Everything about Bituminous Coal totally explained
Bituminous coal is a relatively soft
coal containing a tarlike substance called
bitumen. It is of higher quality than
lignite coal but poorer quality than
anthracite coal.
Bituminous coal is an organic sedimentary rock formed by diagenetic and submetamorphic compression of
peat bog material.
Bituminous coal has been compressed and heated so that its primary constituents are the
macerals
vitrinite,
exinite, etc. The carbon content of bituminous coal is around 60-80%; the rest is composed of water, air, hydrogen, and
sulfur, which have not been driven off from the
macerals.
The heat content of bituminous coal ranges from 21 million to 30 million Btu/ton (24 to 35 MJ/kg) on a moist, mineral-matter-free basis.
Bituminous coal is usually black, sometimes dark brown, often with well-defined bands of bright and dull material. Bituminous coal seams are stratigraphically identified by the distinctive sequence of bright and dark bands and are classified accordingly as either "dull, bright-banded" or "bright, dull-banded" and so on.
Bank Density is approximately 1346 kg/m³ (84 lb/ft³). Bulk density typically runs 833 kg/m³ (52 lb/ft³).
Uses
Bituminous coals are graded according to vitrinite reflectance, moisture content,
volatile content, plasticity and ash content. Generally, the highest value bituminous coals are those which have a specific grade of
plasticity, volatility and low ash content, especially with low
carbonate,
phosphorus and
sulfur.
Plasticity is vital for
coking and
steel-making, where the coal has to behave in a manner which allows it to mix with the iron oxides during smelting. Low phosphorus content is vital for these coals, as phosphorus is a highly deleterious (damaging) element in steel making.
Coking coal is best if it has a very narrow range of volatility and plasticity. This is measured by the
Free Swelling Index test. Tar content, volatile content and swelling index are used to select coals for coke blending.
Volatility is also critical for steel-making and power generation, as this determines the burn rate of the coal. High volatile content coals, while easy to ignite often are not as prized as moderately volatile coals; low volatile coal may be difficult to ignite although it'll contain more energy per unit volume. The smelter must balance the volatile content of the coals to optimize the ease of ignition, burn rate, and energy output of the coal.
Low ash, sulfur, and carbonate coals are prized for power generation because they don't produce much boiler
slag and they don't require as much effort to scrub the flue gases to remove particulate matter. Carbonates are deleterious as they readily stick to the boiler apparatus. Sulfide contents are also deleterious in some fashion as this sulfur is emitted and can form
smog,
acid rain and haze pollution. Again, scrubbers on the flue gases aim to eliminate particulate and sulfur emissions.
Coking coal
When used for many industrial processes, bituminous coal must first be
"coked" to remove volatile components. Coking is achieved by heating the coal in the absence of oxygen, which drives off volatile
hydrocarbons such as
propane,
benzene and other aromatic hydrocarbons, and some sulfur gases. This also drives off a considerable amount of the contained water of the bituminous coal.
Coking coal is used in the manufacture of
steel, where carbon must be as volatile-free and ash-free as possible.
Jurassic coals
Extensive but low-value coals of Jurassic age extend through the
Surat Basin in
Australia, formed in an intracratonic sag basin, and contain evidence of
dinosaur activity in the numerous ash plies. These coals are exploited in
Queensland from the
Walloon Coal Measures which are up to 15m thick of sub-bituminous to bituminous coals suited for coking, steam-raising and oil cracking.
Triassic coals
Coals of
Triassic age are known from the Clarence-Moreton and
Ipswich Basins, near
Ipswich,
Australia and the Esk Trough. Coals of this era are rare, and many contain fossils of flowering plants. Some of the best coking coals are Australian Triassic coals, although most economic deposits have been worked out.
Permian coals
The second largest deposits of the world's bituminous coal are contained within Permian strata in
Russia. Australian deposits in the
Bowen Basin in
Queensland, the
Sydney Basin and
Perth Basin are Permian coal, where thicknesses in excess of 300 m are known. Current reserves and resources are projected to last for over 200 years.
Australia exports the vast majority of its coal for coking and steel making in Japan. Certain Australian coals are the best in the world for these purposes, requiring little to no blending. Some bituminous coals from the Permian and Triassic in Australia are also the most suitable for cracking into
oil.
Vast deposits of
oil shale exist in the Permian sediments of Queensland.
Carboniferous coals
Much
North American coal was created when swamps created organic material faster than it could decay, before the
orogenies that created the
Appalachian Mountains during the
Carboniferous epoch, which is subdivided in American literature into the
Mississippian and
Pennsylvanian eras after the two main coal-bearing time periods.
Bituminous coal is mined in the
Appalachian region, primarily for power generation.
Mining is done via both surface and underground mines.
Pocahontas bituminous coal at one time fueled half the world's navies and today stokes steel mills and power plants all over the globe.
While coal mining is an important part of Appalachia's economy, many miners are afflicted with
black lung disease.
Further Information
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