Catalysis is the key fundamental ingredient to convert elemental mercury in coal-fired power stations into its oxidized forms that are more easily captured by sorbents, ESPs, baghouses, and wet scrubbers, whether the catalyst be unburned carbon (UBC) in the ash or vanadium pentoxide in SCR catalysts. This project has investigated several different types of catalysts that enhance mercury oxidation in several different ways. The stated objective of this project in the Statement of Objectives included testing duct-injection catalysts, catalyst-sorbent hybrids, and coated low-pressure-drop screens. Several different types of catalysts were considered for duct injection, including different forms of iron and carbon. Duct-injection catalysts would have to be inexpensive catalysts, as they would not be recycled. Iron and calcium had been shown to catalyze mercury oxidation in published bench-scale tests. However, as determined from results of an on-going EPRI/EPA project at Southern Research, while iron and calcium did catalyze mercury oxidation, the activity of these catalysts was orders of magnitude below that of carbon and had little impact in the short residence times available for duct-injected catalysts or catalyst-sorbent hybrids. In fact, the only catalyst found to be effective enough for duct injection was carbon, which is also used to capture mercury and remove it from the flue gas. It was discovered that carbon itself is an effective catalyst-sorbent hybrid. Bench-scale carbon-catalyst tests were conducted, to obtain kinetic rates of mercury adsorption (a key step in the catalytic oxidation of mercury by carbon) for different forms of carbon. All carbon types investigated behaved in a similar manner with respect to mercury sorption, including the effect of temperature and chlorine concentration. Activated carbon was more effective at adsorbing mercury than carbon black and unburned carbon (UBC), because their internal surface area of activated carbon was greater. Catalyst coating of low-pressure-drop screens was of particular interest as this project was being developed. However, it was discovered that URS was already heavily involved in the pursuit of this same technology, being funded by DOE, and reporting significant success. Hence, testing of SCR catalysts became a major focus of the project. Three different commercial SCR catalysts were examined for their ability to oxidize mercury in simulated flue-gas. Similar performance was observed from each of the three commercial catalysts, both in terms of mercury oxidation and SO{sub 3} generation. Ammonia injection hindered mercury oxidation at low HCl concentrations (i.e., {approx}2 ppmv), yet had little impact on mercury oxidation at higher HCl concentrations. On the other hand, SO{sub 2} oxidation was significantly reduced by the presence of ammonia at both low and high concentrations of HCl.
