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Re : Temperature range

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  • Tony & Elle Ackland
    ... The temperature at the top of the column is a result of the purity of the vapour you have there. eg if its 78.15 C you have 96.48% purity, 78.24 C is 92.06
    Message 1 of 2 , Feb 24, 2001
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      >within reason what is the allowable temperature range at the
      >top of the collum And what is the ideal temperature

      The temperature at the top of the column is a result of the purity of the
      vapour you have there.
      eg if its 78.15 C you have 96.48% purity, 78.24 C is 92.06 %, 78.74 C is
      90.15 % and so on.

      For me, I target around 78.2C

      There is a table of these values at
      http://www.geocities.com/kiwi_distiller/calc.htm (if you want the detail),
      or a graph of it (easy to understand) at
      http://www.geocities.com/kiwi_distiller/theory.htm#strong

      You should be endevouring to control the tmperature up there by controlling
      the purity of the product you're making. The way to do this is to change
      the height of the column, its packing, or the reflux ratio (eg how much
      liquid you return back down over the packing, compared to how much you take
      off to keep).

      If you're trying to control the heat input to the pot, all you're doing is
      changing the amount of vapour that you're producing. Change the vapour
      flowrate too roughly, and you'll get surging then periods of nothing,
      really upsetting the balance in the column. Decrease it from maximum, and
      you'll be distilling slower than what you can ideally.

      Given that the height of the column, and its packing, don't change within
      the course of a distillation run, your lever really should be the reflux
      ratio.

      If you've got the "pass-through" cooling tubes, like in the Still Maker
      design, these will be condensing a fairly constant amount of vapour. This
      is why changing the heat input will work to some degree - if you're
      condensing out a fixed amount, you can change the ratio by altering the
      total amount. But it's arse about face. Instead, see if you can do it by
      altering the amount of cooling going on with the cooling tubes. Keep the
      vapour flowrate at maximum (ie don't control heat input), and alter the
      amount you're condensing with the tubes. Do this by altering the water
      flowrate through the tubes. The proviso for this is that your still has
      been designed to match the column diameter with the power input being
      supplied to the pot (and hence vapour flowrate). If your column is too
      narrow, then it will "flood" - eg there will be more vapour rising through
      it than desired, and it will push the refluxing liquid back up, rather than
      letting it trickle down through the packing. This is a fundamental flaw
      with the design. Only in this case should you try to run at less than
      maximum heat, as you'll need the lower flowrate just to get things working
      ok. This is where those "lower pass-through" tubes are sometimes of
      benefit - they'll knock out a lot of the vapour prematurely, before it can
      enter the column, and thus reduce the amount in the column. But this is a
      fundamental design problem, and should be addressed by changing the column
      diameter. If you're doing things to reduce the vapour using the column,
      all you're achieving is an extended distilling time.

      This is where the use of pass-through tubes can be a limitation. They may
      not present enough surface area to enable enough cooling to produce the
      amount of reflux you require at the higher purities. There's a couple of
      ways around this - make sure that the column is tall, not short, and that
      you've got some really high surface area packing in there (eg stainless
      steel wool pot scourers). If you've satisfied these two criteria, you
      really don't need a lot of reflux to get the high purity / low temperature
      situation.

      eg - my column is 1.1m tall, and packed with pot scourers. I only need a
      reflux ratio of about 2 (eg return 20 mL back down the column for every 10
      mL kept), to keep the temperature at around 78.2 C. Having a good column
      then means that the low reflux ratio keeps the collection rate fairly high
      - I'm not having to slow things down. With an 1800W element, I'm
      collecting 95%+ purity at around 40-50 mL/minute

      If you can't directly measure the reflux ratio (like with the Nixon-Still
      design), you can still estimate it using a wee calculator I've got at
      http://www.geocities.com/kiwi_distiller/dtw.htm#use_fract

      How high should you let it get ? Again, you can keep it fairly constant by
      slowly increasing the reflux ratio during the course of the run, to deal
      with the slowly decreasing alcohol content in the vapour, as the pot starts
      to run out of alcohol. But there comes a point where you've slowed your
      collection to a dribble, and its still climbing. Depending on your still
      design, this can be an abrupt change, or a gradual one starting a lot
      earlier.

      Looking at the graph at
      http://www.geocities.com/kiwi_distiller/theory.htm#strong , you can decide
      at what lower % purity you want to stop. At it starts to lower,you'll be
      getting into collecting the tails - the fusel oils. I stop collecting for
      purity reasons around 79 C. At this stage I then just open up the valve
      and don't bother refluxing. I'll then collect the vapour from between 79 C
      to 96 C in a seperate bottle. This I'll put in with the next wash, next
      time I distilling. I get about 200-300 mL of liquid in this range.

      Tony
    • Gary Gluyas
      Hello Tony From the above, you mention that your column is 1.1m tall and full of pot scrubbers. Can you remember how many pot scrubbers? Is the column packed
      Message 2 of 2 , Mar 3, 2001
      • 0 Attachment
        Hello Tony

        From the above, you mention that your column is 1.1m tall and full of pot
        scrubbers.

        Can you remember how many pot scrubbers?

        Is the column packed everywhere including top and bottom?

        I am using the plastic balls in my column and was considering a trial using
        pot scrubbers - your comments would be appreciated.

        Cheers

        Gary Gluyas
        gluyas@...

        www.pbsltd.co.nz

        ----------
        From: Tony & Elle Ackland <Tony.Ackland@...>
        To: 'Distillers newsgroup' <Distillers@yahoogroups.com>
        Subject: [Distillers] Re : Temperature range
        Date: Sunday, 25 February 2001 09:16

        >within reason what is the allowable temperature range at the
        >top of the collum And what is the ideal temperature

        The temperature at the top of the column is a result of the purity of the
        vapour you have there.
        eg if its 78.15 C you have 96.48% purity, 78.24 C is 92.06 %, 78.74 C is
        90.15 % and so on.

        For me, I target around 78.2C

        There is a table of these values at
        http://www.geocities.com/kiwi_distiller/calc.htm (if you want the detail),
        or a graph of it (easy to understand) at
        http://www.geocities.com/kiwi_distiller/theory.htm#strong

        You should be endevouring to control the tmperature up there by controlling

        the purity of the product you're making. The way to do this is to change
        the height of the column, its packing, or the reflux ratio (eg how much
        liquid you return back down over the packing, compared to how much you take

        off to keep).

        If you're trying to control the heat input to the pot, all you're doing is
        changing the amount of vapour that you're producing. Change the vapour
        flowrate too roughly, and you'll get surging then periods of nothing,
        really upsetting the balance in the column. Decrease it from maximum, and
        you'll be distilling slower than what you can ideally.

        Given that the height of the column, and its packing, don't change within
        the course of a distillation run, your lever really should be the reflux
        ratio.

        If you've got the "pass-through" cooling tubes, like in the Still Maker
        design, these will be condensing a fairly constant amount of vapour. This
        is why changing the heat input will work to some degree - if you're
        condensing out a fixed amount, you can change the ratio by altering the
        total amount. But it's arse about face. Instead, see if you can do it by
        altering the amount of cooling going on with the cooling tubes. Keep the
        vapour flowrate at maximum (ie don't control heat input), and alter the
        amount you're condensing with the tubes. Do this by altering the water
        flowrate through the tubes. The proviso for this is that your still has
        been designed to match the column diameter with the power input being
        supplied to the pot (and hence vapour flowrate). If your column is too
        narrow, then it will "flood" - eg there will be more vapour rising through
        it than desired, and it will push the refluxing liquid back up, rather than

        letting it trickle down through the packing. This is a fundamental flaw
        with the design. Only in this case should you try to run at less than
        maximum heat, as you'll need the lower flowrate just to get things working
        ok. This is where those "lower pass-through" tubes are sometimes of
        benefit - they'll knock out a lot of the vapour prematurely, before it can
        enter the column, and thus reduce the amount in the column. But this is a
        fundamental design problem, and should be addressed by changing the column
        diameter. If you're doing things to reduce the vapour using the column,
        all you're achieving is an extended distilling time.

        This is where the use of pass-through tubes can be a limitation. They may
        not present enough surface area to enable enough cooling to produce the
        amount of reflux you require at the higher purities. There's a couple of
        ways around this - make sure that the column is tall, not short, and that
        you've got some really high surface area packing in there (eg stainless
        steel wool pot scourers). If you've satisfied these two criteria, you
        really don't need a lot of reflux to get the high purity / low temperature
        situation.

        eg - my column is 1.1m tall, and packed with pot scourers. I only need a
        reflux ratio of about 2 (eg return 20 mL back down the column for every 10
        mL kept), to keep the temperature at around 78.2 C. Having a good column
        then means that the low reflux ratio keeps the collection rate fairly high
        - I'm not having to slow things down. With an 1800W element, I'm
        collecting 95%+ purity at around 40-50 mL/minute

        If you can't directly measure the reflux ratio (like with the Nixon-Still
        design), you can still estimate it using a wee calculator I've got at
        http://www.geocities.com/kiwi_distiller/dtw.htm#use_fract

        How high should you let it get ? Again, you can keep it fairly constant by

        slowly increasing the reflux ratio during the course of the run, to deal
        with the slowly decreasing alcohol content in the vapour, as the pot starts

        to run out of alcohol. But there comes a point where you've slowed your
        collection to a dribble, and its still climbing. Depending on your still
        design, this can be an abrupt change, or a gradual one starting a lot
        earlier.

        Looking at the graph at
        http://www.geocities.com/kiwi_distiller/theory.htm#strong , you can decide

        at what lower % purity you want to stop. At it starts to lower,you'll be
        getting into collecting the tails - the fusel oils. I stop collecting for
        purity reasons around 79 C. At this stage I then just open up the valve
        and don't bother refluxing. I'll then collect the vapour from between 79 C

        to 96 C in a seperate bottle. This I'll put in with the next wash, next
        time I distilling. I get about 200-300 mL of liquid in this range.

        Tony






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