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17132Re: New file uploaded to new_distillers

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  • Harry
    Aug 26, 2005
      --- In new_distillers@yahoogroups.com, Kevin Nowaczyk
      <beakerboy99@y...> wrote:
      > I'd argue that there is a wier just below the up/down
      > arrow representing liquid spill-over. You are
      > correct, there are no downcomers. Are downcomers
      > necesarry though? The last facility I worked in with
      > distillation columns used vertically oriented
      > structured packing, and it's my understanding that
      > columns looking like this are very rare. I'd think
      > that in a well designed column the liquid spill-over
      > could provide enough resistance to the gas flowing
      > through it if the space between the wier and the
      > column wall was sufficiently narrow.
      > Kevin Nowaczyk

      Nice theory, but no cigar. On initial startup the liquid will just
      dump all the way to the reboiler, then any resulting generated
      vapour will rise up the column which has little or no liquid on the
      trays, and nothing to impede its progress through the 'weir' gaps,
      all the way to the top. The amount of downward flow changes with
      each succeeding plate, therefore it is nigh on impossible to design
      for such variation. If you were to design the gaps to just the
      right size for each tray (a monumental task), at some stage in the
      process you would get a buildup of liquid on one or more trays and
      then the column would flood, then dump. Distilling action would be
      lost, meaning a restart. Don't forget the constant depositing of
      fouling agents e.g. calcium & organic matter, which change the tray
      perforations and your carefully engineered weir gaps. A 10mm hole
      (common tray perforation size) with a 1mm buildup around the lip
      will reduce the efficiency by 20%, and this variation alone is
      enough to cause flooding.

      Also, what about equilibration under total reflux at startup? This
      is mandatory when starting up this type of still. The bottom of
      each downcomer must be below the liquid surface of the next lower
      plate to form a vapour seal. These stills depend on pressure
      between trays. Perhaps a crash course in continuous distillation
      theory will help?...
      Left side of screen, goto Links > Distillation Theory.

      regards Harry
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