Reboiler Type

The reboiler representation is selected by choosing the appropriate "Reboiler Type" option. The default type of Kettle (Conventional) is available to all distillation column algorithms. The thermosiphon models are currently only available for the Inside-Out, Enhanced I/O and Sure algorithms.

Additional Information

Kettle Reboilers

This reboiler is modeled as an equilibrium stage with a heat duty. The bottom tray of the column model is the reboiler and the equilibrium liquid from this tray is withdrawn as the column "bottoms" product. All equilibrium vapor is returned to the next tray above the reboiler tray. The "bottoms" product temperature is the same as the reboiler exit temperature.

Thermosiphon Reboilers

Thermosiphon reboilers split the liquid from the bottom of a column with one portion removed as the "bottoms" product and the other portion circulated through a reboiler where it is heated prior to being returned to the column. The circulation is accomplished by pressure differentials related to the fluid density, reboiler height, etc. and the fraction of the circulating fluid that is vaporized is typically lower than that for kettle reboilers. For this type of reboiler, the reboiler exit temperature is higher than the "bottoms" product temperature. It is not possible to model the thermosiphon reboiler with one tray, as with the kettle reboiler, and PRO/II has two models available for thermosiphon reboilers. The reboiler duty is still applied to the bottom tray of the column model as with the kettle reboiler, however the "bottoms" product composition and temperature are not the same as the liquid from this tray which represents the reboiler return streams.

The "Thermosiphon without Baffles" option represents the case when the bottoms product and reboiler circulating fluid are drawn from a common sump, i.e., there is no baffle in the bottom of the column. For this model the temperature and composition of the "bottoms" product and the reboiler feed sump are identical. See Thermosiphon without Baffles for more details on this reboiler model.

The "Thermosiphon with Baffles" option represents the case when the "bottoms" product sump and reboiler feed sump are physically separated by a baffle in the bottom of the column. Furthermore, the reboiler return liquid enters the "bottoms" sump, which overflows the baffle into the reboiler sump. The liquid from the bottom tray of the column is all directed into the reboiler sump. See Thermosiphon with Baffles for more details on this reboiler model.

Thermosiphon reboilers with baffles in which the reboiler return liquid flows into the reboiler sump are equivalent to the "Thermosiphon without Baffles" model for simulation purposes and should be modeled as such.

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