Experimental And CFD Investigations On Centrifugal Flotation Unit For Simulated Oilfield Waste Water Treatment

Flotation is an important technology in oily waste water treatment, which hasbeen widely used for oil/water separation in onshore secondary oil recovery andoffshore petroleum production. However, the large footprint of flotation equipmenthas confined its application to offshore produced water treatment, where the space isstrictly limited. Therefore, coupling flotation technology and centrifugal field can be afeasible way to reduce the footprint in order to apply flotation process to offshorecrude oil industry. Besides air sparged hydrocyclone, low intensity centrifugalflotation units have drawn much attention these years. Based on the concepts ofresidence time and centrifugal intensity, this thesis suggested centrifugal flotation unitwith low centrifugal intensity for oilfield waste water treatment. Both the experimentsand CFD simulations were performed to investigate the oil removal efficiency andanalyze the multiphase flow field.The experiments were carried out in a unit of120mm in diameter. A mixingpump was used to generate microbubbles. Oily water was prepared by diesel. For thefloating oily water treatment, oil was dispersed in water by a static mixer. While forthe emulsified oily water treatment, the emulsion was prepared by pump circulation,with or without emulsifier. The result showed that the oil removal efficiencydecreased with the increasing treatment loading for the floating oily water. Foremulsified oil, it increased at first then decreased with the increasing loading whencoagulant was added. The optimal flow rate was3L/min for both the floating oil andemulsified oil as a compromise between the efficiency and capacity of the unit. Inaddition, the effects of air dissolving pressure and the concentration of oil were alsoinvestigated.In order to obtain the flow field characteristics,3-dimensional computationalfluid dynamics (CFD) simulations were performed for the gas-liquid multiphase flow.Eulerian-Eulerian model was selected to model the gas-liquid flow and the Schiller–Naumann model was used to calculate the momentum exchange term in themomentum equations. Dispersed phase RNG k-? model was used to describe theturbulence. The results of simulation were used to analyze the flow field, the air volume fraction profile and the effect of bubble diameter was investigated. Thesimulated air volume fraction profiles were compared with experimental observation.