Investigation of the oil—gas separation in a horizontal separator for oil-injected compressor units

Abstract

This article presents an investigation of the separation process as well as the separation efficiency for a horizontal oil—gas separator, which is widely used in the oil-injected compressor units. The trajectories of oil droplets with different diameters in the separator were simulated by using the discrete phase model in combination with the gas flow model. The laser diffraction technique (Malvern) was applied to measure the oil concentration and thereby the separation efficiency. By varying the parameters such as the oil injection flowrate, compressor discharge pressure, and oil—gas mixture inlet velocity, the main factors influencing the separation efficiency were identified. The results indicate that the trajectories together with the residence time of the oil droplets in the separator vary significantly with the droplet sizes. The separation efficiency increases from 99.81 to 99.93 per cent as the oil injection flowrate rises from 567 to 1182 l/h. An optimal discharge pressure exists for the separation efficiency, and the highest separation efficiency was obtained at a discharge pressure of 0.65 MPa. The simulated minimum oil droplet that can be separated completely during the first step separation is ∼17 μ m, which has a good agreement with the measured data of 17.7–20.5 μ m.