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Coal
Sedimentary rock
Bituminous coal,the most commoncoal grade
Composition
Primarycarbon
Secondary

Coalis acombustibleblack or brownish-blacksedimentary rock,formed asrock stratacalledcoal seams.Coal is mostlycarbonwith variable amounts of otherelements,chieflyhydrogen,sulfur,oxygen,andnitrogen.[1] Coal is a type offossil fuel,formed when deadplant matterdecays intopeatwhich is converted into coal by the heat and pressure of deep burial over millions of years.[2]Vast deposits of coal originate in formerwetlandscalledcoal foreststhat covered much of the Earth's tropical land areas during the lateCarboniferous(Pennsylvanian) andPermiantimes.[3][4]

Coal is used primarily as a fuel. While coal has been known and used for thousands of years, its usage was limited until theIndustrial Revolution.With the invention of thesteam engine,coal consumption increased.[5]In 2020, coal supplied about a quarter of the world'sprimary energyand over a third of itselectricity.[6]Someironandsteel-making and other industrial processes burn coal.

The extraction and burning of coaldamages the environment,causing premature death and illness,[7]and it is the largestanthropogenicsource ofcarbon dioxidecontributing toclimate change.Fourteen billion tonnes of carbon dioxide were emitted by burning coal in 2020,[8]which is 40% of total fossil fuel emissions[9]and over 25% of total globalgreenhouse gas emissions.[10]As part of worldwideenergy transition,many countries havereduced or eliminated their use of coal power.[11][12]TheUnited Nations Secretary Generalasked governments to stop building newcoal plantsby 2020.[13]

Global coal use was 8.3 billion tonnes in 2022,[14]and is set to remain at record levels in 2023.[15]To meet theParis Agreementtarget of keepingglobal warmingbelow 2 °C (3.6 °F)coal use needs to halvefrom 2020 to 2030,[16]and "phasing down" coal was agreed upon in theGlasgow Climate Pact.

The largest consumer and importer of coal in 2020 wasChina,which accounts for almost half the world's annual coal production, followed byIndiawith about a tenth.IndonesiaandAustraliaexport the most, followed byRussia.[17][18]

Etymology

The word originally took the formcolinOld English,from reconstructedProto-Germanic*kula(n), fromProto-Indo-Europeanroot *g(e)u-lo-"live coal".[19]Germaniccognates include theOld Frisiankole,Middle Dutchcole,Dutchkool,Old High Germanchol,GermanKohleandOld Norsekol.Irishgualis also a cognate via the Indo-European root.[19]

Formation of coal

Example chemical structure of coal

The conversion of dead vegetation into coal is calledcoalification.At various times in the geologic past, the Earth had dense forests[20]in low-lying areas. In these wetlands, the process of coalification began when dead plant matter was protected fromoxidation,usually by mud or acidic water, and was converted intopeat.The resultingpeat bogs,which trapped immense amounts of carbon, 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.[21]The grade of coal produced depended on the maximum pressure and temperature reached, withlignite(also called "brown coal" ) produced under relatively mild conditions, andsub-bituminous coal,bituminous coal,oranthracite coal(also called "hard coal" or "black coal" ) produced in turn with increasing temperature and pressure.[2][22]

Of the factors involved in coalification, temperature is much more important than either pressure or time of burial.[23]Subbituminous coal can form at temperatures as low as 35 to 80 °C (95 to 176 °F) while anthracite requires a temperature of at least 180 to 245 °C (356 to 473 °F).[24]

Although coal is known from most geologicperiods,90% of all coal beds were deposited in theCarboniferousandPermianperiods.[25]Paradoxically, this was during theLate Paleozoic icehouse,a time of globalglaciation.However, the drop in global sea level accompanying the glaciation exposedcontinental shelvesthat had previously been submerged, and to these were added wideriver deltasproduced by increasederosiondue to the drop inbase level.These widespread areas of wetlands provided ideal conditions for coal formation.[26]The rapid formation of coal ended with thecoal gapin thePermian–Triassic extinction event,where coal is rare.[27]

Favorable geography alone does not explain the extensive Carboniferous coal beds.[28]Other factors contributing to rapid coal deposition were highoxygenlevels, above 30%, that promoted intensewildfiresand formation ofcharcoalthat was all but indigestible by decomposing organisms; highcarbon dioxidelevels that promoted plant growth; and the nature of Carboniferous forests, which includedlycophytetrees whosedeterminate growthmeant that carbon was not tied up inheartwoodof living trees for long periods.[29]

One theory suggested that about 360 million years ago, some plants evolved the ability to producelignin,a complex polymer that made theircellulosestems much harder and more woody. The ability to produce lignin led to the evolution of the firsttrees.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.[30][31][32]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,[33]reconstruction of ancestral enzymes by phylogenetic analysis corroborated a hypothesis that lignin degrading enzymes appeared in fungi approximately 200 MYa.[34]

One likely tectonic factor was theCentral 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 amonsoonclimate. This is necessary for the preservation of peat in coal swamps.[35]

Coal is known fromPrecambrianstrata, which predate land plants. This coal is presumed to have originated from residues of algae.[36][37]

Sometimes coal seams (also known as coal beds) are interbedded with other sediments in acyclothem.Cyclothems are thought to have their origin inglacial cyclesthat produced fluctuations insea level,which alternately exposed and then flooded large areas of continental shelf.[38]

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.[39]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.[40]The low oxygen content of coal shows that coalification removed most of the oxygen and much of the hydrogen a process calledcarbonization.[41]

Carbonization proceeds primarily bydehydration,decarboxylation,and demethanation. Dehydration removes water molecules from the maturing coal via reactions such as[42]

2 R–OH → R–O–R + H2O

Decarboxylationremoves carbon dioxide from the maturing coal:[42]

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 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.[43]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 compoundsconvert toaromatic compounds.Similarly, aromatic rings fuse intopolyaromaticcompounds (linked rings of carbon atoms).[44]The structure increasingly resemblesgraphene,the structural element of graphite.

Chemical changes are accompanied by physical changes, such as decrease in average pore size.[45]

Macerals

The macerals are coalified plant parts that retain the morphology and some properties of the original plant. In many coals, individual macerals can be identified visually. Some macerals include:[46]

  • vitrinite, derived from woody parts
  • lipinite, derived from spores and algae
  • inertite, derived from woody parts that had been burnt in prehistoric times
  • huminite,a precursor to vitrinite.

In coalification huminite is replaced by vitreous (shiny)vitrinite.[47]Maturation of bituminous coal is characterized bybitumenization,in which part of the coal is converted tobitumen,a hydrocarbon-rich gel.[48]Maturation to anthracite is characterized bydebitumenization(from demethanation) and the increasing tendency of the anthracite to break with aconchoidal fracture,similar to the way thick glass breaks.[49]

Types

Coastal exposure of the Point Aconi Seam inNova Scotia
Coal ranking system used by theUnited States Geological Survey

As geological processes applypressureto deadbiotic materialover time, under suitable conditions, itsmetamorphic gradeor rank increases successively into:

  • Peat,a precursor of coal
  • Lignite,or brown coal, the lowest rank of coal, most harmful to health when burned,[7]used almost exclusively as fuel for electric power generation
  • 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 makecoke.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 commercialspace heating.
  • Graphite,a difficult to ignite coal which is mostly used in pencils, or powdered forlubrication.
  • Cannel coal(sometimes called "candle coal" ), a variety of fine-grained, high-rank coal with significant hydrogen content, which consists primarily ofliptinite.It is related to boghead coal.

There are several international standards for coal.[50]The classification of coal is generally based on the content ofvolatiles.However the most important distinction is between thermal coal (also known as steam coal), which is burnt to generate electricity via steam; andmetallurgical coal(also known as coking coal), which is burnt at high temperature to makesteel.

Hilt's lawis 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,metamorphismmay cause lateral changes of rank, irrespective of depth. For example, some of the coal seams of theMadrid, New Mexicocoal field were partially converted to anthracite bycontact metamorphismfrom an igneoussillwhile the remainder of the seams remained as bituminous coal.[51]

History

Further information:History of coal mining
Chinese coal miners in an illustration of theTiangong Kaiwuencyclopedia, published in 1637

The earliest recognized use is from theShenyangarea of China where by 4000 BCNeolithicinhabitants had begun carving ornaments from black lignite.[52]Coal from theFushunmine in northeastern China was used to smeltcopperas early as 1000 BC.[53]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.[54]In Europe, the earliest reference to the use of coal as fuel is from the geological treatiseOn Stones(Lap. 16) by the Greek scientistTheophrastus(c. 371–287 BC):[55][56]

Among the materials that are dug because they are useful, those known asanthrakes[coals] are made of earth, and, once set on fire, they burn like charcoal [anthrakes]. They are found in Liguria... and in Elis as one approaches Olympia by the mountain road; and they are used by those who work in metals.

— Theophrastus, On Stones (16)[57]

Outcropcoal was used in Britain during theBronze Age(3000–2000 BC), where it formed part offuneralpyres.[58][59]InRoman Britain,with the exception of two modern fields, "theRomanswere exploiting coals in all the major coalfields inEnglandandWalesby the end of the second century AD ".[60]Evidence of trade in coal, dated to about AD 200, has been found at theRoman settlement at Heronbridge,nearChester;and in theFenlandsofEast Anglia,where coal from theMidlandswas transported via theCar Dykefor use in drying grain.[61]Coal cinders have been found in the hearths ofvillasandRoman forts,particularly inNorthumberland,dated to around AD 400. In the west of England, contemporary writers described the wonder of a permanent brazier of coal on the altar ofMinervaatAquae Sulis(modern dayBath), although in fact easily accessible surface coal from what became theSomerset coalfieldwas in common use in quite lowly dwellings locally.[62]Evidence of coal's use foriron-working in the city during the Roman period has been found.[63]InEschweiler,Rhineland,deposits ofbituminous coalwere used by the Romans for the smelting ofiron ore.[60]

Coal miner in Britain, 1942

No evidence exists of coal being of great importance in Britain before about AD 1000, theHigh Middle Ages.[64]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 ofKing Henry IIIgranted in 1253.[65]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,[64]but by the time ofHenry VIII,it was understood to derive from the way it was carried to London by sea.[66]In 1257–1259, coal fromNewcastle upon Tynewas shipped to London for thesmithsandlime-burners buildingWestminster Abbey.[64]Seacoal Lane and Newcastle Lane, where coal was unloaded at wharves along theRiver Fleet,still exist.[67]

These easily accessible sources had largely become exhausted (or could not meet the growing demand) by the 13th century, when underground extraction byshaft miningoraditswas developed.[58]The alternative name was "pitcoal", because it came from mines.

Coal production of the world in 1908 as presented byThe Harmsworth atlas and Gazetter

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.[68]HistorianRuth Goodmanhas traced the socioeconomic effects of that switch and its later spread throughout Britain[68]and suggested that its importance in shaping the industrial adoption of coal has been previously underappreciated.[68]: xiv–xix 

The development of theIndustrial Revolutionled to the large-scale use of coal, as thesteam enginetook over from thewater wheel.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.[69]In 1947 there were some 750,000 miners in Britain,[70]but the last deep coal mine in the UK closed in 2015.[71]

A grade between bituminous coal and anthracite was once known as "steam coal" as it was widely used as a fuel forsteam locomotives.In this specialized use, it is sometimes known as "sea coal" in the United States.[72]Small "steam coal", also calleddry small steam nuts(DSSN), was used as a fuel for domesticwater heating.

Coal played an important role in industry in the 19th and 20th century. The predecessor of theEuropean Union,theEuropean Coal and Steel Community,was based on the trading of this commodity.[73]

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.[74]

Composition

Coal consists mainly of a black mixture of diverse organic compounds and polymers. Of course, several kinds of coals exist, with variable dark colors and variable compositions. Young coals (brown coal, lignite) are not black. The two main black coals are bituminous, which is more abundant, and anthracite. The % carbon in coal follows the order anthracite > bituminous > lignite > brown coal. The fuel value of coal varies in the same order. Some anthracite deposits contain pure carbon in the form ofgraphite.

For bituminous coal, the elemental composition 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.[40]This composition reflects partly the composition of the precursor plants. The second main fraction of coal is ash, an undesirable, noncombustable mixture of inorganic minerals. The composition of ash is often discussed in terms of oxides obtained after combustion in air:

Ash composition, weight percent
SiO2 20–40
Al2O3 10–35
Fe2O3 5–35
CaO 1–20
MgO 0.3–4
TiO2 0.5–2.5
Na2O&K2O 1–4
SO3 0.1–12[75]

Of particular interest is the sulfur content of coal, which can vary from less than 1% to as much as 4%. Most of the sulfur and most of the nitrogen is incorporated into the organic fraction in the form oforganosulfur compoundsandorganonitrogen compounds.This sulfur and nitrogen arestrongly boundwithin the hydrocarbon matrix. These elements are released as SO2and NOxupon combustion. They cannot be removed, economically at least, otherwise. Some coals contain inorganic sulfur, mainly in the form ofiron pyrite(FeS2). Being a dense mineral, it can be removed from coal by mechanical means, e.g. byfroth flotation.Some sulfate occurs in coal, especially weathered samples. It is not volatilized and can be removed by washing.[46]

Minor components include:

Average content
Substance Content
Mercury(Hg) 0.10±0.01ppm[76]
Arsenic(As) 1.4–71ppm[77]
Selenium(Se) 3ppm[78]

As minerals, Hg, As, and Se are not problematic to the environment, especially since they are only trace components. They become however mobile (volatile or water-soluble) when these minerals are combusted.

Uses

While most coal is used as fuel, other large-scale applications exist.

Coke

Main article:Coke (fuel)
Coke oven at asmokeless fuelplant inWales,United Kingdom

Coke is a solid carbonaceous residue derived fromcoking coal(a low-ash, low-sulfur bituminous coal,[79]also known asmetallurgical coal), which is used in manufacturing steel and other iron-containing products.[79]Coke is made when coking coal is baked 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 areducing agentinsmeltingiron ore in ablast furnace.[80]The carbon monoxide produced by its combustion reduceshematite(aniron oxide) to iron.

2Fe2O3+ 6 CO → 4Fe + 6 CO2)

Pig iron,which is too rich in dissolved carbon, is also produced.

The coke must bestrong enoughto 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 coke-making processes produce byproducts, includingcoal tar,ammonia,light oils, andcoal gas.

Petroleum coke(petcoke) is the solid residue obtained inoil refining,which resembles coke but contains too many impurities to be useful in metallurgical applications.

Production of chemicals

Production of chemicals from coal

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 wascoal gasificationto producesyngas.Primary chemicals that are produced directly from the syngas includemethanol,hydrogen,andcarbon monoxide,which are the chemical building blocks from which a whole spectrum of derivative chemicals are manufactured, includingolefins,acetic acid,formaldehyde,ammonia,urea,and others. The versatility ofsyngasas 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 ofcoal bed methaneis becoming more important.[81]

Because the slate of chemical products that can be made via coal gasification can in general also use feedstocks derived fromnatural gasandpetroleum,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.[82]Much coal to chemical production is in China[83][84]where coal dependent provinces such asShanxiare struggling to control its pollution.[85]

Liquefaction

Main article:Coal liquefaction

Coal can be converted directly intosynthetic fuelsequivalent to gasoline or diesel byhydrogenationorcarbonization.[86]Coal liquefaction emits more carbon dioxide than liquid fuel production fromcrude oil.Mixing in biomass and using CCS would emit slightly less than the oil process but at a high cost.[87]State ownedChina Energy Investmentruns a coal liquefaction plant and plans to build 2 more.[88]

Coal liquefaction may also refer to the cargo hazard when shipping coal.[89]

Gasification

Main articles:Coal gasificationandUnderground coal gasification

Coal gasification, as part of anintegrated gasification combined cycle(IGCC) coal-fired power station, is used to producesyngas,a mixture ofcarbon monoxide(CO) and hydrogen (H2) gas to fire gas turbines to produce electricity. Syngas can also be converted into transportation fuels, such asgasolineanddiesel,through theFischer–Tropsch process;alternatively, syngas can be converted intomethanol,which can be blended into fuel directly or converted to gasoline via the methanol to gasoline process.[90]Gasification combined with Fischer–Tropsch technology was used by theSasolchemical company ofSouth Africato make chemicals and motor vehicle fuels from coal.[91]

During gasification, the coal is mixed withoxygenandsteamwhile also being heated and pressurized. During the reaction, oxygen and water moleculesoxidizethe coal into carbon monoxide (CO), while also releasinghydrogengas (H2). This used to be done in underground coal mines, and also to maketown 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 thewater gas shift reaction,where more hydrogen is liberated:

CO + H2O → CO2+ H2

Electricity generation

Energy density

Main article:Energy value of coal

Theenergy densityof coal is roughly 24megajoulesper kilogram[92](approximately 6.7kilowatt-hoursper kg). For a coal power plant with a 40% efficiency, it takes an estimated 325 kg (717 lb) of coal to power a 100 W lightbulb for one year.[93]

27.6% of world energy was supplied by coal in 2017 and Asia used almost three-quarters of it.[94]

Precombustion treatment

Main article:Refined coal

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 efficiencyimprovements are achievable by improved pre-drying (especially relevant with high-moisture fuel such as lignite or biomass).[95]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

Main article:Coal-fired power station
Castle Gate Power Plantnear Helper, Utah, US
Coal rail cars
Bulldozerpushing coal inLjubljana Power Station,Slovenia

Coal burnt as asolid fuelincoal power stationstogenerate electricityis calledthermal 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.[96]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 forelectricity generation,it is usually pulverized and then burned in a furnace with aboiler(see alsoPulverized coal-fired boiler).[97]The furnace heat converts boiler water tosteam,which is then used to spinturbineswhich turngeneratorsand create electricity.[98]Thethermodynamic efficiencyof 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.[99][100]

A fewintegrated 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, thecoal is gasifiedto createsyngas,which is burned in agas turbineto produce electricity (just like natural gas is burned in a turbine). Hot exhaust gases from the turbine are used to raise steam in aheat recovery steam generatorwhich powers a supplementalsteam turbine.The overall plant efficiency when used to providecombined heat and powercan reach as much as 94%.[101]IGCC power plants emit less local pollution than conventional pulverized coal-fueled plants; however the technology forcarbon capture and storage(CCS) after gasification and before burning has so far proved to be too expensive to use with coal.[102][103]Other ways to use coal are ascoal-water slurry fuel(CWS), which was developed in theSoviet Union,or inan 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.[104]In 2018 global installed capacity was 2TW(of which 1TW is in China) which was 30% of total electricity generation capacity.[105]The most dependent major country is South Africa, with over 80% of its electricity generated by coal;[106]but China alone generates more than half of the world's coal-generated electricity.[107]

Maximum useof coal was reached in 2013.[108]In 2018 coal-fired power stationcapacity factoraveraged 51%, that is they operated for about half their available operating hours.[109]

Coal industry

Main pages:Category:Coal companies,Coal mining,Coal by country,Coal industry in China,Coal industry in Pakistan,Coal industry in India,andCoal companies of Australia

Mining

Main article:Coal mining

About 8,000 Mt of coal are produced annually, about 90% of which is hard coal and 10% lignite. As of 2018just over half is from underground mines.[110]More accidents occur during underground mining than surface mining. Not all countries publishmining accidentstatistics so worldwide figures are uncertain, but it is thought that most deaths occur incoal mining accidents in China:in 2017 there were 375 coal mining related deaths in China.[111]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.[112]

As a traded commodity

See also:Cost of electricity by source
Extensive coal docks seen inToledo, Ohio,1895

China minesalmost half the world's coal, followed byIndiawith about a tenth.[113]Australiaaccounts for about a third of world coal exports, followed byIndonesiaandRussia,[18]while the largest importers areJapanand India. Russia is increasingly orienting its coal exports from Europe to Asia as Europe transitions to renewable energy and subjects Russia to sanctions over its invasion of Ukraine.[18]

The price of metallurgical coal is volatile[114]and much higher than the price of thermal coal because metallurgical coal must be lower in sulfur and requires more cleaning.[115]Coal futures contracts provide coal producers and theelectric power industryan important tool forhedgingandrisk management.

In some countries, new onshorewindorsolargeneration already costs less than coal power from existing plants.[116][117] However, for China this is forecast for the early 2020s[118]and for southeast Asia not until the late 2020s.[119]In India, building new plants is uneconomic and, despite being subsidized, existing plants are losing market share to renewables.[120]

Market trends

Of thecountries 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 of coal. Therefore, international market trends depend onChinese energy policy.[121]Although the government effort to reduce air pollution in China 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.[105]

Major producers

Main article:List of countries by coal production
Coal production by region

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

Production of coal by country and year (million tonnes)[122][113][123][124]
Country 2000 2005 2010 2015 2017 Share (2017)
China 1,384 2,350 3,235 3,747 3,523 46%
India 335 429 574 678 716 9%
United States 974 1,027 984 813 702 9%
Australia 314 375 424 485 481 6%
Indonesia 77 152 275 392 461 6%
Russia 262 298 322 373 411 5%
Rest of World 1,380 1,404 1,441 1,374 1,433 19%
World total 4,726 6,035 7,255 7,862 7,727 100%

Major consumers

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

Consumption of coal by country and year (million tonnes)[125][126]
Country 2008 2009 2010 2011 2012 2013 2014 2015 2016 Share
China 2,691 2,892 3,352 3,677 4,538 4,678 4,539 3,970 coal + 441met coke= 4,411 3,784 coal + 430 met coke = 4,214 51%
India 582 640 655 715 841 837 880 890 coal + 33 met coke = 923 877 coal + 37 met coke = 914 11%
United States 1,017 904 951 910 889 924 918 724 coal + 12 met coke = 736 663 coal + 10 met coke = 673 9%
World Total 7,636 7,699 8,137 8,640 8,901 9,013 8,907 7,893 coal + 668 met coke = 8561 7,606 coal + 655 met coke = 8261 100%

Major exporters

Exports of coal by country and year (million tonnes)[127]
Country 2018 2019 2020 2021
Indonesia 408 443 410 434
Australia 382 393 371 366
Russia 212 223 222 238
United States 105 85 63 77
South Africa 80 79 75 66
Colombia 84 72 68 56
Canada 32 36 32 32
Netherlands 30 28 15 27
Kazakhstan 26 26 25 24
Mongolia 36 36 29 20

Exporters are at risk of a reduction in import demand from India and China.[128][18]

Major importers

Imports of coal by country and year (million tonnes)[129][130]
Country 2018
China 281
India 223
Japan 189
South Korea 149
Taiwan 76
Germany 44
Netherlands 44
Turkey 38
Malaysia 34
Thailand 25

Damage to human health

Deaths caused as a result of fossil fuel use, especially coal (areas of rectangles in chart) greatly exceed those resulting from production ofrenewable energy(rectangles barely visible in chart).[131]

The use of coal as fuel causes health problems and deaths.[132]The mining and processing of coal causes air and water pollution.[133]Coal-powered plants emit nitrogen oxides, sulfur dioxide, particulate pollution, and heavy metals, which adversely affect human health.[133]Coal bed methane extractionis important to avoid mining accidents.

The deadlyLondon smogwas caused primarily by the heavy use of coal. Globally coal is estimated to cause 800,000 premature deaths every year,[134]mostly in India[135]and China.[136][137][138]

Burning coal is a major contributor tosulfur dioxideemissions, which creates PM2.5particulates,the most dangerous form of air pollution.[139]

Coal smokestack emissions causeasthma,strokes,reducedintelligence,arteryblockages,heart attacks,congestive heart failure,cardiac arrhythmias,mercury poisoning,arterial occlusion,andlung cancer.[140][141]

Annual health costs in Europe from use of coal to generate electricity are estimated at up to €43 billion.[142]

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.[143]

A 2017 study in theEconomic Journalfound 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."[144]

Breathing incoal dustcausescoalworker's pneumoconiosisor "black lung", so called because the coal dust literally turns the lungs black.[145]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.[146]

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 includefly ash,bottom ash,andflue-gas desulfurizationsludge, that containmercury,uranium,thorium,arsenic,and otherheavy metals,along with non-metals such asselenium.[147]

Around 10% of coal is ash.[148]Coal ashis hazardous and toxic to human beings and some other living things.[149]Coal ash contains the radioactive elementsuraniumandthorium.Coal ash and other solid combustion byproducts are stored locally and escape in various ways that expose those living nearcoal plantsto radiation and environmental toxics.[150]

Damage to the environment

Main article:Environmental impact of the coal industry
Aerial photograph of the site of theKingston Fossil Plantcoal fly ash slurry spill taken the day afterthe event

Coal mining,coal combustion wastes,andflue gasare causing major environmental damage.[151][152]

Water systems are affected by coal mining.[153]For example, the mining of coal affectsgroundwaterandwater tablelevels and acidity. Spills of fly ash, such as theKingston Fossil Plant coal fly ash slurry spill,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 ofwater scarcity,such as theThar DesertinPakistan,coal mining and coal power plants contribute to the depletion of water resources.[154]

One of the earliest known impacts of coal on thewater cyclewasacid rain.In 2014, approximately 100Tg/S ofsulfur dioxide(SO2) was released, over half of which was from burning coal.[155]After release, the sulfur dioxide is oxidized to H2SO4which scatters solar radiation, hence its increase in the atmosphere exerts a cooling effect on the 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,[156]whereas carbon dioxide remains in the atmosphere for hundreds of years. Release of SO2also contributes to the widespread acidification of ecosystems.[157]

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 ofcoal seam firesare burning at any given time.[158]For example,Brennender Berghas been burning since 1668, and is still burning in the 21st century.[159]

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.[160]TheWhyalla steelworksis one example of a coke producing facility where liquid ammonia was discharged to the marine environment.[161]

Emission intensity

Emission intensityis thegreenhouse gas emitted over the life of a generatorper unit of electricity generated. The emission intensity ofcoal power stationsis 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.[162]

Underground fires

Main article:Coal-seam fire

Thousands of coal fires are burning around the world.[163]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 surfacewildfires.Coal seams can be set on fire byspontaneous combustionor contact with amine fireor 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.[164][165]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 CO2fromfossil fuels.[166][167]InCentralia, Pennsylvania(aboroughlocated in theCoal Regionof the U.S.), an exposed vein of anthracite ignited in 1962 due to a trash fire in the borough landfill, located in an abandonedanthracitestrip minepit. Attempts to extinguish the fire were unsuccessful, and itcontinues to burn underground to this day.The AustralianBurning Mountainwas 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.[168]

At Kuh i Malik inYagnob 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 thePowder River BasininWyomingand in westernNorth Dakotais calledporcelanite,which resembles the coal burning waste "clinker" or volcanic "scoria".[169]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.[170]Wild coal fires in the area were reported by theLewis and Clark Expeditionas well as explorers and settlers in the area.[171]

Climate change

The warming influence (calledradiative forcing) of long-lived greenhouse gases has nearly doubled in 40 years, with carbon dioxide being the dominant driver of global warming.[172]

The largest and most long-term effect of coal use is the release of carbon dioxide, agreenhouse gasthat causesclimate change.Coal-fired power plants were the single largest contributor to the growth in global CO2emissions in 2018,[173]40% of the total fossil fuel emissions,[9]and more than a quarter of total emissions.[8][note 1]Coal mining can emit methane, another greenhouse gas.[174][175]

In 2016 world grosscarbon dioxide emissionsfrom coal usage were 14.5 gigatonnes.[176]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 anatural gas-fired electric plant.[177]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.[178]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.[179]

Pollution mitigation

Emissions controls at acoal fired power plant
These paragraphs are an excerpt fromCoal pollution mitigation.[edit]

Coal pollution mitigation,sometimes labeled as clean coal, is a series of systems and technologies that seek to mitigatehealth and environmental impact of burning coalfor energy. Burning coal releases harmful substances that contribute to air pollution,acid rain,andgreenhouse gasemissions. Mitigation includes precombustion approaches, such as cleaning coal, and post combustion approaches, includeflue-gas desulfurization,selective catalytic reduction,electrostatic precipitators,andfly ashreduction. These measures aim to reduce coal's impact on human health and the environment.

The combustion of coal releases diverse chemicals into the air. The main products are water and carbon dioxide, just like the combustion of petroleum. Also released aresulfur dioxideand nitrogen oxides, as well as some mercury. The residue remaining after combustion,coal ashoften contains arsenic, mercury, and lead. Finally, the burning of coal, especiallyanthracite,can release radioactive materials.[180]

Economics

In 2018US$80 billionwas invested in coal supply but almost all for sustaining production levels rather than opening new mines.[181] In the long term coal and oil could cost the world trillions of dollars per year.[182][183]Coal alone may cost Australia billions,[184]whereas costs to some smaller companies or cities could be on the scale of millions of dollars.[185]The economies most damaged by coal (via climate change) may be India and the US as they are the countries with the highestsocial cost of carbon.[186]Bank loans to finance coal are a risk to the Indian economy.[135]

China is the largest producer of coal in the world. It is the world's largest energy consumer, andcoal in Chinasupplies 60% of its primary energy. However two fifths of China's coal power stations are estimated to be loss-making.[118]

Air pollution from coal storage and handling costs the US almost 200 dollars for every extra ton stored, due to PM2.5.[187]Coal pollution costs the€43 billioneach year.[188]Measures to cut air pollution benefit individuals financially and the economies of countries[189][190]such as China.[191]

Subsidies

See also:Fossil fuel subsidies

Subsidies for coal in 2021 have been estimated atUS$19 billion,not including electricity subsidies, and are expected to rise in 2022.[192]As of 2019G20countries provide at leastUS$63.9 billion[173]of government support per year for the production of coal, including coal-fired power: many subsidies are impossible to quantify[193]but they includeUS$27.6 billionin domestic and international public finance,US$15.4 billionin fiscal support, andUS$20.9 billionin state-owned enterprise (SOE) investments per year.[173]In the EU state aid to new coal-fired plants is banned from 2020, and to existing coal-fired plants from 2025.[194]As of 2018, government funding for new coal power plants was supplied byExim Bank of China,[195]theJapan Bank for International Cooperationand Indian public sector banks.[196]Coal in Kazakhstanwas the main recipient of coal consumption subsidies totalling US$2 billion in 2017.[197]Coal in Turkeybenefited from substantial subsidies in 2021.[198]

Stranded assets

Some coal-fired power stations could becomestranded assets,for exampleChina Energy Investment,the world's largest power company, risks losing half its capital.[118]However, state-owned electricity utilities such asEskomin South Africa,Perusahaan Listrik Negarain Indonesia,Sarawak Energyin Malaysia,Taipowerin Taiwan,EGATin Thailand,Vietnam ElectricityandEÜAŞin Turkey are building or planning new plants.[199]As of 2021 this may be helping to cause acarbon bubblewhich could cause financial instability if it bursts.[200][201][202]

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 theParis Agreement.[105][203][204]In 2019, the Pacific Island nations (in particularVanuatuandFiji) criticized Australia for failing to cut their emissions at a faster rate than they were, citing concerns about coastal inundation and erosion.[205]In May 2021, the G7 members agreed to end new direct government support for international coal power generation.[206]

Protesting against damage to theGreat Barrier Reefcaused byclimate change in Australia

Cultural usage

Coal is theofficial state mineralofKentucky,[207]and the official state rock ofUtah[208]andWest Virginia.[209]TheseUS stateshave a historic link to coal mining.

Some cultures hold that children who misbehave will receive only a lump of coal fromSanta Clausfor Christmas in theirstockingsinstead of presents.

It is also customary and considered lucky inScotlandand theNorth of Englandto give coal as a gift onNew Year's Day.This occurs as part offirst-footingand represents warmth for the year to come.

See also

Notes

  1. ^14.4 gigatonnes coal/50 gigatonnes total

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Sources

Further reading

External links

The WikibookHistorical Geologyhas a page on the topic of:Peat and coal
The WikibookHigh School Earth Sciencehas a page on the topic of:Coal
Wikimedia Commons has media related toCoal.
Look upcoalin Wiktionary, the free dictionary.
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