Installation height of vertical thermosyphon reboiler under vacuum operation
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Recently, I read the book on heat exchanger process design written by Professor Sun Lanyi. In Chapter 5, which deals with reboilers, regarding vacuum distillation, the upper tube sheet of the reboiler must be above the normal liquid level in the tower bottom; under such conditions, the static head is less than the length of the heat exchange tubes. I’m not quite understanding why the vacuum distillation reboiler needs to be at a higher level than the normal liquid level in the tower bottom; please give me some advice
This is to ensure space for the evaporation of liquid inside the reboiler; a slight negative pressure is created by evaporation, thereby inducing siphoning.
Reduce the static pressure at the reboiler inlet to lower the boiling point temperature
Generally speaking, in a vacuum, the volume of the gas is much larger, providing a pathway for gas-liquid transfer； The second point is that vacuum operation is employed, usually to lower the boiling or bubble point. If the liquid level in the tower is higher than that on the tube sheet of the heat exchanger, then the net head is increased, and thus the significance of vacuum operation is reduced