Study And Experiment Of Water-In-Oil Emulsion Demulsification Separating In High Frequency Pulse Centrifugal Separation Device

At present, the oilfield has entered high water content stage in our country.The produced mix liquid mostly exists in the form of emulsions.It is difficult to find a way to solve the emulsion demulsification separation technical problem. Therefore, study and experiment of water-in-oil emulsion demulsification about high frequency pulse centrifugal separation device have important theoretical significance and engineering application value.In this thesis, based on surface and interface physics mechanics, dielectric physics, rheology, fluid dynamics, the emulsion demulsification separation is analysed theoretically, droplet motion and coalescence mechanism is studied theoretically under the condition of the electric field, the centrifugal field and interaction field. Four strength theories are proposed, such as the droplets critical tensile stress theory, the droplets critical elastic strain theory, the droplet critical shear stress theory, the droplets critical total potential energy theory. The distribution of droplet surface charge and the electrical potential change are analyzed under the condition of the applied electric field. The distribution of electric field and flow field inside the drum are analyzed, especially the distribution of tangential velocity and shear stress. At the same time, the force and movement of droplet with the action of electric field and centrifugal field produced by drum rotating are analyzed.Numerical simulation by fluent is used to investigate the impact of different rotation speed, reaction time, volume fraction and other physical parameters for the oil-water separation. A detailed numerical simulation of fluid motion and distribution parameters are obtained. The results showed that when the speed increases, the fluid velocity and pressure increase.Water volume fraction of near the drum wall is greater than the center.With the increasing of time, the water volume fraction of the drum bottom is greater than the top. With the increasing speed and time, water content increases. Rotating speed are the obvious effect on the water content and is superior to the pure gravitational field.The phase field method of Cahn-Hilliard equation in COMSOL software is used to study the deformation and coalescence law of dispersed droplets with high-frequency pulsed electric field. The droplet deformation occurs due to electric power driven. The degree of deformation is proportional to droplet size and electric field intensity, and is inversely proportional to viscosity. When the deformation reaches a certain conditions, the droplet will rupture, which depends on the physical properties of the continuous phase and the dispersed droplets. The droplet is subjected to electric field strength that is periodic changes caused by High-frequency pulsed electric field, the frequency variation of the applied voltage mainly is determined by the cycle frequency and itself physical parameters, with the same physical parameters, the critical rupture electric field intensity is greater than the critical coalesce electric field strength. High-frequency pulse electric field square wave, sine wave, triangle wave, and sawtooth waveform have basically same droplet coalescence law. The analysis shows that square wave is optimal, sine wave and triangular wave take second place and saw tooth wave is worst. When the electric field intensity is low, the power generated by the electric field is not enough to resist fluid interfacial tension and adhesion resistance of fluid, no matter how long the time is, droplet will not coalescence. When the field strength rises to a certain range, the electric drive can withstand resistance, the droplets have a tendency to coalesce, and the electric field strength is proportional to coalescence time. When the electric field intensity is greater than the critical droplet coalescence electric field strength, the droplets themselves deformation occurs, and there is a tendency toward the close direction of the electrode, the increase of the electric field reduces the speed of the droplet coalescence. If electric field continues to increase, the droplets move toward the poles, increasing from the center of the droplet, the droplet can not aggregate, but not broken. Then continue to improve field strength is reached the critical droplet deformation and fracture electric field strength, the droplets will not coalesce but rupture itself. For certain physical parameters, there is an optimum frequency of coalescence. With increasing frequency, the coalescence time generally decreases after the first increase,and the coalescence effect of the low frequency range is superior to the high frequency range.In addition, a high-frequency pulse centrifugal demulsification experiment system is designed and made.This experimental system consists of a liquid supply device, breaking devices, liquid storage device, data acquisition device, the heating temperature control device, a high-frequency pulse power supply and other components. The system can realize the precise control of temperature and flow rate, rotational speed, voltage, frequency and other factors that influencing the effect of demulsification. The new type of emulsion breaking device can achieve centrifugal demulsification, high frequency pulsed electric field demulsification, high frequency pulsed electric field centrifugal coupling or union demulsification, respectively. The multi-parameter separation demulsification experiment including voltage, speed, temperature, time, pulse frequency and other parameters have been carried out to obtain the influence law of emulsion demulsification. It is found that the optimal frequency of the emulsion is decided by its own physical parameters.Voltage on the demulsification effect is most obvious, before critical coalescence electric field intensity, demulsification effect increases with the increasing of voltage. With the increase of temperature, demulsification effect increases.the higher the temperature, the lower the viscosity is, the droplet demulsification coalescence easily is separated. At low rotational speed, the rotating speed is inversely proportional to he coupling demulsification effect, and is proportional to the union action demulsification effect. At high speed, the centrifugal field is counterproductive both the union action and coupling action. At low rotational speed, under the coupling action, the demulsification is proportional to the duration under the union action, the demulsification is also proportional to the duration. At high speed, coupling effect of demulsification is inversely proportional to the action duration, demulsification is no obvious rule under the union action. At low speed, union demulsification effect is superior to the coupling effect of various parameters. For low water content of emulsion, the effect of electric field contribution is greater than the centrifugal field, the centrifugal field plays the role of emulsification or demulsification, depending on the speed and physical properties of the emulsion.