Photograph by Brett Simison
Published March 12, 2009
Burning trees for power may seem backward, dirty, and environmentally hostile.
But a high-tech new way of wood burning holds great potential to save energy, cut costs, and even fight global warming, a new study says.
For example, in the United States wood could sustainably supply "enormous amounts of energy, comparable to power production from hydroelectric [dams]," says the study, to be published in tomorrow's issue of the journal Science.
Already, "advanced wood combustion" is powering a U.S. college and cities across Europe, such as Joensuu, Finland.
Joensuu's "air quality has improved greatly," said city resident Antti Asikainen, a forestry expert at the Finnish Forest Research Institute. "It's a really clean technology."
The city of roughly 58,000 "is heated with a wood and peat mixture, which has replaced small fireplaces and oil burners—they're the worst generators" of pollution, Asikainen said.
To get these wood-burning benefits, cities can't rely on ordinary furnaces.
In advanced wood combustion power plants, intense heat and carefully controlled conditions ensure that nearly all the carbon in the wood is broken down into flammable gases. Then the gases are ignited, burning much more cleanly than a typical smoky home fireplace.
The heat from burning the gas can be used directly for heating or to generate electricity.
The power plants also have filters that remove many of the small particles that come from burning the wood, greatly reducing pollution.
Wood Is Green?
Another early adopter of advanced wood burning is Middlebury College in Vermont, which opened a wood-fired power plant last month.
Middlebury wants to be carbon neutral—eliminating its emissions of the greenhouse gas carbon dioxide (CO2)—by 2016 (interactive graphic: how greenhouse gases cause global warming). Trees suck CO2 out of the air as they grow and then release roughly the same amount of CO2 when they're burned in the advanced power plants, said Jack Byrne, director of the college's Sustainability Integration Office.
So the process of growing, harvesting, and burning wood is close to carbon neutral, Byrne said.
By switching to advanced wood power, "we have a 40 percent reduction in carbon emissions," Byrne said.
And, the Finnish Forest Research Institute's Asikainen said, wood power is possible without depleting forests.
Large amounts of wood can be harvested sustainably from forests, as long as the forests are managed correctly, he said.
Furthermore, if wood harvesters leave nutrient-rich leaves and needles on the forest floor and return leftover ash to forest soils, then "we're not endangering the productivity of the forests," Asikainen added.
Not that all the wood has to come from forests.
U.S. cities produce about 30 million tons of wood from trees that have been trimmed or otherwise removed every year, according to the new study. This debris could be fed into power plants instead of being mulched or sent to landfills, the authors say.
St. Paul, Minnesota, for example, already heats and powers much of its downtown by burning about 250,000 tons of wood collected each year from city trees.
Increased use of wood furnaces can also have financial benefits, said study co-author Dan Richter, a Duke University forest ecology professor.
"In the [U.S.] Northeast, it can help communities move beyond their potentially crippling dependence on fossil heating oil," which has had a wildly fluctuating price, Richter said.
At Middlebury, Byrne expects wood power to save $600,000 in 2009 by cutting the college's fuel oil use by about a million barrels.
"We're quite confident that it will pay for itself" in about 13 years—"less than half the power plant's lifetime," Byrne said.
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