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Coal Gasification
Coal gasification is a technique for breaking down coal into its basic chemical constituents, which can be collected and used as a fuel source, as opposed to burning coal directly.1 During coal gasification, coal is exposed to temperatures that would normally cause it to combust, but by carefully regulating the amount of oxygen in the gasifier, and by adding steam, the coal does not burn but rather separates into a mixture of carbon monoxide and hydrogen - also called syngas. The syngas can then be ‘shifted’ with the addition of more steam to produce more hydrogen and to convert the carbon monoxide into carbon dioxide (CO2).2
Debate over emissions advantages
Coal gasification is frequently touted by proponents as an example of a 'clean coal' technology, although it is heavily disputed whether coal gasification provides a true advantage in reduced CO2 emissions over traditional fuel sources, such as oil--the dominant transportation fuel source world wide.
A comprehensive study3 of coal gasification by the US National Academy of Sciences (NAS), released in May 2009, includes the conclusions that:
- Without geological storage of the carbon dioxide produced in the gasification process, greenhouse gas emission from coal-based fuel would be approximately twice that of oil.
- And with geologic storage of the carbon dioxide, greenhouse gas emissions would be nearly the same as those from oil.
The study also found that for the US to substitute syngas for 21 percent of all the fuel used in the US for transportation, coal mining in the country would have to increase by 50 percent--requiring 2 to 3 coal gasification plants to be built annually for the next 20 years.
The report noted that by mixing some biomass fuel with coal-produced fuel, the result could have some emissions advantages over oil: "Liquid fuels from biomass and coal have the potential to reduce the use of petroleum fuels and CO2 emissions from the US transportation sector over the next 25 years." NAS adds, however, that "substantial investments in research, development, and commercial demonstration projects will be needed to produce these alternative liquid fuels in an environmentally conscious way, and at a level that could impact U.S. dependence on imported oil."4
Footnotes
1: World Coal Institute, Coal gasification, www.worldcoal.org.
2: US Department of Energy, Gasification Technology R&D, fossil.energy.gov.
3: National Research Council, Liquid Transportation Fuels from Coal and Biomass: Technological Status, Costs, and Environmental Impacts (Washington DC: National Academies Press, 2009), NAS/NAE/NRC. 22 May 2009
4: National Academies, With New Technologies, Fuels From Coal and Biomass Could Have Impact in U.S.," Top News, May 20, 2009. 22 May 2009.
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