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Report: Co-Firing Biomass at Coal Power Plants Would Cut Greenhouse Gases by 5% "Co-firing" coal and biomass, with wood pellets making up 10% of the fuel mix, would reduce greenhouse gas emissions from the power generation sector by 5% in the United States and Canada, but it would require about 100 million dry metric tons of biomass a year — "a large amount but within inventory amounts," according to the report, "Life Cycle Emissions and Cost of Producing Electricity from Coal, Natural Gas, and Wood Pellets in Ontario, Canada." The study, published in the January issue of the Journal of Environmental Science and Technology, was primarily focused on the potential for biomass at the Nanticoke and Atikokan generating stations in Ontario. Ontario Power Generation Inc. has been looking into converting coal-fired units at both stations into biomass units as part of its plan to eliminate coal generation by 2014. The study, conducted by researchers at the University of Toronto, was funded by Ontario Power Generation and the Natural Sciences and Engineering Research Council of Canada. According to the article, coal is responsible for a fifth of global greenhouse gas emissions, but power generators have few cost-effective "near-term options" for cutting emissions from coal-fired units. While carbon capture and storage technologies, at least on the commercial scale, are still a decade away, co-firing biomass fuels, such as wood pellets, is one short-term solution with unique advantages for cutting pollution and meeting renewable portfolio standards, the report said. "[B]iomass firing does not have the drawback of being intermittent and … is a favorable option as it requires low capital expenditure by using existing facilities and is applicable for virtually all types of utility coal boilers," the report said. "There are no major technical obstacles to cofiring." Compared to a unit running solely on coal, the report estimated, a unit co-firing at 10% and 20% biomass rates would result in reductions of 9% and 18%, respectively, in greenhouse gas emissions. Emissions from a natural gas-fired, combined-cycle unit are lower, but "natural gas is a fossil fuel that is limited in supply and subject to price volatility, which are factors of concern if moderate to large portions of electricity were to be generated from this resource," the report said. Co-firing coal and wood pellets reduces SOx emissions compared to using only coal, but NOx emissions remain the same, the report said. A coal plant retrofitted to completely run off wood pellets would cut emissions by 91%, reducing NOx emissions by 40% to 47% and SOx emissions by 76% to 81%, the study said. But a fuel cost analysis revealed that a plant running solely on biomass would be one of the most expensive ways of mitigating emissions — in some cases just as expensive as constructing a new natural gas-fired, combined-cycle plant. Co-firing wood pellets at 10%, meanwhile, would increase the cost of electricity by 0.6 cent per kWh at Nanticoke and 0.9 cent per kWh at Atikokan, the report said. The capital costs of co-firing biomass total $225 per kW of biomass capacity, the report said, and pellet delivery costs total $160 per metric ton. The study found, however, that the characteristics of generating systems, the type of biomass fuel used and fluctuating fuel costs significantly affect the benefits of biomass as a generation source. "The following simplistic calculations do not reflect the local nature of these aspects or a host of other issues but are provided for perspective," the report said. Still, biomass-fired generation already has been proved to reduce greenhouse gas, NOx and SOx emissions at commercial plants in the United States, Europe and elsewhere, "but not to our knowledge in Canada," the authors of the report said. The report specifically refers to a 50-MW, wood chip-fueled boiler at the Schiller Coal power station owned by Northeast Utilities subsidiary Public Service Co. of New Hampshire, and FirstEnergy Corp.'s and Southern Co.'s plans to convert some coal units to biomass. Georgia Power Co., a subsidiary of Southern Co., announced last month that it will delay the conversion of its coal-fired Mitchell power plant to biomass until the U.S. Environmental Protection Agency better defines boiler technology rules. American Electric Power Service Corp., a unit of American Electric Power Co. Inc., issued a request for proposals Jan. 29 to supply biomass fuel to three of its coal-fired generating stations to comply with state requirements in Ohio. Coal-fired plants can be retrofitted to feed off biomass fuels through a range of modifications, the report said, from modifying coal boilers to fully replacing them with biomass boilers. The potential for biomass as a widespread generation fuel is "substantial" in the United States and Canada, the report said, "due to abundant resources." The article notes that the benefits of biomass can vary depending on different aspects of production and combustion, such as the use of fertilizer, related N2O emissions, changes in land use and performance of the displaced energy system. Researchers developed models to assess the costs and emissions associated with the entire life cycle of coal, natural gas, pellet co-firing and 100% pellet firing — from production to combustion. Researchers said in the report that theirs is the first study to analyze "100% biomass usage" in a coal-fired generating system. Though the report estimates costs and emissions reductions specifically for Ontario Power Generation's coal plants, researchers said the report speaks generally to the future of both U.S. and Canada power generation. "[T]he results suggest that electricity produced from biomass in existing coal [generation systems] should be considered along with other alternatives, as a means of achieving near-term [greenhouse gas] reductions," the report said.
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