Oscillation characteristics of oil core in the tubular axial vortex separator

Tubular Axial Vortex Separator (TAVS) utilizes a high-speed rotating impeller to create a strong swirling flow for oil-water separation, boasting a single-tube capacity of 10,000 m3/d. It is anticipated to streamline oilfield produced water treatment and reduce carbon emissions. However, prototype tests have revealed that increasing the impeller’s speed does not consistently enhance separation efficiency. To investigate the decline mechanism and establish operational limits, a visualized TAVS test platform was constructed. High-speed cameras recorded oil core deformations, while FFT analysis studied its oscillation. Results showed separation efficiency peaks at 90.4% (water outlet oil droplet size: 55 μm) at 1000 rpm, stable up to 1500 rpm (droplet size rises to 90 μm). However, as rotational speed rises from 2500 to 4000 rpm, efficiency drops significantly (87% to 74.1%), mainly due to enhanced entrainment of large droplets. Above 3500 rpm, the oil core’s radial acceleration is 76.6% of centrifugal acceleration, and its oscillating area nears the oil outlet (Ao/Aout ≈0.85), causing oil discharge through the water outlet. Additionally, FFT confirms the oscillation frequency is directly tied to impeller speed, identifying it as the root cause. Field data corroborates the 1000 rpm optimum, aligning with experiments to support TAVS speed optimization.