Anthracite (Greek aνθρακίτης (anthrakítes), "coal-like," from άνθραξ (ánthrax), coal)[1] is a hard, compact variety of mineral coal that has a high luster. It has the highest carbon count, the fewest impurities, the highest calorific content of all types of coals, which also include bituminous coal and lignite.
Anthracite is the most metamorphosed type of coal (but still represents low-grade metamorphism), in which the carbon content is between 92.1% and 98%.[2][3] 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, and smokeless flame.
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Other terms which refer to anthracite are black coal, hard coal, stone coal (not to be confused with the German Steinkohle or Dutch steenkool which are broader terms meaning all varieties of coal of a stonelike hardness and appearance, like bituminous coal and often anthracite as well, as opposed to lignite, which is softer), blind coal (in Scotland), Kilkenny coal (in Ireland), crow coal (or craw coal from its shiny black appearance), and black diamond. "Blue Coal" is the term for a once-popular and trademarked brand of anthracite, mined by the Glen Alden Coal Company in Pennsylvania, and sprayed with a blue dye at the mine before shipping to its northeastern U.S. markets to distinguish it from its competitors. The imperfect anthracite of north Devon and north Cornwall (around Bude) in England, which is used as a pigment, is known as culm. Culm is also the term used in geological classification to distinguish the strata in which it is found and similar strata in the Rhenish hill countries are known as the Culm Measures. In America, culm is used as an equivalent for waste or slack in anthracite mining.
Anthracite is similar in appearance to the mineraloid jet and is sometimes used as a jet imitation.
Anthracite differs from ordinary bituminous coal by its greater hardness, its higher relative density of 1.3–1.4, and lustre, which is often semi-metallic with a mildly brown 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. Anthracitization is the transformation of bituminous into anthracite.
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.
Anthracite may be considered to be a transition stage between ordinary bituminous 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 is a product of metamorphism and is associated with metamorphic rocks, just as bituminous 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 Western Pennsylvania. In the same way the anthracite region of South Wales is confined to the contorted portion west of Swansea and Llanelli, the central and eastern portions producing steam coal, coking coal and domestic 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 at the same temperature. The chemical composition of some typical anthracites is given in the article coal.
Because of its higher quality, anthracite generally costs two to three times as much as regular coal. In June 2008, anthracite cost as US$150/short ton wholesale.[4]
In southwest Wales, anthracite was burned as a domestic fuel since at least medieval times.[5] It was mined near Saundersfoot.
In the United States, anthracite coal history began in 1790 in Pottsville, Pennsylvania, with the discovery of coal made by the hunter Necho Allen in what is now known as the Coal Region. Legend has it that Allen fell asleep at the base of Broad Mountain and woke to the sight of a large fire because his campfire had ignited an outcropping of anthracite coal. By 1795, an anthracite-fired iron furnace had been built on the Schuylkill River.
Anthracite was first experimentally burned as a residential heating fuel in the USA on 11 February 1808, by Judge Jesse Fell in Wilkes-Barre, Pennsylvania, on an open grate in a fireplace. Anthracite differs from wood in that it needs a draft from the bottom, and Judge Fell proved with his grate design that it was a viable heating fuel.
In spring 1808, John and Abijah Smith shipped the first commercially mined load of anthracite down the Susquehanna River from Plymouth, Pennsylvania, marking the birth of commercial anthracite mining in the United States. From that first mine, production rose to an all-time high of over 100 million tons in 1917.
From the late 19th century until the 1950s, anthracite was the most popular fuel for heating homes and other buildings in the northern United States, until it was supplanted first by oil burning systems and more recently by natural gas systems as well. Many large public buildings, such as schools, were heated with anthracite-burning furnaces through the 1980s.
Current U.S. anthracite production averages around 5 million tons per year. Of that, about 1.8 million tons were mined in the state of Pennsylvania. [6]
The principal use of anthracite today is for a domestic fuel in either hand-fired stoves or automatic stoker furnaces. It delivers high energy per its weight and burns cleanly with little soot, making it ideal for this purpose. Its high value makes it prohibitively expensive for power plant use. Other uses include the fine particles used as filter media, and as an ingredient in charcoal briquettes.
Anthracite is processed into different sizes by what is commonly referred to as a breaker (see coal). The large coal is raised from the mine and passed through breakers with toothed rolls to reduce the lumps to smaller pieces. The smaller pieces are separated into different sizes by a system of graduated sieves, placed in descending order. Sizing is necessary for different types of stoves and furnaces.
During the American Civil War, Confederate blockade runners used anthracite as a smokeless fuel for their boilers to avoid giving away their position to the blockaders.[7]
In the early 20th century United States, the Lackawanna Railroad started using only the more expensive anthracite coal in its passenger locomotives, 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". Similarly, the Great Western Railway in the UK was able to use its access to anthracite (it dominated the anthracite region) to earn a reputation for efficiency and cleanliness unmatched by other UK companies.
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 horsepower the expenditure of fuel is at the rate of only 1 pound per horsepower-hour, and with larger engines it is proportionately less. Large quantities of anthracite for power purposes were formerly exported from South Wales to France, Switzerland and parts of Germany. Commercial mining has now ceased.
Anthracite is an authorised fuel[8] in terms of the United Kingdom's Clean Air Act 1993, meaning that it can be used within a designated Smoke Control Area such as the central London boroughs.
Mining of anthracite coal continues to this day in eastern Pennsylvania, and contributes up to 1% to the gross state product. The Anthracite market size of Pennsylvania is $150 million, by far the highest in the nation.[9] More than 2,000 people were employed in the mining of anthracite coal in 1995. Most of the mining as of that date involved reclaiming coal from slag heaps (waste piles from past coal mining) nearby closed mines. Some underground anthracite coal is also being mined. As petroleum and natural gas have become more expensive, anthracite coal may grow in its importance as an energy source.[10]
Historically from time to time, underground veins of coal have caught fire, often from careless or unfortunate mining activities. The pocket of ignited coal is fed oxygen by vent paths that have not yet been discovered. These can smolder for years. Commonly, exhaust vents in populated areas are soon sensed and are sealed while vents in uninhabited areas remain undiscovered. Occasionally, vents are discovered via fumes sensed by passers-by, often in forested areas. Attempts to extinguish those remaining have at times been futile, and several such combustion areas exist today. The existence of an underground combustion site can sometimes be identified in the winter where fallen snow is seen to be melted by the warmth conducted from below. Proposals for harnessing this heat as geothermal energy have not been successful.
A vein of anthracite that caught fire in Centralia, Pennsylvania in 1962 has been burning ever since, turning the once thriving mining hamlet into a ghost town.[11]
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 (6.3 billion tonnes) of minable reserves. Deposits at Crested Butte, Colorado were mined historically.
Anthracites of newer, Tertiary or Cretaceous age, are found in the Crow's Nest part of the Rocky Mountains in Canada, and at various places in the Andes in Peru.
The common American classification is as follows:
Lump, steamboat, egg and stove coals, the latter in two or three sizes, all three being above 1½ in (38 mm) size on round-hole screens.
| Classification | Minimum Size (inches) | Maximum Size (inches) |
|---|---|---|
| Chestnut | 7/8 | 1 1/2 |
| Pea | 9/16 | 7/8 |
| Buckwheat | 3/8 | 9/16 |
| Rice | 3/16 | 3/8 |
| Barley | 3/32 | 3/16 |
The primary sizes used in the United States for domestic heating are Chestnut, Pea, Buckwheat and Rice, with Chestnut and Rice being the most popular. Chestnut and Pea are used in hand fired furnaces while the smaller Rice and Buckwheat are used in automatic stoker furnaces. Rice is currently the most sought after size due to the ease of use and popularity of that type of furnace.
In South Wales a less elaborate classification is adopted, but great care is exercised in hand-picking and cleaning the coal from particles of pyrites in the higher qualities known as best malting coals, which are used for kiln-drying malt.
Anthracite dust can be made into briquettes and is sold in the United Kingdom under trade names such as Phurnacite, Ancit and Taybrite.
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