Perma Pure Indi-GASS - Manual (Page 5)

GASS Module User Manual
5 Bulletin #217
First step in conditioning the sample is to filter out particulates and aerosols by passing it
through a 1
µ
filter consisting of a borosilicate glass filter element with a fluorocarbon binder.
The element is disposable and will withstand high sample temperatures.
If coalescing is anticipated, the system should be fitted with an automatic filter drain to
periodically remove collected liquid mists (in most cases it is acid mist). The automatic
drain will operate in a vacuum or pressurized system.
1. Vacuum Configuration
Collected liquid is withdrawn from the filter drain port by a strong vacuum. The
vacuum is created by an eductor expanding compressed air through a venturi which
should be controlled in cycles by an adjustable digital timer (provided by customer).
The timer switches a solenoid valve and controls compressed air supply.
2. Pressurized Application
An eductor is not required since a vacuum is not needed to withdraw the sample.
Therefore, the 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
the sample.
The filter heater comes standard with a thermostat wired in and preset at 90°C but if sample
condensate is anticipated, an additional temperature controller should be used in place of
the thermostat to control the heater at a lower temperature.
Eductor generates a vacuum to draw condensate from the filter and to drop pressure of the
purge gas to prevent collapsing of Nafion tubing.
The Perma Pure Nafion membrane dryer is installed downstream of the filter. As sample
enters the dryer, the flow splits into a number of small diameter Nafion membrane tubes
which are arranged in a parallel bundle as shown in the figure below. The shell and multi-
tube moisture exchangers transfer water vapor between two countercurrent flowing gas
streams as seen in the drawing below. 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.
Dry purge gas enters the dryer at the sample outlet end and performs two functions:
1. Provides a medium for the water vapor from the sample to be carried away.
2. Creates the temperature gradient along the length of the dryer.
2. GASS Module Components
Filter:
Automatic
Filter Drain
(optional)
Nafion
Dryer
Filter
Thermo-
couple
(optional)
Purge
Eductor
(optional)