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, 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

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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.

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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.

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Contents:



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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)

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Contents:



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3 Root cause diagnosisSources 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 flowsThe linear sources include: Poor controller tuning Controller interaction Structural problems involving recycles

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3 Root cause diagnosis

Diagnosis has two objectives, the identification and the isolation of the disturbance.

Thornhill and Horch (2007)

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Contents:



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4 Methodology for plant-wide disturbance assessment

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Contents:



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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.

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5 Case study on Paper making process Measurement

0 50 100 150 200 250 300 350 400 450 500-505

V1

0 50 100 150 200 250 300 350 400 450 500-505

V2

0 50 100 150 200 250 300 350 400 450 500-505

V3

0 50 100 150 200 250 300 350 400 450 500-505

V4

0 50 100 150 200 250 300 350 400 450 500-505

V5

0 50 100 150 200 250 300 350 400 450 500-505

V6

0 50 100 150 200 250 300 350 400 450 500-505

V7

i

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5 Case study on Paper making process

Disturbance Power

detection spectra

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Root cause

Diagnosis

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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

|)2ˆ(ˆ| 2ˆ22

max cbicibcibNLI

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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.

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Contents:



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6 ResultsDisturbance detection

Process measurements after mean centering and unit deviation scaling

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ACF of time series for the seven variables

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Power spectra of the seven variables

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6 Resultslinear identification

|)2ˆ(ˆ| 2ˆ22

max cbicibcibNLI

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

00.511.522.533.5

x 10-3

0

0.5

1

1.5

2

2.5

x 10-6

f1

f2

Sq

ua

red

bic

oh

ere

nce

V1

|)2ˆ(ˆ| 2ˆ22

max cbicibcibNLI

Squared Bicoherence calculation for V1- Basis weight valve opening

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6 Results

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

00.511.522.533.5

x 10-3

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

f1

f2

Sq

ua

red

bic

oh

ere

nce

V2

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

00.511.522.533.5

x 10-3

0

1

2

3

4

5

6

7

8

x 10-3

f1

f2

Sq

ua

red

bic

oh

ere

nce

V3

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

00.5

11.5

22.5

33.5

x 10-3

0

1

2

3

4

5

6

7

8

x 10-3

f1

f2

Sq

ua

red

bio

he

ren

ce

V4

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

00.511.522.533.5

x 10-3

0

1

2

3

4

5

6

7

8

x 10-3

f1

f2

Sq

ua

red

bic

oh

ere

nce

V5

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

00.511.522.533.5

x 10-3

0

1

2

3

4

5

6

7

8

x 10-3

f1

f2

Sq

ua

red

bic

oh

ere

nce

V6

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

00.5

11.5

22.5

33.5

x 10-3

0

0.5

1

1.5

2

2.5

3

3.5

x 10-3

f1

f2

Sq

ua

red

bic

oh

ere

nce

V7

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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.

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6 Results: Propagation path

4 The causal map:

The root cause is most likely close to the variable 1 - Basis weight valve opening

Thank you for your attention!

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

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