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Thread: Air Stream Moisture Removal

  1. #1
    Associate Engineer
    Join Date
    Apr 2011

    Air Stream Moisture Removal

    Hello All,

    I have a potentially major issue brewing that needs some help but I'm at a loss. In the process of expanding polystyrene with steam, VOCs are given off that must be captured and sent to a thermal oxidizer. The air stream has high moisture content due to steam. We pass the air through a condenser to drop most of it out, but I am having significant amounts of it still condensing and collecting as it gets to the oxidizer that is outside. Question is how do I dry this air enough so that it doesn't collect at my oxidizer? This is roughly 2,500 cfm at about -3.0" w.c. SP. Are there methods other than expensive refrigeration to dry it? The condensers work by passing the steam through a stainless steel "wool" media which is cooled by process water, thereby condensing the steam and the "dry" air exits the top of the condenser and out to the oxidizer. Problem is it's not dry enough and there's still enough moisture that when it cools it condenses and collects in the oxidizer. I am seeing significant corrosion at the oxidizer due to this. I have spoken with various moisture management companies but mechanical/filtration means only remove droplets and not vapor. Any suggestions?

  2. #2
    Project Engineer
    Join Date
    Oct 2013
    Couldn't you add more condensing units to the stream?

  3. #3
    Lead Engineer
    Join Date
    Aug 2013
    Houston TX USA
    Sorry I am a bit late posting. Your condenser is removing enough moisture to reduce the humidity in the air stream to the dew point at the cooling process water temperature at which point the air leaving the condenser is at essentially full saturation, 100% humidity at that temperature, if you are still getting moisture at your oxidizer then it would appear that the air temperature at the entrance to your oxidizer is lower than the air stream leaving the condenser. On the other hand, even if there were to be no free moisture in your air stream you would still have to deal with residual humidity from your condenser, so there is always going to be some possible oxidation/corrosion in the oxidizer.
    It actually appears that your problem is that the oxidizer is not fabricated from a corrosion resistant material suitable for your operating conditions and the real solution to that problem is to address the material problem at that point. Depending upon the operating temperature of the oxidizer this might be remediated by plating or coating the oxidizer components.

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