Simultaneous removal of Hg0 and SO2 from flue gas using vacuum ultraviolet radiation combining with absorption of urea solution

Abstract

A novel process on simultaneous removal of SO2 and Hg0 from flue gas using vacuum ultraviolet (VUV) radiation combining with absorption of urea solution was developed. Several process parameters (e.g., VUV radiated power, O2 content, solution pH, solution temperature, SO2 content, liquid-gas ratio, urea concentration and Hg0 content) of Hg0 removal process were studied and optimized in a semicontinuous and small-scale photochemical reactor. Products and intermediates of SO2 and Hg0 simultaneous removal were measured. Chemistry of Hg0 removal was also investigated initially. Results show that an increase in VUV radiated power, O2 content or liquid-gas ratio promotes Hg0 removal. Increasing solution temperature, SO2 content or Hg0 content reduces Hg0 removal efficiency. Increasing solution pH or urea concentration has a dual impact on Hg0 removal. SO2 reaches 100% removal efficiency under all test conditions. The highest simultaneous removal efficiency is 100% for SO2 and 98.1% for Hg0. Hg2+ and SO42− are the final products of Hg0 and SO2 oxidation, respectively. Ozone and hydroxyl free radicals are successfully captured. The ozone, oxygen atom and hydroxyl free radicals are proved to be the most important oxidants for oxidation removal of Hg0.