Freewater Knockouts

PFEC manufactures a line of special vessels called Freewater Knockouts. A Freewater Knockout is either a vertical or horizontal vessel which removes a dispersed phase from a continuous phase. The degree of separation depends upon:

  1. The available retention time.
  2. The density differential between the two fluids (larger differential means better separation)
  3. The operating temperature of the flowing fluids.
  4. The presence or absence of slugging flow.
  5. Interfacial area available for separation.

Freewater Knockouts are total liquid knockouts and generally do not have mist extractors. They can be used only on streams where water and oil exist separately and not as an emulsion. The gas phase is recombined with the oil phase and the water phase is dumped to a wastewater disposal unit. These units are always used in conjunction with other equipment. If the oil phase is not recombined with the gas and thereby discharged separately, the vessel is not a freewater knockout but a three-phase separator.

After leaving the first-stage separator‚ the high-pressure liquid portion of the produced fluid stream is directed toward the FWKO pressure vessel. This long‚ horizontal vessel is used to separate free water from degassed crude oil and crude oil-water emulsions‚ due to the differences in the densities of these mediums. Depending on the distance to this device‚ which is normally located at the Central Processing Facility‚ pumping may be required to boost the liquid to the inlet connection of this vessel. As the liquid enters the vessel, the design residence time allows a large portion of the water to separate from the crude‚ collecting in the lower portion of the vessel. The captured water is dumped away for ultimate reuse in water flooding reinjection.