BLAST FURNACES

What is a Blast Furnace? BF is a counter current heat and mass exchanger, in which solid raw materials are charged from the top of the furnace and hot blast is sent through the bottom via tuyeres. The heat is transferred from the gas to the burden and oxygen from the burden to the gas. Gas ascends up the furnace while burden and coke descend down through the furnace. The counter current nature of the reactions makes the overall process an extremely efficient one.

In the blast furnace process iron ore and reducing agents (coke, coal) are transformed to hot metal, and slag is formed from the gangue of the ore burden and the ash of coke and coal. Hot metal and liquid slag do not mix and remain separate from each other with the slag floating on top of the denser iron. The iron can then be separated from the slag in the cast house. The other product from the Blast Furnace is dust laden blast furnace gas, which is further cleaned in the gas cleaning plant and is used as a fuel all over the plant.

The basic raw materials and their functions:-

1) Iron Ore: Iron bearing materials; provides iron to the Hot Metal.

2) Sinter: Iron bearing material. Fines that are generated in the plant are effectively utilized by converting them to sinter. Provides the extra lime required for the iron ore that is charged in the blast furnace.

3) Coke: Acts as a reductant and fuel, supports the burden and helps in maintaining permeable bed.

4) Limestone: Acts as Flux. Helps in reducing the melting point of gangue present in the iron bearing material

5) Manganese Ore: Acts as additive for the supply of Mn in the Hot Metal

6) Quartzite: Acts as an additive

7) Coal Dust: Acts as an auxiliary fuel, reduces coke consumption in the BF

8) Coal Tar: Acts as an auxiliary fuel, reduces coke consumption in the BF

9) Pellets: Iron bearing materials. Although not in use right now, there is a proposal to

utilize the fines below the sinter grade for pellet manufacturing and the pellets formed are going to be charged in the BF.