Coal mining

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Surface coal mining in Wyoming.

Coal mining is the extraction or removing of coal from the earth for use as fuel. A coal mine and its accompanying structures are collectively known as a colliery. For the world history see History of coal mining. See also world coal reserves and major coal exporters

1 Methods of extraction
- 1.1 Surface and mountaintop mining
- 1.2 Underground mining
2 History
3 Modern Mining in America
4 Dangers to miners
5 Safer times in modern mining
6 Environmental impacts and mitigation
7 Footnotes
8 References
9 See also
10 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] Surface and mountaintop mining

If the coal seams are near the surface, the coal is extracted by strip mining. Strip mining exposes the coal by the advancement of an open pit or strip. As the coal is exposed and extracted, the overburden from the still covered coal fills the former pit, and the strip progresses. Most open cast mines in the United States extract bituminous coal. In South Wales open casting for steam coal and anthracite is practiced.

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. 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 notorious for destruction of entire ranges. So is the practice of hollow fills, or filling in valleys with mining debris, covering streams and disrupting ecosystems. ^[1]

[edit] Underground mining

Most coal seams are too deep underground for open cast mining and thus this type of mining is called underground mining. In deep mining, the room and pillar or bord and pillar method progresses along the Mammoth coal vein seam, while pillars and timber are left standing to support the coal mine roof. A most dangerous method of operation in deep mining and is known as robbing the pillars. This is where miners attempt to remove and/or retreat between the timbers in order to get coal out of the main coal seam, allowing the roof to cave in. This method of mining is used principally in the United States and has contributed to many fatalities in the industry of coal mining.

There are four major underground mining methods:

Longwall mining – accounts for about 50% of underground production. The longwall shearer has a face of 1000 feet 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-80% 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” 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 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.

Conventional mining – An older practice that uses explosives 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] 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. 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 in 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.^[2]

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

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

[edit] Modern Mining in America

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.

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. These statistics are provided by the National Mining Association.

[edit] Dangers to miners

Historically, coal mining has been a very dangerous activity. Open cut hazards are principally slope failure, underground mining roof collapse and gas explosions. Most of these risks can be greatly reduced in modern mines, and multiple fatality incidents are now rare in the developed world. ^[3]

However, in lesser developed countries, thousands continue to die annually in coal mines. China, in particular, has the highest number of coal mining related deaths in the world, with official statistic 6,027 deaths in 2004^[4]. To compare, the USA reported 28 deaths in the same year^[5]. Coal production in China (highest in the world) is only double compared with USA^[6].

Chronic lung diseases, such as pneumoconiosis (black lung) were once common in miners, leading to reduced life expectancy.

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: mainly carbon monoxide, suffocates like black damp [also, Carbon monoxide is very toxic, even in concentrations as low as 5 ppm]

There have been many deaths related to the safety conditions that exist in coal mines around the world.

(See: Mining accidents)

Mildred, PA coal sludge

[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 (a measure comparing the rate of incidents to overall number of employees or hours worked) by more than half and fatalities by two-thirds following three prior decades of steady improvement.

According to the Bureau of Labor Statistics, coal mining is not even among the top 10 most dangerous occupations in America per capita. Pilots, truck and taxi drivers, loggers, fishermen, roofers and other occupations face greater on the job risks than coal miners.

[edit] Environmental impacts and mitigation

Coal mining causes adverse environmental impacts. These include:

Release of methane, a dangerous greenhouse gas
Interference with groundwater and water table levels
Impact of water use on flows of rivers and consequential impact on other land-uses
Dust
Subsidence above tunnels, sometimes damaging infrastructure (e.g., roads in the Lake Macquarie area in NSW, Australia).
Rendering land unfit for the common usage of the area.

In addition, burning of coal, mainly for power generation, is a leading contributor to greenhouse gas emissions, climate change and global warming.

Strip mining severely alters the landscape, which has damages environmental value in the surrounding land. Mountaintop removal to remove coal is a large negative change to the environment. While there are sometimes requirements for remediation of the strip mined area, the remediation is often delayed for decades. One of the legacies of coal mining is the low coal content waste forming boney piles.

In response to negative land effects of coal mining and the abundance of abandoned mines in the USA, the federal government enacted the Surface Mining Control and Reclamation Act of 1977 (SMCRA), which requires reclamation plans for future coal mining sites. Reclamation plans must be approved and permitted by federal or state authorities before mining begins. As of 2003, over 2 million acres (8000 km²) of previously mined lands have been reclaimed in the United States.

All forms of mining are likely to generate areas where coal is stacked and where the coal has significant sulphur content, such coal heaps generate highly acidic, metal-laden drainage when exposed to rainfall. These liquors can cause severe environmental damage to receiving water-courses. Coal mining releases approximately twenty toxic release chemicals, of which 85% is said to be managed on site. In modern mining, operations must, under federal and state law, meet standards for protecting surface and ground waters from contamination, including acid mine drainage (AMD). To mitigate these problems, water is continuously monitored at coal mines. The five principal technologies used to control water flow at mine sites are: diversion systems, containment ponds, groundwater pumping systems, subsurface drainage systems, and subsurface barriers. In the case of AMD, contaminated water is generally pumped to a treatment facility that neutralizes the contaminants. Still, AMD remains a large problem, emanating from coal mines abandoned in the United States prior to SMCRA.

It is also thought that coal mining is harmful to the quality of air in the surrounding regions. While burning of coal in power plants is most harmful to air quality, the process of mining can release pockets of hazardous gases. These gases may pose a threat to coal miners as well as a minor source of air pollution.

In recent years, there has also been concern for the safety of miners who work in subsurface coal mines.

[edit] Footnotes

[edit] References

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]