A demister is a device often fitted to
vapor–liquid separator
In chemical engineering, a vapor–liquid separator is a device used to separate a vapor–liquid mixture into its constituent phases. It can be a vertical or horizontal vessel, and can act as a 2-phase or 3-phase separator.
A vapor–liquid ...
vessels to enhance the removal of liquid droplets
entrained in a vapor stream. Demisters may be a mesh-type
coalescer, vane pack or other structure intended to aggregate the mist into droplets that are heavy enough to separate from the vapor stream.
Demisters can reduce the residence time required to separate a given liquid droplet size by reducing the volume and associated cost of separator equipment. Demisters are often used where
vapor quality
In physics, a vapor (American English) or vapour (British English and Canadian English; see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R. H. Petrucci, W. S. Harwood, and F. G. Her ...
is important in regard to entrained liquids, particularly where separator equipment costs are high (e.g., high-pressure systems) or where space or weight savings are advantageous.
For example, in the process of
brine desalination on marine vessels,
brine is
flash-heated into vapor. In flashing, vapor carries over droplets of brine, which have to be separated before condensing, otherwise the
distillate
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating ...
vapor would be contaminated with
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
. This is the role of the demister. Demisted vapor condenses on tubes in the desalination plant, and product water is collected in the
distillate
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating ...
tray.
See also
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Vapor–liquid separator
In chemical engineering, a vapor–liquid separator is a device used to separate a vapor–liquid mixture into its constituent phases. It can be a vertical or horizontal vessel, and can act as a 2-phase or 3-phase separator.
A vapor–liquid ...
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Souders-Brown equation
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Vane type separatorbr>
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Vessel Internalsbr>
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Gas Processors Suppliers Association (GPSA
References
{{DEFAULTSORT:Demister (Vapor)
Chemical equipment
Gas technologies