In the MEROX, C3 and Copper Strip? 1

[consilience1]

Dear everyone

Thesedays I have a experience of copper strip fail with C3 Product which is passed through UOP's Merox, also, we checked H2S in C3, result is yes.
If your plant has UOP's Merox, how do you think the cause of H2S remaining in C3? We have pre-wash column for H2S removal and maintain the proper caustic concentraion.

If caustic carry over from pre-wash column to extractor due to high caustic concentraion, which bad result could be expected?

Thank you.

 

[Jason5000]

What is the % spent on the caustic in your prewash? I believe UOP recommends dumping prewashes and recharging with fresh once % spent, as determined by a UOP lab test method, reaches about 50% spent. Prewashes can spend very rapidly if you have a loss of absorbtion due to emulsions, flooding, or other problems in your upstream amine contactor. If H2S breaks through your prewash to the circulating system I would expect problems with caustic regeneration before H2S breakthrough to final C3 product; H2S can be regenerated by the Merox regenerator but the air demand is much higher than that of mercaptan sulfur.

For problems Merox check:
Prewash % spent - maybe best to dump any prewashes above 30% spent if you're having corrosion problems
Caustic shaker time - adjust Merox injection to target an appropriate shaker
Air rate - is air rate too low, excessively high?
Circulating % NaOH - the extraction and regeneration reactions make water, make sure you're adding enough fresh caustic to keep strength up
Contact - Can you detect in problems in your contactors
Heat - Is your regenerator hot enough, but careful, too hot can lead to accelerated corrosion.

Also for problems with copper strip corrosion make sure the strips and bombs are cleaned well and prepared properly, and remember that the test is somewhat subjective.

Once you have corrosive propane in your propane storage it can be a difficult problem to overcome. Baker Petrolite, or some other refining chemical experts, may be able to provide some "joy juice" to help clear things up.

Good Luck

 

[CJKruger]

lion0061, to have H2S going through the prewash and extractor is unusual - almost impossible if your caustic strength + spent is correct.

Are you sure it is not mercaptans ?

Anyway, I would check the air, catalyst and caustic return (to extractor).

 

[Jason5000]

Another thing that will strongly effect propane corrosion is moisture content. Do you monitor dew point downstream of your propane dryers? Any dew point excursions? Any unusual or inadequate regeneration cycles. How old is your desiccant? If you don't monitor dew point do you do the freeze valve check?

In general H2S AND water together will result in bad propane corrosion results. An old GPSA article I read suggested that some level of H2S alone or a somewhat elevated moisture content alone weren't enough to fail the copper strip test, but together they cause propane corrosion. Also mercaptan sulfur did not seem to have a strong effect on propane corrosion; in fact at low mercaptan and H2S levels mercaptan seemed to suppress copper strip corrosion a bit. The conference notes I read that in are probably going on 30 years old now, though.

Again, good luck. This can be a tough problem once it starts.