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Coal
Example chemical structure of coal
Coal is a fossil fuel formed in swamp ecosystems where plant remains were saved by water and mud from oxidization and biodegradation. Coal is a readily combustible black or brownish-black rock. It is a sedimentary rock, but the harder forms, such as anthracite coal, can be regarded as metamorphic rocks because of later exposure to elevated temperature and pressure. It is composed primarily of carbon along with assorted other elements, including sulfur. It is the largest single source of fuel for the generation of electricity world-wide, as well as the largest world-wide source of carbon dioxide emissions, slightly ahead of petroleum and about double that of natural gas.The EIA reports the following emissions in million metric tons of carbon dioxide:
For 2005 as the official energy statistics of the US Government.[1] Coal is extracted from the ground by coal mining, either underground mining or open pit mining (surface mining).
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As geological processes apply pressure to dead matter over time, under suitable conditions, it is transformed successively into
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:Eberhard Lindner; Chemie für Ingenieure; Lindner Verlag Karlsruhe, S. 258
| Name | 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 |
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 < 8% volatiles).
A 120,000-year-old Stone Age coalstone hunting camp was discovered in 2005 by archaelogists in an opencast coalstone mine in Germany, its first known use being campfire cooking fuel for German hunters.Stone Age Camp Found In Germany Der Spiegel 2007-02-06 accessed 2007-11-19 China Coal Information Institute reports the Chinese mined coalstone for fuel 10,000 years ago at the time of the New Stone Age, or Neolithic Era. "People in Shanxi, now the largest coal production base, have been burning coal as fuel since then."Around the Markets: Future for coal brighter Herald Tribune 2007-04-16 accessed 2007-11-29 Outcrop coal was used in Britain during the Bronze Age (2-3000 years BC), where it has been detected as forming part of the composition of funeral pyres.Britannica 2004: Coal mining: ancient use of outcropping coal. It was also commonly used in the early period of the Roman occupation: 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. Salway, Peter (2001): A History of Roman Britain. Oxford University Press. 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 is now the Somerset coalfield was in common use in quite lowly dwellings locally.Forbes, R J (1966): Studies in Ancient Technology. Brill Academic Publishers, Boston.
However, there is no evidence that the product was of great importance in Britain before the High Middle Ages, after about AD 1000. Mineral coal came to be referred to as "seacoal," probably because it came to many places in eastern England, including London, by sea. This is accepted as the more likely explanation for the name than that it was found on beaches, having fallen from the exposed coal seams above or washed out of underwater coal seam outcrops. 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. In London there is still a Seacoal Lane (off the north side of Ludgate Hill) where the coal merchants used to conduct their business. An 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.
Coal is primarily used as a solid fuel to produce electricity and heat through combustion. World coal consumption is about 6.2 billion tons annually, of which about 75% is used for the production of electricity.[citation needed]China produced 2.38 billion tonnes in 2006 and India produced about 447.3 million tonnes in 2006. 83.2% of China\'s electricity comes from coal. The USA consumes about 1.053 billion tonnes of coal each year, using 90% of it for generation of electricity. The world in total produced 6.19 billion tonnes of coal in 2006.
When coal is used for electricity generation, it is usually pulverized and then burned in a furnace with a boiler. 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. "Standard" steam turbines have topped out with some of the most advanced reaching about 35% thermodynamic efficiency for the entire process, which means 65% of the coal energy is rejected as waste heat into the surrounding environment. Old coal power plants, especially "grandfathered" plants, are significantly less efficient and reject higher levels of waste heat.
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.Balancing economics and environmental friendliness - the challenge for supercritical coal-fired power plants with highest steam parameters in the future (PDF). Retrieved on 2006-10-23.
Other efficient ways to use coal are combined cycle power plants, combined heat and power cogeneration, and an MHD topping cycle.
Approximately 40% of the world electricity production uses coal. The total known deposits recoverable by current technologies, including highly polluting, low energy content types of coal (i.e., lignite, bituminous), might be sufficient for 300 years\' use at current consumption levels, although maximal production could be reached within decades (see World Coal Reserves, below).
A more energy-efficient way of using coal for electricity production would be via solid-oxide fuel cells or molten-carbonate fuel cells (or any oxygen ion transport based fuel cells that do not discriminate between fuels, as long as they consume oxygen), which would be able to get 60%–85% combined efficiency (direct electricity + waste heat steam turbine).[citation needed] Currently these fuel cell technologies can only process gaseous fuels, and they are also sensitive to sulfur poisoning, issues which would first have to be worked out before large scale commercial success is possible with coal. As far as gaseous fuels go, one idea is pulverized coal in a gas carrier, such as nitrogen. Another option is coal gasification with water, which may lower fuel cell voltage by introducing oxygen to the fuel side of the electrolyte, but may also greatly simplify carbon sequestration.
Coke burning
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. Metallurgic coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Coke from coal is grey, hard, and porous and has a heating value of 24.8 million Btu/ton (29.6 MJ/kg). Byproducts of this conversion of coal to coke 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.
High prices of oil and natural gas are leading to increased interest in "BTU Conversion" technologies such as gasification, methanation and liquefaction.
Coal gasification breaks down the coal into its components, usually by subjecting it to high temperature and pressure, using steam and measured amounts of oxygen. This leads to the production of syngas, a mixture mainly consisting of carbon monoxide (CO) and hydrogen (H2).
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. South Africa still uses gasification of coal for much of its petrochemical needs.
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.
Gasification is also a possibility for future energy use, as the produced syngas can be cleaned-up relatively easily leading to cleaner burning than burning coal directly (the conventional way). The cleanliness of the cleaned-up syngas is comparable to natural gas enabling to burn it in a more efficient gas turbine rather than in a boiler used to drive a steam turbine. Syngas produced by gasification can be CO-shifted meaning that the combustible CO in the syngas is transferred into carbon dioxide (CO2) using water as a reactant. The CO-shift reaction also produces an amount of combustible hydrogen (H2) equal to the amount of CO converted into CO2. The CO2 concentrations (or rather CO2 partial pressures) obtained by using coal gasification followed by a CO-shift reaction are much higher than in case of direct combustion of coal in air (which is mostly nitrogen). These higher concentrations of carbon dioxide make carbon capture and storage much more economical than it otherwise would be.
Coals can also be converted into liquid fuels like gasoline or diesel by several different processes. The Fischer-Tropsch process of indirect synthesis of liquid hydrocarbons was used in Nazi Germany for many years and is today used by Sasol in South Africa. Coal would be gasified to make syngas (a balanced purified mixture of CO and H2 gas) and the syngas condensed using Fischer-Tropsch catalysts to make light hydrocarbons which are further processed into gasoline and diesel. Syngas can also be converted to methanol, which can be used as a fuel, fuel additive, or further processed into gasoline via the Mobil M-gas process.
A direct liquefaction process Bergius process (liquefaction by hydrogenation) is also available but has not been used outside Germany, where such processes were operated both during World War I and World War II. SASOL in South Africa has experimented with direct hydrogenation. Several other direct liquefaction processes have been developed, among these being the SRC-I and SRC-II (Solvent Refined Coal) processes developed by Gulf Oil and implemented as pilot plants in the United States in the 1960s and 1970s.Cleaner Coal Technology Programme (October 1999). "Technology Status Report 010: Coal Liquefaction". Department of Trade and Industry (UK). Retrieved on November 23.
Another direct hydrogenation process was explored by the NUS Corporation in 1976 and patented by Wilburn C. Schroeder. The process involved dried, pulverized coal mixed with roughly 1wt% molybdenum catalysts. Hydrogenation occurred by use of high temperature and pressure synthesis gas produced in a separate gasifier. The process ultimately yielded a synthetic crude product, Naphtha, a limited amount of C3/C4 gas, light-medium weight liquids (C5-C10) suitable for use as fuels, small amounts of NH3 and significant amounts of CO2.Phillip A. Lowe, Wilburn C. Schroeder, Anthony L. Liccardi (1976). "Technical Economies, Synfuels and Coal Energy Symposium, Solid-Phase Catalytic Coal Liquefaction Process". The American Society of Mechanical Engineers.
Yet another process to manufacture liquid hydrocarbons from coal is low temperature carbonization (LTC). Coal is coked at temperatures between 450 and 700°C compared to 800 to 1000°C for metallurgical coke. 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. The Karrick process was developed by Lewis C. Karrick, an oil shale technologist at the U.S. Bureau of Mines in the 1920s.
All of these liquid fuel production methods release carbon dioxide (CO2) in the conversion process, far more than is released in the extraction and refinement of liquid fuel production from petroleum. If these methods were adopted to replace declining petroleum supplies, carbon dioxide emissions would be greatly increased on a global scale. For future liquefaction projects, Carbon dioxide sequestration is proposed to avoid releasing it into the atmosphere, though no pilot projects have confirmed the feasibility of this approach on a wide scale. As CO2 is one of the process streams, sequestration is easier than from flue gases produced in combustion of coal with air, where CO2 is diluted by nitrogen and other gases. Sequestration will, however, add to the cost.
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 some authors have suggested could 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 USD per barrel,Diesel Fuel News: Ultra-clean fuels from coal liquefaction: China about to launch big projects - Brief Article. Retrieved on September 9, 2005. (break-even cost). This price, while above historical averages, is well below current oil prices. This makes coal a viable financial alternative to oil for the time being, although production is not great enough to make synfuels viable on a large scale.Welcome to Coal People Magazine. Retrieved on September 9, 2005.
Among commercially mature technologies, advantage for indirect coal liquefaction over direct coal liquefaction are reported by Williams and Larson (2003). Estimates are reported for sites in China where break-even cost for coal liquefaction may be in the range between 25 to 35 USD/barrel of oil.[citation needed]\'
Intensive research and project developments have been implemented from 2001. The World CTL Award is granted to personalities having brought eminent contribution to the understanding and development of Coal liquefaction. The 2008 presentation ceremony will take place at the World CTL 2008 Conference (3 & 4 April, 2008).
The price of coal has gone up from around $30 a tonne in 2000 to around $130 a tonne in 2008.
In North America, a Central Appalachian coal futures contract is currently traded on the New York Mercantile Exchange (trading symbol QL). The trading unit is 1,550 tons 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, the futures contract provides coal producers and the electric power industry an important tool for hedging and risk management.NYMEX.com: Coal. Retrieved on January 16, 2008.
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 tons, and are also quoted in U.S. dollars and cents per ton.ICE: Coal Futures. Retrieved on January 16, 2008.
Coal is the official state mineral of Kentucky 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 coal from Santa Claus for Christmas in their stockings instead of presents.
It is also customary and lucky in Scotland to give coal as a gift on New Year\'s Day. It happen\'s as part of First-Footing and represents warmth for the year to come.
The energy density of coal, i.e. its heating value, is roughly 24 megajoules per kilogram.Fisher, Juliya (2003). Energy Density of Coal. The Physics Factbook. Retrieved on 2006-08-25.
The energy density of coal can also be expressed in kilowatt-hours, the units that electricity is most commonly sold in, to estimate how much coal is required to power electrical appliances. The energy density of coal is 6.67 kWh/kg and the typical thermodynamic efficiency of coal power plants is about 30%. Of the 6.67 kWh of energy per kilogram of coal, about 30% of that can successfully be turned into electricity - the rest is waste heat. Coal power plants obtain approximately 2.0 kWh per kg of burned coal.
As an example, running one 100 watt computer for one year requires 876 kWh (100 W × 24 h × 365 {days in a year} = 876000 Wh = 876 kWh). Converting this power usage into physical coal consumption:
It takes 438 kg (967 pounds) of coal to power a computer for one full year.A similar result, using a lightbulb instead, see
How much coal is required to run a 100-watt light bulb 24 hours a day for a year?. Howstuffworks. Retrieved on 2006-08-25. 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.
Because coal is at least 50% carbon (by mass), then 1 kg of coal contains at least 0.5 kg of carbon, which is where 1 mol is equal to NA (Avogadro Number) particles. This combines with oxygen in the atmosphere during combustion, producing carbon dioxide, with an atomic weight of (12 + 16 × 2 = mass(CO2) = 44 kg/kmol). of CO2 is produced from the present in every kilogram of coal, which once trapped in CO2 weighs approximately .
This can be used to put a carbon-cost of energy on the use of coal power. Since the useful energy output of coal is about 30% of the 6.67 kWh/kg(coal), we can say about 2 kWh/kg(coal) of energy is produced. Since 1 kg coal roughly translates as 1.83 kg of CO2, we can say that using electricity from coal produces CO2 at a rate of about 0.915 kg CO2/kWh, or about 0.254 kg CO2/MJ.
This estimate compares favourably with the U.S. Energy Information Agency\'s 1999 report on CO2 emissions for energy generationCO2 Emissions Report, which quotes a specific emission rate of 950 g CO2/kWh. By comparison, generation from oil in the U.S. was 890 g CO2/kWh, while natural gas was 600 g CO2/kWh. Estimates for specific emission from nuclear power, hydro, and wind energy vary, but are about 100 times lower. See indirect carbon emissions from nuclear power for estimates.
There are hundreds of coal fires burning around the world.Sino German Coal fire project. Retrieved on September 9, 2005. 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. A grass fire in a coal area can set dozens of coal seams on fire.Committee on Resources-Index. Retrieved on September 9, 2005.http://www.fire.blm.gov/textdocuments/6-27-03.pdf. Retrieved on September 9, 2005. Coal fires in China burn 109 million tonnes of coal a year, emitting 200 million tonnes of carbon dioxide. This amounts to 2-3% of the annual worldwide production of CO2 from fossil fuels, or as much as emitted from all of the cars and light trucks in the United States.EHP 110-5, 2002: Forum. Retrieved on September 9, 2005.Overview about ITC\'s activities in China. Retrieved on September 9, 2005. 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. The Australian Burning Mountain was originally believed to be a volcano, but the smoke and ash comes from a coal fire which may have been burning for over 5,500 years.Burning Mountain Nature Reserve. Retrieved on September 9, 2005.
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 mis-interpreted the Ancient Greek descriptions as the evidence of active volcanism in Turkestan (up to the 19th century, when Russian army invaded the area).
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".North Dakota\'s Clinker. Retrieved on September 9, 2005. Clinker is rock that has been fused by the natural burning of coal. In the Powder River Basin approximately 27 to 54 billion tonnes of coal burned within the past three million years.BLM-Environmental Education- The High Plains. Retrieved on September 9, 2005. Wild coal fires in the area were reported by the Lewis and Clark Expedition as well as explorers and settlers in the area.http://www.wsgs.uwyo.edu/Coal/CR01-1.pdf. Retrieved on September 9, 2005.
In 2006, China was the top producer of coal with 38% share followed by the USA and India, reports the British Geological Survey.
At the end of 2006 the recoverable coal reserves amounted around 800 or 900 gigatonnes. The United States Energy Information Administration gives world reserves as 998 000 short tons (equal to 905 gigatonnes), approximately half of it being hard coal. At the current production rate, this would last 164 years.International Energy Outlook 2007 Chapter 5 Coal At the current global total energy consumption of 15 terawatt,BP2006 energy report, and US EIA 2006 overview there is enough coal to provide the entire planet with all of its energy for 57 years.[original research?]
British Petroleum, in its annual report 2007, estimated at 2006 end, there were 909,064 million tons of proven coal reserves worldwide, or 147 years reserves 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. 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.
The United States Department of Energy uses estimates of coal reserves in the region of 1,081,279 million short tons (9.81 × 1014 kg), which is about 4,786 BBOE (billion barrels of oil equivalent).International Energy Annual 2003: Reserves. Retrieved on September 9, 2005. The amount of coal burned during 2001 was calculated as 2.337 GTOE (gigatonnes of oil equivalent), which is about 46 million barrels of oil equivalent per day.IEA Publications Bookshop. Retrieved on September 9, 2005. Were consumption to continue at that rate those reserves would last about 285 years. As a comparison, natural gas provided 51 million barrels (oil equivalent), and oil 76 million barrels, per day during 2001.
However, according to New Scientist,"Coal: Bleak outlook for the black stuff", by David Strahan, New Scientist, Jan. 19, 2008, pp. 38-41. reported reserves of some countries have fallen considerably in recent years, and there is much doubt about the reserves reported by other countries. Using Hubbert peak theory, it seems that the total amount of coal that will ever be mined will attain only about 450 gigatonnes[citation needed]. This is much less than what is assumed in calculations of global warming, and it implies that other sources of energy need to be developed[citation needed].
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, Australia, China, India and South Africa.
Note the table below.
| Country | Bituminous & anthracite | SubBituminous & lignite | TOTAL | Share |
|---|---|---|---|---|
| United States of America | 111,338 | 135,305 | 246,643 | 27.1 |
| Russia | 49,088 | 107,922 | 157,010 | 17.3 |
| China | 62,200 | 52,300 | 114,500 | 12.6 |
| India | 90,085 | 2,360 | 92,445 | 10.2 |
| Australia | 38,600 | 39,900 | 78,500 | 8.6 |
| South Africa | 48,750 | 0 | 48,750 | 5.4 |
| Ukraine | 16,274 | 17,879 | 34,153 | 3.8 |
| Kazakhstan | 28,151 | 3,128 | 31,279 | 3.4 |
| Poland | 14,000 | 0 | 14,000 | 1.5 |
| Brazil | 0 | 10,113 | 10,113 | 1.1 |
| Germany | 183 | 6,556 | 6,739 | 0.7 |
| Colombia | 6,230 | 381 | 6,611 | 0.7 |
| Canada | 3,471 | 3,107 | 6,578 | 0.7 |
| Czech Republic | 2,094 | 3,458 | 5,552 | 0.6 |
| Indonesia | 740 | 4,228 | 4,968 | 0.5 |
| Turkey | 278 | 3,908 | 4,186 | 0.5 |
| Greece | 0 | 3,900 | 3,900 | 0.4 |
| Hungary | 198 | 3,159 | 3,357 | 0.4 |
| Pakistan | 0 | 3,050 | 3,050 | 0.3 |
| Bulgaria | 4 | 2,183 | 2,187 | 0.2 |
| Thailand | 0 | 1,354 | 1,354 | 0.1 |
| North Korea | 300 | 300 | 600 | 0.1 |
| New Zealand | 33 | 538 | 571 | 0.1 |
| Spain | 200 | 330 | 530 | 0.1 |
| Zimbabwe | 502 | 0 | 502 | 0.1 |
| Romania | 22 | 472 | 494 | 0.1 |
| Venezuela | 479 | 0 | 479 | 0.1 |
| TOTAL | 478,771 | 430,293 | 909,064 | 100.0 |
| Country | 2003 | 2004 |
|---|---|---|
| Australia | 238.1 | 247.6 |
| United States | 43.0 | 48.0 |
| South Africa | 78.7 | 74.9 |
| Former Soviet Union | 41.0 | 55.7 |
| Poland | 16.4 | 16.3 |
| Canada | 27.7 | 28.8 |
| China | 103.4 | 95.5 |
| South America | 57.8 | 65.9 |
| Indonesia | 107.8 | 131.4 |
| Total | 713.9 | 764.0 |
| | Energy Portal |
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