Power consumption measurements for ac and pulsed dc for electrostatic coalescence of water-in-oil emulsions

Abstract

True root mean square power consumption measurements for coalescence of well-defined water-in-oil (W/O) emulsions [reverse osmosis water dispersed in Isopar M and stabilized with Paranox 100 surfactant] are presented for a 2-l Teflon insulated electrostatic coalescer. Estimated electricity costs for processing 1000 barrels (42 gal basis) of the emulsion were as low as $0.37 and $0.39 under 60 Hz ac and pulsed dc (i.e., half-wave rectified ac) fields, respectively. These data compare favorably with actual operating costs for an equivalent volume of crude oil for NATCO designed full-scale electrostatic coalescer systems with non-insulated electrodes. Contrary to observations by other investigators including past tests in our own laboratory, ac fields were more effective in increasing coalescence rate than pulsed dc fields. Normalized power consumption data show that the optimized frequency for coalescence with electricity costs as the important factor was at 60 Hz (i.e., the lowest frequency tested) in spite of dramatic increases in throughputs at higher frequencies of 120, 400 and 600 Hz. Comparative tests using identically prepared W/O emulsions showed that the coalescence rate with the present system was up to 11-fold higher as compared to a geometrically similar coalescer using a patented plastic-sealed electrode under identical 600 Hz ac fields.