Flue gas treatment with ozone oxidation: An overview on NOx, organic pollutants, and mercury

Traditional flue gas pollutants treatment technologies are installed with their individual function. Industries usually make simple combination and increase operation load of equipment to face with the increasing stringent environmental stress and emission standard. Especially, these technique routes are not available to industrial boilers and furnaces because of specific conditions, such as unsuitable temperature window, complicated components in flue gas, and flexible operation. Simultaneous removal of multi-pollutants within one or two devices is a prospective direction that can save space occupation and cost. Interestingly, the solubility of NOx and mercury increases with its valance state, and organic pollutants can be degraded into nontoxic small molecules by oxidation. Ozone is a strong gas phase oxidant that can achieve pre-oxidation at low temperature, following by post-absorption to completely remove oxidized products. This review focuses on research progress involved in homogeneous and heterogeneous catalytic oxidation of NOx, organic pollutants, and mercury by ozone, as well as NOx absorption regarding of its full path removal. The reaction mechanism, kinetics, operation parameters, conversion efficiency and ozone residual are all summarized in detail. This paper also systematically reviews various approaches in catalytic ozonation towards improving catalytic activity, selectivity, and stability, as well as lowering temperature, such as active metals, metal loading contents, supports, precursors, and other modification. Finally, the overall technique route of simultaneous removal of multi-pollutants by ozone is analyzed. In conclusion, the ozone oxidation technology is advantaged in flue gas pollutants treatment, including low temperature, no massive adjustment in operation and original devices, saving space, no secondary pollution, N/S sources recovery, and potential to ultra-low emission.