Coal is: black sedimentary rock

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 (especially 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

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, open pit, or strip) mining methods. 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. Sony VAIO VGN-TZ190N/B Battery

Large Open Cast mines can cover an area of many square kilometers and use very large pieces of equipment. 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.Sony VAIO VGN-TZ190N/BC Battery

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.Sony VAIO VGN-TZ191N/XC Battery

The coal is then loaded on to large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used.

Most open cast mines in the United States extract bituminous coal. In Australia and South Africa open cast mining is used for both thermal and metallurgical coals.Sony VAIO VGN-TZ195N/XC Battery

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.Sony VAIO VGN-TZ198N/RC Battery

Area mining

Strip mining exposes the coal by removing the overburden (the earth above the coal seam(s)) in long cuts or strips. The soil from the first strip is deposited in an area outside the planned mining area. Spoil from subsequent cuts is deposited as fill in the previous cut after coal has been removed. Sony VAIO VGN-TZ250N/B Battery

Usually, the process is todrill the strip of overburden next to the previously mined strip.

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. Sony VAIO VGN-TZ250N/N Battery

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 (a 'block' of coal). This block of coal may be drilled and blasted (if hard) or otherwise loaded onto trucks or conveyors for transport to the coal preparation (or wash) plant. Sony VAIO VGN-TZ250N/P Battery

Once this strip is empty of coal, the process is repeated with a new strip being created next to it. This method is most suitable for areas with flat terrain.

Equipment to be used depends on geologic conditions. For example, to remove overburden that is loose or unconsolidated, a bucket wheel excavator might be the most productive. The life of some area mines may be more than 50 years.Sony VAIO VGN-TZ27/N Battery

Contour mining

The contour mining method consists of removing overburden from the seam in a pattern following the contours along a ridge or around a hillside. This method is most commonly used in areas with rolling to steep terrain. Sony VAIO VGN-TZ270N/B Battery

It was once common to deposit the spoil on the downslope side of the bench thus created, but this method of spoil disposal consumed much additional land and created severe landslide and erosion problems. To alleviate these problems, a variety of methods were devised to use freshly cut overburden to refill mined-out areas.Sony VAIO VGN-TZ27N Battery

These haul-back or lateral movement methods generally consist of an initial cut with the spoil deposited downslope or at some other site and spoil from the second cut refilling the first. A ridge of undisturbed natural material 15 to 20 ft (5–6 m) wide is often intentionally left at the outer edge of the mined area. Sony VAIO VGN-TZ28/N Battery

This barrier adds stability to the reclaimed slope by preventing spoil from slumping or sliding downhill.

The limitations on contour strip mining are both economic and technical. When the operation reaches a predetermined stripping ratio (tons of overburden/tons of coal), it is not profitable to continue. Sony VAIO VGN-TZ285N/RC Battery

Depending on the equipment available, it may not be technically feasible to exceed a certain height of highwall. At this point, it is possible to produce more coal with the augering method in which spiral drills bore tunnels into a highwall laterally from the bench to extract coal without removing the overburden.Sony VAIO VGN-TZ28N Battery

Mountaintop removal mining

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." Valley fills occur in steep terrain where there are limited disposal alternatives.Sony VAIO VGN-TZ290EAB Battery

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. Sony VAIO VGN-TZ290EAN Battery

This method usually leaves ridge and hill tops as flattened plateaus. The process is highly controversial for the drastic changes in topography, the practice of creating head-of-hollow-fills, or filling in valleys with mining debris, and for covering streams and disrupting ecosystems.Sony VAIO VGN-TZ290EAP Battery

Spoil is placed at the head of a narrow, steep-sided valley or hollow. In preparation for filling this area, vegetation and soil are removed and a rock drain constructed down the middle of the area to be filled, where a natural drainage course previously existed.Sony VAIO VGN-TZ295N/XC Battery

When the fill is completed, this underdrain will form a continuous water runoff system from the upper end of the valley to the lower end of the fill. Typical head-of-hollow fills are graded and terraced to create permanently stable slopes.

Room and pillar mining

Room and pillar mining consists of coal deposits that are mined by cutting a network of rooms into the coal seam. Sony VAIO VGN-TZ298N/XC Battery

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.Sony VAIO VGN-TZ33/B Battery

However, this can be extracted at a later stage (see Retreat Mining).

Underground mining

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.Sony VAIO VGN-TZ33/N Battery

In deep mining, the room and pillar or bord and pillarmethod 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),Sony VAIO VGN-TZ33/W Battery

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.Sony VAIO VGN-TZ350N/B Battery

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. The mobile roof supports are similar to a large dining-room table, but with hydraulic jacks for legs.Sony VAIO VGN-TZ350N/N Battery

After the large pillars of coal have been mined away, the mobile roof support's legs shorten and it is withdrawn to a safe area. The mine roof typically collapses once the mobile roof supports leave an area.

There are five principal methods of underground mining: Sony VAIO VGN-TZ350N/P Battery

• 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. Sony VAIO VGN-TZ370N/B Battery
• The loosened coal falls on to 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 which advance with the machine as mining progresses. Sony VAIO VGN-TZ37N/G Battery
• 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.Sony VAIO VGN-TZ37N/P Battery
• 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.
• Continuous mining utilizes a machine with a large rotating steel drum equipped with tungsten carbide teeth that scrape coal from the seam.Sony VAIO VGN-TZ37N/R Battery
• 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 five tons of coal a minute, more than a non-mechanised mine of the 1920s would produce in an entire day. Sony VAIO VGN-TZ37N/X Battery
• 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. Sony VAIO VGN-TZ38N/X Battery
• Continuous mining is truly a misnomer, as room and pillar coal mining is very cyclical. In the US, one can generally cut 20 ft (or a bit more with MSHA permission), after which, the face has to be serviced, before it can be advanced again. During servicing, the "continuous" miner moves to another face.Sony VAIO VGN-TZ398U/XC Battery
• Some continuous miners can bolt and 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. Sony VAIO VGN-TZ50B Battery
• This may partly be because incorporation of bolting makes the machines wider, and therefore, less maneuverable.
• 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 on to shuttle cars or conveyors for removal to a central loading area. Sony VAIO VGN-TZ90HS Battery
• 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.Sony VAIO VGN-TZ90NS Battery
• 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. The continuous miner shears coal panels 150 to 200 feet (40 to 60 m) wide and more than a half-mile (1 km) long, having regard to factors such as geological strata.Sony VAIO VGN-TZ90S Battery
• 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 ceiling will collapse and possibly crush or trap workers in the mine.Sony VAIO VPC CW2MFX/PU Battery

Production

Coal is mined commercially in over 50 countries. Over 7,036 Mt/yr of hard coal is currently produced, a substantial increase over the past 25 years. In 2006, the world production of brown coal and lignite was slightly over 1,000 Mt, with Germany the world’s largest brown coal producer at 194.4 Mt, and China second at 100.6 Mt.Sony VAIO VPC S11V9E/B Battery

Coal production has grown fastest in Asia, while Europe has declined. The top coal mining nations (figures in brackets are 2009 estimate of total coal production in millions of tons).

Most coal production is used in the country of origin, with around 16 percent of hard coal production being exported.Sony VAIO VPCB119GJ/B Battery

Global coal production is expected to reach 7,000 Mt/yr in 2030 (Update required, world coal production is already past 7,000 Mt/yr and by 2030 will probably be closer to 13,000 Mt/yr), with China accounting for most of this increase. Steam coal production is projected to reach around 5,200 Mt/yr; coking coal 620 Mt/yr; and brown coal 1,200 Mt/yr.Sony VAIO VPCB11AGJ Battery

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.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.Sony VAIO VPCB11AVJ Battery

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. Sony VAIO VPCB11V9E Battery

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 (JORC) Code used by the Australian Securities Exchange (ASX).Sony VAIO VPCB11X9E Battery

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.Sony VAIO VPCCW18FJ/P Battery

Many jobs require four-year university degrees. Computer knowledge has also become greatly valued within the industry as most of the machines and safety monitors are computerized.

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".Sony VAIO VPCCW18FJ/R Battery

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.

Dangers to miners

Historically, coal mining has been a very dangerous activity and the list of historical coal mining disasters is a long one. Sony VAIO VPCCW18FJ/W Battery

In the US alone, more than 100,000 coal miners were killed in accidents over the past century, with more than 3,200 dying in 1907 alone. Open cut hazards are principally mine wall failures and vehicle collisions; underground mining hazards include suffocation, gas poisoning, roof collapse and gas explosions.Sony VAIO VPCCW19FJ/W Battery

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.Sony VAIO VPCCW1AFJ Battery

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. China, in particular, has the highest number of coal mining related deaths in the world, with official statistics claiming that 6,027 deaths occurred in 2004.Sony VAIO VPCCW1AHJ Battery

To compare, 28 deaths were reported in the US in the same year. Coal production in China is twice that in the US, while the number of coal miners is around 50 times that of the US, making deaths in coal mines in China 4 times as common per worker (108 times as common per unit output) as in the US.Sony VAIO VPCCW1S1E Battery

In 2006, fatal work injuries among miners in the US doubled from the previous year, totaling 47. These figures can in part be attributed to the Sago Mine disaster of January 2006. The 2007 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 US miners.Sony VAIO VPCCW1S1E/B Battery

More recently, the Upper Big Branch Mine disaster in West Virginia killed 29 miners in April 2010.

Chronic lung diseases, such as pneumoconiosis (black lung) were once common in miners, leading to reduced life expectancy. Sony VAIO VPCCW1S1E/L Battery

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).[25] Rates may be higher than reported in some regions.Sony VAIO VPCCW1S1E/P Battery

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, and is formed as a result of corrosion in enclosed spaces so removing oxygenfrom the atmosphere. Sony VAIO VPCCW1S1E/R Battery
• After damp: similar to black damp, after damp consists of carbon monoxide, carbon dioxide and nitrogen and forms after a mine explosion.
• Fire damp: consists of mostly methane, a highly flammable gas.
• Stink damp: so named for the rotten egg smell of the hydrogen sulphide gas, stink damp can explode and is also very toxic.
• White damp: air containing carbon monoxide which is toxic, even at low concentrations .Sony VAIO VPCCW1S1E/W Battery

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,electrical equipment, and ventilation have reduced many of the risks of rock falls, explosions, and unhealthy air quality.Sony VAIO VPCCW21FX/B Battery

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, mining remains the second most dangerous occupation in America.Sony VAIO VPCCW21FX/L Battery

New braces called Atlas Cribs contain a mix of hardwoods and a main lateral element that make these braces stronger than other braces used in the past. The new cribbing system takes up 41 percent less area than existing ones and may be up to 50 percent more efficient in terms of airflow.Sony VAIO VPCCW21FX/R Battery

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, Sony VAIO VPCCW21FX/W Battery

alters current land uses, and to some extent permanently changes the general topography of the area mined,This often results in a scarred landscape with no scenic value. Rehabilitation or reclamation mitigates some of these concerns and is required by Federal Law, specifically the Surface Mining Control and Reclamation Act of 1977.Sony VAIO VPCCW26EC Battery

Mine tailing dumps produce acid mine drainage which can seep into waterways and aquifers, with consequences on ecological and human health. If underground mine tunnels collapse, this can cause subsidence of land surfaces. During actual mining operations, methane, a known greenhouse gas, may be released into the air. Sony VAIO VPCCW26FX/B Battery

And by the movement, storage, and redistribution of soil, the community of microorganisms and nutrient cycling processes can be disrupted.

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.Sony VAIO VPCCW28EC Battery

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. Most Chinese mines are deep underground and do not produce the surface disruption typical of strip mines.Sony VAIO VPCCW28FJ/P Battery

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.Sony VAIO VPCCW28FJ/R Battery

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 in China|aquaculture]] ponds but has more than they need for that purpose.Sony VAIO VPCCW28FJ/W Battery

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.Sony VAIO VPCCW29FJ/W Battery

Colombia

Some of the world's largest coal reserves are located in South America, and an opencast mine at Cerrejón in Colombiais 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). Sony VAIO VPCCW2AFJ Battery

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. Sony VAIO VPCCW2AHJ Battery

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 on to vessels of up to 175,000 tons of dead weight. Sony VAIO VPCCW2S1E Battery

The mine, railroad and port operate 24 hours per day. Cerrejón directly employs 4,600 workers, with a further 3,800 employed by contractors. The reserves at Cerrejón are low-sulfur, low-ash, bituminous coal. The coal is mostly used for electric power generation, with some also used in steel manufacture. Sony VAIO VPCCW2S1E/B Battery

The surface mineable reserves for the current contract are 330 million tons. However, total proven reserves to a depth of 300 metres are 3,000 million tons.

Coalbed methane (CBM) or Coal Bed Methane , coalbed gas or coal mine methane (CMM) is a form of natural gas extracted from coal beds.Sony VAIO VPCCW2S1E/L Battery

In recent decades it has become an important source of energy in United States, Canada, and other countries. Australia has rich deposits where it is known as coal seam gas (abbreviated "CSG" ).

The term refers to methane adsorbed into the solid matrix of the coal. It is called 'sweet gas' because of its lack of hydrogen sulfide.Sony VAIO VPCCW2S1E/P Battery

The presence of this gas is well known from its occurrence in underground coal mining, where it presents a serious safety risk. Coalbed methane, often referred to as CBM, is distinct from a typical sandstone or other conventional gas reservoir, as the methane is stored within the coal by a process called adsorption.Sony VAIO VPCCW2S1E/R Battery

The methane is in a near-liquid state, lining the inside of pores within the coal (called the matrix). The open fractures in the coal (called the cleats) can also contain free gas or can be saturated with water.

Unlike much natural gas from conventional reservoirs, coalbed methane contains very little heavier hydrocarbons such as propane or butane, and no natural gas condensate.Sony VAIO VPCCW2S1E/W Battery

It often contains up to a few percent carbon dioxide. Some coal seams, such as those in certain areas of the Illawarra Coal Measures in NSW, Australia, contain little methane, with the predominant coal seam gas being carbon dioxide.

Permeability of coal bed methane reservoirs

Permeability is key factor for CBM. Coal itself is a low permeability reservoir. Sony VAIO VPCCW2S5C CN1 Battery

Almost all the permeability of a coal bed is usually considered to be due to fractures, which in coal are in the form of cleats and joints. The permeability of the coal matrix is negligible by comparison. Coal cleats are of two types: butt cleats and face cleats, which occur at nearly right angles.Sony VAIO VPCF112FX/B Battery

The face cleats are continuous and provide paths of higher permeability while butt cleats are discontinuous and end at face cleats. Joints are larger fractures through the coal that may cross lithological boundaries. Hence, on a small scale, fluid flow through coal bed methane reservoirs usually follows rectangular paths. Sony VAIO VPCF115FG/B Battery

The ratio of permeabilities in the face cleat direction over the butt cleat direction may range from 1:1 to 17:1. Because of this anisotropic permeability, drainage areas around coal bed methane wells are often elliptical in shape.Sony VAIO VPCF116FGBI Battery

Intrinsic properties affecting gas production

Gas contained in coal bed methane is mainly methane and trace quantities of ethane, nitrogen, carbon dioxide and few other gases. Intrinsic properties of coal as found in nature determine the amount of gas that can be recovered.Sony VAIO VPCF117FJ/W Battery

Porosity

The porosity of coal bed reservoirs is usually very small, ranging from 0.1 to 10%.

Adsorption capacity

Adsorption capacity of coal is defined as the volume of gas adsorbed per unit mass of coal usually expressed in SCF (standard cubic feet, the volume at standard pressure and temperature conditions) gas/ton of coal. Sony VAIO VPCF117HG/BI Battery

The capacity to adsorb depends on the rank and quality of coal. The range is usually between 100 to 800 SCF/ton for most coal seams found in the US. Most of the gas in coal beds is in the adsorbed form. When the reservoir is put into production, water in the fracture spaces is pumped off first. Sony VAIO VPCF118FJ/W Battery

This leads to a reduction of pressure enhancing desorption of gas from the matrix.

Fracture permeability

As discussed before, the fracture permeability acts as the major channel for the gas to flow. The higher the permeability, higher is the gas production.Sony VAIO VPCF119FC Battery

For most coal seams found in the US, the permeability lies in the range of 0.1 to 50 milliDarcies. The permeability of fractured reservoirs changes with the stress applied to them. Coal displays a stress-sensitive permeability and this process plays an important role during stimulation and production operations.Sony VAIO VPCF119FC/BI Battery

Thickness of formation and initial reservoir pressure

The thickness of the formation may not be directly proportional to the volume of gas produced in some areas.

For Example: It has been observed in the Cherokee Basin in Southeast Kansas that a well with a single zone of 1–2 ft of pay can produce excellent gas rates, whereas an alternative formation with twice the thickness can produce next to nothing. Sony VAIO VPCF119FJ/BI Battery

Some coal (and shale) formations may have high gas concentrations regardless of the formation's thickness, probably due to other factors of the area's geology.

The pressure difference between the well block and the sand face should be as high as possible as is the case with any producing reservoir in general.Sony VAIO VPCF11AFJ Battery

Other properties

Other affecting parameters include coal density, initial gas phase concentration, critical gas saturation, irreducible water saturation, relative permeability to water and gas at conditions of Sw = 1.0 and Sg = 1-Swirreducible respectively.Sony VAIO VPCF11AGJ Battery

Extraction

To extract the gas, a steel-encased hole is drilled into the coal seam (100–1500 meters below ground). As the pressure within the coal seam declines due to natural production or the pumping of water from the coalbed, both gas and 'produced water' come to the surface through tubing. Sony VAIO VPCF11AHJ Battery

Then the gas is sent to a compressor station and into natural gas pipelines. The 'produced water' is either reinjected into isolated formations, released into streams, used for irrigation, or sent to evaporation ponds. The water typically contains dissolved solids such as sodium bicarbonate and chloride.Sony VAIO VPCF11JFX/B Battery

Coalbed methane wells often produce at lower gas rates than conventional reservoirs, typically peaking at near 300,000 cubic feet (8,500 m3) per day (about 0.100 m³/s), and can have large initial costs. The production profiles of CBM wells are typically characterized by a "negative decline" in which the gas production rate initially increases as the water is pumped off and gas begins to desorb and flow. A dry CBM well is similar to a standard gas well.Sony VAIO VPCF11M1E Battery

The methane desorption process follows a curve (of gas content vs. reservoir pressure) called a Langmuir isotherm. The isotherm can be analytically described by a maximum gas content (at infinite pressure), and the pressure at which half that gas exists within the coal. Sony VAIO VPCF11M1E/H Battery

These parameters (called the Langmuir volume and Langmuir pressure, respectively) are properties of the coal, and vary widely. A coal in Alabama and a coal in Colorado may have radically different Langmuir parameters, despite otherwise similar coal properties.Sony VAIO VPCF11MFX/B Battery

As production occurs from a coal reservoir, the changes in pressure are believed to cause changes in the porosity and permeability of the coal. This is commonly known as matrix shrinkage/swelling. As the gas is desorbed, the pressure exerted by the gas inside the pores decreases, causing them to shrink in size and restricting gas flow through the coal.Sony VAIO VPCF11S1E Battery

As the pores shrink, the overall matrix shrinks as well, which may eventually increase the space the gas can travel through (the cleats), increasing gas flow.

The potential of a particular coalbed as a CBM source depends on the following criteria. Cleat density/intensity: cleats are joints confined within coal sheets. Sony VAIO VPCF11S1E/B Battery

They impart permeability to the coal seam. A high cleat density is required for profitable exploitation of CBM. Also important is the maceral composition: maceral is a microscopic, homogeneous, petrographic entity of a corresponding sedimentary rock. A high vitrinite composition is ideal for CBM extraction, while inertinite hampers the same.Sony VAIO VPCF11Z1E Battery

The rank of coal has also been linked to CBM content: a vitrinite reflectance of 0.8-1.5% has been found to imply higher productivity of the coalbed.

The gas composition must be considered, because natural gas appliances are designed for gas with a heating value of about 1000 BTU (British thermal units) per cubic foot, or nearly pure methane. Sony VAIO VPCF11Z1E/BI Battery

If the gas contains more than a few percent non-flammable gases such as nitrogen or carbon dioxide, either these will have to be removed or it will have to be blended with higher-BTU gas to achieve pipeline quality. If the methane composition of the coalbed gas is less than 92%, it may not be commercially marketable.Sony VAIO VPCF11ZHJ Battery

Environmental impacts

CBM wells are connected by a network of roads, pipelines, and compressor stations. Over time, wells may be spaced more closely in order to extract the remaining methane. Additionally, the produced water may contain undesirable concentrations of dissolved substances. Water withdrawal may depress aquifers over a large area and affect groundwater flows. Sony VAIO VPCF127HGBI Battery

In Australia, produced water is typically evaporated in large ponds due to the high salinity of the water. When these ponds fail (e.g. Chinchilla) the salinity content has destroyed contiguous soil quality and vegetation. Recently a number of gas companies have commenced operating or developing plant to treat the product water for use as domestic supply, Sony VAIO VPCF137HG/BI Battery

cooling water for power stations or discharge to streams. These plant typically use reverse osmosis to treat the product water.

The environmental impacts of CBM development are considered by various governmental bodies during the permitting process and operation, which provide opportunities for public comment and intervention.Sony VAIO VPCS111FM/S Battery

Operators are required to obtain building permits for roads, pipelines and structures, obtain wastewater (produced water) discharge permits, and prepare Environmental Impact Statements. As with other natural resource utilization activities, the application and effectiveness of environmental laws, regulation, and enforcement vary with location.Sony VAIO VPCS115EC Battery

Violations of applicable laws and regulations are addressed through regulatory bodies and criminal and civil judicial proceedings.

Several environmental and conservation organizations work specifically on advocating for responsible coal bed methane development. Northern Plains Resource Council has been leading this fight in Montana since 1999, and the Citizens Concerned About Coalbed Methane has worked out of Fernie, BC since 1998.Sony VAIO VPCS115FG Battery

Reserves

Coalbed methane reserve estimates vary; however a 1997 estimate from the U.S. Geological Survey predicts more than 700 trillion cubic feet (20 trillion cubic metres) of methane within the US. At a natural gas price of US$6.05 per million Btu (US$5.73/GJ), that volume is worth US$4.37trillion.Sony VAIO VPCS117GG Battery

At least 100 trillion cubic feet (2.8 trillion cubic metres) of it is economically viable to produce.

In Canada, British Columbia is estimated to have approximately 90 trillion cubic feet (2.5 trillion cubic metres) of coalbed gas.Sony VAIO VPCS117GGB Battery

Alberta, to date the only province with commercial coalbed methane wells, is estimated to have approximately 170 trillion cubic feet (4.8 trillion cubic metres) of economically recoverable coalbed methane.

Recent depressed natural gas prices have made CBM less economically viable compared to the past few years.Sony VAIO VPCS118EC Battery

Currently considered a non-renewable resource, there is evidence by the Alberta Research Council, Alberta Geological Survey and others showing coalbed methane is arenewable resource, because the bacterial action that formed the methane is ongoing. Sony VAIO VPCS119FJ/B Battery

The assertion of being renewable, however, has itself become one of debate since it has also been shown that the dewatering that accompanies CBM production destroys the conditions needed for the bacteria to produce methane.In addition, the rate of formation of additional methane is undetermined. Sony VAIO VPCS119GC Battery

This debate is currently causing a right of ownership issue in the Canadian province of Alberta, as only non-renewable resources can legally be owned by the province.Sony VAIO VPCS11AFJ Battery,Sony VAIO VPCS11AGJ Battery,Sony VAIO VPCS11AHJ Battery,Sony VAIO VPCS11AVJ Battery,Sony VAIO VPCS11J7E/B Battery,Sony VAIO VPCS11M1E/W Battery,Sony VAIO VPCS11V9E Battery