Reboilers in Series

[kozar20]

Our client has an existing column with a horizontal thermosiphon reboiler with steam as the heat source. They want to install a forced circulation reboiler upstream of this reboiler and feeding it with a mixed vapor/liquid feed in series. I have never seen this done before. Any comments? I would think that the flashing two phase flow would cause severe problems.

RMS

 

[Homayun]

I have never seen such an operation neither! This is strange.
But I have seen a tower with 2 reboilers and even at different stages..

What is the porpose of this configuraiton?

 

[djack77494]

My philosophy of design is that if I haven't seen a particular design done before (and preferably known that it successfully operated) I won't do it without a lot of testing, handholding, etc. Just think of what you do know concerning various designs. Think about the many pitfalls that you do know about. Many of them offer no clues as to their existance, and it would be very easy to screw up if you just charged ahead without prior knowledge. Why would a new design you know nothing about not have similar pitfalls? Assume the worst and hope for the best.

 

[jamesbanda]

I've not seen this done.

I would urge you to get a decent simulation working of the system and perform some sensitivities.

 

[chemicalengineerthai]

You can do only in parrallel installation but not in series installation.

The existing design thermosyphon will recieve the bubble point ( saturate) liquid and start to have heat at reboiler to get two phase after enter reboiler.

If you put another reboiler before thermosyphon and you have 2 phase flow, you 2nd reboiler will never enogh due to 2 phase already expand which require larger space for separation, if not enough, then similar to water hammer effect, and gas block in the system just before second reboiler.

All nozzle will not be enough (RHo V2 momentum is exceed), pipe vibration, pipe support will shake.

So, you can do only parrallel for different kind of reboiler but not in serie.

 

[unclesyd]

Why not change the thermosiphon reboiler to a forced circulation reboiler. With the proper flow the forced circulation should be able to increase the column loading to a very high level if the thermosiphon reboiler was doing the job.
We changed some vertical thermosiphon reboilers to forced circulation and had to limit recirculation due to overloading the column. We had to change the steam flow to account for the new loading with a slight increase in steam pressure.
like everyone else I've never seen two reboilers in series, only in parallel. Even this arrangement gave some control problems.