| 释义 |
coal
Physics
A brown or black carbonaceous deposit derived from the accumulation and alteration of ancient vegetation, which originated largely in swamps or other moist environments. As the vegetation decomposed it formed layers of peat, which were subsequently buried (for example, by marine sediments following a rise in sea level or subsidence of the land). Under the increased pressure and resulting higher temperatures the peat was transformed into coal. Two types of coal are recognized: humic (or woody) coals, derived from plant remains; and sapropelic coals, which are derived from algae, spores, and finely divided plant material. As the processes of coalification (i.e. the transformation resulting from the high temperatures and pressures) continue, there is a progressive transformation of the deposit: the proportion of carbon relative to oxygen rises and volatile substances and water are driven out. The various stages in this process are referred to as the ranks of the coal. In ascending order, the main ranks of coal are: lignite (or brown coal), which is soft, brown, and has a high moisture content; subbituminous coal, which is used chiefly by generating stations; bituminous coal, which is the most abundant rank of coal; semibituminous coal; semianthracite coal, which has a fixed carbon content of between 86% and 92%; and anthracite coal, which is hard and black with a fixed carbon content of between 92% and 98%. Most deposits of coal were formed during the Carboniferous and Permian periods. More recent periods of coal formation occurred during the early Jurassic and Tertiary periods. Coal deposits occur in all the major continents; the leading producers include the USA, China, Ukraine, Poland, South Africa, India, Australia, and Germany. Coal is used as a fuel and in the chemical industry; by-products include coke and coal tar.
Chemistry
A brown or black carbonaceous deposit derived from the accumulation and alteration of ancient vegetation, which originated largely in swamps or other moist environments. As the vegetation decomposed it formed layers of peat, which were subsequently buried (for example, by marine sediments following a rise in sea level or subsidence of the land). Under the increased pressure and resulting higher temperatures the peat was transformed into coal. Two types of coal are recognized: humic (or woody) coals, derived from plant remains; and sapropelic coals, which are derived from algae, spores, and finely divided plant material. As the processes of coalification (i.e. the transformation resulting from the high temperatures and pressures) continue, there is a progressive transformation of the deposit: the proportion of carbon relative to oxygen rises and volatile substances and water are driven out. The various stages in this process are referred to as the ranks of the coal. In ascending order, the main ranks of coal are: lignite (or brown coal), which is soft, brown, and has a high moisture content; subbituminous coal, which is used chiefly by generating stations; bituminous coal, which is the most abundant rank of coal; semibituminous coal; semianthracite coal, which has a fixed carbon content of between 86% and 92%; and anthracite coal, which is hard and black with a fixed carbon content of between 92% and 98%. Most deposits of coal were formed during the Carboniferous and Permian periods. More recent periods of coal formation occurred during the early Jurassic and Tertiary periods. Coal deposits occur in all the major continents; the leading producers include the USA, China, Ukraine, Poland, UK, South Africa, India, Australia, and Germany. Coal is used as a fuel and in the chemical industry; by-products include coke and coal tar.
Biology
A brown or black carbonaceous deposit derived from the accumulation and alteration of ancient vegetation, which originated largely in swamps or other moist environments. As the vegetation decomposed it formed layers of peat, which were subsequently buried (for example, by marine sediments following a rise in sea level or subsidence of the land). Under the increased pressure and resulting higher temperatures the peat was transformed into coal. Two types of coal are recognized: humic (or woody) coals, derived from plant remains; and sapropelic coals, which are derived from algae, spores, and finely divided plant material. As the processes of coalification (i.e. the transformation resulting from the high temperatures and pressures) continue, there is a progressive transformation of the deposit: the proportion of carbon relative to oxygen rises and volatile substances and water are driven out. The various stages in this process are referred to as the ranks of the coal. In ascending order, the main ranks of coal are: lignite (or brown coal), which is soft, brown, and has a high moisture content; subbituminous coal, which is used chiefly by generating stations; bituminous coal, which is the most abundant rank of coal; semibituminous coal; semianthracite coal, which has a fixed carbon content of between 86% and 92%; and anthracite coal, which is hard and black with a fixed carbon content of between 92% and 98%. Most deposits of coal were formed during the Carboniferous and Permian periods. More recent periods of coal formation occurred during the early Jurassic and Palaeogene periods. Coal deposits occur in all the major continents. Coal is used as a fuel and in the chemical industry; by-products include coke and coal tar. Combustion of coal is a major source of greenhouse gases worldwide, and efforts are under way to develop ‘clean coal’ technology or to phase out its use.
Geology and Earth Sciences
Carbon-rich mineral deposit formed from the remains of fossil plants. These are deposited initially as peat, but burial and increase in temperatures at depth bring about physical and chemical changes. The process of ‘coalification’ results in the production of coals of different ranks (‘coal series’), from peat, through the bituminous coals and lignite, to anthracite. Each rank marks a reduction in the percentage of volatiles and moisture, and an increase in the percentage of carbon. They are termed ‘woody’ or ‘humic’ coals if formed from fragments of trees or bushes. If the major constituents of coal are pollen grains and/or finely divided plant debris, the term ‘sapropelic coal’ is used.
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