Liquid-vapour separators are used to separate vapour stream from a mixed stream of liquid and vapour. They are also called knockout drums. The vessel diameter must be large enough to slow down the gas to a sufficiently low velocity so that the dropplets settle out. Demisting pads can be used to improve the efficieny of the knockout drums. Equation to determine the height of heavy liquid outlet:

where *D* in the above equation is the vessel diameter, *V _{v}* is the volumetric flowrate of gas or liquid,

Type the required values to get the sizing of a knockout drum:

Vapour flow (kg/h)

Liquid flow (kg/h)

Vapour density (*ρ _{v}*, kg/m

Liquid density (*ρ _{l}*, kg/m

Settling velocity (m/s)

Vessel diameter with demister (m)

Vessel diameter without demister (m)