Modelling of Rotary Kiln based Direct Reduction

Abstract

Direct Reduction (DR) is the process by which iron ore, as oxide , is reduced by a reductant , viz., coal or natural gas to the product called sponge iron or Direct Reduced Iron( DRI). Coal based DR is carried out in a rotary kiln reactor where iron ore is reduced usually by noncoking coal . The kiln temperature is maintained at around 1000°C towards the discharge end, the rotati- onal speed is usually kept in the range of 0.4 to 0.7 r.p.m. While the inclination of the kiln is fixed in the range of 1.5° to 2.5°. The kiln rotational speed, coup- led with the inclination, imparts a forward motion to the charge bed of the kiln, thus aiding it to travel towards the discharge end. The charge consisting of iron ore and coal, while traversing the kiln length at high temperature, undergoes two simultaneous reactions, viz., gasification of the coal and reduction of the oxide ore. The oxide ore thus gradually gets converted to the lower oxides and finally, to the metallised poduct, DRI (90 - 95% metallised). However, the hot product from the kiln also contains coal char and ash and these being non-magnetic , are separated from the product DRI (magnetic) by magnetic separation . Before magnetic separation, the hot kiln-discharge product is cooled to about 100°C, usually in a rotary cooler , indirectly cooled by water.