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Bituminous coal, or black coal, is a type of
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
containing a
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...
-like substance called bitumen or
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...
. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. It is typically hard but
friable Friability ( ), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing. The opposite of friable is indurate. Substances that are designated hazardous, ...
. Its quality is ranked higher than lignite and sub-bituminous coal, but lesser than anthracite. It is the most abundant rank of coal, with deposits found around the world, often in rocks of Carboniferous age. Bituminous coal is formed from sub-bituminous coal that is buried deeply enough to be heated to or higher. Bituminous coal is used primarily for electrical power generation and in the
steel industry Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant t ...
. Bituminous coal suitable for smelting iron (''coking coal'' or ''
metallurgical coal Metallurgical coal or coking coal is a grade of coal that can be used to produce good-quality coke. Coke is an essential fuel and reactant in the blast furnace process for primary steelmaking. The demand for metallurgical coal is highly coupled ...
'' ) must be low in sulfur and
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
. It commands a higher price than other grades of bituminous coal (thermal coal) used for heating and power generation. Within the coal mining industry, this type of coal is known for releasing the largest amounts of firedamp, a dangerous mixture of gases that can cause underground explosions. Extraction of bituminous coal demands the highest safety procedures involving attentive gas monitoring, good ventilation and vigilant site management.


Properties

Bituminous coal is a particular ''
rank Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking, such as: Level or position in a hierarchical organization * Academic rank * Diplomatic rank * Hierarchy * ...
'' of
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
, as determined by the amount and type of
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
present in the coal and the amount of energy it can produce when burned. It is higher in rank than sub-bituminous coal but lower in rank than anthracite. Bituminous coal is the most abundant rank of coal. Coal rank is based on several characteristics of the coal. The ''fixed carbon content'' refers to the percentage of the coal that is neither moisture, nor ash, nor volatile matter. When evaluated on a dry, mineral-matter-free basis, the fixed carbon content is the fraction of the coal that is not volatile organic matter. An ''agglomerating'' coal is a coal that softens when heated, forming a hard, gray, porous coke that resists crushing. ''Vitrinite reflectance'' is a measure of how reflective a polished surface of an average particle of ''
vitrinite Vitrinite is one of the primary components of coals and most sedimentary kerogens. Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of rocks. Vitrinite has a shiny appearance resembling gla ...
'' in the coal is. It is determined by how much of the carbon has condensed to an aromatic form from the heat and pressure of deep burial. In the United States, bituminous coal is defined as agglomerating coal yielding at least 10,500
Btu The British thermal unit (BTU or Btu) is a unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is also part of the United States customary units. The modern SI u ...
/lb (24,400 kJ/kg) of energy on combustion (on a moist, mineral-matter-free basis), with a fixed carbon content less than 86% (on a dry, mineral-matter-free basis.) Coal with a higher fixed carbon content is classified as anthracite, while agglomerating coal yielding less than 10,500 Btu/lb (24,400 kJ/kg) or nonagglomerating coal yielding less than 11,500 Btu/lb (26,700 kJ/kg) is classified as sub-bituminous coal. In the international market, bituminous coal is defined as coal with a vitrinite reflectance between 0.5 and 1.9. Vitrinite reflectance is also routinely measured for U.S. coal as a check on its rank classification Bituminous coal is dark brown to black, hard, but
friable Friability ( ), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing. The opposite of friable is indurate. Substances that are designated hazardous, ...
. It is commonly composed of thin bands of alternating bright and dull material. Though bituminous coal varies in its chemical composition, a typical composition is about 84.4% carbon, 5.4% hydrogen, 6.7% oxygen, 1.7% nitrogen, and 1.8% sulfur, on a weight basis. Its bank density (the density of a coal seam prior to breaking up during mining) is about 1346 kg/m3 (84 lb/ft3) while the
bulk density Bulk density, also called apparent density or volumetric density, is a property of powders, granules, and other "divided" solids, especially used in reference to mineral components (soil, gravel), chemical substances, (pharmaceutical) ingredient ...
of extracted coal is up to 833 kg/m3 (52 lb/ft3). Bituminous coal characteristically burns with a smoky flame and softens and swells during combustion. It gets its name from this tendency to form a softened, sticky mass when heated, which reflects the presence of bitumen (mineral tar) in the coal. Though almost all agglomerating coal is of bituminous rank, some bituminous coal is not agglomerating. Non-agglomerating bituminous coal includes cannel coal and
boghead coal Torbanite, also known as boghead coal or channel coal, is a variety of fine-grained black oil shale. It usually occurs as Lens (geology), lenticular masses, often associated with deposits of Permian coals. Torbanite is classified as Lacustrine ...
. These are nonbanded and nonreflective, and break with a conchoidal fracture. Both are ''saprolitic'', in contrast with most bituminous coal, which is ''humic'' (composed of decayed woody tissue of plants). Cannel coal is composed mostly of plant spores, while boghead coal is composed mostly of nonspore algal remains.


Subranks

In the United States, bituminous coal is further divided into subranks based on its heating value and fixed carbon content. Thus bituminous coal is divided into high-, medium-, and low-volatile categories based on fixed carbon content, and high-volatile bituminous coal is further subdivided by energy content. ISO classification of bituminous coal is based on vitrinite reflectance. This classification divides medium rank coal (approximately equivalent to bituminous coal) into four subranks. In order of increasing rank, these are: * Medium D: Vitrinite reflectance of 0.5 to 0.6. Corresponds approximately to ASTM high volatile C bituminous or sub-bituminous A. * Medium C: Vitrinite reflectance of 0.6 to 1.0. Corresponds approximately to ASTM high volatile C to high volatile B bituminous. * Medium B : Vitrinite reflectance of 1.0 to 1.4. Corresponds approximately to ASTM high volatile A to medium volatile bituminous. * Medium A: Vitrinite reflectance of 1.4 to 2.0. Corresponds approximately to ASTM low volatile bituminous.


Uses

Bituminous coal is used primarily for electrical power generation and in the manufacture of steel.


Coking coal

Coking coal (
metallurgical coal Metallurgical coal or coking coal is a grade of coal that can be used to produce good-quality coke. Coke is an essential fuel and reactant in the blast furnace process for primary steelmaking. The demand for metallurgical coal is highly coupled ...
or "met coal") is used in the manufacture of steel. A good coking coal must have excellent agglomeration properties, a high carbon content, and a low content of sulfur,
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, and ash. The best unblended coking coal is high quality medium-volatile bituminous coal. However, since single coals with all the necessary properties are scarce, coking coal is usually a blend of high-volatile bituminous coal with lesser amounts of medium- and low-volatile bituminous coal. Smithing coal is bituminous coal of the highest quality, as free of ash and sulfur as possible, used to manufacture coke for use by
blacksmith A blacksmith is a metalsmith who creates objects primarily from wrought iron or steel, but sometimes from other metals, by forging the metal, using tools to hammer, bend, and cut (cf. tinsmith). Blacksmiths produce objects such as gates, gr ...
s. Coking coal commands a higher price than coal used for energy production. , coking coal in the U.S. sold for about , compared with for bituminous coal generally. The cost of coking coal is about 3.5 times as high as the cost of coal used for electrical power (which includes lower ranks of coal, such sub-bituminous coal and lignite, as well as noncoking bituminous coal.)


Thermal coal

Bituminous coal which lacks the qualities required for use as metallurgical coal is graded as thermal coal. This is used primarily for electrical power generation. The ideal thermal coal is easily ignited but has a high heat content.


Activated carbon

Bituminous coal is used for the production of activated carbon. The coal is first coked, removing volatiles, then steam treated to activate it. Chemical processes for activating coke produced from bituminous coal have also been investigated.


Origin

Like other ranks of coal, bituminous coal forms from thick accumulations of dead plant material that are buried faster than they can decay. This usually takes place in
peat bogs A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg ...
, where falling plant debris is submerged in standing water. The stagnant water excludes oxygen, creates an acidic environment, and slows decay. The dead plant material is converted to
peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficient ...
. Peat is mostly a mixture of
cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...
,
hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all terrestrial plant cell walls.Scheller HV, Ulvskov Hemicelluloses.// Annu Rev ...
, and lignin that originally made up the woody tissue of the plants. Lignin has a weight composition of about 54% carbon, 6% hydrogen, and 30% oxygen, while cellulose has a weight composition of about 44% carbon, 6% hydrogen, and 49% oxygen. Bituminous coal has a composition of about 84.4% carbon, 5.4% hydrogen, 6.7% oxygen, 1.7% nitrogen, and 1.8% sulfur, on a weight basis. This implies that chemical processes during coalification remove most of the oxygen and much of the hydrogen, leaving carbon, a process called ''carbonization''. During coalification, the maturing coal increases in carbon content, decreases in hydrogen and volatiles, increases in its heating value, and becomes darker and more lustrous. Chemical changes include
dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
(which removes oxygen and hydrogen as water), decarboxylation (which removes oxygen as
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
), and demethanation (which removes hydrogen as
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
). By the time the coal reaches bituminous rank, most dehydration and decarboxylation has already taken place, and maturation of bituminous coal is characterized by demethanation. During coalification at bituminous rank, coal approaches its maximum heating value and begins to lose most of its volatile content. As carbonization proceeds, aliphatic compounds (carbon compounds characterized by chains of carbon atoms) are replaced by
aromatic compound Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past grouping ...
s (carbon compounds characterized by rings of carbon atoms) and aromatic rings begin to fuse into polyaromatic compounds (linked rings of carbon atoms). The structure increasingly resembles
graphene Graphene () is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure.
, the structural element of
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...
. This is accompanied by an increase in vitrinite reflectance, used to assess coal rank. During coalification, the pressure of burial reduces the volume of the original peat by a factor of 30 as it is converted to coal. However, the increase in rank of maturing coal mostly reflects the maximum temperature the coal reaches. Neither the maximum pressure, nor the nature of the original plant material, nor the length of burial is nearly as important. The temperature range for maturation of bituminous coal is from . The bitumen that characterizes bituminous coal forms under approximately the same conditions at which
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
is formed in petroleum source rocks. Bituminization is accompanied by peak methane generation in medium to low volatile bituminous coal. This makes these bituminous coals "gassy" and precautions must be taken against methane explosions. If the coal reaches temperatures above about , bitumen breaks down (''debituminization'') and the coal matures to anthracite.


Occurrence and production

Coal deposits are widely distributed worldwide, and range in age from the Devonian (about 360 to 420 million years ago) to Neogene deposits just a few million years old. However, 90% of all coal beds were deposited in the Carboniferous and
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...
periods, which represent just 2% of the Earth's geologic history. Vast deposits of coal formed in
wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The p ...
s—called
coal forest Coal forests were the vast swathes of wetlands that covered much of the Earth's tropical land areas during the late Carboniferous ( Pennsylvanian) and Permian times.Cleal, C. J. & Thomas, B. A. (2005). "Palaeozoic tropical rainforests and their e ...
s—that covered much of the Earth's tropical land areas during the late Carboniferous ( Pennsylvanian) and
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...
times. Bituminous coal is predominantly Carboniferous in age. Most bituminous coal in the United States is between 100 and 300 million years old. Vast deposits of bituminous coal of Pennsylvanian age is found in the Appalachian and Interior Provinces of North America.
Mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...
is done via both surface and underground mines. Historically, the many seams scattered over rugged terrain in the Appalachians have been conducive to mining by small companies, while the great extent and gentle dip of beds further west favors very large-scale operations. The Appalachian coal is notably low in sulfur and is often of metallurgical grade, while the Interior Province coal is much higher in sulfur. The belt of Carboniferous coal fields extends into central Europe, and much of this is bituminous coal. Bituminous coal fields are found in Poland and the Czech Republic, and the Polish deposits are one of the most important of that nation's natural resources. The Czech deposits have been exploited since prehistoric times. The European deposits include the Coal Measures of Britain, which account for most of Britain's coal production and which are mostly bituminous coal. The Westfield coal basin is the largest in Britain. Other significant bituminous coal deposits are found through much of Europe, including France, Germany, and northern Italy. Coal deposition was interrupted by the Permian-Triassic extinction event, but resumed later in the
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...
. Extensive bituminous coal deposits of Permian age are found in Siberia, east Asia, and Australia. These include the Minusinsky coal basin in Siberia, the
Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...
, Bowen, and Sydney Basins in Australia, and the extensive bituminous coal reserves of China. A second peak in coal deposition began in the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
, though most of this is lower rank coal rather than bituminous. In the United States, Cretaceous bituminous coals occur in Wyoming, Colorado and New Mexico. In Canada, the Western Canada Sedimentary Basin of
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
and
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
hosts major deposits of bituminous coal that formed in swamps along the western margin of the
Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea ...
. They range in age from latest
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
or earliest
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
in the Mist Mountain Formation, to
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...
in the Gates Formation. The Intermontane and Insular Coalfields of British Columbia also contain deposits of Cretaceous bituminous coal. , the countries with the greatest estimated ultimately recoverable resources of bituminous coal were the US, 161.6 Gt; India, 99.7 Gt; China, 78.4 Gt; Australia, 51.3 Gt; South Africa, 38.7 Gt; the UK, 26.8 Gt; Germany, 25.2 Gt; Columbia, 7.8 Gt; Indonesia, 5.6 Gt; and France, 4.4 Gt , total world production of bituminous coal (coking coal plus other bituminous coal) was 6.220 Gt. The leading producer is China, with India and the United States a distant second and third. U.S. production of bituminous coal was 238 million short tons in 2020 and represented 44% of all U.S. coal production. Bituminous coal is mined in 18 states, but the five states of West Virginia, Pennsylvania, Illinois, Kentucky, and Indiana produce 74%of U.S. coal.


Hazards and their mitigation

Maturation of bituminous coal at medium and low volatile subrank is accompanied by peak methane generation. This makes these bituminous coals "gassy" and precautions must be taken against methane explosions.
Imidazolium Imidazole (ImH) is an organic compound with the formula C3N2H4. It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. In chemistry, it is an aromatic heterocycle, classified as a diazole, and has non-a ...
-based ionic liquid solvents can reduce spontaneous combustion, which accounts for 2 to 3 percent of global annual
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
emissions. Bituminous coal was once extensively used for home heating in the US. However, bituminous coal is a relatively dirty fuel. The reduction in the use of bituminous coal between 1945 and 1960 is estimated to have saved at least 1923 lives of all ages and 310 infant lives per winter month. Bituminous coal quality is improved with floatation methods, which increase the fraction of vitrinite to yield a cleaner-burning product. The bioconversion of bituminous coal to methane is being actively researched as a clean coal technology.


See also

* Big Vein * Coal assay *
Georges Creek Valley Georges Creek Valley is located in Allegany County, Maryland along the Georges Creek. The valley is rich in wide veins of coal, known historically as " The Big Vein." Coal was once extracted by deep mines but is only mined today through surf ...
*
List of CO2 emitted per million Btu of energy from various fuels Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and larg ...
* List of rock types * Maceral


References


Further reading


Adams, Sean Patrick, . "The US Coal Industry in the Nineteenth Century."
EH.Net Encyclopedia, August 15, 2001 scholarly overview * Buxton, N.K. ''The economic development of the British coal industry: from Industrial Revolution to the present day''. 1979. * * Hatcher, John, et al. ''The History of the British Coal Industry'' (5 vol, Oxford U.P., 1984–87); 3000 pages of scholarly history * Long, Priscilla. '' Where the Sun Never Shines: A History of America's Bloody Coal Industry'' Paragon, 1989. * Netschert, Bruce C. and Sam H. Schurr, ''Energy in the American Economy, 1850–1975: An Economic Study of Its History and Prospects.'
(1960) online
* Veenstra, Theodore A., and Wilbert G. Fritz. "Major Economic Tendencies in the Bituminous Coal Industry," ''Quarterly Journal of Economics'' 51#1 (1936) pp. 106–13
in JSTOR


External links

* http://chemed.chem.purdue.edu/genchem/topicreview/bp/1organic/coal.html * {{DEFAULTSORT:Bituminous Coal Sedimentary rocks Coal Symbols of West Virginia