Liquid-liquid flows and separation
The transport and separation of oil and water is a vital process to the oil and chemical industries. Fluids exiting from oil wells usually consist of gas, oil and water and these three phases need to be transported and separated before they can be processed further. Operation of the primary separators has often proved to be problematic due to the change in composition of the fluids as the well matures, often accompanied by the build up of sand or asphaltenes. These vessels are very expensive to install so there is motivation to improve their design and performance. One major factor affecting separator performance is the phase distribution of the inlet flow, as reflected in the flow pattern and droplet size. In this work, flow pattern boundaries and drop sizes of liquid-liquid dispersions were measured for vertical and horizontal flow of a kerosene and water mixture in a 0.063m tube. Drop size was investigated by using two different laser optical techniques. A laser backscatter technique was employed for concentrated dispersions and a diffraction technique was used at low concentrations. In order to develop a greater understanding of separator performance, a 1/5th-scale model was constructed of diameter 0.6m and length 205m. Residence Time Distributions were obtained for a range of different internal configurations and flow rates using a colorimetric tracer technique. Flow rates of 1.5-4 kg/s oil and 1-4 kg/s water were used and the vessel was equipped with a perforated flow-spreading baffle at the inlet and an overflow weir. Experiments were performed with no internals and with dip or side baffles. The side baffles acted to create quiescent zones within the vessel while the dip baffle caused a local acceleration of both phases. These situations are similar to those that can be caused by blocked internals or existing baffling or structured packing within field separators. A Residence Time Distribution model of a primary separator, the Alternative Path Model, was developed using transfer functions. This model has the ability to reproduce features of the experimental data by representing the flow as a series of continuous stirred tanks in series or in parallel. The model was used to develop parameters that could be used to obtain information about the performance of the separator. This model was also applied to Residence Time Distribution data obtained from field separators by BP Exploration, to relate features of the pilot scale separator to the field vessels.