REQUIREMENTS OF REFRACTORIES FOR ELECTRIC FURNACES1

This article is essentially a survey, giving, however, not generalized statements, but a definite discussion of the refractories problems now existing in the important electric furnace processes. After summarizing some of the general refractory requirements of electric furnace work, the author discusses the specific conditions and refractory requirements in steel, iron, and non-ferrous metal melting, smelting furnaces for producing iron, ferro-alloys and calcium carbide, anti in furnaces for melting refractory materials. The article closes with a summary of outstanding present developments. Varied conditions probably make an ideal, universal refractory almost impossible of attainment. The relatively cheap refractories standardized in fuel-fired furnaces have been very largely used in electric furnaces. There is, however, a growing use for specialized “super-refractories,” even at greatly increased cost, that will stand various especially severe conditions in certain kinds of work. Important recent developments are higher firing temperatures, the use of high aluminous fire clays, and increased experimental work on fused refractories. The commercial production of sufficiently high firing temperatures, and the development of satisfactory bonds for special refractories are at present perplexing problems.     

Interface behaviour and corrosion behaviour of magnesia refractory by alkaline slag in an alkali recovery furnace

The adhesion of Na₂CO₃ slag to the surface of refractories in an alkali recovery furnace can cause corrosion and spall. Magnesia refractories can be used as linings in alkali recovery furnaces owing to their strong corrosion resistance to alkali slag. However, the permeability resistance of magnesia refractories is relatively poor. Hence, the interface and corrosion behaviours of slag cladding on magnesia refractories were studied using sessile drop and static crucible tests. The experimental results showed that an increase in the heating rate positively affected the cladding of the molten column on the refractory surface. The microstructure, element changes, and chemical composition changes of the corroded refractories were analysed using SEM-EDS and XRD. Thermodynamic simulation of the reaction between the slag and refractory was performed using Factsage 7.3. The results indicate that the generated forsterite filled the pores of the magnesia refractories. The microstructure of dense slag-refractory interface layer was formed, which prevented the infiltration of slag phases and alleviated the corrosion of refractories by the slag.     

Service of zirconia refractories in continuous furnaces for quartz glass melting

Data are given on the durability of baddeleyite refractories of grade TsTsPP, which contain no stabilizing additives, in operation in the lining of continuous furnaces for melting quartz glass at the Dzerzhinskii Glass Works. In operation in contact with molten quartz at a temperature of (2000 Mp 10)°C, the average (for a year) durability has increased up to 82.5 days compared with the lining made of refractory sectors of CaO-stabilized ZrO₂, which had a durability in these furnaces up to 25 days. It is noted that the durability of furnace linings made of baddeleyite refractories is limited by the durability of the roof plates. With the use of a water-cooled roof, the durability of the furnace lining was increased up to 267 days, but the heat losses were higher. The results of comparative tests of baddeleyite refractories with different porosity (between 9.6% and 22.3%) and of those based on natural baddeleyite of natural grain size and on electrofused ZrO₂ are given. No differences in their durability have been established. The results of examining the refractories after their operation in furnaces are also considered.Translated from Ogneupory, No. 2, pp. 25 – 28, February, 1994.     

Calculation of the emission of nitrogen oxides in electric resistance heating furnaces

The present paper is devoted to the least studied topic in the field of use of modern electric heating equipment, namely, pollution of the atmosphere by nitrogen oxides and reduction of the intensity of this effect by coating furnace linings. Experimental and theoretical estimates of reduction of the emission of nitrogen oxides in electric furnaces with a lining with an intensifying refractory coating of the IVA-2 and IVAKS-2 types and an algorithm for calculating the emission of nitrogen oxides are presented. The plotted process of metal heating in an electric furnace shows that the use of IVA-2 and IVAKS-2 refractory coatings decreases the emission of nitrogen oxides by 22–28% both in a still oxidizing medium and under forced feeding of air into the heating zone. A method for calculating the characteristics of the process of emission of nitrogen oxides in electric furnaces is suggested. Results of the work can be, applied to heating and heat-treatment furnaces of forging and rolling mills, especially in environmentally vulnerable regions. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp. 21–24, February, 1998.     

Strength of magnesia refractories in combined thermal cyclic and mechanical loading of them

Conclusions As the result of laboratory tests of periclase-chromite refractories produced by different methods (MKhS, MKhV, and MKhVP) under the combined action of thermocyclic and mechanical loads possibilities were revealed of the most effective use of them in relation to the service conditions of plasma and electric arc furnace linings. The results of production tests of MKhS, MKhV, and MKhVP refractories at various furnace lining operating temperatures agree with the laboratory data and make it possible to draw the following conclusions:MKhS parts, as the most heat resistant, may be used successfully in heating the furnace lining working surface to 1700–1750°C, which corresponds to a temperature on the boundary of spalling of the refractory of 1400–1500°C.An increase in the lining operating temperature to 1800–1900°C (1550–1650°C on the boundary of spalling) requires the use of refractories with a combination of such properties as heat resistance and high-temperature strength. These requirements are met to the greatest degree by MKhV parts.In the future for large tonnage plasma and electric arc furnaces with high mechanical loads MKhVP high-strength parts may be recommended for the lining. However, for successful use of these parts it is necessary to aim to increase their heat resistance.Translated from Ogneupory, No. 5, pp. 43–47, May, 1985.     

Reaction of high-alumina refractory with chromium vapors in vacuum

Conclusions The main cause of the failure of high-alumina refractory of mullite composition during service in vacuum furnaces is the chemical reaction of chromium vapors with the alumina, as a result of which a readily melting vitreous silicate substance is formed together with gaseous silicon monoxide and corundum with chromium dissolved in it. Therefore, in order to increase the life of linings of vacuum furnaces it is necessary to use high-alumina refractories with a maximally high content of Al₂O₃.Translated from Ogneupory, No. 6, pp. 38–40, June, 1969.     

Use of aluminum phosphate as a bond for refractory corundum products and washes

Summary The use of aluminum phosphate is desirable for preparing corundum products and washes based on commercial calcined alumina.A composition was developed ensuring strong bonding of corundum refractories and also of corundum refractories with steel and graphite.The bonded refractory components (corundum) are tightly held on graphite components of thermocouples after 15 h operation in the walls of electric arc furnaces at 2000°C.Aluminophosphate bond increases the spalling resistance of corundum products and also raises their strength.     

THE USE OF SILICON-CARBIDE REFRACTORIES IN BOILER FURNACES1

The chief causes of failure of refractories in boiler furnaces are slag adhesion, erosion, and failure of structure, dependent on the type of coals and feeds used. Some of the physical and chemical properties of different types of refractories are given. The development of bonded silicon carbide brick is mentioned. Clinker trouble is eliminated by use of these brick in furnaces using all kinds of present day stoker equipment. Failures due to chemical reaction between iron and silicon carbide, and torch action on a wall produced by a blast of flame under pressure together with medium amounts of iron in the ash are discussed. Air cooling of walls is taken up. Installations of air-cooled silicon-carbide blocks are listed and discussed. Water cooling, the use of preheated air, and conditions of use of the water wall are taken up.     

无芯感应炉用炉衬材料的选择

介绍了感应炉炉衬耐火材料的使用环境 ,分析了感应炉炉衬结构以及在不同的使用环境下的使用情况和材料选择     

Destruction of refractories by carbon monoxide at high temperatures

Conclusions Laboratory tests carried out showed that carbon monoxide at 500 ± 20°C destroys all types of refractories, regardless of their chemical and mineral composition with more or less substantial porosities. Destruction of the refractories occurs more rapidly the higher the porosity and the lower the degree of vitrification.Since the main cause of destruction in refractory in the shaft of a blast furnace is the action of carbon monoxide, the shaft needs to be lined with gas-impermeable refractories. The apparent porosity of the high-density high-grog refractory for the shaft of glass furnaces should be not more than 5–7%. With this density the refractory is practically gas-impermeable, and therefore is not destroyed by carbon monoxide. The optimum content of alumina in high-grog refractories should be considered as 35–37%.In the nature of a discussion. Comments on the articles by A. V. Gorokh and I. M. Galemina, Ogneupory No. 9 (1964).     

Degradation of magnesia-chromite refractory in ZnO-containing ferrous calcium silicate slags

To assess the impact of changes in slag type on the degradation of refractory linings of secondary copper smelters, the degradation behavior of direct-bonded and fused grain magnesia–chromite refractories in ZnO-containing ferrous calcium silicate slags was studied via dynamic refractory finger and static refractory crucible tests at 1200 °C under Ar atmosphere. The effect of ZnO level in the slag and refractory type on the degradation behavior was determined. A combination of microstructural and compositional characterizations of tested refractories, and thermodynamic calculations leads to comprehensive understanding of the degradation mechanism of the refractories. Based on the degradation mechanism, conclusions can be given about the prediction of lifetime of refractory lining when the slag type changes from fayalite-based to ferrous calcium silicate-based slags for secondary copper smelting.     

THE PREVENTION OF DISINTEGRATION OF BLAST FURNACE LININGS1

Theories and observations on the causes of disintegration of fireclay refractories in blast furnaces are given and a process is developed for improving high iron clays for this use. The disintegration of refractories in blast furnace linings is initiated by alteration in the iron spots. Ferric oxide is reduced to ferrous oxide at 500°C and hastens the cracking of 2CO to CO₂+C₁ the carbon being retained by the lining. When Fe₂O₂ is converted to Fe₃O₄ the brick will not disintegrate.     

Mineral formation in chrome-magnesite refractories in rotary furnaces used to produce defluorinated phosphates

Conclusions Silicates of chrome-magnesite refractories in a large or small degree react with the components of the batch and the decomposition products of apatite. With rise in temperature this reaction sharply increases.The silicate bond in the working zones of chrome-magnesite refractories is located in the liquid or plastic state (depending on the positioning of the brick in the lining and the distance from the working surface of the refractory), since the tricalcium phosphates in contact with the refractory forms a eutectic at 1308°C. The eutectic melt easily penetrates deep down into the refractory, filling its pores and cracks. The bond between the grains and sections of periclase and the chromite is weakened under these conditions, the structure is destroyed with a break in the continuity of the individual grains and the sections which are opened by the firing products moving into the furnace.The service life of the chrome-magnesite refractories can be increased by sharply reducing the quantity of melt formed in the working and partly in the sintering zones of the refractory, which can be obtained by reducing the content of silicates (forsterite and montichellite) in the original brick.The use of denser periclase-spinel refractories should also favor an increase in the life of the linings of rotary furnaces in the firing zone.Translated from Ogneupory, No.2, pp.41–46, February, 1967.     

Increasing the heat resistance of refractory linings in autogenous smelting setups for nonferrous metallurgy

Data on Russian and foreign refractory materials used in smelters of nonferrous metals are reviewed. The dependence of the durability of refractories on various factors, including some design features and operating conditions of setups for autogenous smelting of sulfide materials, is considered. Special attention is paid to domestic developments, such as the flare-oxygen and Vanyukov smelting furnaces. A modern trend is to combine linings with inserted cooling elements (jackets) and to create refractory-slag linings. Another trend is a continuing search for a more perfect design for enclosures for the above setups. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp. 34–38, February, 1997.     

Slag resistance of refractories in the lining of an arc steel melting furnace

The interaction of refractories of various grades with liquid slags whose samples were taken in different stages of melting from an electric furnace are investigated by wetting for temperatures ranging from 20 to 1550°C. The compositions of the slags differed in the CaO/SiO₂ proportion and the content of chromium oxide. It has been established that the olivinite refractory has advantages under the conditions of electric melting, which seems to be explainable by its chemical composition and specific pore structure. The results of the investigation were used to develop compositions of gunite powders for torch guniting of linings of the slag belt of an arc steel melting furnace. Translated from Ogneupory, No. 9, pp. 18 – 20, September, 1995.     

Service of refractories in a glass-tank furnace producing glass fiber by the single-stage method

Conclusions Chromium oxide blocks developed by the Ukrainian Scientific-Research Institute of Refractories from fine-grained and coarse-grained compounds, like the chromium oxide refractories S-1215 material made by the Corhart company of the USA, ensure a high resistance in the linings of the tanks of glass furnaces producing glass fiber. Their wear occurs on account of chemical solution in the glass at temperatures above 1500°C.Magnesite-chromite refractories rapidly react with aluminoborosilicate glass and cannot be recommended for the second layer of the structure of the glass tanks.Mullite-corundum refractories are subjected to rapid wear in the crown of glass furnaces due to the interaction with vapors of the glass batch at high temperatures.In order to increase the length of the operation of fiber-producing furnaces we recommend that the first and second layers of the tank lining, the channel, and the feeder be made of chromium oxide refractories, and the suspension walls and roof of the furnace from corundum refractories. These recommendations are being used for building the furnace for a second campaign.Translated from Ogneupory, No. 1, pp. 5–12, January, 1980.     

我国高炉用耐火材料的进展

结合高炉炉身、炉缸、炉底、风口和出铁沟的工作条件,阐述了相应部位用耐火材料的发展进程。     

Corrosion mechanism of lightweight microporous alumina-based refractory by molten steel

Lightweight refractory linings for industrial furnaces have become important subjects of development in high-temperature industries. The reaction mechanism between a lightweight microporous alumina-based refractory material and molten steel was investigated in this study. The main mechanism of refractory damage was structural spalling, caused by steel penetrating the pores. The many micropores in lightweight microporous alumina have high specific surface area and reactivity, inducing the formation of FeO–Fe₂O₃–Al₂O₃ phases. This impeded the further penetration of molten steel and the direct dissolution of refractory oxides, promoting greater resistance to molten steel than that shown by common tabular alumina-based refractories, in which Fe does not react and steel penetration through the pores cannot be retarded.     

Operational experience with coke batteries and preservation of existing coke furnaces 2. Maintenance and information services

Contributions to the Seventeenth Annual Seminar of Coke-Industry Specialists by representatives of companies that maintain Russia’s coke furnaces in operating condition are summarized. Problems in the provision of refractories for the repair and reconstruction of furnace linings are considered, along with new repair methods and the work of research and design organizations on improving coke production.