Underground coal gasification

Underground coal gasification

Underground coal gasification (UCG) is an "in-situ" gasification process carried out in non-mined coal seams using injection and production wells drilled from the surface, which enables the coal to be converted into product gas. The process is flexible in operation and is capable of producing commercial quantities of gas to be used as a chemical feedstock or as fuel for power generation. The technique can be applied to resources that are otherwise not economical to extract and also offers an alternative to conventional coal mining methods for some resources. UCG has the advantage over traditional coal mining and gasification in minimising environmental and social harm. The technology could be used to ensure that coal remains apart of the global energy mix by providing a solution to reduce and abate greenhouse gas emissions (GHG).


The history of UCG can be traced back to the year 1868, When Sir William Siemens first to suggested the underground gasification of waste and slack coal in the mine. [Siemens W., "Transactions of Chemical Society", 21, 279, 1868, [http://www.patentstorm.us/patents/4197911/description.html (citation)] ] Russian chemist Dmitri Mendeleyev, who was credited with conceiving the periodic table, further developed Siemen's idea over the next couple of decades . However, the first experimental work on UCG did not begin until the year 1912 in Durham (UK) under the leadership of Nobel Prize winner Sir William Ramsay. The following year saw Ramsay set about raising money from industrial investors to build the first UCG plant but he was unable to complete this work before the beginning of World War I. Subsequently, all efforts in UCG development in Western Europe were discontinued until the end of the Second World War. Ramsay's work did not go unnoticed: In 1913, Russian exile Vladimir Lenin was reportably somewhat influenced to write "Pravda", a book about a "Great Victory of Technology" which promised to liberate workers from the hazardous work in the nation's mines. Fifteen years later, Stalin charged the USSR based Skochinsky Institute of Mining to run a research and development program during the 1930s, in competition with Germany who were fast developing Fischer Tropsch processing technology. Stalin allocated thousands of workers and an estimated $10 billion (in current terms) to the development of the technology. The first trials in 1937 failed and many top scientists were put on trial with a number being executed. By 1939 the Soviets had successfully begun operating a UCG plant in the Ukraine which was later shut down by German occupation. After the war, the Soviets restarted the UCG program which eventually culminated in the operation of fourteen industrial-scale UCG plants by the end of the 1960s. However, activity subsequently declined due to the discovery of extensive natural gas resources. As a result only one site is still in operation today at Angren in the territory of Uzbekistan.

At about the same time (between the years 1944 and 1959) the shortage in energy, and, the diffusion of the results of the UCG experiments in the USSR during the period 1934–1940, provoked new interest in UCG in Western European coal mining countries. The first research work was directed to the development of UCG in thin seams at shallow depth. The stream method was tested at Bois-la Dame, Belgium in 1948, and in Djerada, Morocco in 1949. The boreholes 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 plant—the P5 Trial— at Newman Spinney in 1958-1959. During the 1960s all European work was stopped, due to an abundance of energy and low oil prices. In the USA, a UCG program was initiated in 1972, which built upon Russian experience, and an extensive field testing program was begun, supported by a number of research institutes and universities. In 1989, the European Working Group on UCG recommended that a series of trials should be undertaken to evaluate the commercial feasibility of UCG. The trial was undertaken by the Spain, the UK and Belgium, and was supported by the European Commission. The largest ongoing program is being conducted by China, which includes 16 UCG trials.cite web
title = Underground Coal Gasification. Current Developments (1990 to date)
publisher = CG Engineering Ltd
url = http://www.coal-ucg.com/current%20developments.html
accessdate = 2007-11-24

The successful demonstration near the town of Chinchilla, some 350 km west of Brisbane, in Queensland, Australia has resulted in a surge of interest in the technology. The Chinchilla demonstration began in December 1999, on a coal lease owned by [http://www.lincenergy.com.au/ucg.php Linc Energy] . Linc licensed the UCG technology from [http://www.ergoexergy.com Ergo Exergy] (Canada), who conducted the demonstration up until the end of the controlled shutdown program, which was completed in April 2003. The demonstration involved the gasification of 35,000 tonnes of coal, and resulted in successful environmental performance as per independent audit reports.


Criteria for underground coal gasification

Underground coal gasification projects have specific requirements regarding the coal seam:

* The seam lies underground at a depth of between 30 and 800 metres (as demonstrated by [http://www.ergoexergy.com Ergo Exergy's] ] technology at Chinchilla);
* The seam thickness is more than 5 metres;
* The ash content of the coal is less than 60%;
* The seam has minimal discontinuities; &
* There are no aquifers nearby (to avoid polluting supplies of drinking water)cite web |author=Andrew Beath | title=Underground Coal Gasification Resource Utilisation Efficiency |publisher=CSIRO Exploration & Mining | url=http://www.carbonenergy.com.au/uploads/File/carbonenergy/presentations/Innovation&ExcellenceCSIRO%20-%20Aug2006.pdf | format=PDF| date=2006-08-18 | accessdate=2007-11-11] .



cite web |author=Katie Walter | title= Fire in the Hole|publisher=Lawrence Livermore National Library | url=https://www.llnl.gov/str/April07/Friedmann.html | format=html| date= accessdate=2008-10-06] The basic underground coal gasification process consists of one production well drilled into the unmined coal-seam for injection of the oxidants, and another production well to bring the product gas to surface "(See Diagram)". The coal seam is ignited via the first well and burns at temperatures as high as 1500 kelvins, generating hydrogen(H), carbon monoxide(CO) and small quantities of methane(CH4) and hydrogen sulphide(H2S) at high pressure. As the coal face burns and the immediate area is depleted, the oxidants injected are controlled by the operator, ultimately with the objective of guiding the burn along the seam.

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 satisfactory. For high pressure break-up of the coal, a hydrofraccing, an electric-linkage, and a reverse combustion may be used with varying degrees.cite web | title=The Basics of UCG|publisher=UCG Partnership | url=http://www.ucgp.com/key-facts/basic-description/ | accessdate=2007-11-11]

There are two different commercially available underground coal gasification methods. One of the methods uses vertical wells and a method of reverse combustion to open up the internal pathways in the coal. The process was used in the Soviet Union and later it was tested in Chinchilla by using air and water as the injected gases. This orginal UCG method has been refined to produced greater energy efficiency by Canadian based company, [http://www.ergoexergy.com Ergo Exergy] , who are widely regarded as the leaders in UCG technology. Ergo Exergy licenses out its εUCG™ technology for use in UCG projects globally.

Another method that was largely developed in the USA creates dedicated inseam boreholes, using drilling and completion technology adapted from oil and gas production. It has a moveable injection point known as CRIP (controlled retraction injection point) and generally uses oxygen or enriched air for gasification.



Underground coal gasification allow access to more coal resources than economically recoverable by traditional technologies. By some estimates it will increase economically recoverable reserves by 600 billion tonnescite book
title = Survey of energy resources
publisher = World Energy Council (WEC)
date = 2007
edition = 21
page = 7
url = http://www.worldenergy.org/documents/ser2007_final_online_version_1.pdf
format = PDF
isbn = 0946121265
accessdate = 2007-11-24
] . The Lawrence Livermore National Laboratory estimates that using UCG could increase recoverable coal reserves in the USA by 300%. According to [http://www.lincenergy.com.au/ucg.php Linc Energy] , the capital and operating costs of the underground coal gasification are lower than in traditional mining.cite web
title = UCG
publisher = Linc Energy
url = http://www.lincenergy.com.au/ucg.php
accessdate = 2007-11-24
] .

UCG product gas is optimally used to fire Combined cycle Gas Turbine(CCGT) powerplants, with some studies suggesting power island efficiences of up to 55%, with a combined UCG / CCGT process efficiency rate of up to 43%. CCGT power plants using UCG product gas instead of Natural Gas(NG) can achieve much higher outputs. In particular, this increase in efficiency over pulverised-coal-fired power stations (and associated upstream processes) results in a large decrease in GHG emissions.

UCG product gas can also be used for:

* Synthesis of liquid fuels at a predicted cost equivalent to US$17/bbl;
* Manufacture of chemicals such as ammonia and fertilizers; &
* Enhanced oil recovery (EOR).

In the roles listed above, UCG product gas replaces the use of natural gas and can provide substantial cost savings. In demonstrating the economic benefits of UCG, South African utility [http://www.eskom.co.za Eskom] , successfully produced gas at a significantly reduced cost of $1 per million BTU's at its Majuba operation, using Ergo Exergy's technology. This is between one third and one sixth of the cost of gas made in an equivalent surface gasifier. The gas is being used to fire an existing 4.2 GW powerplant.

Additional cost savings can be made over traditional coal mining and required coal transport, whereby the UCG process: produces syngas which can piped directly to the end-user, reducing need for rail / road infrastructure; and; lowers the cost of environmental cleanup due to solid waste being confined underground.With regards to new environmental markets, for example an emissions trading scheme,companies whose usual operations involve traditional coal mining and burning may see value in the reduced greenhouse gas emissions (GHG) generated using UCG as an alternative. The forecasted cost savings could be substantial given the projected high cost of carbon abatement for coal industry companies who are impacted by regulatory schemes e.g. the Australian Government's proposed Carbon Pollution Reduction Scheme.

In 2008, Canadian company [http://www.laurusenergy.com Laurus Energy] , advanced their progress in combining UCG and Carbon capture and storage(CCS) to decrease costly externalities and further increase the technology's environmental credentials. This case study is further discussed in the following section.


Environmental and social impacts

Environmental impacts

UCG offers significant benefits to the environment over traditional coal mining or coal gasification methods. Most notably UCG eliminates the need for mining. This results in a number of immediate benefits including the elimination of solid waste discharge and reduction in SOx) and (NOx) Shu-qin, L., Jun-hua, Y (2002). Environmental Benefits of underground coal gasification. Journal of Environmental Sciences, vol. 12, no. 2, pp.284-288] . The reduction of solid waste is a major advantage of UCG over traditional coal mining, where large quantities of coal ash, oxides, waste rock and radioactive waste are common discharges. In the case of UCG, this waste is either avoided or contained underground. Due to the absence of coal mining, Appalachian mountaintops are not stripped bare and remain largely preserved, and, there is no need for tailing and ash damsKrupp, F, Horn, M (2008). Earth: The Sequel. Environmental Defense Fund, New york.] . For comparison, the ash content of UCG syngas is estimated to be appxomiately 10 mg/m³ compared to smoke from burning where ash content may be up to 70 mg/m³. The containment of ash widens the appeal of UCG technology to nations who have abundant low-quality – high ash content coal reserves and who rely on coal for their energy needs. For example, recentlywhen interest in UCG has been growing in India, the world's third largest producer of coal and where coal constitutes 60% of the country's energy mix.

As stated, when coal is combusted underground, NOx and SOx atmospheric GHG emissions are lowered, therefore creating the added advantage in stemming acid rain occurence. Also, reducing NOx emissions has key benefits in mitigating climate change, where NOx has a global warming potential of 296 times that of carbon dioxide (CO2). As mentioned previously, Laurus Energy is currently making efforts to combine UCG with CCS technology. It is estimated that for approximately $25 per tonne, CO2 could be readily captured using commercially available absorbents such as Selexol. Such technology would then seek to compress and reinject some of the CO2 on-site and into the highly permeable depleted gasifer created during the burn process i.e. where the goal used to be . Also, contaminants such as ammonia and hydrogen sulphide can be removed from UCG product gas used to fire CCGT power stations, for example, at a relatively low cost.

The impact of UCG on the water table has been highlighted by some critics as an environmental concern. Organic and often toxic materials (such as Phenol) remain in the underground chamber post gasification and therefore are likely to leech into the water table, should inappropriate site selection occur. Phenol leechate is regarded as the most significant environmental hazard due to its high water solubility and high reactiveness to gasification. However, research has shown that the persistence of such substances in the water is short and that underground water has been shown to recover within two years . One such example where Lawrence Livermore National University conducted a burn at Hoe Creek, Wyoming (USA) highlights the possible negative environmental impacts of UCG. In this case the operating pressure in the burn carvity was greater than the surrounding rock, resulting in contaminants (including the carcinogen benzene) being pushed away from the cavity and out into the potable groundwater. Since this incident scientists have significantly advanced their knowledge of contaminants produced during the UCG process, and as a result a number of steps have been developed to guard against ground water contamination. Since 1999, the ongoing successful containment of water pollution has been demonstrated at Linc Energy's Chinchilla operation.

Lastly, UCG does not require an external water source to operate, exhibiting a major environmental advantage over water-intensive coal mining operations and pulverised-coal-fired energy production methods.

Social impacts

Due to the absence of mining in UCG, a number of social benefits are evident. Firstly, the risk of injury or death to humans is somewhat eliminated given that workers no longer need to enter a mine. Secondly, as the impact on the environment is greatly reduced, local communities do not face the detrimental impacts (e.g. air pollution and large scale land degradation) that traditional mining brings. Lastly, local communities may benefit from the creation of associated infrastructure (e.g. roads), subsidised ennergy, and employee spending in the local economy.


External links

* [http://www.ucgp.com UCG Partnership]
* [http://www.carbonenergy.com.au/ CarbonEnergy PTY LTD (CEPL)] An energy company focusing on bringing the very best in technology to coal energy and liquid fuels projects both in Australia and internationally.
* [http://www.undeerc.org/programareas/undergroundcoalgasification.aspx Energy & Environmental Research Centre (EERC) - UCG overview]
* [http://www.coal.gov.uk/resources/cleanercoaltechnologies/ucgintro.cfm UK government Coal Authority - UCG information resources]
* [http://www.co2sinus.org/index_en.html CO2SINUS] CO2 Storage in in situ Converted Coal Seams - Research Project at the RWTH Aachen University.
* [http://www.ergoexergy.com Ergo Exergy] Licenses advanced εUCG™ technology: Supports projects in South Africa, Australia, Canada, India & Uzbekistan
* [http://www.laurusenergy.com Laurus Energy]

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