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Re: Does size matter?

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  • mavnkaf
    ... see a ... over ... packing. ... to ... Hi Mason. In my case, having a HJ cross flow-dual head still that has about 71 inches x 2 inch column that is packed
    Message 1 of 7 , Nov 26, 2008
      > Hey Neighbor,
      > I recently asked these questions in private to one of the more
      > knowledgeable members and was told that 36" of packing length was
      > sufficient in a 2 inch column to achieve maximum Purity. You do
      see a
      > lot of 48" and even taller columns out there, I had just always
      > wondered if it was necessary. The taller columns may be a carry
      > from the days when Marbles and Rashig Rings were the available
      > They have a small amount of surface area compared to Scrubbers and
      > Structured packing therefore you would need a taller column of them
      > get more theoretical plates. Could one of you reflux guys (Riku,
      > Harry) confirm or deny this assumption?
      > Mason

      Hi Mason.

      In my case, having a HJ cross flow-dual head still that has about 71
      inches x 2 inch column that is packed with Amphora mesh, which does
      include the boiler or the section for the VM take off and cross
      condenser. Yes its tall, but for a reason you did not mention.

      And that is vapor speed through the column. If the ethanol/water
      vapor is too fast through the column packing it will require a
      higher reflux ratio to achieve the % you want, which takes more time.

      My boiler is a 20-litter hot water urn, 20 L to the brim; it's kind
      of small but suits my time frame. The original element is 2400
      watts, I added a still spirits 1100 watt element for the spirit run.

      So as we all know the best wattage element for a spirit run is about
      750 watts, right? I already had the crappy still spirits still, so I
      used the element from that and added to my free hot water urn. To
      compensate for the extra heat/vapor velocity , I needed to add more
      theoretical plates to achieve the separation I hope for. I get 95.
      what ever %, every time. You still got to the heads and tails thing
      but it happens in a shorter period.

      Conclusion: add vapor velocity /element wattage/ reflux ratio to the
      reason if you want? I'm talking about balancing the still, I know
      there's much more to it and Harry was just giving a simple yes and no


      Ps, I'm way over my head on this, but the "vapor velocity" subuject,
      has been talked about before.
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