9 replies to this topic

[Ali_gholamalian]

Dear all

 

In H2SO4 alkylation unit, polymerization is rival reaction. after bad operating, polymers accumulate in Debutaniser column, duty of reboiler decreased, and the polymeric fouling in reboiler shell occurs. The maintenance group try every solvent but there is no way to remove fouling from tube bundle.

Can anyone show me a way to analysis this polymer (solid form), and also get rid of this?

BTW normal heptane did not have any effect.

[Bobby Strain]

Try water.

 

Bobby

[Ali_gholamalian]

Try water.
 
Bobby

Dear Mr. Strain
even hot water does not work.

[Bobby Strain]

Well, step 2 is to call your alky unit licensor. This is a common problem. And, whoever designed your unit did you a great disservice by using a kettle. If this is a continuing problem for you, you might consider replacing it with a vertical unit with boiling in-tube. Or, just add a supplemental exchanger and reduce the temperature on the kettle. Replacement would be best, however.

 

Bobby

[Ali_gholamalian]

because of sanction, licensor is unavailable. so your opinion is change column to a vertical thermosiphon type? would you clear me why you suggest vertical instead of horizontal? For sedimentation of polymers in bottom of reboiler?

[Bobby Strain]

It is not possible to reliably design a horizontal exchanger with boiling on the tubeside. The tube inside is much easier to clean and less subject to fouling. But you need sufficient elevation of the column to permit proper installation of the vertical unit. The design should maintain high velocity, which is achieved by longer tubes.

 

Bobby

[Ali_gholamalian]

yes of-course you're right. I did not see "boiling in tube" in previous post, I assumed your point is boiling in shell and horizontal.
Do you think jet can clean this type of foulling? Height from ground to bottom of column is about 3m. I guess pump on boilup line will satisfy loss of elevation if more height is needed.

[Bobby Strain]

If an exchanger is expected to be fouled, the bundle is designed with square pitch so that it can be cleaned. As to elevation, it is significant if you are drawing from a chimney tray into the reboiler. If this is the case, then you may have room enough for a vertical unit. Sometimes using finned tubes is successful in fouling service; sometimes not. Obviously you need to clean the bundle as best you can with whatever you have available.

 

Good luck.

Bobby

[Ali_gholamalian]

If an exchanger is expected to be fouled, the bundle is designed with square pitch so that it can be cleaned. As to elevation, it is significant if you are drawing from a chimney tray into the reboiler. If this is the case, then you may have room enough for a vertical unit. Sometimes using finned tubes is successful in fouling service; sometimes not. Obviously you need to clean the bundle as best you can with whatever you have available.

 

Good luck.

Bobby

I really appreciate your help.

[Padmakar Katre]

Hi,

Can you please share the wall temperatures and hot fluid/heating medium supply temperature. In addition reboiler control system sketch, if utility is steam then is it pressure controlled or condensate control.

 

Main culprit may be tube wall temperature which enhances polymerization and that leads fouling, lowering hot medium temperature should increase reboiler run length.

 

If it's circulating thermosyphon, increase in column level thereby resulting lower vapor fraction at tube side outlet and ensuring the entire tubes are wet. (I presume it is vertical thermosyphon)

Edited by Padmakar, 18 August 2014 - 05:11 AM.