Improved Desalting of Challenging Crude Slates

Abstract

Crude slates containing a blend of traditional and heavy crude oil are challenging to desalt in most refineries. In addition to the higher crude oil viscosity and reduced oil / brine density difference, heavy crude oil also provides additional challenges in the form of higher crude oil conductivity and solids stabilized emulsions. Blended oils often have a higher solids content which can stabilize rag layers inside the desalters. Many refineries use AC type electrostatic technology operating at line frequency, 50 or 60 Hz. Conventional AC desalters provide limited voltage gradients and are not efficient for treating conductive crude oils. Advancements in electrostatic desalters have resulted in desalters providing stronger electrostatic forces and improved conditions for coalescence of brine droplets. Computational fluid dynamics (CFD) has also provided a better understanding of the oil and brine flow inside refinery desalters, which has lead to the use of improved internals which provide a better fluid distribution, elimination of recirculation areas and allowing higher flow rates at constant BS&W and PTB. More efficient desalting of crude oil in refineries can provide the following benefits: –OPEX:○opportunity to process higher volumes of cheaper opportunity crude oil○reduced volume of wash water○lower operating temperature○lower demulsifier dosage○higher desalter uptime–CAPEX○use of smaller desalters (only applicable for new desalters)○reduced transportation cost This paper describes new enhanced electrostatic desalting technologies, including case studies.