BF hearth protection using titania spinel formation
- BF hearth protection using titania spinel formation
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- In case the hearth temperature increases in a blast furnace due to the wear of hearth refractory by hot metal penetration and mechanical erosion, the formation of titanium carbonitride, which has very high thermal and chemical stability (melting point > 3000 °C), has been used as a conventional method to protect the refractory wear.
Because titanium carbonitride is formed only in the molten iron, the area that can form a protective layer in the hearth is limited. However, there is another possibility to form compounds with high melting point such as magnesium aluminate spinel (m.p 2130 °C), magnesium titanate spinel (m.p 1840 °C) and perovskite (m.p 1980 °C) in the slag phase in case the slag contains high content of Al2O3 and MgO. Because the hearth is made with magnesia-carbon refractory comprising magnesium oxide and carbon, aluminate spinel and magnesium titanate spinel can be formed by the interface reaction between slag and hearth refractory as well as by the adsorption of those compounds to the refractory. If the compounds with high melting point are simultaneously formed in the molten iron and slag by adding TiO2, it might be more effective to form the protective layer and to prevent the refractory wear of hearth. However, the change of slag compositions and the formation of slag compounds can affect the slag viscosity and critical temperature, which might cause serious problems with blast furnace operation.
Therefore, it is necessary to find the optimum slag compositions considering compounds formation, which contribute to the formation of a protective layer, and slag fluidity from the viewpoint of viscosity and critical temperature. In this study, the compositional range of optimum slag was suggested by identifying the compounds based on the measured viscosity data for the given slag compositions.
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