Coke Formation in Reactor Systems

[sshep]

I have a project to install new heat transfer equipment in a paraffin dehydrogenation reaction loop (UOP Pacol Process) with a end of run reaction temperature of about 920F. I have recieved the recommendation that we should sulfide our substantial amount of new metal at start-up to reduce catalyzed coke formation. This recommendation is being challenged by operations, and now I must formulate some response to the question of what the consequences are if we forego sulfiding. Previous projects in this unit and in our other Pacol units have generally sulfided metal prior to putting into service so I have no reference points for not sulfiding.

The current process has some cracking products (CH4, C2's, C3's, etc) in the recycle H2, and our heat exchanger has a low density carbon build-up that must be cleaned every few years to reduce pressure drop and restore heat transfer. I have recieved some good but conflicting opinions from engineers in other units where I have worked that have coke formation histories (ethylene and hydrotreating units). One area of uncertainty is catalyzed vs thermal mechanisms since it is reasonable to believe that a one time sulfiding will not have any effect on thermal decomposition.

Can anyone point me to some literature on this subject?

thanks,
sshep

 

[epoisses]

Sshep, I could not find an answer to your question in available literature, other than the remark that coke formation is a major issue in the Pacol process. Wouldn't you simply want to follow UOP recommendations in order to not lose their performance guarantee if there is one?
If in-situ sulfiding is a problem for Operations, this can generally be done off-site as well by companies like Eurecat.

 

[StoneCold]

Sshep
I would love to give you a differnt opinion but since my limited experience in oil was actually with UOP I would also say sulfide the bare metal to avoid catalyzed coke formation from "active sites" in the metal.

I would also comment that not doing it is certainly more risky than doing it and having the operators complain that you are wasting there time for a couple of weeks. Donuts can always buy your way out of that.

I don't know of any book that comments on it but you might look in the oil & gas journals for articles. I know it was often a subject of discussion at UOP when the temps reached the 900F mark.

Goodluck
StoneCold

 

[epoisses]

once again with my glasses on. Aaaah.. it's not a new unit... In any case I would still consult UOP and follow their advice, which is probably sulfide it. If necessary/required go for ex-situ to gain time and avoid safety issues.