Coal

Struktura chemiczna węgla kamiennego

Sydney Mines Point Aconi Seam 038

Coal Rank USGS

Tiangong Kaiwu Coal Mining

Men of the Mine- Life at the Coal Face, Britain, 1942 D8263

Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dead plant matter decays into peat and is converted into coal by the heat and pressure of deep burial over millions of years. Vast deposits of coal originate in former wetlands—called coal forests—that covered much of the Earth's tropical land areas during the late Carboniferous (Pennsylvanian) and Permian times.

Formation

Coal is formed from the physical and chemical alteration of peat. Peat is composed of plant materials that accumulate in wetlands (bogs and fens), which break down through the process of peatification. This process involves the removal of water and volatile substances and the breakdown of complex molecules into simpler ones. Over geological time, the peat undergoes further transformation into coal through the process of coalification, which involves biochemical and geochemical processes that increase the carbon content and decrease the oxygen content of the material. The degree of change undergone by a coal as it matures from peat to anthracite is known as coalification and is described by the rank of the coal.

Types of Coal

Coal is classified into four main types, or ranks: lignite, sub-bituminous, bituminous, and anthracite, depending on the amounts and types of carbon it contains and the heat energy it can produce. The rank of coal is determined by the degree of transformation from the original plant material to carbon. The process of transformation involves the removal of moisture and volatile matter, leaving a higher concentration of carbon.

Lignite

Lignite, often referred to as brown coal, is the lowest rank of coal and has the lowest energy content. Lignite is crumbly and has high moisture content. It is mainly used in electricity generation.

Sub-Bituminous Coal

Sub-bituminous coal is black in color and has a higher heating value than lignite. It is used primarily as fuel in steam-electric power generation.

Bituminous Coal

Bituminous coal is a dense sedimentary rock, usually black but sometimes dark brown. It is used primarily as fuel in steam-electric power generation and to make coke for the steel industry.

Anthracite

Anthracite is the highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter. Anthracite is used for residential and commercial space heating.

Uses of Coal

Coal is primarily used as fuel to generate electric power in the United States. In coal-fired power plants, coal is combusted and heats water in enormous boilers. The steam from the boilers is used to turn turbines, which generate electricity. In addition to electricity generation, coal is used in industrial processes, such as cement and steel production.

Environmental Impact

The burning of coal is a major source of carbon dioxide, a greenhouse gas that contributes to global warming. Other harmful pollutants released during the burning of coal include sulfur dioxide, nitrogen oxides, and particulate matter. Mining and processing of coal can also have significant environmental impacts, including land degradation, water pollution, and the destruction of habitats.

Future of Coal

The future of coal is uncertain, with many countries moving towards cleaner sources of energy due to concerns about climate change and air pollution. However, coal remains an important energy source, especially in developing countries where it is a relatively cheap and abundant resource.

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