Removal of NO_x and PM from Non-Road Mobile Machinery by the Combination of Ozone Oxidation and Venturi Scrubbing

Non-road mobile machinery (NRMM) emits a significant amount of NO_x and particulate matter (PM), yet there is still a lack of economically feasible purification technologies up to now. In response to this issue, and taking into account the relatively flexible installation conditions for exhaust purification systems in NRMM, this study proposes a novel technical approach for the simultaneous removal of NO_x and PM based on gas-phase O₃ oxidation combined with Venturi scrubbing. The effects of O₃ oxidation on the PM physicochemical properties, O₃ concentration, liquid-to-gas (L/G) ratio, and surfactant addition in the scrubbing liquid on the PM removal and simultaneous removal of PM and NO_x were investigated. The results showed that O₃ oxidation significantly promoted PM removal in the absence of NO, which was attributed to the increase in the hydrophilicity of PM resulting from O₃ oxidation. However, O₃ preferentially reacted with NO, thereby reducing the removal efficiency of PM under the conditions when PM and NO coexisted. Adding surfactants to the scrubbing liquid improved PM removal and increasing the liquid-to-gas ratio improved the removal of both PM and NO_x. When both the O₃/NO molar ratio and liquid-to-gas ratio were 1.5, the removal efficiencies of NO_x and PM reached 87% and 92%, respectively, and O₃ escape was also effectively controlled. These findings demonstrated that the combination of gas-phase O₃ oxidation and Venturi scrubbing is a promising purification technology for NRMM exhausts.