Coal is burned to generate thermal energy, with most used for power generation. Different types of coal are classified by carbon concentration and impurities. Burning coal produces heat, which turns water into steam to generate electricity. Ash is a byproduct that can be recovered for use in cement or separated into basic impurities. Coal is also used to make coke for steelmaking.
Coal burning is a process that involves burning certain types of sedimentary or metamorphic rocks to generate thermal energy. The primary use for burning coal is to fire boilers in power stations, although it has also been burned for other purposes such as heating and a source of power for locomotives. In countries like the United States, only about 10% of the total coal consumed each year is used for purposes other than power generation. Billions of tons of coal are burned each year, accounting for about half of all electricity generated in the world.
There are several types of coal and coal precursors, which are formed when certain biological materials are exposed to very high pressures for long periods of time. Most of these materials were used as fuel, from peat to anthracite coal. High carbon concentrations make coal highly combustible and allow it to burn longer than materials such as wood. Sub-bituminous and bituminous coals are classified as sedimentary rocks and contain more impurities than the harder metamorphic anthracite. All three are commonly used to power coal-fired power generators.
When coal is burned as part of a power generation process, it is typically first pulverized into a fine powder. The coal dust is then ignited inside a furnace connected to a boiler. Burning coal can produce a large amount of heat, which causes the water in the boiler to turn into steam. The steam can then be used to turn turbines capable of generating electricity.
One of the major byproducts of coal burning is ash, which can take the form of bottom ash or fly ash. Many of the impurities in coal can leak out of a power plant as fly ash if proper measures are not taken, while others remain trapped in the bottom ash. Both varieties of ash can be recovered for use in cement or separated into basic impurities such as aluminum and iron, although uranium and other fissile materials are also sometimes found. One way to reduce the amount of ash generated is to burn a slurry of water and coal rather than dust in the air.
Besides power generation, coal burning is also used for various other industrial applications. A common use of coal is to turn it into coke, a very carbon-rich substance. The coking process consists of subjecting some types of coal to very high temperatures without providing sufficient oxygen for complete combustion. Coke has several uses, although it is essential for the operation of blast furnaces in steelmaking.
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