STUDY OF MERCURY OXIDATION BY SCR CATALYST IN AN ENTRAINED-FLOW REACTOR UNDER SIMULATED PRB CONDITIONS

A bench-scale entrained-flow reactor system was constructed for studying elemental mercury (Hg0) oxidation under selective catalytic reduction (SCR) reaction conditions. The system consists of a natural gas burner for producing combustion flue gas, and an electrically heated cylindrical quartz reactor (4 cm I.D., 310.5 cm in length) with SCR catalyst placed in the middle of the reactor. Simulated flue gas was doped with fly ash collected from a subbituminous Powder River Basin (PRB) coal-fired boiler along with other coal combustion flue gas components such as sulfur dioxide (SO2), nitrogen oxides (NOx), hydrogen chloride (HCl), reductant ammonia (NH3) for the NOx reduction reaction over SCR catalyst, and trace Hg0. Concentrations of Hg0 and Hg2+ upstream and downstream of the SCR catalyst were measured using a continuous emission monitor (CEM). The effects of HCl concentration, SCR operating temperature, and feed rate of PRB coal fly ash on Hg0 oxidation were studied. It was concluded that HCl plays an important role of providing a source of Cl for Hg0 oxidation under conditions simulating SCR systems for PRB coal-fired boilers. Good Hg mass balance closure was observed for tests at 20 ppm HCl. Poor Hg mass balance closure a