Coking is a thermal cracking-type operation used to convert petroleum residua to coke, gas, and distillates. Two types of petroleum coking processes are presently operating: (1) Delayed coking, which uses multiple coking chambers to permit continuous feed processing wherein one drum is making coke and one drum is being decoked; and (2) fluid coking, which is a fully continuous process where product coke can be withdrawn as a fluidized solid. Installed capacities for coking in the United States are:
Coker Charge Stocks
Crude oil residua obtained from the vacuum distillation tower as a bottoms fraction are the usual charge stocks to coking. Longer residua, such as atmospheric tower bottoms, may be charged but it is generally not attractive to thermally degrade the gas-oil fraction contained in the longer residua. Other charge stocks to coking are solvent decarbonizer or deasphalter bottoms, bitumens such as Athabasca Tar and Gilsonite, shale oil bottoms, thermal tars, pyrolysis tar from ethylene plants, and decant oil from fluid catalytic cracking. The latter three stocks can be coked to provide a very high quality specialty coke used in graphite articles.