Removal of NO in flue gas using vacuum ultraviolet light/ultrasound/chlorine in a VUV-US coupled reactor

•A novel process on integrated removal of NO and SO2 was proposed.•VUV/US/chlorine coupling system was used to remove NO and SO2.•Key influencing factors, active species and products were investigated.•Mechanism of NO removal was revealed.

Removal process of NO and integrated removal process of NO and SO2 using vacuum ultraviolet light (VUV)/ultrasound (US)/chlorine system in a VUV-US coupled reactor were developed. The feasibility, key influencing factors and mechanism of removal process were investigated. The results reveal that SO2 is almost completely removed in most experimental conditions due to its very high solubility and good reactivity. Addition of US enhances NO removal, and US of lower frequency is more effective than that of higher frequency. Vacuum ultraviolet light was found to be the most effective light source for removal of NO in VUV/US/chlorine system. Removal of NO was enhanced at a higher ClO− concentration, light intensity, ultrasonic energy density or oxygen concentration, but was inhibited with the increase of NO, SO2 or CO2 concentration. Initial solution pH and reaction temperature were found to have double effect on NO removal. The key active species in different systems were detected, indicating that VUV/US/chlorine system had the highest hydroxyl radical yield. High oxygen concentration favors the generation of ozone. NO is mainly removed by oxidations of hydroxyl radical, ClO− and O/O3. Amplification of removal process were also discussed.