Naphtha hydrotreator abnormal high catalyst bed pressure drop

[ProcEng247]

The naphtha hydrotreator unit in my plant is experiencing abnormally high reactor pressure drop. This unit processes coker naphtha feed using a diene reactor and HDS reactor in series. The diene reactor pressure drop is stable and in the normal range, however the HDS reactor pressure drop is seeing an abnormal growth.

Historically, this unit has always been limited by Si uptake (rarely by pressure drop or activity) and typical run length of 2.5 to 3 years. However our previous and current loads have experienced unusually high pressure drop growth. Previous load it was 10psi per month and we changed out catalyst in 1 year. The current load is only a month old with fresh catalyst and we have gained 60psi!!

I'm looking to understand if other naphtha hydrotreators have seen this and what feed contaminants were at play. We have reviewed the hydrotreator operations and see nothing out of the ordinary, implying the source of the pressure drop is the feed.

Another question is around two-phase flow into the HDS reactor. The design is for gas phase reaction, but we suspect possible two phase flow due to lower than recommended inlet temperature. Can this have any effect on the pressure drop?

I'm looking for any info that may be related to the problem we are seeing.

Thanks!

 

[SeanB]

There are some very good articles available online regarding this topic. Just do a Google search for "coker naphtha hydrotreating fouling".
Has your feed changed in any way since the last reactor run? Has throughput increased? Does your coker naphtha feed come directly from the upstream unit or does it go to an intermediate storage?