Might burning coal thousands of feet below the surface be the secret to making coal climate friendly?
That's what fans of underground coal gasification will be saying this week at several sessions and in the keynote speech at the International Pittsburgh Coal Conference, which goes through Wednesday. Momentum is growing worldwide to look closely at the idea, a 150-year-old technique of igniting seams of coal deep under the ground to produce electrical power or chemicals. It's a proven technology: Joseph Stalin launched the first national research program into the idea in 1928 and the Soviets used it for 40 years to produce power. Since then, cheap natural gas and shallow, easy-to-mine coal burned in traditional power plants have prevented the technique from taking off. (graphic courtesy Lawrence Livermore National Laboratory)
But gasifying coal underground is now a hot topic among power companies and scientists, with at least 10 pilot projects around the world planned or underway. The cost benefits and climate advantages are among the reasons that five countries run national research programs on the technique; is the United States falling behind on the next big fossil fuel technology?
Yes, says the nonprofit Clean Air Task Force, a well-respected public health and environment advocacy group, in a report issued last week.
Recent studies suggest that energy obtained using the technique would be cheaper than more popular methods of getting low emissions coal power, like so-called Integrated Gasification Combined Cycle (IGCC), which involves gasifying coal above ground in facilities like the FutureGen project, which the Bush Administration proposed and then killed. The idea would also eliminate the need for strip mining, which is environmentally harmful, or carbon intensive shipping of mined coal.
"The enormous potential of underground coal gasification to meet rising energy demand in a CO2-constrained world warrants a high priority effort by the United States government to speed commercialization," the Task Force study said.
The technology works by drilling two holes on either side of an underground layer of coal. If the layer is not porous, engineers drill horizontally to connect them, allowing gas to flow between the pipes. Then air or oxygen is added to one pipe and the coal ignited underground. There, the coal is partially oxidized; the gas which escapes from the second pipe is a mixture of syngas (carbon monoxide and hydrogen) and carbon dioxide and a little methane. On the surface, the hydrogen is cleanly burned in a turbine to produce electricity and the carbon dioxide, as well as processed carbon monoxide, is liquefied for underground storage.
The advantages of the techniques are myriad, says the Task Force, starting with the fact that it's a cleaner version of “clean coal” than other techniques:
[D]uring gasification, roughly half of the sulfur, mercury, arsenic, tar, ash, and particulates from the used coal remain in the subsurface, and any sulfur or metals that reach the surface arrive in a chemically reduced state, making them relatively simple to remove.
The carbon dioxide that comes out of the ground is at high pressure, saving energy that in IGCC would be required to compress it for underground storage. The coal doesn't have to be mined; the facilities on the ground are much smaller than traditional coal plants with boilers or IGCC plants. The trick is to use the ground itself as a gasifier instead of having to gassify the coal in a vessel—which can cost billions.
The Task Force thinks that the technology could compete economically a natural gas plan that sequesters its carbon. That's a claim most advocates of other coal technologies cannot make.
Last year, Booz Allen Hamilton estimated that underground gasification could cost 40% less than IGCC facilities. And a study that the task force cited suggested that underground gasification with the carbon capture for storage would cost a quarter as much as IGCC.
Traditionally, the coal industry looks for thick layers of coal near the surface so it can mine them relatively easily. With underground gasification, geologists would scope out thinner but broader layers of coal found much deeper. The idea would be to produce power right above those seams. So, the report argues, underground gasification makes sense for new power plants in coal rich states, say in the U.S. midwest. A report by Purdue University scientists in March, in fact, found five promising sites state in Indiana where facilities could be built.
So if underground coal gasification is so great, why are commercial projects exploiting the method so few and far in between? Up till now, the reason is the availability of cheap energy using other means, author Julio Friedmann of the Lawrence Livermore National Laboratory in California tells ScienceInsider. During the late '70s energy crisis, the technology got several demonstrations in the United States, but the coal industry stuck with the methods it liked, especially because they owned rights for coal close to the surface. Plentiful and cheap natural gas was a further disincentive.
Now though, with natural gas prices rising and climate a central concern, Australia, Canada, China, New Zealand, and South Africa all have government-funded R&D projects in this area. "China has minted 100 Ph.D.'s in this area," says John Thompson, director of the Task Force's project on coal transformation. "We are losing."
The United States, he says, has little expertise comparatively, and the clean coal programs funded by the U.S. Department of Energy all but ignore the underground gasification technique. (One earmarked research effort in Utah is examining it.) "It's just not on our radar screen," says DOE Technology Development Manager Gary Stiegel, who says that funding limitations are the main reason that the government has not looked into the technology. He says the cost advantages to the technique might one day prove accurate, but in the meantime, "Nobody's built any so how do you know?"
For its part, the report suggests DOE spend more than $100 million over the next 4 years on science, development, and demonstration efforts to try to catch up.