On the Direct Reduction of Iron Ore in Rotary Kiln

Abstract

An analysis of direct reduction process in the isothermal zone of a rotary kiln has been made. The analysis results in four simultaneous ordinary differential equations and one algebric equation relating the fraction of total oxygen remaining in iron ore, the fraction of total carbon gasified, partial pressures of carbonmonoxide, carbondioxide and nitrogen inside the charge bed as a function of time. The numerical solution of equations shows that upto 90% reduction, the rate of reduction is practically constant and it depends on the following parameters: size of ore particles, reactivity of solid fuel, the ratio of iron oxide to carbon in the charge and the fraction of reactor volume occupied by the charge. For a particular reactivity of solid fuel, particle size of ore and the fraction of reactor volume occupied by the charge, the production rate increases with the increase in the ratio of carbon to iron oxide in the charge till the latter reaches a critical value, when further increase of the ratio dies not effect the production rate appreciably. This critical ratio of carbon to iron oxide in the charge increases with the decrease in the particle size of ore and with the increase in the reactivity of solid fuel but it is practically independent of fraction of reactor volume occupied by the charge. The analysis further shows that the production rate can be increased by increasing the amount of charge per unit reactor volume, using solid fuel of higher reacti- vity and by decreasing the particle size of iron ore.