10 replies to this topic

[empire]

Hi,
In my Naphtha Hydrotreating Unit, we inject Boiler Feed water continuously at downstream of Feed-Reactor Effluent Exchanger. To monitor corrosion we keep track on pH and iron content in sour water at separator boot. Based on UOP guideline, acceptable corrosion rate is <2 ppm wt of Iron with Water injection rate of 3% volume of Feed.
In fact what we've got is Iron content is normally higher than that specification. Fe content depends on pH, our pH varied from 7 to 9 but Fe spiked, from below 2 to 12.Of course, the lab result is sometimes not correct, but we got data for continuous 1 month.
If you have any experience about this matter, please help me.
Thanks.

[Root]

Hi,
In my Naphtha Hydrotreating Unit, we inject Boiler Feed water continuously at downstream of Feed-Reactor Effluent Exchanger. To monitor corrosion we keep track on pH and iron content in sour water at separator boot. Based on UOP guideline, acceptable corrosion rate is <2 ppm wt of Iron with Water injection rate of 3% volume of Feed.
In fact what we've got is Iron content is normally higher than that specification. Fe content depends on pH, our pH varied from 7 to 9 but Fe spiked, from below 2 to 12.Of course, the lab result is sometimes not correct, but we got data for continuous 1 month.
If you have any experience about this matter, please help me.
Thanks.

Check Chloride content in H2 make and increase the wash water injection to more than 3% (may be 4 or 5%) for temporarily, Fe content should not come with RX effulents, there is chance if your CFE leak then the chances are there.

[empire]

We can eliminate the possibility of CFE leakage because Sulfur content of product is stable and on-spec

[iyer]

Are you sure about the 3% or is it a value you came up to with optimization. In units I have seen, it is between 4-8%.
In case of BFW, I would assume it comes to a break tank. Is this nitrogen blanketed or not? Oxygen limit i wash water if I remember right is 50ppb.
Refiners normally make a mistake of basing wash water off the volumetric flow rate while forgetting the feed Nitrogen and Sulfur which may be different from design. Compare the feed N2 and S vs the timing at which the pH was higher and I am quite certain that you will find them higher at higher pH.
Anyways
Step 1 is to increase wash water flow.
Step 2 Check O2 in wash water.

Please get back with your results

[empire]

Dear Iyer,
The specification of 3% and <2ppm wt of Iron comes from UOP guideline. The most important is at injection point at least 25% water remain in liquid phase.
Our water break tank isn't Nitrogen blanketed. I'm not sure about the relationship between Oxygen and corrosion in this case, can you please show me the document about this matter?
Thank you for your help.

[iyer]

Will check and get back to you on the source, but I think it is also mentioned in the wash water specs. 25% should be in liquid phase is the rule, but I still think 3% is on the borderline. Do you have any coker Naphtha in your feed?

[empire]

We dont process coking naphtha, our unit was design for max 100ppm Sulfur. Normally we run with FRN, its S content varies from 10-25 ppm

[empire]

Dear Iyer,
I found the document which mentions about Oxygen impact in corrosion.Maybe it's the cause of our problem.
And 3% is really the borderline.
Another thing, I want to verify the amount of liquid water (25%).Can you please show me the guideline to calculate?
Thank you.

[iyer]

Well Empire
If you can simulate it, it would come up. I dont have anything as such with me, but lemme check. Please keep me posted if ur situation improves.

[empire]

Hi,
we keep water injection rate about 3.2 %vol and it seems to be fine.
Thanks for your help.

[iyer]

No problem, glad to know I was of help