A Knock-out (KO) drum consists of a vertical vessel specially designed to separate vapor and liquid from a two-phase process flow. Inside you’ll find an inlet diffuser and de-entrainment mesh pad designed to maximize the collection of liquid contained in the vapor as it travels to the top of the vessel.
Gravity draws the liquid down to the bottom of the vessel for withdrawal, while the vapor exits the top. Sometimes the process fluid is a pressurized liquid that is relieved into the vessel, causing the liquid to “flash” off a part, or all, of the liquid as vapor. In such case, the unit may be referred to as a ‘flash drum’.
Typically, Chromalox electric process heaters are used in a knock-out drum to increase vaporization of flashed liquid or to vaporize liquid collected in the bottom of the vessel. They can also be used to decrease viscosity of heavy fluids (e.g oils) to improve pump-ability and to maintain a minimum temperature in the vessel for freeze protection.