Foaming in caustic soda Scrubber in steam-cracking ethylene plant

[Ahmed Elzawawi]

In our ethylene plant( steam cracking plant). During operation, we faced foam formation in the caustic soda scrubber to remove acid gases from cracked gas .
What might me the reason for this?

 

[TiCl4]

I'm not in this industry, but a simple Google search seemed to have an AIChE topic devoted to this exact issue. I'm not a member, so can't access this, but perhaps you can or are willing to pay membership fees to access. Acid gases (SO2, Cl2?) don't tend to foam by themselves, so it suggests to me that some organics are being carried over to the caustic scrubber. Salts and rust are also mentioned as being foam stabilizers, and, of course, your L/G ratio will play a large part in foam formation.

https://www.aiche.org/conferences/a.../paper/192g-fouling-and-foaming-caustic-tower

 

[georgeverghese]

Foaming is always caused by contact of caustic (or alkanolamine in other types of acid gas removal towers) with condensed hydrocarbons. These condensed hydrocarbons may be have been
(a) entrained in the CG feed from the upstream scrubber due to high vapor velocity through this KOD or some kind of vapor liquid separation inefficiency in this KOD
(b) condensed out from the CG in the caustic tower itself - this may be due to low operating temperature in the tower which is below the dewpoint temp of CG at the tower operating pressure.
(c) due to the use of anti polymerizing agent such as hydroxyl amine NH2OH (or anti foulant dispersant chemical)in the tower to inhibit aldol condensation reactions (that would lead to formation of red oils in the spent caustic).

So
(a) check the demister in the upstream KOD
(b) keep the tower temp warm enough to prevent hydrocarbon condensation from the high dewpoint temp CG
(c) dope the weak caustic feed with anti foaming agent

Also check that you are removing all red oils accumulating in the recirculating weak caustic solution so that the use of anti foulant dispersant chemical is minimised.

See details in this article on caustic scrubber chemistry and performance issues.

https://www.scribd.com/document/363...ion-Considerations-for-Effective-Performance#

 

[Ahmed Elzawawi]

hi georgeverghese
Thank you for your reply . unfortunately I can not access the link you shared !

 

[georgeverghese]

This is the title of this doc - see if this pops up on Google

Caustic Tower Operation - Considerations For Effective Performance

 

[horacio Torres]

Foaming is a normal issue in caustic scrubber for ethylene plants. Antifoaming chemicals control foam and eeduced the troubles for it.

Horacio

https://www.linkedin.com/company/lagotuy/