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EducationSign InMenuDonateARTICLEARTICLECoalCoalCoal is a nonrenewable fossil fuel that is combusted and used to generate electricity. Mining techniques and combustion are both dangerous to miners and hazardous to the environment; however, coal accounts for about half of the electricity generation in the United States.Grades9 - 12SubjectsEarth Science, Geology, Experiential Learning, Geography, Physical Geography‌‌‌‌‌‌‌‌‌‌‌‌‌‌Loading ...ArticleVocabularyCoal is a black or brownish-black sedimentary rock that can be burned for fuel and used to generate electricity. It is composed mostly of carbon and hydrocarbons, which contain energy that can be released through combustion (burning).Coal is the largest source of energy for generating electricity in the world, and the most abundant fossil fuel in the United States.Fossil fuels are formed from the remains of ancient organisms. Because coal takes millions of years to develop and there is a limited amount of it, it is a nonrenewable resource.The conditions that would eventually create coal began to develop about 300 million years ago, during the Carboniferous period. During this time, Earth was covered in wide, shallow seas and dense forests. The seas occasionally flooded the forested areas, trapping plants and algae at the bottom of a swampy wetland. Over time, the plants (mostly mosses) and algae were buried and compressed under the weight of overlying mud and vegetation.As the plant debris sifted deeper under Earth’s surface, it encountered increased temperatures and higher pressure. Mud and acidic water prevented the plant matter from coming into contact with oxygen. Due to this, the plant matter decomposed at a very slow rate and retained most of its carbon (source of energy).These areas of buried plant matter are called peat bogs. Peat bogs store massive amounts of carbon many meters underground. Peat itself can be burned for fuel, and is a major source of heat energy in countries such as Scotland, Ireland, and Russia.Under the right conditions, peat transforms into coal through a process called carbonization. Carbonization takes place under incredible heat and pressure. About three meters (10 feet) of layered vegetation eventually compresses into a third of a meter (one foot) of coal!Coal exists in underground formations called “coal seams” or “coal beds.” A coal seam can be as thick as 30 meters (90 feet) and stretch 1,500 kilometers (920 miles).Coal seams exist on every continent. The largest coal reserves are in the United States, Russia, China, Australia, and India.In the United States, coal is mined in 25 states and three major regions. In the Western Coal Region, Wyoming is the top producer—about 40 percent of the coal mined in the country is extracted in the state. More than one-third of the nation’s coal comes from the Appalachian Coal Region, which includes West Virginia, Virginia, Tennessee, and Kentucky. Coal extracted from Texas in the Interior Coal Region supplies mostly local markets.Types of CoalCoal is very different from mineral rocks, which are made of inorganic material. Coal is made of fragile plant matter, and undergoes many changes before it becomes the familiar black and shiny substance burned as fuel.Coal goes through different phases of carbonization over millions of years, and can be found at all stages of development in different parts of the world.Coal is ranked according to how much it has changed over time. Hilt's Law states that the deeper the coal seam, the higher its rank. At deeper depths, the material encounters greater temperatures and pressure, and more plant debris is transformed into carbon.PeatPeat is not coal, but can eventually transform into coal under the right circumstances. Peat is an accumulation of partly decayed vegetation that has gone through a small amount of carbonization.However, peat is still considered part of the coal “family” because it contains energy that its original plants contained. It also contains high amounts of volatile matter and gases such as methane and mercury, which are environmentally hazardous when burned.Peat retains enough moisture to be spongy. It can absorb water and expand the bog to form more peat. This makes it a valuable environmental defense against flooding. Peat can also be integrated into soil to help it retain and slowly release water and nutrients. For this reason, peat and so-called “peat moss” are valuable to gardeners.Peat is an important source of energy in many countries, including Ireland, Scotland, and Finland, where it is dehydrated and burned for heat.LigniteLignite coal is the lowest rank of coal. It has carbonized past the point of being peat, but contains low amounts of energy—its carbon content is about 25-35 percent. It comes from relatively young coal deposits, about 250 million years old.Lignite, a crumbly brown rock also called brown coal or rosebud coal, retains more moisture than other types of coal. This makes it expensive and dangerous to mine, store, and transport. It is susceptible to accidential combustion and has very high carbon emissions when burned. Most lignite coal is used in power stations very close to where it was mined.Lignite is mainly combusted and used to generate electricity. In Germany and Greece, lignite provides 25-50 percent of electricity generated by coal. In the U.S., lignite deposits generate electricity mostly in the states of North Dakota and Texas.Sub-Bituminous CoalSub-bituminous coal is about 100 million years old. It contains more carbon than lignite, about 35-45 percent. In many parts of the world, sub-bituminous coal is considered “brown coal,” along with lignite. Like lignite, sub-bituminous coal is mainly used as fuel for generating electricity.Most sub-bituminous coal in the U.S. is mined in the state of Wyoming, and makes up about 47 percent of all of the coal produced in the United States. Outside the U.S., China is a leading producer of sub-bituminous coal.Bituminous CoalBituminous coal is formed under more heat and pressure, and is 100 million to 300 million years old. It is named after the sticky, tar-like substance called bitumen that is also found in petroleum. It contains about 45-86 percent carbon.Coal is a sedimentary rock, and bituminous coal frequently contains “bands,” or strips, of different consistency that mark the layers of plant material that were compressed.Bituminous coal is divided into three major types: smithing coal, cannel coal, and coking coal. Smithing coal has very low ash content, and is ideal for forges, where metals are heated and shaped.Cannel coal was extensively used as a source of coal oil in the 19th century. Coal oil is made by heating cannel coal with a controlled amount of oxygen, a process called pyrolysis. Coal oil was used primarily as fuel for streetlights and other illumination. The widespread use of kerosene reduced the use of coal oil in the 20th century.Coking coal is used in large-scale industrial processes. The coal is coked, a process of heating the rock in the absense of oxygen. This reduces the moisture content and makes it a more stable product. The steel industry relies on coking coal.Bituminous coal accounts for almost half of all the coal that is used for energy in the United States. It is mainly mined in Kentucky, Pennsylvania, and West Virginia. Outside the U.S., nations such as Russia and Colombia rely on bituminous coal for energy and industrial fuel.AnthraciteAnthracite is the highest rank of coal. It has the most amount of carbon, up to 97 percent, and therefore contains the most energy. It is harder, more dense, and more lustrous than other types of coal. Almost all the water and carbon dioxide have been expelled, and it does not contain the soft or fibrous sections found in bituminous coal or lignite.Because anthracite is a high-quality coal, it burns cleanly, with very little soot. It is more expensive than other coals, and is rarely used in power plants. Instead, anthracite is mainly used in stoves and furnaces.Anthracite is also used in water-filtration systems. It has tinier pores than sand, so more harmful particles are trapped. This makes water safer for drinking, sanitation, and industry.Anthracite can typically be found in geographical areas that have undergone particularly stressful geologic activity. For example, the coal reserves on the Allegheny Plateau in Kentucky and West Virginia stretch to the base of the Appalachian Mountains. Here, the process of orogeny, or mountain formation, contributed to temperatures and pressures high enough to create anthracite.China dominates the mining of anthracite, accounting for almost three-quarters of anthracite coal production. Other anthracite-mining countries include Russia, Ukraine, Vietnam, and the United States (mostly Pennsylvania).GraphiteGraphite is an allotrope of carbon, meaning it is a substance made up only of carbon atoms. (Diamond is another allotrope of carbon.) Graphite is the final stage of the carbonization process.Graphite conducts electricity well, and is commonly used in lithium ion batteries. Graphite can also resist temperatures of up to 3,000°C (5,400°F). It can be used in products such as fire-resistant doors, and missile parts such as nose cones. The most familiar use for graphite, however, is probably as pencil “leads.”China, India, and Brazil are the world’s leading producers of graphite.Coal MiningCoal can be extracted from the earth either by surface mining or underground mining. Once coal has been extracted, it can be used directly (for heating and industrial processes) or to fuel power plants for electricity.Surface MiningIf coal is less than 61 meters (200 feet) underground, it can be extracted through surface mining.In surface mining, workers simply remove any overlying sediment, vegetation, and rock, called overburden. Economically, surface mining is a cheaper option for extracting coal than underground mining. About two and a half times as much coal can be extracted per worker, per hour, than is possible with underground mining.The environmental impacts of surface mining are dramatic. The landscape is literally torn apart, destroying habitats and entire ecosystems. Surface mining can also cause landslides and subsidence (when the ground begins to sink or cave in). Toxic substances leaching into the air, aquifers, and water tables may endanger the health of local residents.In the United States, the Surface Mining Control and Reclamation Act of 1977 regulates the process of coal mining, and is an effort to limit the harmful effects on the environment. The act provides funds to help fix these problems and clean up abandoned mining sites.The three main types of surface coal mining are strip mining, open-pit mining, and mountaintop removal (MTR) mining.Surface Mining: Strip MiningStrip mining is used where coal seams are located very near the surface and can be removed in massive layers, or strips. Overburden is usually removed with explosives and towed away with some of the largest vehicles ever made. Dump trucks used at strip mines often weigh more than 300 tons and have more than 3,000 horsepower.Strip mining can be used in both flat and hilly landscapes. Strip mining in a mountainous area is called contour mining. Contour mining follows the ridges, or contours, around a hill.Surface Mining: Open-Pit MiningOpen-pit mining is used when coal is located deeper underground. A pit, sometimes called a borrow, is dug in an area. This pit becomes the open-pit mine, sometimes called a quarry. Open-pit mines can expand to huge dimensions, until the coal deposit has been mined or the cost of transporting the overburden is greater than the investment in the mine.Open-pit mining is usually restricted to flat landscapes. After the mine has been exhausted, the pit is sometimes converted into a landfill.Surface Mining: MTRDuring mountaintop removal mining (MTR), the entire summit of a mountain is stripped of its overburden: rocks, trees, and topsoil.Overburden is often hauled to nearby valleys, earning the process the nickname “valley fill” mining. After the summit is cleared of vegetation, explosives are used to expose the coal seam.After the coal is extracted, the summit is sculpted with overburden from the next mountaintop to be mined. By law, valuable topsoil is supposed to be saved and replaced after mining is done. Barren land can be replanted with trees and other vegetation.Mountaintop removal began in the 1970s as a cheap alternative to underground mining. It is now used for extracting coal mainly in the Appalachian Mountains of the U.S., in states including Virginia, West Virginia, Tennessee, and Kentucky.MTR is probaby the most controversial coal mining technique. The environmental consequences are radical and severe. Waterways are cut off or contaminated by valley fill. Habitats are destroyed. Toxic byproducts of the mining and explosive processes can drain into local waterways and pollute the air.Underground MiningMost of the world’s coal reserves are buried deep underground. Underground mining, sometimes called deep mining, is a process that retrieves coal from deep below the Earth’s surface—sometimes as far as 300 meters (1,000 feet). Miners travel by elevator down a mine shaft to reach the depths of the mine, and operate heavy machinery that extracts the coal and moves it above ground.The immediate environmental impact of underground mining appears less dramatic than surface mining. There is little overburden, but underground mining operations leave significant tailings. Tailings are the often-toxic residue left over from the process of separating coal from gangue, or economically unimportant minerals. Toxic coal tailings can pollute local water supplies.To miners, the dangers of underground mining are serious. Underground explosions, suffocation from lack of oxygen, or exposure to toxic gases are very real threats.To prevent the buildup of gases, methane must be constantly ventilated out of underground mines to keep miners safe. In 2009, about 10 percent of the U.S. methane emissions came from ventilating underground mines; two percent resulted from surface mining.There are three major types of underground coal mining: longwall mining, room-and-pillar mining, and retreat mining.Underground Mining: Longwall MiningDuring longwall mining, miners slice off enormous panels of coal that are about onemeter (three feet) thick, three to four kilometers (2-2.5 miles) long, and 250-400 meters (800-1,300 feet) wide. The panels are moved by conveyor belt back to the surface.The roof of the mine is maintained by hydraulic supports known as chocks. As the mine advances, the chocks also advance. The area behind the chocks collapses.Longwall mining is one of the oldest methods of mining coal. Before the widespread use of conveyor belts, ponies would descend to the deep, narrow channels and haul the coal back to the surface.Today, almost a third of American coal mines use longwall mining. Outside the U.S., that number is even higher. In China, the world’s largest coal producer, more than 85 percent of coal is exracted using the longwall method.Underground Mining: Room and PillarIn the room-and-pillar mining method, miners carve a “room” out of coal. Columns (pillars) of coal support the ceiling and overburden. The rooms are about nine meters (30 feet) wide, and the support pillars can be 30 meters (100 feet) wide.There are two types of room-and-pillar mining: conventional and continuous. In conventional mining, explosives and cutting tools are used. In continuous mining, a sophisticated machine called a continuous miner extracts the coal.In the U.S., most room-and-pillar mining uses a continuous miner. In developing countries, room-and-pillar coal mines use the conventional method.Underground Mining: Retreat MiningRetreat mining is a variation of room-and-pillar. When all available coal has been extracted from a room, miners abandon the room, carefully destroy the pillars, and let the ceiling cave in. Remains of the giant pillars supply even more coal.Retreat mining may be the most dangerous method of mining. A great amount of stress is put on the remaining pillars, and if they are not pulled out in a precise order, they can collapse and trap miners underground.How We Use CoalPeople all over the world have been using coal to heat their homes and cook their food for thousands of years. Coal was used in the Roman Empire to heat public baths. In the Aztec Empire, the lustrous rock was used for ornaments as well as fuel.The Industrial Revolution was powered by coal. It was a cheaper alternative than wood fuel, and produced more energy when burned. Coal provided the steam and power needed to mass-produce items, generate electricity, and fuel steamships and trains that were necessary to transport items for trade. Most of the collieries, or coal mines, of the Industrial Revolution were in northern England, where more than 80 percent of coal was mined in the early 18th century.Today, coal continues to be used directly (heating) and indirectly (producing electricity). Coal is also essential to the steel industry.FuelAround the world, coal is primarily used to produce heat. It is the leading energy choice for most developing countries, and worldwide consumption increased by more than 30 percent in 2011.Coal can be burned by individual households or in enormous industrial furnaces. It produces heat for comfort and stability, as well as heating water for sanitation and health.ElectricityCoal-fired power plants are one of the most popular ways to produce and distribute electricity. In coal-fired power plants, coal is combusted and heats water in enormous boilers. The boiling water creates steam, which turns a turbine and activates a generator to produce electricity.Almost all the electricity in South Africa (about 93 percent) is generated by coal. Poland, China, Australia, and Kazakhstan are other nations that rely on coal for electricity. In the United States, about 45 percent of the nation’s electricity is driven by coal.CokeCoal plays a vital role in the steel industry. In order to produce steel, iron ore must be heated to separate the iron from other minerals in the rock. In the past, coal itself was used to heat and separate the ore. However, coal releases impurities such as sulfur when it is heated, which can make the resulting metal weak.As early as the 9th century, chemists and engineers discovered a way to remove these impurities from coal before it was burned. Coal is baked in an oven for about 12-36 hours at about 1,000-1,100°C (1,800-2,000°F). This drives off impurities such as coal gas, carbon monoxide, methane, tars, and oil. The resulting material—coal with few impurities and high carbon content—is coke. The method is called coking.Coke is burned in a blast furnace with iron ore and air that is about 1,200°C (2,200°F). The hot air ignites the coke, and the coke melts the iron and separates out the impurities. The resulting material is steel. Coke provides heat and chemical properties that gives steel the strength and flexibility needed to build bridges, skyscrapers, airports, and cars.Many of the biggest coal producers in the world (the United States, China, Russia, India) are also among the biggest steel producers. Japan, another leader in the steel industry, does not have significant coal reserves. It is one of the world’s largest coal importers.Synthetic ProductsThe gases that are released during the coking process can be used as a source of power. Coal gas can be used for heat and light. Coal can also be used to produce syngas, a combination of hydrogen and carbon monoxide. Syngas can be used as a transportation fuel similar to petroleum or diesel.In addition, coal and coke byproducts can be used to make synthetic materials such as tar, fertilizers, and plastics.Coal and Carbon EmissionsBurning coal releases gases and particulates that are harmful to the environment. Carbon dioxide is the primary emission.Carbon dioxide is an essential part of our planet’s atmosphere. It is called a greenhouse gas because it absorbs and retains heat in the atmosphere, and keeps our planet at a livable temperature. In the natural carbon cycle, carbon and carbon dioxide are constantly cycled between the land, ocean, atmosphere, and all living and decomposing organisms. Carbon is also sequestered, or stored underground. This keeps the carbon cycle in balance.However, when coal and other fossil fuels are extracted and burned, they release sequestered carbon into the atmosphere, which leads to a build-up of greenhouse gases and adversely affects climates and ecosystems.In 2011, about 43 percent of the electricity in the U.S. was generated from burning coal. However, coal production was responsible for 79 percent of the country’s carbon emissions.Other Toxic EmissionsSulfur dioxide and nitrogen oxides are also released when coal is burned. These contribute to acid rain, smog, and respiratory illnesses.Mercury is emitted when coal is burned. In the atmosphere, mercury is usually not a hazard. In water, however, mercury transforms into methylmercury, which is toxic and can accumulate in fish and organisms that consume fish, including people.Fly ash (which floats away with other gases during coal combustion) and bottom ash (which does not float away) are also released when coal is combusted. Depending on the composition of the coal, these particulates can contain toxic elements and irritants such as cadmium, silicon dioxide, arsenic, and calcium oxide.In the U.S., fly ash must be captured with industrial “scrubbers” to prevent it from polluting the atmosphere. Unfortunately, fly ash is often stored in landfills or power plants, and can drain into groundwater. As a response to this environmental hazard, fly ash is being used as a component of concrete, thereby isolating it from the natural environment.Many countries do not regulate their coal industries as strictly as the U.S., and emissions pollute air and water supplies.Coal FiresUnder the right conditions of heat, pressure, and ventilation, coal seams can self-ignite and burn underground. Lightning and wildfires can also ignite an exposed section of the coal seam, and smoldering fire can spread along the seam.Coal fires emit tons of greenhouse gases into the atmosphere. Even if the surface fire is extinguished, the coal can smolder for years before flaring up and potentially starting a wildfire again.Coal fires can also begin in mines as a result of an explosion. Coal fires in China, many ignited by explosions used in the extraction process, may account for 1% of the world’s carbon emissions. In the U.S., it is more common for abandoned mines to catch fire if trash is burned in nearby landfills.Once coal catches fire and begins smoldering, it is extremely difficult to extinguish. In Australia, the coal fire at “Burning Mountain” has been burning for 5,500 years!Advantages and DisadvantagesAdvantagesCoal is an important part of the world energy budget. It is relatively inexpensive to locate and extract, and can be found all over the world. Unlike many renewable resources (such as solar or wind), coal production is not dependent on the weather. It is a baseload fuel, meaning it can be produced 24 hours a day, 7 days a week, 365 days a year.We use and depend on many things that coal provides, such as heat and electricity to power our homes, schools, hospitals, and industries. Steel, vital for constructing bridges and other buildings, relies on coke for almost all production.Coal byproducts, such as syngas, can be used to make transportation fuels.Coal mining also provides economic stability for millions of people worldwide. The coal industry relies on people with a wide range of knowledge, skills, and abilities. Jobs associated with coal include geologists, miners, engineers, chemists, geographers, and executives. Coal is an industry that is critical to countries in both the developed and developing world.DisadvantagesCoal is a nonrenewable source of energy. It took millions of years to form, and a finite amount of it exists on our planet. Although it is a consistent and reliable source of energy at this point in time, it will not be available forever.Mining is one of the most dangerous jobs in the world. The health hazards to underground miners include respiratory illnesses, such as “black lung,” in which coal dust builds up in the lungs. In addition to disease, thousands of miners die every year in mine explosions, collapses, and other accidents.Burning coal for energy releases toxins and greenhouse gases, such as carbon dioxide. These have an immediate impact on the local air quality, and contribute to global warming, the current period of climate change.Surface mining permanently alters the landscape. In mountaintop removal, the landscape itself is obliterated and ecosystems are destroyed. This increases erosion in the area. Floods and other natural hazards put these areas at great risk.Coal mining can impact local water supplies in several ways. Streams may be blocked, increasing the chances for flooding. Toxins often leach into groundwater, streams, and aquifers.Coal is one of the most controversial energy sources in the world. The advantages of coal mining are economically and socially significant. However, mining devastates the environment: air, land, and water.Fast FactCarbon FiberCarbon fiber, used in everything from lightweight bicycles to bullet-protecting Kevlar vests, is a type of graphite, the highest rank of coal.Fast FactClean Coal“Clean coal” is a term used for any technology that reduces the carbon emissions of coal combustion. Clean coal usually refers to the process of carbon capture, where emissions are trapped and stored underground.Fast FactCoal FossilsCoal puts the “fossil” in “fossil fuel.” Paleontologists have discovered brilliantly preserved fossils of some of the world’s oldest tropical rainforests in coal seams.Fast FactTop Coal Producers (in 2020 and 2021)ChinaIndiaIndonesiaUnited States AustraliaFast FactIt’s the PitsThe North Antelope Rochelle Complex in the U.S. state of Wyoming is the world’s largest coal mine. The open-pit mine has shipped more than 1.4 billion tons of coal since opening in 1983.Articles & ProfilesSF Gate: Positives and Negatives of Coal Energy SourcesEnergy Information Administration: Energy Kids—CoalCoal-Fired Australia, Buffeted by Climate Change, Enacts Carbon TaxNational Geographic Magazine: High Cost of Cheap Coal: The Coal ParadoxU.S. Department of Energy: CoalCreditsMedia CreditsThe audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.WritersAndrew TurgeonElizabeth MorseIllustratorMary Crooks, National Geographic SocietyEditorJeannie Evers, Emdash Editing, Emdash EditingProducerNational Geographic SocietyotherLast UpdatedOctober 19, 2023User PermissionsFor information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.MediaIf a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.TextText on this page is printable and can be used according to our Terms of Service.InteractivesAny interactives on this page can only be played while you are visiting our website. You cannot download interactives.Related ResourcesNational Geographic Headquarters 1145 17th Street NW Washington, DC 20036ABOUTNational Geographic SocietyNatGeo.comNews and ImpactContact UsExploreOur ExplorersOur ProgramsEducationNat Geo LiveStorytellers CollectiveTraveling ExhibitionsJoin UsWays to GiveApply for a GrantCareersdonateget updatesConnectNational Geographic Society is a 501 (c)(3) organization. © 1996 - 2024 National Geographic Society. All rights reserved.Privacy Notice|Sustainability Policy|Terms of Service|Code of Eth

Coal - Wikipedia

Coal - Wikipedia

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1Etymology

2Geology

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2.1Formation

2.1.1Chemistry of coalification

2.2Types

3History

4Chemistry

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4.1Composition

4.2Coking coal and use of coke to smelt iron

4.2.1Use in foundry components

4.2.2Alternatives to coke

4.3Gasification

4.4Liquefaction

4.5Production of chemicals

5Electricity generation

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5.1Energy density

5.2Precombustion treatment

5.3Power plant combustion

6Coal industry

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6.1Mining

6.2As a traded commodity

6.3Market trends

6.4Major producers

6.5Major consumers

6.6Major exporters

6.7Major importers

7Damage to human health

8Damage to the environment

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8.1Emission intensity

8.2Underground fires

8.3Climate change

9Pollution mitigation

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9.1Standards

9.2Satellite monitoring

9.3Combined cycle power plants

9.4Carbon capture and storage

10Economics

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10.1Subsidies

10.2Stranded assets

11Politics

12Transition away from coal

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12.1Peak coal

12.2Switch to cleaner fuels and lower carbon electricity generation

12.3Coal regions in transition

12.4Employment

12.5Bioremediation

13Cultural usage

14See also

15Notes

16References

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16.1Sources

17Further reading

18External links

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Coal

122 languages

AfrikaansالعربيةAragonésԱրեւմտահայերէնArmãneashtiঅসমীয়াAsturianuAymar aruAzərbaycancaবাংলাBanjarBân-lâm-gúБеларускаяБеларуская (тарашкевіца)भोजपुरीBikol CentralБългарскиBosanskiBrezhonegCatalàЧӑвашлаČeštinaCymraegDanskDeitschDeutschDiné bizaadEestiΕλληνικάEmiliàn e rumagnòlEspañolEsperantoEuskaraفارسیFøroysktFrançaisFurlanGaeilgeGàidhligGalego客家語/Hak-kâ-ngî한국어Հայերենहिन्दीHrvatskiIdoBahasa IndonesiaИронÍslenskaItalianoעבריתJawaಕನ್ನಡქართულიҚазақшаKiswahiliKreyòl ayisyenКыргызчаЛаккуLatinaLatviešuLietuviųLigureLimburgsLombardMagyarМакедонскиMalagasyമലയാളംमराठीBahasa MelayuМонголမြန်မာဘာသာNāhuatlNederlandsनेपालीनेपाल भाषा日本語NordfriiskNorsk bokmålNorsk nynorskOccitanOʻzbekcha / ўзбекчаਪੰਜਾਬੀپنجابیپښتوPicardPolskiPortuguêsRomânăRuna SimiРусиньскыйРусскийСаха тылаShqipSicilianuSimple EnglishSlovenčinaSlovenščinaSoomaaligaСрпски / srpskiSrpskohrvatski / српскохрватскиSundaSuomiSvenskaTagalogதமிழ்తెలుగుไทยТоҷикӣTsetsêhestâheseTürkçeУкраїнськаاردوVènetoTiếng ViệtWalon文言Winaray吴语粵語中文

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From Wikipedia, the free encyclopedia

Combustible sedimentary rock composed primarily of carbon

For other uses, see Coal (disambiguation).

CoalSedimentary rockBituminous coal, the most common coal gradeCompositionPrimarycarbonSecondary

hydrogen

sulfur

oxygen

nitrogen

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.[1]

Coal is a type of fossil fuel, formed when dead plant matter decays into peat and is converted into coal by the heat and pressure of deep burial over millions of years.[2] Vast deposits of coal originate in former wetlands called coal forests that covered much of the Earth's tropical land areas during the late Carboniferous (Pennsylvanian) and Permian times.[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 the Industrial Revolution. With the invention of the steam engine, coal consumption increased.[citation needed] In 2020, coal supplied about a quarter of the world's primary energy and over a third of its electricity.[5] Some iron and steel-making and other industrial processes burn coal.

The extraction and use of coal causes premature death and illness.[6] The use of coal damages the environment, and it is the largest anthropogenic source of carbon dioxide contributing to climate change. Fourteen billion tonnes of carbon dioxide were emitted by burning coal in 2020,[7] which is 40% of the total fossil fuel emissions[8] and over 25% of total global greenhouse gas emissions.[9] As part of worldwide energy transition, many countries have reduced or eliminated their use of coal power.[10][11] The United Nations Secretary General asked governments to stop building new coal plants by 2020.[12] Global coal use was 8.3 billion tonnes in 2022.[13] Global coal demand is set to remain at record levels in 2023.[14] To meet the Paris Agreement target of keeping global warming below 2 °C (3.6 °F) coal use needs to halve from 2020 to 2030,[15] and "phasing down" coal was agreed upon in the Glasgow Climate Pact.

The largest consumer and importer of coal in 2020 was China, which accounts for almost half the world's annual coal production, followed by India with about a tenth. Indonesia and Australia export the most, followed by Russia.[16][17]

Etymology

The word originally took the form col in Old English, from Proto-Germanic *kula(n), which in turn is hypothesized to come from the Proto-Indo-European root *g(e)u-lo- "live coal".[18] Germanic cognates include the Old Frisian kole, Middle Dutch cole, Dutch kool, Old High German chol, German Kohle and Old Norse kol, and the Irish word gual is also a cognate via the Indo-European root.[18]

Geology

Coal is composed of macerals, minerals and water.[19] Fossils and amber may be found in coal.[20]

Formation

Example chemical structure of coal

The conversion of dead vegetation into coal is called coalification. At various times in the geologic past, the Earth had dense forests[21] in low-lying wetland areas. In these wetlands, the process of coalification began when dead plant matter was protected from biodegradation and oxidation, usually by mud or acidic water, and was converted into peat. 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.[19] The grade of coal produced depended on the maximum pressure and temperature reached, with lignite (also called "brown coal") produced under relatively mild conditions, and sub-bituminous coal, bituminous coal, or anthracite coal (also called "hard coal" or "black coal") produced in turn with increasing temperature and pressure.[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 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.[25] Paradoxically, this was during the Late Paleozoic icehouse, a time of global glaciation. However, the drop in global sea level accompanying the glaciation exposed continental shelves that had previously been submerged, and to these were added wide river deltas produced by increased erosion due to the drop in base level. These widespread areas of wetlands provided ideal conditions for coal formation.[26] The rapid formation of coal ended with the coal gap in the Permian–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 high oxygen levels, above 30%, that promoted intense wildfires and formation of charcoal that was all but indigestible by decomposing organisms; high carbon dioxide 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.[29]

One theory suggested that about 360 million years ago, some plants evolved the ability to produce lignin, a complex polymer that made their cellulose 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.[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 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.[35]

Coal is known from Precambrian 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 a cyclothem. Cyclothems are thought to have their origin in glacial cycles that produced fluctuations in sea 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] This implies that chemical processes during coalification must remove most of the oxygen and much of the hydrogen, leaving carbon, a process called carbonization.[41]

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

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[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 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.[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 (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).[44] The structure increasingly resembles graphene, the structural element of graphite.

Chemical changes are accompanied by physical changes, such as decrease in average pore size.[45] 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.[46] Maturation of bituminous coal is characterized by bitumenization, in which part of the coal is converted to bitumen, a hydrocarbon-rich gel.[47] 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.[48]

Types

Coastal exposure of the Point Aconi Seam in Nova Scotia

Coal ranking system used by the United States Geological Survey

As geological processes apply pressure to dead biotic material over time, under suitable conditions, its metamorphic grade or rank increases successively into:

Peat, a precursor of coal

Lignite, or brown coal, the lowest rank of coal, most harmful to health when burned,[6] 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, the highest rank of coal, is a harder, glossy black coal used primarily for residential and commercial space heating.

Graphite is difficult to ignite and not commonly used as fuel; it is most used in pencils, or powdered for lubrication.

Cannel coal (sometimes called "candle coal") is a variety of fine-grained, high-rank coal with significant hydrogen content, which consists primarily of liptinite.

There are several international standards for coal.[49] 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.

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 while the remainder of the seams remained as bituminous coal.[50]

History

Further information: History of coal mining

Chinese coal miners in an illustration of the Tiangong Kaiwu encyclopedia, published in 1637

The earliest recognized use is from the Shenyang area of China where by 4000 BC Neolithic inhabitants had begun carving ornaments from black lignite.[51] Coal from the Fushun mine in northeastern China was used to smelt copper as early as 1000 BC.[52] 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.[53] 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):[54][55]

Among the materials that are dug because they are useful, those known as anthrakes [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) [56]

Outcrop coal was used in Britain during the Bronze Age (3000–2000 BC), where it formed part of funeral pyres.[57][58] In Roman Britain, with the exception of two modern fields, "the Romans were exploiting coals in all the major coalfields in England and Wales by the end of the second century AD".[59] 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.[60] Coal cinders have been found in the hearths of villas 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 at Aquae Sulis (modern day Bath), although in fact easily accessible surface coal from what became the Somerset coalfield was in common use in quite lowly dwellings locally.[61] Evidence of coal's use for iron-working in the city during the Roman period has been found.[62] In Eschweiler, Rhineland, deposits of bituminous coal were used by the Romans for the smelting of iron ore.[59]

Coal miner in Britain, 1942

No evidence exists of coal being of great importance in Britain before about AD 1000, the High Middle Ages.[63] 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.[64] 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,[63] but by the time of Henry VIII, it was understood to derive from the way it was carried to London by sea.[65] In 1257–1259, coal from Newcastle upon Tyne was shipped to London for the smiths and lime-burners building Westminster Abbey.[63] Seacoal Lane and Newcastle Lane, where coal was unloaded at wharves along the River Fleet, still exist.[66]

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.[57] 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.[67] Historian Ruth Goodman has traced the socioeconomic effects of that switch and its later spread throughout Britain[67] and suggested that its importance in shaping the industrial adoption of coal has been previously underappreciated.[67]: xiv–xix 

The development of the Industrial Revolution led to the large-scale use of coal, as the steam engine took over from the water 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.[68] In 1947 there were some 750,000 miners in Britain,[69] but the last deep coal mine in the UK closed in 2015.[70]

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.[71] 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 Coal and Steel Community, was based on the trading of this commodity.[72]

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.[73]

Chemistry

Composition

The composition of coal is reported either as a proximate analysis (moisture, volatile matter, fixed carbon, and ash) or an ultimate analysis (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.[40]

The composition of ash, given in terms of oxides, varies:[40]

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[74]

Other minor components include:

Average content

Substance

Content

Mercury (Hg)

0.10±0.01 ppm[75]

Arsenic (As)

1.4–71 ppm[76]

Selenium (Se)

3 ppm[77]

Coking coal and use of coke to smelt iron

Main article: Coke (fuel)

Coke oven at a smokeless fuel plant in Wales, United Kingdom

Coke is a solid carbonaceous residue derived from coking coal (a low-ash, low-sulfur bituminous coal, also known as metallurgical coal), which is used in manufacturing steel and other iron products.[78] 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 smelting iron ore in a blast furnace.[79] The carbon monoxide produced by its combustion reduces hematite (an iron oxide) to iron.

Waste carbon dioxide is also produced (

2

Fe

2

O

3

+

3

C

⟶

4

Fe

+

3

CO

2

{\displaystyle {\ce {2Fe2O3 + 3C -> 4Fe + 3CO2}}}

) 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, so that these do not migrate to the metal.[78]

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 coke-making processes produce byproducts, including coal tar, ammonia, 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. 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.[80] Sea coal can be mixed with the clay lining (the "bod") used for the bottom of a cupola furnace. When heated, the coal decomposes and the bod becomes slightly friable, easing the process of breaking open holes for tapping the molten metal.[81]

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 can be used as the reducing agent[82] and biomass or waste as the source of carbon.[83] Historically, charcoal has been used as an alternative to coke in a blast furnace, with the resultant iron being known as charcoal iron.

Gasification

Main articles: Coal gasification and Underground coal 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 (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, 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.[84] Gasification combined with Fischer–Tropsch technology was used by the Sasol chemical company of South Africa to make chemicals and motor vehicle fuels from coal.[85]

During gasification, the coal is mixed with oxygen and steam while also being heated and pressurized. During the reaction, oxygen and water molecules oxidize the coal into carbon monoxide (CO), while also releasing hydrogen 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

Main article: Coal liquefaction

Coal can be converted directly into synthetic fuels equivalent to gasoline or diesel by hydrogenation or carbonization.[86] 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.[87] State owned China Energy Investment runs a coal liquefaction plant and plans to build 2 more.[88]

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

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 was coal gasification to produce syngas. Primary chemicals that are produced directly from the syngas include methanol, hydrogen and carbon monoxide, which are the chemical building blocks from which a whole spectrum of derivative chemicals are manufactured, including olefins, acetic acid, formaldehyde, 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 is becoming more important.[90]

Because the slate of chemical products that can be made via coal gasification can in general also use feedstocks derived from natural gas and petroleum, 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.[91] Much coal to chemical production is in China[92][93] where coal dependent provinces such as Shanxi are struggling to control its pollution.[94]

Electricity generation

Energy density

Main article: Energy value of coal

The energy density of coal is roughly 24 megajoules per kilogram[95] (approximately 6.7 kilowatt-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.[96]

27.6% of world energy was supplied by coal in 2017 and Asia used almost three-quarters of it.[97]

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 efficiency improvements are achievable by improved pre-drying (especially relevant with high-moisture fuel such as lignite or biomass).[98] 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 Plant near Helper, Utah, US

Coal rail cars

Bulldozer pushing coal in Ljubljana Power Station, Slovenia

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.[99] 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 (see also Pulverized coal-fired boiler).[100] The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity.[101] 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.[102][103]

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%.[104] IGCC power plants emit less local pollution than conventional pulverized coal-fueled plants; however the technology for carbon capture and storage (CCS) after gasification and before burning has so far proved to be too expensive to use with coal.[105][106] Other ways to use coal are as coal-water slurry fuel (CWS), which was developed in the Soviet Union, 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.[107] In 2018 global installed capacity was 2TW (of which 1TW is in China) which was 30% of total electricity generation capacity.[108] The most dependent major country is South Africa, with over 80% of its electricity generated by coal;[109] but China alone generates more than half of the world's coal-generated electricity.[110]

Maximum use of coal was reached in 2013.[111] In 2018 coal-fired power station capacity factor averaged 51%, that is they operated for about half their available operating hours.[112]

Coal industry

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

Mining

Main article: Coal mining

About 8000 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.[113] 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.[114] 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.[115]

As a traded commodity

See also: Cost of electricity by sourceExtensive coal docks seen in Toledo, Ohio, 1895

China mines almost half the world's coal, followed by India with about a tenth.[116] Australia accounts for about a third of world coal exports, followed by Indonesia and Russia,[117][17] while the largest importers are Japan and 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.[118]

The price of metallurgical coal is volatile[119] and much higher than the price of thermal coal because metallurgical coal must be lower in sulfur and requires more cleaning.[120] 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 or solar generation already costs less than coal power from existing plants.[121][122]

However, for China this is forecast for the early 2020s[123] and for southeast Asia not until the late 2020s.[124] In India, building new plants is uneconomic and, despite being subsidized, existing plants are losing market share to renewables.[125]

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 of coal. Therefore, international market trends depend on Chinese energy policy.[126] 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.[108]

Major producers

Main article: List of countries by coal production

Coal production by region

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

Production of coal by country and year (million tonnes)[127][116][128][129]

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

1380

1404

1441

1374

1433

19%

World total

4,726

6,035

7,255

7,862

7,727

100%

Major consumers

Countries with 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)[130][131]

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 + 441 met 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)[132]

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.[133][117]

Major importers

Imports of coal by country and year (million tonnes)[134][135]

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 of renewable energy (rectangles barely visible in chart).[136]

The use of coal as fuel causes ill health and deaths.[137] Mining and processing of coal causes air and water pollution.[138] Coal-powered plants emit nitrogen oxides, sulfur dioxide, particulate pollution and heavy metals, which adversely affect human health.[138] Coal bed methane extraction 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,[139] mostly in India[140] and China.[141][142][143]

Burning coal is a major contributor to sulfur dioxide emissions, which creates PM2.5 particulates, the most dangerous form of air pollution.[144]

Coal smokestack emissions cause asthma, strokes, reduced intelligence, artery blockages, heart attacks, congestive heart failure, cardiac arrhythmias, mercury poisoning, arterial occlusion, and lung cancer.[145][146]

Annual health costs in Europe from use of coal to generate electricity are estimated at up to €43 billion.[147]

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.[148]

A 2017 study in the Economic 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."[149]

Breathing in coal dust causes coalworker's pneumoconiosis or "black lung", so called because the coal dust literally turns the lungs black.[150] 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.[151]

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, and other heavy metals, along with non-metals such as selenium.[152]

Around 10% of coal is ash.[153] Coal ash is hazardous and toxic to human beings and some other living things.[154] 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.[155]

Damage to the environment

Main article: Environmental impact of the coal industry

Aerial photograph of the site of the Kingston Fossil Plant coal fly ash slurry spill taken the day after the event

Coal mining, coal combustion wastes and flue gas are causing major environmental damage.[156][157]

Water systems are affected by coal mining.[158] For example, mining affects groundwater and water table levels and acidity. Spills of fly ash, such as the Kingston 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 of water scarcity, such as the Thar Desert in Pakistan, coal mining and coal power plants contribute to the depletion of water resources.[159]

One of the earliest known impacts of coal on the water cycle was acid rain. In 2014, approximately 100 Tg/S of sulfur dioxide (SO2) was released, over half of which was from burning coal.[160] 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,[161] whereas carbon dioxide remains in the atmosphere for hundreds of years. Release of SO2 also contributes to the widespread acidification of ecosystems.[162]

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 fires are burning at any given time.[163] For example, Brennender Berg has been burning since 1668 and is still burning in the 21st century.[164]

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.[165] The Whyalla steelworks is one example of a coke producing facility where liquid ammonia was discharged to the marine environment.[166]

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.[167]

Underground fires

Main article: Coal-seam fire

Thousands of coal fires are burning around the world.[168] 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 wildfires. Coal seams can be set on fire by spontaneous combustion or contact with a mine 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.[169][170] 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.[171][172] In Centralia, Pennsylvania (a borough located in the Coal Region 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 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.[173]

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 and in western North Dakota is called porcelanite, which resembles the coal burning waste "clinker" or volcanic "scoria".[174] 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.[175] Wild coal fires in the area were reported by the Lewis and Clark Expedition as well as explorers and settlers in the area.[176]

Climate change

The warming influence (called radiative forcing) of long-lived greenhouse gases has nearly doubled in 40 years, with carbon dioxide being the dominant driver of global warming.[177]

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,[178] 40% of the total fossil fuel emissions,[8] and more than a quarter of total emissions.[7][note 1] Coal mining can emit methane, another greenhouse gas.[179][180]

In 2016 world gross carbon dioxide emissions from coal usage were 14.5 gigatonnes.[181] 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-fired electric plant.[182] 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.[183] 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.[184]

Pollution mitigation

Emissions controls at a coal fired power plant

These paragraphs are an excerpt from Coal pollution mitigation.[edit]

Coal pollution mitigation, sometimes labeled as clean coal, is a series of systems and technologies that seek to mitigate health and environmental impact of burning coal for energy. Burning coal releases harmful substances, including mercury, lead, sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon dioxide (CO2), contributing to air pollution, acid rain, and greenhouse gas emissions. Methods include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction focusing on reducing the emissions of these harmful substances. These measures aim to reduce coal's impact on human health and the environment.

Standards

Local pollution standards include GB13223-2011 (China), India,[185] 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.[186] It has also revealed that low use of technology such as SCR has resulted in high NO2 emissions in South Africa and India.[187]

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.[188][189]

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 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.[190]

Economics

In 2018 US$80 billion was invested in coal supply but almost all for sustaining production levels rather than opening new mines.[191]

In the long term coal and oil could cost the world trillions of dollars per year.[192][193] Coal alone may cost Australia billions,[194] whereas costs to some smaller companies or cities could be on the scale of millions of dollars.[195] 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.[196] Bank loans to finance coal are a risk to the Indian economy.[140]

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.[123]

Air pollution from coal storage and handling costs the US almost 200 dollars for every extra ton stored, due to PM2.5.[197] Coal pollution costs the €43 billion each year.[198] Measures to cut air pollution benefit individuals financially and the economies of countries[199][200] such as China.[201]

Subsidies

See also: Fossil fuel subsidies

Subsidies for coal in 2021 have been estimated at US$19 billion, not including electricity subsidies, and are expected to rise in 2022.[202] As of 2019[update] G20 countries provide at least US$63.9 billion[178] of government support per year for the production of coal, including coal-fired power: many subsidies are impossible to quantify[203] but they include US$27.6 billion in domestic and international public finance, US$15.4 billion in fiscal support, and US$20.9 billion in state-owned enterprise (SOE) investments per year.[178] In the EU state aid to new coal-fired plants is banned from 2020, and to existing coal-fired plants from 2025.[204] As of 2018, government funding for new coal power plants was supplied by Exim Bank of China,[205] the Japan Bank for International Cooperation and Indian public sector banks.[206] Coal in Kazakhstan was the main recipient of coal consumption subsidies totalling US$2 billion in 2017.[207] Coal in Turkey benefited from substantial subsidies in 2021.[208]

Stranded assets

Some coal-fired power stations could become stranded assets, for example China Energy Investment, the world's largest power company, risks losing half its capital.[123] However, state-owned electricity utilities such as Eskom in South Africa, Perusahaan Listrik Negara in Indonesia, Sarawak Energy in Malaysia, Taipower in Taiwan, EGAT in Thailand, Vietnam Electricity and EÜAŞ in Turkey are building or planning new plants.[209] As of 2021 this may be helping to cause a carbon bubble which could cause financial instability if it bursts.[210][211][212]

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.[108][213][214] In 2019, the Pacific Island nations (in particular Vanuatu and Fiji) criticized Australia for failing to cut their emissions at a faster rate than they were, citing concerns about coastal inundation and erosion.[215] In May 2021, the G7 members agreed to end new direct government support for international coal power generation.[216]

Protesting against damage to the Great Barrier Reef caused by climate change in Australia

Opposition to coal pollution was one of the main reasons the modern environmental movement started in the 19th century.[citation needed]

Transition away from coal

Main article: Coal phase-out

The annual amount of coal plant capacity being retired increased into the mid-2010s.[217] However, the rate of retirement has since stalled,[217] and global coal phase-out is not yet compatible with the goals of the Paris Climate Agreement.[218]In parallel with retirement of some coal plant capacity, other coal plants are still being added, though the annual amount of added capacity has been declining since the 2010s.[219]

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.[220] Phasing out coal has short-term health and environmental benefits which exceed the costs,[221] but some countries still favor coal,[222] and there is much disagreement about how quickly it should be phased out.[223][224] However many countries, such as the Powering Past Coal Alliance, have already or are transitioned away from coal;[225] the largest transition announced so far being Germany, which is due to shut down its last coal-fired power station between 2035 and 2038.[226] 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.[227] However, low-lying Pacific Islands are concerned the transition is not fast enough and that they will be inundated by sea level rise, so they have called for OECD countries to completely phase out coal by 2030 and other countries by 2040.[215] 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.[228] Phasing down coal was agreed at COP26 in the Glasgow Climate Pact. Vietnam is among few coal-dependent developing countries that pledged to phase out unabated coal power by the 2040s or as early as possible thereafter[229]

Peak coal

A coal mine in Wyoming, US. The US has the world's largest coal reserves.This section is an excerpt from Peak coal.[edit]

Peak coal is the peak consumption or production of coal by a human community.

The peak of coal's share in the global energy mix was in 2008, when coal accounted for 30% of global energy production.[230]

Coal consumption is declining in the United States and Europe, as well as developed economies in Asia.[230] However, consumption is still increasing in India and Southeast Asia,[231] which compensates for the falls in other regions.[232]

Global coal consumption reached an all time high in 2023 at 8.5 billion tons.[233]

Peak coal can be driven by peak demand or peak supply. Historically, it was widely believed that the supply-side would eventually drive peak coal due to the depletion of coal reserves. However, since the increasing global efforts to limit climate change, peak coal in many countries has been driven by demand.[230] This is due in large part to the rapid expansion of natural gas and renewable energy.[230] Many countries have pledged to phase-out coal, despite estimates that project coal reserves to have the capacity to last for centuries at current consumption levels.

Switch to cleaner fuels and lower carbon electricity generation

See also: Natural gas § Power 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.[234] 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 declined as a result of the development of North Sea oil and the subsequent dash for gas 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 provided 30% of the electricity, down from approximately 49% in 2008,[235][236][237] due to plentiful supplies of low cost natural gas obtained by hydraulic fracturing of tight shale formations.[238]

Coal regions in transition

Some coal-mining regions are highly dependent on coal.[239]

Employment

Further information: Just Transition

Some coal miners are concerned their jobs may be lost in the transition.[240] A just transition from coal is supported by the European Bank for Reconstruction and Development.[241]

Bioremediation

The white rot fungus Trametes versicolor can grow on and metabolize naturally occurring coal.[242] The bacteria Diplococcus has been found to degrade coal, raising its temperature.[243]

Cultural usage

Coal is the official state mineral of Kentucky,[244] and the official state rock of Utah[245] and West Virginia.[246] These 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 and the North of England to give coal as a gift on New Year's Day. This occurs as part of first-footing and represents warmth for the year to come.

See also

Geology portalEnergy portal

Biochar – Lightweight black residue, made of carbon and ashes, after pyrolysis of biomass

Carbochemistry – Branch of chemistry

Coal analysis – Measurement of properties of coal

Coal blending – Mixing of mined coal

Coal homogenization – Process of mixing coal to reduce variance

Coal measures (stratigraphic unit)

Health and environmental impact of the coal industry

Fluidized bed combustion – Technology used to burn solid fuels

Fossil fuel phase-out – Gradual reduction of the use and production of fossil fuels

Gytta – type of fine grained sedimentary mudPages displaying wikidata descriptions as a fallback

Coal-mining region – Basin with coal deposits

Mountaintop removal mining – Type of surface mining

The Coal Question – Book by William Stanley Jevons

Tonstein – Type of sedimentary rock

World Coal Association – international non-profit, non-governmental association based in London representing the global coal industryPages displaying wikidata descriptions as a fallback

Notes

^ 14.4 gigatonnes coal/50 gigatonnes total

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Further reading

Freese, Barbara (2003). Coal: A Human History. Penguin Books. ISBN 978-0-7382-0400-0. OCLC 51449422.

Thurber, Mark (2019). Coal. Polity Press. ISBN 978-1509514014.

Paxman, Jeremy (2022). Black Gold : The History of How Coal Made Britain. William Collins. ISBN 9780008128364.

External links

The Wikibook Historical Geology has a page on the topic of: Peat and coal

The Wikibook High School Earth Science has a page on the topic of: Coal

Wikimedia Commons has media related to Coal.

Look up coal in Wiktionary, the free dictionary.

Coal Transitions

World Coal Association

Coal – International Energy Agency

Coal Online – International Energy Agency Archived 19 January 2008 at the Wayback Machine

CoalExit

European Association for Coal and Lignite

Coal news and industry magazine

Global Coal Plant Tracker

Centre for Research on Energy and Clean Air

"Coal" . Encyclopædia Britannica. Vol. 6 (11th ed.). 1911. pp. 574–93.

"Coal" . New International Encyclopedia. 1905.

"Coal" . Collier's New Encyclopedia. 1921.

vteCoalCoal types by grade(lowest to highest)

Xylit

Peat1

Lignite

Sub-bituminous coal

Bituminous coal

Anthracite

Graphite1

Coal combustion

Black coal equivalent

Char

Coal pollution mitigation

Coal preparation plant

Coal-seam fire

Coke

Coal tar

Energy value

Flue gas

Fly ash

Coal mining

Coalfields

Coal dust

Coal gas

Coal refuse

Coal slurry

Coal homogenization

Coal liquefaction

Health and environmental impact of the coal industry

History

Mining regions

Peak coal

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Coal | Uses, Types, Pollution, & Facts | Britannica

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IntroductionHistory of the use of coalIn ancient timesIn EuropeIn the New WorldModern utilizationCoal as an energy sourceConversionProblems associated with the use of coalHazards of mining and preparationPollution from coal utilizationCoal types and ranksCoal typesMaceralsCoal rock typesBanded and nonbanded coalsRanking by coalificationHydrocarbon contentChemical content and propertiesOrigin of coalCoal-forming materialsPlant matterThe fossil recordFormation processesPeatCoalificationStructure and properties of coalOrganic compoundsPropertiesDensityPorosityReflectivityOther propertiesWorld distribution of coalGeneral occurrenceResources and reserves

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coal, one of the most important primary fossil fuels, a solid carbon-rich material that is usually brown or black and most often occurs in stratified sedimentary deposits.coal depositsLocation of the most-important coal occurrences on Earth.(more)Coal is defined as having more than 50 percent by weight (or 70 percent by volume) carbonaceous matter produced by the compaction and hardening of altered plant remains—namely, peat deposits. Different varieties of coal arise because of differences in the kinds of plant material (coal type), degree of coalification (coal rank), and range of impurities (coal grade). Although most coals occur in stratified sedimentary deposits, the deposits may later be subjected to elevated temperatures and pressures caused by igneous intrusions or deformation during orogenesis (i.e., processes of mountain building), resulting in the development of anthracite and even graphite. Although the concentration of carbon in Earth’s crust does not exceed 0.1 percent by weight, it is indispensable to life and constitutes humankind’s main source of energy.This article considers the geological origins, structure, and properties of coal, its usage throughout human history, and current world distribution. For a discussion of the coal-extraction process, see the article coal mining. For a more complete treatment of the processes involved in coal combustion, see the article coal utilization. History of the use of coal In ancient times The discovery of the use of fire helped to distinguish humans from other animals. Early fuels were primarily wood (and charcoal derived from it), straw, and dried dung. References to the early uses of coal are meagre. Aristotle referred to “bodies which have more of earth than of smoke” and called them “coal-like substances.” (It should be noted that biblical references to coal are to charcoal rather than to the rock coal.) Coal was used commercially by the Chinese long before it was used in Europe. Although no authentic record is available, coal from the Fushun mine in northeastern China may have been employed to smelt copper as early as 1000 bce. Stones used as fuel were said to have been produced in China during the Han dynasty (206 bce–220 ce). In Europe James WattArtist's recreation of James Watt inventing the separate condenser for the steam engine, c. 1765.(more)Coal cinders found among Roman ruins in England suggest that the Romans were familiar with coal use before 400 ce. The first documented proof that coal was mined in Europe was provided by the monk Reinier of Liège, who wrote (about 1200) of black earth very similar to charcoal used by metalworkers. Many references to coal mining in England and Scotland and on the European continent began to appear in the writings of the 13th century. Coal was, however, used only on a limited scale until the early 18th century, when Abraham Darby of England and others developed methods of using in blast furnaces and forges coke made from coal. Successive metallurgical and engineering developments—most notably the invention of the coal-burning steam engine by James Watt—engendered an almost insatiable demand for coal. In the New World Up to the time of the American Revolution, most coal used in the American colonies came from England or Nova Scotia. Wartime shortages and the needs of the munitions manufacturers, however, spurred small American coal-mining operations such as those in Virginia on the James River near Richmond. By the early 1830s mining companies had emerged along the Ohio, Illinois, and Mississippi rivers and in the Appalachian region. As in European countries, the introduction of the steam locomotive gave the American coal industry a tremendous impetus. Continued expansion of industrial activity in the United States and in Europe further promoted the use of coal.

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Modern utilization Coal as an energy source coal cutterRail-mounted coal-cutting machine, 19th century. (more)Bełchatów; coalPower plant and coal mine in Bełchatów, Poland.(more)Coal is an abundant natural resource that can be used as a source of energy, as a chemical source from which numerous synthetic compounds (e.g., dyes, oils, waxes, pharmaceuticals, and pesticides) can be derived, and in the production of coke for metallurgical processes. Coal is a major source of energy in the production of electrical power using steam generation. In addition, gasification and liquefaction of coal produce gaseous and liquid fuels that can be easily transported (e.g., by pipeline) and conveniently stored in tanks. After the tremendous rise in coal use in the early 2000s, which was primarily driven by the growth of China’s economy, coal use worldwide peaked in 2012. Since then coal use has experienced a steady decline, offset largely by increases in natural gas use. Conversion In general, coal can be considered a hydrogen-deficient hydrocarbon with a hydrogen-to-carbon ratio near 0.8, as compared with a liquid hydrocarbons ratio near 2 (for propane, ethane, butane, and other forms of natural gas) and a gaseous hydrocarbons ratio near 4 (for gasoline). For this reason, any process used to convert coal to alternative fuels must add hydrogen (either directly or in the form of water). Gasification refers to the conversion of coal to a mixture of gases, including carbon monoxide, hydrogen, methane, and other hydrocarbons, depending on the conditions involved. Gasification may be accomplished either in situ or in processing plants. In situ gasification is accomplished by controlled, incomplete burning of a coal bed underground while adding air and steam. The gases are withdrawn and may be burned to produce heat or generate electricity, or they may be used as synthesis gas in indirect liquefaction or the production of chemicals.

Coal liquefaction—that is, any process of turning coal into liquid products resembling crude oil—may be either direct or indirect (i.e., by using the gaseous products obtained by breaking down the chemical structure of coal). Four general methods are used for liquefaction: (1) pyrolysis and hydrocarbonization (coal is heated in the absence of air or in a stream of hydrogen), (2) solvent extraction (coal hydrocarbons are selectively dissolved and hydrogen is added to produce the desired liquids), (3) catalytic liquefaction (hydrogenation takes place in the presence of a catalyst—for example, zinc chloride), and (4) indirect liquefaction (carbon monoxide and hydrogen are combined in the presence of a catalyst).

Coal | Properties, Formation, Occurrence and Uses

Coal | Properties, Formation, Occurrence and Uses

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Coal

Modified date: 15/08/2023

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Coal is a non-clastic sedimentary rock. They are the fossilized remains of plants and are in flammable black and brownish-black tones. Its main element is carbon, but it can also contain different elements such as hydrogen, sulfur and oxygen. Unlike coal minerals, it does not have a fixed chemical composition and crystal structure. Depending on the type of plant material, varying degrees of carbonization and the presence of impurities, different types of coal are formed. There are 4 recognized varieties. Lignite is the lowest grade and is the softest and least charred. Sub-bituminous coal is dark brown to black. Bituminous coal is the most abundant and is often burned for heat generation. Anthracite is the highest grade and most metamorphosed form of coal. It contains the highest percentage of low-emission carbon and would be an ideal fuel if it weren’t for comparatively less.

Coal is mainly used as a fuel. Coal has been used for thousands of years, but its real use began with the invention of steam engines after the industrial revolution. Coal provides two-fifths of electricity production worldwide and coal is used as the main fuel in iron and steel production facilities.

Name origin: The word originally took the Old English form col from the Proto-Germanic *kula(n), which is supposed to derive from the Proto-Indo-European root *g(e)u-lo- “live coal”.

Color: Black and Brownish black

Hardness: Changeable

Grain size: Fine grained

Group: Non-Clastic Sedimentary Rock

ContentsCoal ClassificationHistorical significanceChemical compositionPhysical propertiesMining and processing of coalExtraction techniques (surface and underground mining)Processing methods (cleaning, crushing, grading, etc.)Coal CompositionCoal FormationOccurrence of CoalCoal Characteristics and PropertiesIntensityPorosityReflectivityOther featuresEconomic and social importance of coalSummary of Key PointsReferences

Coal Classification

As geological processes put pressure on dead biotic material over time under favorable conditions, the degree or order of metamorphic successively increases as follows:

Lignite, the lowest level of coal, the most harmful to health, is used almost exclusively as a fuel for electric power generation

Jet, a compact form of lignite, sometimes polished; Upper Paleolithic Lower-bituminous coal, whose properties range from those of lignite to bituminous coal, was primarily used as an ornamental stone as it was used as a fuel for steam-electric power generation.

Bituminous coal, a dense sedimentary rock, usually black, but sometimes dark brown, often with well-defined bands of shiny and dull material. It is primarily used as a fuel in the production of steam-electric power and in the production of coke. In the UK it is known as steam coal and has historically been used to raise steam in steam locomotives and ships.

Anthracite, the highest grade of coal, is a harder, glossy black coal used primarily for residential and commercial space heating.

Graphite is difficult to ignite and is not commonly used as a fuel; it is most commonly used in pencils or powdered for lubrication.

Channel coal (sometimes called “candle coal”) is a variety of fine-grained, high-grade coal composed primarily of liptinite with significant hydrogen content.

There are several international standards for coal. The classification of coal is generally based on the content of volatile substances. But the most important distinction is thermal coal (also known as steam coal), which is burned to generate electricity through steam; and metallurgical coal (also known as coking coal), which is burned at high temperature to make steel.

Historical significance

Coal has played an important role in human history and has been used as a source of fuel for thousands of years. In ancient times, coal was used to heat and cook food, and for warmth. During the Industrial Revolution, coal became the primary source of energy for powering steam engines and machinery, leading to significant technological advancements in transportation, manufacturing, and other industries. The use of coal also led to the development of mining as a major industry, and helped to spur economic growth in many parts of the world. However, coal use has also been associated with significant environmental impacts, including air and water pollution, and has been a major contributor to climate change. As a result, efforts are underway to transition to cleaner sources of energy and reduce dependence on coal.

Chemical composition

Coal is primarily composed of carbon, hydrogen, oxygen, nitrogen, and sulfur. The exact composition of coal varies depending on its age and origin, but generally, coal can be classified into four major types based on its carbon content: lignite, sub-bituminous, bituminous, and anthracite. Lignite is the youngest type of coal and contains the least amount of carbon, while anthracite is the oldest and has the highest carbon content. Generally, coal with higher carbon content has a higher energy content and burns more efficiently. Coal also contains varying amounts of minerals such as silica, alumina, iron, calcium, sodium, and potassium, which can affect its combustion properties and environmental impact when burned.

Physical properties

Coal has a variety of physical properties, including:

Color: Coal can range in color from black to brown to grayish.

Hardness: Coal can range in hardness from very soft and crumbly, like graphite, to very hard, like anthracite.

Density: Coal has a lower density than many rocks and minerals, making it relatively lightweight.

Porosity: Coal can be very porous, with small spaces between the coal particles.

Conchoidal fracture: Coal often fractures in a smooth, curved pattern, known as conchoidal fracture.

Luster: Coal has a dull to shiny luster, depending on the type of coal.

Streak: Coal produces a black or dark brown streak when rubbed on a white, unglazed porcelain plate.

The physical properties of coal are important for its mining, processing, and use. For example, the hardness of the coal can affect the type of mining method used, while the porosity and density can affect the processing and transportation of the coal.

Mining and processing of coal

Coal is typically extracted from underground or surface mines. Underground mining methods include room and pillar, longwall, and retreat mining, while surface mining methods include strip mining, mountaintop removal, and open-pit mining.

In the room and pillar mining method, tunnels are dug into a coal seam and pillars of coal are left to support the roof. In longwall mining, a long wall of coal is mined in a single slice, while the roof over the mined-out area collapses behind the mining machine. Retreat mining involves the removal of pillars from a previously mined area.

In surface mining, the overlying rock and soil are removed to access the coal. This process can be done by strip mining, in which the overburden is removed in strips, or by mountaintop removal, in which entire mountaintops are removed to access the coal. Open-pit mining is another surface mining technique, in which a large pit is excavated to extract the coal.

Once the coal has been extracted, it is processed to remove impurities and prepare it for use. The processing may include crushing, screening, and washing to remove rock and other impurities, as well as drying to reduce the moisture content of the coal. Coal may also be treated with chemicals to remove sulfur and other impurities, a process known as coal cleaning.

Extraction techniques (surface and underground mining)

Coal mining can be divided into two broad categories: surface mining and underground mining.

Surface mining involves removing the overlying rock, soil, and vegetation to expose the coal seam. This is usually done with large machines that remove the overburden (the material above the coal seam) in layers. There are different surface mining methods, including strip mining, open-pit mining, mountaintop removal mining, and highwall mining. In strip mining, the overburden is removed in long strips, while in open-pit mining, the overburden is removed in a large pit. Mountaintop removal mining involves removing the entire top of a mountain to access the coal seam, while highwall mining is used to recover coal from an exposed vertical face or cliff.

Underground mining involves digging tunnels or shafts into the earth to reach the coal seam. There are two main types of underground mining: room and pillar mining, and longwall mining. In room and pillar mining, the coal seam is mined in a series of rooms, leaving pillars of coal to support the roof. In longwall mining, a machine called a shearer moves back and forth along the coal seam, cutting the coal and dropping it onto a conveyor belt. The roof is supported by hydraulic supports as the machine advances.

After the coal is extracted, it may be processed to remove impurities and prepared for use. The processing may involve crushing, screening, and washing to remove rocks and other materials that are mixed with the coal. The coal may also be treated with chemicals to remove sulfur and other impurities, or it may be converted to liquid or gaseous fuels.

Processing methods (cleaning, crushing, grading, etc.)

After coal is mined, it often needs to be cleaned and processed to remove impurities and prepare it for use. The exact processing methods used can vary depending on the type of coal and its intended use.

One common method of processing coal is through a process known as “washing,” which involves using water, chemicals, and mechanical equipment to separate the coal from impurities like rock, ash, and sulfur. The coal is crushed and mixed with water and chemicals to create a slurry, which is then passed through a series of screens and cyclones to separate the coal from the other materials. The separated coal is then further processed to remove any remaining impurities and graded based on size.

Other processing methods can include crushing and grinding the coal to make it suitable for burning or other uses, as well as processes to remove sulfur and other pollutants from the coal. Depending on the intended use of the coal, additional processing steps may also be required, such as carbonization to produce coke for use in the steel-making process.

Coal Composition

The composition of coal can be analyzed in two ways. The first is reported as a close analysis (moisture, volatile matter, fixed carbon and ash) or a final analysis (ash, carbon, hydrogen, nitrogen, oxygen and sulfur). A typical bituminous coal may have a final analysis on a dry, ash-free basis of 84.4% carbon, 5.4% hydrogen, 6

ASH COMPOSİTİON, WEİGHT PERCENTSiO220-40Al2O310-35Fe2O35-35CaO1-20MgO0.3-4TiO20.5-2.5Na2O & K2O1-4SO30.1-12

Coal Formation

The process of turning dead vegetation into coal is called coalification. In the geological past there were low wetlands and dense forests in various regions. The dead vegetation in these areas has generally started to biodegrade and transform with mud and acidic water.

This trapped the carbon in huge peat bogs that were eventually buried deep by sediments. Then, over millions of years, the heat and pressure of the deep burial caused a loss of water, methane, and carbon dioxide and increased carbon content.

The grade of coal produced depended on the maximum pressure and temperature reached; Lignite (also called “brown coal”) and sub-bituminous coal, bituminous coal or anthracite (also called “hard coal” or “hard coal”) produced under relatively mild conditions is produced with increasing temperature and pressure.

Of the factors involved in charring, temperature is much more important than pressure or burial time. Sub-bituminous 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).

Although coal is known from most geological periods, 90% of all coal deposits were deposited during the Carboniferous and Permian periods, which represent only 2% of Earth’s geological history.

Occurrence of Coal

Coal is a common energy and chemical source. Terrestrial plants necessary for the development of coal were not abundant until the Carboniferous period (358.9 million to 298.9 million years ago), large sedimentary basins containing rocks of Carboniferous age and younger are known on almost every continent, including Antarctica. The presence of large coal deposits in regions with currently arctic or subarctic climates (such as Alaska and Siberia) is due to climate changes and tectonic movement of crustal plates that have moved older continental masses over the Earth’s surface, sometimes through the subtropical and even tropics. regions. Some areas (like Greenland and most of northern Canada) lack coal because the rocks found there predate the Carboniferous Period, and these regions, known as continental shields, lack the abundant terrestrial plant life needed for the formation of large coal deposits.

Coal Characteristics and Properties

Many of the properties of coal vary with factors such as its composition and the presence of mineral matter. Different techniques have been developed to examine the properties of coal. These are X-ray diffraction, scanning and transmission electron microscopy, infrared spectrophotometry, mass spectroscopy, gas chromatography, thermal analysis, and electrical, thermal analysis, and electrical, optical and magnetic measurements.

Intensity

Knowing the physical properties of coal is important in the preparation and use of coal. For example, coal density ranges from about 1.1 to about 1.5 megagrams per cubic metre, or grams per cubic centimeter. Coal is slightly denser than water and significantly less dense than most rocks and mineral matter. Density differences make it possible to improve the quality of a coal by removing most of the rock matter and sulfide-rich particles through heavy liquid separation. 

Porosity

Coal density is controlled in part by the presence of pores that persist throughout charring. Pore ​​sizes and pore distribution are difficult to measure; however, pores appear to have three size ranges:

(1) macropores (diameter greater than 50 nanometers),

(2) mesopores (2 to 50 nanometers in diameter), and

(3) micropores (diameter less than 2 nanometers).

(One nanometer equals 10−9 metres.) Most of a coal’s effective surface area—about 200 square meters per gram—is found in the pores of the coal, not on the outer surface of a piece of coal. The presence of pore space is important in coke production, gasification, liquefaction and high surface area carbon production to purify water and gases. For safety reasons, coal pores may contain significant amounts of adsorbed methane, which can be released during mining operations and form explosive mixtures with air. The risk of explosion can be reduced by adequate ventilation or prior removal of coalbed methane during mining.

Reflectivity

An important property of coal is its reflectivity (or reflectivity), that is, its ability to reflect light. Reflectivity is measured by shining a monochromatic light beam (with a wavelength of 546 nanometers) onto a polished surface of vitrinite macerals in a charcoal sample and measuring the percentage of reflected light with a photometer. Vitrinite is used as its reflectivity gradually changes with increasing degree. Fusinite reflections are very high due to its coal origin and liptinites tend to disappear with increasing degrees. Although very little of the incident light is reflected (ranging from a few tenths of a percent to 12 percent), the value increases with degrees and can be used to grade most coals without measuring the percentage of volatile matter present.

Other features

Other properties such as hardness, grindability, ash fusion temperature, and free swelling index (a visual measurement of the amount of swelling that occurs when a coal sample is heated in a closed crucible) can affect coal mining and preparation. as well as the way a coal is used. Hardness and grindability determine the types of equipment used for mining, crushing and grinding, in addition to the amount of power consumed in their operations. Ash fusion temperature affects furnace design and operating conditions. The free swelling index provides preliminary information on the suitability of a coal for coke production.

Economic and social importance of coal

Coal is an important natural resource that has played a significant role in the development of the modern world. Its economic and social importance can be seen in several areas:

Energy production: Coal is one of the primary sources of energy used for power generation. It is burned in power plants to produce electricity, which is used to power homes, businesses, and industries.

Steel production: Coal is also a key ingredient in the production of steel. When heated, coal releases carbon, which is used to reduce iron ore to iron. This iron is then used to produce steel, which is an essential material for construction, infrastructure, and many other applications.

Job creation: The mining and processing of coal creates jobs and contributes to local economies in many countries. The industry employs a large number of people, including miners, engineers, geologists, and other professionals.

Transportation: Coal is often transported long distances by rail or ship to reach its destination, which can create jobs and contribute to the economy of the areas through which it passes.

Affordable energy: Coal is often a more affordable source of energy compared to other sources, which can help keep energy costs low for consumers and businesses.

Chemical products: Coal is also used as a raw material in the production of a range of chemical products, including plastics, synthetic fibers, fertilizers, and other chemicals.

However, the use of coal also has significant environmental impacts, including greenhouse gas emissions and other air pollutants, as well as negative effects on water quality and land use. These impacts must be carefully considered in any evaluation of the economic and social importance of coal.

Summary of Key Points

Here are some key points about coal:

Coal is a fossil fuel that is formed from the remains of ancient plants that lived millions of years ago.

There are four main types of coal: lignite, sub-bituminous, bituminous, and anthracite, each with different properties and uses.

Coal is an abundant and relatively cheap source of energy, making it an important fuel for power generation, heating, and industrial processes.

Coal mining can have significant environmental and social impacts, including land disturbance, water pollution, and health risks for workers and nearby communities.

Efforts are underway to develop cleaner coal technologies, such as carbon capture and storage, to reduce the environmental impact of coal use.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.

Kopp, O. C. (2020, November 13). coal. Encyclopedia Britannica. https://www.britannica.com/science/coal-fossil-fuel

Wikipedia contributors. (2021, October 26). Coal. In Wikipedia, The Free Encyclopedia. Retrieved 09:57, November 1, 2021, from https://en.wikipedia.org/w/index.php?title=Coal&oldid=1051971849

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3,245FansLike22,909FollowersFollow1,070SubscribersSubscribe Table of ContentsCoal ClassificationHistorical significanceChemical compositionPhysical propertiesMining and processing of coalExtraction techniques (surface and underground mining)Processing methods (cleaning, crushing, grading, etc.)Coal CompositionCoal FormationOccurrence of CoalCoal Characteristics and PropertiesIntensityPorosityReflectivityOther featuresEconomic and social importance of coalSummary of Key PointsReferences

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Coal

Coal

 

Coal is defined as a sedimentary rock composed predominantly of solid organic materials with a greater or lesser proportion of mineral matter. It is derived from the accumulation of plant remains in sedimentary basins, and is altered to solid rock by heat and pressure applied during the basin’s development. Its quality varies according to the content of ash, impurities, and volatile matter which decreases as coal rank gets higher. It has a natural dark brown to black, graphite-like appearance and is primarily used as a fuel. Types of coal according to increasing rank (in terms of hardness, purity and heating value) are peat, lignite, subbituminous, bituminous and anthracite.

 

Worldwide, coal is a sought-after energy source. It has the largest reserve and is often the cheapest of the fuel options. Now that clean coal technologies are available, the demand for coal has remained steady despite the current stringent standard on environmental concerns. The Philippines is largely a coal consuming country with coal having the highest contribution to the power generation mix at 58% in 2021. But, local demand for coal is not limited to power generation. In 2021, the cement industry utilized 6.66% of the country’s coal supply, 7.08% went to other industries such as alcohol, sinter, rubber boots, paper and chemical manufacturing, fertilizer production and smelting processes.

 

The coal industry has never been so robust than these past years. From a historical yearly average of 1.5 million MT, local coal production began increasing at a steady rate since 2002. Within a span of 19 years, annual coal production has reached to as high as 15.3 million MT in 2019 and 14.3 million MT in 2021. Consumption likewise, increase steadily as new coal-fired power plants are installed and industries switch to coal because of the highly volatile price of oil.

 

Potentials

 

The Philippines has a vast potential for coal resources just awaiting full exploration and development to contribute to the attainment of the country's energy self- sufficiency program. As of 31 December 2020, our in-situ coal reserves amount to 315 million metric tons or 13.29% of the country's total coal resource potential of 2.37 billion metric tons.

 

Continuing Exploration and Development Program

 

Recent upswing development in the coal industry encouraged increased interest in coal exploration. There are 21 Coal Operating Contracts in the Development and Production phase, 6 Coal Operating Contracts in the Exploration phase, and 47 small-scale coal mining operators as of May 2022.

 

To supplement these exploration activities, the Coal and Nuclear Minerals Division (CNMD) is actively implementing the Philippine Conventional Energy Contracting Program (PCEPC) for Coal.

 

Investment Opportunities

 

It is but very timely to invest in coal facilities as the price of oil continues to rise with coal being still the cheapest option with abundant supply worldwide. For private companies, the key investment opportunities in the coal sector are (1) the setting-up of coal preparation plants to upgrade the quality of Philippine coals and make them acceptable to current coal users; (2) the expansion of production volumes of higher-rank Philippine coals which can be used without upgrading and/or blending with high-quality imported coal; (3) the introduction of clean coal technologies (i.e., circulating fluidized bed combustion) to ensure utilization of Philippine coals with minimal adverse effects on the environment; and (4) the putting-up of mine-mouth power plants designed to utilize the abundant low-rank coals that have no alternative markets.

 

Introduction of Clean Coal Technologies

 

In the downstream coal sector, particularly the utilization of coal for power generation and cement manufacturing companies, it can introduce clean coal technologies in existing and future power/cement plants to minimize adverse effects of coal on the environment and still be competitive, are definitely welcome.

 

Some Clean Coal Technologies presently being utilized are:

 

(1) Coal washing/preparation – This is a wet method of cleaning low-rank coal by separating coal from the wastes using their specific gravity differences. This method reduces ash and sulfur contents of coal and increases its heating value.

 

(2) Circulating Fluidized Bed (CFB) Combustion Technology – Crushed coal is fed with crushed limestone or dolomite to a fluidized bed furnace with a bed material (silica sand). At a controlled furnace temperature of 800-950 C, the limestone or dolomite due to its reactive CaO or MgO absorbs and reacts with SOx gas, thereby reducing the formation of this gas. At the said temperature, NOx emission is also controlled.

 

(3) Flue Gas Desulfurizer (FGD) - This equipment is installed to control the SOx emissions by spraying or scrubbing the flue gas with limestone slurry whose MgO content absorbs and reacts with SOx to form a stable substance (gypsum).

 

Setting-Up Mine-Mouth Power Plants.

 

Finally, companies wanting to get involved in the Philippine coal sector in a major way are invited to consider putting up coal-fired mine-mouth power plants in the country's major undeveloped coal areas through joint ventures with existing holders of coal operating contracts. As in the case of natural gas and geothermal, private companies are allowed to put up their own plants at the mine site to assure a market for the coal by selling electricity to the grid. 

 

Specific programs, forecast and coal project schedules are found in the Philippine Energy Plan. 

 

Incentives

 

The current coal operating contract (COC) system gives the following incentives to contractors:

• Exemption from all taxes except income tax

• Exemption from payment of tariff duties and compensating tax on importation of machinery/equipment/spare parts/materials required for the coal operations

• Allow entry of alien technical personnel

• The right of ingress to and egress from the COC areas

• Recovery of operating expenses

 

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Coal: Anthracite, Bituminous, Coke, Pictures, Formation, Uses

Coal: Anthracite, Bituminous, Coke, Pictures, Formation, Uses

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Home » Rocks » Sedimentary Rocks » Coal

Coal

What Is Coal and How Does It Form?

Article by: Hobart M. King, PhD, RPG

Bituminous Coal: Bituminous coal is typically a banded sedimentary rock. In this photo you can see bright and dull bands of coal material oriented horizontally across the specimen. The bright bands are well-preserved woody material, such as branches or stems. The dull bands can contain mineral material washed into the swamp by streams, charcoal produced by fires in the swamp, or degraded plant materials. This specimen is approximately three inches across (7.5 centimeters). Photo by the West Virginia Geological and Economic Survey.

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What is Coal?

Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment. Coal is a combustible rock and, along with oil and natural gas, it is one of the three most important fossil fuels. Coal has a wide range of uses; the most important use is for the generation of electricity.

Coal-Forming Environments: A generalized diagram of a swamp, showing how water depth, preservation conditions, plant types, and plant productivity can vary in different parts of the swamp. These variations will yield different types of coal. Illustration by the West Virginia Geological and Economic Survey.

Peat: A mass of recently accumulated to partially carbonized plant debris. This material is on its way to becoming coal, but its plant debris source is still easily recognizable.

Rock & Mineral Kits: Get a rock, mineral, or fossil kit to learn more about Earth materials. The best way to learn about rocks is to have specimens available for testing and examination.

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How Does Coal Form?

Coal forms from the accumulation of plant debris, usually in a swamp environment. When a plant dies and falls into the swamp, the standing water of the swamp protects it from decay. Swamp waters are usually deficient in oxygen, which would react with the plant debris and cause it to decay. This lack of oxygen allows the plant debris to persist. In addition, insects and other organisms that might consume the plant debris on land do not survive well under water in an oxygen-deficient environment.

To form the thick layer of plant debris required to produce a coal seam, the rate of plant debris accumulation must be greater than the rate of decay. Once a thick layer of plant debris is formed, it must be buried by sediments such as mud or sand. These are typically washed into the swamp by a flooding river. The weight of these materials compacts the plant debris and aids in its transformation into coal. About ten feet of plant debris will compact into just one foot of coal.

Plant debris accumulates very slowly. So, accumulating ten feet of plant debris will take a long time. The fifty feet of plant debris needed to make a five-foot thick coal seam would require thousands of years to accumulate. During that long time, the water level of the swamp must remain stable. If the water becomes too deep, the plants of the swamp will drown, and if the water cover is not maintained the plant debris will decay. To form a coal seam, the ideal conditions of perfect water depth must be maintained for a very long time.

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If you are an astute reader you are probably wondering: "How can fifty feet of plant debris accumulate in water that is only a few feet deep?" The answer to that question is the primary reason that the formation of a coal seam is a highly unusual occurrence. It can only occur under one of two conditions: 1) a rising water level that perfectly keeps pace with the rate of plant debris accumulation; or, 2) a subsiding landscape that perfectly keeps pace with the rate of plant debris accumulation. Most coal seams are thought to have formed under condition #2 in a delta environment. On a delta, large amounts of river sediments are being deposited on a small area of Earth's crust, and the weight of those sediments causes the subsidence.

For a coal seam to form, perfect conditions of plant debris accumulation and perfect conditions of subsidence must occur on a landscape that maintains this perfect balance for a very long time. It is easy to understand why the conditions for forming coal have occurred only a small number of times throughout Earth's history. The formation of a coal requires the coincidence of highly improbable events.

Rank

(From Lowestto Highest)

Properties

Peat

A mass of recently accumulated to partially carbonized plant debris. Peat is an organic sediment. Burial, compaction, and coalification will transform it into coal, a rock. It has a carbon content of less than 60% on a dry ash-free basis.

Lignite

Lignite is the lowest rank of coal. It is a peat that has been transformed into a rock, and that rock is a brown-black coal. Lignite sometimes contains recognizable plant structures. By definition it has a heating value of less than 8300 British Thermal Units per pound on a mineral-matter-free basis. It has a carbon content of between 60 and 70% on a dry ash-free basis. In Europe, Australia, and the UK, some low-level lignites are called "brown coal."

Sub Bituminous

Sub bituminous coal is a lignite that has been subjected to an increased level of organic metamorphism. This metamorphism has driven off some of the oxygen and hydrogen in the coal. That loss produces coal with a higher carbon content (71 to 77% on a dry ash-free basis). Sub bituminous coal has a heating value between 8300 and 13000 British Thermal Units per pound on a mineral-matter-free basis. On the basis of heating value, it is subdivided into sub bituminous A, sub bituminous B, and sub bituminous C ranks.

Bituminous

Bituminous is the most abundant rank of coal. It accounts for about 50% of the coal produced in the United States. Bituminous coal is formed when a sub bituminous coal is subjected to increased levels of organic metamorphism. It has a carbon content of between 77 and 87% on a dry ash-free basis and a heating value that is much higher than lignite or sub bituminous coal. On the basis of volatile content, bituminous coals are subdivided into low-volatile bituminous, medium-volatile bituminous, and high-volatile bituminous. Bituminous coal is often referred to as "soft coal"; however, this designation is a layman's term and has little to do with the hardness of the rock.

Anthracite

Anthracite is the highest rank of coal. Unlike other types of coal, it is usually considered to be a metamorphic rock. It has a carbon content of over 87% on a dry ash-free basis. Anthracite coal generally has the highest heating value per ton on a mineral-matter-free basis. It is often subdivided into semi-anthracite, anthracite, and meta-anthracite on the basis of carbon content. Anthracite is often referred to as "hard coal"; however, this is a layman's term and has little to do with the hardness of the rock.

Anthracite coal: Anthracite is the highest rank of coal. It has a bright luster and breaks with a semi-conchoidal fracture.

What is Coal "Rank"?

Plant debris is a fragile material compared to the mineral materials that make up other rocks. As plant debris is exposed to the heat and pressure of burial, it changes in composition and properties. The "rank" of a coal is a measure of how much change has occurred. Sometimes the term "organic metamorphism" is used for this change.

Based upon composition and properties, coals are assigned to a rank progression that corresponds to their level of organic metamorphism. The basic rank progression is summarized in the table here.

Lignite: The lowest rank of coal is "lignite." It is peat that has been compressed, dewatered, and lithified into a rock. It often contains recognizable plant structures.

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What are the Uses of Coal?

Electricity production is the primary use of coal in the United States. Most of the coal mined in the United States is transported to a power plant, crushed to a very small particle size, and burned. Heat from the burning coal is used to produce steam, which turns a generator to produce electricity. Most of the electricity consumed in the United States is made by burning coal.

Coal-Fired Power Plant: Photo of a power plant where coal is burned to produce electricity. The three large stacks are cooling towers where water used in the electricity generation process is cooled before reuse or release to the environment. The emission streaming from the right-most stack is water vapor. The combustion products from burning the coal are released into the tall, thin stack on the right. Within that stack are a variety of chemical sorbents to absorb polluting gases produced during the combustion process. Image copyright iStockphoto / Michael Utech.

Coal has many other uses. It is used as a source of heat for manufacturing processes. For example, bricks and cement are produced in kilns heated by the combustion of a jet of powdered coal. Coal is also used as a power source for factories. There it is used to heat steam, and the steam is used to drive mechanical devices. A few decades ago most coal was used for space heating. Some coal is still used that way, but other fuels and coal-produced electricity are now used instead.

Coke production remains an important use of coal. Coke is produced by heating coal under controlled conditions in the absence of air. This drives off some of the volatile materials and concentrates the carbon content. Coke is then used as a high-carbon fuel for metal processing and other uses where an especially hot-burning flame is needed.

Coal is also used in manufacturing. If coal is heated the gases, tars, and residues produced can be used in a number of manufacturing processes. Plastics, roofing, linoleum, synthetic rubber, insecticides, paint products, medicines, solvents, and synthetic fibers all include some coal-derived compounds. Coal can also be converted into liquid and gaseous fuels; however, these uses of coal are mainly experimental and done on a small scale.

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Frequently Asked Questions

Energy

What is coal?

Coal is a sedimentary deposit composed predominantly of carbon that is readily combustible. Coal is black or brownish-black, and has a composition that (including inherent moisture) consists of more than 50 percent by weight and more than 70 percent by volume of carbonaceous material. It is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time.

Coal is found all over the world—including the United States—predominantly in places where prehistoric forests and marshes existed before being buried and compressed over millions of years. Some of the largest coal deposits are located in the Appalachian basin in the eastern U.S., the Illinois basin in the mid-continent region, and throughout numerous basins and coal fields in the western U.S. and Alaska.

Learn more:  

Coal – A Complex Natural Resource 

U.S. Coal Resources and Reserves Assessment 

 

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What are the types of coal?

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon-rich, and harder material. The four ranks are: Anthracite : The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of...

link

What are the types of coal?

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon-rich, and harder material. The four ranks are: Anthracite : The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of...

Learn More

link

What is coal used for?

Coal is primarily used as fuel to generate electric power in the United States. In coal-fired power plants, bituminous coal, subbituminous coal, or lignite is burned. The heat produced by the combustion of the coal is used to convert water into high-pressure steam, which drives a turbine, which produces electricity. In 2019, about 23 percent of all electricity in the United States was generated by...

link

What is coal used for?

Coal is primarily used as fuel to generate electric power in the United States. In coal-fired power plants, bituminous coal, subbituminous coal, or lignite is burned. The heat produced by the combustion of the coal is used to convert water into high-pressure steam, which drives a turbine, which produces electricity. In 2019, about 23 percent of all electricity in the United States was generated by...

Learn More

link

What is the biggest coal deposit in the United States?

The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal resources, 162 billion short tons of recoverable coal resources, and 25 billion short tons of economic coal resources (also called reserves) in 2013. The coal in the Powder River Basin is subbituminous in rank. Large coal deposits can also...

link

What is the biggest coal deposit in the United States?

The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal resources, 162 billion short tons of recoverable coal resources, and 25 billion short tons of economic coal resources (also called reserves) in 2013. The coal in the Powder River Basin is subbituminous in rank. Large coal deposits can also...

Learn More

link

Which country has the most coal?

As of January 2020, the United States has the largest recoverable coal reserves with an estimated 252 billion short tons of coal remaining, according to the U.S. Energy Information Administration . Learn more: U.S. Coal Resources and Assessment World Coal Quality Inventory

link

Which country has the most coal?

As of January 2020, the United States has the largest recoverable coal reserves with an estimated 252 billion short tons of coal remaining, according to the U.S. Energy Information Administration . Learn more: U.S. Coal Resources and Assessment World Coal Quality Inventory

Learn More

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Cannel Coal

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September 27, 2017

Assessing U.S. coal resources and reserves

The U.S. Coal Resources and Reserves Assessment Project, as part of the U.S. Geological Survey (USGS) Energy Resources Program, conducts systematic, geology-based, regional assessments of significant coal beds in major coal basins in the United States. These assessments detail the quantity, quality, location, and economic potential of the Nation’s remaining coal resources and reserves and provide

Authors

Brian N. Shaffer

By

Energy Resources Program, Central Energy Resources Science Center

September 1, 2003

Coal-A complex natural resource: An overview of factors affecting coal quality and use in the United States With a contribution on coal quality and public health

No abstract available.

Authors

Stanley P. Schweinfurth, Robert B. Finkelman

January 1, 1983

World coal exploration and development

No abstract available.

Authors

Gordon H. Wood

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link

October 23, 2017

Assessments Evolved: USGS Coal Research in the 21st Century

Although often associated with helping fuel the Nation’s growth during the Industrial Revolution, coal is very much part of our space-age present. In...

Read Article

Related Content

FAQ

Label

link

What are the types of coal?

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon-rich, and harder material. The four ranks are: Anthracite : The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of...

link

What are the types of coal?

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon-rich, and harder material. The four ranks are: Anthracite : The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of...

Learn More

link

What is coal used for?

Coal is primarily used as fuel to generate electric power in the United States. In coal-fired power plants, bituminous coal, subbituminous coal, or lignite is burned. The heat produced by the combustion of the coal is used to convert water into high-pressure steam, which drives a turbine, which produces electricity. In 2019, about 23 percent of all electricity in the United States was generated by...

link

What is coal used for?

Coal is primarily used as fuel to generate electric power in the United States. In coal-fired power plants, bituminous coal, subbituminous coal, or lignite is burned. The heat produced by the combustion of the coal is used to convert water into high-pressure steam, which drives a turbine, which produces electricity. In 2019, about 23 percent of all electricity in the United States was generated by...

Learn More

link

What is the biggest coal deposit in the United States?

The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal resources, 162 billion short tons of recoverable coal resources, and 25 billion short tons of economic coal resources (also called reserves) in 2013. The coal in the Powder River Basin is subbituminous in rank. Large coal deposits can also...

link

What is the biggest coal deposit in the United States?

The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal resources, 162 billion short tons of recoverable coal resources, and 25 billion short tons of economic coal resources (also called reserves) in 2013. The coal in the Powder River Basin is subbituminous in rank. Large coal deposits can also...

Learn More

link

Which country has the most coal?

As of January 2020, the United States has the largest recoverable coal reserves with an estimated 252 billion short tons of coal remaining, according to the U.S. Energy Information Administration . Learn more: U.S. Coal Resources and Assessment World Coal Quality Inventory

link

Which country has the most coal?

As of January 2020, the United States has the largest recoverable coal reserves with an estimated 252 billion short tons of coal remaining, according to the U.S. Energy Information Administration . Learn more: U.S. Coal Resources and Assessment World Coal Quality Inventory

Learn More

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Label

link

Cannel Coal

link

Lignite Coal

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Anthracite Coal

link

Cannel Coal

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Peacock Coal

Publications

Label

September 27, 2017

Assessing U.S. coal resources and reserves

The U.S. Coal Resources and Reserves Assessment Project, as part of the U.S. Geological Survey (USGS) Energy Resources Program, conducts systematic, geology-based, regional assessments of significant coal beds in major coal basins in the United States. These assessments detail the quantity, quality, location, and economic potential of the Nation’s remaining coal resources and reserves and provide

Authors

Brian N. Shaffer

By

Energy Resources Program, Central Energy Resources Science Center

September 1, 2003

Coal-A complex natural resource: An overview of factors affecting coal quality and use in the United States With a contribution on coal quality and public health

No abstract available.

Authors

Stanley P. Schweinfurth, Robert B. Finkelman

January 1, 1983

World coal exploration and development

No abstract available.

Authors

Gordon H. Wood

News

Label

link

October 23, 2017

Assessments Evolved: USGS Coal Research in the 21st Century

Although often associated with helping fuel the Nation’s growth during the Industrial Revolution, coal is very much part of our space-age present. In...

Read Article

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Coal - World Distribution, Fossil Fuel, Energy | Britannica

Coal - World Distribution, Fossil Fuel, Energy | Britannica

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coal

Table of Contents

coal

Table of Contents

IntroductionHistory of the use of coalIn ancient timesIn EuropeIn the New WorldModern utilizationCoal as an energy sourceConversionProblems associated with the use of coalHazards of mining and preparationPollution from coal utilizationCoal types and ranksCoal typesMaceralsCoal rock typesBanded and nonbanded coalsRanking by coalificationHydrocarbon contentChemical content and propertiesOrigin of coalCoal-forming materialsPlant matterThe fossil recordFormation processesPeatCoalificationStructure and properties of coalOrganic compoundsPropertiesDensityPorosityReflectivityOther propertiesWorld distribution of coalGeneral occurrenceResources and reserves

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Earth Sciences

World distribution of coal General occurrence coal depositsCoal is a widespread resource of energy and chemicals. Although terrestrial plants necessary for the development of coal did not become abundant until Carboniferous time (358.9 million to 298.9 million years ago), large sedimentary basins containing rocks of Carboniferous age and younger are known on virtually every continent, including Antarctica (not shown on the map). The presence of large coal deposits in regions that now have arctic or subarctic climates (such as Alaska and Siberia) is due to climatic changes and to the tectonic motion of crustal plates that moved ancient continental masses over Earth’s surface, sometimes through subtropical and even tropical regions. Coal is absent in some areas (such as Greenland and much of northern Canada) because the rocks found there predate the Carboniferous Period and these regions, known as continental shields, lacked the abundant terrestrial plant life needed for the formation of major coal deposits. Resources and reserves coal mineSchematic diagram of an underground coal mine, showing surface facilities, access shafts, and room-and-pillar and longwall mining methods. (more)World coal reserves and resources are difficult to assess. Although some of the difficulty stems from the lack of accurate data for individual countries, two fundamental problems make these estimates difficult and subjective. The first problem concerns differences in the definition of terms such as proven reserves (generally only those quantities that are recoverable) and geological resources (generally the total amount of coal present, whether or not recoverable at present). The proven reserves for any commodity should provide a reasonably accurate estimate of the amount that can be recovered under existing operating and economic conditions. To be economically mineable, a coal bed must have a minimum thickness (about 0.6 metre; 2 feet) and be buried less than some maximum depth (roughly 2,000 metres; 6,600 feet) below Earth’s surface. These values of thickness and depth are not fixed but change with coal quality, demand, the ease with which overlying rocks can be removed (in surface mining) or a shaft sunk to reach the coal seam (in underground mining), and so forth. The development of new mining techniques may increase the amount of coal that can be extracted relative to the amount that cannot be removed. For example, in underground mining (which accounts for about 60 percent of world coal production), conventional mining methods leave behind large pillars of coal to support the overlying rocks and recover only about half of the coal present. On the other hand, longwall mining, in which the equipment removes continuous parallel bands of coal, may recover nearly all the coal present. The second problem, which concerns the estimation of reserves, is the rate at which a commodity is consumed. When considering the worldwide reserves of coal, the number of years that coal will be available may be more important than the total amount of coal resources. At present rates of consumption, world coal reserves should last more than 300–500 years. A large amount of additional coal is present in Earth but cannot be recovered at this time. These resources, sometimes called “geologic resources,” are even more difficult to estimate, but they are thought to be as much as 15 times greater than the amount of proven reserves.

World proved reserves of coal*

country/region

million metric tons

share of world total (%)

anthracite and bituminous

subbituminous and lignite

total

*At end of 2016. Proved reserves of coal are generally taken to be those quantities that geological and engineering information indicates with reasonable certainty can be recovered in the future from known deposits under existing economic and operating conditions.

**Less than 0.05%.

Source: BP p.l.c., BP Statistical Review of World Energy (June 2017).

Canada

4,346

2,236

6,582

0.6

Mexico

1,160

51

1,211

0.1

United States

221,400

30,182

251,582

22.1

Total North America

226,906

32,469

259,375

22.8

Brazil

1,547

5,049

6,596

0.6

Colombia

4,881

—

4,881

0.4

Venezuela

731

—

731

0.1

Other South and Central American countries

1,784

24

1,808

0.2

Total South and Central America

8,943

5,073

14,016

1.2

Bulgaria

192

2,174

2,366

0.2

Czech Republic

1,103

2,573

3,676

0.3

Germany

12

36,200

36,212

3.2

Greece

—

2,876

2,876

0.3

Hungary

276

2,633

2,909

0.3

Kazakhstan

25,605

—

25,605

2.2

Poland

18,700

5,461

24,161

2.1

Romania

11

280

291

**

Russian Federation

69,634

90,730

160,364

14.1

Serbia

402

7,112

7,514

0.7

Spain

868

319

1,187

0.1

Turkey

378

10,975

11,353

1.0

Ukraine

32,039

2,336

34,375

3.0

United Kingdom

70

—

70

**

Uzbekistan

1,375

—

1,375

0.1

Other European and Eurasian countries

2,618

5,172

7,790

0.7

Total Europe and Eurasia

153,283

168,841

322,124

28.3

South Africa

9,893

—

9,893

0.9

Zimbabwe

502

—

502

**

Middle East

1,203

—

1,203

0.1

Other African countries

2,756

66

2,822

0.2

Total Africa and Middle East

14,354

66

14,420

1.3

Australia

68,310

76,508

144,818

12.7

China

230,004

14,006

244,010

21.4

India

89,782

4,987

94,769

8.3

Indonesia

17,326

8,247

25,573

2.2

Japan

340

10

350

**

Mongolia

1,170

1,350

2,520

0.2

New Zealand

825

6,750

7,575

0.7

Pakistan

207

2,857

3,064

0.3

South Korea

326

—

326

**

Thailand

—

1,063

1,063

0.1

Vietnam

3,116

244

3,360

0.3

Other Asia-Pacific countries

1,322

646

1,968

0.2

Total Asia-Pacific

412,728

116,668

529,396

46.5

Total world

816,214

323,117

1,139,331

100.0

U.S. coal depositsCoal-bearing areas of the conterminous United States.(more)The quantities of proven coal reserves are typically shown in millions of tons of coal equivalent (MTCE). One ton of coal equivalent equals 1 metric ton (2,205 pounds) of coal with a heating value of 29.3 megajoules per kilogram (12,600 British thermal units per pound). These values suggest that the United States has the largest amount of recoverable coal. Nearly 75 percent of the world’s recoverable coal resources are controlled by five countries: the United States (about 22 percent), Russia (about 15 percent), Australia (14 percent), China (about 13 percent), and India (about 10 percent). Otto C. Kopp The Editors of Encyclopaedia Britannica

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Coal

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Fast FactsView our summary of key facts and information.

Before You Watch Our LectureMaximize your learning experience by reviewing these carefully curated videos and readings we assign to our students.

Our LectureWatch the Stanford course lecture.

Additional ResourcesFind out where to explore beyond our site.

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Fast Facts AboutCoal

Principal Energy Uses: Electricity, HeatForm of Energy: Chemical

Coal is the most carbon-intensive fossil fuel and a huge contributor to climate change, air pollution, and land disruption. It is a combustible, rock-like hydrocarbon mined from the earth that is burned to convert chemical energy to heat. A widely-available and non-renewable resource, coal is still the second-largest source of energy in the world and the most-used fuel for electricity generation.

Significance

Energy Mix

27% of world (#2 resource)

11% of US (#3 resource)

Electricity Generation

35% of world (#1 resource)

22% of US (#2 resource)

Global Coal Use

Electricity: 66%

Heat: 18%

Steel making: 15%

Global Demand

Modest increase:

⬆2%

(2016-2021)

World

Largest Proven Reserves

USA 22%

Largest Producer

China 51%

Largest Consumer

China 55%

U.S.

Largest Proven Reserves

Montana 25%

Largest Producer

Wyoming 41%

Largest Consumer

Texas 8%

Global Trade

Amount Traded

17%

of global consumption

Largest Exporters

Indonesia 31%

Australia 29%

Largest Importer

China 23% 

Drivers

Abundant

Relatively low private costs (but note that high social and environmental costs are not factored into the price)

Easy to store

Sunk cost of infrastructure

Historical dependence of some communities on coal industry

Domestic availability of coal

Barriers

Many externalities: greenhouse gas emissions, heavy metals (e.g., mercury), air pollution (e.g., SO2, NOx), water pollution, coal dust, coal ash, high water use, land subsidence

Health and safety of mine workers, public health impacts on local communities

Regulations are increasing

New coal plants no longer cost competitive in many major markets

Coal-fired power plants are inflexible, may be hard to integrate with increasing renewables

Legacy issues such as abandoned mines and leftover coal ash that require ongoing treatment and management

Climate Impact: High

The most carbon-intensive fossil fuel energy source

Escaping coal bed methane is also a potent greenhouse gas

Environmental Impact: High

Combustion releases air pollutants (e.g., mercury and SO2)

Extraction/mining and coal ash harm landscapes and water quality

Surface mining and mountaintop removal are particularly damaging

Sources

Printable PDF

Updated April 2023

Before You Watch Our Lecture onCoal

We assign videos and readings to our Stanford students as pre-work for each lecture to help contextualize the lecture content. We strongly encourage you to review the Essential readings and videos before watching our lecture on Coal. Include selections from the Optional and Useful list based on your interests and available time.

Essential

How Coal Made Us Rich — And Why It Needs to Go. DW Planet A. February 19, 2021. (8 min)Coal’s history, it’s impact on the environment and society, and why it is hard to stop using it.

This Town Powered America for Decades. What Do We Owe Them? CNN Opinion. Ewen, McKenna. March 16, 2021. (9 minutes)About Gillette, Wyoming – the main supplier of coal to the U.S. for decades – and the decline of the coal industry.

How Coal Mining is Displacing Millions. DW Planet A. April 3, 2021. (12 min)Large-scale open pit mining impacts habitat and communities in India.

The Land of Mountaintop Removal. Smithsonian Channel. August 6, 2013. (3 min)Visuals and statistics about the impact mountain top removal has had on the Appalachian Mountains and it’s communities.

How Huawei’s Use of 5G and AI Is Transforming China’s Coal Mining Industry. South China Morning Post. May 12, 2023. (4 min)Showcases the advancements in mechanization and automation of coal mining.

The Danger of Coal Ash, the Toxic Dust the Fossil Fuel Leaves Behind. PBS NewsHour. August 14, 2019. (10 min)Coal ash is a toxic waste that is left behind after burning coal and is a legacy environmental and health hazard.

Closing the Coal Ash Loophole. Grist. June 20, 2023. (8 pages)Insight into recent coal ash regulations and how coal ash impacts the health of first responders and communities.

How Steel Might Finally Kick Its Coal Habit. Wired. February 6, 2021. (4 pages)An overview of different technologies to produce steel without coal.

Optional and Useful

Coal. NEED.org. 2021. (4 pages)Great overview of coal.

Could Coal Waste Be Used to Make Sustainable Batteries? The New Yorker. August 26, 2022. (5 pages)Can we clean up acid mine drainage by extracting the metals we need for batteries?

Climate Change Challenges: India's Need for Coal. BBC News. September 22, 2021. (3 min)Spotlight on India’s challenges moving away from coal.

In Afghanistan, Coal Mining Relies on the Labor of Children. NPR. December 31, 2022. (5 min)Spotlight on child labor for coal mining. 

The Shocking Danger of Mountaintop Removal – And Why It Must End | Michael Hendryx. TED. June 1, 2018. (14 min)More information about the impact of mountaintop removal for coal mining in the Appalachian Mountains.

Federal Court Reinstates Ban on New Coal Sales on Public Land. The Washington Post. August 12, 2022. (2 pages)Short article on recent reinstatement of the moratorium to issue new coal leases on federal land.

North Dakota Officials Block Wind Power in Effort to Save Coal. NPR. February 25, 2021. (3 min)Example of the tension between coal industry and renewables industry in local governments.

Mining Methods. KGS. January 28, 2009. (2 pages)Concisely describes how coal mining works.

The Big One: Coal Dragline. Edmonton Journal. June 7, 2010. (3 min)The equipment used in open pit coal mining is huge.

Poisonous Ponds: Tackling Toxic Coal Ash Great Lakes Now. September 6, 2022. (27 min)

The TVA is Dumping a Mountain of Coal Ash in Black South Memphis. The Washington Post. August 19, 2022. (11 pages)Spotlight on the racial inequities with plans to relocate coal ash.

Biden Administration Takes Action on Toxic Coal Ash Plaguing Kentucky and Indiana Courier Journal. January 17, 2022. (3 pages)Describes how the Biden administration is taking action on some of the extension applications filed to comply with the 2015 regulations on coal ash rules. Shows the complexities in enacting regulation.

The Coal Plant Next Door. ProPublica. March 22, 2021. (2 pages)An example of the contamination that can come from not properly disposing of coal ash.

Our Lecture onCoal

This is our Stanford University Understand Energy course lecture on coal. We strongly encourage you to watch the full lecture to understand coal as an energy system and to be able to put this complex topic into context. For a complete learning experience, we also encourage you to watch / read the Essential videos and readings we assign to our students before watching the lecture.

Presented by: Diana Gragg, PhD; Core Lecturer, Civil and Environmental Engineering, Stanford University; Explore Energy Managing Director, Precourt Institute for EnergyRecorded on: April 13, 2022   Duration: 70 minutes

Table of Contents

(Clicking on a timestamp will take you to YouTube.)0:00 Introduction to Coal11:36 What is the Significance of Coal?17:09 What is Coal?20:51 How Does the Coal Industry Work (From Mine to Use)?42:07 What are the Environmental and Social Impacts of Coal?1:01:31 How is the Future of Coal Changing?

Lecture slides available upon request.

Embed Code

Additional Resources AboutCoal

Stanford University

Energy Science and Engineering Department   Sally Benson - Carbon capture and storage Freeman Spogli Institute for International StudiesMark Thurber - Energy policy, carbon marketsDavid Victor - Coal, energy policy, climate impact

Government and International Organizations

International Energy Agency (IEA) CoalUS Energy Information Administration (EIA) Coal, Coal ExplainedUS Energy Information Administration (EIA) Today in Energy CoalUS Environmental Protection Agency (EPA) Coal Ash (Coal Combustion Residuals)

Industry Organizations

World Coal AssociationGlobal CCS InstituteAmerican Coal Ash Association

History

Coal: A Human History - Barbara Freese (2003) find at a library near you

Other Resources

Energy Institute Statistical Review of World Energy Coal Chapter (great resource for global coal production and consumption data)National Energy Education Development (NEED) Coal

Next Topic: Introduction to Nuclear Energy Other Energy Topics to Explore

Fast Facts SourcesEnergy Mix: World 2019 (“Global share of total energy supply by source, 2019” in World Energy Balances, IEA 2021). For comparison, also see “Total primary energy supply by fuel, 1971 and 2019” in World Energy Balances, IEA 2021), U.S. 2021 (“Table 1.3 Primary Energy Consumption by Source” in Monthly Energy Review, EIA 2022. For a 2020 summary, see “U.S. total energy statistics”)Electricity Mix: World 2020 (“Share of unabated coal-fired power generation 2020” in Coal, IEA 2022),  U.S. 2021 (Table 7.2a Electricity net generation: Total (all sectors) and 10.6 Solar electricity net generation in Monthly Energy Review, EIA 2022)Demand, estimated: World 2021 (Coal power’s sharp rebound is taking it to a new record in 2021, threatening net zero goals, IEA 2021)Largest Reserves: U.S. 2021 Coal explained: How much coal is left, EIA 2021Largest Producer: China 2021 Coal and Coke Production, EIA 2021)Largest Consumer: China 2021 (Coal and Coke Consumption, EIA 2021)Largest Reserves: Montana 2021 (Coal explained: How much coal is left, EIA 2021)Largest Producer: Wyoming 2021 (Coal Data Browser, EIA 2021Largest Consumer: Texas 2021 (Coal Data Browser, EIA 2021)Total Traded: 17% of Global Consumption in 2020 (Coal 2021: Analysis and forecast to 2024) (PDF)Largest Exporter: In 2020, Indonesia 2020 by weight: 405 Mt, followed by Australia: 372 Mt. (Coal Information: Overview, Exports, IEA 2022). However, Australia is generally the largest exporter by energy content and value of exports (Coal Information: Overview, Trade, IEA 2022).Largest Importer: China 2020: 314 Mt (Coal 2021: Analysis and forecast to 2024) (PDF)More details available on request.Back to Fast Facts

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Energy system

Fossil Fuels

Coal

Coal

Overview

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Programmes

Why is it important?

Coal still supplies just over a third of global electricity generation even though it is the most carbon-intensive fossil fuel. While coal is being gradually replaced in most countries for power generation, it will continue to play a crucial role in iron and steel production until newer technologies are available.

Where do we need to go?

The IEA’s Net Zero Emissions by 2050 Scenario envisions that all unabated coal generation ends by 2040.

What are the challenges?

With energy demand continuing to grow, many countries feel they have little choice but to continue generating power with coal, while some industrial processes require coal’s carbon content. To have a place as a cleaner energy source in the decades to come, governments and the coal industry need to develop and deploy less polluting and more efficient technologies, including but not limited to carbon capture, utilisation and storage (CCUS).

Why is it important?

Chevron down

Coal still supplies just over a third of global electricity generation even though it is the most carbon-intensive fossil fuel. While coal is being gradually replaced in most countries for power generation, it will continue to play a crucial role in iron and steel production until newer technologies are available.

Where do we need to go?

Chevron down

The IEA’s Net Zero Emissions by 2050 Scenario envisions that all unabated coal generation ends by 2040.

What are the challenges?

Chevron down

With energy demand continuing to grow, many countries feel they have little choice but to continue generating power with coal, while some industrial processes require coal’s carbon content. To have a place as a cleaner energy source in the decades to come, governments and the coal industry need to develop and deploy less polluting and more efficient technologies, including but not limited to carbon capture, utilisation and storage (CCUS).

Latest findings

Global coal consumption, 2000-2025

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Key strategies to reduce emissions of existing coal-fired plants in the in the Announced Pledges Scenario, 2022-2050

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0

1

Tracking Coal-fired Electricity Generation

Not on track

For the second year in a row, global coal-fired generation reached an all-time high in 2022, pushing CO2 emissions from coal-fired power plants to record levels and accounting for more than one-third of total electricity generation. High natural gas prices brought on by Russia’s invasion of Ukraine, coupled with extreme weather events, led many regions to turn to coal to secure electricity supplies. While the recent uptick in coal-fired generation is likely to be a temporary glitch in some regions, the overall trend is not on track with the Net Zero Emissions by 2050 Scenario, which calls for immediate reductions and a global decline in unabated coal‐fired generation of around 55% by 2030 compared to 2022 levels, and a complete phase-out by 2040. 

Tracking Clean Energy Progress 2023circle-arrow

Country and regional highlights

Chevron down

G7 countries recognise the need to end construction of new unabated coal-fired power generation

Countries and regions making notable progress include: In June 2023, China started operations at the Taizhou coal-fired power plant in the Jiangsu province, making it the third large-scale coal plant in the world to be equipped with carbon capture technology. In 2022, two new Just Energy Transition Partnerships (JETP) were announced in Indonesia (with a budget of USD 20 billion) and Viet Nam (USD 15.5 billion) to support decarbonisation efforts, including a just transition away from coal power. The Group of 7 (G7) Ministers of Climate, Energy and the Environment released a communiqué recognising the need to end the construction of new unabated coal-fired power generation, as called for in the NZE Scenario. At the end of 2021, Portugal closed its last remaining coal plant, becoming the fourth country in the European Union to do so after Belgium, Austria and Sweden. 

CO2 emissions

Chevron down

Global CO2 emissions from coal-fired power plants reached a new high in 2022

In 2022 CO2 emissions from coal-fired power plants grew by over 2% from the previous year, led in particular by increases in emerging market and developing economies (EMDEs) in Asia. Gas-to-coal switching in many regions was the main driver of this growth.  There are currently three coal power plants fitted with carbon capture, utilisation and storage (CCUS) in operation: Boundary Dam in Canada, and the Jinjie Power and Taizhou Power stations in China. The Taizhou project only recently started operation in June 2023 and has a capacity to capture 500 000 tonnes of CO2 each year. To get on track with the Net Zero Scenario, a global annual average reduction of emissions from coal-fired power plants of around 10% is needed through to 2030. 

Annual change in generation and CO2 emissions from unabated coal-fired power plants in the Net Zero Scenario, 2015-2030

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Energy

Chevron down

Coal-fired power generation continued its rise in 2022, driven by high gas prices and extreme weather events

In 2022 global coal-fired power generation rose by nearly 2%. Though the year-on-year change is far less than the 8% growth seen in 2021 as coal rebounded from Covid-19 lows, last year’s growth surpasses the nearly stagnant annual average growth seen in the five years preceding Covid-19. In absolute terms coal-fired generation continued its record-breaking streak for a second year in a row to around 10 400 TWh.  Asia Pacific: The largest absolute increases were in the Asia Pacific region. Extreme weather events and record-breaking natural gas prices led to higher coal use in electricity generation in the region, up nearly 3% from 2021 levels.  Coal-fired power generation in China grew by around 2% compared to 2021. China continues to add new coal-fired power plants to the grid, with 11 GW added in 2022, driven by energy security concerns, local economic interests, and tendency to pair dispatchable power sources with variable renewable sources.  In India, extreme heatwaves in the summer sharply increased electricity demand, which was primarily met by coal-fired generation. This led to a significant year-on-year increase of more than 8.5% in 2022, with a 20% increase in April through July compared to the same period in the previous year. Europe: Coal-fired generation increased in the European Union by nearly 7% amid low hydropower and nuclear output.  United States: Despite electricity demand increasing in the United States, coal-fired generation fell by almost 8% in 2022, reversing a 15% increase in 2021. The decrease in coal output was balanced by an increase in generation from natural gas and strong growth in renewables.  As a result, coal's share of total global generation remained around 36%. This is not on track with Net Zero Scenario, which calls for immediate reductions and a decline in unabated coal‐fired generation of around 55% by 2030 compared to 2022 levels, reducing coal to around 12% of global generation by 2030. 

Activity

Chevron down

The European Union and United Kingdom resorted to coal to temporarily increase security of supply amid Russia’s continued invasion of Ukraine

Russia's invasion of Ukraine and the ongoing energy crisis have forced the European Union and individual countries to take measures to enhance security of electricity supply amid low nuclear availability and tight gas markets. The United Kingdom and several countries in the European Union have decided – or are discussing plans – to bring reserve capacity back into the market or to postpone closure dates.  Germany accounts for most of the additional coal-fired capacity, with almost 10 GW for the 2022 and 2023 winter. In the Netherlands, the removal of the 35% production cap on coal-fired plants will add another 3.8 GW. Under confirmed plans, overall coal-fired capacity will increase by about 15% (19 GW) to 146 GW in the European Union and the United Kingdom combined. 

Policy

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Countries look to policies to transition coal-dependent regions and workers

In January 2022, Brazil passed legislation to establish a just energy transition programme for the coal-dependent state of Santa Catarina. Under the law, Brazil will phase-out coal-fired power generation by 2040 and set out a plan to prepare the region for the coal phase-out. In Poland, government and mining union delegates have signed a social contract that sets out a specific timetable for discontinuing hard coal mining at each production unit by the end of 2049.  In the Czech Republic, the European Commission approved the budget of CZK 40 billion (Czech Koruna) to transform the coal regions of Karlovy Vary Moravian-Silesian and Ústí with the aim of increasing the quality of life of its inhabitants, restoring the area, and developing clean energy.  

Status of coal phase-down pledges

As of July 2022, 75 countries had agreed to phase out coal or to not develop new unabated coal power plants, collectively accounting for 20% of current coal‐fired generation. Of these countries, 31 have incorporated coal phase‐out targets with specified dates in national plans, most are in Europe, and 80% are advanced economies. They include countries with a strong reliance on coal‐fired power such as Poland, the Czech Republic and Montenegro. As of August 2022, only four countries had completed their phasedowns: Belgium (2016), Austria (2020), Sweden (2020) and Portugal (2021). Seven large countries with a net zero emissions target remain without a coal phasedown plan: Brazil, China, India Japan, Korea, South Africa and the United States. 

Explore all coal policies

Policy and Measures database (PAMS)circle-arrow

International collaboration

Chevron down

Just Energy Transition Partnership expands to Indonesia and Viet Nam

The Just Energy Transition Partnership (JETP) is a programme launched during COP26 in 2021 by France, Germany, the United Kingdom, the United States and the European Union – often called the International Partners Group – to make available the financial resources necessary to accelerate energy transitions and meet climate targets, while ensuring a just transition. During COP26, the International Partners Group announced USD 8.5 billion for JETP in South Africa, and the programme has since expanded to other countries. In November 2022, Japan, the United States and other partners announced USD 20 billion for JETP in Indonesia, and in December 2022 the International Partners Group announced USD 15.5 billion for Viet Nam’s JETP.  

G7 countries recognise the need to end new unabated coal-fired power plants

In April 2023 the Group of 7 (G7) Ministers of Climate, Energy and the Environment released a communiqué recognising the need to end the construction of new unabated coal-fired power generation, as called for in the IEA’s Net Zero Scenario. The G7 leaders noted their intention to work with other countries to end new unabated coal-fired power generation projects world wide as soon as possible, in order to accelerate the clean energy transition in a just manner. 

Private sector strategies

Chevron down

Japanese bank announces plans to phase out funding of coal projects

Opposition to coal is not new, but in recent years an increasing number of governments have announced policies to restrict or prohibit financing for coal projects and investments. Further momentum to restrict financing for coal comes from the financial community, where many institutional investors, pension funds, banks, insurance companies and others have committed to reduce or end their involvement in coal. In February 2023 the Sumitomo Mitsui Banking Corporation (SMBC) announced that it will phase out project and corporate financing of coal mining projects and coal-fired power plants by 2040. Although SMBC did not specify a detailed timeline for the phase-out, it noted that this will include funding for new mines, expansion of existing mines and related infrastructure. 

Acknowledgements

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We would like to thank the following external reviewers:

Andrew Minchener, ICSC TCPEren Cam, IEA

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Policy makers and the private sector

Repurpose, retrofit or retire coal plants while ensuring grid stability and flexibility

Efforts to address emissions from existing coal-fired power plants, including those from the large number of young plants in EMDEs, are essential for reaching net zero goals. Industry should consider a three-pronged approach, and governments should adopt appropriate policies to enable this approach, to stay on track with the phase-out of unabated coal plants by 2040:  Repurpose coal plants (i.e. reducing operations to focus on system adequacy or flexibility services) for flexibility. This means an unabated coal plant produces less electricity over a certain period but remains available at times when the system needs are highest, and is available to ramp up and down to meet needs for flexibility, contributing to the reliability of power systems. Retrofit coal-fired power plants with CCUS: This provides a means to supply low‐emission power from existing coal assets, and provide stability services such as inertia, ramping flexibility, and firm capacity at peak times. This would also make use of existing transmission infrastructure, and allow current plants to be operated so that investments can be recouped, while reducing their carbon footprint. This is particularly important for emerging economies in Asia, where the average age of coal‐fired power plants is only 13 years and new plants continue to be built. Retrofit to co-fire with ammonia or biomass in order to reduce the CO2 emissions intensity of the electricity produced. Retire less-efficient coal plants before they reach the end of their technical lifetimes, and potentially convert the site to another use, in order to cut emissions from unabated coal‐fired power plants. 

Policy makers

Support CCUS deployment in the power sector through targeted and complementary policy instruments

Governments can accelerate CCUS deployment at coal-fired power plants through targeted policies such as a carbon pricing, granting funding for CCUS projects, tax incentives and carbon contracts-for-difference. In addition, increased funding for large-scale demonstration projects can help drive down costs and increase capture rates. Simultaneous support for CO2 transport and storage infrastructure is also vital, and governments can play a key role in identifying and funding strategic CO2 transport networks and storage sites. 

Policy makers

Ensure a just transition for coal-dependent regions, while maintaining energy security needs

Given the dependence of a number of countries and regions on coal, the closure of power plants could have significant economic and social consequences. Coal-dependent regions are often highly specialised “mono-industry” areas, where the economy and the local identity are closely tied to the coal value chain.  Governments should manage closures appropriately and successfully by planning for the impacts on affected workers and communities by facilitating early dialogue with affected stakeholders and establishing the right financial mechanisms to ensure a just transition. Social safety net expansions, retraining and job relocation programmes for coal power plant workers and their communities are essential to ensure that no-one is left behind. Establishing clear long-term energy transition strategies would foster investment in promising technologies, such as CCUS and renewable energy, resulting in stable job creation opportunities. Another crucial goal should be to carefully design relevant interconnected policies to avoid regressive distributional impacts. In addition, governments should pre-emptively manage any potential energy security concerns that may arise from coal plant closures. Recently, South Africa noted that it may need to pause the decommissioning of some coal plants to ensure its energy security needs in the short term. Phasing down and ultimately replacing coal in electricity systems in a secure and affordable manner requires several regulatory and operational changes, including actions to use a wider set of smaller and more distributed sources for grid services.  

Private sector

Increase demonstration activities to co-fire ammonia and biomass in coal-fired power plants

Ammonia, which does not emit CO2 when burned, is an alternative fuel to reduce emissions from coal-fired power plants. To get on track with the Net Zero Scenario, the private sector should begin to evaluate co-firing opportunities and conduct small-scale ammonia co-firing tests, with an eye towards commercial plant application in the coming years. Co-firing sustainable bioenergy is another option to allow coal-fired power facilities to continue contributing to flexibility and ensuring adequate capacity while reducing CO2 emissions. However, the biomass feedstocks used must be considered sustainable in order to ensure a net CO2 emissions reduction from co-firing. 

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