AACHEN, Germany -- Scientists here in the academic heart of Germany's coal-mining region are readying what they say is a disruptive model for the electric utility industry.
Leave the coal deep underground, they say, and forget the death and expense that come with mining. Instead, put a drilling hat on.
By baking coal buried thousands of feet underground using controlled fires and gravity's pressure, they say, previously inaccessible seams can be shifted into easily extracted gas. The gas, pumped up, will fuel turbines. And when most of the coal is gone, inject carbon dioxide to fill the void.
It is a simple concept that could reduce construction costs and eliminate the need to build the extensive pipelines required for CO2 storage at any large scale, said Tomas Fernandez-Steeger, an assistant professor at Aachen University's Department of Engineering Geology and Hydrogeology. "We make space," he said, "before we put something in the space."
The model combines an environmentally problematic but proven technology, underground coal gasification, with recent experiments finding coal seams greedy to trap CO2 but lacking in storage. By filling the hollows created by underground burning with waste CO2, companies could potentially create coal-fired power plants for the same price as current carbon-spewing power stations.
The Aachen project is still theoretical. But it is part of a new wave of startup companies and scientists who have targeted underground coal gasification (UCG), a century-old idea, as the budget-minded savior to curbing greenhouse gas emissions.
In one stroke, advocates say, underground gasification could triple U.S. coal reserves; put an end to dangerous underground and environmentally degrading surface mining; and provide an affordable way to collect CO2 emissions for storage. And it can be done without the technical mishaps and water contamination that have plagued past efforts.
The reality is that coal use in the developing world will double over the next few decades, and with its low costs, UCG holds more promise for reducing emissions than nearly any other option, said John Thompson, director of the coal transition program at the Clean Air Task Force, a nonprofit focused on reducing atmospheric pollution.
"It's a breakthrough on cost with carbon capture and storage," Thompson said.
One recent estimate has placed the cost of UCG plants with CO2 storage as equal to those of surface coal-fired plants without any capture technology. Other estimates have found the synthetic gas UCG produces cheaper than natural gas, even at current depressed levels.
Simply put, it is "coal energy with a natural gas footprint," said Julio Friedmann, leader of the carbon management program at the U.S. Energy Department's Lawrence Livermore National Lab.
China, which has had several recent mining tragedies, has embraced underground gasification. There, it is known as "coal without mining," Thompson said.
One large-scale project is producing synthetic gas out of Inner Mongolia's coal seams. Australia is also operating a large UCG pilot, and more projects are in the pipeline in Asia. Fitfully, UCG is also returning to the United States, where it was intensely studied after the 1970s oil crisis. An Alaskan company, CIRI, has begun the process of building a 100-megawatt UCG plant in the Cook Inlet. The proposal, which would use its CO2 for enhanced oil recovery, is undergoing environmental review.
UCG's profile, should the first projects go smoothly, will rise soon, Thompson said. "If you couple [UCG] with CCS, it is a very, very attractive way of getting energy out of coal," he said, while also allowing the world "to make deep, deep reductions in CO2 by the midcentury."
A 'controllable' problem
Like the rise of unconventional natural gas, underground gasification has seen its viability increase in recent years thanks to the leaps made in drilling technology.
Unlike previous efforts, which often focused on coal seams in the drinking water table -- to sometimes disastrous results -- newer UCG projects would burn coal 2,000 yards underground or more, far removed from groundwater supplies. Such coal would never be accessible in today's mining conditions.
For example, rich deposits of hard coal sit several kilometers underneath Germany's northern reaches, said Rafig Azzam, the leader of the Aachen project and a hydrogeology professor. "It wouldn't be appropriate for normal mining," he said. "But with the drilling techniques we have now, you can reach that."
And down there, Azzam said, "You have much more coal there than we have ever mined before."
Underground gasification works remarkably similarly to gasification reactors, the expensive equipment expected to be at the heart of next-generation coal plants. But rather than using glossy metal chambers to create the pressure needed to transmute coal into gas, UCG substitutes rock, gravity and well-injected oxygen.
Gasification projects rely on two wells, one to carry oxygen down to the seam and the other to evacuate synthetic gas, which flows through permeable coal. Since seams are often stacked, the synthetic gas well can serve multiple deposits, said Thomas Kempka, a scientist at the German Research Center for Geosciences who collaborates with the Aachen team.
The importance of site selection cannot be stressed enough, Thompson said.
"The big challenge with this environmentally is groundwater damage," Thompson said. "But if a site is located below the potable water supply, you really eliminate a lot of the problems that existed in the 1970s."
Those problems were not insignificant. Two UCG projects decades ago in Wyoming resulted in large amounts of organic contaminants -- carcinogens like benzene -- entering the groundwater. One shallow project was poorly operated and its site badly chosen, and the other had drilling problems, according to a report written by Friedmann.
These past environmental problems are sure to haunt UCG, especially in Europe or the United States. UCG is, after all, burning coal.
There will be something like tar production in the seams, though it will likely stay isolated, Fernandez-Steeger said. "We are concerned about pollution," he said.
Modeling pollution paths is the group's main activity, though nearly everyone, including U.S. EPA, who has researched UCG has found pollution to be a "controllable" problem, he added. Whether the public agrees remains to be seen.
Soviet made, American refined
Prior to this recent surge in interest, underground gasification has truly had a pilgrim's progress across the world, taking more than 100 years to develop into the latest, greatest hope for coal.
The Soviet Union adopted UCG after World War II, seeing it as a way to free the worker from the burdens of mining. Despite a successful program, work was abandoned in the 1970s, perhaps due to the discovery of Siberian natural gas.
Still, the Soviet legacy looms, and a Soviet-era UCG plant, recently purchased by an Australian energy company, operates to this day in Uzbekistan.
The United States built off Soviet research during the 1970s oil crisis, drilling 33 pilot projects by the late 1980s, when plummeting energy prices killed the research. Belgium and Spain then hosted projects proving deep coal could be gasified in a safe way.
But there were problems, said Henk Pagnier, a Dutch geologist who worked on the Belgian project. "The whole issue was how do you control the fire underground?" he said "And how do you control your gas quality? Both are not so easy, I can tell you."
Geologists thought they would need a decade or two to get it right, Pagnier added. But those issues have been solved, Kempka said.
Thanks to advances that originated in the United States, no oxygen can reach the coal without human intervention, he said. "You have total control," he said. "Otherwise the process wouldn't work."
The need for maintaining pressure is one reason gasified coal seams could make ideal CO2 storage sites, Kempka said. UCG requires impermeable rock to overhang target coal seams -- the same type of formations necessary for trapping carbon dioxide in more accepted geological formations like sandstone. "Everything has to be tight," he said. "You need the perfect sealing caprock, otherwise you can't hold this pressure."
At first, it seems counterintuitive that coal would hold CO2. But it was a project led by Pagnier, the Dutch geologist, that inspired the Aachen group.
Working in Poland several years ago, Pagnier injected CO2 into a coal seam deep underground. The coal swelled out of eagerness to trap the gas, halting injection. Coal, it seemed, had a strong affinity for holding CO2, though little room to do it.
The central idea of the Aachen group, which requires further study, is that UCG turns the coal left behind into the rough equivalent of activated carbon, riddled with a vast network of internal pores.
For example, 1 gram of activated carbon contains close to the surface area of a basketball court. The amount of space created in the coal, and its propensity to hold CO2, would mean that most seams could hold all of the CO2 emissions they would have otherwise emitted, Azzam said, with the coal moving from 2 percent to 30 percent porosity.
There is a great amount of variability in these projections -- the projections could fall short -- but more certainty is not possible yet, Kempka said. "Just a pilot is not enough to get all this data," he said. "We need a really large-scale operation, which right now is not available."
The upshot of coal-seam storage, rather than the aquifer storage likely to be pursued by UCG projects in the immediate future, would be having source and sink at one point, Azzam said. No pipelines to build, he said. "These types of expenses," he said, "we don't have."
While the Aachen system could be desirable in the long term, it requires far more research on how CO2 will behave among the gasified coal and neighboring rocks. The heat, collapse and chemical reactions that accompany gasfication change coal seams, and real-world tests have not been conducted on how CO2 might behave in such an environment.
For the CO2 tests to happen, more UCG projects will have to get under way. And in the end it is the price of UCG, even when combined with carbon capture and storage, that will have any success driving the technology.
One recent estimate from a Canadian firm, Ergo Exergy Technologies Inc., put the price of developing a UCG plant with CCS below the cost of a standard coal-fired plant that made no attempts to curb emissions. That estimate may not hold, but most estimates agree that UCG can be competitive with natural gas for power generation, even at current deflated prices, according to Lawrence Livermore's Friedmann.
Investors who have balked at the price of CCS coal-fired plants, which will cost more than $1 billion in their earliest incarnations, could find the modular costs of UCG -- say, several hundred million dollars -- easier to swallow, Thompson added.
"The advantage of this is it [requires] much lower capital," he said. "You don't have the mining, so you eliminate that part of the supply chain. You don't have the surface gasifier. ... Basically, you have a much lower capital cost."
The United States, with the harsh divides between oil and gas firms and coal miners, is in some ways poorly suited as a launching point for UCG, Thompson said.
Few domestic firms have expressed interest, though the British oil company BP PLC has partnered with the Lawrence Livermore National Lab to develop the technology (Greenwire, July 16, 2007). Much will depend on the success of CIRI's Alaska project and efforts in Australia and Canada, Thompson said.
The Energy Department could really usher the technology along by independently monitoring the cavities created at the CIRI project and elsewhere for contaminates, to assuage the fears of early adopters, he added.
"We need to exercise caution in these first sites," Thompson said. "But this is a potential game changer."
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