FGD Additives to Segregate and Sequester Mercury in Solid Byproducts

Coal is used to generate more than half of the electricity in the United States. However, coal has a range of mercury-related environmental disadvantages: (1) emissions of mercury via the flue gas, and (2) environmental releases of mercury during subsequent processing and disposal of byproducts. This project will address both concerns through the use of chemical additives in the power plant¿s flue gas desulfurization (FGD) system. These additives will sequester mercury into the liquid phase, prevent mercury re-emissions into the flue gas, prevent precipitation and adsorption of mercury on primary FGD byproducts such as gypsum, and subsequently precipitate mercury from the FGD wastewater as a stable solid byproduct that is segregated from other FGD solid byproducts. In Phase I, laboratory testing using a bench-scale scrubber test apparatus demonstrated that the technology can control re-emissions of mercury and that the mercury can be subsequently removed from the scrubber wastewater and concentrated into a stable solid waste product. An engineering cost analysis demonstrated that the technology would be economical and competitive with other control strategies. Phase II initially will involve additional laboratory testing to further refine the chemistry, and the selection of the additives and process conditions. Then, a larger pilot-scale demonstration will be conducted at two host utility sites, using actual flue gas and the FGD scrubbing slurry from the utility. Commercial Applications and Other Benefits as described by the awardee: The proposed technology should have extensive commercial applications in the electric utility industry at both new and existing coal-fired power plants equipped with wet FGD scrubbing systems. The public would benefit through reduced exposure to mercury emitted from power plant stacks and through reduced exposure to the mercury-containing FGD byproducts during their disposal or re-use in gypsum wallboard products and agriculture applications.