Interference Effect of H2O on Hg0 Removal by a Mercury Sorbent in an Oxyfuel-Combustion Atmosphere

The H2O concentration in an oxyfuel-combustion atmosphere is higher than that in a traditional combustion atmosphere, which will affect the mercury removal process. Therefore, it is necessary to carry out a research on the interference effect of H2O on mercury removal under an oxyfuel-combustion atmosphere. In this paper, corn straw char was modified by NH4Cl, and related experiments were carried out using a fixed-bed reaction system. The characterization results of the sorbent showed that the modification enhanced its physical and chemical adsorption capacities. The addition of H2O in a NO atmosphere was not conducive to mercury removal but could alleviate the toxicity of SO2 on the adsorbent in a SO2 atmosphere. The coexistence of H2O and NO significantly inhibited the mercury removal, but some nitrate ions were generated during the process, which slightly weakened the negative effects of H2O. The coexistence of low-concentration H2O and SO2 would weaken the poisoning effect of SO2 on the mercury sorbent, and high-content H2O would react to generate excess H2SO4 to block the surface pores. SO3 could assist Hg-0 oxidation, while H2O would hinder the transformation of SO2 into SO3. In a HCl atmosphere, highconcentration H2O (20%) inhibited mercury removal, while lower-concentration H2O (5-15%) showed an opposite behavior. The low concentration of H2O did not affect the oxidation of Hg-0 by HCl, and it was accompanied by the formation of substances conducive to mercury removal. The increase of the H2O concentration would hinder the oxidation reaction of HCl and Hg-0.