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FW: 2m Column

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  • Tony & Elle Ackland
    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
    Message 1 of 4 , Feb 1, 2002
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      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
    • 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 2 of 4 , Feb 2, 2002
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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 3 of 4 , Feb 2, 2002
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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 4 of 4 , Feb 2, 2002
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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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