Underground Coal Gasification.

Coal gasification is the conversion of coal into gases that can be used directly as fuel or as feedstocks for the creation of liquid fuels (e.g. hydrocarbons) or for commercial processes such as the production of fertilizers and other chemicals, including pharmaceuticals. As oil stocks begin to run short and an inexorable demand is placed on natural gas to substitute for it, either to be burned per se or indeed turned into synthetic oil, we face an energy supply crisis which will hit civilization across the board, with soaring prices of all goods including food, and even food shortages, since modern agriculture is now entirely underpinned by oil and gas: e.g. oil to run farm machinery and gas to produce hydrogen which is combined with nitrogen to make ammonia, the mainstay raw material for synthetic fertilizers.

If this crisis will begin to bite within a decade following the arrival of Peak Oil, and then grip humankind more determinedly in subsequent decades, what is there that might be implemented to take the place of oil and gas? The only other carbon-based material in substantial abundance is coal, and so we need to dig more of it. There are estimated to be upward of six trillion tonnes of coal available for extraction on earth, and probably much more in locations that are hard to access. For example, some three trillion tonnes of coal have been identified under the sea off the coast of Norway, but this is not amenable to conventional mining and extraction. The UK has around 220 million tonnes of coal (to be compared with the 60 million tonnes or so we use each year, two thirds of which is imported) in known mines and it is thought that a total of 1.5 billion tonnes could be got by extending the existing mining infrastructure - i.e. just keep digging the seams that are already underway. Indeed, some mines that were closed in the 1980's in Yorkshire and in South Wales are now being re-opened, and so there are efforts ongoing in this respect.

It was however, estimated that there are some 190 billion tonnes of coal altogether underlying the UK, particularly if regions under the southern part of the North Sea are included in the tally, as I commented in a previous posting ("Coal May be Crowned King after all!", Monday December 4th, 2006). However, while this would amount apparently to nearly 700 years worth of supply, not all of that is readily accessible, and to dig it out by conventional means, covering an underground area of probably around one third that of the UK mainland, is not a realistic option unless some extremely efficient new technology were devised and implemented by the industry.

As an alternative strategy, the conversion of coal to gas in situ is being considered. The putative process is called Underground Coal Gasification (UCG). In UCG, two boreholes are drilled into a coal-seam underground, one to introduce oxygen and water (to provide steam), and the second to bring the gaseous products of the partial combustion/steam reforming of the coal to the surface. The gas will consist principally of hydrogen and carbon monoxide along with smaller amounts of methane and other flammable hydrocarbons that are formed by in situ pyrolysis of the coal itself in consequence of the high temperatures incurred.

There are many potential advantages to the UCG approach, namely that actual coal extraction is unnecessary, along with the usual detritus of coal mining, e.g. slag-heaps of rock and coal waste (such as engulfed a school at Aberfan, in South Wales, forty years ago, killing 129 children). Furthermore, the process would make available a clean fuel/chemical feedstock gas, and on our own shores. As noted, there is the considerable appeal too that it might be thus possible to utilise huge stocks of coal that would otherwise remain inaccessible. The essential premise of UCG has been shown to work in trials e.g. in Russia, but it is mandatory to evaluate the controllability of the process over sustained periods of operation (we are talking about hundreds of years), and any negative environmental impact on underground aquifers (i.e. groundwater pollution) and on any adjacent strata, such as subsidence. The latter is of particular concern since coal often intersperses rock layers and provides a supporting medium for them and so, if the coal is dug out, either literally, or by conversion from solid to gas, will not the overlying rock simply collapse into the "hole" that has been created?

The gasification of coal seams in situ was first done by the Russians in the 1930's and processes have been in operation since WWII. One, ongoing in Uzbekistan, is still in operation now, and experimental UCG technology is being undertaken in Australia, as advised by experts on the subject from Uzbekistan. In the 1950's, Britain established its own UCG trial in shallow mines in Derbyshire with success, but the National Coal Board later abandoned the project on economic grounds. In the US, technology from the oil and gas industries was adapted in the 1970's to make UCG a more readily controllable process, while in Europe UCG has been applied to work both shallow and deep seams; the latter in Spain during 1992 - 1999, and funded by the British DTI, the EU and Spanish and Belgian organisations.

Hence the overall vista for UCG appears optimistic, and a six-year project has been inaugurated in the UK at a cost of $15 - 20 million, with the following aims:

(1) To improve the accuracy of in-seam drilling.
(2) To examine the implications of burning UCG gas in electricity-generating turbines.
(3) To evaluate the real land-reserve capacity for UCG.
(4) To identify a semi-commercial site to undertake the process.
(5) To work-out the likely costs.
(6) To carry-out a feasibility study of offshore coal-exploitation by UCG methods.

It sounds great, so let's get started! What are our realistic alternatives? Nuclear, renewables on a gargantuan scale, or increasingly vulnerable imports of natural gas from unstable regions of the world. If it works, UCG answers some questions about security of supply, and with carbon-capture technology it could also cut our CO2 emissions. It still doesn't mean we can readily match our current requirements of imported fuel (although UCG gas could be converted into some synthetic fuel using Fisher-Tropsch technology) and so transportation remains almost certain to be curbed on a substantial scale, hence forging local communities/economies, if people need to stay put and it is less feasible to transport food/goods over significant distances.


Related Reading.
http://www.coal.gov.uk/resources/cleanercoaltechnologies/ucgoverview.cfm