Distillation Design and Control Using Aspen Simulation
2. Edition May 2013
512 Pages, Hardcover
Wiley & Sons Ltd
ISBN:
978-1-118-41143-8
John Wiley & Sons
Short Description
The new edition of this book greatly updates and expands the previous edition. It boasts new chapters on the divided wall column and carbon dioxide capture from stack gas, revises the design and control of distillation systems, and explains the use of dynamic simulation to study safety issues in the event of operating failures. Using Aspen Plus to develop rigorous simulations of single distillation columns and sequences of columns, the book considers the economics of capital investment and energy costs to create an optimal system for separation methods in the chemical and petroleum industries.
Learn how to develop optimal steady-state designs for distillation systems
As the search for new energy sources grows ever more urgent, distillation remains at the forefront among separation methods in the chemical, petroleum, and energy industries. Most importantly, as renewable sources of energy and chemical feedstocks continue to be developed, distillation design and control will become ever more important in our ability to ensure global sustainability.
Using the commercial simulators Aspen Plus(r) and Aspen Dynamics(r), this text enables readers to develop optimal steady-state designs for distillation systems. Moreover, readers will discover how to develop effective control structures. While traditional distillation texts focus on the steady-state economic aspects of distillation design, this text also addresses such issues as dynamic performance in the face of disturbances.
Distillation Design and Control Using Aspen(tm) Simulation introduces the current status and future implications of this vital technology from the perspectives of steady-state design and dynamics. The book begins with a discussion of vapor-liquid phase equilibrium and then explains the core methods and approaches for analyzing distillation columns. Next, the author covers such topics as:
* Setting up a steady-state simulation
* Distillation economic optimization
* Steady-state calculations for control structure selection
* Control of petroleum fractionators
* Design and control of divided-wall columns
* Pressure-compensated temperature control in distillation columns
Synthesizing four decades of research breakthroughs and practical applications in this dynamic field, Distillation Design and Control Using Aspen(tm) Simulation is a trusted reference that enables both students and experienced engineers to solve a broad range of challenging distillation problems.
PREFACE TO THE SECOND EDITION xv
PREFACE TO THE FIRST EDITION xvii
1 FUNDAMENTALS OF VAPOR-LIQUID-EQUILIBRIUM (VLE) 1
1.1 Vapor Pressure / 1
1.2 Binary VLE Phase Diagrams / 3
1.3 Physical Property Methods / 7
1.4 Relative Volatility / 7
1.5 Bubble Point Calculations / 8
1.6 Ternary Diagrams / 9
1.7 VLE Nonideality / 11
1.8 Residue Curves for Ternary Systems / 15
1.9 Distillation Boundaries / 22
1.10 Conclusions / 25
Reference / 27
2 ANALYSIS OF DISTILLATION COLUMNS 29
2.1 Design Degrees of Freedom / 29
2.2 Binary McCabe-Thiele Method / 30
2.2.1 Operating Lines / 32
2.2.2 q-Line / 33
2.2.3 Stepping Off Trays / 35
2.2.4 Effect of Parameters / 35
2.2.5 Limiting Conditions / 36
2.3 Approximate Multicomponent Methods / 36
2.3.1 Fenske Equation for Minimum Number of Trays / 37
2.3.2 Underwood Equations for Minimum Reflux Ratio / 37
2.4 Conclusions / 38
3 SETTING UP A STEADY-STATE SIMULATION 39
3.1 Configuring a New Simulation / 39
3.2 Specifying Chemical Components and Physical Properties / 46
3.3 Specifying Stream Properties / 51
3.4 Specifying Parameters of Equipment / 52
3.4.1 Column C1 / 52
3.4.2 Valves and Pumps / 55
3.5 Running the Simulation / 57
3.6 Using Design Spec/Vary Function / 58
3.7 Finding the Optimum Feed Tray and Minimum Conditions / 70
3.7.1 Optimum Feed Tray / 70
3.7.2 Minimum Reflux Ratio / 71
3.7.3 Minimum Number of Trays / 71
3.8 Column Sizing / 72
3.8.1 Length / 72
3.8.2 Diameter / 72
3.9 Conceptual Design / 74
3.10 Conclusions / 80
4 DISTILLATION ECONOMIC OPTIMIZATION 81
4.1 Heuristic Optimization / 81
4.1.1 Set Total Trays to Twice Minimum Number of Trays / 81
4.1.2 Set Reflux Ratio to 1.2 Times Minimum Reflux Ratio / 83
4.2 Economic Basis / 83
4.3 Results / 85
4.4 Operating Optimization / 87
4.5 Optimum Pressure for Vacuum Columns / 92
4.6 Conclusions / 94
5 MORE COMPLEX DISTILLATION SYSTEMS 95
5.1 Extractive Distillation / 95
5.1.1 Design / 99
5.1.2 Simulation Issues / 101
5.2 Ethanol Dehydration / 105
5.2.1 VLLE Behavior / 106
5.2.2 Process Flowsheet Simulation / 109
5.2.3 Converging the Flowsheet / 112
5.3 Pressure-Swing Azeotropic Distillation / 115
5.4 Heat-Integrated Columns / 121
5.4.1 Flowsheet / 121
5.4.2 Converging for Neat Operation / 122
5.5 Conclusions / 126
6 STEADY-STATE CALCULATIONS FOR CONTROL STRUCTURE SELECTION 127
6.1 Control Structure Alternatives / 127
6.1.1 Dual-Composition Control / 127
6.1.2 Single-End Control / 128
6.2 Feed Composition Sensitivity Analysis (ZSA) / 128
6.3 Temperature Control Tray Selection / 129
6.3.1 Summary of Methods / 130
6.3.2 Binary Propane/Isobutane System / 131
6.3.3 Ternary BTX System / 135
6.3.4 Ternary Azeotropic System / 139
6.4 Conclusions / 144
Reference / 144
7 CONVERTING FROM STEADY-STATE TO DYNAMIC SIMULATION 145
7.1 Equipment Sizing / 146
7.2 Exporting to Aspen Dynamics / 148
7.3 Opening the Dynamic Simulation in Aspen Dynamics / 150
7.4 Installing Basic Controllers / 152
7.4.1 Reflux / 156
7.4.2 Issues / 157
7.5 Installing Temperature and Composition Controllers / 161
7.5.1 Tray Temperature Control / 162
7.5.2 Composition Control / 170
7.5.3 Composition/Temperature Cascade Control / 170
7.6 Performance Evaluation / 172
7.6.1 Installing a Plot / 172
7.6.2 Importing Dynamic Results into Matlab / 174
7.6.3 Reboiler Heat Input to Feed Ratio / 176
7.6.4 Comparison of Temperature Control with Cascade CC/TC / 181
7.7 Conclusions / 184
8 CONTROL OF MORE COMPLEX COLUMNS 185
8.1 Extractive Distillation Process / 185
8.1.1 Design / 185
8.1.2 Control Structure / 188
8.1.3 Dynamic Performance / 191
8.2 Columns with Partial Condensers / 191
8.2.1 Total Vapor Distillate / 192
8.2.2 Both Vapor and Liquid Distillate Streams / 209
8.3 Control of Heat-Integrated Distillation Columns / 217
8.3.1 Process Studied / 217
8.3.2 Heat Integration Relationships / 218
8.3.3 Control Structure / 222
8.3.4 Dynamic Performance / 223
8.4 Control of Azeotropic Columns/Decanter System / 226
8.4.1 Converting to Dynamics and Closing Recycle Loop / 227
8.4.2 Installing the Control Structure / 228
8.4.3 Performance / 233
8.4.4 Numerical Integration Issues / 237
8.5 Unusual Control Structure / 238
8.5.1 Process Studied / 239
8.5.2 Economic Optimum Steady-State Design / 242
8.5.3 Control Structure Selection / 243
8.5.4 Dynamic Simulation Results / 248
8.5.5 Alternative Control Structures / 248
8.5.6 Conclusions / 254
8.6 Conclusions / 255
References / 255
9 REACTIVE DISTILLATION 257
9.1 Introduction / 257
9.2 Types of Reactive Distillation Systems / 258
9.2.1 Single-Feed Reactions / 259
9.2.2 Irreversible Reaction with Heavy Product / 259
9.2.3 Neat Operation Versus Use of Excess Reactant / 260
9.3 TAME Process Basics / 263
9.3.1 Prereactor / 263
9.3.2 Reactive Column C1 / 263
9.4 TAME Reaction Kinetics and VLE / 266
9.5 Plantwide Control Structure / 270
9.6 Conclusions / 274
References / 274
10 CONTROL OF SIDESTREAM COLUMNS 275
10.1 Liquid Sidestream Column / 276
10.1.1 Steady-State Design / 276
10.1.2 Dynamic Control / 277
10.2 Vapor Sidestream Column / 281
10.2.1 Steady-State Design / 282
10.2.2 Dynamic Control / 282
10.3 Liquid Sidestream Column with Stripper / 286
10.3.1 Steady-State Design / 286
10.3.2 Dynamic Control / 288
10.4 Vapor Sidestream Column with Rectifier / 292
10.4.1 Steady-State Design / 292
10.4.2 Dynamic Control / 293
10.5 Sidestream Purge Column / 300
10.5.1 Steady-State Design / 300
10.5.2 Dynamic Control / 302
10.6 Conclusions / 307
11 CONTROL OF PETROLEUM FRACTIONATORS 309
11.1 Petroleum Fractions / 310
11.2 Characterization Crude Oil / 314
11.3 Steady-State Design of Preflash Column / 321
11.4 Control of Preflash Column / 328
11.5 Steady-State Design of Pipestill / 332
11.5.1 Overview of Steady-State Design / 333
11.5.2 Configuring the Pipestill in Aspen Plus / 335
11.5.3 Effects of Design Parameters / 344
11.6 Control of Pipestill / 346
11.7 Conclusions / 354
References / 354
12 DIVIDED-WALL (PETLYUK) COLUMNS 355
12.1 Introduction / 355
12.2 Steady-State Design / 357
12.2.1 MultiFrac Model / 357
12.2.2 RadFrac Model / 366
12.3 Control of the Divided-Wall Column / 369
12.3.1 Control Structure / 369
12.3.2 Implementation in Aspen Dynamics / 373
12.3.3 Dynamic Results / 375
12.4 Control of the Conventional Column Process / 380
12.4.1 Control Structure / 380
12.4.2 Dynamic Results and Comparisons / 381
12.5 Conclusions and Discussion / 383
References / 384
13 DYNAMIC SAFETY ANALYSIS 385
13.1 Introduction / 385
13.2 Safety Scenarios / 385
13.3 Process Studied / 387
13.4 Basic RadFrac Models / 387
13.4.1 Constant Duty Model / 387
13.4.2 Constant Temperature Model / 388
13.4.3 LMTD Model / 388
13.4.4 Condensing or Evaporating Medium Models / 388
13.4.5 Dynamic Model for Reboiler / 388
13.5 RadFrac Model with Explicit Heat-Exchanger Dynamics / 389
13.5.1 Column / 389
13.5.2 Condenser / 390
13.5.3 Reflux Drum / 391
13.5.4 Liquid Split / 391
13.5.5 Reboiler / 391
13.6 Dynamic Simulations / 392
13.6.1 Base Case Control Structure / 392
13.6.2 Rigorous Case Control Structure / 393
13.7 Comparison of Dynamic Responses / 394
13.7.1 Condenser Cooling Failure / 394
13.7.2 Heat-Input Surge / 395
13.8 Other Issues / 397
13.9 Conclusions / 398
Reference / 398
14 CARBON DIOXIDE CAPTURE 399
14.1 Carbon Dioxide Removal in Low-Pressure Air Combustion Power Plants / 400
14.1.1 Process Design / 400
14.1.2 Simulation Issues / 401
14.1.3 Plantwide Control Structure / 404
14.1.4 Dynamic Performance / 408
14.2 Carbon Dioxide Removal in High-Pressure IGCC Power Plants / 412
14.2.1 Design / 414
14.2.2 Plantwide Control Structure / 414
14.2.3 Dynamic Performance / 418
14.3 Conclusions / 420
References / 421
15 DISTILLATION TURNDOWN 423
15.1 Introduction / 423
15.2 Control Problem / 424
15.2.1 Two-Temperature Control / 425
15.2.2 Valve-Position Control / 426
15.2.3 Recycle Control / 427
15.3 Process Studied / 428
15.4 Dynamic Performance for Ramp Disturbances / 431
15.4.1 Two-Temperature Control / 431
15.4.2 VPC Control / 432
15.4.3 Recycle Control / 433
15.4.4 Comparison / 434
15.5 Dynamic Performance for Step Disturbances / 435
15.5.1 Two-Temperature Control / 435
15.5.2 VPC Control / 436
15.5.3 Recycle Control / 436
15.6 Other Control Structures / 439
15.6.1 No Temperature Control / 439
15.6.2 Dual Temperature Control / 440
15.7 Conclusions / 442
References / 442
16 PRESSURE-COMPENSATED TEMPERATURE CONTROL IN DISTILLATION COLUMNS 443
16.1 Introduction / 443
16.2 Numerical Example Studied / 445
16.3 Conventional Control Structure Selection / 446
16.4 Temperature/Pressure/Composition Relationships / 450
16.5 Implementation in Aspen Dynamics / 451
16.6 Comparison of Dynamic Results / 452
16.6.1 Feed Flow Rate Disturbances / 452
16.6.2 Pressure Disturbances / 453
16.7 Conclusions / 455
References / 456
17 ETHANOL DEHYDRATION 457
17.1 Introduction / 457
17.2 Optimization of the Beer Still (Preconcentrator) / 459
17.3 Optimization of the Azeotropic and Recovery Columns / 460
17.3.1 Optimum Feed Locations / 461
17.3.2 Optimum Number of Stages / 462
17.4 Optimization of the Entire Process / 462
17.5 Cyclohexane Entrainer / 466
17.6 Flowsheet Recycle Convergence / 466
17.7 Conclusions / 467
References / 467
18 EXTERNAL RESET FEEDBACK TO PREVENT RESET WINDUP 469
18.1 Introduction / 469
18.2 External Reset Feedback Circuit Implementation / 471
18.2.1 Generate the Error Signal / 472
18.2.2 Multiply by Controller Gain / 472
18.2.3 Add the Output of Lag / 472
18.2.4 Select Lower Signal / 472
18.2.5 Setting up the Lag Block / 472
18.3 Flash Tank Example / 473
18.3.1 Process and Normal Control Structure / 473
18.3.2 Override Control Structure Without External Reset Feedback / 474
18.3.3 Override Control Structure with External Reset Feedback / 476
18.4 Distillation Column Example / 479
18.4.1 Normal Control Structure / 479
18.4.2 Normal and Override Controllers Without External Reset / 481
18.4.3 Normal and Override Controllers with External Reset Feedback / 483
18.5 Conclusions / 486
References / 486
INDEX 487
PREFACE TO THE FIRST EDITION xvii
1 FUNDAMENTALS OF VAPOR-LIQUID-EQUILIBRIUM (VLE) 1
1.1 Vapor Pressure / 1
1.2 Binary VLE Phase Diagrams / 3
1.3 Physical Property Methods / 7
1.4 Relative Volatility / 7
1.5 Bubble Point Calculations / 8
1.6 Ternary Diagrams / 9
1.7 VLE Nonideality / 11
1.8 Residue Curves for Ternary Systems / 15
1.9 Distillation Boundaries / 22
1.10 Conclusions / 25
Reference / 27
2 ANALYSIS OF DISTILLATION COLUMNS 29
2.1 Design Degrees of Freedom / 29
2.2 Binary McCabe-Thiele Method / 30
2.2.1 Operating Lines / 32
2.2.2 q-Line / 33
2.2.3 Stepping Off Trays / 35
2.2.4 Effect of Parameters / 35
2.2.5 Limiting Conditions / 36
2.3 Approximate Multicomponent Methods / 36
2.3.1 Fenske Equation for Minimum Number of Trays / 37
2.3.2 Underwood Equations for Minimum Reflux Ratio / 37
2.4 Conclusions / 38
3 SETTING UP A STEADY-STATE SIMULATION 39
3.1 Configuring a New Simulation / 39
3.2 Specifying Chemical Components and Physical Properties / 46
3.3 Specifying Stream Properties / 51
3.4 Specifying Parameters of Equipment / 52
3.4.1 Column C1 / 52
3.4.2 Valves and Pumps / 55
3.5 Running the Simulation / 57
3.6 Using Design Spec/Vary Function / 58
3.7 Finding the Optimum Feed Tray and Minimum Conditions / 70
3.7.1 Optimum Feed Tray / 70
3.7.2 Minimum Reflux Ratio / 71
3.7.3 Minimum Number of Trays / 71
3.8 Column Sizing / 72
3.8.1 Length / 72
3.8.2 Diameter / 72
3.9 Conceptual Design / 74
3.10 Conclusions / 80
4 DISTILLATION ECONOMIC OPTIMIZATION 81
4.1 Heuristic Optimization / 81
4.1.1 Set Total Trays to Twice Minimum Number of Trays / 81
4.1.2 Set Reflux Ratio to 1.2 Times Minimum Reflux Ratio / 83
4.2 Economic Basis / 83
4.3 Results / 85
4.4 Operating Optimization / 87
4.5 Optimum Pressure for Vacuum Columns / 92
4.6 Conclusions / 94
5 MORE COMPLEX DISTILLATION SYSTEMS 95
5.1 Extractive Distillation / 95
5.1.1 Design / 99
5.1.2 Simulation Issues / 101
5.2 Ethanol Dehydration / 105
5.2.1 VLLE Behavior / 106
5.2.2 Process Flowsheet Simulation / 109
5.2.3 Converging the Flowsheet / 112
5.3 Pressure-Swing Azeotropic Distillation / 115
5.4 Heat-Integrated Columns / 121
5.4.1 Flowsheet / 121
5.4.2 Converging for Neat Operation / 122
5.5 Conclusions / 126
6 STEADY-STATE CALCULATIONS FOR CONTROL STRUCTURE SELECTION 127
6.1 Control Structure Alternatives / 127
6.1.1 Dual-Composition Control / 127
6.1.2 Single-End Control / 128
6.2 Feed Composition Sensitivity Analysis (ZSA) / 128
6.3 Temperature Control Tray Selection / 129
6.3.1 Summary of Methods / 130
6.3.2 Binary Propane/Isobutane System / 131
6.3.3 Ternary BTX System / 135
6.3.4 Ternary Azeotropic System / 139
6.4 Conclusions / 144
Reference / 144
7 CONVERTING FROM STEADY-STATE TO DYNAMIC SIMULATION 145
7.1 Equipment Sizing / 146
7.2 Exporting to Aspen Dynamics / 148
7.3 Opening the Dynamic Simulation in Aspen Dynamics / 150
7.4 Installing Basic Controllers / 152
7.4.1 Reflux / 156
7.4.2 Issues / 157
7.5 Installing Temperature and Composition Controllers / 161
7.5.1 Tray Temperature Control / 162
7.5.2 Composition Control / 170
7.5.3 Composition/Temperature Cascade Control / 170
7.6 Performance Evaluation / 172
7.6.1 Installing a Plot / 172
7.6.2 Importing Dynamic Results into Matlab / 174
7.6.3 Reboiler Heat Input to Feed Ratio / 176
7.6.4 Comparison of Temperature Control with Cascade CC/TC / 181
7.7 Conclusions / 184
8 CONTROL OF MORE COMPLEX COLUMNS 185
8.1 Extractive Distillation Process / 185
8.1.1 Design / 185
8.1.2 Control Structure / 188
8.1.3 Dynamic Performance / 191
8.2 Columns with Partial Condensers / 191
8.2.1 Total Vapor Distillate / 192
8.2.2 Both Vapor and Liquid Distillate Streams / 209
8.3 Control of Heat-Integrated Distillation Columns / 217
8.3.1 Process Studied / 217
8.3.2 Heat Integration Relationships / 218
8.3.3 Control Structure / 222
8.3.4 Dynamic Performance / 223
8.4 Control of Azeotropic Columns/Decanter System / 226
8.4.1 Converting to Dynamics and Closing Recycle Loop / 227
8.4.2 Installing the Control Structure / 228
8.4.3 Performance / 233
8.4.4 Numerical Integration Issues / 237
8.5 Unusual Control Structure / 238
8.5.1 Process Studied / 239
8.5.2 Economic Optimum Steady-State Design / 242
8.5.3 Control Structure Selection / 243
8.5.4 Dynamic Simulation Results / 248
8.5.5 Alternative Control Structures / 248
8.5.6 Conclusions / 254
8.6 Conclusions / 255
References / 255
9 REACTIVE DISTILLATION 257
9.1 Introduction / 257
9.2 Types of Reactive Distillation Systems / 258
9.2.1 Single-Feed Reactions / 259
9.2.2 Irreversible Reaction with Heavy Product / 259
9.2.3 Neat Operation Versus Use of Excess Reactant / 260
9.3 TAME Process Basics / 263
9.3.1 Prereactor / 263
9.3.2 Reactive Column C1 / 263
9.4 TAME Reaction Kinetics and VLE / 266
9.5 Plantwide Control Structure / 270
9.6 Conclusions / 274
References / 274
10 CONTROL OF SIDESTREAM COLUMNS 275
10.1 Liquid Sidestream Column / 276
10.1.1 Steady-State Design / 276
10.1.2 Dynamic Control / 277
10.2 Vapor Sidestream Column / 281
10.2.1 Steady-State Design / 282
10.2.2 Dynamic Control / 282
10.3 Liquid Sidestream Column with Stripper / 286
10.3.1 Steady-State Design / 286
10.3.2 Dynamic Control / 288
10.4 Vapor Sidestream Column with Rectifier / 292
10.4.1 Steady-State Design / 292
10.4.2 Dynamic Control / 293
10.5 Sidestream Purge Column / 300
10.5.1 Steady-State Design / 300
10.5.2 Dynamic Control / 302
10.6 Conclusions / 307
11 CONTROL OF PETROLEUM FRACTIONATORS 309
11.1 Petroleum Fractions / 310
11.2 Characterization Crude Oil / 314
11.3 Steady-State Design of Preflash Column / 321
11.4 Control of Preflash Column / 328
11.5 Steady-State Design of Pipestill / 332
11.5.1 Overview of Steady-State Design / 333
11.5.2 Configuring the Pipestill in Aspen Plus / 335
11.5.3 Effects of Design Parameters / 344
11.6 Control of Pipestill / 346
11.7 Conclusions / 354
References / 354
12 DIVIDED-WALL (PETLYUK) COLUMNS 355
12.1 Introduction / 355
12.2 Steady-State Design / 357
12.2.1 MultiFrac Model / 357
12.2.2 RadFrac Model / 366
12.3 Control of the Divided-Wall Column / 369
12.3.1 Control Structure / 369
12.3.2 Implementation in Aspen Dynamics / 373
12.3.3 Dynamic Results / 375
12.4 Control of the Conventional Column Process / 380
12.4.1 Control Structure / 380
12.4.2 Dynamic Results and Comparisons / 381
12.5 Conclusions and Discussion / 383
References / 384
13 DYNAMIC SAFETY ANALYSIS 385
13.1 Introduction / 385
13.2 Safety Scenarios / 385
13.3 Process Studied / 387
13.4 Basic RadFrac Models / 387
13.4.1 Constant Duty Model / 387
13.4.2 Constant Temperature Model / 388
13.4.3 LMTD Model / 388
13.4.4 Condensing or Evaporating Medium Models / 388
13.4.5 Dynamic Model for Reboiler / 388
13.5 RadFrac Model with Explicit Heat-Exchanger Dynamics / 389
13.5.1 Column / 389
13.5.2 Condenser / 390
13.5.3 Reflux Drum / 391
13.5.4 Liquid Split / 391
13.5.5 Reboiler / 391
13.6 Dynamic Simulations / 392
13.6.1 Base Case Control Structure / 392
13.6.2 Rigorous Case Control Structure / 393
13.7 Comparison of Dynamic Responses / 394
13.7.1 Condenser Cooling Failure / 394
13.7.2 Heat-Input Surge / 395
13.8 Other Issues / 397
13.9 Conclusions / 398
Reference / 398
14 CARBON DIOXIDE CAPTURE 399
14.1 Carbon Dioxide Removal in Low-Pressure Air Combustion Power Plants / 400
14.1.1 Process Design / 400
14.1.2 Simulation Issues / 401
14.1.3 Plantwide Control Structure / 404
14.1.4 Dynamic Performance / 408
14.2 Carbon Dioxide Removal in High-Pressure IGCC Power Plants / 412
14.2.1 Design / 414
14.2.2 Plantwide Control Structure / 414
14.2.3 Dynamic Performance / 418
14.3 Conclusions / 420
References / 421
15 DISTILLATION TURNDOWN 423
15.1 Introduction / 423
15.2 Control Problem / 424
15.2.1 Two-Temperature Control / 425
15.2.2 Valve-Position Control / 426
15.2.3 Recycle Control / 427
15.3 Process Studied / 428
15.4 Dynamic Performance for Ramp Disturbances / 431
15.4.1 Two-Temperature Control / 431
15.4.2 VPC Control / 432
15.4.3 Recycle Control / 433
15.4.4 Comparison / 434
15.5 Dynamic Performance for Step Disturbances / 435
15.5.1 Two-Temperature Control / 435
15.5.2 VPC Control / 436
15.5.3 Recycle Control / 436
15.6 Other Control Structures / 439
15.6.1 No Temperature Control / 439
15.6.2 Dual Temperature Control / 440
15.7 Conclusions / 442
References / 442
16 PRESSURE-COMPENSATED TEMPERATURE CONTROL IN DISTILLATION COLUMNS 443
16.1 Introduction / 443
16.2 Numerical Example Studied / 445
16.3 Conventional Control Structure Selection / 446
16.4 Temperature/Pressure/Composition Relationships / 450
16.5 Implementation in Aspen Dynamics / 451
16.6 Comparison of Dynamic Results / 452
16.6.1 Feed Flow Rate Disturbances / 452
16.6.2 Pressure Disturbances / 453
16.7 Conclusions / 455
References / 456
17 ETHANOL DEHYDRATION 457
17.1 Introduction / 457
17.2 Optimization of the Beer Still (Preconcentrator) / 459
17.3 Optimization of the Azeotropic and Recovery Columns / 460
17.3.1 Optimum Feed Locations / 461
17.3.2 Optimum Number of Stages / 462
17.4 Optimization of the Entire Process / 462
17.5 Cyclohexane Entrainer / 466
17.6 Flowsheet Recycle Convergence / 466
17.7 Conclusions / 467
References / 467
18 EXTERNAL RESET FEEDBACK TO PREVENT RESET WINDUP 469
18.1 Introduction / 469
18.2 External Reset Feedback Circuit Implementation / 471
18.2.1 Generate the Error Signal / 472
18.2.2 Multiply by Controller Gain / 472
18.2.3 Add the Output of Lag / 472
18.2.4 Select Lower Signal / 472
18.2.5 Setting up the Lag Block / 472
18.3 Flash Tank Example / 473
18.3.1 Process and Normal Control Structure / 473
18.3.2 Override Control Structure Without External Reset Feedback / 474
18.3.3 Override Control Structure with External Reset Feedback / 476
18.4 Distillation Column Example / 479
18.4.1 Normal Control Structure / 479
18.4.2 Normal and Override Controllers Without External Reset / 481
18.4.3 Normal and Override Controllers with External Reset Feedback / 483
18.5 Conclusions / 486
References / 486
INDEX 487
WILLIAM L. LUYBEN, PhD, is Professor of Chemical Engineering at Lehigh University where he has taught for over forty-five years. Dr. Luyben spent nine years as an engineer with Exxon and DuPont. He has published fourteen books and more than 250 original research papers. Dr. Luyben is a 2003 recipient of the Computing Practice Award from the CAST Division of the AIChE. He was elected to the Process Control Hall of Fame in 2005. In 2011, the Separations Division of the AIChE recognized his contributions to distillation technology by a special honors session.
