Lignite

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Lignite-coal.jpg
Braunkohle als Hausbrand.jpg
A lignite stockpile (above) and a lignite briquette

Lignite, often referred to as brown coal, [1] is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25 to 35 percent, [1] [2] and is considered the lowest rank of coal due to its relatively low heat content. Lignite is mined all around the world and is used almost exclusively as a fuel for steam-electric power generation.

Contents

The combustion of lignite produces less heat for the amount of carbon dioxide and sulfur released than other ranks of coal. As a result, environmental advocates have characterized lignite as the most harmful coal to human health. [3]

Characteristics

Lignite mining, western North Dakota, US (c. 1945) Lignite mining in Western North Dakota.jpg
Lignite mining, western North Dakota, US (c. 1945)

Lignite is brownish-black in color and has a carbon content of 60-70 percent on a dry ash-free basis. However, its inherent moisture content is sometimes as high as 75 percent [1] and its ash content ranges from 6–19 percent, compared with 6–12 percent for bituminous coal. [4] As a result, its carbon content on the as-received basis (i.e., containing both inherent moisture and mineral matter) is typically just 25-35 percent. [2]

Strip mining lignite at Tagebau Garzweiler in Germany Garzweiler surface mine, October 2018, -01.jpg
Strip mining lignite at Tagebau Garzweiler in Germany

The energy content of lignite ranges from 10 to 20 MJ/kg (9–17 million BTU per short ton) on a moist, mineral-matter-free basis. The energy content of lignite consumed in the United States averages 15 MJ/kg (13 million BTU/ton), on the as-received basis. [5] The energy content of lignite consumed in Victoria, Australia, averages 8.6 MJ/kg (8.2 million BTU/ton) on a net wet basis. [6]

Lignite has a high content of volatile matter which makes it easier to convert into gas and liquid petroleum products than higher-ranking coals. Unfortunately, its high moisture content and susceptibility to spontaneous combustion can cause problems in transportation and storage. Processes which remove water from brown coal reduce the risk of spontaneous combustion to the same level as black coal, increase the calorific value of brown coal to a black coal equivalent fuel, and significantly reduce the emissions profile of 'densified' brown coal to a level similar to or better than most black coals. [7] However, removing the moisture increases the cost of the final lignite fuel.

Lignite rapidly degrades when exposed to air. This process is called slacking or slackening. [8]

Uses

Most lignite is used to generate electricity. [2] However, small amounts are used in agriculture, in industry, and even as jewelry. Its historical use as fuel for home heating has continuously declined and is now of lower importance than its use to generate electricity.

As fuel

Layer of lignite for mining in Lom CSA, Czech Republic Lom CSA Most Czech Republic 2016 7.jpg
Layer of lignite for mining in Lom ČSA, Czech Republic
Pendant in lignite (jet) from the Magdalenian culture Pendeloque en lignite Marsoulas MHNT.PRE.2012.0.6.95.jpg
Pendant in lignite (jet) from the Magdalenian culture

Lignite is often found in thick beds located near the surface, making it inexpensive to mine. However, because of its low energy density, tendency to crumble, and typically high moisture content, brown coal is inefficient to transport and is not traded extensively on the world market compared with higher coal grades. [1] [6] It is often burned in power stations near the mines, such as in Australia's Latrobe Valley and Luminant's Monticello plant in Texas. Primarily because of latent high moisture content and low energy density of brown coal, carbon dioxide emissions from traditional brown-coal-fired plants are generally much higher per megawatt generated than for comparable black-coal plants, with the world's highest-emitting plant being Australia's Hazelwood Power Station [9] until its closure in March 2017. [10] The operation of traditional brown-coal plants, particularly in combination with strip mining, is politically contentious due to environmental concerns. [11] [12]

The German Democratic Republic relied extensively on lignite to become energy self-sufficient, and eventually obtained 70% of its energy requirements from lignite. [13] Lignite was also an important chemical industry feedstock via Bergius process or Fischer-Tropsch synthesis in lieu of petroleum, [14] which had to be imported for hard currency following a change in policy by the Soviet Union in the 1970s, which had previously delivered petroleum at below market rates. [15] East German scientists even converted lignite into coke suitable for metallurgical uses (cf. de:Braunkohlenhochtemperaturkoks on the German Wikipedia) and much of the railway network was dependent on lignite either through steam trains or electrified lines mostly fed with lignite derived power. [15] As per the table below, East Germany was the largest producer of lignite for much of its existence as an independent state.

In 2014, about 12 percent of Germany's energy and, specifically, 27 percent of Germany's electricity came from lignite power plants, [16] while in 2014 in Greece, lignite provided about 50 percent of its power needs. Germany has announced plans to phase out lignite by 2038 at the latest. [17] [18] [19] [20] Greece has confirmed that the last coal plant will be shut in 2025 after receiving pressure from the European Union [21] and plans to heavily invest in Renewable energy. [22]


Home heating

Lignite was and is used as a replacement for or in combination with firewood for home heating. It is usually pressed into briquettes for that use. [23] [24] Due to the smell it gives off when burned, lignite was often seen as a fuel for poor people compared to higher value hard coals.

In agriculture

An environmentally beneficial use of lignite is in agriculture. Lignite may have value as an environmentally benign soil amendment, improving cation exchange and phosphorus availability in soils while reducing availability of heavy metals, [25] [26] and may be superior to commercial K humates. [27] Lignite fly ash produced by combustion of lignite in power plants may also be valuable as a soil amendment and fertilizer. [28] However, rigorous studies of the long-term benefits of lignite products in agriculture are lacking. [29]

Lignite may also be used for the cultivation and distribution of biological control microbes that suppress plant pests. The carbon increases the organic matter in the soil while the biological control microbes provide an alternative to chemical pesticides. [30]

Leonardite is a soil conditioner rich in humic acids that is formed by natural oxidation of lignite near the surface of the Earth. [31]

In drilling mud

Reaction with quaternary amine forms a product called amine-treated lignite (ATL), which is used in drilling mud to reduce fluid loss during drilling. [32]

As an industrial adsorbent

Lignite may have potential uses as an industrial adsorbent. Experiments show that its adsorption of methylene blue falls within the range of activated carbons currently used by industry. [33]

In jewelry

Jet is a form of lignite that has been used as a gemstone. [34] The earliest jet artifacts date to 10,000 BCE [35] and jet was used extensively in necklaces and other ornamentation in Britain from the Neolithic until the end of Roman Britain. [36] Jet experienced a brief revival in Victorian Britain. [37]

Geology

Okefenokee Swamp, a modern peat-forming swamp Canal Run shadows (5179305812).jpg
Okefenokee Swamp, a modern peat-forming swamp
Partial molecular structure of a lignin-derived organic molecule in lignite U S Geological Survey Circular 1143 Lignite Structure.png
Partial molecular structure of a lignin-derived organic molecule in lignite

Lignite begins as an accumulation of partially decayed plant material, or peat. Peat accumulates most readily in areas where there is ample moisture, slow subsidence of the land surface, and lack of disturbance by rivers or oceans. Peat swamps are otherwise found in a wide variety of climates and geographical settings. Under these conditions, the area remains saturated with water, which covers dead plant material and protects it from degradation by atmospheric oxygen. Anaerobic bacteria may continue to degrade the peat, but this process is slow, particularly in acid water. Once the peat is buried by other sediments, biological degradation essentially comes to a halt, and further changes are a result of increased temperature and pressure from burial. [38]

Lignite forms from peat that has not experienced deep burial and heating. It forms at temperatures below 100 °C (212 °F), [1] primarily by biochemical degradation. This includes humification, in which microorganisms extract hydrocarbons from the peat and humic acids are formed. The humic acids make the environment more acidic, which slows the rate of further bacterial decay. Humification is still incomplete in lignite, coming to completion only when the coal reaches sub-bituminous rank. [39] The most characteristic chemical change in the organic material during formation of lignite is the sharp reduction in the number of C=O and C-O-R functional groups. [40]

Lignite deposits are typically younger than higher-ranked coals, with the majority of them having formed during the Tertiary period. [1]

Resources and Reserves

List of countries by lignite reserves

Top Ten Countries by lignite reserves (2018) [41]
CountriesLignite reserves (millions of tonnes)
Russia90447
Australia76508
Germany35900
United States30003
Indonesia11728
Turkey10975
China8128
Serbia7112
New Zealand6750
Poland5865

Australia

The Latrobe Valley in Victoria, Australia, contains estimated reserves of some 65 billion tonnes of brown coal. [42] The deposit is equivalent to 25 percent of known world reserves. The coal seams are up to 98 metres thick, with multiple coal seams often giving virtually continuous brown coal thickness of up to 230 metres. Seams are covered by very little overburden (10 to 20 metres). [42]

North America

The largest lignite deposits in North America are the Gulf Coast lignites and the Fort Union lignite field. The Gulf Coast lignites are located in a band running from Texas to Alabama roughly parallel to the Gulf Coast. The Fort Union lignite field stretches from North Dakota to Saskatchewan. Both are important commercial sources of lignite. [8]

Types

Lignite can be separated into two types. The first is xyloid lignite or fossil wood and the second form is the compact lignite or perfect lignite.

Although xyloid lignite may sometimes have the tenacity and the appearance of ordinary wood, it can be seen that the combustible woody tissue has experienced a great modification. It is reducible to a fine powder by trituration, and if submitted to the action of a weak solution of potash, it yields a considerable quantity of humic acid. [43] Leonardite is an oxidized form of lignite, which also contains high levels of humic acid. [44]

Jet is a hardened, gem-like form of lignite used in various types of jewelry. [34]

Production

Germany is the largest producer of lignite, [45] followed by China, Russia, and United States. [46] Lignite accounted for 8% of all U.S. coal production in 2019. [2]

Lignite mined in millions of metric tonnes
Country or territory1970198019902000201020112012201320142015
Flag of East Germany.svg  East Germany 261258.1280 [lower-alpha 1] [lower-alpha 1] [lower-alpha 1] [lower-alpha 1] [lower-alpha 1] [lower-alpha 1] [lower-alpha 1]
Flag of Germany.svg  Germany 108 [lower-alpha 2] 129.9 [lower-alpha 2] 107.6 [lower-alpha 2] 167.7169176.5185.4183178.2178.1
Flag of the People's Republic of China.svg  China 24.345.547.7125.3136.3145147145140
Flag of Russia.svg  Russia 145 [lower-alpha 3] 141 [lower-alpha 3] 137.3 [lower-alpha 3] 87.876.176.477.9737073.2
Flag of Kazakhstan.svg  Kazakhstan [lower-alpha 4] [lower-alpha 4] [lower-alpha 4] 2.67.38.45.56.56.6
Flag of Uzbekistan.svg  Uzbekistan [lower-alpha 4] [lower-alpha 4] [lower-alpha 4] 2.53.43.83.8
Flag of the United States.svg  United States 542.879.977.671.073.671.670.172.164.7
Flag of Poland.svg  Poland 36.967.659.556.562.864.36663.963.1
Flag of Turkey.svg  Turkey 14.544.460.970.072.568.157.562.650.4
Flag of Australia (converted).svg  Australia 32.94667.368.866.769.159.958.063.0
Flag of Greece.svg  Greece 23.251.963.956.558.761.8544846
Flag of India.svg  India 514.124.237.742.343.54547.243.9
Flag of Indonesia.svg  Indonesia 40.051.360.065.060.060.0
Flag of the Czech Republic.svg  Czechoslovakia 828771 [lower-alpha 5] [lower-alpha 5] [lower-alpha 5] [lower-alpha 5] [lower-alpha 5] [lower-alpha 5] [lower-alpha 5]
Flag of the Czech Republic.svg  Czech Republic [lower-alpha 6] [lower-alpha 6] [lower-alpha 6] 50.143.846.643.54038.338.3
Flag of Slovakia.svg  Slovakia [lower-alpha 6] [lower-alpha 6] [lower-alpha 6] 3.72.42.42.3
Flag of Yugoslavia (1946-1992).svg  Yugoslavia 33.764.1 [lower-alpha 7] [lower-alpha 7] [lower-alpha 7] [lower-alpha 7] [lower-alpha 7] [lower-alpha 7] [lower-alpha 7]
Flag of Serbia.svg  Serbia [lower-alpha 8] [lower-alpha 8] [lower-alpha 8] 35.5 [lower-alpha 9] 37.840.63840.129.737.3
Flag of Kosovo.svg  Kosovo [lower-alpha 8] [lower-alpha 8] [lower-alpha 8] [lower-alpha 10] 8.7 [lower-alpha 11] 9 [lower-alpha 11] 8.7 [lower-alpha 11] 8.2 [lower-alpha 11] 7.2 [lower-alpha 11] 8.2 [lower-alpha 11]
Flag of North Macedonia.svg  North Macedonia [lower-alpha 8] [lower-alpha 8] [lower-alpha 8] 7.56.78.27.5
Flag of Bosnia and Herzegovina.svg  Bosnia and Herzegovina [lower-alpha 8] [lower-alpha 8] [lower-alpha 8] 3.4117.176.26.26.5
Flag of Slovenia.svg  Slovenia [lower-alpha 8] [lower-alpha 8] [lower-alpha 8] 3.744.14
Flag of Montenegro.svg  Montenegro [lower-alpha 8] [lower-alpha 8] [lower-alpha 8] [lower-alpha 10] 1.922
Flag of Romania.svg  Romania 26.533.72931.135.534.124.723.625.2
Flag of Bulgaria.svg  Bulgaria 3031.526.329.437.132.526.531.335.9
Flag of Albania.svg  Albania 1.42.13014920
Flag of Thailand.svg  Thailand 1.512.417.818.321.318.318.11815.2
Flag of Mongolia.svg  Mongolia 4.46.65.18.58.39.9
Flag of Canada (Pantone).svg  Canada 69.411.210.39.79.59.08.510.5
Flag of Hungary.svg  Hungary 22.617.3149.19.69.39.69.69.3
Flag of North Korea.svg  North Korea 1010.67.26.76.86.8777
Source: World Coal Association [47]  · U.S. Energy Information Administration [48]  · BGR bund.de Energiestudie 2016 [49]  ·1970 data from World Coal (1987) [50]

no data available

  1. 1 2 3 4 5 6 7 East Germany became a part of Germany as a result of German reunification in 1990.
  2. 1 2 3 Data prior to 2000 are for West Germany only.
  3. 1 2 3 Data prior to 2000 represent the Soviet Union.
  4. 1 2 3 4 5 6 Country was a part of the Soviet Union during this time.
  5. 1 2 3 4 5 6 7 Czechoslovakia dissolved in 1993.
  6. 1 2 3 4 5 6 Country was a part of Czechoslovakia during this time.
  7. 1 2 3 4 5 6 7 Yugoslavia broke up in a process that concluded in 1992.
  8. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Country was a part of Yugoslavia during this time.
  9. 2000 data is for Federal Republic of Yugoslavia.
  10. 1 2 Country was a part of Federal Republic of Yugoslavia during this time.
  11. 1 2 3 4 5 6 Albanians unilaterally declared independence from Serbia, but the country it is not member of UN and its status is heavily disputed.

See also

Related Research Articles

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Fossil fuel power station Facility that burns fossil fuels to produce electricity

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Bioenergy Energy made from biomass or biofuell

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An integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the power generation cycle. Some of these pollutants, such as sulfur, can be turned into re-usable byproducts through the Claus process. This results in lower emissions of sulfur dioxide, particulates, mercury, and in some cases carbon dioxide. With additional process equipment, a water-gas shift reaction can increase gasification efficiency and reduce carbon monoxide emissions by converting it to carbon dioxide. The resulting carbon dioxide from the shift reaction can be separated, compressed, and stored through sequestration. Excess heat from the primary combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine. This process results in improved thermodynamic efficiency compared to conventional pulverized coal combustion.

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A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Coal-fired power stations generate over a third of the world's electricity but cause hundreds of thousands of early deaths each year, mainly from air pollution.

Health and environmental impact of the coal industry

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Refined coal is the product of the application of a coal-upgrading technology that removes moisture and certain pollutants from lower-rank coals such as sub-bituminous and lignite (brown) coals and raising their calorific values. Coal refining or upgrading technologies are typically pre-combustion treatments and/or processes that alter the characteristics of a coal before it is burned. The goals of pre-combustion coal-upgrading technologies are to increase efficiency and reduce emissions when 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. A primary benefit of refined coal is the capacity to reduce the net volume of carbon emissions that is currently emitted from power generators and would reduce the amount of emissions that is proposed to be managed via emerging carbon sequestration methodologies. Refined coal technologies have primarily been developed in the United States, several similar technologies have been researched, developed and tested in Victoria, Australia, including the Densified coal technology developed to alter the chemical bonds of brown coal to create a product that is cleaner, stable, exportable and of sufficiently high calorific value to be a black coal equivalent.

Leonardite is a soft waxy, black or brown, shiny, vitreous mineraloid that is easily soluble in alkaline solutions. It is an oxidation product of lignite, associated with near-surface mining. It is a rich source of humic acid and is used as a soil conditioner, as a stabilizer for ion-exchange resins in water treatment, in the remediation of polluted environments and as a drilling additive. It was named after A. G. Leonard, first director of the North Dakota Geological Survey, in recognition of his work on these deposits.

Maddingley Mine near Bacchus Marsh Railway Station, Victoria, Australia contains a concentration of a particular brown coal (lignite) formation called Leonardite. A relatively high altitude formation, Maddingley brown coal is distinguished as having 60 per cent moisture content and a rich fulvic acid and humic acid content. A declared strategic State mining reserve, the estimated 400 million tonne deposit at Maddingley is the largest of three known deposits of high value Leonardite in the world, the others occurring in Mexico and Germany.

Densified coal is the product of the Coldry Process coal upgrading technology that removes moisture from low-rank coals such as sub-bituminous and lignite/brown coal. The densification process raises the calorific value of low-rank coal to equal or exceed that of many export-grade black coals. Densified coal resulting from the Coldry Process is regarded as a black coal equivalent or replacement for black coal.

Coal in Europe

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Cornelia C. Cameron American geologist

Cornelia Clermont Cameron was an American geologist who researched peat as a soil additive and energy source.

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