Petroleum coke, or petcoke, is a carbonization product of high-boiling hydrocarbon fractions that are residues from petroleum processing (heavy residues). Coke production is the result of carbonization via distillation and cracking processes. The calcined petroleum coke is used as a fuel in the aluminum industry to make carbon anodes for smelting, as graphite electrodes in steel making, and in solid fuel boilers to generate electricity. It is also a raw material in the chemical industry to produce graphite and silicon carbide, and as an industrial refractory for producing cast iron.
High-grade petroleum coke low in sulphur and heavy metals can be used to make carbon anodes for the aluminum industry and as graphite electrodes in steel smelting. The majority of the world's petroleum coke, however, is made into fuel-grade coke for firing in solid fuel boilers to generate electricity. This is because it is lower in sulfur and has a higher calorific value than coal.
Fuel-grade coke is a highly granular carbon material that differs from graphite in its degree of crystallinity, especially in the c direction. It can be brittle, like needle coke, or very porous depending on the gas release process during coking. It can be isotropic or anisotropic, and it may be hard or soft, depending on impurities and other factors. The degree of crystallinity in a coke can be determined by X-ray diffraction and other methods, such as the Fourier transform infrared spectrum.
Because of its high carbon content and low ash content, petcoke is useful as an industrial fuel for power generation in metal and brick industries, in cement kilns, etc. In addition, its combustability can reduce the size of fuel storage facilities and increase plant efficiency. In addition to its high heat output, petcoke is a cleaner fuel than coal and produces fewer greenhouse gases.
However, there are several issues that need to be considered when using petcoke as a substitute for coal in solid fuel power plants. These include pulverization problems, the ash characteristics of the coke, and environmental emissions. Moreover, the prices of oil coke and coal vary over time, which affects fuel selection decisions by power companies.
The low sulfur and sulphur contents of petroleum coke, as well as its low mercury concentrations, make it an ideal substitute for coal in oil refinery boilers. Because of these properties, petroleum coke is a popular alternative to coal in generating electrical power in the United States and some other countries. However, the high volatile matter content of coke can lead to slagging and fouling, as well as a decrease in boiler performance and an increase in trace metal emissions. This can be mitigated by gasification, which is a conversion technology that allows for a zero residue target. All other conversion technologies, such as thermal cracking, catalytic cracking, cooking, deasphalting, and hydroprocessing, cannot achieve this. Therefore, gasification is a necessary precondition for the use of petroleum coke in coal-based power plants.
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