K. Urbaniec (Eds.) Modern Energy Economy in Beet Sugar Factories 1989
-
Upload
vera-ivkovic -
Category
Documents
-
view
84 -
download
10
description
Transcript of K. Urbaniec (Eds.) Modern Energy Economy in Beet Sugar Factories 1989
SUGAR SERIES
Vol. 1. Standard Fabrication Practices for Cane Sugar Mills (Delden) Vol. 2. Manufacture and Refining of Raw Cane Sugar (Baikow) Vol. 3. By-Products of the Cane Sugar Industry (Paturau) Vol. 4. Unit Operations in Cane Sugar Production (Payne) Vol. 5. Noel Deerr: Classic Papers of a Sugar Cane Technologist (Payne,
Compiler) Vol. 6. The Energy Cane Alternative (Alexander) Vol. 7. Handbook of Cane Sugar Engineering (Hugot, 3rd edition) Vol. 8. Management Accounting for the Surgar Cane Industry (Fok Kam) Vol. 9. Chemistry and Processing of Sugarbeet and Sugarcane (Clarke
and GodshalL Editors) Vol. 10. Modern Energy Economy in Beet Sugar Factories (Urbaniec)
sugar series, 10
modern energy economy in beet sugar factories by
K. Urbaniec Division of Thermodynamics, Fluid Mechanics and Heat Transfer, Lund Institute of Technology, Lund, Sweden
Elsevier
Amsterdam — Oxford — New York — Tokyo 1989
ELSEVIER SCIENCE PUBLISHERS B.V. Sara Burgerhartstraat 25 P.O. Box 2 1 1 , 1000 AE Amsterdam, The Netherlands
Distributors for the United States and Canada:
ELSEVIER SCIENCE PUBLISHING COMPANY INC. 655, Avenue of the Americas New York, NY 10010, U.S.A.
ISBN 0-444-87294-9 (Vol. 10) ISBN 0-444-41897-0 (Series)
© Elsevier Science Publishers B.V., 1989
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B.V./ Physical Sciences & Engineering Division, P.O. Box 330, 1000 AH Amsterdam, The Netherlands.
Special regulations for readers in the USA - This publication has been registered with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA . All other copyright questions, including photocopying outside of the U S A , should be referred to the publisher.
No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, Oi fi om any use or operation of any methods, products, instructions or ideas contained in the material herein.
Printed in The Netherlands
FOREWORD
I t has been v e r y demanding o f t ime and e f f o r t to w r i t e a book on the ene rgy
economy o f beet s u g a r f a c t o r i e s , because the re a re so many a s p e c t s o f t h i s
s u b j e c t t ha t dese rve to be p r e s e n t e d . T r y i n g to e x p l a i n how the energy
requ i rements s h o u l d be adapted to the p r i n c i p l e s o f beet s u g a r manu fac tu re ,
I cou ld not a v o i d d i s c u s s i n g c e r t a i n prob lems o f modern beet s u g a r t e c h n o l o g y .
I hope the s u g a r t e c h n o l o g i s t s can u n d e r s t a n d t h a t f rom t h e i r p o i n t o f v i e w ,
t h i s d i s c u s s i o n may seem incomp le te . I t would be a p p r e c i a t e d i f r e a d e r s would
p o i n t out any o m i s s i o n s or e r r o r s which have been o v e r l o o k e d .
T h i s book c o u l d not have been w r i t t e n w i t h o u t the s t i m u l a t i o n and d i r e c t
a s s i s t a n c e o f P r o f e s s o r Jan Dob rzyck i and D r . W i t o l d L e k a w s k i , to whom s p e c i a l
t hanks are e x p r e s s e d . C e r t a i n i d e a s o r i g i n a t e d f rom d i s c u s s i o n s w i t h the l a t e
P r o f e s s o r S t a n i s l a w Z a g r o d z k i d u r i n g the p e r i o d 1 9 7 9 - 1 9 8 0 .
G ra te fu l a p p r e c i a t i o n i s e x p r e s s e d to the f o l l o w i n g f i r m s and i n s t i t u t i o n s
f o r t h e i r a s s i s t a n c e i n p r o v i d i n g t e c h n i c a l i n f o r m a t i o n , i l l u s t r a t i o n s or
s t a t i s t i c a l d a t a :
- Chemadex, Cukropo l and C u k r o p r o j e k t , Warsaw, P o l a n d ;
- D D S , Copenhagen, Denmark;
- F e i t e n & Gu i l l eaume E n e r g i e t e c h n i k , Nordenham, FRG;
- F r a t e l l i B a b b i n i , Fo r i i , I t a l y ;
- GEA Wiegand , E t t l i n g e n , FRG;
- H o l l y Suga r C o r p o r a t i o n , San F r a n c i s c o , USA;
- K ra f twerk U n i o n , M٧ lhe im , FRG;
- I n s t i t u t f ٧ r L a n d w i r t s c h a f t l i c h e T e c h n o l o g i e und Z u c k e r i n d u s t r i e , TU
B r a u n s c h w e i g , FRG;
- I n s t y t u t P rzemys lu C u k r o w n i c z e g o , Warsaw, P o l a n d ;
- P f e i f e r & Langen , C o l o g n e , FRG;
- R a f f i n e r i e T i r l e m o n t o i s e , B r u s s e l s , B e l g i u m ;
- S o c k e r b o l a g e t , Malmφ, Sweden;
- S p r e c k e l s Suga r D i v i s i o n , Amstar C o r p o r a t i o n , San F r a n c i s c o , USA;
- S t o r d B a r t z , B e r g e n , Norway.
A l a r g e p a r t o f the p r e s e n t book was w r i t t e n d u r i n g my s t a y a t the U n i v e r s i t y
o f Lund , Sweden. I am g r a t e f u l to my f r i e n d P r o f e s s o r Gunnar T y l l e r e d , whase
i n v i t a t i o n made my v i s i t to Sweden p o s s i b l e . Gunnar F e l t b o r g and D r . Jan T jebbes
deserve s p e c i a l t h a n k s f o r t h e i r a s s i s t a n c e i n r e a c h i n g the r e l e v a n t i n f o r m a t i o n
on the Swed ish s u g a r i n d u s t r y . Thanks a re a l s o e x p r e s s e d to the pe rsonne l o f the
l i b r a r y o f S o c k e r b o l a g e t i n A r l φ v where I found a p e r f e c t env i ronment f o r my
V I
l i t e r a t u r e s t u d i e s .
F i n a l l y , I would l i k e to thank t hose A m e r i c a n , B e l g i a n , B r i t i s h , B u l g a r i a n ,
C a n a d i a n , C z e c h , D a n i s h , F r e n c h , German, Greek , H u n g a r i a n , I t a l i a n , P o l i s h ,
S o v i e t , Swed ish and Y u g o s l a v c o l l e a g u e s who he lped me - somet imes unknow ing ly -
th rough i n f o r m a t i o n , a d v i c e , and f r i e n d l y d i s c u s s i o n s .
V I I
PREFACE
The 1970s and 1980s w i l l c e r t a i n l y be remembered as a p e r i o d o f impor tan t
developments i n the energy market and changes i n i n d u s t r y ' s a t t i t u d e towards
energy economy. As e n t i r e n a t i o n s were a f f e c t e d by the economic consequences o f
v i o l e n t f l u c t u a t i o n s i n fue l p r i c e s , much i n t e l l e c t u a l e f f o r t and numerous
p r a c t i c a l a c t i o n s were under taken w i t h the aim o f imp rov ing energy u t i l i z a t i o n .
For example , the ene rgy consumpt ion i n Swed ish i n d u s t r y dec reased by 20%
between 1973 and 1 9 8 3 , w h i l e the t o t a l p r o d u c t i o n volume - e x p r e s s e d i n f i x e d
p r i c e s - remained n e a r l y c o n s t a n t . I n F r a n c e , where the i n d u s t r i a l ou tpu t was
a l s o n e a r l y c o n s t a n t i n the same p e r i o d , the ene rgy consumpt ion i n i n d u s t r y was
reduced by 12%. I n the Federa l R e p u b l i c o f Germany, i n d u s t r i a l ou tpu t r o s e 8%
between 1973 and 1 9 8 4 , but the energy consumpt ion dec reased by 18%. A l t h o u g h
few n a t i o n s have been as s u c c e s s f u l as t h o s e named a b o v e , the t r end towards
s a v i n g energy i s now common. I t has a l s o become v i s i b l e i n s u g a r i n d u s t r i e s
t h roughou t the w o r l d .
The book i s devoted to the problems o f i d e n t i f y i n g the p o t e n t i a l f o r , and
then d e s i g n i n g and imp lemen t i ng , e n e r g y - s a v i n g measures i n beet s u g a r f a c t o r i e s .
As the s u g a r i n d u s t r i e s i n v a r i o u s c o u n t r i e s d i f f e r c o n s i d e r a b l y w i t h r e s p e c t
to the economic c o n d i t i o n s f o r f a c t o r y o p e r a t i o n and the l e v e l o f t e c h n o l o g i c a l
deve lopment , the problem range i s ve ry b r o a d . I t may i n c l u d e the e l i m i n a t i o n o f
f a u l t y o r u n r e l i a b l e a u x i l i a r y equ ipment , o r the i n t r o d u c t i o n o f s i m p l e
improvements i n vapour d i s t r i b u t i o n s c hemes , i n f a c t o r i e s ope ra ted i n c o u n t r i e s
where the need f o r e f f i c i e n t energy u t i l i z a t i o n has not r e a l l y been ve ry u r g e n t
up to now. On the o t h e r h a n d , t he re a re some o t h e r c o u n t r i e s where s u g a r
f a c t o r i e s have l ong s i n c e been ve ry hard p r e s s e d to save ene rgy and where
c o n s i d e r a b l e ach ievements have been no ted i n t h i s f i e l d . F u r t h e r p r o g r e s s may
s t i l l be p o s s i b l e t h e r e , but o n l y i f more advanced e n g i n e e r i n g prob lems a re
s o l v e d .
T a k i n g the D a n i s h s u g a r i n d u s t r y as an examp le , i t can be seen f rom F i g . 1
t h a t the f ue l consumpt ion was d e c r e a s i n g s t e a d i l y d u r i n g the 1950s and 1 9 6 0 s .
A t the b e g i n n i n g o f the 1970s the energy economy reached a c e r t a i n s t a t e o f
m a t u r i t y ; s a v i n g s which c o u l d be ach ieved i n a s i m p l e manner - r o u g h l y s p e a k i n g ,
by a v o i d i n g waste o f energy - had a l r e a d y become a r e a l i t y . F u r t h e r p r o g r e s s
became g r a d u a l l y a q u e s t i o n o f how to mod i fy the f a c t o r i e s i n a l l the a s p e c t s
t ha t cou ld be r e l a t e d to r e d u c t i o n s o f the ene rgy demand, i n c l u d i n g the s u g a r
manu fac tu r i ng p r o c e s s , b y - p r o c e s s e s and a u x i l i a r y p r o c e s s e s , equ ipment , c o n t r o l
V I I I
2^ 5h
cn
•Ľ Ö Ĺ ů
§ 3h CP
^0. ^ 0 ,
X · X X
1955 1960 1965 1970 1975 1980 1985
F i g . 1 . Average consumpt ion o f normal fue l ( h e a t i n g v a l u e 29300 k J / k g ) i n beet s u g a r manufactu'^e i n s e l e c t e d European c o u n t r i e s , w i t h t h e i r 1984 s h a r e i n wor ld p r o d u c t i o n o f beet s u g a r g i v e n i n b r a c k e t s .
s y s t e m s , m o n i t o r i n g methods and p r o c e d u r e s , and even o t h e r a r e a s .
In F i g . 1 , the s t a t i s t i c a l da ta on fue l consumpt ion i n Swed ish and French
s u g a r i n d u s t r i e s a re a l s o shown. I t s h o u l d be po in ted ou t t ha t the da ta a re no t
meant to be compared d i r e c t l y , as the d i f f e r e n c e s must be seen as e x p r e s s i o n s
o f numerous d i s s i m i l a r i t i e s between the i n d u s t r i e s c o n c e r n e d . I n d e e d , t he re a re
even some d i f f e r e n c e s i n the methods used to c a l c u l a t e the ave rage ene rgy
consumpt ion : Swed ish data a re based on p r o d u c t i o n s t a t i s t i c s from 6 wh i te s u g a r
f a c t o r i e s (one raw s u g a r f a c t o r y has been e x c l u d e d ) ; D a n i s h data r e p r e s e n t 5
DDS-owned f a c t o r i e s , f o u r o f them p roduc ing wh i te s u g a r o n l y and one wh i te
s u g a r and r a f f i nade ; F rench da ta have been ave raged from 56 f a c t o r i e s , t h e i r
1984 ou tpu t c o n s i s t i n g o f 80% wh i te s u g a r , 15% s y r u p s and 5% raw s u g a r . I n o t h e r
w o r d s , the d i f f e r e n c e s stem p a r t l y f rom the f a c t t ha t p r o d u c t s w i t h d i f f e r e n t
s p e c i f i c energy demands a re i n v o l v e d . N e v e r t h e l e s s , i t can be conc luded from
a compar ison o f t r ends t h a t both i n Sweden and F r a n c e , the deve lopments towards
s i t u a t i o n s s i m i l a r to t h a t i n Denmark a re f a r advanced .
Under such c i r c u m s t a n c e s , i s one j u s t i f i e d i n w r i t i n g a book devoted s o l e l y
to the energy economy? T a k i n g the g l o b a l p e r s p e c t i v e , t he re i s no doubt t h a t
much work on energy problems i s needed i n the s u g a r i n d u s t r y because the re a re
s t i l l c o u n t r i e s - major beet s u g a r p roduce rs - where the s p e c i f i c energy
consumpt ion i n s u g a r manufac ture i s much h i g h e r than i n the c o u n t r i e s named
above . About 60% o f the w o r l d ' s beet s u g a r comes from f a c t o r i e s c o n s u m i n g , on
a v e r a g e , 2 - 3 t imes more ene rgy per u n i t mass o f bee ts than the D a n i s h s u g a r
f a c t o r i e s .
A s e l e c t i o n o f s t a t i s t i c a l da ta on the ene rgy consumpt ion i n beet s u g a r
manufac ture i n s e v e r a l s u g a r - p r o d u c i n g c o u n t r i e s can be seen i n Tab le 1 . A g a i n ,
IX
TABLE 1
Average consumpt ion o f nonnal f ue l ( h e a t i n g v a l u e 29300 k J / k g ) i n beet s u g a r manufac ture - pu lp d r y i n g e x c l u d e d - i n s e l e c t e d c o u n t r i e s .
Sha re i n wo r l d Normal f ue l Count ry p r o d u c t i o n o f beet Year Bee ts worked consumpt ion
s u g a r 1984 (%) (1000 t o n s ) ( k g / 1 0 0 kg b)
USSR 2 3 . 0 3 1980 64300 FRG 8 . 2 4 1984 20189 3 . 1 ^ USA 6 . 8 9 1980 21320 7 . 6 a Po land 4 . 9 2 1984 15500 7 . 4 C z e c h o s l o v a k i a 2 . 2 2 1984 7540 8 . 5 Greece 0 . 6 2 1981 2560 4 . 6
es t ima ted
the reade r s h o u l d be c a u t i o n e d a g a i n s t d i r e c t compar i sons o f the i n d i c e s g i v e n ,
as w i th t hese c o u n t r i e s coming i n t o the p i c t u r e , one has to be aware o f even
more p ro found d i s s i m i l a r i t i e s than t h o s e between F r a n c e , Sweden and Denmark.
Le t us j u s t ment ion c l i m a t i c c o n d i t i o n s , wh ich a f f e c t the ene rgy demand
c o n s i d e r a b l y : i t i s no t unusua l f o r U S S R , P o l i s h and some US f a c t o r i e s to
p r o c e s s f r o z e n bee ts i n the f i n a l s t a g e o f the s e a s o n , w h i l e t h i s i s unheard o f
i n Greece ( i t i s a l s o ex t remely u n l i k e l y i n Sweden, Denmark and F r a n c e ) . On the
o t h e r h a n d , some o f the c o u n t r i e s l i s t e d had never been known f o r a ve r y
e f f e c t i v e energy u s a g e ; n e i t h e r had they r e a l l y been a f f e c t e d by the
d i s t u r b a n c e s i n the i n t e r n a t i o n a l f ue l market because t h e i r n a t i o n a l economic
p o l i c i e s were d e s i g n e d to c o u n t e r a c t the wor ldw ide t r e n d s . I t s e e m s , however ,
t ha t the p r e s e n t economic deve lopments i n t hese c o u n t r i e s f o l l o w the gene ra l
p a t t e r n , thus s t i m u l a t i n g i n t e r e s t i n a r a t i o n a l i z e d ene rgy economy. I n t h a t
r e s p e c t , the answer to the q u e s t i o n f o rmu la ted above seems to be p o s i t i v e .
How c o u l d the book be shaped i n o r d e r to make i t u s e f u l to the peop le
work ing i n v a r i o u s c o u n t r i e s , where the s u g a r i n d u s t r i e s a re c h a r a c t e r i z e d by
d i f f e r e n t l e v e l s o f s o p h i s t i c a t i o n o f the ene rgy economy? I t seems t h a t when
l o o k i n g a t the energy subsys tem and i t s i n t e r a c t i o n s w i th o t h e r s u b s y s t e m s and
w i th the env i ronment o f the f a c t o r y , an at tempt can be made to s y s t e m a t i z e and
e v a l u a t e the most impor tan t e n e r g y - s a v i n g measures t h a t may come i n t o q u e s t i o n .
Such a s y s t e m a t i c rev iew can prove h e l p f u l to the managers and t e c h n o l o g i s t s i n
s u g a r f a c t o r i e s , where a problem may a r i s e o f c h o o s i n g the most a p p r o p r i a t e s e t
o f measures t ha t b e s t f i t the f a c t o r y ' s un ique n e e d s . I t i s a l s o hoped t ha t the
book can be used i n u n i v e r s i t y - l e v e l c o u r s e s on the ene rgy economy o f s u g a r
f a c t o r i e s , and t ha t i t may be o f i n t e r e s t to d e s i g n e n g i n e e r s as we l l as to
s p e c i a l i s t s engaged i n r e s e a r c h i n t h i s a r e a .
As r e g a r d s the scope o f the book , i t must be conc luded t h a t when a t tempt ing
to cove r the e n t i r e problem f i e l d , i t would be i n a p p r o p r i a t e to r e s t r i c t
a t t e n t i o n to the t r a d i t i o n a l l y r e c o g n i z e d energy economy prob lems o n l y . I n s t e a d ,
i t i s n e c e s s a r y to adopt an i n t e r d i s c i p l i n a r y approach aimed a t d e m o n s t r a t i n g
how the energy demand o f a s u g a r f a c t o r y can be a f f e c t e d by the i n t e r a c t i o n s
between a number o f f a c t o r s , namely :
- l a y o u t and parameters o f the energy c o n v e r s i o n and d i s t r i b u t i o n p r o c e s s e s ;
- l a y o u t and parameters o f the s u g a r manu fac tu r i ng p r o c e s s and b y - p r o c e s s e s ;
- c h a r a c t e r i s t i c s o f the equipment and c o n t r o l s y s t e m s ;
- comple teness and accu racy o f the ene rgy m o n i t o r i n g p r o c e d u r e s .
The book c o n s i s t s e s s e n t i a l l y o f t h ree p a r t s . In Chap te rs 1 to 3 , some
t h e o r e t i c a l background i s g i v e n and e n g i n e e r i n g p r i n c i p l e s f o r c r e a t i n g
e f f i c i e n t energy c o n v e r s i o n and u t i l i z a t i o n s u b s y s t e m s i n s u g a r f a c t o r i e s a re
r ev i ewed . More s p e c i f i c a l l y , Chapter 1 p r o v i d e s an i n t r o d u c t o r y s t r u c t u r i n g
o f the problem f i e l d and a rev iew o f the p e r t i n e n t l i t e r a t u r e . Chap te r 2 i s
devoted to mass and energy b a l a n c e s a s t o o l s f o r a n a l y s i n g ene rgy p r o c e s s e s and
s y s t e m s , and to fundamenta ls o f compu te r -a ided a n a l y s i s and d e s i g n o f ene rgy
s u b s y s t e m s . Chapter 3 p r o v i d e s a rev iew o f e s s e n t i a l e n g i n e e r i n g p r o b l e m s , and
methods f o r t h e i r s o l v i n g , r e l a t e d to improv ing heat economy i n e x i s t i n g
f a c t o r i e s o r d e s i g n i n g new, e f f i c i e n t thermal s u b s y s t e m s .
In the i n i t i a l c h a p t e r s , the impor tance i s i n d i c a t e d o f o t h e r a r e a s t ha t do
not s t r i c t l y be long to energy e n g i n e e r i n g but a re c l e a r l y r e l a t e d to an
e f f i c i e n t energy economy. C o n s e q u e n t l y , i n the second p a r t , i . e . , Chap te rs 4
to 7 , recen t developments i n t hese a r e a s and t h e i r impor tance to ene rgy
c o n v e r s i o n and u t i l i z a t i o n i n s u g a r f a c t o r i e s a re d i s c u s s e d . Chapte r 4 i s
devoted to e n e r g y - e f f i c i e n t p r o c e s s e s , and Chapter 5 to equipment d e s i g n .
Con t ro l sys tems and t h e i r r o l e i n s a v i n g ene rgy a re d i s c u s s e d i n Chapte r 6 . I n
Chapte r 7 , methods and p rocedu res f o r m o n i t o r i n g e n e r g y - r e l a t e d a s p e c t s o f
f a c t o r y o p e r a t i o n a re r ev i ewed . In Chap te rs 6 and 7 , computer a p p l i c a t i o n s i n
the r e s p e c t i v e a r e a s a re a l s o d i s c u s s e d .
I t has been the a u t h o r ' s amb i t i on to i l l u s t r a t e the p r e s e n t a t i o n w i th
s u i t a b l e p r a c t i c a l l y - o r i e n t e d examp les . These a re based m o s t l y on the a u t h o r ' s
expe r i ence f rom 9 y e a r s wo rk ing w i t h an e n g i n e e r i n g company s p e c i a l i z i n g i n the
d e s i g n , e r e c t i o n and m o d e r n i z a t i o n o f s u g a r f a c t o r i e s , as wel l f rom an
a d d i t i o n a l 5 y e a r s o f c o n s u l t i n g and r e s e a r c h f o r the s u g a r i n d u s t r y . S h o r t
examples a re p resen ted i n Chap te rs 1 , 2 , 3 and 7 . I n the t h i r d p a r t o f the b o o k ,
i . e . . Chap te rs 8 and 9 , summaries a re g i v e n o f r e a l - l i f e d e s i g n a n a l y s e s o f
ene rgy subsys tems o f s u g a r f a c t o r i e s , c h a r a c t e r i z e d by d i f f e r e n t l e v e l s o f
s o p h i s t i c a t i o n o f the energy economy.
I t s h o u l d be emphas ized t ha t the p r e s e n t book i s not i n tended to g i v e any
p r e s c r i p t i o n s but r a t h e r to s t i m u l a t e t h i n k i n g and i d e a - g e n e r a t i n g . As i t
X I
d e f i n i t e l y cannot r e p l a c e e n g i n e e r i n g handbooks o r d e s i g n a i d s , an at tempt has
been made to a v o i d the r e p e t i t i o n o f b a s i c t h e o r y and fundamental d a t a , such as
thermodynamic d e f i n i t i o n s and t a b l e s o f p r o p e r t i e s o f water and steam o r
p r o p e r t i e s o f s u g a r s o l u t i o n s ; t h e s e can be found e l s e w h e r e . Fo r r e a d e r s who
may need an i n t r o d u c t i o n to the f u n d a m e n t a l s , ample r e f e r e n c e s a re g i v e n to the
n o w - c l a s s i c a l l i t e r a t u r e , and m o s t l y to A m e r i c a n , E n g l i s h and German s o u r c e s .
Then , i n Append ices 1 and 2 , numer ica l a p p r o x i m a t i o n s o f thermodynamic
p r o p e r t i e s o f wa te r , steam and s u g a r s o l u t i o n s a re d i s c u s s e d . I n Append ix 3 ,
a s h o r t rev iew o f u s e f u l r e l a t i o n s h i p s and da ta r e l a t i n g to c e r t a i n heat
t r a n s f e r phenomena i s g i v e n .
When p r e s e n t i n g p h y s i c o - c h e m i c a l and t e c h n i c a l d a t a , e x a m p l e s , c a l c u l a t i o n s ,
e t c . , S I u n i t s o f measure have been used t h r o u g h o u t the book . Fo r r e a d e r s
accustomed to o t h e r u n i t s . Append ix 4 p r o v i d e s a s e l e c t i o n o f c o n v e r s i o n
f a c t o r s .
X I I
L I S T OF SYMBOLS
a j u i c e d r a f t
b c o n c e n t r a t i o n
Β fue l consump t i on , fue l demand
C s p e c i f i c heat
D steam f low
F s u r f a c e a rea
G mass f l ow
h en tha lpy
k o v e r a l l heat t r a n s f e r c o e f f i c i e n t
Μ mass
Ν e l e c t r i c a l e f f e c t , power
ρ p r e s s u r e
Ρ power demand, power ou tpu t
q , Q heat
heat o f combust ion
h e a t i n g v a l u e
S steam ra te
t temperature
Ô a b s o l u t e temperature
Ä Ô , At temperature d i f f e r e n c e
V s p e c i f i c volume
ô t ime , d u r a t i o n
Mos t f r e q u e n t l y used s u b s c r i p t s or s u p e r s c r i p t s :
b b e e t s , c o s s e t t e s
c condensate
j j u i c e
Ρ pu lp
s steam
V vapour
w water
C h a p t e r 1
THE ENERGY SYSTEM AND I T S ROLE IN A SUGAR FACTORY
1.1 SUBSYSTEMS OF A SUGAR FACTORY
The s u g a r m a n u f a c t u r i n g p r o c e s s , b y - p r o c e s s e s and a u x i l i a r y p r o c e s s e s must
be c o n t i n u o u s l y and r e l i a b l y s u p p l i e d w i t h t h e e n e r g y needed t o p e r f o r m a l l t h e
u n i t o p e r a t i o n s i n v o l v e d . By t h e i r v e r y n a t u r e , t h e p r o c e s s e s a r e c h a r a c t e r i z e d
by p r e d e t e r m i n e d v a l u e s o f c e r t a i n i n p u t , o u t p u t and i n t e r m e d i a t e p a r a m e t e r s ;
o t h e r pa ramete rs may be l i m i t e d by c o n s t r a i n t s r e l a t e d t o p r o c e s s r e q u i r e m e n t s ,
f a c t o r y economy, e n v i r o n m e n t p r o t e c t i o n and o t h e r f a c t o r s . C o n s e q u e n t l y , t h e
f reedom o f c h o i c e o f t h e v a l u e s o f pa rame te rs o f t h e e n e r g y c o n v e r s i o n ,
d i s t r i b u t i o n and u t i l i z a t i o n p r o c e s s e s i s s u b s t a n t i a l l y r e s t r i c t e d . To make
t h i n g s even more c o m p l i c a t e d , u n d e r l o c a l c o n d i t i o n s i n a s p e c i f i c f a c t o r y ,
some c o n s t r a i n t s may be g i v e n o n l y i m p l i c i t l y a n d , q u i t e o f t e n , a r e d i f f i c u l t
t o i d e n t i f y .
I n such c i r c u m s t a n c e s , an i n v e s t i g a t i o n o f t h e e n e r g y economy o f a s p e c i f i c
s u g a r f a c t o r y r e q u i r e s s t u d y i n g v a r i o u s a s p e c t s o f i n t e r a c t i o n s between s u g a r
m a n u f a c t u r i n g , b y - p r o c e s s e s and a u x i l i a r y p r o c e s s e s on t h e one s i d e , and e n e r g y
c o n v e r s i o n , d i s t r i b u t i o n and u t i l i z a t i o n p r o c e s s e s on t h e o t h e r . As t h e
i n t e r a c t i o n s a r e t a k i n g p l a c e i n v a r i o u s s e c t i o n s and components o f t h e f a c t o r y ,
i t c o u l d be c o n c l u d e d t h a t i t i s n e c e s s a r y t o s t u d y t h e e n t i r e f a c t o r y i n g r e a t
d e t a i l . H o w e v e r , i t se ldom makes sense t o i n v e s t i g a t e a l l t h e d e t a i l s a t o n c e ,
as a s t r a i g h t f o r w a r d app roach w o u l d r e s u l t i n a l a r g e vo lume o f i n f o r m a t i o n
w h i c h may be d i f f i c u l t t o h a n d l e and i n t e r p r e t . What i s r e a l l y needed f o r
g r a s p i n g t h e s i t u a t i o n and i d e n t i f y i n g p o t e n t i a l e n e r g y s a v i n g s i s s t r u c t u r e d
i n f o r m a t i o n f rom w h i c h , depend ing on s p e c i f i c n e e d s , r e l e v a n t d a t a on t h e
f a c t o r y r e g i o n s o f i n t e r e s t can be e x t r a c t e d .
The c o n c e p t o f s t r u c t u r e d i n f o r m a t i o n on e n e r g y p r o c e s s e s must be seen i n
c o n n e c t i o n w i t h t h e s t r u c t u r e o f t h e s u g a r f a c t o r y i n q u e s t i o n . T h i s does n o t
n e c e s s a r i l y mean i n v e s t i g a t i n g a l l t h e p h y s i c a l componen ts , l i k e b u i l d i n g s ,
p r o c e s s s t a t i o n s o r equ ipment u n i t s ; t h e s t r u c t u r e may be d e f i n e d i n a manner
s u i t e d t o s p e c i f i c n e e d s . I n t h e l i t e r a t u r e , a v a r i e t y o f app roaches a t
d i f f e r e n t l e v e l s o f c o m p l e x i t y can be f o u n d . A t one end o f t h e c o m p l e x i t y s c a l e ,
t h e app roach employed b y , among o t h e r s , S c h i e b l ( r e f . 1) a n d , more r e c e n t l y ,
K a r r e n ( r e f . 2) can be p l a c e d . H e r e , t h e e n e r g y usage i s i d e n t i f i e d by t h e i n p u t
e n e r g y s t r eam w h i c h can a l s o be c o n s i d e r e d as t h e sum o f power house l o s s e s and
p r o c e s s e n e r g y c o n s u m p t i o n ; t h i s means d i v i d i n g t h e f a c t o r y i n t o power house
and p r o c e s s a r e a s , as i n d i c a t e d i n F i g . 1.1. A b i t c l o s e r t o t h e m i d d l e o f t h e
c o m p l e x i t y s c a l e comes t he s t r u c t u r i n g p r i n c i p l e used by Bal oh ( r e f . 3 ) , t h a t
Γ l o s s e s I
I
1
1 1 s t e a m . ^
2 1 1 e lect r ic 2 1 power 1
1 power 1
fue l
F i g , Ί . Ι . S u g a r f a c t o r y d i v i d e d i n t o power house 1 and p r o c e s s a r e a 2 . Mass and e n e r g y s t reams c r o s s i n g t h e bounda ry shown by t h e dashed l i n e a r e d e t e r m i n e d .
i s , d i v i d i n g t h e f a c t o r y i n t o e i g h t main s e c t i o n s and i d e n t i f y i n g t h r e e
d i f f e r e n t a reas o f e n e r g y p r o c e s s e s . T h i s p r i n c i p l e i s shown s c h e m a t i c a l l y i n
F i g . 1 .2 ; n o t e t h a t t h e s t reams o f e l e c t r i c a l power s u p p l i e d t o t h e f a c t o r y
s e c t i o n s a r e n o t c o n s i d e r e d . Mov ing t o t h e o t h e r end o f t h e c o m p l e x i t y s c a l e ,
t h e approach used by Z a g r o d z k i ( r e f . 4 ) can be p r e s e n t e d . As can be seen i n
F i g . 1 .3 , i t r e l i e s on t h e i d e n t i f i c a t i o n o f e n e r g y s t reams t o and f rom
i n d i v i d u a l equ ipment u n i t s , o r g r o u p s o f u n i t s . Note t h a t o n l y a p a r t o f t h e
f a c t o r y , and o n l y the rma l e n e r g y , a r e c o n s i d e r e d .
Examples o f even more d e t a i l e d app roaches can be f ound i n t h e l i t e r a t u r e , as
i i u e _ g a s _ _ : \ s l u d g e .
L ±i -T^ -{-- -i-T
F i g . 1.2. S u g a r f a c t o r y d i v i d e d i n t o : 1 - l ime k i l n w i t h m i l k - o f - l i m e s t a t i o n , 2 - e x t r a c t i o n s t a t i o n , 3 - j u i c e p u r i f i c a t i o n s t a t i o n , 4 - e v a p o r a t o r , 5 -s u g a r h o u s e , 6 - c o n d e n s a t e t a n k s , 7 - p u l p d r y i n g s t a t i o n , 8 - power h o u s e . Mass and e n e r g y s t reams can be i d e n t i f i e d a t t h r e e d i f f e r e n t b o u n d a r i e s : I -e n t i r e f a c t o r y , I I - h e a t economy a r e a . I I I - p r o c e s s h e a t i n g a r e a .
JP
Ε· exhous i j s team,
η
7 • 5H
EV
η η η
F i g . 1.3. Example o f s t r u c t u r i n g o f s u g a r f a c t o r y equ ipment i n v o l v e d i n t h e e n e r g y p r o c e s s e s . Ε - e x t r a c t i o n s t a t i o n , J P - j u i c e p u r i f i c a t i o n s t a t i o n , SH s u g a r h o u s e , EV - e v a p o r a t o r , V - vacuum p a n s , " - Z - e v a p o r a t o r e f f e c t s , 6 -h e a t e r s , 7 - c o n d e n s e r . V a p o u r s t reams c r o s s i r r t h e bounda ry shown by t h e dashed l i n e and t h e b o u n d a r i e s o f J P , EV and SH can be i d e n t i f i e d .
i l l u s t r a t e d i n F i g . 1.4 ( r e f . 5 ) . T a b l e 1.1 d e m o n s t r a t e s how t h i s s t r u c t u r i n g
p r i n c i p l e makes i t p o s s i b l e t o i d e n t i f y t h e consumpt i on o f h e a t i n g media i n
equ ipment u n i t s o r g roups o f u n i t s i n a model f a c t o r y , t hus p r o v i d i n g a
c o n v e n i e n t b a s i s f o r c a l c u l a t i o n s o f t h e o v e r a l l e n e r g y consumpt i on i n t h e
s u g a r m a n u f a c t u r i n g p r o c e s s o r i n i t s p a r t s .
G e n e r a l l y , a s u g a r f a c t o r y may be a n a l y s e d as a who le o r as a sum o f s m a l l e r
p a r t s ( w h i c h , i n t u r n , may be s u b d i v i d e d t o o ) by emp loy ing t h e n o t i o n o f an
open thermodynamic sys tem ( r e f s . 6 , 7 ) . I t can be d e f i n e d as t h e p a r t o f t h e
p h y s i c a l space w h i c h i s c o n t a i n e d w i t h i n p r e s c r i b e d and i d e n t i f i a b l e b o u n d a r i e s .
The s t a t e o f an open thermodynamic sys tem can be d e f i n e d i n te rms o f q u a n t i t i e s
c h a r a c t e r i z i n g mass and e n e r g y s t reams c r o s s i n g i t s bounda ry ( s e e C h a p t e r 2 ) .
By s p l i t t i n g t h e s y s t e m i n t o s u b s y s t e m s , t h e p o s s i b i l i t y i s c r e a t e d o f
d e t e r m i n i n g mass and e n e r g y s t reams and t h e i r pa rame te rs needed t o d e f i n e t h e
s t a t e s o f t h e s u b s y s t e m s . I t s h o u l d be emphas ized t h a t an i n v e s t i g a t o r i s f r e e
t o d e f i n e t h e b o u n d a r i e s o f t h e s y s t e m and i t s subsys tems i n t h e manner b e s t
s u i t e d t o h i s s p e c i f i c n e e d s . T h i s makes i t p o s s i b l e t o decompose c o m p l i c a t e d
m u l t i v a r i a b l e e n g i n e e r i n g prob lems i n t o a number o f s i m p l e r p rob lems t h a t a r e
e a s i e r t o u n d e r s t a n d and s o l v e . A w e l l p l a n n e d sys tem d e c o m p o s i t i o n a l s o
c r e a t e s p o s s i b i l i t i e s o f i n f o r m a t i o n s t r u c t u r i n g , t h i s i n t u r n g i v i n g a b e t t e r
condenir sa te
J P
6 n: 6
T C ,
e x h p u s t steam
5 H(
π
EV
π
7 :
SH
Β
•Θ D 4 X I ®
F i g . 1.4. A n o t h e r example o f s t r u c t u r i n g o f s u g a r f a c t o r y equ ipment i n v o l v e d i n t h e e n e r g y p r o c e s s e s . JP - j u i c e p u r i f i c a t i o n s t a t i o n , SH - s u g a r h o u s e , A , B, C - vacuum pans A , Β and C , TC - t h e r m o c o m p r e s s o r s , EV - e v a p o r a t o r , 1-4 - e v a p o r a t o r e f f e c t s , 5 - e x t r a c t o r , 6 - h e a t e r s , 7 - c o n d e n s e r , 8 - p u l p p r e s s e s , 9 - t h i c k j u i c e t a n k , 10 m e l t e r , 11 - s y r u p t a n k s , 12 - s u g a r d r y e r . Not shown: condensa te c o n n e c t i o n s . V a p o u r and c o n d e n s a t e s t reams c r o s s i n g t h e bounda ry shown by t h e dashed l i n e and t h e b o u n d a r i e s o f J P , EV and SH a r e i d e n t i f i e d .
i n s i g h t i n t o e n e r g y p r o c e s s e s and p o t e n t i a l e n e r g y s a v i n g s .
The i d e a o f t r e a t i n g a s u g a r f a c t o r y as a thermodynamic sys tem i n w h i c h
subsys tems can be d e f i n e d seems t o be so s i m p l e and o b v i o u s t h a t p e o p l e t e n d t o
s h r u g i t o f f . A c t u a l l y , i t may be t r u e t h a t a common-sense a p p r o a c h t o e n e r g y
a n a l y s e s i s e f f e c t i v e enough i n s o l v i n g s i m p l e p r o b l e m s . When c o n s i d e r i n g
c o m p l i c a t e d and s u b t l e q u e s t i o n s , h o w e v e r , one s h o u l d r e c o g n i z e t h e a d v a n t a g e s
o f a d i s c i p l i n e d , t h e o r e t i c a l l y w e l l f ounded thermodynamic a p p r o a c h . As a m a t t e r
o f f a c t , when t h e e n e r g y economy i n c o n t e m p o r a r y s u g a r f a c t o r i e s becomes so
advanced t h a t t h e was te o f e n e r g y i s l a r g e l y e l i m i n a t e d , v i r t u a l l y no e n e r g y -
s a v i n g measure can be r e g a r d e d as s i m p l e . F o l l o w i n g t h e law o f d i m i n i s h i n g
r e t u r n s , i n v e s t m e n t s i n an advanced e n e r g y economy can b r i n g l i m i t e d g a i n s o n l y ,
so t h e economic a n a l y s e s on w h i c h management d e c i s i o n s a r e based must be
TABLE 1.1
Steam and v a p o u r s t reams (kg /100 kg b ) between equ ipment u n i t s o r g r o u p s i n t h e model f a c t o r y shown s c h e m a t i c a l l y i n F i g . 1.4. Dashed l i n e s s e p a r a t e d a t a r e l a t i n g t o J P , SH and E V .
S o u r c e s
R e c e i v e r s E v a p o r a t o r
1 2
e f f e c t s
3 4
O t h e r s o u r c e s
P r e s s w a t e r h e a t e r E x t r a c t o r Raw j u i c e h e a t e r
0.90 1.97
0.92 Vacuum pan v a p o u r
P r e - l i m e d j u i c e h e a t e r s H e a t e r a f t e r 1 s t c a r b o n a t a t i o n H e a t e r b e f o r e 2nd c a r b o n a t a t i o n 2.50
2.85 3.36 2.62
Condensa te
T h i n j u i c e h e a t e r s 2.24 2.43 1.65
T h i c k j u i c e h e a t e r M e l t e r I n d i r e c t l y h e a t e d tanks D i r e c t l y hea ted tanks Remelt h e a t e r Vacuum pans A
Β C
Sugar d r y e r
0.20 0.45 0.58
12.80 3.40 1.31
0.15
0.18
E x h a u s t steam 0.50
Thermocompressors Condense r
10.00 0.90
L i v e steam 4.00
E v a p o r a t o r t o t a l 12.24 24.57 8.37 6.23
r e l i a b l e i n d e e d . T h i s makes i t n e c e s s a r y t o e n s u r e a h i g h a c c u r a c y o f
e n g i n e e r i n g c a l c u l a t i o n s so as t o p r o v i d e r e l i a b l e i n p u t d a t a f o r economic
a n a l y s e s . F o r examples o f t h e a p p l i c a t i o n o f a d i s c i p l i n e d thermodynamic
app roach i n t h e c a l c u l a t i o n s o f e n e r g y b a l a n c e s , see C h a p t e r s 2 , 3 , 8 and 9.
I t s h o u l d be n o t e d t h a t t h e need f o r d e f i n i n g and s u b s e q u e n t l y decompos ing
a thermodynamic sys tem may a r i s e i n p r a c t i c a l s i t u a t i o n s as d i f f e r e n t a s :
( i ) R a t i o n a l i z i n g , o r p l a n n i n g m o d e r n i z a t i o n o f , t h e e n e r g y economy o f an
e x i s t i n g f a c t o r y , when a t h o r o u g h u n d e r s t a n d i n g o f t h e d e f i c i e n c i e s and
l i m i t a t i o n s o f an e x i s t i n g sys tem i s needed as a f o u n d a t i o n f o r p r o p o s e d
improvements . C h a r a c t e r i s t i c p rob lems a r e d i s c u s s e d i n C h a p t e r s 8 and 9.
( i i ) D e s i g n i n g a new f a c t o r y , i n c l u d i n g i t s e n e r g y s u b s y s t e m . T h i s r e q u i r e s
a n a l y s i n g t h e p r o p e r t i e s o f a sys tem w h i c h does n o t y e t e x i s t w i t h t h e aim o f
s h a p i n g i t o p t i m a l l y , as d i s c u s s e d i n C h a p t e r 9.
( i i i ) M o n i t o r i n g t h e e n e r g y p r o c e s s e s d u r i n g f a c t o r y o p e r a t i o n , when p e r i o d i c
e n e r g y consumpt ion checks o r a t t e m p t e d improvements i n r o u t i n e m o n i t o r i n g
p r o c e d u r e s may r e q u i r e l o c a t i n g new measur ing i n s t r u m e n t s f o r more d e t a i l e d
i n f o r m a t i o n on e n e r g y b a l a n c e s , o r p l a c i n g some s e e m i n g l y r e d u n d a n t
measurements i n o r d e r t o o b t a i n i n f o r m a t i o n needed f o r s y s t e m a t i c c r o s s - c h e c k s
on i m p o r t a n t b a l a n c e d a t a . Problems o f t h i s k i n d a r e p r e s e n t e d i n C h a p t e r 7.
1.2 THE THERMAL SYSTEM AND I T S COMPONENTS
1.2.1 D e f i n i t i o n
T a k i n g advan tage o f t h e f l e x i b i l i t y i n h e r e n t i n t h e n o t i o n o f a s y s t e m
b o u n d a r y , a thermodynamic sys tem can be d e f i n e d w i t h i n a s u g a r f a c t o r y so as t o
i n c o r p o r a t e a l l t h e equ ipment u n i t s i n w h i c h the rma l e n e r g y ( h e a t ) c o n v e r s i o n
and u t i l i z a t i o n p r o c e s s e s a r e c a r r i e d o u t . I n t e r c o n n e c t i n g p i p e s a n d , p o s s i b l y ,
r e l e v a n t a u t o m a t i c c o n t r o l c i r c u i t s can a l s o be taken i n t o c o n s i d e r a t i o n . I t
can f u r t h e r be assumed t h a t t h e e l e c t r i c a l e n e r g y i s d i s r e g a r d e d e x c e p t as
a mean ing fu l o u t p u t i n t h e e n e r g y b a l a n c e o f t h e power h o u s e , o r t h a t i t i s
a l s o a c c o u n t e d f o r as a b a l a n c e i n p u t when equ ipment u n i t s o r g r o u p s a r e
a n a l y s e d . I n t he f o l l o w i n g , such a sys tem w i l l be c a l l e d t h e the rma l sys tem o f
a s u g a r f a c t o r y (an example i s shown s c h e m a t i c a l l y i n F i g . 1 . 5 ) . I t s h o u l d be
no ted t h a t i f a l l t h e e n e r g y p r o c e s s e s , i n c l u d i n g power g e n e r a t i o n and
u t i l i z a t i o n , a r e c o n s i d e r e d , t h e n t h e te rm " e n e r g y s y s t e m " w i l l be u s e d .
O d d l y e n o u g h , t h e n o t i o n o f a t he rma l sys tem i s n o t used i n t h e s u g a r
i n d u s t r y . I n t h e l i t e r a t u r e d e v o t e d t o e n e r g y p r o b l e m s , such terms as " t h e r m a l
scheme o f a s u g a r f a c t o r y " ( r e f . 8 ) , " h e a t c i r c u i t r y " ( r e f . 9 ) , o r " h e a t
economy c i r c u i t " ( r e f . 4 ) a r e u s e d , and most o f t e n , t h e o b j e c t unde r
c o n s i d e r a t i o n i s n o t r i g o r o u s l y d e f i n e d . Some a u t h o r s do n o t use any u n i f y i n g
n o t i o n s f o r t h e o b j e c t o f e n e r g y a n a l y s e s a t a l l . F o r e x a m p l e , Hugo t ( r e f . 10)
t r e a t s e v a p o r a t i o n and h e a t i n g i n d e p e n d e n t l y o f what he c a l l s t h e "s team c y c l e " .
F a i l u r e t o r e c o g n i z e t h e i m p o r t a n c e o f t h e e n t i r e t he rma l s y s t e m t o t h e
e n e r g y econoniy may l e a d t o e n e r g y w a s t a g e . To i l l u s t r a t e t h i s p o i n t , t h e a u t h o r
r e c a l l s a s u g a r f a c t o r y he v i s i t e d f o r a s t u d y on p o s s i b l e e n e r g y s a v i n g s ( t h e
f a c t o r y i s s i t u a t e d i n a c o u n t r y known f o r i t s l o n g - s t a n d i n g i n d u s t r i a l
t r a d i t i o n , and f o r q u i t e e f f i c i e n t e n e r g y u t i l i z a t i o n s t i m u l a t e d by i n a d e q u a t e
domes t i c f u e l r e s o u r c e s ) . I n t he power h o u s e , t h e r e were c l e a n and s h i n i n g
i n s u l a t i o n c o v e r s and f r o n t p a n e l s o f somewhat o u t d a t e d , b u t w e l l m a i n t a i n e d ,
b o i l e r s , c a r e f u l l y m a i n t a i n e d t u r b o - g e n e r a t o r s and p e r f e c t l y f u n c t i o n i n g
a u x i l i a r y equ ipment and measur ing i n s t r u m e n t s . Adequate d a t a r e c o r d s were
a v a i l a b l e f o r t h e e v a l u a t i o n o f e n e r g y b a l a n c e s o f t h e power h o u s e . I n t h e
n e i g h b o u r i n g b u i l d i n g c o n t a i n i n g t h e p r o c e s s e q u i p m e n t , h o w e v e r , e v a p o r a t o r
b o d i e s and vacuum pans were s h i n i n g t o o , b u t numerous p r e s s u r e and t e m p e r a t u r e
i n d i c a t o r s were e i t h e r m i s s i n g o r o u t o f o r d e r . On t h e g round f l o o r ,
m a l f u n c t i o n i n g steam t r a p s and l e a k i n g h o t - c o n d e n s a t e l i n e s were f o u n d . Data
r e c o r d s on e n e r g y u t i l i z a t i o n were i n c o m p l e t e and no h e a t b a l a n c e s o f p r o c e s s
equ ipment c o u l d be e s t i m a t e d . I n s h o r t , t h e r e were s i g n s t h a t t h e f a c t o r y
to ammonia ι water tank |
F i g . 1.5. Example o f a scheme o f a the rma l s y s t e m . I - power h o u s e , I I -e v a p o r a t o r . I I I - b e e t h o u s e , I V - s u g a r h o u s e , V - c o n d e n s i n g and c o o l i n g e q u i p m e n t , 1-4 - e v a p o r a t o r e f f e c t s , 5 - e x t r a c t o r , 6 - h e a t e r s , 7 - c o n d e n s e r , 8 - p u l p p r e s s e s , 9 - t h i c k j u i c e t a n k , 10 - m e l t e r , 11 - s y r u p t a n k s , 12 -s u g a r d r y e r , 13 - c o n d e n s a t e t a n k s , 14 - i n t e r m e d i a t e c o n d e n s a t e t a n k , 15 -main f e e d - w a t e r t a n k , 16 - b o i l e r , 17 - t u r b i n e .
managers t r e a t t he power house and t h e p r o c e s s - h e a t i n g a r e a as i f t h e y were n o t
p a r t s o f t he same sys tem i n w h i c h i n t e r a c t i o n s between e n e r g y p r o c e s s e s
d e t e r m i n e t h e o v e r a l l e n e r g y c o n s u m p t i o n . N e e d l e s s t o s a y , t h e f u e l consump t i on
p e r u n i t mass o f b e e t s p r o c e s s e d was v e r y h i g h i n t h i s f a c t o r y .
Now, even i f l a c k o f awareness o f t h e i m p o r t a n c e o f t h e e n t i r e t he rma l
sys tem i s n o t as d r a s t i c , i t may e a s i l y become a cause o f m i s u n d e r s t a n d i n g , o r
f a i l u r e t o r e c o g n i z e , t h e i n t e r d e p e n d e n c e s g o v e r n i n g t h e e n e r g y economy i n
a s u g a r f a c t o r y . On t h e c o n t r a r y , t h e t o t a l app roach o f w h i c h t h e the rma l
s y s t e m c o n c e p t i s o n l y a p a r t makes i t e a s i e r t o g r a s p t h e e s s e n t i a l f e a t u r e s
o f t h e e n e r g y prob lems a n a l y s e d .
1.2.2 Tasks
I t happens a l l t o o o f t e n t h a t t h e s u g a r t e c h n o l o g i s t s a s s i g n a r a t h e r low
p r i o r i t y t o h e a t c o n v e r s i o n and d i s t r i b u t i o n w i t h i n a f a c t o r y , r e q u i r i n g s i m p l y
t h a t t h e h e a t s u p p l y c o v e r t h e p r o c e s s h e a t demand. L e t us o b s e r v e t h a t such
a r e q u i r e m e n t i s ambiguous even i f a l l t h e p r o c e s s pa rame te rs a r e e x a c t l y
s p e c i f i e d , as a d e f i n i t e p r o c e s s h e a t demand can be s a t i s f i e d by v a r i o u s
the rma l sys tems r e q u i r i n g d i f f e r e n t e n e r g y i n p u t s .
A the rma l sys tem can be a n a l y s e d and e v a l u a t e d i n terms o f c e r t a i n n o t i o n s
w h i c h can a l s o be used t o f o r m u l a t e sys tem t a s k s p r e c i s e l y . I n each equ ipment
u n i t i n t h e p r o c e s s h e a t i n g a r e a o f t h e s y s t e m , a c e r t a i n h e a t s t r e a m q^ s h o u l d
be t r a n s f e r r e d t o some p r o c e s s medium. Heat s t reams can be u n i q u e l y d e f i n e d f o r
i n d i v i d u a l equ ipment u n i t s o r g r o u p s o f u n i t s , as a t f i x e d p r o c e s s p a r a m e t e r s ,
hea t b a l a n c e s o f a l l p r o c e s s p a r t s can be s e t up and n e c e s s a r y h e a t i n p u t s can
be i d e n t i f i e d . We a r e t h u s a b l e t o d e f i n e t h e t o t a l h e a t demand as
Ql = q^. ( 1 . 1 )
where η i s t h e t o t a l number o f equ ipment u n i t s o r g r o u p s i n v o l v e d .
I t i s c h a r a c t e r i s t i c o f the rma l sys tems used i n t he s u g a r i n d u s t r y t h a t
m u l t i p l e use o f h e a t t akes p l a c e . Not o n l y i s t h i s t h e u n d e r l y i n g i d e a o f t h e
m u l t i p l e - e f f e c t e v a p o r a t o r , b u t t h e v a p o u r w i t h d r a w n f rom t h e e v a p o r a t o r i s
a l s o used t o h e a t o t h e r equ ipmen t . On t h e o t h e r h a n d , t h e l o s s e s t o t h e
e n v i r o n m e n t a n n i h i l a t e a p a r t o f t h e h e a t c i r c u l a t i n g i n t h e s y s t e m . T h e r e f o r e ,
t h e r e q u i r e d ( n e t ) h e a t i n p u t t o t h e s y s t e m , i s d i f f e r e n t f r om (and u s u a l l y
much s m a l l e r t h a n ) t h e t o t a l h e a t demand.
I t s h o u l d be p o i n t e d o u t t h a t Q2 i s n o t i d e n t i c a l t o t h e p r i m a r y e n e r g y
i n p u t t o t h e f a c t o r y ( s e e S e c t i o n 1 . 2 . 4 ) . I n F i g . 1 .6 , t h e h e a t s t reams and n e t
h e a t demand a r e i l l u s t r a t e d i n a Sankey d iag ram r e p r e s e n t i n g e n e r g y p r o c e s s e s
i n a the rma l s y s t e m . F o r t h e sake o f s i m p l i c i t y , t h e s u g a r m a n u f a c t u r e i s
d i v i d e d i n t o f i v e s u b p r o c e s s e s ( t h a t i s , t h e r e a r e f i v e equ ipment g r o u p s ) .
ki ln gas,water , cossettes
pulp, heat loss
carbonatatii gas.
heat loss
heat loss ^
k evaporator y l osses
vacuum pan vapour
condensate to boiler
F i g . 1.6. Heat s t reams q . and n e t h e a t demand Qp i n a Sankey d iag ram r e p r e s e n t i n g t h e h e a t f l o w s i n a s u g a r f a c t o r y . 1 - e x t r a c t i o n , 2 - j u i c e p u r i f i c a t i o n , 3 - t h i n j u i c e h e a t i n g , 4 - e v a p o r a t i o n , 5 - c r y s t a l l i z a t i o n .
From t h e p o i n t o f v i e w o f e n e r g y economy, i t i s d e s i r a b l e t h a t t h e r a t i o
Κ = Q T / Q 2 ( 1 . 2 )
i s as l a r g e as p o s s i b l e ; i t t e l l s how many t imes on a v e r a g e t h e h e a t i n p u t i s
c i r c u l a t e d i n o r d e r t o s a t i s f y t h e t o t a l h e a t demand. I n t h e f o l l o w i n g , Κ i s
c a l l e d t h e e f f e c t i v e n e s s r a t i o o f t h e the rma l s y s t e m . The v a l u e o f Κ depends on
t h e sys tem l a y o u t , t h a t i s , t h e number and t y p e s o f equ ipment u n i t s , as w e l l as
v a p o u r and c o n d e n s a t e d i s t r i b u t i o n r o u t e s . F o r a sys tem o f known l a y o u t , t h e
e f f e c t i v e n e s s r a t i o may v a r y , depend ing on t h e the rma l p r o p e r t i e s o f equ ipment
u n i t s and pa rame te rs c h a r a c t e r i z i n g t h e p r o c e s s e s o f e n e r g y d i s t r i b u t i o n and
u t i l i z a t i o n . V a l u e s o f Κ as l a r g e as between 4 and 5 have been r e p o r t e d f o r
s u g a r f a c t o r i e s ( r e f s . 1 1 , 1 2 ) . The t e c h n i q u e s used t o i n c r e a s e Κ a r e d i s c u s s e d
i n C h a p t e r s 3 , 8 and 9. H o w e v e r , d i f f e r e n t l a y o u t s , equ ipment and e n e r g y
p r o c e s s e s l e a d t o d i f f e r e n t i a t e d c o s t s o f i n v e s t m e n t , ma in tenance and o p e r a t i o n .
F o r t h i s r e a s o n , t h e r e i s u s u a l l y a p r a c t i c a l r e q u i r e m e n t imposed on Κ t h a t i t s
10
v a l u e s h o u l d be as l a r g e as a l l o w e d by t h e economic c o n s t r a i n t s and c r i t e r i a
a c c o r d i n g t o w h i c h t h e r e s u l t s o f f a c t o r y o p e r a t i o n a r e e v a l u a t e d . I t may be
n o t e d t h a t w i t h t h e e n e r g y c o s t s v a r y i n g between 3% and 17% o f t h e c o s t o f s u g a r
i n v a r i o u s c o u n t r i e s , t h e most economic v a l u e s o f Κ may be w i d e l y d i f f e r e n t i a t e d .
A l s o , unde r t i m e - v a r y i n g economic c o n d i t i o n s r e s u l t i n g f rom e l e c t r i c i t y t a r i f f s
w h i c h v a r y f rom month t o month d u r i n g t h e autumn and w i n t e r p e r i o d , v a r i a t i o n s
o f t h e e f f e c t i v e n e s s r a t i o d u r i n g p r o d u c t i o n may be j u s t i f i e d ( r e f . 1 3 ) .
I t s h o u l d be n o t e d t h a t o t h e r i n d i c e s have a l s o been p r o p o s e d i n t h e
l i t e r a t u r e f o r e v a l u a t i o n o f t h e e n e r g y p r o c e s s e s t a k i n g p l a c e i n t h e the rma l
s y s t e m . German s o u r c e s ( r e f . 12) employ t h e n o t i o n o f e f f i c i e n c y o f t h e the rma l
sys tem d e f i n e d by t h e f o r m u l a
η = 1 - Q2/Q1 = 1 - 1/K ( 1 . 3 )
1.2.3 B u i l d i n g b l o c k s
The sys tem p a r t s shown i n F i g . 1.5 a r e component g roups o r i n d i v i d u a l
components t h a t c u s t o m a r i l y r e c e i v e s e p a r a t e t r e a t m e n t i n e n e r g y a n a l y s e s .
A l t h o u g h t h e s e p a r t s a r e c e r t a i n l y i m p o r t a n t , such a " d e e p " d e c o m p o s i t i o n does
n o t c o n t r i b u t e much t o u n d e r s t a n d i n g o f t h e e s s e n t i a l f e a t u r e s o f e n e r g y
p r o c e s s e s . A b e t t e r i n s i g h t i s g a i n e d by l o o k i n g a t t h e subsys tems d e f i n e d
a c c o r d i n g t o a n o t h e r d e c o m p o s i t i o n p r i n c i p l e , i n d i c a t e d by t h e dashed l i n e s i n
F i g . 1.5 and a d d i t i o n a l l y i l l u s t r a t e d by t h e scheme shown i n F i g . 1 . 7 ( a ) . The
f u n c t i o n o f t h i s v e r s i o n o f t h e the rma l s y s t e m can be summar ized as f o l l o w s :
- u s i n g p r i m a r y e n e r g y s u p p l i e d i n f u e l , combined g e n e r a t i o n o f h e a t ( c a r r i e d
away by steam e x t r a c t e d f rom t h e t u r b i n e e x h a u s t ) and e l e c t r i c a l power t akes
p l a c e i n t he power h o u s e ,
- hea t s u p p l i e d i n h e a t i n g steam t o t h e e v a p o r a t o r s t a t i o n g e n e r a t e s v a p o u r s
( o f w h i c h a sma l l f r a c t i o n may be d i r e c t e d t o t h e c o n d e n s e r ) and h o t c o n d e n s a t e ;
t he t o t a l q u a n t i t y o f w a t e r e v a p o r a t e d i s p r e d e t e r m i n e d by t h e n e c e s s i t y o f
t r a n s f o r m i n g t h i n j u i c e i n t o t h i c k j u i c e ,
- a p a r t o f t he h o t c o n d e n s a t e i s r e t u r n e d t o t h e power h o u s e ; t h e v a p o u r s and
t h e rema in i ng c o n d e n s a t e a r e used t o t r a n s p o r t h e a t t o t h e j u i c e h e a t e r s , vacuum
pans and o t h e r p r o c e s s equ ipment i n t h e b e e t house and s u g a r h o u s e ,
- a f r a c t i o n o f h e a t s u p p l i e d t o t h e p r o c e s s i s d i s s i p a t e d t o t h e e n v i r o n m e n t
o r c a r r i e d away by o u t f l o w i n g p r o d u c t s o r was te m e d i a , and t h e main p a r t i s
c a r r i e d away by v a p o u r s g e n e r a t e d i n vacuum p a n s ,
- t h e vacuum pan v a p o u r s a r e n o t u t i l i z e d b u t d i r e c t e d t o t h e c o n d e n s e r , where
t h e i r e n e r g y i s a b s o r b e d and removed i n b a r o m e t r i c w a t e r ( i . e . , c o o l i n g w a t e r
mixed w i t h condensed v a p o u r s ) ; t h i s e n e r g y must be f i n a l l y d i s s i p a t e d t o t h e
e n v i r o n m e n t i n a s y s t e m component n o t shown i n t h e scheme ( e . g . c o o l i n g t o w e r s ,
c o o l i n g p o n d , r i v e r o r l a k e ) .
11
-Ό C
t í 3 c χ : -Μ <o
4-> υ χ : to o χ : *f- χ •Μ 3 ω •Γ- C 5 «3 + J
Ε (Ο ^ <ϋ S- ^ — <ο I σ> ω
· » 3 + J ι— 4Λ to <ο <ο o e s
• ι - ω to ω ι to S ίΟ -Μ UD
ι— ω ο XI ·«
<ο ο to " Ι - C
· · ο -σ · (Λ <υ α i-Ε C ο (υ <υ C ο (Λ ο ι -σ to r— LO Q .
t— Ε • ' ^
ío $- <υ Q . Ε <U «Λ S. ^ Ζ( O) ω -M O SZ Z3
4 J ^ + J Μ- · ι - <0 S-o 5 σ> <υ σ) to Ε <υ -o <υ Q . s ^ ι 4-> >> ι
C O s- o «»f— O to to I
Μ- to 13 <U O CT»
Μ- ι - ^ O CL
E -Μ J -to O (U 0) ω α <υ >» ο. ί- -σ
• ι - 3 1 U ο Q . C Ο-ΓΟ I — •Γ- ίΟ Ζ3
i- > - ο . ^ ο ω
C7)4-> 4-> i -C - r - ίΟ 3 •Γ- 5 $- 4->
Ο <ο S- ^ CL $-Ο U ro <υ 5 — > Q .
0) ε (Λ Ο ^ ο . «^-Γ-ο «S ω ^ ο > ίΛ
ι— 3 I ^ C ο
<0 ^ 00 0> Q . C i - -·.- ε ω J -
^ 5 ο · — 13 ο V ) •Γ- ο Q . V ) J D > I S-= ^ . ^ i •
ο C S-1^ >> ο
. «ο $ ο . ι— Ν -σ <ο
•I- > • r— O l
σ>·Γ- Γ - I •Γ- 4-> Ζ3
12
The f o l l o w i n g b u i l d i n g b l o c k s can t hus be named w i t h i n t h e s y s t e m : power h o u s e ,
m u l t i p l e - e f f e c t ( m u l t i - s t a g e ) e v a p o r a t o r , p r o c e s s equ ipment i n t h e b e e t house
and i n t h e s u g a r h o u s e , and c o n d e n s e r ( a l s o r e p r e s e n t i n g a s s o c i a t e d c o o l i n g
e q u i p m e n t ) . I n F i g . 1 . 7 ( a ) , t h e w i d t h o f t h e s t r i p s l i n k i n g t h e b l o c k s i n d i c a t e
a p p o x i m a t e l y t h e p r o p o r t i o n a t e e n e r g y s t reams c i r c u l a t e d .
The e s s e n t i a l l a y o u t o f e n e r g y c o n v e r s i o n and d i s t r i b u t i o n p r o c e s s e s
e x p l a i n e d above i s by f a r t h e most commonly a p p l i e d i n c o n t e m p o r a r y s u g a r p l a n t s .
L e t us use i t as a s t a r t i n g p o i n t f o r a s h o r t p r e s e n t a t i o n o f o t h e r p o s s i b l e
l a y o u t s . F o r t he sake o f s i m p l i c i t y , i t w i l l be assumed t h a t t h e pa rame te rs o f
t he s u g a r m a n u f a c t u r i n g p r o c e s s a r e f i x e d , t h a t i s , t h e t o t a l hea t demand
remains c o n s t a n t .
Suppose t h a t i n s t e a d o f d i r e c t i n g t h e e n t i r e e n e r g y s t ream c a r r i e d by vacuum
pan vapou rs t o t h e c o n d e n s e r , a p a r t o f i t i s r e - u s e d i n p r o c e s s h e a t i n g , as
shown s c h e m a t i c a l l y i n F i g . 1 . 7 ( b ) . A p r e r e q u i s i t e ( i . e . an a d d i t i o n a l
c o n s t r a i n t t o be s a t i s f i e d ) f o r t h i s i s t h e e x i s t e n c e o f l o w - t e m p e r a t u r e p r o c e s s
p a r t s where t he t e m p e r a t u r e o f vacuum pan v a p o u r s c o u l d be r e g a r d e d as
s u f f i c i e n t l y h i g h t o a l l o w e f f i c i e n t h e a t i n g . I f p r a c t i c a b l e , t h i s g i v e s t h e
p o s s i b i l i t y o f s a v i n g e n e r g y by r e d u c i n g t h e demand f o r v a p o u r s f rom t h e
e v a p o r a t o r a n d , c o n s e q u e n t l y , d e c r e a s i n g steam demand a t t h e e v a p o r a t o r i n l e t .
H o w e v e r , t h i s p o s s i b i l i t y can be r e a l i z e d o n l y i f t h e e v a p o r a t i o n p r o c e s s i s
m o d i f i e d so as t o s a t i s f y t h e c o n d i t i o n s t h a t t h e t o t a l q u a n t i t y o f w a t e r
e v a p o r a t e d remains unchanged .
Now, suppose t h a t an a t t emp t i s made t o a p p l y one o f t h e above l a y o u t s , b u t
i t t u r n s o u t t h a t t he demand f o r v a p o u r s f rom t h e e v a p o r a t o r i s so sma l l t h a t
t h e r e q u i r e d q u a n t i t y o f w a t e r can be e v a p o r a t e d o n l y i f a l a r g e v a p o u r f l o w t o
t h e c o n d e n s e r i s a l l o w e d . T h i s must be i n t e r p r e t e d as an i n d i c a t i o n t h a t a n o t h e r
e n e r g y - s a v i n g b l o c k s h o u l d be added t o t h e s y s t e m , as shown i n F i g . 1 . 7 ( c ) .
A v a p o u r compresso r r a i s i n g t h e p r e s s u r e o f a p a r t o f t h e v a p o u r s makes i t
p o s s i b l e t o r e c y c l e t h e compressed steam and t o use i t f o r h e a t i n g p u r p o s e s i n
t he e v a p o r a t o r . The r e c y c l e d h e a t d e c r e a s e s t h e h e a t demand a t t h e e v a p o r a t o r
i n l e t , r e s u l t i n g i n a h e a t s a v i n g as shown i n t h e scheme.
As f a r as t h e s u g a r m a n u f a c t u r i n g p r o c e s s i s c o n c e r n e d , m u l t i - s t a g e
e v a p o r a t i o n w i t h v a p o u r w i t h d r a w a l , u t i l i z a t i o n o f vacuum pan v a p o u r s , and
v a p o u r c o m p r e s s i o n a r e t h e main e n e r g y c o n v e r s i o n p r o c e s s e s and t hus a l s o t h e
main f u n c t i o n s o f t h e b u i l d i n g b l o c k s o f t he rma l s y s t e m s . P o s s i b l e v a r i a n t s o f
t h e b u i l d i n g b l o c k s and t h e i r v a r i o u s c o m b i n a t i o n s a r e p r e l i m i n a r i l y p r e s e n t e d
i n t h e r e m a i n i n g S e c t i o n s o f t h i s C h a p t e r . Note t h a t any the rma l s y s t e m has t o
s a t i s f y t h e p r o c e s s - i m p o s e d c o n s t r a i n t s men t ioned a b o v e . O t h e r c o n s t r a i n t s and
t h e i n t e r a c t i o n s between them, seen f rom d i f f e r e n t p o i n t s o f v i e w , a r e d i s c u s s e d
when p r e s e n t i n g t h e d e t a i l s o f t h e b u i l d i n g b l o c k s i n t h e f o l l o w i n g S e c t i o n s and
13
C h a p t e r s .
An i m p o r t a n t b y - p r o c e s s employed i n a m a j o r i t y o f c o n t e m p o r a r y b e e t s u g a r
f a c t o r i e s i s p u l p d r y i n g . I t i s n o t unusua l t h a t i t r e q u i r e s 35% o r even more
o f t h e f a c t o r y ' s o v e r a l l ( i . e . , f o r s u g a r m a n u f a c t u r e and p u l p d r y i n g
c o n s i d e r e d j o i n t l y ) demand f o r p r i m a r y e n e r g y . From t h e p o i n t o f v i e w o f e n e r g y
u t i l i z a t i o n a t y p i c a l d r y i n g p l a n t , c o n s i s t i n g o f a d r y e r and a f u r n a c e where
f u e l i s bu rned i n o r d e r t o g e n e r a t e h o t g a s e s , i s r a t h e r p r i m i t i v e .
C o n s e q u e n t l y , much a t t e n t i o n has r e c e n t l y been d e v o t e d t o r a t i o n a l i z i n g t h e
e n e r g y usage i n p u l p d r y i n g . P o s s i b l e e n e r g y s a v i n g m o d i f i c a t i o n s o f t h e p r o c e s s
l a y o u t and pa ramete rs a r e d i s c u s s e d i n S e c t i o n 1 .2 .8 .
I n a s u g a r f a c t o r y emp loy ing p u l p d r y i n g , an e n e r g y - s a v i n g p o t e n t i a l e x i s t s
a l s o i n t h e the rma l c o u p l i n g between t h i s p r o c e s s and o t h e r f a c t o r y a r e a s . An
e a r l y i d e a , d e v e l o p e d s e v e r a l decades a g o , was t o mix h o t f l u e gas f rom b o i l e r s
w i t h a i r s u p p l i e d t o t h e f u r n a c e , t hus r e d u c i n g t h e f u e l consumpt i on i n t h e
d r y i n g p l a n t . More r e c e n t l y , bo th t h e u t i l i z a t i o n o f d r y e r o u t l e t gas i n t h e
p r o c e s s h e a t i n g i n s u g a r manu fac tu re and t h e u t i l i z a t i o n o f w a s t e h e a t f rom
s u g a r manu fac tu re i n t h e p u l p d r y i n g were i n t r o d u c e d , as shown s c h e m a t i c a l l y i n
F i g . 1 . 7 ( d ) . U s i n g t h e s e t e c h n i q u e s , t h e c o n s t r a i n t s imposed on t h e the rma l
sys tem by t h e s u g a r m a n u f a c t u r i n g p r o c e s s a r e f a v o u r a b l y m o d i f i e d , c r e a t i n g new
p o s s i b i l i t i e s o f e n e r g y s a v i n g s . The u n d e r l y i n g c o n c e p t s a r e d i s c u s s e d i n
S e c t i o n 1 .2 .9 .
1.2.4 Power house
The w o r k i n g p r i n c i p l e o f t h e power houses i n c o n t e m p o r a r y s u g a r f a c t o r i e s
c o n s i s t s o f b u r n i n g f u e l i n a b o i l e r w h i c h s u p p l i e s l i v e steam t o a b a c k
p r e s s u r e t u r b i n e . The t u r b i n e d r i v e s an e l e c t r i c a l g e n e r a t o r w h i c h s u p p l i e s
e l e c t r i c a l power t o t he f a c t o r y ; s i m u l t a n e o u s l y , t h e steam f rom t h e t u r b i n e
e x h a u s t i s d e l i v e r e d t o t h e e v a p o r a t o r s t a t i o n .
T h e r e a r e two i m p o r t a n t c o n s t r a i n t s r e s u l t i n g f rom t h e p r o p e r t i e s o f t h e
power house equ ipment and a f f e c t i n g t h e c h a r a c t e r i s t i c s o f t h e e n t i r e the rma l
s y s t e m :
( i ) The c o n v e r s i o n o f l i v e - s t e a m e n e r g y t a k i n g p l a c e i n t h e t u r b i n e i s
c h a r a c t e r i z e d by a d e f i n i t e r a t i o between e n e r g y c o n v e r t e d i n t o e l e c t r i c i t y and
e x h a u s t - s t e a m e n e r g y w h i c h i s a v a i l a b l e f o r h e a t i n g . From t h e demand
c h a r a c t e r i s t i c s o f t h e e n t i r e f a c t o r y , a d i f f e r e n t p r o p o r t i o n between t h e power
demand and n e t h e a t demand may r e s u l t . O n l y i f t h e e v e n t u a l mismatch p rob lem i s
e f f e c t i v e l y r e s o l v e d by some s p e c i a l measures ( s e e S e c t i o n 1 .5 .3 ) can t h e power
house be r e g a r d e d as a s u i t a b l e e n e r g y s o u r c e f o r a p a r t i c u l a r t he rma l s y s t e m .
( i i ) The c o n v e r s i o n o f p r i m a r y e n e r g y i n t o l i v e - s t e a m e n e r g y t a k i n g p l a c e i n t h e
b o i l e r i s a s s o c i a t e d w i t h e n e r g y l o s s e s o f t h e o r d e r o f 10-20% o r even more .
14
The r e s u l t i n g demand f o r p r i m a r y e n e r g y i s equa l t o t h e sum o f l i v e - s t e a m
e n e r g y and b o i l e r l o s s e s . O n l y i f t h e the rma l c o n n e c t i o n between t h e power
house and p r o c e s s h e a t i n g i s m o d i f i e d can t h e s e l o s s e s be p a r t l y r e c o v e r e d ,
r e s u l t i n g i n a r e d u c t i o n o f t h e t o t a l e n e r g y l o s s f rom t h e the rma l sys tem and
t hus r e d u c i n g t h e demand f o r p r i m a r y e n e r g y .
The prob lems i n d i c a t e d may come i n t o q u e s t i o n i n new o r e x i s t i n g f a c t o r i e s
o p e r a t e d u n d e r d i f f e r e n t l o c a l c o n d i t i o n s and s u b j e c t t o t he i n f l u e n c e o f
d i f f e r e n t economic f a c t o r s . As t h i s d e f i n e s an a r r a y o f w i d e l y d i v e r s i f i e d
s i t u a t i o n s , i t can h a r d l y be imag ined t h a t a steam b o i l e r and a b a c k - p r e s s u r e
t u r b i n e do r e a l l y p r o v i d e a u n i v e r s a l power house s o l u t i o n . A d i s c u s s i o n o f
v a r i o u s s i t u a t i o n s and s o l u t i o n s i s p r e s e n t e d i n S e c t i o n 1.5.
1.2.5 E v a p o r a t o r
The dom ina t i ng e v a p o r a t o r a r rangemen t i s t h a t u s i n g t h e m u l t i p l e - e f f e c t ,
p a r a l l e l - f l o w p r i n c i p l e s c h e m a t i c a l l y shown i n F i g . 1.5. T h r e e t o s i x e f f e c t s
a r e u s e d , f o u r o r f i v e b e i n g t h e commonest s o l u t i o n . The o r i g i n a l i d e a o f u s i n g
t he hea t as many t imes as t h e r e a r e e f f e c t s i n t h e e v a p o r a t o r ( R i l l i e u x
p r i n c i p l e ) has been m o d i f i e d by v a p o u r w i t h d r a w a l f o r h e a t i n g p u r p o s e s . W h i l e
t h i s r e s u l t s i n w o r s e h e a t u t i l i z a t i o n i n t h e e v a p o r a t o r i t s e l f , t h e v a p o u r
w i t h d r a w a l t u r n s o u t t o be d e c i s i v e i n e n s u r i n g a h i g h l y e f f i c i e n t h e a t
u t i l i z a t i o n i n t h e e n t i r e s u g a r f a c t o r y . T h i s p rob lem i s a d d i t i o n a l l y d i s c u s s e d
i n C h a p t e r 3 , and p r a c t i c a l examples a r e g i v e n i n C h a p t e r s 8 and 9.
As a b u i l d i n g b l o c k i n a the rma l s y s t e m , t h e e v a p o r a t o r s h o u l d be adap ted t o
t h e p r o c e s s - i m p o s e d c o n s t r a i n t a l r e a d y m e n t i o n e d , namely t h e p r e d e t e r m i n e d
p e r c e n t a g e o f w a t e r t o be e v a p o r a t e d . A n o t h e r i m p o r t a n t c o n s t r a i n t i s c o n c e r n e d
w i t h t h e j u i c e t e m p e r a t u r e i n t h e h e a t i n g chamber o f t h e f i r s t e v a p o r a t o r
e f f e c t , name ly , i n o r d e r t o p r e v e n t e x c e s s i v e the rma l decay o f s u c r o s e , t h i s
t e m p e r a t u r e must n o t e x c e e d 125-130°C. A number o f p r o p o s a l s on e v a p o r a t o r
a r rangemen t have been made w h i c h aim t o e n s u r e e f f i c i e n t h e a t u t i l i z a t i o n w h i l e
a l s o s a t i s f y i n g t h e c o n s t r a i n t s ; t h e s e p r o p o s a l s have been r e v i e w e d e l s e w h e r e
( r e f . 3 ) . A q u i n t u p l e - e f f e c t e v a p o r a t o r , w i t h p a r a l l e l f l o w o f j u i c e and v a p o u r
i n e f f e c t s 1 t h r o u g h 4 and c o u n t e r - f l o w i n e f f e c t 5, i s shown s c h e m a t i c a l l y i n
F i g . 1.8.
I n modern the rma l sys tems where t h e h e a t i n g needs have been r e d u c e d t o
a minimum, t h e o v e r a l l demand f o r v a p o u r s w i t h d r a w n f rom t h e e v a p o r a t o r may be
l e s s than t h e amount o f w a t e r t o be e v a p o r a t e d , t h u s making t h e w a t e r
p e r c e n t a g e c o n s t r a i n t d i f f i c u l t t o s a t i s f y . An i n c r e a s e d f l o w o f l a s t - e f f e c t
v a p o u r t o t h e c o n d e n s e r can h a r d l y be a c c e p t e d , as t h i s wou ld be a d i r e c t
e n e r g y l o s s r e q u i r i n g a c o r r e s p o n d i n g i n c r e a s e o f t h e h e a t i n g steam s u p p l y t o
t h e f i r s t e f f e c t . H o w e v e r , t h i s s i t u a t i o n can be changed i f u n c o n v e n t i o n a l
e v a p o r a t i o n s t a g e s hea ted w i t h l o w - t e m p e r a t u r e o r was te h e a t a r e a t t a c h e d t o
15
e x h a u s t s team ' \ -
η 128°C
\ th in j u i ce
14 .5%DS.90°C
th ick ju ice 7 2 % D S . 9 4 ° C _
F i g . 1.8. Scheme o f a m u l t i p l e - e f f e c t e v a p o r a t o r f e a t u r i n g c o u n t e r - f l o w o f j u i c e and h e a t i n g v a p o u r i n t he f i f t h e f f e c t . 1-5 - e v a p o r a t o r e f f e c t s , 6 - j u i c e h e a t e r s .
t h e c l a s s i c a l e v a p o r a t o r . An i n t r o d u c t i o n t o p o s s i b l e s o l u t i o n s based on t h i s
p r i n c i p l e i s g i v e n i n S e c t i o n 1 .2 .6 . As an a l t e r n a t i v e , t h e c l a s s i c a l m u l t i
s t a g e e v a p o r a t i o n can be combined w i t h v a p o u r c o m p r e s s i o n , as o u t l i n e d i n
S e c t i o n 1 .2 .7 .
I n each e v a p o r a t o r e f f e c t , w h i l e v a p o u r i s g e n e r a t e d a t a c e r t a i n r a t e ,
condensa te must be d r a i n e d a t an a p p r o x i m a t e l y equa l r a t e f rom t h e h e a t i n g
chamber. The c o n d e n s a t e i s f l a s h e d ( f l a s h - e v a p o r a t e d ) , g e n e r a t i n g a d d i t i o n a l
v a p o u r , t h e e n e r g y o f w h i c h can be u t i l i z e d i n t h e s u b s e q u e n t e f f e c t s . Among
v a r i o u s a r rangements o f t h e c o n d e n s a t e s u b s y s t e m , t h e cascade f l a s h shown
s c h e m a t i c a l l y i n F i g . 1.5 i s t he most e f f e c t i v e s o l u t i o n . F i r s t - e f f e c t and
p o s s i b l y s e c o n d - e f f e c t c o n d e n s a t e a r e t y p i c a l l y used as b o i l e r f e e d - w a t e r , w h i l e
t he condensa tes f rom t h e r e m a i n i n g e f f e c t s can be u t i l i z e d i n t h e p r o c e s s
h e a t i n g and f o r o t h e r p u r p o s e s . V a r i o u s a s p e c t s o f t h e c o n d e n s a t e usage a r e
d i s c u s s e d i n C h a p t e r s 3 , 8 and 9.
The impo r t ance o f t he e v a p o r a t o r t o t h e e n e r g y c o n v e r s i o n and d i s t r i b u t i o n i n
a the rma l sys tem imposes s p e c i a l r e q u i r e m e n t s on t h e e v a p o r a t i o n p r o c e s s , as
w e l l as t he a s s o c i a t e d equ ipment and c o n t r o l s y s t e m s . New deve lopmen ts i n t h e s e
a reas a r e m a i n l y d i s c u s s e d i n C h a p t e r s 5 and 6.
1.2.6 U t i l i z a t i o n o f l o w - t e m p e r a t u r e o r was te h e a t
As t h e vacuum pans a r e s u p p l i e d w i t h t h e h e a t r e q u i r e d f o r s u g a r b o i l i n g , and
the p r o c e s s media a r e c o n t i n u o u s l y hea ted i n o r d e r t o s t a b i l i z e t h e t e m p e r a t u r e s
needed f o r i m p o r t a n t u n i t o p e r a t i o n s , s t reams o f l o w - t e m p e r a t u r e h e a t become
a v a i l a b l e , m a i n l y i n vacuum pan v a p o u r s and s p e n t c a r b o n a t a t i o n g a s . T h e r e a r e
s t i l l many f a c t o r i e s where t h e l o w - t e m p e r a t u r e h e a t i s c o n s i d e r e d u s e l e s s , so
t he vapou rs a r e d i r e c t e d t o t h e c o n d e n s e r and t h e c a r b o n a t a t i o n gas i s
d i s c h a r g e d d i r e c t l y t o t h e a tmosphe re . H o w e v e r , i f t h e s u g a r m a n u f a c t u r i n g
p r o c e s s i s so a r r a n g e d t h a t i n c e r t a i n p a r t s o f t h e w a t e r and j u i c e f l o w s t h e
t empe ra tu re i s low enough ( t h a t i s , l o w e r t han t h e t e m p e r a t u r e o f vacuum pan
16
v a p o u r s o r s p e n t c a r b o n a t a t i o n g a s ) , t h e n t he l o w - t e m p e r a t u r e h e a t can be
u t i l i z e d . T y p i c a l " c o l d " media a r e raw j u i c e a n d , i n some i n s t a n c e s , w a t e r
s u p p l i e d t o t h e e x t r a c t o r , and p r e - l i m e d j u i c e .
One o f t h e o b s t a c l e s t o u t i l i z i n g l o w - t e m p e r a t u r e h e a t i s t h a t t h e n e c e s s a r y
equ ipment may be a b i t t r o u b l e s o m e . I n a j u i c e h e a t e r hea ted by vacuum pan
v a p o u r s , t h e s p e c i f i c volume o f v a p o u r i s so l a r g e t h a t i t n e c e s s i t a t e s a h i g h
f l o w v e l o c i t y . T h i s i n v o l v e s t he r i s k , among o t h e r s , o f t ube v i b r a t i o n a n d , as
t he w a t e r c o n t e n t i n v a p o u r f l o w i n g t h r o u g h t h e h e a t e r i n c r e a s e s , t u b e e r o s i o n .
When r e c o v e r i n g t he c a r b o n a t a t i o n h e a t l o s s i n a s u r f a c e hea t e x c h a n g e r , a low
f i l m c o e f f i c i e n t o f h e a t t r a n s f e r between t h e gas and t h e h e a t i n g s u r f a c e i s
u n a v o i d a b l e , and t hus a r e l a t i v e l y l a r g e h e a t i n g s u r f a c e a r e a may be r e q u i r e d .
I n t he case o f c a r b o n a t a t i o n - g a s r e c i r c u l a t i o n , p o w e r - e x p e n s i v e pumping may a l s o
be n e c e s s a r y .
P r o v i d i n g r e l i a b l e and n o t t o o c o s t l y equ ipment i s a v a i l a b l e , t h e
r e c i r c u l a t e d l o w - t e m p e r a t u r e h e a t can r e p l a c e an e q u i v a l e n t p o r t i o n o f t h e hea t
i n vapou rs w i t h d r a w n f rom t h e e v a p o r a t o r , t hus making i t p o s s i b l e t o r e d u c e t h e
h e a t i n g steam demand a t t he e v a p o r a t o r i n l e t . The h e a t i n g by vacuum pan v a p o u r s
i s a d d i t i o n a l l y d i s c u s s e d i n C h a p t e r 3 , and t h e t e c h n i q u e s used t o r e d u c e t h e
c a r b o n a t a t i o n h e a t l o s s i n C h a p t e r 4 .
C e r t a i n s t reams o f l o w - t e m p e r a t u r e hea t l e a v i n g t h e f a c t o r y a r e so d i f f i c u l t
t o u t i l i z e t h a t t h e y a r e t r a d i t i o n a l l y c a l l e d " w a s t e h e a t " . (Some a u t h o r s use
t h i s te rm f o r a l l t h e hea t s t reams t h a t a r e f i n a l l y d i s c h a r g e d t o t h e
e n v i r o n m e n t , i n c l u d i n g t h e l o w - t e m p e r a t u r e h e a t ) . I t may i n c l u d e , among o t h e r
componen ts , h e a t c a r r i e d by o u t l e t gas f rom t h e p u l p d r y e r , e x c e s s c o n d e n s a t e
f rom t h e e v a p o r a t o r and even b a r o m e t r i c w a t e r p r i o r t o e n t e r i n g t h e c o o l i n g
t o w e r s . I t s h o u l d be emphas ized t h a t t h e u t i l i z a t i o n o f was te h e a t i s now
r e a l i z a b l e , a l t h o u g h n o t a lways e c o n o m i c a l l y f e a s i b l e .
Both l o w - t e m p e r a t u r e and was te hea t can be u t i l i z e d i n j u i c e and s y r u p
e v a p o r a t i o n pe r fo rmed a t a s u f f i c i e n t l y low t e m p e r a t u r e , t h a t i s , u n d e r h i g h
vacuum. S p e c i a l v a p o u r - and g a s - h e a t e d e v a p o r a t o r s a r e b e i n g d e v e l o p e d f o r t h i s
p u r p o s e , as d i s c u s s e d i n C h a p t e r 5. A l t e r n a t i v e methods o f u t i l i z a t i o n o f l o w -
t e m p e r a t u r e hea t employ the rma l c o n n e c t i o n s between s u g a r m a n u f a c t u r e and p u l p
d r y i n g . T h i s i s p a r t i c u l a r l y i n t e r e s t i n g i f t h e s o - c a l l e d l o w - t e m p e r a t u r e d r y i n g
i s a p p l i e d , as o u t l i n e d i n S e c t i o n 1 .2 .9 .
1.2.7 Vapou r compresso rs
As i n d i c a t e d i n S e c t i o n 1.2.3 a b o v e , v a p o u r c o m p r e s s i o n i s a t e c h n i q u e w h i c h
can be used t o r e s o l v e a c o n f l i c t between t h e p o t e n t i a l r e d u c t i o n s o f t h e v a p o u r
demand and t he p r o c e s s c o n s t r a i n t on w a t e r q u a n t i t y t o be e v a p o r a t e d f rom j u i c e .
By i n t r o d u c i n g v a p o u r c o m p r e s s i o n t o t h e the rma l s y s t e m , i t becomes p o s s i b l e t o
e v a p o r a t e the r e q u i r e d w a t e r amount w h i l e r e c i r c u l a t i n g t h e p o r t i o n o f t h e
17
e v a p o r a t i o n h e a t w h i c h exceeds t h e hea t demand o f v a p o u r - h e a t e d equ ipment
o u t s i d e t h e e v a p o r a t o r .
Most o f t e n , t h e v a p o u r t o be compressed i s t aken f rom th-e f i r s t e f f e c t a n d ,
i t s p r e s s u r e r a i s e d , i s s u p p l i e d t o t he h e a t i n g chamber o f t h e same e f f e c t .
A the rma l machine t r a n s f e r r i n g , a t t he expense o f w o r k , h e a t f rom a l o w -
t e m p e r a t u r e body t o a h i g h - t e m p e r a t u r e body i s known as a h e a t pump. I n a
t y p i c a l the rma l sys tem i n a s u g a r f a c t o r y , t h e r e a r e numerous p o t e n t i a l h e a t
pump a p p l i c a t i o n s o t h e r than h e a t r e c i r c u l a t i o n i n t h e f i r s t e v a p o r a t o r e f f e c t .
G e n e r a l l y , t he e n e r g y t r a n s p o r t i s i n i t i a t e d a t t h e h i g h e s t t e m p e r a t u r e / p r e s s u r e
l e v e l c o r r e s p o n d i n g t o t h e pa ramete rs o f l i v e steam and t h e n c o n t i n u e d a t t h e
g r a d u a l l y d e c r e a s i n g t e m p e r a t u r e s and p r e s s u r e s o f media c i r c u l a t e d i n v a r i o u s
p a r t s o f t h e the rma l s y s t e m . The l o w e s t l e v e l , a t w h i c h t h e e n e r g y t r a n s p o r t i s
t e r m i n a t e d , i s d e f i n e d by t h e t e m p e r a t u r e o f b a r o m e t r i c w a t e r and t h e
a t m o s p h e r i c p r e s s u r e . T h e o r e t i c a l l y , t h e h e a t pump p r i n c i p l e can be a p p l i e d
between any two d i f f e r e n t t e m p e r a t u r e / p r e s s u r e l e v e l s . By s u p p l y i n g e n e r g y (as
e l e c t r i c a l power o r l i v e s team) t o t h e h e a t pump, i t becomes p o s s i b l e t o
r e c i r c u l a t e a c e r t a i n amount o f h e a t , t hus c u t t i n g down t h e n e t h e a t demand o f
t he therma l s y s t e m .
I n r e a l i t y , t h e number o f f e a s i b l e h e a t pump a p p l i c a t i o n s i n a t he rma l
sys tem i s l i m i t e d . F o r e x a m p l e , t h e h e a t r e c o v e r y f rom t h e b a r o m e t r i c w a t e r ,
a l t h o u g h r e a l i z a b l e , c a n n o t be pe r fo rmed by v a p o u r c o m p r e s s i o n ; i n s t e a d , i t
r e q u i r e s complex and c o s t l y m a c h i n e r y , making t h e s o l u t i o n uneconomic . F i g u r e
1.9 shows f i v e p o s s i b l e l o c a t i o n s o f v a p o u r compresso rs t o r e c i r c u l a t e h e a t i n
a the rma l sys tem w i t h a q u a d r u p l e - e f f e c t e v a p o r a t o r . I t s h o u l d be p o i n t e d o u t
t h a t t h e s e l o c a t i o n s a r e by no means e q u i v a l e n t t o each o t h e r . I n g e n e r a l , i f
e n e r g y s a v i n g s a r e t o be o b t a i n e d , t hen t h e h e a t r e c i r c u l a t i o n t a k i n g p l a c e i n
a c e r t a i n p a r t o f t h e the rma l s y s t e m must be c o o r d i n a t e d w i t h mass and e n e r g y
Γ "
e x h a u s t ) s t e a m
6
F i g . 1.9. P o s s i b l e l o c a t i o n s o f v a p o u r c o m p r e s s o r s r e l a t i v e t o e s s e n t i a l components o f a the rma l sys tem w i t h a q u a d r u p l e - e f f e c t e v a p o r a t o r s u p p l y i n g s e c o n d - e f f e c t v a p o u r t o vacuum-pan h e a t i n g . 1-4 - e v a p o r a t o r e f f e c t s , 5 - vacuum p a n s , 6 - c o n d e n s e r .
s team
c o m p r e s s e d
v a p o u r
v a p o u r
F i g . 1.10. Work ing p r i n c i p l e o f a j e t - t y p e c o m p r e s s o r .
f l o w s i n o t h e r p a r t s o f t he s y s t e m . F o r e x a m p l e , i f vacuum pan v a p o u r i s
compressed and r e - u s e d t o hea t t h e vacuum p a n s , t h e n t h e demand f o r v a p o u r f rom
the e v a p o r a t o r i s r e d u c e d . As t h e amount o f w a t e r t o be removed f rom j u i c e must
be h e l d c o n s t a n t , t h e d i s t r i b u t i o n o f v a p o u r s w i t h d r a w n f rom t h e e v a p o r a t o r
must be p r o p e r l y a d j u s t e d ; o t h e r w i s e , i t may be n e c e s s a r y t o i n c r e a s e t h e e n e r g y
l o s s r e s u l t i n g f rom t h e f l o w o f l a s t - e f f e c t v a p o u r t o t h e c o n d e n s e r , pe rhaps
making t h e i d e a o f v a p o u r c o m p r e s s i o n m e a n i n g l e s s .
As r e g a r d s t h e e q u i p m e n t , b o t h j e t - t y p e compresso rs ( t h e r m o c o m p r e s s o r s ) and
mechan ica l compresso rs ( t u r b o c o m p r e s s o r s ) can be u s e d . The j e t - t y p e c o m p r e s s o r
( F i g . 1.10) must be c o n t i n u o u s l y s u p p l i e d w i t h l i v e s t eam, b y - p a s s i n g t h e t u r b o
g e n e r a t o r and n o t c o n t r i b u t i n g t o e l e c t r i c i t y g e n e r a t i o n . Depend ing on t h e
i n l e t and o u t l e t p r e s s u r e s o f t h e v a p o u r c o m p r e s s e d , t he c o m p r e s s i o n r a t i o , i . e .
t h e r a t i o o f v a p o u r mass f l o w t o l i v e - s t e a m mass f l o w , v a r i e s as shown i n T a b l e
1.2 ( t h e v a l u e s g i v e n s h o u l d be i n t e r p r e t e d as t h e h i g h e s t a t t a i n a b l e , w h i l e
t h e a c t u a l v a l u e s may a l s o depend on compresso r q u a l i t y ) .
The mechan ica l compresso r ( F i g . 1.11) i s d r i v e n by a m o t o r , t o w h i c h e n e r g y
must be s u p p l i e d c o n t i n u o u s l y . A t p r e s e n t , e l e c t r i c moto rs a r e g e n e r a l l y
r e g a r d e d as most e c o n o m i c , b u t steam t u r b i n e s a r e a l s o used as c o m p r e s s o r
d r i v e s . As a c o n s e q u e n c e , t h e a p p l i c a t i o n o f a mechan ica l c o m p r e s s o r e i t h e r
i n c r e a s e s t h e f a c t o r y ' s power demand, o r r e q u i r e s a c e r t a i n f l o w o f l i v e steam
b y - p a s s i n g t he t u r b o - g e n e r a t o r t o be s u p p l i e d t o t h e c o m p r e s s o r d r i v e .
When c o n s i d e r i n g a l l t he p o s s i b l e s i t u a t i o n s r e l a t e d t o t h e f a c t o r y ' s power
b a l a n c e and hea t b a l a n c e and t h e p o s s i b i l i t y o f c o o p e r a t i o n w i t h an e x t e r n a l
TABLE 1.2
E s t i m a t e d a t t a i n a b l e v a l u e s o f t h e c o m p r e s s i o n r a t i o o f j e t compresso rs o p e r a t e d a t d i f f e r e n t l o c a t i o n s i n t h e the rma l sys tem shown i n F i g . 1.9 a t l i v e - s t e a m paramete rs 38 b a r and 450°C.
L o c a t i o n Compress ion r a t i o
a - 1s t e f f e c t v a p o u r t o e x h a u s t steam 2.4 b - 2nd e f f e c t v a p o u r t o e x h a u s t steam 1.1 c - vacuum pan v a p o u r t o e x h a u s t steam 0.3 d - 3 rd e f f e c t v a p o u r t o 2nd e f f e c t v a p o u r 1.5 e - vacuum pan v a p o u r t o 2nd e f f e c t v a p o u r 0.7
19
F i g . 1.11. T y p i c a l s i n g l e - s t a g e c e n t r i f u g a l c o m p r e s s o r f o r t h e c o m p r e s s i o n o f f i r s t e v a p o r a t o r e f f e c t v a p o u r . A t volume f l o w 50 000 m^/h and r o t a t i o n a l v e l o c i t y 5000 rpm, t h e r o t o r d i a m e t e r i s a b o u t 0.9 m.
power g r i d , i t must be c o n c l u d e d t h a t t h e r e i s no u n i v e r s a l l y o p t i m a l v a p o u r
compress i on t e c h n i q u e . Depending on t h e c o n s t r a i n t s t o be s a t i s f i e d and t h e
economic r e l a t i o n s between t he n e c e s s a r y i n v e s t m e n t s and t h e a t t a i n a b l e e n e r g y
s a v i n g , one t y p e o f equ ipment o r a c o m b i n a t i o n o f bo th may p r e v a i l . Unde r West
European c o n d i t i o n s , i t i s g e n e r a l l y b e l i e v e d t h a t t h e e l e c t r i c a l l y d r i v e n
mechan ica l compresso r r e c i r c u l a t i n g f i r s t - e f f e c t v a p o u r i s most e c o n o m i c .
A l t h o u g h t h i s seems t o be p r o v e d by a number o f r e c e n t i n v e s t m e n t s ( r e f . 1 4 ) ,
t h e e n e r g y - e f f i c i e n t Dan ish f a c t o r i e s employ t u r b i n e - d r i v e n c o m p r e s s o r s
r e c i r c u l a t i n g s e c o n d - e f f e c t v a p o u r ( p o s s i b l y i n c o m b i n a t i o n w i t h j e t - t y p e
c o m p r e s s o r s ) . T h e r e a r e a l s o numerous West European s u g a r f a c t o r i e s r e l y i n g on
j e t - t y p e compresso rs and a t t a i n i n g e x c e l l e n t r e s u l t s ( r e f s . 1 5 , 1 6 ) . I n E a s t e r n
E u r o p e , where t h e economic c o n d i t i o n s a r e d i f f e r e n t , j e t - t y p e c o m p r e s s o r s a r e
u s u a l l y p r e f e r a b l e t o mechan ica l ones ( r e f . 5 ) .
I t may be added t h a t j e t - t y p e compresso rs have r e c e n t l y been s e l e c t e d f o r
v a p o u r c o m p r e s s i o n c i r c u i t s i n Greek and Czech s u g a r f a c t o r i e s ( r e f s . 1 7 , 1 8 ) .
The a p p l i c a t i o n s o f v a p o u r compresso rs a r e d i s c u s s e d i n g r e a t e r d e t a i l i n
C h a p t e r s 3 , 8 and 9.
1.2.8 Pu lp d e h y d r a t i o n
The p u l p d e h y d r a t i o n p r o c e s s i s t y p i c a l l y o p e r a t e d i n p a r a l l e l w i t h t h e
s u g a r m a n u f a c t u r i n g p r o c e s s ( F i g . 1 . 1 2 ( a ) ) . The d e h y d r a t i o n u s u a l l y c o n s i s t s o f
mechan ica l p r e s s i n g o f t h e p u l p t o a d r y - s u b s t a n c e c o n t e n t o f t h e o r d e r o f
20
(α)
(c)
pw
Lt lue_äqs_J
PP
fuel
αίΓ
(b) α I
ä;i
I
>-! σ ι
t o
1 u 2 3 1 2 3
pw PP d p i
dp
4
dp
CL Ό CL ¿1 σ ι ·
• •
1
1 I
2 3 1 2 3
pw
(d)
PP d p |
α o CL I I
ι
' t lue gas
•
1 I
2 3 1 2 3
pw
PP d p |
F i g . 1.12. P o s s i b l e schemes f o r t h e p u l p d e h y d r a t i o n p r o c e s s : ( a ) t h e r m a l l y i n d e p e n d e n t , ( b ) t h e r m a l l y i n d e p e n d e n t w i t h gas r e c i r c u l a t i o n , ( c ) p a r t l y h e a t e d w i t h b o i l e r f l u e g a s , ( d ) w i t h t h e u t i l i z a t i o n o f b o i l e r f l u e g a s . pw - p r e s s w a t e r , pp - p r e s s e d p u l p , dp - d r i e d p u l p ; 1 - p r e s s e s , 2 - f u r n a c e , 3 - d r y e r .
20% DS and s u b s e q u e n t the rma l d r y i n g t o abou t 90% DS. W h i l e t h e a v e r a g e e n e r g y
demand i s abou t 1000 kJ p e r kg w a t e r r emoved , t h e c o n t r i b u t i o n s o f t h e two
p r o c e s s e s t o t h i s f i g u r e a r e v e r y d i f f e r e n t i n d e e d . The mechan ica l p r e s s i n g
r e q u i r e s 40-80 k J e l e c t r i c a l e n e r g y p e r kg w a t e r r emoved , w h i l e t h e h e a t demand
i n the rma l d r y i n g i s abou t 3000 kJ p e r kg w a t e r . The d r y i n g and t h e s u b s e q u e n t
p e l l e t i n g o f t h e d r i e d p u l p a r e a l s o a s s o c i a t e d w i t h a power e x p e n d i t u r e o f t h e
o r d e r o f 0.6 kWh p e r 100 kg b e e t p r o c e s s e d .
When compared t o t h e s u g a r m a n u f a c t u r e , t h e u t i l i z a t i o n o f p r i m a r y e n e r g y
s u p p l i e d t o the rma l d r y i n g o f t h e p u l p i s r a t h e r p o o r . A c t u a l l y , i t c a n n o t be
b e t t e r i n a p r o c e s s s t a r t i n g f rom f u e l combus t i on i n a h i g h e x c e s s o f a i r , w h i c h
i s e q u i v a l e n t t o m i x i n g t h e o r e t i c a l l y p o s s i b l e h i g h - t e m p e r a t u r e c o m b u s t i o n gases
w i t h c o l d a i r . T h e r e i s a l s o a l a r g e t e m p e r a t u r e d i f f e r e n c e between t h e gases
and t h e p u l p i n t he d r y e r . F i n a l l y , t h e e n e r g y s t ream i s c a r r i e d away by t h e
o u t l e t gases a f t e r p e r f o r m i n g o n l y one pass t h r o u g h t h e d r y e r .
S u b s t a n t i a l e n e r g y s a v i n g s a r e p o s s i b l e i n p u l p d e h y d r a t i o n i f more w a t e r i s
removed by p r e s s i n g and l e s s by d r y i n g . T h i s can be a c h i e v e d by i n t r o d u c i n g
m ino r p r o c e s s m o d i f i c a t i o n s and a p p l y i n g improved p u l p p r e s s e s , as d i s c u s s e d i n
C h a p t e r 4 . As f a r as t h e c l a s s i c a l the rma l d r y i n g i s c o n c e r n e d , i t can be
c o n c l u d e d t h a t t h e p o s s i b i l i t i e s o f c u t t i n g down t h e e n e r g y e x p e n d i t u r e p e r u n i t
mass o f e v a p o r a t e d w a t e r a r e r a t h e r l i m i t e d . The o n l y e f f e c t i v e e n e r g y - s a v i n g
t e c h n i q u e i s t h e r e c i r c u l a t i o n o f gases f rom the d r y e r o u t l e t , e i t h e r t o t h e
21
d r y e r i n l e t o r t o t h e f u r n a c e i n l e t ( F i g . 1 . 1 2 ( b ) ) . S a v i n g s o f up t o 10-12% o f
t he p r i m a r y e n e r g y i n p u t can be a t t a i n e d ( r e f s . 1 9 , 2 0 ) . H o w e v e r , an e n t i r e l y new
f i e l d o f p o t e n t i a l e n e r g y s a v i n g s can be opened i f t h e p u l p d r y i n g becomes
t h e r m a l l y i n t e g r a t e d w i t h t he s u g a r m a n u f a c t u r e .
1.2.9 Thermal c o u p l i n g between p u l p d r y i n g and s u g a r manu fac tu re
The e n e r g y b a l a n c e o f p u l p d r y i n g can be c o n s i d e r a b l y improved by u t i l i z i n g
t h e was te h e a t f rom t h e b o i l e r f l u e g a s , as shown s c h e m a t i c a l l y i n F i g s . 1 . 1 2 ( c )
and 1 . 1 2 ( d ) . P o s s i b l e s a v i n g s can be e s t i m a t e d a t up t o 12-15% o f t h e d r y e r ' s
h e a t demand.
P a r a l l e l o p e r a t i o n o f a d r y e r hea ted by f l u e gas and a d r y e r w i t h i t s own
f u r n a c e , a l t h o u g h r e a l i z a b l e , has s e r i o u s drawbacks and i s n o t t o be recommended
( r e f . 1 9 ) . I n an a l t e r n a t i v e s y s t e m , t h e b o i l e r f l u e gas r e p l a c e s t h e a i r
admixed w i t h t h e combus t i on gas i n t h e o u t l e t o f t h e d r y i n g - p l a n t f u r n a c e . As
t he f l u e gas t e m p e r a t u r e i s h i g h e r than t h e a i r t e m p e r a t u r e , l e s s combus t i on gas
and thus l e s s f u e l w i l l be consumed f o r a d e f i n i t e t e m p e r a t u r e a t t h e d r y e r
i n l e t . I t i s a l s o p o s s i b l e t o mix t h e b o i l e r f l u e gas w i t h t h e c o m b u s t i o n a i r
p r i o r t o t h e f u r n a c e , r a i s i n g t h e t e m p e r a t u r e i n t h e f u r n a c e i n l e t and making i t
p o s s i b l e t o r e d u c e t h e f u e l demand.
G e n e r a l l y , t h e use o f b o i l e r f l u e gas s e t s s p e c i a l r e q u i r e m e n t s on t h e d r y e r
c a p a c i t y . As shown i n t h e i n v e s t i g a t i o n s o f drum d r y e r s ( r e f . 2 0 ) , t h e most
e f f e c t i v e h e a t u t i l i z a t i o n i s a t t a i n e d a t a c e r t a i n o p t i m a l l o a d o f t h e d r y e r ' s
drum. Load d e v i a t i o n s f rom the o p t i m a l v a l u e cause t h e h e a t consump t i on p e r kg
w a t e r t o i n c r e a s e .
The d i s p r o p o r t i o n i n e n e r g y u t i l i z a t i o n e f f i c i e n c y o f p u l p d r y i n g and s u g a r
manu fac tu re has r e c e n t l y i n s p i r e d r a t i o n a l i z a t i o n measures aimed a t i n t e n s i f y i n g
t he e n e r g y usage i n f a c t o r i e s emp loy i ng p u l p d r y i n g . A t t h e h i g h - t e m p e r a t u r e end
o f t h e p u l p d r y i n g p r o c e s s , e l e c t r i c i t y g e n e r a t i o n ( p r e f e r a b l y i n a g a s - t u r b i n e
s e t ) i s p r o p o s e d t o u t i l i z e t h e the rma l p o t e n t i a l o f t h e h e a t o b t a i n e d t h r o u g h
f u e l c o m b u s t i o n . The changed r e q u i r e m e n t s o f power house o p e r a t i o n a s s o c i a t e d
w i t h g a s - t u r b i n e a p p l i c a t i o n s a r e d i s c u s s e d i n S e c t i o n 1.5.
A t t h e l o w - t e m p e r a t u r e end o f p u l p d r y i n g , a t t e m p t s a r e made t o use w a s t e
h e a t i n t he o u t l e t gases f rom t h e d r y e r f o r h e a t i n g p u r p o s e s i n s u g a r
m a n u f a c t u r e . As t h e o u t l e t gases c o n t a i n d u s t p a r t i c l e s accompanied by s u l p h u r
d i o x i d e , t h i s must be seen i n c o n n e c t i o n w i t h gas c l e a n i n g . Where gas c l e a n i n g
( p o s s i b l y i n c l u d i n g d e s u l p h u r i z a t i o n ) i s r e q u i r e d f o r e n v i r o n m e n t a l r e a s o n s , i t
may be a d v i s a b l e t o comp le te t h e n e c e s s a r y equ ipment w i t h a h e a t - r e c o v e r y
c i r c u i t . The r e c o v e r e d h e a t can be u t i l i z e d i n j u i c e h e a t i n g o r e v a p o r a t i o n , as
has been demons t ra ted i n p r o t o t y p e p l a n t s ( r e f s . 2 1 , 2 2 ) , T h i s c r e a t e s a d d i t i o n a l
p o s s i b i l i t i e s o f s a t i s f y i n g t h e w a t e r remova l c o n s t r a i n t w h i c h i s so i m p o r t a n t
t o t he e n e r g y b a l a n c e o f s u g a r m a n u f a c t u r e .
22
A n o t h e r g roup o f r a t i o n a l i z a t i o n measures o r i g i n a t e s f rom t h e i d e a o f
s p l i t t i n g t he p u l p d r y i n g p r o c e s s i n t o p a r t s pe r fo rmed a t d i f f e r e n t t e m p e r a t u r e
l e v e l s ( r e f s . 9 , 1 9 , 2 3 ) . W h i l e t h e h i g h - t e m p e r a t u r e p r o c e s s i s e s s e n t i a l l y
i d e n t i c a l t o c o n v e n t i o n a l d r y i n g , t h e l o w - t e m p e r a t u r e p r o c e s s c r e a t e s new
p o t e n t i a l f o r t he u t i l i z a t i o n o f was te hea t f rom s u g a r manu fac tu re and
r e d u c t i o n s i n o v e r a l l e n e r g y demand o f t h e f a c t o r y . Waste h e a t can be r e c o v e r e d
f rom vacuum pan v a p o u r s , c o n d e n s a t e , s p e n t c a r b o n a t a t i o n gas and even b a r o m e t r i c
w a t e r , r a i s i n g t h e t e m p e r a t u r e o f a i r s u p p l i e d t o t h e l o w - t e m p e r a t u r e d r y e r t o
55-60°C. By remov ing a s u b s t a n t i a l p a r t o f t h e w a t e r f rom t h e p u l p , t h e f u e l
demand can be r e d u c e d i n t h e f i n a l d r y i n g , where t h e r e q u i r e d d r y s u b s t a n c e
c o n t e n t o f t h e d r i e d p u l p i s a t t a i n e d . The economic p o t e n t i a l s s o c i a t e d w i t h
t h i s s o l u t i o n has a l r e a d y been demons t ra ted i n i n d u s t r i a l - s c a l e p l a n t s
( r e f . 2 4 ) .
V e r y p r o m i s i n g c o n c e p t s o f e n e r g y - s a v i n g the rma l c o u p l i n g between p u l p d r y i n g
and o t h e r s u g a r f a c t o r y subsys tems a r e based on t he a p p l i c a t i o n s o f steam
d r y e r s . The i d e a o f steam d r y i n g i s n o t new t o t h e s u g a r i n d u s t r y , b u t i t i s
o n l y r e c e n t l y t h a t i t has become p o s s i b l e t o i n c l u d e t h e d r y e r s - w h e t h e r
s u p p l i e d w i t h l i v e s t eam, o r w i t h e x h a u s t steam o r v a p o u r f rom t h e e v a p o r a t o r -
i n t o the rma l sys tems u s i n g t h e p r i n c i p l e o f m u l t i p l e h e a t u t i l i z a t i o n w h i c h i s
so c h a r a c t e r i s t i c o f s u g a r m a n u f a c t u r e . I f used i n c o m b i n a t i o n w i t h medium- o r
l o w - t e m p e r a t u r e d r y i n g ( r e f s . 2 5 , 2 6 ) , steam d r y i n g makes i t p o s s i b l e t o
e l i m i n a t e p r i m a r y e n e r g y i n p u t t o t h e p u l p d r y i n g p l a n t and t o a t t a i n
c o n s i d e r a b l e o v e r a l l e n e r g y s a v i n g s .
I t must be a d m i t t e d t h a t t h e the rma l c o u p l i n g between p u l p d r y i n g and s u g a r
manu fac tu re g e n e r a l l y r e q u i r e s t h e a p p l i c a t i o n o f r a t h e r c o s t l y e q u i p m e n t .
T h e r e f o r e , t h e p r a c t i c a b l e e n e r g y s a v i n g s a r e h i g h l y dependen t on economic
f a c t o r s , l i k e t he c o s t s o f f u e l and p o w e r , and t h e c a p i t a l c o s t . W i th t h e
e x c e p t i o n o f t he u t i l i z a t i o n o f b o i l e r f l u e g a s , a l l t h e t e c h n i q u e s men t ioned
above s h o u l d be r e g a r d e d as new deve lopmen ts r a t h e r t han s t a n d a r d i n d u s t r i a l
p r a c t i c e ( f o r a more d e t a i l e d d i s c u s s i o n , see C h a p t e r 4 ) .
1.3 HEAT DEMAND
1.3.1 Scope o f t h e prob lems
Sugar i n d u s t r y p e o p l e t e n d t o t h i n k o f t h e l i n k between h e a t economy and t h e
s u g a r m a n u f a c t u r i n g p r o c e s s i n terms o f how much f u e l s h o u l d be b u r n t i n t h e
b o i l e r s i n o r d e r t o make t h e p r o c e s s r u n . As f u e l p r i c e s go u p , h o w e v e r , t h e
q u e s t i o n o f how t h e p r o c e s s can be a l t e r e d i n o r d e r t o r e d u c e t h e h e a t demand
becomes more and more i m p o r t a n t .
I n S e c t i o n 1 .2 , t h r e e q u a n t i t i e s were i n t r o d u c e d t o e x p r e s s t h e
c h a r a c t e r i s t i c s o f t h e h e a t economy: t o t a l h e a t demand n e t h e a t demand
23
and e f f e c t i v e n e s s r a t i o K. The t r a d i t i o n a l app roach s u g g e s t s t h a t t h e h e a t
economy can be improved by e n s u r i n g t h a t t h e the rma l sys tem i s w e l l d e s i g n e d ,
c a r e f u l l y o p e r a t e d and w e l l m a i n t a i n e d . T h i s means t h a t a t a g i v e n Q- j , a l a r g e Κ
s h o u l d be a t t a i n e d so t h a t Q2 = Q-j /K w i l l become s u f f i c i e n t l y s m a l l .
The p r o c e s s - o r i e n t e d app roach stems f rom t h e o b s e r v a t i o n t h a t t h e n e t h e a t
demand can a l s o be c u t down by r e d u c i n g t h e sum o f h e a t s t reams ( t o t a l h e a t
demand) Q-j. T h i s r e q u i r e s a d j u s t i n g t h e p r o c e s s so as t o make s u g a r m a n u f a c t u r e
l e s s e n e r g y - i n t e n s i v e .
I t s h o u l d be emphas ized t h a t i n i n d u s t r i a l p r a c t i c e , t h e measures t aken t o
i n c r e a s e Κ s h o u l d be t r e a t e d on an equa l b a s i s w i t h t h o s e aimed a t r e d u c i n g Q-j .
I n o t h e r w o r d s , e n e r g y - s a v i n g p r o c e s s a d j u s t m e n t s a r e as i m p o r t a n t as the rma l
sys tem improvements s e r v i n g t h e same p u r p o s e .
I n t h i s S e c t i o n , we s h a l l s t u d y t h e i n f l u e n c e o f p r o c e s s pa rame te rs on t he
sum o f hea t s t reams Q-j . T a k i n g i n t o a c c o u n t t h a t t h e number o f pa rame te rs
c h a r a c t e r i z i n g t h e s u g a r m a n u f a c t u r i n g p r o c e s s and t h e b y - p r o c e s s e s may be q u i t e
l a r g e , we s h a l l r e s t r i c t o u r t r e a t m e n t t o t h e most i m p o r t a n t pa ramete rs t h a t can
a l s o be c o n s i d e r e d a d j u s t a b l e . B e f o r e d i s c u s s i n g t h e d e t a i l s , h o w e v e r , l e t us
ment ion some l i m i t a t i o n s o f t h i s a p p r o a c h .
T h e r e i s much t r u t h i n t h e s a y i n g t h a t s u g a r i s e s s e n t i a l l y p r o d u c e d i n t h e
b e e t f i e l d s and t he f a c t o r y i s o n l y p r o c e s s i n g i t . The i n f l u e n c e o f b e e t g r o w i n g
on t he f a c t o r y ' s h e a t demand i s a t l e a s t t w o f o l d :
( i ) An i n c r e a s e d s u g a r c o n t e n t o f b e e t s i s e q u i v a l e n t t o a r e l a t i v e r e d u c t i o n o f
t h e i n t a k e o f w a t e r and n o n - s u g a r s t o t h e s u g a r m a n u f a c t u r i n g p r o c e s s . As t h e
s u g a r c o n t e n t i s i n c r e a s e d f rom 16 t o 19%, a h e a t s a v i n g ( p e r 1 kg s u g a r
p r o d u c e d ) o f t h e o r d e r o f 6% can be o b t a i n e d .
( i i ) A r e d u c e d c o n t e n t o f n o n - s u g a r s i n b e e t s , t h a t i s , a h i g h e r j u i c e p u r i t y ,
p o s i t i v e l y a f f e c t s t h e mass b a l a n c e s o f t h e p u r i f i c a t i o n and c r y s t a l l i z a t i o n
p r o c e s s e s . As r a w - j u i c e p u r i t y i s i n c r e a s e d f rom 88.5 t o 90%, t h e r e s u l t i n g h e a t
s a v i n g ( p e r 1 kg b e e t ) amounts t o abou t 3%.
U n d e r s t a n d a b l y e n o u g h , d e s p i t e t h i s i n t e r e s t i n g e n e r g y - s a v i n g p o t e n t i a l , i t
i s i m p o s s i b l e t o a d j u s t t he b e e t p r o p e r t i e s q u i c k l y by t a k i n g some t e c h n i c a l l y -
o r i e n t e d measures . T h e r e f o r e , t h e p rob lems o f b e e t g r o w i n g must be c o n s i d e r e d
as be ing beyond t h e scope o f t h e p r e s e n t book .
The e n e r g y demands o f s u g a r manu fac tu re may v a r y c o n s i d e r a b l y , depend ing on
t he t y p e and q u a l i t y o f t he s u g a r . When c o n s i d e r i n g t h e e n t i r e f a c t o r y , o t h e r
f a c t o r s o f impo r tance a r e t h e t y p e and q u a l i t y o f t h e b y - p r o d u c t s , w h e t h e r o r
n o t t h i c k - j u i c e s t o r a g e f o r s u b s e q u e n t p r o c e s s i n g i s e m p l o y e d , w h e t h e r o r n o t
s y r u p s a r e s o l d , e t c . I n t h e c o n t e m p o r a r y s u g a r i n d u s t r y , w h i t e s u g a r
manu fac tu re and t h e c l a s s i c a l o p e r a t i o n a r e d o m i n a n t , b e i n g o f t e n accompanied by
the p r o d u c t i o n o f d r i e d p u l p . Ou r t r e a t m e n t w i l l t h e r e f o r e c o n c e n t r a t e on w h i t e
24
s u g a r f a c t o r i e s , w i t h p u l p d r y i n g t aken i n t o a c c o u n t .
R e t u r n i n g now t o t h e p rob lems t h a t a r e w e l l w i t h i n t h e scope o f t h i s b o o k ,
l e t us quo te t h e f o l l o w i n g a c c o u n t g i v e n by S c h i e b l ( r e f . 1) h a l f a c e n t u r y a g o :
" T h e h e a t i n g steam demand can be d e c r e a s e d i f t h e f o l l o w i n g c o n d i t i o n s a r e
s a t i s f i e d :
- t h e steam demand f o r a u x i l i a r y p u r p o s e s and f o r s u g a r wash i n c e n t r i f u g a l s i s
d e c r e a s e d ,
- t h e f a c t o r y i s o p e r a t e d a t low j u i c e d r a f t ,
- a h i g h c o n c e n t r a t i o n o f t h i c k j u i c e i s m a i n t a i n e d .
A t t h e p r e s e n t s t a t e o f deve lopment o f b e e t s u g a r t e c h n o l o g y , t h e r e a r e no o t h e r
p o s s i b i l i t i e s o f d e c r e a s i n g t h e h e a t demand."
T h i n g s have changed c o n s i d e r a b l y s i n c e t h e s e words were p u b l i s h e d . T h e r e i s
a v a s t l i t e r a t u r e d e v o t e d t o t he methods o f r e d u c i n g t he h e a t demand f o r s u g a r
m a n u f a c t u r e , and t he most i m p o r t a n t s o u r c e s w i l l be r e f e r r e d t o i n t h e
f o l l o w i n g .
I n s t e a d o f naming a few s e l e c t e d e n e r g y - s a v i n g m e a s u r e s , as S c h i e b l d i d ( a n d ,
a c t u a l l y , many o t h e r a u t h o r s t o o ) , l e t us adop t a top -down a p p r o a c h , f i r s t
t a k i n g a b r o a d e r v i e w o f t h e f i e l d o f e x i s t i n g p o s s i b i l i t i e s and t h e n t r y i n g t o
d e f i n e s m a l l e r a reas o f s p e c i a l i n t e r e s t . The n o t i o n o f t h e sum o f h e a t s t reams
can be u t i l i z e d as a s t a r t i n g p o i n t . F o r a s p e c i f i c s u g a r f a c t o r y , i t can be
c o n v e n i e n t l y s p l i t i n t o t h r e e components
where Q ] Q i s t h e sum o f h e a t s t reams t h a t a r e n e c e s s a r y f o r c a r r y i n g o u t u n i t
o p e r a t i o n s t o w h i c h hea t must be d e l i v e r e d , l i k e h e a t i n g , e v a p o r a t i o n ,
c r y s t a l l i z a t i o n and d r y i n g ; Q-j^ i s t h e t o t a l hea t s t ream needed t o b a l a n c e h e a t
d i s s i p a t i o n f rom t h e s e o p e r a t i o n s , and Q-j ^ i s t h e t o t a l h e a t s t ream needed t o
h e a t t h e rooms i n t h e f a c t o r y b u i l d i n g s .
The l a s t q u a n t i t y i s d e l i b e r a t e l y , even i f u n t y p i c a l l y , c o n s i d e r e d t o g e t h e r w i t h
t h e p r o c e s s h e a t demand. As f a r as t h e e n e r g y s u p p l y v i a t h e the rma l sys tem i s
c o n c e r n e d , t h e r e i s no r e a s o n f o r a s e p a r a t e t r e a t m e n t because room h e a t i n g i s
a l s o n e c e s s a r y f o r f a c t o r y o p e r a t i o n .
L e t us o b s e r v e t h a t a t d e f i n i t e p r o c e s s p a r a m e t e r s , components Q-j^ and Q-j^
may depend on f a c t o r s t h a t a r e n o t s p e c i f i c t o t h e p r o c e s s , l i k e t h e q u a l i t y o f
the rma l i n s u l a t i o n o r t h e e f f i c i e n c y o f room h e a t i n g e q u i p m e n t . C o n s e q u e n t l y , i t
may be p o s s i b l e t o c u t down Q-j^ and Q - , ^ , t hus r e d u c i n g t h e t o t a l h e a t s t r e a m ,
w i t h o u t i n t r o d u c i n g any changes t o t h e p r o c e s s . E n e r g y s a v i n g s o f t h i s k i n d a r e
t h e e a s i e s t t o a c h i e v e and w i l l be d i s c u s s e d f i r s t .
The component Q-j^ can be c u t down by a v a r i e t y o f t e c h n i q u e s , t h a t can be
g rouped w i t h r e g a r d t o t h e p r i n c i p l e s a c c o r d i n g t o w h i c h t h e e n e r g y i s s a v e d .
L e t us d e f i n e t h r e e g r o u p s :
25
- r e d u c t i o n s o f t he w a t e r i n t a k e t o t h e s u g a r m a n u f a c t u r i n g p r o c e s s ,
- r e d u c t i o n s o f t he w a t e r t r a n s f e r f rom o t h e r f a c t o r y s e c t i o n s t o t h e s u g a r
h o u s e ,
- i n t r o d u c t i o n o f m o d i f i e d o r new e n e r g y - e f f i c i e n t p r o c e s s e s .
T h i s S e c t i o n i s d e v o t e d t o t h e e n e r g y - s a v i n g measures t h a t can be t a k e n
i n d e p e n d e n t l y o f , o r w i t h i n t he f ramework o f , t h e c o n v e n t i o n a l s u g a r
m a n u f a c t u r i n g p r o c e s s . M o d i f i e d o r new p r o c e s s e s a r e d i s c u s s e d i n C h a p t e r 4 .
1.3.2 H e a t i n g o f f a c t o r y b u i l d i n g s
I n t h o s e p a r t s o f t h e f a c t o r y b u i l d i n g s where a c o m f o r t a b l e t e m p e r a t u r e i s
needed f o r w o r k i n g p e o p l e , h e a t i n g may be n e c e s s a r y d u r i n g t h e o p e r a t i n g and
a p a r t o f t he o f f - s e a s o n p e r i o d . W h i l e t h e f a c t o r y i s i n o p e r a t i o n , t h e h e a t
demand Q ^ ^ i s a sma l l f r a c t i o n o f t h e sum o f t h e h e a t s t reams and t h u s n o t v e r y
i m p o r t a n t t o t he d e s i g n o f t h e the rma l s y s t e m , and c o n t r i b u t e s v e r y l i t t l e t o
the n e t h e a t demand o f t h e f a c t o r y . Depend ing on t h e c l i m a t i c c o n d i t i o n s and t h e
p r o c e s s h e a t demand, h o w e v e r , t he h e a t consumpt i on i n room h e a t i n g d u r i n g t h e
e n t i r e h e a t i n g p e r i o d may be r e s p o n s i b l e f o r 4-6% o f t he f a c t o r y ' s t o t a l annua l
e n e r g y c o n s u m p t i o n .
As c u t t i n g down the hea t demand i n room h e a t i n g i n s t a l l a t i o n s r e q u i r e s
s o l v i n g prob lems t h a t a r e n o t s p e c i f i c t o t h e s u g a r i n d u s t r y , no d e t a i l s w i l l be
d i s c u s s e d h e r e . The main p o i n t s t o be c o n s i d e r e d , p a r t i c u l a r l y i n o l d e r
f a c t o r i e s , a r e :
- improvements o f t he the rma l i n s u l a t i o n o f f a c t o r y b u i l d i n g s ,
- r e d u c t i o n o f t h e h e a t l o s s e s f rom t h e h e a t d i s t r i b u t i o n sys tem ( b y i m p r o v i n g
the rma l i n s u l a t i o n o f t h e h o t - w a t e r p i p e s , i n t r o d u c i n g e f f e c t i v e f l o w c o n t r o l
me thods , e t c . ) ,
- i n t r o d u c t i o n o f a u t o m a t i c r o o m - t e m p e r a t u r e c o n t r o l t o p r e v e n t l o c a l
o v e r h e a t i n g , t hus e l i m i n a t i n g h e a t l o s s e s caused by e x c e s s i v e v e n t i l a t i o n .
When s e l e c t i n g s u i t a b l e h e a t s o u r c e s t o c o v e r t h e hea t demand f o r h e a t i n g
p u r p o s e s , use can be made o f w a s t e - h e a t s u p p l i e s t h a t a r e c h a r a c t e r i s t i c o f t h e
s u g a r i n d u s t r y . As shown i n a s t u d y c a r r i e d o u t f o r a Swed ish s u g a r f a c t o r y
( r e f . 2 7 ) , more than 90% o f t h e hea t demand f o r room h e a t i n g d u r i n g o p e r a t i o n s
can be c o v e r e d by s u p p l y i n g h o t c o n d e n s a t e f rom vacuum p a n s . Unde r M i d d l e -
European c l i m a t i c c o n d i t i o n s , t h i s c o r r e s p o n d s t o 1/4 o f t h e f a c t o r y ' s annua l
hea t consumpt ion f o r h e a t i n g p u r p o s e s , o r an e q u i v a l e n t o f 1-1.5% o f t h e t o t a l
annual e n e r g y c o n s u m p t i o n .
U s i n g more advanced t e c h n i q u e s , t he was te h e a t can be accumu la ted d u r i n g
o p e r a t i o n s and u t i l i z e d f o r h e a t i n g d u r i n g t h e o f f - s e a s o n p e r i o d . F o r e x a m p l e ,
warm w a t e r can be s t o r e d u n d e r g r o u n d and l a t e r s u p p l i e d t o a h e a t pump. The
r e a l i z a b l e s a v i n g s have been e s t i m a t e d a t 60-70% o f t h e f a c t o r y ' s annua l h e a t
consumpt ion f o r h e a t i n g p u r p o s e s , t h a t i s , 2 .4-4 .2% o f t h e t o t a l annua l e n e r g y
26
c o n s u m p t i o n . H o w e v e r , t h e economic p o t e n t i a l o f t h i s s o l u t i o n depends h e a v i l y on
f u e l and power p r i c e s , as w e l l as c a p i t a l c o s t . F o r e x a m p l e , a c o m b i n a t i o n o f
cheap f u e l and r e l a t i v e l y c o s t l y power c o u n t e r a c t s t h e p r o f i t a b i l i t y o f h e a t -
pump a p p l i c a t i o n s , j u s t i f y i n g r a t h e r t h e u t i l i z a t i o n , d u r i n g t h e o f f - s e a s o n
p e r i o d , o f a c o n v e n t i o n a l h e a t i n g sys tem i n w h i c h hea t i s g e n e r a t e d by b u r n i n g
f u e l i n a b o i l e r . F o r such a s o l u t i o n t o be c o m p e t i t i v e , a h i g h b o i l e r
e f f i c i e n c y i s r e q u i r e d .
1.3.3 Heat d i s s i p a t i o n f rom t h e p r o c e s s
Heat l o s s e s f rom t h e s u g a r m a n u f a c t u r i n g p r o c e s s t o t h e e n v i r o n m e n t a r e
caused b y :
- mass and h e a t exchange between t h e a tmosphere and f r e e s u r f a c e s o f h i g h -
t e m p e r a t u r e media i n open t a n k s , s i p h o n s and d i s t r i b u t o r s ,
- hea t exchange between t he a i r and t h e s u r f a c e s o f p r o c e s s equ ipment and
p i p i n g .
I n F i g . 1 .13, t h e e s t i m a t e d h e a t d i s s i p a t i o n f rom t h e w a t e r s u r f a c e i n an
open v e s s e l , a t t y p i c a l ambien t t e m p e r a t u r e , i s shown as a f u n c t i o n o f w a t e r
t e m p e r a t u r e ( r e f . 2 8 ) . A s i m i l a r r a t e o f h e a t d i s s i p a t i o n can be e x p e c t e d a t
20000
10 000
- 5000
o ω χ
2000
1000
500
200
water agi tated
\ \
W ( 3ter at rest
40 50 60 70 80
Water temperature (°C)
90 100
F i g . 1.13. Heat l o s s f rom t h e s u r f a c e o f w a t e r i n an open tank ( a f t e r r e f . 2 8 ) .
27
f r e e j u i c e s u r f a c e s i n t h e j u i c e p u r i f i c a t i o n s t a t i o n , w h i l e t h e h e a t t r a n s f e r
between a i r and m a s s e c u i t e s u r f a c e s i n open v e s s e l s i s l e s s i n t e n s i v e . I f no
p r e c a u t i o n s a r e t a k e n , t h e combined e f f e c t o f h e a t l o s s e s f rom t h e f r e e s u r f a c e s
o f p r o c e s s media i n open v e s s e l s and s i p h o n s may e a s i l y a t t a i n a l e v e l
c o r r e s p o n d i n g t o h e a t i n g - s t e a m consumpt ion o f t h e o r d e r 1-3 kg/100 kg b e e t . I t
i s t hus a d v i s a b l e t o m i n i m i z e t h e a r e a o f f r e e c o n t a c t between a t m o s p h e r i c a i r
and h i g h - t e m p e r a t u r e med ia , by p r o p e r l y s h a p i n g t h e equ ipment u n i t s o r a p p l y i n g
s c r e e n s o r c o v e r s mounted on t h e e q u i p m e n t .
Heat l o s s e s f rom t h e s u r f a c e s o f p r o c e s s equ ipment and p i p i n g depend on t h e
t o t a l s u r f a c e a r e a and t he q u a l i t y o f t he rma l i n s u l a t i o n . When s h a p i n g t h e
equ ipment and p i p i n g i n new o r m o d e r n i z e d f a c t o r i e s , c a r e s h o u l d be t aken o f
t he t r a n s p o r t r o u t e s o f h i g h - t e m p e r a t u r e m e d i a , so t h a t t h e o u t e r s u r f a c e a r e a
o f t h e p i p e s i s m i n i m i z e d . Heat l o s s e s w i l l a l s o be reduced i f t h e number o f
ba re v a l v e s and o t h e r p i p i n g components a l o n g t h e t r a n s p o r t r o u t e s i s m i n i m i z e d .
N o r m a l l y , h e a t l o s s e s f rom a b a r e v a l v e a r e l a r g e r t han f rom 1 m o f t h e p i p e .
The p i p e - l e n g t h e q u i v a l e n t o f a h e a t - d i s s i p a t i n g b a r e f l a n g e i s u s u a l l y abou t
0.5 m. I n F i g . 1.14, t h e e s t i m a t e d h e a t d i s s i p a t i o n f rom b a r e p i p e s , a t t y p i c a l
ambient t e m p e r a t u r e , i s shown as a f u n c t i o n o f t h e t e m p e r a t u r e o f t h e f l u i d
c o n t a i n e d i n t h e p i p e s ( r e f . 2 8 ) .
I t i s d i f f i c u l t t o g i v e q u a n t i t a t i v e i n f o r m a t i o n on t he e n e r g y s a v i n g s w h i c h
4000
2000
_ 1000 4 α Q .
α Φ
100 150
Fluid temperature (°C)
200
F i g . 1.14. Heat l o s s f rom t h e s u r f a c e o f a b a r e p i p e ( a f t e r r e f . 2 8 ) .
28
can be a t t a i n e d by i m p r o v i n g t h e the rma l i n s u l a t i o n , as t h i s depends on t h e
i n i t i a l l o s s l e v e l t o w h i c h t h e s a v i n g s must be compared . I n F i g . 1 .15, t h e
r e l a t i o n s h i p between hea t d i s s i p a t i o n and i n s u l a t i o n t h i c k n e s s a t a d e f i n i t e
p i p e d i a m e t e r i s shown ( r e f . 2 8 ) . Unde r g i v e n economic c o n d i t i o n s , t h e r e i s
a t r a d e - o f f between t h e c o s t o f i n s u l a t i o n and t h e c o s t o f e n e r g y l o s t t o t h e
e n v i r o n m e n t . Depending on l o c a l c o n d i t i o n s , t h e e c o n o m i c a l l y j u s t i f i e d l o s s
l e v e l ( t o be a c c o u n t e d f o r when c o n s i d e r i n g i n s u l a t i o n improvemen ts ) may v a r y
( r e f . 2 9 ) . I t can be e s t i m a t e d t h a t t h e " e n e r g y e q u i v a l e n t " o f t h e d i f f e r e n c e
between p o o r and s a t i s f a c t o r y i n s u l a t i o n o f p r o c e s s equ ipment and p i p i n g i s o f
t he o r d e r o f 4-6% o f t h e sum o f t h e h e a t s t r e a m s .
300
25 50 75 100 Insulat ion thickness (mm)
F i g . 1.15. Heat l o s s f rom t h e s u r f a c e o f an i n s u l a t e d p i p e as a f u n c t i o n o f i n s u l a t i o n t h i c k n e s s ( a f t e r r e f . 2 8 ) .
The hea t d i s s i p a t i o n can a l s o be e f f e c t i v e l y r educed by d e c r e a s i n g t h e
t e m p e r a t u r e l e v e l o f t h e p r o c e s s o r i t s s e c t i o n s . The hea t f l u x r e s u l t i n g f rom
f r e e c o n v e c t i o n f rom a s u r f a c e a t a b s o l u t e t e m p e r a t u r e Τ t o an e n v i r o n m e n t
c h a r a c t e r i z e d by a b s o l u t e t e m p e r a t u r e T ^ i s a f u n c t i o n o f t h e d i f f e r e n c e
ΔΤ = Τ - T g , namely
q ^ = Α ^ ( Δ Τ ) ^ · 2 5 ( ^ 5 )
where i s a c o n s t a n t depend ing on g e o m e t r i c f a c t o r s .
P r o v i d i n g t he t e m p e r a t u r e d i f f e r e n c e ΔΤ i s sma l l i n compar i son w i t h t h e s u r f a c e
t e m p e r a t u r e T , t h e r a d i a t i o n h e a t f l u x can be e x p r e s s e d by t h e f o l l o w i n g
a p p r o x i m a t e r e l a t i o n s h i p
= A ^ T V ( 1 . 6 )
where A ^ i s a c o n s t a n t depend ing on s u r f a c e p r o p e r t i e s and g e o m e t r i c f a c t o r s .
29
I t f o l l o w s f rom t h e above f o r m u l a e t h a t i f t h e s u r f a c e t e m p e r a t u r e Τ i s
d e c r e a s e d a t a c o n s t a n t e n v i r o n m e n t t e m p e r a t u r e T ^ , t h e n t h e r e l a t i v e r e d u c t i o n
i n o v e r a l l h e a t f l u x + q^^ i s l a r g e r t h a n t h e r e l a t i v e r e d u c t i o n i n
t e m p e r a t u r e d i f f e r e n c e Τ - T ^ . T a k i n g i n t o a c c o u n t t h a t t he h e a t l o s s r e d u c t i o n
a p p l i e s t o a t o t a l o f 2-3% o f t h e sum o f t h e h e a t s t r e a m s , o n l y a s u b s t a n t i a l
t e m p e r a t u r e r e d u c t i o n i s r e a l l y i n t e r e s t i n g . O b v i o u s l y , any t e m p e r a t u r e changes
must be t r e a t e d c a u t i o u s l y because o f t he r i s k o f i n t e r f e r i n g w i t h t h e p r o c e s s .
I t has been d e m o n s t r a t e d i n p r a c t i c e t h a t t h e t e m p e r a t u r e i n t h e j u i c e
p u r i f i c a t i o n s t a t i o n can be s u b s t a n t i a l l y r e d u c e d . I n s s p e c i f i c f a c t o r y , t h i s
i s p o s s i b l e o n l y t o the e x t e n t w h i c h can be a c c e p t e d f rom t h e p o i n t o f v i e w o f
p u r i f i c a t i o n r e s u l t s . No g e n e r a l p r e s c r i p t i o n s can be g i v e n h e r e , as t h e
p r a c t i c a b l e t e m p e r a t u r e changes a r e c o n s t r a i n e d by such l o c a l f a c t o r s as b e e t
q u a l i t y and i t s v a r i a t i o n s , r e q u i r e d p u r i f i c a t i o n e f f e c t , equ ipment p r o p e r t i e s
and so o n . Under t h e c o n d i t i o n s c h a r a c t e r i s t i c o f Greek s u g a r f a c t o r i e s ,
p o s s i b l e t e m p e r a t u r e a d j u s t m e n t s have been d i s c u s s e d i n t h e l i t e r a t u r e ( r e f . 3 0 ) .
The p u r i f i c a t i o n method c o n s i d e r e d i s a c l a s s i c a l one c o m p r i s i n g p r o g r e s s i v e
p r e - l i m i n g , main l i m i n g , and d o u b l e - s t a g e c a r b o n a t a t i o n and f i l t r a t i o n . I n F i g .
1.16, t he j u i c e t e m p e r a t u r e i s shown as a f u n c t i o n o f t h e a v e r a g e t ime i t t akes
f o r t he j u i c e t o r e a c h c o n s e c u t i v e p r o c e s s s e c t i o n s . A t a g i v e n p r o c e s s i n g
c a p a b i l i t y , t h i s t ime r e p r e s e n t s t h e volume o f p r o c e s s equ ipment and p i p i n g as
40 60 T i m e ( m i n i
100
F i g . 1.16. J u i c e t e m p e r a t u r e v s . t ime i n j u i c e p u r i f i c a t i o n s t a t i o n s : A - w i t h h o t main l i m i n g o n l y , Β - w i t h c o l d and h o t main l i m i n g . 1 - e x t r a c t i o n , 2 -p r e - l i m i n g , 3 - h e a t i n g o f p r e - l i m e d j u i c e , 4 - main l i m i n g , 5 - 1 s t c a r b o n a t a t i o n , 6 - j u i c e h e a t i n g b e f o r e 1 s t f i l t r a t i o n , 7 - 1 s t f i l t r a t i o n , 8 -j u i c e h e a t i n g b e f o r e 2nd c a r b o n a t a t i o n , 9 - 2nd f i l t r a t i o n , 10 - h e a t i n g o f t h i n j u i c e ( a f t e r r e f . 3 0 ) .
30
w e l l a s , by a n o n l i n e a r t r a n s f o r m a t i o n , t h e a r e a o f o u t e r s u r f a c e s o f equ ipment
and p i p i n g . The d iag ram v i s u a l i z i n g t e m p e r a t u r e as a f u n c t i o n o f t ime t h u s
demons t ra tes t h e h e a t d i s s i p a t i o n p o t e n t i a l o f t he j u i c e p u r i f i c a t i o n s t a t i o n .
As can be s e e n , t h i s p o t e n t i a l ( a p p r o x i m a t e l y r e p r e s e n t e d by t h e s u r f a c e a r e a
under t h e r e s p e c t i v e c u r v e ) i s much s m a l l e r i n case Β than i n case A . T h i s i s
a r e s u l t o f t he a p p l i c a t i o n o f main l i m i n g pe r fo rmed e s s e n t i a l l y a t a low
t e m p e r a t u r e , w i t h a smal l h i g h - t e m p e r a t u r e s e c t i o n o n l y . O t h e r c o n t r i b u t i n g
f a c t o r s a r e : s h o r t r e t e n t i o n t ime o f t h e f i l t r a t i o n o p e r a t i o n s , and a r e l a t i v e l y
low t e m p e r a t u r e o f t h e second c a r b o n a t a t i o n . I t i s r e a l i s t i c t o e x p e c t t h a t i n
case B, t he h e a t consumpt ion w i l l be l e s s t han h a l f o f t h a t i n case A . A l t h o u g h
t he e x a c t f i g u r e wou ld depend on l o c a l c o n d i t i o n s , i t can be e s t i m a t e d t h a t t h e
h e a t demand i n j u i c e p u r i f i c a t i o n w i l l be r e d u c e d t o as low a l e v e l as t h e
e q u i v a l e n t o f abou t 5 kg h e a t i n g steam p e r 100 kg b e e t .
A n o t h e r i n t e r e s t i n g s t u d y on p o s s i b l e t e m p e r a t u r e r e d u c t i o n s i n t h e j u i c e
p u r i f i c a t i o n s t a t i o n has been p u b l i s h e d by S o v i e t a u t h o r s ( r e f . 3 1 ) . I t has been
shown i n a s p e c i f i c s u g a r f a c t o r y t h a t t h e a v e r a g e t e m p e r a t u r e can be d e c r e a s e d
i f p r e - c a r b o n a t a t i o n i s i n t r o d u c e d a t 60°C w i t h t h e CaO r a t e abou t 45% o f t h e
t o t a l . A l t h o u g h t he t e m p e r a t u r e o f t h e f i r s t c a r b o n a t a t i o n remains unchanged a t
85°C, t he hea t l o s s o c c u r r i n g t h e r e i s s u b s t a n t i a l l y r e d u c e d due t o a l o w e r CaO
r a t e (40% o f t he t o t a l , a g a i n s t 80% i n t he o r i g i n a l p r o c e s s ) . The t e m p e r a t u r e o f
t h e second c a r b o n a t a t i o n i s d e c r e a s e d f rom 95^C t o 75^C. The r e s u l t i n g r e d u c t i o n
i n t he hea t d i s s i p a t e d f rom t h e j u i c e p u r i f i c a t i o n p r o c e s s t o t h e e n v i r o n m e n t
can be e s t i m a t e d a t abou t 60%.
P o t e n t i a l t e m p e r a t u r e r e d u c t i o n s i n o t h e r s e c t i o n s o f t h e s u g a r m a n u f a c t u r i n g
p r o c e s s a r e l i m i t e d , b u t s t i l l p o s s i b l e . A n o t h e r s t u d y by S o v i e t a u t h o r s ( r e f .
32) i n d i c a t e s t h a t i n a s p e c i f i c f a c t o r y , t h e b o i l i n g t e m p e r a t u r e s o f A , Β and C
m a s s e c u i t e s can be d e c r e a s e d by abou t 5 K, 10 Κ and 15 K, r e s p e c t i v e l y . A l t h o u g h
t h e new t e m p e r a t u r e reg ime i s aimed a t c u t t i n g down the s u g a r l o s s e s caused by
thermal decay o f s u c r o s e i n vacuum p a n s , t h e hea t d i s s i p a t i o n f rom t h e s u g a r
house can a l s o be r e d u c e d .
1.3.4 Water i n t a k e t o t he p r o c e s s
Most o f t he w a t e r s u p p l i e d t o t h e s u g a r m a n u f a c t u r i n g p r o c e s s i n b e e t s o r
o t h e r mass s t reams ( F i g . 1.17) must u l t i m a t e l y be removed , m a i n l y as v a p o u r o r
as h o t c o n d e n s a t e . The a s s o c i a t e d hea t e x p e n d i t u r e i s a p p r o x i m a t e l y p r o p o r t i o n a l
t o t he amount o f w a t e r s u p p l i e d . I f t h i s amount i s r e d u c e d , and p r o v i d i n g t h e r e
i s no s e r i o u s i n t e r f e r e n c e w i t h t h e p r o c e s s , t hen e n e r g y s a v i n g s can be
o b t a i n e d . The most i m p o r t a n t measures based on t h i s p r i n c i p l e a r e :
- r e d u c t i o n o f t he j u i c e d r a f t ,
- e l i m i n a t i o n o f u n n e c e s s a r y w a t e r a d d i t i o n s t o t h e j u i c e , p a r t i c u l a r l y i n t h e
j u i c e p u r i f i c a t i o n s t a t i o n .
31
water
cosset tes pressed pulpl
..LX sludge
vapour vapour
sugar to d r y e r
molasses
condensate
F i g . 1.17. Main s t reams o f w a t e r and w a t e r - c o n t a i n i n g media e n t e r i n g o r l e a v i n g a s u g a r f a c t o r y . 1 - p r o c e s s a r e a , 2 - e x t r a c t i o n s t a t i o n , 3 - j u i c e p u r i f i c a t i o n s t a t i o n , 4 - e v a p o r a t o r , 5 - s u g a r h o u s e , 6 - c o n d e n s a t e t a n k , 7 - c o n d e n s e r .
- r e d u c t i o n o f t h e w a t e r i n t a k e t o t h e s u g a r h o u s e .
I t i s a l s o p o s s i b l e t o r educe t h e t o t a l w a t e r i n t a k e by i n t r o d u c i n g new
p r o c e s s e s ; e n e r g y - s a v i n g measures o f t h i s k i n d a r e c o n s i d e r e d i n C h a p t e r 4 .
The j u i c e d r a f t , i . e . t h e r a t i o o f r a w - j u i c e f l o w t o c o s s e t t e s f l o w , c a n n o t
be j u d g e d on t he b a s i s o f hea t e x p e n d i t u r e o n l y , as i t i s c e r t a i n l y one o f t h e
most i m p o r t a n t v a r i a b l e s g o v e r n i n g t h e e x t r a c t i o n p r o c e s s , i n f l u e n c i n g a l s o t h e
s u g a r l o s s i n e x h a u s t e d c o s s e t t e s . The s u g a r l o s s depends a l s o on b e e t q u a l i t y ,
c o s s e t t e s q u a l i t y , and on pH and t e m p e r a t u r e d i s t r i b u t i o n s i n t h e e x t r a c t o r , and
t h o s e f a c t o r s may v a r y d u r i n g t he o p e r a t i n g p e r i o d . I t may t h e r e f o r e be
n e c e s s a r y t o v a r y t h e j u i c e d r a f t so as t o keep t h e s u g a r l o s s a t an a c c e p t a b l y
low l e v e l , and t h i s r e q u i r e m e n t may e v e n t u a l l y c l a s h w i t h t h e e n e r g y - b a s e d
r e q u i r e m e n t o f d r a f t m i n i m i z a t i o n .
I f t h e e n e r g y s a v i n g s a r e l a r g e e n o u g h , t h e n t he l o c a l economic c o n d i t i o n s
may s t i m u l a t e d r a f t r e d u c t i o n even a t t h e c o s t o f i n c r e a s e d s u g a r l o s s
( p a r t i c u l a r l y i f s u g a r r e t e n t i o n i n c r e a s e s t h e v a l u e o f e x h a u s t e d c o s s e t t e s s o l d
as f o d d e r ) . T h i s s i t u a t i o n has been a n a l y s e d f o r t r o u g h - and t o w e r - t y p e
e x t r a c t o r s ( r e f . 3 3 ) . Assuming a s u g a r c o n t e n t i n p r e s s e d p u l p o f abou t 2%, i . e .
a s u g a r l o s s abou t 0.6%, j u i c e d r a f t v a l u e s as low as 95.5% f o r a t r o u g h - t y p e
e x t r a c t o r and 98.6% f o r a t o w e r - t y p e e x t r a c t o r have been c o n s i d e r e d . The
r e s u l t i n g e n e r g y s a v i n g s have been e s t i m a t e d a t 5-10% o f t h e f a c t o r y ' s demand
f o r p r i m a r y e n e r g y .
A c t u a l l y , t he p r i c e s o f f u e l s and s u g a r seem t o s t i m u l a t e f a c t o r y o p e r a t i o n
a t an e x t r a c t i o n l o s s s u b s t a n t i a l l y l o w e r t han t h e above v a l u e , so t h e j u i c e
d r a f t s h o u l d be reduced by m o d i f y i n g t h e e x t r a c t i o n p r o c e s s . T h i s depends m a i n l y
on equ ipment a d j u s t m e n t s ( s e e C h a p t e r 5 ) .
32
The w a t e r i n t a k e t o t h e j u i c e p u r i f i c a t i o n s t a t i o n r e s u l t s m a i n l y f rom m i l k -
o f - l i m e a d d i t i o n s t o t he j u i c e and c a r b o n a t a t i o n s l u d g e s w e e t e n i n g - o f f i n t h e
f i l t e r s . A t y p i c a l m i l k - o f - l i m e c o m p o s i t i o n i s 20% CaO and 80% w a t e r , and t h e
CaO r a t e i s o f t h e o r d e r o f 2 kg p e r 1 kg b e e t . The w a t e r i n t a k e i n t h e m i l k - o f -
l ime can be m i n i m i z e d by m a i n t a i n i n g a low CaO r a t e and h i g h CaO c o n c e n t r a t i o n ,
b u t under no c i r c u m s t a n c e s can a r e d u c t i o n o f t h e j u i c e p u r i f i c a t i o n e f f e c t be
a l l o w e d . T h e r e f o r e , a p r e r e q u i s i t e f o r t h i s k i n d o f e n e r g y s a v i n g i s t o a p p l y
p r o p e r l y d e s i g n e d p r o c e s s equ ipment and e f f e c t i v e a u t o m a t i c c o n t r o l o f key
p r o c e s s v a r i a b l e s . U n n e c e s s a r y w a t e r can a l s o be l a r g e l y e l i m i n a t e d i f l i m e
s l a k i n g i s pe r fo rmed u s i n g j u i c e t apped f rom a p r o p e r l y s e l e c t e d p l a c e i n t h e
j u i c e p u r i f i c a t i o n s t a t i o n ( t y p i c a l l y , j u i c e s e p a r a t e d f rom s u b s i d e r s l u d g e i s
u s e d ) .
The s i t u a t i o n w i t h t he s l u d g e s w e e t e n i n g - o f f i s t o some e x t e n t s i m i l a r t o
t h a t w i t h c o s s e t t e s e x h a u s t i o n , namely t h a t t h e r e i s a t r a d e - o f f between t h e
amount o f w a t e r s u p p l i e d and t h e s u g a r l o s s i n s l u d g e . Depend ing on t h e
f i l t r a t i o n scheme and equ ipment u s e d , w a t e r i n t a k e can be l i m i t e d t o 2-4 kg p e r
100 kg b e e t , t h i s r e s u l t i n g i n a f i n a l s u g a r c o n t e n t o f t h e s l u d g e be low
0 .5-0 .7%.
Water i n t a k e t o t h e s u g a r house may be r e q u i r e d f o r :
- d i l u t i o n o f s y r u p s , when t h e p r o c e s s r e q u i r e m e n t s a r e t h a t t h e i r c o n c e n t r a t i o n
has t o be d e c r e a s e d t o a d e f i n i t e v a l u e ,
- s u g a r m e l t i n g ,
- s u g a r wash i n c e n t r i f u g a l s ,
- magma c o n c e n t r a t i o n c o n t r o l d u r i n g s u g a r b o i l i n g i n vacuum p a n s ,
- v i s c o s i t y c o n t r o l d u r i n g C - m a s s e c u i t e c r y s t a l l i z a t i o n ,
- i o n - e x c h a n g e p r o c e s s e s .
V a r i o u s components o f t h e w a t e r i n t a k e , and t h e i r p r o p o r t i o n s , depend on t h e
c r y s t a l l i z a t i o n scheme a p p l i e d . As t h e q u a l i t y o f t h i c k j u i c e and t h e p r o p e r t i e s
o f n o n - s u g a r s v a r y d u r i n g o p e r a t i o n s , i t may be n e c e s s a r y t o a d j u s t t h e s e
components a c c o r d i n g l y . F o r a g i v e n c r y s t a l l i z a t i o n scheme, s p e c i f i c measures
can be taken t o m i n i m i z e t h e t o t a l w a t e r i n t a k e .
The need f o r t h e d i l u t i o n o f s y r u p s u s u a l l y r e s u l t s f rom t h e f i l t r a t i o n
r e q u i r e m e n t s . F o r e x a m p l e , r e m e l t f i l t r a t i o n i s t y p i c a l l y pe r f o rmed a t a d r y
s u b s t a n c e c o n t e n t be low 68%, and i f t h e r e m e l t c o n c e n t r a t i o n exceeds t h i s v a l u e ,
t hen w a t e r must be added . Howeve r , t h e c r y s t a l l i z a t i o n schemes can be so
d e s i g n e d as t o m i n i m i z e o r even e l i m i n a t e t h e need f o r w a t e r a d d i t i o n t o s y r u p s
i n normal o p e r a t i n g c o n d i t i o n s . I t i s a l s o p o s s i b l e t o e l i m i n a t e t h e w a t e r
i n t a k e t o t h e m e l t i n g o p e r a t i o n , u s i n g t h i n j u i c e i n s t e a d .
The w a t e r i n t a k e t o t he vacuum pans can be reduced t o a n e g l i g i b l y sma l l
v a l u e , p r o v i d i n g o t h e r measures a r e t aken t o s e c u r e e f f i c i e n t s u p e r s a t u r a t i o n
33
c o n t r o l d u r i n g t he s u g a r b o l i n g p r o c e s s . To some e x t e n t , t h i s depends on t h e
c r y s t a l l i z a t i o n scheme, b u t vacuum pan au toma t i on ( a u t o m a t i c b o i l i n g c o n t r o l )
seems t o be a d e c i s i v e f a c t o r . T h i s p rob lem i s a d d i t i o n a l l y d i s c u s s e d i n S e c t i o n
1.3.5 and C h a p t e r 6.
The amount o f w a t e r s u p p l i e d t o b a t c h c e n t r i f u g a l s can be o p t i m i z e d w i t h
r e s p e c t t o c r y s t a l l i z a t i o n n e e d s , t h a t i s , f o r maximum y i e l d o f c r y s t a l l i n e
s u g a r o f a d e f i n i t e q u a l i t y ( r e f s . 3 4 , 3 5 ) . A p r e r e q u i s i t e f o r t h e o p t i m i z a t i o n
i s t h a t t h e w a t e r wash o p e r a t i o n s h o u l d be t r e a t e d as a p a r t o f t h e c e n t r i f u g i n g
c y c l e i n w h i c h t i m e , r o t a t i o n a l v e l o c i t y and t h e a p p l i c a t i o n o f s y r u p wash can
a l s o c o n t r i b u t e t o t he f i n a l r e s u l t s . The w a t e r wash o p t i m i z e d i n t h i s manner
can a l s o be c o n s i d e r e d as o p t i m a l w i t h r e s p e c t t o t h e e n e r g y consumpt ion o f t h e
s u g a r h o u s e . E x p e r i e n c e p r o v e s , h o w e v e r , t h a t t h e o p t i m i z a t i o n r e s u l t s may be
v e r y s e n s i t i v e t o l o c a l c o n d i t i o n s . An example o f an o p t i m i z e d c y c l e f o r
A m a s s e c u i t e c e n t r i f u g i n g i n a s p e c i f i c b a t c h c e n t r i f u g a l i s shown i n F i g . 1.18.
Water i n t a k e t o C m a s s e c u i t e c r y s t a l 1 i z e r s t y p i c a l l y s e r v e s t h e p u r p o s e o f
b r i n g i n g down m a s s e c u i t e v i s c o s i t y . As t h e v i s c o s i t y a l s o depends on t h e
t e m p e r a t u r e , i t i s a l s o p o s s i b l e t o o b t a i n a v i s c o s i t y r e d u c t i o n by i n c r e a s i n g
the t e m p e r a t u r e o f t h e m a s s e c u i t e . T h i s app roach has i t s l i m i t a t i o n s , h o w e v e r ,
as t o o h i g h a t e m p e r a t u r e may a d v e r s e l y a f f e c t c r y s t a l l i z a t i o n e f f i c i e n c y .
A n o t h e r v i s c o s i t y - c o n t r o l method w h i c h r e d u c e s t h e w a t e r i n t a k e employs t h e
a d d i t i o n o f mo lasses t o t he m a s s e c u i t e .
I t s h o u l d be p o i n t e d o u t t h a t a n e t w a t e r i n t a k e may a l s o r e s u l t f rom d i r e c t
use o f steam i n t he s u g a r h o u s e . T h i s a p p l i e s t o such o p e r a t i o n s a s :
- vacuum-pan s t e a m i n g ,
- steam wash i n c e n t r i f u g a l s ,
- d i r e c t h e a t i n g o f s y r u p s i n s t o r a g e t a n k s .
1200 Γ
α 1000
800
600
400
200 o
er
^ / ii \ : J I I! 1 114 41-3 ι
I I I I . I I 1 I
\ ^ 4 ^.5
D 60 120 T ime ( s )
180
g r e e n w a s h
F i g . 1.18. O p t i m i z e d c e n t r i f u g i n g c y c l e f o r A m a s s e c u i t e . 1 - c h a r g i n g , 2 -s y r u p w a s h , 3 - w a t e r w a s h , 4 - d i s c h a r g i n g , 5 - c l e a n i n g ( c o u r t e s y D O S ) .
34
T h e r e i s no doub t t h a t t h e s e o p e r a t i o n s s h o u l d be a v o i d e d , o r t h e equ ipment and
i n s t r u m e n t a t i o n s h o u l d make i t p o s s i b l e t o m i n i m i z e t h e steam c o n s u m p t i o n . F o r
e x a m p l e , t h i s can be done w i t h modern a i r - t i g h t s teaming sys tems w h i c h can a l s o
be i n s t a l l e d i n o l d e r vacuum p a n s .
1.3.5 T h i c k j u i c e c o n c e n t r a t i o n and c r y s t a l l i z a t i o n scheme
I t was ment ioned i n S e c t i o n 1.3.1 t h a t t h e hea t demand o f t h e c r y s t a l l i z a t i o n
p r o c e s s can be d e c r e a s e d by r e d u c i n g t h e w a t e r i n t a k e t o t h e s u g a r h o u s e . T h i s
i s a complex q u e s t i o n , o f w h i c h o n l y a p a r t b e l o n g s t o t h e p rob lem f i e l d
d i s c u s s e d i n t h e p r e c e d i n g S e c t i o n . The r e m a i n i n g p a r t s a r e :
- m a i n t a i n i n g a h i g h t h i c k - j u i c e c o n c e n t r a t i o n ,
- o p t i m i z i n g t he scheme and pa ramete rs o f t h e c r y s t a l l i z a t i o n p r o c e s s .
F i g u r e 1.19 shows t h e e s t i m a t e d r e l a t i o n s h i p between t h e hea t demand o f
a s u g a r house emp loy ing t h e c l a s s i c a l t h r e e - b o i l i n g scheme, and t h e
c o n c e n t r a t i o n o f t h i c k j u i c e . When r e d u c i n g t h e w a t e r i n t a k e i n t he t h i c k - j u i c e
s t ream by 50%, t h a t i s , f rom 11.60 t o 5.80 kg p e r 100 kg b e e t , t h e h e a t demand
can be d e c r e a s e d by n e a r l y 1/3 o f i t s i n i t i a l v a l u e (assumed t o c o r r e s p o n d t o
65% D S ) . T h i s i s an i n d i c a t i o n o f a c o n s i d e r a b l e e n e r g y - s a v i n g p o t e n t i a l
a s s o c i a t e d w i t h p o s s i b l e a d j u s t m e n t s o f t h e t h i c k - j u i c e c o n c e n t r a t i o n . H o w e v e r ,
i t s u t i l i z a t i o n depends on w h e t h e r o r n o t c e r t a i n c o n s t r a i n t s can be met .
W a t e r in t h i c k j u i c e ( kg /100 kg b )
11 10 9 8 7
62 64 66 68 70 72 74
C o n c e n t r a t i o n o f t h i c k j u i c e ( % D S )
F i g . 1.19. Heat demand o f t h e t h r e e - b o i l i n g c r y s t a l l i z a t i o n p r o c e s s , as a f u n c t i o n o f t h i c k - j u i c e c o n c e n t r a t i o n .
The d i f f i c u l t i e s appea r a l r e a d y i n t h e e v a p o r a t i o n p r o c e s s , as i n a s p e c i f i c
m u l t i p l e - e f f e c t e v a p o r a t o r , i n c r e a s e d o u t l e t c o n c e n t r a t i o n may r e q u i r e p r o l o n g e d
j u i c e r e t e n t i o n t i m e , and t h e f i n a l e f f e c t s have t o be o p e r a t e d a t i n c r e a s e d d r y
s u b s t a n c e c o n t e n t . T h i s i n d u c e s t h e r i s k o f e x c e s s i v e the rma l decay o f s u c r o s e
and c o l o u r b u i l d - u p , as w e l l as dangerous i n c r u s t a t i o n s w h i c h may be i n i t i a t e d
35
by c o n c e n t r a t i o n f l u c t u a t i o n s i n t h e l a s t e f f e c t . When a t t e m p t i n g t o i n c r e a s e
t h e c o n c e n t r a t i o n o f t h i c k j u i c e , e v a p o r a t o r d e s i g n and t e m p e r a t u r e l e v e l s i n
a l l e f f e c t s , as w e l l as t h e e v a p o r a t o r c o n t r o l s y s t e m , s h o u l d be r e v i e w e d a n d ,
i f n e c e s s a r y , m o d i f i e d f o r s a f e r o p e r a t i o n . E x p e r i e n c e p r o v e s t h a t i t i s n o t
o n l y i n t he i n i t i a l e f f e c t s o p e r a t e d a t h i g h e s t t e m p e r a t u r e s , b u t a l s o i n t h e
f i n a l e f f e c t s , where t h e s i t u a t i o n may become c r i t i c a l w i t h r e s p e c t t o c o l o u r
b u i l d - u p . T h i s may n e c e s s i t a t e r e p l a c i n g t h e e v a p o r a t o r b o d i e s c o n c e r n e d by new
ones e n s u r i n g reduced j u i c e r e t e n t i o n t i m e .
A n o t h e r p rob lem i s a s s o c i a t e d w i t h t h i c k - j u i c e f i l t r a t i o n a t c o n c e n t r a t i o n s
e x c e e d i n g 65-67% DS. C o n v e n t i o n a l f i l t e r s a r e n o t s u i t e d t o h i g h e r
c o n c e n t r a t i o n s and s h o u l d pe rhaps be r e p l a c e d by c e n t r i f u g a l s e p a r a t o r s , wh i ch
have p r o v e d t o work s a t i s f a c t o r i l y i n numerous f a c t o r i e s . T h e r e i s a l s o
a p o s s i b i l i t y o f a p p l y i n g c o n v e n t i o n a l f i l t e r s , n o t n e x t t o t h e e v a p o r a t o r
o u t l e t bu t p r i o r t o t h e l a s t e v a p o r a t o r e f f e c t ; one p o s s i b l e a r rangemen t i s
shown i n F i g . 1.20 ( r e f . 3 6 ) .
e x h a u s t s t e a m
thin j u i ce ϊ [ U % D S . 125°C
r t 3a
Γ 5 5 ^ 6 0 % D S ^
110 °C
3b
] Γ t h i ck ju ice 7 5 % D S . 9 6 %
F i g . 1.20. J u i c e f i l t e r F between e v a p o r a t o r b o d i e s i n t h e t h i r d e f f e c t o f a " f o u r - a n d - a - h a l f - e f f e c t " e v a p o r a t o r ( a f t e r r e f . 3 6 ) .
As r e g a r d s t he o p t i m i z a t i o n o f t h e c r y s t a l l i z a t i o n scheme and p a r a m e t e r s ,
t h i s i s n e c e s s i t a t e d by i n c r e a s e d c o n c e n t r a t i o n s o f t h i c k j u i c e and s y r u p s
because new prob lems a r e c r e a t e d i n t h e b o i l i n g p r o c e s s . Wh i te s u g a r b o i l i n g i n
a b a t c h - t y p e vacuum pan can be r o u g h l y d i v i d e d i n t o t h r e e s t a g e s ( F i g . 1 . 2 1 ) :
( 1 ) E v a p o r a t i o n o f t he i n i t i a l l y drawn u n d e r s a t u r a t e d s o l u t i o n u n t i l a
s u p e r s a t u r a t i o n o f abou t 1.15 i s a t t a i n e d . A h i g h c o n c e n t r a t i o n o f t h i c k j u i c e
i s f a v o u r a b l e w i t h r e s p e c t t o e n e r g y economy, as i t r e s u l t s i n l e s s h e a t
consumed d u r i n g t h i s s t a g e .
( 2 ) Seed ing and c r y s t a l f o r m a t i o n , f o l l o w e d by s l o w c r y s t a l g r o w t h as t h e vacuum
pan i s l o a d e d t o i t s maximum c h a r g e . I n o r d e r t o m a i n t a i n t h e i n t e n s i v e
c i r c u l a t i o n r e q u i r e d f o r u n i f o r m s y r u p s u p e r s a t u r a t i o n and u n i f o r m magma
s t r u c t u r e , t he e v a p o r a t i o n i s c o n t i n u e d w i t h accompany ing i n t a k e s o f
u n d e r s a t u r a t e d s o l u t i o n s . T h e r e i s a r i s k t h a t t h e t h i c k j u i c e c o n c e n t r a t i o n may
36
S t a g e s :
F i g . 1.21. S tages o f t h e w h i t e - s u g a r b o i l i n g p r o c e s s : 1 - e v a p o r a t i o n , 2 -s e e d i n g , c r y s t a l f o r m a t i o n and s l o w c r y s t a l g r o w t h , 3 - a c c e l e r a t e d c r y s t a l g r o w t h .
t u r n o u t t o be j u s t t o o h i g h f o r i n t a k e s meant t o b r i n g t h e s u p e r s a t u r a t i o n down
t o t he r e q u i r e d v a l u e .
( 3 ) A c c e l e r a t e d c r y s t a l g r o w t h as t h e s t r i k e i s t h i c k e n e d u n t i l t h e d e s i r e d
c r y s t a l c o n t e n t has been r e a c h e d . An e v e n t u a l i n t a k e o f h i g h - c o n c e n t r a t i o n t h i c k
j u i c e c o u l d a g a i n be f a v o u r a b l e .
Because o f t h e d i f f i c u l t i e s w h i c h may o c c u r i n s t a g e ( 2 ) , t h e i n t r o d u c t i o n o f
h i g h - c o n c e n t r a t i o n t h i c k j u i c e and s y r u p s c a n n o t be r e g a r d e d as a m ino r
m o d i f i c a t i o n o f t h e c r y s t a l l i z a t i o n p r o c e s s . The s u p e r s a t u r a t i o n can o f c o u r s e
be a d j u s t e d by t a k i n g i n w a t e r , b u t t h i s wou ld c o u n t e r a c t h e a t s a v i n g s . The
p rob lem becomes l e s s c r i t i c a l when s t i r r e d vacuum pans a r e u s e d , making i t
e a s i e r t o m a i n t a i n u n i f o r m s u p e r s a t u r a t i o n i n t h e e n t i r e s t r i k e vo lume .
O p e r a t i o n a l s a f e t y can be f u r t h e r improved by e q u i p p i n g t h e pans w i t h a u t o m a t i c
b o i l i n g c o n t r o l s . The b e s t s o l u t i o n seems t o be t o r e l y on c r y s t a l f o o t i n g ,
w h i c h can h a r d l y be r e g a r d e d as a l i m i t e d m o d i f i c a t i o n b u t r a t h e r as a new
p r o c e s s ; i t i s t h e r e f o r e d i s c u s s e d i n C h a p t e r 4 .
I f t he f o o t i n g p r o c e s s t u r n s o u t t o be t o o advanced w i t h r e g a r d t o t h e s u g a r
house equ ipment a v a i l a b l e , t hen t he c r y s t a l l i z a t i o n scheme w i t h two j u i c e
c o n c e n t r a t i o n s can be a p p l i e d ( r e f . 3 7 ) . I t s e s s e n t i a l i d e a c o n s i s t s o f
t h i c k e n i n g a p a r t o f t h e j u i c e f l o w t o a c o n c e n t r a t i o n e x c e e d i n g 70% DS, w h i l e
t h e r ema in i ng p a r t i s t apped i m m e d i a t e l y a f t e r f i l t r a t i o n , t h a t i s , a t
65-67% DS. H i g h - c o n c e n t r a t i o n j u i c e i s used f o r i n t a k e s d u r i n g t h e f i r s t and
t h i r d s t a g e s o f t h e b o i l i n g p r o c e s s , w h i l e t h e a v a i l a b i l i t y o f l o w - c o n c e n t r a t i o n
j u i c e makes i t e a s i e r t o p e r f o r m t h e c r i t i c a l second s t a g e . I t s h o u l d be made
c l e a r t h a t t h i s method does n o t a l l o w f u l l u t i l i z a t i o n o f t h e h e a t - s a v i n g
p o t e n t i a l o f t he c o n c e n t r a t i o n o f t h i c k j u i c e . I t has been r e p o r t e d t h a t i f
a h a l f o f t he t h i c k - j u i c e s t ream a f t e r f i l t r a t i o n i s t h i c k e n e d t o 74% DS and
t h e o t h e r h a l f remains a t 67% DS, t h e n t h e f a c t o r y ' s steam demand can be r e d u c e d
by abou t 2 kg/100 kg b ( r e f . 3 8 ) . I f t h e e n t i r e t h i c k - j u i c e s t r eam was t h i c k e n e d
37
t o 74% DS, t hen a c c o r d i n g t o F i g . 1.18 a 15% r e d u c t i o n , t h a t i s , by
3.2 kg/100 kg b , w o u l d be p o s s i b l e .
1.4 POWER DEMAND
1.4.1 Scope o f t h e p rob lems
Wi th combined g e n e r a t i o n o f h e a t and e l e c t r i c i t y , t h e l a r g e r t h e steam f l o w
e x t r a c t e d f rom t h e t u r b i n e e x h a u s t , t h e more power can be p roduced i n t h e
e l e c t r i c a l g e n e r a t o r . I n a s u g a r f a c t o r y e q u i p p e d w i t h a p r o p e r l y d i m e n s i o n e d
t u r b o - g e n e r a t o r , and where t h e h e a t consump t i on e x c e e d s t h e e q u i v a l e n t o f
40-45 kg steam p e r 100 kg b e e t , t h e e l e c t r i c a l power s h o u l d be amp le .
The t r e n d towards f u e l s a v i n g s i m p l i e s a r e d u c e d steam f l o w t h r o u g h t h e
t u r b i n e . A t t h e same t i m e , economic f a c t o r s s t i m u l a t e a t e n d e n c y t o mechan ize
and automate a l l t h e u n i t o p e r a t i o n s i n t h e s u g a r i n d u s t r y , t h i s r e s u l t i n g i n
i n c r e a s e d power demand. The i n t r o d u c t i o n o f new e l e c t r i c i t y - c o n s u m i n g equ ipmen t
needed f o r e n v i r o n m e n t a l p r o t e c t i o n , l i k e s l u d g e p r e s s e s , w a s t e - w a t e r t r e a t m e n t
p l a n t s , e t c . , o r t h e a p p l i c a t i o n o f mechan ica l v a p o u r c o m p r e s s o r s , may a l s o
i n c r e a s e t h e power demand. C o n s e q u e n t l y , an i n c r e a s i n g number o f s u g a r f a c t o r i e s
a r e r e a c h i n g t h e p o i n t o f imba lance between t h e steam demand and power demand,
and s p e c i a l measures may be r e q u i r e d t o s e c u r e a r e l i a b l e e n e r g y s u p p l y . I t t hus
becomes i n c r e a s i n g l y i m p o r t a n t t o have s u f f i c i e n t i n f o r m a t i o n on t h e r e l a t i o n
between t h e power demand and t h e f a c t o r y ' s a b i l i t y t o g e n e r a t e i t s own power .
From t h e p o i n t o f v i e w o f e n e r g y b a l a n c e s , a d e s c r i p t i o n o f t h e power demand i n
terms o f t i m e - a v e r a g e d f i g u r e s i s n e e d e d . F o r t h e d i m e n s i o n i n g o f p o w e r -
g e n e r a t i n g and p o w e r - d i s t r i b u t i n g equ ipment and f o r r e l i a b l e c o n t r o l o f t h e
o p e r a t i o n o f t h e e n t i r e e l e c t r i c a l s u b s y s t e m , t h e i n s t a n t a n e o u s demand and i t s
v a r i a t i o n s s h o u l d a l s o be d e f i n e d .
1.4.2 Power ne twork
The e l e c t r i c i t y i s p r o d u c e d as a l t e r n a t i n g c u r r e n t i n a t h r e e - p h a s e s u p p l y .
When compared t o t h e d i r e c t - c u r r e n t i n s t a l l a t i o n s s t i l l i n use i n many
f a c t o r i e s , m o s t l y f o r h i s t o r i c a l r e a s o n s , a l t e r n a t i n g - c u r r e n t sys tems o f f e r t h e
advan tages o f :
- easy t r a n s f o r m a t i o n f rom h i g h t o low v o l t a g e ,
- economic s o l u t i o n f o r power t r a n s m i s s i o n and u t i l i z a t i o n i n l a r g e and medium-
s i z e u n i t s ,
- low c o s t o f t h e m o t o r s .
The s y n c h r o n o u s t h r e e - p h a s e g e n e r a t o r s employ t h r e e g r o u p s o f f i x e d w i n d i n g s
i n w h i c h t h e a l t e r n a t i n g c u r r e n t i s i n d u c e d , and a r o t a t i n g w i n d i n g s u p p l i e d
w i t h d i r e c t c u r r e n t f rom a dynamo ( e x c i t e r ) s i t u a t e d a t t h e end o f t h e r o t o r
s h a f t . The power o u t p u t o f t h e g e n e r a t o r i s c o n t r o l l e d by t h e e x c i t e r c u r r e n t .
S m a l l e r t u r b o - g e n e r a t o r s a r e g e n e r a l l y o f g e a r e d t y p e : t h e t u r b i n e runs a t up t o
38
20 000 rpm a n d , t h r o u g h r e d u c t i o n g e a r s , d r i v e s a g e n e r a t o r r u n n i n g a t 1500 rpm.
A t h i g h e r o u t p u t r a t i n g s , t h e t u r b i n e runs a t 3000 rpm w i t h d i r e c t d r i v e t o
a g e n e r a t o r .
I n o r d e r t o m in im i ze e n e r g y l o s s e s , e l e c t r i c i t y g e n e r a t i o n and t r a n s m i s s i o n
s h o u l d be pe r fo rmed a t low c u r r e n t a n d , c o r r e s p o n d i n g l y , h i g h v o l t a g e . T y p i c a l
v o l t a g e l e v e l s employed a r e s e v e r a l t housands v o l t s . The t r a n s f o r m a t i o n t o t h e
v o l t a g e l e v e l o f motors and o t h e r power r e c e i v e r s ( i . e . power -consuming d e v i c e s )
t akes p l a c e i n t r a n s f o r m e r s w h i c h a r e c o n v e n i e n t l y p l a c e d w i t h i n c l o s e range o f
t h e r e c e i v e r s . The h i g h - v o l t age p a r t o f t he power ne twork i s s e p a r a t e d by
c i r c u i t - b r e a k e r s f rom e n e r g y s o u r c e s ( t h a t i s , g e n e r a t o r s o r s u p p l y l i n e s f rom
t h e e x t e r n a l g r i d ) and t r a n s f o r m e r s . The l o w - v o l t a g e w i n d i n g o f a t r a n s f o r m e r i s
t y p i c a l l y c o n n e c t e d v i a a power c a b l e o r b a r t o a s w i t c h b o a r d , f u r t h e r e n e r g y
d i s t r i b u t i o n t a k i n g p l a c e t o l o c a l s w i t c h b o a r d s o r d i r e c t l y t o l a r g e i n d i v i d u a l
r e c e i v e r s . P o s s i b l e power ne twork a r rangements and t h e i r c o n n e c t i o n s t o t h e
e x t e r n a l power g r i d a r e d i s c u s s e d i n t h e l i t e r a t u r e ( r e f . 3 9 ) .
Among t h e r e c e i v e r s c o n n e c t e d t o t h e power n e t w o r k , a s y n c h r o n o u s e l e c t r i c
motors a r e o f p a r t i c u l a r i m p o r t a n c e . The c o n v e r s i o n o f e l e c t r i c a l i n t o
mechan ica l e n e r g y t a k i n g p l a c e i n t h e s e motors i s accompanied by a l t e r n a t i n g
m a g n e t i z a t i o n o f t h e a c t i v e i r o n . Wi th t h e c h a r a c t e r i s t i c f r e q u e n c y o f t h e
c u r r e n t (50 Hz i n E u r o p e , 60 Hz i n U S ) , t he e l e c t r i c a l e n e r g y i s consumed and
r e c o v e r e d c o r r e s p o n d i n g t o m a g n e t i z a t i o n and c o u n t e r - m a g n e t i z a t i o n . As a r e s u l t ,
i n a d d i t i o n t o t h e f l o w o f e l e c t r i c a l power b e i n g c o n v e r t e d i n t o mechan i ca l work
( c a l l e d e f f e c t i v e power N ^ ) , m a g n e t i z a t i o n e n e r g y i s o s c i l l a t i n g between t h e
s o u r c e and t h e m o t o r s . T h i s i m p l i e s t h a t t he c o n d u c t o r s o f power c a b l e s a r e
c a r r y i n g some a d d i t i o n a l c u r r e n t ; t h e a d d i t i o n a l power i s c a l l e d t h e r e a c t i v e
p o w e r , N ^ . The a c t u a l l o a d o f t h e s o u r c e i s equa l t o t h e g e o m e t r i c sum o f
e f f e c t i v e and r e a c t i v e p o w e r , a l s o c a l l e d t h e a p p a r e n t power N ^ . T h i s phenomenon a
i s u s u a l l y c h a r a c t e r i z e d by t h e s o - c a l l e d power f a c t o r cos φ = Ng/Ng^ ( 1 . 7 )
where φ i s t he phase l a g between t h e e f f e c t i v e power and t h e a p p a r e n t p o w e r .
G e n e r a l l y , each power r e c e i v e r i n a power ne twork can be c h a r a c t e r i z e d , a t
each i n s t a n t , by a s p e c i f i c power f a c t o r . F o r t h r e e - p h a s e a s y n c h r o n o u s m o t o r s ,
w h i c h a r e by f a r t h e most i m p o r t a n t moto rs f o r s u g a r f a c t o r i e s , t h e power f a c t o r
i s a f u n c t i o n o f motor d e s i g n , power r a t i n g and l o a d f a c t o r . I n F i g . 1 .22 ,
a t y p i c a l r e l a t i o n s h i p between t h e power f a c t o r , power r a t i n g and l o a d f a c t o r i s
shown f o r e n c l o s e d - t y p e , 4 - p o l e motors o f J a p a n e s e make w o r k i n g a t 50 Hz ( r e f .
2 8 ) . As can be s e e n , t he l o a d d e v i a t i o n f rom t h e motor r a t i n g i s d e c i s i v e i n
r e d u c i n g cos φ.
The a v e r a g e d power f a c t o r s o f t he r e c e i v e r s d e f i n e t he power f a c t o r o f t h e
g e n e r a t o r . I n a f a c t o r y i n w h i c h no s p e c i a l measures a r e t aken t o improve i t .
39
0.25 0.5 0.75 Load factor
1.0
F i g . 1.22. Power f a c t o r o f e n c l o s e d - t y p e , 4 - p o l e i n d u c t i o n motors o p e r a t e d a t 50 Hz ( a f t e r r e f . 2 8 ) .
cos φ i s u s u a l l y i n t h e range 0 . 6 5 - 0 . 7 0 . L e t us o b s e r v e t h a t t h e maximum
e f f e c t i v e power o f t h e g e n e r a t o r i s d e t e r m i n e d by t h e mechan ica l o u t p u t o f t h e
t u r b i n e . The e l e c t r i c d i m e n s i o n i n g o f t h e g e n e r a t o r m u s t , h o w e v e r , be adap ted
t o t he a p p a r e n t p o w e r , t h a t i s , t h e t u r b i n e o u t p u t d i v i d e d by t h e power f a c t o r .
I n an e x i s t i n g f a c t o r y , t h e r e a c t i v e power o s c i l l a t i n g i n t h e power ne two rk may
cause t h e a p p a r e n t power t o e x c e e d t h e l e v e l f o r w h i c h t h e g e n e r a t i n g and
d i s t r i b u t i n g equ ipment i s d i m e n s i o n e d , even i f t h e t u r b i n e o u t p u t i s
s u f f i c i e n t l y l a r g e t o s u p p l y t h e Sys tem w i t h e f f e c t i v e power . I n o r d e r t o
p r e v e n t t h i s s i t u a t i o n , t h e power f a c t o r o f t h e g e n e r a t o r can be m o d i f i e d by
g e n e r a t i n g r e a c t i v e power i n power c a p a c i t o r s . The c a p a c i t o r s can be c o n n e c t e d
e i t h e r t o t h e main s w i t c h b o a r d o f t h e power h o u s e , o r t o t h e l o c a l s w i t c h b o a r d s
where r e c e i v e r s r e s p o n s i b l e f o r a low power f a c t o r a r e c o n n e c t e d . As i n d i c a t e d
a b o v e , t h e s e r e c e i v e r s a r e a s y n c h r o n o u s motors and p a r t i c u l a r l y ones l o a d e d
be low t h e i r nominal o u t p u t s .
D i s r e g a r d i n g t h e case o f i m p r o p e r l y d i m e n s i o n e d m o t o r s , i t can t h u s be
c o n c l u d e d t h a t when a t t e m p t i n g t o max imize t h e power f a c t o r , c a r e s h o u l d be
taken o f :
- b a t c h c e n t r i f u g a l d r i v e s d u r i n g most o f t h e i r w o r k i n g c y c l e ,
- d r i v e s o f pumps and fans emp loy i ng f l o w c o n t r o l by t h r o t t l i n g d u r i n g t h e
p e r i o d s o f r educed f l o w .
L e t us n o t e t h a t t h e power f a c t o r s o f t h e moto rs men t ioned may v a r y as t h e i r
l oads a r e c h a n g e d , and i t may be n e c e s s a r y t o v a r y t h e r e a c t i v e power g e n e r a t e d
i n t he c a p a c i t o r s a c c o r d i n g l y . H o w e v e r , i f t h e o p e r a t i o n o f a g r o u p o f l a r g e
motors can be c o n t r o l l e d f o r n e a r l y c o n s t a n t t o t a l power c o n s u m p t i o n , i t may
40
a l s o become e a s i e r t o c o n t r o l t h e o v e r a l l r e a c t i v e power o f t h e e n t i r e g r o u p .
T h i s p r i n c i p l e i s a p p l i e d i n t he g r o u p c o n t r o l o f b a t c h c e n t r i f u g a l d r i v e s ( s e e
S e c t i o n 1 . 4 . 3 ) .
1.4.3 Shap ing t he power demand
The s p e c i f i c power demand o f c o n t e m p o r a r y s u g a r f a c t o r i e s i s u s u a l l y o f t h e
o r d e r 2-4 kWh p e r 100 kg b e e t . I t i s i n t e r e s t i n g t o n o t e t h e i n f l u e n c e o f t h e
economy o f s c a l e , namely a l a r g e r p r o c e s s i n g c a p a b i l i t y u s u a l l y i m p l i e s a l o w e r
power demand p e r u n i t mass o f b e e t s p r o c e s s e d . I n F i g . 1 .23, t h e c o n t i n u o u s l i n e
r e p r e s e n t s S o v i e t da ta on t h e s o - c a l l e d b a s i c power demand ( e x c l u d i n g power
consumed i n p u l p d r y i n g and w a s t e - w a t e r t r e a t m e n t ) o f w h i t e - s u g a r m a n u f a c t u r e i n
f a c t o r i e s w i t h p r o c e s s i n g c a p a b i l i t i e s up t o 9000 t o n s p e r day ( r e f . 4 0 ) . The
d i s c r e t e p o i n t s i n t h e d iag ram r e p r e s e n t s t a t i s t i c a l d a t a on o v e r a l l power
c o n s u m p t i o n , i n c l u d i n g p u l p d r y i n g , i n a few West European w h i t e - s u g a r f a c t o r i e s
d u r i n g t he 1985 s e a s o n ; owing t o d i f f e r e n c e s i n p r o c e s s e s and equ ipment
e m p l o y e d , t he i n f l u e n c e o f t h e economy o f s c a l e i s n o t a p p a r e n t f rom t h e s e d a t a .
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
o o JZ
TD C Ό Ε α; •Ό
χ
3 4 5 6 7
P r o c e s s i n g c a p a b i l i t y ( 1 0 0 0 t / d )
F i g . 1.23. S p e c i f i c power demand as a f u n c t i o n o f t h e p r o c e s s i n g c a p a b i l i t y . The l i n e i n d i c a t e s S o v i e t da ta on w h i t e - s u g a r m a n u f a c t u r e , and t h e p o i n t s -s t a t i s t i c a l da ta on 5 West European f a c t o r i e s .
The c o n t r i b u t i o n s od v a r i o u s f a c t o r y s e c t i o n s t o t h e o v e r a l l power demand may
v a r y , depend ing on l o c a l c o n d i t i o n s . F o r e x a m p l e , t h e e n e r g y consumed by pump
d r i v e s depends on h e i g h t d i f f e r e n c e s between p i e c e s o f equ ipment l o c a t e d a l o n g
t h e t r a n s p o r t r o u t e s o f a l i q u i d . The f o l l o w i n g a p p r o x i m a t e i n d i c e s d e s c r i b e
a t y p i c a l s t r u c t u r e o f t he power demand o f w h i t e - s u g a r m a n u f a c t u r e i n f a c t o r i e s
w i t h p r o c e s s i n g c a p a b i l i t i e s o f 4000-6000 t o n s p e r d a y :
41
- e x t r a c t i o n s t a t i o n 10-12%,
- j u i c e p u r i f i c a t i o n and j u i c e t r a n s p o r t 20-25%,
- s u g a r house 14-20%,
- l ime k i l n , m i l k - o f - l i m e p r e p a r a t i o n and k i l n - g a s pumping 12-16%,
- o t h e r p u r p o s e s 36-43%.
A t t h e p r e s e n t s t a t e o f deve lopmen t o f power ne two rks and t h e i r e q u i p m e n t ,
v a r i o u s t e c h n i q u e s can be used t o m o d i f y t h e power demand t owa rds b e t t e r e n e r g y
economy. F o u r app roaches can be e m p l o y e d .
( i ) I n t r o d u c t i o n o f a l t e r n a t i v e p r o c e s s e s c h a r a c t e r i z e d by a l o w e r power demand.
( i i ) A p p l i c a t i o n o f new equ ipment c h a r a c t e r i z e d by a b e t t e r e f f i c i e n c y o f power
u t i l i z a t i o n .
( i i i ) A p p l i c a t i o n o f a l t e r n a t i v e c o n t r o l methods a t t h e l o c a l (equipm.ent) l e v e l ,
p r e v e n t i n g t h e l o s s e s o f e n e r g y d e l i v e r e d t o e l e c t r i c a l l y d r i v e n e q u i p m e n t ,
p a r t i c u l a r l y unde r v a r i a b l e l o a d .
( i v ) I n t r o d u c t i o n o f new c o n t r o l methods a t t h e subsys tem o r sys tem l e v e l ,
making i t p o s s i b l e t o i n f l u e n c e t h e t ime v a r i a t i o n s o f power demand.
The p o s s i b i l i t i e s o f i n t r o d u c i n g a l t e r n a t i v e p r o c e s s e s v a r y f rom f a c t o r y t o
f a c t o r y , depend ing on t h e o p p o r t u n i t i e s t o i n v e s t , u s u a l l y i n c o n n e c t i o n w i t h
f a c t o r y e x t e n s i o n s . F o r e x a m p l e , h y d r a u l i c b e e t u n l o a d i n g and t r a n s p o r t ,
r e q u i r i n g t h a t abou t 3 m^ w a t e r p e r 1 t b e e t r e c e i v e d i s pumped, i s more e n e r g y -
i n t e n s i v e than d r y u n l o a d i n g and t r a n s p o r t . Power s a v i n g s r e p o r t e d f rom F r e n c h
f a c t o r i e s where t he d r y method has been implemented a r e o f t h e o r d e r o f 0 .3 kWh
p e r 100 kg b e e t ( r e f . 4 1 ) . D i f f e r e n t methods o f d i r t s e p a r a t i o n , h o w e v e r , may
d i f f e r w i t h r e s p e c t t o t h e power c o n s u m p t i o n .
I n t h e p a s t , t o o l i t t l e a t t e n t i o n was p a i d t o t h e power demands o f v a r i o u s
p r o c e s s e s . Now t h i s i s b e g i n n i n g t o c h a n g e , as has been i n d i c a t e d by some r e c e n t
p u b l i c a t i o n s i n w h i c h t h e i n f l u e n c e o f p r o c e s s pa rame te rs on t h e e n e r g y demand
i s s t u d i e d ( r e f s . 4 2 , 4 3 ) . The e n e r g y i n t e n s i t y o f new p r o c e s s e s i s a d d i t i o n a l l y
d i s c u s s e d i n C h a p t e r 4 .
As r e g a r d s t h e e l e c t r i c a l e q u i p m e n t , t h e o p e r a t i o n o f b a t c h c e n t r i f u g a l
d r i v e s w h i c h a r e t h e cause o f l o a d peaks i s p a r t i c u l a r l y i m p o r t a n t . F o r economic
r e a s o n s , a t r e n d has been e s t a b l i s h e d t o w a r d s l a r g e - c a p a c i t y m a c h i n e s , t o d a y
r e a c h i n g 1000-1700 kg p e r c h a r g e . The moments o f i n e r t i a o f r o t o r s i n t h e
l a r g e s t machines a r e o f t h e o r d e r 1000-1400 kg m . I n o r d e r t o a c c e l e r a t e such
r o t o r s t o t y p i c a l r o t a t i o n a l v e l o c i t i e s o f 1000-1500 rpm i n a b o u t 20 w o r k i n g
c y c l e s p e r h o u r , motors r e a c h i n g a power l e v e l o f 250-300 kW a r e r e q u i r e d . E v e r y
a c c e l e r a t i o n s e c t i o n o f t h e c e n t r i f u g i n g c y c l e causes a l a r g e t e m p o r a r y l o a d ,
w h i l e e v e r y d e c e l e r a t i o n s e c t i o n a l l o w s t h e p o s s i b i l i t y o f r e t u r n i n g power t o
t he e l e c t r i c a l subsys tem o f t h e f a c t o r y . The o p e r a t i o n o f b a t c h - c e n t r i f u g a l
d r i v e thus r e s u l t s i n t i m e - v a r y i n g e f f e c t i v e and r e a c t i v e l o a d s . I t i s t h e r e f o r e
42
e s s e n t i a l t h a t d u r i n g t h e o p e r a t i o n o f a g r o u p o f c e n t r i f u g a l s , t h e c y c l e s o f
i n d i v i d u a l machines a r e c o o r d i n a t e d i n o r d e r t o a v o i d s i m u l t a n e o u s a c c e l e r a t i o n
o f s e v e r a l u n i t s .
The c o n t r o l o f b a t c h c e n t r i f u g a l s a c c o r d i n g t o t h i s p r i n c i p l e c o n s t i t u t e s
an example o f equ ipment o p e r a t i o n c o n t r o l a t t h e l o c a l ( equ ipmen t g r o u p , o r
s t a t i o n ) l e v e l . T h i s s o l u t i o n i s p a r t i c u l a r l y u s e f u l f o r l a r g e power r e c e i v e r s
c h a r a c t e r i z e d by s u b s t a n t i a l l o a d v a r i a t i o n s .
I n t h e c o n t e m p o r a r y s u g a r i n d u s t r y , pe rhaps t h e l a r g e s t p o w e r - s a v i n g
p o t e n t i a l i s a s s o c i a t e d w i t h t h e d r i v e s o f pumps and f a n s . On a v e r a g e , t h e s e
machines a r e r e s p o n s i b l e f o r abou t 60% o f t h e e l e c t r i c a l e n e r g y consumed i n
a s u g a r f a c t o r y . D imens ioned f o r t h e l a r g e s t p o s s i b l e f l o w s o f m e d i a , t h e pumps
and fans a r e c o n t r o l l e d u s i n g methods w h i c h i n d u c e e n e r g y l o s s e s , t h a t i s , f l o w
b y - p a s s i n g o r t h r o t t l i n g . T h i s i s a d e c i s i v e f a c t o r i n c a u s i n g i n c r e a s e d
s p e c i f i c power consumpt ion when t h e f a c t o r y ' s p r o c e s s i n g c a p a b i l i t y f a l l s be low
i t s nominal l e v e l ( F i g . 1 . 24 ) . Wi th modern d r i v i n g s y s t e m s , o l d e r c o n t r o l
methods can be r e p l a c e d by t h e v a r i a b l e speed c o n t r o l w h i c h i s d i s c u s s e d i n
C h a p t e r 6. T y p i c a l s a v i n g s a r e o f t h e o r d e r o f 20-40% o f t h e e n e r g y consumed
when u s i n g t h e o r i g i n a l methods .
o o " 1.6 •α
i 1. φ •o ir '• φ o
o- 1.0 50 60 70 80 90 100
A v e r a g e to nomina l d a i l y capab i l i t y ( % )
F i g . 1.24. R a t i o o f a c t u a l t o nominal s p e c i f i c power demand as a f u n c t i o n o f t h e u t i l i z a t i o n o f p r o c e s s i n g c a p a b i l i t y .
A t t h e f a c t o r y l e v e l , a t i m e - v a r y i n g t o t a l power demand may cause
d i f f i c u l t i e s i n s e c u r i n g a r e l i a b l e power s u p p l y . Load peaks e x c e e d i n g t h e
g e n e r a t i n g c a p a b i l i t y o f t h e e l e c t r i c a l subsys tem c a n n o t be met w i t h o u t
s u p p l y i n g power f rom t h e e x t e r n a l g r i d . I n o r d e r t o a v o i d u n n e c e s s a r y e n e r g y
p u r c h a s e s , o r i f no e l e c t r i c i t y s u p p l i e s f rom o u t s i d e t h e f a c t o r y a r e a v a i l a b l e ,
such peaks must be e l i m i n a t e d by t e m p o r a r i l y d i s c o n n e c t i n g c e r t a i n power
r e c e i v e r s . T h i s can be done w i t h o u t r e d u c i n g t h e t o t a l e n e r g y amount r e q u i r e d
f o r normal f a c t o r y o p e r a t i o n , t h a t i s , by c o n t r o l l i n g t h e power demand o n l y when
i t app roaches i t s maximum.
43
The power r e c e i v e r s t o be d i s c o n n e c t e d a r e s e l e c t e d so as n o t t o cause any
damage t o normal f a c t o r y o p e r a t i o n . T y p i c a l l y , t h e s e a r e a e r a t o r s o f w a s t e - w a t e r
t r e a t m e n t p l a n t s , a i r c o n d i t i o n i n g sys tems o f s u g a r and p e l l e t s i l o s , and
e l e c t r i c room h e a t e r s .
E x p e r i e n c e p r o v e s t h a t c o n t r o l o f t h e maximum power demand can be e f f e c t i v e
o n l y i f automated l o a d - m o n i t o r i n g and l o a d - d i s c o n n e c t i n g equ ipment i s u s e d . The
n e c e s s a r y e l e c t r o n i c equ ipment can be r a t h e r i n e x p e n s i v e , as p r o v e d by
a p p l i c a t i o n examples p r e s e n t e d i n t h e l i t e r a t u r e ( r e f s . 4 5 , 4 6 ) . The sys tem i s
measur ing t h e i n s t a n t a n e o u s power demand and compar ing i t w i t h t h e g e n e r a t i n g
c a p a c i t y . I f a p r e d e t e r m i n e d c r i t i c a l d i f f e r e n c e between t h e s e two q u a n t i t i e s
i s a p p r o a c h e d , t h e n a g r o u p o f r e c e i v e r s i s d i s c o n n e c t e d . I n a b r o a d e r l o a d
r a n g e , t h e sys tem o p e r a t i o n i s u s u a l l y s e m i - a u t o m a t i c , a l l o w i n g f o r t h e
i n t e r v e n t i o n o f human o p e r a t o r s , and i t may a l s o i n c o r p o r a t e t r e n d m o n i t o r i n g ,
s i g n a l l i n g o f c r i t i c a l s i t u a t i o n s , p r i n t i n g o f p r o c o t o l s and r e p o r t s , e t c . As
an o p t i o n , t h e m o n i t o r i n g o f t he r e a c t i v e power and t h e a u t o m a t i c c o n t r o l o f
t he power c a p a c i t o r s t o improve t h e power f a c t o r can a l s o be i n c l u d e d .
1.5 INTERACTION BETWEEN POWER GENERATION AND HEAT ECONOMY
1.5.1 E n e r g y p o l i c y c o n s i d e r a t i o n s
The t a s k o f t h e power house can be u n d e r s t o o d as t r a n s f o r m i n g t h e p r i m a r y
e n e r g y s u p p l i e d t o t he f a c t o r y i n t o t h e n e c e s s a r y n e t h e a t i n p u t Q2 and power
i n p u t P ' . The n e t h e a t i n p u t i s o f t e n e x p r e s s e d as t h e mass f l o w o f steam
r e q u i r e d t o c a r r y i t ; t h i s f l o w w i l l be c a l l e d steam demand i n t h e f o l l o w i n g .
Assuming t h e s o - c a l l e d normal steam p a r a m e t e r s , t h a t i s , d r y s a t u r a t i o n s t a t e a t
tg = lOO^C and s p e c i f i c h e a t o f e v a p o r a t i o n r^ = 2256.9 k J / k g , t h e steam demand
can be d e f i n e d as
D' = Q2 / r3 ( 1 . 8 )
The above c o n v e n t i o n i s t o some e x t e n t s i m i l a r t o t h e use o f t h e w i d e l y known
c o n c e p t o f t h e demand f o r normal f u e l ( h e a t i n g v a l u e 29 300 k J / k g ) i n e x p r e s s i n g
t h e demand f o r p r i m a r y e n e r g y . I t s h o u l d be added t h a t i n t h e p r e s e n t b o o k , t h e
te rm "demand" u s u a l l y a p p l i e s t o a p r e d i c t e d o r c a l c u l a t e d q u a n t i t y . I f measured
i n an e x i s t i n g f a c t o r y , t he c o r r e s p o n d i n g q u a n t i t y w i l l r a t h e r be c a l l e d
" c o n s u m p t i o n " .
The most w i d e l y a p p l i e d method o f s u p p l y i n g t h e n e c e s s a r y e n e r g y i n p u t s i s t o
r e l y on combined g e n e r a t i o n o f h e a t and e l e c t r i c i t y i n a steam c y c l e e q u i p p e d
w i t h a b o i l e r and a b a c k - p r e s s u r e t u r b i n e , shown s c h e m a t i c a l l y i n F i g . 1.25
( r e f s . 3 8 , 4 6 , 4 7 ) . N e v e r t h e l e s s , t h e economic c o n d i t i o n s f o r t h i s method b e i n g
w o r k a b l e v a r y c o n s i d e r a b l y between d i f f e r e n t c o u n t r i e s and even between
d i f f e r e n t f a c t o r y l o c a t i o n s .
T a k i n g a g l o b a l p e r s p e c t i v e , t h e r e i s no d o u b t t h a t combined g e n e r a t i o n saves
44
fue l
s t e a m l o s s f 10%
\ f u e l /100%|
c o n d e n s a t e a i r 0 .5%
' l o s s 1.1%
h e a t ^ 76 %
p o w e r 13.4%
F i g . 1.25. E n e r g y sys tem l a y o u t and Sankey d iag ram ( l i v e steam 80 b a r and 520 C , b a c k - p r e s s u r e 3 b a r ) f o r t h e a p p l i c a t i o n o f a b a c k - p r e s s u r e steam t u r b i n e . 1 - b o i l e r , 2 - t u r b i n e , 3 - p r o c e s s .
p r i m a r y e n e r g y and reduces a i r p o l l u t i o n . Where h e a t i n g i s n e c e s s a r y , power can
a d d i t i o n a l l y be o b t a i n e d , u s i n g t h i s me thod , a t t h e expense o f abou t h a l f as
much f u e l as i n a the rma l power p l a n t e q u i p p e d w i t h c o n d e n s i n g t u r b o - g e n e r a t o r s .
T h i s means a l s o t h a t h a l f as much b o i l e r f l u e gas i s d i s c h a r g e d t o t h e
a tmosphere .
A f t e r t h e b i t t e r l e s s o n s o f t h e 1970s, many c o u n t r i e s now r e c o g n i z e t h e
i n d u s t r i a l power houses as b e i n g i m p o r t a n t t o t h e i r e n e r g y p o l i c i e s and l o n g -
term p l a n n i n g i n t h i s f i e l d . Depending on t h e economic s i t u a t i o n and a v a i l a b l e
e n e r g y r e s o u r c e s , governments t r y t o cope w i t h w o r l d market deve lopmen ts by
i n f l u e n c i n g , d i r e c t l y o r i n d i r e c t l y ( e . g . by t a x r e g u l a t i o n s ) , t h e f u e l p r i c e s ,
power p r i c e , and c a p i t a l c o s t . The economic c o n d i t i o n s t hus c r e a t e d f o r power
house o p e r a t i o n may v a r y c o n s i d e r a b l y , as can be demons t ra ted by t h e examples o f
e l e c t r i c i t y p u r c h a s e s i n two i m p o r t a n t b e e t - s u g a r p r o d u c i n g c o u n t r i e s - USSR and
USA. I n t h e USA, a t y p i c a l s i t u a t i o n i s t h a t steam s a v i n g s s h o u l d n o t be
compromised t o keep the e l e c t r i c i t y and steam i n b a l a n c e , as p u r c h a s e d
e l e c t r i c i t y i s c h e a p e r than power g e n e r a t i o n w i t h o u t f u l l u t i l i z a t i o n o f t h e
e x h a u s t s team. C o n t r a r y t o t h a t , i t may be j u s t i f i e d i n t he USSR t o g e n e r a t e
e l e c t r i c i t y w i t h some steam b l o w - o f f even under normal o p e r a t i n g c o n d i t i o n s
( r e f s . 4 8 , 4 9 ) .
F l u c t u a t i n g f u e l p r i c e s s t i m u l a t e an i n t e r e s t i n g deve lopmen t w h i c h has become
v i s i b l e i n f u e l - i m p o r t i n g c o u n t r i e s , namely t h e d i v e r s i f i c a t i o n o f f u e l s t o
e l i m i n a t e t h e dependence on f u e l o i l w h i c h was dominant b e f o r e t h e o i l c r i s e s .
F r a n c e and Sweden can be named as examples o f c o u n t r i e s where t h e s u g a r
i n d u s t r i e s r educed t h e p e r c e n t a g e o f f u e l o i l i n t h e t o t a l e n e r g y consumpt i on
f rom more than 95% t o abou t 50%. I n bo th c o u n t r i e s , t he p e r c e n t a g e o f n a t u r a l
gas was c o n s i d e r a b l y i n c r e a s e d abou t 1985. I n t h e s u g a r i n d u s t r i e s i n o t h e r
c o u n t r i e s , l i k e Denmark, use o f b i t u m i n o u s c o a l as t h e main s u b s t i t u t e f o r f u e l
o i l was p r e f e r r e d .
As r e g a r d s t h e d e c i s i o n s on power house i n v e s t m e n t , w h i c h a r e u s u a l l y
a s s o c i a t e d w i t h l a r g e c a p i t a l e x p e n d i t u r e s , t h e f o l l o w i n g f a c t o r s s h o u l d be
c o n s i d e r e d :
45
- t h e p o s s i b i l i t y o f p u r c h a s i n g power f rom t h e e x t e r n a l g r i d , g r i d r e l i a b i l i t y ,
and t he p o s s i b i l i t y o f s e l l i n g power t o t h e g r i d ,
- f u e l p r i c e ,
- t he r a t i o o f f u e l p r i c e t o power p r i c e ,
- c a p i t a l c o s t ,
- i f a p p l i c a b l e , t h e p r i c e o f power s o l d t o t h e g r i d .
As t h e p a y - b a c k p e r i o d s o f power house i n v e s t m e n t s may be r e l a t i v e l y l o n g , t h e r e
i s t h e r i s k o f f u t u r e f l u c t u a t i o n s o f t h e above f a c t o r s a f f e c t i n g t h e outcome o f
i n v e s t m e n t d e c i s i o n s . As a r e s u l t , t h e r e i s an i n c r e a s i n g i n t e r e s t i n
a l t e r n a t i v e t e c h n o l o g i e s f o r hea t and power g e n e r a t i o n t o r e p l a c e o r supp lement
t h e e x i s t i n g steam c y c l e s .
1.5.2 S o l u t i o n s based on c o n n e c t i o n t o a power g r i d
A s e e m i n g l y e x o t i c a l t e r n a t i v e i s t o a v o i d t h e use o f f u e l s and r e l y on t h e
e x t e r n a l g r i d as t h e o n l y s o u r c e o f e n e r g y . T h i s can be an o p t i m a l s o l u t i o n i f
cheap h y d r o e l e c t r i c power i s a v a i l a b l e , as d e m o n s t r a t e d by a B r a z i l i a n cane
s u g a r f a c t o r y u s i n g e l e c t r i c a l l y hea ted b o i l e r s t o g e n e r a t e steam ( r e f . 5 0 ) .
The a v a i l a b i l i t y o f h y d r o e l e c t r i c power a l s o p l a y e d a d e c i s i v e r o l e i n a d o p t i n g
t h e e x t e r n a l g r i d a l t e r n a t i v e i n t h e A a r b e r g f a c t o r y i n S w i t z e r l a n d n e a r l y f o u r
decades ago ( r e f . 5 1 , 5 2 ) . A s o p h i s t i c a t e d the rma l sys tem e m p l o y i n g v a p o u r
compress i on was a p p l i e d t h e r e i n o r d e r t o a c h i e v e e f f i c i e n t e n e r g y u t i l i z a t i o n
i n s u g a r m a n u f a c t u r e , and s p e c i a l a r rangemen ts were made t o s e l l p r e s s e d p u l p
w i t h o u t d r y i n g . F o l l o w i n g t he changes i n S w i t z e r l a n d ' s e n e r g y b a l a n c e , h o w e v e r ,
i n v e s t m e n t s were made i n t h e e a r l y 1970s p r e p a r i n g f u t u r e power s u p p l i e s f rom
a d e d i c a t e d g e n e r a t i n g u n i t . As h y d r o e l e c t r i c power i s now c o v e r i n g a b o u t 60% o f
t he c o u n t r y ' s e n e r g y demands, a steam c y c l e w i t h a b a c k - p r e s s u r e t u r b i n e has
been p u t i n t o o p e r a t i o n i n A a r b e r g ( r e f . 53) t o s u p p l y n e a r l y h a l f o f t h e power
consumed i n t h e f a c t o r y .
I n s p i t e o f t h e g l o b a l advan tages o f t h e combined g e n e r a t i o n o f h e a t and
e l e c t r i c i t y , l o c a l economic c o n d i t i o n s may j u s t i f y s o l u t i o n s c o n s i s t i n g o f steam
g e n e r a t i o n i n l o w - p r e s s u r e b o i l e r s and power p u r c h a s e s f rom t h e e x t e r n a l g r i d .
I f t h e g r i d r e l i a b i l i t y i s s u f f i c i e n t l y h i g h , t h i s s o l u t i o n i s f u l l y f l e x i b l e
w i t h r e g a r d t o t he r a t i o between h e a t and power consumed. When r e l y i n g on t h i s
a l t e r n a t i v e t o d a y , h o w e v e r , i t i s a d v i s a b l e t o keep open t h e o p t i o n t o a p p l y
combined g e n e r a t i o n i n t h e f u t u r e .
R e t u r n i n g now t o t h e a p p l i c a t i o n o f p o w e r - g e n e r a t i n g u n i t s based on t h e steam
c y c l e , l e t us o b s e r v e t h a t a b a c k - p r e s s u r e t u r b i n e i s j u s t a s p e c i a l case o f
a steam t u r b i n e . I f we d e f i n e A as t h e r a t i o o f steam demand D' ( k g / h ) t o power
demand P' (kW)
A = D ' / P ' ( 1 . 9 )
then f o r A>10, a b a c k - p r e s s u r e t u r b i n e i s u s u a l l y t h e b e s t c h o i c e . F o r A<10,
46
a c o n d e n s i n g / e x t r a c t i o n t u r b i n e ( F i g . 1.26) s h o u l d be r e g a r d e d as a s e r i o u s
a l t e r n a t i v e . I t assumes the use o f e x t r a c t i o n steam i n s t e a d o f e x h a u s t steam
f rom a b a c k - p r e s s u r e u n i t , w h i l e t he r e m a i n i n g steam f l o w i n g t o t h e c o n d e n s e r
g e n e r a t e s some e x t r a power . A l t h o u g h t h i s s o l u t i o n i s e x p e n s i v e , i t can a l s o be
o p e r a t e d d u r i n g t h e o f f - s e a s o n p e r i o d i f power can be s o l d t o t h e e x t e r n a l g r i d .
T h i s seems t o be p a r t i c u l a r l y a t t r a c t i v e t o i n d u s t r i a l combines o f w h i c h t h e
s u g a r f a c t o r y i s o n l y a p a r t , and where h e a t and power a r e needed d u r i n g t h e
o f f - s e a s o n p e r i o d . Examples o f t h i s s o l u t i o n can be f ound i n t h e B u l g a r i a n and
S o v i e t s u g a r i n d u s t r i e s , as w e l l as i n cane s u g a r f a c t o r i e s i n r e g i o n s where
power s u p p l i e s t o t he g r i d a r e r e q u i r e d ( r e f s . 5 4 - 5 6 ) .
s t e a m
f u e l
1 L
1 til -Θ 3
Ί k ' . c o n d e n s a t e
F i g . 1.26. E n e r g y sys tem l a y o u t f o r t h e a p p l i c a t i o n o f a c o n d e n s i n g / e x t r a c t i o n t u r b i n e . 1 - b o i l e r , 2 - t u r b i n e , 3 - p r o c e s s , 4 - c o n d e n s e r .
1.5.3 S o l u t i o n s based on a b a c k - p r e s s u r e t u r b i n e
I n a s u g a r f a c t o r y e q u i p p e d w i t h i t s own power h o u s e , a mismatch p rob lem
between t h e power demand and power p r o d u c t i o n may o c c u r . The e l e c t r i c a l o u t p u t
Ρ o f a b a c k - p r e s s u r e t u r b o - g e n e r a t o r can be e x p r e s s e d as a f u n c t i o n o f steam
f l o w D
Ρ = D/S ( 1 . 1 0 )
where S i s t he steam r a t e , i . e . t he steam consumpt ion p e r u n i t power p r o d u c e d
( k g / k W h ) , o f t he t u r b o - g e n e r a t o r .
D i v i d i n g t h e above e q u a t i o n by t h e d a i l y p r o c e s s i n g c a p a b i l i t y o f t h e f a c t o r y
R, we o b t a i n
P/R = ( D / R ) / S ( 1 . 1 1 )
Assuming a c o n s t a n t steam r a t e , t h i s i s a l i n e a r r e l a t i o n s h i p i l l u s t r a t e d i n
F i g . 1.27. L e t us now e x p r e s s t h e f a c t o r y ' s e n e r g y demand by two i n d i c e s
p ' = P ' / R and d ' = D ' / R r e p r e s e n t i n g power demand and steam demand, r e s p e c t i v e l y ,
p e r u n i t d a i l y c a p a b i l i t y . Two d i f f e r e n t s i t u a t i o n s can be imag ined f o r a b a c k
p r e s s u r e t u r b o - g e n e r a t o r c h a r a c t e r i z e d by steam r a t e S :
( i ) P' < d ' / S
T h i s means t h a t t h e steam f l o w c o v e r i n g t h e f a c t o r y ' s hea t demand i s
47
60 b a r / 5 0 0 ° C / 40 ba r7 420 °C
10 20 30 40 50 60
S team d e m a n d ( k g / I O O k g b )
F i g . 1.27. Power g e n e r a t e d as a f u n c t i o n o f t h e steam f l o w t h r o u g h a b a c k -- p r e s s u r e t u r b i n e .
s u f f i c i e n t l y l a r g e t o g e n e r a t e power needed (d-j i n F i g . 1 . 2 7 ) . The f a c t o r y i s
l i k e l y t o be s e l f - s u f f i c i e n t w i t h r e s p e c t t o power g e n e r a t i o n ,
( i i ) P' > d ' / S
The steam f l o w c o v e r i n g t h e f a c t o r y ' s h e a t demand i s t o o smal l t o s a t i s f y t h e
power demand ( d ^ i n F i g . 1 . 2 7 ) , and s e l f - s u f f i c i e n c y w i t h r e s p e c t t o power
g e n e r a t i o n i s i m p o s s i b l e o r v e r y d i f f i c u l t t o a c h i e v e .
Case ( i ) i s a f a v o u r a b l e s i t u a t i o n . I f no e l e c t r i c i t y s a l e s t o t h e e x t e r n a l
g r i d a r e p o s s i b l e , t hen a p a r t o f t he l i v e steam s h o u l d be d i r e c t e d t o
a t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n and s u p p l i e d t o t h e p r o c e s s , t h u s b y - p a s s i n g
t he t u r b i n e . T h i s i s t he most w i d e l y used s o l u t i o n ; i t i s e x t e n s i v e l y d e s c r i b e d
i n t he l i t e r a t u r e ( r e f . 3 9 ) .
Case ( i i ) n e c e s s i t a t e s a c r i t i c a l r e v i e w o f t h e s t r u c t u r e o f t h e power demand,
and a c t i o n s aimed a t s a v i n g power u s i n g t h e t e c h n i q u e s men t ioned i n S e c t i o n
1 .4 .3 . I f no m e a n i n g f u l improvements can be a t t a i n e d , t hen i t becomes n e c e s s a r y
t o m o d i f y t he power house c o n c e p t assumed. T h e r e a r e s e v e r a l p o s s i b l e s o l u t i o n s
i n w h i c h t h e b a c k - p r e s s u r e steam c y c l e remains dom inan t :
- e l e c t r i c i t y p u r c h a s e s f rom t h e e x t e r n a l g r i d t o c o v e r t h e d e f i c i t ;
- u s i n g steam f rom t h e t u r b i n e e x h a u s t t o h e a t combus t i on a i r s u p p l i e d t o t h e
b o i l e r s o r p u l p - d r y e r f u r n a c e , t hus i n c r e a s i n g t h e steam f l o w t h r o u g h t h e
t u r b i n e ;
- i n s t a l l i n g a new b a c k - p r e s s u r e t u r b i n e c h a r a c t e r i z e d by a l o w e r steam r a t e
( i n F i g . 1 .27, t h i s i s i n t e r p r e t e d as moving t o t h e t u r b i n e c h a r a c t e r i s t i c s
shown by t h e dashed l i n e ) ,
- i n s t a l l i n g a new b o i l e r g e n e r a t i n g steam a t a h i g h e r p r e s s u r e and an
a d d i t i o n a l " t o p p i n g " b a c k - p r e s s u r e t u r b i n e ( F i g . 1 . 2 8 ( a ) ) , and s u p p l y i n g steam
48
(α)
fuel
fuel
c o n d e n s a t e
( b )
s t e a m 3 3 fue l
s t e a m
H 3
c o n d e n s a t e
F i g . 1.28. E n e r g y sys tem l a y o u t s f o r t h e m o d e r n i z a t i o n o f c o n v e n t i o n a l b a c k -- p r e s s u r e steam c y c l e s : ( a ) w i t h a t o p p i n g t u r b i n e , ( b ) w i t h a c o n d e n s i n g t u r b i n e . 1 - b o i l e r , 2 - t u r b i n e , 3 - p r o c e s s , 4 - c o n d e n s e r , 5 - t o p p i n g t u r b i n e , 6 - c o n d e n s i n g t u r b i n e .
f rom the e x h a u s t o f t h e " t o p p i n g " t u r b i n e t o t he e x i s t i n g t u r b i n e ;
- i n s t a l l i n g an a d d i t i o n a l c o n d e n s i n g t u r b i n e t o be s u p p l i e d w i t h a p a r t o f t h e
e x h a u s t steam f l o w ( F i g . 1 . 2 8 ( b ) ) ;
- i n cases where a the rma l c o n n e c t i o n between t h e f a c t o r y and an e x t e r n a l h e a t
r e c e i v e r ( e . g . a d i s t r i c t h e a t i n g s y s t e m ) i s p o s s i b l e , a p p l y i n g a b a c k - p r e s s u r e /
/ e x t r a c t i o n t u r b i n e ( r e f . 5 7 ) .
The complement ing power p u r c h a s e s f rom t h e e x t e r n a l g r i d a r e e c o n o m i c a l l y
a t t r a c t i v e , p r o v i d i n g t h e power p r i c e i s s u f f i c i e n t l y low i n r e l a t i o n t o t h e
f u e l p r i c e . T h i s s o l u t i o n i s w i d e l y used nowadays ; v a r i o u s a s p e c t s o f t h e
c o o p e r a t i o n w i t h t h e e x t e r n a l g r i d , i n c l u d i n g t e c h n i c a l d e t a i l s r e l a t e d t o t h e
power n e t w o r k , a r e d i s c u s s e d i n t h e l i t e r a t u r e ( r e f . 3 9 ) .
I n t e r e s t i n g deve lopments can be seen i n F r a n c e , where t h e power t a r i f f s a r e
d i f f e r e n t i a t e d depend ing on t h e t ime o f y e a r , t h e p r i c e s r i s i n g i n O c t o b e r and
November and r e a c h i n g a maximum i n December. T h i s s t i m u l a t e s power p u r c h a s e s i n
t h e i n i t i a l s t a g e o f t h e s e a s o n , w h i l e e l e c t r i c s e l f - s u f f i c i e n c y i s p r e f e r r e d
l a t e r o n . T h e r e f o r e , t i m e - d e p e n d e n t o p e r a t i o n o f t h e e n e r g y sys tems i n t h e s u g a r
i n d u s t r y i s p r o p o s e d so t h a t t h e power demand can v a r y ( r e f . 1 3 ) . D u r i n g t h e
i n i t i a l weeks o f t h e season power can be p u r c h a s e d t o o p e r a t e advanced v a p o u r -
compress i on c i r c u i t s , making i t p o s s i b l e t o m i n i m i z e t h e steam demand and t h u s
a l s o t he f u e l c o n s u m p t i o n . L a t e r o n , no power w i l l be p u r c h a s e d , and t h e f u e l
consumpt ion w i l l be a l l o w e d t o i n c r e a s e .
The second s o l u t i o n f rom t h e above l i s t can be a p p l i e d o n l y i f t h e i n s t a l l e d
b o i l e r and t u r b i n e c a p a c i t i e s a r e l a r g e enough t o a l l o w f o r a steam f l o w
i n c r e a s e . I t r e q u i r e s i n s t a l l i n g s t eam-hea ted a i r p r e h e a t e r s i n w h i c h t h e e n e r g y
o f t h e c o n d e n s i n g e x h a u s t steam can be t r a n s f e r r e d t o t h e combus t i on a i r . The
t e m p e r a t u r e range o v e r w h i c h a i r p r e h e a t i n g must be c o n t a i n e d i s l i m i t e d , t h u s
49
l i m i t i n g t h e a t t a i n a b l e s t e a m - f l o w i n c r e a s e . Where a i r p r e h e a t i n g a p p l i e s t o t h e
b o i l e r s o n l y , t he power g e n e r a t i o n can be i n c r e a s e d by abou t 7-8%. An a n a l y s i s
o f r e l e v a n t e n e r g y b a l a n c e s , i n c l u d i n g t h e case o f p r e h e a t i n g o f a i r d i r e c t e d t o
t h e p u l p - d r y e r f u r n a c e , can be found i n t h e l i t e r a t u r e ( r e f . 5 8 ) .
The t h i r d s o l u t i o n , i . e . a b a c k - p r e s s u r e t u r b i n e w i t h an improved steam r a t e ,
can o n l y be a p p l i e d p r o v i d i n g t h e p r e s s u r e and t e m p e r a t u r e o f t h e l i v e steam a r e
i n c r e a s e d , w h i c h a l s o r e q u i r e s i n s t a l l i n g a new b o i l e r . F i g u r e 1.29 shows
a d iag ram i n d i c a t i n g t he steam r a t e , and t he r a t i o o f t h e e l e c t r i c a l e n e r g y
p roduced t o t he i n p u t o f p r i m a r y e n e r g y i n f u e l d e l i v e r e d , as f u n c t i o n s o f l i v e -
steam p r e s s u r e ( t h e r e may be some s c a t t e r i n t h e d a t a because t h e q u a l i t y o f
t u r b i n e s s u p p l i e d by v a r i o u s m a n u f a c t u r e r s may v a r y ) . L e t us n o t e t h a t t h e steam
r a t e can be r e d u c e d n o t o n l y by i n c r e a s i n g l i v e - s t e a m p r e s s u r e and t e m p e r a t u r e
b u t a l s o by a p p l y i n g t h e r e h e a t c y c l e . F o r a p r o p o s e d u n i t o p e r a t e d a t l i v e -
steam paramete rs 80 b a r and 500^0, w i t h r e h e a t a t 30 b a r and 450^0, an
e s t i m a t e d steam r a t e i s 5.5 kg/kWh ( r e f . 5 9 ) .
The r e m a i n i n g c o n c e p t s named a t t he end o f t h e above l i s t , r e q u i r i n g
r e l a t i v e l y complex power house l a y o u t s , m i g h t be c o n s i d e r e d when s o l v i n g f a c t o r y
e x t e n s i o n o r m o d e r n i z a t i o n p r o b l e m s . I t has been p r o v e d u n d e r s p e c i f i c economic
c o n d i t i o n s t h a t a t o p p i n g t u r b i n e o p e r a t e d a t steam pa rame te rs 100 b a r and 540°C,
h a v i n g t he advan tage o f l a r g e r power p r o d u c t i o n , may be a t l e a s t e c o n o m i c a l l y
e q u i v a l e n t t o an a d d i t i o n a l b a c k - p r e s s u r e t u r b i n e s u p p l i e d w i t h steam a t 40 b a r
and 440°C ( r e f . 6 0 ) . As r e g a r d s an a d d i t i o n a l c o n d e n s i n g t u r b i n e , t h i s i s a
t y p i c a l s o l u t i o n i n cane s u g a r f a c t o r i e s i n w h i c h a l l bagasse i s b u r n e d , and t h e
e l e c t r i c i t y s u r p l u s i s s o l d t o t he e x t e r n a l g r i d ( r e f s . 6 1 , 6 2 ) .
15
SI
o
£ o φ
LH
ι ^ 500
520 °C
\ \ x \
V \
500
\ \ x \
V \
X 4 0 ° C •
400 ° c / ' — ^
'360°C -
20 40 60 80
1 14
•D
L-- 12 0; — - 12 > >%
c . t : o υ
• o Ζ >Χ> cnSí
• 10 Φ^ C ο
φ D
LL Η 8
P r e s s u r e ( b a r )
F i g . 1.29. Steam r a t e , and p e r c e n t a g e o f f u e l e n e r g y c o n v e r t e d t o e l e c t r i c i t y , as f u n c t i o n s o f l i v e steam pa ramete rs a t b a c k - p r e s s u r e 3 b a r .
50
I t s h o u l d be p o i n t e d o u t t h a t a new b o i l e r - t u r b i n e u n i t o p e r a t e d a t i n c r e a s e d
steam p a r a m e t e r s , o r an a d d i t i o n a l b o i l e r - t u r b i n e u n i t , r e q u i r e l a r g e
i n v e s t m e n t s , i n c l u d i n g c o s t l y f o u n d a t i o n s and pe rhaps b u i l d i n g s . I n o r d e r t o
a v o i d t h i s , a l t e r n a t i v e p o w e r - g e n e r a t i o n t e c h n o l o g i e s may be c o n s i d e r e d . The
a l t e r n a t i v e s o l u t i o n s a r e c h a r a c t e r i z e d by l o w e r i n v e s t m e n t c o s t s , and e l i m i n a t e
t h e r i g i d r e l a t i o n s h i p between t h e steam f l o w and t h e power g e n e r a t e d t h a t i s
c h a r a c t e r i s t i c o f t h e steam c y c l e .
1.5.4 C o m b u s t i o n - e n g i n e based s o l u t i o n s
A c o n c e p t w h i c h has r e c e i v e d much a t t e n t i o n i s t o a p p l y g a s - t u r b i n e d r i v e n
g e n e r a t i n g s e t s , w h i c h a r e a v a i l a b l e t o d a y w i t h power r a t i n g s up t o 100 MW. A t
t he p r e s e n t s t a t e o f deve lopmen t o f g a s - t u r b i n e t e c h n o l o g y , h o w e v e r , t h i s l i m i t s
t h e c h o i c e o f f u e l s t o l i q u i d o r gaseous t y p e s .
A g a s - t u r b i n e s e t i n c l u d e s a c o m p r e s s o r r a i s i n g t h e p r e s s u r e o f t h e
a t m o s p h e r i c a i r t o abou t 3-5 b a r and d e l i v e r i n g i t t o a combus t i on chamber where
t h e f u e l i s b u r n e d . Hot combus t i on gases s u b s e q u e n t l y expand i n a t u r b i n e , w h i c h
i s t y p i c a l l y mounted on t h e same s h a f t as t h e c o m p r e s s o r . The r o t a t i o n a l
v e l o c i t y may be as h i g h as 10 000 rpm, so t h e r e i s u s u a l l y a r e d u c i n g g e a r b o x
between t h e t u r b i n e - c o m p r e s s o r s e t and t h e e l e c t r i c a l g e n e r a t o r . The gas
p r e s s u r e i n t h e t u r b i n e e x h a u s t e q u a l s a t m o s p h e r i c p r e s s u r e , and t h e t e m p e r a t u r e
i s t y p i c a l l y abou t 430-550°C. The scheme o f a gas t u r b i n e s e t and a t y p i c a l
Sankey d iag ram a r e shown i n F i g . 1.30. The w e i g h t s and d i m e n s i o n s o f two g a s -
t u r b i n e d r i v e n c o n t i n u o u s - d u t y g e n e r a t i n g s e t s a r e g i v e n i n F i g . 1.31.
fuel
2 h
Qir I
-Θ exhaus t g a s compressor
work 38.3%
h e a t 7 0 . 6 %
IV p o w e r ^ 2 7 5 %
F i g . 1.30. Work ing p r i n c i p l e o f a g a s - t u r b i n e s e t and a c o r r e s p o n d i n g Sankey d i a g r a m . 1 - c o m p r e s s o r , 2 - combus t i on chamber , 3 - t u r b i n e .
An e a r l y i d e a was t o c o n n e c t t h e gas t u r b i n e t o a l o w - p r e s s u r e b o i l e r , i n
w h i c h t h e e n e r g y o f gases l e a v i n g t h e t u r b i n e e x h a u s t can be used t o g e n e r a t e
h e a t i n g s team, as shown s c h e m a t i c a l l y i n F i g . 1 . 32 (a ) ( r e f . 6 3 ) . From t h e p o i n t
o f v i e w o f t h e e n e r g y economy, t h i s s o l u t i o n e n s u r e s t h e l a r g e s t power o u t p u t a t
a g i v e n hea t demand. H o w e v e r , a b o i l e r hea ted by gases a t a r e l a t i v e l y l ow
i n i t i a l t e m p e r a t u r e i s so c o s t l y t h a t t h e economic r e s u l t m i g h t be q u e s t i o n a b l e .
51
(α) (b )
- c 1?
7m 15m
F i g . 1.31. Examples o f g a s - t u r b i n e d r i v e n g e n e r a t i n g s e t s , ( a ) r a t i n g 2.5 MW, w e i g h t 18 t , ( b ) 6.2 MW, 60 t . 1 - a i r i n l e t , 2 - gas o u t l e t , 3 - g e n e r a t o r .
(a) I f u e l I
( b )
2 3 2 3
I f ue l I
0 - 1
g a s g a s
p o w e r 2 7 5 %
heaf 41.6%
p o w e r 2 7 5 %
h e a t 61.7%
p o w e r 20 .0%
"hea t 69 .4%
F i g . 1.32. E n e r g y sys tem l a y o u t s and t y p i c a l Sankey d iagrams f o r t h e a p p l i c a t i o n o f gas t u r b i n e s , ( a ) i n c o n n e c t i o n t o a l o w - p r e s s u r e steam b o i l e r , ( b ) i n c o n n e c t i o n t o a p u l p d r y e r , ( c ) as a t o p p i n g u n i t . 1 - gas t u r b i n e , 2 - s team b o i l e r , 3 - p r o c e s s , 4 - p u l p d r y e r , 5 - steam t u r b i n e .
52
A more a t t r a c t i v e s o l u t i o n c o n s i s t s o f s u p p l y i n g t h e gases f rom t h e t u r b i n e
e x h a u s t d i r e c t l y t o p u l p d r y i n g , as i l l u s t r a t e d i n F i g . 1 . 3 2 ( b ) ( r e f s . 6 4 - 6 7 ) .
A p r o t o t y p e i n s t a l l a t i o n w i t h a gas t u r b i n e r a t e d a t 1200 kW i s o p e r a t e d i n
a F r e n c h f a c t o r y ( r e f . 4 1 ) . Assuming t h a t t h e t o t a l amount o f p u l p p r e s s e d t o
22% DS i s d r i e d t o 90% DS, and t h e e n e r g y b a l a n c e o f t h e t u r b i n e i s e s s e n t i a l l y
i d e n t i c a l t o t h a t shown i n F i g . 1.30, power can be g e n e r a t e d a t t h e r a t e o f
abou t 1.9 kWh p e r 100 kg b e e t .
The most advanced and e c o n o m i c a l l y a t t r a c t i v e c o n c e p t i s based on t h e
a p p l i c a t i o n o f a t o p p i n g g a s - t u r b i n e f rom w h i c h t h e e x h a u s t gases a r e s u p p l i e d
t o a steam b o i l e r e q u i p p e d w i t h i t s own f u r n a c e , as shown s c h e m a t i c a l l y i n
F i g . 1 . 3 2 ( c ) . By b u r n i n g a d d i t i o n a l f u e l i n t h e b o i l e r f u r n a c e , t he t e m p e r a t u r e
o f t h e gases can be r a i s e d , w h i c h a l l o w s t h e h e a t t r a n s f e r s u r f a c e s t o be made
as compact as i n a c o n v e n t i o n a l b o i l e r and t hus no more c o s t l y . The g a s - t u r b i n e
s e t and t he s t e a m - t u r b i n e s e t t o g e t h e r g e n e r a t e more power t han a c o n v e n t i o n a l
steam c y c l e . An i n t e r e s t i n g f e a t u r e o f t h i s s o l u t i o n , demons t ra ted i n a f u l l -
s c a l e i n d u s t r i a l a p p l i c a t i o n i n t h e chemica l i n d u s t r y ( r e f . 6 9 ) , i s t h a t t h e
t o p p i n g g a s - t u r b i n e can be c o n n e c t e d t o a c o n v e n t i o n a l b o i l e r a f t e r m o d e s t l y
e x p e n s i v e b o i l e r m o d i f i c a t i o n s .
The economic j u s t i f i c a t i o n o f t h e t h r e e v a r i a n t s d e s c r i b e d depends on f u e l
and e l e c t r i c i t y p r i c e s , as w e l l as c a p i t a l c o s t . I n s p e c i a l economic c o n d i t i o n s ,
namely h i g h power p r i c e , low D i e s e l - o i l p r i c e and a r e l a t i v e l y l a r g e power
demand d u r i n g t h e o f f - s e a s o n p e r i o d , i t m igh t be p r a c t i c a l t o c o n s i d e r a t o p p i n g
D i e s e l e n g i n e c o n n e c t e d t o a b a c k - p r e s s u r e steam c y c l e , o r t o a p u l p d r y e r
e q u i p p e d w i t h an a u x i l i a r y f u r n a c e ( r e f s . 7 0 , 7 1 ) . D u r i n g t h e o f f - s e a s o n p e r i o d ,
t h e e n g i n e can be o p e r a t e d f o r t h e p u r p o s e o f power g e n e r a t i o n o n l y .
A l t h o u g h r e l y i n g on e x i s t i n g t e c h n o l o g y , t h e f e a s i b i l i t y o f t h e a p p l i c a t i o n
o f D i e s e l e n g i n e and gas t u r b i n e i n t h e s u g a r i n d u s t r y y e t remains t o be
demons t ra ted i n p r a c t i c e . I t can be n o t e d t h a t a f t e r t h e f i r s t wave o f i n t e r e s t
i n c o m b u s t i o n - e n g i n e based s o l u t i o n s i n t h e l a t e 1970s, no l a r g e - s c a l e
i n v e s t m e n t s were u n d e r t a k e n , and some s c e p t i c i s m based on economic
c o n s i d e r a t i o n s was e x p r e s s e d i n t h e l i t e r a t u r e ( r e f . 7 2 ) .
1.5.5 U n c o n v e n t i o n a l t he rma l c o u p l i n g between t h e power house and t h e hea t
economy
A c o n v e n t i o n a l app roach t o t h e l i n k between t h e power house and t h e s u g a r
m a n u f a c t u r i n g p r o c e s s assumes t h a t t h e power house i s f u n c t i o n i n g as an e n e r g y
s o u r c e , and t h e p r o c e s s as an e n e r g y r e c e i v e r . An e n e r g y s t ream f l o w i n g i n t h e
r e v e r s e d i r e c t i o n , namely t h e c o n d e n s a t e r e t u r n e d f rom t h e e v a p o r a t o r t o t h e
b o i l e r s , i s se ldom t r e a t e d as a p a r t o f e n e r g y c o n v e r s i o n and u t i l i z a t i o n
p r o c e s s e s b u t r a t h e r as an a r rangemen t t o s e c u r e p r o p e r q u a l i t y o f t h e b o i l e r
f e e d w a t e r .
53
A c o n s i d e r a b l e e n e r g y - s a v i n g p o t e n t i a l i s a s s o c i a t e d w i t h t h e p o s s i b i l i t y o f
r e c u p e r a t i n g l o w - t e m p e r a t u r e h e a t f rom c e r t a i n s e c t i o n s o f t h e p r o c e s s and
r e t u r n i n g i t f o r r e - u s e i n o t h e r s e c t i o n s . A d i f f i c u l t y i n h e r e n t i n t h i s
app roach i s t o f i n d p r o c e s s media w i t h t e m p e r a t u r e s low enough t o make t h e
a b s o r p t i o n o f t h e r e c u p e r a t e d h e a t p o s s i b l e . ( I t i s p r e c i s e l y f o r t h i s r e a s o n
t h a t l o w - t e m p e r a t u r e p u l p d r y i n g i s so i n t e r e s t i n g as an e n e r g y - s a v i n g m e a s u r e ,
because a i r d i r e c t e d t o a l o w - t e m p e r a t u r e d r y e r i s h e a t e d by w a s t e h e a t w h i c h
wou ld o t h e r w i s e be d i s s i p a t e d t o t h e e n v i r o n m e n t . )
The l o w - t e m p e r a t u r e h e a t can a l s o be r e t u r n e d t o t h e power h o u s e , by h e a t i n g
combus t ion a i r s u p p l i e d t o t h e b o i l e r f u r n a c e s . By making i t p o s s i b l e t o c u t
down t he f u e l consumpt ion i n t h e b o i l e r s , t h i s s o l u t i o n can be e c o n o m i c a l l y
j u s t i f i e d i f t h e f u e l s a v i n g i s l a r g e enough t o pay back t h e i n v e s t m e n t i n t h e
h e a t - r e c u p e r a t i n g and a i r - h e a t i n g e q u i p m e n t .
The d e t a i l s o f t h e the rma l c o u p l i n g between t h e power house and t h e h e a t
economy may v a r y . A s o l u t i o n implemented i n a B e l g i a n f a c t o r y has been d e s c r i b e d
i n t h e l i t e r a t u r e ( r e f . 7 3 ) . The hea t i s r e c o v e r e d f rom s p e n t c a r b o n a t a t i o n gas
i n a d i r e c t - c o n t a c t h e a t e r where t h e t e m p e r a t u r e o f c i r c u l a t i n g w a t e r i s r a i s e d
f rom 50'^C t o a b o u t 80°C ( s e e a l s o S e c t i o n 4 . 2 . 2 ) . Water i s s u b s e q u e n t l y pumped
t o a i r p r e h e a t e r s c o n n e c t e d t o t h e b o i l e r s ( a l t e r n a t i v e l y , i t can be pumped t o
a i r p r e h e a t e r s c o n n e c t e d t o t h e s u g a r d r y e r ) . F u e l s a v i n g s o f t h e o r d e r o f
0.1 kg normal f u e l p e r 100 kg b e e t have been r e p o r t e d f o r t h i s s o l u t i o n .
A i r p r e h e a t e r s can a l s o be s u p p l i e d w i t h h e a t r e c o v e r e d f rom vacuum-pan
v a p o u r s c o n d e n s i n g i n a s p e c i a l c o n d e n s e r ( r e f . 7 4 ) . The t e m p e r a t u r e o f h e a t -
c a r r y i n g w a t e r a t t h e c o n d e n s e r o u t l e t i s a b o u t 58-59°C. F o r t h i s r e a s o n , t h e
economic j u s t i f i c a t i o n o f t h i s s o l u t i o n m igh t be more d i f f i c u l t t o e s t a b l i s h .
F o r a compar i son w i t h o t h e r methods o f u t i l i z a t i o n o f vacuum-pan v a p o u r , see
S e c t i o n 3 . 3 . 1 .
REFERENCES
1 K. S c h i e b l , W 'á rmewi r t scha f t i n d e r Z u c k e r i n d u s t r i e , Τ . S t e i n k o p f f V e r l a g , D r e s d e n / L e i p z i g , 1939.
2 Β. K a r r e n , The p o t e n t i a l f o r e n e r g y s a v i n g i n t h e b e e t s u g a r i n d u s t r y . S u g a r J . , 4 4 ( 1 ) (1981) 8 -13 .
3 T . B a l o h , W ä r m e w i r t s c h a f t , i n : F . S c h n e i d e r ( E d . ) , T e c h n o l o g i e des Z u c k e r s , S c h a p e r V e r l a g , H a n n o v e r , 1968, p p . 705-776.
4 S . Z a g r o d z k i , Gospodarka C i e p l n a C u k r o w n i , WNT, Warszawa , 1979. 5 K. U r b a n i e c , S p r e z a n i e oparow w g o s p o d a r c e c i e p l n e j c u k r o w n i , G a z . C u k r o w . ,
90 (9 ) (1982) 134-136. 6 T . D . E a s t o p and A . McConkey , A p p l i e d Thermodynamics f o r E n g i n e e r i n g
T e c h n o l o g i s t s , 3 rd e d n . , Longman, London and New Y o r k , 1978. 7 G . J . Van Wylen and R . E . S o n n t a g , Fundamenta ls o f C l a s s i c a l T h e r m o d y n a m i c s ,
3 rd e d n . , W i l e y , New Y o r k , 1985. 8 T . B a l o h , Wärmeat las f ü r d i e Z u c k e r i n d u s t r i e , S c h a p e r V e r l a g , H a n n o v e r , 1975. 9 P. V a l e n t i n , E n e r g y c o n s e r v a t i o n s t u d i e s i n t h e b e e t s u g a r i n d u s t r y . I n t .
Sugar J . , 82(982) (1980) 303-309.
54
10 Ε. H u g o t , Handbook o f Cane S u g a r E n g i n e e r i n g , 3 rd e d n . , E l s e v i e r , Amsterdam, 1986.
11 P. V a l e n t i n , U b e r d i e B e e i n f l u s s u n g des P r i m ä r e n e r g i e v e r b r a u c h s i n d e r Z u c k e r i n d u s t r i e , Ζ . Z u c k e r i n d . , 26 (8 ) (1976) 525-534.
12 P. Mosel ( e t a l . ) , O p t i m i e r u n g von E i n d i c k u n g s p r o z e s s e n i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 104(12) (1979) 1101-1107.
13 P. G i r a u d , R e d u i r e l e s c o u t s e n e r g e t i q u e s p a r 1 ' u t i l i s a t i o n de l ' e l e c t r i c i t e , I n d . A l i m . A g r i e , 102 (7 -8 ) (1985) 707-710.
14 Κ . Ε . A u s t m e y e r , B rüdenkompress ion i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 108(8) (1983) 715-728.
15 R. M i c h e l , P h . T e r n y n c k and P h . B o n n e n f a n t , R e a l i s a t i o n du p o s t e d ' e v a p o r a t i o n dans une u s i n e de 12 000 t / j de b e t t e r a v e s s t o c k a n t 60% du s i r o p p r o d u i t en campagne, I n d . A l i m . A g r i e , 9 4 ( 7 - 8 ) (1977) 701-705.
16 R e p e r t o i r e des S u c r e r i e s e t R a f f i n e r i e s b e i g e s , S u c r . B e i g e , (102) (1984) 21-74.
17 P. C h r i s t o d o u l o u , B e t r i e b s e r f a h r u n g e n m i t dem E i n s a t z e i n e r Wärmepumpe i n V e r d a m p f s t a t i o n e i n e r Z u c k e r f a b r i k , Z u c k e r i n d . , 109(7) (1984) 628-634.
18 P. Ho f fman, O p t i m a l i z a c e e n e r g e t i c k e h o h o s p o d a r s t v i c u k r o v a r u L o v o s i c e , L i s t y C u k r . , 102(7) (1986) 155-161.
19 F. Baunack , T r o c k n u n g , i n : F . S c h n e i d e r ( E d . ) , T e c h n o l o g i e des Z u c k e r s , Schape r V e r l a g , H a n n o v e r , 1968, p p . 845-883.
20 T h . C r o n e w i t z , Wege z u r r a t i o n e l l e n E n e r g i e v e r w e n d u n g b e i d e r S c h n i t z e l -t r o c k n u n g i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 105(2) (1980) 129-139.
21 F . Amding, Abwärmenutzung z u r Saf tanwärmung im Zusammenhang m i t d e r S c h n i t z e l t r o c k n u n g , Z u c k e r i n d . , 110(8) (1985) 675-679.
22 P. V e r m e u l e n , Sa f t e i ndamp fung m i t t e l s T r o c k n u n g s a b g a s be i dessen R e i n i g u n g , Z u c k e r i n d . , 110(8) (1985) 681-685.
23 K . E . Aus tmeye r and W. P o e r s c h , N i e d e r t e m p e r a t u r t r o c k n u n g - G r u n d l a g e n und B e t r a c h t u n g e n z u r W i r t s c h a f t l i c h k e i t , Z u c k e r i n d . , 108(9) (1983) 861-868, 108(11) (1983) 1033-1041, 109(5) (1984) 411-419, 110(1) (1985) 28-34.
24 E. S c h r ö t e r , D ie N i e d e r t e m p e r a t u r t r o c k n u n g i n L e h r t e - F u n k t i o n s w e i s e und E r f a h r u n g e n , Z u c k e r i n d . , 111(6) (1986) 545-548.
25 K . E . Aus tmeye r and U . B u n e r t , Abwärmenutzung im Zusammenhang m i t d e r S c h n i t z e l t r o c k n u n g , Z u c k e r i n d . , 110(8) (1985) 659-670.
26 M. Kunz and P. V a l e n t i n , S c h n i t z e l t r o c k n u n g ohne P r i m ä r e n e r g i e e i n s a t z u n t e r a u s s c h l i e s s l i c h e r Nu tzung d e r Abwärme- und E i n d a m p f p o t e n t i a l e d e r Z u c k e r f a b r i k , Z u c k e r i n d . , 111(8) (1986) 741-750.
27 G . F e l t b o r g , Ä t g ä r d e r f ö r a t t minska u p p v ä r m n i n g s k o s t n a d e r n a v i d e t t s o c k e r b r u k , S o c k e r b o l a g e t r e p o r t , 1985.
28 Gu ide Book f o r F a c t o r y E n g i n e e r s on E n e r g y C o n s e r v a t i o n D i a g n o s i s , UNIDO Document I S . 4 4 9 , V i e n n a , 1984.
29 J . S . Hogg ( e t a l . ) . The r o l e o f t h e r m o g r a p h i c s u r v e y i n g i n e n e r g y c o n s e r v a t i o n . I n t . Suga r J . , 85(1011) (1983) 67-71.
30 P. C h r i s t o d o u l o u , D ie O p t i m i e r u n g d e r E n e r g i e w i r t s c h a f t i n d e r Z u c k e r f a b r i k , Ζ . Z u c k e r i n d . , 27 (7 ) (1977) 441-446, 27 (8 ) (1977) 509-515.
31 O . V . M o r o z , A . A . L i p e t s and D.M. K o r i l k e v i c h , P u t i umensheniya p o t e r t e p l a na s t a n t s i i d e f e k o s a t u r a t s i i , Sakh . P r o m . , ( 9 ) (1985) 45-47 .
32 Y u . D . Kot ( e t a l . ) , P r o i z v o d s t v e n n y e i s p y t a n i y a n i z k o t e m p e r a t u r n o g o r e z h i m a , Sakh . P r o m . , ( 2 ) (1985) 20-22 .
33 P . - V . Schmid t and E. Manzke , Zu F r a g e n d e r E n e r g i e w i r t s c h a f t be i d e r T e i l e x t r a k t i o n , L e b e n s m i t t . - I n d . , 2 4 ( 1 ) (1977) 21 -24 , 2 4 ( 2 ) (1977) 77-80.
34 T . P . Ma t v i enko ( e t a l . ) , P r o b e l i v a n i e sakha ra s pr imenen iem v t o r o g o o t t e k a u t f e l y a I k r i s t a l l i z a t s i i , Sakh . P r o m . , ( 8 ) (1984) 31-34.
35 P. M o s e l , H . - R . Kemter and T h . C r o n e w i t z , Z u r Anwendung e i n e r S i r u p d e c k e b e i p e r i o d i s c h a r b e i t e n d e n Z e n t r i f u g e n , Z u c k e r i n d . , 111(3) (1986) 211-216.
36 H. V o g e l e r . E i n Weg z u r hohen D i c k s a f t d i c h t e und d e r e n w i r t s c h a f t l i c h e N u t z u n g , Z u c k e r , 30(12) (1977) 676-683.
37 H . - J . Krombach, M ö g l i c h k e i t e n z u r Senkung des H e i z d a m p f V e r b r a u c h e s im Z u c k e r h a u s , Z u c k e r i n d . , 106(9) (1981) 793-804.
38 W. L e k a w s k i , M o d e r n i z a c j a G o s p o d a r k i C i e p l n e j C u k r o w n i , S T C , Warszawa , 1986.
55
39 W. v . P r o s k o w e t z , K r a f t z e n t r a l e , i n : F . S c h n e i d e r ( E d . ) , T e c h n o l o g i e des Z u c k e r s , S c h a p e r V e r l a g , H a n n o v e r , 1968, p p . 676-704.
40 B . P . E f a n o v and A . G . K u t k o v o y , N o r m i r o v a n i e r askhoda e l e k t r i c h e s k o i e n e r g i i V s a k h a r n o i p r o m y s h l e n n o s t i , S a k h . P r o m . , ( 2 ) (1986) 39-43.
41 C . Longue E p e e , L e c t u r e p r e s e n t e d a t t h e I n t e r n a t i o n a l E x h i b i t i o n SVEKLOVODSTVO, K i e v , May 1986.
42 B. M a y r h o f e r and P. K n e d l i k , D ie R e i n i g u n g von Z u c k e r r ü b e n m i t t e l s L u f t s t r o m , Z u c k e r i n d . , 108(2) (1983) 138-140, 111(2) (1986) 128-132.
43 A . I . Khomenko, O t e p l o v o i e k o n o m i c h n o s t i s i s t e m d i f f u z i y a - d e f e k a t s i y a , S a k h . P r o m . , (11 ) (1983) 42 -47 .
44 V . N . F i l o n e n k o and A . N . Z a g o r u y k o , N e r i t m i c h n o s t r a b o t y s v e k l o s a k h a r n o g o zavoda i u d e l n y e r a s k h o d y e n e r g o r e s u r s o v , S a k h . P r o m . , ( 6 ) (1986) 37-40.
45 U . Zimmer and A . Dambach, S t rombezugsüberwachung im Werk P l a t t l i n g d e r Süddeu tschen Z u c k e r - A G , Z u c k e r i n d . , 108(10) (1983) 940-942.
46 R . A . H . C h i l v e r s , C o n t r o l o f maximum e n e r g y demand u s i n g a m i c r o p r o c e s s o r s y s t e m , P r o c . SASTA, 58 (1984) 111-115.
47 G . H . P i a t t , Steam t u r b i n e deve lopmen t i n t h e b e e t s u g a r i n d u s t r y . I n t . S u g a r J . , 82(982) (1980) 297-302.
48 B . L . K a r r e n , E f f i c i e n c y c o n s i d e r a t i o n s i n t h e use o f p r o c e s s s t e a m . S u g a r J . , 4 7 ( 2 ) (1984) 13-15.
49 V . N . F i l o n e n k o , E f f e k t i v n o s t m e r o p r i y a t i i po s n i z h e n y u r a s k h o d a e n e r g o r e s u r s o v i s b a l a n s i r o v a n n o s t e n e r g o p o t r e b l e n i y a sakha rnogo z a v o d a , Sakh . P r o m . , ( 7 ) (1986) 43-46.
50 J . A . B e z e r r a , The use o f e l e c t r i c b o i l e r s i n s u g a r r e f i n e r i e s as an a l t e r n a t i v e s o u r c e o f s t eam. S u g a r I n d . T e c h n o l . , 44 (1985) 277-297.
51 H . R . B r u n n e r , W. Hoppe and G . v . L e n g y e l - K o n o p i , B e t r a c h t u n g e n z u r E n t w i c k l u n g d e r e n e r g e t i s c h e n K o n z e p t i o n d e r Z u c k e r f a b r i k + R a f f i n e r i e A a r b e r g A G , Z u c k e r i n d . , 106(1) (1981) 42 -47 .
52 H . R . B r u n n e r , D ie Thermokompress ion i n d e r Z u c k e r f a b r i k + R a f f i n e r i e A a r b e r g A G , G e s c h i c h t e - E n t w i c k l u n g - A u s b l i c k , Z u c k e r i n d . , 108(8) (1983) 729-736.
53 H . R . B r u n n e r ( e t a l . ) . D ie V e r d a m p f s t a t i o n d e r Z u c k e r f a b r i k + R a f f i n e r i e A a r b e r g AG und das M u l t i - E n e r g i e - S c h e m a , Z u c k e r i n d . , 110(5) (1985) 393-398.
54 W. L e i b i g , B a s i c e n e r g y and i t s u t i l i z a t i o n i n t h e cane s u g a r i n d u s t r y , Z u c k e r i n d . , 103(5) (1978) 412-416.
55 G . D e r m a l , E n e r g y i n a cane s u g a r c o m p l e x : an o r i g i n a l t e c h n i c a l s o l u t i o n f o r i t s most e f f i c i e n t u s e . Suga r J . , 4 4 ( 6 ) (1981) 5 -8 .
56 T . T o r i s s o n , The p o t e n t i a l f o r g e n e r a t i o n o f p u b l i c e l e c t r i c i t y i n cane s u g a r f a c t o r i e s . S u g a r y A z ú c a r , 7 9 ( 4 ) (1984) 21-31.
57 L. B e r g f o r s , H. H u t t u n e n and J . V i l j a n e n , 20 J a h r e Fernwärmeerzeugung i n d e r Z u c k e r f a b r i k T u r e n k i , Z u c k e r i n d . , 109(7) (1984) 634-637.
58 Κ . Ε . Aus tmeye r and U . B u n e r t , M ö g l i c h k e i t e n z u r V e r b e s s e r u n g d e r E n e r g i e w i r t s c h a f t b e i d e r Z u c k e r g e w i n n u n g , i n : P r o c . 17th C I T S , C o p e n h a g e n , 1983, p p . 333-369.
59 Ε. O t o r o w s k i , R a c j o n a l n e g o s p o d a r o w a n i e p a r a ζ k o t l o w , G a z . C u k r o w . , 9 3 ( 2 ) (1985) 204-206.
60 V . S . Mokhor t and V . N . C h i k i r i s o v , T e k h n i k o - e k o n o m i c h e s k o e s r a v n e n i e r e k o n s t r u k t s i i TEC sakha rnykh z a v o d o v s u s t a n o v k o i n a d s t r o y k i v y s o k o g o d a v l e n i y a , Sakh . P r o m . , ( 7 ) (1983) 40 -42 .
61 R. A n t o i n e , E l e c t r i c i t y e x p o r t f rom cane s u g a r f a c t o r i e s , i n : F . O . L i c h t s Gu ide t o t h e S u g a r F a c t o r y Mach ine I n d u s t r y , F . O . L i c h t GmbH, R a t z e b u r g , 1984, p p . A75-A88.
62 T . E n g b e r g , Steam and power g e n e r a t i o n i n t h e s u g a r i n d u s t r y . I n t . S u g a r J . , 86(1031) (1984) 286-287.
63 N. M a r i g n e t t i and G . M a n t o v a n i , B e t r a c h t u n g e n ü b e r den E i n s a t z d e r G a s t u r b i n e i n d e r Z u c k e r i n d u s t r i e , Z u c k e r , 2 7 ( 9 ) (1974) 470-474.
64 U . H a n t s c h , E i n s a t z von G a s t u r b i n e n i n Z u c k e r f a b r i k e n , Z . Z u c k e r i n d . , 25 (1 ) (1975) 31-32.
65 H. P o h l e r t , D ie Verwendung von G a s t u r b i n e n i n Z u c k e r f a b r i k e n , Z u c k e r , 30(2 ) (1977) 75-76.
56
66 W . J . L e i b i g , Use o f gas t u r b i n e s i n t h e s u g a r i n d u s t r y . S u g a r J . , 40 (12 ) (1978) 13-15.
67 M. B r u h n s , B e i t r a g z u r w i r t s c h a f t l i c h e n B e u r t e i l u n g e i n e r Z u c k e r f a b r i k m i t B rüdenkompress ion und G a s t u r b i n e i n d e r S c h n i t z e l t r o c k n u n g , Z u c k e r i n d . , 107(10) (1982) 945-957.
68 H. L ö f f e l and D. T h i n i u s , G a s t u r b i n e n e i n s a t z im Rahmen d e r K r a f t - W ä r m e -K o p p l u n g , BWK, 37(12) (1985) 482-487.
69 H. L ö f f e l and M. S c h u l z , G a s t u r b i n e f ü r E n e r g i e v e r s o r g u n g s s y s t e m e i n e s I n d u s t r i e b e t r i e b e s , BWK, 36 (6 ) (1984) 243-248.
70 H. Huber and H. L i c h a , E i n Weg z u r Sommerst romerzeugung i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 104(1) (1979) 25-29.
71 H . - U . R e i c h e l , Gedanken z u r E n t w i c k l u n g des P r i m ä r e n e r g i e e i n s a t z e s - Dampf und St rom i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 107(10) (1982) 936-939.
72 P. V a l e n t i n , D i s k u s s i o n s b e i t r a g z u "Wärmepumpen i n d e r Z u c k e r i n d u s t r i e " , Z u c k e r i n d . , 108(8) (1983) 746-748.
73 Anonymous, R e c u p e r a t i o n t he rm ique s u r buees de seconde c a r b o n a t a t i o n a l a R a f f i n e r i e Notre-Dame a O r e y e , S u c r . B e l g e , 103 (1985) 5-11.
74 T e c h n i c a l i n f o r m a t i o n f rom Wiegand K a r l s r u h e GmbH, E t t l i n g e n , 1986.
57
C h a p t e r 2
ENERGY BALANCES
2.1 PRINCIPLES OF ESTABLISHING ENERGY BALANCES
The e n e r g y b a l a n c e o f a s u g a r f a c t o r y , o r a p a r t o f i t , can be a n a l y s e d on
t h e b a s i s o f t h e f i r s t law o f t h e r m o d y n a m i c s , w h i c h i s e s s e n t i a l l y a s t a t e m e n t
o f t h e p r i n c i p l e o f t he c o n s e r v a t i o n o f e n e r g y . The f i r s t law o f thermodynamics
can be r i g o r o u s l y s t a t e d i n t h e fo rm o f a ma themat i ca l e q u a t i o n , p r o v i d e d t h e
o b j e c t unde r c o n s i d e r a t i o n i s unamb igous l y d e f i n e d as a thermodynamic s y s t e m
( r e f s . 1 , 2 ) . As a l r e a d y ment ioned i n S e c t i o n 1.1, t h e i d e n t i f i c a t i o n o f a
p r e s c r i b e d and i d e n t i f i a b l e bounda ry i s n e c e s s a r y f o r sys tem d e f i n i t i o n ; t h e
boundary s e p a r a t e s t h e sys tem f rom i t s s u r r o u n d i n g s . Once t h e b o u n d a r y has been
d e f i n e d , t h e f i r s t law o f thermodynamics s t a t e s s i m p l y t h a t i n any p r o c e s s , t h e
e n e r g y d e l i v e r e d t o t h e sys tem must equa l t h e sum o f t h e e n e r g y s t o r e d i n i t and
t he e n e r g y removed t o t h e s u r r o u n d i n g s . The mathemat i ca l f o r m u l a t i o n t akes
a c c o u n t o f t h e f a c t t h a t e n e r g y can be a t t r i b u t e d t o m a t t e r c o n t a i n e d i n t h e
sys tem o r , p o s s i b l y , f l o w i n g a c r o s s i t s b o u n d a r y , and t h a t e n e r g y can a l s o be
t r a n s f e r r e d t o and f rom t h e s u r r o u n d i n g s as h e a t and w o r k . I f t h e b o u n d a r y has
been so d e f i n e d t h a t t h e r e i s no mass t r a n s f e r a c r o s s i t , t h e n t h e sys tem i s
s a i d t o be c l o s e d . E n e r g y can e n t e r o r l e a v e a c l o s e d sys tem o n l y as h e a t o r
w o r k .
I n most p rob lems d i s c u s s e d i n t h i s b o o k , h o w e v e r , a t y p i c a l s i t u a t i o n i s t h a t
t he o b j e c t unde r c o n s i d e r a t i o n has t o be i n t e r p r e t e d as an open s y s t e m , t h a t i s ,
i t s boundary has t o be d e f i n e d so as t o a l l o w f o r mass t r a n s f e r t o and f rom t h e
s u r r o u n d i n g s . Such a bounda ry i s sometimes c a l l e d a c o n t r o l s u r f a c e and t h e
sys tem encompassed , a c o n t r o l vo lume .
A p r e r e q u i s i t e f o r d e t e r m i n i n g t h e e n e r g y b a l a n c e o f an open sys tem i s t h a t
t he mass f l o w s c r o s s i n g t h e sys tem bounda ry a r e known. I n c e r t a i n e n g i n e e r i n g
p r o b l e m s , h o w e v e r , i t may i n i t i a l l y be n e c e s s a r y t o c a l c u l a t e some unknown mass
f l o w s . I f t h i s i s t he c a s e , t hen one has t o use a mass b a l a n c e e q u a t i o n w h i c h i s
an e x p r e s s i o n o f t h e law o f mass c o n s e r v a t i o n
M 3 = Δ Μ + ( 2 . 1 )
where i s t h e mass d e l i v e r e d t o t he s y s t e m , Δ Μ i s t h e i n c r e a s e o f t h e s y s t e m
mass, and i s t h e mass removed f rom t h e s y s t e m .
The above e q u a t i o n h o l d s f o r t h e f i n i t e t ime p e r i o d d u r i n g w h i c h t h e
measurements t o d e t e r m i n e M ^ , Δ Μ and have been p e r f o r m e d . I n t h e p rob lems
c o n s i d e r e d h e r e , mass i n f l o w and o u t f l o w u s u a l l y r e s u l t f rom m u l t i p l e mass f l o w s
^ s l ' ^ s 2 » - * ' ^ s p e n t e r i n g t he sys tem and G ^ ^ ^ r 2 " * ' ^ r q " '^s iv ing i t ( F i g . 2 . 1 ) .
58
mass flows entering the system BOUNDARY
niass Uows leaving the systenn
work
F i g . 2 .1 . Mass and e n e r g y b a l a n c e s o f an open thermodynamic s y s t e m .
I t may t h e r e f o r e be c o n v e n i e n t t o e x p r e s s t h e mass b a l a n c e f o r u n i t t ime
% } ' Gsp = ^V^t + ^ ^ + + . . + G , q ( 2 . 2 )
where M^ i s t h e sys tem mass, i . e . t h e mass c o n t a i n e d w i t h i n t h e sys tem b o u n d a r y .
A t y p i c a l case o f an open sys tem i s a s t e a d y - s t a t e sys tem w h i c h i s
c h a r a c t e r i z e d by t i m e - i n v a r i a n t mass and c o n s t a n t mass f l o w s . As t h e t ime
d e r i v a t i v e o f t h e sys tem mass e q u a l s z e r o , t h e b a l a n c e e q u a t i o n becomes
^ s i ^ h z ^1 ^ ^ 2 ^ - - ^ ^ q ( 2 . 3 )
Hav ing de te rm ined t h e mass f l o w s c r o s s i n g t h e sys tem b o u n d a r y , we can r e t u r n
t o t h e main p r o b l e m . A g e n e r a l fo rm o f t h e e n e r g y b a l a n c e e q u a t i o n i s
E3 = ΔΕ + E^ ( 2 . 4 )
where E^ i s t h e e n e r g y d e l i v e r e d t o t h e s y s t e m , ΔΕ i s t h e i n c r e a s e o f t h e
s y s t e m ' s e n e r g y , and E^, i s t h e e n e r g y removed f rom t h e s y s t e m .
U s i n g t h e mass f l o w s and e x p r e s s i n g t h e b a l a n c e f o r u n i t t i m e , we o b t a i n f o r
t h e sys tem shown i n F i g . 2.1
- ^V^t ^ L + G^^h^T . G^^VZ qVq ' ( 2 - 5 )
where h ^ ^ . . , h^p and h ^ - j , . . , h^^ a r e t h e e n t h a l p i e s p e r u n i t mass i n i n f l o w i n g
and o u t f l o w i n g s t r e a m s , E^ i s t h e e n e r g y a s s o c i a t e d w i t h t h e m a t t e r c o n t a i n e d
w i t h i n t h e sys tem b o u n d a r y , L i s t h e mechan ica l power (work p e r u n i t t i m e ) and
Q i s t h e the rma l power ( h e a t p e r u n i t t i m e ) d e l i v e r e d t o t h e s y s t e m . I n s t e a d y -
s t a t e s y s t e m s , t h e t ime d e r i v a t i v e o f E^ i s z e r o , a l l t h e q u a n t i t i e s c o n c e r n e d
a r e c o n s t a n t , and the e n e r g y b a l a n c e e q u a t i o n becomes
• ^ s l ^ s l ' %2\2 h p h , - L * ^ ^ ^ ^ - \ 2 \ 2 ' - ^ V r q " ^ ( ^ . 6 )
I t i s assumed i n e q n s . ( 2 . 5 ) and ( 2 . 6 ) t h a t t h e s i g n o f t h e work i s p o s i t i v e i f
i t i s removed f rom t h e s y s t e m , w h i l e t h e s i g n o f t h e h e a t i s p o s i t i v e i f i t i s
59
d e l i v e r e d t o t h e s y s t e m . The r e s u l t s o f t h e c a l c u l a t i o n s i n w h i c h t h e s e
e q u a t i o n s a r e used a r e c o r r e c t o n l y i f t h i s s i g n c o n v e n t i o n i s o b s e r v e d . One
s h o u l d a l s o be aware o f c e r t a i n i n h e r e n t l i m i t a t i o n s o f t h e b a l a n c e e q u a t i o n s ,
as w e l l as o f t h e c o n d i t i o n s f o r t h e i r c o r r e c t u s e . The d e t a i l s o f t h e prob lems
may v a r y , depend ing on t h e p u r p o s e f o r w h i c h t h e e q u a t i o n s a r e s e t u p , as
e x p l a i n e d b e l o w .
( i ) I n t h e d e s i g n a n a l y s e s , i t i s u s u a l l y assumed t h a t t h e e q u i p m e n t , i n c l u d i n g
a u x i l i a r y d e v i c e s , i s w o r k i n g i n a c c o r d a n c e w i t h t h e t e c h n i c a l s p e c i f i c a t i o n s ,
i . e . t h a t t h e r e a r e no m a l f u n c t i o n i n g steam t r a p s , u n r e l i a b l e v a l v e s , l e a k i n g
p a c k i n g s , e t c . A n o t h e r t y p i c a l assump t i on i s t h a t t h e p r o c e s s i n g c a p a b i l i t y i s
c o n s t a n t (most o f t e n , t h e nominal o r maximum c a p a b i l i t y v a l u e i s assumed) . Even
t h e s e s e e m i n g l y o b v i o u s a s s u m p t i o n s , h o w e v e r , c o n s t i t u t e an i d e a l i z a t i o n o f t h e
e n e r g y p r o c e s s e s a n a l y s e d . The r e a l p r o c e s s e s w i l l c e r t a i n l y be c h a r a c t e r i z e d by
f l u c t u a t i n g p a r a m e t e r s , t h e p r o c e s s i n g c a p a b i l i t y may d e v i a t e f rom t h e v a l u e
assumed, and t h e r e w i l l be some unknown f l o w s o f t h e p r o c e s s media l e a k i n g
between sys tem p a r t s and f rom t h e sys tem t o t h e s u r r o u n d i n g s . Unde r such
c i r c u m s t a n c e s , a l t h o u g h i t i s e s s e n t i a l n o t t o i n t r o d u c e any s i g n i f i c a n t
s y s t e m a t i c e r r o r s i n t o t h e b a l a n c e r e l a t i o n s h i p s , i t i s a l s o m e a n i n g l e s s t o
c o m p l i c a t e t h e b a l a n c e e q u a t i o n s by i n t r o d u c i n g f a c t o r s w h i c h can a c t u a l l y be
n e g l e c t e d w i t h o u t i n c r e a s i n g t h e o v e r a l l u n c e r t a i n t y m a r g i n . T h i s a p p l i e s , i n
t he f i r s t p l a c e , t o t h e e n e r g y s t reams a s s o c i a t e d w i t h t h e h e a t o f
c r y s t a l l i z a t i o n o f s u g a r and t h e mechan ica l work s u p p l i e d t o t h e p r o c e s s
e q u i p m e n t , as t h e i r o r d e r o f magn i tude may be comparab le w i t h t h a t o f t h e
unknown l o s s e s t o t he s u r r o u n d i n g s .
( i i ) I n t h e p r o c e s s m o n i t o r i n g a p p l i c a t i o n s , a number o f d i f f e r e n t s i t u a t i o n s
s h o u l d be r e c o g n i z e d . When i n v e s t i g a t i n g an e x i s t i n g f a c t o r y t o be m o d e r n i z e d ,
t h e c a l c u l a t i o n e r r o r s s h o u l d n o t e x c e e d t h e u n c e r t a i n t y m a r g i n c h a r a c t e r i s t i c
o f t h e s u b s e q u e n t d e s i g n c a l c u l a t i o n s . I n t h e r o u t i n e m o n i t o r i n g t a s k s aimed a t
p r o v i d i n g t h e f a c t o r y managers w i t h i n f o r m a t i o n on how e f f i c i e n t l y t h e e n e r g y i s
u t i l i z e d , t h e s p e c i f i c r e q u i r e m e n t s may v a r y depend ing on t h e e x p e c t e d f a c t o r y
p e r f o r m a n c e . U s u a l l y , t h e d e s i r e d a c c u r a c y i s s i m i l a r t o t h a t t y p i c a l o f t h e
d e s i g n p r o b l e m s . H o w e v e r , t h e r e may be s p e c i a l cases i n w h i c h r a t h e r h i g h
a c c u r a c y i s r e q u i r e d , f o r e x a m p l e , when t h e g u a r a n t e e t e s t s o f equ ipment u n i t s
o r e n t i r e s t a t i o n s have t o be m o n i t o r e d .
( i i i ) As a r u l e , t h e b a l a n c e c a l c u l a t i o n s r e l a t i n g t o s u g a r f a c t o r i e s , o r p a r t s
o f them, a r e pe r f o rmed unde r t h e assump t i on o f s t e a d y - s t a t e c o n d i t i o n s , u s i n g
e q n s . ( 2 . 3 ) and ( 2 . 6 ) . W h i l e t h i s may be p e r f e c t l y c o r r e c t i n most c a s e s , g r e a t
c a r e i s recommended i n i n t e r p r e t i n g t h e r e s u l t s o f e x p e r i m e n t a l i n v e s t i g a t i o n s .
I f t he measurements have been pe r fo rmed w i t h o u t s t r i c t l y m a i n t a i n i n g s t e a d y -
s t a t e c o n d i t i o n s , t h e n n e g l e c t o f t i m e - d e r i v a t i v e s o f and E^ i n e q n s . ( 2 . 2 )
60
and ( 2 . 5 ) , r e s p e c t i v e l y , may become a s o u r c e o f e r r o r s .
2.2 INPUT DATA FOR ENERGY BALANCE CALCULATIONS
2.2.1 N a t u r e o f t he i n p u t d a t a
The c a l c u l a t i o n p r i n c i p l e s p r e s e n t e d i n t h e p r e v i o u s S e c t i o n can be a p p l i e d
t o any thermodynamic sys tem w i t h i n a s u g a r f a c t o r y . F o r a p a r t i c u l a r s y s t e m ,
a s e t o f b a l a n c e e q u a t i o n s can be f o r m u l a t e d , making i t p o s s i b l e t o d e t e r m i n e
t h e v a l u e s o f as many unknown v a r i a b l e s as t h e r e a r e e q u a t i o n s i n t h e s e t . F o r
each e n e r g y b a l a n c e p r o b l e m , an a p p r o p r i a t e s e t o f i n p u t d a t a must be a v a i l a b l e .
I f some r e q u i r e m e n t s have been imposed on t h e s t r u c t u r i n g o f t h e b a l a n c e
r e s u l t s , t h a t i s , i f t h e sys tem i s t o be c o n s i d e r e d as t h e sum o f s p e c i f i c
s u b s y s t e m s , bo th t h e s e t o f e q u a t i o n s and t he s e t o f i n p u t d a t a s h o u l d be
p r e p a r e d i n a manner making i t p o s s i b l e t o s a t i s f y t h e s e r e q u i r e m e n t s . T h i s
i m p l i e s , i n t u r n , t h e n e c e s s i t y n o t o n l y t o a c c o u n t f o r t h e s y s t e m s t r u c t u r e ,
b u t a l s o t o s a t i s f y t h e c o n s t r a i n t s t h a t a r e c h a r a c t e r i s t i c o f t h e s u g a r
m a n u f a c t u r i n g p r o c e s s . F i n a l l y , t h e i n p u t da ta s h o u l d be c o m p l e t e , t h a t i s ,
among t he q u a n t i t i e s a p p e a r i n g i n t h e b a l a n c e e q u a t i o n s , o n l y as many can be
l e f t unknown as t h e r e a r e e q u a t i o n s i n t h e s e t .
The g u i d e l i n e s f o r a d e s c r i p t i o n o f t h e s t r u c t u r e o f a thermodynamic s y s t e m
and i t s subsys tems have been f o r m u l a t e d i n S e c t i o n 1.1, and t y p i c a l s t r u c t u r a l
e lements e n c o u n t e r e d i n the rma l sys tems o f s u g a r f a c t o r i e s have been d i s c u s s e d
i n S e c t i o n 1.2.
C l o s e l y a s s o c i a t e d w i t h t h e i n f o r m a t i o n on t h e sys tem s t r u c t u r e i s t h e
i n f o r m a t i o n on t h e thermodynamic p r o p e r t i e s o f t h e p r o c e s s media and on t h e
equ ipment c h a r a c t e r i s t i c s . I n t h e e q u a t i o n s p r e s e n t e d i n t h e p r e c e d i n g S e c t i o n ,
t h e e n t h a l p i e s o f t h e p r o c e s s media a p p e a r . The e n t h a l p i e s can be d e t e r m i n e d as
f u n c t i o n s o f t e m p e r a t u r e , p r e s s u r e o r o t h e r p a r a m e t e r s . I n p r a c t i c a l
c a l c u l a t i o n s , i n v e r s e f u n c t i o n s may a l s o be n e e d e d , as w e l l as a number o f o t h e r
thermodynamic f u n c t i o n s n o t n e c e s s a r i l y r e l a t e d t o t h e n o t i o n o f e n t h a l p y . The
thermodynamic f u n c t i o n s can be f ound i n d iag ram o r t a b u l a r fo rm i n t h e
l i t e r a t u r e , and t h e i r n u m e r i c a l a p p r o x i m a t i o n s a r e d i s c u s s e d i n A p p e n d i c e s 1
and 2.
As r e g a r d s t h e equ ipment d a t a , two k i n d s o f them a r e o f p a r t i c u l a r
i m p o r t a n c e :
- h e a t l o s s c o e f f i c i e n t s ,
- e q u a t i o n s e x p r e s s i n g t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t s .
A p o s s i b l e app roach t o t h i s p a r t o f t h e e n e r g y - b a l a n c e da ta w i l l be p r e s e n t e d i n
t h e r e m a i n i n g S e c t i o n s o f t h i s C h a p t e r , The v a l u e s o f t h e h e a t l o s s c o e f f i c i e n t s
and t he e q u a t i o n s d e s c r i b i n g t h e h e a t t r a n s f e r c h a r a c t e r i s t i c s o f t h e equ ipment
a r e d i s c u s s e d i n Append i x 3.
As r e g a r d s t h e p r e p a r a t i o n o f da ta on t h e s u g a r m a n u f a c t u r i n g p r o c e s s .
61
t he use o f e q u a t i o n s o f p r o c e s s mass b a l a n c e s h o u l d be named f i r s t . The mass
f l o w s o f t h e p r o c e s s media r e p r e s e n t e d i n t h e e n e r g y b a l a n c e e q u a t i o n s have t o
s a t i s f y t h e e q u a t i o n s o f t h e p r o c e s s mass b a l a n c e . A p r a c t i c a l consequence i s
t h a t t h e m a s s - b a l a n c e i n v e s t i g a t i o n - e x p e r i m e n t a l , t h e o r e t i c a l , o r a
c o m b i n a t i o n o f b o t h - must be comp le ted b e f o r e t h e e n e r g y - b a l a n c e p rob lem i s
a p p r o a c h e d .
S e t t i n g up t h e e q u a t i o n s o f t h e mass b a l a n c e o f a s u g a r m a n u f a c t u r i n g p r o c e s s
can be a d i f f i c u l t p r o b l e m i n i t s e l f . U s u a l l y , i t r e q u i r e s i d e n t i f y i n g t h e
p r o c e s s scheme and c a l c u l a t i n g t h e f l o w s o f mass componen ts : w a t e r , d r y m a t t e r ,
s u c r o s e , and - i f a p p l i c a b l e - s u c r o s e c r y s t a l s . The c a l c u l a t i o n s can be
pe r fo rmed m a n u a l l y ; p o s s i b l y , t w o - o r t h r e e - c o m p o n e n t d iag rams f o r s u g a r
s o l u t i o n s can be used t o s i m p l i f y t h e manual w o r k . Examples o f t h e u p - t o - d a t e
app roach t o t h i s t y p e o f c a l c u l a t i o n method can be f ound i n t h e l i t e r a t u r e
( r e f s . 3 - 5 ) . I n c r e a s i n g l y o f t e n , h o w e v e r , t h e p r o c e s s mass b a l a n c e s a r e
c a l c u l a t e d w i t h t h e a i d o f computer p rog rams . The methods used i n c o m p u t e r i z e d
c a l c u l a t i o n s a r e based e i t h e r on t h e p r o c e s s s i m u l a t i o n app roach ( r e f s . 6 -8 ) o r
on t h e s o l u t i o n o f a sys tem o f l i n e a r e q u a t i o n s ( r e f . 9 ) .
2 .2 .2 Example
The s u g a r m a n u f a c t u r i n g p r o c e s s i s t o be c o n s i d e r e d f o r a f a c t o r y f e a t u r i n g
a t r o u g h - t y p e e x t r a c t o r , a c l a s s i c a l j u i c e p u r i f i c a t i o n s t a t i o n w i t h s u b s e q u e n t
j u i c e d e c a l c i f i c a t i o n and a s t a n d a r d - l i q u o r - b a s e d , t h r e e - b o i l i n g c r y s t a l l i z a t i o n
scheme. The pa rame te rs d e f i n i n g t h e o v e r a l l p r o c e s s c h a r a c t e r i s t i c s a r e g i v e n i n
T a b l e 2 .1 . The scheme o f t h e b e e t house i s shown i n F i g . 2.2 and t h e
c o r r e s p o n d i n g mass b a l a n c e da ta a r e p r e s e n t e d i n T a b l e 2 . 2 . The scheme o f t h e
s u g a r house i s shown i n F i g . 2.3 and t h e mass b a l a n c e d a t a a r e p r e s e n t e d i n
T a b l e 2 . 3 . L e t us a n a l y s e t h e p r o c e s s scheme and t h e mass b a l a n c e d a t a f rom t h e
p o i n t o f v i e w o f t h e i r s u i t a b i l i t y as i n p u t da ta f o r e n e r g y b a l a n c e
c a l c u l a t i o n s .
TABLE 2.1
E s s e n t i a l p r o c e s s da ta f o r t h e Examp le .
Name D imens ion V a l u e
P o l a r i z a t i o n o f c o s s e t t e s % 18.0 J u i c e d r a f t % 110.0 CaO r a t e :
p r e - l i m i n g kg/100 kg b 0.28 main l i m i n g
kg/100 kg b 1.52
2nd c a r b o n a t a t i o n II II 0.22 T h i c k j u i c e c o n c e n t r a t i o n % DS 56.0 Mo lasses p u r i t y % 62.0
62
feed water
ΙΛ
o c !5
Ε
en TD
-D (Λ
Χ )
(Λ
cossettes
EXTRACTOR
HEATER i_
HEATER I
y. L - w e t pulp raw juice
4
press water
PRESSES
pressed pulp
HEATERS to drying
sweet water
PRE-LIMING
HEATERS
MAIN LIMING
1
Φ
Φ
•σ
to lime slaking
i Φ Φ
CARBONATATION I
HEATERS
THICKENERS I
ju ice
VACUUM FILTERS
HEATER
Φ Φ
ω
water -
CARBONATATION I I
THICKENERS Π
s ludge^
thin ju ice to heating and evapora t ion .
SAFETY FILTERS
DECALCI FICATION
1 SULPHITATION
thin juice to sugar house^
ju ice
F i g . 2 . 2 . Scheme o f t he b e e t house c o n s i d e r e d i n t h e Examp le .
63
TABLE 2.2
Mass b a l a n c e o f t h e b e e t house i n t h e Example
No. St ream name T o t a l f l o w
(kg /100 kg b ) C o n c e n t r a t i o n
(% DS) P u r i t y
(%)
1 C o s s e t t e s 100.00 86.90 2 Wet p u l p 84.60 3 P r e s s e d p u l p 27.04 19.00 4 D r i e d p u l p 5.58 92.00 5 P r e s s w a t e r 57.56 0.90 74.50 6 Feed w a t e r 37.04 7 Raw j u i c e 110.00 18.16 88.11 8 J u i c e t o main l i m i n g 135.84 17.88 9 J u i c e t o c a r b o n a t a t i o n I 143.46 17.99
10 J u i c e f rom vacuum f i l t e r s 13.73 12.00 92.38 11 J u i c e t o t h i c k e n e r s I 157.19 17.47 12 J u i c e t o c a r b o n a t a t i o n I I 124.50 16.28 91.48 13 S u b s i d e r s l u d g e I 32.69 20.00 14 Subs i d e r s l u d g e I t o vacuum f i l t e r s 20.69 15 S w e e t e n i n g - o f f w a t e r t o vacuum
f i l t e r s 12.72
16 S l u d g e 8.48 50.00 17 Sweet w a t e r f rom vacuum f i l t e r s 11.02 7.00 89.00 18 J u i c e t o t h i c k e n e r s I I 127.30 92.04 19 S u b s i d e r s l u d g e I I t o p r e - l i m i n g 3.59 18.00 20 J u i c e t o s a f e t y f i l t e r s 125.42 15.76 92.03 21 J u i c e t o s u l p h i t a t i o n 123.71 22 J u i c e t o d e c a l c i f i c a t i o n 118.50 16.68 92.03 23 S w e e t e n i n g - o f f w a t e r t o
d e c a l c i f i c a t i o n 7.00
24 Sweet w a t e r f rom d e c a l c i f i c a t i o n 3.50 1.08 88.00 25 T h i n j u i c e t o e v a p o r a t i o n 122.00 15.51 92.04 26 M i l k - o f - l i m e t o p r e - l i m i n g 1.41 27 " main l i m i n g 7.62 28 " " c a r b o n a t a t i o n I I 1.09 29 K i l n gas t o c a r b o n a t a t i o n I 3.80 30 II II II II J J 0.79
The scheme and t h e da ta d e s c r i b i n g t h e b e e t house p r o v i d e a comp le te
d e f i n i t i o n o f a l l t he mass s t reams t o w h i c h h e a t s h o u l d be d e l i v e r e d . I t i s
p o s s i b l e t o d e t e r m i n e , f o r each s t r e a m , t h e mass f l o w and t h e m a t e r i a l
p r o p e r t i e s a f f e c t i n g t h e e n t h a l p y ( o r t h e s p e c i f i c h e a t ) . No t e m p e r a t u r e s a r e
g i v e n , h o w e v e r , t h i s i m p l y i n g t h a t t h e t e m p e r a t u r e r e q u i r e m e n t s s h o u l d be
s e p a r a t e l y c o n s i d e r e d , p o s s i b l y t o g e t h e r w i t h t h e s t r u c t u r e o f t h e p a r t o f t h e
therma l sys tem w h i c h i s a s s o c i a t e d w i t h t h e b e e t h o u s e .
The scheme o f t h e s u g a r house seems t o be i n c o m p l e t e , as no h e a t i n g
o p e r a t i o n s a r e s p e c i f i e d . The mass b a l a n c e d a t a d e f i n e c o m p l e t e l y a l l t h e t i m e -
a v e r a g e d mass f l o w s o f media w i t h i n t h e s u g a r h o u s e . Once t h e h e a t i n g
o p e r a t i o n s have been s p e c i f i e d ( t y p i c a l l y , h e a t i n g o f t h i c k j u i c e d e l i v e r e d t o
t he s u g a r house and s y r u p s s t o r e d i n i n t e r m e d i a t e t anks i s r e q u i r e d ) , i t w i l l be
p o s s i b l e t o i d e n t i f y a l l t h e mass f l o w s and m a t e r i a l p r o p e r t i e s t h a t a r e
64
thick juice
MELTER
FILTER
standard liquor
VACUUM PANS A 1
1 MIXERS A
1 CENTRIFUGALS A
sugar A
green " syrup A "
1 1 Γ
Q . 13
sz ΙΛ O
VACUUM PANS Β
MIXERS Β 1
1 CENTRIF UGALS Β
sugar Β
1 σ ι >>
3 ί VACUUM PANSC
I
MAGMA MIXER
• white sugar
MIXERS C
z r : CENTRIFUGALS C
L- sugar C —-I
- magma-
molasses
F i g . 2 . 3 . Scheme o f t h e s u g a r house c o n s i d e r e d i n t h e Examp le .
TABLE 2.3
Mass b a l a n c e o f t h e s u g a r house i n t h e Examp le .
No. S t ream name T o t a l f l o w
(kg /100 kg b ) C o n c e n t r a t i o n
{% DS) P u r i t y
{%)
1 T h i c k j u i c e 33.61 56.00 92.02 2 S t a n d a r d l i q u o r 39.88 62.62 93.60 3 A m a s s e c u i t e 29.09 92.50 93.46 4 Green s y r u p A t o vacuum pans C 2.79 82.50 84.60 5 II II II II II g 5.80 82.50 84.60 6 · magma 3.82 82.50 84.60 7 Wash s y r u p A 2.65 75.50 91.96 8 A s u g a r 14.80 99.10 99.85 9 Β m a s s e c u i t e 13.35 92.80 87.18
10 Green s y r u p Β 6.25 83.80 74.20 11 Wash s y r u p Β 1.26 79.50 86.18 12 Β s u g a r 6.27 98.10 98.40 13 C m a s s e c u i t e 7.92 93.50 76.94 14 C s u g a r 3.62 97.10 93.50 15 Magma 7.44 89.60 89.29 16 Mo lasses 4.66 83.50 62.00
65
r e l e v a n t t o t h e e n e r g y b a l a n c e c a l c u l a t i o n s . A g a i n , t h e t e m p e r a t u r e r e q u i r e m e n t s
can c o n v e n i e n t l y be s p e c i f i e d when d e f i n i n g t h e s t r u c t u r e o f t h e a s s o c i a t e d p a r t
o f t he the rma l s y s t e m .
2.3 EXTERNAL ENERGY BALANCE OF A SUGAR FACTORY
The e n e r g y demand i n a s u g a r f a c t o r y i s u l t i m a t e l y d e t e r m i n e d by t h e
i n t e r a c t i o n s between t he s u g a r m a n u f a c t u r i n g p r o c e s s , t h e the rma l sys tem and t h e
power h o u s e . When s o l v i n g c e r t a i n e n g i n e e r i n g p r o b l e m s , i t may be o f i n t e r e s t t o
i n v e s t i g a t e key i n t e r a c t i o n pa ramete rs and t o i d e n t i f y o r e v a l u a t e e s s e n t i a l
p r o p e r t i e s o f t h e t h r e e f a c t o r y subsys tems named, w i t h o u t a n a l y s i n g t h e i r
d e t a i l s . T h i s can be done by s e t t i n g up t h e s o - c a l l e d e x t e r n a l mass and e n e r g y
b a l a n c e o f t h e f a c t o r y . Examples o f a p p l i c a t i o n o f t h i s app roach can be f ound i n
t he l i t e r a t u r e ( r e f s . 1 0 , 1 1 ) .
L e t us c o n s i d e r an open thermodynamic s y s t e m c o m p r i s i n g t h e main p r o c e s s
equ ipment and the rma l equ ipment f rom t h e e x t r a c t i o n s t a t i o n t o t h e s u g a r h o u s e ,
t h a t i s , e x c l u d i n g t h e b e e t wash ing and s l i c i n g s t a t i o n , s u g a r áryer^ l i m e k i l n ,
power h o u s e , b a r o m e t r i c c o n d e n s e r and b a r o m e t r i c - w a t e r c o o l i n g c i r c u i t . A b l o c k
d iagram r e p r e s e n t i n g t h e sys tem i s shown i n F i g . 2 . 4 . I t can be seen t h a t most
mass f l o w s t o and f rom t h e sys tem a r e r o u t i n e l y measured f o r p r o c e s s c o n t r o l
pu rposes o r can be deduced f rom such measurements , so o n l y a few mass f l o w s
s h o u l d be a d d i t i o n a l l y de te rm ined i n o r d e r t o d e s c r i b e t h e mass b a l a n c e f u l l y .
SYSTEM BOUNDARY
Spen t q a s from 1 s f / 2 n d carb.
vapour I 4-
1 cosseHes ^
E S 1
1 E S
1 1 —
o •α α χί 1 δ
J P
^ \ — s i
vapour
EV SH
steann
VQPOur
I sugar
molasse^
F i g . 2 . 4 . B l o c k scheme i l l u s t r a t i n g t h e e x t e r n a l e n e r g y b a l a n c e o f a s u g a r f a c t o r y . ES - e x t r a c t i o n s t a t i o n , JP - j u i c e p u r i f i c a t i o n s t a t i o n , EV -e v a p o r a t o r , SH - s u g a r h o u s e . 1 - b e e t wash ing and s l i c i n g e q u i p m e n t , 2 - l ime k i l n and m i l k - o f - l i m e s t a t i o n , 3 - power h o u s e , 4 - s u g a r d r y i n g and packag ing s t a t i o n , 5 - c o n d e n s e r and c o o l i n g c i r c u i t .
66
The number o f t e m p e r a t u r e ( a n d , p o s s i b l y , p r e s s u r e ) measurements r e q u i r e d t o
i d e n t i f y t h e e n t h a l p i e s o f f l o w i n g media i s a l s o s m a l l .
The i n t e r n a l c o m p l e x i t i e s o f t h e sys tem d e f i n e d above need n o t be known f o r
t h e e x t e r n a l e n e r g y b a l a n c e , w h i c h can be d e s c r i b e d by i n t r o d u c i n g t h e
q u a n t i t i e s c h a r a c t e r i z i n g t h e f l o w i n g media i n t o e q n s . ( 2 . 5 ) o r ( 2 . 6 ) . The n e t
h e a t demand i s r e p r e s e n t e d by t h e h e a t s t ream i n t h e steam d e l i v e r e d f rom t h e
power house and we a r e f r e e t o s t u d y how t o r e d u c e i t by a d j u s t i n g o t h e r
s t r e a m s . O f c o u r s e , i t i s d e s i r a b l e t h a t t h e sum o f o u t f l o w i n g e n e r g y s t reams
s h o u l d be as sma l l as p o s s i b l e , w h i c h can be o b t a i n e d by l i m i t i n g t h e o u t f l o w i n g
mass f l o w s a n d / o r d e c r e a s i n g t h e t e m p e r a t u r e s o f t h e media l e a v i n g t h e s y s t e m .
I n t h e f i r s t p l a c e t h i s a p p l i e s t o v a p o u r s t r e a m s , because t h e v a p o u r e n t h a l p i e s
a r e h i g h e s t . I t i s t h u s e s s e n t i a l t o m i n i m i z e t h e v a p o u r f l o w f rom t h e l a s t
e v a p o r a t o r e f f e c t t o t h e c o n d e n s e r , and t h e e n e r g y o f t h e vacuum pan v a p o u r s
s h o u l d be u t i l i z e d as much as p o s s i b l e b e f o r e t h e v a p o u r s e n t e r t h e c o n d e n s e r .
S i m i l a r recommendat ions a p p l y t o e x c e s s c o n d e n s a t e f rom t h e e v a p o r a t o r , and
s p e n t c a r b o n a t a t i o n g a s .
An i m p o r t a n t c o n c l u s i o n can be drawn f rom t h e e x t e r n a l e n e r g y b a l a n c e , namely
t h a t as l ong as e x c e s s c o n d e n s a t e (ammoniacal w a t e r ) f rom t h e e v a p o r a t o r i s
s u p p l i e d as f r e s h w a t e r t o t h e e x t r a c t i o n s t a t i o n , and t h e c o n d e n s e r l o s s f rom
t h e l a s t e v a p o r a t o r e f f e c t i s h e l d c o n s t a n t , t h e n e t hea t demand i s i n d e p e n d e n t
o f t he amount o f w a t e r e v a p o r a t e d i n t h e e v a p o r a t o r . I f t h e above c o n d i t i o n s a r e
s a t i s f i e d , t hen t h e j u i c e d r a f t can be i n c r e a s e d o r c o n d e n s a t e can be added t o
j u i c e w i t h o u t n e c e s s a r i l y i n c r e a s i n g t h e n e t h e a t demand. On t h e o t h e r h a n d , any
i n t a k e o f e x t r a w a t e r f rom o u t s i d e t h e s y s t e m , f o r example t o vacuum p a n s ,
i n e v i t a b l y i n c r e a s e s t h e n e t hea t demand.
As r e g a r d s t h e c a l c u l a t i o n s o f t h e e n e r g y s t r e a m s , i t s h o u l d be o b s e r v e d t h a t
i f a h i g h a c c u r a c y o f t he e x t e r n a l b a l a n c e i s r e q u i r e d , t h e n i t i s n e c e s s a r y t o
a c c o u n t f o r t h r e e e n t r i e s w h i c h a r e t r a d i t i o n a l l y n e g l e c t e d i n e n g i n e e r i n g
a n a l y s e s .
( i ) Heat o f c a r b o n a t a t i o n r e a c t i o n . Assuming t h a t i t i s g e n e r a t e d a t t h e r a t e o f
70 k J p e r 1 mol o f CaO and t h a t t h e e f f e c t i v e CaO r a t e i s 1.9%, we o b t a i n an
e n e r g y s t ream o f abou t 2400kJ/100 kg b , t h i s b e i n g e q u i v a l e n t t o 1.1 kg steam
p e r 100 kg b.
( i i ) Heat o f c r y s t a l l i z a t i o n o f s u g a r . A t 75°C, t h i s i s 82 k J / k g . M u l t i p l e
c r y s t a l l i z a t i o n - d i s s o l v i n g o p e r a t i o n s i n t h e s u g a r house can be d i s r e g a r d e d , on
t h e assumpt ion t h a t t h e h e a t g e n e r a t e d e q u a l s t h e h e a t a b s o r b e d . H o w e v e r , t h e
s u g a r s t ream l e a v i n g t h e s u g a r house c o r r e s p o n d s t o a d e f i n i t e amount o f h e a t
g e n e r a t e d . A t a t y p i c a l s u g a r y i e l d , t h i s c o r r e s p o n d s t o abou t 0.5 kg steam p e r
100 kg b.
( i i i ) Mechan i ca l work s u p p l i e d t o t he p r o c e s s . Power consumed by t h e motors
67
d r i v i n g t h e pumps, s t i r r e r s and o t h e r equ ipment i s c o n v e r t e d t o mechan i ca l work
and f i n a l l y d i s s i p a t e d - a p a r t t o t h e p r o c e s s m e d i a , and t h e r e s t t o t h e
e n v i r o n m e n t . Assuming a t y p i c a l equ ipment c o n f i g u r a t i o n and a 50:50 e n e r g y
d i s s i p a t i o n , t h e s t ream o f mechan ica l work a b s o r b e d by t h e p r o c e s s media can be
e s t i m a t e d a t abou t 0.8 kg steam p e r 100 kg b.
TABLE 2.4
E x t e r n a l mass and e n e r g y b a l a n c e s o f a s u g a r f a c t o r y c o n s i d e r e d as a thermodynamic sys tem shown s c h e m a t i c a l l y i n F i g . 2 . 4 .
Mass f l o w T e m p e r a t u r e E n t h a l p y E n t h a l p y s t ream No. Name (kg /100 kg b ) ( O Q ) ( k J / k g ) ( M J / l O O kg b )
I n f l o w i n g s t reams
1 C o s s e t t e s 100.0 12 45 4.5 2 M i l k - o f - l i m e 11.9 40 150 1.8 3 K i l n gas 5.3 35 80 0.4 4 Heat o f - - - 2.4
c a r b o n a t a t i o n r e a c t i o n 5 Wash w a t e r t o c e n t r i f u g a l s 1.4 15 63 0.1 6 Wash steam (7 b a r ) t o 1.2 165 2762 3.3
c e n t r i f u g a l s 7 C r y s t a l l i z a t i o n h e a t - - - 1.2 8 Mechan i ca l work t o p r o c e s s - - - 1.8 9 Steam ( 3 . 4 b a r ) t o 52.0 138 2730 142.0
e v a p o r a t o r and vacuum pan s teaming
T o t a l 1-9 171.8 _ _ 157.5
O u t f l o w i n g s t reams
10 P r e s s e d p u l p 14.35% DS 34.3 40 160 5.5 11 C a r b o n a t a t i o n s l u d g e 8.5 60 150 1.3
50% DS 12 Sweet w a t e r t o l ime 6.7 65 267 1.8
s l a k i n g 13 Gas f rom l s t / 2 n d 6.3 82/92 7.3
c a r b o n a t a t i o n 14 Vacuum f i l t e r v a p o u r 0.6 65 2618 1.6 15 V a p o u r f rom t h e l a s t 8.4 90 2660 22.3
e v a p o r a t o r e f f e c t 16 Condensa te t o b o i l e r s 60.2 114 478 28.8 17 Vacuum pan v a p o u r 20.3 62 2613 53.0 18 Suga r f rom c e n t r i f u g a l s 14.2 70 97 1.4 19 H e a t i n g v a p o u r t o s u g a r 0.9 125 2713 2.4
d r y e r 20 Mo lasses 5.0 50 115 0.6 21 C o o l i n g o f C m a s s e c u i t e - - - 0.6 22 Wash steam d i s s i p a t e d f rom 1.0 165 2762 2.8
c e n t r i f u g a l s 23 Steam d i s s i p a t e d f rom 0.5 138 2730 1.4
vacuum pans
T o t a l 10-23 166.9 - - 130.8
24 V a r i o u s l e a k s and h e a t 4 .9 - - 26.7 l o s s e s
T o t a l 10-24 171.8 - - 157.5
68
A q u e s t i o n may be posed abou t t h e pu rpose o f a c c o u n t i n g f o r t h e s e r e l a t i v e l y
smal l i ncoming e n e r g y s t r e a m s , w h i l e s i m u l t a n e o u s l y c a l c u l a t i n g n o t - s o - w e l l
d e f i n e d l o s s e s caused by t h e l e a k s o f media and t h e h e a t t r a n s f e r t o t h e
e n v i r o n m e n t . The answer i s t h a t i t i s o n l y when a l l t h e incoming e n e r g y s t reams
a r e known t h a t i t becomes p o s s i b l e t o e v a l u a t e t h e l o s s e s r e a l i s t i c a l l y . O f
c o u r s e , one can a l s o imag ine e n g i n e e r i n g p rob lems i n w h i c h a p p r o x i m a t e
c a l c u l a t i o n s o f t h e e n e r g y b a l a n c e a r e s u f f i c i e n t t o a r r i v e a t a c o r r e c t
s o l u t i o n , t h i s i m p l y i n g t h a t v e r y sma l l e n e r g y s t reams need n o t be t aken i n t o
a c c o u n t .
I n T a b l e 2 . 4 , an example i s p r e s e n t e d o f t h e e x t e r n a l e n e r g y b a l a n c e w i t h t h e
h e a t o f t h e c a r b o n a t a t i o n r e a c t i o n , h e a t o f c r y s t a l l i z a t i o n o f s u g a r and
mechan ica l work taken i n t o a c c o u n t . As can be s e e n , t h e u n c o n t r o l l a b l e e n e r g y
l o s s e s c o r r e s p o n d t o abou t 19% o f t h e e n e r g y s t ream d e l i v e r e d i n t h e h e a t i n g
s team. Had t h e sma l l i ncoming s t reams been n e g l e c t e d , t h e l o s s e s wou ld have been
c a l c u l a t e d a t abou t 15% o f t h e steam e n e r g y , t h i s b e i n g a c l e a r u n d e r e s t i m a t e .
L e t us o b s e r v e a l s o t h a t t h e d e f i n i t i o n o f t h e thermodynamic sys tem so as t o
e x c l u d e t h e s u g a r d r y e r i s a m a t t e r o f c o n v e n i e n c e . The h e a t demand o f t h e d r y e r
can be c a l c u l a t e d s e p a r a t e l y f rom t h e w a t e r c o n t e n t i n s u g a r l e a v i n g t h e
c e n t r i f u g a l s . Had t h e d r y e r been i n c l u d e d , i t wou ld have been n e c e s s a r y t o
a c c o u n t f o r t h e s t reams o f a i r e n t e r i n g and l e a v i n g t h e s y s t e m , a i r e n t h a l p y
b e i n g a f u n c t i o n o f h u m i d i t y and t e m p e r a t u r e . T h i s wou ld make t h e b a l a n c e
c a l c u l a t i o n s a l i t t l e more l a b o r i o u s .
I t s h o u l d be f i n a l l y no ted t h a t t h e t o t a l hea t demand a n d , c o n s e q u e n t l y ,
t h e e f f e c t i v e n e s s r a t i o o f t h e therma l sys tem c a n n o t be c a l c u l a t e d f rom t h e
e x t e r n a l e n e r g y b a l a n c e . T h i s i s i l l u s t r a t e d by T a b l e 2.4 w h i c h c o n t a i n s t h e
i n f l o w i n g and o u t f l o w i n g e n e r g y s t reams b u t n o t t h e ones c i r c u l a t i n g i n t h e
p r o c e s s .
2.4 MASS AND HEAT BALANCES OF HEAT RECEIVERS
2.4.1 I n t r o d u c t o r y remarks
I t i s o f t e n n e c e s s a r y t o i n v e s t i g a t e t h e mass and h e a t b a l a n c e s o f a s u g a r
f a c t o r y i n o r d e r t o d e t e r m i n e t h e d e t a i l s c o r r e s p o n d i n g t o t h e i n d i v i d u a l
equ ipment u n i t s . Such a s i t u a t i o n may a r i s e when d e s i g n i n g a new the rma l sys tem
f o r g i v e n paramete rs o f t he s u g a r m a n u f a c t u r i n g p r o c e s s , o r when a n a l y s i n g t h e
e n e r g y econorny o f an e x i s t i n g s u g a r f a c t o r y . I n o r d e r t o a r r i v e a t a s o l u t i o n ,
i t i s n e c e s s a r y t o i d e n t i f y a l l t h e h e a t s t reams q^. d e f i n e d i n S e c t i o n 1 . 2 . 2 ;
t h i s makes i t a l s o p o s s i b l e t o c a l c u l a t e t h e t o t a l h e a t demand, t h e n e t h e a t
demand and t he e f f e c t i v e n e s s r a t i o o f t h e the rma l s y s t e m . Examples o f
f o r m u l a t i o n o f t h i s k i n d o f p rob lem can be found i n t h e l i t e r a t u r e ( r e f s .
1 2 - 1 4 ) .
V i r t u a l l y a l l the rma l sys tems i n c o r p o r a t e such equ ipment as j u i c e h e a t e r s .
69
e x t r a c t o r s , hea ted i n t e r m e d i a t e s t o r a g e tanks and vacuum p a n s . G e n e r a l f o r m u l a e
used i n b a l a n c e c a l c u l a t i o n s o f t h e equ ipment u n i t s named a r e p r e s e n t e d i n t h e
f o l l o w i n g . The b a l a n c e s o f o t h e r e q u i p m e n t , n o t c o n s i d e r e d h e r e , can be m o d e l l e d
i n a s i m i l a r manner.
2 .4 .2 J u i c e h e a t e r s
J u i c e h e a t e r s a r e c e r t a i n l y among t h e most i m p o r t a n t components o f t h e
therma l s y s t e m s , as i t i s v i a t h e h e a t e r s t h a t a l a r g e p a r t o f t h e t o t a l h e a t
demand i s t r a n s f e r r e d t o t h e p r o c e s s . The b a l a n c e c a l c u l a t i o n f o r a h e a t e r i s
r a t h e r s i m p l e , b u t t h e p rob lem o f c o o r d i n a t i n g i t w i t h t h e c a l c u l a t i o n s o f o t h e r
p a r t s o f t he the rma l sys tem may be d i f f i c u l t t o s o l v e .
L e t us c o n s i d e r t h e e v a l u a t i o n o f t h e h e a t exchange i n a h e a t e r c h a r a c t e r i z e d
by a g i v e n h e a t i n g s u r f a c e a r e a F and o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t k,
s u p p l i e d w i t h h e a t i n g v a p o u r a t t e m p e r a t u r e t ^ , w h i l e t h e r e q u i r e d f i n a l
t e m p e r a t u r e o f t h e f l u i d hea ted i s t ^ . The q u a n t i t i e s d e t e r m i n i n g t h e mass and
h e a t b a l a n c e s o f t he h e a t e r a r e i n d i c a t e d i n F i g . 2 . 5 ( a ) . ( I t s h o u l d be n o t e d
t h a t t h e c a l c u l a t i o n p r o c e d u r e t o be a p p l i e d i n t h e case o f an unknown h e a t i n g
s u r f a c e a rea i s g i v e n i n r e f . 1 4 . )
(a) (b)
G , t i ,
G v i t v ^ -h-i-H-
iliü i Μ i! ι ι ι ; ι
-h-i-H-
iliü i Μ i! ι ι ι ; ι Ι Μ I I
t2 ,
G c . t c i , t t t t t Miii liiii t t t t t Miii liiii ι ι ι ι ι M i l l
F i g . 2 . 5 . P r i n c i p l e o f mass and h e a t b a l a n c e s o f j u i c e h e a t e r s : ( a ) v a p o u r -h e a t e d , ( b ) c o n d e n s a t e - h e a t e d .
I f t h e f l u i d t e m p e r a t u r e a t t h e h e a t e r i n l e t i s t - j , t h e n t h e r e s u l t i n g f i n a l
t e m p e r a t u r e w i l l be
t2 = - ( t v - t i ) e x p ( - F k / ( ( l + n ) G C ) ) ( 2 . 7 )
where η i s t he h e a t l o s s c o e f f i c i e n t and C i s t h e j u i c e s p e c i f i c h e a t .
N e g l e c t i n g condensa te s u b c o o l i n g , t h e mean l o g a r i t h m i c t e m p e r a t u r e d i f f e r e n c e
can be c a l c u l a t e d as
A t = ( t ^ - t i ) / l n ( ( t ^ - t^)/(t^ - t 2 ) ) ( 2 . 8 )
T a k i n g t he s u b c o o l i n g i n t o a c c o u n t , t h e a p p r o x i m a t e v a l u e o f t h e o u t l e t
t e m p e r a t u r e o f t he c o n d e n s a t e i s
^ c = + 1 ^ ^ 2 ) / δ ( 2 . 9 )
70
D e n o t i n g t h e e n t h a l p y o f d r y s a t u r a t e d steam a t t e m p e r a t u r e t by h " ( t ) , v a p o u r
e n t h a l p y i s t h u s h^ = h " ( t ^ ) , and assuming a l l t h e e n t h a l p i e s a r e e x p r e s s e d i n
k J / k g , condensa te e n t h a l p y i s h^= 4.19 t ^ .
The h e a t t r a n s f e r r e d f rom v a p o u r t o j u i c e i n t h e h e a t e r i s
q = (1 + n ) G C ( t 2 - t ^ ) ( 2 . 1 0 )
and t he h e a t i n g v a p o u r demand
Gv = q / ( h v - \ ) ( 2 . 1 1 )
The f u r t h e r c o u r s e o f t h e c a l c u l a t i o n s depends now on t h e r e l a t i o n between t h e
two f i n a l t e m p e r a t u r e s , t h e r e q u i r e d t ^ and r e s u l t i n g t 2 . Too low a t2 v a l u e i s
an i n d i c a t i o n o f i n s u f f i c i e n t hea t s u p p l y . I n o r d e r t o e n s u r e c o r r e c t h e a t i n g ,
t h e h e a t i n g s u r f a c e a r e a s h o u l d be i n c r e a s e d , o r a n o t h e r h e a t e r s h o u l d be
p l anned n e x t t o t h e one b e i n g e v a l u a t e d ; i n e i t h e r c a s e , i t i s n e c e s s a r y t o
r e p e a t t h e c a l c u l a t i o n a c c o r d i n g t o e q n s . ( 2 . 7 ) - ( 2 . 1 1 ) w i t h a new s e t o f i n p u t
d a t a . I f t ^ t u r n s o u t t o be t o o h i g h , t h e n t h e c o n c l u s i o n c o u l d be drawn t h a t
t o o much hea t w i l l be t r a n s f e r r e d t o t h e j u i c e . I t i s p o s s i b l e t o l e a v e t h e
h e a t i n g s u r f a c e a r e a u n c h a n g e d , h o w e v e r , as i n r e a l i t y , t h e t e m p e r a t u r e c o n t r o l
c i r c u i t w i l l a d j u s t t h e v a p o u r consumpt ion so as t o o b t a i n t h e r e q u i r e d f i n a l
j u i c e t e m p e r a t u r e t ^ . C o n s e q u e n t l y , t h e h e a t t r a n s f e r r e d becomes
q ^ = (1 + n ) G C ( t ^ - t ^ ) ( 2 . 1 2 )
and t h e r e s u l t i n g l o g a r i t h m i c t e m p e r a t u r e d i f f e r e n c e i s
A t ^ = ( t f - t ^ ) / l n ( ( t f - t ^ ) / ( t ^ - t 2 ) ) ( 2 . 1 3 )
The r e s u l t i n g t e m p e r a t u r e and e n t h a l p y o f t h e c o n d e n s a t e a r e
t ^ ^ = ( 6 t ^ + t ^ + t i ) / 8 ( 2 . 1 4 )
and
h ^ f = 4.19 t ^ ^ ( 2 . 1 5 )
and t h e h e a t i n g v a p o u r demand i s
G v f = q f / ( h v - h ^ f ) ( 2 . 1 6 )
I t i s a l s o p o s s i b l e t o d e t e r m i n e t h e e f f e c t i v e ( i . e . , minimum r e q u i r e d ) h e a t i n g
s u r f a c e a r e a as
= q ^ / ( k A t ^ ) ( 2 . 1 7 )
I n t h e case o f c o n d e n s a t e - h e a t e d h e a t e r s , t h e c o u r s e o f t h e c a l c u l a t i o n s and
t h e s u b s e q u e n t d e c i s i o n - m a k i n g p r o c e d u r e may be d i f f e r e n t . T y p i c a l l y , c o n d e n s a t e
mass f l o w G ^ and i n l e t t e m p e r a t u r e t^-j a r e known, a l o n g w i t h h e a t i n g s u r f a c e
a r e a F , o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t k and r e q u i r e d f i n a l t e m p e r a t u r e t ^
o f t h e l i q u i d h e a t e d . The q u a n t i t i e s d e t e r m i n i n g t h e mass and h e a t b a l a n c e s o f
t h e h e a t e r a r e i n d i c a t e d i n F i g . 2 . 5 ( b ) . C o u n t e r - c u r r e n t o p e r a t i o n o f t h e h e a t e r
i s assumed.
71
The d i f f i c u l t y i n i n i t i a t i n g t h e c a l c u l a t i o n s i s t h e u n c e r t a i n t y abou t t h e
f i n a l t e m p e r a t u r e s o f bo th t h e l i q u i d hea ted and t h e c o n d e n s a t e . I t can be
r e s o l v e d by making an i n i t i a l guess t2^- on t h e o u t l e t t e m p e r a t u r e o f t h e l i q u i d
( l a t e r o n , we w i l l be a b l e t o check how good t h e guess i s ) . I t t hus becomes
p o s s i b l e t o e s t i m a t e t h e o u t l e t t e m p e r a t u r e o f t h e c o n d e n s a t e
\ 2 = ^ c l - ^ " ) ^ ^ ( ^ 2 i - t i ) ) / ( 4 . 1 9 ( 2 . 1 8 )
The r e s u l t i n g mean l o g a r i t h m i c t e m p e r a t u r e d i f f e r e n c e i s t h u s
At = ( ( t ^ T - t^^) - ( t ^ 2 - ^ ΐ ) ) / " ' " ( ( ^ ο 1 " ^ 2 i ) / ( ^ c 2 - ^ l ) ) ( 2 · ^ ^ )
and t he h e a t t r a n s f e r r e d can be e s t i m a t e d as
q = kFAt ( 2 . 2 0 )
I t now becomes p o s s i b l e t o c a l c u l a t e an improved a p p r o x i m a t i o n o f t h e f i n a l
t e m p e r a t u r e o f t h e l i q u i d hea ted
t2 = t^ + q / ( ( l + n ) G C ) ( 2 . 2 1 )
I f | t 2 - t2^-| > t ^ , where t ^ i s t h e assumed t e m p e r a t u r e - e r r o r t o l e r a n c e , t h e n
a new guess on t h e v a l u e o f t2^- s h o u l d be made and t h e c a l c u l a t i o n s s h o u l d be
r e p e a t e d , s t a r t i n g f rom e q n . ( 2 . 1 8 ) . Once an a c c e p t a b l e v a l u e o f t 2 has been
f o u n d , t h e c o u r s e o f t h e c a l c u l a t i o n s depends on t h e r e l a t i o n between t2 and
t h e r e q u i r e d f i n a l t e m p e r a t u r e t ^ . I f t 2 i s t o o l o w , t h e n t h e h e a t i n g s u r f a c e
a r e a s h o u l d be i n c r e a s e d , o r a n o t h e r h e a t e r s h o u l d be p l anned i m m e d i a t e l y
f o l l o w i n g t he one b e i n g e v a l u a t e d . I n e i t h e r c a s e , t h e c a l c u l a t i o n s a c c o r d i n g
t o e q n s . ( 2 . 1 8 ) - ( 2 . 2 1 ) must be r e p e a t e d w i t h a new s e t o f i n p u t d a t a . Too h i g h
a t2 v a l u e s h o u l d be i n t e r p r e t e d as an i n d i c a t i o n o f t o o l a r g e a c o n d e n s a t e
f l o w o r t oo l a r g e a h e a t i n g s u r f a c e a r e a . The r e a l i s t i c v a l u e o f t h e h e a t
t r a n s f e r r e d i s
q ^ = (1 + n ) G C ( t ^ - t ^ ) ( 2 . 2 2 )
and t h e f i n a l c o n d e n s a t e t e m p e r a t u r e can be c a l c u l a t e d as
^c2 = ^ c l ^ V ( ^ - ^ ^ ^ c ) ( 2 . 2 3 )
The r e s u l t i n g mean l o g a r i t h m i c t e m p e r a t u r e d i f f e r e n c e i s
Lt^ = ( ( t ^ ^ - t ^ ) - ( t ^ 2 - t i ) ) / l n ( ( t c l - t f ) / ( t c 2 • ^ l ) ) ( 2 . 2 4 )
and t he e f f e c t i v e h e a t i n g s u r f a c e a r e a can be d e t e r m i n e d as
= q ^ / ( k A t f ) ( 2 . 2 5 )
A c o n v e n i e n t f e a t u r e o f t h e f o r m u l a e g i v e n above i s t h a t t h e y a r e e a s y t o
a r r a n g e i n a manner f a c i l i t a t i n g t h e c a l c u l a t i o n s f o r a g r o u p o f h e a t e r s
s u p p l i e d w i t h v a r i o u s h e a t i n g med ia . T y p i c a l l y , a d e f i n i t e t e m p e r a t u r e o f t h e
l i q u i d i s r e q u i r e d a t t h e l a s t h e a t e r o u t l e t and t h e h e a t t r a n s f e r s u r f a c e
a reas a r e g i v e n f o r a l l t h e h e a t e r s . The c a l c u l a t i o n s can be c o m p u t e r i z e d
a c c o r d i n g t o t he f l o w d iag ram shown i n F i g . 2 . 6 . I f t h e i n i t i a l assump t i ons a r e
c o r r e c t , then the temperatures of the l i q u i d between heaters are d e t e r m i n e d and
72
" d e n s a t e W heated L
assign evaporator
effect
t2,ec^n.(2.7)
At^.tcf^^r^vf'^f eans.(2.12)-
(2.17) eons. ( 2 . 8 ) -
(2.11)
set next t^ ecj,ual to
STQP1 ^ 1= ί +1
guess
ecins.(2-ie)-C2.21)
eans. (2 .22) -(2.25)
i CANNOT BE ,ATTAIN ED
I ^ STOP 2 ^
new t 2 i
F i g . 2 . 6 . F low d iag ram o f t h e c a l c u l a t i o n s f o r a g r o u p o f j u i c e h e a t e r s .
73
STOP 1 i s r e a c h e d . I f t h e c a l c u l a t i o n s p r o v e t h a t t h e r e q u i r e d f i n a l t e m p e r a t u r e
o f t he l i q u i d canno t be a t t a i n e d , t h e n a message i s o u t p u t and t h e a c t i o n i s
t e r m i n a t e d a t STOP 2 , t h i s i m p l y i n g t h a t t h e i n p u t da ta must be m o d i f i e d . I t
s h o u l d be o b s e r v e d t h a t a s i n g l e h e a t e r can be c a l c u l a t e d as a s p e c i a l case o f
a h e a t e r g r o u p , t h i s making i t p o s s i b l e t o a p p l y t h e a l g o r i t h m t o most h e a t e r
a r rangements e n c o u n t e r e d i n t he s u g a r i n d u s t r y .
2 . 4 . 3 E x t r a c t o r
A c h a r a c t e r i s t i c f e a t u r e o f t he mass and hea t b a l a n c e s o f t h e e x t r a c t o r i s
t h a t i t may be n e c e s s a r y t o s p l i t t he c a l c u l a t i o n s i n t o p a r t s c o r r e s p o n d i n g t o
v a r i o u s p r o c e s s r e q u i r e m e n t s imposed on e x t r a c t o r p a r t s . The d e t a i l s depend on
e x t r a c t o r d e s i g n , and may v a r y f rom f a c t o r y t o f a c t o r y . C a l c u l a t i o n s o f a t o w e r -
t y p e e x t r a c t o r have been d e s c r i b e d i n t h e l i t e r a t u r e ( r e f . 1 3 ) . I n t h e
f o l l o w i n g , a p o s s i b l e p r o c e d u r e o f t h e a p p r o x i m a t e b a l a n c e c a l c u l a t i o n s o f
a t r o u g h - t y p e (DOS) e x t r a c t o r i s p r e s e n t e d .
The q u a n t i t i e s d e t e r m i n i n g t h e mass and h e a t b a l a n c e s a r e i n d i c a t e d i n
F i g . 2 . 7 . The i d e a o f s p l i t t i n g t h e e q u a t i o n s i n t o two g roups stems f rom t h e
f a c t t h a t c o r r e c t e x t r a c t i o n depends on e f f e c t i v e h e a t i n g o f t h e incoming
c o s s e t t e s i n e x t r a c t o r zone A ; t h i s can be r e f l e c t e d by a r e q u i r e m e n t t h a t t h e
t e m p e r a t u r e s o f t h e j u i c e and c o s s e t t e s between zones A and Β be s u f f i c i e n t l y
h i g h .
cosseites
req,ulrecl temperatures: cossettes t juice t^j
fresh v\ oter Gw.tw pulp
vapour
F i g . 2 . 7 . P r i n c i p l e o f mass and e n e r g y b a l a n c e s o f a t r o u g h - t y p e e x t r a c t o r .
The t o t a l hea t demand o f t h e e x t r a c t o r i s a p p r o x i m a t e l y
Q = (1 + « . ) ( G j h j . GpCptp - 4 . 1 9 ( G ^ t ^ - G p ^ t p J - G ^ C ^ t ^ ) ( 2 . 2 6 )
where m i s t he h e a t l o s s c o e f f i c i e n t , h j i s t h e e n t h a l p y o f j u i c e a t t e m p e r a t u r e
t j , Cp i s t h e s p e c i f i c h e a t o f p u l p , and C^^ i s t h e s p e c i f i c h e a t o f c o s s e t t e s .
74
The e s t i m a t e d t e m p e r a t u r e and e n t h a l p y o f t h e c o n d e n s a t e a t t h e o u t l e t o f zone A
can be c a l c u l a t e d as
t c A = ( " ^ A ' C jtj - Stb) / (S- ' ' (Vj ^ *rb)/2)/8 ( 2 . 2 7 )
= 4.19 t , , ( 2 . 2 8 )
The r e s u l t i n g h e a t demand o f zone A i s
Qa = (1 + m)(G^^Cj^( t^^ - t ^ ) - G.(h^. - h.}) (2.29)
and t he h e a t i n g v a p o u r demand i n zone A i s
S = V ( ^ A - ^ca) (2.30) The t e m p e r a t u r e and e n t h a l p y o f t h e c o n d e n s a t e a t t h e o u t l e t o f zone Β a r e
e s t i m a t e d as
tcB = ("^B ' ( V j ' Vb)/2 - ( V „ - GpwSw ' W^^% ' Sw ' (2-31)
The hea t demand o f zone Β i s t hus
Qb = Q - Qa
and t h e h e a t i n g v a p o u r demand i n zone Β i s
% = v ( ^ B • ^ b )
(2.32)
(2.33)
(2.34)
2.4.4 S u g a r house equ ipment
The e n e r g y p r o c e s s e s i n t h e s u g a r house a r e dominated by t h e h e a t consumpt i on
i n t h e vacuum p a n s , t y p i c a l l y b a t c h p a n s . I n t h e mass and h e a t b a l a n c e
c a l c u l a t i o n s , t h e d i s c r e t e n a t u r e o f vacuum pan h e a t i n g i s u s u a l l y d i s r e g a r d e d
and t he c a l c u l a t i o n s a r e pe r f o rmed f o r t h e e n t i r e m a s s e c u i t e s t reams i n t h e
r e s p e c t i v e s t r i k e s . The q u a n t i t i e s d e t e r m i n i n g t h e mass and h e a t b a l a n c e s o f a
f i c t i v e c o n t i n u o u s pan r e p r e s e n t i n g b a t c h pans a r e i n d i c a t e d i n F i g . 2 . 8 ( a ) .
( Q ) a evaporated water Ge.te
syrups:
(b)
G v > t v ^
Ac
G,b,-t,
massecuite
F i g . 2.8. P r i n c i p l e o f mass and h e a t b a l a n c e s o f s u g a r house e q u i p m e n t : ( a ) ( a ) vacuum p a n , ( b ) s y r u p t a n k .
75
From the p r o c e s s d a t a , t h e sum o f i ncoming mass f l o w s o f s y r u p s and t h e a v e r a g e
v a l u e s o f t h e i r s p e c i f i c h e a t s , i n i t i a l t e m p e r a t u r e s and c o n c e n t r a t i o n s can be
de te rm ined as
G = Σ G . ( 2 . 3 5 )
^a = ( 2 . 3 6 )
t ^ = ( Σ G . C . t . ) / ( G C ^ ) ( 2 . 3 7 )
b^ = ( Σ G . b . ) / G ( 2 . 3 8 )
The mass f l o w o f t h e e v a p o r a t e d w a t e r ( i . e . , vacuum pan v a p o u r ) i s
= G ( l - b ^ / b ^ ) ( 2 . 3 9 )
Hav ing d e t e r m i n e d t h e s p e c i f i c h e a t o f t h e m a s s e c u i t e C ^ , and t h e e n t h a l p y o f
t he vacuum-pan v a p o u r h^ = h " ( t g ) , t h e t i m e - a v e r a g e d h e a t demand i s e x p r e s s e d as
q = (1 + u ) ( G ^ h g + (G - G g ) C ^ t ^ - G C ^ t ^ ) ( 2 . 4 0 )
where u i s t h e h e a t l o s s c o e f f i c i e n t .
L e t us o b s e r v e t h a t even t hough t h e h e a t o f s u g a r c r y s t a l l i z a t i o n i s n e g l e c t e d
h e r e , t h e f o r m u l a can y i e l d c o r r e c t h e a t demand v a l u e s p r o v i d i n g t h e h e a t l o s s
c o e f f i c i e n t i s a p p r o p r i a t e l y d e f i n e d . The e s t i m a t e d v a l u e s o f t h e t e m p e r a t u r e
and e n t h a l p y o f t h e c o n d e n s a t e a r e
^ c = ^ ^ ^ V)/^ ( 2 . 4 1 )
h^ = 4.19 t ^ ( 2 . 4 2 )
and t he t i m e - a v e r a g e d h e a t i n g v a p o u r demand i s
% = q / ( ^ - ^ ) ( 2 - 4 3 )
A s u b s t a n t i a l s h a r e o f t h e h e a t demand o f t h e s u g a r house i s a s s o c i a t e d w i t h t h e
tanks i n w h i c h t h i c k j u i c e , r u n - o f f , r e m e l t a n d , p o s s i b l y , o t h e r media a r e
t e m p o r a r i l y s t o r e d and hea ted t o d e f i n i t e t e m p e r a t u r e s . The q u a n t i t i e s
d e t e r m i n i n g t h e mass and h e a t b a l a n c e s o f an i n d i r e c t l y hea ted tank s u p p l i e d
w i t h h e a t i n g v a p o u r a t t e m p e r a t u r e t ^ a r e i n d i c a t e d i n F i g . 2 . 8 ( b ) . A f t e r
d e t e r m i n i n g t h e i n l e t and o u t l e t e n t h a l p i e s o f t h e s y r u p h-j and h ^ , and assuming
t h e hea t l o s s c o e f f i c i e n t m i s known, t h e h e a t demand can be c a l c u l a t e d as
q = (1 + m)G(h2 - h^ ) ( 2 . 4 4 )
The t e m p e r a t u r e and e n t h a l p y o f t h e c o n d e n s a t e can be e s t i m a t e d as
= (^S ^ 1 ^ ^ 2 ) / ^ (2 - ' ^5 )
h^ = 4.19 t ^ ( 2 . 4 6 )
and t h e h e a t i n g v a p o u r demand i s
^ = q / ( ^ - h^ ) ( 2 . 4 7 )
76
2.5 MASS AND HEAT BALANCES OF A M U L T I P L E - E F F E C T EVAPORATOR
2 . 5 . Ί I n t r o d u c t i o n
The m u l t i p l e - e f f e c t e v a p o r a t o r i s a p r o c e s s s t a t i o n i n w h i c h j u i c e t h i c k e n i n g
takes p l a c e ; i t can a l s o be seen as a b u i l d i n g b l o c k p l a y i n g a d e c i s i v e r o l e i n
t h e m u l t i p l e u t i l i z a t i o n o f e n e r g y i n t h e the rma l s y s t e m . The a c c u r a c y o f t h e
c a l c u l a t i o n s o f e v a p o r a t o r b a l a n c e s d e t e r m i n e s t h e a c c u r a c y w i t h w h i c h t h e mass
and hea t f l o w s w i t h i n t he therma l sys tem can be c a l c u l a t e d . I t s h o u l d t h e r e f o r e
be no ted t h a t i n t h e l i t e r a t u r e , two t e n d e n c i e s c o n c e r n i n g t h e methods o f
e v a p o r a t o r c a l c u l a t i o n s can be i d e n t i f i e d .
( i ) R e l y i n g on s i m p l i f i e d mathemat ica l models w h i c h e n a b l e one t o make
c a l c u l a t i o n s m a n u a l l y , o r w i t h t h e a i d o f a p o c k e t c a l c u l a t o r . A l t h o u g h such
methods a r e c e r t a i n l y u s e f u l i n many a p p l i c a t i o n s , t h e r e i s t h e r i s k t h a t t h e
u s e r may be unaware o f t h e magn i tude o f t h e e r r o r m a r g i n . Because o f t h e
c a l c u l a t i o n e r r o r , i t may be i m p o s s i b l e t o use t h e s e methods i n c e r t a i n d e s i g n
prob lems o r i n t h e o p t i m i z a t i o n o f e v a p o r a t o r s .
( i i ) U s i n g d e t a i l e d mathemat ica l models w h i c h may r e q u i r e t h e c a l c u l a t i o n s t o be
c o m p u t e r i z e d . A number o f models o f t h i s k i n d have been d e s c r i b e d i n t h e
l i t e r a t u r e . H o w e v e r , i t may sometimes be d i f f i c u l t t o use them because t h e
p u b l i c a t i o n s do n o t s p e c i f y model a c c u r a c y and no i n f o r m a t i o n i s g i v e n on the
numer i ca l p rob lems o f model u s e . I n t h e case o f c a l c u l a t i o n methods r e l y i n g on
t h e i t e r a t i v e improvements o f i n i t i a l l y guessed v a l u e s o f unknown v a r i a b l e s ,
an i m p r o p e r l y chosen n u m e r i c a l p r o c e d u r e may c a r r y t h e r i s k o f u n c o n t r o l l a b l e
n u m e r i c a l e r r o r s .
Both app roaches men t ioned w i l l be s t u d i e d i n t h e f o l l o w i n g . A c o n v e n i e n t
s t a r t i n g p o i n t i s t h e s o - c a l l e d g e n e r a l i z e d e v a p o r a t o r s t r u c t u r e . I t can be
u n d e r s t o o d as a s e t o f a l l p o s s i b l e components and t h e i r c o n n e c t i o n s i n
a m u l t i p l e - e f f e c t e v a p o r a t o r . Once a mathemat ica l model o f t h e g e n e r a l i z e d
s t r u c t u r e has been f o r m u l a t e d , one can e a s i l y g e n e r a t e a u n i q u e model o f a
s p e c i f i c e v a p o r a t o r v e r s i o n .
F i g u r e 2.9 shows s c h e m a t i c a l l y a r e p e t i t i v e b l o c k o f t h e s t r u c t u r e o f a c o -
c u r r e n t ( p a r a l l e l f l o w ) m u l t i p l e - e f f e c t e v a p o r a t o r c o m p r i s i n g an a r b i t r a r y
number o f e f f e c t s . The f o l l o w i n g c o n n e c t i o n s between t h e b l o c k and i t s
s u r r o u n d i n g s ( i n c l u d i n g n e i g h b o u r i n g b l o c k s ) can be taken i n t o a c c o u n t :
- v a p o u r w i t h d r a w a l f o r h e a t i n g pu rposes and c o n d e n s a t e r e t u r n f rom h e a t
r e c e i v e r s ,
- s u p p l y o f v a p o u r o b t a i n e d by c o n d e n s a t e f l a s h e v a p o r a t i o n ,
- condensa te w i t h d r a w a l f o r h e a t i n g o r o t h e r p u r p o s e s ( t o t h e r e c e i v e r s o u t s i d e
t h e e v a p o r a t o r ) ,
- condensa te s u p p l y t o t h e c o n d e n s a t e tank i n t h e n e x t e v a p o r a t o r e f f e c t .
I n t h e f o l l o w i n g , t he e f f e c t s o f an N - e f f e c t e v a p o r a t o r w i l l be numbered
77
extracted vapour I
steam I or ;
heating vapour t '
ν ν
i - th effect
to condenser
juice I G Ó . ^ ¿ , b t G'. t.' b.' i I Ά "ί-ΐ ' ί-ΐ' i-1 • I ψ t ' Β
condensate' flash vapouH^
condensatej
returned I condensate
extracted \ condensate!
i - r 1-1
I L
G i , t ¿ • \ EVAPORATOR BOUNDARY
F i g . 2 . 9 . Scheme o f t h e i - t h r e p e t i t i v e b l o c k i n an N - e f f e c t e v a p o r a t o r and t h e symbols used i n t h e mathemat i ca l m o d e l .
1 , 2 , . . , N . C e r t a i n v a r i a b l e s w i l l be i n d e x e d 0 a t i n l e t and N+1 a t o u t l e t .
A t y p i c a l s e t o f i n p u t da ta f o r e v a p o r a t o r c a l c u l a t i o n s c o m p r i s e s t h e
f o l l o w i n g p a r a m e t e r s :
- t h i n j u i c e mass f l o w G ^ ,
- c o n c e n t r a t i o n o f t h i n j u i c e and t h i c k j u i c e Bj^,
- t h i n j u i c e t e m p e r a t u r e t ¿ .
The mass f l o w o f w a t e r t o be e v a p o r a t e d can be c a l c u l a t e d as
G = G¿(1 - b Q / B ^ ) ( 2 . 4 8 )
The f o l l o w i n g p r o c e s s pa ramete rs a r e i n d e p e n d e n t o f t h e mass and e n e r g y b a l a n c e s
and must be s p e c i f i e d b e f o r e b e g i n n i n g t h e c a l c u l a t i o n s :
- t e m p e r a t u r e and p r e s s u r e o f t h e h e a t i n g steam s u p p l i e d t o t h e f i r s t e f f e c t 4-S „ s
P p
- t e m p e r a t u r e d i f f e r e n c e s A t ^ A t 2 , . . , ät^ be tween t h e h e a t i n g steam o r v a p o u r ,
and t he v a p o u r g e n e r a t e d f rom j u i c e ; a l t e r n a t i v e l y , t e m p e r a t u r e d i f f e r e n c e s
between t he h e a t i n g steam o r v a p o u r , and t h e j u i c e , can be s p e c i f i e d .
From the c a l c u l a t i o n s o f o t h e r components o f t h e the rma l s y s t e m , t h e
f o l l o w i n g da ta must a l s o be known:
- mass f l o w s o f v a p o u r s w i t h d r a w n f rom t h e i n d i v i d u a l e f f e c t s f o r h e a t i
pu rposes G ^ , G ^ , . . , G ^ ; ng
78
- mass f l o w s and t e m p e r a t u r e s o f c o n d e n s a t e s r e t u r n e d t o t h e c o n d e n s a t e t a n k s ,
G!|*, G 2 9 . . J GJJ and tp t 2 j . . j tjj;
- c o n d e n s a t e w i t h d r a w a l / s u p p l y c o e f f i c i e n t s r ^ i ^ 2 " * » ' ^Ν '
F o r t h e i - t h e f f e c t , r^ = 0 means t h a t t he e n t i r e c o n d e n s a t e s t r e a m i s w i t h d r a w n
t o t h e s u r r o u n d i n g s , w h i l e r . = 1 means t h a t t he e n t i r e c o n d e n s a t e s t ream i s
s u p p l i e d t o t h e tank i n t h e e f f e c t numbered ( i + 1 ) .
F o r known e v a p o r a t o r d e s i g n s and known c h a r a c t e r i s t i c s o f t h e the rma l
i n s u l a t i o n i n t he i n d i v i d u a l e f f e c t s , t h e f o l l o w i n g the rma l d a t a can be
s p e c i f i e d :
- s u b c o o l i n g ( r e l a t i v e t o t h e s a t u r a t i o n t e m p e r a t u r e ) o f t h e condensa tes l e a v i n g
t he c o n s e c u t i v e h e a t i n g chambers s ^ S 2 » . . , S j ^ ;
- v a p o u r t e m p e r a t u r e d rops due t o t h r o t t l i n g i n t h e p i p e s l i n k i n g n e i g h b o u r i n g
e f f e c t s d p d 2 , . . , d^^;
- hea t l o s s c o e f f i c i e n t s o f t h e e v a p o r a t o r b o d i e s e ^ e 2 , . . , ej^ and c o n d e n s a t e
tanks C p 0 2 » . . > C j^ .
Hav ing s p e c i f i e d a l l t h e i n p u t d a t a , one i s a b l e t o d e t e r m i n e t he v a p o u r
t e m p e r a t u r e s i n t h e e n t i r e e v a p o r a t o r ( f o r e f f e c t s numbered i = 1, 2 , . . , N) as
tV = t ? - A t . ( 2 . 4 9 )
t l , - t ^ - d,. ( 2 . 5 0 )
I t now becomes p o s s i b l e t o c o n s t r u c t a mathemat i ca l d e s c r i p t i o n o f t h e m u l t i
s t a g e e v a p o r a t i o n p r o c e s s , i n t h e fo rm o f a sys tem o f e q u a t i o n s c o n t a i n i n g
unknown mass f l o w s , t e m p e r a t u r e s and j u i c e c o n c e n t r a t i o n s i n o r between t h e
i n d i v i d u a l e v a p o r a t o r e f f e c t s . The f o l l o w i n g thermodynamic f u n c t i o n s must be
known i n o r d e r t o f o r m u l a t e t h e e n e r g y b a l a n c e r e l a t i o n s h i p s :
- h ' ^ ( t , b ) , j u i c e e n t h a l p y as a f u n c t i o n o f t e m p e r a t u r e and c o n c e n t r a t i o n ,
- A T ( t , b ) , b o i l i n g p o i n t e l e v a t i o n as a f u n c t i o n o f t e m p e r a t u r e and
c o n c e n t r a t i o n ,
- h " ( t ) , e n t h a l p y o f d r y s a t u r a t e d steam as a f u n c t i o n o f t e m p e r a t u r e ,
- h ' ( t ) , e n t h a l p y o f s a t u r a t e d w a t e r as a f u n c t i o n o f t e m p e r a t u r e .
2 .5 .2 S i m p l i f i e d model
The mathemat ica l d e s c r i p t i o n o f a s i n g l e e v a p o r a t o r e f f e c t becomes much
e a s i e r t o h a n d l e i f t h e h e a t l o s s e s and c o n d e n s a t e r e t u r n s a r e n e g l e c t e d and t h e
amount o f v a p o u r e v a p o r a t e d f rom j u i c e i s s e t equa l t o t h e amount o f h e a t i n g
v a p o u r o r steam condensed ( t h a t i s , t h e i n f l u e n c e o f t h e t e m p e r a t u r e and
c o n c e n t r a t i o n on t h e j u i c e e n t h a l p y i s d i s r e g a r d e d ) . These assumpt i ons can be
w r i t t e n down, f o r i = 1, 2 , . . , N, as e.¡ = c^. = 0 , οξ* = 0 , and
G^ = G^ - GT + G^^ . , ( 2 . 5 1 )
where G Í i s t h e mass f l o w o f c o n d e n s a t e f l a s h v a p o u r , t o be c a l c u l a t e d f rom t h e
79
r e l a t i o n s h i p
= ( G ' + G ^ _ ^ ) ( h ^ ^ - h ^ ) / ( h [ - h^ ) ( 2 . 5 2 )
where t h e e n t h a l p i e s h ^ ^ , h9 and h t a p p l y t o t h e s u b c o o l e d c o n d e n s a t e l e a v i n g
t h e h e a t i n g chamber , t h e condensa te i n t h e t a n k , and t h e f l a s h v a p o u r ,
r e s p e c t i v e l y . These e n t h a l p i e s a r e d e t e r m i n e d as
h ^ ' = h ' ( t ^ - s . ) ( 2 . 5 3 )
= h ' ( t ^ ^ ^ ) ( 2 . 5 4 )
h f = h " ( t ^ ^ T ) ( 2 . 5 5 )
The mass f l o w o f c o n d e n s a t e t o t h e tank i n t h e n e x t e f f e c t i s
G? = r . ( G ^ + G ^ . ^ - G f ) ( 2 . 5 6 )
The mass b a l a n c e o f t he e v a p o r a t o r can now be d e t e r m i n e d by s o l v i n g an e q u a t i o n
w i t h t he mass f l o w o f t h e l a s t - e f f e c t v a p o u r t o t h e c o n d e n s e r , G ^ ^ ^ , as t h e
unknown v a r i a b l e . L i n k i n g t h e mass b a l a n c e s o f t h e e f f e c t s numbered
N, N - 1 , . . , i , f o r m u l a t e d i n a c c o r d a n c e w i t h e q n . ( 2 . 5 1 ) , we o b t a i n
= ¿ « ^ N - k - i k ) ^ ( 2 . 5 7 )
On t h e o t h e r h a n d , we can c o n c l u d e f rom t h e mass b a l a n c e o f t h e e n t i r e
e v a p o r a t o r t h a t
G ^ ^ l = (G - ^ E ^ i ( G y - G Í ) ) / N ( 2 . 5 8 )
where G i s d e f i n e d by e q n . ( 2 . 4 8 ) .
The m a s s - b a l a n c e e q u a t i o n can now be o b t a i n e d by s u b s t i t u t i n g , f o r
i = Ν , N - 1 , . . , 1, e q n s . ( 2 . 5 3 ) - ( 2 . 5 6 ) i n t o e q n . ( 2 . 1 1 ) , t hus d e t e r m i n i n g g [ as
f u n c t i o n s o f G ^ _ ^ ^ , and s u b s e q u e n t l y s u b s t i t u t i n g t h e s e f u n c t i o n s i n t o e q n .
( 2 . 5 8 ) . F o r a s p e c i f i c number o f e f f e c t s N, t h i s can be done a n a l y t i c a l l y . I t i s
a l s o p o s s i b l e t o d e v i s e a s i m p l e a l g o r i t h m d e l i v e r i n g n u m e r i c a l s o l u t i o n s f o r
a r b i t r a r y N , as shown i n F i g . 2 . 1 0 ( a ) . The a l g o r i t h m i s based on a c h a i n o f
s u b s t i t u t i o n s g e n e r a t i n g an e q u a t i o n o f t h e fo rm
" l l -η<^Μ) ( 2 - 5 9 )
T h i s e q u a t i o n can be s o l v e d by i t e r a t i v e l y i m p r o v i n g a p p r o x i m a t e s o l u t i o n s t o
s a t i s f y t h e c o n d i t i o n
IG^^I - f ( G ^ ^ ^ ) | < g ( 2 . 6 0 )
where g i s a s u f f i c i e n t l y sma l l number.
In o r d e r t o s i m p l i f y t h e f l o w d i a g r a m , t h e c a l c u l a t i o n o f t h e c o n d e n s a t e
mass f l o w a c c o r d i n g t o e q n . ( 2 . 5 6 ) i s n o t shown i n F i g . 2 . 1 0 ( a ) . As t h i s
8 0
(α) eqn.(2A8)
(b )
for i = 1.2. . . . N
eqns.{2.49).(2.58)
{2.53)- (2.55)
Gi = 0
for i=N,N-1,..,1
eqn.(2.57) eqn.(2.52)
- J -
G ^ ^ ^ from(2.58)
eqn.(2A8)
for i=1.2, . . . N
eqns.{2.49).(2.50)
(2.53)-(255).(2.80)
initial guesses
for G ^ , ^
F i g . 2 . 1 0 . F low d iag ram o f t h e a l g o r i t h m s o f e v a p o r a t o r c a l c u l a t i o n s : ( a ) u s i n g t h e s i m p l i f i e d m o d e l , ( b ) u s i n g t h e d e t a i l e d m o d e l .
c a l c u l a t i o n i s pe r f o rmed b e f o r e c h e c k i n g c o n d i t i o n ( 2 . 6 0 ) , t h e mass b a l a n c e o f
t h e e v a p o r a t o r becomes unamb iguous l y d e f i n e d . Known v a p o u r and c o n d e n s a t e f l o w s
make i t p o s s i b l e t o c a l c u l a t e j u i c e f l o w s and c o n c e n t r a t i o n s , f o r
i = 2 , 3 , . . , N - 1 , as
= Q J . ^ - G ? ( 2 . 6 1 )
C o n s e q u e n t l y , b o i l i n g p o i n t e l e v a t i o n s and e f f e c t i v e t e m p e r a t u r e d i f f e r e n c e s i n
t h e e f f e c t s numbered i = 1 , 2 , . . , Ν a r e
Δ Τ . = AT(tr, b . ) ( 2 . 6 3 )
81
A t . = t^ - (tV + Δ Τ . ) ( 2 . 6 4 )
Known t e m p e r a t u r e s and j u i c e c o n c e n t r a t i o n s now make i t p o s s i b l e t o e s t i m a t e
o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s k . i n each e f f e c t , u s i n g g raphs o r f o r m u l a e
c h a r a c t e r i z i n g t h e e v a p o r a t o r d e s i g n a p p l i e d . C o n s e q u e n t l y , h e a t t r a n s f e r
s u r f a c e a reas can be c a l c u l a t e d as
F,. = G^ (h? - h f ) / ( k . A t . ) ( 2 . 6 5 )
2 .5 .3 D e t a i l e d model
I t was o b s e r v e d a l ong t ime ago t h a t t h e a c c u r a c y o f t h e s i m p l i f i e d model may
be i n s u f f i c i e n t when s o l v i n g c e r t a i n e n g i n e e r i n g p rob lems ( r e f . 1 5 ) . The
s y s t e m a t i c e r r o r i n h e r e n t i n t h e s i m p l i f i e d model r e s u l t s m a i n l y f rom n e g l e c t e d
changes i n j u i c e e n t h a l p y between c o n s e c u t i v e e v a p o r a t o r e f f e c t s , n e g l e c t e d h e a t
l o s s e s t o t h e s u r r o u n d i n g s , and i n c o m p l e t e d e s c r i p t i o n o f t h e c o n d e n s a t e f l a s h .
More d e t a i l e d mathemat i ca l models have been c o n s i d e r e d by v a r i o u s a u t h o r s
( r e f s . 1 6 - 1 8 ) . A comp le te s e t o f e q u a t i o n s d e s c r i b i n g a s i n g l e e v a p o r a t o r e f f e c t
i s p r e s e n t e d b e l o w . I t i s assumed t h a t t h e j u i c e c o n c e n t r a t i o n i s known, w h i c h
i m p l i e s t h a t some h i g h e r - o r d e r a l g o r i t h m must s u p p l y c o n c e n t r a t i o n s f o r each
c a l c u l a t i o n s t e p c o r r e s p o n d i n g t o a s i n g l e e f f e c t . T h e r e f o r e , t h e model may
i n c l u d e e q n s . ( 2 . 6 3 ) and ( 2 . 6 4 ) . The e n t h a l p y o f t h e j u i c e i s
h * = h J ( t ^ ' , b . ) ( 2 . 6 6 )
The mass f l o w o f t h e v a p o u r o b t a i n e d i s
G? = G- - G ( + G ^ ^ ^ ( 2 . 6 7 )
The mass f l o w o f t h e h e a t i n g v a p o u r r e q u i r e d t o e v a p o r a t e t h i s amount o f w a t e r
can be c a l c u l a t e d as
G^ = ((1 + e . ) / ( h ^ - h f ) ) ( G ? ( h y - hl^) - G J ( h J _ ^ - h J ) ) ( 2 . 6 8 )
where t h e e n t h a l p y h ? ^ i s d e f i n e d by e q n . ( 2 . 5 3 ) and t h e e n t h a l p y hV o f v a p o u r
g e n e r a t e d i s d e f i n e d as
= h " ( t ^ ) ( 2 . 6 9 )
The t o t a l mass f l o w o f t h e c o n d e n s a t e e n t e r i n g t h e tank i s
G - ^ = G^_. , + G^ + G C ( 2 . 7 0 )
and i t s a v e r a g e t e m p e r a t u r e can be c a l c u l a t e d a p p r o x i m a t e l y as
t f = ( G ? ( t ^ - s . ) + G ^ . ^ t ^ . ^ + G ; ' t ^ ) / G f ( 2 . 7 1 )
The condensa te e n t h a l p y a t t h e a v e r a g e t e m p e r a t u r e i s
h f = h ' ( t f ) ( 2 . 7 2 )
82
The mass f l o w o f t h e condensa te f l a s h v a p o u r i s
= G f ( h f - h ^ ) / ( ( h i - h ^ ) ( l + c . ) ) ( 2 . 7 3 )
and t he mass f l o w o f t he c o n d e n s a t e w i t h d r a w n t o t h e s u r r o u n d i n g s i s
G^ = G9^ - - G ^ ( 2 . 7 4 )
I t i s now p o s s i b l e t o d e t e r m i n e t he mass f l o w o f t h e j u i c e a t t h e o u t l e t as
GJ = G J . ^ - G? ( 2 . 7 5 )
and t he j u i c e c o n c e n t r a t i o n a t t h e o u t l e t as
b i = b ^ - i G ^ - j / G ^ ' ( 2 . 7 6 )
As i n t he s i m p l i f i e d m o d e l , t h e above e q u a t i o n s can be f o r m u l a t e d f o r t h e
e f f e c t s numbered 1, 2 , . . , Ν and t h e n combined i n t o one e q u a t i o n ( w i t h one
unknown v a r i a b l e G^^^^) ana logous t o e q n . ( 2 . 5 9 ) . As t h e c h a i n o f s u b s t i t u t i o n s
i s r a t h e r c o m p l i c a t e d , t h e e q u a t i o n can o n l y be s o l v e d n u m e r i c a l l y . C o n t r a r y t o
t h e s i m p l i f i e d m o d e l , d i r e c t i t e r a t i o n s may n o t c o n v e r g e ; i t i s t h e r e f o r e
n e c e s s a r y t o use o t h e r n u m e r i c a l methods . The e q u a t i o n i s c o n v e n i e n t l y r e w r i t t e n
i n t h e fo rm
'^l,-n^l^)-0 ( 2 . 7 7)
I n F i g . 2 . 1 0 ( b ) , t h e f l o w d iag ram o f t h e a l g o r i t h m based on a p p l i c a t i o n o f t h e
s e c a n t method i s shown. A p r e r e q u i s i t e f o r a s u c c e s s f u l i t e r a t i v e c o m p u t a t i o n i s
t o f i n d two i n i t i a l a p p r o x i m a t i o n s o f t h e unknown v a r i a b l e f o r w h i c h e r r o r s o f
e q n . ( 2 . 7 7 ) have o p p o s i t e s i g n s . I t i s u s u a l l y p o s s i b l e t o s e t G ^ ^ ^ = 0 as t h e
f i r s t a p p r o x i m a t i o n , and G^^-j r e s u l t i n g f rom t h e i n i t i a l c h a i n o f s u b s t i t u t i o n s
as t he s e c o n d . When c o m p u t e r i z i n g t h e a l g o r i t h m , i t i s recommended t o check t h e
e r r o r s i g n s f o r bo th a p p r o x i m a t i o n s a n d , i f n e c e s s a r y , t o m o d i f y one o f them
b e f o r e t h e i t e r a t i v e p r o c e s s i s s t a r t e d . Some i n i t i a l a p p r o x i m a t i o n s have a l s o
t o be found f o r s e v e r a l o t h e r v a r i a b l e s whose v a l u e s a r e n o t known as l o n g as
G ^ ^ ^ i s unknown. B e f o r e e n t e r i n g t h e i t e r a t i o n l o o p , i t can be assumed t h a t f o r
i = 2 , 3 , . . , N-1 , t he c o n c e n t r a t i o n s and t h e mass f l o w s o f t h e j u i c e a r e
b. = b._^ + ( B ^ - b Q ) / N ( 2 . 7 8 )
and
G J = G J . ^ b . . i / b . ( 2 . 7 9)
The i n i t i a l guesses f o r t h e mass f l o w s o f t h e f l a s h v a p o u r s f o r i = 1, 2 , . . , N-1
can be
G f = 0.005 G^ ( 2 . 8 0 )
The i t e r a t i o n s i n t h e i n t e r n a l l o o p can be t e r m i n a t e d i f , i n two s u b s e q u e n t
83
i t e r a t i o n s numbered n-1 and n , t h e j u i c e c o n c e n t r a t i o n s a t t h e e v a p o r a t o r o u t l e t
do n o t d i f f e r by more t h a n t h e assumed t o l e r a n c e b^
|bi") - b ( " - 1 ) | < ( 2 . 8 1 )
A f t e r c o m p l e t i n g t h e i t e r a t i o n l o o p c o n t r o l l e d by t h e s e c a n t me thod , a l l t h e
mass f l o w s w i t h i n t h e m u l t i p l e - e f f e c t e v a p o r a t o r a r e known. E q u a t i o n s ( 2 . 6 4 ) and
( 2 . 6 5 ) can t h e n be used t o d e t e r m i n e t h e h e a t exchange a r e a s i n t h e i n d i v i d u a l
e v a p o r a t o r b o d i e s .
2 .5 .4 Example
The d i f f e r e n c e between t h e s i m p l i f i e d model and t h e d e t a i l e d model can be
demons t ra ted by a n u m e r i c a l examp le . The i n p u t d a t a f o r a q u i n t u p l e - e f f e c t
e v a p o r a t o r a r e shown i n T a b l e 2 . 5 , and t h e r e s u l t s o f t h e c a l c u l a t i o n s p e r f o r m e d
u s i n g bo th models a r e shown i n T a b l e 2 . 6 . As can be s e e n , w h i l e t h e r e s u l t s
p roduced by t h e d e t a i l e d model a r e f u l l y a c c e p t a b l e , t h e s i m p l i f i e d model y i e l d s
a n e g a t i v e v a p o u r f l o w f rom t h e l a s t e v a p o r a t o r e f f e c t t o t h e c o n d e n s e r , w h i c h
i s p h y s i c a l l y i m p o s s i b l e .
TABLE 2.5
Main i n p u t da ta f o r t h e mass and h e a t b a l a n c e s o f a q u i n t u p l e - e f f e c t e v a p o r a t o r .
T h i n j u i c e mass f l o w ( t / h ) 219.9 T h i n j u i c e t e m p e r a t u r e ( O C ) 127.0 T h i n j u i c e c o n c e n t r a t i o n {% DS) 14.1 T h i c k j u i c e c o n c e n t r a t i o n (% DS) 52.0 H e a t i n g steam t e m p e r a t u r e ( O C ) 139.0
E f f e c t No. 1 2 3 4 5
Mass f l o w o f v a p o u r w i t h d r a w n ( t / h ) 4.75 49.00 8.10 8.10 6.93 Tempera tu re d i f f e r e n c e between h e a t i n g ( K ) 9.2 8.1 6.8 12.3 13.5 s t e a m / v a p o u r and v a p o u r g e n e r a t e d
( K )
TABLE 2.6
E x c e r p t s f rom t h e c a l c u l a t e d mass and e n e r g y b a l a n c e s o f a q u i n t u p l e - e f f e c t e v a p o r a t o r ( a l l mass f l o w s i n t / h ) .
Q u a n t i t y E f f e c t No. S i m p l i f i e d
model D e t a i l e d
model
Mass f l o w o f v a p o u r g e n e r a t e d 1 67.60 66.85 2 64.01 63.22 3 16.09 15.60 4 9.11 9.66 5 3.10 5.03
Mass f l o w o f c o n d e n s a t e f l a s h 1 1.16 0.98 v a p o u r 2 1.08 0.76
3 1.13 1.00 4 2.08 2.28 5 2.26 2.67
Mass f l o w o f v a p o u r t o t h e c o n d e n s e r - 1 . 5 8 0.76
84
I t s h o u l d be n o t e d t h a t t h e d i f f e r e n c e i n v a p o u r f l o w s t o t h e c o n d e n s e r r e s u l t s
f rom d i f f e r e n t app roaches o f t h e models t o t h e j u i c e f l a s h phenomenon a t t h e
i n l e t t o each s t a g e . As t h i s phenomenon i s d i s r e g a r d e d i n t h e s i m p l i f i e d model
( t h e i n f l u e n c e o f t e m p e r a t u r e and c o n c e n t r a t i o n on j u i c e e n t h a l p y i s n e g l e c t e d ) ,
t h e t o t a l amount o f v a p o u r s g e n e r a t e d i n t h e e v a p o r a t o r i s u n d e r e s t i m a t e d , and
so i s t he v a p o u r f l o w f rom t h e l a s t e f f e c t .
2.6 MASS AND HEAT BALANCES OF A THERMAL SYSTEM
2.6.1 P r i n c i p l e s o f u t i l i z a t i o n o f t h e r e s u l t s o f b a l a n c e c a l c u l a t i o n s
The a l g o r i t h m s used t o c a l c u l a t e t h e m u l t i p l e - e f f e c t e v a p o r a t o r and t h e h e a t
r e c e i v e r s can be combined i n t o one a l g o r i t h m o f a d e t a i l e d mass and h e a t
b a l a n c e o f t h e the rma l s y s t e m . To make a d i s t i n c t i o n f rom t h e e x t e r n a l e n e r g y
b a l a n c e , t h i s p r i n c i p l e i s sometimes c a l l e d e v a p o r a t o r - r e c e i v e r a p p r o a c h . I n
o r d e r t o t u r n t he combined a l g o r i t h m i n t o a t o o l f o r e n g i n e e r i n g a n a l y s e s , i t
s h o u l d be g e n e r a l enough t o make i t p o s s i b l e t o c a l c u l a t e t h e b a l a n c e s o f
v a r i o u s h y p o t h e t i c a l t he rma l s y s t e m s . The a l g o r i t h m s h o u l d a l s o make i t e a s y
f o r t h e u s e r t o h a n d l e p r a c t i c a l s i t u a t i o n s a s s o c i a t e d w i t h s o l v i n g e n g i n e e r i n g
p r o b l e m s . F o r e x a m p l e , when d e s i g n i n g a new the rma l s y s t e m , t h e r e s u l t s o f t h e
c a l c u l a t i o n o f an e v a p o r a t o r m igh t p r o v e t h a t t h e assumed d i s t r i b u t i o n o f
v a p o u r s t o t h e i n d i v i d u a l r e c e i v e r s i s i n c o m p a t i b l e w i t h t h e r e q u i r e d v a l u e o f
t h i c k j u i c e c o n c e n t r a t i o n . A l t e r n a t i v e l y , f o r o t h e r s e t s o f i n p u t d a t a , t h e
r e s u l t s m igh t i n d i c a t e t h a t t he j u i c e t e m p e r a t u r e s assumed i n c e r t a i n p l a c e s
c a n n o t be r e a c h e d . I n b o t h c a s e s , t h e d e s i g n p r o c e d u r e r e q u i r e s t h a t some
changes t o t h e i n p u t da ta be i n t r o d u c e d , and two b a s i c t y p e s o f changes can be
i m a g i n e d : c o r r e c t i o n s o f t h e mass b a l a n c e , o r m o d i f i c a t i o n s o f t h e s t r u c t u r e o f
t he the rma l s y s t e m . Once t h e i n p u t d a t a have been c h a n g e d , t h e c a l c u l a t i o n s must
be r e p e a t e d .
A s l i g h t l y d i f f e r e n t s i t u a t i o n a r i s e s when i n v e s t i g a t i n g t h e mass and h e a t
b a l a n c e s o f an e x i s t i n g s y s t e m . U s u a l l y , t h e b a l a n c e s can be c a l c u l a t e d f rom
i n p u t da ta w h i c h i n c l u d e o n l y a p a r t o f t h e d a t a o b t a i n e d f rom t h e measurements .
The r e s u l t s a r e t hen s e t a g a i n s t t h e r e m a i n i n g measurement d a t a , and an a t t e m p t
i s made t o i n t e r p r e t p o s s i b l e d i s c r e p a n c i e s . Once a h y p o t h e s i s f o r t h e cause o f
t h e d i s c r e p a n c i e s has been f o r m u l a t e d , changes t o t h e i n p u t d a t a a r e i n t r o d u c e d
and t he b a l a n c e c a l c u l a t i o n s a r e r e p e a t e d . ( T h e a p p l i c a t i o n s o f t h i s p r o c e d u r e
a r e men t ioned i n C h a p t e r 3 . )
I t can be c o n c l u d e d f rom t h e above examples t h a t t h e a n a l y s e s o f e n e r g y
b a l a n c e s o f t e n r e q u i r e r e p e t i t i v e c a l c u l a t i o n s . T h i s must be seen i n c o n n e c t i o n
w i t h t he h a n d l i n g o f c o n s i d e r a b l e vo lumes o f d a t a and t h e r e p e t i t i v e use o f
thermodynamic f u n c t i o n s . The p r e s e n t a t i o n o f t h e b a l a n c e r e s u l t s i s a l s o a n o n -
t r i v i a l p r o b l e m , because i t i s n e c e s s a r y t o show a l l t h e d e t a i l s w h i c h may be
needed t o a n a l y s e t h e c o r r e c t n e s s o f t h e b a l a n c e and t o i d e n t i f y t h e n e c e s s a r y
85
changes i n t he i n p u t d a t a .
2 . 6 . 2 C o m p u t e r - a i d e d b a l a n c e c a l c u l a t i o n s
The c h a r a c t e r i s t i c f e a t u r e s o f t h e e n g i n e e r i n g t a s k s d i s c u s s e d i n t h e
p r e c e d i n g S e c t i o n j u s t i f y t h e use o f computers t o automate d a t a h a n d l i n g ,
c a l c u l a t i o n s and p r e s e n t a t i o n o f r e s u l t s . Con tempora ry c o m p u t e r s , i n c l u d i n g t h e
s o - c a l l e d p r o f e s s i o n a l p e r s o n a l c o m p u t e r s , a r e v e r y w e l l s u i t e d t o t h i s k i n d o f
a p p l i c a t i o n . As r e g a r d s t h e d a t a h a n d l i n g , t h e p rob lems can c o n v e n i e n t l y be
s o l v e d u s i n g s t a n d a r d d a t a - b a s e programs t o c r e a t e and upda te t h e d a t a f i l e s .
The c a l c u l a t i o n p r o g r a m , i n c l u d i n g t h e thermodynamic f u n c t i o n s , can be w r i t t e n
i n some h i g h - l e v e l programming l a n g u a g e , l i k e B a s i c , F o r t r a n o r P a s c a l . The
program s h o u l d r e a d most i n p u t d a t a f rom t h e f i l e s , p o s s i b l y a c c e p t i n g t h e
r e m a i n i n g d a t a f rom t h e k e y b o a r d , and t h e r e s u l t s s h o u l d p r e f e r a b l y be s t o r e d i n
t h e f i l e s . I t i s a l s o i m p o r t a n t t o have h i g h l y f l e x i b l e p r e s e n t a t i o n programs
a v a i l a b l e , t o make i t p o s s i b l e t o s e l e c t f rom t h e f i l e s and t o d i s p l a y o r p r i n t
o n l y t h e p a r t o f t h e r e s u l t s w h i c h i s r e a l l y needed a t a p a r t i c u l a r moment.
I t s h o u l d be p o i n t e d o u t t h a t t o c o m p u t e r i z e t h e b a l a n c e c a l c u l a t i o n s i s
pe rhaps more a p rob lem o f o r g a n i z a t i o n t han o f t h e e n g i n e e r i n g a c t i v i t i e s
c o n t e n t . T h e r e f o r e , no s p e c i f i c g u i d e l i n e s on p rogram d e s i g n w i l l be d i s c u s s e d
h e r e , as i t i s n e v e r p o s s i b l e t o e l i m i n a t e t h e need f o r a c a r e f u l a n a l y s i s o f
t h e p r a c t i c a l r e q u i r e m e n t s and c o n d i t i o n s f o r p rog ram u s e . I t may be o f some
i n t e r e s t , h o w e v e r , t o t ake a l o o k a t t h e main f e a t u r e s o f a p r o g r a m , d e v e l o p e d
w i t h t h e p a r t i c i p a t i o n o f t h e p r e s e n t a u t h o r , and l a t e r used i n hund reds o f
a p p l i c a t i o n s ( r e f . 1 9 ) . Most a p p l i c a t i o n cases were r e l a t e d t o d e s i g n p r o b l e m s ,
b u t s e v e r a l dozens o f mass and h e a t b a l a n c e s were a l s o c a l c u l a t e d when
i n v e s t i g a t i n g e n e r g y economy prob lems i n e x i s t i n g s u g a r f a c t o r i e s .
The p rogram was g r a d u a l l y improved d u r i n g t h e p e r i o d 1975-1980, as i t was
d e s i g n e d and coded f o r new v e r s i o n s o f m i c r o c o m p u t e r s . A s i m p l i f i e d f l o w d i a g r a m
v i s u a l i z i n g t h e e s s e n t i a l a c t i o n s and d e c i s i o n s l e f t t o t h e p rogram u s e r and t h e
e s s e n t i a l b l o c k s o f r o u t i n e s p e r f o r m e d by t h e compu te r i s shown i n F i g . 2 .11 . I t
can be seen t h a t t h e d i a l o g u e between t h e u s e r and t h e compute r p l a y s an
i m p o r t a n t r o l e i n t h e f u n c t i o n i n g o f t h e p r o g r a m . I n a d d i t i o n , i t has been t aken
i n t o a c c o u n t t h a t a comp le te a p p l i c a t i o n c y c l e c o m p r i s i n g d a t a i n p u t ,
c a l c u l a t i o n s , p o s s i b l e da ta m o d i f i c a t i o n s and r e - c a l c u l a t i o n s , p r e s e n t a t i o n o f
i n t e r m e d i a t e and f i n a l r e s u l t s , and f i n a l p rob lem a n a l y s i s may r e q u i r e
a c o n s i d e r a b l e t i m e . T h e r e f o r e , i t has been made p o s s i b l e t o i n t e r r u p t , and
l a t e r r e s t a r t , p rog ram a c t i o n a t s e v e r a l p o i n t s between t h e r o u t i n e b l o c k s . The
r e s u l t i n g f l e x i b i l i t y o f p rogram use t u r n e d o u t t o be a c r u c i a l f a c t o r i n i t s
s u c c e s s f u l a p p l i c a t i o n s .
Much a t t e n t i o n has been p a i d t o t h e u s e r ' s c o n v e n i e n c e when u t i l i z i n g t h e
da ta i n p u t r o u t i n e s , as l a r g e d a t a vo lumes a r e a l w a y s a s s o c i a t e d w i t h t h e r i s k
86
key in update
calculations of heat receivers, printouts
:ey in data on thernnal
syslenr) details
corrected At
F i g . 2 .11. S i m p l i f i e d f l o w d iag ram o f a computer program c a l c u l a t i n g t h e mass and hea t b a l a n c e s o f the rma l sys tems o f s u g a r f a c t o r i e s . The boxes marked * deno te d i s k e t t e memory.
o f t y p i n g e r r o r s . I n p u t d a t a a r e l o g i c a l l y d i v i d e d i n t o segments r e l a t e d t o t h e
p r o c e s s mass b a l a n c e , equ ipment p a r a m e t e r s , p r o c e s s h e a t i n g r e q u i r e m e n t s and
the rma l sys tem s t r u c t u r e . W i t h i n each segmen t , a s e r i e s o f e r g o n o m i c a l l y
87
o p t i m i z e d s c r e e n f o rma ts p r o v i d e s g u i d a n c e f o r t h e u s e r and c r o s s - c h e c k s on d a t a
c o r r e c t n e s s and c o n s i s t e n c y , as w e l l as a l l o w i n g c o n v e n i e n t i n t r o d u c t i o n o f a l l
n e c e s s a r y changes and c o r r e c t i o n s t o t h e d a t a a l r e a d y s t o r e d i n t h e compute r
memory.
C o n c e r n i n g t h e o u t p u t s , bo th t o v i d e o s c r e e n and h a r d c o p y , a number o f
o p t i o n s have been i n t r o d u c e d t o e n a b l e t h e u s e r t o choose t h e volume and t h e
fo rm o f t he o u t p u t i n f o r m a t i o n . Among o t h e r s , i t i s p o s s i b l e t o choose f rom f o u r
l anguages f o r o u t p u t d e s c r i p t i o n s . A s e c t i o n o f p r i n t o u t w i t h t h e t e x t i n
E n g l i s h i s shown i n F i g . 2 .12 .
I F A B L Ö ü f E V A P O R A T O R P A R A M E T E R S T A B L E 1
P A F ; : A M E T E R D E S C R I P T I O N
14 Η e 3 1 I. Ι Ί SI S t e a M t E ΐϊι Ρ e r a t Υ E
2 . V a Ρ o u r t e in Ρ E & t u r e
3 . J Υ ;J. C E t E ι ϊ ι ρ e A t ϊ · e
4 • L H I E f U I t θ iTi Ρ E A t . d i f f E r E N c e 5 . E.' V 3 Ρ o a t :I. o Η E F f e C t
¿ . Ε Η t r y S B E Β ι ϊ ι q i.j A i ί t I t \:i 7 *\}aFOIJ r f o r hea t i η η e e d S
8 . J U I C E Q u a n t i t y a f t e r E F F E C T
9. J U i C e C O Ι Ί C E ι ί t r *aF tEr ef f ect 1 0 . U A Ρ O IJ Ρ e S S Υ ν e
1 1 . Τ A Γι S F e r e d H e a t Α Υ a γί t i t y
U N I T
C
C
C
C
% P B
% P B
% P B
% P B
B X
M P A
A T A
KW
E F F E C T N U M B E R
1 ! 2 ! 3 : 4 : 5 136. 0 ! 1 2 8 . 8 Ί 1 2 1 . 5 1110 . 4 ! 9 9 . 8
I I I I I I I I 1 2 9 . 8 ! 1 2 2 . 5 1 1 1 1 . 4 1 1 0 0 . 8 ! 9 0 . 1 I I I I I I I I 1 3 0 . 3 ! 1 2 3 . 2 Ί 1 1 3 . 9 ! 1 0 4 . 4 I 9 4 . 5
5 . 7 ! 5 . 5 ! 7 . 3 ! 5 . 4 ! 4 . 4
J I J J
3 2 . 1 9 ! 2 0 . 3 5 ! 2 5 . 1 5 ! 4 . 3 4 ! 1 . 8 1
! ! ! ! 3 3 . 1 1 Ί 2 5 . 6 5 ! 2 4 . 6 1 ! 3 . 9 4 ! 1 . 4 6
I I I ! 7 . 0 2 ! 2 . 3 6 ! 2 1 . 7 7 ! 4 . 2 3 ! 1 . 8 2
8 2 . 8 3 ! 5 6 . 4 8 ! 3 1 . 3 2 ! 2 6 . 9 9 ! 2 5 . 1 8
1 9 . 7 6 ! 2 8 . 9 8 ! 5 2 . 2 5 ! 6 0 . 6 4 ! 6 5 . 0 1
! ! ! ! 0 . 2 6 8 ! 0 . 2 1 4 ! 0 . 1 5 0 ! 0 . 1 0 4 ! 0 . 0 7 1
2 . 7 3 ! 2 . 1 8 ! 1 . 5 3 ! 1 . 0 6 ! 0 . 7 ; ;
2 0 5 4 7 ! 1 6 0 6 6 ! 1 5 5 6 2 ! 2 5 2 8 ! 9 4 7
F i g . 2 .12 . P a r t o f a p r i n t o u t f rom a compute r p rogram c a l c u l a t i n g t h e mass and hea t b a l a n c e s o f the rma l sys tems o f s u g a r f a c t o r i e s ( c o u r t e s y Chemadex) .
2.7 EXERGY BALANCES
2.7.1 T h e o r e t i c a l backg round
When i n t r o d u c i n g t h e e n e r g y b a l a n c e e q u a t i o n s ( 2 . 5 ) and ( 2 . 6 ) , we have i n
f a c t a c c e p t e d a c o n v e n t i o n a c c o r d i n g t o w h i c h t h e r e p r e s e n t a t i o n o f t h e e n e r g y
f l o w i s based on t he e n t h a l p y o f m a t t e r e n t e r i n g o r l e a v i n g t h e thermodynamic
s y s t e m . The same c o n v e n t i o n i s used when r e p r e s e n t i n g t h e e n e r g y f l o w i n
88
a Sankey d i a g r a m . L e t us o b s e r v e , n o w e v e r , t h a t i f t h e r e f e r e n c e pa rame te rs i n
t h e d e f i n i t i o n o f t h e e n t h a l p y a r e changed ( f o r e x a m p l e , z e r o e n t h a l p y assumed
a t 20°C i n s t e a d o f a t O ^ C ) , t h e n t h e r e p r e s e n t a t i o n o f t h e e n e r g y f l o w i s
changed t o o , even though t h e e s s e n c e o f t h e e n e r g y b a l a n c e does n o t change a t
a l l . I n o r d e r t o a c c e n t u a t e t h e f a c t t h a t t h e e n e r g y b a l a n c e r e p r e s e n t a t i o n i s
so dependent on t h e n o t i o n o f e n t h a l p y , some a u t h o r s have adop ted t h e terms
" e n t h a l p y b a l a n c e " and " e n t h a l p y f l o w d i a g r a m " ( r e f s . 1 4 , 2 0 ) .
The e n t h a l p y - b a s e d e n e r g y b a l a n c e s a r e i n d i s p e n s a b l e t o t h e d e s i g n a n a l y s e s ,
and p a r t i c u l a r l y t o t h e p r e p a r a t i o n o f t h e d a t a f o r equ ipment s e l e c t i o n
d e c i s i o n s . The same a p p l i e s t o t h e m o n i t o r i n g o f e n e r g y p r o c e s s e s , i n c l u d i n g
t h e d e t e r m i n a t i o n o f t he e n e r g y c o n s u m p t i o n . I n a n a l y s e s aimed a t t h e
i d e n t i f i c a t i o n o f t h e e n e r g y - s a v i n g p o t e n t i a l o f p o s s i b l e the rma l sys tem
improvemen ts , h o w e v e r , t h e e n t h a l p y - b a s e d b a l a n c e s can be e x p e c t e d t o d e l i v e r
o n l y a p a r t o f t h e i n f o r m a t i o n r e q u i r e d . The r e a s o n i s t h a t i n r e a l - l i f e
s y s t e m s , t h e e f f i c i e n c y o f e n e r g y u t i l i z a t i o n can be r e d u c e d n o t o n l y by d i r e c t
h e a t l o s s e s t o t h e e n v i r o n m e n t , b u t a l s o by i n d i r e c t l o s s e s known as t h e
the rma l d e g r a d a t i o n o f e n e r g y . F o r e x a m p l e , i f a c e r t a i n amount o f e n e r g y has
been t r a n s f e r r e d f rom a h i g h - t e m p e r a t u r e medium t o a l o w - t e m p e r a t u r e o n e , t h e n
t h e range o f p o s s i b i l i t i e s f o r t h e u t i l i z a t i o n o f t h i s amount o f e n e r g y i s
n a r r o w e d . A s i m i l a r e f f e c t i s o b t a i n e d when t h e f l o w o f an e n e r g y - c a r r y i n g
medium i s t h r o t t l e d down f rom a h i g h e r t o a l o w e r p r e s s u r e . G e n e r a l l y , t h e
p r o c e s s e s r e s u l t i n g i n t h e the rma l d e g r a d a t i o n o f e n e r g y a r e c a l l e d i r r e v e r s i b l e
p r o c e s s e s .
W h i l e t he d i r e c t e n e r g y l o s s e s can be q u a n t i t a t i v e l y d e s c r i b e d on t h e
c o n c e p t u a l b a s i s p r o v i d e d by t h e f i r s t law o f t h e r m o d y n a m i c s , t h e i n d i r e c t
l o s s e s c a n n o t . A q u a n t i t a t i v e d e s c r i p t i o n o f t h e i n d i r e c t e n e r g y l o s s e s r e q u i r e s
use o f t h e n o t i o n s a s s o c i a t e d w i t h t h e second law o f t h e r m o d y n a m i c s , and
p a r t i c u l a r l y t h e n o t i o n o f e n t r o p y . F o r a thermodynamic sys tem w h i c h i s i s o l a t e d
f rom i t s s u r r o u n d i n g s , t h e second law s p e c i f i e s t h a t f o r any i n f i n i t e s i m a l l y
sma l l change o f s t a t e o f t h e s y s t e m , t h e change o f e n t r o p y ( d e n o t e d S ) must be
n o n - n e g a t i v e
dS > 0 ( 2 . 8 1 )
where t h e i n e q u a l i t y s i g n a p p l i e s t o i r r e v e r s i b l e , and t h e e q u a l i t y s i g n t o
r e v e r s i b l e , p r o c e s s e s . I n a f i n i t e p r o c e s s i n i t i a t e d a t s t a t e 1 and t e r m i n a t e d
a t s t a t e 2 , t h e e n t r o p y i n c r e a s e
2 AS = / dS ( 2 . 8 2 )
1
can be u n d e r s t o o d as a measure o f t h e e n e r g y d e g r a d a t i o n caused by t h e p r o c e s s .
As t h e e n t r o p y i s a lways a t t r i b u t e d t o t h e m a t t e r c o n t a i n e d i n t h e s y s t e m , i t
can a l s o be e x p r e s s e d p e r 1 kg mass; i t w i l l t h e n be c a l l e d s p e c i f i c e n t r o p y .
8 9
and deno ted s .
I n an a t t emp t t o c o n s t r u c t a u n i f i e d t h e o r e t i c a l app roach t o b o t h d i r e c t
e n e r g y l o s s e s and e n e r g y d e g r a d a t i o n , a new thermodynamic f u n c t i o n c a l l e d e x e r g y
has been i n t r o d u c e d w i t h t he d e f i n i t i o n
e = h - hQ - T Q ( S - S Q ) ( 2 . 8 3)
where s u b s c r i p t 0 deno tes t h e s t a t e o f thermodynamic e q u i l i b r i u m w i t h t h e
e n v i r o n m e n t . T Q t hus deno tes t h e e n v i r o n m e n t t e m p e r a t u r e and h g , S Q t h e e n t h a l p y
and e n t r o p y , r e s p e c t i v e l y , a t t h e pa rame te rs c o r r e s p o n d i n g t o t h e s t a t e o f
e q u i l i b r i u m ; h and s deno te e n t h a l p y and e n t r o p y , r e s p e c t i v e l y , a t t h e
pa ramete rs f o r w h i c h e x e r g y i s d e f i n e d .
An e x e r g y l o s s t a k i n g p l a c e i n a p r o c e s s can be i n t e r p r e t e d as an i n d i c a t i o n
t h a t , f o l l o w i n g d i r e c t e n e r g y l o s s e s o r t he rma l d e g r a d a t i o n o f e n e r g y ( t h i s
r e s u l t i n g i n e n t h a l p y c h a n g e , e n t r o p y change o r a c o m b i n a t i o n o f b o t h ) , t h e
s t a t e o f t h e sys tem moves c l o s e r t o thermodynamic e q u i l i b r i u m w i t h t h e
e n v i r o n m e n t . O b v i o u s l y , t h i s i s a s s o c i a t e d w i t h a r e d u c t i o n o f t h e range o f
p o s s i b i l i t i e s f o r t h e u t i l i z a t i o n o f sys tem e n e r g y .
U s i n g t h e n o t i o n o f e x e r g y , t h e p r o c e s s e s o f e n e r g y c o n v e r s i o n and
d i s t r i b u t i o n can be d e s c r i b e d by e x e r g y b a l a n c e s . A g r a p h i c a l r e p r e s e n t a t i o n o f
t h e e x e r g y b a l a n c e ( t h a t i s , t h e e x e r g y f l o w d i a g r a m ) i s known as t h e Grassmann
d i a g r a m . I t can g e n e r a l l y be s t a t e d t h a t t h e e x e r g y - b a s e d app roach i s v e r y
g r a p h i c and u s e f u l i n compar i sons o f d i s s i m i l a r s o l u t i o n s o f e n e r g y p r o c e s s e s .
Examples o f s u c c e s s f u l a p p l i c a t i o n s o f e x e r g y a n a l y s e s t o s u g a r t e c h n o l o g y
prob lems can be f ound i n t h e l i t e r a t u r e ( r e f s . 2 2 , 2 3 ) .
As r e g a r d s i n d u s t r i a l p r a c t i c e , i t can be o b s e r v e d t h a t once a few s o l u t i o n
c o n c e p t s have been s e l e c t e d f o r an e n e r g y p r o c e s s , i t becomes n e c e s s a r y t o
d e t e r m i n e t h e p r o c e s s p a r a m e t e r s , s e l e c t t h e equ ipment and e s t i m a t e t h e c o s t s .
O f c o u r s e , c o s t e s t i m a t e s s h o u l d be based on t h e e n t h a l p y b a l a n c e s , p o s s i b l y
p r e p a r e d i n p a r a l l e l w i t h t h e e x e r g y b a l a n c e s . I f t h e f i e l d o f p o s s i b l e
s o l u t i o n s i s l i m i t e d , as i s r a t h e r c h a r a c t e r i s t i c o f t h e s u g a r i n d u s t r y , t h e n
t he e n t h a l p y b a l a n c e a l o n e i s e f f e c t i v e enough as a t o o l f o r s o l v i n g most e n e r g y
e n g i n e e r i n g p r o b l e m s . A f t e r a l l , t h e e x e r g y b a l a n c e i s n o t h i n g more t han a n o t h e r
c o n v e n t i o n f o r d e s c r i b i n g t h e e n e r g y p r o c e s s e s .
2 . 7 . 2 Example
Compare e n t h a l p y - f l o w and e x e r g y - f l o w r e p r e s e n t a t i o n s o f e n e r g y c o n v e r s i o n
and u t i l i z a t i o n i n t h e p u l p d r y i n g p r o c e s s . The amount o f p u l p d e l i v e r e d t o
a d r u m - t y p e d r y e r i s 2 4 kg p e r 1 0 0 kg b e e t , t h e d r y s u b s t a n c e c o n t e n t changes
f rom 2 0 % t o 9 0 % , t h e gas t e m p e r a t u r e i n t h e drum i s 9 0 0 ° C a t i n l e t and l l O ^ C a t
o u t l e t , and t h e e n e r g y consumpt ion i s 2 9 0 0 k J p e r kg w a t e r removed . O t h e r d a t a
a re as f o l l o w s : f u e l used - o i l , f u r n a c e e f f i c i e n c y 0 . 9 3 , h e a t l o s s c o e f f i c i e n t
90
o f t h e d r y e r drum 0 . 0 3 , e n v i r o n m e n t t e m p e r a t u r e 20 C .
E n e r g y c o n v e r s i o n and u t i l i z a t i o n i n t he p u l p d r y i n g p r o c e s s can be d i v i d e d
i n t o t h r e e s t e p s : f u e l c o m b u s t i o n , a i r adm ix i ng t o t h e combus t i on g a s , and
d r y i n g . The Sankey d iag ram ( e n t h a l p y f l o w r e p r e s e n t a t i o n ) i s shown i n
F i g . 2 . 1 3 ( a ) and t h e Grassmann d iag ram ( e x e r g y f l o w r e p r e s e n t a t i o n ) i n
F i g . 2 . 1 3 ( b ) .
( a ) ( b )
fuel 100% fue l 100%
loss Λ ) .
7% VI
loss I
L.
exhaust gas 102.1% exhaus t gas 11.9%
, . pressed Η pulp 0.4%
dr ied pulp 0.1%
F i g . 2 .13 . E n t h a l p y - f l o w ( a ) and e x e r g y - f l o w ( b ) r e p r e s e n t a t i o n s o f t h e p u l p d r y i n g p r o c e s s . 1 - f u r n a c e , 2 - m i x i n g chamber , 3 - d r y e r d rum.
The e n t h a l p y - f l o w app roach seems t o s u g g e s t t h a t s i g n i f i c a n t e n e r g y s a v i n g s
c o u l d o n l y be o b t a i n e d by c u t t i n g down t h e e n t h a l p y f l o w i n t h e gas a t t h e d r y e r
o u t l e t , as t he d i r e c t e n e r g y l o s s e s a r e s m a l l .
I n t h e e x e r g y - f l o w r e p r e s e n t a t i o n , h o w e v e r , c o n s i d e r a b l e e x e r g y l o s s e s a r e
a t t r i b u t e d t o t h e f u r n a c e , t h e m i x i n g chamber and t h e d r y e r d rum. S t a r t i n g f rom
t h e l a s t p r o c e s s s t e p , t h e e x e r g y l o s s i n t h e d r y e r c o u l d be r e d u c e d by
d e c r e a s i n g t h e i n i t i a l gas t e m p e r a t u r e . T h e n , i n t h e m i x i n g chamber , one c o u l d
imag ine t h e e l i m i n a t i o n o f a i r a d m i x i n g , w h i c h i s t h e cause o f t h e e x e r g y l o s s
o c c u r r i n g t h e r e . I n s t e a d , gas c o o l i n g by h e a t exchange w i t h a s t e a m - g e n e r a t i n g
t ube bund le c o u l d be a p p l i e d , and by d e l i v e r i n g steam t o a t u r b o - g e n e r a t o r ,
e l e c t r i c a l e n e r g y c o u l d be p roduced w i t h o u t any e x t r a e n e r g y s u p p l y f rom t h e
e n v i r o n m e n t . F i n a l l y , i n t h e f u r n a c e , t h e e x e r g y l o s s i s u n a v o i d a b l e , as i t i s
a s s o c i a t e d w i t h t h e v e r y n a t u r e o f t h e combus t i on p r o c e s s .
2.8 ANALYSIS OF TRANSIENT ENERGY PROCESSES USING COMPUTER SIMULATION
I n e n g i n e e r i n g prob lems r e l a t e d t o t h e a u t o m a t i c c o n t r o l and m o n i t o r i n g o f
e n e r g y p r o c e s s e s , i t may be n e c e s s a r y t o s t u d y t he dynamic b e h a v i o u r o f t h e
the rma l sys tem unde r c h a n g i n g o p e r a t i n g c o n d i t i o n s . F o r e x a m p l e , i t may be
91
n e c e s s a r y t o e v a l u a t e p o s s i b l e consequences o f t h e a p p l i c a t i o n s o f v a r i o u s
c o n t r o l sys tems w i t h r e s p e c t t o t h e e n e r g y l o s s e s accompany ing t r a n s i e n t s t a t e s
o f t h e e v a p o r a t o r . Prob lems o f t h i s k i n d can be a n a l y s e d w i t h t h e a i d o f
computer s i m u l a t i o n methods .
The e s s e n c e o f computer s i m u l a t i o n i s i l l u s t r a t e d by t h e scheme i n F i g . 2 .14 .
F o r t h e sys tem unde r i n v e s t i g a t i o n ( i . e . , an equ ipment u n i t , a p r o c e s s s t a t i o n
o r a f a c t o r y s e c t i o n ) , an adequate mathemat i ca l model must be f o r m u l a t e d i n
terms o f v a r i a b l e s r e p r e s e n t i n g t h e key p r o c e s s pa rame te rs and t h e e x p r e s s i o n s
( i . e . , e q u a t i o n s , i n e q u a l i t i e s and f u n c t i o n s ) r e p r e s e n t i n g t h e r e l a t i o n s h i p s
between t h e p a r a m e t e r s . Hav ing t r a n s f o r m e d t h e model i n t o a compute r p r o g r a m ,
one i s a b l e t o c a r r y o u t c a l c u l a t i o n s o f t h e b e h a v i o u r o f t h e sys tem i n s t e a d y -
s t a t e and dynamic c o n d i t i o n s .
SYSTEM
1^ II 11
MATHEMATICAL MODEL
input data reflecting operating conditions
_ L _ COMPUTER PROGRAM
' I engineering decisions regarding
sysfenrTproperties.automatic controls, etc.
simulation results predicting system behaviour
F i g . 2 .14 . P r i n c i p l e o f t h e i n v e s t i g a t i o n o f o p e r a t i o n a l c h a r a c t e r i s t i c s o f t e c h n o l o g i c a l sys tems w i t h t h e a i d o f compute r s i m u l a t i o n .
S i m u l a t i o n o f t h e e v a p o r a t o r can be r e g a r d e d as a r e p r e s e n t a t i v e example o f
s i m u l a t i o n prob lems r e l a t e d t o t he e n e r g y economy. The p e r t i n e n t l i t e r a t u r e
r e f l e c t s t h e deve lopmen t o f compute r s i m u l a t i o n t e c h n i q u e s d u r i n g t h e l a s t two
d e c a d e s . I n an e a r l y s t u d y , a l i n e a r i z e d e v a p o r a t o r model s u i t e d t o programming
on an ana log computer was p r o p o s e d ( r e f . 2 4 ) . L a t e r o n , a l e a n i n g t o w a r d s
d i g i t a l computers has been g e n e r a l l y a d o p t e d . S e v e r a l p u b l i c a t i o n s can be named
where e v a p o r a t o r models a r e d e s c r i b e d u s i n g d i f f e r e n t i a l e q u a t i o n s s o l v e d by
such n u m e r i c a l methods as t h e o r t h o g o n a l c o l l o c a t i o n method ( r e f . 2 5 ) , t h e
c o r r e c t o r - p r e d i c t o r method ( r e f . 26) and R u n g e - K u t t a i n t e g r a t i o n ( r e f . 2 7 ) . The
models assume t h e use o f s p e c i a l computer p r o g r a m s , w r i t t e n i n t h e F o r t r a n
l a n g u a g e . To t he knowledge o f t h e p r e s e n t a u t h o r , h o w e v e r , none o f t h e s e
programs has been w i d e l y a p p l i e d .
An a l t e r n a t i v e app roach t o e v a p o r a t o r s i m u l a t i o n assumes t h e a p p l i c a t i o n o f
w i d e l y c i r c u l a t e d g e n e r a l - p u r p o s e s i m u l a t i o n p r o g r a m s . Such programs e n a b l e one
92
t o s o l v e t y p i c a l d i f f e r e n t i a l e q u a t i o n s e n c o u n t e r e d i n t h e s i m u l a t i o n o f
t r a n s i e n t s t a t e s o f v a r i o u s t e c h n o l o g i c a l s y s t e m s . A p r e r e q u i s i t e f o r s u c c e s s f u l
a p p l i c a t i o n o f a s p e c i f i c p rogram i s t o f o r m u l a t e t h e e v a p o r a t o r model i n
a manner c o m p a t i b l e w i t h t h e r e q u i r e m e n t s adop ted by t h e program d e s i g n e r . T h i s
app roach has been implemented i n p r a c t i c e u s i n g a w i d e l y known IBM program
( r e f . 2 8 ) .
Examples o f s i m u l a t i o n r e s u l t s d e s c r i b i n g t h e dynamic b e h a v i o u r o f m u l t i p l e -
e f f e c t e v a p o r a t o r s a r e g i v e n i n F i g . 2 .15 .
( a ) ( b )
iJllUUlr vapour flow
withdrawn from 3rd effect
j r d effect
ju ice temperatures
vapour flow withdrawn from 2nd effect
I
1000 2000
T i m é i s )
3000 4000
3rd effect
vapour consumption
5th effect
5 10
Time (min)
15
F i g . 2 .15 . Examples o f s i m u l a t i o n r e s u l t s d e s c r i b i n g t h e dynamic b e h a v i o u r o f q u i n t u p l e - e f f e c t e v a p o r a t o r s , ( a ) j u i c e t e m p e r a t u r e s a t v a r i a b l e v a p o u r w i t h d r a w a l f rom t h e t h i r d e f f e c t , d i s c h a r g e - c o n t r o l l e d j u i c e l e v e l s ( a f t e r r e f . 2 6 ) , ( b ) consumpt ion o f h e a t i n g v a p o u r s a t v a r i a b l e v a p o u r w i t h d r a w a l f rom t h e second e f f e c t , f e e d - c o n t r o l l e d j u i c e l e v e l s ( a f t e r r e f . 2 8 ) .
REFERENCES
1 T . D . E a s t o p and A . McConkey , A p p l i e d Thermodynamics f o r E n g i n e e r i n g T e c h n o l o g i s t s , 3 rd e d n . , Longman, London and New Y o r k , 1978.
2 G . J . Van Wylen and R . E . S o n n t a g , Fundamenta ls o f C l a s s i c a l The rmodynam ics , 3 rd e d n . , W i l e y , New Y o r k , 1985.
3 J . C u e l , Le b i l a n t he rm ique en s u c r e r i e , S u c r . F r . , 119(21) (1978) 424-434, 119(22) (1978) 455-466.
4 P.W. van d e r Poel ( e t a l . ) , Z u c k e r h a u s s c h e m a t a , e i n B e i s p i e l von I n f o r m a t i o n s v e r b e s s e r u n g m i t H i l f e d e r e l e k t r o n i s c h e n D a t e n v e r a r b e i t u n g , Z u c k e r , 28 (3 ) (1975) 122-131.
5 T . B a l o h , Z u c k e r t e c h n o l o g i s c h e Rechnungen m i t dem Dre ikomponen ten -D iag ramm, Z u c k e r i n d . , 107(6) (1982) 515-525.
6 A . K u b a s i e w i c z , W. Lekawski and K. U r b a n i e c , Automated d e s i g n c a l c u l a t i o n s o f b e e t s u g a r p l a n t s u s i n g m i c r o c o m p u t e r COMPUCORP 425 G , P r o c . 3 rd Symp. Use o f Computers i n Chemica l E n g i n e e r i n g , G l i w i c e , 1974, p p . 213-217.
7 L.W. W e i s s , Computer p rogram t o a i d s u g a r end o p e r a t i o n s . Paper p r e s e n t e d a t 21s t ASSBT M e e t i n g , San D i e g o , 1981.
8. H . R . D e l a n e y , D. G o t t h a r d and J . B . N i c h o l s , Use o f an e n e r g y model i n s u g a r r e f i n i n g . I n t . Suga r J . , 85(1014) (1983) 171-176.
9 R . G . H o e k s t r a , A f l e x i b l e computer p rogram f o r f o u r - c o m p o n e n t m a t e r i a l b a l a n c e s i n s u g a r i n d u s t r y b o i l i n g h o u s e s . I n t . Suga r J . , 85(1016) (1983) 227-232, 85(1017) (1983) 262-265.
93
10 P.M. S i l i n , V o p r o s y T e k h n o l o g i i Sakha rnykh V e s h c h e s t v , P i s h c h e p r o m i z d a t , Moskva , 1950.
11 W. Lekawski and K. U r b a n i e c , M o d e r n i s i e r u n g d e r W 'á rmewi r t scha f t i n Z u c k e r f a b r i k e n , Z u c k e r i n d . , 108(4) (1983) 338-343.
12 Κ. U r b a n i e c and Α . K u b a s i e w i c z , Mode le matematyczne d í a p r o j e k t o w a n i a w i e l o d z i a l o w y c h i n s t a l a c j i w y p a r n y c h , I n z . C h e m . , 7 ( 1 ) (1977) 207-221.
13 T . B a l o h , W ä r m e w i r t s c h a f t , i n : F . S c h n e i d e r ( E d . ) , T e c h n o l o g i e des Z u c k e r s , S c h a p e r V e r l a g , H a n n o v e r , 1968, p p . 705-776.
14 Τ . B a l o h , Wärmeat las f ü r d i e Z u c k e r i n d u s t r i e , S c h a p e r V e r l a g , H a n n o v e r , 1975.
15 A . L . Webre , E v a p o r a t i o n and h e a t i n g , i n : D. S p e n c e r and G . P . Meade ( E d s . ) , Cane Suga r Handbook, W i l e y , New Y o r k , 1948, p p . 134-174.
16 Τ . B a l o h , Wärmetechn ische Berechnung d e r V e r d a m p f s t a t i o n , Z u c k e r - B e i h e f t e , 3 ( 2 ) (1956) 29-74.
17 G . K imenov, E n e r g e t i s c h e U n t e r s u c h u n g e n an e i n e r m e h r s t u f i g e n Ve rdamp f s t a t i o n a l s DampfUmformer, Z u c k e r , 2 5 ( 7 ) (1972) 225-230.
18 V . U r b a n , Matemat i cky model c u k r o v a r n i c k e p r u t o k o v e o d p a r k y p r a c u j i c i se s t o u p a j i c i v r s t v o u , L i s t y C u k r . , 8 9 ( 6 ) (1973) 114-118.
19 G . B a t o r and K. U r b a n i e c , P r o j e k t i e r u n g von Ve rdamp fan lagen i n Z u c k e r f a b r i k e n m i t H i l f e von Compu te rn , Z u c k e r i n d . , 103(12) (1978) 1035-1042.
20 T . B a l o h , E n e r g i e w i r t s c h a f t b e i E i n d a m p f u n g s - und T r o c k n u n g s p r o z e s s e n , Z u c k e r i n d . , 105(1) (1980) 50-61.
21 T . B a l o h , Me thod ik be i e x e r g e t i s c h e n U n t e r s u c h u n g e n i n Z u c k e r f a b r i k e n , Z u c k e r i n d . , 106(1) (1981) 29-40.
22 0. A u e r s w a l d , E x e r g e t i s c h e A n a l y s e e i n e r Z u c k e r f a b r i k m i t B rüdenkompress ion am B e i s p i e l d e r Z u c k e r f a b r i k A a r b e r g , S c h w e i z , Z u c k e r i n d . , 106(9) (1981) 804-815.
23 T . B a l o h , S t u d i e e i n e r Z u c k e r f a b r i k m i t B r ü d e n k o m p r e s s i o n , Z u c k e r i n d . , 109(4) (1984) 285-294.
24 0. W i k l u n d , The c a l c u l a t i o n and c o n t r o l o f m u l t i p l e e f f e c t e v a p o r a t o r s . S o c k e r H a n d l . , 22 (1 ) (1968) 1-22.
25 υ. B o l m s t e d t and Α . J e r n q v i s t , S i m u l a t i o n o f t h e s t e a d y - s t a t e and dynamic b e h a v i o u r o f m u l t i p l e e f f e c t e v a p o r a t i o n p l a n t s . Comp. A i d e d D e s . , 8 ( 3 ) (1976) 142-148, 9 ( 1 ) (1977) 29-40.
26 Μ. M ä k e l ä , Ma temat i sches F o r m u l i e r e n und d i g i t a l e s S i m u l i e r e n e i n e r V e r d a m p f s t a t i o n i n d e r R ü b e n z u c k e r i n d u s t r i e , Z u c k e r i n d . , 106(11) (1981) 989-993.
27 A . L e b e r t ( e t a l . ) , S i m u l a t i o n s u r o r d i n a t e u r d ' u n e v a p o r a t e u r de s u c r e r i e a m u l t i p l e e f f e t s , I n d . A l i m . A g r i e , 9 7 ( 7 - 8 ) (1980) 691-698.
28 Κ. U r b a n i e c and M. S z c z e n i o w s k i , N a c h b i l d u n g e i n e r m e h r s t u f i g e n Ve rdamp f s t a t i o n u n t e r Verwendung des CSMP-Sys tems, Z u c k e r i n d . , 105(7) (1980) 628-631.
94
C h a p t e r 3
SELECTED PROBLEMS OF HEAT ECONOMY
3.1 ANALYSIS AND EVALUATION OF THE HEAT ECONOMY
3.1.1 M e t h o d o l o g i c a l h i n t s
Any a t t emp t t o improve t h e hea t economy o f a s u g a r f a c t o r y b e g i n s w i t h t h e
a c q u i s i t i o n o f i n f o r m a t i o n on t h e e x i s t i n g s t a t e o f t h i n g s , and an i n i t i a l
e f f o r t may be needed t o e s t a b l i s h t h e t y p e and amount o f i n f o r m a t i o n t h a t w i l l
be s u f f i c i e n t . The aim o f an i n i t i a l i n v e s t i g a t i o n i s t o r e a c h a c e r t a i n l e v e l
o f knowledge o f t h e s t r u c t u r e o f t he the rma l s y s t e m , i t s mass and h e a t b a l a n c e s ,
and t he c h a r a c t e r i s t i c s o f t h e equ ipmen t . T h i s s h o u l d e n a b l e one t o p e r f o r m an
o v e r a l l e v a l u a t i o n and t o f o r m u l a t e a d i a g n o s i s o f t he d e f i c i e n c i e s o f t h e h e a t
economy.
L e t us o b s e r v e t h a t i f t h e d i a g n o s i s can be made v e r y a c c u r a t e , t hen i t may
become e a s i e r t o o u t l i n e p o s s i b l e improvements and t h e way t h e y can be
implemented i n t h e f a c t o r y . T h e r e f o r e , i t i s a l w a y s a d v i s a b l e t o have more t han
minimum i n f o r m a t i o n a t h a n d , and a d e t a i l e d knowledge o f t h e scheme o f t h e s u g a r
m a n u f a c t u r i n g p r o c e s s , t h e v a l u e s o f p r o c e s s p a r a m e t e r s , and t h e c h a r a c t e r i s t i c s
o f p r o c e s s equ ipment and c o n t r o l sys tems i s p a r t i c u l a r l y u s e f u l .
I t can t h u s be g e n e r a l l y c o n c l u d e d t h a t t h e more d e t a i l e d a r e t h e a v a i l a b l e
d a t a , t he e a s i e r i t i s t o p e r f o r m an a n a l y s i s o f t h e e x i s t i n g s t a t e o f t h e h e a t
economy. T h e r e i s no p o i n t , h o w e v e r , i n i n v e s t i g a t i n g d e t a i l s w h i c h may be
c o s t l y t o o b t a i n b u t w i l l e v e n t u a l l y t u r n o u t i r r e l e v a n t t o t h e p rob lems o f
i n t e r e s t . T h i s a p p l i e s , i n p a r t i c u l a r , t o t h e mass and h e a t b a l a n c e s , t h e
d e t a i l s o f w h i c h may be d i f f i c u l t t o e s t a b l i s h u n l e s s t ime -consum ing and c o s t l y
measurements a r e p e r f o r m e d . E x p e r i e n c e p r o v e s t h a t a s a t i s f a c t o r y l e v e l o f
knowledge o f t h e b a l a n c e d a t a can o f t e n be o b t a i n e d t h r o u g h a p p r o x i m a t e a n a l y s e s
o f thermodynamic sys tems p r o p e r l y d e f i n e d w i t h i n a f a c t o r y . A p p r o x i m a t e b a l a n c e
c a l c u l a t i o n s can be pe r fo rmed on t h e b a s i s o f e s s e n t i a l d a t a e x t r a c t e d f rom
r o u t i n e f a c t o r y r e c o r d s . I f t he a n a l y s i s i s i n t e n d e d t o c r e a t e a b a s i s f o r
l i m i t e d m o d i f i c a t i o n s o f an e x i s t i n g f a c t o r y , t h i s app roach i s o f t e n , b u t n o t
a l w a y s , e f f e c t i v e enough . A d i s c u s s i o n o f l i m i t e d - s c a l e m o d i f i c a t i o n s o f the rma l
s y s t e m s , i n c l u d i n g p r a c t i c a l e x a m p l e s , i s g i v e n i n C h a p t e r 8.
A d i f f e r e n t s i t u a t i o n a r i s e s when t h e u n d e r l y i n g i n t e n t i o n i s t o m o d e r n i z e
t h e f a c t o r y e x t e n s i v e l y . I n t h i s c a s e , i n - d e p t h s t u d i e s o f new s o l u t i o n s ,
i n c l u d i n g mass and hea t b a l a n c e s c o r r e s p o n d i n g t o bo th t he e x i s t i n g s t a t e and
t he mode rn i zed f a c t o r y , a r e i n d i s p e n s a b l e .
A summary o f i n f o r m a t i o n r e q u i r e m e n t s a s s o c i a t e d w i t h t y p i c a l m o d e r n i z a t i o n s ,
i n c l u d i n g p r a c t i c a l e x a m p l e s , i s g i v e n i n C h a p t e r 9. The need t o a n a l y s e more
95
da ta does n o t n e c e s s a r i l y mean, h o w e v e r , t h a t t h e i n i t i a l s t a t e o f t h e hea t
economy must be known i n f u l l d e t a i l . A g a i n , a p p r o x i m a t e b a l a n c e c a l c u l a t i o n s
t u r n o u t t o be e f f e c t i v e enough i n t y p i c a l m o d e r n i z a t i o n c a s e s .
A p r a c t i c a l c o r r e l a t i o n seems t o e x i s t between t he l e v e l o f s o p h i s t i c a t i o n o f
t h e hea t economy and t he amount o f work needed t o p r e p a r e a d e c i s i o n on t h e most
s u i t a b l e and c o s t - e f f e c t i v e improvemen ts . When t a l k i n g t o t h e managers o f
e n e r g y - e f f i c i e n t f a c t o r i e s , one can u s u a l l y c o n c l u d e t h a t t h e y have a g r a s p o f
t h e s i t u a t i o n and a r e w e l l aware o f t h e a r e a s where improvements a r e n e e d e d , as
w e l l as t he s o l u t i o n s t h a t may come i n t o q u e s t i o n . On t h e o t h e r h a n d , i n a n o t -
s o - e f f i c i e n t f a c t o r y , i t may be t h a t t h e m a n a g e r ' s p e r c e p t i o n o f e n e r g y p rob lems
i s i n c o m p l e t e , no p rob lem h i e r a r c h y e x i s t s and t h e r e i s a l o t o f u n c e r t a i n t y
abou t p o s s i b l e c o u r s e s o f a c t i o n .
F o r an e n e r g y s p e c i a l i s t , t he l a t t e r case c o n s t i t u t e s a r e a l l y c h a l l e n g i n g
s i t u a t i o n . L e t us assume t h a t t he s t a r t i n g p o i n t o f t he i n v e s t i g a t i o n o f a h e a t
economy i s t h e m a n a g e r ' s d i s s a t i s f a c t i o n w i t h t h e e x i s t i n g s t a t e , b u t t h a t t h e r e
i s no c l e a r i d e a o f t h e e x t e n t o f t h e r a t i o n a l i z a t i o n measures needed and t h e
p r i o r i t i e s o f t h e p rob lems t o be s o l v e d . P r i o r t o f o r m u l a t i n g a d i a g n o s i s and
p r o p o s i n g a s e t o f r e m e d i e s , i t i s n e c e s s a r y t o c o l l e c t i n f o r m a t i o n r e l a t e d t o
t he f o l l o w i n g q u e s t i o n s :
( i ) C o n s i d e r i n g t he e x i s t i n g p o s s i b i l i t i e s and l i m i t a t i o n s r e s u l t i n g f rom i t s
l a y o u t and t h e c h a r a c t e r i s t i c s o f t h e e q u i p m e n t , does t h e r e a l pe r f o rmance o f
t h e the rma l sys tem match t h e e x p e c t e d pe r fo rmance ? I f n o t , what a r e t h e r e a s o n s
and how can t h e y be e l i m i n a t e d ?
( i i ) What a r e t h e d e c i s i v e f a c t o r s e n a b l i n g t h e the rma l sys tems t o s a t i s f y t h e
a c t u a l t o t a l hea t demand a t t h e n e t h e a t demand r e c o r d e d , and how can t h e
e f f e c t i v e n e s s r a t i o be i n c r e a s e d ?
( i i i ) What a re t he l i m i t a t i o n s imposed on t h e e n e r g y economy by t he e x i s t i n g
scheme and pa rame te rs o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s and by t h e
c h a r a c t e r i s t i c s o f p r o c e s s equ ipment and c o n t r o l sys tems ? How can t h e s e f a c t o r s
be a d j u s t e d t o r e d u c e t h e t o t a l hea t demand ?
( i v ) How e f f e c t i v e a r e t h e e n e r g y m o n i t o r i n g p r o c e d u r e s based on t h e e x i s t i n g
i n s t r u m e n t a t i o n , and what a c t i o n s can be taken t o improve them ?
I n p r a c t i c e , i t i s n o t p o s s i b l e t o o b t a i n d i r e c t l y p i e c e s o f i n f o r m a t i o n t h a t
f a l l n e a t l y i n t o one o f t h e f o u r c a t e g o r i e s m e n t i o n e d . V e r y o f t e n , one has t o
i d e n t i f y , i n t e r p r e t and s o r t symptoms w h i c h may p o i n t a t some i n f o r m a t i o n
r e l a t e d t o more t han one c a t e g o r y .
T h e r e a r e t h r e e main t e c h n i q u e s o f i d e n t i f y i n g t he symptoms w h i c h
c h a r a c t e r i z e t h e f u n c t i o n i n g o f t he the rma l s y s t e m :
- t o a n a l y s e t h e d a t a i n t h e r o u t i n e f a c t o r y r e c o r d s , t o q u e s t i o n t h e managers
and the t e c h n i c a l p e r s o n n e l , and t o i n s p e c t t he f a c t o r y ( p r e f e r a b l y when i n
96
o p e r a t i o n ) ,
- t o s e t up and t o i n v e s t i g a t e t h e e x t e r n a l mass and e n e r g y b a l a n c e s o f t h e
f a c t o r y ,
- t o a n a l y s e t h e mass and h e a t b a l a n c e s o f t h e the rma l sys tem and i t s
components .
I n more c o m p l i c a t e d c a s e s , i t may be u s e f u l t o s p l i t t h e s y m p t o m - f i n d i n g
p r o c e d u r e i n t o two p a r t s . I n i t i a l l y , b a s i c d a t a a r e c o l l e c t e d t o make t he
b a l a n c e c a l c u l a t i o n s p o s i b l e . Once t h e mass and e n e r g y b a l a n c e s have been
e s t a b l i s h e d , t he f i g u r e s o b t a i n e d and t h e p r e l i m i n a r y d i a g n o s i s a r e compared
w i t h t h e r e a l i t y .
As r e g a r d s t he a n a l y s e s o f t he b a l a n c e f i g u r e s , a v a r i e t y o f t e c h n i q u e s can
be c o n s i d e r e d . I t i s p o p u l a r t o d e f i n e s e v e r a l s e t s o f i n p u t d a t a i n a manner
a l l o w i n g t h e changes o f c e r t a i n i m p o r t a n t f a c t o r s t o be s t u d i e d , and t o
c a l c u l a t e s e v e r a l mass and e n e r g y b a l a n c e s f rom w h i c h i n f o r m a t i o n on t h e
impor tance o f t h e s e f a c t o r s can be e x t r a c t e d . More advanced methods f o r e n e r g y
a n a l y s e s a r e d i s c u s s e d i n C h a p t e r 9.
3 .1 .2 C o l l e c t i n g e s s e n t i a l i n f o r m a t i o n
I n a d d i t i o n t o the r e q u i r e m e n t s men t ioned i n t h e p r e c e d i n g S e c t i o n , i t
f o l l o w s f rom t h e d i s c u s s i o n p r e s e n t e d i n C h a p t e r s 1 and 2 t h a t i n f o r m a t i o n on
t h e e n e r g y economy s h o u l d a l s o be w e l l s t r u c t u r e d . T h i s can be a c h i e v e d u s i n g
t h e top -down a p p r o a c h , t h a t i s , p r e s e n t i n g t h e o v e r a l l p i c t u r e f i r s t , t h e n
a n a l y s i n g t h e e s s e n t i a l b u i l d i n g b l o c k s o f t he therma l s y s t e m , and f i n a l l y
i n v e s t i g a t i n g the c h a r a c t e r i s t i c s o f t h e equ ipment u n i t s .
The f i r s t s t e p s h o u l d be d e v o t e d t o i d e n t i f i c a t i o n o f t h e schemes and
pa ramete rs o f t he s u g a r m a n u f a c t u r i n g p r o c e s s and t he e n e r g y p r o c e s s e s . A l l t h e
d a t a taken f rom t h e e x i s t i n g documents s h o u l d be v e r i f i e d , p r e f e r a b l y d u r i n g
normal f a c t o r y o p e r a t i o n when any changes o r m o d i f i c a t i o n s r e l a t i v e t o t he
documented s t a t e can e a s i l y be o b s e r v e d . When document ing t h e d a t a a c q u i r e d , i t
i s a d v i s a b l e t o p r e s e n t them i n fo rms f a c i l i t a t i n g easy i d e n t i f i c a t i o n o f t he
i n f o r m a t i o n s t r u c t u r e and t he r e l a t i o n s between i m p o r t a n t segments o f
i n f o r m a t i o n . A l t h o u g h t he c o n v e n t i o n a l schemes and t a b l e s l i k e t h o s e used i n t h e
p r e s e n t book a r e s u f f i c i e n t l y e f f e c t i v e i n most p r a c t i c a l a p p l i c a t i o n s , i t may
p r o v e u s e f u l t o combine them w i t h o t h e r fo rms e n a b l i n g one t o l o o k a t t he d a t a
f rom a d i f f e r e n t a n g l e . F i g u r e 3.1 shows an example o f a d iag ram w h i c h makes i t
p o s s i b l e t o match t he a v a i l a b l e h e a t i n g media t o t h e p r o c e s s media t h a t must be
hea ted ( r e f . 1 ) .
Among t h e main f e a t u r e s o f t h e the rma l s y s t e m , t h e s t a b i l i t y o f t h e
o p e r a t i n g pa rame te rs i s o f u tmost i m p o r t a n c e . I n most f a c t o r i e s , pa ramete r
f l u c t u a t i o n s may o c c u r even under p e r f e c t l y normal o p e r a t i n g c o n d i t i o n s , m o s t l y
because t h e r e a r e v a p o u r demand f l u c t u a t i o n s due t o t he b a t c h w i s e o p e r a t i o n
97
c o s s e t t e s
rec i rcu lated ju ice * . p r e s s w a t e r
m a k e - u p water
p re - l imed j u i c e σ J l imed j u i c e ~ c l e a r j u i c e —
t h i n j u i c e TD Φ Ε ω υ o
ju ice in 1 s t e f fec t v a c u u m p a n s A χ
s y r u p s — v a c u u m p a n s Β χ
room h e a t i n g
1s t -e f fec t v a p o u r 2 n d - e f f e c t v a p o u r
c o n d e n s ó t e 3 r d - e f f e c t v a p o u r χ
n o n c o n d e n s a b l e s — v a p o u r f rom vacuum pans A χ
r ec i r cu la ted j u i c e p r e s s w a t e r —
•o Ε en c o
15 20 30 AO 50 60 70 80 90 100 110 120 130
T e m p e r a t u r e { °C )
' i n the e x t r a c t i o n s t a t i o n
F i g . 3 .1 . G r a p h i c a l compendium o f t h e p r o c e s s media t o be h e a t e d , o r hea t r e c e i v e r s , and t he h e a t i n g med ia .
o f vacuum p a n s . Any paramete r change i n t r o d u c i n g a d e v i a t i o n f rom a b a l a n c e d
s t a t e o f t h e the rma l sys tem c r e a t e s t h e r i s k o f i n c r e a s e d e n e r g y l o s s .
T y p i c a l l y , t h e immediate causes o f t h e l o s s a r e i n c r e a s e d v a p o u r f l o w f rom t h e
l a s t e v a p o r a t o r e f f e c t t o t he c o n d e n s e r , o r r e d u c e d t h i c k - j u i c e c o n c e n t r a t i o n
w h i c h r a i s e s t h e h e a t demand o f t h e s u g a r h o u s e . A t v e r y r a p i d pa ramete r
c h a n g e s , t h e r e may be u n f a v o u r a b l e emergency d i s c h a r g e s o f h i g h - t e m p e r a t u r e
media w i t h i n t he therma l sys tem o r even d i r e c t l y t o t h e e n v i r o n m e n t ( e x a m p l e s :
open ing s a f e t y v a l v e s on a steam p i p e l i n e o r on an e v a p o r a t o r b o d y , o v e r f l o w i n g
h o t - j u i c e t a n k s , e t c . ) .
I t f o l l o w s f rom t h e above i n t r o d u c t i o n t h a t a b n o r m a l l y l a r g e pa ramete r
f l u c t u a t i o n s w h i c h a r e d i f f i c u l t t o dampen s h o u l d be t r e a t e d as a symptom o f
dange rous d e f i c i e n c i e s o f t h e the rma l s y s t e m . The u n d e r l y i n g f a c t o r s a r e most
f r e q u e n t l y as f o l l o w s :
- t o o smal l a h e a t i n g s u r f a c e a r e a i n t h e e v a p o r a t o r e f f e c t f rom w h i c h v a p o u r i s
s u p p l i e d t o vacuum p a n s ,
- a f a u l t y c o n t r o l sys tem i n t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n , w h i c h i s
d e c i s i v e i n s t a b i l i z i n g t h e p r e s s u r e and t e m p e r a t u r e o f t he e x h a u s t s team,
- a f a u l t y c o n d e n s a t e d r a i n a g e subsys tem c a u s i n g p e r i o d i c a c c u m u l a t i o n o f t he
condensa te i n t h e h e a t i n g chambers o f e v a p o r a t o r b o d i e s .
The e n e r g y consumpt ion o f a s u g a r f a c t o r y may be i n f l u e n c e d n o t o n l y by
98
u n c o n t r o l l a b l e paramete r f l u c t u a t i o n s b u t a l s o by r o u t i n e pa ramete r a d j u s t m e n t s ,
l i k e t h o s e a s s o c i a t e d w i t h a t e m p o r a r i l y i n t r o d u c e d r e d u c t i o n o f t h e p r o c e s s i n g
c a p a b i l i t y . G e n e r a l l y , t h e r e s p o n s e s o f a the rma l sys tem t o changes o f t h i s
k i n d a r e w o r t h s t u d y i n g as an i n d i c a t i o n o f p o s s i b l e sys tem d e f i c i e n c i e s t h a t
need t o be c o r r e c t e d . On t h e o t h e r h a n d , even c o r r e c t l y f u n c t i o n i n g sys tems
w i t h p e r f e c t pa ramete r s t a b i l i z a t i o n a r e a d v e r s e l y a f f e c t e d by c o n t i n u e d
d e v i a t i o n s f rom t h e i r nominal o p e r a t i n g p a r a m e t e r s . T h i s phenomenon s h o u l d be
s t u d i e d w i t h t h e aim o f i d e n t i f y i n g p o s s i b l e i n d i c a t i o n s o f t he e x i s t e n c e o f an
e n e r g y - s a v i n g s t r a t e g y f o r t h e f a c t o r y o p e r a t i o n . Most n o t a b l y , a d a i l y
p r o c e s s i n g c a p a b i l i t y f a l l i n g be low i t s nominal l e v e l u s u a l l y causes t h e e n e r g y
consumpt ion p e r u n i t mass o f b e e t s p r o c e s s e d t o i n c r e a s e . T h e r e a r e r a t h e r few
f a c t o r i e s , h o w e v e r , where t h e managers a r e f u l l y aware o f t h e c o n s e q u e n c e s , i n
te rms o f a d d i t i o n a l f u e l bu rned p e r u n i t mass o f b e e t s p r o c e s s e d , o f a d e c i s i o n
t o reduce t he p r o c e s s i n g c a p a b i l i t y . A n o t h e r i m p o r t a n t f a c t o r i s t he j u i c e
d r a f t , w h i c h a f f e c t s bo th t h e s u g a r l o s s i n e x h a u s t e d c o s s e t t e s and the e n e r g y
demand o f t h e p r o c e s s .
F i g u r e s 3.2 and 3.3 show t h e r e s u l t s o f s t u d i e s o f t h e f u e l consumpt ion under
chang ing o p e r a t i n g c o n d i t i o n s i n two s u g a r f a c t o r i e s w i t h d i f f e r e n t p r o c e s s i n g
c a p a b i l i t i e s . S t a t i s t i c a l d a t a f rom 9 seasons were taken t o c o n s t r u c t t he
d i a g r a m s , and b r a c k e t s deno te seasons c h a r a c t e r i z e d by abnormal c l i m a t i c
c o n d i t i o n s , unusua l b e e t p r o p e r t i e s , e t c .
The a b i l i t y o f t h e therma l s y s t e m ' s p i p i n g t o c r e a t e c o r r e c t f l o w c o n d i t i o n s
f o r a l l t he e n e r g y - c a r r y i n g media i s a n o t h e r i m p o r t a n t p o i n t t o be i n v e s t i g a t e d .
I t i s n o t o n l y t he f l o w c o n d i t i o n s d u r i n g normal f a c t o r y o p e r a t i o n , b u t a l s o
t h o s e i n d u c e d by f a c t o r y s t a r t - u p o r pa ramete r f l u c t u a t i o n s , t h a t may a f f e c t
e n e r g y l o s s e s and equ ipment s a f e t y . The symptoms o f a b n o r m a l i t i e s a re pa ramete r
i n s t a b i l i t i e s , e x c e s s i v e p i p e v i b r a t i o n s , h y d r a u l i c s h o c k s , e t c . G e n e r a l l y ,
t h r e e f a c t o r s a r e o f c r i t i c a l impo r tance t o t he f u n c t i o n i n g o f t h e p i p i n g :
( i ) The d i m e n s i o n s o f t h e p i p e s d e t e r m i n e t he f l o w v e l o c i t i e s under bo th normal
and abnormal o p e r a t i n g c o n d i t i o n s . F low v e l o c i t i e s , i n t u r n , d e t e r m i n e p r e s s u r e
l o s s e s t h a t may e a s i l y become a cause o f d i s t u r b a n c e s i n the rma l sys tem
o p e r a t i o n , such as p r e s s u r e l o s s e s i n t h e v a p o u r p i p e s l i n k i n g t h e e v a p o r a t o r
w i t h t h e vacuum p a n s , o r i n t h e p i p e l i n e s between t h e vacuum pans and t h e
c o n d e n s e r . I t i s recommended t o keep t h e p r e s s u r e l o s s between t h e e v a p o r a t o r
and t he vacuum pans be low 0.1 b a r , w h i c h c o r r e s p o n d s t o a c o n d e n s a t i o n -
t e m p e r a t u r e d rop o f l e s s t han 2 K. ( L e t us o b s e r v e t h a t i n bo th cases m e n t i o n e d ,
t h e p i p e d i m e n s i o n s s h o u l d be based on maximum v a p o u r f l o w s . ) F low v e l o c i t i e s
w h i c h can be recommended f o r d i f f e r e n t p i p e d i m e n s i o n s a r e d i s c u s s e d i n t h e
l i t e r a t u r e ( r e f s . 3 , 4 , 6 ) .
( i i ) The s l o p e s o f h o r i z o n t a l s e c t i o n s o f t he p i p e l i n e s a l l o w g r a v i t a t i o n a l f l o w
99
4.3
A . 2 h
4.1
cn O O
4.0
3.9
cn ^. 3.8
o Ε Ιο c
3.7
c o α Ε D (Λ C O
o
3.6
3.5
3.4
(71)
3.3
3.2
94 96 98 100 102 104
A v e r a g e to n o m i n a l d a i l y c a p a c i t y { % )
F i g . 3 . 2 . Fue l consumpt ion v s . a v e r a g e d a i l y c a p a c i t y i n two s u g a r f a c t o r i e s w i t h nominal c a p a c i t i e s o f 2100 t / d ( p o i n t s ) and 5800 t / d ( c r o s s e s ) .
o f t he condensa te t o take p l a c e . The recommended s l o p e o f c o n d e n s a t e l i n e s i s a t
l e a s t 2%. The h o r i z o n t a l s e c t i o n s o f steam and v a p o u r l i n e s s h o u l d be i n c l i n e d
t o o , i n o r d e r t o make i t p o s s i b l e t o d r a i n t h e c o n d e n s a t e f o r m i n g t h e r e d u r i n g
t he s t a r t - u p o f t he therma l s y s t e m .
( i i i ) Condensa te d r a i n a g e equ ipment a t t a c h e d t o steam and v a p o u r l i n e s i s
e s s e n t i a l . T h i s i s a p r e r e q u i s i t e f o r a s a f e s t a r t - u p o f t h e the rma l s y s t e m .
An i n s p e c t i o n o f t he p i p i n g aimed a t c h e c k i n g t h e d i m e n s i o n s and s l o p e s , and
t he a v a i l a b i l i t y o f a u x i l i a r y equ ipment ( s e e a l s o S e c t i o n 7 . 7 . 4 ) , can be
combined w i t h a p r e l i m i n a r y i n s p e c t i o n o f t h e the rma l i n s u l a t i o n and can
p r e f e r a b l y be e x t e n d e d t o i n c l u d e an i n s p e c t i o n o f t he i n s u l a t i o n o f t h e main
f a c t o r y equ ipmen t . W h i l e i t i s r e l a t i v e l y e a s y t o g e t a g e n e r a l q u a l i t a t i v e
100
4.3
0 0 ,4 .0
^ § 39
1 ^-^
3.8 [
120 122 124 126 128 130 132 Average juice draft (% )
F i g . 3 . 3 . Fue l consumpt ion v s . a v e r a g e j u i c e d r a f t i n a 2100 t / d f a c t o r y .
p i c t u r e o f t h e s t a t e o f the rma l i n s u l a t i o n , t h e magn i tude o f h e a t d i s s i p a t i o n
l o s s e s remains unknown u n l e s s a s p e c i a l i n v e s t i g a t i o n i s u n d e r t a k e n . A v e r y
e f f e c t i v e t e c h n i q u e w h i c h can be u t i l i z e d f o r t h i s pu rpose i s t h e r m o g r a p h i c
s u r v e y i n g w i t h t he a i d o f i n f r a - r e d - s e n s i t i v e cameras . The u n d e r l y i n g
p r i n c i p l e s , and examples o f t he a p p l i c a t i o n o f t he rmography i n B r i t i s h s u g a r
f a c t o r i e s , a r e p r e s e n t e d i n t he l i t e r a t u r e ( r e f . 2 ) .
A n o t h e r i m p o r t a n t f e a t u r e o f t h e the rma l sys tem i s i t s a b i l i t y t o g u a r a n t e e
s a f e b o i l e r o p e r a t i o n w i t h o u t u n n e c e s s a r y e n e r g y l o s s e s . N o r m a l l y , t h e
condensa tes f rom the t anks i n t h e f i r s t and second e v a p o r a t o r e f f e c t s a r e
s u p p l i e d as f e e d w a t e r t o t he b o i l e r s . I f t he q u a l i t y o f t he c o n d e n s a t e i n a
c e r t a i n tank becomes u n a c c e p t a b l e w i t h r e g a r d t o s a f e b o i l e r o p e r a t i o n , t h e n t h e
e n t i r e amount o f t he h o t condensa te must be removed f rom t h i s p a r t i c u l a r t ank
and f rom the therma l s y s t e m . When r e p l a c i n g i t by make-up w a t e r , abou t 20 kg o f
normal f u e l must be burned i n o r d e r t o hea t 1 m^ w a t e r t o t h e r e q u i r e d
t e m p e r a t u r e .
T h e r e a re s e v e r a l p o s s i b l e causes o f t he d e g r a d a t i o n o f t he q u a l i t y o f
c o n d e n s a t e :
( a ) Too much o f t he gaseous p r o d u c t s o f therma l decay o f s u c r o s e , o r c e r t a i n
nonsuga rs p r e s e n t i n v a p o u r and d i s s o l v e d i n t he c o n d e n s a t e . T h i s phenomenon
endangers the q u a l i t y o f t he condensa te o b t a i n e d f rom f i r s t - e f f e c t v a p o u r .
( b ) J u i c e p e n e t r a t i n g t he h e a t i n g chambers o f t h e e v a p o r a t o r b o d i e s o r h e a t e r s
t h r o u g h l e a k i n g t u b e s . N o r m a l l y , t h e p r e s s u r e d i f f e r e n c e between t he h e a t i n g
chamber and t h e j u i c e space i n an e v a p o r a t o r body wou ld p r e s s t he c o n d e n s a t e
i n t o j u i c e , bu t t he d i r e c t i o n o f l e a k s may be t e m p o r a r i l y r e v e r s e d due t o
p r e s s u r e f l u c t u a t i o n s .
101
( c ) F i r s t - e f f e c t j u i c e c a r r i e d o v e r as foam o r sma l l d r o p l e t s t o t h e h e a t i n g
chamber o f t h e second e f f e c t . T h i s may be caused by e x c e s s i v e f o a m i n g , t o o h i g h
f l o w v e l o c i t y i n t h e v a p o u r chamber o f t h e f i r s t e f f e c t a n d / o r i n e f f i c i e n t
e n t r a i n m e n t s e p a r a t o r s . I t s h o u l d be emphas ized t h a t no s e p a r a t o r can be
c o n s i d e r e d as f u l l y r e l i a b l e a t t o o h i g h v a p o u r - f l o w v e l o c i t i e s ( e x c e e d i n g
1-1.2 m/s i n t h e v a p o u r c h a m b e r ) . I t may t h e r e f o r e happen t h a t a s e p a r a t o r works
p e r f e c t l y w e l l under normal o p e r a t i n g c o n d i t i o n s , b u t j u i c e c a r r y o v e r o c c u r s a t
a b n o r m a l l y low v a p o u r p r e s s u r e s i n d u c e d by pa ramete r f l u c t u a t i o n s i n t h e the rma l
s y s t e m .
The r i s k o f j u i c e c a r r y o v e r i s a l w a y s p r e s e n t i n t h e h e a t i n g chamber o f t h e
second e v a p o r a t o r e f f e c t . I n the rma l sys tems emp loy i ng v a p o u r c o m p r e s s i o n , t h e
f i r s t e f f e c t may a l s o be e n d a n g e r e d . S p e c i a l p r e c a u t i o n s must be t aken t o
m i n i m i z e t h e consequences o f condensa te p o l l u t i o n i n such sys tems ( s e e S e c t i o n
3 . 4 . 4 ) .
A p a r t f rom t h e immediate causes o f t h e p r e s e n c e o f unwanted s u b s t a n c e s i n
t h e c o n d e n s a t e , i t s h o u l d be p o s s i b l e t o d e t e c t t h e danger and t o r e a c t q u i c k l y ,
p r e v e n t i n g b o i l e r damage. To a l a r g e e x t e n t , t h i s depends on t h e i n s t r u m e n t a t i o n
and m o n i t o r i n g p r o c e d u r e s r e l a t i n g t o t h e c o n d e n s a t e c o n t r o l , as w e l l as on t he
p r o c e d u r e s o f r e p l a c i n g t he d i s c a r d e d c o n d e n s a t e by make-up w a t e r .
3 .1 .3 I n t e r p r e t i n g e x t e r n a l b a l a n c e s
By a n a l y s i n g t he e x t e r n a l e n e r g y b a l a n c e and t h e p r o c e s s mass b a l a n c e
t o g e t h e r , i t becomes p o s s i b l e t o d e t e r m i n e c e r t a i n f a c t o r s c a u s i n g e x c e s s i v e
e n e r g y consumpt ion i n a f a c t o r y . These f a c t o r s may be r e l a t e d t o any o f t h e f o u r
q u e s t i o n s l i s t e d i n S e c t i o n 3 . 1 . 1 . As an e x a m p l e , l e t us c o n s i d e r t he e x t e r n a l
e n e r g y b a l a n c e shown i n C h a p t e r 2 , T a b l e 2 . 4 , t o g e t h e r w i t h t he d e s i g n d a t a on
t he p r o c e s s mass b a l a n c e summarized i n T a b l e 3 .1 .
The consumpt ion o f h e a t i n g steam i s c e r t a i n l y v e r y l a r g e ; when c o n v e r t e d t o
normal s team, i t amounts t o 46.7 kg/100 kg b. The main r e a s o n s can be summar ized
as f o l l o w s :
( i ) The t h i c k - j u i c e c o n c e n t r a t i o n o f 65% DS i s r e l a t i v e l y l o w ; t h i s i s c e r t a i n l y
one o f t he p r o c e s s c o n s t r a i n t s w h i c h c o u l d be m o d i f i e d t o d e c r e a s e t h e t o t a l
h e a t demand. Even a t t h i s c o n c e n t r a t i o n , h o w e v e r , t he mass f l o w o f vacuum-pan
v a p o u r s ( T a b l e 2 . 4 , e n t r y 16) i s t o o l a r g e , e x c e e d i n g t he d e s i g n v a l u e ( T a b l e
3 .1 , e n t r y 35) by n e a r l y 13%. T h i s may be caused by t o o l a r g e a w a t e r i n t a k e t o
t he vacuum pans a n d , p r o b a b l y , t o o much wash w a t e r s u p p l i e d t o t h e c e n t r i f u g a l s .
E x c e s s i v e w a t e r i n t a k e s t o t he s u g a r house can a l s o be r e g a r d e d as a p r o c e s s
c o n s t r a i n t t o be m o d i f i e d .
( i i ) The e l e v a t e d t e m p e r a t u r e i n t h e p r e - l i m i n g tank i s m a i n t a i n e d by r e c y c l i n g
a l a r g e f l o w o f h o t j u i c e a f t e r f i r s t c a r b o n a t a t i o n ( T a b l e 3 .1 , e n t r y 9 ) . T h i s
i s a p r o c e s s c o n s t r a i n t p r e v e n t i n g t h e raw j u i c e f rom b e i n g hea ted by l o w -
102
TABLE 3.1
Summary o f t h e d e s i g n da ta on p r o c e s s mass b a l a n c e o f t he f a c t o r y d e s c r i b e d by t h e e x t e r n a l e n e r g y b a l a n c e shown i n T a b l e 2 . 4 .
No. St ream name T o t a l f l o w
(kg /100 kg b) C o n c e n t r a t i o n
(% DS)
1 C o s s e t t e s , p o l . 17.5% 100.0 2 Wet p u l p 90.0 3 P r e s s e d p u l p 34.3 14.35 4 P r e s s w a t e r 55.7 5 Feed w a t e r ( c o n d e n s a t e ) 49.3 6 Raw j u i c e , p u r i t y 88% 115.0 7 J u i c e t o main l i m i n g 176.4 8 J u i c e t o c a r b o n a t a t i o n I 188.3 9 J u i c e f rom c a r b o n a t a t i o n I r e c y c l e d t o
p r e - 1 i m i n g 40.0 10 J u i c e t o d e c a n t e r 148.0 11 S u b s i d e r s l u d g e I t o vacuum f i l t e r s 21.3 12 ^ S u b s i d e r s l u d g e I r e c y c l e d t o p r e - l i m i n g 15.0 13 J u i c e t o s a f e t y f i l t e r s I 130.2 14 J u i c e t o c a r b o n a t a t i o n I I 129.8 15 J u i c e t o t h i c k e n e r s I I 129.0 16 S u b s i d e r s l u d g e I I r e c y c l e d t o p r e - l i m i n g 5.0 17 T h i n j u i c e t o b u f f e r tank 124.0 18 Water ( c o n d e n s a t e ) added f o r c o n t r o l
p u r p o s e s 5.0 19 T h i n j u i c e t o e v a p o r a t o r 129.0 14.3 20 M i l k - o f - l i m e t o p r e - l i m i n g 1.4 21 M i l k - o f - l i m e t o main l i m i n g 9.9 22 M i l k - o f - l i m e t o c a r b o n a t a t i o n I I 0.6 23 T h i c k j u i c e 24.8 65.0 24 Water ( c o n d e n s a t e ) t o r e m e l t Β 3.8 25 Wash w a t e r t o c e n t r i f u g a l s 1.2 26 Condensa te f rom steam wash 0.2 27 Water ( c o n d e n s a t e ) added t o m a s s e c u i t e C 0.3 28 Condensa te f rom vacuum-pan s teaming 0.2 29 Water ( c o n d e n s a t e ) i n t a k e t o vacuum pans 2.5 30 Condensa te f rom d i r e c t h e a t i n g o f s y r u p s 1.1 31 Sugar A t o d r y i n g 14.2 99.1 32 M o l a s s e s 5.0 33 Vapou rs f rom s e l f - e v a p o r a t i o n o f s y r u p s 0.5 34 Water e v a p o r a t e d i n vacuum pans 18.0
t e m p e r a t u r e v a p o u r s f rom t h e l a s t e v a p o r a t o r e f f e c t o r f rom t h e vacuum p a n s . I f
t h i s c o n s t r a i n t can be e l i m i n a t e d , t hen improved u t i l i z a t i o n o f l o w - t e m p e r a t u r e
v a p o u r s becomes p o s s i b l e .
( i i i ) The v a p o u r f l o w f rom t h e l a s t e v a p o r a t o r e f f e c t t o t he c o n d e n s e r ( T a b l e
2 . 4 , e n t r y 14) i s v e r y l a r g e . I t i s ha rd t o b e l i e v e t h a t t h i s can be c o m p a t i b l e
w i t h t h e i n t e n t i o n o f t he d e s i g n e r o f t h e the rma l sys tem o r w i t h t h e w i s h e s o f
t h e o p e r a t i n g p e r s o n n e l . I f an i n s u f f i c i e n t u t i l i z a t i o n o f t h e l a s t - e f f e c t
v a p o u r f o r h e a t i n g p u r p o s e s had i n d e e d been p l a n n e d , i t wou ld have t o be
i n t e r p r e t e d as a thermal sys tem d e f i c i e n c y r e q u i r i n g immediate a c t i o n . More
l i k e l y a r e t he f o l l o w i n g r e a s o n s :
103
- v a p o u r l e a k s t h r o u g h condensa te d r a i n a g e l i n e s i n t he e v a p o r a t o r a r e a , and
pe rhaps t o o much v a p o u r i s w i t h d r a w n a l o n g w i t h t h e n o n c o n d e n s a b l e gases f rom
t h e p r e c e d i n g e v a p o r a t o r e f f e c t , t o g e t h e r c a u s i n g an u n c o n t r o l l a b l e v a p o u r
i n f l o w t o t h e l a s t e f f e c t ,
- f l u c t u a t i o n s i n t h e t h i n - j u i c e f l o w , i n c o m b i n a t i o n w i t h t o o sma l l a volume o f
t he t h i n - j u i c e tank b e f o r e t he e v a p o r a t o r , t h u s f o r c i n g condensa te i n t a k e s t o
t he j u i c e as t h e j u i c e l e v e l i n t h e t ank f a l l s t o o low o r t h e c o n c e n t r a t i o n o f
t h i c k j u i c e becomes t o o h i g h .
The f a c t o r s named above must be seen as i n d i c a t i o n s t h a t t h e therma l sys tem i s
n o t w o r k i n g as o r i g i n a l l y p l a n n e d because o f d e f i c i e n c i e s o f t h e a u x i l i a r y
equ ipmen t .
( i v ) Poor c o n d i t i o n o f t he the rma l i n s u l a t i o n , d i r e c t hea t d i s s i p a t i o n f rom open
t anks c o n t a i n i n g h i g h - t e m p e r a t u r e med ia , and u n c o n t r o l l a b l e l e a k s o f v a p o u r o r
condensa te cause r e l a t i v e l y l a r g e h e a t l o s s e s t o t h e e n v i r o n m e n t ( T a b l e 2 . 4 ,
e n t r y 2 3 ) . A f a c t - f i n d i n g v i s i t t o t he f a c t o r y i n q u e s t i o n w o u l d p r o b a b l y l e a d
t o t he c o n c l u s i o n t h a t bo th t he the rma l sys tem and t h e p r o c e s s equ ipment s h o u l d
be improved i n t h a t r e s p e c t .
3 .1 .4 I n t e r p r e t i n g e v a p o r a t o r - r e c e i v e r b a l a n c e s
I t i s p e r f e c t l y normal t h a t t h e r e a l steam consumpt ion o f an e v a p o r a t o r i s
1-2 kg/100 kg b g r e a t e r than t h e steam demand d e t e r m i n e d f rom t h e m a s s - b a l a n c e
and e n e r g y - b a l a n c e c a l c u l a t i o n s . T h i s i s a r e s u l t o f f l u c t u a t i o n s o f t h e
o p e r a t i n g pa rame te rs t h a t a r e d i s r e g a r d e d i n t h e b a l a n c e e q u a t i o n s based on t h e
s t e a d y - s t a t e a p p r o a c h . A d i f f e r e n c e l a r g e r t han t h a t named a b o v e , h o w e v e r , may
i n d i c a t e t h a t t h e the rma l sys tem does n o t work as d e s i g n e d and p l a n n e d . I t i s
i m p o s s i b l e t o s t u d y t he r e a s o n s f o r t h i s s i t u a t i o n u s i n g t he e x t e r n a l - b a l a n c e
approach o n l y . I n o r d e r t o o b t a i n more i n f o r m a t i o n on t h e e n e r g y p r o c e s s e s , t h e
mass and e n e r g y b a l a n c e s o f t h e e v a p o r a t o r and v a p o u r r e c e i v e r s s h o u l d be
d e t e r m i n e d and a n a l y s e d .
L e t us c o n s i d e r an e x t e n s i o n o f t he example p r e s e n t e d i n t h e p r e c e d i n g
S e c t i o n . I n F i g . 3 . 4 , t h e v a p o u r and c o n d e n s a t e d i s t r i b u t i o n scheme o f t h e same
f a c t o r y i s shown t o g e t h e r w i t h t h e r e s u l t s o f mass- and h e a t - b a l a n c e
c a l c u l a t i o n s pe r f o rmed u s i n g t h e e v a p o r a t o r - r e c e i v e r a p p r o a c h .
As i t t u r n s o u t , t he c a l c u l a t e d steam demand i s 2.0 kg/100 kg b l e s s t han t h e
consumpt ion i n d i c a t e d i n t h e e x t e r n a l b a l a n c e , w h i l e t h e c a l c u l a t e d mass f l o w o f
l a s t - e f f e c t v a p o u r d i r e c t e d t o t h e c o n d e n s e r i s 3.9 kg/100 kg b l e s s t h a n t h e
e x t e r n a l - b a l a n c e v a l u e . T h i s may be an i n d i c a t i o n o f steam and v a p o u r l e a k s
t h r o u g h t h e steam t r a p s i n t h e c o n d e n s a t e d r a i n a g e l i n e s a n d / o r t h r o u g h t h e
v e n t i n g l i n e s , o r t h r o u g h c e r t a i n v a l v e s w h i c h may be c l o s e d b u t a r e n o t f u l l y
t i g h t . ( A d d i t i o n a l i n d i c a t i o n s o f l e a k s o f steam o r h e a t i n g v a p o u r can be
104
sugar house 1.1
O , 00
Ö σι c % Ε σ Ι ο 'S öl c 3
50.8 A9.0
heater 3.1 ex t r .2 .^ 39.4
127'C
137'"C
vacuum pons 19.9 heaters 9.1
heaters11.4 8.8
115°C
126*C
o I
ö
extr. 0.8
1.5 2.9
lorc
114'C
|115°C h |115°C
90°C
100'C
. Γ—in Λ — 1-(^iorcH^90°c
18.0
JO.O 0j 0.0
tn! CD CM*
86.7 to COndensate receivers
condensate returns
F i g . 3 . 4 . E x c e r p t s f rom mass and h e a t b a l a n c e s o f t he the rma l sys tem p r e v i o u s l y c o n s i d e r e d i n S e c t i o n 3 .1 .3 ( f l o w s g i v e n i n kg/100 kg b ) .
o b t a i n e d by c h e c k i n g t e m p e r a t u r e s and p r e s s u r e s i n t h e e v a p o r a t o r e f f e c t s .
U s u a l l y , v a p o u r l e a k i n g t o a s p e c i f i c e f f e c t i n d u c e s a t e n d e n c y t o w a r d s
t e m p e r a t u r e and p r e s s u r e i n c r e a s e s w h i c h a r e accompanied by r e d u c e d e v a p o r a t i o n .
I f t h e l e a k s a r e s i g n i f i c a n t , t hen i t may be d i f f i c u l t t o m a i n t a i n a h i g h t h i c k -
j u i c e c o n c e n t r a t i o n a t t h e e v a p o r a t o r o u t l e t . )
F i g u r e 3.5 shows t h e r e s u l t s o f mass- and h e a t - b a l a n c e c a l c u l a t i o n s p e r f o r m e d
f o r t h e same therma l sys tem under t h e f o l l o w i n g assump t i ons c o n c e r n i n g t h e steam
and v a p o u r l e a k s :
( i ) E x h a u s t steam l e a k i n g , a t t h e r a t e o f 1 kg/100 kg b , t h r o u g h a steam t r a p i n
t h e f i r s t e f f e c t and a c o n d e n s a t e f l a s h p i p e t o second e f f e c t v a p o u r .
( i i ) E x h a u s t steam l e a k i n g , a t t h e r a t e o f 1 kg/100 kg b , t h r o u g h t h e same steam
t r a p as above and a n o t h e r steam t r a p a t t h e o u t l e t o f t h e c o n d e n s a t e t ank i n t h e
f i r s t e f f e c t , t o t h e condensa te tank i n t h e f o u r t h e f f e c t .
( i i i ) F i r s t - e f f e c t v a p o u r l e a k i n g , a t t h e r a t e o f 1 kg/100 kg b , t h r o u g h a steam
t r a p i n t he second e f f e c t t o s e c o n d - e f f e c t v a p o u r .
( i v ) S e c o n d - e f f e c t v a p o u r l e a k i n g , a t t h e r a t e o f 5 kg/100 kg b , t h r o u g h a
f a u l t y condensa te d r a i n a g e subsys tem i n t h e vacuum-pan s t a t i o n , t o t h i r d - e f f e c t
v a p o u r .
As can be s e e n , t h e c a l c u l a t e d steam demand i s now 52.9 kg/100 kg b and t h e mass
f l o w o f t h e l a s t - e f f e c t v a p o u r t o t h e c o n d e n s e r i s 7.4 kg/100 kg b ; b o t h v a l u e s
105
sugar house 1.1
QO d
I •5 o in
Oil
Ε
I 53.7 51.9
heater 3 J extr. 2 .6 A 0.2
il27.5t
138 C
v a c u u m pans 19 .9-^5.0 heaters 9.1
heaterslLA 4.3
CN II A
W 5 t h \w..sX.^9-\iWc
S i
1lA.5t
126.5 C
CO |Γ- = ·
extr. 0 . 8 1.6
liase
C S l | CD
m.5°c h h i A . s t H » H i 0 4 ' c 1-0-19o°c
9 0 °C
103°C
18 .0
10.0
condensate returns
I I 8 5 . 3 to condensate receivers ~ ^
F i g . 3 . 5 . E x c e r p t s f rom mass and h e a t b a l a n c e s o f t h e the rma l sys tem p r e v i o u s l y c o n s i d e r e d i n S e c t i o n 3 . 1 . 3 , w i t h steam and v a p o u r l e a k s taken i n t o a c c o u n t .
a r e p r e t t y c l o s e t o t he r e a l f i g u r e s .
Steam and v a p o u r l e a k s o c c u r r i n g i n t h e c o n d e n s a t e d r a i n a g e subsys tem
c o n s t i t u t e j u s t one p o s s i b l e t y p e o f d e v i a t i o n f rom t h e c o r r e c t o p e r a t i o n o f t h e
therma l s y s t e m . A n o t h e r t y p e o f d e v i a t i o n i s a s s o c i a t e d w i t h l e a k i n g e v a p o r a t o r
t u b e s . As t h e condensa te i s p r e s s e d i n t o j u i c e , t h e r e q u i r e d t h i c k - j u i c e
c o n c e n t r a t i o n may be i m p o s s i b l e t o m a i n t a i n , b u t t h e r e a s o n w i l l be d i f f i c u l t t o
i d e n t i f y . Depend ing on t h e methods o f b a l a n c e c a l c u l a t i o n s a p p l i e d , t h e mass and
e n e r g y b a l a n c e s d e r i v e d f rom t h e v a l u e s o f t h e pa rame te rs measured may i n d i c a t e ,
f o r examp le , t h a t t h e r e i s a c e r t a i n v a p o u r f l o w e n t e r i n g t h e e v a p o r a t o r (when
u s i n g t h e e v a p o r a t o r - b a l a n c e a l g o r i t h m p r e s e n t e d i n C h a p t e r 2 , a r e v e r s e d v a p o u r
f l o w f rom t h e c o n d e n s e r t o t h e l a s t e v a p o r a t o r e f f e c t may be o b t a i n e d ) .
The i n v e s t i g a t i o n s o f e v a p o r a t o r - r e c e i v e r b a l a n c e s can c o n v e n i e n t l y be
e x t e n d e d by d e t e r m i n i n g t h e o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s i n t h e e v a p o r a t o r
b o d i e s , j u i c e h e a t e r s , vacuum pans and o t h e r e q u i p m e n t . ( T h e methods o f
m o n i t o r i n g t h e n e c e s s a r y d a t a and c a l c u l a t i n g t h e c o e f f i c i e n t s a r e d i s c u s s e d i n
C h a p t e r 7 . ) A b n o r m a l l y low h e a t t r a n s f e r i n t e n s i t i e s may be caused by t h e
f o l l o w i n g f a c t o r s e n c o u n t e r e d i n a l l t y p e s o f e v a p o r a t o r s and h e a t e x c h a n g e r s :
- s c a l e b u i l d - u p a f f e c t i n g h e a t i n g s u r f a c e s ;
- t o o h i g h a condensa te l e v e l i n t h e h e a t i n g chamber , due t o i n e f f i c i e n t
condensa te d r a i n a g e ;
106
- d e c r e a s e d v a p o u r c o n d e n s a t i o n t e m p e r a t u r e , due t o t h e p r e s e n c e o f
noncondensab le g a s e s ;
- d e c r e a s e d v a p o u r c o n d e n s a t i o n t e m p e r a t u r e due t o t h e t h r o t t l i n g o f t h e v a p o u r
f l o w .
I n R o b e r t - t y p e e v a p o r a t o r s , t h e o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s a r e
r e d u c e d when t o o h i g h j u i c e l e v e l s a re m a i n t a i n e d . Too low a h e a t t r a n s f e r
c o e f f i c i e n t i n t he f i r s t e v a p o r a t o r e f f e c t may a l s o i n d i c a t e t h a t t h e j u i c e
t e m p e r a t u r e a t t he e v a p o r a t o r i n l e t i s t o o l o w .
I n m u l t i p l e - p a s s t u b u l a r h e a t e r s , t h e hea t t r a n s f e r i n t e n s i t y may be
d e c r e a s e d when t he j u i c e - s i d e s e a l s between t h e passes a r e l e a k i n g . Leaky s e a l s
may cause t h e j u i c e f l o w i n c e r t a i n passes t o d e c r e a s e , w h i c h i s e q u i v a l e n t t o
a r e d u c t i o n o f t he e f f e c t i v e h e a t i n g s u r f a c e a r e a .
3.2 FUNDAMENTALS OF CORRECT OPERATION OF A THERMAL SYSTEM
3.2.1 Condensa te d r a i n a g e
One o f t he e s s e n t i a l r e q u i r e m e n t s o f p r o p e r steam o r v a p o u r h e a t i n g i s a
r e l i a b l e c o n d e n s a t e d r a i n a g e . W h i l e no condensa te s h o u l d accumu la te i n t h e
h e a t i n g chambers o f t he e q u i p m e n t , as t h i s wou ld r educe t h e e f f e c t i v e o v e r a l l
h e a t t r a n s f e r c o e f f i c i e n t , n e i t h e r s h o u l d v a p o u r o r steam be a l l o w e d t o f l o w
t h r o u g h condensa te l i n e s , as t h i s w o u l d be e q u i v a l e n t t o s h o r t - c i r c u i t i n g t h e
therma l s y s t e m . These c o n d i t i o n s can be s a t i s f i e d p r o v i d i n g t h e e n t i r e d r a i n a g e
subsys tem i s p r o p e r l y d e s i g n e d and m a i n t a i n e d . I m p o r t a n t p o i n t s a r e t h e
d imens ions o f t he components , t he l o c a t i o n s o f t h e c o n d e n s a t e - o u t l e t n o z z l e s ,
t h e p o s i t i o n i n g o f t h e condensa te p i p e s and t h e i r v e n t i n g , t h e t y p e , d i m e n s i o n s
and p o s i t i o n i n g o f t h e steam t r a p s and c o n n e c t i o n o f t h e c o n d e n s a t e p i p e s t o
c o r r e c t l y s e l e c t e d r e c e i v e r s . I n t h e e x i s t i n g l i t e r a t u r e , t h e r e a r e r e l a t i v e l y
few s o u r c e s i n w h i c h p r o p e r a t t e n t i o n has been p a i d t o t h e s e p rob lems ( r e f s .
3 , 4 ) .
The d e t a i l s o f a condensa te d r a i n may v a r y , depend ing on t h e p r e s s u r e l e v e l
i n t h e a s s o c i a t e d h e a t i n g chamber. A t h i g h e r p r e s s u r e s c o r r e s p o n d i n g t o e x h a u s t
steam and f i r s t - o r s e c o n d - e f f e c t v a p o u r , t h e c o n d e n s a t e u s u a l l y f l o w s o u t by
g r a v i t y and t h e escape o f v a p o u r i s p r e v e n t e d by a steam t r a p . F u r t h e r d e t a i l s
may depend on t h e t y p e o f steam t r a p s e l e c t e d . Fou r t y p e s a r e most w i d e l y
a p p l i e d i n b e e t - s u g a r f a c t o r i e s :
- f l o a t t y p e ;
- n o z z l e t y p e ;
- N i e s s n e r co lumns ;
- l e v e l c o n t r o l c i r c u i t s a c t i n g as steam t r a p s .
O t h e r d e s i g n s a r e a l s o known ( r e f s . 3 , 4 ) and new deve lopmen ts have r e c e n t l y been
r e p o r t e d ( r e f . 5 ) .
107
A f l o a t - t y p e steam t r a p as shown i n F i g . 3 . 6 ( a ) i s a v e r y p o p u l a r d e v i c e .
A f l o a t opens o r c l o s e s t h e d i s c h a r g e v a l v e , depend ing on t h e c o n d e n s a t e l e v e l
i n t he t r a p . P r o v i d i n g i t i s w e l l m a i n t a i n e d and i t s s i z e has been c o r r e c t l y
chosen w i t h r e g a r d t o t h e a c t u a l o p e r a t i n g c o n d i t i o n s , t h i s d e v i c e e n s u r e s
a r e l i a b l e condensa te d r a i n a g e even a t l a r g e f l o w c h a n g e s . I t s h o u l d be p o i n t e d
o u t , h o w e v e r , t h a t t h e t r a p t h r o u g h p u t depends n o t o n l y on i t s s i z e , b u t a l s o
on t he p r e s s u r e d i f f e r e n c e between t he i n l e t and o u t l e t n o z z l e s .
M a l f u n c t i o n s o f f l o a t - t y p e steam t r a p s a r i s e m o s t l y because o f wear i n t h e
moving p a r t s . A damaged v a l v e s e a t o r v a l v e head may cause v a p o u r l e a k s , and
a damaged l e v e r sys tem may r e s u l t i n v a l v e l o c k - o u t , c a u s i n g i n s u f f i c i e n t
condensa te d r a i n a g e o r steam l e a k s . I t s h o u l d a l s o be remembered t h a t b e f o r e
normal s t e a m - t r a p o p e r a t i o n i s a t t a i n e d d u r i n g a f a c t o r y s t a r t - u p , v e n t i n g o f
t he t r a p chamber i s n e c e s s a r y . C o n s e q u e n t l y , t h e a p p l i c a t i o n s o f f l o a t - t y p e
steam t r a p s a r e a s s o c i a t e d w i t h a r e q u i r e m e n t f o r a c a r e f u l m a i n t e n a n c e . I t i s
t h e r e f o r e n e c e s s a r y t o i n s t a l l t h e d e v i c e s i n e a s i l y a c c e s s i b l e p l a c e s and t o
e q u i p t he d r a i n a g e l i n e s w i t h s h u t - o f f v a l v e s and b y - p a s s s e c t i o n s . I f t h e s e
c o n d i t i o n s a r e n o t s a t i s f i e d , t hen l e a k y steam t r a p s may e a s i l y become a cause
o f r e d u c e d e v a p o r a t o r t h r o u g h p u t o r i n c r e a s e d steam c o n s u m p t i o n .
( a ) ( b )
3J 2 \
F i g . 3 . 6 . Steam t r a p s : ( a ) f l o a t t y p e , ( b ) n o z z l e t y p e . 1 - i n l e t , 2 - o u t l e t , 3 - v e n t , 4 - v a l v e , 5 - f l o a t , 6 - d i a p h r a g m s , 7 - t h r o u g h p u t a d j u s t m e n t s p i n d l e .
A n o t h e r t y p e o f steam t r a p i s t h e n o z z l e d e s i g n shown i n F i g . 3 . 6 ( b ) . I t s
w o r k i n g p r i n c i p l e c o n s i s t s o f t h r o t t l i n g t h e v a p o u r f l o w w h i l e a l l o w i n g f o r a
r e l a t i v e l y f r e e c o n d e n s a t e f l o w . The t h r o t t l i n g e f f e c t i s o b t a i n e d i n a n o z z l e
e q u i p p e d w i t h a sys tem o f d iaphragms w i t h h o l e s o f a r e a s a d j u s t e d t o t h e
o p e r a t i n g c o n d i t i o n s . T h i s d e v i c e i s sma l l and e a s y t o i n s t a l l , and as t h e r e a r e
no c o n s t a n t l y moving p a r t s , a h i g h mechan ica l r e l i a b i l i t y i s e n s u r e d . H o w e v e r ,
t he e f f i c i e n c y o f t he steam t r a p may v a r y w i t h v a r i a b l e o p e r a t i n g c o n d i t i o n s .
108
and f o r condensa te f l o w s w e l l be low t h e i r nominal v a l u e , v a p o u r l e a k s a r e
u n a v o i d a b l e .
I n c e r t a i n d e s i g n s , i t i s p o s s i b l e t o a d j u s t t h e p o s i t i o n o f t he d iaphragms
f o r changed t h r o u g h p u t . T h r o t t l i n g t h e f l o w t o o much, h o w e v e r , may cause t h e
condensa te l e v e l i n t he h e a t i n g chamber t o r i s e e x c e s s i v e l y . N o z z l e - t y p e steam
t r a p s a r e t h e r e f o r e p r e f e r r e d where condensa te d r a i n a g e f rom equ ipment hea ted
w i t h an a lmos t c o n s t a n t steam f l o w , l i k e e v a p o r a t o r s , i s r e q u i r e d .
Vapour l e a k s caused by r a p i d f l o w changes o f s h o r t d u r a t i o n can be e l i m i n a t e d
i f t he n o z z l e - t y p e t r a p i s p r e c e d e d by a w a t e r s e a l i n a U - t u b e , F i g . 3 . 7 ( a ) .
A t r educed f l o w , t he condensa te l e v e l i n t h e i n l e t l e g o f t h e U - t u b e i s l o w e r e d ,
r e d u c i n g t h e p r e s s u r e d i f f e r e n c e a c r o s s t h e steam t r a p and t h u s r e d u c i n g i t s
t h r o u g h p u t . T h i s s o l u t i o n can be recommended f o r t h e c o n n e c t i o n s between t h e
condensa te t anks c o l l e c t i n g t h e c o n d e n s a t e s f rom t h e i n d i v i d u a l e v a p o r a t o r
e f f e c t s . S i m i l a r a r rangemen ts a r e a l s o n e c e s s a r y when a p p l y i n g n o z z l e - t y p e steam
t r a p s i n t h e condensa te d r a i n s a t t a c h e d t o b a t c h vacuum p a n s , where p e r i o d i c
changes o f t he condensa te f l o w o c c u r . T h i s a p p l i c a t i o n case i s s c h e m a t i c a l l y
shown i n F i g . 3 . 7 ( b ) .
( a )
Ε in
I- l . J
(b )
Ε
i - t h e f f e c t v a p o u r
1 t o ( i * l ) t h e f f e c t
1 ' "
L.J
v a p o u r
F i g . 3 . 7 . Recommended a r rangemen ts o f condensa te d r a i n s f e a t u r i n g n o z z l e - t y p e steam t r a p s : ( a ) between two condensa te t a n k s , ( b ) between a vacuum pan and a condensa te m a n i f o l d . 1 - steam t r a p , 2 - n o n - r e t u r n v a l v e , 3 - vacuum p a n , 4 - condensa te m a n i f o l d .
A N i e s s n e r column i s a s i m p l e and s e l f - r e g u l a t i n g d e v i c e r e q u i r i n g o n l y t h a t
enough space i s a v a i l a b l e f o r i t s i n s t a l l a t i o n . The p l a c i n g o f t h e column
r e l a t i v e t o t he h e a t i n g chamber i s shown i n F i g . 3 . 8 . The e f f e c t i v e h e i g h t Η
s h o u l d be l a r g e enough t o g u a r a n t e e t h a t t h e w a t e r s e a l can work p r o p e r l y even
i f t he p r e s s u r e d i f f e r e n c e between t h e h e a t i n g chamber and t h e c o l u m n ' s v a p o u r
chamber i n c r e a s e s due t o pa ramete r f l u c t u a t i o n s o r t o f o u l e d h e a t i n g s u r f a c e s
i n t h e e v a p o r a t o r s t a t i o n . Component s h o u l d be n o t l e s s t han 3 m t o
compensate f o r t h e p r e s s u r e f l u c t u a t i o n s , and component s h o u l d be sma l l
enough t o p r e v e n t t he condensa te f rom a c c u m u l a t i n g i n t he h e a t i n g chamber a t
109
c o n d e n s a t e
F i g . 3 .8 . Scheme o f a condensa te d r a i n a g e l i n e f e a t u r i n g a N i e s s n e r co lumn. 1 - e v a p o r a t o r , 2 - l e v e l g a u g e , 3 - t h r o t t l i n g v a l v e .
a r e d u c e d p r e s s u r e d i f f e r e n c e a c r o s s t h e co lumn . These r e q u i r e m e n t s can be
s t a t e d i n t h e form o f i n e q u a l i t i e s
where Δρ and Δρ . a r e t h e maximum and minimum p r e s s u r e d i f f e r e n c e s , γ i s max mi η c
t h e d e n s i t y o f c o n d e n s a t e i n t h e c e n t r a l p i p e , and g i s t h e a c c e l e r a t i o n o f
g r a v i t y .
I f t h e h e i g h t i s t o o s m a l l , t h e e f f i c i e n c y o f t h e column can be improved by
i n s t a l l i n g a t h r o t t l i n g v a l v e a t t h e c o n d e n s a t e i n l e t . T h i s causes t h e
condensa te l e v e l i n t h e i n l e t p i p e t o r i s e , t h u s c r e a t i n g an a d d i t i o n a l
s a f e g u a r d a g a i n s t v a p o u r e n t e r i n g t he co lumn .
A l l t h e s h o r t c o m i n g s o f t h e c l a s s i c a l steam t r a p s can be a v o i d e d by a p p l y i n g
a c o n t r o l c i r c u i t c o n s i s t i n g o f a l e v e l t r a n s d u c e r , c o n t r o l l e r and c o n t r o l
v a l v e . I t i s a r r a n g e d t o m a i n t a i n a s t a b l e w a t e r s e a l i n t h e d r a i n a g e l i n e . Such
a d e v i c e i s h i g h l y r e l i a b l e , and e a s y t o o p e r a t e and m a i n t a i n . When used i n
a condensa te d r a i n a g e subsys tem c o n n e c t e d t o a m u l t i p l e - e f f e c t e v a p o r a t o r , i t
can e l i m i n a t e t h e steam o r v a p o u r l e a k s between t h e e v a p o r a t o r e f f e c t s
c o m p l e t e l y . A q u a d r u p l e - e f f e c t e v a p o r a t o r w i t h a c o n d e n s a t e d r a i n a g e subsys tem
emp loy ing t h i s i d e a i s shown s c h e m a t i c a l l y i n F i g . 3 . 9 . The c o n d e n s a t e d r a i n a g e
f rom the f i r s t and second e f f e c t s , and t he c o n d e n s a t e f l o w between t h e
condensa te t a n k s , a r e l e v e l - c o n t r o l l e d .
110
to main condensate tank
condensate re turned from heaters and vacuum pans
F i g . 3 . 9 . Scheme o f a condensa te d r a i n a g e subsys tem f e a t u r i n g l e v e l - c o n t r o l l e d h y d r a u l i c s e a l s and condensa te t a n k s .
I n a condensa te d r a i n c o n n e c t e d t o a h e a t i n g chamber o p e r a t e d a t a low
p r e s s u r e , t he escape o f v a p o u r can be e f f e c t i v e l y p r e v e n t e d w i t h o u t u s i n g a
steam t r a p ; i t i s enough t o c o n n e c t t he d r a i n a g e p i p e t o t h e bot tom p a r t o f a
c l o s e d c o n d e n s a t e tank i n w h i c h a c e r t a i n minimum l e v e l o f t he c o n d e n s a t e i s
a l w a y s m a i n t a i n e d . Sometimes t h e d r a i n a g e p i p e can be formed as a U - t u b e , o r
s i p h o n , w i t h t h e two l i q u i d columns i n t h e l e g s o f t he U - t u b e a c t i n g as a
p r e s s u r e - b a l a n c i n g d e v i c e and a h y d r a u l i c s e a l . The s i p h o n can a l s o be used t o
l e t t h e condensa te f l o w f rom one v e s s e l t o a n o t h e r when a d e f i n i t e p r e s s u r e
d i f f e r e n c e between t he v e s s e l s i s t o be m a i n t a i n e d . I t i s i m p o r t a n t t o choose
t h e h e i g h t o f t h e s i p h o n w i t h a s u f f i c i e n t s a f e t y marg in o f a t l e a s t 50%, making
i t p o s s i b l e t o n e u t r a l i z e t h e p r e s s u r e f l u c t u a t i o n s and t h e condensa te f l a s h i n
t h e l o w - p r e s s u r e l e g o f t h e U - t u b e . I n o r d e r t o a v o i d t h e r i s k o f t h e l i q u i d
column b e i n g d e s t r o y e d by t he f l a s h v a p o u r , t he d i a m e t e r o f t h e l o w - p r e s s u r e l e g
s h o u l d be s u f f i c i e n t l y l a r g e t o l i m i t t h e f l o w v e l o c i t y o f t h e c o n d e n s a t e
(assumed t o be f r e e o f v a p o u r b u b b l e s ) t o abou t 0.6 m/s .
I n t he condensa te d r a i n a g e subsys tem shown i n F i g . 3 . 9 , t h e f l o w o f
c o n d e n s a t e s f rom t h e t h i r d and f o u r t h e v a p o r a t o r e f f e c t s and f rom t h e j u i c e
h e a t e r s s u p p l i e d w i t h s e c o n d - , t h i r d - and f o u r t h - e f f e c t v a p o u r s i s
g r a v i t a t i o n a l . As t he condensa te t a n k s a r e l e v e l - c o n t r o l l e d , t h e d r a i n a g e p i p e s
can be c o n n e c t e d t o t h e condensa te t a n k s w i t h o u t u s i n g s i p h o n s .
S p e c i a l condensa te d r a i n a g e p rob lems a r e a s s o c i a t e d w i t h i n t e r m i t t e n t
o p e r a t i o n o f t he b a t c h vacuum p a n s , t h e l a r g e d i s t a n c e between t h e pans and t h e
in
e v a p o r a t o r be ing a c o n t r i b u t i n g f a c t o r . The r e a s o n i s t h a t t h e p r e s s u r e i n t h e
h e a t i n g chambers o f t h e i n d i v i d u a l pans i s s u b j e c t t o l a r g e f l u c t u a t i o n s . D u r i n g
s teaming and o t h e r a u x i l i a r y phases o f t h e b o i l i n g c y c l e , t h e v a p o u r s u p p l y
v a l v e i s c l o s e d w h i l e t he v e n t i n g v a l v e rema ins o p e n , t h i s c a u s i n g t h e p r e s s u r e
i n t h e h e a t i n g chamber t o f a l l . D u r i n g t h e s y r u p - t h i c k e n i n g p h a s e , when t h e h e a t
demand i s l a r g e s t , a l a r g e v a p o u r f l o w r e s u l t s i n a c o n s i d e r a b l e p r e s s u r e l o s s
i n t he s u p p l y l i n e . As t h e v a p o u r f l o w i s much s m a l l e r d u r i n g t h e c r y s t a l - g r o w t h
p h a s e , t he c o r r e s p o n d i n g p r e s s u r e l o s s i s a l s o s m a l l e r . As a c o n s e q u e n c e , even
i f a l l t h e vacuum pans a r e s u p p l i e d w i t h v a p o u r f rom t h e same e v a p o r a t o r e f f e c t ,
t he p r e s s u r e d i f f e r e n c e between t he h e a t i n g chambers o f two vacuum p a n s , one o f
them i n t h e s y r u p - t h i c k e n i n g and t h e o t h e r i n t h e c r y s t a l - g r o w t h p h a s e , may
e a s i l y a t t a i n v a l u e s abou t 0.5 b a r .
I f a condensa te d r a i n c a n n o t a d e q u a t e l y r e s p o n d t o p r e s s u r e f l u c t u a t i o n s ,
t h e r e may be a t e n d e n c y t o w a r d s c o n d e n s a t e a c c u m u l a t i o n i n t h e h e a t i n g chamber
d u r i n g t h e p e r i o d s o f d e c r e a s e d p r e s s u r e . On t h e o t h e r h a n d , when t h e p r e s s u r e
i s r a i s e d , a v a p o u r l e a k may o c c u r i n t h e c o n d e n s a t e l i n e . D r a i n a g e m a l f u n c t i o n s
a re p o s s i b l e even w i t h c o r r e c t l y w o r k i n g steam t r a p s , when t h e d e v i c e s a r e
i n s t a l l e d t o o h i g h ( r e l a t i v e t o t h e h e a t i n g chamber) o r t h e i r o u t l e t s a r e
c o n n e c t e d t o a m a n i f o l d o f t o o smal l a d i a m e t e r .
L e t us a n a l y s e t h e o p e r a t i o n o f a c o n d e n s a t e d r a i n a g e subsys tem e q u i p p e d w i t h
f l o a t - t y p e steam t r a p s , as shown i n F i g . 3 .10 . The c o n d e n s a t e m a n i f o l d i s
c o n n e c t e d t o t h e c o n d e n s a t e tank i n t h e e v a p o r a t o r e f f e c t n e x t t o t h e one
s u p p l y i n g t h e h e a t i n g v a p o u r . Even though t h e c o n d e n s a t e l e a v i n g t h e h e a t i n g
i-th effect vapour
\ Ζ 7 to( i^1) th effect^ vapour
F i g . 3 .10 . P r i n c i p l e o f c o n d e n s a t e d r a i n a g e f rom vacuum pans u s i n g f l o a t - t y p e steam t r a p s and a c o n d e n s a t e m a n i f o l d c o n n e c t e d t o a t a n k .
chambers o f t h e vacuum pans may be s u b c o o l e d , t h a t i s , i t s t e m p e r a t u r e may be
l o w e r t han t h a t o f t he h e a t i n g v a p o u r , i t b e g i n s t o b o i l as soon as i t has
passed t he t r a p and i s e x p o s e d t o t h e p r e s s u r e c o r r e s p o n d i n g t o t h e n e x t
e v a p o r a t o r e f f e c t . The r e s u l t i n g i n c r e a s e o f a v e r a g e s p e c i f i c vo lume i n d u c e s an
112
i n c r e a s e d f l o w v e l o c i t y and a l a r g e r p r e s s u r e l o s s i n t h e m a n i f o l d , t h i s l e a d i n g
t o a r e d u c e d sys tem t h r o u g h p u t and a t e n d e n c y t o w a r d s c o n d e n s a t e a c c u m u l a t i o n i n
t h e i n d i v i d u a l d r a i n s and h e a t i n g chambers .
The s i t u a t i o n d e s c r i b e d can be p r e v e n t e d by i n c r e a s i n g t h e h e i g h t o f t h e
condensa te l e g i n t h e l i n e c o n n e c t i n g t h e h e a t i n g chamber and t h e steam t r a p ,
t h a t i s , by i n s t a l l i n g t h e steam t r a p a t l e a s t 5-6 m be low t h e c o n d e n s a t e o u t l e t
n o z z l e . I n l a r g e - c a p a c i t y s u g a r f a c t o r i e s where t h e vacuum pans must be l o c a t e d
a t a r e l a t i v e l y l ong d i s t a n c e f rom the e v a p o r a t o r , i t i s a d v i s a b l e t o i n s t a l l
a s e p a r a t e condensa te tank c o l l e c t i n g t he c o n d e n s a t e f rom the vacuum p a n s .
Mutua l i n t e r f e r e n c e between t h e pans can be p r e v e n t e d by e l i m i n a t i n g t h e
m a n i f o l d , t h a t i s , c o n n e c t i n g t h e i n d i v i d u a l d r a i n a g e l i n e s d i r e c t l y t o t h e
condensa te t a n k .
Among o t h e r d r a i n a g e v e r s i o n s , a s o l u t i o n based on t h e a p p l i c a t i o n o f a n o n
r e t u r n v a l v e i n s t e a d o f a steam t r a p i s p a r t i c u l a r l y s e n s i t i v e t o t h e r e l a t i o n
between t he l e v e l d i f f e r e n c e and t h e magn i tude o f p r e s s u r e f l u c t u a t i o n s .
R e l i a b l e o p e r a t i o n can be a c h i e v e d u s i n g t h e c o n f i g u r a t i o n shown i n F i g . 3 .11 ,
where t he l e v e l - c o n t r o l p r i n c i p l e i s i n t r o d u c e d t o e l i m i n a t e t h e v a p o u r l e a k s
accompany ing p r e s s u r e peaks i n t h e h e a t i n g chambers o f t he p a n s .
10-12m
F i g . 3 .11. Scheme o f condensa te d r a i n a g e f rom vacuum pans u s i n g n o n - r e t u r n v a l v e s and a l e v e l - c o n t r o l l e d condensa te t a n k .
3 .2 .2 V e n t i n g o f n o n c o n d e n s a b l e s
The e l e v a t e d j u i c e t e m p e r a t u r e i n t h e e v a p o r a t o r causes the rma l decay o f
am ides , b i c a r b o n a t e s , i n v e r t s u g a r and s u c r o s e . As a r e s u l t , ammonia and c a r b o n
d i o x i d e a r e p r o d u c e d . I n a d d i t i o n , p r e s s u r e d r o p s a s s o c i a t e d w i t h j u i c e f l o w
between t he c o n s e c u t i v e e v a p o r a t o r e f f e c t s c o n t r i b u t e t o t h e l i b e r a t i o n o f a i r
d i s s o l v e d i n t h e j u i c e . The p r e s e n c e o f t h e s e gases (known as n o n c o n d e n s a b l e s )
i n h e a t i n g v a p o u r s s h o u l d be r e g a r d e d as an i m p o r t a n t f a c t o r t o be k e p t under
c o n t r o l .
I t i s d i f f i c u l t t o e v a l u a t e t h e amount o f n o n c o n d e n s a b l e s p r o d u c e d i n t h e
e v a p o r a t o r . The amount o f ammonia was e s t i m a t e d a t 0.015 kg/100 kg b by C l a a s s e n
113
( r e f . 7) and 0.005-0.017 kg/100 kg b by D o b r z y c k i ( r e f . 8 ) . The t o t a l amount o f
noncondensab les was e s t i m a t e d a t 0 .024-0.032 kg/100 kg b by Gorokh ( r e f . 9 ) .
An e s t i m a t e g i v e n by Koren ( r e f . 1 0 ) o f t h e c o n c e n t r a t i o n o f n o n c o n d e n s a b l e s i n
t h i r d - e f f e c t v a p o u r f rom a q u a d r u p l e - e f f e c t e v a p o r a t o r was 2 .0-5 .6%. I t seems
t h a t t he a c t u a l f i g u r e s c h a r a c t e r i z i n g t h e p r o c e s s i n g o f b e e t s o f i n f e r i o r
q u a l i t y ( f o l l o w i n g p r o l o n g e d s t o r a g e o r f r o s t damage) may be even h i g h e r .
A t a c o n s t a n t t o t a l p r e s s u r e o f t h e g a s / v a p o u r m i x t u r e i n t h e h e a t i n g chamber
o f an e v a p o r a t o r b o d y , t h e b u i l d - u p o f n o n c o n d e n s a b l e s causes t he p a r t i a l
p r e s s u r e o f v a p o u r t o d e c r e a s e . As a r e s u l t , t h e c o n d e n s a t i o n t e m p e r a t u r e
d e c r e a s e s and t h e e f f e c t i v e t e m p e r a t u r e d i f f e r e n c e between h e a t i n g v a p o u r and
j u i c e i s r e d u c e d . L e t us o b s e r v e t h a t when a t y p i c a l t e m p e r a t u r e d i f f e r e n c e o f
10 Κ i s r e d u c e d by as l i t t l e as 1 .5-2.0 K, t h e r e s u l t i n g r e d u c t i o n o f t h e amount
o f hea t t r a n s f e r r e d i s 15-20%. More d a t a i l l u s t r a t i n g t h e impac t o f
noncondensab les on t h e t e m p e r a t u r e d i f f e r e n c e a f f e c t i n g t he hea t t r a n s f e r a r e
p r e s e n t e d i n T a b l e 3 . 2 .
I t s h o u l d be p o i n t e d o u t t h a t t h e r e a r e a l s o o t h e r d i s a d v a n t a g e o u s
consequences o f t h e p r e s e n c e o f n o n c o n d e n s a b l e s . W h i l e t he f i l m c o e f f i c i e n t o f
h e a t t r a n s f e r a t a h e a t i n g s u r f a c e where t h e c o n d e n s a t i o n o f pu re steam t a k e s
p l a c e i s o f t h e o r d e r o f 10 000 W / ( m ^ K ) , i t does n o t e x c e e d 100 W/(m^K) a t
a s u r f a c e exposed t o a i r . C o n s e q u e n t l y , when t h e s u r f a c e i s exposed t o a m i x t u r e
o f v a p o u r and n o n c o n d e n s a b l e s , t h e f i l m c o e f f i c i e n t o f h e a t t r a n s f e r may be
s u b s t a n t i a l l y r e d u c e d . A t 0 .5-1.0% n o n c o n d e n s a b l e s i n t h e m i x t u r e , t h e r e d u c t i o n
o f t he c o e f f i c i e n t r e l a t i v e t o i t s p u r e - v a p o u r v a l u e i s abou t 50-60%. G e n e r a l l y ,
t h e f i l m c o e f f i c i e n t o f hea t t r a n s f e r i s i n v e r s e l y p r o p o r t i o n a l t o t h e s q u a r e
r o o t o f t h e mass c o n c e n t r a t i o n o f n o n c o n d e n s a b l e s ( r e f . 1 2 ) .
I n o r d e r t o p r e v e n t an e x c e s s i v e c o n c e n t r a t i o n o f n o n c o n d e n s a b l e s , t h e g a s /
v a p o u r m i x t u r e s h o u l d be c o n t i n u o u s l y v e n t e d . W h i l e i t i s p o p u l a r i n p r a c t i c e t o
d i s c h a r g e t h e m i x t u r e t o t h e c o n d e n s e r o r d i r e c t l y t o t h e a t m o s p h e r e , cascade
v e n t i n g between c o n s e c u t i v e e v a p o r a t o r e f f e c t s has been recommended by some
a u t h o r s . The a d v a n t a g e s o f t h i s method a r e h i g h l y d u b i o u s because o f t h e
a c c u m u l a t i o n o f n o n c o n d e n s a b l e s i n f i n a l e v a p o r a t o r e f f e c t s , t h i s making i t
n e c e s s a r y t o v e n t t o t he c o n d e n s e r anyway . A n o t h e r consequence o f cascade
v e n t i n g i s t h a t a t c o n s t a n t h e a t i n g - v a p o u r demand i n t h e the rma l s y s t e m , w a t e r
e v a p o r a t i o n i n t h e e v a p o r a t o r i s r e d u c e d because t h e v a p o u r v e n t e d r e p l a c e s
a p a r t o f t h e v a p o u r w h i c h w o u l d o t h e r w i s e be g e n e r a t e d i n t he a c t u a l e v a p o r a t o r
e f f e c t i t s e l f .
The most e f f e c t i v e method t o v e n t t h e e v a p o r a t o r b o d i e s i s t o l e t t h e e n t i r e
amount o f v a p o u r f rom the p r e c e d i n g e f f e c t f l o w t h r o u g h t h e h e a t i n g chamber i n
t he n e x t e f f e c t . As a p a r t o f t he n o n c o n d e n s a b l e s becomes d i s s o l v e d i n t h e
c o n d e n s a t e , t h e r e s t i s s u p p l i e d i n t h e h e a t i n g v a p o u r t o t h e j u i c e h e a t e r s .
114
TABLE 3.2
R e d u c t i o n o f t h e e f f e c t i v e t e m p e r a t u r e d i f f e r e n c e due t o t h e p r e s e n c e o f a i r i n t h e c o n d e n s i n g v a p o u r , as a f u n c t i o n o f mass c o n c e n t r a t i o n o f a i r , t o t a l p r e s s u r e and t h e o r e t i c a l t e m p e r a t u r e d i f f e r e n c e A t .
( b a r ) ( K ) 2.5 5 7.5 10
0.3 5 11.5 22.9 34.8 48.1 10 5.8 11.5 17.4 24.0 15 3.8 7.6 11.6 16.0 20 2.9 5.7 8.7 12.0
0.5 5 12.6 25.4 39.0 52.1 10 6.3 12.7 19.5 26.0 15 4 .2 8.5 13.0 17.4 20 3.2 6.4 9.8 13.0
0.75 5 13.3 27.2 41.2 55.0 10 6.7 13.6 20.6 27.5 15 4 .4 9.1 13.7 18.3 20 3.3 6.8 10.3 13.8
1.0 5 14.7 28.6 43.9 58.4 10 7.3 14.3 21.9 29.2 15 4 .9 9.5 14.6 19.5 20 3.7 7.1 11.0 14.7
1.5 5 15.2 30.9 46.6 62.4 10 7.6 15.5 23.3 31.2 15 5.1 10.3 15.5 20.8 20 3.8 7.8 11.7 15.6
2.0 5 15.8 32.2 48.8 66.0 10 7.9 16.1 24.4 33.0 15 5.3 10.7 16.3 22.0 20 4 .0 8.1 12.2 16.5
2.5 5 16.6 33.6 51.0 69.0 10 8.3 16.8 25.5 34.5 15 5.5 11.2 17.0 23.0 20 4 .2 8.2 12.8 17.9
3.0 5 17.0 35.0 52.6 71.2 10 8.5 17.5 26.3 35.6 15 5.7 11.7 17.5 23.7 20 4 .3 8.8 13.5 17.8
3.5 5 17.8 35.6 54.0 73.2 10 8.9 17.8 27.0 36.6 15 5.9 11.9 18.0 24.4 20 4 .5 8.9 13.5 18.3
vacuum pans and o t h e r r e c e i v e r s . An i n c r e a s e d c o n c e n t r a t i o n o f n o n c o n d e n s a b l e s
i n t h e h e a t i n g chambers o f h e a t r e c e i v e r s causes l e s s i n c o n v e n i e n c e t h e r e t han
i n t h e e v a p o r a t o r , because t h e a c t u a l t e m p e r a t u r e d i f f e r e n c e s a r e l a r g e r t han
t h o s e c h a r a c t e r i s t i c o f t h e e v a p o r a t o r b o d i e s .
A v e n t i n g sys tem based on v a p o u r w i t h d r a w a l f rom t h e h e a t i n g chambers o f
115
a q u a d r u p l e - e f f e c t e v a p o r a t o r i s shown s c h e m a t i c a l l y i n F i g . 3.12 ( r e f . 6 ) . The
e n t i r e amount o f n o n c o n d e n s a b l e s l i b e r a t e d i n t h e f i r s t e f f e c t and abou t h a l f o f
t he gases f rom t h e second e f f e c t a r e d i r e c t e d t o t h e h e a t e r b e f o r e t h e second
c a r b o n a t a t i o n . T h i r d - e f f e c t v a p o u r and n o n c o n d e n s a b l e s w i t h d r a w n f rom t h e
h e a t i n g chamber o f t h e f o u r t h e f f e c t a r e s u p p l i e d t o t h e h e a t e r b e f o r e h o t main
l i m i n g . I n o r d e r t o m i n i m i z e v a p o u r l o s s e s when v e n t i n g t h e h e a t i n g chambers o f
t h e h e a t e r s named, a u t o m a t i c c o n t r o l can be a p p l i e d by u t i l i z i n g t h e phenomenon
o f c o n d e n s a t i o n t e m p e r a t u r e changes accompany ing t h e changes o f gas
c o n c e n t r a t i o n . The s i g n a l f rom t h e j u i c e - t e m p e r a t u r e c o n t r o l l e r i s a c t i n g , v i a
c o r r e c t i o n e l e m e n t s , on a c o n t r o l v a l v e i n t h e v a p o u r s u p p l y l i n e and a n o t h e r i n
t h e v e n t i n g l i n e . The c o r r e c t i o n e lemen ts a r e t r a n s f o r m i n g t h e s i g n a l i n such
a way t h a t a t t o o h i g h a j u i c e t e m p e r a t u r e , t h e v e n t i n g v a l v e c l o s e s f i r s t and
t h e v a p o u r v a l v e s e c o n d . A t t o o low a j u i c e t e m p e r a t u r e , t h e v a p o u r v a l v e opens
f i r s t and t h e v e n t i n g v a l v e s e c o n d .
Media heated:
α - thin juice
b - clear juice
c - limed juice
steam iL
Pi to the
condenser
F i g . 3 .12 . Scheme o f a v e n t i n g subsys tem f e a t u r i n g a u t o m a t i c c o n t r o l o f t h e d i s c h a r g e o f n o n c o n d e n s a b l e s f rom t h e h e a t i n g chambers o f j u i c e h e a t e r s .
P r a c t i c a l e x p e r i e n c e w i t h t h e above s o l u t i o n i s s a t i s f a c t o r y . N o r m a l l y , t h e
v e n t i n g v a l v e opens o n l y t e m p o r a r i l y , a t t o o low j u i c e t e m p e r a t u r e s i n d u c e d by
j u i c e - f l o w f l u c t u a t i o n s . When t h e v e n t i n g v a l v e c l o s e s , t h e c o n c e n t r a t i o n o f
n o n c o n d e n s a b l e s i n t h e h e a t i n g chamber i s i n c r e a s e d t o a l e v e l e n a b l i n g t h e
gases t o become d i s s o l v e d i n t h e c o n d e n s a t e and d r a i n e d w i t h o u t v a p o u r l o s s .
Howeve r , t h e c o n d e n s a t e s h o u l d be d i r e c t e d t o t h e ammonia-water t ank r a t h e r t han
t o t he condensa te t a n k , because t h e gases l i b e r a t e d by t h e c o n d e n s a t e f l a s h may
o t h e r w i s e r e - e n t e r t h e e v a p o r a t o r .
A n o t h e r c o n t r o l method f o r t h e v e n t i n g o f n o n c o n d e n s a b l e s f rom t h e h e a t i n g
chambers o f e v a p o r a t o r b o d i e s has been t e s t e d i n t h e P o l i s h s u g a r i n d u s t r y
116
( r e f . 1 3 ) . The b u i l d - u p o f n o n c o n d e n s a b l e s t a k i n g p l a c e i n a h e a t i n g chamber can
be d e t e c t e d by compar ing t he t e m p e r a t u r e s o f t h e h e a t i n g v a p o u r f l o w i n g i n t h e
i n l e t n o z z l e and t h a t c o n d e n s i n g a t t h e h e a t i n g s u r f a c e . The s i g n a l f rom a
s p e c i a l t r a n s m i t t e r measur ing t h e t e m p e r a t u r e d i f f e r e n c e may be s u p p l i e d t o an
a u t o m a t i c c o n t r o l l e r open ing t h e v e n t i n g v a l v e .
3 .2 .3 S c a l e p r e v e n t i o n and removal
A c o n s i d e r a b l e q u a n t i t y o f t h e i m p u r i t i e s p r e s e n t i n t h i n j u i c e becomes l e s s
s o l u b l e as t he c o n c e n t r a t i o n o f t h e j u i c e r i s e s , and some o f t h e s e i m p u r i t i e s
may d e p o s i t on t h e h e a t i n g s u r f a c e s o f t he e v a p o r a t o r b o d i e s , f o r m i n g a h a r d
s c a l e . Be ing a poo r c o n d u c t o r o f h e a t , t h e s c a l e d e c r e a s e s t h e h e a t t r a n s f e r
c o e f f i c i e n t s a c r o s s t h e h e a t i n g s u r f a c e s . C o n s e q u e n t l y , t h e e v a p o r a t o r
t h r o u g h p u t i s r e d u c e d and can be a d j u s t e d t o t h e r e q u i r e d v a l u e o n l y i f t h e
t e m p e r a t u r e d i f f e r e n c e s a re i n c r e a s e d , w i t h i n c r e a s e d steam consumpt ion as a
r e s u l t .
The d i s a d v a n t a g e o u s e f f e c t s o f s c a l e f o r m a t i o n depend on t h e the rma l
c o n d u c t i v i t y o f d e p o s i t s and t he s c a l e t h i c k n e s s . The g o v e r n i n g e q u a t i o n i s
k = l / ( l / a ^ + ό / λ + ό ^ / λ ^ + Ι / α ^ ) ( 3 . 4 )
where k i s t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t , a-j and a r e t h e f i l m
c o e f f i c i e n t s o f h e a t t r a n s f e r on t h e j u i c e s i d e and t he v a p o u r s i d e ,
r e s p e c t i v e l y , δ and a re t he t h i c k n e s s e s o f t h e tube w a l l and t h e d e p o s i t
l a y e r , r e s p e c t i v e l y , and λ and a r e t h e the rma l c o n d u c t i v i t i e s o f t h e t u b e
m a t e r i a l and d e p o s i t s , r e s p e c t i v e l y .
The therma l c o n d u c t i v i t y o f d e p o s i t s may v a r y i n t h e range 0 .08-2 .00 W / ( m K ) ,
depend ing on t h e chemica l c o m p o s i t i o n and s t r u c t u r e o f t h e d e p o s i t e d s u b s t a n c e .
T h e r e f o r e , a v e r y t h i n s c a l e may be enough t o a f f e c t t h e h e a t t r a n s f e r
s e r i o u s l y . The l a r g e r t he i n i t i a l o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t
c o r r e s p o n d i n g t o a c l e a n h e a t i n g s u r f a c e , t he more p ronounced i s t h i s e f f e c t , as
shown i n F i g . 3 .13 .
The k i n d o f s c a l e d e p o s i t e d by t he j u i c e d u r i n g e v a p o r a t i o n o b v i o u s l y depends
on many f a c t o r s , and p r i n c i p a l among them i s t h e c o m p o s i t i o n o f m i n e r a l s a l t s i n
t h e raw j u i c e . The j u i c e p u r i f i c a t i o n method a l s o has a marked e f f e c t , as w e l l
as t h e a p p l i c a t i o n o f j u i c e d e c a l c i f i c a t i o n t e c h n i q u e s .
I t i s p o s s i b l e t o p r e v e n t t h e f o r m a t i o n o f s c a l e by u s i n g v a r i o u s a d d i t i o n
p r o d u c t s , a l t h o u g h no p a r t i c u l a r p r o d u c t i s u n i v e r s a l l y e f f i c i e n t i f used w i t h
d i f f e r e n t raw j u i c e p r o p e r t i e s and d i f f e r e n t p u r i f i c a t i o n methods . I n t h e D a n i s h
s u g a r i n d u s t r y , where t he c o n t e n t o f c a l c i u m s a l t s i n b e e t s i s u s u a l l y v e r y l o w ,
s c a l e p r e v e n t i o n i s s i m p l y based on soda a d d i t i o n t o t h e second c a r b o n a t a t i o n .
A number o f m a n u f a c t u r e r s a r e o f f e r i n g p r e p a r a t i o n s based on o r g a n o p h o s p h a t e s
o r p o l y e l e c t r o l y t e s as s c a l e - p r e v e n t i n g a g e n t s , c l a i m i n g a r e d u c t i o n o f s c a l i n g
117
SI
o
1.0
0 .8 φ
0 . 6
ο υ
Ο.Α
C 0.2
Initial heat transfer coefficient:
1 0 0 0 W/(m*K)
2 0 0 0 W/(m^K) 3 0 0 0 W/(m^K)
0 0.2 0 Λ 0.6 O B 1.0
Scale thickness (mm)
F i g . 3 .13 . O v e r a l l h e a t t r a n s f e r c o e f f i c i e n t as a f u n c t i o n o f s c a l e t h i c k n e s s a t s c a l e c o n d u c t i v i t y 0.97 W/ (mK) .
i n t h e e v a p o r a t o r o f up t o 90%. A d i s c u s s i o n o f t h e p r o p e r t i e s o f t h e s e a g e n t s ,
as w e l l as methods o f a p p l i c a t i o n and e x p e r i e n c e s a r i s i n g i n s u g a r f a c t o r i e s ,
can be f o u n d i n t h e l i t e r a t u r e ( r e f s . 1 4 , 1 5 ) .
A n o t h e r s c a l e - p r e v e n t i o n t e c h n i q u e i s based on t h e a c t i v a t i o n o f m o l e c u l e s o f
m i n e r a l s a l t s d i s s o l v e d i n j u i c e i n an e l e c t r i c f i e l d o r i n a m a g n e t i c f i e l d .
The a c t i v a t e d m o l e c u l e s t e n d t o remain i n s u s p e n s i o n r a t h e r t han d e p o s i t i n g on
t he h e a t - e x c h a n g e s u r f a c e s , and some r e p o r t s i n d i c a t e t h a t t h e s c a l e becomes
more e a s i l y removed , sometimes b e i n g changed i n t o m i c r o c r y s t a l 1 i n e mud. The
a c t i v a t i n g d e v i c e c o n s i s t s o f a t u b e , u s u a l l y p l a c e d i n t h e p i p e p r e c e d i n g t h i n -
j u i c e h e a t e r s , and f i e l d - g e n e r a t i n g c i r c u i t r y . Thousands o f u n i t s o f t h i s k i n d
have been s e t i n o p e r a t i o n i n v a r i o u s i n d u s t r i e s d u r i n g t h e l a s t f o u r d e c a d e s .
As r e g a r d s t h e s u g a r i n d u s t r y , i t seems t h a t t h i s method does n o t g i v e v e r y
d e f i n i t e r e s u l t s , and t h e r e have been v a r y i n g r e p o r t s on i t s e f f i c i e n c y ( r e f s .
3 , 1 6 - 1 9 ) . Howeve r , i t c a n n o t be e x c l u d e d t h a t some o f t he u n f a v o u r a b l e r e p o r t s
have r e s u l t e d f rom m i s u n d e r s t a n d i n g s , as t h e e v a l u a t i o n o f t h e e f f i c i e n c y o f
s c a l e p r e v e n t i o n i s a s u r p r i s i n g l y complex p r o b l e m . The a s s o c i a t e d d i f f i c u l t i e s
have been d i s c u s s e d i n a r e c e n t a r t i c l e d e v o t e d t o s t u d i e s o f s c a l e f o r m a t i o n
d u r i n g raw j u i c e e v a p o r a t i o n ( r e f . 2 0 ) .
I t s h o u l d f i n a l l y be p o i n t e d o u t t h a t s c a l e p r e v e n t i o n must a l s o i n c l u d e
p r o p e r p r o c e d u r e s f o r e v a p o r a t o r o p e r a t i o n unde r abnormal c o n d i t i o n s , l i k e t h e
s t a r t - u p w i t h w a t e r r e p l a c i n g j u i c e i n t h e e v a p o r a t o r b o d i e s , o r t h e a d d i t i o n o f
w a t e r t o t h i n j u i c e i n emergency s i t u a t i o n s a r i s i n g where t h e j u i c e f l o w becomes
t o o s m a l l . I n p r i n c i p l e , t h e w a t e r added s h o u l d be o f c o n d e n s a t e o r f e e d - w a t e r
q u a l i t y . The use o f u n t r e a t e d w a t e r must be a v o i d e d even d u r i n g v e r y s h o r t
p e r i o d s , because o f t he r i s k o f f o r m a t i o n o f v e r y t r o u b l e s o m e d e p o s i t s .
V a r i o u s p r o c e d u r e s have been a d v o c a t e d f o r c l e a n i n g e v a p o r a t o r t u b e s and
o t h e r i n c r u s t e d h e a t i n g s u r f a c e s . The commonest p r a c t i c e i s t o b o i l f o r s e v e r a l
h o u r s w i t h c a u s t i c soda s o l u t i o n , t h e n wash w i t h w a t e r and b o i l w i t h d i l u t e
118
h y d r o c h l o r i c a c i d . The d e t a i l s o f t h e p r o c e d u r e must be d e f i n e d so as t o a v o i d
t h e r i s k o f c o r r o s i v e damage t o t h e equ ipmen t , and p a r t i c u l a r l y t o t h e h e a t i n g
t u b e s . I n c o n n e c t i o n w i t h t h i s r e q u i r e m e n t , o t h e r c h e m i c a l s ( i n h i b i t o r s ,
a c t i v a t o r s and p a s s i v a t o r s ) have been d e v e l o p e d t o make i t e a s i e r t o c o n t r o l t h e
c l e a n i n g p r o c e s s . The t y p e and amount o f c h e m i c a l s and t h e b o i l i n g t ime may v a r y
f rom f a c t o r y t o f a c t o r y , depend ing on t h e s c a l e p r o p e r t i e s and tube m a t e r i a l
u s e d . A good a c c o u n t o f t h e p rob lems a s s o c i a t e d w i t h t h e i m p l e m e n t a t i o n o f
chemica l c l e a n i n g methods ( i n t he P o l i s h s u g a r i n d u s t r y ) can be f ound i n t h e
l i t e r a t u r e ( r e f s . 2 1 - 2 4 ) . S p e c i a l i z e d chemica l companies a r e p r e s e n t l y o f f e r i n g
e x t e n d e d i n d i v i d u a l c l e a n i n g and c o n s e r v a t i o n methods , on t he b a s i s o f s c a l e
samp les , s c a l e d - t u b e s e c t i o n s , r e s i n s a m p l e s , e t c .
Where chemica l c l e a n i n g has n o t p r o v e d e f f e c t i v e , mechan ica l o r h y d r a u l i c
t ube c l e a n e r s can be u s e d . E l e c t r i c a l d e s c a l e r s a r e w i d e l y known, c o n s i s t i n g o f
an e l e c t r i c motor and a f l e x i b l e s h a f t t e r m i n a t i n g i n a t o o l w i t h s e r r a t e d
r o l l e r s , w h i c h i s d r i v e n a t a h i g h s p e e d . One o r two passages o f t h e t o o l f o r
each t ube a re u s u a l l y s u f f i c i e n t t o remove t h e s c a l e .
3.3 FUNDAMENTALS OF CORRECT U T I L I Z A T I O N OF CONDENSATES AND VAPOURS
3.3.1 Condensa tes
The u t i l i z a t i o n o f t he e n e r g y o f c o n d e n s a t e s t a k e s p l a c e i n t h e the rma l
c i r c u i t r y a t t a c h e d t o t h e condensa te t a n k s . P r o v i d i n g t h e d r a i n a g e subsys tem i s
w o r k i n g c o r r e c t l y , t he t a s k o f most condensa te t a n k s i s t o a c t as f l o w
s t a b i l i z e r s and t o s e c u r e p r o p e r c o n d i t i o n s f o r t h e c o n d e n s a t e - f l a s h p r o c e s s . As
t h e i n f l o w i n g condensa te i s e x p a n d i n g t o t h e p r e s s u r e m a i n t a i n e d i n t h e t a n k ,
f l a s h v a p o u r , assumed t o be d r y s a t u r a t e d s team, i s g e n e r a t e d ( s e e a l s o S e c t i o n
2 . 5 ) . As a s e c o n d a r y e f f e c t , t h e gases d i s s o l v e d i n t h e condensa te a re
1 i b e r a t e d .
The f l a s h p r o c e s s s h o u l d c o n v e n i e n t l y be pe r f o rmed i n t h i n c o n d e n s a t e l a y e r s
o r s t r e a m s . I n a h o r i z o n t a l t a n k , t h i s can be a c c o m p l i s h e d by s u p p l y i n g t h e
condensa te t o t he upper p a r t and p r e f e r a b l y t o a s p e c i a l n o z z l e p l a c e d above t h e
l i q u i d l e v e l , as shown i n F i g . 3 . 1 4 ( a ) . I t s h o u l d be o b s e r v e d t h a t when
i n t r o d u c i n g t he condensa te be low t h e l i q u i d l e v e l , v a p o u r g e n e r a t i o n may
i n i t i a l l y be i n h i b i t e d by t h e h y d r a u l i c p r e s s u r e , and s u b s e q u e n t i n t e n s i v e
b o i l i n g i n a l a r g e l i q u i d vo lume may i n d u c e tank v i b r a t i o n s .
I n F i g . 3 . 1 4 ( b ) , a scheme f o r a v e r t i c a l t a n k d e s i g n e d t o s a t i s f y t h e
r e q u i r e m e n t s o f e f f i c i e n t c o n d e n s a t e f l a s h i s shown. H i g h - t e m p e r a t u r e c o n d e n s a t e
i s s u p p l i e d f rom be low v i a a n o z z l e t o a s i e v e t r a y p l a c e d above t h e l i q u i d
l e v e l . A p o s s i b l e s u p p l y o f l o w - t e m p e r a t u r e condensa te i s d i r e c t e d t o a n o z z l e
p l a c e d be low t h e o u t l e t n o z z l e . The tank i s u s u a l l y e q u i p p e d w i t h an a u t o m a t i c
l e v e l - c o n t r o l c i r c u i t .
119
(α) ( b )
jT I Χ nozzle nozzle
h i
baffle
sieve tray
Γ
F i g . 3 .14 . D e s i g n p r i n c i p l e s o f c o n d e n s a t e t a n k s : ( a ) h o r i z o n t a l t y p e , ( b ) v e r t i c a l t y p e ( c o u r t e s y Chemadex) . 1 - e x p a n d i n g c o n d e n s a t e , 2 - s u b c o o l e d c o n d e n s a t e , 3 - o u t f l o w i n g c o n d e n s a t e , 4 - f l a s h v a p o u r .
I t s h o u l d be o b s e r v e d t h a t t h e a v a i l a b l e e n e r g y o f t h e c o n d e n s a t e may e i t h e r
be s u p p l i e d t o t h e e v a p o r a t o r i n t h e f l a s h v a p o u r , o r t r a n s f e r r e d t o j u i c e o r
o t h e r media i n c o n d e n s a t e - h e a t e d h e a t e r s . H o w e v e r , i f a p a r t o f t h e h e a t i n g -
v a p o u r demand i s s a t i s f i e d by t h e f l a s h v a p o u r , and t h e c o n d e n s e r l o s s i s
c o n s t a n t , t hen l e s s w a t e r w i l l be e v a p o r a t e d f rom j u i c e i n t h e e v a p o r a t o r . I n
t h e a r rangement shown s c h e m a t i c a l l y i n F i g . 3 . 1 5 ( a ) , a b o u t 1.4 kg f l a s h v a p o u r
i s o b t a i n e d pe r 100 kg b e e t , t h i s r e d u c i n g w a t e r e v a p o r a t i o n i n t h e f i r s t and
second s t a g e s by abou t 2.8 kg/100 kg b. T h i s f i g u r e can be c u t down by a p p l y i n g
d o u b l e - s t a g e condensa te e x p a n s i o n , w h i c h r e q u i r e s u s i n g two c o n d e n s a t e t a n k s as
shown i n F i g . 3 . 1 5 ( b ) . I n t h e f i r s t t a n k , t h e c o n d e n s a t e i s f l a s h e d t o t h e
f i r s t - e f f e c t p r e s s u r e , g e n e r a t i n g abou t 0.7 kg v a p o u r p e r 100 kg b e e t . S e c o n d -
s t a g e f l a s h p r o d u c e s a n o t h e r 0.7 kg v a p o u r p e r 100 kg b e e t . As a r e s u l t , w a t e r
e v a p o r a t i o n w i l l be r e d u c e d by 0.7 + 2 -0 .7 = 2.1 kg/100 kg b , i . e . , 25% l e s s
t han i n t h e p r e v i o u s c a s e .
The f i r s t s t a g e o f t he c o n d e n s a t e f l a s h c h a i n p r e s e n t e d above can be r e p l a c e d
by a h e a t e r t o w h i c h t h i n j u i c e f rom a n o t h e r h e a t e r , hea ted by f i r s t - e f f e c t
v a p o u r , i s s u p p l i e d . T h i s s o l u t i o n , shown s c h e m a t i c a l l y i n F i g . 3 . 1 5 ( c ) , r e d u c e s
w a t e r e v a p o r a t i o n i n t h e e v a p o r a t o r by o n l y 1.4 kg/100 kg b.
A n o t h e r p o s s i b i l i t y o f r e p l a c i n g c o n d e n s a t e f l a s h i n a t a n k by c o n d e n s a t e
c o o l i n g i n a h e a t e r can be f o u n d i n c o n n e c t i o n w i t h t h e l a s t e v a p o r a t o r e f f e c t .
More s p e c i f i c a l l y , t he l a s t - e f f e c t c o n d e n s a t e t ank can be o p e r a t e d a t a p r e s s u r e
equal t o t h a t i n t h e h e a t i n g chamber ( i n s t e a d o f t h a t i n t h e v a p o u r c h a m b e r ) .
120
(α)
35 Τ 126°C 116°C
" 136'C 125°C
(b )
^ 3 : ^ © _ _ .
( c )
35
126°C 35
_ Γ 136"C
116C
125 C
I ^ . J ^ r ^ L - S -3.3:6 0
126°C
136°C I 116'C
125-C
Ö
34.3 Ί
F i g . 3 .15 . Schemes o f u t i l i z a t i o n o f f i r s t - e f f e c t condensa te i n a q u a d r u p l e -e f f e c t e v a p o r a t o r : ( a ) s i n g l e - s t a g e f l a s h , ( b ) d o u b l e - s t a g e f l a s h , ( c ) t h i n j u i c e h e a t i n g , f o l l o w e d by s i n g l e - s t a g e f l a s h ( f l o w s i n kg/100 kg b ) .
T h i s makes i t p o s s i b l e t o s u p p l y t h e c o n d e n s a t e t o a h e a t e r i n s t a l l e d as t h e
n e x t h e a t i n g s t a g e a f t e r t h e one hea ted by t h e l a s t - e f f e c t v a p o u r . I f a p p l i e d
i n s t e a d o f a f l a s h s t a g e , t h i s s o l u t i o n i n c r e a s e s w a t e r e v a p o r a t i o n i n t h e
e v a p o r a t o r by 1.8-2.5 kg/100 kg b.
I f t he p r i n c i p l e s o f c o r r e c t u t i l i z a t i o n o f c o n d e n s a t e s a r e o b s e r v e d , t h e n
t h e condensa te subsys tem c o n s i s t i n g o f t a n k s , p i p i n g , f i t t i n g s , c o n t r o l s and
measur ing i n s t r u m e n t s l o o k s i m i l a r i n d i f f e r e n t f a c t o r i e s . A l t e r n a t i v e l y , t h e
e s s e n t i a l components can be combined i n t o a s i n g l e p i e c e o f equ ipment known as
t h e compound t a n k . W h i l e t h e compartments o f t h e compound tank c o r r e s p o n d t o t h e
i n d i v i d u a l t a n k s o f t he c o n v e n t i o n a l s o l u t i o n , l e s s p i p i n g and f i t t i n g s can be
u s e d . Depending on l o c a l c o n d i t i o n s , i t may a l s o be e a s i e r t o f i n d a p l a c e f o r
a s i n g l e compound tank r a t h e r t han m u l t i p l e i n d i v i d u a l t a n k s .
121
3 .3 .2 V a p o u r s
The r o l e o f t h e m u l t i p l e - e f f e c t e v a p o r a t o r s t a t i o n i n t h e hea t economy o f
s u g a r f a c t o r i e s has been d i s c u s s e d p r e l i m i n a r i l y i n S e c t i o n 1 .2 .5 . I t s i n f l u e n c e
on t h e n e t h e a t demand o f t he s u g a r m a n u f a c t u r i n g p r o c e s s i s based on t h e
m o d i f i e d R i l l i e u x p r i n c i p l e , t h a t i s , u s i n g t h e h e a t r e p e t i t i v e l y i n t h e
c o n s e c u t i v e e v a p o r a t o r e f f e c t s , and s i m u l t a n e o u s l y d e l i v e r i n g f r a c t i o n s o f t h e
h e a t t o t h e v a p o u r r e c e i v e r s c o n n e c t e d t o each e f f e c t . As a r e s u l t , t h e
e v a p o r a t i o n c o e f f i c i e n t , i . e . t h e r a t i o o f t h e mass o f w a t e r e v a p o r a t e d t o t h e
mass o f h e a t i n g steam consumed i n t he f i r s t e f f e c t , may r e a c h 2 . 3 - 2 . 8 i n a
q u a d r u p l e - e f f e c t and 3 .2 -3 .5 i n a q u i n t u p l e - e f f e c t , e v a p o r a t o r . The l a r g e r t h e
e v a p o r a t i o n c o e f f i c i e n t , t h e l a r g e r can be t h e e f f e c t i v e n e s s r a t i o
c h a r a c t e r i z i n g t h e the rma l s y s t e m .
Numerous t h e o r e t i c a l a n a l y s e s and p r a c t i c a l l y - o r i e n t e d s t u d i e s have been
d e v o t e d t o t h e op t ima l d i s t r i b u t i o n o f v a p o u r s f rom m u l t i p l e - e f f e c t e v a p o r a t o r s
( r e f s . 2 5 - 3 3 ) . T h e i r r e s u l t s can be summar ized i n two r u l e s , t o be o b s e r v e d when
d e s i g n i n g a new therma l sys tem o r m o d e r n i z i n g an e x i s t i n g o n e :
( i ) Each h e a t i n g o p e r a t i o n s h o u l d be a c c o m p l i s h e d u s i n g v a p o u r a t t h e l o w e s t
p o s s i b l e t e m p e r a t u r e .
( i i ) Vapour f l o w f rom the l a s t e v a p o r a t o r e f f e c t t o t h e c o n d e n s e r s h o u l d
approach z e r o .
The t e m p e r a t u r e s o f v a p o u r s f rom the e v a p o r a t o r e f f e c t s a r e d e t e r m i n e d by
t h e number o f e f f e c t s , t h e d e s i g n o f e v a p o r a t o r b o d i e s and t h e h e a t i n g - s u r f a c e
a r e a s i n t h e i n d i v i d u a l e f f e c t s . S i m u l t a n e o u s l y , t h e pa rame te rs o f t h e s u g a r
m a n u f a c t u r i n g p r o c e s s d e t e r m i n e t h e v a p o u r demand and t h e t e m p e r a t u r e r e q u i r e d
f o r t he h e a t i n g o p e r a t i o n s . C o n s e q u e n t l y , i t i s p o s s i b l e t o a s s i g n , t o each
h e a t i n g o p e r a t i o n , a s p e c i f i c e v a p o r a t o r e f f e c t f rom w h i c h h e a t i n g v a p o u r a t
a s u i t a b l e t e m p e r a t u r e can be w i t h d r a w n .
The p o s s i b i l i t i e s f o r u s i n g v a p o u r s f rom d i f f e r e n t e v a p o r a t o r e f f e c t s i n
a g i v e n h e a t i n g o p e r a t i o n a r e l i m i t e d by t h e r e q u i r e d f i n a l t e m p e r a t u r e o f t h e
medium h e a t e d , and by t he minimum t e m p e r a t u r e d i f f e r e n c e ( t e m p e r a t u r e p i n c h )
c h a r a c t e r i s t i c o f t h e h e a t i n g a p p a r a t u s . The r e l a t i o n s between t h e t e m p e r a t u r e s
a r e i l l u s t r a t e d i n F i g . 3 .16 . I t can t h u s be c o n c l u d e d t h a t t h e e f f e c t i v e n e s s o f
t h e u t i l i z a t i o n o f v a p o u r s d e p e n d s , t o a c e r t a i n e x t e n t , on t h e h e a t i n g
equ ipment a v a i l a b l e . A q u a n t i t a t i v e a n a l y s i s o f t h i s r e l a t i o n s h i p can be based
on t he e q u a t i o n e x p r e s s i n g t h e hea t Q t r a n s f e r r e d i n u n i t t ime between t h e
v a p o u r and t h e medium hea ted as
Q = kFAT ( 3 . 5 )
where k i s t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t , F i s t h e h e a t i n g - s u r f a c e a r e a ,
and Δ Τ i s t he mean t e m p e r a t u r e d i f f e r e n c e between h e a t i n g v a p o u r and t h e medium
h e a t e d .
122
\_ D
2 Ο.
Τν vapour
Η-<
pinch
required f inal
temperature
0 100 Heating surface area p a s s e d ( % )
F i g . 3 .16 . Tempera tu re c h a r a c t e r i s t i c s o f j u i c e h e a t i n g . ΔΤ - mean t e m p e r a t u r e d i f f e r e n c e , T ^ - a c t u a l v a p o u r t e m p e r a t u r e , T ^ - l o w e s t p o s s i b l e v a p o u r t e m p e r a t u r e .
F o r a g i v e n amount o f hea t t r a n s f e r r e d , i t may be p o s s i b l e t o r e d u c e t h e mean
t e m p e r a t u r e d i f f e r e n c e (and t h e minimum t e m p e r a t u r e d i f f e r e n c e ) o n l y i f t h e
p r o d u c t kF i s i n c r e a s e d . C o n s e q u e n t l y , t h e p r i n c i p l e o f s e l e c t i o n o f v a p o u r a t
t h e l o w e s t p o s s i b l e t e m p e r a t u r e i m p l i e s t h a t t h e equ ipment c h a r a c t e r i z e d by
a smal l minimum t e m p e r a t u r e d i f f e r e n c e , w h i c h i s e q u i v a l e n t t o a l a r g e k F ,
s h o u l d be p r e f e r r e d . Howeve r , l a r g e kF can o n l y be o b t a i n e d u s i n g h i g h - i n t e n s i t y
h e a t t r a n s f e r , o r l a r g e h e a t i n g - s u r f a c e a r e a s , o r bo th - t h i s i n d u c i n g i n c r e a s e d
h e a t e r c o s t . A t g i v e n u n i t p r i c e s o f e n e r g y and h e a t - e x c h a n g i n g e q u i p m e n t , t h e r e
i s a t r a d e - o f f between t h e e f f e c t i v e n e s s o f t h e e n e r g y u t i l i z a t i o n and t he
i n v e s t m e n t c o s t o f t he h e a t e r s , and an optimum e x i s t s f o r t h e minimum
t e m p e r a t u r e d i f f e r e n c e . ( A c t u a l l y , i t may be p o s s i b l e t o t r e a t t h i s phenomenon
as a b a s i s o f e n e r g y - s y s t e m a n a l y s i s and d e s i g n , as shown i n S e c t i o n 9 . 4 . 3 . )
As r e g a r d s v a p o u r - h e a t e d j u i c e h e a t e r s , i t i s b e l i e v e d a t p r e s e n t t h a t t h e
economic v a l u e s o f t h e minimum t e m p e r a t u r e d i f f e r e n c e s h o u l d n o t e x c e e d 5-10 K,
l o w e r v a l u e s c o r r e s p o n d i n g t o h i g h e r f u e l p r i c e s . T y p i c a l h e a t i n g o p e r a t i o n s
s h o u l d t h u s be a c c o m p l i s h e d u s i n g v a p o u r s a t t e m p e r a t u r e s n o t h i g h e r t han 5-10 Κ
above t h e r e q u i r e d f i n a l j u i c e t e m p e r a t u r e . Even s m a l l e r t e m p e r a t u r e d i f f e r e n c e s
may be adop ted when h e a t i n g w i t h l o w - t e m p e r a t u r e v a p o u r s ( s e e S e c t i o n 3 . 3 . 4 ) .
The l a r g e s t component o f t h e h e a t i n g - v a p o u r demand i s a s s o c i a t e d w i t h t h e
s u g a r b o i l i n g p r o c e s s . S u p p l y i n g t h e vacuum pans w i t h v a p o u r a t t h e l o w e s t
p o s s i b l e t e m p e r a t u r e i s d e c i s i v e i n o p t i m i z i n g t h e d i s t r i b u t i o n o f v a p o u r s f rom
t h e e v a p o r a t o r . F o r t h i s r e a s o n , l e t us t ake a c l o s e r l o o k a t t h e h e a t i n g
r e q u i r e m e n t s o f s u g a r b o i l i n g .
I n t he case o f b a t c h vacuum p a n s , t h e n o t i o n o f t h e minimum t e m p e r a t u r e
d i f f e r e n c e must be adap ted t o t h e d i s c o n t i n u o u s n a t u r e and o t h e r s p e c i a l
f e a t u r e s o f t h e b o i l i n g p r o c e s s . I t i s known t h a t t h e magma t e m p e r a t u r e may be
u n e v e n l y d i s t r i b u t e d i n t h e s t r i k e v o l u m e , t h e d i s t r i b u t i o n b e i n g dependen t on
t h e pan d e s i g n a n d , p o s s i b l y , s t i r r e r e f f i c i e n c y ( r e f s . 3 4 - 3 6 ) . F o r t h e sake o f
123
s i m p l i c i t y , l e t us assume t h a t t h e t e m p e r a t u r e c o n d i t i o n s i n t h e magma can be
a d e q u a t e l y d e s c r i b e d u s i n g t h e mean magma t e m p e r a t u r e . A t c o n s t a n t vacuum,
f o l l o w i n g changes o f t h e b o i l i n g - p o i n t e l e v a t i o n as t h e magma c o n c e n t r a t i o n i s
i n c r e a s e d , t h i s t e m p e r a t u r e v a r i e s d u r i n g t h e b o i l i n g c y c l e as shown
a p p r o x i m a t e l y i n F i g . 3 .17 . F o r t h e same r e a s o n , t h e o v e r a l l h e a t t r a n s f e r
c o e f f i c i e n t a t t he h e a t i n g s u r f a c e v a r i e s as i n d i c a t e d i n t h e same d i a g r a m .
S i m u l t a n e o u s l y , t h e c o n d e n s a t i o n t e m p e r a t u r e i n t h e h e a t i n g chamber may v a r y ( a s
d i s c u s s e d i n S e c t i o n 3 . 1 . 2 ) , becoming t e m p o r a r i l y l o w e r t han t h e t e m p e r a t u r e o f
v a p o u r f rom t h e a s s o c i a t e d e v a p o r a t o r e f f e c t .
oH76
20 UO 60 80 100 Time after seeding (m in )
F i g . 3 .17 . Mean magma t e m p e r a t u r e as a f u n c t i o n o f t ime d u r i n g w h i t e - s u g a r b o i l i n g i n two d i f f e r e n t vacuum pans ( a f t e r r e f . 3 4 ) .
The range o f c h o i c e s o f v a p o u r t e m p e r a t u r e v a l u e s f o r pan h e a t i n g i s l i m i t e d
by t h e b o i l i n g t ime r e q u i r e m e n t w h i c h i s e s s e n t i a l t o bo th t h e s u g a r house
t h r o u g h p u t and p r o d u c t q u a l i t y . A t a g i v e n h e a t i n g - s u r f a c e a r e a , t h e amount o f
h e a t t r a n s f e r r e d s h o u l d be l a r g e enough t o e n s u r e t h a t t he s t r i k e can be
comp le ted w i t h i n t h e r e q u i r e d b o i l i n g t ime τ . I n a d d i t i o n , t h e h e a t t r a n s f e r r e d
p e r u n i t t ime s h o u l d be s u f f i c i e n t l y l a r g e t o make c o r r e c t s t r i k e f i n i s h i n g
p o s s i b l e .
I n o r d e r t o s i m p l i f y t h e f o r m u l a t i o n o f t h e r e q u i r e m e n t s , l e t us assume t h a t
changes o f t h e v a p o u r - c o n d e n s a t i o n t e m p e r a t u r e a r e n e g l i g i b l y s m a l l . T h i s a l l o w s
us t o r e s t r i c t o u r a t t e n t i o n t o t h e f o l l o w i n g pa rame te r s t h a t a p p r o x i m a t e l y
d e s c r i b e t h e t e m p e r a t u r e c y c l e ( F i g . 3 . 1 8 ) :
- t i m e - a v e r a g e d mean magma t e m p e r a t u r e T ^ ;
- h i g h e s t mean magma t e m p e r a t u r e T ^ ;
- vapou r t e m p e r a t u r e T ^ .
124
Time (min)
F i g . 3 .18 . Tempera tu re c y c l e accompany ing t h e s u g a r b o i l i n g p r o c e s s .
The t e m p e r a t u r e c y c l e i s accompanied by t he h e a t t r a n s f e r c y c l e ( F i g . 3 . 1 9 ) ,
w h i c h can be c h a r a c t e r i z e d by t h e f o l l o w i n g pa rame te rs i l l u s t r a t e d i n F i g . 3 .20 :
- t i m e - a v e r a g e d o v e r a l l hea t t r a n s f e r c o e f f i c i e n t k^; a
- l o w e s t o v e r a l l hea t t r a n s f e r c o e f f i c i e n t k^;
- hea t demand p e r one s t r i k e Q^^.
U s i n g t he pa rame te rs l i s t e d a b o v e , i t i s p o s s i b l e t o d e r i v e a s i m p l e
mathemat ica l model o f t he hea t t r a n s f e r r e l a t i o n s h i p s i n a b o i l i n g c y c l e . The
v a p o u r t e m p e r a t u r e s h o u l d be chosen t o s a t i s f y t h e i n e q u a l i t y
w h i c h can be r e w r i t t e n as
Τ < Τ
( 3 . 6 )
V( V) ' a ν ( 3 . 7 )
D e n o t i n g t he maximum a l l o w a b l e h e a t t r a n s f e r r e d p e r u n i t t ime by Q ^ , a n o t h e r
i n e q u a l i t y can be c o n s t r u c t e d t o r e f l e c t t h e c o n d i t i o n s o f s t r i k e f i n i s h i n g as
< V\ - ( 3 . 8 )
o r
( 3 . 9 )
F i g . 3 .19 . O v e r a l l hea t t r a n s f e r c o e f f i c i e n t as a f u n c t i o n o f t ime d u r i n g w h i t e -s u g a r b o i l i n g i n two d i f f e r e n t vacuum pans ( a f t e r r e f . 3 4 ) .
125
Time
F i g . 3 .20 . Heat t r a n s f e r c y c l e accompany ing t h e s u g a r b o i l i n g p r o c e s s .
The above f o r m u l a e a re meant t o p r o v i d e o n l y a q u a l i t a t i v e p i c t u r e o f t h e
therma l a s p e c t s o f s e l e c t i o n o f t h e v a p o u r t e m p e r a t u r e . As i n d i c a t e d by ( 3 . 7 )
and ( 3 . 9 ) , f o r a s p e c i f i c p r o d u c t and a g i v e n vacuum-pan d e s i g n , t h e t e m p e r a t u r e
o f t h e h e a t i n g v a p o u r must be h i g h e r t han a c e r t a i n t h r e s h o l d v a l u e . Most
con tempo ra ry pan d e s i g n s make i t p o s s i b l e t o b o i l w h i t e s u g a r a t a v a p o u r
t e m p e r a t u r e 107-120°C, and l o w - g r a d e p r o d u c t s a t 102-110°C.
From t h e r e a s o n i n g p r e s e n t e d a b o v e , t h e c o n c l u s i o n can be drawn t h a t t h e
v a p o u r t e m p e r a t u r e s e l e c t i o n f o r vacuum-pan h e a t i n g i s v e r y much i n f l u e n c e d by
t h e c o n d i t i o n s o f t h e f i n a l p a r t o f t h e s t r i k e - t h i c k e n i n g p h a s e . A c t u a l l y , t h e
u t i l i z a t i o n o f v a p o u r s f rom t h e e v a p o r a t o r can be improved i f v a p o u r a t a l o w e r
t e m p e r a t u r e i s s u p p l i e d d u r i n g most o f t h e b o i l i n g c y c l e , t h i s b e i n g f o l l o w e d by
h e a t i n g a t a h i g h e r t e m p e r a t u r e when t h e f i n a l p a r t o f t h e s t r i k e - t h i c k e n i n g
phase i s a p p r o a c h e d . A l t h o u g h t h i s i d e a i s c e r t a i n l y r e a l i z a b l e and t h e r e have
been examples o f i t s p r a c t i c a l a p p l i c a t i o n i n b a t c h vacuum pans ( r e f . 3 7 ) , one
has t o r eckon w i t h s i d e - e f f e c t s c o n s i s t i n g o f a d d i t i o n a l f l u c t u a t i o n s o f
e v a p o r a t o r pa rame te rs accompany ing t h e moment o f s w i t c h i n g f rom l o w - t o h i g h -
t e m p e r a t u r e v a p o u r ( t h e f l u c t u a t i o n s r e s u l t i n g , u n a v o i d a b l y , i n an e x t r a e n e r g y
l o s s ) . Howeve r , t h e p o t e n t i a l g a i n s can e a s i l y be a t t a i n e d u s i n g c o n t i n u o u s
vacuum p a n s . A d i s c u s s i o n o f t h e deve lopmen t and a p p l i c a t i o n s o f c o n t i n u o u s pans
i s p r e s e n t e d i n C h a p t e r 5.
R e t u r n i n g now t o t he b a t c h vacuum p a n s , i t can be seen i n F i g s . 3.17 and 3.19
t h a t t h e h i g h e s t mean magma t e m p e r a t u r e t e n d s t o be h i g h e r , and t h e o v e r a l l h e a t
t r a n s f e r c o e f f i c i e n t s i s m a r k e d l y l o w e r , i n t h e n a t u r a l - c i r c u l a t i o n vacuum p a n s .
Both f a c t o r s a c t i n t h e same d i r e c t i o n , making i t n e c e s s a r y t o s e t t h e
d i f f e r e n c e between t he t i m e - a v e r a g e d magma t e m p e r a t u r e and t h e v a p o u r
t e m p e r a t u r e l a r g e r t han i n s t i r r e r - e q u i p p e d p a n s . I t can t h u s be c o n c l u d e d t h a t
t he s t i r r e r - e q u i p p e d vacuum pans make i t p o s s i b l e t o a c c e p t a l o w e r h e a t i n g -
vapou r t e m p e r a t u r e , t h u s s t i m u l a t i n g b e t t e r u t i l i z a t i o n o f v a p o u r s f rom t h e
e v a p o r a t o r .
126
C o n c l u d i n g t h e d i s c u s s i o n o f t h e r u l e o f h e a t i n g w i t h v a p o u r a t t h e l o w e s t
p o s s i b l e t e m p e r a t u r e , l e t us o b s e r v e t h a t i t s a p p l i c a t i o n l e a d s t o s h i f t i n g t h e
e v a p o r a t o r l o a d t owa rds l o w - t e m p e r a t u r e e f f e c t s . As a c o n s e q u e n c e , t h e
e v a p o r a t i o n c o e f f i c i e n t i s i n c r e a s e d and t h e n e t h e a t demand o f t h e f a c t o r y may
be r e d u c e d . I n t he l i t e r a t u r e , examples can be f o u n d o f s u c c e s s f u l a p p l i c a t i o n s
o f t h i s r u l e i n m o d e r n i z a t i o n o f e v a p o r a t o r s t a t i o n s ( r e f s . 3 7 , 3 8 ) .
The second r u l e f o r m u l a t e d a t t h e b e g i n n i n g o f t h i s S e c t i o n , t o m a i n t a i n t h e
v a p o u r f l o w t o t h e condense r c l o s e t o z e r o , means s i m p l y t h a t t h e v a p o u r must
n o t be w a s t e d . On t h e o t h e r h a n d , i t i s n e c e s s a r y t o e v a p o r a t e as much w a t e r i n
t h e e v a p o r a t o r as needed t o a t t a i n a p r e d e t e r m i n e d t h i c k - j u i c e c o n c e n t r a t i o n .
I n a s u g a r f a c t o r y c h a r a c t e r i z e d by a l a r g e hea t demand, so much v a p o u r must be
w i t h d r a w n f rom t h e e v a p o r a t o r f o r h e a t i n g p u r p o s e s t h a t t h i s c o n s t r a i n t i s e a s y
t o s a t i s f y . I f t he hea t demand has been d e c r e a s e d , h o w e v e r , t hen t h e t o t a l
v a p o u r w i t h d r a w a l m igh t be i n s u f f i c i e n t , and i n c r e a s e d v a p o u r f l o w t o t h e
condense r wou ld be t he o n l y p o s s i b i l i t y t o keep t h e t h i c k - j u i c e c o n c e n t r a t i o n
c o n s t a n t . Such a s i t u a t i o n s h o u l d be i n t e r p r e t e d as i n d i c a t i n g t h e n e c e s s i t y t o
m o d i f y t h e a c t u a l e v a p o r a t o r c o n f i g u r a t i o n . G e n e r a l l y , t h r e e s o l u t i o n s can be
c o n s i d e r e d , e i t h e r s e p a r a t e l y o r i n c o m b i n a t i o n :
( 1 ) r e p l a c i n g s e l e c t e d e v a p o r a t o r b o d i e s by o t h e r s w i t h l a r g e r h e a t i n g s u r f a c e s
a n d / o r h i g h e r o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s ;
( 2 ) i n c r e a s i n g t he number o f e v a p o r a t o r e f f e c t s ;
( 3 ) i n t r o d u c i n g a v a p o u r c o m p r e s s i o n c i r c u i t .
The p r i n c i p l e o f t h e f i r s t s o l u t i o n can be seen i n e q n . ( 3 . 5 ) , w h i c h has been
f o r m u l a t e d f o r a h e a t e r b u t a p p l i e s as w e l l t o an e v a p o r a t o r b o d y . F o r a
p r e d e t e r m i n e d amount o f hea t t o be t r a n s f e r r e d f rom h e a t i n g v a p o u r t o j u i c e , an
i n c r e a s e d o v e r a l l hea t t r a n s f e r c o e f f i c i e n t a n d / o r e n l a r g e d h e a t i n g - s u r f a c e a r e a
make i t p o s s i b l e t o r educe t h e mean t e m p e r a t u r e d i f f e r e n c e between v a p o u r and
j u i c e . An a p p l i c a t i o n o f t h i s p r i n c i p l e i s i l l u s t r a t e d i n F i g . 3 .21 , w h i c h shows
v a p o u r t e m p e r a t u r e s i n a q u i n t u p l e - e f f e c t e v a p o r a t o r b e f o r e and a f t e r
m o d e r n i z a t i o n o f t h e 4 t h - e f f e c t b o d y . F o l l o w i n g a r e d u c t i o n o f t h e mean
t e m p e r a t u r e d i f f e r e n c e i n t h e 4 th e f f e c t , t h e t e m p e r a t u r e s o f t h e 4 t h - and 5 t h -
e f f e c t v a p o u r s a r e i n c r e a s e d , making i t e a s i e r t o u t i l i z e t h e s e v a p o u r s f o r
h e a t i n g p u r p o s e s . I t t h u s becomes p o s s i b l e t o s u p p l y 4 t h - and 5 t h - e f f e c t v a p o u r s
t o c e r t a i n r e c e i v e r s t h a t have p r e v i o u s l y been hea ted by 3 r d - and 4 t h - e f f e c t
v a p o u r s , r e s p e c t i v e l y . As a r e s u l t , t h e n e t h e a t demand may be r e d u c e d .
An i n c r e a s e d number o f e v a p o r a t o r e f f e c t s i s an o b v i o u s s o l u t i o n i n s u g a r
f a c t o r i e s where t r i p l e - o r q u a d r u p l e - s t a g e e v a p o r a t o r s a r e u s e d . A t p r e s e n t ,
most e n e r g y e f f i c i e n t f a c t o r i e s r e l y on q u i n t u p l e - e f f e c t e v a p o r a t o r s . T h i s
s h o u l d be seen as an e n t i r e f a m i l y o f e v a p o r a t o r s o l u t i o n s , each c h a r a c t e r i z e d
by a un ique d i s t r i b u t i o n o f h e a t i n g v a p o u r s . Vacuum pans may be hea ted by 2 n d - ,
127
IAO
α 130
t 120 3
ξ 110 α φ 100
90
1 2 3 A 5 Evaporator effect No.
F i g . 3 .21. T e m p e r a t u r e d i s t r i b u t i o n i n a q u i n t u p l e - e f f e c t e v a p o r a t o r . Dashed l i n e s i n d i c a t e r e s u l t s o f t h e m o d e r n i z a t i o n o f f o u r t h - e f f e c t body ( c o u r t e s y C u k r o p r o j e k t ) .
3 r d - , 4 t h - , o r even 5 t h - e f f e c t v a p o u r , o r two d i f f e r e n t v a p o u r s . The l a s t
e f f e c t may work as a c o n c e n t r a t o r , t h a t i s , w i t h v a p o u r w i t h d r a w a l t o t h e
condense r o n l y , o r v a p o u r may a l s o be w i t h d r a w n f o r h e a t i n g p u r p o s e s . Depend ing
on t h e d e s i g n o f t h e e v a p o r a t o r b o d i e s , i t may be n e c e s s a r y t o i n c r e a s e t h e
e x h a u s t - s t e a m p r e s s u r e above t h e l e v e l w h i c h i s s u f f i c i e n t i n q u a d r u p l e - e f f e c t
e v a p o r a t o r s .
Up t o now, s e x t u p l e - e f e c t e v a p o r a t o r s a r e se ldom used i n t y p i c a l w h i t e - s u g a r
f a c t o r i e s . Examples a r e known o f f a c t o r i e s where s e x t u p l e - s t a g e e v a p o r a t o r
s t a t i o n s have been c o n v e r t e d back t o q u i n t u p l e - e f f e c t o n e s , t o make t h e
o p e r a t i o n e a s i e r . S u c c e s s f u l a p p l i c a t i o n s o f s e x t u p l e - e f f e c t e v a p o r a t o r s have
been r e p o r t e d f rom P l a t t l i n g , FRG, and B u c y - l e - L o n g , F r a n c e ( r e f . 3 9 ) . H o w e v e r ,
t h e s e a r e n o t o r d i n a r y f a c t o r i e s , as t h i c k - j u i c e s t o r a g e i s a p p l i e d i n
P l a t t l i n g , and v a p o u r c o m p r e s s i o n i s employed i n t h e the rma l sys tem a t B u c y - l e -
Long .
The i n t r o d u c t i o n o f a v a p o u r - c o m p r e s s i o n c i r c u i t i s men t ioned above as a
t h i r d p o s s i b i l i t y t o m o d i f y an e v a p o r a t o r c o n f i g u r a t i o n . T h i s t e c h n i q u e i s
d i s c u s s e d i n g r e a t e r d e t a i l i n S e c t i o n 3 . 4 .
3 .3 .3 The r o l e o f vacuum sys tems
The a t t a i n a b l e vacuum l e v e l d e f i n e s t h e l o w e s t t e m p e r a t u r e t o w h i c h h e a t
f l o w s can be d i r e c t e d w i t h i n a the rma l s y s t e m . F o r t h i s r e a s o n , t h e f u n c t i o n i n g
o f t h e l a s t e v a p o r a t o r e f f e c t and t h e s u g a r b o i l i n g under vacuum a r e v e r y
i m p o r t a n t t o t h e e f f e c t i v e n e s s o f e n e r g y c o n v e r s i o n p r o c e s s e s t a k i n g p l a c e i n
t he therma l s y s t e m . The d i s c u s s i o n o f t h i s s u b j e c t was i n i t i a t e d i n t h e
p r e c e d i n g S e c t i o n by a n a l y s i n g t h e r e l a t i o n s h i p s c h a r a c t e r i s t i c o f vacuum-pan
128
h e a t i n g . The h i g h e r t he vacuum, t h a t i s , t h e l o w e r t h e p r e s s u r e i n t h e
c o n d e n s e r , t h e l o w e r can be t h e t i m e - a v e r a g e d mean magma t e m p e r a t u r e and t h u s
t h e l o w e r can be t he h e a t i n g - v a p o u r t e m p e r a t u r e , t h i s c o n t r i b u t i n g t o improved
h e a t economy.
As r e g a r d s t he l a s t e v a p o r a t o r e f f e c t , t he vacuum l e v e l d e t e r m i n e s t h e
p r e s s u r e and t h u s t h e j u i c e - b o i l i n g t e m p e r a t u r e . T h i s , i n t u r n , d e f i n e s t h e
t e m p e r a t u r e span a v a i l a b l e f o r t h e m u l t i - s t a g e e v a p o r a t i o n p r o c e s s (be tween t h e
e x h a u s t - s t e a m t e m p e r a t u r e i n t h e f i r s t s t a g e and j u i c e t e m p e r a t u r e i n t h e l a s t ) ,
and i n d i r e c t l y d e f i n e s t h e t e m p e r a t u r e s o f h e a t i n g v a p o u r s and c o n d e n s a t e s f rom
t h e i n d i v i d u a l e v a p o r a t o r e f f e c t s .
I n t he vacuum sys tem o f a s u g a r f a c t o r y , vacuum i s p r o d u c e d i n one o r more
c o n d e n s e r s . The p r e s s u r e i n t h e condense r i s equa l t o t he sum o f t he w a t e r -
s a t u r a t i o n p r e s s u r e c o r r e s p o n d i n g t o t h e t e m p e r a t u r e o f t h e c o n d e n s i n g v a p o u r ,
and t h e p r e s s u r e o f t h e noncondensab le g a s e s . Howeve r , a c o n n e c t i o n between t h e
c o n d e n s e r and an equ ipment u n i t o p e r a t e d under vacuum may i n c l u d e n o z z l e s ,
p i p e s , f i t t i n g s , e n t r a i n m e n t s e p a r a t o r s a n d , p e r h a p s , h e a t i n g chambers o f
h e a t e r s . The f l o w o f v a p o u r t h r o u g h t h e c o n n e c t i o n i s i n e v i t a b l y a s s o c i a t e d w i t h
a p r e s s u r e d r o p , so t he a v a i l a b l e p r e s s u r e i s h i g h e r , i . e . , t h e a v a i l a b l e vacuum
i s l o w e r t han t h a t i n t he c o n d e n s e r ( a c t u a l l y , a p a r t o f t h i s p r e s s u r e d r o p may
o c c u r i n t h e condense r i t s e l f ) . I f , i n a d d i t i o n , t he n o n c o n d e n s a b l e s t e n d t o
accumu la te i n t h e c o n d e n s e r , t h e n t h e i r p r e s s u r e may cause t h e t o t a l p r e s s u r e
i n t h e condense r t o i n c r e a s e , t h i s r e d u c i n g t he a v a i l a b l e vacuum even f u r t h e r .
As a r e s u l t , t h e t e m p e r a t u r e i n t h e equ ipment u n i t may be i n c r e a s e d and a h i g h e r
h e a t i n g - v a p o u r t e m p e r a t u r e may become n e c e s s a r y .
O b v i o u s l y , a t e n d e n c y t o w a r d s i n c r e a s e d t e m p e r a t u r e s o f h e a t i n g v a p o u r s w o u l d
have a d e t r i m e n t a l e f f e c t on t h e h e a t economy. I t can be p r e v e n t e d , h o w e v e r , by
p a y i n g p r o p e r a t t e n t i o n t o t h r e e f a c t o r s c h a r a c t e r i z i n g t he vacuum s y s t e m :
( i ) A v a p o u r - c o n d e n s a t i o n t e m p e r a t u r e c l o s e t o t he i n l e t t e m p e r a t u r e o f c o o l i n g
w a t e r e n t e r i n g t h e c o n d e n s e r ;
( i i ) E f f e c t i v e e v a c u a t i o n o f n o n c o n d e n s a b l e s f rom the c o n d e n s e r ;
( i i i ) S u f f i c i e n t l y smal l p r e s s u r e d r o p s between t h e equ ipment o p e r a t e d under
vacuum and t h e c o n d e n s e r .
M i n i m i z a t i o n o f t h e t e m p e r a t u r e d i f f e r e n c e between t he c o n d e n s i n g v a p o u r and
t h e c o o l i n g w a t e r i s an i m p o r t a n t r e q u i r e m e n t t o be a c c o u n t e d f o r i n c o n d e n s e r
d e s i g n . A d i s c u s s i o n o f t h e a d v a n t a g e s and d i s a d v a n t a g e s o f v a r i o u s d e s i g n s can
be f ound i n t h e l i t e r a t u r e ( r e f s . 3 , 4 0 ) . Many f a c t o r i e s r e l y on s i m p l e , and
q u i t e e f f e c t i v e , c o u n t e r - c u r r e n t s h e l f - t y p e b a r o m e t r i c c o n d e n s e r s . An o u t l i n e o f
a d e s i g n p r e s e n t l y used i n D a n i s h s u g a r f a c t o r i e s can be seen i n F i g . 3 .22 .
A n o t h e r condense r d e s i g n , implemented r e c e n t l y i n t he S o v i e t s u g a r i n d u s t r y ,
c o n s i s t s o f two v e s s e l s c o n n e c t e d i n s e r i e s ( F i g . 3 . 2 3 ) . Vapour e n t e r i n g t h e
129
cooling ρ — ^ water Τ τ - ^ ^
vapour
to vacuum pump
barometric water
F i g . 3 .22 . O u t l i n e o f a c o u n t e r - c u r r e n t s h e l f - t y p e b a r o m e t r i c c o n d e n s e r ( c o u r t e s y D O S ) .
F i g . 3 .23 . Scheme o f a b a r o m e t r i c c o n d e n s e r f e a t u r i n g a c o - c u r r e n t v e s s e l ( a ) and a c o u n t e r - c u r r e n t v e s s e l ( b ) . 1 - v a p o u r i n l e t , 2 - c o o l i n g w a t e r i n l e t , 3 - w a t e r o u t l e t , 4 - vacuum l i n e .
130
f i r s t v e s s e l i s s u b j e c t t o c o - c u r r e n t c o o l i n g as w a t e r f l o w s down t h e s h e l v e s .
The f i r s t p o r t i o n o f w a t e r can be w i t h d r a w n f rom t h e upper p a r t o f t h e v e s s e l .
P r o v i d i n g t h i s w a t e r does n o t mix w i t h t h e main c o o l i n g - w a t e r s t r e a m , t h e upper
p a r t o f t h e f i r s t v e s s e l can be t r e a t e d as an e n t r a i n m e n t s e p a r a t o r . I t i s a l s o
p o s s i b l e t o u t i l i z e t h i s p a r t o f t he c o n d e n s e r as a d i r e c t - c o n t a c t h e a t e r ; f o r
examp le , f r e s h w a t e r s u p p l i e d t o t h e e x t r a c t o r can be hea ted t h e r e . C o - c u r r e n t
c o o l i n g ( u s i n g w a t e r f rom t h e main c o o l i n g c i r c u i t ) c o n t i n u e s i n t h e l o w e r p a r t
o f t he v e s s e l , t h i s be ing f o l l o w e d by c o u n t e r - c u r r e n t c o o l i n g i n t h e second
v e s s e l . I n compar i son t o vacuum sys tems emp loy ing s i m p l e c o u n t e r - c u r r e n t
c o n d e n s e r s , t h i s d e s i g n i s c l a i m e d t o r e d u c e t h e c o o l i n g - w a t e r demand by 25-30%
( r e f . 4 1 ) .
The e v a c u a t i o n o f n o n c o n d e n s a b l e s f rom t h e c o n d e n s e r i s e f f e c t e d u s i n g vacuum
pumps, u s u a l l y o f t h e w a t e r - r i n g t y p e . I n a d d i t i o n t o t h e g e n e r a l c o n d e n s e r
d e s i g n , t h e l o c a t i o n and d i m e n s i o n o f t h e g a s - w i t h d r a w a l n o z z l e i s i m p o r t a n t , as
i t may o r may n o t e n s u r e t h a t t h e gas e v a c u a t i o n i s s u f f i c i e n t and t h e gas
t e m p e r a t u r e i s as low as p o s s i b l e . ( T h e l o w e r t h i s t e m p e r a t u r e , t h e s m a l l e r i s
t he e n e r g y e x p e n d i t u r e i n t h e vacuum pump d r i v e . )
As r e g a r d s t h e p r e s s u r e d r o p s a l o n g t h e v a p o u r p a t h s between equ ipment u n i t s
and t h e c o n d e n s e r , some s p e c i f i c p rob lems may a r i s e depend ing on t h e scheme o f
t h e vacuum i n s t a l l a t i o n . I n t h e case o f i n d i v i d u a l c o n d e n s e r s , i t i s e s s e n t i a l
t o choose channe l d i m e n s i o n s i n a c c o r d a n c e w i t h maximum v a p o u r - f l o w v a l u e s ( f o r
examp le , v a p o u r c h a n n e l s a t t a c h e d t o a vacuum pan s h o u l d be d i m e n s i o n e d f o r t h e
v a p o u r f l o w e x p e c t e d d u r i n g t h e s y r u p - t h i c k e n i n g phase o f t he b o i l i n g c y c l e ) . I f
a c e n t r a l c o n d e n s e r i s e m p l o y e d , t h e n a d e l i c a t e p rob lem a r i s e s o f f l o w
d i s t r i b u t i o n i n p a r a l l e l s e c t i o n s o f t h e vacuum p i p i n g .
L a r g e d i a m e t e r s o f n o z z l e s , v a l v e s and p i p e s i n d u c e a t e n d e n c y t o w a r d s
s e l e c t i n g t o o smal l d i m e n s i o n s , t h i s r e s u l t i n g i n t o o l a r g e p r e s s u r e d r o p s .
T r a d i t i o n a l l y , c a l c u l a t i o n s o f t h e vacuum p i p i n g have been based on t h e
recommended v a l u e s o f f l o w v e l o c i t i e s i n s e r t e d i n t o i n c o m p r e s s i b l e - f l o w f o r m u l a e
e x p r e s s i n g t h e p r e s s u r e d r o p ( r e f . 3 ) . I t can be p r o v e d , h o w e v e r , t h a t n e g l e c t
o f t h e v a p o u r c o m p r e s s i b i l i t y may cause a s y s t e m a t i c e r r o r o f abou t 10% o f t h e
c a l c u l a t e d p r e s s u r e d rop ( r e f . 4 2 ) . An example o f c a l c u l a t i o n s o f t h e vacuum
p i p i n g u s i n g c o m p r e s s i b l e - f l o w f o r m u l a e can be f o u n d i n t h e l i t e r a t u r e
( r e f . 4 3 ) .
I t s h o u l d be added t h a t t h e above d i s c u s s i o n c a n n o t be c o n s i d e r e d as a
comple te p r e s e n t a t i o n o f t h e r e q u i r e m e n t s r e l a t i n g t o e f f i c i e n t vacuum s y s t e m s .
F o r examp le , s t a b i l i t y o f t h e vacuum l e v e l i s v e r y i m p o r t a n t t o bo th t h e h e a t
economy and t he r e l i a b i l i t y o f vacuum-pan o p e r a t i o n . The s t a b i l i t y r e q u i r e m e n t s
t o be a c c o u n t e d f o r i n t h e c o n d e n s e r d e s i g n a r e r e v i e w e d i n t h e l i t e r a t u r e
( r e f . 4 4 ) .
131
3 .3 .4 U t i l i z a t i o n o f l o w - p r e s s u r e v a p o u r s
I n S e c t i o n 1.2, u t i l i z a t i o n o f l o w - t e m p e r a t u r e h e a t and c e r t a i n p rob lems
a s s o c i a t e d w i t h t he equ ipment used f o r t h i s p u r p o s e were p r e l i m i n a r i l y
d i s c u s s e d . I n t h i s a r e a , t h e u t i l i z a t i o n o f vacuum-pan v a p o u r s i s o f p a r t i c u l a r
i m p o r t a n c e . T h i s p rob lem has much i n common w i t h t h e u t i l i z a t i o n o f l a s t - e f f e c t
v a p o u r f rom t h e e v a p o r a t o r .
The p o s s i b i l i t i e s o f h e a t i n g w i t h vacuum-pan v a p o u r s a re l i m i t e d by t h e i r low
t e m p e r a t u r e , 55-65°C. A p o p u l a r s o l u t i o n known f rom l e s s e f f i c i e n t the rma l
sys tems i s t o h e a t f r e s h w a t e r s u p p l i e d t o t h e e x t r a c t o r . T h i s can be d o n e , f o r
examp le , i n t he i n l e t p a r t o f t h e d o u b l e - v e s s e l c o n d e n s e r men t i oned i n t h e
p r e c e d i n g S e c t i o n ; i t has been r e p o r t e d t h a t w a t e r t e m p e r a t u r e s as h i g h as 1-2 Κ
be low the v a p o u r t e m p e r a t u r e can be a t t a i n e d ( r e f . 4 5 ) . I n h i g h l y e f f i c i e n t
thermal s y s t e m s , h o w e v e r , t h e e x t r a c t o r s h o u l d r a t h e r be s u p p l i e d w i t h e x c e s s
c o n d e n s a t e , and o t h e r methods o f u t i l i z a t i o n o f vacuum-pan v a p o u r s s h o u l d be
p r e f e r r e d .
A t y p i c a l e n e r g y - e f f i c i e n t s o l u t i o n i s t o h e a t raw j u i c e i n a h e a t e r o f
a s u i t a b l e d e s i g n . I t seems t h a t h o r i z o n t a l l y - o r v e r t i c a l l y - a r r a n g e d t u b u l a r
h e a t e r s a re most f r e q u e n t l y u s e d , w h i l e a p p l i c a t i o n s o f s p i r a l h e a t e r s a r e a l s o
known. Raw j u i c e can be hea ted t o t h e 50-55°C r e q u i r e d f o r h o t p r e - l i m i n g , t h i s
making i t p o s s i b l e t o u t i l i z e 4-5 kg vacuum-pan v a p o u r p e r 100 kg b e e t . The 2
h e a t i n g s u r f a c e a r e a r e q u i r e d i s t y p i c a l l y o f t h e o r d e r 70-110 m p e r 100 t / d
p r o c e s s i n g c a p a b i l i t y . I f t h e t e m p e r a t u r e i n t h e p r e - l i m e r i s l o w e r , t h e n p r e -
l imed j u i c e can be hea ted i n s t e a d .
The l e a d i n g p r i n c i p l e o f h e a t i n g w i t h vacuum-pan v a p o u r s i s t o aim a t as h i g h
a v a p o u r - c o n d e n s a t i o n t e m p e r a t u r e i n t h e h e a t e r as p o s s i b l e . C o n s e q u e n t l y ,
v a p o u r s f rom pans A a re p r e f e r r e d t o t h o s e f rom Β and C p a n s . P r o p e r p r e c a u t i o n s
s h o u l d a l s o be taken a g a i n s t t h e i n f l u e n c e o f noncondensab le gases c o n s i s t i n g
m a i n l y o f a i r l i b e r a t e d f rom j u i c e and s y r u p s d u r i n g t h e t h i c k e n i n g p h a s e , a i r
e n t e r i n g t h e vacuum pans d u r i n g t h e i n t e r v a l s between t h e b o i l i n g c y c l e s , and
a i r l e a k i n g i n t o t h e vacuum s y s t e m . The volume o f n o n c o n d e n s a b l e s i s u s u a l l y
abou t 1% o f t he v a p o u r vo l ume .
The i n f l u e n c e o f n o n c o n d e n s a b l e s i s e l i m i n a t e d i f t h e h e a t e r i s p r o p e r l y
c o n n e c t e d t o t h e vacuum s y s t e m . I n F i g . 3 .24 , two d i f f e r e n t s o l u t i o n s a r e shown
s c h e m a t i c a l l y . I n case ( a ) , t h e e n t i r e v a p o u r f l o w f rom t h e vacuum pans i s
d i r e c t e d t o t h e h e a t e r and t o t h e c o n d e n s e r , t h i s e f f e c t i v e l y p r e v e n t i n g t h e
a c c u m u l a t i o n o f n o n c o n d e n s a b l e s . The h e a t e r d e s i g n must be adap ted t o a v e r y
l a r g e volume f l o w o f v a p o u r , w h i c h r e q u i r e s a r e l a t i v e l y l a r g e h e a t e r d i a m e t e r
and s p a r s e l y p l a c e d t u b e s , so as n o t t o e x c e e d a v a p o u r p r e s s u r e d rop o f
0 .01-0 .02 b a r . Two s u i t a b l e d e s i g n s i n w h i c h a v a p o u r - f l o w v e l o c i t y o f up t o
40-50 m/s has been assumed a r e shown s c h e m a t i c a l l y i n F i g s . 3.25 (one v a p o u r -
132
(α) (b )
3
- 0
3
Ν /
F i g . 3 .24 . H e a t e r a r rangemen ts s u i t e d t o h e a t i n g w i t h vacuum-pan v a p o u r s : ( a ) h e a t e r s u p p l i e d w i t h t h e e n t i r e v a p o u r f l o w , ( b ) h e a t e r s u p p l i e d w i t h a p a r t o f t he v a p o u r f l o w . 1 - h e a t e r , 2 - foam c a t c h e r , 3 - c o n d e n s e r .
s i d e pass and f o u r j u i c e - s i d e p a s s e s ) and 3.26 ( two and t w e l v e p a s s e s ,
r e s p e c t i v e l y ) . O t h e r d e s i g n s have a l s o been p r e s e n t e d i n t h e l i t e r a t u r e ( r e f .
4 7 ) . G e n e r a l l y , t he h e a t e r d i m e n s i o n s a r e v e r y l a r g e and i t may be d i f f i c u l t t o
f i n d a p l a c e i n an e x i s t i n g f a c t o r y where such a u n i t can be i n s t a l l e d .
I n case ( b ) , t he h e a t e r i s c o n n e c t e d t o a v a p o u r l i n e p a r a l l e l t o t h e main
v a p o u r m a n i f o l d . The v a p o u r f l o w t h r o u g h t h e h e a t e r i s t y p i c a l l y 25-30% o f t h e
t o t a l f l o w , t h i s making i t p o s s i b l e t o r e d u c e t h e d i m e n s i o n s o f t h e u n i t . As t h e
d i a m e t e r s o f t he v a p o u r p i p e s can a l s o be r e d u c e d , i t becomes e a s i e r t o i n s t a l l
t he h e a t e r i n a manner f a c i l i t a t i n g c o n v e n i e n t a c c e s s f o r r e p a i r and
m a i n t e n a n c e . Vapour f rom t h e h e a t e r o u t l e t i s d i r e c t e d t o t h e main v e s s e l o f
a d o u b l e - v e s s e l main c o n d e n s e r (when a c o n d e n s i n g sys tem s i m i l a r t o t h a t
p r e s e n t e d i n S e c t i o n 3 .3 .3 i s a p p l i e d ) , o r t o an i n d i v i d u a l c o n d e n s e r . I n t h i s
c a s e , t h e volume c o n c e n t r a t i o n o f n o n c o n d e n s a b l e s a t t h e v a p o u r o u t l e t may
a t t a i n 4-5%, d e c r e a s i n g t h e c o n d e n s a t i o n t e m p e r a t u r e by abou t 1-1.5 K. I t i s
t h e r e f o r e recommended t o adap t t h e h e a t e r d e s i g n t o t h e f o l l o w i n g r e q u i r e m e n t s
o f e f f i c i e n t v e n t i n g :
uice
8 nn
— C7>
vapour
F i g . 3 .25 . Scheme o f a t u b u l a r h e a t e r hea ted w i t h vacuum-pan v a p o u r , h e a t i n g s u r f a c e a r e a 125 m2. 1 - t u b e s , 2 - i n t e r m e d i a t e t ube s h e e t s , 3 - c o n d e n s a t e -s e p a r a t i n g b a f f l e , 4 - p r o t e c t i v e s c r e e n s ( a f t e r r e f . 4 6 ) .
(α)
133
(b)
baffle
external wall
holes
F i g . 3 .26 . Scheme o f a t u b u l a r h e a t e r h e a t e d w i t h vacuum-pan v a p o u r , h e a t i n g s u r f a c e a r e a 250 m^ ( c o u r t e s y Chemadex) . ( a ) g e n e r a l l a y o u t , ( b ) d e t a i l o f t h e b a f f l e , t o p v i e w .
- v a p o u r - f l o w v e l o c i t y i n t h e f r e e - f l o w ( i . e . d i s r e g a r d i n g t h e p r e s e n c e o f
h e a t i n g t u b e s ) h e a t e r c r o s s - s e c t i o n a r e a c l o s e t o t h e v a p o u r i n l e t s h o u l d be
10-15 m/s , t o p r e v e n t t he d i f f u s i o n o f n o n c o n d e n s a b l e s ;
- c o l d j u i c e s h o u l d e n t e r t h e h e a t i n g t u b e s i n t h e v i c i n i t y o f t h e v a p o u r
o u t l e t , t o s t i m u l a t e i d e n t i c a l f l o w d i r e c t i o n s o f bo th v a p o u r and
n o n c o n d e n s a b l e s .
The above comments and recommendat ions a p p l y a l s o t o t h e h e a t e r s s u p p l i e d
w i t h v a p o u r s f rom t h e l a s t e v a p o r a t o r e f f e c t . A d i s c u s s i o n o f a h e a t e r
a r rangement f o r r a w - j u i c e h e a t i n g u s i n g f i f t h - e f f e c t v a p o u r can be f o u n d i n t h e
l i t e r a t u r e ( r e f . 4 8 ) .
A number o f a l t e r n a t i v e methods o f u t i l i z a t i o n o f l o w - t e m p e r a t u r e v a p o u r s
have a l s o been p r o p o s e d . I n t h e S o v i e t s u g a r i n d u s t r y , d i r e c t - c o n t a c t h e a t e r s
f o r r a w - j u i c e h e a t i n g a r e i n use ( F i g . 3 . 2 7 ) . W h i l e t h i s equ ipment i s s i m p l e and
easy t o imp lement , t h e a d v a n t a g e s o f i t s a p p l i c a t i o n a r e f a r f rom o b v i o u s ,
because t h e j u i c e becomes d i l u t e d w i t h c o n d e n s a t e , t h u s r e q u i r i n g i n c r e a s e d
e v a p o r a t i o n i n t h e e v a p o r a t o r . I n o r d e r t o r e d u c e t h e n e t h e a t demand, i t i s
n e c e s s a r y t o a d j u s t t he d i s t r i b u t i o n o f t h e h e a t i n g v a p o u r s p r i o r t o t h e
imp lemen ta t i on o f a d i r e c t - c o n t a c t h e a t e r ( r e f . 5 0 ) .
A n o t h e r method o f u t i l i z a t i o n o f vacuum-pan v a p o u r s employs an i n t e r m e d i a t e
134
View A
F i g . 3 .27 . Scheme o f a d i r e c t - c o n t a c t j u i c e h e a t e r hea ted w i t h vacuum-pan v a p o u r . 1 - j u i c e i n l e t , 2 - j u i c e o u t l e t , 3 - v a p o u r , 4 - n o n c o n d e n s a b l e s .
w a t e r c i r c u i t f o r hea t t r a n s p o r t t o a i r p r e h e a t e r s i n t h e b o i l e r s o r i n t h e
d r y i n g s t a t i o n s ( s u g a r d r y e r , l o w - t e m p e r a t u r e p u l p d r y e r , e t c . ) . A c o n d e n s e r -
h e a t e r ( " h o t c o n d e n s e r " ) w h i c h has been d e s i g n e d f o r such a p p l i c a t i o n s i s shown
s c h e m a t i c a l l y i n F i g . 3 .28 . A t l e a s t one m a n u f a c t u r e r i s now o f f e r i n g a comp le te
c i r c u i t w h i c h c o n s i s t s o f a c o n d e n s e r - h e a t e r , w a t e r t a n k , pump, and a s p i r a l
hea t e x c h a n g e r f o r r a w - j u i c e h e a t i n g . I t i s c l a i m e d t h a t t h i s s o l u t i o n i s more
economic t han a c o n v e n t i o n a l r a w - j u i c e h e a t e r s u p p l i e d w i t h vacuum-pan v a p o u r .
I n a number o f F r e n c h and West German s u g a r f a c t o r i e s , vacuum-pan v a p o u r s
a re u t i l i z e d i n s p e c i a l e v a p o r a t o r s f o r t h i c k e n i n g j u i c e o r Β s y r u p . As
imp lemen ta t i on o f t h i s method i s v e r y much dependen t on t h e a v a i l a b i l i t y o f
s u i t a b l e equ ipmen t , i t i s d i s c u s s e d i n C h a p t e r 5. I t i s w o r t h n o t i n g t h a t i n t h e
f a c t o r i e s where t h i s method i s a p p l i e d , t h e t o t a l a r e a o f t h e h e a t i n g s u r f a c e s
o f t h e equ ipment hea ted by vacuum-pan v a p o u r s may a t t a i n 380-400 m p e r 1000 t / d
p r o c e s s i n g c a p a b i l i t y .
3.4 VAPOUR COMPRESSION
3.4.1 Compress ion o f v a p o u r s f rom t h e e v a p o r a t o r
An i n t r o d u c t i o n t o t he a p p l i c a t i o n o f v a p o u r c o m p r e s s i o n t e c h n i q u e s was
p r e s e n t e d i n S e c t i o n 1 .2 .7 . T h e r e i s a v a s t l i t e r a t u r e d e v o t e d t o t h e p rob lems
o f comb in ing v a p o u r compress i on c i r c u i t s w i t h v a r i o u s e n e r g y sys tems i n t h e
135
to vacuum pump
1
condensate
water 39 C
cooling water 30"c
cooling ^ water 35 C
φ ) vapour
water 56 C
F i g . 3 .28 . Condenser t o w e r f o r t h e c o n d e n s a t i o n o f vacuum-pan v a p o u r ( c o u r t e s y W i e g a n d ) .
s u g a r i n d u s t r y ( r e f s . 2 , 3 , 5 1 - 5 9 ) . Wor th recommending a l s o i s a b r o c h u r e w h i c h
summar izes t h e p r e s e n t s t a t e - o f - t h e - a r t i n t h e f i e l d o f a p p l i c a t i o n s o f
mechan ica l v a p o u r compresso rs i n v a r i o u s p r o c e s s i n d u s t r i e s ( r e f . 6 0 ) . I n t h i s
S e c t i o n , we s h a l l c o n c e n t r a t e on t h e two s o l u t i o n s most f r e q u e n t l y used i n s u g a r
f a c t o r i e s , namely t h o s e emp loy ing t h e c o m p r e s s i o n o f v a p o u r s f rom t h e f i r s t and
t h e second e v a p o r a t o r e f f e c t s .
I t was i n d i c a t e d i n S e c t i o n 1.2.7 t h a t b e f o r e t h e i n t r o d u c t i o n o f a v a p o u r
compress ion c i r c u i t i n t o a the rma l s y s t e m , i t may be n e c e s s a r y t o r e a r r a n g e t h e
d e t a i l s o f t he d i s t r i b u t i o n o f v a p o u r s f rom t h e e v a p o r a t o r . L e t us c o n s i d e r t h e
example o f a r a t h e r i n e f f i c i e n t the rma l sys tem c h a r a c t e r i z e d by a r e l a t i v e l y
l a r g e steam demand, namely 47.9 kg/100 kg b, c o n s i s t i n g o f :
- h e a t i n g steam a t t h e pa rame te rs c o r r e s p o n d i n g t o t h e t u r b i n e e x h a u s t , s u p p l i e d
t o t h e e v a p o r a t o r and t he s u g a r d r y e r , 46.4 kg/100 kg b;
- l i v e steam t h r o t t l e d t o 7 b a r , s u p p l i e d t o t h e c e n t r i f u g a l s , 1.5 kg/100 kg b.
The f a c t o r y c o n s i d e r e d employs a t r o u g h - t y p e e x t r a c t o r , s u p p l i e d w i t h f r e s h
w a t e r f rom o u t s i d e t h e f a c t o r y , a c l a s s i c a l j u i c e - p u r i f i c a t i o n s t a t i o n , a
q u a d r u p l e - e f f e c t e v a p o r a t o r i n w h i c h t h e j u i c e i s t h i c k e n e d f rom 15.5% DS t o
136
65% DS, and a t h r e e - b o i l i n g c r y s t a l l i z a t i o n scheme. The e s s e n t i a l f e a t u r e s o f
t h e v a p o u r d i s t r i b u t i o n scheme and t h e v a p o u r f l o w s a r e g i v e n i n T a b l e 3 . 3 . L e t
us n o t e t h a t t he f l o w o f l a s t - e f f e c t v a p o u r t o t h e c o n d e n s e r can be r e g a r d e d as
s u f f i c i e n t l y s m a l l , and u n l e s s t h e v a p o u r d i s t r i b u t i o n i s c h a n g e d , no v a p o u r
s t ream i s d i r e c t l y a v a i l a b l e f o r a p o s s i b l e v a p o u r - c o m p r e s s i o n c i r c u i t .
TABLE 3.3
Steam and v a p o u r s t reams (kg /100 kg b) between s o u r c e s and r e c e i v e r s i n a the rma l sys tem consuming 47.9 kg steam p e r 100 kg b e e t .
S o u r c e s
R e c e i v e r s E v a p o r a t o r e f f e c t s O t h e r s
1
P r e s s - w a t e r h e a t e r 1 .95 E x t r a c t o r 2.17 0 .21 R a w - j u i c e h e a t e r condensa te H e a t e r s b e f o r e main l i m i n g 6 .80 H e a t e r a f t e r 1s t c a r b o n a t a t i o n 3.22 H e a t e r b e f o r e 2nd c a r b o n a t a t i o n 2.86 T h i n - j u i c e h e a t e r s 2.52 3.38 T h i c k - j u i c e h e a t e r 0.15 M e l t e r 0.20 I n d i r e c t l y - h e a t e d s y r u p t a n k s 0.45 D i r e c t l y - h e a t e d s y r u p t anks 0.58 Remelt h e a t e r 0.20 Vacuum pans A 12.80
Β 3.40 C 1.31
Vacuum-pan s teaming 1.50 C e n t r i f u g a l s 7 ba r steam 1.50 Sugar d r y e r e x h a u s t steam 0.50 Condense r 0.71
E v a p o r a t o r t o t a l 2.52 32.22 8. .96 0.71
I t can be c o n c l u d e d f rom t h e d a t a p r e s e n t e d i n T a b l e 3.3 t h a t t h e h e a t
economy can be improved by i n t r o d u c i n g t h e u t i l i z a t i o n o f f o u r t h - e f f e c t v a p o u r
and vacuum-pan v a p o u r s . An a d d i t i o n a l improvement can be o b t a i n e d by s u p p l y i n g
t h e e x t r a c t o r w i t h e x c e s s c o n d e n s a t e , i n s t e a d o f f r e s h w a t e r s u p p l i e d a t a l o w e r
i n i t i a l t e m p e r a t u r e . L e t us assume t h a t t h e s e changes a r e i n t r o d u c e d w i t h o u t any
m o d i f i c a t i o n s o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s ; most n o t a b l y , t h e t h i c k - j u i c e
c o n c e n t r a t i o n remains a t 65% DS.
F o l l o w i n g t h e u t i l i z a t i o n o f t h e vacuum-pan v a p o u r s i n r a w - j u i c e h e a t i n g and
o t h e r hea t -economy improvemen ts , t h e demand f o r h e a t i n g v a p o u r s f rom t h e
e v a p o r a t o r i s r e d u c e d . I n o r d e r t o keep t h e t h i c k - j u i c e c o n c e n t r a t i o n c o n s t a n t ,
t h i s can be compensated f o r by a r t i f i c i a l l y w i t h d r a w i n g a s u f f i c i e n t l y l a r g e
v a p o u r s t ream f rom t h e e v a p o r a t o r . L e t us assume t h a t t h i s s t ream can be t a k e n
f rom t h e f i r s t e v a p o r a t o r e f f e c t .
137
The e s s e n t i a l f e a t u r e s o f t h e improved v a p o u r d i s t r i b u t i o n scheme, i n c l u d i n g
t h e f l o w s o f h e a t i n g v a p o u r s f rom t h e e v a p o r a t o r and vacuum p a n s , a r e shown i n
T a b l e 3 . 4 . As can be s e e n , a v a p o u r s t ream o f 10 kg/100 kg b i s w i t h d r a w n f rom
t h e f i r s t e f f e c t . T h i s v a p o u r can be compressed t o t h e e x h a u s t - s t e a m p r e s s u r e
and u t i l i z e d i n t he h e a t i n g chamber o f t h e f i r s t e f f e c t , c u t t i n g down t h e demand
f o r e x h a u s t steam s u p p l i e d t o t h e e v a p o r a t o r .
TABLE 3.4
Steam and v a p o u r s t reams (kg /100 kg b) between s o u r c e s and r e c e i v e r s i n t h e m o d i f i e d the rma l s y s t e m .
S o u r c e s
R e c e i v e r s E v a p o r a t o r e f f e c t s O t h e r s
1
P r e s s - w a t e r h e a t e r 1. ,97 E x t r a c t o r 0. .90 0.92 R a w - j u i c e h e a t e r vacuum-pan v a p o u r H e a t e r s b e f o r e main l i m i n g 2.85 3. ,36 c o n d e n s a t e H e a t e r a f t e r 1 s t c a r b o n a t a t i o n 2.62 H e a t e r b e f o r e 2nd c a r b o n a t a t i o n 2, .50 T h i n - j u i c e h e a t e r s 2. .24 2, .43 1.65 T h i c k - j u i c e h e a t e r 0.15 M e l t e r 0, .20 I n d i r e c t l y - h e a t e d s y r u p t a n k s 0, .45 D i r e c t l y - h e a t e d s y r u p t anks 0, .58 Remel t h e a t e r 0.18 Vacuum pans A 12, .80
Β 3 .40 C 1 .31
Vacuum-pan s teaming 1 .50 C e n t r i f u g a l s 7 ba r steam 1.50 Sugar d r y e r e x h a u s t steam 0.50 Condenser 0, .09 To be w i t h d r a w n 10, .00 (5 .00) *
E v a p o r a t o r t o t a l 12, .24 26 .07 8.37 5, .42
V a p p l i e s t o c o m p r e s s i o n o v e r two s t a g e s
B e f o r e d i s c u s s i n g p o s s i b l e s o l u t i o n s f o r t h e v a p o u r c o m p r e s s i o n c i r c u i t , l e t
us assume t h e f o l l o w i n g v a l u e s o f t h e e n e r g y c o n v e r s i o n and d i s t r i b u t i o n
p r o c e s s e s i n t h e f a c t o r y :
- l i v e steam p r e s s u r e 38 ba r and t e m p e r a t u r e 450°C;
- e x h a u s t steam t e m p e r a t u r e 135°C, f i r s t - e f f e c t v a p o u r t e m p e r a t u r e 126°C ( d r y
s a t u r a t e d steam i n bo th c a s e s , t h a t i s , p r e s s u r e s o f 3.13 ba r and 2.39 b a r ,
r e s p e c t i v e l y ) ;
- power consumpt ion i n t h e f a c t o r y 3 kWh p e r 100 kg b e e t ;
- steam r a t e o f t h e t u r b o - g e n e r a t o r 8 kg /kWh;
- on a v e r a g e , 37.4 % o f t h e h e a t i n g s team, i . e . 17.36 kg/100 kg b , d e l i v e r e d
138
f rom t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n .
L e t us a l s o o b s e r v e t h a t 62.6% o f t he h e a t i n g - s t e a m f l o w d e l i v e r e d v i a t h e
t u r b i n e makes i t p o s s i b l e t o g e n e r a t e 3.63 kWh p e r 100 kg b e e t , so t h e f a c t o r y
i s a b l e t o s e l l an e l e c t r i c i t y s u r p l u s o f t h e o r d e r o f 20% o f i t s own power
c o n s u m p t i o n .
3 .4 .2 Mechan i ca l v s . j e t - t y p e compresso rs
To b e g i n w i t h , l e t us c o n s i d e r a compress i on c i r c u i t emp loy ing an
e l e c t r i c a l l y - d r i v e n , s i n g l e - s t a g e mechan ica l c o m p r e s s o r . The v a p o u r c o m p r e s s i o n
p r o c e s s i s shown i n t he M o l l i e r d iag ram i n F i g . 3 .29 . S p e c i f i c power consumpt ion
( p e r 1 kg v a p o u r ) can be c a l c u l a t e d as
P 3 = ( h , 3 - h ^ l ) / { n , n ^ ) ( 3 . 1 0 )
where h^-j i s t h e e n t h a l p y o f f i r s t - e f f e c t v a p o u r , h^^ i s t h e f i n a l v a p o u r
e n t h a l p y i n t he i s e n t r o p i c compress i on p r o c e s s , i s t h e c o m p r e s s i o n e f f i c i e n c y
and i s t he mechan ica l e f f i c i e n c y .
Assuming = 0 .68 , = 0.95 and u s i n g t he pa ramete r v a l u e s l i s t e d i n t h e
p r e c e d i n g S e c t i o n ( e n t h a l p y v a l u e s a c c o r d i n g t o U . G r i g u l l ( E d . ) , P r o p e r t i e s o f
Water and Steam i n S l - U n i t s , 2nd e d n . , S p r i n g e r - V e r l a g , B e r l i n - H e i d e l b e r g - N e w
Y o r k , 1979) , we o b t a i n
Pg = (2764.1 - 2 7 1 4 . 4 ) / ( 0 . 6 8 - 0 . 9 5 ) = 76.9 k J / k g = 0.0214 kWh/kg
2800
Oí
1^2750 o JZ ·•-· c ÜJ
2700
6.95 7.00 7.05 7.10 715
Entropy ( k ^ i R g K ) )
F i g . 3 .29 . Compress ion o f f i r s t - e f f e c t v a p o u r i n a mechan ica l c o m p r e s s o r .
139
The e n t h a l p y o f t he compressed v a p o u r i s
h^^ = h^^ + ( h ^ ^ - h ^ ^ ) / n ^ = 2714.4 + (2764.1 - 2 7 1 4 . 4 ) / 0 . 6 8 = 2787.5 k J / k g
T h i s c o r r e s p o n d s t o a t e m p e r a t u r e o f 163.2°C, t h a t i s , 28.2 Κ above t h e
s a t u r a t i o n t e m p e r a t u r e . The compressed v a p o u r s h o u l d be d e s u p e r h e a t e d by
condensa te i n j e c t i o n and t h e n d i r e c t e d t o t h e h e a t i n g chamber o f t h e f i r s t
e v a p o r a t o r e f f e c t . Assuming t h e c o n d e n s a t e e n t h a l p y c o r r e s p o n d i n g t o t h e l i q u i d
s a t u r a t e d s t a t e a t t h e e x h a u s t - s t e a m p r e s s u r e , t h a t i s , h^ = 567.7 k J / k g , t h e
mass o f condensa te needed t o d e s u p e r h e a t 1 kg compressed v a p o u r can be
c a l c u l a t e d as
= ( h ^ c " • ^ ) ( 2 · ^ ^ '
where h^ i s t h e e n t h a l p y o f e x h a u s t steam (assumed t o be d r y s a t u r a t e d steam a t
3.13 ba r p r e s s u r e ) .
A f t e r i n s e r t i n g t h e e n t h a l p y v a l u e s , we o b t a i n
m^ = (2787.5 - 2 7 2 6 . 6 ) / ( 2 7 2 6 . 6 - 567.7) = 0.028 kg /kg
U s i n g t h e r e s u l t s o f t h e above c a l c u l a t i o n s , we can summarize t h e
consequences o f i n t r o d u c i n g a v a p o u r - c o m p r e s s i o n c i r c u i t based on a mechan ica l
compresso r as f o l l o w s .
( i ) H e a t i n g steam demand i s r e d u c e d by 10 · (1 + 0.028) = 10.28 kg/100 kg b , i . e .
by abou t 21.5% o f t h e i n i t i a l steam demand. T h i s makes i t p o s s i b l e t o c u t down
t h e l i v e steam f l o w t h r o u g h t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n t o l e s s t han
41% o f i t s i n i t i a l v a l u e .
( i i ) Power demand i s i n c r e a s e d by 10-0.0214 = 0.214 kWh/100 kg b , i . e . by abou t
7% o f t h e i n i t i a l v a l u e .
L e t us o b s e r v e t h a t t he power o u t p u t remains u n a f f e c t e d , t h i s i m p l y i n g t h a t
t h e r e i s a change i n t h e power b a l a n c e , namely a r e d u c t i o n o f t h e e l e c t r i c i t y
s u r p l u s w h i c h can be s o l d t o t h e e x t e r n a l g r i d .
A d i f f e r e n t r e s u l t i s o b t a i n e d when t h e e l e c t r i c motor d r i v i n g t h e compresso r
i s r e p l a c e d by a steam t u r b i n e . Assuming a steam r a t e o f abou t 12 kg/kWh w h i c h
i s t y p i c a l o f sma l l s i n g l e - s t a g e t u r b i n e s , 2.56 kg l i v e steam p e r 100 kg b e e t i s
needed t o d r i v e t h e c o m p r e s s o r , and t h e expanded steam f rom t h e t u r b i n e e x h a u s t
can be mixed w i t h t h e compressed v a p o u r . I n t h i s c a s e , a r e d u c t i o n o f t h e
h e a t i n g - s t e a m demand and a s i m u l t a n e o u s i n c r e a s e o f t h e l i v e - s t e a m demand
r e s u l t i n a n e t s a v i n g o f abou t 21.5% o f t h e i n i t i a l steam demand, w h i l e t h e
power o u t p u t and t h e power demand remain unchanged . I t i s t h e r e f o r e w e l l w o r t h
c o n s i d e r i n g a t u r b i n e - d r i v e n compresso r as an i n t e r e s t i n g a l t e r n a t i v e t o an
e l e c t r i c a l l y - d r i v e n o n e .
Recen t examples o f t h e a p p l i c a t i o n o f e l e c t r i c a l l y - d r i v e n c o m p r e s s o r s have
been d i s c u s s e d i n t h e l i t e r a t u r e ( r e f s . 6 1 - 6 4 ) . T u r b i n e - d r i v e n c o m p r e s s o r s a r e
known t o be a p p l i e d i n D a n i s h s u g a r f a c t o r i e s (whe re s e c o n d - e f f e c t v a p o u r i s
140
compressed , see S e c t i o n 3 . 4 . 3 ) .
The v a p o u r - c o m p r e s s i o n p r o c e s s can a l s o be pe r fo rmed u s i n g j e t - t y p e
c o m p r e s s o r s . T y p i c a l l y , m u l t i p l e compresso rs a r e i n s t a l l e d i n a s i n g l e
compress i on c i r c u i t f o r r e a s o n s o f f l o w c o n t r o l ( s e e S e c t i o n 3 . 4 . 4 ) . An
i d e a l i z e d compress ion p r o c e s s i n a j e t - t y p e compresso r s u p p l i e d w i t h l i v e steam
i s shown i n t h e M o l l i e r d iag ram i n F i g . 3 .30 . I n o r d e r t o c a l c u l a t e t h e steam
demand, f i n a l v a p o u r e n t h a l p y , e t c . , t h e f o l l o w i n g i n d i c e s c h a r a c t e r i z i n g t h e
i d e a l i z e d p r o c e s s must be known:
- compress i on r a t i o u ( s e e T a b l e 1 . 2 ) ,
3A00
3300
CT3200
>;3100 o £ C
ÜJ 3000
2900
2800
2700
2600 6.95 7.00 7.05 710 7.15
Entropy ( k j / (kg K))
F i g . 3 .30 . Compress ion o f f i r s t - e f f e c t v a p o u r i n a j e t - t y p e c o m p r e s s o r .
141
- e f f i c i e n c y o f t h e l i v e - s t e a m n o z z l e ,
- e f f i c i e n c y o f t h e m ixed -s team ( i . e . , compressed v a p o u r ) n o z z l e η ^ .
The l i v e - s t e a m demand can be d e t e r m i n e d as
= D / u ( 3 . 1 2 )
where i s t h e v a p o u r f l o w .
Assuming u = 2 .40 , we o b t a i n f o r t h e c o m p r e s s i o n c i r c u i t under c o n s i d e r a t i o n
D^ = 10/2.40 = 4.17 kg/100 kg b.
The e n t h a l p y o f t he l i v e s team, a f t e r e x p a n s i o n i n t h e n o z z l e t o t h e p r e s s u r e
o f f i r s t - e f f e c t v a p o u r , can be c a l c u l a t e d as
^ c = ^ " " Ns^ l ( ^ - ^ ^ ^
where h-j i s t he i n i t i a l l i v e - s t e a m e n t h a l p y , and h-j^ i s t h e f i n a l steam e n t h a l p y
i n t h e i s e n t r o p i c e x p a n s i o n p r o c e s s .
I n s e r t i n g e n t h a l p y v a l u e s and assuming n-j = 0 .90 , we o b t a i n
h^^ = 3333.9 - (3333.9 - 2 6 7 3 . 8 ) · 0 . 9 0 = 2739.0 k J / k g .
The e n t h a l p y b a l a n c e o f m i x i n g expanded steam w i t h f i r s t - e f f e c t v a p o u r can be
w r i t t e n as
D l ^ l e ' ^ ^ ^ = C l ^ \K ( 3 . 1 4 )
where h^ i s t h e m ixed -s team e n t h a l p y .
The m ixed -s team e n t h a l p y can t h u s be c a l c u l a t e d as
h^ = (4 .17 -2739 .8 + 1 0 - 2 7 1 4 . 4 ) / ( 4 . 1 7 + 10) = 2721.9 k J / k g .
From a s e p a r a t e e n t r o p y b a l a n c e , we can d e t e r m i n e t h e e n t r o p y o f m ixed steam as
s = 7.0852 k J / ( k g K ) , w h i c h c o r r e s p o n d s t o a s l i g h t l y s u p e r h e a t e d s t a t e . The
e n t h a l p y o f mixed steam a f t e r c o m p r e s s i o n i n t h e n o z z l e t o t h e e x h a u s t - s t e a m
p r e s s u r e can be c a l c u l a t e d as
V = ^ ^ ( ^ s - ( 3 . 1 5 )
where h^^ i s t h e f i n a l steam e n t h a l p y i n t h e i s e n t r o p i c c o m p r e s s i o n p r o c e s s .
I n s e r t i n g e n t h a l p y v a l u e s and assuming = 0 . 8 7 , we o b t a i n
h^^ = 2721.9 + (2772.0 - 2 7 2 1 . 9 ) / 0 . 8 7 = 2779.4 k J / k g .
T h i s c o r r e s p o n d s t o a t e m p e r a t u r e o f 159.4°C, t h a t i s , 24.4 Κ above t h e
s a t u r a t i o n t e m p e r a t u r e . Assuming t h a t m ixed steam i s d e s u p e r h e a t e d u s i n g
condensa te i n j e c t i o n , we can c a l c u l a t e t h e mass o f c o n d e n s a t e p e r 1 kg steam
f rom e q n . ( 3 . 1 1 )
m^ = (2779.4 - 2 7 2 6 . 6 ) / ( 2 7 2 6 . 6 - 567.7) = 0.024 kg /kg
The t o t a l f l o w o f s a t u r a t e d steam s u p p l i e d by t h e v a p o u r - c o m p r e s s i o n c i r c u i t
i s t h u s
s ^ ^ 1 ^ v ' ^ ^ "^c ' ^ ^ ^ ^ ^ ^ ^ ^ - ^ 2 4 ) = 14.52 kg/100 kg b.
We can now summarize t he r e s u l t s o f t h e i n t r o d u c t i o n o f j e t - t y p e c o m p r e s s o r s
142
t o t h e v a p o u r - c o m p r e s s i o n c i r c u i t as f o l l o w s .
( i ) The h e a t i n g - s t e a m demand i s r e d u c e d by 14.52 kg/100 kg b b u t t h e l i v e - s t e a m
demand i s i n c r e a s e d by 4.17 kg/100 kg b. The r e s u l t i n g n e t steam s a v i n g i s
10.35 kg/100 kg b , i . e . , abou t 21.6% o f t h e i n i t i a l steam demand.
( i i ) The l i v e - s t e a m f l o w t h r o u g h t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n can be
c u t down t o abou t 16% o f i t s i n i t i a l v a l u e ; h o w e v e r , an even l a r g e r l i v e - s t e a m
f l o w must be s u p p l i e d t o t h e c o m p r e s s o r s .
( i i i ) The power o u t p u t and t he power demand remain u n a f f e c t e d by v a p o u r
c o m p r e s s i o n .
Recen t examples o f t he a p p l i c a t i o n o f j e t - t y p e compresso rs can be found i n
t he l i t e r a t u r e ( r e f s . 6 5 , 6 6 ) . Howeve r , p r a c t i c a l r e s u l t s may d i f f e r
s u b s t a n t i a l l y f rom t h o s e i n d i c a t e d i n t h e above c a l c u l a t i o n , as e x p l a i n e d i n t h e
n e x t S e c t i o n .
3 .4 .3 S e l e c t i n g t he most s u i t a b l e compress i on t e c h n i q u e
A compar i son o f t he v a l u e s o f e s s e n t i a l q u a n t i t i e s c h a r a c t e r i z i n g t he e n e r g y
b a l a n c e s r e s u l t i n g f rom t h e a p p l i c a t i o n s o f t h e t h r e e s o l u t i o n s d e s c r i b e d i n t h e
p r e c e d i n g S e c t i o n i s shown i n T a b l e 3 .5 . As can be s e e n , t h e steam s a v i n g s a r e
a lmos t i d e n t i c a l . The j e t - t y p e c o m p r e s s o r s and t h e t u r b i n e - d r i v e n mechan i ca l
compresso r o f f e r t h e advan tage o f an unchanged power b a l a n c e , w h i l e t h e
e l e c t r i c a l l y - d r i v e n mechan ica l compresso r i n c r e a s e s t h e power demand. I t s h o u l d
be p o i n t e d o u t , h o w e v e r , t h a t t h i s c o n c l u s i o n h o l d s o n l y i f t h e steam s a v i n g
r e l a t i v e t o t h e o r i g i n a l t he rma l sys tem w i t h o u t v a p o u r c o m p r e s s i o n does n o t
exceed t h e l i v e - s t e a m f l o w o r i g i n a l l y d i r e c t e d t o t h e t h r o t t l i n g - d e s u p e r h e a t i n g
s t a t i o n . I n o r d e r t o demons t ra te how d i f f e r e n t r e s u l t s can be o b t a i n e d under
d i f f e r e n t c o n d i t i o n s , a n o t h e r example i s p r e s e n t e d b e l o w .
TABLE 3.5
Compar ison o f e n e r g y b a l a n c e s r e s u l t i n g f rom t h e a p p l i c a t i o n o f v a r i o u s v a p o u r -compress i on t e c h n i q u e s i n a s u g a r f a c t o r y c h a r a c t e r i z e d by an i n i t i a l steam demand o f 47.9 kg/100 kg b.
Q u a n t i t y W i t h o u t
Compressor
D imens ion v a p o u r e l e c t r i c a l l y - • t u r b i n e - j e t -c o m p r e s s i o n d r i v e n d r i v e n t y p e
(kg /100 kg b ) 47.90 37.62 37.62 37.55 (%) 100 78.5 78.5 78.4
(kWh/100 kg b ) 3.000 3.214 3.000 3.000 (%) 100 107 100 100
(kWh/100 kg b ) 3.630 3.630 3.630 3.630 (%) 100 100 100 100
(kWh/100 kg b ) 0.630 0.416 0.630 0.630 (%) 100 66 100 100
143
L e t us assume t h a t t h e i n i t i a l h e a t i n g - s t e a m demand o f t h e f a c t o r y under
c o n s i d e r a t i o n i s 36.4 kg/100 kg b and a l l t h e r e m a i n i n g pa rame te r s o f t h e e n e r g y
c o n v e r s i o n and d i s t r i b u t i o n p r o c e s s e s a r e t h e same as i n t h e f a c t o r y p r e v i o u s l y
c o n s i d e r e d . The a v e r a g e steam f l o w t h r o u g h t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n
i s 7.36 kg/100 kg b , i . e . 19.4% o f t h e t o t a l h e a t i n g - s t e a m f l o w . I f we now
c o n s i d e r t h e a p p l i c a t i o n s o f t h r e e v a p o u r - c o m p r e s s i o n c i r c u i t s a n a l o g o u s t o
t h o s e p r e v i o u s l y s p e c i f i e d , t hen t h e r e s u l t i n g r e l a t i v e m o d i f i c a t i o n s o f t h e
e n e r g y b a l a n c e t u r n o u t t o be e n t i r e l y d i f f e r e n t f rom t h o s e f ound i n t h e
p r e v i o u s c a s e . As t he r e d u c t i o n s o f t he h e a t i n g - s t e a m f l o w e x c e e d t h e l i v e - s t e a m
f l o w o r i g i n a l l y s u p p l i e d t o t he t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n , t h e steam
f l o w t h r o u g h t h e t u r b i n e and t h e power o u t p u t d e c r e a s e as shown i n T a b l e 3 . 6 .
These e f f e c t s a r e most p ronounced i n t h e case o f j e t - t y p e c o m p r e s s o r s , c a u s i n g
t he s u g a r f a c t o r y t o become h e a v i l y dependen t on e l e c t r i c i t y s u p p l i e s f rom t h e
e x t e r n a l g r i d . When a p p l y i n g a mechan ica l c o m p r e s s o r , a smal l power s u r p l u s can
be e x p e c t e d i n t h e case o f an e l e c t r i c d r i v e , and a smal l power d e f i c i t i n t h e
case o f a t u r b i n e d r i v e .
TABLE 3.6
Compar ison o f e n e r g y b a l a n c e s r e s u l t i n g f rom t h e a p p l i c a t i o n o f v a r i o u s v a p o u r -c o m p r e s s i o n t e c h n i q u e s i n a s u g a r f a c t o r y c h a r a c t e r i z e d by an i n i t i a l steam demand o f 37.9 kg/100 kg b.
Q u a n t i t y W i t h o u t
Compressor
D imens ion v a p o u r e l e c t r i c a l l y - • t u r b i n e - j e t -c o m p r e s s i o n d r i v e n d r i v e n t y p e
(kg /100 kg b) 37.90 27.62 27.62 27.55 (%) 100 72.9 72.9 72.9
(kWh/100 kg b ) 3.000 3.214 3.000 3.000 (%) 100 100 100 100
(kWh/100 kg b ) 3.630 3.270 2.950 2.182 (%) 100 90 81 60
(kWh/100 kg b ) 0.630 0.056 -0 .050 -0 .818 (%) 100 9 -8 -130
I t s h o u l d be emphas ized t h a t T a b l e s 3.5 and 3.6 j u s t summarize t h e r e s u l t s o f
t h e a n a l y s e s c o n c e r n e d w i t h two p a r t i c u l a r s u g a r f a c t o r i e s e q u i p p e d w i t h
p a r t i c u l a r c o m p r e s s i o n c i r c u i t s . These d a t a c a n n o t be c o n s i d e r e d as s u f f i c i e n t
b a s i s f o r g e n e r a l c o n c l u s i o n s . I n r e a l - l i f e e n g i n e e r i n g p rob lems i t i s e s s e n t i a l
t o a c c o u n t f o r t h e i n f l u e n c e o f t h e t y p e o f c o m p r e s s i o n equ ipment on t h e
i n v e s t m e n t c o s t s , as w e l l as o t h e r f a c t o r s o f p r a c t i c a l i n t e r e s t . Depend ing on
t h e i n i t i a l steam-demand l e v e l , t h e r e q u i r e m e n t s imposed on t h e c o m p r e s s i o n
c i r c u i t can be d i f f e r e n t l y f o r m u l a t e d i n d i f f e r e n t f a c t o r i e s . The d e s i g n o f
a v a p o u r c o m p r e s s i o n c i r c u i t can t h u s be c o n s i d e r e d as a m u l t i - v a r i a b l e d e c i s i o n
144
p r o b l e m , i n w h i c h equ ipment t y p e and v a p o u r f l o w s can be o p t i m i z e d f o r t h e b e s t
o v e r a l l economic r e s u l t s .
I n t h i s c o n t e x t , l e t us men t ion t h e p o s s i b i l i t y o f t h e a p p l i c a t i o n o f v a p o u r
c o m p r e s s i o n o v e r two e v a p o r a t i o n s t a g e s . T h e r e a r e i m p o r t a n t p r a c t i c a l
c o n s i d e r a t i o n s w h i c h can j u s t i f y such a s o l u t i o n . I t i s n o t unusua l t h a t t h e
c o n c e n t r a t i o n o f o r g a n i c gaseous s u b s t a n c e s i n t h e f i r s t - e f f e c t v a p o u r i s so
h i g h t h a t when t h e v a p o u r i s compressed and r e c i r c u l a t e d t o f i r s t - e f f e c t
h e a t i n g , t h e q u a l i t y o f f i r s t - e f f e c t condensa te becomes a d v e r s e l y a f f e c t e d . I f
t h e pa rame te rs o f t h e condensa te do n o t s a t i s f y t he r q u i r e m e n t s o f f e e d - w a t e r
q u a l i t y , t h e n a p rob lem i s c r e a t e d w i t h p o s s i b l e a d v e r s e c o n s e q u e n c e s , as
d i s c u s s e d i n S e c t i o n 3 . 1 . 2 . I t i s t h e r e f o r e w o r t h n o t i n g t h a t t he c o n c e n t r a t i o n
o f o r g a n i c gaseous s u b s t a n c e s i n s e c o n d - e f f e c t v a p o u r i s u s u a l l y 3-4 t imes
s m a l l e r t han t h a t i n f i r s t - e f f e c t v a p o u r ( r e f . 6 5 ) .
L e t us r e t u r n f o r a moment t o T a b l e 3 . 4 , i n w h i c h t h e mass f l o w s o f v a p o u r s
f rom t h e e v a p o r a t o r and vacuum pans i n t h e m o d i f i e d the rma l sys tem a r e
p r e s e n t e d . I f we assume t h a t i n s t e a d o f f i r s t - e f f e c t v a p o u r , v a p o u r i s w i t h d r a w n
f rom t h e second e f f e c t t o t h e c o m p r e s s i o n c i r c u i t , t h e n t he r e q u i r e d mass f l o w
o f t h a t v a p o u r can be c a l c u l a t e d f rom t h e c o n s t r a i n t o f c o n s t a n t t h i c k - j u i c e
c o n c e n t r a t i o n . The r e s u l t i n g f l o w v a l u e i s shown i n T a b l e 3.4 i n b r a c k e t s ; i t i s
o n l y h a l f o f t h e e q u i v a l e n t f l o w o f f i r s t - e f f e c t v a p o u r . As a c o n s e q u e n c e , t h e
i n c r e a s e s i n t h e t o t a l v a p o u r f l o w f rom bo th t h e f i r s t and second e v a p o r a t o r
e f f e c t s a r e s m a l l e r t han t h e i n c r e a s e r e s u l t i n g f rom v a p o u r c o m p r e s s i o n o v e r one
e v a p o r a t i o n s t a g e . The o u t l e t c o n c e n t r a t i o n o f j u i c e i n t he f i r s t e f f e c t i s
l o w e r t han i n t he o t h e r s o l u t i o n , t h i s making i t p o s s i b l e t o m a i n t a i n a l a r g e r
v a l u e o f t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t i n t he f i r s t e f f e c t . I t may
t h e r e f o r e be e a s i e r , w i t h r e s p e c t t o t h e r e q u i r e d h e a t i n g - s u r f a c e a r e a i n t h e
f i r s t e v a p o r a t o r e f f e c t , t o implement v a p o u r c o m p r e s s i o n o v e r two s t a g e s . I t can
be added t h a t t h i s s o l u t i o n i s g e n e r a l l y a p p l i e d i n D a n i s h s u g a r f a c t o r i e s and
has a l s o been i n t r o d u c e d t o t h e Greek s u g a r i n d u s t r y .
3 .4 .4 C o n t r o l c o n s i d e r a t i o n s r e l a t i n g t o v a p o u r c o m p r e s s i o n
When s u p p l y i n g t he compressed v a p o u r f rom t h e f i r s t o r second e v a p o r a t o r
e f f e c t t o f i r s t - e f f e c t h e a t i n g , one has t o r eckon w i t h t he r i s k o f j u i c e
c a r r y o v e r c a u s i n g a t e m p o r a r y s u g a r p r e s e n c e i n t h e f i r s t - e f f e c t c o n d e n s a t e . I n
o r d e r t o manage emergency s i t u a t i o n s e f f e c t i v e l y , i t may be a d v i s a b l e t o i n s t a l l
two e v a p o r a t o r b o d i e s and two c o r r e s p o n d i n g c o n d e n s a t e t a n k s i n t h e f i r s t
e f f e c t . I f t h e c o m p r e s s e d - v a p o u r s t ream i s d i r e c t e d t o t h e h e a t i n g chamber o f
one b o d y , and t he o t h e r body i s hea ted w i t h pu re e x h a u s t s team, t h e n t h e r i s k o f
condensa te p o l l u t i o n i s l i m i t e d t o o n l y a p a r t o f t h e condensa te s t r e a m . An
example o f steam and v a p o u r c o n n e c t i o n s i n a v a p o u r c o m p r e s s i o n c i r c u i t
145
u t i l i z i n g t h i s i d e a i s shown i n F i g . 3 . 3 1 ( a ) .
A n o t h e r p o s s i b i l i t y f o r p r e v e n t i n g j u i c e d r o p l e t s f rom b e i n g c a r r i e d o v e r t o
f i r s t - e f f e c t condensa te i s t o w i t h d r a w t h e v a p o u r s t ream t o be c o m p r e s s e d , n o t
d i r e c t l y f rom t h e e f f e c t i n w h i c h v a p o u r i s p r o d u c e d b u t f rom t h e h e a t i n g
chamber o f t h e n e x t e f f e c t . T h i s makes i t p o s s i b l e t o wash t h e v a p o u r t o be
w i t h d r a w n w i t h w a t e r c o n d e n s i n g i n t he h e a t i n g chamber. A c c o r d i n g t o t h i s
p r i n c i p l e , t h e Dan i sh s u g a r f a c t o r i e s employ t h e w i t h d r a w a l o f s e c o n d - e f f e c t
v a p o u r v i a t he h e a t i n g chamber o f t he t h i r d e f f e c t , as shown s c h e m a t i c a l l y i n
F i g . 3 . 3 1 ( b ) .
( b )
F i g . 3 .31. Schemes o f steam and v a p o u r c o n n e c t i o n s p r e v e n t i n g t h e p o l l u t i o n o f f i r s t - e f f e c t c o n d e n s a t e by j u i c e c a r r y o v e r i n t h e compressed v a p o u r : ( a ) c o m p r e s s i o n o v e r one e v a p o r a t i o n s t a g e , ( b ) c o m p r e s s i o n o v e r two e v a p o r a t i o n s t a g e s . 1-3 - e v a p o r a t o r e f f e c t s , 4 - c o m p r e s s o r , 5 - t u r b i n e , 6 - e x h a u s t s team, 7 - l i v e s team, 8 - h e a t i n g v a p o u r t o t h e n e x t e f f e c t , 9 -n o n c o n d e n s a b l e s .
When i n t r o d u c i n g v a p o u r c o m p r e s s i o n t o a the rma l s y s t e m , i t i s d e s i r a b l e t o
e l i m i n a t e , o r a t l e a s t t o r e d u c e , t h e use o f t h e t h r o t t l i n g - d e s u p e r h e a t i n g
s t a t i o n i n c o n t r o l l i n g t h e sys tem t h r o u g h p u t . As r e g a r d s c o m p r e s s i o n c i r c u i t s
emp loy ing mechan ica l c o m p r e s s o r s , t h i s i s s i m p l y a q u e s t i o n o f s e l e c t i n g one o f
t he f l o w - c o n t r o l t e c h n i q u e s a p p l i c a b l e t o gas-pumping equ ipment ( s e e C h a p t e r 7 ) .
The c o n t r o l t e c h n i q u e s e l e c t e d may a f f e c t t h e e n e r g y l o s s e s o c c u r r i n g i n t h e
therma l sys tem under chang ing l o a d s . T h e r e a r e examples o f a p p l i c a t i o n o f t he
most e f f i c i e n t v a r i a b l e - s p e e d c o n t r o l ( r e f . 5 9 ) , and t h e l e s s e f f i c i e n t b y - p a s s
c o n t r o l ( w h i c h happens t o be employed i n t h e scheme shown i n F i g . 3 . 3 1 ( a ) ) .
The case o f j e t - t y p e compresso rs i s d i f f e r e n t , as t h e s e d e v i c e s a r e
e s s e n t i a l l y d e s i g n e d t o work a t d e f i n i t e v a p o u r f l o w s and t h e c o n t r o l ma rg i ns
a re v e r y n a r r o w . I f t he f l o w d e v i a t e s f rom i t s nominal v a l u e , t h e n t h e
e f f i c i e n c y o f a compresso r f a l l s o f f r a p i d l y . I n o r d e r t o make i t p o s s i b l e t o
v a r y t h e c o m p r e s s i o n - c i r c u i t l o a d w i t h o u t s e r i o u s l y r e d u c i n g c o m p r e s s i o n
146
e f f i c i e n c y , i t i s n e c e s s a r y t o a r r a n g e j e t - t y p e compresso rs o f d i f f e r e n t
t h r o u g h p u t s i n b a t t e r i e s , l i k e t h e one shown i n F i g . 3 .32 . A p o p u l a r s o l u t i o n
c o n s i s t s o f u s i n g f o u r c o m p r e s s o r s , t h e i r t h r o u g h p u t s c r e a t i n g a g e o m e t r i c
s e r i e s 1 :2 :4 :8 ( r e f . 6 5 ) . A c o n t r o l sys tem t a k e s c a r e o f t u r n i n g on compresso r
c o m b i n a t i o n s w i t h t o t a l t h r o u g h p u t s g r e a t e r t h a n , b u t c l o s e t o , t h e r e q u i r e d
v a p o u r - f l o w v a l u e s . U s i n g t h i s p r i n c i p l e , t h e a v e r a g e e f f i c i e n c y o f t h e b a t t e r y
a t v a r i a b l e l o a d s may be r e d u c e d o n l y i n s i g n i f i c a n t l y . I t may be added t h a t
t h e shap ing o f t h e compresso r b a t t e r y becomes l e s s i m p o r t a n t when a s t a b l e
e v a p o r a t o r l o a d i s e n s u r e d . I n two Dan i sh s u g a r f a c t o r i e s , v a p o u r c o m p r e s s i o n
c i r c u i t s a r e a p p l i e d w i t h t h e b a t t e r i e s c o m p r i s i n g f o u r and f i v e j e t - t y p e
c o m p r e s s o r s , t he t h r o u g h p u t s o f w h i c h c r e a t e t h e s e r i e s 1 : 1 . 9 4 : 1 . 9 4 : 4 . 5 and
1 : 1 . 0 7 : 2 . 1 4 : 2 . 6 : 4 . 8 4 , r e s p e c t i v e l y .
F i g . 3 .32 . Scheme o f a b a t t e r y o f j e t - t y p e c o m p r e s s o r s . 1 - l i v e s team, 2 - v a p o u r , 3 - compressed v a p o u r .
3 .4 .5 Compress ion o f vacuum-pan v a p o u r s
I t f o l l o w s f rom t h e p r e c e d i n g s e c t i o n s t h a t t h e a p p l i c a t i o n o f a v a p o u r
compress i on c i r c u i t i n an e x i s t i n g the rma l sys tem may n e c e s s i t a t e i n t r o d u c i n g
s u b s t a n t i a l changes i n t he d i s t r i b u t i o n o f v a p o u r s and c o n d e n s a t e s , as w e l l as
i n s t a l l i n g p o s s i b l e r e p l a c e m e n t s f o r some o f t h e e x i s t i n g e v a p o r a t o r b o d i e s .
Because o f l a c k o f space i n t h e e x i s t i n g b u i l d i n g s , o r f o r economic r e a s o n s ,
t h i s may sometimes be d i f f i c u l t t o a c c e p t . I n o r d e r t o w iden t h e c h o i c e o f
p o s s i b l e s o l u t i o n s , t h e c i r c u i t s compress ing vacuum-pan v a p o u r s have been
d e v e l o p e d and implemented i n a few European s u g a r f a c t o r i e s .
A c t u a l l y , t h i s i d e a had a l r e a d y been a p p l i e d f o u r decades ago i n t h e S w i s s
147
f a c t o r y a t A a r b e r g , u s i n g e l e c t r i c a l l y - d r i v e n mechan ica l c o m p r e s s o r s c o n n e c t e d
t o bo th t h e e v a p o r a t i o n and vacuum-pan s t a t i o n s ( r e f . 6 7 ) . The e n t i r e s t ream o f
vacuum-pan v a p o u r s i s compressed f rom 0.25 ba r t o 1.2 ba r p r e s s u r e and
r e c i r c u l a t e d t o pan h e a t i n g . M u l t i - s t a g e c o m p r e s s o r s a r e used f o r t h i s p u r p o s e ;
i n o r d e r t o m i n i m i z e t h e power c o n s u m p t i o n , i n t e r - s t a g e v a p o u r c o o l i n g by
condensa te i n j e c t i o n i s emp loyed . As a r e s u l t , 1 .14-1.16 kg h e a t i n g v a p o u r i s
o b t a i n e d f rom 1 kg vacuum-pan v a p o u r a t a power consumpt ion o f 0 .12 -0 .13 kWh p e r
1 kg vacuum-pan v a p o u r . The power consumpt ion o f t h e s i n g l e - s t a g e compresso rs
i n s t a l l e d i n t h e e v a p o r a t o r a r e a i s 0 .013-0.018 kWh p e r 1 kg v a p o u r c o m p r e s s e d .
As men t ioned i n S e c t i o n 1.5, h o w e v e r , t h e A a r b e r g s o l u t i o n was m o t i v a t e d by
a v e r y s p e c i a l e n e r g y p o l i c y i n w h i c h t h e a v a i l a b i l i t y o f cheap h y d r o e l e c t r i c
power p l a y e d a fundamenta l r o l e . T h e r e f o r e , i t can h a r d l y be r e g a r d e d as a model
e n e r g y sys tem t o be i m i t a t e d on a w i d e r b a s i s . A m o d i f i e d v e r s i o n o f t h e A a r b e r g
sys tem i n c o n n e c t i o n w i t h a f a c t o r y i n w h i c h t he power i s g e n e r a t e d bo th i n
a s t e a m - c y c l e - b a s e d power house and i n a g a s - t u r b i n e g e n e r a t i n g s e t has been
a n a l y s e d by Ba loh ( r e f . 6 8 ) .
I n t h e s o l u t i o n s w h i c h a r e now c o m e r c i a l l y o p e r a t e d i n two F r e n c h f a c t o r i e s
( a w h i t e - s u g a r f a c t o r y and a r e f i n e r y ) , a p a r t o f t h e vacuum-pan v a p o u r s i s
compressed and r e c i r c u l a t e d t o vacuum-pan h e a t i n g ( r e f s . 3 9 , 6 9 ) . L e t us n o t e
t h a t w h i l e t h e A a r b e r g f a c t o r y employs b a t c h vacuum p a n s , t h e F r e n c h
i n s t a l l a t i o n s a r e b u i l t a round c o n t i n u o u s vacuum p a n s . The u n d e r l y i n g i d e a i s t o
reduce t he demand f o r h e a t i n g v a p o u r s f rom t h e e v a p o r a t o r , t h u s making i t
p o s s i b l e t o c u t down t h e h e a t i n g - s t e a m demand. I t s h o u l d be p o i n t e d o u t t h a t
a r e d u c t i o n o f t h e w i t h d r a w a l o f v a p o u r s f rom t h e e v a p o r a t o r has t o be
compensated f o r , so as t o keep t he t h i c k - j u i c e c o n c e n t r a t i o n c o n s t a n t . F o r t h i s
r e a s o n , a r e a r r a n g e m e n t o f t h e v a p o u r - d i s t r i b u t i o n scheme, o r t h e a p p l i c a t i o n o f
a n o t h e r v a p o u r compress i on c i r c u i t i n t h e e v a p o r a t o r a r e a , o r a c o m b i n a t i o n o f
bo th measu res , may be n e e d e d . I f i t i s s u f f i c i e n t t o r e a r r a n g e t h e v a p o u r
d i s t r i b u t i o n o n l y , t h e n t h e n e c e s s a r y i n v e s t m e n t s i n t h e e v a p o r a t o r a r e a may be
l e s s e x t e n s i v e and e a s i e r t o p e r f o r m t han t h o s e n e c e s s i t a t e d by o t h e r v a p o u r
compress ion t e c h n i q u e s .
A d i s a d v a n t a g e o f s o l u t i o n s emp loy ing t h e c o m p r e s s i o n o f vacuum-pan v a p o u r s
i s t h e i r l a r g e power c o n s u m p t i o n . I f an e l e c t r i c a l l y - d r i v e n compresso r i s
a p p l i e d , t hen t h e hea t s a v i n g can be a t t a i n e d a t t h e c o s t o f a p o w e r - c o n s u m p t i o n
i n c r e a s e P^. I n a d d i t i o n , depend ing on t h e i n i t i a l l e v e l o f t h e steam
c o n s u m p t i o n , t h e hea t s a v i n g may be accompanied by a d e c r e a s e P ^ o f t h e power
o u t p u t . As t h e l i v e - s t e a m demand i s r e d u c e d , l e s s a i r w i l l be consumed i n t h e
b o i l e r s and l e s s was te h e a t w i l l be t r a n s p o r t e d i n b a r o m e t r i c w a t e r t o t h e
c o o l i n g t o w e r s , t h i s r e s u l t i n g i n a power-demand d e c r e a s e P ^ . The r e l a t i o n
between t he f u e l s a v i n g and t h e power b a l a n c e change Δ Ρ = P ^ + P ^ - P ^ i s
148
d e t e r m i n e d by t h e pa rame te rs o f t h e compress i on p r o c e s s , as w e l l as by t h e
t u r b i n e steam r a t e and b o i l e r e f f i c i e n c y .
When t h e steam f l o w t h r o u g h t h e t u r b i n e i s r e d u c e d by G ^ , t he r e s u l t i n g
d e c r e a s e o f t h e power o u t p u t i s
P, = G / S ( 3 . 1 6 )
where S i s t h e steam r a t e o f t h e t u r b i n e .
The r e d u c t i o n o f t he hea t demand by causes t he f u e l demand t o d e c r e a s e by
ß r = V(%Vb) ( 3 . 1 7 )
where i s t he h e a t i n g v a l u e o f t h e f u e l , i s t h e s t e a m - p i p i n g e f f i c i e n c y ,
and i s t h e b o i l e r e f f i c i e n c y .
TABLE 3.7
E n e r g y - b a l a n c e m o d i f i c a t i o n s r e s u l t i n g f rom the i m p l e m e n t a t i o n o f vacuum-pan v a p o u r compress ion ( u s i n g mechan ica l c o m p r e s s o r s ) i n two s u g a r f a c t o r i e s c h a r a c t e r i z e d by d i f f e r e n t t u r b i n e steam r a t e s and b o i l e r e f f i c i e n c i e s . E n t r i e s 4-12 a r e g i v e n pe r 1 kg vacuum-pan v a p o u r compressed .
No. Name D imens ion F a c t o r y
1 Steam r a t e , S 2 B o i l e r e f f i c i e n c y , 3 S t e a m - p i p i n g e f f i c i e n c y , η 4 R e d u c t i o n o f t h e steam ^
f l o w t h r o u g h t h e t u r b i n e , G^ 5 R e d u c t i o n o f t h e power o u t p u t , P^ 6 R e d u c t i o n o f t he power demand, P^ 7 Compressor power demand, P^ 8 Change o f t h e power b a l a n c e ,
Pc ^ Pr - Pd 9 Hea t s a v i n g i n t h e e v a p o r a t o r
10 Heat s a v i n g i n t h e t u r b i n e 11 O v e r a l l h e a t s a v i n g , 12 N o r m a l - f u e l s a v i n g , B^
I I I
kg/kWh 8.0 10.5 0.90 0.75 0.98 0.95
kg 1.2 1.2 kWh 0.150 0.114 kWh 0.020 0.020 kWh 0.179 0.179
kWh 0.309 0.273 kJ 2805 2805 kJ 570 502 k J 3375 3307 kg 0.131 0.158
I n T a b l e 3 . 7 , t he c a l c u l a t e d e n e r g y - b a l a n c e changes r e s u l t i n g f rom t h e
i m p l e m e n t a t i o n o f t h e c o m p r e s s i o n o f vacuum-pan v a p o u r s i n two s u g a r f a c t o r i e s
e q u i p p e d w i t h d i f f e r e n t b o i l e r s and t u r b i n e s a r e compared. O b v i o u s l y , an
economic g a i n can be a t t a i n e d o n l y i f t he v a l u e o f t he f u e l saved e x c e e d s t h e
v a l u e o f t h e e l e c t r i c e n e r g y p u r c h a s e d f rom t h e e x t e r n a l g r i d :
B^c^ > APCg ( 3 . 1 8 )
where c^ and c^ a r e t h e p r i c e s o f f u e l and powe r , r e s p e c t i v e l y .
I t s h o u l d be p o i n t e d o u t t h a t t h i s i s o n l y a n e c e s s a r y , b u t n o t a s u f f i c i e n t ,
c o n d i t i o n f o r t h e economic j u s t i f i c a t i o n o f vacuum-pan v a p o u r c o m p r e s s i o n , as
a s e r i o u s economic e v a l u a t i o n r e q u i r e s t h e i n v e s t m e n t s c o s t s t o be t aken i n t o
a c c o u n t .
149
The above i n e q u a l i t y can be t r a n s f o r m e d t o t he f o l l o w i n g fo rm
c^/Cg > Δ Ρ / Β ^ ( 3 . 1 9 )
I t can now be o b s e r v e d t h a t f a c t o r i e s e q u i p p e d w i t h l o w - e f f i c i e n c y b o i l e r s and
t u r b i n e s a r e c h a r a c t e r i z e d by s m a l l e r v a l u e s o f t h e r a t i o Δ Ρ / Β ^ , t h i s i m p l y i n g
t h a t t h e i n e q u a l i t y i s e a s i e r t o s a t i s f y . T h i s does n o t mean, h o w e v e r , t h a t an
o u t d a t e d power house c r e a t e s a b a s i s f o r t h e economic g a i n s f rom vacuum-pan
v a p o u r c o m p r e s s i o n . A c t u a l l y , i t may happen t h a t t h e i n v e s t m e n t s aimed a t
i n c r e a s i n g t h e power house e f f i c i e n c y w i l l , e c o n o m i c a l l y , be more e f f e c t i v e t han
t h o s e r e q u i r e d f o r imp lement ing a v a p o u r - c o m p r e s s i o n c i r c u i t .
I n s t e a d o f an e l e c t r i c a l l y - d r i v e n c o m p r e s s o r , j e t - t y p e compresso rs can be
a p p l i e d . U s i n g l i v e steam a t 38 ba r and 450°C, 2 . 5 - 3 . 0 kg steam a r e needed t o
compress 1 kg vacuum-pan v a p o u r f rom 0.25 t o 1.2 b a r . A f t e r i n j e c t i n g t h e
condensa te t o d e s u p e r h e a t t h e mixed s team, 4 . 1 - 4 . 7 kg s a t u r a t e d steam i s
o b t a i n e d p e r 1 kg vacuum-pan v a p o u r .
A v a p o u r c o m p r e s s i o n c i r c u i t o f t h i s k i n d , o p e r a t e d i n p a r a l l e l w i t h a
c i r c u i t i n w h i c h v a p o u r f rom t h e second e v a p o r a t o r e f f e c t i s c o m p r e s s e d , has
been p r o p o s e d i n t h e l i t e r a t u r e ( r e f . 5 8 ) . C o n s i d e r i n g j o i n t l y t h e f l o w s o f l i v e
steam s u p p l i e d t o bo th c o m p r e s s i o n c i r c u i t s , 5 . 5 - 7 . 0 kg l i v e steam p e r 1 kg
vacuum-pan v a p o u r s h o u l d be s u p p l i e d t o j e t - t y p e c o m p r e s s o r s . The r e d u c t i o n o f
t he n e t hea t demand i s e q u i v a l e n t t o abou t 1.65 kg steam p e r 1 kg vacuum-pan
v a p o u r compressed .
Due t o a r e l a t i v e l y l a r g e l i v e - s t e a m demand, t h e f i e l d o f p o t e n t i a l
a p p l i c a t i o n s o f t h i s t e c h n i q u e seems t o be l i m i t e d t o t h e m o d e r n i z a t i o n o f
f a c t o r i e s i n w h i c h a s u b s t a n t i a l p a r t o f t h e h e a t i n g - s t e a m f l o w must be s u p p l i e d
f rom t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n . Under such c o n d i t i o n , - l i v e steam can
be d i r e c t e d t o t h e compresso rs w i t h o u t a f f e c t i n g t h e power o u t p u t o f t h e power
h o u s e . On t h e o t h e r h a n d , i f t h e e n t i r e steam f l o w has o r i g i n a l l y been s u p p l i e d
v i a t he t u r b i n e , t h e n u s i n g l i v e steam i n a v a p o u r - c o m p r e s s i o n c i r c u i t r e s u l t s
i n a r e d u c t i o n o f t h e power o u t p u t o f abou t 0 . 4 - 0 . 5 kWh p e r 1 kg vacuum-pan
v a p o u r compressed . T h i s seems t o be a c c e p t a b l e o n l y i f s u f f i c i e n t l y cheap power
i s a v a i l a b l e f rom an e x t e r n a l e l e c t r i c g r i d .
A n o t h e r d i s a d v a n t a g e o f j e t - t y p e c o m p r e s s o r s i s t h e i r l i m i t e d f l e x i b i l i t y
under v a r i a b l e - l o a d c o n d i t i o n s . When used i n c o n n e c t i o n w i t h b a t c h vacuum p a n s ,
t h e compress i on c i r c u i t i s e x p e c t e d t o compensate f o r q u i c k changes o f h e a t i n g -
v a p o u r demand. T h i s r e q u i r e m e n t i s much e a s i e r t o s a t i s f y when a p p l y i n g a
mechan ica l c o m p r e s s o r . T h e r e a r e b e t t e r chances f o r a c o m p e t i t i v e p o s i t i o n o f
j e t - t y p e compresso rs i n f a c t o r i e s emp loy ing c o n t i n u o u s vacuum p a n s , e s p e c i a l l y
i f t he i n d i c e s g i v e n above c o u l d be improved by i n c r e a s i n g t h e c o m p r e s s i o n
r a t i o . T h i s m igh t be p o s s i b l e when r e p l a c i n g c o n v e n t i o n a l s i n g l e - n o z z l e d e v i c e s
by t he m u l t i p l e - n o z z l e , v a r i a b l e t h r o a t - a r e a d e s i g n ( " s t a t o - c o m p r e s s o r s " )
150
a c c o r d i n g t o a F r e n c h p a t e n t . A d i s c u s s i o n o f t h e a p p l i c a t i o n o f m u l t i p l e - n o z z l e
compresso rs i n a v a p o u r c o m p r e s s i o n c i r c u i t r e c i r c u l a t i n g v a p o u r f rom a
c o n t i n u o u s vacuum pan can be f ound i n t h e l i t e r a t u r e ( r e f . 7 0 ) . F o r a d e v i c e
u t i l i z i n g l i v e steam a t 24 ba r and 320°C and r a i s i n g t h e v a p o u r p r e s s u r e f rom
0.3 ba r t o 1.2 b a r , a c o m p r e s s i o n r a t i o o f 0.70 has been r e p o r t e d ( r e f . 7 1 ) .
T h i s v a l u e i s t w i c e t h a t a t t a i n a b l e i n a s i n g l e - n o z z l e c o m p r e s s o r .
REFERENCES
1 B. Goublomme, Comment a b o r d e r l e p rob leme de l a r e d u c t i o n des c o u t s e n e r g e t i q u e s dans l e s s u c r e r i e s , S u c r . B e i g e , 103 (1985) 27-30.
2 J . S . Hogg ( e t a l . ) . The r o l e o f t h e r m o g r a p h i c s u r v e y i n g i n e n e r g y c o n s e r v a t i o n . I n t . Sugar J . , 85(1011) (1983) 67-71.
3 E. H u g o t , Handbook o f Cane Sugar E n g i n e e r i n g , 3 rd e d n . , E l s e v i e r , Amsterdam, 1986.
4 T . B a l o h , W ä r m e w i r t s c h a f t , i n : F . S c h n e i d e r ( E d . ) , T e c h n o l o g i e des Z u c k e r s , Schaper V e r l a g , H a n n o v e r , 1968, p p . 705-776.
5 I . F r i e d m a n n , E i n n e u e r , l e i s t u n g s f ä h i g e r Kondensa tab i e i t e r i n d e r Z u c k e r i n d u s t r i e d e r DDR, Z u c k e r i n d . , 110(12) (1985) 1094-1095.
6 W. L e k a w s k i , M o d e r n i z a c j a G o s p o d a r k i C i e p l n e j C u k r o w n i , S T C , Warszawa, 1986. 7 H. C l a a s s e n , D i e Z u c k e r f a b r i k a t i o n m i t b e s o n d e r e r B e r ü c k s i c h t i g u n g des
B e t r i e b e s , 7 th e d n . , Magdeburg , 1943. 8 J . D o b r z y c k i , Chemiczne Pods tawy T e c h n o l o g i i C u k r u , WNT, Warszawa, 1984. 9 V . N . Gorokh and K . O . S h t a n g e e v , K o l i c h e s t v o g a z o v p o s t u p a y u s h c h i k h ν
k o n d e n s a t o r n u y u u s t a n o v k u sakharnogo z a v o d a , Sakh . P r o m . , ( 4 ) (1976) 64-65. 10 R . V . K o r e n , 0 r a t s i o n a l n o i r a z r a b o t k e a p p a r a t o v i skhem k o n d e n s a t s i i
t e k h n o l o g i c h e s k i k h p a r o v sakha rnogo z a v o d a , Sakh . P r o m . , ( 6 ) (1981) 45 -49 . 11 R. Wasmund, Uber den E i n f l u s s d e r im He izdampf b e f i n d l i c h e n L u f t a u f das
T e m p e r a t u r g e f ä l l e be i W ä r m e ü b e r t r a g u n g s p r o z e s s e n , Z . Z u c k e r i n d . , 26 (1 ) (1976) 13-18.
12 H. S c h r ä d e r , Der E i n f l u s s von I n e r t g a s e n a u f den Wärmeübergang be i d e r K o n d e n s a t i o n von Dämpfen, C h e m . - I n g . - T e c h n . , 38 (1966) 1091-1094.
13 S . Z a g r o d z k i and J . D o b r z y c k i , Removal o f i n c o n d e n s a b l e gases f rom c a l a n d r i a s . I n t . Sugar J . , 71 (1969) 235-237.
14 P. D e v i l l e r s ( e t a l . ) , L ' e n t a r t r a g e en e v a p o r a t i o n , p r e v e n t i o n e t l u t t e , S u c r . F r . , 9 4 ( 5 ) (1977) 217-226.
15 H. G r u s z e c k a , Badan ia i ocena s r o d k a A n t i p r e x z a p o b i e g a j a c e g o z a r a s t a n i u p o w i e r z c h n i g r z e j n e j w y p a r k i , G a z . C u k r o w . , 93 (2 ) (1985) 43-44 .
16 T . W . B a k e r , E v a p o r a t i o n and H e a t i n g , i n : G . T . Meade and J . C . Chen ( E d s . ) , Cane Sugar Handbook, W i l e y , New Y o r k , 1977, p p . 185-235.
17 W. S t a n k i e w i c z , Wplyw z a r a s t a n i a p o w i e r z c h n i g r z e j n e j w y p a r k i na z a g e s z c z a n i e sokow, G a z . C u k r o w . , 78(10) (1970) 233-236.
18 D. S p a n o v i c , A p p l i c a t i o n de I ' a p p a r e i l CEPI en vue de l a p r o t e c t i o n des e v a p o r a t e u r s en s u c r e r i e , S u c r . B e i g e , 89 (8 ) (1970) 403-406.
19 S . I . N e d z v e s k i i ( e t a l . ) , E l e k t r o m a g n i t n a y a o b r a b o t k a s a k h a r n y k h r a s t v o r o v , Sakh . P r o m . , ( 7 ) (1977) 50-53.
20 G . Rösner and G . P o l l a c h , B e l a g s b i l d u n g s s t u d i e n m i t H i l f e von L a b o r v e r damp fe rn , Z u c k e r i n d . , 111(2) (1986) 125-127.
21 B. K u t e r m a n k i e w i c z , Wygotowywanie w y p a r k i bez z a t r z y m y w a n i a p r z e r o b u burakow, G a z . C u k r o w . , 78 (8 ) (1970) 188-190.
22 S . L a w n i c k i , O c z y s z c z a n i e r u r e k w y p a r k i ζ osadow w Cukrown i P r u s z c z p r z e z w y k w a s z a n i e , G a z . C u k r o w . , 78(11) (1970) 271-273.
23 S . L a w n i c k i and E . Z a b i e r e k , Kwasowe o c z y s z c z a n i e p o w i e r z c h n i g r z e j n y c h apa ra tow w y p a r n y c h , G a z . C u k r o w . , 81 (9 ) (1973) 229-230.
24 H. D a b r o w s k i , Z a r a s t a n i e i metody wygo towywan ia p o w i e r z c h n i g r z e j n y c h w y p a r k i , G a z . C u k r o w . , 87(11) (1979) 245-249.
151
25 Κ. S c h i e b l , W ä r m e w i r t s c h a f t i n d e r Z u c k e r i n d u s t r i e , T . S t e i n k o p f f V e r l a g , D r e s d e n / L e i p z i g , 1939.
26 S . Z a g r o d z k i , Wplyw uk l adu s t a c j i w y p a r n e j na gospoda rke c i e p l n a , G a z . C u k r o w . , 72 (1 ) (1964) 1-7.
27 S . Z a g r o d z k i , Porownan ie z u z y c i a p a r y w n i e k t o r y c h uk l adach w y p a r k i w i e l o -d z i a l o w e j , G a z . C u k r o w . , 78 (7 ) (1970) 157-163.
28 S . Z a g r o d z k i , Wplyw uk l adu s t a c j i w y p a r n e j na w i e l k o s c p o w i e r z c h n i o g r z e w a l n e j o r a z z u z y c i e p a r y i w e g l a , G a z . C u k r o w . , 78 (8 ) (1970) 181-185.
29 G . K imenov , E n e r g e t i s c h e U n t e r s u c h u n g e n an e i n e r m e h r s t u f i g e n Ve rdamp f -Sta t ion a l s Dampfumformer, Z u c k e r , 25 (7 ) (1972) 225-230.
30 S . N i e s p o d z i n s k i , A . G a t y s and D. S z w e d o w i c z , Wplyw s t a c j i w y p a r n e j na o s z c z e d n o s c p a l i w a w c u k r o w n i , G a z . C u k r o w . , 90 (10) (1982) 161-163.
31 C . H . I v e r s o n , W i t h e r g o e s t t h o u , oh B T U ? , S u g a r . J . , 45 (11) (1983) 17-22. 32 B. K a r r e n , The p o t e n t i a l f o r e n e r g y s a v i n g i n t h e b e e t s u g a r i n d u s t r y .
L e c t u r e p r e p a r e d f o r t he Bee t Sugar I n s t i t u t e C o u r s e , 1980. 33 B. K a r r e n , E x p e r i e n c e o f e n e r g y s a v i n g i n t h e Canad ian s u g a r i n d u s t r y , i n :
P . O . L i c h t s Gu ide t o t h e Sugar F a c t o r y Mach ine I n d u s t r y , F . O . L i c h t GmbH, R a t z e b u r g , 1984, p p . A75-A88.
34 H. S c h i w e c k , M ö g l i c h k e i t e n z u r Senkung des E n e r g i e b e d a r f e s im Z u c k e r h a u s , Z u c k e r , 30(10) (1977) 525-535.
35 I . S . G u l y i , A . G . S h c h e r b a t y u k and B . V . Kuzmenko, Κ t ep lovomu r a s c h e t u v a k u u m - a p p a r a t o v , Sakh . P r o m . , ( 6 ) (1984) 52-53.
36 K . E . A u s t m e y e r , A n a l y s i s o f s u g a r b o i l i n g and i t s t e c h n i c a l c o n s e q u e n c e s . I n t . Sugar J . , 88 ( 1 9 8 6 ) , P a r t I (1045) 3 - 7 , P a r t I I (1046) 23-29 , P a r t I I I (1047) 50-55.
37 E. Krupka and J . S z a d k o w s k i , Gospodarka c i e p l n a w Cukrowni G o s l a w i c e , G a z . C u k r o w . , 89 (1 ) (1981) 2 -5 .
38 L . L . N e v i l l e , E n e r g y r e c o v e r y f rom t h e e v a p o r a t o r s t a t i o n s . Sugar J . , 46 (4 ) (1983) 5-8 .
39 D. B r o t , Recompress ion mechanique de v a p e u r s de c u i t e e t e v a p o r a t i o n 6 e f f e t s a l a s u c r e r i e B u c y - l e - L o n g , I n d . A l i m . A g r i e , 102(7 -8 ) (1985) 681-684.
40 S . A . Z o z u l y a and A . I . Khomenko, 0 r a t s i o n a l n o i skheme vakuum-k o n d e n s a t s i o n n o i u s t a n o v k i , Sakh . P r o m . , ( 7 ) (1984) 37-42 .
41 S . A . Z o z u l y a ( e t a l . ) , P r i m e n e n i e k o n d e n s a t o r o v t i p a A2-PKB ν s o s t a v e vakuum-kondensa t s i onnykh u s t a n o v o k s a k h a r n y k h z a v o d o v , Sakh . P r o m . , ( 7 ) (1986) 27-30.
42 V . N . G o r o k h , B . F . Us and K . O . S h t a n g e e v , R a s c h e t d a v l e n i y a ν vakuumnoi s i s t e m e sakha rnogo z a v o d a , Sakh . P r o m . , (11 ) (1983) 47-48 .
43 V . N . G o r o k h , B . F . Us and K . O . S h t a n g e e v , R a s c h e t vakuumnoi s i s t e m y s a k h a r nogo z a v o d a s uchetom szh imaemos t i p a r a , Sakh . P r o m . , ( 6 ) (1985) 40-44 .
44 J . G . Z i e g l e r , B a r o m e t r i c c o n d e n s e r s - good and b a d . Sugar J . , 38 ( A p r i l 1976) 39-41.
45 S . A . Z o z u l y a and G . D . B o b r o v n i k , O p y t n a l a d k i i e k s p l u a t a t s i i k o n d e n s a t o r o v t i p a A2-PKB, Sakh . P r o m . , ( 7 ) (1983) 37-39 .
46 Y u . S . R a z l a d i n ( e t a l . ) , I s p o l z o v a n i e u t f e l n o g o p a r a d l y a n a g r e v a d i f f u z i o n -nogo s o k a , Sakh . P r o m . , ( 3 ) (1984) 41-44.
47 V . N . Gorokh ( e t a l . ) , P o d o g r e v a t e l d i f f u z i o n n o g o s o k a , obog revaemy i u t f e l n y m parom, Sakh . P r o m . , ( 8 ) (1981) 36-39.
48 Y u . S . R a z l a d i n ( e t a l . ) , P r i m e n e n i e s e k t s i o n n o g o p o d o g r e v a t e l y a d l y a n a g r e v a n i y a sakharnogo soka v t o r i c h n y m parom 5 ko rpusa v y p a r n o i u s t a n o v k i , Sakh . P r o m . , ( 6 ) (1986) 33-36.
49 V . l . Dovgopo l ( e t a l . ) , Nag rev d i f f u z i o n n o g o soka ν p a r o k o n t a k t n y k h p o d o g r e -v a t e l y a k h , Sakh . P r o m . , ( 7 ) (1976) 45-48 .
50 V . N . Gorokh ( e t a l . ) , E f f e k t i v n o s t i s p o l z o v a n i y a u t f e l n o g o p a r a d l y a n a g r e v a d i f f u z i o n n o g o s o k a , Sakh . P r o m . , ( 6 ) (1983) 26-30.
51 G . V e r n o i s , D ie mechan ische B r ü d e n v e r d i c h t u n g i n Z u c k e r f a b r i k e n , Z u c k e r e r z e u g u n g , (11) (1962) 286-289.
52 S. Z a g r o d z k i , Po rownan ie uk l adu w y p a r k i w i e l o d z i a l o w e j ζ ukladem w y p a r k i ζ t e r m o s p r e z a n i e m , G a z . C u k r o w . , 78 (6 ) (1970) 136-138.
152
53 S . M . Z a g r o d z k i J r . , E n e r g y s a v i n g s w i t h a f o u r - e f f e c t e v a p o r a t o r and t u r b o c o m p r e s s o r . Sugar J . , 4 2 ( 9 ) (1980) 9 -13 .
54 A . F e n y e s , H ö s z i v a t t y u s b e p a r l a s a c u k o r g y a r b a n , C u k o r i p a r , 28 (6 ) (1975) 222-227.
55 H. L ü h r s , E i n s a t z d e r t e r m i s c h e n ode r mechan ischen B r ü d e n v e r d i c h t u n g i n d e r Z u c k e r i n d u s t r i e , V D I - B e r . , (383) (1980) 35-37 .
56 C . H . I v e r s o n , Mechan i ca l v a p o r - r e c o m p r e s s i o n - f a l l i n g f i l m e v a p o r a t i o n . Sugar J . , 44 (1 ) (1981) 15-20.
57 Κ. U r b a n i e c , S p r e z a n i e oparow w g o s p o d a r c e c i e p l n e j c u k r o w n i , G a z . C u k r o w . , 90 (9 ) (1982) 134-136.
58 K . E . A u s t m e y e r , B rüdenkompress ion i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 108(8) (1983) 715-728.
59 J . B o z e c , E v o l u t i o n de l a consommation t he rm ique dans Γ i n d u s t r i e s u c r i e r e , I n d . A l i m . A g r i e , 100(7 -8 ) (1983) 477-480.
60 Mechan ische B r ü d e n k o m p r e s s i o n , V D I - G e s e l 1 s c h a f t E n e r g i e t e c h n i k , D ü s s e l d o r f , 1987.
61 T . L u b i e n s k i , E r s t e S c h r i t t e i n d e r B r ü d e n k o m p r e s s i o n , Z u c k e r i n d . , 105(11) (1980) 1087-1088.
62 H. W e i d n e r , D i e B rüdenkompress ion i n e i n e r R o h z u c k e r f a b r i k , Z u c k e r i n d . , 108(8) (1983) 736-742.
63 U . J a c o b s e n , Der e i n s t u f i g e R a d i a l k o m p r e s s o r , Z u c k e r i n d . , 108(8) (1983) 742-746.
64 M. B u r t i n and J . - C . G i o r g i , Recompress ion de l a v a p e u r : l a s o l u t i o n o r i g i n a l e de l a s u c r e r i e de G u i g n i c o u r t , S u c r . F r . , 125(82) (1984) 117-121.
65 P. C h r i s t o d o u l o u , B e t r i e b s e r f a h r u n g e n m i t dem E i n s a t z e i n e r Wärmepumpe i n d e r V e r d a m p f S t a t i o n e i n e r Z u c k e r f a b r i k , Z u c k e r i n d . , 109(7) (1984) 628-634.
66 P .Ho f fman , O p t i m a l i z a c e e n e r g e t i c k e h o h o s p o d a r s t v i c u k r o v a r u L o v o s i c e , L i s t y C u k r . , 102(7) (1986) 155-161.
67 H . R . B r u n n e r , D i e Thermokompress ion i n der Z u c k e r f a b r i k + R a f f i n e r i e A a r b e r g A G , G e s c h i c h t e - E n t w i c k l u n g - A u s b l i c k , Z u c k e r i n d . , 108(8) (1983) 729-736.
68 T . B a l o h , S t u d i e e i n e r Z u c k e r f a b r i k m i t B r ü d e n k o m p r e s s i o n , Z u c k e r i n d . , 109(4) (1984) 285-294.
69 J . - C . G i o r g i , La r e c o m p r e s s i o n de v a p e u r de c u i t e , i n : P r o c . 17th C I T S , Copenhagen , 1983, p p . 279-290.
70 J . C u e l , Economies d ' e n e r g i e en r a f f i n e r i e p a r u t i l i z a t i o n e t / o u r e c o m p r e s s i o n de v a p e u r s i s s u e s d'une c u i t e c o n t i n u e a s s o c i e e a de m a l a x e u r s - c r i s t a l 1 i s e u r s Continus sous v i d e p r o f o n d , I n d . A l i m . A g r i e , 103(7-8 ) (1986) 669-675.
71 C . Longue E p e e , L e c t u r e p r e s e n t e d a t the I n t e r n a t i o n a l E x h i b i t i o n SVEKLOVODSTVO, K i e v , May 1986.
153
C h a p t e r 4
ENERGY SAVINGS BY PROCESS MODIFICATIONS
4.1 INTRODUCTION
I n s y s t e m a t i c a l l y e s t a b l i s h i n g ways t o r e d u c e t h e n e t h e a t demand, we
s e p a r a t e d measures aimed a t r e d u c i n g t h e h e a t demand o f t he i n d i v i d u a l p r o c e s s e s
f rom t h o s e f a c i l i t a t i n g an i n c r e a s e o f t h e e f f e c t i v e n e s s r a t i o o f t h e the rma l
s y s t e m . When b e g i n n i n g a d i s c u s s i o n o f e n e r g y - s a v i n g p r o c e s s m o d i f i c a t i o n s , one
m igh t pe rhaps e x p e c t t h a t o n l y measures b e l o n g i n g t o t h e f o r m e r g roup w o u l d be
c o n s i d e r e d . A c t u a l l y , t h e p rob lem i s more i n v o l v e d as t h e r e a r e examples o f
p r o c e s s e s t h a t have been i n t r o d u c e d f o r t h e s o l e p u r p o s e o f making the rma l
sys tem improvements p o s s i b l e . M o r e o v e r , a p r o c e s s may a f f e c t t h e e n e r g y demand
d i r e c t l y ( ow ing t o a d i r e c t r e l a t i o n s h i p between e n e r g y demand and p r o c e s s
p a r a m e t e r s ) o r i n d i r e c t l y ( ow ing t o t h e i n f l u e n c e on t h e pa rame te rs o f o t h e r
p r o c e s s e s ) . F i n a l l y , t he power demand o f a p r o c e s s may a l s o become an i m p o r t a n t
i s s u e .
I t i s sometimes d i f f i c u l t t o t e l l w h e t h e r a c e r t a i n e n e r g y s a v i n g can be
a t t r i b u t e d t o a p r o c e s s improvement o r t o deve lopmen ts i n equ ipment o r c o n t r o l
s y s t e m s . T h i s C h a p t e r p r e s e n t s a r e v i e w o f p rob lems i n w h i c h r e - t h i n k i n g o f
p r o c e s s r e q u i r e m e n t s p l a y s a p a r t i c u l a r l y i m p o r t a n t r o l e . O f c o u r s e , t h i s i s
j u s t a c o n v e n t i o n ; t h e n e x t two c h a p t e r s a r e d e v o t e d t o complementary p rob lems
where equ ipment and c o n t r o l sys tems come i n t o t h e f o r e g r o u n d .
The p r e s e n t a u t h o r i s aware o f t h e f a c t t h a t i t i s n o t e a s y t o c o v e r a b r o a d
p rob lem f i e l d i n w h i c h new deve lopmen ts a r e s t e a d i l y t a k i n g p l a c e . I t i s h o p e d ,
h o w e v e r , t h a t i d e n t i f i c a t i o n o f t h e main d i r e c t i o n s o f e f f o r t can have a l a s t i n g
v a l u e . I n t h i s c o n t e x t , c e r t a i n p u b l i c a t i o n s o r p u b l i c a t i o n s e r i e s d e s e r v e t o be
n o t e d , as t h e y p r o v i d e d i n v a l u a b l e h e l p i n t h e s t u d i e s o f w o r l d w i d e t r e n d s
( r e f s . 1 -3 ) . I n t h e f o l l o w i n g , t h e s u b j e c t i s s p l i t i n t o f o u r p a r t s :
- j u i c e p u r i f i c a t i o n ;
- s u g a r c r y s t a l l i z a t i o n ;
- u n c o n v e n t i o n a l p r o c e s s e s ;
- p u l p d e h y d r a t i o n .
I t m igh t be a rgued t h a t t h e c o n c e p t o f p r e s e n t i n g p r o c e s s e s as means t o
reduce e n e r g y demand i s t a k i n g t h i n g s t o o f a r ; a f t e r a l l , t h e s u g a r i n d u s t r y i s
n o t a f i e l d o f e n e r g y - s a v i n g c o n t e s t s . I t s h o u l d t h e r e f o r e be p o i n t e d o u t t h a t
t he p r i o r i t i e s o f d i f f e r e n t a s p e c t s o f f a c t o r y o p e r a t i o n have been d i s c u s s e d i n
C h a p t e r 1. Even i f t h e p r e s e n t C h a p t e r may be f o u n d p r o v o c a t i v e , i t i s hoped
t h a t i t can s t i m u l a t e u s e f u l i d e a s w h i c h w i l l e v e n t u a l l y f i n d t h e i r way i n t o
p r a c t i c e .
154
4 .2 J U I C E P U R I F I C A T I O N
4.2.1 I n f l u e n c e on t h e e n e r g y demand
Bee t s u g a r f a c t o r i e s a l l o v e r t h e w o r l d employ t h e method o f p u r i f i c a t i o n o f
raw j u i c e based on l ime and ca rbon d i o x i d e a d d i t i o n s . The aim o f j u i c e
p u r i f i c a t i o n i s t o remove nonsuga rs as f a r as p o s s i b l e , i n o r d e r t o p r o d u c e
c l e a r t h i n j u i c e w i t h h i g h p u r i t y and s t a b i l i t y p r e v e n t i n g q u a l i t y changes
d u r i n g e v a p o r a t i o n . Due t o v a r y i n g b e e t c o m p o s i t i o n and d i f f e r e n t methods o f
h a r v e s t i n g , t r a n s p o r t , s t o r a g e and e x t r a c t i o n , many v e r s i o n s o f t h e j u i c e
p u r i f i c a t i o n method a r e i n u s e . The v e r s i o n s may d i f f e r w i t h r e s p e c t t o t h e
d i s t r i b u t i o n o f l ime between i n d i v i d u a l p r o c e s s s t a g e s , t h e amount o f r e c y c l e d
j u i c e o r s l u d g e , t h e t e m p e r a t u r e s and r e s i d e n c e t imes c h a r a c t e r i z i n g v a r i o u s
p r o c e s s s t a g e s .
I n a r e f e r e n c e v e r s i o n o f t he c l a s s i c a l j u i c e p u r i f i c a t i o n method , t he t o t a l
r e q u i r e m e n t o f CaO amounts t o 80-95% o f t he c o n t e n t o f nonsuga rs i n raw j u i c e .
10-12% goes t o the p r e - 1 i m e r , 5-7% to t he j u i c e p r i o r t o second c a r b o n a t a t i o n
and t he rema inder i s added t o t he main l i m e r . The t e m p e r a t u r e s a r e 55-65°C i n
t h e p r e - l i m i n g , 85°C i n t h e main l i m i n g and f i r s t c a r b o n a t a t i o n , and 94°C i n
t h e second c a r b o n a t a t i o n ( r e f . 4 ) .
The pa rame te rs named above d e f i n e t h e therma l c h a r a c t e r i s t i c s o f t h e j u i c e
p u r i f i c a t i o n p r o c e s s . I t s i n f l u e n c e on t he t o t a l e n e r g y demand i n s u g a r
manu fac tu re i s more c o m p l i c a t e d t han j u s t d i r e c t l y c o n t r i b u t i n g t o t h e h e a t
demand. I n t h e f i r s t p l a c e , t h i n j u i c e q u a l i t y d e t e r m i n e s the r e q u i r e m e n t s on
t h e s u g a r c r y s t a l l i z a t i o n p r o c e s s , t h u s a f f e c t i n g t h e e n e r g y demand i n t h e s u g a r
house ( s e e S e c t i o n 4 . 3 ) . T h e n , t he t e m p e r a t u r e i n p r e - l i m i n g i s d e c i s i v e i n
w h e t h e r o r o r n o t i t i s p o s s i b l e t o u t i l i z e l o w - t e m p e r a t u r e hea t (vacuum-pan
v a p o u r s , l a s t - e f f e c t v a p o u r , c o n d e n s a t e ) i n raw j u i c e h e a t i n g . A c t u a l l y , t h i s
p o s s i b i l i t y depends a l s o on t h e t e m p e r a t u r e o f raw j u i c e and o t h e r f a c t o r s , so
one s h o u l d pe rhaps i n v e s t i g a t e i t by a n a l y s i n g a subsys tem c o m p r i s i n g e x t r a c t i o n
and j u i c e p u r i f i c a t i o n ( r e f . 5 ) . F o r examp le , i f l a r g e f l o w s o f h o t j u i c e o r
s u b s i d e r s l u d g e a r e r e c y c l e d t o t h e p r e - 1 i m e r f rom f i r s t o r second
c a r b o n a t a t i o n , t h e n l e s s h e a t i n g o f raw j u i c e i s n e e d e d . T h i s must be
compensated f o r by more hea t d e l i v e r e d t o o t h e r s t a g e s o f j u i c e h e a t i n g , where
t h e t e m p e r a t u r e s a r e t o o h i g h t o a l l o w t h e u t i l i z a t i o n o f l o w - t e m p e r a t u r e h e a t .
I t s h o u l d a l s o be o b s e r v e d t h a t l a r g e r e c y c l e s may r e q u i r e c o n s i d e r a b l e power
consumpt ion i n j u i c e pumping.
C o n c e r n i n g d i r e c t e n e r g y l o s s e s a s s o c i a t e d w i t h j u i c e p u r i f i c a t i o n ,
a q u a l i t a t i v e d i s c u s s i o n o f t h e i r r e d u c t i o n by p r o c e s s t e m p e r a t u r e changes has
been g i v e n i n S e c t i o n 1 .3 .3 . The main p a r t o f t h e s e l o s s e s , amount ing under
c e r t a i n c i r c u m s t a n c e s t o as much as 1/10 o f t h e n e t hea t demand o f t h e
f a c t o r y , o c c u r s i n t h e c a r b o n a t a t i o n s . I n t he f o l l o w i n g , t h e e n e r g y - s a v i n g
155
p o t e n t i a l a s s o c i a t e d w i t h t he c a r b o n a t a t i o n p r o c e s s i s d i s c u s s e d .
4 . 2 . 2 Heat b a l a n c e o f c a r b o n a t a t i o n
A t y p i c a l a r rangemen t o f t h e equ ipment a s s o c i a t e d w i t h t h e c a r b o n a t a t i o n
p r o c e s s i s shown i n F i g . 4 . 1 . Gas f rom t h e l ime k i l n , c o n t a i n i n g C O ^ , i s d e -
d u s t e d , washed and d e l i v e r e d t o a w a t e r - r i n g c o m p r e s s o r . I t s p r e s s u r e r a i s e d t o
1 .6-1 .8 b a r and a t a t e m p e r a t u r e abou t 35°C, t h e gas f l o w s t o two s e p a r a t e ,
a t m o s p h e r i c - p r e s s u r e c a r b o n a t a t i o n t a n k s , where i t i s b r o u g h t i n t o c o n t a c t w i t h :
- i n f i r s t c a r b o n a t a t i o n - j u i c e a f t e r main l i m i n g , d e l i v e r e d a t a b o u t 85°C,
- i n second c a r b o n a t a t i o n - j u i c e a f t e r f i r s t f i l t r a t i o n , d e l i v e r e d a t a b o u t
94°C.
I n bo th c a r b o n a t a t i o n t a n k s , mass and h e a t exchange t a k e s p l a c e between t h e
j u i c e and t h e c a r b o n a t a t i o n g a s . As t h e gas f l o w s f rom t h e b u b b l e r t o t h e j u i c e
s u r f a c e , i t s p r e s s u r e f a l l s t o a t m o s p h e r i c p r e s s u r e and t h e t e m p e r a t u r e
i n c r e a s e s , f i n a l l y a p p r o a c h i n g t h e j u i c e t e m p e r a t u r e . The gas a l s o becomes
s a t u r a t e d w i t h v a p o u r e v a p o r a t e d f rom j u i c e . I t s e n t h a l p y r a i s e d c o n s i d e r a b l y
above t h e i n l e t v a l u e , t h e s p e n t gas i s d i s c h a r g e d t o t h e a t m o s p h e r e , t h i s
c a u s i n g an e n e r g y l o s s .
LIME KILN J D E - D U S T E R
I water I
WASHER
5^
limed juice_ CARBONATATION I CARBONATATION I I
COMPRESSOR
clear juice_
F i g . 4 . 1 . Scheme o f t h e equ ipment a r rangemen t a s s o c i a t e d w i t h t h e c a r b o n a t a t i o n p r o c e s s .
The l o s s can be s t u d i e d u s i n g e q n . ( 2 . 6 ) . F o r t h e thermodynamic sys tem
c o m p r i s i n g a s i n g l e t ank shown i n F i g . 4 . 2 , t h e e n e r g y b a l a n c e i s
• ^ j i ^ j i ^ ^ ^ ^ ^ = Vj2^ V V ' E ( ' · ^ '
where G j ^ and G^-j a r e t h e mass f l o w s o f j u i c e and c a r b o n a t a t i o n gas ( u n d e r s t o o d
as d r y g a s ) , r e s p e c t i v e l y , a t i n l e t ; G^^ and G ^ ^ a r e t h e mass f l o w s o f t h e same
media a t o u t l e t ; h^^ and h^^ a r e t h e e n t h a l p i e s o f j u i c e a t i n l e t and o u t l e t ;
hg^ and h^^ a r e t h e e n t h a l p i e s o f c a r b o n a t a t i o n gas ( p e r 1 kg d r y g a s ) a t i n l e t
and o u t l e t ; Qp i s t he h e a t o f c a r b o n a t a t i o n r e a c t i o n , and i s t h e h e a t
d i s s i p a t e d t o t h e e n v i r o n m e n t by r a d i a t i v e and c o n v e c t i v e h e a t exchange ( b o t h
Qp and a r e e x p r e s s e d p e r u n i t t i m e ) .
The b a l a n c e e q u a t i o n can be r e w r i t t e n t o r e f l e c t t h e f a c t t h a t t h e e n e r g y l o s t
156
Gas Gg2 Gas Gg i
Juice out
Gj2 '^\2
J u i c e in
Gji.hj i
F i g . 4.2. C a r b o n a t a t i o n tank as a thermodynamic s y s t e m . F o r e x p l a n a t i o n o f t h e s y m b o l s , see t e x t .
by d i s c h a r g i n g s p e n t gas and by h e a t exchange w i t h t h e e n v i r o n m e n t has a c t u a l l y
been removed f rom t h e j u i c e
( 4 . 2 )
( 4 . 3 )
( 4 . 4 )
V g 2 - ^ g l ^ l ^ = ^ • i ^ ' j i - «j2^2 ^ \ The h e a t l o s s can t h u s be e x p r e s s e d e i t h e r as
\ - %2\2 - Λ^ " o r as
Q L = G j ^ h - T - G j 2 h j 2 ^ Q R
Now, l e t us o b s e r v e t h a t t h e h e a t o f r e a c t i o n c a n n o t be n e g l e c t e d i n e n e r g y
b a l a n c e s . I f we assume t h a t i t i s g e n e r a t e d a t 70 kJ /kmo l ( r e f . 6) and t h a t t h e
amount o f CaO i n v o l v e d i n b o t h c a r b o n a t a t i o n s i s 2 kg/100 kg b , t h e n we a r r i v e
a t t h e v a l u e = 2500 kJ /100 kg b , t h i s b e i n g e q u i v a l e n t t o a steam amount
abou t 1.1 kg/100 kg b.
The above e x p r e s s i o n s e n a b l e us t o e v a l u a t e t h e magn i tude o f t h e combined
h e a t l o s s f rom t h e c a r b o n a t a t i o n s . I n t h e r e f e r e n c e v e r s i o n o f t h e p r o c e s s
men t ioned i n t h e p r e c e d i n g S e c t i o n , a t 40% CO^ c o n t e n t , one needs a p p r o x i m a t e l y
3.4 k g / l O O kg b o f k i l n gas i n f i r s t c a r b o n a t a t i o n and 0.7 k g / l O O kg b i n second
c a r b o n a t a t i o n . Even a t t h e most advan tageous p r o c e s s p a r a m e t e r s , t h e combined
l o s s c a n n o t be e x p e c t e d t o be l o w e r t han 5000 kJ /100 kg b , o r a steam e q u i v a l e n t
157
o f abou t 2.2 kg/100 kg b. G e n e r a l l y , assuming t h a t as much gas i s d e l i v e r e d t o
t h e p r o c e s s as needed t o n e u t r a l i z e t h e a c t i v e CaO i n t h e j u i c e , t h e e n e r g y l o s s
depends on t h e f o l l o w i n g f a c t o r s :
- CaO r a t e ;
- j u i c e t e m p e r a t u r e ;
- CO^ c o n t e n t i n incoming k i l n g a s ;
- CO2 u t i l i z a t i o n .
A t low i n i t i a l CO2 c o n t e n t , s a y 30% and a t l i m i t e d CO2 u t i l i z a t i o n , t h e combined
c a r b o n a t a t i o n h e a t l o s s can r e a c h 10 000-12 000 kJ /100 kg b , o r a steam
e q u i v a l e n t o f 4 . 4 - 5 . 3 kg/100 kg b. I n modern b e e t s u g a r f a c t o r i e s c h a r a c t e r i z e d
by steam demand o f t h e o r d e r o f 30 kg steam p e r 100 kg b e e t , t h e c a r b o n a t a t i o n
h e a t l o s s t h u s becomes one o f t h e l a r g e s t i d e n t i f i a b l e components o f t h e n e t
hea t demand.
A number o f s o l u t i o n s have been p r o p o s e d t o r e d u c e t h e c a r b o n a t a t i o n h e a t
l o s s by c u t t i n g down gas f l o w and o u t l e t e n t h a l p y . W i t t e and Sch iweck ( r e f . 6)
d e s c r i b e a sys tem based on r e c y c l i n g s p e n t gas f rom second t o f i r s t
c a r b o n a t a t i o n . The f l o w o f k i l n gas t o f i r s t c a r b o n a t a t i o n can be r e d u c e d by
10%; t he r e s u l t i n g steam s a v i n g has been e s t i m a t e d a t 0.5 kg/100 kg b , t h a t i s ,
up t o 1/5 o f t h e c a r b o n a t a t i o n l o s s . The same r e f e r e n c e r e p o r t s r e s u l t s o f
e x p e r i m e n t s w i t h a r a w - j u i c e h e a t e r h e a t e d by s p e n t c a r b o n a t a t i o n g a s . No
e s t i m a t e o f t h e a t t a i n a b l e e n e r g y s a v i n g i s g i v e n ; t h e s a v i n g w o u l d p r o b a b l y be
d e t e r m i n e d by an economic t r a d e - o f f between t h e v a l u e o f e n e r g y s a v e d and t h e
h e a t e r c o s t .
A n o t h e r s o l u t i o n based on a s i m i l a r app roach has been r e p o r t e d by a B e l g i a n
team ( r e f . 7 ) . Spen t gas f rom second c a r b o n a t a t i o n i s b r o u g h t i n t o d i r e c t
c o n t a c t w i t h w a t e r ; t he r e c u p e r a t e d h e a t a b s o r b e d by t h e w a t e r i s t h e n used t o
p r e h e a t a i r d e l i v e r e d t o t h e b o i l e r s o r t o t h e s u g a r d r y e r . The i m p l e m e n t a t i o n
i n a s u g a r f a c t o r y r e s u l t e d i n an e s t i m a t e d e n e r g y s a v i n g o f t h e o r d e r o f 1 kg
steam pe r 100 kg b e e t . S i m i l a r r e s u l t s have been r e p o r t e d f rom F r e n c h s u g a r
f a c t o r i e s where w a t e r i s hea ted by s p e n t gases f rom bo th c a r b o n a t a t i o n s i n a
s p e c i a l c o n d e n s e r , t o w h i c h an e x h a u s t f a n f o r gas pumping i s c o n n e c t e d ( r e f . 8 ) .
I n F i g . 4 . 3 , t h e e s s e n c e o f t h e s o l u t i o n s r e v i e w e d above i s p r e s e n t e d i n
a s i m p l i f i e d Sankey d i a g r a m . T h e y can be c l a s s i f i e d as h e a t r e c u p e r a t i o n
t e c h n i q u e s n o t a f f e c t i n g t h e p r i n c i p l e o f t h e c a r b o n a t a t i o n p r o c e s s .
4 . 2 . 3 M o d i f i c a t i o n s o f c a r b o n a t a t i o n
C a r b o n a t a t i o n h e a t l o s s can a l s o be r e d u c e d by c h a n g i n g p r o c e s s p a r a m e t e r s
i n a way f a c i l i t a t i n g a r e d u c t i o n o f t h e d i f f e r e n c e Mg2hg2 " ' ^g l ' ^g l
( 4 . 3 ) . More s p e c i f i c a l l y , i t i s p o s s i b l e t o r e d u c e t h e gas e n t h a l p y i n c r e a s e , as
w e l l as t o improve CO^ u t i l i z a t i o n , t h u s c u t t i n g down t h e gas f l o w . Two
158
2
heat transferred from ju ice
to gas ) o h <
IA ? c ) a> a, 1 s%
/— / energy of kiln gas
1 energy recycled to the process
\ carbonatat ion loss
F i g . 4 . 3 . E n e r g y - f l o w p r i n c i p l e o f sys tems r e d u c i n g t h e c a r b o n a t a t i o n hea t l o s s by r e c u p e r a t i o n .
t e c h n i q u e s can be used f o r t h i s pu rpose ( r e f . 9 ) :
- h e a t i n g and h u m i d i f i c a t i o n o f t h e k i l n gas p r i o r t o c a r b o n a t a t i o n ;
- c a r b o n a t a t i o n a t i n c r e a s e d p r e s s u r e .
The p r i n c i p l e on w h i c h bo th methods a r e based can be e x p l a i n e d i n a g r a p h
showing c a r b o n a t a t i o n gas e n t h a l p y ( p e r 1 kg o f d r y g a s ) as a f u n c t i o n o f
t e m p e r a t u r e and p r e s s u r e ( F i g . 4 . 4 ) . The g r a p h has been c o n s t r u c t e d u s i n g t h e
r e l a t i o n s h i p between e n t h a l p y p e r 1 kg d r y gas and m o i s t u r e c o n t e n t an
t e m p e r a t u r e , and t h e r e l a t i o n s h i p between m o i s t u r e c o n t e n t , t o t a l p r e s s u r e and
1 2 Pressure ( b a r )
F i g . 4 . 4 . E n t h a l p y o f c a r b o n a t a t i o n gas v s . p r e s s u r e and t e m p e r a t u r e .
159
( 4 . 5 )
p a r t i a l p r e s s u r e o f steam
X = ( m g / m g ) P g / ( p - Pg)
where X i s t h e m o i s t u r e c o n t e n t i n kg /kg d r y g a s , m^ i s t h e mo la r w e i g h t o f
s team, m^ i s t h e a v e r a g e mo la r w e i g h t o f g a s , p^ i s t h e p a r t i a l p r e s s u r e o f
s team, and ρ i s t h e t o t a l p r e s s u r e .
I n t h e g r a p h , examples a r e shown o f t h e e n t h a l p y i n c r e a s e o f c a r b o n a t a t i o n
gas i n t h e c o n v e n t i o n a l p r o c e s s ( c a s e A) and o f gas w h i c h has been p r e l i m i n a r i l y
hea ted t o 70°C w i t h accompany ing h u m i d i f i c a t i o n , a t 1.3 ba r o u t l e t p r e s s u r e
( c a s e B ) . The e n t h a l p y i n c r e a s e i n case A i s 1830 k J / k g d r y g a s , and i n case Β
960 k J / k g d r y g a s . T a k i n g i n t o a c c o u n t t h a t case Β w o u l d a l s o i n v o l v e a
r e d u c t i o n o f t h e gas f l o w due t o b e t t e r CO^ u t i l i z a t i o n , t h e combined h e a t l o s s
can i n t h i s e x e m p l a r y case be abou t 50% o f t h a t i n t h e c o n v e n t i o n a l p r o c e s s .
The f i r s t i d e a i s gas h e a t i n g and h u m i d i f i c a t i o n a t t h e expense o f was te h e a t
f rom o t h e r s e c t i o n s o f t h e s u g a r m a n u f a c t u r e . Waste h e a t can be a v a i l a b l e i n h o t
condensa te e x t r a c t e d d i r e c t l y f rom t h e e v a p o r a t i o n s t a t i o n ( a t 95-100°C) o r i n
t he condensa te w h i c h has a l r e a d y passed j u i c e h e a t e r s ( a b o u t 75°C) . Mass and
hea t exchange t a k i n g p l a c e i n t h e c a r b o n a t a t i o n t ank between t h e h e a t e d ,
h u m i d i f i e d k i l n gas and t h e j u i c e t h e n r e s u l t s i n l e s s e v a p o r a t i o n f rom t h e
j u i c e and s m a l l e r j u i c e t e m p e r a t u r e d r o p . C o n s e q u e n t l y , even t hough t h e
t e m p e r a t u r e and h u m i d i t y o f t h e s p e n t gas a r e i d e n t i c a l t o t h o s e i n t h e
c o n v e n t i o n a l p r o c e s s , t h e hea t l o s s i s r e d u c e d by abou t 1 /3, i . e . a t l e a s t
0.8 kg steam p e r 100 kg b e e t . An improvement o f CO^ u t i l i z a t i o n o f t h e o r d e r
10-15% can a l s o be e x p e c t e d . T h i s method can be c l a s s i f i e d as a p r o c e s s
m o d i f i c a t i o n , and i t s w o r k i n g p r i n c i p l e i s shown i n a Sankey d iag ram i n
F i g . 4 . 5 ( a ) .
As r e g a r d s t he c o n f i g u r a t i o n o f t h e e q u i p m e n t , t h i s method r e q u i r e s add ing t o
(B)
CD ^ cr <
5
o I/)
COMPRESSOR
Ι Λ additional
i pumping power Ι
F i g . 4 . 5 . E n e r g y - f l o w p r i n c i p l e s o f t he m o d i f i e d c a r b o n a t a t i o n s : ( a ) w i t h gas h e a t i n g and h u m i d i f i c a t i o n , ( b ) a t i n c r e a s e d p r e s s u r e . 1 - e n e r g y o f k i l n g a s , 2 - hea t t r a n s f e r r e d f rom j u i c e t o g a s , 3 - e n e r g y o f s p e n t g a s .
160
t h e c a r b o n a t a t i o n tank a s c r u b b e r f i l l e d w i t h R a s c h i g r i n g s o r some o t h e r t y p e
o f p a c k i n g . T h e r e , gas f l o w i n g i n an upward d i r e c t i o n i s hea ted and h u m i d i f i e d
by c o n d e n s a t e d i s p e r s e d on t h e p a c k i n g s u r f a c e .
The second method i m p l i e s t h a t t h e p r o c e s s c a n n o t be pe r f o rmed i n a
c o n v e n t i o n a l a t m o s p h e r i c - p r e s s u r e c a r b o n a t a t i o n t a n k ; i n s t e a d , a p r e s s u r e v e s s e l
s h o u l d be a p p l i e d and t he gas pump s h o u l d be o p e r a t e d a t i n c r e a s e d p r e s s u r e . The
thermodynamic consequence o f i n c r e a s e d p r e s s u r e i s t h a t t h e p a r t i a l p r e s s u r e o f
s a t u r a t e d steam i n t h e s p e n t gas remains c o n s t a n t ( i t depends on j u i c e
t e m p e r a t u r e o n l y ) , so t h e f i n a l m o i s t u r e c o n t e n t p e r 1 kg d r y gas i s r e d u c e d .
T h i s r e s u l t s i n r e d u c e d f i n a l e n t h a l p y p e r 1 kg d r y g a s . C o n s e q u e n t l y , j u i c e
e v a p o r a t i o n and j u i c e t e m p e r a t u r e d r o p caused by mass and h e a t exchange between
t h e j u i c e and t h e gas a r e s m a l l e r t han i n t h e a t m o s p h e r i c - p r e s s u r e p r o c e s s .
The w o r k i n g p r i n c i p l e o f c a r b o n a t a t i o n a t i n c r e a s e d p r e s s u r e i s i l l u s t r a t e d
i n F i g . 4 . 5 ( b ) . A t a gas p r e s s u r e above t he j u i c e s u r f a c e i n t h e tank abou t
1.7 b a r , t h e o v e r a l l h e a t l o s s can be r e d u c e d by n e a r l y 1 /2 , i . e . a t l e a s t
1.2 kg steam p e r 100 kg b e e t . T h i s e f f e c t can be m a g n i f i e d i f t h e gas i s
p r e h e a t e d and h u m i d i f i e d b e f o r e i t e n t e r s t he c a r b o n a t a t i o n t a n k s .
Advan tageous the rma l e f f e c t s o f i n c r e a s e d c a r b o n a t a t i o n p r e s s u r e have been
v e r i f i e d i n l a b o r a t o r y - s c a l e e x p e r i m e n t s ( r e f . 1 0 ) . C o n c e r n i n g t h e combined
e f f e c t o f i n c r e a s e d p r e s s u r e and gas h e a t i n g and h u m i d i f i c a t i o n , some i n i t i a l
r e s u l t s i n d i c a t e t h a t i t may be r e a l i s t i c t o e x p e c t an improvement i n CO^
u t i l i z a t i o n by a f a c t o r o f 1 .2 , i . e . i n f i r s t c a r b o n a t a t i o n , f rom a b o u t 70% t o
84%. T h i s w o u l d c o n t r i b u t e t o a r e d u c t i o n o f t h e c a r b o n a t a t i o n h e a t l o s s by 2 / 3 ,
i . e . a t l e a s t 1.6 kg steam p e r 100 kg b e e t .
A l t h o u g h t h e the rma l e f f e c t s can be r e g a r d e d as e x p e r i m e n t a l l y v e r i f i e d , t h e
a p p l i c a t i o n p o t e n t i a l o f c a r b o n a t a t i o n a t i n c r e a s e d p r e s s u r e i s n o t o b v i o u s , as
i t depends on economic f a c t o r s . I n p a r a l l e l t o t h e g a i n r e s u l t i n g f rom f u e l
s a v i n g s , one has t o c o n s i d e r on t h e c o s t s i d e :
- i n c r e a s e d i n v e s t m e n t c o s t s o f gas c o m p r e s s o r s and c a r b o n a t a t i o n t a n k s ;
- i n c r e a s e d power consumpt ion i n gas c o m p r e s s o r s .
C o n s e q u e n t l y , t h e o v e r a l l economic r e s u l t i s v e r y much dependen t on season
l e n g t h , f u e l p r i c e , power c o s t and c a p i t a l c o s t ( r e f . 1 1 ) .
4 .3 SUGAR CRYSTALL IZAT ION
4.3.1 Scope o f t h e p rob lems
The e n e r g y demand o f t h e s u g a r house u s u a l l y c o r r e s p o n d s t o 50-70% o f t h e n e t
h e a t demand and 14-20% o f t h e t o t a l power demand o f a w h i t e - s u g a r f a c t o r y . I n
a f a c t o r y c h a r a c t e r i z e d by d e f i n i t e l e v e l s o f equ ipment q u a l i t y and p r o c e s s
a u t o m a t i o n , t h e e x a c t f i g u r e s depend on t h e l a y o u t and pa rame te r s o f t h e s u g a r
c r y s t a l l i z a t i o n p r o c e s s . ( L e t us r e c a l l t h a t i n t h e p r e s e n t book , we a r e m a i n l y
161
i n t e r e s t e d i n t h r e e - b o i l i n g c r y s t a l l i z a t i o n . )
T a k i n g i n t o a c c o u n t t h a t a l a r g e p a r t o f t h e f a c t o r y ' s h e a t demand i s
c o n c e r n e d , a p rob lem m igh t be posed o f a r r a n g i n g t h e c r y s t a l l i z a t i o n p r o c e s s so
as t o m i n i m i z e t h e hea t demand o f t h e s u g a r h o u s e . O n l y s i m p l i f i e d p rob lem
f o r m u l a t i o n s can be a t temp ted and o n l y a p p r o x i m a t e s o l u t i o n s s o u g h t , h o w e v e r ,
because t h e r e i s a m u l t i t u d e o f p r o c e s s c o n s t r a i n t s a s s o c i a t e d w i t h s u g a r o u t p u t
and s u g a r q u a l i t y . A c t u a l l y , one m igh t even n o t e t h a t t h e c r y s t a l l i z a t i o n
p r o c e s s i s v e r y much dependen t on t h e q u a l i t y o f j u i c e s e n t e r i n g t h e s u g a r
h o u s e . T h i s w o u l d i m p l y t h a t i n o r d e r t o a r r a n g e t h e c r y s t a l l i z a t i o n p r o c e s s
o p t i m a l l y , t he e n t i r e f a c t o r y s h o u l d be c o n s i d e r e d . N e e d l e s s t o s a y , such an
approach wou ld n o t be v e r y p r a c t i c a l i f one had t o c o n c e n t r a t e on t h e e n e r g y
economy.
L e t us o b s e r v e t h a t t h e p rob lem becomes even more complex i f we a l l o w f o r
p o s s i b l e m o d i f i c a t i o n s o f t h e equ ipmen t , m a i n l y vacuum p a n s , as w e l l as
m o d i f i c a t i o n s o f t h e a u t o m a t i c c o n t r o l s y s t e m s . F o r t h e sake o f s i m p l i c i t y o f
p r e s e n t a t i o n , t h e s e q u e s t i o n s a r e c o n s i d e r e d s e p a r a t e l y i n C h a p t e r s 5 and 6. I t
s h o u l d n e v e r t h e l e s s be a d m i t t e d t h a t s a v i n g e n e r g y by r a t i o n a l i z i n g t h e s u g a r
c r y s t a l l i z a t i o n p r o c e s s i m p l i e s t h e n e c e s s i t y o f t o u c h i n g t h e most i n t r i c a t e
p rob lems o f s u g a r t e c h n o l o g y .
T h r e e i m p o r t a n t e n e r g y - s a v i n g c o n c e p t s a r e d i s c u s s e d i n t h e p r e s e n t S e c t i o n :
- t h e Dan i sh c r y s t a l l i z a t i o n scheme;
- c o o l i n g c r y s t a l l i z a t i o n ;
- c r y s t a l f o o t i n g t e c h n i q u e s .
4 . 3 . 2 Dan i sh c r y s t a l l i z a t i o n scheme
The e s s e n t i a l i d e a o f t h e Dan i sh c r y s t a l l i z a t i o n scheme i s t o e n s u r e t h a t
t he q u a l i t y o f Β p r o d u c t i s h i g h enough t o mix i t w i t h A p r o d u c t , and t o t r e a t
t h e m i x t u r e as w h i t e s u g a r . T h i s r e d u c e s t h e combined m a s s e c u i t e c i r c u l a t i o n
c o n s i d e r a b l y , b r i n g i n g abou t a r e d u c t i o n o f t h e t o t a l h e a t e x p e n d i t u r e i n s u g a r
b o i l i n g . As a f i r s t a p p r o x i m a t i o n , t h e h e a t s a v i n g can be e s t i m a t e d as t h e h e a t
r e q u i r e d t o e v a p o r a t e t h e amount o f w a t e r t h e o r e t i c a l l y needed t o d i s s o l v e
Β s u g a r , p l u s t he amount o f wash w a t e r needed when c e n t r i f u g i n g t h i s s u g a r as
A s u g a r . When compared t o a c o n v e n t i o n a l t h r e e - b o i l i n g scheme i n w h i c h t h i c k
j u i c e a t 72% DS i s used t o d i s s o l v e Β s u g a r , t h e steam s a v i n g i s o f t h e o r d e r o f
9-13% o f t h e w h i t e s u g a r o u t p u t , o r - u s i n g v a l u e s c h a r a c t e r i s t i c o f D a n i s h
f a c t o r i e s - abou t 1 .2-1 .7 kg/100 kg b. I f t h e c o n v e n t i o n a l scheme employs
d i s s o l v i n g Β s u g a r i n w a t e r , t h e n t h e s a v i n g amounts t o 12-14% o f t h e w h i t e
s u g a r o u t p u t , o r abou t 1 .6-1 .9 kg steam p e r 100 kg b e e t .
The s u g a r house scheme a p p l i e d i n DOS s u g a r f a c t o r i e s and t h e scheme o f s u g a r
f l o w t h r o u g h c r y s t a l l i z a t i o n s t a g e s a r e shown i n F i g . 4 . 6 . The main q u a l i t y
162
Fig
. 4
.6.
Suga
r ho
use
(a)
and
flow
of
suga
r (b
) ac
cord
ing
to t
he
Dan
ish
crys
tall
izat
ion
sche
me.
VP
B,
VPC
- va
cuum
pan
s Β
and
C;
CB,
CC
-
cen
trif
ug
als
Β a
nd C
(c
ourt
esy
DD
S).
163
r e q u i r e m e n t c o n c e r n e d w i t h Β s u g a r i s i t s low c o l o u r . I t i s known t h a t i n a
number o f c o u n t r i e s , t h e a t t e m p t s t o implement t h e D a n i s h scheme f a i l e d because
t h i s r e q u i r e m e n t c o u l d n o t be s a t i s f i e d r e l i a b l y . T h i s i s u n d e r s t a n d a b l e , as t h e
c o n d i t i o n s f o r a r e l i a b l e o p e r a t i o n o f t h e D a n i s h scheme - i n t e n d e d m a i n l y t o
p r e v e n t c o l o u r b u i l d - u p - have been s p e c i f i e d as f o l l o w s ( r e f . 1 2 ) .
( i ) I n t h e j u i c e p u r i f i c a t i o n , c o l o u r i n g m a t t e r e x h i b i t i n g s p e c i a l a f f i n i t y t o
s u g a r s h o u l d be e l i m i n a t e d . T h i s r e q u i r e s t h e p o l y m e r i z a t i o n o f p h e n o l i c
compounds so t h a t t h e y can be removed w i t h t h e s l u d g e , as w e l l as d e s t r o y i n g
i n v e r t s u g a r . I n p r a c t i c a l t e r m s , an a d e q u a t e l y l o n g j u i c e r e t e n t i o n t ime s h o u l d
be e n s u r e d a t an a l k a l i n i t y l e v e l e x c e e d i n g 0 . 4 - 0 . 5 g C a O / l O O ml ( w h i c h
c o r r e s p o n d s t o main l i m i n g ) .
( i i ) F i r s t f i l t r a t i o n must be e f f e c t i v e enough t o keep t h e s l u d g e c o n t e n t i n
t he f i l t r a t e be low 20 ppm.
( i i i ) S u l p h i t a t i o n o f t h i n j u i c e s h o u l d e n s u r e a pH v a l u e o f abou t 8.7 a t 20°C.
( i v ) I n t h e s u g a r h o u s e , pH v a l u e s s h o u l d be k e p t l o w e r t han 8 . 5 - 9 . 0 .
( v ) No u n n e c e s s a r y r e c y c l e s o f n o n s u g a r s and c o l o u r i n g m a t t e r s h o u l d be
t o l e r a t e d i n t h e s u g a r h o u s e .
( v i ) H igh c r y s t a l q u a l i t y s h o u l d be e n s u r e d i n b o i l i n g o f C s u g a r .
( v i i ) H i g h - p r e c i s i o n c e n t r i f u g i n g o f m a s s e c u i t e s i s r e q u i r e d .
P r a c t i c a l e x p e r i e n c e p r o v e s t h a t c o n d i t i o n s ( i v ) - ( v i i ) can be r e l i a b l y met
o n l y i f t h e s u g a r house o p e r a t i o n i s v e r y w e l l s t a b i l i z e d w i t h r e s p e c t t o t h e
q u a l i t y o f b o i l i n g and t he t e m p e r a t u r e s o f m a s s e c u i t e s b e f o r e c e n t r i f u g i n g . I n
s i m p l e t e r m s , i t can be c o n c l u d e d t h a t t h e D a n i s h c r y s t a l l i z a t i o n scheme i s
p r a c t i c a b l e o n l y i n w e l l e q u i p p e d , h i g h l y au toma ted , c a r e f u l l y m a i n t a i n e d and
s k i l f u l l y o p e r a t e d s u g a r f a c t o r i e s , and a s u f f i c i e n t l y h i g h b e e t q u a l i t y seems
t o be a p r e r e q u i s i t e . The q u a l i t y r e q u i r e m e n t s s h o u l d be u n d e r s t o o d t o a p p l y t o
b e e t s a t t h e e n t r a n c e t o t h e s l i c i n g s t a t i o n , t h a t i s , w i t h t h e consequences o f
b e e t d e t e r i o r a t i o n d u r i n g t r a n s p o r t and s t o r a g e t a k e n i n t o a c c o u n t . Among t h e
q u a l i t y pa rame te rs c o n c e r n e d , t h e amino-N c o n t e n t seems t o be o f c o n s i d e r a b l e
i m p o r t a n c e . I n Denmark, i t i s kep t be low 100 mg Ν p e r 100 g s u g a r as p r a c t i c a l
e x p e r i e n c e has shown t h a t h i g h e r amino-N c o n t e n t s make i t d i f f i c u l t t o o b t a i n
a s u f f i c i e n t l y h i g h p u r i t y o f t h i c k j u i c e ( r e f . 1 3 ) .
4 . 3 . 3 C o o l i n g c r y s t a l l i z a t i o n
The c o o l i n g c r y s t a l l i z a t i o n i s n o t a new i d e a , as i t i s g e n e r a l l y a p p l i e d i n
C m a s s e c u i t e c r y s t a l l i z a t i o n and i t has a l s o been p r a c t i s e d i n t he
c r y s t a l l i z a t i o n o f h i g h - p u r i t y m a s s e c u i t e s i n t h e cane s u g a r i n d u s t r y . W h i l e t h e
e v a p o r a t i n g c r y s t a l l i z a t i o n employs t h e e v a p o r a t i o n o f w a t e r f o r t h e
s u p e r s a t u r a t i o n c o n t r o l , t h e c o o l i n g c r y s t a l l i z a t i o n r e l i e s on a r e d u c t i o n o f
t he s o l u b i l i t y o f s u c r o s e i n w a t e r w i t h d e c r e a s i n g t e m p e r a t u r e . T h i s phenomenon
164
i s i l l u s t r a t e d i n a d iag ram i n F i g . 4 .7 ( a f t e r r e f . 1 4 ) . I t has been e s t i m a t e d
t h a t f o r h i g h - p u r i t y m a s s e c u i t e s , a t e m p e r a t u r e d e c r e a s e o f 2 Κ makes i t
p o s s i b l e t o i n c r e a s e t h e c r y s t a l y i e l d by 1% ( r e f . 1 5 ) .
4.0 Γ
3.5μ
-ο L.
D φ O o
CO
3 .ομ
2.5k
2 . 0 L - ^ AO 50 60 70 80
Temperature (**C)
F i g . 4 . 7 . S o l u b i l i t y o f s u c r o s e i n w a t e r as a f u n c t i o n o f t e m p e r a t u r e ( a f t e r r e f . 1 4 ) .
The m a s s e c u i t e can be c o o l e d i n an a t m o s p h e r i c - p r e s s u r e w a t e r - c o o l e d
c r y s t a l 1 i z e r . An equ ipment c o n f i g u r a t i o n making i t p o s s i b l e t o combine
e v a p o r a t i n g c r y s t a l l i z a t i o n and " p u r e - c o o l i n g " c r y s t a l l i z a t i o n i n t o one
c r y s t a l l i z a t i o n s t a g e i s s c h e m a t i c a l l y shown i n F i g . 4 .8 ( a f t e r r e f . 1 6 ) . The
m a s s e c u i t e i s d i s c h a r g e d f rom vacuum pans t o c o n v e n t i o n a l m i x e r s , f rom w h i c h i t
i s d i r e c t e d t o c o o l i n g c r y s t a l 1 i z e r s where an adequate r e t e n t i o n t ime - up t o
4-5 h f o r A , and 6-7 h f o r Β m a s s e c u i t e - must be e n s u r e d . As t h e m a s s e c u i t e i s
cooling water
VACUUM PANS
— Í — massecuite
i MIXERS
COOLING CRYSTALLIZERS
CENTRIFUGALS
sugar
vapour to the condenser
syrup
CONCENTRATOR
syrup to the next^ crystallization stage
HEATER
syrup
F i g . 4 . 8 . Scheme o f a c r y s t a l l i z a t i o n s t a g e emp loy ing e v a p o r a t i n g c r y s t a l l i z a t i o n and " p u r e - c o o l i n g " c r y s t a l l i z a t i o n .
165
c o o l e d down f rom t h e i n i t i a l t e m p e r a t u r e o f 70°C t o a b o u t 40-50°C, t h e c r y s t a l
c o n t e n t can be s u b s t a n i t a l l y i n c r e a s e d , i t s a t t a i n a b l e f i n a l v a l u e depend ing on
t h e DS c o n t e n t o f t h e r e c i r c u l a t e d s y r u p . F o r a c r y s t a l 1 i z e r d e s i g n known as
a c o o l i n g - c r y s t a l l i z a t i o n t o w e r t e s t e d i n t h e s u g a r i n d u s t r y i n FRG, t h e
a t t a i n a b l e r e l a t i v e i n c r e a s e o f t h e c r y s t a l c o n t e n t i s shown as a f u n c t i o n o f
f i n a l m a s s e c u i t e t e m p e r a t u r e and s y r u p DS c o n t e n t i n F i g . 4 . 9 . H o w e v e r , t h e
p o t e n t i a l f o r improvement o f c r y s t a l y i e l d i n d i c a t e d i n t h i s d iag ram t u r n s o u t
t o be d i f f i c u l t t o a c h i e v e owing t o t h e p rob lems o f m a i n t a i n i n g a s u f f i c i e n t l y
i n t e n s i v e hea t t r a n s f e r between t h e m a s s e c u i t e and t h e c o o l i n g s u r f a c e s .
0.50 Γ
ω ω S 0.A0 ϋ c
t 0-30
-L 0.20 o
<^ 0.10
0 - L 70 60 50 40 30 F ind massecuite temperature {°C)
F i g . 4 . 9 . R e l a t i v e i n c r e a s e o f t h e c r y s t a l c o n t e n t i n t h e c o o l i n g -c r y s t a l l i z a t i o n t o w e r v s . f i n a l m a s s e c u i t e t e m p e r a t u r e and DS c o n t e n t o f r e c i r c u l a t e d s y r u p ( a f t e r r e f . 1 7 ) .
A n o t h e r method o f c o o l i n g c r y s t a l l i z a t i o n , i n v e n t e d i n F r a n c e , employs a
vacuum c r y s t a l 1 i z e r i n w h i c h m a s s e c u i t e i s b o i l i n g as i t expands t o a p r e s s u r e
as low as abou t 0.09 b a r . The c r y s t a l 1 i z e r i s fo rmed as a h o r i z o n t a l c y l i n d r i c a l
v e s s e l e q u i p p e d w i t h a r i b b o n s t i r r e r , and t h e r e q u i r e d r e t e n t i o n t ime i s a b o u t
1 h . A p o s s i b l e equ ipment c o n f i g u r a t i o n i s shown s c h e m a t i c a l l y i n F i g . 4 . 1 0 . The
f l o w o f r e c i r c u l a t e d s y r u p (80-82% DS) i s a b o u t h a l f o f t h e t o t a l s y r u p f l o w .
P r a c t i c a l v a l u e s o f t h e r e l a t i v e c r y s t a l - y i e l d i n c r e a s e a r e abou t 0 .25 -0 .30
( i . e . , t he c r y s t a l c o n t e n t o f t h e m a s s e c u i t e i s i n c r e a s e d by a f a c t o r o f 1.25-
1 .30 ) .
As t h e c o o l i n g c r y s t a l l i z a t i o n makes i t p o s s i b l e t o i n c r e a s e t h e c r y s t a l
y i e l d i n a c r y s t a l l i z a t i o n s t a g e w i t h o u t a d d i t i o n a l h e a t e x p e n d i t u r e , i t can be
used t o r e d u c e t h e hea t demand o f t h e s u g a r h o u s e . The a t t a i n a b l e s a v i n g s depend
on t h e c o o l i n g method a p p l i e d and t h e l a y o u t o f t h e c r y s t a l l i z a t i o n scheme.
T a k i n g a c o n v e n t i o n a l t h r e e - b o i l i n g scheme w i t h t h i c k - j u i c e c o n c e n t r a t i o n o f
75% DS as a b a s i s f o r c o m p a r i s o n s , i t can be c o n c l u d e d t h a t t h e same w h i t e - s u g a r
166
80°C CONTINUOUS VACUUM PAN
massecuite
O.IAbar 68-70°C
0.09 bar 55-60°C
VACUUM CRYSTALLIZER1
VACUUM CRYSTALLIZER 2
CENTRIFUGALS
to the next crystal l izat ion
stage
BO-eS^'C
HEATER
syrup
sugar
F i g . 4 . 1 0 . Scheme o f a c r y s t a l l i z a t i o n s t a g e emp loy ing e v a p o r a t i n g c r y s t a l l i z a t i o n and c o o l i n g c r y s t a l l i z a t i o n under vacuum ( a f t e r r e f . 1 8 ) .
o u t p u t can be o b t a i n e d u s i n g t w o - b o i l i n g schemes f e a t u r i n g combined e v a p o r a t i o n -
and c o o l i n g - c r y s t a l l i z a t i o n o f t h e w h i t e s u g a r . I n t h e case o f " p u r e - c o o l i n g "
c r y s t a l l i z a t i o n , assuming a c r y s t a l - y i e l d i n c r e a s e abou t 0 .32 , t h e t h e o r e t i c a l
hea t demand ( c a l c u l a t e d f rom t h e r e q u i r e d e v a p o r a t i o n ) o f t h e s u g a r house i s
r e d u c e d by 48%. I f vacuum c r y s t a l l i z a t i o n i s employed and t h e c r y s t a l y i e l d i n
w h i t e - s u g a r c r y s t a l l i z a t i o n i n c r e a s e s by 0 .33 , t h e r e s u l t i n g r e d u c t i o n o f t h e
t h e o r e t i c a l hea t demand i s n e a r l y 53% ( r e f . 1 6 ) .
The e n e r g y - s a v i n g p o t e n t i a l o f c o o l i n g c r y s t a l l i z a t i o n has y e t t o be
i n v e s t i g a t e d . Up t o now, t h e deve lopmen t i n t h i s a r e a has been s t i m u l a t e d m a i n l y
by t h e i n d u s t r y ' s i n t e r e s t i n i m p r o v i n g s u g a r q u a l i t y . The u n d e r l y i n g i d e a i s t o
t ake advan tage o f bo th t h e n e g l i g i b l e c o l o u r i n c r e a s e c h a r a c t e r i s t i c o f t h e
c o o l i n g c r y s t a l l i z a t i o n , and t h e r e d u c t i o n o f t h e amount o f s y r u p s accompany ing
t he c r y s t a l - y i e l d i n c r e a s e . The l a t t e r f a c t o r makes i t p o s s i b l e t o r e d u c e s y r u p
r e c i r c u l a t i o n i n t he c r y s t a l l i z a t i o n scheme, t h i s r e s u l t i n g i n r e d u c e d c o l o u r
b u i l d - u p . I n a d d i t i o n , new p o s s i b i l i t i e s t o c o n t r o l t h e c r y s t a l g r o w t h a r e
c r e a t e d , t h i s making i t p o s s i b l e t o c o n t r o l f i n a l c r y s t a l s i z e and g r a n u l o m e t r i c
d i s t r i b u t i o n . Howeve r , when a t t e m p t i n g t o d e s i g n a c r y s t a l l i z a t i o n p r o c e s s
a iming t o r educe t he hea t demand o f t h e s u g a r h o u s e , one w o u l d have t o c o n s i d e r
c r y s t a l - q u a l i t y c o n s t r a i n t s w h i c h have n o t been f u l l y i n v e s t i g a t e d so f a r
( r e f . 1 9 ) .
4 . 3 . 4 C r y s t a l f o o t i n g t e c h n i q u e s
The c o n c e p t o f c r y s t a l f o o t i n g o p e r a t i o n was i n t r o d u c e d w i t h t h e e s s e n t i a l
aim o f i m p r o v i n g c r y s t a l q u a l i t y and e s p e c i a l l y t o make t h e g r a n u l o m e t r i c
d i s t r i b u t i o n more u n i f o r m . The u n d e r l y i n g i d e a i s t o r a t i o n a l i z e t h e i n i t i a l
167
phase o f t h e s u g a r b o i l i n g p r o c e s s as d i s c u s s e d i n S e c t i o n 1 .3 .5 . I n s t e a d o f
p e r f o r m i n g i t i n e v e r y s t r i k e i n e v e r y vacuum p a n , t h e i n i t i a l s y r u p t h i c k e n i n g
and c r y s t a l f o r m a t i o n i s c o n c e n t r a t e d i n a s p e c i a l i z e d u n i t . The seed magma
o b t a i n e d t h e r e i s s u b s e q u e n t l y d e l i v e r e d t o vacuum pans where t h e b o i l i n g can be
s t a r t e d d i r e c t l y f rom the c r y s t a l g r o w t h p h a s e .
A c r y s t a l f o o t i n g t e c h n i q u e can be i n t r o d u c e d i n t o c r y s t a l l i z a t i o n schemes i n
a v a r i e t y o f w a y s , depend ing on t h e k i n d o f f o o t i n g u n i t and t h e scheme i n
q u e s t i o n . A s i m p l e method c o n s i s t s o f p r e p a r i n g t h e seed magma e v e r y second
s t r i k e i n a s e l e c t e d b a t c h vacuum pan t o a b o u t 2 /3 o f i t s v o l u m e , pumping a h a l f
o f t h e magma t o a n o t h e r pan and s u b s e q u e n t l y b o i l i n g s u g a r i n bo th pans i n
p a r a l l e l . P r a c t i c a l e x p e r i e n c e p r o v e s t h a t i t may r e d u c e t h e a v e r a g e b o i l i n g
t ime by abou t 20%. Fewer s y r u p - t h i c k e n i n g phases pe r f o rmed i n t h e e n t i r e vacuum-
pan s t a t i o n r e d u c e t h e s t a t i o n ' s h e a t demand by a few p e r c e n t .
A n o t h e r method c o n s i s t s o f p r e p a r i n g t h e seed magma as a m i x t u r e o f s y r u p s
and c r y s t a l l i n e Β and C s u g a r s i n a s p e c i a l m i x e r . When d e l i v e r i n g t h e magma t o
vacuum pans A , t he b o i l i n g o f A s u g a r can be s t a r t e d f rom the c r y s t a l g r o w t h
p h a s e . E x p e r i m e n t s have d e m o n s t r a t e d t h e p o s s i b i l i t y o f r e d u c i n g t h e a v e r a g e
b o i l i n g t ime by abou t 25% and c u t t i n g down t h e h e a t demand by 5% ( r e f . 2 0 ) .
A method w h i c h r e c e i v e d much a t t e n t i o n i n t h e l a t e 1970s i s t o mix g r e e n
s y r u p A and n o n - a f f i n e d C s u g a r t o seed magma s u b s e q u e n t l y used i n vacuum pans
B. I t has been p r o v e d n o t t o b r i n g any s i g n i f i c a n t e n e r g y s a v i n g s . The h e a t
demand can be e f f e c t i v e l y r e d u c e d , h o w e v e r , i f t h i s p r o c e d u r e i s a p p l i e d t o
a p a r t o f t h e C - s u g a r s t ream o n l y a n d , i n a d d i t i o n , p a r t o f t h e Β s u g a r i s m ixed
w i t h wash s y r u p A t o seed magma used i n vacuum pans A ( F i g . 4 . 1 1 ) . Such a
" d o u b l e - f o o t i n g " t e c h n i q u e shows an e n e r g y - s a v i n g p o t e n t i a l o f t h e o r d e r o f up
t o 3 kg steam p e r 100 kg b e e t ( r e f s . 2 1 , 2 2 ) .
The b e s t c o n t r o l o f c r y s t a l q u a l i t y can be a t t a i n e d when a p p l y i n g a s p e c i a l
f o o t i n g u n i t i n w h i c h bo th c o o l i n g - and e v a p o r a t i n g - c r y s t a l 1 i z a t i o n , used a t
d i f f e r e n t s t a g e s o f t h e w o r k i n g c y c l e , a r e employed t o p r o d u c e t h e seed magma.
The equ ipment c o n f i g u r a t i o n can be e i t h e r a c o m b i n a t i o n o f a s e p a r a t e
c r y s t a l l i z e r and a vacuum p a n , o r a s i n g l e p i e c e s c h e m a t i c a l l y shown i n F i g .
4.12 ( r e f s . 2 3 , 2 4 ) . I f comp le ted w i t h t h i c k - j u i c e c o n d i t i o n i n g making i t
p o s s i b l e t o c o n t r o l t h i c k - j u i c e p a r a m e t e r s a c c u r a t e l y a t t h e e n t r a n c e t o t h e
s u g a r h o u s e , t h e c r y s t a l f o o t i n g t e c h n i q u e p r o v i d e s a v e r y e f f e c t i v e t o o l f o r
m a s t e r i n g s u g a r c r y s t a l l i z a t i o n a t h i g h t h i c k - j u i c e c o n c e n t r a t i o n s .
A p r e r e q u i s i t e f o r i t s s u c c e s s f u l a p p l i c a t i o n i s t h a t t h e s u g a r house i s
e q u i p p e d w i t h s t i r r e d vacuum pans o f s u i t a b l e d e s i g n and w i t h e f f e c t i v e
a u t o m a t i c b o i l i n g c o n t r o l s ; t h e s e q u e s t i o n s a r e d i s c u s s e d m a i n l y i n C h a p t e r s 5
and 6. I n c o n c l u s i o n , t h e impo r tance o f t h e c r y s t a l f o o t i n g t e c h n i q u e s t o t h e
e n e r g y economy does n o t l i e i n some d i r e c t e n e r g y - s a v i n g e f f e c t s b u t r a t h e r i n
168
thin juice thick juice
4 Β remelt Β seed magma
U L L I STAGE A
MELTER Β FOOTING UNIT Β
" — Β s u g a r -
i STAGE Β
C seed magma C remelt
FOOTING UNIT C MELTER C
STAGE C
white sugar
W<hrixi- • C suga r •
molasses
F i g . 4 ,11 . S i m p l i f i e d scheme o f t h r e e - b o i l i n g w h i t e - s u g a r c r y s t a l l i z a t i o n u s i n g " d o u b l e f o o t i n g " .
i t s p o t e n t i a l t o u t i l i z e e f f e c t i v e l y t h e i n f l u e n c e o f i n c r e a s e d t h i c k - j u i c e
c o n c e n t r a t i o n on t h e hea t demand i n t h e s u g a r house ( s e e S e c t i o n 1 . 3 . 5 ) .
( a ) slurry
cooling water
® condenser
Γ-CXl·
ISOLUTION * * TANK
I MIXER
HXl -thick juice
remelt
syrup
steam
to vacuum pans ^
y supersaturation about 1.05
* y 7/.-75V0DS
r—t><l—' "5<
CONDITIONED IREMELT* TANK
MIXER
to vacuum
5Γ m
pans
F i g . 4 . 1 2 . F o o t i n g u n i t s emp loy ing bo th e v a p o r a t i n g - and c o o l i n g - c r y s t a l l i z a t i o n t o p roduce seed magma: ( a ) w i t h a vacuum pan and a w a t e r - c o o l e d s t i r r e d v e s s e l ( a f t e r r e f . 2 3 ) , ( b ) w i t h a s p e c i a l l y d e s i g n e d vacuum p a n / c r y s t a l 1 i z e r and v a c u u m - c o n t r o l l e d c o o l i n g ( a f t e r r e f . 2 4 ) .
169
4.4 UNCONVENTIONAL ENERGY-SAVING PROCESSES IN SUGAR MANUFACTURE
4.4.1 U n d e r l y i n g c o n c e p t s
The s u g a r m a n u f a c t u r i n g p r o c e s s emp loy i ng e x t r a c t i o n , j u i c e p u r i f i c a t i o n w i t h
l ime and c a r b o n d i o x i d e , j u i c e t h i c k e n i n g by e v a p o r a t i o n and f i n a l l y ,
c r y s t a l l i z a t i o n , i s a p p a r e n t l y a s s o c i a t e d w i t h a c e r t a i n minimum e n e r g y
e x p e n d i t u r e w h i c h c a n n o t be f u r t h e r r e d u c e d . Assuming an o p t i m a l c o n f i g u r a t i o n
o f t h e the rma l s y s t e m , an e s t i m a t e o f t h e minimum i n p u t o f p r i m a r y e n e r g y abou t
2.3 kg normal f u e l p e r 100 kg b e e t has been g i v e n i n D a n i s h s o u r c e s ( r e f . 2 5 ) .
Even though t h i s v a l u e can s t i l l be d i s c u s s e d , p r a c t i c a l e x p e r i e n c e p r o v e s t h a t
e x t r e m e l y low hea t demand i n c o n v e n t i o n a l s u g a r m a n u f a c t u r e can o n l y be a t t a i n e d
a t t h e expense o f i n c o n v e n i e n t p r o c e s s m o d i f i c a t i o n s , t h e s e i n t u r n r e q u i r i n g
m o d i f i e d equ ipment and c o n t r o l s y s t e m s , as w e l l as i n c r e a s e d c o m p l e x i t y o f t h e
the rma l s y s t e m . I t seems t h a t t h e r e i s no o t h e r way i n w h i c h t h e c o n s t r a i n t s
i n h e r e n t i n t h e c o n v e n t i o n a l s u g a r m a n u f a c t u r i n g p r o c e s s can be s a t i s f i e d .
A number o f a l t e r n a t i v e p r o c e s s e s m i g h t p o s s i b l y be employed i n s u g a r
manu fac tu re t o remove o r change t h e c o n s t r a i n t s imposed on e n e r g y c o n v e r s i o n and
u t i l i z a t i o n t e c h n i q u e s . T h i s m igh t open e n t i r e l y new p o s s i b i l i t i e s f o r e n e r g y
demand r e d u c t i o n s .
To b e g i n w i t h , t h e i n i t i a l phase o f s u g a r m a n u f a c t u r i n g c o n s i s t s i n f a c t o f
j u i c e s e p a r a t i o n ; t h i s can be done by methods o t h e r t han e x t r a c t i o n . N e x t , j u i c e
p u r i f i c a t i o n can be p e r f o r m e d , a t l e a s t p a r t l y , w i t h o u t l ime and C O ^ .
E v a p o r a t i o n i s n o t t h e o n l y method s u i t e d t o j u i c e t h i c k e n i n g ; s i m i l a r l y ,
e v a p o r a t i n g - c r y s t a l 1 i z a t i o n can be a i d e d o r even r e p l a c e d by o t h e r methods o f
s e p a r a t i o n o f c r y s t a l l i n e s u g a r . C o n s e q u e n t l y , one can imag ine a s u g a r f a c t o r y
w i t h o u t e x t r a c t o r s , l i m e r s , c a r b o n a t a t i o n t a n k s , e v a p o r a t o r s and vacuum p a n s .
F o r t h e t ime b e i n g , such a v i s i o n b o r d e r s on s c i e n c e f i c t i o n , so no a t t e m p t w i l l
be made t o a n a l y s e i t as a w h o l e . I f one l o o k s a t t h e componen ts , h o w e v e r , t h e n
t he a p p l i c a t i o n p r o s p e c t s t u r n o u t t o be more r e a l i s t i c . I n t h e f o l l o w i n g , s h o r t
r e v i e w s o f t h e most p r o m i s i n g c o n c e p t s a r e g i v e n .
4 . 4 . 2 J u i c e s e p a r a t i o n
As an a l t e r n a t i v e t o e x t r a c t i o n , j u i c e s e p a r a t i o n f rom r a s p e d o r s l i c e d b e e t
b r e i can be c o n s i d e r e d . T h i s method was w i d e l y used i n t h e 19th c e n t u r y and
u l t i m a t e l y abandoned because t h e r e c o v e r y o f s u c r o s e was n o t s u f f i c i e n t l y
c o m p l e t e . I t i s now be ing s t u d i e d , h o w e v e r , w i t h some s u b s t a n t i a l m o d i f i c a t i o n s .
One p o s s i b l e v e r s i o n i s t o a p p l y l o w - t e m p e r a t u r e , c o u n t e r - c u r r e n t wash ing o f
b e e t b r e i ( r e f . 2 6 ) . The p r i n c i p l e o f t h e p r o c e s s and i t s e s s e n t i a l p a r a m e t e r s
a re g i v e n i n F i g . 4 . 1 3 ( a ) and t h e r e t e n t i o n t ime o f t h e b r e i can be e s t i m a t e d a t
10 m i n u t e s . The key p rob lem i s t o d e s t r o y c e l l membranes e f f e c t i v e l y so t h a t
s u g a r can be washed o u t a t low t e m p e r a t u r e . T h i s may r e q u i r e d o u b l e - s t a g e
170
(α) disintegrated beet
tissue 23VoDS acid f i l t rat ion
aid p reserva t ive water
raw juice 16.4% D S *
( b ) powdered lime 0.6
disintegrated ^
beet t issue 100
press juice
^ ^ A S H - "
-STAGE U
- - W A S H - '
. ^ S T A G E 2 .
" - W A S H - - '
.^STAGE 3 . PRESS
^ ^ A S H - "
-STAGE U
" - W A S H - - '
.^STAGE 3 .
b re i3 Ί
PRESS
pressed brei 35% DS
TANK 80°C
water 12.5 powdered lime
1 Γ PRESS 1 PRESS 2 35 bar 70 bar
raw juice
• pressed brei AOVoDS
F i g . 4 . 1 3 . Schemes o f j u i c e s e p a r a t i o n f rom b e e t b r e i : ( a ) t r i p l e - s t a g e c o u n t e r -c u r r e n t wash ing and p r e s s i n g o f b r e i , ( b ) d o u b l e - s t a g e p r e s s i n g . Mass f l o w s g i v e n i n kg/100 kg b. * / i n c l u d i n g 2% f i b r e s u b s t a n c e .
d i s i n t e g r a t i o n o f t h e b e e t t i s s u e : f i r s t i n a d i s k m i l l , t h e n i n a homogen ize r
o r a b e a t e r m i l l . S u c r o s e r e c o v e r y can be e s t i m a t e d as 0.97 m u l t i p l i e d by t h e
e f f i c i e n c y o f d i s i n t e g r a t i o n o f c e l l membranes. An e f f i c i e n c y o f 0.95 can e a s i l y
be o b t a i n e d , r e s u l t i n g t h u s i n s u c r o s e r e c o v e r y abou t 0 .92 . A t 16% s u g a r i n
b e e t s , 13.8% s u g a r i n raw j u i c e can be o b t a i n e d .
The a d v a n t a g e s o f t h e p r o c e s s a r e :
- h i g h p u r i t y o f s e p a r a t e d j u i c e ;
- no hea t e x p e n d i t u r e ;
- h i g h v a l u e o f c o n c e n t r a t e d b r e i as animal f e e d .
The most s e r i o u s d i s a d v a n t a g e i s t h e r e l a t i v e l y h i g h power demand o f t h e
d i s i n t e g r a t i o n equ ipmen t : 0.44 kWh/100 kg b has been r e p o r t e d f rom a p r o t o t y p e
i n s t a l l a t i o n . N e v e r t h e l e s s , economic c o m p e t i t i v e n e s s a g a i n s t c o n v e n t i o n a l
e x t r a c t i o n has a l r e a d y been c l a i m e d a t sma l l p r o c e s s i n g c a p a b i l i t i e s up t o
1200 t / d .
A n o t h e r s o l u t i o n employs d o u b l e - s t a g e p r e s s i n g o f b e e t b r e i a t e l e v a t e d
t e m p e r a t u r e ( r e f . 2 7 ) . The p r o c e s s i s s c h e m a t i c a l l y shown i n F i g . 4 . 1 3 ( b ) ; t h e
r e t e n t i o n t ime o f t h e b r e i can be e s t i m a t e d a t 20 m i n u t e s . D o u b l e - s t a g e p r e s s i n g
o f f e r s t h e a d v a n t a g e s o f v e r y h i g h s u c r o s e r e c o v e r y and v e r y h i g h c o n t e n t o f
d r y s u b s t a n c e i n t h e p r e s s e d b r e i . A t 16% s u g a r i n b e e t s , 15.5% s u g a r i n raw
j u i c e seems t o be a r e a l i s t i c f i g u r e . As t h i s p r o c e s s has been t e s t e d on
171
a l a b o r a t o r y s c a l e o n l y , f u r t h e r r e s e a r c h i s needed b e f o r e any e v a l u a t i o n can be
g i v e n o f i t s t e c h n i c a l and economic f e a s i b i l i t y .
4 . 4 . 3 J u i c e p u r i f i c a t i o n and t h i c k e n i n g
J u i c e p u r i f i c a t i o n i s a p r o c e s s e s s e n t i a l l y aimed a t remov ing n o n s u g a r s , and
j u i c e t h i c k e n i n g one aimed a t remov ing e x c e s s w a t e r f rom s u g a r s o l u t i o n s . These
f u n c t i o n s can be pe r f o rmed emp loy ing membrane f i l t r a t i o n p r o c e s s e s ( r e f s . 28-30)
known as u l t r a f i l t r a t i o n and h y p e r f i 1 t r a t i o n ; t h e l a t t e r t e c h n i q u e i s a l s o
c a l l e d r e v e r s e o s m o s i s . The c h a r a c t e r i s t i c s o f b o t h p r o c e s s e s a r e g i v e n i n
T a b l e 4 . 1 . U l t r a f i l t r a t i o n c o n c e n t r a t e s h i g h - m o l e c u l a r s u b s t a n c e c o l l o i d s and
suspended p a r t i c l e s , w h i l e h y p e r f i 1 t r a t i o n c o n c e n t r a t e s l o w - m o l e c u l a r s u b s t a n c e s
and s e p a r a t e s t h e s o l v e n t . The a p p r o x i m a t e l i m i t between t h e two p r o c e s s e s i s
a m o l e c u l a r w e i g h t o f 500-1000.
TABLE 4.1
Main f e a t u r e s o f u l t r a f i l t r a t i o n and h y p e r f i 1 t r a t i o n p r o c e s s e s .
U l t r a f i l t r a t i o n H y p e r f i 1 t r a t i o n
Minimum s i z e o f p a r t i c l e s s e p a r a t e d ( m i c r o n s ) 10-200 1-10 Examples o f s u b s t a n c e s n o t s e p a r a t e d w a t e r , e t h a n o l , w a t e r , e t h a n o l , Examples o f s u b s t a n c e s n o t s e p a r a t e d
l a c t i c a c i d . l a c t i c a c i d s u g a r s , s a l t s . l o w e r o r g a n i c compounds
P r e s s u r e range ( b a r ) 1-10 20-100 A p p l i c a t i o n s o u t s i d e s u g a r i n d u s t r y s e p a r a t i o n o f w a t e r
p r o t e i n s d e s a l i n a t i o n
The membranes, u s u a l l y 100-400 m i c r o n s t h i c k , a r e m a n u f a c t u r e d f rom p o l y m e r i c
m a t e r i a l s c a s t on a p o l y e s t e r o r p o l y p r o p y l e n e s u p p o r t . The d i f f e r e n c e between
u l t r a f i l t r a t i o n and h y p e r f i 1 t r a t i o n membranes l i e s i n t h e i r s t r u c t u r e s . The s i z e
o f t he membrane i s l i m i t e d by i t s s t r e n g t h . The membranes a r e mounted i n modu les
p r o v i d i n g a l s o n e c e s s a r y f l o w c h a n n e l s ; t u b u l a r , s p i r a l - w o u n d , p l a t e - a n d - f r a m e
and h o l l o w - f i b r e d e s i g n s a r e u s e d . The modules can be c o n n e c t e d t o g e t h e r and
e q u i p p e d w i t h pumps, v a l v e s , t a n k s , a u t o m a t i c c o n t r o l s , e t c . , t o c r e a t e a
membrane f i l t r a t i o n sys tem as shown s c h e m a t i c a l l y i n F i g . 4.14 ( r e f . 3 0 ) .
An u l t r a f i l t r a t i o n u n i t can be i n c o r p o r a t e d i n s u g a r m a n u f a c t u r e as j u i c e
p u r i f i c a t i o n equ ipmen t , a c c o r d i n g t o a scheme shown i n F i g . 4.15 ( r e f . 3 0 ) .
W h i l e t he p u r i t y o f u l t r a f i l t e r e d j u i c e can be as h i g h as t h a t o f t h i n j u i c e
l e a v i n g c o n v e n t i o n a l p u r i f i c a t i o n s t a t i o n s , i n v e r t s u g a r i s however n o t
e l i m i n a t e d , t h i s g i v i n g r i s e t o e x c e s s i v e c o l o u r f o r m a t i o n . T h e r e f o r e , f u r t h e r
t r e a t m e n t w i t h 0.05 kg l ime p e r 100 kg b e e t , o r by i o n e x c h a n g e , may be
n e c e s s a r y .
The a d v a n t a g e s o f u l t r a f i l t r a t i o n a r e l ime s a v i n g and e l i m i n a t i o n o f
172
sugar solution
water
permeate
concentrate
F i g . 4 .14 . Scheme o f a membrane f i l t r a t i o n sys tem ( a f t e r r e f . 3 0 ) .
water
raw juice ] SCREENING — ^ P R E - T R E A T M E N T —
ULTRAFILTRATION 80°C
thin juice SULPHITATION
CLARIFICATION OR FILTRATION
sludge
permeate
LIMING
concentrate
F i g . 4 .15 . J u i c e p u r i f i c a t i o n scheme i n c l u d i n g an u l t r a f i l t r a t i o n u n i t ( a f t e r r e f . 3 0 ) .
c a r b o n a t a t i o n hea t l o s s e s . I f a c h i e v e d d u r i n g a f a c t o r y e x t e n s i o n , t h i s can make
i n v e s t m e n t i n t h e l ime k i l n u n n e c e s s a r y . C o s t e s t i m a t e s based on p i l o t - s c a l e
t r i a l s can be f ound i n the l i t e r a t u r e ( r e f . 3 1 ) .
A h y p e r f i l t r a t i o n u n i t can be used t o remove w a t e r f rom j u i c e , t h u s r e d u c i n g
t h e e v a p o r a t o r l o a d . Two p o s s i b l e l o c a t i o n s i n a s u g a r m a n u f a c t u r i n g l i n e a r e
shown s c h e m a t i c a l l y i n F i g . 4.16 ( r e f . 3 2 ) . A t t h e p r e s e n t s t a t e o f deve lopmen t
o f h y p e r f i 1 t r a t i o n membranes, 30-35% DS seems t o be t h e upper l i m i t o f
p r a c t i c a b l e j u i c e c o n c e n t r a t i o n s . T h i s c o r r e s p o n d s t o an a t t a i n a b l e steam s a v i n g
o f t h e o r d e r o f 2.7 kg/100 kg b. Power consumpt ion i n j u i c e pumping, h o w e v e r ,
may be as h i g h as 0.8 kWh/100 kg b. C o s t e s t i m a t e s o b t a i n e d by e x t r a p o l a t i n g t h e
f i g u r e s f rom p i l o t - s c a l e t e s t s a r e g i v e n i n t h e l i t e r a t u r e ( r e f . 3 1 ) .
The p rob lem w i t h t h e membrane f i l t r a t i o n sys tems p r e s e n t l y a v a i l a b l e i s t h a t
module s i z e s a r e r e l a t i v e l y s m a l l , t h i s i n c r e a s i n g t h e i n v e s t m e n t c o s t s o f
l a r g e - c a p a c i t y u n i t s . The c o s t o f membranes i s a l s o h i g h . N e v e r t h e l e s s , i f t h e
f u e l c o s t i s h i g h , i t may be j u s t i f i e d t o c o n s i d e r e n e r g y - s a v i n g membrane
f i l t r a t i o n sys tems as s e r i o u s a l t e r n a t i v e s t o e x t e n s i o n s o f t h e c o n v e n t i o n a l
equ ipmen t . F u r t h e r deve lopmen ts i n membrane t e c h n o l o g y can be e x p e c t e d t o
173
improve t h e c o m p e t i t i v e n e s s o f such s o l u t i o n s ; i n t h e f i r s t p l a c e , t h i s seems t o
a p p l y t o h y p e r f i 1 t r a t i o n ( r e v e r s e o s m o s i s ) u n i t s .
cossettes EXTRACTION
pulp
row juice HYPERFILTRATION VERSION 1
concentrate
permeate
LIMING
CARBONATATION
thick juice EVAPORATION
Ε 1
permeate
t FILTRATION
"1 concentrate HYPERFILTRATION SULPHITATION
VERSION 2 SULPHITATION
s ludge
F i g . 4 . 16 . P o s s i b l e l o c a t i o n s o f h y p e r f i 1 t r a t i o n u n i t s i n a scheme o f a s u g a r m a n u f a c t u r i n g p r o c e s s ( a f t e r r e f . 3 2 ) .
4 . 4 . 4 Sugar c r y s t a l l i z a t i o n
The p o s s i b i l i t i e s f o r a r a d i c a l change i n s u g a r c r y s t a l l i z a t i o n methods
depend v e r y much on t he r e s u l t s t h a t can be o b t a i n e d i n t h e p r e c e d i n g s e c t i o n s
o f t h e s u g a r m a n u f a c t u r i n g l i n e . I f h i g h enough t h i c k - j u i c e p u r i t y c o u l d be
assumed, t h e n t h e c o m p l i c a t e d m u l t i - s t a g e c r y s t a l l i z a t i o n c o u l d be r e p l a c e d , f o r
examp le , by s p r a y d r y i n g . I m p l i c a t i o n s on t h e e n e r g y s i d e , as w e l l as t h e
consequences f o r i n v e s t m e n t c o s t s , wou ld be enormous.
S t a y i n g w i t h i n t h e f rames d e f i n e d by t h e p r e s e n t s t a t e o f deve lopmen t o f
j u i c e s e p a r a t i o n and p u r i f i c a t i o n , m u l t i - s t a g e c r y s t a l l i z a t i o n seems t o be t h e
o n l y f e a s i b l e s o l u t i o n . C o n s i d e r a b l e e n e r g y s a v i n g s can be o b t a i n e d , h o w e v e r , i f
t h e e v a p o r a t i n g c r y s t a l l i z a t i o n i s r e p l a c e d by some l e s s e n e r g y - i n t e n s i v e
method. A d o p t i n g t he i d e a u s e d , f o r examp le , i n c e r t a i n European p a t e n t s
c o n c e r n e d w i t h mo lasses d e s u g a r i z a t i o n , t h e a p p l i c a t i o n o f f r e e z e
c r y s t a l l i z a t i o n has been p r o p o s e d ( r e f s . 3 3 , 3 4 ) . I t s p r i n c i p l e r e q u i r e s a
r e f r i g e r a n t s u b s t a n c e t o be added t o t h e s u c r o s e s o l u t i o n . As t h e r e f r i g e r a n t
a b s o r b s h e a t f rom the s o l u t i o n , t h e w a t e r c r y s t a l l i z e s . E v e n t u a l l y , t h i s b r i n g s
abou t t he s u p e r s a t u r a t i o n o f t h e s o l u t i o n and t h e f o r m a t i o n o f s u g a r c r y s t a l s .
I n t h e n e x t s t e p , s u g a r i s s e p a r a t e d f rom i c e c r y s t a l s t h a t a r e s u b s e q u e n t l y
washed w i t h w a t e r . Sugar c r y s t a l s a r e washed w i t h s y r u p , d r a i n e d , f i l t e r e d and
c e n t r i f u g e d .
T h i s method i s so new t o t h e s u g a r i n d u s t r y t h a t a l o t o f work i s needed t o
c l a r i f y i t s a p p l i c a t i o n p o t e n t i a l . On t h e e n e r g y s i d e , t h e c h o i c e o f t h e
r e f r i g e r a n t and t h e c o n c e p t o f t h e r e f r i g e r a t i o n c i r c u i t seem t o be d e c i s i v e i n
d e t e r m i n i n g t h e a t t a i n a b l e s a v i n g s .
174
4.5 PULP DEHYDRATION
4.5.1 L i n e s o f deve lopment
I t i s c h a r a c t e r i s t i c o f h i s t o r i c a l deve lopmen ts i n t he s u g a r i n d u s t r y t h a t
e n e r g y usage i n t he s u g a r m a n u f a c t u r i n g p r o c e s s has been t r e a t e d more s e r i o u s l y
than t h a t i n d r y i n g t h e p u l p . F o l l o w i n g t h e e n e r g y c r i s e s o f t h e 1970s, i t was
r e a l i z e d t h a t w h i l e t h e e n e r g y sys tems o f s u g a r manu fac tu re a r e r a t h e r e l a b o r a t e
and s t e a d i l y i m p r o v i n g , r e l a t i v e l y p r i m i t i v e p u l p - d r y i n g sys tems can be
r e s p o n s i b l e f o r as much as 1/3 o f t h e p r i m a r y - e n e r g y i n p u t in a s u g a r f a c t o r y .
T h i s s t i m u l a t e d much r e s e a r c h and numerous p r a c t i c a l a c t i o n s w h i c h g r a d u a l l y
began t o g i v e p r a c t i c a l r e s u l t s . I n c e r t a i n c o u n t r i e s , t h e e n e r g y s a v i n g s i n
p u l p d r y i n g have been q u i t e s p e c t a c u l a r , as can be seen i n F i g . 4 . 1 7 . The
p r o g r e s s was a c h i e v e d owing t o combined deve lopmen ts i n p r o c e s s e s , equ ipment
and c o n t r o l s y s t e m s . I n t he p r e s e n t a u t h o r ' s o p i n i o n , h o w e v e r , r e - t h i n k i n g o f
p r o c e s s r e q u i r e m e n t s p l a y e d a p a r t i c u l a r l y i m p o r t a n t r o l e .
1978 1980 1982 1984
F i g . 4 . 1 7 . S t a t i s t i c a l d a t a on e n e r g y consumpt ion i n p u l p d r y i n g i n FRG and Sweden, 1977-1985. The v a l u e s g i v e n f o r bo th c o u n t r i e s a r e n o t d i r e c t l y comparab le because o f t he d i f f e r e n c e s i n mo lasses d o s a g e .
I t s h o u l d n o t be f o r g o t t e n t h a t t h e e s s e n t i a l p rob lem w i t h t h e we t p u l p i s
how t o u t i l i z e i t . The most w i d e l y a c c e p t e d s o l u t i o n c o n s i s t s o f p r e s s i n g ,
d r y i n g and p e l l e t i n g the p u l p so t h a t i t can be e a s i l y s t o r e d , t r a n s p o r t e d and
s o l d as animal f e e d a d d i t i v e . T h e r e a r e numerous o t h e r p r o p o s a l s , h o w e v e r , t h a t
a l s o d e s e r v e s e r i o u s c o n s i d e r a t i o n . Depend ing on economic and v a r i o u s l o c a l
( e . g . , e n v i r o n m e n t a l ) c o n d i t i o n s i n a p a r t i c u l a r f a c t o r y , t h e b e s t c h o i c e may
v a r y .
An i n t e r e s t i n g p o s s i b i l i t y i s t o a v o i d t r e a t i n g t h e p u l p as a b y - p r o d u c t and
t o u t i l i z e i t w i t h t h e aim o f i m p r o v i n g t h e f a c t o r y ' s e n e r g y b a l a n c e . T h i s can
be done by c o n v e r t i n g t h e p r e s s e d p u l p t o b i o g a s i n an a n a e r o b i c f e r m e n t a t i o n
p r o c e s s . I t has been demons t ra ted i n l a b o r a t o r y - s c a l e e x p e r i m e n t s , and p a r t l y
c o n f i r m e d i n a p i l o t p l a n t , t h a t 90% o f t h e o r g a n i c m a t t e r p r e s e n t i n p u l p can
175
be c o n v e r t e d t o methane, t h e r e s t b e i n g a was te w h i c h needs t o be d i s p o s e d o f
( r e f . 2 , 3 5 ) . B i o g a s g e n e r a t e d f rom t h e e n t i r e amount o f p u l p can be s u p p l i e d t o
t he b o i l e r s . A l t e r n a t i v e l y , a p a r t o f t h e p u l p may be c o n v e r t e d t o methane,
wh i ch i s s u b s e q u e n t l y bu rned i n a d r y e r f u r n a c e , making i t p o s s i b l e t o d r y t h e
rema in ing p a r t . The economic p o t e n t i a l o f b i o g a s p r o d u c t i o n f rom t h e p u l p has
y e t t o be demons t ra ted i n a f u l l - s c a l e i n d u s t r i a l a p p l i c a t i o n .
A s o l u t i o n w i d e l y p r a c t i s e d i s t o s e l l t h e p r e s s e d p u l p d i r e c t l y , as f o d d e r .
I f t r a n s p o r t and s t o r a g e a r e p r o v i d e d by t h e c u s t o m e r s , t h e a d v a n t a g e s a r e
g r e a t . I t can be seen f rom t h e e x p e r i e n c e s o f numerous c o u n t r i e s , h o w e v e r , t h a t
t he o v e r a l l c o s t s o f t h e e n t i r e d i s t r i b u t i o n and s t o r a g e sys tem - s e r v i n g a
p r o d u c t w h i c h c o n t a i n s abou t 80% w a t e r - may be h i g h e r t han t h e v a l u e o f s a v i n g s
o b t a i n e d i n t h e f a c t o r y . T h e r e f o r e , t h i s s o l u t i o n may be d i f f i c u l t t o
s u b s t a n t i a t e i n w e l l - b a l a n c e d economies . N e e d l e s s t o s a y , i t a l s o r e q u i r e s l o n g -
te rm m a r k e t i n g .
A n o t h e r p o s s i b i l i t y c o n s i s t s o f s t o r i n g t h e p r e s s e d p u l p i n t h e f a c t o r y a r e a .
T h i s r e q u i r e s t h e a p p l i c a t i o n o f a s u i t a b l e p r e s e r v a t i o n p r o c e d u r e e n s u r i n g p u l p
f e r m e n t a t i o n aimed a t l a c t i c a c i d f o r m a t i o n ( r e f s . 3 7 , 3 7 ) . The s i m p l e s t method
i s t o e n s i l e t h e p u l p i m m e d i a t e l y a f t e r p r e s s i n g , t h a t i s , a t 45-50°C. A c o r r e c t
f e r m e n t a t i o n i s a t t a i n e d i f t h e e n s i l e d p u l p i s c o o l e d a t a d a i l y r a t e o f
0 . 5 - 1 . 0 K. No chemica l a d d i t i v e s a r e r e q u i r e d , b u t t h e a d d i t i o n o f m o l a s s e s has
been shown t o i n c r e a s e l a c t i c a c i d f o r m a t i o n . A l t e r n a t i v e l y , c o o l e d p u l p can be
e n s i l e d , p o s s i b l y w i t h chemica l p r e s e r v a t i v e s o r i n a 85:15 m i x t u r e w i t h b e e t
f r a g m e n t s . S u c c e s s f u l i n d u s t r i a l a p p l i c a t i o n s o f p u l p e n s i l a g e a r e known.
R e t u r n i n g now t o t h e p u l p d e h y d r a t i o n me thod , r e f e r e n c e can be made t o
S e c t i o n s 1.2.8 and 1.2.9 where t h e i m p o r t a n c e o f e n e r g y - s a v i n g p r o c e s s
m o d i f i c a t i o n s was s t r e s s e d . I n F i g . 4 . 1 8 ( a ) , t h e i n f l u e n c e o f t h e f i n a l DS
c o n t e n t on t h e s p e c i f i c e n e r g y demand i n mechan i ca l and the rma l d e h y d r a t i o n i s
shown. The e n e r g y demand p e r u n i t mass o f w a t e r removed by mechan ica l p r e s s i n g
i s v e r y low a t low DS c o n t e n t , b u t i t i n c r e a s e s r a p i d l y a t DS c o n t e n t s above
a c e r t a i n l i m i t . C o n c e r n i n g the rma l d r y i n g , i t s s p e c i f i c e n e r g y demand i s
r e l a t i v e l y c o n s t a n t o v e r a w ide range o f DS c o n t e n t s . The i n t e r s e c t i o n p o i n t
between t h e a p p l i c a t i o n r a n g e s o f bo th me thods , h o w e v e r , i s d e t e r m i n e d by
o v e r a l l economic r e s u l t s r a t h e r t han by e n e r g y i s s u e s o n l y . I t t u r n s o u t t h a t
w i t h i n c r e a s i n g DS c o n t e n t , t h e i n v e s t m e n t c o s t s o f p r e s s e s i n c r e a s e more
r a p i d l y t han t h e s p e c i f i c e n e r g y demand, s h i f t i n g t h e i n t e r s e c t i o n p o i n t t o w a r d s
l o w e r DS v a l u e s .
Numerous s t u d i e s o f a p p l i c a t i o n r a n g e s o f bo th d e h y d r a t i o n methods have been
p u b l i s h e d ( r e f . 3 8 - 4 3 ) . A g raph d e p i c t i n g t h e r e l a t i o n s h i p between p r e s s i n g and
thermal d r y i n g i s shown i n F i g . 4 . 1 8 ( b ) . As can be s e e n , a t 8% DS i n e x h a u s t e d
c o s s e t t e s , i n c r e a s i n g t h e DS c o n t e n t o f p r e s s e d p u l p f rom 22% t o 30% r e s u l t s i n
176
(α)
Ο Φ ϊ I
^1
III·"" g I
I l l l l l l l l l l l l á l l l " " " ' t h e r m a l
mechanical
J 0 20 40 60 80 100
Final DS content in pu lp(%)
20 40 60 80
DS content in pulp ( % )
F i g . 4 .18 . C h a r a c t e r i s t i c s o f mechan ica l and therma l p u l p d e h y d r a t i o n : ( a ) s p e c i f i c e n e r g y demand v s . f i n a l DS c o n t e n t , ( b ) w a t e r amount i n p u l p v s . DS c o n t e n t ( a f t e r r e f . 5 1 ) .
an i n c r e a s e o f w a t e r amount removed by therma l d e h y d r a t i o n o f abou t 1/7.
S i m u l t a n e o u s l y , t h e w a t e r amount removed by the rma l d e h y d r a t i o n i s r e d u c e d by
abou t 1/3.
I n t h e f o l l o w i n g , t h r e e e n e r g y - s a v i n g t e c h n i q u e s r e l a t e d t o p u l p d e h y d r a t i o n
t e c h n o l o g y a r e d i s c u s s e d :
- p r e s s i n g a t i n c r e a s e d f i n a l DS c o n t e n t o f t h e p u l p ;
- l o w - t e m p e r a t u r e d r y i n g ;
- steam d r y i n g .
4 . 5 . 2 P r e s s i n g t o h i g h DS c o n t e n t
A mechan ica l p r e s s o f c o n t e m p o r a r y d e s i g n u t i l i z e s t h e combined e f f e c t o f
p r e s s u r e and r e t e n t i o n t ime on t h e f i n a l DS c o n t e n t o f t h e p u l p . T h i s phenomenon
has been e x t e n s i v e l y s t u d i e d f o r d i f f e r e n t p r e s s d e s i g n s ; sample r e s u l t s a r e
shown i n F i g . 4.19 ( r e f . 4 4 ) . The nominal r e t e n t i o n t i m e , c o r r e s p o n d i n g t o t h e
nominal c a p a c i t y o f t h e p r e s s , d e t e r m i n e s i t s d i m e n s i o n s and t h u s t h e i n v e s t m e n t
c o s t . When t h e r o t a t i o n a l v e l o c i t y o f t he r o t o r i s r e d u c e d , l o n g e r r e t e n t i o n
t ime i s e n s u r e d and a h i g h e r DS c o n t e n t can be a t t a i n e d ; t h i s i m p l i e s , h o w e v e r ,
t h a t t h e c a p a c i t y u t i l i z a t i o n d e c r e a s e s . T h e r e f o r e , r e a l p r o g r e s s i s a c h i e v e d
o n l y i f t h e p r e s s d e s i g n i s improved t o g i v e a h i g h DS c o n t e n t i n t h e most
economica l o p e r a t i n g c o n d i t i o n s .
Up t o now, t he e s t a b l i s h e d p r e s s m a n u f a c t u r e r s i n t r o d u c e d o n l y l i m i t e d
changes t o t h e i r p r o d u c t s ( r e f s . 4 4 , 4 5 ) . Among t h e new d e s i g n s , a F r e n c h
s o l u t i o n a t t a i n i n g 50% DS was s u c c e s s f u l l y t e s t e d , bo th on p i l o t and i n d u s t r i a l
s c a l e s ( r e f . 4 2 ) . The c o n c e p t o f p u l p c e n t r i f u g i n g a l s o d e s e r v e s t o be n o t e d .
177
10 20 30 40 Retention time (min)
50 60
F i g . 4 . 19 . A t t a i n a b l e DS c o n t e n t o f p r e s s e d p u l p v s . r e t e n t i o n t ime and p r e s s u r e .
I t i s a w e l l known phenomenon t h a t t h e r e s u l t s o f p r e s s i n g a r e t o some e x t e n t
dependen t on t he p r o p e r t i e s o f t h e we t p u l p , most n o t a b l y on t h e c o n d i t i o n o f
p e c t i n s . I f t he p e c t i n s a r e decomposed d u r i n g e x t r a c t i o n , p r e s s i n g becomes
d i f f i c u l t . F o r t h i s r e a s o n , t o o h i g h t e m p e r a t u r e s and t o o l ong p u l p r e t e n t i o n
t imes i n t he e x t r a c t o r s h o u l d be a v o i d e d , as w e l l as p u l p r e c y c l e s . M o r e o v e r ,
advan tageous e f f e c t s can be a c h i e v e d by c o n t r o l l e d i n f e c t i o n by l a c t i c a c i d
b a c t e r i a , g i v i n g low pH o f t h e p u l p and good p r e s s i n g . As t h i s a l s o causes t he
s u g a r l o s s e s i n t h e e x t r a c t i o n t o i n c r e a s e , t h e f e a s i b i l i t y o f t h e method i s n o t
o b v i o u s . A r e f e r e n c e can be made t o f u l l - s c a l e e x p e r i m e n t s i n two A u s t r i a n
f a c t o r i e s , where m i c r o b i a l i n f e c t i o n i n t o w e r e x t r a c t o r s was c o n t r o l l e d t h r o u g h
c o n t i n u o u s f o r m a l i n d o s i n g v i a h i g h - p r e c i s i o n m e t e r i n g sys tems ( r e f . 4 6 ) . I n one
c a s e , t h e r e s u l t s were c l e a r l y p o s i t i v e ; i n t h e o t h e r f a c t o r y , t h e v a l u e o f
s u g a r l o s t a n n i h i l a t e d t h e e f f e c t o f e n e r g y s a v i n g . I t can a l s o be men t ioned
t h a t t h e r e have been examples o f i m p r o v i n g we t p u l p p r o p e r t i e s by d o s i n g
s u l p h u r i c a c i d t o p r e s s w a t e r (pH v a l u e abou t 4 ) .
I n r e c e n t y e a r s , m a i n l y on an e m p i r i c a l b a s i s , t h e a d d i t i o n o f p r e s s i n g a i d s
has become w i d e s p r e a d ( r e f s . 4 4 , 4 7 ) . C a l c i u m s a l t s - C a ( H S 0 2 ) 2 , C a C l 2 , CaSO^ -
a re t he most p o p u l a r because o f t h e i r low c o s t . The a i d s a r e added i n s o l u t i o n
o r s l u r r y t o t h e e x t r a c t i o n f e e d w a t e r o r t o t h e p u l p a t t h e e x t r a c t o r o u t l e t .
T e s t s o f l i m i n g o f f r e s h c o s s e t t e s have a l s o been p e r f o r m e d ( r e f . 4 8 ) . D i f f e r e n t
r a t i o s o f a i d / b e e t s a r e u s e d , bu t 500 g p e r 1 t b e e t i s a b o u t t h e upper l i m i t .
More s y s t e m a t i c s t u d i e s o f t h e e f f e c t o f p r e s s i n g a i d s , p u b l i s h e d r e c e n t l y ,
de te rm ine an upper l i m i t o f t h e l o a d i n g o f c a l c i u m s a l t s a t 4 m i l l i g r a m
e q u i v a l e n t s p e r 100 g b e e t ( r e f . 4 9 ) . The i n c r e a s e i n the d r y s u b s t a n c e c o n t e n t
o f t he p r e s s e d p u l p i s 3-4%. I t has a l s o been e s t a b l i s h e d t h a t t h e a i d s
c o n t a i n i n g t r i v a l e n t i o n s , e . g . k^^{SO^)^, may r a i s e t h e p u l p DS c o n t e n t even
f u r t h e r .
178
The amounts o f s a l t s used as p r e s s i n g a i d s a r e so sma l l t h a t t h e y seem t o
d i s a p p e a r i n t h e j u i c e p u r i f i c a t i o n p r o c e s s , a l t h o u g h s l i g h t l y i n c r e a s e d s u g a r
l o s s i n mo lasses can be e x p e c t e d e s p e c i a l l y when u s i n g C a C l ^ ( r e f . 5 0 ) . The
c o n d i t i o n s change when mo lasses i s added t o t h e p u l p . I t i s known t h a t i t s
o s m o t i c e f f e c t on p u l p p a r t i c l e s r a i s e s t h e amount o f w a t e r t h a t can be removed
f rom t h e p u l p . A f t e r add ing as much m o l a s s e s as 3-4 kg/100 kg b , h o w e v e r , t h e
s u g a r c o n t e n t i n t h e p r e s s f i l t r a t e may become so h i g h t h a t i t c a n n o t be
r e c y c l e d t o t he e x t r a c t o r ( p a r t i c u l a r l y i f t h e mo lasses i s added i n t h e second
p r e s s i n g , see b e l o w ) . One p o s s i b l e s o l u t i o n i s t o t h i c k e n t h e f i l t r a t e i n
a s p e c i a l e v a p o r a t o r and t o r e c y c l e i t t o t h e p r e s s e s ( r e f . 3 8 ) .
The improvements i n p r e s s d e s i g n , p u l p c o n d i t i o n i n g i n t h e e x t r a c t o r and
a p p l i c a t i o n o f p r e s s i n g a i d s can be combined w i t h d o u b l e - s t a g e p r e s s i n g . I t was
i n i t i a l l y t e s t e d w i t h o u t p r e s s i n g a i d s , g i v i n g a DS i n c r e a s e o f up t o 10% above
t h a t a t t a i n e d i n t h e f i r s t s t a g e . U s i n g p r e s s i n g a i d s , 35-40% DS i n t h e p u l p can
be a t t a i n e d , b u t an e c o n o m i c a l l y j u s t i f i e d l e v e l seems t o be somewhat l o w e r .
4 . 5 . 3 L o w - t e m p e r a t u r e d r y i n g
I t was men t ioned i n S e c t i o n 1.2.8 t h a t owing t o t h e p r o c e s s l a y o u t and
p a r a m e t e r s , t h e e n e r g y u t i l i z a t i o n i n c o n v e n t i o n a l the rma l d r y i n g i s p o o r .
Assuming t h a t h i g h - t e m p e r a t u r e gases s h o u l d be f e d t o t h e d r y e r , b u r n i n g o f f u e l
c a n n o t be a v o i d e d and o n l y a p a r t o f t h e e n e r g y demand can be s a t i s f i e d
u t i l i z i n g b o i l e r f l u e g a s e s . T h e r e f o r e , a p r o p o s a l has been made t o i n t r o d u c e
a d r y i n g p r o c e s s w i t h t h e i n i t i a l gas t e m p e r a t u r e low enough t o u t i l i z e was te
hea t f rom t h e s u g a r m a n u f a c t u r i n g p r o c e s s . C a l l e d l o w - t e m p e r a t u r e d r y i n g , t h i s
p r o c e s s has p r o v e d t e c h n o l o g i c a l l y f e a s i b l e i n a few a p p l i c a t i o n s . As t h e c o s t
o f t h e n e c e s s a r y equ ipment i s v e r y h i g h , h o w e v e r , i t c a n n o t be seen as t h e
u l t i m a t e e n e r g y - s a v i n g s o l u t i o n b u t r a t h e r as a n o t h e r new sys tem component t o be
u t i l i z e d i n e n e r g y - e f f i c i e n t f a c t o r i e s .
The s t reams o f was te h e a t t h a t can be c o n s i d e r e d f o r u t i l i z a t i o n a r e
a v a i l a b l e i n t h e f o l l o w i n g med ia :
- b a r o m e t r i c w a t e r ;
- vacuum pan v a p o u r ;
- condensa te (ammonia w a t e r ) ;
- s p e n t c a r b o n a t a t i o n g a s ;
- v a p o u r s f rom l ime s l a k i n g ;
- f l u e gas f rom b o i l e r s ;
- p o s s i b l y , s p e n t gas f rom h i g h - t e m p e r a t u r e p u l p d r y i n g .
H e a t i n g o f a i r has been e x t e n s i v e l y s t u d i e d i n a number o f p u b l i c a t i o n s ( r e f s .
5 1 - 5 4 ) . The a t t a i n a b l e t e m p e r a t u r e i s o f t h e o r d e r o f 50-70°C. The e x a c t v a l u e
s e l e c t e d , as w e l l as o t h e r p r o c e s s pa rame te rs - i n c l u d i n g a i r h u m i d i t y a t t h e
179
d r y e r o u t l e t - d e t e r m i n e t h e e n e r g y demand p e r 1 kg w a t e r removed f rom t h e p u l p ,
as a p p r o x i m a t e l y shown i n t h e d iag ram o f F i g . 4 . 2 0 . When compared t o h i g h -
t e m p e r a t u r e d r y i n g , s a y a t 500°C a i r t e m p e r a t u r e a t t h e d r y e r i n l e t , 40-80% more
e n e r g y p e r 1 kg w a t e r i s needed i n l o w - t e m p e r a t u r e d r y i n g ( a t a i r h u m i d i t y
chang ing f rom 50% t o 90%). I n o r d e r t o m i n i m i z e t h e s p e c i f i c e n e r g y demand, t h e
o u t l e t t e m p e r a t u r e s h o u l d be low and o u t l e t h u m i d i t y h i g h , t h i s i m p l y i n g t h a t i t
i s v e r y d i f f i c u l t t o d r y t h e p u l p t o a h i g h DS c o n t e n t . C o n s e q u e n t l y , l o w -
t e m p e r a t u r e d r y i n g i s most s u i t a b l e as a f i r s t s t a g e p r e c e d i n g h i g h - t e m p e r a t u r e
d r y i n g , where t h e f i n a l DS c o n t e n t can be a t t a i n e d . I t has been p r o v e d t h a t such
a s o l u t i o n can save more e n e r g y t han a p a r a l l e l c o m b i n a t i o n o f bo th t y p e s o f
d r y i n g ( r e f . 5 1 ) .
— — air temperature at d rye r inlet — a i r humidity at d rye r outlet
5500 Γ
20 AO 60 80
Air temperature at d ryer outlet {°C)
100 120
F i g . 4 . 2 0 . S p e c i f i c e n e r g y demand i n l o w - and med ium- tempera tu re d r y i n g as a f u n c t i o n o f p r o c e s s pa rame te rs ( a f t e r K . K r ö l l , T r o c k n u n g s t e c h n i k , 2nd e d n . , S p r i n g e r - V e r l a g , B e r l i n , 1978) .
A p o s s i b l e d e s i g n f o r a l o w - t e m p e r a t u r e d r y e r o f t h e t r a v e l l i n g - s c r e e n t y p e
i s shown s c h e m a t i c a l l y i n F i g . 4.21 ( t h e d r y e r c o n s i s t s o f m u l t i p l e c e l l s l i k e
t h e one shown i n c r o s s - s e c t i o n ) . I t i s c h a r a c t e r i z e d by a s p e c i f i c power demand
abou t 50 kWh p e r 1 t w a t e r removed , t h e a i r f a n s b e i n g r e s p o n s i b l e f o r most o f
i t and t h e c o n v e y o r and s c r e e n d r i v e s f o r t h e r e s t . The pa rame te rs o f a l o w -
t e m p e r a t u r e d r y e r o p e r a t e d i n a s u g a r f a c t o r y i n FRG a r e l i s t e d i n T a b l e 4 . 2 .
O t h e r d e s i g n s have been d e s c r i b e d i n t h e l i t e r a t u r e ( r e f s . 5 5 - 5 7 ) .
As t he i n t r o d u c t i o n o f l o w - t e m p e r a t u r e d r y i n g has a d i s a d v a n t a g e o u s e f f e c t on
180
A pulp in
4- A-A air out
i L
7 - - - r - - z - z - . - ^
\ / _ o u i pulp out
A i F i g . 4 .21 . Scheme o f a l o w - t e m p e r a t u r e d r y e r ( a f t e r r e f . 5 3 ) . 1 - a i r h e a t e r , 2 - a i r f a n , 3 - a i r d i s t r i b u t o r and s c r e e n .
TABLE 4.2
Paramete rs o f a l o w - t e m p e r a t u r e d r y e r ( a f t e r r e f . 5 1 ) .
VäTüe pe r 1 t w a t e r removed a t
e v a p o r a t i n g c a p a c i t y ( t / h ) Q u a n t i t y T o t a l v a l u e
25 30
Thermal c a p a c i t y (kW) ρ 34600 1384 1153 H e a t i n g s u r f a c e a r e a i n a i r h e a t e r s (m ) 43370 1735 1446 A i r f l o w ( t / h ) 2830 113 94 Power demand, i n c l u d i n g w a s t e - h e a t r e c o v e r y equ ipment (kW) ^ 1500 60 50 A v e r a g e a i r t e m p e r a t u r e a t h e a t e r o u t l e t ( C) 50 A v e r a g e p u l p r e t e n t i o n t ime (m in ) 25 D imens ions (m) ^ 36X16X19 T o t a l s c r e e n a r e a (m ) 600 T o t a l w e i g h t ( t ) 1600
t h e power b a l a n c e o f t h e f a c t o r y , a p r o p o s a l was made t o c r e a t e an a d d i t i o n a l
therma l c o n n e c t i o n between p u l p d r y i n g and s u g a r m a n u f a c t u r e , w i t h t h e aim o f
i n c r e a s i n g the steam demand o f t h e e v a p o r a t i o n s t a t i o n , w i t h o u t i n c r e a s i n g t h e
p r i m a r y - e n e r g y i n p u t t o t h e f a c t o r y . I n t h i s way , t h e steam f l o w t h r o u g h t h e
t u r b i n e can be i n c r e a s e d and a d d i t i o n a l power g e n e r a t e d . Assuming t h a t t h e
a d d i t i o n a l c o n n e c t i o n c o n s i s t s o f s u p p l y i n g t h i r d - e f f e c t v a p o u r t o an a i r
h e a t e r , an a i r t e m p e r a t u r e abou t 90°C can be a t t a i n e d ; t h i s s o l u t i o n i s known as
med ium- tempera tu re d r y i n g . As can be seen i n F i g . 4 . 2 0 , i t s s p e c i f i c e n e r g y
demand does n o t d i f f e r s i g n i f i c a n t l y f rom t h a t o f l o w - t e m p e r a t u r e d r y i n g . The
a i r f l o w and s c r e e n s u r f a c e i n t h e d r y e r can be c o s i d e r a b l y r e d u c e d , h o w e v e r ,
t h i s r e s u l t i n g i n reduced power demand and i n v e s t m e n t c o s t s . U s i n g medium-
181
t e m p e r a t u r e d r y i n g f o l l o w e d by c o n v e n t i o n a l d r y i n g w i t h b o i l e r f l u e g a s , t h e
t o t a l p u l p amount can be d r i e d u s i n g o n l y was te and l o w - t e m p e r a t u r e h e a t f rom
o t h e r f a c t o r y s e c t i o n s . A s u i t a b l e l a y o u t o f t h e e n e r g y sys tem i s shown
s c h e m a t i c a l l y i n F i g . 4.22 ( a f t e r r e f . 5 8 ) .
steam
fuel
9 0 Ϊ
3 r d - e f f e c t ^ I vapour
pressed pulp
flue gas 205°C dried pulp
F i g . 4 . 2 2 . E n e r g y sys tem l a y o u t f o r d o u b l e - s t a g e p u l p d r y i n g u s i n g was te and l o w - t e m p e r a t u r e h e a t f rom b o i l e r s and s u g a r m a n u f a c t u r e ( a f t e r r e f . 5 8 ) . 1 - b o i l e r , 2 - t u r b i n e , 3 - s u g a r m a n u f a c t u r i n g p r o c e s s , 4 - med ium- tempera tu re d r y e r , 5 - c o n v e n t i o n a l d r y e r .
4 . 5 . 4 Steam d r y i n g
I n t h e s e a r c h f o r a l t e r n a t i v e s t o c o n v e n t i o n a l t he rma l d e h y d r a t i o n , steam
d r y i n g has r e c e i v e d much a t t e n t i o n i n r e c e n t y e a r s . I n a d d i t i o n t o t h e o b v i o u s
p r o p e r t y o f making i t easy t o i n t e g r a t e t h e h e a t economy i n s u g a r m a n u f a c t u r e
and p u l p d r y i n g , t h i s method can a l s o improve t h e q u a l i t y o f t h e p u l p , as i t i s
d r i e d i n t h e absence o f a i r and t h u s w i t h o u t t h e r i s k o f o x i d a t i o n . Among f o u r
i n d u s t r i a l - s c a l e steam d r y e r s p r e s e n t l y i n o p e r a t i o n ( r e f s . 1 3 , 5 9 - 6 1 ) , t h e
Swed ish u n i t p r o d u c e s h i g h - q u a l i t y d r i e d p u l p w h i c h i s s u b s e q u e n t l y t r a n s f o r m e d
t o a f o o d a d d i t i v e ( r e f . 62) and t h e r e m a i n i n g ones seem t o be used m a i n l y f o r
t he pu rpose o f i m p r o v i n g e n e r g y economy.
The thermodynamic mechanism o f steam d r y i n g i s somewhat d i f f e r e n t f rom t h a t
o f c o n v e n t i o n a l d r y i n g . The d r i v i n g f o r c e o f t h e mass exchange between a p u l p
p a r t i c l e and t h e h e a t i n g a g e n t i s t h e d i f f e r e n c e between t h e steam t e m p e r a t u r e
and t he s a t u r a t i o n t e m p e r a t u r e a t t h e p r e s s u r e m a i n t a i n e d i n t h e d r y e r . As t h e
t e m p e r a t u r e o f t he p a r t i c l e e n t e r i n g t h e d r y e r i s l o w e r t han t h e steam
t e m p e r a t u r e , t he p a r t i c l e may i n i t i a l l y a b s o r b w a t e r by c o n d e n s a t i o n .
E v a p o r a t i o n b e g i n s a f t e r t h e s a t u r a t i o n t e m p e r a t u r e has been a t t a i n e d a t t h e
p a r t i c l e s u r f a c e , and t he s a t u r a t i o n zone i s g r a d u a l l y e x t e n d e d t o t h e c e n t r e o f
t he p a r t i c l e . O n l y i n t he l a y e r s f rom w h i c h w a t e r has been removed can t he
p a r t i c l e t e m p e r a t u r e d i f f e r s i g n i f i c a n t l y f rom t h e s a t u r a t i o n v a l u e , w h i c h i s
u n l i k e l y t o happen i n a w e l l d e s i g n e d d r y e r . I n t h i s way o v e r h e a t i n g o f t h e p u l p
182
0.5 1.0 1.5 2.0 Water content ( k g / k g DS)
2.5
F i g . 4 . 2 3 . Changes o f a v e r a g e p u l p t e m p e r a t u r e and w a t e r c o n t e n t d u r i n g steam
d r y i n g ( a f t e r r e f . 3 8 ) .
The steam t e m p e r a t u r e s r e p o r t e d a r e i n t h e range 132-189^0. The w o r k i n g
p r i n c i p l e s o f two d r y e r d e s i g n s a r e shown s c h e m a t i c a l l y i n F i g . 4 . 2 4 . I t seems
t h a t t h e s o l u t i o n s have y e t t o be o p t i m i z e d w i t h r e s p e c t t o t h e i r economic
f e a s i b i l i t y .
The d r y e r a p p l i e d i n a s u g a r f a c t o r y i n FRG i s o f t h e t r a v e l l i n g - s c r e e n t y p e
( F i g . 4 . 2 4 ( a ) , a f t e r r e f . 6 1 ) . The d i m e n s i o n s g i v e n a p p l y t o a u n i t r a t e d 20 t / h
e v a p o r a t e d w a t e r . The d r y e r c o n s i s t s o f n i n e c e l l s l i k e t h e one shown i n c r o s s -
s e c t i o n . The s a t u r a t i o n t e m p e r a t u r e o f t h e r e c i r c u l a t e d v a p o u r i s 132°C. Due t o
t h e p r e s e n c e o f c i r c u l a t i o n f a n s , i t s s p e c i f i c power demand i s s i m i l a r t o t h a t
o f a l o w - t e m p e r a t u r e d r y e r , t h a t i s , abou t 50 kWh/1 t w a t e r . As t h e d r y e r i s
(a) vapour
pulp in
40 m
pulp out
condensate vapour
F i g . 4 . 24 . w o r k i n g p r i n c i p l e s o f steam d r y e r s : ^7!^|5",^^;Π;α. ( b ) f l u i d i z e d b e d . 1 - h e a t e r , 2 - s c r e e n s , 3 - f a n , 4 t l u i a i z e o
can be a v o i d e d , w i t h a p o s i t i v e e f f e c t on t h e q u a l i t y o f t h e f i n a l p r o d u c t .
A d iag ram o f p u l p t e m p e r a t u r e changes d u r i n g steam d r y i n g i s shown i n F i g . 4 . 2 3 .
183
hea ted by e x h a u s t s team, i t s p r e s e n c e i n an e n e r g y sys tem f a c i l i t a t e s i n c r e a s e d
power g e n e r a t i o n . I f combined w i t h a l o w - t e m p e r a t u r e d r y e r used i n t h e i n i t i a l
p r o c e s s s t a g e , t h i s d e s i g n makes i t p o s s i b l e t o d r y t h e e n t i r e p u l p amount
w i t h o u t d i r e c t e x p e n d i t u r e o f p r i m a r y e n e r g y . A s u i t a b l e e n e r g y - s y s t e m l a y o u t i s
shown s c h e m a t i c a l l y i n F i g . 4 . 2 5 ( a ) .
( a ) Qir I
pressed pulp
flue gas
steam
fuel
(b)
waste heat
vapour
steam
fuel - Θ
vapour
steam ^ I ^ 1
pressed pulp dried pulp
U partly dried pulp
dried pulp
F i g . 4 .25 . E n e r g y sys tem l a y o u t s f o r s t e a m - d r y i n g o f t h e p u l p : ( a ) d o u b l e - s t a g e d r y i n g , steam d r y e r hea ted w i t h e x h a u s t steam ( a f t e r r e f . 3 8 ) , ( b ) steam d r y e r hea ted w i t h h i g h - p r e s s u r e steam ( a f t e r r e f s . 1 3 , 6 3 ) . 1 - b o i l e r , 2 - t u r b i n e , 3 - s u g a r m a n u f a c t u r i n g p r o c e s s , 4 - l o w - t e m p e r a t u r e d r y e r , 5 - steam d r y e r , 6 - w a s t e - h e a t r e c o v e r y s u b s y s t e m , 7 - v a p o u r w a s h e r .
A D a n i s h d e s i g n emp loy ing t h e c e l l u l a r f l u i d i z e d - b e d t e c h n i q u e i s shown i n
F i g . 4 . 2 4 ( b ) ( a f t e r r e f s . 1 3 , 6 3 ) . The f l u i d i z e d bed c o n s i s t s o f m u l t i p l e c e l l s
a r r a n g e d i n a c i r c l e s u r r o u n d i n g t h e t u b u l a r h e a t e r s i t u a t e d i n t h e c e n t r e o f
a v e r t i c a l v e s s e l . I n a p r o t o t y p e a p p l i c a t i o n , t h e d r y e r i s r a t e d 6 t / h
e v a p o r a t e d w a t e r . I t i s hea ted by steam a t 12 ba r and 220°C f rom a b o i l e r w h i c h
happens t o be a v a i l a b l e i n t h e f a c t o r y i n q u e s t i o n ; t h i s steam does n o t
184
c o n t r i b u t e t o power g e n e r a t i o n . The v a p o u r p r e s s u r e i s m a i n t a i n e d a t 3.5 ba r and
t he t e m p e r a t u r e i s 162°C above t he f l u i d i z e d bed and 189°C a t t h e h e a t e r o u t l e t .
The r e c i r c u l a t e d v a p o u r f l o w i s 35-40 t imes l a r g e r t han t h e w a t e r e v a p o r a t i o n .
As v a p o u r e n e r g y i s d i r e c t e d t o t h e e v a p o r a t o r s t a t i o n , t he hea t consumpt i on i n
s u g a r manu fac tu re can be r e d u c e d . A p o s s i b l e e n e r g y - s y s t e m l a y o u t i s shown
s c h e m a t i c a l l y i n F i g . 4 . 2 5 ( b ) .
C o n s i d e r a b l e hea t s a v i n g s can be imag ined i n s u g a r f a c t o r i e s emp loy ing s team-
d r y i n g o f t h e p u l p and v a p o u r c o m p r e s s i o n . F o r examp le , i t i s p r o p o s e d t o
s u p e r h e a t v a p o u r w i t h d r a w n f rom the second e v a p o r a t o r e f f e c t and s u b s e q u e n t l y
compressed , and t o d e l i v e r i t t o a steam d r y e r ( r e f . 6 4 ) . T h i s w o u l d make i t
p o s s i b l e t o i n t e g r a t e e n e r g y economy i n s u g a r manu fac tu re and p u l p d r y i n g i n
v a r i o u s t y p e s o f e n e r g y s y s t e m s , i n c l u d i n g t h o s e emp loy ing gas t u r b i n e s .
REFERENCES
1 L. R o s e n b e r g , T e c h n o l o g i c a l changes i n some o f E u r o p e ' s s u g a r p r o d u c i n g c o u n t r i e s . S u g a r . J . , 4 6 ( 5 ) (1983) 7-11.
2 E. R e i n e f e l d , Uber d i e Kampagne 1985, Z u c k e r i n d . , 111(4) (1986) 303-313. 3 E.W. K r a u s e , New equ ipment and p r o c e s s e s i n t h e s u g a r i n d u s t r y , i n : F . O .
L i c h t Yearbook and D i r e c t o r y , R a t z e b u r g , 1985, p p . E5 -E36 . 4 H. S c h i w e c k , T h . C r o n e w i t z and G . W i t t e , Some t h o u g h t s on t he c l a s s i c a l
method o f j u i c e p u r i f i c a t i o n . Sugar J . , 47(11) (1985) 18-22. 5 A . I . Khomenko, 0 t e p l o v o i e k o n o m i c h n o s t i s i s t e m d i f f u z i y a - d e f e k a t s i y a ,
Sakh . P r o m . , (11 ) (1983) 42-47 . 6 G . W i t t e and H. S c h i w e c k , D i e Ausnu t zung des Wärme inha l t es von C a r b o n a t a -
t i o n s b r ü d e n , Z u c k e r i n d . , 109(8) (1984) 706-710. 7 Anonymous, R e c u p e r a t i o n t h e r m i q u e s u r buees de seconde c a r b o n a t a t i o n a l a
R a f f i n e r i e Notre-Dame a O r e y e , S u c r . B e i g e , 103 (1985) 5-11. 8 T e c h n i c a l i n f o r m a t i o n f rom F i v e s - C a i l Babcock , L i l l e , 1986. 9 W. Lekawski and K. U r b a n i e c , E n e r g y s a v i n g t h r o u g h m o d i f i c a t i o n o f t h e
c a r b o n a t a t i o n p r o c e s s , Z u c k e r i n d . , 110(9) (1985) 810-813. 10 Τ . B o g u m i l , E x p e r i m e n t a l i n v e s t i g a t i o n s o f t h e c a r b o n a t a t i o n p r o c e s s a t
i n c r e a s e d p r e s s u r e , Z u c k e r i n d . , 111(6) (1986) 565-568. 11 Κ. U r b a n i e c , Heat economy improvements a s s o c i a t e d w i t h t h e c a r b o n a t a t i o n
p r o c e s s i n b e e t s u g a r p l a n t s . Paper p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e " Improvement o f t h e Bee t Sugar P r o d u c t i o n " , Warszawa, May 1987.
12 R . F . Madsen, V e r s c h i e d e n e Z u c k e r h a u s k o n z e p t e und i h r E i n f l u s s a u f den E n e r g i e v e r b r a u c h , Z u c k e r i n d . , 111(12) (1986) 1121-1126.
13 R . F . Madsen, P r o g r e s s i n Dan i sh s u g a r p r o d u c t i o n w i t h i n t h e p a s t d e c a d e , Paper p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e " Improvement o f t h e B e e t Sugar P r o d u c t i o n " , Warszawa, May 1987.
14 K. Wagne rowsk i , D. Dabrowska and C . D a b r o w s k i , Prob leme d e r M e l a s s e r s c h ö p f u n g , Ζ . Z u c k e r i n d . , 12(9) (1962) 664-671.
15 Η. S c h i w e c k , M ö g l i c h k e i t e n z u r Senkung des E n e r g i e b e d a r f s im Z u c k e r h a u s , Z u c k e r , 30(10) (1977) 525-534.
16 K . E . Aus tmeyer and R. Marwede, E n t w u r f und B i l a n z i e r u n g w e i t e r f ü h r e n d e r Z u c k e r h a u s k o n z e p t e , Z u c k e r i n d . , 112(3) (1987) 193-201.
17 S. M a t u s c h , P r a k t i s c h e E r f a h r u n g e n m i t den K ü h l u n g s k r i s t a l 1 i s a t o r KKT, Z u c k e r i n d . , 112(4) (1987) 274-276.
18 H. E i c h h o r n , A r b e i t s w e i s e m i t k o n t i n u i e r l i c h e n Vakuum-Ma ischen , System B e g h i n - S a y , i n d e r R a f f i n e r i e E l s d o r f , Z u c k e r i n d . , 112(2) 114-117.
19 D. S c h l i e p h a k e , K . E . Aus tmeyer and R. Hempelmann, K ü h l u n g s k r i s t a l l i s a t i o n von Magmen h ö h e r e r R e i n h e i t , Z u c k e r i n d . , 110(4) (1987) 269-273.
20 A . R . S a p r o n o v , V . l . T u z h i l k i n and A . P . S h c h e r e n k o , Sovremennye n a p r a v l e n i y a ν u l u c h s h e n i i k r i s t a l l i z a t s i i s a k h a r a , Sakh . P r o m . , ( 5 ) (1985) 42-44 .
185
21 Ε. R e i n e f e l d , Über d i e Kampagne 1979, Z u c k e r i n d . , 105(4) (1980) 329-340. 22 E. R e i n e f e l d , Über d i e Kampagne 1981, Z u c k e r i n d . , 107(5) (1982) 369-380. 23 K . E . A u s t m e y e r , A n a l y s i s o f s u g a r b o i l i n g and i t s t e c h n i c a l c o n s e q u e n c e s .
I n t . Sugar J . , 88 ( 1 9 8 6 ) , P a r t I (1045) 3 - 7 , P a r t I I (1046) 23-29 , P a r t I I I (1047) 50-55.
24 H. Sch iweck and M. M u n i r , Das H e r s t e l l e n e i n e s gemeinsames K r i s t a l l f u s s magmas f ü r W e i s s z u c k e r - 1 und -2 nach dem V e r f a h r e n d e r Süddeu tschen Z u c k e r - A G , Paper p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e " Improvement o f t he Bee t Sugar P r o d u c t i o n " , Warszawa, May 1987.
25 R . F . Madsen and W. Ko fod N i e l s e n , D ie Kampagne 1977 i n d e r " A / S De Danske S u k k e r f a b r i k k e r " , Z u c k e r i n d . , 103(10) (1978) 831-839.
26 Anonymous, E rzeugung von R ü b e n r o h s a f t d u r c h m e h r s t u f i g e G e g e n s t r o m -Auswaschung von z e r k l e i n e r t e m Rübenmate r i a l be i n i e d r i g e n T e m p e r a t u r e n , Z u c k e r i n d . , 110(8) (1985) 709-710.
27 J . M . R a n d a l l , R . H . Edwards and E. Z a r a g o s a , E x p r e s s i o n o f j u i c e f rom s u g a r bee t t i s s u e . Paper p r e s e n t e d a t 23rd ASSBT M e e t i n g , San D i e g o , F e b r u a r y 1985.
28 T . B a l o h , Reversosmose i n d e r T e c h n o l o g i e des Z u c k e r s , Ζ . Z u c k e r i n d . , 25 (8 ) (1975) 452-456.
29 S . E . B i c h s e i and A . M . S a n d r e , A p p l i c a t i o n o f membrane t e c h n o l o g y t o j u i c e c o n c e n t r a t i o n . I n t . Sugar J . , 84(1005) (1982) 266-268.
30 W. Ko fod N i e l s e n , S . K r i s t e n s e n and R . F . Madsen, P r o s p e c t s and p o s s i b i l i t i e s i n a p p l i c a t i o n o f membrane f i l t r a t i o n sys tems w i t h i n t h e b e e t and cane s u g a r i n d u s t r y . Sugar T e c h . R e v . , 9 ( 1 ) (1982) 59-117.
31 T . R . Hanssens ( e t a l . ) . U l t r a f i l t r a t i o n as an a l t e r n a t i v e f o r raw j u i c e p u r i f i c a t i o n i n t h e b e e t s u g a r i n d u s t r y , Z u c k e r i n d . , 109(2) (1084) 152-156.
32 W. Cape l i n . Bee t j u i c e c o n c e n t r a t i o n by r e v e r s e o s m o s i s . I n t . Sugar J . , 84(1007) (1982) 323-324.
33 P . J . Wrobel and J . A . H e i s t , Sugar c r y s t a l l i z a t i o n f rom b e e t j u i c e s and mo lasses u s i n g t h e h y d r a t e f r e e z i n g p r o c e s s . I n t . Sugar J . , 89(1062) (1987) 111-117.
34 S . E . B i c h s e l , M. C l e a r y and T . S . B a r r o n , Steam consumpt ion r e d u c t i o n by e u t e c t i c f r e e z e c r y s t a l l i z a t i o n o f s u c r o s e . Paper p r e s e n t e d a t 23rd ASSBT M e e t i n g , San D i e g o , F e b r u a r y 1985.
35 K. B u c h h o l z ( e t a l . ) , U n t e r s u c h u n g e n z u r B i l d u n g von B i o g a s aus R ü b e n p r e s s -s c h n i t z e l n , Z u c k e r i n d . , 11(9) (1986) 837-845.
36 E. T h i e r , K o n s e r v i e r u n g s t e c h n i s c h e und w i r t s c h a f t l i c h e A s p e k t e des P r e s s s c h n i t z e l a b s a t z e s , Z u c k e r i n d . , 106(1) (1981) 60-65.
37 J . B e c k h o f f and C . H e l l e r , P r e s s s c h n i t z e l - e i n e A l t e r n a t i v e z u r S c h n i t z e l t r o c k n u n g , Z u c k e r i n d . , 108(3) (1983) 213-217.
38 M. Kunz and P. V a l e n t i n , S c h n i t z e l t r o c k n u n g ohne P r i m ä r e n e r g i e e i n s a t z u n t e r a u s s c h l i e s s l i c h e r Nu tzung de r Abwärme- und E i n d a m p f P o t e n t i a l e d e r Z u c k e r f a b r i k , Z u c k e r i n d . , 111(8) (1986) 741-750.
39 T h . C r o n e w i t z ( e t a l . ) . Über den E i n f l u s s v e r s c h i e d e n e r G r ö s s e n a u f den E n e r g i e b e d a r f und S t a u b e m i s s i o n von S c h n i t z e l t r o c k n u n g s a n l a g e n u n t e r B e r ü c k s i c h t i g u n g des V e r w e i l Z e i t v e r h a l t e n s d e r S c h n i t z e l während d e r T r o c k n u n g , Z u c k e r , 28 (8 ) (1975) 401-410.
40 H. H u b e r , Bestimmung des o p t i m a l e n E n e r g i e v e r b r a u c h s f ü r d i e E n t w ä s s e r u n g d e r e x t r a h i e r t e n S c h n i t z e l , Z u c k e r , 30 (9 ) (1977) 485-489.
41 T h . C r o n e w i t z , Wege z u r r a t i o n e l l e n E n e r g i e v e r w e n d u n g be i d e r S c h n i t z e l -t r o c k n u n g i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 105(2) (1980) 129-139.
42 M. Demaux, P r e s s a g e e t sechage des p u l p e s de b e t t e r a v e s . F a c t e u r s de r e d u c t i o n des c o u t s . I n d . A l i m . A g r i e , 102 (7 -8 ) (1985) 723-730.
43 Μ. Demaux, C o u t de l ' e n e r g i e e t p r e s s a g e des p u l p e s de b e t t e r a v e s , I n d . A l i m . A g r i e , 103(7 -8 ) (1986) 661-667.
44 O p t i m i e r u n g d e r mechan ischen S c h n i t z e l a b p r e s s u n g , Z u c k e r i n d . , 106(11) (1981) 965-981.
45 Symposium: " S c h n i t z e l a b p r e s s u n g - S tand 1987" , Z u c k e r i n d . , 112(7) (1987) 571-579.
46 F. Hol l a u s and G . P o l l a c h , V e r b e s s e r u n g d e r S c h n i t z e l a b p r e s s u n g d u r c h g e s t e u e r t e I n f e k t i o n , Z u c k e r i n d . , 111(11) (1986) 1025-1030.
186
47 P. C a u l k i n s , G . Holman and L . Norman, Gypsum - c o s t - e f f e c t i v e p r e s s i n g a i d . Sugar J . , 47 (12) (1985) 21-23.
48 J . M . R a n d a l l , W. Camirand and E . M . Z a r a g o s a , E n e r g y r e d u c t i o n by c o s s e t t e l i m i n g , Z u c k e r i n d . , 107(1) (1982) 38-46.
49 Κ. B u c h h o l z , R. T a r r a c h and K . - M . B l i e s e n e r , Chemische A s p e k t e d e r mechan ischen S c h n i t z e l e n t w ä s s e r u n g , Z u c k e r i n d . , 111(1) (1986) 23-27 .
50 E . R e i n e f e l d , Über d i e Kampagne 1980, Z u c k e r i n d . , 106(5) (1981) 397-406. 51 D. S c h r ö d e r , E i n i g e Gedanken zum E i n s a t z e i n e r N i e d e r t e m p e r a t u r t r o c k n u n g
i n n e r h a l b d e r S c h n i t z e l t r o c k n u n g , Z u c k e r i n d . , 108(2) (1983) 126-135. 52 P. V a l e n t i n , E r h ö h t e Abwärmenutzung d e r Z u c k e r f a b r i k i n d e r N i e d e r
t e m p e r a t u r t r o c k n u n g , Z u c k e r i n d . , 108(11) (1983) 1025-1033. 53 K . E . Aus tmeyer and W. P o e r s c h , N i e d e r t e m p e r a t u r t r o c k n u n g - G r u n d l a g e n und
B e t r a c h t u n g e n z u r W i r t s c h a f t l i c h k e i t , Z u c k e r i n d . , 108(9) (1983) 861-868, 108(11) (1983) 1033-1041, 109(5) (1984) 411-419, 110(1) (1985) 28-34.
54 H. K l e b e r , Anwärmung von L u f t f ü r d i e N i e d e r t e m p e r a t u r - T r o c k n u n g , Z u c k e r i n d . , 110(8) (1985) 686-688.
55 W. K u n z , D ie N i e d e r t e m p e r a t u r t r o c k n u n g i n V e r b i n d u n g m i t d e r t r a d i t i o n e l l e n S c h n i t z e l t r o c k n u n g , Z u c k e r i n d . , 108(9) (1983) 868-870.
56 Anonymous, N i e d e r t e m p e r a t u r - S c h n i t z e l t r o c k n u n g i n d e r Z u c k e r f a b r i k A r t e n a y , Z u c k e r i n d . , 108(2) (1983) 135.
57 E . S c h r ö t e r , D i e N i e d e r t e m p e r a t u r t r o c k n u n g i n L e h r t e - F u n k t i o n s w e i s e und B e t r i e b s e r f a h r u n g e n , Z u c k e r i n d . , 111(6) (1986) 545-549.
58 K . E . Aus tmeyer and U . B u n e r t , Abwärmenutzung im Zusammenhang m i t d e r S c h n i t z e l t r o c k n u n g , 110(8) (1985) 659-670.
59 Anonymous, P i l o t a n l a g e f ü r S c h n i t z e l t r o c k n u n g m i t t e l s Dampf, Z u c k e r i n d . , 110(1) (1985) 54.
60 Anonymous, Dampf t rockne r f ü r S c h n i t z e l , Z u c k e r i n d . , 110(8) (1985) 707-708. 61 Anonymous, S team-hea ted p u l p d r y e r , i n : F . O . L i c h t Yearbook and D i r e c t o r y ,
R a t z e b u r g , 1986, p p . G5-G9 . 62 C . Gudmundson, p e r s o n a l commun ica t i on . 63 A . S l o t h J e n s e n ( e t a l . ) . Bee t p u l p d r y i n g i n s u p e r h e a t e d steam under
p r e s s u r e , Z u c k e r i n d . , 112(10) (1987) 886-891. 64 Ε . O t o r o w s k i , P u l p d r y i n g . Paper p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e
" Improvement o f t he Bee t Sugar P r o d u c t i o n " , Warszawa, May 1987.
187
C h a p t e r 5
EQUIPMENT DESIGN FOR E F F I C I E N T ENERGY U T I L I Z A T I O N
5.1 SCOPE OF THE PROBLEMS
The deve lopments o f e n e r g y - s a v i n g p r o c e s s e s and equ ipment a r e m u t u a l l y
d e p e n d e n t . W h i l e t h e p r o c e s s r e q u i r e m e n t s i n f l u e n c e equ ipment d e s i g n , i t i s t h e
a t t a i n a b l e equ ipment c h a r a c t e r i s t i c s w h i c h a r e o f t e n d e c i s i v e i n c o n s t r a i n i n g
t h e pa rame te rs o f a p r o c e s s . T h i s a p p l i e s t o l a r g e s e c t i o n s o f t h e s u g a r
m a n u f a c t u r i n g p r o c e s s i n w h i c h i n t e r a c t i o n s between numerous i n t e r c o n n e c t e d
equ ipment u n i t s a r e t a k i n g p l a c e ( j u i c e p u r i f i c a t i o n , s u g a r c r y s t a l l i z a t i o n ,
e t c . ) , as w e l l as t o u n i t o p e r a t i o n s p e r f o r m e d i n s p e c i a l i z e d equ ipment
( e x t r a c t i o n , h e a t i n g , e t c . ) .
By i n t r o d u c i n g s e l e c t i v e d e s i g n changes o r a p p l y i n g e n t i r e l y new equ ipment
d e s i g n s , i t becomes p o s s i b l e t o c u t down t h e power demand and t h e t o t a l h e a t
demand o f a s u g a r f a c t o r y . I n a d d i t i o n , improved c h a r a c t e r i s t i c s o f t h e
equ ipment u n i t s o f w h i c h a the rma l sys tem i s composed may c o n t r i b u t e t o an
improved e f f e c t i v e n e s s r a t i o and t h u s r e d u c e d n e t h e a t demand. C o n s i d e r a b l e
p r o g r e s s has been a c h i e v e d i n t h e s e a r e a s i n r e c e n t y e a r s . I n t h e p r e s e n t
C h a p t e r , d e s i g n t r e n d s a r e r e v i e w e d r e l a t i n g t o t h e f o l l o w i n g e q u i p m e n t :
- e x t r a c t o r s ,
- e v a p o r a t o r s ,
- h e a t e x c h a n g e r s ,
- vacuum p a n s ,
- c e n t r i f u g a l s .
5.2 EXTRACTORS
The e s s e n t i a l f u n c t i o n o f an e x t r a c t o r can be d e s c r i b e d as c o u n t e r - c u r r e n t
l e a c h i n g o f c o s s e t t e s . I n i t i a l the rma l breakdown o r d e n a t u r a t i o n o f c e l l
membranes i s r e q u i r e d t o make s u c r o s e e x t r a c t i o n p o s s i b l e . D e n a t u r a t i o n b e g i n s
a t 50-60°C and becomes a lmos t i n s t a n t a n e o u s a t t e m p e r a t u r e s above 90°C. F o r t h i s
r e a s o n , i t i s n e c e s s a r y t o s u p p l y hea t t o t h e e x t r a c t o r , w h i c h i s t h u s a l s o
a component o f t h e the rma l s y s t e m .
As t h e d r i v i n g f o r c e o f s u c r o s e e x t r a c t i o n i s t h e d i f f e r e n c e o f c o n c e n t r a t i o n
between t h e c o s s e t t e s and t h e e x t r a c t i n g j u i c e , t h e c o n c e n t r a t i o n o f t h e j u i c e
can n e v e r exceed t h a t i n t h e e x t r a c t e d m a t e r i a l . T a k i n g i n t o a c c o u n t t h a t t h e
c o s s e t t e s c o n t a i n abou t 95% c e l l j u i c e , t h e j u i c e d r a f t can n e v e r be l o w e r t han
95%; t o a t t a i n t h i s t h e o r e t i c a l l i m i t , an i d e a l e x t r a c t o r o f i n f i n i t e l e n g t h
wou ld be r e q u i r e d . I n r e a l i t y , i n o r d e r t o i n c r e a s e t h e d r i v i n g f o r c e and
reduce equ ipment s i z e , e x c e s s w a t e r i s f e d t o t h e e x t r a c t o r , t h i s c a u s i n g
188
i n c r e a s e d j u i c e d r a f t . The p r a c t i c a l r ange o f j u i c e d r a f t s i s 105-140%.
From t h e t r e n d t owa rd e n e r g y s a v i n g , two b a s i c r e q u i r e m e n t s t o w h i c h
e x t r a c t o r d e s i g n e r s must r e s p o n d f o l l o w :
- p r o d u c t i o n o f c o l d raw j u i c e , w h i c h a l l o w s t h e r e c o v e r y o f l o w - t e m p e r a t u r e
hea t w h i c h wou ld o t h e r w i s e be w a s t e d ;
- t h e p o s s i b i l i t y o f o p e r a t i n g t h e e x t r a c t o r a t low j u i c e d r a f t , w h i c h r e s u l t s
i n a r e d u c t i o n o f t he amount o f w a t e r t o be e v a p o r a t e d .
U s i n g a c l a s s i f i c a t i o n w i t h r e s p e c t t o t h e way t h e c o s s e t t e s a re t r a n s p o r t e d
w i t h i n t h e e x t r a c t o r , f o u r d e s i g n s a r e t h e most w i d e l y used t o d a y : t o w e r t y p e ,
s c r o l l ( o r t r o u g h ) t y p e , moving bed ( o r b e l t ) t y p e and drum t y p e . T h e i r w o r k i n g
p r i n c i p l e s a r e shown s c h e m a t i c a l l y i n F i g . 5 .1 . As can be s e e n , t he p r o d u c t i o n
o f c o l d raw j u i c e has been c h a r a c t e r i s t i c o f t he t r o u g h - t y p e (DOS) e x t r a c t o r
o n l y . I n t h i s d e s i g n , hea t i s t r a n s f e r r e d t o t h e e x t r a c t i o n m i x t u r e f rom v a p o u r
c o n d e n s i n g i n h e a t i n g j a c k e t s a t t a c h e d t o t he t r o u g h . I t seems t h a t a t l a r g e
c a p a c i t i e s , h o w e v e r , t he h e a t i n g j a c k e t s a r e n o t e f f e c t i v e enough t o e n s u r e
a c o r r e c t t e m p e r a t u r e d i s t r i b u t i o n i n t h e e x t r a c t i o n m i x t u r e , so 3000 t / d i s t h e
p r a c t i c a l l i m i t o f t he c a p a c i t y o f t r o u g h - t y p e e x t r a c t o r s t o d a y .
T h e r e i s no c o n s t r a i n t o f t h i s k i n d r e l a t i n g t o t h e o t h e r e x t r a c t o r t y p e s .
(a)
Μ
h 5 (b) Μ
( Μ e
\-
7 ^ Γ 6
F i g . 5 .1 . Work ing p r i n c i p l e s o f e x t r a c t o r s : ( a ) t o w e r , ( b ) moving b e d , ( c ) t r o u g h , ( d ) drum. Μ - h e a t e x c h a n g e r c o s s e t t e s - j u i c e ( m i x e r ) , Η - j u i c e h e a t e r . 1 - c o s s e t t e s , 2 - f r e s h w a t e r , 3 - p r e s s w a t e r , 4 - raw j u i c e , 5 -e x h a u s t e d c o s s e t t e s , 6 - s team, 7 - r e c i r c u l a t e d j u i c e , 8 - e x t r a c t i o n m i x t u r e .
189
because h e a t i s s u p p l i e d v i a s e p a r a t e hea t e x c h a n g e r s t o t h e j u i c e r e c i r c u l a t e d
a t t he r a t e o f up t o 300%. O r i g i n a l l y i n v e n t e d t o d e l i v e r h o t raw j u i c e , t h e s e
d e s i g n s must be m o d i f i e d by add ing a h e a t e x c h a n g e r ( m i x e r ) i n w h i c h j u i c e i s
c o o l e d , i n c o u n t e r - f l o w , by incoming c o s s e t t e s . The m i x e r can be i n s t a l l e d as a
s e p a r a t e u n i t , b u t i n new d r u m - t y p e d e s i g n s , i t can a l s o be s t r u c t u r a l l y
i n t e g r a t e d w i t h t h e e x t r a c t o r p r o p e r . The a d d i t i o n o f a m i x e r r e s u l t s i n
i n c r e a s e d i n v e s t m e n t c o s t s , w h i c h can a p p a r e n t l y be o f f - s e t by c o s t r e d u c t i o n s
a s s o c i a t e d w i t h e n e r g y s a v i n g s .
The a p p l i c a t i o n o f m i x e r s i n new e x t r a c t i o n s t a t i o n s can be c o n s i d e r e d as
s t a n d a r d p r a c t i c e nowadays , and m i x e r s a r e a l s o added t o t h e e x i s t i n g e x t r a c t o r s
( r e f . 1 ) . One case has been r e p o r t e d o f a t r o u g h - t y p e a p p a r a t u s ( f o r m e r l y used
as an e x t r a c t o r ) a p p l i e d as a m i x e r l i n k e d t o a d r u m - t y p e e x t r a c t o r ( r e f . 2 ) .
The a t t a i n a b l e j u i c e t e m p e r a t u r e i s u s u a l l y 11-15 Κ above t h e c o s s e t t e s
t e m p e r a t u r e . Depend ing on t h e e x t r a c t o r t y p e and l o c a l c o n d i t i o n s , steam s a v i n g s
o f t he o r d e r o f 0.5 kg/100 kg b have been r e p o r t e d ( r e f . 3 ) ; t h i s f i g u r e s h o u l d
be t r e a t e d c a u t i o u s l y , as i t depends on t h e accompany ing c o r r e c t i o n s o f t h e
therma l sys tem as w e l l . As p o i n t e d o u t by G e n i e ( r e f . 4 ) , h o w e v e r , i t makes
l i t t l e sense t o i n v e s t t o o much i n a m i x e r subsys tem because t h e the rma l r e t u r n s
d i m i n i s h i f a c e r t a i n m i x e r s i z e i s exceeded a n d , i n a d d i t i o n , s u c r o s e l o s s e s
i n c r e a s e as a r e s u l t o f i n c r e a s e d b a c t e r i a l a c t i v i t y on a c c o u n t o f low
t e m p e r a t u r e s and l ong r e t e n t i o n t i m e s .
Lower i ng o f t h e j u i c e d r a f t has a l r e a d y been d i s c u s s e d i n S e c t i o n 1 .3 .4 .
Be ing a l w a y s a p remise f o r r e d u c e d e n e r g y c o n s u m p t i o n , i t becomes a lmos t a
n e c e s s i t y i n modern s u g a r f a c t o r i e s i n w h i c h hea t consumpt ion has been d e c r e a s e d
t o a c e r t a i n l e v e l . The a s s o c i a t e d d e c r e a s e i n t h e demand f o r h e a t i n g v a p o u r s
may l e a d t o t he i m p o s s i b i l i t y o f f u l l u t i l i z a t i o n o f v a p o u r s f rom t h e
e v a p o r a t i o n p r o c e s s , u n l e s s v a p o u r c o m p r e s s i o n i s a p p l i e d . L o w e r i n g o f t h e j u i c e
d r a f t wou ld be much more c o n v e n i e n t , b u t i t r a i s e s e x t r a c t o r d e s i g n p rob lems
wh i ch s t i l l remain t o be s o l v e d . A b e t t e r u n d e r s t a n d i n g o f t h e d e s i g n
r e q u i r e m e n t s has been a c h i e v e d i n r e c e n t y e a r s , owing t o advances i n t h e t h e o r y
o f t h e e x t r a c t i o n p r o c e s s ( r e f s . 5 - 8 ) .
Each e x t r a c t o r can be c h a r a c t e r i z e d by a number o f mass t r a n s f e r u n i t s , w h i c h
can be d e f i n e d as t h e number o f s t e p s i n a p e r f e c t b a t c h e x t r a c t o r t h a t w o u l d be
r e q u i r e d t o p r o d u c e t he same j u i c e f rom t h e same c o s s e t t e s w i t h t h e same l o s s o f
s u g a r i n e x h a u s t e d c o s s e t t e s ( f o r ma themat i ca l f o r m u l a e , see r e f . 6 ) . P r a c t i c a l
v a l u e s range f rom 8 t o 16; t h e h i g h e r t h e f i g u r e t h e b e t t e r i s t h e e x t r a c t o r ,
and t h e l o w e r t h e j u i c e d r a f t t h a t can be m a i n t a i n e d a t a g i v e n s u g a r l o s s . F o r
t he d r u m - t y p e d e s i g n , t he r e q u i r e m e n t s have been summar ized by G e n i e ( r e f . 4 ) i n
a g raph ( F i g . 5 . 2 ) . As can be s e e n , a r e d u c t i o n i n j u i c e d r a f t r e q u i r e s a
s t r u c t u r a l change i n e x t r a c t o r d e s i g n ; i . e . , an i n c r e a s e d number o f t r a n s f e r
190
101 evaporated water less per 100 kg beets
I L 10 15
No. of t ransfer units
20
F i g . 5 . 2 . R e d u c t i o n o f j u i c e d r a f t v s . number o f t r a n s f e r u n i t s o f e x t r a c t o r f o r 0.2% s u c r o s e l o s s on b e e t s and 18% DS i n p r e s s e d p u l p ( a f t e r r e f . 4 ) .
u n i t s . S i m i l a r r e l a t i o n s h i p s e x i s t f o r o t h e r e x t r a c t o r t y p e s , t h i s s t i m u l a t i n g
a l s o numerous m o d e r n i z a t i o n s o f e x i s t i n g u n i t s . When i n c r e a s i n g t h e h e i g h t o f
a t o w e r o r t h e l e n g t h o f a t r o u g h , o t h e r improvements a r e i n t r o d u c e d as w e l l ,
p a r t i c u l a r l y e a s i l y c o n t r o l l e d d r i v e s , improved m i x i n g / t r a n s p o r t i n g e l e m e n t s ,
more e f f e c t i v e h e a t - s u p p l y s u b s y s t e m s , e t c . ( r e f s . 1 , 9 - 1 1 ) .
5.3 EVAPORATORS
5.3.1 C o n v e n t i o n a l a p p l i c a t i o n s
I t was p o i n t e d o u t i n S e c t i o n 3 .3 .2 t h a t a h i g h h e a t t r a n s f e r i n t e n s i t y
s h o u l d be r e g a r d e d as an i m p o r t a n t f e a t u r e o f t h e e v a p o r a t o r s . A t low e n e r g y
c o s t , i n t e n s i v e hea t t r a n s f e r has been t r e a t e d as a means t o r e d u c e h e a t i n g
s u r f a c e a r e a s and t h u s i n v e s t m e n t c o s t s . The t r e n d t o w a r d s e n e r g y s a v i n g s
i n i t i a t e d changes i n t h e a t t i t u d e o f d e s i g n e r s . I n a m u l t i p l e - e f f e c t e v a p o r a t o r
s t a t i o n , a h i g h p r i o r i t y i s g i v e n nowadays t o m a i n t a i n i n g v a p o u r t e m p e r a t u r e s
f a c i l i t a t i n g u t i l i z a t i o n o f l o w - g r a d e h e a t f rom t h e f i n a l e f f e c t s . As a
c o n s e q u e n c e , t e m p e r a t u r e d i f f e r e n c e s between v a p o u r s i n c o n s e c u t i v e e f f e c t s may
be s m a l l e r t han t h o s e recommended i n t h e p a s t , even a t t h e expense o f l a r g e r
h e a t i n g s u r f a c e a r e a s .
The t r a d e - o f f between h e a t i n g s u r f a c e a r e a and t e m p e r a t u r e d i f f e r e n c e has
been s t u d i e d by numerous a u t h o r s ( r e f s . 1 2 - 1 5 ) . A l t h o u g h no u n i v e r s a l d e s i g n
p r e s c r i p t i o n s have been f o r m u l a t e d , t h i s work n e v e r t h e l e s s c o n t r i b u t e s t o b e t t e r
u n d e r s t a n d i n g o f t h e r e l a t i o n s h i p s i n v o l v e d . L e t us c o n s i d e r an a p p r o x i m a t e
f o r m u l a g i v e n by Ba loh ( r e f . 15) f o r t h e op t ima l t e m p e r a t u r e d i f f e r e n c e Δ Τ ^ ^ ^ i n
an e v a p o r a t o r e f f e c t i n w h i c h t h e j u i c e t e m p e r a t u r e ( a b s o l u t e v a l u e ) i s Τ
( 5 . 1 )
where c , i s t h e annual c o s t o f 1 m h e a t i n g s u r f a c e a r e a , c i s t h e e n e r g y c o s t , a β
T ^ i s t he e n v i r o n m e n t t e m p e r a t u r e , k i s t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t ,
and τ i s t h e d u r a t i o n o f t he o p e r a t i n g s e a s o n .
191
As can be s e e n , t h e t e m p e r a t u r e d i f f e r e n c e i n an e v a p o r a t o r body s h o u l d be
r e d u c e d a t h i g h e n e r g y c o s t , h i g h l y i n t e n s i v e h e a t t r a n s f e r and p r o l o n g e d
s e a s o n s . I t s h o u l d be i n c r e a s e d , h o w e v e r , when t h e e v a p o r a t o r c o s t i n c r e a s e s
r e l a t i v e t o t h e e n e r g y c o s t , o r when t h e c a p i t a l c o s t i s i n c r e a s e d .
A n o t h e r i m p o r t a n t f e a t u r e o f t h e e v a p o r a t o r s i s t h e j u i c e r e t e n t i o n t ime and
i t s d i s t r i b u t i o n . A t j u i c e t e m p e r a t u r e s above 105°C, t h e r e t e n t i o n t ime
d e t e r m i n e s t h e amount o f h y d r o l i z e d s u c r o s e and decomposed i n v e r t s u g a r , t h i s
a f f e c t i n g c o l o u r f o r m a t i o n i n t h e j u i c e . As p o i n t e d o u t i n S e c t i o n 4 . 3 , a h i g h
j u i c e c o l o u r , n e c e s s i t a t i n g a l a r g e m a s s e c u i t e c i r c u l a t i o n , may i n d i r e c t l y
i n c r e a s e t h e e n e r g y demand o f t he s u g a r h o u s e . The p rob lem o f c o l o u r f o r m a t i o n
i n t h e e v a p o r a t o r s t a t i o n has been s t u d i e d i n r e c e n t y e a r s ( r e f . 16) and t h e
a s s o c i a t e d r e q u i r e m e n t on e v a p o r a t o r d e s i g n i s f a i r l y c l e a r : t h e mean j u i c e
r e t e n t i o n t ime s h o u l d be as s h o r t as p o s s i b l e , and t h e r e t e n t i o n t ime spec t rum
s h o u l d be c o n c e n t r a t e d c l o s e t o t h e mean v a l u e .
From the v a r i e t y o f r e q u i r e m e n t s men t i oned a b o v e , i t i s n e c e s s a r y t o e v a l u a t e
t he e x i s t i n g e v a p o r a t o r d e s i g n s c r i t i c a l l y . A t l e a s t t h r e e d i s a d v a n t a g e o u s
p r o p e r t i e s o f t h e p o p u l a r R o b e r t - t y p e e v a p o r a t o r can be i d e n t i f i e d :
- a p a r t o f t h e a v a i l a b l e t e m p e r a t u r e d i f f e r e n c e becomes l o s t because o f t h e
h y d r o s t a t i c h e a d ;
- t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t d e c r e a s e s r a p i d l y w i t h i n c r e a s i n g j u i c e
c o n c e n t r a t i o n ; i n t h e l a s t e v a p o r a t o r e f f e c t , i t s v a l u e may be 5-6 t imes s m a l l e r
t han t h a t i n t h e f i r s t e f f e c t ;
- mean j u i c e r e t e n t i o n t ime i s o f t h e o r d e r o f s e v e r a l m i n u t e s ; i n a d d i t i o n ,
owing t o n a t u r a l c i r c u l a t i o n i n a r e l a t i v e l y l a r g e l i q u i d v o l u m e , t h e s p e c t r u m
o f r e t e n t i o n t i m e s i s r a t h e r w i d e .
F o r t h i s r e a s o n o t h e r e v a p o r a t o r t y p e s , p a r t i c u l a r l y t h i n - f i l m t y p e s , have
r e c e i v e d a t t e n t i o n i n r e c e n t y e a r s . Among numerous d e s i g n s t h a t a r e r e v i e w e d
e l s e w h e r e ( r e f . 1 7 ) , t h e f a l l i n g - f i l m e v a p o r a t o r s seem t o be b e s t s u i t e d t o t h e
r e q u i r e m e n t s . T h r e e v e r s i o n s o f t h e t u b u l a r f a l l i n g - f i l m d e s i g n a r e shown
s c h e m a t i c a l l y i n F i g . 5.3 (where a s k e t c h o f a R o b e r t - t y p e u n i t i s a l s o g i v e n
f o r c o m p a r i s o n ) . T h i n j u i c e i s s p r e a d on t h e v e r t i c a l t u b e b u n d l e by means o f
a d i s t r i b u t o r d e v i c e , and f l o w s as a f i l m on t h e i n n e r t u b e w a l l f rom t o p t o
bo t t om. The t u b e s used i n t h e s u g a r i n d u s t r y a r e 6-12 m l o n g . I n o r d e r t o
p r e v e n t v i b r a t i o n s , t h e t u b e s a r e l e d t h r o u g h b a f f l e s p l a c e d abou t 2 m a p a r t . As
a r e s u l t o f h e a t i n g t h e c h e s t w i t h e x h a u s t steam o r v a p o u r , v a p o u r i s g e n e r a t e d
f rom the j u i c e . H a v i n g l e f t t h e t ube b u n d l e , t h e c o n c e n t r a t e d j u i c e f a l l s i n t o
t h e e v a p o r a t o r base and t h e v a p o u r f l o w s t h r o u g h a s e p a r a t o r t o t h e o u t l e t
n o z z l e .
The f u n c t i o n i n g o f t h e j u i c e d i s t r i b u t i o n d e v i c e i s o f c r i t i c a l impo r tance t o
t h e e f f i c i e n c y and r e l i a b i l i t y o f t he f a l l i n g - f i l m e v a p o r a t o r . I f w e t t i n g o f
192
O)
^ ^ 1 } .ττ-ττ^\
0 0
-mi-ir IL 11
Fig.
5.
3.
Fal
lin
g-f
ilm
eva
pora
tors
(c
ourt
esy
Wie
gand
) an
d a
Rob
ert-
type
ev
apor
ator
, (a
) fa
llin
g-f
ilm
un
it w
ith
adja
cent
ce
ntr
ifu
gal
se
para
tor,
(b
) w
ith
inte
gra
ted
sepa
rato
r at
the
ba
se,
(c)
wit
h ex
tern
al
vapo
ur
duct
s an
d in
teg
rate
d se
para
tor
at t
he
top.
1
- ju
ice
inle
t,
2 -
reci
rcul
ated
ju
ice
to
the
dis
trib
uto
r,
3 -
juic
e o
utl
et,
4
- he
atin
g-st
eam
in
let,
5
- co
nden
sate
o
utl
et,
6
- va
pour
ou
tlet
.
193
a t ube w a l l becomes i n s u f f i c i e n t , t h e r e i s a r i s k t h a t t h e l i q u i d f i l m w i l l t e a r
a p a r t , t h i s r e s u l t i n g i n s c a l e f o r m a t i o n on t h e t ube w a l l . I t i s t h e r e f o r e
e s s e n t i a l t h a t t h i s d e v i c e works w i t h o u t c l o g g i n g , e n s u r i n g a l s o u n i f o r m j u i c e
d i s t r i b u t i o n on t he t u b e - s h e e t s u r f a c e . The w o r k i n g p r i n c i p l e s o f f o u r p a t e n t e d
d i s t r i b u t o r d e s i g n s a r e shown i n F i g . 5 .4 .
(a)
v v v v v v v v v v v v v v v v
( b )
1
A A / V A A A A A A A A A
F i g . 5 .4 . J u i c e d i s t r i b u t i o n d e v i c e s employed i n f a l l i n g - f i l m e v a p o r a t o r s : ( a ) and ( b ) c i r c u l a r a r r a n g e m e n t s , ( c ) b a r s and tube i n s e r t s under m u l t i p l e n o z z l e s , ( d ) b a f f l e s under a s p r i n k l e r .
I n o r d e r t o a v o i d i n s u f f i c i e n t t ube w e t t i n g a t r e d u c e d l o a d , a r e c i r c u l a t i o n
pump can be a t t a c h e d t o t h e e v a p o r a t o r . U s i n g r e c i r c u l a t i o n , s a f e o p e r a t i o n can
be a c h i e v e d a t l o a d s as low as abou t 40% o f t he nominal v a l u e .
An e s t i m a t e o f t he a t t a i n a b l e o v e r a l l hea t t r a n s f e r c o e f f i c i e n t o f t he
f a l l i n g - f i l m e v a p o r a t o r as a f u n c t i o n o f j u i c e c o n c e n t r a t i o n i s shown i n
F i g . 5.5 ( a f t e r r e f . 1 8 ) , w i t h an a n a l o g o u s r e l a t i o n s h i p c h a r a c t e r i s t i c o f t he
R o b e r t - t y p e d e s i g n . As can be s e e n , w h i l e t h e r e i s no n o t i c e a b l e d i f f e r e n c e i n
i n t he f i r s t e v a p o r a t o r e f f e c t , t he v a l u e o f k a t j u i c e c o n c e n t r a t i o n s 35-70% DS
i n a f a l l i n g - f i l m u n i t can be up t o 100% above t h a t i n a R o b e r t - t y p e e v a p o r a t o r .
F o r t h i s r e a s o n , r e p l a c e m e n t s o f R o b e r t - t y p e u n i t s by f a l l i n g - f i l m ones i n f i n a l
194
- 3500
S 3000
o 2500h
fj^ 2000
ge
5 o
1000
- \ \
\
/ fa l l inc film
-Rot
-
20 30 AO 50 60 Mean juice concentration ( % DS)
70
F i g . 5 .5 . O v e r a l l hea t t r a n s f e r c o e f f i c i e n t s o f R o b e r t and f a l l i n g - f i l m e v a p o r a t o r s ( a f t e r r e f . 1 8 ) .
e v a p o r a t o r e f f e c t s have been u n d e r t a k e n i n numerous f a c t o r i e s .
The mean j u i c e r e t e n t i o n t ime i n a f a l l i n g - f i l m u n i t i s t y p i c a l l y abou t
1.5 m i n . T a k i n g s p e c i a l measu res , i t can be c u t down t o l e s s than 30 s ( r e f . 1 9 ) ,
t h i s r e q u i r i n g p r o p e r p r e c a u t i o n s i n t h e f i e l d o f a u t o m a t i c c o n t r o l and s a f e t y
d e v i c e s . A s , i n a d d i t i o n , t he spec t rum o f r e t e n t i o n t imes i s q u i t e n a r r o w ,
f a l l i n g - f i l m u n i t s match v e r y w e l l t h e r e q u i r e m e n t s o f a p p l i c a t i o n i n t h e
i n i t i a l e v a p o r a t o r e f f e c t s . I t has a l s o been r e p o r t e d t h a t a t low j u i c e
c o n c e n t r a t i o n s , o n l y n e g l i g i b l e s c a l i n g may o c c u r i n a f a l l i n g - f i l m e v a p o r a t o r
even though s c a l e f o r m a t i o n was a s e r i o u s p rob lem i n a R o b e r t - t y p e u n i t
p r e v i o u s l y u s e d .
I n t h e f i r s t e v a p o r a t o r e f f e c t , t h e p rob lem o f e n t r a i n m e n t s e p a r a t i o n becomes
c r i t i c a l because o f t he r i s k t h a t j u i c e c a r r y o v e r w i l l l e a d t o t h e p r e s e n c e o f
s u g a r i n t h e s e c o n d - e f f e c t c o n d e n s a t e . I t seems t h a t t h e deve lopmen t o f
d i f f e r e n t e n t r a i n m e n t s e p a r a t o r s has advanced so f a r t h a t t h e y can be s a f e l y
a p p l i e d w i t h i n t h e i r r e s p e c t i v e r a n g e s o f o p e r a t i o n ( r e f s . 2 0 - 2 3 ) . C e n t r i f u g a l
s e p a r a t o r s a r e c h a r a c t e r i z e d by a r e l a t i v e l y l a r g e v a p o u r v e l o c i t y , 10-40 m /s ,
and a p r e s s u r e d rop o f 10-100 mm H^O. The p o p u l a r " z i g z a g " and c u r v i l i n e a r
b a f f l e s a re most e f f e c t i v e a t v a p o u r v e l o c i t i e s 3-12 m/s , w i t h r e s u l t i n g
p r e s s u r e d r o p s 12-25 mm H^O. F i n a l l y , mesh pads can be used a t 1.5-10 m/s and
12-50 mm H2O. W h i l e t h e c e n t r i f u g a l s e p a r a t o r s c a n n o t s t o p v e r y f i n e j u i c e
d r o p l e t s s m a l l e r t han 10 m i c r o n s , t he mesh pads a r e e f f e c t i v e down t o a d r o p l e t
d i a m e t e r o f 5 m i c r o n s . The l a t t e r d e s i g n i s however p rone t o p a r t i a l c l o g g i n g
by d r y s u b s t a n c e s o f t h e j u i c e , t h i s r e s u l t i n g i n t h e pe r fo rmance d e t e r i o r a t i n g
w i t h t i m e . I n o r d e r t o p r e v e n t d e p o s i t b u i l d - u p , p e r i o d i c a l wash ing w i t h w a t e r
may be r e q u i r e d . A d e t a i l o f a f a l l i n g - f i l m e v a p o r a t o r w i t h e n t r a i n m e n t
s e p a r a t i o n augmented by a mesh pad i s shown s c h e m a t i c a l l y i n F i g . 5 .6 .
195
^condensate
MESH PAD
F i g . 5 .6 . I n t e g r a t e d e n t r a i n m e n t s e p a r a t o r e q u i p p e d w i t h a mesh pad a t t h e base o f a f a l l i n g - f i l m e v a p o r a t o r .
5 .3 ,2 U n c o n v e n t i o n a l a p p l i c a t i o n s
I t was men t ioned i n S e c t i o n 1.2.5 t h a t s u b s t a n t i a l r e d u c t i o n s o f t h e t o t a l
h e a t demand i n s u g a r manu fac tu re may cause t h e o v e r a l l v a p o u r demand i n t h e
e v a p o r a t o r t o become s m a l l e r t han t h e amount o f w a t e r t o be e v a p o r a t e d f rom
j u i c e . A p o s s i b l e s o l u t i o n t o t h i s p rob lem i s t o combine c o n v e n t i o n a l m u l t i
s t a g e e v a p o r a t i o n w i t h one o r two e v a p o r a t i o n s t a g e s hea ted by was te h e a t ; l o w -
t e m p e r a t u r e v a p o u r s o b t a i n e d i n t h e a d d i t i o n a l e v a p o r a t o r s can be d i r e c t e d t o
t h e c o n d e n s e r . I t s h o u l d be o b s e r v e d t h a t t h i s i s an a l t e r n a t i v e t o a v a p o u r
c o m p r e s s i o n c i r c u i t i n w h i c h an e q u i v a l e n t amount o f f i r s t - o r s e c o n d - e f f e c t
v a p o u r i s r e c i r c u l a t e d . Compared w i t h v a p o u r c o m p r e s s i o n , i t has t h e a d v a n t a g e
o f n o t a f f e c t i n g t h e power b a l a n c e o f t h e f a c t o r y .
Two d i f f e r e n t c o n c e p t s o f u n c o n v e n t i o n a l e v a p o r a t i o n have been implemented i n
p r a c t i c e r e c e n t l y .
( i ) T h i c k e n i n g o f j u i c e between c o n v e n t i o n a l e v a p o r a t i o n s t a g e s o r a f t e r t h e
l a s t e v a p o r a t o r e f f e c t , u s i n g vacuum-pan v a p o u r s ( r e f s . 2 4 - 2 6 ) .
( i i ) P r e - e v a p o r a t i o n o f t h i n j u i c e p r i o r t o t h e c o n v e n t i o n a l m u l t i - s t a g e
e v a p o r a t i o n p r o c e s s , u s i n g o u t l e t gases f rom p u l p d r y i n g ( r e f . 2 7 ) .
A n o t h e r p r o p o s a l , s t i l l i n t h e d e s i g n s t a g e , c o n s i s t s o f p r e - e v a p o r a t i n g a p a r t
o f t h e t h i n j u i c e f l o w i n a d o u b l e - e f f e c t e v a p o r a t o r hea ted by vacuum-pan
v a p o u r s ( r e f . 2 8 ) .
I t i s c h a r a c t e r i s t i c o f a l l t h e s e c o n c e p t s t h a t i n o r d e r t o u t i l i z e t h e l o w -
g rade h e a t , t h e j u i c e t e m p e r a t u r e i n t h e e v a p o r a t o r s h o u l d be s u f f i c i e n t l y l o w .
The j u i c e i s t h e r e f o r e c o o l e d down p r i o r t o e n t e r i n g t h e s p e c i a l e v a p o r a t o r and
warmed up a f t e r l e a v i n g i t .
196
I n case ( i ) , a t 0.12 bar e v a p o r a t i o n p r e s s u r e and 54 C nominal j u i c e
t e m p e r a t u r e , t h e r e i s a p rob lem t h a t t h e j u i c e may become s u p e r s a t u r a t e d a t
u n d e s i r a b l e paramete r f l u c t u a t i o n s . F o r t h i s r e a s o n , i f t h e assumed t h i c k - j u i c e
c o n c e n t r a t i o n exceeds 72-73% DS, t hen t h e s p e c i a l e v a p o r a t o r i s more s a f e l y
u t i l i z e d p r i o r t o t he l a s t e v a p o r a t o r e f f e c t , as shown i n F i g . 5 . 7 ( a ) . A t l o w e r
c o n c e n t r a t i o n s , i t can be a t t a c h e d t o t h e e v a p o r a t o r o u t l e t . F i g . 5 . 7 ( b ) . The
p rob lem w i t h t he s p e c i a l e v a p o r a t o r i s t h a t t he p r e s s u r e s o f t h e h e a t i n g v a p o u r
and t he v a p o u r g e n e r a t e d f rom j u i c e a r e v e r y l o w . As a c o n s e q u e n c e , l a r g e c r o s s -
s e c t i o n s o f t he f l o w c h a n n e l s a re r e q u i r e d and h i g h v a p o u r v e l o c i t i e s a re
d i f f i c u l t t o a v o i d i n c e r t a i n e v a p o r a t o r p a r t s .
F i g . 5 . 7 . J u i c e e v a p o r a t i o n u s i n g vacuum-pan v a p o u r s i n c o n n e c t i o n w i t h c o n v e n t i o n a l f o u r - s t a g e e v a p o r a t i o n : ( a ) between s t a g e s 3 and 4 , ( b ) a f t e r s t a g e 4 . 1 - s p e c i a l e v a p o r a t o r , 2 - hea t e x c h a n g e r , 3 - s team, 4 - vacuum-pan v a p o u r , 5 - t h i n j u i c e , 6 - t h i c k j u i c e .
To t he knowledge o f t h e p r e s e n t a u t h o r , a l l t he e v a p o r a t o r s hea ted by vacuum-
pan v a p o u r s a re o f t he f a l l i n g - f i l m t y p e . A t l e a s t one m a n u f a c t u r e r i s known t o
o f f e r a d e s i g n n o t v e r y d i f f e r e n t f rom t h o s e shown i n F i g . 5 . 3 ; i t s h o u l d be
c o n n e c t e d t o a s e p a r a t e condense r ( r e f . 2 6 ) . A compet ing s o l u t i o n c o n s i s t s o f
an e v a p o r a t o r , condense r and j u i c e tank i n t e g r a t e d i n a t o w e r - l i k e u n i t shown
s c h e m a t i c a l l y i n F i g . 5.8 ( a f t e r r e f . 2 4 ) . The mass and hea t b a l a n c e d a t a g i v e n
i n t he f i g u r e c o r r e s p o n d t o a s u g a r f a c t o r y w i t h a p r o c e s s i n g c a p a b i l i t y o f
7200 t / d . As can be s e e n , t he s p e c i a l e v a p o r a t o r makes i t p o s s i b l e t o e v a p o r a t e
8.3 kg w a t e r pe r 100 kg b e e t u s i n g o n l y s e c o n d a r y hea t w i t h o u t c o n t r i b u t i n g t o
p r o c e s s h e a t i n g .
197
EVAPORATOR
vacuum pan vapour 60°C. 7.7 kg/100 kg b_
ju ice 53%DS
^ ^cool ing water 28°C
1 β barometric water 38^C^
THICK JUICE TANK
F i g . 5 .8 . F a l l i n g - f i l m e v a p o r a t o r hea ted by vacuum-pan v a p o u r and f e a t u r i n g an i n t e g r a t e d condense r and t h i c k - j u i c e tank ( a f t e r r e f . 2 4 ) .
The s o l u t i o n under ( i i ) i s known f rom a p r o t o t y p e a p p l i c a t i o n i n a 6000 t / d
s u g a r f a c t o r y ( r e f . 2 7 ) . A c t u a l l y , i t was s t i m u l a t e d by t h e n e c e s s i t y o f
c l e a n i n g t h e o u t l e t gases f rom the p u l p d r y e r . Due t o v e r y s t r i n g e n t
e n v i r o n m e n t a l r e q u i r e m e n t s , d o u b l e - s t a g e c l e a n i n g ( c y c l o n e s f o l l o w e d by a
w a s h e r ) was a d o p t e d . The a v a i l a b i l i t y o f c l e a n gas a t 68°C made i t p o s s i b l e t o
i n c l u d e a g a s - h e a t e d e v a p o r a t o r i n t h e new i n s t a l l a t i o n . As t h e v a p o u r p r e s e n t
i n t he gas condenses i n t he h e a t i n g chamber , t h e u n i t can be e x p e c t e d t o
f u n c t i o n as an a d d i t i o n a l g a s - c l e a n i n g s t a g e i n w h i c h t h e f i n e s t d u s t p a r t i c l e s
a r e s e p a r a t e d w h i l e SO^ and NO^ d i s s o l v e i n w a t e r .
The f l o w o f t h i n j u i c e d e l i v e r e d t o p r e - e v a p o r a t i o n i s 110 t / h , i . e . , a b o u t
1/3 o f t h e t o t a l t h i n j u i c e f l o w . The i n f l o w i n g j u i c e a t 15.6% DS i s c o o l e d down
t o 60°C and expanded t o 44°C i n t he e v a p o r a t o r s ; t h e o u t f l o w i n g j u i c e a t
21.5% DS i s warmed up t o 90°C. Two f a l l i n g - f i l m e v a p o r a t o r s w i t h o u t j u i c e
c i r c u l a t i o n were i n s t a l l e d f o r t h i s a p p l i c a t i o n . Each u n i t has a h e a t i n g s u r f a c e 2
o f 1750 m c o n s i s t i n g o f t u b e s 51 mm o u t e r d i a m e t e r and 8 m l o n g . The t u b e s a r e
p e r i o d i c a l l y washed on t h e gas s i d e , u s i n g h o t w a t e r i n t r o d u c e d a t t h e upper
t ube s h e e t and f l o w i n g i n a f i l m on t he o u t e r t u b e w a l l s .
198
To comple te t h i s r e v i e w , a n o t h e r unusua l e v a p o r a t o r a p p l i c a t i o n can be
m e n t i o n e d . The medium t h i c k e n e d i s g r e e n s y r u p Β l e a v i n g a Q u e n t i n u n i t . I n
o r d e r t o make t h e i o n exchange p r o c e s s p o s s i b l e , t h e s y r u p i s d i l u t e d t o 64% DS
b e f o r e e n t e r i n g t h i s u n i t , w h i c h r e q u i r e s add ing up t o 2.9 kg w a t e r p e r 100 kg
b e e t . As t h e d i l u t e d s y r u p i s r e t u r n e d t o t he c r y s t a l l i z a t i o n s u b s y s t e m , t h i s
w a t e r must be e v a p o r a t e d . I f i t i s done i n C vacuum p a n s , t h e n a c o r r e s p o n d i n g
i n c r e a s e o f t h e hea t demand o f t h e s u g a r house can be e x p e c t e d . A l t e r n a t i v e l y ,
e x c e s s w a t e r can be e v a p o r a t e d u s i n g was te h e a t .
W i th i t s t e m p e r a t u r e r e d u c e d t o 50°C, s i m i l a r l y t o t h e case d i s c u s s e d a b o v e ,
t h e s y r u p i s d e l i v e r e d t o an e v a p o r a t o r hea ted by vacuum-pan v a p o u r s . A f a l l i n g -
f i l m u n i t ( w i t h o u t s y r u p r e c i r c u l a t i o n ) e q u i p p e d w i t h i t s own c o n d e n s e r has been
s e l e c t e d f o r t h i s a p p l i c a t i o n . The main p o i n t s o f t h e d e s i g n a n a l y s i s and a
summary o f o p e r a t i o n a l r e s u l t s can be f ound i n t h e l i t e r a t u r e ( r e f . 2 8 ) . T h i s
s o l u t i o n has much i n common w i t h t h e e v a p o r a t o r shown i n F i g . 5 .8 .
5.4 HEAT EXCHANGERS
T h e r e a re no r e v o l u t i o n a r y new d e s i g n s i n t h e j u i c e h e a t e r f i e l d , b u t t h e
r e q u i r e m e n t s d i s c u s s e d i n S e c t i o n 3 .3 .2 n e c e s s i t a t e a more c a r e f u l app roach t o
t he e x i s t i n g v a r i e t y o f c h o i c e s . From t h e p o i n t o f v i e w o f e n e r g y u t i l i z a t i o n ,
t h r e e f a c t o r s s h o u l d be taken i n t o a c c o u n t :
- t h e the rma l r e s i s t a n c e o f t h e h e a t i n g s u r f a c e , p a r t i c u l a r l y under r e a l
o p e r a t i n g c o n d i t i o n s , a s s o c i a t e d w i t h t h e r i s k o f s c a l e b u i l d - u p ;
- t he p o s s i b i l i t y o f m a i n t a i n i n g an e c o n o m i c a l l y j u s t i f i e d r e l a t i o n s h i p between
t h e hea t t r a n s f e r i n t e n s i t y and t h e p r e s s u r e d r o p i n t h e l i q u i d h e a t e d ;
- t he p o s s i b i l i t y o f o b t a i n i n g pu re c o u n t e r - f l o w , w h i c h i s e s p e c i a l l y i m p o r t a n t
i n t he case o f r e c u p e r a t i o n o f l o w - t e m p e r a t u r e h e a t .
T h r e e w i d e l y used j u i c e h e a t e r d e s i g n s a r e shown s c h e m a t i c a l l y i n F i g . 5 . 9 .
The f a c t o r s men t ioned above a r e d e c i s i v e i n q u a l i f y i n g t h e p l a t e h e a t e x c h a n g e r
as t he d e s i g n w h i c h can be adap ted most e a s i l y t o d i f f e r e n t o p e r a t i n g
c o n d i t i o n s . I n a d d i t i o n t o v e r y h i g h o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t s , p l a t e
hea t e x c h a n g e r s g i v e t he u s e r a r e a l chance o f easy m a i n t e n a n c e , as t h e y a r e
o f f e r e d t o d a y w i t h :
- v a r i o u s channe l g e o m e t r i e s p r o v i d i n g f o r s e l f - c l e a n i n g e f f e c t s , and t h u s
s u i t e d t o p a r t i c l e - c o n t a i n i n g l i q u i d s ;
- p l a t e m a t e r i a l s s u i t e d t o v a r i o u s c o r r o s i o n r e q u i r e m e n t s ;
- p a c k i n g m a t e r i a l s w h i c h make i t p o s s i b l e t o o p e r a t e p l a t e h e a t e x c h a n g e r s
s a f e l y a t t e m p e r a t u r e s up t o 260°C.
I n e a r l y a p p l i c a t i o n s i n t h e s u g a r i n d u s t r y , t h e c l a s s i c a l v e r s i o n o f t h e
p l a t e hea t e x c h a n g e r was dominan t . As i t i s c h a r a c t e r i z e d by v e r y smal l p l a t e
s p a c i n g (somet imes l e s s than 1 mm), s c a l e b u i l d - u p n o t o n l y causes a r e d u c t i o n
199
(α) (b)
Ε (c )
1 ^
F i g . 5 .9 . Schemes o f j u i c e h e a t e r s : ( a ) t u b u l a r , ( b ) p l a t e , ( c ) s p i r a l . 1 - i n f l o w i n g j u i c e , 2 - o u t f l o w i n g j u i c e , 3 - h e a t i n g v a p o u r , 4 - c o n d e n s a t e , 5 - s p e n t v a p o u r .
o f t h e hea t t r a n s f e r i n t e n s i t y , b u t a l s o a r a p i d i n c r e a s e o f t h e p r e s s u r e d r o p
on t h e j u i c e s i d e . T h i s e x c l u d e s t h e use o f c l a s s i c a l p l a t e h e a t e r s i f t h e r e i s
a r i s k o f heavy s c a l i n g , as on raw j u i c e and p a r t i c u l a r l y i n t h e t e m p e r a t u r e
range o f p r o t e i n d e p o s i t ( b e l o w 70°C) .
I n r e c e n t y e a r s , a new g e n e r a t i o n o f p l a t e h e a t e r s has been i n t r o d u c e d t o t h e
marke t . The m o d i f i e d d e s i g n i s l e s s s e n s i t i v e t o s c a l e b u i l d - u p . A s i d e - e f f e c t
o f t h e changed f l o w - c h a n n e l g e o m e t r y , h o w e v e r , i s t h a t t h e o v e r a l l h e a t t r a n s f e r
c o e f f i c i e n t i s s m a l l e r t han i n t he c l a s s i c a l v e r s i o n . A summary o f o p e r a t i o n a l
r e s u l t s o b t a i n e d w i t h t he new p l a t e h e a t e r s used on raw j u i c e can be f o u n d i n
t h e l i t e r a t u r e ( r e f . 3 0 ) .
T h e r e a r e s t i l l c e r t a i n a p p l i c a t i o n s i n a s u g a r f a c t o r y where o t h e r h e a t
e x c h a n g e r d e s i g n s can p r o f i t a b l y be u s e d . Examples can be c i t e d o f s u g a r
f a c t o r i e s e q u i p p e d w i t h v a r i o u s t y p e s o f j u i c e h e a t e r s o p t i m a l l y s e l e c t e d f o r
t h e r e q u i r e m e n t s c h a r a c t e r i s t i c o f e v e r y h e a t i n g s t a g e . T a b l e 5.1 g i v e s a
summary o f t h e da ta on t u b u l a r , s p i r a l and p l a t e h e a t e r s i n s t a l l e d i n a 6600 t / d
West European f a c t o r y . I t i s i n t e r e s t i n g t o n o t e , h o w e v e r , t h a t i n t h e D a n i s h
s u g a r i n d u s t r y , o n l y t u b u l a r h e a t e r s a r e used and t h e p l a t e u n i t s have been
200
TABLE 5.1
J u i c e h e a t e r s o f d i f f e r e n t d e s i g n s i n a 6600 t / d s u g a r f a c t o r y .
L o c a t i o n H e a t i n g medium H e a t e r t y p e H e a t i n g s u r f a c e
a r e a (m^)
Raw j u i c e 5th v a p o u r t u b u l a r 250X2 II II condensa te s p i r a l 38X2
P r e - l i m e d j u i c e vacuum-pan v a p o u r II 150X2 II II condensa te II 69X2 II II 4 th v a p o u r t u b u l a r 150X2
C l e a r j u i c e 3 rd v a p o u r p l a t e 83* T h i n j u i c e II II II 345*
II II 2nd v a p o u r II 210* II II 1s t v a p o u r II 83+116 II II e x h a u s t steam II 64+89
s i n g l e u n i t ( o t h e r h e a t e r s a r e i n s t a l l e d two i n p a r a l l e l )
f ound t o o d i f f i c u l t t o v e n t ( r e f . 3 1 ) .
A n o t h e r j u i c e h e a t e r d e s i g n w h i c h d e s e r v e s t o be men t ioned i s t h e segmented
t u b u l a r h e a t e r i n t r o d u c e d i n t h e S o v i e t s u g a r i n d u s t r y ( r e f s . 3 2 - 3 4 ) . I t i s
c h a r a c t e r i z e d by j u i c e v e l o c i t y abou t 3 m/s o r even h i g h e r , t h i s r e d u c i n g s c a l e
b u i l d - u p . As can be seen i n F i g . 5 .10 , t h e j u i c e f l o w pa th i s s t r e a m l i n e d t o
e n s u r e a low p r e s s u r e l o s s . A p p a r e n t l y , t h e c o n d i t i o n s f o r t he f l o w o f t he
h e a t i n g v a p o u r a r e f a r f rom opt imum, and t h e use o f v a p o u r e j e c t o r s f o r
improvement o f t he hea t t r a n s f e r has been r e p o r t e d ( r e f . 3 3 ) .
3 condensate
heating vapour
Top view J u i c e out
F i g . 5 .10 . Scheme o f a segmented t u b u l a r h e a t e r .
201
I n hea t e x c h a n g e r a p p l i c a t i o n s o t h e r t han j u i c e h e a t i n g between e x t r a c t i o n
and e v a p o r a t i o n , t he t r e n d s a r e s i m i l a r . A l t h o u g h t h e t u b u l a r d e s i g n i s s t i l
v e r y much i n u s e , t h e demand f o r e x c h a n g e r s e n s u r i n g a h i g h h e a t t r a n s f e r
i n t e n s i t y i s i n c r e a s i n g . F o r examp le , i n t h e u n c o n v e n t i o n a l e v a p o r a t i o n c i r c u i t s
d i s c u s s e d i n t he p r e c e d i n g S e c t i o n , i t i s e s s e n t i a l t h a t t h e t e m p e r a t u r e o f
j u i c e r e t u r n e d t o t h e p r o c e s s i n g l i n e i s as c l o s e as p o s s i b l e t o t h e i n i t i a l
t e m p e r a t u r e . As a r u l e , p l a t e hea t e x c h a n g e r s a r e s e l e c t e d f o r t h i s a p p l i c a t i o n .
S t i l l a n o t h e r u s e f u l f e a t u r e o f t he p l a t e h e a t e x c h a n g e r s i s t h e i r compac tness ,
w h i c h makes them easy t o i n s t a l l i n a l i m i t e d s p a c e , t h i s b e i n g a c h a r a c t e r i s t i c
r e q u i r e m e n t o f f a c t o r y m o d e r n i z a t i o n s o r e x t e n s i o n s .
5.5 VACUUM PANS
5.5.1 B a t c h - t y p e u n i t s
The therma l a s p e c t s o f vacuum-pan d e s i g n were p r e l i m i n a r i l y d i s c u s s e d i n
S e c t i o n 3 . 3 . 2 . I t can be no ted t h a t a l a r g e o v e r a l l hea t t r a n s f e r c o e f f i c i e n t
and a l a r g e h e a t i n g s u r f a c e a r e a a re c e r t a i n l y d e s i r a b l e f e a t u r e s o f t h e b a t c h -
t y p e u n i t s . T a k i n g i n t o a c c o u n t t he e s s e n t i a l r o l e o f t h e b o i l i n g p r o c e s s i n
s u g a r m a n u f a c t u r e , h o w e v e r , o t h e r r e q u i r e m e n t s s h o u l d pe rhaps be g i v e n even
h i g h e r p r i o r i t y . Most o f a l l , t he vacuum pan s h o u l d e n s u r e a r e a s o n a b l y s h o r t
b o i l i n g t i m e , h i g h c r y s t a l y i e l d and h i g h c r y s t a l q u a l i t y . A c t u a l l y , t h e s e
f a c t o r s can a l s o be l i n k e d t o t h e e n e r g y demand:
- i n c r e a s e d c r y s t a l y i e l d r e s u l t s i n r e d u c e d m a s s e c u i t e c i r c u l a t i o n ;
- improved c r y s t a l q u a l i t y c o n t r i b u t e s t o b e t t e r c o n d i t i o n s f o r c e n t r i f u g i n g ;
i . e . , l o w e r w a t e r consumpt ion i n c e n t r i f u g a l s and t h u s a r e d u c e d amount o f
s y r u p s .
On t he b a s i s o f advances o f t h e t h e o r y o f c r y s t a l l i z a t i o n and accumu la ted
e x p e r i e n c e , t h e i n a d e q u a c i e s o f b a t c h vacuum pans a r e now r e l a t i v e l y w e l l
u n d e r s t o o d . The h e a t i n g s u r f a c e a r e a i s t y p i c a l l y t o o l a r g e d u r i n g t h e f i r s t
s t a g e o f t h e b o i l i n g c y c l e ( c f . S e c t i o n 1 . 3 . 5 ) . A h i g h w a t e r e v a p o r a t i o n r a t e
r e s u l t i n g f rom bubb le b o i l i n g causes t h e o c c u r r e n c e o f z o n e s o f t o o h i g h
s u p e r s a t u r a t i o n , where c r y s t a l c o n g l o m e r a t e s a r e c r e a t e d o r s e c o n d a r y n u c l e a t i o n
t a k e s p l a c e . I n t he r e g i o n s c l o s e t o t h e h e a t i n g s u r f a c e , where t h e t e m p e r a t u r e
i s h i g h e r , t he s o l u t i o n may be u n d e r s a t u r a t e d , c a u s i n g t h e c r y s t a l s t o d i s s o l v e .
As t he l o c a l p r o c e s s e s a r e i m p o s s i b l e t o c o n t r o l , t h e g r a n u l o m e t r i c d i s t r i b u t i o n
o f c r y s t a l s i s a d v e r s e l y a f f e c t e d .
D u r i n g t h e l a s t s t a g e o f t h e b o i l i n g c y c l e , t h e h e a t i n g s u r f a c e a r e a i s
u s u a l l y t o o s m a l l . The e v a p o r a t i o n r a t e i s i n s u f f i c i e n t t o m a i n t a i n t h e d e s i r e d
c o n c e n t r a t i o n g r a d i e n t i n t h e s o l u t i o n a t t h e s u r f a c e s o f c r y s t a l s .
The s i t u a t i o n can be improved i f an e f f i c i e n t s t i r r e r i s i n s t a l l e d i n t h e
vacuum p a n . D u r i n g s o l u t i o n t h i c k e n i n g and c r y s t a l f o r m a t i o n , i n t e n s i v e m i x i n g
202
r e d u c e s t h e d a n g e r s o f l o c a l o v e r - and u n d e r - s a t u r a t i o n . I n t h e h i g h l y v i s c o u s
m a s s e c u i t e o b t a i n e d d u r i n g the l a s t s t a g e o f t h e b o i l i n g , t h e s t i r r e r h e l p s t o
i n c r e a s e t he c i r c u l a t i o n , t h i s i n c r e a s i n g t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t
and i n t e n s i f y i n g t h e e v a p o r a t i o n . P o s i t i v e e f f e c t s can a l s o be o b t a i n e d by
chang ing t h e way t h e vacuum pan i s u t i l i z e d i n t h e s u g a r b o i l i n g p r o c e s s , t h a t
i s , by emp loy ing t h e c r y s t a l f o o t i n g t e c h n i q u e , i n t r o d u c i n g c o n t r o l l e d vacuum
c h a n g e s , e t c . ( r e f s . 3 5 , 3 6 ) ; t h e s e methods have been r e v i e w e d i n S e c t i o n 4 . 3 .
(a) (b) ( c )
F i g . 5 .11. Examples o f s t i r r e r a r rangemen ts i n b a t c h vacuum p a n s : ( a ) s t i r r e r w i t h i n c a l a n d r i a , i n w a r d c i r c u l a t i o n , ( b ) s t i r r e r above c a l a n d r i a , ou twa rd c i r c u l a t i o n , ( c ) s t i r r e r be low c a l a n d r i a , ou twa rd c i r c u l a t i o n ( a f t e r r e f . 3 6 ) .
I t s h o u l d be added t h a t a t p r e s e n t , t h e r e q u i r e m e n t s o f t h e c r y s t a l g r o w t h
s t a g e o f t h e b o i l i n g c y c l e a r e n o t f u l l y known. W h i l e r e s e a r c h i n t h i s a r e a
c o n t i n u e s , t he p r e s e n t s t a t e o f knowledge on t h e d e s i g n o f modern vacuum pans
can be summarized as f o l l o w s .
( i ) Among v a r i o u s t y p e s o f pans shown i n F i g . 5 .11 , t h e c a l a n d r i a d e s i g n s w i t h
ample downtakes and f l a t o r s t r e a m l i n e d bot toms a r e p r e f e r r e d t o o t h e r s o l u t i o n s
( r e f s . 3 6 , 3 7 ) .
( i i ) The hyd rodynam ics o f m a s s e c u i t e c i r c u l a t i o n seem t o be w e l l u n d e r s t o o d .
The o p t i m i z a t i o n o f l e n g t h and d i a m e t e r o f h e a t i n g t u b e s and t h e d i a m e t e r o f
t h e downtake has been s t u d i e d ( r e f s . 3 8 , 3 9 ) .
( i i i ) I t has t aken a l ong t ime t o a r r i v e a t a s a t i s f a c t o r y d e s i g n o f s t i r r e r
p r o p e l l e r s and a p r o p e r a r rangement o f n o z z l e s r e l a t i v e t o t h e s t i r r e r and t h e
h e a t i n g s u r f a c e ( F i g . 5 . 1 2 ) . The speed o f p r o p e l l e r r o t a t i o n i s c a r e f u l l y
s e l e c t e d , t o e n s u r e i n c r e a s e d hea t t r a n s f e r d u r i n g t h e l a s t s t a g e o f t h e b o i l i n g
c y c l e , w h i l e a l s o keep ing t h e power demand a t as low a l e v e l as p o s s i b l e ( r e f s .
3 6 , 4 0 ) .
The a d v a n t a g e s o f f o r c e d c i r c u l a t i o n a r e so e v i d e n t t h a t i t has become
p o p u l a r t o i n s t a l l s p e c i a l l y d e s i g n e d s t i r r e r s i n o l d , n a t u r a l - c i r c u l a t i o n
vacuum p a n s . I t has been p r o v e d by measurements made i n a vacuum pan i n s t a l l e d
i n Β s t r i k e t h a t such a s t i r r e r can i n c r e a s e t h e h e a t t r a n s f e r c o e f f i c i e n t
d u r i n g t h e f i n a l s t a g e o f b o i l i n g ( a t magma c o n c e n t r a t i o n 90-93% DS) by
100-400%, and s h o r t e n t h e b o i l i n g t ime by 1/3 ( r e f . 1 ) .
203
F i g . 5 .12 . Deve lopment o f f o r c e d - c i r c u l a t i o n vacuum p a n s : ( a ) d e s i g n p r o p o s a l f rom 1896, ( b ) d e s i g n f rom 1949, ( c ) scheme o f a vacuum pan f o r a f t e r p r o d u c t b o i l i n g ( a f t e r r e f . 4 0 ) . 1 - j u i c e i n l e t , 2 - v a p o u r o u t l e t , 3 - m a s s e c u i t e o u t l e t , 4 - h e a t i n g chamber , ( 5 ) s t i r r e r .
As p r a c t i c a l e x p e r i e n c e p r o v e s , i f a s o p h i s t i c a t e d mechan ica l d e s i g n o f a
b a t c h vacuum pan i s combined w i t h e f f e c t i v e a u t o m a t i c b o i l i n g c o n t r o l s , t h e n
t h e r e s u l t s can be r e a l l y s a t i s f a c t o r y . N e v e r t h e l e s s , t h e s u g a r t e c h n o l o g i s t s
a re now aware o f t h e f a c t t h a t i n b a t c h p a n s , n o t h i n g more t han a t r a d e - o f f
between c o n f l i c t i n g r e q u i r e m e n t s o f d i f f e r e n t s t a g e s o f b o i l i n g can be a t t a i n e d .
S u b s t a n t i a l l y improved r e s p o n s e t o t he p r o c e s s r e q u i r e m e n t s can o n l y be e n s u r e d
i n c o n t i n u o u s vacuum p a n s .
5 .5 .2 C o n t i n u o u s u n i t s
I t has l ong been known t h a t t h e r e i s an e n e r g y - s a v i n g p o t e n t i a l i n c o n t i n u o u s
vacuum p a n s . One o f t h e r e a s o n s i s t h e i r i n h e r e n t a b i l i t y t o e l i m i n a t e t h e
f l u c t u a t i o n s o f t h e h e a t i n g v a p o u r demand. The r e s u l t i n g s t a b l e l o a d on t h e
e v a p o r a t o r s t a t i o n makes i t p o s s i b l e t o s t a b i l i z e t h i c k - j u i c e c o n c e n t r a t i o n and
t o a v o i d c o n d e n s e r l o s s e s e f f e c t i v e l y , w i t h r e d u c e d n e t h e a t demand as a r e s u l t .
A d i r e c t e n e r g y s a v i n g i s a l s o o b t a i n e d because s teaming a f t e r e v e r y
d i s c o n t i n u o u s b o i l i n g c y c l e i s no l o n g e r n e c e s s a r y . The advances i n b a t c h
vacuum-pan d e s i g n and h i g h l y e f f i c i e n t c o n t r o l s y s t e m s , h o w e v e r , made i t more
d i f f i c u l t f o r c o n t i n u o u s vacuum pans t o compete . D u r i n g t h e 1970s, v a r i o u s t y p e s
o f c o n t i n u o u s pans were t r i e d : g r o u p s o f i n t e r c o n n e c t e d b a t c h p a n s , h o r i z o n t a l
s i n g l e - o r m u l t i p l e - c o m p a r t m e n t u n i t s , c r y s t a l l i z a t i o n t o w e r , e t c . ( r e f s . 38,
4 1 - 4 4 ) . T h e r e were r e p o r t s t h a t s a t i s f a c t o r y o p e r a t i o n o f c e r t a i n d e s i g n s had
been o b t a i n e d , b u t m a i n l y on l o w - g r a d e s t r i k e s . Even t hough t h e number o f
c o n t i n u o u s pans was s l o w l y i n c r e a s i n g , t h e r e were a l s o r e p o r t s t h a t some o f them
204
were taken o u t o f o p e r a t i o n because o f u n s a t i s f a c t o r y r e s u l t s ( r e f . 4 5 ) . Two
p rob lems p r o v e d t o be most d i f f i c u l t t o s o l v e :
- t h e p e r i o d f o r w h i c h c o n t i n u o u s o p e r a t i o n c o u l d be m a i n t a i n e d was r a t h e r
s h o r t , because o f i n c r u s t a t i o n s w i t h i n t h e u n i t , e s p e c i a l l y on h i g h - p u r i t y
m a s s e c u i t e s ;
- t he g r a n u l o m e t r i c d i s t r i b u t i o n o f c r y s t a l s was w i d e r than t h a t a t t a i n a b l e i n
w e l l o p e r a t e d , modern ba t ch p a n s .
As p o i n t e d o u t by Aus tmeyer and F r a n k e n f e l d ( r e f . 4 6 ) , i n p r a c t i c e no
c o n t i n u o u s vacuum pan c o u l d be s u c c e s s f u l l y implemented w i t h o u t c r y s t a l f o o t i n g .
I t seems now, h o w e v e r , t h a t accumu la ted e x p e r i e n c e i s b e g i n n i n g t o b r i n g
p o s i t i v e r e s u l t s . S e v e r a l u n i t s o f a w e l l known h o r i z o n t a l m u l t i p l e - c o m p a r t m e n t
d e s i g n (80 pans d e l i v e r e d o r o r d e r e d up t o 1986) a r e now o p e r a t e d w i t h c r y s t a l
f o o t i n g ( r e f . 2 5 ) . A u n i t r a t e d 31 t / h Β m a s s e c u i t e , w i t h h e a t i n g s u r f a c e a r e a o f
540 m^, i s s u p p l i e d w i t h 12.5 t / h seed magma. S i m i l a r a p p a r a t u s r a t e d a t
17.5 t / h C m a s s e c u i t e , w i t h a h e a t i n g s u r f a c e a r e a o f 754 m , i s s u p p l i e d w i t h
6.1 t / h seed magma. Bo th u n i t s a r e hea ted w i t h v a p o u r a t 100°C, o f w h i c h a p a r t
i s i n j e c t e d d i r e c t l y i n t o t h e magma w i t h t h e aim o f i m p r o v i n g c i r c u l a t i o n .
A summary o f o p e r a t i o n a l r e s u l t s can be f ound i n t h e l i t e r a t u r e ( r e f . 4 7 ) . As
t h e f l o w o f seed magma l a r g e r t han 30% o f t he vacuum pan o u t p u t i s a c l e a r
d i s a d v a n t a g e , r e s e a r c h i s under way t o r educe t h i s f i g u r e . T h e r e a r e r e p o r t s
t h a t by m o d i f y i n g pan d e s i g n and c o n t r o l p r i n c i p l e s , o p e r a t i o n w i t h l e s s than
5% seed magma w i l l be p o s s i b l e ( r e f . 4 8 ) .
From t h e d e s i g n p r i n c i p l e men t i oned a b o v e , a new v e r s i o n o f a h o r i z o n t a l
c o n t i n u o u s pan e v o l v e d i n Sou th A f r i c a ( r e f . 4 9 ) . On t he b a s i s o f p o s i t i v e
Φ 6.75m
F i g . 5 .13 , Scheme o f a c o n t i n u o u s vacuum p a n , o f L a n g r e n e y t y p e ( a f t e r r e f . 5 2 ) . 1 - s t a n d a r d l i q u o r , 2 - seed magma, 3 - m a s s e c u i t e , 4 - h e a t i n g s u r f a c e s , 5 - s t i r r e r .
205
r e s u l t s o b t a i n e d i n the cane s u g a r i n d u s t r y , i t has r e c e n t l y been i n t r o d u c e d t o
a European b e e t s u g a r f a c t o r y ( r e f . 5 0 ) .
A n o t h e r h o r i z o n t a l s i n g l e - c o m p a r t m e n t d e s i g n was m o d i f i e d by a d o p t i n g a
c i r c u l a r shape o f v e s s e l w i t h a s t i r r e d o u t l e t s e c t i o n , as shown i n F i g . 5.13
( r e f s . 5 1 , 5 2 ) . The d i m e n s i o n s g i v e n i n t h e f i g u r e a p p l y t o a u n i t r a t e d a t
17 t / h C m a s s e c u i t e , w i t h h e a t i n g s u r f a c e a r e a o f 620 m^. I t i s n o r m a l l y
F i g . 5 .14. Scheme o f a c o n t i n u o u s vacuum p a n , o f BMA t y p e ( a f t e r r e f . 54) 1 - f e e d l i q u o r , 2 - seed magma, 3 - m a s s e c u i t e , 4 - v a p o u r , 5 - h e a t i n g s u r f a c e s , 6 - s t i r r e r s , 7 - s team.
206
o p e r a t e d w i t h c r y s t a l f o o t i n g . Numerous a p p l i c a t i o n s o f t h i s u n i t a r e known i n
t he cane s u g a r i n d u s t r y ; i t i s a l s o used i n C s t r i k e i n a F r e n c h b e e t s u g a r
f a c t o r y ( r e f . 5 1 ) .
The t o w e r d e s i g n has r e c e n t l y been adop ted by a n o t h e r m a n u f a c t u r e r , and t h e
r e s u l t s seem t o be b e t t e r t h i s t i m e . The u n i t c o n s i s t s o f a cascade o f s e v e r a l
c r y s t a l l i z a t i o n chambers , where t h e m a s s e c u i t e f l o w s f rom t h e t o p t o w a r d s t h e
bot tom under g r a v i t y , as shown i n F i g . 5.14 ( r e f s . 3 6 , 5 3 , 5 4 ) . The d i m e n s i o n s
g i v e n i n t h e f i g u r e a p p l y t o a u n i t r a t e d a t 45 t / h A m a s s e c u i t e , w i t h a h e a t i n g
s u r f a c e a r e a o f 1590 m^. The seed and t h e f e e d s o l u t i o n a r e f e d c o n t i n u o u s l y
i n t o t h e f i r s t chamber ; p a r t o f t he f e e d s o l u t i o n i s a l s o f e d t o chambers 2
t o 4 . Each c r y s t a l l i z a t i o n chamber i s adap ted t o t h e o p e r a t i o n a l r e q u i r e m e n t s
o f t h e r e l e v a n t p a r t o f t he b o i l i n g c y c l e i n te rms o f v o l u m e , h e a t i n g s u r f a c e ,
s t i r r e r c h a r a c t e r i s t i c s , e t c . F o r examp le , t he s t i r r e r s used i n t h e upper
chambers a r e h i g h - s p e e d a g i t a t o r s , w h i l e t h o s e i n t h e l o w e r chambers a r e l o w -
speed t u r b i n e s t i r r e r s augment ing m a s s e c u i t e c i r c u l a t i o n . I n c r u s t a t i o n s f o r m i n g
i n c e r t a i n chambers can be removed i n d i v i d u a l l y w i t h o u t f u l l y i n t e r r u p t i n g
o p e r a t i o n o f t h e u n i t . The t o w e r i s hea ted w i t h v a p o u r a t 90°C and a h i g h h e a t
t r a n s f e r i n t e n s i t y i s m a i n t a i n e d by c o n t r o l l i n g t h e m a s s e c u i t e l e v e l s i n t h e
i n d i v i d u a l chambers .
The c r y s t a l l i z a t i o n t o w e r s a r e o p e r a t e d s u c c e s s f u l l y i n A s t r i k e i n a few
f a c t o r i e s i n FRG. A r e d u c t i o n o f steam demand by abou t 5% has been r e p o r t e d f rom
one f a c t o r y . A l t h o u g h c o r r e c t i o n s and improvements a r e s t i l l b e i n g i n t r o d u c e d
i n t o t h i s d e s i g n , t h e o p e r a t i o n a l r e s u l t s a r e s a t i s f a c t o r y ( r e f s . 5 5 , 5 6 ) . The
f l o w o f seed magma i s k e p t be low 20% o f t h e pan o u t p u t .
5.6 CENTRIFUGALS
5.6.1 I n t r o d u c t i o n
The d i r e c t i n f l u e n c e o f c e n t r i f u g a l s on t h e e n e r g y consumpt ion i n a f a c t o r y
i s a s s o c i a t e d w i t h e l e c t r i c i t y - c o n s u m i n g d r i v i n g m o t o r s . Even more i m p o r t a n t ,
h o w e v e r , i s t h e i n d i r e c t i n f l u e n c e a s s o c i a t e d w i t h t h e q u a l i t y o f c e n t r i f u g e d
s u g a r and w i t h t h e e f f i c i e n c y o f s y r u p s e p a r a t i o n , because t h e s e f a c t o r s a f f e c t
t he mass f l o w s and t h u s t h e o v e r a l l e n e r g y consumpt ion i n t h e s u g a r h o u s e . I n
t h e c o n t e m p o r a r y s u g a r i n d u s t r y , b o t h b a t c h and c o n t i n u o u s c e n t r i f u g a l s a r e i n
u s e . Modern d e s i g n s o f bo th mach ines a r e shown s c h e m a t i c a l l y i n F i g . 5 .15 . Each
o f them has i t s a d v a n t a g e s and d i s a d v a n t a g e s ; t h i s a p p l i e s t o e n e r g y p rob lems
as w e l l as t o o t h e r a s p e c t s o f s u g a r c e n t r i f u g i n g ( r e f . 5 7 ) .
5 .6 .2 B a t c h mach ines
The deve lopmen t o f b a t c h c e n t r i f u g a l s has f o r many y e a r s been c h a r a c t e r i z e d
by a t r e n d t o w a r d s b i g g e r b a s k e t s , i . e . i n c r e a s e d c a p a c i t y . T h i s i s t h e cause
o f t h e p rob lem w i t h l a r g e - c a p a c i t y i r r e g u l a r l y r u n n i n g e l e c t r i c a l d r i v e s
207
F i g . 5 .15. Schemes o f c e n t r i f u g a l s : ( a ) b a t c h m a c h i n e , ( b ) c o n t i n u o u s mach ine . 1 - d r i v i n g m o t o r , 2 - b a s k e t , 3 - m a s s e c u i t e i n l e t , 4 - s u g a r o u t l e t , 5 -s y r u p - c o l l e c t i n g c a s i n g , 6 - s u g a r - c o l l e c t i n g c a s i n g , 7 - wash n o z z l e s .
ment ioned i n S e c t i o n 1 .4 .3 . D u r i n g t h e 1970s and 1980s, much e f f o r t was s p e n t on
t he deve lopment o f d r i v e s t h a t can work e f f i c i e n t l y a t t h e speed changes
c h a r a c t e r i s t i c o f t h e c e n t r i f u g i n g c y c l e .
Many fo rms o f e l e c t r i c a l d r i v e have been a p p l i e d t o t h e b a t c h m a c h i n e s . I n
t he 1970s, p o l e - c h a n g e a s y n c h r o n o u s a l t e r n a t i n g c u r r e n t mo to rs became v e r y
p o p u l a r . The p r i n c i p l e o f speed c o n t r o l can be seen i n t h e e q u a t i o n e x p r e s s i n g
t h e number o f r e v o l u t i o n s o f an a s y n c h r o n o u s motor ( i n rpm)
η = ( 6 0 f / p ) ( l - s ) ( 5 . 2 )
where f i s t h e s t a t o r f r e q u e n c y , ρ i s t h e number o f p o l e s , and s i s t h e motor
s l i p .
The s l i p can be d e f i n e d as
s = ( n ^ - n ) / n ^ ( 5 . 3 )
where n^ i s t h e s y n c h r o n o u s number o f r e v o l u t i o n s .
208
S t a n d a r d s i n g l e - s p e e d a s y n c h r o n o u s moto rs c o n n e c t e d t o a f i x e d - f r e q u e n c y s o u r c e
have a l a r g e s l i p d u r i n g r u n n i n g - u p , t h i s b e i n g t h e cause o f e n e r g y l o s s e s . I n
p o l e - c h a n g e m o t o r s , m u l t i p l e w i n d i n g s w i t h d i f f e r e n t numbers o f p o l e s a r e
i n s t a l l e d . By s w i t c h i n g f rom one w i n d i n g t o a n o t h e r , s t e p - c h a n g e s o f t h e number
o f r e v o l u t i o n s can be o b t a i n e d . I n t h i s w a y , a v e r a g e s l i p and a s s o c i a t e d e n e r g y
l o s s e s d u r i n g r u n n i n g - u p can be r e d u c e d . By r e d u c i n g f o u r t o f i v e d i f f e r e n t
speeds r a t h e r than a s i n g l e - s p e e d m o t o r , l o s s e s can be r e d u c e d by 75-80%. I n
a d d i t i o n , e l e c t r i c a l r e g e n e r a t i v e b r a k i n g can be u t i l i z e d f o r p a r t i a l r e c o v e r y
o f t he k i n e t i c e n e r g y o f t h e mass b e i n g c e n t r i f u g e d .
Advances i n s e m i c o n d u c t o r t e c h n o l o g y made i t p o s s i b l e f o r d i r e c t c u r r e n t
d r i v e s t o become h i g h l y c o m p e t i t i v e i n r e c e n t y e a r s . The c o m p l i c a t e d and c o s t l y
Ward -Leona rd sys tems have been r e p l a c e d by s i m p l e and r o b u s t t h y r i s t o r -
c o n t r o l l e d d r i v e s ( r e f . 5 8 ) . As t h e d . c . motor i s n o t dependen t on c u r r e n t
f r e q u e n c y , t h e r e a r e no s l i p l o s s e s d u r i n g r u n n i n g - u p and b r a k i n g . More
e f f i c i e n t e n e r g y r e c o v e r y t e c h n i q u e s can a l s o be a p p l i e d i n d . c . d r i v e s . F o r
t h i s r e a s o n , t he d . c . motor uses l e s s e n e r g y t han a . c . mo to rs w i t h p o l e - c h a n g e .
A n o t h e r s o l u t i o n based on t h e a p p l i c a t i o n o f s e m i c o n d u c t o r d e v i c e s i s t h e
f r e q u e n c y c o n v e r t e r a . c . d r i v e ( r e f s . 5 9 , 6 0 ) . The speed c o n t r o l p r i n c i p l e
c o n s i s t s o f v a r y i n g t h e s t a t o r f r e q u e n c y ; i t i s a l s o n e c e s s a r y t o v a r y t h e
v o l t a g e p r o p o r t i o n a t e l y t o t h e f r e q u e n c y . The f r e q u e n c y c o n v e r t e r c o n v e r t s t h e
c o n s t a n t a l t e r n a t i n g q u a n t i t i e s o f t h e mains i n t o v a r i a b l e v a l u e s s u i t a b l e f o r
t h e speed s e t t i n g s o f t h e m o t o r . T h i s e n a b l e s t h e speed o f t h e motor t o be
i n f i n i t e l y v a r i a b l e . I f a c o n v e r t e r w i t h a d i r e c t c u r r e n t i n t e r m e d i a t e c i r c u i t
i s u s e d , t h e n e n e r g y r e c o v e r y when b r a k i n g i s p o s s i b l e w i t h o u t any a d d i t i o n a l
e f f o r t : t he motor i s s i m p l y o p e r a t i n g as a g e n e r a t o r and f e e d i n g e n e r g y back
i n t o t h e ma ins . The mains s i d e o f t h e c o n v e r t e r can a l s o be e q u i p p e d w i t h an
o s c i l l a t i o n c i r c u i t w h i c h compensates t h e b a s i c amount o f t h e c o n t r o l r e a c t i v e
powe r , t h u s e n s u r i n g a h i g h power f a c t o r .
The a v e r a g e e f f i c i e n c y o f t h e f r e q u e n c y c o n v e r t e r a . c . d r i v e i s comparab le
w i t h t h a t o f t h e d . c . d r i v e . The power d iag rams o f bo th d r i v e s i n a c e n t r i f u g i n g
c y c l e a r e compared i n F i g . 5.16 ( a f t e r r e f s . 5 8 - 6 0 ) .
Modern c e n t r i f u g a l d r i v e s a r e s u p p l i e d w i t h comp le te c o n t r o l s f o r t h e
t e c h n o l o g i c a l f l o w o f o p e r a t i o n s . E l e c t r o n i c c i r c u i t s t e n d t o d o m i n a t e , and
m i c r o p r o c e s s o r a p p l i c a t i o n s a r e i n c r e a s i n g l y f r e q u e n t . F o r t h e c y c l i c s e q u e n c e ,
a memory programmable c o n t r o l i s u t i l i z e d . I n many c a s e s , n o t o n l y i s t h e who le
c y c l e a u t o m a t i c b u t g r o u p s o f mach ines a r e a l s o a u t o m a t i c a l l y l i n k e d , f o r smooth
b a t t e r y o p e r a t i o n .
The b a t c h s u g a r c e n t r i f u g a l i s n e a r l y 150 y e a r s o l d . I t can now be c o n s i d e r e d
a v e r y t h o r o u g h l y d e v e l o p e d m a c h i n e , and f u r t h e r p r o g r e s s c o n s i s t s o f t h e
r e f i n e m e n t o f d e t a i l s . Among t he d e t a i l s w h i c h a re r e l a t e d t o e n e r g y p r o b l e m s .
209
filling speeding up centrifuging braking discharging
F i g . 5 .16. Power - t ime d iagrams o f b a t c h c e n t r i f u g a l d r i v e s : ( a ) f r e q u e n c y c o n v e r t e r a . c . d r i v e , ( b ) d . c . d r i v e ( a f t e r r e f s . 5 8 - 6 0 ) . Shaded a r e a s i n d i c a t e e n e r g y r e c o v e r e d d u r i n g b r a k i n g .
wash sys tems s h o u l d be named. As a l r e a d y men t i oned i n S e c t i o n 1 .3 .4 , t h e
o p t i m i z a t i o n o f w a t e r wash i s i m p o r t a n t t o t h e e n e r g y consumpt ion i n t h e s u g a r
h o u s e . Modern wash sys tems s h o u l d t h e r e f o r e be f l e x i b l e enough t o make i t
p o s s i b l e t o o p t i m i z e t h e s p r a y g e o m e t r y , as w e l l as t h e t i m i n g and d u r a t i o n o f
t he wash . Examples o f c o n s i d e r a b l e improvements i n m a s s e c u i t e c i r c u l a t i o n
o b t a i n e d by wash o p t i m i z a t i o n can be f o u n d i n t h e l i t e r a t u r e ( r e f . 6 1 ) .
5 .6 .3 C o n t i n u o u s mach ines
Wi th r e s p e c t t o power demand, c o n t i n u o u s c e n t r i f u g a l s a r e c l e a r l y p r e f e r a b l e
t o b a t c h t y p e s . The d r i v e i s u s u a l l y f rom a s t a n d a r d a . c . m o t o r . The motor i s
smal l compared w i t h t h a t o f a b a t c h mach ine , s i n c e t h e h i g h a c c e l e r a t i n g /
d e c e l e r a t i n g l o a d s a r e no l o n g e r p r e s e n t .
The dom ina t i ng c o n t i n u o u s - a c t i o n d e s i g n p r i n c i p l e i s t h a t o f a v e r t i c a l - a x i s ,
c o n e - b a s k e t mach ine . The pe r f o rmance o f t h e c o n t e m p o r a r y c o n t i n u o u s c e n t r i f u g a l
i n l o w - g r a d e s t a t i o n s i s u s u a l l y e q u i v a l e n t t o t h a t o f t h e b a t c h mach ine . I n
t he c e n t r i f u g i n g o f h i g h - p u r i t y m a s s e c u i t e s , h o w e v e r , t h e c o n t i n u o u s c e n t r i f u g a l
i s g e n e r a l l y i n f e r i o r t o t h e b a t c h one ( r e f . 6 2 ) . I n c e r t a i n a p p l i c a t i o n s ,
c o n t i n u o u s c e n t r i f u g i n g i s f o l l o w e d by a f i n i s h i n g c r y s t a l t r e a t m e n t i n b a t c h
mach ines .
The main d i s a d v a n t a g e o f c o n t i n u o u s c e n t r i f u g i n g i s t h e c r y s t a l damage
r e s u l t i n g f rom c o l l i s i o n s o f c r y s t a l s , e j e c t e d a t a h i g h s p e e d , w i t h t h e s u g a r -
210
c o l l e c t i n g c a s i n g . T h i s has a d i r e c t d e t r i m e n t a l e f f e c t on t h e g r a n u l o m e t r i c
d i s t r i b u t i o n o f c r y s t a l s ; i n d i r e c t l y , i n c r e a s e d m a s s e c u i t e c i r c u l a t i o n i n t h e
s u g a r house can be a r e s u l t . F o l l o w i n g y e a r s o f r e s e a r c h work on t h i s p rob lem
( r e f s . 2 5 , 6 3 ) , a t l e a s t one m a n u f a c t u r e r i s now o f f e r i n g a d e v i c e w h i c h can be
i n s t a l l e d i n c o n t i n u o u s mach ines t o r educe c r y s t a l damage. Formed as a wheel
p l a c e d between t h e baske t and t h e c a s i n g , i t i s r o t a t e d a t a speed l o w e r t han
t h a t o f t h e b a s k e t ( r e f . 6 4 ) .
A n o t h e r p rob lem i s t h a t t h e wash a c t s d i f f e r e n t l y i n a c o n t i n u o u s m a c h i n e ,
so t h e wash c o n t r o l canno t be q u i t e so f i n e as w i t h a w e l l d e s i g n e d b a t c h
mach ine . The s i t u a t i o n improves as work on t h e r e f i n e m e n t o f wash sys tems and
o t h e r d e t a i l s c o n t i n u e s . T a k i n g i n t o a c c o u n t t h a t t h e c o n t i n u o u s machine i s 50
y e a r s y o u n g e r t han t he b a t c h o n e , i t seems t h a t i t s e n e r g y - s a v i n g p o t e n t i a l has
n o t y e t been f u l l y u t i l i z e d .
REFERENCES
1 E. R e i n e f e l d , Über d i e Kampagne 1981, Z u c k e r i n d . , 107(5) (1982) 369-380. 2 C . Longue E p e e , L e c t u r e p r e s e n t e d a t t h e I n t e r n a t i o n a l E x h i b i t i o n
SVEKLOVODSTVO, K i e v , May 1986. 3 Anonymous, Le t a p i s - e c h a n g e u r j u s - c o s s e t t e du t y p e DE SMET, S u c r . B e i g e ,
103 (1985) 12. 4 G . V . G e n i e , E n e r g y s a v i n g t h r o u g h more e f f i c i e n t b e e t d i f f u s e r s , Z u c k e r i n d . ,
108(7) (1983) 643-647. 5 Τ . B a l o h , V e r f a h r e n s t e c h n i s c h e D a r s t e l l u n g d e r E x t r a k t i o n , Ζ . Z u c k e r i n d . ,
27 (6 ) (1977) 363-372. 6 G . V . G e n i e , J u i c e e x t r a c t i o n i n t he b e e t s u g a r f a c t o r y . Sugar T e c h . R e v . ,
9 ( 2 ) (1982) 119-270. 7 G . V . G e n i e , Computer s i m u l a t i o n o f s t e p w i s e d i f f u s e r s , Z u c k e r i n d . ,
109(5) (1984) 456-460. 8 G . V . G e n i e , Computer s i m u l a t i o n and mathemat i ca l m o d e l l i n g o f d i f f u s i o n ,
Z u c k e r i n d . , 111(2) (1986) 149-154. 9 R . F . Madsen and W. Ko fod N i e l s e n , D i e Kampagne 1977 i n d e r " A / S De Danske
S u k k e r f a b r i k k e r " , Z u c k e r i n d . , 103(10) (1978) 831-839. 10 S . V . M a r k i t a n ( e t a l . ) , Nag rev c i r k u l i r u y u s h c h e g o soka pa rokon tak tnym
sposobom, Sakh . P r o m . , ( 9 ) (1980) 43-46. 11 K. Vukov and I . S i p o s , V e r s u c h e z u r e n e r g i e s p a r e n d e r E rhöhung d e r g e w i n n
ba ren Zuckermenge be i d e r R ü b e n e x t r a k t i o n , Paper p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e " Improvement o f t h e Bee t Suga r P r o d u c t i o n " , Warszawa, May 1987.
12 P. V a l e n t i n , D i e A b h ä n g i g k e i t des H e i z w ä r m e b e d a r f s von H e i z f 1 ä c h e n g r ö s s e und R o h s a f t a b z u g , Z u c k e r i n d . , 104(8) (1979) 695-701.
13 P. Mosel ( e t a l . ) , O p t i m i e r u n g von E i n d i c k u n g s p r o z e s s e n i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 104(12) (1979) 1101-1106.
14 A . A . Knyazev and V . N . G o r o k h , V l i y a n i e u d e l n o i p l o s h c h a d i p o v e r k h n o s t i n a g r e v a v y p a r n o i u s t a n o v k i na r a s k h o d t e p l o v o i e n e r g i i d l y a t e k h n o l o g i c h e s k i k h nuzhd s v e k l o s a k h a r n o g o z a v o d a , Sakh . P r o m . , ( 3 ) (1976) 41-43 .
15 T . B a l o h , O p t i m i e r u n g von Z u c k e r f a b r i k s a n l a g e n u n t e r B e r ü c k s i c h t i g u n g des E n e r g i e h a u s h a l t s , Z u c k e r , 29(10) (1976) 541-548.
16 K. V u k o v , I . Körmendy and H.M. L o k o , A u f e n t h a l t s z e i t und S a f t v e r f ä r b u n g i n e i n e r V e r d a m p f s t a t i o n , Z u c k e r i n d . , 108(12) (1983) 1144-1149.
17 S . Z a g r o d z k i and A . K u b a s i e w i c z , Hea t economy i n b e e t s u g a r f a c t o r y e v a p o r a t i o n . Sugar T e c h . R e v . , 5 ( 1 / 2 ) (1977/78) 1-154.
18 P. T o b e , F a l l i n g - f i l m e v a p o r a t o r s f o r t h e cane s u g a r i n d u s t r y , W i e g a n d , E t t l i n g e n , 1986.
211
19 U . C u r d t s , L e c t u r e p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e " Improvement o f t h e B e e t Sugar P r o d u c t i o n " , Warszawa, May 1987.
20 A . K u b a s i e w i c z , W y p a r k i . K o n s t r u k c j a i O b l i c z a n i e , WNT, Warszawa, 1977. 21 Anonymous, S e p a r a t e u r s de g o u t t e s EUROFORM pou r i n s t a l l a t i o n s d ' e v a p o r a t i o n
dans 1 ' i n d u s t r i e s u c r i e r e , S u c r . F r . , 118(June 1977) 262-265. 22 J . Kwasn iak , P o l i s h P a t e n t 79 895. 23 D.M. Humm, E n t r a i n m e n t s e p a r a t o r s f o r vacuum pans and e v a p o r a t o r s . Sugar J . ,
44(12) (1982) 8-14. 24 E. R e i n e f e l d , Über d i e Kampagne 1984, Z u c k e r i n d . , 110(5) (1985) 367-377. 25 Ε . R e i n e f e l d , Über d i e Kampagne 1985, Z u c k e r i n d . , 111(4) (1986) 303-313. 26 T e c h n i c a l i n f o r m a t i o n f rom Wiegand , i n : F . O . L i c h t s Yearbook and D i r e c t o r y ,
R a t z e b u r g , 1983, p p . H71-H74. 27 P. V e r m e u l e n , Sa f t e i ndamp fung m i t t e l s T r o c k n u n g s a b g a s be i dessen R e i n i g u n g ,
Z u c k e r i n d . , 110(8) (1985) 681-685. 28 W. L e k a w s k i , p e r s o n a l commun ica t i on . 29 Ε . Hess and H . v . Mal l a n d , E i n d i c k u n g s a n l a g e f ü r Rohzucke r 2 - A b l a u f ,
Z u c k e r i n d . , 109(4) (1985) 295-300. 30 N . R . T w a i t e , H . J . D a v e n p o r t and E . K . M a c d o n a l d , E n e r g y r e d u c t i o n and p r o c e s s
i n t e g r a t i o n . I n t . Suga r J . , 88(1055) (1986) 217-219, 88(1056) (1986) 230-236.
31 Ν. L o f t , p e r s o n a l commun i ca t i on . 32 A . A . Pochechun ( e t a l . ) , P r o i z v o d s t v e n n y e i s p y t a n i y a s e k t s i o n n o g o p o d o g r e v a
t e l y a soka p e r e d I I s a t u r a t s i e i , Sakh . P r o m . , ( 2 ) (1983) 43-45 . 33 Y u . S . R a z l a d i n ( e t a l . ) , Nagrev d i f f u z i o n n o g o soka ν s e k t s i o n n y k h a p p a r a t a k h
d l y a z a v o d a moshchnos tyu 6 t y s . t , Sakh . P r o m . , ( 1 ) (1984) 35-38. 34 V . G . B e l i k ( e t a l . ) , S e k t s i o n n y e p o d o g r e v a t e l i , Sakh . P r o m . , ( 6 ) (1986)
35-37. 35 H. S c h i w e c k , M ö g l i c h k e i t e n z u r Senkung des E n e r g i e b e d a r f s im Z u c k e r h a u s ,
Z u c k e r , 30(10) (1977) 525-535. 36 K . E . A u s t m e y e r , A n a l y s i s o f s u g a r b o i l i n g and i t s t e c h n i c a l c o n s e q u e n c e s .
I n t . Sugar J . , 88 ( 1 9 8 6 ) , P a r t I (1045) 3 - 7 , P a r t I I (1046) 23-29 , P a r t I I I (1047) 50-55.
37 C h . M o l l e r , Sugar b o i l i n g t h e o r y and p r a c t i c e . I n t . Sugar J . , 85(1045) (1983) 163-165.
38 E. H u g o t , Handbook o f Cane Sugar E n g i n e e r i n g , 3 r d e d n . , E l s e v i e r , Amsterdam, 1986.
39 H . N . Gupta and S . J . Pande, Optimum d e s i g n o f a vacuum p a n . I n t . Sugar J . , 88(1048) (1986) 66-68.
40 E r f a h r u n g e n m i t R ü h r w e r k s - A p p a r a t e n , Z u c k e r i n d . , 105(3) (1980) 227-244. 41 Μ. D m i t r o v s k i and A . Η . Kokke, US P a t e n t 3 981 739. 42 A . G e n a r t , I n s t a l l a t i o n d ' u n c r i s t a l 1 i s e u r c o n t i n u a l a R a f f i n e r i e N o t r e -
Dame a O r e y e , S u c r . B e i g e , 98(11) (1979) 337-345. 43 F. L a n g r e n e y , E r s t e E r g e b n i s s e des k o n t i n u i e r l i c h a r b e i t e n d e n E i n d a m p f -
k r i s t a l l i s a t o r s , B a u a r t " L a n g r e n e y " , Z . Z u c k e r i n d . , 26(12) (1976) 772-776. 44 W. W o z n i a k i e w i c z and M. W i e k l u k , P o l i s h P a t e n t 54 086. 45 K. T e s c h , E r f a h r u n g e n m i t R ü h r w e r k s - K o c h a p p a r a t e n i n d e r Z u c k e r f a b r i k
O c h s e n f u r t , Z u c k e r i n d . , 105(3) (1980) 240-242. 46 K . E . Aus tmeyer and T h . F r a n k e n f e l d , Der Weg z u r k o n t i n u i e r l i c h e n K r i s t a l l
f u s s g e w i n n u n g , Z u c k e r i n d . , 112(1) (1987) 36-45 . 47 H. H e r o l d , K o n s t r u k t i o n und A r b e i t s w e i s e d e r k o n t i n u i e r l i c h e n Kochappa ra te
von F i v e s - C a i l Babcock i n E l s d o r f , Z u c k e r i n d . , 112(2) (1987) 118-122. 48 Anonymous, Seed ing a c o n t i n u o u s vacuum pan w i t h l e s s t h a n 10% magma,
Z u c k e r i n d . , 112(3) (1987) 211. 49 P.W. R e i n , E x p e r i e n c e w i t h c o n t i n u o u s vacuum pans i n T o n g a a t - H u l e t t S u g a r ,
I n t . Sugar J . , 89(1058) (1987) 28-34. 50 H . - E . U e c k e r , K o n t i n u i e r l i c h e r K o c h a p p a r a t B a u a r t T o n g a a t - H u l e t t ,
Z u c k e r i n d . , 112(3) (1987) 202-203. 51 F . L a n g r e n e y , Le p o i n t s u r l e c r i s t a l 1 i s e u r c o n t i n u non c o m p a r t i m e n t e ,
I n d . A l i m . A g r i e , 102(7 -8 ) (1985) 673-678.
212
52 Anonymous, Le c r i s t a l 1 i s e u r c o n t i n u ( L i c . L a n g r e n e y ) a l a S u c r e r i e de M a r i e , I n d . A l i m . A g r i e , 102(7-8 ) (1985) 713-717.
53 Ε . R e i n e f e l d , Über d i e Kampagne 1983, Z u c k e r i n d . , 109(5) (1984) 399-411. 54 E . D . B o s s e , A new e v a p o - c r y s t a l 1 i z a t i o n t o w e r f o r w h i t e s u g a r and low raw
p r o d u c t s . Sugar y A z ú c a r , 8 1 ( 5 ) (1986) 33-56. 55 Κ. Her rman , Neue Systeme z u r k o n t i n u i e r l i c h e n K o c h a r b e i t - BMA-Verdampfungs-
K r i s t a l l i s a t i o n s t u r m , Z u c k e r i n d . , 112(4) (1987) 277-280. 56 J . Be low , D ie V K T - A n l a g e i n L e h r t e , Z u c k e r i n d . , 112(4) (1987) 280-284. 57 J . O . S m i t h , Recen t p r o g r e s s i n s u g a r c e n t r i f u g i n g . Sugar T e c h . R e v . ,
4 ( 1 ) (1976/77) 49-87 . 58 Η. G r a s s , S p e z i a l a n t r i e b e f ü r d i e Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 107(9) (1982)
863-868. 59 H. G r a s s , D i e E n t w i c k l u n g e l e k t r i s c h e r Z u c k e r z e n t r i f u g e n a n t r i e b e ,
Z u c k e r i n d . , 110(2) (1985) 132-136. 60 T e c h n i c a l i n f o r m a t i o n f rom Fe i t en&Gu i1 leaume E n e r g i e t e c h n i k , Nordenham,
1985. 61 E. R e i n e f e l d , Über d i e Kampagne 1982, Z u c k e r i n d . , 108(4) (1983) 307-319. 62 P. C r e d o z , J . Ledoux and G . J o u r n e t , The deve lopmen t o f c o n t i n u o u s
c e n t r i f u g i n g i n t h e f i e l d o f h i g h - p u r i t y s u g a r s , Sugar y A z ú c a r , 75 (2 ) (1980) 34-42 .
63 Ε . R e i n e f e l d , Über d i e Kampagne 1980, Z u c k e r i n d . , 106(5) (1981) 397-407. 64 Anonymous, K r i s t a l l r a d z u r V e r r i n g e r u n g von K r i s t a l 1bruch i n k o n t i n u i e r l i
chen Z e n t r i f u g e n , Z u c k e r i n d . , 112(1) (1987) 34.
213
C h a p t e r 6
AUTOMATIC CONTROL FOR E F F I C I E N T ENERGY U T I L I Z A T I O N
6.1 SCOPE OF THE PROBLEMS
A u t o m a t i c p r o c e s s c o n t r o l i s i n d i s p e n s a b l e t o t h e c o n t e m p o r a r y s u g a r
i n d u s t r y . When imp lement ing o p t i m i z e d p r o c e s s e s o r p u t t i n g improved equ ipment
i n t o o p e r a t i o n , t h e a u t o m a t i c c o n t r o l o f t e n p l a y s a l e a d i n g r o l e i n e n s u r i n g
t h a t t h e i n t e n t i o n s o f a t e c h n o l o g i s t o r an equ ipment d e s i g n e r become a r e a l i t y .
To a l a r g e e x t e n t , t h i s i s a l s o t r u e i n t h e case o f improvements i n t r o d u c e d i n t o
t h e e n e r g y economy.
T h i s C h a p t e r p r e s e n t s a r e v i e w o f t h e a p p l i c a t i o n s o f a u t o m a t i c c o n t r o l t h a t
a r e p a r t i c u l a r l y u s e f u l i n o p t i m i z i n g e n e r g y c o n v e r s i o n and u t i l i z a t i o n i n t h e
s u g a r f a c t o r y . A c t u a l l y , t h e f u n c t i o n i n g o f a u t o m a t i c c o n t r o l s can be r e l a t e d t o
t h e e n e r g y economy i n a v a r i e t y o f w a y s . To b e g i n w i t h , examples can be named o f
a u t o m a t i c c i r c u i t s c o n t r o l l i n g e n e r g y p r o c e s s e s d i r e c t l y , such as combus t i on
c o n t r o l i n a b o i l e r o r i n a p u l p d r y i n g f u r n a c e ( r e f . 1 ) . T h i s t y p e o f c o n t r o l
a p p l i c a t i o n w i l l n o t be d i s c u s s e d h e r e , h o w e v e r , as i t i s n o t s p e c i f i c t o t h e
s u g a r i n d u s t r y .
A n o t h e r g roup o f a u t o m a t i c c o n t r o l c i r c u i t s s e r v e s t h e p u r p o s e o f s t a b i l i z i n g
p r o c e s s p a r a m e t e r s , w h i c h has some i n f l u e n c e on t h e e n e r g y demand o f t h e
p r o c e s s e s a f f e c t e d . T h i s can be e x e m p l i f i e d by t h e a u t o m a t i c c o n t r o l o f m i l k - o f -
l ime d e n s i t y and m i l k - o f - l i m e f l o w t o t h e j u i c e p u r i f i c a t i o n s t a t i o n . H e r e , t he
s e t t i n g s a r e a l w a y s a r r a n g e d t o e n s u r e t h e CaO doses r e q u i r e d by t h e j u i c e
p u r i f i c a t i o n p r o c e s s . C o n s e q u e n t l y , t he amount o f e x c e s s w a t e r i n t r o d u c e d i n
m i l k - o f - l i m e t o t h e p r o c e s s v a r i e s depend ing on t h e q u a l i t y o f t h e a u t o m a t i c
c o n t r o l , w i t h v a r y i n g hea t demand i n t h e e v a p o r a t i o n p r o c e s s as a r e s u l t . I n
p r i n c i p l e , a u t o m a t i c c o n t r o l s o f t h i s k i n d need n o t be d i s c u s s e d i n g r e a t e r
d e t a i l , as t h e e n e r g y - r e l a t e d r e q u i r e m e n t s on t h e i r o p e r a t i o n a r e r a t h e r
o b v i o u s . One p o s s i b l e e x c e p t i o n i s t h e f l o w c o n t r o l , e s p e c i a l l y i n a p p l i c a t i o n s
c o n c e r n e d w i t h l a r g e f l u i d s t r e a m s . I n t h i s c a s e , t h e w o r k i n g p r i n c i p l e o f t h e
c o n t r o l module may d i r e c t l y i n f l u e n c e t h e power demand o f f l u i d pumping under
chang ing f l o w s .
C e r t a i n c o n t r o l sys tems can be r e l a t e d t o t h e e n e r g y economy because t h e y
a f f e c t p o s s i b l e f l u c t u a t i o n s o f steam and v a p o u r f l o w s i n t h e the rma l s y s t e m .
Such f l u c t u a t i o n s can i n d u c e e x t r a hea t l o s s e s c h a r a c t e r i s t i c o f t r a n s i e n t
s t a t e s o f t h e e v a p o r a t o r , w i t h a d e t r i m e n t a l e f f e c t on t h e t i m e - a v e r a g e d
e f f e c t i v e n e s s r a t i o o f t h e the rma l s y s t e m . L e t us n o t e t h a t t h e r e a r e examples
o f a u t o m a t i c c o n t r o l s m a i n l y s e r v i n g t h e p u r p o s e o f s t a b i l i z a t i o n o f f l o w s o f
p r o c e s s med ia , l i k e t h e sys tem o f c o o r d i n a t i o n o f f l o w s i n t h e j u i c e
214
p u r i f i c a t i o n s t a t i o n , o r t h e sys tem o f c o o r d i n a t i o n o f b a t c h equ ipment o p e r a t i o n
i n t he s u g a r h o u s e . A p p l i c a t i o n s o f such sys tems r e s u l t i n s t a b l e hea t demand i n
r e s p e c t i v e s e c t i o n s o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s , l e a d i n g t o r e g u l a r i z e d
e v a p o r a t o r o p e r a t i o n .
P a r t i c u l a r l y i m p o r t a n t a p p l i c a t i o n s o f a u t o m a t i c c o n t r o l a re c o n c e r n e d w i t h
p r o c e s s e s i n w h i c h t h e r e q u i r e m e n t s o f s u g a r m a n u f a c t u r e a r e l i n k e d t o g e t h e r
w i t h t h o s e o f e n e r g y economy. I t was p o i n t e d o u t i n t h e p r e c e d i n g c h a p t e r s t h a t
t h e r e q u i r e m e n t s b e l o n g i n g t o t h e s e two g r o u p s o f t e n c o n f l i c t . The way such
c o n f l i c t s a r e r e s o l v e d may d e p e n d , t o a l a r g e e x t e n t , on t h e c o n t r o l s ys tem
a p p l i e d . The a s s o c i a t e d m u l t i v a r i a b l e , m u l t i - o b j e c t i v e c o n t r o l p rob lems a r e
o f t e n v e r y d i f f i c u l t t o s o l v e , h o w e v e r . T h i s s t i m u l a t e s t h e use o f computer
t e c h n o l o g y , w h i c h i s p a r t i c u l a r l y w e l l s u i t e d t o complex c o n t r o l t a s k s .
I t can be c o n c l u d e d f rom t h e above i n t r o d u c t i o n t h a t v a r i o u s a s p e c t s o f
a u t o m a t i c c o n t r o l and v a r i o u s c o n t r o l a p p l i c a t i o n s may a f f e c t t h e e f f i c i e n c y o f
e n e r g y u t i l i z a t i o n i n a s u g a r f a c t o r y . I n t h e s u b s e q u e n t S e c t i o n s , s i x d i f f e r e n t
p rob lem a r e a s a r e d i s c u s s e d :
- deve lopment o f compu te r -based c o n t r o l s y s t e m s ;
- f l o w c o n t r o l u s i n g v a r i a b l e speed d r i v e s ;
- e x t r a c t i o n c o n t r o l ;
- e v a p o r a t i o n c o n t r o l ;
- s u g a r c r y s t a l l i z a t i o n c o n t r o l ;
- p u l p d r y i n g c o n t r o l .
6 .2 COMPUTER-BASED CONTROL SYSTEMS
I t i s c h a r a c t e r i s t i c o f c o n v e n t i o n a l c o n t r o l t e c h n o l o g y t h a t t h e app roach t o
a p p l i c a t i o n s c o n s i s t s o f i d e n t i f y i n g n e c e s s a r y c o n t r o l f u n c t i o n s and s e l e c t i n g
s u i t a b l e c o n t r o l modules w h i c h add up t o a s y s t e m . I n t h e case o f a complex
c o n t r o l t a s k , a m u l t i t u d e o f c o n t r o l modules o r a s p e c i a l i z e d c o n t r o l l e r must be
a p p l i e d . F o r t h i s r e a s o n , such t a s k s may be v e r y c o s t l y t o au tomate .
The a d v e n t o f d i g i t a l computers made i t p o s s i b l e t o change t h e c o n v e n t i o n a l
a p p r o a c h . I n s t e a d o f p e r f e c t i n g t h e sys tem by a d d i n g , each t i m e , modules f o r
a d d i t i o n a l f u n c t i o n s , a s i n g l e module - t h a t i s , t h e c e n t r a l p r o c e s s o r o f t h e
computer - can be u t i l i z e d f o r i n f o r m a t i o n p r o c e s s i n g . A l l t h e n e c e s s a r y
o p e r a t i o n s , i n c l u d i n g c o m p u t a t i o n s , a r e c a r r i e d o u t s e q u e n t i a l l y a c c o r d i n g t o
a p r e - e s t a b l i s h e d p rog ram. The speed o f t h e computer i s u s u a l l y h i g h enough t o
f o l l o w t h e e v o l u t i o n o f s i g n a l s coming f rom t h e i n s t a l l a t i o n b e i n g c o n t r o l l e d .
T h e r e a re numerous examples o f c o m p u t e r - o r m i c r o p r o c e s s o r - b a s e d sys tems
e f f e c t i v e l y r e p l a c i n g c o n v e n t i o n a l l o o p s c o n t r o l l i n g combus t i on i n b o i l e r s and
p u l p d r y i n g f u r n a c e s , d e l i v e r y o f m a t e r i a l s t o l ime k i l n s , m i l k - o f - l i m e f l o w t o
j u i c e p u r i f i c a t i o n , o p e r a t i o n o f f i l t e r s t a t i o n s , c o o r d i n a t i o n o f f l o w s i n t h e
215
m a n u f a c t u r i n g l i n e between e x t r a c t i o n and e v a p o r a t i o n , e t c . { r e f s . 2 - 9 ) .
S i g n i f i c a n t e n e r g y s a v i n g s r e s u l t i n g f rom improved c o n t r o l have been r e p o r t e d i n
some c a s e s ( r e f s . 2 , 3 , 8 ) .
Owing t o t h e deve lopment o f ha rdware and s o f t w a r e , t h e computer i s no l o n g e r
s o l e l y a d a t a p r o c e s s i n g machine b u t a l s o an e n g i n e e r i n g t o o l c a p a b l e o f
c o n t r o l l i n g complex i n s t a l l a t i o n s , as w e l l as c o l l e c t i n g d a t a f o r d i r e c t
management o f t h e p r o c e s s o r f o r t r a n s m i s s i o n t o o t h e r c o m p u t e r s . T h i s
s t i m u l a t e s n o t o n l y t he r e p l a c e m e n t o f c o n v e n t i o n a l c o n t r o l l o o p s by compu te r -
c o n t r o l l e d equ ipmen t , b u t a l s o t h e deve lopmen t o f d a t a a c q u i s i t i o n , t r a n s m i s s i o n
and p r o c e s s i n g sys tems t h a t c o u l d n o t e x i s t w i t h o u t computer t e c h n o l o g y . Two
p o s s i b l e p r i n c i p l e s o f a r c h i t e c t u r e o f complex c o m p u t e r - b a s e d c o n t r o l sys tems
a r e shown i n F i g . 6 .1 . The f u n c t i o n s o f such sys tems can be t a i l o r e d t o t h e
needs o f i n d i v i d u a l s t a t i o n s , p r o c e s s s e c t i o n s o r even an e n t i r e f a c t o r y and can
i n c l u d e a u t o m a t i c p r o c e s s c o n t r o l as w e l l as d a t a m o n i t o r i n g , p r o c e s s i n g and
r e c o r d i n g , h a n d l i n g o f a l a r m s , e t c .
(Q)
PROCESS
(b)
PROCESS
F i g . 6 .1 . Schemes o f complex c o m p u t e r - b a s e d c o n t r o l s y s t e m s : ( a ) h i e r a r c h i c a l s y s t e m , ( b ) d i s t r i b u t e d s y s t e m . 1 - s u p e r v i s o r y c o m p u t e r , 2 - dua l p r o c e s s c o n t r o l compu te r , 3 - d i s k s t o r a g e , 4 - c o n t r o l l o o p s , 5 - l o c a l c o n t r o l c o m p u t e r s , 6 - l o c a l a r e a n e t w o r k s i n c l u d i n g m u l t i p l e c o n t r o l l o o p s , 7 - i n p u t / o u t p u t i n t e r f a c e , 8 - d a t a b u s , 9 - d a t a commun ica t ion l i n k .
The impo r tance o f computer t e c h n o l o g y t o t h e d e s i g n and o p e r a t i o n o f s u g a r
f a c t o r i e s has been d i s c u s s e d e l s e w h e r e ( r e f s . 1 0 - 1 9 ) . C o n c e r n i n g e n e r g y economy,
new p o s s i b i l i t i e s o f improved e n e r g y u t i l i z a t i o n a r e d e r i v e d f rom t h e f o l l o w i n g
f e a t u r e s o f c o m p u t e r - b a s e d c o n t r o l s y s t e m s :
- i n t e g r a t i o n o f c o n t r o l o f i n d i v i d u a l s t a t i o n s , w i t h i n t e r a c t i o n s between them
taken i n t o a c c o u n t ;
216
- i n t e g r a t i o n o f management and u t i l i z a t i o n o f d a t a o r i g i n a t i n g f rom v a r i o u s
s o u r c e s , such as t h e l a b o r a t o r y , a u t o m a t i c measur ing i n s t r u m e n t s , c o u n t e r s ,
f a c t o r y r e c o r d s , e t c .
I t i s f e l t t h a t t h e s e new p o s s i b i l i t i e s have n o t y e t been f u l l y r e a l i z e d .
Examples o f t h e i r u t i l i z a t i o n a r e men t ioned i n t h e s u b s e q u e n t S e c t i o n s and i n
C h a p t e r 7.
6.3 FLOW CONTROL USING VARIABLE SPEED DRIVES
6.3.1 I n t r o d u c t i o n
I t has a l r e a d y been men t ioned i n S e c t i o n 1.4.3 t h a t t h e d r i v e s o f pumps, f a n s
and compresso rs a r e t y p i c a l l y r e s p o n s i b l e f o r abou t 60% o f t h e e l e c t r i c a l e n e r g y
consumed i n a s u g a r f a c t o r y . Among the l a r g e s t power consumers , t h e f o l l o w i n g
mach ines can be named:
- b o i l e r f e e d pumps;
- b e e t pumps;
- main j u i c e pumps i n t h e j u i c e p u r i f i c a t i o n s t a t i o n ;
- w a s t e - w a t e r pumps;
- f o r c i n g f a n s and e x h a u s t f a n s i n t h e b o i l e r h o u s e ;
- mechan ica l v a p o u r c o m p r e s s o r s ;
- a i r f a n s i n l o w - t e m p e r a t u r e p u l p d r y e r s .
As t h e p r o c e s s i n g c a p a b i l i t y o f t h e f a c t o r y o r t h e t h r o u g h p u t s o f t h e i n d i v i d u a l
s t a t i o n s v a r y , t h e f l o w s o f media d e l i v e r e d by pumps and f a n s a r e v a r i e d t o o .
T h i s i s e n s u r e d by a u t o m a t i c modules w h i c h a d j u s t t h e f l o w s t o t he r e q u i r e d
v a l u e s . W i th t h e f l o w c o n t r o l methods w i d e l y a p p l i e d , t he most economica l
o p e r a t i o n o f t h e sys tem c o m p r i s i n g t h e mach ine , i t s d r i v e and t h e c o n t r o l module
i s a c h i e v e d a t t h e maximum f l o w . A t r e d u c e d f l o w , e n e r g y d i s s i p a t i o n t a k e s p l a c e
i n t h e sys tem and t h e d r i v e consumes more power t han r e a l l y n e c e s s a r y .
U s i n g v a r i a b l e speed c o n t r o l , t h e power consumed by t he d r i v e o f a pump o r
a f a n can be m i n i m i z e d f o r any f l o w v a l u e . The a t t a i n a b l e s a v i n g depends on t h e
c o n t r o l method r e p l a c e d ; t y p i c a l l y , i t i s o f t h e o r d e r o f 20-40% o f t h e
e l e c t r i c a l e n e r g y consumed by t h e d r i v e d u r i n g t h e e n t i r e o p e r a t i o n .
6 .3 .2 Pump d r i v e s
The t a s k o f t h e pump a t a g i v e n l i q u i d f l o w i s t o g e n e r a t e a p r e s s u r e h i g h
enough t o overcome the p r e s u r e l o s s i n t h e h y d r a u l i c sys tem t o w h i c h t h e l i q u i d
i s d e l i v e r e d . The p r e s s u r e l o s s i s an a p p r o x i m a t e l y q u a d r a t i c f u n c t i o n o f t h e
f l o w , w h i l e t h e p r e s s u r e g e n e r a t e d by a r o t o d y n a m i c pump a t a c o n s t a n t r a t e o f
r e v o l u t i o n depends on t h e f l o w , a c c o r d i n g t o t h e pump c h a r a c t e r i s t i c s .
C o n s e q u e n t l y , t h e p r e s s u r e e q u i l i b r i u m between an u n c o n t r o l l e d pump and t h e
h y d r a u l i c sys tem i s o b t a i n e d a t a d e f i n i t e f l o w v a l u e , as shown i n F i g . 6 . 2 .
When the r e q u i r e d f l o w d e v i a t e s f rom t h e e q u i l i b r i u m v a l u e , i t i s n e c e s s a r y t o
217
Flow ( k g / s )
F i g . 6 . 2 . Pump c h a r a c t e r i s t i c s ( 1 ) and p r e s s u r e l o s s i n a h y d r a u l i c sys tem ( 2 ) . Hs - s t a t i c h e a d , - dynamic h e a d , Η - e f f e c t i v e h e a d , G - e q u i l i b r i u m f l o w . Dashed l i n e s i n d i c a t e pump c h a r a c t e r i s t i c s a t d i f f e r e n t r a t e s o f r e v o l u t i o n .
overcome the mismatch between t h e c h a r a c t e r i s t i c s o f t h e pump and t h a t o f t h e
h y d r a u l i c s y s t e m .
U s i n g a b y - p a s s c o n t r o l , a d i f f e r e n c e i s c r e a t e d between t h e f l o w o f l i q u i d
p a s s i n g t h r o u g h t h e pump and t h e f l o w o f t h e l i q u i d d e l i v e r e d t o t h e s y s t e m .
The pump i s o p e r a t e d a t a f l o w l a r g e r than r e a l l y n e e d e d , and t h e e x c e s s l i q u i d
i s r e c i r c u l a t e d t o t h e s u c t i o n n o z z l e . T h i s i s accompanied by e n e r g y d i s s i p a t i o n
i n t he b y - p a s s v a l v e . The power consumed by t h e pump d r i v e can be e x p r e s s e d as
= ( G ^ + G ^ ) g H / n b = N^,^ + ( 6 . 1 )
where G^ i s t h e mass f l o w o f l i q u i d d e l i v e r e d t o t h e h y d r a u l i c s y s t e m , G^ i s t h e
mass f l o w o f r e c i r c u l a t e d l i q u i d , g i s t h e a c c e l e r a t i o n o f g r a v i t y , Η i s t h e
e f f e c t i v e pump h e a d , x]^ i s t h e pump e f f i c i e n c y , i s t h e power consumed t o
d e l i v e r t h e f l o w o f l i q u i d r e a l l y n e e d e d , and i s t h e power l o s t by l i q u i d
r e c i r c u l a t i o n .
A method w h i c h i s by f a r t h e most p o p u l a r i n t h e s u g a r i n d u s t r y c o n s i s t s o f
f l o w c o n t r o l by t h r o t t l i n g . U s i n g a t h r o t t l i n g v a l v e i n s t a l l e d between t h e
d i s c h a r g e n o z z l e o f t he pump and t h e h y d r a u l i c s y s t e m , t h e dynamic head can be
changed and t h u s a d i f f e r e n c e can be c r e a t e d between t h e p r e s s u r e g e n e r a t e d by
t he pump and t he p r e s s u r e a t t h e sys tem i n l e t . The pump i s o p e r a t e d a t an
e f f e c t i v e head l a r g e r t han r e a l l y n e e d e d , w h i c h i s accompanied by e n e r g y
d i s s i p a t i o n i n t h e t h r o t t l i n g v a l v e . The power consumed by t h e pump d r i v e can be
e x p r e s s e d as
\ = G^g (H + H ^ / n ^ = N^^ + ( 6 . 2 )
where i s t h e e f f e c t i v e head l o s t by t h r o t t l i n g , i s t h e pump e f f i c i e n c y ,
N^^ i s t he power consumed t o d e l i v e r mass f l o w G ^ a t e f f e c t i v e head H , and N-j i s
t he power l o s t by t h r o t t l i n g . I t s h o u l d be n o t e d t h a t i s d i f f e r e n t f rom τ]^
because t h e pump i s o p e r a t e d a t a n o t h e r r e g i o n o f i t s c h a r a c t e r i s t i c s .
T y p i c a l l y , t h e e f f i c i e n c y o f a r o t o d y n a m i c pump o p e r a t e d a t c o n s t a n t speed
218
d e c r e a s e s when moving away f rom t h e nominal o p e r a t i n g c o n d i t i o n s , t h i s
c o n t r i b u t i n g t o t he e n e r g y d i s s i p a t i o n i n d u c e d by t h e t h r o t t l i n g c o n t r o l .
The e n e r g y d i s s i p a t i o n e f f e c t s c h a r a c t e r i s t i c o f t h e f l o w c o n t r o l methods
d i s c u s s e d above can be e l i m i n a t e d by u s i n g a v a r i a b l e speed c o n t r o l . I t s
p r i n c i p l e can be seen i n F i g . 6 . 2 , where pump c h a r a c t e r i s t i c s c o r r e s p o n d i n g t o
d i f f e r e n t speeds a r e i n d i c a t e d by dashed l i n e s . By v a r y i n g t h e r e v o l u t i o n r a t e
o f t h e pump i m p e l l e r , t he e f f e c t i v e pump head can be n e a r l y i d e a l l y a d j u s t e d t o
t h e c h a r a c t e r i s t i c s o f t he h y d r a u l i c s y s t e m . C o n s e q u e n t l y , t h e pump d r i v e
consumes o n l y as much power as r e a l l y needed t o d e l i v e r t h e r e q u i r e d f l o w o f t h e
l i q u i d . A n o t h e r advan tage o f a v a r i a b l e r e v o l u t i o n speed i s t h a t t h e e f f i c i e n c y
o f t h e pump d e v i a t e s o n l y n e g l i g i b l y f rom i t s maximum v a l u e . A compar i son o f
power consumpt ion f o r v a r i a b l e speed c o n t r o l and t h r o t t l i n g c o n t r o l i s shown i n
F i g . 6 . 3 .
100
- 80 c
o I 60 3 § AO
20
0 20 AO 60 80 100 Flow ( 7 · )
F i g . 6 . 3 . Power consumed by a pump d r i v e a t v a r i a b l e f l o w . 1 - c o n t r o l by t h r o t t l i n g , 2 - v a r i a b l e speed c o n t r o l .
I n a s p e c i f i c a p p l i c a t i o n , t he e n e r g y s a v i n g w h i c h can be a t t a i n e d by u s i n g
v a r i a b l e speed c o n t r o l depends on t h e l o a d c h a r a c t e r i s t i c s o f t h e pump. The
f e a s i b i l i t y o f t he method i s a m a t t e r o f e c o n o m i c s , as t h e v a l u e o f e n e r g y saved
s h o u l d be we ighed a g a i n s t t h e i n c r e a s e d i n v e s t m e n t c o s t o f t h e d r i v e ( r e f . 2 0 ) .
6 .3 .3 Fan d r i v e s
The f l o w o f gas d e l i v e r e d by a f a n can a l s o be v a r i e d by u s i n g a b y - p a s s o r
t h r o t t l i n g c o n t r o l a c c o r d i n g t o t h e p r i n c i p l e s d i s c u s s e d i n t h e p r e c e d i n g
S e c t i o n ; one p o s s i b l e d i f f e r e n c e i s t h a t t h e t h r o t t l i n g v a l v e can be i n s t a l l e d
i n t h e s u c t i o n l i n e o f t h e f a n . A n o t h e r c o n t r o l method used i n c o n n e c t i o n w i t h
l a r g e - c a p a c i t y f a n s o p e r a t e d a t c o n s t a n t speed employs t h e p o s i t i o n i n g o f i n l e t
219
g u i d e vanes f o r a v a r i a b l e p e r i p h e r a l component o f t h e gas v e l o c i t y a t i n l e t .
A c c o r d i n g t o E u l e r ' s pump and t u r b i n e e q u a t i o n , t h e t h e o r e t i c a l head can be
e x p r e s s e d as
"2 "2u l ^ l u ^ ( 6 . 3 )
where u i s t h e v e l o c i t y o f t r a n s p o r t a t i o n a t t h e mean r o t o r d i a m e t e r , c^ i s
t h e p e r i p h e r a l component o f t h e gas v e l o c i t y , and t h e s u b s c r i p t s deno te 1 -
i n l e t and 2 - o u t l e t ; g i s t h e a c c e l e r a t i o n o f g r a v i t y .
As can be s e e n , t he t h e o r e t i c a l head - and t h u s t h e e f f e c t i v e head t o o - v a r i e s
as c ^^ i s v a r i e d . When t h e a n g l e o f i n c l i n a t i o n o f t h e i n l e t g u i d e vanes i s
changed , t he gas f l o w e n t e r i n g t h e f a n r o t o r i s a l s o c h a n g e d . T h i s c o n t r o l
method i s more economica l t han c o n t r o l by t h r o t t l i n g , p a r t i c u l a r l y a t f l o w s
s m a l l e r t han 70-75% o f t h e maximum v a l u e .
S i m i l a r l y t o t h e case o f t h e pump, h o w e v e r , i t i s v a r i a b l e speed c o n t r o l
w h i c h e n s u r e s t h e most e n e r g y - e f f i c i e n t f a n o p e r a t i o n . A compar i son o f power
consumpt ion c u r v e s r e p r e s e n t i n g t h r e e d i f f e r e n t c o n t r o l methods i s shown i n
F i g . 6 . 4 . O b v i o u s l y , t h e f e a s i b i l i t y o f v a r i a b l e speed c o n t r o l i n a s p e c i f i c f a n
a p p l i c a t i o n depends on economic f a c t o r s ( r e f . 2 0 ) .
20 40 60 Flow ( " /«)
80 100
F i g . 6 . 4 . Power consumed by a f a n d r i v e a t v a r i a b l e f l o w . 1 - c o n t r o l by t h r o t t l i n g , 2 - p o s i t i o n i n g o f i n l e t g u i d e v a n e s , 3 - v a r i a b l e s p e e d .
6.4 EXTRACTION CONTROL
The dynamic r e s p o n s e o f t h e e x t r a c t i o n p r o c e s s p e r f o r m e d i n c o n t e m p o r a r y
c o n t i n u o u s e x t r a c t o r s i s v e r y s l o w . U s i n g c o n v e n t i o n a l c o n t r o l c i r c u i t s , t h e
t ime span between s e t - p o i n t a d j u s t m e n t and a t t a i n m e n t o f a d e s i r e d r e s u l t i s o f
t h e o r d e r o f s e v e r a l h o u r s . M a i n l y f o r t h i s r e a s o n , a human o p e r a t o r i s o f t e n
unab le t o c o n t r o l t h e e x t r a c t i o n p r o c e s s v e r y e f f e c t i v e l y , a l t h o u g h good r e s u l t s
can c e r t a i n l y be a c h i e v e d by e x p e r i e n c e d p e r s o n n e l . I f a d i s t u r b a n c e , such as
t o o l a r g e a j u i c e d r a f t , i s d e t e c t e d , t h e n s e v e r a l h o u r s may be needed t o b r i n g
t he s i t u a t i o n back t o n o r m a l . I n t h e meant ime, t h e f a c t o r y must be o p e r a t e d
220
under abnormal c o n d i t i o n s i n d u c i n g an e x c e s s i v e h e a t c o n s u m p t i o n .
E f f e c t i v e e x t r a c t i o n c o n t r o l can be e n s u r e d i f t h e c o n v e n t i o n a l c o n t r o l l e r s
a r e r e p l a c e d by a compu te r -based c o n t r o l s y s t e m . T h i s makes i t p o s s i b l e t o
m o n i t o r t h e t r e n d s o f pa rame te rs measured and t o employ c o n t r o l a l g o r i t h m s
p r e v e n t i n g u n d e s i r a b l e s i t u a t i o n s . The s t a b i l i z a t i o n o f e x t r a c t i o n pa rame te r s
f a c i l i t a t e s e f f i c i e n t e n e r g y usage i n t h e e n t i r e s u g a r m a n u f a c t u r i n g p r o c e s s .
I f a d i s t u r b a n c e o c c u r s , t h e computer i s a b l e t o r e s t o r e t h e d e s i r e d paramete r
reg ime more q u i c k l y than a human o p e r a t o r .
V a r i o u s e x t r a c t o r t y p e s men t ioned i n S e c t i o n 5.2 r e q u i r e d i f f e r e n t app roaches
t o t h e i r c o n t r o l . The e s s e n t i a l f e a t u r e s o f c o n t r o l sys tems used i n c o n n e c t i o n
w i t h t o w e r , drum and m o v i n g - b e d e x t r a c t o r s have been p r e s e n t e d i n t h e l i t e r a t u r e
( r e f s . 1 4 , 2 1 , 2 2 ) . C o n t r o l o f t h e t r o u g h e x t r a c t o r i s p a r t i c u l a r l y s i m p l e , and
can be summarized he re f o r i l l u s t r a t i o n p u r p o s e s . An o u t l i n e o f a t r o u g h
e x t r a c t o r , w i t h i n d i c a t i o n s o f t h e measured and c o n t r o l l e d p a r a m e t e r s , i s g i v e n
i n F i g . 6 .5 . The i n p u t s a r e as f o l l o w s ( r e f . 6 ) :
- l e v e l s i n b e e t s i l o ;
- b e l t w e i g h e r on b e l t f o r c o s s e t t e s ;
- c o s s e t t e s l e v e l a t j u i c e e n d ;
- 4 b u b b l e - t u b e l e v e l s a t i n t e r m e d i a t e p o i n t s i n t h e t r o u g h ;
- f r e s h - w a t e r f l o w ;
- p r e s s - w a t e r f l o w ;
- l e v e l i n p r e s s - w a t e r t a n k .
The e s s e n t i a l t a s k o f t he c o n t r o l sys tem i s t o keep t h e l e v e l o f t h e c o s s e t t e s
Speed control of slicing machines
Speed control of h e l i c e s ^
^ Θ— Juice flow control
Press water and fresh water flow control
Temperature control
F i g . 6 . 5 . Work ing p r i n c i p l e o f t h e a u t o m a t i c c o n t r o l o f a t r o u g h e x t r a c t o r ( a f t e r r e f . 6 ) . P o i n t s o f measurements : C - r a t e o f d e l i v e r y o f c o s s e t t e s , L0 -L6 - l e v e l s , T 0 - T 5 - t e m p e r a t u r e s , F l and F2 - f l o w s .
221
i n t he e x t r a c t o r s a t i s f a c t o r y under a l l c o n d i t i o n s . I n a d d i t i o n , t h e computer
t a k e s c a r e o f t h e t e m p e r a t u r e c o n t r o l , as w e l l as o f t h e s t a r t - u p and s h u t - d o w n
p r o c e d u r e s , i n c l u d i n g s t a r t i n g and s t o p p i n g o f a l l m o t o r s , open ing and c l o s i n g
o f main v a p o u r v a l v e , e t c .
The computer can a l s o be c h a r g e d w i t h d r a f t o p t i m i z a t i o n . T h i s p rob lem
o r i g i n a t e s f rom t h e f a c t t h a t t h e d r a f t and t he s u g a r l o s s i n e x h a u s t e d
c o s s e t t e s a r e i n t e r r e l a t e d . The i n f l u e n c e o f t h e d r a f t on e n e r g y demand can be
c a l c u l a t e d f rom t h e e v a p o r a t o r hea t b a l a n c e . The s u g a r c o n c e n t r a t i o n i n
e x h a u s t e d c o s s e t t e s can be e x p r e s s e d u s i n g S i l i n ' s f o r m u l a
b^ = ( ( a - l ) b ^ / ( a e x p ( ( ( a - 1 ) / a ) ( A T L x / y ) ) - 1) ( 6 . 4 )
where a i s t h e j u i c e d r a f t , b^ i s t h e s u g a r c o n c e n t r a t i o n i n t h e incoming
c o s s e t t e s , A i s a c h a r a c t e r i s t i c c o n s t a n t , Τ i s t h e a b s o l u t e t e m p e r a t u r e , L i s
t he l e n g t h o f 100 g c o s s e t t e s , τ i s t h e e x t r a c t i o n t i m e , and μ i s t h e j u i c e
v i s c o s i t y .
F o r g i v e n p r i c e s o f s u g a r and f u e l , i t t h u s becomes p o s s i b l e t o e x p r e s s t h e
v a l u e o f s u g a r l o s t i n e x h a u s t e d c o s s e t t e s , and t h e v a l u e o f t h e n e c e s s a r y
e n e r g y i n p u t , as f u n c t i o n s o f t he j u i c e d r a f t . T h i s makes i t p o s s i b l e t o
d e t e r m i n e t h e op t ima l d r a f t v a l u e .
A more r e l i a b l e d e t e r m i n a t i o n o f t h e s u g a r l o s s can be a c h i e v e d u s i n g o n - l i n e
measurements o f t h e s u g a r c o n t e n t o f t h e p r e s s w a t e r . Examples a r e a l s o known o f
t h e a p p l i c a t i o n s o f i n d u s t r i a l r e f r a c t o m e t e r s w i t h a u t o m a t i c j u i c e samp l i ng f o r
o n - l i n e measurements o f t h e j u i c e c o n c e n t r a t i o n . F u r t h e r m o r e , t h e o p t i m i z a t i o n
model can be e x t e n d e d t o i n c o r p o r a t e t h e consequences o f t h e e x t r a c t i o n o f
n o n s u g a r s , by p r e d i c t i n g t h e d i s t r i b u t i o n o f t h e e x t r a c t e d s u g a r between w h i t e
s u g a r and m o l a s s e s . I n t h i s c a s e , t h e op t ima l d r a f t depends a l s o on t h e p r i c e o f
m o l a s s e s .
Summaries o f o p e r a t i o n a l r e s u l t s o b t a i n e d w i t h c o m p u t e r - b a s e d e x t r a c t i o n
c o n t r o l can be f o u n d i n t h e l i t e r a t u r e ( r e f s . 2 1 , 2 3 ) . The r e p o r t e d r e d u c t i o n s o f
t h e j u i c e d r a f t a r e o f t h e o r d e r o f 1-2%.
6.5 EVAPORATION CONTROL
I t f o l l o w s f rom t h e c h a r a c t e r i s t i c s o f t h e the rma l sys tem t h a t two a s p e c t s o f
a u t o m a t i c e v a p o r a t i o n c o n t r o l a r e p a r t i c u l a r l y i m p o r t a n t t o t h e e n e r g y economy,
namely e f f e c t i v e s t a b i l i z a t i o n o f t h e c o n c e n t r a t i o n o f t h i c k j u i c e , and
e f f e c t i v e s t a b i l i z a t i o n o f v a p o u r p r e s s u r e s i n t h e i n d i v i d u a l e v a p o r a t o r
e f f e c t s . As p o i n t e d o u t by Z a g r o d z k i t h r e e decades ago ( r e f . 2 4 ) , p r e s s u r e
s t a b i l i z a t i o n i n t h e e f f e c t f rom w h i c h v a p o u r i s w i t h d r a w n f o r vacuum-pan
h e a t i n g i s a d e c i s i v e f a c t o r i n e n s u r i n g s t a b l e e v a p o r a t o r o p e r a t i o n .
O t h e r c o n t r o l r e q u i r e m e n t s a r e l i n k e d t o t h e c h a r a c t e r i s t i c f e a t u r e s o f t h e
m u l t i p l e - e f f e c t e v a p o r a t o r s t a t i o n . I t i s e s s e n t i a l t o e n s u r e economica l
222
Operation o f t he ind iv idua l e f f e c t s , t h a t i s , t o maintain optimal c o n d i t i o n s f o r
hea t t r a n s f e r and t o m in im i ze s u c r o s e d e c a y . C o n c e r n i n g t h e p r o c e s s d y n a m i c s ,
f l e x i b l e a d a p t a t i o n o f t h e e v a p o r a t i n g c a p a c i t y o f t h e e n t i r e s t a t i o n t o
changes i n t h e f l o w o f t h i n j u i c e e n t e r i n g t h e e v a p o r a t o r i s p r i m a r i l y r e q u i r e d .
When p e r f o r m i n g t he n e c e s s a r y f u n c t i o n s , t h e a u t o m a t i c c o n t r o l sys tem s h o u l d
be a b l e t o e l i m i n a t e d i s t u r b a n c e s r e s u l t i n g f rom f l u c t u a t i o n s o f t h e f o l l o w i n g
q u a n t i t i e s :
- t h i n j u i c e f l o w and c o n c e n t r a t i o n ;
- j u i c e l e v e l s i n t h e e v a p o r a t o r b o d i e s ;
- h e a t i n g v a p o u r demand ( e s p e c i a l l y v a p o u r w i t h d r a w n f o r vacuum-pan h e a t i n g ) .
To t h e g e n e r a l r e q u i r e m e n t s l i s t e d a b o v e , v a r i o u s e x t e n s i o n s can be added
depend ing on t h e t y p e o f e v a p o r a t o r emp loyed . F o r examp le , t h e R o b e r t t y p e and
f a l l i n g - f i l m e v a p o r a t o r s a r e p r e f e r a b l y f e e d - c o n t r o l l e d , w h i l e t h e c l i m b i n g - f i l m
e v a p o r a t o r must be p r o v i d e d w i t h a h y d r a u l i c s e a l a t t h e o u t l e t , t h i s i m p l y i n g
d i s c h a r g e c o n t r o l . M o r e o v e r , owing t o t h e d i f f e r e n c e s i n j u i c e vo lumes
c o n t a i n e d , t h e dynamic r e s p o n s e o f t h e t h i n - f i l m e v a p o r a t o r s i s s e v e r a l t imes
f a s t e r t han t h a t o f t h e R o b e r t e v a p o r a t o r s .
The m u l t i t u d e o f r e q u i r e m e n t s c h a r a c t e r i z i n g v a r i o u s e v a p o r a t o r s t a t i o n s can
be met o n l y by a p p l y i n g v a r i o u s c o n t r o l s y s t e m s . T y p i c a l s o l u t i o n s a r e r e v i e w e d
e l s e w h e r e ( r e f s . 2 5 - 2 7 ) . The p r o c e s s e s t o be c o n t r o l l e d a r e v e r y comp lex ,
h o w e v e r , as t h e y c o n s i s t o f i n t e r r e l a t e d r a p i d phenomena o f h e a t t r a n s f e r and
r e l a t i v e l y s l o w phenomena o f mass t r a n s f e r . F o r t h i s r e a s o n , i t may be d i f f i c u l t
t o a t t a i n s a t i s f a c t o r y r e s u l t s w i t h t y p i c a l c o n t r o l s y s t e m s , and t h e v a r i a t i o n s
f ound i n p r a c t i c e seem t o be i n f i n i t e . T h i s can be e x e m p l i f i e d by a u t o m a t i c
c o n t r o l o f t h e c o n c e n t r a t i o n o f t h i c k j u i c e . Fou r d i f f e r e n t s o l u t i o n s a r e shown
s c h e m a t i c a l l y i n F i g . 6 . 6 . The sys tems under ( a ) , ( b ) and ( c ) a r e t o o p r i m i t i v e
t o p e r f o r m s a t i s f a c t o r i l y under a l l c o n d i t i o n s . B e t t e r r e s u l t s can be o b t a i n e d
w i t h t he f o u r t h s y s t e m , i n w h i c h t h e f l o w o f v a p o u r f rom t h e l a s t e v a p o r a t o r
e f f e c t i s measured and compared w i t h t h e r e q u i r e d v a l u e d e t e r m i n e d on t h e b a s i s
o f measurements o f j u i c e fow and c o n c e n t r a t i o n b e f o r e t h e l a s t e f f e c t . T h i s
p r i n c i p l e can be a l s o m o d i f i e d by i n t r o d u c i n g a c o r r e c t i o n o f t h e r e q u i r e d
v a p o u r f l o w depend ing on t h i c k - j u i c e c o n c e n t r a t i o n measured .
I t may be added t h a t even more complex sys tems o f s t a b i l i z a t i o n o f t h i c k -
j u i c e c o n c e n t r a t i o n a r e e n c o u n t e r e d i n p r a c t i c e . A t r e q u i r e d c o n c e n t r a t i o n
v a l u e s a p p r o a c h i n g 75% DS, due w e i g h t s h o u l d be g i v e n t o t h e s a f e t y r e q u i r e m e n t
c o n c e r n e d w i t h t h e r i s k o f t h i c k j u i c e becoming s u p e r s a t u r a t e d . As t h e s t a t e o f
s a t u r a t i o n depends on j u i c e t e m p e r a t u r e , a d d i t i o n a l measurements become
n e c e s s a r y and e x t e n d e d d e c i s i o n - m a k i n g must be i n c l u d e d i n t h e c o n t r o l
a l g o r i t h m .
A l t h o u g h good r e s u l t s can be o b t a i n e d u s i n g c o n v e n t i o n a l e v a p o r a t o r c o n t r o l .
223
(α)
to condenser
η -βίο) to condenser
F i g . 6 .6 . P o s s i b l e s o l u t i o n s o f t h e a u t o m a t i c c o n t r o l o f t h i c k - j u i c e c o n c e n t r a t i o n : ( a ) t h i c k - j u i c e r e c i r c u l a t i o n , ( b ) t h i n - j u i c e b y - p a s s , ( c ) v a r i a b l e p r e s s u r e i n t h e l a s t e v a p o r a t o r e f f e c t , ( d ) v a r i a b l e v a p o u r f l o w f rom n e x t t o t h e l a s t e f f e c t t o t h e c o n d e n s e r . D, F - measurements o f d e n s i t y and f l o w , r e s p e c t i v e l y ; R, C - r e g i s t r a t i o n and c o n t r o l , r e s p e c t i v e l y ; U F , FFRC - e lements r e s p o n s i b l e f o r t h e c o m p u t a t i o n o f r e q u i r e d f l o w v a l u e and t he compar i son between a c t u a l and r e q u i r e d f l o w v a l u e s , r e s p e c t i v e l y .
224
t h e above example can be seen as an i n d i c a t i o n o f t he f a c t t h a t e f f e c t i v e
c o n t r o l a l g o r i t h m s must be q u i t e c o m p l i c a t e d , and t h e i r i m p l e m e n t a t i o n u s i n g
c o n v e n t i o n a l c o n t r o l t e c h n o l o g y may be r a t h e r c o s t l y . F o r t h i s r e a s o n , c o m p u t e r -
based e v a p o r a t o r c o n t r o l i s now g a i n i n g p o p u l a r i t y ( r e f s . 1 , 3 , 1 4 , 2 2 ) . A s o l u t i o n
r e c e n t l y implemented i n a s e x t u p l e - e f f e c t e v a p o r a t o r can be c i t e d as an example
( r e f . 2 8 ) . The f u n c t i o n s pe r f o rmed by t h e computer p rogram a r e l o g i c a l l y d i v i d e d
i n t o t h r e e modu les .
( i ) P r e s s u r e c o n t r o l .
( i i ) S u p p r e s s i o n o f f l u c t u a t i o n s o f j u i c e c o n c e n t r a t i o n .
( i i i ) S t a b i l i z a t i o n o f t h i c k - j u i c e c o n c e n t r a t i o n a t a p r e d e t e r m i n e d l e v e l .
The l o c a t i o n s o f t h e c o n t r o l v a l v e s i n t h e e v a p o r a t o r scheme and t h e p o i n t s o f
measurement o f t h e e s s e n t i a l v a r i a b l e s a r e shown s c h e m a t i c a l l y i n F i g . 6 . 7 .
Module ( i ) i s r e s p o n s i b l e f o r a d j u s t m e n t s o f t h e p o s i t i o n o f t h e b y - p a s s v a l v e
between f i r s t - and f o u r t h - e f f e c t v a p o u r , as w e l l as o f t h e p o s i t i o n s o f t h e
v a l v e s on v a p o u r l i n e s c o n n e c t e d t o t h e c o n d e n s e r . Module ( i i ) a d j u s t s t h e
p o s i t i o n o f t he v a l v e c o n t r o l l i n g t h i n - j u i c e f l o w t o t h e i n l e t o f t h e f o u r t h
e f f e c t . The t h i r d module c o n t r o l s t h e b y - p a s s f l o w o f f o u r t h - t o s i x t h - e f f e c t
v a p o u r and t he f l o w o f s i x t h - e f f e c t v a p o u r t o t h e c o n d e n s e r . I f t h e
c o n c e n t r a t i o n o f t h i c k j u i c e t e n d s t o be t o o l o w , t h e b y - p a s s v a l v e c l o s e s and
t h e v a p o u r f l o w t o t h e c o n d e n s e r i s i n c r e a s e d . I n t h e o p p o s i t e c a s e , t h e b y - p a s s
f l o w i s i n c r e a s e d , t h i s be ing e q u i v a l e n t t o " n e g a t i v e c o n d e n s a t i o n " o f s i x t h -
e f f e c t v a p o u r .
I n t o t a l , t h e sys tem u t i l i z e s 28 ana log i n p u t s ( f l o w s , p r e s s u r e s and
c o n c e n t r a t i o n s ) , 6 b i n a r y i n p u t s ( s t a t e o f a c t i v a t i o n o f c o n t r o l f u n c t i o n s ) and
6 ana log o u t p u t s ( v a r i a b l e s c o n t r o l l e d ) .
thin juice
1 2 3 U 5 6
lb
to ^^condenser
thick juice
F i g . 6 . 7 . Work ing p r i n c i p l e o f t h e a u t o m a t i c c o n t r o l o f a s e x t u p l e - e f f e c t e v a p o r a t o r ( a f t e r r e f . 2 8 ) . P o i n t s o f measurement : a -d - f l o w s , e and f -c o n c e n t r a t i o n s , g - j - p r e s s u r e s .
225
6.6 SUGAR CRYSTALL IZAT ION CONTROL
6.6.1 I n t r o d u c t i o n
The use o f a u t o m a t i c c o n t r o l i n t he s u g a r house was i n i t i a l l y s t i m u l a t e d by
t he r e q u i r e m e n t s o f s u g a r q u a l i t y , r e q u i r i n g r e p r o d u c i b l e r e s u l t s o f t h e
c r y s t a l l i z a t i o n p r o c e s s . R i s i n g e n e r g y c o s t s e x p o s e d t h e s i g n i f i c a n c e o f c o n t r o l
methods f o r i n c r e a s i n g t he e f f i c i e n c y o f e n e r g y u t i l i z a t i o n . The f o l l o w i n g
f a c t o r s a s s o c i a t e d w i t h t h e q u a l i t y o f p r o c e s s c o n t r o l a r e p a r t i c u l a r l y
i m p o r t a n t :
- e f f e c t i v e s t a b i l i z a t i o n o f p r o c e s s p a r a m e t e r s ;
- e x a c t d i s t r i b u t i o n o f mass f l o w s i n t h e c r y s t a l l i z a t i o n scheme;
- smooth w i t h d r a w a l o f h e a t i n g v a p o u r s f rom t h e e v a p o r a t o r s t a t i o n ;
- e n e r g y - e f f i c i e n t s u g a r b o i l i n g i n vacuum p a n s .
P r a c t i c a l e x p e r i e n c e p r o v e d t h a t good r e s u l t s can be a t t a i n e d i f a t w o - l e v e l
approach t o t h e c o n t r o l o f t h e s u g a r house i s a d o p t e d . The l o w e r l e v e l i n c l u d e s
t h e c o n t r o l l e r s o f t h e i n d i v i d u a l equ ipment u n i t s , w h i l e t h e upper l e v e l i s
c r e a t e d t o e n s u r e t h e c o o r d i n a t i o n o f i n t e r r e l a t e d p r o c e s s e s . A n o t h e r p r a c t i c a l
c o n c l u s i o n i s t h a t t h e c o m p l e x i t y o f c o n t r o l a l g o r i t h m s j u s t i f i e s t h e use o f
compu te r -based c o n t r o l s y s t e m s .
A p r e r e q u i s i t e f o r t h e e f f e c t i v e n e s s o f s u g a r house c o n t r o l i s t h e
s t a b i l i z a t i o n o f p r o c e s s i n p u t s . I n c o n t e m p o r a r y s u g a r f a c t o r i e s o p e r a t e d a t
t h i c k - j u i c e c o n c e n t r a t i o n s a p p r o a c h i n g 75% DS, t h e s t a b i l i z a t i o n o f pa rame te rs
o f t h e t h i c k j u i c e and s y r u p s becomes c r i t i c a l . I n o r d e r t o e n s u r e r e p r o d u c i b l e
r e s u l t s o f f e e d i n t a k e s t o t h e vacuum pans and t o r e d u c e t h e amount o f w a t e r
drawn f o r c o n t r o l p u r p o s e s , t h e r i s k o f u n d e s i r a b l e c r y s t a l f o r m a t i o n s h o u l d be
e l i m i n a t e d . As t h e s t a t e o f s a t u r a t i o n depends a l s o on s o l u t i o n t e m p e r a t u r e ,
t h i s i s no l o n g e r o n l y a q u e s t i o n o f c o n t r o l l i n g t h e c o n c e n t r a t i o n .
The t h i c k - j u i c e pa rame te rs can be s t a b i l i z e d i n a c o n d i t i o n e r shown
s c h e m a t i c a l l y i n F i g . 6 .8 . The j u i c e l e a v i n g t h e e v a p o r a t o r i s expanded i n a
v e s s e l i n s t a l l e d b e f o r e t h e t h i c k - j u i c e t a n k . The r e q u i r e d j u i c e t e m p e r a t u r e i s
m a i n t a i n e d by c o n t r o l l i n g t he p r e s s u r e . The v e s s e l i s a l s o l e v e l - c o n t r o l l e d . I f
t he s e l f - e v a p o r a t i o n o f t h i c k j u i c e i n c r e a s e s t h e c o n c e n t r a t i o n above t h e
r e q u i r e d v a l u e , t h e n t h e o u t l e t s t ream i s d i l u t e d w i t h t h i n j u i c e .
6 .6 .2 Sugar b o i l i n g
The e s s e n t i a l p a r t o f t h e hea t consumed i n t h e b a t c h vacuum pan i s needed t o
e v a p o r a t e w a t e r f rom s u g a r s o l u t i o n . I n t h e f i r s t phase o f t h e b o i l i n g c y c l e ,
t h e i n i t i a l l y drawn s o l u t i o n i s t h i c k e n e d i n o r d e r t o a t t a i n t h e r e q u i r e d
s u p e r s a t u r a t i o n . I n t h e r e m a i n i n g p h a s e s , w a t e r i n s u g a r s o l u t i o n s o r , i n some
i n s t a n c e s , pu re w a t e r i s drawn t o t h e vacuum pan f o r c o n t r o l p u r p o s e s . Water
i n t a k e s immed ia te l y a f t e r s e e d i n g a r e r e q u i r e d t o s t a b i l i z e t h e s u p e r s a t u r a t i o n .
226
to condenser
to sugar house
F i g . 6 . 8 . Scheme o f a u t o m a t i c t h i c k - j u i c e c o n d i t i o n i n g . 1 - c o n d i t i o n i n g v e s s e l , 2 - t h i c k - j u i c e t a n k . P, L , D - p r e s s u r e , l e v e l and d e n s i t y , r e s p e c t i v e l y ; I , C - i n d i c a t i o n and c o n t r o l , r e s p e c t i v e l y .
L a t e r o n , c r y s t a l g r o w t h i s a s s o c i a t e d w i t h t h e need t o draw w a t e r m a i n t a i n i n g
t he b a l a n c e between e v a p o r a t i o n and c r y s t a l l i z a t i o n . F i n a l l y , w a t e r may be drawn
i n o r d e r t o keep t h e s t r i k e b e f o r e i t i s d i s c h a r g e d .
The impor tance o f an a u t o m a t i c b o i l i n g c o n t r o l t o e f f i c i e n t e n e r g y
u t i l i z a t i o n l i e s i n e l i m i n a t i n g t h e i n f l u e n c e o f i n d e t e r m i n i s t i c f a c t o r s -
a s s o c i a t e d w i t h t he i n t e r v e n t i o n s o f a human o p e r a t o r - on t h e amount o f w a t e r
drawn and t h u s on e n e r g y s p e n t d u r i n g t h e b o i l i n g c y c l e . The e s s e n t i a l f u n c t i o n s
o f c o n t e m p o r a r y a u t o m a t i c c o n t r o l s can be summarized as f o l l o w s ( r e f s . 2 9 - 3 5 ) .
( i ) C o n t i n u o u s measur ing o f t h e s y r u p and m a s s e c u i t e l e v e l s f o r a u t o m a t i c
c h a r g i n g , a u t o m a t i c t h i c k e n i n g and a u t o m a t i c change o f f e e d s u p p l y , vacuum and
h e a t i n g v a p o u r s u p p l y .
( i i ) C o n t i n u o u s c o n t r o l o f s u p e r s a t u r a t i o n , u s u a l l y by measur ing t h e d i e l e c t r i c
v a l u e o r c o n d u c t i v i t y o f t h e m a s s e c u i t e .
( i i i ) C o n t i n u o u s c o n t r o l o f t he vacuum l e v e l i n t h e p a n .
( i v ) C o n t i n u o u s c o n t r o l o f t h e h e a t i n g v a p o u r s u p p l y d u r i n g t h e who le c y c l e .
( v ) C o n t i n u o u s c o n t r o l o f t h e m a s s e c u i t e t e m p e r a t u r e .
( v i ) C o n t i n u o u s measur ing o f t h e power consumpt ion o f t he s t i r r e r , t h i s a l l o w i n g
f i n a l t h i c k e n i n g t o t h e optimum m a s s e c u i t e c o n c e n t r a t i o n b e f o r e d i s c h a r g e .
I n a compu te r -based c o n t r o l s y s t e m , t h e computer a l s o t a k e s c a r e o f a l l v a l v e
o p e r a t i o n s d u r i n g s t a r t i n g and s t o p p i n g o f t he vacuum-pan c y c l e .
The f u n c t i o n s under ( i i i ) and ( i v ) a r e p a r t i c u l a r l y u s e f u l i n m i n i m i z i n g h e a t
c o n s u m p t i o n . A t t h e b e g i n n i n g o f t h e c r y s t a l g r o w t h p h a s e , i t i s d e s i r a b l e t o
i n c r e a s e t h e t e m p e r a t u r e o f t h e s u g a r s o l u t i o n ; t h i s can be done by i n c r e a s i n g
t h e p r e s s u r e i n t h e p a n . I n t h i s w a y , t he c r y s t a l l i z a t i o n can be i n c r e a s e d
w i t h o u t s p e n d i n g a d d i t i o n a l e n e r g y t o i n t e n s i f y e v a p o r a t i o n . L a t e r o n , when t h e
c r y s t a l g r o w t h becomes l i m i t e d by t h e e v a p o r a t i o n , t h e p r e s s u r e s h o u l d be
227
r e d u c e d , t h i s r e s u l t i n g i n r e d u c e d s o l u t i o n t e m p e r a t u r e and t h u s i n c r e a s e d h e a t
f l u x a t t h e h e a t i n g s u r f a c e . An a d d i t i o n a l e n e r g y - s a v i n g e f f e c t i s a l s o
o b t a i n e d , namely e x t r a c r y s t a l l i z a t i o n due t o r e d u c e d s o l u b i l i t y o f s u c r o s e
( i . e . , w i t h o u t h e a t e x p e n d i t u r e ) . The p r i n c i p l e o f p r o g r a m - c o n t r o l l e d
t e m p e r a t u r e changes d u r i n g t h e b o i l i n g c y c l e i s shown i n F i g . 6 . 9 ( a ) . When
p e r f o r m i n g t h e t e m p e r a t u r e r e d u c t i o n , t h e c o n t r o l a l g o r i t h m s h o u l d a v o i d
e x c e s s i v e t e m p e r a t u r e g r a d i e n t s , w i t h t h e a s s o c i a t e d r i s k o f f a l s e g r a i n
f o r m a t i o n .
(a) (b )
lower limit
Time Time
F i g . 6 . 9 . P r i n c i p l e s o f p r o g r a m - c o n t r o l l e d changes o f i m p o r t a n t v a r i a b l e s d u r i n g t h e a u t o m a t i c b o i l i n g c y c l e : ( a ) t e m p e r a t u r e , ( b ) h e a t i n g - v a p o u r f l o w . 1 - e v a p o r a t i o n o f t he i n i t i a l l y drawn s o l u t i o n , 2 - s e e d i n g and c r y s t a l f o r m a t i o n , 3 - c r y s t a l g r o w t h , 4 - t ime i n t e r v a l o f f l o w c o n t r o l u s i n g o p t i m i z a t i o n a l g o r i t h m .
The c o n t r o l o f h e a t i n g v a p o u r s u p p l y makes i t p o s s i b l e t o a v o i d u n n e c e s s a r y
w a t e r i n t a k e s accompanying t h e advanced c r y s t a l g r o w t h p h a s e . D u r i n g t h i s p a r t
o f t h e b o i l i n g c y c l e , t h e c o n t r o l a l g o r i t h m a d j u s t s t h e s e t - p o i n t v a l u e o f t h e
v a p o u r f l o w depend ing on t h e d r y s u b s t a n c e c o n t e n t o f t h e s o l u t i o n drawn and t h e
r a t e a t w h i c h t he m a s s e c u i t e l e v e l i s r a i s e d . The p r i n c i p l e o f p r o g r a m -
c o n t r o l l e d changes o f t h e v a p o u r f l o w i s shown i n F i g . 6 . 9 ( b ) .
The f u n c t i o n s under ( i ) and ( i i i ) can be u t i l i z e d t o v a r y t h e d u r a t i o n o f t h e
b o i l i n g c y c l e , a c c o r d i n g t o t h e r e q u i r e m e n t s d e f i n e d by t he u p p e r - l e v e l c o n t r o l .
More s p e c i f i c a l l y , i t i s p o s s i b l e t o r a i s e t h e m a s s e c u i t e l e v e l a t a
p r e d e t e r m i n e d r a t e , t h u s a f f e c t i n g t h e t ime needed t o r e a c h t h e maximum. I n
a d d i t i o n , t he s e t - p o i n t v a l u e o f t h e vacuum l e v e l and t h e moment when i t s change
i s i n i t i a t e d can be a d j u s t e d i n o r d e r t o i n f l u e n c e t h e r a t e o f c r y s t a l g r o w t h .
The c o m p l e x i t y o f c o m p u t e r - b a s e d b o i l i n g c o n t r o l s can be i l l u s t r a t e d by t h e
pa rame te rs o f one o f t h e sys tems a v a i l a b l e on t h e marke t ( r e f . 3 6 ) . I t uses 8
ana log and 32 d i g i t a l i n p u t s , as w e l l as 4 a n a l o g and 16 d i g i t a l o u t p u t s .
228
Communicat ion w i t h t h e u s e r i s p o s s i b l e v i a d i s p l a y , p r i n t e r , k e y b o a r d and u s e r -
d e f i n e d p u s h - b u t t o n s . The sys tem i s a l s o e q u i p p e d w i t h a da ta communica t ion
c h a n n e l , w h i c h p e r m i t s da ta t r a n s m i s s i o n t o and f rom t h e upper c o n t r o l l e v e l .
6 .6 .3 C o o r d i n a t i o n o f s u g a r house o p e r a t i o n s
The r e p r o d u c i b l e r e s u l t s o f automated s u g a r b o i l i n g make i t p o s s i b l e t o
u n d e r t a k e t h e t a s k o f c o o r d i n a t i n g t h e p r o c e s s e s o f m u l t i - s t a g e c r y s t a l l i z a t i o n
t o a c h i e v e t he b e s t o v e r a l l r e s u l t s . The c o n c e p t o f t h e q u a l i t y o f r e s u l t s ,
h o w e v e r , i s f a r f rom o b v i o u s . L e t us f o r m u l a t e two h y p o t h e t i c a l o b j e c t i v e s o f
c o o r d i n a t i o n :
- m a x i m i z i n g w h i t e s u g a r o u t p u t p e r 100 kg b e e t p r o c e s s e d ;
- m a x i m i z i n g s u g a r house t h r o u g h p u t , e x p r e s s e d i n amount o f t h i c k j u i c e
p r o c e s s e d i n u n i t t i m e .
On t h e b a s i s o f t h e s e o b j e c t i v e s , two d i f f e r e n t c o n t r o l s t r a t e g i e s can be
d e f i n e d ; i t i s a l s o p o s s i b l e t o combine them i n t o one compromise s t r a t e g y ( r e f .
3 7 ) . A n a l o g o u s l y , one can imag ine t he m i n i m i z a t i o n o f t h e e n e r g y demand b e i n g
a c c e p t e d as one o f t h e c o n t r o l o b j e c t i v e s , and s e a r c h i n g f o r e n e r g y s a v i n g s
be ing i n c l u d e d i n t he c o n t r o l s t r a t e g y .
I n any c o n t r o l s t r a t e g y , a c c o u n t s h o u l d be t aken o f numerous c o n s t r a i n t s
r e l a t e d t o t h e i n t e r a c t i o n o f c o n t i n u o u s and b a t c h e q u i p m e n t , s t o r a g e vo lumes
a v a i l a b l e , l i m i t a t i o n s o f h e a t i n g v a p o u r s u p p l y , e t c . P r a c t i c a l e x p e r i e n c e
p r o v e s t h a t v i o l a t i o n s o f t h e s e c o n s t r a i n t s a r e t h e p r i m a r y cause o f t h e
d i s t u r b a n c e s o c c u r r i n g i n m a n u a l l y o p e r a t e d c r y s t a l l i z a t i o n s u b s y s t e m s .
A t t h e p r e s e n t s t a t e o f deve lopmen t o f c o o r d i n a t i o n c o n t r o l , a t t e n t i o n i s
c o n c e n t r a t e d on a v o i d i n g d i s t u r b a n c e s i n mass and e n e r g y f l o w s w i t h i n t h e s u g a r
h o u s e . A c o n t r i b u t i n g f a c t o r i s t h a t t h e e x i s t i n g c r y s t a l l i z a t i o n subsys tems and
t h e i r e n v i r o n m e n t a r e o f t e n n o t p a r t i c u l a r l y s u i t e d t o a u t o m a t i c s u g a r house
o p e r a t i o n . T h i s r e s u l t s i n a m u l t i t u d e o f s p e c i a l c o n s t r a i n t s t o be a c c o u n t e d
f o r i n t h e c o n t r o l a l g o r i t h m s . T y p i c a l examples a r e : l i m i t e d c a p a c i t y o f t h e
vacuum s y s t e m , t o o smal l s t o r a g e t a n k s , l i m i t e d range o f o p e r a t i o n o f t h e
e v a p o r a t o r c o n t r o l , e t c . F o r t h i s r e a s o n , t h e g e n e r a l o b j e c t i v e s o f c o o r d i n a t i o n
i n t h e e s t a b l i s h e d sys tems a r e l e s s i m p o r t a n t t han t h e c o n t r o l f u n c t i o n s aimed
a t s a t i s f y i n g t h e c o n s t r a i n t s , l i k e s c h e d u l i n g o f o p e r a t i o n o f b a t c h vacuum pans
and c e n t r i f u g a l s , p r e v e n t i n g tank o v e r f l o w , e t c . ( r e f s . 3 8 - 4 1 ) . These f u n c t i o n s
c o n s i s t m a i n l y o f s u p e r v i s i n g t h e l e v e l s i n s y r u p t a n k s and m a s s e c u i t e m i x e r s
and a d j u s t i n g t h e w o r k i n g c y c l e s o f t h e b a t c h equ ipmen t . I n t h i s manner ,
a r e g u l a r i z a t i o n o f s u g a r house o p e r a t i o n can be o b t a i n e d .
The r e s u l t s o b t a i n e d w i t h t h e c o o r d i n a t i o n sys tems a r e c l e a r l y p o s i t i v e .
The a t t a i n a b l e e n e r g y s a v i n g s can be i l l u s t r a t e d by r e d u c t i o n o f t h e amount o f
w a t e r drawn t o b a t c h vacuum pans i n a s u g a r f a c t o r y i n FRG ( r e f . 4 2 ) . A f t e r
imp lement ing t h e c o o r d i n a t i o n s y s t e m , w a t e r i n t a k e s t o vacuum pans C were
229
reduced f rom t h e i n i t i a l l e v e l o f a b o u t 30 kg p e r 1 t magma t o z e r o . I n A
s t r i k e , w a t e r i n t a k e s were n e a r l y h a l v e d f rom abou t 12 t o 7 kg p e r 1 t magma.
I t i s f e l t t h a t f u r t h e r improvements a r e needed i n t h e methods o f
c o o r d i n a t i o n o f s u g a r house o p e r a t i o n . The e x i s t i n g c o o r d i n a t i o n sys tems do n o t
f u l l y u t i l i z e t h e t e c h n o l o g i c a l p o t e n t i a l o f i n t e g r a t e d c o n t r o l o f i n d i v i d u a l
s t a t i o n s and i n t e g r a t e d management o f d a t a on t h e d e t a i l s o f t h e s u g a r
c r y s t a l l i z a t i o n p r o c e s s .
6.7 PULP DRYING CONTROL
The goa l o f t h e p u l p d r y i n g p r o c e s s i s t o d r y t h e incoming p r e s s e d p u l p t o
a d e f i n i t e m o i s t u r e c o n t e n t . T y p i c a l l y , t h e f i n a l m o i s t u r e c o n t e n t o f t h e d r i e d
p u l p s h o u l d n o t be l o w e r t han 5-6%; i n t h e s u b s e q u e n t p e l l e t i n g , i t i s
e v e n t u a l l y i n c r e a s e d t o 9-11%. These v a l u e s a r e d e s i r a b l e w i t h r e s p e c t bo th t o
e n e r g y economy and t h e keep ing q u a l i t y o f t h e d r i e d p u l p .
The t a s k o f t h e a u t o m a t i c c o n t r o l s ys tem i s t o keep t h e f i n a l m o i s t u r e
c o n t e n t o f t h e d r i e d p u l p a t a p r e d e t e r m i n e d l e v e l . I t s h o u l d be p o s s i b l e t o
e l i m i n a t e d i s t u r b a n c e s r e s u l t i n g m a i n l y f rom f l u c t u a t i o n s o f t h e r a t e o f
d e l i v e r y o f p r e s s e d p u l p , t h e m o i s t u r e c o n t e n t o f p r e s s e d p u l p , and t h e q u a l i t y
o f p r e s s e d p u l p . The r e v i e w o f c o n t r o l p rob lems p r e s e n t e d be low i s l i m i t e d t o
t h e p rob lems c h a r a c t e r i s t i c o f d r u m - t y p e d r y e r s hea ted by combus t i on g a s e s .
C o n t r o l o f t h e combus t i on p r o c e s s i s e x c l u d e d f rom t h e r e v i e w as i t i s n o t
s p e c i f i c t o t h e s u g a r i n d u s t r y .
T h e r e a r e two main r e a s o n s f o r t h e d i f f i c u l t i e s e n c o u n t e r e d i n p u l p d r y i n g
c o n t r o l :
- a c c u r a t e measurements o f t h e m o i s t u r e c o n t e n t o f t h e p u l p a r e d i f f i c u l t t o
make;
- t h e p r o c e s s i s c h a r a c t e r i z e d by a l a r g e r a t i o o f gas f l o w t o p r e s s e d p u l p
f l o w ; i t s v a l u e depends on t h e d e t a i l s o f t h e p r o c e s s , and i s o f t h e o r d e r 2-4
i n h i g h - t e m p e r a t u r e d r y e r s ( l o w e r v a l u e s b e i n g c h a r a c t e r i s t i c o f d r y e r s
f e a t u r i n g gas r e c i r c u l a t i o n o r u t i l i z a t i o n o f b o i l e r f l u e g a s ) .
Because o f t h e f i r s t p r o b l e m , most a u t o m a t i c c o n t r o l sys tems p r e s e n t l y i n use
r e l y on measurement o f t h e e x i t gas t e m p e r a t u r e , i n d i r e c t l y r e p r e s e n t i n g t h e
f i n a l m o i s t u r e c o n t e n t o f t h e d r i e d p u l p . Depend ing on t h e a c t u a l v a l u e
measured , t h e sys tem a d j u s t s t h e e n e r g y i n p u t t o t h e d r y e r f u r n a c e . P o s s i b l e
c o r r e c t i o n s o f s e t t i n g s a r e i n t r o d u c e d a c c o r d i n g t o t h e r e s u l t s o f t h e
l a b o r a t o r y a n a l y s e s o f d r i e d p u l p s a m p l e s . The w o r k i n g p r i n c i p l e o f t h e d r y e r
c o n t r o l a f f e c t s t h e way t he d r y e r o p e r a t o r s a c t . I n o r d e r t o a v o i d t h e r i s k o f
t o o h i g h f i n a l m o i s t u r e c o n t e n t , t h e y t e n d t o o v e r d r y t he p u l p , w i t h t o o l a r g e
an e n e r g y consumpt ion as a r e s u l t .
The g a s / p u l p r a t i o , a l o n g w i t h a l a r g e s p e c i f i c volume o f t h e g a s , r e s u l t s i n
a c o n s i d e r a b l e d i f f e r e n c e between t h e r e t e n t i o n t ime o f t h e gas and t h a t o f
230
t he p u l p i n t h e d r y e r drum. W h i l e t h e t ime needed f o r t he p u l p t o r e a c h t h e
d r y e r o u t l e t i s o f t he o r d e r o f one h o u r , t he r e t e n t i o n t ime o f t h e gas may be
s e v e r a l s e c o n d s . F o r t h i s r e a s o n , i f a d i s t u r b a n c e o c c u r s and t he h e a t b a l a n c e
o f t he d r y e r c h a n g e s , t h e e x i t gas t e m p e r a t u r e i s changed w i t h i n s e c o n d s , b u t
15-20 m inu tes a r e needed b e f o r e t h e f i n a l m o i s t u r e c o n t e n t o f t h e d r i e d p u l p
i s c h a n g e d . T h i s t ime l ag i s t h e u n d e r l y i n g cause o f t h e d i f f i c u l t i e s a s s o c i a t e d
w i t h c o n t r o l l i n g t r a n s i e n t p r o c e s s e s i n t h e d r y e r . F o r examp le , i n p u l p d r y i n g
s t a t i o n s e q u i p p e d w i t h two o r more d r y e r s w o r k i n g i n p a r a l l e l , one o f them i s
d e s t i n e d t o a b s o r b t h e s w i n g s i n t h e p r o c e s s . When e x p e c t i n g f l u c t u a t i o n s o f t h e
p a r a m e t e r s , t h e o p e r a t o r u s u a l l y t r i e s t o c a t c h t h e w o r s t c o n d i t i o n . A t y p i c a l
r e s u l t i s t h a t t h e e x i t gas t e m p e r a t u r e t e n d s t o be t o o h i g h , and t h e e n e r g y
consumpt ion l a r g e r than r e a l l y n e c e s s a r y .
V a r i o u s sys tems o f a u t o m a t i c p u l p d r y i n g c o n t r o l have been p r o p o s e d t o
overcome t h e t y p i c a l d i f f i c u l t i e s men t ioned above ( r e f s . 4 3 , 4 4 ) . C o n s i d e r a b l e
improvements have been a t t a i n e d by u s i n g new methods o f measurement o f t h e
m o i s t u r e c o n t e n t o f t h e p u l p ( r e f s . 2 2 , 4 5 ) . As t h e c o n t r o l f u n c t i o n s a r e
e x t e n d e d and c o n t r o l a l g o r i t h m s become i n c r e a s i n g l y c o m p l e x , h o w e v e r , t h e
c o n v e n t i o n a l sys tems become c o m p l i c a t e d and c o s t l y . A c o n t r i b u t i n g f a c t o r i s
t h a t t h e e n e r g y - s a v i n g e x t e n s i o n s o f t h e p u l p d r y i n g p r o c e s s , l i k e u t i l i z a t i o n
o f b o i l e r f l u e gas o r gas r e c i r c u l a t i o n , r e q u i r e t h e a d d i t i o n o f e x t r a c o n t r o l
l o o p s t o t he b a s i c s y s t e m .
A l t h o u g h an e x p e r i e n c e d d r y e r o p e r a t o r can a t t a i n v e r y good r e s u l t s u s i n g
a c o n v e n t i o n a l c o n t r o l sys tem and new deve lopmen ts a r e s t i l l p o s s i b l e i n t h i s
f i e l d ( r e f . 4 6 ) , t he f u t u r e i s c e r t a i n l y i n c o m p u t e r - b a s e d s y s t e m s . The
advan tages o f computer a p p l i c a t i o n have been c l e a r l y d e m o n s t r a t e d i n a s u g a r
f a c t o r y i n FRG, where computer t e c h n o l o g y was i n t r o d u c e d as a l o g i c a l s t e p i n
dr ied pulp
F i g . 6 .10 . P o i n t s o f measurement o f main v a r i a b l e s i n t h e a u t o m a t i c c o n t r o l o f a p u l p d r y e r : 1 - combus t ion gas t e m p e r a t u r e , 2 - t e m p e r a t u r e i n t h e drum, 3 - o u t l e t t e m p e r a t u r e , 4 - f i n a l m o i s t u r e c o n t e n t , 5 - f u e l f l o w , 6 - a i r f l o w , 7 - f e e d e r c a p a c i t y , 8 - i n i t i a l m o i s t u r e c o n t e n t . F - f u r n a c e , D - d r u m , A - a f t e r d r y e r .
231
i m p r o v i n g t h e e x i s t i n g p u l p d r y i n g c o n t r o l s ( r e f . 4 7 ) . The mathemat i ca l model o f
t he p r o c e s s dynamics was i d e n t i f i e d on t h e b a s i s o f measurements r e c o r d e d i n t h e
a c t u a l p u l p d r y i n g s t a t i o n , u s i n g a method c o m p r i s i n g c o r r e l a t i o n a n a l y s i s and
e s t i m a t i o n o f model p a r a m e t e r s . A s k e t c h o f a d r y e r , w i t h i n d i c a t i o n o f i n p u t
and o u t p u t v a r i a b l e s o f t h e m o d e l , i s shown i n F i g . 6 .10 .
The computer c o n t r o l s t h r e e d r y e r s w o r k i n g i n p a r a l l e l . I t was e s t i m a t e d t h a t
t he imp lemen ta t i on o f t h i s sys tem r e s u l t e d i n a f u e l s a v i n g o f abou t 2.5%. I t i s
n o t e w o r t h y t h a t t h i s s a v i n g was o b t a i n e d r e l a t i v e t o d r y e r o p e r a t i o n s u p e r v i s e d
by e x p e r i e n c e d o p e r a t o r s u s i n g w e l l - f u n c t i o n i n g c o n v e n t i o n a l c o n t r o l s . S i m i l a r
r e s u l t s a r e r e p o r t e d f rom o t h e r cases o f a p p l i c a t i o n o f c o m p u t e r - b a s e d d r y e r
c o n t r o l s .
REFERENCES
1 J . D o b r z y c k i , A u t o m a t y z a c j a w P r z e m y s l e C u k r o w n i c z y m , WNT, Warszawa, 1974. 2 Anonymous, B o i l e r f u e l c o s t s r e d u c e d . Sugar J . , 4 4 ( 9 ) (1982) 21. 3 J . A . H e i n b a u g h , D i r e c t d i g i t a l c o n t r o l o f t h e b o i l e r h o u s e , p u l p d r i e r , and
m u l t i - e f f e c t e v a p o r a t o r s . Paper p r e s e n t e d a t 23rd ASSBT M e e t i n g , San D i e g o , F e b r u a r y 1985.
4 J . A . F i t z p a t r i c k , The a p p l i c a t i o n o f compute rs and e l e c t r o n i c s t o p r o c e s s c o n t r o l i n Thames R e f i n e r y , I n t . Sugar J . , 82(980) (1980) 231-236.
5 J . S . Hogg and D . F . A . H o r s l e y , The use o f sma l l compute rs i n B r i t i s h b e e t s u g a r f a c t o r i e s . I n t . Sugar J . , 82(980) (1980) 240-243.
6 R . F . Madsen, P r o g r e s s i n Dan i sh s u g a r p r o d u c t i o n w i t h i n t h e p a s t d e c a d e . Paper p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e " Improvement o f Bee t Sugar P r o d u c t i o n " , Warszawa, May 1987.
7 K .A . S c h u l t e s , M i k r o c o m p u t e r g e s t e u e r t e D i c k s a f t f i l t e r s t a t i o n , Z u c k e r i n d . , 104(11) (1979) 1029-1031.
8 P. S l u g o c k i , R e g u l a c j a p r z e p l y w u mas w Cukrown i C h e l m z a , G a z . C u k r . , 93 (4 ) (1985) 79-81.
9 M. S t a s z c z a k , A . B r a t e k and E . K u l a s z y n s k i , M i k r o p r o c e s o r o w y s y s t e m k o o r d y n a c j i p r z e p l y w u mas w s u r o w n i Cukrown i R o p c z y c e , G a z . C u k r . , 9 3 ( 5 - 6 ) (1985) 73-75.
10 H. Kemter , E i n neue r Weg be i d e r P r o z e s s a u t o m a t i s i e r u n g i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 103(11) (1978) 939-945.
11 G . W i n d a l , A p p o r t des t e c h n i q u e s modernes en a u t o m a t i s a t i o n de s u c r e r i e , I n d . A l i m . A g r i e , 9 6 ( 7 - 8 ) (1979) 737-745.
12 Η. P a s c h o l d , E i n s a t z von P r o z e s s r e c h n e r n i n b e l g i s c h e n und n i e d e r l ä n d i s c h e n Z u c k e r f a b r i k e n , Z u c k e r i n d . , 105(4) (1980) 343-344.
13 L . W e n z e l , B e i s p i e l e von A u t o m a t i s i e r u n g s k o n z e p t e n i n Z u c k e r f a b r i k e n , Z u c k e r i n d . , 107(10) (1982) 934-936.
14 G . W i n d a l , L ' i n f o r m a t i q u e i n d u s t r i e l l e dans 1 ' o p t i m i s a t i o n e n e r g e t i q u e du p r o c e d e de f a b r i c a t i o n , i n : P r o c . 17th C I T S , Copenhagen , 1983, p p . 45-65 .
15 H . S . B i r k e t t , Computer a p p l i c a t i o n s . Sugar J . , 46(10) (1984) 10-12. 16 Anonymous, A u t o m a t i s a t i o n e t i n f o r m a t i q u e i n d u s t r i e l l e , S u c r . F r . ,
127(103) (1986) 110-114. 17 P. Mosel ( e t a l . ) , P r o z e s s a u t o m a t i s i e r u n g und Daten-Management m i t dem neuen
D C I - S y s t e m im Werk P l a t t l i n g d e r S ü d d e u t s c h e n Z u c k e r - A G , Z u c k e r i n d . , 111(4) (1986) 321-328.
18 T h . C r o n e w i t z , W e c h s e l w i r k u n g e n be i d e r E n t w i c k l u n g von D a t e n v e r a r b e i t u n g und V e r f a h r e n s t e c h n i k - M ö g l i c h k e i t e n d e r P r o z e s s f ü h r u n g i n d e r Z u k u n f t , Z u c k e r i n d . , 112(2) (1987) 103-107.
19 P. P e t e r s , A u t o m a t i s i e r u n g s - und P r o z e s s d a t e n e r f a s s u n g s a n i agen i n s ü d d e u t s c h e n Z u c k e r f a b r i k e n - e i n e S t a n d o r t b e s t i m m u n g , Z u c k e r i n d . , 112(2) (1987) 107-114.
232
20 J . M e r k l , E n e r g i e e i n s p a r u n g m i t d r e h z a h l r e g e ! b a r e n D r e h s t r o m a n t r i e b e n i n d e r Z u c k e r i n d u s t r i e , Z u c k e r i n d . , 110(2) (1985) 1082-1089.
21 P. M o s e l , E r f a h r u n g e n m i t e inem P r o z e s s r e c h n e r f ü r v o l l a u t o m a t i s c h e n B e t r i e b d e r E x t r a k t i o n , Z u c k e r , 27(10) (1974) 528-541.
22 P.W. van d e r P o e l , N . H . M . de V i s s e r and C . C . B l e y e n b e r g , Deve lopments i n computer and o n - l i n e c o n t r o l i n t h e b e e t s u g a r f a c t o r y . Sugar T e c h . R e v . , 9 ( 1 ) (1982) 1-58.
23 G . W i n d a l , B. P o r t a l e s and D. Maes, Le p o i n t s u r Γ a u t o m a t i s a t i o n des d i f f u s e u r s Continus p a r l e p rocede I R I S , S u c r . F r . , 126(93) (1985) 145-149.
24 S . Z a g r o d z k i , 0 zasadach samoczynne j r e g u l a c j i s t a c j i w y p a r n e j , G a z . C u k r o w . , 60 (4 ) (1958) 105-108.
25 W. Grasmann and 0. P a r i s e k , Messen und Rege ln des D u r c h f l u s s e s und d e r D i c h t e von D i c k s a f t und D ü n n s a f t , Z u c k e r , (1969) 432-438.
26 D ie Rege lung d e r V e r d a m p f s t a t i o n i n d e r Z u c k e r f a b r i k , T e c h n i c a l i n f o r m a t i o n f rom S iemens , F ü r t h , 1975.
27 T . W . B a k e r , E v a p o r a t i o n and h e a t i n g , i n : G . T . Meade and J . C . Chen ( E d s . ) , Cane Sugar Handbook, W i l e y , New Y o r k , 1977, p p . 185-235.
28 J . C . G i o r g i , P. G i r a u d and A . D e l e u r e n c e , G e s t i o n au tomat ique de l ' a t e l i e r d ' e v a p o r a t i o n , S u c r . F r . , 126(93) (1985) 123-128.
29 H . - F . K o r n , D ie P r a x i s des k o n t r o l l i e r t e n und a u t o m a t i s i e r t e n K o c h e n s , Z u c k e r , 19(13) (1966) 337-349.
30 R . J . Bass and J . Donovan , M i c r o p r o c e s s o r c o n t r o l o f s u g a r b o i l i n g , S u c r . B e i g e , 95 (8 ) (1976) 421-433.
31 G . Windal and A . D e l e u r e n c e , R e s u l t a t s i n d u s t r i é i s de l a c o n d u i t e des c u i t e s pa r m i c r o - o r d i n a t e u r , S u c r . F r . , 9 6 ( 3 ) (1979) 121-122.
32 P.W. van d e r Poel ( e t a l . ) , A u t o m a t i s i e r u n g d e r K o c h s t a t i o n d e r C S M - Z u c k e r -f a b r i k B r e d a , Z u c k e r i n d . , 107(2) (1982) 113-117.
33 P.W. van d e r Poel ( e t a l . ) , E n e r g i e e i n s p a r u n g e n be i d e r V e r d a m p f u n g s k r i s t a l l i s a t i o n , Z u c k e r i n d . , 108(10) (1983) 934-939.
34 D. Hoks , A u t o m a t i c a l l y c o n t r o l l e d s u g a r b o i l i n g s y s t e m . Sugar J . , 46 (7 ) (1983) 8 -9 .
35 S . C . H . McCarey and F. F e a r n s i d e , A s p e c t s o f a u t o m a t i c s u g a r b o i l i n g a t Newark f a c t o r y . I n t . Sugar J . , P a r t I 87(1043) (1985) 208-213, P a r t I I 87(1044) (1985) 223-227.
36 G . R . M o l l e r , A a n i s h m i c r o p r o c e s s o r c o n t r o l l e r f o r t h e pan f l o o r . Sugar y A z ú c a r , 80 (7 ) (1985) 33-35.
37 D. P i o t r o w s i c i and K. U r b a n i e c , Op t ima l c o n t r o l o f b a t c h - c o n t i n u o u s c r y s t a l ! f z a t i on o f s u g a r . Paper p r e s e n t e d a t 7 th I n t e r n a t i o n a l C o n g r e s s CHISAr^B l , P r a g u e , September 1981.
38 G . W i n d a l , A u t o m a t i s a t i o n pa r m i c r o - o r d i n a t e u r des c u i t e s 2eme e t 3eme j e t de l a S u c r e r i e de T o u r y , S u c r . F r . , 9 4 ( 3 ) (1977) 129-135.
39 G . Windal and A . D e l e u r e n c e , G e s t i ó n a s s i s t e e du c h a n t i e r de p r e m i e r j e t , S u c r . F r . , 9 6 ( 3 ) (1979) 123-126.
40 G . Windal and A . D e l e u r e n c e , A p p l i c a t i o n a l a c r i s t a l 1 i s a t i o n du p r o c e d e Cheops de g e s t i ó n c o o r d o n n e e , I n d . A l i m . A g r i e , 9 8 ( 7 - 8 ) (1981) 581-588.
41 Β. H a r r i s o n and J . R u z i c k a , S u p e r v i s o r y c o n t r o l and d a t a a c q u i s i t i o n f o r p r o c e s s . Sugar J . , 48 (1 ) (1985) 5 -9 .
42 W. Assenmacher , Η. Merensky and K. W ö h r l e , A u t o m a t i s c h e S t e u e r u n g e i n e r K o c h s t a t i o n m i t d i s k o n t i n u i e r l i c h e n K o c h a p p a r a t e n , Z u c k e r i n d . , 111(6) (1986) 549-554.
43 F. Baunack , T r o c k n u n g , i n : F . S c h n e i d e r ( E d . ) , T e c h n o l o g i e des Z u c k e r s , Schaper V e r l a g , H a n n o v e r , 1968, p p . 845-883.
44 H .A . P a s c h o l d , D i e Rege lung von a d i a b a t i s c h e n und n i c h t - a d i a b a t i s c h e n T r o c k n e r n am B e i s p i e l von Trommel - und d a m p f b e h e i z t e n R ö h r e n b ü n d e l t r o c k n e r n , Z u c k e r i n d . , 103(12) (1978) 1036-1030.
45 H. Kemter , Rege lung von S c h n i t z e l t r o m m e l t r o c k n e r n , Z u c k e r , 30(1 ) (1977) 7-10 . 46 H . P . G i l d e r s l e e v e , Bee t p u l p d r y i n g c o n t r o l . Sugar J . , 44 (5 ) (1981) 15-18. 47 P. Mosel ( e t a l . ) , Führung e i n e r T r o m m e l t r o c k n e r a n l a g e f ü r P r e s s s c h n i t z e l
m i t e inem P r o z e s s r e c h n e r , Z u c k e r i n d . , 105(6) (1980) 554-561.
233
C h a p t e r 7
MONITORING OF THE HEAT CONSUMPTION
7.1 INTRODUCTORY REMARKS
7.1.1 Scope o f t h e p rob lems
The r e q u i r e m e n t s o f hea t economy i n a s u g a r f a c t o r y a r e , on t h e one hand , t o
e n s u r e a c o n t i n u o u s hea t s u p p l y t o a l l s e c t i o n s o f t h e p r o c e s s and t o m a i n t a i n
p r o p e r o p e r a t i n g c o n d i t i o n s f o r t h e f a c t o r y e q u i p m e n t , as t h e s e a r e t h e
p r e r e q u i s i t e s f o r smooth f a c t o r y o p e r a t i o n , and on t h e o t h e r h a n d , t o m i n i m i z e
hea t consumpt ion i n t he p r o c e s s . A l l t h e s e t a s k s c a n n o t be f u l f i l l e d w i t h o u t
m o n i t o r i n g h e a t consumpt ion i n i n d i v i d u a l equ ipment u n i t s and p r o c e s s s t a t i o n s ,
o v e r s e e i n g equ ipment o p e r a t i o n , i d e n t i f y i n g causes f o r hea t l o s s e s and
d e t e r m i n i n g t h e p o s s i b i l i t i e s f o r improvements i n h e a t economy.
I t i s t r a d i t i o n a l l y u n d e r s t o o d t h a t t he p rob lem a r e a under c o n s i d e r a t i o n
i n c l u d e s :
- f u e l and f u e l s t o r a g e ;
- f u e l combus t ion and steam g e n e r a t i o n i n b o i l e r s ;
- e l e c t r i c i t y g e n e r a t i o n i n t h e power h o u s e ;
- steam and v a p o u r u t i l i z a t i o n f o r p r o c e s s p u r p o s e s .
A long w i t h s a t i s f y i n g t h e s p e c i f i c needs o f t h e s u g a r i n d u s t r y , i t i s
n e c e s s a r y i n most c o u n t r i e s t o m o n i t o r f a c t o r y o p e r a t i o n a c c o r d i n g t o g e n e r a l
r e g u l a t i o n s c o n c e r n i n g t h e o p e r a t i o n o f e n e r g y - s u p p l y equ ipmen t . The r e g u l a t i o n s
u s u a l l y r e q u i r e keep ing o p e r a t i n g r e c o r d s and p e r i o d i c a l l y e v a l u a t i n g them f rom
t h e p o i n t o f v i e w o f e n e r g y u t i l i z a t i o n . T h i s a p p l i e s i n p a r t i c u l a r t o such
equ ipment a s :
- steam and w a t e r b o i l e r s ;
- t u r b i n e s ;
- l a r g e hea t r e c e i v e r s ( h e a t e x c h a n g e r s , d r y e r s , e t c . ) ;
- c o n t r o l l i n g and measur ing equ ipmen t .
I t can be s t a t e d t h a t , u n l i k e d e s i g n p r o b l e m s , m o n i t o r i n g p rob lems a s s o c i a t e d
w i t h t he hea t economy i n s u g a r f a c t o r i e s a r e n o t v e r y w e l l c o v e r e d i n t h e
l i t e r a t u r e . I n t h i s C h a p t e r , t h e b a s i c f a c t o r s needed t o m o n i t o r and e v a l u a t e
hea t economy c o r r e c t l y and e f f e c t i v e l y under a c t u a l o p e r a t i n g c o n d i t i o n s a r e
b r o u g h t t o g e t h e r .
As o n l y t h e most i m p o r t a n t t o p i c s can be d i s c u s s e d h e r e , t h e h i g h e s t p r i o r i t y
i s a t t r i b u t e d t o p rob lems d i r e c t l y a s s o c i a t e d w i t h e n e r g y s a v i n g s . The p rob lems
o f c o n t r o l l i n g s p e c i f i c a s p e c t s o f t h e o p e r a t i o n o f i n d i v i d u a l mach ines and
equ ipment u n i t s a r e r e g a r d e d as be ing beyond t h e scope o f t h i s C h a p t e r .
I t has been assumed t h r o u g h o u t t h i s C h a p t e r t h a t t h e s u g a r f a c t o r y under
234
c o n s i d e r a t i o n i s c h a r a c t e r i z e d by an a v e r a g e l e v e l o f p r o c e s s i n s t r u m e n t a t i o n .
The advanced measur ing and a u t o m a t i c m o n i t o r i n g sys tems used i n some modern
p l a n t s a r e l a r g e l y i g n o r e d h e r e .
7 .1 .2 T h e o r e t i c a l background
I n t h e p u b l i c a t i o n s d e v o t e d s o l e l y t o t h e e n e r g y economy ( r e f s . 1 - 4 ) , and
a l s o i n t he s p e c i a l c h a p t e r s i n w e l l known books on b e e t s u g a r t e c h n o l o g y ( r e f s .
5 - 9 ) , m o n i t o r i n g o f t he hea t consumpt ion i s t r e a t e d o n l y m a r g i n a l l y . The
i n f o r m a t i o n g a t h e r e d i n t h e s e s o u r c e s may p r o v e i n s u f f i c i e n t as a b a s i s f o r
p r a c t i c a l e n g i n e e r i n g a n a l y s e s a s s o c i a t e d w i t h t h i s p r o b l e m . I t may t h e n become
n e c e s s a r y t o r e l y on g e n e r a l t h e o r e t i c a l r e l a t i o n s h i p s , p a r t i c u l a r l y i n such
f i e l d s as t h o s e l i s t e d b e l o w .
( i ) The f i r s t law o f t he rmodynamics , as a b a s i s f o r d e t e r m i n i n g t h e e n e r g y
b a l a n c e s o f therma l p r o c e s s e s and f l o w s i n s t a t i o n s , equ ipment o r equ ipment
p a r t s . T h i s i m p o r t a n t m a t t e r has been d i s c u s s e d i n g r e a t e r d e t a i l i n S e c t i o n
2 .1 . F o r an e x t e n s i v e t h e o r e t i c a l t r e a t m e n t r e f s . 10 and 11, o r o t h e r l i t e r a t u r e
on a p p l i e d t he rmodynamics , may be c o n s u l t e d .
( i i ) The thermodynamics o f w a t e r and s team, w h i c h a r e t h e b a s i c media i n t h e
thermal p r o c e s s e s . The books men t ioned above a l s o i n c l u d e c h a p t e r s d e v o t e d t o
t h i s t o p i c . T a b l e s o f thermodynamic f u n c t i o n s a r e g i v e n i n r e f s . 12, 13 and
o t h e r s o u r c e s , w h i l e f o r n u m e r i c a l a p p r o x i m a t i o n s f o r c a l c u l a t o r - o r c o m p u t e r -
a i d e d c a l c u l a t i o n s . A p p e n d i x 1 may be c o n s u l t e d .
( i i i ) C o m b u s t i o n . T h i s p r o c e s s i s p a r t i c u l a r l y w o r t h a t t e n t i o n , because i t may
g i v e r i s e t o c o n s i d e r a b l e e n e r g y l o s s e s ; l i t e r a t u r e as a b o v e .
( i v ) Heat t r a n s f e r , as a g roup o f phenomena c o n t r i b u t i n g t o t h e mechanism o f
most hea t l o s s e s . I n a d d i t i o n t o t h e above l i t e r a t u r e , r e f s . 14 and 15 can be
recommended.
( v ) The f o u n d a t i o n s o f i n d u s t r i a l measurement , as a b a s i s f o r t h e d a t a g a t h e r i n g
and da ta i n t e r p r e t a t i o n on w h i c h hea t -economy m o n i t o r i n g must r e l y . F o r
t e c h n i c a l d e t a i l s and f o r i n f o r m a t i o n on e r r o r a n a l y s i s , r e f s . 15-18 may be
c o n s u l t e d .
I t s h o u l d be added t h a t p r o p e r a n a l y s i s and e f f e c t i v e s o l v i n g o f t h e p rob lems
a s s o c i a t e d w i t h t h e u t i l i z a t i o n o f steam and v a p o u r f o r p r o c e s s p u r p o s e s o f t e n
r e q u i r e deep u n d e r s t a n d i n g o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s .
An e s s e n t i a l p r o c e s s i n hea t -economy m o n i t o r i n g i s t o i d e n t i f y t h e h e a t
b a l a n c e s o f t h e o b j e c t s under c o n s i d e r a t i o n , i . e . equ ipment u n i t s , p r o c e s s
s t a t i o n s , o r even t h e e n t i r e f a c t o r y . The i d e n t i f i c a t i o n o f a h e a t b a l a n c e
c o n s i s t s o f e s t a b l i s h i n g t h e bounda ry o f a thermodynamic s y s t e m , d e t e r m i n i n g t h e
mass and e n e r g y s t reams c r o s s i n g t h e b o u n d a r y , and r e c o g n i z i n g t h e magn i tude o f
each s t r e a m . I n p r a c t i c e , i t r e q u i r e s t h a t measurements o f t h e a p p r o p r i a t e
235
pa ramete rs a re t a k e n . Not a l l pa rame te rs need t o be known, h o w e v e r , as t h e
t h e o r e t i c a l b a l a n c e d e s c r i p t i o n e n a b l e s one t o c o n s t r u c t a sys tem o f e q u a t i o n s .
The measurements s h o u l d s u p p l y as many pa ramete r v a l u e s as r e q u i r e d f o r
d e t e r m i n i n g t he r e m a i n i n g ones f rom t h e e q u a t i o n s .
When p e r f o r m i n g t h e measurements , i t i s n e c e s s a r y t o o b s e r v e t h e c o n f o r m i t y
o f t h e s t a t e o f t he thermodynamic sys tem c o n s i d e r e d w i t h t h e c o n d i t i o n s f o r
w h i c h t h e t h e o r e t i c a l b a l a n c e d e s c r i p t i o n has been f o r m u l a t e d . I n p a r t i c u l a r ,
when u s i n g t h e f o r m u l a e o r i g i n a t i n g f rom e q n s . ( 2 . 3 ) o r ( 2 . 6 ) , s t e a d y - s t a t e
c o n d i t i o n s must be m a i n t a i n e d t h r o u g h o u t t h e t e s t p e r i o d . I f f l u c t u a t i o n s o f t h e
pa rame te rs c a n n o t be a v o i d e d , t h e t e s t p e r i o d s h o u l d be l ong enough t o e n s u r e
t h e v a l i d i t y o f mean v a l u e s ( t h e recommendat ions c o n c e r n i n g t e s t d u r a t i o n s f o r
i n d i v i d u a l s t a t i o n s a r e g i v e n b e l o w ) .
I n an e x i s t i n g f a c t o r y , t h e p r e r e q u i s i t e f o r measurements l e a d i n g t o a
c o r r e c t h e a t b a l a n c e i s t h a t t h e sys tem be e q u i p p e d w i t h good measu r i ng
equ ipmen t . C l e a r l y , e r r o n e o u s measurements may l e a d t o a f a l s e b a l a n c e and
f i n a l l y t o wrong c o n c l u s i o n s . I t i s t h u s recommended t h a t more measu r ing
i n s t r u m e n t s be i n s t a l l e d t han a r e t h e o r e t i c a l l y needed f o r s o l u t i o n o f t h e
sys tem o f b a l a n c e e q u a t i o n s . Measurement d a t a can t h e n be checked by compar ing
b a l a n c e r e s u l t s o b t a i n e d i n d i f f e r e n t w a y s .
7 .1 .3 Example
When i n v e s t i g a t i n g t he e n e r g y b a l a n c e o f t h e s u g a r h o u s e , i t i s n e c e s s a r y t o
overcome d i f f i c u l t i e s due t o t h e p e r i o d i c o p e r a t i o n o f t h e vacuum pans and
c e n t r i f u g a l s . F o r examp le , t he mass and e n e r g y b a l a n c e s o f a b a t c h vacuum pan
noncondensable gases
A U X I L I A R Y B O U N D A R I E S | "
cooling , A - b 1 water ' / r , ^ - " '
S U G A R H O U S E E Q U I P M E N T
~ " S Y S T E M " B O U N D A R Y ~ "
leaks
I ' heat losses
' sugar
4 -molasses
condensate
J
F i g . 7 .1 . E n e r g y b a l a n c e o f t h e s u g a r h o u s e .
236
s h o u l d be a n a l y s e d f o r t he e n t i r e b o i l i n g c y c l e , w i t h t he a i d o f b a l a n c e
r e l a t i o n s h i p s based on e q n s . ( 2 . 1 ) and ( 2 . 4 ) . F o r s t a b i l i z e d s u g a r house o u t p u t ,
h o w e v e r , t h e b a l a n c e can r e l y on t h e r e l a t i o n s h i p s c o n c e r n i n g s t e a d y - s t a t e
c o n d i t i o n s , i . e . e q n s . ( 2 . 3 ) and ( 2 . 6 ) . The sys tem bounda ry i s p l a c e d as shown
i n F i g . 7 .1 , where an a u x i l i a r y bounda ry f o r t h e c o n d e n s e r b a l a n c e i s a l s o
i n d i c a t e d . The measurements n e c e s s a r y f o r e s t a b l i s h i n g the b a l a n c e s s h o u l d be
pe r f o rmed o v e r an adequate t i m e , so t h a t r e l i a b l e mean v a l u e s can be c a l c u l a t e d
f o r steam and condensa te f l o w s , b a r o m e t r i c w a t e r t e m p e r a t u r e , e t c . I n an o v e r a l l
e n e r g y b a l a n c e f o r t he s u g a r h o u s e , one can n e g l e c t r e l a t i v e l y smal l e n e r g y
s t reams such as c r y s t a l l i z a t i o n hea t and work pe r f o rmed by d r i v i n g moto rs
( e s p e c i a l l y i n m i x e r s , c e n t r i f u g a l s and pumps) . A n o t h e r c o n v e n i e n t assump t i on i s
t h a t t h e mass l o s s e s caused by u n c o n t r o l l a b l e l e a k s ( l e a k i n g s e a l s , e v a p o r a t i o n
f rom open t a n k s , e t c . ) a r e t r e a t e d j o i n t l y as mass s t ream G ^ ^ . The e n e r g y l o s s e s
i n l e a k s , h o w e v e r , may c o n v e n t i o n a l l y be added t o t h o s e r e s u l t i n g f rom hea t
t r a n s f e r t o t he e n v i r o n m e n t , and t r e a t e d j o i n t l y as hea t Q . Assuming t h a t a l l
t he rema in ing q u a n t i t i e s shown i n F i g . 7.1 have been d e f i n e d f rom t h e
measurements , t he e q u a t i o n s o f mass and e n e r g y b a l a n c e s can be w r i t t e n as
• sl " %2 " %3 " ^ 4 " <^s5 = ^1 ^ 2 * ^ 3 + ^ 4 + ^ 5
%A^ ^ S2^2 ^ ^ s 3 ^ 3 ^ «^54^4 ^ ^ 5 ^ 5 =
= ^^^^ * \z\z' ^ 3 ^ 3 ^ ^ 4 ^ 4 - ^
Hence t he t o t a l l eak s t ream and t o t a l u n c o n t r o l l a b l e hea t l o s s a r e
^ 5 = » sl ^ hz * " '^s4 ^ - ( ^ 1 ^ ^2 * ^ 3 * ^ 4 ^
Q - G^^h^T + G 2 2 ^ ^ 3 ^ 3 " ^ 4 ^ 4 -
- (Sl^l * S2^2 ' ^ S 3 h s 3 ^ 4 ^ 4 + Ss^S^
T y p i c a l b a l a n c e d a t a and r e s u l t s a r e g i v e n i n T a b l e 7 .1 .
TABLE 7.1
Mass and e n e r g y b a l a n c e o f t h e s u g a r h o u s e , c a l c u l a t e d f o r 100 kg b e e t .
St ream name G
(kg /100 kg b ) t
( °C) h
( k J / k g ) G-h
( k J / 1 0 0 kg b )
k I n l e t
1 T h i c k j u i c e 28.6 103.3 306 8752 2 T h i n j u i c e 2.4 95 371 890 3 Water 9.4 80 335 3149 4 V a p o u r s 26.4 2754 72706 5 C o o l i n g w a t e r 360.0 20 84 30240
j O u t l e t
1 Sugar 14.0 20 23 322 2 M o l a s s e s 3.6 20 105 378 3 Condensa te 25.2 95 398 10030 4 B a r o m e t r i c w a t e r 382.0 55 230 87860 5 Leaks 2.0 Hea t l o s s e s 17147
237
7 .1 .4 M o n i t o r i n g and r e d u c t i o n o f t h e h e a t consumpt ion
The hea t economy i n a s u g a r f a c t o r y can be t r e a t e d as a sys tem kep t i n
o p e r a t i o n by a f u e l s u p p l y . As t h i s sys tem i s r e l a t i v e l y c o m p l i c a t e d , i t s
f u n c t i o n i n g can be e v a l u a t e d o n l y on t h e b a s i s o f r e c o r d e d v a l u e s o f c e r t a i n
pa ramete rs c h a r a c t e r i z i n g s e l e c t e d the rma l p r o c e s s e s . I t has been s u g g e s t e d
above t h a t t h e d a t a on sys tem o p e r a t i o n can be a p p l i e d t o i d e n t i f y h e a t l o s s e s
and t h e i r p o s s i b l e r e d u c t i o n . M o n i t o r i n g r e s u l t s t h u s e n a b l e one t o p o i n t o u t
w h e r e , and i n what manner , t h e e x i s t i n g i n s t a l l a t i o n can be improved and what
e f f e c t s can be e x p e c t e d .
E x p e r i e n c e p r o v e s t h a t i f no s y s t e m a t i c m o n i t o r i n g o f t h e hea t economy has
been c a r r i e d o u t p r e v i o u s l y , i n i t i a t i n g such a c t i o n may i m m e d i a t e l y y i e l d
advan tageous r e s u l t s . An i n v e n t o r y and d o c u m e n t a t i o n o f t h e e x i s t i n g the rma l
s y s t e m , even w i t h o u t hea t b a l a n c e s , e n a b l e s one t o d i s c o v e r t h e a b n o r m a l i t i e s
w h i c h a r e n o t v i s i b l e i n t h e f u n c t i o n i n g o f i n d i v i d u a l equ ipment u n i t s and
s t a t i o n s , l i k e e r r o r s i n c o n d e n s a t e l i n e s c a u s i n g i n c o m p l e t e u t i l i z a t i o n o f
condensa te e n e r g y , and e r r o r s i n v a p o u r l i n e s c a u s i n g sma l l u n c o n t r o l l a b l e
v a p o u r f l o w s between e v a p o r a t o r e f f e c t s . The most i m p o r t a n t c o n c l u s i o n on ways
t o r e d u c e h e a t consumpt ion can o f c o u r s e be drawn f rom t h e hea t b a l a n c e s o f
i n d i v i d u a l s t a t i o n s and o f t h e e n t i r e f a c t o r y . I t i s a n o t h e r m a t t e r , h o w e v e r ,
i n what manner t h e c o n c l u s i o n s a r e implemented i n p r a c t i c e . I n p r i n c i p l e , t h e
improvements a r e a l w a y s aimed a t r e d u c i n g h e a t consumpt i on p e r u n i t amount o f
raw m a t e r i a l , o r u n i t amount o f s u g a r . The e s s e n t i a l a i m , h o w e v e r , i s t o r e d u c e
m a n u f a c t u r i n g c o s t s . The economic f a c t o r s s h o u l d f i n a l l y d e c i d e w h e t h e r t h e
p o t e n t i a l r e d u c t i o n o f hea t consumpt ion i s u t i l i z e d o r n o t .
I t s h o u l d a l s o be remembered t h a t o n l y i n e x c e p t i o n a l c a s e s can t h e measures
r e d u c i n g hea t consumpt ion be r e g a r d e d as " p u r e " h e a t economy c o r r e c t i o n s . As
a r u l e , c o r r e c t i v e a c t i o n s a r e c o n c e r n e d w i t h t h e f a c t o r s a f f e c t i n g bo th p r o c e s s
and hea t economy. As an examp le , c o n s i d e r t h e c o n c e n t r a t i o n o f t h i c k j u i c e ,
a pa ramete r whose impo r tance t o t h e h e a t consumpt ion i n s u g a r m a n u f a c t u r e has
been d i s c u s s e d i n S e c t i o n 1 .3 .5 . Any c o r r e c t i o n o f t h i s p a r a m e t e r , h o w e v e r , i s
u n t h i n k a b l e w i t h o u t p r i o r a n a l y s i s o f p o s s i b l e consequences i n s u g a r y i e l d and
s u g a r q u a l i t y .
7.2 QUALITY OF WATER AND STEAM
7.2.1 Scope o f t h e q u a l i t y i n s p e c t i o n
I n o r d e r t o m a i n t a i n p r o p e r o p e r a t i n g c o n d i t i o n s f o r b o i l e r s and t u r b i n e s ,
i t i s n e c e s s a r y t o i n s p e c t t he q u a l i t y o f w a t e r and steam i n t h e the rma l sys tems
o f s u g a r f a c t o r i e s s y s t e m a t i c a l l y a n d , i f r e q u i r e d , t o t ake c o r r e c t i v e a c t i o n .
The aim o f t h e i n s p e c t i o n i s t o e s t a b l i s h , by measurement o r l a b o r a t o r y
a n a l y s i s , t h e amounts o f i m p u r i t i e s i n :
- f e e d w a t e r s u p p l i e d t o t h e b o i l e r ;
238
- b o i l e r w a t e r and s team;
- c o n d e n s a t e , p a r t i c u l a r l y f rom t h e e v a p o r a t i o n s t a t i o n .
The pa rame te rs o f make-up w a t e r a re a l s o i m p o r t a n t , and t h u s t h e q u a l i t y
i n s p e c t i o n i n c l u d e s a n a l y s e s o f raw w a t e r and o f w a t e r a t t h e i n d i v i d u a l s t a g e s
o f t h e p u r i f i c a t i o n p r o c e s s .
Wi th r e s p e c t t o t h e i r p h y s i c a l p r o p e r t i e s , t he i m p u r i t i e s can be c l a s s i f i e d
a s :
- mechan ica l i m p u r i t i e s , w i t h p a r t i c l e s i z e s above 0.1 m i c r o n , a p p e a r i n g as
suspended m a t t e r o r s e d i m e n t ;
- c o l l o i d a l i m p u r i t i e s , w i t h p a r t i c l e s between 1 nm and 0.1 m i c r o n , c r e a t i n g
s u s p e n s o i d s ;
- m o l e c u l a r i m p u r i t i e s , w i t h p a r t i c l e s be low 1 nm a p p e a r i n g i n s o l u t i o n s .
W i th r e s p e c t t o t he chemica l p r o p e r t i e s , t h e c u m u l a t i v e c o n c e n t r a t i o n s o f
c e r t a i n g r o u p s o f compounds a re i m p o r t a n t ( e x a m p l e s : h a r d n e s s , a l k a l i n i t y ) , b u t
so a l s o t he i n d i v i d u a l c o n c e n t r a t i o n s o f some s p e c i f i c e lemen ts and compounds
( e x a m p l e s : o x y g e n , S i O ^ ) .
Owing t o t h e e x t r e m e l y h i g h q u a l i t y r e q u i r e m e n t s o f w a t e r and steam t h a t
r e s u l t f rom t h e advanced p o w e r - g e n e r a t i o n t e c h n o l o g i e s used i n l a r g e - s c a l e
e l e c t r i c i t y g e n e r a t i o n , t h e p rob lem o f q u a l i t y i n s p e c t i o n and c o n t r o l has
e v o l v e d i n t o an e n t i r e b ranch o f e n g i n e e r i n g s c i e n c e ( r e f . 1 9 ) . O n l y a sma l l
p a r t o f i t i s r e a l l y a p p l i c a b l e t o the rma l sys tems a s s o c i a t e d w i t h s u g a r
t e c h n o l o g y .
The d e t a i l s and p r i n c i p l e s o f q u a l i t y i n s p e c t i o n o f w a t e r and steam may v a r y
i n d i f f e r e n t s u g a r f a c t o r i e s , i n a c c o r d a n c e w i t h i n s t a l l a t i o n o r equ ipment
t y p e s , l o c a l c o n d i t i o n s o r l o c a l r e g u l a t i o n s . As a r u l e , t h e c h i e f t e c h n o l o g i s t
and c h i e f power e n g i n e e r j o i n t l y bea r t h e r e s p o n s i b i l i t y f o r i n s p e c t i o n
p r i n c i p l e s ; somet imes, t h e agreement o f t h e equ ipment m a n u f a c t u r e r i s r e q u i r e d .
7 .2 .2 Condensa te
The aim o f t h e i n s p e c t i o n o f c o n d e n s a t e f rom t h e e v a p o r a t o r s t a t i o n i s t o
e s t a b l i s h w h e t h e r o r n o t i t i s s u i t a b l e as a f e e d - w a t e r component t h a t can be
r e t u r n e d t o t h e b o i l e r h o u s e . ( T h e q u a l i t y o f d i r e c t f e e d w a t e r f o r t h e b o i l e r s
i s i n s p e c t e d s e p a r a t e l y . ) A t t e n t i o n s h o u l d be f o c u s e d on m o l e c u l a r i m p u r i t i e s
and p a r t i c u l a r l y on s u g a r c o n c e n t r a t i o n , w h i c h may i n d i c a t e l e a k i n g t u b e s i n
t h e e v a p o r a t o r o r t h e p r e s e n c e o f j u i c e d r o p l e t s i n v a p o u r s f rom t h e f i r s t
e f f e c t .
The p r e s e n c e o f s u g a r makes i t p r a c t i c a l l y i m p o s s i b l e t o d i r e c t c o n d e n s a t e
t o t h e b o i l e r , as t h i s m igh t cause f o u l i n g o f t h e h e a t i n g s u r f a c e and o t h e r
dange rous e f f e c t s . As h i g h c o n d e n s a t e t e m p e r a t u r e may i n d u c e t he d e c o m p o s i t i o n
o f s u c r o s e w h i c h t h e n becomes u n d e t e c t a b l e , o p e r a t o r s a r e recommended t o r e l y on
239
t h e d e t e r m i n a t i o n o f oxygen c o n s u m p t i o n , w h i c h i s a measure o f t he c o n c e n t r a t i o n
o f o r g a n i c compounds. A c c o r d i n g l y , a n a l y s e s i n c o n d e n s a t e q u a l i t y i n s p e c t i o n
t y p i c a l l y dea l w i t h p H , s u g a r p r e s e n c e and o x y g e n c o n s u m p t i o n .
As f a r as t h e c o n d e n s a t e b y - p a s s i n g t h e b o i l e r s i s c o n c e r n e d , t h e i n s p e c t i o n
i a aimed a t d e t e c t i o n o f s u g a r as an i n d i c a t i o n o f imp rope r o p e r a t i o n o f
equ ipment ( j u i c e d r o p l e t s o r j u i c e foam i n v a p o u r s ) , o r l e a k i n g t u b e s . R o u t i n e
i n s p e c t i o n may r e l y on samples t aken f rom c o n d e n s a t e t a n k s . Once t h e p r e s e n c e
o f s u g a r i n a t ank has been d e t e c t e d , h o w e v e r , i t may become n e c e s s a r y t o o b t a i n
condensa te samples f rom the o u t l e t p i p e s c o n n e c t e d t o t h e i n d i v i d u a l equ ipment
u n i t s .
An i m p o r t a n t f a c t o r t o be a c c o u n t e d f o r i n e n s u r i n g t h e e f f i c i e n c y o f
condensa te q u a l i t y i n s p e c t i o n i s t h e f r e q u e n c y o f a n a l y s e s . D e t e c t i o n o f s u g a r
i n condensa te f rom t h e f i r s t and second e v a p o r a t o r e f f e c t s s h o u l d be p e r f o r m e d
c o n t i n u o u s l y . I f t h e r e a r e no a u t o m a t i c a n a l y s e r s , t h i s means t h a t t h e t e s t s a r e
r e p e a t e d o v e r a c y c l e o f s e v e r a l m i n u t e s a t a p o s i t i o n i n t he v i c i n i t y o f t h e
e v a p o r a t o r . A c c u r a t e l a b o r a t o r y t e s t s f o r s u g a r , t o g e t h e r w i t h o x y g e n
consumpt ion measurements , a r e r e q u i r e d a t l e a s t e v e r y 2 h o u r s . O t h e r c o n d e n s a t e
a n a l y s e s may be pe r f o rmed w i t h t h e same f r e q u e n c y , as i n t h e case o f f e e d - w a t e r
i n s p e c t i o n . An example o f a comp le te s e t o f c o n d e n s a t e a n a l y s e s , a c c e p t e d by t h e
b o i l e r m a n u f a c t u r e r f o r a s p e c i f i c s u g a r f a c t o r y , i s g i v e n i n T a b l e 7 . 2 .
TABLE 7.2
Example o f a s e t o f condensa te a n a l y s e s .
Q u a n t i t y D imens ion T e s t s ^ p e r ^ 8 - h o u r
pH 4 T o t a l h a r d n e s s m v a l / l i t r e 1 Oxygen consumpt ion mg KMnO¿^ / l i t r e 4 A l k a l i n i t y m v a l / l i t r e 2 Sugar p r e s e n c e 4*
* / number o f l a b o r a t o r y t e s t s aimed a t v e r i f i c a t i o n o f r o u t i n e t e s t s
7 .2 .3 Feed w a t e r and make-up w a t e r
Feed w a t e r s u p p l i e d t o t h e b o i l e r s c o n s i s t s o f e v a p o r a t o r c o n d e n s a t e t o w h i c h
make-up w a t e r i s added . The demand f o r make-up w a t e r i s u s u a l l y o n l y a few
p e r c e n t on b e e t s . G e n e r a l l y , q u a l i t y r e q u i r e m e n t s c o n c e r n i n g f e e d w a t e r depend
on t h e b o i l e r t y p e and steam p r e s s u r e . I n some c o u n t r i e s , s t a n d a r d s o r o t h e r
r e g u l a t i o n s have been i n t r o d u c e d i n t h i s f i e l d . Q u a l i t y recommendat ions i s s u e d
i n Be lg ium can be f ound i n t h e l i t e r a t u r e ( r e f . 2 0 ) . B e l o w , t h e r e q u i r e m e n t s
f o r m u l a t e d i n P o l i s h r e g u l a t i o n s ( r e f . 21) a r e r e v i e w e d .
The f e e d w a t e r must be c o l o u r l e s s and f r e e f rom mechan ica l i m p u r i t i e s . A pH
240
above 7 i s r e q u i r e d and t he oxygen consumpt ion s h o u l d be as low as p o s s i b l e ,
p r e f e r a b l y be low 5-10 mg K M n O ^ / l i t r e . The w a t e r h a r d n e s s s h o u l d be as low as
p o s s i b l e , b u t i t s a l l o w a b l e upper l i m i t depends on t h e b o i l e r t y p e , steam
p r e s s u r e and t he hea t f l u x a t t h e h e a t i n g s u r f a c e ( f o r examp le , i n t h e case o f
w a t e r - t u b e r a d i a n t b o i l e r s a t 40 ba r o p e r a t i n g p r e s s u r e , f e e d w a t e r w i t h a
h a r d n e s s o f up t o 0.01 m v a l / l i t r e can be a c c e p t e d ) . The o x y g e n c o n t e n t s h o u l d be
as smal l as p o s s i b l e , n o t e x c e e d i n g 0 .02 -0 .03 m g / l i t r e f o r modern b o i l e r s . The
CO^ c o n t e n t - w i t h w h i c h t h e danger o f c o r r o s i v e a c t i o n i s a s s o c i a t e d - must n o t
exceed 20 m g / l i t r e .
Depending on t he b o i l e r p r e s s u r e , d i f f e r e n t l e v e l s o f a l k a l i n i t y and o f t h e
c o n t e n t o f s i l i c o n d i o x i d e , phospha tes and i r o n compounds can be a c c e p t e d . The
c o n c e n t r a t i o n o f o i l - t y p e i m p u r i t i e s c a n n o t e x c e e d a l i m i t w h i c h has been
d e f i n e d a t 10 m g / l i t r e f o r o l d e r b o i l e r s w i t h l a r g e w a t e r vo lume and a t 0 . 5 - 1 . 0
m g / l i t r e f o r modern b o i l e r s o p e r a t e d a t 40 ba r steam p r e s s u r e .
The same r e g u l a t i o n d e f i n e s t h e s e t o f o b l i g a t o r y f e e d - w a t e r a n a l y s e s . F o r
t he most w i d e l y used b o i l e r t y p e s , i t i s n e c e s s a r y t o d e t e r m i n e :
- p H ;
- oxygen c o n s u m p t i o n ;
- h a r d n e s s ;
- d i s s o l v e d oxygen c o n t e n t ;
- mechan ica l i m p u r i t i e s ;
- a l k a l i n i t y ;
- S i O ^ c o n c e n t r a t i o n ;
- CO^ c o n c e n t r a t i o n ;
- o i l - t y p e i m p u r i t i e s ;
- w a t e r a p p e a r a n c e .
F o r o l d e r b o i l e r s o p e r a t e d a t a p r e s s u r e be low 16 b a r , o n l y t h e f i r s t 5
a n a l y s e s on t h e l i s t a n d , a d d i t i o n a l l y , t he d e t e r m i n a t i o n o f t e m p o r a r y h a r d n e s s ,
a r e o b l i g a t o r y . An i m p o r t a n t s e c t i o n o f t h e r e g u l a t i o n s s t i p u l a t e s t h a t f o r
modern b o i l e r s n o t men t ioned i n t h e g e n e r a l s e c t i o n , t h e r e q u i r e m e n t s f o r m u l a t e d
by t h e b o i l e r ' s m a n u f a c t u r e r a r e d e c i s i v e .
W a t e r - q u a l i t y i n s p e c t i o n i n t h e w a t e r - t r e a t m e n t i n s t a l l a t i o n s may be aimed a t
c o n t r o l l i n g t h e f i n a l r e s u l t o f t h e t r e a t m e n t , t o g e t h e r w i t h t h e r e s u l t s o f u n i t
o p e r a t i o n s such as c o a g u l a t i o n , f i l t r a t i o n , d e c a r b o n i z a t i o n , and s o f t e n i n g .
The d e t a i l e d i n s p e c t i o n scheme s h o u l d be adap ted t o l o c a l c o n d i t i o n s , w h i c h
means t o t he p r o p e r t i e s o f t h e raw w a t e r , t he t r e a t m e n t p r o c e s s s t r u c t u r e and
r e q u i r e m e n t s imposed on f e e d - w a t e r p a r a m e t e r s . I n t h e case o f i o n exchange
t r e a t m e n t , c o n t r o l o f t h e i o n - e x c h a n g e r a c t i v i t y must be i n c l u d e d .
C o n c e r n i n g t h e f r e q u e n c y o f a n a l y s e s , t h e r e q u i r e m e n t s f o r m u l a t e d by t h e
b o i l e r m a n u f a c t u r e r a re b i n d i n g on o p e r a t o r s . U s u a l l y , a comp le te s e t o f
241
a n a l y s e s s h o u l d be pe r f o rmed t h r e e t imes a d a y , i . e . once p e r 8 - h o u r w o r k i n g
s h i f t . Loca l c o n d i t i o n s may make i t n e c e s s a r y t o p e r f o r m c e r t a i n a n a l y s e s more
f r e q u e n t l y , w h i l e o t h e r s may even be o m i t t e d . I n t h e case o f new b o i l e r s ,
h o w e v e r , such changes must be a c c e p t e d by t h e m a n u f a c t u r e r .
An example o f a comple te s e t o f w a t e r a n a l y s e s i n t he d i f f e r e n t s t a g e s o f
a t r e a t m e n t p r o c e s s , and f e e d - w a t e r a n a l y s e s a c c e p t e d by t h e b o i l e r m a n u f a c t u r e r ,
i s shown i n T a b l e 7 . 3 .
7 .2 .4 B o i l e r w a t e r and steam
Steam g e n e r a t i o n i n b o i l e r s i s i n h e r e n t l y a s s o c i a t e d w i t h t h e i n c r e a s i n g
c o n c e n t r a t i o n o f i m p u r i t i e s i n t he b o i l e r w a t e r . T h i s , i n t u r n , c r e a t e s t he
danger o f d i s t u r b a n c e s i n b o i l e r o p e r a t i o n .
Mechan i ca l i m p u r i t i e s o f o r g a n i c o r i g i n t e n d t o i n c r e a s e b o i l e r f o a m i n g ; i f
combined w i t h m i n e r a l i m p u r i t i e s , t h e y cause t h e f o r m a t i o n o f a dange rous k i n d
o f b o i l e r s c a l e . Mechan i ca l i m p u r i t i e s o f m i n e r a l o r i g i n m igh t become
t r a n s f o r m e d i n t o s l u d g e o r h a r d b o i l e r s c a l e . C o l l o i d a l i m p u r i t i e s a l s o cause
foaming and s l u d g e f o r m a t i o n ; c o l l o i d a l s i l i c o n d i o x i d e i s p a r t i c u l a r l y
d a n g e r o u s , as i t becomes t r a n s f o r m e d i n t o b o i l e r s c a l e w h i c h i s v e r y d i f f i c u l t
t o remove. O i l o r l u b r i c a n t p r e s e n t i n b o i l e r w a t e r becomes s i n t e r e d on t h e
h e a t i n g s u r f a c e s , making h e a t t r a n s f e r more d i f f i c u l t ; e v e n t u a l l y , t h i s may l e a d
t o b u r n i n g o f t h e b o i l e r t u b e s . S i m i l a r e f f e c t s a r e i n d u c e d by t h e p r e s e n c e o f
o r g a n i c m o l e c u l a r i m p u r i t i e s ( e . g . s u c r o s e ) , w h i l e m i n e r a l m o l e c u l a r i m p u r i t i e s
cause s c a l e f o r m a t i o n o r c o r r o s i o n .
Q u a l i t y i n s p e c t i o n o f b o i l e r w a t e r i s aimed a t d e t e r m i n i n g w h e t h e r o r n o t t h e
c o n c e n t r a t i o n o f i m p u r i t i e s e x c e e d s t h e a l l o w a b l e l i m i t . The i n s p e c t i o n
r e q u i r e m e n t s can be f o r m u l a t e d by t h e b o i l e r m a n u f a c t u r e r o r by b o i l e r
i n s p e c t i o n a u t h o r i t i e s . The g e n e r a l p r i n c i p l e i s t h a t t h e c o n c e n t r a t i o n o f
i m p u r i t i e s must be smal l enough t o e n s u r e :
- e l i m i n a t i o n o f c o r r o s i o n p r o c e s s e s ;
- l i m i t a t i o n o f b o i l e r s c a l e and s l u d g e f o r m a t i o n ;
- m a i n t a i n i n g t h e p r o p e r steam p u r i t y , w h i l e h e a t l o s s e s r e s u l t i n g f rom t h e
b o i l e r blowdown a r e kep t r e a s o n a b l y s m a l l .
A c c o r d i n g t o P o l i s h r e g u l a t i o n s , q u a l i t y i n s p e c t i o n o f t h e b o i l e r w a t e r
s h o u l d c o m p r i s e , f o r most b o i l e r s , p a r t i c u l a t e and d i s s o l v e d m a t t e r , a l k a l i n i t y ,
S i O ^ c o n t e n t and P^O^ c o n t e n t . F o r o l d e r b o i l e r s , i t i s enough t o d e t e r m i n e
p a r t i c u l a t e and d i s s o l v e d m a t t e r , and a l k a l i n i t y .
I n o r d e r t o o b t a i n a t e m p o r a r y pH i n c r e a s e and t o c o u n t e r a c t s l u d g e
p r e c i p i t a t i o n , phospha te may be added t o b o i l e r w a t e r . H o w e v e r , e f f e c t i v e
c o n t r o l o f t h e c o n c e n t r a t i o n o f i m p u r i t i e s r e l i e s on b o i l e r b lowdown. W i th t h e
r e s u l t s o f a n a l y s e s o f b o i l e r w a t e r and make-up w a t e r , i t i s p o s s i b l e t o
p r e d e t e r m i n e t h e n e c e s s a r y blowdown r a t e i n o r d e r t o m a i n t a i n a c o n s t a n t d e s i r e d
242
TABL
E 7.
3 Ex
ampl
e of
a s
et o
f an
alys
es f
or m
ake-
up w
ater
an
d fe
ed w
ater
(r
adia
nt
bo
iler
s,
40
bar
stea
m p
ress
ure
).
Uppe
r nu
mbe
r -
test
s pe
r 8-
hour
s
hif
t,
low
er
num
bers
-
allo
wab
le
valu
es.
_ W
ater
Aft
er
Aft
er
Qua
ntity
W
ith
Fil
tere
d
"^^^
^""^
^^
^^"^
Fe
ed
coag
ulan
t »-
T>T^
erea
g^
^han
ge
deso
rpti
on
exch
ange
H+
N
a+
1 in
24
h 8.
5-11
.0
O
O
7.0-
9.5
7.0
-9.5
Oxy
gen
cons
umpt
ion
, 4„
o/
, u
1 (m
g K
MnO
^/lit
re)
1 24
h
5.0-
10.0
Tota
l ha
rdne
ss
i o/
i u
—!
1 (m
va
l/li
tre
) 1
m
24
h Q
05
0.05
-0.1
0
Oxy
gen
cont
ent
1 (m
g/l
itre
) 0.
02-0
.03
PpOc
con
tent
1
(mg
/lit
re)
1.0-
3.0
Fe c
onte
nt
τ .
. 1
in 2
4 h
J ^
(mg
/lit
re)
1 in
24
h
^^^^
Q
5
Q
Q5
0.03
-0.0
5
Oil
cont
ent
irre
gu
lar
(mg
/lit
re)
0.05
-1.0
0
243
c o n c e n t r a t i o n i n t h e b o i l e r w a t e r ( f o r d e t a i l s , see r e f . 2 2 ) . I t s h o u l d be
emphas ized t h a t e x c e s s i v e blowdown means a l o s s o f e n e r g y and s h o u l d t h e r e f o r e
be a v o i d e d .
Steam l e a v i n g t h e b o i l e r c o n t a i n s i m p u r i t i e s o r i g i n a t i n g f rom t h e b o i l e r
w a t e r , p a r t i c u l a r l y i f foaming o c c u r s . Such i m p u r i t i e s - e s p e c i a l l y s i l i c o n
d i o x i d e and i r o n compounds - a r e d a n g e r o u s , as t h e y f a l l i n t o t h e t u r b i n e and
t h e r e fo rm d e p o s i t s w h i c h a f f e c t t h e d u r a b i l i t y o f t h e t u r b i n e e l emen ts and
d i s t u r b t h e i r f u n c t i o n ( e . g . h i n d e r t h e movement o f v a l v e p a r t s ) . C o n t r o l o f
steam p u r i t y s h o u l d be by c o n t r o l o f t h e i m p u r i t y c o n t e n t o f t h e b o i l e r w a t e r .
The l i m i t o f i m p u r i t y c o n c e n t r a t i o n i n s team, as w e l l as t h e method o f i t s
i n s p e c t i o n , s h o u l d be d e t e r m i n e d by c o n s u l t a t i o n w i t h t h e b o i l e r and t u r b i n e
m a n u f a c t u r e r s , and f i n a l l y v e r i f i e d i n p r a c t i c a l o p e r a t i o n . T y p i c a l l y , s team
q u a l i t y m o n i t o r i n g s h o u l d i n c l u d e :
- S i O ^ c o n c e n t r a t i o n ;
- o v e r a l l Fe c o n c e n t r a t i o n ;
- e l e c t r i c a l c o n d u c t i v i t y o f t h e c o n d e n s a t e a t 20°C.
The f r e q u e n c y o f a n a l y s e s o f b o i l e r w a t e r and steam s h o u l d f o l l o w t h e
r e q u i r e m e n t s o f t h e b o i l e r m a n u f a c t u r e r : t y p i c a l l y , t h e r e q u i r e d f r e q u e n c y i s
t w i c e d a i l y . P r a c t i c a l e x p e r i e n c e p r o v e s , h o w e v e r , t h a t f o r e f f i c i e n t q u a l i t y
c o n t r o l , t h e b a s i c pa rame te rs o f b o i l e r w a t e r (pH and e l e c t r i c a l c o n d u c t i v i t y )
must be d e t e r m i n e d more f r e q u e n t l y .
An example o f a s e t o f b o i l e r w a t e r and steam a n a l y s e s , a c c e p t e d by t h e
b o i l e r m a n u f a c t u r e r f o r a s p e c i f i c s u g a r f a c t o r y , i s g i v e n i n T a b l e 7 .4 .
TABLE 7.4
Example o f a s e t o f b o i l e r w a t e r and steam a n a l y s e s .
Q u a n t i t y D imens ion A l l o w a b l e
v a l u e s T e s t s p e r
8 - h o u r s h i f t
B o i l e r w a t e r
pH E l e c t r i c a l c o n d u c t i v i t y A l k a l i n i t y " p " P2O5 c o n t e n t SÍO2 c o n t e n t
yS /cm m v a l / 1 i t r e m g / 1 i t r e m g / 1 i t r e
7 50-5000 0 . 1 - 6 . 0
3-10 ca 25
4 1-2
1 2
i r r e g u l a r
Steam Fe c o n t e n t SÍO2 c o n t e n t
m g / 1 i t r e m g / 1 i t r e
max. 0.02 max. 0.02
1 1
7 .2 .5 Sampl ing o f w a t e r and steam
Water samples a r e c o l l e c t e d and p r e s e r v e d i n g l a s s b o t t l e s w h i c h a r e washed
i n advance w i t h soap o r soda s o l u t i o n , t h e n t a p w a t e r and f i n a l l y w i t h d i s t i l l e d
w a t e r . S i m i l a r l y washed g l a s s p l u g s , o r c o r k s b o i l e d i n d i s t i l l e d w a t e r , a r e
u s e d . The method o f samp l i ng w a t e r s h o u l d be a d a p t e d t o t h e t y p e o f w a t e r s o u r c e
and t o t h e a n a l y s i s r e q u i r e d ( r e f . 2 3 ) . F o r e x a m p l e , raw w a t e r f rom a pump o r
244
a p i p e l i n e s h o u l d f l o w f o r abou t 10 m inu tes b e f o r e a sample i s c o l l e c t e d ; i f
t h e a n a l y s i s i s c o n c e r n e d w i t h t h e c o n t e n t o f d i s s o l v e d g a s , sample a e r a t i o n
must be a v o i d e d .
Condensa te and b o i l e r w a t e r a r e sampled a c c o r d i n g t o s t a n d a r d methods ( r e f .
24) and samp l ing equ ipment can a l s o be s t a n d a r d i z e d ( r e f . 2 5 ) . Condensa te samples
can be o b t a i n e d t h r o u g h s p e c i a l gauge cocks i n s t a l l e d i n r e l e v a n t p i p e l i n e s , o r
t h r o u g h d r a i n cocks t h a t a r e p a r t s o f w a t e r - l e v e l i n d i c a t o r s . The l a t t e r
p o s s i b i l i t y i s p a r t i c u l a r l y i m p o r t a n t i f t h e condensa te p r e s s u r e i s l o w e r t han
t he a t m o s p h e r i c p r e s s u r e ; o t h e r w i s e , d r a i n cocks o r a i r - e s c a p e cocks a t t h e
steam t r a p s can be u s e d .
F e e d - w a t e r and b o i l e r - w a t e r samples must be c o o l e d . U s u a l l y , s i m p l e c o i l -
t y p e , w a t e r - c o o l e d hea t e x c h a n g e r s a r e i n s t a l l e d i n c o n n e c t i o n w i t h t he r e l e v a n t
t e s t c o c k s . I t s h o u l d be p o i n t e d o u t t h a t such c o o l e r s may be s u b j e c t t o
h y d r a u l i c t e s t s , t o g e t h e r w i t h t h e e n t i r e b o i l e r .
Sample c o o l i n g i s a l s o n e c e s s a r y i n t h e case o f steam s a m p l i n g ; steam i s
c o l l e c t e d i n condensa te form ( r e f . 2 6 ) . L i k e f e e d - w a t e r and b o i l e r - w a t e r
s a m p l i n g , condensa te f l o w must be a l l o w e d p r i o r t o sample c o l l e c t i o n , so t h a t
any i m p u r i t i e s i n i t i a l l y p r e s e n t i n t he p i p e and i n t he c o o l e r a r e washed away.
7 .2 .6 D e t e r m i n a t i o n o f p h y s i c a l p r o p e r t i e s
From t h e p o i n t o f v i e w o f s u i t a b i l i t y f o r h e a t economy s y s t e m s , o n l y
p h y s i c a l p r o p e r t i e s o f w a t e r r e l a t e d t o t h e c o n c e n t r a t i o n o f i m p u r i t i e s a r e
i m p o r t a n t .
The appearance o f w a t e r i s e v a l u a t e d by t r a n s p a r e n c y and t u r b i d i t y t e s t s .
Such t e s t s a r e g e n e r a l l y s t a n d a r d i z e d ( r e f . 2 7 ) .
The measure o f c o n c e n t r a t i o n o f n o n - v o l a t i l e i m p u r i t i e s i n w a t e r i s t h e d r y
m a t t e r c o n t e n t , i . e . t he amount o f d r y m a t t e r r e m a i n i n g a f t e r 1 l i t r e o f w a t e r
has been e v a p o r a t e d ; i t s w e i g h t i s d e t e r m i n e d a f t e r d r y i n g a t 105°C. T e s t
p r o c e d u r e s a r e a l s o s t a n d a r d i z e d ( r e f . 2 8 ) .
The t o t a l s a l t c o n t e n t i n w a t e r can be e x p r e s s e d i n d i r e c t l y by t h e w a t e r
d e n s i t y . F o r r a p i d measurements o f d e n s i t y , ae rome te r s c a l i b r a t e d i n k g / l i t r e
o r d e g r e e s Baume (°Bé) can be u s e d .
The c o n t e n t o f s a l t s , a c i d s and bases can be e x p r e s s e d by t h e s p e c i f i c
e l e c t r i c a l c o n d u c t i v i t y o f t h e w a t e r . As t h i s depends on t e m p e r a t u r e , i t i s
measured a t 20°C. I n t he case o f measurements made a t d i f f e r e n t t e m p e r a t u r e s ,
c o n d u c t i v i t y v a l u e s s h o u l d be c o r r e c t e d a c c o r d i n g t o s t a n d a r d i z e d f o r m u l a e . As
c o n d u c t i v i t y measurements can e a s i l y be r e c o r d e d a u t o m a t i c a l l y , t h e y a r e w i d e l y
a p p l i e d i n w a t e r and steam q u a l i t y i n s p e c t i o n . M e a s u r i n g p r o c e d u r e s a r e
s t a n d a r d i z e d ( r e f . 2 9 ) .
245
7 .2 .7 T o t a l h a r d n e s s and t e m p o r a r y h a r d n e s s
Hardness i s a measure o f t h e t e n d e n c y o f w a t e r t o p r o d u c e d e p o s i t s and t o
fo rm b o i l e r s c a l e . Ha rdness i s caused by c a l c i u m and magnesium s a l t s t h a t appear
as b i c a r b o n a t e s , Ca(HC02)2 ^Qi^^O^'^Z' s a l t s o f i n o r g a n i c a c i d s ; t h a t
i s , s u l p h a t e s , c h l o r i d e s and n i t r a t e s ( C a S O ^ , M g C l ^ , Cdi(HÖ^)^) and o t h e r s . Water
h a r d n e s s can be e x p r e s s e d i n d e g r e e s , o r g r a m - e q u i v a l e n t s o r m i l l i g r a m -
e q u i v a l e n t s p e r u n i t vo lume . I n s e v e r a l European c o u n t r i e s , t h e s o - c a l l e d German
deg ree o f h a r d n e s s has been a p p l i e d ; i t c o r r e s p o n d s t o 10 g CaO i n 1 m* o f
w a t e r , o r 10 mg CaO i n 1 l i t r e .
The t o t a l h a r d n e s s o f w a t e r can be d e t e r m i n e d u s i n g t h e v e r s e n a t e method ,
t h a t i s , by t i t r a t i n g t he w a t e r sample w i t h sodium v e r s e n a t e ( r e f . 3 0 ) .
T o t a l h a r d n e s s can be r e g a r d e d as t h e sum o f t e m p o r a r y h a r d n e s s , caused by
c a l c i u m and magnesium b i c a r b o n a t e s , and permanent h a r d n e s s , caused by o t h e r
c a l c i u m and magnesium s a l t s . Tempora ry h a r d n e s s can be d e t e r m i n e d by t i t r a t i n g
w a t e r w i t h h y d r o c h l o r i c a c i d .
7 .2 .8 Oxygen consumpt ion and s u g a r c o n t e n t
Oxygen consumpt ion and a r e l a t e d q u a n t i t y , t h e chemica l o x y g e n demand, a r e
c o n v e n t i o n a l measures o f t h e c o n c e n t r a t i o n o f o r g a n i c i m p u r i t i e s and some o t h e r
e a s i l y o x i d i z a b l e i n o r g a n i c compounds.
The oxygen consumpt ion can be d e t e r m i n e d by t i t r a t i n g w a t e r w i t h p o t a s s i u m
permanganate s o l u t i o n . I t i s e x p r e s s e d i n t h e m i l l i g r a m s o f KMnO^ used t o
o x i d i z e t he i m p u r i t i e s i n 1 l i t r e o f w a t e r . By c o n v e r t i n g t h i s q u a n t i t y i n t o
t h e oxygen amount, we o b t a i n t h e chemica l o x y g e n demand.
T e s t s o f t he p r e s e n c e o f s u c r o s e i n w a t e r (2 m g / 1 i t r e o r more) can be
pe r f o rmed u s i n g t h e w e l l known a l p h a - n a p h t o l method . W i t h l a r g e r s u g a r
c o n c e n t r a t i o n s , c l a s s i c a l a n a l y s i s t e c h n i q u e s known i n s u g a r t e c h n o l o g y can be
a p p l i e d ( r e f . 3 1 ) . C o n d u c t o m e t r i c and o t h e r methods f o r c o n t i n u o u s measurement ,
p a r t i c u l a r l y s u i t a b l e f o r c o n d e n s a t e q u a l i t y m o n i t o r i n g , a r e a l s o i n u s e .
7 .2 .9 Hydrogen i o n c o n t e n t , a l k a l i n i t y and o t h e r p r o p e r t i e s
The v a l u e o f pH i n aqueous s o l u t i o n s can be d e t e r m i n e d by c o l o r i m e t r i c
a n a l y s i s o r by e l e c t r i c a l measurement . The l a t t e r method i s t h e most w i d e l y
u s e d ; i t c o n s i s t s o f measur ing t h e e l e c t r o m o t i v e f o r c e o f t h e s o - c a l l e d
p H - m e t r i c c e l l , i . e . two e l e c t r o d e s immersed i n t h e s o l u t i o n . I t s h o u l d be
p o i n t e d o u t , h o w e v e r , t h a t t h e measu r i ng e r r o r i s h i g h l y dependen t on t h e
e l e c t r o d e c o n d i t i o n . T h e r e f o r e , pH me te rs s h o u l d be t e s t e d o f t e n by measu r ing
t h e pH v a l u e s o f two r e f e r e n c e s o l u t i o n s . F o r r e l i a b l e measurement , i t i s
n e c e s s a r y t o e l i m i n a t e t h e p o s s i b i l i t y o f a c c i d e n t a l l y p o l l u t i n g w a t e r samples
w i t h any i m p u r i t i e s . The t e m p e r a t u r e o f t h e w a t e r t e s t e d s h o u l d be 20°C.
A l k a l i n i t y o f w a t e r i s caused by t h e p r e s e n c e o f h y d r o x i d e s and s a l t s o f
246
e lements b e l o n g i n g t o t h e p o t a s s i u m and c a l c i u m g r o u p s . I t can be d e t e r m i n e d by
t i t r a t i n g w a t e r w i t h h y d r o c h l o r i c a c i d .
O t h e r chemica l a n a l y s e s i m p o r t a n t f o r w a t e r q u a l i t y i n s p e c t i o n a r e :
- oxygen ( u n d e r s t o o d as d i s s o l v e d f r e e o x y g e n ) c o n t e n t ;
- c a r b o n d i o x i d e c o n t e n t ;
- phospha te c o n t e n t ;
- s i l i c o n d i o x i d e c o n t e n t ;
- o i l ( u n d e r s t o o d as o i l - t y p e i m p u r i t i e s ) c o n t e n t ;
- i r o n ( u n d e r s t o o d as t o t a l i r o n i n v a r i o u s compounds) c o n t e n t .
7.3 FUEL ANALYSIS
7.3.1 Sampl ing o f f u e l s
F u e l s a r e e v a l u a t e d u s i n g t h e r e s u l t s o f l a b o r a t o r y t e s t s p e r f o r m e d on an
a v e r a g e d l a b o r a t o r y samp le . Samples s h o u l d be t aken f rom t h e f u e l t r a n s p o r t s
d u r i n g u n l o a d i n g , so t h a t n e c e s s a r y c l a i m s t o t h e s u p p l i e r can be made, and a l s o
f rom the f u e l s t ream i n t r o d u c e d t o t h e b o i l e r f u r n a c e , so t h a t t h e a c t u a l
h e a t i n g v a l u e can be a c c o u n t e d f o r i n t h e e n e r g y b a l a n c e . The most i m p o r t a n t
p r o p e r t i e s o f coa l and o t h e r s o l i d f u e l s a r e t h e p e r c e n t a g e s o f c o m b u s t i b l e
m a t t e r , m o i s t u r e and a s h . The c h a r a c t e r i s t i c s o f i m p o r t a n t c o a l t y p e s a r e
s t a n d a r d i z e d i n many c o u n t r i e s ( r e f . 3 2 ) . I n t h e case o f l i q u i d f u e l s , such
p r o p e r t i e s as v i s c o s i t y , t h e p e r c e n t a g e s o f s u l p h u r and vanadium o x i d e , and
f i n a l l y t h e p e r c e n t a g e o f w a t e r , a r e p a r t i c u l a r l y i m p o r t a n t . F o r d e t a i l s ,
n a t i o n a l s t a n d a r d s s h o u l d be c o n s u l t e d ( r e f . 3 3 ) .
C o r r e c t samp l ing o f f u e l i s a p r e r e q u i s i t e f o r r e l i a b l e d e t e r m i n a t i o n o f i t s
p r o p e r t i e s . The f o l l o w i n g c o n c e p t s a r e a p p l i e d i n d e f i n i n g samp l i ng p r o c e d u r e s :
- a p a r e n t l o t i s t h e amount o f a d e f i n i t e t y p e o f f u e l , n o t g r e a t e r t han
1000 t o n s ;
- a p r i m a r y sample i s a sample t aken f rom one p l a c e i n t h e p a r e n t l o t , o r a
s i n g l e sample taken f rom a f l o w i n g - f u e l s t r e a m ;
- a g r o s s sample i s a sample c o n t a i n i n g a l l p r i m a r y s a m p l e s ;
- an a v e r a g e d sample i s a p a r t o f t h e g r o s s sample d e s t i n e d f o r l a b o r a t o r y
a n a l y s e s .
I n t h e case o f c o a l o r o t h e r s o l i d f u e l s , i t i s d e s i r e d t h a t each p a r t i c l e i n
t h e p a r e n t l o t be g i v e n t he same p r o b a b i l i t y o f b e i n g chosen f o r t h e sample as
e v e r y o t h e r p a r t i c l e , d e s p i t e d i f f e r e n c e s i n p a r t i c l e s i z e o r s h a p e . P r i m a r y
samples s h o u l d p r e f e r a b l y be c o l l e c t e d f rom a f u e l s t ream on a c o n v e y o r , w i t h
t h e f r e q u e n c y a d j u s t e d t o t h e s i z e o f t h e p a r e n t l o t and t o t h e r e q u i r e d number
o f samp les . D i r e c t samp l ing f rom r a i l w a y c a r s , t r u c k s o r f u e l p i l e s i s a l l o w e d
o n l y i f t h e r e i s no p o s s i b i l i t y o f samp l i ng f rom c o n v e y o r s . The g r o s s sample i s
fo rmed by m i x i n g a l l p r i m a r y s a m p l e s ; c a r e s h o u l d be t aken t h a t t h e samples a r e
247
hand led so as t o m i n i m i z e changes i n f u e l p r o p e r t i e s . F o r d e t a i l s , see t h e
a p p r o p r i a t e s t a n d a r d s ( r e f . 3 4 ) .
I n t h e case o f l i q u i d f u e l s , i t i s i m p o r t a n t t o a p p l y t h e same method o f
samp l ing when c o l l e c t i n g t h e p r i m a r y samples f rom w h i c h t h e a v e r a g e d sample w i l l
be o b t a i n e d . Sampl ing o f f u e l s i n s t o r a g e t a n k s s h o u l d be pe r f o rmed i n such
a way t h a t no p a r t i c u l a r l a y e r o f l i q u i d i s p r e f e r r e d ; i f a b a t c h o f l i q u i d i s
run i n t o a t a n k , t hen t h e f i r s t samp l ing s h o u l d o c c u r n o t e a r l i e r t han two h o u r s
l a t e r . Sampl ing f rom p i p e l i n e s may e i t h e r be done c o n t i n u o u s l y , p r o p o r t i o n a l l y
t o t h e f u e l f l o w , o r p e r i o d i c a l l y a t c o n s t a n t f r e q u e n c y ; p e r i o d s w i t h c o n s t a n t
f l o w c o n d i t i o n s a r e p r e f e r r e d .
The p r i m a r y sample vo lume i s d e f i n e d by t h e c a p a c i t y o f t h e samp l i ng d e v i c e ,
and s h o u l d be f i x e d f o r a g i v e n f u e l l o t . The g r o s s sample vo lume s h o u l d be
l a r g e enough f o r t h e p r e p a r a t i o n o f an a v e r a g e d sample o f a t l e a s t 3 kg . I n t h e
case o f a r b i t r a t i o n a n a l y s e s pe r f o rmed i n two o r t h r e e d i f f e r e n t l a b o r a t o r i e s ,
a v e r a g e d samples o f up t o 9 kg may be r e q u i r e d . F o r d e t a i l s on samp l ing o f
l i q u i d f u e l s , see r e f . 35.
7 .3 .2 D e t e r m i n a t i o n o f coa l p r o p e r t i e s
The m o i s t u r e c o n t e n t i s c e r t a i n l y one o f t h e most i m p o r t a n t p r o p e r t i e s o f
s o l i d f u e l s , as i t can a d v e r s e l y i n f l u e n c e b o i l e r c a p a c i t y and e f f i c i e n c y .
A h i g h m o i s t u r e c o n t e n t makes f u e l i g n i t i o n more d i f f i c u l t , w h i l e t h e h e a t i n g
v a l u e d e c r e a s e s .
A t low t e m p e r a t u r e s o f f l u e gas a p p r o a c h i n g t h e b o i l e r o u t l e t , c o n d e n s a t i o n
o f v a p o u r s o r i g i n a t i n g f rom f u e l m o i s t u r e i n t h e p r e s e n c e o f SO^ and SO^ causes
c o r r o s i o n o f b o i l e r p a r t s . A t f r e e z i n g ambien t t e m p e r a t u r e s , f u e l m o i s t u r e may
cause s e r i o u s p rob lems i n t r a n s p o r t a t i o n and u n l o a d i n g .
I n chemica l a n a l y s e s , t h e c o n c e p t s o f f r e e , i n h e r e n t and t o t a l m o i s t u r e a r e
a p p l i e d . F r e e m o i s t u r e i s t he p a r t o f t h e w a t e r i n s o l i d f u e l t h a t e v a p o r a t e s
w h i l e a t t a i n i n g e q u i l i b r i u m w i t h t h e e n v i r o n m e n t ( w a t e r removed by d r y i n g a t
ambien t t e m p e r a t u r e ) . I n h e r e n t m o i s t u r e i s t h e p a r t o f t h e w a t e r t h a t rema ins i n
t h e f u e l a f t e r a t m o s p h e r i c d r y i n g ; i t can be d e t e r m i n e d by f i n d i n g t h e mass
decrement o f f u e l w i t h o u t f r e e m o i s t u r e , a d d i t i o n a l l y d r i e d a t 1 0 5 - l l Ü ° C .
A s h , i . e . m i n e r a l m a t t e r , d e c r e a s e s t h e h e a t i n g v a l u e o f f u e l . A h i g h ash
c o n t e n t makes t he combus t i on p r o c e s s more d i f f i c u l t , and r e d u c e s b o i l e r c a p a c i t y
and e f f i c i e n c y . F l y ash i n f l u e gas may be r e s p o n s i b l e f o r t h e f o u l i n g o f
h e a t i n g s u r f a c e s and e r o s i o n wear o f b o i l e r p a r t s . I n o r d e r t o d e t e r m i n e t h e ash
c o n t e n t , a c o a l sample o f 1-2 g mass i s bu rned i n a l a b o r a t o r y oven a t 815^C,
and t he r e s i d u e i s a d d i t i o n a l l y r o a s t e d .
C o m b u s t i b l e m a t t e r i n c o a l i n c l u d e s t h e e l emen ts t h a t t a k e p a r t i n t h e
combus t ion p r o c e s s , i . e . c a r b o n , h y d r o g e n and s u l p h u r . Knowledge o f t h e c o n t e n t
o f c o m b u s t i b l e e lemen ts may be e s p e c i a l l y i m p o r t a n t i f t h e r e i s no p o s s i b i l i t y
248
o f d i r e c t l y d e t e r m i n i n g t he combus t i on h e a t o r h e a t i n g v a l u e o f t h e f u e l , as
t h e s e q u a n t i t i e s can be a l t e r n a t i v e l y c a l c u l a t e d by an i n d i r e c t method ( s e e
S e c t i o n 7 . 3 . 4 ) . Sometimes i t may be i m p o r t a n t t o d e t e r m i n e t h e c o n t e n t o f
c o m b u s t i b l e m a t t e r i n b o i l e r a s h , as t h i s w o u l d a l l o w c a l c u l a t i o n o f t h e e n e r g y
l o s s r e s u l t i n g f rom i n c o m p l e t e c o m b u s t i o n .
F o r d e t a i l s o f coa l a n a l y s i s and s t a n d a r d s c o n c e r n i n g t h e l a b o r a t o r y
p r o c e d u r e s , t he l i t e r a t u r e s h o u l d be c o n s u l t e d ( r e f . 3 6 , 3 7 ) .
7 .3 .3 P r o p e r t i e s o f f u e l o i l
Perhaps t h e most i m p o r t a n t p r o p e r t y o f f u e l o i l i s t he v i s c o s i t y . L i g h t f u e l
o i l s o f v i s c o s i t y up t o 2°E ( d e g r e e s E n g l e r ) a t 20^C may be s u p p l i e d t o t h e
b u r n e r s w i t h o u t p r i o r h e a t i n g . Heavy f u e l o i l s o f h i g h v i s c o s i t y must be hea ted
e i t h e r o n c e , i . e . b e f o r e pumping, o r t w i c e , i . e . b e f o r e pumping and b e f o r e
d i s p e r s i n g i n b u r n e r s . The n e c e s s a r y t e m p e r a t u r e (up t o 150°C) depends on t h e
o i l t y p e , and can be f ound i n d iag rams o r nomographs ( r e f . 3 3 ) .
O t h e r e s s e n t i a l pa rame te rs a re t h e s u l p h u r c o n t e n t and vanadium o x i d e
c o n t e n t . S u l p h u r i s i m p o r t a n t n o t o n l y f o r e n v i r o n m e n t a l r e a s o n s ; i t may be
r e s p o n s i b l e f o r l o w - t e m p e r a t u r e c o r r o s i o n i n t h e o u t l e t p a r t s o f t h e b o i l e r .
Vanadium o x i d e , V20^ , may cause h i g h - t e m p e r a t u r e c o r r o s i o n o f b o i l e r p a r t s .
7 .3 .4 Heat o f combus t i on and h e a t i n g v a l u e
The h e a t o f c o m b u s t i o n , Q ^ , i s t h e amount o f e n e r g y r e l e a s e d pe r u n i t
q u a n t i t y o f f u e l i n compressed o x y g e n a t c o n s t a n t v o l u m e ; i t i s a d d i t i o n a l l y
assumed t h a t t h e f u e l t e m p e r a t u r e b e f o r e combus t i on and t h e t e m p e r a t u r e o f t h e
combus t ion p r o d u c t s i s 20°C, and t h e w a t e r i n i t i a l l y p r e s e n t i n t h e f u e l , o r
c r e a t e d by b u r n i n g o f h y d r o g e n , i s f i n a l l y c o n d e n s e d .
The d e t e r m i n a t i o n o f h e a t o f combus t i on i s one o f t he most i m p o r t a n t
l a b o r a t o r y measurements needed f o r hea t -economy m o n i t o r i n g , and t h u s p a r t i c u l a r
c a r e and a c c u r a c y i s r e q u i r e d . The s t a n d a r d method a p p l i c a b l e t o s o l i d and
l i q u i d f u e l s i s t he b o m b - c a l o r i m e t e r method . The a p p a r a t u s i s r e q u i r e d t o meet
a s t a n d a r d s p e c i f i c a t i o n , and t h e p r o c e d u r e used i s a l s o s t a n d a r d i z e d ( r e f . 3 7 ) .
The bomb i s a smal l s t a i n l e s s - s t e e l v e s s e l i n w h i c h a smal l mass o f t h e f u e l
( a b o u t 1 g ) i s h e l d i n a c r u c i b l e ( F i g . 7 . 2 ) . I f t h e f u e l i s s o l i d , i t i s
u s u a l l y c r u s h e d and t hen p r e s s e d i n t o t h e fo rm o f a p e l l e t i n a s p e c i a l p r e s s .
The p e l l e t i s i g n i t e d by f u s i n g a p i e c e o f w i r e w i t h w h i c h i t i s i n c o n t a c t ; t h e
p e l l e t can a l s o be made w i t h t h e f u s e w i r e p a s s i n g t h r o u g h i t .
The w i r e fo rms p a r t o f an e l e c t r i c a l c i r c u i t w h i c h can be comp le ted by a
f i r i n g b u t t o n w h i c h i s s i t u a t e d i n a p o s i t i o n remote f rom t h e bomb. I f a l i q u i d
f u e l i s be i ng t e s t e d , i t i s c o n t a i n e d i n a g e l a t i n e c a p s u l e and t h e f i r i n g may
be a s s i s t e d by i n c l u d i n g i n t h e c r u c i b l e a l i t t l e p a r a f f i n o f known h e a t o f
c o m b u s t i o n . The c r u c i b l e c a r r y i n g t h e f u e l i s l o c a t e d i n t h e bomb, and t h e t o p
249
o f t he bomb i s sc rewed down. Oxygen i s t h e n a d m i t t e d s l o w l y u n t i l t h e p r e s s u r e
i s 20-35 b a r , depend ing on t he f u e l t y p e . The bomb i s l o c a t e d i n t h e c a l o r i m e t e r
and a measured q u a n t i t y o f w a t e r i s pou red i n t o t h e c a l o r i m e t e r .
F i g . 7 . 2 . Scheme o f t h e bomb c a l o r i m e t e r . 1 - i n s u l a t i n g c o v e r , 2 - w a t e r , 3 - bomb, 4 - i n s u l a t i n g f e e t , 5 - f u e l sample i n a c r u c i b l e .
The c a l o r i m e t e r i s c l o s e d , t h e e x t e r n a l c o n n e c t i o n s t o t he c i r c u i t a r e made,
and an a c c u r a t e thermometer o f t h e f i x e d - r a n g e o r t h e Beckman t y p e i s immersed
t o a p r o p e r dep th i n t h e w a t e r . The w a t e r i s s t i r r e d by a m o t o r - d r i v e n s t i r r e r
and t e m p e r a t u r e o b s e r v a t i o n s a r e t aken e v e r y m i n u t e . A t t h e end o f t h e f i f t h
m i n u t e , t he c h a r g e i s f i r e d and t e m p e r a t u r e r e a d i n g s a r e t aken e v e r y 10 seconds
u n t i l t h e r e a d i n g s b e g i n t o f a l l ; t h e n , t he f r e q u e n c y o f r e a d i n g s can a g a i n be
r e d u c e d t o e v e r y m i n u t e . The measured t e m p e r a t u r e r i s e , w h i c h s h o u l d n o t e x c e e d
2-3 K, i s c o r r e c t e d f o r v a r i o u s l o s s e s a c c o r d i n g t o t h e f o r m u l a e g i v e n i n t h e
r e s p e c t i v e s t a n d a r d s . The hea t o f combus t i on o f t h e f u e l t e s t e d i s f i n a l l y
c a l c u l a t e d f rom the h e a t b a l a n c e e q u a t i o n , a l s o g i v e n i n t h e s t a n d a r d s , and t h e
measur ing e r r o r can be e s t i m a t e d .
I f , f o r any r e a s o n , t he bomb c a l o r i m e t e r method c a n n o t be u s e d , b u t t h e
chemica l c o n s t i t u t i o n o f t h e f u e l i s known, t h e n i t i s p o s s i b l e t o c a l c u l a t e
t he hea t o f combus t ion u s i n g a p p r o p r i a t e f o r m u l a e . F o r e x a m p l e , i n t h e case o f
European coa l t y p e s , t h e s o - c a l l e d D u l o n g ' s f o r m u l a may be a p p l i e d
= 341C + 1444{H - (0 + Ν - l ) / 8 ) + 93S ( k J / k g ) ( 7 . 1 )
where C , H , 0 , N , and S a re t h e p e r c e n t a g e s o f c a r b o n , h y d r o g e n , o x y g e n ,
n i t r o g e n and s u l p h u r .
The a c c u r a c y o f t h e s e s o - c a l l e d i n d i r e c t methods f o r d e t e r m i n a t i o n o f t h e h e a t
o f combus t i on i s l i m i t e d . A t a c a r b o n c o n t e n t o f a b o u t 86%, and an o x y g e n
c o n t e n t be low 7.5%, t h e a c c u r a c y o f t h e D u l o n g ' s f o r m u l a i s a b o u t ±2%.
250
The h e a t i n g v a l u e o f t h e f u e l i s equa l t o t h e h e a t o f combus t i on minus t h e
l a t e n t h e a t o f t h e w a t e r coming f rom t h e f u e l d u r i n g c o m b u s t i o n . T h i s
c o r r e s p o n d s t o t h e f a c t t h a t w a t e r v a p o u r formed i n f u r n a c e s i s e m i t t e d i n t h e
f l u e gas t o t h e a tmosphe re , and t h e l a t e n t h e a t i s l o s t ( c o n t r a r y t o a bomb
c a l o r i m e t e r measurement ) .
The h e a t i n g v a l u e o f t h e f u e l , Q ^ , can be c a l c u l a t e d as a f u n c t i o n o f t h e
combus t ion h e a t , Q ^ , t h e h y d r o g e n p e r c e n t a g e Η and t h e m o i s t u r e p e r c e n t a g e W.
A g a i n , d e t a i l e d f o r m u l a e can be f o u n d i n t h e r e l e v a n t s t a n d a r d s . F o r e x a m p l e ,
P o l i s h S t a n d a r d s s t a t e t h a t f o r l i q u i d f u e l s
= - 25 .19(9H + W) ( k J / k g ) ( 7 . 2 )
and f o r s o l i d f u e l s
= - 24 .55 (8 .9H + W) ( k J / k g ) ( 7 . 3 )
I t i s n o t e w o r t h y t h a t i n t h e case o f l i q u i d f u e l s , e m p i r i c a l f o r m u l a e a r e
a v a i l a b l e f o r c a l c u l a t i o n o f t h e h y d r o g e n c o n t e n t as a f u n c t i o n o f t h e h e a t o f
c o m b u s t i o n , w h i l e t h e h y d r o g e n c o n t e n t i n s o l i d f u e l s must be e x p e r i m e n t a l l y
d e t e r m i n e d .
I n d i r e c t c a l c u l a t i o n o f t h e h e a t i n g v a l u e u s i n g t h e f o r m u l a e g i v e n i n t h e
l i t e r a t u r e i s a l s o p o s s i b l e . F o r examp le , t h e f o l l o w i n g f o r m u l a may be a p p l i e d
t o European coa l t y p e s :
= 339(C - 0 . 7 5 ( 0 / 2 ) ) + 1193(H - 0 . 1 2 5 ( 0 / 2 ) ) + 105S - 25W. ( k J / k g ) ( 7 . 4 )
where i s t he p e r c e n t a g e o f i n h e r e n t m o i s t u r e ; o t h e r symbo ls as a b o v e .
7 .3 .5 Fue l s t o r a g e i n s p e c t i o n
Coa l p i l e s s h o u l d be v i s u a l l y i n s p e c t e d d a i l y d u r i n g t h e f i r s t 3 months a f t e r
t h e i r d e l i v e r y and t w i c e a week t h e r e a f t e r . A f i r e h a z a r d i s i n d i c a t e d b y :
- s p o t - w i s e d r y i n g o f t he p i l e s u r f a c e a f t e r r a i n f a l l ;
- e s c a p i n g steam c l o u d s ;
- d e p o s i t s o f ash and s u l p h u r a p p e a r i n g on t h e p i l e s u r f a c e ;
- e s c a p i n g smoke o f c h a r a c t e r i s t i c o d o u r .
A more p r e c i s e i n s p e c t i o n p r o c e d u r e r e q u i r e s t h a t t h e t e m p e r a t u r e o f t he c o a l
i n t h e p i l e s be measured . The s t a n d a r d measurement f r e q u e n c y i s t w i c e a week
d u r i n g t he f i r s t 2 months and once e v e r y two weeks t h e r e a f t e r . A c o a l
t e m p e r a t u r e above 45°C s h o u l d be i n t e r p r e t e d as an i n d i c a t i o n o f f i r e h a z a r d . I f
t h e t e m p e r a t u r e r i s e s above 60°C, t h e r e l e v a n t f u e l l o t must i m m e d i a t e l y be
d i r e c t e d t o t h e f u r n a c e .
A c c o r d i n g t o P o l i s h r e g u l a t i o n s , c o a l - s t o r a g e y a r d s w i t h c a p a c i t i e s l a r g e r
t han 500 t o n s must be e q u i p p e d w i t h permanent t e m p e r a t u r e - m e a s u r i n g s y s t e m s ,
c o n s i s t i n g o f i n s t r u m e n t s spaced l e s s t han 5 m a p a r t . The s i m p l e s t i n s t r u m e n t i s
a m e r c u r y - i n - g l a s s thermometer p l a c e d i n s i d e a s t e e l t ube t h a t can be i n s e r t e d
251
i n t h e f u e l l a y e r . S p e c i a l s i g n a l l i n g the rmometers o r remote measu r i ng sys tems
can a l s o be a p p l i e d .
Fue l o i l i s h e l d i n s t o r a g e t a n k s o u t s i d e t h e b o i l e r h o u s e , and an
i n t e r m e d i a t e tank w i t h a c a p a c i t y o f a b o u t 8 - h o u r s ' b o i l e r s u p p l y i s u s u a l l y
i n s t a l l e d i n , o r c l o s e t o , t h e b o i l e r h o u s e . As h e a v y o i l r e q u i r e s h e a t i n g
b e f o r e i t can be pumped t o t h e b u r n e r s , t e m p e r a t u r e c o n t r o l i n t h e t a n k s and
p i p e l i n e s i s e s s e n t i a l . A s t a n d a r d s o l u t i o n t o t h i s p rob lem i s an a u t o m a t i c a l l y
c o n t r o l l e d h e a t i n g sys tem comp le te w i t h r e m o t e - t e m p e r a t u r e measurements and
d e v i c e s w a r n i n g o f e x c e s s t e m p e r a t u r e .
7.4 BOILERS
7.4.1 Methods o f measurement
The b o i l e r s can be r e g a r d e d as a s p e c i a l p a r t o f t h e the rma l s y s t e m , where
c o n s i d e r a b l e e n e r g y l o s s e s can o c c u r o r c o n s i d e r a b l e e n e r g y s a v i n g s can be
a t t a i n e d . E n e r g y d e l i v e r e d i n f u e l can be e f f i c i e n t l y u t i l i z e d i f b o i l e r s a r e
m a i n t a i n e d i n p r o p e r c o n d i t i o n . B o i l e r e f f i c i e n c y i s one o f t h e i m p o r t a n t
i n d i c e s t o be s y s t e m a t i c a l l y checked and c a r e f u l l y w a t c h e d , because even sma l l
d e v i a t i o n s f rom i t s op t ima l v a l u e , i f m a i n t a i n e d f o r a l o n g p e r i o d , may cause
c o n s i d e r a b l e e n e r g y l o s s e s .
I n some c o u n t r i e s , g e n e r a l s a f e t y r e g u l a t i o n s may a p p l y t o t h e b o i l e r s
i n s t a l l e d i n s u g a r f a c t o r i e s . T h i s can be e x e m p l i f i e d by t h e s o - c a l l e d
"Measurement l i s t f o r b o i l e r o p e r a t i o n " . T a b l e 7 . 5 , w h i c h i s o b l i g a t o r y i n
Po land ( r e f . 2 1 ) . I t s t a t e s wha t pa rame te r s s h o u l d be r e c o r d e d a t l e a s t e v e r y
h o u r , f o r r o u t i n e c h e c k i n g o f b o i l e r o p e r a t i o n .
A b o i l e r scheme w i t h an i n d i c a t i o n o f pa rame te r s needed f o r t h e b o i l e r e n e r g y
b a l a n c e i s shown i n F i g . 7 . 3 . The e s s e n t i a l p rob lem o f b o i l e r c h e c k i n g i s t o
t g . p g . D Tsuperheated steam
ι Η JTT Κ
\ \ \ \ \ \ \ \ ^ \ \ \ \ \ f e e d - w a t e r ^ ^ | j \ ^ p ^ . t ^ 21
F i g . 7 . 3 . Scheme o f a b o i l e r . M e a s u r i n g p o i n t s a r e i n d i c a t e d a c c o r d i n g t o t h e l i s t o f measurements . T a b l e 7 .5 .
252
TABLE 7.5
Measurement l i s t f o r b o i l e r o p e r a t i o n , a c c o r d i n g t o P o l i s h r e g u l a t i o n s ( r e f . 2 1 ) .
No. Parameter B o i l e r c a p a c i t y 3 ^ ^ ^ ^ ^
1-5 t / h above 5 t / h
1 F e e d - w a t e r p r e s s u r e χ χ p^ 2 Steam p r e s s u r e a t b o i l e r o u t l e t r χ p^ 3 Steam p r e s s u r e i n b o i l e r drum χ χ 4 F e e d - w a t e r t e m p e r a t u r e χ χ t ^ 5 Tempera tu re a f t e r f e e d - w a t e r h e a t e r χ χ 6 Steam t e m p e r a t u r e a t b o i l e r o u t l e t χ χ 7 B l a s t a i r p r e s s u r e χ χ 8 A i r p r e s s u r e b e f o r e a i r h e a t e r χ r 9 A i r p r e s s u r e a f t e r a i r h e a t e r - r
10 F l u e gas t e m p e r a t u r e b e f o r e f e e d - w a t e r h e a t e r r r
11 F l u e gas t e m p e r a t u r e b e f o r e a i r h e a t e r - r 12 F l u e gas t e m p e r a t u r e b e f o r e ch imney χ χ 13 A i r t e m p e r a t u r e b e f o r e a i r h e a t e r - r 14 A i r t e m p e r a t u r e a f t e r a i r h e a t e r - r 15 D r a u g h t i n f u r n a c e above s t o k e r r χ 16 D r a u g h t b e f o r e f e e d - w a t e r h e a t e r r r 17 D r a u g h t a f t e r s u p e r h e a t e r r r 18 D r a u g h t b e f o r e a i r h e a t e r - r 19 D r a u g h t b e f o r e ch imney χ χ 20 CO2 c o n t e n t i n f l u e gas b e f o r e ch imney x * χ 21 F e e d - w a t e r f l o w χ χ 22 Steam f l o w x * * χ D 23 C o m b u s t i b l e m a t t e r i n ash r χ 24 Fue l f l o w χ χ Β
* 7 * * 7 X = r e q u i r e d ; r = recommended; e x c e p t h a n d - f i r e d f u r n a c e s ; o n l y i n b o i l e r s e q u i p p e d w i t h s u p e r h e a t e r s .
de te rm ine how much e n e r g y i s consumed i n t h e g e n e r a t i o n o f a d e f i n i t e amount o f
steam a t t h e r e q u i r e d p r e s s u r e and t e m p e r a t u r e . Two i n d i c e s can be u s e d , t h e
b o i l e r e f f i c i e n c y η and t he e n e r g y consumpt ion p e r 1 kg steam q .
η = D ( h ^ - h^ ) / (BQ^) -100% ( 7 . 5 )
where D i s t h e mass o f steam g e n e r a t e d i n t he b o i l e r , h^ i s t h e e n t h a l p y o f
steam a t t h e b o i l e r o u t l e t , h i s t h e e n t h a l p y o f f e e d w a t e r , Β i s t h e mass o f w
f u e l consumed i n t h e b o i l e r f u r n a c e , and i s t h e h e a t i n g v a l u e o f f u e l .
The e n e r g y consumpt ion p e r 1 kg steam can be c a l c u l a t e d as
q = BQ^/D ( 7 . 6 )
I n o r d e r t o d e t e r m i n e t he above i n d i c e s , i n a d d i t i o n t o t h e h e a t i n g v a l u e o f
f u e l , t he f o l l o w i n g q u a n t i t i e s must be f ound f rom measurements :
- t h e mass o f f u e l consumed;
- t h e mass o f steam g e n e r a t e d ;
- t he steam p r e s s u r e and t e m p e r a t u r e ( f o r e n t h a l p y d e t e r m i n a t i o n ) ;
- t he mass o f f e e d w a t e r d e l i v e r e d t o t h e b o i l e r ( c h e c k on s t e a m - f l o w
253
measurement ) ;
- t h e f e e d - w a t e r t e m p e r a t u r e ( f o r e n t h a l p y d e t e r m i n a t i o n ) .
The amount o f s o l i d f u e l i s w e i g h e d , p r e f e r a b l y by an a u t o m a t i c s c a l e w h i c h
i s c a l i b r a t e d d a i l y . I n t h e absence o f s c a l e s , a v o l u m e t r i c method can be u s e d .
F u e l - o i l consumpt ion can be measured by f l o w me te rs i n s t a l l e d i n t he s u p p l y
p i p e l i n e . F o r a c c u r a t e hea t b a l a n c e s , i t i s recommended t h a t f l o w r e a d i n g s be
taken e v e r y f i v e m i n u t e s .
The amount o f steam i s measured by f l o w me te rs and e v e n t u a l l y checked a g a i n s t
t he i n d i c a t i o n s o f a w a t e r meter i n s t a l l e d on t he f e e d - w a t e r s u p p l y l i n e . I f a
h i g h - a c c u r a c y b a l a n c e i s r e q u i r e d , i t i s recommended t h a t t he s o o t b l o w e r s and
t he b o i l e r blowdown a re t e m p o r a r i l y c u t o f f ; i f t h e blowdown c a n n o t be a v o i d e d ,
t hen a p p r o p r i a t e c o r r e c t i o n s must be i n t r o d u c e d i n t h e f e e d - w a t e r meter
i n d i c a t i o n s .
Mean v a l u e s o f t h e w a t e r and steam p a r a m e t e r s can be e s t i m a t e d w i t h t h e a i d
o f t e m p e r a t u r e and p r e s s u r e r e c o r d s f rom t h e r e c o r d i n g i n s t r u m e n t s . F o r a c c u r a t e
e n e r g y b a l a n c e s , t h e pa rame te rs can be c a l c u l a t e d as mean v a l u e s o f i n s t r u m e n t
r e a d i n g s taken e v e r y 15 m i n u t e s .
A r o u t i n e b o i l e r check c o n s i s t s o f o b s e r v i n g t h e i n d i c a t i o n s o f t he i n s t a l l e d
measur ing i n s t r u m e n t s and r e c o r d i n g t h e i m p o r t a n t r e a d i n g s a t l e a s t e v e r y h o u r .
I n f o r m a t i o n g a t h e r e d i n t h i s way g e n e r a l l y e n a b l e s us t o e v a l u a t e b o i l e r
o p e r a t i o n , e s p e c i a l l y f u e l c o n s u m p t i o n , and t o e s t a b l i s h how i t i s i n f l u e n c e d by
l o a d f l u c t u a t i o n s r e s u l t i n g f rom o p e r a t i o n o f t h e s u g a r f a c t o r y .
P e r i o d i c checks s h o u l d be aimed a t a n a l y s i n g t h e e n e r g y b a l a n c e s o f t he
b o i l e r u n i t s a t l e a s t e v e r y 10 d a y s . E n e r g y b a l a n c e c a l c u l a t i o n s s h o u l d be based
on t h e r e s u l t s o f measurements t aken e v e r y 15 m inu tes d u r i n g a 6 - h o u r t e s t
p e r i o d ( r e f . 3 9 ) . The p r e r e q u i s i t e f o r a r e l i a b l e e n e r g y b a l a n c e i s s t a b i l i z e d
b o i l e r o p e r a t i o n d u r i n g t h a t t i m e .
7 .4 .2 Combus t ion e v a l u a t i o n
The e s s e n t i a l r e q u i r e m e n t s t o be a c c o u n t e d f o r i n combus t i on e v a l u a t i o n a r e
r e l a t e d t o t h e phenomena o c c u r r i n g i n t h e b o i l e r f u r n a c e . The combus t i on p r o c e s s
i n c l u d e s f u e l d e c o m p o s i t i o n and o x i d a t i o n o f c o m b u s t i b l e componen ts , i . e .
c a r b o n , s u l p h u r and h y d r o g e n , i n t o ca rbon d i o x i d e , s u l p h u r d i o x i d e and w a t e r ,
r e s p e c t i v e l y . Two b a s i c r e q u i r e m e n t s f o r e f f e c t i v e combus t i on a r e t h u s a
s u f f i c i e n t l y h i g h t e m p e r a t u r e and an adequa te o x y g e n s u p p l y .
E v a l u a t i o n o f t he combus t ion p r o c e s s i s based on f l u e - g a s a n a l y s i s , aimed a t
d e t e r m i n i n g t he c o n t e n t o f c a r b o n d i o x i d e , c a r b o n monox ide and o x y g e n . The
measured CO^ c o n t e n t e n a b l e s us t o e v a l u a t e t h e combus t i on p r o c e s s by compar i son
w i t h t he t h e o r e t i c a l CO^ c o n t e n t c a l c u l a t e d f rom s t o i c h o m e t r i c r e l a t i o n s h i p s . I f
t h e r e a l CO^ c o n t e n t i s l o w e r t han t h e t h e o r e t i c a l v a l u e , and t he 0^ c o n t e n t i s
h i g h , t h i s i n d i c a t e s an e x c e s s i v e a i r s u p p l y o r a l e a k y b o i l e r e x h a u s t c h a n n e l .
254
From s i m u l t a n e o u s f u r n a c e t e m p e r a t u r e and d r a u g h t measurements , i t i s p o s s i b l e
t o d e t e r m i n e t h e r e a s o n s f o r t h e s i t u a t i o n .
The CO c o n t e n t i n d i c a t e s i n c o m p l e t e c o m b u s t i o n , r e s u l t i n g e i t h e r f rom
i n a d e q u a t e a i r f e e d o r , i n t h e case o f s o l i d f u e l s , f rom t o o t h i c k a f u e l l a y e r
on t h e s t o k e r .
The u l t i m a t e goa l o f combus t i on e v a l u a t i o n i s t o d e t e r m i n e t h e e n e r g y l o s s e s
r e s u l t i n g f rom t h e combus t ion p r o c e s s and t o t ake a p p r o p r i a t e c o r r e c t i v e
measu res . The ch imney l o s s depends on t h e CO^ c o n t e n t and t h e f l u e - g a s
t e m p e r a t u r e . T h i s i s t h e l a r g e s t o f t h e e n e r g y l o s s e s , n o r m a l l y amount ing t o
8-12% o f t h e e n e r g y d e l i v e r e d i n t h e f u e l . I n o l d e r b o i l e r t y p e s , i t can e x c e e d
20%. The ch imney l o s s can be c a l c u l a t e d f rom t h e S i e g e r t f o r m u l a
= a ( t ^ - t ^ (%) ( 7 . 7 )
0.10
0.09
0.08
0.07
0.05
0.04
1
16 18 CO2 content in f lue gas (%)
20 22
F i g . 7 .4 . C o e f f i c i e n t α i n t h e S i e g e r t f o r m u l a ( a f t e r r e f . 4 0 ) . S o l i d l i n e s -c o a l and l i g n i t e , dashed l i n e s - wood .
255
where α i s a c o e f f i c i e n t depend ing on t h e c o n t e n t , f u e l t y p e and t h e f u e l
m o i s t u r e c o n t e n t ( t h e v a l u e o f α can be f o u n d i n F i g . 7 . 4 ) , t ^ i s t h e f l u e - g a s
t e m p e r a t u r e a t t h e b o i l e r o u t l e t i n and t ^ i s t h e ambien t t e m p e r a t u r e i n °C.
F o r g a s - and o i l - f i r e d b o i l e r s , f o r m u l a e e x p r e s s i n g t h e ch imney l o s s as a
f u n c t i o n o f CO^ and 0^ c o n t e n t i n t h e f l u e gas and t e m p e r a t u r e d i f f e r e n c e
t - t can be f ound i n t h e l i t e r a t u r e , and even c a l c u l a t o r p rograms t o g 3
automate t h e c a l c u l a t i o n s o f t h e ch imney l o s s have been p u b l i s h e d ( r e f . 4 1 ) .
The i n c o m p l e t e combus t ion l o s s , S j , depends i n p r i n c i p l e on t h e c o n t e n t o f
c o m b u s t i b l e gases ( C O , h y d r o c a r b o n s ) i n t h e f l u e g a s . I t amounts t o 0 .5-1.5%
i n b o i l e r s e q u i p p e d w i t h modern f u r n a c e s , and up t o 5% i n o l d e r b o i l e r s w i t h
h a n d - f i r e d f u r n a c e s . Due t o measurement d i f f i c u l t i e s , d e t e r m i n a t i o n o f t h e
i n c o m p l e t e combus t ion l o s s u s u a l l y r e l i e s on t h e CO c o n t e n t o f t h e f l u e g a s .
F i g . 7 .5 . We see t h a t 1% CO i n f l u e gas c o r r e s p o n d s t o an e n e r g y l o s s o f
a p p r o x i m a t e l y 4-6%.
The ash l o s s , S ^ , depends on t h e c o m b u s t i b l e m a t t e r c o n t e n t i n t h e a s h . T h i s
depends m o s t l y on t h e f u e l t y p e and t h e f u r n a c e t y p e . The ash l o s s i n o i l - f i r e d
CO content in f lue gas (%)
0.3 O.A 0.6 0.8 1.0 1.5
10 8 6 5 4 3 2 1.5 1.0 0.8 0.6 Incomplete combustion loss (%)
F i g . 7 .5 . I n c o m p l e t e combus t i on l o s s S j ( a f t e r r e f . 4 0 ) .
2 5 6
Mass of ash as α percentage of fuel mass (%)
3 A 5 6 7 8 9 1 0 1 1 1 2 1 3 Κ 1 5 1 6
A s h l o s s ( % )
F i g . 7 . 6 . Ash l o s s ( a f t e r r e f . 3 7 ) .
b o i l e r s does n o t exceed 1 . 5 % , w h i l e i n t h e case o f c o a l - f i r e d b o i l e r s , i t can be
0 . 5 - 4 . 0 % i n pu l v e r i z e d - c o a l f u r n a c e s , 5 - 1 4 % i n s t o k e r - f i r e d b o i l e r s , and 6 - 1 8 %
i n h a n d - f i r e d f u r n a c e s . The ash l o s s can be e s t i m a t e d as a f u n c t i o n o f t he ash
mass and t h e c o m b u s t i b l e m a t t e r c o n t e n t C i n t h e ash samples ( F i g . 7 . 6 ) .
The r a d i a t i o n hea t l o s s , S ^ , i s caused by therma l r a d i a t i o n f rom b o i l e r w a l l s .
I t depends on b o i l e r c a p a c i t y ( F i g . 7 . 7 ) . T y p i c a l v a l u e s a r e 0 . 5 % i n l a r g e
b o i l e r s and up t o 1 0 % i n smal l b o i l e r s w i t h i n s u f f i c i e n t the rma l i n s u l a t i o n .
3.2
θ 2 Λ
o .1.6
^0.8 α:
\ \
8 10 ' lA '18 20 AO 60 80 100 12 16
Boiler capacity ( t / h )
F i g . 7 . 7 . R a d i a t i o n l o s s S R ( a f t e r r e f . 4 0 ) . 1 - b o i l e r s e q u i p p e d w i t h a i r h e a t e r s and f e e d - w a t e r h e a t e r s , 2 - b o i l e r s w i t h o u t h e a t e r s .
257
7 . 4 . 3 Steam g e n e r a t i o n
A steam g e n e r a t i o n check s h o u l d be d i r e c t e d t o t h r e e e s s e n t i a l a r e a s :
o p e r a t i o n a l s a f e t y , t h e b a s i c o p e r a t i n g pa rame te r s and t h e c o r r e c t n e s s o f t h e
steam g e n e r a t i o n p r o c e s s . S a f e t y r e q u i r e m e n t s c o n c e r n i n g measur ing and
s i g n a l l i n g equ ipmen t , as w e l l as o v e r - p r e s s u r e p r o t e c t i o n , a re g o v e r n e d by
s a f e t y r e g u l a t i o n s i n most c o u n t r i e s and a r e o m i t t e d h e r e .
As t o b a s i c o p e r a t i n g p a r a m e t e r s , t h e d e v i a t i o n s f rom t h e i r nominal v a l u e s
canno t exceed t he l i m i t s t h a t a r e r e q u i r e d by o t h e r p o w e r - h o u s e e q u i p m e n t ,
m a i n l y t h e t u r b i n e s and t h e steam t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n . The steam
p r e s s u r e and t e m p e r a t u r e a r e a u t o m a t i c a l l y s t a b i l i z e d i n modern b o i l e r s , and
t h u s t he t a s k o f t he o p e r a t i n g p e r s o n n e l i s l i m i t e d t o c h e c k i n g t he c o r r e c t n e s s
o f t he a u t o m a t i c c o n t r o l .
As t o t h e steam g e n e r a t i o n p r o c e s s , i t s h o u l d be remembered t h a t i t c o n s i s t s
o f t he p r o c e s s e s i n t h r e e b o i l e r p a r t s : f e e d - w a t e r h e a t e r , b o i l e r p r o p e r and
s u p e r h e a t e r . These p r o c e s s e s can be e v a l u a t e d on t h e b a s i s o f t h e r e s u l t s o f
measurements s p e c i f i e d i n S e c t i o n 7 . 4 . 1 . R e c o r d i n g i n s t r u m e n t s s h o u l d p r e f e r a b l y
be u s e d ; o t h e r w i s e , r e a d i n g s t aken a t l e a s t e v e r y hou r s h o u l d be i n c l u d e d i n
o p e r a t i o n r e p o r t s .
7 . 4 . 4 E n e r g y b a l a n c e o f t he b o i l e r
I t i s recommended t h a t e n e r g y b a l a n c e s be s e t up a t l e a s t e v e r y t e n days
( t e s t c o n d i t i o n s a r e e x p l a i n e d i n S e c t i o n 7 . 4 . 1 ) . I n a d d i t i o n t o pa ramete r
v a l u e s , t h e h e a t i n g v a l u e o f t he f u e l must a l s o be known. The mean v a l u e s o f t h e
pa rame te rs a re a p p l i e d i n t he c a l c u l a t i o n s .
The e n e r g y o f t he f u e l s u p p l i e d t o t h e b o i l e r , Q p , i s t r a n s f o r m e d i n t o steam
e n e r g y , Q ^ , and e n e r g y l o s s e s , Qj^.
Qp = Q 3 + Q L ( 7 . 8 )
The e n e r g y s u p p l i e d can be c a l c u l a t e d as
Qp = B Q H ( 7 . 9 )
where Β i s t he mass o f f u e l s u p p l i e d t o t h e b o i l e r , and Q^ i s t h e h e a t i n g v a l u e
o f t he f u e l .
The e n e r g y consumed i n steam g e n e r a t i o n can be c a l c u l a t e d f rom t h e f o r m u l a
Qs = D ( h ^ - h^) ( 7 . 1 0 )
where D i s t he mass o f steam g e n e r a t e d , a c c o r d i n g t o f l o w measurement a t t h e
b o i l e r o u t l e t , h^ i s t he e n t h a l p y o f steam ( f o u n d i n steam t a b l e s o r d i a g r a m s ,
f o r t he measured p r e s s u r e p^ and t e m p e r a t u r e t ^ ) , and h i s t h e e n t h a l p y o f t he
s s w
f e e d w a t e r ( f o u n d i n t a b l e s f o r t he measured t e m p e r a t u r e t ^ ) .
I f Qp and Q^ have been c a l c u l a t e d , t h e b o i l e r e f f i c i e n c y can a l s o be
c a l c u l a t e d a c c o r d i n g t o e q n . ( 7 . 5 ) . The a c c u r a c y o f t h e e f f i c i e n c y v a l u e depends
258
m a i n l y on measur ing e r r o r s i n t h e measurements o f steam f l o w and f u e l mass. I n
some i n s t a n c e s , b o i l e r e f f i c i e n c y can be c a l c u l a t e d more a c c u r a t e l y i f t h e h e a t
l o s s e s have been d e t e r m i n e d ( s e e S e c t i o n 7 . 4 . 2 ) . The r e l e v a n t f o r m u l a i s
η = 100 - ( S ^ + S j + S^ + S^) (%) ( 7 . 1 1 )
7 .4 .5 Example
A c o a l - f i r e d b o i l e r has been t e s t e d and t h e f o l l o w i n g d a t a summarize t h e t e s t
r e s u l t s :
- coa l c o n s u m p t i o n , Β = 5550 k g / h ;
- coa l h e a t i n g v a l u e , = 21440 k J / k g ;
- steam f l o w , D = 32900 k g / h ;
- steam e n t h a l p y , h^ = 3172 k J / k g ;
- f e e d - w a t e r e n t h a l p y , h , = 488 k J / k g . w
The e s s e n t i a l e n e r g y b a l a n c e components a r e t h u s :
- e n e r g y s u p p l i e d t o t he b o i l e r
Qp = 5550-21440 = 1.19-10^ k J / h ;
- e n e r g y consumed i n steam g e n e r a t i o n
Q 3 = 32900· (3172 - 488) = 0 .88-10^ k J / h ;
- e n e r g y l o s s
Q L = Qp - Q 3 = 0 .31-10^ k J / h .
I t i s now p o s s i b l e t o c a l c u l a t e t he b o i l e r e f f i c i e n c y
η = ( 0 . 8 8 - 1 0 ^ / 1 . 1 9 · 1 0 ^ ) · 1 0 0 = 73.9%
and t h e e n e r g y consumpt ion p e r 1 kg steam
q = 5550-21440/32900 = 3617 k J / k g .
7.5 TURBO-GENERATORS
7.5.1 Method o f measurement
The e s s e n t i a l p rob lem o f t u r b o - g e n e r a t o r c h e c k i n g i s t o d e t e r m i n e t h e h e a t
consumpt ion i n e l e c t r i c i t y g e n e r a t i o n . I t i s c o n v e n t i o n a l l y e x p r e s s e d as t h e
steam r a t e , S , t h a t i s , t he mass o f steam consumed i n t h e t u r b o - g e n e r a t o r p e r
1 kWh o f e l e c t r i c a l e n e r g y p r o d u c e d :
S = M/E (kg /kWh) ( 7 . 1 2 )
where Μ i s t h e mass o f steam s u p p l i e d t o t h e t u r b i n e w i t h i n a c e r t a i n t ime
p e r i o d i n kg , and Ε i s t h e e l e c t r i c a l e n e r g y p r o d u c e d a t t h e same t ime i n kWh.
The same i n d e x can a l s o be c a l c u l a t e d as
S = D/N (kg /kWh) ( 7 . 1 3 )
where D i s t h e mass f l o w o f steam i n k g / h , and Ν i s t h e e l e c t r i c a l e f f e c t o f
t h e t u r b o - g e n e r a t o r i n kW.
259
The e s s e n t i a l i n f o r m a t i o n c o n t a i n e d i n t h e S v a l u e can a l t e r n a t i v e l y be
e x p r e s s e d u s i n g t h e c o n c e p t o f t h e o v e r a l l e f f i c i e n c y o f t h e t u r b o - g e n e r a t o r
( s e e S e c t i o n 7 . 5 . 5 ) . I n o r d e r t o c a l c u l a t e bo th i n d i c e s , t h e f o l l o w i n g
measurements a r e n e c e s s a r y :
- steam amount, Μ ( k g ) o r steam mass f l o w , D ( k g / h ) ;
- amount o f e l e c t r i c a l e n e r g y , Ε (kWh) o r e l e c t r i c a l e f f e c t , Ν ( k W ) ;
- i n l e t p r e s s u r e o f s team, p^ ( b a r ) ;
- i n l e t t e m p e r a t u r e o f s team, t ^ ( ° C ) ;
- o u t l e t t e m p e r a t u r e o f s team, t^ ( °C ) ( r e q u i r e d o n l y f o r t h e c a l c u l a t i o n o f
o v e r a l l e f f i c i e n c y ) .
The way i n w h i c h t h e t e s t i s p e r f o r m e d and t h e f r e q u e n c y o f t h e measurements
d e t e r m i n e how t h e t e s t r e s u l t s can be i n t e r p r e t e d . A r o u t i n e check i s based on
measurements r e p e a t e d e v e r y 30 m i n u t e s ; t u r b i n e o p e r a t i o n i s d e t e r m i n e d by steam
g e n e r a t i o n i n t h e b o i l e r and by t h e accompany ing e l e c t r i c a l and the rma l l o a d s .
The r e s u l t i n g S v a l u e r e f l e c t s n o t o n l y t h e t u r b o - g e n e r a t o r q u a l i t y b u t a l s o
t he method o f i t s u t i l i z a t i o n under a c t u a l l o a d c o n d i t i o n s .
As t o t h e p e r i o d i c c h e c k i n g , t h i s i s aimed a t t e s t i n g t u r b i n e o u t p u t and
e f f i c i e n c y under s t a b i l i z e d o p e r a t i n g c o n d i t i o n s . The t u r b i n e s h o u l d be b r o u g h t
i n t o the rma l e q u i l i b r i u m i n a d v a n c e , b e f o r e t h e t e s t i s i n i t i a t e d ; t h e l o a d
s h o u l d be s t a b i l i z e d and t h e n h e l d c o n s t a n t d u r i n g t h e e n t i r e t e s t . I t i s
recommended t h a t t h e f r e q u e n c y o f t h e measurements be r e l a t e d t o t h e d u r a t i o n o f
t h e t e s t . F o r examp le , t he recommendat ion o f r e f . 42 i s t h a t t h e t e s t d u r a t i o n
can be 15 o r 60 m i n u t e s , and t h e recommended measu r i ng f r e q u e n c y i s shown i n
T a b l e 7 .6 .
TABLE 7.6
Recommended f r e q u e n c y o f i n s t r u m e n t r e a d i n g s i n t u r b o - g e n e r a t o r t e s t s .
Measurement ^ ^ " ^ ^ ^ P " 15 m i n u t e s 60 m inu tes
E l e c t r i c a l e f f e c t 1 min 1 min Steam f l o w 1 min 1 min Tempera tu re o f incoming steam 1 min 5 min P r e s s u r e o f incoming steam 1 min 5 min Tempera tu re o f e x h a u s t steam 1 min 5 min P r e s s u r e o f e x h a u s t steam 1 min 5 min E l e c t r i c i t y meter i n d i c a t i o n s b e g i n n i n g and Steam c o u n t e r i n d i c a t i o n s end o f t e s t
7 .5 .2 Steam consumpt ion
The t r u e steam c o n s u m p t i o n , a q u a n t i t y on w h i c h t h e b a l a n c e and t h e r o u t i n e
c h e c k i n g o f t h e t u r b o - g e n e r a t o r a r e b a s e d , can be d e t e r m i n e d f rom s t e a m - c o u n t e r
i n d i c a t i o n s a t t h e b e g i n n i n g and end o f t h e t e s t . I t i s n e c e s s a r y t o m o d i f y t h e
260
c o u n t e r i n d i c a t i o n s i f t h e steam p r e s s u r e and t e m p e r a t u r e d e v i a t e f rom t h e
nominal f l o w - m e t e r v a l u e s a t t h e t ime o f t h e t e s t . I n t h e case o f p e r i o d i c
checks aimed a t t h o r o u g h t u r b i n e i n s p e c t i o n , t h e steam consumpt ion v a l u e s h o u l d
be a d d i t i o n a l l y c o r r e c t e d f o r p r e s s u r e and t e m p e r a t u r e d e v i a t i o n s , a c c o r d i n g t o
t h e f o r m u l a
D = - M ^ ) f ^ / T ( k g / h ) ( 7 . 1 4 )
where τ i s t he t e s t d u r a t i o n i n h , M-j and a r e t h e m o d i f i e d c o u n t e r
i n d i c a t i o n s a t t h e b e g i n n i n g and a t t h e end o f t h e t e s t i n kg , and fj^ i s a
c o r r e c t i o n f a c t o r .
I f t h e measurements a re taken f rom a steam f l o w meter and η m o d i f i e d f l o w
v a l u e s D p D2, . . , D ^ have been r e c o r d e d , t hen t he f o l l o w i n g f o r m u l a i s u s e d :
D = O ^ f , ( 7 . 1 5 )
where D ^ i s t h e mean v a l u e o f t he steam f l o w . I f some measurements f a l l beyond
t h e ±2.5% i n t e r v a l a round t h e mean v a l u e , t h i s i s c a l c u l a t e d as
D = ( d / n ) Σ / D T ) 2 ( 7 . 1 6 ) ^ i = l ^
O t h e r w i s e , t h e mean a r i t h m e t i c v a l u e s h o u l d be t a k e n .
The c o r r e c t i o n f a c t o r , f j^ , i s c a l c u l a t e d f o r a b a c k - p r e s s u r e t u r b i n e as t h e
p r o d u c t o f t h r e e c o e f f i c i e n t s r e f l e c t i n g t h e d e v i a t i o n s o f i n l e t p r e s s u r e , i n l e t
t e m p e r a t u r e and o u t l e t p r e s s u r e f rom t h e i r nominal v a l u e s . The d a t a on t h e s e
c o e f f i c i e n t s s h o u l d be s u p p l i e d i n d iag ram o r t a b l e fo rm by t h e t u r b i n e
m a n u f a c t u r e r .
7 .5 .3 T u r b o - g e n e r a t o r power o u t p u t
I n power o u t p u t measurements , t he same g e n e r a l p r i n c i p l e i s a p p l i e d as i n t h e
case o f steam c o n s u m p t i o n . The b a l a n c e and r o u t i n e c o n t r o l o f t h e t u r b o
g e n e r a t o r s h o u l d be based on a c t u a l o u t p u t v a l u e s , w h i l e i n p e r i o d i c c o n t r o l ,
c o r r e c t i o n s f o r t h e d e v i a t i o n s o f o p e r a t i n g pa rame te r s a r e n e c e s s a r y .
I n t he case o f measurements t aken f rom an e l e c t r i c m e t e r , t h e t u r b o - g e n e r a t o r
power o u t p u t i s c a l c u l a t e d as
Ν = (E2 - E ^ ) A f p / T (kW) ( 7 . 1 7 )
where τ i s t h e t e s t d u r a t i o n i n h , E^ and E2 a r e t h e e l e c t r i c meter i n d i c a t i o n s
a t t h e b e g i n n i n g and a t t h e end o f t e s t i n kWh, A i s t h e e l e c t r i c meter c o n s t a n t
and f p i s t h e c o r r e c t i o n f a c t o r .
I f t he r e a d i n g s a re taken f rom a power o u t p u t m e t e r , t h e n t h e f o l l o w i n g
f o r m u l a i s u s e d :
Ν = N^fp (kW) ( 7 . 1 8 )
where i s t h e mean a r i t h m e t i c v a l u e o f t h e power o u t p u t , i n kW.
The c o r r e c t i o n f a c t o r , f ^ , i s a g a i n c a l c u l a t e d on t h e b a s i s o f t u r b i n e
261
c h a r a c t e r i s t i c s , t a k i n g i n t o a c c o u n t t h e pa ramete r d e v i a t i o n s f rom t h e i r nominal
v a l u e s .
7 .5 .4 T u r b o - g e n e r a t o r e n e r g y b a l a n c e
I n t h e e n e r g y b a l a n c e o f a t u r b o - g e n e r a t o r , a l l i ncoming and o u t g o i n g mass
and e n e r g y f l o w s s h o u l d be a c c o u n t e d f o r :
- incoming s team;
- e x h a u s t s team;
- e l e c t r i c a l e n e r g y p r o d u c e d ;
- hea t d i s s i p a t e d t o t he e n v i r o n m e n t .
The scheme o f a t u r b o - g e n e r a t o r w i t h an i n d i c a t i o n o f t h e sys tem bounda ry and
e n e r g y s t reams i s shown i n F i g . 7 . 8 ( a ) .
(a) SYSTEM BOUNDARY
live steam TURBINE
r heat loss
L
electrical effect
>
exhaust steam
F i g . 7 .8 . E n e r g y c o n v e r s i o n p r i n c i p l e o f a t u r b o - g e n e r a t o r w i t h a b a c k - p r e s s u r e t u r b i n e , ( a ) e n e r g y b a l a n c e scheme, ( b ) steam e x p a n s i o n p r o c e s s shown i n t h e M o l l i e r d i a g r a m .
Assuming t h a t t h e f l o w s o f incoming steam and e x h a u s t steam a r e e q u a l , i t
f o l l o w s f rom the f i r s t law o f thermodynamics t h a t
Dh^ = Ν + Dk^ - Q ( 7 . 1 9 )
where Q i s t h e hea t l o s s , and h^ and h-j a r e t h e e n t h a l p i e s o f incoming steam and
e x h a u s t s team, r e s p e c t i v e l y .
7 .5 .5 T u r b i n e and t u r b o - g e n e r a t o r e f f i c i e n c y
The p r o c e s s t h a t i s t h e o r e t i c a l l y p o s s i b l e i n a steam t u r b i n e c o n s i s t s o f
t r a n s f o r m i n g i n t o mechan ica l work a p a r t o f t he steam e n e r g y , equa l t o t h e
262
i s e n t r o p i c e n t h a l p y d rop w i t h t h e e x p a n s i o n f rom i n i t i a l t o f i n a l steam
p r e s s u r e . T h i s i s shown i n t h e M o l l i e r d i a g r a m , F i g . 7 . 8 ( b ) . As t h e r e a r e a l w a y s
f r i c t i o n l o s s e s and i n t e r n a l l e a k s a s s o c i a t e d w i t h steam e x p a n s i o n i n t h e
t u r b i n e , t h e r e a l p r o c e s s f o l l o w s t h e p a t t e r n shown i n t h e d i a g r a m , w h i l e o n l y
a p a r t o f t he i s e n t r o p i c e n t h a l p y d rop i s t r a n s f o r m e d i n t o mechan ica l w o r k .
The u t i l i z a t i o n o f t h e i s e n t r o p i c e n t h a l p y d rop i n a t u r b i n e can be e x p r e s s e d
by t h e s o - c a l l e d i n t e r n a l e f f i c i e n c y
^ i = ( ^ - - ^2^ ( ^ - 2 0 )
where h^ i s t he t h e o r e t i c a l e n t h a l p y v a l u e a f t e r i s e n t r o p i c e x p a n s i o n t o t h e
f i n a l p r e s s u r e , and t he r e m a i n i n g symbo ls a r e as a b o v e .
The v a l u e o f t h e i n t e r n a l e f f i c i e n c y i s o f p r i m a r y impo r t ance i f t h e combined
g e n e r a t i o n o f hea t and e l e c t r i c i t y i s c o n s i d e r e d . The h i g h e r t h e e f f i c i e n c y
v a l u e , t h e l a r g e r t he amount o f e l e c t r i c a l e n e r g y t h a t can be g e n e r a t e d f rom t h e
same amount o f s team. I f t h e p e r i o d i c t u r b i n e i n s p e c t i o n s r e v e a l t h a t t h e
i n t e r n a l e f f i c i e n c y i s d e c r e a s i n g , t h e n one may e x p e c t t h a t t h e c o n t r o l v a l v e s ,
i n t e r n a l s e a l s o r b l a d e sys tem r e q u i r e r e p a i r .
A c t u a l l y , o n l y a p a r t o f t h e mechan ica l work o b t a i n e d i n t h e t u r b i n e can be
t r a n s f o r m e d i n t o e l e c t r i c a l e n e r g y . E n e r g y l o s s e s i n t h e t u r b o - g e n e r a t o r a r e
caused by f r i c t i o n i n t he b e a r i n g s and p o s s i b l y i n t h e t r a n s m i s s i o n gea r between
t h e t u r b i n e and g e n e r a t o r , e n e r g y consumpt ion i n a u x i l i a r y mechanisms, and h e a t
d i s s i p a t i o n i n t he g e n e r a t o r w i n d i n g . These l o s s e s a r e c o n v e n t i o n a l l y a lowed
f o r , t o g e t h e r w i t h l o s s e s caused by steam l e a k s t h r o u g h t h e t u r b i n e s e a l s and by
hea t d i s s i p a t i o n f rom the s u r f a c e o f t h e t u r b i n e c y l i n d e r .
The o v e r a l l u t i l i z a t i o n o f t h e i s e n t r o p i c e n t h a l p y d rop i n a t u r b o - g e n e r a t o r
can be e x p r e s s e d by t h e o v e r a l l e f f i c i e n c y
= n . . 3 6 0 0 / ( S ( h ^ - h ^ ) ) ( 7 . 2 1 )
I t f o l l o w s f rom e q n s . ( 7 . 2 0 ) and ( 7 . 2 1 ) t h a t once t he q u a n t i t i e s d i s c u s s e d i n
S e c t i o n s 7 . 5 . 1 - 7 . 5 . 4 have been d e t e r m i n e d , i t becomes p o s s i b l e t o c a l c u l a t e t h e
i n t e r n a l e f f i c i e n c y o f t h e t u r b i n e and t h e o v e r a l l e f f i c i e n c y o f t h e t u r b o
g e n e r a t o r . No s i m p l e method e x i s t s , h o w e v e r , f o r d e t e r m i n a t i o n o f t h e t u r b i n e
mechan ica l e f f i c i e n c y , η ^ , t h e t r a n s m i s s i o n gea r e f f i c i e n c y , η ^ ^ , and t h e
g e n e r a t o r e f f i c i e n c y , η ^ . I t can t h u s be u s e f u l t o remember t h a t
V t g ' ^ g = ( ^ - 2 2 )
7 .5 .6 Example
A t u r b o - g e n e r a t o r d r i v e n by a b a c k - p r e s s u r e t u r b i n e has been t e s t e d and t h e
f o l l o w i n g d a t a summarize t h e t e s t r e s u l t s (mean v a l u e s ) :
- e l e c t r i c a l e f f e c t , N^ = 6593 kW; m
- steam f l o w , = 58830 k g / h ;
263
- i n l e t p r e s s u r e and t e m p e r a t u r e o f s team, p^ = 34.33 b a r , t ^ = 433.2°C
( e n t h a l p y h^ = 3300 k J / k g ) ;
- o u t l e t p r e s s u r e and t e m p e r a t u r e o f s team, p-j = 3.52 b a r , t^ = 193.3°C
( e n t h a l p y h^ = 2851 k J / k g ) .
C o r r e c t i o n f a c t o r s , f rom d iagrams s u p p l i e d by t h e t u r b i n e m a n u f a c t u r e r , a r e
f ^ = 1-0.997-0.99 = 0.987 = 1 / f^ .
The c o r r e c t e d v a l u e s o f t h e e l e c t r i c a l e f f e c t and steam f l o w a r e t h u s
Ν = 6593/0.987 = 6679 kW,
D = 58830-0.987 = 58064 k g / h .
The steam r a t e i s
S = 58064/6679 = 8 . 6 9 kg/kWh.
The t h e o r e t i c a l e n t h a l p y v a l u e a f t e r i s e n t r o p i c e x p a n s i o n t o t h e o u t l e t
p r e s s u r e , f rom steam t a b l e s , i s h^ = 2732 k J / k g .
The i n t e r n a l t u r b i n e e f f i c i e n c y i s
η. = (3300 - 2851) / (3300 - 2732) = 0 .790.
The o v e r a l l t u r b o - g e n e r a t o r e f f i c i e n c y i s
= 0 .790-3600 / (8 .69 (3300 - 2851) ) = 0 .729.
7.6 PROCESS HEATING EQUIPMENT
7.6.1 E v a p o r a t o r
J u i c e t h i c k e n i n g i n a m u l t i p l e - e f f e c t e v a p o r a t o r depends on h e a t t r a n s m i s s i o n
f rom t h e h e a t i n g steam t o t h e v a p o u r s . C a s c a d e - t y p e h e a t i n g o f c o n s e c u t i v e
e v a p o r a t o r e f f e c t s e n s u r e s m u l t i p l e u t i l i z a t i o n o f hea t i n t h e c o n s e c u t i v e
e v a p o r a t i o n s t a g e s . Heat i s f u r t h e r u t i l i z e d i n s u g a r b o i l i n g , j u i c e h e a t i n g and
o t h e r p r o c e s s s e c t i o n s .
P r o p e r f u n c t i o n i n g o f t h e e v a p o r a t o r s t a t i o n i s v e r y much dependen t on t h e
f u n c t i o n i n g o f t h e i n d i v i d u a l e v a p o r a t o r e f f e c t s and t h e i r a u x i l i a r y e q u i p m e n t .
The c a s c a d e - h e a t i n g p r i n c i p l e works w e l l o n l y i f i n t e n s i v e hea t t r a n s f e r i s
e n s u r e d i n each e f f e c t .
I n t he case o f R o b e r t - t y p e e v a p o r a t o r s , t h e j u i c e l e v e l i n t h e h e a t i n g t u b e s
i s o f p r i m a r y i m p o r t a n c e . A c c o r d i n g t o some s o u r c e s ( r e f . 6 ) , t h e o p t i m a l j u i c e
l e v e l i s 20-30% o f t ube h e i g h t . The v a l u e s g i v e n i n o t h e r s o u r c e s a r e 10-15%
h i g h e r ( r e f . 8 ) . Even i f a d i f f e r e n c e o f , s a y , 10% tube h e i g h t has a l i m i t e d
i n f l u e n c e on t h e h e a t t r a n s f e r i n t e n s i t y , i t s h o u l d be remembered t h a t marked
d e v i a t i o n s f rom t h e s e v a l u e s wou ld have an u n f a v o u r a b l e e f f e c t on j u i c e
t h i c k e n i n g .
F o r t h e c o r r e c t o p e r a t i o n o f f a l l i n g - f i l m e v a p o r a t o r s , s u f f i c i e n t l i q u i d
w e t t i n g o f t h e tube w a l l i s n e c e s s a r y . Too sma l l a j u i c e f l o w i s a s s o c i a t e d
w i t h t h e r i s k t h a t t h e f i l m w i l l t e a r a p a r t , t h i s r e s u l t i n g i n l o c a l
s u p e r s a t u r a t i o n and i n c r u s t a t i o n s f o r m i n g on t h e t ube w a l l . P r a c t i c a l e x p e r i e n c e
p r o v e s t h a t l i q u i d w e t t i n g can be e v a l u a t e d u s i n g volume f l o w p e r u n i t l e n g t h o f
264
tube c i r c u m f e r e n c e a t t he o u t l e t . As a f i r s t a p p r o x i m a t i o n o f minimum w e t t i n g
f o r t he e v a p o r a t i o n o f s u g a r s o l u t i o n s , t h e v a l u e o f 15 1 i t r e s / ( h - c m ) can be
u s e d .
Heat t r a n s f e r can a l s o be h i n d e r e d by i r r e g u l a r i t i e s i n steam c o n d e n s a t i o n on
t he o u t e r s u r f a c e s o f t he h e a t i n g t u b e s . T h i s can be a v o i d e d i f n o n c o n d e n s a b l e s
a r e v e n t e d e f f e c t i v e l y , and i f t h e condensa te d r a i n a g e p r e v e n t s t h e c o n d e n s a t e
l e v e l f rom r i s i n g above t h e o u t l e t n o z z l e s . Ex t reme c a r e i s recommended h e r e , as
bo th l e a k i n g steam t r a p s and e x c e s s i v e v e n t i n g may cause u n n e c e s s a r y v a p o u r
l o s s e s . F o r d e t a i l s , see condensa te d r a i n a g e under S e c t i o n 3.2.1 and v e n t i n g
under S e c t i o n 3 . 2 . 2 .
I n many s u g a r f a c t o r i e s , s c a l e b u i l d - u p on t he i n t e r n a l s u r f a c e s o f h e a t i n g
t u b e s and t h e accompanying r e d u c t i o n o f t h e hea t t r a n s f e r i n t e n s i t y may l e a d t o
a s i t u a t i o n where t h e t o t a l t e m p e r a t u r e d e c r e a s e i n t h e e v a p o r a t o r ( f r o m
h e a t i n g - s t e a m t e m p e r a t u r e t o t h i c k - j u i c e t e m p e r a t u r e ) becomes i n s u f f i c i e n t f o r
t he r e q u i r e d j u i c e t h i c k e n i n g . I f t he p r o c e s s i n g c a p a b i l i t y i s h e l d c o n s t a n t ,
a l o w e r c o n c e n t r a t i o n o f t h i c k j u i c e must be a l l o w e d w h i c h , i n t u r n , causes
i n c r e a s e d hea t consumpt ion i n t h e s u g a r house and f i n a l l y i n t h e e n t i r e s u g a r
f a c t o r y . The s i t u a t i o n can be b r o u g h t back t o normal i f t h e s c a l e i s removed .
A c t u a l l y , e a r l i e r s c a l e removal i s recommended, as i t a l l o w s e l i m i n a t i o n o f n o n -
op t ima l hea t u t i l i z a t i o n ; a l s o , i t i s e a s i e r t o remove t h e t h i n n e r s c a l e l a y e r s .
The c h o i c e o f t he moment a t w h i c h s c a l e removal s h o u l d be u n d e r t a k e n can be
based on o b s e r v a t i o n o f t he o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t s i n t h e e v a p o r a t o r
e f f e c t s . T h i s r e q u i r e s measur ing t h e q u a n t i t i e s needed t o c a l c u l a t e t he h e a t
t r a n s f e r c o e f f i c i e n t s .
As p r e s e n t e d a b o v e , t h e p u r p o s e o f t h e e v a p o r a t o r check i s t o d e t e r m i n e t h e
c o u r s e o f t h e m u l t i - s t a g e e v a p o r a t i o n p r o c e s s , and p o s s i b l y t o i n t r o d u c e some
p r o c e s s c o r r e c t i o n s aimed a t r e d u c t i o n o f t h e steam c o n s u m p t i o n . I n a w e l l
d e s i g n e d and p r o p e r l y m a i n t a i n e d e v a p o r a t o r , i t w o u l d be enough t o check t h e
t e m p e r a t u r e d i f f e r e n c e s i n t h e i n d i v i d u a l e f f e c t s and t h e o v e r a l l c o n c e n t r a t i o n
i n c r e a s e . I f , h o w e v e r , t e c h n i c a l c h a r a c t e r i s t i c s and c o r r e c t n e s s o f o p e r a t i o n
have t o be i n v e s t i g a t e d , t h e n t h e f o l l o w i n g measurements a r e n e c e s s a r y :
- steam f l o w t o t h e f i r s t e f f e c t , ( kg /100 kg b ) ;
- t e m p e r a t u r e and p r e s s u r e i n h e a t i n g chambers o f i n d i v i d u a l e f f e c t s , t p t ^ ,
. . , ( ° C ) ; p^ , p^ , . . , ( b a r ) ;
- t e m p e r a t u r e and p r e s s u r e i n v a p o u r chambers o f i n d i v i d u a l e f f e c t s , t p t^, . . ,
( ° C ) ; p^ , p^ , . . , ( b a r ) ;
- t h i n - j u i c e f l o w , G¿ (kg /100 kg b ) ;
- t h i n - j u i c e t e m p e r a t u r e , t ^ , and j u i c e t e m p e r a t u r e i n t he i n d i v i d u a l e f f e c t s ,
t l t ¡ , . . , ( ° C ) ;
- t h i n - j u i c e c o n c e n t r a t i o n , b^ , and j u i c e c o n c e n t r a t i o n s a t c o n s e c u t i v e o u t l e t s ,
265
b p b^ , . . , (% D S ) .
I t i s i m p o r t a n t t o adap t t he measur ing t e c h n i q u e s t o t he p e c u l i a r i t i e s o f
m u l t i - s t a g e e v a p o r a t i o n , p a r t i c u l a r l y i n t e m p e r a t u r e d e t e r m i n a t i o n . I n t h e
f o l l o w i n g , i t i s assumed t h a t t h e the rmometers i n t h e v a p o u r chambers a r e p l a c e d
c l o s e t o t he t o p o f t h e h e a t i n g t u b e s , t h u s i n d i c a t i n g t h e t e m p e r a t u r e s o f t h e
s u p e r h e a t e d v a p o u r s ( s a t u r a t i o n t e m p e r a t u r e + b o i l i n g p o i n t e l e v a t i o n ) .
I t s h o u l d be p o i n t e d o u t t h a t r e l i a b i l i t y o f t he t e s t r e s u l t s can be a c h i e v e d
o n l y i f t he measurements a re pe r f o rmed d u r i n g s t e a d y - s t a t e e v a p o r a t o r o p e r a t i o n ,
when paramete r and j u i c e - l e v e l o s c i l l a t i o n s a r e l i m i t e d . Ex t reme c a r e i s
recommended when c o l l e c t i n g j u i c e samples f o r c o n c e n t r a t i o n measurements . I n
p r i n c i p l e , t e s t cocks f o r j u i c e samp l ing s h o u l d be p r o v i d e d w i t h w a t e r c o o l e r s ,
so t h a t t h e j u i c e can be c o o l e d t o abou t 20°C. D u r i n g t h e t e s t , t h e cocks a r e
opened so t h a t a s t e a d y j u i c e f l o w i s e n s u r e d , and t h e samples a r e c o l l e c t e d i n
v e s s e l s l a r g e enough t o e n s u r e c o n c e n t r a t i o n a v e r a g i n g .
S u f f i c i e n t samp l ing a c c u r a c y can be o b t a i n e d even i f t he j u i c e samples have
n o t been c o o l e d . T h e n , h o w e v e r , t he c o n c e n t r a t i o n v a l u e s d e t e r m i n e d i n t h e
l a b o r a t o r y s h o u l d be c o r r e c t e d f o r s e l f - e v a p o r a t i o n e f f e c t s ( t h e s e e f f e c t s must
be t aken i n t o a c c o u n t i n t h e samples o f t h i n j u i c e and j u i c e f rom t h e f i r s t and
second e v a p o r a t o r e f f e c t s ) . I f t he l a b o r a t o r y - e s t i m a t e d c o n c e n t r a t i o n v a l u e
i s b * , t h e n t h e t r u e c o n c e n t r a t i o n i s
b = b * / ( l + Am) (% DS) ( 7 . 2 3 )
where Am i s t he mass o f w a t e r e v a p o r a t e d f rom 1 kg o f j u i c e
Am = (h - h J / ( 2 6 7 6 - h ) ( k g ) ( 7 . 2 4 ) a
where h i s t h e j u i c e e n t h a l p y i n t h e t e s t cock o u t l e t , w h i c h can be c a l c u l a t e d
as a p p r o x i m a t e l y
h = 4.19(1 - 0 . 5 2 b / 1 0 0 ) t ( k J / k g ) ( 7 . 2 5 )
and h i s t h e e n t h a l p y o f t h e b o i l i n g j u i c e a t a t m o s p h e r i c p r e s s u r e . F o r t y p i c a l a
j u i c e c o n c e n t r a t i o n s , i t can be c a l c u l a t e d as
t h i n j u i c e h^ = 421 - 2.19b ( k J / k g )
j u i c e a f t e r f i r s t e f f e c t h^ = 423 - 2.20b ( k J / k g ) a
j u i c e a f t e r second e f f e c t h = 430 - 2.23b ( k J / k g ) . a
Once t h e above q u a n t i t i e s have been measu red , i t becomes p o s s i b l e t o
i d e n t i f y t h e c o u r s e o f t he m u l t i - s t a g e e v a p o r a t i o n p r o c e s s . From t h e d r y m a t t e r
b a l a n c e e q u a t i o n f o r t h e i - t h e v a p o r a t o r e f f e c t
G¿bo = GJb . ( 7 . 2 6 )
we can c a l c u l a t e t h e j u i c e f l o w
= G ¿ b Q / b . ( kg /100 kg b ) ( 7 . 2 7 )
N e x t , t he mass o f e v a p o r a t e d w a t e r can be c a l c u l a t e d
266
W. = G^_^ - ( kg /100 kg b ) ( 7 . 2 8 )
The e f f e c t i v e t e m p e r a t u r e d i f f e r e n c e i n t h e i - t h e f f e c t i s
A t . = - ( 7 . 2 9 )
( T h i s f o r m u l a i s v a l i d o n l y i f tV i s t h e v a p o u r t e m p e r a t u r e measured i n t h e
v a p o u r chamber c l o s e t o t h e j u i c e s u r f a c e . I f t h e t e m p e r a t u r e i s measured a t t h e
v a p o u r chamber o u t l e t , t hen t h e e f f e c t i v e d i f f e r e n c e must be r e d u c e d by t h e
v a l u e o f b o l i n g p o i n t e l e v a t i o n . )
U s i n g t h e q u a n t i t i e s d e t e r m i n e d a c c o r d i n g t o t h e above f o r m u l a e , t h e o v e r a l l
h e a t t r a n s f e r c o e f f i c i e n t can be d e t e r m i n e d f rom a g r a p h g i v e n i n r e f . 2 . I t i s
a l s o p o s s i b l e t o a p p l y a s i m p l e i t e r a t i v e a l g o r i t h m w h i c h can c o n v e n i e n t l y be
c o m p u t e r i z e d . The a l g o r i t h m uses t h e thermodynamic f u n c t i o n s h " ( t ) and h ' ( t ) ,
i . e . e n t h a l p i e s o f d r y s a t u r a t e d steam and s a t u r a t e d w a t e r as f u n c t i o n s o f
t e m p e r a t u r e , and h ' ^ ( t , b ) , i . e . j u i c e e n t h a l p y as a f u n c t i o n o f t e m p e r a t u r e and
c o n c e n t r a t i o n . The amount o f h e a t t r a n s f e r r e d i n u n i t t ime i s
= (1 + e . ) ( W . ( h " ( t ^ ) - h ' ( t p ) + G ^ ( h J ( t ^ . p b . . ^ ) - h J ( t J , b . ) ) ) ( 7 . 3 0 )
where e / i s t h e h e a t l o s s c o e f f i c i e n t o f t h e i - t h e v a p o r a t o r e f f e c t .
The o v e r a l l hea t t r a n s f e r c o e f f i c i e n t can be c a l c u l a t e d f rom t h e f o r m u l a
k. = Q . / ( F . A t . ) ( 7 . 3 1 )
I n c o n c l u s i o n , l e t us s p e c i f y t h e recommendat ions f o r e v a p o r a t o r c h e c k i n g .
A r o u t i n e check s h o u l d c o n s i s t s o f r e c o r d i n g t h e j u i c e and v a p o u r t e m p e r a t u r e s
i n t h e i n d i v i d u a l e f f e c t s and t h e c o n c e n t r a t i o n s o f t h i n and t h i c k j u i c e . The
r e c o r d i n g f r e q u e n c y s h o u l d be a t l e a s t e v e r y 0 . 5 - 1 . 0 h o u r .
I n p e r i o d i c c h e c k s , a more d e t a i l e d i n v e s t i g a t i o n o f t h e e v a p o r a t o r ,
i n c l u d i n g t h e d e t e r m i n a t i o n o f hea t t r a n s f e r c o e f f i c i e n t s , i s n e c e s s a r y . I n
o r d e r t o e n s u r e t he r e l i a b i l i t y o f r e s u l t s , t e s t d u r a t i o n s o f a t l e a s t 4-6 h o u r s
s h o u l d be a d o p t e d . I n t h e case o f h e a t t r a n s f e r o b s e r v a t i o n s , t h e t e s t s s h o u l d
be pe r f o rmed e v e r y 10 d a y s , and even more f r e q u e n t l y when marked d r o p s i n h e a t
t r a n s f e r c o e f f i c i e n t s have been o b s e r v e d .
7 .6 .2 Example
I n a s u g a r f a c t o r y o p e r a t e d a t a c a p a c i t y o f 4000 t / d , a 4 - h o u r t e s t o f t h e
e v a p o r a t o r s t a t i o n has been p e r f o r m e d . The h e a t t r a n s f e r a r e a s i n f o u r 2
c o n s e c u t i v e e v a p o r a t o r e f f e c t s a r e : 2100, 2400, 2100 and 1050 m . The mean
v a l u e s o f t h i n - j u i c e f l o w and t h i n - j u i c e c o n c e n t r a t i o n a r e Gjj = 124.9 kg/100 kg
b e e t , bg = 13.9% DS. O t h e r t e s t d a t a a r e g i v e n i n t h e upper p a r t o f T a b l e 7 . 7 .
U s i n g e q n s . ( 7 . 2 7 ) , ( 7 . 2 8 ) and ( 7 . 2 9 ) , j u i c e f l o w s , amounts o f w a t e r
e v a p o r a t e d and e f f e c t i v e t e m p e r a t u r e d i f f e r e n c e s can be c a l c u l a t e d , as shown i n
t h e c e n t r e o f T a b l e 7 . 7 .
267
F i n a l l y , t h e g raph g i v e n i n r e f . 2 can be u s e d . The r e s u l t i n g v a l u e s o f
o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t s a r e shown i n t h e l o w e r p a r t o f T a b l e 7 . 7 .
TABLE 7.7
Example o f e v a p o r a t o r t e s t r e s u l t s .
E f f e c t No . 1 2 3 4
J u i c e c o n c e n t r a t i o n a t o u t l e t (% DS) 21 35 52 60 Tempera tu re i n h e a t i n g chamber ( °C) 134.0 127.4 119.7 110.0 Tempera tu re i n v a p o u r chamber ( °C) 128.5 121.0 112.9 103.7
J u i c e f l o w (kg /100 kg b ) 82.0 49.3 33.2 28.7 Water e v a p o r a t i o n (kg /100 kg b ) 43.0 32.7 16.1 4.5 E f f e c t i v e t e m p e r a t u r e d i f f e r e n c e ( K ) 5.5 6.4 6.8 6.3
Heat t r a n s f e r c o e f f i c i e n t ( W i m h ) ) 3.84 2.20 1.14 0.70
7 .6 .3 E x t r a c t o r
The e s s e n t i a l e x t r a c t o r f u n c t i o n s , i . e . p r o p e r e x h a u s t i o n o f c o s s e t t e s and
o b t a i n i n g h i g h - p u r i t y raw j u i c e , a r e dependen t on r a p i d h e a t i n g o f t h e i n f l o w i n g
c o s s e t t e s f o r d e n a t u r a t i o n o f l i v i n g c e l l s , f o l l o w e d by e x t r a c t i o n a t a
t e m p e r a t u r e l e v e l o f 70-74°C. The p a r t o f t h e h e a t economy r e l a t e d t o e x t r a c t i o n
i s aimed p r e c i s e l y a t t h a t o p e r a t i o n . The f o l l o w i n g d i s c u s s i o n a p p l i e s m o s t l y t o
t he t r o u g h - t y p e (DOS) e x t r a c t o r s , b u t t h e g e n e r a l recommendat ions and comments
on m o n i t o r i n g p r i n c i p l e s and methods a r e a l s o v a l i d f o r o t h e r e x t r a c t o r t y p e s .
T h e r e a r e f o u r h e a t i n g j a c k e t s i n t r o u g h - t y p e e x t r a c t o r s ; two o f them a r e
u s u a l l y hea ted by s e c o n d - e f f e c t v a p o u r a t a t e m p e r a t u r e o f 112-115°C, w h i l e t h e
o t h e r two a r e hea ted by t h i r d - e f f e c t v a p o u r a t 103-105°C. E x t r a c t o r m o n i t o r i n g
i s aimed m a i n l y a t c h e c k i n g w h e t h e r t h e r e q u i r e m e n t s o f e x t r a c t i o n t e m p e r a t u r e
and c o r r e c t n e s s o f h e a t s u p p l y a r e f u l f i l l e d . The p r e r e q u i s i t e f o r c o r r e c t
e x t r a c t o r o p e r a t i o n i s e f f i c i e n t c o n d e n s a t e d r a i n a g e and e f f i c i e n t v e n t i n g o f
h e a t i n g j a c k e t s ; t h e c o n t r o l p rob lems i n t h i s a r e a were d i s c u s s e d i n S e c t i o n s
3.2.1 and 3 . 2 . 2 . O t h e r the rma l p rob lems c a n n o t be s e p a r a t e d f rom t h e e x t r a c t i o n
p r o c e s s i t s e l f . F o r c o r r e c t i n t e r p r e t a t i o n o f t h e check r e s u l t s , i t i s
recommended t h a t c o n s i d e r a t i o n be g i v e n t o h e a t t r a n s f e r i n two p a r t s o f t h e
e x t r a c t o r : A - c o s s e t t e s h e a t i n g z o n e ; Β - e x t r a c t i o n p r o c e s s zone (whe re t h e
t e m p e r a t u r e s o f j u i c e and c o s s e t t e s a r e e q u a l ) , as shown i n F i g . 7 . 9 . G d e n o t e s
t he mass f l o w i n k g / l O O kg b , t i s t h e t e m p e r a t u r e i n °C, and C i s t h e s p e c i f i c
hea t i n k J / ( k g K ) . The s u b s c r i p t s d e n o t e : b , c o s s e t t e s ; pw, p r e s s w a t e r ; w , f r e s h
w a t e r ; j , raw j u i c e ; p , p u l p ( e x h a u s t e d c o s s e t t e s ) ; m, j u i c e - c o s s e t t e s m i x t u r e
between zones A and B.
U s i n g t h e d e f i n i t i o n o f t h e e f f i c i e n c y o f h e a t exchange between j u i c e and
c o s s e t t e s a c c o r d i n g t o r e f . 43
Ε = 1 0 0 . G . C . ( t ^ - t j ) / ( G ( ^ C ^ , ( t ^ - t ( , ) ) (%) ( 7 . 3 2 )
268
G j C j t j Β
Τ"
Gw CvA/t V
GpCptp
F i g . 7 .9 . Heat b a l a n c e scheme o f t h e t r o u g h e x t r a c t o r . A - f r o n t p a r t , Β - r e a r p a r t . Fo r t h e e x p l a n a t i o n o f s y m b o l s , see t e x t .
we can e x p r e s s t he hea t demand f o r c o s s e t t e s h e a t i n g as
= ( (100 - E ) / E ) G j ^ C ^ ( t ^ - t ^ ) ( k J / 1 0 0 kg b) ( 7 . 3 3 )
T a k i n g i n t o a c c o u n t t h a t = 1 0 0 - G / a , where a i s t h e raw j u i c e d r a f t i n %, t he
r e l a t i o n s h i p s between e x t r a c t i o n pa rame te rs can be shown d i a g r a m m a t i c a l l y
( F i g . 7 . 1 0 ) . I t can e a s i l y be seen t h a t t he the rma l phenomena a re h i g h l y
dependen t on such p r o c e s s f a c t o r s a s :
- c o s s e t t e s q u a l i t y , as l o w e r q u a l i t y causes a d e c r e a s e d Ε v a l u e ;
80 h
S 60
c D O Ε O ^ A O O Οι
Χ
20 h
50
A O
L_ Ζ)
Ε ο. Ε Φ
Φ ο
30
20
10
5 10 Cossettes temperature (°C)
15
α = 115 α=120
α=110
^ Ε = 8 0 /
E = go
Ε = 70
Ε =80
Ε =90
Ε = 100
F i g . 7 .10 . R e l a t i o n s h i p between e x t r a c t i o n pa rame te rs i n t h e f r o n t p a r t o f t h e e x t r a c t o r ( a f t e r r e f . 4 3 ) . a - j u i c e d r a f t ( % ) , Ε - hea t exchange e f f i c i e n c y {%
269
- d e - a e r a t i o n o f t he j u i c e - c o s s e t t e s m i x t u r e , as i n s u f f i c i e n t d e - a e r a t i o n causes
Ε t o d e c r e a s e ;
- j u i c e d r a f t , as i t s i n c r e a s e i m m e d i a t e l y causes i n c r e a s e d h e a t consumpt ion i n
t he e x t r a c t o r ;
- s t a b i l i z a t i o n o f t he j u i c e l e v e l a t t he o u t l e t s c r e e n , as an i n c o r r e c t j u i c e
l e v e l may a l s o reduce t he v a l u e o f E .
The d iag ram a l s o d e m o n s t r a t e s t h a t c o r r e c t e x t r a c t o r o p e r a t i o n n e c e s s a r i l y
i n v o l v e s v a r i a b l e j u i c e t e m p e r a t u r e as a f u n c t i o n o f t h e c o s s e t t e s t e m p e r a t u r e .
I f t h e c o s s e t t e s t e m p e r a t u r e i s l o w , a l o w e r j u i c e t e m p e r a t u r e s h o u l d be
a c c e p t e d , w i t h s u b s e q u e n t j u i c e h e a t i n g i n t h e h e a t e r s b e f o r e t h e p u r i f i c a t i o n
s t a t i o n . The op t ima l t e m p e r a t u r e d i f f e r e n c e between j u i c e and c o s s e t t e s i s
10-15 K.
I n o r d e r t o a c h i e v e a comp le te e v a l u a t i o n o f t h e the rma l c o n d i t i o n s , t he
e x t r a c t o r check s h o u l d i f p o s s i b l e c o n s i s t o f measu r i ng a l l t he q u a n t i t i e s
i n c l u d e d i n t h e h e a t b a l a n c e ( s e e F i g . 7.9 and t h e e x p l a n a t i o n o f s y m b o l s ) . F o r
c o r r e c t i n t e r p r e t a t i o n o f t he t e s t r e s u l t s , t h e f o l l o w i n g d a t a a r e a l s o
n e c e s s a r y :
- t he c o s s e t t e s l e n g t h ;
- t h e j u i c e d r a f t ;
- comments on c o s s e t t e s q u a l i t y , d e - a e r a t i o n o f t h e j u i c e - c o s s e t t e s m i x t u r e and
t h e j u i c e l e v e l a t t h e o u t l e t s c r e e n .
Known v a l u e s o f t he i n w a r d and o u t w a r d mass f l o w s make i t p o s s i b l e t o
c a l c u l a t e t h e t h e o r e t i c a l hea t demand ( w i t h o u t l o s s e s t o t h e e n v i r o n m e n t ) f rom
t h e e n e r g y b a l a n c e e q u a t i o n
F o r hea t -economy m o n i t o r i n g p u r p o s e s , t h e r e a l h e a t consumpt ion w o u l d be
i n t e r e s t i n g , bu t t he measur ing equ ipment c o n v e n t i o n a l l y i n s t a l l e d a t t h e
e x t r a c t o r s does n o t a l l o w f o r such a measurement . I f a d d i t i o n a l equ ipment f o r
t h e d e t e r m i n a t i o n o f c o n d e n s a t e f l o w i s i n s t a l l e d , t h e n c o n d e n s a t e f l o w s ( e q u a l
t o v a p o u r f l o w s ) and Gg , i n kg/100 kg b , can be d e t e r m i n e d . P r o v i d i n g t h a t
t he v a p o u r t e m p e r a t u r e s t ^ and t g , and c o n d e n s a t e t e m p e r a t u r e s t ^ ^ and t ^ g , a r e
a l s o measured , i t becomes p o s s i b l e t o c a l c u l a t e t h e h e a t consumpt ion i n bo th
p a r t s o f t h e e x t r a c t o r
QA = S ^ ^ A " " ^ - ^ ^ ^ C A ) ^9 b) ( 7 . 3 5 )
Qß = Gg(hg - 4 . 1 9 t ^ g ) ( k J / 1 0 0 kg b) ( 7 . 3 6 )
where h^ and hg a r e t h e e n t h a l p i e s o f v a p o u r s i n k J / k g , a t t e m p e r a t u r e s t ^ and
t g , r e s p e c t i v e l y .
Depend ing on t h e c o s s e t t e s t e m p e r a t u r e , t h e v a p o u r consumpt ion i n P a r t A i s
1 .5-2.0 kg/100 kg b. I n P a r t B, a v a p o u r f l o w o f up t o 1 kg/100 kg b i s r e q u i r e d
270
w i t h o u t p r e s s - w a t e r h e a t i n g , o r somewhat l e s s i f t h e p r e s s w a t e r i s h e a t e d .
Tempera tu re m o n i t o r i n g a t t h e e x t r a c t o r must be r o u t i n e l y pe r f o rmed d u r i n g
t he e n t i r e o p e r a t i o n s . A h e a t b a l a n c e d e t e r m i n a t i o n , p o s s i b l y i n c l u d i n g
c o n d e n s a t e - f l o w measurements , may become n e c e s s a r y i f unusua l p rob lems o c c u r i n
e x t r a c t o r o p e r a t i o n .
7 .6 .4 J u i c e h e a t e r s
The hea t s u p p l y t o t he j u i c e o r o t h e r media i n t h e h e a t e r s i s aimed a t
a t t a i n i n g t he t e m p e r a t u r e needed f o r such u n i t o p e r a t i o n s as l i m i n g ,
c a r b o n a t a t i o n , f i l t r a t i o n , e t c . A t t e n t i o n s h o u l d be d i r e c t e d , h o w e v e r , n o t o n l y
t o t he f u n c t i o n i n g o f each p a r t i c u l a r h e a t e r , b u t a l s o t o t h e o p e r a t i o n o f a l l
h e a t e r s v i e w e d as an i m p o r t a n t p a r t o f t h e hea t economy. From t h a t p o i n t o f
v i e w , hea t economy m o n i t o r i n g s h o u l d compr i se c h e c k i n g t h e t e m p e r a t u r e s o f t h e
media f o r t h e i r c o r r e s p o n d e n c e w i t h p r o c e s s r e q u i r e m e n t s , as w e l l as i n s p e c t i n g
t he s u i t a b i l i t y o f t h e d i s t r i b u t i o n o f h e a t i n g media ( c o n d e n s a t e and v a p o u r s
f rom the e v a p o r a t o r and vacuum p a n s ) . The e s s e n t i a l p r i n c i p l e o f h e a t - s a v i n g
media d i s t r i b u t i o n i s t o s u p p l y t h e h e a t e r w i t h a medium a t a t e m p e r a t u r e h i g h
enough t o hea t t h e j u i c e , b u t n o t t o o h i g h . Depend ing on h e a t e r d e s i g n , hea t
t r a n s f e r a r e a and j u i c e v e l o c i t y , t h e v a p o u r t e m p e r a t u r e s h o u l d be n o t h i g h e r
than 5-10 Κ above t h e f i n a l j u i c e t e m p e r a t u r e ( s e e a l s o S e c t i o n 3 .3 .2 on
u t i l i z a t i o n o f v a p o u r s ) .
R e g a r d i n g i n d i v i d u a l h e a t e r s , t h e y s h o u l d be t h o r o u g h l y i n s p e c t e d f o r t h e i r
f u n c t i o n i n g as hea t r e c e i v e r s . I n t h e case o f v a p o u r h e a t i n g , t h e c o n d e n s a t e
l e v e l i n t h e h e a t i n g chamber i s p a r t i c u l a r l y i m p o r t a n t ( s e e a l s o S e c t i o n 3.2.1
on condensa te d r a i n a g e ) . The c o n d e n s a t e l e v e l s h o u l d n o t be a l l o w e d t o r i s e
above t h e o u t l e t n o z z l e s , as t h i s w o u l d r e d u c e t h e e f f e c t i v e o v e r a l l hea t
t r a n s f e r c o e f f i c i e n t , making i t more d i f f i c u l t t o a t t a i n t h e p r o p e r j u i c e
t e m p e r a t u r e . S i m i l a r p rob lems o c c u r i f h e a t t r a n s f e r i s hampered by t h e
a c c u m u l a t i o n o f n o n c o n d e n s a b l e s ; t h e h e a t e r check s h o u l d t h u s i n c l u d e i n s p e c t i o n
o f t h e v e n t s ( s e e S e c t i o n 3 . 2 . 2 ) . The h e a t t r a n s f e r i n t e n s i t y can a l s o be
reduced by s c a l e b u i l d - u p i n t h e h e a t i n g t u b e s ; t h i s i s a n o t h e r p rob lem t o be
a c c o u n t e d f o r i n t he i n s p e c t i o n .
I n o r d e r t o make c a l c u l a t i o n s o f h e a t b a l a n c e p o s s i b l e , t h e f o l l o w i n g
measurements a r e r e q u i r e d :
- j u i c e mass f l o w , G (kg /100 kg b ) ;
- j u i c e i n l e t t e m p e r a t u r e , t^ ( ^ C ) ;
- j u i c e o u t l e t t e m p e r a t u r e , t ^ ( ° C ) ;
- j u i c e c o n c e n t r a t i o n , b (% D S ) ;
- v a p o u r o r condensa te ( s e e b e l o w ) mass f l o w , G^ (kg /100 kg b ) ;
- v a p o u r t e m p e r a t u r e , t ^ , and c o n d e n s a t e t e m p e r a t u r e , t ^ ( °C) ( o r , i n t h e case
271
o f condensa te h e a t i n g , i n i t i a l and f i n a l t e m p e r a t u r e s , t ^ - j , t ^ ^ ( ° ^ ) »
condensa te l e v e l i n t he h e a t i n g chamber s h o u l d be wa tched a t t h e same t i m e ) .
The measurements s h o u l d be pe r f o rmed d u r i n g s t e a d y - s t a t e h e a t e r o p e r a t i o n ,
p o s s i b l y a t t he j u i c e f l o w c o r r e s p o n d i n g t o t he nominal p r o c e s s i n g c a p a b i l i t y o f
t he f a c t o r y . The recommended t e s t d u r a t i o n i s a t l e a s t 1-2 h o u r s , w i t h an
i n s t r u m e n t - r e a d i n g f r e q u e n c y o f 5-10 m i n u t e s . A f t e r mean pa ramete r v a l u e s have
been c a l c u l a t e d , t he hea t t r a n s f e r i n t e n s i t y s h o u l d be e v a l u a t e d f i r s t . I f t he
c o r r e c t v a l u e o f t h e v a p o u r ( o r i n l e t c o n d e n s a t e ) t e m p e r a t u r e i s accompanied by
an i n s u f f i c i e n t j u i c e t e m p e r a t u r e i n c r e a s e ( w i t h p r o p e r condensa te d r a i n a g e and
v e n t i n g ) , t hen s c a l i n g on t he h e a t i n g s u r f a c e s may be s u s p e c t e d .
A t known j u i c e - m a s s f l o w , G , t he hea t consumed can be c a l c u l a t e d as
Q = G C ( t 2 - t ^ ) ( l + n ) ( k J / 1 0 0 kg b ) ( 7 . 3 7 )
where the s p e c i f i c hea t o f t he j u i c e , C ( k J / ( k g K ) ) , can be f ound i n t a b l e s o r
c a l c u l a t e d as a f u n c t i o n o f t h e j u i c e c o n c e n t r a t i o n , b, and η i s t h e hea t l o s s
c o e f f i c i e n t .
On v a p o u r h e a t i n g , hea t consumpt ion on t h e v a p o u r s i d e can be d e t e r m i n e d o n l y
i f p e r f e c t o p e r a t i o n o f t h e steam t r a p s i s e n s u r e d ( t h a t i s , o n l y i f steam
leakage i n t h e condensa te s t ream i s e l i m i n a t e d ) . The condensa te f l o w can be
measured by a v o l u m e t r i c method , by c a t c h i n g t he c o n d e n s a t e i n a s p e c i a l
c o n t a i n e r . The h e a t consumpt ion can t hen be c a l c u l a t e d as
Q = G ^ ( h " - 4 . 1 9 t ^ ) ( k J / 1 0 0 kg b) ( 7 . 3 8 )
where h" d e n o t e s v a p o u r e n t h a l p y i n k J / k g . I n t h e case o f condensa te h e a t i n g , t he c o r r e s p o n d i n g f o r m u l a i s
Q = G ^ - 4 . 1 9 ( t ^ ^ - t ^ 2 ) kg b) ( 7 . 3 9 )
As t o t h e f r e q u e n c y o f h e a t e r check measurements , an i n s p e c t i o n o f
t e m p e r a t u r e s b e f o r e most i m p o r t a n t u n i t o p e r a t i o n s s h o u l d be p e r f o r m e d r o u t i n e l y
d u r i n g t he e n t i r e s e a s o n . Any i r r e g u l a r i t i e s n o t i c e d i n t he d i s t r i b u t i o n o f
h e a t i n g media t o t h e i n d i v i d u a l h e a t e r s must i m m e d i a t e l y be c o r r e c t e d . D e t a i l e d
i n v e s t i g a t i o n s o f h e a t e r o p e r a t i o n may be r e q u i r e d i f d i f f i c u l t i e s o c c u r i n t h e
h e a t i n g o f p r o c e s s med ia .
7 .6 .5 Ba tch vacuum pans
Sugar b o i l i n g i s a d e c i s i v e o p e r a t i o n f o r s u g a r y i e l d and s u g a r q u a l i t y . The
b o i l i n g t i m e , combined w i t h i n s t a l l e d pan v a p a c i t y , can be a l i m i t a t i o n t o s u g a r
f a c t o r y p r o c e s s i n g c a p a b i l i t y . I n a d d i t i o n , t h e h e a t consumpt ion f o r s u g a r
b o i l i n g may i n v o l v e 40-50% o f t he t o t a l p r o c e s s - h e a t c o n s u m p t i o n . As a
c o n s e q u e n c e , i n v e s t i g a t i o n s o f hea t consumpt ion i n vacuum pans must be ser: as
one o f t he most s e r i o u s t a s k s i n hea t -economy m o n i t o r i n g .
I n p r a c t i c e , a hea t economy check i n t h e s u g a r house canno t be s e p a r a t e d f rom
272
a t e c h n o l o g i c a l check . The r e a s o n i s t h a t t he h e a t consumpt ion f o r s u g a r b o i l i n g
depends on t h e amounts and c o n c e n t r a t i o n s o f t h i c k j u i c e and r e m e l t , as w e l l as
on t he amount o f w a t e r i n t r o d u c e d i n t o t h e s u g a r house v i a such o p e r a t i o n s as
d i l u t i o n o f s y r u p s , wash ing and i n t a k e s t o vacuum p a n s .
The t o t a l consumpt ion o f v a p o u r s f o r s u g a r b o i l i n g i n a vacuum pan ( o r i n
a g roup o f vacuum pans ) can be e x p r e s s e d as t h e sum
= + G ^ (kg /100 kg b ) ( 7 . 4 0 )
where G^ i s t he v a p o u r consumpt ion f o r b o i l i n g s u g a r s o l u t i o n s , and G ^ i s t h e
v a p o u r consumpt ion f o r t h e e v a p o r a t i o n o f a d d i t i o n a l w a t e r f rom i n t a k e s . Both
q u a n t i t i e s depend on t e c h n o l o g i c a l pa rame te rs a c c o r d i n g t o t he f o r m u l a e ( r e f . 8)
G ^ = u M ^ Í C g í t ^ - t ^ ) + (1 - b ^ / b ^ ) ( h ^ - h ) ) / ( h ^ - h^) ( kg /100 kg b ) ( 7 . 4 1 )
G ^ = W(h^ - h ) / ( h ^ - h^) (kg /100 kg b) ( 7 . 4 2 )
where u i s t h e l o s s c o e f f i c i e n t ( 1 . 1 - 1 . 2 ) , i s t h e t o t a l amount o f s u g a r
s o l u t i o n s s u p p l i e d t o t he vacuum pan i n kg/100 kg b , bj^ i s t h e f i n a l
c o n c e n t r a t i o n o f m a s s e c u i t e i n % DS, i s t he mean s p e c i f i c h e a t o f t h e
s o l u t i o n s i n k J / ( k g K ) , t|^ i s t h e b o i l i n g t e m p e r a t u r e i n °C, t ^ i s t h e mean
i n i t i a l t e m p e r a t u r e o f t h e s o l u t i o n s i n °C, h , i s t h e e n t h a l p y o f t h e vacuum-pan w
v a p o u r , h i s t h e e n t h a l p y o f w a t e r a t t e m p e r a t u r e t ^ , h^ i s t h e e n t h a l p y o f t h e
h e a t i n g v a p o u r , h^ i s t he condensa te e n t h a l p y ( a l l e n t h a l p i e s i n k J / k g ) , and W
i s t he amount o f w a t e r f rom i n t a k e s , i n kg/100 kg b.
The above r e l a t i o n s h i p s p r o v e t h a t t h e most i m p o r t a n t f a c t o r i n o b t a i n i n g
hea t s a v i n g s i n s u g a r b o i l i n g i s adhe rence t o t h e t e c h n o l o g i c a l g u i d e l i n e s . I t
i s p a r t i c u l a r l y i m p o r t a n t t o m a i n t a i n h i g h v a l u e s i n t h e c o n c e n t r a t i o n s o f t h i c k
j u i c e , s y r u p s and r e m e l t . S h o u l d any o f t h e c o n c e n t r a t i o n s d e c r e a s e , t h e
r e s u l t i n g d e c r e a s e i n b^ v a l u e wou ld r e s u l t i n an i n c r e a s e d v a l u e o f v a p o u r
c o n s u m p t i o n , G ^ . Water i n t a k e s t o vacuum pans s h o u l d be r e d u c e d t o a minimum; o t h e r w i s e , t h e f a c t o r G wou ld cause an u n n e c e s s a r y i n c r e a s e i n v a p o u r
w
c o n s u m p t i o n . On t h e o t h e r h a n d , t h e vacuum i n t he pans i s a l s o i m p o r t a n t , as
t h i s i s t h e e s s e n t i a l f a c t o r i n e n s u r i n g i n t e n s i v e h e a t t r a n s f e r , w h i c h i s
n e c e s s a r y t o m a i n t a i n s h o r t b o i l i n g t imes w i t h o u t i n c r e a s i n g e n e r g y e x p e n d i t u r e .
As t o t he i n d i v i d u a l vacuum p a n s , t h e i r o p e r a t i o n as hea t r e c e i v e r s s h o u l d
be t h o r o u g h l y i n v e s t i g a t e d . The most i m p o r t a n t p o i n t s a r e :
- condensa te d r a i n a g e f rom t h e h e a t i n g chamber ;
- v e n t i n g o f t he h e a t i n g chamber ;
- e l i m i n a t i o n o f i n c r u s t a t i o n s f rom the hea t t r a n s f e r s u r f a c e .
The measurements needed f o r m o n i t o r i n g p u r p o s e s a r e :
- b o i l i n g t e m p e r a t u r e , t j ^ ;
- v a p o u r p r e s s u r e , Pj^;
- h e a t i n g - v a p o u r t e m p e r a t u r e , t ^ ;
273
- condensa te t e m p e r a t u r e , t ^ .
V a l u e s o f t he above pa rame te rs e n a b l e u s , e v e n t u a l l y , t o d e t e r m i n e t h e e n t h a l p y
v a l u e s a p p e a r i n g i n e q n s . ( 7 . 3 9 ) and ( 7 . 4 0 ) . ( I t s h o u l d be p o i n t e d o u t t h a t
p e r f o r m i n g t he measurements e n t a i l s ove rcoming s p e c i f i c o b s t a c l e s r e l a t e d t o
suga r b o i l i n g ( r e f . 1 6 ) . ) A t t h e end o f t he s t r i k e , t h e amount o f m a s s e c u i t e M^,
and t he f i n a l c o n c e n t r a t i o n b|^, become known.
The measurements s h o u l d compr i se a t l e a s t two s t r i k e s . The f r e q u e n c y o f
i n s t r u m e n t r e a d i n g s s h o u l d be adap ted t o t h e s t r i k e d u r a t i o n ( a t l e a s t 10-15
r e a d i n g s ) .
U s i n g t h e e s t i m a t e d mean v a l u e o f t h e c o n c e n t r a t i o n o f s u g a r s o l u t i o n s
s u p p l i e d t o t h e vacuum p a n , t h e amount o f w a t e r e v a p o r a t e d f rom t h e s o l u t i o n s
can be c a l c u l a t e d as
= M ^ ( b . / b ^ - 1) ( kg /100 kg b) ( 7 . 4 3 )
D i r e c t measurement o f t he t o t a l v a p o u r consumpt ion i s o f t e n i m p o s s i b l e f o r
l a c k o f f l o w me te rs a t i n d i v i d u a l vacuum p a n s . P r o v i d i n g t h a t c o n d e n s a t e
d r a i n a g e and v e n t i n g do n o t cause v a p o u r l e a k s , v o l u m e t r i c d e t e r m i n a t i o n o f t h e
condensa te amount, equa l t o G ^ , can p o s s i b l y be u s e d . Condensa te f l o w can a l s o
be measured w i t h t h e a i d o f an i n d u c t i v e f l o w meter i n s t a l l e d as shown
s c h e m a t i c a l l y i n F i g . 7. 11. A c o n d e n s a t e tank e q u i p p e d w i t h a w a t e r - l e v e l
i n d i c a t o r and a s e p a r a t e s i g h t g l a s s make i t p o s s i b l e t o check t h e i n t e g r a l o f
t he f l o w meter r e c o r d s , and t o check t h e c o n d i t i o n s f o r c o r r e c t measurement
( l a r g e movements o f t he condensa te column must be a v o i d e d ) .
Wi th p r o p e r vacuum-pan o p e r a t i o n , t h e v a p o u r consumpt ion d u r i n g one s t r i k e
F i g . 7 .11. Measurement o f t he c o n d e n s a t e f l o w f rom t h e h e a t i n g chamber o f a vacuum pan ( a f t e r r e f . 4 4 ) . 1 - vacuum p a n , 2 - c o n d e n s a t e tank w i t h a w a t e r -l e v e l i n d i c a t o r , 3 - f l o w m e t e r , 4 - s i g h t g l a s s , 5 - p r e s s u r e - b a l a n c i n g p i p e .
274
s h o u l d n o t exceed t he v a l u e
G. = ( 1 . 0 2 t o 1.15)W^ ( k g / l O O kg b ) ( 7 . 4 4 ) L e
I n r e f . 6, t h e upper l i m i t o f 1.20Wg i s m e n t i o n e d , b u t t h i s seems t o be
i n a p p r o p r i a t e i n t h e s e days o f e n e r g y s h o r t a g e s .
A v e r y u s e f u l a d d i t i o n t o t h e m o n i t o r i n g t e c h n i q u e s d e s c r i b e d above i s t h e
measurement o f t o t a l v a p o u r consumpt ion i n vacuum p a n s . T h i s r e q u i r e s
i n s t a l l a t i o n o f a f l o w meter on t h e main p i p e l i n e s u p p l y i n g v a p o u r t o t h e p a n s .
Even though t h i s method i s n o t e n t i r e l y a c c u r a t e when a p p l i e d t o s a t u r a t e d
s team, i t g i v e s a much-needed p r a c t i c a l o r i e n t a t i o n . F o r r o u t i n e vacuum-pan
c h e c k s , a c t u a l f l o w v a l u e s and f l o w o s c i l l a t i o n s can be e s t i m a t e d , w h i l e i n
p e r i o d i c c h e c k s , t h e o v e r a l l l e v e l o f v a p o u r consumpt ion and abnormal
consumpt ion jumps can be e v a l u a t e d and a n a l y s e d . I n p r i n c i p l e , i f t h e
c o n f i g u r a t i o n o f t he s u p p l y p i p e s a l l o w s , v a p o u r - f l o w measurement equ ipment
c o u l d be i n s t a l l e d a t each i n d i v i d u a l p a n .
7 .6 .6 O t h e r hea t r e c e i v e r s
I n a d d i t i o n t o t he main h e a t r e c e i v e r s d i s c u s s e d a b o v e , t h e r e a r e numerous
smal l h e a t r e c e i v e r s i n a s u g a r p l a n t : t h e s u g a r d r y e r , m e l t e r , hea ted s t o r a g e
t a n k s ( c o n t a i n i n g t h i c k j u i c e , r e m e l t , s y r u p s , m o l a s s e s , e t c . ) , n o z z l e sys tems
f o r wash ing and s t e a m i n g , and mo lasses pumping s y s t e m . I f u s e d , cube s u g a r
p r o d u c t i o n and p u l p p e l l e t i n g a l s o c o n t r i b u t e t o hea t c o n s u m p t i o n .
As each o f t h e i n d i v i d u a l hea t r e c e i v e r s men t ioned above i s r e s p o n s i b l e f o r
a v e r y sma l l p o r t i o n o f t h e t o t a l h e a t c o n s u m p t i o n , t h e y a r e u s u a l l y p o o r l y
s u p e r v i s e d o r even t r e a t e d m a r g i n a l l y . N e v e r t h e l e s s , t h e y d e s e r v e more a t t e n t i o n ,
as t h e i r combined hea t consumpt ion may c o n s t i t u t e a c o n s i d e r a b l e p o r t i o n o f t h e
t o t a l .
The e s s e n t i a l p rob lem i n t he m o n i t o r i n g o f smal l hea t r e c e i v e r s i s t h e
d e t e c t i o n o f e x c e s s i v e - t h a t i s , o u t o f a l l p r o p o r t i o n t o p r o c e s s
r e q u i r e m e n t s - consumpt ion o f steam o r v a p o u r s . Even i f t h e equ ipment i s
p r o p e r l y m a i n t a i n e d , t h i s may happen because o f o p e r a t o r e r r o r s ; t y p i c a l c a s e s
a r e s u g a r wash ing and t he s t e a m i n g - o u t o f vacuum p a n s .
App rox ima te v a l u e s o f the rma l pa rame te rs and t he consumpt ion o f h e a t i n g
media i n v a r i o u s u n i t s a r e g i v e n i n T a b l e 7 .8 . The o p e r a t i o n o f t h e s u g a r d r y e r
r e q u i r e s t h a t some p r o c e s s pa rame te rs a re a d d i t i o n a l l y measu red . I t i s
recommended t h a t t h e m o i s t u r e c o n t e n t i n s u g a r f rom c e n t r i f u g a l s be m a i n t a i n e d
a t 0 .5-1 .5%, t h e a i r f l o w a t 5-15 kg/100 kg b , and t h e a i r t e m p e r a t u r e a t
110-120°C.
Smal l hea t r e c e i v e r s s h o u l d be examined a t t h e b e g i n n i n g o f t h e s e a s o n , and
a l s o f o l l o w i n g t e m p o r a r y s h u t - d o w n s o r equ ipment r e p a i r s . I n t h e case o f
equ ipment where hea t consumpt ion depends on o p e r a t o r q u a l i f i c a t i o n s , a d d i t i o n a l
275
TABLE 7.8
H e a t i n g o f v a r i o u s smal l h e a t r e c e i v e r s .
Equipment H e a t i n g medium Consumpt ion ( kg /100 kg b )
Sugar d r y e r e x h a u s t s team, I s t - e f f e c t v a p o u r be low 1.0
S t o r a g e t a n k s ( comb ined) 2 n d - e f f e c t v a p o u r be low 1.5 M e l t e r 2 n d - e f f e c t v a p o u r 0 . 2 - 0 . 3 Sugar wash ing steam 5 b a r , 200°C 1 .5-2 .0 S t e a m i n g - o u t o f vacuum pans e x h a u s t s team,
1 s t - o r 2 n d - e f f e c t v a p o u r be low 1.5 Pu lp p e l l e t i n g steam 5 ba r be low 0.2
s p o t checks a r e recommended ( t h i s a p p l i e s t o s u g a r wash ing i n c e n t r i f u g a l s and
t o t h e s t e a m i n g - o u t o f vacuum pans and p i p e l i n e s ) .
7.7 AUXIL IARY EQUIPMENT
7.7.1 T h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n
The t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n s e r v e s t o r educe t h e steam p r e s s u r e and
d e c r e a s e i t s t e m p e r a t u r e so t h a t c e r t a i n d e f i n i t e v a l u e s o f bo th p a r a m e t e r s a r e
a t t a i n e d . I n the rma l s y s t e m s , such s t a t i o n s a r e a p p l i e d t o t r a n s f o r m l i v e steam
i n t o l o w - p r e s s u r e s team, t o supp lemen t t h e t u r b i n e - e x h a u s t s team, o r t h e
i n t e r m e d i a t e - p r e s s u r e steam ( u s u a l l y abou t 5 b a r ) t o be used i n c e n t r i f u g a l s .
The t h r o t t l i n g - d e s u p e r h e a t i n g p r o c e s s i s shown i n t h e M o l l i e r d i ag ram i n
F i g . 7 .12 . The p r e s s u r e r e d u c t i o n c o n s i s t s o f t h r o t t l i n g t h e steam f l o w i n a
r e d u c i n g v a l v e a t c o n s t a n t e n t h a l p y (segment A B ) . The t e m p e r a t u r e i s d e c r e a s e d
by i n j e c t i n g w a t e r a t s t a t e D i n such an amount ( a u t o m a t i c a l l y c o n t r o l l e d ) t h a t
a f t e r m i x i n g i t w i t h steam a t s t a t e B, t h e f i n a l s t a t e o f t h e m i x t u r e C i s c l o s e
t o s a t u r a t i o n . I n p r a c t i c e , steam a t t h e o u t l e t o f t h e t h r o t t l i n g - d e s u p e r h e a t i n g
s t a t i o n may be s l i g h t l y s u p e r h e a t e d , t h a t i s , i t s t e m p e r a t u r e may be 30-40 Κ
above t h e s a t u r a t i o n t e m p e r a t u r e .
F o r t h e e n t i r e the rma l s y s t e m , t h e f u n c t i o n i n g o f t h e t h r o t t l i n g -
d e s u p e r h e a t i n g s t a t i o n t h a t s u p p l i e s make-up steam t o t h e e x h a u s t steam i s o f
p a r t i c u l a r i m p o r t a n c e . The demand f o r e x h a u s t steam f l u c t u a t e s , f o l l o w i n g t h e
changes i n e v a p o r a t o r l o a d s . The t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n s h o u l d
compensate f o r t h e s e f l u c t u a t i o n s , so t h a t c o n s t a n t p r e s s u r e i s m a i n t a i n e d a t
t h e i n l e t t o t h e h e a t i n g chamber o f t h e f i r s t e v a p o r a t o r e f f e c t .
The check o f t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n s h o u l d be aimed a t
v e r i f i c a t i o n o f t h e p r o c e s s p a r a m e t e r s . I n a d d i t i o n t o t h e mean pa ramete r
v a l u e s , f l u c t u a t i o n s o f a c t u a l v a l u e s a r e a l s o i m p o r t a n t . D u r i n g a t e s t o f a t
l e a s t 1-2 h o u r s , t h e f o l l o w i n g i n s t r u m e n t r e a d i n g s a r e r e q u i r e d e v e r y 5 m i n u t e s :
- l i v e steam p r e s s u r e and t e m p e r a t u r e ;
276
Entropy
F i g . 7 .12 . Work ing p r i n c i p l e o f t he t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n . SC - s a t u r a t i o n c u r v e , p^ - p r e s s u r e o f l i v e s team, pg - p r e s s u r e o f make-up s team; A - s t a t e o f steam a t i n l e t , Β - s t a t e o f steam a f t e r r e d u c i n g v a l v e , C - s t a t e o f steam a t o u t l e t , D - s t a t e o f w a t e r b e f o r e d e s u p e r h e a t e r .
- steam p r e s s u r e a f t e r t he r e d u c i n g v a l v e ;
- steam p r e s s u r e and t e m p e r a t u r e a f t e r t h e d e s u p e r h e a t e r ;
- p r e s s u r e and t e m p e r a t u r e o f w a t e r s u p p l i e d t o t h e d e s u p e r h e a t e r .
F l u c t u a t i o n s o f steam p r e s s u r e can be e s t i m a t e d s i m p l y by i n c r e a s i n g t h e
f r e q u e n c y o f t he i n s t r u m e n t r e a d i n g s , f o r example t o e v e r y m i n u t e . T e m p e r a t u r e
f l u c t u a t i o n s can be e v a l u a t e d o n l y r o u g h l y , as t h e l ag o f i n d u s t r i a l
thermometers i s t o o l a r g e . The r e s u l t s s h o u l d be e v a l u a t e d a g a i n s t t he f o l l o w i n g
g u i d e l i n e s :
- a t t he mean i n l e t - p r e s s u r e v a l u e , c o n s t r a i n e d w i t h i n t he r e g i o n ±5% a round t h e
nominal v a l u e , t h e t o l e r a n c e o f t h e mean v a l u e o f t he r e d u c e d p r e s s u r e i s a l s o
- v e r y good r e d u c e d - p r e s s u r e s t a b i l i z a t i o n means t h a t p r e s s u r e f l u c t u a t i o n s do
n o t exceed ±2% o f i t s mean v a l u e . Howeve r , l a r g e r f l u c t u a t i o n s can be a l l o w e d ,
p r o v i d e d t h a t d i s t u r b a n c e s i n t h e sys tem o p e r a t i o n ( e s p e c i a l l y t he t u r b i n e ) a r e
a v o i d e d ;
- t he steam t e m p e r a t u r e a f t e r t he d e s u p e r h e a t i n g s h o u l d be h i g h e r than t h e
s a t u r a t i o n t e m p e r a t u r e , because t h i s i s t he o n l y way t o e l i m i n a t e t h e
u n c o n t r o l l a b l e p r e s e n c e o f e x c e s s w a t e r . Howeve r , s u p e r h e a t i n g s h o u l d n o t
exceed 40 K.
I n o r d e r t o i n t e r p r e t t e s t r e s u l t s c o r r e c t l y , a t t e n t i o n s h o u l d be g i v e n t o
t he o p e r a t i n g c o n d i t i o n s . T h e r e a r e a t l e a s t t h r e e r e q u i r e m e n t s f o r normal
277
o p e r a t i o n o f t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n ; name ly , l o a d f l u c t u a t i o n s
s h o u l d be no more i n t e n s i v e than under a v e r a g e o p e r a t i n g c o n d i t i o n s , t h e b o i l e r
l o a d s h o u l d be r e a s o n a b l y l o w e r t han i t s maximum c a p a c i t y , and t h e p r e s s u r e o f
w a t e r s u p p l i e d t o t h e d e s u p e r h e a t e r s h o u l d be a t l e a s t 4 b a r h i g h e r t han t h e
reduced steam p r e s s u r e .
I t i s recommended t h a t t h e t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n i s checked a t
t he b e g i n n i n g o f t h e season and t h e n p e r i o d i c a l l y e v e r y t e n days o r two weeks .
7 .7 .2 B a r o m e t r i c c o n d e n s e r s
The v a p o u r - c o n d e n s i n g s t a t i o n p l a y s an i m p o r t a n t r o l e , as i t i n f l u e n c e s such
i m p o r t a n t p r o c e s s e s as s u g a r b o i l i n g , w h i l e a l s o i n t e r a c t i n g w i t h t h e the rma l
sys tem because i t a b s o r b s l a r g e amounts o f hea t t o be d i s s i p a t e d t o t h e
e n v i r o n m e n t . An i m p o r t a n t p r o c e s s r e q u i r e m e n t i s t h a t t he c o n d e n s e r s s h o u l d
e n s u r e t he c o n s t a n t low p r e s s u r e ( h i g h vacuum) t h a t i s n e c e s s a r y t o o b t a i n low
b o i l i n g t e m p e r a t u r e s and r a p i d t h i c k e n i n g o f s u g a r s o l u t i o n s i n t he b a t c h vacuum
p a n s . A therma l r e q u i r e m e n t i s t h a t t he t e m p e r a t u r e o f b a r o m e t r i c w a t e r s h o u l d
be as low as p o s s i b l e , bu t h i g h enough t o e n s u r e r a p i d hea t d i s s i p a t i o n i n t h e
c o o l i n g t o w e r s . I n d o u b l e - s t a g e c o n d e n s i n g s y s t e m s , i t may be i m p o r t a n t t o g e t
w a t e r f rom t h e f i r s t s t a g e w i t h a t e m p e r a t u r e s u f f i c i e n t l y h i g h t o s e r v e as f e e d
w a t e r f o r t h e e x t r a c t i o n p r o c e s s . S i m u l t a n e o u s l y , t h e o p e r a t i o n o f t h e v a p o u r -
condens ing s t a t i o n i s dependen t on e f f i c i e n t e v a c u a t i o n o f n o n c o n d e n s a b l e s by
vacuum pumps and a l s o on hea t d i s s i p a t i o n f rom t h e c o o l i n g t o w e r s .
The e s s e n t i a l p rob lem i n c o n d e n s e r i n s p e c t i o n i s t o d e t e r m i n e t h e c o o l i n g -
w a t e r consumpt ion w h i l e c o l l e c t i n g i n f o r m a t i o n on t h e c o n d e n s a t i o n p r o c e s s . T h i s
makes i t p o s s i b l e t o check w h e t h e r p r o c e s s r e q u i r e m e n t s a r e s a t i s f i e d , and
whe the r t he w a t e r consumpt ion can be d e c r e a s e d . The recommended c o n d e n s e r - t e s t
d u r a t i o n i s 4-6 h o u r s . The f o l l o w i n g measurements s h o u l d be r e c o r d e d e v e r y 20-30
m i n u t e s :
- t h e vacuum i n t h e condense r a t t h e v a p o u r i n l e t n o z z l e l e v e l ;
- t h e vacuum i n t h e upper p a r t o f t h e c o n d e n s e r above t h e c o o l i n g w a t e r i n l e t ;
- t h e t e m p e r a t u r e o f t he v a p o u r s s u p p l i e d t o t h e c o n d e n s e r ;
- t he mass f l o w o f c o o l i n g w a t e r ;
- t he t e m p e r a t u r e o f t he c o o l i n g w a t e r b e f o r e t h e c o n d e n s e r ;
- t he t e m p e r a t u r e o f t h e b a r o m e t r i c w a t e r a t t he c o n d e n s e r o u t l e t ( a t bo th
o u t l e t s i n a d o u b l e - s t a g e c o n d e n s i n g s t a t i o n ) .
T e s t r e s u l t s s h o u l d be i n t e r p r e t e d a g a i n s t t h e f o l l o w i n g g u i d e l i n e s :
- t h e d e s i r a b l e vacuum i n t h e c o n d e n s e r c e n t r e i s abou t 0.8 b a r (600 mm H g ) , as
a g a i n s t 0.88 ba r (660 mm Hg) i n i t s upper p a r t ;
- t h e d e s i r a b l e t e m p e r a t u r e o f t h e b a r o m e t r i c w a t e r i n a s i n g l e - s t a g e c o n d e n s e r
i s 45-50°C;
278
- i n a d o u b l e - s t a g e c o n d e n s e r , t h e t e m p e r a t u r e o f t he b a r o m e t r i c w a t e r s h o u l d
be 60-65°C i n t he f i r s t s t a g e and 40-45°C i n t h e second s t a g e ;
- t he d i f f e r e n c e between t h e s a t u r a t i o n t e m p e r a t u r e a t a c t u a l c o n d e n s e r p r e s s u r e
and t he b a r o m e t r i c w a t e r t e m p e r a t u r e s h o u l d n o t e x c e e d 5 K.
O p e r a t i n g c o n d i t i o n s a t t he t ime o f t he t e s t s h o u l d be a c c o u n t e d f o r i n t h e
e v a l u a t i o n o f t e s t r e s u l t s . The e f f i c i e n c y o f t he vacuum pumps and t h e
t e m p e r a t u r e o f t he c o o l i n g w a t e r a r e e s p e c i a l l y i m p o r t a n t , as w e l l as v a p o u r -
f l o w f l u c t u a t i o n s , because a t e m p o r a r y f l o w i n c r e a s e may i n d u c e l o w e r e d vacuum.
Under normal f a c t o r y - o p e r a t i n g c o n d i t i o n s , p o s s i b l e d i f f i c u l t i e s i n
m a i n t a i n i n g a p p r o p r i a t e vacuum, as w e l l as t o o l a r g e a d i f f e r e n c e between
s a t u r a t i o n and b a r o m e t r i c - w a t e r t e m p e r a t u r e s , i n d i c a t e t h a t t he condense r i s
o v e r l o a d e d by e x c e s s i v e v a p o u r f l o w . I n t h i s c a s e , t he f l o w v e l o c i t y o f t h e
v a p o u r s i n t h e f r e e - f l o w c r o s s - s e c t i o n a r e a o f t h e c o n d e n s e r s h o u l d be v e r i f i e d .
The a p p r o x i m a t e v a l u e ( n e g l e c t i n g h e a t l o s s e s t o t h e e n v i r o n m e n t ) o f t h e v a p o u r
mass f l o w , G^, can be c a l c u l a t e d f rom the e q u a t i o n s o f c o n d e n s e r mass and
e n e r g y b a l a n c e s
+ = G , (7.45)
where G. i s t he unknown mass f l o w o f b a r o m e t r i c w a t e r i n k g / h , G, i s t h e known
D W mass f l o w o f c o o l i n g w a t e r i n k g / h , and h ^ , h^ and hj^ a re e n t h a l p i e s i n k J / k g ,
w h i c h can be d e t e r m i n e d as f u n c t i o n s o f known t e m p e r a t u r e s t ^ , t ^ and t ^ . Upon
d e t e r m i n a t i o n o f t h e v a p o u r mass f l o w
^ = • - \ ^ ( k g / h ) (7.47)
t he f l o w v e l o c i t y can be c a l c u l a t e d as
w = G^vy((TTd2/4)-3600) ( m / s ) (7.48) where v ^ i s t he s p e c i f i c v o l u m e , i n m'^/kg, o f d r y s a t u r a t e d steam a t t e m p e r a t u r e
t ^ , and d i s t h e i n n e r d i ame te r o f t h e condense r b o d y , i n m. The f l o w v e l o c i t y
s h o u l d n o t exceed 50-60 m/s .
I t i s recommended t h a t t h e c o n d e n s e r s a r e checked a t t he b e g i n n i n g o f t h e
s e a s o n ; a f t e r t h a t , i n s p e c t i o n s h o u l d be u n d e r t a k e n whenever d e v i a t i o n s f rom
normal c o n d e n s e r o p e r a t i o n o c c u r .
7.7.3 Steam t r a p s
As emphas ized i n S e c t i o n 3.2.1, one o f t h e e s s e n t i a l r e q u i r e m e n t s o f p r o p e r
steam o r v a p o u r h e a t i n g i s r e l i a b l e condensa te d r a i n a g e . T h i s r e q u i r e m e n t can be
s a t i s f i e d , p r o v i d i n g t h a t t h e e n t i r e sys tem i s p r o p e r l y d e s i g n e d and m a i n t a i n e d .
I n p r a c t i c e , i t i s n o t unusua l t h a t d e s i g n e r r o r s o r m a k e s h i f t m o d i f i c a t i o n s
cause steam consumpt ion i n i n d i v i d u a l equ ipment u n i t s t o i n c r e a s e by 25-50% above t he a c t u a l n e e d . I t s h o u l d be u n d e r s t o o d he re t h a t t he p r e r e q u i s i t e f o r
279
r o u t i n e c h e c k i n g o f steam t r a p s i s t o e l i m i n a t e such e r r o r s .
Check ing o f steam t r a p s i s aimed a t d e t e c t i n g and e l i m i n a t i n g m a l f u n c t i o n i n g
t r a p s . Condensa te d r a i n a g e can be o b s e r v e d a t w a t e r - l e v e l gauges t h a t i n d i c a t e
t h e condensa te l e v e l i n t h e h e a t i n g chambers o f t h e r e l e v a n t a p p a r a t u s . N o z z l e -
t y p e steam t r a p s a r e o f t e n e q u i p p e d w i t h s i g h t - g l a s s e s t h a t make i t p o s s i b l e t o
o b s e r v e steam l e a k s . When i r r e g u l a r i t i e s a r e d e t e c t e d , i t may be n e c e s s a r y t o
r e f e r t o t h e measur ing i n s t r u m e n t s i n t h e the rma l s y s t e m ; h o w e v e r , i f t h e
p r e s s u r e d rop a c r o s s t he t r a p does n o t d i f f e r much f rom i t s nominal v a l u e , t r a p
damage can be s u s p e c t e d . A damaged t r a p must be r e p l a c e d w i t h o u t d e l a y .
Steam t r a p o p e r a t i o n can a l s o be i n v e s t i g a t e d u s i n g an u l t r a s o n i c sound
d e t e c t o r ( r e f . 4 5 ) . A l e s s r e l i a b l e method employs a s t e t h o s c o p e , o r even a
metal r o d t o u c h i n g t he t r a p s u r f a c e (an i n i t i a l t r i a l s h o u l d be made t o e n s u r e
t h a t t h i s method i s e f f i c i e n t ) .
7 .7 .4 Steam and v a p o u r p i p e l i n e s
The equ ipment and machines i n a the rma l sys tem a re i n t e r c o n n e c t e d by
p i p e l i n e s f o r t r a n s p o r t o f s team, v a p o u r o r w a t e r . Steam and v a p o u r p i p e l i n e s
a re p a r t i c u l a r l y i m p o r t a n t because o f t h e i r i n f l u e n c e on t h e e n e r g y u t i l i z a t i o n .
I t s h o u l d be p o i n t e d o u t t h a t c o r r e c t o p e r a t i o n o f a steam p i p e l i n e d e p e n d s ,
i n t he f i r s t p l a c e , on s a t i s f y i n g b a s i c c o n s t r u c t i o n r u l e s such as p i p e -
p o s i t i o n i n g w i t h t he s l o p e needed f o r c o n d e n s a t e f l o w - o f f , a p p l y i n g n e c e s s a r y
d r a i n a g e and v e n t i n g , p r o v i d i n g a p p r o p r i a t e the rma l i n s u l a t i o n , i n s t a l l i n g b y
pass l i n e s , e t c . These r u l e s a r e p a r t i c u l a r l y i m p o r t a n t f o r s a f e s t a r t - u p and
s h u t - d o w n , as w e l l as f o r t h e smooth r e p a i r and ma in tenance o f i n d i v i d u a l
equ ipment u n i t s w i t h o u t a f f e c t i n g t he o p e r a t i o n o f t h e e n t i r e s y s t e m . I t i s n o t
unusua l i n p r a c t i c e , h o w e v e r , t o f i n d t h a t t h e s e r u l e s a r e n o t c o m p l e t e l y
s a t i s f i e d due t o d e s i g n e r r o r s o r m a k e s h i f t m o d i f i c a t i o n s . I t s h o u l d be
u n d e r s t o o d he re t h a t t h e p r e r e q u i s i t e f o r normal p i p e l i n e c h e c k i n g i s t o
e l i m i n a t e e r r o r s o f t h a t k i n d .
Check ing o f steam p i p e l i n e s i s aimed a t :
- s t eam- leakage d e t e c t i o n and e l i m i n a t i o n ;
- t h e r m a l - i n s u l a t i o n i n s p e c t i o n and r e p a i r .
S team- leakage d e t e c t i o n c o n s i s t s o f f i n d i n g l e a k a g e s t o t h e e n v i r o n m e n t and
u n c o n t r o l l e d f l o w s t h r o u g h f a u l t y d r a i n s o r v e n t s , as w e l l as f l o w s i n d u c e d by
l e a k i n g v a l v e s i n b y - p a s s o r r e s e r v e l i n e s . T h i s may be a d i f f i c u l t t a s k i n
complex p i p i n g s y s t e m s ; i t can be made e a s i e r i f t he rmometers and manometers a r e
i n s t a l l e d i n a l l t h e p i p i n g s e c t i o n s . I t i s s u f f i c i e n t t o p e r f o r m s t e a m - l e a k a g e
checks a t t h e b e g i n n i n g o f t h e season and a f t e r t e m p o r a r y s h u t - d o w n s o r
equ ipment r e p a i r s .
The aim o f t h e checks o f the rma l i n s u l a t i o n i s t o i d e n t i f y and e l i m i n a t e
280
u n n e c e s s a r y h e a t l o s s e s f rom the p i p e l i n e s u r f a c e . Wet o r damaged i n s u l a t i o n
s e c t i o n s s h o u l d immed ia te l y be r e p a i r e d . I n cases o f we t i n s u l a t i o n , i t i s
enough t o e l i m i n a t e t h e w a t e r i n f l o w , as hea t f l u x f rom the p i p e s u r f a c e w i l l
cause s u b s e q u e n t d r y i n g . I n s u l a t i o n c h e c k i n g s h o u l d be pe r f o rmed a t t h e f a c t o r y
s t a r t - u p , and a f t e r equ ipment o r p i p i n g r e p a i r s . A t t e n t i o n s h o u l d be d i r e c t e d
t o p i p e s e c t i o n s c l o s e t o f i t t i n g s , hange rs and compensa t ion p i e c e s .
7 .7 .5 V e n t s
The h e a t i n g chambers o f equ ipment hea ted by v a p o u r s , such as e v a p o r a t o r s ,
j u i c e h e a t e r s and p r i m a r i l y vacuum p a n s , s h o u l d be c o n t i n u o u s l y v e n t e d .
Noncondensab le gases p r e s e n t i n c o n d e n s i n g v a p o u r s t e n d t o accumu la te i n t h e
l o w e r r e g i o n s o f h e a t i n g chambers . I t i s u s u a l l y a t t h e s e p o i n t s , and
p a r t i c u l a r l y where t h e v a p o u r p a t h s e n d , t h a t v e n t i n g n o z z l e s s h o u l d be
i n s t a l l e d ( r e f . 4 6 ) ; t he n o z z l e s s h o u l d be c o n n e c t e d t o p i p e s e q u i p p e d w i t h
v a l v e s t h a t make i t p o s s i b l e t o c o n t r o l t he f l o w .
I f v e n t i n g does n o t p r e v e n t t h e a c c u m u l a t i o n o f noncondensab le g a s e s , t hen
t h e i r i n c r e a s e d p a r t i a l p r e s s u r e causes t he p a r t i a l p r e s s u r e o f t he steam t o
d e c r e a s e , w h i c h i n t u r n d e c r e a s e s t he c o n d e n s a t i o n t e m p e r a t u r e . I n s u f f i c i e n t
v e n t i n g t h u s r e s u l t s i n a d e c r e a s e d e f f e c t i v e t e m p e r a t u r e d i f f e r e n c e and l e s s
i n t e n s i v e hea t t r a n s f e r w h i c h means:
- d e c r e a s e d j u i c e e v a p o r a t i o n i n t h e e v a p o r a t o r s ;
- d e c r e a s e d f i n a l j u i c e t e m p e r a t u r e i n t h e h e a t e r s ;
- l o n g e r b o i l i n g t ime i n t h e ba t ch vacuum p a n s .
V e n t i n g a l w a y s causes a c e r t a i n amount o f steam t o e s c a p e , t o g e t h e r w i t h t he
noncondensab le g a s e s . I t i s t h u s i m p o r t a n t t o r educe t h a t amount t o a minimum
a n d , i f p o s s i b l e , t o r e c o v e r h e a t f rom t h e e s c a p i n g m i x t u r e . Most o f t e n , v e n t i n g
p i p e s a re c o n n e c t e d a t s e l e c t e d p l a c e s i n t h e therma l s y s t e m , as e x p l a i n e d i n
S e c t i o n 3 . 2 . 2 .
When c o n t r o l l i n g t h e f l o w o f a g a s - v a p o u r m i x t u r e , i t i s recommended t h a t t h e
v a l v e s p i n d l e be t u r n e d n o t more t han 1/4 t o 1/3 r e v o l u t i o n a t a t i m e . I t s h o u l d
be o b s e r v e d t h a t t h i s k i n d o f f l o w c o n t r o l i s r e a l i z a b l e o n l y i n t h e case o f
v e n t s opened t o the a t m o s p h e r e , as e x c e s s i v e v e n t i n g i s i n d i c a t e d t h e r e by
v i s i b l e steam o u t f l o w .
The a c c u r a t e c o n t r o l o f v e n t i n g t h a t i s p a r t i c u l a r l y needed i n t he
e v a p o r a t o r s wou ld r e q u i r e i n s t a l l a t i o n o f p r e c i s i o n thermometers a t t he steam
n o z z l e b e f o r e the h e a t i n g chamber i n l e t and i n t he h e a t i n g chamber c l o s e t o
t he v e n t i n g n o z z l e . Open ing o f t h e c o n t r o l v a l v e s h o u l d r e s u l t i n a t e m p e r a t u r e
d i f f e r e n c e o f abou t 1 K. As i t i s p r a c t i c a l l y i m p o s s i b l e t o measure such a smal l
t e m p e r a t u r e d i f f e r e n c e w i t h adequate a c c u r a c y i t i s recommended t h a t , i n s t e a d o f
two t he rmome te r s , a s p e c i a l measur ing sys tem be used i n c l u d i n g f o u r r e s i s t a n c e
281
thermometers and an e l e c t r i c a l b r i d g e e q u i p p e d w i t h f o u r r e s i s t o r s ( r e f . 4 7 ) .
T h i s i s p a r t i c u l a r l y u s e f u l i n t he second and t h i r d e v a p o r a t o r e f f e c t s where t h e
c o n c e n t r a t i o n o f n o n c o n d e n s a b l e s i s h i g h e s t .
Check ing o f v e n t i n g sys tems s h o u l d p r i m a r i l y be c a r r i e d o u t a t t h e b e g i n n i n g
o f t he s e a s o n , a f t e r t e m p o r a r y s h u t - d o w n s and a f t e r equ ipment r e p a i r s . A l s o i n
cases o f i r r e g u l a r i t i e s , i n d i c a t e d by t o o low f i n a l j u i c e t e m p e r a t u r e s i n t h e
h e a t e r s o r t o o s l o w s u g a r b o i l i n g i n t h e vacuum p a n s , a v e n t i n g check s h o u l d be
a s t a n d a r d r o u t i n e .
7.8 PULP DRYER
7.8.1 Methods o f measurement
I t i s assumed t h r o u g h o u t t h i s S e c t i o n t h a t t h e d r y e r under c o n s i d e r a t i o n i s
a c l a s s i c a l d r u m - t y p e d r y e r hea ted by combus t i on g a s e s . Compared t o a the rma l
sys tem i n s u g a r m a n u f a c t u r e , a p u l p d r y e r e q u i p p e d w i t h i t s own f u r n a c e i s
e x t r e m e l y p r i m i t i v e , as t he hea t i s u t i l i z e d o n l y once ( t h e same a p p l i e s t o
d r y e r s u t i l i z i n g f l u e gases f rom b o i l e r s ) . Any h e a t l o s s i n p u l p d r y i n g i s t h u s
i r r e c o v e r a b l e , and t h a t i s why t he d r y i n g p r o c e s s s h o u l d be c a r e f u l l y m o n i t o r e d .
A d r u m - t y p e p u l p d r y e r i s shown s c h e m a t i c a l l y i n F i g . 7 .13 , t o g e t h e r w i t h
a l i s t o f q u a n t i t i e s t h a t appear i n t h e mass and h e a t b a l a n c e s .
pressed pulp
B . Q H
exhaust gas t 2 . C 0 2
F i g . 7 .13 . P o i n t s o f measurement i n p u l p d r y e r c h e c k . 1 - f u r n a c e , 2 - f e e d e r , 3 - a f t e r d r y e r . F o r t he e x p l a n a t i o n o f s y m b o l s , see t e x t .
The e s s e n t i a l p rob lem o f m o n i t o r i n g e n e r g y usage i n a p u l p d r y e r i s t o
de te rm ine t h e hea t consumpt ion w h i l e d r y i n g a d e f i n i t e amount o f p u l p . The h e a t
consumpt ion can c o n v e n t i o n a l l y be e x p r e s s e d by two i n d i c e s : t he d r y e r
e f f i c i e n c y , η, and the hea t consumpt ion f o r t he e v a p o r a t i o n o f 1 kg o f w a t e r , q .
The d r y e r e f f i c i e n c y can be d e f i n e d as
282
where i s t h e t h e o r e t i c a l h e a t demand f o r e v a p o r a t i n g w a t e r f rom t h e p u l p i n
k J , Β i s t h e f u e l consumpt ion i n kg , and i s t h e h e a t i n g v a l u e o f f u e l i n
k J / k g .
The hea t consumpt ion f o r e v a p o r a t i o n o f 1 kg w a t e r can be c a l c u l a t e d f rom t h e
f o r m u l a
q = BQ^/W ( k J / k g ) ( 7 . 5 0 )
where W i s t h e mass o f w a t e r e v a p o r a t e d i n t h e d r y e r i n kg .
I n o r d e r t o de te rm ine t h e above i n d i c e s , i t i s n e c e s s a r y t o measure t he
f o l l o w i n g q u a n t i t i e s :
- mass o f f u e l consumed, Β ( k g ) ;
- h e a t i n g v a l u e o f f u e l , ( k J / k g ) ;
- mass o f p r e s s e d p u l p , ( k g ) , o r mass o f d r i e d p u l p , G^ ( k g ) ;
- mass o f mo lasses added b e f o r e t h e d r y e r , G ^ ( k g ) ;
- d r y m a t t e r c o n t e n t i n p r e s s e d p u l p , s^ ( % ) , i n d r i e d p u l p , S2 ( % ) , and i n
m o l a s s e s , s ^ ( % ) ;
- p r e s s e d p u l p t e m p e r a t u r e b e f o r e t h e d r y e r , t^^ ( ° C ) ;
- gas t e m p e r a t u r e b e f o r e t h e d r y e r drum, t^ ( ° C ) , and a t t h e d r y e r o u t l e t ,
( °C ) .
I n o r d e r t o a t t a i n s a t i s f a c t o r y measur ing a c c u r a c y , c a r e i s r e q u i r e d i n t a k i n g
r e p r e s e n t a t i v e p u l p samples f o r t h e d e t e r m i n a t i o n o f d r y m a t t e r c o n t e n t .
Tempera tu re measurements b e f o r e t h e d r y e r o u t l e t a r e a l s o v e r y i m p o r t a n t . The
f l u e gas t e m p e r a t u r e b e f o r e t he drum must n o t be measured a t t h e f u r n a c e o u t l e t ,
bu t i n s t e a d where t he f l u e gas has a l r e a d y been mixed w i t h s e c o n d a r y a i r ( f e d
f o r t e m p e r a t u r e a d j u s t m e n t p u r p o s e s ) and a l s o w i t h a i r l e a k i n g i n t h r o u g h gaps
between t h e f u r n a c e and t he drum, as w e l l as a round t he p u l p i n t a k e . T e m p e r a t u r e
d e t e c t o r s s h o u l d t h u s be i n s t a l l e d a t t he drum beyond t he p u l p i n t a k e . As t o t h e
o u t l e t t e m p e r a t u r e measurements , s y s t e m a t i c e r r o r s due t o i r r e g u l a r i t i e s o f t he
t e m p e r a t u r e d i s t r i b u t i o n i n t h e drum o u t l e t must be a v o i d e d . The r i g h t p l a c e f o r
t e m p e r a t u r e measurement i s t h e o u t l e t n o z z l e o f t he e x h a u s t f a n .
A v e r y u s e f u l a d d i t i o n t o t he above measurements i s d e t e r m i n a t i o n o f t h e CO2
c o n t e n t i n t he gas a t t he d r y e r o u t l e t . Gas samples s h o u l d be taken f rom t h e
o u t l e t n o z z l e o f t h e e x h a u s t f a n .
I n t h e case o f a p e r i o d i c d r y e r c h e c k , i t i s recommended t h a t t h e sys tem o f
measur ing used makes i t p o s s i b l e t o d e t e r m i n e t h e hea t consumpt ion i n d i c e s and
a l s o t o i d e n t i f y t h e r e a s o n s f o r any i r r e g u l a r i t i e s d e t e c t e d . P a r t i c u l a r l y
u s e f u l a re t h e measurements o f CO2 c o n t e n t i n t h e gas b e f o r e t h e d r y e r drum and
a t t he d r y e r o u t l e t , as t he d i f f e r e n c e i n CO2 c o n t e n t shows w h e t h e r t h e drum i s
p r o p e r l y s e a l e d . I n a d d i t i o n , i f t he o u t l e t CO2 c o n t e n t and t e m p e r a t u r e a r e
known, t h e n app rox ima te v a l u e s o f hea t consumpt ion and gas h u m i d i t y can be f o u n d
i n t h e d iagrams g i v e n i n r e f . 8 o r o t h e r s o u r c e s .
283
R o u t i n e d r y e r m o n i t o r i n g s h o u l d be based on i n s t r u m e n t r e a d i n g s t aken e v e r y
h o u r . Then t he mean v a l u e s o f pa rame te rs ( c a l c u l a t e d o v e r t h e e n t i r e t e s t
p e r i o d ) r e f l e c t n o t o n l y t h e q u a l i t y o f t h e d r y e r - f u r n a c e s y s t e m , b u t a l s o t h e
i n f l u e n c e o f d i s t u r b a n c e s i n t h e o p e r a t i n g c o n d i t i o n s , such as c h a n g i n g m o i s t u r e
c o n t e n t o r mass f l o w o f t h e p r e s s e d p u l p .
I n p e r i o d i c c h e c k s , t he i n v e s t i g a t i o n s a r e aimed a t t he d e t e r m i n a t i o n o f
d r y e r e f f i c i e n c y . R e l i a b l e t e s t r e s u l t s can o n l y be o b t a i n e d i f t h e d r y e r l o a d
i s s t a b i l i z e d and no s i g n i f i c a n t d i s t u r b a n c e s o c c u r . O t h e r w i s e , t h e the rma l
c a p a c i t y o f t h e d r y e r may i n t r o d u c e a c o n s i d e r a b l e h e a t - b a l a n c e e r r o r . The t e s t
d u r a t i o n s h o u l d be 8-12 h o u r s , w i t h pa ramete r r e a d i n g s taken e v e r y 30 m inu tes
and p u l p samples c o l l e c t e d e v e r y h o u r .
7 .8 .2 Mass and hea t b a l a n c e s o f a p u l p - d r y i n g p l a n t
The mass b a l a n c e can be a n a l y s e d on t h e b a s i s o f t h e e q u a t i o n d e s c r i b i n g t h e
d r y m a t t e r s t ream
G^s^ = G2S2 ( 7 . 5 1 )
P r o v i d e d t h a t t h e p u l p samples a r e r e a l l y r e p r e s e n t a t i v e , v e r y a c c u r a t e v a l u e s
o f s^ and S2 can be o b t a i n e d f rom l a b o r a t o r y a n a l y s e s . T h u s , e q n . ( 7 . 5 1 ) makes
i t p o s s i b l e t o v e r i f y t h e i n d i c a t i o n s o f t h e p r e s s e d - p u l p s c a l e s . The mass o f
d r i e d p u l p l e a v i n g t h e d r y e r , G ^ , can be d e t e r m i n e d by d i r e c t i n g t h e d r i e d p u l p
i n t o a c o n t a i n e r . Once t h e b a t c h has been w e i g h e d , one can c a l c u l a t e G^ f rom
e q n . ( 7 . 5 1 ) .
The mass o f w a t e r e v a p o r a t e d i n t h e d r y e r can be c a l c u l a t e d as
W = G^(S2 - S ^ ) / S 2 + G^(S2 - s ^ ) / s 2 ( k g ) ( 7 . 5 2 )
The t h e o r e t i c a l hea t demand f o r w a t e r e v a p o r a t i o n can be c a l c u l a t e d as
= W(h^ - h^) ( k J ) ( 7 . 5 3 )
where h^ i s t he e n t h a l p y o f t h e v a p o u r s i n t h e gas a t t h e d r y e r o u t l e t i n k J / k g ,
and h^ i s t h e e n t h a l p y o f w a t e r i n t h e p r e s s e d p u l p i n k J / k g . The e n t h a l p y h^
can be d e t e r m i n e d f rom steam t a b l e s o r d i a g r a m s . A c t u a l l y , v a p o u r s i n t h e o u t l e t
gases a r e s u p e r h e a t e d ; t h e t e m p e r a t u r e i s t ^ and t h e p r e s s u r e s h o u l d be
u n d e r s t o o d as t h e p a r t i a l p r e s s u r e o f H^O i n g a s . H o w e v e r , a s a t i s f a c t o r y
a p p r o x i m a t i o n i s o b t a i n e d by assuming t h a t t h e p r e s s u r e i s 1 ba r ( t h e r e s u l t i n g
e r r o r does n o t e x c e e d 1%). The o t h e r e n t h a l p y v a l u e i s h^ = 4 .19 tp^ ( k J / k g ) .
7 .8 .3 Economica l p u l p d r y e r o p e r a t i o n
I n a r e a s o n a b l y w e l l o p e r a t e d p u l p d r y e r w i t h an i n d i v i d u a l f u r n a c e , a
t y p i c a l e f f i c i e n c y v a l u e i s 0 . 7 5 - 0 . 8 5 , w h i l e h e a t consumpt ion p e r 1 kg
e v a p o r a t e d w a t e r does n o t e x c e e d 3140-3560 k J / k g .
I n a d r y e r hea ted by b o i l e r f l u e g a s , t h e e f f i c i e n c y v a l u e c o n v e n t i o n a l l y
c a l c u l a t e d p e r t o t a l amount o f f u e l consumed i n t h e b o i l e r i s 0 . 1 0 - 0 . 1 5 , and
284
t he hea t consumpt ion ( c a l c u l a t e d i n t h e same way) amounts t o 21500-28000 k J / k g .
Keep ing the thermal i n d i c e s o f a d r y e r a t an a p p r o p r i a t e l e v e l r e q u i r e s good
u n d e r s t a n d i n g o f t he r e l a t i o n s h i p s t h a t a f f e c t i t s hea t b a l a n c e , s c h e m a t i c a l l y
shown i n a s i m p l i f i e d Sankey d iag ram i n F i g . 7 .14 .
( i ) The s m a l l e s t p o s s i b l e h e a t consumpt ion i s r e l a t e d t o t he t h e o r e t i c a l h e a t
demand, c a l c u l a t e d a c c o r d i n g t o e q n . ( 7 . 5 3 ) .
( i i ) Pu lp d r y i n g r e q u i r e s t h a t t he e n e r g y i n t r o d u c e d i n t o the d r y i n g gas must
exceed t he t h e o r e t i c a l demand by t h e combined e n e r g y l o s s i n t h e o u t l e t g a s ,
p l u s t he hea t l o s s f rom the d r y e r drum.
( i i i ) I n o r d e r t o g e n e r a t e t h e r i g h t amount o f gas a t t h e p r o p e r t e m p r e r a t u r e ,
i t i s n e c e s s a r y t o burn an amount o f f u e l t h a t c o r r e s p o n d s t o t he above amount
o f e n e r g y , p l u s combus t ion l o s s e s and hea t l o s s f rom the f u r n a c e t o t he
e n v i ronment .
ω l_ φ >
•σ ω
o QJ Χ
χ Cí ώ
Losses from furnace
Cf m
Heat theoretically needed
Exhaust and radiation
losses
F i g . 7 .14. Heat b a l a n c e o f t h e p u l p d r y i n g p l a n t .
I t f o l l o w s f rom ( i ) t h a t p r o c e s s t o l e r a n c e s s h o u l d be o b s e r v e d , and t h e f i n a l
d r y m a t t e r c o n t e n t i n d r i e d p u l p s h o u l d n o t exceed t h e r e q u i r e d v a l u e .
The need t o m i n i m i z e t he e x h a u s t l o s s i s a p p a r e n t i n ( i i ) ; t h e o u t l e t gas
t e m p e r a t u r e s h o u l d n o t exceed 90-115°C, and t h e gas f l o w s h o u l d be m i n i m a l . An
e q u i v a l e n t f o r m u l a t i o n o f t h e l a t t e r r e q u i r e m e n t i s t o keep t h e gas t e m p e r a t u r e
b e f o r e t he d r y e r drum r a t h e r h i g h , a t 800-900°C.
F i n a l l y , ( i i i ) i m p l i e s t h a t gas g e n e r a t i o n s h o u l d p r o c e e d w i t h e x c e s s a i r
be low 100-150%; o t h e r w i s e , t he gas t e m p e r a t u r e b e f o r e t h e d r y e r drum w o u l d be
t o o l o w . I n a c t u a l combus t ion c o n d i t i o n s , t h e amount o f e x c e s s a i r i s l o w e r .
The rema in ing a i r ( s e c o n d a r y a i r ) i s i n t r o d u c e d s e p a r a t e l y b e f o r e t he drum i n l e t
and u t i l i z e d f o r g a s - t e m p e r a t u r e a d j u s t m e n t . U n c o n t r o l l a b l e a i r l e a k s t h r o u g h
t h e gaps between t h e drum and t he f u r n a c e , and a t t he p u l p i n t a k e , a r e c l e a r l y
d i s a d v a n t a g e o u s , l e a d i n g sometimes t o an u n a c c e p t a b l y l a r g e t e m p e r a t u r e d r o p .
The l e a k s may a l s o cause t e m p e r a t u r e d i s t r i b u t i o n i r r e g u l a r i t i e s o v e r t he drum
285
c r o s s - s e c t i o n , hamper ing t h e p u l p - d r y i n g p r o c e s s .
I n keep ing t h e e n t i r e a i r f e e d under c o n t r o l , CO^ measurement i n t h e gas a t
t he d r y e r o u t l e t i s e s p e c i a l l y u s e f u l . P r o v i d i n g t h e chemica l c o m p o s i t i o n o f t h e
f u e l and t he r e q u i r e d e x c e s s a i r a r e known, i t i s p o s s i b l e t o d e t e r m i n e t h e
d e s i r a b l e v o l u m e t r i c c o m p o s i t i o n o f t he f l u e gas b e f o r e t h e d r y e r drum. T a k i n g
i n t o a c c o u n t t h e f u e l m o i s t u r e and t h e w a t e r e v a p o r a t e d f rom t h e p u l p , t h e
recommended c o n t e n t a t t h e d r y e r o u t l e t can a l s o be d e t e r m i n e d ( a n d ,
p r e f e r a b l y , e x p e r i m e n t a l l y v e r i f i e d ) . The d r y e r o p e r a t o r s h o u l d keep t h e a c t u a l
c o n t e n t c l o s e t o t he recommended v a l u e , a v o i d i n g l o w e r v a l u e s t h a t i n d i c a t e
t o o much e x c e s s a i r .
As a c o n c l u d i n g comment t o ( i i i ) , i t s h o u l d be s t a t e d t h a t t h e f u r n a c e must
be m a i n t a i n e d i n p r o p e r c o n d i t i o n i n o r d e r t o keep combus t i on l o s s e s and h e a t
d i s s i p a t i o n a t a minimum.
As a m a t t e r o f f a c t , p u l p - d r y i n g o p e r a t i o n c o n s i s t s o f ma tch ing t h e
r e q u i r e m e n t s on t h e e f f e c t o f t h e d r y i n g p r o c e s s and t h e e n e r g y c o n s u m p t i o n .
The pa ramete r v a l u e s g i v e n above make i t p o s s i b l e t o a c h i e v e a compromise i n
d r y e r c a p a c i t y , c l o s e t o i t s nominal l e v e l . C a p a c i t y changes r e q u i r e m o d i f y i n g
paramete r v a l u e s , wh i ch c a u s e s , as a r u l e , i n c r e a s e o f h e a t c o n s u m p t i o n . F o r
t h i s r e a s o n , t h e f i r s t p r i n c i p l e o f p u l p - d r y e r o p e r a t i o n i s t o keep t h e c a p a c i t y
c o n s t a n t ; i f p o s s i b l e , c l o s e t o i t s nominal v a l u e .
7 .8 .4 Example
An o i l - f i r e d , d r u m - t y p e p u l p d r y e r has been t e s t e d i n a 12-hour t e s t and t h e
f o l l o w i n g d a t a summarize t h e t e s t r e s u l t s :
- mass o f f u e l o i l consumed, Β = 14077 kg ;
- o i l h e a t i n g v a l u e , = 40400 k J / k g ;
- mass o f p r e s s e d p u l p , G-j = 223510 kg ;
- mass o f mo lasses added b e f o r e d r y e r , G ^ = 8975 kg ;
- d r y m a t t e r c o n t e n t i n p r e s s e d p u l p , s-j = 17%, i n d r i e d p u l p , S2 = 90.8%, and
i n m o l a s s e s , s = 76.3%;
- p r e s s e d p u l p t e m p e r a t u r e b e f o r e d r y e r , t^-j = 20 C ;
- gas t e m p e r a t u r e b e f o r e d r y e r drum, t-j = 803^0, and a t d r y e r o u t l e t , t2 = 102°C.
The mass o f w a t e r e v a p o r a t e d i n t h e d r y e r
W = 223510(90.7 - 1 7 ) / 9 0 . 7 + 8975(90.7 - 7 6 . 3 ) / 9 0 . 7 = 183042 kg
The v a p o u r e n t h a l p y a t t he d r y e r o u t l e t , f rom steam t a b l e s
h^ = 2682 k J / k g
The t h e o r e t i c a l hea t demand
= 183042(2682 - 4 .19 -20) = 4 .756-10^ kJ
The d r y e r e f f i c i e n c y
η = 4 .756-10^ / (14077-40400) = 0.836
286
The hea t consumpt ion f o r e v a p o r a t i o n o f 1 kg w a t e r
q = (14077·40400) /183042 = 3106 k J / k g
7.9 COMPUTER-AIDED MONITORING
I t can be c o n c l u d e d f rom p r e c e d i n g S e c t i o n s o f t h i s C h a p t e r t h a t once methods
o f i d e n t i f i c a t i o n o f t h e h e a t b a l a n c e s needed t o s u p e r v i s e t h e h e a t economy
i n a s u g a r f a c t o r y have been e s t a b l i s h e d , t h e m o n i t o r i n g p r o c e d u r e s can be
r o u t i n e l y a p p l i e d on a r e p e t i t i v e b a s i s . The p r a c t i c a l m o n i t o r i n g t h e n c o n s i s t s
m a i n l y o f da ta a c q u i s i t i o n , da ta p r o c e s s i n g and r e p o r t g e n e r a t i n g , and can be
automated w i t h t he a i d o f a d i g i t a l compu te r . T h i s a p p l i e s , i n t he f i r s t p l a c e ,
t o t he r o u t i n e m o n i t o r i n g t a s k s ( r o u t i n e c h e c k s ) w h i c h a r e pe r f o rmed most o f t e n ,
so t h a t t he i n i t i a l e f f o r t needed t o p r e p a r e c o m p u t e r i z e d t o o l s can be p a i d back
most q u i c k l y .
The impor tance o f c o m p u t e r - a i d e d m o n i t o r i n g t o t h e e n e r g y economy l i e s i n t h e
f a c t t h a t , by r e d u c i n g t h e amount o f r e p e t i t i v e and t e d i o u s work a s s o c i a t e d w i t h
the p r e p e r a t i o n o f t he hea t b a l a n c e s , i t c r e a t e s t he p o s s i b i l i t y o f
s y s t e m a t i c , d e t a i l e d e v a l u a t i o n o f t he e n e r g y p r o c e s s e s . T h i s a p p l i e s n o t o n l y
t o t h e i n d i v i d u a l s t a t i o n s d i s c u s s e d i n S e c t i o n s 7 . 2 - 7 . 8 , b u t a l s o t o t he e n t i r e
therma l s y s t e m . On t h i s b a s i s i t becomes p o s s i b l e t o c o n t r o l and o p t i m i z e , i n
r e s p e c t o f t he e n e r g y economy o f t h e e n t i r e f a c t o r y , t h e o p e r a t i n g c o n d i t i o n s a t
t h e most d e c i s i v e p r o c e s s s t a t i o n s .
A g e n e r a l scheme o f t h e d a t a f l o w on w h i c h c o m p u t e r - a i d e d m o n i t o r i n g o f t h e
f a c t o r y o p e r a t i o n i s based can be seen i n F i g . 7 .15 . The p r a c t i c a l a p p l i c a t i o n s
o f t he g e n e r a l i d e a a r e d i f f e r e n t i a t e d w i t h r e s p e c t t o d a t a a c q u i s i t i o n
t e c h n i q u e s , d a t a - b a s e s t r u c t u r e and v o l u m e , t he d a t a - b a s e u p d a t i n g and s e a r c h
t e c h n i q u e s u s e d , u s e r programs a v a i l a b l e and d a t a p r e s e n t a t i o n methods emp loyed .
By a d o p t i n g t h i s k i n d o f s t r u c t u r i n g o f da ta p r o c e s s i n g f u n c t i o n s , h o w e v e r , one
i s a b l e t o a p p l y w i d e l y c i r c u l a t e d , w e l l p r o v e n s o f t w a r e components f a c i l i t a t i n g
MEASURING INSTRUMENTS
DATA INPUT USER TERMINALS TERMINALS
Software system
Updating programs
1 Data acquisi t ion
1 programs
Data
base
User programs T T
Search
programs
PRINTER
PLOTTER
F i g . 7 .15 . Scheme o f da ta f l o w i n c o m p u t e r - a i d e d m o n i t o r i n g o f t h e f a c t o r y o p e r a t i o n .
287
smooth i m p l e m e n t a t i o n and h i g h r e l i a b i l i t y o f t h e m o n i t o r i n g s y s t e m .
M o n i t o r i n g o f t h e e n e r g y economy can be t r e a t e d as one o f t h e f u n c t i o n s o f
an e x t e n s i v e m o n i t o r i n g sys tem c o v e r i n g v a r i o u s a s p e c t s o f f a c t o r y o p e r a t i o n , o r
i t can be pe r f o rmed by a s p e c i a l i z e d s y s t e m . The d a t a management f o r m o n i t o r i n g
p u r p o s e s can be i n t e g r a t e d w i t h t h a t r e q u i r e d f o r c o m p u t e r - b a s e d a u t o m a t i c
c o n t r o l , o r can be t r e a t e d i n d e p e n d e n t l y o f t h e a u t o m a t i c c o n t r o l f u n c t i o n s .
Among t h e m o n i t o r i n g p rob lems w h i c h must be s o l v e d i n o r d e r t o r e c o g n i z e t h e
c o n d i t i o n o f t h e e n e r g y p r o c e s s e s , e v a p o r a t o r m o n i t o r i n g i s o f c r i t i c a l
i m p o r t a n c e . I t d e t e r m i n e s t he q u a l i t y o f i n f o r m a t i o n on t he most i m p o r t a n t
pa ramete rs o f t he e n e r g y p r o c e s s e s , and i s d e c i s i v e i n c r e a t i n g p o s s i b i l i t i e s
o f c o r r e c t l y d i a g n o s i n g t h e i n a d e q u a c i e s o f t h e e n e r g y economy.
The s i m p l e s t app roach t o e v a p o r a t o r m o n i t o r i n g i s t o use a p a r t o f t h e d a t a
on f a c t o r y o p e r a t i o n , s t o r e d o f f - l i n e i n t h e computer memory f o r s t a t i s t i c a l
p u r p o s e s , f o r d e t e r m i n a t i o n o f t he t r e n d s i n pa ramete r v a l u e s and f o r p e r i o d i c
mass and h e a t b a l a n c e c a l c u l a t i o n s . The e v a p o r a t i o n p r o c e s s can be i d e n t i f i e d i n
terms o f a v e r a g e v a l u e s o f t h e p a r a m e t e r s , t y p i c a l l y c a l c u l a t e d once p e r day o r
once pe r s h i f t . An example o f a p p l i c a t i o n o f t h i s app roach can be f o u n d i n
r e f . 45.
A more advanced e v a p o r a t o r m o n i t o r i n g p r o c e d u r e i s based on o n - l i n e r e c o r d i n g
o f t h e e s s e n t i a l p a r a m e t e r s , measured c o n t i n u o u s l y i n t he i n d i v i d u a l e f f e c t s ,
and o f f - l i n e s t o r i n g o f t he da ta on j u i c e c o n c e n t r a t i o n s p e r i o d i c a l l y d e t e r m i n e d
by l a b o r a t o r y a n a l y s e s . The c a l c u l a t i o n s o f mass and h e a t b a l a n c e s can o n l y be
pe r f o rmed u s i n g t i m e - a v e r a g e d v a l u e s o f t h e pa rame te r s c o r r e s p o n d i n g t o t h e
p e r i o d s between l a b o r a t o r y a n a l y s e s . H o w e v e r , t h e r e c o r d e d v a l u e s o f p r e s s u r e s ,
t e m p e r a t u r e s and f l o w s can be d i s p l a y e d o r p r i n t e d , t h u s making i t p o s s i b l e t o
p e r f o r m d e t a i l e d a n a l y s e s o f pa ramete r changes d u r i n g f a c t o r y o p e r a t i o n .
Examples o f a p p l i c a t i o n o f t h i s t y p e o f m o n i t o r i n g p r o c e d u r e s have been
ment ioned i n t h e l i t e r a t u r e ( r e f . 4 9 ) .
A m o n i t o r i n g p r o c e d u r e o f f e r i n g a lmos t c o n t i n u o u s a v a i l a b i l i t y o f comp le te
da ta on t he e v a p o r a t i o n p r o c e s s i s t o measure c o n t i n u o u s l y , and t o r e c o r d o n
l i n e , a l l t h e pa rame te rs needed t o c a l c u l a t e t h e mass and h e a t b a l a n c e s . T h i s
does n o t n e c e s s a r i l y mean t h a t a l l t h e j u i c e c o n c e n t r a t i o n v a l u e s c h a r a c t e r i z i n g
the s t a t e o f t h e e v a p o r a t o r have t o be a u t o m a t i c a l l y measu red . I t i s p o s s i b l e t o
i d e n t i f y c e r t a i n d e t a i l s o f t he mass and h e a t b a l a n c e s o f t h e e v a p o r a t o r u s i n g
i n d i r e c t measurements , as d e m o n s t r a t e d by an example r e p o r t e d i n r e f . 50. The
amount o f hea t t r a n s f e r r e d i n t h e e v a p o r a t o r b o d i e s can be d e t e r m i n e d u s i n g t h e
measurements o f condensa te f l o w , and t h e c o n d e n s e r l o s s f rom t h e l a s t e f f e c t can
be c a l c u l a t e d by measur ing t h e v a p o u r f l o w t o t h e c o n d e n s e r . I t i s i n t e r e s t i n g
t o no te t h a t t he s p e c i a l hea t -economy m o n i t o r i n g sys tem d e s c r i b e d i n r e f . 50
employs a d a t a a c q u i s i t i o n u n i t h a n d l i n g 64 i n p u t s i g n a l s , and t h e da ta
288
( i n c l u d i n g t he c a l c u l a t i o n s o f t h e mass and hea t b a l a n c e s ) a re p r o c e s s e d by two
h a n d - h e l d programmable c a l c u l a t o r s .
I t can be e x p e c t e d t h a t t h e deve lopmen t o f computer t e c h n o l o g y and t h e r i s i n g
impo r tance o f e n e r g y economy w i l l r e s u l t i n w i d e s p r e a d use o f c o m p u t e r - a i d e d
m o n i t o r i n g o f e n e r g y p r o c e s s e s . Numerous m o n i t o r i n g sys tems o f t h i s k i n d a r e
p r e s e n t l y be i ng implemented i n v a r i o u s c o u n t r i e s .
REFERENCES
Symbols o f N a t i o n a l S t a n d a r d s used b e l o w : ASTM - USA, BS - G r e a t B r i t a i n , NF -F r a n c e , DIN - FRG, COST - USSR, PN - P o l a n d .
1 K. S c h i e b l , W ä r m e w i r t s c h a f t i n d e r Z u c k e r i n d u s t r i e , Τ . S t e i n k o p f f V e r l a g , D r e s d e n / L e i p z i g , 1939.
2 Τ . B a l o h , Wärmeat las f ü r d i e Z u c k e r i n d u s t r i e , Schaper V e r l a g , H a n n o v e r , 1975.
3 S . Z a g r o d z k i and A . K u b a s i e w i c z , Heat economy i n b e e t s u g a r f a c t o r y e v a p o r a t i o n , Sugar T e c h . R e v . , 5 ( 1 / 2 ) (1977/78) 1-154.
4 S . Z a g r o d z k i , Gospodarka C i e p l n a C u k r o w n i , WNT, Warszawa, 1979. 5 P. H o n i g , P r i n c i p l e s o f Sugar T e c h n o l o g y , E l s e v i e r , Amsterdam, 1963. 6 F. S c h n e i d e r ( E d . ) , T e c h n o l o g i e des Z u c k e r s , Schaper V e r l a g , H a n n o v e r , 1968. 7 R .A . M c G i n n i s ( E d . ) , Bee t Sugar T e c h n o l o g y , Beet Sugar Dev . F o u n d . ,
F o r t C o l l i n s , 1971. 8 J . D o b r z y c k i ( E d . ) , P o r a d n i k I n z y n i e r a - C u k r o w n i c t w o , WNT, Warszawa, 1973. 9 D. Urban ( e t a l . ) , Z u c k e r h e r s t e l l u n g , F a c h b u c h v e r l a g , L e i p z i g , 1980.
10 F. B o s n j a k o v i c , T e c h n i s c h e Thermodynamik , T . S t e i n k o p f f V e r l a g , D r e s d e n , 1965.
11 T . D . Eas top and A . McConkey, A p p l i e d Thermodynamics f o r E n g i n e e r i n g T e c h n o l o g i s t s , 3 rd e d n . , Longmans, London and New Y o r k , 1978.
12 U . G r i g u l l ( E d . ) , P r o p e r t i e s o f Water and Steam i n S l - U n i t s , 2nd e d n . , S p r i n g e r - V e r l a g , B e r l i n - H e i d e l b e r g - N e w Y o r k , 1979.
13 M.P. V u k a l o v i c h , T e p l o f i z i c h e s k i e S v o i s t v a Vody i Vodyanogo P a r a , M a s h i n o s t r o e n i e , Moskva , 1967.
14 J . P . Holman, Heat T r a n s f e r , 5 th e d n . , M c G r a w - H i l l , H a m b u r g - L o n d o n - P a r i s , 1981.
15 J . C h u d z i n s k i ( e t a l . ) , P o r a d n i k T e r m o e n e r g e t y k a , 2nd e d n . , WNT, Warszawa, 1974.
16 J . D o b r z y c k i , A u t o m a t y z a c j a w P r z e m y s l e C u k r o w n i c z y m , WNT, Warszawa, 1974. 17 J . S tanek ( E d . ) , Handbuch d e r M e s s t e c h n i k i n d e r B e t r i e b s k o n t r o l l e ,
A k a d e m i e v e r l a g , L e i p z i g , 1979. 18 R .P . B e n e d i c t , Fundamenta ls o f T e m p e r a t u r e , P r e s s u r e , and F low Measurements ,
W i l e y , New Y o r k , 1969. 19 R. F r e i e r , K e s s e l s p e i s e w a s s e r , K ü h l w a s s e r - T e c h n o l o g i e , B e t r i e b s a n a l y s e ,
W a l t e r de G r u y t e r , B e r l i n , 1963. 20 F. C o g e t and M. W i n k e l , Le t r a i t e m e n t des eaux de c h a u f f e r i e s dans l e s
s u c r e r i e s , S u c r . B e i g e , 102 (1984) 5-11. 21 R e g u l a t i o n s o f t h e P o l i s h M i n i s t r y o f M i n i n g and E n e r g y ( i n P o l i s h ) ,
M o n i t o r P o l s k i , (51) ( 1 9 6 7 ) . 22 R . H . L . Howe, B o i l e r - w a t e r c o n t r o l f o r e f f i c i e n t steam p r o d u c t i o n , i n :
R. Greene ( E d . ) , P r o c e s s E n e r g y C o n s e r v a t i o n , M c G r a w - H i l l , New Y o r k , 1982, p p . 185-188.
23 Sampl ing o f i n d u s t r i a l w a t e r , ASTM D 510-68, BS 1328:1968; PN-74 /C-04620 . 24 Sampl ing o f w a t e r f rom b o i l e r s , ASTM 860-54, BS 1328:1968; PN-74 /C-04620 . 25 Equipment f o r samp l ing i n d u s t r i a l w a t e r and s team, ASTM 1192-70;
PN-74/C-04620. 26 Sampl ing o f s team, ASTM 1066-69; BS 3285; PN-74/C-04621. 27 Appearance o f w a t e r , ASTM D 1889-71; BS 2690: P a r t 9 ; NF Τ 90-002 /50 ;
PN-79 /C-04583.
289
28 P a r t i c u l a t e and d i s s o l v e d m a t t e r i n w a t e r , ASTM D 1888-67; NF Τ 90-029 /70 ; COST 18164-72; PN-78/C-04541.
29 E l e c t r i c a l c o n d u c t i v i t y o f w a t e r , ASTM D 1125-61; BS 2690: P a r t 9 ; NF Τ 90-031 /73 ; PN-77 /C-04542.
30 Water h a r d n e s s , ASTM D 1126-67; BS 1427:1962; NF Τ 90-003 /58 ; PN-71 /C-04554. 31 F. S c h n e i d e r ( E d . ) , Sugar A n a l y s i s - ICUMSA M e t h o d s , ICUMSA, P e t e r b o r o u g h ,
1979. 32 Coal and o t h e r s o l i d f u e l s , NF Μ 10-002; GOST 19292-73; PN-82/G-97001. 33 Fue l o i l s , ASTM D 396-73; BS 2869; NF Μ 15-010 and 011/68; DIN 51603-66;
GOST 10585-63; PN-75/C-96024. 34 Sampl ing o f c o a l , ASTM D 2234-72; BS 1017:1977; NF Μ 01-001; DIN 51701;
GOST 16479-70; PN-80/G-04502. 35 Sampl ing o f l i q u i d f u e l s , ASTM D 270; BS 3195:1959; NF Μ 07-001 /60 ;
DIN 51570; GOST 2517-60; PN-66 /C-04000 . 36 A . A . A v d e e v a , B . S . B e l o s e l s k i i and M.N. K r a s n o v , K o n t r o l T o p l i v a ν E l e k t r o -
s t a n t s i y a k h , E n e r g i y a , Moskva , 1973. 37 H. K a r o l c z u k , R a c j o n a l n a Gospodarka Weglem E n e r g e t y c z n y m , WNT, Warszawa,
1978. 38 Heat o f combus t i on by bomb c a l o r i m e t e r . S o l i d f u e l s , BS 1016: P a r t 5;
DIN 51900; GOST 147-74; PN-81/G-04513. L i q u i d f u e l s , ASTM D 240-64; NF Μ 07-030/65; GOST 6712-53; PN-71 /C-04062 .
39 Requ i remen ts and a c c e p t a n c e t e s t s , steam b o i l e r s , I S O / T C - 6 4 P u b l i c a t i o n s No. 40-50 ( 1 9 5 7 - 5 9 ) ; DIN 1942; PN-72/M-3128.
40 P. O r l o w s k i , K o t l y Parowe w E n e r g e t y c e P r z e m y s l o w e j , WNT, Warszawa, 1976. 41 T . A . S t o a , C a l c u l a t i n g b o i l e r e f f i c i e n c y and e c o n o m i c s , i n : R. Greene ( E d . ) ,
P r o c e s s E n e r g y C o n s e r v a t i o n , M c G r a w - H i l l , New Y o r k , 1982, p p . 245-250. 42 Requ i rements and a c c e p t a n c e t e s t s , steam t u r b i n e s , l E C No. 45 /1970;
PN-71/M-35520. 43 A . K u b a s i e w i c z and W. L e k a w s k i , P r z e b i e g wymiany c i e p l a w e k s t r a k t o r z e
ko ry towym, G a z . C u k r o w . , 83 (3 ) ( 1 9 7 5 ) . 44 K . E . A u s t m e y e r , A n a l y s i s o f s u g a r b o i l i n g and i t s t e c h n i c a l c o n s e q u e n c e s .
I n t . Sugar J . , 88 ( 1 9 8 6 ) , P a r t I (1045) 3 - 7 , P a r t I I (1046) 23-29 , P a r t I I I (1047) 50-55.
45 S . J . V a l l e r y , A re y o u r steam t r a p s w a s t i n g e n e r g y ? , i n : R. Greene ( E d . ) , P r o c e s s E n e r g y C o n s e r v a t i o n , M c G r a w - H i l l , New Y o r k , 1982, p p . 170-184.
46 D. V o i t and A . H u t s i n p i 1 l e r , A p r a c t i c a l app roach t o t h e v e n t i n g o f n o n c o n d e n s a b l e s . Paper p r e s e n t e d a t 23rd ASSBT M e e t i n g , San D i e g o , F e b r u a r y 1985.
47 S . Z a g r o d z k i and J . D o b r z y c k i , Removal o f i n c o n d e n s a b l e gases f rom c a l a n d r i a s . I n t . Sugar J . , 71 (1969) 235-237.
48 B . L . K a r r e n and M.K. F a v i e l l , A computer app roach t o t e c h n i c a l r e c o r d s i n t he b e e t s u g a r f a c t o r y l a b o r a t o r y , S u c r . B e i g e , 99 (2 ) (1980) 63-80.
49 D. P i o t r o w s k i and K. U r b a n i e c , Anwenderprogramme f ü r den P r o z e s s r e c h n e r e i n s a t z i n Z u c k e r f a b r i k e n , Z u c k e r i n d . , 106(2) (1981) 135-138.
50 C h . M o l l e r and H. J a n s d o r f , Heat economy and s u p e r v i s o r y computer c o n t r o l . I n t . Sugar J . , 87(1034) (1985) 26-31.
290
C h a p t e r 8
S T E P - B Y - S T E P IMPROVEMENTS OF E X I S T I N G ENERGY SYSTEMS
8.1 THE S T E P - B Y - S T E P APPROACH
8.1.1 I n t r o d u c t i o n
From t h e t e c h n i c a l s t a n d p o i n t , i t i s d i f f i c u l t t o make a c l e a r d i s t i n c t i o n
between s t e p - b y - s t e p improvements and an e x t e n s i v e m o d e r n i z a t i o n o f a s u g a r
f a c t o r y . Managers o f f a c t o r i e s o p e r a t e d under d i f f e r e n t c o n d i t i o n s wou ld
p r o b a b l y i n t e r p r e t t h e s e two terms d i f f e r e n t l y , depend ing on t he economic
r e s o u r c e s w h i c h a re a v a i l a b l e t o them. I t seems, h o w e v e r , t h a t t he most d i s t i n c t
d i f f e r e n c e s between s t e p - b y - s t e p improvements and a m o d e r n i z a t i o n can be f o u n d
i n the me thodo logy o f i m p l e m e n t a t i o n o f changes d e c i d e d upon .
W h i l e t h e m o d e r n i z a t i o n o f a f a c t o r y c o n s i s t s o f a package o f e x t e n s i v e
changes t o be i n t r o d u c e d a t o n c e , s t e p - b y - s t e p improvements may i n v o l v e numerous
s m a l l e r u n d e r t a k i n g s s p r e a d o v e r a l o n g e r t ime p e r i o d . On t h e b a s i s o f r e p e a t e d
r e v i e w s o f t he f a c t o r y ' s n e e d s , t h e o b j e c t i v e s a r e p e r i o d i c a l l y upda ted and
r a t i o n a l i z a t i o n measures a r e s e l e c t e d f rom a l i m i t e d f i e l d o f p o s s i b l e
s o l u t i o n s , t he l i m i t a t i o n s be ing d e f i n e d by t h e a v a i l a b l e economic r e s o u r c e s .
C o n s e q u e n t l y , improvements i n t h e ene rgy -economy a r e a can be d e c i d e d upon and
implemented o n l y i f t h e y r e a l l y a r e more u r g e n t than o t h e r a c t i o n s a l s o
c o n s i d e r e d d e s i r a b l e . H i g h p r i o r i t y i s u s u a l l y a s s i g n e d , h o w e v e r , t o measures
wh i ch improve s u g a r y i e l d o r p r o d u c t q u a l i t y , o p e r a t i o n a l s a f e t y and equ ipment
r e l i a b i l i t y , w h i l e a l s o b e n e f i t i n g e n e r g y economy.
W i t h i n t he g e n e r a l f rame t h u s o u t l i n e d , v a r i o u s c o u r s e s o f a c t i o n may be
adop ted i n a s p e c i f i c f a c t o r y i n a c c o r d a n c e w i t h t h e l o c a l c o n d i t i o n s . P o s s i b l e
r a t i o n a l i z a t i o n measures i n t he a r e a o f e n e r g y economy i n s u g a r manu fac tu re can
be s y s t e m a t i z e d by d i s t i n g u i s h i n g between t h r e e ways t o reduce t h e e n e r g y demand,
( i ) B r i n g i n g t h e e n e r g y - s y s t e m o p e r a t i o n i n t o p a r i t y w i t h i t s nominal
c a p a b i l i t i e s , by e l i m i n a t i n g u n n e c e s s a r y d e v i a t i o n s f rom t h e r e q u i r e d c o u r s e o f
e n e r g y p r o c e s s e s and i m p r o v i n g m a l f u n c t i o n i n g subsys tems and components o f t h e
e n e r g y s y s t e m . T y p i c a l measures a r e as f o l l o w s :
- e l i m i n a t i n g steam and v a p o u r l e a k s i n t he condensa te l i n e s ;
- e l i m i n a t i n g the causes o f abnormal pa ramete r f l u c t u a t i o n s ;
- i m p r o v i n g condensa te d r a i n a g e f rom s team- and v a p o u r - h e a t e d e q u i p m e n t ;
- i m p r o v i n g t he w i t h d r a w a l o f n o n c o n d e n s a b l e s f rom t h e h e a t i n g chambers o f
e v a p o r a t o r s and h e a t e r s ;
- p r e v e n t i n g t h e f o r m a t i o n o f s c a l e ;
- s e c u r i n g p r o p e r q u a l i t y o f t h e condensa te r e t u r n e d f rom t h e e v a p o r a t o r t o t h e
b o i l e r s ;
291
- s e c u r i n g p r o p e r f u n c t i o n i n g o f t h e measu r ing i n s t r u m e n t s w h i c h a r e e s s e n t i a l
i n m o n i t o r i n g e n e r g y c o n v e r s i o n , d i s t r i b u t i o n and u t i l i z a t i o n p r o c e s s e s .
( i i ) Reduc ing t h e t o t a l e n e r g y demand o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s . Among
o t h e r s , t h e f o l l o w i n g measures can be u n d e r t a k e n :
- r e d u c i n g t h e hea t d i s s i p a t i o n f rom t h e p r o c e s s equ ipment and p i p i n g t o t h e
e n v i r o n m e n t ;
- r e d u c i n g t h e e n e r g y consumpt ion f o r a u x i l i a r y p u r p o s e s i n t h e p r o c e s s p l a n t ;
- r e d u c i n g t h e w a t e r i n t a k e t o t h e p r o c e s s ;
- r e d u c i n g t h e t o t a l w a t e r i n t a k e t o t h e s u g a r h o u s e ;
- r e p l a c i n g o u t d a t e d p r o c e s s - e q u i p m e n t u n i t s by new ones f a c i l i t a t i n g a b e t t e r
e n e r g y economy;
- i m p r o v i n g t h e a u t o m a t i c c o n t r o l s f o r b e t t e r e n e r g y u t i l i z a t i o n i n t h e p r o c e s s .
( i i i ) I m p r o v i n g t h e c a p a b i l i t i e s o f t he e n e r g y s y s t e m , i n c l u d i n g t h e
e f f e c t i v e n e s s r a t i o o f t h e therma l s y s t e m . T y p i c a l measures a r e as f o l l o w s :
- r e d u c i n g t h e e n e r g y l o s s e s and t h e e n e r g y consumpt ion f o r a u x i l i a r y p u r p o s e s
i n t he power h o u s e ;
- i m p r o v i n g t h e power f a c t o r o f t h e e l e c t r i c a l s u b s y s t e m ;
- r e d u c i n g t h e hea t d i s s i p a t i o n f rom t h e components o f t h e e n e r g y sys tem t o t h e
e n v i r o n m e n t ;
- i m p r o v i n g t h e u t i l i z a t i o n o f c o n d e n s a t e s ;
- i m p r o v i n g t h e u t i l i z a t i o n o f l o w - p r e s s u r e v a p o u r s ;
- o p t i m i z i n g t h e u t i l i z a t i o n o f v a p o u r s f rom t h e e v a p o r a t o r ;
- r e p l a c i n g o u t d a t e d e n e r g y - s y s t e m equ ipment by more modern and e f f i c i e n t
m a c h i n e r y ;
- i m p r o v i n g a u t o m a t i c c o n t r o l s t o a c h i e v e b e t t e r e f f i c i e n c y o f e n e r g y c o n v e r s i o n
and d i s t r i b u t i o n p r o c e s s e s .
8 .1 .2 Rev iew o f examples
T h e r e i s a v a s t l i t e r a t u r e d e v o t e d t o s t e p - b y - s t e p improvements i n t h e e n e r g y
economy o f s u g a r f a c t o r i e s , a l t h o u g h i t i s f e l t t h a t p rob lems o f r a t i o n a l i z a t i o n
o f power b a l a n c e s a r e n o t a d e q u a t e l y c o v e r e d . Some p u b l i c a t i o n s s i m p l y p r e s e n t
p a r t i c u l a r measures unde r t aken i n s p e c i f i c f a c t o r i e s ( r e f s . 1 , 2 ) . V e r y v a l u a b l e
i n f o r m a t i o n can be f ound i n t h e a r t i c l e s a t t e m p t i n g t o draw g e n e r a l i z e d
c o n c l u s i o n s f rom t h e e x p e r i e n c e s o f c o n s u l t a n t s , e n g i n e e r i n g companies o r s u g a r
i n d u s t r y managers i n v o l v e d i n e n e r g y - r a t i o n a l i z a t i o n programmes implemented i n
a number o f s u g a r f a c t o r i e s ( r e f s . 3 - 1 2 ) .
The most i n t e r e s t i n g g roup o f p u b l i c a t i o n s i s t h a t d e v o t e d t o t h e e x p e r i e n c e s
accumu la ted i n s p e c i f i c f a c t o r i e s d u r i n g l o n g e r p e r i o d s o f s t e p - b y - s t e p
improvements ( r e f s . 1 3 - 1 6 ) . As p r e s e n t a t i o n s o f t h i s k i n d a r e r a t h e r s c a r c e , l e t
us a d d i t i o n a l l y c o n s i d e r two examples o f s t e p - b y - s t e p improvement programmes
292
wh i ch have been e f f e c t e d d u r i n g a p e r i o d o f 15 y e a r s i n Swed ish s u g a r f a c t o r i e s .
The da ta p r e s e n t e d be low have been e x t r a c t e d by t h e p r e s e n t a u t h o r f rom t h e
p u b l i s h e d o p e r a t i o n s r e p o r t s .
The p r o c e s s i n g c a p a b i l i t i e s o f t he f a c t o r i e s c o n s i d e r e d a r e 2100 and 5800
t o n s p e r d a y . As bo th f a c t o r i e s be long t o t he same company, i t can be assumed
t h a t t h e y have been s u b j e c t t o t he p r e s s u r e o f i d e n t i c a l economic s t i m u l a t o r s
and t h a t t h e same l e v e l o f t e c h n o l o g i c a l e x p e r t i s e has been a v a i l a b l e t o them.
T h e i r s t a r t i n g p o s i t i o n s i n 1970 can be summarized as f o l l o w s :
- bo th f a c t o r i e s were equ ipped w i t h t o w e r - t y p e e x t r a c t o r s , c l a s s i c a l j u i c e
p u r i f i c a t i o n s t a t i o n s , q u i n t u p l e - e f f e c t e v a p o r a t o r s and t h r e e - b o i l i n g
c r y s t a l l i z a t i o n schemes w i t h t h e a f f i n a t i o n o f C s u g a r ;
- bo th f a c t o r i e s were e q u i p p e d w i t h o i l - f i r e d b o i l e r s o p e r a t e d a t l i v e - s t e a m
pa rame te rs 40 ba r and 430°C;
- i n bo th c a s e s , abou t 10% o f t he power demand was c o v e r e d by power p u r c h a s e s
f rom the e x t e r n a l g r i d ;
- as t h e f l u e gases f rom b o i l e r s i n t h e l a r g e r o f t he two f a c t o r i e s were
u t i l i z e d i n t he p u l p - d r y e r f u r n a c e , no e c o n o m i z e r s were i n s t a l l e d t h e r e , t h i s
r e s u l t i n g i n a b o i l e r e f f i c i e n c y 8% l o w e r t h a n t h a t i n t h e s m a l l e r f a c t o r y ;
- f o l l o w i n g i n v e s t m e n t s made d u r i n g 1950s and 1960s, t h e l a r g e r f a c t o r y was
g e n e r a l l y e q u i p p e d w i t h more modern m a c h i n e r y and a u t o m a t i c c o n t r o l c i r c u i t s .
T a b l e s 8.1 and 8.2 l i s t t he r a t i o n a l i z a t i o n measures t h a t were implemented i n
t he e n e r g y economy and o t h e r r e l a t e d a r e a s i n bo th f a c t o r i e s d u r i n g t h e p e r i o d
1970-1985. The r e s u l t s were c a r e f u l l y c o n t r o l l e d a s , s t a r t i n g f rom the f i r s t o i l
c r i s i s i n 1974, t he f a c t o r i e s adop ted e n e r g y - m o n i t o r i n g p r o c e d u r e s based on
f r e q u e n t 24 -hou r e n e r g y - c o n s u m p t i o n t e s t s . I n a d d i t i o n , d e t a i l e d i n v e s t i g a t i o n s
o f t he e n e r g y economy emp loy ing one-week t e s t p e r i o d s were pe r f o rmed e v e r y
second o r t h i r d y e a r .
I n bo th f a c t o r i e s , t he m o d i f i c a t i o n s o f j u i c e h e a t i n g and t h e improvements
i n t r o d u c e d i n t he s u g a r houses seem t o have p l a y e d a d e c i s i v e r o l e i n r e d u c i n g
t he e n e r g y c o n s u m p t i o n . The t o t a l w a t e r i n t a k e and t he m a s s e c u i t e c i r c u l a t i o n
were r e d u c e d i n t he s u g a r h o u s e s , and t he pa ramete r f l u c t u a t i o n s o r i g i n a t i n g
f rom b a t c h w i s e o p e r a t i o n o f t he s u g a r house equ ipment were s u b s t a n t i a l l y
1 i m i t e d .
I n t he l a r g e r f a c t o r y , most o f t he i n v e s t m e n t s p r o p o s e d t o implement t h e
ene rgy -economy improvements were pe r f o rmed d u r i n g t h e a c t u a l p e r i o d . On t h e
c o n t r a r y , t he managers o f t he s m a l l e r f a c t o r y were n e i t h e r a b l e t o m o d e r n i z e t h e
t owe r e x t r a c t o r f o r l o w e r j u i c e d r a f t , n o r a b l e t o m o d i f y t h e j u i c e p u r i f i c a t i o n
s t a t i o n f o r l o w e r CaO r a t e ( t h r o u g h o u t t he p e r i o d o f i n t e r e s t i n c l u d i n g t h e 1985
s e a s o n , t h e CaO r a t e was 20-25% h i g h e r than i n t he l a r g e r f a c t o r y ) .
N e v e r t h e l e s s , t h e r e s u l t s o f t h e 1 5 - y e a r deve lopmen ts a r e q u i t e i m p r e s s i v e i n
293
TAB
LE
8.Ί
En
erg
y-s
avin
g
an
d
oth
er
rela
ted
m
ea
sure
s in
tro
du
ce
d
19
70
-19
85
, a
nd sta
tisti
ca
l d
ata
o
n
no
rma
l-fu
el
(he
ati
ng
va
lue
2
93
00
kJ/k
g)
co
nsu
mp
tio
n
in
sug
ar
ma
nu
factu
re
in
a
58
00
t/d
facto
ry.
\/,^
^w,
c^r
^^
'-c
A^
^^
-A^
^
No
rma
l fu
el
cons
umed
Y
ea
r S
pe
cif
ica
tio
n
^^^^^^^
19
66
-19
69
3.7
0-4
.17
1970
A
uto
ma
tic
bo
ilin
g
co
ntr
ols
in
sta
lle
d
on
va
cuu
m
pa
ns
C.
3.9
3
1971
T
wo
n
ew
li
me
d-j
uic
e
he
ate
rs
wit
h
incre
ase
d
he
ati
ng
su
rfa
ce
a
rea
s in
sta
lle
d.
He
ati
ng
3
.79
su
rfa
ce
a
rea
in
fo
urt
h
eva
po
rato
r e
ffe
ct
inc
rea
se
d.
Te
mp
era
ture
co
ntr
oll
ers
in
sta
lle
d
on
h
ea
ters
b
efo
re fi
rst
an
d
seco
nd
ca
rbo
na
tati
on
. 19
72
Le
ve
l c
on
tro
lle
rs
ins
tall
ed
o
n
wa
ter
se
als
(a
cti
ng
a
s st
ea
m
tra
ps
) in
co
nd
en
sate
3
.58
d
rain
ag
e
lin
es
fr
om
2
nd
, 3
rd
an
d
4th
e
va
po
rato
r e
ffe
cts
. 19
74
Th
erm
al
insu
lati
on
o
f fu
el
tan
ks
imp
rove
d.
Ne
w
bo
ile
r fo
r o
ff-s
ea
so
n
he
ati
ng
a
nd
ro
om
3.5
6
tem
pe
ratu
re
co
ntr
oll
ers
in
sta
lle
d.
On
e
ne
w
vacu
um
pan
A
e
qu
ipp
ed w
ith
a sti
rre
r a
nd
an
a
ir-t
igh
t,
low
-pre
ss
ure
ste
am
ing
syste
m i
nsta
lle
d.
1975
T
hre
e
co
nti
nu
ou
s a
ffin
ati
on
c
en
trif
ug
als
in
sta
lle
d.
On
e
co
nti
nu
ou
s ce
ntr
ifu
ga
l 3
.23
in
sta
lle
d
in
Β
str
ike
fo
r a
cce
pta
nce te
sts
. 19
76
Fo
ur
co
nti
nu
ou
s c
en
trif
ug
als
in
sta
lle
d
in
Β
str
ike
. O
ne
co
nti
nu
ou
s ce
ntr
ifu
ga
l 3
.42
in
sta
lle
d
in
C
str
ike
fo
r a
cce
pta
nce te
sts
. 19
77
Ne
w
ste
am
ing
-ou
t sy
ste
m
usin
g
se
co
nd
-eff
ect
va
po
ur
ins
tall
ed
in
a
ll va
cuum
p
an
s A
. 3
.21
19
78
Op
tim
iza
tio
n
of
C-m
asse
cu
ite
sta
tio
n
co
mp
lete
d.
3.3
6
1979
E
con
om
ize
r in
sta
lle
d
in
on
e
bo
ile
r.
Ve
nti
ng
o
f n
on
con
de
nsa
ble
s im
pro
ve
d.
Wa
ter
inta
ke
3
.38
to
ca
rbo
na
tati
on
slu
dg
e
sw
ee
ten
ing
-off
re
du
ce
d.
1980
F
low
m
ete
r in
sta
lle
d
on
w
ate
r su
pp
ly
to
the
su
ga
r h
ou
se.
3.2
8
1982
S
tirr
er
ins
tall
ed
in
o
ne
va
cuu
m
pa
n
A.
3.2
0
1983
T
ow
er
extr
acto
r m
od
ern
ize
d
for
low
er
juic
e
dra
ft.
Au
tom
ati
c b
oil
ing
c
on
tro
ls
on
va
cuu
m
3.1
8
pa
ns
A
mo
de
rniz
ed
. C
on
de
nsa
te-h
ea
ted
pla
te
he
at
exc
ha
ng
er
ins
tall
ed
a
s th
ick
-ju
ice
he
ate
r in
ste
ad
o
f a
tub
ula
r h
ea
t e
xch
an
ge
r h
ea
ted
by
thir
d-e
ffe
ct
va
po
ur.
19
84
Syr
up
w
ash
teste
d
in
on
e
ce
ntr
ifu
ga
l in
A str
ike
. 3
.15
19
85
Imp
rove
d
oil
bu
rne
rs
ins
tall
ed
in
o
ne
bo
ile
r.
Mic
roc
om
pu
ter-
ba
se
d
bo
ile
r co
ntr
ol
3.1
3
syst
em
im
ple
me
nte
d.
294
TAB
LE
8.2
En
erg
y-s
avin
g
an
d
oth
er
rela
ted
m
ea
sure
s in
tro
du
ce
d
19
70
-19
85
, a
nd sta
tisti
ca
l d
ata
on
no
rma
l-fu
el
(he
ati
ng
v
alu
e
29
30
0 kJ/k
g)
co
nsu
mp
tio
n
in
sug
ar
ma
nu
factu
re
in
a
21
00
t/d
fac
tory
.
^ e
.jr-
4.·
N
orm
al
fue
l co
nsum
ed
Ye
ar
Sp
ec
ific
ati
on
^
^^
/^^
^
19
67
-19
70
3.8
8-4
.02
1971
N
ew
m
ea
su
rin
g
instr
um
en
ts
insta
lle
d
on
the
eva
po
rato
r sta
tio
n.
Eq
uip
me
nt
op
era
tors
4
.09
instr
ucte
d
on
the
pri
nc
iple
s
of
smo
oth
o
pe
rati
on
o
f A
-ma
sse
cu
ite sta
tio
n.
1972
E
ne
rgy
econ
omy
an
aly
se
d
an
d
eq
uip
me
nt
mo
de
rniz
ati
on
p
rog
ram
me
pro
po
se
d.
3.9
8
1973
T
he
rma
l in
su
lati
on
re
pla
ce
d
on
thre
e
eva
po
rato
r b
od
ies
an
d
on
e
co
nd
en
sa
te
tan
k.
4.1
7
1974
S
tirr
er
insta
lle
d
in
on
e
vacu
um
pan
A.
New
b
oile
r fo
r o
ff-s
ea
so
n
he
ati
ng
insta
lle
d.
3.9
6
1975
N
ew
m
ea
su
rin
g
instr
um
en
ts
insta
lle
d
on
the
extr
acto
r a
s w
ell
as
on
va
cuum
p
an
s Β
a
nd
C.
3.4
9
1977
P
erf
orm
an
ce
of
C-m
asse
cu
ite
sta
tio
n
an
aly
se
d
an
d
mo
de
rniz
ati
on
p
rop
ose
d.
3.6
6
1978
C
on
tin
uo
us
ce
ntr
ifu
ga
ls
insta
lle
d
for
incre
ase
d
thro
ug
hp
ut
of
C-m
asse
cu
ite
sta
tio
n.
3.7
7
1979
A
uto
ma
tic
tem
pe
ratu
re
co
ntr
ol
cir
cu
it
insta
lle
d
on
exh
au
st
ste
am
su
pp
ly
to
the
3.6
5
eva
po
rato
r sta
tio
n.
Le
ve
l co
ntr
olle
rs
insta
lle
d
on
wa
ter
se
als
(a
cti
ng
a
s st
ea
m t
rap
s)
in
co
nd
en
sa
te
dra
ina
ge
lin
es
b
etw
ee
n
eva
po
rato
r e
ffe
cts
3
an
d
4
as
we
ll
as
4
an
d
5.
1980
S
yru
p
was
h im
ple
me
nte
d
in
ce
ntr
ifu
ga
ls
A
an
d
B.
En
erg
y ec
onom
y a
na
lyse
d.
3.7
3
1981
C
he
mic
al
sc
ale
p
reve
nti
on
im
ple
me
nte
d.
3.4
5
1982
S
tea
m-t
urb
ine
dri
ve
n
kiln
-ga
s
pum
ps
rep
lace
d
by
ne
w e
lec
tric
all
y-d
riv
en
o
ne
s.
Ne
w
3.4
0
he
ate
r fo
r th
in ju
ice
insta
lle
d.
Va
po
ur
dis
trib
uti
on
sc
hem
e a
dju
ste
d
for
be
tte
r u
tiliza
tio
n
of
low
-te
mp
era
ture
va
po
urs
. E
ne
rgy
econ
omy
an
aly
se
d.
1983
A
uto
ma
tic
leve
l-co
ntr
ol
cir
cu
its
in
th
e
eva
po
rato
r sta
tio
n
mo
de
rniz
ed
. S
pir
al
he
at
3.4
6
exc
ha
ng
ers
h
ea
ted
by
co
nd
en
sa
te
an
d
fou
rth
-eff
ect
vap
ou
r im
ple
me
nte
d
as
raw
-ju
ice
he
ate
rs.
Inte
gra
ted
a
uto
ma
tic
co
ntr
ol
of
the
be
et
ho
use
im
ple
me
nte
d.
1984
S
tirr
ers
in
sta
lle
d
in
all
vacu
um
pa
ns
A.
Co
nti
nu
ou
s ce
ntr
ifu
ga
ls
insta
lle
d
in
Β str
ike
. 3
.14
Pro
gra
mm
ab
le
co
ntr
ol
of
A
ce
ntr
ifu
ga
ls
imp
lem
en
ted
. C
he
mic
al
sc
ale
p
reve
nti
on
im
pro
ve
d.
1985
3
.23
295
bo th c a s e s . The f u e l consumpt ion e x p r e s s e d i n kg normal f u e l p e r 100 kg b e e t has
been reduced by abou t 20% i n t he l a r g e r f a c t o r y and by abou t 30% i n t he s m a l l e r .
I n o r d e r t o i n i t i a t e ene rgy -economy improvements u s i n g t h e s t e p - b y - s t e p
a p p r o a c h , s u f f i c i e n t i n f o r m a t i o n must be a v a i l a b l e on t h e e x i s t i n g s t a t e o f
t h i n g s and p o s s i b l e c o u r s e s o f a c t i o n . I n t h e f o l l o w i n g , two examples a re
p r e s e n t e d o f t h e r e s u l t s o f s t u d i e s i n t e n d e d t o c r e a t e c o n v e n i e n t s t a r t i n g
p o i n t s f o r s t e p - b y - s t e p improvements .
The f i r s t example ( S e c t i o n 8 .2 ) i s r e p r e s e n t a t i v e o f r a t h e r s m a l l , n o t - s o -
modern f a c t o r i e s c h a r a c t e r i z e d by r a t h e r p o o r e n e r g y u t i l i z a t i o n and v e r y
l i m i t e d i n i t i a l knowledge o f measures t h a t can be taken t o improve i t . The
i n i t i a l f u e l consumpt ion i n s u g a r manu fac tu re i s abou t 6.7 kg normal f u e l p e r
100 kg b e e t . P o s s i b l e improvements a r e s t u d i e d on t he b a s i s o f mass and hea t
b a l a n c e s w h i c h a r e c a l c u l a t e d u s i n g i n p u t d a t a e x t r a c t e d f rom r o u t i n e f a c t o r y
r e c o r d s . The h e a t s a v i n g w h i c h can be o b t a i n e d by t a k i n g t h e most u r g e n t
r a t i o n a l i z a t i o n measures (a imed m a i n l y a t r e d u c i n g t h e e n e r g y w a s t e ) i s
e s t i m a t e d a t abou t 20% o f t he i n i t i a l hea t c o n s u m p t i o n . I n o r d e r t o p r e p a r e
d e c i s i o n s on f u r t h e r improvemen ts , a d e t a i l e d d e s i g n s t u d y i s recommended.
The second example ( S e c t i o n 8 .3 ) i s c o n c e r n e d w i t h a m e d i u m - c a p a c i t y s u g a r
f a c t o r y c h a r a c t e r i z e d by a q u i t e e f f e c t i v e e n e r g y economy. The i n i t i a l f u e l
consumpt ion i n s u g a r manu fac tu re i s 3.5 kg normal f u e l pe r 100 kg b e e t . An
a n a l y s i s o f ways t o improve t he hea t economy i s pe r f o rmed u s i n g t h e r e s u l t s o f
measurements o f t he pa rame te rs o f e n e r g y c o n v e r s i o n and u t i l i z a t i o n p r o c e s s e s .
I n t h i s manner , a r e l i a b l e b a s i s i s c r e a t e d f o r e v a l u a t i o n o f t he consequences
o f smal l improvements o f t h e v a p o u r d i s t r i b u t i o n . The e s t i m a t e d hea t s a v i n g i s
o f t he o r d e r o f 2% o f t he i n i t i a l hea t c o n s u m p t i o n .
The e x p e r i e n c e p r o v e s t h a t even h i g h l y e f f i c i e n t modern e n e r g y sys tems can be
improved u s i n g t he s t e p - b y - s t e p a p p r o a c h . To i l l u s t r a t e t h i s p o i n t . S e c t i o n 8.4
p r e s e n t s a summary o f e n e r g y - s a v i n g measures t aken d u r i n g a 1 0 - y e a r p e r i o d i n
a l a r g e r a w - s u g a r f a c t o r y . A t p r e s e n t , t h e f a c t o r y i s consuming l e s s t han 2 kg
normal f u e l p e r 100 kg b e e t . T h i s example i n d i c a t e s a l s o t h e impo r tance o f
c o o r d i n a t i n g t he hea t and power b a l a n c e s a t a v e r y low hea t demand. I n a d d i t i o n ,
t he d i f f i c u l t y i s demons t ra ted o f d i s t i n g u i s h i n g between s t e p - b y - s t e p
improvements and a m o d e r n i z a t i o n . A l t h o u g h t h e g e n e r a l app roach t o t h e
improvements can be c o n s i d e r e d as e v o l u t i o n a r y , some o f t h e s t e p s t aken i n v o l v e
e x t e n s i v e t e c h n o l o g i c a l changes and r a t h e r c o s t l y i n v e s t m e n t s .
8.2 FACTORY CHARACTERIZED BY POOR I N I T I A L ENERGY U T I L I Z A T I O N
8.2.1 I n t r o d u c t o r y remarks
The example p r e s e n t e d i n t h i s S e c t i o n i s based on a r e a l case i n v e s t i g a t e d by
t he p r e s e n t a u t h o r a few y e a r s a g o . The c o n s u l t a n t was i n v i t e d t o t h e f a c t o r y i n
296
q u e s t i o n by a manager whose i n t e r e s t i n e n e r g y economy was o b v i o u s l y s t i m u l a t e d
by t h e r a p i d l y r i s i n g o i l p r i c e s a t t h a t t i m e . A n o t h e r c o n t r i b u t i n g f a c t o r was
t h e p l a g u e o f f r e q u e n t b o i l e r f a i l u r e s t h a t s e r i o u s l y a f f e c t e d t h e o p e r a t i o n a l
r e s u l t s . T h e r e was an e x p e c t a t i o n t h a t some q u i c k a c t i o n s c o u l d be u n d e r t a k e n
d u r i n g t h e s u b s e q u e n t o f f - s e a s o n p e r i o d , w i t h t he aim o f a c h i e v i n g s u b s t a n t i a l
e n e r g y s a v i n g s a l r e a d y i n t he n e x t s e a s o n . The manager was r e a d y t o c o n t i n u e
t he r a t i o n a l i z a t i o n o f t he e n e r g y economy i n coming y e a r s , b u t he made i t c l e a r
t h a t i n t h e f o r e s e e a b l e f u t u r e , no i n v e s t m e n t f u n d s w o u l d be a v a i l a b l e f o r an
e x t e n s i v e m o d e r n i z a t i o n o f t h e f a c t o r y .
The i n v i t a t i o n came as t he season app roached i t s e n d . No a c t u a l d a t a were
a v a i l a b l e on t h e d e t a i l s o f t he f a c t o r y ' s e n e r g y b a l a n c e . As t h e r e was no t ime
l e f t f o r p r e p a r i n g a d d i t i o n a l measurements , i t became c l e a r t h a t e v a l u a t i o n o f
t he mass and e n e r g y b a l a n c e s s h o u l d be pe r f o rmed on t h e b a s i s o f t h e d a t a
e x t r a c t e d f rom t h e f a c t o r y r e c o r d s o r measured by t h e e x i s t i n g i n s t r u m e n t a t i o n .
8 .2 .2 B a s i c f a c t o r y d a t a and scheme o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s
P r o c e s s i n g c a p a b i l i t y : 2100 t / d .
P o l a r i z a t i o n o f c o s s e t t e s : 16.18%.
E x t r a c t o r : t r o u g h - t y p e .
J u i c e d r a f t : 120%.
R a w - j u i c e c o n c e n t r a t i o n and p u r i t y : 15.80% DS and 86.82%.
Pu lp p r e s s e d t o : 17.3% DS.
P o l a r i z a t i o n o f p r e s s e d p u l p : 1%.
K i l n g a s : 30-32% CO^ v o l .
J u i c e p u r i f i c a t i o n a c c o r d i n g t o t he c l a s s i c a l scheme, c o m p r i s i n g :
- h o t p r e - l i m i n g a t 45°C, CaO r a t e 0.30 kg/100 kg b;
- main l i m i n g a t 85°C, CaO r a t e 2.01 kg/100 kg b ;
- c a r b o n a t a t i o n I a t 80-85°C;
- d o u b l e - s t a g e f i l t r a t i o n I ;
- c a r b o n a t a t i o n I I a t 93-97°C;
- s i n g l e - s t a g e f i l t r a t i o n I I .
P u r i f i c a t i o n e f f e c t : 36%.
T h i n - j u i c e c o n c e n t r a t i o n and p u r i t y : 15.63% DS and 91.19%.
E v a p o r a t o r s t a t i o n : q u a d r u p l e - e f f e c t , R o b e r t - t y p e b o d i e s .
T h i c k - j u i c e c o n c e n t r a t i o n : 61.4% DS.
Sugar h o u s e :
- r a w - s u g a r a d d i t i o n 3.21 kg/100 kg b;
- t h r e e - b o i l i n g scheme w i t h t h e a f f i n a t i o n o f C s u g a r and raw s u g a r ;
- Β s u g a r me l t ed i n w a t e r ;
- m i x t u r e o f a f f i n e d C s u g a r and raw s u g a r m e l t e d i n t h i n j u i c e .
297
Sugar o u t p u t ( i n c l u d i n g s u g a r i n t r o d u c e d as raw s u g a r ) : 15.73 kg/100 kg b.
Power h o u s e :
- o i l - f i r e d b o i l e r s , s i x u n i t s r a t e d 12.5 t / h and one 6.5 t / h , a v e r a g e
e f f i c i e n c y abou t 80%;
- l i v e steam pa ramete rs 25 ba r and 425°C;
- two b a c k - p r e s s u r e t u r b i n e s r a t e d 3 MW e a c h ;
- b a c k - p r e s s u r e 3.3 b a r .
Steam s u p p l y t o t he s u g a r m a n u f a c t u r i n g p r o c e s s :
- l i v e steam t h r o t t l e d t o 4 .9 ba r t o t h e c e n t r i f u g a l s ;
- h e a t i n g steam 3.3 bar ( e x h a u s t steam and t h r o t t l e d l i v e steam) t o t he
rema in ing r e c e i v e r s .
H e a t i n g steam c o n s u m p t i o n : 56-57 kg/100 kg b.
Normal f u e l c o n s u m p t i o n : abou t 6.5 kg/100 kg b.
The schemes o f t h e bee t house and s u g a r house a r e shown i n F i g s . 8.1 and 8 . 2 ,
r e s p e c t i v e l y .
8 .2 .3 Scheme o f t he therma l sys tem
The scheme i s shown i n F i g . 8 . 3 . T h e r e a r e s e v e r a l q u e s t i o n a b l e d e t a i l s t o
a c c o u n t f o r i n t h e e v a l u a t i o n o f t he hea t economy:
- t h e h e a t i n g sys tems o f t h e f a c t o r y b u i l d i n g s and s u g a r s i l o s a r e s u p p l i e d w i t h
e x h a u s t s team;
- m e l t e r , r e m e l t h e a t e r , t h i n - j u i c e h e a t e r and s y r u p t a n k s a r e h e a t e d by e x h a u s t
s team;
- s t e a m i n g - o u t o f vacuum pans i s p e r f o r m e d u s i n g e x h a u s t s team;
- most condensa te f rom s team- and v a p o u r - h e a t e d e q u i p m e n t , and t h e c o n d e n s a t e
f rom t h e h e a t i n g s y s t e m s , i s w a s t e d ;
- t he f o u r t h e v a p o r a t o r e f f e c t i s o p e r a t e d as a c o n c e n t r a t o r , i m p l y i n g t h a t t h e
e v a p o r a t o r i s e s s e n t i a l l y o p e r a t e d as a t r i p l e - e f f e c t ;
- t he v a p o u r d i s t r i b u t i o n scheme i s r a t h e r p r i m i t i v e and t h e t e m p e r a t u r e s o f t h e
v a p o u r s s u p p l i e d t o t h e i n d i v i d u a l h e a t e r s do n o t s a t i s f y t he r e q u i r e m e n t o f
minimum t e m p e r a t u r e d i f f e r e n c e s ;
- t h e scheme o f t he c o n d e n s a t e subsys tem i n t he e v a p o r a t o r a r e a i s a l s o
p r i m i t i v e , r e s u l t i n g i n poo r u t i l i z a t i o n o f t h e c o n d e n s a t e e n e r g y ;
- t he h e a t i n g s u r f a c e a r e a s o f t he e v a p o r a t o r b o d i e s and most j u i c e h e a t e r s a r e
v e r y l a r g e .
8 .2 .4 A d d i t i o n a l i n f o r m a t i o n a c q u i r e d i n t h e f a c t o r y
I n t h e p r o c e s s h e a t i n g a r e a , a number o f m a l f u n c t i o n i n g subsys tems and
components were i d e n t i f i e d :
- a l l t h e steam t r a p s were o f t he f l o a t t y p e and some o f them were l e a k i n g
v a p o u r t o t he condensa te l i n e s ;
298
feed water
S c
.5
01 Ε
o ι
1
cossettes
• press water
EXTRACTOR
raw juice wet pulp —J
HEATERS
PRESSES
pressed pulp
to drying
PRE-LIMING
MAIN LIMING
HEATERS
•D Ό (Λ ι -
(Λ
Ζ) (/)
CARBONATATION I
THICKENERS I
juice
HEATER
1 Γ CARBONATATION I I
THICKENERS I I
τ
HEATER
i i r~ juice -J_J: sweet water
VACUUM FILTERS
Τ
to lime slaking
sludge water
to evaporation^
FILTERS
HEATERS
thin j thin j uice
f
SULPHITATION |
to sugar house^
ju ice sludge^
F i g . 8 . 1 . Scheme o f e x t r a c t i o n and j u i c e p u r i f i c a t i o n .
299
thic
k ju
ice
thin
juic
e w
ater
ro
w su
gar
VACU
UM P
ANS
A [
VACU
UM P
ANS
Β |
VACU
UM P
ANS
C |
I M
IXER
S A
^ I
MIX
ERS
Β | ^
MIX
ERS
C [
ω
I (-
r- I
Ol
I
' I
CENT
RIFU
GALS
A I
?
á I
CENT
RIFU
GALS
ΒI
f CE
NTRI
FUGA
LS C
suga
r A
suga
r Β
suga
r C
I ME
LTER
Β
I M
IXER
|
MIX
ER
affin
atio
n m
asse
cuite
^ I
»ELT
ER C
I
I I 'Ώ
J°M
J
^ I
777^
I
riR
I AF
FINA
TION
I
ΏST
I
I ^"
-TŁR
I
οω
I
CENT
RIFU
GALS
|
o
whi
te s
ugar
|
| f
| |
f m
olas
s
Fig.
8.
2.
Sche
me
of t
he
suga
r ho
use.
300
to boi ler — — house — 1 L to 6^
F i g . 8 . 3 . Scheme o f t h e the rma l sys tem i n the p r o c e s s h e a t i n g a r e a . Condensa te d r a i n a g e l i n e s n o t shown i n t he p i c t u r e a r e c o n n e c t e d t o t h e sewer s y s t e m . The meaning o f numbers d e n o t i n g equ ipment u n i t s i s i d e n t i c a l t o t h a t i n F i g . 1.5.
- s t a r t - u p v e n t s i n s e v e r a l steam t r a p s were kep t p e r m a n e n t l y o p e n , l e a k i n g
v a p o u r t o t he e n v i r o n m e n t ;
- v e n t i n g o f noncondensab les was c l e a r l y i n a c h a o t i c c o n d i t i o n , h e a t e r v e n t s
be ing kep t c l o s e d and vacuum-pan v e n t s l e a k i n g t o o much v a p o u r t o t h e
e n v i r o n m e n t ;
- a number o f measur ing i n s t r u m e n t s were m i s s i n g o r o u t o f o r d e r .
I n t he power house a r e a , t he equ ipment seemed t o be r a t h e r w e l l m a i n t a i n e d .
Among t h e measur ing i n s t r u m e n t s , f l u e gas a n a l y s e r s were o u t o f o r d e r and steam
f l o w meters were c l e a r l y n o t w o r k i n g r e l i a b l y . The most s e r i o u s p rob lem seemed
t o be t he poo r q u a l i t y o f make-up w a t e r , w i t h r e s u l t i n g c o r r o s i o n damage
f r e q u e n t l y o c c u r r i n g i n t he b o i l e r t u b e s .
C o n c e r n i n g t he hea t d i s t r i b u t i o n and u t i l i z a t i o n p r o c e s s e s , a number o f
301
d e f i c i e n c i e s i n t he thermal sys tem and i n t h e s u g a r m a n u f a c t u r i n g p r o c e s s can be
immed ia te l y i d e n t i f i e d :
- e x c e s s i v e hea t l o s s e s due t o l a r g e s e c t i o n s o f the rma l i n s u l a t i o n b e i n g i n
poo r c o n d i t i o n o r m i s s i n g ( e . g . a few h e a t e r s , v a p o u r p i p e l i n e s f rom t h e t h i r d
e v a p o r a t o r e f f e c t and a number o f c o n d e n s a t e p i p e s ) ;
- e x c e s s i v e hea t consumpt ion i n t he r o o m - h e a t i n g s y s t e m , due t o l a c k o f room
t e m p e r a t u r e c o n t r o l ;
- e x c e s s i v e hea t l o s s e s due t o u n c o v e r e d t a n k s i n t h e s u g a r house (most o f t h e
e x i s t i n g c o v e r s kep t p e r m a n e n t l y o p e n ) ;
- n o n - o p t i m a l o p e r a t i o n o f t he e v a p o r a t o r and e x c e s s i v e pa ramete r f l u c t u a t i o n s
due t o i n a d e q u a t e a u t o m a t i c c o n t r o l s .
I t g r a d u a l l y became c l e a r d u r i n g t he v i s i t t o t h e f a c t o r y t h a t i t s e n e r g y -
economy p rob lems were caused m a i n l y by a was te o f hea t i n t h e p r o c e s s h e a t i n g
a r e a . T h i s was accompanied by a was te o f c o n d e n s a t e s , and t h u s e x c e s s i v e
consumpt ion o f make-up w a t e r w h i c h must be added t o t h e b o i l e r f e e d . When
o v e r l o a d i n g t h e w a t e r - t r e a t m e n t s t a t i o n by a l a r g e f l o w o f p o l l u t e d r i v e r w a t e r ,
t he q u a l i t y o f make-up w a t e r became u n s a t i s f a c t o r y . T h i s c o n t r i b u t e d t o
a c c e l e r a t e d c o r r o s i o n , w h i c h was t h e immediate cause o f b o i l e r - t u b e f a i l u r e s .
T a k i n g i n t o a c c o u n t t h a t no p o w e r - b a l a n c e p rob lems were d e t e c t e d and t h a t t he
power house seemed t o be w e l l m a i n t a i n e d and o p e r a t e d , t h e above c o n c l u s i o n s
p o i n t a t p r o c e s s h e a t i n g as t h e e s s e n t i a l p rob lem t o w h i c h a t t e n t i o n s h o u l d be
d i r e c t e d when p e r f o r m i n g s u b s e q u e n t s t a g e s o f t h e a n a l y s i s .
8 .2 .5 Mass b a l a n c e o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s
The c a l c u l a t e d mass b a l a n c e o f t h e b e e t house i s shown i n T a b l e 8 . 3 . The
pa rame te rs o f t he e x t r a c t i o n and j u i c e p u r i f i c a t i o n p r o c e s s e s can be r e g a r d e d as
e s s e n t i a l l y c o r r e c t .
The c a l c u l a t e d mass b a l a n c e o f t he s u g a r house i s shown i n T a b l e 8 . 4 . The
pa rame te rs o f g r e e n s y r u p s A and B, i . e . h i g h p u r i t i e s and r e l a t i v e l y low
c o n c e n t r a t i o n s , i n d i c a t e t h a t t o o much wash w a t e r i s s u p p l i e d t o A and Β
c e n t r i f u g a l s . As a r e s u l t , c r y s t a l s d i s s o l v e i n e x c e s s w a t e r , c a u s i n g a r e d u c e d
c r y s t a l y i e l d and i n c r e a s e d c i r c u l a t i o n o f m a s s e c u i t e s i n t h e s u g a r h o u s e . T h i s
c o n t r i b u t e s t o t h e e x c e s s i v e h e a t demand i n t h e s u g a r h o u s e .
8 .2 .6 Heat b a l a n c e o f t he the rma l sys tem and h e a t economy e v a l u a t i o n
The hea t b a l a n c e c a l c u l a t i o n s were p e r f o r m e d a c c o r d i n g t o t h e e v a p o r a t o r -
r e c e i v e r a p p r o a c h . The r e s u l t s , e x p r e s s e d i n steam and v a p o u r f l o w s , a r e shown
i n T a b l e 8 . 5 . The b a l a n c e da ta seem t o c o n f i r m t h e i m p r e s s i o n g a i n e d f rom t h e
r e v i e w o f t he the rma l sys tem scheme t h a t t h e v a p o u r and condensa te d i s t r i b u t i o n
i s r a t h e r p r i m i t i v e . I t can a l s o be seen t h a t t h e c a l c u l a t e d steam demand i s
3 .5 -4 .5 kg/100 kg b l e s s t han t h e steam consumpt i on t aken f rom t h e f a c t o r y
302
TABLE 8.3
Mass b a l a n c e o f t h e b e e t h o u s e .
No. St ream name T o t a l f l o w C o n c e n t r a t i o n P u r i t y
No. St ream name (kg /100 kg b) (% DS) (%)
1 C o s s e t t e s 100.00 85.70
2 Wet p u l p 85.00 3 P r e s s e d p u l p 30.70 17.30 4 P r e s s w a t e r 54.30 1.50 5 F r e s h w a t e r 50.70 6 Raw j u i c e 120.00 15.17 86.82 7 J u i c e t o p r e - l i m i n g 123.76 8 J u i c e t o main l i m i n g 125.28 9 J u i c e t o c a r b o n a t a t i o n I 135.35
10 J u i c e f rom vacuum f i l t e r s 17.37 11 J u i c e t o t h i c k e n e r s I 152.45 12 J u i c e t o c a r b o n a t a t i o n I I 130.20 13 S u b s i d e r s l u d g e I 22.25 14 S w e e t e n i n g - o f f w a t e r t o vacuum f i l t e r s ; 14.33 15 S ludge 9.55 16 Sweet w a t e r f rom vacuum f i l t e r s 9.55 17 J u i c e t o t h i c k e n e r s I I 130.16 18 S u b s i d e r s l u d g e I I t o p r e - l i m i n g 3.76 19 J u i c e t o f i n e f i l t e r s 126.40 20 T h i n j u i c e 126.40 13.56 91.19 21 T h i n j u i c e t o e v a p o r a t i o n 119.57 22 M i l k - o f - l i m e t o p r e - l i m i n g 1.52 23 M i l k - o f - l i m e t o main l i m i n g 10.07 24 K i l n gas t o c a r b o n a t a t i o n I 4.49 25 K i l n gas t o c a r b o n a t a t i o n I I 0.40
r e c o r d s . Most p r o b a b l y , t h i s i s an i n d i c a t i o n o f steam a n d / o r v a p o u r l e a k s
o c c u r r i n g i n t h e condensa te d r a i n a g e s u b s y s t e m .
On t he b a s i s o f t he da ta t h u s a c q u i r e d , t h e f o l l o w i n g g e n e r a l c o n c l u s i o n s
were d r a w n .
( i ) The the rma l sys tem i s c l e a r l y w o r k i n g l e s s e f f e c t i v e l y t han c o u l d be
e x p e c t e d on t h e b a s i s o f i t s d e s i g n and equ ipment c h a r a c t e r i s t i c s . The most
i m p o r t a n t r e a s o n s a r e :
- steam and v a p o u r l e a k s w i t h i n t h e sys tem o r d i r e c t l y t o t he e n v i r o n m e n t ;
- u n r e l i a b l e v e n t i n g o f n o n c o n d e n s a b l e s ;
- e x c e s s i v e hea t d i s s i p a t i o n t o t h e e n v i r o n m e n t .
( i i ) The d e s i g n and pa rame te rs o f t he s u g a r m a n u f a c t u r i n g p r o c e s s i n t h e s u g a r
house a r e a a r e c o n t r i b u t i n g t o t h e e x c e s s i v e t o t a l h e a t demand. The e s s e n t i a l
d e f i c i e n c i e s a r e :
- u n n e c e s s a r y w a t e r i n t a k e t o Β r e m e l t ;
- t o o l a r g e w a s h - w a t e r consumpt ion i n A and Β c e n t r i f u g a l s .
( i i i ) The e f f e c t i v e n e s s o f t h e h e a t d i s t r i b u t i o n scheme i n t he p r o c e s s h e a t i n g
a r e a i s t o o l o w . The u n d e r l y i n g r e a s o n s a r e :
- was te o f c o n d e n s a t e s ;
303
TABLE 8.4
Mass b a l a n c e o f t he s u g a r h o u s e .
7Γ ¡ri77~T7Z T o t a l f l o w C o n c e n t r a t i o n P u r i t y No. St ream name ^^^^^^^ ./ o/ ^
1 T h i c k j u i c e 26.24 61.40 91 .14 2 T h i n j u i c e 6.83 13.56 91 .19 3 Raw s u g a r 3.21 98.73 98.70 4 A m a s s e c u i t e 41.33 91.90 93.74 5 Green s y r u p A 24.15 79.70 89.00 6 Wash s y r u p A 3.84 74.19 91.94 7 Whi te s u g a r 15.73 99.95 99.80 8 Β m a s s e c u i t e 18.51 92.00 88.39 9 Green s y r u p Β 8.15 81.80 79.20
10 Wash s y r u p Β 3.79 74.18 85.69 11 Β s u g a r 7.59 99.50 97.50 12 C m a s s e c u i t e 13.32 94.60 82.93 13 C s u g a r 8.56 98.50 92.50 14 M o l a s s e s 4.76 87.60 63.60 15 A f f i n a t i o n m a s s e c u i t e 21.26 90.00 91.93 16 A f f i n a t i o n s y r u p 11.04 78.81 87.42 17 A f f i n e d C s u g a r 10.65 98.00 95.69 18 Β r e m e l t 11.86 65.00 97.55 19 C - a f f . r e m e l t 17.48 65.00 95.32 20 Water t o c e n t r i f u g a l s A 1.53 21 Steam t o c e n t r i f u g a l s A 1.03 22 Water t o c e n t r i f u g a l s Β 1.02 23 Water t o Β r e m e l t 4.11
TABLE 8.5
Steam and v a p o u r f l o w s (kg /100 kg b) between s o u r c e s and r e c e i v e r s i n t he p r o c e s s - h e a t i n g a rea o f t h e the rma l s y s t e m .
S o u r c e s No. R e c e i v e r s E x h a u s t E v a p o r a t o r e f f e c t s n4-höv-c
steam 1 2 3 4 ^^"^^^^
1 E x t r a c t o r 1.18 1.85 2 R a w - j u i c e h e a t e r s 1.23 c o n d e n s a t e 3 L i m e d - j u i c e h e a t e r s 0.44 6.30 4 H e a t e r i n c a r b o n a t a t i o n I 1.30 5 C l e a r - j u i c e h e a t e r 3.67 6 T h i n - j u i c e h e a t e r s 5.85 7 T h i c k - j u i c e h e a t e r 0.45 8 M e l t e r 0.40 9 I n d i r e c t l y - h e a t e d s y r u p t a n k s 0.38
10 D i r e c t l y - h e a t e d s y r u p t a n k s 0.55 11 Remel t h e a t e r 0.36 12 Vacuum pans A 18.61 13 Vacuum pans Β 3.46 14 Vacuum pans C 2.67 15 Vacuum-pan s teaming 1.80 16 O t h e r smal l r e c e i v e r s 0.50 17 Sugar d r y e r 0.50 18 Condense r 0.58 19 E v a p o r a t o r t o t a l 5.85 30.03 10.67 0.58 20 E x h a u s t - s t e a m consumpt ion 51.58
304
thic
k ju
ice
thin
ju
ice
raw
sugar
VAC
UU
M
PAN
S A
V
AC
UU
M
PAN
S Β
V
AC
UU
M
PAN
S C
<
' I
' <
C
D
' I
' C
D
* I
' ^
MIX
ER
S A
^
Φ
MIX
ER
S Β
^
MIX
ER
S C
CEN
TRIF
UG
ALS
A I
Γ
• I
CE
NTR
IFU
GA
LS Β
I
Γ
CE
NTR
IFU
GA
LS C
I
suga
r A
su
gar
Β
suga
r C
-slu
mps—
^ j
^ 1
LI-*—,
|—I 1—,
I M
ELT
ER
B
I I
""-ψ
I
I I
^ ^
j affin
atio
n
mas
secu
ite
φ
Mp
iTP
Rr
rpm
pit
Β
AFF
INA
TIO
N
Ε
^^^^
^ C
re
me
ltB
^
| M
IXER
S
c
I 7
^
I I
AFFI
NAT
ION
I §
^
I '^"-^
'^ I
I C
EN
TRIF
UG
ALS
|
σ
wh
ite s
ugar
| I
| |
| t
mo
lass
es
Fig
. 8
.4.
Mo
dif
ied
sc
hem
e o
f th
e
sug
ar
ho
us
e.
305
- no u t i l i z a t i o n o f f o u r t h - e f f e c t v a p o u r ;
- i n a d e q u a t e u t i l i z a t i o n o f t h i r d - e f f e c t v a p o u r ;
- u n n e c e s s a r y h e a t i n g w i t h e x h a u s t s team;
- u n n e c e s s a r y u t i l i z a t i o n o f e x h a u s t steam f o r a u x i l i a r y p u r p o s e s .
8 .2 .7 P o s s i b l e improvements and i m p l e m e n t a t i o n s t r a t e g y
E v a l u a t i o n o f t h e hea t economy i n d i c a t e s t h a t s u b s t a n t i a l improvements can be
o b t a i n e d by t a k i n g v a r i o u s r a t i o n a l i z a t i o n measu res . As t he pa rame te rs o f t he
equ ipment a r e s u f f i c i e n t l y w e l l s u i t e d t o t h e f a c t o r y ' s n e e d s , t he s t e p - b y - s t e p
approach a v o i d i n g l a r g e i n v e s t m e n t s seems t o be s u f f i c i e n t t o c u t down t h e hea t
consumpt ion c o n s i d e r a b l y .
The imp lemen ta t i on s t r a t e g y e v o l v e s n a t u r a l l y f rom t h e f o l l o w i n g l o g i c a l
sequence o f c o r r e c t i v e a c t i o n s .
( i ) F i r s t , t h e was te o f e n e r g y s h o u l d be i m m e d i a t e l y e l i m i n a t e d by r e p a i r i n g o r
r e p l a c i n g a l l t h e m a l f u n c t i o n i n g a u x i l i a r y components o f t h e therma l s y s t e m ,
t h a t i s :
- l e a k i n g steam t r a p s ;
- u n r e l i a b l e v e n t s ;
- i n o p e r a t i v e measur ing i n s t r u m e n t s .
( i i ) S e c o n d , t h e t o t a l hea t demand o f t he s u g a r m a n u f a c t u r i n g p r o c e s s s h o u l d be
reduced b y :
- r e p a i r i n g o r i n s t a l l i n g damaged o r m i s s i n g s e c t i o n s o f t h e the rma l i n s u l a t i o n
i n t h e p r o c e s s h e a t i n g a r e a ;
- e l i m i n a t i n g t he use o f e x h a u s t steam f o r a u x i l i a r y p u r p o s e s and r e p l a c i n g i t
by f i r s t - o r s e c o n d - e f f e c t v a p o u r ;
- m o d i f y i n g t he c r y s t a l l i z a t i o n scheme t o t h e fo rm shown i n F i g . 8 . 4 , t h u s
c u t t i n g down the t o t a l w a t e r i n t a k e t o t he s u g a r house (B r e m e l t i s p r e p a r e d
u s i n g t h i n j u i c e i n s t e a d o f w a t e r ) ;
- r e d u c i n g t h e consumpt ion o f wash w a t e r i n A and Β c e n t r i f u g a l s ;
- r e d u c i n g t h e t o t a l w a t e r i n t a k e t o t h e s u g a r house even f u r t h e r by i n c r e a s i n g
t he t h i c k - j u i c e c o n c e n t r a t i o n .
The e s t i m a t e d mass b a l a n c e o f t he s u g a r house a f t e r w a t e r i n t a k e r e d u c t i o n s i s
shown i n T a b l e 8 . 6 .
( i i i ) The e f f e c t i v e n e s s r a t i o o f t he the rma l sys tem s h o u l d be i m p r o v e d . F i r s t o f
a l l , i t i s n e c e s s a r y t o e l i m i n a t e t h e was te o f c o n d e n s a t e s by i n s t a l l i n g
condensa te d r a i n a g e l i n e s l i n k i n g a l l t h e h e a t e r s w i t h p r o p e r l y s e l e c t e d
r e s p e c t i v e condensa te t a n k s . W h i l e i m p r o v i n g t h e e n e r g y r e c o v e r y , t h i s w i l l
r educe t he d e f i c i t o f make-up w a t e r and c o n t r i b u t e t o improved b o i l e r
r e l i a b i l i t y . F u r t h e r improvement i n t h i s r e s p e c t can be o b t a i n e d by r e p l a c i n g
t he o l d - f a s h i o n e d steam h e a t i n g o f f a c t o r y b u i l d i n g s by w a t e r h e a t i n g . To
comple te t h e c o r r e c t i v e a c t i o n s r e l a t e d t o t h e c o n d e n s a t e subsys tem
306
T o t a l f l o w C o n c e n t r a t i o n P u r i t y No. St ream name ^ ^ ^ / ^ ^ ^ (o/^j
1 T h i c k j u i c e 24.57 65.00 91.14 2 T h i n j u i c e 7.91 13.56 91.19 3 Raw s u g a r 3.21 98.73 98.70 4 A m a s s e c u i t e 31.27 92.00 94.11 5 Green s y r u p A 12.43 81.00 85.00 6 Wash s y r u p A 3.25 76.93 92.91 7 Wh i te s u g a r 16.05 99.96 99.95 8 Β m a s s e c u i t e 11.80 93.00 86.29 9 Green s y r u p Β 5.24 83.00 72.00
10 Wash s y r u p Β 1.26 79.27 85.29 11 Β s u g a r 5.66 99.50 97.50 12 C m a s s e c u i t e 7.86 93.50 76.87 13 C s u g a r 3.55 98.50 95.50 14 Mo lasses 4.62 83.50 60.00 15 A f f i n a t i o n m a s s e c u i t e 11.99 90.50 92.33 16 A f f i n a t i o n s y r u p 6.17 78.64 84.69 17 A f f i n e d C s u g a r 6.06 99.00 98.52 18 Β r e m e l t 9.73 65.00 97.03 19 C a f f . r e m e l t 10.06 65.00 97.91 20 Water t o c e n t r i f u g a l s A 0.47 21 Steam t o c e n t r i f u g a l s A 0.16 22 Water t o c e n t r i f u g a l s Β 0.35 23 Water t o c r y s t a l 1 i z e r s C 0.31
i t i s n e c e s s a r y t o a d d , t o t h e e x i s t i n g equ ipment and p i p i n g , a c o n d e n s a t e tank
and a few f l a s h - v a p o u r c o n n e c t i o n s making i t p o s s i b l e t o u t i l i z e f u l l y t h e
a v a i l a b l e condensa te e n e r g y i n t h e e v a p o r a t o r .
The n e x t s t e p t o improve t h e e f f e c t i v e n e s s r a t i o c o n s i s t s o f e l i m i n a t i n g
p r o c e s s - e q u i p m e n t h e a t i n g w i t h e x h a u s t s team, i m p r o v i n g u t i l i z a t i o n o f t h i r d -
e f f e c t v a p o u r and i n t r o d u c i n g t h e u t i l i z a t i o n o f f o u r t h - e f f e c t v a p o u r . T h i s
amounts t o a r e c o n s t r u c t i o n o f t he v a p o u r d i s t r i b u t i o n scheme and must be
c o o r d i n a t e d w i t h t h e i n s t a l l a t i o n o f t h e condensa te d r a i n a g e l i n e s men t i oned
b e f o r e .
The m o d i f i e d v a p o u r d i s t r i b u t i o n scheme i s shown i n F i g . 8 . 5 . I n o r d e r t o
take f u l l advan tage o f t h e r e c o n s t r u c t i o n o f t h e e v a p o r a t i o n s u b s y s t e m , t h e
e v a p o r a t o r s h o u l d a l s o be e q u i p p e d w i t h a u t o m a t i c l e v e l c o n t r o l s .
Equipment r e p a i r and changes n e c e s s a r y f o r i n t r o d u c i n g t h e m o d i f i c a t i o n s
men t ioned under ( i ) and ( i i ) can e a s i l y be comp le ted d u r i n g one o f f - s e a s o n
p e r i o d . I t can be e s t i m a t e d t h a t t h e r e s u l t i n g r e d u c t i o n o f t h e steam
consumpt ion w i l l be a t l e a s t 4 . 5 - 5 . 0 kg/100 kg b. As r e g a r d s r e c o n s t r u c t i o n o f
t h e v a p o u r d i s t r i b u t i o n scheme, i t must be p r e c e d e d by a d e s i g n s t u d y on t h e
n e c e s s a r y p i p i n g m o d i f i c a t i o n s . A p r e l i m i n a r y h e a t b a l a n c e ( e x p r e s s e d i n steam
and v a p o u r f l o w s ) o f t h e m o d i f i e d the rma l sys tem i s p r e s e n t e d i n T a b l e 8 . 7 . As
TABLE 8.6
M o d i f i e d mass b a l a n c e o f t h e s u g a r h o u s e .
307
to ammonia water
i tank
ί
5
Ϊ
r - m -
exhaust steam -4^ :
to boiler -——M3I j ' ljj
7
Β
-Ε
- Q -
exhaust steam
house
to 6*
. J
F i g . 8 . 5 . M o d i f i e d scheme o f t h e the rma l sys tem i n t h e p r o c e s s h e a t i n g a r e a . Condensa te d r a i n a g e l i n e s n o t shown i n t he p i c t u r e a r e c o n n e c t e d t o t h e ammonia w a t e r t a n k . The meaning o f numbers d e n o t i n g equ ipment u n i t s i s i d e n t i c a l t o t h a t i n F i g . 1.5.
can be s e e n , t h e steam consumpt ion can be r e d u c e d t o abou t 41.8 kg/100 kg b ,
w h i c h i s n e a r l y 10 kg/100 kg b l e s s t han i n d i c a t e d i n t he h e a t b a l a n c e o f t h e
e x i s t i n g the rma l sys tem ( T a b l e 8 . 5 ) .
I t s h o u l d be p o i n t e d o u t t h a t even a f t e r t h e c o m p l e t i o n o f t h e
r a t i o n a l i z a t i o n programme p r o p o s e d a b o v e , t h e h e a t economy w i l l remain r a t h e r
p r i m i t i v e , as t h e e f f e c t i v e n e s s r a t i o o f a the rma l sys tem w i t h o u t f u l l
u t i l i z a t i o n o f t h e l o w - t e m p e r a t u r e h e a t c a n n o t be v e r y h i g h . U n l e s s a d e t a i l e d
d e s i g n s t u d y i s p e r f o r m e d , i t i s i m p o s s i b l e t o d e t e r m i n e w h e t h e r o r n o t t h e
a p p l i c a t i o n o f more advanced s o l u t i o n s c o u l d be e c o n o m i c a l l y v i a b l e . I t i s
t h e r e f o r e recommended t o e v a l u a t e t h e e n e r g y economy a g a i n a f t e r two o r t h r e e
y e a r s o f t h e s t e p - b y - s t e p improvement programme, and t o r e p e a t t h e a n a l y s i s o f
p o s s i b l e e n e r g y - s a v i n g measu res . The i n d i v i d u a l measures can be e v a l u a t e d
308
TABLE 8.7
Steam and v a p o u r f l o w s (kg /100 kg b) between s o u r c e s and r e c e i v e r s i n t he p r o c e s s - h e a t i n g a r e a o f t h e m o d i f i e d the rma l s y s t e m .
No. R e c e i v e r s S o u r c e s E x h a u s t E v a p o r a t o r e f f e c t s
steam Ί 2 3 4 "
1 E x t r a c t o r 1 .18 1 .87 2 R a w - j u i c e h e a t e r s 0, .30 condensa te 3 L i m e d - j u i c e h e a t e r s 2.44 4, .33 4 H e a t e r i n c a r b o n a t a t i o n I 1.32 5 C l e a r - j u i c e h e a t e r s 1, .14 2.54 6 T h i n - j u i c e h e a t e r s 2.21 2 .99 7 T h i c k - j u i c e h e a t e r 0, .35 8 9
M e l t e r I n d i r e c t l y - h e a t e d s y r u p t a n k s
0, 0,
.40
.30 10 D i r e c t l y - h e a t e d s y r u p t anks 0, .24 11 Remelt h e a t e r 0, .26 12 Vacuum pans A 13, .04 13 Vacuum pans Β 2, .87 14 Vacuum pans C 1, .42 15 Vacuum-pan s t e a m i n g - o u t 1, .80 16 O t h e r smal l r e c e i v e r s 0 .50 17 Sugar d r y e r 0 .50 18 Condenser 1. .02 19 E v a p o r a t o r t o t a l 2.21 25. .99 8.16 4. .63 20 E x h a u s t - s t e a m consumpt ion 41 , .77
e c o n o m i c a l l y , c r e a t i n g a b a s i s f o r d e c i s i o n s on t h e f u t u r e c o u r s e o f a c t i o n . I f
t he l a c k o f i n v e s t m e n t f u n d s c o n t i n u e s , t h e n e x t s t a g e o f t he s t e p - b y - s t e p
improvement programme can be p l a n n e d ; o t h e r w i s e , a m o d e r n i z a t i o n o f t he f a c t o r y
can be c o n s i d e r e d .
8.3 FACTORY CHARACTERIZED BY GOOD I N I T I A L ENERGY U T I L I Z A T I O N
8.3.1 I n t r o d u c t o r y remarks
The example p r e s e n t e d i n t h i s S e c t i o n i s based on a r e a l case i n v e s t i g a t e d
by a s p e c i a l i z e d team a few y e a r s ago i n Sweden ( r e f . 1 7 ) . The i n v e s t i g a t i o n was
p l anned i n advance by the f a c t o r y manager ( as a r u l e , e v e r y Swed ish s u g a r
f a c t o r y has i t s e n e r g y economy i n v e s t i g a t e d e v e r y t h i r d o r f o u r t h y e a r ) .
The f a c t o r y was known f o r i t s r a t h e r low steam c o n s u m p t i o n , abou t 30-32 kg
pe r 100 kg b , r e s u l t i n g f rom i n v e s t m e n t s pe r f o rmed m a i n l y i n t h e 1950s and 1960s
and s t e p - b y - s t e p improvements i n t r o d u c e d i n t h e 1970s. F o r economic r e a s o n s , t h e
s t e p - b y - s t e p app roach i s a l s o l i k e l y t o remain t h e o n l y p r a c t i c a l method o f
i n t r o d u c i n g improvements i n t he f o r e s e e a b l e f u t u r e .
I t was p l anned t o a c q u i r e t h e n e c e s s a r y da ta d u r i n g 5 measurements s e s s i o n s
o r g a n i z e d a p p r o x i m a t e l y e v e r y two weeks f rom t h e b e g i n n i n g t o t he end o f t h e
s e a s o n . T h i s a r rangement was f o r s t u d y i n g t h e pa rame te rs o f t h e hea t u t i l i z a t i o n
p r o c e s s e s as f u n c t i o n s o f t i m e , t h u s making i t p o s s i b l e t o i d e n t i f y t he
309
i n f l u e n c e o f t h e s c a l e b u i l d - u p . The u l t i m a t e goa l was t o p r e p a r e a comp le te
s u r v e y o f t h e hea t u t i l i z a t i o n i n t h e s u g a r m a n u f a c t u r i n g p r o c e s s and f o r
a u x i l i a r y p u r p o s e s , and p a r t i c u l a r l y i n t h e e v a p o r a t o r s t a t i o n , s u g a r house and
a number o f smal l steam r e c e i v e r s . On t h e b a s i s o f t h e s u r v e y r e s u l t s , t h e most
e f f e c t i v e measures t o reduce t h e hea t demand c o u l d be d e t e r m i n e d .
D u r i n g t h e o f f - s e a s o n p e r i o d p r e c e d i n g t h e a c t u a l s e a s o n ' s o p e r a t i o n s , a
s p e c i a l measur ing sys tem i n d e p e n d e n t o f t h e f a c t o r y ' s measu r ing i n s t r u m e n t s was
i n s t a l l e d w i t h t h e aim o f p r o v i d i n g v e r y a c c u r a t e d a t a on t h e most i m p o r t a n t
p a r a m e t e r s , namely p r e s s u r e s and t e m p e r a t u r e s i n t h e e v a p o r a t i o n s u b s y s t e m ,
i n c l u d i n g c o n d e n s a t e t a n k s . O r i f i c e s were i n s t a l l e d i n t h e main v e n t i n g l i n e s
i n o r d e r t o make i t p o s s i b l e t o e v a l u a t e t h e f l o w s o f n o n c o n d e n s a b l e s .
A r rangements were a l s o made w i t h t h e l a b o r a t o r y t o p e r f o r m a number o f e x t r a
a n a l y s e s , m o s t l y o f t he d r y s u b s t a n c e c o n t e n t and p o l a r i z a t i o n ( a s w e l l as
a l k a l i n i t y and c a l c i u m s a l t s i n t h e case o f samples taken f rom t h e j u i c e
p u r i f i c a t i o n s t a t i o n ) o f j u i c e and s y r u p s a m p l e s . The p o i n t s o f samp l i ng were
p l a n n e d t o a c h i e v e a h i g h a c c u r a c y o f i d e n t i f i c a t i o n o f t he p r o c e s s mass b a l a n c e
and o f t h e the rma l p r o p e r t i e s o f a l l t h e i m p o r t a n t mass s t r e a m s . I n t h e
e v a p o r a t o r a r e a , j u i c e samples were t o be c o l l e c t e d i n a manner a l l o w i n g
d e t e r m i n a t i o n o f i n l e t and o u t l e t j u i c e c o n c e n t r a t i o n s i n a l l t he e v a p o r a t o r
b o d i e s .
I t was p l a n n e d t o a c q u i r e t h e r e m a i n i n g d a t a f rom t h e o r d i n a r y f a c t o r y
i n s t r u m e n t a t i o n , and t o take c e r t a i n i n s t r u m e n t r e a d i n g s s o l e l y f o r t h e pu rpose
o f c r o s s - c h e c k i n g t h e i n d i c a t i o n s o f t h e s p e c i a l measu r ing s y s t e m . A f t e r
c a l c u l a t i n g t he t ime a v e r a g e d v a l u e s o f t h e key p a r a m e t e r s , e v e r y measurement
p e r i o d ( l a s t i n g abou t one w o r k i n g s h i f t ) was e x p e c t e d t o p r o d u c e abou t 300 d a t a
t o be used i n t h e hea t b a l a n c e c a l c u l a t i o n s .
8 . 3 .2 B a s i c f a c t o r y d a t a and scheme o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s
P r o c e s s i n g c a p a b i l i t y : 3700 t / d .
P o l a r i z a t i o n o f c o s s e t t e s : 15.7%.
E x t r a c t o r : t r o u g h - t y p e .
J u i c e d r a f t : 120%.
R a w - j u i c e c o n c e n t r a t i o n : 15.0%.
P u l p p r e s s e d t o : 21.4% DS.
K i l n g a s : 36-38% CO^ v o l .
J u i c e p u r i f i c a t i o n a c c o r d i n g t o t he c l a s s i c a l scheme, c o m p r i s i n g :
- h o t p r e - l i m i n g a t 60-65°C;
- main l i m i n g a t abou t 85°C;
- c a r b o n a t a t i o n I a t 80-85°C;
- d o u b l e - s t a g e f i l t r a t i o n I ;
- c a r b o n a t a t i o n I I a t 92-95°C;
310
- d o u b l e - s t a g e f i l t r a t i o n I I .
T h i n - j u i c e c o n c e n t r a t i o n : 14.2% DS.
E v a p o r a t o r : q u i n t u p l e - e f f e c t , f a l l i n g - f i l m b o d i e s i n t h e f i r s t and f i f t h
e f f e c t s , R o b e r t - t y p e b o d i e s i n t h e r e m a i n i n g e f f e c t s .
T h i c k - j u i c e c o n c e n t r a t i o n : 64.8% DS.
Sugar h o u s e :
- t h r e e - b o i l i n g scheme w i t h t h e a f f i n a t i o n o f C s u g a r ;
- a f f i n e d C s u g a r me l t ed i n t h i n j u i c e ;
- s t a n d a r d l i q u o r p r e p a r e d f rom t h i c k j u i c e , Β s u g a r and C - a f f . r e m e l t .
Power h o u s e :
- o i l - f i r e d b o i l e r r a t e d 50 t / h , e f f i c i e n c y 91%;
- l i v e - s t e a m pa rame te rs 60 ba r and 470°C;
- b a c k - p r e s s u r e t u r b i n e r a t e d 6 MW;
- b a c k - p r e s s u r e 3.5 b a r .
Steam s u p p l y t o t h e s u g a r m a n u f a c t u r i n g p r o c e s s : steam 3.5 bar ( i n p r i n c i p l e ,
e x h a u s t steam o n l y , and t h r o t t l e d l i v e steam i f n e c e s s a r y ) .
H e a t i n g steam c o n s u m p t i o n : 30-32 kg/100 kg b.
Normal f u e l c o n s u m p t i o n : abou t 3.6 kg/100 kg b.
The schemes o f t h e b e e t house and s u g a r house a r e shown i n F i g s . 8.6 and 8 . 7 ,
r e s p e c t i v e l y . I t can immed ia te l y be seen t h a t t h e s u g a r m a n u f a c t u r i n g p r o c e s s
has been c a r e f u l l y p l a n n e d t o m i n i m i z e w a t e r i n t a k e s and t o e l i m i n a t e
u n n e c e s s a r y r e c y c l i n g o f t h e p r o c e s s med ia .
8 .3 .3 Scheme o f t h e therma l sys tem
The scheme i s shown i n F i g . 8 . 8 . A number o f d e t a i l s d e s e r v e t o be n o t e d , as
t h e y i n d i c a t e t h a t a h i g h d e g r e e o f r a t i o n a l i z a t i o n o f t h e e n e r g y economy has
a l r e a d y been a t t a i n e d .
I n t he p r o c e s s h e a t i n g a r e a , t h r e e f a c t o r s make i t p o s s i b l e t o a t t a i n a h i g h
e f f e c t i v e n e s s r a t i o :
- t h e a p p l i c a t i o n o f a q u i n t u p l e - e f f e c t e v a p o r a t o r s t a t i o n and t h e u t i l i z a t i o n
o f f i f t h - e f f e c t v a p o u r i n r a w - j u i c e h e a t i n g ;
- t he u t i l i z a t i o n o f t he vacuum-pan v a p o u r s i n r a w - j u i c e h e a t i n g ;
- t h e u t i l i z a t i o n o f t h e c o n d e n s a t e i n h e a t i n g p r e - l i m e d j u i c e .
The e v a p o r a t o r s t a t i o n c o n s i s t s o f n i n e b o d i e s , two o f them o f t h e f a l l i n g -
f i l m t y p e and t he rema inde r o f t h e R o b e r t t y p e . A scheme o f j u i c e and v a p o u r
c o n n e c t i o n s , i n c l u d i n g v e n t i n g l i n e s , i s shown i n F i g . 8 . 9 . ( H e a t i n g s u r f a c e
a r e a s a r e g i v e n i n T a b l e 8 . 9 . )
A f a l l i n g - f i l m body i n t h e f i r s t e v a p o r a t o r e f f e c t i s c h a r a c t e r i z e d by a
l a r g e o v e r a l l hea t t r a n s f e r c o e f f i c i e n t w h i c h rema ins n e a r l y c o n s t a n t t h r o u g h o u t
t h e s e a s o n . T h i s i s a d e c i s i v e f a c t o r keep ing t h e e v a p o r a t i o n c a p a c i t y a t a h i g h
l e v e l , even i f s c a l e b u i l d - u p t a k e s p l a c e i n t h e second and t h i r d e f f e c t s .
311
(/) o CT»
c Ξί
cosset tes
α;
• σ
Χ3
1
• p ress water -
Γ HEATER
EXTRACTOR
HEATERS
PRE-L IMING
HEATERS
MAIN LIMING
CARBONATATION I
THICKENERS I
τ
ω
HEATERS
FILTERS
CARBONATATION I I
HEATERS
THICKENERS Π
milk-of - lime
i LIME SLAKING — Γ Τ
ju ice CaO
I
f L-wet pulp —J PRESSES I-raw juice I \ 1
i
VACUUM FILTERS
water
HEATERS
thin ju ice
l _ i SAFETY FILTERS
- ju ice -
1
pressed pulp
to dry ing
sludge
to evaporation
to sugar house
F i g . 8 . 6 . Scheme o f e x t r a c t i o n and j u i c e p u r i f i c a t i o n . 1 - h e a t e x c h a n g e r i n wh i ch condensa te ( f r e s h w a t e r ) warms up p r e s s w a t e r .
3 1 2
thin
thi
ck
juic
e ju
ice
| ^
"}
^ j
I VA
CUUM
PAN
S A
I I
VACU
UM P
ANS
Β VA
CUUM
PAN
S C
MIX
ERS
A M
IXER
S Β
MIX
ERS
C
CENT
RIFU
GALS
A
CENT
RIFU
GALS
Β
CENT
RIFU
GALS
C
g su
garC
15
—
was
h sy
rup
A—
—I
Logr
een
syru
p A
—I
I »
syru
p Β
—I—
• ^
|
. su
gar
B-
1 |
^^IX
ER
|
——
—
^ af
finat
ion
mas
secu
ite
>,
MELT
ER
I I
^
I 1
I AF
FINA
TION
I
I I
1 I
I M
IXER
S I
g
g AF
FINA
TION
£
CENT
RIFU
GALS
I ^
^ ,
f>—
af
fined
sug
ar C
'
' '
MELT
ER C
I I
white
sug
ar
mol
asse
;
Fig.
8.
7.
Sche
me
of t
he
suga
r ho
use.
313
— hot feed water
from 13
saturated i steam 6Ab ί 16 i CM
Ε
fuel - a _ i _ ^ m a k e - u p
water
• power
• OIL TANKS
PULP DRYING & PELLETING
STORAGE HOUSES
FACTORY BUILDING
OFFICE BUILDING
FROM BOILER BLOWDOWN
F i g . 8 . 8 . Scheme o f t he the rma l s y s t e m . 14 - e x t r a c t o r , 18 - p r e s s - w a t e r h e a t e r ; t h e r ema in i ng numbers have t h e same meaning as i n F i g . 1.5. D u r i n g t h e measurements , h e a t e r 6"*" was o u t o f o p e r a t i o n .
314
to the 2nd thin juice heater
thin juice 1
1
2A
π 2B
π
3A1
π 3B
π
3Α2
ΑΑ A B
to condenser
thick juice
F i g . 8 . 9 . Scheme o f j u i c e and v a p o u r c o n n e c t i o n s i n t h e e v a p o r a t o r s t a t i o n . D o t t e d l i n e s i n d i c a t e v e n t i n g c o n n e c t i o n s .
A n o t h e r f a l l i n g - f i l m body i n t h e f i f t h e v a p o r a t o r e f f e c t a l s o p l a y s an i m p o r t a n t
r o l e . I t s l a r g e hea t t r a n s f e r c o e f f i c i e n t makes i t p o s s i b l e t o keep t h e
t e m p e r a t u r e o f t h e f i f t h - e f f e c t v a p o u r s u f f i c i e n t l y h i g h t o u t i l i z e t h e l o w -
t e m p e r a t u r e h e a t , even d u r i n g t he f i n a l weeks o f t h e s e a s o n . T h i s w o u l d be v e r y
d i f f i c u l t t o a c h i e v e w i t h a R o b e r t - t y p e b o d y .
V e n t i n g l i n e s f rom c e r t a i n e v a p o r a t o r b o d i e s and v e n t i n g l i n e s f rom s e l e c t e d
h e a t e r s a r e c o n n e c t e d t o v a p o u r s u p p l y p i p e s o f o t h e r h e a t e r s . T h i s makes i t
p o s s i b l e t o u t i l i z e t he e n e r g y o f t h e m i x t u r e o f v a p o u r and n o n c o n d e n s a b l e s
p r i o r t o d i s c h a r g i n g i t t o t he e n v i r o n m e n t o r t o t h e c o n d e n s e r .
P l a t e hea t e x c h a n g e r s a r e a p p l i e d as c l e a r - j u i c e h e a t e r s ( b e f o r e
c a r b o n a t a t i o n I ) and as j u i c e h e a t e r s a f t e r c a r b o n a t a t i o n I I . Owing t o t h e i r
l a r g e hea t t r a n s f e r c o e f f i c i e n t s , t h e s e h e a t e r s can be s u p p l i e d w i t h v a p o u r s o f
r e l a t i v e l y low t e m p e r a t u r e s .
I n t h e power house a r e a , b o i l e r blowdown i s p e r f o r m e d v i a a f l a s h tank
c o n n e c t e d t o t h e e x h a u s t - s t e a m p i p e l i n e . F l a s h v a p o u r o b t a i n e d f rom t h e b o i l e r
w a t e r ( s u b s e q u e n t l y d i s c h a r g e d t o t h e sewer sys tem) i s t h u s mixed w i t h e x h a u s t
s team. A n a l o g o u s l y , t he v e n t i n g l i n e f rom t h e main f e e d - w a t e r t ank i s c o n n e c t e d
t o t h e p i p e s u p p l y i n g t h i r d - e f f e c t v a p o u r t o t h e h e a t i n g chamber o f t h e f o u r t h
e v a p o r a t o r e f f e c t . I n t h i s a r r a n g e m e n t , t h e f e e d w a t e r i s f l a s h e d f rom t h e
p r e s s u r e ^ o f s e c o n d - e f f e c t v a p o u r t o t h a t o f t h i r d - e f f e c t v a p o u r .
8 .3 .4 I n f o r m a t i o n o b t a i n e d f rom t h e measurements
U s i n g t h e r e c o r d e d v a l u e s o f j u i c e c o n c e n t r a t i o n s , as w e l l as v a p o u r and
condensa te t e m p e r a t u r e s measured i n t h e e v a p o r a t o r a r e a , mass and hea t b a l a n c e s
o f t h e e v a p o r a t o r were c a l c u l a t e d f o r each measurement s e s s i o n . An example o f
a comple te s e t o f i n p u t d a t a and c a l c u l a t i o n r e s u l t s ( c o r r e s p o n d i n g t o t h e
315
TABL
E 8
.8
Mas
s an
d he
at b
alan
ces
of
the
evap
orat
or
stat
ion
. Bo
dy 4
B w
as
disc
onne
cted
dur
ing
the
actu
al
mea
sure
men
t se
ssio
n.
Evap
orat
or
body
1
2A
2B
3
A1
3A
2 3B
4
A
4B
5
Inpu
t da
ta:
« H
eatin
g su
rfac
e ar
ea
(m^^
) 12
00
12
10
800
880
800
1200
1
10
0 86
0 70
0 Ju
ice
conc
entr
atio
n (%
DS
) in
let
14
.2
18
.8
18
.8
29
.3
40
.0
25
.2
44
.8
59
.7
ou
tlet
1
8.8
2
9.3
2
5.2
4
0.0
4
8.0
4
0.9
5
5.7
6
4.8
Va
pour
tem
pera
ture
( C
) he
atin
g ch
ambe
r 1
37
.4
12
5.2
1
24
.7
11
5.6
1
15
.3
11
5.6
1
08
.2
91
.3
vapo
ur
cham
ber
12
8.8
1
17
.0
11
7.8
1
08
.8
10
7.1
1
07
.9
92
.5
77
.7
Con
dens
ate
tem
pera
ture
(°
C)
13
6.0
1
26
.7
12
6.0
1
17
.3
11
8.3
1
17
.3
11
4.7
9
1.7
Fl
ow o
f no
ncon
dens
able
s (k
g/10
0 kg
b
) 0
.07
0.1
0 0
.14
0.1
0 0
.10
0.1
4 0
.07
0.1
0 R
esul
ts:
Juic
e te
mpe
ratu
re (
°C)
inle
t 1
33
.0
12
8.8
1
28
.8
11
7.0
1
08
.8
11
7.8
1
08
.0
93
.5
ou
tlet
1
28
.8
11
7.0
1
17
.8
10
8.8
1
08
.1
10
7.9
9
3.5
8
0.7
Ju
ice
flow
(k
g/10
0 kg
b
) in
let
11
3.7
5
0.5
3
5.3
3
2.4
2
3.7
2
6.4
3
6.0
5
1.7
* o
utl
et
85
.8
32
.4
26
.4
23
.7
19
.8
16
.2
29
.0
24
.9
Vapo
ur f
low
(k
g/10
0 kg
b
) he
atin
g ch
ambe
r 2
7.8
1
7.8
9
.0
8.7
4
.4
10
.3
6.7
3
.5
vapo
ur
cham
ber
27
.9
18
.1
9.0
8
.7
4.1
1
0.3
7
.1
4.2
C
onde
nsat
e fl
ow
(kg/
100
kg
b)
27
.7
17
.7
8.9
8
.7
4.3
1
0.2
6
.6
4.5
H
eat
flu
x at
he
atin
g su
rfac
e (k
W/m
^) ^
2
0.6
1
3.2
9
.8
8.9
4
.7
7.7
5
.5
4.5
O
vera
ll he
at t
ran
sfer
co
effi
cien
t (W
/(m
^K))
2400
16
0 1
42
0 1
31
0 66
0 10
00
37
5 43
0
*/ re
circ
ula
tio
n fl
ow
3 1 6
second s e s s i o n , i . e . t h e t h i r d week o f t h e s e a s o n ) i s g i v e n i n T a b l e 8 . 8 . As can
be s e e n , t he r e s u l t s i n c l u d e hea t f l u x e s and o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s
i n t h e i n d i v i d u a l e v a p o r a t o r b o d i e s . T h i s makes i t p o s s i b l e t o e v a l u a t e t h e
i n f l u e n c e o f s c a l e b u i l d - u p on t h e hea t t r a n s f e r i n t e n s i t y i n t h e e v a p o r a t o r
s t a t i o n .
The o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s i n t h e i n d i v i d u a l e v a p o r a t o r e f f e c t s
a r e shown as f u n c t i o n s o f t ime i n F i g . 8 .10 . As can be s e e n , t h e t e n d e n c i e s
c h a r a c t e r i s t i c o f R o b e r t - t y p e b o d i e s have been r e g i s t e r e d i n e f f e c t s 2 -4 . The
r e d u c t i o n o f t h e hea t t r a n s f e r i n t e n s i t y i n t he f o u r t h e f f e c t was so d r a s t i c
a f t e r f i v e weeks t h a t a s t a n d - b y body (48) was c o n n e c t e d t o t h i s e f f e c t . As
r e g a r d s the f a l l i n g - f i l m b o d i e s , no s c a l e b u i l d - u p i s v i s i b l e i n t h e f i r s t
e f f e c t , w h i l e t h e hea t t r a n s f e r i n t e n s i t y i n t he f i f t h e f f e c t d e c r e a s e s l i k e
t h a t i n R o b e r t - t y p e b o d i e s .
U s i n g t he r e c o r d e d v a l u e s o f t he t e m p e r a t u r e s o f h e a t i n g v a p o u r s , as w e l l as
j u i c e t e m p e r a t u r e s and j u i c e f l o w s , t he hea t b a l a n c e s o f j u i c e h e a t e r s were
2500
- 2000
ε
§ 1500
ΙΛ C
I 1000
α χ :
6 500h
1st effect
4 6
Time (weeks)
10
F i g . 8 .10 . Changes o f t he a v e r a g e d o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s i n t h e e v a p o r a t o r s t a t i o n ( s t a n d - b y body c o n n e c t e d t o t h e f o u r t h e f f e c t a f t e r 5 w e e k s ) .
317
c a l c u l a t e d f o r each measurement s e s s i o n . An example o f a comp le te s e t o f i n p u t
da ta and c a l c u l a t i o n r e s u l t s ( c o r r e s p o n d i n g t o t h e second s e s s i o n ) i s g i v e n i n
T a b l e 8 . 9 . As t h e r e s u l t s i n c l u d e t h e o v e r a l l hea t t r a n s f e r c o e f f i c i e n t s o f t he
i n d i v i d u a l h e a t e r s , t h e e f f e c t s o f s c a l e b u i l d - u p i n t h e h e a t e r s can be s t u d i e d .
TABLE 8.9
Heat b a l a n c e s o f t h e j u i c e h e a t e r s .
Medium hea ted Raw j u i c e P r e -
1 i med j u i c e
C l e a r j u i c e J u i ce a f t e r 2nd c a r b . ' *
T h i n j u i c e Medium hea ted
1 2
P r e -1 i med j u i c e
1* 2*
J u i ce a f t e r 2nd c a r b . ' * 1 2 3 4
I n p u t d a t a : H e a t i n g s u r f a c e a r e a (m^) 125 125 259 70.2 70.8 100 150 150 150 150 H e a t i n g v a p o u r . e x e f f e c t No. ^ 5 5 4 4 4 3 3 2 1 h a u s t t e m p e r a t u r e ( C) 77.7 77.7 92.5 92.5 92.5 108.1 108.1 117.3 128.8 137.4 J u i c e t e m p e r a t u r e ( C)
i n l e t 42.3 42.3 75.1 80.7 88.7 85.0 95.5 105.5 116.0 124.4 o u t l e t 60.1 58.8 84.3 88.7 91.5 98.5 105.5 116.0 124.4 133.0
J u i c e f l o w (kg /100 kg b) 56.6 106.4 147.2 138.2 138.2 116.8 113.7 113.7 113.7 113.7
R e s u l t s : Vapour demand (kg /100 kg b ) 3.09 2.86 1.86 1.86 0.65 2.70 1 .96 2.08 1 .69 1.76 O v e r a l l hea t t r a n s f e r c o e f f i c i e n t (W/ (m2K) ) 950 850 720 3660 4280 1680 1970 2790 1340 1360
V p l a t e hea t e x c h a n g e r s
The o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t s i n t h e i n d i v i d u a l j u i c e h e a t e r s a r e
shown as f u n c t i o n s o f t ime i n F i g . 8 .11 . These c o e f f i c i e n t s a re g e n e r a l l y v e r y
h i g h , w h i c h i n d i c a t e s t h a t t h e h e a t e r s a r e u t i l i z e d e f f e c t i v e l y . The e f f e c t s o f
t h e s c a l e b u i l d - u p can be seen e x a c t l y where t h e y m igh t be e x p e c t e d , namely i n
r a w - j u i c e , p r e - 1 i m e d - j u i c e and c l e a r - j u i c e h e a t e r s .
I t can be c o n c l u d e d t h a t t he j u i c e - t e m p e r a t u r e p r o f i l e s d e t e r m i n e d d u r i n g t h e
measurement s e s s i o n s a r e e s s e n t i a l l y c o r r e c t . A compar i son o f t e m p e r a t u r e
p r o f i l e s c o r r e s p o n d i n g t o t h e b e g i n n i n g and end o f t h e season i s shown i n
F i g . 8 .12 . N o t e w o r t h y a re t h e v e r y smal l v a l u e s - somet imes as low as 2 Κ - o f
t he minimum t e m p e r a t u r e d i f f e r e n c e i n t h e t h i n - j u i c e h e a t e r s , w h i c h a r e o f
t u b u l a r d e s i g n .
The e x h a u s t steam consumpt ion was d e t e r m i n e d a t 30 .5 -34 .0 kg/100 kg b i n
measurement s e s s i o n s 1-4. I t i n c r e a s e d t o 43.1 kg/100 kg b i n measurement
s e s s i o n 5, w h i c h was r e p r e s e n t a t i v e o f t h e f i n a l s t a g e o f t h e s e a s o n . C o n c e r n i n g
318
4000 h
3000 h
2000 h
clear juice (PHE)
c ω 'ο
I o
(Λ C O
1000 h
3000 h α o»
2
O
2000 h
1000 h
A 6 Time (weeks)
F i g . 8 .11. O v e r a l l hea t t r a n s f e r c o e f f i c i e n t s i n t he j u i c e h e a t e r s as f u n c t i o n s o f t i m e . PHE - p l a t e hea t e x c h a n g e r s . * d e n o t e s two h e a t e r s c o n n e c t e d i n p a r a l l e i .
319
F i g . 8 .12 . T e m p e r a t u r e s o f h e a t i n g v a p o u r s ( dashed l i n e s ; numbers deno te e v a p o r a t o r e f f e c t s ) and j u i c e ( s o l i d l i n e s ) . T h i c k l i n e s - f i r s t week o f t h e s e a s o n , t h i n l i n e s - t e n t h week o f t h e s e a s o n .
t he hea t consumpt ion components , p a r t i c u l a r a t t e n t i o n was p a i d t o t h e s u g a r
h o u s e . The h e a t i n g - v a p o u r demand o f t h e vacuum pans was c a l c u l a t e d on t h e b a s i s
o f t h e mass b a l a n c e o f t h e s u g a r c r y s t a l l i z a t i o n p r o c e s s . The demand f i g u r e s
c o r r e s p o n d i n g t o t h e f i v e measurement s e s s i o n s were c o n t a i n e d i n t h e range
14 .1-16 .8 kg/100 kg b , w i t h a t e n d e n c y t o i n c r e a s e as t h e season p r o g r e s s e d . As
t he v a p o u r used i n vacuum-pan s t e a m i n g - o u t was s u p p l i e d v i a a s e p a r a t e s u p p l y
l i n e , i t was p o s s i b l e t o measure i t s consumpt ion d i r e c t l y , and i n measurement
s e s s i o n s 1-4 t h e r e s u l t s were n e a r l y i d e n t i c a l , a t 0 . 9 - 1 . 0 kg/100 kg b. The
v a l u e d e t e r m i n e d i n measurement s e s s i o n 5 was 1.4 kg/100 kg b.
I n a d d i t i o n t o t he e x h a u s t s team, s a t u r a t e d b o i l e r steam ( w i t h d r a w n f rom t h e
b o i l e r drum) t h r o t t l e d t o 12 ba r i s s u p p l i e d t o t h e f a c t o r y f o r such p u r p o s e s as
h e a t i n g f u e l o i l b e f o r e t he b u r n e r s , as w e l l as o i l a t o m i z a t i o n i n t h e b u r n e r s
i n s t a l l e d i n t h e b o i l e r f u r n a c e and i n t h e l ime k i l n . I n t h e f i v e measurement
s e s s i o n s , t he consumpt ion o f 12 ba r steam remained n e a r l y c o n s t a n t a t
0 .3 -0 .4 kg/100 kg b.
320
8 .3 .5 Heat b a l a n c e o f t h e therma l sys tem
The hea t b a l a n c e c a l c u l a t i o n s were pe r f o rmed i n t h e f o l l o w i n g manner :
- u s i n g t h e r e s u l t s o f f l o w measurements ( o r t he c a l c u l a t e d mass b a l a n c e d a t a )
and t he t e m p e r a t u r e v a l u e s measu red , t he v a p o u r o r steam consumpt ion was
d e t e r m i n e d f o r a l l hea t r e c e i v e r s , and t h e t o t a l consumpt ion o f v a p o u r s f rom t h e
i n d i v i d u a l e v a p o r a t o r e f f e c t s was c a l c u l a t e d ;
- u s i n g t he v a l u e s o f t h e e v a p o r a t o r pa rame te rs measu red , t h e mass and hea t
b a l a n c e s o f t h e e v a p o r a t o r , i n c l u d i n g v a p o u r f l o w s ( a v a i l a b l e f o r p r o c e s s
h e a t i n g ) f rom t h e i n d i v i d u a l e f f e c t s , were c a l c u l a t e d .
Owing t o measurement e r r o r s , t h e t o t a l v a p o u r consumpt ion may d i f f e r f rom
t h e c a l c u l a t e d a v a i l a b l e v a p o u r f l o w . I f t h e d i f f e r e n c e i s l e s s t han
TABLE 8.10
Steam and v a p o u r f l o w s (kg /100 kg b ) between s o u r c e s and r e c e i v e r s i n t he thermal s y s t e m .
No. R e c e i v e r s E x h a u s t steam 1
S o u r c e s E v a p o r a t o r e f f e c t s O t h e r s
10
11
12 13
14 15 16 17 18 19
20 21 22 23
E x t r a c t o r R a w - j u i c e h e a t e r s P r e - 1 i m e d - j u i c e h e a t e r s C l e a r - j u i c e h e a t e r s H e a t e r a f t e r c a r b o n a t a t i o n I I 2.70 T h i n - j u i c e h e a t e r s 1.76 1.69 2.08 1.96 O i l t a n k s 0.25 Pu lp d r y i n g and p e l l e t i n g 0.02 H e a t i n g o f p r o d u c t s t o r e s 0.50 H e a t i n g o f f a c t o r y b u i l d i n g s 0.19 H e a t i n g o f o f f i c e b u i l d i n g s 0.16 Main f e e d - w a t e r tank 0.13 M o l a s s e s and a f f . - s y r u p t a n k s 0.12 M e l t e r C 0.02 Sy rup A t anks 0.37 Sy rup Β t anks 0.12 M e l t e r Β 0.33 Vacuum pans A , B, C 14.13 Vacuum-pan s t e a m i n g - o u t 0.86 C e n t r i f u g a l s 0.22 Sugar d r y e r 0.48 E v a p o r a t o r t o t a l 1.8 4.4 E x h a u s t - s t e a m consumpt ion 30.6 O i l b u r n e r s i n b o i l e r and l ime k i l n
0.83
1.86 2.51
5.95 vacuum-pan v a p o u r
condensa te
18.8 5.2 6.0
12 ba r steam 24
321
1 kg/100 kg b , t hen t he a c c u r a c y o f t h e measurements can be r e g a r d e d as
s a t i s f a c t o r y . I t can be added t h a t t h i s v a l u e i s e q u i v a l e n t t o d e t e r m i n i n g j u i c e
c o n c e n t r a t i o n s i n t he f i r s t and second e v a p o r a t o r e f f e c t s w i t h an a c c u r a c y o f
0.1% DS.
The hea t b a l a n c e d e t e r m i n e d u s i n g t h e r e s u l t s o f t h e second measurement
s e s s i o n ( t h i r d week o f t he s e a s o n ) i s p r e s e n t e d i n T a b l e 8 .10 .
8 .3 .6 E v a l u a t i o n o f t he hea t economy and i d e n t i f i c a t i o n o f p o s s i b l e improvements
The r e s u l t s o f t h e measurements and t h e s u b s e q u e n t hea t b a l a n c e c a l c u l a t i o n s
c o n f i r m e d t h a t t h e hea t economy i s q u i t e e f f e c t i v e . No s u b s t a n t i a l d i s c r e p a n c i e s
were o b s e r v e d between t he p o t e n t i a l e f f e c t i v e n e s s o f t h e e n e r g y c o n v e r s i o n and
d i s t r i b u t i o n p r o c e s s e s and t he r e a l b e h a v i o u r o f t h e the rma l s y s t e m . From
a d e t a i l e d r e v i e w o f t he hea t r e c e i v e r s , h o w e v e r , a number o f p o s s i b l e smal l
improvements o f hea t u t i l i z a t i o n can be i d e n t i f i e d .
As r e g a r d s t he s u g a r h o u s e , i t was o b s e r v e d d u r i n g s e s s i o n 5 t h a t t h e v a p o u r
consumpt ion i n vacuum-pan s t e a m i n g - o u t changed w i t h o u t a p p a r e n t r e a s o n ; t h i s
i n d i c a t e s t h a t i f more a t t e n t i o n i s p a i d t o t he f u n c t i o n i n g o f t h e s teaming
equ ipmen t , t hen v a p o u r can be s a v e d . As some smal l s y r u p t a n k s a r e hea ted by
f i r s t - e f f e c t v a p o u r , a hea t s a v i n g can be o b t a i n e d u s i n g s e c o n d - e f f e c t v a p o u r
i n s t e a d . F u r t h e r m o r e , some o t h e r s y r u p t a n k s a r e d i r e c t l y hea ted by s e c o n d -
e f f e c t v a p o u r w i t h o u t any a r rangemen ts t o s e c u r e a u n i f o r m t e m p e r a t u r e
d i s t r i b u t i o n i n t h e s y r u p vo lume . T h i s i s a s s o c i a t e d w i t h a r i s k o f l o c a l l y
o v e r h e a t e d zones c a u s i n g e x c e s s i v e hea t c o n s u m p t i o n . T h i s s i t u a t i o n can be
improved e i t h e r by imp lement ing i n d i r e c t h e a t i n g , o r by i n s t a l l i n g m i x i n g
d e v i c e s i n d i r e c t l y hea ted t a n k s .
As r e g a r d s smal l e x h a u s t - s t e a m r e c e i v e r s , some o f them can a c t u a l l y be
s u p p l i e d w i t h f i r s t - o r s e c o n d - e f f e c t v a p o u r . I n t h e f i r s t p l a c e , t h i s a p p l i e s
t o o i l - t a n k h e a t i n g , as w e l l as t o h e a t i n g o f f a c t o r y b u i l d i n g s . The h e a t i n g
sys tem i n t h e o f f i c e b u i l d i n g can a l s o be s u p p l i e d w i t h s e c o n d - e f f e c t v a p o u r .
F i n a l l y , i t was o b s e r v e d t h a t t h e f l o w o f t h e m i x t u r e o f v a p o u r and
noncondensab les w i t h d r a w n f rom t h e e v a p o r a t o r by v e n t i n g c o u l d be r e d u c e d
w i t h o u t any a d v e r s e e f f e c t s i n t h e hea t t r a n s f e r i n t e n s i t y . The a s s o c i a t e d
e n e r g y - s a v i n g p o t e n t i a l can be u t i l i z e d , p r o v i d i n g t h e o p e r a t i n g p e r s o n n e l
o p e r a t e t he v e n t i n g sys tem more c a r e f u l l y .
The e s t i m a t e d e f f e c t s o f t h e improvements l i s t e d above were c a l c u l a t e d u s i n g
a computer p rogram f o r e v a p o r a t o r b a l a n c e c a l c u l a t i o n s . The r e s u l t s a r e l i s t e d
i n T a b l e 8 .11. O n l y i n t he case o f r e p l a c i n g e x h a u s t steam by v a p o u r s i n t h e
h e a t i n g o f c e r t a i n r e c e i v e r s , h o w e v e r , can t h e e s t i m a t e s be t r e a t e d as t h e
v a l u e s o f e x p e c t e d s a v i n g s . O t h e r e s t i m a t e s , o b t a i n e d on t h e " i f - t h e n " b a s i s ,
i n d i c a t e t h e o r d e r o f magn i tude b u t l e a v e a marg in o f u n c e r t a i n t y abou t t h e
322
TABLE 8.11
E s t i m a t e d h e a t i n g - s t e a m s a v i n g s r e s u l t i n g f rom v a r i o u s improvements o f t h e h e a t economy.
~ I 77. ~ E s t i m a t e d steam No. S p e c i f i c a t i o n 3 ^ ^ . ^ g
1 Reduc ing t he v a p o u r consumpt ion i n vacuum-pan s t e a m i n g - o u t by 15% 0, .06
2 R e p l a c i n g f i r s t - e f f e c t v a p o u r by s e c o n d - e f f e c t v a p o u r i n t h e h e a t i n g o f smal l s y r u p t a n k s 0 .02
3 Reduc ing t h e consumpt ion o f s e c o n d - e f f e c t v a p o u r i n t he d i r e c t h e a t i n g o f s y r u p t a n k s 0 .20
4 R e p l a c i n g e x h a u s t steam by f i r s t - and s e c o n d - e f f e c t v a p o u r i n t he h e a t i n g o f o i l t anks and f a c t o r y b u i l d i n g s 0 .28
5 R e p l a c i n g e x h a u s t steam by s e c o n d - e f f e c t v a p o u r i n t he h e a t i n g o f t h e o f f i c e b u i l d i n g 0, .06
6 Reduc ing t he f l o w o f v a p o u r - n o n c o n d e n s a b l e s m i x t u r e w i t h d r a w n f rom t h e e v a p o r a t o r by 25% 0, .10
a t t a i n a b l e v a l u e s o f t h e s a v i n g s . (Mos t n o t a b l y , t h i s a p p l i e s t o t h e vacuum-pan
s t e a m i n g - o u t and t o t he v e n t i n g o f n o n c o n d e n s a b l e s . I f r e d u c t i o n s o f t h e v a p o u r
f l o w s by 15% and 25%, r e s p e c t i v e l y , can be a t t a i n e d , t hen steam s a v i n g s o f
0.06 kg/100 kg b and 0.10 kg/100 kg b , r e s p e c t i v e l y , seem t o be w i t h i n r e a c h .
The assump t i ons on v a p o u r - f l o w r e d u c t i o n , h o w e v e r , can o n l y be p r o v e d by
p r a c t i c a l r e s u l t s . ) T h e r e f o r e , T a b l e 8.11 can o n l y be r e g a r d e d as a r e v i e w o f
p o s s i b l e r a t i o n a l i z a t i o n measures and t h e i r r e l a t i v e i m p o r t a n c e , bu t n o t t h e i r
a b s o l u t e e f f e c t s .
8.4 FACTORY FEATURING AN ADVANCED ENERGY SYSTEM
8.4.1 I n t r o d u c t o r y remarks
A l t h o u g h t h e p r e s e n t book i s assumed t o be c o n c e r n e d m a i n l y w i t h w h i t e - s u g a r
f a c t o r i e s , i t seems r e a s o n a b l e t o g i v e , i n t h i s S e c t i o n , a summary o f s t e p - b y -
s t e p improvements i n t r o d u c e d on an advanced e n e r g y sys tem i n a r a w - s u g a r
f a c t o r y . P u t t i n g a s i d e t h e p r o c e s s - s p e c i f i c a s p e c t s o f t h i s p a r t i c u l a r c a s e , i t
may be i n t e r e s t i n g t o see how much e n e r g y can be s a v e d , and how i m p o r t a n t t h e
power b a l a n c e becomes i n a modern f a c t o r y u t i l i z i n g e n e r g y v e r y e f f i c i e n t l y .
The i n f o r m a t i o n p r e s e n t e d be low i s e x t r a c t e d p a r t l y f rom p u b l i c a t i o n s ( r e f s .
18,19) and p a r t l y f rom the m a t e r i a l o b t a i n e d d i r e c t l y f rom P f e i f e r & L a n g e n
Company, C o l o g n e , FRG ( r e f . 1 9 , 2 0 ) .
The A p p e l d o r n f a c t o r y was e r e c t e d i n t he p e r i o d 1975-77. I t s main p r o d u c t i s
raw s u g a r d e s t i n e d f o r f u r t h e r p r o c e s s i n g i n a r e f i n e r y owned by t h e same
company.
The i n i t i a l p r o c e s s i n g c a p a b i l i t y was 4500 t / d . Howeve r , t h e equ ipment was
d imens ioned t o make i t p o s s i b l e t o i n c r e a s e t he p r o c e s s i n g c a p a b i l i t y w i t h o u t
f u r t h e r heavy i n v e s t m e n t . The l a y o u t o f t he p r o c e s s s t a t i o n s and t h e main
323
f a c t o r y b u i l d i n g were a l s o d e s i g n e d t o f a c i l i t a t e f u t u r e e x t e n s i o n s . F o l l o w i n g
t h e e v o l u t i o n o f f u e l and power p r i c e s i n FRG, advan tage was taken o f t h e s e
s p e c i a l f e a t u r e s o f t he A p p e l d o r n f a c t o r y , and a number o f improvements were
i n t r o d u c e d a im ing t o improve t h e o v e r a l l economic r e s u l t s a n d , i n p a r t i c u l a r , t o
r e d u c e t he e n e r g y c o s t s .
A t t h e i n i t i a l steam consumpt ion l e v e l o f abou t 27 kg/100 kg b, t h e f a c t o r y
c o u l d i n p r i n c i p l e be c o n s i d e r e d as r a t h e r e n e r g y - e f f i c i e n t . W i th c a r e f u l l y
d e s i g n e d p r o c e s s and therma l sys tem schemes as w e l l as modern equ ipment and
a u t o m a t i c c o n t r o l s , i t was p o s s i b l e t o p r e v e n t u n n e c e s s a r y e n e r g y was te and t o
keep t h e e n e r g y c o n v e r s i o n , d i s t r i b u t i o n and u t i l i z a t i o n p r o c e s s e s w e l l under
c o n t r o l . T h e r e f o r e , when d e s i g n i n g and imp lemen t ing t h e improvemen ts , a t t e n t i o n
was t u r n e d t o two g r o u p s o f r a t i o n a l i z a t i o n m e a s u r e s :
- r e d u c i n g t h e t o t a l e n e r g y demand o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s ;
- i m p r o v i n g t he c a p a b i l i t i e s o f t he e n e r g y s y s t e m .
8 .4 .2 E v o l u t i o n o f t h e s u g a r m a n u f a c t u r i n g p r o c e s s
The f a c t o r y i s e q u i p p e d w i t h a t o w e r e x t r a c t o r , c l a s s i c a l j u i c e p u r i f i c a t i o n
s t a t i o n , m u l t i p l e - s t a g e e v a p o r a t o r s t a t i o n and b a t c h - t y p e c r y s t a l l i z a t i o n
equ ipmen t . I n i t i a l l y , a j u i c e d r a f t abou t 125 kg/100 kg b was m a i n t a i n e d . The
e v a p o r a t o r s - f o u r R o b e r t - t y p e and two f a l l i n g - f i l m u n i t s , w i t h h e a t i n g s u r f a c e 2
a r e a s o f 2000 m each - were a r r a n g e d i n a q u i n t u p l e - e f f e c t s t a t i o n . A t a t h i n -
j u i c e c o n c e n t r a t i o n abou t 14% DS, a t h i c k - j u i c e c o n c e n t r a t i o n o f 66% DS was
m a i n t a i n e d .
The i n i t i a l v e r s i o n o f t h e s u g a r house was based on a s i n g l e - b o i l i n g
c r y s t a l l i z a t i o n p r o c e s s , w i t h raw s u g a r and s y r u p as t h e f i n a l p r o d u c t s . I n
o r d e r t o p roduce mo lasses needed i n t h e p u l p - d r y i n g p l a n t , a l o w - g r a d e p r o d u c t
s t a g e was added t o t h e c r y s t a l l i z a t i o n scheme. I n 1978, t h e c a p a c i t y o f t he l o w -
g rade s t a t i o n was s u f f i c i e n t t o p r o c e s s abou t h a l f o f t h e s y r u p f l o w . A t 66% DS
t h i c k - j u i c e c o n c e n t r a t i o n , t h e t h e o r e t i c a l w a t e r e v a p o r a t i o n i n t h e s u g a r house
was 8.7 kg/100 kg b.
F o l l o w i n g a d j u s t m e n t s o f t h e f a c t o r y e q u i p m e n t , t h e p r o c e s s i n g c a p a b i l i t y
a t t a i n e d 5000 t / d a l r e a d y i n 1979. I n o r d e r t o r e d u c e t he e n e r g y demand, t h e
w a t e r i n t a k e t o t h e p r o c e s s was r e d u c e d by g r a d u a l l y d e c r e a s i n g t h e j u i c e d r a f t
t o 117%. I n 1981, t h e e v a p o r a t i o n p r o c e s s was m o d i f i e d by a t t a c h i n g a v a p o u r
compress i on c i r c u i t t o t h e e v a p o r a t o r s t a t i o n and r e a r r a n g i n g v a p o u r and
condensa te d i s t r i b u t i o n t o t h e hea t r e c e i v e r s . As t h i s made i t p o s s i b l e t o
i n c r e a s e t h i c k - j u i c e c o n c e n t r a t i o n t o 68% DS, t h e hea t demand o f t h e s u g a r house
was r e d u c e d . Howeve r , a Q u e n t i n s t a t i o n was i n s t a l l e d i n t h e s u g a r house and t h e
c a p a c i t y o f t he l o w - g r a d e s t a t i o n was e x t e n d e d t o p r o c e s s t h e e n t i r e s y r u p f l o w ,
t h i s i n c r e a s i n g t h e hea t demand.
324
I n 1986, t he p r o c e s s i n g c a p a b i l i t y was r a i s e d t o 6200 t / d . Owing t o e x t e n s i o n
o f t h e e x t r a c t o r ( t h e a v e r a g e e x t r a c t i o n t ime was changed f rom 87 t o 120 m i n ) ,
t he j u i c e d r a f t a t t a i n e d a v e r y low v a l u e o f 109%. A new f a l l i n g - f i l m u n i t w i t h 2
a h e a t i n g s u r f a c e a r e a o f 2500 m was i n s t a l l e d as t h e f i f t h e v a p o r a t o r e f f e c t ,
and t h e t h i c k - j u i c e c o n c e n t r a t i o n was i n c r e a s e d t o 72-73% DS. Even t hough t h e
c r y s t a l l i z a t i o n scheme was t r a n s f o r m e d t o i n c o r p o r a t e " t w o - a n d - a - h a l f - b o i l i n g "
( r aw s u g a r s I and I I , and a l o w - g r a d e p r o d u c t ) , h i g h t h i c k - j u i c e c o n c e n t r a t i o n
and t he i n t r o d u c t i o n o f c r y s t a l f o o t i n g r e s u l t e d i n t h e t h e o r e t i c a l w a t e r
e v a p o r a t i o n i n t h e s u g a r house be ing r e d u c e d t o 8.2 kg/100 kg b.
8 .4 .3 E v o l u t i o n o f t h e therma l sys tem
The 1978 v e r s i o n o f t h e therma l sys tem i s shown s c h e m a t i c a l l y i n F i g . 8 .13 ,
t o g e t h e r w i t h t he da ta on mass and hea t b a l a n c e s . The e v a p o r a t o r consumed
26.8 kg steam pe r 100 kg b. Owing t o a r a t h e r low hea t demand o f t he s u g a r
h o u s e , i t was i m p o s s i b l e t o u t i l i z e t he e n t i r e amount o f v a p o u r s , and a
r e l a t i v e l y l a r g e f l o w o f l a s t - e f f e c t v a p o u r t o the c o n d e n s e r had t o be a c c e p t e d .
The condensa te e n e r g y was n o t f u l l y u t i l i z e d . I n t h e power h o u s e , one t u r b o
g e n e r a t o r d r i v e n by a b a c k - p r e s s u r e t u r b i n e s u p p l i e d w i t h l i v e steam a t 58 bar
and 500°C was enough t o c o v e r t he power demand o f t h e f a c t o r y . Howeve r , a p a r t
o f t h e h e a t i n g - s t e a m f l o w had t o be s u p p l i e d v i a t h e t h r o t t l i n g - d e s u p e r h e a t i n g
s t a t i o n .
F o l l o w i n g t he e x t e n s i o n s o f t he f a c t o r y and t he r e s u l t i n g i n c r e a s e i n power
demand, a second t u r b o - g e n e r a t o r was i n s t a l l e d i n t he power h o u s e . A t h e o r e t i c a l
p o s s i b i l i t y a r o s e t o s e l l t h e power s u r p l u s t o t h e e x t e r n a l g r i d ; h o w e v e r , t h e
f a c t o r y was o f f e r e d a power p r i c e w h i c h t u r n e d o u t t o be t o o low t o c o v e r t h e
c o s t . T h i s s t i m u l a t e d a t h o r o u g h a n a l y s i s and r e - o r i e n t a t i o n o f t h e e n e r g y
p o l i c y t owa rds f a r - r e a c h i n g power and hea t s a v i n g s .
I t was d e c i d e d t o m o d i f y t h e the rma l sys tem by i n t r o d u c i n g t he c o m p r e s s i o n o f
f i r s t - e f f e c t v a p o u r i n an e l e c t r i c a l l y - d r i v e n mechan ica l c o m p r e s s o r . I n o r d e r t o
change t h e mass and h e a t b a l a n c e s o f t h e e v a p o r a t o r , r a w - j u i c e h e a t i n g w i t h
vacuum-pan v a p o u r s and p r e - 1 i m e d - j u i c e h e a t i n g w i t h condensa te were imp lemen ted .
T h i s made i t p o s s i b l e t o r e c i r c u l a t e 27.3 kg f i r s t - e f f e c t v a p o u r p e r 100 kg b e e t
i n t he v a p o u r - c o m p r e s s i o n c i r c u i t , and t o d e c r e a s e t h e h e a t i n g - s t e a m consumpt i on
i n t h e e v a p o r a t o r t o 23.6 kg/100 kg b. The 1981 v e r s i o n o f t h e the rma l sys tem i s
shown s c h e m a t i c a l l y i n F i g . 8 .14 .
Among t h e m o d i f i c a t i o n s i n t r o d u c e d a f t e r 1981, e x t e n s i o n o f t he e v a p o r a t o r
s t a t i o n p l a y e d t he main r o l e . F o l l o w i n g t he i n s t a l l a t i o n o f a f a l l i n g - f i l m 2
e v a p o r a t o r w i t h a h e a t i n g s u r f a c e a r e a o f 2500 m i n t h e l a s t e f f e c t , t h e t o t a l 2
h e a t i n g s u r f a c e a r e a o f t h e e v a p o r a t o r r e a c h e d 14500 m . T h i s made i t p o s s i b l e
t o m a i n t a i n 73% DS t h i c k - j u i c e c o n c e n t r a t i o n a t r e d u c e d t e m p e r a t u r e d i f f e r e n c e s
i n t h e i n d i v i d u a l e f f e c t s . I t t h u s became p o s s i b l e t o d e c r e a s e t he t e m p e r a t u r e
325
Fig.
8
.14
. S
imp
lifi
ed
sche
me
of
the
ther
mal
sy
stem
of
the
App
eldo
rn
fact
ory
, 19
81
vers
ion
(aft
er
ref.
18
).
Fig.
8
.13
. S
imp
lifi
ed
sche
me
of
the
ther
mal
sy
stem
of
the
App
eldo
rn
fact
ory
, 19
78 v
ersi
on
(aft
er
ref.
18
).
Stea
m a
nd
vapo
ur
flow
s ar
e gi
ven
in
kg/lO
O
kg b
.
326
Fig.
8.
16.
Sim
pli
fied
sch
eme
of t
he
ther
mal
sy
stem
of
the
App
eldo
rn
fact
ory
, 19
86 v
ersi
on
(aft
er
ref.
18).
Fig. 8.15.
Scheme o
f the
util
izat
ion
of c
ondensate
in t
he A
ppel
dorn f
actory (after
ref. 18).
327
(and t h e c o r r e s p o n d i n g s a t u r a t i o n p r e s s u r e ) o f t h e h e a t i n g s team, t h i s r e s u l t i n g
i n an i n c r e a s e d i s e n t r o p i c e n t h a l p y d r o p i n t h e t u r b i n e and an i n c r e a s e o f t h e
power g e n e r a t e d . Owing t o l o w e r j u i c e t e m p e r a t u r e s i n t h e i n d i v i d u a l e v a p o r a t o r
e f f e c t s , s u c r o s e decay was a l s o r e d u c e d , w i t h a c o n s i d e r a b l e r e d u c t i o n o f t h i c k -
j u i c e c o l o u r as a r e s u l t ( r e f . 1 7 , 1 8 ) .
V e r y i n t e n s i v e u t i l i z a t i o n o f t h e c o n d e n s a t e e n e r g y was a l s o implemented
( F i g . 8 . 1 5 ) . I n a s e r i e s o f hea t e x c h a n g e r s c o n n e c t e d t o t h e room h e a t i n g
s y s t e m , 1 i m e d - j u i c e and r a w - j u i c e h e a t i n g , f u e l - o i l h e a t i n g and w a s t e - w a t e r
t r e a t m e n t s y s t e m , t he t e m p e r a t u r e o f t he c o n d e n s a t e f a l l s f rom i t s i n i t i a l
v a l u e o f 92°C t o as low as 37°C. I n a d d i t i o n , depend ing on t h e t e m p e r a t u r e
l e v e l , p a r t s o f t he condensa te s t ream a re u t i l i z e d a s :
- wash w a t e r i n t h e c e n t r i f u g a l s ;
- s w e e t e n i n g - o f f w a t e r i n t he s l u d g e p r e s s e s ;
- f r e s h w a t e r i n t h e e x t r a c t o r .
The scheme o f t h e thermal s y s t e m , w i t h t h e da ta on mass and hea t b a l a n c e s
c h a r a c t e r i s t i c o f t he 1986 s e a s o n , a r e shown i n F i g . 8 .16 . As can be s e e n , t h e
h e a t i n g - s t e a m consumpt ion i n t h e e v a p o r a t o r was r e d u c e d t o 18.5 kg/100 kg b.
8 .4 .4 E v o l u t i o n o f t h e power b a l a n c e
When d e s i g n i n g t h e A p p e l d o r n s u g a r f a c t o r y , much e f f o r t was s p e n t on e n s u r i n g
a low power demand. F o r examp le , j u i c e pumps i n t h e e x t r a c t i o n and j u i c e
p u r i f i c a t i o n s t a t i o n s were e q u i p p e d w i t h t h y r i s t o r - c o n t r o l l e d d . c . d r i v e s ,
making i t p o s s i b l e t o a p p l y v a r i a b l e speed c o n t r o l . As a r e s u l t , power
consumpt ion as low as 2.54 kWh/100 kg b was a c h i e v e d i n t h e f i r s t s e a s o n .
The i n s t a l l a t i o n o f an e l e c t r i c a l l y - d r i v e n v a p o u r compresso r caused t h e power
demand o f t h e f a c t o r y t o i n c r e a s e by 13%. I n o r d e r t o r e s t o r e t h e r e l a t i o n
between power g e n e r a t e d and power consumed, a number o f r a t i o n a l i z a t i o n measures
were t a k e n :
- an e x t e n s i o n o f t he p r o c e s s i n g c a p a b i l i t y o f t h e f a c t o r y t ook p l a c e w i t h o u t
any e x t e n s i o n o f t h e b e e t s t o r a g e y a r d s ;
- t he e x i s t i n g w a s t e - w a t e r t r e a t m e n t p l a n t was r e p l a c e d by an a n a e r o b i c p l a n t
c h a r a c t e r i z e d by a l o w e r e n e r g y demand;
- o n l y a p a r t o f t he p r e s s e d p u l p was d i r e c t e d t o t he d r y i n g p l a n t (50% i n 1986) .
A r e v i e w was a l s o u n d e r t a k e n o f t h e e l e c t r i c d r i v e s and e l e c t r i c a l l y - d r i v e n
machines i n t h e e n t i r e f a c t o r y . F o r examp le , a l l t he t r o u g h c o n v e y o r s were
i n v e s t i g a t e d t o i d e n t i f y t h o s e t h a t c o u l d be r e p l a c e d by more e n e r g y - e f f i c i e n t
b e l t c o n v e y o r s . Howeve r , p a r t i c u l a r a t t e n t i o n was p a i d t o t h e f l o w m a c h i n e r y
and t h e p o s s i b i l i t i e s o f r e p l a c i n g t h r o t t l i n g c o n t r o l by v a r i a b l e speed c o n t r o l ,
o r i n t r o d u c i n g i n t e r m i t t e n t i n s t e a d o f c o n t i n u o u s o p e r a t i o n . T a k i n g advan tage o f
f a l l i n g p r i c e s o f f r e q u e n c y - c o n t r o l l e d a . c . d r i v e s , v a r i a b l e - s p e e d d r i v e s were
implemented i n b e e t pumps and k i l n - g a s c o m p r e s s o r s , as w e l l as i n p u l p p r e s s e s .
328
TABL
E 8.
12
Powe
r co
nsum
ed a
nd p
ower
su
pplie
d to
th
e A
ppel
dorn
su
gar
fact
ory
, in
kW
h/10
0 kg
b
(aft
er
ref.
18).
1977
19
78
1979
19
80
1981
19
82
1983
19
84
1985
19
86
Bee
t st
orag
e ya
rds
0.27
2 0.
261
0.27
6 0.
294
0.26
4 0.
290
0.23
3 0.
164
0.14
0 0.
160
Bee
t ho
use
0.87
0 0.
860
0.85
6 0.
843
1.01
8 0.
980
0.96
3 0.
945
0.92
2 0.
830
Suga
r ho
use
0.61
4 0.
610
0.61
2 0.
633
0.60
9 0.
584
0.55
4 0.
642
0.63
0 0.
670
Pul
p-dr
ying
p
lan
t 0.
338
0.33
4 0.
350
0.34
3 0.
330
0.33
4 0.
271
0.26
0 0.
210
0.28
0 Po
wer
hous
e 0.
155
0.15
7 0.
160
0.15
4 0.
142
0.15
4 0.
159
0.15
8 0.
160
0.17
3 W
ater
ci
rcu
its
and
com
pres
sed-
air
supp
ly
0.15
5 0.
157
0.17
6 0.
156
0.16
2 0.
149
0.16
0 0.
157
0.13
0 0.
140
Was
te-w
ater
tre
atm
ent
0.13
3 0.
201
0.22
8 0.
260
0.25
1 0.
263
0.17
8 0.
200
0.11
0 0.
110
Vapo
ur
com
pres
sor
0.39
0 0.
410
0.38
0 0.
290
0.24
0 0.
330
Powe
r ge
nera
ted
2.47
3 2.
506
2.61
2 2.
642
3.02
2 3.
012
2.75
2 2.
640
2.41
4 2.
534
Powe
r pu
rcha
sed
0.06
4 0.
074
0.04
6 0.
041
0.14
4 0.
152
0.14
6 0.
176
0.12
8 0.
159
Tota
l po
wer
su
pplie
d 2.
537
2.58
0 2.
658
2.68
3 3.
166
3.16
4 2.
898
2.81
6 2.
542
2.69
3
TABL
E 8.
13
Powe
r co
nsum
ed a
nd p
ower
su
pplie
d to
th
e A
ppel
dorn
su
gar
fact
ory
, in
kW
h/t
suga
r (a
fter
re
f. 18
).
1977
19
78
1979
19
80
1981
19
82
1983
19
84
1985
19
86"
Bee
t st
orag
e ya
rds
20.8
9 18
.63
19.2
8 21
.73
18.8
0 20
.94
16.5
4 11
.63
9.49
10
.70
Bee
t ho
use
66.7
9 61
.49
59.8
4 62
.23
73.3
4 71
.94
69.8
8 67
.76
65.4
8 53
.30
Suga
r ho
use
47.1
4 43
.62
42.8
0 46
.71
43.3
0 42
.16
39.4
7 45
.57
43.7
0 42
.90
Pulp
-dry
ing
pla
nt
25.9
4 23
.85
24.4
7 25
.34
23.4
8 24
.08
19.3
1 18
.30
14.8
1 18
.20
Powe
r ho
use
11.9
0 11
.19
11.2
0 11
.41
10.0
7 11
.10
11.3
0 11
.24
10.9
4 11
.20
Wat
er
circ
uit
s an
d co
mpr
esse
d-ai
r su
pply
11
.90
11.1
9 12
.07
11.5
2 11
.49
10.7
6 11
.40
11.1
5 9.
27
8.80
W
aste
-wat
er
trea
tmen
t 10
.18
14.1
7 15
.95
19.2
1 17
.52
19.0
3 12
.70
14.2
5 7.
70
8.70
Va
pour
co
mpr
esso
r 26
.60
28.4
0 25
.80
19.8
0 16
.20
20.5
0 Po
wer
ge
nera
ted
189.
82
179.
12
182.
42
195.
14
214.
39
217.
42
195.
96
187.
30
168.
65
164.
00
Powe
r pu
rcha
sed
4.92
5.
32
3.19
3.
01
10.2
1 10
.99
10.4
4 12
.40
8.94
10
.30
Tota
l po
wer
su
pplie
d 19
4.74
18
4.44
18
5.61
19
8.15
22
4.60
22
8.41
20
6.40
19
9.70
17
7.59
17
4.30
329
As a r e s u l t , t h e t o t a l i n s t a l l e d power o f t h e d . c . d r i v e s r e a c h e d a l e v e l o f
3200 kW, and t h a t o f t he f r e q u e n c y - c o n t r o l l e d a . c . d r i v e s 1900 kW, w i t h t h e
v a r i a b l e speed d r i v e s d o m i n a t i n g i n t h e b e e t house and i n t h e s u g a r h o u s e . As
r e g a r d s t h e equ ipment i n s t a l l e d i n t he power house and i n t h e p u l p - d r y i n g
p l a n t , i t t u r n e d o u t t h a t t h e p o t e n t i a l e n e r g y s a v i n g s a r e t o o smal l t o j u s t i f y
t he i n v e s t m e n t c o s t s o f v a r i a b l e - s p e e d d r i v e s t h e r e .
The e v o l u t i o n o f t h e power consumpt ion i n s e v e n s e c t i o n s o f t h e f a c t o r y (and
t he v a p o u r c o m p r e s s o r ) i s i l l u s t r a t e d i n T a b l e s 8.12 and 8 .13 . As can be s e e n ,
t h e power consumpt ion o f t he v a p o u r compresso r has been o f f - s e t by t h e power
s a v i n g s a t t a i n e d i n t he b e e t s t o r a g e y a r d s , b e e t h o u s e , p u l p - d r y i n g p l a n t , w a t e r
s u p p l y sys tem and w a s t e - w a t e r t r e a t m e n t p l a n t . I t i s a l s o i n t e r e s t i n g t o see
t h a t i n t he s u g a r h o u s e , w h i l e t he power consumpt ion p e r 100 kg b e e t has
i n c r e a s e d due t o t he e x t e n s i o n s o f t he c r y s t a l l i z a t i o n scheme, a r e d u c t i o n o f
t he power consumpt ion p e r 1 t s u g a r was a c h i e v e d .
I n T a b l e s 8.12 and 8 . 1 3 , d a t a a r e a l s o g i v e n on t h e power s u p p l i e d t o t h e
f a c t o r y . I t can be c o n c l u d e d f rom t h e s t e e p i n c r e a s e s o f power g e n e r a t e d and
p u r c h a s e d w h i c h took p l a c e i n 1981 t h a t t h e hea t s a v i n g men t ioned i n t he
p r e c e d i n g S e c t i o n was a t t a i n e d a t t h e expense o f i n c r e a s e d power c o n s u m p t i o n .
I t can a l s o be seen t h a t t he measures t aken t o a d j u s t t h e power g e n e r a t i o n t o
chang ing power demand were q u i t e e f f e c t i v e , as a t p r e s e n t , t h e power p u r c h a s e d
does n o t e x c e e d 5-6% o f t he t o t a l power s u p p l i e d .
REFERENCES
1 L. S z y d l o , W. Lekawski and K. U r b a n i e c , M o d e r n i z a c j a g o s p o d a r k i c i e p l n e j Cukrown i K l e c i n a , G a z . C u k r o w . , 9 3 ( 7 - 8 ) (1985) 134.
2 N .K . P o l i s h c h u k , I s p o l z o v a n i e e n e r g o r e s u r s o v na E rken -Shakharskom sakharnom z a v o d e , Sakh . P r o m . , ( 6 ) (1986) 39-40.
3 K. U r b a n i e c , Ocena p r a k t y c z n y c h m o z l i w o s c i o s z c z e d z a n i a p a l i w a w g o s p o d a r c e e n e r g e t y c z n e j c u k r o w n i , G a z . C u k r o w . , 8 9 ( 4 ) (1981) 80-81.
4 Y u . D . G o l o v n y a k and L . G . B e l o s t o t s k i i , S h i r o k o v n e d r y a t nauchnye r a z r a b o t k i d l y a s n i z h e n i y a raskhoda t o p l i v a , Sakh . P r o m . , ( 8 ) (1981) 21-24.
5 K. U r b a n i e c , R a c j o n a l i z a c j a g o s p o d a r k i c i e p l n e j w c u k r o w n i a c h , G a z . C u k r o w . , 92 (2 ) (1984) 27-28.
6 C . H . I v e r s o n , W i t h e r g o e s t t h o u , oh BTU ? , Sugar J . , 45 (11) (1983) 17-22. 7 J . B o z e c , E v o l u t i o n de l a consommation t h e r m i q u e dans 1 ' i n d u s t r i e s u c r i e r e ,
I n d . A l i m . A g r i e , 100(7 -8 ) (1983) 477-480. 8 Anonymous, E n e r g y p rogram a t I m p e r i a l S u g a r , Sugar J . , 4 7 ( 1 ) (1984) 20. 9 B. K a r r e n , E x p e r i e n c e o f e n e r g y s a v i n g i n t he Canad ian s u g a r i n d u s t r y , i n :
F . O . L i c h t s Gu ide t o t h e Sugar F a c t o r y Mach ine I n d u s t r y , F . O . L i c h t GmbH, R a t z e b u r g , 1984, p p . A75-A88.
10 L . L . N e v i l l e , H o l l y Sugar C o r p o r a t i o n ' s c a p i t a l improvement p r o g r a m , Sugar y A z ú c a r , 80 (2 ) (1985) 49 ,52 .
11 G . K o w a l s k a , Po rzadkowan ie g o s p o d a r k i c i e p l n e j na p r z y k l a d z i e cuk rown i w i e l k o p o l s k i c h , G a z . C u k r o w . , 94 (4 ) (1986) 52-53.
12 W. L e k a w s k i , M o d e r n i z a c j a G o s p o d a r k i C i e p l n e j C u k r o w n i , S T C , Warszawa, 1986. 13 E . V . M l o d z y a n o w s k i i , V . S . B e r e z y u k and K . N . S a v c h u k , Ekonomnoe i s p o l z o v a n y e
e n e r g o r e s u r s o v , Sakh . P r o m . , ( 7 ) (1981) 22-27 . 14 E. Krupka and J . S z a d k o w s k i , Gospodarka c i e p l n a w Cukrown i G o s l a w i c e ,
G a z . C u k r o w . , 89 (1 ) (1981) 2 -5 .
330
15 A . I . Khomenko, Ekonomya t o p i i v n o - e n e r g e t i c h e s k i k h r e s u r s o v - i t o g i i z a d a c h i , Sakh . P r o m . , (2) (1983) 35-39.
16 L . P . I g n a t e v ( e t a l . ) , O p y t r a b o t y po s n i z h e n i y u raskhoda t o p i i v n o -e n e r g e t i c h e s k i k h r e s u r s o v na A l e k s a n d r i i s k o m sakharnom z a v o d e , Sakh . P r o m . , (10) (1985) 32-34.
17 G. F e l t b o r g , p e r s o n a l commun ica t i on . 18 H. W e i d n e r , D i e B rüdenkompress ion i n e i n e r R o h z u c k e r f a b r i k , Z u c k e r i n d . ,
108(8) (1983) 736-742. 19 υ . C u r d t s , E i n Weg z u r V e r b e s s e r u n g d e r W ä r m e w i r t s c h a f t e i n e r R o h z u c k e r
f a b r i k - am B e i s p i e l d e r Z u c k e r f a b r i k A p p e l d o r n , Paper p r e s e n t e d a t t h e I n t e r n a t i o n a l C o n f e r e n c e " Improvement o f Bee t Sugar P r o d u c t i o n " , Warszawa, May 1987.
20 A . Co l sman , p e r s o n a l commun ica t i on .
331
C h a p t e r 9
DESIGN OF MODERNIZED OR NEW ENERGY SYSTEMS
9.1 THE MODERNIZATION OF ENERGY SYSTEMS
C o n t r a r y t o the s t e p - b y - s t e p a p p r o a c h c o n s i d e r e d i n t h e p r e c e d i n g C h a p t e r ,
m o d e r n i z a t i o n o f a s u g a r f a c t o r y i n v o l v e s e x t e n s i v e changes t h a t a r e i n t r o d u c e d
e i t h e r a l l a t once o r i n a few s t e p s pe r f o rmed d u r i n g c o n s e c u t i v e o f f - s e a s o n
p e r i o d s . T y p i c a l l y , t h i s i s a s e r i o u s and c o s t l y u n d e r t a k i n g , v e r y se ldom aimed
s o l e l y a t e n e r g y s a v i n g s . Most o f t e n t h e r e a r e s e v e r a l t e c h n o l o g i c a l o b j e c t i v e s ,
among w h i c h an e x t e n s i o n o f t h e p r o c e s s i n g c a p a b i l i t y has a l e a d i n g r o l e and
the o t h e r s s e r v e the pu rpose o f c u t t i n g down m a n u f a c t u r i n g c o s t s . As t h e
u n d e r t a k i n g has t o be comp le ted w i t h i n a d e f i n i t e c o s t / t i m e f r amework , i t may be
d i f f i c u l t t o a r r i v e a t an i n i t i a l p rob lem f o r m u l a t i o n , and even more so t o f i n d
t he s o u g h t - a f t e r s o l u t i o n . T h e r e f o r e , m o d e r n i z a t i o n u s u a l l y r e q u i r e s t he
e x p e r t i s e o f s p e c i a l i z e d e n g i n e e r i n g compan ies .
P u b l i c a t i o n s r e l a t e d t o t h e m e t h o d o l o g i c a l p rob lems o f m o d e r n i z a t i o n o f s u g a r
f a c t o r i e s a r e r a t h e r s c a r c e , as t h i s s u b j e c t i s r e g a r d e d as a p a r t o f t h e know-
how o f t h e companies i n v o l v e d . A book and a few a r t i c l e s can be f ound r e v i e w i n g
t h e g e n e r a l d e s i g n p r o c e d u r e s , as w e l l as t h e s p e c i a l i z e d q u e s t i o n s o f e n e r g y
economy improvements ( r e f s . 1 - 3 ) .
The i n v e s t i g a t i o n o f m o d e r n i z a t i o n r e q u i r e m e n t s b e g i n s w i t h d r a w i n g up an
i n v e n t o r y o f e x i s t i n g f a c t o r y s u b s y s t e m s . The number o f subsys tems t y p i c a l l y
d e f i n e d i s 25-30. F o r e v e r y s u b s y s t e m , c r u c i a l d a t a on p r o c e s s a p p a r a t u s and
machines a r e r e g i s t e r e d , as w e l l as on a s s o c i a t e d e l e c t r i c a l e q u i p m e n t , c o n t r o l
c i r c u i t r y and measur ing i n s t r u m e n t s . D raw ings a r e s i m u l t a n e o u s l y p r e p a r e d o f
e s s e n t i a l f a c t o r y b u i l d i n g s , t o g e t h e r w i t h a s i t e p l a n . The i n f o r m a t i o n t h u s
a c q u i r e d makes i t p o s s i b l e t o e v a l u a t e t h e f a c t o r y ' s t e c h n o l o g i c a l base and t h e
s t a t e o f t h e b u i l d i n g s .
The n e x t s t e p u s u a l l y c o n s i s t s o f d i s c u s s i n g t h e da ta w h i c h a r e p a r t i c u l a r l y
i m p o r t a n t t o d e t e r m i n a t i o n o f t h e o b j e c t i v e s and i d e n t i f i c a t i o n o f t h e c o s t - and
t i m e - r e l a t e d c o n s t r a i n t s o f t h e m o d e r n i z a t i o n . The da ta o f c r u c i a l i m p o r t a n c e
a r e as f o l l o w s :
- b e e t p o l a r i z a t i o n ;
- s u g a r l o s s e s i n t h e m a n u f a c t u r i n g p r o c e s s , i n c l u d i n g t h e i r d i s t r i b u t i o n
between e x t r a c t i o n , c a r b o n a t a t i o n s l u d g e , mo lasses and u n d e f i n e d l o s s ;
- p u r i t i e s o f raw j u i c e , t h i c k j u i c e and m o l a s s e s ;
- t he main f e a t u r e s o f t h e j u i c e p u r i f i c a t i o n scheme, i n c l u d i n g t e m p e r a t u r e s o f
e s s e n t i a l p r o c e s s s t e p s ;
- CaO r a t e s and main f e a t u r e s o f t h e l i m e - s l a k i n g p r o c e s s ;
332
- t he main f e a t u r e s o f t he p u l p - p r e s s i n g and p u l p - d r y i n g p r o c e s s e s ;
- t he main f e a t u r e s o f t he s u g a r c r y s t a l l i z a t i o n scheme and s u g a r b o i l i n g
p r o c e s s ;
- au toma t i on r e q u i r e m e n t s ;
- e n v i r o n m e n t a l p r o t e c t i o n r e q u i r e m e n t s ;
- the f u e l t y p e and the e x p e c t e d l e v e l o f f u e l demand i n t h e power house and i n
the p u l p - d r y i n g p l a n t ;
- power consumpt ion r e q u i r e m e n t s .
Hav ing a c q u i r e d n e c e s s a r y knowledge o f t h e c o n d i t i o n o f t h e f a c t o r y and t he
p r i o r i t i e s o f t he m o d e r n i z a t i o n o b j e c t i v e s , t he d e s i g n e n g i n e e r s s h o u l d be a b l e
t o c a l c u l a t e and p r e p a r e s k e t c h e s o f r e c o n s t r u c t i o n p r o p o s a l s f o r t h e most
i m p o r t a n t f a c t o r y s e c t i o n s . Depending on s p e c i f i c c o n d i t i o n s , t he f o l l o w i n g
m a t e r i a l may be r e q u i r e d :
- scheme o f b e e t r e c e p t i o n , u n l o a d i n g , t r a n s p o r t and s t o r a g e ;
- mass b a l a n c e s o f e x t r a c t i o n , j u i c e p u r i f i c a t i o n , e v a p o r a t i o n and s u g a r
c r y s t a l l i z a t i o n ;
- h e a t b a l a n c e o f t he therma l s y s t e m ;
- h e a t b a l a n c e o f t he p u l p - d r y i n g p l a n t ;
- v e r i f i c a t i o n o f r a t i n g o f t h e e x i s t i n g equ ipment and recommendat ions on t he
s e l e c t i o n o f new equ ipment u n i t s ;
- e n e r g y ( h e a t and power ) b a l a n c e o f t h e power h o u s e .
C o m p l e t i o n o f t h i s s t e p makes i t p o s s i b l e t o d e t e r m i n e t h e scope o f
equ ipment p u r c h a s e s and c o n s t r u c t i o n w o r k , as w e l l as t o p l a n d i s m a n t l i n g o f
t he e x i s t i n g e q u i p m e n t , c o n s t r u c t i o n w o r k , a s s e m b l i n g o f new equ ipment and
p i p i n g , i n s t a l l a t i o n o f e l e c t r i c a l equ ipment and c o n t r o l c i r c u i t r y , e t c .
The s o l u t i o n s a r e u s u a l l y p r e p a r e d i n a number o f v e r s i o n s and d e s c r i b e d i n a
r e p o r t on p o s s i b l e and recommended c o u r s e s o f a c t i o n , c o s t p r o j e c t i o n s and
p r e l i m i n a r y t i m e - s c h e d u l e s . T h i s c o n s t i t u t e s a b a s i s f o r d e c i s i o n - m a k i n g on
d e t a i l e d m o d e r n i z a t i o n d e s i g n s .
The d e c i s i o n s t e p d e s e r v e s most a t t e n t i o n as i t d e t e r m i n e s , t o a g r e a t
e x t e n t , the economic r e s u l t s o f t h e e n t i r e u n d e r t a k i n g . The c o s t s t r u c t u r e o f
a t y p i c a l m o d e r n i z a t i o n case i s c h a r a c t e r i z e d by a p p r o x i m a t e l y equa l
c o n t r i b u t i o n s o f t he f o l l o w i n g c o s t componen ts :
- t he c o s t o f t he c o n s t r u c t i o n w o r k ;
- t he c o s t o f p u r c h a s i n g and a s s e m b l i n g t he main e q u i p m e n t ;
- t he c o s t o f p i p i n g , e l e c t r i c a l e q u i p m e n t , c o n t r o l and i n s t r u m e n t a t i o n
c i r c u i t r y , e n g i n e e r i n g s e r v i c e s , e t c .
P r i o r t o making t h e d e c i s i o n s , one can a l s o c o n s i d e r t h e m o d e r n i z a t i o n c o s t s as
a sum o f two componen ts :
( i ) t he c o s t o f t h e i n c r e a s e o f p r o c e s s i n g c a p a b i l i t y ;
333
( i i ) the c o s t o f t he o p t i m i z a t i o n o f d e t a i l e d s o l u t i o n s .
I t can be e s t i m a t e d t h a t component ( i i ) i s t y p i c a l l y o f t he o r d e r o f 15-20% o f
t he t o t a l c o s t . By o p t i m i z i n g t he s o l u t i o n s , h o w e v e r , one may i n f l u e n c e t h e
economic r e s u l t s o f t he m o d e r n i z a t i o n t o a d e g r e e comparab le w i t h t h a t
a s s o c i a t e d w i t h t he p r o c e s s i n g - c a p a b i l i t y i n c r e a s e . A c t u a l l y , t h i s i s where t h e
impo r t ance o f improvements o f t h e e n e r g y economy l i e s . I t i s n o t unusua l t h a t
t h e s e improvements a r e d e c i s i v e i n o p t i m i z i n g t h e m o d e r n i z a t i o n s o l u t i o n s .
O p t i m i z a t i o n o f t h e e n e r g y economy o f a m o d e r n i z e d s u g a r f a c t o r y i s a
d e c i s i o n p rob lem unde r many c o n s t r a i n t s . W i t h i n t h e f i e l d o f f e a s i b l e s o l u t i o n s ,
each e n e r g y - s a v i n g t e c h n i q u e o f t h o s e c o n s i d e r e d i n C h a p t e r s 3 t o 7 and
s y s t e m a t i z e d i n S e c t i o n 8.1 can be c o n s i d e r e d f o r a p p l i c a t i o n . The s e t o f
t e c h n i q u e s s a t i s f y i n g t he c o n s t r a i n t s and p r o m i s i n g t h e b e s t economic r e s u l t s
c o n s t i t u t e s t h e d e s i r e d s o l u t i o n ( s e e a l s o S e c t i o n 9 . 4 ) .
I t can be c o n c l u d e d f rom t h e above i n t r o d u c t i o n t h a t i t i s d i f f i c u l t t o
r e p o r t a m o d e r n i z a t i o n example i n g r e a t d e t a i l . As a r u l e , t h e p r e s e n t a t i o n s
p u b l i s h e d a r e v e r y c o n c i s e and f e w , i f a n y , t e c h n i c a l d e t a i l s a r e g i v e n
( r e f s . 4 - 7 ) . T r y i n g t o change t h i s s i t u a t i o n a l i t t l e w i t h o u t e x c e e d i n g t h e
space a v a i l a b l e i n t h e p r e s e n t b o o k , summaries a r e p r e s e n t e d i n S e c t i o n s 9.2
and 9.3 o f two r e a l - l i f e c a s e s : one f a c t o r y c h a r a c t e r i z e d b y r a t h e r p o o r
i n i t i a l e n e r g y u t i l i z a t i o n and a n o t h e r i n w h i c h t h e e n e r g y economy was q u i t e
d e c e n t . Bo th m o d e r n i z a t i o n s were u l t i m a t e l y aimed a t e x t e n s i o n s o f t h e
p r o c e s s i n g c a p a b i l i t y , t h i s b e i n g v e r y much dependen t on improvements o f t h e
e n e r g y economy. Pu lp d r y i n g was n o t t aken i n t o c o n s i d e r a t i o n .
The p r e s e n t a t i o n s c o n c e n t r a t e on t h e most r e l e v a n t p a r t s o f t h e m o d e r n i z a t i o n
c o n c e p t s , namely t h o s e c o n c e r n e d w i t h p o s s i b l e v e r s i o n s o f t h e r e c o n s t r u c t e d
thermal sys tems and t h e i r h e a t b a l a n c e s . I t i s n o t e w o r t h y , h o w e v e r , t h a t t h e
impo r tance o f t h e power b a l a n c e s has a l s o come i n t o f o c u s . I n t h e f i r s t e x a m p l e ,
p r e s e n t e d i n S e c t i o n 9 . 2 , owing t o a r e l a t i v e l y l a r g e n e t h e a t demand, t h e
f a c t o r y i s g e n e r a l l y a b l e t o s e l l a power s u r p l u s t o t h e e x t e r n a l g r i d . I t i s
o n l y t he most e n e r g y - e f f i c i e n t v e r s i o n o f t h e the rma l sys tem w h i c h r e d u c e s t h e
steam f l o w t h r o u g h t h e t u r b i n e t o a v a l u e l e s s t h a n t h a t r e q u i r e d f o r e l e c t r i c a l
s e l f - s u f f i c i e n c y . The second example p r e s e n t e d i n S e c t i o n 9.3 i s c o n c e r n e d w i t h
an e n e r g y sys tem i n w h i c h p o s s i b l e s i g n i f i c a n t h e a t s a v i n g s a r e accompanied by
a w i d e n i n g power d e f i c i t . I n t h i s s i t u a t i o n , measures t o r e d u c e t h e power
demand become an i m p o r t a n t p a r t o f t h e m o d e r n i z a t i o n , and t h e magn i t ude o f
complementary power p u r c h a s e s f rom t h e e x t e r n a l g r i d t akes a p l a c e i n t h e
e v a l u a t i o n o f m o d e r n i z a t i o n v e r s i o n s .
C o n c l u d i n g t h i s C h a p t e r and t h e e n t i r e b o o k , a summary i s g i v e n i n S e c t i o n
9.4 o f p r i n c i p l e s o f e n e r g y - s y s t e m d e s i g n u s i n g o p t i m i z a t i o n me thods .
334
9.2 FACTORY CHARACTERIZED BY POOR I N I T I A L ENERGY U T I L I Z A T I O N
9.2.1 I n t r o d u c t o r y remarks
The f a c t o r y was e r e c t e d a t t h e b e g i n n i n g o f t h i s c e n t u r y . I n t h e 1930s and
1940s s a t e l l i t e p r o d u c t i o n f a c i l i t i e s were b u i l t , i n c l u d i n g an a l c o h o l
d i s t i l l e r y , a c a r b o n d i o x i d e p l a n t and a m a c h i n e - s h o p . A f t e r numerous
e x t e n s i o n s and m o d e r n i z a t i o n s o f t h e s u g a r f a c t o r y , a p r o c e s s i n g c a p a b i l i t y o f
3000 t / d was a t t a i n e d i n the 1960s. By comb in ing t h e s t e p - b y - s t e p app roach w i t h
two l i m i t e d - s c a l e m o d e r n i z a t i o n s d u r i n g a p e r i o d o f s e v e r a l y e a r s e n d i n g l a t e
i n t he 1970s, t he b u l k o f t he o l d p r o c e s s equ ipment was r e p l a c e d by new
m a c h i n e r y . The p r o c e s s i n g c a p a b i l i t y was t hen i n c r e a s e d t o 3900 t o n s p e r d a y ,
w i t h t h e maximum t h r o u g h p u t o f t he e x t r a c t i o n s t a t i o n e s t i m a t e d a t a b o u t
5000 t / d .
As t h e r e were o n l y min imal i n v e s t m e n t s i n t he the rma l sys tem d u r i n g t he most
r e c e n t p e r i o d o f f a c t o r y improvemen ts , symptoms o f i n a d e q u a t e i n s t a l l e d b o i l e r
c a p a c i t y became v i s i b l e a t t h i s p r o c e s s i n g c a p a b i l i t y . The managing s t a f f was
aware o f t he o u t d a t e d h e a t economy and t h e f a c t t h a t no f u r t h e r f a c t o r y
e x t e n s i o n s can be p l anned u n l e s s t h e the rma l sys tem i s t h o r o u g h l y m o d e r n i z e d .
As a m a t t e r o f f a c t , t h i s s i t u a t i o n was n o t u n e x p e c t e d . I t was d e l i b e r a t e l y
a l l o w e d t o c o i n c i d e w i t h t h e n e c e s s a r y i n s t a l l a t i o n o f r e p l a c e m e n t s f o r two o l d
e v a p o r a t o r b o d i e s i n the 2nd e f f e c t , t h e i r c e r t i f i c a t e s o f p r e s s u r e - v e s s e l
o p e r a t i o n above 2 b a r b e i n g due t o e x p i r e . C o n s e q u e n t l y , an e n g i n e e r i n g company
was h i r e d t o d e s i g n the n e c e s s a r y r e c o n s t r u c t i o n o f t h e therma l s y s t e m .
A number o f c o n s t r a i n t s and assump t i ons were f o r m u l a t e d i n advance by t h e
managing s t a f f o f t he f a c t o r y :
- the e n e r g y s a v i n g s s h o u l d make i t p o s s i b l e t o i n c r e a s e t h e p r o c e s s i n g
c a p a b i l i t y t o 5000 t / d , b u t t he n e s e s s a r y e x t e n s i o n s o f t h e p r o c e s s equ ipment
w i l l be c o n s i d e r e d a t a l a t e r d a t e ;
- no i n v e s t m e n t f unds a r e a v a i l a b l e f o r m o d e r n i z a t i o n o f t h e power house
e q u i p m e n t ;
- t he f a c t o r y has t o be s e l f - s u f f i c i e n t i n power , as t h e e x t e r n a l g r i d i s n o t
r e l i a b l e enough d u r i n g t h e w i n t e r p e r i o d o f peak l o a d s ;
- steam consumpt ion i n t he p r o d u c t i o n f a c i l i t i e s o u t s i d e t h e s u g a r f a c t o r y i s
w e l l under c o n t r o l and need n o t be a n a l y s e d ;
- i n t he s u g a r f a c t o r y , t he j u i c e d r a f t s h o u l d be i n c r e a s e d and t he c r y s t a l l i z
a t i o n scheme s h o u l d be a d j u s t e d t o i n c r e a s e t h e s u g a r o u t p u t ;
- due t o the c h a r a c t e r i s t i c s o f t h e e x i s t i n g t h i c k - j u i c e f i l t r a t i o n e q u i p m e n t ,
t h i c k - j u i c e c o n c e n t r a t i o n s h o u l d n o t exceed 65% DS.
Under such c i r c u m s t a n c e s , t h e t a s k o f t h e d e s i g n e r s was l e s s c o m p l i c a t e d
than i n a t y p i c a l case o f f a c t o r y m o d e r n i z a t i o n . I t was p o s s i b l e t o l i m i t t he
335
e x t e n t o f t he i n v e n t o r y o f t he e x i s t i n g f a c t o r y subsys tems t o t he c o l l e c t i o n o f
e s s e n t i a l d a t a r e q u i r e d f o r c a l c u l a t i o n s o f t h e mass and h e a t b a l a n c e s o f t h e
therma l s y s t e m . O n l y f o r t he case o f t h e e v a p o r a t o r s t a t i o n and h e a t e r s
( t o g e t h e r w i t h t h e a s s o c i a t e d p i p i n g and a u x i l i a r y equ ipmen t ) were d e t a i l e d
schemes and l a y o u t d r a w i n g s p r e p a r e d . An i n v e n t o r y o f t h e r e l e v a n t s u p p o r t i n g
s t r u c t u r e s was a l s o drawn u p , and a s e p a r a t e e x a m i n a t i o n o f t he measur ing
i n s t r u m e n t s and c o n t r o l c i r c u i t s was u n d e r t a k e n .
9 .2 .2 B a s i c f a c t o r y d a t a
P r o c e s s i n g c a p a b i l i t y : 3900 t / d .
P o l a r i z a t i o n o f c o s s e t t e s : 14.0-14.5%.
E x t r a c t i o n s t a t i o n : two t r o u g h - t y p e e x t r a c t o r s .
J u i c e d r a f t : 108%.
R a w - j u i c e c o n c e n t r a t i o n and p u r i t y : 15.29% DS, 88.5%.
Pu lp p r e s s e d t o : 10.5% DS and 15.0% DS ( 4 / 5 and 1/5 o f t h e w e t - p u l p f l o w ,
r e s p e c t i v e l y ; t he f o r m e r p a r t i s s o l d t o f a r m e r s and t h e l a t t e r d i r e c t e d t o
a d r y e r ) .
K i l n g a s : 26.8% CO2 v o l .
J u i c e p u r i f i c a t i o n a c c o r d i n g t o t h e c l a s s i c a l scheme, c o m p r i s i n g :
- h o t p r e - l i m i n g a t 50°C, CaO r a t e 0.22 kg/100 kg b ;
- main l i m i n g a t 8 6 ^ C , CaO r a t e 1.30 kg/100 kg b ;
- 1 s t c a r b o n a t a t i o n a t 82°C;
- d e c a n t i n g and f i l t r a t i o n ;
- 2nd c a r b o n a t a t i o n a t 94°C, CaO r a t e 0.10 kg/100 kg b ;
- d o u b l e - s t a g e 2nd f i l t r a t i o n .
T h i n - j u i c e c o n c e n t r a t i o n and p u r i t y : 13.42% D S , 92.40%.
E v a p o r a t o r : q u a d r u p l e - e f f e c t , R o b e r t - t y p e b o d i e s .
T h i c k - j u i c e c o n c e n t r a t i o n : 60-62.5% DS.
Sugar h o u s e :
- s t a n d a r d - l i q u o r based t h r e e - b o i l i n g scheme w i t h t h e a f f i n a t i o n o f C s u g a r ;
- Β s u g a r and a f f i n e d C s u g a r m e l t e d i n t h i n j u i c e ;
- s t a n d a r d l i q u o r p r e p a r e d f rom t h i c k j u i c e and r e m e l t .
Sugar o u t p u t : 10.89 kg/100 kg b.
Power h o u s e :
- c o a l - f i r e d b o i l e r s , two u n i t s r a t e d 30 t / h and t h r e e u n i t s r a t e d 20 t / h ,
a v e r a g e e f f i c i e n c y abou t 60%;
- l i v e steam paramete rs 22 b a r , 320°C;
- two b a c k - p r e s s u r e t u r b i n e s r a t e d 3.3 MW e a c h , steam r a t e s a b o u t 11 kg /kWh;
- b a c k - p r e s s u r e 3.2 b a r .
The f a c t o r y s e l l s a power s u r p l u s t o t he e x t e r n a l g r i d .
336
I cocí VC
I 3
Fig.
9.
1.
Sche
me
of t
he t
herm
al
syst
em a
nd m
ass
and
heat
bal
ance
d
ata,
fo
r fa
cto
ry
befo
re m
oder
niza
tion
(t
hic
k-ju
ice
conc
entr
atio
n 60
% D
S).
C
onde
nsat
es o
btai
ned
from
vap
our
stre
ams
mar
ked
* ar
e di
scha
rged
to
th
e se
wer
sy
stem
.
337
Steam s u p p l y t o t he s u g a r m a n u f a c t u r i n g p r o c e s s :
- l i v e steam t h r o t t l e d t o 6 b a r t o t he c e n t r i f u g a l s and vacuum-pan s t e a m i n g ;
- h e a t i n g steam 3.2 b a r ( e x h a u s t steam and t h r o t t l e d l i v e s team) t o t h e
r e m a i n i n g r e c e i v e r s .
Steam consumpt ion a c c o r d i n g t o measurements : 44 .5 -48 .6 kg/100 kg b .
Power c o n s u m p t i o n : e s t i m a t e d a t abou t 2.5 kWh/100 kg b.
Normal f u e l c o n s u m p t i o n : 6 .20-7 .00 kg/100 kg b.
I t s h o u l d be n o t e d t h a t i n p a r a l l e l t o s u p p l y i n g e n e r g y t o t h e s u g a r f a c t o r y ,
t he power house s u p p l i e s power and steam t o t h e f o l l o w i n g p r o d u c t i o n f a c i l i t i e s :
- a l c o h o l d i s t i l l e r y ;
- c a r b o n - d i o x i d e p l a n t ;
- m a c h i n e - s h o p .
The combined power demand o f t h e s e f a c i l i t i e s does n o t e x c e e d 0.8 MW, and t h e
h e a t i n g steam demand i s o f t h e o r d e r o f 6 t / h . The demand on 6 b a r steam i s
n e g l i g i b l y s m a l l .
The scheme o f v a p o u r and c o n d e n s a t e d i s t r i b u t i o n , and t h e main r e s u l t s o f t h e
mass and h e a t b a l a n c e c a l c u l a t i o n s o f t h e the rma l sys tem o f t h e s u g a r f a c t o r y
b e f o r e m o d e r n i z a t i o n , a r e shown i n F i g . 9 .1 . I t can i m m e d i a t e l y be r e c o g n i z e d
t h a t t h e r e a r e a few q u e s t i o n a b l e d e t a i l s t h a t s h o u l d be e l i m i n a t e d :
- the q u a d r u p l e - e f f e c t e v a p o r a t o r i s e s s e n t i a l l y o p e r a t e d as a t r i p l e - e f f e c t one
because t h e r e i s no h e a t i n g w i t h l a s t - s t a g e v a p o u r ;
- the 1 s t - and 2 n d - e f f e c t c o n d e n s a t e s a r e f l a s h e d t o t h e a t m o s p h e r e ;
- a s i g n i f i c a n t p a r t o f t h e c o n d e n s a t e s i s w a s t e d ;
- the f l o w o f c o n d e n s a t e r e t u r n e d t o t h e power house i s t o o sma l l t o e n s u r e an
adequate f e e d - w a t e r s u p p l y .
A c t u a l l y , vacuum-pan s teaming w i t h 6 b a r steam - as men t ioned e a r l i e r - a l s o
b e l o n g s t o t h i s l i s t .
A n o t h e r o b s e r v a t i o n i s t h a t t h e c a l c u l a t e d demand on h e a t i n g steam i s l o w e r
than the consumpt ion found i n t he measurements . Two main r e a s o n s f o r t h i s
d i s c r e p a n c y can be i d e n t i f i e d :
- v a p o u r l e a k s t h r o u g h f l o a t - t y p e steam t r a p s i n t he c o n d e n s a t e d r a i n a g e l i n e s
i n the e v a p o r a t o r a r e a ;
- f r e q u e n t pa ramete r i n s t a b i l i t i e s , caused by i n a d e q u a t e t h r o u g h p u t and u n s t a b l e
c o n t r o l s o f t he t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n d e l i v e r i n g 3.2 b a r s team.
I t s h o u l d be added t h a t t he f o l l o w i n g q u e s t i o n a b l e d e t a i l s , n o t shown i n
F i g . 9 . 1 , were a l s o f ound i n the v a p o u r d i s t r i b u t i o n scheme:
- e x t r a c t o r h e a t i n g by I s t - e f f e c t v a p o u r o n l y ; t h i s was m o t i v a t e d by t h e f a c t
t h a t i t h e l p e d t o p r o v i d e a h i g h t e m p e r a t u r e o f t h e e x t r a c t i o n m i x t u r e , t hus
making i t p o s s i b l e t o m a i n t a i n a v e r y low j u i c e d r a f t ;
- m u l t i p l e - s t a g e h e a t i n g o f p r e - l i m e d j u i c e and t h i n j u i c e where v a p o u r s a t
338
the t e m p e r a t u r e s r e q u i r e d i n t he f i n a l s t a g e s were a l s o used i n t he p r e c e d i n g
s t a g e s ; t h i s c o n t r i b u t e d t o i n a d e q u a t e u t i l i z a t i o n o f l o w - t e m p e r a t u r e v a p o u r s .
9 .2 .3 F i e l d o f s o l u t i o n s
The e n g i n e e r i n g team p r o p o s e d t h e f o l l o w i n g s t r a t e g y o f m o d e r n i z a t i o n , t o be
implemented i n two s t e p s .
( i ) W h i l e i n s t a l l i n g the n e c e s s a r y r e p l a c e m e n t s o f t h e e v a p o r a t o r b o d i e s i n t h e
2nd e f f e c t , the rma l sys tem c o r r e c t i o n s can be i n t r o d u c e d t o r e d u c e t h e n e t h e a t
demand and make i t p o s s i b l e t o o p e r a t e t h e f a c t o r y a t a h i g h e r j u i c e d r a f t and
i n c r e a s e d s u g a r o u t p u t .
( i i ) The e v a p o r a t o r and t h e v a p o u r d i s t r i b u t i o n scheme can be r e c o n s t r u c t e d t o
improve the e f f e c t i v e n e s s r a t i o o f t h e the rma l sys tem and t hus r e d u c e t h e n e t
h e a t demand even f u r t h e r .
When a n a l y s i n g t he o p e r a t i o n o f t h e e x t r a c t i o n s t a t i o n a t a h i g h e r j u i c e
d r a f t , i t was c o n c l u d e d t h a t bo th t h e f l o w o f e x t r a c t i o n f e e d - w a t e r and t he f l o w
o f p r e s s w a t e r can be i n c r e a s e d . The d r y s u b s t a n c e c o n t e n t o f t h e p r e s s e d p u l p
can be i n c r e a s e d t o 11.2% DS and 15.6% DS ( 4 / 5 and 1/5 o f t h e w e t - p u l p f l o w ,
r e s p e c t i v e l y ) , t h i s b e i n g w e l l w i t h i n the o p e r a t i n g range o f t h e e x i s t i n g p u l p
p r e s s e s . I n t h i s w a y , more p r e s s w a t e r i s o b t a i n e d and a d d i t i o n a l e n e r g y
s a v i n g s i n p u l p d r y i n g become p o s s i b l e . C o n c e r n i n g t h e c r y s t a l l i z a t i o n scheme,
i t t u r n e d o u t t h a t an i n c r e a s e d s u g a r o u t p u t r e q u i r e s a l a r g e r m a s s e c u i t e
c i r c u l a t i o n , t h i s making an i n c r e a s e d h e a t demand o f t h e s u g a r b o i l i n g p r o c e s s
u n a v o i d a b l e even a t t h i c k - j u i c e c o n c e n t r a t i o n o f 65% DS (as compared t o 60% DS
p r i o r t o t he m o d e r n i z a t i o n ) .
Two therma l sys tem v e r s i o n s were p r o p o s e d f o r s t e p ( i ) and t h r e e v e r s i o n s f o r
s t e p ( i i ) . I n t h e f o l l o w i n g , t h e s e v e r s i o n s a r e d e n o t e d A l , A2 and 81, 82 , 83.
Each o f them assumes t h a t t he f o l l o w i n g changes a r e i n t r o d u c e d t o t he the rma l
s y s t e m :
- vacuum-pan s teaming i s pe r f o rmed u s i n g 2 n d - e f f e c t v a p o u r ;
- c o n d e n s a t e s f rom a l l i m p o r t a n t v a p o u r r e c e i v e r s a r e r e t u r n e d t o the c o n d e n s a t e
tanks ( t h i s r e q u i r e s i n s t a l l i n g new t a n k s , as t h e vo lumes o f t h e e x i s t i n g ones
a r e t o o sma l l t o accommodate i n c r e a s e d c o n d e n s a t e f l o w s ) ;
- cascade f l a s h i n g o f c o n d e n s a t e s i s a p p l i e d ;
- e x t r a c t o r s a r e hea ted by 1 s t - and 3 r d - e f f e c t v a p o u r ;
- m u l t i p l e - s t a g e j u i c e h e a t i n g i s pe r fo rmed u s i n g v a p o u r s o f d i f f e r e n t
t e m p e r a t u r e s , s t a r t i n g f rom t h e l o w e s t p o s s i b l e t e m p e r a t u r e ( i n some v e r s i o n s ,
t h i s may r e q u i r e i n s t a l l i n g new h e a t e r s , as t h e h e a t i n g s u r f a c e a r e a s o f t h e
e x i s t i n g ones may be t o o sma l l when u t i l i z e d a t r e d u c e d t e m p e r a t u r e
d i f f e r e n c e s ) ;
- l e v e l - c o n t r o l l e d h y d r a u l i c s e a l s a r e a p p l i e d i n t h e c o n d e n s a t e d r a i n a g e l i n e s
c o n n e c t e d t o e v a p o r a t o r b o d i e s l a and l b ;
339
No. E x i s t i n g A l A2 Bl B2 B3
l a 1500 1500 1500 1500 1500 1500 l b 1500 1500^ 1500^ 1500^ 1500^ 1500^ 2a 1460 1800^ 1800? 1800^ 1800f 1800^ 2b 1460 1800^ 1800^ 1800^ 1800^ 1800^ 3a 1320 1320 1460 1320 1460 1460 3b - 1460 1460 1460 1460 1460 4 900 900 1320 900 1320 1320 5 - - - - 900 900
' new b o d i e s
A2. Q u a d r u p l e - e f f e c t e v a p o r a t o r w i t h i n c r e a s e d h e a t i n g s u r f a c e a r e a s i n the 2 n d ,
3 rd and 4 th e f f e c t s ; and the f o l l o w i n g a d j u s t m e n t s o f t h e the rma l s y s t e m :
- 4 t h - e f f e c t v a p o u r i s u t i l i z e d i n r a w - j u i c e and 1 i m e d - j u i c e h e a t i n g ;
- o t h e r d e t a i l s a r e e s s e n t i a l l y i d e n t i c a l t o t h o s e o f v e r s i o n A l .
F o r more i n f o r m a t i o n , see F i g . 9 . 3 . I t i s n e c e s s a r y t o i n s t a l l f o u r new
c o n d e n s a t e tanks i n t h i s v e r s i o n .
- a new t h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n t o s u p p l y 3.2 b a r steam i s i n s t a l l e d
and e q u i p p e d w i t h an a u t o m a t i c c o n t r o l c i r c u i t s t a b i l i z i n g e x h a u s t - s t e a m
p r e s s u r e .
The c o n f i g u r a t i o n s o f t he e v a p o r a t o r s t a t i o n employed i n t h e d i f f e r e n t
v e r s i o n s a re p r e s e n t e d i n T a b l e 9 .1 . The main f e a t u r e s o f t h e i n d i v i d u a l
v e r s i o n s a r e r e v i e w e d b e l o w .
A l . Q u a d r u p l e - e f f e c t e v a p o r a t o r w i t h i n c r e a s e d h e a t i n g s u r f a c e a r e a s i n t he 2nd
and 3 rd e f f e c t s , and t he f o l l o w i n g a d j u s t m e n t s o f t h e therma l s y s t e m :
- 4 t h - e f f e c t v a p o u r i s u t i l i z e d i n r a w - j u i c e h e a t i n g and i n d i r e c t h e a t i n g o f
e x t r a c t i o n f e e d - w a t e r i n a p r e c o n d e n s e r ;
- an a d d i t i o n a l c o n d e n s a t e tank i s i n s t a l l e d t o c o l l e c t t h e c o n d e n s a t e d r a i n e d
f rom the 3 rd e v a p o r a t o r e f f e c t ;
- a u t o m a t i c l e v e l c o n t r o l l e r s a r e i n s t a l l e d i n 2nd - and 3 r d - e f f e c t c o n d e n s a t e
tanks t o e n s u r e e f f e c t i v e h y d r a u l i c s e a l s i n r e s p e c t i v e c o n d e n s a t e d r a i n a g e
l i n e s .
The d i s t r i b u t i o n o f v a p o u r s and c o n d e n s a t e s , and t h e r e s u l t s o f mass and h e a t
b a l a n c e c a l c u l a t i o n s , a r e shown i n F i g . 9 . 2 . I n a d d i t i o n t o two new e v a p o r a t o r
b o d i e s ( w h i c h a r e a l s o i n c l u d e d i n o t h e r m o d e r n i z a t i o n v e r s i o n s ) , t h i s v e r s i o n
r e q u i r e s i n s t a l l i n g f o u r new c o n d e n s a t e t a n k s .
TABLE 9.1
E v a p o r a t o r c o n f i g u r a t i o n s i n d i f f e r e n t m o d e r n i z a t i o n v e r s i o n s .
2 Body H e a t i n g s u r f a c e a r e a (m )
340
> ß
!Ν3
O o CO
O'Z
6-U
9Ό
8V8
5 ĆÉ'!
6Ό
en
TI ^ 1
-e 1000
Fig
. 9
.2.
Sch
eme
of
the
m
od
ern
ize
d th
erm
al
syst
em
, v
ers
ion
A
l.
341
1 i2
1 1 i2
1 en en
CO
. 1 Ă —
L. I
ε'9 17
]^ I'll •
r _ . _
. tí <£>
- 5 h ~¡Mm ®
L mi
¿o
1 . ^
é ir?"
Lr2j
L J S I I
—j
LA — Č -
IDOO
Fig
. 9
.3.
Sch
eme
of
the
m
od
ern
ize
d th
erm
al
syst
em
, v
ers
ion A
2.
342
B l . Q u a d r u p l e - e f f e c t e v a p o r a t o r w i th vapour c o m p r e s s i o n , a n d :
- a h e a t i n g scheme s i m i l a r to t ha t o f v e r s i o n A l ;
- vacuum-pan vapour i s u t i l i z e d in r a w - j u i c e h e a t i n g ;
- i n a d d i t i o n to the b a s i c condensa te subsys tem i d e n t i c a l to t ha t o f v e r s i o n A l ,
an au tomat ic l e v e l c o n t r o l l e r i s i n s t a l l e d i n the 4 t h - e f f e c t condensa te tank and
a condensa te tank f l a s h e d to 4 t h - e f f e c t vapour i s i n s t a l l e d as a f i n a l l i n k i n
the condensa te tank c h a i n ;
- compress ion o f I s t - e f f e c t vapour i s performed u s i n g j e t - t y p e c o m p r e s s o r s ;
- compressed vapour i s d i r e c t e d to the h e a t i n g chamber o f body l a ;
- exhaus t steam i s d i r e c t e d to the h e a t i n g chamber o f body l b ;
- i n o rde r to reduce compress ion work , a temperature d i f f e r e n c e o f 6 Κ i s
ma in ta ined a c r o s s the h e a t i n g s u r f a c e i n body l a , w h i l e the c o r r e s p o n d i n g
f i g u r e in body lb i s 10 K;
- s e p a r a t e condensa te tanks a re i n s t a l l e d to c o l l e c t condensa tes from b o d i e s l a
and l b .
The d i s t r i b u t i o n scheme f o r vapou rs and condensa tes and e x c e r p t s from the mass
and heat ba lance data a re shown i n F i g . 9 . 4 . T h i s v e r s i o n r e q u i r e s i n s t a l l i n g
s i x new condensa te t anks and one new h e a t e r .
B 2 . Q u i n t u p l e - e f f e c t e v a p o r a t o r , a n d :
- condensa te tank c o l l e c t i n g 5 t h - e f f e c t condensa te i s no t connected to the
condensa te tank c h a i n ;
- condensa te i s u t i l i z e d in h e a t i n g p r e - l i m e d j u i c e , p r e h e a t i n g a i r be fo re the
s u g a r d r y e r , k i l n - g a s h e a t i n g and h u m i d i f i c a t i o n be fo re the c a r b o n a t a t i o n t a n k s ,
and room h e a t i n g ;
- vacuum-pan v a p o u r s a re u t i l i z e d in r a w - j u i c e h e a t i n g ;
- vacuum pans A are heated by 2 n d - e f f e c t v a p o u r , but vacuum pans Β and C by 3 r d -
e f f e c t vapour ( the h e a t i n g s u r f a c e a r e a s i n vacuum pans A tu rned out to be too
s m a l l , p r e c l u d i n g the use o f vapour a t a lower t e m p e r a t u r e ) ;
- t h i n - j u i c e h e a t i n g i n the f i n a l s t a g e i s per formed u s i n g exhaus t s team.
For more i n f o r m a t i o n , see F i g . 9 . 5 . I t i s n e c e s s a r y to i n s t a l l f i v e new
condensa te tanks and th ree new h e a t e r s i n t h i s v e r s i o n .
B 3 . Q u i n t u p l e - e f f e c t e v a p o r a t o r w i th vapour c o m p r e s s i o n , a n d :
- a h e a t i n g scheme e s s e n t i a l l y the same as i n v e r s i o n B 2 ;
- a c o n t i n u o u s c h a i n o f condensa te tanks a p p l i e d between the 2nd and 5 th
e v a p o r a t o r e f f e c t s ;
- t h i c k j u i c e a f t e r the 4 th e f f e c t i s d i r e c t e d to the s u g a r house where
s t a n d a r d l i q u o r i s p r e p a r e d ;
- s t a n d a r d l i q u o r i s re tu rned to the 5 th e f f e c t and t h i ckened to 11% D S ;
- compress ion o f I s t - e f f e c t vapour i s per formed u s i n g an e l e c t r i c a l l y - d r i v e n
mechanica l c o m p r e s s o r ;
343
Fig
. 9
.4.
Sch
eme
of
the
m
od
ern
ize
d th
erm
al
syst
em
, ve
rsio
n
Bl.
Not
sho
wn
: ra
w-j
uic
e
he
ati
ng
usin
g
vacu
um-p
an
vap
ou
r.
344
> o
o
o ů
§ Ol Ł Ć) 3 O
in
ι χ:
c o Q.
Ĺ D S
CO
S IT)
o tν CO
ö
3
09 61
9-91 ευ
CM ? ^ CM
t ε·ιε
. t í 5
o "
¿O ..Él
1 SJ
ir>! F
ig.
9.5
. S
chem
e o
f th
e
mo
de
rniz
ed
the
rma
l sy
ste
m,
ve
rsio
n
B2
. N
ot
sho
wn
: ra
w-j
uic
e
he
ati
ng
usin
g
vacu
um-p
an
vap
ou
r.
345
cn
O
CD c o,
C O
t — . z - f
. IΝ σ T—4
Ă - . - , in!
Fig
. 9
.6.
Sch
eme
of
the
m
od
ern
ize
d th
erm
al
syst
em
, v
ers
ion
B3
. N
ot
show
n:
raw
-ju
ice
he
ati
ng
usin
g
vacu
um-p
an
vap
ou
r.
346
- compressed vapour i s d i r e c t e d to the h e a t i n g chamber o f body l a ;
- exhaus t steam i s d i r e c t e d to the h e a t i n g chamber o f body l b ;
- i n o r d e r to reduce compressor power demand, a temperature d i f f e r e n c e o f 6 Κ
i s ma in ta ined between the h e a t i n g chamber and vapour chamber i n body l a , w h i l e
the c o r r e s p o n d i n g f i g u r e i n body l b i s 10 K;
- s e p a r a t e condensa te tanks are i n s t a l l e d to c o l l e c t condensa tes from b o d i e s l a
and l b .
The d i s t r i b u t i o n scheme f o r vapou rs and c o n d e n s a t e s , and s e l e c t e d r e s u l t s o f
mass and heat ba lance c a l c u l a t i o n s , a re shown i n F i g . 9 . 6 . T h i s v e r s i o n r e q u i r e s
i n s t a l l i n g s i x new condensa te t anks and f i v e new h e a t e r s .
9 . 2 . 4 Compar ison o f s o l u t i o n s
When a n a l y s i n g the m o d e r n i z a t i o n s t r a t e g y o u t l i n e d i n the p reced ing S e c t i o n s ,
each v e r s i o n o f the modern ized f a c t o r y can be c h a r a c t e r i z e d by a v e c t o r o f
a t t r i b u t e s c o m p r i s i n g inves tment c o s t , fue l s a v i n g and power demand i n c r e a s e .
U s i n g the ac tua l p r i c e s o f fue l and power, the consequences o f m o d e r n i z a t i o n
can thus be e x p r e s s e d i n economic t e rms . The economic data can a l s o be combined
i n t o some s y n t h e t i c i n d e x , l i k e the p e r i o d o f r e t u r n on i nves tmen t . T h i s makes
i t p o s s i b l e to compare the s o l u t i o n s and to s e l e c t the most f e a s i b l e one o f
v e r s i o n s B l , B2 and B 3 .
The Inves tmen t c o s t was c a l c u l a t e d on the b a s i s o f p r i c e s quoted by the
s u p p l i e r s o f the main equipment ( e v a p o r a t o r b o d i e s , j u i c e h e a t e r s , condensa te
t a n k s , pumps and vapour c o m p r e s s o r s ) . To the equipment p r i c e s , the f o l l o w i n g
es t ima ted c o s t components were added :
- p i p i n g and a u x i l i a r y equ ipment ;
- measur ing d e v i c e s and con t r o l c i r c u i t s ;
- thermal i n s u l a t i o n ;
- d e s i g n documen ta t i on ;
- c o n s t r u c t i o n work ;
- a s s e m b l i n g o f equ ipment , p i p i n g and i n s t r u m e n t a t i o n .
Es t ima ted v a l u e s o f the a t t r i b u t e s o f the m o d e r n i z a t i o n v e r s i o n s were taken
from r e s u l t s o f the d e s i g n a n a l y s i s summarized i n the p r e v i o u s S e c t i o n .
I t was agreed w i th the f a c t o r y managers t h a t no d e t a i l e d economic a n a l y s i s i s
r e q u i r e d , because the impor tance o f the r e c o n s t r u c t i o n o f the thermal sys tem
l i e s ma in l y i n making i t p o s s i b l e to ex tend the p r o c e s s i n g c a p a b i l i t y ; however ,
t h i s w i l l be d e s i g n e d and a n a l y s e d a t a l a t e r d a t e . In o rde r to reduce the
comp lex i t y o f the compar ison o f the v a r i o u s v e r s i o n s , approx imate v a l u e s
( n e g l e c t i n g the i n f l u e n c e o f c a p i t a l c o s t ) o f the p e r i o d o f r e t u r n on
i n v e s t m e n t , i n y e a r s , were c a l c u l a t e d a c c o r d i n g to the fo rmu la
τ = I / A ( 9 . 1 )
where I i s the inves tment c o s t and A i s the annual s a v i n g .
347
The r e s u l t s o f the compara t i ve a n a l y s i s a re summarized i n Tab le 9 . 2 . Due to
f l u c t u a t i o n s o f p r i c e s and c u r r e n c y exchange r a t e s i n the i n t e r n a t i o n a l marke t ,
i t would make l i t t l e sense to quote the a b s o l u t e l e v e l o f the economic e s t i m a t e s
i n the o r i g i n a l c u r r e n c y . A t the moment o f p u b l i c a t i o n o f the p r e s e n t b o o k ,
a coup le o f y e a r s a f t e r the a n a l y s i s was comp le ted , these data would be o f
h i s t o r i c a l v a l u e o n l y . T h e r e f o r e , the c o s t s and s a v i n g s a re g i v e n r e l a t i v e to
the inves tmen t c o s t a s s o c i a t e d w i th the m o d e r n i z a t i o n v e r s i o n Al ( t h i s c o s t i s
taken as ^00%),
TABLE 9 . 2
Compar ison o f main t e c h n i c a l and economic parameters o f d i f f e r e n t m o d e r n i z a t i o n v e r s i o n s .
Thermal sys tem v e r s i o n E x i s t i n g Al A2 Bl B2 B3
H e a t i n g - s t e a m demand ( k g / 1 0 0 kg b) 4 2 . 4 4 1 . 2 4 0 . 3 3 7 . 7 3 6 . 8 3 1 . 9 6 bar steam demand ( k g / 1 0 0 kg b) 2 . 5 1.0 1.0 1.0 1.0 1.0 Norma l - fue l demand ( k g / 1 0 0 kg b) 6 . 0 0 5 . 6 2 5 . 5 0 5 . 1 2 4 . 6 0 3 . 0 7 L i v e - s t e a m demand i n vapour compress ion ( k g / 1 0 0 kg b) - - - 6 . 1 0 - -Power demand i n vapour compress ion (kWh/100 kg b) - - - - - 0 . 3 2 Condensate f low to the b o i l e r house
( k g / 1 0 0 kg b) 4 0 . 5 4 6 . 5 4 5 . 2 4 7 . 0 4 1 . 5 3 5 . 7 Tota l h e a t i n g s u r f a c e a rea i n the^ e v a p o r a t o r (m ) 8140 10280 10420 10280 11740 11740 R e l a t i v e inves tmen t c o s t (%) - 100 111 116 148 234 Va lue o f coa l saved per s e a s o n {7o) - 58 70 107 157 205 Approx imate p e r i o d o f r e t u r n on inves tmen t ( y e a r s ) - 1 .73 1 .59 1 .08 0 . 9 4 1 .14
As can be seen i n Tab le 9 . 2 , v e r s i o n s B l , B2 and B3 are e c o n o m i c a l l y more
a t t r a c t i v e than Al and A 2 . T h i s i n d i c a t e s t h a t a f t e r the f i r s t m o d e r n i z a t i o n
s t e p has been comp le ted , the second s t e p s h o u l d be taken as soon as p o s s i b l e .
Among the Β v e r s i o n s , i t i s Bl t ha t i s c h a r a c t e r i z e d by the l owes t i nves tmen t
c o s t ; B3 o f f e r s the l a r g e s t fue l s a v i n g , and B2 seems to p r o v i d e a t r a d e - o f f
between inves tmen t c o s t and fue l s a v i n g .
From the data g i v e n i n S e c t i o n 9 . 2 . 2 , the t o t a l power demand (vapour
compress ion exc luded ) o f the s u g a r f a c t o r y a t the p r o c e s s i n g c a p a b i l i t y o f
5000 t / d , p l u s o the r p r o d u c t i o n f a c i l i t i e s , can be es t ima ted a t 6 . 0 MW. Add ing
a 10% s a f e t y m a r g i n , the power demand w i l l equal the r a t i n g o f the t u r b i n e s .
To genera te 6 . 6 MW in the t u r b o - g e n e r a t o r s , a steam f low o f about 73 t / h i s
r e q u i r e d . S u b t r a c t i n g 6 t / h consumed o u t s i d e the s u g a r f a c t o r y , a minimum
h e a t i n g - s t e a m demand o f 67 t / h , o r 3 2 . 2 k g / 1 0 0 kg b , i s o b t a i n e d . Look ing now a t
the c h a r a c t e r i s t i c s o f v e r s i o n B 3 , i t can be seen t ha t the t o t a l power demand,
vapour compress ion i n c l u d e d , amounts to 6 . 7 MW and the h e a t i n g - s t e a m demand i s
348
a l i t t l e l e s s than the minimum v a l u e . T h i s e x c l u d e s the p o s s i b i l i t y o f
implement ing v e r s i o n B3 w i thou t p u r c h a s i n g power from the ex te rna l g r i d , o r
mode rn i z i ng the power h o u s e . T h e r e f o r e , v e r s i o n B3 does no t s a t i s f y the
c o n s t r a i n t s l i s t e d i n S e c t i o n 9 . 2 . 1 .
9 . 3 FACTORY CHARACTERIZED BY GOOD I N I T I A L ENERGY U T I L I Z A T I O N
9 . 3 . 1 I n t r o d u c t o r y remarks
The f a c t o r y was b u i l t in the e a r l y 1970s w i th an i n i t i a l p r o c e s s i n g
c a p a b i l i t y o f 4000 t ons per day . The i n i t i a l f ue l consumpt ion was about 5 . 3 kg
normal fue l per 100 kg bee t . Du r i ng a p e r i o d o f about ten y e a r s , r e l y i n g m o s t l y
on the s t e p - b y - s t e p a p p r o a c h , the p r o c e s s i n g c a p a b i l i t y was i n c r e a s e d to
5900 t / d . T h i s was accompanied by the o p t i m i z a t i o n o f the s u g a r manu fac tu r i ng
p r o c e s s w i th r e s p e c t to the fue l demand, and numerous improvements o f the
thermal s y s t e m . Among o t h e r s , the u t i l i z a t i o n o f vacuum-pan vapou rs i n two
t u b u l a r r a w - j u i c e h e a t e r s was i n t r o d u c e d , a l ong w i th improvements o f the
u t i l i z a t i o n o f low- tempera tu re p r imary vapours and c o n d e n s a t e . As a r e s u l t ,
n o r m a l - f u e l consumpt ion dec reased to 3 . 5 - 3 . 7 k g / 1 0 0 kg b.
When a p r o c e s s i n g c a p a b i l i t y o f 5900 t / d was a t t a i n e d , d i f f i c u l t i e s a r o s e i n
m a i n t a i n i n g p roper v a l u e s o f c r u c i a l p r o c e s s pa rame te rs . The tempera tu res o f
e x t r a c t i o n and main l i m i n g tended to be too l ow , and the c o n c e n t r a t i o n o f t h i c k
j u i c e d e c r e a s e d . T h i s was accompanied by vacuum- leve l i n s t a b i l i t i e s d i s t u r b i n g
the s u g a r b o i l i n g p r o c e s s . An e v a l u a t i o n o f the mass and heat b a l a n c e s o f the
e v a p o r a t o r i n d i c a t e d a l s o a l a r g e f low o f l a s t - e f f e c t vapour t o the c o n d e n s e r .
A f t e r the r e s u l t s o f the s e a s o n had been r e v i e w e d , i t was conc luded t h a t the
o p e r a t i o n a l d i f f i c u l t i e s caused too h i g h s u g a r l o s s e s . I t a l s o became c l e a r t ha t
no f u r t h e r r e d u c t i o n o f the energy consumpt ion i s p o s s i b l e u n l e s s the e x i s t i n g
p r o c e s s equipment and thermal sys tem a re mode rn i zed . C o n s e q u e n t l y , an
e n g i n e e r i n g team was c a l l e d i n to a n a l y s e the s i t u a t i o n and to d e s i g n the
n e c e s s a r y m o d i f i c a t i o n s .
A d e t a i l e d i n v e n t o r y o f 12 f a c t o r y subsys tems i n the s u g a r m a n u f a c t u r i n g l i n e
was p r e p a r e d , s t a r t i n g from the beet wash ing s t a t i o n and end ing a t the C
m a s s e c u i t e s t a t i o n . A rev iew o f impor tan t parameters o f 15 o t h e r s u b s y s t e m s was
a l s o c a r r i e d o u t . Wh i le most o f the data needed to i n i t i a t e a m o d e r n i z a t i o n
s t u d y i n the heat economy area were o b t a i n e d , i t was found t h a t the data on the
f a c t o r y ' s power ba lance were no t s u f f i c i e n t l y d e t a i l e d . Tak i ng i n t o accoun t t ha t
the modern ized f a c t o r y cannot be s e l f - s u f f i c i e n t i n power, i t became c l e a r t h a t
ways to reduce the power demand i n a l l r e l e v a n t f a c t o r y s u b s y s t e m s s h o u l d be
s t u d i e d and p roper measures s h o u l d be t a k e n . I t was t h e r e f o r e recommended t h a t :
- measurements be made o f the power consumpt ion i n major power r e c e i v e r s d u r i n g
the nex t s e a s o n , to a n a l y s e the r a t i n g o f motors and t r a n s f o r m e r s ;
- a d e t a i l e d s t udy be under taken o f the w a t e r - s u p p l y and was te -wa te r t rea tment
349
Subsystems, with the aim o f reducing the power demand;
- a d e t a i l e d s t udy be under taken o f f low c o n t r o l r equ i remen ts i n the s u g a r
manu fac tu r i ng p r o c e s s , w i th the aim o f m o d e r n i z i n g the c o n t r o l sys tems f o r
be t t e r ene rgy u t i l i z a t i o n .
9 . 3 . 2 B a s i c f a c t o r y data and heat ba lance
P r o c e s s i n g c a p a b i l i t y : 5900 t / d .
P o l a r i z a t i o n o f c o s s e t t e s : 15 .7%.
E x t r a c t i o n s t a t i o n : two t h r o u g h - t y p e e x t r a c t o r s .
J u i c e d r a f t : 115%.
Raw- ju i ce c o n c e n t r a t i o n and p u r i t y : 15.0% DS and 8 8 . 4 % .
Pu lp p r e s s e d t o : 27 .6% D S .
K i l n g a s : 35% CO^ v o l .
J u i c e p u r i f i c a t i o n a c c o r d i n g to the c l a s s i c a l scheme, c o m p r i s i n g :
- ho t p r e - l i m i n g a t 4 5 - 5 0 ° C ;
- main l i m i n g a t 79 -80°C ( r e q u i r e d tempera tu re : 8 2 - 8 5 ° C ) ;
- 1 s t c a r b o n a t a t i o n a t 77°C ( r e q u i r e d tempera tu re : 8 0 - 8 2 ° C ) ;
- d o u b l e - s t a g e 1 s t f i l t r a t i o n ;
- 2nd c a r b o n a t a t i o n a t 9 6 ° C ;
- d o u b l e - s t a g e 2nd f i l t r a t i o n .
D e c a l c i f i c a t i o n o f t h i n j u i c e by ion exchange .
T h i n - j u i c e c o n c e n t r a t i o n and p u r i t y : 15.4% DS and 9 1 . 8 % .
E v a p o r a t o r : q u a d r u p l e - e f f e c t , R o b e r t - t y p e b o d i e s ; N i e s s n e r columns a p p l i e d i n
the condensa te d r a i n a g e s u b s y s t e m .
T h i c k - j u i c e c o n c e n t r a t i o n : 61 .9% DS ( r e q u i r e d v a l u e : 65% D S ) .
S u g a r h o u s e :
- t h r e e - b o i l i n g scheme w i th the a f f i n a t i o n o f C s u g a r ;
- 60% o f Β s y r u p p r o c e s s e d i n a Quent in u n i t .
Power h o u s e :
- o i l - f i r e d b o i l e r s , ave rage e f f i c i e n c y 92%;
- l i v e steam parameters 40 b a r , 4 3 0 ^ 0 ;
- b a c k - p r e s s u r e 2 . 9 b a r ;
- f eed -wa te r pump d r i v e n by a steam t u r b i n e .
Steam s u p p l y to the s u g a r manu fac tu r i ng p r o c e s s :
- l i v e steam t h r o t t l e d to 8 bar to the c e n t r i f u g a l s ;
- h e a t i n g steam 2 . 9 bar ( exhaus t steam and t h r o t t l e d l i v e steam) to the
rema in ing r e c e i v e r s .
Hea t ing steam c o n s u m p t i o n : 3 5 . 5 k g / 1 0 0 kg b.
Power c o n s u m p t i o n : 2 . 8 5 kWh/100 kg b.
Normal fue l c o n s u m p t i o n : 3 . 6 8 k g / 1 0 0 kg b.
The s i m p l i f i e d scheme o f vapour and condensa te d i s t r i b u t i o n , and the r e s u l t s
350
ó) irS ů Q;
O - C
t o
ů CjD. c ^-^
o Q .
(Ë
Ĺ 3 Ü o
tn
o 3 Ü o ů
o
s X
ů s
ç CO ¿•0
O o O CN LO CM CÑJ W l _ r
6·9ε CO
I cnjI
o o o " CM
CNJ CO
Ν'ΝZ
1!0 ÉČĐ^ Fig
. 9
.7.
Sch
eme
of
the
th
erm
al
syst
em
a
nd
m
ass
an
d
he
at
ba
lan
ce
da
ta,
for
facto
ry
be
fore
m
od
ern
iza
tio
n.
351
O CO o . «;í- CO C\J CM
O (Ô> O .
CO CM CO
O »— O . 00 oo I— ^
o r -O . CM é— LO
O ·
I—
O O O .
>
c
ů
(T3 O CO O . ^ CO CM CM
O σ> o · CO
CM CO
o Éď · CO CO I— ^
O 1— O . CM Ă— LO
O o . I— KO
o o o . o <
4-> c ö
ů
o o . LT)
o CO o . ^ CO CM CM
o CT» o . ^ CO CM CO
O r - o r -o . o . 00 00 CM I— ^ I— LO
o o · ^ LO I— LO
o o o · o ^
o S-Q .
c o
ίο CL
> O)
c o
«5
ů o S- -Éďß 4->
<Ό ů í. o +J <o c :
O) í. u 13 C CO o
o c +J
•I- 0) +-> I— (ő 23 đ: o
ta o o o · ^ I— CM CM
ta o Éď . 'd- o CM CM
«3 o Éď . o CM CM
o o · ^ CO CM CO
o CO o · CM CM
o CO o . »d- CT» CM CM
O f — Ď ß ď , o . 00 00 CM 1^ Ă— ^ I— LO
o o . 00 o r— ^
o ^ o . CM 00 <—
o 1^ o ^ o . o · 00 o CM 00
o o . «d- LO r - LO
o o o . ^ o f— LO
Đ3 o o o . ^ o I— LO
o o o · o ^
to o o o . o o I—
Đ3 o o o · o o I— r-
cu o
T3
to
o Éď . 00 o
o CO o . ^ CT> CM CM
o o · 00 o
o ^ o · CM 00 I— ^
o o o · ^ o t— LO
o o o . o o
to
O)
c o
CO o
CT> to Lü o —I Q . OQ to «t >
o 00 o · 00 .—
CM
o CM o . 00 r -
O LO o . ^ LO CM CO
o o o . ^ LO CM CO
o o o . 00 CT» ·— ^
o LO o . 00 00 r - ^
o o o . CM LO .— LO
o CT» o · CM Ă é— LO
' fa
llin
g-f
ilm
ty
pe
, te
mp
ora
rily
un
used
352
o f mass and heat ba lance c a l c u l a t i o n s o f the thermal sys tem be fo re m o d e r n i z a t i o n
a re shown in F i g . 9 . 7 . No d e t a i l s o f the vapour and condensa te c o n n e c t i o n s i n
the p r o c e s s h e a t i n g a rea a re g i v e n , as t h e s e were found e n t i r e l y c o r r e c t .
9 . 3 . 3 F i e l d o f s o l u t i o n s
The e n g i n e e r i n g team proposed the f o l l o w i n g s t r a t e g y o f m o d e r n i z a t i o n , to be
implemented in f o u r s t e p s .
( i ) I n t r oduce equipment m o d i f i c a t i o n s and minor thermal sys tem c o r r e c t i o n s ,
aimed a t s e c u r i n g p roper p r o c e s s parameters and e l i m i n a t i n g u n n e c e s s a r y energy
l o s s e s .
( i i ) Conver t the e x i s t i n g e v a p o r a t o r i n t o a q u i n t u p l e - e f f e c t o n e , i n o r d e r to
a t t a i n a h i g h c o n c e n t r a t i o n o f t h i c k j u i c e and to i n c r e a s e the e f f e c t i v e n e s s
r a t i o o f the thermal s y s t e m .
( i i i ) I n c r e a s e the h e a t i n g s u r f a c e a rea i n the f i r s t e f f e c t (two a l t e r n a t i v e 2
s o l u t i o n s can be c o n s i d e r e d : the e x i s t i n g R o b e r t - t y p e body w i t h 1800 m
h e a t i n g - s u r f a c e a rea can be e i t h e r removed from the f a c t o r y , o r o n l y t e m p o r a r i l y
d i s c o n n e c t e d ) .
( i v ) I n t r o d u c e a vapour compress ion c i r c u i t and a d d i t i o n a l l y i n c r e a s e the
e f f e c t i v e n e s s r a t i o o f the thermal sys tem th rough improved u t i l i z a t i o n o f low-
temperature vapours (each s o l u t i o n c o n s i d e r e d i n the p reced ing s t e p g e n e r a t e s
two p o s s i b l e v e r s i o n s ) .
The p roposa l can be c o n v e n i e n t l y rev iewed by summar iz ing the main f e a t u r e s
o f two i n te rmed ia te s o l u t i o n s t ha t may r e s u l t from the comp le t ion o f s t e p s ( i )
and ( i i ) , as wel l a s f o u r p o s s i b l e v e r s i o n s among which a c h o i c e must be made
when e x e c u t i n g s t e p s ( i i i ) and ( i v ) . Tab le 9 . 3 shows c o n f i g u r a t i o n s o f the
e v a p o r a t o r s t a t i o n f o r a l l v e r s i o n s , t oge the r w i th data on the j u i c e
c o n c e n t r a t i o n s .
A l . An i n te rmed ia te s o l u t i o n r e s u l t i n g from s t e p ( i ) :
- steam j a c k e t s o f the e x t r a c t o r s a re heated by 2 n d - and 3 r d - e f f e c t v a p o u r s , and
2 n d - e f f e c t vapour i s a d d i t i o n a l l y i n j e c t e d i n t o the e x t r a c t i o n m i x t u r e , but no te
tha t vapour i n j e c t i o n may a d v e r s e l y a f f e c t the e f f e c t i v e n e s s r a t i o , be ing
p r i m a r i l y aimed a t s e c u r i n g a c o r r e c t temperature d i s t r i b u t i o n i n the e x t r a c t i o n
p r o c e s s ;
- the b u f f e r tank between p r e - l i m i n g and hot main l i m i n g i s conve r ted to a l ime r
i n which c o l d main l i m i n g can be pe r fo rmed ;
- one o f the h e a t e r s used h i t h e r t o f o r r a w - j u i c e h e a t i n g w i th vacuum-pan vapour
i s conve r ted to l i m e d - j u i c e h e a t i n g ( p r i o r to hot main l i m i n g ) w i th l a s t - e f f e c t
v a p o u r , a change which does not a f f e c t the e f f e c t i v e n e s s r a t i o ( the f low o f
l a s t - e f f e c t vapour to the condenser was anyway too l a r g e ) but s e c u r e s a c o r r e c t
temperature i n the hot main l i m i n g ;
- k i l n - g a s hea t i ng and h u m i d i f i c a t i o n a p p a r a t u s i s i n s t a l l e d be fo re the 1 s t
353
c a r b o n a t a t i o n ;
- a new b u f f e r tank i s i n s t a l l e d a f t e r the 2nd c a r b o n a t a t i o n to s e c u r e an
adequate j u i c e r e t e n t i o n t ime needed to s t a b i l i z e CaCO^ c r y s t a l s ;
- improved steam t r a p s are i n s t a l l e d i n condensa te d r a i n a g e l i n e s o f vacuum pans
A , and au tomat ic l e v e l con t r o l i s a t t ached to the condensa te tank c o l l e c t i n g
condensa tes from the h e a t i n g chambers o f the vacuum p a n s ;
- improved v e n t i n g o f the h e a t i n g chambers o f the vacuum pans i s implemented;
- improved v e n t i n g o f the h e a t i n g chambers o f the 2nd e v a p o r a t o r e f f e c t and o f
the j u i c e hea te r s heated w i th 1 s t - and 2 n d - e f f e c t vapours i s implemented;
- p i p e s o f i n c r e a s e d d iameters are i n s t a l l e d i n the c o n n e c t i o n s between the
vacuum pans and the c o n d e n s e r , as we l l as between the l a s t e v a p o r a t o r e f f e c t and
the c o n d e n s e r ;
- the C m a s s e c u i t e s t a t i o n i s extended by i n s t a l l i n g two v e r t i c a l - t y p e
c r y s t a l 1 i z e r s w i th a c a p a c i t y o f 150 m^ e a c h .
In s p i t e o f a number o f improvements i n t r o d u c e d to the thermal s y s t e m , the
measures l i s t e d above cannot be expec ted to reduce the fue l c o n s u m p t i o n .
A c t u a l l y , when b r i n g i n g p r o c e s s h e a t i n g back to n o r m a l , the t o t a l heat demand i s
i n c r e a s e d . Heat s a v i n g s can o n l y be o b t a i n e d by t a k i n g the next m o d e r n i z a t i o n
s t e p .
Conce rn ing the power demand, two minor improvements were p r o p o s e d :
- a t h y r i s t o r - c o n t r o l l e d d . c . d r i v e i n s t a l l e d i n the o u t l e t s e c t i o n o f the beet
washer ( to make bee t - f l ow con t r o l p o s s i b l e , and to save p o w e r ) ;
- a t h y r i s t o r - c o n t r o l l e d d . c . d r i v e a p p l i e d i n the j u i c e pump a f t e r 1 s t
c a r b o n a t a t i o n ( to min imize the i n f l u e n c e o f pumping on the s t r u c t u r e o f d e p o s i t s
to be f i l t e r e d , and to save power ) . I t s h o u l d be o b s e r v e d , however , t h a t an
i n c r e a s e o f the t o ta l power demand can be expec ted f o l l o w i n g the i n s t a l l a t i o n o f
a s t i r r e d c o l d main l imer and two C m a s s e c u i t e c r y s t a l 1 i z e r s .
A 2 . Another i n te rmed ia te s o l u t i o n , r e s u l t i n g f rom s t e p ( i i ) :
- the e v a p o r a t o r s t a t i o n i s extended by i n s t a l l i n g two f a l l i n g - f i l m b o d i e s w i t h
h e a t i n g s u r f a c e a r e a s o f 1400 m and 1000 m , to be used as the 4 th and 5th
e f f e c t s , r e s p e c t i v e l y ;
- no changes a re i n t r o d u c e d to the 1 s t and 2nd e v a p o r a t o r e f f e c t s , but the 3 rd
e f f e c t i s extended by add ing a R o b e r t - t y p e body p r e v i o u s l y used i n the 4 th
e f f e c t ;
- the condensa te d r a i n a g e subsys tem i s ex tended by i n s t a l l i n g two condensa te
t anks a t t ached to new e v a p o r a t o r b o d i e s ;
- a t h i c k - j u i c e c o n d i t i o n e r o f the vacuum type i s i n s t a l l e d a t the e v a p o r a t o r
o u t l e t to s t a b i l i z e the f i n a l c o n c e n t r a t i o n o f the t h i c k j u i c e , by means o f
s e l f - e v a p o r a t i o n o r t h i n - j u i c e i n t a k e , a t a l e v e l o f 70% D S .
The d i s t r i b u t i o n o f vapours and condensa tes and the r e s u l t s o f mass and heat
354
r l , ^! gl •Ľ Q
ç (NJ'
o
1 o
o
tν tν
Ă'"
ΐ'οε ö
- £ - ñ οε
ĂĆ7 9*1 J i
0ε·3 1!0 Éâç^ Fig
. 9
.8.
Sche
me
of
the
m
od
ern
ize
d th
erm
al
syst
em,
ve
rsio
n IK
Z.
355
1Ŕ
C D ,
liJ 00 1-
ů
9 6 Ί 1!0 Ιθπ^ Fig
. 9
.9.
Sch
eme
of
the
m
od
ern
ize
d th
erm
al
syst
em
, ve
rsio
n
Bl.
356
9 6 Ί 1!0 Ιθπ^ body
?
a!°
;esp
1ctive
ΝyK
' m
od
ern
ize
d th
erm
al
syst
em
, ve
rsio
ns
B2
and C
I (f
all
ing
-fil
m or
Ro
be
rt-t
yp
e u
nit
insta
lle
d a
s
357
ba lance c a l c u l a t i o n s o f the modern ized thermal sys tem a re shown i n F i g . 9 . 8 .
I n o r d e r to s t a b i l i z e the e x t r a c t i o n parameters and t h i c k - j u i c e c o n c e n t r a t i o n ,
as we l l as to m in im ize heat l o s s e s caused by the v e n t i n g o f n o n c o n d e n s a b l e s , i t
was a l s o p roposed to i n s t a l l some a d d i t i o n a l c o n t r o l equ ipment :
- au tomat i c c o n t r o l o f the temperature d i f f e r e n c e between raw j u i c e and incoming
c o s s e t t e s , by means o f a v a r i a b l e f l ow o f vapour i n j e c t e d i n t o the e x t r a c t i o n
m i x t u r e ;
- au tomat i c c o n t r o l o f the t h i c k - j u i c e c o n c e n t r a t i o n a t the o u t l e t o f the t h i c k
j u i c e c o n d i t i o n e r ;
- au tomat i c c o n t r o l o f the v e n t i n g o f the vacuum p a n s ;
- au tomat i c c o n t r o l o f the v e n t i n g o f the c l e a r - j u i c e hea te r (heated by 2 n d -
e f f e c t v a p o u r ) .
B l . Compress ion o f 2 n d - e f f e c t v a p o u r .
I n a d d i t i o n to the changes d e s c r i b e d a b o v e , a f a l l i n g - f i l m body w i t h a 2
h e a t i n g s u r f a c e a rea o f 2400 m i s i n s t a l l e d as the 1 s t e v a p o r a t o r e f f e c t
( r e p l a c i n g the o l d R o b e r t - t y p e b o d y ) . I n the vapour c o m p r e s s i o n c i r c u i t , 2 n d -
e f f e c t vapour i s r e c y c l e d to the h e a t i n g chamber o f the I s t - e f f e c t u s i n g an
e l e c t r i c a l l y - d r i v e n mechanica l c o m p r e s s o r . Other changes a re as f o l l o w s :
- t h i c k - j u i c e c o n c e n t r a t i o n 74% D S ;
- r a w - j u i c e h e a t i n g i n a s p i r a l hea te r u s i n g ho t water f rom a "ho t c o n d e n s e r " i n
which vacuum-pan vapours a re c o n d e n s e d ;
- p r e - l i m e d j u i c e h e a t i n g w i t h l a s t - e f f e c t vapour i n two t u b u l a r heat e x c h a n g e r s
p r e v i o u s l y used as raw j u i c e h e a t e r s ;
- t h i n - j u i c e h e a t i n g i n f o u r s t a g e s ;
- the s t e a m - t u r b i n e d r i v e n feed -wa te r pump r e p l a c e d by an e l e c t r i c a l l y - d r i v e n
o n e .
The d i s t r i b u t i o n o f vapou rs and condensa tes and the r e s u l t s o f mass and heat
ba lance c a l c u l a t i o n s o f t h i s v e r s i o n a re shown i n F i g . 9 . 9 . I t can be f u r t h e r
es t ima ted t ha t the combined power demand o f the vapour compresso r and the f e e d -
water pump i s about 920 kW. Owing to reduced heat demand, the power demand o f
the c o m b u s t i o n - a i r f a n s and the b a r o m e t r i c - w a t e r pumps can s i m u l t a n e o u s l y be
reduced by about 300 kW.
B 2 . Compress ion o f I s t - e f f e c t vapour to a f a l l i n g - f i l m body .
Two f a l l i n g - f i l m b o d i e s , 1500 m^ ( l a ) and 2400 m^ ( l b ) , a re i n s t a l l e d i n the
1 s t e v a p o r a t o r e f f e c t and I s t - e f f e c t vapour i s r e c y c l e d to the h e a t i n g chamber
o f body l a u s i n g an e l e c t r i c a l l y - d r i v e n mechan ica l c o m p r e s s o r . A new tank i s
i n s t a l l e d to c o l l e c t the condensa te d r a i n e d f rom body l a . Other d e t a i l s remain
the same as i n the p reced ing v e r s i o n , excep t t h a t the e x h a u s t - s t e a m tempera ture
i s 3 Κ l owe r , r e s u l t i n g i n a lower b a c k - p r e s s u r e and thus more power genera ted
i n the t u r b o - g e n e r a t o r . Fo r data on mass and heat b a l a n c e s , see F i g . 9 . 1 0 .
358
The combined power demand o f the vapour compressor and the f eed -wa te r pump i s
about 660 kW. The power demand r e d u c t i o n r e s u l t i n g f rom reduced heat demand i s
the same as i n v e r s i o n B l .
C I . Compress ion o f I s t - e f f e c t vapour to a R o b e r t - t y p e body.
A f a l l i n g - f i l m body , 2400 m^, i s added to the e x i s t i n g R o b e r t - t y p e body i n
the 1 s t e v a p o r a t o r e f f e c t . The vapour compress ion c i r c u i t remains i d e n t i c a l to
t ha t o f the p reced ing v e r s i o n , but the compressed vapour i s r e c y c l e d to the
h e a t i n g chamber o f body l b . As the h e a t i n g s u r f a c e a rea o f the R o b e r t - t y p e body
i s l a r g e r than t ha t o f the f a l l i n g - f i l m body , the temperature d i f f e r e n c e between
h e a t i n g - s t e a m and vapour can be r e d u c e d , r e s u l t i n g i n a reduced power demand by
the compresso r . The mass and heat b a l a n c e s a re n e a r l y the same as i n the
p reced ing v e r s i o n . The combined power demand o f the compressor and the f e e d -
water pump i s about 600 kW. The power-demand r e d u c t i o n i n the rema in ing
equipment i s i d e n t i c a l to t h a t i n v e r s i o n s Bl and B 2 .
C 2 . Thermocompress ion o f I s t - e f f e c t v a p o u r .
The e v a p o r a t o r s t a t i o n i s i d e n t i c a l to t ha t o f the p r e c e d i n g v e r s i o n but the
I s t - e f f e c t vapour i s compressed u s i n g j e t - t y p e c o m p r e s s o r s . Wh i le the mass and
heat b a l a n c e s o f the thermal sys tem i n the p r o c e s s - h e a t i n g a rea remain i d e n t i c a l
to t hose o f v e r s i o n s B2 and C I , the mass and energy b a l a n c e s o f the power house
and the 1 s t e v a p o r a t o r e f f e c t a re changed as shown i n F i g . 9 . 1 1 . The power
demand o f the feed -wa te r pump i s app rox ima te l y equal to the power-demand
r e d u c t i o n r e s u l t i n g from reduced heat demand, so the t o t a l power demand i s equal
to t ha t o f v e r s i o n s A l , A2 and B l .
l osses 0.5
F i g . 9 . 1 1 . E x c e r p t s from mass and heat b a l a n c e s o f the modern ized thermal s y s t e m , v e r s i o n C 2 .
359
9 . 3 . 4 Compar ison o f s o l u t i o n s
An approx imate economic a n a l y s i s o f the m o d e r n i z a t i o n p r o p o s a l was p r e p a r e d ,
to compare the s o l u t i o n s ( B l , B 2 , CI and C2) and to s e l e c t the most f e a s i b l e
v e r s i o n . The gene ra l approach adopted was s i m i l a r to t h a t p r e s e n t e d i n S e c t i o n
9 . 2 . 4 , w i th the f o l l o w i n g e x t e n s i o n s :
- the v e c t o r o f a t t r i b u t e s i n c l u d e s a d d i t i o n a l s u g a r p r o d u c t i o n ;
- when a n a l y s i n g the inves tmen t c o s t , i t s h o u l d be taken i n t o accoun t t ha t i f a
c e r t a i n equipment u n i t i s removed from the f a c t o r y i n q u e s t i o n , i t can be
c o n s i d e r e d f o r a p p l i c a t i o n i n o t h e r s u g a r f a c t o r i e s o f the same company;
- the p o s s i b i l i t y o f f u t u r e changes i n fue l and power p r i c e s s h o u l d be a l l owed
f o r ;
- when c a l c u l a t i n g the p e r i o d o f r e t u r n on i n v e s t m e n t , c a p i t a l c o s t and
i n c r e a s e d main tenance c o s t s h o u l d be accoun ted f o r .
In v e r s i o n s Bl and B 2 , removal o f the e x i s t i n g R o b e r t - t y p e body from the 1 s t
e v a p o r a t o r e f f e c t was assumed. As i t can be a p p l i e d i n ano the r s u g a r f a c t o r y ,
the va lue o f t h i s equipment u n i t was deducted f rom the i nves tmen t c o s t s o f t h e s e
v e r s i o n s .
The es t ima ted r e s u l t s o f the m o d e r n i z a t i o n , t h a t i s , the fue l s a v i n g , power
demand i n c r e a s e and a d d i t i o n a l s u g a r p r o d u c t i o n , were taken f rom the d e s i g n
a n a l y s i s p resen ted i n the p r e v i o u s S e c t i o n . Two economic e s t i m a t e s were
determined f o r fue l s a v i n g s and power demand i n c r e a s e s :
1 . u s i n g the ac tua l p r i c e s o f fue l o i l and power ;
2 . u s i n g the f o r e c a s t ave rage p r i c e s f o r the i n i t i a l s e a s o n s w i t h the modern ized
f a c t o r y ; e . g . f o r a p e r i o d o f t h ree y e a r s , a f ue l o i l p r i c e i n c r e a s e d by 50% and
power p r i c e by 35%.
The c a p i t a l c o s t and i n c r e a s e d main tenance c o s t were j o i n t l y e s t i m a t e d , u s i n g
an e q u i v a l e n t i n t e r e s t r a te o f 0 . 1 3 . As a f i r s t a p p r o x i m a t i o n , the p e r i o d o f
r e t u r n on i n v e s t m e n t , i n y e a r s , was c a l c u l a t e d u s i n g the fo rmu la
τ = I / ( A - r l ) ( 9 . 2 )
where I i s the i nves tmen t c o s t , A i s the annual s a v i n g , and r i s the e q u i v a l e n t
i n t e r e s t r a t e .
The r e s u l t s o f the compara t i ve a n a l y s i s a re shown i n Tab le 9 . 4 . As i n Tab le
9 . 2 i n S e c t i o n 9 . 2 . 4 , the c o s t s a re g i v e n r e l a t i v e to the i nves tmen t c o s t o f
a s e l e c t e d v e r s i o n . I t has been assumed t ha t the i nves tmen t c o s t a s s o c i a t e d w i th
mode r n i za t i on s t e p ( i ) i s 100%.
The con ten t s o f Tab le 9 . 4 can be summarized as f o l l o w s :
- the i n te rmed ia te s o l u t i o n s a re e c o n o m i c a l l y h i g h l y a t t r a c t i v e ;
- the economic r e s u l t s o f f u r t h e r i nves tmen ts i n the ene rgy economy a re
dependent on developments i n the fue l ma rke t ;
360
TAB
LE 9
.4
Com
pari
son
of
mai
n te
ch
nic
al
an
d
econ
omic
p
ara
me
ters
o
f d
iffe
ren
t m
od
ern
iza
tio
n v
ers
ion
s.
Ve
rsio
n E
xis
tin
g
Al
A2
Β
C
Bl B
2 C
I C
2
Pro
cess
ing
ca
pa
bilit
y
5900
60
00
6000
60
00
6000
60
00
6000
60
00
6000
Fu
el-
oil
de
man
d (k
g/1
00
kg
b)
2.6
8
2.7
5
2.3
0
2.3
0
2.3
0
1.9
5
1.9
5
1.9
5
2.0
9
Fu
el-
oil
s
av
ing
rela
tive
to
e
arl
ier
ve
rsio
n
(kg
/10
0
kg
b)
- -0
.07
0.3
8
0.3
8
0.3
8
0.3
5
0.3
5
0.3
5
0.2
1
Pow
er
dem
and
(kW
h/1
00
kg
b)
2.8
5
2.8
5
2.8
5
2.8
5
2.8
5
3.0
3
2.9
5
2.9
4
2.8
5
Pow
er-d
eman
d in
cre
ase
(kW
) -
- -
- -
62
0
36
0
300
Su
ga
r-o
utp
ut
incre
ase
(k
g/1
00
kg
b
- 0
.42
--
--
--
-T
ota
l e
va
po
rato
r h
ea
tin
g
su
rfa
ce
a
rea
(m2
72
00
7200
96
00
1020
0 10
200
1020
0 1
17
00
12
000
1200
0
Inve
stm
ent
co
st
(%)
- T
OO
4
2
69
^ 7
6^
32 5
7 3
9
22
Va
lue
of
fue
l o
il sa
ved
per
sea
son
(%)
- a
t a
ctu
al
pri
ce
-
-5.3
34 3
4 3
4 2
6 2
6 2
6
16
- a
t fo
reca
st
pri
ce
-
- 38
45
45
42
42
42
25
Co
st
of
ad
dit
ion
al
pow
er
purc
hase
d per
sea
son
{%)
- a
t a
ctu
al
pri
ce
-
- 10
6
5-
- a
t fo
reca
st
pri
ce
-
- -
- -
14
8
7
-V
alu
e o
f a
dd
itio
na
l su
ga
r p
rod
uce
d per
seas
on
W
- 199
-
Pe
rio
d
of
retu
rn
on
in
vest
me
nt
(ye
ars
) -
at
actu
al
pri
ce
s -
0.5
4
1.5
2
.8
3.1
2
.7
4.4
2
.4
1.7
-
at
fore
ca
st
pri
ce
s -
- 1
.3
1.9
2
.2
1.3
2
.1
1.3
1
.0
^/
inclu
din
g
the
co
st
of
ve
rsio
n
A2
361
- among the v e r s i o n s c o n s i d e r e d , CI and C2 a re c h a r a c t e r i z e d by the s h o r t e s t
p e r i o d s o f r e t u r n on i n v e s t m e n t .
9 . 4 OPTIMIZATION OF ENERGY SYSTEMS
9 . 4 . 1 P r a c t i c a l meaning o f d e s i g n o p t i m i z a t i o n
With the t r a d i t i o n a l d e s i g n me thods , improvements a re i n t r o d u c e d to ene rgy
sys tems u s i n g the l e a r n i n g - b y - e x p e r i e n c e a p p r o a c h . When e v a l u a t i n g the r e s u l t s
o b t a i n e d from s u g a r f a c t o r y o p a r a t i o n , the o p e r a t o r s and d e s i g n e r s l e a r n f rom
t h e i r m i s t a k e s . As a new f a c t o r y i s e r e c t e d o r an e x i s t i n g one i s m o d e r n i z e d ,
a t tempts a re made to improve the energy economy i n r e l a t i o n to e a r l i e r
s o l u t i o n s . The r e s u l t s a re ve ry much dependent on the e n g i n e e r ' s i n t u i t i o n and
e x p e r i e n c e , and i t may be i m p o s s i b l e to determine j u s t how c l o s e a d e s i g n i s to
the rea l minimum energy demand. On the o t h e r h a n d , i t i s i n c r e a s i n g l y o f t e n
r e q u i r e d t ha t e n e r g y - c o s t s a v i n g s s h o u l d be ba lanced a g a i n s t c a p i t a l i n ves tmen ts
and economic and o p e r a t i n g c o n s t r a i n t s to i d e n t i f y the most c o s t - e f f e c t i v e
d e s i g n i n any g i v e n s i t u a t i o n . I n o r d e r to make i t p o s s i b l e f o r e n g i n e e r s to use
t h i s a p p r o a c h , new compute r -a ided methods have been p roposed f o r e n e r g y - s y s t e m
d e s i g n .
In the f o l l o w i n g , s h o r t rev iews a re g i v e n o f the u n d e r l y i n g p r i n c i p l e s o f
sys tem s y n t h e s i s by mathemat ical programming and the p r o c e s s i n t e g r a t i o n
t e c h n i q u e . Both methods o r i g i n a t e d f rom the needs o f gene ra l p r o c e s s e n g i n e e r i n g ,
and p a r t i c u l a r l y from the n e c e s s i t y to shape ene rgy sys tems o f complex and o f t e n
e n t i r e l y new chemical p r o c e s s e s r a t i o n a l l y , where i t may be i m p o s s i b l e to use
the e v o l u t i o n a r y a p p r o a c h . I n the s u g a r i n d u s t r y , the s i t u a t i o n i s d i f f e r e n t
because the p r o c e s s has changed r e l a t i v e l y l i t t l e o v e r many d e c a d e s . When
a p p l i e d to an e x i s t i n g s u g a r f a c t o r y , the new methods migh t j u s t i n d i c a t e t h a t
the p r o c e s s i s o p e r a t i n g c l o s e to minimum ene rgy demand and any improvement can
be ach ieved o n l y by i n t r o d u c i n g new u n i t o p e r a t i o n s and equ ipment . When new
s o l u t i o n s are c o n s i d e r e d , however , the new methods may prove u s e f u l i n s t u d y i n g
t h e i r e n e r g y - s a v i n g p o t e n t i a l and max im iz ing p o s s i b l e p r o f i t s .
9 . 4 . 2 E n e r g y - s y s t e m s y n t h e s i s u s i n g mathemat ica l programming methods
"Mathemat ica l programming" i s the common name o f s e v e r a l mathemat ica l
t echn iques t ha t at tempt to s o l v e prob lems by m i n i m i z i n g o r max im iz i ng a f u n c t i o n
( c a l l e d the o b j e c t i v e f u n c t i o n ) o f s e v e r a l independent v a r i a b l e s . T y p i c a l
i n d u s t r i a l a p p l i c a t i o n s i n c l u d e de te rm in i ng the optimum a l l o c a t i o n o f r e s o u r c e s
( i . e . , c a p i t a l , raw m a t e r i a l s , manpower, e t c . ) to o b t a i n maximum p r o f i t o r
minimum c o s t f o r the p r o j e c t , c h o o s i n g the optimum v a l u e s o f d e s i g n v a r i a b l e s to
o b t a i n minimum c o s t o r maximum th roughpu t o f the equipment u n i t , e t c . Opt imal
a l l o c a t i o n o f r e s o u r c e s o r opt imal v a l u e s o f d e s i g n v a r i a b l e s must be determined
under c o n d i t i o n s where the re a re a l t e r n a t i v e u s e s o f r e s o u r c e s o r a l t e r n a t i v e
362
d e s i g n s , and where p h y s i c a l , economic and o t h e r c o n s t r a i n t s must be met. The
c o n s t r a i n t s take the form o f e q u a t i o n s o r i n e q u a l i t i e s c o n t a i n i n g the same
problem v a r i a b l e s as appear i n the o b j e c t i v e f u n c t i o n .
R e s t r i c t i n g our a t t e n t i o n to the energy economy o f s u g a r f a c t o r i e s , we can
s t a t e tha t f o r a g i v e n scheme and known parameters o f the s u g a r m a n u f a c t u r i n g
p r o c e s s , a l t e r n a t i v e e n e r g y - s y s t e m d e s i g n s can be c o n s i d e r e d . Each d e s i g n i s
d e f i n e d by :
- a sys tem s t r u c t u r e ( i . e . a s e t o f components and t h e i r c o n n e c t i o n s ) ;
- parameters o f the energy c o n v e r s i o n , d i s t r i b u t i o n and u t i l i z a t i o n p r o c e s s e s
( f l ows o f e n e r g y - c a r r y i n g med ia , t e m p e r a t u r e s , e t c . ) .
Le t us assume t h a t the s e t o f p o s s i b l e sys tem s t r u c t u r e s i s l i m i t e d to a few
v e r s i o n s and the problem c o n s i s t s o f de te rm in ing the v a l u e s o f η unknown
v a r i a b l e s ×2, . . , x^ c h a r a c t e r i z i n g the components and the ene rgy p r o c e s s e s
o f each v e r s i o n . The c o n s t r a i n t s e t t h a t d e s c r i b e s a t y p i c a l ene rgy sys tem
c o n s i s t s l a r g e l y o f the f o l l o w i n g r e l a t i o n s h i p s .
( i ) E q u a t i o n s f o r the mass and energy b a l a n c e s f o r p r o c e s s u n i t s and equipment
i tems c o n s i d e r e d , i n c l u d i n g m u l t i p l e - e f f e c t e v a p o r a t o r , j u i c e h e a t e r s , e x t r a c t o r ,
t u r b i n e , e t c .
( i i ) E q u a t i o n s f o r heat and power demand.
( i i i ) Upper and lower bounds f o r the independent v a r i a b l e s .
( i v ) E q u a t i o n s and i n e q u a l i t i e s t ha t a re f a c t o r y - d e p e n d e n t .
U s i n g the n o t a t i o n χ = (X ] ,X2> . . fXp )5 we may w r i t e down the gene ra l form o f the
c o n s t r a i n t s e t as
fT(x) = 0 i = 1 , 2 , . . , ρ ( 9 . 3 )
^ j ( x ) < 0 j = 1 , 2 , . . , q ( 9 . 3 )
The o b j e c t i v e f u n c t i o n f o r an ene rgy sys tem can range from ve ry s i m p l e to
q u i t e complex. The s i m p l e s t c o n s i s t o f a s i n g l e v a r i a b l e r e p r e s e n t i n g , f o r
example , the l i v e steam demand, o r the t o t a l fue l demand. I n e i t h e r c a s e , the
o b j e c t i v e f u n c t i o n i s m i n i m i z e d .
A comprehens ive o b j e c t i v e can be d e f i n e d as the sum o f o p e r a t i n g expenses
( i n c l u d i n g f u e l , e l e c t r i c power, f eed -wa te r make-up f o r the b o i l e r , e t c . ) and
the c o s t ^ f c a p i t a l r e c o v e r y , p l u s a r e t u r n on inves tmen t f o r major equ ipment .
F o r a new energy sys tem ( i n a modern ized o r an e n t i r e l y new f a c t o r y ) a t the
d e s i g n s t a g e , t h i s o b j e c t i v e f u n c t i o n r e p r e s e n t s the t o t a l v a r i a b l e c o s t o f the
sys tem and i s a l s o m i n i m i z e d .
Between the two t ypes o f o b j e c t i v e f u n c t i o n ment ioned a b o v e , f u n c t i o n s o f
i n te rmed ia te comp lex i t y can be i m a g i n e d . S e l e c t i o n o f a p a r t i c u l a r o b j e c t i v e
f u n c t i o n , to r e f l e c t the w i s h e s and e x p e c t a t i o n s o f the d e c i s i o n - m a k e r s , i s
o f t en t r e a t e d as a pa r t o f the d e s i g n s t u d y . I n a p r e l i m i n a r y d e s i g n , i t may be
s u f f i c i e n t to m in im ize the t o t a l steam o r fue l demand. I n a d e t a i l e d d e s i g n , the
363
o b j e c t i v e f u n c t i o n s h o u l d i n c l u d e a l l the e s s e n t i a l f a c t o r s t h a t a f f e c t the
economic r e s u l t s o f f a c t o r y o p e r a t i o n .
Hav ing s p e c i f i e d the o b j e c t i v e f u n c t i o n F(x^) , we can fo rmu la te the
mathemat ica l programming problem which i s an a b s t r a c t r e p r e s e n t a t i o n o f the
problem o f opt imal s y n t h e s i s o f the ene rgy s y s t e m . Among a l l the p o s s i b l e x ' s we
a re s e e k i n g such an xP ( i . e . , x°,X2>.. »2< ) t h a t the o b j e c t i v e f u n c t i o n a t t a i n s
i t s minimum
F ( x ° ) = mjn F ( x ) ( 9 . 5 )
Of c o u r s e , x ° can be accepted o n l y i f i t s a t i s f i e s the c o n s t r a i n t s ( 9 . 3 ) and
( 9 . 4 ) .
From the mathemat ical p o i n t o f v iew the p rob lem, c o n s i s t i n g o f c o n d i t i o n s
( 9 . 3 ) - ( 9 . 5 ) , can be e i t h e r l i n e a r o r n o n l i n e a r . I n the former c a s e , the
f u n c t i o n s F , f , and f . must be l i n e a r , t h a t i s , i t s h o u l d be p o s s i b l e to e x p r e s s ' J η
each o f them i n the form ^E^aj^Xj^, where a p a2» . . j a re known c o n s t a n t s . I f
a t l e a s t one o f the f u n c t i o n s i n v o l v e d i s n o n l i n e a r , then the e n t i r e problem i s
s a i d to be n o n l i n e a r . Depending on the prob lem t y p e , d i f f e r e n t mathemat ica l
p rocedures must be a p p l i e d to f i n d a s o l u t i o n .
I t i s an i n h e r e n t p r o p e r t y o f the problems o f e n e r g y - s y s t e m o p t i m i z a t i o n t ha t
some o f the r e l a t i o n s h i p s ment ioned under ( i ) , ( i i ) and ( i v ) a re n o n l i n e a r . I n
p r i n c i p l e , i t may be p o s s i b l e to t r a n s f o r m such r e l a t i o n s h i p s i n t o l i n e a r ones
and to app l y wel l p r o v e n , r e l i a b l e l i n e a r programming methods to f i n d a s o l u t i o n
( r e f . 8 ) . I t has a l s o been demons t ra ted , however , t h a t n o n l i n e a r prob lems can be
e f f e c t i v e l y s o l v e d u s i n g a p p r o p r i a t e numer ica l methods ( r e f s . 9 , 1 0 ) . Fo r
example , opt imal s y n t h e s i s o f a thermal sys tem f e a t u r i n g a q u a d r u p l e - e f f e c t
e v a p o r a t o r has been fo rmu la ted and s o l v e d as a n o n l i n e a r programming prob lem
w i th 2 4 - 2 6 v a r i a b l e s and 19 -24 c o n s t r a i n t s , the e x a c t number o f v a r i a b l e s and
c o n s t r a i n t s depending on the sys tem s t r u c t u r e c o n s i d e r e d ( r e f . 1 1 ) .
I t i s worth n o t i n g t ha t the f i r s t s u c c e s s f u l a t tempts to i n t r o d u c e the
methods o f opt imal sys tem s y n t h e s i s to the s u g a r i n d u s t r y took p l ace a t the
b e g i n n i n g o f the 1 9 7 0 s , when t h i s approach was r e l a t i v e l y new. I t can be seen i n
the l i t e r a t u r e , however , t ha t a w ide r i n t e r e s t i n the a p p l i c a t i o n o f
o p t i m i z a t i o n methods to the food i n d u s t r i e s began some ten y e a r s l a t e r ( r e f s .
1 2 , 1 3 ) . T a k i n g advantage o f the development o f mathemat ica l t e c h n i q u e s , i t i s
now p o s s i b l e to o p t i m i z e the sys tem s t r u c t u r e a l o n g w i t h the parameters o f the
components and p r o c e s s e s .
9 . 4 . 3 E n e r g y - s y s t e m d e s i g n u s i n g the techn ique o f p r o c e s s i n t e g r a t i o n
A d i s a d v a n t a g e o f the opt imal s y n t h e s i s approach d i s c u s s e d i n the p r e c e d i n g
S e c t i o n i s t h a t the t r a n s l a t i o n o f r e a l - l i f e d e s i g n problems to a b s t r a c t
mathemat ical fo rmulae i s both d i f f i c u l t and t i m e - c o n s u m i n g . Even w i th computer
364
programs tha t automate the min imum-seek ing c o m p u t a t i o n s , a l o t o f e f f o r t must be
spen t on the i d e n t i f i c a t i o n o f c o n s t r a i n t s and t h e i r mathemat ica l f o r m u l a t i o n ,
p r e p a r a t i o n o f i n p u t data i n accordance w i th the mathemat ica l c o n v e n t i o n a s s u m e d ,
e t c . Once the o p t i m i z a t i o n r e s u l t s have been o b t a i n e d , however , the d e s i g n e r s
tend to t r e a t the f i g u r e s w i th some s u s p i c i o n because they a re u s u a l l y unab le to
con t r o l i n t u i t i v e l y the p r o c e s s o f a r r i v i n g a t a s o l u t i o n . A b e t t e r i n s i g h t can
o n l y be g a i n e d i n an i n d i r e c t manner , by r e p e a t i n g the o p t i m i z a t i o n compu ta t i ons
f o r m u l t i p l e s e t s o f i n p u t data and a n a l y s i n g the s o l u t i o n ' s s e n s i t i v i t y to
changes o f impor tan t i n p u t parameters ( l i k e the p r i c e s o f f ue l and power , c a p i t a l
c o s t r a t e , e t c . ) . Owing to the a s s o c i a t e d work load and the p s y c h o l o g i c a l b a r r i e r ,
t h i s approach may be d i f f i c u l t to adopt as a p a r t o f the e n g i n e e r i n g a c t i v i t i e s .
P r o c e s s i n t e g r a t i o n i s a t echn ique to f a c i l i t a t e s y s t e m a t i c thermodynamic
a n a l y s i s o f comp l i ca ted energy s y s t e m s . O r i g i n a t i n g from the work on mathemat ica l
t o o l s to s y n t h e s i z e e n e r g y - o p t i m a l heat exchanger networks ( r e f s . 1 4 , 1 5 ) , i t can
he lp the u s e r to unde rs tand how and where a v a i l a b l e energy can b e s t be s u p p l i e d
and r e - u s e d w i t h i n the p r o c e s s , and a t what temperature i t s h o u l d be r e j e c t e d
from the p r o c e s s ( r e f s . 1 6 , 1 7 ) .
An i n t r o d u c t i o n to the r e a s o n i n g c h a r a c t e r i s t i c o f p r o c e s s i n t e g r a t i o n can be
g i v e n by u s i n g the s o - c a l l e d compos i te c u r v e s i n a g raph showing cumu la t i ve heat
l o a d s as f u n c t i o n s o f tempera tu re . The g raph can be c o n s t r u c t e d f rom mass and
heat ba lance data c o n s i s t i n g o f the mass f l o w , en tha lpy o r s p e c i f i c h e a t , s u p p l y
temperature and r e q u i r e d ( t a r g e t ) temperature f o r each p r o c e s s s t r e a m .
The hot compos i te r e p r e s e n t s the amount o f heat a v a i l a b l e a t v a r i o u s
tempera tures o f the hot p r o c e s s media (exhaus t s t e a m , h e a t i n g v a p o u r s , condensa te
c o n d e n s a t e , e t c . ) . T h i s heat must be removed to dec rease the e n t h a l p i e s o f the
ho t med ia , i n accordance w i t h the assumed methods o f t h e i r u t i l i z a t i o n . The c o l d
compos i te r e p r e s e n t s the amount o f heat r e q u i r e d a t v a r i o u s tempera tu res o f the
c o l d p r o c e s s media ( c o s s e t t e s , p r e s s w a t e r , j u i c e i n v a r i o u s s t a g e s o f the
p r o c e s s , s y r u p s , e t c . ) . T h i s heat must be s u p p l i e d to i n c r e a s e the tempera tu res
o f the c o l d media to t h e i r r e q u i r e d v a l u e s , as d e f i n e d by the p r o c e s s n e e d s .
Assuming a h y p o t h e t i c a l s i t u a t i o n t ha t the re i s no heat r e c o v e r y i n the ene rgy
s y s t e m , i t would be n e c e s s a r y to s u p p l y the e n t i r e heat amount r e p r e s e n t e d by
the c o l d compos i te i n the b o i l e r f u e l . S i m u l t a n e o u s l y , the heat amount a v a i l a b l e
i n the hot media would need to be removed from the p r o c e s s u s i n g c o o l i n g wa te r .
U s i n g heat r e c o v e r y , t ha t i s , a l l o w i n g f o r some o f the heat a v a i l a b l e i n the ho t
s t reams to cove r the heat demand o f the c o l d s t r e a m s , i t becomes p o s s i b l e to
reduce the fue l demand. T h i s can be done i n a v a r i e t y o f w a y s , and e x p e r i e n c e
p roves t ha t some o f the h e a t - r e c o v e r y s o l u t i o n s may be p r e f e r a b l e to o t h e r s .
The p o t e n t i a l f o r heat r e c o v e r y by heat exchange between hot and c o l d p r o c e s s
media can be i n v e s t i g a t e d by f i x i n g the r e l a t i v e p o s i t i o n s o f the hot and c o l d
365
100 150 200
Heat load (MW)
150
Heat load (MW)
F i g . 9 . 1 2 . Examples o f cumu la t i ve heat l o a d s as f u n c t i o n s o f t empera tu re . 1 -hot c o m p o s i t e , 2 - c o l d c o m p o s i t e , 3 - p i n c h p o i n t , 4 - minimum heat s u p p l y , 5 - minimum heat r e j e c t i o n .
compos i te c u r v e s , as shown i n F i g . 9 . 1 2 . The d i s t a n c e between them i n the
d i r e c t i o n o f the temperature a x i s must be g r e a t e r t h a n , o r equal t o , the minimum
accep tab le temperature d i f f e r e n c e c h a r a c t e r i s t i c o f the hea t -exchange equipment
a v a i l a b l e ( i n a way, t h i s temperature d i f f e r e n c e r e f l e c t s the a t t a i n a b l e o v e r a l l
heat t r a n s f e r c o e f f i c i e n t , see S e c t i o n 3 . 3 . 2 ) . Once the minimum temperature
d i f f e r e n c e has been d e f i n e d , the r e l a t i v e p o s i t i o n s o f both c u r v e s become f i x e d
and the amounts o f heat to be s u p p l i e d , exchanged and r e j e c t e d can be de te rm ined .
I t a l s o becomes p o s s i b l e to i d e n t i f y the p i n c h p o i n t , t ha t i s , the p o i n t on the
graph where the compos i te c u r v e s a re s e p a r a t e d by the minimum temperature
d i f f e r e n c e .
The p inch p o i n t s e p a r a t e s two d i s t i n c t r e g i o n s o f the p r o c e s s . A t
tempera tures above the p i n c h - p o i n t t empe ra tu re , a l l the heat a v a i l a b l e i n the
hot media can be t r a n s f e r r e d to the c o l d m e d i a , and the heat d e f i c i t must be
ba lanced by s u p p l y i n g f u e l . Below the p i n c h - p o i n t t empe ra tu re , a l l the h e a t i n g
needs o f the c o l d media can be s a t i s f i e d u s i n g the heat a v a i l a b l e i n the hot
med ia , and the s u r p l u s heat must f i n a l l y be r e j e c t e d . I t can thus be conc luded
t ha t the re s h o u l d be no heat t r a n s f e r a c r o s s the p i n c h , as any heat amount
t r a n s f e r r e d w i l l i n c r e a s e the d e f i c i t i n the upper r e g i o n ; t h i s w i l l l ead to
i n c r e a s e d fue l demand, and more i n s t a l l e d h e a t i n g s u r f a c e a rea than r e a l l y
needed. Heat t r a n s f e r a c r o s s the p i nch s h o u l d t h e r e f o r e be a v o i d e d i n a new
d e s i g n . When i n v e s t i g a t i n g p o s s i b l e improvements i n an e x i s t i n g f a c t o r y , the
366
p i n c h - p o i n t temperature s h o u l d be determined and the c a s e s o f i n c o r r e c t h e a t i n g
s h o u l d be i d e n t i f i e d .
I t s h o u l d be p o i n t e d ou t t h a t the above c o n c l u s i o n s r e l a t i n g to the e n e r g y
t a r g e t s and heat t r a n s f e r a r rangements can be drawn be fo re i n i t i a t i n g d e s i g n
work , and the i n f o r m a t i o n thus a c q u i r e d can be t r ea ted as a d e s i g n g u i d e l i n e .
A c t u a l l y , i f the p i n c h - p o i n t temperature i s known, then a d d i t i o n a l i n f o r m a t i o n
can be ob ta i ned r e g a r d i n g o t h e r energy p r o c e s s e s t o o . Fo r examp le , i t s h o u l d be
c l e a r t ha t a vapour compress ion c i r c u i t can save energy o n l y i f i t t akes the
heat from below the p inch and s u p p l i e s i t to a temperature l e v e l above the p i nch
p o i n t where t he re i s a heat d e f i c i t . T h i s i s an unambiguous c r i t e r i o n making i t
p o s s i b l e to i d e n t i f y economic a p p l i c a t i o n s o f vapour c o m p r e s s i o n .
As can be seen i n F i g . 9 . 1 2 , w h i l e the minimum accep tab le temperature
d i f f e r e n c e a f f e c t s the r e l a t i v e p o s i t i o n s o f the compos i te c u r v e s , i t a l s o
de termines the w id th o f the r e g i o n o f o v e r l a p r e p r e s e n t i n g p o s s i b l e heat
e x c h a n g e , and the w id th o f the r e g i o n r e p r e s e n t i n g n e c e s s a r y heat s u p p l y . T a k i n g
i n t o accoun t the c o s t s o f h e a t - e x c h a n g e r s u r f a c e s and energy and a p p l y i n g
compute r -a ided o p t i m i z a t i o n methods , i t becomes p o s s i b l e to f i n d the most
economic v a l u e o f the minimum temperature d i f f e r e n c e . The r e s u l t i n g d e s i g n
g u i d e l i n e s can then be t r e a t e d as opt imal w i th r e s p e c t to o v e r a l l f a c t o r y
economy. U s i n g t hese g u i d e l i n e s , the most economic e n e r g y - s y s t e m o p t i o n s to be
c o n s i d e r e d i n the d e t a i l e d d e s i g n a re e a s i l y i d e n t i f i e d .
REFERENCES
1 N . P . Romensk i i ( E d . ) , R e k o n s t r u k t s i y a i Tekhn i cheskoe P e r e v o o r u z h e n i e Sakharnykh Zavodov , T e k h n i k a , K i e v , 1 9 8 5 .
2 H. Wunsch , E r k e n t n i s s e und E r f a h r u n g e n bei der P lanung von K a p a z i t δ t s e rwe i te rungen i n Z u c k e r f a b r i k e n , Z u c k e r i n d . , 1 0 7 ( 1 0 ) ( 1982 ) 9 3 2 - 9 3 4 .
3 W. Lekawski and K. U r b a n i e c , M o d e r n i s i e r u n g der Wδrmewi r tscha f t i n Z u c k e r f a b r i k e n , Z u c k e r i n d . , 1 0 8 ( 4 ) (1983) 3 3 8 - 3 4 3 .
4 R. M i c h e l , P h . Ternynck and P h . B o n n e n f a n t , R e a l i s a t i o n du pos te d ' e v a p o r a t i o n dans une u s i n e de 12000 t / j de b e t t e r a v e s s t o c k a n t 60% du s i r o p p r o d u i t en campagne, I n d . A l i m . A g r i e , 9 4 ( 7 - 8 ) (1977 ) 7 0 1 - 7 0 5 . Η. C y r k l a f f (e t a l . ) , M o d e r n i z a c j a g o s p o d a r k i c i e p l n e j cukrowni Che lmza , Gaz . C u k r o w . , 9 2 ( 7 - 8 H . R . B runner (e t a l .
(1984) 1 5 6 - 1 5 7 . , D ie Ve rdamp fs ta t i on der Z u c k e r f a b r i k + R a f f i n e r i e
Aa rbe rg AG und das M u l t i - E n e r g i e - S c h e m a , Z u c k e r i n d . , 1 1 0 ( 5 ) (1985 ) 3 9 3 - 3 9 8 . / P . Hof fman, Optimal i z a c e e n e r g e t i c k e h o h o s p o d a r s t v i c u k r o v a r u L o v o s i c e ,
L i s t y C u k r . , 1 0 2 ( 7 ) (1986 ) 1 5 5 - 1 6 1 . 8 J . K . C l a r k and N . E . He im i ck , How to op t im i ze the d e s i g n o f s team s y s t e m s ,
i n : R. Greene ( E d . ) , P r o c e s s Energy C o n s e r v a t i o n , M c G r a w - H i l l , New Y o r k , 1 9 8 2 , pp . 1 5 3 - 1 6 4 .
9 A . Kubas iew icz (e t a l . ) , Op tyma l i zac ja g o s p o d a r k i c i e p l n e j cukrowni za pomoca maszyny matematyczne j , Gaz . C u k r o w . , 8 3 ( 7 ) (1975 ) 1 6 5 - 1 6 7 .
10 A . Kubas iew icz (e t a l . ) . Optimum d e s i g n o f thermal sys tems o f s u g a r p l a n t s . Paper p resen ted a t V I I I I n t e r n a t i o n a l Confe rence on I n d u s t r i a l E n e r g e t i c s , Gdansk , September 1 9 7 5 .
11 A . Kubas iew icz (e t a l . ) . Some a s p e c t s o f computer ized d e s i g n o f thermal sys tems o f beet s u g a r p l a n t s , i n : P r o c . Symp. Computers i n the D e s i g n and E r e c t i o n o f Chemical P l a n t s , K a r l o v y V a r y , September 1 9 7 5 , pp . 5 9 9 - 6 0 7 .
367
12 I . S a g u y , O p t i m i z a t i o n t h e o r y , t e c h n i q u e s , and t h e i r imp lementa t ion i n the food i n d u s t r y : i n t r o d u c t i o n . Food T e c h n . , ( 1982 ) ( 7 ) 8 7 .
13 D. Depeyre and P h . L u c a s , S y n t h e s e de p rocedes e t a m e l i o r a t i o n e n e r g e t i q u e du procede s u c r i e r , I n d . A l i m . A g r i e , 1 0 2 ( 7 - 8 ) ( 1985 ) 7 4 3 - 7 4 8 .
14 Β . L i n n h o f f and J . R . F l o w e r , S y n t h e s i s o f heat exchanger n e t w o r k s , A I C h E J . , 2 4 ( 4 ) (1978 ) 6 3 3 - 6 5 4 .
15 D. Bo land and B. L i n n h o f f , The p r e l i m i n a r y d e s i g n o f ne tworks f o r heat exchange by s y s t e m a t i c methods , Chem. E n g i n e e r , (1979 ) (4 ) 2 2 2 - 2 2 8 .
16 B. Goublomme, Comment abo rde r le probleme de l a r e d u c t i o n des c o u t s e n e r g e t i q u e s dans l e s s u c r e r i e s , S u c r . B e i g e , 103 (1985 ) 2 7 - 3 0 .
17 N . R . T w a i t e , H . J . Davenpor t and E . K . M a c d o n a l d , Energy r e d u c t i o n and p r o c e s s i n t e g r a t i o n . I n t . S u g a r J . , 88 ( 1 9 8 6 ) , P a r t I : ( 1055 ) 2 1 7 - 2 1 9 , P a r t I I : ( 1056 ) 2 3 0 - 2 3 6 .
368
Appendix 1
NUMERICAL APPROXIMATIONS OF THERMODYNAMIC PROPERTIES OF WATER AND STEAM
Data on the thermodynamic p r o p e r t i e s o f water and steam are i n d i s p e n s a b l e
to e n g i n e e r i n g c a l c u l a t i o n s r e l a t e d to the energy economy o f s u g a r f a c t o r i e s .
Most o f ten used are data on the p r o p e r t i e s o f s a t u r a t e d water and d ry s a t u r a t e d
s team, as wel l as superhea ted s team. They can be found i n genera l t a b l e s o f
the p r o p e r t i e s o f water and steam ( r e f . 1 ) , o r i n s p e c i a l i z e d t a b l e s , d iag rams
and nomographs where the ranges o f the parameters are adapted to the needs o f
the s u g a r i n d u s t r y ( r e f . 2 ) .
In computer ized c a l c u l a t i o n s , o r when u s i n g h a n d - h e l d programmable
c a l c u l a t o r s to automate p a r t s o f the c a l c u l a t i o n p r o c e d u r e s , t a b l e s o r d iag rams
o f thermodynamic p r o p e r t i e s s h o u l d p r e f e r a b l y be r ep l aced by s u i t a b l e f u n c t i o n a l
r e l a t i o n s h i p s . T h i s requ i rement i s nowadays r e c o g n i z e d by the p u b l i s h e r s o f
i n t e r n a t i o n a l l y known t a b l e s o f thermodynamic p r o p e r t i e s o f water and s t e a m ,
where mathemat ical formulae are a l s o g i v e n f o r most thermodynamic f u n c t i o n s
( r e f . 1 ) . These formulae are i n t e n d e d , however , to combine thermodynamic
c o n s i s t e n c y w i th h i g h accu racy over broad ranges o f parameter v a l u e s . To s a t i s f y
t h i s c o n d i t i o n , the mathemat ical e x p r e s s i o n s c o n s i s t o f many terms and the
c o e f f i c i e n t s are g i v e n w i th s e v e r a l - d i g i t a c c u r a c y . Such fo rmulae may be
i n c o n v e n i e n t to u s e , e s p e c i a l l y when r e l y i n g on smal l -memory comput ing hardware .
However, i f the parameter ranges are narrow and the accu racy c o n d i t i o n s a re no t
ve ry s t r i n g e n t , then the l eng thy e x p r e s s i o n s can be rep laced by more c o n c i s e
o n e s . Numerous s imp le fo rmulae d e s i g n e d f o r use w i t h i n d e f i n i t e i n t e r v a l s o f
parameter v a l u e s can be found in the l i t e r a t u r e , and some o f them have been
e l abo r a ted to s a t i s f y the needs o f the s u g a r i n d u s t r y .
The most impor tan t app rox ima t i on fo rmulae a re g i v e n i n Tab le A l . U n l e s s
o the rw i se s t a t e d , t h e i r ranges o f v a l i d i t y s h o u l d be unde rs tood to c o i n c i d e w i th
the ranges o f parameters no rma l l y encounte red i n the s u g a r i n d u s t r y . The maximum
r e l a t i v e d i f f e r e n c e between the t a b u l a t e d data and the a p p r o x i m a t i o n s does no t
exceed 0 .3% and the ave rage e r r o r i s t y p i c a l l y l e s s than 0 . 1 % .
REFERENCES
1 U. G r i g u l l ( E d . ) , P r o p e r t i e s o f Water and Steam i n S l - u n i t s , 2nd e d n . , S p r i n g e r - V e r l a g , B e r l i n - H e i d e l b e r g - N e w Y o r k , 1979 .
2 T. B a l o h , Wδrmeat las f ٧ r d ie Z u c k e r i n d u s t r i e , Schaper V e r l a g , Hannove r , 1 9 7 5 . 3 A . I l l y e s , Anwendung von N δ h e r u n g s g l e i c h u n g e n i n der Wδrmetechn ik ,
Ζ . Z u c k e r i n d . , 2 6 ( 1 2 ) (1976) 7 6 3 - 7 6 5 . 4 . G, Ba to r and Κ. U r b a n i e c , P r o j e k t i e r u n g von Verdampfan lagen i n Z u c k e r f a b r i k e n
mi t H i l f e von Computern, Z u c k e r i n d . , 103 (12 ) (1978) 1 0 3 5 - 1 0 4 2 . 5 W. Reed , The smal l programmable c a l c u l a t o r i n a s u g a r r e f i n e r y . S u g a r J . ,
P a r t I : January 1 9 7 9 , 1 3 - 2 0 , P a r t I I : Feb rua ry 1 9 7 9 , 1 3 - 2 0 .
369 TA
BLE
Al
Ap
pro
xim
ati
on
form
ula
e fo
r th
erm
od
yna
mic
fu
ncti
on
s o
f w
ate
r an
d st
ea
m
(te
mp
era
ture
in
p
ressu
re
in
ba
r,
en
tha
lpy
in
kJ
/kg
, s
pe
cif
ic
volu
me
in
m^
/kg
).
Sp
ec
ific
ati
on
^^"^
^^^
R
efe
ren
ce
va
lid
ity
Sa
tura
tio
n
tem
pe
ratu
re a
s
0.2
5-6
.0 b
ar
t^^^ =
1
59
.52
ρ^·
""^^
^ -
59
.96
3
a fu
ncti
on
of
pre
ssu
re
t^^^
=
(58
5.4
3 +
2
02
.2
log
p
)/(4
.98
7
- lo
g
p)
- 1
7.7
8 5
^
Sa
tura
tio
n
pre
ssu
re a
s
65
-16
0°C
p
^^^
=
((t
+
59
.96
)/1
59
.52
)^'^
^^
3
a fu
ncti
on o
f te
mp
era
ture
p,,.
=
ex
p(2
.30
26
(11
.06
6 t
- 4
34
)/(1
.8
t +
3
96
) -
2.6
74
4)
5^
sa
t
afS
1S
L?io
roT
Sera
f"e
2
0-1
60
°C
h'
=
1.5
43
. 4
.12
20
t .
0.5
44
94
(t2
/10
00
) 4
En
tha
lpy
of
dry
sa
tura
ted
st
ea
m
20
-16
0°C
h
" =
2
50
0 +
1
.81
3 t
+
(0.4
71
t^
- 0
.01
10
4
t^)/
10
00
4
as a
fu
ncti
on o
f te
mp
era
ture
6
5-1
60
°C
h"
=
13
09
.1
+
54
6.3
5(t
+
5
9.9
6)°
·^^°^
3
Sp
ecif
ic
volu
me
of
sa
tura
ted
w
ate
r ^.^
^ o
^
^,
^
y^
^^
^^
_
^^
^^
^
_
0
00
35
3 ^2
^ 3
as
a
fun
cti
on
of
tem
pe
ratu
re
^
^
Sp
ec
ific
vo
lum
e o
f dry
sa
tura
ted
0
.25
-1.2
b
ar
v"
=
1/(
0.1
05
+
0.6
10
5 ρ
-
0.0
30
3 p
^)
3
ste
am
a
s
a
fun
cti
on
of
pre
ssu
re
1.2
-6.0
b
ar
v"
=
1/(
0.0
53 +
0
.54
62
ρ -
0.0
04
55
3 p
^)
3
En
tha
lpy
of
su
pe
rhe
ate
d
ste
am
a
s
h
=
10
77
.81
+
0.7
74
58
t +
0
.00
01
37
t^
- ^a
Srlssuie
"""
^^"^
P^^
^^^^
^ -
13
0.5
3(p
+
0
.68
9)(
log
ρ +
1
.16
15
)/(1
.8
t -
21
8)
' B
riti
sh
u
nit
s
use
d in
th
is
refe
ren
ce
370
Appendix 2
NUMERICAL APPROXIMATIONS OF THERMODYNAMIC PROPERTIES OF SUGAR SOLUTIONS
Data on the thermodynamic p r o p e r t i e s o f s u g a r s o l u t i o n s can be found i n
the t a b l e s and d iag rams g i v e n i n r e f . 1 and o t h e r s o u r c e s . As i n the p r o p e r t i e s
o f water and s team, when c a l c u l a t i n g the energy b a l a n c e s , these da ta s h o u l d
p r e f e r a b l y be a v a i l a b l e i n the form o f f u n c t i o n a l r e l a t i o n s h i p s . Mos t p u b l i s h e d
r e l a t i o n s h i p s are based on data measured f o r pure s u c r o s e s o l u t i o n s and thus
y i e l d o n l y approx imate v a l u e s when used f o r t e c h n i c a l s u g a r s o l u t i o n s . However,
i n t y p i c a l e n g i n e e r i n g c a l c u l a t i o n s , t h e i r a c c u r a c y can be rega rded as
s u f f i c i e n t l y h i g h .
A few app rox ima t i on fo rmulae a re g i v e n i n Tab le A 2 . U n l e s s o the rw i se s t a t e d ,
the ranges o f v a l i d i t y s h o u l d be unde rs tood to c o i n c i d e w i th the ranges o f
parameters n o r m a l l y encounte red in the s u g a r i n d u s t r y . The maximum r e l a t i v e
d i f f e r e n c e between the t a b u l a t e d data and the a p p r o x i m a t i o n s does no t exceed
0.5% except f o r the second d e n s i t y f o r m u l a , the maximum e r r o r o f wh ich i s
about 2%.
REFERENCES
1 T. B a l o h , Wδrmeat las f ٧ r d i e Z u c k e r i n d u s t r i e , Schaper V e r l a g , Hannover , 1975 . 2 A . I l l y e s , Anwendung von N δ h e r u n g s g l e i c h u n g e n i n der Wδrmetechn ik ,
Ζ . Z u c k e r i n d . , 2 6 ( 1 2 ) (1976) 7 6 3 - 7 6 5 . 3 G. Ba to r and Κ. U r b a n i e c , P r o j e k t i e r u n g von Verdampfan lagen i n Z u c k e r f a b r i k e n
mi t H i l f e von Computern , Z u c k e r i n d . , 103 (12 ) (1978) 1 0 3 5 - 1 0 4 2 . 4 W. R e e d , The smal l programmable c a l c u l a t o r i n a s u g a r r e f i n e r y . S u g a r J . ,
Pa r t I : January 1 9 7 9 , 1 3 - 2 0 , P a r t I I : Feb rua ry 1 9 7 9 , 1 3 - 2 0 .
371
TAB
LE A
2
Ap
pro
xim
ati
on
form
ula
e fo
r th
erm
od
yna
mic
fu
ncti
on
s
of
su
ga
r so
luti
on
s
(te
mp
era
ture
in
°C
, b
.p.e
. in
K
, co
nce
ntr
ati
on
in
%
DS
, p
uri
ty in
%
, e
nth
alp
y in
k
J/k
g,
sp
ec
ific
h
ea
t in
k
J/(
kg
K),
d
en
sit
y in
k
g/m
^).
Sp
ec
ific
ati
on
Sid
itν
R
efe
ren
ce
Bo
ilin
g-p
oin
t e
lev
ati
on
, a
s
20
-14
0°C
Δ
Τ =
f,
+
(t
/10
0)f
p +
(t
/10
0)^
f-.
3
a fu
ncti
on o
f co
nce
ntr
ati
on
10
-90%
D
S
^
and
wa
ter
sa
tura
tio
n
tem
pe
ratu
re
f-j
=
ex
p(-
1.5
25
4 +
0
.02
29
62
b +
0
.00
02
16
3 b
)
- 0
.2
f2
=
ex
p(-
3.2
02
1
+
0.0
06
67
43
b
- 0
.00
01
16
1 b
^)
- 0
.15
f3
=
ex
p(-
1.4
27
8 -
0.0
24
38
2 b
+
0
.00
06
04
7 b
^)
Sp
ec
ific
h
ea
t a
s
a
fun
cti
on
of
C
=
4.1
94 +
t(
t -
72
)/1
08
15
5 -
tem
pe
ratu
re,
co
nce
ntr
ati
on
an
d
_
(b/1
00
)(2
.72
2
- 0
.00
75
t .
0.0
04
6(1
00
- r)
) ^
Sp
ec
ific
h
ea
t a
s
a
fun
cti
on o
f
tem
pe
ratu
re
an
d
co
nce
ntr
ati
on
C =
4
.18
68 -
0.0
25
58
14
b +
0
.00
00
75
36
bt
(pu
rity
a
bo
ut
90%
) E
nth
alp
y a
s
a
fun
cti
on o
f ^n
, T/
inO
r o
te
mp
era
ture
a
nd
co
nce
ntr
ati
on
in
ano/
nc h
=
1
.5 +
(4
.12
2 -
0.0
25
12
b)t
+
(5
.5 +
0
.37
5 b
)(t/
10
0)'
^ 3
(p
uri
ty
ab
ou
t 9
0%
) '"
'^"/
^
Spi
ννtrr
/aνr
^coν
^nνν
atio
n ρ
=
^^
^-^
"
0-0
^38
3 t
- 0
.00
38
4
. (b
t)/(
0.2
46 t
- 0
.26
8)
2
De
nsity
as
a
fun
cti
on o
f co
nce
ntr
ati
on
(te
mp
era
ture
10
-70%
D
S ń
=
1
02
2.5
3 b
^'
^^-^
'^^^
exp
(0.0
05
55
3 b
) 70
-130
OC
)
372
Appendix 3
CALCULATIONS OF HEAT TRANSFER PHENOMENA
I t was assumed th roughou t Chapter 2 and o the r r e l e v a n t p a r t s o f the p r e s e n t
book t h a t data on the thermal p r o p e r t i e s o f equipment a re a v a i l a b l e whenever
needed i n the c a l c u l a t i o n s o f ene rgy b a l a n c e s o f f a c t o r y s u b s y s t e m s . In p r a c t i c e ,
such data a re o f ten unknown f o r s p e c i f i c equipment u n i t s , and i n o rde r to make
the ba lance c a l c u l a t i o n s p o s s i b l e , c e r t a i n a s s u m p t i o n s may be r e q u i r e d . The aim
o f t h i s Appendix i s to s y n t h e s i z e i n f o r m a t i o n which can prove h e l p f u l i n making
r e a l i s t i c a s s u m p t i o n s about the c h a r a c t e r i s t i c s o f thermal equ ipment .
In the energy ba lance o f an equipment u n i t , heat l o s s e s to the env i ronment
are accounted f o r by m u l t i p l y i n g the heat e f f e c t i v e l y t r a n s f e r r e d w i t h i n the
u n i t by the heat l o s s c o e f f i c i e n t . I t s h o u l d be emphasized t ha t d i f f e r e n t
d e f i n i t i o n s o f such c o e f f i c i e n t s can be found i n the l i t e r a t u r e , and t h e i r
ac tua l v a l u e s may depend on equipment d e s i g n , the e f f i c i e n c y o f thermal
i n s u l a t i o n and l o c a l c o n d i t i o n s ( f o r example , ou tdoor l o c a t i o n o f a p a r t i c u l a r
u n i t ) . I n the fo rmulae g i v e n i n Chapter 2 , the f o l l o w i n g v a l u e s o f heat l o s s
c o e f f i c i e n t s can be u s e d :
- j u i c e h e a t e r s 0 . 0 3 - 0 . 0 5 ;
- e x t r a c t o r s 0 . 0 5 - 0 . 1 0 ;
- vacuum pans 0 . 0 3 - 0 . 1 2 ;
- s y r u p t anks 0 . 0 3 - 0 . 0 5 .
As r e g a r d s the e v a p o r a t o r s , exper imenta l work has been repo r ted on the
de te rm ina t i on o f heat l o s s c o e f f i c i e n t s . Zag rodzk i and S o k o l o w s k i ( r e f . 1) found
tha t the heat l o s s c o e f f i c i e n t o f a R o b e r t - t y p e e v a p o r a t o r body i n the second
e f f e c t o f a q u a d r u p l e - e f f e c t e v a p o r a t o r was 0 . 0 0 1 5 ; w i th an a d d i t i o n a l
i n s u l a t i o n l a y e r , the c o e f f i c i e n t was reduced to 0 . 0 0 0 9 . These r e s u l t s are in
good agreement w i th the va lue o f 0 . 0 0 1 1 measured by Hogg e t a l . ( r e f . 2 ) . Tak ing
i n t o accoun t heat d i s s i p a t i o n from j u i c e , vapour and condensa te p i p e l i n e s ,
a c o e f f i c i e n t va lue o f 0 . 0 0 2 5 was recommended by the l a t t e r a u t h o r s , w h i l e i n
o l d e r s o u r c e s , v a l u e s o f up to 0 . 0 3 can be found ( r e f . 3 ) .
I t seems t ha t f o r most e v a p o r a t o r s , a heat l o s s c o e f f i c i e n t between 0 . 0 0 2 5
and 0 . 0 1 can be assumed. When u s i n g the c a l c u l a t i o n a l g o r i t h m p resen ted i n
Chapter 2 , i d e n t i c a l v a l u e s can u s u a l l y be assumed f o r both the e v a p o r a t o r body
and the condensate tank .
The v a l u e s o f o v e r a l l heat t r a n s f e r c o e f f i c i e n t s used i n the d e s i g n
c a l c u l a t i o n s o f thermal sys tems are d e c i s i v e i n e n s u r i n g a p roper c h o i c e o f
the a r e a s o f h e a t i n g s u r f a c e s in equipment u n i t s . As the p r a c t i c a l v a l u e s o f
heat t r a n s f e r c o e f f i c i e n t s may v a r y w i th t i m e , depending on s c a l e b u i l d - u p .
373
i t i s d i f f i c u l t to c o r r e l a t e d e s i g n data and r e a l i t y . A l t h o u g h the f i l m
c o e f f i c i e n t s o f heat t r a n s f e r c h a r a c t e r i z i n g c l e a n h e a t i n g s u r f a c e s can be
c a l c u l a t e d u s i n g d i m e n s i o n l e s s r e l a t i o n s h i p s known from the t heo ry o f heat
t r a n s f e r and w ide l y c i t e d in the l i t e r a t u r e , i t i s common to r e l y i n s t e a d on
p r a c t i c a l l y v e r i f i e d f i g u r e s . Care s h o u l d be t a k e n , however , o f the
c o m p a t i b i l i t y o f a l l da ta used i n the e q u a t i o n g o v e r n i n g heat t r a n s f e r a c r o s s
the h e a t i n g s u r f a c e
Q = k F At
where Q i s the heat t r a n s f e r r e d i n u n i t t i m e , k i s the o v e r a l l heat t r a n s f e r
c o e f f i c i e n t , F i s the h e a t i n g s u r f a c e a r e a , and At i s the mean temperature
d i f f e r e n c e .
In the j u i c e h e a t e r s , i t i s e s s e n t i a l t ha t the va lue o f k be determined u s i n g
the same d e f i n i t i o n o f the h e a t i n g s u r f a c e a rea as assumed i n the ac tua l
c a l c u l a t i o n . For t u b u l a r h e a t e r s , the i n n e r s u r f a c e a rea o f the tubes i s
t y p i c a l l y u s e d . Depending on the tube d iameter and wa l l t h i c k n e s s , i t may d i f f e r
by up to 12-15% from the ou te r s u r f a c e a rea o f the t u b e s .
For vapou r -hea ted t u b u l a r hea te r s ope ra ted a t c o r r e c t v a l u e s o f the j u i c e
f low v e l o c i t y , the o v e r a l l heat t r a n s f e r c o e f f i c i e n t s d e f i n e d a t the i n n e r
s u r f a c e area o f the tubes can u s u a l l y be assumed as f o l l o w s :
- raw j u i c e 6 0 0 - 8 0 0 W / ( m ^ K ) ;
- c l e a r j u i c e 700 -1000 W / ( m ^ K ) ;
- t h i n j u i c e 9 0 0 - 1 2 0 0 W / ( m ^ K ) ;
- t h i c k j u i c e and s y r u p s 4 0 0 - 6 0 0 W / ( m ^ K ) .
These v a l u e s can be t r ea ted as rough e s t i m a t e s o n l y ( c f . exper imenta l v a l u e s
c i t e d in Chapter 8 ) . As r e g a r d s p l a t e and s p i r a l h e a t e r s , the s c a t t e r o f
p r a c t i c a l v a l u e s o f heat t r a n s f e r c o e f f i c i e n t s i s so l a r g e t h a t one can o n l y
r e l y on the data s u p p l i e d by the equipment m a n u f a c t u r e r s .
In the case o f e v a p o r a t o r s , d e f i n i t i o n s o f both the h e a t i n g s u r f a c e a rea and
the e f f e c t i v e temperature d i f f e r e n c e are e s s e n t i a l . The temperature d i f f e r e n c e ,
a c c o r d i n g to the d e f i n i t i o n g i v e n i n Chapter 2 and most f r e q u e n t l y used i n the
l i t e r a t u r e , i s
At = t^ - ( t^ + ΔΤ)
where t^ i s the temperature o f the h e a t i n g steam (vapou r ) c o n d e n s i n g i n the
h e a t i n g chamber, t^ i s the temperature o f s a t u r a t e d vapour i n the vapour chamber
and AT i s the b o i l i n g p o i n t e l e v a t i o n . However, some a u t h o r s take the e f f e c t i v e
temperature d i f f e r e n c e as
At = t^ ^ t^
Adop t i ng t h i s d e f i n i t i o n , the v a l u e s o f the o v e r a l l heat t r a n s f e r c o e f f i c i e n t
c a l c u l a t e d f o r e v a p o r a t o r e f f e c t s opera ted a t h i g h e r j u i c e c o n c e n t r a t i o n s
(50-70% DS) may be up to 50-60% g r e a t e r than those c o r r e s p o n d i n g to the
374
d e f i n i t i o n o f At adopted i n the p r e s e n t book .
For a p r o p e r l y d imens ioned and c o r r e c t l y ope ra ted R o b e r t - t y p e e v a p o r a t o r ,
the o v e r a l l heat t r a n s f e r c o e f f i c i e n t can be c a l c u l a t e d from B a l o h ' s fo rmu la
( r e f . 3)
k = 5 . 2 3 - 1 0 ^ ( b 2 ^ + b^^^ + 800) (W{mh)) where b^.^ and b^^^ are j u i c e c o n c e n t r a t i o n s ( i n % DS) a t i n l e t and o u t l e t ,
r e s p e c t i v e l y . T h i s fo rmu la i s known to g i v e somewhat too h i g h v a l u e s o f the heat
t r a n s f e r c o e f f i c i e n t a t the h i g h e s t j u i c e c o n c e n t r a t i o n s .
Approx imate v a l u e s o f the o v e r a l l heat t r a n s f e r c o e f f i c i e n t i n both R o b e r t -
type and f a l l i n g - f i l m e v a p o r a t o r s a re a l s o g i v e n , as f u n c t i o n s o f mean j u i c e
c o n c e n t r a t i o n , i n F i g . 5 . 5 .
REFERENCES
1 S . Zag rodzk i and A . S o k o l o w s k i , Pomiary s t r a t c i e p l n y c h w apa ra tach wypa rnych , Gaz. C u k r o w . , 8 1 ( 4 ) (1973 ) 8 1 - 8 5 .
2 J . S . Hogg (e t a l . ) . The r o l e o f the rmograph ic s u r v e y i n g in energy c o n s e r v a t i o n . I n t . S u g a r J . , 8 5 ( 1 0 1 1 ) (1983) 6 7 - 7 1 .
3 T. B a l o h , Wδrmeat las f ٧ r d ie Z u c k e r i n d u s t r i e , Schaper V e r l a g , Hannover , 1 9 7 5 .
375
Appendix 4
and from g i v e n tj^ i n Κ
tp = 1.8(t,^ - 2 7 3 . 1 5 ) + 32 .
UNITS OF MEASUREMENT
The S I sys tem o f u n i t s used th roughou t t h i s book i s based on the f o l l o w i n g
u n i t s :
- mass i n k i l o g r a m s ( k g ) ;
- l eng th i n metres (m) ;
- t ime i n seconds ( s ) .
The temperature i s measured i n deg rees C e l s i u s ( ° C ) , and the a b s o l u t e
temperature i n K e l v i n s ( K ) . The temperature d i f f e r e n c e i s e x p r e s s e d i n K.
The met r i c sys tem o f u n i t s ( a l s o known as the t e c h n i c a l sys tem) i s based on
the f o l l o w i n g u n i t s :
- f o r ce in k i l o g r a m s f o r c e , o r k i l o p o n d s ( k g f o r k p ) ;
- l e n g t h i n m;
- t ime in s .
The mass i s measured i n k g . The temperature i s measured i n ^ C , and the a b s o l u t e
temperature i n deg rees K e l v i n ( ° K ) . The temperature d i f f e r e n c e can be e x p r e s s e d
i n °C o r \ .
The B r i t i s h sys tem o f u n i t s ( a l s o known as p o u n d - s e c o n d - f o o t sys tem) i s
based on the f o l l o w i n g u n i t s :
- mass i n pounds ( l b . ) ;
- l eng th i n f e e t ( f t . ) ;
- t ime in seconds (denoted s e c ) .
The f o r ce i s e x p r e s s e d i n pounds f o r c e ( I b f . ) . The temperature i s measured i n
degrees F a h r e n h e i t ( ^ F ) . The temperature d i f f e r e n c e i s a l s o e x p r e s s e d i n ^ F .
The c o n v e r s i o n from S I to me t r i c o r B r i t i s h u n i t s can be performed u s i n g
the c o n v e r s i o n f a c t o r s g i v e n in Tab le A 4 .
The c o n v e r s i o n fo rmu la f o r c a l c u l a t i o n o f the temperature i n °F from a g i v e n
temperature t^ i n °C i s
tp = 1.8 t(. + 32
376
TAB
LE A
4
Co
nve
rsio
n ta
ble
-
SI
to m
etr
ic
and
Bri
tish
un
its.
Qu
an
tity
S
I u
nit
M
etr
ic
eq
uiv
ale
nt
Bri
tis
h e
qu
iva
len
t
Mas
s 1
kg
1
kg
2
.20
46
22
lb.
Le
ng
th
1
m
1
m =
10
0 cm
3
.28
02
84
ft.
=
39
.37
in.
Are
a 1
m
^
1
m^
=
10^
cm
^ 1
0.7
64
sq
.ft.
=
1550
sq
.in
.
Vol
ume
1
m^
1
m"^
3
5.3
14
7 c
u.f
t.
=
6102
4 c
u.i
n.
De
nsit
y 1
kg
/m^
1
kg/m
^ 0
.06
24
28
lb./
cu
.ft.
Fo
rce
1
kg
m
/s^
= 1
Ν
0.1
01
97
2 kg
f 0
.04
62
54
Ibf.
Pre
ssu
re
1
N/m
^ =
1
P
a
1.0
19
72
-10
"^
kgf/
cm^
0.02
0885
5 Ib
f./s
q.f
t.
=
1.4
50
38
-10
"^
p.s
.i.
1 b
ar
=
10^
P
a 1
.01
97
2 kg
f/cm
^ 2
08
8.5
5 Ib
f./s
q.f
t.
=
14
.50
38
p.s
.i.
Wo
rk,
energ
y 1
Ν
m =
1
J
0.1
01
97
2 kg
f m
0
.73
75
62
ft.-
Ibf.
1 kJ =
10^ J
1
01
.97
2 kg
f m
7
37
.56
2 ft
.-Ib
f
Hea
t 1
J
2.3
88
46
-10
"^
kca
l 9
.47
81
7-1
0"^
BT
U
1 kJ
0
.23
88
46
kca
l 0
.94
78
17
BT
U
Pow
er
1
J/s
=
1
W
0
.10
19
72
kg
f m
/s
0.7
37
56
2 ft
.-Ib
f./s
ec
.
1 kW
=
10^
W
1
01
.97
2 kg
f m
/s
73
7.5
62
ft.-
Ibf.
/se
c.
He
ati
ng
v
alu
e
1
kJ
/kg
0
.23
88
46
kc
al/
kg
0
.42
99
23
BT
U/l
b.
Te
mp
era
ture
d
iffe
ren
ce I
K
1°C
1
.8°F
Sp
ec
ific
h
ea
t 1
k
J/(
kg
K)
0.2
38
84
6 k
ca
l/(k
g°C
) 0
.23
88
46
BT
U/(
lb.°
F)
The
rmal
co
nd
ucti
vit
y 1
W
/(m
K
) 0
.86
0 k
ca
l/(m
h
^C)
0.5
77
81
6 B
TU
/(ft
.h°F
)
Hea
t tr
an
sfe
r c
oe
ffic
ien
t 1
W
/(m
^K)
0.8
60
kca
l/(m
^h°C
) 0
.17
61
10
BT
U/(
sq
.ft.
h°F
)
377
INDEX
A i r p r e h e a t i n g , 1 5 7 , 342 A l k a l i n i t y o f wa te r , 2 3 8 , 2 4 3 , 245 Apparen t power, 38 Appearance o f wa te r , 2 4 0 , 244 Ash con ten t o f c o a l , 247
Ba romet r i c c o n d e n s e r , see condenser Ba romet r i c wa te r , 2 , 1 0 , 1 6 , 2 2 , 6 5 , 2 7 7 , 357 Batch c e n t r i f u g a l , 3 3 , 2 0 6 , 228 Batch vacuum p a n , 7 4 , 1 1 0 , 1 2 2 , 1 2 5 , 1 4 7 , 1 6 7 , 2 0 1 , 2 2 5 , 2 2 8 , 2 3 5 , 2 7 1 , 2 7 7 , 280 B i o g a s p r o d u c t i o n , 175 B o i l e r blowdown, 2 4 1 , 2 4 3 , 2 5 5 , 313 B o i l e r check , 253 B o i l e r e f f i c i e n c y , 2 6 , 1 4 8 , 2 5 1 , 2 5 8 , 2 9 2 , 3 1 0 , 3 3 5 , 349 B o i l e r l o s s :
a s h , 255 ch imney, 254 incomplete c o m b u s t i o n , 255 r a d i a t i o n , 256
B o i l e r water q u a l i t y , 241 B o i l i n g p o i n t e l e v a t i o n , 7 8 , 1 2 3 , 2 6 5 , 3 7 0 , 373 Bomb c a l o r i m e t e r , 248 Boundary o f thermodynamic s y s t e m , 3 , 6 , 5 7 , 234 B . p . e . , see b o i l i n g p o i n t e l e v a t i o n
C a r b o n a t a t i o n , 5 , 2 9 , 6 1 , 6 3 , 6 6 , 154 , 1 5 9 , 2 9 6 , 2 9 8 , 3 0 2 , 3 0 9 , 3 1 1 , 318 C a r b o n a t a t i o n g a s , 2 , 9 , 1 5 , 2 2 , 5 3 , 6 5 , 1 5 5 , 1 5 7 , 178 C e n t r i f u g a l d r i v e , 3 9 , 4 1 , 2 0 7 , 209 Chemical c l e a n i n g o f t u b e s , 117 C l o s e d thermodynamic s y s t e m , 57 Co lou r b u i l d - u p , 3 4 , 1 6 3 , 166 Combined g e n e r a t i o n o f heat and e l e c t r i c i t y , 1 0 , 4 3 , 262 Combus t ib le ma t te r :
i n a s h , 2 5 2 , 255 in c o a l , 247
Composi te c u r v e , 364 Compress ion r a t i o , 1 8 , 140 , 150 Condensa te :
d r a i n a g e , 1 5 , 9 7 , 9 9 , 1 0 3 , 1 0 5 , 1 0 9 , 1 1 1 , 1 1 8 , 2 6 4 , 2 7 0 , 2 7 2 , 2 7 8 , 2 9 0 , 2 9 3 , 3 0 2 , 3 3 2 , 338
f l a s h i n g ( f l a s h - e v a p o r a t i o n ) , 1 5 , 7 6 , 7 9 , 8 2 , 119 p o l l u t i o n , 1 0 1 , 144 q u a l i t y , 100 , 117 , 2 3 9 , 290
Condensate t a n k , 2 , 7 , 3 1 , 7 6 , 7 9 , 8 1 , 1 0 0 , 1 0 8 , 1 1 0 , 1 1 2 , 1 1 8 , 1 2 0 , 1 4 4 , 2 3 9 , 2 7 3 , 2 9 4 , 3 0 5 , 3 3 8 , 3 4 2 , 3 4 6 , 353
Condense r , 3 , 7 , 1 0 , 1 4 , 1 7 , 3 1 , 4 6 , 4 8 , 6 5 , 7 7 , 7 9 , 8 3 , 9 7 , 1 0 2 , 1 0 4 , 1 1 3 , 1 2 1 , 1 2 6 , 1 2 8 , 1 3 0 , 134 , 2 2 3 , 2 7 7 , 2 8 7 , 3 4 8 , 352
C o n t i n u o u s c e n t r i f u g a l , 2 0 6 , 2 0 9 , 2 9 3 , 294 C o n t i n u o u s vacuum p a n , 1 2 5 , 1 4 7 , 1 4 9 , 1 6 6 , 203 Con t ro l s u r f a c e , 57 Con t ro l vo lume, 57 C o o l i n g - c r y s t a l l i z a t i o n tower , 165 C o s s e t t e s m i x e r , 189 C r y s t a l f o o t i n g , 3 6 , 166 , 2 0 4 , 324
378
C r y s t a l 1 i z a t i o n : c o o l i n g , 1 6 3 , 167 e v a p o r a t i n g , 1 6 3 , 167 , 173 f r e e z e , 173 under vacuum, 165
C r y s t a l l i z a t i o n scheme: D a n i s h , 161 s i n g l e b o i l i n g , 323 t h r e e - b o i l i n g , 3 4 , 6 1 , 1 6 1 , 1 6 5 , 2 9 2 , 2 9 6 , 3 1 0 , 3 3 5 , 349 t w o - a n d - a - h a l f - b o i l i n g , 324 t w o - b o i l i n g , 166 w i th c r y s t a l f o o t i n g , 1 6 6 , 168 w i th two j u i c e c o n c e n t r a t i o n s , 36
C r y s t a l l i z a t i o n tower , 2 0 3 , 206
Decompos i t i on o f a s y s t e m , 3 , 10 D u l o n g ' s f o r m u l a , 249
E f f e c t i v e power, 38 E f f e c t i v e n e s s r a t i o , 9 , 2 3 , 9 5 , 1 2 1 , 1 8 7 , 2 1 3 , 2 9 1 , 3 1 0 , 3 3 8 , 352 E l e c t r i c a l c o n d u c t i v i t y o f wa te r , 243 E l e c t r i c a l d e s c a l e r , 118 Energy b a l a n c e , 5 , 8 , 5 7 , 6 0 , 6 5 , 8 4 , 8 7 , 9 6 , 1 0 3 , 1 5 5 , 2 3 4 , 2 5 3 , 2 5 7 , 2 6 1 , 2 6 9 ,
2 7 8 , 2 9 6 , 382 Energy s y s t e m , 5 , 1 7 4 , 1 8 1 , 1 8 3 , 2 9 0 , 2 9 5 , 3 2 2 , 3 3 3 , 3 6 2 , 364 E n t h a l p y b a l a n c e , 88 En t ra inment s e p a r a t o r , 1 0 1 , 1 3 0 , 194 E u l e r ' s e q u a t i o n , 219 E v a p o r a t i o n , 6 , 1 2 , 2 4 , 3 5 , 1 4 4 , 1 4 7 , 2 1 3 , 2 1 5 , 2 2 1 , 2 2 6 , 2 6 4 , 2 8 7 , 307 E v a p o r a t i o n c o e f f i c i e n t , 121 E v a p o r a t o r :
c l i m b i n g - f i l m , 222 d o u b l e - e f f e c t , 195 f a l l i n g - f i l m , 1 9 1 , 2 2 2 , 2 6 3 , 3 1 0 , 3 1 4 , 3 1 6 , 3 2 3 , 3 5 3 , 3 5 7 , 374 m u l t i p l e - e f f e c t , 8 , 1 2 , 1 5 , 3 4 , 7 6 , 8 3 , 1 2 1 , 1 9 0 , 2 2 1 , 2 6 3 , 3 2 3 , 349 q u a d r u p l e - e f f e c t , 17 , 1 2 0 , 1 2 6 , 2 9 6 , 3 3 5 , 3 3 9 , 342 q u i n t u p l e - e f f e c t , 1 4 , 8 3 , 1 2 6 , 1 3 5 , 2 9 2 , 3 1 0 , 3 2 3 , 342 R o b e r t - t y p e , 1 0 6 , 1 9 1 , 2 2 2 , 2 6 3 , 2 9 6 , 3 1 0 , 3 1 4 , 3 1 6 , 3 2 3 , 3 3 5 , 3 4 9 , 3 5 2 , 3 5 7 ,
3 5 9 , 3 7 2 , 374 s e x t u p l e - e f f e c t , 127 , 224 t r i p l e - e f f e c t , 1 2 6 , 2 9 7 , 337 t h i n - f i l m , 1 9 1 , 222
Evapo ra to r check , 2 6 4 , 266 E v a p o r a t o r - r e c e i v e r a p p r o a c h , 8 4 , 1 0 3 , 301 E x e r g y , 8 9 , 90 Ex te rna l energy b a l a n c e , 6 5 , 8 4 , 1 0 1 , 103 E x t r a c t o r :
b e l t t y p e , see mov ing-bed type drum t y p e , 1 8 8 , 2 2 0 , mov ing-bed t y p e , 1 8 8 , 220 s c r o l l t y p e , see t r ough type tower t y p e , 3 1 , 7 3 , 1 8 8 , 2 2 0 , 2 9 2 , 323 t r ough t y p e , 3 1 , 6 1 , 7 3 , 1 3 5 , 1 8 8 , 2 2 0 , 2 6 7 , 2 9 6 , 3 0 9 , 3 3 5 , 349
E x t r a c t o r check , 269
Feed-water q u a l i t y , 238 F i l m c o e f f i c i e n t o f heat t r a n s f e r , 1 6 , 1 1 3 , 1 1 6 , 373 F l o a t - t y p e steam t r a p , 1 0 6 , 1 1 1 , 2 9 7 , 337
379
Flow c o n t r o l : by p o s i t i o n i n g o f i n l e t gu ide v a n e s , 219 by t h r o t t l i n g , 4 2 , 2 1 7 , 219 b y - p a s s , 4 2 , 1 5 5 , 2 1 7 , 219 v a r i a b l e s p e e d , 4 2 , 1 4 5 , 2 1 6 , 2 1 8 , 327
F r e q u e n c y - c o n v e r t e r ( - c o n t r o l l e d ) a . c . d r i v e , 2 0 8 , 3 2 7 , 329 Fuel s t o r a g e , 2 3 3 , 250
Gas t u r b i n e , 2 1 , 5 0 , 184 Grassmann d i a g r a m , 89
Hardness o f wa te r , 2 3 8 , 2 4 0 , 2 4 2 , 245 Heat b a l a n c e , 6 , 8 , 1 8 , 6 8 , 7 3 , 7 6 , 8 4 , 9 6 , 1 0 4 , 2 6 8 , 2 7 0 , 2 8 1 , 2 8 3 , 2 8 7 , 3 0 1 ,
3 0 6 , 3 0 9 , 3 1 4 , 3 2 0 , 3 2 4 , 3 2 7 , 3 3 2 , 3 3 6 , 3 3 9 , 3 4 2 , 3 4 6 , 3 4 9 , 352 Heat l o s s :
by d i s s i p a t i o n to the env i ronmen t , 2 4 , 2 6 , 1 0 0 , 1 0 3 , 1 5 5 , 2 8 4 , 2 9 1 , 301 by f r e e c o n v e c t i o n , 28 by r a d i a t i o n , 28
Heat l o s s c o e f f i c i e n t , 6 0 , 6 9 , 7 3 , 7 5 , 7 8 , 8 9 , 2 6 6 , 2 7 1 , 372 Heat o f c a r b o n a t a t i o n r e a c t i o n , 6 6 , 155 Heat o f combus t i on , 248 Heat o f c r y s t a l l i z a t i o n o f s u g a r , 5 9 , 6 6 , 7 5 , 236 Heat pump, 1 7 , 25 Hea te r , see j u i c e heater Hea t ing and hum id i f i c a t i o n o f k i l n g a s , 1 5 8 , 3 4 2 , 352 Hea t ing v a l u e o f f u e l , 1 4 8 , 2 4 6 , 2 5 2 , 257 Hot c o n d e n s e r , 134 , 357 Hydrogen i on c o n t e n t , see pH H y p e r f i l t r a t i o n , 171
J u i c e c a r r y o v e r , 1 0 1 , 1 4 4 , 194 J u i c e d r a f t , 2 4 , 3 0 , 6 1 , 6 6 , 9 8 , 1 8 7 , 2 1 9 , 2 2 1 , 2 6 8 , 2 9 2 , 2 9 6 , 3 0 9 , 3 2 3 , 3 3 4 ,
3 3 8 , 349 J u i c e h e a t e r :
c o n d e n s a t e - h e a t e d , 6 9 , 1 1 9 , 2 7 1 , 293 d i r e c t - c o n t a c t , 130 , 133 p l a t e , 1 9 8 , 2 9 3 , 3 1 4 , 3 1 7 , 373 segmented, 200 s p i r a l , 1 3 1 , 1 9 9 , 2 9 4 , 3 5 7 , 373 t u b u l a r , 1 0 6 , 1 3 1 , 1 9 9 , 2 9 3 , 373 v a p o u r - h e a t e d , 6 9 , 1 2 2 , 271
J u i c e heater check , 271 J u i c e p u r i f i c a t i o n , 2 , 2 3 , 2 9 , 4 1 , 6 1 , 1 1 6 , 1 3 5 , 1 5 3 , 1 6 3 , 1 6 9 , 1 7 1 , 2 1 3 , 2 1 6 ,
2 9 2 , 2 9 6 , 3 0 9 , 3 1 1 , 3 2 3 , 3 3 1 , 3 3 5 , 349 J u i c e s e p a r a t i o n , 169
K i l n g a s , 9 , 6 2 , 6 7 , 1 5 5 , 1 5 7 , 1 5 9 , 2 9 6 , 3 0 9 , 3 3 5 , 349
Law o f mass c o n s e r v a t i o n , 57 Law o f thermodynamics :
f i r s t , 5 7 , 8 8 , 2 3 4 , 261 s e c o n d , 88
L e v e l - c o n t r o l l e d h y d r a u l i c (water ) s e a l , 1 0 6 , 1 0 9 , 1 1 2 , 2 9 3 , 2 9 4 , 3 3 8 , 342 L i n e a r programming, 363
Mass b a l a n c e , 5 7 , 6 1 , 6 3 , 6 7 , 7 4 , 7 9 , 8 3 , 9 4 , 1 0 1 , 2 3 5 , 2 8 1 , 2 8 3 , 2 8 7 , 2 9 6 , 3 0 1 , 3 0 5 , 3 1 4 , 3 3 2 , 3 3 5 , 3 3 7 , 3 3 9 , 352
Mean l o g a r i t h m i c temperature d i f f e r e n c e , 69 Membrane f i l t r a t i o n , 171 Minimum temperature d i f f e r e n c e , 1 2 1 , 365 M o i s t u r e con ten t o f c o a l , 247 Motor s l i p , 207
380
Net heat demand, 8 , 2 2 , 2 5 , 6 6 , 9 5 , 1 2 1 , 1 4 9 , 1 5 3 , 1 6 0 , 187 , 2 0 3 , 3 3 3 , 338 N i e s s n e r co lumn, 1 0 6 , 1 0 8 , 349 N o n c o n d e n s a b l e s , 9 7 , 1 1 2 , 1 1 5 , 1 2 8 , 130 , 2 6 4 , 2 7 0 , 2 8 0 , 2 9 0 , 3 0 0 , 3 0 2 , 3 0 9 , 314 N o n l i n e a r programming, 363 Normal f u e l , 4 3 , 53 Normal steam pa rame te r s , 43 N o z z l e - t y p e steam t r a p , 1 0 6 , 279 Number o f mass t r a n s f e r u n i t s , 189
O b j e c t i v e f u n c t i o n , 362 Open thermodynamic s y s t e m , 3 , 5 7 , 65 Optimal s y n t h e s i s , 363 O v e r a l l heat t r a n s f e r c o e f f i c i e n t , 6 0 , 6 9 , 8 1 , 1 0 6 , 1 1 6 , 1 2 1 , 1 2 4 , 1 4 4 , 1 9 3 ,
1 9 8 , 2 0 1 , 2 6 4 , 2 6 6 , 2 7 0 , 3 1 5 , 3 6 5 , 372 O v e r a l l t u r b o - g e n e r a t o r e f f i c i e n c y , 2 5 9 , 262 Oxygen consumpt ion o f wa te r , 2 3 9 , 2 4 2 , 245 Oxygen con ten t o f wa te r , 2 4 0 , 2 4 2 , 246
pH, 2 3 9 , 2 4 2 , 245 P e r i o d o f r e t u r n on i nves tmen t , 3 4 6 , 359 P inch p o i n t , 365 P o l e - c h a n g e a . c . motor , 207 Power c a p a c i t o r , 3 9 , 43 Power demand, 1 3 , 1 8 , 3 7 , 4 0 , 4 5 , 1 5 3 , 1 6 0 , 170 , 1 7 9 , 1 8 2 , 187 , 2 0 9 , 2 1 3 , 3 2 7 ,
3 3 2 , 3 3 4 , 3 3 7 , 3 4 6 , 3 5 3 , 357 Power f a c t o r , 3 8 , 4 3 , 2 0 8 , 290 Power h o u s e , 1 , 6 , 1 0 , 3 9 , 4 3 , 4 5 , 4 9 , 5 2 , 1 4 9 , 2 3 3 , 2 9 0 , 2 9 7 , 3 0 0 , 3 1 0 , 3 1 4 ,
3 2 4 , 3 3 2 , 3 3 5 , 3 3 7 , 348 Power ne twork , 37 P r e s s i n g a i d s , 177 Pu lp d e h y d r a t i o n , 1 9 , 1 5 3 , 174 Pu lp d r y e r :
drum t y p e , 2 1 , 8 9 , 2 2 9 , 2 8 1 , 285 f l u i d i z e d - b e d t y p e , 183 low- tempera tu re , 2 2 , 5 3 , 179 s team, 2 2 , 182 t r a v e l l i n g - s c r e e n t y p e , 1 7 9 , 182
Pu lp d rye r check , 282 Pu lp d rye r e f f i c i e n c y , 2 8 1 , 2 8 3 , 285 Pu lp d r y i n g :
h i g h - t e m p e r a t u r e , 2 2 , 179 low- tempera tu re , 1 6 , 2 2 , 1 7 6 , 178 medium-temperature, 2 2 , 178 s team, 2 2 , 181
Pu lp e n s i l a g e , 175 Pu lp f e r m e n t a t i o n , 175 Pu lp p r e s s i n g , 1 9 , 176 , 178
Quent in u n i t , 1 9 8 , 3 2 3 , 349
R e a c t i v e power, 3 8 , 43 Reverse o s m o s i s , see h y p e r f i l t r a t i o n
S a m p l i n g : f u e l , 246 j u i c e , 265 s team, 244 wa te r , 243
Sankey d i a g r a m , 8 , 4 4 , 5 0 , 8 8 , 9 0 , 1 5 8 , 283 S c a l e , 1 0 5 , 1 1 6 , 1 9 3 , 198 , 2 4 1 , 2 4 5 , 2 6 4 , 2 7 0 , 3 0 9 , 3 1 6 , 372 Secan t method, 8 0 , 82 Seed magma, 167 , 204 S i e g e r t ' s f o r m u l a , 254
381
S i l i n ' s f o r m u l a , 221 S i m u l a t i o n , 6 1 , 91 S ludge s w e e t e n i n g - o f f , 3 2 , 302 S o l u b i l i t y o f s u c r o s e , 1 6 3 , 1 6 6 , 227 S t e a d y - s t a t e c o n d i t i o n s , 5 8 , 9 1 , 235 Steam demand, 1 6 , 4 3 , 4 6 , 1 3 5 , 1 3 9 , 1 4 2 , 1 4 9 , 3 0 1 , 3 3 7 , 3 4 7 , 362 Steam q u a l i t y , 2 3 7 , 243 Steam r a t e , 4 6 , 4 9 , 137 , 1 3 9 , 1 4 8 , 2 5 8 , 2 6 3 , 335 Steam t r a p , 6 , 5 9 , 1 0 3 , 1 0 6 , 1 1 1 , 2 7 8 , 2 9 3 , 3 0 0 , 353 Steam t u r b i n e :
b a c k - p r e s s u r e , 1 3 , 4 4 , 4 7 , 2 6 0 , 2 9 7 , 3 1 0 , 324 b a c k - p r e s s u r e / e x t r a c t i o n , 48 c o n d e n s i n g , 48 c o n d e n s i n g / e x t r a c t i o n , 46 t o p p i n g , 46
Sugar b o i l i n g : c o n t r o l , 3 3 , 2 0 3 , 2 2 6 , 293 p r o c e s s , 1 5 , 3 2 , 3 5 , 1 1 1 , 1 2 2 , 1 2 5 , 1 2 7 , 1 6 7 , 2 0 1 , 2 0 3 , 2 2 5 , 2 2 7 , 2 7 1 , 332
Sugar l o s s : i n exhaus ted c o s s e t t e s , 3 1 , 1 8 9 , 221 i n s l u d g e , 32
S u r r o u n d i n g s o f thermodynamic s y s t e m , 5 7 , 88
Temperature p i n c h , see minimum temperature d i f f e r e n c e Thermal decay o f s u c r o s e , 14 , 3 0 , 3 4 , 100 Thermal d e g r a d a t i o n o f e n e r g y , 88 Thermal i n s u l a t i o n , 2 5 , 2 7 , 7 8 , 9 9 , 1 0 3 , 2 7 9 , 2 9 3 , 3 0 1 , 3 0 5 , 3 4 4 , 372 Thermal s y s t e m , 6 , 1 0 , 1 6 , 2 3 , 6 0 , 6 5 , 6 8 , 8 4 , 8 8 , 9 0 , 9 4 , 1 0 0 , 1 0 3 , 1 2 1 , 1 2 7 ,
1 3 1 , 1 3 6 , 1 4 5 , 1 5 3 , 187 , 2 1 3 , 2 2 1 , 2 5 1 , 2 7 5 , 2 7 7 , 2 7 9 , 2 8 7 , 2 9 7 , 3 0 0 , 3 0 5 , 3 1 0 , 3 2 0 , 3 2 3 , 3 3 2 , 3 3 4 , 3 4 0 , 3 4 3 , 3 4 8 , 3 5 4 , 373
Thermodynamic f u n c t i o n s , 6 0 , 7 8 , 8 4 , 8 9 , 2 3 4 , 3 6 8 , 370 Thermodynamic s y s t e m , 3 , 6 , 5 7 , 6 0 , 6 7 , 8 8 , 2 3 4 , 235 Thermograph ic s u r v e y i n g , 100 T h r o t t l i n g - d e s u p e r h e a t i n g s t a t i o n , 4 7 , 9 7 , 1 3 8 , 1 4 2 , 1 4 5 , 1 4 9 , 2 5 7 , 2 7 5 , 324 T h y r i s t o r - c o n t r o l l e d d . c . d r i v e , 2 0 8 , 3 2 7 , 353 Tota l heat demand, 8 , 1 2 , 2 2 , 6 8 , 9 5 , 1 8 7 , 1 9 5 , 3 0 2 , 3 0 5 , 3 2 3 , 353 Tu rb ine e f f i c i e n c y :
i n t e r n a l , 262 m e c h a n i c a l , 262
T u r b o - g e n e r a t o r check , 258
T u r b o - g e n e r a t o r e f f i c i e n c y , see o v e r a l l t . - g . e .
U l t r a f i l t r a t i o n , 171
Vacuum-pan check , 272 Vacuum-pan s t e a m i n g - o u t , 3 3 , 2 0 3 , 2 7 5 , 3 0 8 , 3 1 9 , 337 Vacuum-pan s t i r r e r , 1 2 2 , 1 2 5 , 2 0 2 , 2 0 4 , 206 Vapour c o m p r e s s i o n , 1 1 , 1 6 , 1 2 6 , 1 3 4 , 1 3 7 , 1 4 0 , 1 4 2 , 1 4 4 , 1 4 7 , 1 4 9 , 1 8 4 , 1 9 5 ,
3 2 4 , 3 4 2 , 3 4 7 , 3 5 7 , 3 6 0 , 366 Vapour compresso r :
e l e c t r i c a l l y d r i v e n , 1 3 8 , 1 4 2 , 1 4 5 , 1 4 7 , 1 4 9 , 3 2 4 , 3 4 2 , 357 j e t t y p e , 1 8 , 1 4 0 , 1 4 2 , 1 4 5 , 1 4 9 , 3 2 4 , 3 4 2 , 358 m e c h a n i c a l , 1 8 , 1 3 8 , 1 4 2 , 1 4 5 , 147 , 1 4 9 , 3 2 7 , 3 4 2 , 357 t u r b i n e d r i v e n , 1 3 9 , 142
Ven t i ng (o f n o n c o n d e n s a b l e s ) , 1 1 2 , 1 1 5 , 2 6 4 , 2 7 0 , 2 7 2 , 2 8 0 , 2 9 0 , 3 0 0 , 3 0 3 , 3 1 4 , 3 5 3 , 357
Waste h e a t , 1 4 , 2 1 , 2 5 , 5 3 , 147 , 1 5 9 , 1 7 8 , 1 8 0 , 185
382
Water i n t a k e : to j u i c e p u r i f i c a t i o n s t a t i o n , 32 to C m a s s e c u i t e c r y s t a l 1 i z e r s , 33 to p r o c e s s , 3 0 , 2 9 1 , 3 1 0 , 323 to s u g a r h o u s e , 3 2 , 3 4 , 2 9 1 , 3 0 2 , 305 to vacuum p a n s , 3 2 , 6 6 , 1 0 1 , 2 2 5 , 2 2 8 , 271