The Study On Elemental Mercury Capture In Simulated Flue Gas By Modified Gangue Fly Ash

Mercury in coal combustion-derived flue gas is present in three forms:elemental mercury, oxidized mercury, and particulate-bound mercury. Oxidized mercury is water soluble and therefore can be effectively captured by wet flue gas desulfurization systems as a co-benefit. The majority of particulate-bound mercury can be collected by electrostatic precipitators or fabric filters. Elemental mercury is the most difficult to remove by the existing pollution control devices because of its low solubility in water and stable chemical properties. The key point of the researching on this paper is the removal of elemental mercury.Fly ash is a kind of cheap natural minerals in China, but the efficiency of mercury removal is not high. The fly ash were modified by impregnating NaBr, NH4Br, CuBr2 and metal oxide CuCe to prepare NaBr/FA, NH4Br/FA, CuBr2/FA and Cu/FA, CuCe/FA to enhance the performance for removal of elemental mercury. The effect of modified materials, bromide loadings, adsorbent temperatures and gas compositions on the performance of mercury removal efficiency was studied in a fixed bed.The results indicate that the chemical adsorption of fly ash raises dramatically as it has been modified by NH4Br and CuBr2 - Hg capacity shows an upward trend when increasing amounts of these two chemicals-. When loadings is greater than 10% and adsorbent temperature is greater than 100℃, mercury removal efficiency of CuBr2/FA achieves to 100%. Mercury removal efficiency of NaBr/FA remained at low levels and didn’t change with loadings and adsorbent temperatures. Fly ash modified by three kinds of active substances follows the different mechanism of mercury removal, which lead to the different removal efficiency of elemental mercury. Hg removal efficiencies of three kinds of bromide modified fly ash follow the order: CuBr2>NH4Br>NaBr. O2, SO2 and HCl both can enhance the Hg removal efficiencies of bromide modified fly ash.Cu-Ce modified fly ash adsorbent its best copper cerium molar ratio is 2:1, the best loadings is 10%, the optimum reaction temperature is 100℃. Hg removal efficiency of the best modified fly ash adsorbent samples is 97%, reaction conditions: temperature 100℃; flow rate 200 ml/min; Hg concentration 40 μg/m3; 200 mg sorbent; N2 only; Time is 4h. O2 can enhance the Hg removal efficiencies of CuCe/FA, Hg removal over CuCe/FA sorbents follows the Mars-Maessen mechanism. The results also show that SO2 inhibits the Hg removal efficiencies of Cu/FA. The addition of CeO2 can improve the sulfur resistance of the adsorbent. HCl reacts with lattice oxygen in adsorbent, generating active chlorine which can oxidize Hg and improve Hg removal efficiencies of CuCe/FA.