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These applications are unique in that stack gas is very wet and hot. You must maintain temperatures above the dew point during extraction at the sample probe and transport to the sample conditioning cabinet.

The problem areas start with the transition from the sample probe to the tubing bundle. While the sample maintain temperatures are generally in the range of 150 to 180§C the stack gas may be 200 to 350§C when it is extracted. The extraction temperatures can quickly exceed the maximum allowable temperature for the process tube and many electric tracers so it must be cooled before it is transported. Because stack gas does not have a high specific heat providing adequate cooling is almost never a problem but it must be considered in the design of the system.

Since the stack gas cools very rapidly precautions must be taken to insure that it does not cool below the dew point of any component in the sample. The best method to insure adequate temperature maintenance is to place a heated metal housing around the sample probe.



It is important to bring the tubing bundle into the enclosure to eliminate the possibility of cold spots. The bundle must be supported and strain relief provided. This can be provided by using a heat shrink entry seal with a mesh support grip. The heat shrink entry seal provides; support for the bundle, a weatherproof connection to the sample probe box, and an insulated transition. The mesh grip provides the mechanical support attaching the bundle to the probe housing.

The bundle must be supported as it is routed down the stack. This support should begin no further than 1 meter from the probe housing.