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Re: FW: 2m Column

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  • peter_vcb
    Tony, if i have a column tall enough eg 2 or 3 metres do i really need any reflux at all. could i run it without a condenser at the top of the column and just
    Message 1 of 4 , Feb 2 5:06 AM
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      Tony, if i have a column tall enough eg 2 or 3 metres do i really
      need any reflux at all. could i run it without a condenser at the top
      of the column and just have it coming out into a normal liebeg
      condenser?

      --- In new_distillers@y..., Tony & Elle Ackland <Tony.Ackland@c...>
      wrote:
      > Graeme,
      >
      > Your email address doesnt like me, so I'll reply publically .....
      For
      > everyone else .. the question was essentially "how does a taller
      column let
      > you run it faster" ?
      >
      >
      > Your 1.2m column presently does about ten redistillations up its
      length, to
      > get the purity you're presently getting. But to achieve that
      purity, you
      > need to run it at a particular reflux ratio (I'm assuming about 4 -
      eg you
      > keep 1 and return 4 parts back to the column).
      >
      > By increasing the column length to 2m, you'd now have about 16
      > redistillations (HETP) happening.
      >
      > But you know you only need say 10 for the purity - so if you keep
      the
      > existing reflux ratio, not a lot further will be going on in those
      extra 6
      > stages.
      >
      > But heres the trick - if you decrease your reflux ratio - eg keep
      more,
      > return less, you will degrade the effectivenesss of those stages,
      but it
      > doesnt matter - as you have so many of them "spare". But - you've
      > increased your collection rate. So your 16 stages are now only
      working
      > like 10, but you're still happy with the purity, as its the same as
      what
      > you had prior. But you're collecting it heaps faster.
      >
      > And it doesnt require any more heat input. You're just using the
      spare
      > refining capacity of the taller column.
      >
      > Unfortunately, my calculations on this aren't too precise - so I
      cant
      > detail the exact trade-off between extra height and going faster.
      Four
      > times does sound heaps, but entirely permissable. All I can say is
      give it
      > a try. There will be benefit in going taller.
      >
      > Tony
    • Tony & Elle Ackland
      ... Just scale them up to keep the same number per meter ... 18 x (2/1.2) = 30 Tony
      Message 2 of 4 , Feb 2 11:15 AM
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        > On the subject of scrubbers I have 18 on the 1.2 column. How many
        > should one have on the 2m?

        Just scale them up to keep the same number per meter ...
        18 x (2/1.2) = 30


        Tony
      • Tony & Elle Ackland
        ... You will always need some reflux. Without that liquid flowing back down over the packing, there will be nothing to purify the rising vapour. You d just
        Message 3 of 4 , Feb 2 6:46 PM
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          > if i have a column tall enough eg 2 or 3 metres do i really
          > need any reflux at all.

          You will always need some reflux. Without that liquid flowing back down
          over the packing, there will be nothing to purify the rising vapour.
          You'd just have a tall pot still.

          If you didn't insulate the column, then there might be some condensing
          happening on the sides of the column, and refluxing, but thats not what you
          want. Its too uncontrolled, and wont do the job properly. You want the
          reflux to be a deliberate action, generated above the top of the packing
          (so that it gets to flow down over all the packing). If it were just off
          side cooling, then its not using the full height of the column, and it wont
          be distributed well through the packing.

          A taller column will allow you to run less reflux (eg say 3:1 instead of
          4:1), but it will always require reflux, and still a good proportion of it.
          A taller column is only of use if the reflux is using all that height.

          Tony
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