ISU looks to burn wood in coal plant

Wood biomass co-firing blends wood chips with coal in utility boilers to cut sulfur emissions, lower greenhouse gases, and diversify fuel. Supported by USDA subsidies, it offers renewable energy despite higher BTU costs and challenges.

A western Iowa entrepreneur hopes his supply of wood chips or pellets can turn the Iowa State University power plant from an ugly duckling to a swan.

The 104-year-old ISU plant burns not just coal, but a higher-sulfur variety from Illinois and Kentucky. The boilers were designed decades ago to burn Iowa coal that may have two or three times more sulfur than the Wyoming coal used most commonly by utilities.

The ISU plant has kept itself within environmental regulations by adding limestone to the coal fuel.

Bob Ravlin, who has access to wood from the lodgepole forests of Wyoming and Colorado, has supplied wood chips for generation for experimental burns at the ISU plant since June.

"We have an application for a permit from the Iowa Department of Natural Resources to enable the plant to burn wood biomass, a process that often triggers questions about biomass plans in local reviews," said Ravlin, who operates his NextGen Biofuels business from his hometown of Underwood in western Iowa.

Jeffrey Witt, assistant director of utilities for Iowa State, said wood chips were blended at rates of up to 15 percent with the coal in a form of coal/biomass co-firing with no harmful impact on the plant's boilers.

"We had looked at corn stover as an alternative fuel and it just wasn't economical or practical for utility boilers," said Witt. "But wood biomass may work."

Wood biomass is one of the energy sources, along with wind power, used as an alternative to the coal that now supplies more than two-thirds of the power of U.S. electric utilities, as some utilities turn to wood for generation to diversify supply.

Coal has long been the mainstay of utility fuels because of its cheap and plentiful supply in the United States.

But despite dogged use of scrubbers and other pollution control devices, coal remains the most polluting of utility fuels.

Wood biomass is a contender as an alternative fuel because, unlike wind energy, it can be stored, and recent biomass breakthroughs have increased industry interest as well. The U.S. Department of Agriculture has endorsed wood biomass as a utility fuel and has a two-year subsidy program for experiments.

Ravlin and Witt hope that the ISU plant can become one of the "conversion facilities," in USDA lingo, and qualify for subsidies that might cover much of the difference in cost between biomass and coal.

As Witt notes, the cost difference is a factor. Coal costs about $4.15 per million British thermal units, which is the way utilities measure the heat generated by a fuel.

Natural gas, which is coming on strong as a utility fuel thanks to big discoveries in shale formations in the Southwest, Pennsylvania and New York, now costs around $5 per million BTUs, amid an ongoing power source debate over alternatives. Gas is prone to price spikes, such as a climb above $12 per thousand cubic feet two years ago.

The current cost for wood is around $8 per million BTUs, which necessitates some kind of public subsidy.

Wood biomass is one alternative being tested in old coal plants to help older, coal-burning utility generators cut down their greenhouse gases.

The University of Iowa's power plant in Iowa City has experimented with burning oat hulls from a processing plant at Cedar Rapids, so far with no apparent negative impact on the boilers.

The city-owned utility at Cedar Falls also has tried different biomass fuels.

"Wood pellets and chips already are used to burn in stoves," Ravlin said. "You can buy the pellets at hardware stores."

The smaller wood chips are the preferred biomass rather than pellets, which are less environmentally friendly because they require more energy to make.

Chips aren't perfect. Witt and Ravlin note that when mixed with coal in storage, the chips tend to settle through the coal mix and segregate at the bottom of the coal pile.

"There are various ways to mix them to solve the segregation problem, but it does have to be fixed," Witt said.

But the wood biomass is generally environmentally friendly. While wood still emits particulates mostly ash and its fast-burning heat is a source of nitrogen oxide, wood fuel enables a utility to reduce the sulfur emissions that are the heart of any utility's pollution problems.

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