Special Report

Squeezing Cleaner Energy from Coal’s Waste

Coal mine methane could soon transform from problematic waste to valuable fuel

Elk Creek is the first methane-to-energy project at a coal mine west of the Mississippi and the largest of its kind nationwide. (Aspen Skiing Company)

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The law recognizes methane alongside continually replenished resources like wind and solar as a renewable resource, a policy strongly opposed by some environmental groups and green energy advocates. Jeremy Nichols, director of climate and energy programs for the non-profit environmental advocacy group WildEarth Guardians, says classifying methane "is not the purpose of a renewable energy standard." But using methane for energy, he says, beats the status quo of venting it to the atmosphere. “At end of the day,” he says, “it's making the best of a bad thing.” And over time, experts say bringing methane under the new mandate could increase demand among Colorado utilities for electricity from projects like Elk Creek.

Change is afoot at the federal level, too. President Obama has directed federal agencies to "develop a comprehensive methane strategy" and the Environmental Protection Agency has identified around 50 U.S. coal mines that show promise for capturing waste methane and burning it or converting it to electricity.

Methane energy proponents are hopeful that a forthcoming vote in California will ultimately make the technology more profitable coast to coast. The state’s air regulators are slated to vote soon on a proposal to reward methane abatement projects under its cap-and-trade program, which is designed to help the state reduce its greenhouse gas emissions to 1990 levels by the year 2020. If approved, the protocol would allow coal mine operators and methane emitters nationwide to earn credits for reducing their emissions. California polluters expecting to exceed the state’s maximum emission allowance could then purchase these credits as a way to negate their overage.

"You need a very good price on carbon to make [methane mitigation] viable," says Clark Talkington, a senior consultant with Advanced Resources International, which develops energy and carbon sequestration projects. "I know there are several projects sitting on the sidelines, so if California comes through, it would definitely drive those forward."

At Elk Creek, for example, 84 percent of methane captured from the mine—enough to generate $1 million worth of electricity—is simply burned because Holy Cross lacks the budget and desire to purchase more energy from the project, and no other customers have been found. "We definitely have our eye on another project," says ASC's Schendler. "But the barrier is getting a power purchase agreement from another utility that is at an acceptable price." ASC would lose money on the project if it sold electricity at the typical wholesale rate of 3.5 cents per kilowatt hour.

Innovation in the Works

Beyond policy, innovative techniques are making it possible to scavenge methane from very dilute sources, such as the ventilated air in mine shafts, and use it as fuel for generators. At a large coal mine in China's Henan Province, ventilated air with methane concentrations as low 0.3 percent is used to heat water for mine facilities. The system loops ventilated coal mine air through chambers that increase its temperature until methane molecules break down into carbon dioxide and water, and the heat from this reaction is captured.

In Australia, a coal plant owned by BHP Billiton combines ventilated air methane with highly concentrated methane that has been drained into boreholes drilled near the mine before mining begins. Mixed together, methane from the vents and the drains can be burned as fuel. This system generates heat to produce steam, which in turn runs a small power plant producing an average of 10 gigawatt hours per year.

Other scientists are looking to develop better filters for separating the methane in ventilated air from unneeded gases like carbon dioxide and nitrogen. Scientists with the University of California, Berkeley and the Lawrence Livermore National Laboratory, for example, have looked at a highly sorbent material marked by nano-scale pores called nanoporous zeolites. The group has used computer models to test nearly 100,000 different zeolite structures, says Amitesh Maiti, a materials physicist at the Lawrence Livermore lab.

At this point, the research remains in early stages. "The material might not be as pure in real life as we see in these models," Maiti says. Yet if a nanoporous zeolite or other material can be developed that readily captures methane molecules, it could dramatically reduce the cost of generating electricity from the highly diluted waste methane of coal mines. In the process, it could make this source of methane too valuable as a fuel to carry on its previous mantle as a harmful, nuisance waste to be thrown away. 


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