CFD Simulation of Three-Phase Separator: Effects of Size Distribution

The gas/oil/water separation in a three-phase horizontal separator, employed by the ADCO company in Abu Dhabi, was studied previously using the Eulerian-Eulerian with the k-ε model assuming mono-dispersed secondary phases (oil and water). The separator was equipped with new internals due to the increasing amounts of water and Gas-to-Oil Ratio GOR from the field. The approach allowed the description of several features of the internal flow but the prediction of the overall efficiency was largely overestimated compared to the measured value from the field. The source of the discrepancy could be traced back to the assumption of mono-dispersed secondary phases and possibly to the unknown structure of the size distribution at the inlet of the separator preventing thus a correct modeling of drag between the phases and, hence, influencing momentum and secondary phases (oil and water) dispersion. Investigations, using the Population Balance Model, for size distribution, were conducted. Normal and Skewed distributions were employed to represent, only, the secondary water phase due to the limitation of the population model used to only one secondary phase. The paper presents, in addition to the separation efficiency, the internal multiphase flow behavior in terms of overall and local phase distributions. The simulations with PBM model showed a clear improvement of the results in terms of separation efficiency compared with field tests although no experimental data related to the size distribution were available.