Technology Solutions
Integrated technology targets mercury emissions A small power plant in Eastlake, OH, is gearing up for a commercial-scale demonstration of a new technology for removing multiple pollutants, including mercury, from the emissions of coal-fired power plants. The electro-catalytic oxidation technology is sufficiently promising to have attracted the investment of American Electric Power, one of the nation's largest power generators. Developed by Powerspan Corp., of New Durham, NH, the electrocatalytic oxidation system is a threepart process that works in conjunction with the electrostatic precipitators that are used in at least 1200 U.S. plants to capture coarse and fine particulate matter. None of the component technologies is new, but Powerspan holds a patent on the way in which they are combined to target power plant emissions. For
example, the technology deploys a high-voltage plasma called a barrier discharger, which has been used in ozone generation for more than 50 years. This barrier discharger, which is also known as a gas reactor, electrically oxidizes NOx, S02, and mercury to form dilute acid aerosols and particulates that can be collected by the electrostatic precipitator, according to Powerspan. From there, the technology employs an acid byproduct recovery system to separate the solids from the dilute acids; concentrates the acids; and removes the heavy metals. The technology uses existing plant systems, requires no chemical reagents, and generates no new waste streams. The approach of targeting all the major pollutants from coal-fired power plants is the best way to reduce emissions, says Ken Colburn,
Conventional power plant with electro-catalytic oxidation Electro-catalytic oxidation can work with the electrostatic precipitators (ESPs) found in more than 90% of the nation's coal-fired power plants to target all of the major pollutants resulting from coal combustion.
Source: Powerspan Corp.
3 7 8 A • SEPTEMBER 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
director of the air resources division of the New Hampshire Department of Environmental Services. There is a lot of push in the direction of these integrated control strategies because individual pollutant control is not the smart way to deal with these emissions, agrees Praveen Amar, director of science and policy for the Northeast States for Coordinated Air Use Management, an interstate agencv including eight states and two EPA regions. The Powerspan technology is expected to cost 25% less to install and 50% less to operate than current NOx control technologies like selective catalytic reduction (SCR), according to Guy Pipitone, vice president of FirstEnergy Corp., the power company that plans to construct the $10.5 million commercial-scale demonstration at the 50-MW Ohio plant. The technology's ability to effectively operate with high-sulfur coal actually makes it preferable to SCR, a popular technology for reducing power plants' NO emissions he adds. Under many operating conditions however electro-catalytic oxidation would have to be used in combination with some other NO reducing technology like low-NO ^ burners or selective noncatalytic deduction according to FirstEnerev's Ralph DiNicola manager of public relations Rut he still expects the tprhnoloffv to result in cost savings FirstEnergy has been operating a pilot-scale demonstration of the technology at another Ohio plant since 1998. In those tests, electrocatalytic oxidation reduced NO.,. emissions by 76%, cut S0 2 levels by 44%, and achieved 68% mercury removal. In addition to trapping more than 99% of the fine particulates in the flue gas, the technology captured 88% of the hydrochloric acid and 99.9% of the hydrofluoric acid, both of which are chemicals that must be reported to EPA's Toxics Release Inventory (TRI). It also captured than 99% of a number of other © 2000 American Chemical Society
heavy metals including arsenic, chromium, copper, and nickel. To achieve these reductions, the electro-catalytic oxidation system requires about 5% of the plant's power output. "This is a very large [amount]," Amar cautions. Powerspan is actively trying to reduce the power draw, says Stephanie Procopis, the company's director of marketing. She points out that some of this cost may be offset by sales of the nitric and sulfuric acids generated by the process. But she acknowledges that these acids are most likely to be cost-competitive only if they can be sold locally to a customer. The technology's ability to sequester mercury could make it an attractive option if EPA decides to regulate utilities' mercury emissions; the agency is under a court-ordered mandate to make a determination by mid-December. Coal-fired power plants emit roughly one-third of the anthropogenic mercury in the United States, making them the largest source of airborne mercury according to EPA. A National Academy of Sciences report on methylmercury issued in mid-July correlated the methylmercury that is believed to form in water bodies as the result of airborne deposition with health risks There is also a movement afoot to target mercury emissions from coalfired power plants at the European Union level as well, Amar says. And the North American Free Trade Agreement's Commission for Environmental Cooperation has made recommendations for mercury reductions, he says. Although electro-catalytic oxidation was not one of the technologies that EPA was reviewing to support the U.S. decision about whether to regulate utilities' mercury emissions, the agency is interested in examining the performance and cost capabilities of otiier potential technologies, according to Ravi Srivastava, a chemical engineer with the U.S. EPA's Air Pollution Prevention and Control Division. There is some reason to believe that the activated carbon injection technology currently being reviewed by EPA may not work appropriately under the higher temperatures associated with larger power plants Colburn says This should not be a problem with electro-catalvtic oxidation he says —KELLYNS.BETTS
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