SERVICE

OF

NONPOWDERABLE

HIGH-TEMPERATURE

DINAS

STOVES

V. D. Tsigler, V. L. and I. F. Usatikov

OF

IN

BLAST

FURNACES

Bulakh,

UDC 666.763.3:669.162.231

In connection with the i n c r e a s e d t e m p e r a t u r e s of the blow, the s e r v i c e conditions of r e f r a c t o r i e s in the h i g h - t e m p e r a t u r e zones of b l a s t furnace s t o v e s , e s p e c i a l l y in the c h e c k e r s , a r e undergoing c e r t a i n changes. TABLE 1. P r o p e r t i e s of the Dinas after Service* 4 I r !

~

The Ukrainian Institute has developed a technology for dinas which is not r e a d i l y e m b r i t t l e d (nonpowdering type) for s e r v i c e in the h i g h - t e m p e r a t u r e zones of the stoves working with a t e m p e r a ture under the cupola of up to 1550~ In 1966 using the developed technology the Red A r m y Dinas F a c t o r y manufactured a batch of these products using Ovruch q u a r t z i t e s for the stoves of the b l a s t furnace at the Zaporozhe Steel F a c t o r y [1]. The c h e m i c a l c o m position of the products was 94.0-94.8% SIO2, 2.0-2.2% CaO, 1.72.0% Fe20 3.

~.~

1

Lower Upl~r

1700 19,9 1,86 2,32 1670 14,8 2,00 2.36

2

Lower Upper

1680

The p r o p e r t i e s of the products were: r e f r a c t o r i n e s s 17001710~ r e f r a c t o r i n e s s under load of 2 k g / c m 2 1620-1640~ comp r e s s i v e s t r e n g t h 372-765 k g / c m 2, apparent p o r o s i t y 17.7-21.5%, a p p a r e n t density 1.9-1.95 g / c m 3, density 2.35-2.38 g / c m 3, a f t e r expansion at 1450~ 0.17-0.20%, coefficient of t h e r m a l conductivity at 1200~ on the hot face 1.51-1.59 k c a l / ( m .h .deg), at 1400~

20,0 1,88 2,34 1650 15,9 1,98 2,36

* Temperature of initial deformation in the upper part of the brick 2 was 1650~ lSUa . . . . . . . . . . . . . . . . . . . . . .

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Fig. 2

F i g . 1. Drying and heating cycles for stove No. 8 at the Z a p o r o z h e Steel Plant: 1) actual; 2) stated. Rate of t e m p e r a t u r e r i s e up to 500~ 4 deg/h, f r o m 500 to 700~ 5 deg/h, above 700~ 10 deg/h. At a cupola t e m p e r a t u r e of 700~ b l a s t f u r nace gas was t r a n s m i t t e d through the b u r n e r , and a i r was injected; at a cupola t e m p e r a t u r e of 920~ the fan to the b u r n e r was switched on. F i g . 2 . Dinas c h e c k e r b r i c k (1, 2) a f t e r 3 y e a r s ' o p e r a t i o n . 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 . 31, June, 1972.

T r a n s l a t e d f r o m Ogneupory, NO. 6; pp. 28-

9 1972 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00.

375

TABLE 2. Chemical Composition of Dinas after Service, % Brick

1

2

Part of bric~

! Lower Upper Lower Upper

TABLE 3. Typical Mineral C o m position of Dinas after Service Content'."%0

68

I

Lower 82--85 1--2 4--5 10--i] Upper 86--90 1--2 3-4 6--8

SiO~

AlzOs-~-TiOsFe20~ CaO MgO

loss on

NazO

K,O

ignition

92,90

90,00

2,04 2,26

1,44 2,70

2,89 0,22 3,87 0,22

0,13 0,17

0,12 0, 17

0,22 0,38

91,74 89~70

2,01 2, 16

1,79 4,40

3,42 t 0,20 2,55 0,22

0,17 0,19

0,17 0,19

0,08 0,24

1.76-1.77 k c a l / ( m 9h . deg), specific heat at 12 00~ and at 1400~ 0.31 c a l / ( g . d e g ) .

0.2 9 c a l / ( g 9deg),

Studies were also made of the deformation p r o p e r t i e s of the l o w - e m b r i t t l e m e n t dinas at different t e m p e r a t u r e s , loads, and times. Studies showed that at 1450~C a load of 10 k g / c m 2, and at 1500~C with a load of 6 k g / c m 2, in a period of 10 h, there is no deformation in the silica brick; at 1550~C and with a load of 4 k g / c m 2 the b r e a k down of the dinas c o m m e n c e d after 3 h 10 min, at 1600~C and a load of 2 k g / c m 2 failure was noted a f t e r 40 min.

Lower 87--89Nil 1"2 10--12 Upper 85--90Trace Nil 10--15

Using the l o w - e m b r i t t l e m e n t dinas in the stoves of the blast furnace at the Zaporozhe Steel F a c t o r y , we built h i g h - t e m p e r a t u r e zones as follows: the cupola, walls, combustion chamber, and c h e c k e r s (about 45% of the total height). In building the walls, in o r d e r to compensate for the thermal expansion and residual additional expansion in the silica b r i c k during s e r v i c e , using calculations of the planning division of the Zaporozhe Steel F a c t o r y , we specified the construction after e v e r y 3-5 bricks of combustible inserts 5 mm thick; with this purpose in mind, the dimensions of the dinas checker products a c r o s s the thickness were reduced to 128 m m instead of 130 m m for f i r e b r i c k as used in the lower zone of the checkers in the stoves, The s t r u c t u r e of the walls and the cupola w e r e made with silica plasticized m o r t a r MG-1 (GOST 5338-60). 2

The stove after drying and w a r m i n g in a period of 15 days in J a n u a r y 1967 was then put into operation. The drying cycle and the heating cycle are shown in Fig. 1. During the y e a r the t e m p e r a t u r e under the cupola in the stove was 1450~ then we noticed overheating of the cupola housing, in connection with which the t e m p e r a t u r e under the cupola was reduced to 1350~ The cause of the overheating was established after examination of the external s u r f a c e of the cupola s t r u c t u r e . Heat insulation of the dinas s t r u c t u r e was made f r o m tripoli b r i c k in one l a y e r 125 m m thick. At a subcupola t e m p e r a t u r e of 1450~ and a relatively enhanced thermal conductivity for the l o w - e m b r i t t l e ment dinas in contact with the dinas - t r i p o l i brick, the t e m p e r a t u r e apparently reached 900~ (possibly higher), which led to the sintering of the tripoli brick, breaking up (with gaps up to 30-40 mm) of the s e p a r a t e b r i c k s , and loss in their thermal insulation p r o p e r t i e s . To prevent this phenomena, subsequently it was decided to make the heat-insulating s t r u c t u r e of the cupola with a double l a y e r of m o r e effective lightweight r e f r a c t o r i e s . During paired parallel operation of the stoves in the blast furnace the working cycle for the e x p e r i mental unit was as follows: gas period time 2 h 20 min, air period 2 h, t e m p e r a t u r e under the cupola 1350~ at the c o m m e n c e m e n t , and 1200~C at the end of the air period, t e m p e r a t u r e on the joint of the dinas f i r e b r i c k checker 850~ at the s t a r t and 680~C at the finish of the air period. During stoppage of ~he blast f u r nace non draft," the extraction of the combustion products was done without the experimental stove. After 2 y e a r s 10 months operation the state of the dinas s t r u c t u r e in the experimental stove was e x amined after cooling for 10 days; under these conditions the t e m p e r a t u r e under the cupola in the f i r s t 48 h was reduced f r o m 1350 to 500r The dinas s t r u c t u r e of the cupola, c h e c k e r s , and combustion chamber was found to be in a s a t i s f a c t o r y state. The working surface of the dinas b r i c k of the cupola was d a r k - g r a y in color without scaling, c r a c k s , or fusion. The internal s u r f a c e of the s t r u c t u r e of the cupola contained five v e r t i c a l shallow c r a c k s 1-2 mm wide, passing a c r o s s the joints between the b r i c k s ; they had f o r m e d obviously during cooling of the cupola.

376

The working surface of the checker was horizontal without p r o t r u b e r a n c e s and shrinkage cavities; the cells of the checkers were clean without clogging up by dust or displacement. We did not o b s e r v e any fusion of the individual b r i c k s in the cells of the c h e c k e r s ; they were easily s e p a r a t e d without f o r c e . The working s u r f a c e of the s t r u c t u r e in the upper part of the dinas combustion c h a m b e r , was clean, and unslagged, while the lower part made f r o m chamotte b r i c k was fused. In o r d e r to study the changes in the p r o p e r t i e s of the l o w - e m b r i t t l e m e n t dinas in s e r v i c e we selected two bricks f r o m the f i r s t row of the checker (Fig.2). The dimensions of the b r i c k s being studied were 230 • 130 • 38 m m and were p r a c t i c a l l y entirely p r e s e r v e d . The s u r f a c e of the b r i c k 1 was shiny, dark brown in color, without t r a c e s of destruction; in the upper part of the brick there were s e p a r a t e dark gray spots f o r m e d due to saturation with oxides which had been c a r r i e d in with the air and the gas. In the central part of the b r i c k there were lighter nonshiny bands at the site of contact with other b r i c k s in the c h e c k e r . The surface of the upper half of the b r i c k 2 was dark gray in color with t r a c e s of some destruction, and in the lower part it was shiny, and dark brown in c o l o r . There was no zoned s t r u c t u r e in the f r a c t u r e of the b r i c k . The p r o p e r t i e s of the dinas after s e r v i c e a r e given in Table 1, and the chemical composition in Table 2. T h e r e was no a f t e r - e x p a n s i o n of the dinas at 1450~ The r e s u l t s of the study show that the w o r k e d dinas undergoes a certain reduction in the r e f r a c t o r i n e s s at the top of the b r i c k s , while the r e f r a c t o r i n e s s of the lower part r e m a i n s p r a c t i c a l l y the same as b e f o r e s e r v i c e . T h e r e was no substantial densification of the upper part of the b r i c k as a r e s u l t of the absorption of iron oxides (see Table 2). In the lower s e c tions the apparent p o r o s i t y was unaltered. The dinas after s e r v i c e had the minimum density, which indicates completion on it of the quartz degeneration p r o c e s s e s . This is confirmed by p e t r o g r a p h i c analysis (Table 3). The increased density at the top of the product is due to the saturation by migrated oxides, the density of which is much higher than the density of the silica modification. It is typical that the low e m b r i t t l e m e n t dinas after s e r v i c e is distinguished by a reduced thermal expansion, which at 200~ is 0.22%, at300~ 0.4%, at 500~ 0.63%, at 800~ 0.78%, at 1000~ 0.94%, and at 1400~ 0.90%. Study of the spent b r i c k s under the m i c r o s c o p e indicates a uniformly grained s t r u c t u r e . The s p e c i mens consist of tridymite, solid solutions of pseudowollastonite, cristolbalite with iron metasilicate, and glass. The tridymite is present in the form of prisms, and m o r e rarely in the form of tablets and pit-like twinnings; in this case in the upper part of the bricks the content of tridymite is greater than in the lower. In brick 1 and the lower part of brick 2 the glass phase is colored brown, in s o m e sections the glass has recrystallized with the formation of very thin dendritic crystals of cristobalite and brown grains, classified probably as a solid solution between the pseudowollastonite and the iron metasilicate (CaSiO~-FeSiO~). In the upper part of the brick 2 the glass phase is black, and opaque as a result of impurities of iron oxides. Rarely skeletal crystals of eristobalite can be seen. Studies of the dinas after s e r v i c e in the upper row of the checkers showed that because of the action of the high t e m p e r a t u r e s in the low embrittlement dinas the p r o c e s s e s involved in the quartz transitions were completed without e m b r i t t l e m e n t of the s t r u c t u r e , and the hot p r o p e r t i e s were only slightly changed. Thus, the low e m b r i t t l e m e n t dinas is suitable for s e r v i c e in the high t e m p e r a t u r e zones of the walls, c h e c k e r s , and cupola of the stoves of blast furnaces operating at subcupola t e m p e r a t u r e s of 1450~ The use of this kind of dinas in the last five y e a r s has s p r e a d rapidly: at the p r e s e n t time m o r e than 15 stoves a r e in operation, including a block of stoves for a blast furnace with a volume of 3000 m 3. Using dinas in the h i g h - t e m p e r a t u r e zones we should b e a r in mind that it has special p r o p e r t i e s : the tendency of dinas to expand during heating, and during s e r v i c e . To prevent the action of dinas expansion the Institute U k r g i p r o m e z has developed a design for a stove with an independently supported cupola. The use of dinas is effective if the s t r u c t u r e made f r o m it during operation will operate in variable t e m p e r a t u r e conditions of 800-1550-800~C. In c o n t r a s t to aluminosilieate r e f r a c t o r i e s , during s e r v i c e of which in h i g h - t e m p e r a t u r e stoves with certain conditions there is a growth of the cells in the c h e c k e r s , dinas sucks up the oxides, and so the cells

377

r e m a i n clean for a long t i m e . However, to p r e v e n t s l a g erosion and d e t e r i o r a t i o n of the hot p r o p e r t i e s of the dinas, and also to prolong the life, when putting a b l a s t furnace on draft it is n e c e s s a r y to "turn off~ the stove. In the operation of h i g h - t e m p e r a t u r e stoves it is i m p o r t a n t to specify careful cleaning of the a i r used for heating. CONCLUSIONS Experience with the use of low-powdered (low embrittlement) dinas in the high-temperature zones (walls, cupolas, combustion chamber, and checkers) of blast furnace stoves showed that at subcupola temperatures of 1350-1450~C after 3 years service the original physieochemieal properties of the product were not impaired, and the structure had preserved its satisfactory condition. A study of the properties of low-powdered dinas after service showed that despite the reduction in the density as a result of additional transition in the quartz, the structure of the dinas is not embrittled, but is densified. Considering the relatively good deformation properties of the low-embrittlement be tested in the operation of stoves with subeupola temperatures of 1500-1550~

378

dinas, its use should