Saturday, 21 July 2007

China simplifies method for turning coal to gas

Chinese researchers have demonstrated a cheap, simple way to convert underground coal into gas. The new method could make it more economical to exploit coal seams that are otherwise difficult to reach, but also raises environmental concerns.

Coal gas was commonly used in the 19th century to light cities, and is still manufactured today in some plants above ground. Coal is heated in the presence of oxygen and steam, producing methane, hydrogen, carbon monoxide and carbon dioxide.

The process would be cheaper, however, if the coal did not have to be mined and transported first.
"The Chinese been working on this process, and they're quite keen on it, for 20 years now," says Michael Green, Director of UCG Engineering in the UK, which consults on underground coal gasification. "They're trying to [create] a very cheap process, without high technology."

But Green says more efficient methods are also being developed in the West that use directional drilling to create combustion chambers, and which feed fires with pure oxygen instead of air.

However, environmentalists worry that coal gasification will release too much carbon dioxide into the atmosphere, accelerating climate change.

Green says that underground coal gasification could be combined with carbon sequestration. But he notes that the Chinese experiment was conducted on a relatively shallow coal seam, which could also risk contaminating groundwater. Proposed Western projects would occur much deeper, he says.
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