Performance Evaluation of a Multi-Branch Liquid-Gas Pipe Separator using Computational Fluid Dynamics

The present thesis aims to evaluate the performance of a multi-branch gas-liquid separator by means of 3D computational fluid dynamics (CFD). Thus, numerical simulations of the two-phase system were performed using various operating conditions to determine the potential of such a separator in terms of separation efficiency and slug handling capacity. The separation efficiency was measured by quantifying the liquid carry over and gas blowby. The capability of 4 multiphase models in a commercial software to represent realistic flow distributions and separation of an oil-gas mixture in the multi-branch separator was evaluated. The inhomogeneous mixture model was the multiphase model providing the most realistic results and best convergence behaviour and was employed for simulations performed to quantify the performance of the separator. The effect of the pressure difference between the two outlets on separation performance was analyzed using multiple different pressures in the gas outlet. A small variation in outlet pressure was found to have a large effect on the flow distribution. Optimal operating conditions regarding the pressure difference between the two outlets have been found. Inlet conditions with various volume fractions showed a small effect on the gas separation performance and no effect on the liquid separation performance and flow distribution. Hydrodynamic slug flow at two different frequencies was studied. A high separation performance, similar to simulations with stable inlet conditions, was seen for the high-frequency slugs while the longer slugs resulted in a slightly reduced performance. Thus, the multi-branch separator showed well slug-handling abilities for the studied slug flow conditions