A
coker or
coker unit is an
oil refinery processing unit that converts the residual oil from the vacuum distillation column or the atmospheric distillation column into low molecular weight
hydrocarbon gases,
naphtha, light and heavy
gas oils, and
petroleum coke. The process thermally
cracks the long chain hydrocarbon molecules in the residual oil feed into shorter chain molecules leaving behind the excess carbon in the form of petroleum coke.