Petroleum coke, commonly known as Petcoke or coke, is a byproduct of the coker process when refining crude oil. In the petroleum coker unit, the specific process of delayed coking takes place. Residual oils, produced from the various distillation processes used in petroleum refining, are treated at high pressure and temperature in the presence of steam, leaving behind the solid petcoke after driving off the remaining light and heavy oils, gases, and volatiles.
Petcoke can either be anode grade (lower in metals and sulfur) or fuel grade (higher in metals and sulfur). The raw, solid material produced in the coker unit is often referred to as green coke. Green coke can be used for cement production, metal smelting, electricity generation, and the raw material for calcined coke.
Green coke is used as the raw material to produce calcined coke. Calcining is a process in which green coke is subjected to elevated temperatures in a rotary kiln or hearth which removes residual volatile hydrocarbons from the coke. Calcined petcoke can then be combined with pitch to create anodes. These anodes are then used to assist the chemical process that converts aluminum oxide into aluminum. Calcined coke can also be used in steel production.