Investigation Of The Movement And Coalescence Characteristics Of Droplets In Electrical Field

Petroleum demulsification is an essential process in the oil-field industries. From the perspective of energy efficiency, the electrical treating method is optimal to make tiny water-droplets coalesce into bigger ones and settle out. Utill now, there're not enough studies of coalescence mechanism in electric field, neither a theoretical system. In this paper, the electrostatic coalescence characteristics of horizontal water-doublets in the 50-400Hz sinusoidal AC electric field have been investigated. Also, the effects of oil&water physical properties and electric field parameters on the coalescence have been studied. The main conclusions are as following:The forces acting on the horizontal water-doublets before coalescing in the AC electric field are simplified and analyzed. According to the different center distances and whether there's the film-thinning force, the force expressions have been derived piecewise. Combined with Newton's second law, it's shown that through the integrating of the law expressions, the displacements of water-boublets change with the relationship x=Ae^Bt+Ct+D. But with the different center distances and different force expressions, the coefficients of relationship are different. Based on the micro-experimental datas, the 6s movement process of water doublets before coalescence is analyzed in two piecewise parts, and using the curve x=Ae^Bt+Ct+D to fit the datas achieves a good consistency, separately. In addition, the 6s continuous motion process is analyzed and fitted using the quartic curve x=at⁴+bt³+ct²+dt+e, also achieving good consistency.Under the same electric field conditions, the velocity of big doublets in relative motion before coalescence is faster than that of small ones, and the bigger the doublets are, the greater the deformation degree is and the shorter the coalescence time is. The viscosity of continuous phase influences the relative motion speed and coalescence time due to its drag force, but it does not obviously influence the deformation degree of water doublets. The more viscous the oil is, the slower the relative motion is and the longer the coalescence time is. It's found that only when the conductivity difference of the dispersed phase is large, the relative motion speed and coalescence time differ from each other remarkbly. The great conductivity of dispersed droplets increases the relative motion speed and decreases the coalescence time. For smaller droplets, the influence of conductivity becomes indistinct. In addition, only when the difference of the oil-water interfacial tension is large, it influences the relative motion apparently, and for the smaller droplets the effect will be weakened. However, with the decrease of the interfacial tension, the maximum deformation degree increases, and the coalescence time is shortened significantly.The applied electric field is the main driving force to cause droplet coalescence. The great electric field strength can significantly increase the relative motion speed, increase the deformation degree and decrease the coalescence time. In an appropriate range of electric field strength, increasing the electric field intensity can improve the efficiency of electrostatic coalescence, and promote oil and water separation. In this micro-experiment, the frequency range is 50-400Hz. The frequency of electric field exceeds the inherent frequency of water droplets, so they can not respond to the change of the applied field. Thereby, in the50-400Hz electric field, the AC field frequency approximately does not affect the relative motion velocity, the deformation degree and the coalescence time.