Underground Coal Gasification: Another Head of the Clean Coal Hydra
by Matthew McDermott, New York, NY on 09.17.08
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.
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Not sure how it impacts environmentally, but Interesting thought.
30 plants (in CHINA) without testing the impacts is not good.
This seems like a pretty stupid idea overall. By intentionally setting fire to underground coal they are setting themselves up for lawsuits in the future. I grew up in Pennsylvania where you can sometimes see smoke puffing out of the ground. This is the result of accidental underground coal fires. According to my father, some of these have been burning for over 50 years. When the fire burns far enough away from the generation plant, it will find enough natural vents that the pressure will go out through those rather than at the generation plant. At that point the plant won't be financially viable and there will be no way to put the fire out. It will continue to burn slowly for years to come. It will surely work its way away from the generation plant's property and into coal owned by others. Of course the company would likely have been dismantled by that time and wouldn't be around to sue for lost income. Some people (such as my family) own land that has coal under it which we don't intend to mine for ecological reasons. An underground fire would violate our intentions. Also, as the article mentioned, there would be water contamination and subsidence which would also cause damage after the company had disappeared.
Reminds me of the label you see on the back of a mercury battery which says "DIspose of properly." Nobody has defined what properly is in this context. How will they handle the following?
It seems to me that some of the design discussion cited might be quite disingenuous. The main point of "injecting" C02 back into the mine cavity may very well be to control the oxygen level in the combustion zone, preventing a runaway pyrolysis reaction that wiould potentially plug the soil and rock pores enroute to the extraction well. preventing economic extraction of the distilled combustibles and allowing offgasing at uncontrolled places.
A fair amount of CO, particulate matter, and mercury is ALSO going to come up with the distillate gases. How do they plan to manage that? Inject pure oxygen? Build chillers,s crubbers, and bag houses that consume electicity and discharge toxic wastewater?
Obviously, in China, they just look the other way about these issues. Same in Russia. If that's the cost estimating basis used by these engineers they are nuts. Advanced pollution control will be needed just as it is needed in above ground coal gasification schemes.
There is no magic bullet for cost super cheap "clean coal".
For the project engineers and dreamers behind this idea. Wet soil pores are not an effective means of keeping the C02 underground for milennia. Look up "carbonic acid, formation of" and also "weathering" in a geology book if you have one. This thing called Google might help too.
Shouldn't be allowed unless CO2 is actually sequestered.
Is there a working coal CCS operation, or working pilot project anywhere? Coal CCS seems like fusion power: not demonstrated, for some time in the indefinite future, not to be relied upon. DB
correct me if i'm wrong, but isn't lighting a coal seam on fire a bad idea? There's no way for them to accurately map out every small thread of a coal seam, and I'd rather not risk having an uncontrollable underground fire the likes of Centralia, PA.
CCS is not strictly necessary, for example the CO2 can be sequestered by mining olivine, pulverizing it and dipersing it over the oceans. This costs perhaps 2 or 3 cents/kWh.
However, the contamination issues are real. A more interesting proposal involves underground methanization (turning coal into methane) by bacteria. This doesn't have much contamination issues, and an extensive methane infrastructure already exists in many countries (natural gas infrastructure).
There is one clean coal technologies you may not heard is Underground Coal Gasification.It Is an older technology.If we combine Clean Coal with carbon capture and storage in situ they will have found a way to keep burning coal and avoid the associated greenhouse gas emissions.
This site contains the detail explanation about under ground coal gasification.The CO2 produced in Clean Coal is captured and converts in to liquid and preserves under the earth.
As technologies have increased day by day the processes like CTL and UCG processes become more effective and apart from them new processes may posses.