Optimise NH 3 injection flow rates Optimise wash water rates Generate integrity operating envelopes Estimate corrosion rates. Corrosion monitoring: Guarding infrastructure integrity Corrosion in CDU overheads caused unplanned and costly unit outages. 8 Eliminating or minimising corrosion in the overhead system of CDUs was challenging, as it could lead to pipe leaks. This corrosion stemmed from aqueous corro- sion attributed to hydrogen chloride forming from hydrol- ysis of inorganic chlorides in crude preheat and furnace processes. Factors such as ammonium and/or hydrochlo- ride salts that absorb moisture often cause corrosion above the dew point. Mitigation strategies involved optimising the injection of chemical agents or dew point control in the overhead system. This complexity made the overhead system one of the most vulnerable parts of each distilla- tion unit. As shown in Figure 7 , the corrosion digital twin provided a comprehensive solution that consolidated pro- cesses as well as chemical and corrosion data to streamline monitoring from a single location. The corrosion control delivered the following benefits: Minimised corrosive conditions Prevented excessive corrosion, thereby extending the service life of the pipe and process equipment Reduced and prevented unpredictable shutdowns or accidents Cut maintenance costs. The corrosion digital twin achieved these outcomes by tracking the following parameters: • Ionic dew point temperature • Salting point temperature • Aqueous phase condensation temperature and pH • Neutralising ammonia injection rate • Boot water pH • Wash water injection rate. An electrolyte-based fluid package with the proprietary OLI and Petro-SIM digital twin of the CDU overhead was developed to demonstrate the capabilities of a corrosion- monitoring digital solution. It provided key information to confirm corrosion mechanisms, rates, and comprehensive operational guidelines.
Real time optimisation Planning & scheduling Enhanced unit monitoring Decarbonisation studies
New Data Set Alert
Digital Twin
AMM
AMM Proposed Calibrated & Tuned model
Simulation / LP health scores Actionable alerts Best calibration case Calibration & tuning factors
Figure 5 Automated model maintenance
Online prediction and monitoring of corrosion indicator parameters. a. Ionic dew point temperature and pH b. Salting point temperature c. Aqueous phase condensation temperature and pH The following objectives were set to guide the deployment of a digital twin to monitor corrosion in the refinery’s CDU overhead section and optimise operations: the process is maintained at desired operating conditions by reviewing process constraints, reducing process variability. During actual plant operations, equipment availability, eco- nomic conditions, and process disturbances result in changes in optimum conditions, as shown in Figure 6 . Hence, the optimum operating conditions need to be re-calculated in real time. The RTO of set points requires two models: the economic model and the operating model. The economic model functions to minimise costs while maximising product values, and the operating model is a steady-state process model to identify the operating limits for the process variable. Case study: Showcasing digital twin applications This case study minimises corrosion for a refinery overhead system. As part of their digitalisation journey to improve asset reliability, this client sought a centralised corrosion monitoring system. To address corrosion issues in the crude distillation units’ (CDU) overhead system, KBC (A Yokogawa Company) deployed a corrosion digital twin.
Traditional: DCS only
Modern: APC + DCS
New standard: RTO + APC+ DCS
Control with uctuation
Minimise uctuation
Minimise uctuation + maximise pro t
Optimal setpoint
Manual setpoint
Process data (ex. Product properties)
Figure 6 Control systems
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PTQ Q1 2024
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