Mechanisms governing the fate of mercury in coal-fired power systems

This paper summarizes the results of a significant research and development investment to understand the fundamental mechanisms governing the speciation of mercury in coal-fired power systems. An extensive experimental search was conducted through all the parameter variations characterizing the majority of full-scale U.S. coal-fired power plants, in an effort to quantify the impact each parameter variation had on mercury oxidation and removal from the gas phase. As a result of this extensive investigation, the mechanisms responsible for mercury speciation differences observed for different coal types, power plants, and pollution control devices were elucidated. Specifically, unburned carbon was found to catalytically enhance mercury oxidation, while the actual differences in chlorine concentration from plant to plant were found to be of secondary importance to carbon. In addition, synergistic enhancement of mercury capture by carbon and calcium in flyash was quantitatively described for various coal-fired configurations, such as coal blending and sorbent injection, including development of contour plots of mercury removal at an ESP inlet and exit as a function of carbon and calcium concentration at the ESP inlet.