PRINCIPLE OF OPERATION
INSTALLATION SPECIFICATIONS
3. SPLIT SAMPLE METHOD
PD™-Series gas dryers are shell and multi-tube
moisture exchangers that transfer water vapor
between two countercurrent flowing gas streams
as shown in the figure above. The dryers consist
of a bundle of Nafion® polymer tubes surrounded
by an outer tube.
Dry purge gas flowing over the exterior surface of
the Nafion tubing continuously extracts water
vapor from the gas stream inside the tubing. The
driving force is the difference in water concentration on the opposite sides of the tubing wall. The
purge gas then carries the water vapor away .
When installing PD-Series gas dryers, the
following rules apply:
- Sample pressure equal to or greater than purge
pressure
- Sample gas pressure not to exceed 80 psig
- Purge gas pressure not to exceed 10 psig
- T emperatures must not exceed 120°C for SA,
SS, KS or KA models, and 90°C for PP or PS
models
- If sample dew point is above ambient temperature, inlet of dryer must be heated (contact
factory for details)
- Purge air of -40°C dew point at a flow rate of two
to three times sample flow
- Sample and purge air must flow countercurrent
to each other
WARNING!
When connecting any fitting to the purge
ports of the dryer , be sure not to tighten
the threaded fitting more than 5 turns.
More turns may cause the fitting to
damage the element header just below.
FLOW
METER
INSTRUMENT
AIR
INLET
DRY
SAMPLE
EXHAUST
WET
SAMPLE
INLET
PURGE
EXHAUST
PD DRYER
DRY
SAMPLE
OUTLET
NEEDLE
VALVE
PRESSURE
REGULATOR
GAS
ANALYZER
Figure 1 - Typical Setup
2. REFLUX METHOD
The reflux setup, shown in Figure 2, returns dry
sample back to the dryer for use as the purge
after it has gone through the analyzer . Since this
method uses all of the dry sample as the purge
gas, only the sample flow required for analysis
passes through the dryer . This results in high
drying efficiency.
The vacuum on the purge gas should be at least
15” of Hg, with a higher vacuum preferable. This
vacuum level is necessary to provide the desired
2:1 purge-to-sample flow ratio based on the actual
volumetric flow.
The split sample method, shown in Figure 3,
diverts some of the sample from the main stream
to be used as the purge gas. More sample
passes through the dryer than is required for the
analysis, lowering the drying efficiency somewhat.
The following equation can be used to determine
the purge flow rate required for the split sample
method. Any unit s may be used as long as they
are consistent.
NOTE: Pressure units must be in absolute terms.
Vp = V
s
(Ps/2Pv) - 1
Where:
Vp = Purge flowrate (indicated on flowmeter)
Vs = Sample flowrate (indicated on flowmeter)
Ps = Sample pressure (in absolute units)
Pv = Purge pressure (in absolute units)
GAS
FLOW
ANALYZER
EXHAUST
SAMPLE
METER
1. STANDARD METHOD
The most efficient way to set up PD-Series dryers
is to have sample enter through the 1/4” NPT port
and the purge gas enter through the 1/8” NPT port
at the opposite end (see Figure 1). Purge gas
should be instrument air or other dry gas. If no
dry purge air is available, one of the following
methods may be used.
WET
SAMPLE
INLET
PD DRYER
VACUUM GAUGE
Figure 2 - Reflux Setup
VACUUM PUMP
NEEDLE
VALVE
DRY
SAMPLE
OUTLET
EXHAUST
FLOW
METER
GAS
ANALYZER
WET
SAMPLE
INLET
PD DRYER
PUMP
VACUUM GAUGE
(OPTIONAL)
VACUUM PUMP
(OPTIONAL)
PURGE
AIR
FLOW
METER
Figure 3 - Split Sample Setup
NEEDLE
VALVE
DRY
SAMPLE
OUTLET
PRESSURE
GAUGE
EXHAUST
NEEDLE
VALVE
TO ROTATE FITTINGS
Adjusting end fittings without following
the steps below may cause twisting of
membrane tubing and void warranty .
5. Repeat steps 2-4 for other end.
6. Remove one o-ring from tube header (see
Figure 5).
7. Pull tube element from opposite end of dryer.
PERFORMANCE
PD-Series dryer’s performance vary according to
dryer lengths, flowrates and the number of
Nafion tubes.
T ool Needed:
- Phillips head screwdriver
1. T urn locking screw 2-3 turns on end of dryer
(not necessary to take screw out).
2. Position fittings as needed. Do not rotate
more than 180 degrees from original
position and check to see tubing inside
shell is not twisted.
3. Align purge port to hole in shell tube (see
Figure 4).
4. Tighten locking screw.
Sample Port
Check for Alignment
TO DISASSEMBLE DRYER
T ools Needed:
- Phillips head screwdriver
- unsharpened pencil with eraser
Tube Header
Figure 5
TO ASSEMBLE DRYER
T ool Needed:
- Phillips head screwdriver
1. Install one thick o-ring onto grooved tube
header (Refer to Figure 6).
2. Slip opposite tube header into dryer shell.
3. Install other thick o-ring onto groove.
4. Push one thin o-ring into groove inside
coupling (for SS and AL shells slip o-ring on
shell across two holes).
5. Firmly push coupling over tube header.
6. Align purge port with hole in shell tube.
7. Tighten locking screws until underside of
screw head contacts top of boss.
8. Repeat steps 4-7 for opposite end.
PD™ -Series
Gas Dryer
User Manual
1. Loosen locking screws on both ends of dryer.
2. Insert eraser end of pencil into one sample
port until it rests on tube header face.
3. Hold dryer vertically and place other end of
pencil down onto a hard, slip resistant surface.
4. While supporting shell tube, push lower end
fitting down with consistent pressure until it
slips off shell tube. Do not attempt to pull
fitting from shell tube; doing this is likely to
damage dryer element tubing.
Nafion® is a registered trademark of DuPont
PD™ is a trademark of Perma Pure LLC.
Bulletin# 204a
Figure 6
Performance Curve
Replacement parts:
Dryer element:
PD-50T-(12, 24, 48,72)E-M
Includes one set of o-rings
Extra o-ring set of 4:
PD-50T-3M
PERMA PURE
8 Executive Drive
Toms River, N.J. 08755
Phone: 732/244-0010
Fax: 732/244-8140
e-mail: info@permapure.com
Web Site: www.permapure.com
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