Mechanism-Guided Waveform Modulation for Accelerated Electrocoalescence in Rationally Designed Concentric Cylindrical Electrocoalescers

Electrocoalescence is the technology of choice for crude-oil dehydration and desalting, yet the performance remains limited by the commonly used combination of 50–60 Hz AC power supplies and parallelly configured electrode pairs which produce spatially uniform electric fields. This work explores enhancement of electrocoalescence performance using concentric cylindrical electrode pairs that impose centripetal dielectrophoretic force on brine droplets through spatial variation in the electric field, in combination with judiciously chosen temporally modulated multistage voltage waveforms and corresponding electric fields, applied across the pair of electrodes. The design space is governed by the competing mechanisms. Increasing the outer-to-inner electrode radius ratio ( R o / R i ) enhances field gradients and accelerates dielectrophoretic force-driven droplet migration near the inner electrode but weakens the field near the outer boundary to a value below the critical value required for coalescence to occur by dipolar forces. Higher applied potentials restore strong fields across the annular space and promote beneficial postcoalescence rebound, but also increase the risk of conductive droplet-chain formation and electrical breakdown. We hypothesized that this impasse can be resolved by optimally selecting the electrode diameter ratio and temporally modulating the electric potential difference applied across the electrodes. Several electrode diameter ratios and electric-field modulation programs were tested in a batch experimental setup. The combination of electric-field inhomogeneity from the selected concentric geometry and suitable temporal modulation yielded a 4.5-fold decrease in incubation time required to initiate coalescence, a 4-fold reduction in the time required to reach 60% absolute separation, and a 2.5-fold reduction in the time required to reach 90% absolute separation, relative to the unmodulated “parallel-plate” baseline, across varying water and salt concentrations. These findings can guide the development of electrocoalescers with substantially improved performance, even for high water-cut and high-salinity emulsions, overcoming major limitations of currently employed industrial electrocoalescers.