Steel production through the conventional blast furnace route requires coking coal in abundance, which is a limited resource in our country and is also becoming scarce world over.
Hence, a new technology – TISCO Direct Reduction (TDR) technology was evolved that helped in the reduction of iron ore by using abundantly available non-coking coal.
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 commercialised with the commissioning of Tata Sponge Iron Limited.
Manufacturing sponge iron by the TDR process
|W.H.R.B.||Waste Heat Recovery Boiler|
Raw Material Treatment
Iron ore 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 950-1050oC. 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.
Sponge Iron Storage & Despatch
The overall process extends to a period of 10 to 12 hours inside the kiln. During this time, iron ore is optimally reduced and the hot reduced sponge iron along with semi-burnt coal is discharged to a rotary cooler for indirect cooling to a temperature of around 120°C. Sponge iron being magnetic in nature, the discharge from cooler consisting of sponge iron, char & other contaminations are routed through electromagnetic separators, to separate other impurities from sponge iron.
The product is then screened in size fractions of lump (+3 mm) and fines(0-3 mm). Separate bins are installed to preserve its quality, reduce reoxidation and facilitate faster loading on to the trucks. Just below the bunkers, automatic bagging machines have been installed for bagging sponge iron which are then sent through rakes through company’s private railway siding or through trucks, as per customers’ preference.
Fully computerised operation of kilns through a mathematical model, customised for use by IIT,BBS has helped the company to ensure reduced level of human intervention in the production process which has in turn enabled production of consistent quality product.