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Coal is a black carnbonaceous black sedimentary rock containing combustible properties.
is a fossil fuel comprised of the altered remains of prehistoric vegetation that originally accumulated in swamps and peat bogs. Most coal was formed during the Carboniferous period, the first coal age that spanned from 360 million to 290 million years ago.[1] It exists as a solid but very brittle carbonaceous black sedimentary combustible rock containing carbon, hydrogen, oxygen, nitrogen, and a small amount of sulfur and other trace elements.[2] Coal is extracted through coal mining operations that are carried out underground or on the surface.


[edit] Process

Coal was formed when sediment, built up and combined with the tectonic movement in the earth’s crust, buried plant vegetation at great depths in swamps and peat bogs. The buried vegetation was subjected to extreme temperatures and pressures. Temperatures and pressures caused the plant vegetation to undergo  physical and chemical changes that transformed it into peat and then coal. This transformation of coal as it is subjected pressure and temperature and matures from peat to hard coal is called coalification. Coalification describes the physical and chemical properties of coal, often referred to as the coal's ranking.[3]  There are different types of coal, ranging from low- to high-ranking coal. In fact, the harder a coal is, the higher its ranking. The quality of coal depends primarily on four factors: type of vegetation from which the coal originated, depth of burial, temperatures and pressures, and duration of time coal has to form in a deposit.

[edit] Types

There are four different types of coals used in the world today. These coals are distinguished as either low-ranking or high-ranking. Low-ranking coals contain a low amount of carbon and a high oxygen and hydrogen content. Globally, low-ranking coals comprise about 47 percent of all coal consumed globally. High-ranking coals account for about 53 percent.

  • Lignite is the softest form of coal with a low organic maturity and color range of various shades of brown to deep black. It is considered a low-ranking coal useful largely as fuel for power generation.
  • Sub-bituminous is coal that has continued to experience the effects of pressure and temperature over a longer period of time than lignite coal. As a result, sub-bituminous coal has a higher organic maturity even though it is still considered a low-ranking coal. Sub-bituminous coal is used in power generation, cement manufacturing, and for other industrial purposes.
  • Bituminous coal is formed through advanced chemical and physical changes, which cause it to become harder and blacker or with well-defined bands of bright and dull material. It is further subdivided according to thermal (steam) coal and metallurgical (coking) coal. Steam coal is used in power generation, cement manufacturing, and for other industrial purposes. Coking coal is used in steel and iron manufacturing. Under certain conditions, bituminous coal can even continue to form until it becomes anthracite. Bituminous coal is a high-ranking coal.
  • Anthracite is the hardest form of coal and also the highest-ranking coal; it is used mostly for residential and commercial space heating.

[edit] Global Coal Reserves 

There is an estimated 847 billion tons of proven coal reserves worldwide. That amount is equivalent to about 130 years worth at current production rates.[4] The largest coal reserves are located in the USA, Russia, China, and India. There exist recoverable coal reserves in about 70 countries worldwide.[5] A proven recoverable reserve refers to the tonnage of coal that has been proven by drilling and is economically and technically extractable.

[edit] Coal Production

According to the World Coal Institute, about 5,540 million tons of hard coal is produced world wide and of that, 935 million tons consists of lignite brown coal. The top five coal-producing countries in the world are China, the USA, India, Australia, and South Africa. Most of the coal produced is used by the country that produces it. Only 16 percent of all hard coal produced gets exported to international markets.[6]

[edit] Coal Mining

Coal is produced through various underground and surface mining methods. Underground coal mining accounts for around 60 percent of global coal production. In some countries such as Australia, surface coal mining takes precedence over underground methods. Approximately 80 percent of the coal produced in Australia comes from surface mining operations. In the USA, the surface mining of coal only accounts for about 67 of the total amount of coal produced domestically.[7]

[edit] Uses

Coal is used in many different applications. Of these, the most significant is its use in electricity generation, steel production, cement manufacturing, and as a liquid fuel. As of 2000, global consumption of coal has grown more than any other fuel. China, the U.S., India, Japan, and Russia account for 72 percent of total global coal consumption. Of these, Asia has the largest coal market for coal, accounting for 56 percent of global coal consumption.[8]

Some other uses of coal include alumina fineries, paper manufacturers, and the chemical and pharmaceutical industries. Many chemical products are produced from the coal by-products. Refined coal tar is used in chemical manufacturing to create creosote oils, naphthalene, phenol, and benzene. Ammonia gas recovered from coking ovens is used in the manufacturing of ammonia salts, nitric acid, and agricultural fertilizers. In addition, many other by-products made from coal include soap, aspirin, solvents, dyes, plastics, and fibers such as rayon and nylon.[9]

[edit] References

  1. What is Coal? World Coal Institute. 22-06-2009.
  2. What is Coal? RockTalk Volume 8, Number 2, 2005. 22-06-2009.
  3. What is Coal? World Coal Institute. 22-06-2009.
  4. Where is Coal Found? World Coal Institute. 22-06-2009.
  5. Where is Coal Found? World Coal Institute. 22-06-2009.
  6. Coal Mining. World Coal Institute. 22-06-2009.
  7. Coal Mining. World Coal Institute. 23-06-2009.
  8. Uses of Coal. World Coal Institute. 22-06-2009.
  9. Uses of Coal. World Coal Institute. 22-06-2009.