Burning coal underground has potential

Underground Coal Gasification (UCG) converts deep, unmineable seams into syngas for power and fuels, leveraging advanced drilling; pilots target hydrogen, methane, CCS integration, lower costs, and energy security within five to seven years.

Burning coal underground could be one of the next breakthroughs to increase the world's energy supply, similar to establishment of Canadian oil sands, executives and academics told a conference in London.

The world could exploit huge additional coal reserves that are too deep or remote to mine, using a technology that burns the fuel hundreds of meters underground.

But the approach is so far untested on a commercial scale, making the initial expense a concern for governments and investors who must face clean coal realities when backing early projects.

"The potential is huge," said Gordon Couch, from the International Energy Agency's Clean Coal Center.

"It needs a series of successful demonstrations. Despite 50 years of trials no commercial use has been demonstrated. Current pilots could result in commercial opportunities within five to seven years."

Higher energy prices and security fears, particularly in countries such as the United States that still rely heavily on coal, and in particular advances in drilling — the biggest single cost — were focusing new attention on underground coal gasification (UCG).

The technology involves injecting air or oxygen into a coal seam, which is burned and heated to produce and then pipe to the surface an energy-rich gas that contains hydrogen, methane and carbon dioxide, and according to one report CO2 capture is possible for commercial coal generation under certain designs.

The gas could be burned to produce electricity or liquefied and turned into a liquid carbon fuel that, according to some, shows how coal can be green in limited contexts.

"We believe strongly that UCG is the next frontier for us," said Dzung Nguyen from Canada's Alberta Energy Research Institute.

"Thirty years ago no-one had heard of the oil sands industry, now it's the biggest oil reserve in North America," he said, adding that investment had cut by one third the cost of extracting heavy oil from sands in Alberta.

Successful UCG could access 628 billion tons of coal from Alberta's Mannville seam alone, 1,400 meters underground and too deep for mining, said Nguyen.

That compares with global coal production now of 6 billion tons a year, according to the IEA's Couch.

Half of Germany's coal reserves were below 1,500 meters and too deep for mining, said Thomas Kempka from the German Research Center for Geosciences, noting that coal generation in Germany is expected to remain significant.

Researchers are working on particular problems, especially the danger of contaminating groundwater, as well as the extra greenhouse gas emissions from a new focus on burning high-carbon coal, with critics arguing that clean coal isn't climate-friendly when the full system is considered.

"When you burn coal it produces benzenes, weird aromatic compounds, tarry materials, ideally you want these generated in a totally sealed way," said Michael Stephenson, head of science energy at the British Geological Survey.

Research had to establish whether heating coal underground, cracking bedrock above and drawing in water, could contaminate surface supplies, he said.

Greenhouse gas emissions from the process could be cut by storing the carbon dioxide underground using an equally experimental technology called carbon capture and storage (CCS), though there are many carbon storage myths and realities to weigh in project planning.

"We see UCG and CCS together as a bridging technology to the deployment of renewable energy" such as wind and solar power, said Germany's Kempka.

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