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 meltergasifier 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.