Abstract
Computational simulations of a full-scale, horizontal liquid-liquid gravity separator have been undertaken by Southwest Research Institute (SwRI®) to model the batch separation of oil and water flow in two different software packages. Separator modeling using computational fluid dynamics (CFD) represents a powerful and economical option for design, but caution must be used in the setup and interpretation of data. Many examples are available in literature of poor agreement between simulation results and experimental/field data. Results require interpretation before taking them at face value due to the complexity of the various submodels that can be utilized. This work offers an evaluation of multiphase flow modeling techniques in both ANSYS® Fluent® and in Siemens PLM STAR-CCM+®, and provides a unique comparison between the CFD solvers that cover a broad range of flow rates, water cuts, and viscosities. Verification of the accuracy of each software package to reproduce empirical results while reducing computational resources has been accomplished.
The performance of a horizontal gravity separator with perforated baffles has been investigated using CFD. The simulations were carried out using an Eulerian-Eulerian multiphase approach, using monodisperse water droplets in an oil-continuous phase. Separation efficiencies and fluid concentration percentages at several locations throughout the test separator were compared against experimental results for a wide range of inlet flow rates, water cuts, and oil viscosities. Initial computational results indicated that the horizontal liquid-liquid separator can be modeled within 7% accuracy of the local experimental separation efficiency values for the various test conditions in both software packages. An additional simulation with a modification to a known drag model in Fluent showed a significant improvement to the oil-in-water (OiW) concentration in comparison to the same simulation conducted in STAR-CCM+. This effort demonstrates the capability of reliable modeling of multiphase flow fields inside of horizontal gravity separators and offers a viable option for aiding in the design of separation equipment.
