Process Control

Myke King is Director of Whitehouse Consulting which provides process control consulting and training services. He has been running courses for industry covering all aspects of process control for the past 30 years (over 150 courses to over 1,500 delegates).Myke graduated from Cambridge University in 1974 with a master’s degree in Chemical Engineering. After University he joined Exxon to work as control engineer in their oil refinery in the UK, later managing the process control section. In 1983 he co-founded the consulting company KBC Process Automation, which was later sold to Honeywell. He thus has about 40 years of relevant experience - working in over 30 countries providing services to over 100 companies.

• Preface xAbout the Author xv1. Introduction 12. Process Dynamics 32.1 Definition 32.2 Cascade Control 102.3 Model Identification 122.4 Integrating Processes 262.5 Other Types of Process 292.6 Robustness 313. PID Algorithm 353.1 Definitions 353.2 Proportional Action 363.3 Integral Action 413.4 Derivative Action 433.5 Versions of Control Algorithm 493.6 Interactive PID Controller 513.7 Proportional‐on‐PV Controller 563.8 Nonstandard Algorithms 643.9 Tuning 653.10 Ziegler‐Nichols Tuning Method 663.11 Cohen‐Coon Tuning Method 723.12 Tuning Based on Penalty Functions 733.13 Manipulated Variable Overshoot 773.14 Lambda Tuning Method 803.15 IMC Tuning Method 803.16 Choice of Tuning Method 833.17 Suggested Tuning Method for Self‐Regulating Processes 843.18 Tuning for Load Changes 873.19 Tuning for SP Ramps 893.20 Tuning for Unconstrained MV Overshoot 913.21 PI Tuning Compared to PID Tuning 923.22 Tuning for Large Scan Interval 943.23 Suggested Tuning Method for Integrating Processes 973.24 Measure of Robustness 993.25 Implementation of Tuning 1003.26 Tuning Cascades 1013.27 Loop Gain 1043.28 Adaptive Tuning 1053.29 Initialisation 1063.30 Anti‐Reset Windup 1083.31 On‐Off Control 1094. Level Control 1124.1 Use of Cascade Control 1124.2 Parameters Required for Tuning Calculations 1134.3 Tight Level Control 1204.4 Averaging Level Control 1224.5 Error‐Squared Controller 1294.6 Gap Controller 1324.7 Impact of Noise on Averaging Control 1344.8 Potential Disadvantage of Averaging Level Control 1364.9 General Approach to Tuning 1374.10 Three‐Element Level Control 1395. Signal Conditioning 1435.1 Instrument Linearisation 1435.2 Process Linearisation 1455.3 Control of pH 1475.4 Constraint Conditioning 1515.5 Pressure Compensation of Distillation Tray Temperature 1535.6 Compensation of Gas Flow Measurement 1535.7 Filtering 1555.8 Exponential Filter 1575.9 Nonlinear Exponential Filter 1615.10 Moving Average Filter 1615.11 Least Squares Filter 1635.12 Tuning the Filter 1695.13 Control Valve Characterisation 1705.14 Equal Percentage Valve 1725.15 Split‐Range Valves 1786. Feedforward Control 1846.1 Ratio Algorithm 1856.2 Bias Algorithm 1886.3 Deadtime and Lead‐Lag Algorithms 1906.4 Tuning 1946.5 Laplace Derivation of Dynamic Compensation 1997. Deadtime Compensation 2017.1 Smith Predictor 2017.2 Internal Model Control 2067.3 Dahlin Algorithm 2068. Multivariable Control 2108.1 Constraint Control 2108.2 SISO Constraint Control 2118.3 Signal Selectors 2138.4 Relative Gain Analysis 2178.5 Niederlinski Index 2268.6 Condition Number 2278.7 Steady State Decoupling 2298.8 Dynamic Decoupling 2318.9 MPC Principles 2378.10 Parallel Coordinates 2398.11 Enhanced Operator Displays 2408.12 MPC Performance Monitoring 2429. Inferentials and Analysers 2489.1 Inferential Properties 2489.2 Assessing Accuracy 2569.3 Laboratory Update of Inferential 2629.4 Analyser Update of Inferential 2669.5 Monitoring On‐Stream Analysers 26810. Combustion Control 27010.1 Fuel Gas Flow Correction 27010.2 Measuring NHV 27810.3 Dual Firing 28010.4 Heater Inlet Temperature Feedforward 28110.5 Fuel Pressure Control 28410.6 Firebox Pressure 28710.7 Combustion Air Control 28810.8 Boiler Control 29910.9 Fired Heater Pass Balancing 30011. Compressor Control 30611.1 Polytropic Head 30611.2 Load Control (Turbo‐Machines) 31011.3 Load Control (Reciprocating Machines) 31411.4 Anti‐Surge Control 31512. Distillation Control 32212.1 Key Components 32512.2 Relative Volatility 32512.3 McCabe‐Thiele Diagram 32812.4 Cut and Separation 33312.5 Effect of Process Design 34512.6 Basic Controls 35012.7 Pressure Control 35012.8 Level Control 36412.9 Tray Temperature Control 38212.10 Pressure Compensated Temperature 39312.11 Inferentials 40212.12 First‐Principle Inferentials 41112.13 Feedforward on Feed Rate 41312.14 Feed Composition Feedforward 41612.15 Feed Enthalpy Feedforward 41812.16 Decoupling 41912.17 Multivariable Control 42412.18 On‐Stream Analysers 43312.19 Towers with Sidestreams 43312.20 Column Optimisation 43512.21 Optimisation of Column Pressure 43812.22 Energy/Yield Optimisation 44113. APC Project Execution 44413.1 Benefits Study 44413.2 Benefit Estimation for Improved Regulatory Control 44513.3 Benefits of Closed‐Loop Real‐Time Optimisation 45513.4 Basic Controls 45813.5 Basic Control Monitoring 45913.6 Inferential Properties 46413.7 Organisation 46413.8 Vendor Selection 46813.9 Safety in APC Design 47113.10 Alarms 47114. Statistical Methods 47314.1 Central Limit Theorem 47314.2 Generating a Normal Distribution 47514.3 Quantile Plots 47714.4 Calculating Standard Deviation 47814.5 Skewness and Kurtosis 48014.6 Correlation 48014.7 Confidence Interval 48114.8 Westinghouse Electric Company Rules 48414.9 Gamma Function 48514.10 Student t Distribution 48614.11 χ2 Distribution 48914.12 F Distribution 49214.13 Akaike Information Criterion 49714.14 Adjusted R2 49914.15 Levene’s Test 50014.16 Box‐Wetz Ratio 50114.17 Regression Analysis 50214.18 Outliers 51314.19 Model Identification 51414.20 Autocorrelation and Autocovariance 51814.21 Artificial Neural Networks 52714.22 Repeatability 53314.23 Reproducibility 53314.24 Six‐Sigma 53514.25 Data Reconciliation 53515. Mathematical Techniques 54015.1 Fourier Transform 54015.2 Recursive Filters 54815.3 Lagrangian Interpolation 55315.4 Padé Approximation 55715.5 Laplace Transform Derivations 56015.6 Laplace Transforms for Processes 56315.7 Laplace Transforms for Controllers 56915.8 I‐PD versus PI‐D Algorithm 57215.9 Direct Synthesis 57315.10 Predicting Filter Attenuation 57815.11 Stability Limit for PID Control 57915.12 Ziegler‐Nichols Tuning from Process Dynamics 58315.13 Partial Fractions 58615.14 z‐Transforms and Finite Difference Equations 588References 594Index 596