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energy that grows back: Burning wood considered carbon neutral

With greenhouses gases and global warming capturing everyone's attention these days, people who promote burning biomass to generate electricity note that wood is a carbon-neutral fuel, at least in the long run.

With greenhouses gases and global warming capturing everyone's attention these days, people who promote burning biomass to generate electricity note that wood is a carbon-neutral fuel, at least in the long run.

Wood combustion spews carbon into the air, contributing to the buildup of gases most scientists say is spurring global warming. But the new trees that grow where the cut tree had been eventually will absorb that carbon, offsetting the increase.

With some biomass, such as grass, harvesting and burning the fuel may lead to a net decline of carbon in the atmosphere. That's because the root system of the grass continues to grow, and new grass absorbs carbon even between cuttings. Some researchers say there may be some tree varieties that do the same. Aspen forests, for example, continue to grow underground after cutting and quickly re-sprout with more stems than were cut.

It remains to be seen whether such forests truly are long-term carbon sinks or if other interactions in the ecosystem may mitigate any gain. Also, the energy used to harvest and process biomass and get it to the powerplant releases carbon, making the end product somewhat less carbon-neutral.

Under orders from the state to start churning out more electricity from renewable fuels, Minnesota Power officials are looking out their office windows for the next big thing.

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Wood.

They're intercepting pallets, paper mill waste and demolition materials that had been headed to landfills. They're grinding them to pieces and churning out steam and electricity in Duluth and Grand Rapids.

And they're looking at leftover treetops and limbs at logging sites across the Northland's forests.

Minnesota Power supplies about 1 million megawatt hours of electricity from renewable sources. But they must more than double that, adding an estimated 1.5 million megawatt hours, by 2020, company spokesman Eric Olson said.

"Biomass will need to be a significant piece of our renewable portfolio in order to meet the state mandate,'' Olson said. "We already know how to use biomass. It's available. It's local. It's renewable. It's going to be a big part of the mix for us.''

While the company plans on expanding biomass electrical generation, no details have been released on where or how big a new biomass plant might be.

How much wood is available to burn is unclear. Wood prices are historically high. Private land available for logging is shrinking as more forest is developed or moved out of timber management. There's already pressing demand on public forests from sawmills, board plants and paper mills.

While biomass burners generally use leftovers from traditional logging practices, the overall demand for wood fiber could eclipse supply. The economics of removing large amounts of low-value wood from the forest isn't certain.

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"What we don't want is to get into competition with our biggest [electrical] customers for the wood that they need for their mills,'' said Mike Polzin, renewable fuels coordinator for Minnesota Power. "We're going to remain a secondary customer, using the byproduct.''

It's also not clear how much more wood the forest can provide without ecological consequences. Leaving some leftovers from logging on the forest floor is critical for bird and wildlife habitat and to help re-charge the soil for the next growth of trees.

Despite the unknowns, the allure of a locally produced, renewable fuel is too much to ignore.

In addition to any new Minnesota Power project and the company's two wood-burning boilers, the Minntac taconite plant in Mountain Iron uses waste wood for some of its fuel needs. The new Laurentian Energy Authority boilers in Hibbing and Virginia are burning tons of wood every hour. Meanwhile, the Bois Forte Band of Ojibwe is eyeing a possible wood-to-ethanol plant that would use local waste wood, and a similar facility is being built in Little Falls.

Don Arnosti, forestry coordinator for the Minnesota-based Institute for Agriculture and Trade Policy, said Minnesota Power and others eyeing biomass for new energy production should move carefully.

"There's a real danger if we start demanding our forest give up a certain amount of energy, if we build new plants and assign a quota to our forest to come up with the fuel ... rather than first determining how much energy is sustainably available and going from there,'' Arnosti said.

State mandate

Minnesota imports a larger percent of its electricity than any other state, and much of that is produced from coal. Burning coal is cheap, but it contributes to the load of mercury in fish and to carbon dioxide pollution and a warming climate.

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In an effort to lessen those problems and keep energy dollars in the state, Minnesota lawmakers and Gov. Tim Pawlenty last month approved landmark legislation requiring that Minnesota's big electric utilities make 25 percent of their electricity from renewable sources by 2020.

To satisfy that law, Minnesota Power is looking at adding even more wind generators to replace electricity currently generated by burning coal. And the utility has hydroelectric dams that create electricity.

But windmills are expensive, don't turn when it's calm and aren't welcome in all communities. And it's not likely federal regulators will approve any new dams on Northland rivers.

"So we're looking at the third W: wood," Polzin said. "We think there's opportunity there. But there are also some challenges."

Minnesota Power is generating electricity from wood at its Hibbard plant in West Duluth and at its plant adjacent to the Blandin paper mill in Grand Rapids. Each plant burns about 70 percent wood and 30 percent coal to provide steam sold to paper mills and generate electricity to sell.

"There's no reason any wood should ever go into a landfill again,'' said Norm Opack, owner of Demolicious, the Duluth company that supplies Minnesota Power with its shredded waste wood in Duluth. "We can take a lot more than we're getting. But we have to change the way people think about [wood waste.] It's too valuable to be buried.''

Burning on the Range

Terry Leoni, Virginia Public Utilities manager who helps oversee the new Laurentian Energy wood burning project in Virginia and Hibbing, said there are ample logging leftovers in the forest to supply the boilers. The plant has months of supply already on hand.

The two plants are burning 36 tons of wood every hour, every day to produce steam to heat their communities and electricity to sell to Xcel Energy and Minnesota Power. Laurentian hopes to reach 100 percent capacity -- burning 50 tons of wood per hour -- in coming months.

But Leoni agrees that northern Minnesota can't support infinite biomass burners.

"The capacity for more [biomass energy projects] is there. Am I concerned that it could get out of hand? Yes,'' Leoni said. "I think our lawmakers realize that we can't oversaturate our area with [biomass] projects everywhere.''

Arnosti said accumulating wood to burn for energy may be a good way for loggers to make extra money from a logging site primarily intended for mills. It may also be a way to help pay for logging that's intended to create wildlife habitat, fire prevention or forest thinning for productivity.

"We've been doing it since 1973. It works for us,'' said Tom McCabe, owner of Duluth-based McCabe Forest Products. His company sells so called "non-merchantable'' timber -- tree tops, stems and branches -- to Minnesota Power and other industries in Duluth.

"It's about 25 percent of our business,'' McCabe said of biomass. "I'm not sure what's going to happen with the markets. But there's [supply] out there if the demand comes.''

Arnosti said harvesting for biomass may never pay for itself without subsidies. His group has been studying the cost of harvesting biomass from forest plots, and researching the environmental impacts, in conjunction with the U.S. Forest Service and Laurentian. The final report is due in August, but some aspects already are clear, he said.

"Biomass isn't the entire solution. Minnesota Power can't get to 25 percent renewable [only] by burning tree tops,'' Arnosti said. "It would be a recipe for collapse of our forests and a recipe for perpetual conflict between the users of our forests, from recreation to the paper mills ... We'd be killing the golden goose for everyone."

John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at jmyers@duluthnews.com.
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