Conditions for Minimizing Direct Reduction in Smelting Reduction Iron Making

Abstract

In a 2 stage-smelting reduction process, it is favorable to lower the reduction degree of iron ore in a pre-reducing unit by lowering 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 coal ratio. In this case, the direct reduction ratio is determined by the reducibility of Pre-Reduced Iron ore (PRI) and the reactivity of coal with CO₂. PRI was made into pellets and its reducibility was measured in various temperatures and H₂ contents. Coal was carbonized in melter-gasifier condition and then its reactivity with CO₂ was measured in various temperatures and CO₂ contents. 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 drawn as the product of the CO₂ content in the ascending gas and the reaction rate constant of coal with CO₂ and the way to minimize the direct reduction ratio was discussed with that diagram.