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Pressure distillation column startup and tuning

Start the model Continuous pressure distillation column with default parameters (benzene-toluene mixture, benzene mass fraction 35%, non condensable 2%, 10 trays+boiler, feed tray n°5)

Operating conditions are: feed 2000 kg.h-1, reflux ratio 4, pressure 1.4 to 1.6 bar a, steam to reboiler ~600 kg.h-1, distillate specification 95% of benzene, residue specification 5% of benzene

  • Column bottom is already filled, fill it up to 100% level, then open degazing valve at 80% and dispose cooling water on condenser
  • Start heating bottom with heating steam flow controller at 600 kg.h-1
  • Follow temperature profile in thermosiphon reboiler, and at boiling, vapor rising up in the column
  • When vapor reach condenser, purge non condensable gas and close the degazing valve to keep pressure around 1.5 bar a
  • When reflux drum level reach 30%, start reflux pump and put cascade reflux drum level -> reflux flow control in operation
  • When you think it's time, set feed flow control up to 1000 kg.h-1, feed pre-heater at boiling temperature, cascade bottom level -> residue flow rate control, cascade reflux ratio -> distillate flow rate, and overhead pressure control on degazing at 1.5 bar a
  • When column is on specification, start increase the feed up to 2000 kg.h-1
  • When you succeded in controlling the column, try to find the feed limit of the column
  • If the limit is on degazing flow rate, let the pressure increase, and/or change degazing valve cv
  • If the limit is on reboiler, decrease the operating pressure, or increase steam network pressure and/or reboiler heating area


  • This column is also able to treat feed without non condensable, operating though with the condenser flooding pressure controller
  • You can see with this model what happen in case of heat excess (pressure relief valve), or heat default (vaccuum breaker)