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Further Fractionating fabrication Frustrations

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  • Thomas Hart
    A question for anyone who can help. If I retrofit my reflex still with a condensing unit that allows recirculation of my distillate to promote fractionization
    Message 1 of 2 , Apr 6, 2001
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      A question for anyone who can help.

      If I retrofit my reflex still with a condensing unit that allows
      recirculation of my distillate to promote fractionization (if that is a real
      word), how do make sure that the distillate actually recirculates and
      doesn't just pool? An additional concern is pressure build up in a looping
      system.

      I have seen two designs. One has basically a cooled extension of the column
      with a valve to the regular condenser. My guess is that this valve serves
      as a pressure relief primarily, but I imagine there is a degree of vapor
      that passes through and is not recirculated. The second design is basically
      a condenser with an open top which the vapor enters at a mid-point, rises,
      hopefully condenses before it exits and then trickles back down into the
      Reflux column via a port in the side just above the packing. I assume this
      design is open ended so as to allow for pressure relief.

      In the first example I see how the distillate simply flows back, and I
      imagine the amount sent on to the condenser is of little significance, but
      there is loss none the same. The second system raises concerns for me as
      well. Is the loss of vapor through the open top a concern? I would guess
      it would not be if this unit is tall enough, but how is this gauged?
      Additionally, since this unit is an external loop, isn't there going to be a
      problem with column vapor rising up through its outlet as well as its inlet?

      Maybe I am over thinking all of this, but I want to get it right. Which is
      better, are these real issues, and are there other designs I should
      consider?

      Finally, wouldn't increasing the flow rate through the coil in the head of
      my still accomplish the same thing as either of the above?

      Thanks for your help with all this. I hope it doesn't keep you up at night.
      I need to let it go and get back to Sundays sermon as I haven't figured out
      how fractionating columns relates to Palm Sunday.

      Peace-
      Tom
      the Stillpastor
    • Kev
      Tom, AFAIK the way to stop the pooling is to make sure that gravity is working for you. Introduced back into the column, the condensed liquid will fall back
      Message 2 of 2 , Apr 8, 2001
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        Tom,

        AFAIK the way to stop the pooling is to make sure that gravity is
        working for you. Introduced back into the column, the condensed
        liquid will fall back down the column before turning back into vapour
        and rising back up again.

        Pressure release - yes, that's the reason for the open ended design
        on a 100% reflux system.

        How do you kow you're not losing loads of good stuff to the air? You
        over-engineer your condensor to make sure that all the liquid is
        taken out of the expanded gas well before releasing it into the open.

        > Additionally, since this unit is an external loop, isn't there
        going to be a
        > problem with column vapor rising up through its outlet as well as
        its inlet?

        That's exactly the problem that I had with my modified still. The
        Nixon / Stone design has the inlet and back-flow pipes sharing the
        same tube - vapour rises to the top of the tube, liquid flows back on
        the bottom. This seems like the best design, other than playing with
        a non-return valve on the flow-back pipe, which is my next project.
        Watch this space!

        > Finally, wouldn't increasing the flow rate through the coil in the
        head of
        > my still accomplish the same thing as either of the above?

        Yes, if your head returns the distillate back down the column. You'd
        not get as fine a level of control doing this, but it'd more or less
        work, yes.

        Good luck!

        Kev.
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