(639a) High Temperature Mercury Oxidation Catalyst for Mercury Emissions Control

The use of different coals and different air pollution control device configurations within coal-fired power plants pose a great challenge for cost-effective mercury technology solutions to meet the new impending Mercury and Air Toxics Standards (MATS) rule. This study aims to develop Hg(0) oxidation catalysts that can work at typical SCR unit temperatures of 350-400 °C.  Selected mercury oxidation catalysts prepared onto TiO₂ were tested in both a lab-scale fixed-bed reactor and a bench-scale reactor with structured catalysts at 370 °C. Two different simulated flue gas conditions representing eastern bituminous coal and PRB coal were used.  Both fresh and spent catalysts were characterized by SEM-EDX, XAFS, FTIR, and XPS.

Under high HCl conditions, 95% Hg(0) oxidation could be achieved while minimizing metal loadings. The addition of cerium also improved the performance under high SO₂ conditions (up to 2000 ppm).  For low chlorine-containing PRB and lignite coals, the injection of CaBr₂ to the boiler is a viable solution.  The catalysts were also optimized to work with low bromine content (less than 5 ppm in the form of HBr) and the amount of CaBr₂ needed could be significantly reduced. Any significant SO₃ or NO_x gas generation was not observed over the catalysts.  The mercury oxidation catalysts can be installed at the tail section of the existing SCR unit.  Oxidized mercury in the form of HgCl₂ or HgBr₂ is highly soluble in water and can be captured in the subsequent wet FGD process.