Dynamic demulsification of oil-in-water emulsions with electrocoalescence: Diameter distribution of oil droplets

The oil-in-water (O/W) emulsions, especially oily wastewater from EOR oilfield, generally contain small oil droplets in the continuous water phase, which is difficult to be removed with conventional oil separation process such as precipitation, flotation. The electrostatic coalescence is a promising pretreatment step to induce the oil droplets coalescence and promote the oil separation efficiency of conventional methods. In order to explore the feasibility of electrostatic demulsification for O/W emulsions, the influence of operating parameters including electric voltage, pulsatile frequency, water content of emulsions and hydraulic retention time (HRT) on oil diameter distribution of the emulsions were studied using dynamic demulsification experiment. The volume percentage of oil droplets with a diameter exceeding 40 μm (denoted as DG40) was adopted as the main indicator of demulsification results, it increased from 0 (the original emulsions) to 65.62% (the treated emulsions) at the optimal operation parameters including water content of emulsions 90 vol%, electric voltage 150 V, pulsatile frequency 1000 Hz, duty cycle ratio 0.5, hydraulic retention time (HRT) 60 s. Furthermore, the water separation efficiency for emulsions reached 82.5% at 11 min of the dynamic experiment duration. The results of this study showed that applying pulsatile electric field could be a feasible and effective technology for emulsified oil droplets coalescence in O/W emulsions.