Anthracite coal

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Anthracite (Greek Ανθρακίτης, literally "a form of coal", from Anthrax [Άνθραξ], coal) is a hard, compact variety of mineral coal that has a high luster. It has the highest carbon count and is the best burning of all coals. Anthracite coal is the highest of the metamorphic rank, in which the carbon content is between 92% and 98%. The term is applied to those varieties of coal which do not give off tarry or other hydrocarbon vapours when heated below their point of ignition. Anthracite ignites with difficulty and burns with a short blue flame, without smoke.

Other terms having the same meaning are blue coal, hard coal, stone coal (not to be confounded with the German Steinkohle), blind coal (in Scotland), Kilkenny coal (in Ireland), and black diamond. The imperfect anthracite of north Devon, which however is only used as a pigment, is known as culm, the same term being used in geological classification to distinguish the strata in which it is found, and similar strata in the Rhenish hill countries which are known as the Culm Measures. In America, culm is used as an equivalent for waste or slack in anthracite mining.

Contents

Properties

Anthracite is similar in appearance to the mineraloid jet, and is sometimes used to imitate it.

Physically, anthracite differs from ordinary bituminous coal by its greater hardness, higher density, 1.3-1.4, and lustre, the latter being often semi-metallic with a somewhat brownish reflection. It contains a high percentage of fixed carbon and a low percentage of volatile matter. It is also free from included soft or fibrous notches and does not soil the fingers when rubbed.

The moisture content of fresh-mined anthracite generally is less than 15 percent. The heat content of anthracite ranges from 22 to 28 million Btu per short ton (26 to 33 MJ/kg) on a moist, mineral-matter-free basis. The heat content of anthracite coal consumed in the United States averages 25 million Btu/ton (29 MJ/kg), on the as-received basis (i.e., containing both inherent moisture and mineral matter). Note: Since the 1980s, anthracite refuse or mine waste has been used for steam electric power generation. This fuel typically has a heat content of 15 million Btu/ton (17 MJ/kg) or less.

Anthracite may be considered to be a transition stage between ordinary bituminous coal and graphite, produced by the more or less complete elimination of the volatile constituents of the former; and it is found most abundantly in areas that have been subjected to considerable earth-movements, such as the flanks of great mountain ranges. Anthracite coal is a product of metamorphism and is associated with metamorphic rocks, just as bituminous coal is associated with sedimentary rocks. For example, the compressed layers of anthracite that are deep mined in the folded (metamorphic) Appalachian Mountains of the Coal Region of northeastern Pennsylvania are extensions of the layers of bituminous coal that are strip mined on the (sedimentary) Allegheny Plateau of Kentucky and West Virginia, and Eastern Pennsylvania. In the same way the anthracite region of South Wales is confined to the contorted portion west of Swansea and Llanelly, the central and eastern portions producing steam, coking and house coals.

Structurally it shows some alteration by the development of secondary divisional planes and fissures so that the original stratification lines are not always easily seen. The thermal conductivity is also higher, a lump of anthracite feeling perceptibly colder when held in the warm hand than a similar lump of bituminous coal at the same temperature. The chemical composition of some typical anthracites is given in the article coal.


Economic value

Pottsville, Pennsylvania anthracite coal history began in 1790 with the discovery of coal made by the hunter Necho Allen in what is called the Coal Region. Legend has it that Allen fell asleep at the base of the Broad Mountain and woke to the sight of a large fire. His campfire had ignited an outcropping of anthacite coal. By 1795, an anthracite fired iron furnace was established on the Schuylkill River.

Anthracite was first experimentally burned as a fuel on February 11, 1808 by Judge Jeese Fell in Wilkes-Barre, Pennsylvania on a open grate in a fireplace. It delivers high energy per its weight and burns cleanly with little soot, making it a sought after variety of coal and hence of higher value. It is also used as a filter medium.

The principal use of anthracite is as a smokeless fuel. In the eastern from the United States, it is largely employed as domestic fuel, usually in close stoves or furnaces, as well as for steam purposes, since, unlike that from South Wales, it does not decrepitate when heated, or at least not to the same extent. For proper use, however, it is necessary that the fuel should be supplied in pieces as nearly uniform in size as possible, a condition that has led to the development of the breaker which is so characteristic a feature in American anthracite mining (see coal). The large coal as raised from the mine is passed through breakers with toothed rolls to reduce the lumps to smaller pieces, which are separated into different sizes by a system of graduated sieves, placed in descending order. Each size can be perfectly well burnt alone on an appropriate grate, if kept free from larger or smaller admixtures.

In the early 20th century United States, the Lackawanna Railroad started using only the more expensive anthracite coal, dubbed themselves "The Road of Anthracite," and advertised widely that travelers on their line could make railway journeys without getting their clothing stained with soot. The advertisements featured a white-clad woman named Phoebe Snow and poems containing lines like "My gown stays white / From morn till night / Upon the road of Anthracite".

Formerly, anthracite was largely used, both in America and South Wales, as blast-furnace fuel for iron smelting, but for this purpose it has been largely superseded by coke in the former country and entirely in the latter. An important application has, however, been developed in the extended use of internal combustion motors driven by the so-called "mixed," "poor," "semi-water" or "Dowson gas" produced by the gasification of anthracite with air and a small proportion of steam. This is probably the most economical method of obtaining power known; with an engine as small as 15 horse-power the expenditure of fuel is at the rate of only 1 lb per horse-power hour, and with larger engines it is proportionately less. Large quantities of anthracite for power purposes are now exported from South Wales to France, Switzerland and parts of Germany.

Major Reserves

The largest fields of anthracite coal in the United States are found in Northeastern Pennsylvania called the Coal Region, where there are 7 billion short tons (6.4 petagrams) of minable reserves. Deposits at Crested Butte, Colorado were mined historically. Anthracite deposits of an estimated 3 billion short tons (2.7 Pg) in Alaska have never been mined.

Anthracites of newer, tertiary or cretaceous age, are found in the Crow's Nest part of the Rocky Mountains in Canada, and at various points in the Andes in Peru.

Classifications

The common American classification is as follows:--

Lump, steamboat, egg and stove coals, the latter in two or three sizes, all three being above 1-1/2 in. size on round-hole screens.

Chestnut below 1-1/2 inch above 7/8 inch
Pea " 7/8 " " 9/16 "
Buckwheat " 9/16 " " 3/8 "
Rice " 3/8 " " 3/16 "
Barley " 3/16 " " 3/32 "

From the pea size downwards the principal use is for steam purposes. In South Wales a less elaborate classification is adopted; but great care is exercised in hand-picking and cleaning the coal from included particles of pyrites in the higher qualities known as best malting coals, which are used for kiln-drying malt and hops.

References


External links

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