A demister, is a device often fitted to vapor liquid separator vessels to enhance the removal of liquid droplets entrained

Entrainment (engineering)

Entrainment as commonly used in various branches of engineering may be defined as the entrapment of one substance by another substance. For example:* The entrapment of liquid droplets or solid particulates in a flowing gas, as with smoke....

 in a vapor stream. Demisters may be a mesh type coalescer

Coalescer

A Coalescer is a technological device performing coalescence. They are primarily used to separate emulsions into their components via various processes; operating in reverse to an emulsifier....

, 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 thereby reducing the volume and associated cost of separator equipment. Demisters are often used where vapor quality

Vapor quality

In thermodynamics, vapor quality is a quantitative description of the usefulness of a vapor to do mechanical work. The quality of a fluid is the percentage of mass that is vapor; i.e. saturated vapor has a "quality" of 100%, and saturated liquid has a "quality" of 0%...

 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

Brine

Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

 desalination on marine vessels, brine

Brine

Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

 is flash heated into vapor

Flash evaporation

Flash evaporation is the partial vapor that occurs when a saturated liquid stream undergoes a reduction in pressure by passing through a throttling valve or other throttling device. This process is one of the simplest unit operations...

. In flashing, vapor carries over droplets of brine which have to be separated before condensing, otherwise the distillate vapor would be contaminated with salt

Salt

In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...

. This is the role of the demister. Demisted vapor condenses on tubes in the desalination plant, and product water is collected in the distillate tray.

See also

• Souders-Brown equation
  Souders-Brown equation
  The Souders-Brown equation has been the tool for obtaining the maximum allowable vapor velocity in vapor–liquid separation vessels...
  
  
• CWMS
• Separator
  Separator
  Separator can refer to:* Cream separator, separates cream from milk* Community separator, a term of urban planning* Separator , of an oil production plant* Vapor-liquid separator, separates a vapor-liquid mixture...
  
  
• Vane type separator
• Vessel Internals
• Gas Processors Suppliers Association (GPSA)