Burning Biomass with Fossil Fuels

August 22, 2007

Ken Silverstein, EnergyBiz Insider

Cutting greenhouse gas emission need not be a distant dream or expensive. Advocates of co-firing bio-mass with coal or natural gas say that it is an effective way for utilities to begin now to reduce their carbon footprints.

Biomass consists of any fuel produced from organic matter. That includes forest waste, agricultural waste, organic waste and municipal waste. Biomass produced from wood chips, for example, can be mixed with certain types of coal before the new compound is combusted. It can all be accomplished, say experts, without having to change the fuel-firing system.

"It is a technology that is available and it does not require a substantial investment by utilities," says Janusz Kozinski, dean of the College of Engineering at the University of Saskatchewan. "Effectively, there are zero emissions associated with some bio-fuels."

About 20 utilities in North America are now using wood chips to replace 5-25 percent of the needed coal or natural gas. State laws that have been enacted to require utilities to offer some green power are the impetus for the changes. Among non-hydro renewable sources, biomass plays a key role today with 7,000 MW of installed capacity and producing 37 billion kilowatt hours of electricity each year, says the U.S. Department of Energy's Energy Information Administration. The Energy Department also says that the co-firing of biomass and fossil-fired fuels is the most immediate step that utilities can take to cut their carbon dioxide (CO2) emissions.

Biomass crops, such as trees, absorb CO2. When burned, however, the biomass material releases the CO2 back into the atmosphere. But, such discharges are considered "neutral," meaning that the plants absorbed the same amount as the materials released -- unlike traditional fossil fuels that essentially discharge all new CO2 into the air.

The Energy Department is working with utilities seeking to expand biomass generation. Alliant Energy is developing a combined-cycle plant that uses corn starch as a feedstock. United Technologies, meanwhile, is testing a biomass gasifier coupled with a fuel cell and steam turbine options that run on wood residue. Similarly, Progress Energy is developing a biomass gasification process that uses wood waste. The advantage of using industrial waste byproducts, as opposed to agricultural crops such as corn, is that it does not contribute to food shortages.

According to Dr. Kozinski, it generally takes twice as much biomass to create the same amount of energy as coal. So, one kilogram of coal produces one unit of energy. To replace that, 2 kilograms of biomass would be required. At the same time, any industrial operation utilizing the technology needs to assure it would have a continuous supply of the underlying feedstock while also making certain that the biomass and the coal are compatible before they would be mixed and burned.

Striking Proposition

Building a biomass plant from scratch is a hugely expensive undertaking. Estimates are that it cost twice as much as a coal plant. But, co-firing the two together is working now and especially in Europe that has signed the global warming pact, the Kyoto Protocol. Sweden, for example, gets 19 percent of energy from bark, straw and wood chips and expects to receive 40 percent from such sources by 2020.

The main problem in Europe, however, is that food crops are the central fuel source. By substituting industrial waste, though, utilities could reduce their carbon output without driving up the market value for food commodities. That's what Evergreen BioFuels is trying to do. It says that its woody fibers can be co-fired with coal without the need to replace or retrofit the current plant infrastructure.

"Thirty percent of CO2 emissions are generated by utilities and industry in the U.S," says Mark Drisdelle, CEO of Montreal-based Evergreen. "The Earth doesn't have a decade or more to wait for a solution for climate change."

Why are so few of the nation's utilities using this concept? Until federal legislation is adopted to cap or tax carbon output, Drisdelle says that many power companies don't have the financial or legal incentives. Right now, though, biomass entrepreneurs are in the process of educating more such companies about these types of alternatives.

Mining coal and harvesting biomass are both involved processes. In the final analysis, however, biomass is more attractive, says Drisdelle. Anthracite coal, for example, has more BTUs than bio-fuels. But, it also contains large quantities of sulfur, nitrogen oxide, particulate matter, mercury and CO2. With ever-stricter environmental laws and in a carbon constrained world, the value of facilities that use biomass will rise.

That's been the experience of the Public Service Co. of New Hampshire. Utilities in its neck of the woods are flocking to its door to buy biomass-derived power from it. The company took three well-functioning coal-fired boilers that were profiting and then converted those facilities into ones that could also burn wood chips. The change cost $75 million. But the new 50-megawatt facility actually has lower operational costs and higher earnings. Moreover, the utility's overall emissions have been drastically reduced.

The changes were made because New Hampshire implemented a renewable portfolio standard requiring its own utilities to supply a quarter of its energy from sustainable sources by 2025. Meanwhile, neighboring utilities are also required to offer their customers green options. For now, it's a seller's market in the New England region. That could change if an increasing number of utilities begin offering biomass alternatives.

"The point is if we compare the cost of producing a ton of coal with a ton of wood chips, it is ultimately cheaper to use the industrial waste," says Drisdelle. "If we look at the full life-cycle benefits, bio-energy is better because of the environmental benefits."

Large power plants need viable and cost effective solutions to cut their carbon footprints. Co-firing biomass with prevalent fossil fuels is one answer. It's a striking proposition: Act now to reduce greenhouse gas emissions or wait two decades when arcane technologies are finally commercialized.

For more on this topic, visit the Energy Central Generation Technologies Topic Center.

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Ken Silverstein
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