By product slot type coke ovens:

Coal is indirectly heated in these ovens which have separate chambers for carbonization and combustion. A battery of 10 to 100 ovens can be installed at a time. Gaseous fuels like coke oven gas are burnt in the comnustion chamber. Is needs to be assured that carbonization gases do not mix with combustion gases. By products recovered are ammonia, tar, crude benzol, and coke oven gas.

The carbonization chamber is 12m x 14m x 500mm size which has a volume of 50 cu.m leading to about 40 tons of coal per charge giving about 50 to 60 tons of coke per day throughput. The two ends are provided with doors and roof is provided with 3 to 4 holes for charging of coal. Additional hole is made for carbonization gases to escape through the standpipe.

The combustion chamber consists of flues built in the dividing wall between the two neighbouring carbonization chambers and also the two end of the walls of the battery. The coke oven gases are supplied in these flues to supply the heat. Modern coke ovens are provided with regenerators beneath the ovens. The heat recovered in the regenerator is utilized in preheating the gases and air. Coke oven gases cannot be preheated as the hydrocarbons crack forming coke on the walls of the regenerator.

The coke ovens are made of silica bricks which are preferred over fire bricks mainly because of the higher stability requirements at very high temperatures of 1350 to 1450 C.

Operation : coal crushed till all of it is less than 3mm in size. It is stored in service bunkers from where it is loaded onto the carriage carts which travel on rail lines overhead the battery to charge it with coal. After carbonization is complete the coke is sent for quenching – wet(with water) or dry(with hot gases) on the coke wharf.