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Coal is a
combustible A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
black or brownish-black
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
, formed as rock strata called
coal seams Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron fro ...
. Coal is mostly
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 ...
with variable amounts of other elements, chiefly
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
, sulfur,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
, and
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
. Coal is formed when dead
plant matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
decays into
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 ...
and is converted into coal by the heat and pressure of deep burial over millions of years. Vast deposits of coal originate in former
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. Many significant coal deposits are younger than this and originate from the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
and Cenozoic eras. Coal is used primarily as a fuel. While coal has been known and used for thousands of years, its usage was limited until the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
. With the invention of the steam engine, coal consumption increased. In 2020, coal supplied about a quarter of the world's
primary energy Primary energy (PE) is an energy form found in nature that has not been subjected to any human engineered conversion process. It is energy contained in raw fuels, and other forms of energy, including waste, received as input to a system. Prim ...
and over a third of its
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describ ...
. Some
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
and steel-making and other industrial processes burn coal. The extraction and use of coal causes premature death and illness. The use of coal damages the environment, and it is the largest anthropogenic source of
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 ...
contributing to
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
. Fourteen billion tonnes of carbon dioxide was emitted by burning coal in 2020, which is 40% of the total fossil fuel emissions and over 25% of total global
greenhouse gas emissions 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 ...
. As part of worldwide energy transition, many countries have reduced or eliminated their use of coal power. The
United Nations Secretary General The secretary-general of the United Nations (UNSG or SG) is the chief administrative officer of the United Nations and head of the United Nations Secretariat, one of the six principal organs of the United Nations. The role of the secretary-g ...
asked governments to stop building new
coal plants A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts capacity. They generate about a th ...
by 2020. Global coal use peaked in 2013. To meet the Paris Agreement target of keeping
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
below coal use needs to halve from 2020 to 2030, and phasing out coal was agreed upon in the
Glasgow Climate Pact The Glasgow Climate Pact is an agreement reached at the 2021 United Nations Climate Change Conference (COP26). The pact is the first climate agreement explicitly planning to reduce unabated coal usage. A pledge to "phase out" coal was change ...
. The largest consumer and importer of coal in 2020 was China, which accounts for almost half the world's annual coal production, followed by
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
with about a tenth.
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
and Australia export the most, followed by
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
.


Etymology

The word originally took the form ''col'' in
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th c ...
, from
Proto-Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic bran ...
*''kula''(''n''), which in turn is hypothesized to come from the
Proto-Indo-European Proto-Indo-European (PIE) is the reconstructed common ancestor of the Indo-European language family. Its proposed features have been derived by linguistic reconstruction from documented Indo-European languages. No direct record of Proto-Indo- ...
root *''g''(''e'')''u-lo-'' "live coal". Germanic cognates include the
Old Frisian Old Frisian was a West Germanic language spoken between the 8th and 16th centuries along the North Sea coast, roughly between the mouths of the Rhine and Weser rivers. The Frisian settlers on the coast of South Jutland (today's Northern Fri ...
''kole'',
Middle Dutch Middle Dutch is a collective name for a number of closely related West Germanic dialects whose ancestor was Old Dutch. It was spoken and written between 1150 and 1500. Until the advent of Modern Dutch after 1500 or c. 1550, there was no overarc ...
''cole'',
Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () Dutch may also refer to: Places * Dutch, West Virginia, a community in the United States * Pennsylvania Dutch Country People E ...
''kool'',
Old High German Old High German (OHG; german: Althochdeutsch (Ahd.)) is the earliest stage of the German language, conventionally covering the period from around 750 to 1050. There is no standardised or supra-regional form of German at this period, and Old High ...
''chol'',
German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
''Kohle'' and
Old Norse Old Norse, Old Nordic, or Old Scandinavian, is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and their overseas settlemen ...
''kol'', and the
Irish Irish may refer to: Common meanings * Someone or something of, from, or related to: ** Ireland, an island situated off the north-western coast of continental Europe ***Éire, Irish language name for the isle ** Northern Ireland, a constituent unit ...
word ''gual'' is also a cognate via the
Indo-European The Indo-European languages are a language family native to the overwhelming majority of Europe, the Iranian plateau, and the northern Indian subcontinent. Some European languages of this family, English, French, Portuguese, Russian, Dutc ...
root.


Geology

Coal is composed of
macerals A maceral is a component, organic in origin, of coal or oil shale. The term 'maceral' in reference to coal is analogous to the use of the term 'mineral' in reference to igneous or metamorphic rocks. Examples of macerals are inertinite, vitrinite, ...
,
minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed ...
and water. Fossils and
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In ...
may be found in coal.


Formation

The conversion of dead vegetation into coal is called coalification. At various times in the geologic past, the Earth had dense forests in low-lying wetland areas. In these wetlands, the process of coalification began when dead plant matter was protected from
biodegradation Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegrada ...
and
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
, usually by mud or acidic water, and was converted into
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 ...
. This trapped the carbon in immense
peat bog 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; a ...
s that were eventually deeply buried by sediments. Then, over millions of years, the heat and pressure of deep burial caused the loss of water, methane and carbon dioxide and increased the proportion of carbon. The grade of coal produced depended on the maximum pressure and temperature reached, with lignite (also called "brown coal") produced under relatively mild conditions, and sub-bituminous coal, bituminous coal, or anthracite coal (also called "hard coal" or "black coal") produced in turn with increasing temperature and pressure. Of the factors involved in coalification, temperature is much more important than either pressure or time of burial. Subbituminous coal can form at temperatures as low as while anthracite requires a temperature of at least . Although coal is known from most geologic periods, 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. Paradoxically, this was during the
Late Paleozoic icehouse The late Paleozoic icehouse, also known as the Late Paleozoic Ice Age (LPIA) and formerly known as the Karoo ice age, was an ice age that began in the Late Devonian and ended in the Late Permian, occurring from 360 to 255 million years ago (Mya), ...
, a time of global
glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
. However, the drop in global sea level accompanying the glaciation exposed continental shelfs that had previously been submerged, and to these were added wide
river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...
s produced by increased
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
due to the drop in base level. These widespread areas of wetlands provided ideal conditions for coal formation. The rapid formation of coal ended with the coal gap in the
Permian–Triassic extinction event The Permian–Triassic (P–T, P–Tr) extinction event, also known as the Latest Permian extinction event, the End-Permian Extinction and colloquially as the Great Dying, formed the boundary between the Permian and Triassic geologic periods, as ...
, where coal is rare. Favorable geography alone does not explain the extensive Carboniferous coal beds. Other factors contributing to rapid coal deposition were high
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
levels, above 30%, that promoted intense
wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...
s and formation of charcoal that was all but indigestible by decomposing organisms; high
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 ...
levels that promoted plant growth; and the nature of Carboniferous forests, which included
lycophyte The lycophytes, when broadly circumscribed, are a vascular plant (tracheophyte) subgroup of the kingdom Plantae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldes ...
trees whose
determinate growth In biology and botany, indeterminate growth is growth that is not terminated in contrast to determinate growth that stops once a genetically pre-determined structure has completely formed. Thus, a plant that grows and produces flowers and fruit ...
meant that carbon was not tied up in
heartwood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin t ...
of living trees for long periods. One theory suggested that about 360 million years ago, some plants evolved the ability to produce lignin, a complex polymer that made their
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 ...
stems much harder and more woody. The ability to produce lignin led to the evolution of the first
trees In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are u ...
. But bacteria and fungi did not immediately evolve the ability to decompose lignin, so the wood did not fully decay but became buried under sediment, eventually turning into coal. About 300 million years ago, mushrooms and other fungi developed this ability, ending the main coal-formation period of earth's history. Although some authors pointed at some evidence of lignin degradation during the Carboniferous, and suggested that climatic and tectonic factors were a more plausible explanation, reconstruction of ancestral enzymes by phylogenetic analysis corroborated a hypothesis that lignin degrading enzymes appeared in fungi approximately 200 MYa. One likely tectonic factor was the
Central Pangean Mountains The Central Pangean Mountains were an extensive northeast–southwest trending mountain range in the central portion of the supercontinent Pangaea during the Carboniferous, Permian and Triassic periods. They were formed as a result of collision ...
, an enormous range running along the equator that reached its greatest elevation near this time. Climate modeling suggests that the Central Pangean Mountains contributed to the deposition of vast quantities of coal in the late Carboniferous. The mountains created an area of year-round heavy precipitation, with no dry season typical of a
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal osci ...
climate. This is necessary for the preservation of peat in coal swamps. Coal is known from Precambrian strata, which predate land plants. This coal is presumed to have originated from residues of algae. Sometimes coal seams (also known as coal beds) are interbedded with other sediments in a
cyclothem In geology, cyclothems are alternating stratigraphy, stratigraphic sequences of Marine (ocean), marine and non-marine sediments, sometimes interbedded with coal seams. Historically, the term was defined by the European coal geologists who worked ...
. Cyclothems are thought to have their origin in
glacial cycle An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gree ...
s that produced fluctuations in
sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...
, which alternately exposed and then flooded large areas of continental shelf.


Chemistry of coalification

The woody tissue of plants is composed mainly of cellulose, hemicellulose, and lignin. Modern peat is mostly lignin, with a content of cellulose and hemicellulose ranging from 5% to 40%. Various other organic compounds, such as waxes and nitrogen- and sulfur-containing compounds, are also present. 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 must remove most of the oxygen and much of the hydrogen, leaving carbon, a process called ''carbonization''. Carbonization proceeds primarily by
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 ...
, decarboxylation, and demethanation. Dehydration removes water molecules from the maturing coal via reactions such as :2 R–OH → R–O–R + H2O :2 R-CH2-O-CH2-R → R-CH=CH-R + H2O Decarboxylation removes carbon dioxide from the maturing coal and proceeds by reaction such as :RCOOH → RH + CO2 while demethanation proceeds by reaction such as :2 R-CH3 → R-CH2-R + CH4 :R-CH2-CH2-CH2-R → R-CH=CH-R + CH4 In each of these formulas, R represents the remainder of a cellulose or lignin molecule to which the reacting groups are attached. Dehydration and decarboxylation take place early in coalification, while demethanation begins only after the coal has already reached bituminous rank. The effect of decarboxylation is to reduce the percentage of oxygen, while demethanation reduces the percentage of hydrogen. Dehydration does both, and (together with demethanation) reduces the saturation of the carbon backbone (increasing the number of double bonds between carbon). 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 A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...
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. Chemical changes are accompanied by physical changes, such as decrease in average pore size. The macerals (organic particles) of lignite are composed of ''huminite'', which is earthy in appearance. As the coal matures to sub-bituminous coal, huminite begins to be replaced by vitreous (shiny) ''vitrinite''. Maturation of bituminous coal is characterized by ''bitumenization'', in which part of the coal is converted to bitumen, a hydrocarbon-rich gel. Maturation to anthracite is characterized by ''debitumenization'' (from demethanation) and the increasing tendency of the anthracite to break with a conchoidal fracture, similar to the way thick glass breaks.


Types

As geological processes apply
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
to dead
biotic material Biotic material or biological derived material is any material that originates from living organisms. Most such materials contain carbon and are capable of decay. The earliest life on Earth arose at least 3.5 billion years ago.Schopf, JW, Kudr ...
over time, under suitable conditions, its
metamorphic grade Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of che ...
or rank increases successively into: *
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 ...
, a precursor of coal * Lignite, or brown coal, the lowest rank of coal, most harmful to health, used almost exclusively as fuel for electric power generation ** Jet, a compact form of lignite, sometimes polished; used as an ornamental stone since the
Upper Palaeolithic The Upper Paleolithic (or Upper Palaeolithic) is the third and last subdivision of the Paleolithic or Old Stone Age. Very broadly, it dates to between 50,000 and 12,000 years ago (the beginning of the Holocene), according to some theories coin ...
* Sub-bituminous coal, whose properties range between those of lignite and those of bituminous coal, is used primarily as fuel for steam-electric power generation. * Bituminous coal, a dense sedimentary rock, usually black, but sometimes dark brown, often with well-defined bands of bright and dull material. It is used primarily as fuel in steam-electric power generation and to make coke. Known as steam coal in the UK, and historically used to raise steam in steam locomotives and ships * Anthracite coal, the highest rank of coal, is a harder, glossy black coal used primarily for residential and commercial
space heating Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
. *
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 ...
is difficult to ignite and not commonly used as fuel; it is most used in pencils, or powdered for lubrication. * Cannel coal (sometimes called "candle coal") is a variety of fine-grained, high-rank coal with significant hydrogen content, which consists primarily of
liptinite In coal geology, liptinite is the finely-ground and macerated remains found in coal deposits. It replaced the term exinite as one of the four categories of kerogen. Liptinites were originally formed by spores, pollen, dinoflagellate cysts, leaf c ...
. There are several international standards for coal. The classification of coal is generally based on the content of
volatiles Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances. On planet Earth, the term ...
. However the most important distinction is between thermal coal (also known as steam coal), which is burnt to generate electricity via steam; and
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 ...
(also known as coking coal), which is burnt at high temperature to make steel.
Hilt's law Hilt's law is a geological law that states the deeper the coal, the higher its rank (grade). The law holds true if the thermal gradient is entirely vertical, but metamorphism may cause lateral changes of rank, irrespective of depth. Increasing ...
is a geological observation that (within a small area) the deeper the coal is found, the higher its rank (or grade). It applies if the thermal gradient is entirely vertical; however,
metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...
may cause lateral changes of rank, irrespective of depth. For example, some of the coal seams of the
Madrid, New Mexico Madrid (/ˈmædrɪd/, Spanish: aˈðɾið is a census-designated place (CDP) in Santa Fe County, New Mexico, United States. It is part of the Santa Fe, New Mexico Metropolitan Statistical Area. The population was 149 at the 2000 census and 204 i ...
coal field were partially converted to anthracite by
contact metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of che ...
from an igneous sill while the remainder of the seams remained as bituminous coal.


History

The earliest recognized use is from the Shenyang area of China where by 4000 BC
Neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several p ...
inhabitants had begun carving ornaments from black lignite. Coal from the
Fushun Fushun (, formerly romanised as ''Fouchouen'', using French spelling, also as Fuxi ()) is a prefecture level city in Liaoning province, China, about east of Shenyang, with a total area of , of which is the city proper. Situated on the Hun Rive ...
mine in northeastern China was used to smelt
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
as early as 1000 BC. Marco Polo, the Italian who traveled to China in the 13th century, described coal as "black stones ... which burn like logs", and said coal was so plentiful, people could take three hot baths a week. In Europe, the earliest reference to the use of coal as fuel is from the geological treatise ''On Stones'' (Lap. 16) by the Greek scientist
Theophrastus Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek philosopher and the successor to Aristotle in the Peripatetic school. He was a native of Eresos in Lesbos.Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routle ...
(c. 371–287 BC):
Outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
coal was used in Britain during the
Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second prin ...
(3000–2000 BC), where it formed part of funeral
pyre A pyre ( grc, πυρά; ''pyrá'', from , ''pyr'', "fire"), also known as a funeral pyre, is a structure, usually made of wood, for burning a body as part of a funeral rite or execution. As a form of cremation, a body is placed upon or under the ...
s.Britannica 2004: ''Coal mining: ancient use of outcropping coal'' In
Roman Britain Roman Britain was the period in classical antiquity when large parts of the island of Great Britain were under occupation by the Roman Empire. The occupation lasted from AD 43 to AD 410. During that time, the territory conquered wa ...
, with the exception of two modern fields, "the
Romans Roman or Romans most often refers to: *Rome, the capital city of Italy * Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a lette ...
were exploiting coals in all the major coalfields in
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
and
Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...
by the end of the second century AD". Evidence of trade in coal, dated to about AD 200, has been found at the Roman settlement at Heronbridge, near Chester; and in the
Fenlands The Fens, also known as the , in eastern England are a naturally marshy region supporting a rich ecology and numerous species. Most of the fens were drained centuries ago, resulting in a flat, dry, low-lying agricultural region supported by a ...
of East Anglia, where coal from the Midlands was transported via the
Car Dyke The Car Dyke was, and to a large extent still is, an long ditch which runs along the western edge of the Fens in eastern England. It is generally accepted as being of Roman age and, for many centuries, to have been taken as marking the western ...
for use in drying grain. Coal cinders have been found in the hearths of villas and
Roman forts In the Roman Republic and the Roman Empire, the Latin word ''castrum'', plural ''castra'', was a military-related term. In Latin usage, the singular form ''castrum'' meant 'fort', while the plural form ''castra'' meant 'camp'. The singular and ...
, particularly in
Northumberland Northumberland () is a county in Northern England, one of two counties in England which border with Scotland. Notable landmarks in the county include Alnwick Castle, Bamburgh Castle, Hadrian's Wall and Hexham Abbey. It is bordered by land ...
, dated to around AD 400. In the west of England, contemporary writers described the wonder of a permanent brazier of coal on the altar of
Minerva Minerva (; ett, Menrva) is the Roman goddess of wisdom, justice, law, victory, and the sponsor of arts, trade, and strategy. Minerva is not a patron of violence such as Mars, but of strategic war. From the second century BC onward, the Rom ...
at
Aquae Sulis Aquae Sulis (Latin for ''Waters of Sulis'') was a small town in the Roman province of Britannia. Today it is the English city of Bath, Somerset. The Antonine Itinerary register of Roman roads lists the town as ''Aquis Sulis.'' Ptolemy records t ...
(modern day Bath), although in fact easily accessible surface coal from what became the Somerset coalfield was in common use in quite lowly dwellings locally. Evidence of coal's use for
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
-working in the city during the Roman period has been found. In
Eschweiler Eschweiler (, Ripuarian: ) is a municipality in the district of Aachen in North Rhine-Westphalia in Germany on the river Inde, near the German-Belgian-Dutch border, and about east of Aachen and west of Cologne. History * Celts (fi ...
,
Rhineland The Rhineland (german: Rheinland; french: Rhénanie; nl, Rijnland; ksh, Rhingland; Latinised name: ''Rhenania'') is a loosely defined area of Western Germany along the Rhine, chiefly its middle section. Term Historically, the Rhinelands ...
, deposits of bituminous coal were used by the Romans for the smelting of iron ore. No evidence exists of coal being of great importance in Britain before about AD 1000, the
High Middle Ages The High Middle Ages, or High Medieval Period, was the period of European history that lasted from AD 1000 to 1300. The High Middle Ages were preceded by the Early Middle Ages and were followed by the Late Middle Ages, which ended around AD 150 ...
. Coal came to be referred to as "seacoal" in the 13th century; the wharf where the material arrived in London was known as Seacoal Lane, so identified in a charter of King Henry III granted in 1253. Initially, the name was given because much coal was found on the shore, having fallen from the exposed coal seams on cliffs above or washed out of underwater coal outcrops, but by the time of Henry VIII, it was understood to derive from the way it was carried to London by sea. In 1257–1259, coal from
Newcastle upon Tyne Newcastle upon Tyne ( RP: , ), or simply Newcastle, is a city and metropolitan borough in Tyne and Wear, England. The city is located on the River Tyne's northern bank and forms the largest part of the Tyneside built-up area. Newcastle is ...
was shipped to London for the smiths and
lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...
-burners building
Westminster Abbey Westminster Abbey, formally titled the Collegiate Church of Saint Peter at Westminster, is an historic, mainly Gothic church in the City of Westminster, London, England, just to the west of the Palace of Westminster. It is one of the Unite ...
. Seacoal Lane and Newcastle Lane, where coal was unloaded at wharves along the
River Fleet The River Fleet is the largest of London's subterranean rivers, all of which today contain foul water for treatment. Its headwaters are two streams on Hampstead Heath, each of which was dammed into a series of ponds—the Hampstead Ponds a ...
, still exist. These easily accessible sources had largely become exhausted (or could not meet the growing demand) by the 13th century, when underground extraction by
shaft mining Shaft mining or shaft sinking is the action of excavating a mine shaft from the top down, where there is initially no access to the bottom. Shallow shafts, typically sunk for civil engineering projects, differ greatly in execution method from ...
or
adit An adit (from Latin ''aditus'', entrance) is an entrance to an underground mine which is horizontal or nearly horizontal, by which the mine can be entered, drained of water, ventilated, and minerals extracted at the lowest convenient level. Adit ...
s was developed. The alternative name was "pitcoal", because it came from mines. Cooking and home heating with coal (in addition to firewood or instead of it) has been done in various times and places throughout human history, especially in times and places where ground-surface coal was available and firewood was scarce, but a widespread reliance on coal for home hearths probably never existed until such a switch in fuels happened in London in the late sixteenth and early seventeenth centuries. Historian Ruth Goodman has traced the socioeconomic effects of that switch and its later spread throughout Britain and suggested that its importance in shaping the industrial adoption of coal has been previously underappreciated. The development of the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
led to the large-scale use of coal, as the steam engine took over from the
water wheel A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a wheel (usually constructed from wood or metal), with a number of blades or bucket ...
. In 1700, five-sixths of the world's coal was mined in Britain. Britain would have run out of suitable sites for watermills by the 1830s if coal had not been available as a source of energy. In 1947 there were some 750,000 miners in Britain but the last deep coal mine in the UK closed in 2015. A grade between bituminous coal and anthracite was once known as "steam coal" as it was widely used as a fuel for steam locomotives. In this specialized use, it is sometimes known as "sea coal" in the United States. Small "steam coal", also called ''dry small steam nuts'' (DSSN), was used as a fuel for domestic water heating. Coal played an important role in industry in the 19th and 20th century. The predecessor of the
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been de ...
, the European Coal and Steel Community, was based on the trading of this commodity. Coal continues to arrive on beaches around the world from both natural erosion of exposed coal seams and windswept spills from cargo ships. Many homes in such areas gather this coal as a significant, and sometimes primary, source of home heating fuel.


Chemistry


Composition

The composition of coal is reported either as a proximate analysis (moisture, volatile matter, fixed carbon, and ash) or an
ultimate analysis Ultimate or Ultimates may refer to: Arts, entertainment, and media Music Albums * ''Ultimate'' (Jolin Tsai album) * ''Ultimate'' (Pet Shop Boys album) *''Ultimate!'', an album by The Yardbirds *'' The Ultimate (Bryan Adams Album)'', a compilati ...
(ash, carbon, hydrogen, nitrogen, oxygen, and sulfur). The "volatile matter" does not exist by itself (except for some adsorbed methane) but designates the volatile compounds that are produced and driven off by heating the coal. A typical bituminous coal may have an ultimate analysis on a dry, ash-free basis of 84.4% carbon, 5.4% hydrogen, 6.7% oxygen, 1.7% nitrogen, and 1.8% sulfur, on a weight basis. The composition of ash, given in terms of oxides, varies: Other minor components include:


Coking coal and use of coke to smelt iron

Coke is a solid carbonaceous residue derived from
coking 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 ...
(a low-ash, low-sulfur bituminous coal, also known as ''metallurgical coal''), which is used in manufacturing steel and other iron products. Coke is made from coking coal by baking in an oven without oxygen at temperatures as high as 1,000 °C, driving off the volatile constituents and fusing together the fixed carbon and residual ash. Metallurgical coke is used as a fuel and as a
reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth me ...
in
smelting Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a ...
iron ore in a blast furnace. The carbon monoxide produced by its combustion reduces hematite (an iron oxide) to iron. Waste carbon dioxide is also produced together with pig iron, which is too rich in dissolved carbon so must be treated further to make steel. Coking coal should be low in ash, 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 ...
, so that these do not migrate to the metal. The coke must be strong enough to resist the weight of overburden in the blast furnace, which is why coking coal is so important in making steel using the conventional route. Coke from coal is grey, hard, and porous and has a heating value of 29.6 MJ/kg. Some cokemaking processes produce byproducts, including
coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psorias ...
,
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
, light oils, and coal gas.
Petroleum coke Petroleum coke, abbreviated coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracki ...
(petcoke) is the solid residue obtained in oil refining, which resembles coke but contains too many impurities to be useful in metallurgical applications.


Use in foundry components

Finely ground bituminous coal, known in this application as sea coal, is a constituent of
foundry sand Molding sand, also known as foundry sand, is a sand that when moistened and compressed or oiled or heated tends to pack well and hold its shape. It is used in the process of sand casting for preparing the mold cavity. Green sand Green sand is an a ...
. While the molten metal is in the mould, the coal burns slowly, releasing reducing gases at pressure, and so preventing the metal from penetrating the pores of the sand. It is also contained in 'mould wash', a paste or liquid with the same function applied to the mould before casting. Sea coal can be mixed with the clay lining (the "bod") used for the bottom of a
cupola furnace A cupola or cupola furnace is a melting device used in foundries that can be used to melt cast iron, Ni-resist iron and some bronzes. The cupola can be made almost any practical size. The size of a cupola is expressed in diameters and can range ...
. When heated, the coal decomposes and the bod becomes slightly friable, easing the process of breaking open holes for tapping the molten metal.


Alternatives to coke

Scrap steel can be recycled in an
electric arc furnace An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to ...
; and an alternative to making iron by smelting is
direct reduced iron Direct reduced iron (DRI), also called sponge iron, is produced from the direct reduction of iron ore (in the form of lumps, pellets, or fines) into iron by a reducing gas or elemental carbon produced from natural gas or coal. Many ores are suit ...
, where any carbonaceous fuel can be used to make sponge or pelletised iron. To lessen carbon dioxide emissions
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
can be used as the reducing agent and biomass or waste as the source of carbon. Historically, charcoal has been used as an alternative to coke in a blast furnace, with the resultant iron being known as
charcoal iron Charcoal iron is the substance created by the smelting of iron ore with charcoal. All ironmaking blast furnaces were fueled by charcoal until Abraham Darby introduced coke as a fuel in 1709. The more economical coke soon replaced charcoal in Bri ...
.


Gasification

Coal gasification, as part of an
integrated gasification combined cycle integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the electr ...
(IGCC) coal-fired power station, is used to produce syngas, a mixture of
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
(CO) and hydrogen (H2) gas to fire gas turbines to produce electricity. Syngas can also be converted into transportation fuels, such as
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
and
diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...
, through the
Fischer–Tropsch process The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatu ...
; alternatively, syngas can be converted into methanol, which can be blended into fuel directly or converted to gasoline via the methanol to gasoline process. Gasification combined with Fischer–Tropsch technology was used by the
Sasol Sasol Limited is an integrated energy and chemical company based in Sandton, South Africa. The company was formed in 1950 in Sasolburg, South Africa and built on processes that were first developed by German chemists and engineers in the early ...
chemical company of
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
to make chemicals and motor vehicle fuels from coal. During gasification, the coal is mixed with
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
and steam while also being heated and pressurized. During the reaction, oxygen and water molecules
oxidize Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
the coal into carbon monoxide (CO), while also releasing
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
gas (H2). This used to be done in underground coal mines, and also to make
town gas Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous ...
, which was piped to customers to burn for illumination, heating, and cooking. : 3C (''as Coal'') + O2 + H2O → H2 + 3CO If the refiner wants to produce gasoline, the syngas is routed into a Fischer–Tropsch reaction. This is known as indirect coal liquefaction. If hydrogen is the desired end-product, however, the syngas is fed into the
water gas shift reaction Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...
, where more hydrogen is liberated: : CO + H2O → CO2 + H2


Liquefaction

Coal can be converted directly into
synthetic fuel Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by refo ...
s equivalent to gasoline or diesel by
hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organ ...
or
carbonization Carbonization 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 complex proces ...
. Coal liquefaction emits more carbon dioxide than liquid fuel production from crude oil. Mixing in biomass and using CCS would emit slightly less than the oil process but at a high cost. State owned
China Energy Investment China Energy Investment Corporation, more commonly known as China Energy (), is a state-owned mining and energy company administrated by the SASAC of the State Council of the People's Republic of China. History On August 28, 2017, SASAC announce ...
runs a coal liquefaction plant and plans to build 2 more. Coal liquefaction may also refer to the cargo hazard when shipping coal.


Production of chemicals

Chemicals have been produced from coal since the 1950s. Coal can be used as a feedstock in the production of a wide range of chemical fertilizers and other chemical products. The main route to these products was coal gasification to produce syngas. Primary chemicals that are produced directly from the syngas include methanol,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
, which are the chemical building blocks from which a whole spectrum of derivative chemicals are manufactured, including olefins, acetic acid,
formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
, ammonia,
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
and others. The versatility of syngas as a precursor to primary chemicals and high-value derivative products provides the option of using coal to produce a wide range of commodities. In the 21st century, however, the use of
coal bed methane Coalbed methane (CBM or coal-bed methane), coalbed gas, coal seam gas (CSG), or coal-mine methane (CMM) is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, Au ...
is becoming more important. Because the slate of chemical products that can be made via coal gasification can in general also use feedstocks derived from
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
and
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 ...
, the chemical industry tends to use whatever feedstocks are most cost-effective. Therefore, interest in using coal tended to increase for higher oil and natural gas prices and during periods of high global economic growth that might have strained oil and gas production. Coal to chemical processes require substantial quantities of water. Much coal to chemical production is in China where coal dependent provinces such as Shanxi are struggling to control its pollution.


Electricity generation


Energy density

The energy density of coal is roughly 24 megajoules per kilogram (approximately 6.7
kilowatt-hours A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bi ...
per kg). For a coal power plant with a 40% efficiency, it takes an estimated of coal to power a 100 W lightbulb for one year. 27.6% of world energy was supplied by coal in 2017 and Asia used almost three-quarters of it.


Precombustion treatment

Refined coal is the product of a coal-upgrading technology that removes moisture and certain pollutants from lower-rank coals such as sub-bituminous and lignite (brown) coals. It is one form of several precombustion treatments and processes for coal that alter coal's characteristics before it is burned. Thermal efficiency improvements are achievable by improved pre-drying (especially relevant with high-moisture fuel such as lignite or biomass). The goals of precombustion coal technologies are to increase efficiency and reduce emissions when the coal is burned. Precombustion technology can sometimes be used as a supplement to postcombustion technologies to control emissions from coal-fueled boilers.


Power plant combustion

Coal burnt as a solid fuel in coal power stations to generate electricity is called thermal coal. Coal is also used to produce very high temperatures through combustion. Early deaths due to air pollution have been estimated at 200 per GW-year, however they may be higher around power plants where scrubbers are not used or lower if they are far from cities. Efforts around the world to reduce the use of coal have led some regions to switch to natural gas and electricity from lower carbon sources. When coal is used for
electricity generation Electricity generation is the process of generating electric power from sources of primary energy. For utilities in the electric power industry, it is the stage prior to its delivery ( transmission, distribution, etc.) to end users or its s ...
, it is usually pulverized and then burned in a furnace with a
boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centr ...
(see also
Pulverized coal-fired boiler A pulverized coal-fired boiler is an industrial or utility boiler that generates thermal energy by burning pulverized coal (also known as powdered coal or coal dust since it is as fine as face powder in cosmetic makeup) that is blown into the fireb ...
).Total World Electricity Generation by Fuel (2006)
. Source: IEA 2008.
The furnace heat converts boiler water to steam, which is then used to spin
turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...
s which turn generators and create electricity. The
thermodynamic efficiency In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For a ...
of this process varies between about 25% and 50% depending on the pre-combustion treatment, turbine technology (e.g.
supercritical steam generator A supercritical steam generator is a type of boiler that operates at supercritical pressure, frequently used in the production of electric power. In contrast to a subcritical boiler in which bubbles can form, a supercritical steam generator op ...
) and the age of the plant. A few
integrated gasification combined cycle integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the electr ...
(IGCC) power plants have been built, which burn coal more efficiently. Instead of pulverizing the coal and burning it directly as fuel in the steam-generating boiler, the coal is gasified to create syngas, which is burned in a
gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...
to produce electricity (just like natural gas is burned in a turbine). Hot exhaust gases from the turbine are used to raise steam in a
heat recovery steam generator A heat recovery steam generator (''HRSG'') is an energy recovery heat exchanger that recovers heat from a hot gas stream, such as a combustion turbine or other waste gas stream. It produces steam that can be used in a process (cogeneration) or us ...
which powers a supplemental steam turbine. The overall plant efficiency when used to provide combined heat and power can reach as much as 94%. IGCC power plants emit less local pollution than conventional pulverized coal-fueled plants; however the technology for
carbon capture and storage Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
after gasification and before burning has so far proved to be too expensive to use with coal. Other ways to use coal are as
coal-water slurry fuel Coal-water slurry fuel is a combustible mixture of fine coal particles suspended in water. It can be used to power boilers, gas turbines, diesel engines and heating and power stations. Characteristics A coal-water slurry fuel is defined by a num ...
(CWS), which was developed in the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
, or in an MHD topping cycle. However these are not widely used due to lack of profit. In 2017 38% of the world's electricity came from coal, the same percentage as 30 years previously. In 2018 global installed capacity was 2 TW (of which 1TW is in China) which was 30% of total electricity generation capacity. The most dependent major country is South Africa, with over 80% of its electricity generated by coal; but China alone generates more than half of the world's coal-generated electricity. Maximum use of coal was reached in 2013. In 2018 coal-fired power station
capacity factor The net capacity factor is the unitless ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. The theoretical maximum energy output of a given installation is def ...
averaged 51%, that is they operated for about half their available operating hours.


Coal industry


Mining

About 8000 Mt of coal are produced annually, about 90% of which is hard coal and 10% lignite. just over half is from underground mines. More accidents occur during underground mining than surface mining. Not all countries publish
mining accident A mining accident is an accident that occurs during the process of mining minerals or metals. Thousands of miners die from mining accidents each year, especially from underground coal mining, although accidents also occur in hard rock mining. ...
statistics so worldwide figures are uncertain, but it is thought that most deaths occur in coal mining accidents in China: in 2017 there were 375 coal mining related deaths in China. Most coal mined is thermal coal (also called steam coal as it is used to make steam to generate electricity) but metallurgical coal (also called "metcoal" or "coking coal" as it is used to make coke to make iron) accounts for 10% to 15% of global coal use.


As a traded commodity

China mines almost half the world's coal, followed by
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
with about a tenth. Australia accounts for about a third of world coal exports, followed by
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
and
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...
, while the largest importers are Japan and India. The price of metallurgical coal is volatile and much higher than the price of thermal coal because metallurgical coal must be lower in sulfur and requires more cleaning. Coal futures contracts provide coal producers and the
electric power industry The electric power industry covers the generation, transmission, distribution and sale of electric power to the general public and industry. The commodity sold is actually energy, not power, e.g. consumers pay for kilowatt-hours, power multip ...
an important tool for hedging and risk management. In some countries new onshore
wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...
or solar generation already costs less than coal power from existing plants. However, for China this is forecast for the early 2020s and for southeast Asia not until the late 2020s. In India building new plants is uneconomic and, despite being subsidized, existing plants are losing market share to renewables.


Market trends

Of the countries which produce coal China mines by far the most, almost half the world's coal, followed by less than 10% by India. China is also by far the largest consumer. Therefore, market trends depend on Chinese energy policy. Although the effort to reduce pollution means that the global long-term trend is to burn less coal, the short and medium term trends may differ, in part due to Chinese financing of new coal-fired power plants in other countries.


Major producers

Countries with annual production higher than 300 million tonnes are shown.


Major consumers

Countries with annual consumption higher than 500 million tonnes are shown. Shares are based on data expressed in tonnes oil equivalent.


Major exporters

Exporters are at risk of a reduction in import demand from India and China.


Major importers


Damage to human health

The use of coal as fuel causes ill health and deaths. Mining and processing of coal causes air and water pollution. Coal-powered plants emit nitrogen oxides, sulfur dioxide, particulate pollution and heavy metals, which adversely affect human health.
Coal bed methane extraction Coalbed methane extraction (CBM extraction) is a method for extracting methane from a coal deposit. Coal bed methane (CBM) is one of the factors restricting safe production of coal in underground coal mines. It is also a form of high-quality energ ...
is important to avoid mining accidents. The deadly London smog was caused primarily by the heavy use of coal. Globally coal is estimated to cause 800,000 premature deaths every year, mostly in India and China. Burning coal is a major emitter of sulfur dioxide, which creates PM2.5
particulates Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The t ...
, the most dangerous form of air pollution. Coal smokestack emissions cause
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
,
strokes A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop funct ...
, reduced
intelligence Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning, emotional knowledge, reasoning, planning, creativity, critical thinking, and problem-solving. More generally, it can be des ...
,
artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...
blockages,
heart attacks A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may tr ...
,
congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...
, cardiac arrhythmias, mercury poisoning, arterial occlusion, and
lung cancer Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. Lung carcinomas derive from transformed, malign ...
.Coal Pollution Damages Human Health at Every Stage of Coal Life Cycle, Reports Physicians for Social Responsibility
. ''Physicians for Social Responsibility''. psr.org (18 November 2009)
Annual health costs in Europe from use of coal to generate electricity are estimated at up to €43 billion. In China, improvements to air quality and human health would increase with more stringent climate policies, mainly because the country's energy is so heavily reliant on coal. And there would be a net economic benefit. A 2017 study in the ''
Economic Journal ''The Economic Journal'' is a peer-reviewed academic journal of economics published on behalf of the Royal Economic Society by Oxford University Press. The journal was established in 1891 and publishes papers from all areas of economics.The edito ...
'' found that for Britain during the period 1851–1860, "a one standard deviation increase in coal use raised infant mortality by 6–8% and that industrial coal use explains roughly one-third of the urban mortality penalty observed during this period." Breathing in
coal dust Coal dust is a fine powdered form of which is created by the crushing, grinding, or pulverizing of coal. Because of the brittle nature of coal, coal dust can be created during mining, transportation, or by mechanically handling coal. It is a form ...
causes
coalworker's pneumoconiosis Coal workers' pneumoconiosis (CWP), also known as black lung disease or black lung, is an occupational type of pneumoconiosis caused by long-term exposure to coal dust. It is common in coal miners and others who work with coal. It is similar to ...
or "black lung", so called because the coal dust literally turns the lungs black from their usual pink color. In the US alone, it is estimated that 1,500 former employees of the coal industry die every year from the effects of breathing in coal mine dust. Huge amounts of coal ash and other waste is produced annually. Use of coal generates hundreds of millions of tons of ash and other waste products every year. These include fly ash, bottom ash, and flue-gas desulfurization sludge, that contain mercury,
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
,
thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
,
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
, and other heavy metals, along with non-metals such as
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
. Around 10% of coal is ash:
coal ash 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 de ...
is hazardous and toxic to human beings and some other living things. Coal ash contains the radioactive elements
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
and
thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
. Coal ash and other solid combustion byproducts are stored locally and escape in various ways that expose those living near
coal plants A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts capacity. They generate about a th ...
to radiation and environmental toxics.


Damage to the environment

Coal mining and coal fueling of
power stations A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many po ...
and industrial processes can cause major environmental damage. Water systems are affected by coal mining. For example, mining affects
groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...
and
water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...
levels and acidity. Spills of fly ash, such as the
Kingston Fossil Plant coal fly ash slurry spill The Kingston Fossil Plant coal fly ash slurry spill was an environmental and industrial disaster that occurred on Monday December 22, 2008, when a dike ruptured at a coal ash pond at the Tennessee Valley Authority's Kingston Fossil Plant in ...
, can also contaminate land and waterways, and destroy homes. Power stations that burn coal also consume large quantities of water. This can affect the flows of rivers, and has consequential impacts on other land uses. In areas of
water scarcity Water scarcity (closely related to water stress or water crisis) is the lack of fresh water resources to meet the standard water demand. There are two types of water scarcity: physical or economic water scarcity. Physical water scarcity is whe ...
, such as the
Thar Desert The Thar Desert, also known as the Great Indian Desert, is an arid region in the north-western part of the Subcontinent that covers an area of and forms a natural boundary between India and Pakistan. It is the world's 20th-largest desert, a ...
in
Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-lar ...
, coal mining and coal power plants would use significant quantities of water. One of the earliest known impacts of coal on the
water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly cons ...
was acid rain. In 2014 approximately 100 Tg/S of sulfur dioxide (SO2) was released, over half of which was from burning coal. After release, the sulfur dioxide is oxidized to H2SO4 which scatters solar radiation, hence its increase in the atmosphere exerts a cooling effect on climate. This beneficially masks some of the warming caused by increased greenhouse gases. However, the sulfur is precipitated out of the atmosphere as acid rain in a matter of weeks, whereas carbon dioxide remains in the atmosphere for hundreds of years. Release of SO2 also contributes to the widespread acidification of ecosystems. Disused coal mines can also cause issues. Subsidence can occur above tunnels, causing damage to infrastructure or cropland. Coal mining can also cause long lasting fires, and it has been estimated that thousands of
coal seam fire A coal-seam fire is a burning of an outcrop or underground coal seam. Most coal-seam fires exhibit smouldering combustion, particularly underground coal-seam fires, because of limited atmospheric oxygen availability. Coal-seam fire instances ...
s are burning at any given time. For example,
Brennender Berg The Brennender Berg (Burning Mountain) is a natural monument located in a deep and narrow gorge between Dudweiler and Sulzbach in Saarland, Germany. It is a smouldering coal-seam fire that ignited in 1668 and continues to burn today. History ...
has been burning since 1668 and is still burning in the 21st century. The production of coke from coal produces ammonia, coal tar, and gaseous compounds as byproducts which if discharged to land, air or waterways can pollute the environment. The
Whyalla steelworks The Whyalla Steelworks is a fully integrated steelworks and the only manufacturer of rail in Australia. Iron ore is mined in the Middleback Range to feed the steelworks, resulting in the distribution of finished steel products of over 90 different ...
is one example of a coke producing facility where liquid ammonia was discharged to the marine environment.


Emission intensity

Emission intensity An emission intensity (also carbon intensity or C.I.) is the emission rate of a given pollutant relative to the intensity of a specific activity, or an industrial production process; for example grams of carbon dioxide released per megajoule o ...
is the greenhouse gas emitted over the life of a generator per unit of electricity generated. The emission intensity of
coal power station A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts capacity. They generate about a th ...
s is high, as they emit around 1000 g of CO2eq for each kWh generated, while natural gas is medium-emission intensity at around 500 g CO2eq per kWh. The emission intensity of coal varies with type and generator technology and exceeds 1200 g per kWh in some countries.


Underground fires

Thousands of coal fires are burning around the world. Those burning underground can be difficult to locate and many cannot be extinguished. Fires can cause the ground above to subside, their combustion gases are dangerous to life, and breaking out to the surface can initiate surface
wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...
s. Coal seams can be set on fire by
spontaneous combustion Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high te ...
or contact with a
mine fire A coal-seam fire is a burning of an outcrop or underground coal seam. Most coal-seam fires exhibit smouldering combustion, particularly underground coal-seam fires, because of limited atmospheric oxygen availability. Coal-seam fire instances ...
or surface fire. Lightning strikes are an important source of ignition. The coal continues to burn slowly back into the seam until oxygen (air) can no longer reach the flame front. A grass fire in a coal area can set dozens of coal seams on fire. Coal fires in China burn an estimated 120 million tons of coal a year, emitting 360 million metric tons of CO2, amounting to 2–3% of the annual worldwide production of CO2 from fossil fuels. In
Centralia, Pennsylvania Centralia is a borough and near- ghost town in Columbia County, Pennsylvania, United States. It is part of Northeastern Pennsylvania. Its population has declined from 1,000 in 1980 to five residents in 2020 because a coal mine fire has been bur ...
(a
borough A borough is an administrative division in various English-speaking countries. In principle, the term ''borough'' designates a self-governing walled town, although in practice, official use of the term varies widely. History In the Middle A ...
located in the
Coal Region The Coal Region is a region of Northeastern Pennsylvania. It is known for being home to the largest known deposits of anthracite coal in the world with an estimated reserve of seven billion short tons. The region is typically defined as compri ...
of the U.S.), an exposed vein of anthracite ignited in 1962 due to a trash fire in the borough landfill, located in an abandoned anthracite
strip mine Surface mining, including strip mining, open-pit mining and mountaintop removal mining, is a broad category of mining in which soil and rock overlying the mineral deposit (the overburden) are removed, in contrast to underground mining, in whic ...
pit. Attempts to extinguish the fire were unsuccessful, and it continues to burn underground to this day. The Australian
Burning Mountain Burning Mountain, the common name for Mount Wingen, is a hill near Wingen, New South Wales, Australia, approximately north of Sydney just off the New England Highway. It takes its name from a smouldering coal seam running underground through ...
was originally believed to be a volcano, but the smoke and ash come from a coal fire that has been burning for some 6,000 years. At Kuh i Malik in
Yagnob Valley The Yaghnob Valley is a valley in north-west Tajikistan, between the southern slope of the Zarafshan Range and the northern slope of the Gissar Range. The valley is formed by the Yaghnob River and belongs to the Zarafshan basin. It lies betwe ...
,
Tajikistan Tajikistan (, ; tg, Тоҷикистон, Tojikiston; russian: Таджикистан, Tadzhikistan), officially the Republic of Tajikistan ( tg, Ҷумҳурии Тоҷикистон, Jumhurii Tojikiston), is a landlocked country in Centr ...
, coal deposits have been burning for thousands of years, creating vast underground labyrinths full of unique minerals, some of them very beautiful. The reddish siltstone rock that caps many ridges and buttes in the
Powder River Basin The Powder River Basin is a geologic structural basin in southeast Montana and northeast Wyoming, about east to west and north to south, known for its extensive coal reserves. The former hunting grounds of the Oglala Lakota, the area is very s ...
in
Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the s ...
and in western
North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the indigenous Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minnesota to the east, So ...
is called ''porcelanite'', which resembles the coal burning waste "clinker" or volcanic "
scoria Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) '' ...
". Clinker is rock that has been fused by the natural burning of coal. In the Powder River Basin approximately 27 to 54 billion tons of coal burned within the past three million years. Wild coal fires in the area were reported by the
Lewis and Clark Expedition The Lewis and Clark Expedition, also known as the Corps of Discovery Expedition, was the United States expedition to cross the newly acquired western portion of the country after the Louisiana Purchase. The Corps of Discovery was a select gr ...
as well as explorers and settlers in the area.


Climate change

The largest and most long-term effect of coal use is the release of carbon dioxide, a greenhouse gas that causes
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
. Coal-fired power plants were the single largest contributor to the growth in global CO2 emissions in 2018,Gençsü (2019), p. 8 40% of the total fossil fuel emissions, and more than a quarter of total emissions. Coal mining can emit methane, another greenhouse gas. In 2016 world gross
carbon dioxide emissions 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 la ...
from coal usage were 14.5 gigatonnes. For every megawatt-hour generated, coal-fired electric power generation emits around a tonne of carbon dioxide, which is double the approximately 500 kg of carbon dioxide released by a
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
-fired electric plant. In 2013, the head of the UN climate agency advised that most of the world's coal reserves should be left in the ground to avoid catastrophic global warming. To keep global warming below 1.5 °C or 2 °C hundreds, or possibly thousands, of coal-fired power plants will need to be retired early.


Pollution mitigation


Standards

Local pollution standards include GB13223-2011 (China), India, the
Industrial Emissions Directive The Industrial Emissions Directive (Directive 2010/75/EU of the European Parliament and of the Council of 24 November 2010 on industrial emissions (integrated pollution prevention and control)) is a European Union directive which commits Europea ...
(EU) and the Clean Air Act (United States).


Satellite monitoring

Satellite monitoring is now used to crosscheck national data, for example
Sentinel-5 Precursor Sentinel-5 Precursor (Sentinel-5P) is an Earth observation satellite developed by ESA as part of the Copernicus Programme to close the gap in continuity of observations between Envisat and Sentinel-5. Overview Sentinel-5 Precursor is the first m ...
has shown that Chinese control of SO2 has only been partially successful. It has also revealed that low use of technology such as SCR has resulted in high NO2 emissions in South Africa and India.


Combined cycle power plants

A few
Integrated gasification combined cycle integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the electr ...
(IGCC) coal-fired power plants have been built with coal gasification. Although they burn coal more efficiently and therefore emit less pollution, the technology has not generally proved economically viable for coal, except possibly in Japan although this is controversial.


Carbon capture and storage

Although still being intensively researched and considered economically viable for some uses other than with coal;
carbon capture and storage Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
has been tested at the
Petra Nova The Petra Nova project is a coal-energy-sector/clean-energy project designed to reduce carbon emissions from one of the boilers of a Fossil fuel power station, coal burning power plant in Thompsons, Texas. It is a multi-million dollar project take ...
and
Boundary Dam Boundary Dam is a concrete arch gravity-type hydroelectric dam, finished in 1967, on the Pend Oreille River, in the U.S. state of Washington. The dam is located in the northeast corner of Washington state. It is operated by Seattle City Light an ...
coal-fired power plants and has been found to be technically feasible but not economically viable for use with coal, due to reductions in the cost of solar PV technology.


Economics

In 2018 was invested in coal supply but almost all for sustaining production levels rather than opening new mines. In the long term coal and oil could cost the world trillions of dollars per year. Coal alone may cost Australia billions, whereas costs to some smaller companies or cities could be on the scale of millions of dollars. The economies most damaged by coal (via climate change) may be India and the US as they are the countries with the highest
social cost of carbon The social cost of carbon (SCC) is the marginal cost of the impacts caused by emitting one extra tonne of greenhouse gas (carbon dioxide equivalent) at any point in time, inclusive of 'non-market' impacts on the environment and human health. Th ...
. Bank loans to finance coal are a risk to the Indian economy. China is the largest producer of coal in the world. It is the world's largest energy consumer, and coal in China supplies 60% of its primary energy. However two fifths of China's coal power stations are estimated to be loss-making. Air pollution from coal storage and handling costs the US almost 200 dollars for every extra ton stored, due to PM2.5. Coal pollution costs the each year. Measures to cut air pollution benefit individuals financially and the economies of countries such as China.


Subsidies

Subsidies for coal in 2021 have been estimated at , not including electricity subsidies, and are expected to rise in 2022.
G20 The G20 or Group of Twenty is an intergovernmental forum comprising 19 countries and the European Union (EU). It works to address major issues related to the global economy, such as international financial stability, climate change mitigatio ...
countries provide at least of government support per year for the production of coal, including coal-fired power: many subsidies are impossible to quantify but they include in domestic and international public finance, in fiscal support, and in state-owned enterprise (SOE) investments per year. In the EU state aid to new coal-fired plants is banned from 2020, and to existing coal-fired plants from 2025. As of 2018, government funding for new coal power plants was supplied by
Exim Bank of China The Export–Import Bank of China (Chexim - China Exim Bank) () is one of two institutional banks in China chartered to implement the state policies in industry, foreign trade, economy, and foreign aid to other developing countries, and provi ...
, the
Japan Bank for International Cooperation The , JBIC, is a Japanese public financial institution and export credit agency that was created on October 1, 1999, through the merger of the Japan Export-Import Bank (JEXIM) and the Overseas Economic Cooperation Fund (OECF). JBIC became the in ...
and Indian public sector banks. Coal in Kazakhstan was the main recipient of coal consumption subsidies totalling US$2 billion in 2017.
Coal in Turkey Coal supplies over a quarter of Turkey's primary energy. The heavily subsidised coal industry generates over a third of the country's electricity and emits a third of Turkey's greenhouse gases. Most coal mined in Turkey is lignite (brown ...
benefited from substantial subsidies in 2021.


Stranded assets

Some coal-fired power stations could become stranded assets, for example
China Energy Investment China Energy Investment Corporation, more commonly known as China Energy (), is a state-owned mining and energy company administrated by the SASAC of the State Council of the People's Republic of China. History On August 28, 2017, SASAC announce ...
, the world's largest power company, risks losing half its capital. However, state-owned electricity utilities such as
Eskom Eskom Hld SOC Ltd or Eskom is a South African electricity public utility. It was established in 1923 as the Electricity Supply Commission (ESCOM) and was also known by its Afrikaans name Elektrisiteitsvoorsieningskommissie (EVKOM). Eskom repre ...
in South Africa,
Perusahaan Listrik Negara PT Perusahaan Listrik Negara (Persero) ( 'State Electricity Company', abbreviated as PLN) is an Indonesian government-owned corporation which has a monopoly on electric power distribution in Indonesia and generates the majority of the country' ...
in Indonesia,
Sarawak Energy Sarawak Energy is the electric utility company of the Malaysian state of Sarawak. It is one of Malaysia's three electrical companies, the other two being Tenaga Nasional, supplying the Peninsular Malaysia, and Sabah Electricity, which serves t ...
in Malaysia,
Taipower The Taiwan Power Company (, Taipower; ) is a state-owned electric power industry providing electricity to Taiwan and off-shore islands of the Republic of China. History Taipower was established on 1 May 1946. Its origins can be traced to 1919 ...
in Taiwan,
EGAT The Electricity Generating Authority of Thailand (EGAT) ( th, การไฟฟ้าฝ่ายผลิตแห่งประเทศไทย; ) is a state enterprise, managed by the Ministry of Energy, responsible for electric power ge ...
in Thailand,
Vietnam Electricity Vietnam Electricity (full name: Vietnam Electricity Group, abbreviated name: EVN, vi, Tập đoàn Điện lực Việt Nam) is the largest power company in Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Re ...
and
EÜAŞ The Electricity Generation Company ( tr, Elektrik Üretim A.Ş.; EÜAŞ) is the largest electric power company in Turkey. Owned by the government, it produces and trades electricity throughout the country. History EÜAŞ was founded by the gov ...
in Turkey are building or planning new plants. As of 2021 this may be helping to cause a
carbon bubble The carbon bubble is a hypothesized bubble in the valuation of companies dependent on fossil-fuel-based energy production, resulting from future decreases in value of fossil fuel reserves as they become unusable in order to meet carbon budget ...
which could cause financial instability if it bursts.


Politics

Countries building or financing new coal-fired power stations, such as China, India, Indonesia, Vietnam, Turkey and Bangladesh, face mounting international criticism for obstructing the aims of the Paris Agreement. In 2019, the Pacific Island nations (in particular
Vanuatu Vanuatu ( or ; ), officially the Republic of Vanuatu (french: link=no, République de Vanuatu; bi, Ripablik blong Vanuatu), is an island country located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is east of no ...
and Fiji) criticized Australia for failing to cut their emissions at a faster rate than they were, citing concerns about coastal inundation and erosion. In May 2021, the G7 members agreed to end new direct government support for international coal power generation.


Opposition to coal

Opposition to coal pollution was one of the main reasons the modern
environmental movement The environmental movement (sometimes referred to as the ecology movement), also including conservation and green politics, is a diverse philosophical, social, and political movement for addressing environmental issues. Environmentalists a ...
started in the 19th century.


Transition away from coal

In order to meet global climate goals and provide power to those that do not currently have it coal power must be reduced from nearly 10,000 TWh to less than 2,000 TWh by 2040. Phasing out coal has short-term health and environmental benefits which exceed the costs, but some countries still favor coal, and there is much disagreement about how quickly it should be phased out. However many countries, such as the
Powering Past Coal Alliance The Powering Past Coal Alliance (PPCA) is a group of 166 countries, cities, regions and organisations aiming to accelerate the fossil-fuel phase out of coal-fired power stations, except the very few which have carbon capture and storage. It ha ...
, have already or are transitioned away from coal; the largest transition announced so far being Germany, which is due to shut down its last coal-fired power station between 2035 and 2038. Some countries use the ideas of a " Just Transition", for example to use some of the benefits of transition to provide early pensions for coal miners. However, low-lying Pacific Islands are concerned the transition is not fast enough and that they will be inundated by
sea level rise Globally, sea levels are rising due to human-caused climate change. Between 1901 and 2018, the globally averaged sea level rose by , or 1–2 mm per year on average.IPCC, 2019Summary for Policymakers InIPCC Special Report on the Ocean and Cry ...
, so they have called for
OECD The Organisation for Economic Co-operation and Development (OECD; french: Organisation de coopération et de développement économiques, ''OCDE'') is an intergovernmental organisation with 38 member countries, founded in 1961 to stimulate e ...
countries to completely phase out coal by 2030 and other countries by 2040. In 2020, although China built some plants, globally more coal power was retired than built: the
UN Secretary General The secretary-general of the United Nations (UNSG or SG) is the chief administrative officer of the United Nations and head of the United Nations Secretariat, one of the six principal organs of the United Nations. The role of the secretary-g ...
has also said that OECD countries should stop generating electricity from coal by 2030 and the rest of the world by 2040. Phasing down coal was agreed at
COP26 The 2021 United Nations Climate Change Conference, more commonly referred to as COP26, was the 26th United Nations Climate Change conference, held at the SEC Centre in Glasgow, Scotland, United Kingdom, from 31 October to 13 November 2021. The ...
in the
Glasgow Climate Pact The Glasgow Climate Pact is an agreement reached at the 2021 United Nations Climate Change Conference (COP26). The pact is the first climate agreement explicitly planning to reduce unabated coal usage. A pledge to "phase out" coal was change ...
.


Peak coal


Switch to cleaner fuels and lower carbon electricity generation

Coal-fired generation puts out about twice as much carbon dioxide—around a tonne for every megawatt hour generated—as electricity generated by burning natural gas at 500 kg of greenhouse gas per megawatt hour. In addition to generating electricity, natural gas is also popular in some countries for heating and as an automotive fuel. The use of
coal in the United Kingdom 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 de ...
declined as a result of the development of
North Sea oil North Sea oil is a mixture of hydrocarbons, comprising liquid petroleum and natural gas, produced from petroleum reservoirs beneath the North Sea. In the petroleum industry, the term "North Sea" often includes areas such as the Norwegian Sea ...
and the subsequent
dash for gas The Dash for Gas was the 1990s shift by the newly privatized companies in the electricity sector of the United Kingdom towards generation of electricity using natural gas. Gas consumption peaked in 2001 and has been in decline since 2010. The key ...
during the 1990s. In Canada some coal power plants, such as the
Hearn Generating Station The Richard L. Hearn Generating Station (named after Richard Lankaster Hearn) is a decommissioned electrical generating station in Toronto, Ontario, Canada. The plant was originally fired by coal, but later converted to burn natural gas. The pl ...
, switched from coal to natural gas. In 2017,
coal power in the US Coal generated about 22% of the Electricity sector of the United States, electricity at utility-scale facilities in the United States in 2021, down from 39% in 2014. In 2021, coal supplied of primary energy to electric power plants, which ...
provided 30% of the electricity, down from approximately 49% in 2008, due to plentiful supplies of low cost natural gas obtained by hydraulic fracturing of tight shale formations.


Coal regions in transition

Some
coal-mining region Coal mining regions are significant Natural resource#Extraction, resource extraction industries in many parts of the world. They provide a large amount of the fossil fuel energy in the world economy. The China, People's Republic of China is the la ...
s are highly dependent on coal.


Employment

Some coal miners are concerned their jobs may be lost in the transition. A just transition from coal is supported by the European Bank for Reconstruction and Development.


Bioremediation

The white rot fungus ''
Trametes versicolor ''Trametes versicolor''also known as ''Coriolus versicolor'' and ''Polyporus versicolor''is a common polypore mushroom found throughout the world. Meaning 'of several colors', ''versicolor'' reliably describes this fungus that displays a varie ...
'' can grow on and metabolize naturally occurring coal. The bacteria
Diplococcus A diplococcus (plural diplococci) is a round bacterium (a coccus) that typically occurs in the form of two joined cells. Types Examples of gram-negative diplococci are '' Neisseria spp.'' and ''Moraxella catarrhalis.'' Examples of gram-positiv ...
has been found to degrade coal, raising its temperature.


Cultural usage

Coal is the official state mineral of
Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia ...
and the official state rock of
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
; both
US states In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sov ...
have a historic link to coal mining. Some cultures hold that children who misbehave will receive only a lump of coal from Santa Claus for Christmas in their
stocking Stockings (also known as hose, especially in a historical context) are close-fitting, variously elastic garments covering the leg from the foot up to the knee or possibly part or all of the thigh. Stockings vary in color, design, and transpare ...
s instead of presents. It is also customary and considered lucky in
Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...
and the North of England to give coal as a gift on New Year's Day. This occurs as part of
first-footing In Scottish, Northern English, and Manx folklore, the first-foot ( gd, ciad-chuairt, gv, quaaltagh/qualtagh) is the first person to enter the home of a household on New Year's Day and is seen as a bringer of good fortune for the coming year. Simi ...
and represents warmth for the year to come.


See also

* * * * * * (stratigraphic unit) * * * * * * * * *


Notes


References


Sources

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Further reading

* * *


External links


Coal Transitions

World Coal Association

Coal – International Energy Agency

Coal Online – International Energy Agency

CoalExit

European Association for Coal and Lignite

Coal news and industry magazine

Global Coal Plant Tracker

Centre for Research on Energy and Clean Air
* * * {{Authority control Coal mining Economic geology Fuels Sedimentary rocks Solid fuels