Petroleum coke (petcoke) is a solid byproduct of crude oil refining. It is useful in the production of carbon electrodes for aluminum industry and graphite electrodes used for steel making, as fuel in the firing of solid fuel boilers used to generate electricity, and as a raw material in cement kilns. In the United States, 55 refineries with coking facilities produced slightly over 76,000 short tons per day of petcoke in 1990.
The coking process converts heavy hydrocarbon fractions of refined crude oil into the lighter fractions needed for automobile and jet fuel consumption and petrochemical manufacturing. The heavy and residual fractions are heated to very high temperatures in a coking unit, where they break down into smaller molecules. The heavier molecules burn and vaporize, leaving behind the solid residue known as petroleum coke.
Coke is available in two forms: fuel grade and calcined grade. Fuel grade coke is low in sulfur and metals and high in heat content, whereas calcined coke has the acicular morphology that makes it suitable for use as a reducing agent in blast furnaces, where it is used to "steal" oxygen from iron ore to prevent the oxidation of the molten steel.
Calcined coke is also used in the manufacture of refractory materials, due to its ability to withstand extremely high temperatures and abrasion. It is also used in power generation, where it is burned in pulverized coal (PC) boilers, which are the predominant large combustion systems for electric power generation in the United States and many other industrialized economies of the world. PC boilers are either wall- or tangentially fired and are the most common large combustion systems for petroleum coke in the United States.
During its coking and combustion processes, petroleum coke produces greenhouse gases and other harmful pollutants that can negatively impact air quality and human health. Moreover, the smelting of petroleum coke in blast furnaces emits sulfur dioxide and nitrogen oxides, which contribute to acid rain.
As the world strives towards sustainable energy practices, petroleum coke must evolve its role to align with global sustainability goals. To do so, it must be used more efficiently in the metallurgical and power industries while new technologies develop to reduce its environmental footprint.
Whether used as a fuel or a reducing agent in blast furnaces, coke is essential to the steelmaking process. It provides the heat necessary to melt and liquefy iron ore in the BF and acts as a “trickling column,” ensuring optimal distribution of slag and iron, while preventing the deposition of carbon at the bottom of the trough. In addition, it is a valuable raw material in the production of refractory materials and as a fuel in power plants.
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