Combined Feed Heat Exchanger Fouling

[recklesskid]

Hi!

We have a Welded Plate Heat Exchanger (Packinox, Combine Feed Heat Exchanger) in our Continuous Catalyst Regeneration Unit (CCRU). We have long been experiencing increased Hot Approach Temperature in the exchanger and we already chemically cleaned it (2 years ago) with soda ash since we suspected that the foulant is ammonium chloride. However, we did not see any improvement in the duty of Packinox since then. What could most propbably have fouled the Packinox? And how can we address them?

Thank you very much!

 

[ash9144]

Plate and frame HEX are bad for fouling. They have fairly low velocities and it allows any scale to plate out. The only thing I've seen effective is to break apart the plate assembly and pressure wash or chemical soak.

 

[recklesskid]

Thank you ash9144 for the information.

From your experience, what chemical was used for soaking and was the foulant identified? If so, what was it?

Thanks in advance.

 

[ash9144]

Never bothered to identify foulants. Just recognize that the stream fouls and clean at some regular interval.

 

[Chance17]

If you can't afford the production loss, it may be economical to buy an installed spare.

 

[rmw]

I disagree with Ash's take. I will agree with his statement regarding their fouling up quickly if the PHE is poorly designed. If a PHE is designed so that the velocities are in the range they need to be, then the velocities are adequate to not only enhance heat transfer but to minimize fouling.

Unfortunately, too often, every one puts their fudge factors on things, PHE's included during the design process so that when they get installed they are way over sized.

Doubly unfortunately for you, with a PHE, you can remove enough plates to get the velocity up into the range where it is "happy", but in your case, depending on just exactly what you mean by "welded plate", that might not be possible.

Check with the manufacturer and see what flow they recommend through this unit and if you can alter your process in any way in order to get it, make the necessary changes.

rmw

 

[148bvd]

Welded PHEs are just like what they are described. The plates are fully welded on the seams, closed, have no gaskets, and can not be opened/dismantled for cleaning unlike a standard gasketed PHE. They are cheap and normally used for clean fluids like water, alcohol, etc. Hence, if you use it for fluids with suspended particles, you are in trouble, you get foulings, thermal efficiencies goes down, etc.
My recommendation: change to a gasketed PHE.

 

[lt5q5p]

Your problem starts with your reactors. To answer your question first, You didn't do as good of a chemical wash as you could have. I would be willing to bet that this exchanger has been cleaned before with better results. Make sure to use an organic and inorganic solvent in the wash. You will also need to test the washing effluent. You want to determine when you have dissovled all of the available contaminates and also make sure your not eating away at good metal. This will also ensure you have removed all the sulfur and ammonia build up.
Now for the solution your managers are not going to like. You are going to have to spend more money on catalyst. At the start of your run you need to maximize temperatures to convert ALL the nitrogen and sulfur. As your conversion start to drift down you will have to change out your catalyst. If you do this then you have fewer issues. Alternativly you need to get better control on your Chloride addition. As catalyst ages it will take up chloride at varying rates. You will have to determine what these rates are.

 

[chief]

there is a chemical cleaner called SAF-ACID. Used to shift scale on boiler tubes. Highly effective, circulate and heat and add a handful of household salt to really get it to rumble.

Offshore Engineering&Design

 

[MJCronin]

Was the PHE relocated from some other service ?

Or was it designed, selected and purchase for it's current service ?

 

[recklesskid]

Thanks everyone.

@MJCronin: It's designed, selected and purchased for the current service.

 

[786392]

Dear recklesskid Hello/Good Afternoon,

Just review
Using KMnO4(Potassium PerManganate) Weak Concentration Solution it may prove good cleaning solution.

Or try Orange peel/ skin uniform lowest possible viscosity slurry use as cleansing agent!

Kindly do review the process conditions for

any trace unnoticeable air or oxygen entry possibility into the system, since this may induce such fouling products generation

In order to ensure long sustainable service from the PHE in question.


Good luck for success.

Best Regards
Qalander(Chem)

 

[chemjock]

There should be no ammonia if your upstream NHT is operating properly.