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# definitions - Coal

## coal(n.)

1.fossil fuel consisting of carbonized vegetable matter deposited in the Carboniferous period

2.a hot fragment of wood or coal that is left from a fire and is glowing or smoldering

## coal(v.)

1.take in coal"The big ship coaled"

2.supply with coal

3.burn to charcoal"Without a drenching rain, the forest fire will char everything"

## Coal(n.)

1.(MeSH)A natural fuel formed by partial decomposition of vegetable matter under certain environmental conditions.

# Merriam Webster

CoalCoal (kōl), n. [AS. col; akin to D. kool, OHG. chol, cholo, G. kohle, Icel. kol, pl., Sw. kol, Dan. kul; cf. Skr. jval to burn. Cf. Kiln, Collier.]
1. A thoroughly charred, and extinguished or still ignited, fragment from wood or other combustible substance; charcoal.

2. (Min.) A black, or brownish black, solid, combustible substance, dug from beds or veins in the earth to be used for fuel, and consisting, like charcoal, mainly of carbon, but more compact, and often affording, when heated, a large amount of volatile matter.

☞ This word is often used adjectively, or as the first part of self-explaining compounds; as, coal-black; coal formation; coal scuttle; coal ship. etc.

☞ In England the plural coals is used, for the broken mineral coal burned in grates, etc.; as, to put coals on the fire. In the United States the singular in a collective sense is the customary usage; as, a hod of coal.

Age of coal plants. See Age of Acrogens, under Acrogen. -- Anthracite or Glance coal. See Anthracite. -- Bituminous coal. See under Bituminous. -- Blind coal. See under Blind. -- Brown coal or Brown Lignite. See Lignite. -- Caking coal, a bituminous coal, which softens and becomes pasty or semi-viscid when heated. On increasing the heat, the volatile products are driven off, and a coherent, grayish black, cellular mass of coke is left. -- Cannel coal, a very compact bituminous coal, of fine texture and dull luster. See Cannel coal. -- Coal bed (Geol.), a layer or stratum of mineral coal. -- Coal breaker, a structure including machines and machinery adapted for crushing, cleansing, and assorting coal. -- Coal field (Geol.), a region in which deposits of coal occur. Such regions have often a basinlike structure, and are hence called coal basins. See Basin. -- Coal gas, a variety of carbureted hydrogen, procured from bituminous coal, used in lighting streets, houses, etc., and for cooking and heating. -- Coal heaver, a man employed in carrying coal, and esp. in putting it in, and discharging it from, ships. -- Coal measures. (Geol.) (a) Strata of coal with the attendant rocks. (b) A subdivision of the carboniferous formation, between the millstone grit below and the Permian formation above, and including nearly all the workable coal beds of the world. -- Coal oil, a general name for mineral oils; petroleum. -- Coal plant (Geol.), one of the remains or impressions of plants found in the strata of the coal formation. -- Coal tar. See in the Vocabulary. -- To haul over the coals, to call to account; to scold or censure. [Colloq.] -- Wood coal. See Lignite.

CoalCoal, v. t. [imp. & p. p. Coaled (?); p. pr. & vb. n. Coaling.]
1. To burn to charcoal; to char. [R.]

Charcoal of roots, coaled into great pieces. Bacon.

2. To mark or delineate with charcoal. Camden.

3. To supply with coal; as, to coal a steamer.

CoalCoal, v. i. To take in coal; as, the steamer coaled at Southampton.

# definition (more)

definition of Wikipedia

char

# analogical dictionary

roche carbonée (fr)[Classe]

coal[ClasseHyper.]

outil du dessinateur (fr)[ClasseParExt.]

noir (fr)[Caract.]

chemistry[Domaine]

Coal[Domaine]

fossil fuel - vegetable matter[Hyper.]

coal - char[Dérivé]

coal (n.)

mineral[Classe]

combustible solide (fr)[Classe]

chose solide (fr)[ClasseParExt.]

coal[Classe]

(coal)[Thème]

(steam engine)[Thème]

coal[Classe]

houille (fr)[Classe]

coal (n.)

factotum[Domaine]

part[Domaine]

cake, part, piece - burn, combust[Hyper.]

factotum[Domaine]

SelfConnectedObject[Domaine]

fragment[Hyper.]

char, coal[Dérivé]

coal (n.)

mettre une récolte à l'abri (fr)[Classe]

roche carbonée (fr)[Classe]

coal[ClasseHyper.]

outil du dessinateur (fr)[ClasseParExt.]

noir (fr)[Caract.]

chemistry[Domaine]

Coal[Domaine]

barn, grange, shed[GenV+comp]

coal - coal - char, coal[Dérivé]

get hold of, take[Analogie]

gather in, take in[Hyper.]

coal[Dérivé]

coal (v.)

roche carbonée (fr)[Classe]

coal[ClasseHyper.]

outil du dessinateur (fr)[ClasseParExt.]

noir (fr)[Caract.]

factotum[Domaine]

Putting[Domaine]

chemistry[Domaine]

Coal[Domaine]

give - fossil fuel - vegetable matter[Hyper.]

coal[Dérivé]

coal (v.)

roche carbonée (fr)[Classe]

coal[ClasseHyper.]

outil du dessinateur (fr)[ClasseParExt.]

noir (fr)[Caract.]

factotum[Domaine]

SelfConnectedObject[Domaine]

chemistry[Domaine]

Coal[Domaine]

burn, combust[Cause]

coal (v.)

# Coal

Composition Sedimentary rock Anthracite coal carbon hydrogen, sulfur, oxygen, nitrogen

Coal (from the Old English term col, which has meant "mineral of fossilized carbon" since the 13th century) [1] is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal 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. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.[2]

Throughout history, coal has been a useful resource. It is primarily burned for the production of electricity and/or heat, and is also used for industrial purposes such as refining metals. A fossil fuel, coal forms when dead plant matter is converted into peat, which in turn is converted into lignite, then sub-bituminous coal, then bituminous coal, and lastly anthracite. This involves biological and geological processes that take place over a long period of time.

Coal is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide anthropogenic sources of carbon dioxide releases. Gross carbon dioxide emissions from coal usage are slightly more than those from petroleum and about double the amount from natural gas.[3] Coal is extracted from the ground by mining, either underground by shaft mining through the seams or in open pits.

The top hard and brown coal producers in 2010 (and 2009) were (in millions of tons): China 3,162 (2,971), United States 997 (985), India 571 (571), Australia 420 (399), Indonesia 336 (301), Russia 324 (297), South Africa 255 (247), Poland 134 (135), Kazakhstan 111 (101), and Colombia 74 (73).[4]

Bituminous coal

## Formation

Example chemical structure of coal

About 300 million years ago, the earth had dense forests in low-lying wetland areas. Due to natural processes such as flooding, these forests were buried under the soil. As more and more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. For the process to continue, the plant matter was protected from biodegradation and oxidization, usually by mud or acidic water. This trapped the carbon in immense peat bogs that were eventually covered and deeply buried by sediments. Under high pressure and high temperature dead vegetation were slowly converted to coal. As coal contains mainly carbon, the conversion of dead vegetation into coal is called carbonization.[5]

The wide shallow seas of the Carboniferous period provided ideal conditions for coal formation, although coal is known from most geological periods. 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 known from Precambrian strata, which predate land plants — this coal is presumed to have originated from residues of algae.[6][7]

## Types

Coastal exposure of the Point Aconi Seam (bituminous coal; Pennsylvanian).
Approximate position of continents toward the end of the Carboniferous Period. The light blue represents shallow seas where many of today's coal deposits are found, as opposed to deeper waters which gave rise to oil-bearing rocks derived from marine species.

As geological processes apply pressure to dead biotic material over time, under suitable conditions it is transformed successively into:

• 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. It is also used as a conditioner for soil to make it more able to retain and slowly release water.
• Lignite, or 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 the Upper Palaeolithic
• Sub-bituminous coal, whose properties range from those of lignite to those of bituminous coal, is used primarily as fuel for steam-electric power generation and is an important source of light aromatic hydrocarbons for the chemical synthesis industry.
• Bituminous coal is a dense sedimentary rock, usually 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 used for heat and power applications in manufacturing and to make coke
• 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.[8] Small steam coal (dry small steam nuts or DSSN) was used as a fuel for domestic water heating
• Anthracite, the highest rank of coal, is 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, is difficult to ignite and is not commonly used as fuel — it is mostly used in pencils and, when powdered, as a lubricant.

The classification of coal is generally based on the content of volatiles. However, the exact classification varies between countries. According to the German classification, coal is classified as follows:[9]

German Classification English Designation Volatiles % C Carbon % H Hydrogen % O Oxygen % S Sulfur % Heat content kJ/kg
Braunkohle Lignite 45-65 60-75 6.0-5.8 34-17 0.5-3 <28470
Flammkohle Flame coal 40-45 75-82 6.0-5.8 >9.8 ~1 <32870
Gasflammkohle Gas flame coal 35-40 82-85 5.8-5.6 9.8-7.3 ~1 <33910
Gaskohle Gas coal 28-35 85-87.5 5.6-5.0 7.3-4.5 ~1 <34960
Fettkohle Fat coal 19-28 87.5-89.5 5.0-4.5 4.5-3.2 ~1 <35380
Esskohle Forge coal 14-19 89.5-90.5 4.5-4.0 3.2-2.8 ~1 <35380
Magerkohle Non baking coal 10-14 90.5-91.5 4.0-3.75 2.8-3.5 ~1 35380
Anthrazit Anthracite 7-12 >91.5 <3.75 <2.5 ~1 <35300
Percent by weight

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 (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".

### Hilt's Law

Hilt's Law is a geological term that states that, in a small area, the deeper the coal, the higher its rank (grade).[10] The law holds true if the thermal gradient is entirely vertical, but metamorphism may cause lateral changes of rank, irrespective of depth.

## Early uses as fuel

Chinese coal miners in an illustration of the Tiangong Kaiwu encyclopedia, published in 1637

The earliest reference to the use of coal as fuel is from the geological treatise On stones (Lap. 16) by the Greek scientist Theophrastus (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. 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.[11]

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.[12][13] 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".[14] 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 the Midlands was transported via the Car Dyke for use in drying grain.[15] Coal cinders have been found in the hearths of villas and military 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.[16] Evidence of coal's use for iron-working in the city during the Roman period has been found.[17] In Eschweiler, Rhineland, deposits of bituminous coal were used by the Romans for the smelting of iron ore.[14]

There is no evidence that the product was of great importance in Britain before the High Middle Ages, after about AD 1000.[18] Mineral coal came to be referred to as "seacoal" in the 13th century; the wharf where the material arrived in London was known as Seacoal Lane, so identified in a charter of King Henry III granted in 1253.[19] Initially the name was given because much coal was found on the shore, having fallen from the exposed coal seams on cliffs above or washed out of underwater coal outcrops,[18] but by the time of Henry VIII it was understood to derive from the way it was carried to London by sea.[20] In 1257–59, coal from Newcastle was shipped to London for the smiths and lime-burners building Westminster Abbey.[18] Seacoal Lane and Newcastle Lane, where coal was unloaded at wharves along the River Fleet, are still in existence.[21] (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 adits was developed.[12] 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.[22] In 1947, there were some 750,000 miners,[23] but by 2004 this had shrunk to some 5,000 miners working in around 20 collieries.[24]

In ancient China, coal was used as fuel by the 4th century AD, but there was little extensive use until the 11th century.[25]

## Uses today

Coal-fired power plants provide 49% of consumed electricity in the United States. This is the Castle Gate Plant near Helper, Utah.
Coal rail cars

### 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[26] and is expected to increase 48% to 9.98 billion short tons by 2030.[27] 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.[28]

When coal is used for electricity generation, it is usually pulverized and then combusted (burned) in a furnace with a boiler.[29] The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity. The thermodynamic 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. Increasing the combustion temperature can boost this efficiency even further.[30] 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,[29][31] and in 2012 about one third of the United States' electricity came from coal down from approximately 49% in 2008.[32][33] As of 2012 in the United States use of coal to generate electricity was declining as plentiful supplies of natural gas obtained by hydraulic fracturing of tight shale formations became available at low prices.[32] 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.[34]

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

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.[quantify] However, consumption is increasing and maximal production could be reached within decades (see world coal reserves, below).

### Coking coal and use of coke

Coke oven at a smokeless fuel plant in Wales, United Kingdom

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. Metallurgical coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace.[35] The coking coal should be low in sulfur and phosphorus so that they do not migrate to the metal. The result is pig iron, and is too rich in dissolved carbon, so it must be treated further to make steel.

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 is direct reduced iron, where any carbonaceous fuel can be used to make sponge or pelletised iron. 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.

### 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. 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.

During gasification, the coal is mixed with oxygen and steam (water vapor) while also being heated and pressurized. During the reaction, oxygen and water molecules oxidize 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.

(Coal) + O2 + H2O → H2 + CO

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.

CO + H2O → CO2 + H2

High prices of oil and natural gas are leading to increased interest in "BTU Conversion" technologies such as gasification, methanation and liquefaction. The Synthetic 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). 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.

### 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 either hydrogenated or carbonized. Hydrogenation processes are the Bergius process,[36] the SRC-I and SRC-II (Solvent Refined Coal) processes and the NUS Corporation hydrogenation process.[37][38] 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. 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.[39]

Coal liquefaction methods involve carbon dioxide (CO2) emissions in the conversion process. 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. 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.[40] For most future synthetic fuel projects, Carbon dioxide sequestration is proposed to avoid releasing it into the atmosphere. Sequestration will, however, add to the cost of production. Currently, all US and at least one Chinese synthetic fuel projects,[41] 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. 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.

### 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. It is also contained in mould wash, a paste or liquid with the same function applied to the mould before casting.[42] 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.[43]

## Cultural usage

Coal is the official state mineral of Kentucky[44] (even though coal is not a mineral) and the official state rock of Utah.[45] Both U.S. states have a historic link to coal mining.

Some cultures hold that children who misbehave will receive only a lump of coal from Santa Claus for Christmas in their stockings instead of presents.

It is also customary and considered lucky in Scotland and the North of England to give coal as a gift on New Year's Day. This occurs 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). 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.[46]

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.[47]

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.[48]

## Environmental effects

Aerial photograph of Kingston Fossil Plant coal fly ash slurry spill site taken the day after the event

There are a number of adverse health[49] and environmental effects of coal burning[50] especially in power stations, and of coal mining. These effects include:

## Economic aspects

Coal liquefaction 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. 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,[54] 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, 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.

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.[55] This is probably because China prefers not to be dependent on foreign oil, instead utilizing its enormous domestic coal reserves. 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.[56]

China is by far the largest producer of coal in the world.[57] It has now become the world's largest energy consumer[58] but relies on coal to supply about 70% of its energy needs.[59] An estimated 5 million people work in China's coal-mining industry.[60]

## Energy density

The energy density of coal, i.e. its heating value, is roughly 24 megajoules per kilogram.[61]

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. 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. 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:

$\frac{876 \ \mathrm{kW \cdot h}}{2.0 \ \mathrm{kW} \cdot \mathrm{h/kg}} = 438 \ \mathrm{kg \ of \ coal} = 966 \ \mathrm{pounds \ of \ coal}$

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.[62] One should also take into account transmission 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.

## 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

$\frac{0.8 \ \mathrm{kg}}{\mathrm{12} \cdot \mathrm{kg/kmol}} = \frac{2}{30} \ \mathrm{kmol}$ , where 1 mol equals to NA (Avogadro Number) atoms.

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

$\frac{2}{30} \ \mathrm{kmol} \cdot \frac{44 \ \mathrm{kg}}{\mathrm{kmol}} = \frac{88}{30} \ \mathrm{kg} \approx 2.93 \ \mathrm{kg}$.

This can be used to calculate an emission factor for CO2 from the use of coal power. Since the useful energy output of coal is about 31% of the 6.67 kWh/kg(coal),[63] 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.

The U.S. Energy Information Agency's 1999 report on CO2 emissions for energy generation,[64] 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. 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.[65] Those burning underground can be difficult to locate and many cannot be extinguished. 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. A grass fire in a coal area can set dozens of coal seams on fire.[66][67] Coal fires in China burn an estimated 120 million tons of coal a year, emitting 360 million metric tons of CO2, amounting to 2-3% of the annual worldwide production of CO2 from fossil fuels.[68][69] In Centralia, Pennsylvania (a borough located in the Coal Region of the United States), an exposed vein of anthracite 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. 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.[70]

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. 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).[citation needed]

The reddish siltstone rock that caps many ridges and buttes in the Powder River Basin in Wyoming and in western North Dakota is called porcelanite, which resembles the coal burning waste "clinker" or volcanic "scoria".[71] Clinker is rock that has been fused by the natural burning of coal. In the Powder River Basin approximately 27 to 54 billion tons of coal burned within the past three million years.[72] Wild coal fires in the area were reported by the Lewis and Clark Expedition as well as explorers and settlers in the area.[73]

## Production trends

Coal output in 2005
A coal mine in Wyoming, United States. The United States has the world's largest coal reserves.

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

### World coal reserves

The 948 billion short tons of recoverable coal reserves estimated by the Energy Information Administration are equal to about 4,196 BBOE (billion barrels of oil equivalent).[74] The amount of coal burned during 2007 was estimated at 7.075 billion short tons, or 133.179 quadrillion BTU's.[75] 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.

BP, in its 2007 report, estimated at 2006 end that there were 147 years reserves-to-production ratio based on proven coal reserves worldwide. This figure only includes reserves classified as "proven"; exploration drilling programs by mining companies, particularly in under-explored areas, are continually providing new reserves. 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. Speculative projections predict that global peak coal production may occur sometime around 2025 at 30 percent above current production, depending on future coal production rates.[76]

Continental United States coal regions

Of the three fossil fuels, coal has the most widely distributed reserves; coal is mined in over 100 countries, and on all continents except Antarctica. The largest reserves are found in the USA, Russia, China, India and Australia. Note the table below.

Proved recoverable coal reserves at end-2008 (million tons (teragrams))[77]
Country Bituminous & Anthracite SubBituminous Lignite TOTAL Percentage of World Total
United States 108,501 98,618 30,176 237,295 22.6
Russia 49,088 97,472 10,450 157,010 14.4
China 62,200 33,700 18,600 114,500 12.6
Australia 37,100 2,100 37,200 76,500 8.9
India 56,100 0 4,500 60,600 7.0
Germany 99 0 40,600 40,699 4.7
Ukraine 15,351 16,577 1,945 33,873 3.9
Kazakhstan 21,500 0 12,100 33,600 3.9
South Africa 30,156 0 0 30,156 3.5
Serbia 9 361 13,400 13,770 1.6
Colombia 6,366 380 0 6,746 0.8
Canada 3,474 872 2,236 6,528 0.8
Poland 4,338 0 1,371 5,709 0.7
Indonesia 1,520 2,904 1,105 5,529 0.6
Brazil 0 4,559 0 4,559 0.5
Greece 0 0 3,020 3,020 0.4
Bosnia and Herzegovina 484 0 2,369 2,853 0.3
Mongolia 1,170 0 1,350 2,520 0.3
Bulgaria 2 190 2,174 2,366 0.3
Pakistan 0 166 1,904 2,070 0.3
Turkey 529 0 1,814 2,343 0.3
Uzbekistan 47 0 1,853 1,900 0.2
Hungary 13 439 1,208 1,660 0.2
Thailand 0 0 1,239 1,239 0.1
Mexico 860 300 51 1,211 0.1
Iran 1,203 0 0 1,203 0.1
Czech Republic 192 0 908 1,100 0.1
Kyrgyzstan 0 0 812 812 0.1
Albania 0 0 794 794 0.1
North Korea 300 300 0 600 0.1
New Zealand 33 205 333-7,000 571-15,000[78] 0.1
Spain 200 300 30 530 0.1
Laos 4 0 499 503 0.1
Zimbabwe 502 0 0 502 0.1
Argentina 0 0 500 500 0.1
All others 3,421 1,346 846 5,613 0.7
Total world 404,762 260,789 195,387 860,938 100

### Major coal producers

The reserve life is an estimate based only on current production levels and proved reserves level for the countries shown, and makes no assumptions of future production or even current production trends. Countries with annual production higher than 100 million tonnes are shown. For comparison, data for the European Union is also shown. Shares are based on data expressed in tonnes oil equivalent.

Production of Coal by Country and year (million tonnes) [79]
Country 2003 2004 2005 2006 2007 2008 2009 2010 Share Reserve Life (years)
China 1834.9 2122.6 2349.5 2528.6 2691.6 2802.0 2973.0 3240.0 48.3 % 35
USA 972.3 1008.9 1026.5 1054.8 1040.2 1063.0 975.2 984.6 14.8 % 241
India 375.4 407.7 428.4 449.2 478.4 515.9 556.0 569.9 5.8 % 106
EU 637.2 627.6 607.4 595.1 592.3 563.6 538.4 535.7 4.2 % 105
Australia 350.4 364.3 375.4 382.2 392.7 399.2 413.2 423.9 6.3 % 180
Russia 276.7 281.7 298.3 309.9 313.5 328.6 301.3 316.9 4.7 % 495
Indonesia 114.3 132.4 152.7 193.8 216.9 240.2 256.2 305.9 5.0 % 18
South Africa 237.9 243.4 244.4 244.8 247.7 252.6 250.6 253.8 3.8 % 119
Germany 204.9 207.8 202.8 197.1 201.9 192.4 183.7 182.3 1.2 % 223
Poland 163.8 162.4 159.5 156.1 145.9 144.0 135.2 133.2 1.5 % 43
Kazakhstan 84.9 86.9 86.6 96.2 97.8 111.1 100.9 110.8 1.5 % 303
Total World 5,301.3 5,716.0 6,035.3 6,342.0 6,573.3 6,795.0 6,880.8 7,273.3 100 % 118

### Major coal exporters

Countries with annual export higher than 10 million tonnes are shown.

Exports of Coal by Country and year (million short tons)[80][81][82]
Country 2003 2004 2005 2006 2007 2008 2009 Share
Australia 238.1 247.6 255.0 255.0 268.5 278.0 288.5 26.5%
Indonesia 107.8 131.4 142.0 192.2 221.9 228.2 261.4 24.0%
Russia 41.0 55.7 98.6 103.4 112.2 115.4 130.9 12.0%
Colombia 50.4 56.4 59.2 68.3 74.5 74.7 75.7 6.9%
South Africa 78.7 74.9 78.8 75.8 72.6 68.2 73.8 6.8%
USA 43.0 48.0 51.7 51.2 60.6 83.5 60.4 5.5%
China 103.4 95.5 93.1 85.6 75.4 68.8 38.4 3.5%
Canada 27.7 28.8 31.2 31.2 33.4 36.5 31.9 2.9%
Vietnam 6.9 11.7 19.8 23.5 35.1 21.3 28.2 2.6%
Kazakhstan 30.3 27.4 28.3 30.5 32.8 47.6 25.7 2.4%
Poland 28.0 27.5 26.5 25.4 20.1 16.1 14.6 1.3%
Total 713.9 764.0 936.0 1,000.6 1,073.4 1,087.3 1,090.8 100%

### Major coal importers

Countries with annual import higher than 30 million tonnes are shown.

Imports of Coal by Country and year (million short tons)[83]
Country 2006 2007 2008 2009 Share
Japan 199.7 209.0 206.0 182.1 17.5%
China 42.0 56.2 44.5 151.9 14.5%
South Korea 84.1 94.1 107.1 109.9 10.6%
India 52.7 29.6 70.9 76.7 7.4%
Taiwan 69.1 72.5 70.9 64.6 6.2%
Germany 50.6 56.2 55.7 45.9 4.4%
United Kingdom 56.8 48.9 49.2 42.2 4.1%
Total 991.8 1,056.5 1,063.2 1,039.8 100%

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