Compressed Air Dryers
The air all around us contains water vapour. Humidity refers to the quantity of
vapour contained within a given volume of air. When a compressor draws-in air
from it's surrounding environment, it also takes-in the water. If a dryer is
not used, this water can lead to rusted pipes and components. Excessive water
in a compressed air system can also wash lubricant from where it is needed in
downstream components.
Compressed air dryers are used to remove water from an air system. On an
average day, a 500 cfm compressor can take in 90 gallons of water vapour.
If an
aftercooler
is used, it can remove about half of that water. Without a
dryer, this water would go through the pneumatic equipment before being blown
out into the atmosphere.
There are several types of dryers:
Refrigerant Dryers
Refrigerant dryers are the least expensive option for many compressed air
systems. Although not as efficient as other options, the refrigerated dryer's
low initial cost and low operating cost make it a popular choice.
The
dewpoint
of refrigerant dryers is limited to about 36°F (2°C). This relatively high
dewpoint level makes the refrigerant dryer unsuitable for applications that
require extremely dry air.
Twin-Tower Regenerative Dessicant Dryers
Twin-tower dessicant dryers use two towers containing dessicant to dry
compressed air. One tower actively dries the air, while the second tower
regenerates. Regeneration occurs by redirecting a portion of the dry output air
through the regenerating tower thereby drying the dessicant within. This
process continues until the active tower becomes saturated with moisture at
which point the controls contained within the dryer exchange the active and
regenerating towers.
Dewpoints of -40°F (-40°C) are possible
A coalescing filter must always be used before a dryer to ensure that the air
entering the dryer is free of oils. Contaminated air can quickly coat the
dessicant and render it useless.
It is also recommended that the output air from the dryer is filtered to remove
any dessicant dust.
