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restabilising columns during a run

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  • peter_vcb
    while running at low power my output would stop altogether as time went on and % decreased. at 500W i was getting output near the end at 86C. if i lowered the
    Message 1 of 7 , Jun 23, 2003
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      while running at low power my output would stop altogether as time
      went on and % decreased. at 500W i was getting output near the end at
      86C. if i lowered the power until i was at full reflux for a while i
      could then increase the power past 500W and collect at 78-80C for a
      while before it gradually it went up again to the mid 80s. i presume
      the column was restabilising and the alcohol was getting a chance to
      gather at the top. theres no real advantage to doing this at the end
      of a run if you collect and reuse tail. but i have wondered if it is
      worth doing this at the start of a run. just as you are coming to the
      main run is it worth restabilising the column for a while to get the
      last traces of heads out?
    • Mike Nixon
      peter_vcb wrote: Subject: [Distillers] restabilising columns during a run while running at low power my output would stop altogether as time went on and %
      Message 2 of 7 , Jun 23, 2003
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        peter_vcb wrote:
        Subject: [Distillers] restabilising columns during a run

        while running at low power my output would stop altogether as time went on and % decreased. at 500W i was getting output near the end at 86C. if i lowered the power until i was at full reflux for a while i could then increase the power past 500W and collect at 78-80C for a while before it gradually it went up again to the mid 80s. i presume the column was restabilising and the alcohol was getting a chance to gather at the top. theres no real advantage to doing this at the end of a run if you collect and reuse tail. but i have wondered if it is worth doing this at the start of a run. just as you are coming to the main run is it worth restabilising the column for a while to get the last traces of heads out?
        =========================
        Hi Peter,
        Always a good idea to keep the reflux ratio as high as you can when extracting the heads as the boiling points of most of the heads components are very close to that of ethanol, which makes their separation difficult.  This is why standard procedure is to leave the column to stabilise under full reflux before taking anything off at all, to give time for those components to concentrate at the top of the column, then keep the first rate of extraction as slow as you can so as not to upset that delicate balance.  Stopping this slow collection from time to time is also good practice, and for the reasons you give.  Maintaining low power during this phase helps also, as this maximises the amount of separation inside the column.  It's the way Mike McCaw and I always do it as that extra little patience at the beginning is well worth while.  Once the heads have been bled off, you can safely increase the power and rate of collection as it is relatively easy to keep the tails components suppressed until the end.  Keep those heads to put in the next batch though, together with the tails.  Both contain a very high proportion of ethanol that you can recover next time round.
        Mike N
         
      • spoliatio
        Mike Can you advise me please.... I have a 1.2 M x 50mm column on a 12 ltr boiler with a single pass of 15mm copper tube through the top of the col. acting as
        Message 3 of 7 , Jun 25, 2003
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          Mike
          Can you advise me please.... I have a 1.2 M x 50mm column on a 12 ltr
          boiler with a single pass of 15mm copper tube through the top of the
          col. acting as the reflux condenser, this just above a full
          compliment of your copper packing ( excellent ).
          Q. I am never sure how to acheive the equilibrum discussed with this
          system as by adjusting the water flow or power input via my
          controller I can choose whatever temperature I want at the takeoff
          point.
          I am in the habit of setting this temperature at about 76C and
          leaving it there for half an hour then bringing it up to " a drip a
          second " in the fond hope that I am removing the heads. What
          temperature should I aim for ???
          Cheers
          Spoliatio

          --- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:
          > peter_vcb wrote:
          > Subject: [Distillers] restabilising columns during a run
          >
          > while running at low power my output would stop altogether as time
          went on and % decreased. at 500W i was getting output near the end at
          86C. if i lowered the power until i was at full reflux for a while i
          could then increase the power past 500W and collect at 78-80C for a
          while before it gradually it went up again to the mid 80s. i presume
          the column was restabilising and the alcohol was getting a chance to
          gather at the top. theres no real advantage to doing this at the end
          of a run if you collect and reuse tail. but i have wondered if it is
          worth doing this at the start of a run. just as you are coming to the
          main run is it worth restabilising the column for a while to get the
          last traces of heads out?
          > =========================
          > Hi Peter,
          > Always a good idea to keep the reflux ratio as high as you can when
          extracting the heads as the boiling points of most of the heads
          components are very close to that of ethanol, which makes their
          separation difficult. This is why standard procedure is to leave the
          column to stabilise under full reflux before taking anything off at
          all, to give time for those components to concentrate at the top of
          the column, then keep the first rate of extraction as slow as you can
          so as not to upset that delicate balance. Stopping this slow
          collection from time to time is also good practice, and for the
          reasons you give. Maintaining low power during this phase helps
          also, as this maximises the amount of separation inside the column.
          It's the way Mike McCaw and I always do it as that extra little
          patience at the beginning is well worth while. Once the heads have
          been bled off, you can safely increase the power and rate of
          collection as it is relatively easy to keep the tails components
          suppressed until the end. Keep those heads to put in the next batch
          though, together with the tails. Both contain a very high proportion
          of ethanol that you can recover next time round.
          > Mike N
        • Mike Nixon
          spoliatio wrote: Subject: [Distillers] Re: restabilising columns during a run ... again Mike Mike Can you advise me please.... I have a 1.2 M x 50mm column on
          Message 4 of 7 , Jun 25, 2003
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            spoliatio wrote:
            Subject: [Distillers] Re: restabilising columns during a run ... again Mike

            Mike
            Can you advise me please.... I have a 1.2 M x 50mm column on a 12 ltr boiler with a single pass of 15mm copper tube through the top of the col. acting as the reflux condenser, this just above a full compliment of your copper packing ( excellent ).

            Q. I am never sure how to acheive the equilibrum discussed with this system as by adjusting the water flow or power input via my
            controller I can choose whatever temperature I want at the takeoff point.
            I am in the habit of setting this temperature at about 76C and leaving it there for half an hour then bringing it up to " a drip a
            second " in the fond hope that I am removing the heads. What temperature should I aim for ???
            =============================
            Hokay esteemed Senator.  let's just clear up a wee point about columns first.
             
            A packed column with no imposed cooling at the top is a simple reflux still and the separation you get depends solely on the height of the column and the sort of packing you have inside (which controls the amount of 'natural' reflux inside the column).  Output is taken directly off the top and the rate it comes out and its purity/strength can be controlled by boiler power.
             
            A compound still is a simple reflux column with imposed cooling at the top to provide more reflux in that region than that which you get with the packing alone. A true compound column will have enough cooling at the top to condense all the vapor that gets to the top. Output is also taken from the top, but via a tap which either controls the rate at which liquid or vapor is drawn off.  Boiler power is kept constant.
             
            The columns of both stills are insulated against heat loss as liquid condensing on the column walls tends to return to the boiler almost immediately, reducing the efficiency of separation.
             
            Now what you seem to have is something in between.  The 15mm cooling tube at the top is unlikely to be efficient enough to always act like a compound still reflux condenser in that it will only be able to cope if the boiler power is turned up beyond a certain amount, so you have to watch that input power.  From what you say, you are balancing the heat input so it matches the cooling ability of that cooling tube, and leaving it like this for half an hour or so.  You then either increase the boiler power or reduce the cooling water flow so product starts coming out the top.
             
            Now this will enable the contents of the column to stabilise like a compound column, and if very carefully done it will produce the same results.  During stabilisation, the lightest fractions with the lowest boiling point will accumulate at the top and can then be bled off slowly to remove them as heads.  You can judge when the column has stabilised by watching the temperature at the top.  It will start off high, then slowly fall as the concentration of the lightest fractions increases and the boiling point of the resulting mix at the top is lowered.  When it has remained at a steady temperature for half an hour or so, then you will have built up this mixture in the top so that it extends down a few inches to form a reservoir of heads at the same temperature, with the temperature below this reservoir getting higher and higher.
             
            When you start bleeding off the heads, the temperature at the top should remain steady (the precise value will vary from still to still and from wash to wash), then start to rise until it reaches a new steady reading.  At this point you know that you have now got rid of the heads and are into the main run.  Note that, as it is important ... you do NOT try and control the temperature ... you leave the molecules to sort that out themselves and let them tell you what is happening!
             
            As I said, what you have is something between a simple reflux still and a compound still.  Using it carefully, you can achieve the same strength and purity as a compound still.  However, the penalty you pay is that you have to do this constant juggling act to control heat put into the sytem at the bottom and heat taken out at the top.  The advantage of a true compound still is that it takes away almost all the need for difficult adjustment.  You can set your boiler to match the maximum rate at which you want to run (remembering that faster means dirtier), and rely on your top reflux condenser to deal with all you throw at it without any need for adjustment.  That leaves you free to watch the thermometer to see what is going on in the top of the column, and to control the amount of imposed reflux you apply by the turn of a single tap or gate valve.  The best advice I can give (if you want to carry on with your present still) is to leave the top cooling tube running at full all the time and do all your adjustments with the boiler power alone.  That way you have only one thing to control ... guided by two things:  the rate at which product is coming out the top (zero during stabilisation) and what you read on the thermometer.  At the risk of being more boring than I already am, please let me stress that you should read the thermometer for guidance, not 'control' it!
             
            Let's hope that amongst all that verbosity you find the answer you were looking for :-)
            All the best,
            Mike N
            Per varios usus artem experientia fecit.
             
          • spoliatio
            ... ltr boiler with a single pass of 15mm copper tube through the top of the col. acting as the reflux condenser, this just above a full compliment of your
            Message 5 of 7 , Jun 26, 2003
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              > Mike
              > Can you advise me please.... I have a 1.2 M x 50mm column on a 12
              ltr boiler with a single pass of 15mm copper tube through the top of
              the col. acting as the reflux condenser, this just above a full
              compliment of your copper packing ( excellent ).
              >
              > Q. I am never sure how to acheive the equilibrum discussed with
              this system as by adjusting the water flow or power input via my
              > controller I can choose whatever temperature I want at the takeoff
              point.
              > I am in the habit of setting this temperature at about 76C and
              leaving it there for half an hour then bringing it up to " a drip a
              > second " in the fond hope that I am removing the heads. What
              temperature should I aim for ???
              > =============================
              > Hokay esteemed Senator. let's just clear up a wee point about
              columns first.
              >
              > A packed column with no imposed cooling at the top is a simple
              reflux still and the separation you get depends solely on the height
              of the column and the sort of packing you have inside (which controls
              the amount of 'natural' reflux inside the column). Output is taken
              directly off the top and the rate it comes out and its
              purity/strength can be controlled by boiler power.
              >
              > A compound still is a simple reflux column with imposed cooling at
              the top to provide more reflux in that region than that which you get
              with the packing alone. A true compound column will have enough
              cooling at the top to condense all the vapor that gets to the top.
              Output is also taken from the top, but via a tap which either
              controls the rate at which liquid or vapor is drawn off. Boiler
              power is kept constant.
              >
              > The columns of both stills are insulated against heat loss as
              liquid condensing on the column walls tends to return to the boiler
              almost immediately, reducing the efficiency of separation.
              >
              > Now what you seem to have is something in between. The 15mm
              cooling tube at the top is unlikely to be efficient enough to always
              act like a compound still reflux condenser in that it will only be
              able to cope if the boiler power is turned up beyond a certain
              amount, so you have to watch that input power. From what you say,
              you are balancing the heat input so it matches the cooling ability of
              that cooling tube, and leaving it like this for half an hour or so.
              You then either increase the boiler power or reduce the cooling water
              flow so product starts coming out the top.
              >
              > Now this will enable the contents of the column to stabilise like a
              compound column, and if very carefully done it will produce the same
              results. During stabilisation, the lightest fractions with the
              lowest boiling point will accumulate at the top and can then be bled
              off slowly to remove them as heads. You can judge when the column
              has stabilised by watching the temperature at the top. It will start
              off high, then slowly fall as the concentration of the lightest
              fractions increases and the boiling point of the resulting mix at the
              top is lowered. When it has remained at a steady temperature for
              half an hour or so, then you will have built up this mixture in the
              top so that it extends down a few inches to form a reservoir of heads
              at the same temperature, with the temperature below this reservoir
              getting higher and higher.
              >
              > When you start bleeding off the heads, the temperature at the top
              should remain steady (the precise value will vary from still to still
              and from wash to wash), then start to rise until it reaches a new
              steady reading. At this point you know that you have now got rid of
              the heads and are into the main run. Note that, as it is
              important ... you do NOT try and control the temperature ... you
              leave the molecules to sort that out themselves and let them tell you
              what is happening!
              >
              > As I said, what you have is something between a simple reflux still
              and a compound still. Using it carefully, you can achieve the same
              strength and purity as a compound still. However, the penalty you
              pay is that you have to do this constant juggling act to control heat
              put into the sytem at the bottom and heat taken out at the top. The
              advantage of a true compound still is that it takes away almost all
              the need for difficult adjustment. You can set your boiler to match
              the maximum rate at which you want to run (remembering that faster
              means dirtier), and rely on your top reflux condenser to deal with
              all you throw at it without any need for adjustment. That leaves you
              free to watch the thermometer to see what is going on in the top of
              the column, and to control the amount of imposed reflux you apply by
              the turn of a single tap or gate valve. The best advice I can give
              (if you want to carry on with your present still) is to leave the top
              cooling tube running at full all the time and do all your adjustments
              with the boiler power alone. That way you have only one thing to
              control ... guided by two things: the rate at which product is
              coming out the top (zero during stabilisation) and what you read on
              the thermometer. At the risk of being more boring than I already am,
              please let me stress that you should read the thermometer for
              guidance, not 'control' it!
              >
              > Let's hope that amongst all that verbosity you find the answer you
              were looking for :-)
              > All the best,
              > Mike N
              > Per varios usus artem experientia fecit. Yea Yea Yea
              ===============================================
              Wacha Mike
              That makes it nice and clear, it looks as though I was getting there
              eventually, by guesswork. - Thanks.
              I shall print out your advice and commit it to memory while I wait
              patiently for a good thermometer reading.
              However, the output is very reasonable with this outfit ( in the low
              90's )so I am loath to tear it apart and put a pucker reflux
              condenser at the top.

              As one of my trusted friends in the Senate used to say in those
              boring R&D meetings in the Forum. "Si fractum non sit, noli id
              reficere " You remember, those soul destroying discussions on things
              like chariot wheel bearing life and harness fixing angles...... all
              that consequent paper work and the hassle with the scribes over
              quills. !!!

              I will complete the 3/4 finished Compleat column and keep this one in
              reserve.
              Best regards
              Spoliatio
              Die dulci fruere
            • Mike Nixon
              spoliatio wrote: Subject: [Distillers] Re: restabilising columns during a run ... and again Mike As one of my trusted friends in the Senate used to say in
              Message 6 of 7 , Jun 26, 2003
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                spoliatio wrote:
                Subject: [Distillers] Re: restabilising columns during a run ... and again Mike

                As one of my trusted friends in the Senate used to say in those boring  R&D meetings in the Forum. "Si fractum non sit, noli id
                reficere "  You remember, those soul destroying discussions on things like  chariot wheel bearing life and harness fixing angles...... all that consequent paper work and the hassle with the scribes over quills. !!!
                 
                Best regards
                Spoliatio
                Die dulci fruere
                ==========================
                Do I ever ... sigh .... but trusted friends in the Senate?  Wasn't Marcus Junius Brutus heard to say 'Die dulci fruere' just before the knife slipped home? :-)
                Mike N









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              • spoliatio
                Mike As one of my trusted friends in the Senate used to say in those boring R&D meetings in the Forum. Si fractum non sit, noli id ... things like chariot
                Message 7 of 7 , Jun 28, 2003
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                  Mike

                  As one of my trusted friends in the Senate used to say in those
                  boring R&D meetings in the Forum. "Si fractum non sit, noli id
                  > reficere " You remember, those soul destroying discussions on
                  things like chariot wheel bearing life and harness fixing
                  angles...... all that consequent paper work and the hassle with the
                  scribes over quills. !!!
                  >
                  > Best regards
                  > Spoliatio
                  > Die dulci fruere
                  > ==========================
                  > Do I ever ... sigh .... but trusted friends in the Senate? Wasn't
                  Marcus Junius Brutus heard to say 'Die dulci fruere' just before the
                  knife slipped home? :-)
                  > Mike N
                  ======================================
                  Mike
                  Oh yes but as he pointed out at te time he was using the vernacular
                  and it still means …… Have a nice day !! ?? :-)
                  Cheers
                  Spoliatio
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