User Manual

1.0 System and Component Description

MicroGASS™ System

The Perma Pure MicroGASS™ system prepares gas samples for analysis by electrochemical

sensor (ECS) and other analyzers when the sample is too humid for analysis but not

condensing at ambient temperature. ECS analyzers suffer reliability problems when the sample

is either too wet or too dry. MicroGASS systems reduce sample humidity to the ideal range for

ECS (typically 20-80%RH), while also removing dust or dirt particles. MicroGASS sampling

systems offer full corrosion resistance and very high selectivity to water vapor, so complex

samples can be processed without loss of analyte gases. Nafion® dryer technology is the

driving force behind this system. Operating as a self-contained unit, the MicroGASS

incorporates a built-in pump to draw the sample gas through a filter and MD-Series™ Nafion®

dryer. Clean sample gas then flows to the sensor where the measurement is made. After

exhausting from the analyzer and returning to the system, the gas passes through a needle

valve and expands, causing a reduction in vapor pressure. It then re-enters the dryer to be used

as a purge gas. Because the purge gas is generated from the sample gas exhaust stream of the

sensor, the MicroGASS gas conditioning process is self-regenerating. No maintenance, other

than regular replacement of the particulate filter element, is required. System power is supplied

by a standard 115 or 220 VAC circuit

Particulate Filter

The particulate filter’s function is to remove small amounts of particulate matter from the sample

stream that could, over time, contaminate the system and degrade performance of the system.

High levels of particulate matter should be removed by alternate means upstream of the

MicroGASS system. This is typically accomplished with a heated filter at the point of sample gas

extraction.

Nafion

Membrane Dryer

The dryer consists of a Nafion

membrane tube housed inside a tubular shell. The sample inlet

portion of the dryer is heated to provide rapid removal of the water and to prevent condensation.

Nafion transfers water vapor with a higher efficiency at elevated temperatures yet will allow for

drying to lower water concentration at lower temperatures. For this reason, only the inlet portion

is heated. As wet sample gas enters the Nafion

tube, water vapor is transferred through the

membrane and carried off by a counter-current gas flow at a reduced pressure. The driving

force for this process is the difference in partial vapor pressure of water between the sample

and purge gas flows. In the MicroGASS system, the dried sample gas flow is returned from the

gas sensor or analyzer, expanded to about 1/2 atm pressure and then passed through the shell

portion of the dryer as the purge gas. While all of this may be confusing and sounds like black

magic, it’s not. The sample gas leaves the system with the same water content that it entered

with. What is important to note is that the majority of the water vapor is essentially short-

circuited inside the dryer. The sample gas flow from the system to the sensor and back is the

only section of the plumbing where the humidity of the sample gas is low and condensation

cannot occur. Some of the water vapor will condense as the sample gas exits the system