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.

One of the primary functions of Saudi Aramco Gas-Oil Separation Plants (also known as GOSPs) is to separate emulsified water from the crude. The water is typically highly concentrated with salt, so crude desalting is required to meet the standard quality specifications. GOSPs are typically designed with standard Proportional-Integral-Derivative (PID) controllers to control demulsifier and wash water flow for injection into wet crude. Demulsifier and wash water injection rates are normally left to operator judgement. The challenge with manual adjustment of flowrate is the high risk of overdosing or underdosing as there are several variables that impact the required demulsifier and wash water rates. Overdosing will result in wastage of demulsifier and wash water and higher operating expenditures. Underdosing may lead to operational upsets and potentially off-spec crude production. To overcome this challenge, innovative schemes (Smart Demulsifier Control & Wash Water Ratio Control) have been developed in-house. Smart Demulsifier Control optimizes the separation efficiency (or percentage of total produced water separated) of an upstream High Pressure Production Trap (HPPT or 3-Phase Separator) based on a dynamic target by adjusting the demulsifier injection rate and concentration in the wet crude. Simultaneously, wash water ratio control ensures that an adequate wash water rate is injected to satisfy salt-in-crude specifications. These control schemes eliminate the need for operators to determine the required dosage rate, thereby avoiding both overdosing and underdosing of demulsifier and wash water. The Smart Demulsifier Control (SDC) scheme controls demulsifier injection using two control layers. The first layer controls the Concentration of the Demulsifier in the Wet Crude so that demulsifier flow is automatically adjusted based on the Production Rate to achieve the set point concentration determined by the second layer of control. The second layer adjusts the demulsifier concentration to control the Separation Efficiency of the HPPT, or the amount of water separated in the HPPT vs. the Dehydrator, to achieve the Target Separation Efficiency Set Point determined by a site specific process model. In case of a dehydrator upset, another PID controller with more aggressive tuning will override the HPPT Separation PID Controller to set the required demulsifier concentration to mitigate the upset. Wash water ratio control scheme controls the flow of wash water to ensure that the salt-in-crude specification is met. A site specific target ratio is determined through a salt mass balance. These innovative controls have reduced desalting train upsets by 78% as the process related upsets are practically eliminated. This is achieved while optimizing the demulsifier dosage where 20-40% of demulsifier dosage reduction was realized, especially during the winter season. Moreover, savings of 20% wash water have been achieved throughout the utilization of these self-calculated and smart controls that were developed in-house with minimal costs.

The Static Mixer is a motionless mixer in which fluids are injected and rapidly mixed by combination of alternate vortex shedding and intense shear zone turbulence. It is a compact mixing plate with injection nozzles on two sides to ensure excellent distribution (figure 1 below). Moreover, it has bent tabs (which are designed using Computational Fluid Dynamics Modeling) to generate an efficient mixing with minimal pressure drop and maximum salt removal & chemical effectivness of the crude oil. This subject technology is aimed to optimize the wash water (underground water) & treating chemicals consumption in Gas Oil Separation Plants (GOSP). Also, it is aimed to achieve efficient blending between the crude oil stream and secondary streams resulting in high process efficiency with low consumptions of resources.