Some treaters use an electrode section. Figure 6-11 illustrates a typical design of a horizontal electrostatic treater. The flow path in an electrostatic treater is the same as a horizontal treater. The only difference is that an AC and/or DC electrostatic field is used to promote coalescence of the water droplets.
Procedures for designing electrostatic coalescers have not been published. Since coalescence of droplets in an electric field is so dependent
on the characteristics of the particular emulsion to be treated, it is unlikely that a general relationship of water droplet size to use in the settling equations can be developed. Field experience tends to indicate that electrostatic treaters are efficient at reducing water content in the crude below the 0.5 to 1.0% basic sediment and water (BS&W) level. This makes them particularly attractive for desalting applications. However, for normal crude treating, where 0.5 to 1.0% BS&W is acceptable, it is recommended that they be sized as heater-treaters. By trial and error after installation, the electric grids may be able to allow treating to occur at lower temperatures.