COAL Chemische Eigenschaften,Einsatz,Produktion Methoden
Chemische Eigenschaften
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.
Vorbereitung Methode
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
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.
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 Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
