Bituminous coal
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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 Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...
containing a tar-like substance called
bitumen Bitumen ( , ) is an immensely viscosity, viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American Engl ...
or asphalt. 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. 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 The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
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. Bituminous coal suitable for smelting iron (''coking coal'' or '' metallurgical coal'') must be low in
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
and
phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
. It commands a higher price than other grades of bituminous coal (thermal coal) used for heating and power generation. Within the
coal mining Coal mining is the process of resource extraction, extracting coal from the ground or from a mine. Coal is valued for its Energy value of coal, energy content and since the 1880s has been widely used to Electricity generation, generate electr ...
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'' 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 Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...
, as determined by the amount and type of
carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
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'' 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/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. 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 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 Bitumen ( , ) is an immensely viscosity, viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American Engl ...
(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. These are nonbanded and nonreflective, and break with a conchoidal fracture. Both are ''sapropelic'', 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 Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
.


Coking coal

Coking coal ( metallurgical coal or "met coal") is used in the manufacture of
steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...
. 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; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
, 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, other metals, by forging the metal, using tools to hammer, bend, and cut (cf. tinsmith). Blacksmiths produce objects such ...
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 mus ...
, 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 is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...
. Peat is mostly a mixture of
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...
,
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 embryophyte, terrestrial plant cell walls. Cellulose is crystalline, strong, an ...
, and
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidit ...
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 (which removes oxygen and hydrogen as water), decarboxylation (which removes oxygen as
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
), 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 abundance of methane on Earth makes ...
). 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 Carbonization or carbonisation is the conversion of organic matters like plants and dead animal remains into carbon through destructive distillation. Complexity in carbonization Carbonization is a pyrolytic reaction, therefore, is considered a ...
proceeds, aliphatic compounds (carbon compounds characterized by chains of carbon atoms) are replaced by aromatic compounds (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, the structural element of
graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...
. 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 chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...
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 The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
(about 360 to 420 million years ago) to
Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...
deposits just a few million years old. However, 90% of all coal beds were deposited in the
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
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 251.902 Mya. It is the s ...
periods, which represent just 2% of the Earth's geologic history. Vast deposits of coal formed in
wetland A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor ( anoxic) processes taking place, especially ...
s—called
coal forest Coal forests were the vast swathes of freshwater swamp and riparian forests that covered much of the lands on Earth's tropical regions during the late Carboniferous ( Pennsylvanian) and Permian periods.Cleal, C. J. & Thomas, B. A. (2005). "Pala ...
s—that covered much of the Earth's tropical land areas during the late
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
( 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 251.902 Mya. It is the s ...
times. Bituminous coal is predominantly
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
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
Appalachia Appalachia ( ) is a geographic region located in the Appalachian Mountains#Regions, central and southern sections of the Appalachian Mountains in the east of North America. In the north, its boundaries stretch from the western Catskill Mountai ...
n and Interior Provinces of North America.
Mining Mining is the Resource extraction, extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agriculture, agricultural processes, or feasib ...
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 Middle Triassic. 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 Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
, 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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
, 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 a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...
and
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
hosts major deposits of bituminous coal that formed in swamps along the western margin of the Western Interior Seaway. They range in age from latest
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
or earliest
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
in the Mist Mountain Formation, to
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...
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; Colombia, 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-based ionic liquid solvents can reduce spontaneous combustion, which accounts for 2 to 3 percent of global annual
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
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 1,923 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

* The Big Vein * Coal analysis * Georges Creek Valley * Greenhouse gas emissions#Carbon dioxide (CO2) * List of rock types * Maceral * Coking factory


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



* {{DEFAULTSORT:Bituminous Coal Sedimentary rocks Coal Symbols of West Virginia