3. 4. 5. 6. 7. 8. 9. 10.

Zangs Ludger, F a c h b e r i c h t e H[ittenpraxis, Metallweiter., No. 2, 77-82 (1978). S. Yasukava, I s h i k a w a j i m e - H a r i m a Giho, 1__5.5,No. 2, 259-270 (1975). R. A s s e n m a c h e r et al., P r o c . 3rd Inst. Iron and Steel Cong., Chicago 1978, Metals P a r k , Ohio (1979),pp. 570-579. Yu. N. Tuluevskii et al., Chern. Metall., Byull. NTI, No. 14 (754), 27-29 (1975). G . G . A r i s t o v et al., in: Steelmelting Production: Supplement to the journal " S t a [ ' , " Moscow (1958), pp. 241-252. Iomota Dzyundzi et al., Taikabutsu, 2._99, No. 229, 87-90 (1977). E. E i s e r m a n n et al., E l e k t r o w a e r m e Int., 3_~2, No. 5, 256-261 (1974). A . S . P l y a s h k e v i c h et aL, Stal', No. 3, 208-213 (1976).

SERVICE OF

OF

BLAST V.

DINAS

IN

HIGH-TEMPERATURE

STOVES

FURNACES L.

Bulakh

and

N.

V.

UDC

Pitak

666.762.2:669.162.231.8

A wide range of r e f r a c t o r i e s is used in the USSR and abroad for building the stoves of blast furnaces. F i r e c l a y , dinas, and high alumina a r t i c l e s a r e commonplace. Information exists on the use of corundum, m a g n e s i t e , and f o r s t e r i t e b r i c k s for this purpose. The USSR has developed and introduced into industry a method for producting dinas for stoves; it has outstandingly good p r o p e r t i e s and r e c o m m e n d s itself for service. At the Krivoi Rog steel works, an examination was made of stoves after 3.5 y e a r s operation at subcupola t e m p e r a t u r e s of 1350~ The cupola, walls, combustion c h a m b e r , and c h e c k e r s in the h i g h - t e m p e r a t u r e zone of this stove were made of dinas; the upper c o u r s e of the c h e c k e r s was made of aluminous brick VGO-62 with 62% by weight A1203. The stove was stopped because of the e x c e s s i v e heating of the guard plate in the hotblast connecting pipe (sleeve) and the i n c r e a s e in the a e r o d y n a m i c r e s i s t a n c e of the c h e c k e r s . It was established that the s t r u c t u r e of the cupola in the stove was in a good condition, free of scaling and slag erosion. We o b s e r v e s e v e r a l c r a c k s 5-10 m m wide and stretching to 2.5-3 m, passing only through the m a t e r i a l joints of the s t r u c t u r e f r o m the base of the cupola. These c r a c k s developed, apparently, during cooling of the cupola. The internal s u r f a c e of the cupola s t r u c t u r e is clean, without fusion or slag deposits. The upper c o u r s e of the c h e c k e r made of aluminous brick is strongly slagged over the entire height of the b r i c k and was melted into a monolith, the cells lost their r e g u l a r g e o m e t r i c a l shape. The section of the upper c o u r s e of the c h e c k e r was reduced in c o m p a r i s o n with the original by 35-40%. TABLE 1. P r o p e r t i e s of Dinas after Service in the C h e c k e r s of Stoves * Cornpressive Course ofcheckersin Refractoriness 3ensity, g/crns 3pen porosity,% under load 0.2 strength, MPa above MPa...~ 94.5 7,7--8,1 2,38 1510 SecondT 57.4 9,4-- 10,0 2,37 1640 92.6 18,3--21,0 2,33 1670 ThirdJ" . . . . 65.3 16,7--20,4 2,32 1660 79.9 16,1--19,1 2,32 1680 FourthJ" 112,5 18,6--20,0' 2,32 1650 69.1 15,3--17,3 2,33 1670 Fifth . . * P r o p e r t i e s of dinas before s e r v i c e : RUL 0.2 MPa 1640~ density, 2.36-2.37 g/cm3; open p o r o s i t y , 17.0-20.8%; c o m p r e s s i v e strength, 4 1 . 2 - 6 6 . 0 MPa. The n u m e r a t o r shows the f a c t o r s for the top of the brick, and the denominator the bottom. Ukrainian S c i e n t i f i c - R e s e a r c h Institute of R e f r a c t o r i e s . 34, N o v e m b e r , 1981. 0034-3102/81/1112-0565507.50

T r a n s l a t e d f r o m Ogneupory, No. 11, pp. 31-

9 1982 Plenum Publishing C o r p o r a t i o n

565

F i g . 1. E x t e r n a l a p p e a r a n c e of corroded dinas brick. A f t e r the r e m o v a l of the f i r s t c o u r s e of the c h e c k e r , m a d e of V G O - 6 2 b r i c k , i t w a s r e v e a l e d t h a t the s e c o n d and s u b s e q u e n t c o u r s e s of the c h e c k e r m a d e of d i n a s w e r e in e x c e l l e n t c o n d i t i o n . T h e r e g u l a r g e o m e t r i c a l s h a p e s of the c e l l s w e r e p r e s e r v e d o v e r the e n t i r e a r e a of the c h e c k e r and the c e l l s w e r e c l e a n . The s h a p e of the c h e c k e r b r i c k s w a s c o m p l e t e l y p r e s e r v e d . S o m e of the b r i c k s in the s e c o n d c o u r s e of the c h e c k e r h a d t r a c e s of s l a g e r o s i o n and c o r r o s i o n . T h e c h e c k e r b r i c k s f r o m t h e s e c o n d and s u b s e q u e n t c o u r s e s c o u l d be f r e e l y r e m o v e d . T h e s t r u c t u r e s of the w a l l s w e r e in a s a t i s f a c t o r y c o n d i t i o n ; in the u p p e r p a r t t h e r e w e r e t r a c e s of d e p o s i t i o n s f o r m e d u n d e r s l a g a c t i o n . T h e d i n a s s t r u c t u r e of the c o m b u s t i o n c h a m b e r s w i t h o u t s c a l i n g , c r a c k s , or slagging was not deformed. In e x a m i n i n g t h e s t o v e s , we s e l e c t e d s p e c i m e n s of d i n a s a r t i c l e s f r o m the s e c o n d to t h e fifth c o u r s e s of t h e c h e c k e r s . T h e p r o p e r t i e s of t h e a r t i c l e s a r e shown in T a b l e 1. A f t e r s e r v i c e in t h e u p p e r c o u r s e s of the c h e c k e r , the d i n a s p o s s e s s e d a high m e c h a n i c a l s t r e n g t h and a r e d u c e d d e n s i t y ; i t did n o t h a v e a f t e r - e x p a n s i o n when h e a t e d to 1450~ w h i c h i n d i c a t e d t h a t the q u a r t z i s f u l l y c o n v e r t e d . T h e p o r o s i t y of t h e d i n a s in s e r v i c e h a r d l y a l t e r e d . It i s p o s s i b l e t h a t i t at f i r s t i n c r e a s e d s o m e w h a t on a c c o u n t of t h e i n v e r s i o n s in t h e q u a r t z , and then w a s r e d u c e d a s a r e s u l t of r e c r y s t a l l i z a t i o n , and the f i l l i n g of the p o r e s by o x i d e s b r o u g h t in with the d u s t , a i r , and g a s . T h e t e m p e r a t u r e of i n i t i a l d e f o r m a t i o n u n d e r l o a d of 0.2 Ml>a f o r the b r i c k s ( e x c e p t the u p p e r d i n a s c o u r s e of t h e c h e c k e r s ) i n c r e a s e d by 20-40~ T h e c h e m i c a l c o m p o s i t i o n of the d i n a s a f t e r s e r v i c e i s shown in T a b l e 2. D u r i n g s e r v i c e in the u p p e r c o u r s e s of the c h e c k e r s the d i n a s s i l i c a c o n c e n t r a t i o n w a s s o m e w h a t r e d u c e d b e c a u s e of t h e i n c r e a s e i n t h e a m o u n t of i r o n and c a l c i u m o x i d e s c a r r i e d in with t h e d u s t on t h e a i r and g a s . A p a r t i c u l a r l y h i g h c o n c e n t r a t i o n of i r o n o x i d e s w a s n o t e d in t h e u p p e r p a r t of the b r i c k t a k e n f r o m the s e c o n d c o u r s e of the c h e c k e r s . T h e a m o u n t of a b s o r b e d i r o n o x i d e s w a s r e d u c e d in the t h i r d c o u r s e of t h e c h e c k e r s , w h i l e t h e r e w a s no a b s o r p t i o n by the r e f r a c t o r y in t h e f o u r t h c o u r s e . T A B L E 2.

C h e m i c a l C o m p o s i t i o n of D i n a s a f t e r S e r v i c e *

Course of stove checker Second . . . . . . Third Fourth

..... ....

Sit:).

Al,t:),+TiO 2

Weight parts, "~o Fe,O, C~O MgO

1,70

17,28

1,58

I I I I

2,71 1,66 1,88 1,50

~ 3,50 2--~ 1,80

4-~ 2,97 ~ 2,4,

93,40 t

1,34

2-~

~

88,76 I 91,78 91,68 93,78

Trace

alkalis I l.t:).i.:~ 0,51

I

I

0,04

I

- -

0,10

0,42 I 0--~ 0,27 I 0,32 I 0,25 I 0,36 10,20

0-~

] 0,33

~

*Chemical composition of dinas before service: 93.52% SiO2, 1.657o AIzO3 + TiO2, 2.27% Fe203, 2.0%CaO, 0. 06% MgO, 0.04% alkalis, 0.2% loss on ignition. The numerator shows the data for the top of the brick and the denominator f o r the b o t t o m . LOSS on ignition. 566

TABLE 3.

P r o p e r t i e s of Dinas Brick after Service Typical mineral composition (volume %)

Chemical composition (wt.%) Refractory Z

one

Si02

Least changed 92,14 1,73 Transition !90,44 2,07 Fused edge Fused, lacelike Lateral surface

gTg

t-1203q TiO, F%Os

3--1 0,28 1,57 1,36 4,29 10,36 10,21 0,32 28--30155--571 4--1

89,74 2,35

1,73 4,41 0,63 0,20 0,26

86,62 2,44

1,60 6,4010,8110,10 I

I

187,76 2,13 2,17 5,67[0, I0,22

0,36 18--201587601 5--7 0,16 23--25157--591 5--7

6--8 6--8 6--8 7--9 8--10

Dinas a r t i c l e s serving in the c h e c k e r s acquire a zoned s t r u c t u r e , absorb slags, and are tridymitized. The bond of the dinas is well t r i d y m i t i z e d and in the main, c o n s i s t s of c o a r s e p r i s m s and pitlike twinnings of t r i d y m i t e (maximum c r y s t a l size 500-1100, predominant 100-250 ~m), forming growths and a g l a s s y substance. The c r y s t a l s of t r i d y m i t e are s o m e t i m e s c o r r o d e d and cracked; inclusions of skeletal a g g r e g a t e s of magnetite a r e also s o m e t i m e s seen. The gaps between the c r y s t a l s are filled with brownish g l a s s y substance, strongly saturated with magnetite and fine g r a i n s of hematite. Also encountered are sections that can probably be classified as i r o n - - c a l c i u m silicates of the hedenbergite type. The g r a i n s of quartzite a r e completely converted and do not p o s s e s s c l e a r outlines; they are to be identified among the bonding bodies through their c r y s t a l s of tridymite which are much l e s s in evidence. The m a x i m u m size of the tridymite c r y s t a l s is 50-100, predominantly 1 0 - 5 0 ~ m . The thin needles, p r i s m s , and pitlike twirmings of tridymite penetrate the c o l o r l e s s , and m o r e r a r e l y , light-yellow g l a s s y substance. Quartz and cristobalite are absent. The magnetite and hematite content is reduced as we move away f r o m the p e r i p h e r y of the working zone inside the brick, and also f r o m the upper c o u r s e of the c h e c k e r into the lower courses. The c r y s t a l s of tridymite a r e much l a r g e r in the working zone (especially in the bond) and s m a l l e r in the thickness of the brick. The pore size in the bricks is reduced from the second c o u r s e of the c h e c k e r s to the fifth. The t h e r m a l conductivity of the dinas c h e c k e r b r i c k after s e r v i c e was 15-20% higher than before s e r v i c e (conductivity of dinas before s e r v i c e 1.75-1.85, after s e r v i c e 2.05-2.15 W / ( m . K) at 1400~ which is due to the r e c r y s t a l l i z a t i o n of the silica at high t e m p e r a t u r e s , the entry of oxides and the formation of growths of c o a r s e c r y s t a l s . The r i s e in the t h e r m a l conductivity of dinas in s e r v i c e positively affects the heat-exchange work of the stoves. Thus, during s e r v i c e the p r o p e r t i e s of the dinas were improved. T h e r e were falls in the true density and porosity, i n c r e a s e s in the m e c h a n i c a l strength and t h e r m a l conductivity, and also a fall in a f t e r - c o n t r a c tion during heating to 1450~ Anomalous wear in the brick was revealed n e a r the wall s t r u c t u r e of the c h a m b e r s of the c h e c k e r s after an investigation of stove No. 16 at the I i ' i c h steel works; in e a r l i e r studies of the stoves this was not observed. In a c c o r d a n c e with the specified r e c o m m e n d a t i o n s , the stove was made of a h i g h - t e m p e r a t u r e version of dinas (for possible operation at subcupola t e m p e r a t u r e s of 1500-1550~ with individual resting of the cupola on an additional wall not connected with the main wall. The stove operated for 6 months at a subcupola t e m p e r a t u r e of 1350~ It was stopped and cooled because o f the formation of a blowout in the housing of the cupola trap. The lining of the cupola, the combustion c h a m b e r s , and c h e c k e r s were in excellent condition. The height of the lining of the main (radial) wall over the c h e c k e r level was 825 m m (11 c o u r s e s of brick). No changes o c c u r r e d in the g e o m e t r i c a l f o r m of the main wall; t h e r e was no cracking. In the top p a r t of the wall we detected g r o o v e s of various depths due to the c o r r o s i o n of the r e f r a c t o r y by fusible slag melts. The channels o c c u r r e d only on the wall of the c h e c k e r c h a m b e r and were absent f r o m the combustion c h a m b e r side. Many of the channels t e r m i n a t e d at the level of the c h e c k e r surface. The formation of the g r o o v e s in the dinas s t r u c t u r e was helped by the action of the reducing a t m o s p h e r e in the g a s e o u s period with the simultaneous effect of fusible dust that was brought in. The possibility of this is indirectly c o n f i r m e d by the p r e s e n c e

567

Fig. 2.

Breakdown of c e l l s at the c h e c k e r periphei:y.

even in the waste c o m b u s t i o n p r o d u c t s of up to 17o c a r b o n monoxide. The e x t e r n a l a p p e a r a n c e of the dinas a r t i c l e s e x t r a c t e d f r o m the v e r y d e e p e s t c h a n n e l s is shown in F i g . 1. The p r o p e r t i e s of the dinas r e f r a c t o r y a f t e r s e r v i c e a r e shown in Table 3. The i n v e s t i g a t i o n of the dinas a r t i c l e s e s t a b l i s h e d that q u a r t z i s a b s e n t f r o m all zones. This i n d i c a t e s the high d e g r e e of t r a n s f o r m a t i o n in the dinas. The c e n t r a l p a r t of the b r i c k which c o n s i s t s of the l e a s t changed and t r a n s i t i o n zones, c o n s i s t s of e r i s t o b a l i t e , t r i d y m i t e , and a l a r g e amount of g l a s s with a high r e f r a c t i v e index t y p i c a l of dinas. A p p r o a c h i n g the upper working (lacelike) and side s u r f a c e s of the b r i c k we note o x i d e - e n r i c h m e n t of the dinas: aluminum, c a l c i u m , m a g n e s i u m , and i r o n brought into the working space by dust in the a i r and g a s , which l e a d s to a change in the g l a s s y s u b s t a n c e of the dinas, a r e d u c t i o n in i t s v i s c o s i t y and p a r t i a l outflow of m e l t under the action of m e c h a n i c a l and t h e r m a l s t r e s s e s , and during cooling -c r y s t a l l i z a t i o n of s i l i c a t e s f r o m it. The content of g l a s s in the bond i s r e d u c e d , t h e r e is a fall in i t s r e f r a c t i v e index, and a g r a d u a l p a r t i a l d e s t r u c t i o n of the t r i d y m i t e of the bond with the f o r m a t i o n of a "lace" s t r u c t u r e . The r e d u c t i o n in the SiO 2 content f r o m the c e n t e r to the edge zones a l s o i n d i c a t e s the p r o b a b i l i t y of v o l a t i l i z a t i o n of s i l i c o n monoxide, f o r m e d as a r e s u l t of the d e c o m p o s i t i o n of s i l i c a under the action of r e d u c i n g conditions. Some s t e e l p l a n t s have o b s e r v e d breakdown in the d i m e n s i o n s of the c e l l s in the p e r i p h e r a l s e c t i o n s of the u p p e r c o u r s e s of stove c h e c k e r s which i s due to the c o m p e n s a t i o n g a p s being to s m a l l (Fig. 2). On the b a s i s of an a n a l y s i s of the s e r v i c e of r e f r a c t o r i e s in the s t o v e s of b l a s t f u r n a c e s , we can conclude that dinas i s a r e s i s t a n t m a t e r i a l and s a t i s f i e s the d e m a n d s p l a c e d on b r i c k for the h i g h - t e m p e r a t u r e zones of s t o v e s working at subcupola t e m p e r a t u r e s of up to 1550~ The use of dinas i n c r e a s e s the b l a s t t e m p e r a t u r e in s o m e m e t a l l u r g i c a l f a c t o r i e s to 1200-1360~ while e n s u r i n g p r o l o n g e d and r e l i a b l e working of the stove c h e c k e r s . The f i r s t s t o v e s built with dinas have been working f o r m o r e than 10-14 y e a r s . To p r e v e n t the d e s t r u c t i o n of the p e r i p h e r y c e l l s , we r e c o m m e n d the following gap s i z e s between the c h e c k e r and the w a l l s ( a c r o s s the zones): with s i x - s i d e d c h e c k e r s -- 50 m m for dinas, 30 m m f o r MKV-72 and ShV-42 r e f r a c t o r i e s ; 20 m m f o r ShV-37 and ShV-28; for c h e c k e r s with s q u a r e c e l l s -- 75 m m for dinas, 40 m m for MKV-72 and ShV-42 and 20 m m for ShV-37 and ShV-28. In o r d e r to i n c r e a s e the s e r v i c e life of the c h e c k e r s , it i s n e c e s s a r y to e s t a b l i s h in all b l a s t f u r n a c e s d e v i c e s which will e n s u r e d r a f t in the f u r n a c e s and a l s o to s p e c i f y c e n t r a l feed and cleaning of a i r f o r c o m bustion.

568