• Our desalter is facing a rag layer issue when we process cabinda crude. The brine turns black. It seems like our current emulsion breaker can not solve this problem. Is there any ideas or recommendations?



  • N Sekar Murthy, Ashphil Consultancy, nssvdvr@gmail.com

    Analysis of the rag layer specially the asphaltenes to solids (sand, silt, and other suspended solids) ratio will throw light on the problem being faced. Some refiners witness such problem while processing slop which could induce crude incompatibility with such paraffinic crude. Perhaps it may be worth pulling out slop for couple of days from crude unit and process elsewhere in secondary units. Additionally, approach your local Veolia water technologies representative. They have extensive knowledge on demulsifier and get the right formulation to mitigate this issue. Poor desalting is typically associated with poor dewatering and water shot into d/s heaters and fractionation tower which wastes energy other than corrosion in OH section. Good luck.


  • Ben Morgan, Baker Hughes, ben.morgan@bakerhughes.com

    A deeper dive into the composition of the rag layer can help identify what are the emulsion-stabilising components in order to check whether the existing desalter program is fit for purpose when processing Cabinda.

    Furthermore, its important to understand the impact of Cabinda with respect to the other crudes in the diet in terms asphaltene stability. Destabilised asphaltenes have emulsion stabilising properties. We would suggest a combination of lab analysis and desktop review as the first step.


  • Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

    According to the datasheet of the Cabinda crude oil, this is a light  and sweet crude oil which probably contains high amounts of paraffinic hydrocarbons. To realize an adequate analysis it's important to know if the refinery is processing only the Cabinda crude or under blending with heavier crudes, in this case we can saw chemical instability between the crudes leading to asphaltenes precipitation which stabilize emulsions reducing the separation efficiency in  the desalter vessels and provoke the change in the brine colour. In this case, it's possible to solve the problem by applying a crude stabiliser agent which is dosed independently of the emulsion breaker agent.

    Another approach is analyze the incompatibility between the Cabinda crude with the another crude oils processed by the refinery and take anticipatory actions like reduce the processed flow rate in the crude oil distillation unit to ensure a higher residence time in the dessalters when processing a crude blending with high incompatibility potential, or avoid to process crude oils chemical incompatible with the Cabinda crude.