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HIGH TEMPERATURE CYCLONES

by

PETER A. PATTERSON, M.Eng.

A thesis submitted to the Faculty of Graduate Studies and Rp.search of McGill university in partial

fulfillment of the requirements for the degree of Doctor of Philosophy

Department of Chemical Engineering McGill University, Montreal

0Peter patterson, 1989

February, 1989

• +1 National Ubrary . of canada

Bibliothèque nationale du.Cana!la .

Canadian Theses Servicé Service des thèses canadiennes

Ottawa. Canada KIA ON4

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ISBN 0-315-52508-8

Canada

HIGH TEMPERATURE CYCLONES

P.A. Patterson

Chemical Engineering Department McGill University, Montreal

Quebec, Canada H3A 2A7

ABSTRACT

Gas-solids separation was studied in a 102 mn, dia~eter

conventional cyclone operated with air heated to

te~peratures between 300 K and 2 000 K. Cyclone pressure

drops, fractional and overall collection efficiencies were

measured as functions of temperature, gas throughput, dust

loading and cyclone geometry. Alumina and silica of 100 %

less than 44 pm mass median diameter were used as test

dusts. Inlet velocities ranged from 3 to 42 mis and inlet

dust loadings were between 0.3 and 215 g/m3.

Empirical models were derived to correlata the experimental

results for the cyclone collection efficiency, press~re

drop, tangential velocity and 50 % cut size. The

performance of the cyclones at very high temperatures was

not significantly different from the room temperature

behavior, provided that the effect of ternperature on

particle, gas and flow properties was adequately treated.

cyclone à heute temp6rature

P.A. Patterson

RÉSUMÉ

La séparation gaz-solides fut étudiée dans un cyclone

conventionnel de 102 mm de diamètre opéré dans l'air

chauffé à des températures entre 300 et 2 000 K. La chute

de pression dans le cyclone et les efficacités de

collection fractionnelle et totale ont été mesurées en

fonction de la température, de la charge en poussières, de

la géométrie du cyclone et du débit de gaz le traversant.

Des poussières d'alumine et de silice de moins de 44 pm de

diamètre moyen furent utilisées comme particules d'essai.

La vitesse et la charge en ~~ussière à l'entrée du cyclone

variaient de 3 à 42 mjs et de 0.3 à 235 gjm3 respectivement.

Des modèles empiriques ont été dérivés afin de corréler les

résultats expér •. lllentaux sur l'efficacité de collection, la

perte de pression, la vitesse tangentielle et le diamètre

de pertes à 50%. La performance des cyclones à haute

température comparé à ceux opérant à te~pérature ambiante

est sensiblement la même en autant que les effets de

température sur les particules et les propriétés du gaz et

du flux soient traités adéquatement.

TO MY FATHER

ACKNOlfLEOOEHBNTS

The author wishes to thank all those who contributed

directly or indirectly to the presentation of thi~ ehesis:

Prof. Munz for his guidance, patience and generosity

throughout the course of this project.

Ors. W.H. Gauvin, M.E. Weber, D. Berk, A. Mujumdar and

J.L. Meunier; the plasma group: Earle, Roberto, Paul S.,

Paul P., Peter T., Maysa, Murray, Gang-Qiang, Bogdan; summer

students: John, Colin, Bruno and Gillian for their advice,

practical assistance and moral support.

The Chemical Engineering non-academic staff: Mr. Krish, Mr.

Dumont, Mr. Habib, Alain, Walter, Herb, Don, Lou, Pat and

Anne for their professional 'assistance.

Mr. stanl~y Henry of the Electrical Engineering workshop for

solving many electrical problems (inclùding my TV).

The Natural Sciences and Engineering Research council of

Canada, and the Ministry of Education of Quebec for their

financial support.

And most of all, my family for their love and support.

'. ., ,. ".

• / ~ . .

.'

TABLE OP CONTENTS

-ABSTRACT

RÉSUMÉ

ACKNOWLEDGEMENTS

TABLE OF CONTENTS

I.J:ST OF FIGURES

LIST OF TABLES

GENERAL INTRODUCTION

CHAPTER 1

:HAPTER 2

GENERAL CYCLONE THEORY AND PRACTICE

Introduction Types of cyclones High Temperature cyclone Studies Summary

EXPERIMENTAL PROCEDURES

Introduction

Experimental Apparatus The cyclone The Plasma Generator The cyclone Inlet Channel The Inlet and Out let Diagnostic

Sactions The Particle Feeder The Particle Sample Train

Data Acquisition and Analysis Particle selection Criteria Characterization of the Powders operating Procedure

Summary

ii

~

i

ii

'1

xi

1

3 3 5

23

25

25 25 27 30 32

35 37

40 40 42 49

52

C CHAPTER 3 GAS AND PARTICLE FLOW PATTERNS

Literature Review 53

Experimental Results and Discussion 62 Particle Deposition Patterns 63 Pressure and Velocity Measurements 67

The Pressure Probe 67 Tlle Pressure Probe Location 72 Room Temperature Experiments 73

Profiles Obtained with Large 73 diameter gas outlet

Profiles obtained with small 81 Diameter Gas Outlet

Profiles for small vs Large 85 Diameter Gas Outlet

High Temperature Runs 88 Comparisons with Predicted Profiles 94 Correlation of the Experimental 95

Summary 104

CHAPTER 4 COLLECTION EFFICIENCY STUDY

Introduction 106

Lit3rature Review 107 Modelling the Collection Performance 107

of Cyclones The Rosin et al. Study 112 The Lapple Study 115 The Sproull Study 116 The Leith and Licht Study 118 The Deitz Study 121 The Mothes and Loffler Study 125 Effect of OUst Load on Collection 131

Efficiency summary of Literature Review 138

Experimental Results and Discussion 140 Operating Conditions 140 Correlation with Dimensionless Groups 141 Effect of operating Conditions on 149

Grade Efficiency Curves Comparisons with Predicted Grade 158

Efficiency CUrves Comparisons with Predicted Overall 160

Collection Efficiencies The Loading Effect 163

C The Rosin et al. Model 165

Hi

o

CRAPTER 5

The Lapple Model The Sproull MOdel The Leith and Licht Model The Masin and Koch Hodel The Deitz Model The Mothes and Loffler Model

Summary

CYCLONE PRESSURE DROP STUDY

167 171 171 174 174 178

181

Li~erature Review 184 The Effect of OUst Load on 196

Pressure Drop

Experimental Results and Discussion 201 Analysis of the Euler Number 202 Predicted vs Experimental Pressure 209

Drops su~ary 221

CONCLUSIONS 224

CONTRIBUTIONS TO KNOWLEDGE 227

RECOMMENDATIONS 229

NOMENCLATURE 230

REFERENCES 238

APPENDIX 1 - RAW DATA 246

APPENDIX 2 - TEMPERATURE MEASUREMENT 247

iv

Figure

1-1

1-2

1-3

1-4

1-5

1-6

1-7

1-8

1-9

1-10

2-1

2-2

2-3

2-4

2-5

2-6a

2-6b

c

HaT OP lIGURES

Four basic types o! cyclones (CapIan, 1977)

Examples of some commercial cyclones (perry and Chilton, 1973)

The variation of air viscosity with temperature.

The A.P.T. test rig and grade efficiency curves (parker et al., 1981).

Correlation of the A.P.T. data (Parker et al., 1981).

Dimensions of the Exxon miniplant cyclones (Hoke et al., 1980).

Comparisons of Exxon data with the Leith and Licht model (Hoke et al., 1980).

cyclone dimensions in stream 1 of the CURL test rig (Pillai and Wood, 1981).

Comparisons of CURL data with the Leith and Licht (1972) model (pillai and Wood, 1981).

The Grimethorpe cyclone and data (Wheeldon et al., 1986).

The experimental apparatus (Il, 12, 13 are electrical isolation sections).

The test cyclone.

The inlet diagnostics section.

The outlet diagnostics section.

The Tafa particle feeder.

The particulate sampling train.

Orientation of the slots on successive stages of the cascade impactor.

v

6

8

11

13

15

16

19

21

22

26

28

33

34

36

38

39

2-7

2-8

2-9

2-10

3-1

3-2

3-3

3-4

3-5

3-6

3-7

3-8

3-9

3-10

3-11

3-12

3-13

3-14

3-15

photographs of the test dusts: a) alumina, b) silica. '

In1et particle size distributions of alumina

Inlet pa~icle size distributions of silica

Effect of inlet velocity and dust load on dispersion and measured size distribution

The van Tongeren (1975) cyclone with rust bypass

The velocity profiles of ter Linden (1949)

Particle deposition patterns on the walls of the cyclone.

The 5-channel pressure probe (Reydon, 1978)

Pressure probe location and coordinate system

Total velocity profiles vs inlet flowrate for cyclone Cl.

Tangential velocity profiles vs flowrate for cyclone Cl.

Radial velocity profiles vs flowrate for cyclone Cl.

Axial .elocity profiles vs flowrate for cyclone Cl.

Oiagram showing the flow zones in the cyclone

Tangential velocity profiles vs flowrate cyclone C2.

Radial velocity profiles vs flowrate for cyclone C2.

Axial velocity profiles vs flowr.ate for cyclone C2.

Tangential velocity profiles vs gas outlet configuration for an inlet velocity of 8 mis

Radial velocity profiles vs gas outlet configuration for an inlet velocity of 8 mis

vi

43

44

45

48

55

57

64

69

71

74

76

77

79

82

83

84

86

87

c 3-16

3-17

3-18

3-19

3-20

3-21

3-22

3-23

3-24

4-1

4-2

4-3

4-4a

4-4b

4-5

4-6

Axial velo city profiles vs gas out 1 et configuration for an inlet velocity of 8 m/s

éomparison of tangential velocity profiles at high and lo~ temperatures.

Comparison of radial velocity profiles at high and low temperatures.

Comparison of axial velocity profiles at high and low temperatures.

Wall tangential velocity/mean inlet velocity vs annulus Reynolds number.

comparison of experimental with predicted tangential velocity profiles: cyclone Cl at 300 K.

Comparison of experimental with predicted tangential velocity profiles: cyclone Cl at 1300 K.

Comparison of experimental with predicted tangential velocity profiles: cyclone C4 at 300 K.

Comparison of experimental with predicted tangential velocity profiles: cyclone C4 at 1300 K.

Theoretical vs actual grade efficiency curves (stairmand, 1975).

TI.e Staimand (1951) cyclones and grade efficicncy curves.

T"e nomalized grade efficiency curve and cyclone configuration of Lapple (1951).

The cyclone cross-section for the Leith and Licht (1972) model.

Comparison of the Leith and Licht model with other models.

The geometry for the Deitz (1979) model.

Comparison of the Deitz (1979) model with experimental data.

vii

89

91

92

93

97

98

101

102

103

110

114

117

119

119

123

126

4-7

4-8

4-9

4-10

4-11

4-12

4-13

4-14

4-15

4-16

4-17

4-18

4-19

4-20

4-21a

4-21b

4-21c

The geometry for the Mothes,and Loffler 128 (1984, 1988) model.

Comparisons of theory with experiment for 132 the Mothes and Lo:fler (1984, 1988) model.

/ariation of separation efficiency due to 139 agglomeration with particle size (Mothes and Loffler, 1985).

dpa vs Re.stin 0.5 both both dusts. 145

dpa vs separation number for both dusts. 148

Penetration vs Re.stino.5 for both dusts 150

Penetration vs separation number for alumina 151

Penetration vs separation number for silica 152

Grade efficiency curves showing the effects 153 of temperature, inlet velocity and dust load.

Grade efficiency c~rves showing the effects 155 of particle type and dust load.

Grade efficiency curves showing the effects 157 of outlet dimensions and dust load.

Grade efficiency curves suowing comparison 159 of experimental with predicted data for poor operating conditions.

Grade efficiency curves showing comparison 161 of experimental with predicted data for good operating conditions.

Experimentally measurêd collection efficiency 166 vs dust loading.

Predicted vs experimental overall collection 168 efficiency for the Rosin et al. (1932) model with no load correction.

Predicted vs experimental overall collection 169 efficiency for the Rosin et al. (1932) model with A.P.I. (1975) loa' correction.

Predicted vs experimental overall collection 170 efficiency for Rosin et al. (1932) model with A.P.I. (1975) load correction (A = 0.26)

viii

c

c

4-22 Predicted vs experimental overall collection 172 efficiency for Lapple (1951) model with A.P.I. (1975) load correction (A = 0.26).

4-23 predicted vs experimental overall collection 173 efficiency for Sproull (1970) model with A.P.I. (1975) load correction (A = 0.26).

4-24 Pr.edicte~ vs experimEntal overall efficiency 175 for Leith & Lic:lt (1972) model with A.P.I. (1975) load correction (A = 0.26).

4-25 Predicted vs experimental overall efficiency 176 for Masin & Koch (1984) model with A.P.I. (1975) load correction. (A = 0.26).

4-26 Predicted vs experimental overall efficiency 177 for the Deitz (1981) model with A.P.I. (1975) load correction (A = 0.26).

4-27 Predicted vs experimenta1 overa1l efficiency 179 for the Mothes & Laffler (1984) model with A.P.I. (1975) load correction (A = 0.26).

4-28 Predicted vs experimental overall efficiency 182 for a modified Mothes & Laffler (1984) model with A.P.I. (1975) load correction (A = 0.26).

~-1 Total and static pressure profiles measured 190 by ter Linden (1949).

5-2 Variation of pressure drop reduction with 198 dust load (Sproull, 1966).

5-3

5-4

5-5

5-6

5-7

Variation of pressure drop ratio and velocity profiles with dust load (Yuu et al. 1978).

Variation of pressure drop with barrel velocity he ad for dust-free flow.

Variation of pressure drop with barrel velocity head for dust-laden gas.

Variation of zero-load Euler number with cyclone geometric parameter.

V~riation of Euler number ratio with dust load.

ix

200

204

205

207

208

5-8

5-9

5-10

5-11

5-12

5-13

5-14

5-15

A2-1

A2-2

comparison of experimental data·with pressure drop ~redicted by the Wheeldon et al. (1986) model. <

Comparison of experimental data with pre&sure drop predicted by the Masin and Koch (1986) model.

Comparison of experimental data with pressure drop predicted by the Shepherd and Lapple (1939, 1940) model.

Comparison of experimental data with pressure drop predicted by the Ca~al and Martinez-Benet (1982) model.

Compar~ ~ of experimental data with pressurt urop predicted by the Stairmand (1949) mvdel.

Comparison of experimental data with pressure drop predicted by the Alexander (1949) model.

comparison of experimental d~ta with pressure drop predicted by thp. model derived from the experimental data (method 1).

comparison of experimental data with pressure drop predicted by the model derived from the experimental data (method 2).

Measured vs corrected tempcrature for runs with alumina.

Measured vs corrected temperature for runs with silica.

x

212

213

215

216

218

219

220

222

255

256

Table

4-1

4-2

5-1

5-2

Al-l

Al-2

Al-3

Al-4

Al-5

c

Lxsr OF TABLES

Summary of correlation coeffi~ients for dimensionless group study

Summary of Performance Xndices for collection efficiency models

Co~~a~ison of Euler numbers

Summary of Performance Indices for pressure drop models

Alumina Experimental Data - High Temperature - 5.08 cm outlet

Alumina Experimental Data - High Temperature - 2.54 cm outlet

Alumina Experimental Data - room temperature

Silica Experimental Data - high temperature

silica Experimental Data - room temperature

xi

~

144

164

203

210

247

248

249

250

251

o

GENERAL INTRODUCTION

c

GENERAL, INTRODUCTION •

The separation of-solids from gases at high temperatures is

a very important problem in the areas of .energy conservation

and conversion. Processes SUCII as advanced coal conversion, . . combustion and biomass conversion produce large quantities

of gas at temperatures above 1 000 K which are contaminated

with micron-sized particles. In some cases, these gases

must be cleaned at high tempe ratures to minimize the loss in

enthalpy. Recent developments in high te~perature plasma

processing are also expected to require high temperature gas

cleaning.

Conventional cyclones are popular for l1igh temperature gas

cleaning because of their simplicity and low maintenance

requirements. They are currently the only gas cleaning

device which can be used on an indus trial scale at very high

temperatures. Despite the apparent simplicity of the equip­

ment and its governing principles, the characterization of

particle removal performance is still not clearly defined

and ia largely empirical (Zhou et al., 1988: Mothes and Lof­

fler, 1988). only limited experimental data have been

reported for high temperature operation, and these are

insufficient for thorough evaluation of the effects of tem­

perature on the particle collection mechanism&.

o 2

The objective of this study was ~o gain a fundamental under-

standing of the behavior of conventional cyclones and to

study how they performed at very high temperatures. Collec­

tion efficiencies an1 pressure drops w~re m~asured at gas

temperatures up to 2 000 K with silica and alumina as the

test dusts. The gas throughput, dust loading and cyclone

geometry were the other operating variables. Standard con­

ditions are defined as 298 K and 101 kpa in this thesis.

The thesis is arranged in six chapters. Chapter 1 gives a

broad overview of cyclone practice and a review of rele~ant

studies of cyclones at elevated temperatures. Chapter 2

contains descriptions of the experimental apparatus and

procedures. Chapter 3 deals with the flow patterns in cyc­

lones with discussion~ of published studies and observations

made in the presenc study. Chapters 4 and 5 de scribe col­

lection efficiency and pressure drop studies with emphasis

on math~catical models capable of predicting cyclone perfor­

mance. The raw experimental da~a are included in the appen­

dices.

CRAP'rER 1

GENERAL CYCLONE TJŒORY AND PRAC'l'ICE

c

o ClIAP'l'BR 1

GBNERAL CYCLONE THBORY AND PRACTICB

INTRODUCTION

cyclones have been used for over a cent«~ to separate sol­

ids fro~ gases (1885, German patent 39219). Their simple

design, high efficiency for large partic1es and 10w mainte­

nance costs still cake them the most common gas c1~aning

device in use today. The various types of cyclones common1y

used are described briefly in this chaptcr, fo110wed by a

discussion of their use at high temperatures.

TYPBS OP' CYCLONES

The necessary e1ements of a cyclone are the f10w inlet which

produces the vortex, an axial outlet for cleaned gas, and a

dust discharqe or collector (The~ore & Buonicore, 1976;

caplan, 1977; Heumann, 1983). These three elements have

been coJW.l.ned in many ways and Flgure 1-1 shows the four

basic classifications. The combination of tangential inlet

with axial dust discharge (known as the ~onventional cyc­

lone), is the most common arrangem~nt and was the focus of

this study.

lAI TO"'l'/I"o' illll' ..... GI.cI>Or;1

CCI Aue' iIIlI' GIlet dllotho'VI

4

-

~ 1

IBI T.IIQtIll ••• "" .. pt fi phI'OI c""l'IOu;.

lOI Al .. ' 1/1'" Pt'Ipft.rol CSIKhO,'iI'

Figure 1-1 Four basic types of cyclones (Caplan, 1977).

-0

5

CYclones are used either as individual units, as a composite

of two or more swirl chambers, or as banks of small units in

parallel to form a multicyclone (Figure 1-2). The diameter

can vary from around one centimeter (miniature sampling cyc­

lones) to several meters in commercial units. Many accesso­

ries sucn as inlet vanes, baffles and vortex shields have

been used in attempts to enhance the dust collection and

reduce the pressure drop; however, improving one of these

usually results in making the other worse.

HIGH TEMPERATURE CYCLONE STODIES

cyclones are popular for high temperature gas cleaning

because of their simplicity and low maintenance require­

ments. The largest application of cyclones ;3 for the

recovery of regenerated catalyst fines in petroleum refinery

cata1ytic cracking units (Saxena et al., 1982). In modern

units, temperatures can approach 973 K and pressures,

400 kPa.

The~e has been recent interest in hot gas cleanup systems

for pressurized f1uidized bed combustion of coal in power

generation. Applica~ions at temperatures up to 1 500 K and

pressures up to 5 000 kpa are being considered, with cyc­

lones as the primary gas c1eaning device (Razqaitis,

6

.. ....

.......... _~5r-o..r ... .....

Figure 1-2

v--........ III

C" Cil

_fl_ ... - .... '----""" .....

Ccl

III

Examples ot some commercial cyclones (Perry and Chilton, 1973)

T

1977: Heyer and Edwards, 1978: Horrison, 1979: Gil~s, 1981,

1982: Henry et al., 1981, 1982). Only limited experimental

data have been reported for cyclones oper~ting at very high

temperature and these-a:? insufficl"_-t- for the evaluation of

the effects of temperature and press_. • on the particle col­

lection mechanisms.

The principal effect of high temperatures on the performance

of cyclones, is that the gas viscosity illcreases, leading to

an increase in the drag force on the particles and a

subsequent decrease in the inertial separation potential of

the cyclone. Figure 1-3 shows that the viscosity of air

increases by a factor of three as the temperature increases

from 300 to 2 000 K.

The gas density on the other hand varies inversely with tem­

perature leading to an enhancement in the collection effi­

ciency at elevated temperatures. However, the density

effect is usually negligible since the determining factor is

the difference between particle and gas densities, and the

particle density remains much higher than the gas density.

Theoretical models for cyclone performance do not usually

conta in the operating temperature as an explicit function,

but rather, it appears implicitly ~~ a function of visco­

sity, gas density and other terms such as the vortex law

exp one nt en).

,~

7.0r-1 -----------------1

6.0 co •

0 a.. 6.0 • 10

0 -x 4.0 >-t-H CI)

8 3.01 ./

CI) H >

2.0

1.0~1~----==------~------~------~------J 200 600 Hm 1400

TEWERATURE. K 1800 2200

Fi9u~e 1-3 The variation of air viscosity with temperature.

~

0>

o

9

0n9 ol the earliest _tudies of cyclones at high temperatures

was repo~ted by Parent ~1946). He studied cyclones of 5.0

and 7.6 cm diameter at temperature~ up to 1 030 K using fly­

ash of les& than 1~0 pm as the ' ~st dust. He observed the

inverse variation of efficiency with temperature, and the

direct variation with gas throughput. The dust loads stu­

died were very low (0.0003 to 0.005 g/m3) and did not influ­

ence the collection efficiency in this range.

Later, Alexander (1949) studied cyclones measuring 3.2 to

120 cm in diameter operated at temperatures up to 1 373 K.

The only high temperature results published, were for a

10 cm cyclone. He used silica dust with a mear diameter of

5.0 pm, and he measured static pr&ssures, ve Jcities and

directions of flow within the cyclone using a symmetrical

Pitot probe. The collection efficiencies were determined

for total catches and not fractional catches (with frac­

tional catches, the dust is divided into several size ranges

or fractions, and the amount caught in each fraction is

measuxed). The empirical correlations devcloped by Alex­

ander are discussed in Chapters 3 and 5 of this thesis.

Yellot~ and Broadley (1955), described tests done on 5.0 and

7.6 cm diameter Aerotec cyclones (reported earlier by Par­

ent, 1946), and on a variety of straight-through tubes rang-

10

ing in diameter from 21 to 41 cm. The tests were carried

out at temperatures up to 977 K and pressures up to 500 kPa.

The tubes were tested both individually and Ir. batteries of

up to 60 units in parallel. The expected de crea se in ove­

rall collection efficiency with increasing gas temperature

was observed. ~ellott and Broadley measured overall collec­

tion efficiencies only and not fractional collection effi­

ciencies.

More recent'y, smith et al. (1979) described the development

and calibration of a five-stage cyclone sampling system,

with the cyclones ranging from 1.5 to 4.5 cm in diameter.

They used particles ranging frQm 0.3 to 8.0 pm in diameter

and with densities between 1.03 and 2.04 g/cm3 • Tests were

carried out at temperatures up to 477 K and flow rates up to

0.03 m3/min at atmospheric pressure. They found that the

50 % cut-size was proportional to (pppo.5/Qm) where m was

between 0.63 and 1.11.

Parker et al. (1981) reported an experimental study carried

out at Applied Particulate Technologi~s (A.P.T.). The test

cyclone was a 5.0 cm diameter conventional cyclone operated

at temperatures up to 973 K, pressures up to 2 500 kPa, a~d

inlet velocities up to 5.2 mis (Figure 1-4a). They showed

that the collection efficiency decreased sharply with

increased temperature (Figure 1-4b), and that available the-

o

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..... ... ... ...

'" .. , . ... .. . ... .. . ur ~~~~~=::.:.:...._-..J !--!- --- ,a'" I, ••••• • t. " ........

"'''110' ................ " •. , •• ~ __ .. lM> .... UcH 11).

Figul:e 1-4 The A.P.T. test (Parker et .' 1.. 1

rig and grade efficiency curves 19~1).

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12

oretical models could not predict the observed effects of

temperature and pressure (?igure 1-4c). However, their 50 %

cat-size data (expressed as aerodynami~ diameters) corre­

l~ted weIl against the product of a Reynolds number and the

square root of a Stokes number (Figure 1-5).

The Reynolds number was based on the cyclone diameter and

the mean inlet velocity, while the Stokes number was based

on the mass median diameter of the feed dust (dpg)' the

inlet veloci~t (Vi) and the hydraulic diameter of the

inlet (dH). This definition of the Stokes number differs , from the usual practice of using the 50 % cut-size and the

c~clone diameter. In crder to avoid confusion, the Parker

et al. definition will be referred to as the inlet Stokes

number (Stin) and the other one as the cyclone Stokes num­

ber (stso). The inlet Stokes number was given as:

(1-1)

Unexpectedly, me st of the cor~~lation for the Parker et al.

data was due te the Reynolds number and this could not be

explained by the authors. The inverse variation of cut-size

with Reynolds number is inconsistent, since the gas density

term in the numerator incorrectly predicts that decrcasing

the gas density (by increasing the temperature for example)

o

c • • • • ~ • :II ::! • ~ ,. u .. • •

, .... •••• •••• 1 •••

, ... ••••

o •• o •• o ••

0.1

0.1

13

8

o ...... 1 ..... 1&

o 0 00

00

tO' ,,' 1,4 tO"

Figure 1-5

Data correlation wilh 50% eut diameters.

Correlation of the A.P.T. data (parker et al., 1981).

c

14

would lead to higher cut-sizes. The Parker et al. work 1s

discussed further in Chapter 4.

Hoke et al. (1980, Ernst et al., 1982) studied the perfor­

mance of three cyciones in series in a pressurized fluidized

bed co~ustion miniplant at Exxon. The cyclones had diame­

ters of 15.2, 17.8 and 32.4 cm respectively, and other

dimensions as shown in Figure 1-6. The co~ustor was oper­

ated at up to 1 173 K and 900 kPa.

The first cyclone was used primari1y to recycle flyash to

the co~ustor, so that the secondary cyclone was in effect

the first clean-up cyclone. The overall collection effi­

ciency of the secondary cyclone was 90-95 % with the col­

lected dust having a mean diameter of 20-25 pm, while the

dust penetrating the cyclone had a mean size of 3.0 to

5.0 pm. The tertiary cyclone collected around 90 % of the

dust leaving the second cyclone. About 80 % of the dust

penetrating the third cyclone was less than 5 pm with an

average particle size of around 1 to 3 pm. The final par­

ticle concentration was usually 0.03 to 0.15 g/m3 at room

t~perature and pressure. These efficiencies were higher

than those predicted by available models (for example Leith

and Licht, 1972) and could not be explained by the authors

(Figure 1-7).

o

SYMIOL

15

CYCLCNE DE!JGN DIMlNliIONS

-Iwl­INL!r D t

sa:nCN 1.

DE!OlmCN

Inl.t T,.,. ...,.1 Di ..... 1It

Inlat Wlcth In"t Hel"'" ·O"' .. t PIpe in_lion ..... 1 H.l;ht ConoHolght Out"t PIpe or ..... 1It O"' .. t/ln .. t JMIo DI_lit of C#.e DI Ion­f'-"Ctlon

T T ho ".

1 l T l

DIMENSIONS ICMI CYCLONE CYCLONE CYCLONE

NO. 1 NO. 2 NO. 3

T~ntlal 32.4 7.62

25.4 20.3 43.2 45.7 14.6 0.17

12.7 a.cyc ..

Tan;entlel 17.1 4.45

10.2 13.3 35.6 35.6 .. ., 1.37 '.0

CI-.

Tongontlal 15.2 3.'1 7.62

Il.4 40.' 20.3 6.2 1.~

'.0 CI~

Dimensions ot the Exxon ~iniplant cyclones (Hoke et al., 1980).

~

~ -~ Q !!i z 2 Id :t 0 u

TEiTlAAY CYCLONE COLLECTION EFFICIENCY (IUN 105)

1 1 ~_. a. ~ .... 100 • ..

J ............. .. • • .........

111

60'-'renure

....... ...... ...... ......... 700 k'. uS'e 14.' MII'/.In 15 "ue

...... , •

.... '\ ......

• •

TeMj>l ... ture Flow rate Inlat V.loclty 'renure cltop 4 k'.

' ... ...... .. ... .............

• IAlSTON FILT(J/C..:lUllU COUNTEI • CASCADE IMPACTOI .. LEml AND lICIIT MODEL (nILOaETICAl)

1

•

............ r

• 01 lIt , 1 1 1 l' , 1 l , , , ~

15 10 9 • 7 6 5 4 3 2 1 .9 •• .7 .6 .5

PAITICLE SIZE, .....

Figuro 1-7 Compnrioono ot Exxon dntn with tho I.oith and Licht modol (lloko ot nl., 1980).

~

... CIl'

)

o

o

17

An evaluation of several particulate samp1ing systens was

also done in the Exxon study. The streacs-entering and

leaving the third cyclone were sampled with a Balston Filter

particulate sampling system, and a high-temperature high­

pressure (HTHP) sampling system containing either a 5-cy­

clone sampler (mentioned earlier, Smith et. al., 1979), a

University of Washington 7-stage cascade impactor, or an

Applied Particle Technology (APT) high-tecperature high­

pressure cascade impactor. The Balston filter elements con­

sisted of borosilicate glass fibers bonded with an epoxy

resin.

The study found that while the Balston fil ter could give

good concentration measurecents, problens arose in obtaining

the particle size distribution. The Coulter Counter which

was used to measure the size of the dust col1ected on the

Balston filter, gives the volumetrie diameter whereas the

cyclone sees the aerodynamic equivalent diameter. It was

also not certain whether or not Agglomeration occurred in

the cyclone or in the fil ter, and to what degree agglomer­

ates were redispersed before being measured by the counter.

The 5-cyclone sampler was four.d to be unsuitable for HTHP

sampling due to: 1) the very dilute nature and small size of

the ~articulates in the flue gas stream: 2) the size resolu­

tion of the cyclone train which was too poor: and 3) system

c

18

leaks and contamination from anti-seize compounds in the

fittings.

The results obtained from the 7-stage cascade impactor were

indeterminate since it was run at flowrates which were too

high, leading to wash-off of parti cl es from the early stages

to later stages. On the other hand, good results were

obtained with the APT cascade impactor containing inconel

shim substrates. The flyash particles were very adhesive at

the samplinq conditions, allowing the use of the bare metal

substrates.

Pillai and Wood (1981. also Lane et al. 1982. Hoy and Rob­

erts, 1980) reported on a 1 OOO-hour test program on a

PFBC facility at the Coal utilization Research Laboratory

(CURL) in Leatherhead England. The off-gas from the cOmbus­

tor in the test rig was split into two streams, each con­

taining three cyclones in series. The stream-1 cyclones had

diameters of 50.8, 39 and 33 cm respectively with dimensions

as shown in Figure 1-8. The cyclones were tested at temper­

atures up to 1 088 K, pressures up to 6uO kpa and inlet

velocities up to 33 mis.

The overall collection efficiency of the first cyclone

agreed we11 with that predicted by the Leith and Licht

model, whereas the second and third cyclone overall effi-

(1

Figure 1-8

H

19

~ 1 •

1 s o i

1

L.I----!-I--; 1

1 1 1

STAGE 1 B:%ao.c::rr.ttr 101

• _lr-S1 0/0.0.46 bIO.o.21 A/D.O.30 5/0.0.9 h/C.'.l1 H/D.J.eo

9/0'0.'5

STAGE 2 SOCy DoOn'<' ... ID.

·390IMI"-]""" 0/0_0'6 b/D.D.21 A/O,0.19 5/0'0.9 n/C. !.32 H/D.J80 . 9/0.0.27

STAGE J

aoor :loG.,.'''' '0' • J30_lr-., 0/0 .o.~

b/C.0.19 .4/0_0.5 5/0.0.9

"'0.'.5 H/O.'.O BIO. 0.38

Cjclone dimensions in stream 1 of the CURL test :dg (Pillai and Wood, 1981)_

c

(

c

20

ciencies were poorly pred~cted by the same model.

Figure 1-9 shows that the grade efficiencies for thp three

cyclones did not agree with those predicted by the Laith and

Licht model.

It was also found that for the second cyclone in stream-l,

there was a decrease in the grade efficiency for particles

above 4.0 pm. The stage-3 cyclone on the other hand, had

flat grade efficiencies for particles in the range 0.8 to

15 pm (Figure 1-9). The reasons given for this unexpected

behavior were: 1) large errors due to the sma11 amount of

material collected by the cyclone; 2) the dust was too fine

for inertial separation; and 3) agglomeration of particles

after collection by the cyclones resulting in lower calcu­

lated efficiencies for larger particles.

Wheeldon et al. (1936) reported on the performance of two

parallel pairs of cyclones in the off-gas stream of the Gri­

methorpe PFBC facility in South Yorkshire, England. Each

pair consisted of two cyclones operating in series. The

cyclones were 1.2 m in diameter with the proportions shown

in Figure 1-10a. The operating pressure varied between 6

and 12 atmospheres, temperatures between 900 and 1 183 K,

velocities between 16 and 27 mis and du st loads up to

140 91m3 • Efficiencies up to 98.6 % with cut-sizes of

around 3.5 pm uere measured.

"'or-,..--:--­, l , ft ,"~"'"

" " ' . . " " ••

• ; JO

i 10

~

i • 1 ~Ll. ..•.. , . t "-:.. .. t &. •••••

~ 10 ••• ••

~ . ~ 1 1 S~·\%I: 1

l " " di .. III fi tJ tt

ft • • ••••

"

;; 1 ..

21

· ... . · ... .

· ... , f :

. 1 1 ~ kl ..

i '" .. "1

:,-.-.. , ... -- "'-*--

: .~: -~ .. - .. . . . .. .

f i r" , .

..

! ..

l ,,,''l'~GE. Z. , 1

... h-• ...i...-_--,,;;-, -_.-:L........:~!J.L~l- _1--I-J.....L..l-!.U,!.

Figure 1-9

.. ,., ...... :"" .... I~.'

· ..... · ... , 1 ..

1 1 1 , l '

.. Comparisons of CURL data with the Leith and Licht (1972) model (Pillai and Wood, 1981).

c

...,.t-.a. ..... •

•

fi IIIIJ'

,]

u .. _ fi"'"''''''

1 ~

i i

•

22

STOlU !.Mf' '0' Jtt4.1:!'( .IJIQ UCOtClh' UC\O!!fi

yruY1 "un MI 19.19!t§

.­. "" .... . ". "..., c"a ....

~ .. .. • ft •

• "NI' • Ne...,.., U'''''I''',,-...

:r ~.:·t'·' .. le •

Il .. H .. .M

K' ,. 'M

• ( i 1

•• Il " • • » J 1 M ; • ~ • • & ., • .. 'm ... " .......... C'lQ,I;oC ...... " •• '

" " " H

• Nltru. , _hIN. • ..n. ..... ,.atM ._'IPUIIM

IIC#M1UUR G .... O[ q'l!!!5! 1!:!,V!.S fat ne ""UIX '!SR S(l1'!!9HIJ an2!!fS

--..

-_...-........ ,AdCl lIrCo ....... -

Figure 1-10 The Grimathorpe cyclone and data (Wheeldon et al., 1986).

.23

The ~yclone collection performancè'was characterized by a

cyclone Stokes number defined by the 50 % cut diameter, the

gas velocity in the body of the cyclone [vb = 4Q/~dc2], and

the cyclone diameter:

stso = d pS02ppVb

18pdc (1-2)

The StokeF number varied inversely with collection effi-

ciency and dust load (Figure 1-10b) while the operating

prp.ssure had no influpnce on the collection efficiency. The

effect of temper~ture was accounted for by the viscosity

term in the Stokes number. The grade efficiency curves

(Fiqure 1-10c) showed 'fish-hook' tails explained by the

authors as being due to agglomeration of fine p~rticles in

the cyclone; the agglomerates later break down during the

particle size analysis. The reason for the reduction in

e!ficiency above 8 pm for the secondary cyclones was not

clear, but the authors felt that it was due to strongly

bonded agglomerates with effective densities lower than the

individual particle àensities.

SUHK1.RY

cyclones are used for high temperature particulat~ removal

c

24

mainly because of their simplicity and low maintenance

requirements. Most of the published studies of cyclones

operating at high temperatures were for applications in the

petroleum industry or in fluidized bed coal combustion sys­

tems. These studies included cyclones varying from 1.5 to

120 cm in diameter operating at temperatures up to 1 380 K.

Comparisons of operating data with predicted grade effi­

ciency curves and total collection efficiency data showed

that the performance of cyclones is still not adequately

predicted over a wide range of operating conditions.

CHAP'rER 2

EXPERIMENTAL PROCEDURES

c

(

INTRODUCTION

mmnER2

EXPERIMENTAL PROCEDURES

The first section of this chapter contains descriptions of

the experimental apparatus. This is followed by an outline

of the particle selection criteria and dust characteriza­

tion, and conclu~es with an outline of the operating and

analytical procedures.

EXPERIMENTAL A~PARATUS

A schematic diagram of the experimental test rig is shown in

Figure 2-1. The main components were the cyclone, the

plasma generating system to heat the air stream, the par­

ticle feeder, the inlet and outlet diagnostic sections, and

the particle sampling train. T,lese components are discussed

in the following sections. The cyclone and the inlet and

outlet channels were made out of 316L stainless steel and

were thp~ally insulated.

The cyclone

A sche~atic diagram of the cyclone and its dimensions is

e ~

,

T') 'k AIR VENT ~ pnRTICLE

l uÛl FEE DER

H PlRSHR 'R:l "'TE"PERATURE TORCII PARTlCLES

PRESSURE ~Ffl~1 Il 12 18

PLASMA 1 1 •

'''88.']1' GENERATOR

r l CYCLONE VENTURI ® 1 1 nlllER I!l

AIR PARTlCLE8 IN TEIIPERRTURE --~ J 1 BlH

- --

Figuro 2-1 Tho oxporimontnl nppnrntus (Il, I2, I3 nro oloctricnl isolntion soctions).

N CI

c

27

shown in Figure 2-2. The cyclone had a 10.2 cm i.d. diame­

ter barrel and a rectangular inlet measuring 2.54 cm by 5.08

cm on the inside. The cyclone dimensions were measurable to

within 1 mm. The top of the cyclone was constructed with

the flexibility to change the dimensions of the gas outlet

duct: outlet diameters of 2.54 and 5.08 cm, and engagement

heights of 7.0 and 10.8 cm were studied. The four outlet

configurations were labeled as follows: Cl - 5.08 cm diame­

ter by 10.8 cm long. C2 - 2.54 cm èiameter by 10.8 cm long.

C3 - 5.08 cm diameter by 7.0 cm long and. C4 - 2.54 cm

diameter by 7.0 cm long. Cyclone C3 was the standard design

of Lapple (1951. Perry & Chilton, 1973). The dust was col­

lected in a sealed bin below the cone of the cyclone and

weighed at the end of each run.

The Plasma Generator

A 35 kW TAFA radio frequency plasma generating system was

used to heat air from room temperature to above 2 000 K.

The system consisted of a LEPEL 35 kW rectifier operating at

a frequency ot 4 MHz, and a TAFA Hodel 56 plasma torch. The

plasma vas confined by a 5.08 cm (2 inches) i.d. water­

cooled quartz tube as it passed through the torch. The

presence of this quartz tube limited the operation of the

torch to around atmospheric pressure.

28

o

cm

de 10.2 œ 2.54. 8.OB bo 2.154 ho 8.OB

S 7.0. 10.8 ZI 20.3 ~ 20.3 Zo 18.2 1 2.154

CYC. œ S -lIt-Na.

CI 8.08 10.8 Zo CZ 2.154 10.8

l C3 8.08 7.0 C4 2.154 7.0

Figure 2-2 The test cyclone.

c

29

The use of a plas=a torch to supply the required heat is a

novelty in the study of cyclones at high te=peratures. The

torch allows the use of a wide variety of gases in a con­

trolled che=ical at=osphere at te=peratures which cannot be

achieved in co=bustion syste=s, and by electrical resistance

heating ele=ents. The use of air (whose physical and ther­

=odyna=ic properties are weIl known) instead of a co=bustion

product with =ore che=ical species, reduces uncertainties in

calculations involving the gas properties.

The plas=a torch was always started with argon since it is a

=onato=ic gas and ionizes much easier than air to for= the

plas=a. The energy efficiency of this type of plasma gener­

ating system is of the order of 20 to 40 percent and it

varies with gas throughput~ thus, around 8 to 16 k~ was

transferred to the gas passing through the torch. The flow­

rate of air passing through the torch was between 0.05 and

0.11 m3/min and the temperature of the gas was between 2 000

K and 6 000 K at the exit of the torch (ba~ed on a heat bal­

ance).

A second strea= of air at roo= te=perature was added to the

plasma in a "tee" section just below the exit of the torch,

and a third stream (used as the particle carrier gas) was

added in a Venturi section about 15 c= further downstream.

o

30

. The resulting cixtures were around 2 000 K and less, with

flowrates between 0.19 and 1.18 standard c3/cin. The maxi­

cuc error licits on the measured temperatures and flowrates

were cstiDated to be ± 2 % of the determined values.

The torch was at a potential of around 1 000 volts during •

operation. Whenever the cyclone vas connected to the torch,

the large cass of cetal acted as an electrical energy sink

even when the cyclone vas not grounded. This forced the

torch to operate at very high powers and resulted in the

crackinq of cany quartz tubes. This problec was solved by

insertinq three electrical isolation sections in the inlet

channel thus breaking the single metal cass into four iso­

lated sections and reducing the voltage tetween the torch

and the cyclone in three steps.

The cyclone Inlet Channel

The cyclone inlet channe! began with a 5.08 CD diameter 90

degree elbow through which part of the supplementary air was

fed (Figure 2-1). The elbow was conncctcd to one leg of a

tee section and the second leg of the tee was connected to

the plasca torch. The other part of the supplecentary air

was injected through four tubes ot 5 am internal diameter

• placed tangentially around the top of the tee section just

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31

below the exit of the torch. The outlet of the tee was

separated from a Venturi section by a donut-shaped block of

transite (an asbestos composite) measuring 5.08 cm thick by

5.08 cm inside diameter by 10.2 cm outside diameter (Il in

Figure 2-1). This transite block was the first of the three

electrica1 isolation sections mentioned above.

The Venturi section was 15.2 cm long and had diameters of

5.08 cm at each end and 2.54 cm at the throat. Two 5 mm

i.d. particle feed ports were instal1ed in the wall at the

throat of the Venturi, perpendicular to the wall and diame­

trical1y opposed to each other. The particles were fed this

way in order to take advantage of the high turbulence in the

expanding section of the Venturi to disperse the particles.

The second electrical isolation section was placed after the

Venturi mixer and was again a transite donut, but measuring

only 2.54 cm thick (12 in Figure 2-1).

A 30.5 cm long rectangular section with a 2.54 cm by 5.08 cm

cross-section followed the Venturi. The purpose of this

section was to give the flow a chance to develop before

reaching the inlet diagnostic section. A three mm thick

asbestos gasket placed between these two sections was used

as the third electrical isolati~n section (13 in Fig-

ure 2-1).

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32

The Inlet and outlet Diagnostic sections

The inlet and outlet diagnostic sections contained probes

for the measurement of temperature, pressure and for par­

ticle sampling, as shown in Figures 2-3 and 2-4. The inlet

diagnostic section was rectangular, 15 cm long and ended 10

cm upstream of the cyclone barrel. The outlet diagnostic

section was 5.08 cm in diameter and the probe tips were 15

cm beyond the roof of the cyclone when the 5.08 cm diameter

out let was used, and 23 cm from the roof when a 2.54 cm out-

let diameter was used. The longer outlet was made by

inserting a 2.54 to 5.08 cm expansion section between the

cyclone outlet and the diagnostic section.

The static pressure was measured through a 3.2 mm tube in

the wall of the inlet duct perpendicular to the flow, while

the impact pressure was measured through a similar tube pro­

jecting into the channel and parallel to the flow. The dif­

ferences between the static and impact pressures were used

to compute the inlet velocity while the cyclone pressure

drop was measured by the difference between the inlet and

outlet static pressures. The pressures were measured by an

HKS Baratron Type 77 electronic pressure meter in the range

of 0.1 to 400 N/m2 (0.001 to 3 mmHg), and by a Magnehelic

mechanlcal gage in the range 400 to 2 450 N/m2 (3 to 20

,.,

WALL THERMOCOUPLE

\---t~ " PRESSURE PROBES

PARTICLE SAMPLE PROBE

Figure 2-3 Tho inlet diagnostics section.

~ --

THERMO­COUPLE

~

~

o

THERMO­COUPLE -_---==== PARTICLE:_~'=== SAMPLE PROBE

PRESSURE PROBES

34'

~ALL "..." THERMO­COUPLE

Figure 2-4 The outlet diagnostics section.

(

c

35

mmHg). Both devices were estimated to have maximum error

limits c' ± 2 % of the scale reading.

The inlet gas temperature was measured by a 3.2 lDlD dialnet~r

chromel-alumel (type-K) thermocouple aligned paralle: to the

flow and ';'n the same plane as the .ressure and particle

eampling probes. The wall temp~rature was measured directly

cpposite the gas tEmperature thermocouple and was l'sed to

corrEct the temperatu~e measured by the gas thermocouple for

radiation heat losses (see calculations in Appendix A2).

The temperatures were recorded by à Thermo Ele~ccl~ 24 chan­

nel strip-chart recorder.

The Particle peedcr

A TArA vibrating bowl feeder was used to fEed the test dust

into th., cyc~o ... e inlet channE'l. The feeder (shown in Figure

2-5) consisted of a conical storage hopper which fed th2

powder onto a bowl with a spiralling ramp around its

perimeter. The bowl was made to ~ibrate with an amplitude

proportional to the voltage applied to the vibrator, and

ticles in the bowl liIoved at a proportio •• ate1:~te upward in a

spira'. and through a hole at the top of the ramp. The

feeder was emptied after each run and the amount ~f powder

fed was determined by weight differ.ence. Fe~d =ates of up

SEEDED GAS OUT

, '

36

. .

~ GAS IN

1+-4--- STORAGE CANISTER

f4--4--- VIBRATING BOWL

I---j.--- VIBRATOR

Figure 2-5 The Tafa particl~ feeder.

37

to 700 g/min. with al'lmina and 160 g/min. with silica were

used. The maximum error limits for the dust feed rate were

estimated to be ± 1 g/min.

The Partic1e Samp1ing Train

The particle sampling train is shown schemat.cally in Fig­

ure ~-6. Only one cascade impactor was available, 50 samp­

ling was done on only one stream (either the inlet or the

outlet) in an experiment. The sample probe was a 5 mm

inside diameter stainless steel tube tapered at the end to

form a nozzle which was aligned parallel to the axis of the

channel.

The probe was connected to a Sierra 220 cascade impactor

where particle size distributions were measured for aervJy­

namic diameters in the r~nge of 50 to 0.1 p~. The impactor

was supplied with 10 stages but only the first seven were

used since the last three stages measured particle sizes

below 0.1 pm in diameter and introduced large pressure drops

into the impactor. The cut··sizes of the impactor stages

were determined from data supplied by the manufacturer.

Each impactor stage had four rectanqular slots in a spoke­

like arrangement centered on the axis of the impactor.

c

> -- --- -- -- --or

. . •

., > > Il :::r

. .. CASCADE II1PACTOR

MAIN STREAM

METER

ŒSJ---RECORDER

FLOW TRANSDUCER SAMPLE

r-----:::>~ ST REA M

PUMP

Figure 2-6a The particulate sarnpling train.

o

.c.> 1~{

"

,"," ,

, , "\

"

" '\.

c

39

o o

pol.~ ----of g=

_---A--~ ..... ..•. .... ....

.. .~

~ "

~ .... , ,

~L.i<J ~··········ï ............. Ë···········] ........ -­............

/)r~~ </ , , , , . , . , ........

position of slot.s on oc' .. ocsnt stoges

Figure 2-6b Orientation of the slots on successive stages of the cascade impactor.

o

o

40

The slots were rotated through 45 degrees cn adjacent stages

leading to a circumferential rather than a radial flow of

gas between stages. This arrangement minimized particle

losses at the cyli~drical walls. The slots on the lst stage

measured 3.6 mm by 13 mm while those on the 7th stage were

4 0.15 mm by 5.8 mm.

Fiberglass was used as the collection substrate on each

plate and for the back-up filter. The substrates supplied

by the manufacturer had slots of one size only measuring

4 mm by 14 mm, which meant that a significant area around

the slots on the smaller stages. This situation was

improved by designing a die and cutting new substrates with

smaller slots (measuring 2 mm by 13 mm) which were used on

stages five to seven.

The flowrate of gas through the impactor was monitored using

a Matheson Series 8110 mass flow transducer which preceded

the sampling pump used to ensure a steady flow of gas

through the sample train.

DATA ACQUISITION AND ANALYSIS

Particle selection criteria

The du st used in most of the previous studies of cyclones at

c

41

high tempe ratures was usually flyash having fairly wide size

distributions, and densities that were not precisely known.

Salcedo (1981) showed that the particle density cou Id vary

between size fractions for powders consisting of several

chemical species. The varied composition and wide size dis­

tribution of flyash. together with inaccuracies in the par-. ticle size determination could lead to difficulties in eval-

uating the fractional collection efficiencies and in com-

pleting fractional mass balances. Furthermore, at very high

temperatures, combustion of some of the flyash particl~s

could occur within the cyclone, leading to more uncertain­

ties in evaluating the cyclone performance.

Considering the above, the following criteria were specified

in choosing the test dusts:

1. They should have relatively high melting points.

2. They should not react with air at temperatures below

2 000 K.

3. Their densities should be weIl defined.

4. They should be readily available.

Several refractory oxides meet these criteria and alumina

(grade C70-FG obtained from ALCAN) and silica (grade AC-8130

obt~ined from Anachemia) were selected for this research.

The powders were sieved and the fraction below 44 pm used in

o

o

this study. The fine particle size was used because the

collection efficiency is known to be close to 100 % above 50

pm and it was more beneficial to study the sizes where the

performance is uncertain. The particle densities were 3.9

and 2.6 for the alumina and silica respectively.

Characterization of the Povders

Analyses were done to determine the particle size distribu­

tion, shape and density using microscopes, an x-ray sedi­

graph and agas pycnometer in addition to the cascade impac­

tor.

An optical microscope (Reichert - Zetopan) and a scanning

electron microscope (model JEOL CX100) were used to observe

the shape and size of samples collected on each stage of the

cascade impactor and from the cyclone inlet and bin. These

observations showed that the alumina particles were mostly

rounded but a few were elongated whereas, the silica par­

ticles were more angular and also had some elongated par­

tic les (Figure 2-7a,b).

In both cases, individual as well as clusters of particles

vere observed. For alumina, the individual particle sizes

ranged from 0.4 to 30 pm while the loosely agglomerated

clusters measured up to 140 pm in diameter. The silica

(

a

(

b

( Figure 2-7

43

alumina

sllica

Photographs ot the test dusts: a) alunina, h) silica.

~ • Q

60 lUI Inlet. 1lJat. No. V.locl tu Lood

ml. glrrfl

40/- c ffi03 16 23 o MilS 21 28

N +M36 27 3

~ "MOI 7 6

• OAA3Q 4 120

~ 00 III Sed 1 grq:.h

~ ~ 20r ! 1 II' 1 \. \\ \\ X \ t .... ~

\0 t- ~

.~--I ",., t'A

\.0 \0.0 60.0 PARTICLE SIZE. f..I1l

, , Figure 2-8 Inlct particlo sizo distributions ot alumina.

~ ~

60 lUl Inlet Ibtt No. Veloolty Lood

mie glnP

40~ OSAOI 28 2 c SItIU 9 3

N

3J~ + SII'IX3 6 9 051004 6 9

• .SItœ 9 9

~ • Sad 1 grq:tl

~ ~ 20~ /' ~d>-r"'." \ 1\ 1 ~

~ ~ ~ \II ... !Il

10

0 '- 1 ft !

0.2 !! [J-I 1.0 10.0 60.0

PffiTIQ.e SIZE. f-ITI

Figura 2-9 Inlet particle size distributions of silica.

,

o

46

agglomerated less than the alumina with clusters up to

around 70 pm and discrete particles between 0.15 and 40 pm

being observed.

The theoretical cut-size for each impactor stage fell within

the range of particle sizes observed by the microscope for

both alumina and silica. The SEM observations also con­

firmed that there was an overlap of particle sizes on adja­

cent stages, but the average particle size decreased pro­

gressively from the top to the bottom of the impactor.

A Micromeritics Sedigraph 5000D-Particle Size Analyzer was

used as another way of measuring the particle size distribu­

tion. with this technique, the powdered sample was dis­

persed in a liquid and the ra~e of settling was detected by

an X-ray beam. Stokes' law was assumed and the rate of set­

tling was related to the particle size and density, and the

liquid density and viscosity. The output of the instrument

was a plot of the cumulative percent undersize versus the

Stokes equivalent spherical diameter.

Figures 2-8 and 2-9 show comparisons of size distributions

obtained with the sedigraph comparcd with cascade impactor

distributions for alumina and silica. The distributions

obtained with the sedigraph are shown for comparison but

were not used since the cyclone sees the aerodynamic diame-

c

ter as measured by the impactor, rathar than the diameter

of particles settling in a liquid as rneasured by the sedi­

graph. The distribution measured by the sedigraph also

depended on the degree of dispersion or flocculation of the

particles in the test liquid.

The inlet size distribution measured by the cascade impactor

depended on the inlet velocity and on the dust load. Theor­

etically, at high velocities and low or intermediate dust

loads, the incoming particles are weIl dispersed so the

measured size distribution is closest to the true distribu­

tion (Figure 2-10a). At low velocities and low or interme­

diate dust loads, the largest particles settle in the inlet

channel so the size distribution ente ring the cyclone is

finer than the original distribution (Figure 2-10b). At

very high dust loads, agglomeration of the particles results

in a coarse size distribution (Figure 2-10c).

These trends were experimentally ob~erved and the inlet dis­

tributions measured under various operating conditions are

shown in Figures 2-8 and 2-9. The ~lumina and silica were

bimodally distributed. The major peak for alumina occurred

at around 4 to 5 #m with the minor peak occurring at around

25 #m. For silica, the trend was reverse~ with the major

peak occurring around 25 #m and the minor peak or sadd le

point around 4 to 5 #m.

48

• • • • • • • HIg, Velocltl:l • • • (0) • • • • • • Law 01'" Mad 1 un Lccd • •

• • • • •

•

Law Veloeltl:l

Law 01'" HIg, Loo:f • (b) •

~.... . ...... .. ~ .

, . ... .; .. • • • • •• ••••••••• • . • e. .' ... " . . ' .. •• • • • : . . . .. . . . .

HIg, Locd

Medlun 01'" HIg, Veloel tl:l

•

Figure 2-10 Effect of inlet velocity and dust load on dispersion and measured size distribution.

c

49

The inlet 50 % cut-sizes varied from 2.5 to 5.1 ~m for alu­

mina a~d 4.5 to 10.~ ~~ with silica while the dp16/dp84

ratio varied from 0.11 to 0.19 for alumina and 0.12 to 0.18

for si1ica. dp16 and dp84 are the particle sizes be10w

which 16 % and 84 % of the particles lie. For a log-normal

size dis~ributiont the standard deviation is given by ~ither

dp84/dp50 or dp50/dp16t so dp16/dp84 is equiva1ent to the

inverse of the variance and is a measure of the width of the

distribution.

OPERATïNG PROCErryREB

The following procedure was followed for a typical r:n:

l ._ 1mpactor substrates were weighed an~ the impactor

installed in the sample line.

2. The particle feeder WQS loaded with a • 'own ~ass of

powder.

3. The plasMa generator was warmeu up and the torch ignited

with argon.

4. The plasma gas was switched ta air after around two to

50

five minutas of stable operation with argon.

5. The system is allowed to heat up for between five and 30

minutes depending on the test beirag done.

6. The sample pump was turned on and the sample flow

adjusted to the predetermined isokinetic flowrate.

7. ~bout one minute later, the parti~le feeder was

turned on at the pres et voltage and the feed was main­

tained for the d~sired time (usually 3 minutes).

8. The feeder was switched off, the sample pump turned ~ff,

th.. pl'!.sma generator turned off and the gas flow

stopped, all within five seconds.

9. The mass of powder left in the feeder at tha end of the

run was measured and subtractea from the initial '!.mount

to determine the amount of powder fed.

10. Tite impactor substr,ates were re-weighed to determine the

m~ss collected on each stage.

11. The cyclone was allowed to cool bcfore the inlet

section, the roof and the bin were opened and the dust

deposited in tt-"! inlet chan .. «l, on the walls of the

c

51

cyclone and in the coll~ction bin were collected

separately.

The mass of powder ~ntering the cyclone (HF) was taken as

the difference betwaen the powder fed by the feeder and that

deposited in ~he inlet. The powder collected (HC) was taken

as the S~4 of the powder deposited ~n the walls ~ç the cyc­

lone and that collected in the bill. The inlet size distri­

but.ùn (xif) wa~ Qeasured with the cascade impactor on the

inlet for some initial rvn~ and then th~ impactor was used

on the outlet for subsequent runs to mcasure the outl~t dis­

tribution (xio)' The operating conditions were matched in

choosing the appropriate inlet size distribution for mass

balance calculations. The mass balanc,'s were completed over

the length of time for which powder was fed:

Ovarall mdSS balance:

(7.-1)

Fractional mass ~alance:

(2-2)

The two unknowns - the out~et mass (Ho) and the collected

dust size distribution (xie) - were determined from these

o 52

equations and the ~verall and fractional collection effi­

ciencies given by Mc/MF and (McXif)/(MFxif) respectively.

SU!lHARY

A 10.2 CD i.d. cyclone with four out let configurations w~s

used in this study. The high temperatures were attained

using an induction plasma sYf".tem ol'?rating with air. Inlet

and outlet diagnostic sections enabled the measuremLnts of

temperature pressures and gas and particle flowrates. Mass

balances yielded overall and fractional collection effi­

ciencies and the pressures measurements yielded the cyclone

pressure drop.

CHAP'l'ER 3

GAS AND PARTICLE FLOW PATTERNS

CllAPTBR 3

GAS ~ PAR'l'ICLB PLOW PATTBRNS

LI'l'BRA'l'URB RBVlmf

Some earlier experimental studies of flow patterns and col­

lection performance in cyclones were reported by prockat

(1930), Whiton (1932), Rosin et al. (1932), van Tongeren

(1935), Shepherd and Lapple (1939, 1940), Alexander (1949),

ter Linden (1949), Iinoya (1954) and Smith (1962). These

and other works have been reviewed by Stern et al. (1955),

Jackson (1963), Caplan (1977) and more recently by Saxena et

al. (1982), ogawa (1984) and Leith (1984).

Cyclones operate by converting the inertia of the incoming

stream to centrifugal forces in a confined vortex, causing

the parti cl es to move towards the wall and be separated from

the gas. The gas flow pat~ern has been described by van

Tongeren (1935) as a combination of double-eddy and a dou­

ble-spiral flow patterns as shown in Figure 3-1. The upper

eddy is formed in the annulus between the cyclone wall and

the exit 1uct, with a weak up~ard flow along the outer wall.

The dOUble-spiral p~ttern refers to the downward spiralling

flow around the walls of the cyclone and the upward flow in

the core below the gas exit duct.

c

(

c

54

According to van Tongeren, dust accumulates under the rooi

of t~e cyclone and is supported by the upward force of the

upper eddy current. Eventually, the weight of the dust is

sufficient to overcome the effect of the cddy current so it

falls suddenly and some of it escapes tbrough the gas out­

let. If the particles are sticky (for example hot flyash)

the accumulation on the r~of can form a sol id blcck which

does not fall readily and may haoper the operation of the

cyclone. Some cyclones (such as the one shown in Figure

3-1) are modified to take advantage of the upper eddy by

having a dust bypass which skims the dust from tha top of

the cyclone and re-injects it just above the dust outlet.

The gas ente ring the annular region at the top of the cyc­

lone is s~~cezed by the gas already in the cyclone, to about

half of the inlet width (Theodore & Buonicore, 1976). Inlet

vanes, helical and Involute inlets have been used in

atte~pts to reduce the effects of this Interference between

the two gas streams. Inlet vanes tend to decrease the col­

lection efficiency since they retard the formation of a vor­

tex in the annulus.

Theodore and Buonicore (1976) also pointed out that the con­

ical portion of the cyclone is not necessary to reverse the

dIrection of the vortex although it reduces the length of

cyclone needed to do so. The cone brings tho pa~icles to a

o

û

o

lower

55

Inner ~'\J...i?~--- sp 1 ra 1

eddy outer

IU'!}\,~"+---------it-

spI raI

Figure 3-1 The van Tongeren (1935) cyclone vith dust bypass.

(

(

56

central point making them easier to handle and dispose.

Care should be taken not to make the cone too small; other­

wise the vortex core will contact the wall and re-entrain

the collected dust.

Ter Linden (1949) measured static pressures and three compo­

nents of gas velocities inside a cyclone with a helical

inlet. Figure 3-2 shows that the tangential velocity is the

main component except at the core where the upward axial

velocity is predominant. The tangential velocity increased

from the wall to the center, reaching a maximum at about

65 % of the distance from the wall to the axis, then

decreased quickly as the axis was approached. The tangen­

tial velocity in the outer part of the cyclone up to the

maxima was given as a function of the velocity at the wall

(Vtw) and a vortex exponent (n):

(3-1)

with n = 0.52. According to ter Linden, the wall velocity

does not deviate much from the velocity of the gas in the

inlet duct.

The r~dial velocity measured by ter Linden was relatively

small and directed inward from the wall to around the radius

o

J 1

/

VIridoo olT..,...wVcIoàq Y,IDoI_ Vcb=7 Y ... ~_Io.C"-

---T.....,.w-,.. ------~.._,..

57

T!aL.~ , ,UTC~ .. a 1

tnQl"Jf'r ... ,."",&IS Id ac.t 1

ri i

j -n,:!:\~I7"""'~l~~7t"::""';d lI'.t.rc "fUUI.I •• • _,.,.cw,.,,· ",ocm •

.. , "'lUS"' SICI .~~~~~~~~~~

.\ 1

\ /W\ / ~"1 \ 1 \ 1 \ 1 ''r-I--l-'Ir-i

Figure 3-2 The velocity profiles of ter Linden (1949).

c

58

of the exit duct, and directed outwards from the axis to

around the gas exit duct radius. The axial velocity pro­

files revealed the reversal of flow in the cyclone, with the

axial flow being downward close to the wall and upward in

the core.

Alexander (1949) measured static pressures and ve10cities in

cyclones of 3.2 to 120 cm in diameter. He observed that if

the cyclone was sufficient1y long, the vortex did not run

the full length and was completely reversed at a distance

below the gas exit duct that he termed the "natural length".

This length depended on the cyclone geometry but not on the

gas velocity and was given by the empirical expression:

[d 2] 1/3

Ln = 2.3 de A~ (3-2)

Alexander also derived expressions f~r the ratio of the tan­

gential velocity at the wall to the mean inlet velocity, and

for the vortex exponent as fun ct ions of cyclone diameter and

temperature:

(3-3)

n = (3-4)

fi

59

(3-5)

with dc in centimeters.

Abrahamson et al. (1978) discussed in some detail, the

effects of particle bouncinq on the walls, aqqlomeration,

dust pick-up from the collection bin, and saltation from the

walls and bin. (Saltation is the entrainment of particles

from the surface of a layer of p~rticles into a qas stream).

He measured velocity and static pressure distributions in

du st collection bins of various sizes attached to a 30 cm

diameter cyclone at room temperature. He found thdt the

vortex in the cyclone persists in the bin and that there is

a considerable exchanqe of qas between the cyclone and the

bin. Abrahamson also found that the collection efficiency

varied' inversely with the level of dust in the bin and

directly with the inlet dust concentration. No mathematical

modellinq was presented in his study.

Meissner and Loffler (1978) developed an empirical model to

describe the tanqential velocity profile in the cyclone bar­

rel at room temperature. The velocity at the wall is higher

than the me an inlet velocity due to the vena contracta in

the entry reqion. He found that for friction-free flow, the

c

60

wall velocity (Vtw*) was related to the me an inlet velocity

(vi) by the expression:

= - --- + 0.889 [-0.204 bc ]-1

(3-6)

This equation predicts that the tangential velocity at the

wall would be 1.27 times the mean inlet velocity for the

cyclone used in the present study, with both the 2.54 and

5.08 diameter gas outlets. A wall friction coefficient (ee)

was used to account for the friction at the walls, and the

wall velocity (Vtw) was determined to be:

Vtw 1 [[ -- = ----* 0.25 vb eehz

where:

h * z

~ h *Vt *] O. 5 ] + ~e z w _ 0.5 Vb

(3-7)

(3-8)

with Vb being the gas velocity in the cyclone barrel, hc

the height of the inlet and hz the height of the cylindrical

portion of the cyclone barrel.

Meissner and Loffler did a differential angular momentum

balance to calculate the radial variation of tangential

o

61

velocity as:

Vtw r [ [rJ] - = - 1 + D 1-Vt rc r

(3-9)

where:

+ h] sin ~c

(3-10)

D is a parameter accounting for the exchange of angular

momentum between the wall and the gas and ~c is the angle

the cone makes with the cylindrical portion of the cyclone.

The wall friction coefficients of the body (ee)' the top of

the cyclone (eD) and the conica! section (eK) were measured

and found to lie between 0.0065 and 0.0075 for cyclones with

smocth walls at room temperature.

The radial velocity in the outer part of the cyclone was

determined by assuming that the gas flowed uniformly into

the core region through an imaginary cylinder formed by the

axial extension of the gas outlet duct. The radial velocity

was then given by:

(3-11)

(

c

c

62

the conclusion that stso varied inversely with dust lQad.

Pursuing the same argument and using an anëlysis s;milar to

Wheeldon et al., it was calculated that the cyclone used in

this study would have sts l varying between 1.0 x 10-4 and

2.2 x 10-4 depending .~~ the gas outlet configuration. In

comparison. the measured stso varied between 4.0 x 10-4 and

3.6 x 10-1 , and ~here was no corrblation between stso and

the dust load. It was concluded that a single stso for ea.,

cyclone configuration did not adequately charac~erize the

performance of thb cyclone in tàis study.

Parker et al. (198\) showed that their data could r corre­

lal~d by plotting the p:od~ct of the Reynolds number (Re)

anà the s~uare root of the inlet Stokes number (~tin)

a;ainst the experimen~ally dete~dined SO % cut-size on log­

log coordin

'63

Particlo Deposition Patter"s

A ribbon-like pattern was som&times formed by t~· pùrticles

on the ~alls of the cyclone depending on the inlet flowrate

and dust concentration. The width of the ribbon in the

axial direction was equal. to the height of the inlHt at the

entrance to the cyclor.e. and increased te. about twice that

height after about cn~ ro',tion (Figure 3-3a). These pat-

t!.l:ns indicated that: the -:jas made between three and six

rotations in moving down the cyclone.

Relatively co~centrated depo~its of particles usually accum­

ulated in the corners formed by the intersection of the roof

an~ the r.ycJone barrel, and by the roof and the gas outlet

duct. These deposits are evidence of the ?èdv formed in the

upper sectior. of the cyclone as first described by van Ton­

geren (1935). ·rlJ.e occurrence of these eddies was further

confirmed by the pres~nce of streaks in the deposited layer

close te. the roof. These streaks were djrected upwards at

angles of around 20 to 30 degrees t~ the horizontal on the

wall of the cyclone barrel.

The deposition patterns also indicat~d that ~~e flow in the

annu~.l!s bE'tween the cyclone wall and the gas outl~t duct was

highly turbulent especially in the region where the incoming

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a

b

Figure 3-3

64

particle deposition patt3rns on the ~alls of the cyclone.

c

65

flow met the flow already in the cyclone (Figure 3.3b).

~his behavi~u~ was most noticeable for runs with low or

in~ermediate du st loads (less than 10 g/m3); then it was

clear that the deposits on both the barrel and the outer

wall of the gas outlet duct were thicker than on the sur­

T.vunding walls, and the deposition pattern r.ad a rough

appearance.

There was a tendency for the deposits on the cyclone barrel

to start aDout one to five centimeters further downstream of

the entrance at high temperatures than at lower tempera­

tures. This occurrence could not be zttributed entirely to

the temperature due to the relationship between the volumet­

rie flowrate, inlet velocity, dust loading and temperature.

It is however consistent in that it shows that the particles

reach the ~all at a later time, leading tu lower collection

efficiencies.

Deposits on the inner wall of the gas exit tube started at

around 0.5 to l cm above the lower edge, and exten~ed

upwards. A pattel~ of streaks was observed, upwardly

inclined at more than 45 degraes to the horizont~l for most

runs. This pattern is consist6nt with the notion that the

inner vortex has a higher axial co~ponent than the outer

vortex. It is also consistent with the theory that par­

ticles are separated fro~ the upward inner vortex as weIl as

o

66

from the downward outer vorte~. Models such as the Dietz

(1981) and Mothes and Laffler (1984, 1988) models take this

into account, whereas models such as the Rosin et al. (1932)

model assume that separation occurs only as the gas moves

downward.

The absence of particles within 0.5 to 1 cm of the lower

edge on the inside of the gas outlet duct, can be attributed

to the small inward flow of gas being entrained beneath the

lip of the duct from the eddy current in the upper part of

the cyclone. This stream of gas tend~ to contain only the

fine st particles, and !orms a layer of gas of lON dust con­

centration at the bottom of the gas exit. This layer

extends for up to 1 ~ into the gas outlet before the gas is

fully mixed with the inner vortex leaving the cyclone.

Particle deposition patterns indicated that the vortex usu­

ally ran the full length of the cyclone and that there was a

region of high swirl at the base of the cone when the larger

(5.08 cm ) diameter outlet was used. This ter.dency was best

illustrated by the presence of deep grooves in the dust

deposited at the bottom of the cone, for runs in which high

dust loads were used.

Alexancler's (1949) empirical equation predicted that the

natural length would be 12 cm for the 2.54 cm diameter out-

67

let and 23 cm for the 5.08 cm diameter outlet for the cyc­

lone used in this study. Alexander also stated that the

vortex in cyclones that were slightly longer ~han thr calcu­

lated natural lenqth, is likely to run the full length of

the cyclone. This appeared to be the case with the 5.08 cm

diameter outlet. The actual length of the cyclone below the

gas out let duct was either 1.3 or 1.5 times the calculated

natural length with the 5.08 cm diameter outlet. This com­

pares with ratios ~i 2.5 and 2.8 for the 2.54 cm diameter

outlet.

PRESSURE 2UlD VELOCITY HEASOREHBNTS

The Pressure Probe

A three-dilUp.nsional 5--channel pressure probe (shown in Fig­

ure 3-4) was us cd tIJ maasut'e ve~.ocity and static pressure

profiles in the cyclone. T.he prcbe waz manufactur,d by

United Sensors and Control corporation (~odel No.

DA-250-48-H-44-Cd) and was previously used anù d~scribed in

detail by Bank (197~) and Reydon (1978).

The probe was ~ounted on a stand which allowcd it t~ bB

rotate:i through 360 degrees aro:.md its major axis aud to be

moved known distances along the same axis. 'fhe probe was

68

6.4 mm in diameter and had five taps of 0.8 ~ inside diame­

ter arranged on flat wedges that were eut into the cyl indri­

cal surface of the probe about 13 mm from the tip. This

arrangement allowed the measurement of total and static

pressures at a point, and hence the calculation of the total

velocity and its co~ponents.

Referring to Figure 3-4, hole Pl was centrally located and

permitted the calculation of the total velocity (dynamic)

pressure. Taps P2 and P3 were on planes ± 45 degrees to the

plane of Pl and all~wed the measurement of the yaw angle

pressures and the stream static pressure. Taps P4 and P5

were in the same plane as Pl and wera used to determine the

pitch angle pressures. The differential pressures were

measured by an MKS Baratron electronic pressure transducer

and a Magnehelic mechanical gage (described in Chapter 2).

Velocity-static pressure measurements were made by first

aligning the probe with tap Pl in a horizontal plane and

facing the flow. In this position, the angle to the hori­

zontal was zero and the pressure (P3-P2) was measured. The

probe was then rotated until (P3-P2) was zero (that is P3 =

P2) and the angle through ~hich the probe was rotated was

measured as the angle the flow ~ade with the horizontal

plane (.1». At this fixed angle (4)), the pressures

(PI-Patm)' (P2-Patm), (Pl-P2) and (P~-P5) were measured.

69

. , . '. " . ,. :,.1' ..

• f' •

4

Figure 3-4 The 5-channel pressure probe (Reydon, 1978).

o

70

The velocity pressure (PT-PS)' the direction of the velocity

vector relative to the probe (e), and the static pressure

relative to atmospheric pressure were calculated from the

following equations (Reydon, 1978):

(3-13)

K(e) (3-14)

F(e) (3-15)

(3-16)

The magnitude of the total velocity and its three components

were given by the following equations, using the coordinate

system shown in Figure 3-5c:

(3-17)

Vt = V sin(e) (tangential) (3-18)

Vz = V sin(~) cos(e) (axial) (3-19)

vr = V cos(~) cos(e) (radial) (3-20)

71

(b)

lae •• o

Vz

1)-------

c Figur~ 3-5 Pressure probe location and coordinate system.

o

o

72

In the above equations, C, K, and F are calibration factors

for the probe that were supplied by the manufacturer, and Cp

is a standard pressure probe coefficient that is approxi­

mately 1.

The Pressure Probe Location

The location of the pressure probe in the cyclone is shown

in Figure 3-5a,b. The probe was inserted radially through a

port in the wall of the cyclone, 13 cm from the roof and

perpendicular to the axis of the inlet channel. Four gas

outlet duct configurations, (Cl to C4 in Figure 2-2), were

used. The cross-sectional area of the probe projecting into

the cyclone varied from 0.8 to 3.25 cm2 , depending on its

radial position. This probe area corresponded to around 1

to 4 % of the cyclone cross-sectional area when viewed from

above.

Since gas velocity distributions have been measured in

detail by other researchers (Shepherd & Lapple, 1939; ter

Linden, 1949; Alexander, 1949; Iinoya, 1954; Ogawa, 1984),

the measurements made in the present research were done

mainly to verify that some of the standard assumptions about

the flow pattern were applicable to the cyclone used in this

research.

c

c

73

Room Temperature Experiments

Profiles Obtained with Large Diameter Gas Outlet

Velocity profiles were measured at room temperature using

the four outlet configurations (Figure 2-2) and mean inlet

velocities between 2.75 and 15.2 mis. The measured veloci­

ties were normalized by dividing by the calculated mean

inlet velocities. The radial position (r) was normalized by

dividing by the cyclone radius (rc).

Figure 3-6 shows the variation of the total velocity (V)

across the radius of the cyclone with the outlet configura­

tion Cl (5.08 cm diameter, 10.8 cm long). The mean inlet

velocities for the three profiles shown were 2.75, 7.75 and

15.2 mis. The legend in this figure also shows the inlet

flowrate in standard litres per minute (slpm). The total

velocities increased from the wall towards the center,

peaked at around 0.35 of the cyclone radius, and then

decreased towards the axis of the cyclone. Furthermore, the

velocity ratios varied directly with inlet velocity at each

radial position so that the profiles were parallel to each

other across most of the cyclone.

@

2.8

2.61-

2.41-

2.21-

>- 2.0 l-I-U 1.81-0 ~ 1.61-

1- 1.41-t~~

2 1.21-...... ~ 1.0

5 0.81-1-

0.61-

0.4L 0.2

0.0 0.1

Outlet IÀCt

-_.0... ..... -- ......... IJ-" .... 0 .... ....

Ynlet Flowrate slpm mis

o t 177 16.20 A BOO 7.76 o 213 2.76

••••••••• A ..... "'"-A···· ....... - 0 ." .... ...- - --.. "" ." ". '-1----__

0 . ~

•••••• • .. A. •.•••••••• 0" • •• /.1 .••••.•.•••..• ll. ~o O~~ ........ A

1

O 'l .t:.

1 1 1 1 1 1

0.3 0.4 0.6 0.6 0.7 0.8 RADIAL POSITION. r/R

-0

--'-

0.9

Figure 3-6 Total velocity profiles vs inlet flowrate for cyclone Cl.

9

1.0

~

" "

75

The maxima in the velocity profiles usually occurred at

radial positions that were less than the gas outlet radius.

These maxima indic?~~ a transition from a strongly spiral-

1ing region to a core region with little rotational motion.

The radius of the core region was about 0.7 of the outlet

tube radius, which is within the range of 0.5 to 1.0 as

stated by many researchers (for example sta~ .~and, 1951,

Leith & Licht, 1972: Deitz, 1981).

Figure 3-7 shows the tangential velocity profiles corre­

sponding to the total velocity profiles of Figure 3-6. The

shapes of these profiles and their magnitude are very simi­

lar to the total velocity profiles especially in the outer

part of the cyclone. This indicates that the tangential

component was dominant across most of the cyclone except in

the innermost region around the axis.

Figure 3-8 shows the radial velocity profiles for the runs

discussed above. This figure shows that the radial velocity

was relatively low and directed inwards from the wall

towards the center in the outer part of the cyclone. On the

other hand, the radial velocity was directed outwards from

the axis to around 0.35 of the cyclone radius, coinciding

with the maxima in the total and tangcntial velocity pro­

files. The radial component iF sometimes neglected or is

assumed to be constant along the length of the cyclone.

~

2.8

2.61-

2.41->-1- 2.21-..... u Cl 2.01-...J W :> 1.81-1-w 1.61--1 Z :::: 1.41-...J a: 1.21-..... 1-Z 1.01-w (!)

~ 0.81-1-

0.61-

0.41-

0.2 0.0

_.

Out/et tu::t

,.-,.-1:1- .. C""~ .............

"0

A •• ••••• .. ·····A.... .. ......

Inlet Flowrate alpm mla

01177 16.20 A 600 7.76 o 213 2.76

U e. .... .... .... ... .. . _ .. c.. •• ' '" . A .' 0'" 'oU."-

Y,,' .......... ---C-

.' "·A-; ....... --• .. ... A. "'0 " .. O

..... ' . ...... A

o

_. _L -'- -'-

0.1 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.9 1.0 RADIAL POSITION. r/R

Figure 3-7 Tangential velocity profiles vs flowrate for cyclone Cl.

~

àI

@

t .el 1 1.4 OuUat [u;t

t .21-

t .ot ~ 0.8 .... g 0.6

lnlat Flowrata slpm mis

c 1177 ÂBOO o 213

16.20 7.75 2.75

rrl 0.4 __ g-----~c-----~ St. ::>: ----. -_·ü tu 0.2 ~g.:;,. "...... ...... " .............. ,u ............ .

-' ~ 0.0 / .... ~ I~"

§ ~~:: /.:,/ a::: .'·u -0 6 .... . 0 .....

-0.8 t ····

-t.O~----~----~----~----~----~~----~----~-----L----~----~

0.0 O. t 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.9 RADIAL POSITION. r/R

Figure 3-8 Radial velocity profiles vs flowrate for cyclone Cl.

t .0

o

::l

c

78

The corresponding axial velocity profiles for the same runs

are shown in Figure 3-9. This figure shows that the three

normalized velocity profiles are indistinguishabJe under the

experimental conditions. The figure clearly shows the down­

ward flow of gas close to the wall and the reversed flow in

the inner part of the cyclone. The interface between the

dowllflow and upflow regions occurred at around 0.6 of the

cyclone radius and did not coincirle with either the gas out­

let radius, or the maxima in the tangential and total velo­

city profiles.

These observations led to conclusions similar to those made

by pervov (1974), that there are three regions in the cyc­

lone when viewed from above (Figure 3-10):

1) a downward spiralling outer region around the wall,

2) an upward strongly rotating inner annular region and

3) an innermost core where the flow is mainly axially

upward with little or no spiralling motion.

The transition between regions 1 and 2, occurred at around

0.6 of the cyclone radius while the transition between

regions 2 and 3 occurred at around 0.35 of the cyclone

radius (or around 0.7 of the gas outlet radius).

e

1.8

1.6t-

1.4 t-

1.2t-

>- 1.0t-t-G 0.8t-e ~ 0.6t-

I:ü 0.4 t-

Outlet tblt

~~ ....... .... ...... 6: .. ..........

Inlet Flowrate alpin mis

CII77 16.20 .t::. eoo 7.76 o 213 2.76

2 0.2" I-t

~ 0.0 I-t ~ -0.2t-

..,,;.: ••••• "!- ...... r.1

·····.'Ii·............ ....,.. ______________ ~ 1

o~~&', .. ~ .. "':-0:.",

'~""6-., < ""0 - ..... Li

-0.4t-

-0.6t -0.8~---~---~---~---~---~---~--~------~---~~

0.0 O. t 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.9 t .0 RAOIFL POSITION. r/R

Figure 3-9 Axial velocitl' profiles vs flowrate for cyclone Cl.

o

" ID

c

c

boundorld between downflow end upflow

80

,----.... .. .. .. "," .. , " , ,

1 \ 1 \

1 \ 1 \

1 1 1 1 \ 1 \ 1 \ 1 \ 1

gos outl et duct

core raglon

Figure 3-10 Diagram showing the flow zones in the cyclone.

81

Profiles obtained vith Small Diameter Gas Outlet

Figure 3-11 shows tangential velocity profiles obtained with

gas o4tlet configuration C2 (2.54 cm diameter and 10.8 cm

long). There was a distinc~ change in the slopes of the

curves half way between the axis and the wall, and maxima at

around 0.25 of the cyclone radius. The location of the max­

ima in this case coincided with the outlet tube radius,

(compared to 0.5 to 0.75 outlet diameters with the larger

outlet).

The corresponding radial velocity profiles are shown in Fig­

ure 3-12. A relatively constant inward flow in the outer

part of the cyclone anà flow in the opposite direction

within the core was again observed. The transition was

around 0.25 of the cyclone radius, coinciding with the

radius of the gas outlet duct and the maxima in the tangen­

tial velocity profiles.

The axial velocity profiles for cyclone C2 are shown in Fig­

ure 3-13. The transition from the downflow to the upflow

regions occurred halfway between the axis and the wall. This

coincided with the location of the change in elope of the

tangential velocity profiles. This figure also shows that

the axial velocity increased sharply within the core and

~

2.8

2.6

2.4

(latlat Il.ct

.0- ..... , , , , "

Inlat Flowrata slpm mis

~ 2.2 ' '0 ' , 'A....... , l ,'_ •••.•• ,

Clin A BOO o 213

16.20 7.76 ....

g 2.0 l ,,' -"A, ' " " , ~ ~ ,

l " •••• ,

2.75 ...J w ::-t-w ...J :z .... ....... ...J a:: .... t-:z w Cl)

:z a: t-

1.8

1.6

1.4

1.2

' ,,' " '0 R ~ , . '. .. .... .... ..... ....... 0

"À ...... " ........ 0-......... ........... A '0.-,.

./ 0............... ~ ............. A .......... /:1

/' "0 - ~· .. · ......... A o

1.0 o

0.2'~---L---L---L--~--~--~--~--....I---....I-~

0.0 O. t 0.2 0.3 0.4 0.5 0.6 0.7 0.8 o.g t .0 RADIAL POSITION. r/R

Figure 3-11 Tangantial velocity profiles vs flowrate cyclone C2.

~

CI

""

o

1.6

1.4

1.2

1.0

?: 0.8 1-4 g 0.6

~ 0.4

~ 0.2 1-4 0.0

~ -0.2 1-4

n..sUat n..sct lnlet Flowrata .Ipm mla

Clin 15.20 A 600 7.75

,O-~......... 0 ZI3 Z.75 I/!i.·····... .....0 '.: ...... -...........

L- Â.... -0------0 ( •••••••• /1 ------,R:: . ............. ----.1':1 1 ~ • A······........ . ............ ~ 1 0 3

:"1

/' :, , , , , , ~ -0.4

-0.6 Â: , , -0.8

, , 1

-1.0 0.0 0.1

--'-

0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.9 1.0 RADIAL POSITION. rlR

Figure 3-12 Radial velocity profiles vs flowrate for cyclone C2.

o

CD

'"

~

1.81 U 1 \

1.6 ~ \ 1 ~llel D.x:l A \

1.4 ~ '. \ '. \ ·e. \ 1.2 t- ... \ '. \ e.. \

>- 1.01-l­

0.8t

O -'. \

~\ .. 'q

'"4 ' I-! . , -', ,

Q '.' - -'. , -'. , '.' 'f, ~

U

~ 0.6

Inlel Flowrate slpm mis -

U 1177 16.20 A eoo 7.76 o 213 2.76

fij 0.41-

2 0.21-

&,':., ~~ ,

o~~ I-!

~ 0.0 a: ~ -0.21-a:

"~Q~ , ...... . u .. ..

.... 0 .. ~~:.:.· ..... -A ~::r -,

-0.8 ' ---J 0.0 0.1 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.9 1.0

RADIA- POSITION. rlR

Figure 3-13 Axial velocity profiles vs flowrate for cyclone C2.

~

0>

"'"

o

o

85

became stronger with increased flowrate.

Profiles for Bmall vs Large Diameter Gas Outlet

Figure 3-14 shows a comparison of tangential velocity pro­

files for the four gas outlet configurations (Cl ~o C4) at

a me an inlet velocity of 7.75 m/s. These plots show that

the profiles were similar for the same outlet diameter, and

that the length of the outlet did not greatly affect the

profiles. Furthermore, the velocities were similar in the

outer half of the cyclone but were noticeably higher with

the smaller diameter gas outlet in the inner regions.

The radial velocity profiles in Figure 3-15 show the almost

constant inward drift of gas from the wall towards the cen­

ter, and the flow in the opposite direction in the central

region. The radial velocity was high~= for the small outlet

diameter configurations since the same flow had to enter the

core at a smaller radius. This is consistent with the

hypothesis that the gas passes into the core through an

imaginary cylinder of radius ri' and the radial velocity is

given as [vr = Q/2~rilj.

Figure 3-15 also shows the tendency for the change in direc­

tion of ~he radial velocity to be closer to the ~xis with

~

2.8

2.6 Gas Outlat D..ct Dlcmatar Length

2.4

2.2 >-:: 2.0 u Cl 1.8 ...J w > 1.6 1-w 1.4 ...J z ..... 1.2 " ...J a: 1.0 ..... 1-

ffi 0.8 (!) z: a: 0.6 1-

0.4

0.2 0.0 0.1

.. 0-- ......... , --- ~ ...

dalDo sIDo

""/-----. .....::2" ,,~ '~.

OCI CC2 lIE Cl .C4

0.6 0.26 0.6 0.26 cI'. ,,~

• cr.:;::::::.~.. ······~Iil .... -:.~n__ • .... ............. -..-;:-.- --1.0 1.0 0.7 0.7

... III

... . ........ ._-.".... . -~--~

~ll lIE

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.0 RADIAL POSITION. r/R

Figure 3-14 Tangential velocity profiles vs gas outlct configuration for an inlet velocity of 8 rn/s.

1.0

~

ex> ."

e

1.6

1.41-

1.21-

1.01-

0.81- c-~ .. , .. , .... ''-'"'''' c .. ~~

Gas Oull B l Il..cl DlanelQr Length

OCI CC2 lIEC3 -C4

CdelDe) (aIDe)

0.6 1.0 0.26 1.0 0.6 0.7 0.26 0.7

~ 0.61-.... 1 1 • ...- ... 0-___ LI , . '. ___ ·----....;.;.==.::.=...::.::.ac -..0

;/ "" •••••••••••• • •••••••••••• ·lIE·· •••••••••••. >IL ............ li: g 0.41--' ~ 0.21-

, . .... .. ___ -.()----o---..("'":;.--- v :/ ... ····0 , ..

t- 0 0 ... w • , -' , z 02 ' . ...... - . , . .. .... ,/:Il ~ -0.4 Î ......... c/ c ciIL ..... .,/' ~ -0.6 ~I;/

-0.8 -' -1.0~'--~~--~--~--~~--~--~----L---~--~--~

0.0 0.1 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.0 t .0 RADIAL POSITION. r/R

Figure 3-15 Radial ve10city profiles vs gas outlet configuration for an inlet velocity of 8 rn/s.

o

0> ...

c

88

the short cutlets (C3, C4) than with the long outlets (Cl,

C2). The reason for t.his is that the core was shaped like

an inverted cone with the base being the bottom of the gas

outlet duct. Since the probe location was fixed axially,

the short outlet corresponded to a longer distance below the

gas exit duct, and the observed core diameter was therefore

smaller.

The axial profiles shown in Figure 3-16 ~erc ~imilar in the

outer part of the cyclone with the transition between upf!ow

and downflow occurring at around 0.6 of the cyclone radius.

On the other hand, ti~e axial velocity in the inner region

was higher with the smaller diameter outlet than with the

larger outlet since the same amount of gas had to flow

through the smaller diameter channel.

High Temperature Runs

Measurements with the pressure probe at high ~emperatures

were limited because parts of the probe were bonded with

silver solder. This meant that the probe could not be used

at very high temperatures for the length of time needed to

make extensive measurements. In order to take the non­

isothermal conditions into account, the average temperature

between the inlet and outlet to the cyclone was used to

e

1.8

1.6

1.4

1.2

1.0

>- 0.8 1-

t; 0.6 0 m 0.4'· > 1- 0.2 w ...J :z 0.0 .... "-...J -0.2 a: .... ~ -0.4

-0.6

-0.8 0.0 0.1

Gas eut 1 at I:lJot Dlcmatar Length

deIDc aIDe

OCI OC2 lIEC3 .C4

0.6 0.26 0.6 2.6

-~~ ..... . ........... , "~·············lIE

0.. ";::':"""':::---"::0

~""::~

1.0 1.0 0.7

7

0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.9 1.0 RADIAL POSITION. r/R

Figure 3-16 \~ial velocity profiles vs gas outlet configuration for an inlet velocity of 8 rn/s.

o

CI) co

,

c

90

calculat the velocities from the presRure measurements. In

the worse case, the temperature in the outer region would be

close to the ir.let temperature, while the temperaturc in the

inner region would be close to the outlet temperature.

Figure 3-17 shows tangential velocity profiles obtained with

outlet configuration C3 (5.08 cm diameter, 7.0 cm long) for

flowrate~ of 0.6 and 1.18 standard m3jmin at room and ele­

vated temperatures. These plots show that the profiles were

similar except for the high temperature 0.6 stal1ard m3jmin

run, which was lower than the others except close to the

axis. A probable explanation for the low profile ls that

this run had the highest temperature of the four shown

(1 300 K); thus the gas viscosity was highest and

consequently, the transference of rotational velocity was

least.

The radial velocity profiles (Figure 3-18) were similar in

the outer part of the cyclone except for the high tempera­

ture 0.6 standard m3jmin run, which was again much lower

than the others, and indicated that the inward flow of gas

extended much cl oser to the axis than in the other cases.

The axial velocity profiles (Figure 3-19) also show that the

hottest run had lower velocity ratios than the others across

the cyclone.

e

2.8

2.61-

2.41-:0-r- 2.21-.... g 2.01--J w

1.8~ > r-

1.61-w -J :z:

1.41-.... ...... -J a: 1.2 t-.... t-:z: 1.0 t-w CD ~ 0.81-t-

0.6 t-

0.4 t-

0.2 0.0

, 1 ,

C

_.

1

, , ,

•

,

Outl et IlJot GIn VIn TIn C Ipm) Cmls) CK)

c 600 7.16 + 1177 16.20 A 600 33.00 01177 44.00

1 --+ ............ /~---~ .... + /, ... -~ ~

,... --- O::-----~â: _+ /' - ·_~---C ~ 1::., ......... . "

........ 1::.,...... A A ............

....... ~ •...•......•

1 1 _.

1

300 300

1300 000

•

0.1 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.9 1.0 RADIAL POSITION. r/R

Figure 3-17 cornparison of tangential velocity profiles at high and low ternperatures.

o

co -

..

~

1.8

1.61- Out! et CU::t 1 Gin Vin Tin (Ipm) (mis) CK)

1.41- -o BOO 7.76 300 1.21- +l1n 16.20 300

Il BOO 33.00 1300 >-t-

1.01- o lIn 44.00 000 I-f g 0.81-..J g! 0.61-

l:ü 0.41--' :s 0.21-...... ëÈ 0.0 t-4

ê -0.21-0::

-OAt -0.6

-0.8 0.0

_l~ __ ..1. -'- • ..L • ..J. ..J.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.0 1.0 RADIAL POSITION. rlR

Figura 3-18 comparison of radial valocity pr~filas at high and low tcmpcraturas.

~

co N

e

1.8

1.6 l-

1.41-

1.21-

>-1.01-

.... ~ 0.81-e irl 0.61- c.. > 1- 0.41-w ~ 0.21-... :::i 0.0 a: ~ -0.21-a:

-0.41-

Outlet D.J:=t 1 Gin Vin Tin (Ipm) (mla) CK) -C 600 7.76 300

+ lIn 16.20 300 A eoo 33.00 1300 o lIn 44.00 000

-----~---~ Il.............. ~ .. _+~_ .... ~~:-:-_____ _ ............... ~.~

~. ~~ •••••••• I\.

""0 .. -0.6t _0.81.--.1.--.1.---'----'---'---'---1---'---1----1

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 O.g 1.0 RADIAL POSITION. r/R

Figur~ 3-19 comparison of axial volocity prOfiles at high and low temporatures.

o

,~

Comparisons vith predicted Profiles

Tangential velocity profiles in cyclones are usually deter­

mined by assuming an appropriate vortex law model with the

one in equation 3-1 being the most common. This equation

requires the determination of a vortex exponent and the

velocity at a known radial position (usually at the wall).

Alexander's (1949) models for the wall velocity (equa­

tion 3-3) and the vortex exponent (equations 3-4 and 3-5)

are perhaps the most widely used expressions for this pur­

pose. Equations 3-4 and 3-5 predicted vortex exponent val­

ues of 0.5 at room temperature and 0.2 at 1 300 K for the

cyclone used in this study.

There is no fo~al definition of the wall velocity: strictly

speaking, the velocity at the wall is zer , with a sharp

drop occurring within the boundary layer. In the analysis

of flow patterns within cyclones, the wall velocity is not

usually taken as zero, but is taken to be the free stream

velocity just outside the boundary layer. Because of the

difficulty of making measurements close to the wall, the

wall velo city is usually dete~ined by extrapolation of the

measured profile to the wall, ignoring any points that indi­

cate the sharp drop in velocity within the boundary layer.

This method is adequate when the sha~~ drop in velocity is

95-

observed close to the wall, but becomes subjective vhen the

decrease in velocity is graduaI.

The tangential velocity at the wall (Vtw) has been taken to

h'ive va ..... les ranging from around one to several times the

mean inlet velocity. The measurements made in this study

indicated that the velocity close to the wall was usually

between 0.9 and 1.2 times the me an inlet velocity. This

compares with Alexander's model (equation 3-3) which pre­

dicted wall velocities of 1.52 and 1.07 times the inlet

velocity for outlet diameters of 2.54 and 5.08 cm respec­

tively. Muschelknautz's (1972, 1980) presented a plot which

predicts values of 0.95 and 1.25 for the 2.54 and 5.0a cm

dia~eter outl~ts in the cyclone used in this study. Meis­

sner and Loffler's (1978) model (equation 3-6) predicted a

value of 1.27 for both outlet diameters.

Correlation of the Experimental Data

The measurements made in this study showed that the tangen­

tial velocity at the wall depended on the inlet gas velo­

city, temperature and the outlet diameter. This combination

of variables suggests that a Reynolds number might be used

to correlate the wall velocity with the flow conditions and

outlet dimensions. A Reynol~ number (Rea) was defined

c

96

based on the me an inlet velocity (vi), and the hydraulic

diameter of the annulus between the outlet duct and the

wall:

(3-21)

This Reynolds number was correlated with the wall to inlet

vclocity ratio using a power law model. The resulting plot

is shown in Figure 3-20, with the regrcssion coefficient

being 0.95 and the model given by:

(3-22)

Equation 3-1 was used to calculate the local tangential

velocity in the outer part of the cyclone while the velocity

in the core was assumed to be directly proportional to the

radial position. The radius of the core region was taken to

be at 0.75 of the gas outlet radius. Equation 3-22 was used

to calculate the wall velocity and the vortex exponent was

calculated by Alexander's models (equations 3-4 and 3-5).

The resulting curve is shcwn as the solid line labeled "new

model" in Figure 3-21. This figure shows the experimental

data compared with predicted velocities using the 2.54 cm

~ 0

2.0 1

Vtw/Vln - 0.202 Reo. teg

R - 0.95

~ t-i

H ~

a yaY'ê • • 1

~ t-i _0---

~ ------,.

0

1.0 ~ 0>

0.8 ' ' ,

Œ3 IE4 REYtU.DS t-Ut-I3ER

Figuro 3-20 Wnll tnngentinl volocitY/menn inlot velocity vs nnnulus Reynolds number.

tE6

co ....

~

2.8l 2.6; /

2.4 ~ / ,/'. \~ "'Uat [).ct 1

. / \. / / \ ""-1: 2.21-

1.8 / ' • "-tii t . / .... -.. " " -1.6 / /' .... ............... '" "'

Z

' •• ' ". ... • , .. ' ". ... ........

0-4

g 2.01--1 w >

0-4 • ,...... ... .. ........

...... / ' , .. ' ". .. '-... . /

'.' ...... ............ -1 ' • " .. a: ,.iI ..... .... .. - ,. '" - . t- J' , ,.... . ...... -'" -....... Z /

'/ .•••• :-........... ,: .... --.,. ~ w" .... =- ~ CD ~.,~... • ••••••• ::-.11- ' ..

Z 0 / 1: •• ~ ... ",.8 J -, '"--0- ... -..;: ••••

0.6 /il --• Experimentai

O.4t A'l , 0.2 ( - ,

0.0 O. t 0.2

..... Alexa lder C 1949) --- Naw IfOdel - ·-Malaenar & Loffler C 1972) ---Maleener & Loffler Cvtw - vin)

-'- --L --'- , , 0.3 0.4 0.6 0.6 0.7

RADIAL POSITION. r/R

_. 0.8 0.9 t .0

Figure 3-21 comparison ot experimental with predicted tangential velocity profiles: cyclone Cl nt 300 K.

~

10 CI

o

o

99

diameter gas outlet at room temperature and an inlet velo­

city of 7.75 ~/s. The other profiles shown in this figure

are: the original Alexander (1949) model with the wall velo­

city calculated from equation 3-3; the Heissner and Loffler

(1978) model (equation 3-9); and the Heissner and Loffler

model with the wall velocity being equal to the mean inlet

velocity instead of that calculated from equation 3-6.

Figure 3-21 shows that the Alexander model with both the

original and the new wall velocity agreed well with the

experimental data. On the other hand, the Heissner and

Loffler models greatly over-predicted the tangential velo­

cities across the cyclone. The high values calculated by

the Heissner and Loffler model can be explained by cons id­

ering equations 3-9 and 3-10. For the cyclone used in this

study, D was approximately 0.04, so equation 3-9 reduces to:

Vt _rc = (0.96 to 1) Vtw r

(3-23)

Comparing this equation with equation 3-1, the vortex

exponent in the Heissner and Loffler model is approximately

1.0, which is expected only for a gas of zero viscosity and

with no friction~l effects. The vortex exponent of 0.5

predicted by Alexander's model is more reasonable and was

confirmed by the experi~ental data.

c

c

100

Figure 3-22 shows a similar plot obtained at a temperature

of 1 300 K with the same outlet configuration. In this

case A1exander's model under-predicèed the vortex exponent,

giving a value of 0.2 while a value of 0.3 fitted the data

better. The Meissner and Loffler model once again greatly

over-predicted the velocities across the cyclone radius.

Figure 3-23 is a similar plot obtained with the small

(2.54 cm) diameter gas outlet at room temperature. There

was aga in good agreement between the experimental data and

the profile predicted by the new model except ~or the point

at a relative radius of 0.25. In this case, the predictions

of both the Alexander and the Meissner and Loffler models

were much greater than the measured velocities. The expla­

nation for the high values predicted by the Meissner model

was the same as above (n approximately equal to 1.0),

whereas the over-prediction of the Alexander model over­

prediction was due to the high wall velocity ratio cal cu­

lated for the small diameter outlet (1.52). Once again, the

calculated vortex exponent (0.5) agreed with the experimen­

tal data like it did in Figure 3-21.

Figure 3-24 shows the results of another high temperature

run but with the small diameter outlet. We again see that

the vortex exponent was under-estimated at high temperature

c

2.8 l 1 \ 1 2.6; / .. ~.I Outlet D..Ict

2.41->-1- 2.21-..... u o 2.01--'

. / ' \ / l' \.

/ ' '\ ". . / \, "'-. / ' ,,"'"

1- 1.8 . ,1 ,,,-.,,,,, ~ 1.6 / / '''.. ."",.

w >

~ 14 /. , " "'-... ...... . / •...... ..................... -.1 .. - •.•.• "' .... a: 1 2· ..... ............... .... ............ ...... 1 ' .. ,.--- ... - .............. --..... .... , ....... - .................... .... 1- /.. .. ---_ • . •..• ~ ..••••. z 1 0 .. - " - ------ - .... ~ W • • •• , .- --------, .' , . --CD l, .. ', ~ 0.8 1) ...... / • Experimentai 1- . , o 6 1/ ..... ~' . "'AlaXŒldar C IQ4Q)

. Il .. .,' ---New modal 0.4 t f' . ./' -·-Melsener 8 Laffler (IQ72)

... ; ---Meleener 8 Laffler Cvtw - vin) .. -, 0.2 y 1

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 RADIAL POSITION. r/R

0.8 o.g 1.0

Figure 3-22 Comparison of experimental with prcdicted tangential velocity profiles: cyclone Cl at 1300 K.

.,

... o ...

~

2.8

2.6

2.4

ç 2.2 ..... g 2.0 -l

~ 1.8

l:i:i t .6 2 ...... t.4 ~ CI: t.2 )-t

~ 1.0 C!' ~ 0.8 t- 0.6

0.4

.- 1-- ". -~ '. . . . . IT f /\ .......... .\ \ /

•• : 1 \ "':'\ '\. I f,' \, .. ~,...... . '1 , '\ ••• "

/',' ! ! ", ', ..... , ... , .. ".~ . .., " ..... : l ", •••••••• :1 .... '" .~ •••• ., ., '" ...... . Il ! ' ", '.', " ....................... . . , .""' "-., : 1 ........ '~ .........

. , " . "~ Il . • """.... ___ , il " ________ .. __ " ~-, . li If ___ ' ____ ,

fi If li/i

,

:J :1 ./ , i, il :, i ri

• experimentai ..... Alextnder \: t(49)

---New IIlOCYJI - ·-t-te1 eer.er 8 Laffler C 1972) ---Meleener 8 Laffler Cvtw - vin)

0.2 111 '.

0.0 0.1 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.0 R~IAL POSITION. rlR

1.0

Figure 3-23 Compar~son of experimental with predicted tangential velocity profiles: cyclone C4 at 300 K.

~

... o N

e

2.81 1 1 1 \ \

2.6 • j l '

2.4 Il \, >-., \ ~ 2.2 Il ...... . u . '. , o ., / ..... "

2.0 " i ......... "' ""-.... , ...... "-...... ...... -" ....... ,

1 6 L. Il : ... "" .................. :~ .. . • l" j. '''" ~: .................. .

, 1.4 II f· ,"'-"""-.. •• .......... .............--.1 ., ...... - ......--......

a: 1 2 l'1' f " -------- • ............ ...... . ---_ ....... ~ t;: : 1 --------- ---........, ru tOi 1 ---------':.-

~ 0:8 ~ l/ • Experimentai t- (} 6 1 f / .... Alexmcler (1949)

• i' --- New model o 4 K j/ -.-Melsenar 8 Laffler (1972) • f/ ---Malaenar 8 Latr'ier (vtw - vin)

0.2LM.~i--~-- ~ __ ~ ____ ~ __ ~ ____ L-__ -L __ ~~ __ ~ __ ~

0.0 0.1 0.2 0.3 0.4 0.6 0.6 0.7 0.8 0.0 1.0 RAOIFL POSITION. rlR

Figure 3-24 compa~ison of experimental with predicted tangential velocity profiles: cyclorJ C4 at 1300 K.

o

~

:3' ,

'.

(

c

104

by the Alexander model: a value of 0.2 was predicted while

0.3 fit the data better. In addition to that, the predic­

tions of the original Alexander model were consistently

hi~her due to the high calculated wall velocity ratio

(1.52) •

BUHKARY

It was found that the tangential velocity profileb depended

on the wall velocity and vortex exponent. Experimental

measurements showed that the wall to inlet velocity ratio

depend on the flow conditions and the outlet diameter. A

Reynolds number was defined for the annulus between the cyc­

lone wall and t.he gas outlet duct, and this number was cor­

related wi~h t.he wall to inlet vElocity ratio.

In general, the new wall velocity model along with Alex­

ander's vortex exponent model agreed with the experimental

lata for room temperature runs with both the small and large

diameter outlets. At high temperatures, the vortex exponent

was under-estimated by the ~lexander Dodel. A vortex

exponent of 0.3 fit the data better than the predicted 0.2.

Furthermore, the wall velocity was overpredicted by the

Alexander model for the small diameter gas outlet (2.54 cm),

while the new model gave better estima tes with both the

105

small and large diameter gas outlets. It is recommended

that the new wall velocity model (equation 3-22) be used

with the Alexander vortex exponent model to determine the

tangential velocity profiles.

c

CRAP'l'ER ..

COLLECTION EFFICIENCY STODY

c

106

CRAPTER 4

COLLECTION EPJ'ICIEHCY STUDY

INTRODUCTION

The variables affecting the performance of cyclones can be

classified into four groups:

1. Particle properties - density, size and shape.

2. Gas properties - te~perature, pressure, density, viscosity.

3. Cyclone geo~etry - inlet, outlet barrel di~ensions.

4. System properties - gas and particle flowrat~, inlet velocity, dust load.

The accurate prediction of the perforv.ance of cyclones over

a wide range of operating conditicns is understandably a

formidable task when the nuœber of variables is considered.

Detailed n~erical ~odels nave been developed to design and

predict the performance of cyclones, however, it is ~ore

often the case tb~t a si~ple easy-to-use model is required

for prelimtll<1!.ry or nun-critical applications. Many si~pli­

fi cd an~lytical modcls have been developed for this purpose

and so~e of these are discussed below.

c

107

This chapter examines the performance of cyclones as meas­

ured by the collection efficiency or the particle eut-size.

A reviev is presented of the existing theoretical ~odels

used for correlating and predicting the collection perfor­

mance, followed by discussions of the experimenta1 results

obtained in the present study.

LITERA'l'URE REVIn

Hodel1ing The Collection Performance of cyclones

For a particle in the cyclone, the main forces acting on it

are the centrifugal force (Fe) tending to ~ovc it to the

wall and the viscous drag force (Fv ) acting in the opposite

direction. There are other forces, such as gravit y,

diffusion, thermophoresis and electrostatic forces, which

are negligible in most cases but would have to be considered

in some systems (Calvert and Parker, 1976). The resultant

of these forces determines the motion of the particle.

In this study, the gravit y force was negligible because of

the small mass of the particles, while electrostatic forces

were also negligible since the partiel es were not chargpd

and the cyclone was grounded. Diffusion and thermophoretic

forces could not be ruled out withollt some preliminary cal-

o

o

108

culations since very fine particles «44 p=) vere used in

this study. At least one model (Mothes and Loftler, 1984,

1988) takes diffusion effects into consideration, as will be

discussed later.

Studies by Talbot et al. (1980), Dwyer (1967), Derjaguin and

Yala=ov (1965), Fuchs (1964) and others, have shown that in

order for thercophoretic forces to be significant, particle

sizes must be of the order of 1 p= or less, while tempera­

ture gradients must be of the order of 50 Kjcm or greater.

The temperature gradient in the radial direction had the

greatest effect on the dust separation in the cyclone. The

highest temperature gradient in this study was esti=ated to

be arou~d 100 Kjcm at the wall of the barrel with the wall

being at a lower temperature than the gas. At the same

time, less than 10 \ of the particles were below 1 pm and at

best, about 30 \ of these were estimated to be in the high

ature gradient region close to the wall. These conditions

are marginal for thercophoresis to occur and at best, the

collection efficiency WGuld be enhanced for the 3 \ of sub­

micron-sized particles close to the wall. The thercopho­

reeic effect was negligible for mose runs and marginal at

best, so it was ignored in this study.

A simplified force balance taking into account only the cen-

c

109

trifugal and viscous forces gives:

(4-1)

Assucing that the particles are spherical, and that Stokes

law is valid for the viscous drag on the particles, the '

force balance beco~es:

(4-2)

,

This equation is the starting point for ~ost of the theoret­

ical cyclone ~odels. Theoretically, at a given radial poai­

tion there is a critical size of particle (of given density)

for which these forces just balance so that there is no net

radial ~ovement of the particle. If the radial position is

at the exit duct radius, then this particle size is often

referred to as the "theoretical cut-size". If all of the

particles came in at the same radial position then the effi­

cieney would be 100 t for all particles greater than the

cut-size, and zero for smaller particles. The shape of a

plot ot collection efficieney versus particle size (grade or

fractional efficieney curve) for the Ideal cyclone will then

be a step function as shown in Figure 4-1.

In practice, the particles enter at difterent radial posi-

o

100

UJ N ... Cf)

C UJ l-Cl: 1-Cf)

1- 50 a: c UJ :> 0 z: UJ 0:

~

0

1 1 1 1 1 1 1 1 1 1 1 1 I 1 1

ac tua 1 curV.

\ "1 1

1

110

Th.or.t Ica 1 curV~

:on. of r.duc.d .ffl c I.nc 'l du. to • dd'lln;, bou:'lcln; •••

zon. of Incr.as.d _.fficl.nc'l du. to

collision, flocculatlon •••

PARTICLE SIZE •

th.or.tlcal lI:ut-slz~

Figure 4-1 Theoretical vs actual grade efficiency curves (Stair.aand, 1975).

(

111

tions and many particles smaller than the theoretical cut­

size are separated with the coarser particles due to agglom­

eration and their radial position upon entering the cyclone.

In addition to that, many particles coarser than the theo­

retical cut-size escape vith the clean gas due to secondary

flows, bouncing from the walls and short-circuiting from the

inlet duct directly into the gas outlet stream. As a

result, the grade efficiency curve tends to be "sn shaped

and the cut-size refers to the particle size collected with

50 t efficiency (Figure 4-1).

stairmand (1951) described the preparation and use of grade

efficiency curves to evaluate the performance of cyclones

and to predict their behavior over a limited range of oper­

ating conditions about which the curves were prepared. He

gave experimental data for tests performed on a 20 cm diame­

ter "high efficiency" cyclone and a "high gas rate" cyclone

of the same diameter (Figure 4-2). In both cases, the per­

formance curves were always concave downwards and asymptoti­

cally approached 100 t collection efficiency with increasing

particle size, and ~p.ro efficiency for decreasing particle

size.

Abrahamson and Allen (1986) defined a dimensionless effec­

tive particle size by taking the square-root of the ratio of

the radial particle velocity to the radial gas velocity at

112

the qas outlet radius. This definition was claimed to brinq

toqether the grade efficiency curves for a wide variety and

sizes of cyclones. An important difficulty in usinq this

method is the uncertainty involved in determining the gas

and particle radial velocities in the cyclone.

The ultimate objective of theoretical cyclone studies is to

be able to predict the grade efficiency curves for given

cyclone dimensions and operating conditions. This curve

allows the determination of the overall collection effi­

ciency as weIl as the cut-size. If the curve cannot be pre­

dicted, it is still desirable to be able to predict the ove­

raIl collection efficiency or the critical and cut-sizes.

Some studies aimed at achieving these goals are discussed

below.

The Rosin, Rammler and Intelmann study

One of the earliest theoretical cyclone studies was done by

Rosin et al. (1932). They made several simplifying assump­

tions, the main one being that the qas stream kept the shape

of the inlet duct as it moved do~ the cyclone. They also

assumed that the tangential velocity was equal to the me an

inlet velocity and that the particle acceleration and the

radia~ gas velocity were negligible. The force balance in

c

(

(

113

equation 4-2, was reduced to equating the centrifugaI and

viscous drag forces resulting in:

(4-3)

They went on to show that the smallest particle that

could be collected in the cyclone can be determined by the

e::pression:

dpmin (4-4)

This diameter is usually referred to as the 100 % critical

cut-size. The main problem with using equ~'\on 4-4 is that

the number of rotations made by the gas (Ns ) must be known

beforehand or must be predicted by one of the few

correlations a"ailable (API, 1975: crawford, 1976). One of

these correlations, presented by Theodore and Buonicore

(1976) was given as:

(4-5)

where the effective cyclone volume (Vc ) is divided by the

gas flowrate (Q) to obtain the mean residence time, which is

"","

C, .... , ... tor" _n. •

.,,. .. u,. w,· ,u,.

.... -ur' "-'1i:~::l;:!.JL

•

--1%.1-

.. 1

• "

... . i~

.,"~ YiUUtl.

"'''lf.

114

~

'a ~'O

ï 10

"10 " ~so w w.., ~ :i sa

>0

10

o

TUT CU"VI 10" Ik 1 •• CYC:WHr SO '.twc&NtlT. 'VILOQTY l ,"'/cc. soua C[N$UT IH AI" AT wc.

1 1 1 1 1

1

10 20)O~SOtO ..... TCLC .. tt~

'ttfir".."u cvn. (01 hi,,. f6:ocllq qdOltC

1

,.

niT OJ .. vl 10 .. ' ... ..: .. eTCtONt. JO ""M INtn vlLoan 1&",«, ,QUO DU'I"n IN ~ .. AT ~c.

100

,0 .10

.~

C '0 • 2 tO

t so w

11 40

2'0 • '0

10

o

1/

1/

1

10 '0 )0 .0 so 60 10 , .... ,tC"C "" o.<aoflt)

HI,,. i" ,.'" qd.,.. :,,,,,, "tpfII1.,., 'u(fltNlt(. (V,.,. rI' AIt" 'f' ,.1. (rdOftC

Figure 4-2 The stairmand (1951) cyclones and grade efficiency curvas.

t

.115

then multipliE'd by vi to obtain the mean length of the path

the gas makes in the cyclone. Theodore & Buonicore also

stated that for large diameter cyclones, the number of spi­

rals correlates well with the inlot ve!ocity and can be

expressed approximately as:

Ns = 1.54 ln(vi) - 0.37 with vi in mis (4-6)

Ter Linden (1949), developed a similar model to the Rosin et

al. model and showed that the largest particle that will not

be collected in the cyclone is given by ta king the radial

position (in equation 4-3) to be that of the gas outlet

duct:

(4-7)

~he main diffioulty in using this expression is in knowlng

the radial and t.angential velocities of the gas (vrg

and Vt).

The Lapp10 stUdy

Lapple (1951) showed that the 50 % cut-size r.ould be given

by an e~lation analogous to Rosin et al.'s equ~tion (4-4),

o

116

if the inlet width (S) is used instead of the cyclone diame-

ter:

(4-8)

Lapple then established a normalized grade efficiency curve

for which the fractional collection efficiency was plotted

against t~e particle size (dp) divided by the cut-size

(dp50) calculated by equation 4-8 (Figure 4-3b). This

normalized curve is applicable to cyclones with the configu­

ration shown in Figure 4-3a, which corresponds to cyc:one C3

used in this study (see Figure 2-1).

The Sproull study

Sproull (1970) proposed a particle collection effidency

model of the form:

e .. 1 - e-wO (4-9)

wh.1re

w = (4-9a)

c

c

1! I~ ~ ê<i 8 70 oa. 60 • eo ;; 40 'a ~ ,:: u c .. ~ 'ü

" o

30

20

, , • •

:/

Il

117

•

Section A-A

• • 1 ••

• • • • • 1 l , • 1 1

1 1 1 ........ Il 1/ 1 lA' 1

" 1 1 1 1

. . • • 1 1

1 1 1

1 1 1 1 1

· • i !

· · : i • ~ • , 1 • : •

• , •• • • 1

1 1

/ 1 1 ~ '~ n40S 07 W 3.0 4.0 50 7.0 10.0 8 Fbrflde size mio,lOp/Dpcl

Rebtioruhip betwcen conection efticicncy and pmicle size for cyclODes oE Fig.

Figure 4-3 The normalized grade etticiency curve and cyclone configuration 0: Lapple (1951).

118

In this equation, 0 is the surface area of the bal" -lof the

cyclone divided by the gas throughput. The drift wüocity

(w) is equivalent to the radial velocity vrp in equation 4-3

with r being replaced by the cyclone diameter (de>. '1:he

drift velocity is the main uncertainty in this mod~l, and

the exponential function causes the calculated collection

efficiency to be sensitive to the variables affecting this

velocity.

The Leith , Licht 8tudy

Leith and Licht (1972), used a different approach to the

earlier researchers and attempted to account for the contin­

ual back-mixing of uncollected particles due to turbulence

and secondary flows within the cyclone. They assu~ ., that a

uniform concentration of uncollected dust is maintained in

the gas flowing through any horizontal cross-section of the

cyclone. Referring to Figure 4-4a, they considered a hori­

zontal cross-section of the cyclone. In time dt, all par­

ticles a distance dR or less from the wall will move to the

wall and be collected. Heanwhile, particles travel a dis­

'cance Rda tangentially and dz vertically. The number of

parti~les in che sector is:

c

Figure 4-4a

Figure 4-4b

c

119

The cyclone cross-section for the Leith a~d Licht (1972) model.

- • B .. ,. r-y '19561

_. St ... , r....,. (1'101

-- PrCSCfll TheOlJ

.z

comparison of the Leith and Licht model with other models.

120

(4-10)

and the number of particles removed from the sector is:

Hence, the fraction of particles removed in time dt is:

-d(np) = 2rcdR - (dR)2 = np rc2

2dR (4-11)

Integrating up to the average residence time for a particle

in the cyclone yields a predictive equation for the collec­

tion efficiency given by:

E = 1 - exp[-2(~)1/(2n+2)]

where:

p d 2v (n+1) p p tw

18pdc

(4-12)

(4-13)

(4-14)

c

c

121

(4-15)

(4-16)

The three di~ensionless para=eters in equation 4-12 are: G -

a geometric design constant: ~ - a ~odified i~paction par­

a=eter si~ilar to the Stokes nucber: and n - the vortex 1aw

exponent. Figure 4-4b shows a co~parison of~he Leith and

Licht ~odel with experi~ental data of stair=and (1951) and

other theoretical ~odels.

The Leith and Licht ~odel does not take into account par­

ticle agglo~eration and the loading effect, both of which

improve the collection efficiency. The ~odel is therefore

likely to underesti~ate the perfo~ance of the cyclone in

non-di lute syste~. continuation of the work of Leith and

Licht led to the fo~ulation of overall design approaches

and other developments by Leith and Kehta (1973), Koch and

Licht (1977), Asla=i and Licht (1978) and Kasin and Koch

(1984).

The Deitz study

Dietz (1979, 1981) identified two other features of the

o

122

Leith and Licht model which were inadequately treated.

Firstly, although the distribution ot gas rcsidence times

within the cyclone is recognized, only the average residence

time i~ used in their analysis (the shorter residence times

can lead to lower collection efficiency). Secondly, the

Licht and Leith model is not consistent with the actual gas

flow pattern. If turbulent mixing is an important factor in

determining cyclone efficiency, then the interchange of par­

ticles between the upflowinq and downflowing sections of the

cyclone must be included. Thus, by assuming that the gas is

uniformly mixcd across a horizontal section of the cyclone,

Leith and Licht ignore the reverse flow nature of the cyc­

lone.

In an attempt to o~ercome the deficiencies of the Leith and

Licht model, Deitz developed an analytical expression for

the collection efficiency, based on a three-region model for

the fluid flow in the cyclone. The three regions are the

entrance region, the downflow (annular) region, and the

upflow (core) region (Figure 4-5). TUrbulence is assumed to

main tain uniform radial concentration profiles in each

region, and particle interchange is allowed between the

annular and core regions. Conservation of particles in each

regicn requires that:

·1

c

I-!-l t

1 • Oc ........

1 1

1 ..

1 1 • 1 1 ........ 1 1

2 1 1 1 " n 1 ...... 1 • 1

1 1 1 1 1 1

123

z·o

I-~

a..w 1

z· 1

i 1 , , , 1

~ 1

u~ i 1 1 Z 1

~t ! 1 -'a..w 1

-;-çw( 1 1 1 1 l , 1 1 1 ! ! 1

r···, Ile

Figure 4-5 The geo=etry for the Deitz (1979) =odel.

1 1

o

124

Region 1:

(4-17)

Region 2:

(4-18)

Region 3: ,

(4-19)

Qv(z) is the axial volucetric flowrate, rw(z) is the

particle flux to the cycl?ne wall, rv(z) is the radius of

the core region and rv(z) is the flux of particles fro~ the

annular region to the core region. Stokes' law was used for

the drag force which was ~quated with the centrifugaI force

in order to dete~ine the radial particle velocity. It was

further assuced that:

1. The radial gas velocity into the core region is con­stant.

2. The tangential velocity do es not vary axially.

3. A ~odified free vortex law describes the radial variation of the tangential velocity.

4. The radius of thE: core region is equal to that of the exit tube.

:

The reà~lt was a model for the efficiency of the cyclone

c given by:

where:

_

r~c~u:.rw:....+_r~v:...v~r=--+_r..:v_U~r KO = 2rvur

125

(4-20)

(4-21)

(4-22)

(4-23)

Ur and vr are the radial velocities of the particle and gas

respectively. The Dietz model agreed weIl with data

obtained from the secondary cyclone of the Exxon miniplant

(Ernst et al., 1982; Hoke et al.,1980) as shown in Figure

4-6. The Exxon cyclone had a diameter of 18 cm and was

operated (for the selected data) at up to 948 K, 10 kPa and

55 mIs inlet velocity.

The Mothes , Lorf1er study

Mothes and Loffler (1984, 1988) reported the development of

a model similar to Dietz's (1981i but with four regions

o • --.0-,-

'" w_ .... '-'" -~-<-o--~-----.... c;,._ ,,-

• ,;. .. .... •• .... nt

1)0.

. ,. ...

.. '" l'l' • ,~. . - .~ .

.... .... -•• .. .. '!II' ... ... H' : .. ~.

:h"- :". .. th ..

. ...... h.· h.·

. . --

•• • ... ,~. ... • •• • • .... n-l' U " .- ... ...

lO' •• ., :.,. .. :,. .. :,. ... .... .. ' h.' -

.. . ... Compuison bttwtfll dat-o". aM: tI~rimcct rOf SHOII'oJlI,~ CJcloot al [UN'S mialp!aal (ru J%.l~

126

,:\ _u

('[ l' ,

" • -- .. . . .. . COlipariao.'mrcn lMor7 ,ocI npcrl:atDI rOf .... 04 .... " '7_ al E .... \ ..wpla .. (na

l%.l~

i:l II

• .

i~ li •

--"

,

, ,

. . ---

, , ,

.. .. ;

Computl4D bd"Cflllhrory and npcrfllltilf fot ICCOM..ult (JdODC Il [su.", mmiplanl (nlll ... o4ll~

--

_.

•

. --- . .. ... eoaparisoa bdwua iMoI'J.04 Uptr"'.tDlrot

ucoa41Uct C)'doDt &1 Essoa" miniplard (ruD lf']~

•

•

. -- .. .. .. .. . Co.pathoa ~wtu 1Mor7'" npcrl""'1 rot ItCODd1taCt Cldo .. Il [11011°, .infplant (m n.4~

Fiqure 4-6 , Comparison of the Deitz (1979) model with experimental data.

c

127

instead of three. The new model takes into account the

friction occurring at the walls of the cyclone (which affects

the velocity profiles), and a particle diffusivity which

accounts for the influence of turbulence on the particle

separation. The qualitative results presented include:

1. The tangential velocity depends only on the radius and

does not vary axially. The radial profile is determined

by the cyclone geometry, wall roughness and particle

concentration.

2. The mean motion of the particles primarily determines

the cut of the cyclone while the diffusive (turbulent)

motion influences the shape of the grade efficiency

curve.

3. Particles must be prevented f.rom entering the upward

flow and must be deposited on the wall during their r~s­

idence time.

4. Re-entrainment of particles occurs in the lower part of

the cyclone and from the hopper due to increased turbu­

lence.

The physical cyclone model used by Mothes and Loffl~r (1984,

1988) is shown in Figure 4-7. The radius ra of the actual

(1

Figure 4-7

Exil cice

128

"

l,II' 1.ld

',l':'f=iC'W1\c.l,rj hl''''': I,~I'.II

I,lz-4Z .

i,lII i.1II ri

1r:-~':"""''':'''''''..l''H----' Ij--------I--'-0' . 1 i,I','1- i- C 1 j

~------~--------~~

The geometry for the Mothes and Loffler (1984, 1988) mode!.

129

c'llinder and cone cyclone was changed to ra* = (VcI'lth)o.e.

instead of changing the cyclone height (as Deitz did). This

method does not affect the radial ve1ocity, which is

important in determining the remova1 efficiency. The three

ve1oc1ty comp~nents were given in Chapter 3 (equations 3-9

to 3-12). The axial vo1um~tric f10wrate was given by:

Q(z) (4--24)

Mass balances simi1ar to Deitz yieid2d the fo11)wing expres­

sions for each region:

Region 1:

(4-25)

( 4-26)

w(ra *) :. - (4-27)

Region 2:

d dz[Q(Z)C2(Z)] = -2~ra*j2(ra*) + -~~ij2,4(ri) (4-28)

j2(r~*) = w(ra~)C2{Z) (4-29)

(4-30)

with:

Region 3:

= ppX2Vt 2 (·>:i)

18Jlr i

13v

j2(1)~!ra2-ri2)-j4(1)~ri2_j3(ra*)2~ra*(h-l) .. 0

j3(ra*) = W(ra*)c3 - mw/2~ra*(h-l)

1 = h - (h-ht)/lO

assuming 10 % of gas flows through this region

Region 4:

with j2,4 given by equation 4-30.

These equations were solved for cl(z) to c4(z) and the

cc:lection efficiency calculateâ as:

(4-31)

(4-32)

(4-33 )

(4-34 )

(4-35)

_C::,.4 (.:...h-=t~) e .. 1 - ( 4-36)

The Mothes and Loffler model agreed best with their exper­

imental data when a particle diffusivity of 0.0125 m2/s was

c

131

used (Figure 4-8e). The mcdel predicted the effect of other

operating parameters uith varying degrees-of success (Fig­

ure 4-8a,d). The mcdel al 50 compared iavorably with the

models of Deitz (1981) and Muschelknautz (1972) ln predict­

ing the shape of gr~de efficiency curves (Figure {-Sf). 1c

should be noted that in Figure 4-8f, the curve predict~d by

th~ Leith and Licht (1972) model was straight anè over­

predicted the collection efficiency for small particle

size:>: a similar trend was noticed with most ·,f the data

obtained in the present study.

Effect of Dust Load on Collection Efficiency

Increasing the cIust load has two opposing effects on the

collection efficiency: firstly, it causes a decrease in the

tangential velocity and as a result decreases the separation

potential. Barth (1956), Muschelknautz (1967, 19'/0) and

measurements by Yuu et al. (197S) attributed this to an

increase in the friction factor at the \.11 in the presence

of particles. On the other hand as the dust concentration

increases, particle collisions increase and fine particles

which would not be removed individually, are swept to the

wal1s along with the larger particles. The scrubbing effect

is usual1y dominant and depends on the du st concentration as

weIl ~s on the size distribution of the fred dust.

'1, .,71'':)",' ~!~ - 1 ~ I .... u ". r ... "n .. /-

~ ';!

t' ••• 'a 1 .,-a s U',-·t~l,. -CAO_

oz c _'s· .ut. ,. o.. 0. 0'111 .-'t~ OAll' •

1 i .. l! w ,

u os , • • . .. Pa~Sln c/~ ..

E!f.ç: çf dllo:'\,ftr cf eXit pIpe en u-. ctr.~ •• ,..ey of stS':.tJ"on.

""Ç7j ..

, •• Ion .. ~ ~ •• n· a. n •• otn .. S .......

c..tcqs-'i,

.. ,. r.r-f-_~. O'It •

..~ .

Etred 01 ln. width 01 En •• ntranct on """'ICllncy of stPlratlOn.

,.In-"III 0./.'" .. -UH_ • .... en_ .... " Il .". uns'· .·Un_ ..... ... ...... ,. ., ..... u .. li

.l. ____ ~~~~::::~ ____ ~.~': ... ::n:m:J:.u::J'.

u u z " ... ,,,.l'IJCIt weaJ".m

Elttct of coefflClenl of ~tUd. "If'us-on on ln. ,tf'JCltncy of stp.lrauon.

1. , •• t.C'h ..

-â '.I""='" ~

t;·,u~.

.... t) .. .. a" .. ·.n· a •• , S'

1! o..uus-',. •• ~ j

,,,. ~

us. • U li , , • 1 ..

PutlC" SIle ""-

Eftec1 of gu UlfOug"put on th, tlflCl.ncy of stp.)/lElon.

.~

• '.n~""' • '".OH ..

S ... I.,n,.. , • c • ." ilS ", ... ,. OI-

~ 1 a..'OflU,.),. • JIf

,. • !JI

~ .. ! •

" U UI , • . .. E!ftct 01 cycrone " .. gnl on th, tlf-a,ncy 01

""'"tlon.

~

8 " ~ a a 1 .. ~ .. 5

'1 •• n-". ,. ... " .. .. ItJ"_ Il • 's· I·un .. ",,1"" ./ .... 0'" a,.to,n-'" 'JCtn'"fMiI.

......

-,,/' . //

/// ~ ,I-l ... '..... 111711

• ,1 -....... l'U)I l,' -DoM. IIUIt

;0.." ~ - .... " ........ ,.·,U' ·,~J~----~.~I~--~----·,;-----~,--~.~~.~ ..

PII'ICIt sau rI".n

Companson of VlfIOUS fNU'I.mauul mfIC"'J.

Figur-a 4-8 Comparisons of theory with experiment for the Mothes and Latfier (1984, 1988) model.

'L'

c

c

133

Ogawa (1985) analyzed the effuct of dust load on the collec­

tion efficiency using a model based on the probabilities of

interchange of deposited and dispersed dusts withit. the cyc­

lone. He showed that the eff.iciency depends on thb dust

load according to an expression of the form:

(4-37)

where bl is a dimensionless number and kl (m3jg) is a

coefficient d~pending on the inlet size distribution, cyc­

lone dimensions and inlet velocity. bl and kl were measured

to he 0.032 and -0.0157 for a 90 mm diameter conventional

cyclone with flyash (2.06 pm mean diameter) at velocities of

14 to 16 mjs. The small negative k indicates that the co]­

lect;on efficiency decreased slightly with dust load con­

trary to expectations. On the other hand, in the same

study, the measured efficiency increased with dust load for

axial cyclones of roughly the same diameter.

Ogawa (1982) referred to another empirical expression devel­

oped by the American PetroleU3 Institu~e (API, 1955):

[c ]0.2 Ea = 100 - (100-Eo) c: (4-38)

o

o

134

where the subscript "0" refers to a reference load arbi­

trarily taken as one unit (1 gr/ft3).

A more recent correlation developed by the API (1975) was

based on plots of overall collection efficiency vs du st load

on probability - log coordinates. The model was of the

form:

pee) = P(Eo) + A log L (4-39)

where pee) and P(Eo) are the probabilities associated with

the collection efficiencies at zero loaa (Eo) and higher

loads (E), A is an experimentally determined parameter and L

is the du st loading in gr/ft3 (1 gr/ft3 = 2.29 g/m3). The

parameter A was numerically fitted by Hasin and Koch (1986)

to a polyncmial in the base efficiency:

A = 0.67 - 2.11Eo + 5.63E02 - 4.oeo3 (4-40)

Approximating the probability function by In[(l-e)/E], equa­

tion 4-39 became:

In(l-e) = In[ 1~ ] 1+eo ( -1)

(4-41)

• Masin and Koch also used a correlation developed by Sproull

c

(

135

(1966) to account for the effect of 10ad on the effective

viscosity of the system:

(4-42)

Hasin and Koch used these 10ad corrections and a saltation

correction to modify the Leith and Licht (1972) model,

resulting in the expression:

•

[ ~AiG ]0.41/(n+l)

= -2.3 SF 2 LF.dc

(4-43)

where LF is the viscosity load correction in equation 4-42,

~ and G are the stokes number and the cyclone configuration

factor defined by Leith and Licht (equatioll 4-13 and 4-14),

and n is the vortex exponent. The saltatio.1 factor (SF) was

used to account for the decrease in efficiency that occurs

at high velocity as a result of re-entrainme.lt of particles

from the cyclone walls. A correlation dcveloped by Kalen

and Zenz (1973) was used to calculate the saltation velocity

and the saltation factor defined as:

with k { = 0.41 for 1 < vi/vs < 2.5 = -0.31 otherwise

(4-44)

o

136

The resulting correlation was claimed to improve the collec­

tion efficiency predictions over a wide range of operating

conditions. however, with the high degree of empiricism in

the model and the scatter still remaining in the data, the

authors reconmended experimental verification for critical

applications.

Mothes and Loffler (1985) noted that the agglomeration pro­

cess consists of two parts: firstly, the particle motion

leading to collisions, and se~ondly, the impact behavior

after the collision. The relative motion of the particles

can be due to several things:

1. Different terminal velocities to the wall of par­ticles of different sizes.

2. The relative motion of neighboring particles caused by the velocity gradient of the gas.

3. Particles following the turbulent velocity fluctu­ations.

4. Electrostatic effects with charged particles.

The first effect is usually the dominant one in cyclones.

Mothes and Loffler analyzed the agglomeration process in

three steps: first, the deposition efficiency of fine par­

ticles on a large particle settling towards the wall was

determined. second, the gas volume cleaned by a large par-

c

137

ticle on its way to the cyclone wall was determined: and

third, the change of fine particle concentration caused by

the cleaning effect of the large particles was calculated.

The resulting expression for the collection efficiency under

high load conditions (e) was given as:

e(x) = l - [l-eo (X)][l-eA(X)]

EA(x) = 1 - exp[-CV(XG).Vx(XG,x)]

(4-45)

(4-46)

where eA(x) is the separation efficiency due to agglo~er­

ation, Cv(XG) is the effective vol~e concentration of the

cleaning big particles, and Vx(XG,x) is the gas vol~e

cleaned by a big particle. Vx(XG,x) takes into account the

relative velocity between the large and s~all particles, and

the deposition efficiency of fine particles on a big par­

ti~le.

Mothes and Loffler showed that for a 15 PD cleaning par­

ticle, the variation of deposition efficiency with the size

of the smaller particles was calculated to have a maximua

(at 2 to 3 pm). This maxim~ occurred since the impact

efficiency varied directly with particle size while the

adhesion probability varied inversely with particle size

(large particles rebound almost co~pletely after collision).

The result was that the calculated separation efficiency due

to agglo~eration also had ~axi~a when plotted against par-

o

o

ticle size as shown in Figure 4-9.

The main problem with using this model is in defining the

size of the cleaning particle. In a system with a continu­

ous size distribution, there is a continuous distribution of

cleaning particle sizes and a simultaneous distribution of

small particle sizes. It is therefore not expected that a

weIl defined maximum will be observed in the plot of effi­

ciency due to agglomeration versus particle size.

summary of Literature Review

It has been shown that the collection efficiencies of cyc­

lones depend on the properties of the dusts, the gas proper­

ties system properties, (especially the gas flowrate and

inlet dust load) , and the cyclone geometry. The large number

of variables make mathematical modelling of cyclone oper­

ations a non-trivial task. The result is that prediction of

cyclone performance still depends mainly on empirical corre­

lations. llevertheless, a few models based on fundamenta!

theory have met with varying degrees of success in

predicting the collection efficiencies over a reasonable range of

operating conditions.

c

" -~ >-u c .. ~OS -.. C .2 -'" ~ '" Co .. ..

0 Q2

Figure 4-9

c

139

1 1 1 c.tg/mJ C/C:et't ~t:,..~·"

, .. 150 mm .000

t. 1 SOm", b •• LSmm

2500 h. 1220'"'" Y •• Il'mls

COIl"'''''9 petllel. "'t

1000

9 •• soo ~'. o.,

SO 100 ~

0-' 0.6 o.s 1 15 2 3 , 6 8 10 20

particle size x/llm

Variation of separation e!ficiency due to agglomeration with particle siz~ (Mothes and Lo!!ler, 1985).

140

EXPERIMENTAL RESULTS AND DISCUSSION

operating Conditions

The raw experimental data are tabulated in Tables A1-1 to

Al-5 of Appendix 1. The principal controllable variable was

the volumetrie gas flowrate which directly affected the

inlet velocity, gas temperature, dust loading an~ cyclone

pressure drop. The flowrate had a strong influence on tem­

perature because the flow of gas through the torch was con­

fined to a range of 0.05 to 0.11 standard m3/min and the

power of the generator was maintained near its design limit

of 40 kW when used with air. The power could not be

increased when the supplementary air at room temperature was

mixed with the plasma: this resulted in a drop in tempera­

ture inversely proportional to the flowrate of supplementary

air.

The maximum flowrate used at room temperature was around

1.18 standard m3/min, giving an inlet velocity of 15 mis.

The highest flowrate used at high temperature was 0.98 stan­

dard m3/min, resulting in temperatures of around 900 K and

inlet velocities of around 40 mis. The lowest flowrates

used were around 0.2 standard m3/min; this was the lower

limit necessary to avoid melting the cyclone inlet duct

close ~o the exit of the torch. The highest tempe rature of

(

(

141

2 000 Kwas obtained at a flow rate of 0.194 standard m3/min

and an inlet velocity of 17 mis. The dust load varied from

0.3 to 23S q/m3 for alumina and from 1.1 to 80 q/m3 for

silica.

Correlation With DimenRionless Groups

In evaluating the performance of cyclones we can examine the

variation of either the overall or the fractional collection

efficiency with changes in specifie variables (for example

inlet velocity, dust load, temperature), or with dimension­

less groups such as the Reynolds or Stokes numbers.

A common practice is to characterize the cyclone performance

by the cyclone Stokes number (stSO ) defined in equation 1-2.

The data of Wheeldon et al. (1986) and the measurements made

in this study showed that it was difficult to characterize

the cyclone by a single number such as the Stokes number.

For example, the cyclones in the Wheeldon et al. study were

predicted to have a single stso of 1.29 x 10-4 while the

measured values ranged between 0.4 x 10-4 and 1.96 x 10-4•

This variation was attributed to the variation in dust load,

and a plot was shown of stso versus du st load (Figure

1-10b). The author of this thesis thinks that the scatter

in this plot was too great to justify the lines drawn and

142

the conclusion that stso varied inversely with dust load.

Pursuing the same argument and using an analysis similar to

Wheeldon et al., it was calculated that the cyclone used in

this study would have stso varying between 1.0 x 10-4 and

2.2 x 10-4 depending on the gas outlet configuration. In

comparison, the measured stso varied between 4.0 x 10-4 and

3.6 x 10-1 , and there was no correlation between stso and

the dust load. It was concluded that a single stso for each

cyclone configuration did not adequately characterize the

performance of the cyclone in this study.

Parker et al. (1981) showed that their data could be corre­

lated by plotting the product of the Reynolds number (Re)

and the square root of the inlet Stokes number (st in)

against the experimentally determined SO % cut-size on log­

log coordinates. The cut-size was reported as aerodynamic

diameters (dpa ) defined as the physical diameter (dPSO)

times the square root of the product of the slip correction

parameter (C') and the particle density (pp). The Reynolds

number was based on the cyclone diameter and the mean inlet

velocity, while the Stokes number was based on the mass

median diameter of the feed du st and the hydraulic diameter

of the inlet (equation 1-1).

The inlet Stokes number (stin) defined by Parker et al. is

c

(

143

interesting in that it is based on kncwn operating condi-

tiors (dp~l' Pp' ·'i' Il. H) and can be used as a predictive

parameter if it can be co~related against the collection

eff~ ciency or the 50 % cut-size. On the ':ltth· ... nd, the

cyclo.le Stokes numbe= (st50) ls used to chal.'acterize the

cyclone and consists of independent variables (pp' vb' Ilr

de) and the dependent variahle (dp50).

Their method was tested with our data and Figure 4-10 shows

the results obtained with silica and alu~ina, compared with

the data of Parker et al. (1981). We see that our data fol­

lowed the expected trend but that the slope of the Parker et

al. data was steeper. The correlation coefficient (R) ~as

0.67 for our data whereas it was 0.97 for t~e Parker data.

Further aralysis showed that most of th, correlation for the

Parker et al. data was due to the Reynolds number \~ = 0.97)

rather than the Stokes number (R = 0.~9) while the opposite

was true for our data (R = 0.71 for stin' and 0.55 for Re).

The results of these analyses are shown in Table 4-1 along

'Ii th the critical R required for significance at the 95 \

confid~nce level.

The variation ~f cut-size with Reynolds numbar is theoretic~lly

inconsistent, since the gas density term in the num~rator of the

Reynolds number inco~rectly predicts that decreasing the gas d~n-

144

TABLE C-:l,

summary of Correlation coefficients tor Dimension1ess Group study

CORRELATION COEFFICIENT

Independent Re.St. 0.5 St in. L'oc. Er<! Variables ln Re st in

y - dpai c - 0.2; d - 2

Alumina 0.67 0.58 0.70 0.87 Silica 0.66 0.49 0.79 0.91 Both 0.67 0.5S 0.71 0.85 Parker 0.97 0.97 0.59 0.60

Y = l-e; c = 0.5; d - 2

Alumina 0.63 0.58 J.60 0.90 Silica 0.51 0.37 0.63 0.92 Both 0.50 0.46 0.46 0.72

Critical R at 95 % confidence level

Alumina 0.34 0.;:7 0.27 0.38 Silica 0.40 0.32 0.32 0.44 Both 0.25 0.21 0.21 0.29 Parker 0.52 0.43 0.43 0.58

c

145

~-:~------------------~~ - -~ ~ ln o -

10 • o ,..,. c

"I:f O+J -en

+

(') o -

•

~

N

" .... -,., CI .Sl /:: ::s s:: 1/1 CI :.: o "'" CIl ~

1 CIl 'tl ..... o s:: >. CI CI:

CIl >

oa Co

'tl

o .... 1 ...

sity (by increasing the temperature for example) would lead to

higher cut-sizes. Since stin includes the inlet v~!ocity and the

gas viscosity (as does Re) and also takes into account the inlet

particle size and the particle density, it is justifiable to use

the Stokes number alone or with dimensionless groups other than

the Reynold~ number.

Considering the wide range of du st loads used in this study

and the tendency for the collection efficiency to increase

with increased load, it was felt that a loading factor

should be included with the Stokes number for correlating

the data. 1 dimen"ionless load factor Lv was defined as the

inlet volumetrie dust load: the volume oe particles per unit

volume of gas at the inlet conditions.

The rationale behind using this parameter was that the load

effect is due to eh~ in~reased number of particle-particle

collisions and the prob~oility of collisions occurring is

s~rongly dependent on the volume occupied bl the particles"

In Addition to that, the defined paramcter also takes the

temperature of the g~s Into account and for a given mass

flowrate of gas and particles, increasing the temperature

iowers th~ dust load, leading to lower collection efficten­

cies.

It has been shown by other wo~kers (Alexander, 1949 for

c

(

c

147

example) and in this study that the collection efficiency

increases (or cut-size decreases) as the ratio of barrel

diameter to gas outlet diameter increases. This prompted

the definition of aecond dimensionless pa~ameter (Er = dclde) which was included with the Stokes number for

correlating the data. The cyclona diameter in the numerator

replaces that in thp Reynolds number so the combinat ion of

Stinl Lv and Er is theoretic~lly more cor.sistent than the

Re.stino.5 combination. A new separation number was defined

as:

(4-47)

Non-linear regression analyses on our data determined that c

and d should be 0.2 and 2 respectively for correlation

against the 50 % aerodynamic diameter. Figure 4-11 shows

the resulting plot for silica and alumina and for the data

of Parker using the same values for c and d. The correla­

tion coefficient was 0.85 for the combined alumina and sil-

Ica data whil~ it was 0.60 for the Parker data (Table 4-1).

The correlations with alumina and silica con$idered sepa-

rately were higher than when they were combined. The model

for the combined data was:

d p 50 = 3Sn-O. 2 w~th Sn = St- .T_~0.2.Er2 1n -v (4-48)

148

,... -(1) CD -.., •

0 ... ID lB 2 8 :; N

• <3 ~ ON •

~=i 0

--0 • • • <3d1 a:UlD.. 0"0 0:

0<3+ '41: <3~~ <39 0

ft i :> 'a <1

+ 8~ + + + t <l' 't:/ .t +

++ + J + + 0

o • o

N 0

o -0

0

-

++

+

-·b -.

• o (')

• • - o

'D L-W . 0 > -l .

C ,.J

en

• CI

"" CI ::s '0

J:

"" o ,Q

~

~ ~ CI ,Q JO ::s s: s: o .... "" e ~ Co CI (Il

~ ., 'Oc.

... ... 1 ...

(

(

c

When the overall collection efficiency data were studied

instead of the 50 % cut-size, it was found that the penetra­

tion (l-e) rather than the efficiency (e) should be used for

the log-log plot. There was much scatter in the plot of

penetration vs the Reynolds-Stokes number combination used

by Parker et al. as shown in Figure 4-12.

The new separation parameter showed a much st ronger rela­

tionship with the penetration and was best correlated with c

a~d d (in equation 4-47) being 0.5 and 2 respectively. The

resulting plots are shown in Figures 4-13 and 4-14 for alu­

mina and silica respectively and the corr~lation coeffi­

cients are given in Table 4-1.

Effect o~ Operating conditions on Grade Efficiency CUrvos

The grade efficiency curves are usually more useful for ana­

lyzing the performance of cyclones since they show how the

efficiency varies with particle size and can be integrated

to give the overall collection efficiency. They are also

use fuI for evaluating how weIl a theoretical model works,

since a theory which accurately predicts the shape of the

grade efficiency curve is also likely to successfully pre­

dict the effect of changes in the operating conditions.

Three figures of grade efficiency curves are discussed here

~~

I.OOL~--------------------------------------------~

o

OAlunlna ASlllca

R - 0.60 .-. A A

Cl "'''' '" 0 ,6 '" '" o ~ 0 ~A - 8 '" 0 0

Ct

::: 0 Il' (J '" '" '" '" !li 0",-" 0 0.

0

0 '" 0 '" 0 ~ ft 0 '" ' 0- '" <>.r"" S. 0 _ ~ '" - ~ ~o~ _ ~ 0 "co A 00 ~ ·0.10 00 A Z 0

8 0 0 ~ 0

i o ot ' ", , , , , , , , , , ft 1

• 103 t04 t05 6xt05 Re· eSt In)O.6

Figure 4-12 penetration vs Reynolds number-(stokes number)lj2 for both dusts.

~

1.00, ..,

,.., a a -~ .... W

1 -..., Z 0.101-a t-f

;

AllIlllna

c OCI cold " ~Ct ~t

'" ~ CC3 hot c .......... ~ ~ li( C4 cold

.N:::....k f + C4 hot

~~ë/!~A + 0 - 0.6 ~~KO ~ d-2

00 c R - 0.00

49 ,.",

++~

0.01' ,,' • 1 0

-1 •• " pl

, , ft

1 • "pl ro '''11'

st'n.LyC.Erd 102

Figure 4-13 Penetration vs separation number tor alumina.

~

-ur -

152

N 0 -

+ j"

o .(.lI

% • cs

u ooi

0 ~

O<l . - ooi c:I

't;<l ,. 0

./: <l

II ... L.. ,. W CI

0 • .Il 0 El

o P<l > ::2 ...J s::

O:ll<l • s:: C 0

ooi o+J ~

CI) CI ,. - cs ~<l c.

CI c:I

<lI c:I >

<lt

s:: 0

ooi

SI ~ 1J 1J 10 cs

fi 8] 8] • • ,. ON 0 ~

CI • 1 • s::

--~~ - CI (/) UUUU Cl1J c::: 1 Ilo

O<lll+ . 0 - ... ri

• 1 ... 8 0 - CI - 0 ,. • • • ::2 - 0 0 C'

[001/;;3-1] 'NOI18~!3N3d ooi ~

~ ~

l00t- lK-·_·_·)I{_·- ---- .-~._ _--- -::-:,.-_ ..... ·u - -----~ .,. .. ---- -0---- - - - --

00 1 /" .......... .---N ' .. ...".-/ .. .,/ • 80 . + ,,,0",,..,

>-u 70 1 1 / .. / m • , 1

I-t

60 1 / " / u I-t

H: . , P / w

60 1 j Ij RLn Vin Tin Cln eff Z 0 40 l' f/ No. mis K g/m3 Z I-t t-U :JO ! fI 0 SAOB 3 2Q5 4B 73 w -' J )1{ SAOQ 15 295 4A 00 -' 0 20. + SAZ8 15 1664 50 86 u

IO~ L 1 <> SA29 17 1836 3 61

al.. j, a 2 4 6 8 10 12 14

PARTICLE SIZE. 1..1111

Figure 4-15 Grade efficiency curves showing the effects of temperature, inlet velocity and du st load.

-(Il Col

154

to illustrate some of the trends found in this study.

Figure 4-15 shows four grade efficiency curves obtained with

silica at the conditions shown in the legend. The overall

and fractional collection efficicncy increased as the curves

go from right to left and from bottom to top. The right

hand side of the curves pass through points around 30 ~m and

are not extrapolated as they might appear to be.

Runs SAOS and SA09 in this figure showed that for similar

temperatures and dust loads, the collection efficiency was

significantly higher at the higher inlet velocity for par­

ticle sizes up to around 10 ~m and were both close to 100 %

above 10 ~m. Runs SA09 and SA2S show that for the same

inlet velocity and similar loads, the efficiency varied

inversely with temperature. The difference was not as dra­

matic as the velocity effect, and was most significant

between 1 and 6 ~m.

Runs SA2S and SA29 in the same figure illustrate that

increasing the dust load resulted in significantly higher

collection efficiencies. The curve obtained at the lower

dust load (SA29) did not approach 100 %, but leveled off at

around 95 %. The largest differences occurred between runs

SA09 and SA29 and showed that for similar velocities, the

combined effect of two favorable conditions (low temperature

~ ~

toot- ~ n----A----~------------~""n-n---~ .. -/Jr9- ".......... .•........ ................................... .. ............. ,.,::... ---.----.--.

001-PC'" .,..,-' _. '-'

fJr-o-:t N

r~ •

~ Il RLn Vin TIn Cln eff .... 00 u No. mis K g/m 3 Z ....

~ 60 o AA43 16 298 1 89

B 40 A AA48 16 298 4 93 ....

~ 3J c SAil 16 298 6 87

lIE SAf6 16 298 f 78 20

10 ~ c,

o,ojl~ 0 2 4 6 8 fO f2 14

PARTICLE SIZE. f-ITl

Figure 4-16 Grade efficiency curves showing the effects of partic1e type and dust load.

-(Il (Il

156

and high load) resulted in much higher efficiencies th an the

combined effect of unfavorably high temperature and low dust

load.

Figure 4-16 shows grade efficiency curves for runs obtained

with silica and alumina at room temperature and agas flow­

rate of 1.18 standard m3jmin. The efficiencies were rela­

tively high and the grade efficiency curves were almost

identical (except for run SA1S) because of the favorable

conditions of low temperature and high gas flowrates.

Lines AA43 and SA1S show that for a dust load of 1 gjam3,

the efficiency was higher with alumina for all particle

sizes as expected by its higher density. The four lines

show that with silica, the overall efficiency increased 9 %

(going from 78 to 87 %) as the load went from 1 to S gjam3,

while it went up 4 % for a similar increase in du st load

with alumina. In general, the load effect was larger with

silica than it was with alumina, and the silica grade effi­

ciency curves were lower than the alumina curves. This is

consistent with the premise that the load effect depends

largely on the volume occupied by the particles.

Figure 4-17 shows grade efficiency plots obtained with alu­

mina at high temperatures and at a flowrate of 0.213 stan­

dard m3jmin. Run AA48 and AC01 were obtained with the

~

N ~

>-

~ .... (--~ a ....

~

-- -----l lOO [ ~... ,. .. : . .!!.:!::.-. ~'""':~~:;'--~;;..::o.~.oo.::... ... _ .... '

l " ." ................. . •

001- /;).:9 ao 70

00

60

40

.'~ ù :, , :,

'J!., lb' . ~

li • 1

li :li 1- Il

li

RLn No.

o AA05

A AA48 rl ACQl

li( AD12

Vin rn/a

16

17 17 16

Tin Cln aff K 91m3 Z

1773 18(Y'1

1803

174::1

2\ 77 36 84

35 84 20 84

2Ot- '.:

lOt- i/ 0~.~o~-----~-------:6----~8----~10~--~12~--~14 024

PMTICLE sr:l:. J-m

Figure 4-17 Grade efficiency curves showing the effects of outlet dimensions and dust load.

~

-ln ~

158

5.08 cm diameter out let and outlet J.engths of 10.8 and

7.0 cm respecti~ely. The curves and the overall collec~ion

efficiency were the sa~e, showing that the outlet length did

not notice"lbly affect the performance of the c~·clone. On

the other h~nd, the outlet diameter had a seronger effect on

the collection effici~ncy as illustrated ~y line AA05

(5.08 cm diameterj and AD12 (2.54 ~~ diameter).

O~her comparisons of grade efficiency curves could be made

for other operating and geometric vaciabJ.es but the discus­

sion becomes too exhaustivp. when a large number of data are

being analy?ed. At this point, it becomes cl~ar why it is

~aluable t have a theoretlcal model which accurately pre­

dict~ the grade efficiency curves ~ver a wide range of

operating conditions.

Compariaons With Predicted Grade Effi'::i1lDCY CUrves

The exper::~ntal grade efficiency data were com~arpd wi~h

tha predjctions of the models of Rosin et a~. (1937.), Lapple

(1951), Sproull (1970), Leith and Licht (197 2), Masin and

Koch (1986), Deitz (1981), anù Mothes and Laffler (1984,

1988) • r'lgure 4-18 shows the data obtained for one exper­

iment compared with the predictions of the theoretical ~od­

els- The legand shows the type of particle, \ohe experimen-

~

N

•

~ .... U .... Hi z o ....

~ 8

l00 l -~.~=~-•• .,....-- - - - ':':':":"ft ...................... ::: ·!lI. 1 - - -

/ ......... -..,..-.- --.. .. ..... ----- -;"...-- 'li __ .---. .---

00 L / ..... -;:;,-- __ .-r . __ .. ..,....-.

BOt- / j';:..---;>,/ .... ........... .... ~ ;'/ ,: ,

70l- // /,:1/ , .. ~./ , 1 : ,/

, ! : 1.

6Ol- 1,/,' /y 6Ol- ri / 1

1 .~

-10 l- -'1 ! .1l 3Ol- J ;: ft

\ //. . ," 2Ol- 1 I~r" 10 l- ?,~ ...

( .. ' ~

aL.' • '

• 5111 ca. 17 mie • 1836 K.

S/i2Q

3 g/m3 BI %

• Experlr:lllC"ltel Date ••••••• Roeln et cl. (IQ'J2) -. - LDp/lle ll96l) - - Sproull (1070) ---- Lai th 4 Llcht (\072) -Haaln 4 Koch (1084) ---- Del tz (W81l --- Mothes 4 Loffler (1B84)

a 2 4 6 8 10 12 1-1 PARTICLE srzE. pm

Figure (-18 Grade efficiency cu~ves showing comparison of experimental with prcdicted data for poor opcrating conditions.

~

-01 <D

160

tal run number, inlet velocity, dust load, inlet temperature

and overall collection efticiency. For this experiment,

there was wide disagreement amongst the predictions of the

various models, with th~ ~itz model agreeing best with the

experimental results.

Figure 4-19 is a similar plot for an experiment a~ room teM­

perature, with alumina. The hi1her particle density and low

temperature in this case lrsultcd in a higher overall col­

lection efficiency (93 %). Furthermore, the predicted grade

efficiency curves agrp.ed better th an in the previous case

and are cl oser to the experimental data. The curves pre­

dicted by the Leith and Licht Dodel and~' the Masin et al.

model were usually flattar th,m the other models .md usually

overpredicted the efficiencies in the small part1cle size

range. In general, it was found that the agreement amongst

the moè,ls was best under favorable operating conditions

(hi"" overall collection efficiency) and worst for poor

operating cor~itions.

C~Apariaona wit~ predicted OVerall Collection Efficiencieo

In ord9r to make a better comparis~n of how weIl the models

worked over a wide range of operating conditions, the pre­

dicted overall collect.on efriciencies and 50 % cut-sizes

~

N

•

~ I-t c.J

~ (5 ....

~

....... .:.:.::.:.:.. -'I:"'Z.---:""I.-----------~ . .;~.:_.a~", ,-IIIIt'lii __ " Z,,,""""':::" :,,"';I~' - - 11--.;....--.v~ '- ..... --- __ ' . ;;..- --. . ,' ....

1 ex}

00

80 'ft ./ /,.//

70 t- 1;' !4~" ''fIl Alunlna AA46

16 nt/a. 3 glm3

300 K. 03 r 60H / ~l 50 ri! ,IV • Experimentai Data 40 rI . ······Rosln et al. (1932)

'i -'-L~ple(I001) h ~ - - Sproull (1970)

~ ,t -"- Lei th 4 Llcht (1972)

~() i~ - Hasln 4 Koch (1984) ~ ----Caltz (1981)

10 .1/ --- Mothes 4 Loffler (1984)

OIJr~----~----~----~------~----~----~----~

30

o 2 4 6 8 to t2 14 PARTIa..e SIZe. f-IITI

Figure 4-19 Grade efficiency curves showing comparison of experimental with predicted data for good oparating conditions.

e'\

-'" o

162

were plotted against the experimentally determined values.

The original assucptions made in deriving each model was

used along with Masin and Koch's (1986) approximation to the

load correction of the API (1975), (equations 4-40 and

4-41).

A performance index similar to that used by Rudnick et al.

(1986) and Leith (1987), was used to asses how well the

models predicted the experimental overall collection effi-

ciencies. The efficiencies were transformed into the number

of transfer units (N) defined by:

N = -ln P (4-49)

where P is the penetration (1-e). This transformation

serves the purpose of giving equal weights to the same per­

centage differences at low and high efficiencies. Troe per­

formance index (PI) was defined for each model as:

PI = I(Nm-Np)2 ~ I(A2) ( 4-50) nm nm

where Hm and Np are the measured and pred~cted number of

transfer units, and nm is the number of measurements made.

The performance index can be shown to be made up of two

parts: the variance of Ais:

(

n-1 (I(â»2 n(n-1)

163

(4-51)

where â avg is the mean difference between Nm and Np. For

large n~, equations 4-50 and 4-51 qive:

(4-52)

This indicates that PI consists of a measure of t~e average

difference between Hm and Np (âavg2), and a measure of the

scatter about the parity line of the theory vs experiment

plot (oô 2 ). The ~erformance index varies inversely with the

>-ccuracy with which the ~odel predicts the data, so the best

mcdal should have the lowect index. The resuîting plots are

disc~ssed in the followinq sections and the performance

indices and regression coefficients are summarized in

Table 4-2. The colle~~ion ef~iciencie~ are plotted instead

of the penetrations si~ce collection efficiency is the more

~h~ Lcading Et!ect

7he experimental efficiency was plottp.d against the dust

0

164

TABLE 4-2

summary ot Pertormance Indices tor Collection Etticiency Modela

Model Method* R

Rosin et al. (1932) a) 0.325 b) 0.536 c) 0.511

Lapple (1951) a) 0.264 b) 0.524 c) 0.493

Sproull (1970) a) 0.142 b) 0.409 c) 0.293

Leith & Licht (1972) a) 0.544 b) 0.581 c) 0.700

Masin & Koch (1984) a) 0.544 b) 0.719 c) 0.701

Deitz (1979) a) 0.524 b) 0.644 c) 0.693

Mothes & Laffler (1984) a) 0.720 b) 0.742 c) 0.886

Modified Mothes & Laffler 0.892

* a) mod&l with no load correction b) model with API (1975) load correction

(eqn. 4-39) with A given by eqn. 4-40

PI

0.517 1.006 0.301

0.791 0.744 0.284

1.045 2.7911 2.224

0.261 1.448 0.380

0.261 0.231 0.377

0.694 0.790 0.214

0.451 0.816 0.089 0.085

c) model with API (1975) load correction and A = Ae (Fig. 4-20)

c

165

load on probability-log scales (as in the API study) giving

the graph shown in Figure 4-20. The general trend of effi­

ciency increasing with load was observed. The slope of the

regression line through the data was 0.26 and was taken as

the experimentally dete~ined load correction exponent (Ae).

The slope is dimensionless assuming that the reference load

is 1 g/m3 • The value of 0.26 for Ae compares with the

values determLned from equation 4-40 where A varied between

0.67 and 0.19 as the efficiency varied between 0 \ and

100 %. The performance index was usually lower when Ae was

used, compared to when the A from equation 4-40 was used

with the models tested.

The Rosin et al. Hodel

One of the main requirements for using the Rosin et al.

(1932) model is that the number of spirals made by the gas

in the cyclone must be Known. Particle deposition patterns

on the walls indicat~d that the gas made at least two rota­

tions in the upper part of the barrel and one to four more

turns close to the bot tom of the cone for a total of three

to six spirals. Equation 4-5 predicted that the number of

spirals would vary between 5.0 and 6.5 and equation 4-6 pre­

dicts 0.7 to 5.5 spirals for the range of flowrates used in

this study.

~

00.0

97.6 N

• ~ 00.0

t-4 U t-4

~OO.O

Z "0 o _

~OO.O 70.0

60.0

o alunlna cold <> .1 1 ICXJ co Id C alunlna hot - 1011 val • • "alunlna hot - hlgh val. + slllCXJ hot - 1011 vsl. • si 1 ICXJ hot - hlgh vol •

• o 0 •

• <> ----o • • <>~.....---.

• n c;-; <> -- -00 C C+

<>,

• • • + +

C

g

+

slope Cf\,) - 0.26

60.0 1 , , , ft , , , ft , , , t 1 0 , , , , , ft 1

0.3 1.0 10.0 100.0 300.0 INLET OOST LOAOING. g/m3

Figure 4-20 Experimentally measured collection effic!ency vs dust loading.

~

-Cl Cl

c

167

Figure 4-21a shows the experimenta1 overall collection effi­

ciencies plotted against the efficiency predicted by the

Rosin et al. model using the more fundamental equation (4-5)

to determine the number of spirals in the cyclone. The

loading effect was not taken into account in this figure.

We see that there was much scatter in the data and that the

predicted values were generally lower than the experimental

values. The performance index was 0.52.

The Hasin and Koch load correction model (equations 4-40 and

4-41) was used with the Rosin model to give the plot shown

in Fi~Jre 4-21b. This correction resulted in the calculated

efficiencies being higher than the experimental efficien­

cies. The agreement was better when the experimentally

determined Ae (0.26) was used instead of equation 4-40.

This is shown in Figure 4-21c where the performance index

was 0.43 in this case.

The Lapple model

The Lapple (1951) model was based on a normaljzed grade

efficiency plot (Figure 4-3) with the 50 t cut-size being

the same as that calculated for the Rosin et al. models.

The agreement betv~en the experimental and calculated effi-

e ~

100 1

cuolcna ~I.try

o CI - cold li! OO~ CI - hot

+ ca - hot N 'IJ. C3 - hot

• c C4 - cold

ti li C4 - hot

iD eo A-a .... R - 0.32 u PI - 0.62 ....

Hi

o .0(".61. IJ. Y II1II •••

Il 7--" (f/JO C • ~ + + IJ.

• - • 0.-(J C C

~. c+

~ 70

• y '" li q. l(-o _ Cl

00 ~

.... ~ Q.

IJ. li

00

00

o 0

'lJ CD C

60 ~K ___ .....L ___ --JL..-___ ..L-_

60 00 70 eo 00 100

EXPERltverrAL EFFIClEOCV. %

Figure 4-21a predicted vs experimental overall collection efficiency for the Rosin et al. (1932) model with no load correction.

~

lm. cuo1ona QlnlWtry OK lE lE.o'-~ ~

o CI - cold ~ fil; •

oo~ CI - hot

o lE-' '=1/+

+ C2 - hot .0 '. 7c:ff D

N A C3 - hot

OEA 0 0 0

ci 0 C4 - cold

0

• C4 - hot lE lE lE cV

§ 00 R - 0.64 lE • A;/ • D

8 PI - 1.01

~ 70~ // D

~ A

u .....

~ n. BO

A - 0.67 - 2.11Eo + 6.63EQ2 - 4.0E03

0060 00 70 8) 00 lm

E>.?ERltENTFl. EFFICIel::Y. %

Figure 4-2lb Predicted vs experimental overall collection eiCiciency for the Rosin et al. (1932) model with A.P.l. (1975) load correction.

~

-0> .D

@ ~

100 1

A - 0.26 lIE. lIO li( R - 0.51 . ~~ PI - 0.00

001-.. ~~. []

• 00" Q [] + + 11.~ ~

N ri' 016/ g"D + D • ~

lKl .... • 0 11&

ifi Il [] .... • U .... n/ o 0 lb li( []

fi) 70 Il cyolona 1-u geomatru ....

~ o CI - cold II( CI - hot n. 00 + c..~ - hot Il C3 - hot

[] [] C4 - cold • C4 - hot

1/ 60

60 00 70 lKl 00 \00

EXPERltENTFL EFFIClEOCY. %

Figure 4-21c Predicted vs experimental overall collection efficiency for Ro~in et al. (1932) model with A.P.I. (1975) load correction (A = 0.26)

-... 0

171

ciencies was again best when the experimentally determined

load exponent (Ae) was used with the load correction mod~l

of equation 4-39. The resulting plot is shown in Fig-

ure 4-22. Furthermore, the Lappl model predicted the

experimental data with roughly the same degree of accuracy

as the Rosin et al. model Figure 4-21c. The performance

indices were both around ~.3.

The sproull model

The predictions of the Sproull (1970) model (equation 4-9)

along with the load correction of equation 4-39 and Ae are

shown in Figure 4-23. In thi~ case, the efficiencies calcu­

lated for runs at high temperatures were distinctly higher

than the e~~erimental values. On the other hnnd the room

temperature predictions agreed rensonably well with the

experimental data. The large deviations at high lempera­

tures we~e due to the higher velocities (for a given mass

flowrate) being squared in equation 4-9a.

The Leith and Licht model

Th~ efficiencies predicted by the Leith and Licht (1972)

model (equation 4-12) with the load correction of equation

~ ~

100 1

A - 0.26 R - 0 • ..0 -Jt9/ • PI - 0.28

001- · ~.O •••• "!..~ •• N o.... ~ + +

"~80 + •

~ o· 0 0 0 eo •• 0 • ..... . A 0 [leP 0 u • .....

~ • 0. 0 70

~ 0 cyclone

A geaœtry .. ~ --

~ OCt - cold • CI - hot a.. 00 + C2 - hot

0 A C3 - hot o C4 - cold • C4 - hot

1/ 60

60 00 70 80 00 100

EXPERUENTfl. s=FIClel:Y. %

Figure 4-22 Predicted vs experimental overall collectior. efficiency for La~ple (1951) model with A.P.l. (1975) load correction (A = 0.26).

-" 1\)

e ~

100, li li li( ~p. r+ill1 +

A - 0.26 .... V R - 0.29 li il 0 PI -~2.22 ~ li 0 C

-. li OO~ ;e 001- li o 0 C li o 0 :r ..

J o c

o 0 •

t n/ 0

m c c .... u .... lb

70

~ c

c:uolone gaanatry ....

m OCt - cold li CI - hot

0- 00 + C2 - hot ~ C3 - hot C C4 - cold • C4 - hot

1/ 60

100 60 00 70 00 00

EXPERItENTFL EFFIClEOCV. %

Fig. 4-23 Predicted vs experimental overall collection efficiency for Sproull (1970) model with A.P.l. (1975) load correction (A D 0.26).

-'" (..)

lU

4-39 are shown in Figures 4-24. The agreement b9tween the

calculated and experimental values were not as good as with

the Rosin et al. and the Lapple models. The Licht and Leith

model tended to overestimate the collection efficiency at

both low and high temperatures.

The Hasin end Koch model

Figure 4-25 shows the results obtained with the Hasin and

Koch (1984) model (equation 4-43). The load correction in

this case was given by equation 4-39 and was accompanied by

a saltation correction as discussed in the literature

review. These corrections tended to overestimate the col­

lection effic.Jncies when either A (from equation 4-40) or

the experimentally determined Ae (0.26) was used.

The Deitz model

The graph obtained from the Deitz (1981) model (equa-

tion ~-20) along with the load correction of equation 4-39

is shown in Figure 4-26. The load-corrected efficiencies

obtained with either the calculated A (equation 4-40) or the

experimental Ae (0.26) was better than for the other models

discussed so far. This was not surprising since this model

o 0

100 1

A - 0.26

• Il ~~~11 + R - 0.70 PI • 0.38 Il lB~ • Il Il Il i\'llltllElflI(i P+ 0 001- ($> • .e Pt. 9>. C/

N ~II • ~ A ~ 0

• Il A O~~ • ~

Il 80 • t-4 A u

t-4

~

~ 70

CUOICX'l9 geallstry

t-4

~ o CI - cold • CI - hot Il.. 00 + C2 - hot A C3 - hot DC4-cold • C4 - hot

1/ 60

50 00 70 80 00 100 EXPERltENTFl. s=FICIENCY. %

Figure 4-24 Predicted vs experim~ntal overall efficiency for Leith & Licht (1972) modal with A.P.I. (1975) load correction (A a 0.26).

-.... (Il

~

100 1

CllPIc:v-. get F 1 ti'\l

o CI - cold • 00 f.W CI - hot

+ C2 - hot .. .A C3 - hot

• D C4 - oold

~ • C4 - hot • 80

R - ~.72 • M u PI - 0.23 M

~

~ 70r /'

M

~ eo"

A - 0.87 - 2.IIEa + 5.C3EQe - 4.0e03

mK ~

m eo 70 80 00 100 EXPERllENTFL EFFICIecV. %

Figure 4-25 Predicted vs experimontal overall efficiency for Masin & Koch (1984) model with A.P.l. (1975) load correction. (A - 0.26).

~

-" C1l

~

100 1

A - 0.2C 0 R - 0.e9 :<J~ll PI - 0.21

001-IIi

VO 0

Il 1l0~~~ ~ N Il.':8>0++ • o ~ 1l0' 0 Il

~ Oll 1l~~1l0 • ao t-t 0ll :QA 0+ u IV t-t :/ . ~

70 Il 0

m A • CUOlone u ()QOmBtry t-t

~ OCI - cold • Il CI - hot 0... :rl + C2 - hot

0 A C3 - hot o C4 - cold • C4 - hot

1/ 60

60 00 70 ao 00 100 EXPERltENTfL EFFICIEflCV. %

Figure 4-26 Predicted vs experimcntal overall efficiency for the Deitz (1981) model with A.P.l. (1975) load correction (A a 0.26).

o

-.... ....

178

takes into account some of the inconsistencies of previous

models as discussed earlier. However, it was observed that

the efficiencies calculated for the runs with the small

diamgter gas outlet (C2 and C4) were noticeably lower than

for the larger diameter outlet. At this point, this was not

too much of a concern since the larger diameter is the more

standard size for cyclonen.

The Hothes and Lottler model

Figure 4-27 shows the collection efficiencies predicted by

the Mothes and Loffler (1984, 1988) model plotted against

the experimentally determined values. This model was given

as equations 4-24 to 4-36 in this chapter. ~~~tion 4-39

was again used for the load correction nlong with Ae' The

agreement between the calculated and experimental values was

better than for the,other models. as reflected in the lower

performance index of 0.089.

Several ~odifications were m~de in an attempt to improve the

predictions of the original Mothes and Loffler model. , "

Firstly, it was shown in Chapter 3 that Mothes and Loffler

used a tangential vclocity model (equation 3-9) that consis­

tently over-estimated the velocities measured in the present

study. The Mothes and Loffler velocity model was thus

8 0

\00 1

A - 0.28 R - 0.89 :~~iI + PI - 0.089 ,. .

001- ~ .~~.~QJI .Q~"9> + N

0°· .'i (~o. •

~ 80

o~~ H U • II H

~ 70

~ Il CUOlcna gaonat l1l

H

~ OCI - cold • CI - hot

D- 00 • + C2 - hot Il C3 - hot II C4 - cold • C4 - hot.

t/ 60

60 00 70 80 00 100 EXt~ItENTfl.. EFFICIBCV. %

Fig. 4-27 Predicted vs experimental overall efficiency for the Mothes & Loffler (1984) model with A.P.l. (1975) load correction (A a 0.26).

, , ,

" ,

,

oc • ,

, " " ,

, "

" • >

" .. • \

~

' ~ .. " , ,

c

180

replaced with the one derived from the experimental data

obtained in this study (equation 3-22). Alexander's models

(equ~tions 3-2 and 3-5) were used to calculate the vortex

exponent and the tangential velocit~' at the boundary between

the inner core and the outer vortex. The diameter of this

boundary was taken to be 0.75 of the outlet duct diameter,

instead of the actual outlet diameter.

Another modification was to calculate the particle diffusi­

vit Y instead of using a fixed assumed value. Mothes and

Laffler estimated that the particle diffusivity was between

0.00625 and 0.2, with a value of 0.0125 working best with

'cheir data. This was cOIr:lared with the range of 0.05 to

0.01 found by Abrahamson (1981). Weinstock (1978) showed

that the particle turbulent diffusion coefficient could be

given by the expression:

[m-l]vo'Lo

Dt = m 4'11°.5 (4-53)

where m is a constant taken as 5/3, vo ' is the root Mean

square fluctuating velocity and Lo is the outer scale length

of the turbulence. Abrahamson (1981) showed that vo ' could

be taken as approximately O.lvtw and 10 as 'IIrc. He also

showed that for the particle sizes used in this study, we

can ignore the correction for diffusivities of larger par-

181

ticles which do not follow the gas flow completely. These

relationships were used to calculate the particle diffusi­

vit Y for each expcriment. The calculated values ranged from

0.004 to 0.04 under the experimental conditions used in this

study.

The modifications discussed above were applied to the Mothes

and Laffler model and used along with the A.P.l. (1975) load

correction (equation 4-39). Figurs 4-28 shows that the data

was symmetrically distributed about the parity line and

there was no segregation of the data according to cyclone

geometry or operating temperature. The maximum deviation

between predicted and experimental efficiencies was around

8 %, which was reasonable considering the complexity of the

flow within the cyclone and the wide range of operating con­

ditions. The performance index was 0.085. These factors

make the modified Mothes and Laffler model the most success­

ful of the models tested for predicting the overall collec­

tion effiencies in this study.

SUHHARY

The conclusions drawn from the experimental study regarding

the collection efficiency dnd cut-size are summarized as

~ ~

100 1

A - 0.26 Rf - 0.89 .~~rr .. + PI - 0.1:85

001- ""'IVoy • of

•• ·C};D ... ;~cl1I N • .L{~(p + • o Of!

~ 80 o· -Vo!!'·01 .... O· li" A u .... _/ D

~ ~

70 A CUOlone

gElaIIBt ru 1 U .... o CI - cold

~ • • CI - hot 80 + C2 - hot

A C3 - hot D C4 - cold • C4 - hot

1/ 60

60 80 70 80 00 100 1-'D?6813c EXPERltENTFL EFFICIBCY. %

Fig. 4-28 Predicted vs experimental overall efficiency for a modified Mothes & Loffler (1984) model with A.P.l. (1975) load correction (A = 0.26).

-Cl> -~

182

follows:

1) The overall collection efficiency varied inversely vith

temperature for the same inlet velocity and dust load.

This can be attributed to the increase in viscosity with

temperature.

2) The efficiency increased with dust load and the load effect

was stronger at high temperature than at low tempera-

ture. The load effect was also strongest at low loads

and decreased as the load increased.

3) The efficiencies obtained with the smaller diameter

!2.54 cm) outlet were about 5 to 10 % h!gher than with

the larger (5.08 cm) outlet.

4) There was generally wide disagreement amongst the pre­

dictions of the theoret.l.,.al models for the same operat­

ing conditions. The ClJ.sa'Jreement was widest for poor

operating conditions (low collection efficiencies).

5) The best agreement between calculated and experimental

collection efficiencies was obtained v.lt~ the ~othes and

Loffler (1984, 1988) model. The agreement vas improved

when t.he model was modified to include some of the

results obtained in this study.

<,

CHAPTER 5

CYCLONE PRPoSSURE DROP STUDY

c

~~ER5

CYCLONE PRESSURE DROP STODY

LITERATORE REVIEW

The cyclone pressure drop is one of the important factors

that determines the operating co st of cyclones. The pres­

sure drop is usually expressed as the number of inlet velo­

city heads (NH) where the inlet velocity head is defined as

(PfVi 2f2), where [pf ~ Pg + Cv(pp-Pg)] and Cv is the volume

of dust per unit volume of gas, thus:

(5-1)

Licht (1980) summarized the phenomena that contribute to the

total pressure drop across the cyclone as follows:

1. Loss due to frictional flow in the entrance duct.

2. Exit loss due to the sudden expa~sion of the gas stream from the inlet duct into,the barrel.

3. Friction loss at the walls in the body of the cyclone.

4. Kinetic energy loss due to turbulence within the cyclone.

•

c

185

5. Entrance loss due to the sudden contraction of the gas stream at the entrance to the exit duct.

6. Static he ad loss due to the difference in elevation between the inlet and outlet ducts.

7. Recovery of energy in the.outlet duct.

8. Loss duc to frictional flow '~rough the outlet duct.

The kinetic energy losses (4) are usually the most important

and most models are developed around this. The operating

temperature is not usually considered explicitly but is

taken into account through the variables that it aff~cts

(for example the gas density and viscosity).

Perhaps the most cited study of pressure drop in cyclones

was that of Shepherd and Lapple (1939, 1940), who used a

30 cm glass cyclone of conventional design. They studied

the effects of cyclone size, dust loading, cyclone geometry

and internaI modifications (baffles and vanes for example)

on the cyclone pressure drop. Impact and static pressures

were measured in the cyclone with a Pitot proba consisting

of two adjacent 2.0 mm i.d. copper tubes • •

Shepherd and Lapple found that the pressure drop for a given

cyclone arrangement, when expressed in terms of inlet velo-

186

city heads (Na), was independent of gas flowrate. The same

study found that the cyclone friction loss increased when

the inlet width, inlet height and exit duct length were

increased. In contrast, the pressure drop decreased with

increased exit duct diameter, and increased dust loading.

straightening vanes inserted in the exit duct and extended

below it, ~lso reduced the pressure drop whereas, baffles

placed below the exit duct usually resulted in an increase

in the pressure drop across the cyclone. The effects of

these variables on the collection efficiency were not dis-

cussed by the authors.

Shephord and Lapple supported their experimental str1y with

a theoretical treatment of the pressure drop in the cyclone:

starting with the Bernoulli theorem, the pressure drop

acroes the cyclone expressed as number of velocity heads

(Na) was given by:

(5-2)

wher~ Fcv is the friction loss factor associated with the

cyclone barrel, Fev is that in the exit duct, Ai and Ao are

the inlet and outlet areas respectively. Fev can be evalu­

ated f.rom the Fanning equation and was given by:

c

4 fLe [Ai] 2 Fev = -- --de Ao

187

(5-3)

where "f" may be read from an appropriate curve or may be

assumed to be 0.005 for normal cyclone operating conditions.

Le and de are the equivalent length and diameter of the exit

duct respectively. It was assumed that the frictior loss

factor in the cyclone (Fcv) was equivalent to the energy

required to produce the high velocity inner vortex observed

in reverse flow cyclones. Assuming negligible entrance

los ses and the vortex law exponent (n) equal to 0.5,

together with a correlation of their experimental data,

Shepherd and Lapple obtained the expression:

(5-4)

where kwas 7.5 when an inlet vane was used and 16 without

the inlet vane. Substituting equations 5-3 and 5-4 into

equation 5-2 resulted in the expression:

(5-5)

This model is one of the standard models used for the theo-

o

188

retical treatment of pressure drop in cyclones and is often

approximated by using only the first term on the right hand

side of the equation.

staircand (1949) did a theoretical de~lvation of the pres­

sure drop in a cyclone considering los ses i~ the inlet, the

cyclone and the exit duct. The three components combine to

give the total pressure loss according to the expression:

(5-6)

where ~ is the ratio of the tangential velocity at ~he mean

inlet radius to the mean inlet velocity and was given by:

(5-7)

where As is the inlet area, As is the surface area exposed

to the rotating gas and f is the friction factor. 9 was

calculated to be approximately 0.5 and 0.4 for the 2.54 cm

and 5.08 diameter gas outlets for the cyclones used in this

study.

Ter Linden (1949) measured static and total pressures in a

cyclone (diameter not given) a .. d obtained the profiles shown

c

169

,.

in Figure 5-1. These ~rofiles show that the pressure was , .

high throughout t~e cyclone except for a core of low pres-

sure in the center of the cyclone. The lo~ pressure core

extended the full length of the cyclone into the dust bun~er

and was roughly 0.4 times the diameter of the gas exit duct.

The low pressure existing in the dust collection bin (or

outlet valve) is important since if it is not air tight, air

would be drawn into the bottom of the cyclone, carrying dust

with it and thus lowering ~~e collection efficiency. Ter

Linden did not give a mathematical model to describe the

observed pressure distributions.

Alexander (1949, 1950) developed a model based on the theory

that the cyclone pressure drop is due ta the sum of the

energy losses by gas in passing between the wall and exit

radii, and the energy lost ln the outgoing gas. The first

component was in turn made up of the difference between two

elements: 1) the pressure difference between a layer of gas

at the wall, and a layer of gas at the outlet radius (poten­

tial energy); and 2) the difference in velocity (kinetic)

energy between the wall and the outlet radius. The energy

lost in the outgoing gas was also made up of two components:

1) the energy lost by the gas in going from the outlet

radius to a smaller radius r; and 2) the ro~ational ener~l

of the gas contained within the outlet radius.

Figure :3-1

STAnc: na:uat., "' YUOCTT_'·U t1(TI.(J l'II SIC.I

1 •

• INUT 1

190,

, L __ q

srArc n~i-----=:=m~==-----: +to l1It. fNATlI. 4

vtlOCTT-10·' tUTlU tu SIC.

\ • • • • • • \ \

DUST CUIUT

/ / 1

Toul a:>d Satie P=su:cs al Dilf=l Poicu iD • Cyclone

---Swic~ -:.---- ToaJ p=

Total and static pressure profiles measured by ter Linden (1949).

c

191

The resulting model derived by Alexander for pressure drop

expressed as number of wall velocity heads (NHw) was:

(5-8)

fA is a factor accounting for the energy loss in the out­

going gas and varies between 1.9 and 2.4 as the vortex expo­

nent (n) varies between zero and 0.8. The wall velocity was

shown to be approximately 2.15[Ai/(dcde)]0.5 times the inlet

velocity, so the right hand side of the equation should be

multiplied by 4.62[Ai/(dcdel] to obtain thp. number of inlet

velocity heads.

The American petroleum Institute (API, 1975), used a model

in which the total pressure drop was considered ta be made

up of five components:

1. Inlet contraction loss.

2. Solids contraction loss.

3. Barrel loss.

4. ReversaI loss.

5. Exit contraction loss.

The first two components apply to cyclones which are

immersed in a vessel such as above a fluidized bed combus-

192

tor. The inlet contraction loss was given as:

(5-9)

where kl is a function of the ratio of the cyclone inlet ... area to the external vessel area, and is approximately 0.5

for a ratio uf zero. The solid~ acr.eleration loss depends

on the dust load (Ca~ and was givcn as:

(5-10)

The particle velaci.c.ies in the inlet (vpi) and in the

external vessel (vpv) are usually taken as the gas velocity

for fine particles.

The barrel loss (dPb) was taken as the equivalent of the

straight -;lpe loss evaluated at the inlet velocity (Vi),

with the diameter being the inlet hydraulic diameter (dH)'

and the length being that described by Ns rotations of the

gas around the barrel, thus:

(5-11)

where i is the Fanning friction factor with the Reynolds

c

c

193

number evaluated at the inlet conditions.

The reversaI head loss is due to the flow going from the

barrel to the exit pipe and was taken as one inlet velocity

head:

(5-12)

The exit contraction loss is the difference between the

velocity head based or. the superficial velocity through the

barrel cross-section (PgVb2/2), and that in the exit pipe

(PgVe2/2), and was given by:

with k1 in this case being a function of the ratio of the

cyclone cross-sectional area to the exit duct area.

Masin and Koch (1986} gave a working form of the API model

as:

(5-14)

194

CasaI and Hartinez-Benet (1982) did a statistical analysis

of published experimental data to derive the following equa-

tion for the pressure drop across the cyclone based on the

number of inlet velocity hcads:

[A. ] 2

NH = 11.3 d:2 + 3.33 inlet velocity heads (5-15)

This expression is similar to the simplified Shepherd and

Lapple model but with the number of velocity heads given a

non-zero intercept. The model was claimed to fit the

selected data better than more complicated expressions given

for example by Shepherd and Lapple (1939), Stairmand (1949),

and Alexander (1949).

Masin and Koch (1986) recommended using the Shepherd and

Lapple (1939) or the CasaI and Martinez-Benet (1982) models

for pressure drops up to 0.2 Pa. For higher pressure drops,

they suggested using the API (1975) model modified so that

the maximum change in vclocity was considered for calcul at­

ing the expansion or contraction losses. This was done by

using the greater of the in let or outlet velocity to deter­

mine the friction factor, and by replacing the first term in

equation 5-14 with (l+Pg).

Wheeldon et al. (1986) analyzed their data by defining the

c.

c

195

pressure drop in terms of the velocity in the body of the

cyclone (vb) and the Euler number (Eu), where Eu is the

number of barrel velocity heads:

1 dP = EU0'2PgVb2 (5-16)

with

vb = 4Qv

(5-16a) ?Id 2 c

They added a term to the Shepherd and Lapple (1939) model to

account for the height of the cyclone, and showed that the

Euler number under zero load (Elle)' could be estimated by

the expression:

(5-17)

The constant in this equation was based on an Euler number

of 320 for the standard Stairmand (1949) high efficiency

cyclone. Equation 5-17 predicted an Euler number of 535 for

both the primary and secondary cyclones used in the Wheeldon

et al. study. On the other hand, the experimental data

yielded values of 296 for the primaries and 534 for the sec­

ondaries even though both sets were geometrically similar.

The low value for the primaries was attributed to the higher

o

196

dust loadings going into these units.

The Effect of Dust Load on Pressure Drop

It hag ge~€rally been found that the pressure drop decreases

as the inlet dust load is increased (Kriegel, 1968; Knowl­

ton and Bachovchin, 1977; Bryant et al., 1983). This is

contrary to the effect whereby the effective gas density

increases with dust load and should cause a corresponding

increase in the pressure drop. The observed pressure drop

reduction must therefore be exp1ained by other phenomena.

One factor is that increasing the dust load is usua1ly

accompanied by an increase in the overall collection effi­

ciency. Consequently, there are fewer particles in the out­

let gas stream so the energy loss in the outlet region is

lower and results in lower pressure drops ~t high inlet dust

loads.

Sproull (1966) used an analysis of pressure drop in a pipe

described by Fanning's equation:

dP = p v 2 -f~ dx

2rH (5-18)

(

197

Replacing f with data from Moody (1944), this equation

was given as:

(5-19)

where ks is a constant, dl 3S the pipe diameter and x is the

length of the pipe. If dust is added to the gas for a fixed

flowrate, then only the density (Pg) and viscosity (p) ~ould

be affected. Since the added dust increases the effective

density, then the observed pressure drop reduction must be

due to a decrease in the effective gas viscosity. Equa­

tion 5-19 was used to generate the plot ~f viscosity vs du st

loading shown in Figure 5-2. An empirical expression was

given by equation 4-42 for the visccsity-Ioad effect.

Barth (1956) and Muschelknautz (1967, 1970) attributed the

reduction in pressure drop to the increase in the fricticn

factor at thR walls, and the consequent decrease in the tan­

gential velocities in thR cyclone. Experimental studies by

Yuu et al. (1978) founr éhat in general, the pressure 6rop

was lowered by 35 % for loads between 0.2 and 50 g/m3 and by

larger amounts above 50 g/m3 (Figure 5-3a). This trend was

linked to the observation that at low loads, the uarticles

which stuck to the walls, w~re confined to a small area of

the ~alls, whereas at higher loads, this area suddenly

~~

0

-10

N \

• -20 z a {"6 .~" ... ti ::l

-~ ID 1 ?:

1, 1.3

~

... -40 B

x

U) ~ 1.1 ~ ... • > hl 1 ... > 0.91" -1-60

0.7' '-00 o 60 100 160 200 260

ruST LORD. l;J/"~

Figure 5-2 Variation of pressure drop reduction with dust load (Sproull, 1966).

~

-Il) ())

-'

c

c

199

widened to cover the entire cyclone barrel.

Yuu et al. (1978) also showed that the pressure drop

decreased as the inlet velocity was increased up to 10 mIs

then remained constant at ~igher velocities. It was post­

ulated that the amount of particles sticking to the walls

varied directly with the inlet veloc:ty. The measured

radial profiles of tangential velocity varied inversely with

dust load (Figure 5-3b) and it was shown that the velocities

outside of the wall region, were lowered when the walls were

deliberately coated with particles and dust-free air was

passed through the cyclone (Figure 5-3c).

Briggs (1946) showed that for a constant '·olumetric flow­

rate, the pressure drop varied with dust load according to

the expression:

(5-20)

with Ca beinq the du st lo~d in g/m3 and dPo the pressure

drop at zero load. Masin and Koch (1986) used a similar

load correction while Wheeldon et al. (1986) used an expres­

sion of a simiiar form but with constants proposed by Smo­

lik (1975):

(5-21)

1.0

0.7 r~ .

t-~

• . •

• • • . . • • 6

200

. . ... ~ '-' • . . ..... • Ui -20nys

1 •• · ... ·1 t ..... /d .64 !-... -. "&t·-• 1IC .... ~ -..: XXI:(

Sig ... Maten~1 10 ... 1"",1 '.(q/ml • e., · , o ,P.V.C.Powderl ·163 A 1 Fly ôISh i 27 " 1 Mang.nese 1 18 .

OJQ2'OJ 0.5 0.7 1 2 3

u.leOCmI.,

• ! :5

°o~----'-i~~--~;-----~ re ... , u, YS , (U,· 11.0 =1 ... ).

1.33 a? 2.00

0(" cl?" 4.37

• • , •• li • · 5 7 10 20 30 50 70 100 200 JOO C (gtm'l

" YS C.

"

la

-­. .,.. "\i •

o 50 r ("""1 IQCI r.4

Dis<n'boéoo ::( ...... :éo;I.doœa il lino aac&o

Figu:-:e 5-3 Variation of pressure drop ratio and velocity profiles with dust load (Yuu et al. 1978).

,

c

c

201

The difference between the pressure drop (or Euler number)

ratios predicted by equations 5-20 and 5-21 increases with

load. For example, below 0.1 g/m3 both equations give a

ratio of close to one whereas at 100 g/m3 equation 5-20

gives a ratio of ~.5 and equation 5-21 gives 0.91. The

Briggs model (equation 5-20) has been used extensively, and

gives a more conservative estimate of the pressure drop.

The loading effect could also be affected by the size dis­

tribution of the dust. This can happen due to agglomeration

and settling of the particles for example. Sproull (1966)

mentioned that a coarse dust is less effective than a fine

dust at the same concentration in reducing the friction

factor or the effective viscosity of the gas.

EXPERIMENTAL RESULTS AND DISCUSSION

The pressure drop across the cyclone was measured in each

experiment as described in Chapter 2. The measured pressure

drops ranged from 50 to 2 700 Pa and are listed with the

experimental data in Tables A1-1 to Al-5 of Appendix 1. The

data were analyzed in terms of the Euler number in a way

similar to Wheeldon et al. (1986). The measured pressure

drops were then compared with the predictions of models by

202

Shepherd and Lapple (1939,1940), Alexander (1949), cas al and

Martinez (1~82), Masin and Koch (1986) and Whee1don et al.

(1986). The load effect was accounted for by the Briggs'

(1946) expression (equation 5-20), and by "the Smolik (1975)

model (equation 5-21).

Ana1ysis of the Eu1ar HUmber

The Euler numbers defined by equation 5-16 were calculated

from equation 5-17 to vary between 271 and 1219 for the

cyclone configurations used in this study. These values are

listed in column 2 of Table 5-1. In comparison, the expe­

rimentally determined zcro-load Euler numbers (EUe> varied

between 199 and 722 (column 3 of TaDle 5-1).

The experimental Euler numbers were determined by plotting

the cyclone pressure drop against the pressure drop associ­

ated witn one barrel velocity head, and measuring the slope

of the regression line for each cyclone geometry. Fig-

ure 5-4 shows the plot obtained with the cyclone under dust­

free conditions while Figure 5-5 shows the plot obtained

with the dust-laden gas. These figures show that the Euler

numbers were higher for the smaller diameter gas outlets (C2

and C4) and that the length of the gas outlet affected the

Euler number.

~ ~

'l'AB LB 5-1

COKPARISON OP BULBR NUKBBRS

ZERO-LOAD (EUC> MEAN WITH LOAD

Eqn. 5-17 Fig. 5-4 Eqn. 5-22 Fig. 5-5

stairmand (1949) 320 206

'" Whooldon ot al. (1986) 0 Co>

primarios 545 352 296

Socondarios 545 352 534

This study - Cl 305 238 197 202

C2 1219 646 787 540

C3 271 199 175 153

C4 1083 722 698 622

o

:nxl

i 2600 •

~2CXX)

1600

ce ~Ioo)

m~

1 CUO lone gaometru o CI -ce AC3 lIE C4

00-"'" o 1 2 3 4 6 6 7 a 0 10 8ffiREL vaOCITY I-EAO. Pa

Figuro 5-4 variat:ion of proDDuro drop wit:h barrol volocit:y hoad tor dUDt:-troo tlow.

~

.. o ~

~

:DX). } }

cE 2600 •

~2(XX)

WI&D 0.

œ ~ICXXJ

cuolarw gea.try

o CI -C2 AC3 lIEC4

îlE

lIE

lIE §

600 ~ ,Ji) _~ ~ ~ 0

o/; .. ~. ." ·

1 o

:Eu-640

o

•

o 1 2 3 4 6 6 7 8 9 10 a:F.R8.. vaOCITY I-ERJ. Pa

Figuro 5-5 Variation of rt'oDGUrO drop with barX'ol volocity hoad for dUDt-lndon gaG.

~

N o ln

., 206

A more general way to determine the zero-load Euler number

(Eue) was by fitting the right han~ side of equation 5-17 to

the experimental data. This was done by plotting the zero­

load pressure drop against the group of variables on the

right-hand side of equation 5-17 and measurinq the slope of

the regression line (Figure 5-6). The slope was 18 so the

resulting equation was:

(5-22)

The new set of zero-load Euler numbers (Eue) predieted by

equation 5-22 are given in eolumn 4 of Table 5-1.

Taking the dust loading into aeeount, equation 5-20 ean be

rewritten in the form:

(5-23)

thus a plot of [l-Eu/Eue ] versus Ca on log-log eoordinates

should yield a straight line with a slope of nbn and an

intereept nan• Figure 5-7 shows this plot with the exper-\

imental regression line shown as the sol id line with the . , equation:

~

HXX) 1

CUOIa-. 0011- g.DII.try

Eml- o CI I::.œ

! 700L cc) 1( CC

fXX)

~003 r:l

400

:m

ZOCI

lOCI

rJ a la

Cl>~ ,'" _,of

II(

1(

1(

1::.

B'N', .. trlo do do dol! do paranetlllr - ba ha dei ZI+ZZ-S

20 30 40 GEOtETRIC PARREfER

60

Figure 5-6 Variation of zero-load Euler numbor with cyclono goomotric parametcr.

~

'" ~

o

....

i

2.001r---------------------------------------~

1.00

cuoltnl .,......try

OCI - oold lIE CI - hot +C2 - hot AC3 - hot Il C4 - oold • C4 - hot

• lIE ... (fll lIE +" A A .... ,

"'-~+~ lIE- ...... ~ •

lIE OQ,~ lb ....... . • (j Il ..... .

Il .' + .. ' .!.. 0.10

0.'31

_.~_O.~ c ....

• • . ....... 0·'6 , Il •••••••••• ~ .....

\~~- .

... ... ...'"

0:' ......... tI:.o ......

O$Y,'" # ...... lIE

~ ... ",

...... \' ...... ...... ... .' .' •••• . ...

.... . ' .' .' .' .' .... .... .. '

.' ~ .... o-..... .,. . ... ~. .' .' ....... , .. ·····0

.... 0.01 l , ft , r' ,.- ft ft , , ft , ft , , , ft ft , , 1

0.6 1.0 10.0 100.0 600.0 II'LET OOST LORJ. glm3

Figure 5-7 Variation of Euler number ratio with dust load.

~

~ o 0>

,

c

209

(5-24)

The dotted line in Figure 5-7 was obtained from the Brjggs ,

(1945) equation (5-20), while the broken line represents the

Wheeldon et al. (1986) model (equation 5-21). The plot

shows that there was much scatter in the data and that the

Wheeldon et al. model would predict the performance with

roughly the same degree of accuracy as the experimental

regression line. The Briggs model on the other hand gives a

more conservative estimate of the load effect as mentioned

earlier.

Predicted vs Exp~rimenta1 pressure Drops

The evaluation of the models was completed by plotting the

predicted pressure drop against the experimental pressure

drop on log-log scales. A performance index similar to that

described in Chapter 4 (equations 4-49 to 4-52) was used to

measure the agreement between the experimental data and the

predictions of the theoretical models. The ca1culated per­

formance indices are summarized in Table 5-2 along with the

me an deviation squared and the variance. The devlation is a

measure of the distribution about the parity line while the

variance is a measure of the scatter in the data.

210.

o TA3LE 5·2

SUl'l'l'lary of Perforlllnce Indices for Prnsure Drop Models

Wl>El FIGURE tJ.2 0 2 PERFORAANCE NO. INDEX

~eeldon et .1. (1986) 5·a 0.0606 0.1304 0.1909 (equotlons 5·17 and 5·21)

Ma.ln , Koch (1986) 5·9 0.2712 0.3278 0.5990 (equotlons 5·14 and 5·20)

Shepherd , lapple (1939, 1940) 5·10 0.5223 0.1577 0.6799 (equotlons 5·5 and 5·20)

Ca.al , Martlnez·Benet (1982) 5·11 0.3778 0.2844 0.6622 (equotlons 5·15 and 5·20)

Stalnoond (1949) 5·12 0.3098 0.1214 0.4312 (equotlons 5·6 and 5·20)

Ale.onder (1949) 5·13 0.0407 0.0952 0.1359 (equotlons 5·a and 5·20)

ExperimentaI model 1 5·14 0.0029 0.0816 0.0845 (<qUItlon 5·24, Fig 5·4)

ExperimentaI DOdeI 2 5·15 0.0060 0.0816 0.0925 (equotlons 5·22 and 5·24)

c

211

Figure 5-8 sho~s the experiment~lly determined pressure drop

plotted agalnst the pressure drop predicted by the models

used by Wheeldon et al. (1936). These were given as equa­

tion 5-17 along with the load correcti~n given by equa-

tion 5-21. The figure shows tha~ the pressure drops were

reasonably weIl predicted but with a tendency fo!" the :>re­

dicted values to be higher than the experimental values. The

largest deviations occurred for runs with high du st loads,

in which case equation 5-21 predicted large decreases in the

pressure drop due to the dust loading.

It can also be seen that ~ost of the room temperature pre­

di,ctions agrep.d excellently with the experimental values

while the high temperature predictions wece generally higher

than the experimental values. The high predictions cou Id be

due to two factors: firstly, at high temperatur~s the velo­

cities ",ere hiq~er for the same mass flowrates so t. ... 2 c:t1cu­

lated number of velocity heads were much higher. Secondly,

the du~t load decreased at higher temperatures (for the same

mass fl,wrates) so the calculated Euler numbers were gener­

ally t. tc;'her fct' the high temperature runs. The performance

index was 0.19 with the scatter in the data (variance) being

higher than the deviation from the patity line.

Figure 5-9 shows a similar plot for the pressure drops pre-

c

lOOllO~ 71

~ •

& 151CXX1

~ § 100

1

CUCllona g.cmat.ry

OC1 - cold .C1 - hot +œ - hot 11 C3 - hot CC4 - cold • C4 - hot

•• o~ • '" y

li( I_~

11 • ! ~é-(J1f" ~)..r0

J.!-,~6 I~:~/o

L.~O li( _ 1~"'A 0

0- 0 cg 0 70 -o

IOV '!'l''' ",t", ",'

la 100 ICXX1 10CXX1 EXPERltENTFL PRESSl..RE œtF. Pa

Figare 5-8 Comparison of experimental data with pressure drop predicted by the Wheeldon et al. (1986) model.

o

,.. -,..

~

J(XY.Xh 71

.f • es

P.ilOOl

~ Œ

§ 100

ID ~

cuolona gIICI.etry

OCt - oold lE Ct - hot +C2 - hot AC3 - hot CC4 - oold .C4 - ho~ ... **- li(

A .- ... ~!fl •• CC

/i-.. CI) • C . IllE "'.r.tI + al>

jt/lt:P+ 00

li( ii:l~ ! C C

0<0000

o C QI

oC)

IO~V---~~~~~~--~--~~~~~--~~~~~-u

10 100 1000 10000 EXPERlt-ENTfL PRESSl..R: œlF. Pa

Figure 5-9 comparison of experimcntal data with pressure drop predicted by the Masin and Koch (1986) model.

~

N -w

214

dicted by the Hasin and Koch (1986) version of the

API (1975) mode1 (equation 5-14). In t~is case, the loading

effect was accounted for by the model \~sed by Hasin & Koch

(equation 5-20). The scatter in thir. plot was more than

with the Wheeldon et al. model, and in most cases the pre­

dicted values were lower than the experimental values. The

performance index was higher in this case (0.60) and both

the deviaticn and the variance were high. The discrepancy

betw~en the calculated values at low and high temperatures

was more noticeable in this case.

Figure 5-10 sho~'s the plot obtained for the Shepherd and

Lapple (1939, 1940) model as determined from equations 5-5

and 5-20. In this case only the first term of equation 5-5

was used with the constant k having a \l'alue of 16. A simi­

lar distribution was obtained for the predictions of the

Casal and Hartinez-Benet (1982) model (equation 5-15) as

shown in Figure 5-11. The similarity in the plots was due

to the similarity between the two models as discussed ear­

lier in this chapter. In both cases, the predicted pressure

drops were ~?stly higher than the experimental values, and

in a few cases, the predicted values were almost one order

of ~agnitude higher. The performance indices were 0.68 and

0.66 respectively with the higher contributions coming from

the deviations from the parity line.

~

1 (XXX) r 71

e. •

~Icœ

~ § 100

1

ouolcne gtICIl.try

OC! - oold -CI - hot +C2 - hot AC3 - hot CC4 - oold • C4 - hot.

• rI'. .. ~ ~

_ + J< -

A +1 ?~

iil"lilE~/-~/ _ ,Ir - -,.~A 0

Q C0<o0 Or?"

o 0

la v , ,o,.J

la 100 1000 1 (XXX) EXPERllENTfL PRESSlŒ ŒUF. Pa

Fi9ure 5-10 Comparison of exparimcntal data with pressure drop predicted by the Shcpherd and Lapplo (1939, 1940) mo~el.

~

1\) .. CIl

9

HXXXh 51

~ •

~Icxx)

§ 100

1

CVllcna Q«X,.lry

OCI - cold .CI - hot +C2 - hot AC3 - hot C C4 - cold .C4 - hot

.... ~ ••• C

+

+11 g Dt A I*~

... I!IE/ ~llliiii .... 00

c r.n •• i" • !»lIE A ..n () ./

0<h0' _0

° 10~V--~~~~~~--~~~~~~~--~~~~~

100 1000 10000 10 EXPERltENTFL PREsst..R: œœ. Pa

Figure 5-11 cOhlparison of experimental data with pressure drop predictod by tho Casai and Martinoz-Donot (1982) modol.

~

j\) .. 01

c

(

217

The pressure drops calculated from the Stairmand (1949)

model were generally lower than the experimental values as

shown in Figure 5-12. Equation 5-6 was used along with

Briggs' (1946) load correction model (equation 5-20). There

was little segregation of the data for the cold and hot

runs. The performance index was 0.43 vith the main contri­

bution coming from the deviation from the parity line.

The predictions of the Alexander (1949) model (equation 5-8)

are shown in Figure 5-13. The Briggs modql (equation 5-20)

vas used aga in to determine the loading effect. The plot

shows that there was good agreement between the predicted

and experimental values throughout the range of pressure

drops. Furthermore, there was no segregation between the

low and high temperature data. The performance index was

0.14 which vas the lowest of the theoretical models tested.

Figures 5-14 and 5-15 show plots obtained from the models

derived from the experimental data obtained in this study.

In both cases, the Euler number was calculated from the

equation of t~e experimental regression line obtainad from

the plot of Euler number ratio vs dust loading (equation

5-24). The difference between the two plots was in the

method used to determine the zero-load Euler numl'2r (Eue).

Figure 5-14 (method 1) was obtained by determining the zero-

c

. '

Hxm, /1

e. •

& I5IŒXl

~ § 100

1

cuolone gecawtry

OCI - cold • CI - hot + C2 - hot. âC3 - hot C C4 - cold • C4 - hot.

~",D[J

c.~.[J

• • ~ ~D .... " • l.b~ "'"

.. ' il!90

~ ,.,,IIE"'.

1{4( illE

[J (DT '#Il. '0 (J

'" r~<oO 00

o

IO~o-°' 10

~~~~~~ ........ ~ .... ~~~~~~ ........ ~ .... ~~~~~~ 100 IŒXl IQ(XXl

EXPERlt-ENTfL ~E œoP. Pa

Figura 5-12 Compnrison of exporimentnl data with pressura drop pradictod by tho stnirmnnd (1949) modol.

~

N ... Cl)

~

HXXXh 71

e. •

~1(xx)

5 1'00

cuo 1 cne g.cn.t.ry

OCI - oold • CI - hot +C2 - hot AC3 - hot Il C4 - oold .C4 - hot

IJIJ • fi'!/d

•• ~,7.. A .. Jh.~ 11: 7f( (J'j)

o

+~I!~O

ft~ • 1( ,,6~

Il • riV. ~/cro -o~O

./

10 V ""'" ""... ""

10 100 1000 10000 EXPERlt-ENTFL PRESSl.Π[R(F. Pa

Figura 5-13 compnrison of oxporlmontnl dntn with pro99uro drop prodictcd by tho Aloxnndor (1949) modol.

r\

N ... CD

c

.. HXXXh 51

~ •

~Hxx)

~ If

§ 100

1

cuolcna gIIQIl. t.ry

OCI - oold • CI - hot. +œ - hot. âC3 - hot c C4 - oold • C4 - hot.

• • • ~ll-c . .., • }IE.4

â ,/fFütJ

ttr!<>~ .~~ ..

.1y<-â7 08 c M d:r''b 0 00

o /6

10~K--~~~~~~--~~~~~~--~~~~~~

la 100 1000 10000 EXPERltENTFL PRESSlRE œcP. Pa

Figura 5-14 compnrioon of axparimantnl dntn with praosura drop pradicted by tha modal derived from the experilllentnl dntn (mcthod 1).

o

,.. '" o

,

c

221

load Euler numbers from the slopes of the plot of pressure

drop vs barrel velocity head (Figure 5-4). The points in

Figure 5-14 wcre symmetrically distributed about the parity

line as indicated by the low squared deviation of 0.0029.

The performance index was correspondingly low (0.084) indi­

cating a reasonably good fit of the experimental data.

Figure 5-15 was obtained by determining Euc from its rela­

tionship with the cyclone geometry (equation 5--22). The

performance index was higher than for Figure 5-14 reflecting

the increased uncertainty in using equation 5-22. Neverthe­

less, it is more convenient to use this equation than it is

to determine the Euc for each cyclone configuration from

Figure 5-4. In any case, the decrease in the agreement

between the calculated and experimental values was small so

either method would yield similar result.

SUHMARY

Several theoretical models exist for calculating the pres­

sure drop across thp. cyclone as a function of operating

conditions. The ~ressure drop is often analyzed in terms of

the number of inlet velocity heads (NH) or the number of

barrel velocity heads (Euler number, Eu). It has been found

that the pressure drop varies inversely with the inlet dust

o

HXXXh 7,

e.. • ~ 151ŒXl

i § 100

1

cuolone geaa.try

o CI - cald .CI - hot +C2 - hot AC3 - hot o C4 - cald .C4 - hot

. -• 4--0

l\/~ A ~lIE t:rC~

+ .... J(.. • v:r, ~ _ .,JA'if lIE li ;;1I(:i

lIE rt.A~ 08 o "'~~ CO '0 0

10~V~--~~~~~~----~~~~~~----~~~~~~

10 100 1000 1(0)0 EXPERltENTfL PRESSlΠrRCP. Pa

Figure 5-15 comparison of experimental data with pressure drop predicted by the model derived from the experimental data (method 2).

@

1\) 1\) 1\)

c

223

load and some authors have proposed power law models to

de scribe the relationship.

The experimental data showed the expected inverse variation

of pressure drop with load, but there was much scatter in

the data. The model proposed by Alexander (_949) agreed

with the experimental data better than any of the existing

models tested. Empirical models were derived for the Euler

numbers without and with dust loads.

CONCLUSIONS

o

(

c

c

224

CONCLUSIONS

The main features of this study arc sUMmariz~ . as follows:

1. A 10.2 cm àiamr..t .. ;c cyclo.~~ Illas studied at room ana

elevated temperatures. Temperatures up to 2 000 K were

used and are higher than previously reported for

cyclones. Alumina and silica of less than 44 ~m mass

median diameter were used as test 1usts in air.

2.

'3.

Cyclone preG~UI~ d~op~, fractional and overall collec

tion efficier.~i?~ ware moasured as functions of tempera­

ture, gas throughput, dust loading and gas outlet geo,3-

e.try.

Tangelltial, radial and dxial vel.:.city profiles were

measured in the cyclone barrel at room and elevated tem­

peratures. The Alexander (1949) model (equations 3-3 to

3-5) predicted the profiles reasonably weil. An empiri­

cal model (equatian 3-22) was derived to correlate the

tangential velocity at the wall with the Reynolds number

of the gas in the annulus between the cyclone wall and

the .)utl€>': duct.

4. The inlet dust loading had a strong effect on the col­

lection eff!ciency and pressure drop. The load effect

225

., . increased rapidly at low dust loads (1 to 5 g/m~), and

1eveled off at loads above 50 g/m3•

5. A correlation was developed relating the 50 % cut-size

and the penetration to a dimensionless separation number

(Sn). The separation number was defined in equation

4-47 and comprised an inlet Stokes number (Stin)' the

inlet volumetrie dust loading (Lv) and the ratio of the

cyclone diameter to the gas out let diameter (Er).

S. The best agreement between calculated and experimental

overail collection efficiencies occured with the Mothes

and Loffler (1984, 1988) model (equations 4-26 to 4-36)

along with an A.P.I. (;955 or 1975) load correction

model (equation 4-39). The agreenent was improved when

the tangential velocities were calculated using the

model derived in this study (equation 3-22) and the vor­

tex exponent calculated by the Alexander (1949) mode]s

(equations 3-4 to 3-5).

7. The pressure drop across the cyclone was best predicted

by the l.lexander (1949) model (equation 5-8) along with

the load correction model of Briggs (1946) (equation

~-20). The agreement between calculated and • experimental values was lmproved when the experimental

c

8.

c

226

data was fitted to a model for the Euler r~mbfJr under

load (equation 5-22).

The performance of the cyclones at very high temp~ra­

tures was not significantly different from the room tem­

perature operation, provided that the temperature effect

on the particle, gas and (low properties was adequately

treated.

CONTRIBUTIONS TO XNOWLEDGE

c

c

227

CONTRIBUTIONS TO XNOWLEDGE

The following contributions to knowledge have been made by

the author:

1. Collection efficiencies and pressure drops were measured

at temperûtures higher than previously :epo=ted for co~­

vention~l cyclone~.

2. An empirical model was derived relating the wall tangen­

tial velocity to the Reynolds nucber of the gas in the

annulus between the gas outlet and the cyclone barrel

(equation 3-22).

3. A new separation parameter (Sn) was defined which can

pre~ict the collection efficiency and cut-size from

known operating conditions (equation 4-47). The new

parameter includes an inlet Stokes number (stin)' the

inlet volumetrie dust load (Lv) and the ratio of the

cyclone diameter to the gas outlet diameter (Er).

4. An existing model (Mothes and Loffler (1984, 1988) was

modified to improve the predictions of collection effi­

ciency. The modifications included the replacem

o

o

22&

s. A new coefficient was obtained for a relationship

between the zero-load Euler number and the cyclone

dimensions (equation 5-22).

6. New parameter values were obtained for a model relating

the Euler number to the inlet dust loading.

c

RECOHlŒNDATIONS

(

o

o

RECOKKEHDATIONS

Thp following are reco~endations for future work:

1. A study should be done at high pressures in addition to

the high tempe ratures used in this project. This would

require the use of a different type of heat source since

the RF torch used here cannot be used at high pressures.

2. Larger-sized cyclones should be studied at the high

temperatures used in this study. This would require

using a more powerful plasma generating system or pre­

heating the air to a high temperature in order to handle

the larger gas flows.

3. A more extensive study of gas flow patterns in the

cyclone at very high temperatures should be done.

Ideally, a non-intrusive method of flow visualization

and velocity measurement (Laser-Doppler anemometry for

example) should be used. This could require making the

cyclone out of a transparent, high-temperature material

such as quartz.

4. A continuous system should be studied at high tempera­

tures. This would address issues such as reentrainment

of particles trom the bins which can occur in batch sys-

c

c

229a

tems. This would require on-line weight and particle

size measurement instead of a cascade impactor.

o

NOHENCLATURE

(

(

c

a

A

Ae

Ai

Ao

At

b

B

bc

bl

c

C'

d

230

HOKENC~TURE

constant

load exponent, equation 4-39

experimental load exponent

inlet cross-sectional area, m2

outlet cross-sectional area, m2

thermocouple surface area, m2

constant

inlet width, m

inlet width, m

dimensionless coefficient

load parameter exponent

5-channel pressure probe calibration factor

inlet dust loading, g/m3

calibration factor of heat-flux gauge

no. concentration of particles, no./m3

reference dust load (usually 1 gr/ft3)

constant pressure heat capacity, J/kg/K

pressure probe calibration factor

volumetrie du st load, m3 dust/m3 gas

particle concentrations in region~ 1 to 4, g/m3

cyclone configuration number (Figure 2-1)

CUnningham slip correction factor

exponent of outlet diameter to cyclone diameter ratio

momentum exchange parameter

cyclone barrel diameter, m

dH

di!

dl

dp

Dp

dpa

dpc

dpg

dpmin

dpSO

dp84

dP

dPb

dPe

dP' ~

dPr

dPs

dPo

dt

Dt

da

Er

Eu

Euc

f

0 F

231

inlet hydraulic diameter [4hcbe/2(hc+bc)], m

difference between measured and predicted values

pipe diameter, m

particle diameter, m

particle diffusivity

aerodynamic cut-size [dpso(C'pp)o.s], m.(kg/m3)0.s

cyclone cut-size, m

mean mass diameter of the test dUGt, m

diameter of smallest particle that can be collected.

SO % cut-size, m

84 % cut-size, m

cyclone pressure drop, Pa

barrel pressure loss, Pa

exit contraction loss, Pa

inlet contraction pressure loss, Pa

reversaI pressure head loss, Pa

solids acceleration loss, Pa

zero-load pressure drop, Pa

thermocouple diameter, m

particle turbulent diffusivity

angle swept by particle in horizontal plane

outlet diameter ratio [de/de]

Euler number

zero-load Euler number

Fanning friction factor

S-channel pressure probe calibration factor

232

c energy loss factor

inertial force of a particle

Fc centrifugaI force acting on a particle

Fcv friction loss factor for cyclone barrel

Fev friction loss factor in the exit duct

Ftw shape factor from thermocouple to walls

Fv drag force acting on a particle

G geometric parameter

h cyclone height, m

hc inlet height, m

hf heat transfer coefficient, Wjm2jK

ht height of gas outlet duct, m

hz height of cylindrical portion of cyclone, m

hz* modified height of cylindrical portion of ~zclone, m

II-I3 electrical isolation sections in inlet duct.

jc dust outlet diameter, m

jl,4 particle fluxes, no.jm2js

k constant

K 5-channel pressure probe calibration factor

Ka inlet heightjcyclone diameter

Kb inlet widthjcyclone diameter

Kc volume parame ter

kf thermal conductivity of gas, WjmjK

kl load coefficient

ks constant

thermal conductivity of wall

233

constant

Ko geometric parameter

Kl flow parameter

K2 geometric parameter

L du st loading, gjm3

le height of cylindrical part of barrel, m

Le equivalent length of the exit duct, m

LF load factor

Lo turbulence scale length, m

Ln Ilatural length of vortex in cyclone barrel, m

Lv inlet volumetrie dust load, m3 particlesjm3 gas

m constant

mass of dust collected in cyclone, kg

mass of du st entering cyclone, kg

mass of dust leaving cyclone, kg

vortex exponent

N number of transfer units

Nm measured number of transfer units

NH inlet velocity head

NHw number of wall velocity heads

np number of particles in sector

Np predicted number of transfer units

Ns number of spirals made by gas in the barrel

Nu ~usselt number

P penet~ation, [l-e]

Patm atmospheric pressure, Pa

(

(

(

Nu Nusselt nwnber

P penetration, [l-e]

Patm atmospheric pressure, Pa

Ps static pr~ssure, Pa

PT total pressure, Pù

Pl -5 pressures measured by pressure probe taps, Pa

rI performance index

Pr Prandtl number

Q volumetrie flowrate, m3/min

Qin inlet volumetric flowrate, m3/min

Qo inlet volumetrie flo' 'rate, m3/min

Qv axial volumetric fl~wrate, m3/_ i n

r

R

radial position i~ cyclone, m

regression coefficient

ra* modified radiur of cyclone, m

rc cyc~?ne radius, m

re exit dllct radius, m

ri exit du ct radius, m

rv r.~dius of boundary between upflow and downflow

Re Reyno'is nu~ber [dcUcg/~Pg]

Rea ~eynolds number in annulus formed by gas exit duct

S engagement le~gth, m

Sc engagement length, m

SF saltation factor

5~. se~aration parameter [StinoLvCoErd]

inlet Stokes number [C'dplppuc..l/9~gdH]

235

Tin inlet gas temperature, K

Tt thermocouple temperature, K

Tw wall temperature, K

u tangent '.al velocity component, mis

Uc mean inl~t velocity, mis

ur radial velocity of pa~ticle at radius r, mis

Urw radial velocity of the particle at the wall, mis

v axial velocity component, mis

V gas velocity, mis

vb barrel velocity, lQv/~rc2], mis

Vc effective cyclone volume, m3

vi inlet gas velocity, mis

Vnl voll'me of cyclone at natural length, m3

vo ' root mean square fluc~uating velocity, mis

vpi inlet particle velocity, mis

vpv partjcle velocity in external vessel, mis

v r radial velocity, mis

vr~ radial particle veloc~t.y, mis

vrg radial gas velocity, mis

Vs volume in annulus formed by exit duct, m3

Vs saltation vclocity, mis

Vt tangential veloclty, miR

Vt;w wall tangential veloc!.ty , mis

Vtw~ wall tangential velocity for frictionless flow, mis

Vv gas velocity in external vessel, mis

·'x volume cleaned by a big particle, m3

c

236

Vz axial velocity, mis

Vl stairmand barrel velocity term

w radial velocity component, mis

x length of pipe, m

~lC mass fra?tion of i for collected dust

xif mass fraction of i for feed dust

xio mass fraction of i for escaping dust

xG di"meter -f bjg cleaning particlc, m

y tangential velocity at mean inlet radius/mean inlet

velocity

z axial distance, m

Greek symbols

rv,w particle fluxes no./m2/s

6 difference between measured and predicted values

E collection efficiency

Ea efficiency under load

EA separation efficiency due to agglomeration

~o zero load efficicncy

Et total emissivity

o angle flow makes with the axis of the pressu~e probe

# gas viscosity, Pa.s

#g gas viscosity, Pa.s

#app viscusity under load, Pa.s

e wall friction coefficients

Pf combined density of gas and particles, kg/m3

237

Pg gas density, kg/m3

Pp particle density, kg/m3

o Stefan-Boltzmann constant

~ impaction parameter

o specifie su~face area of the barrel of the cyclone

~ angle flow makes with the axis of the pressure probe

~c angle between cylindrical and conical sections

REPERENCES

c

REPERENCES

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Koch,W.H. and Licht,W., "New Design Approach Boosts cyclone Efficiency," Chem. Eng., 81, Nov (1977).

Kriegel,E., "Effect of OUst Loading on the Throughput and Pressu!e Drop of cyclone Collectors," Aufbereitungs Tech­nik, 1, 1-8, (1968).

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242

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243

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APPENDIX 1

RAW DATA

(

c

APPENDIX 1

RAW DATA

OPERATING CONDITIONS , RA. DATA

Tables Al-l and Al-~ shuw data for experiments don~ at ele­

vated tecperatures using alumina as the test dust, and for

c~· .lon/! out let diameters" 5.08 atld 2.54 cm respecti vely.

The rows in these tables ar: ~rranged :n order ?f decreasing

inlet temperature. Runs where the 50 % cut-size is not r'ven

~ere done with the câscade imp~ctor a~ the cyclone inlet 50

the fractional mass bala~ces could not ~e completed. m~ble

Al-3 shows d~ta for -oom temperature experiments done with

alumina; the rows in this table are arranged in order of

increasing inlet velocity. Data for exp~riments done wit~

silica are given in Tables Al-4 and Al-5 for high and low

tempe ratures respectivaly.

247

TAlLE AI'I AltnfN ExptrfDef'\tll DIU· "ft: leqletlture t::U\S • S.CS (a. outle!

_ .... Inlet Standard Inlet Pressure ~t COllection 50 X

Number Teœperlture Flowt,t- ~eloclty Drop Load Efflclency Cut'slze [::] ~;.h~ IWol (Pli (g,a'51 !XI !/Je]

Cyclone cotltt: S,08 ca dl~terc 10.8 ~ long

M20 2000 0.194 17 53 31.8 83.1 1.84 MI3 1886 0.194 16 64 22.5 71.8 M22 1870 0.210 17 67 21.4 85.6 1.65 A..'21 1863 ~ • .aG 19 al 22.9 84.5 1.68 M41 1816 0.194 15 61 1.4 44.7 2.25 M48 1799 0.213 17 67 35.2 84.0 1.79 M05 lm 0.213 16 71 20.9 76.8 ~.20

MOI 1758 0.213 16 80 18.4 73.0 M03 In6 0.<13 16 67 23.3 75.7 M06 1"20 0.213 16 61 27.0 74.4 2.18 M04 1720 0.213 16 67 24.~ 70.3

MI8 1696 0.274 20 133 15.4 82.9 1.99 M02 16&9 0.213 15 71 40.9 50.5

AA36 1604 0.329 '.3 213 4.4 78.5 1.86 Ml!- 1~66 0.351 24 248 1~.2 88.2 '.~2 MI7 1542 0.329 22 11'2 19.8 86.4 1.42 MI2 1541 0.329 22 208 18.9 91.3 MIO 1525 0.373 25 240 22.6 811.6 1.51 .wa til7 0.423 U 427 234.6 QI.9 0.27

HI5 1505 0.3~ 21 144 22.6 M.9 1.48 MI6 1489 0.329 21 208 28.2 82.9 .-.-. MOS 1487 0.329 21 19~ 4~.3 85.3 1.61

AA.1S 1486 0.424 27 '.GO 2.7 67.7 M09 1480 0.373 24 293 ze. ~ 82.9 1.87 AA37 \478 0.423 27 400 183.1 88.4 106 MI9 1459 0.421 27 3't3 15.2 91.~ I.Z4 MO' 1442 0.329 21 196 35.1 85.9 1.80 AA34 1433 0.421 26 413 4.3 31.1 1.82 Mil 1295 0.463 32 S33 30.7 80.5 1.67 AM7 1221 0.603 32 667 0.7 71.5 1.68 AA44 1206 0.603 31 539 13.0 92.5 1.06 AMO /71 0.984 41 1813 2.1 89.3 ~).26

AA39 927 0.084 39 \421 38.1 95.5 0.95

~.5!!1.!.tl: 5·98 ca dl ..... tsr. 7.0 ca lm

AC'l2 1847 0.213 17 93 1.4 55.7 2.n '':CI 1803 0.213 17 67 3S.4 84.0 1.7Ç AC04 1388 0.429 26 427 40.5 88.6 I.S8 AC03 1380 C.<29 26 413 ".0 75.9 1.91 AC06 1230 G '3 ~ 293 48.0 89.6 1.52 AC05 1208 0.603 " 681 1.8 79.e 1.62

248

IULE AI·2 Aluolna Exptrl~tal Data· HIgh I""POrat .. e Runs • 2.54 CD outlet

RU'I Inlet St~rd Inle! PrHsut"'t Oust COllectIon Cut-hu:ber Tecrptret'Jt'e Flowr.,« Velocfty Drop LNd Efffcloncy She

(KI ~/.Inl 1of,1 (Pa) (g/"J) (%) (JJa)

Cyelont> out'ft: 2.54 os df5ftettt'. 10.8 CIl tenq

AS02 1913 o.m 18 2!2 15.4 93.9 0.74 AS03 1564 0.329 22 629 15.8 94.8 D.2S A80~ 1554 0.329 22 629 18.7 97.9 0.23

Cyç!oneo outtet; 2.54 CIl dl!I!nIUfr. 7.0 aI.Jsei

ADOI 1791 0.213 16 300 2.5 79.1 I.al ADI2 1740 0.213 16 29l 20.3 84.4 1.54 AD02 IT<I 0.213 16 295 87.0 89.5 0.33 AD04 1560 0.429 29 U3 19.8 93.4 1.13 AD03 14:"'1 0.429 26 1421 0.9 87.5 1.21 AD06 1340 0.603 34 2646 4.5 93.5 0.71 ADOS I29T 0.603 33 2058 ~5.7 95.9 0.66

c

249

TABlE Al·3 Al~lna E~rlment •• Dlta • Rooœ Te=perltur~ Runs

RU'I Standord Inlet Pressure Oust C<llIectlon eut· Nu:ber f~?Wrate Veloclty Drcp Load Efflclency SI.e

~,.Inl IaIsl [Pol [g,.,ll !Xl [,.al

Cyc:1one outtfS: S.OS Ç! dl?SU''-, 10.8 CI! tons

Ml4 0.321 1 53 73.7 84.0 1.77 AA30 0.321 • ;1 120.2 81.6 M28 0.401 5 91 62.3 89.0 1.52 U29 0.401 5 ~< 75.9 89.7 1.53 Ml6 0.463 6 160 ~.5 90.8 1.47 M14 0.463 6 104 eo.5 86.9 1.65 AA25 0.561 7 20Ç 54.8 90.9 1.47 AA32 •• 574 7 260 15.3 86.5 1.22 Ml7 0.574 7 253 65.7 92.1 1.30 AA45 1.177 15 1039 0.3 84.3 1.14 M43 1.177 15 IOW 1.3 89.3 1.18 M46 1.177 15 1039 3.5 92.6 1.18 M.l 1.177 15 640 91.8 92.7 1.19

Cyel 2e' ouUtt, 2.54 ça dheu," , 7 ,Q ca long

ADl1 0.213 3 69 5.8 eo.5 1.90 AD07 0.213 3 64 44.5 86.4 1.67 ADl0 0.603 8 833 9.7 92.5 1.07 ADDa 1.050 13 2666 8.4 92.7 1.13 AD09 1.177 15 2~ 14.0 96.0 0.90

250

c

TAlLE AI·4 5111.0 Experleontol Ooto • High Teoperotur~ Runs

R .... Inlet stondord Inlet Pressure Oust Collection CUt· Nu=btr '~rature flowrlte Veloelty Drop Load (ft 1 el enc:y SI ..

[KI [,.l,_lnl t-/sl [Pol [gI,.l1 [%1 [11111

Cyete out(~t; 5,08 CIl dlet,,, , 10,8 Ç!!! 1"""

SA29 1835 0.213 17 77 3.1 61 3.05 SAZ2 1676 0.260 19 107 9.3 78 2.05 SAZ8 '664 0.213 15 53 50.3 M 1.80 SA20 1605 0.308 21 133 8.1 71 2.51 SAI8 1566 0.308 21 147 3.1 67 2.62 SA03 1539 0.423 28 413 2.1 73 2.46 SAOI 1505 0.423 28 413 1.9 79 SA2S 1499 0.305 20 160 61,7 90 1.52 SA16 1474 0.423 27 453 7.9 §6 1.46 SA23 1459 0.429 27 373 8.1 1!2 1.84 SAZ4 1432 0.429 27 373 53.9 90 1.57 SA19 1352 0.600 35 66; 4.5 76 1.93 SAZI 1300 0.603 34 539 11.6 88 1.41 SAZ7 1196 0.600 31 392 58.0 90 1.28 SAZ6 1048 0.600 36 588 49.6 89 1.28 SA17 991 0.9M 42 1331 9.1 89 1.20 SA16 846 0.936 34 1157 8.7 87 1.46

tyettn out"t; br" ce d'~te ... 1.0 ~

51>05 1876 0.213 17 293 13.9 84 1.75 SI>'J2 1439 0.429 26 1079 10.8 90 1.49 51>07 1256 0,603 32 lue 23.9 89 1.~3

SOO4 Il25 0.603 31 1866 14.1 91 1.11

c

251

TABLE AI·5 Sil l,a Experloental Oata • Roao Tooperature Runs

R .... Standar<l Intet Pressure Oust CoUectlon CUt· Nlr.Iler Flowrate V.loclty Orop L~ Efflcloncy Sile

~/1I1n] [Jo/si [l'al [g/.,ll IXI II/III

Cye1m ClUttetj 5.0& ca dfeUt, 10.8 ca long

SAlO 0.212 3 20 30.1 71 2.59 SA08 0.212 3 13 48.0 73 2.55 SAI2 0.424 5 107 15.8 79 2.12 SA07 o ~24 5 72 34.4 74 2.57 SAI4 J.424 5 85 38.9 84 2.00 SA04 0.869 Il 573 6.2 67 SA05 0.869 Il 467 6.9 78 1.74 SA06 0.869 Il 547 25.5 85 1.71 SAI5 1.177 15 1012 1.1 78 1.50 SAli 1.177 15 933 5.4 87 1.46 SA09 I.ITI 15 933 '~.2 90 1.39 SAI3 1.177 15 579 79.7 92 1.30

Cyclone outles; 2'54 ça dhnerrt , 7 .0 (li long

S003 0.213 3 43 56.3 87 1.91 SOO6 0.603 8 5M 46.1 92 1.14 SOOI 1.177 15 2353 22.3 95 0.96

c

APPENDIX 2

TEMPERATURE HEASUREHENT

o

o

252

APPENDIX 2

TEMPERATURE HEABUREHENT

The arrangement of the thermocouples for measuring the inlet

and outlet gas temperatures were shown in F;gures 2-3 and

2-4. The alignment of the tip of the thermocouples paraI leI

to the axes of the channel has the advantage that the tem­

perature gradient along the tip of the thermocouple is

negligible, therefore conduction heat losses can be

neglected. A heat balance around the tip of the thermo­

couple reduces to equating the convective and radiative heat

fluxes:

(A2-1)

where hf is an average heat transfer coefficient, At is the

surface area of the thermocouple, 0 is the Stefan-Boltzman

constant, Et is the total emissivity (0.98) and Ftw is the

view factor from the thermocouple to the wall (taken to be

one).

Since hf was not kno~n, a second equation was needed in

order to determine hf and Tg. Several empirical

correlations for forced convectiop heat transfer from a

sphere or cylinder to agas were tried including those of

Hilpert (1933), McAdam (1954) and Whitaker (1972). The

(

<:

(

253

correlations that generally gave the most conservative

estimates of Tg were some presented by Clift et al. (1978)

which were derived from a collection of published data:

Nu -= 1 + prl/3[1 + 1] 1/3 ReO•41 Re·Pr

Nu = 1 + 0.677ReC•47 100<Re:S:4000

Nu = 1 + 0.272ReO•S8 4 OOO<Re:S: leS

1<Re<100 (A2-2a)

(A2-2b)

(A2-2c)

where Nu [=hfdtfkf] is the Nusselt number. The Reynolds

number [Re -= pvdtfp] was based on the thermocouple diameter

with the gas properties evaluated at the film temperature

[(Tg+Tt)/2]. The Reynolds number ranged between 100 and

2 000. The Prandtl number [Pr = cpp/kf] was also determined

at the film temperature, and was always close to 0.7.

A trial and error procedure was used to determine hf and Tg

stllrting by guessing Tg, calculating h from equati.," A2-2,

calculating a new Tg from equation A2-1 and comparing it to

the guessed value. The assumed and calculated Tg usually

converged to within 1 K in two to six Iterations.

The wall temperature was measured by a thermucouple strapped

to the outer wall of the channels directly opposite the gas

temperature thermocouples. A heat-flux gauge was taped to

€}

2000 1

loocr A 1U'Tl1 na

o Inlet

1000 l- Il Outlet ~

• ~ 1400

ml200

~ 1000'· fi)

WOOD 12 8000

400~/ 1./

200 200 40CJ 00) BOO 1000 1 zoo 1400 1000

tEAStRED TEWERATlR:. K

Figure A2-1 Measured vs correctcd tcmpcraturc for runs with alumina.

1 BOO 2000

~

'" '" '"

~

2(XX) 1

1800~ Slllca '6

o lnlet

~ 100) [ C Outlet

Q>

~ • ~

2 0,

1400 ~tj

1 zoo 1

1000

~ !:Po:

800 Ole/'

w o:r Π0 00) u

-100

ZOO~V~ __ -L ____ ~ ____ ~~ ____ ~ ____ ~ ____ ~ ____ ~ ____ ~ ____ ~

zoo 400 00) 800 1000 1200 1-100 Hm 1800 2(XX) tEASt.RED TePERATœE. K

Figure A2-2 Measured vs corrected temperature for runs with silica.

~

N (II 0>