Removal of mercury from flue gas using coal gasification slag

Abstract

Coal combustion often produces mercury emissions. Coal gasification fine slag (FS) was used to remove Hg0 from flue gas. To increase the removal efficiency, two ionic liquids (IL-T and IL-B) were immobilized on the surface of FS. The mercury removal performance was evaluated in a fixed-bed reactor in the presence of SO2 + O2. The experimental results showed that the mercury removal efficiency increased when the adsorbents were supported by ionic liquids (FS-T and FS-B). The effect of 0.6% SO2 on the capture of Hg0 was negligible for all three adsorbents. The total mercury removal efficiencies exceeded 90% for FS-T and FS-B in the atmosphere of 0.6% SO2 + 6% O2. When the initial mercury concentration was 60 μg/m3, the effective adsorption time was about 80 min for FS and longer than 120 min for FS-T and FS-B. In the presence of 0.6% SO2 + 6% O2, Hg0 and Hg2+ were detected in exhaust gas using FS and FS-B and in solid phase using the three adsorbents. According to XPS analysis, an oxidation reaction occurred on the surface of FS and FS-T. For FS-B, the Br− anion of IL-B was the active site and oxidized Hg0 to Hg2+ on the surface as well as in the gas phase.