Mercury Measurement and Characterization at Constellation Power Source Generation’s Coal-Fired Units

There are current efforts in Maryland to model the atmospheric deposition of mercury releases from certain types of plants in Maryland, study bioaccumulation, and study the economic impacts of fish consumption advisories, to better understand the implications of mercury emissions. The program described in this report complements these existing programs by providing direct measurement of mercury emissions from coal-fired power plants in Maryland. MDE required that all coal-fired generating units in Maryland perform specific stack tests in 2003 to determine the amount and nature of their mercury emissions using a test method called the Ontario Hydro Method (ASTM Method 6784-02). Constellation Power Source Generation (CPSG) and the Maryland Department of Natural Resources Power Plant Research Program (PPRP) developed a cooperative project to expand the scope of the MDE-required testing. The focus of the cooperative project was to provide process-level data to help generators better understand how mercury changes as it passes through the combustion and flue gas stages of the plant, and so aid the facility to better design control strategies.

Three flue gas mercury test methodologies were employed: the Ontario Hydro method required by MDE, a dry sorbent trap method that is currently proposed by EPA as Method 324, and a continuous emissions monitoring method. Testing was conducted during two separate sampling campaigns—one prior to the ozone season and one during the ozone season when additional NOx control systems are employed by CPSG. Concurrent with the flue gas sampling, mercury concentrations in the coal and the ash were determined to calculate mercury mass balances.