MERCURY SPECIATION SAMPLING AT NEW CENTURY ENERGY'S VALMONT STATION

Abstract

The 1990 Clean Air Act Amendments required the U.S. Environmental Protection Agency (EPA) to determine whether the presence of mercury in the stack emissions from fossil fuel-fired electric utility power plants poses an unacceptable public health risk. EPA's conclusions and recommendations were presented in the ''Mercury Study Report to Congress'' and ''Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units''. The first report addressed both the human health and environmental effects of anthropogenic mercury emissions, while the second addressed the risk to public health posed by the emission of mercury and other hazardous air pollutants from steam electric generating units. Although these reports did not state that mercury controls on coal-fired electric power stations would be required given the current state of the art, they did indicate that the EPA views mercury as a potential threat to human health. Therefore, it was concluded that mercury controls at some point may be necessary. EPA also indicated that additional research/information was necessary before any definitive statement could be made. In an effort to determine the amount and types of mercury being emitted into the atmosphere by coal-fired power plants, EPA in late 1998 issued an information collection request (ICR) that required all coal-fired power plants to analyze their coal and submit the results to EPA on a quarterly basis. In addition, about 85 power stations were required to measure the speciated mercury concentration in the flue gas. These plants were selected on the basis of plant configuration and coal type. The Valmont Station owned and operated by New Century Energy in Boulder, Colorado, was selected for detailed mercury speciation of the flue gas as part of the ICR process. New Century Energy, in a tailored collaboration with EPRI and the U.S. Department of Energy, contracted with the Energy & Environmental Research Center (EERC) to do a study evaluating the behavior of mercury at the Valmont Station. The activities conducted at the Valmont Station by the EERC not only included the sampling needed to meet the requirements of the ICR, but involved a much more extensive mercury research program. The following objectives for the sampling at New Century Energy's Valmont Station were accomplished: (1) Successfully complete all of the mercury sampling and reporting requirements of the ICR. (2) Determine the variability in mercury concentrations at the stack using mercury continuous emission monitors (CEMs). (3) Calculate mercury mass balances and emission rates. (4) Determine the mercury concentration in the fly ash as a function of particle size. (5) Determine the impact of a fabric filter on mercury emissions for a western bituminous coal.