Underground coal gasification
UCG is an in-situ gasification process, carried out in non-mined coal seams using injection of oxidants and steam.
The technique can be applied to coal resources that are otherwise unprofitable or technically complicated to extract by traditional mining methods.
[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.
[5] After World War II, the Soviet activities culminated in the operation of five industrial-scale UCG plants in the early 1960s.
[7] 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.
[4][5] In cooperation with Sandia National Laboratories and Radian Corporation, Livermore conducted experiments in 1981–1982 at the WIDCO Mine near Centralia, Washington.
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.
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.
Injection wells are used to supply the oxidants (air, oxygen) and steam to ignite and fuel the underground combustion process.
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.
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 approach is intended to provide access to the greatest quantity of coal per well set and also allows greater consistency in production gas quality.
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 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: 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.
[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.
[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.
[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.
[4] Combining UCG with CCS (Carbon capture and storage) technology allows re-injecting some of the CO2 on-site into the highly permeable rock created during the burning process, i.e. the cavity where the coal used to be.
[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.
"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".
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.
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.
Newer UCG technologies and practices claim to address environmental concerns, such as issues related to groundwater contamination, by implementing the "Clean Cavern" concept.
