Three-phase Eulerian computational fluid dynamics of air–water–oil separator under off-shore operation

Abstract

A three-phase transient Eulerian computational fluid dynamics (CFD) model was developed to investigate the effect of three angular motions (rolling, yawing, and pitching) on the separation efficiency of an air–water–oil separator. The horizontal cylindrical separator included a feed inlet, a gravity separation zone with a coalescer for water and oil separation, and a mist elimination zone. The CFD model consisted of the continuity, momentum, and standard k-ε turbulence equations. The CFD equations were solved in a moving reference frame to take into account the angular motions. The exit pressures at the water and oil outlets were controlled using a user-defined function since the CFD model without pressure control resulted in backflow from the water outlet, which was not realistic. CFD cases, such as no motion, rolling, yawing, 2° pitching, and 4° pitching with a period of 8 s were simulated with exit pressure control. The angular motions with pressure control showed a stable cyclic behavior with a high oil separation efficiency. However, the 4° pitching motion decreased the oil recovery to 93% with 77% water purity at the water outlet.