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) of Sponge Iron.
Non coking coal that is greater than 3mm in size is fed into the Kiln. Coal that is less than 3mm (coal fines) is not at all desired in the process as it gets air borne inside the kiln and doesn’t take part in reduction process. Generally, less than 3mm coal (coal fines) is screened out. This is expensive and the cost of production goes up substantially.
We are looking for a solution to make briquettes from these coal fines so that they can be charged from the feed / inlet end of the kiln with Iron Ore and coal. Similar to coal lumps, the briquettes must sustain all mechanical forces due to tumbling of the burden and should travel at least 10m before it is fully burnt to release heat.
We have made various attempts to form briquettes of coal fines using Molasses / Bentonite / Sodium Silicate as binders but the strength achieved is not sufficient for the intended use. The strength of such briquettes must be at least 80%CCS (Cold Crushing Strength) of coal and the binder must be able to sustain its property at 850-950 oC.
We are looking for a solution to make briquettes from coal fines (less than 3mm) which will maintain their shape i.e. will not crumble inside the Kiln due to various factors mentioned above.