Effects of Quench Rate, NO, and Quartz Surface Area on Gas Phase Oxidation of Mercury by Bromine

Oxidized mercury species may be formed in combustion systems through gas-phase reactions between elemental mercury and halogens, such as chorine or bromine. Injection of bromine compounds or brominated sorbents have been shown to affect mercury speciation and removal in coal-fired power plants. This study examines how bromine species affect mercury oxidation in the gas-phase. Experiments were conducted in a bench-scale, laminar, methane fired (300 W), quartz-lined reactor in which gas composition (Br2, NOx), quench rate, and quartz surface area were varied. Speciated mercury was measured using a wet conditioning system and continuous emissions monitor (CEM). Oxidation levels ranged from 13% to 80% with a quench rate of 450 K/s and bromine concentrations ranging from 3.5 to 41 ppmv equivalent HBr. A lower quench rate (220 K/s) increased oxidation by about one third. Most of the experiments were conducted with 30 ppm NO (dry). Mercury oxidation was unaffected by the presence of 500 ppmv NO. The surface area was increased by inserting a bundle of thin-walled quartz tubes. The insert decreases the reactor residence time by about 5 %. Tripling the interior, quartz surface area of the reactor from 1000 cm to 3000 cm did not appreciably affect the extent of oxidation. The experimental results were compared to detailed kinetic modeling predictions.