BLAST FURNACE PROCESS AUTOMATIC CONTROL I

A. N. Pokhvisnev, I. F. Kurunov, Y. S. Yusf in , V. M. Klempert

Moscow S t e e l and Al loys I n s t i t u t e

Despi te t h e s u b s t a n t i a l change i n b l a s t fu rnace ironmaking technology due t o the use of oxygen, n a t u r a l gas and f u e l o i l a s w e l l a s e l e v a t e d top gas p ressure and o t h e r f a c t o r s promoting t h e b l a s t furnace p rocess , t h e b l a s t furnace foreman con t inues t o play t h e most important p a r t i n s o l v i n g problems a s t o how t o g e t t h e maximum product ion r a t e a t t h e minimum expense. Automatic c o n t r o l i n ironmaking aims a t l i m i t i n g the foreman's r o l e i n the process and reducing i t t o c e r t a i n l i m i t s .

This problem has been the s u b j e c t of i n v e s t i g a t i o n f o r a long period of time a t t h e Ore Working Department of Moscow S t e e l and Al loys I n s t i t u t e .

I n 1939, t o accommodate b l a s t fu rnace c o n t r o l , P ro fessor A . N. Pokhvisnev [ l ] proposed a n index c a l c u l a t e d both from top gas a n a l y s i s and m a t e r i a l balance and f i x i n g t h e ins tan taneous va lue of coke r a t e conforming t o t h e gas composition involved. Schemat ica l ly i t can' be expressed a s a simple formula, p = O b / c g , where Ob i s t h e oxygen pass ing from burden m a t e r i a l s i n t o furnace gases and C i s t h e

g g a s i f i e d carbon. Given t h e top gas a n a l y s i s , t h i s r e l a t i o n s h i p may be convenient ly expressed i n terms of volumetr ic u n i t s ;

C02 + 0.5 CO - BN2 P = where C02 + CO = O 2 ( b l ) I N 2 ( b l )

I f r e q u i r e d , i t may a l s o be expressed i n u n i t s of weight ;

With hydrogen p resen t i n t h e fu rnace gas ( n a t u r a l gas o r o t h e r hydrocarbon i n j e c t i o n ) and oxygen-enriched b l a s t , t h e formula n a t u r a l l y becomes mor'e compl icated;

I n formula ( 3 ) , 0 .5H20( ) r e p r e s e n t s oxygen taken from t h e burden by hydrogen. This can be computed from t e e hydrogen balance us ing a r a t h e r cumbersome formula [2 ] . The use of a computer i s a good p r a c t i c e f o r making such c a l c u l a t i o n s quickly . I n

most i n s t a n c e s , i t i s a c c u r a t e enough t o s p e c i f y the r a t e of hydrogen u t i l i z a t i o n ( T H ~ ) w i t h i n the l i m i t s of 0.40 - 0.45. Then;

I n the even t of oxygen-enriched b l a s t and n a t u r a l gas i n j e c t i o n the c o e f f i c i e n t B r e p r e s e n t s the combined b l a s t oxygen-nitrogen r e l a t i o n s h i p . I t i s expressed a s fo l lows:

where

w - percentage oxygen i n oxygen enr iched dry b l a s t , X - b l a s t mois ture c o n t e n t , grams/nm3, 6 - percentage n a t u r a l gas i n combined b l a s t .

There i s another no l e s s important index r e p r e s e n t i n g t h e r e l a t i o n s h i p between i n d i r e c t r educ t ion oxygen and s o l u t i o n l o s s carbon;

When the va lue of H20(g) i s ignored, the index i s one h a l f of the one more o f t e n used, C02/(C02 + CO) , which 1s the r a t e of carbon monoxide u t i l i z a t i o n . The q/p r e l a t i o n s h i p immediately o f f e r s a genera l va lue of the oxide i n d i r e c t r e d u c t i o n r a t i o r e l a t e d t o both the r a t e of gas use and t h e s p e c i f i c carbon r a t e .

I n t h i s manner, the b l a s t furnace c o n d i t i o n s dur ing any p a r t i c u l a r period of time can be c h a r a c t e r i z e d by the above i n d i c e s .

The i n d i c e s under d i s c u s s i o n can be supplemented wi th d a t a on the h e a t i n p u t per u n i t of oxygen removed from the burden m a t e r i a l s ( index M ) . When t h i s i s t h e c a s e , c a l c u l a t i o n of t h e i n d i c e s may s e r v e a s t h e b a s i s f o r q u a n t i t a t i v e recommendations i n va ry ing coke r a t e , b l a s t temperature and humidity [ 3 ] .

Index M can be found from the fo l lowing c o n s i d e r a t i o n s ; the h e a t q u a n t i t y l i b e r a t e d on t h e format ion of 100 nm3 of gas of a g iven composit ion i s ;

95760 28080 a Kca 1 9, = - 22.4 C02 + - 22.4 100 nm' of gas

the h e a t c o n t e n t of 1 nm3 of b l a s t i s , W = c x t b l '

where

c - h e a t c a p a c i t y tbl - b l a s t temperature

100 N2 the b l a s t volume r a t e , per 100 nm3 of g a s , amounts t o

(100 - w) and the hea t from

the h o t b l a s t i s ;

t h e t o t a l h e a t i s then ;

Kca 1 100 nmj of gas

Oxygen i n t h e furnace gas comprises t h e sum of oxygen i n b l a s t and t h a t removed from t h e burden m a t e r i a l s . B l a s t oxygen can be found i n accordance wi th n i t r o g e n c o n t e n t i n the gas. By t h i s means t h e burden oxygen i s r evea led from t h e fo l lowing express ion ;

nm Ob = C02 + 0.5 CO - BN2

100 nmJ of gas

Dividing t h e previously obta ined va lue of Q by t h e oxygen removed from t h e burden, we produce t h e amount of h e a t per normal cub ic meter of oxygen removed from t h e burden m a t e r i a l s .

The formula t a k e s t h e fo l lowing form;

L 4275C02 + 1254CO + 100-w W

Kca 1 M = Q/ob =

C02 + 0.5CO - BN2 '2(burden)

I f we c a l c u l a t e t h e magnitude of j ( t h e number of oxygen normal cubic meters pass ing i n t o gas per u n i t weight of i r o n on the b a s i s of i t s composi t ion) , then the h e a t consumption per u n i t weight of i r o n i s t h i s ;

Kca 1 M x j

U.W. of i r o n

where j = 0.26 t o 0.30 nm3 0 /kg of i r o n . 2

Through t h e use of these two v a l u e s , one can analyze the b l a s t furnace o p e r a t i o n and automatica l l y c o n t r o l i t s thermal cond i t ions .

The f i r s t checking of t h e o u t l i n e d c o n t r o l method took p lace i n 1941 on the b l a s t fu rnace No. 7 , Dzerzhinsky S t e e l P l a n t and the thermal cond i t ions cont:rol wi th the h e l p of index "M" was performed f o r t h e f i r s t time i n 1942 on a furnace of Magnitogorsky m e t a l l u r g i c a l combine. Gas ana lyses and computations were made manua 1 ly .

The experiments were a success and demonstrated f a i r promptness of the c o n t r o l method under t e s t and i t s s u i t a b i l i t y f o r b l a s t furnaces . But many d i f f i c u l t i e s a r o s e from t h e p r a c t i c e of manually making gas ana lyses and c a l c u l a t i n g t h e c o n t r o l parameter. This kep t t h e proposed and t e s t e d b l a s t fu rnace c o n t r o l method from being promoting a t t h a t time. A t t he end of t h e 19501s , means of automat ic top gas ana lyses came i n t o be ing a long wi th t h e f a s t spread of computers i n t h i s countr:y and overseas . This gave impetus t o r e s e a r c h work on developing the b l a s t fu rnace thermal c o n d i t i o n s automat ic c o n t r o l systems. I n v e s t i g a t i o n s i n t h i s d i r e c t i o n were continued a t t h e Moscow S t e e l and Alloy I n s t i t u t e . The method, mentioned above and t e s t e d i n 1942, of b l a s t fu rnace thermal c o n d i t i o n s c o n t r o l through t h e use of top gas composit ion, formed t h e b a s i s of t h e i n v e s t i g a t i o n s .

A t t h e same time a s t h i s method continued t o be advanced, t h e poss i lb i l i t i . e s f o r u s i n g o t h e r sources of in fo rmat ion about the b l a s t fu rnace process f o r t h e same purposes were a l s o s t u d i e d . The r e s u l t was t h a t i n 1964-1965 a new method of b l a s t fu rnace thermal c o n d i t i o n s c o n t r o l based on t h e composit ion and q u a n t i t y of charged m a t e r i a l s , b l a s t volume wi th a d d i t i o n s was developed [ 4 ] . I n t h i s method, i n p lace

of t h e pe rcen t of t h e top gas c o n s t i t u e n t s , determined from a n a l y s i s , t h e i r q u a n t i t i e s c a l c u l a t e d from t h e composit ion and tonnage of charged m a t e r i a l s , b l a s t volume, and q u a n t i t y of i n j e c t e d a d d i t i o n s a r e made use o f . Q u a n t i t i e s of carbon d iox ide and carbon monoxide can be found from balance equa t ions of oxygen and carbon p resen t i n f ixed volumes of top gas :

co2 = 2 o2 ( i n gas)

- ' ( in gas) - H2°(reduc)

'O = ' ( in gas) + H2°(reduc) - 2 O2 ( i n gas)

Amounts of oxygen 02(in and carbon C(in pass ing i n t o gas can be c a l c u l a t e d from t h e composiffEh of burden m a t e r i a l s '(burden and 02(in burden , b l a s t and i n j e c t e d a d d i t i o n s O ~ ( ~ d d ) and C(add). Quant i ty o& water vapor r e s u l t i n g from r e d u c t i o n (H20(reduc)) can be es t imated assuming t h e . v a l u e of hydrogen u t i l i z a t i o n r a t e t o be cons tan t . I f we make c a l c u l a t i o n s per some u n i t of burden m a t e r i a l s ( f o r example, per one charge) and keep i n mind t h a t whi le i n the fu rnace each volume of charge r e a c t s wi th gases which vary i n composit ion and q u a n t i t y , we can d e r i v e t h e fo l lowing equat ions f o r a 2 and CO volumes (normal cub ic meters per one charge) ;

- - "2 = 2( O2(in bur.) O2(in b l a s t ) ) - ( ' ( in bur . )

t

- - C

(add) ) ' H2°(reduc) ;

- - + 0 C0 = bur.) + ' ( in add) ) - 2 ( 0 2 ( i n b u r . ) 2 ( b l ) ) + '

For a g iven charge , t h e l i n e denotes the process i n t e g r a l c h a r a c t e r i s t i c s f o r a period of time when t h e burden m a t e r i a l s a r e i n the furnace .

- - I n o t h e r words, va lues of 5 2 ( i n b l a s t ) , C(add) and H20(reduc

1 c o n s t i t u t e t h e

average wi th time q u a n t i t i e s of oxygen i n t h e b l a s t , carbon I n he i n j e c t e d a d d i t i v e s and r e d u c t i o n water vapor per g iven charge of burden m a t e r i a l s .

To c a l c u l a t e the above v a l u e s , a s w e l l a s q u a n t i t i e s of h e a t added by t h e h o t b l a s t and consumed by decomposit ion of t h e i n j e c t e d a d d i t i v e s i n t h e h e a r t h per g iven charge of burden m a t e r i a l s , t h e mean o p e r a t i n g time of t h i s charge i n t h e fu rnace has t o be e s t i m a t e d , i . e . ,

a = - minutes per charge n (17)

where

a - r e s i d a n c e time of burden m a t e r i a l s i n t h e fu rnace (conven t iona l ly taken c o n s t a n t and equal t o 240 - 420 minutes depending upon t h e volume and working c o n d i t i o n s of the b l a s t f u r n a c e ) ,

n - number of charges f i l l e d i n t h e time period "a".

Using t h e obta ined va lues of CO, C02, H20(reduc i t i s p o s s i b l e t o c a l c u l a t e the same b l a s t fu rnace process i n d i c e s which a r e es t imated from t h e top gas composition.

The method, formulated h e r e , has been app l i ed t o c a l c u l a t e the index M b r e p r e s e n t i n g t h e h e a t i n p u t per u n i t of oxygen i n t h e burden m a t e r i a l s jo in ing the furnace gas. There i s a formula t o i c a l c u l a t e Mg from the gas composition:

where:

C02, CO, N2, H20(reduc) - t h e i r con ten t i n the d ry top g a s , percent by volume ;

(r - combined b l a s t volume - t o i t s n i t rogen con ten t r a t i o

a = 100/(100-u)

- S u b s t i t u t i n g z2, 00 and H20 reduc) i n t h e above formula r e s u l t s i n the same index

of h e a t inpu t (Kcal) per u n i t ok burden l o s s oxygen (one nm3 0 2 bVrden), but i t i s c a l c u l a t e d from the composit ion of burden, b l a s t and i n j e c t e d a 6 d l t i v e s

- - - 3 Values of 02 , 0 2 b l , Cb, Caddy H20reduc should be expressed he re i n nm /charge; va lues of wb?, Qadd - i n callc charge. The checking of index Mb f o r conf idence, i . e . , whether i t i s i n conformity wi th t h e furnace thermal c o n d i t i o n s , has been c a r r i e d ou t by c a l c u l a t i n g t h e same from t h e d a t a of b l a s t furnaces working under d i f f e r e n t cond i t ions .

The assessment of convergence was done through p l o t t i n g the diagrams and computing the normalized i n t e r c o r r e l a t i o n func t ions .

b Table 1 d i s p l a y s t h e i n t e r c o r r e l a t i o n c o e f f i c i e n t s between index M and s i l i c o n

con ten t i n the i r o n f o r d i f f e r e n t va lues of time o f f s e t s . Opera t ing cond i t ions and o t h e r c h a r a c t e r i s t i c s of t h e b l a s t furnaces a r e a l s o given i n Table 1. The time i n t e r v a l between c a s t s i s used he re a s a t ime-uni t .

I n a l l i n s t a n c e s index had a p o s i t i v e and r e l i a b l e r e l a t i o n s h i p wi th s i l i c o n con ten t both i n absence of a time o f f s e t and when f o r e c a s t i n g f o r one o r two c a s t s , i . e . , f o r 2.5 t o 5 h r s .

Figure 1, g i v i n g t h e curves of Mb and s i l i c o n changes, i l l u s t r a t e s a cons ide rab le c h i l l followed by a h e a t i n g up of t h e furnace . The po in t s of both curves a-re s h i f t e d from one ano the r f o r one c a s t , i . e . , f o r 2.5 h r s .

b Thus, index M , c a l c u l a t e d from the b l a s t furnace working d a t a under d i f f e r e n t

c o n d i t i o n s , adequate ly accounts f o r changes i n the furnace thermal cond i t ions . C o r r e l a t i o n c o e f f i c i e n t s f o r M~ and s i l i c o n a t t e s t t o the r e l i a b l e r e l a t i o n s h i p of Mb and s i l i c o n c o n t e n t i n the i r o n i n a l l cases .

Table 1. S t a t i s t i c a l R e l a t i o n s h i p Between M~ and S i l i c o n Content i n t h e I r o n

Time of b

M and S i l i c o n Content S t e e l P l a n t B l a s t Furnace Working F o r e c a s t i n g I n t e r c o r r e l a t i o n Coeff i -

S1 No. B l a s t Furnace Condi t ions Cas t s C a s t s c i e n t

1 "Azovs t a l " , 17 19 cum 99% s i n t e r , l imes tone , 160 December, 1964 n a t u r a l g a s , oxygen

(30-31 pe rcen t )

"Azovstal", 1719 cum 96% s i n t e r , l imes tone , June , 1965 n a t u r a l g a s , oxygen

(27-28 pe rcen t )

"Azovs t a l l 1 , 17 19 cum 80% s i n t e r , limes tone , October , 1965 a tmospher ic a i r b l a s t

Tcherepovets s t e e l 100% f luxed s i n t e r , p l a n t , 2000 cum n a t u r a l g a s , oxygen J a n u a r y , 1966 (22-23 pe rcen t )

Novo-Lipetsk s t e e 1 100% f luxed s i n t e r , p l a n t , 2000 cum. n a t u r a l g a s , oxygen J a n u a r y , 1966 (25-26 pe rcen t )

(hours) 0 0.29 1 0.29 2 0 .23 3 0.17

Tes t on a B l a s t Furnace w i t h t h e use of a Com~ute r

I n January - February , 1968 and 1969, a n a lgor i thm t o check and c o n t r o l t h e b l a s t furnace thermal c o n d i t i o n s , developed a t t h e Moscow S t e e l and Al loys I n s t i t u t e , was t e s t e d on one of t h e fu rnaces of t h e "Azovstal" S t e e l P l a n t equipped wi th a computer and s u i t a b l e ins t rumenta t ion [5 ] . The b a s i s f o r t h e a lgor i thm i s t h e checking of t h e fu rnace thermal c o n d i t i o n s through t h e c a l c u l a t e d i n d i c e s of thermal c o n d i t i o n s ( ~ g and M ~ ) and e v a l u a t i n g t h e q u a n t i t a t i v e recommendations t o change t h e fu rnace o p e r a t i n g c o n d i t i o n s accord ing t o v a r i a t i o n s of t h e i n d i c e s . On t r i a l s i n January - February , 1968, t h e index M~ was made use of t o check t h e fu rnace thermal c o n d i t i o n s and determine t h e c o n t r o l l i n g e f f e c t s , thermal c o n d i t i o n s c o n t r o l being c a r r i e d o u t a t the same time by the index Mg.

A coke charge s i z e ( i . e . , t h e o r e load) served t h e r e a s a- c o n t r o l l i n g e f f e c t , m e t a l l i c burden of a charge being v a r i e d i n t h e even t o f ! b u r d e n changing only (F igure 2). I

Determining t h e c o n t r o l l i n g e f f e c t ( i . e . , e v a l u a t i n g t h e requ i red s i z e oE a coke charge t o main ta in the s p e c i f i e d s i l i c o n c o n t e n t i n the i r o n ) was performed a t hour ly i n t e r v a l s by d e v i a t i o n of magnitude and s i g n of ~ b - i n d e x from i t s mean v a l u e s f o r two e a r l i e r hours . This was done wi th t h e use of a s p e c i a l l y made l o g i c a l c h a r t , where numerical v a l u e s of Mb-index and recommended changAs of coke r a t e per charge were s e l e c t e d from t h e e a r l i e r exper ience and c a l c u l a t i o n s .

According t o the c h a r t , magnitude and s i g n of c o n t r o l l i n g e f f e c t s a r e determined b b a s per magnitude and s i g n of M1 and M2 parameters , which r e p r e s e n t d i f f e r e n c e s

between mean va lues of Mb i n d i c e s per hour f o r a d j a c e n t hour ly per iods of time.

The f i r s t d i f f e r e n c e g i v e s only an i n d i c a t i o n of the fu rnace thermal c o n d i t i o n s d e v i a t i o n h i t h e r and t h i t h e r a t a p a r t i c u l a r length of time a s compared wi th the previous one. The second d i f f e r e n c e a l r e a d y makes i t p o s s i b l e t o judge about the tendency of t h e fu rnace thermal c o n d i t i o n s t o change and fo l lowing t h e i r va lue t o s t r e n g t h e n t h e c o n t r o l l i n g a c t i o n on r e t e n t i o n tendency of t h e fu rnace t o c h i l l o r t o warm-up and weaken o r e l i m i n a t e them i n t h e oppos i t e case .

b I f t h e value of M1 exceeds t h e range of i n s e n s i t i v e n e s s (LOO ~ c a l / n ~ : n ~ of Ozb) , b u t l e s s than 200 Kcal, then i t i s recommended by the t a b l e t o change coke r a t e by 25 kg per cha r e ( a l l accompanying f i g u r e s a r e taken f o r a coke charge equa l t o 6-7 tons ) . When Mf runs i n t o 200-500 Kcal, then coke r a t e s h a l l be changed by 50 kg per cha rge , and i f i t i s more than 500 Kcal, t h e coke r a t e s h a l l b e changed by 150 kg per charge.

b b

The zone of i n s e n s i t i v e n e s s f o r M2 runs a s high a s 200 Kcal. I f the va lues of M2 a r e w i t h i n t h e l i m i t s of 200-500 Kcal , coke r a t e s h a l l be changed by 50 kg per charge. I f they exceed 500 Kcal than the chan e s h a l l be 150 kg. The s i g n of coke r a t e changing i s assumed o p p o s i t e t o t h a t of Mf and M!.

The development of t h e mentioned Table of C o n t r o l l i n g Act ions was p r i m a r i l y based on t h e a v a i l a b l e p o s s i b i l i t i e s t o c o n t r o l t h e b l a s t fu rnace thermal c o ~ t d i t i o n s through t h e use of a computer o p e r a t i n g a s a "foreman's adviser" . I n t h i s c a s e , i t was p r i m a r i l y intended t o c a r r y ou t t h e q u a l i t a t i v e c o n t r o l , when t o i n f l u e n c e heat ing-up of t h e furnace . I t s o p e r a t i n g personnel most commonly changed the coke r a t e only by 100 kg, r e g a r d l e s s t h e magnitude of the heat ing-up d e v i a t i o n , and i n t h e even t of a severe c h i l l , by the a d d i t i o n of one o r s e v e r a l sk ip loads of coke.

I n 1968 t e s t s were c a r r i e d o u t f o r the period of time from January 22nd up t o February 5 t h , when low-phosphorus manganese s t e e l q u a l i t y i r o n of increased s i l i c o n c o n t e n t was smelted i n t h e b l a s t furnace .

! U n t i l t h e t e s t s were s t a r t e d , the fu rnace worked r a t h e r smoothly, though i t s c e n t r e was over loaded w i t h m e t a l l i c burden and the o p e r a t i o n was s o l e l y pe r iphera 1 ( t h a t could be observed from t h e c h a r t of C02 d i s t r i b u t i o n round a r a d i u s ) .

The over loading of t h e furnace c e n t r e was a s s i s t e d by a g r e a t q u a n t i t y of supp l i ed s i n t e r of h igh b a s i c i t y , con ta in ing 30-35 percent of below 5 mm f i n e s r e s u l t i n g from numerous rechargings .

A 1 1 d a t a t o be processed by a computer can be c l a s s i f i e d i n t o two groups:

1. The informat ion which a r r i v e s a t t h e computer from t h e cont inuously a l i v e sensors ( t e n i n number) o f : top gas composition (C02, CO, H2), h o t b l a s t volume, temperature and humidi ty , cold b l a s t p ressure and temperature , oxygen con ten t i n b l a s t , n a t u r a l gas r a t e . The sensors were quest ioned every 3-4 seconds. The a r r i v i n g informat ion was averaged over hour ly i n t e r v a l s of time. The computer au tomat ica l ly took account of number of charges (bo th o rd ina ry and blank) d e l i v e r e d i n t o t h e furnace per each hour.

2. The second group of d a t a comprises the informat ion on the amount and composit ion of the charged m a t e r i a l s . This kind of an informat ion was in t roduced i n t o the computer manually. The time of s i n t e r (wi th changed chemical composit ion) a r r i v a l a t t h e fu rnace top was t e n t a t i v e l y determined from the m a t e r i a l of previous composit ion remaining i n b i n s and from i t s hour ly consumption a t the furnace .

There were th ree s toppages of t h e furnace dur ing t h e t e s t s (January 23rd, 25th and 26th) t o r e p l a c e burned coo l ing members and t o do some maintenance work. Besides , on January 23rd, a hanging of the burden m a t e r i a l s occurred. To improve gas d i s t r i b u t i o n i n the fu rnace , a p o r t i o n of "washing-out" burden m a t e r i a l s was charged ( f i v e b lank charges , t h r e e o rd ina ry charges , 25 tons of furnace c l i n k e r , two o rd ina ry charges , 25 tons of furnace c l i n k e r ) . For the period of time from the l a s t s toppage (on January 26th) and up t o t h e end of the t e s t , t he b l a s t furnace worked smoothly w i t h o u t ' s t o p p a g e s , hangings , d i s t u r b a n c e s of the s l a g tapping and h o t metal c a s t i n g schedules . Yet burden changes were being made dur ing t h a t period of t ime, by varying the r e l a t i o n between domestic and f o r e i g n s i n t e r a s w e l l a s manganese o r e per charge .

A s noted above, on t h e s e t e s t s the computer opera ted a s a "foreman's adviser" . A t the beginning of each hour the d a t a , accumulated and averaged f o r the previous one, was computed according t o the programmed formula, the r e s u l t a n t d i f f e r e n c e s of

b b M1 and M2 were analyzed i n accordance wi th the l o g i c a l t a b l e and the f i n a l r e s u l t s ( i n c l u d i n g va lues of ~ g , M~ and the recommended v a r i a t i o n s of the coke feed s i z e ) were brought o u t and p r in ted by a p r i n t i n g device of t h e computer.

The adopted zones of i n s e n s i t i v e n e s s and c o n t r o l ranges were checked dur ing the f i r s t two days of t h e t e s t s (January 23rd and 24 th ) . The recommendations, produced by the computer i n the course of t h i s p e r i o d , were not considered. The r e a l t e s t was s t a r t e d on January 25th and completed on February 5 t h a t 3:00 p.m.

F i f t y a c t i v e and 20 pass ive recommendations were produced by the computer f o r the period of t e s t s up t o the 5 t h of February. The a c t i v e one was aimed a t changing t h e b l a s t furnace work ing ,cond i t ions by means of varying the coke r a t e , whi le the pass ive recommendation was d i r e c t e d t o main ta in the e x i s t i n g c o n d i t i o n s of t h e furnace Tho success ive hour ly recommendations of t h e same s i g n produced by a computer were taken a s one recommendation.

Simultaneous examination of the changing of fu rnace thermal c o n d i t i o n s and t h e computer's recommendations (Figure 2) makes i t poss ib le t o draw a conc lus ion t o t h e e f f e c t t h a t e s s e n t i a l l y a l l recommendations took t h e c o r r e c t account of the furnace -'

heating-up and i t s tendency toward changing. Only two a c t i v e recommendations proved t o be wrong (one of these r e s u l t e d from the e a r l i e r stoppage of t h e f u r n a c e , the

o t h e r one was connected t o the burden changing).

The two week period of t e s t i n g has been subdivided i n t o n ine i n t e r v a l s of four days each, beginning from January 25 th , 26th and s o f o r t h . The number of executed recommendations i n these per iods (1-9) increased by the end of the t e s t s :

Period No. 1 2 3 4 5 6 7 8 9 Executed re-

commendations 4 4 3 3 3 4 7 7 7

The p ropor t ion of h o t meta l c a s t s w i t h s i l i c o n c o n t e n t s equal t o 0.7-1.0 percent ( s p e c i f i e d 0.8-0.9) had a l s o increased by the end of the t e s t s (Figure 3 ) . S i l i c o n con ten t v a r i a n c e dur ing the ind ica ted per iods ranged r e s p e c t i v e l y a s fo l lows:

Period No. 1 2 3 4 5 6 7 8 9

Average s i l i c o n c o n t e n t , 0.93 0.89 0.91 0.86 0.92 0.87 0.88 0.93 0.92 pe rcen t

Roo t-mean- square de- v i a t i o n , 0.23 0.19 0.18 0.20 0.22 0.15 0.19 0.16 0.14 percent

This provides the reason t o b e l i e v e t h a t a more c l o s e fo l lowing of the recommendations favoured t h e s t a b i l i t y of furnace hea t ing .

Over t h e whole t e s t i n g p e r i o d , the i n d i c e s Mb and Mg took account of the furnace h e a t i n g adequate ly enough. The i n t e r c o r r e l a t i o n normalized f u n c t i o n s between these i n d i c e s and s i l i c o n c o n t e n t , computed f o r t h e t e s t i n g pe r iod , d isplayed t h e a v a i l a b i l i t y of p o s i t i v e and r e l i a b l e r e l a t i o n s h i p .

Tabulated i n Table 1 , the i n t e r c o r r e l a t i o n c o e f f i c i e n t s be tween Mb and s i l i c o n c o n t e n t i n most of the c a s e s had maximum va lues i n the absence of a s h i f t bet.ween t h e moments of computation of both parameters. The a v a i l a b i l i t y of the maximum c o r r e l a t i o n between Mb and s i l i c o n c o n t e n t i n the f o r e c a s t i n g range, obta ined dur ing the t e s t s i n 1968, i s l i k e l y t o be connected wi th changing of the dynamic c h a r a c t e r i s t i c s of t h e b l a s t furnace process and c a l l s f o r f u r t h e r study.

The Mg-index has been b e s t a s s o c i a t e d wi th s i l i c o n con ten t i n i r o n i n the absence of a s h i f t between both parameters wi th t ime, i . e . , i t descr ibed furnace h e a t i n g a t t h e moment of time under review and could have been used t o c o n t r o l the furnace thermal c o n d i t i o n s by mois ture c o n t e n t and temperature of the a i r b l a s t .

b The M - index fo recas ted t h e change of s i l i c o n con ten t f o r two hours ahead and

t e s t s proved t h a t t h i s favoured the t imely producing of recommendations d i r e c t e d t o changing coke r a t e .

When t e s t i n g t h e a lgor i thm i n 1969 (from January 28th up t o February 6 t h ) , the planned resea rch program ( t h e computer recommendations being ind i spensab le t o i t s f u l f i l l m e n t ) f a i l e d due t o u n s t a b l e o p e r a t i o n of the computer. To compute the Mb-index, i t i s necessary t o accumulate the d a t a f o r four hours . This i s the reason why, i n case of the fu rnace s toppage, the recommendations were produced by the computer only four hours a f t e r t h e furnace s t a r t i n g .

A s a r e s u l t of the t e s t s i n 1969, t h e b l a s t furnace working d a t a had been accumulated f o r t h a t period of time. A f t e r t h e t e s t s were over , the i n d i c e s ~ g , Mb and t h e i r i n t e r c o r r e l a t i o n f u n c t i o n s wi th s i l i c o n con ten t were computed from t h i s

d a t a (F igure 4b).

During t h e t e s t s i n 1968, the Mg-index had n o t been demonstrated t o have a r e l i a b l e r e l a t i o n s h i p wi th s i l i c o n c o n t e n t , (F igure 4 a ) . The fol lowing f a c t o r s probably a r e t h e r e a s o n s ; bad work of gas a n a l y z e r s ; v a r i a b l e o x i d a t i o n of t h e m e t a l l i c burden r e s u l t e d from t h e varying p ropor t ion of p e l l e t s i n t h e fu rnace charge (from 1.0 t o 2.5 tons per cha rge) ; and a l s o f l u c t u a t i o n s i n t h e combined b l a s t composition.

b There has been found a p o s i t i v e and c l o s e t o s u b s t a n t i o n a l r e l a t i o n s h i p between

M and s i l i c o n c o n t e n t ( r a t i o r/ar = 2.4) f o r a f o r e c a s t i n g time equal t o four hours.

During t h e t e s t s i n 1969, t h e b l a s t furnace working was smooth and i t s thermal c o n d i t i o n s f l u c t u a t e d cons ide rab ly l e s s .

For t h e t e s t s conducted i n 1968 and 1969, t h e ranges of s i l i c o n con ten t v a r i a t i o n amounted t o 0.5- 1.65 and 0.25-0.85 p e r c e n t , r e s p e c t i v e l y , and those of Mb were w i t h i n t h e l i m i t s of 7400-9600 and 8400-9800 ~ c a l / n m ~ of 02(in burden), r e s p e c t i v e l y .

The narrowing o f t h e f l u c t u a t i o n s i n the furnace thermal c o n d i t i o n s has been by f a r a n important r eason why t h e c loseness of t h e r e l a t i o n s h i p between Mb and Mg i n d i c e s , on t h e one hand, and. s i l i c o n con ten t i n i r o n , on t h e o t h e r , d e c r e a s e d . . '

Conc l u s i o n

We came t o t h e conc lus ion t h a t , depending upon s p e c i f i c c o n d i t i o n o f t h e b l a s t fu rnace working and accuracy of sens ing u n i t s ( o r t r a n s m i t t e r s ) , t h e fo l lowing v e r s i o n s of t h e b l a s t fu rnace process thermal c o n d i t i o n s c o n t r o l and r e g u l a t i o n a r e p r a c t i c a b l e :

1. by top gas composit ion on ly , i . e . , by o u t l e t parameters ( t h e most world-wide known way) ;

2. by tonnage and composit ion of charge burden m a t e r i a l s on ly ;

3. a combined c o n t r o l method, when top gas a n a l y s i s a s w e l l a s burden m a t e r i a l s d a t a a r e put t o use.

T h e o r e t i c a l l y speak ing , any of t h e l i s t e d v e r s i o n s must produce t h e same r e s u l t s , because t h e phys ica l sense of the c a l c u l a t e d index of the fu rnace thermal c o n d i t i o n s remains i n v a r i a b l e ; bu t i n r e a l c o n d i t i o n s of t h e fu rnace working, these v e r s i o n s of c a l c u l a t i o n b r i n g about d i f f e r e n t r e s u l t s o n account of d i s s i m i l a r e r r o r of i n i t i a l d a t a . The discrepancy may become a s b i g a s 8-10 pe rcen t . Here i s a n example. While conduct ing t e s t s a t one of the s t e e l p l a n t s (USSR) where a combined scheme of c a l c u l a t i o n had been adop ted , the magnitude of Mb-index, es t imated from d a t a on q u a n t i t y and composit ion of burden m a t e r i a l s , was found t o be s y s t e m a t i c a l l y i n excess of t h e same f o r Mg-index by 800-900 Kcal , i . e . , 9 pe rcen t of t h e a b s o l u t e value of the Mb-index. I n a d d i t i o n , a phase s h i f t of 2-3 hours between f l u c t u a t i o n s of the Mg and Mb-index was observed a t t h e same time. The l a t t e r f a c t suggested t h a t t h e Mb-index (which provides longer f o r e c a s t i n g t ime) should be used t o c o n t r o l o r e load, whi le the Mg-index should be used t o c o n t r o l h e a t c o n t e n t of a i r b l a s t . Such d i s t r i b u t i o n of f u n c t i o n s i s a s s o c i a t e d wi th a subs t a n t i o n a l t r a n s p o r t a t i o n l a g a s f a r a s o r e load i s concerned and complete absence of t h a t f o r h e a t con ten t of b l a s t .

I n a d d i t i o n , t h e e x i s t i n g p o s s i b i l i t y of s e l e c t i n g ~ one ou t of t h e t h r e e c a l c u l a t i o n v e r s i o n s widens the scope of a p p l i c a t i o n of t h e descr ibed a l g o r i t h m f o r those b l a s t fu rnaces which have n o t been equipped wi th ins t rumenta t ion f o r cont inuous top gas a n a l y s i s . I n such a c a s e , r o u t i n e top gas a n a l y s i s w i l l be of use t o check the r e s u l t s obta ined s o l e l y on t h e b a s i s of d a t a on composit ion and q u a n i t i t y

of charged burden m a t e r i a l s .

The f i n d i n g s presented i n t h i s paper o f f e r t h e b a s i s f o r cons ide r ing t h e suggested method and a lgor i thm f o r thermal c o n t r o l w i l l f i n d a p p l i c a t i o n i n the p r a c t i c e of b l a s t fu rnace process c o n t r o l .

L i t e r a t u r e References

1. A. N. Pokhvisnev, Control of BF Process by Means of Measuring the Composition of Top Gas; Theory and P r a c t i c e of Meta l lu rgy , 1939, /I8

2. A. N. Pokhvisnev, L. Y. Rozhewski and N. K. Z h i l k i n , On t h e Problem of Automation of t h e BF Process S t a l , 1963, No. 10, pp. 875-878

3. A. N. Pokhvisnev, Rapid Heat Balance of the BF Process Symposium on "Problems of Ferrous Metal lurgy" , Vol. X X I I I , M e t a l l u r g i z d a t , 1946, pp. 23-33

4. A. N. Pokhvisnev, I. F. Kurunov, Y. S. Yusf in , L. Y. Rozhewski, Y. Mirny, "On the Problem of C a l c u l a t i o n of the Thermal Condi t ion of a B Furnace", I z v e s t i g a Vysshykh Uchebnykh Zavedeniy, Chernaya M e t a l l u r g i y a , 1966, //7, pp. 25-29, I

/ I l l , pp. 20121

5. A . N. Pokhvisnev, I. F. Kurunov, V. M. Klempert, S. T. P l i skanovsk i , G. T. Kaminski, I n v e s t i g a t i o n of the Algori thm f o r C o n t r o l l i n g the Thermal Condi t ion of a B l a s t Furnace, S t a l , 1971, / / I , pp. 9-12

0.4 6\" I .- - 0.2 $ :::F,OJ>Gj .6 0.0

6 7 8 9 1 0 1 2 3 4 5 6 7 8 9 1 0 1 2

1-3-66 1-4-66

CONSECUTIVE CASTS

4 1121201 4 ( 1 2 1 2 0 1 4 1 1 2 1 2 0 1 4 112120( 8 16 24 8 16 29 8

1-27-68 I 1-28-68 1 1-29-68 1-30-68

Fig. 1. Varying of in index and s i l i c o n

l6 T " l6 2T Fig. 2 . Comparison of t h e recommended

con ten t i n i r o n dur ing c a s t s a t b l a s t and a c t u a l coke r a t e ( t o n s oer charge) and 3 fu rnaces w i t h 2000 m e f f e c t i v e volume. h o t b l a s t mois tu re wi th s i l i c o n con ten t

Tcherepovets S t e e l P l a n t , January 3-5, i n i r o n dur ing t e s t s i n January 1968. 1966.

Si-% OPERATING PERIODS

Fig . 3. Char t of s i l i c o n c o n t e n t i n i r o n d u r i n g c a s t s f o r 1-9 p e r i o d s i n January- Tebruary 1968.

F ig . 4 A . I n t e r c o r r e l a t i o n f u n c t i o n s between M~ and Mg i n d i c e s and s i l i c o n con ten t i n i r o n i n t h e p rocess of t e s t s between January-February 1968.

-0.3 -16 -12 -8 - 4 0 + 4 +8 +I2 +I6

HOURS

Fig . 4B. I n t e r c o r r e l a t i o n f u n c t i o n s between M~ and ~g i n d i c e s and s i l i c o n con ten t i n i r o n i n t h e p r o c e s s of t e s t s i n January-February 1969.

DISCUSSION

A. K. Garbee

Senior Research Engineer, Raw Materials & Smelting Section, Research & Technology

Armco S t e e l Corporation, Middletown, Ohio

The cont r ibu t ion of Pk. Pokhvisnev and h i s colleagues t o t he 1972 Ironurnking Conference i s appreciated. Vx. Pokhvisnev, i n pa r t i cu l a r , has long been involved with the thermochemistry of b l a s t furnace processes. The work done over t he years a t t h e Moscow I n s t i t u t e of S t e e l and Alloys in applying thermochemical concepts t o t h e b l a s t furnace operat ion cons t i t u t e s a s ign i f i can t e f f o r t . The Ore Working Department i s t o be commended f o r t h a t e f f o r t .

The evolut ion of b l a s t furnace cont ro l schemes, in general , has been a gradual one. The implementation of these cont ro l techniques has been a f a r slower process. This slow r a t e may be changing.

As the authors noted, t h e b l a s t furnace operator has t h e r e spons ib i l i t y f o r g e t t i q mximum hot metal production a t ninimum cost . The rap id ly escalat ing cost of raw mater ia l s , e spec i a l ly coke, make maxhium ef f ic iency a t t he b l a s t furnace e s s e n t i a l t o a successful s t e e l p lan t . Implementation of a cont ro l algorithm designed t o f u l f i l l t h e cont ro l o r operator guide and da ta logging funct ions should be a s t r a t e g i c par t of any plan t o improve t h e e f f ic iency of a b l a s t furnace operation.

I n t h e preceding pa.per, t h e authors have l i s t e d t h r e e conceptual approaches t o t he cont ro l and regula t ion of t he t h e m 1 conditions in t h e b l a s t furnace. The cont ro l algorithm can be based on

1 ) t op gas ana lys is ,

2) quant i ty and character of charge mater ials , o r

3) t o p gas ana lys i s and cha,rge mater ia l s da ta combined.

Any one of t h e th ree might be appropriate f o r a given furnace operation. Experience with the c i t e d h s s i a n furnace indicated t h a t t he burden based index ( K ~ ) should be used t o cont ro l the ore load, with the to^ gas based index (#) reserved f o r cont ro l l ing t h e hot b l a s t .

There i s l i t t l e t o disagree with i n t h e development of t h e various cont ro l ind ices . The same subject i s discussed by Pokhvisnev e t a l . i n t he January 1971 i s sue of "Stee l i n t h e USSR. I'

I The burden based index i s of p a r t i c u l a r i n t e r e s t , because the working condition o f a b l a s t furnace i s l a rge ly dependent on charge make-up. However, t h i s algorithm is dealing with a complex system. Several questions a r i s e regarding t h e hardware required t o put t h e algorithm i n t o pract ice.

With what accuracy a r e charge weights known?

How a r e representa t ive samples of burden mater ia l s obtained?

What i s t h e t a r g e t coke moisture, and what i s t h e quenching p rac t i ce recommended f o r achieving t h a t no i s tu re in a uniform manner?

Can a s p e c i f i c coke savings be ascribed t o the use of t h e cont ro l technique?

It would be he lp fu l t o have answers t o these quest ions i n the near f u t u r e i n order t o properly i d e n t i f y t h e p r a c t i c a l v e r s a t i l i t y of t h e b l a s t furnace cont ro l algorithms and t o show how read i ly these concepts can be reduced t o prac t ice .

D i s c u s s i o n of œ: last Fu rnace P roces s Automatic

c o n t r o l " by A . N . Pokhvisnev e t a1

D . H . Wakelin

Jones & Laughl in S t e e l Corpora.t ion

P i t t s b u r g h , Pa. 15230

D i s c u s s i o n

T h i s p a p e r b r i n g s u s u p t o - d a t e w i t h p r o g r e s s on a u t o m a t i c c o n t r o l of t h e b l a s t f u r n a c e p r o c e s s i n t h e S o v i e t Union. P r o f e s s o r P o k h v i s n e v was one of t h e f i r s t p r o p o n e n t s o f t h e u s e o f t o p g a s a n a l y s i s t o q u a n t i f y t h e t r a n s i e n t t h e r m a l s t a t e of t h e b l a s t f u r n a c e and i s a t r u e e x p e r t i n t h i s f i e l d .

To r e a d t h e p a p e r i s somewhat l i k e l o o k i n g i n a m i r r o r f o r t h o s e of u s i n t h e U. S. who have a t t e m p t e d c o n t r o l b a s e d on t o p g a s a n a l y s i s . F i r s t t h e r e i s t h e p rob lem of t h e t o p g a s s y s t e m a v a i l a b i l i t y and a c c u r a c y , t h e n t h e s h o r t d a t a p e r i o d s w i t h n o t a l w a y s c o n c l u s i v e c o r r e l a t i o n s be tween c a l c u l a t e d t h e r m a l l e v e l s and h o t m e t a l c h e m s t r y and f i n a l l y t h e r e a l s t u m b l i n g b l o c k - smooth, c o n t i n u o u s f u r n a c e o p e r a t i o n .

F o r t h o s e who d o n o t have s u f f i c i e n t l y c o n t i n u o u s g a s a n a l y s i s , P r o f e s s o r P o k h v i s n e v h a s d e r i v e d e q u a t i o n s b a s e d on t h e c o m p o s i t i o n and q u a n t i t i e s of t h e m a t e r i a l s c h a r g e d , t h e b l a s t and i n j e c t e d a d d i t i v e s t h a t a r e u s e d . T h i s s u b s t i t u t e s f o r t h e s a m p l i n g and a n a l y s i s p r o b l e m s of t o p g a s s y s t e m s t h o s e a s s o c i a t e d w i t h raw m a t e r i a l s , w h i c h may be m n o r i f a c o n s i s t e n t b u r d e n i s a v a i l a b l e .

I t i s u n f o r t u n a t e t h a t t h e a u t h o r s d o n o t have more e x p e r i m e n t a l d a t a . The manner i n which t h e r e s u l t s f rom t h e o n - l i n e t e s t i n 1 9 6 8 a r e p r e s e n t e d i s r a t h e r c o n f u s i n g . Twelve d a y s of t r i a l have been c o n v e r t e d i n t o n i n e o v e r l a p p i n g p e r i o d s of f o u r d a y s e a c h , and f o u r t e e n a c t u a l e x e c u t e d recommenda t ions have been made t o a p p e a r a s i f f o r t y - t w o o f t h e f i f t y compute r

s u g g e s t i o n s were f o l l o w e d .

The s h o r t p e r i o d s u s e d f o r d e v e l o p j n g t h e c o r r e l a t i o n f u n c t i o n s between Mg, M~ and p i g - i r o n s i l i c o n c o n t e n t have u n d o u b t e d l y c o n t r i b u t e d t o t h e s i 7 e o f t h e f o r e c a s t t i m e s be tween them. C o n t r a r y t o t h e r e s u l t s shown i t would seem more l o g i c a l f o r t h e h e a t i n d e x Mg c a l c u l a t e d f rom t o p g a s a n a l y s i s t o have a t l e a s t a s g r e a t a f o r e c a s t t i m e v e r s u s s i l i c o n c o n t e n t a s t h e h e a t i n p u t j.ndex M~ d o e s . The c a l c u l a t i o n of M~ u s e s mean i n p u t v a r i a b l e s a v e r a g e d f rom t h e t i m e of c h a r g i n g t o a r r i v a l o f m a t e r i a l a t t h e bottorn of t h e f u r n a c e , w h e r e a s ~9 t a k e s i n t o a c c o u n t t r a n s i e n t c h a n g e s o c c u r r i n g i n . m a t e r i a l y e t t o a r r i v e a t t h e h e a r t h .

I F i n a l l y t h e r e i s t h e q u e s t i o n of t h e smooth f u r n a c e o p e r a t i o n . I n t h i s d i s c u s s o r ' s mind i t i s ve ry p robab l e t h a t i n p r o j e c t s of t h i s n a t u r e t h e e f f o r t s expended i n upg rad ing raw m a t e r i a l s , i n s t r u m e n t a t i o n and f u r n a c e a v a i l a b i l i t y i n o r d e r t o o b t a i n a s u f f i c i e n t l y s t a b l e o p e r a t i on, produce b e n e f i t s beyond which t h e c l o s e d l o o p computer c o n t r o l can show only marg ina l improvement.