Petroleum coke, abbreviated
coke or petcoke, is a final carbon-rich solid
material that derives from oil refining, and is
one type of the group of fuels referred to as
cokes. Petcoke is the coke that, in particular,
derives from a final cracking process—a
thermo-based chemical engineering process that
splits long chain hydrocarbons of petroleum into
shorter chains—that takes place in units termed
coker units. (Other types of coke are derived
from coal.) Stated succinctly, coke is the
“carbonization product of high-boiling
hydrocarbon fractions obtained in petroleum
processing (heavy residues)”. Petcoke is
also produced in the production of synthetic
crude oil (syncrude) from bitumen extracted from
Canada’s oil sands and from Venezuela’s
Orinoco oil sands.
In petroleum coker units, residual oils from
other distillation processes used in petroleum
refining are treated at a high temperature and
pressure leaving the petcoke after driving off
gases and volatiles, and separating off
remaining light and heavy oils. These processes
are termed “coking processes”, and
most typically employ chemical engineering plant
operations for the specific process of delayed
coking.
This coke can either be fuel grade (high in
sulfur and metals) or anode grade (low in sulfur
and metals). The raw coke directly out of the
coker is often referred to as green coke. In
this context, “green” means
unprocessed. The further processing of green
coke by calcining in a rotary kiln removes
residual volatile hydrocarbons from the coke.
The calcined petroleum coke can be further
processed in an anode baking oven to produce
anode coke of the desired shape and physical
properties. The anodes are mainly used in the
aluminium and steel industry.
Petcoke is over 80% carbon and emits 5% to 10%
more carbon dioxide (CO2) than coal on a
per-unit-of-energy basis when it is burned. As
petcoke has a higher energy content, petcoke
emits between 30 and 80 percent more CO2 than
coal per unit of weight. The difference between
coal and coke in CO2 production per unit of
energy produced depends upon the moisture in the
coal, which increases the CO2 per unit of energy
– heat of combustion – and on the volatile
hydrocarbons in coal and coke, which decrease
the CO2 per unit of energy.