underground coal mining: see coal mining.

coal tar, product of the destructive distillation of bituminous coal. Coal tar can be distilled into many fractions to yield a number of useful organic products, including benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. These substances, called the coal-tar crudes, form the starting point for the synthesis of numerous products—notably dyes, drugs, explosives, flavorings, perfumes, preservatives, synthetic resins, and paints and stains. The residual pitch left from the fractional distillation is used for paving, roofing, waterproofing, and insulation.

coal mining, physical extraction of coal resources to yield coal; also, the business of exploring for, developing, mining, and transporting coal in any form. Strip mining is the process in which the overburden (earth and rock material overlying the coal) is removed to expose a coal seam or coal bed. Excavators either dispose of the overburden or store the waste material for replacement after the coal has been extracted. Once exposed, the coal is usually removed in a separate operation. Surface soil is often stripped separately and spread back onto the reclaimed surface. The environment can also be protected by seeding or planting grass or trees on the fertilized restored surface of a strip mine. The term strip mining is most often used in reference to coal mining, although the process may also be used to extract certain metallic ores as well. Sometimes the terms open-pit, open-cast, or surface mining are used in the same sense, although they usually refer to metalliferous mining or the mining of other minerals. Underground coal mining is the extraction of coal from below the surface of the earth. The coal is worked through tunnels, passages, and openings that are connected to the surface for the purpose of the removal of the coal. Mechanical equipment breaks the coal to a size suitable for haulage. Alternatively, the coal is drilled, and the resultant holes are loaded with explosives and blasted in order to break the coal to the desired size. In order to protect the miners and equipment in an underground coal mine, much attention is paid to maintaining and supporting a safe roof or overhead ceiling for the extraction openings. Long-wall mining is a method of underground mining believed to have been developed in Shropshire, England, near the end of the 17th cent. A long face, or working section, of coal, some 600 ft (180 m) in length, is operated at one time. The miners and machinery at the working face are usually protected by hydraulic jacks or mechanical props which are advanced as the coal is extracted. The excavated, or gob, area is either allowed to cave in, or is filled in by waste material called stowing. The Anderton shearer is a widely used coal cutter and loader for long-wall mining. It shears coal from the face as it moves in one direction and loads coal onto an armored conveyor as it travels back in the opposite direction. It is ordinarily used for coal seams greater than 3.5 ft (9.1 cm) in thickness.

coal gas, gas obtained in the destructive distillation of soft coal, as a byproduct in the preparation of coke. Its composition varies, but in general it is made up largely of hydrogen and methane with small amounts of other hydrocarbons, carbon monoxide (a poisonous gas), carbon dioxide, and nitrogen. It is used as a fuel and illuminant.

coal, fuel substance of plant origin, largely or almost entirely composed of carbon with varying amounts of mineral matter.

Types

There is a complete series of carbonaceous fuels, which differ from each other in the relative amounts of moisture, volatile matter, and fixed carbon they contain. Of the carbonaceous fuels, those containing the largest amounts of fixed carbon and the smallest amounts of moisture and volatile matter are the most useful to humans. The lowest in carbon content, peat, is followed in ascending order by lignite and the various forms of coal—subbituminous coal or black lignite (a slightly higher grade than lignite), bituminous coal, semibituminous (a high-grade bituminous coal), semianthracite (a low-grade anthracite), and anthracite.

Lignite and subbituminous coal, because of the high percentage of moisture they contain, tend to crumble on exposure to the air. Bituminous coal, being more consolidated, does not crumble easily; it is a deep black in color, burns readily, and is used extensively as fuel in industries and on railroads and in making coke. Anthracite, which is nearly pure carbon, is very hard, black, and lustrous and is extensively used as a domestic fuel. Cannel coal, a dull, homogeneous variety of bituminous coal, is composed of pollen grains, spores, and other particles of plant origin. It ignites and burns easily, with a candlelike flame, but its fuel value is low.

Formation

The vegetable origin of coal is supported by the presence in coal of carbonized fibers, stems, leaves, and seeds of plants, which can be detected with the naked eye in the softer varieties and with the microscope in harder coal. Sometimes carbonized tree stumps have been found standing in layers of coal. The general interpretation of these facts is that coal originated in swamps similar to present-day peat bogs and in lagoons, probably partly from plants growing in the area and partly from plant material carried in by water and wind. From the thickness of coal seams, it is assumed that the coal swamps were located near sea level and were subject to repeated submergence, so that a great quantity of vegetable matter accumulated over a long period of time.

The initial processes of disintegration and decomposition of the organic matter were brought about by the action of bacteria and other microorganisms. Peat, the first product formed, is altered to form lignite and coal through metamorphism. The pressure of the accumulated layers of overlying sediments and rock upon the submerged plant matter forced out much of the water and caused some of the volatile substances to escape and the nonvolatile carbon material to form a more compact mass. The greater the stress exerted in the process of metamorphism, the higher was the grade of coal produced. Cannel coal was probably formed in ponds, rather than in lagoons or swamps, as it occurs in lenticular masses and is frequently found to contain fossil fish. Coal was formed chiefly in the Carboniferous period of geologic time, but valuable deposits date also from the Permian, Triassic, Jurassic, Cretaceous, and Tertiary periods.

Natural Occurrence

Coal is found in beds or seams interstratified with shales, clays, sandstones, or (rarely) limestones. It is usually underlaid by an underclay (a layer of clay containing roots of plants). The coal is removed by strip (surface) mining or underground mining methods (see coal mining).

The chief coal fields of the United States are the Appalachian (from N Pennsylvania into Alabama), the Eastern Interior (Illinois, Kentucky, and Indiana), the Northern Interior (Michigan), the Western Interior (Iowa, Kansas, Missouri, Oklahoma, and Arkansas), the Rocky Mountain (Colorado, Wyoming, Utah, New Mexico, Montana, and North Dakota), the Pacific (Washington), and the Gulf Coast (Texas, Arkansas, and Louisiana). In Europe the chief coal-producing countries are Germany, Russia, Ukraine, and Poland. There are valuable coal fields in China, India, Indonesia, Australia, South Africa, and Korea but few in South America.

cannel coal: see coal.

brown coal: see lignite.

bituminous coal: see coal.

European Coal and Steel Community (ECSC), 1st treaty organization of what has become the European Union; established by the Treaty of Paris (1952). It is also known as the Schuman Plan, after the French foreign minister, Robert Schuman, who proposed it in 1950. Member nations of ECSC pledged to pool their coal and steel resources by providing a unified market for their coal and steel products, lifting restrictions on imports and exports, and creating a unified labor market. Economically, the Coal and Steel Community achieved early success; between 1952 and 1960 iron and steel production rose by 75% in the ECSC nations, and industrial production rose 58%. When overproduction of coal became a problem after 1959, especially in Belgium, the ECSC demonstrated its flexibility by reducing Belgium's coal-producing capacity by 30% and by making available large sums of money to aid in retraining miners and developing new industries. The ECSC had, by 1970, granted about $150 million in aid to retrain over 400,000 coal miners. The executive machinery of the ECSC provided an important precedent for the future growth of a united Europe: the nine-member High Authority, which became a part of the European Commission in 1967, was chosen by the member governments and made independent of those governments. Its independence was guaranteed by providing the authority with its own source of income.

Dark-brown to black coal, intermediate in rank between lignite and bituminous coal. It contains less water and is harder than lignite, making it easier to transport, store, and use. It has lower heating value than bituminous coal, but its sulfur content is often low, so that a number of coal-fired electric-power plants have switched from bituminous to subbituminous coal and lignite (which also tends to have relatively low sulfur). Subbituminous deposits are found in the U.S., Canada, Brazil, Germany, Russia, Ukraine, Australia, and China.

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or hard coal

Coal containing more fixed carbon than any other form of coal and the lowest amount of volatile (quickly evaporating) material, giving it the greatest heat value. The most valuable of the coals, it is also the least plentiful, making up less than 2percnt of all coal reserves in the U.S., with most of the known deposits occurring in the East. Anthracites are black and have a brilliant, almost metallic lustre. Hard and brittle, they can be polished and used for decorative purposes. They are difficult to ignite but burn with a pale-blue flame and require little attention to sustain combustion. In the past they were used for domestic heating, but today they have given way to other sources of energy (e.g., natural gas and electricity).

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or kerosine

Organic compound, a clear, oily, highly flammable liquid with a strong odour, distilled from petroleum (10–25percnt of total volume). It is a mixture of about 10 different types of fairly simple hydrocarbons, depending on its source. It is less volatile than gasoline, boiling at 285–610 °F (140–320 °C). It is burned in lamps, heaters, and furnaces and is used as a fuel or fuel component for diesel and tractor engines, jet engines, and rockets and as a solvent for greases and insecticides.

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Extraction of coal deposits from the Earth's surface and from underground. Because coal was the basic energy source that fueled the Industrial Revolution, the resulting industrial growth supported the large-scale exploitation of coal deposits. In the late 20th century, open pit mines replaced underground mines as the principal source of coal in the industrial nations. The mining of coal from surface and underground deposits today is a highly productive, mechanized operation.

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Solid, usually black but sometimes brown, carbon-rich material that occurs in stratified sedimentary deposits. One of the most important fossil fuels, it is found in many parts of the world. Coal is formed by heat and pressure over millions of years on vegetation deposited in ancient shallow swamps (see peat). It varies in density, porosity, hardness, and reflectivity. The major types are lignite, subbituminous, bituminous, and anthracite. Coal has long been used as fuel, for power generation, for the production of coke, and as a source of various compounds used in synthesizing dyes, solvents, and drugs. The search for alternative energy sources has periodically revived interest in the conversion of coal into liquid fuels; technologies for coal liquefaction have been known since early in the 20th century.

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or soft coal

Most abundant form of coal. It is dark brown to black and has a relatively high heat value. Widely abundant and with the broadest range of commercial uses, it has long been used for steam generation in electric power plants and industrial boiler plants. Certain varieties are also used to make coke, a hard substance of almost pure carbon that is important for smelting iron ore. One major problem is that burning large quantities of bituminous coal that has a medium to high sulfur content contributes to air pollution and produces acid rain. Seealso subbituminous coal.

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Administrative agency designed to integrate the coal and steel industries of France, West Germany, Italy, Belgium, the Netherlands, and Luxembourg. It originated in the plan of Robert Schuman (1950) to establish a common market for coal and steel by those countries willing to submit to an independent authority. Created in 1952, the ECSC came to include all members of the European Union. It initially removed barriers to trade in coal, coke, steel, pig iron, and scrap iron; it later supervised the reduction of its members' excess production. In 1967 its governing bodies were merged into the European Community. When the treaty expired in 2002, the ECSC was dissolved.

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