Designing Controls for the Process Industries

429 Pages·2017·9.73 MB·English

by  Seames, Wayne

Designing Controls for
the Process Industries

Designing Controls for
the Process Industries
Wayne Seames
CRC Press
Taylor & Francis Group
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Contents
List of Figures ......................................................................................................xiii
List of Tables .....................................................................................................xxvii
Preface ..................................................................................................................xxix
Author ...............................................................................................................xxxiii
1. Processing System Fundamentals ...............................................................1
1.1 Continuous Processing .........................................................................3
1.2 Batch Processing ....................................................................................4
1.3 Semi-Batch Processing ..........................................................................4
1.4 Unit Operations .....................................................................................7
1.5 Dynamics: The Speed of Information Flow in Processes ................8
1.6 Recycle Loops ......................................................................................11
1.7 Documenting Process Flow ...............................................................12
1.8 Batch and Semi-Batch Process Drawings ........................................19
1.9 Distributed Control Systems .............................................................22
1.9.1 Elements of the Distributed Control System .....................26
1.9.2 Programmable Logic Control Systems ...............................28
1.10 Symbology for Control Systems .......................................................29
1.10.1 Other, Less Common, Symbols ............................................35
Problems ..........................................................................................................36
Reference .........................................................................................................38
2. Control System Fundamentals ...................................................................39
2.1 Overview of Basic Unit Operations ..................................................39
2.1.1 Motive Force (Momentum Transfer) ...................................39
2.1.2 Heat Transfer ..........................................................................39
2.1.3 Mass Transfer ..........................................................................40
2.1.4 Reactions .................................................................................40
2.2 Independent and Dependent Process Variables .............................40
2.2.1 Control (Independent) Variables .........................................40
2.2.2 Measurement (Dependent) Variables .................................42
2.3 Feedback Control Loop ......................................................................43
2.4 Disturbance Variables .........................................................................49
2.5 Feed Forward Contributions to Control ..........................................53
2.6 Related Variables .................................................................................56
2.7 Ratio Control Loops ............................................................................58
2.8 Cascade Loops .....................................................................................61
2.9 Feed Forward/Feedback Cascade Control Loops ..........................68
2.10 Process and Safety Systems ...............................................................69
2.11 Sequential Logic Control ....................................................................74
Problems ..........................................................................................................78
vii
viii Contents
3. Motive Force Unit Operations Control .....................................................83
3.1 Incompressible Fluids: Pumps ..........................................................83
3.2 Compressible Fluids: Compressors, Blowers, and Fans ................92
3.2.1 Other Compressible Fluid Devices: Expanders and
Turbines ...................................................................................97
3.3 Solids Handling Devices ..................................................................100
3.3.1 Solids Mixed with Gases and Liquids ..............................100
3.3.2 Physical Motive Force Devices...........................................102
3.3.3 Using Physical Pressure or Gravity Directly on the
Solid for Short Distance Transport ....................................103
3.4 Startup and Shutdown for Large Motive Force Systems ............107
3.5 Equipment Protection Systems .......................................................107
3.6 Switching Controls for Parallel Motive Force Units ....................108
Problems ........................................................................................................110
4. Heat Transfer Unit Operations Control ..................................................113
4.1 Fluid-Fluid Heat Transfer ................................................................113
4.1.1 Heating or Cooling a Process Stream to a Specified
Temperature Using a Utility Stream .................................114
4.1.2 Vaporizing a Liquid Process Stream Using a Utility
Stream ....................................................................................117
4.1.3 Condensing a Gaseous Process Stream Using a
Utility Stream ........................................................................119
4.1.4 Process-Process Heat Transfer ............................................122
4.1.4.1 Cross Exchanger with Phase Change ................125
4.2 Direct Mixing Heat Transfer ............................................................130
4.3 Electrical Resistance Heat Transfer .................................................133
4.4 Fired Heaters ......................................................................................134
4.5 Monitoring and Adapting for Heat Exchanger Fouling and
Scaling .................................................................................................138
4.6 Switching Controls for Parallel Heat Transfer Units ...................139
Problems ........................................................................................................141
5. Separation Unit Operations Controls .....................................................145
5.1 Single-Stage Separation ....................................................................145
5.1.1 The Flash Drum ....................................................................145
5.1.2 The Phase (Gravity) Separator ...........................................149
5.2 Multistage Distillation Overall Concepts ......................................150
5.2.1 Overhead System Controls for Distillation ......................157
5.2.1.1 Overhead System with a Partial Condenser ....157
5.2.1.2 Overhead Control Scheme with Total
Condenser..............................................................158
5.2.2 Bottoms System Controls for Distillation .........................160
Contents ix
5.3 Liquid-Based Absorption/Adsorption/Extraction/Leaching
System Controls .................................................................................163
5.3.1 Single-Stage, Once-Through Absorption ..........................164
5.3.2 Single-Stage, Once-Through Extraction ...........................166
5.3.3 Multistage Absorption with Solvent Recovery ...............168
5.4 Solid-Based Absorption/Adsorption/Extraction/Leaching
System Controls .................................................................................175
5.4.1 Once-Through Solid Sorbent Systems ..............................175
5.4.2 Fluidized Bed Solid Sorbent Systems ...............................177
5.4.3 Fixed Bed Regenerated Solid Sorbent Systems ...............181
Problems ........................................................................................................190
6. Reaction Unit Operations Control ...........................................................195
6.1 Continuous Flow Reactors ...............................................................195
6.1.1 A Heterogeneous Binary Reaction of Two Liquid
Reactants ...............................................................................197
6.1.2 Safety Control Systems .......................................................201
6.2 CSTR-Type Reactors .........................................................................203
6.3 Batch Reaction Systems ....................................................................207
6.4 Batch Reactors in Continuous Processes .......................................209
Problems ........................................................................................................215
7. Other Control Paradigms ..........................................................................219
7.1 Using Intermediate Calculations in Control Loops .....................219
7.1.1 Using CALC Blocks in Blending Applications ................221
7.1.2 Using CALC Blocks to Monitor Heat Exchanger
Performance ..........................................................................223
7.2 Inferential Control .............................................................................227
7.3 High and Low Select Controls ........................................................231
7.4 Override Control ...............................................................................233
7.5 Split Range Control ...........................................................................233
7.6 Allocation Control .............................................................................235
7.7 Constraint Control ............................................................................235
Problems ........................................................................................................238
8. Controller Theory .......................................................................................241
8.1 On/Off Control .................................................................................241
8.2 PID Control ........................................................................................243
8.2.1 Proportional Response Control ..........................................246
8.2.2 Integral Control ....................................................................248
8.2.3 Derivative Control ...............................................................250
8.2.4 Combined PID Control Algorithm ....................................251
8.3 Modifications to Minimize Derivative Kick ..................................252