DESCRIPTION OF FACILITIES FOR SPONGE IRON PLANT
- Day Bins
- Rotary Kiln and cooler
- Off Gas System including waste heat power generation
- Product processing facilities and product storage bins
DAY BINS
The Day Bin building for DRI Kiln have separate bins for storage of about one day’s requirement of screened iron ore (5-20mm) coal (3-25mm) injection coal (3-15mm) and dolomite (2-8mm). Weigh feeders are provided to draw various materials in the required proportion from the bins and deliver to the conveyors for feeding into the kiln.
Rotary kiln and cooler
Rotary kiln of a certain dia and length are provided for reduction of iron ore into sponge iron using non-coking coal as reductant. Other main components of kiln are:
- Feed end and discharge end housing of welded steel construction with refractory lining including feed chute
- Pneumatic cylinder actuated labyrinth air seal complete with auto lubricating system at feed end and discharge end.
- On board equipments like fans, manifolds, valves, piping, actuators, air inlet parts, slip ring housing etc.
- Cooling fans at feed end and discharge end
- Fuel-on system consisting of compressed pipeline with cooling fans
- Feed end double flap valves and dust valves
The kiln will be lined with high alumina castable refractories throughout its length with dams at feed end and discharge end.
The kiln feed from the charging end consist of screened iron ore, coal, and dolomite. Air is supplied to the kiln through air ports provided on kiln periphery along the kiln length. This ensures a controlled combustion resulting in a very even temperature profile. A part of required coal will be thrown from discharge end pneumatically into the kiln. Necessary rotary feeder, compressor, piping, and valves will be provided for the injection system.
In the kiln, the iron ore is dried and heated to the reduction temperature of about 1000 C. The iron oxide of the ore is reduced to metallic iron by carbon monoxide generated in the kiln from coal. The heat required for the reduction process is also supplied by the combustion of coal. Thermocouple installed along the length of the kiln shell determines the thermal profile of the kiln. The temperature inside the kiln is controlled by regulating the amount of combustion air admitted into the kiln through ports with the help of fans mounted on the kiln shell and by controlled coal injection. The reduced material from the kiln is cooled indirectly in a rotary cooler by water spray. At the discharge end, the cooler will act as a screening section, which separates all the accretions larger than 50 mm from the reduced material.
These lumps are discharged separately via lump gate. Rest of the material is discharged on a conveyor via double flap valve.
The cooled product is conveyed to the product processing building by a system of belt conveyors. The products from the cooler discharge contain sponge iron, char and spent dolomite. In the product processing building, the product will be first screened in a double deck screen having 3mm and 20mm screens. The screened product i.e. +3mm to +20 mm and -3mm fraction is subjected to magnetic separation. The magnetic fraction of 3 to 20mm is stored in separate product storage bins. Char generated in the plant is stored separately for use as fuel in the power plant.
DRI Kiln enable the company to be self reliant in the arena of Power requirement for production of Steel and dependence on import of Power from the State Grid at a higher cost can be reduced substantially. Cheaper Power availability through this CPP route will help the company to have lesser production cost of Steel, which is especially of consequence when high Power intensive Induction Furnaces are in use.
Selection of the System Scheme and Unit Size has been influenced by the prime consideration that in the event of any forced outage of any one of the two DRI Kilns with associated WHRBs, the Captive Power Plant shall be in a position to generate Net MVA to meet the Power requirement of steel plant as below:
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