TDR Technology
Scarcity of Coking Coal
Production of steel through the conventional blast furnace route requires coking coal, of which India has limited reserves. Therefore, evolution of a technology for the reduction of iron ore using abundantly available non coking coal was contemplated, giving birth to direct reduced iron technology.
Research at Tata Steel
Tata Steel undertook an in-house research initiative in 1972. A 10 TPD pilot plant was installed to study the feasibility of such a process route. After successful operations, the process was patented in 1978 as TISCO Direct Reduction (TDR) technology, which was later commercialized with the opening of Tata Sponge Iron Limited.
Process
Iron ore (haematite) and non-coking coal are the prime raw materials for the production of sponge iron. These are charged into a rotary kiln in requisite proportion along with some dolomite. Coal plays a dual role in the process by acting as a reductant as well as a fuel for providing heat to maintain the requisite temperature inside the kiln at 950-1050C. The reduction process occurs in solid state. The crucial factor in this reduction process is the controlled combustion of coal and its conversion to carbon monoxide to remove oxygen from the iron ore.
The overall process requires a duration of approximately ten to twelve hours inside the kiln, during which iron ore is optimally reduced and discharged to a rotary cooler for cooling below 120°C., before coming out into the finished product circuit.