Residence time distributions and flow behaviour within primary crude oil-water separators treating well-head fluids

Within primary crude oil separators used by the oil industries, the residence time distribution of both organic and aqueous phases has been obtained for the purpose of flow diagnostics. This paper describes the application of the Alternative Path Model developed by Simmons et al. (2002) to give a quantitative description of the hydrodynamics and mixing within several field separators. Parameters developed from the model are used to describe the degree of mixing within the vessels. The model shows that vessel performance is affected by the internal configuration (flow smoothing baffles and separation plates) and the primary separation duty (gas-liquid or oil-water). The presence of baffling is shown to reduce the turbulence within the flow for oil-water separation, but less so for gas-oil separation, which had the overall effect of increasing mixing levels, perhaps due to the buoyancy of the fast rising gas bubbles. The presence of secondary peaks on some of the measured residence time distributions indicates the presence of secondary flows within the main body of the separators. This was most noticeable when the differential velocity between the oil and water phases was high.