Knock out vessels are used to separate solids and liquids from the gas stream. Knock out drums can be installed horizontal or vertical. In a vertical arrangement the knock out drum can have a side inlet with a larger exit which will reduce the velocity the gasses. Another method for using a vertical drum is to use a tangential inlet. With a tangential knock out drum, the gasses enter and spin around the wall of the vessel. While spinning the fluidic friction of the gas along the wall will "scrub out" much of the entrained liquid. Baffles are also used in a vertical drum to disrupt and slow down the gas prior to exit. These drums must be equipped with a liquid level gauge or indicator to know the when the KOD needs to be drained. Material of construction can be as per the compatibility with the fluid. Automatic as well as manual drain controls can be included to prevent the accumulation of liquid.
For both varieties of separator, the gas outlet may be surrounded by a spinning mesh screen or grating, so that any liquid that does approach the outlet, strikes the grating, is de-accelerated, and thrown away from the outlet. The vapour travels through the gas outlet at a design velocity which minimizes the entrainment of any liquid droplets in the vapour as it exits the vessel. The feed to a vapour–liquid separator may also be a liquid that is being partially or totally flashed into a vapour as it enters the separator.
Cyclone Separators are used in the vessel (Knock out drums) for more effective separation of liquid from the gas stream. The Cyclone separator is an entrainment eliminator. It is gas device that employ a centrifugal force generated by a spinning gas stream to separate the particulate matter, which could be solid or liquid, from the carrier gas. The number of cyclone separators is based on the efficiency required and the pressure drop desired across the vessel.
The centrifugal force due to a high rate of spin flings the dust particles to the outer walls of the cylinder and the cone. The particles then slide down the walls and into the storage hopper. The cleaned gas reverses its downward spiral and forms a smaller ascending spiral. A vortex finder tube that extends downward into the cylinder aids in directing the inner vortex out of the device. This proper designing of the knock out drum results in higher efficiency which reduces product loss; downstream corrosion; contamination; and damage to downstream equipment such as compressors, molecular sieve driers, and blowers.