| Description |
This thesis examines gas-phase oxidation of mercury by chlorine and bromine. Experiments were carried out in a bench-scale, laminar, 300 W, methane-fired, quartzlined reactor in which quench rate, flue gas composition, and reactor surface were varied. All species were introduced through the flame. This study examined conditioning system chemistry and found the majority of previously reported oxidation in this reactor was occurring in the KC1 solution. Modeling predicted up to 3.5 ppm CI2 could be formed in the reactor. This CI2 forms hypochlorite in solution which oxidizes elemental mercury. Less than 10 ppm Cl2 was injected along with flue gas directly into the KC1 solution. This produced oxidation up to 95%, comparable to previously reported levels of gasphase oxidation. This oxidation in solution is removed by Na2S203 or sufficient levels of SO2, which reduce the hypochlorite ion. These results bring into question laboratory scale experimental data on mercury oxidation where wet chemistry was used to partition metallic and oxidized mercury without the presence of sufficient levels of SO2. For further experimentation, 0.5 wt% Na2S203 was added to the KC1 solution. Homogeneous oxidation experiments were then repeated. Gas-phase oxidation was reduced drastically and ranged from 2% to 8% with reactor chlorine concentrations ranging from 100 to 500 ppmv (as HC1). Oxidation was unaffected by 500 ppm NO or 400 ppm S02 . Kinetic modeling parameters for a two-step oxidation mechanism were fit to the experimental data using a high quench rate (440 K/s). The model under-predicted the experimental data taken at a lower quench rate (210 K/s) and predicted increased oxidation at lower temperatures. Using bromine as the oxidant, gas-phase oxidation ranged from 18% to 78% with reactor bromine concentrations ranging from 6.7 to 41.4 ppmv (as HBr), a quench rate of 450 K/s, and 30 ppm NO (dry as measured). Oxidation increased by one third using a lower quench rate (220 K/s). Increasing the reactor surface area from 1000 crn to 3000 cm increased oxidation by 15%. Increasing the NO concentration from 30 ppm to 500 ppm had no effect. These results suggest that bromine oxidizes much more elemental mercury than chlorine. |
