image: Ergo Exergy
Here's one clean coal technology you may not have heard of: Underground Coal Gasification. An older technology—the Soviets first explored utilizing it in the 1930s; Uzbekistan has had a plant running using this method for 50 years—it is being reinvestigated in a number of countries, with China leading the way, the Wall Street Journal reports.
Now, proponents of UCG are hoping that if they can combine it with carbon capture and storage in situ they will have found a way to keep burning coal and avoid the associated greenhouse gas emissions. There seem to be a lot of 'ifs' in this technology, but this is how it works:A Bit Like An Intentionally Set Coal Mine Fire...
As TreeHugger John Laumer once described it, underground coal gasification is a little bit like a coal mine fire: A simplified description perhaps but not hugely off.
WSJ has a more descriptive summary of the process:
A borehole is drilled down to the coal seam, which is then ignited. Oxygen is forced down through the borehole to feed the combustion. Gases produced by the combustion are then forced out a second borehole to the surface, where they are harnessed to turn turbines or for the production of chemicals.
Concerns: Land Subsidence, Groundwater Contamination
The first concern that immediately popped to mind is what would happen when all the coal was consumed; would there be subsidence of the land above? According to Julio Friedmann, of the Lawrence Livermore National Laboratory, if the site is chosen properly and the surrounding rock strata is strong the risk of subsidence is small.
Friedmann also told the Wall Street Journal that another risk, underground water contamination, can be mitigated if operators pressurize the cavity properly.
An even greater concern, a technological unknown, is the carbon capture and storage prospects of UCG. The idea would be to pump CO2 back into the cavity left underground after burning the coal. However, the same concerns that apply to all CCS projects would apply here: Will the cavity be large enough to actually hold all the CO2 produced, how long will it be able to be stored (leakage?), will doing this increase costs so much that the whole thing is unprofitable?
Considering that by some estimates utilization of UCG could increase recoverable coal reserves by 300-400% globally, in the quest to maximize profits, the temptation might be to fudge a bit on choosing the proper rock strata and pressurization schemes, these reassurances about UCG's safety don't assuage my concerns.
Where is Underground Coal Gasification Being Used?
In the United States, underground coal gasification is being investigated for use in the Powder River Basin along the Wyoming-Montana border. In the UK, the hope is that the process will make more coal reserves recoverable under the North Sea. India is hoping to use UCG to increase access to 350 million tons of coal recently discovered in Gujarat and West Bengal. The leader though in China: 30 underground coal gasification projects are currently underway at various stages of preparation.
As John also said when he wrote about UCG, "Oh...great".
For some more on how this all works from a company which calls UGC "True Energy" (so tread a bit skeptically) check out Ergo Exergy.
via :: Wall Street Journal
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