PDO's First Advanced Process Control Technology Optimizing Condensate & LPG Production

Abstract

Abstract Condensate production needs to be stabilized before exporting it. True Vapor Pressure (TVP) is the standard measure for condensate volatility and is used for Condensate product specification. Petroleum Development Oman (PDO) exports condensate with a TVP limit below 100 kPa. Whenever the limit is violated, Condensate production is automatically diverted to an off-spec tank for re-processing to bring the TVP below the limit before exporting it. Liquified Petroleum Gas (LPG) is also produced from the volatile condensate with C3 mol% and C5+ mole% specification limits below 18% and 2% respectively. Optimum operation is a point where condensate production is maximized up to the TVP specification limit at the expense of LPG production, and LPG production is maximized up to the specification limits at the expense of flash gas production. The higher the TVP the higher the condensate production, and the higher the C3% the higher the LPG production. However, due to complex process dynamics (excessive time delays between causes and effects) and limitations of the base-layer control systems (the standard setup used in PDO) in dealing with such dynamics, it is practically impossible to continuously perform corrective setpoint changes by the operator. Therefore, the margin between the TVP maximum operating limit and the actual operating point was maintained conservatively at 80 kPa to absorb the variations in TVP without violating the limit and initiating offspec mode. Advanced Process Control (APC) is an established digital technology that has been deployed successfully in the process industry for decades to handle such scenarios and maximize the output of similar processes without violating any limits. The technology employs a predictive model of the process dynamics to anticipate changes before they happen and apply corrective actions proactively to maintain a steady and optimal operation. The feasibility study to implement APC for the condensate Stabilization System was concluded in December 2020 and showed that APC will yield an economic value. The APC application was then designed and commissioned in October 2021 with 100% in-house capabilities and have resulted in benefits in line with the estimations of the feasibility study. The success of APC implementation in PDO opens up the door to upstream specific applications to solve optimization challenges that were not possible to solve using existing standard control system (DCS). Figure 1 demonstrates the benefits gained from deploying APC for the Condensate Stabilization System. Figure 1 Demonstration of APC Benefits