Q & A > Question Details
Our company has two serial desalters. Wash water at pH 7-7.5 level is injected, and brine of pH 6 is released. Not long ago, Brazilian crude(Lula) was mixed at about 30 percent, and the pH dropped to 4.5. The TAN value of Lula is low at 0.3 level. I cut naphtha and checked for organic acids, but this isn't a particularly large amount. Our chemical vendor gave the opinion that this was because there were a lot of salts crystallized in the crude oil. However, even after analyzing metal and ash, there was not much. We need to analyze the cause; does someone have similar experience?
28/12/2020 A: Ravi Vaghela, Bharat Petroleum Corporation Limited, ravi.vaghela.712@gmail.com
During processing of Lula crude, we have also faced quite similar issues of pH drop but not this low. Did you find an increase in the overhead chlorides during Lula processing? As this crude contains low molecular weight organic acids, the chlorides tend to increase drastically in the overhead, causing severe corrosion. You might have also noticed deteriorating brine quality while processing this crude.
02/12/2020 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Did you analyze the brine to see what was causing the low pH? Sometimes organic acids are added at the production platform for various reasons. Some of those acids will end up in the crude. Sometimes strong acids are injected downhole. While these acids are not supposed to end up in the crude they can. The presence of strong acids would typically be an intermittent thing while organic acids are more likely to be used continuously. It’s not clear what “cut the naphtha and checked for organic acids” entailed. Depending on what was actually done, it may or may not tell you whether you really have organic acids present or not.
26/11/2020 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
The naphthenic acids may be in the kero/diesel cut, but lowering the pH to 4.5 leads me to believe that something else is going on. Is it possible that the Lula contains dissolved CO2 or H2S? Or that a mineral acid present in the crude slate from production methods? What is the BS&W of the Lula crude? What is the pH of water separated off of the Lula crude storage tanks?
26/11/2020 A: Nagarathinam S Murthy, Ashphil Consultancy, Chennai, nssvdvr@gmail.com
Check the distribution of chloride species (Na, Ca and Mg) in the crude when Lula crude is high on the diet (30%) and other normal days. The excess CaCl2 in the feed can dip the pH apart from other species like H2S, HCl and light organic acids. Also, most sour crudes do bring in tramp amines which keeps the brine pH higher. Check whether Lula crude displaced any of the crudes with relatively higher tramp amines. TAN is not an indicator for drop in pH across desalters.