Shaohua Qiao

Catalytic Oxidation of Elemental Mercury over the Modified Catalyst Mn/α-Al2O3 at Lower Temperatures

In order to facilitate the removal of elemental mercury (Hg(0)) from coal-fired flue gas, catalytic oxidation of Hg(0) with manganese oxides supported on inert alumina (alpha-Al2O3) was investigated at lower temperatures (373-473 K). To improve the catalytic activity and the sulfur-tolerance of the catalysts at lower temperatures, several metal elements were employed as dopants to modify the catalyst of Mn/alpha-Al2O3. The best performance among the tested elements was achieved with molybdenum (Mo) as the dopant in the catalysts. It can work even better than the noble metal catalyst Pd/alpha-Al2O3. Additionally, the Mo doped catalyst displayed excellent sulfur-tolerance performance at lower temperatures, and the catalytic oxidation efficiency for Mo(0.03)-Mn/alpha-Al2O3 was over 95% in the presence of 500 ppm SO2 versus only about 48% for the unmodified catalyst. The apparent catalytic reaction rate constant increased by approximately 5.5 times at 423 K. In addition, the possible mechanisms involved in Hg(0) oxidation and the reaction with the Mo modified catalyst have been discussed.

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

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)x10(-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 10mg/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.

Removal Characteristics of Hydrogen Sulfide in Biofilters with Fibrous Peat and Resin

The removal characteristics of hydrogen sulfide were studied experimentally in the biofilters with fibrous peat and resin as the packed materials. The factors that influenced the removal efficiency of hydrogen sulfide were investigated. The biofilter with 100% of the peat showed higher removal capacity than the resin biofolter, but the gas flow resistance was lower in the latter. The mixture of the peat and resin as the packed material of the biofilter was proved to be an advisable method to keep the high removal capacity and reduce the gas flow resistance for a long-term operation. The flow resistance can decrease by 50% when 50% of the resin mixed with the peat, but the removal capacity was still considerable high. In addition, the removal kinetics in the biofilters were discussed, and the main kinetics parameters were determined experimentally. The maximum removal rate of hydrogen sulfide, Vmax , was about 620, 210 and 480 g/m3h in the biofilters with 100% peat, 100% resin and 50% peat mixture, respectively. The result was helpful to the design and optimization of the biofilter.

Preliminary Study on Oxidation of Elemental Mercury in the Presence of Gaseous Oxidants

Elemental mercury in coal-fired flue gas is difficult to be removed efficiently by traditional Air Pollution Control Devices (APCD). It has been proved to a promising approach to convert elemental mercury to oxidized mercury, which is soluble and ready to be captured. The oxidants for the direct oxidation of elemental mercury by gas phase reaction were studied, and gaseous iodine was investigated in this paper. The reaction kinetics between elemental mercury and oxidants were determined experimentally. Iodine showed high performance to the oxidation of elemental mercury among these oxidants, and the 2nd rate constant was about 1.95times10-16cm3-molecules-1ldrs-1 at around 297 K. In addition, sulfur dioxide had very slight impact on the reaction kinetics between elemental mercury and iodine. However, nitric oxide showed a significant inhibition effect on this reaction.