There are two common ways to deal with process exhaust effluent: heating the forelines and components to maintain the effluent in a gaseous state until it enters the scrubber, or trapping the effluent in a place where you can access it easily for regular maintenance. Many installations have both, and we recommend this approach for the really harsh effluent applications such as LPCVD Silicon Nitride. For more information on the heating approach, there are other blog posts on this site. This post focuses on trapping techniques.
Standard and custom foreline traps range in complexity from sealed, coaxial traps (to prevent oil backstreaming), to triple-pass water cooled traps (for removing condensable gases which contaminate mechanical pump oil or other components of the system). There can be as much as a 200% increase in maintenance intervals once a trap is installed.
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The question that arises is ‘what type of trap should I use in my application?’ The answer depends on what you are trying to accomplish. The following table can be used as a general guide to selecting which type of trap will best suit your application:
|Trap Type →||Metal Sieve||Molecular||Cold||Particulate|
|Condensables – Low Vapor Pressure||B||B||A||A|
|Condensables – High Vapor Pressure||C||C||A||C|
Blank = Not suitable for this application
C = Good performance
B = Better performance
A = Best performance