Brominated Activated Carbon for Coal-fired Power Plant Mercury Emission Control

Coal-burning power plants have been the largest unregulated source of mercury emissions in the United States, sending 48 tons of mercury into the air annually. In 2005, the U.S. Environmental Protection Agency promulgated its Clean Air Mercury Rule (CAMR), requiring coal-fired power plants to reduce their mercury emissions by approximately 20% beginning in 2010. Numerous states are already requiring swifter and higher mercury reduction levels than what is federally required. For the majority of the coal-fired power plants, the leading candidate technology to comply with the new mercury regulations is the injection of powdered activated carbon (PAC) mercury sorbents into the flue gas in front of the plant’s existing particulate control devices. This opens a potential U.S. market for activated carbon that could exceed $500 M per year. Flue gas conditions, including very short contact times, about 1-2 seconds, very low Hg concentrations, about 10μg/m, and high flue gas temperatures, about 160-200°C, make the mercury adsorption of activated carbon far below its equilibrium capacity. Our studies indicate that a bromination pretreatment can significantly increase the mercury adsorption of activated carbon. A family of PAC based brominated mercury sorbents have been developed and are conmmercially manufactured. The characterization of the brominated carbon sorbent and its mercury performance compared to plain activated carbon, including the results from the full-scale power plant trials, is presented in this paper.