3 replies to this topic

Greetings!!

I am a new hire and have a few questions about vertical reboilers.........

in one of our projects, the heat exchanger engineer designed a vertical reboiler where the reboiler tubeside outlet nozzle will be connected directly to the column return nozzle.

I would like to know the reason for this? Why no pipring from the reboile tubeside outlet to the column nozzle.

Also, would the column vendor have to do a stress analysis to account for this load on his design.........

I know about stab-in reboilers but it seems odd to have such a big HX hanging out there.......

Is this a common practice is the field?

Any other info about vertical reboilers would be appreciated.

Have a nice day!

kellie

[Technocrat]

dear kelly,

as i understand, vertical reboilers are thermosiphon type reboilers i.e. liquid from tower bottom or the bottommost tray is withdrawn and fed to the reboiler. heat is applied at one side of the reboiler. the liquid gets partially vaporised and hence its density is reduced. the liquid flows from the reboiler inlet to the reboiler outlet due to this difference in density of liquid at reboiler inlet and reboiler outlet. the oultelt flow is a two phase flow (vapor-liquid mixture) hence the pressure drop on the outlet line is more. hence the reboiler outlet is directly connected to the column to minimise pressure drop in the outlet line. any extra pressure drop in the outlet line will increase liquid level in the column. if this liquid level reaches the reboiler outlet nozzle then there will be severe flooding of the bottm tray and the total column get flooded after some time.

regards.

[Zauberberg]

Hello Ms Kellie,

We have exactly the same type of reboilers you decribed, employed at two gasoline redistillation columns. No additional piping is required.
More info about reboilers:

www-unix.ecs.umass.edu/~rlaurenc/Courses/che333/Reference/exchanger.pdf
www.kolmetz.com/pdf/Resolving-Process-Distillation-Equipment-Opportunities.pdf
www.wlv.com/products/databook/ch5_2.pdf
www.tkk.fi/Units/ChemEng/news/2002/aiche2002/aiche2002_102c.pdf

Best regards

[joerd]

Also, directly connecting the reboiler to the column prevents that a piping stress engineer will try to put an expansion loop in your return line - something that you definitely don't want!