Differentiated use of refractories in blast-furnace hot blast stoves

Conclusions In the service of blast furnace hot blast stoves the lining and checkerwork fail in individual zones as the result of deformation of the refractories, formation of cracks, and chemical corrosion of the lining under the action of low-melting dust at high temperatures.It was shown that the deformation of aluminosilicate refractories depends not only upon temperature, load, and hold but also to a large degree upon the physicochemical properties of the parts, especially upon the composition and quantity of impurities.On the basis of an analysis of the service of refractories in hot blast stoves recommendations were developed on differentiated use of refractories in the different zones of the lining and checkerwork.For lining of the walls and the checkerwork of high-temperature hot blast stoves operating with a blast temperature up to 1300°C (temperature under the crown 1500–1550°C) the use of the following forms of refractories (GOST 20901-75) is recommended: 1550–1200°C temperature zone — type DV dinas parts; 1200–1100°C temperature zone — type MKV-72 mullite-corundum parts; 1100–900°C temperature zone — type ShV-42 chamotte parts; 900–700°C temperature zone — type ShV-37 chamotte parts; 700–400°C temperature zone — type ShV-28 chamotte parts.To line the lower portion of the combustion chamber mullite-corundum parts of types MK-80 to Technical Specification 14-8-405-82 or MKV-72 must be used.Lining of the crown, the inner wall of the combustion chamber, the hot blast lines, and the gas burners must be done with mortars corresponding to the types of refractories used (dinas and VT-1) with the addition of 10–12% orthophosphoric acid.Type MKRP-340 mullite-silica fiber parts to GOST 23619-79 and other fiber materials are recommended for use as the compensation gap filler up to temperatures of not higher than 1150°C, and asbestos-vermiculite plates to GOST 13450-68 in the up to 600°C temperature zone.The shell of the hot blast stove in the high temperature zone must be covered with thermal-insulation gunited concrete.Translated from Ogneupory, No. 7, pp. 44–50, July, 1986.     

Service of nonpowderable dinas in high-temperature stoves of blast furnaces

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 physicochemical 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 dinas, its use should be tested in the operation of stoves with subcupola temperatures of 1500–1550°C.Translated from Ogneupory, No. 6, pp.28–31, June, 1972.     

Study of the service of high-alumina and kaolin refractories in the checkers and structure of blast-furnace stoves

Conclusions The structure of kaolin brick in the high-temperature zone of the stove after 6.7–7.2 years service at subcupola temperatures of 1300°C underwent substantive external and structural changes.In the structure of the stove made from high-alumina brick VGO-62 after six years service we detected substantially less change.In the kaolin brick of the upper rows of the checker three clearly defined zones are formed: working (slag), impregnated with alkalis, the transition zone (porcelain-type), and the least-changed zone. During the service of high-alumina refractories mullite crystallizes, which confirms the results of work carried out previously.Owing to the creep of kaolin and high-alumina refractories 4–5% shrinkage of the brick occurs in the upper rows of the checker, and at a depth of 2.5–6.0 m — 1.5–2.0%. The height of the checker diminishes under these conditions by 0.8–1.0 m.The densification of the structure of the upper rows of the checker corresponds to a reduction in porosity and an increase in the density of the brick.The temperature of initial deformation under load of 2 kg/cm² of the slagged kaolin refractories taken from the upper rows of the checker diminishes by 150–200°C, and in the lower layers of the checker it does not alter. This factor for high-alumina refractories in service increases by 160–190°C. In the high-temperature zone of the stoves it is desirable to test dense, high-alumina refractories containing 72–75% Al₂O₃.Translated from Ogneupory, No. 5, pp.14–19, May, 1972.     

Damage to stoves and measures to eliminate it

Conclusions As a result of investigations into newly developed refractories and a study of their service conditions in the stoves of blast furnaces, three basic types of failure in the structure and the checkers were determined:the formation of vertical cracks in the dome and walls; deformation of the checkers and the upper part of the combustion chamber; and failure of the lower part of the combustion chamber. The formation of cracks can be eliminated by selecting the optimum joints, and by using a design in the stoves which takes into account the properties of the refractories under variable temperatures.In order to reduce the deformation of the checkers and the combustion chamber it is recommended that these zones be made of refractories possessing the minimum creep, in the first case dinas with low embrittlement factors, and high-alumina products made of kaolin and calcined alumina.The lower part of the combustion chamber should be built from high-alumina and kaolin refractories possessing a high resistance to thermal shock.It is found that the upper rows of the checker become saturated with fusible compounds, formed when batch dust falls on the material, which means a substantial reduction in their thermal-mechanical properties, contributing to an increase in the deformation under load.To increase the blast temperature to 1300–1400°C it is necessary to use, in the high-temperature zones, mullite, mullite-corundum refractories based on kaolin, and low-embrittlement dinas with the compulsory completion of a number of measures: installation of an emission combustion chamber, removal of the dome load from the working walls, the use of perforated checkers, the construction of a special device for putting the furnace on draft, purification of the gases and air to remove dust and fusible substances, a reduction in the heating period, and the organization of paired-parallel operation of the stoves.Translated from Ogneupory, No. 1, pp. 23–32, January, 1972.     

Thermal strength,deformation, and thermal fatigue characteristics of dinas products before and after service in the high-temperature zones of the hot-blast stoves

Conclusions The deformation and strength characteristics of the dinas specimens (drawn from the industrial walling and checkerwork products before and after service) were studied under uniaxial tension and compression at a temperature up to 1600°C.It was established that their ultimate strength decreases with increasing test temperature and that the load-bearing capacity is insignificant at 1570–1600°C; when subjected to cyclic heating (1250 1450°C) in the laboratory tests as well as during service in a hotblast stove operating under alternating oxidizing and reducing environmental conditions, dinas bricks exhibit embrittlement and softening (their tensile and compressive strength characteristics differ by almost 10 times).The obtained data showed that the limiting temperature at which the strength characteristics of dinas abruptly decrease under a constant stress and multiple cyclic action of alternating atmospheres amounts to 1600°C; this fact must be taken into account when designing and operating hot-blast stoves.Translated from Ogneupory, No. 6, pp. 19–22, June, 1986.     

Creep of a dinas based mortar used in coke ovens

Conclusions Owing to the competition of the growth process occuring due to the phase transformations of quartz, the compressive creep of the specimens of the MDK-1 dinas mortar is low and in the 1100–1300°C range, it amounts to 0.2–0.3% within a period of 50 h at a stress of 0.6 N/mm²; and it amounts to 2–2.5% at 1400°C under the same conditions. A stress level of 0.2 N/mm² is insufficient to suppress the growth of the mortar (in the original mortar specimens as well as in the specimens fired at the test temperature for a period of 10 h). The deformability of the constituent specimens having a mortar joint is determined mainly by the deformation of the mortar layer.The rigidity of the experimental dinas mortar indicates its low capacity to relax the stresses in the coke oven lining.Translated from Ogneupory, No. 6, pp. 1–5, June, 1989.     

Effect of some production factors on the life of dinas refractories at high temperatures in reducing conditions

Conclusions A reduction in the maximum grain size of dinas batches and an increase in pressing force ensure high apparent density in the articles, which increases their resistance to the action of solid reducing agents.The optimum firing temperature for dinas refractories should be considered as 1400°C; an increase or reduction in this by 40°C causes a fall in the resistance of the dinas to reduction, which is connected with the incompletion of the processes of crystallization (at 1360°C) and excess embrittlement of the structure (at 1440°C).Prolonging isothermal soaking of specimens during their first firing contributes to more complete mineral formation, growth and ordering of the crystals of the high-temperature modifications, which increases the material's resistance to the action of the reducing agents.Translated from Ogneupory, No. 8, pp. 31–37, August, 1981.     

High-temperature abrasion of refractories

Conclusions The most rapid abrasion in dinas refractories occurs in the 700–900°C range; periclase 800–1000°C; mullite-corundum articles exhibit a smooth increase in abrasion with rise in temperature. The abrasion of refractory concretes is much higher than for bricks.It is possible by determining the abrasion resistance to carry out quality control of the firing process, and also to check the quality of linings made from concretes.Translated from Ogneupory, No. 1, pp. 13–14, January, 1991.     

Thermal expansion of dinas — The basis of drying and heating the lining of coke batteries

Conclusions To determine the optimum condition for drying and heating up of coke batteries accurate data on the thermal expansion of dinas parts intended for lining the various zones of the coke ovens is necessary.A design of quartz dilatometer providing of dinas in the 20–750° range has been developed.Translated from Ogneupory, No. 5, pp. 42–46, May, 1989.     

Study of some properties of quartz ceramics in a wide temperature range

Conclusions The strength of quartz ceramics determined during short-term loading gradually increases with temperature rise to 1100°C. Differences in the short-term strength connected with porosity at elevated temperatures are preserved.The creep of quartz ceramics obeys an empirical rule for the creep in the range 1100–1300°C. At higher temperatures the process sharply deviates from the normal rule in connection with the cristobalite formation in the material. The rate of deformation of the porous materials compared with dense materials increases by an order of magnitude.The gas permeability of the quartz ceramic with an apparent porosity of up to 8% is very slight. However, the specimens are not vacuum tight.Marked volatilization of quartz ceramics occurs in vacuum only at temperatures above 1200–1300°C.The electric conductivity of quartz ceramics is the same as that of fused quartz, and hardly changes with density changes in the porosity range 1–10%.Translated from Ogneupory, No. 4, pp. 45–51, April, 1971.     

Use of magnesite refractories in the chequerwork of the air heaters of blast furnaces

Conclusions Magnesite refractories are a promising material for use in the upper rows of the chequerwork, particularly where it is necessary to increase the thermal capacity of the air heaters without increasing their dimensions.When the magnesite refractories are used, the mass of the chequerwork and the unit load on the subchequerwork grid and the lower rows of the chequerwork are increased.The improved efficiency of magnesite refractories in the chequework of air-heaters by comparison with other types of refractory is becouse of their high storage capacity for heat as a result of the increased apparent density and better thermophysical characteristics.The magnesite refractory used in the chequerwork should contain a minimal amount of impurities, particularly of Fe₂O₃.When magnesite refractories are used to replace dinas, the cost per ton of chequerwork increases 50% while for the replacement of mullite by magnesite, the cost per ton of chequerwork is reduced by 16%.Contact between the magnesite refractories and the dinas (without a load) is permissible at a temperature not higher than 1450°C; with sillimanite, at not more than 1350°C.In order to prevent the action of finely dispersed particles of dust and alkali oxides accidentally introduced into the air heaters it is sensible for the upper row of chequerwork to be made from sillimanite or mullite refractories.The theoretical extreme temperature for the use of magnesite refractories in the chequerwork of the air heaters (allowing for creep and the interaction with other types of refractories) is 1650°C for M-I type blocks and for M-II, not more than 1450°C. For greater safety it is recommended that the ultimate working temperatures be reduced by 150°C.Taking into account the favorable experience abroad in using magnesite blocks in the chequerwork of air heaters, it is necessary to carry out industrial tests of the magnesite products in the upper zones of the chequerwork.Translated from Ogneupory, No. 7, pp. 32–36, July, 1982.     

Statistical data on thermal expansion in dinas refractories for coking ovens

Conclusions Statistical data have been obtained on the temperature dependence of the thermal expansion for dinas refractories for coking ovens in the range from 20 to 1400°C. The temperature coefficient of linear expansion does not vary monotonically as the temperature rises and has peaks near the temperatures of the phase transformations in tridimite, cristobalite, and quartz, at which the values attained are 50·10^–6, 80·10^–6 and 10·10^–6 K^–1 correspondingly. The averaged TCLE should be considered as standard reference ones. The thermalexpansion curves for dinas brick show hysteresis due to the phase transitions in silica.Translated from Ogneupory, No. 5, pp. 30–33, May, 1987.     

Features of the production technology and the properties of the components made from Al2O3 and SiO2 of different particle-size distributions

Conclusions It is recommended that the mullite-silica products made from polydispersed mixtures of alumina and silica in the presence of oxide additives be fired at a temperature of 1380–1410°C according to the firing regime of the dinas refractories. We obtained products containing a mixture of iron and calcium oxides (maintaining their total content not exceeding 3% and a 21 ratio). Oxide additions exceeding 3.5% have a negative effect on the technological effectivenesss and the properties of the products.In the absence of additives, mullite-silica products must be fired at 1550–1600°C maintaining the heating and cooling rates below 30°C/h. The mullite-silica products based on the polydispersed mixtures of corundum and crystalline quartz are recommended for the linings of the units used in the production of steel and cast iron and for lining coke-ovens and other thermal units (furnaces).Translated from Ogneupory, No. 7, pp. 9–12, July, 1988.     

Effect of the firing medium and other technological parameters on the properties and phase composition of dinas articles on dry mineralizers

The effect of the gaseous firing medium and other technological factors (grain composition of the charge, pressing pressure, temperature and time of the hold at the final firing temperature) on the properties of dinas and the degree of transformation of silica in it is investigated. On the basis of results of a comparative analysis of the phase compositions and properties of specimens the following parameters are recommended as optimum technological parameters for fabricating dinas on dry mineralizers that provide high operating characteristics for the articles: the maximum grain size of quartzite is 2 mm, the pressing pressure is at least 50 MPa, the firing temperature is 1420°C, the duration of the hold is 44 h. Petrographic and x-ray analyses are used to show the preferableness of firing dinas in a reducing medium, which promotes a fuller transformation of quartz in the dinas and provides high operating properties for the articles.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 14–17, June, 1996.The work has been done in collaboration with L. M. Khvostishkova. The physicochemical properties of the specimens were investigated in specialized laboratories of the Ukrainian Research Institute of Refractories.     

Determining the maximum possible rates of single sided heating of refractories

Conclusions Tests on refractories on a special rig showed that the permitted heating rates on the hot face, without producing important changes in the engineering properties, are as follows: for dinas refractories 3 deg/min, magnesite 7.5 deg/min, and chrome — magnesite and magnesite — chromite up to 20 deg/min. These rates are greater than the calculated rates which may be due to the effect of structural heterogeneities in the product. However, the use of such heating rates for the refractories in the structure of heating units is possible after careful practical checking in industrial conditions.Translated from Ogneupory, No. 4, pp. 51–55, April, 1971.     

Firing dinas in a tunnel kiln with natural gas

Conclusions The firing of products for open-hearth, cooking, and glass furnaces and electric-steel furnaces was developed in a tunnel kiln 180 m long. Firing can be done on a level with other types of fuel with natural gas, the combustion of which should be done with double duct burners.For the firing of dinas products it is necessary to prolong the firing zone and this permits maximum temperatures to operate over a large section. With an annual output of 55,000 tons of products, the goods in the kiln are well cooled. The temperature of the goods upon discharge from the kiln does not exceed 40–50°C.During a four-year working period the factory staff substantially improved the working factors of the kiln. The specific fuel consumption for firing products in a tunnel kiln of this type is very low.Translated from Ogneupory, No. 8, pp. 22–25, August, 1969.     

Lining fireboxes in a high-pressure steam boiler

Conclusions The service conditions of the lining in high-pressure steam boilers with gas turbine blowing are characterized by a heating temperature above 1500–1550°C on the working surface and repeated sharp changes in temperature at rates of up to 100 deg/min during heating and up to 85 deg/min during cooling. In these conditions it is advisable to use silicon carbide refractories which are the most heat-resistant.The developed designs for the refractory linings to go into the fireboxes of high-pressure boilers have satisfactory heat-insulating properties. Owing to the combination of silicon carbide products with the ramming body, the choice of the most optimum product shape, and making them from silicon carbide with a complex oxynitride bond, such linings are very resistant and recommended for wide use.Translated from Ogneupory, No.2, pp. 18–23, February, 1970.     

The thermomechanical and deformation properties of fibrous heat-insulation refractories

Conclusions An analysis was carried out of the deformation characteristics in uniaxial compression and of the creep and compression strength at temperatures of 400–1100°C of heat-insulation slabs produced from kaolin wool and an organic adhesive.The impregnation with an organic adhesive reduces the deformation of the slabs at temperatures of 20–600°C to a significant extent.The kaolin wool heat-insulation slabs can be used as compensation and construction material for the regenerations of blast furnaces including large-capacity furnaces because the slabs are capable of supporting long-term loads up to 1 kg/cm² at temperatures of 20–1100°C.Translated from Ogneupory, No. 7, pp. 51–54, July, 1976.     

Spalling resistance of oxide products

Summary Articles made of magnesia can be recommended for operation infrequently changing temperature conditions, and with changes of the order of 400° C in the range 1900–1500° C, and for shorter periods of operation with temperature variations of up to 900° C in the range 1900–1000° C.     

A high-alumina lining for crucible-type induction furnaces

Conclusions In crucible-type induction furnaces, the durability of a lining of compound MLM-1 (Technical Specifications 14-8-119-74) is several times higher than that of a quartzite lining or a sintered lining based on corundum and kyanite-sillimanite concentrate. The compound can be recommended for crucible furnaces when melting high-grade cast iron and steel.The density of compound MKE-78 can be increased by adding up to 20% synthetic corundum No. 6 and 3–4% orthophosphoric acid solution. Its high refractoriness makes it possible to use this lining as well for melting steel with a casting temperature of 1680–1700°C Its durability in this case is at least 2 months.Translated from Ogneupory, No. 3, pp. 24–28, March, 1977.