What is Sponge Iron:
Sponge iron is a metallic product produced through direct reduction of iron ore in the solid state. It is a substitute for scrap and is mainly used in making steel through the secondary route.
What is a Kiln:
Rotary kiln is a refractory lined horizontal steel cylinder (72 – 80 M long & 4.2m in diameter) which is slightly inclined (1.432o) towards out let side and the cylinder is rotated (0.35-0.7 RPM) by Motor – Gear arrangement. The inner surface of kiln is made of a refractory castable material which primarily consists of 60-80% monolithic Alumina.
How Sponge Iron is made:
Sponge iron making process is removal of oxygen from sized ore in solid state. To do this - iron ore, non coking coal and a small quantity of Dolomite is fed into the rotary kiln. Non-coking coal acts as reductant at bed temperature of 1050 oC and the dolomite acts as a desulphurizing compound. The whole reduction process takes place inside a rotary kiln in a reducing atmosphere for 10-12 hours to produce Directly Reduced Iron (DRI) or Sponge Iron.
To produce every tonne of sponge Iron, the charge mix (mainly) includes roughly 1.6 MT of iron ore (size 5-18mm), 1 MT of coal (size 3-30mm) and 0.045 MT of dolomite (size 3-8mm).
During the normal plant operation, the rotary kiln gets accreted (Fused mass of Raw Material fines start clinging on the inner refractory wall of the kiln), due to instability in the process parameters. These accretions weigh anywhere between 10 - 100 Kg. Due to accretion, quality of product becomes inconsistent and the life of the kiln gets shortened, often leading to shortening of campaign life (number of days the kiln was in continuous operation, before undergoing shutdown). The Accretion build up also blocks the raw material input ports and restricts feeding of coal from the discharge end of the kiln, which affects the product quality adversely.
Not only does this accretion reduce the campaign life, it makes it difficult to maintain the consistency in process parameters resulting in the kiln operating below its full capacity.
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