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Coal
Coal is a fossil fuel extracted from the ground by deep mining, coal mining (open-pit mining or strip mining). It is a readily combustible black or brownish-black sedimentary rock. It is composed primarily of carbon and hydrocarbons, along with assorted other elements, including sulfur. Often associated with the Industrial Revolution, coal remains an enormously important fuel and is the most common source of electricity world-wide. In the United States, for example, the burning of coal generates over half the electricity consumed by the population. United States
Etymology
Coal is thought ultimately to derive its name from the Old English col but this actually meant charcoal at the time; coal was not mined prior to the late Middle Ages. Mineral coal was referred to as sea-coal, either because it was found on beaches occasionally having fallen from the exposed coal seams above, or because it was easier to transport by sea rather than on the very poor road system (in London, England there is still a sea coal road/lane where the coal merchants conducted their business). It is associated with the astrological sign Capricorn. It is carried by thieves to protect them from detection and to help them to escape when pursued. It is an element of a popular ritual associated with New Year's Eve. To dream of burning coals is a symbol of disappointment, trouble, affliction and loss, unless they are burning brightly, when the symbol gives promise of uplifting and advancement. Santa Claus is said to leave a lump of coal instead of Christmas presents in the stockings of naughty children.
Composition and creation
Carbonacous material forms more than 50 percent by weight and more than 70 percent by volume of coal (this includes inherent moisture). Coal is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time. Much coal was formed from ancient plants that grew in swamp ecosystems. When such plants died, their biomass was deposited in anaerobic, aquatic environments where low oxygen levels prevented their decay and oxidation (rotting and release of carbon dioxide). Successive generations of this type of plant growth and death formed thick deposits of unoxidized organic matter that were subsequently covered by sediments and compacted into carbonaceous deposits such as peat or bituminous or anthracite coal. Evidence of the types of plants that contributed to carbonaceous deposits can occasionally be found in the shale and sandstone sediments that overlie coal deposits, and, with special techniques, within the coal itself. The greatest coal-forming time in geologic history was during the Carboniferous era (280 to 345 million years ago).
Harmful effects of coal burning
Combustion of coal, like any other compound containing carbon, produces carbon dioxide (CO2), along with varying amounts of sulfur dioxide (SO2) depending on where it was mined. Sulfur dioxide reacts with water to form sulfurous acid. If sulfur dioxide is discharged into the atmosphere, it reacts with water vapor and is eventually returned to the Earth as acid rain. Emissions from coal-fired power plants represent the largest source of artificial carbon dioxide emissions, according to most climate scientists a primary cause of global warming. Many other pollutants are present in coal power station emissions. Some studies claim that coal power plant emissions are responsible for tens of thousands of premature deaths annually in the United States alone. Modern power plants utilize a variety of techniques to limit the harmfulness of their waste products and improve the efficiency of burning, though these techniques are not widely implemented in some countries, as they add to the capital cost of the power plant. To eliminate CO 2 emissions from coal plants, carbon sequestration has been proposed but is not yet in large-scale use. Coal also contains many trace elements, including arsenic and mercury, which are dangerous if released into the environment. Coal also contains low levels of uranium, thorium, and other naturally-occurring radioactive isotopes whose release into the environment may lead to radioactive contamination. While these substances are trace impurities, if a great deal of coal is burned, significant amounts of these substances are released. If coal liquefaction or gasification is used to make petrochemicals, a great deal of carbon dioxide is produced in the process. However, if sequestration or some other process were used to dispose of this by-product, fuels produced from this process would be less polluting. Some process do not have a much greater total impact on carbon dioxide levels than ones refined from petroleum. Others may be less polluting still. Research in this field is ongoing.
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