In a processing operation, a flash tank is a vessel used to separate the gas created from liquid when it is flashed from a high pressure to a low pressure.
Condensate from the process enters the flash tank at high pressure. As condensate enters the low pressure flash tank, part of the condensate flashes into steam. Steam condensate drops to the bottom of the tank and is discharged. Steam vapors rise and are likewise discharged. They may be metered and recombined to create a known steam cut or may each be separately used further in the process.