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44588Re: Reflux

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  • Harry
    Feb 27, 2009
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      --- In Distillers@yahoogroups.com, "alaray_992000" <carsonar@...>
      wrote:
      >
      > Sorry for my lack of information.
      > My system and procedures are as follows.
      > I brew 2 brews of 57 litres each containing 12 and a half kg
      Dextrose
      > and 3kg Sugar. This is brewed with Heat Wave yeast. Each 57 litre
      is
      > stripped giving 17 litres (34 litres total) for the 2nd
      distillation.
      > The still is 60 litre S/S with a column of 1.15 metres x 50mm S/S
      non
      > packed for stripping and for the 2nd distillation a 1.95 mitre x
      50mm
      > S/S column packed with Structured Pure Copper Mesh Column Packing
      > with a gap of 100mm from the return pipe from the offset head to
      the
      > top of the packing.
      > The still is heated by a 2400 watt element controlled by a Helios
      SSR
      > controller which allows me to strip at 100% and then on the 2nd
      > distillation turn power down to 30%. I reflux normally between 30 –
      > 50% heat settings. My 2nd distillation gives me an output of
      between
      > 13 and 14 litres at 94/95%. I re-distil any distillation below 93%.
      > In the past things have gone well with output of 95% for 13 litres
      > with top of column temps reducing from 80at start to as low as 76
      > during distillation. I am at a loss as to why I could not get the
      top
      > of column temp below 86. To my knowledge I did not deviate from
      > normal procedures.
      >


      Sounds like you're doing everything right. Looking for
      possibilities...

      The temp at the top of the packed column is an indication of the
      ratio of [ethanol : water] vapours passing the probe. At 86°C
      measured, it's somewhere around 75% ethanol to 25% water (assuming a
      binary mix for simplicity. It's not, as there are minute amounts of
      other substances involved, but I digress...).

      Now this is fine for a flavoured spirit (e.g whisk(e)y or rum) but
      not good enough for GNS or vodka. And it's certainly not good enough
      for a packed-column reflux run.

      To increase purity (therefore separation) in a 50mm Ø you need to:
      A. Increase the coolant flow
      B. Decrease the product takeoff
      C. decrease the energy input

      A combination of A & B will increase the reflux ratio, thereby
      improving separation. 'C' is necessary if you are overdriving the
      still, creating more vapour than the still column was designed to
      handle.



      It's entirely possible that your controller has developed a fault and
      you may be applying more power than you think. I find it suspicious
      that in previous runs the temp was dropping below the BP of ethanol.
      This indicates either a LOT of heads or not enough power being
      applied to maintain the boil. From your above description of the run
      in question, I'd be checking the accuracy of the controller with a
      multimeter. Some of them are not designed for continuous duty cycle.

      Also check the coolant system for correct operation. There may be a
      blockage of some sort restricting flow and upsetting reflux ratio.

      Let us know the results.


      Slainte!
      regards Harry
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