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Plant-wide disturbance assessment with an application on a paper making process

Plant-wide disturbance assessment with an application on a paper making process. Zhang Di, M.Sc , Chen g Hui, M.Sc , Jämsä-Jounela Sirkka-Liisa, Professor 29 Jan, 2009 15th Nordic Process Control Workshop. Contents:. 1 Introduction 2 Plant-wide disturbance detection

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Plant-wide disturbance assessment with an application on a paper making process

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  1. Plant-wide disturbance assessment with an application on a paper making process Zhang Di, M.Sc,Cheng Hui, M.Sc,Jämsä-Jounela Sirkka-Liisa, Professor 29 Jan, 2009 15th Nordic Process Control Workshop

  2. Contents: • 1 Introduction • 2 Plant-wide disturbance detection • 3 Root cause diagnosis • 4 Methodology for plant-wide disturbance assessment • 5 Case study on Paper making process • 6 Results

  3. 1 Introduction: • There are many pieces of process equiment and control loops in one typical industrial plant, and they interact with each other instead of isolating from each other. • So disturbance may propagate through the plant and affect a large number of process variables, evolving into a plant-wide problem. • The widespread nature of the disturbacne then makes it difficult to identify its orgin.

  4. 1 Introduction: • A plant-wide approach means the distrbution of a distrubance is mapped out, and the location and nature of the cause of the disturbance are determined with a high probability of being right first time . • The alternative is a time consuming procedure of testing each control loop in turn until the root cause is found.

  5. Contents: • 1 Introduction • 2 Plant-wide disturbance detection • 3 Root cause diagnosis • 4 Methodology for plant-wide disturbance assessment • 5 Case study on Paper making process • 6 Results

  6. 2 Plant-wide disturbance detection More from the single loop disturbance detection, the plant-wide disturbance detection includes the identification of clusters of measurements having similar dynamic behaviour. Thornhill and Horch (2007)

  7. Contents: • 1 Introduction • 2 Plant-wide disturbance detection • 3 Root cause diagnosis • 4 Methodology for plant-wide disturbance assessment • 5 Case study on Paper making process • 6 Results

  8. 3 Root cause diagnosis Sources of persistent dynamic plant-wide disturbance The non-linear sources include: For example: • Control valves with excessive static friction • On-off and split-range control • Sensors faults • Process non-linearities leading to limit cycles • Hydrodynamic instability such as slugging flows The linear sources include: • Poor controller tuning • Controller interaction • Structural problems involving recycles

  9. 3 Root cause diagnosis • Diagnosis has two objectives, the identification and the isolation of the disturbance. Thornhill and Horch (2007)

  10. Contents: • 1 Introduction • 2 Plant-wide disturbance detection • 3 Root cause diagnosis • 4 Methodology for plant-wide disturbance assessment • 5 Case study on Paper making process • 6 Results

  11. 4 Methodology for plant-wide disturbance assessment

  12. Contents: • 1 Introduction • 2 Plant-wide disturbance detection • 3 Root cause diagnosis • 4 Methodology for plant-wide disturbance assessment • 5 Case study on Paper making process • 6 Results

  13. Testing environment :APROS interface The basis weight valve is under concern because the poor performance caused by the malfunction of valves is quite common in industry.

  14. 5Case study on Paper making process Measurement

  15. 5Case study on Paper making process Disturbance Power detection spectra

  16. 5Case study on Paper making process Root cause Diagnosis

  17. 5 Case study on Paper making process • In Choudhury et al. (2004), the existence of non-linearity in a system can be decided by the Gaussian test and the nonlinearity test. • If the signal is non-Gaussian it goes through another test to determine its linearity. • The nonlinearity index (NLI) is provided as shown

  18. 5 Case study on Paper making process • If the process is identified as linear, the root diagnosis path presented by Bauer and Thornhill (2007) is applied to find the disturbance propagation path and to build the causal diagraph. • Basic idea: To get to know the cause-and-effect relationship through the time delays between process variables. • Procedure: 1 Time delay estimation (cross-correlation function) 2 Build the causality matrix 3 Consistency check It is used to verify and ascertain the results. The limit is N-2.

  19. Contents: • 1 Introduction • 2 Plant-wide disturbance detection • 3 Root cause diagnosis • 4 Methodology for plant-wide disturbance assessment • 5 Case study on Paper making process • 6 Results

  20. 6 ResultsDisturbance detection Process measurements after mean centering and unit deviation scaling

  21. 6 ResultsDisturbance detection ACF of time series for the seven variables

  22. 6 ResultsDisturbance detection Power spectra of the seven variables

  23. 6 Resultslinear identification Squared Bicoherence calculation for V1 - Basis weight valve opening

  24. 6 Results

  25. 6 Results: propagation path 1 Causality matrix: 2 Consistency check: 3 Then: It is used to verify and ascertain the results. The limit is N-2.

  26. 6 Results: Propagation path 4 The causal map: The root cause is most likely close to the variable 1 - Basis weight valve opening

  27. Thank you for your attention!

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