Dual Roles of Nano-Sulfide in Efficient Removal of Elemental Mercury from Coal Combustion Flue Gas within a Wide Temperature Range

摘要

Nanostructured zinc sulfide (Nano-ZnS) has been demonstrated to be an efficient adsorbent for removal of elemental mercury (Hg-0). However, the Hg-0 removal performance deteriorates once the flue gas temperature deviates from the optimal temperature of 180 degrees C. In this study, ultraviolet (UV) light, which is generally generated through corona discharge in electrostatic precipitators (ESPs), was adopted to enhance Hg-0 removal by Nano-ZnS. With the UV irradiation, Nano-ZnS exhibited excellent performance in Hg-0 removal within a much wide temperature range from room temperature to 240 degrees C. A Hg-0 removal efficiency of 99% was achieved at 60 degrees C even under extremely adverse conditions, that is, gas flow with an extremely high gas hourly space velocity but without hydrogen chloride. At low temperatures, Hg-0 was mainly oxidized by superoxide radicals (center dot O-2(-) ) and hydroxyl radicals (center dot OH) generated by UV photostimulation to form mercuric oxide (HgO). At high temperatures, most Hg-0 was immobilized as mercuric sulfide (HgS), as both the enhanced chemisorption and the accelerated transformation of HgO to HgS facilitated the formation of HgS. Compared with commercial activated carbon, injection of Nano-ZnS can utilize the UV in ESPs to warrant a higher Hg-0 removal efficiency within a much wider temperature range.