Numerical investigation of air-injected deoiling hydrocyclones using population balance model.

• Air injection shifts oil droplets to the central region and enhances the separation efficiency. • The migration velocity of oil droplets toward the center is increased using air injection. • The length of the reverse flow region is increased by the air injection. • Air injection with the small diameter of air bubbles enhances the separation efficiency. The need to have an efficient oil-water separator leads to improve and optimize the hydrocyclones. One way to improve the efficiency of a deoiling hydrocyclone is using air injection. In the present study, the effects of air injection on the three-phase flow field, oil droplet distribution, separation efficiency, and the working principles of deoiling hydrocyclones are investigated using the Eulerian-Eulerian multi-fluid model. The numerical results of two and three-phase flow are in good agreement against the experimental data. The oil core which is formed at the center of the deoiling hydrocyclones disappeared due to the air injection. The injected air creates an air-core inside the deoiling hydrocyclone and flows out through the overflow. The results show that the air injection increases the migration velocity of oil droplets and the length of the reverse flow region, leading to the enhancement of the separation efficiency. The air injection also increases the turbulence level and consequently increases the breakup rate of the oil droplets inside the deoiling hydrocyclone with air injection. Therefore, the air-liquid ratio and the injected bubble diameter should be regulated to increase the efficiency of the air-injected deoiling hydrocyclone. The results of different air injection diameters show that the small injection diameter is preferable due to the more penetration inside the deoiling hydrocyclone and increase the reverse flow region. The simulation results show that the air injection with bubble diameter of 42 μm increases the hydrocyclone efficiency up to 95.6%. [ABSTRACT FROM AUTHOR]