Coal mining

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Coal mining is the extraction or removing of coal from the earth by mining. When coal is used for fuel in power generation it is referred to as steaming or thermal coal. Coal that is used to create coke for steel manufacturing is referred to as coking or metallurgical coal.^[1] In the United States, UK, and South Africa, a coal mine and its accompanying structures are collectively known as a colliery. In Australia, 'colliery' usually only refers to an underground coal mine.^[2]

Contents 1 Methods of extraction 1.1 Modern surface mining 1.2 Underground mining 2 Production 3 History 4 Modern mining 5 Dangers to miners 6 Safer times in modern mining 7 Environmental impacts 8 See also 9 References 10 Further reading 11 External links

[edit] Methods of extraction

The most economical method of coal extraction from coal seams depends on the depth and quality of the seams, and also the geology and environmental factors of the area being mined. Coal mining processes are generally 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.

[edit] Modern surface mining

When coal seams are near the surface, it may be economical to extract the coal using open cut (also referred to as open cast or open pit) mining methods. Typically, for coal, strip mining is used. Strip mining exposes the coal by the advancement of an open pit or strip. The earth above the coal seam(s) is known as overburden. A strip of overburden next to the previously mined strip is usually drilled. The drill holes are filled with explosives and blasted. The overburden is then removed using large earthmoving equipment such as draglines, shovel and trucks, excavator and trucks, or bucket-wheels and conveyors. This overburden is put into the previously mined (and now empty) strip. When all the overburden is removed, the underlying coal seam will be exposed as a strip known as a 'block'. This 'block' of coal may be drilled and blasted (if hard) or otherwise loaded on to trucks or conveyors for transport to the coal preparation (or wash) plant. Once this strip is empty of coal, the process is repeated with a new strip being created next to it.

Open cast 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. Opencast coal mines can cover many square kilometers.^[3]

Most open cast mines in the United States extract bituminous coal. In South Wales open casting for steam coal and anthracite is practiced. In Australia and South Africa open cast mining is used for both thermal and metallurgical coals. Surface mining accounts for around 80% of production in Australia, while in the USA it is used for about 67% of production. Globally, about 40% of coal production involves surface mining.^[4]

Mountaintop removal is a form of surface mining that takes place at the topmost portion of a mountain, and is a technique that is commonly applied in Appalachia in the United States. Utilized for the past 30 years, mountaintop mining involves removing the highest part of the mountain for the maximum recovery of coal. The process is highly controversial for the drastic changes in topography, the practice of hollow fills, or filling in valleys with mining debris, and for covering streams and disrupting ecosystems.^[5]

[edit] Underground mining

Main article: Underground mining

Most coal seams are too deep underground for opencast mining and mining these seams involves underground mining. Underground mining currently accounts for about 60% 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 coal 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 referred to as second mining or retreat mining is commonly started. This is when miners remove the coal in the pillars, thereby recovering as much coal from the coal seam as possible. A work area that is 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 other equipment have left a work area. The mobile roof supports are similar to a large dining room table, but with hydraulic jacks for legs. After the large pillars of coal have been mined away, the mobile roof support legs shorten, and the mobile roof supports travel out to a safe area. The mine roof typically collapses once the mobile roof supports leave an area.

There are four major underground mining methods:

• Longwall mining – accounts for about 50% 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 a pan line that takes the coal to the conveyor belt for removal from the work area. Longwall systems have their own hydraulic roof supports for overlying rock that advance with the machine as mining progresses. As the longwall mining equipment moves forward, overlying rock that is no longer supported by the coal that has been removed 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% coal recovery rate where the surrounding geology allows their use.

• Continuous mining– Utilize a machine with a large rotating steel drum equipped with tungsten carbide teeth 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 “rooms” or work areas cut into the coalbed – it can mine as much as five tons of coal a minute – more than a non-mechanised miner of the 1920s would produce in an entire day. Continuous miners account for about 45% of underground coal production, and also utilize conveyors to 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.

• Blast mining – 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% of total underground production in the U.S. today.

• Shortwall mining– A method that accounts for less than 1% of deep coal production, shortwall involves the use of a continuous mining machine with moveable roof supports, similar to longwall. The continuous miner shears coal panels 150-200 feet wide and more than a half-mile long, depending on other things like the strata of the Earth and the transverse waves.

[edit] Production

Coal is mined commercially in over 50 countries. Over 4 970 Mt of hard coal is currently produced, a nearly 80% increase over the past 25 years.^[7] In 2005, the world production of brown coal and lignite was 906 Mt, with Germany the world’s largest brown coal producer.

Coal production has grown fastest in Asia, while Europe has declined. The top five coal mining nations (figures in brackets are 2006 estimate of hard coal production)^[8] are:

• China (2 482 Mt)
• USA (990 Mt)
• India (427 Mt)
• Australia (309 Mt)
• South Africa (244 Mt)

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

Global coal production is expected to reach 7 Gt in 2030, with China accounting for most of this increase. Steam coal production is projected to reach around 5200 Mt; coking coal 620 Mt; and brown coal 1200 Mt.^[9]

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.^[10]

[edit] History

Main article: History of coal mining

The oldest continuously worked deep-mine in the UK and possibly the world is Tower Colliery at the northern end of the south Wales valleys in the heart of the South Wales coalfield. This colliery was started in 1805 and at the end of the 20th century it was bought out by its miners rather than being allowed to be closed.

The World Championships in coal-carrying take place every Easter Monday, at Ossett, West Yorkshire, UK. The race starts from the site of the old Savile & Shaw Cross colliery.

The first commercial coal mines in the United States were started in 1748 in Midlothian, Virginia, near Richmond, Virginia.^[11]

In the 1880s, Coal-cutting machines became available (prior to that, coal was mined underground by hand using a pick and shovel.)

By 1912, surface mining was underway with steam shovels specifically designed for coal mining.

[edit] Modern mining

Technological advancements have made coal mining today more productive than it has ever been. To keep up with technology and to extract coal as efficiently as possible modern mining personnel must be highly skilled and well trained in the use of complex, state-of-the-art instruments and equipment. Future coal miners have to be highly educated and many jobs require four-year college degrees. Computer knowledge has also become greatly valued within the industry as most of the machines and safety monitors are computerized.

In the United States, the increase in technology has significantly decreased the mining workforce from 335,000 coal miners working at 7,200 mines fifty years ago to 104,824 miners working in fewer than 2,000 mines today. As some might see this as a sign that coal is a declining industry its advances has reported an 83% increase of production from 1970 to 2004^{[citation needed]}.

[edit] Dangers to miners

Historically, coal mining has been a very dangerous activity and the list of historical coal mining disasters is a long one. Open cut hazards are principally mine wall failures and vehicle collisions; underground mining hazards include roof collapse and gas explosions. 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.^[12]

However, in lesser developed countries and some developed countries, many miners continue to die annually, either through direct accidents in coal mines or through adverse health consequences from working under poor conditions. China, in particular, has the highest number of coal mining related deaths in the world, with official statistic 6,027 deaths in 2004.^[13] To compare, the USA reported 28 deaths in the same year.^[14] Coal production in China is twice that of the United States,^[15] while the number of coal miners is around 50 times that of the USA, making deaths in coal mines in China 4 times as common per worker (50 times as common per unit output) as in the USA.

When compared to industrial countries such as China, the U.S. fatality rate is low.^[specify] However in 2006 fatal work injuries among U.S. miners doubled from the previous year, totaling 47.^[16] These figures can in part be attributed to the Sago Mine disaster. The recent mine accident in Utah's Crandall Canyon Mine, where nine miners were killed and six entombed, speaks to the increase in occupational risks faced by U.S. miners.^[17]

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 4000 new cases of black lung every year in the USA (4% of workers annually) and 10 000 new cases every year in China (0.2% of workers).^[18] Rates may be higher than reported in some regions.

Build-ups of a hazardous gas are known as damps, possibly from the German word "Dampf" which means steam or vapor:

• Black damp: a mixture of carbon dioxide and nitrogen in a mine can cause suffocation.
• After damp: similar to black damp, an after damp consists of carbon dioxide and nitrogen and forms after a mine explosion.
• Fire damp: consists of mostly methane, a flammable gas.
• Stink damp: so named for the rotten egg smell of the sulfur, a stink damp can explode.
• White damp: air containing carbon monoxide which is toxic, even at low concentrations]

See also: Mining accidents

[edit] Safer times in modern mining

Improvements in mining methods (e.g. longwall mining), hazardous gas monitoring (such as safety-lamps or more modern electronic gas monitors), gas drainage, and ventilation have reduced many of the risks of rock falls, explosions, and unhealthy air quality. Statistical analyses performed by the U.S. 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, mining remains the second most dangerous occupation in America.^[19]

[edit] Environmental impacts

Main article: Environmental effects of coal

Coal mining can result in a number of adverse effects on the environment. Open cast coal mines leaves areas of land that is no longer usable and leaves a scarred landscape with no scenic value. Rehabilitation can mitigate some of these concerns. Mine tailing dumps produce acid mine drainage which can seep into waterways and aquifers with consequences on ecological and human health. Subsidence of land surfaces due to collapse of mine tunnels can also occur. During the mining operation methane, a potent greenhouse gas and a constituent of fire damp, can be released.

[edit] See also

• Acid mine drainage
• Black lung disease
• Coal Measures
• Coal mining debate
• Coal slurry impoundment
• Coal-mining region
• Hurrying
• Mine fire
• Problems in coal mining
• World Coal Institute
• Coal mining in Australia

[edit] References

[edit] Further reading

• Daniel Burns. The modern practice of coal mining (1907)
• Hughes. Herbert W, A Text-Book of Mining: For the Use of Colliery Managers and Others (London, many editions 1892-1917), the standard British textbook for its era.
• James Tonge. The principles and practice of coal mining (1906)
• Charles V. Nielsen and George F. Richardson. 1982 Keystone Coal Industry Manual (1982)
• Hayes, Geoffrey. Coal Mining (2004), 32 pp
• A.K. Srivastava. Coal Mining Industry in India (1998) (ISBN 81-7100-076-2)
• Chirons, Nicholas P. Coal Age Handbook of Coal Surface Mining (ISBN 0-07-011458-7)
• Saleem H. Ali. Minding our Minerals, 2006. [1]
• National Energy Information Center, Greenhouse Gases, Climate Change, Energy, <http://www.eia.doe.gov/oiaf/1605/ggccebro/chapter1.html>. Retrieved on 16 October 2007 

• The Department of Trade and Industry, The Coal Authority, <http://www.coal.gov.uk/resources/cleanercoaltechnologies/CoalMineandbedmethane.cfm>. Retrieved on 16 October 2007 

[edit] External links

• Abandoned Mine Research
• of Wollongong - educational resource on longwall mining
• National Coal Mining Museum for England
• World Coal Institute - Coal Mining
• NIOSH Coal Workers' Health Surveillance Program
• Prudue University - Petroleum and Coal