Effect of coal ash on ring behavior of iron-ore pellet powder in kiln

Abstract

Ring formation as a troublesome problem for grate-kiln production of iron-ore oxide pellet makes the quality of pellet declining, production efficiency reducing, and production cost increasing. Pellet powder and coal ash are the raw material of ring. Bonding strength, microstructure and composition of coal ash, iron-ore pellet powder, and their mixed powder were investigated to analyze the effect of coal ash on ring behavior of pellet powder and observe the forming of powder ring in kiln. Results showed that coal ash not only changes chemical composition of pellet powder, but also influences its bonding process. The proportion of hematite decreases while that of mullite and quartz increases with the rise of coal ash. High temperature (not less than 1250°C) is a necessary condition to make powder form ring. Fe2O3 recrystallization of pellet powder is the primary manner for powder briquettes. Pure pellet powder is difficult to form ring because of its insufficient Fe2O3 recrystallization at beginning of formation, but their weak bonding can be intensified by coal ash. The combined actions of glassy phase silicide, liquation phase aluminosilicate and liquid phase of low melting substance make the ash briquette with tight structure and high strength in the initial of roasting which is difficult to be destroyed and maintain in rotary kiln as the original ring. Then with the continuous of high temperature roasting, sufficient Fe2O3 recrystallization makes the original ring further strong and unbreakable, and evolve to the final ring which is indestructible and malignant.