Steel is a vital material used in buildings, cars and electrical appliances. Its strength, flexibility and durability make it a highly desirable metal. During the steelmaking process, high temperatures and carbon are required to drive chemical reactions and provide a source of energy. The production of iron and steel accounts for 7% of industrial emissions in the United States.
Petroleum coke (also known as petcoke or coal coke) is a solid, black fuel with a high carbon content. It is the result of the conversion of low-ash and low-sulphur bituminous coal to petroleum products by a process called coking. Petroleum coke is also formed by geologic processes such as volcanic eruptions. Coke has a very high energy value and produces carbon monoxide, hydrogen and water when burned. Its ash content is typically less than 0.5%.
During the steelmaking process, petroleum coke is fired in a blast furnace to supply carbon dioxide, heat and other fuel for the production of liquid blast-furnace iron (BF iron). BF iron is a major raw material for the manufacture of steel and contains 3.5% to 4.5% carbon, 0.4 to 1.2 percent silicon, 0.6 to 1.2 percent manganese and up to 0.04 percent sulfur. Coke is also injected into the blast furnace to provide permeability and to stir and mix the iron ore, pellets and sinter. This mixing enhances the chemical reactions, purges hydrogen and nitrogen, improves heat transfer, raises the carbon dioxide vapor pressure and helps to control the temperature of the kiln.
The Bessemer steel process, named after Henry Bessemer of England, was the first method discovered for mass-producing steel. The original process used a blast furnace that blew air through bars of carbon-free wrought iron, producing pig iron which was then melted into steel in a crucible. This process took up to three hours to complete and required up to 3 tons of coke per ton of steel produced. The Bessemer process reduced the time to half an hour and only required enough coke to melt pig iron, reducing the cost to PS7 a long ton.
Blast furnaces are now commonly equipped to use natural gas in place of coke for the same purposes, as the addition of gas reduces CO2 emissions and allows for greater energy efficiency. The introduction of cofiring with coal has also allowed plants to achieve similar results with lower capital and operating costs.
Various types of petroleum coke have been tested for cofiring with WCF, including flexicoke, hard coke and soft coke. Regardless of type, petroleum coke has a high calorific value and is an excellent fuel for generating steam. Nevertheless, the ashes of petroleum coke are problematic for power generation and may produce undesirable side effects such as corrosion, deposit formation or fouling. The ash quality of coke depends on the volatile matter and sulfur contents of crude oil refined from which it originated. For example, a high sulfur pet coke will produce significant amounts of sulfur dioxide and other pollutants during combustion.
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