Underground Coal-Gasification, Coal-to-Liquids Fuel Project in Australia
15 August 2005
Syntroleum Corporation and Australian-based Linc Energy are planning to develop a coal-to-liquids (CTL) project in Australia that integrates Syntroleum’s air-based Fischer-Tropsch technology (earlier post) with Linc Energy’s underground coal gasification (UCG) technology.
This will be the first such project to combine the two technologies for the production of synthetic diesel from coal.
The CTL work will be part of Linc Energy’s ongoing Chinchilla Project (350 km west of Brisbane) which also includes early development of an integrated power plant.
Under the terms of the Memorandum of Agreement (MOA), Linc Energy is licensing Syntroleum’s CTL technology, with options for Syntroleum’s equity participation in these projects. Under the MOA, Linc Energy and Syntroleum will jointly fund a series of technology demonstration programs in advance of developing engineering designs for the CTL projects.
Linc’s underground gasification process has the potential to significantly reduce the capital cost of the CTL plants. They have produced commercial volumes of nitrogen-diluted syngas which we believe have the characteristics uniquely suitable for Syntroleum’s air-based FT process.—Ken Roberts, SVP of business development, Syntroleum
|Simplified UCG Process|
Underground Coal Gasification (UCG) is a process through which coal is converted in-situ to a syngas that can be used as a fuel for power generation or as a chemical feedstock—e.g., to feed into a Fischer-Tropsch process for the generation of synthetic diesel.
UCG has been used in the Former Soviet Union for some 40 years.
In general terms, UCG uses adjacent boreholes drilled into a coal seam (typically > 100m depth). The injection wells are used to feed a pressurized oxidant such as air or oxygen/steam into the coal seam and to trigger the and subsequent down-hole ignition. The production wells recover the product gases.
The UCG syngas, which undergoes sulfur removal and additional conditioning at the surface, is similar to syngas obtained from conventional surface coal gasification systems, but production is achieved at a much lower cost.
According to Ergo Exergy, the providers of the UCG technology used by Linc, typical gas recovered using air injection may have calorific values in the range 3.5 to 5.0 MJ/m3, depending on specific site conditions, with approximately twice these values being achieved with oxygen injection.
UCG differs from conventional above-ground gasification in a number of ways:
Coal is not mined and chemical processes are arranged to occur in the virgin coal seam in situ.
The process wells (the collective terms for the injection and production wells in a UCG project) must be connected within the coal seam by the links of low hydraulic resistance to allow production of commercial quantities of gas.
Process water for gasification usually comes from the coal itself and surrounding rocks, and its influx must be carefully regulated.
No ash or slag removal and handling are necessary since they predominantly stay behind in the underground cavities.
The process must be confined within a hydraulic system created in the coal seam so that no leakage of the product is possible and no contamination of the underground environment can occur. Such a hydraulic system is called an underground gasifier, and its design is the most crucial part of a UCG operation.
A Life Cycle Analysis of UCG electricity production by BHP Billiton Newcastle Technology Center in Australia concluded that:
UCG-CCGT (Underground Coal Gasification-Combined Cycle Gas Turbine) has the potential to be one of the lowest greenhouse gas (GGE) coal-based technologies, and compares with the emerging IGCC (Integrated Gasification Combined Cycle) and more radical ultra-supercritical developments—it would generate around 25% less GGE than the most efficient of Australian coal-fired power stations.
UCG-CCGT, however, emits more GGE than does a natural-gas-fired CCGT process due primarily to the higher carbon to hydrogen ratio of the gasified coal product.
NOx values are equivalent to other combined cycle type power stations.
UCG-CCGT requires smaller amounts of water compared to other combined cycle technologies, as gasification water requirement is provided by controlling ingress of water from aquifers surrounding the wells and gasification voids. Some of this water is extracted as condensate and reused for cooling purposes.
Syntroleum’s strategic focus for its gas-to-liquids process is smaller fields of stranded natural gasfields of less than 5 Tcf in size, that do not have large—and highly expensive—GTL or LNG plants associated with them, or pipelines. Syntroleum’s compact technology is more mobile, and in theory can be more economically deployed to these distributed—and stranded—resources.
The UCG technology is designed for similarly “stranded”—remote and/or difficult to mine—coalfields. The two technologies complement each other in their capabilities of enabling producers to extract product from such resources.
The first commercial phase of the Chinchilla Project, which Linc Energy plans for next year, involves installation of a 30-40 MW power plant which will provide electricity to local markets. The second commercial phase of the Chinchilla Project, which plans for a 17,000-barrel-per-day Syntroleum CTL plant and power plant expansion, will be developed over the next several years.
Ergo Exergy, GE Power Systems: The Chinchilla IGCC Project to Date: Underground Coal Gasification and Environment (2002)
LINC Energy, Ergo Exergy, GE Power Systems: An IGCC Project at Chinchilla (2001)
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