Petroleum coke is the carbon-rich byproduct of the oil refining process. It is produced by heating heavy crude oil to very high temperatures in a thermal cracking unit, causing the large hydrocarbon molecules in the crude oil to break down and form smaller ones. The heat and pressure in the cracking unit also transforms the petroleum coke into a hard solid called petcoke.
Petroleum coke has a number of uses in the steel production process. It is used as a fuel in power plants and to produce a type of steel called coke-based briquetted iron (CBI). Petroleum coke has a much higher calorific value than most fossil fuels, so it can be used to replace coal in power plant boilers. Coke-based briquetted iron is less expensive than traditional pig iron because it does not require a blast furnace to produce.
In addition to the energy and cost benefits of coke-based briquetted iron, petroleum coke has other advantages in the steel production process. It provides the carbon needed to carburize the liquid hot metal, which improves its mechanical properties. It also plays a critical thermal role in the arc furnace, where it is used as a source of heat for melting and remelting the steel slag and iron oxides. Coke is also used in the grate area of the blast furnace to control the slag flow and provide a better gas distribution pattern.
Coke-based briquetted iron can be used in iron ore-based steel smelting plants to produce finished steel products such as wire rod and rolled product. In addition, it can be used to produce other metals such as tin and zinc, which are important raw materials in many industrial applications. Coke-based smelting is also an environmentally friendly alternative to conventional smelting methods.
As with coal, petroleum coke can be stored in large piles for easy transport. It can be loaded into trucks, railcars, and conveyor systems for transportation to the steel mill. It must be kept in a dry environment since it will become a hard solid if wet.
In some cases, the lower volatile content of petroleum coke makes it possible to be blended with coal in electric generating boilers. A typical blend is 20% to 30% by weight on a calorific basis. This is often done to lower the overall costs of electricity generation.
Despite the lower volatility, it is not advisable to use petroleum coke in PC boilers that operate under low pressure because it could lead to oxidation and corrosion of boiler equipment. In general, it is best to use petroleum coke only in high-pressure cyclone and BNR boilers.
Some refineries use a process known as fluid coking to convert crude oil into other petroleum products, such as gasoline, diesel fuel, and kerosene. This process involves injecting a stream of hot crude oil into a fluidized bed of coke, where it is heated to high temperatures in order to break down larger hydrocarbon molecules into smaller ones. Afterwards, the coke is mixed with coal in a coke oven to make metallurgical coke for steel production. Coke from this process is considered to be superior in quality because it has a lower reactivity to CO2 and higher mechanical strength than coke made using other conversion technologies such as thermal cracking, catalytic cracking, cooking, deasphalting, or hydroprocessing.
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