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Aeration ControlSystem Design
Aeration ControlSystem Design
A Practical Guide to Energy andProcess Optimization
Thomas E. Jenkins, PEJenTech Inc.
Copyright # 2014 by John Wiley & Sons, Inc. All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Cataloging-in-Publication Data:
Jenkins, Thomas E., 1950-
Aeration control system design : a practical guide to energy and process optimization / Thomas E.
Jenkins, PE, JenTech Inc. – First edition.
pages cm
Includes index.
ISBN 978-1-118-38998-0 (hardback)
1. Sewage–Purification–Aeration. 2. Water–Aeration. 3. Supervisory control systems. 4. Sewage
disposal plants–Energy conservation. I. Title.
TD758.J47 2013
628.1065–dc23
2013020446
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents
Preface xi
Acknowledgments xiii
List of Figures xv
List of Tables xxi
1 Introduction 1
1.1 Basic Concepts and Objectives / 2
1.2 Safety / 9
1.3 The Importance of an Integrated Approach / 10
1.4 Importance of Operator Involvement / 13
1.5 The Benefits of Successful Aeration Process Automation / 14
1.5.1 Energy Cost Reduction / 14
1.5.2 Treatment Performance / 18
1.5.3 Improved Equipment Life / 18
Example Problems / 19
2 Initial System Assessment 21
2.1 Define Current Operations / 24
2.1.1 Energy Cost / 25
2.1.2 Energy Consumption Patterns / 29
v
2.1.3 Influent and Effluent Process Parameters / 35
2.1.4 Treatment Performance / 36
2.2 Evaluate Process and Equipment / 37
2.3 Benchmark Performance / 40
2.4 Estimate Potential Energy Savings and Performance Improvement / 42
2.5 Prepare Report / 45
Example Problems / 47
3 Aeration Processes 49
3.1 Process Fundamentals / 49
3.1.1 Peripheral Equipment and Processes / 55
3.1.2 BOD Removal / 62
3.1.3 Nitrification / 66
3.1.4 Denitrification / 67
3.2 Loading Variations and Their Implications / 68
3.3 Process Limitations and Their Impact on Control Systems / 70
Example Problems / 74
4 Mechanical and Diffused Aeration Systems 77
4.1 Oxygen Transfer Basics / 78
4.2 Types of Aerators / 87
4.2.1 Mechanical Aerators / 88
4.2.2 Mechanical Aeration Control Techniques / 90
4.2.3 Diffused Aeration / 95
4.2.4 Diffused Aeration Control Techniques / 103
4.3 Savings Determinations / 106
Example Problems / 111
5 Blowers and Blower Control 113
5.1 Common Application and Selection Concerns / 114
5.1.1 Properties of Air / 114
5.1.2 Effect of Humidity / 119
5.1.3 Pressure Effects / 123
5.1.4 Common Performance Characteristics / 125
5.2 Positive Displacement Blowers and Control Characteristics / 134
5.2.1 Types and Characteristics / 134
5.2.2 Lobe Type PD Blowers / 134
vi CONTENTS
5.2.3 Screw Blowers / 138
5.2.4 Control and Equipment Protection Considerations / 141
5.3 Dynamic Blowers / 143
5.3.1 Types and Characteristics / 144
5.3.2 Multistage Centrifugal Blowers / 150
5.3.3 Geared Single Stage Centrifugal Blowers / 152
5.3.4 Turbo Blowers / 154
5.3.5 Control and Protection Considerations / 155
Example Problems / 157
6 Piping Systems 161
6.1 Design Considerations / 162
6.1.1 Layout / 162
6.1.2 Pipe Size / 172
6.1.3 Pipe Material / 174
6.2 Pressure Drop / 178
6.3 Control Valve Selection / 182
Example Problems / 187
7 Instrumentation 191
7.1 Common Characteristics and Electrical Design Considerations / 192
7.2 Pressure / 202
7.3 Temperature / 205
7.4 Flow / 209
7.5 Analytic Instruments / 216
7.5.1 Dissolved Oxygen / 217
7.5.2 Offgas Analysis / 221
7.5.3 pH and ORP / 224
7.6 Motor Monitoring and Electrical Measurements / 224
7.7 Miscellaneous / 226
Example Problems / 230
8 Final Control Elements 233
8.1 Valve Operators / 234
8.2 Guide Vanes / 238
8.3 Motor Basics / 239
8.4 Motor Control / 247
8.5 Variable Frequency Drives / 251
Example Problems / 259
CONTENTS vii
9 Control Loops and Algorithms 261
9.1 Control Fundamentals / 264
9.1.1 Discrete Controls / 264
9.1.2 Analog Control / 267
9.1.3 Proportional-Integral-Derivative / 271
9.1.4 Deadband Controllers / 274
9.1.5 Floating Control / 276
9.2 Dissolved Oxygen Control / 280
9.3 Aeration Basin Air Flow Control / 287
9.4 Pressure Control / 288
9.5 Most-Open-Valve Control / 291
9.6 Blower Control and Coordination / 293
9.7 Control Loop Timing Considerations / 302
9.8 Miscellaneous Controls / 303
Example Problems / 305
10 Control Components 309
10.1 Programmable Logic Controllers / 310
10.1.1 System Architecture / 314
10.1.2 Program Structure / 315
10.1.3 Communications Networks / 318
10.1.4 Accommodating Instrument Inaccuracy and Failure / 322
10.2 Distributed Control Systems / 323
10.3 Human Machine Interfaces / 323
10.3.1 Supervisory Control and Data Acquisition / 325
10.3.2 Touchscreens / 327
10.4 Control Panel Design Considerations / 328
Example Problems / 330
11 Documentation 333
11.1 Specification Considerations / 335
11.2 Data Lists / 338
11.3 Process and Instrumentation Diagrams / 341
11.4 Ladder and Loop Diagrams / 342
11.5 One-Line Diagrams / 344
11.6 Installation Drawings / 345
11.7 Loop Descriptions / 347
11.8 Operation and Maintenance Manuals / 348
Example Problems / 349
viii CONTENTS
12 Commissioning 351
12.1 Inspection / 354
12.2 Testing / 357
12.3 Tuning / 361
12.4 Training / 365
12.5 Measurement and Verification of Results / 368
Example Problems / 369
13 Summary 371
13.1 Review of Integrated Design Procedure / 371
13.2 Potential Problem Areas / 374
13.3 Benefits / 375
Example Problems / 375
Appendix A: Example Problem Solutions 377
Appendix B: List of Equations and Variables 447
Bibliography 485
Index 487
CONTENTS ix
Preface
This is an engineering manual.
There are a lot of excellent resources available for energy conservation in
wastewater treatment facilities. They contain a great deal of useful information
on developing and implementing energy conservation programs. Most of them
discuss aeration in general and automated aeration control in particular. Many of
them include case histories identifying successful implementations of aeration
control and showing the resulting savings. A few identify unsuccessful attempts
and how to avoid problems.
To the best of my knowledge none of the available resources provide the detailed
engineering procedures required to design, commission, and test an aeration control
system. To the best of my knowledge none of the available resources provide detailed
guidance on applying the multiple engineering disciplines—mechanical, electrical,
and environmental—necessary for successful system design.
The information in this book is the result of over 30 years experience in analyzing
energy consumption in wastewater treatment plants. It includes the lessons learned in
the design of over 200 aeration control systems. This is hard-won knowledge, and
was gained by personal experience in all of the tasks needed to develop concepts, sell
management on the cost-effectiveness, get operator buy-in, and work through the
inevitable start-up issues. The intent is to explain the nuts and bolts details of what to
do—and what not to do—in designing aeration control systems.
There are two concepts that appear repeatedly in this book. First, there are no hard
and fast rules. Steady-state operation is virtually nonexistent in wastewater treat-
ment. This leads to the second concept. Whenever possible the assistance and input
of equipment manufacturers should be obtained in order to obtain the highest level of
precision possible in calculations.
xi
Unfortunately, equipment manufacturers may not be responsive enough to meet
the tight deadlines associated with many energy conservation and control designs.
Worse, in some cases the information obtained may not be pertinent or even accurate.
A thorough knowledge of the many aspects of aeration system operation is necessary
to filter good information from bad and to make independent evaluations when
outside sources fail. My intent is to provide that knowledge.
Another theme that appears throughout this text is “reasonable accuracy.” One
unfortunate side effect of the wide availability of computers, math software, and
advanced modeling programs is the tendency to create elaborate analyses of various
alternatives. The results, calculated to 10 or 20 digits, are reassuring and intellectu-
ally satisfying. There is a tendency to forget that the elaborate calculations are all
based on initial assumptions that are only correct to two or three significant digits!
There is a time for detailed and precise calculations, and sophisticated modeling
can provide insight into relationships between variables that would be difficult to
achieve in any other way. However, when the early stages of the design process
require deciding between multiple alternatives, it is generally adequate to use what
used to be called “slide rule accuracy.” Then, when the problem has been narrowed
and the needed supporting data gathered, more advanced calculation methods can be
used for the final analysis and design confirmation.
This book will show in detail how to predict savings, how to design systems that
meet the mechanical, electrical, and process requirements, and how to commission
the systems to secure successful operation. It is wide ranging in scope, but focused on
providing practical guidance to creating aeration control systems that the operators
will feel comfortable leaving in automatic.
xii PREFACE
Acknowledgments
First and foremost the credit for making this book possible goes to my wife, Ginny. I
know—everybody says that. In this case Ginny has earned the credit a hundred times
over. She gave me support and encouragement, of course. But more than that she
backed me 30 years ago when I had “an idea,” supported me when I began a business
to commercialize that idea, figured out how to feed our family through the long lean
years getting started, and for many years handled the finances for the business purely
as an act of love. “Thanks” is inadequate, but all I have.
I also need to thank our employees. Over the years they contributed their hard
work, ideas, and expertise to improving and implementing aeration control systems.
All of them were important, but a special “thank you” goes to Tim Hilgart. He stuck
it out through the tough times and was in it for the long haul. In my long career I have
met no better engineer or finer man.
Finally, I want to thank my brother Paul and all of the plant operators I have
worked with over the years. These professionals contributed insights, ideas, and
encouragement. Some also contributed harsh and much needed criticism because
they knew and understood reality in a way that no engineer really can. I hope this
book repays their efforts by helping engineers design solutions—not problems!
THOMAS E. JENKINS
Milwaukee, WI
xiii
