Numerical simulation and experimental research on the oil removal efficiency during the oily wastewater separation by hydrocyclone

Some oil and gas fields in China are located in the north, and in winter, oil fields face technical difficulties in separating oil and water from high viscosity condensate produced fluids. This article proposes a low-temperature oil-water separation scheme using a preheated hydrocyclone, with a focus on studying the separation effect of oil-water mixtures with different oil contents by varying the overflow diversion ratio and inlet flow rate of the hydrocyclone. The structure of the cyclone was optimized using response surface methodology (RSM) through three-dimensional modeling. The Euler multiphase flow model was used to study the distribution characteristics of the flow field and phase volume fraction of the oil-water two-phase medium inside the hydraulic cyclone under different injection parameters. The results show that when the oil content of the mixed liquid is 10% and the viscosity of the oil phase is 27-31mPa·s, an increase in the overflow diversion ratio is beneficial for the rapid separation of low-density phase media. If the diversion ratio is too high, it will cause the liquid flowing out of the overflow port to form an oily mixture again. In our experiment, the optimal overflow diversion ratio is 0.2, and the effective oil removal efficiency can reach 92%. The influence of the oil content in the mixed liquid on the oil-water separation efficiency of the cyclone is achieved through the interaction of viscous drag and centrifugal force on the radial partial pressure and tangential flow velocity. As the oil content and viscosity of the mixed liquid increase, the radial flow resistance experienced by the cylindrical and conical sections of the cyclone will increase. The radial partial pressure, pressure gradient, and radial flow velocity of the aqueous medium will also decrease, and the separation efficiency will also decrease accordingly.