Three Dimensional CFD Simulation of Gas-Liquid Separation in a Two-Phase Separator with a Vane Pack Mist Eliminato

Oil well production is the extraction of petroleum liquids and gaseous hydrocarbons from porous formations within the earth. Two and three phase separators are used in the bulk separation of liquids from the gases, notably natural gas. Prior to compression, the residual fine mist water and oil droplets are removed from the natural gas sales stream by a combination of gas gravity settling and droplet impaction on vane pack surfaces in two phase separators. Industry standards published by API and GPSA provide various methods for sizing the separator diameter. The sizing methods are conservative and based on a plug flow assumption.;This research utilized ANSYS FLUENT R18.1 CFD software to three-dimensionally simulate the steady-state, incompressible, multiphase flow of a methane-water mixture in a full-scale, 48" diameter vertical separator fitted with a down flow inlet diverter and a vane pack mist extractor. Multiphase one-way coupled Discrete Phase Modelling was performed on the continuous phase flow field to determine the gas gravity settling fraction and vane pack trapping efficiency. Constant diameter water droplets and Rosin-Rammler diameter distributions ranging from 0.1 mum to 250 mum were evaluated with continuous phase separator inlet velocities up to 80 ft/s at 40 psig and 650 psig. The results show that the flow field is highly complex and three dimensional. Many areas of the flow field exceed the Souders Brown terminal velocity computed with industry standard methods. Gas gravity settling is a strong function of pressure. Less than 5% of water droplets settle out of the gas at 650 psig. Vane Pack trapping efficiencies are predicted to be as high as 100% depending on droplet diameters greater than 20 mum. Droplets 15 mum and less pass through the vane pack. Pressure drop across the vane pack is minimal. CFD has proven to be a useful tool for evaluating separator and vane pack performance.