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Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s, has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United Kingdom and South Africa, a coal mine and its structures are a colliery, a coal mine - a pit, and the above-ground structures - a pit head. In Australia, "colliery" generally refers to an underground coal mine. In the United States, "colliery" has been used to describe a coal mine operation but nowadays the word is not commonly used.

Coal mining has had many developments over the recent years, from the early days of men tunneling, digging, and manually extracting the coal on carts to large open cut and long wall mines. Mining at this scale requires the use of draglines, trucks, conveyors, hydraulic jacks and shearers.

History


Small-scale mining of surface deposits dates back thousands of years.

The Industrial Revolution, which began in Britain in the 18th century and later spread to continental Europe and North America, was based on the availability of coal to power steam engines. International trade expanded rapidly when coal-fed steam engines were built for the railways and steamships.

Until the late nineteenth-century coal was mined underground using a pick and shovel, and children were often employed underground in dangerous conditions.[2] Coal-cutting machines were introduced in the 1880s.

Mineworkers used rodents (mostly mice) and birds (canaries) underground to track the amount of concentrated carbon monoxide in the shafts.

Methods of extraction


The most economical method of coal extraction from coal seams depends on the depth and quality of the seams, and the geology and environmental factors. Coal mining processes are differentiated by whether they operate on the surface or underground. Many coals extracted from both surface and underground mines require washing in a coal preparation plant. Technical and economic feasibility are evaluated based on the following: regional geological conditions; overburden characteristics; coal seam continuity, thickness, structure, quality, and depth; strength of materials above and below the seam for roof and floor conditions; topography (especially altitude and slope); climate; land ownership as it affects the availability of land for mining and access; surface drainage patterns; groundwater conditions; availability of labor and materials; coal purchaser requirements in terms of tonnage, quality, and destination; and capital investment requirements.[4]

Surface mining and deep underground mining are the two basic methods of mining.

Coal that occurs at depths of 180 to 300 ft (55 to 90 m) are usually deep mined, but in some cases surface mining techniques can be used.

When coal seams are near the surface, it may be economical to extract the coal using open cut (also referred to as open cast, open pit, mountaintop removal or strip) mining methods. Opencast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. This equipment can include the following: Draglines which operate by removing the overburden, power shovels, large trucks in which transport overburden and coal, bucket wheel excavators, and conveyors. In this mining method, explosives are first used in order to break through the surface or overburden, of the mining area. The overburden is then removed by draglines or by shovel and truck. Once the coal seam is exposed, it is drilled, fractured and thoroughly mined in strips. The coal is then loaded onto large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used.[6]

Most open cast mines in the United States extract bituminous coal. In Canada (BC), Australia and South Africa, open cast mining is used for both thermal and metallurgical coals. In New South Wales open casting for steam coal and anthracite is practiced. Surface mining accounts for around 80 percent of production in Australia, while in the US it is used for about 67 percent of production. Globally, about 40 percent of coal production involves surface mining.[6]

Strip mining exposes coal by removing earth above each coal seam.

It is often necessary to fragment the overburden by use of explosives.

Equipment to be used depends on geological conditions.

The contour mining method consists of removing overburden from the seam in a pattern following the contours along a ridge or around the hillside.

The limitations of contour strip mining are both economic and technical.

Mountaintop coal mining is a surface mining practice involving removal of mountaintops to expose coal seams, and disposing of associated mining overburden in adjacent "valley fills."

Mountaintop removal combines area and contour strip mining methods. In areas with rolling or steep terrain with a coal seam occurring near the top of a ridge or hill, the entire top is removed in a series of parallel cuts. Overburden is deposited in nearby valleys and hollows.

Spoil is placed at the head of a narrow, steep-sided valley or hollow.

Most coal seams are too deep underground for opencast mining and require underground mining, a method that currently accounts for about 60 percent of world coal production.[6] In deep mining, the room and pillar or bord and pillar method progresses along the seam, while pillars and timber are left standing to support the mine roof. Once room and pillar mines have been developed to a stopping point (limited by geology, ventilation, or economics), a supplementary version of room and pillar mining, termed second mining or retreat mining, is commonly started. Miners remove the coal in the pillars, thereby recovering as much coal from the coal seam as possible. A work area involved in pillar extraction is called a pillar section.

Modern pillar sections use remote-controlled equipment, including large hydraulic mobile roof-supports, which can prevent cave-ins until the miners and their equipment have left a work area.

There are six principal methods of underground mining:

  • Longwall mining accounts for about 50 percent of underground production. The longwall shearer has a face of 1,000 feet (300 m) or more. It is a sophisticated machine with a rotating drum that moves mechanically back and forth across a wide coal seam. The loosened coal falls onto an armored chain conveyor or pan line that takes the coal to the conveyor belt for removal from the work area. Longwall systems have their own hydraulic roof supports which advance with the machine as mining progresses. As the longwall mining equipment moves forward, overlying rock that is no longer supported by coal is allowed to fall behind the operation in a controlled manner. The supports make possible high levels of production and safety. Sensors detect how much coal remains in the seam while robotic controls enhance efficiency. Longwall systems allow a 60-to-100 percent coal recovery rate when surrounding geology allows their use. Once the coal is removed, usually 75 percent of the section, the roof is allowed to collapse in a safe manner.[6]
  • Continuous mining utilizes a Continuous Miner Machine with a large rotating steel drum equipped with tungsten carbide picks that scrape coal from the seam. Operating in a "room and pillar" (also known as "bord and pillar") system—where the mine is divided into a series of 20-to-30-foot (5–10 m) "rooms" or work areas cut into the coalbed—it can mine as much as 14 tons of coal a minute, more than a non-mechanised mine of the 1920s would produce in an entire day. Continuous miners account for about 45 percent of underground coal production. Conveyors transport the removed coal from the seam. Remote-controlled continuous miners are used to work in a variety of difficult seams and conditions, and robotic versions controlled by computers are becoming increasingly common. Continuous mining is a misnomer, as room and pillar coal mining is very cyclical. In the US, one can generally cut 20 feet (6 meters) (or a bit more with MSHA permission) (12 meters or roughly 40 ft in South Africa before the Continuous Miner goes out and the roof is supported by the Roof Bolter), after which, the face has to be serviced, before it can be advanced again. During servicing, the "continuous" miner moves to another face. Some continuous miners can bolt and rock dust the face (two major components of servicing) while cutting coal, while a trained crew may be able to advance ventilation, to truly earn the "continuous" label. However, very few mines are able to achieve it. Most continuous mining machines in use in the US lack the ability to bolt and dust. This may partly be because incorporation of bolting makes the machines wider, and therefore, less maneuverable.
  • Room and pillar mining consists of coal deposits that are mined by cutting a network of rooms into the coal seam. Pillars of coal are left behind in order to keep up the roof. The pillars can make up to forty percent of the total coal in the seam, however where there was space to leave head and floor coal there is evidence from recent open cast excavations that 18th-century operators used a variety of room and pillar techniques to remove 92 percent of the in situ coal. However, this can be extracted at a later stage (see retreat mining).[6]
  • Blast mining or conventional mining, is an older practice that uses explosives such as dynamite to break up the coal seam, after which the coal is gathered and loaded onto shuttle cars or conveyors for removal to a central loading area. This process consists of a series of operations that begins with “cutting” the coalbed so it will break easily when blasted with explosives. This type of mining accounts for less than 5 percent of total underground production in the US today.
  • Shortwall mining, a method currently accounting for less than 1 percent of deep coal production, involves the use of a continuous mining machine with movable roof supports, similar to longwall.
  • Retreat mining is a method in which the pillars or coal ribs used to hold up the mine roof are extracted; allowing the mine roof to collapse as the mining works back towards the entrance. This is one of the most dangerous forms of mining, owing to imperfect predictability of when the roof will collapse and possibly crush or trap workers in the mine.

Production


Coal is mined commercially in over 50 countries.

Coal production has grown fastest in Asia, while Europe has declined.

Most coal production is used in the country of origin, with around 16 percent of hard coal production being exported.

Coal reserves are available in almost every country worldwide, with recoverable reserves in around 70 countries. At current production levels, proven coal reserves are estimated to last 147 years.[14] However, production levels are by no means level, and are in fact increasing and some estimates are that peak coal could arrive in many countries such as China and America by around 2030. Coal reserves are usually stated as either (1) "Resources" ("measured" + "indicated" + "inferred" = "resources", and then, a smaller number, often only 10-20% of "resources", (2) "Run of Mine" (ROM) reserves, and finally (3) "marketable reserves", which may be only 60% of ROM reserves. The standards for reserves are set by stock exchanges, in consultation with industry associations. For example, in ASEAN countries reserves standards follow the Australasian Joint Ore Reserves Committee Code (JORC) used by the Australian Securities Exchange.

Modern mining


Technological advancements have made coal mining today more productive than it has ever been.

The use of sophisticated sensing equipment to monitor air quality is common and has replaced the use of small animals such as canaries, often referred to as "miner's canaries".[15]

In the United States, the increase in technology has significantly decreased the mining workforce.

Safety


Historically, coal mining has been a very dangerous activity and the list of historical coal mining disasters is a long one. In the US alone, more than 100,000 coal miners were killed in accidents in the twentieth century,[18] 90 percent of the fatalities occurring in the first half of the century.[19] More than 3,200 died in 1907 alone.[20]

Open cut hazards are principally mine wall failures and vehicle collisions; underground mining hazards include suffocation, gas poisoning, roof collapse, rock burst, outbursts, and gas explosions.

Firedamp explosions can trigger the much-more-dangerous coal dust explosions, which can engulf an entire pit. Most of these risks can be greatly reduced in modern mines, and multiple fatality incidents are now rare in some parts of the developed world. Modern mining in the US results in approximately 30 deaths per year due to mine accidents.[21]

However, in lesser developed countries and some developing countries, many miners continue to die annually, either through direct accidents in coal mines or through adverse health consequences from working under poor conditions.

Mine disasters have still occurred in recent years in the US,[25] Examples include the Sago Mine disaster of 2006, and the 2007 mine accident in Utah's Crandall Canyon Mine, where nine miners were killed and six entombed.[26] In the decade 2005-2014, US coal mining fatalities averaged 28 per year.[27] The most fatalities during the 2005-2014 decade were 48 in 2010, the year of the Upper Big Branch Mine disaster in West Virginia, which killed 29 miners.[28]

Chronic lung diseases, such as pneumoconiosis (black lung) were once common in miners, leading to reduced life expectancy. In some mining countries black lung is still common, with 4,000 new cases of black lung every year in the US (4 percent of workers annually) and 10,000 new cases every year in China (0.2 percent of workers).[29] The use of water sprays in mining equipment reduces the risk to miners' lungs.[30] Build-ups of a hazardous gas are known as damps, possibly from the German word "Dampf" which means steam or vapor:

Noise is also a contributing factor to potential adverse effects on coal miners' health.

Noise exposures vary depending on the method of extraction.

In the 1966 Aberfan disaster in Wales, a colliery spoil tip collapsed, engulfing a school and killing 116 children and 28 adults. Other accidents involving coal waste include the Martin County coal slurry spill (USA, 2000) and the Obed Mountain coal mine spill (Canada, 2013).

Improvements in mining methods (e.g. longwall mining), hazardous gas monitoring (such as safety-lamps or more modern electronic gas monitors), gas drainage, electrical equipment, and ventilation have reduced many of the risks of rock falls, explosions, and unhealthy air quality. Gases released during the mining process can be recovered to generate electricity and improve worker safety with gas engines.[33] Another innovation in recent years is the use of closed circuit escape respirators, respirators that contain oxygen for situations where mine ventilation is compromised.[34] Statistical analyses performed by the US Department of Labor's Mine Safety and Health Administration (MSHA) show that between 1990 and 2004, the industry cut the rate of injuries by more than half and fatalities by two-thirds. However, according to the Bureau of Labor Statistics, even in 2006, mining remained the second most dangerous occupation in America, when measured by fatality rate.[35] However, these numbers include all mining, with oil and gas mining contributing the majority of fatalities; coal mining resulted in only 47 fatalities that year.[35]

Environmental impacts


Coal mining can result in a number of adverse effects on the environment.

Surface mining of coal completely eliminates existing vegetation, destroys the genetic soil profile, displaces or destroys wildlife and habitat, degrades air quality, alters current land uses, and to some extent permanently changes the general topography of the area mined.[36] This often results in a scarred landscape with no scenic value. Of greater concern, the movement, storage, and redistribution of soil during mining can disrupt the community of soil microorganisms and consequently nutrient cycling processes. Rehabilitation or reclamation mitigates some of these concerns and is required by US Federal Law, specifically the Surface Mining Control and Reclamation Act of 1977.

Mine dumps (tailings) could produce acid mine drainage which can seep into waterways and aquifers, with consequences on ecological and human health.

If underground mine tunnels collapse, they cause subsidence of the ground above. Subsidence can damage buildings, and disrupt the flow of streams and rivers by interfering with the natural drainage.

Coal production is a major contributor to global warming: burning coal generates large quantities of carbon dioxide and mining operations can release methane, a known greenhouse gas, into the atmosphere. The coal mining industry is working to improve its public image.[37]

Legality of coal mining


A court in Australia has cited climate change in ruling against a new coal mine.[38]

Coal mining by country


Top 10 hard and brown coal producers in 2012 were (in million metric tons): China 3,621, United States 922, India 629, Australia 432, Indonesia 410, Russia 351, South Africa 261, Germany 196, Poland 144, and Kazakhstan 122.[39][40]

Coal is mined in every state of Australia, but mainly in Queensland, New South Wales and Victoria.

In 2007, 428 million tonnes of coal was mined in Australia.[10] In 2007, coal provided about 85% of Australia's electricity production.[41] In fiscal year 2008/09, 487 million tonnes of coal was mined, and 261 million tonnes was exported.[42] In fiscal year 2013/14, 430.9 million tonnes of coal was mined, and 375.1 million tonnes was exported.[43] In 2013/14, coal provided about 69% of Australia's electricity production.[44]

In 2013, Australia was the world's fifth-largest coal producer, after China, the United States, India, and Indonesia.

Canada was ranked as the 15th coal producing country in the world in 2010, with a total production of 67.9 million tonnes. Canada's coal reserves, the 12th largest in the world, are located largely in the province of Alberta.[45]

The first coal mines in North America were located in Joggins and Port Morien, Nova Scotia, mined by French settlers beginning in the late 1600s. The coal was used for the British garrison at Annapolis Royal, and in construction of the Fortress of Louisbourg.

Compared to other South American countries Chile has limited coal resources.

The People's Republic of China is by far the largest producer of coal in the world, producing over 2.8 billion tons of coal in 2007, or approximately 39.8 percent of all coal produced in the world during that year.[10] For comparison, the second largest producer, the United States, produced more than 1.1 billion tons in 2007. An estimated 5 million people work in China's coal-mining industry. As many as 20,000 miners die in accidents each year.[48] Most Chinese mines are deep underground and do not produce the surface disruption typical of strip mines. Although there is some evidence of reclamation of mined land for use as parks, China does not require extensive reclamation and is creating significant acreages of abandoned mined land, which is unsuitable for agriculture or other human uses, and inhospitable to indigenous wildlife. Chinese underground mines often experience severe surface subsidence (6–12 meters), negatively impacting farmland because it no longer drains well. China uses some subsidence areas for aquaculture ponds but has more than they need for that purpose. Reclamation of subsided ground is a significant problem in China. Because most Chinese coal is for domestic consumption, and is burned with little or no air pollution control equipment, it contributes greatly to visible smoke and severe air pollution in industrial areas using coal for fuel. China's total energy uses 67% from coal mines.

Some of the world's largest coal reserves are located in South America, and an opencast mine at Cerrejón in Colombia is one of the world's largest open pit mines. Output of the mine in 2004 was 24.9 million tons (compared to total global hard coal production of 4,600 million tons). Cerrejón contributed about half of Colombia's coal exports of 52 million tons that year, with Colombia ranked sixth among major coal exporting nations. The company planned to expand production to 32 million tons by 2008. The company has its own 150 km standard-gauge railroad, connecting the mine to its coal-loading terminal at Puerto Bolívar on the Caribbean coast. There are two 120-car unit trains, each carrying 12,000 tons of coal per trip. The round-trip time for each train, including loading and unloading, is about 12 hours. The coal facilities at the port are capable of loading 4,800 tons per hour onto vessels of up to 175,000 tons of dead weight. The mine, railroad and port operate 24 hours per day.

The expansion of the Cerrejón mine has been blamed for the forced displacement of local communities.[49][50]

Germany has a long history of coal mining, going back to the Middle Ages. Coal mining greatly increased during the industrial revolution and the following decades. The main mining areas were around Aachen, the Ruhr and Saar area, along with many smaller areas in other parts of Germany. These areas grew and were shaped by coal mining and coal processing, and this is still visible even after the end of the coal mining.

Coal mining reached its peak in the first half of the 20th century.

Coal mining in India has a long history of commercial exploitation starting in 1774 with John Sumner and Suetonius Grant Heatly of the East India Company in the Raniganj Coalfield along the Western bank of Damodar River. Demand for coal remained low until the introduction of steam locomotives in 1853. After this, production rose to an annual average of 1 Mt and India produced 6.12 Mt per year by 1900 and 18 Mt per year by 1920, following increased demand in the First World War, but went through a slump in the early thirties. The production reached a level of 29 Mt by 1942 and 30 Mt by 1946. After independence, the country embarked upon five-year development plans. At the beginning of the 1st Plan, annual production went up to 33 Mt. During the 1st Plan period, the need for increasing coal production efficiently by systematic and scientific development of the coal industry was being felt. Setting up the National Coal Development Corporation (NCDC), a Government of India undertaking, in 1956 with the collieries owned by the railways as its nucleus was the first major step towards planned development of Indian Coal Industry. Along with the Singareni Collieries Company Ltd. (SCCL) which was already in operation since 1945 and which became a government company under the control of Government of Andhra Pradesh in 1956, India thus had two Government coal companies in the fifties. SCCL is now a joint undertaking of Government of Telangana and Government of India.

The richest Japanese coal deposits have been found on Hokkaido and Kyushu.

Japan has a long history of coal mining dating back into the Japanese Middle Ages. It is said that coal was first discovered in 1469 by a farming couple near Ōmuta, central Kyushu.[51] In 1478, farmers discovered burning stones in the north of the island, which led to the exploitation of the Chikuhõ coalfield.[52]

Following Japanese industrialization additional coalfields were discovered northern Japan.

Russia ranked as the fifth largest coal producing country in 2010, with a total production of 316.9 Mt. Russia has the world's second largest coal reserves.[54] Russia and Norway share the coal resources of the Arctic archipelago of Svalbard, under the Svalbard Treaty.

Spain was ranked as the 30th coal producing country in the world in 2010. The coal miners of Spain were active in the Spanish Civil War on the Republican side. In October 1934, in Asturias, union miners and others suffered a fifteen-day siege in Oviedo and Gijon. There is a museum dedicated to coal mining in the region of Catalonia, called Cercs Mine Museum.

In October 2018, the Sánchez government and Spanish Labour unions settled an agreement to close ten Spanish coal mines at the end of 2018. The government pre-engaged to spend 250 million Euro to pay for early retirements, occupational retraining and structural change. In 2018, about 2,3 per cent of the electric energy produced in Spain was produced in coal-burning power plants.[55]

South Africa is one of the ten largest coal producing countries[56][57] and the fourth largest coal exporting country[58] in the world.

In Taiwan, coal is distributed mainly in the northern area. All of the commercial coal deposits occurred in three Miocene coal-bearing formations, which are the Upper, the Middle and the Lower Coal Measures. The Middle Coal Measures was the most important with its wide distribution, great number of coal beds and extensive potential reserves. Taiwan has coal reserves estimated to be 100-180 Mt. However, coal output had been small, amounting to 6,948 metric tonnes per month from 4 pits before it ceased production effectively in 2000.[59] The abandoned coal mine in Pingxi District, New Taipei has now turned into the Taiwan Coal Mine Museum.[60]

In 2012 coal production in Ukraine amounted to 85.946 million tonnes, up 4.8% from 2011.[61] Coal consumption that same year grew to 61.207 million tonnes, up 6.2% compared with 2011.[61]

More than 90 percent of Ukraine's coal production comes from the Donets Basin.[62] The country's coal industry employs about 500,000 people.[63] Ukrainian coal mines are among the most dangerous in the world, and accidents are common.[64] Furthermore, the country is plagued with extremely dangerous illegal mines.[65]

Before the industrial revolution much of the coal was used near to its production, although there was an active trade along the North Sea coast supplying coal to Yorkshire and London.[1]

Many coalfields were developed in the industrial revolution.

The United Kingdom was ranked as the 24th coal producing country in the world in 2010, with a total production of 18.2 million tonnes. Coal mining in the United Kingdom probably dates to Roman times; coal production increased significantly during the Industrial Revolution in the 19th century and peaked during World War I. As a result of its long history with coal Britain's economically recoverable coal reserves have decreased,[67] and more than twice as much coal is now imported than produced.[68]

Coal was mined in America in the early 18th century, and commercial mining started around 1730 in Midlothian, Virginia.[69]

The American share of world coal production remained steady at about 20 percent from 1980 to 2005, at about 1 billion short tons per year. The United States was ranked as the second highest coal producing country in the world in 2010, and possesses the largest coal reserves in the world. In 2008 then-President George W. Bush stated that coal was the most reliable source of electricity.[70] However, in 2011 President Barack Obama said that the US should rely more on "clean" sources of energy that emit lower or no carbon dioxide pollution.[71] For a time, while domestic coal consumption for electric power was being displaced by natural gas, exports were increasing.[72] US net coal exports increased ninefold from 2006 to 2012, peaked at 117 million short tons in 2012, then declined to 63 million tons in 2015. In 2015, 60% of net US exports went to Europe, 27% to Asia.US coal production increasingly comes from strip mines in the western United States, such as from the Powder River Basin in Wyoming and Montana.[73]

Coal has come under continued price pressure from natural gas and renewable energy sources, which has resulted in a rapid decline of coal in the U.S. and several notable bankruptcies including Peabody Energy. On 13 April 2016 it reported, that its revenue had reduced by 17 percent as coal prices fell and that it had lost two billion dollars the previous year.[74] It then filed Chapter 11 bankruptcy on 13 April 2016.[74] The Harvard Business Review discussed retraining coal workers for solar photovoltaic employment because of the rapid rise in U.S. solar jobs.[75] A 2016 study indicated that this was technically possible and would account for only 5% of the industrial revenue from a single year to provide coal workers with job security in the energy industry as whole.[17]

President Donald Trump pledged to bring back coal jobs during the 2016 US presidential election, and as president he announced plans to reduce environmental protection, particularly by repealing the Clean Power Plan (CPP). However, industry observers have warned that this might not lead to a boom in mining jobs[76] A 2019 projection by the Energy Information Administration estimated that coal production without CPP would decline over coming decades at a faster rate than indicated in the agency's 2017 projection, which had assumed the CPP was in effect.[77]

See also


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