Research On Electrostatic Oil Cleaning Technology Based On Inorganic Dielectric Material With High Dielectric Constant And Multi-dimensional Gradient Electric Field

Impurities in petroleum can make exacerbation of equipment corrosion and inactivation of catalyst so as to degrade product quality.Therefore,it is very important to clean and remove impurities.Compared with other methods of cleaning oil,electrostatic oil purification technology is gradually applied because it can remove fine solid impurity particles,and the purification effect is better and pollution is not caused again.The conventional electrostatic oil cleaning equipment are mainly flat electrode structure and cylindrical electrode structure.Among them,the flat electrode produces a uniform electric field and only adsorbs the charged impurities in the oil.Although the cylindrical electrode can generate a non-uniform electric field,the generated electric field gradient is small,which limits adsorption capacity for neutral impurities in oil.It results in low cleaning oil efficiency and purification accuracy.In view of the above problems,we improve the gradient of non-uniform electric field by developing the electrode structure of electrostatic oil cleaning equipment and introducing the inorganic dielectric ceramic powders with high dielectric constant,based on the theory of dielectrophoresis and field flow separation technology.The obtained scientific research results are shown as follows:（1）To solve the problem that the electric field gradient of the electrostatic oil purification technology is not high enough,a“battlement”type electrode structure was designed and the inorganic dielectric ceramic powders with high dielectric constant was introduced,and a new electrostatic oil cleaning equipment that can generate multi-dimensional high gradient electric field has been developed.On this basis,the simulation model of the“battlement”type electrostatic oil cleaning equipment was established by using COMSOL Multiphysics software.Through numerical analysis,it is found that the potential distribution of the“battlement”type electrostatic oil cleaning equipment is non-uniform,and there is a large electric field gradient between the plates of the“battlement”type electrode.The simulation results of the movement of impurities in the oil show that the impurity particles in the non-uniform electric field move along the“battlement”type plate,the whole purification process only takes 4.8 minutes to achieve the desired effect.（2）BaTiO₃ and Ba_0.7Sr_0.3TiO₃ ceramics were synthesized by conventional solid-state reaction method.The effects of preparation process on microstructure and electrical properties have been systematically investigated.The results show that the BaTiO₃ ceramics is a single tetragonal phase with an average grain size of 80μm.The dielectric constant exceeds 1000 in the clean oil operating temperature range（30⁴0 ^oC）,and the dielectric constant has good temperature stability.The sintering temperature has a significant effect on the microstructure and electrical properties of Ba_0.7Sr_0.3TiO₃ ceramics.The results show that the Ba_0.7Sr_0.3TiO₃ceramics sintered at 1350¹450 ^oC are single pseudo-cubic perovskite structure.The average grain size of Ba_0.7Sr_0.3TiO₃ ceramics sintered at 1350 ^oC,1400 ^oC,and 1450 ^oC was 9μm,12μm,and 24μm,respectively.There is obvious broadening dielectric peak and frequency dispersion phenomenon in Ba_0.7Sr_0.3TiO₃ ceramics and obvious ferroelectric hysteresis loops above the Curie temperature,indicating that it is a typical relaxor ferroelectrics.The Ba_0.7Sr_0.3TiO₃ ceramic powders prepared at 1350 ^oC has a large dielectric constant and a low dielectric loss（the dielectric constant is above 8000 in the temperature range of 30⁴0 ^oC,and the dielectric loss is<1%）.On this basis,BaTiO₃ and Ba_0.7Sr_0.3TiO₃ ceramic powders suitable for electrostatic cleaning were prepared.（3）The oil purification experiment was carried out by using an electrostatic oil cleaning equipment with a“battlement”type electrode structure.The influences of the type and strength of the electric field,the purification time,and the with/without of the dielectric materials on the oil cleaning have been systematically studied.The results show that as purification time increases,the degree of oil pollution is significantly reduced,but the degree of oil pollution tends to be stable after the purification time reaches 20 minutes.The effect of AC electric field for cleaning oil is slightly better than that of the DC electric field.After 60 minutes of purification by a 20 kV/cm industrial frequency electric field,the removal rate can reach 99.64%（>0.1μm）.By introducing BaTiO₃/Ba_0.7Sr_0.3TiO₃ ceramic powders with high dielectric constant,compared with the purification effect of with/without of dielectric and different dielectrics under 20 kV/cm industrial frequency electric field.It was found that the electrostatic cleaning effect of the two ceramic powders with high dielectric constant is better than that without dielectric materials.The purification oil effect of Ba_0.7Sr_0.3TiO₃ ceramic powders is obviously better than that of BaTiO₃ ceramic powders.After 20 kV/cm for 50 min,the pollution degree of oil（≥4μm）purified by the Ba_0.7Sr_0.3TiO₃ ceramic powder is<12.In order to further confirm the purification oil effect and determine whether the oil has undergone significant changes after being treated by the high electric field,the original oil（the oil mixed with impurities）and the purified oil are tested.It was found that the degree of oil pollution after electrostatic cleaning reduced to some extent relative to the original oil,and the purification oil effect was the best when Ba_0.7Sr_0.3TiO₃ ceramic powders were introduced.There were no significant changes in the viscosity,color,and copper strip test for petroleum products after the electrostatic oil cleaning.