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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

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