Coke is the solid carbon material produced by the destructive distillation process of bituminous low-ash coal. The product is sometimes also known as petroleum coke (or pet coke), which refers to its source, crude oil. It is mostly composed of carbon, with smaller amounts hydrogen, nitrogen and sulfur. It has a high carbon content and is used to replace coal and other fuels in the power industry.
The most important uses of metallurgical grade petroleum coke are in the manufacture of anodes for aluminium, steel and titanium smelting and for producing synthetic graphite. The coke needs to be free of metal impurities while also being strong enough in order to support the heavy loads that are placed inside the furnace. This is why it is necessary to use a type of coke that has been calcined, or refined petroleum coke.
In addition to its use as a fuel, metallurgical coke has other valuable chemical properties that make it a desirable feedstock. By gasifying the calcined material, a range of fertilisers can be produced. By using this method, ammonia and urea/ammonium-nitrate can be produced as well as valuable nitrogen compounds including diammoniumphosphate and ammoniumcarbonate. Metalurgical coke is also used in the production glass, paper, and paint.
Early coke production was done by heating the coal in large hexaphedron or beehive shaped ovens. American battery had up to two hundred of these. The resulting gases were then used to generate heat to power the coking processes. Gases produced by coke were stored in "gas works", which was then distributed to homes, businesses, factories, and other industrial and commercial users via underground pipe networks. This was a common practice until the advent of natural gas in the 1960s.
Today, a wide range of technologies is available to burn or gasify petroleum coke. In coal-fired boilers, the most common use is to burn fuel coke in order to generate electricity. This is a very energy-intensive process and produces significant quantities of greenhouse gases, but it is important to note that a substantial proportion of the gross calorific value of petroleum coke is retained in the form of unburned hydrocarbons. For example, flue-gas desulfurisation technology is used extensively to combat the environmental issues associated with using this high sulfur feedstock. The alternative is to gasify petroleum coke using a fluidised bed to produce syngas, which then can be combined with oxygen in a combustion to produce electricity.
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