Underground coal gasification is a relatively old technique capable of producing a synthesis gas that has many applications as a source of energy. This technology is capable of accessing low-grade coal reserves that would otherwise be uneconomical to mine. Underground coal gasification is a relatively complex process that, in its simplest form, involves the burning of coal in-situ and extracting the synthesis gas containing mostly hydrogen and carbon dioxide. Field tests in the U.S. and a recent trial in Australia have developed this technology to a level that commercial applications can be considered.
With the current high price of crude oil and likely future trends, it is a suitable time to look for alternate sources for production of liquid fuels such as gasoline. Gas-to-liquid technology is one such method that involves the reaction of a synthesis gas in a Fischer-Tropsch plant. Fischer-Tropsch technology is also a relatively old process that has been on hold since world war two where the Germans required a technique to create liquid fuels from coal. Fischer-Tropsch plants have been in use for serval decades producing useful gasoline with most notably cleaner burring characteristics.
It follows that a gas-to-liquid plant can utilise an underground coal gasification synthesis gas to produce gasoline. A design in Queensland Australia, utilising a coal seam in the Surat Basin, with similar gasification techniques as that used in the Australian trial is implemented. Modifications to this design are introduced to insure a higher quality synthesis gas with the addition of an air separation plant to provide an oxygen rich feed gas and use of a deeper coal seam. This design ensures that a suitable synthesis gas can be produced to feed the Fischer-Tropsch process without any significant work to the gas.
An economic analysis of this design showed that gasoline could be produced on a small, medium and large scale that results in a cheaper consumer price than current oil derived gasoline at 90 cents per litre. It is however, conceded that this integrated technology is not yet mature enough to attract investment commitments from energy companies, but marks a potential for future interest when oil-derived gasoline become too expensive to produce.