High Efficiency Static Mixer Technology for Crude Desalting

Abstract A high-efficiency static mixer was installed at the inlet of a desalter vessel at a Saudi Aramco gas-oil separation plant (GOSP) under an initiative to field trial new technologies to enhance crude quality of low water and salt content, and to optimize wash water consumption used in the desalting. This paper describes a high-efficiency static mixer assessment through Computational Fluid Dynamics (CFD) modeling and an extensive field trial. The technology, which is the first of its kind implemented in Saudi Aramco, is a compact wafer style mixer with a specially designed orifice plate. Enhanced turbulent mixing of wash water with wet crude oil improves desalting efficiency, resulting in lower desalter outlet salt-in-crude concentration and/or reduced wash water consumption. The compact design of the mixer and the restricted lengths of upstream and downstream straight run piping requirements makes this mixer ideal for installation in congested areas without the adequate space for conventional spool static mixers. The high- efficiency static mixer produced a 17% reduction of wash water consumption after installation downstream the conventional mixing valves and upstream the desalter inlet at the Saudi Aramco facility while maintaining the salt-content at 5-6 pounds per thousand barrels of crude oil. A total saving of more than 8½ million gallons of wash water was achieved during the nine month field trial. Further analysis by Saudi Aramco, including CFD modeling, identified the potential to improve mixer performance and gain further reductions in wash water rates by optimizing the mixer location.