Effect of Carbon Aggregates on the Properties of Carbon Refractories for a Blast Furnace
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INTRODUCTION
THE blast furnace (BF) is used at the beginning of the iron production process to reduce the iron oxide ores. Because of the need to increase productivity in recent years, it has become necessary to enlarge the BF volume and increase the hot metal temperature. In the lower portion of a BF where the molten iron accumulates—especially in the portion below the iron notch—the surface of the lining refractory layer is in contact with the molten metal at a temperature between 1400 C and 1600 C. Thereafter, the lining refractory layer is often worn and damaged by various factors, such as the molten metal penetration, thermal stresses, carbon dissolution, carbon oxidation, and alkalia attack.[1–3] Thus, it has been of worldwide consensus that hearth carbon refractories are the main culprit that determine the life expectancy of a BF. To prolong the life of a BF, higher requirements for the properties of BF carbon refractories are suggested, especially for the thermal conductivity, microporous structure, molten iron erosion, and alkali-attack resistance, because a strong microporous structure can prevent the penetration of molten iron and thereby prevent the formation of embrittle structure. Highthermal conductivity can control the interfacial viscosity of molten iron and form the hardened layer of XILAI CHEN, Ph.D. Student, YAWEI LI, YUANBING LI, and LEI ZHAO, Professors, SHAOBAI SANG, SHUJING LI, and SHENGLI JIN, Teachers, and SHAN GE, Senior Engineer, are with the State Key Laboratory Breeding Base of Refractories and Ceramics, Wuhan University of Science and Technology, Hubei, PR China 430070. Contact e-mail: [email protected] Manuscript Submitted June 3, 2009. Article published online January 5, 2010. 420—VOLUME 41B, APRIL 2010
metal—the so-called scull—to provide greater protection to the furnace hearth and bottom by increasing corrosion resistance and cooling capability.[4–8] Regretfully, so far in China, the longevity of carbon refractories for a BF has not reached satisfactory levels, which may be mainly attributed to the poor properties of the carbon aggregates (approximately 60–70 pct[9,10]) used in carbon refractories. The anthracite resource is abundant, and most carbon refractories for a BF are made by using calcined anthracite as the main carbon aggregates in China because of its excellent volume stability and anti-molten iron erosion[11,12]; graphite, silicon, and ceramic phases are added as well. Graphite such as flaky graphite and/ or artificial graphite can effectively increase the thermal conductivity of such materials. Si is in situ of formed SiC whiskers to reduce the pore size and improve the microporous structure. Ceramic phases such as corundum, magnesia, and andalusite etc. can increase the molten iron erosion resistance. The properties of carbon refractories are primarily interrelated with those of carbon aggregates. Some investigations have been done on the carbon aggregates for carbon refractories. The results are summarized as follows: (1) the graphitized anthracite can contribut
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