Microbubble-based process for the enhancement of microfine and heavy oil droplets swirl separation in axial inlet hydrocyclone

Because of the pressing demand for environmental governance and resource utilization of pollutants, the separation of oil in oily wastewater has become a research hotspot in water treatment, with swirl de-oiling being one of the most effective separation technologies. However, the current swirl separation technology has significant shortcomings when separating microfine and heavy oil droplets. In this study, a new process based on composite force field enhanced separation was developed to enhance swirl separation of microfine and heavy oils by injecting microbubbles into the axial inlet hydrocyclone. The performance between the standard swirl and the proposed swirl air flotation processes in separating microfine and heavy oil was evaluated for overall separation efficiency, particle grade efficiency, and outlet particle size distribution. The results showed that the swirl air flotation process enhanced the separation efficiency by 24.2 % and 15.9 % for heavy oil (density of 950 kg/m3) and light oil (density of 825 kg/m3) with particle size distribution of EP2, respectively. The main enhancement was in the particle size range of 11.2–58.9 μm, and the largest enhancement in separation capability was achieved for oil droplets with a particle size of 16.4–35.3 μm, with an enhancement of approximately 18 %. Furthermore, the introduction of a swirl-stabilizing tube improved the separation effect and anti-fluctuation of the device. This study provides insights supporting practical applications of swirl air flotation and a provides basis for further studies aimed at broadening the axial inlet hydrocyclone application range.