Bromine gas was evaluated for converting elemental mercury (Hg0) to oxidized mercury, a form that can readily be captured by the existing air pollution control device. The gas-phase oxidation rates of Hg0by Br2decreased with increasing temperatures. SO2, CO, HCl, and H2O had insignificant effect, while NO exhibited a reverse course of effect on the Hg0oxidation: promotion at low NO concentrations and inhibition at high NO concentrations. A reaction mechanism involving the formation of van der Waals clusters is proposed to account for NO's reverse effect. The apparent gas-phase oxidation rate constant, obtained under conditions simulating a flue gas without flyash, was 3.61 × 10-17cm3·s-1molecule-1·s-1at 410 K corresponding to a 50% Hg0oxidation using 52 ppm Br2in a reaction time of 15 s. Flyash in flue gas significantly promoted the oxidation of Hg0by Br2, and the unburned carbon component played a major role in the promotion primarily through the rapid adsorption of Br2which effectively removed Hg0from the gas phase. At a typical flue gas temperature, SO2slightly inhibited the flyash-induced Hg0removal. Conversely, NO slightly promoted the flyash induced Hg0removal by Br2. Norit Darco-Hg-LH and Darco-Hg powder activated carbons, which have been demonstrated in field tests, were inferred for estimating the flyash induced Hg0oxidation by Br2. Approximately 60% of Hg0is estimated to be oxidized with the addition of 0.4 ppm of gaseous Br2into full scale power plant flue gas.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry