Underground coal gasification

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Underground coal gasification
Process type chemical
Industrial sector(s) oil and gas industry
coal industry
Feedstock coal
Product(s) coal gas
Leading companies Africary
Linc Energy
Carbon Energy
Main facilities Angren Power Station (Uzbekistan)
Majuba Power Station (South Africa)
Chinchilla Demonstration Facility (Australia)
Inventor Carl Wilhelm Siemens
Year of invention1868
Developer(s) African Carbon Energy
Ergo Exergy Technologies
Skochinsky Institute of Mining

Underground coal gasification (UCG) is an industrial process which converts coal into product gas. UCG is an in-situ gasification process, carried out in non-mined coal seams using injection of oxidants and steam. The product gas is brought to the surface through production wells drilled from the surface. [1]

Contents

The predominant product gases are methane, hydrogen, carbon monoxide and carbon dioxide. Ratios vary depending upon formation pressure, depth of coal and oxidant balance. Gas output may be combusted for electricity production. Alternatively, the gas output can be used to produce synthetic natural gas, or hydrogen and carbon monoxide can be used as a chemical feedstock for the production of fuels (e.g. diesel), fertilizer, explosives and other products.

The technique can be applied to coal resources that are otherwise unprofitable or technically complicated to extract by traditional mining methods. UCG offers an alternative to conventional coal mining methods for some resources. It has been linked to a number of concerns from environmental campaigners. [2]

History

The earliest recorded mention of the idea of underground coal gasification was in 1868, when Sir William Siemens in his address to the Chemical Society of London suggested the underground gasification of waste and slack coal in the mine. [3] [4] Russian chemist Dmitri Mendeleyev further developed Siemens' idea over the next couple of decades. [4] [5]

In 1909–1910, American, Canadian, and British patents were granted to American engineer Anson G. Betts for "a method of using unmined coal". [4] [5] The first experimental work on UCG was planned to start in 1912 in Durham, the United Kingdom, under the leadership of Nobel Prize winner Sir William Ramsay. However, Ramsay was unable to commence the UCG field work before the beginning of the World War I, and the project was abandoned. [4] [5]

Initial tests

In 1913, Ramsay's work was noticed by Russian exile Vladimir Lenin who wrote in the newspaper Pravda an article "Great Victory of Technology" promising to liberate workers from hazardous work in coal mines by underground coal gasification. [4] [5] [6]

Between 1928 and 1939, underground tests were conducted in the Soviet Union by the state-owned organization Podzemgaz. [6] The first test using the chamber method started on 3 March 1933 in the Moscow coal basin at Krutova mine. This test and several following tests failed. The first successful test was conducted on 24 April 1934 in Lysychansk, Donetsk Basin, by the Donetsk Institute of Coal Chemistry. [5]

The first pilot-scale process started 8 February 1935 in Horlivka, Donetsk Basin. Production gradually increased, and, in 1937–1938, the local chemical plant began using the produced gas. In 1940, experimental plants were built in Lysychansk and Tula. [5] After World War II, the Soviet activities culminated in the operation of five industrial-scale UCG plants in the early 1960s. However, Soviet activities subsequently declined due to the discovery of extensive natural gas resources. In 1964, the Soviet program was downgraded. [5] As of 2004 only Angren site in Uzbekistan and Yuzhno-Abinsk site in Russia continued operations. [7]

Post-war experiments

After World War II, the shortage in energy and the diffusion of the Soviets' results provoked new interest in Western Europe and the United States. In the United States, tests were conducted in 1947–1958 in Gorgas, Alabama. The experiments were carried out in a partnership between Alabama Power and the US Bureau of Mines. The experiments at Gorgas continued for seven years until 1953, at which point the US Bureau of Mines withdrew its support for them after the US Congress withdrew funding. In total 6,000 tons of coal were combusted by 1953 in these experiments. The experiments succeeded in producing combustible synthetic gas. [8] The experiments were reactivated after 1954, this time with hydrofracturing using a mixture of oil and sand, but finally discontinued in 1958 as uneconomical. [9] From 1973–1989, extensive testing was carried out. The United States Department of Energy and several large oil and gas companies conducted several tests. Lawrence Livermore National Laboratory conducted three tests in 1976–1979 at the Hoe Creek test site in Campbell County, Wyoming. [4] [5]

In cooperation with Sandia National Laboratories and Radian Corporation, Livermore conducted experiments in 1981–1982 at the WIDCO Mine near Centralia, Washington. [4] In 1979–1981, an underground gasification of steeply dipping seams was demonstrated near Rawlins, Wyoming. The program culminated in the Rocky Mountain trial in 1986–1988 near Hanna, Wyoming. [5] [7]

In Europe, the stream method was tested at Bois-la-Dame, Belgium, in 1948 and in Jerada, Morocco, in 1949. [7] The borehole method was tested at Newman Spinney and Bayton, United Kingdom, in 1949–1950. A few years later, a first attempt was made to develop a commercial pilot plan, the P5 Trial, at Newman Spinney Derbyshire in 1958–1959. [5] [7] The Newman Spinney project was authorised in 1957 and comprised a steam boiler and a 3.75 MW turbo-alternator to generate electricity. [10] The National Coal Board abandoned the gasification scheme in summer 1959. [10] During the 1960s, European work stopped, due to an abundance of energy and low oil prices, but recommenced in the 1980s. Field tests were conducted in 1981 at Bruay-en-Artois, in 1983–1984 at La Haute Deule, France, in 1982–1985 at Thulin, Belgium and in 1992–1999 at the El Tremedal site, Province of Teruel, Spain. [4] In 1988, the Commission of the European Communities and six European countries formed a European Working Group. [7]

In New Zealand, a small scale trial was operated in 1994 in the Huntly Coal Basin. In Australia, tests were conducted starting in 1999. [7] China has operated the largest program since the late 1980s, including 16 trials. [4] [11]

Process

The underground coal gasification process. UCGprocessfigure-01.png
The underground coal gasification process.

Underground coal gasification converts coal to gas while still in the coal seam (in-situ). Gas is produced and extracted through wells drilled into the unmined coal seam. Injection wells are used to supply the oxidants (air, oxygen) and steam to ignite and fuel the underground combustion process. Separate production wells are used to bring the product gas to the surface. [7] [12] The high pressure combustion is conducted at temperature of 700–900 °C (1,290–1,650 °F), but it may reach up to 1,500 °C (2,730 °F). [4] [7]

The process decomposes coal and generates carbon dioxide (CO
2), hydrogen (H
2), carbon monoxide (CO) and methane (CH
4). In addition, small quantities of various contaminants including sulfur oxides (SO
x), mono-nitrogen oxides (NO
x), and hydrogen sulfide (H
2S) are produced. [7] As the coal face burns and the immediate area is depleted, the volumes of oxidants injected are controlled by the operator. [4]

There are a variety of designs for underground coal gasification, all of which provide a means of injecting oxidant and possibly steam into the reaction zone, and also provide a path for production gases to flow in a controlled manner to the surface. As coal varies considerably in its resistance to flow, depending on its age, composition and geological history, the natural permeability of the coal to transport the gas is generally not adequate. For high pressure break-up of the coal, hydro-fracturing, electric-linkage, and reverse combustion may be used in varying degrees. [4] [12]

The simplest design uses two vertical wells: one injection and one production. Sometimes it is necessary to establish communication between the two wells, and a common method is to use reverse combustion to open internal pathways in the coal. Another alternative is to drill a lateral well connecting the two vertical wells. [13] UCG with simple vertical wells, inclined wells, and long deflected wells was used in the Soviet Union. The Soviet UCG technology was further developed by Ergo Exergy and tested at Linc's Chinchilla site in 1999–2003, in Majuba UCG plant (2007) and in Cougar Energy's failed UCG pilot in Australia (2010).

In the 1980s and 1990s, a method known as CRIP (controlled retraction and injection point) was developed (but not patented) by the Lawrence Livermore National Laboratory and demonstrated in the United States and Spain. This method uses a vertical production well and an extended lateral well drilled directionally in the coal. The lateral well is used for injection of oxidants and steam, and the injection point can be changed by retracting the injector. [13]

Carbon Energy was the first to adopt a system which uses a pair of lateral wells in parallel. This system allows a consistent separation distance between the injection and production wells, while progressively mining the coal between the two wells. This approach is intended to provide access to the greatest quantity of coal per well set and also allows greater consistency in production gas quality. [14]

A new technology has been announced in May 2012 by developer Portman Energy wherein a method called SWIFT (Single Well Integrated Flow Tubing) uses a single vertical well for both oxidant delivery and syngas recovery. The design has a single casing of tubing strings enclosed and filled with an inert gas to allow for leak monitoring, corrosion prevention and heat transfer. A series of horizontally drilled lateral oxidant delivery lines into the coal and a single or multiple syngas recovery pipeline(s) allow for a larger area of coal to be combusted at one time. The developers claim this method will increase syngas production by up to ten (10) times above earlier design approaches. The single well design means development costs are significantly lower and the facilities and wellheads are concentrated at a single point reducing surface access roads, pipelines and facilities footprint.[9] The UK patent office have advised that the full patent application GB2501074 by Portman Energy be published 16 October 2013.

A wide variety of coals are amenable to the UCG process and coal grades from lignite through to bituminous may be successfully gasified. A great many factors are taken into account in selecting appropriate locations for UCG, including surface conditions, hydrogeology, lithology, coal quantity, and quality. According to Andrew Beath of CSIRO Exploration & Mining other important criteria include:

According to Peter Sallans of Liberty Resources Limited, the key criteria are:

Economics

Underground coal gasification allows access to coal resources that are not economically recoverable by other technologies, e.g., seams that are too deep, low grade, or that have a thin stratum profile. [4] By some estimates, UCG will increase economically recoverable reserves by 600 billion tonnes. [17] Lawrence Livermore National Laboratory estimates that UCG could increase recoverable coal reserves in the US by 300%. [18] Livermore and Linc Energy claim that UCG capital and operating costs are lower than those for traditional mining. [4] [19]

UCG product gas is used to fire combined cycle gas turbine (CCGT) power plants, with some studies suggesting power island efficiencies of up to 55%, with a combined UCG/CCGT process efficiency of up to 43%. CCGT power plants using UCG product gas instead of natural gas can achieve higher outputs than pulverized-coal-fired power stations (and associated upstream processes), resulting in a large decrease in greenhouse gas (GHG) emissions.[ citation needed ]

UCG product gas can also be used for:

In addition, carbon dioxide produced as a by-product of underground coal gasification may be re-directed and used for enhanced oil recovery.[ citation needed ]

Underground product gas is an alternative to natural gas and potentially offers cost savings by eliminating mining, transport, and solid waste. The expected cost savings could increase given higher coal prices driven by emissions trading, taxes, and other emissions reduction policies, e.g. the Australian Government's proposed Carbon Pollution Reduction Scheme.[ citation needed ]

Projects

Cougar Energy and Linc Energy conducted pilot projects in Queensland, Australia based on UCG technology provided by Ergo Exergy until their activities were banned in 2016. [20] [21] [22] [23] [24] [25] Yerostigaz, a subsidiary of Linc Energy, produces about 1 million cubic metres (35 million cubic feet) of syngas per day in Angren, Uzbekistan. The produced syngas is used as fuel in the Angren Power Station. [26]

In South Africa, Eskom (with Ergo Exergy as technology provider) is operating a demonstration plant in preparation for supplying commercial quantities of syngas for commercial production of electricity. [27] [28] [29] African Carbon Energy [30] has received environmental approval for a 50 MW power station near Theunissen in the Free State province and is bid-ready to participate in the DOE's Independent Power Producer (IPP) gas program [31] where UCG has been earmarked as a domestic gas supply option.

ENN has operated a successful pilot project in China.[ citation needed ]

In addition, there are companies developing projects in Australia, UK, Hungary, Pakistan, Poland, Bulgaria, Canada, US, Chile, China, Indonesia, India, South Africa, Botswana, and other countries. [27] According to the Zeus Development Corporation, more than 60 projects are in development around the world.

Environmental and social impacts

Eliminating mining eliminates mine safety issues. [32] Compared to traditional coal mining and processing, the underground coal gasification eliminates surface damage and solid waste discharge, and reduces sulfur dioxide (SO
2) and nitrogen oxide (NO
x) emissions. [4] [33] For comparison, the ash content of UCG syngas is estimated to be approximately 10 mg/m3 compared to smoke from traditional coal burning where ash content may be up to 70 mg/m3. [18] However, UCG operations cannot be controlled as precisely as surface gasifiers. Variables include the rate of water influx, the distribution of reactants in the gasification zone, and the growth rate of the cavity. These can only be estimated from temperature measurements, and analyzing product gas quality and quantity. [4]

Subsidence is a common issue with all forms of extractive industry. While UCG leaves the ash behind in the cavity, the depth of the void left after UCG is typically greater than that with other methods of coal extraction. [4]

Underground combustion produces NO
x and SO
2 and lowers emissions, including acid rain.

Regarding emissions of atmospheric CO
2, proponents of UCG have argued that the process has advantages for geologic carbon storage. [4] Combining UCG with CCS (Carbon capture and storage) technology allows re-injecting some of the CO
2 on-site into the highly permeable rock created during the burning process, i.e. the cavity where the coal used to be. [34] Contaminants, such as ammonia and hydrogen sulfide, can be removed from product gas at a relatively low cost.[ citation needed ]

However, as of late 2013, CCS had never been successfully implemented on a commercial scale as it was not within the scope of UCG projects and some had also resulted in environmental concerns. In Australia in 2014 the Government filed charges over alleged serious environmental harm stemming from Linc Energy's pilot Underground Coal Gasification plant near Chinchilla in the Queensland's foodbowl of the Darling Downs. [35] When UCG was banned in April, 2016 the Queensland Mines Minister Dr Anthony Lynham stated "The potential risks to Queensland's environment and our valuable agricultural industries far outweigh any potential economic benefits. UCG activity simply doesn't stack up for further use in Queensland." [25]

Meanwhile, as an article in the Bulletin of Atomic Sciences pointed out in March 2010 that UCG could result in massive carbon emissions. "If an additional 4 trillion tonnes [of coal] were extracted without the use of carbon capture or other mitigation technologies atmospheric carbon-dioxide levels could quadruple", the article stated, "resulting in a global mean temperature increase of between 5 and 10 degrees Celsius". [36] [37]

Aquifer contamination is a potential environmental concern. [4] [38] Organic and often toxic materials (such as phenol) could remain in the underground chamber after gasification if the chamber is not decommissioned. Site decommissioning and rehabilitation are standard requirements in resources development approvals whether that be UCG, oil and gas, or mining, and decommissioning of UCG chambers is relatively straightforward. Phenol leachate is the most significant environmental hazard due to its high water solubility and high reactiveness to gasification. The US Dept of Energy's Lawrence Livermore Institute conducted an early UCG experiment at very shallow depth and without hydrostatic pressure at Hoe Creek, Wyoming. They did not decommission that site and testing showed contaminants (including the carcinogen benzene) in the chamber. The chamber was later flushed and the site successfully rehabilitated. Some research has shown that the persistence of minor quantities of these contaminants in groundwater is short-lived and that ground water recovers within two years. [33] Even so, proper practice, supported by regulatory requirements, should be to flush and decommission each chamber and to rehabilitate UCG sites.

Newer UCG technologies and practices claim to address environmental concerns, such as issues related to groundwater contamination, by implementing the "Clean Cavern" concept. [39] This is the process whereby the gasifier is self-cleaned via the steam produced during operation and also after decommissioning. Another important practice is maintaining the pressure of the underground gasifier below that of the surrounding groundwater. The pressure difference forces groundwater to flow continuously into the gasifier and no chemical from the gasifier can escape into the surrounding strata. The pressure is controlled by the operator using pressure valves at the surface. [39]

See also

Related Research Articles

Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.

<span class="mw-page-title-main">Gasification</span> Form of energy conversion

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

In industrial chemistry, coal gasification is the process of producing syngas—a mixture consisting primarily of carbon monoxide (CO), hydrogen, carbon dioxide, methane, and water vapour —from coal and water, air and/or oxygen.

<span class="mw-page-title-main">Sasol</span> South African integrated energy and chemical company

Sasol Limited is an integrated energy and chemical company based in Sandton, South Africa. The company was formed in 1950 in Sasolburg, South Africa, and built on processes that German chemists and engineers first developed in the early 1900s. Today, Sasol develops and commercializes technologies, including synthetic fuel technologies, and produces different liquid fuels, chemicals, coal tar, and electricity.

<span class="mw-page-title-main">National Energy Technology Laboratory</span> United States research lab

The National Energy Technology Laboratory (NETL) is a U.S. national laboratory under the Department of Energy Office of Fossil Energy. NETL focuses on applied research for the clean production and use of domestic energy resources. It performs research and development on the supply, efficiency, and environmental constraints of producing and using fossil energy resources while maintaining affordability.

Coal liquefaction is a process of converting coal into liquid hydrocarbons: liquid fuels and petrochemicals. This process is often known as "Coal to X" or "Carbon to X", where X can be many different hydrocarbon-based products. However, the most common process chain is "Coal to Liquid Fuels" (CTL).

<span class="mw-page-title-main">Synthetic fuel</span> Fuel from carbon monoxide and hydrogen

Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by reforming of natural gas.

<span class="mw-page-title-main">Coal pollution mitigation</span>

Coal pollution mitigation, sometimes labeled as clean coal, is a series of systems and technologies that seek to mitigate health and environmental impact of burning coal for energy. Burning coal releases harmful substances that contribute to air pollution, acid rain, and greenhouse gas emissions. Mitigation includes precombustion approaches, such as cleaning coal, and post combustion approaches, include flue-gas desulfurization, selective catalytic reduction, electrostatic precipitators, and fly ash reduction. These measures aim to reduce coal's impact on human health and the environment.

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 electricity 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.

Plasma gasification is an extreme thermal process using plasma which converts organic matter into a syngas which is primarily made up of hydrogen and carbon monoxide. A plasma torch powered by an electric arc is used to ionize gas and catalyze organic matter into syngas, with slag remaining as a byproduct. It is used commercially as a form of waste treatment, and has been tested for the gasification of refuse-derived fuel, biomass, industrial waste, hazardous waste, and solid hydrocarbons, such as coal, oil sands, petcoke and oil shale.

Carbon capture and storage (CCS) is a technology that can capture carbon dioxide CO2 emissions produced from fossil fuels in electricity, industrial processes which prevents CO2 from entering the atmosphere. Carbon capture and storage is also used to sequester CO2 filtered out of natural gas from certain natural gas fields. While typically the CO2 has no value after being stored, Enhanced Oil Recovery uses CO2 to increase yield from declining oil fields.

<span class="mw-page-title-main">Mining in New Zealand</span>

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<span class="mw-page-title-main">Bioenergy with carbon capture and storage</span>

Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon dioxide (CO2) that is produced.

<span class="mw-page-title-main">Linc Energy</span>

Linc Energy was an Australian energy company that specialised in coal-based synthetic fuel production, as well as conventional oil and gas production. It was engaged in development and commercialisation of proprietary underground coal gasification technology. Produced gas was used for production of synthetic fuel through gas-to-liquid technology, and was also used for power generation. The company had its headquarters in Brisbane, Queensland.

Moreton Resources Limited is an Australian coal mining company. In 2007–2013 it was specialized on underground coal gasification and electric power production by produced syngas. In addition to Australia, the company planned underground coal gasification projects in the United Kingdom, India, Pakistan, China, and Mongolia.

Carbon Energy Corporation is an Australian global energy technology provider and services company with expertise in unconventional syngas extraction utilising its proprietary Underground Coal Gasification (UCG) technology. It operates an underground coal gasification pilot plant at Bloodwood Creek, Queensland, Australia. In 2009, Carbon Energy signed an agreement with the Chilean company Antofagasta Minerals to develop an underground coal gasification project in Mulpún, Chile. The Company is headquartered in Brisbane, Australia, is listed on the Australian Securities Exchange (ASX) as CNX and is quoted on the OTCQX International Exchange as CNXAY in the United States.

<span class="mw-page-title-main">Hi-Gen Power</span>

Hi-Gen Power was a London-based developer of projects combining underground coal gasification with carbon capture and storage and alkaline fuel cells. It was established in 2009 to commercialize alkaline fuel cells developed by the fuel cell manufacturer AFC Energy. It is affiliated with B9 Gas.

<span class="mw-page-title-main">Kemper Project</span> Power station in Mississippi, US

The Kemper Project, also called the Kemper County energy facility or Plant Ratcliffe, is a natural gas-fired electrical generating station currently under construction in Kemper County, Mississippi. Mississippi Power, a subsidiary of Southern Company, began construction of the plant in 2010. The initial, coal-fired project was central to President Obama's Climate Plan, as it was to be based on "clean coal" and was being considered for more support from the Congress and the incoming Trump Administration in late 2016. If it had become operational with coal, the Kemper Project would have been a first-of-its-kind electricity plant to employ gasification and carbon capture technologies at this scale.

Coal gasification is a process whereby a hydrocarbon feedstock (coal) is converted into gaseous components by applying heat under pressure in the presence of steam. Rather than burning, most of the carbon-containing feedstock is broken apart by chemical reactions that produce "syngas." Syngas is primarily hydrogen and carbon monoxide, but the exact composition can vary. In Integrated Gasification Combined Cycle (IGCC) systems, the syngas is cleaned and burned as fuel in a combustion turbine which then drives an electric generator. Exhaust heat from the combustion turbine is recovered and used to create steam for a steam turbine-generator. The use of these two types of turbines in combination is one reason why gasification-based power systems can achieve high power generation efficiencies. Currently, commercially available gasification-based systems can operate at around 40% efficiencies. Syngas, however, emits more greenhouse gases than natural gas, and almost twice as much carbon as a coal plant. Coal gasification is also water-intensive.

Lower-temperature fuel cell types such as the proton exchange membrane fuel cell, phosphoric acid fuel cell, and alkaline fuel cell require pure hydrogen as fuel, typically produced from external reforming of natural gas. However, fuels cells operating at high temperature such as the solid oxide fuel cell (SOFC) are not poisoned by carbon monoxide and carbon dioxide, and in fact can accept hydrogen, carbon monoxide, carbon dioxide, steam, and methane mixtures as fuel directly, because of their internal shift and reforming capabilities. This opens up the possibility of efficient fuel cell-based power cycles consuming solid fuels such as coal and biomass, the gasification of which results in syngas containing mostly hydrogen, carbon monoxide and methane which can be cleaned and fed directly to the SOFCs without the added cost and complexity of methane reforming, water gas shifting and hydrogen separation operations which would otherwise be needed to isolate pure hydrogen as fuel. A power cycle based on gasification of solid fuel and SOFCs is called an Integrated Gasification Fuel Cell (IGFC) cycle; the IGFC power plant is analogous to an integrated gasification combined cycle power plant, but with the gas turbine power generation unit replaced with a fuel cell power generation unit. By taking advantage of intrinsically high energy efficiency of SOFCs and process integration, exceptionally high power plant efficiencies are possible. Furthermore, SOFCs in the IGFC cycle can be operated so as to isolate a carbon dioxide-rich anodic exhaust stream, allowing efficient carbon capture to address greenhouse gas emissions concerns of coal-based power generation.

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  34. ↑ Krupp, Fred; Horn, Miriam (2009). Earth: The Sequel: The Race to Reinvent Energy and Stop Global Warming. New York: Norton & Company. ISBN   978-0-393-33419-7.
  35. ↑ "Queensland government hits Underground Coal Gasification player Linc Energy with environmental damage charges". 15 April 2014.
  36. ↑ "The Untold Story Of The Dangerous New Experiment Coal Companies Want To Bring To America | ThinkProgress". ThinkProgress . Archived from the original on 13 November 2013.
  37. ↑ "Is underground coal gasification a sensible option?". 29 March 2010.
  38. ↑ National Research Council (U.S.). Committee on Ground-Water Resources in Relation to Coal Mining (1981). Coal mining and ground-water resources in the United States: a report. United States National Academies. p. 113. ISBN   9780309031868.
  39. 1 2 Burton, Elizabeth A. (2019). "Best Practices in Underground Coal Gasification". Best Practices in Underground Coal Gasification. osti.gov.

Further reading

"Beyond fracking", New Scientist feature article (Fred Pearce), 15 February 2014

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