The gas conditioning is accomplished by filtering and drying of the sample through a membrane of Nafion. The dryer is installed downstream of the filter. When the sample enters the dryer within the system will remove the water vapor from the sample hot, before they cool and condense. This is a considerable advantage over other systems because it avoids the possibility of losing any analytes soluble in water.
The Nafion is not only highly resistant to chemical attacks, but also has a very selective absorption. exhibits highly selective absorption.
The gases d ‘environmental interest such as carbon monoxide, carbon dioxide, nitrogen oxides, sulfur dioxide, hydrochloric acid and others, are completely retained within the sample. With the exception of ammonia, virtually all compounds routinely monitored in an application CEMS are totally retained within the sample flow.
The first step in conditioning the sample is the filtering of particles. The sample gas enters the Group Permeation through a system to bulkhead or, in the case of line heated, this is directly connected to the filter.
After the filter the sample passes through a heated pump, this means that the membrane works in conditions of positive pressure so as to reinforce its capacity for removal of ‘water.
After pumping, the sample enters the Nafion dryer. Gas travels the length of the tube by means of a temperature gradient. The water vapor is absorbed in a selective way and moves through the walls of the tubes pushed by the difference in partial pressure of water vapor on the opposite sides of the membrane.
The flow of purge gas should be -40 ° C dew point air, nitrogen or argon. If this is not available, ETG offers a generator of dry air, as an option to dry the air purge. In addition to bring away the water in the form of steam, the purge gas are suitable to cool the dryer. The elimination of gas helps to establish a good temperature gradient along the dryer ‘.