Preheating the liquid above bubble point temperature 2

[arun2298589]

I would like to know that preheating of liquid above the bubble point temperature, just before it enters into the distillation column will give any saving in the energy consumption in terms of reboiler heat duty

 

[Latexman]

The reboiler will use less energy with a heated feed versus a cold feed. Of course, the preheater will use more energy by the same amount as the reboiler saves.


Good luck,
Latexman

 

[Montemayor]

arun2298589:

Latexman is correct, but he left out the part about you flashing into the feed tray section and possibly injecting excessive flash vapors in the rectification section (the tower section above the feed tray) than the tower was originally designed to handle.

By preheating the feed to a level where you have reduced the reboiler duty, you have switched the relative V/L ratios around inside the tower. Now, you are handling more vapor above the feed tray than you did originally; if you don't have the mechanical capacity to handle the vapors in that region, you may cause a "choked" condition (nothing to do with sonic flow) and blow your tray seals - upsetting the entire tower operation.

Before you do this, I recommend you check out the reslting hydraulics and vapor velocities. A lot depends on what is inside the tower: trays or packing. You may not have the design flexibility.


Art Montemayor
Spring, TX