Styrene overhead condenser: Design criteria to minimize polymer formation and typical HX types

[Peregrino7]

A shell-and-tube heat exchanger for handling an easily polymerizable substance (condensing in the shell side) needs to be designed (with a removable bundle for easy mechanical cleaning). Working conditions are around 50/60ºC and near vacuum pressure. I'm looking for any guidelines or previous experience for heat exchanger design in order to minimize the formation of polymers in the shellside. Condensing fluid is Styrene and cooling water is used in the tubeside.

It is also very helpful to have an idea of a typical design for this service that you have seen in similar plants (Overhead condenser for styrene column).

Thanks in advance for your response or any insight.



PGh.

 

[EdStainless]

Since you know that it will need to be cleaned people would typically use a square pitch tube bundle with fairly large tube spacing.
It is also common to use a combination of bypass and recirculation lines to allow the cooling water temp to be kept in a very narrow range. Too warm and you don't condenser enough (and polymerize too much)and too cold and you just set solids formation.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

Styrene melts at -30 C so solidification isn't an issue. How do you keep it from polymerizing? Eliminate liquid hold-up so that uninhibited liquid styrene condensate a) can't sit anywhere for any extended period of time and b) stays cold. A baffle-free U tube design oriented vertically downward with condensation on the shell (basically a "cold finger") discharging into a cold-traced condensate receiver is one option that could do that. Obviously the condensed phase needs to be handled with care until a polymerization inhibitor can be mixed with it.

Polymer/monomer handling equipment is also frequently taken to a fairly high surface polish to discourage the formation of "stalactites" as well as to make it easier to dislodge polymer should it start to form.

 

[EdStainless]

You have to watch the polishing though, I know with some waxes it just assure a tighter bond and makes residues impossible to ever remove.
The idea of u-tubes in the U down position is very sound for this service.

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P.E. Metallurgy, Plymouth Tube

 

[Peregrino7]

Thanks for your comments. They've been very valuable. I guess a heat exchanger TEMA type with removable bundle is a must.
BEU would be an option instead of an AES type (with floating head), since AES type would promote stagnation of liquid in the area between shell and floating head.
For U tube design, it is not clear for me if a horizontal U bend is preferred than a Vertical U bend (see links bellow with pictures) Is there an advantage of using one or another?
Thanks for your advice.



PGh.