Reduction of HgCl2 to Hg0 in flue gas at high temperature. Part Ⅰ: Influences of oxidative species

Abstract

The reduction of gaseous oxidized mercury Hg2+(g) to elemental mercury Hg0(g) is a key technology to obtain the total flue gas mercury in the mercury continuous emission monitoring system (Hg-CEMS). Investigation of the reduction of HgCl2(g) to Hg0(g) in the high-temperature decomposition (HTD) was conducted with/without oxidative components in a fixed bed reactor. The chemical reaction path was discussed in-depth by thermodynamic calculation and theoretical analysis. The results show that the higher the temperature, the higher the efficiency of HgCl2(g) reduction. The chlorine species produced in the HTD process inhibit the conversion rate because of re-oxidation on Hg0(g). For eliminating the negative effect of Cl radicals and promoting the reactive sites, a quartz filler with appropriate size demonstrates a good performance for enhancing the decomposition of HgCl2(g). However, the presence of O2 and HCl leads to the complete failure of HgCl2(g) HTD because O2 greatly promotes the combination of Hg0(g) with chlorine. Compared with HCl molecules, Cl atoms are more active in thermodynamic favor in speeding up re-oxidation of Hg0(g). Active Cl atoms are the most crucial factor hindering HTD reaction due to their high reaction initiative and low activation energy.