Effect of Silica in Ash of Coke on Carburization and Melting of Iron

Abstract

Reducing energy consumption in ironmaking process is essential for decreasing the amount of carbon dioxide emission from the blast furnace process. To effectively reduce carbon dioxide emission, a faster reduction of iron ore, as well as the acceleration of carburization and melting of the reduced iron is important. Understanding the ash behavior of coke in blast furnace is necessary for controlling carburization because ash prevents carburization. In this study, the following were investigated:

1) Condensation behavior of the ash components on the surface of coke by gasification under the simulated blast furnace condition

2) Melting behavior of iron tablet by the direct contact with coke plate

3) In-situ observation of the melting behavior of coke-iron composite and effect of deashing treatment

4) In-situ observation of the melting behavior of Fe–Si alloy using graphite

The results revealed that ash condenses on the coke surface via gasification, and the ash coverage ratio of the coke surface increases with increasing in the coke reactivity. In addition, the melting of iron by carburization with coke proceeds at lower temperature when the coke reactivity is high. However, the effect of ash coverage on this behavior is significantly higher than that of coke reactivity, and an increase in the ash coverage ratio suppresses the carburization and melting of iron. In addition, during holding at high temperature, SiO₂ in ash is reduced to Si, and it alloys with metallic iron. Furthermore, an increase in Si concentration in metallic iron increases the melting temperature of Fe–Si system. Consequently, carburization and melting iron are suppressed.

Silicon and carbon concentration of iron sample after carburization using as-polished and gasified coke.