The performance of iodine on the removal of elemental mercury from the simulated coal-fired flue gas

Abstract

In order to facilitate the removal of elemental mercury (Hg 0) in flue gas, iodine was used as the oxidant to convert Hg 0 to the oxidized or particulate-bound form. The removal of Hg 0 by the homogenous gas phase reaction and the heterogeneous particle-involved reactions was investigated under various conditions, and a method to test the particle-involved reaction kinetics was developed. Iodine was found to be efficient in Hg 0 oxidation, with a 2nd-order rate constant of about 7.4(±0.2) × 10 −17 cm 3 molecules −1 s −1 at 393 K. Nitric oxide showed significant inhibition in the homogenous gas reaction of Hg 0 oxidation. The oxidation of Hg 0 with iodine can be greatly accelerated in the presence of fly-ash or powder activated carbon. SO 2 slightly reduced Hg 0 removal efficiency in the particle-involved reaction. It was estimated that Hg 0 removal efficiency was as high as 70% by adding 0.3 ppmv iodine into the flue gas with 20 g/m 3 of fly-ash. In addition, the predicted removal efficiency of Hg 0 was as high as 90% if 10 mg/m 3 of activated carbon and 0.3 ppmv iodine were injected into the flue gas with fly-ash. The results suggest that the combination of iodine with fly-ash and/or activated carbon can efficiently enhance the removal of Hg 0 in coal-fired flue gas.