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 energy and over a third of itselectricity.[6] Someiron andsteel-making and other industrial processes burn coal.
The largest consumer and importer of coal in 2020 wasChina, which accounts for almost half the world's annual coal production, followed byIndia with about a tenth.Indonesia andAustralia export the most, followed byRussia.[17][18]
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 theCarboniferous andPermian periods.[25] Paradoxically, this was during theLate Paleozoic icehouse, a time of globalglaciation. However, the drop in global sea level accompanying the glaciation exposedcontinental shelves that had previously been submerged, and to these were added wideriver deltas produced by increasederosion due 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 gap in 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 highoxygen levels, above 30%, that promoted intensewildfires and formation ofcharcoal that was all but indigestible by decomposing organisms; highcarbon dioxide levels that promoted plant growth; and the nature of Carboniferous forests, which includedlycophyte trees whosedeterminate growth meant that carbon was not tied up inheartwood of 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 theircellulose stems 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 amonsoon climate. This is necessary for the preservation of peat in coal swamps.[35]
Coal is known fromPrecambrian strata, 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 cycles that 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]
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 compounds convert toaromatic compounds. Similarly, aromatic rings fuse intopolyaromatic compounds (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
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]
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 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 theMadrid, New Mexico coal field were partially converted to anthracite bycontact metamorphism from an igneoussill while the remainder of the seams remained as bituminous coal.[51]
Chinese coal miners in an illustration of theTiangong Kaiwu encyclopedia, published in 1637
The earliest recognized use is from theShenyang area of China where by 4000 BCNeolithic inhabitants had begun carving ornaments from black lignite.[52] Coal from theFushun mine in northeastern China was used to smeltcopper as 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.
Outcrop coal 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, "theRomans were exploiting coals in all the major coalfields inEngland andWales by 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 theFenlands ofEast Anglia, where coal from theMidlands was transported via theCar Dyke for use in drying grain.[61] Coal cinders have been found in the hearths ofvillas andRoman 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 ofMinerva atAquae Sulis (modern dayBath), although in fact easily accessible surface coal from what became theSomerset coalfield was 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 coal were 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 III granted 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 Tyne was shipped to London for thesmiths andlime-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 mining oradits was 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 Goodman has 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 Revolution led to the large-scale use of coal, as thesteam engine took 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 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 is a mixture of diverse organic compounds and polymers. Several kinds exist, with variable dark colors and composition. Young coals (brown coal, lignite) are not completely black. The two main black coals are bituminous, which is more abundant, and anthracite. The type of coal with the highest percentage of carbon in its chemical composition is anthracite, followed by bituminous, then lignite, and finally 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:
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 compounds andorganonitrogen compounds. This sulfur and nitrogen arestrongly bound within the hydrocarbon matrix. These elements are released as SO2 and NOx upon 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]
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
Most coal is used as fuel. 27.6% of world energy was supplied by coal in 2017 and Asia used almost three-quarters of it.[79] Other large-scale applications also exist. Theenergy density of coal is roughly 24megajoules per kilogram[80] (approximately 6.7kilowatt-hours per 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.[81]
In 2022, 68% of global coal use was used for electricity generation.[82]: 11 Coal burnt incoal power stations togenerate electricity is calledthermal coal. It is usually pulverized and then burned in a furnace with aboiler.[83] The furnace heat converts boiler water tosteam, which is then used to spinturbines which turngenerators and create electricity.[84] Thethermodynamic 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.[85][86]
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 gasified to createsyngas, which is burned in agas 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 aheat recovery steam generator which powers a supplementalsteam turbine. The overall plant efficiency when used to providecombined heat and power can reach as much as 94%.[87] IGCC power plants emit less local pollution than conventional pulverized coal-fueled plants. 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.[88] In 2018 global installed capacity was 2TW (of which 1TW is in China) which was 30% of total electricity generation capacity.[89] The most dependent major country is South Africa, with over 80% of its electricity generated by coal;[90] but China alone generates more than half of the world's coal-generated electricity.[91] Efforts around the world to reduce the use of coal have led some regions to switch to natural gas andrenewable energy. In 2018 coal-fired power stationcapacity factor averaged 51%, that is they operated for about half their available operating hours.[92]
Coke is a solid carbonaceous residue that is used in manufacturing steel and other iron-containing products.[93] Coke is made whenmetallurgical coal (also known ascoking 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 agent insmelting iron ore in ablast furnace.[94] The carbon monoxide produced by its combustion reduceshematite (aniron oxide) to iron.
2 Fe2O3 + 6 CO → 4 Fe + 6 CO2
Pig iron, which is too rich in dissolved carbon, is also produced.
The coke must bestrong 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 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 gasification to 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 ofsyngas 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 ofcoal bed methane is becoming more important.[95]
Because the slate of chemical products that can be made via coal gasification can in general also use feedstocks derived fromnatural gas andpetroleum, 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.[96] Much coal to chemical production is in China[97][98] where coal dependent provinces such asShanxi are struggling to control its pollution.[99]
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 asgasoline anddiesel, 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.[104] Gasification combined with Fischer–Tropsch technology was used by theSasol chemical company ofSouth Africa to make chemicals and motor vehicle fuels from coal.[105]
During gasification, the coal is mixed withoxygen andsteam while also being heated and pressurized. During the reaction, oxygen and water moleculesoxidize the coal into carbon monoxide (CO), while also releasinghydrogen gas (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:
About 8,000 Mt of coal are produced annually, about 90% of which is hard coal and 10% lignite. As of 2018[update] just over half is from underground mines.[106] The coalmining industry employs almost 2.7 million workers.[107] More accidents occur during underground mining than surface mining. Not all countries publishmining accident statistics 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.[108] 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.[109]
China mines almost half the world's coal, followed byIndia with about a tenth.[110] At 471 Mt and a 34% share of global exports, Indonesia was the largest exporter by volume in 2022, followed by Australia with 344 Mt and Russia with 224 Mt.[111] Other major exporters of coal are the United States, South Africa, Colombia, and Canada.[82]: 118 In 2022, China, India, and Japan were the biggest importers of coal, importing 301, 228, and 184 Mt respectively.[82]: 117 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[112] and much higher than the price of thermal coal because metallurgical coal must be lower in sulfur and requires more cleaning.[113] Coal futures contracts provide coal producers and theelectric power industry an important tool forhedging andrisk management.
In some countries, new onshorewind orsolar generation already costs less than coal power from existing plants.[114][115]However, for China this is forecast for the early 2020s[116] and for southeast Asia not until the late 2020s.[117] In India, building new plants is uneconomic and, despite being subsidized, existing plants are losing market share to renewables.[118]
In many countries in the Global North, there is a move away from the use of coal and former mine sites are being used as a tourist attraction.[119]
In 2022, China used 4520 Mt of coal, comprising more than half of global coal consumption. India, the European Union, and the United States, were the next largest consumers of coal, using 1162, 461, and 455 Mt respectively.[82]: 114 Over the past decade, China has almost always accounted for the lion's share of the global growth in coal demand.[120] 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.[89]
Preliminary analysis byInternational Energy Agency (IEA) indicates that global coal exports reached an all-time high in 2023. Through to 2026, the IEA expects global coal trade to decline by about 12%, driven by growing domestic production in coal-intensive economies such as China and India andcoal phase-out plans elsewhere, such as in Europe.[111] While thermal coal exports are expected to decline by about 16% by 2026, exports of metallurgical coal are expected to slightly increase by almost 2%.[111]
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).[122]
The use of coal as fuel causes health problems and deaths.[123] The mining and processing of coal causes air and water pollution.[124] Coal-powered plants emit nitrogen oxides, sulfur dioxide, particulate pollution, and heavy metals, which adversely affect human health.[124]Coal bed methane extraction is important to avoid mining accidents.
The deadlyLondon smog was caused primarily by the heavy use of coal. Globally coal is estimated to cause 800,000 premature deaths every year,[125] mostly in India[126] and China.[127][128][129]
Burning coal is a major contributor tosulfur dioxide emissions, which creates PM2.5particulates, the most dangerous form of air pollution.[130]
Annual health costs in Europe from use of coal to generate electricity are estimated at up to €43 billion.[133]
In China, early deaths due to air pollution coal plants 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.[134] Improvements to China's air quality and human health would grow 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.[135]
A 2017 study in theEconomic Journal 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."[136]
Breathing incoal dust causescoalworker's pneumoconiosis or "black lung", so called because the coal dust literally turns the lungs black.[137] 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.[138]
Around 10% of coal is ash.[140]Coal ash is hazardous and toxic to human beings and some other living things.[141] Coal ash contains the radioactive elementsuranium andthorium. Coal ash and other solid combustion byproducts are stored locally and escape in various ways that expose those living nearcoal plants to radiation and environmental toxics.[142]
Water systems are affected by coal mining.[145] For example, the mining of coal affectsgroundwater andwater table levels 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 Desert inPakistan, coal mining and coal power plants contribute to the depletion of water resources.[146]
One of the earliest known impacts of coal on thewater cycle wasacid rain. In 2014, approximately 100Tg/S ofsulfur dioxide (SO2) was released, over half of which was from burning coal.[147] After release, the sulfur dioxide is oxidized to H2SO4 which 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,[148] whereas carbon dioxide remains in the atmosphere for hundreds of years. Release of SO2 also contributes to the widespread acidification of ecosystems.[149]
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 fires are burning at any given time.[150] For example,Brennender Berg has been burning since 1668, and is still burning in the 21st century.[151]
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.[152] TheWhyalla steelworks is one example of a coke producing facility where liquid ammonia was discharged to the marine environment.[153]
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.[154]
The largest and most long-term effect of coal use is the release of carbon dioxide, agreenhouse gas that causesclimate change. Coal-fired power plants were the single largest contributor to the growth in global CO2 emissions in 2018,[155] 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.[156][157]
In 2016 world grosscarbon dioxide emissions from coal usage were 14.5 gigatonnes.[158] 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.[159] The emission intensity of coal varies with type and generator technology and exceeds 1200 g per kWh in some countries.[160] 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.[161] 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.[162]
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 combustion or contact with amine fire 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.[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 CO2 fromfossil fuels.[166][167]
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).[168] 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.
Carbon capture and storage (CCS) can be used to capture carbon dioxide from theflue gas of coal power plants and bury it securely in an underground reservoir. Between 1972 and 2017, plans were made to add CCS to enough coal and gas power plants to sequester 161 million tonnes ofCO 2 per year, but by 2021 98% of these plans had failed.[169] Cost, the absence of measures to address long-term liability for stored CO2, and limited social acceptability have all contributed to project cancellations.[170]: 133 As of 2024, CCS is in operation at only four coal power plants and one gas power plant worldwide.[171]
"Clean coal" and "abated coal"
Coal industry groups promote the idea of "clean coal". In one video by theAmerican Coalition for Clean Coal Electricity, coal lumps are portrayed as characters singing carols with names like "Frosty the Coalman."[172]
Since the mid-1980s, the term "clean coal" has been widely used with various meanings.[173] Initially, "clean coal technology" referred to scrubbers and catalytic converters that reduced the pollutants that cause acid rain. The scope then expanded to include reduction of other pollutants such as mercury.[173] Recently, the term has come to encompass the use of CCS to reduce greenhouse gas emissions (GHG).[173]
In political discourse, the term has been erroneously used to imply that coal itself can be clean.[173] For instance, it has been suggested that "clean coal" can be produced and exported.[173] Even with scrubbers and some CCS, coal still has a fairly high environmental impact.[173]
In discussions on greenhouse gas emissions, another common term is "abatement" of coal use. In the2023 United Nations Climate Change Conference, an agreement was reached to phase down unabated coal use.[174] Since the termabated was not defined, the agreement was criticized for being open to abuse.[174] Without a clear definition, is possible for fossil fuel use to be called "abated" if it uses CCS only in a minimal fashion, such as capturing only 30% of the emissions from a plant.[174]
The IPCC considers fossil fuels to be unabated if they are "produced and used without interventions that substantially reduce the amount of GHG emitted throughout the life-cycle; for example, capturing 90% or more from power plants."[175][176]
Economics
In 2018US$80 billion was invested in coal supply but almost all for sustaining production levels rather than opening new mines.[177]In the long term coal and oil could cost the world trillions of dollars per year.[178][179] Coal alone may cost Australia billions,[180] whereas costs to some smaller companies or cities could be on the scale of millions of dollars.[181] 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.[182] Bank loans to finance coal are a risk to the Indian economy.[126]
China is the largest producer of coal in the world. It is the world's largest energy consumer, andcoal in China supplies 60% of its primary energy. However two fifths of China's coal power stations are estimated to be loss-making.[116]
Air pollution from coal storage and handling costs the US almost 200 dollars for every extra ton stored, due to PM2.5.[183] Coal pollution costs the€43 billion each year.[184] Measures to cut air pollution benefit individuals financially and the economies of countries[185][186] such as China.[187]
Subsidies for coal in 2021 have been estimated atUS$19 billion, not including electricity subsidies, and are expected to rise in 2022.[188] As of 2019[update]G20 countries provide at leastUS$63.9 billion[155] of government support per year for the production of coal, including coal-fired power: many subsidies are impossible to quantify[189] but they includeUS$27.6 billion in domestic and international public finance,US$15.4 billion in fiscal support, andUS$20.9 billion in state-owned enterprise (SOE) investments per year.[155] In the EU state aid to new coal-fired plants is banned from 2020, and to existing coal-fired plants from 2025.[190] As of 2018, government funding for new coal power plants was supplied byExim Bank of China,[191] theJapan Bank for International Cooperation and Indian public sector banks.[192]Coal in Kazakhstan was the main recipient of coal consumption subsidies totalling US$2 billion in 2017.[193]Coal in Turkey benefited from substantial subsidies in 2021.[194]
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.[89][199][200] In 2019, the Pacific Island nations (in particularVanuatu andFiji) criticized Australia for failing to cut their emissions at a faster rate than they were, citing concerns about coastal inundation and erosion.[201] In May 2021, the G7 members agreed to end new direct government support for international coal power generation.[202]
Some cultures hold that children who misbehave will receive only a lump of coal fromSanta Claus for Christmas in theirstockings instead of presents.
It is also customary and considered lucky in Scotland to give coal as a gift onNew Year's Day. This occurs as part offirst-footing and represents warmth for the year to come.[206]
FutureCoal – international non-profit, non-governmental association based in London representing the global coal industryPages displaying wikidata descriptions as a fallback
^McGhee, George R. (2018).Carboniferous Giants and Mass Extinction: The Late Paleozoic Ice Age World. New York: Columbia University Press. p. 98.ISBN9780231180979.
^Koonin, Steven E. (2021).Unsettled: What Climate Science Tells Us, What It Doesn't, and Why It Matters. Dallas: BenBella Books. p. 44.ISBN9781953295248.
^Floudas, Dimitrios; Binder, Manfred; Riley, Robert; Barry, Kerrie; Blanchette, Robert A.; Henrissat, Bernard; Martínez, Angel T.; Otillar, Robert; Spatafora, Joseph W.; Yadav, Jagjit S.; Aerts, Andrea; Benoit, Isabelle; Boyd, Alex; Carlson, Alexis; Copeland, Alex; Coutinho, Pedro M.; de Vries, Ronald P.; Ferreira, Patricia; Findley, Keisha; Foster, Brian; Gaskell, Jill; Glotzer, Dylan; Górecki, Paweł; Heitman, Joseph; Hesse, Cedar; Hori, Chiaki; Igarashi, Kiyohiko; Jurgens, Joel A.; Kallen, Nathan; Kersten, Phil; Kohler, Annegret; Kües, Ursula; Kumar, T. K. Arun; Kuo, Alan; LaButti, Kurt; Larrondo, Luis F.; Lindquist, Erika; Ling, Albee; Lombard, Vincent; Lucas, Susan; Lundell, Taina; Martin, Rachael; McLaughlin, David J.; Morgenstern, Ingo; Morin, Emanuelle; Murat, Claude; Nagy, Laszlo G.; Nolan, Matt; Ohm, Robin A.; Patyshakuliyeva, Aleksandrina; Rokas, Antonis; Ruiz-Dueñas, Francisco J.; Sabat, Grzegorz; Salamov, Asaf; Samejima, Masahiro; Schmutz, Jeremy; Slot, Jason C.; St. John, Franz; Stenlid, Jan; Sun, Hui; Sun, Sheng; Syed, Khajamohiddin; Tsang, Adrian; Wiebenga, Ad; Young, Darcy; Pisabarro, Antonio; Eastwood, Daniel C.; Martin, Francis; Cullen, Dan; Grigoriev, Igor V.; Hibbett, David S. (29 June 2012). "The Paleozoic Origin of Enzymatic Lignin Decomposition Reconstructed from 31 Fungal Genomes".Science.336 (6089):1715–1719.Bibcode:2012Sci...336.1715F.doi:10.1126/science.1221748.hdl:10261/60626.OSTI1165864.PMID22745431.S2CID37121590.
^Stanley, Steven M.Earth System History. New York: W.H. Freeman and Company, 1999.ISBN0-7167-2882-6 (p. 426)
^Andriesse, J. P. (1988). "The Main Characteristics of Tropical Peats".Nature and Management of Tropical Peat Soils. Rome: Food and Agriculture Organization of the United Nations.ISBN92-5-102657-2.
^abReid, William (1973). "Chapter 9: Heat Generation, Transport, and Storage". In Robert Perry; Cecil Chilton (eds.).Chemical Engineers' Handbook (5 ed.).
^Ulbrich, Markus; Preßl, Dieter; Fendt, Sebastian; Gaderer, Matthias; Spliethoff, Hartmut (December 2017). "Impact of HTC reaction conditions on the hydrochar properties and CO2 gasification properties of spent grains".Fuel Processing Technology.167:663–669.doi:10.1016/j.fuproc.2017.08.010.
^abHatcher, Patrick G.; Faulon, Jean Loup; Wenzel, Kurt A.; Cody, George D. (November 1992). "A structural model for lignin-derived vitrinite from high-volatile bituminous coal (coalified wood)".Energy & Fuels.6 (6):813–820.doi:10.1021/ef00036a018.
^Ibarra, JoséV.; Muñoz, Edgar; Moliner, Rafael (June 1996). "FTIR study of the evolution of coal structure during the coalification process".Organic Geochemistry.24 (6–7):725–735.Bibcode:1996OrGeo..24..725I.doi:10.1016/0146-6380(96)00063-0.
^Li, Yong; Zhang, Cheng; Tang, Dazhen; Gan, Quan; Niu, Xinlei; Wang, Kai; Shen, Ruiyang (October 2017). "Coal pore size distributions controlled by the coalification process: An experimental study of coals from the Junggar, Ordos and Qinshui basins in China".Fuel.206:352–363.Bibcode:2017Fuel..206..352L.doi:10.1016/j.fuel.2017.06.028.
^Carol, Mattusch (2008).Oleson, John Peter (ed.).Metalworking and Tools. The Oxford Handbook of Engineering and Technology in the Classical World. Oxford University Press. pp. 418–38 (432).ISBN978-0-19-518731-1.
^"το δ' εκ της κατακαύσεως ὅμοιον γίνεται γη κεκαυμένη. οὓς δε καλοῦσιν ευθὺς ἄνθρακας των ὀρυττομένων δια την χρείαν εισί γεώδεις, ἐκκαίονται δε και πυροῦνται καθάπερ οἱ ἄνθρακες. εισὶ δε περί τε την Λιγυστικὴν ὅπου και το ἤλεκτρον, και εν τη Ήλεία βαδιζόντων Όλυμπίαζε την δι' ὄρους, οΐς και οἱ χαλκεΐς χρῶνται."ΠΕΡΙ ΛΙΘΩΝ, p. 21.
^abBritannica 2004:Coal mining: ancient use of outcropping coal
^"Arsenic in Coal"(PDF). pubs.usgs.gov. 28 March 2006.Archived(PDF) from the original on 9 May 2013. Retrieved22 February 2013.
^Lakin, Hubert W. (1973). "Selenium in Our Enviroment [sic]".Selenium in Our Environment – Trace Elements in the Environment. Advances in Chemistry. Vol. 123. p. 96.doi:10.1021/ba-1973-0123.ch006.ISBN978-0-8412-0185-9.
^Ritchie, Hannah; Roser, Max (2021)."What are the safest and cleanest sources of energy?".Our World in Data.Archived from the original on 15 January 2024. Data sources: Markandya & Wilkinson (2007); UNSCEAR (2008; 2018); Sovacool et al. (2016); IPCC AR5 (2014); Pehl et al. (2017); Ember Energy (2021).
^Human Impacts on Atmospheric Chemistry, by PJ Crutzen and J Lelieveld, Annual Review of Earth and Planetary Sciences, Vol. 29: 17–45 (Volume publication date May 2001)
^Sun, Dong; Fang, Jing; Sun, Jingqi (2018). "Health-related benefits of air quality improvement from coal control in China: Evidence from the Jing-Jin-Ji region".Resources, Conservation and Recycling.129:416–423.Bibcode:2018RCR...129..416S.doi:10.1016/j.resconrec.2016.09.021.
^"Utah State Rock – Coal".Pioneer: Utah's Online Library. Utah State Library Division.Archived from the original on 2 October 2011. Retrieved7 August 2011.
.jpg)
.jpg)
_(cropped).jpg)
_(cropped).jpg)
.jpg)
