A coker or coker unit is an oil refinery processing unit that converts the residual oil from the vacuum distillation column into low molecular weight hydrocarbon gases, naphtha, gentle and heavy gas oils, and petroleum coke. The method thermally cracks the lengthy chain hydrocarbon molecules within the residual oil feed into shorter chain molecules forsaking the excess carbon within the type of petroleum coke.

This petroleum coke can both be fuel grade (high in sulphur and metals) or anode grade (low in sulphur and metals). The raw coke from the coker is also known as green coke.[1] In this context, “green” means unprocessed. The additional processing of inexperienced coke by calcining in a rotary kiln removes residual unstable hydrocarbons from the coke. The calcined petroleum coke may be further processed in an anode baking oven in order to provide anode coke of the desired shape and bodily properties. The anodes are mainly used within the aluminium and steel business.