Effects of metal ions on Hg0 re-emission under air and oxy-fuel combustion atmospheres in a WFGD system

Abstract

The effects of metal ions, including Fe2+, Fe3+, Mn2+, and Cu2+, on Hg0 re-emission were investigated in a simulated wet flue gas desulfurization (WFGD) system under air and oxy-fuel combustion atmospheres. The results show that in the presence of metal ions, Hg0 re-emission is enhanced under a N2 atmosphere but inhibited under N2/9%O2, air, and oxy-fuel combustion atmospheres. In the inhibition cases, Hg2+ reduction and Hg0 re-emission were accelerated in the initial stages of the experiments. Fortunately, Fe2+, Fe3+, Mn2+, and Cu2+ have a positive impact on mercury stabilization in the liquid phase, and the precipitates of Fe2+/Fe3+ can also adsorb mercury in the solid phase, thus offsetting the acceleration of Hg0 re-emission in the initial stage. Therefore, Hg0 re-emission is suppressed by metal ions under N2/9%O2, air, and oxy-fuel combustion atmospheres. With an increase in CO2 concentration, the inhibition of Fe2+, Fe3+, and Cu2+ was intensified, whereas the suppression by Mn2+ was slightly weakened. Under an oxy-fuel combustion atmosphere, increasing O2 concentration would promote the inhibition of Mn2+ on Hg0 re-emission, but hardly affect the inhibitory effect of Cu2+.