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

Abstract

The H 2 O 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 H 2 O on mercury removal under an oxyfuelcombustion atmosphere. In this paper, corn straw char was modified by NH 4 Cl, 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 H 2 O in a NO atmosphere was not conducive to mercury removal but could alleviate the toxicity of SO 2 on the adsorbent in a SO 2 atmosphere. The coexistence of H 2 O and NO significantly inhibited the mercury removal, but some nitrate ions were generated during the process, which slightly weakened the negative effects of H 2 O. The coexistence of low-concentration H 2 O and SO 2 would weaken the poisoning effect of SO 2 on the mercury sorbent, and high-content H 2 O would react to generate excess H 2 SO 4 to block the surface pores. SO 3 could assist Hg 0 oxidation, while H 2 O would hinder the transformation of SO 2 into SO 3 . In a HCl atmosphere, highconcentration H 2 O (20%) inhibited mercury removal, while lower-concentration H 2 O (5−15%) showed an opposite behavior. The low concentration of H 2 O 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 H 2 O concentration would hinder the oxidation reaction of HCl and Hg 0 .

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