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Coal is a combustible 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 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 ma ...
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-to ...
, 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 ...
, and nitrogen. 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 Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...
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 waters, anoxic) processes prevailing, especially in t ...
s called coal forests that covered much of the Earth's tropical land areas during the late Carboniferous ( Pennsylvanian) and Permian times. Many significant coal deposits are younger than this and originate from the Mesozoic 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. With the invention of the
steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be ...
, coal consumption increased. In 2020, coal supplied about a quarter of the world's primary energy 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 describe ...
. Some
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
and
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
-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 t ...
contributing to climate change. 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. As part of worldwide energy transition, many countries have reduced or eliminated their use of coal power. The United Nations Secretary General asked governments to stop building new coal plants by 2020. Global coal use peaked in 2013. To meet the Paris Agreement target of keeping global warming 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 changed ...
. The largest consumer and importer of coal in 2020 was
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
, 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 List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
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 Gui ...
and
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
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-ei ...
.


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 ...
, 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 br ...
*''kula''(''n''), which in turn is hypothesized to come from the Proto-Indo-European 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 Fries ...
''kole'', Middle Dutch ''cole'', Dutch ''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 Hig ...
''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 settlement ...
''kol'', and the Irish 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, Du ...
root.


Geology

Coal is composed of macerals,
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 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 biodegra ...
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 ...
, usually by mud or acidic water, and was converted into
peat Peat (), also known as turf (), is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...
. This trapped the carbon in immense peat bogs 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 Anthracite, also known as hard coal, and black coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the hig ...
(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 periods, which represent just 2% of the Earth's geologic history. Paradoxically, this was during the Late Paleozoic icehouse, 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 bet ...
. 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 deltas 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 d ...
due to the drop in
base level In geology and geomorphology a base level is the lower limit for an erosion process. The modern term was introduced by John Wesley Powell in 1875. The term was subsequently appropriated by William Morris Davis who used it in his cycle of erosion ...
. 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, ...
, 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 ...
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 t ...
levels that promoted plant growth; and the nature of Carboniferous forests, which included lycophyte trees whose determinate growth meant that carbon was not tied up in heartwood 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 wa ...
stems much harder and more woody. The ability to produce lignin led to the evolution of the first trees. 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, 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 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 stratigraphic sequences of marine and non-marine sediments, sometimes interbedded with coal seams. Historically, the term was defined by the European coal geologists who worked in coal basins formed during ...
. 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 standardis ...
, 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, 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 compounds (carbon compounds characterized by rings of carbon atoms) and aromatic rings begin to fuse into polyaromatic compounds (linked rings of carbon atoms). The structure increasingly resembles
graphene Graphene () is an allotrope of carbon consisting of a Single-layer materials, 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 a ...
to dead biotic material over time, under suitable conditions, its metamorphic grade or rank increases successively into: *
Peat Peat (), also known as turf (), is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...
, 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 * 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 Anthracite, also known as hard coal, and black coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the hig ...
, the highest rank of coal, is a harder, glossy black coal used primarily for residential and commercial space heating. *
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 la ...
is difficult to ignite and not commonly used as fuel; it is most used in pencils, or powdered for lubrication. *
Cannel coal Cannel coal or candle coal is a type of bituminous coal, also classified as terrestrial type oil shale. Hutton(1987) Dyni (2006), pp. 3–4 Speight (2012), pp. 6–7 Due to its physical morphology and low mineral content cannel coal is considered ...
(sometimes called "candle coal") is a variety of fine-grained, high-rank coal with significant hydrogen content, which consists primarily of liptinite. There are several international standards for coal. The classification of coal is generally based on the content of volatiles. 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 (also known as coking coal), which is burnt at high temperature to make
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
. Hilt's law 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 may cause lateral changes of rank, irrespective of depth. For example, some of the coal seams of the Madrid, New Mexico coal field were partially converted to anthracite by contact metamorphism from an igneous
sill Sill may refer to: * Sill (dock), a weir at the low water mark retaining water within a dock * Sill (geology), a subhorizontal sheet intrusion of molten or solidified magma * Sill (geostatistics) * Sill (river), a river in Austria * Sill plate, ...
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 pa ...
inhabitants had begun carving ornaments from black lignite. Coal from the Fushun 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 pink ...
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 (c. 371–287 BC): Outcrop 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 pri ...
(3000–2000 BC), where it formed part of funeral pyres.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 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 ...
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 of East Anglia, where coal from the Midlands was transported via the Car Dyke for use in drying grain. Coal cinders have been found in the hearths of
villas Villas may refer to: Places * Villas, Florida, United States * Villas, Illinois, United States * Villas, New Jersey, United States * Las Villas, a region of Spain * Las Villas (Cuba), a former Cuban Province * The Villas, a housing estate in St ...
and Roman forts, particularly in Northumberland, 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 R ...
at Aquae Sulis (modern day
Bath Bath may refer to: * Bathing, immersion in a fluid ** Bathtub, a large open container for water, in which a person may wash their body ** Public bathing, a public place where people bathe * Thermae, ancient Roman public bathing facilities Plac ...
), 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 Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
-working in the city during the Roman period has been found. In Eschweiler, Rhineland, 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 periodization, 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 ...
. 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-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 United ...
. 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 an ...
, 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 or adits 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 led to the large-scale use of coal, as the
steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be ...
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 buckets ...
. 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 union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...
, 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 Proximates are used in the analysis of biological materials as a decomposition of a human-consumable good into its major constituents. They are a good approximation of the contents of packaged comestible goods and serve as a cost-effective and ea ...
(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 met ...
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 c ...
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 Ea ...
, 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 pso ...
,
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 ...
, light oils, and coal gas. Petroleum coke (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 rang ...
. 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; and an alternative to making iron by smelting is direct reduced iron, 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-to ...
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.


Gasification

Coal gasification, as part of an integrated gasification combined cycle (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 simpl ...
(CO) and hydrogen (H2) gas to fire gas turbines to produce electricity. Syngas can also be converted into transportation fuels, such as gasoline 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 engi ...
, through the Fischer–Tropsch process; 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 southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
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 ...
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 ...
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-to ...
gas (H2). This used to be done in underground coal mines, and also to make town gas, 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, where more hydrogen is liberated: : CO + H2O → CO2 + H2


Liquefaction

Coal can be converted directly into synthetic fuels equivalent to gasoline or diesel by hydrogenation or carbonization. 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-to ...
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 simpl ...
, 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 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 carbon d ...
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 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, 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, central ...
(see also Pulverized coal-fired boiler).Total World Electricity Generation by Fuel (2006)
. Source: IEA 2008.
The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity. The thermodynamic efficiency of this process varies between about 25% and 50% depending on the pre-combustion treatment, turbine technology (e.g. supercritical steam generator) and the age of the plant. A few integrated gasification combined cycle (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 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 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 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 (CWS), which was developed in the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
, 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 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 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 List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
with about a tenth.
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
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 Gui ...
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-ei ...
, while the largest importers are
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
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 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 ...
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 Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
, 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. Th ...
, 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, reduced intelligence, artery 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 ...
, congestive heart failure, 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, mali ...
.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 edit ...
'' 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 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 b ...
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, thorium,
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, b ...
, and other heavy metals, along with non-metals such as selenium. 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 wh ...
is hazardous and toxic to human beings and some other living things. Coal ash contains the radioactive elements uranium and thorium. Coal ash and other solid combustion byproducts are stored locally and escape in various ways that expose those living near coal plants to radiation and environmental toxics.


Damage to the environment

Coal mining and coal fueling of power stations 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 Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...
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, 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, ...
in
Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...
, 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 co ...
was acid rain. In 2014 approximately 100 Tg/S of
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
(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 is one example of a coke producing facility where liquid ammonia was discharged to the marine environment.


Emission intensity

Emission intensity is the greenhouse gas emitted over the life of a generator per unit of electricity generated. The emission intensity of coal power stations 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 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 (a borough 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 compris ...
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 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, Tajikistan, 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 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 t ...
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, ...
is called ''porcelanite'', which resembles the coal burning waste "clinker" or volcanic " scoria". 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. 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 an ...
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 carbon d ...
-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 (EU) and the Clean Air Act (United States).


Satellite monitoring

Satellite monitoring is now used to crosscheck national data, for example Sentinel-5 Precursor 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 (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 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 coal burning power plant in Thompsons, Texas. It is a multi-million dollar project taken up by NRG Energy and JX ...
and Boundary Dam 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. 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 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 Japan Bank for International Cooperation 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 benefited from substantial subsidies in 2021.


Stranded assets

Some coal-fired power stations could become
stranded assets Stranded assets are "assets that have suffered from unanticipated or premature write-downs, devaluations or conversion to liabilities". Stranded assets can be caused by a variety of factors and are a phenomenon inherent in the 'creative destructi ...
, 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 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 the ...
in Malaysia, Taipower 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 g ...
in Thailand, Vietnam Electricity and EÜAŞ in Turkey are building or planning new plants. As of 2021 this may be helping to cause a carbon bubble 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 ...
and
Fiji Fiji ( , ,; fj, Viti, ; Fiji Hindi: फ़िजी, ''Fijī''), officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consis ...
) 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 has ...
, 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 Cr ...
, so they have called for OECD 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 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 changed ...
.


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 dead ...
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 Se ...
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, switched from coal to natural gas. In 2017,
coal power in the US Coal generated about 22% of the 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 made up 90% of coal's contribution to U ...
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 resource extraction industries in many parts of the world. They provide a large amount of the fossil fuel energy in the world economy. The People's Republic of China is the largest producer of coal in the world, ...
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'' can grow on and metabolize naturally occurring coal. The bacteria Diplococcus has been found to degrade coal, raising its temperature.


Cultural usage

Coal is the official state mineral of Kentucky and the official state rock of Utah; both US states 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 stockings instead of presents. It is also customary and considered lucky in
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...
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