Catalytic oxidation and heterogeneous capture of elemental gas-phase mercury.

摘要

The ability of three sorbents, activated carbon, char and mordenite, to adsorb mercury is determined using simulated flue gas containing 10-15 mu g/m3 of mercury, in a laboratory-scale, fixed-bed adsorption system. The adsorption performance of the three sorbents is compared by, adsorption rate, rather than the adsorption capacity. The effect of temperature, sorbent loading, mercury concentration and acid gases such as NO and SO2 on the adsorption rate is investigated and presented in this dissertation. The mercury adsorption rate is in the range of 3000 to 3900 ng/hr for all three sorbents and increases with temperature, mercury concentration and acid gas concentration. Temperature is the major factor affecting the mercury adsorption rate on activated carbon and char while the rate of mercury adsorption on the zeolite sorbent is more strongly affected by the mercury concentration in the flue gas stream.; In a separate set of experiments, the effect of oxidizing agents on mercury oxidation and retention in a selective catalytic reduction (SCR) system, in a laboratory-scale using commercial vanadium-titania catalysts is investigated. Four oxidizing agents, HCl, H2SO 4, HBr and HI are introduced into the system. As the concentration of HCl, increases in the flue gas to a maximum of 35 ppm, oxidation of mercury increases up to a maximum of 85%. HBr and HI almost completely oxidize mercury in the flue gas, individually, at very low concentrations. H2SO4 does not contribute well to mercury oxidation. Temperature and space velocity are also shown to affect the mercury oxidation rates in expected ways. A kinetic model accounting for three reactions and mass transfer has been developed and is presented to better understand the experimental results. Fitting unknown kinetic parameters to the data and generation of accurate results shows that the model may be robust and predictive.