Petroleum Coke

Petcoke is the coke that, in particular, derives from a final crackingprocess–a catalytic 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, or 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 catalytically 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 engineeringplant operations for the specific process of delayed coking.

A delayed coking unit.A schematic flow diagram of such a unit, where residual oilenters the process at the lower left (see →), proceeds via pumps to the main fractionator(tall column at right), the residue of which, shown in green, is pumped via a furnace into the coke drums (two columns left and center) where the final carbonization takes place, at high temperature and pressure, in the presence of steam.
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 in order 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 90 percent carbon and emits 5 to 10 percent 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 CO2than coal per unit of weight. The difference between coal and coke in CO2 production per unit energy produced depends upon the moisture in the coal (increases the CO2 per unit energy – heat of combustion) and volatile hydrocarbon in coal and coke (decrease the CO2 per unit energy).