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Coal - fuel of the future?
14 Dec, 2009 04:38 pm
Two pieces of news provide evidence of a fightback by coal. American Electric Power's Mountaineer plant in West Virginia is reporting significant success for its small scale carbon capture project. And the UK has just licensed exploratory boreholes for offshore Underground Coal Gasification (UCG), a woefully under-researched technology that may make CO2 sequestration easier. The scale of the challenge facing the globe's coal users is enormous but with determined research and development, the fuel may remain usable for power generation in a low-carbon world.
Vattenfall's Schwarze Pumpe coal plant has been separating CO2 for a year or so. It hasn't been putting the gas back into the ground because of resistance from citizens not wanting CO2 under their back yards. AEP started collecting and storing some of the CO2 from its Mountaineer electric power plant in early autumn 2009 using Alstom's chilled ammonia process and injected the gas into permeable rocks 2.5km underneath the plant. Today' process captures the CO2 from just 20 MW of the plants output. An upscaling of the plant will multiply this ten-fold by 2015. Today (December 9th 2009), the Wall Street Journal reports that the plant's operators are pleased with the early success. AEP says that the energy penalty from operating the carbon dioxide separation and sequestering process is less than expected. (The Alstom process uses energy to heat the ammonia to separate the CO2 after it has been captured). AEP's CEO is reported as saying that the cost increase is no more than 4 US cents a kilowatt hour. Even this, however, would approximately double the cost of electricity produced at the plant. The optimism at AEP matches Vattenfall's cautiously upbeat projections for the long-run cost of CCS when capturing the CO2 from a large power station's entire output.
Clean Coal Ltd
Underground Coal Gasification (UCG) drives off useful combustible gases from coal seams. The gases are then burnt to produce electricity in a conventional gas power station. The technology has been known about for a century or more but technological advances have been slow. In recent years, the level of interest around the world has increased, partly as a result of concerns about climate change but also because of worries over the long-term availability of natural gas.
UCG is a 'clean' process in that it avoids the need for mining and burning coal and extracting sulphur and other pollutants. But it does face real environmental challenges in, for example, avoiding the pollution of local water supplies around the gasification sites. UGC is also not truly 'clean' in that it offers only a marginal improvement on conventional coal power stations in the amount of CO2 it produces. (This fact tends not to be mentioned by UGC proponents). The world leader in UCG, Linc Energy of Australia, puts CO2 output per kwh of electricity at around 750 grams, compared to 400 grams for a combined cycle gas-fired power station.
The advantage of UCG is that may offer cheaper sequestration of CO2 than a conventional coal station as well as much lower capital costs to build than a surface coal gasification plant. The gas coming up from the coal seam will be largely hydrogen, carbon monoxide, methane and carbon dioxide. CO2 can be stripped from the combustible gases relatively easily because it is at high pressure. The remaining gases are then burnt in a gas turbine, producing water and nearly pure CO2. It may - only may - be possible to reinject the gas into the coal seam for permanent storage. Some industry proponents think that this technique will eventually offer the lowest cost carbon capture and storage from coal.
The UK government has just licensed some experimental wells to be drilled by Clean Coal Ltd, a US/UK company run by industry pioneers. The wells will be in thin seams of offshore coal that would never be economic to exploit by conventional mining techniques. Offshore drilling also avoids some of the problems of subsidence that may occur when the coal is gasified underground in onshore locations.
The company's press release says
The UK Coal Authority has awarded Clean Coal Ltd licences to investigate the potential for underground coal gasification at 5 sites in the UK. If the investigations over the next 12-18 months prove to be successful, commercial operations could start by 2014/15 and could lead to underground coal gasification producing 3-5% of the UK's total energy requirement by that date.
This statement is over-ambitious. Other UCG projects around the world have taken much longer and gas production from underground coal is still something of an art. Although the Soviet Union ran UCG plants, only one of these remains open today. One of the leading scientists in the field, Dr Julio Friedmann of the US Lawrence Livermore lab. Says 'a large number of basic science questions remain in the field of UCG'1.
Importantly, the Clean Coal press release is very vague about carbon capture and storage at its UK sites. Powerfuel, which is intending to use mined coal for surface gasification in Yorkshire, has been more specific and recently achieved EU funding for its plans. Without CO2 capture, Clean Coal Ltd is unlikely to be able to move forward in the UK or elsewhere but the quickening worldwide pace of interest in UCG is a good sign.
The UK's huge reserves of coal make it particularly important that the country invests in the research and development necessary to take the technology forward. Unfortunately, as ever, we are late to the game. China has graduated over 100 PhDs in UCG from one mining university and Linc in Australia is far more advanced with its plans for onshore gasification. As with several other technologies, the arguments for investing hundreds of millions in UK research and development over the next five years are overwhelmingly strong.
1Page 8 of his chapter in the Clean Air Task Force report of September 2009 Coal without Carbon.
Originally published on Carbon Commentary