Perma Pure GASS-2040 - Manual (Page 8)

8 GASS-2040 User Manual | Original Instructions
Dry purge gas enters the dryer at the sample outlet end and performs two functions:
1. Provides a medium for water vapor from the sample to be carried away.
2. Creates a temperature gradient along length of dryer.
Ambient purge air enters the dryer at sample outlet, keeping that portion of dryer cooled.
This counter current flow is required to produce a temperature gradient along the length of
the dryer. To effectively maintain the gradient, the temperature of purge gas exhaust is
monitored and controlled by an electronic temperature controller. As purge gas passes
through the dryer it is heated to the desired sample inlet temperature. This gradient allows for both
rapid vapor removal and decreased final dew point. If the purge gas temperature begins to fall
below the programmed temperature, the system’s backplate will heat. An aluminum heating block
will conduct energy from the backplate to the dryer’s shell tube. Purge gas traveling through the
dryer’s shell acquires heat from the shell. This process allows final temperature of the purge gas to
be closely controlled and a consistent temperature gradient will be maintained.
2. Pressurized Configuration:
An eductor is not required since a vacuum is not needed to withdraw the sample.
Therefore, condensate withdraw is directly controlled by the solenoid valve. Cycle
times can be varied and will be dependent on the amount of liquid present in sample.
2.4 Sample Pump (optional):
The sample pump draws the sample gas and supplies it to the analyzer. It supplies up to 10
liters per minute of sample gas flow. The pump is typically plumbed between the coalescing filter
and membrane dryer or between the coalescing filter and the ammonia scrubber (if present). The
head of the pump is located in the heated section of the system while the motor is located in the
control section. This configuration keeps pump head at a temperature above dew point of the
sample preventing condensation from forming. Included with the optional sample pump is a vortex
cooling tube that helps keep the control enclosure at an acceptable temperature. The PLC controls
the valve that supplies air to the vortex tube. Compressed air requirements are approximately 4
scfm @ 80psi.
2.5 Nafion ® Dryer:
The Perma Pure Nafion membrane dryer is installed downstream of the filter. As sample
enters the dryer, flow splits into a number of small diameter Nafion tubes arranged in a parallel
bundle as shown in Figure 3 below. After sample enters one of these tubes it comes in contact with
the Nafion membrane walls. The membrane selectively removes water vapor from the sample by a
process of permeation distillation. Water vapor travels through the tubing walls driven by the
difference in partial water vapor pressure on the opposing sides of the membrane. As the sample
flows from inlet to outlet water is continually removed, reducing the sample dew point as it travels
through the dryer.
Figure 3