Vapor-liquid separator

A vapor–liquid separator is a device used in several industrial applications to separate a vapor–liquid mixture.

A vapor–liquid separator may also be referred to as a Flash Drum, Breakpot, Knock-out drum, Knock-out pot, Compressor suction drum or Compressor Inlet Drum. When used to remove suspended water droplets from streams of air, it is often called a demister.

For the common variety, gravity is utilized in a vertical vessel to cause the liquid to settle to the bottom of the vessel, where it is withdrawn.

In low gravity environments such as a space station, a common liquid separator will not function because gravity is not usable as a separation mechanism. In this case, centrifugal force needs to be utilised in a spinning centrifugal separator to drive liquid towards the outer edge of the chamber for removal. Gaseous components migrate towards the center.

For both varieties of separator, the gas outlet may itself be surrounded by a spinning mesh screen or grating, so that any liquid that does approach the outlet strikes the grating, is accelerated, and thrown away from the outlet.

The vapor travels through the gas outlet at a design velocity which minimises the entrainment of any liquid droplets in the vapor as it exits the vessel.

The feed to a vapor–liquid separator may also be a liquid that is being partially or totally flashed into a vapor and liquid as it enters the separator.

The separator is only effective as long as there is an air space inside the chamber. The separator can fail if either the mixed inlet is overwhelmed with supply material, or the liquid drain is unable to handle the volume of liquid being collected. The separator may therefore be combined with some other liquid level sensing mechanism such as a sight glass or float sensor. In this manner, both the supply and drain flow can be regulated to prevent the separator from becoming overloaded. (Agastya, Bayu)

Vapor–liquid separators are very widely used in a great many industries and applications, such as:

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