Simulation of Free Interface Shape and Complex Two-phase Flow Behavior in a Gas-liquid Cylindrical Cyclone Separator

The Gas Liquid Cylindrical Cyclone (GLCC) separator is an attractive compact separator alternative to the conventional vessel-type two-phase flow separator. Thus, it is important to develop predictive tools for design and to be able to improve the technology of the GLCC. Previous studies on the GLCC have focused on mechanistic models capable of predicting the operational envelope for liquid carry-over and on understanding the flow field in the GLCC. This study investigates the effects of the free interface between the gas and liquid on the flow field below the GLCC inlet. CFD simulations of single-phase and two-phase flow are carried out. A commercially available CFD code (CFX 4.1) is used to model two-phase flow in an axisymmetric geometry that represents the GLCC configuration. Two multiphase flow models, namely, the multi-fluid model and the homogenous (or free-interface) model are used. Both models are capable of predicting the free interface that forms between the gas and liquid phases. The predictions of the free interface shape are compared to flow visualization experiments. Good agreement is obtained between the observations and the simulations. INTRODUCTION Developing compact separators remains a critical and yet overlooked problem for the oil and gas industry. This is an important issue since the future of the oil and gas industry lies in offshore production. The Gas-Liquid Cylindrical Cyclone (GLCC) separator is an attractive alternative to the conventional vessel-type two-phase flow separator, especially for offshore platforms in oil and gas production operations. The GLCC is shown schematically in Figure 1. The gas and liquid mixture flows through an inclined inlet section, to enhance stratification, prior to reaching a tangential inlet slot. As a result of the tangential inlet, a vortex is formed causing the gas and liquid to separate due to the centrifugal force. The liquid moves toward the wall and downward, while the gas flows to the center and exits from the top. For certain operating conditions, some liquid droplets flow with the gas and move up toward the gas leg. This phenomenon is referred to as liquid carry-over. On the other hand, some gas bubbles may be entrained with the liquid and exit from the bottom of the GLCC (gas carry-under). Experimental observations indicate that a free interface forms between the gas and liquid phases that has a parabolic shape. Gas bubbles that are entrained in the liquid phase below the interface are forced to migrate toward the center of the vortex to form a gas bubble filament due to the centrifugal force.