Coke-making

Secondary fuels are those which do not occur in nature but they are produced from primary (natural reserves) reserves to meet certain specific requirements. It must be clearly noted that coke does not occur in nature.

One of the important secondary fuels is coke. Coke is an important raw material in the blast furnace iron-making. It is a source of chemical and thermal energy in the blast furnace. Coke also helps maintaining permeability of the burden which is required for flow of gases ascending upwards in the blast furnace. It must be clearly noted that coke does not occur in nature.

How coke is produced

Coke is produced by heating coal to high temperature out of contact of air until all volatile matters are removed. The process is called “carbonization” or “Destructive distillation of coal”.

Coal consists of complex organic compounds in which C, H, N, O, and S atoms are bonded together. As a result of heating these bonds are broken and new bonds are formed between atoms of elements like , , , ,, and other complex hydrocarbons like , etc.

The mass of coal during heating fuses and becomes plastic. It swells during coking and then resolidifies. The structure of coke depends much on fusion, swelling and resolidification. Difference in behaviour of different types of coal account for the difference in structure of coke. For example non coking coal may decompose without becoming plastic at any stage. Mixing of two different varieties of coal i.e. non- coking coal with coking coal result in control over coke properties.