Anthracite
Anthracite, also known as hard coal and black coal, is a hard, compact variety of coal that has a submetallic lustre. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the highest ranking of coals.
The Coal Region of Northeastern Pennsylvania in the United States has the largest known deposits of anthracite coal in the world with an estimated reserve of seven billion short tons. China accounts for the majority of global production; other producers include Russia, Ukraine, North Korea, South Africa, Vietnam, Australia, Canada, and the United States. The total production of anthracite worldwide in 2023 was 632 million short tons.
Anthracite is the most metamorphosed type of coal, but still represents low-grade metamorphism, as found in the anthracite of the Narragansett Basin in Rhode Island which is of greenschist metamorphic facies. The carbon content of anthracite is between 86% and 97%. 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 is difficult to ignite, and burns with a short, blue, and smokeless flame.
Anthracite is categorized into several grades. Standard grade anthracite is used predominantly in power generation, and high grade and ultra high grade are used predominantly in the metallurgy sector. Anthracite accounts for about 1% of global coal reserves, and is mined in only a few countries around the world.
Names
Anthracite derives from the Greek anthrakítēs, literally "coal-like". Other terms which refer to anthracite are black coal, hard coal, stone coal, dark coal, coffee coal, blind coal, Kilkenny coal, crow coal or craw coal, 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.Culm has different meanings in British and American English. In British English, culm is the imperfect anthracite, located predominantly north Devon and Cornwall, which was used as a pigment. The term is also used to refer to some carboniferous rock strata found in both Britain and in the Rhenish hill countries, also known as the Culm Measures. In Britain, it may also refer to coal exported from Britain during the 19th century. In American English, "culm" refers to the waste or slack from anthracite mining, mostly dust and small pieces not suitable for use in home furnaces.
Properties
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 luster, which is often semi-metallic with a mildly green 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 coal into anthracite.
The moisture content of fresh-mined anthracite generally is less than 15 percent. The heat content of anthracite ranges from 26 to 33 MJ/kg on a moist, mineral-matter-free basis. The heat content of anthracite coal consumed in the United States averages 29 MJ/kg, on the as-received basis, containing both inherent moisture and mineral matter.
Since the 1980s, anthracite refuse or mine waste has been used for coal power generation in a form of recycling. The practice known as reclamation is being applied to culm piles antedating laws requiring mine owners to restore lands to their approximate original condition.
Chemically, anthracite may be considered as 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 stresses and pressures, such as the flanks of great mountain ranges. Anthracite is associated with strongly deformed sedimentary rocks that were subjected to higher pressures and temperatures just as bituminous coal is generally associated with less deformed or flat-lying sedimentary rocks. The compressed layers of anthracite that are deep mined in the folded Ridge and Valley Province of the Appalachian Mountains of the Coal Region of East-central Pennsylvania are extensions of the same layers of bituminous coal that are mined on the generally flat lying and undeformed sedimentary rocks further west on the Allegheny Plateau of Kentucky and West Virginia, Eastern Ohio, 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.
Anthracite 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 feels perceptibly colder when held in the warm hand than a similar lump of bituminous coal at the same temperature.
Anthracite has a history of use in blast furnaces for iron smelting; however, it lacked the pore space of metallurgical coke, which eventually replaced anthracite.
History of mining and use
In southwest Wales, anthracite has been burned as a domestic fuel since at least medieval times, when it was mined near Saundersfoot. More recently, large-scale mining of anthracite took place across the western part of the South Wales Coalfield until the late 20th century.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 outcrop of anthracite coal.
By the late 18th century, it was known in the United States that anthracite could be burnt, but the techniques required to do so were unknown. Anthracite differs from wood and bituminous coal in that it has a higher ignition temperature and needs a fresh air draft from the bottom to burn. Several claims are made about who "first" burnt anthracite coal in the United States around this time, and all such claims originate from Pennsylvania. The city of Pottsville, Pennsylvania claims that their town was founded around an anthracite-fired iron furnace purchased by John Potts in 1806, which was built on the Schuylkill River in 1795. Pennsylvanian Charles V. Hagner recalls in his 1869 book that an unnamed employee of Josiah White and Erskine Hazard accidentally burnt anthracite in their rolling mill at the Falls of the Schuylkill River at some point between 1812 and 1815. Judge Jesse Fell is claimed to be the first person to burn anthracite for the purposes of residential heating in the USA in Wilkes-Barre, Pennsylvania on 11 February 1808. Judge Fell used an open grate in his fireplace to burn anthracite, as an experiment to prove that it was a viable residential 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.
The difficulty of igniting anthracite inhibited its early use, especially in blast furnaces for smelting iron. With the development of the hot blast in 1828, which used waste heat to preheat combustion air, anthracite became a preferred fuel, accounting for 45% of US pig iron production within 15 years. Anthracite iron smelting was later displaced by coke.
From the late 19th century until the 1950s, anthracite was the most popular fuel for heating homes and other buildings in the northern US, until it was supplanted by oil-burning systems, and more recently natural gas systems. Many large public buildings, such as schools, were heated with anthracite-burning furnaces through the 1980s.
During the American Civil War, Confederate blockade runners used anthracite as a smokeless fuel for their boilers to avoid revealing their position to the blockaders.
The invention of the Wootten firebox enabled locomotives to directly burn anthracite efficiently, particularly waste culm. In the early 20th century US, the Delaware, Lackawanna and Western 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 to earn a reputation for efficiency and cleanliness unmatched by other UK companies.
Internal combustion motors driven by the so-called "mixed", "poor", "semi-water" or "Dowson gas" produced by the gasification of anthracite with air were at one time the most economical method of obtaining power, requiring only, or less. Large quantities of anthracite for power purposes were formerly exported from South Wales to France, Switzerland and parts of Germany.
Commercial anthracite mining in Wales ceased in 2013, although a few large open cast sites remain, along with some relatively small drift mining operations. Commercial anthracite mining is still ongoing in Pennsylvania; the state produced a "total of 4,614,391 tons of coal, predominately from surface coal mines" in 2015.