Interpretation of the flow characteristics of a primary oil-water separator from the Residence Time Distribution

The separation of oil and water mixtures is a vital process in the oil and chemical industries. Fluids exiting from oil wells. usually consist of gas; oil and water and the primary stage of phase separation is usually performed by horizontal gravity separators. The performance of these vessels is inferred from in-situ measurements of the Residence Time Distribution (RTD). To relate the features of the RTD to the flow characteristics, a colorimetric tracer technique was used to obtain data from a pilot-scale separator. This separator had a diameter of 0.6 m and length 2.5 m. Flow rates of 1.5-3 kg s(-1) kerosene, and 1-2.5 kg s(-1) water, were used and different internal baffles were installed to mimic conditions in existing field separators. Differences in the Mean Residence Time (MRT) obtained from the experiments compared with the estimated MRT (based on dividing the volume throughput of each phase by the volume it occupies) leads to differences of approximately +/-60%. These differences were found to be more sensitive to flowrate than the internal configurations used in the vessel. When significant changes were observed due to internals, these were when the internals used (dip baffles) interfered with the location of the oil-water interface.