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RE: [Distillers] much info already gained... hungry for more.

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  • Tony & Elle Ackland
    Ben,The scrubbers (or marbles or whatever else you ve chosen for packing) only provide surface area, for the refluxing liquid to spread out over, so that
    Message 1 of 2 , Jun 23, 2001
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      The scrubbers (or marbles or whatever else you've chosen for packing) only
      provide surface area, for the refluxing liquid to spread out over, so that
      it will quickly come to equilbrium with the rising vapour, so that the two
      of them can do a mini-distillation of their own. This is the idea of the
      packed column - you end up doing the equivalent of many distillations. The
      energy for this is from the fact that condensing water out of the vapour
      stream releases energy which can be used to vapourise alcohol out of the
      falling liquid.

      The graph at http://www.geocities.com/kiwi_distiller/theory.htm shows how
      the liquid temperature, its purity, and the resulting vapour purity are all
      related. This relationship is fixed - hardwired, and you can't change it
      (other than say using a vacuum).

      The blue line (liquid) shows how the pot, with say originally 15% alcohol,
      will boil at 90C to start with, slowly increasing towards 100C as the
      amount of alcohol in the liquid decreases (So if you have a thermometer in
      the pot, you can actually tell how much alcohol is left!)

      If the pot is boiling at say 93C, then the vapour coming off will also be
      at 93C. The red line shows that this vapour will have a purity of around
      55%. As the vapour rises up through the packed column, and gets to swap
      water for alcohol from the falling liquid, its purity will increase. The
      temperature of it is shown by the red line. So if you've got enough height
      of packing, and sufficient liquid falling (refluxing), you may get it up to
      say 90% purity. At this point it will be at around 79C. So the vapour
      temperature at the top of the column can tell you how pure it is up there.

      So, you're looking at a temperature gradient, starting at the pot/bottom of
      the column of 93C, decreasing up the height of the column, to around say

      This "cooling" is due to the energy used to swap the ethanol and water
      between the vapour and the liquid. If you cool the liquid too much when
      you condense the vapour to form the reflux, then this energy will be going
      into heating the liquid back up to equilbrium temperature, rather than
      using it to help purify the vapour.

      Does this help, or would you like some numbers, examples etc of the energy
      transfer that is taking place, doing the cooling etc ? I have an
      interactive calculator which does it at
      http://www.geocities.com/kiwi_distiller/heatmass.htm , but it doesn't have
      a lot of the explanation of the detail.

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