Petroleum coke is the solid byproduct from oil refining. It is used as a fuel in power generation plants and in the production of carbon electrodes for aluminum smelting, graphite electrodes for steel making and as an energy source in rotary kilns producing cement (Figure 7.8). The United States produces over 1.5 million tons per year of petroleum coke, which is a significant fraction of global production (Energy Information Administration 1999).
Natural petroleum coal is an amorphous brown-black material that has a low content of carbon, a large specific gravity and macroporosity. It can hold water, steam, and other volatile compounds. It is made by heating coal or oil in the absence air, a procedure called coking.
After coking petroleum coke in a coke oven, it is subjected to heat and pressure for a further process. This removes volatile components and increases its carbon content. The resulting calcined petroleum coke is a high-purity carbon product, which has a number of industrial applications, including power generation and production of graphite electrodes for steelmaking. The calcining of crude petroleum coke removes any mercury or other heavy metals, which are present after crude oil is refined.
The gasification and conversion of petroleum sludge and non-volatile refinery waste streams (such as visbreaker, atmospheric, vacuum, deasphalter, and vacuum sludge) into clean transportation fuels produces a cleaner alternative to fossil fuels. The gasification process can reduce the environmental impact by turning fossil fuels into high-value materials, such as hydrogen and carbon nanomaterials.
The use of petroleum as a blend fuel in ironmaking reduces the formation of slag. This is because, unlike coal-based coke, petcoke does not have a significant amount of ash inerts that must be fluxed with limestone and disposed of as slag during direct reduction ironmaking. This minimizes the amount of slag required to make liquid iron, which is a considerable cost savings.
The ability of petroleum coke to bind molten metals during reductive smelting is another advantage in the use of this blending fuel for ironmaking. The coke, as a carbon-rich source in the melting reaction, prevents the oxidation of molten metal and increases its workability. Petcoke can also lower the temperature of the system by reducing the kinetics energy.
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