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Chen Q.,Harbin University of Science and Technology | Liang W.,Harbin University of Science and Technology | Song C.,Harbin University of Science and Technology | Liu Z.,Design Institute of Daqing Oilfield | And 2 more authors.
Gaodianya Jishu/High Voltage Engineering | Year: 2014

In electric dehydration of crude oil, the type and intensity of the applied electric field determine the efficiency and the electric field stability. To obtain an appropriate type and intensity of dehydration electric field for crude oil emulsions with various initial moisture contents, we tested the dehydration effectiveness of crude oil emulsion in laboratory experiments under AC and DC electric field, respectively. We also theoretically analyzed the dehydration mechanism, consequently established a water droplet motion model in electric field, and obtained the expressions of the electrodispersion field intensity and the electrophoretic velocity of water droplets. The results show that there exists optimal critical electric field strength: once the electric field exceeds this critical value, electrodispersion occurs and it lowers the electric dehydration efficiency. Compared with that under DC electric field, the dehydration of emulsion with high moisture content under AC electric field is faster and the dehydration electric field is more stable. However, the DC electric field can enhance the dehydration effectiveness for emulsions with low moisture content, which can be used for deep purification. The proposed theoretical model can well explain the dehydration phenomenon under different voltages, and it provides a theoretical foundation for determining the optimal intensity and type of dehydration electric field for oil emulsion with different moisture contents. Source


Chen Q.,Harbin University of Science and Technology | Liang W.,Harbin University of Science and Technology | Song C.,Harbin University of Science and Technology | Liu Z.,Design Institute of Daqing Oilfield | And 2 more authors.
Huagong Xuebao/CIESC Journal | Year: 2014

In order to improve the efficiency of oil dehydration and maintain the stability of dehydration electric field to satisfy the technical requirements of compactness and efficiency on onshore and offshore oil processing platform, effects of pulsed electric field strength and frequency on the emulsion dehydration are studied. The relationship between water droplet deformation and electric field strength is derived based on the telescopic model and force balance of water droplet. The expression of applied electric field frequency is obtained based on the vibration kinetic model and force balance with water droplet vibration, so that the optimal dehydration electric field frequency can be determined theoretically. The results show that there exist optimal dehydration electric field strength and frequency during electric dehydration of emulsion. The dehydration rate first increases with the external electric field, and then declines when the external electric field exceeds the critical breakdown strength, with the dehydration electric unstable. When the external electric field frequency reaches the resonance frequency of water droplet, the amplitude of water droplet is the maximum and the dehydration effect is the best. ©All Rights Reserved. Source


Chen Q.,Harbin University of Science and Technology | Song C.,Harbin University of Science and Technology | Liang W.,Harbin University of Science and Technology | Zheng T.,Harbin University of Science and Technology | And 3 more authors.
Huagong Xuebao/CIESC Journal | Year: 2015

Kinetics behavior of droplet deformation under electric field is important in the research on emulsion electric dehydration mechanism. In order to study the dynamic behavior of water droplets under non-uniform electric field, a simulation model of droplet under non-uniform electric field was established through the phase field method based on Cahn-Hilliard formulation. The distributions of charge density and electric field force on the droplet surface as well as the coupling effect of flow field and electric field were investigated during the process of droplet deformation, moving and coalescence. The influences of droplet size, electric field strength and non-uniform coefficient on droplet behavior were simulated and analyzed. The experimental study on the emulsion dehydration under non-uniform electric field was conducted by using the small dehydration test system in laboratory, and the droplets motion in the emulsion under different conditions was observed and analyzed by high-speed camera. The distribution of polarization charges was different on the droplet surface under non-uniform electric field, increasing from the center to both ends of the droplet. The values of polarization charge and Maxwell stress at droplet's one end surface closed to electric field concentrated area were the largest. The increase of electric field strength, electric field non-uniformity coefficient or droplet diameter could lead to larger droplet deformation, faster moving of droplet to concentrated electric field area, and higher coalescence rate. ©, 2015, Chemical Industry Press. All right reserved. Source


Chen Q.,Harbin University of Science and Technology | Song C.,Harbin University of Science and Technology | Liang W.,Harbin University of Science and Technology | Liu Z.,Design Institute of Daqing Oilfield | And 2 more authors.
Gaodianya Jishu/High Voltage Engineering | Year: 2016

Droplet deformation and motion behavior under electric field are important contents in the research of electric dehydration mechanism. In order to research movement characteristics under different electric field types, a simulation model of droplet was established through the phase field method under uniform and non-uniform electric field. The distributions of charge density and electric field force on the droplet surface as well as the coupling effect of flow field and electric field were investigated during the process of droplet deformation, moving and coalescence. Moreover, the droplet deformation and motion behavior were simulated and analyzed under uniform and non-uniform electric field. The results show that the tensile deformation and migration of water droplets will both occur under AC non-uniform electric field. The distribution of polarization charges is different on the droplet surface under non-uniform electric field, increasing from the center to both ends of the droplet. The values of polarization charge and Maxwell stress at droplet's one end surface closed to electric field concentrated area are the largest. The electric field makes the surrounding fluid of water droplets to rotate and to generate different intensity flow fields, then the flow field and the dipole attraction force will both make the droplets coalescence rate faster. Within a certain range, the improvement of electric field intensity can increase collision probability and dipoalr interaction of water droplets under the non-uniform electric field when compared with uniform electric field. However, the higher strength of electric field can also make water droplets broken easily. © 2016, High Voltage Engineering Editorial Department of CEPRI. All right reserved. Source


Chen Q.,Harbin University of Science and Technology | Song C.,Harbin University of Science and Technology | Liang W.,Harbin University of Science and Technology | Liu Z.,Design Institute of Daqing Oilfield | And 2 more authors.
Gaodianya Jishu/High Voltage Engineering | Year: 2015

In order to improve the dewatering efficiency of onshore and offshore oil platform, we studied the dehydration characteristics of emulsion under non-uniform electric field with coaxial cylindrical electrode structure. Through analyzing water droplets polarization characteristics in non-uniform electric field, we established the models for the water droplet polarization and bearing stress, and analyzed the dynamic characteristics of droplet movement, droplet coalescence, and rupture. The results show that the emulsion dehydration speed increases with the non-uniform coefficient. Within a certain range, the improvement of non-uniform coefficient of the electric field can reduce the moisture content of emulsion eventually. However, the higher non-uniform coefficient of electric field can also cause electric dispersion. In non-uniform electric field, the dielectrophoresis force of water droplets and dipole coalescence force between the droplets are proportional to electric field intensity, water droplet radius, and non-uniform coefficient of electric field, and they are inversely proportional to the distance between the center of the electrode and water droplet, and the distance between the water droplets. The scattered electric field intensity for water droplets is related to surface charge density of water droplet, droplet size, and surface tension. When the water droplet is charged, its scattered electric field intensity will decrease. The established dehydration model for non-uniform electric field can explain the phenomenon of electric dehydration, and it can provide a theory basis for the high efficient dehydrator design. ©, 2015, Science Press. All right reserved. Source

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