Q & A > Question Details
Our desalter unit is working fine, the crude oil outlet to the CDU is "clean", there is no water and low metals content. However, there is an issue with the outlet water. When the desalter is "washing" low sulphur content crude oil the water has a huge content of oil in water, grams per liter, and what looks like asphaltenes on the interface. When running high sulphur crude this issue doesn't occur. We did some lab tests; strangely we can not get the same outcome as what happens in the desalter. The water is clean and there are no issues on the water interface. Does anyone know what might be the issue?
 
Answers
13/08/2020 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
I have seen cases with light sweet crudes in desalters operating at low temperatures where there were heavy waxes that remained as solids which hung up at the interface and caused rag layer & oil under carry problems.

The other possibility is asphaltene stability issues. If you haven't already done so, you need to check the asphaltene stability of your crude. If that looks OK, try washing your crude with some of your desalter wash water and then recheck the asphaltene stability. Sometimes there can be chemical interactions between acids or bases in the wash water and the crude oil that impact the asphaltene stability. The more extreme either high or low the pH is on your wash water, the more likely this is to be a problem.