THERMOCHEMICAL STUDY OF MERCURY OXIDATION

摘要

Experiments conducted in a simple laboratory apparatus confirmed an hypothesis that arntemperature window exists for mercury oxidation by chlorine species. This window exists in therntemperature range of about 700 – 900 ℃ and is represented by a low, but sustainable populationrnof free radicals which are believed to initiate the conversion of HCl into free chlorine atoms andrnthen to molecular chlorine. The experimental data were used as a calibration point for therndevelopment of a kinetic submechanism to describe mercury oxidation by chlorine. Thernmechanism predicts that the rate-limiting step in mercury oxidation by chlorine is the chlorineradicalrnattack on elemental mercury. Subsequently the resulting HgCl radical can react quicklyrnwith even small concentrations of molecular chlorine, HCl, Cl?, or HOCl. The predicted raternconstant for the initial attack of Cl? on mercury was in the expected range of about 10~(16) cm~6?molrn~(-2)?s~(-1).rnOnce calibrated using the experimental data the submechanism and a kinetic model were used tornexplore other options for mercury control and their implications under extant conditions of coalrncombustion flue gas where both mercury and HCl concentrations are low.