By-Product coke-oven

Metallurgical coke (coke used in blast furnace iron making) is produced in by-product coke ovens. By-product coke ovens are flexible in treating different types of coal and to control the coke properties.

Coke is charged batch wise into silica lined or refractory lined retorts and these retorts are heated externally by burning gaseous fuels. Note that retorts are heated indirectly and coal is heated through heat transferred from the walls of the retort. Coal near the wall of the retort is heated faster than coal near the centre.  As a result, coke near the wall swells much earlier than coal at the centre. Therefore, proper distribution of coal in the retort would be desirable.

The volatile matter from the coal is collected in the by-product recovery plant where by product are separated from each other. It takes around 18 hours to convert one batch of coal into coke. Coke is discharge from the other end of the retort by mechanical hopper into a car, where it is wet quenched.

Note that hot coke so produced cannot be used directly into blast furnace hence coke is cooled to room temperature. During wet quenching of coal considerable amount of sensible heat is lost and pollutants are discharged in atmosphere. This aspect of coke making is dealt separately in next lecture with a quantitative illustration.

The quality of coke depends both on temperature and rate of heating. Metallurgical grade coke is produced at temperature higher than.

Among the by-products, coke oven gas possesses both sensible heat and potential energy. Coke oven gas is used as a fuel to heat the furnace and also in heating the coke oven. The leakage of atmospheric air into coke oven must be avoided as the air causes oxidation of C and results in decrease in yield.