'Green coal' to get a tryout: Charred wood shows promise as renewable option but challenges remain

Jan 13, 2009 (The News & Observer - McClatchy-Tribune Information Services via COMTEX) -- PGN | Quote | Chart | News | PowerRating -- North Carolina is about to become the nation's test case for what marketers call "green coal" -- wood that has been baked into charcoal.

If successful, the experiment -- a partnership of sorts between Progress Energy, N.C. State University and an Asheville start-up -- could mark the end of the state's reliance on dirty coal.

But the option of locally grown fuel is not without challenges and environmental concerns. Still, advocates of the process believe the technology is on the verge of a breakthrough.

"This is probably closer to reality than anything I have seen up to here," said NCSU professor Mike Boyette in the Department of Biological and Agricultural Engineering. "We're moving in the direction where some portion of our energy will come from biomass."

The process is not as simple as collecting dead branches from the forest floor. The wood has to be treated in an industrial oven until it turns to charcoal. It remains to be seen if the experimental ovens can mass-produce charred wood of a uniform quality that won't clog power plants sensitively calibrated to burn coal.

Progress Energy this year plans to test the idea by adding charred wood at its coal-fired Cape Fear power plant in the Chatham County community of Moncure. The wood will come from two sources: NCSU's agricultural extension service, which has been developing a wood baking technology; as well as from Integro Earth Fuels, a 2-year-old Asheville company that's betting on the increasing importance of wood as a clean energy source.

In a state that depends on out-of-state coal for half its electricity, burning wood waste holds appeal because it's local, clean and renewable. When burned, wood releases significantly less sulphur and almost no mercury. And wood doesn't add to the atmospheric greenhouse gases that are believed to cause global warming.

Charred wood, a type of biomass, would be a major breakthrough because it can be pulverized into a fine powder for burning in existing power plants, potentially displacing a third of the coal in some plants, advocates say. By blending wood with coal, Progress wouldn't have to build a separate power plant for incinerating wood chips, thus eliminating a multimillion-dollar expense from the green energy equation.

Progress expects a state environmental permit as early as this month to burn up to 240 tons of the material, initially offsetting about 5 percent of the coal the Cape Fear plant would normally burn. The company is accumulating charred wood delivered for the past month from N.C. State University's agricultural extension program, which is producing small batches. Progress will run the test as as soon as it accumulates enough fuel, possibly this summer.

Burning wood to generate electricity would help Progress comply with state law requiring power companies to tap renewable resources.

"It has a lot of promise as a renewable option for us," said Grant Blume, Progress Energy's lead strategic engineer.

Challenges

Despite the early enthusiasm, many obstacles remain. The process of torrefaction is so experimental that it has only been tested in a power plant once, in the Netherlands in 2005, for a 24-hour period. Even if power plants can burn the fuel successfully, electric utilities won't sign long-term contracts for charred wood if they lack confidence they can count on steady supplies. Currently there are no commercial suppliers in the world.

But that could soon change. Integro is developing an industrial-scale wood-baking apparatus, called a torrefaction reactor, in Person County, about 20 miles north of Durham. Integro plans to bake wood chips for one hour between 500 degrees and 535 degrees, drawing out more than 99 percent of the water and cooking away the bonding agents that reinforce wood tissue. Agri-Tech Producers in Columbia, S.C., is developing several competing facilities, including a torrefaction site that it plans to have in eastern North Carolina by 2010. Europeans also are advancing the technology: RWE Innogy, a German concern, last summer announced plans for a facility to be built this year in Europe.

Integro expects to be in commercial production this fall, beginning by processing five tons of charred wood per hour, and operating around the clock. It would ramp up to 20 tons per hour by 2010. Integro has letters of intent from Progress Energy and two other potential customers in North Carolina, contingent on successful tests, but has not signed a contract yet to sell the fuel.

Integro and others developing the technology will have to demonstrate that their torrefaction ovens can consistently produce fuel that rivals coal in quality. And the producers will need to depend on reliable sources for wood scraps from paper mills and forestry operations, without incurring cost overruns if there's a wood shortage or if quality suffers. As is, torrefied wood costs about 30 percent more than coal today, but the cost disparity could be erased if coal values surge as they did last summer.

In its marketing materials, Integro refers to the charred wood as "green coal" because the fuel can be farmed or collected in the wild without dynamiting mountaintops. In Europe, RWE markets the fuel as "biocoal."

"It looks like coal, it acts like coal, but it's green," said Walt Dickinson, Integro's chief executive. "You can't grow coal, but you can grow trees."

Risky venture

Integro plans to obtain scrap pine and pulp wood from paper mills and forestry operations by collecting branches shaved off tree trunks and left on the forest floor. It would harvest wood within about 40 miles of its Person County facility.

Dickinson acknowledged Integro is running a high risk in developing a facility that will cost about $16 million. If the torrefaction process fails the test and utilities balk, the company would fall back on making wood pellets for home heating and for small power plants that burn wood chips.

Such power plants generate power in the state, mostly at paper mill operations that recycle their own scrap wood and pulp. But instead of wood charred under high temperatures, they use regular wood, a much less efficient source of fuel.

Farming wood for fuel raises its own set of issues. The benefits of reducing reliance on coal would be negated if natural habitats are destroyed to create single species tree farms, said Dee Eggers, a professor of environmental studies at UNC-Asheville. Every stray branch removed from the forest floor means that much organic material won't replenish the soil with nutrients. The forestry practices would have to be managed to minimize damage, she said.

"It's not purely an environmental positive," Eggers said.

john.murawski@newsobserver.com or 919-829-8932

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