Perma Pure PD-Series - Manual

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.
Figure 2 - Reflux Setup
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 some-
what.
The following equation can be used to determine
the purge flow rate required for the split sample
method. Any units may be used as long as they
are consistent.
NOTE: Pressure units must be in absolute terms.
V
p
= V
s
(P
s
/2P
v
) - 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)
Figure 3 - Split Sample Setup
INSTALLATION SPECIFICATIONS
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.
1. STANDARD METHOD
3. SPLIT SAMPLE METHOD
WARNING!
PRINCIPLE OF OPERATION
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 concentra-
tion on the opposite sides of the tubing wall. The
purge gas then carries the water vapor away.
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.
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
- Temperatures 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 tempera-
ture, 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
EXHAUST
VACUUM PUMP
NEEDLE
VALVE
VACUUM GAUGE
GAS
ANALYZER
PD DRYER
FLOW
METER
DRY
SAMPLE
OUTLET
W ET
SAMPLE
INLET
EXHAUST
VACUUM PUMP
VACUUM GAUGE
GAS
ANALYZER
PD DRYER
DRY
SAMPLE
OUTLET
WET
SAMPLE
INLET
PUMP
(OPTIONAL)
(OPTIONAL)
PURGE
AIR
FLOW
METER
NEEDLE
VALVE
SAMPLE
FLOW
METER
NEEDLE
VALVE
PRESSURE
GAUGE
EXHAUST
NEEDLE
VALVE
GAS
ANALYZER
PD DRYER
FLOW
METER
DRY
SAMPLE
OUTLET
WET
SAMPLE
INLET
INSTRUMENT
AIR
INLET
DRY
SAMPLE
EXHAUST
PURGE
EXHAUST
PRESSURE
REGULATOR