Petroleum coke

Petroleum coke (often abbreviated pet coke or petcoke) is a carbonaceous solid delivered from oil refinery coker units or other cracking processes. Coking processes that can be employed for making petcoke include contact coking, fluid coking, flexicoking and delayed coking. Other coke has traditionally been delivered from coal.

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 CO₂ than 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).

There are at least four basic types of petroleum coke, namely, needle coke, honeycomb coke, sponge coke and shot coke. Different types of petroleum coke have different microstructures due to differences in operating variables and nature of feedstock. Significant differences are also to be observed in the properties of the different types of coke, particularly ash and volatile matter contents.

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