2
1.2 Receiving, Storing, and Moving
A.
Receiving - This shipment has been thoroughly
checked, packed and inspected before leaving our
plant. It was received in good condition by the carrier
and was so acknowledged.
Upon receipt, check for visible loss or damage. If this
shipment shows evidence of loss or damage at time
of delivery to you, insist that a notation of this loss or
damage be made on the delivery receipt by the
carrier’s agent.
Also check for concealed loss or damage. When a
shipment has been delivered to you in apparent good
order, but concealed damage is found upon unpack-
ing, notify the carrier immediately and insist on his
agent inspecting the shipment. Reporting damages
to the freight forwarder is the responsibility of the
consignee.
B. Storing - Store the dryer indoors to prevent damage
to any electrical or mechanical components. All
packaging material should be left in place until the
dryer is in position.
C. Moving - The dryer frame is designed to be lifted by a
fork truck. The dryer may also have lifting lugs for use
with an overhead crane. Be sure to attach to all of the
lift points and use appropriate spreader bars to
prevent damage to the dryer.
CAUTION:
Never lift the dryer by attaching hooks or
slings to the air inlet and outlet connections or
piping, or to any part other than the lifting lugs.
Severe structural damage could result.
2.0 Equipment Function and Operation
A. Function
Blower purge type regenerative desiccant dryers are
an economical and reliable way to dry compressed air
to dew points below the freezing point of water.
Desiccant dryers lower the dew point of compressed
air by adsorbing the water vapor present in the
compressed air onto the surface of the desiccant.
Adsorption continues until equilibrium is reached
between the partial pressure of the water vapor in
the air and that on the surface of the desiccant.
These dryers continuously dry compressed air by
using two identical towers, each containing a desic-
cant bed. While one tower is on-line drying the
compressed air, the other tower is off-line being
regenerated.
The towers are alternated on- and off-line so that dry
desiccant is always in contact with the wet com-
pressed air, resulting in a continuous supply of dry air
downstream. The switching from one tower to the
other is controlled by a PLC on either a fixed time
basis (standard) or a demand basis (optional).
B. One Stage Regeneration (Standard)
When a tower is placed off-line, it is slowly depressur-
ized and the desiccant is regenerated as follows. The
blower draws in ambient air which is heated. This
heated air flows through the desiccant bed, desorbs
the moisture from the desiccant, and carries the
desorbed water out of the dryer. The blower and
heater are turned off when the desiccant bed is fully
heated. The tower is then repressurized to full line
pressure. This prevents desiccant bed movement
and downstream pressure loss when the tower goes
back on-line.
C. Two Stage Regeneration (Optional)
When a tower is placed off-line, it is slowly depressur-
ized and the desiccant is regenerated in a two stage
process. First, a blower draws in ambient air which is
heated. This heated air flows through the desiccant
bed, desorbs the moisture from the desiccant, and
carries the desorbed water out of the dryer. The first
stage continues until the desiccant bed is fully
heated. In the second stage, a portion of the dry
compressed air (4.5% maximum, 0.8% average) is
diverted from the main air flow and throttled to near
atmospheric pressure. This extremely dry, low
pressure air passes through the hot off-line tower,
partially cooling the desiccant bed and reducing the
dew point spike after tower change over. At the end
of the second stage, the tower is repressurized to full
line pressure. This prevents desiccant bed movement
and downstream pressure loss when the tower goes
back on-line.
D. Temperature and dew point spike
When a regenerated tower is placed on-line, there will
be a temperature spike and a dew point spike. With
two-stage regeneration the temperature spike is
reduced by approximately 25
°
F (14
°
C) and the dew
point spike by 20
°
F (11
°
C) in comparison to a dryer
with one stage regeneration. The outlet temperature
and dew point will return to design conditions in less
than thirty minutes.
Left Tower Drying Right Tower
1st Stage Regeneration
Figure 2.1
Left Tower Drying Right Tower
2nd Stage Regeneration
