The electrostatic coalescer has proved to be an efficient means of separating water-in-oil type emulsions. Engineering design and better understanding of the mechanisms of droplet–droplet electrocoalescence should lead to the enhancement and development of new types of electrocoalescer. Almost all the electrocoalescers in the oil and petroleum industries use AC electric fields for the separation of water-in-oil emulsions. However, some research work reported in literature indicates some promising performance for pulsed DC electric fields. The existence of an optimum electric field and frequency has been reported, but it has not been widely confirmed [12]. However, it may be intuitively expected that differences in the mechanical and electrical relaxation times of the droplets could give rise to the existence of an optimum voltage and frequency. Further, research is needed to elucidate this issue. Recent work shows that, under a pulsed DC electric field, chains of water droplets are usually created during periods of high voltage, followed by rapid coalescence during periods of reduced or no voltage. Therefore, a further improvement in the electrostatic coalescence technology with respect to the applied electric field may be achieved by operating the coalescer at an optimum voltage and frequency with reference to the condition of the emulsion, as well as the design of the coalescer itself to give the best electric field configuration. In a water-in-oil emulsion with a high content of dispersed water, insulating the electrode may be necessary. This is because the high water content tends to produce over-stressing of the electrical coalescer due to a direct conductive path between the electrodes. A further enhancement can be achieved when the electrostatic coalescer is coupled with a centrifugal force or when employing a multi-stage separator. Moreover, various combinations for emulsion treatment have also been utilised. Besides centrifugal force, heating has also been used with electrical treatment. It has been shown that chemical addition would further enhance electrocoalescence of water droplets in oil emulsions. Other methods that can be combined with electrical treatment are filtration, pressure application and mixing, which enhance the separation efficiency in various ways.
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