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We have low PH (3 to 4) in the CDU overhead but in same time we have low chloride values ( 3 to 10 ) and already we injected high values of neutralizing amine and corrosion inhibiter. What is the reason that causes this drop in PH value?

Jul-2023

Answers

Salem Ghoul, Mellitah O&G Co, smghoul@gmail.com

API 571 3.7.7 Inspection and Monitoring f) The pH should be monitored where water is known to accumulate in the process, particularly at the overhead accumulation drum of the crude tower. If a low pH is found that cannot be accounted for by the level of chlorides measured, additional acids, potentially including organic acids, are likely present. Table 3-7-1—Light Organic Acid Corrosion Equivalency Factors Acid HCl Equivalent Factor Formic 0.76 Acetic 0.61 Propionic 0.49 Methyl propionic 0.41 Butanoic 0.41 3-methyl butanoic 0.36 Pentanoic 0.36 Hexanoic 0.31 Heptanoic 0.28

Jan-2025
Salem Ghoul, Mellitah O&G Co, smghoul@gmail.com

If you get the answer and the problem was solved, can you please share the steps you performed.

Mar-2024
sam lordo, Becht, salordo@comcast.net

As mentioned already, this scenario suggests that you have organic acids which can buffer causing increasing neutraliser demand. have your chemical supplier run a detailed water analysis to include , not only pH, Cl, metals, Nh3, H2S, SOx species, amines and orgain acids...

If corrosion is an issue and the organic acids are causing the increase in neutraliser demand, then the approach commonly taken is to adjust the ph to 5-5.5 and double to triple the filming amine dosage.

Nov-2023
Joan de la Paz, Baker Hughes, joan.paz@bakerhughes.com

On top of previous comments please check the kind of crude processed. may be medium-high TAN (mostly from Santos basin, Brazil) and if furnace T is relatively high can drive to decomposition of the big molecules into smaller ones (acetic or propionic) that can stabilize the low pH. (this also is in line with the high neutralizer consumption). will be interesting also to see the Fe values.

Oct-2023
Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com

To get that low of pH with low chloride while adding significant amounts of neutralizer, it sounds like you have other strong acids present besides HCl.

If you haven't done so already, check the pH of the water leaving your Desalter. If that's also low, the acids are probably coming in with your crude. Various strong acids can be used in certain upstream well activities and can find their way into the crude oil. If you use overhead boot water in your Desalter wash water, you'll need to desalt your crude in the lab to check for pH and ionic species present as low desalter pH could be due to the overhead water.

Oxygen ingress into the crude unit can also lead to reactions with H2S that form sulfuric or sulfurous acid. An ion chromatograph of the overhead boot water will tell you what ionic species are present and give you clues about what is going on.

Sep-2023
Walter Militello, Nalco Champion Co, wmilitello@nalco.com

HCl is not the only acid that can be present in the condensed water. Many acids are there, with mid and low strength, but still able to reduce significantly the pH, is not completely neutralised. A proper analytical test about strong and weak acids can help for the troubleshooting. Nalco has proprietary analytical method to asses the weak and strong acids concentration. some crude oils are naturally rich of weak acids (organic acids) and pH control at OVH is not easy.

Additionally I would evaluate the amine neutraliser, if single component, bi-component, amine(s) nature and concentration.

Sep-2023
Mohamed Salman, Midor, msalman1351@gmail.com

If chloride values are low, pH can be lower due to high H2S content, or high weak acid content where in this case high injection of neutralizing amine will not increase pH as required. Keep monitoring Fe content in sour water to ensure there is no high corrosion rate. Weak acid is mainly resulted from crude types, or processing refinery Slops.

Jul-2023
N Sekar Murthy, Ashphil Consultancy, nssvdvr@gmail.com

Request your lab to assess the ionic load on the OH boot water of CDU. Low mol wt organic acids, H2S, Sulphurous acid, etc. can be a reality in boot water specially in the refinery having coker in the configuration. Consumption of neutralizer can shoot up with any of these acids present in OH.

Jul-2023
Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

It's important analyze the content of chloride salts (MgCl2 and CaCl2) in the processed crude, these salts can suffer hydrolysis and generate hydrogen chloride (HCl) which can cause drastic reduction in the pH. According to the concentration of chloride salts in the crude oil it's possible to minimize this problem injection sodium hydroxide (NaOH) upstream of the dessalting vessels aiming to neutralize the hydrochlorides compounds.

Jul-2023