Effects of NOx, α-Fe2O3, γ-Fe2O3, and HCl on mercury transformations in a 7-kW coal combustion system

An abundance of Hg2+, HCl, and γ-Fe2O3 in Blacksville flue gas and the inertness of injected α-Fe2O3 with respect to heterogeneous Hg0 oxidation in Absaloka and Falkirk flue gases suggested that γ-Fe2O3 catalyzes Hg2+ formation and that HCl is an important Hg0 reactant. The filtration of Absaloka and Falkirk combustion flue gases at 150 °C through fabric filters with ≈60 g/m2 γ-Fe2O3 indicated that about 30% of the Hg0 in Absaloka and Falkirk flue gases was converted to Hg2+ and/or Hg(p). HCl injection (100 ppmv) into the Absaloka combustion flue gas converted most of the Hg0 to Hg2+, whereas HCl injection into the Falkirk flue gas converted most of the Hg0 and Hg2+ to Hg(p). Additions of γ-Fe2O3 and HCl did not have a synergistic effect on Hg0 oxidation. The filtration of Absaloka and Falkirk flue gases through much greater fabric filter loadings of 475 g/m2 γ-Fe2O3 essentially doubled the baghouse Hg[tot] removal efficiency to about 50%. Results from this investigation demonstrate the importance of evaluating potential Hg0 reactants and oxidation catalysts in actual coal combustion flue gases.