In the petroleum industry, dehydration and desalting of a crude oil−brine emulsion are critical to further processing and refining of crude. The process of dehydration and desalting is typically done in large units called electrocoalescers. Enhancing the performance of an electrocoalescer includes the ability to dehydrate the emulsion in a shorter time, that is to increase the rate of separation of water while keeping the operation safe. The work proposes the enhancement of separation based on AC electric field modulation. The modulated waveform is composed of a high amplitude electric field step, followed by a low amplitude electric field step, and the process is repeated. The work demonstrates the efficacy of the technique through several experiments and their analysis. The work includes designing and optimizing the electrical waveform and then demonstrating the faster kinetics of electrocoalescence achieved in comparison with the conventional practice. The main advantage of modulation is facilitation of chaining of drops during the high voltage period, followed by their effective coalescence in the low voltage period. The effect of the modulation field and period has been investigated, and optimization of the time periods of the high field and the low field steps is carried out. Our analysis indicates that an increase in the fraction of the total period spanned by the high field improves the water separation, while a relatively weaker dependence is found on the total period. The electric field was applied both in directions parallel and perpendicular to the gravity, and performances were compared. It was found that the parallel configuration was better than the perpendicular configuration.
Electrocoalescence has long been known for the separation of a water‐in‐oil emulsion. An associated challenge with electrocoalescers is the undesired noncoalescence and consequently chain formation of aqueous phase droplets. This leads to low separation efficiency and damage of electrical equipment. Recently Hasib et al. proposed an electric field modulated scheme that showed significant improvement in dehydration of water‐in‐oil emulsions. They investigated the range of modulation parameters when the scheme is most effective. The fundamental process in electrostatic dehydration of an emulsion is the interaction between a pair of water droplets. In the present study, two suspended aqueous drops in insulated oil experiments are compared for their behavior under unmodulated and modulated electric fields. Further, a model is developed and the experimental behavior under unmodulated and modulated electric fields is compared with numerical solutions. The model predicts the experimental observations accurately by balancing electrostatic, electrophoresis, dipolar, and resisting viscous drag forces, ignoring the end (bridge) effect during the contact. The study shows that the increase in the rate of dehydration of a water‐in‐oil emulsion under modulated electric fields with an increase in duty ratio and its near independence on the modulation time period can be explained by the two‐drop studies. However, several other processes such as multidrop interactions as well as scavenging of fine droplets by charged droplets created as intermediates in the interaction of two droplets cannot be explained by the two‐drop studies.
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