Mercury oxidation by chlorine-containing species and scrubbing in a wet flue gas desulfurization system.

摘要

This research is particularly related to mercury control technologies. The state of the art in mercury emission control is generally classified into two categories: Mercury Transformation and Mercury Capture. In this research, two chapters (3 & 4) are specifically related to mercury transformation and another two (5 & 6) are related to mercury capture.; Chapter 3 investigates the capabilities of HCl and Cl2 on Hg0 oxidation. The resulting data indicated that both were effective in the combustor. However, HCl was less effective in a quartz reactor. Subsequently, the inhibitory effects of NO and SO2 were identified in the quartz reactor. The result and mechanism showed that the presence of H2O was necessary for NO and SO2 to have an inhibitory effect probably by scavenging Cl and Cl2 in the flue gas.; Chapter 4 studies the capability of gold catalyst in catalytically promoting Hg0 oxidation by chlorine. Gold was selected as catalyst because of its inertial property in adsorbing H2O, SO2 and NO. This property was demonstrated critical to avoid the inhibitory effects of NO and SO2 on Hg0 oxidation.; Chapter 5 presents recent insights, theoretically and experimentally, into the effects of aqueous S(IV) species (sulfite or bisulfite) on Hg 0 reemissions. Evidence indicated that bisulfate, rather than sulfite, was the primary species in the wet flue gas desulfurization (FGD) scrubber that caused Hg0 to be reemitted. The Hg0 reemission in S(IV) solution was also simulated by fitting experimental data, showing that the Hg0 reemission was proportional to HSO3 - concentration, but inversely proportional to total S(IV) concentration. When industrial limestone was used to validate the gained mechanism, it appeared that limestone was also capable of suppressing Hg0 reemission by adsorbing HgCl2 onto its alkaline surfaces.; Chapter 6 particularly relates to mercury control in wet flue gas desulfurization systems. The effects of such scrubber operating parameters as liquid/gas (L/G), SO2 concentration, and slurry pH on mercury capture and reemission were investigated. The result indicated that the capture of oxidized mercury across the scrubber was strongly dependent upon the water solubility of HgCl 2, and insensitive to slurry pH and SO2 concentration. Increasing the L/G increased the reemission source by delivering more Hg2+ back to the spray tower and enhanced the contact surfaces.