A cheap way of removing methane from the foul air that emerges from underground coal mines could slash global emissions of this potent greenhouse gas -- and generate electricity on the side.
Molecule for molecule, methane is many times more powerful a greenhouse gas than carbon dioxide. So although considerably less methane is released into the atmosphere, it is the second biggest cause of climate change after CO2. The world's coal mines are estimated to emit 25 million tonnes of methane a year. This is roughly as much as leaks from the world's oil and gas fields, and has the same global warming potential as the annual emissions of CO2 from Britain.
Methane emissions from coal mines occur at low concentrations, typically between 1 and 10 parts in a 1000. This makes it difficult and expensive to eliminate.
Now Richard Trottier of Natural Resources Canada, a government agency, claims to have developed the first cost-effective method of banishing these methane emissions. The system uses a secret catalyst to oxidise the methane to water and CO2.
While the reaction requires heat to get going, once it begins the process generates enough heat to maintain the reaction -- and even generate electricity. "If concentrations of methane in the mine air are above three parts per thousand, the heat from the methane oxidation can be recovered and converted to electric power for the grid," says Trottier.
A pilot plant in Phalen, Nova Scotia, completes its first test phase in February. It consists of two units, each containing a catalyst. Hot air from one passes through the other unit, heating it enough to start the reaction. The flow is reversed roughly every half hour to keep both units hot. The output air can be as hot as 800 °C.
Trottier has already begun the next stage, a US$800 000 demonstration plant also at the halen mine that will handle up to 8 cubic metres of mine air each second. That is enough to gobble up methane with a global warming potential equal to the CO2 output of a community of 2000 people. Its electricity-generating potential has attracted the interest of Nova Scotia Power, which is a partner in the project.
Under the terms of the Kyoto Protocol, agreed by more than 160 nations in 1997, countries can count cuts in methane emissions from coal mines and other sources towards meeting their commitments to cut emissions of greenhouse gases over the next decade. Companies that reduce their emissions should qualify for tradable pollution credits.
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