CONTROL OF DIRECT REDUCTION IN SMELTING REDUCTION IRONMAKING

Abstract

In two stage-smelting reduction process, it is desirable to decrease the reduction degree of iron ore in a pre-reducing unit by reducing its temperature to avoid any troubles due to stickiness of high reduced iron ore. However, less pre-reduced iron ore can induce direct reduction in a melter-gasifier, which can increase the consumption of coal. In this case, the portion of direct reduction can be determined by the reducibility of Pre-Reduced Iron ore (PRI) and the reactivity of coal with CO2. PRI was prepared in the form of pellets, and its reducibility was evaluated at various temperatures in an atmosphere containing H2. Coal was carbonized in melter-gasifier condition, and then its reactivity with CO2 was measured at several temperatures and CO2-containing gas mixture. The possibility that direct reduction takes place in a melter-gasifier was high because the PRI pellet was reduced more slowly than unreduced iron ore, and the char reacted more actively than coke. The direct reduction rate in a melter-gasifier was roughly estimated as the product of the CO2 content in the ascending gas and the reaction rate constant of coal with CO2. Based on the diagram, the way of minimizing the portion of direct reduction was discussed.