Investigation On Coalescence And Separation Characteristics Of Electrostatic Coalescence Separator

Electrostatic coalescence method is capable of removing water from oil of low water content,and for its features such as high efficiency,energy saving and environmental friendliness,electrostatic coalescence method is favored by more and more researchers.Western researchers proposed the crude oil dewatering method that separating electrostatic coalescence process from gravity settling process,but this method had exposed the problem that after the coalescence process,droplets will be re-emulsified by severe shear from elbows and valve of the pipelines.Therefore,this article combines coaxial cylindrical insulated electrode with traditional gravity separator,and the new type electrostatic coalescence separator was designed to avoid re-emulsification.In this paper,the insulation material of the coaxial cylindrical insulated electrode was screened and insulation structure was designed.The basic separation mechanism of electrostatic coalescence separator was expounded and based on Maxwell-Wagner model,the distribution characteristics of electric field of the coaxial cylindrical insulated electrode system was investigated from the angle of dielectric polarization.The laboratory prototype of electrostatic coalescence separator was designed and constructed,and the flow evaluation experiment loop system for electrostatic coalescence and separation was designed and built.The structural parameter of oil-water premixed blender was optimized with simulation software—Mixsim.The physical parameters of experimental medium were measured and oil-water emulsion of 4 water content was prepared.The effects of electric field intensity,frequency,flow rate and water content on coalescence of water droplets,oil-water separation of the electrostatic coalescence separator were investigated with flow evaluation experiment.The results of experiments show that high strength electric field could promote the quick coalescence process,but in order to avoid “electric dispersion” phenomenon,the electric field strength could not be too high.With the increase of the frequency of electric field,droplets coalescence efficiency shows a trend of increase,however,there is an obvious inflection point of frequency at about 100 Hz,and the higher the water content,the earlier the inflection point emerges.With the increase of flow rate,the time during which emulsion is in electric field decreases,so the droplets coalescence efficiency would be reduced.The multiple of droplets size increasement would be improved with the increase of water content,and with the increase of flow rate,the multiple of droplets size increasement of emulsion of different water content would converge.Electrode voltage and frequency were key determinants of power consumption of electrostatic coalescence separator,and to process 1 m3 of emulsion,it would only consume 7.742×10-3 to 1.996 kilowatt hour,so electrostatic coalescence separator was very economical and reliable.The laminar flow in the coalescence flow channel of electrostatic coalescence separator was simplified to two-dimensional plane Couette flow.Based on the phase-field method,the electric field and shearing field are coupled to establish the numerical model of movements and coalescence of double-droplets under the coupling effect of electric field and shearing field.The law of movements and coalescence of double-droplets and the effects of geometry parameters,electrical parameters,flow parameters and physical parameters on coalescence rate of double-droplets are investigated through simulation.The results show that the numerical model was proved to be accurate by micro experiment.The dynamic behavior of double-droplets under the coupling effect of electric field and shearing field can be divided into three types: non-coalescing,coalescing and breaking up after coalescing;the efficiency of coalescence under the coupling effect of shearing field and electric field exceeds that under the effect of single field by 63% to 94%.The effect of electric frequency on coalescence time appears to be a u-shaped curve.The coalescence efficiency would be improved with the increase of shear strength,but the droplets could not coalesce for inadequately drainage if the shear strength was too high.Reducing the viscosity of the continuous phase could significantly reduced the viscous drag force which hinders droplet coalescence and could improve coalescence efficiency.The effect of electric field would change the influence of interfacial tension on droplets coalescence.The relationship between coalescence time and ?Y/R appers to be an exponential function relation,it could be used to determine the critical water content of rapid coalescence and effective coalescence.The results of experimental research and numerical simulation are completed and compared to each other to guide the optimized design of electrostatic coalescence separation equipment and optimization of working parameters.