Freewater Knockouts (FWKO) are essentially two phase separators that take advantage of settling to separate free water from the production stream. Their purpose is not to break the emulsion or fully dry the oil but to remove the water that is easily separated from the process.
Unwanted water in the process stream can increase the cost of treatment by reducing the size of equipment and energy requirements of subsequent steps. The stream might be preheated prior to the knockout to help the water break out of the emulsion. Typically this will be done with a heat exchanger with heat that would otherwise be wasted.
Some freewater knockouts separate the gas from the production stream and others pass it through to be removed later in the process. Running the vessel at high pressures will prevent the gas from breaking out of the emulsion.
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