Removal of NOx 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 NOx 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 NOx 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 NOx 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 NOx. When both the O3/NO molar ratio and liquid-to-gas ratio were 1.5, the removal efficiencies of NOx 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.