Testing was scheduled to begin Aug. 16 at an Ohio powerplant that has been emitting an acid cloud that descends on the town of Cheshire like a fog.
|SURPRISED Gavin's plant's clean-air retrofit has produced unexpected results. (Photo courtesy of American Electric Power Co. Inc.)|
The blue plume first appeared in June shortly after Columbus, Ohio-based American Electric Power Co. Inc. added a selective catalytic reduction (SCR) device to the 2,600-Mw coal-fired Gavin plant. The $200-million system reduces nitrogen oxide (NOx) emissions, but also produces SO3 as an unwanted byproduct, says Paul Chodak, AEP's environmental optimization group manager. "We've been able to trace the cloud to the conversion of SO2 to SO3," he says.
The SCR reduces NOx by converting it to nitrogen and water vapor. "The water vapor and SO3 combine to make sulfuric acid (H2SO4), which comes out of the stack as an aerosol," says Chodak. The plume touches the ground only on hot, humid days. Some days there will be more than one, but on other days there are none, says Chodak.
The Environmental Protection Agency does not regulate SO3 air emissions, but the Electric Power Research Institute, Palo Alto, Calif., has been testing ways to reduce SO3 in powerplants because it corrodes boilers and often reduces energy efficiency. Under a research project financed in part by the Dept. of Energy, EPRI engineers will inject magnesium hydroxide into the Gavin plant's boiler to precipitate SO3 from the flue gas.
The institute has tested the method at FirstEnergy Corp.'s Bruce Mansfield coal-fired plant with good results, says George Offen, EPRI area manager for emissions and by-products management. "If the plant did not have an SCR we know we could reduce the SO3. But with an SCR it could react with the catalyst and make it less effective for NOx reduction," he says. The test will last 23 days.
The SCR is an important part of the plant's clean-air compliance plan, but AEP is willing to temporarily bypass the system when conditions are right for a plume to touch the ground, says Chodak. The plant also is burning low-sulfur coal for now because the scrubbers used to reduce the SO2 emissions produced by the plant's normal high-sulfur coal also produce SO3. The amount was not enough to cause a problem until the SCR was added, says Chodak.
The sulfuric acid clouds, while disturbing and potentially hazardous to the town's people, do not violate the plant's air-quality permit and no enforcement actions have been taken by epa. But officials in the Chicago regional office are keeping an eye on the plant. "We are strongly encouraging AEP to find a solution and put an end to this," says George Czerniak, chief of air enforcement.