How is sponge iron made?

Now a days,sponge iron is a household name in steel making process.There are different methods to manufacture sponge iron but in India largely coal based process are carried out.In this process iron ore lumps (5-20mm)are feed into a horizontaly inclined vessel named as Rotary kiln (length 40mt. and dia 3mt.) from one end with required quantity of coal(5-20mm).The kiln revolves in a certain rotation and during the travel time iron ore is reduced by coal and converted to sponge iron .To reduce the iron certain temperatures are maintained with the help of coal and air supplied through fans mounted in the kiln.The temp. are regulated by dampers provided with the fans. Some imp. reactions that take place inside the kiln are given below,

The following reaction takes place inside the kiln.

Fe2O3 + 3 CO = 2 Fe + CO2

However the reduction from oxide to metal does not occurs in one step but by a gradual removal of oxygen giving rise to various intermediate oxides the reduction chain may be expressed as follows:

2 Fe2O3 ------------------------- 2 Fe3O4 ------------------- 6 FeO -------------6 Fe

Hematite Magnetite Wustite Iron

The degree of reduction between each stage is as follows:

11% 22% 67%

3Fe2O3--------------------- 2Fe3O4-------------------------- 6FeO--------------6 Fe

The byproduct of above reaction is carbon die oxide (CO2).

This Co2 reacts with carbon from coal to produce CO.

CO2 + C = 2 CO.

The above reaction is known as bound ward reaction which is reversible.

The above kiln dia and length can produce 100MT of sponge/day.Though all reaction takes place in solid state the product from the kiln transfered to a rotary drum called COOLER ,where sponge iron from the klin are cooled indirectly by water and temp. decreased from 1100˚C to 150˚C.Further the discharge material transfered to separation chamber by conveyor belts where magnetic sponge is separated from char by magnetic separators and stored in bunkers.

With development and research production quantity also increased from 100MT TO 500MT by increasing the size of kilns.