Fires burning underground

The Science pages of the NYTimes carried a story about underground fires burning years and years, even smoldering for centuries. Did you know?

Fires are burning in thousands of underground coal seams from Pennsylvania to Mongolia, releasing toxic gases, adding millions of tons of heat-trapping carbon dioxide to the atmosphere and baking the earth until vegetation shrivels and the land sinks.

The coal fires are similar to those that smoldered for months beneath the wreckage of the World Trade Center, in that they involve buried fuels and are sustained and intensified by slight drafts of air and heat locked into surrounding rubble or rock.

In 2002, Maureen Sullivan at Slate asked about a Colorado fire that's been burning since 1910, "How can a fire burn underground for 92 years, and why hasn't anyone put it out before now?" Coal fires can reach temperatures of 1200 degrees Fahrenheit, so water dumped on them evaporates instead of putting them out.

Burning 250 years?
The Smithsonian reports that across the globe, thousands of coal fires are burning. More than forty-five years ago in Centralia, Pennsylvania, "a vast honeycomb of coal mines at the edge of the town caught fire. An underground inferno has been spreading ever since, burning at depths of up to 300 feet, baking surface layers, venting poisonous gases and opening holes large enough to swallow people or cars. The conflagration may burn for another 250 years, along an eight-mile stretch encompassing 3,700 acres, before it runs out of the coal that fuels it."

Underground coal fires are burning in Pennsylvania, West Virginia, Utah, Colorado, Kentucky and Wyoming.

Scientists believe that anywhere from 20 million to 200 million tons burn from underground coal fires in China alone - producing 1% of the world's excess carbon dioxide each year. (Coal consumption in the United States during 2000 was just over one billion tons.) India's coal fires are more numerous. A coal seam inside Australia's Burning Mountain has been smoking for over 5500 years.

There are so many perpetual coal fires it might be possible to extract the heat to generate electricity after capping and directing the heat source with vertical thermal extraction.

Chemicals and fuel can be extracted from the internal gases as well. A proposal for China will ignite an underground coal mine for an above ground coal-gasification power and chemical plant, keeping the sulfur, tar, particulates and mercury underground. In some parts of the world, if it's too costly to bring coal to the surface, British Petroleum and others believe they can burn the coal while it's still underground.

Here's an excellent synopsis of underground coal fires, Fire in the Hole - Coal’s Underground Secret.