Control of Slopping in Basic Oxygen Steel Making

8/4/2019 Control of Slopping in Basic Oxygen Steel Making

1/72

McMaster University

DigitalCommons@McMaster

Open Access Dissertations and Theses Open Dissertations and Theses

5-1-1981

Control of Slopping in Basic Oxygen SteelmakingGeorge K. Cuthill

This Thesis is brought to you for free and open access by the Open Dissertations and Theses at DigitalCommons@McMaster. It has been accepted for

inclusion in Open Access Dissertations and Theses by an authorized administrator of DigitalCommons@McMaster. For more information, please

contact [email protected].

Recommended CitationCuthill, George K., "Control of Sl opping in Basic Oxygen Steelmaking" (1981). Open Access Dissertations and Theses. Paper 2933.http://digitalcommons.mcmaster.ca/opendissertations/2933
http://digitalcommons.mcmaster.ca/http://digitalcommons.mcmaster.ca/opendissertationshttp://digitalcommons.mcmaster.ca/open_dissmailto:[email protected]:[email protected]://digitalcommons.mcmaster.ca/open_disshttp://digitalcommons.mcmaster.ca/opendissertationshttp://digitalcommons.mcmaster.ca/


2/72

CONTROL OF SLOPPING IN'-BASICOXYGEN STEELMAKING

by-GEORGE K. CUTHILL, B.Sc.

A ThesisSubmitted to the School o f Graduate Stu d ies

in P a r t i a l F u l f i l ~ e n t o f the Requirements'\

fo r the Degree.Master o f Engineering

McMaster Un iv ersity

".

May 1981

....

".'


3/72

..

-

l .

CONTROL OF SLOPPING IN BASICOXYGEN STEELMAKING

I


4/72

. .MASTER OF' ENGINEERING(Metallurgy &Materials Science)

"

M ~ M A S T E R t l N I ~ E R S I T YHamilton, OntarioTITLE: Control of Slopping in Basic OxygenSteelmakingAUTHOR:SUPERVISORS:

George'K. Cuthil l , B.Sc.Dr. W-K. LuDr. T. R. Meadowcroft (Stelco)

NUMBER OF PAGES: (vit1.) \ 62

'- .-,--

-, .

. ( i i )


5/72

ABSTRACT

J Methods for controll ing slopping (slag ?verflow)were studied in the Steel Company of Canada's Hilton Worksbasic oxygen furnace insta l la t ion. A l ink was established

between slopping and various o ~ e r a t i ~ ~ ~ c o n d i t i o n s by draw-/ '1ing'on .the experience of the f u r ~ a c e operators ana by

,examining ingot yield data . . An on-line 'control syst,em was~ e v e l o p e d which used c h a n g e ~ ip the temperatu re of thefurnace waste gases tor signal when corrective action shouldbe taken to prevent slopping. During t r i a l s , this system

"reduced slopping and in cr ea sed ingo t yield by ~ r o x ~ m a t e l yone percent.

The chemical composition of slag from normal andslopping heats was studied in an attempt to determine why" ? .slopping occurs. The resul ts pf this study support a mech-anism proposed by F. Bardenheuer (Ref. 21) ~ h i c h relatesincreases in slag foaming in the B.O.F. to the precipitat iqn"f dicalcium s i l icate and qverpxidation.

,

-( i i i )

"" .


6/72

. . \ACKNOWLEDGEMENTS

I wish to thank the Steel Company of Canada Ltd.b&th for i ts f inancial support and for i ts sponsorship of ' :this project.

;

An industr ial research project owes i ts successto many people; I am grateful to the members of Stelco'sBasic Oxygen Steelmaking Department and Research ~ n Develop-ment Department for their unstinting cooperation. I ampart icularly indebted to Mr. K. W. Heyer, Mr. J. E. Laitand Mr. D. C. Telfer for their vi ta l contributions to thisstudy. Special t h a ~ k ~ go t o ~ r . T. R. Meadowcroft for hisguidance and support.

,rThe advice of Dr. W-K. Lu and other members ofthe McMaster University Department of Metallurgy regardingthe p repa ra tion o f this thesis. is also gratefully a c k n p w l e ~ g e d .,

(iv)


7/72

,

TABLE OF CONTENTS

S4

1

1212

Page

.B a c k g ! o ~ n ~ ~ 0 ~ - L i n e Control

.INTRODl(CTION..Background: Off-line Control

Characteristics of S10ppr-Heats at Ste1coON-LINE CONTROL TRIALS AT STELCO

RELATJON BETWEEN OPERATING CONDITIONSAND SLOPPING 4

Devefopment of Equipment for Measur-ing the Waste Gas Temperature 193.3. Development and ~ e s t i n g of Procedures' f o r Controlling Slopping , 23

CHA'PTER 4 OBSERVATIONS'ON THE MECHANISM OFSLOPPING 36

CHAPTER 1CHAPTER 2

2.12. 2

CHAPTER 33.13.2

APPENDIX 1'1: 1.Description of Procedures for Sampiingand Analyzing Slag

Mechanism of Slag Foaming Proposedby F. BardenheuerInves ti ga tion of the Mechanism ofSlopping at .Ste1co .Use of the Mechanism to ExplainHow O p e r a ~ i n g Conditions C a u s ~Slopping' , CONCLUSIONS

,.

4.14. 2

. 4.3..

CHAPTER SREFERENCESAPPENDIX I:

2.

,Description of B.O.F. OperationatSte1coGlossary

3639

424S

6146SlS4

. (v)


8/72

(

APPENDIX III : Factors Affecting Ingot Yield

..

co

Page58

(v i ) , -


9/72

,LIST OF FIGURES

..

J Figure 1Figure '1.Figure 3Figure 4

Figure 5Figure 6Figure 7Figure 8Figure 9Figure 10

Sections through a,BOF Showing theDevelopment of a Foaming SlagIn fluence of Slop Severity on AverageIngot Yield (BEU Ingots)Effect of Vessel Life on BEU YieldInfluence of Hot Metal Silicon, Hot.Metal Manganese and Lance Life on BEU. Yield (Vessel Life 0-800 heats)Typical LanceNozzle Wear (Mach 2.2Lance) -Thermocouple Assembly for Measuring theWaste Gas TemperatureCross Section through Stelco's HiltogWorks BOF ShopWaste Gas Temperature Trace -Normal Heat.Per iod dur ing the Blow at whichSloppingStartsWaste ~ a Temperature Trace - SloppingHeat

2I 79

10

11212224

2526

0'

Figure 11 .Changes to the Oxygen Flow Rate inResponse to the Waste Gas Temperature Manual Control Procedure, 28Figure 12

.Figure 13

Changes to the Oxygen Flow Rate inResponse to the Waste Gas Temperature Control CircuitComposition of the Slag at 10 and 15Minutes into the Blow

3240,Figure IIA.l Cross Section through Stelco' s Hi! tonWorks BOF Shop

.'

( v a )

53


10/72

. ,LIST OF TABLES

JV--

Table 1Table 2

Table 3

Monitoring Systems for Con trol lingSloppingComparison of the Average Ingot YieldAchieved on Control and Normal Heats( 0 - 5 ~ 0 heats on lining)Comparison of the Average Ingot YieldAchieved on Control and Normal Heats(0-500 heats on l ining) .

13

30

33Table IAI Composition, in Weight P e r ~ e n t , ofi lag Samples taken from Stelco's

OFs 48TabIe IAII Slag Composition Ranges Used by IRSID 50\ .. "

\\ ,,,

,. ,(

".

.. ( v t t t ).}

."-


11/72

._ .. ,.',. - - .

,)

CHAPTER 1INTRODUCTION

"All went'quietly at f i r s t , but after about 10

-minutes a rapid change took place, a voluminous white flameand an e v e r ~ i n c r e a s i n g stream of sparks be ing ejected fromthe mouth of the vessel , followed by explosions and evolu-tions of molten slag and metal, the apparatus becoming averi table volcano in a sta te of active eruption.", [27].This graphic account describes one of Sir Henry Bessemer'sf i r s t experiments in pneumatic s t e e l m a k i n ~ , however, i t couldequally 'well apply'to the slopping of a modeYn basic oxygenfurnace. Despite the advances in steelmaking technology,9which have taken place since Bessemer's day , slopping remains.-a problem which has never completely been solyed.,Slopping is related to the process of slag formation..in b a s i c ~ oxygen steelmaking. As oxygen is injected intoa basic oxygen furnace , carbon, s il icon ,manganese and ironare oxidized (a more complete description of B.O.F. operationis given in Appendix I I ) . The resul t ing s i l ica , iron oxideand m a ~ g a n e s e oxide react with fluxes charged into the vesseland the r ef ractory l in ing of the furnace forming a ~ l a g . Theoxid ation o f carbon generates carbon monoxide, some o ~ whichr ~ s e s through the slag making i t foam (figure 1). Normallythere is enough space i n s i ~ e the furnace to contain thisfoaming, however, occasionally the capacity of the f u r n a ~ e


12/72

_. _ __ . . . . . . ._ ..... 41."- . ."

- 2 - ,

._ . '_ ' _ __._. . . . _ . _. _ .__ . ~ .... u ., ,._. ,'

;

Figure 1: Sections through a BOF Showing theDevelopment of a Foaming Slag

')

Omln

7min

20mln

oxygon Jot

!Imin

13min_ nm l l:>GO metallic bath_ gas-slag-motalomuilion

(After Chatterje,e [22)) I

t


13/72

... - 3 - \

.,.

'--...'

.\Yis exceeded and the slag overflows. This overflow of slagis referred to as slopping .

Slopping creates several problems for s teel producers.Since iron is los t along with the slag, slopping reduces theamount of hot metal and scrap which can be recovered asusable product. This decrease in yield increases the costper ton of steel produced ,in B.O.F. shops. Also, the numberof t ~ of steel which can be produced by a furnace perhour is reduced, because the operation of the furnace must'be delayed to take co{;ective action to stop slopping and toremove e je cte d s la g. By reducing the number of heats which.slop, furnace productivity could be increased and operatingcosts lowered. 1Many diff icul t ies face an investigator trying todevelop a workable method for preventing slopping. One majorproblem is the large n U ~ b e r of factors, many of which areinterrelated, which affect the operation of ' a basic oxygenfurnace. Isolat ing those factors which are related toslopping r equire s la rg e amounts of data and demands carefulanalysis. Time, money and the phy sic al constraints of basicoxy'gen furnace operation l imi t the depth to which the problemof slopping can be studied. Ultimately, the degree ofsuccess which is achieved depends upon the invest igator ' sabil i ty to make the best use of the resources at hand. Thist ~ e s i s describes a study into methods of controlling sloppingwhich was carried out in the Steel Company of Canada Ltd. 'sHilton Works, basic oxygen furnace shop.


14/72

- ,CHAPTER 2

RELATION BETWEEN OPERATIONCONDITIONS AND SLOPPING.'2.1 Background: Off-line Control

All methods of controlling B.O.F. slopping can becategorized as either on-line or off- l ine systems. In onl ine control systems, corrections are made during the blowin response to some ' real time' signal which indicateswhether the heat is about to slop. In off- l ine control,systems, on the other hand, the cor rect ive act ion is taken

,before the blow star ts and, is based on past experience ofhow various operating conditions affect slopping.

Off-line systems for controlling slopping seek toreduce the number of heats which slop by either eliminatingor minimi zing the effect of factors which have been fo'undto cause slopping. The following factors have been reportedin the l i terature as causes of slopping:(i) Hot metal si l icon above 1 .2 percent [ 1 , 2 ] ;'( i i ) Hot metal manganese outside the range 0.5-0 .9

percent [1 ,3 ,4] ;( i i i ) Charging more than the fllornace's designed capacity [1] ;(iv) Use of fluorspar to speed lime dissolution [1 ,5] ;(v) Use of iron oxide as a coolant [1] ;(vi) Use of a newly relined furnace [ 6] ;'(vii) ~ h o i c e of oxygen lance design [7,8];

- 4 -


15/72

- 5 -

(vi i i ) Blowing with. the lance higher above the steel bath' \than normal [5,7].Because operating conditions vary from c o m p a ~ y to

company, some of these factors will be more of a problemin one B.O.F. shop than ano the r (e .g. , the amount of overcharging varies from company to company).

A v, r ie ty of action s can consti tute off- l ine controlof slopping. For example, rest r ict ing the aim manganesecontent of the hot metal for the B.O.F. [3] and regularlychecking the lance to bath separation [7] are both off- l inemethods of control. Because problems ui f fer , off- l inecontrol practices vary from company to company. Off-linecontrol practices can often only be implemented to a l imitedextent because they confl ic t with other aspects of a company'soperation. For example, although i t is desirable toeliminate overcharging to reduce slopping, thp need toproduce as much s tee l as possible from existing s!eelmakingfaci l i t ies may dforce a company to exceed the design capacity

'.of their B.O.F.s.(

2.2 Characteris t ics of Slopping Heats at StelcoBefore attempting to improve methods of off- l ine

control, the factors which are linked to slopping in Stelco 'sIB.O.F. operation had to be ident i f ied. Rather than examining

a l l the factors reported in the l i t e ra tu ra , Stelco's B.O.F.operators were asked which of the factors they fe l t were


16/72

- p

most important. These men reported, based on their operat-ing experience, that the following factors caused slopping:(i) .Vessel l ining l i f e less than approximate ly 400 heats.(ii) . Use of an oxygen lance with damaged nozzles.( i i i ) Hot metal manganese concentrat ion 'greater than

approximately 1.2 percent.(iv) Hot metal s i l icon concentration greater than

approximately 1.0 percent.- )

An attempt was t ~ made to qua?tify the effect ofeach of these four f a c t o ~ on shop operation. Since recordsare not kept of which heats slop, ingot yield was used asa measure of the severi ty of slopping. As. figure 2 shows,the average tngotyield drops as slopping b ec ome s moresevere. Ingot yield was also used because i t is an indicatorof p roduct iv it y f ami li ar to the B.O.F. supervisors - (This~ a an important consideration since . these were the men mostconcerned with the problem).

Only heats teemed into 24 x 28 inch big end up ingotmolds were selected for th is study. Attention was restr ic tedto these heats because of the small ingot size (the 5.9 tonB.E.U. ingot is the smallest size produced a t Stelco. )

-Iron losses are most l ikely to reduce the number of ingotsproduced on th ese h ea ts so that th eir yield is very sensi t iveto the effect of slopping. Data was collected on over 3000heats produced between October, 1975 and October, 1976.

In analyzing th is data, heats with s im tla r lin ing


17/72


18/72


19/72


20/72


21/72


22/72


23/72


24/72


25/72


26/72


27/72


28/72


29/72


30/72


31/72


32/72


33/72


34/72


35/72


36/72


37/72


38/72


39/72


40/72


41/72


42/72


43/72


44/72


45/72


46/72


47/72


48/72


49/72


50/72


51/72


52/72


53/72


54/72


55/72


56/72


57/72


58/72


59/72


60/72


61/72


62/72


63/72


64/72


65/72


66/72


67/72


68/72


69/72


70/72


71/72


72/72

Control of Slopping in Basic Oxygen Steel Making

Documents

Transcript of Control of Slopping in Basic Oxygen Steel Making