Preparation of fly ash adsorbents utilizing non-thermal plasma to add S active sites for Hg0 removal from flue gas

Abstract

This paper proposed a method of preparing efficient, cost-effective and eco-friendly fly ash (FA) adsorbents utilizing non-thermal plasma technology in H2S atmosphere to remove elemental mercury (Hg0) in the coal-fired flue gas. Characterization of fly ash samples showed plasma treatment had little effect on porous structure, surface morphology and crystal structure of fly ash samples. It was found that elemental sulfur (S) particles, which were active site for Hg0 removal, was incorporated successfully on the adsorbents’ surface. The loaded S particles showed superior Hg0 oxidation ability and low remission possibility. The Hg0 removal experiments were conducted in a bench-scale fixed-bed reactor. After plasma treatment, the initial Hg0 removal efficiency of modified fly ash had increased significantly compared to raw fly ash (2.8–3.6 times). The effects of treatment time (0.5–5 min), adsorption temperature (60–180 °C) and flue gas components on Hg0 removal efficiency were also analyzed in the present study. The Hg0 removal efficiency had a positive correlation with adsorption temperature. HCl, O2 and NO in the flue gas could promote the removal of Hg0, whereas SO2 had an adverse effect. The Hg0 adsorption performance was better with longer treatment time largely due to more S was loaded on the fly ash surface, which was confirmed by XPS and SEM results. Additionally, the temperature-programmed decomposition (TPD) experiments further proved existing species of mercury in used modified fly ash were black HgS and red HgS. Finally, the mechanism of fly ash adsorbents modified by non-thermal plasma technology to remove Hg0 was proposed.