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Product Name: | COAL | Synonyms: | COAL | CAS: | | MF: | | MW: | 0 | EINECS: | | Product Categories: | | Mol File: | Mol File | |
Chemical Properties | Coal is an organic, combustible, rock-like natural substance
that occurs in various forms from hard and brittle anthracite
to soft and friable lignite. Coal is sometimes classified into
two types: hard coal and soft coal. These terms do not,
however, have a standardized meaning. One definition
calls anthracite hard coal and places all other coal types in
the soft coal category. A more common convention is that of
Speight, in which anthracite and bituminous coals are
termed hard coal and lignite and brown coal are classified as
soft coal. | Production Methods | Coal exists as distinct seams of mineral laid down as
sedimentary deposits within the earth. The seams are
extracted by surface (strip) or underground mining. Surface
mining generally involves the removal of rock and other
strata to uncover the top or side of a coal seam.
Using blasting and/or mechanical means, the coal is fractured
and removed from the mine by train or truck. There are two
main types of underground mining: room and pillar and
longwall (each accounting for 50% of U.S. production in
2010). Room and pillar mining is the traditional method of
mining, whereby pillars of coal are left to support the roof. These pillars may later be removed or
“robbed,” a process that provides better reclamation of the
coal but speeds up subsidence of the overlying strata. Room
and pillar operations are commonly undertaken using conventional
mining or continuous mining. In the former
method, the bottom of the coal seam is undercut first,
followed by blasting to bring the coal down. In continuous
mining, a machine with a rotating cutting head removes the
coal from the coal face. Longwall mining, of more recent
origin, involves removing “slices” of coal from the edge of
the seam by large coal cutting machines. All of
the coal is extracted, and the roof is left to collapse as the coal
face advances. A lesser-used method of underground mining
is the shortwall system, which is a hybrid of the longwall
and continuous mining methods and is used principally in
Australia. After extraction, coal is typically crushed and
cleaned. Cleaning can involve screening for size, removal
of impurities by wet or dry methods, and drying. | Definition | coal: A brown or black carbonaceousdeposit derived from the accumulationand alteration of ancient vegetation,which originated largely inswamps or other moist environments.As the vegetation decomposedit formed layers of peat, whichwere subsequently buried (for example,by marine sediments following arise in sea level or subsidence of theland). Under the increased pressureand resulting higher temperaturesthe peat was transformed into coal.Two types of coal are recognized:humic (or woody) coals, derived fromplant 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 transformationof the deposit: the proportionof carbon relative to oxygenrises and volatile substances andwater are driven out. The variousstages in this process are referred toas the ranks of the coal. In ascendingorder, the main ranks of coal are: lignite(or brown coal), which is soft,brown, and has a high moisture content;subbituminous coal, which isused chiefly by generating stations;bituminous coal, which is the mostabundant rank of coal; semibituminouscoal; semianthracite coal, whichhas a fixed carbon content of between86% and 92%; and anthracitecoal, which is hard and black with afixed carbon content of between 92%and 98%. Most deposits of coal were formedduring the Carboniferous and Permianperiods. More recent periods ofcoal formation occurred during theearly Jurassic and Tertiary periods.Coal deposits occur in all the majorcontinents; the leading producers includethe USA, China, Ukraine,Poland, UK, South Africa, India, Australia,and Germany. Coal is used as afuel and in the chemical industry; byproductsinclude coke and coal tar. | Definition | A black mineral that consists
mainly of carbon, used as a fuel and as a
source of organic chemicals. It is the fossilized
remains of plants that grew in the
Carboniferous and Permian periods and
were buried and subjected to high pressures
underground. There are various types
of coal, classified according to their increasing
carbon content. | Agricultural Uses | Coal is a brown or black carbonaceous deposit, formed largely by the accumulation and alteration of ancient vegetation in swamps and other moist environments. The vegetation decomposes, forms layers of peat, and gets subsequently buried deep in the earth where, under increased pressure and temperatures, the peat gets transformed into coal. This, in short, is the process of coalification. Two types of coals are known - humic coal or woody coal (derived from plant remains) and sapropelic coal (derived from algae, spores and finely divided plant materials). As the process of coalification continues, the proportion of carbon rises relative to oxygen, and volatile substances and water are expelled. Various intermediates in the coalification process are referred to as the ranks of coal. Some of them are lignite or brown coal (soft and brown with a high moisture content), sub-bituminous coal (used mainly for power generation) and bituminous coal (the most abundant type of coal). Other varieties are semi-bituminous coal, semi-anthracite coal (with a fwed carbon content of 86 to 92%) and anthracite coal (hard and black, with a fwed carbon content of 92 to 98%). Coal is used as a fuel and in the chemical industry. When coal is heated in the absence of air, its volatile components are expelled and it is converted into coke. When bituminous coal is subjected to destructive distillation, it is converted into a thick black liquid, called coal tar. Coal has varying amounts of ash and clinker and impurities like clays and sulphur (between 0.5% and 3%). The calorific value of coal increases with its grade till it reaches the anthracite level. The design of coal burning (or gasifying) facilities is dictated by its calorific content and impurities. Based on its moisture percentage, coal is specified with values of volatile combustible matter, fixed carbon, ash and percentages of carbon, hydrogen, oxygen, nitrogen and sulphur. Coal, used for the large-scale production of hydrogen, is probably the world's largest source for producing ammonia. Coal-based power generation units and fertilizer production units are located near coal mines. Coal is also an important source of raw material for the chemical industry. Pyrolysis or distillation of coal yields coal tar and hydrocarbon gases which are upgraded by hydrogenation or methanation to synthetic crude oil and fuel gas, respectively. Catalytic hydrogenation yields hydrocarbon oils and gasoline. Gasification produces synthesis gas (CO+H) from which ammonia and other fertilizers are made. However, coal creates environmental pollution and entails high plant costs. As a result, its use at the current scale may decline in the years to come. | Carcinogenicity | There is little epidemiologic evidence
of a relationship between coal mine dust exposure and
lung cancer development, although a link with silica dust
exposure has been reported. Histological
evaluation of lung tumors in coal miners reveals that these
tumors vary little in cell type or pathological features from
those associated with cigarette smoking.
Elevated stomach cancer rates have been reported in
studies of U.S. underground coal miners compared to general
population rates. A mechanistic
explanation for coal dust-induced stomach cancer suggests
that swallowed coal dust mixes with nitrates in food and
under the acidic conditions in the stomach, nitrosation of
organic material associated with this coal dust occurs, resulting
in the production of carcinogenic products. Evidence
indicates that nitrosation of coal dust extracts become
mutagenic and can cause neoplastic transformations in mammalian
cells. Some evidence of elevated stomach
cancer mortality in coal miners has also been observed in
more recent studies in the United Kingdom, Germany, and
United States. |
| COAL Preparation Products And Raw materials |
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