Major DRI production processes are either gas based or coal based. Feed material in a DRI process is either iron ore sized to 10 to 30mm or iron ore pellets produced in an iron ore pellet plant.
In a coal based plant, the reactor for the reduction reaction is an inclined horizontal rotary kiln. In this kiln, both coal and the iron ore feed material is charged from the same end of the kiln. During the movement of feed material forward the oxidation reaction of carbon in coal and reduction reaction of CO gas is carefully balanced. A temperature profile ranging from 800-1050 deg C is maintained along the length of the kiln at different zones and as the material flows down due to gravity the ore is reduced. In a coal based process, non-coking thermal coal is used. The carbon of the coal acts as a reducing agent in the process.
The reduction DRI process is as follows
The basic reduction reactions in a coal based DRI process is as follows
C+ O2 = CO2
CO2 +C = 2 CO
3Fe2O3 + CO = 2Fe3O4 + CO2
Fe3O4 + CO = 3FeO + CO2
FeO + CO = Fe + CO2