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I. Compressed air is the
phantom utility. Industry has to have it, but it
can’t buy it. Industry can buy electricity and water. They
have to make their own compressed air.
II.
Why compress air? Compressed air is used as a source of
energy, much like electricity. Compressed air is stored
energy. How is it used in industry?
A. Pneumatic motors
B. Pneumatic cylinders
C. Operate or position valves and
instruments
D. Operate control devices
E. Convey materials
1. Push product through a pipe, i.e.
cement and plastic pellets
2. Convey materials along a
tray or belt
3. Align, rotate or flip
materials, i.e. push empty Coke cans to one side of a
conveying belt to allow their proper entry into the next
machine
4. Remove a bad product, i.e.
an electronic eye determines that a can has fallen and
removes the can with a blast of compressed air
F. Dry, heat or cool materials or finished
products
G. Operate pneumatic tools
H. Spray abrasive material under pressure
to remove coating
I. Painting or coating application
J. Inflate tires or other components
K. The list for the uses of compressed air
is endless
III.
Why use compressed air in lieu of electricity?
A. Compressed air is safer
1. Non-sparking
2. Not explosive
B. Compressed air is typically
non-damaging to the component. You can stall a pneumatic
motor and cause no damage
IV.
What makes up the air that we breathe, the air that we
compress?
A. 78% Nitrogen
B. 21% Oxygen
C. 1% Argon and other rare gases
V.
Qualities of ambient air:
A. Humidity, we complain about the
amount of gaseous water held by the
air
B. Particulate matter, dust, pollen and
other matter
C. Hydrocarbons
1. Oil vapors
2. Engine exhaust waste
3. Industrial waste,
pollutants
D. One cubic foot of air weighs 0.07
pounds.
E. Ambient air at sea level is 0 PSI (0
PSIG for gauge pressure) or 14.7 PSIA for absolute pressure.
VI.
Characteristics of compressed air:
A. An air compressor takes ambient air and
compresses it an average of eight-fold. 117 PSI is eight
times one atmosphere (14.7). Most air compressors operate
between 100 PSI and 125 PSI. Air compressors basically
take eight coffee cans of ambient air and shove it into one
coffee can.
B. We now have eight times the
contaminants:
1. Eight times the water.
a. A 100 HP air
compressor operating at full load for a twenty-four hour day
at ambient conditions of 95 F and 40% average humidity takes
in fifty-five gallons (a drum) of water a day!
b. This water
must be removed at each drain. Poor removal of water at any
drain in this system will overload the downstream equipment!
c. The ability
to remove water directly relates to the operating
temperature of the equipment. It is critical to keep the
coolers of the air compressor and air dryer clean. The
cooling air supply to these coolers must be ambient
temperature or lower!
2. Eight times the
particulate matter. Automobile manufacturers filter
ambient air before it is compressed for use in the internal
combustion engine. We are eight times more contaminated.
This damaging matter can easily be removed via a particulate
filer. This is usually accomplished after the air
compressor and before the air dryer.
3. Eight times the
hydrocarbons. An industrial ambient atmosphere is
typically measured at 15 PPM hydrocarbons. After we
compress the air we now have 120 PPM of damaging oils in the
airstream. Instruments and other components operating on
the compressed air will fail with this level of oil in the
compressed air. A coalescer filter is used to
coalesce or remove the hydrocarbons. To coalesce means
to bring together the aerosols molecules and drain them
away. While this is not really a filter, we name the
component a coalescer filter.
4. The air compressor
discharge is a contaminant. An oil flood rotary screw air
compressor typically has an oil carry-over which adds more
hydrocarbons and metal fines (particulates) to the airstream.
C. Definitions of Useable Compressed Air
1. Plant Air
a. 90 – 125 PSI
b. 38 F pressure
dewpoint (refrigerated air dryer)
c. Minimal
particulate and hydrocarbon removal
2. Instrument Air
a. 40 – 90 PSI
b. 0 F pressure
dewpoint
c. 99.997% removal
of particulate and hydrocarbon removal
3. Specialty Air
a. Medical Air
b. Pharmaceutical
Air
c. Breathing Air
d. High Pressure
Air
VII.
What makes up a typical industrial compressed air system?
A. Air compressor
1. Rotary screw 5 – 500 HP, 15
CFM – 2,000 CFM
2. Reciprocating (piston style
like automobile engine) ˝ HP – 30 HP
3. Double acting reciprocating
50 HP – 350 HP
4. Centrifugal 200 HP – 1,100
HP
B. Rotary screw air compressor components:
1. Intake air filter.
Critical component for lubricant and compressor air end life
2. Controls
3. Air end. This is the
rotating device that compresses the air. Rotary screws
compressor are preferred due to the continuous compression
across the screw rotors. Compressor lubricant is injected
as the ambient air is compressed. Thus this style of
compression is referred to as oil flooded.
4. Air oil separator
5. Coolant thermal regulation
valve
6. Oil filter
7. Aftercooler
a. Air cooled or
water cooled
b. Integral on
rotary screw air compressors
c. Required to
cool the compressed air
d. Moisture
separator follows to remove liquid water and hydrocarbons.
This drain point is typically responsible for 45% of the
water removal.
C. Particulate filter
1. Delta pressure gauge
2. Combination strainer ball valve
3. Electronic drain valve.
This drain must operate to prevent liquid slugging of the
air dryer!
D. Air Receiver
1. ASME coded and U-stamped
for safe working pressure
2. Pressure gauge
a. 0-200 PSI
b. Most pressure
gauges are accurate to plus or minus 2% and accurate only on
the middle one third of the gauge face
3. Pressure relief valve
4. Condensate drain valve
E. Refrigerated air dryer
1. Air dryer refrigeration
system much like a small window unit air conditioner. The
difference is the media being cooled; the compressed air is
pressurized and remains enclosed in copper tubes or similar
material.
2. Compressed air heats up
in the compression cycle. Charles law of physics sates that
if we reduce the volume (compress) of a gas we produce heat
as a byproduct. As we increase the temperature of air we
increase the water holding capacity. When we utilize the
compressed air we expand back to atmosphere (back to eight
coffee cans). Charles law states that the temperature will
drop as we release the energy (decompress). The water
holding capacity of the air drops and liquid water appears
at the discharge of the pneumatic device.
Let’s use
the example of blasting a metal part to near white metal
condition. We use compressed air to convey an abrasive
material to collide with the metal object removing paint and
oil. The metal is now exposed and without oxidation
protection. The compressed air energy is released, the
pressure drops and the water holding capacity of the air is
reduced. We end up with liquid water draining from the
metal part. Thirty minutes after we cleaned the part
rusting has begun.
A
refrigeration air dryer is necessary to lower the
temperature of the compressed air and remove the water from
the airstream. Compressed air is a closed system. Once
the water is properly removed via air drying, water can no
longer create problems on the manufacturing floor.
3. When the compressed air
enters a refrigerant air dryer its temperature is reduced by
the cold compressed air leaving the dryer. This serves a
dual purpose. First this air to air temperature exchange
lowers the temperature of the entering compressed air.
Secondly this heat exchange increases the temperature of the
dry compressed air restoring the full pneumatic power; hot
compressed air has more energy than cold compressed air.
This is why you will see some of our air receiver
installations after the refrigerant dryer, painted an
absorbing color and exposed to the sun.
Next the
refrigerant is used to chill or lower the compressed air
temperature to approximately 38 F. This level of moisture
removal is referred to as 38 F pressure dewpoint. This is
equivalent to 95% removal of water.
4. Older refrigerants are
considered ozone depleting. Customers utilizing R-12 in
older air dryers should be encouraged to upgrade the
refrigerant air dryer to modern refrigerants.
5. Refrigerant systems can
only be repaired by certified refrigerant technicians.
Refrigerant must not be release to the atmosphere. Air
dryer repairs are commonly performed by qualified
refrigerant subcontractors.
6. Refrigerant air dryers
are only as good as the condensate drain following the
dryer. This drain is critical to the removal of water form
the airstream. An electronic drain valve with a
combination strainer ball valve preceding the valve is
highly recommended.
7. Absorption Dryers as
alternate. For applications that require superior moisture
removal, absorption dryers utilize desiccant in an absorbing
(versus adsorption) method for water removal. This style of
dryer is commonly referred to as regeneration or pressure
swing. Sophisticated instrumentation, pharmaceuticals,
neutraceuticals, aerospace and electronics are industries
that must use this type of moisture removal.
F. Coalescer filter. This filter should be
installed after a refrigerant dryer or before a desiccant
absorbent dryer. Its job is to remove hydrocarbons
(oil), but it often removes water. When this filter is
installed after a refrigerant dryer, a manual petcock is
used to evaluate the amount of oil carryover from the air
compressor.
G. Alternate location for air receiver.
In an effort to reduce the power cost associated with the
production of compressed air it is critically important to
create ‘true compressed air storage’. An air receiver will
not necessarily create compressed air storage. We recommend
that the air receiver be installed after the moisture has
been removed and all filtration is accomplished. With the
air receiver installed last, we can create a large buffer
between the supply of compressed air (the compressed air
system) and the demand for compressed air (the plant).
Storage
of compressed air is accomplished by creating a controlled
pressure drop across the air receiver. In layman’s
terminology, we must put a high pressure in the air receiver
and take the air out at a lower pressure. This creates
storage, reduces the consumption pressure in the plant and
lowers the operational cost significantly. A properly
designed and selected pressure reducing device and a very
accurate pressure gauge are required.
H. Condensate/waste oil separation
1. Considered a hazardous
waste by the EPA
2. Generally easy to separate
back to harmless water and compressor waste oil
I. Distribution air piping system
1. Loop header system
2. Properly designed
compressed air drops
3. Avoid quick connectors
4. Pipe, valve and fitting
selection
5. Materials
6. Subcontract installations
The Writer of 'Compressed Air
Systems 101' can be reached at 727-847-4900. |
800-761-4298
