About 1.6 trillion tons of unmineable coal in the US is recoverable using UCG. (Image courtesy of ErgoExergy Inc.)
Really Clean Coal
June / July 2006
Volume 4 Number 3
Imagine a form of energy that is clean, cheap and safe and is found deep underground—€”energy that turns coal into a gas rich in methane and hydrogen that can be used to generate electricity, synthetic natural gas or liquid fuel such as the gasoline we put in our cars, energy produced by a process that can be used as a substitute for mining, bringing the heat and chemical energy of coal to the surface in a useable form, while storing the carbon dioxide used to extract the coal deep underground.
Underground Coal Gasification (UCG) may just be the process we need to cure the ills of the energy market. UCG can tap into coal deposits up to 5,000 feet below the ground, something not attainable through conventional mining.
"This is an opportunity to increase the use of coal without the hazards of mining," said Julio Friedmann, group leader of Lawrence Livermore National Laboratory's carbon management program.
By pumping (or injecting) either air or oxygen into an unmined seam and igniting the coal, coal is converted into product gas (syngas) that can be used for different forms of energy. The underground cavity formed by the process can be pressurized to prevent leakage and protect the groundwater surrounding the cavity. The syngas is delivered to a site where it is converted to natural gas, electricity, liquid fuels (diesel and jet fuel) or ammonia-based fertilizers. There is also extra hydrogen left over—€”"the cheapest way to make hydrogen," according to Friedmann.
Livermore recently received a grant from the Department of Energy to further study UCG. In addition, LLNL recently signed a memorandum of understanding with Ergo Exergy Inc. of Canada to begin collaborative field and laboratory research.
More than one-third of the gas produced from UCG is hydrogen, according to Ray Smith, an LLNL mechanical engineer who reexamined UCG a couple of years ago.
"Using UCG, the United States has hundreds and hundreds of years worth of natural gas and hydrogen if we go after it," he said. UCG can be used for power in an Integrated Gasification Combined Cycle (IGCC) power plant or as a supplement and substitute fuel in the existing coal-fired and natural gas power plants.
Power plants, however, are one of the biggest producers of carbon dioxide. "CO2 emissions are a big deal," Friedmann said, "and contribute to global warming."
And as the nation and states such as California move toward cutting their CO2 emissions dramatically in the next decade, there is a pressing need for alternative sources of energy that either don't produce CO2 or find a way to store or sequester it. In California, Governor Arnold Schwarzenegger has proposed that greenhouse gas emissions be reduced to 2000 levels by 2010; to 1990 levels by 2020; and to 80 percent below 1990 levels by 2050.
Friedmann said UCG has the built-in capability to capture CO2 by separating it from the syngas at the surface level. Up to one-third of the CO2 produced to make syngas could be stored underground in the cavity formed by the UCG process, according to Smith. The remainder could be stored in a neighboring formation.
"As the price of energy and gas has gone up and the environmental requirements have been raised so that we have to get rid of high quantities of CO2, we really could have our cake and eat it, too," Smith said. "We could get the energy out and keep it clean."
According to the California Energy Commission, the state produces about 16 percent of the natural gas it uses, 42 percent of the petroleum and 77.7 percent of the electricity. The remaining energy is imported and consists of electricity and natural gas purchases from Canada, the Pacific Northwest, the Rocky Mountain states and the Southwest; and crude oil imported from Alaska and foreign countries.
Livermore researchers have a 20-year history of research and development in UCG. Though the research originally began in the mid-1940s, Livermore's involvement began in the 1970s during that decade's energy crisis.
But at the time, the cost to use UCG was more expensive than coal mining, and UCG hadn't been fine-tuned enough to ensure that the water table would not be contaminated, Friedmann said. And UCG was not commercialized in the past because of the large drop in oil and natural gas prices in the mid-1980s. But UCG has since been reassessed so that potable groundwater sits well above the coal cavity, protecting it from potential leakage. "With proper siting, simulation and modeling we can properly contain all these contaminants," Smith said.
LLNL chemical engineer Ravi Upadhye says UCG has improved so significantly that companies are starting to see the benefits of investing in it. "We understand how to do the UCG process without environmental damage," he said. "And producing too much hydrogen is not a negative, it's a positive." With rising gas and electricity demands and higher prices today, UCG can be deployed at a competitive rate. About 1.6 trillion tons of unmineable coal in the United States is recoverable using UCG. Unlike traditional surface gasification facilities, with UCG there is no need to purchase gasifiers or build ash and slag management facilities. In addition, there is a reduced operating expense because there is no need to purchase, transport, store or prepare coal. This not only reduces cost but also the environmental footprint of coal facilities
Because gasification in UCG is underground, the facilities produce no sulfur oxides or nitrogen oxides, both regulated pollutants, thereby reducing environmental management costs. Particulates are generated at half the rate of their surface equivalents, and no ash is produced.
But one of the biggest advantages of UCG is fuel supply certainty: the supply of syngas is local and continuous.
There is growing evidence that the ErgoExergy Inc. technology works: several commercial projects are under way in Australia, India, South Africa, New Zealand and Canada.
Anne M. Stark is a public information officer at Lawrence Livermore National Laboratory.
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