NUMERICAL-SIMULATION OF THE GAS-LIQUID FLOW IN A ROTARY GAS SEPARATOR

The presence of free gas at the pump intake adversely affects the perf ormance of an electrical submersible pump (ESP) system, often resultin g in low efficiency and causing operational problems. One method of re ducing the amount of free gas that the pump has to process is to insta ll a rotary gas separator. The gas-liquid flow associated with the dow nhole installation of a rotary separator has been investigated to addr ess its overall phase segregation performance. A mathematical model wa s developed to investigate factors contributing to gas-liquid separati on and to determine the efficiency of the separator. The drift-flux ap proach was used to formulate this complex two-phase flow problem. The turbulent diffusivity was modeled by a two-layer mixing-length model a nd the relative velocity between phases was formulated based on publis hed correlations for flows with similar characteristics. The well-know n numerical procedure of Patankar-Spalding for single-phase flow compu tations was extended to this two-phase flow situation. Special discret ization techniques were developed to obtain consistent results. Specia l underrelaxation procedures were also developed to keep the gas void fraction in the interval [0, 1]. Predicted mixture velocity vectors an d gas void fraction distribution for the two-phase flow inside the cen trifuge are presented. The model's predictions are compared to data ga thered on a field scale experimental facility to support its invaluabl e capabilities as a design tool for ESP installations.