Reduction of HgCl2 to Hg0 in flue gas at high temperature. Part Ⅱ: Acid remover

Abstract

Eliminating the adverse effects of oxidative species on the reduction of HgCl2(g) to Hg0(g) in the high-temperature decomposition (HTD) is a prerequisite to ensuring the accuracy of the total gaseous mercury in Hg-CEMS. To overcome the influences of the oxidative species on the reduction of HgCl2(g) in HTD, an efficient acid remover (AR) was developed. Combining characterization and thermodynamic calculation with fixed-bed experiments, the mechanisms of how the acid remover (AR) deteriorates the re-oxidation of Hg0(g) and boosts the reduction of HgCl2(g) were explored thoroughly. The results show that CaO is the best active material which is synthesized by the optimum precursor of Ca(CH3COO)2. γ-Al2O3 is confirmed as the optimal support material with the best synthesis mass ratio to the precursor of 30%. In an atmosphere where 10 ppm HCl and 4% O2 coexist, the HgCl2(g) HTD efficiency can reach 97.2% with CaO/30%γ-Al2O3 contrasted to 0% without the AR. This is due to the high deacidification reactivity and abundant microstructure of the prepared CaO-based AR. The productive alkaline sites of CaO/30%γ-Al2O3 can enhance the absorption of acidic species and adsorb weakly acidic HgCl2(g) molecules to strengthen their reduction reaction.