Study On Dynamic Demulsification Of Crude Oil Emulsions Via Ultrasound

The form of crude oil usually lies as emulsion, and the dispersive structure and component are very complicated. The aqueous particulate usually exists in oil. There are many unuseful components in oil such as NaCl, CaCl₂, MgCl₂, etc., which can destroy the refining of crude oil. The cost of removing them, especially water, from oil will be increased. The excessive water can make the operation of distillation tower unstable and increase the consumption of energy. The salts in crude oil will hydrolyze to HC1, which is corrosive intensely. At the same time, these salts will deposit on the wall of pipes, reduce the efficiency of heat transport, increase flow resistance, and even block up the pipe. Moreover, the salts and water in crude oil can poison catalysts, so crude oil must be dewatered and desalted before refining.The main methods of crude oil emulsion breaking can be physical, electrical, and chemical. Usually these three ways are used jointly. But sometimes, they aren't practical for some types of crude oil, especially for further crude oil mined. Due to complexity of chemical components and its emulsion structure, it is difficult to demulsify with electrical or chemical methods. If these types of crude oil enter the electrical desalting device, they will destroy the electrical field. So it is emergent to find out other ways to demulsify them. The domestic and foreign researches indicate that crude oil emulsion breaking by ultrasound irradiation is a new method in future.Experiments were designed to demulsify the RUNING crude oil with ultrasound combined with electrical desalting according to the actual desalting process of the oil refinery. The results of dehydration and desalting of crude oil were compared between with ultrasound combined with electrical desalting and with electrical desalting only. The salt content of the crude oil treated by ultrasound combined with electrical desalting could be reduced from 39.46mg/L to 2.2mg/L and water content can be reduced to 0.13% in the optimum experimental conditions. However, after treated by electrical desalting in the same condition, the salt content of the crude oil and the water content can only be reduced to 7.12mg/L and 0.57%respectively. Moreover, after the radiation of ultrasound, it could be observed with microscope that the sizes of water drops grew and amounts reduced. The factors of effecting emulsion breaking by ultrasound, such as sound field, frequency, power of ultrasound, operation temperature, pressure drop of mixing valve, dosage of demulsifying agent and voltage of desalting tank were studied. Monofactorial and multiple factors' orthogonal experiments of demulsification were carried out. The optimum conditions for crude oil desalting in standing field are: flow of oil 20L/h, flow of water lL/h, voltage of desalting tank 6kV, operation temperature 80 °C, ultrasound frequency 10kHz, in standing wave field, power of ultrasound 150W, pressure drop of mixing valve 0.4MPa, demulsifying agent dosage 30ppm. The final salt content in this condition is 1.95mg/L predicted by Statistica6.0. This result was proved creditable by the experiments in the same condition. This salt content of crude oil meets the demands (under 6.00mg/L) of refinery. After treatment in the standing wave field and then in reverberation field, the salt content and water content of the crude oil could be reduced to 1.51 mg/L and 0.06% respectively, which were superior to the results (2.11 mg/L and 0.13%) of being treated in the standing wave field or the results (3.61mg/L and 0.24%) of being treated in reverberation field.We don't consider that ultrasound treatment can completely replace electric desalting process. However, the process of demulsification with ultrasound is not influenced by character of crude oil. So treatment with ultrasound can be considered as pretreatment of electrical treatment, and it can intensify electric desalting by lightening the charge of electric desalting device.