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A compressed air dryer is a device for removing water vapor from
compressed air.Compressed air dryers are commonly found in a wide
range of industrial andcommercial facilities.
The process of air compression concentrates atmospheric
contaminants, includingwater vapor. This raises the dew point of
the compressed air relative to free
atmospheric air and leads to condensation within pipes as the
compressed air coolsdownstream of the compressor.
Excessive water in compressed air, either in the liquid or vapor
phase, can cause avariety of operational problems for users of
compressed air. These include freezingof outdoor air lines;
corrosion of equipment; fouling of processes and products.
There are various types of compressed air dryers. Their
performance characteristicsare typically defined by the dew
point.
Regenerative desiccant dryers, often called "regens" or "twin
tower" dryers
Refrigerated dryers Deliquescent dryers Membrane dryers
Vapor is removed from compressed air to prevent condensation
from occurring andto prevent moisture from interfering in sensitive
industrial processes.
Characteristics
A regenerative desiccant dryer typically delivers a dew point of
between-40(-40C) F and -100F (-73C)
A refrigerated dryer delivers a dew point not lower than
approximately 35F
(2C) A deliquescent dryer delivers a dew point suppression that
fluctuates with air
temperature. Typically this suppression is 20F below the
compressed airtemperature.
Refrigerated Dryer
Refrigeration dryers employ two heat exchangers, one for
air-to-air and one for airto refrigeration. However, there is also
a single TRISAB heat exchanger thatcombines both functions. The
compressors used in this type of dryer are usually ofthe hermetic
type and the most common gas used is R-134a. The goal of having
two
heat exchangers is that the cold outgoing air cools down the hot
incoming air andreduces the size of compressor required. At the
same time the increase in thetemperature of outgoing air prevents
re-condensation.
As of the year 2000, most manufacturers started producing energy
saving dryersthat do not make use of a hot-gas by pass. These
dryers can save up to 40% in totalenergy and can consume only 10%
of the max power when idle. They employ digitalcontrol and
sometimes variable speed compressors.
http://en.wikipedia.org/wiki/Dew_pointhttp://en.wikipedia.org/wiki/Heat_exchangerhttp://en.wikipedia.org/wiki/Gas_compressorhttp://en.wikipedia.org/wiki/R-134ahttp://en.wikipedia.org/wiki/Heat_exchangerhttp://en.wikipedia.org/wiki/Gas_compressorhttp://en.wikipedia.org/wiki/R-134ahttp://en.wikipedia.org/wiki/Dew_point
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Some manufacturers are marketing compressors with built in
refrigeration dryers,but these have had a mixed acceptance in the
market.
Commonly a coalesing prefilter is installed immediately upstream
of a refrigerateddryer to remove lubricating oil and other
contaminants that have the potential tofoul the dryer's heat
exchangers.
Deliquescent Dryer
A deliquescent dryer typically consists of a pressure vessel
filled with a hygroscopicmedia that absorbs water vapor. The media
gradually dissolvesor deliquescestoform a solution at the base of
the pressure vessel. The liquid must be regularlydrained from the
vessel and new media must be added. The media is usually intablet
or briquette form.
Deliquescent dryers have no moving parts and don't require
electrical power foroperation. Common applications therefore often
involve remote, hazardous, or
mobile worksites. Deliquescent dryers are used for removing
water vapor fromcompressed air, natural gas, and waste gases such
as landfill gas and digester gas.
The performance of a deliquescent dryer, as measured by outlet
dew point, is highlydependent on the temperature of the air or gas
being processed, with coolertemperatures resulting in better
performance.
Desiccant Dryer
The term "desiccant dryer" refers to a broad class of dryers.
Other terms commonlyused are regenerative dryer and twin tower
dryer, and to a lesser extent adsorptiondryer.
The compressed air is passed through a pressure vessel filled
with an adsorbentmedia such as activated alumina, silica gel,
molecular sieve or other desiccantmaterial. The desiccant can bring
the dew point of the air down to -40 degreesCelsius or below. This
means that the air will not condense water until it is cooled to-40
degrees Celsius. In practice two cylinders with desiccant are used;
one is dryingthe air, while the other vessel is being regenerated.
The switching of the vesselsand the regeneration sequence is
typically done automatically via solenoid operatedvalves.
The regeneration of the desiccant vessel can be during three
different methods:
Heatless "pressure-swing" drying which uses part of the dry
compressed aircoming from the other vessel to dry the desiccant in
the vessel beinggenerated at lower pressure.
Heated dryer, this can use a hot air blower, so there is no loss
of compressedair.
Heat of compression. This can only be used with an oilfree
compressor.
http://en.wikipedia.org/wiki/Silica_gelhttp://en.wikipedia.org/wiki/Desiccanthttp://en.wikipedia.org/wiki/Silica_gelhttp://en.wikipedia.org/wiki/Desiccant
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Membrane dryer
Membrane dryer refers to a dehumidication membrane that removes
water vaporfrom compressed air. It is used in pneumatic components,
air bearings, air spindles,medical equipment, air guns and
pneumatic brakes for vehicles & trains.
