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6 novembre 2011 7 06 /11 /novembre /2011 10:12

Coal is a combustible black or brownish-black sedimentary rock normally occurring normally occurring in rock strata in layers or veins calledcoal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Sony VAIO VGN-SR41M/P Battery

Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, with smaller quantities of sulfur, oxygen and nitrogen.

Formation

Coal begins as layers of plant matter accumulating at the bottom of a body of water. Sony VAIO VGN-SR41M/S Battery

For the process to continue, the plant matter must be protected from biodegradation and oxidization, usually by mud or acidic water. This traps their carbon in immense peat bogs that are eventually covered over and deeply buried by sediments. Sony VAIO VGN-SR49VN/H Battery

Under this compression the plant material is metamorphosed into coal: over time, the chemical and physical properties of the plant remains are changed by geological action to create a solid material.

The wide shallow seas of the Carboniferous period provided ideal conditions for coal formation, although coal is known from most geological periods. Sony VAIO VGN-SR51B/P Battery

The exception is the coal gap in the Lower Triassic, where coal is rare: presumably a result of the mass extinction which prefaced this era. Coal is even known from Precambrian strata, which predate land plants: this coal is presumed to have originated from algal residues.Sony VAIO VGN-SR51B/S Battery

Coal, a fossil fuel, is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide anthropogenic sources ofcarbon dioxide releases. Gross carbon dioxide emissions from coal usage are slightly more than those from petroleum and about double the amount from natural gas.Sony VAIO VGN-SR51MF Battery

Coal is extracted from the ground by mining, either underground by shaft mining through the seams or in open pits.

Types

As geological processes apply pressure to dead biotic material over time, under suitable conditions it is transformed successively into:Sony VAIO VGN-SR51MF/P Battery

  • Peat, considered to be a precursor of coal, has industrial importance as a fuel in some regions, for example, Ireland and Finland. In its dehydrated form, peat is a highly effective absorbent for fuel and oil spills on land and water Sony VAIO VGN-SR51MF/S Battery
  • Lignite, also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since theUpper Palaeolithic Sony VAIO VGN-SR51MF/W Battery
  • Sub-bituminous coal, whose properties range from those of lignite to those of bituminous coal are used primarily as fuel for steam-electric power generation. Additionally, it is an important source of light aromatic hydrocarbons for the chemical synthesis industry.Sony VAIO VGN-SR51MR Battery
  • Bituminous coal, dense sedimentary rock, black but sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and to make coke Sony VAIO VGN-SR59VG Battery
  • Steam coal is a grade between bituminous coal and anthracite, once widely used as a fuel for steam locomotives. In this specialized use it is sometimes known as sea-coal in the U.S.[5] Small steam coal (dry small steam nuts or DSSN) was used as a fuel for domestic water heating Sony VAIO VGN-SR59VG/H Battery
  • Anthracite, the highest rank; a harder, glossy, black coal used primarily for residential and commercial space heating. It may be divided further into metamorphically altered bituminous coal and petrified oil, as from the deposits in Pennsylvania
  • Graphite, technically the highest rank, but difficult to ignite and is not so commonly used as fuel: it is mostly used in pencils and, when powdered, as a lubricant.Sony VAIO VGN-SR70B/S Battery

The middle six grades in the table represent a progressive transition from the English-language sub-bituminous to bituminous coal, while the last class is an approximate equivalent to anthracite, but more inclusive (the U.S. anthracite has < 6% volatiles).

Cannel coal (sometimes called "candle coal"), is a variety of fine-grained, high-rank coal with significant hydrogen content. It consists primarily of "exinite" macerals, now termed "liptinite".Sony VAIO VGN-SR72B/P Battery

Hilt's Law

Hilt's Law is a geological term that states that, in a small area, the deeper the coal, the deeper its rank (grade).[7] The law holds true if the thermal gradient is entirely vertical, but metamorphism may cause lateral changes of rank, irrespective of depth.Sony VAIO VGN-SR72B/S Battery

Early uses as fuel

The earliest reference to the use of coal as fuel is from the geological treatise On stones (Lap. 16) by the Greek scientistTheophrastus (c. 371–287 BC):

Among the materials that are dug because they are useful, those known as coals are made of earth, and, once set on fire, they burn like charcoal.Sony VAIO VGN-SR73JB/S Battery
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.

Outcrop coal was used in Britain during the Bronze Age (3000–2000 BC), where it has been detected as forming part of the composition of funeral pyres.Sony VAIO VGN-SR74FB/S Battery

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". Evidence of trade in coal (dated to about AD 200) has been found at the inland port of Heronbridge, near Chester, and in the Fenlands of East Anglia, where coal from theMidlands was transported via the Car Dyke for use in drying grain. Sony VAIO VGN-SR90FS Battery

Coal cinders have been found in the hearths of villas andmilitary 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.Sony VAIO VGN-SR90NS Battery

Evidence of coal's use for iron-working in the city during the Roman period has been found.[14] In Eschweiler, Rhineland, deposits of bituminous coal were used by the Romans for the smelting of iron ore.[11]

There is no evidence that the product was of great importance in Britain before the High Middle Ages, after about AD 1000.Sony VAIO VGN-SR90S Battery

Mineral coal came to be referred to as "seacoal" in the 13th century; the wharf where the material arrived in London was known asSeacoal Lane, so identified in a charter of King Henry III granted in 1253.Initially the name was given because much coal was found on the shore, Sony VAIO VGN-SR90US Battery

having fallen from the exposed coal seams on cliffs above or washed out of underwater coal outcrops,[15] but by the time of Henry VIII it was understood to derive from the way it was carried to London by sea.[17] In 1257–59, coal fromNewcastle was shipped to London for the smiths and lime-burners building Westminster Abbey.Sony VAIO VGN-SR91NS Battery

Seacoal Lane and Newcastle Lane where coal was unloaded at wharves along the River Fleet, are still in existence.((See Industrial processes below for modern uses of the term.)

These easily accessible sources had largely become exhausted (or could not meet the growing demand) by the 13th century, when underground mining from shafts or aditswas developed.Sony VAIO VGN-SR91PS Battery

The alternative name was "pitcoal," because it came from mines. It was, however, the development of the Industrial Revolution that led to the large-scale use of coal, as the steam engine took over from the water wheel. In 1700, 5/6 of the world's coal was mined in Britain. Without coal, Britain would have run out of suitable sites for watermills by the 1830s.Sony VAIO VGN-SR91S Battery

In 1947, there were some 750,000 miners, but by 2004 this had shrunk to some 5,000 miners working in around 20 collieries.

In ancient China, coal was used as fuel by the 4th century AD, but there was little extensive use until the 11th century.Sony VAIO VGN-SR91US Battery

Coal as fuel

Coal is primarily used as a solid fuel to produce electricity and heat through combustion. World coal consumption was about 6.75 billion short tons in 2006[23] and is expected to increase 48% to 9.98 billion short tons by 2030.Sony VAIO VGN-SR92NS Battery

China produced 2.38 billion tons in 2006. India produced about 447.3 million tons in 2006. 68.7% of China's electricity comes from coal. The USA consumes about 14% of the world total, using 90% of it for generation of electricity.

When coal is used for electricity generation, it is usually pulverized and then combusted (burned) in a furnace with a boiler. Sony VAIO VGN-SR92PS Battery

The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity. Thethermodynamic efficiency of this process has been improved over time. Simple cycle steam turbines have topped out with some of the most advanced reaching about 35% thermodynamic efficiency for the entire process. Sony VAIO VGN-SR92S Battery

Increasing the combustion temperature can boost this efficiency even further.Old coal power plants, especially "grandfathered" plants, are significantly less efficient and produce higher levels of waste heat. At least 40% of the world's electricity comes from coal,and in 2008 approximately 49% of the United States' electricity came from coal.Sony VAIO VGN-SR92US Battery

The emergence of the supercritical turbine concept envisions running a boiler at extremely high temperatures and pressures with projected efficiencies of 46%, with further theorized increases in temperature and pressure perhaps resulting in even higher efficiencies.Sony VAIO VGN-SR93DS Battery

An experimental way of coal combustion is in a form of coal-water slurry fuel (CWS, which was well-developed in Russia (since the Soviet Union time). CWS significantly reduces emissions saving the heating value of coal. Other ways to use coal are combined heat and power cogeneration and an MHD topping cycle.Sony VAIO VGN-SR93JS Battery

The total known deposits recoverable by current technologies, including highly polluting, low energy content types of coal (i.e., lignite, bituminous), is sufficient for many years. However, consumption is increasing and maximal production could be reachedwithin decades (see World Coal Reserves, below).Sony VAIO VGN-SR93PS Battery

Coking coal and use of coke

Coke is a solid carbonaceous residue derived from low-ash, low-sulfur bituminous coal from which the volatile constituents are driven off by baking in an oven without oxygen at temperatures as high as 1,000 °C (1,832 °F) so that the fixed carbon and residual ash are fused together. Sony VAIO VGN-SR93YS Battery

Metallurgical coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. The coking coal should be low in sulphur and phosphorus so that they do not migrate to the metal. The product is cast iron and is too rich in dissolved carbon, and so must be treated further to make steel.Sony VAIO VGN-SR94FS Battery

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. However, the alternative route to is direct reduced iron, where any carbonaceous fuel can be used to make sponge or pelletised iron.Sony VAIO VGN-SR94GS Battery

Coke from coal is grey, hard, and porous and has a heating value of 24.8 million Btu/ton (29.6 MJ/kg). Some cokemaking processes produce valuable by-products that include coal tar, ammonia, light oils, and "coal gas".

Petroleum coke is the solid residue obtained in oil refining, which resembles coke but contains too many impurities to be useful in metallurgical applications.Sony VAIO VGN-SR94HS Battery

Gasification

Coal gasification can be used to produce syngas, a mixture of carbon monoxide (CO) and hydrogen (H2) gas. This syngas can then be converted into transportation fuels like gasoline and diesel through the Fischer-Tropsch process.Sony VAIO VGN-SR94VS Battery

This technology is currently used by the Sasol chemical company of South Africa to make gasoline from coal and natural gas. Alternatively, the hydrogen obtained from gasification can be used for various purposes such as powering a hydrogen economy, making ammonia, or upgrading fossil fuels.Sony VAIO VGN-SZ35B/B Battery

During gasification, the coal is mixed with oxygen and steam (water vapor) while also being heated and pressurized. During the reaction, oxygen and water moleculesoxidize the coal into carbon monoxide (CO) while also releasing hydrogen (H2) gas. This process has been conducted in both underground coal mines and in coal refineries.Sony VAIO VGN-SZ54B/B Battery

If the refiner wants to produce gasoline, the syngas is collected at this state and routed into a Fischer-Tropsch reaction. If hydrogen is the desired end-product, however, the syngas is fed into the water gas shift reaction where more hydrogen is liberated.Sony VAIO VGN-SZ55B/B Battery
High prices of oil and natural gas are leading to increased interest in "BTU Conversion" technologies such as gasification, methanation and liquefaction. TheSynthetic Fuels Corporation was a U.S. government-funded corporation established in 1980 to create a market for alternatives to imported fossil fuels (such as coal gasification). Sony VAIO VGN-SZ55GN/B Battery
The corporation was discontinued in 1985.

In the past, coal was converted to make coal gas, which was piped to customers to burn for illumination, heating, and cooking. At present, the safer natural gas is used instead.Sony VAIO VGN-SZ56 Battery

Liquefaction

Coal can also be converted into liquid fuels such as gasoline or diesel by several different processes. In the direct liquefaction processes, the coal is eitherhydrogenated or carbonized. Hydrogenation processes are the Bergius process,the SRC-I and SRC-II (Solvent Refined Coal) processes and the NUS Corporation hydrogenation process.Sony VAIO VGN-SZ561N Battery

In the process of low-temperature carbonization, coal is coked at temperatures between 360 °C (680 °F) and 750 °C (1,380 °F). These temperatures optimize the production of coal tars richer in lighter hydrocarbons than normal coal tar. The coal tar is then further processed into fuels. Sony VAIO VGN-SZ562N Battery

Alternatively, coal can be converted into a gas first, and then into a liquid, by using the Fischer-Tropsch process. An overview of coal liquefaction and its future potential is available.

Coal liquefaction methods involve carbon dioxide (CO2) emissions in the conversion process. Sony VAIO VGN-SZ57N Battery

If coal liquefaction is done without employing either carbon capture and storage technologies or biomass blending, the result is lifecycle greenhouse gas footprints that are generally greater than those released in the extraction and refinement of liquid fuel production from crude oil. Sony VAIO VGN-SZ58GN Battery

If CCS technologies are employed, reductions of 5-12% can be achieved in CTL plants and up to a 75% reduction is achievable when co-gasifying coal with commercially demonstrated levels of biomass (30% biomass by weight) in CBTL plants.For most future synthetic fuelprojects, Carbon dioxide sequestration is proposed to avoid releasing it into the atmosphere. Sony VAIO VGN-SZ58GN/C Battery

Sequestration will, however, add to the cost of production. Currently all US and at least one Chinese synthetic fuel projects,include sequestration in their process designs.

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.Sony VAIO VGN-SZ58N Battery

It is one form of several pre-combustion treatments and processes for coal that alter coal's characteristics before it is burned. The goals of pre-combustion coal technologies are to increase efficiency and reduce emissions when the coal is burned. Depending on the situation, pre-combustion technology can be used in place of or as a supplement to post-combustion technologies to control emissions from coal-fueled boilers.Sony VAIO VGN-SZ61MN/B Battery

Industrial processes

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. Sony VAIO VGN-SZ61VN/X Battery

It is also contained in mould wash, a paste or liquid with the same function applied to the mould before casting. 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.Sony VAIO VGN-SZ61WN/C Battery

Cultural usage

Coal is the official state mineral of Kentucky (even though coal is not a mineral) and the official state rock of Utah. Both U.S. states have a historic link to coal mining.

Some cultures uphold that children who misbehave will receive only a lump of coal from Santa Claus for Christmas in their stockings instead of presents.Sony VAIO VGN-SZ640N/B Battery

It is also customary and lucky in Scotland and the North of England to give coal as a gift on New Year's Day. It happens as part of First-Footing and represents warmth for the year to come.

Coal as a traded commodity

In North America, Central Appalachian coal futures contracts are currently traded on the New York Mercantile Exchange (trading symbol QL). Sony VAIO VGN-SZ645P3 Battery

The trading unit is 1,550 short tons (1,410 t) per contract, and is quoted in U.S. dollars and cents per ton. Since coal is the principal fuel for generating electricity in the United States, coal futures contracts provide coal producers and the electric power industry an important tool for hedging and risk management.Sony VAIO VGN-SZ650N/C Battery

In addition to the NYMEX contract, the IntercontinentalExchange (ICE) has European (Rotterdam) and South African (Richards Bay) coal futures available for trading. The trading unit for these contracts is 5,000 tonnes (5,500 short tons), and are also quoted in U.S. dollars and cents per ton.Sony VAIO VGN-SZ660N/C Battery

The price of coal increased from around $30.00 per short ton in 2000 to around $150.00 per short ton as of September 2008. As of October 2008, the price per short ton had declined to $111.50. Prices further declined to $71.25 as of October 2010.

Environmental effects

There are a number of adverse health and environmental effects of coal burning  especially in power stations, and of coal mining.Sony VAIO VGN-SZ670N/C Battery

These effects include:

  • Coal-fired power plants shortened nearly 24,000 lives a year in the United States, including 2,800 from lung cancer
  • Generation of hundreds of millions of tons of waste products, including fly ash, bottom ash, flue gas desulfurization sludge, that contain mercury, uranium, thorium, arsenic, and other heavy metals  Sony VAIO VGN-SZ680ND Battery
  • Acid rain from high sulfur coal
  • Interference with groundwater and water table levels
  • Contamination of land and waterways and destruction of homes from fly ash spills such as Kingston Fossil Plant coal fly ash slurry spill
  • Impact of water use on flows of rivers and consequential impact on other land-uses  Sony VAIO VGN-SZ691N/X Battery
  • Dust nuisance
  • Subsidence above tunnels, sometimes damaging infrastructure
  • Uncontrollable underground fires which may burn for decades or centuries.
  • Coal-fired power plants without effective fly ash capture are one of the largest sources of human-caused background radiation exposure  Sony VAIO VGN-SZ71E/B Battery
  • Coal-fired power plants emit mercury, selenium, and arsenic which are harmful to human health and the environment
  • Release of carbon dioxide, a greenhouse gas, which causes climate change and global warming according to the IPCCand the EPA. Coal is the largest contributor to the human-made increase of CO2 in the air  Sony VAIO VGN-SZ71VN/X Battery

Economic aspects

Coal liquification is one of the backstop technologies that could potentially limit escalation of oil prices and mitigate the effects of transportation energy shortage that will occur under peak oil. This is contingent on liquefaction production capacity becoming large enough to satiate the very large and growing demand for petroleum. Sony VAIO VGN-SZ71WN/C Battery

Estimates of the cost of producing liquid fuels from coal suggest that domestic U.S. production of fuel from coal becomes cost-competitive with oil priced at around $35 per barrel, with the $35 being the break-even cost. With oil prices as low as around $40 per barrel in the U.S. as of December 2008,Sony VAIO VGN-SZ74B/B Battery

liquid coal lost some of its economic allure in the U.S., but will probably be re-vitalized, similar to oil sand projects, with an oil price around $70 per barrel.

United States

Some of the simplest economic costs of coal come in the form of subsidies and tax breaks which are not reflected in the market price of coal (for example the estimated $4.6 billion in coal-related subsidies in the 2009 stimulus package). Sony VAIO VGN-SZ750N/C Battery

Coal mining and combustion projects require major investments, and the risks and costs of those investments are often passed on to taxpayers via infrastructure subsidies and loan guarantees. An extreme example of this is the Healy Clean Coal Plant (HCCP),Sony VAIO VGN-SZ75B/B Battery

which has cost the State of Alaska and the Federal Government nearly $300 million since the mid 1990s yet is not producing power in return. Similarly, a recent study in Kentucky determined that the government spends $115 million more on subsidies for the coal industry in the state than it receives in taxes or other benefits.Sony VAIO VGN-SZ76 Battery

Taxpayers also pay the costs of cleaning up environmental disasters caused by the coal industry. Cleanup of the recent coal ash spill in Tennessee is estimated to cost up to $1 billion, not including pending litigation. Now that the cleanup at this site has been taken over by the EPA under the Superfund law, most of this cost will be borne by the US taxpayer.Sony VAIO VGN-SZ770N/C Battery

The health impacts of coal pollution have enormous economic costs, through health care costs and lost productivity. The Ontario government study estimated these costs as billions of dollars within Ontario alone. A similar recent study in West Virginia found that the cost associated with premature death due to coal mining was five times greater than all measurable economic benefits from the mining.Sony VAIO VGN-SZ77N Battery

Other industries depend on the ecosystems coal mining destroys. This economic impact on industries such as recreational fishing, commercial fishing, and tourism is particularly relevant in Alaska. Almost 55,000 direct jobs (full time equivalent basis, FTE) are closely linked to the health of Alaska's ecosystems. Sony VAIO VGN-SZ780 Battery

These jobs make up more than a quarter of Alaskan FTE employment and produce almost $2.6 billion of income for Alaska workers. These 55,000 ecosystem-dependent jobs dwarf the 350 estimated jobs that would be created by a project such as the Chuitna Coal strip mine.Sony VAIO VGN-SZ78N Battery

Negative effects on the economy lead to worse health in the population, which has an impact on health care costs, compounding the economic impact. Some people have used this to argue that coal has additional benefits to society. The argument is that coal provides cheap electricity, which is a boon to the economy, therefore health is improved, and health care costs are lowered.Sony VAIO VGN-SZ791N/X Battery

While this additional health effect should indeed be considered, it should be applied after the economic impacts discussed above. Once the costs of pollution, global warming, and habitat destruction are added to the benefits of cheap electricity, the economic impact of coal is no longer positive, and this additional health effect only makes it even more costly.Sony VAIO VGN-SZ84NS Battery

China

In China, due to an increasing need for liquid energy in the transportation sector, coal liquefaction projects were given high priority even during periods of oil prices below $40 per barrel.  This is probably because China prefers not to be dependent on foreign oil, instead utilizing its enormous domestic coal reserves. Sony VAIO VGN-SZ84PS Battery

As oil prices were increasing during the first half of 2009, the coal liquefaction projects in China were again boosted, and these projects are profitable with an oil barrel price of $40.

China is by far the largest producer of coal in the world.Sony VAIO VGN-SZ84S Battery

It has now become the world's largest energy consumer  but relies on coal to supply about 70% of its energy needs. An estimated 5 million people work in China's coal-mining industry.

Among commercially mature technologies, advantages for indirect coal liquefaction over direct coal liquefaction are reported by Williams and Larson (2003).Sony VAIO VGN-SZ84US Battery

Energy density

The energy density of coal, i.e. its heating value, is roughly 24 megajoules per kilogram.

The energy density of coal can also be expressed in kilowatt-hours, the units that electricity is most commonly sold in, per units of mass to estimate how much coal is required to power electrical appliances.Sony VAIO VGN-SZ85NS Battery

One kilowatt-hour is 3.6 MJ, so the energy density of coal is 6.67 kW·h/kg. The typical thermodynamic efficiency of coal power plants is about 30%, so of the 6.67 kW·h of energy per kilogram of coal, 30% of that—2.0 kW·h/kg—can successfully be turned into electricity; the rest is waste heat. Sony VAIO VGN-SZ85S Battery

So coal power plants obtain approximately 2.0 kW·h per kilogram of burned coal.

As an example, running one 100-watt lightbulb for one year requires 876 kW·h (100 W × 24 h/day × 365 day/year = 876000 W·h = 876 kW·h). Converting this power usage into physical coal consumption:Sony VAIO VGN-SZ85US Battery

For a coal power plant with a 40% efficiency, it takes 325 kg (714 lb) of coal to power a 100 W lightbulb for one year.One should also take into accounttransmission and distribution losses caused by resistance and heating in the power lines, which is in the order of 5–10%, depending on distance from the power station and other factors.Sony VAIO VGN-SZ94NS Battery

Carbon intensity

Commercial coal has a carbon content of at least 70%. Coal with a heating value of 6.67 kWh per kilogram as quoted above has a carbon content of roughly 80%, which is, where 1 mol equals to NA (Avogadro Number) atoms.Sony VAIO VGN-SZ94PS Battery

Carbon combines with oxygen in the atmosphere during combustion, producing carbon dioxide, with an atomic weight of (12 + 16 × 2 = 44 kg/kmol). The CO2 released to air for each kilogram of incinerated coal is therefore .This can be used to calculate an emission factor for CO2 from the use of coal power.Sony VAIO VGN-SZ94S Battery

Since the useful energy output of coal is about 30% of the 6.67 kWh/kg(coal), the burning of 1 kg of coal produces about 2 kWh of electrical energy. Since 1 kg coal emits 2.93 kg CO2, the direct CO2 emissions from coal power are 1.47 kg/kWh, or about 0.407 kg/MJ.Sony VAIO VGN-SZ94US Battery

The U.S. Energy Information Agency's 1999 report on CO2 emissions for energy generation,quotes a lower emission factor of 0.963 kg CO2/kWh for coal power. The same source gives a factor for oil power in the U.S. of 0.881 kg CO2/kWh, while natural gas has 0.569 kg CO2/kWh.Sony VAIO VGN-SZ95NS Battery

Estimates for specific emission from nuclear power, hydro, and wind energy vary, but are about 100 times lower.

Underground fires

There are thousands of coal fires burning around the world.Those burning underground can be difficult to locate and many cannot be extinguished. Sony VAIO VGN-SZ95S Battery

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. Sony VAIO VGN-SZ95US Battery

A grass fire in a coal area can set dozens of coal seams on fire. Coal fires in China burn 109 million tons of coal a year, emitting 360 million metric tons of CO2. This contradicts the ratio of 1:1.83 given earlier,[clarification needed] but it amounts to 2-3% of the annual worldwide production of CO2 from fossil fuels.Sony VAIO VGN-TZ121 Battery

In Centralia, Pennsylvania (a borough located in the Coal Region of the United States), an exposed vein of coal 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. Sony VAIO VGN-TZ13 Battery

The Australian Burning Mountain was originally believed to be a volcano, but the smoke and ash comes from a coal fire that has been burning for some 6,000 years.

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.Sony VAIO VGN-TZ130N/B Battery

Local people once used this method to mine ammoniac. This place has been well-known since the time of Herodotus, but European geographers misinterpreted the Ancient Greek descriptions as the evidence of active volcanism in Turkestan (up to the 19th century, when the Russian army invaded the area).Sony VAIO VGN-TZ131 Battery

The reddish siltstone rock that caps many ridges and buttes in the Powder River Basin (Wyoming), and in western North Dakota is called porcelanite, which also may resemble the coal burning waste "clinker" or volcanic "scoria". Clinker is rock that has been fused by the natural burning of coal. Sony VAIO VGN-TZ132/N Battery

In the Powder River Basin approximately 27 to 54 billion tons of coal burned within the past three million years.Wild coal fires in the area were reported by the Lewis and Clark Expedition as well as explorers and settlers in the area.

Production trends

In 2006, China was the top producer of coal with 38% share followed by the USA and India, according to the British Geological Survey.Sony VAIO VGN-TZ132N Battery

World coal reserves

The 930 billion short tons of recoverable coal reserves estimated by the Energy Information Administration are equal to about 4,116 BBOE (billion barrels of oil equivalent).The amount of coal burned during 2007 was estimated at 7.075 billion short tons, or 133.179 quadrillion BTU's.Sony VAIO VGN-TZ150N/N Battery

This is an average of 18.8 million BTU per short ton. In terms of heat content, this is about 57,000,000 barrels (9,100,000 m3) of oil equivalent per day. By comparison in 2007, natural gas provided 51,000,000 barrels (8,100,000 m3) of oil equivalent per day, while oil provided 85,800,000 barrels (13,640,000 m3) per day.Sony VAIO VGN-TZ160CB Battery

BP, in its 2007 report, estimated at 2006 end that there were several million tons of proven coal reserves worldwide, or 147 yearsreserves-to-production ratio. This figure only includes reserves classified as "proven"; exploration drilling programs by mining companies, particularly in under-explored areas, are continually providing new reserves.Sony VAIO VGN-TZ160N/B Battery

In many cases, companies are aware of coal deposits that have not been sufficiently drilled to qualify as "proven". However, some nations haven't updated their information and assume reserves remain at the same levels even with withdrawals. Sony VAIO VGN-TZ16GN/B Battery

Collective projections generally predict that global peak coal production may occur sometime around 2025 at 30 percent above current production in the best case scenario, depending on future coal production rates.

The goal of coal mining is to remove coal from the ground. Coal is valued for its energy content, and since the 1880s has been widely used to generate electricity.Sony VAIO VGN-TZ16N Battery

Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United States, United Kingdom, and South Africa, a coal mine and its structures are a "colliery". In Australia, "colliery" generally refers to an underground coal mine.Sony VAIO VGN-TZ16N/B Battery

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 exponentially when coal-fed steam engines were built for the railways and steamships.Sony VAIO VGN-TZ17/N Battery

The new mines that grew up in the 19th century depended on men and children to work long hours in often dangerous working conditions. There were many coalfields, but the oldest were in Newcastle and Durham, South Wales, Scotland and the Midlands, such as those atCoalbrookdale.Sony VAIO VGN-TZ170N/B Battery

The oldest continuously worked deep-mine in the United Kingdom is Tower Colliery in South Wales valleys in the heart of the South Wales coalfield. This colliery was developed in 1805, and its miners bought it out at the end of the 20th century, to prevent it from being closed.Sony VAIO VGN-TZ170N/N Battery

Tower Colliery was finally closed on 25 January 2008, although production continues at the Aberpergwm drift mine owned by Walter Energy of the USA nearby.

Coal was mined in America in the early 18th century, and commercial mining started around 1730 in Midlothian, Virginia.Sony VAIO VGN-TZ17GN/B Battery

Coal-cutting machines were invented in the 1880s. Before this invention, coal was mined from underground with a pickand shovel. By 1912 surface mining was conducted with steam shovels designed for coal mining.

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. Sony VAIO VGN-TZ17N Battery

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 acoal preparation plant. Technical and economic feasibility are evaluated based on: regional geologic conditions; overburden characteristics; Sony VAIO VGN-TZ18/N Battery

coal seam continuity, thickness, structure, quality, and depth; strength of materials above and below the seam for roof and floor conditions; topography (e

specially altitude and slope); climate; land ownership as it affects the availability of land for mining and access; surface drainage patterns; ground water conditions;Sony VAIO VGN-TZ180N/RC Battery

availability of labor and materials; coal purchaser requirements in terms of tonnage, quality, and destination; and capital investment requirements.

Surface mining and deep underground mining are the two basic methods of mining. Sony VAIO VGN-TZ185N/WC Battery

The choice of mining method depends primarily on depth of burial, density of the overburden and thickness of the coal seam. Seams relatively close to the surface, at depths less than approximately 180 ft (50 m), are usually surface mined.

Coal that occurs at depths of 180 to 300 ft (50 to 100 m) are usually deep mined, but in some cases surface mining techniques can be used.Sony VAIO VGN-TZ18GN/X Battery

For example, some western U.S. coal that occur at depths in excess of 200 ft (60 m) are mined by the open pit methods, due to thickness of the seam 60–90 feet (20–30 m). Coals occurring below 300 ft (100 m) are usually deep mined. Although there are open pit mining operations working on coal seams up to 1000–1500 feet (300–450 m) below ground level, for instance Tagebau Hambach in Germany.Sony VAIO VGN-TZ18N Battery

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