Key Parameters Calibration and Benefits Evaluation of a Closed Loop Performance Monitoring System

The paper presents results from field validation of a closed loop performance monitoring system installed on several units of a refinery plant. The system supervises more than 1200 base control loops and evaluates performance periodically, after scheduled data acquisitions followed by off-line analysis. The first point taken into account is a comparison between verdicts issued by the system and indications by control operators: the large number of issued verdicts indicating scarce performance, but considered still acceptable by operators, results practically in False Alarm and forced to revisit the criterion adopted to classify a response as excessively oscillatory. New threshold values for the widely used Hägglund criterion (1995) were found and similar criteria were proposed and compared in order to match operators practical indications. The efficiency of criteria and threshold values depend on the type of loop (i.e. flow, pressure, level or temperature). The second point examined concerns validation of valve stiction diagnosis: indications from the monitoring systems are compared with evidence before and after plant shut down. Results confirm that oscillations in valves indicated as sticky disappeared after the operation, while many valves which underwent the maintenance procedure on the basis of a time schedule did not require it. Therefore, a systematic application of diagnostics tools for maintenance scheduling would be beneficial in order to focus on real needs and avoid unnecessary revision costs..