Ask a
Question:
Can
moisture damage my compressed air system?
ANSWER:
Liquid
water in a compressed air stream increases the cost of operation. It
contributes to unnecessary product rejects and countless hours of unscheduled
maintenance. Air tool lubricant gets washed away creating unnecessary wear.
Highly acidic, this condensed water eats away at air motors and valves and,
contaminates finished goods.
Invest in the correct drying technology for your application and the compressed
air lines stay dry. Dry air will also pay your big dividends for years to come.
Ask a Question:
How
does damaging moisture get in your compressed air system?
ANSWER:
At
an ambient temperature of 75°F and 75% relative humidity, a typical 100 HP (500
scfm) air compressor inhales 90 gallons of water vapor every 24 hours.
Discharging air at 100°F and 100 psig, a well maintained aftercooler may remove
about 57 gallons. That leaves 33 gallons inside your air system.
At the CAGI ADF 100 design standard of 38°F, a refrigerated dryer removes an
additional 29 gallons. The remaining 4 gallons safely pass through the system
as water vapor. Because there is usually a rise in air temperature during
compression, condensation often does not occur within your compressor itself.
Condensation in your compressed air system usually happens as compressed air
cools when passing through the discharge piping. This condensed water must be
drawn out of your line by a separator and a trap. While approximately
two-thirds of the water vapor is converted to liquid from the system in an
effective aftercooler, there is still a lot of water vapor remaining in the
compressed air which is "saturated" at the exit temperature from the
aftercooler.
Compressed Air Dryers have been designed and developed to help remove water
vapor from the compressed air in a controlled manner in order to provide you
with a required "quality of dry air" needed for your equipment and
processes.
Ask a Question:
How
DRY should my compressed air be?
ANSWER:
"Dryness"
can be relative. Air that is dry for one type of application my not be
dry enough for another. There will always some moisture present in your compressed
air system regardless of the degree of drying.
There are different types of dryers available with varying degrees of moisture
removal. First - you need to determine the required "degree of
dryness" for your Compressed Air System, which is specified in the
"Pressure Dew Point" (PDP) at a certain pressure.
It is not a good practice to specify a pressure dew point a lot lower than your
application's requirements. This can result in more costly equipment and
increased operating expenses. Determining the PRESSURE DEW POINT TEMPERATURE
will help you determine the "dew point class" of the dryer you need.
Ask a Question:
What is "PRESSURE DEW POINT"?
ANSWER:
Pressure Dew Point - For a given pressure, the temperature at which
water VAPOR will begin to condense INTO liquid water.
Ask a Question:
What pressure dew point do I need?
ANSWER:
First - here's some information to help you understand pressure
dew point: The lowest pressure dew point class for a refrigerated
dryer is Class 4. Class 4 delivers a pressure dew point of +38°F.
Refrigerated dryers should not operate below the Class 4 range because the
water vapor will freeze in the dryer. The highest pressure dew point for a
refrigerated dryer is Class 6. Class 6 delivers a pressure dew point of
+50°F.
The highest practical pressure dew point because higher pressure dew point
causes condensation in downstream piping.
WAYS TO DETERMINE PRESSURE DEW POINT:
1. Ask
the Manufacturer what the pressure dew point (PDP) requirements are for your
equipment.
2. You can CALCULATE PRESSURE DEW POINT
TEMPERATURE you need. Here's how:
1.
Determine the lowest ambient temperature your compressed air piping system will
be exposed to.
Check the location of air lines throughout air conditioned or unheated areas
underground or between buildings.
(For
example, your compressor and piping is inside your facility and the lowest air
temperature it would ever be exposed to is 58ºF.)
2. Now you
need to take that temperature number and lower it by 20º.
(For
example, your 58ºF lowest ambient temperature -20º = (38º PDP NEEDED)
This
will give the PRESSURE DEW POINT TEMPERATURE needed to prevent liquid water
forming
downstream.
Determining the PRESSURE DEW POINT TEMPERATURE will help you determine the
"dew point class" of the dryer you need. These
"classifications" are industry standards for compressed air dryers as
established by the ISO (International Organization for Standardization).
ISO 8573.1 AIR QUALITY CLASSES of PRESSURE DEW POINTS THAT APPLY TO
REFRIGERATED AIR DRYERS:
Class 4 maximum pressure dew point +38 º F
Class 5 maximum pressure dew point +45 º F
Class 6 maximum pressure dew point +50 º F
The lower the dew point, the dryer the
air.
These
"classifications" are industry standards for compressed air dryers
are established by the ISO (International Organization for Standardization).
Ask a Question:
What
is the most popular type of compressed air dryer?
ANSWER:
The
REFRIGERATED AIR DRYER has
become the most widely used dryer in general industrial plant air applications,
providing a pressure dew point of 35°F to 39°F.
Refrigerated dryers deliver 33°F to 39°F dew point to provide the best value
with low initial cost and low cost of operation. They are the best choice when
the ambient temperature where the compressed air is used will remain higher
than the pressure dew point. A 33°F to 39°F dew point is ideal for most indoor
areas wherepeople comfort is maintained.
Ask a Question:
How
does a Refrigerated Air Dryer work?
ANSWER:
The
basic principle is similar to a domestic refrigerator or home air conditioning
system. The compressed air is cooled in an air-to-refrigerant heat
exchanger to about 35°F, at which point the condensed moisture is drained off.
The air is then reheated in an air-to-air heat exchanger by means of the
incoming air, which also is pre-cooled before entering the air-to-refrigerant
heat exchanger.
This means that the compressed air leaving the dryer has a pressure dew point
of 35°F to 40°F. A lower dew point is not feasible in this type of dryer
as the condensate would freeze at
32°F or lower. In a non-cycling refrigerated dryer, the refrigerant
circulates continuously through the system.
Because both the flow of compressed air and ambient temperatures vary, a hot
gas bypass valve is often used to regulate the flow of the refrigerant and
maintain stable operating conditions within the refrigerant system.
Usually in most designs, the refrigerant evaporated within the air-to-refrigerant
heat exchanger (evaporator) and is condensed after compression by an air- or
water-to-refrigerant heat exchanger (condenser.) This type of design provided a
rapid response to changes in operating loads.
Four Advantages of Refrigerated Air
Dryers:
- Low initial capital cost
- Relatively low operating cost
- Low maintenance costs
- Not damaged by lubricant in the
air system
*Refrigerated air dryers
do have a limited dew point capability. Where a pressure dew point of less than
35°F is required, a refrigerant-type dryer cannot be used.
For
more in-depth information visit
Refrigerated Air Dryer Basics.
Compressed
air definitions you should know from Compressed Air & Gas Institute:
Dew
Point - The
temperature at which moisture in the air will begin to condense if the air is
cooled at constant pressure. At this point the relative humidity is
100%.Dew points may be expressed at an operating pressure or at atmospheric
pressure. Operating pressure should be specified when using
"pressure dew point."
Pressure Drop
- Loss of pressure in a compressed air system or component due to friction or
restriction. Typically, the pressure drop through a compressed air dryer is 3
to 5 psi and should be taken into account in system requirements.
SOURCES:
"Improving
Compressed Air System Performance- A sourcebook for industry" U.S.
Department of Energy Energy Efficiency and Renewable Energy; "Best
Practices for Compressed Air Systems" by CA;
Compressed Air & Gas
Institute (CAGI).
