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ENERGY AND PROCESSOPTIMIZATION FOR THEPROCESS INDUSTRIES

ENERGY AND PROCESSOPTIMIZATION FOR THEPROCESS INDUSTRIES

FRANK (XIN X.) ZHU

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Zhu, Frank Xin X.

Energy optimization for the process industries / Frank Xin X. Zhu. – First

edition.

pages cm

Includes index.

ISBN 978-1-118-10116-2 (hardback)

1. Process engineering. 2. Manufacturing processes–Cost control. 3.

Manufacturing processes–Environmental aspects. 4. Energy conservation. I.

Title.

TS176.Z53 2013

658.5–dc23

2013020443

Printed in the United States of America

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To Jane, Kathy, and Joshua

These three remain: faith, hope, and love.

The greatest of these is love.

1 Corinthians 13:13

CONTENTS

PREFACE xv

PART 1 BASIC CONCEPTS AND THEORY 1

1 Overview of this Book 3

1.1 Introduction, 3

1.2 Who is this Book Written for?, 4

1.3 Five Ways to Improve Energy Efficiency, 5

1.4 Four Key Elements for Continuous Improvement, 7

1.5 Promoting Improvement Ideas in the Organization, 8

2 Theory of Energy Intensity 9

2.1 Introduction, 9

2.2 Definition of Process Energy Intensity, 10

2.3 The Concept of Fuel Equivalent (FE), 11

2.4 Energy Intensity for a Total Site, 13

2.5 Concluding Remarks, 15

Nomenclature, 15

References, 15

3 Benchmarking Energy Intensity 16

3.1 Introduction, 16

3.2 Data Extraction from Historian, 17

vii

3.3 Convert All Energy Usage to Fuel Equivalent, 17

3.4 Energy Balance, 21

3.5 Fuel Equivalent for Steam and Power, 23

3.6 Energy Performance Index (EPI) Method, 29


Nomenclature, 33

Reference, 34

4 Key Indicators and Targets 35


4.2 Key Indicators Represent Operation Opportunities, 36

4.3 Define Key Indicators, 39

4.4 Set up Targets for Key Indicators, 45

4.5 Economic Evaluation for Key Indicators, 49

4.6 Application 1: Implementing Key Indicators into an “Energy

Dashboard,” 53

4.7 Application 2: Implementing Key Indicators to Controllers, 56

4.8 It is Worth the Effort, 57

Nomenclature, 58

References, 58

PART 2 ENERGY SYSTEM ASSESSMENTMETHODS 59

5 Fired Heater Assessment 61


5.2 Fired Heater Design for High Reliability, 62

5.3 Fired Heater Operation for High Reliability, 68

5.4 Efficient Fired Heater Operation, 73

5.5 Fired Heater Revamp, 80

Nomenclature, 81

References, 81

6 Heat Exchanger Performance Assessment 82


6.2 Basic Concepts and Calculations, 83

6.3 Understand Performance Criterion—U Values, 89

6.4 Understanding Pressure Drop, 94

6.5 Heat Exchanger Rating Assessment, 96

6.6 Improving Heat Exchanger Performance, 106

Appendix: TEMATypes of Heat Exchangers, 109

Nomenclature, 110

References, 111

viii CONTENTS

7 Heat Exchanger Fouling Assessment 112


7.2 Fouling Mechanisms, 113

7.3 Fouling Mitigation, 114

7.4 Fouling Mitigation for Crude Preheat Train, 117

7.5 Fouling Resistance Calculations, 119

7.6 A Cost-Based Model for Clean Cycle Optimization, 121

7.7 Revised Model for Clean Cycle Optimization, 125

7.8 A Practical Method for Clean Cycle Optimization, 128

7.9 Putting All Together—A Practical Example of Fouling Mitigation, 130

Nomenclature, 136

References, 137

8 Energy Loss Assessment 138


8.2 Energy Loss Audit, 139

8.3 Energy Loss Audit Results, 147

8.4 Energy Loss Evaluation, 149

8.5 Brainstorming, 150

8.6 Energy Audit Report, 152

Nomenclature, 153

References, 153

9 Process Heat Recovery Targeting Assessment 154


9.2 Data Extraction, 155

9.3 Composite Curves, 156

9.4 Basic Concepts, 159

9.5 Energy Targeting, 160

9.6 Pinch Golden Rules, 160

9.7 Cost Targeting: Determine Optimal DTmin, 162

9.8 Case Study, 165

9.9 Avoid Suboptimal Solutions, 169

9.10 Integrated Cost Targeting and Process Design, 171

9.11 Challenges for Applying the Systematic

Design Approach, 172

Nomenclature, 174

References, 174

10 Process Heat Recovery Modification Assessment 175


10.2 Network Pinch—The Bottleneck of Existing Heat

Recovery System, 176

CONTENTS ix

10.3 Identification of Modifications, 179

10.4 Automated Network Pinch Retrofit Approach, 181

10.5 Case Studies for Applying the Network Pinch Retrofit Approach, 183

References, 194

11 Process Integration Opportunity Assessment 195


11.2 Definition of Process Integration, 196

11.3 Plus and Minus (þ/�) Principle, 198

11.4 Grand Composite Curves, 199

11.5 Appropriate Placement Principle for Process Changes, 200

11.6 Examples of Process Changes, 205

References, 222

PART 3 PROCESS SYSTEM ASSESSMENT AND OPTIMIZATION 225

12 Distillation Operating Window 227


12.2 What is Distillation?, 228

12.3 Distillation Efficiency, 229

12.4 Definition of Feasible Operating Window, 232

12.5 Understanding Operating Window, 232

12.6 Typical Capacity Limits, 253

12.7 Effects of Design Parameters, 255

12.8 Design Checklist, 257

12.9 Example Calculations for Developing

Operating Window, 257


Nomenclature, 277

References, 279

13 Distillation System Assessment 281


13.2 Define a Base Case, 281

13.3 Calculations for Missing and Incomplete Data, 284

13.4 Building Process Simulation, 287

13.5 Heat and Material Balance Assessment, 288

13.6 Tower Efficiency Assessment, 292

13.7 Operating Profile Assessment, 295

13.8 Tower Rating Assessment, 298

13.9 Column Heat Integration Assessment, 300

13.10 Guidelines for Reuse of an Existing Tower, 302

x CONTENTS

Nomenclature, 303

References, 304

14 Distillation System Optimization 305


14.2 Tower Optimization Basics, 306

14.3 Energy Optimization for Distillation System, 312

14.4 Overall Process Optimization, 318


References, 326

PART 4 UTILITY SYSTEM ASSESSMENT AND OPTIMIZATION 327

15 Modeling of Steam and Power System 329


15.2 Boiler, 330

15.3 Deaerator, 333

15.4 Steam Turbine, 334

15.5 Gas Turbine, 338

15.6 Letdown Valve, 339

15.7 Steam Desuperheater, 341

15.8 Steam Flash Drum, 342

15.9 Steam Trap, 342

15.10 Steam Distribution Losses, 344

Nomenclature, 344

References, 344

16 Establishing Steam Balances 345


16.2 Guidelines for Generating Steam Balance, 346

16.3 AWorking Example for Generating Steam Balance, 347

16.4 A Practical Example for Generating Steam Balance, 357

16.5 Verify Steam Balance, 362


Nomenclature, 365

Reference, 365

17 Determining True Steam Prices 366


17.2 The Cost of Steam Generation from Boiler, 367

17.3 Enthalpy-Based Steam Pricing, 371

17.4 Work-Based Steam Pricing, 372

CONTENTS xi

17.5 Fuel Equivalent-Based Steam Pricing, 373

17.6 Cost-Based Steam Pricing, 376

17.7 Comparison of Different Steam Pricing Methods, 377

17.8 Marginal Steam Pricing, 379

17.9 Effects of Condensate Recovery on Steam Cost, 384


Nomenclature, 385

References, 385

18 Benchmarking Steam System Performance 386


18.2 Benchmark Steam Cost: Minimize Generation Cost, 387

18.3 Benchmark Steam and Condensate Losses, 389

18.4 Benchmark Process Steam Usage and Energy Cost Allocation, 394

18.5 Benchmarking Steam System Operation, 396

18.6 Benchmarking Steam System Efficiency, 397

Nomenclature, 402

References, 402

19 Steam and Power Optimization 403


19.2 Optimizing Steam Header Pressure, 404

19.3 Optimizing Steam Equipment Loadings, 405

19.4 Optimizing On-Site Power Generation Versus Power Import, 407

19.5 Minimizing Steam Letdowns and Venting, 412

19.6 Optimizing Steam System Configuration, 413

19.7 Developing Steam System Optimization Model, 417

Nomenclature, 422

Reference, 422

PART 5 RETROFIT PROJECT EVALUATION AND

IMPLEMENTATION 423

20 Determine the True Benefit from the OSBL Context 425


20.2 Energy Improvement Options Under Evaluation, 426

20.3 A Method for Evaluating Energy Improvement Options, 429

20.4 Feasibility Assessment and Make Decisions for Implementation, 442

21 Determine the True Benefit from Process Variations 447


21.2 Collect Online Data for the Whole Operation Cycle, 448

xii CONTENTS

21.3 Normal Distribution and Monte Carlo Simulation, 449

21.4 Basic Statistics Summary for Normal Distribution, 456

Nomenclature, 458

Reference, 458

22 Revamp Feasibility Assessment 459


22.2 Scope and Stages of Feasibility Assessment, 460

22.3 Feasibility Assessment Methodology, 462

22.4 Get the Project Basis and Data Right in the Very Beginning, 465

22.5 Get Project Economics Right, 466

22.6 Do Not Forget OSBL Costs, 470

22.7 Squeeze Capacity Out of Design Margin, 471

22.8 Identify and Relax Plant Constraints, 472

22.9 Interactions Between Process Conditions, Yields, and Equipment, 473

22.10 Do Not Get Misled by False Balances, 474

22.11 Prepare for Fuel Gas Long, 475

22.12 Two Retrofit Cases for Shifting Bottlenecks, 477


Nomenclature, 480

References, 480

23 Create an Optimization Culture with Measurable Results 481


23.2 Site-Wide Energy Optimization Strategy, 482

23.3 Case Study of the Site-Wide Energy Optimization Strategy, 487

23.4 Establishing Energy Management System, 492

23.5 Energy Operation Management, 496

23.6 Energy Project Management, 499

23.7 An Overall Work Process from Idea Discovery to Implementation, 500

References, 502

INDEX 503

CONTENTS xiii

PREFACE

In recent years, there has been an increased emphasis on industrial energy optimi-

zation. However, there are no dedicated books available to discuss basic concepts,

provide practical methods, and explain industrial application procedures. This book

is written to fill this gap with the following people in mind: managers, engineers,

and operators working in the process industries. The book is aimed at providing

practical tools to people who face challenges and wish to find opportunities for

improved processing energy efficiency. I hope that this book is able to convey

concepts, theories, and methods in a straightforward and practical manner.

With these objectives in mind, the focal discussions in this book center around five

kinds of energy improvement opportunities. The first is minimizing heat losses via

diligence. In reality, steam generated in the boiler house is distributed through an

extensive network of steam pipelines to end users. The losses in steam distribution

can be 10–20% of fuel fired in boilers. Hence, the net boiler efficiency could be 10–

20% lower from the user’s point of view.

The second is operation improvement opportunities, which occur due to the age of

processes, the nature of operation variations. This usually involves establishing the

best operation practices and optimizing process conditions. The third opportunity

comes from improved heat recovery within and across process units, which requires

design changes to process flow schemes and heat exchange schemes. The fourth is

the use of state-of-the-art processes and equipment technology for enhanced

processing efficiency. The fifth and final opportunity comes from better operation

and planning of the energy supply system. In this book, these opportunities will be

discussed and the methods for opportunity identification, assessment, and imple-

mentation will be introduced.

xv

As the book covers a wide range of topics, I have attempted to organize the

materials in such a way that aids the reader to locate the relevant materials quickly,

to be able to understand them readily, and to apply them in the right context.

Furthermore, the structure of the book is carefully designed to help readers avoid

losing sight of the forest for the trees. The book starts with a provision of an overall

context of the process energy optimization, followed by concepts and theory to gain a

basic understanding of the energy metrics, gradually transitions to practical assess-

ment methods from equipment- to system-based evaluations, and culminates in

establishing an effective energy management system to sustain the benefits. There-

fore, the features of material organizations need to be explained:

� An overview of process energy optimization is provided in Chapter 1. Basic

concepts for process energy efficiency are introduced in Chapters 2–4 in Part 1.

These concepts include energy intensity for determining process-specific

energy use, energy benchmarking for setting the energy baseline and identify-

ing the improvement gap, and key energy indicators for determining what

operating parameters to monitor and what are their operating targets.

� Energy assessment methods are presented in Part 2. Chapter 5 focuses on

reliable and efficient operation for process-fired heaters, while Chapter 6

discusses process energy loss analysis. Chapters 7 and 8 are dedicated to

heat exchanger performance assessment as well as fouling mitigation. Methods

for heat recovery targeting and retrofit design are explained in Chapters 9

and 10, while process integration methods are illustrated in Chapter 11.

� Part 3 is dedicated to process assessment. The concept of operating window for

fractionation is introduced in Chapter 12 where the calculation methods for

determining the operating window are explained. Fractionation system assess-

ment and optimization are discussed in Chapters 13 and 14.

� The steam and power system must supply energy in an efficient manner if one

wishes to achieve high energy efficiency for an overall processing site. Thus,

methods for steam and power system assessment and optimization are provided

in Part 4. Steam and power system modeling is explained in Chapter 15.

Chapter 16 covers steam and power balances. Chapter 17 discusses practical

steam pricing methods. Chapter 18 focuses on steam system benchmarking. By

putting the models and opportunities together, Chapter 19 discusses how to

build mathematical models for steam and power optimization.

� Finally, Part 5 is dedicated to techno-economical analysis of energy modifica-

tions as well as establishing an effective energy management system. To avoid

bad investment, true benefits must be determined by considering outside system

battery limit conditions and process variations, which are discussed in Chapters

20 and 21. The goal of the capital project evaluation is to achieve minimum

investment cost. The key to achieving this goal is to explore alternative design

options for each improvement idea and find economical solutions to overcome

process/equipment limits. Detailed discussions are given in Chapter 22.

The last chapter, Chapter 23, condenses the ideas presented in the other

xvi PREFACE

chapters by explaining how to establish an effective energy management

system to sustain the benefits gained from implementation through a case study.

It is my sincere hope that readers will find the methods and techniques discussed

herein useful for analysis, optimization, engineering design, and monitoring,

which are required to identify, assess, implement, and sustain energy improvement

opportunities. More importantly, I hope that this book can help readers build

mental models in terms of key parameters and their limits and interactions. You

can then revisit these methods whenever you need them.

Clearly, it was not a small effort to write this book; but it was the strong need of

practical methods for helping people to improving industrial energy efficiency that

spurred me to writing. In this endeavor, I owe an enormous debt of gratitude to

many colleagues at UOP and Honeywell for their generous support to this effort.

First of all, I would like to mention Geoff Miller, vice president of UOP, who has

provided encouragement and support. I am very grateful to many colleagues for

constructive suggestions and comments on the materials contained in this book,

and I apologize if any names are unmentioned. I would especially like to thank

John Petri for his critical readings of Chapter 4, Darren Le Geyt and Dennis Clary

for Chapter 5, Phil Daly and Lillian Huppler for Chapter 6, Zhanping (Ping) Xu for

Chapter 12, and Chuck Welch for Chapter 15; their comments have improved these

chapters. Tom King provided meticulous line-by-line reading of the entire first

draft and identified pedagogical lapses, typos, better expressions, and better

sources of information. My sincere gratitude also goes to Charles Griswold,

Margaret (Peg) Stine, and Mark James for their review of the book. I would

like to thank all of my colleagues for their help with the book and my debt to them

is very great, but I would like to stress that any deficiencies are my responsibility.

This book reflects my own opinions and not that of UOP and Honeywell.

I would also like to thank my co-publishers, AIChE and John Wiley, for their

help. Special thanks go to Steve Smith at AIChE and Michael Leventhal at

John Wiley for guidance. The copyediting and typesetting by Vibhu Dubey at

Thomson Digital is very helpful in polishing the book.

Finally, I am truly grateful to my family: my wife Jane and my children Kathy and

Joshua, for their understanding, unwavering support, and generosity of spirit in

tolerating the absentee paterfamilias during the writing of this book. Jane, my

beloved wife, produced beautiful drawings for many figures in the book with her

graphic design skills and Kathy helped to polish this book with her linguistic skills.

Your contributions to this book and to my life are deeply appreciated.

FRANK ZHU

Long Grove, Illinois, USA

May 7, 2013

PREFACE xvii

PART 1

BASIC CONCEPTS AND THEORY

1OVERVIEW OF THIS BOOK

1.1 INTRODUCTION

Energy management is a buzzword nowadays. What is the objective of energy

management in the process industry? It is not simply energy minimization. The

ultimate goal of energy management is to control energy usage in the most efficient

manner to make production more economical and efficient. To achieve this goal,

energy use must be optimized with the same rigor as how product yields and process

safety are managed.

The time of “let the plant engineers do their technical work” is long gone. The

reduction of the technical workforce due to automation and technology advances has

also increased the level of responsibility on business management of plant opera-

tions, often resulting in fewer workers taking on more tasks. Furthermore, it is often

the case that plant managers and engineers are ill-prepared to take on widespread

responsibilities, particularly when working under time pressures. This in turn results

in their devoting less time on plant operation and equipment reliability and

maintenance. Therefore, the current challenge for energy optimization is: How

can we develop effective enablers to support engineers and management?

In addition, plant management and engineers are presented with modern man-

agement concepts and techniques. Not all these methods are easily translatable or

applicable to any given company. Even if implemented, some of these methods

require tailor-made revisions to fit into specific applications. The challenge here

becomes:Which methods should be selected and how to implement them for specific

circumstances?

3

Energy and Process Optimization for the Process Industries, First Edition. Frank (Xin X.) Zhu.� 2014 by the American Institute of Chemical Engineers, Inc. Published 2014 by JohnWiley & Sons, Inc.

This reminds me of a project I led a few years into the new millennium. My

company took on a project to provide technical support to a large oil refining

plant and I was tasked with leading a team of engineers to spearhead this effort.

When I met with the general manager of the refinery plant, his words were brief.

“My plant spends huge amounts of money on operating costs, in the order of

hundreds of million dollars per year.” The general manager started after a quick

introduction. “I know someone out there can help my plant to cut down the

energy cost by more than 10%. I hope it is you.” These simple words from the

general manager became a strong motivation like a heavy weight on my shoulder.

I took the challenge and worked with the team and the plant staff to achieve the

goal. By the end of the fifth year, a survey team from corporate management

came on site. After reviewing the data and various utility costs, the team issued

the statement that the plant had achieved the corporate goal of saving 10% energy

costs. Our efforts were successful and the results were recognized by the plant

and corporate management.

Over time, I applied the methods and tools I had developed over the course of my

career to other projects I was staffed on in the past 10 years. The theory and practice

of these methods and experience has become the foundation of this book. The book

will present the core of a systematic approach covering energy optimization strategy,

solution methodology, supporting structure, and assessment methods. In short, it will

describe what it takes to make sizable reductions in energy operating costs for

process plants and how to sustain energy-saving benefits. The benefits of this

effective approach include identification of large energy-saving projects via applying

assessment methods, capturing hidden opportunities in process operation via use of

key energy indicators, closing of various loose ends in steam system and off-site

utilities via good steam balances, optimizing utility system operation via setting up

appropriate steam prices, and maintaining continuous improvement via regular

review and performance matrices.

The concepts, methods, and tools presented in this book provide a glimpse of

recent advances in energy utilization techniques based on simultaneous optimization

of process and energy considerations. The case studies show that very substantial

improvements in energy utilization can be made by applying these methods and tools

not only in new investment projects but also in existing plants.

1.2 WHO IS THIS BOOKWRITTEN FOR?

This book is written with the following people in mind: managers, engineers, and

operators working in the process industries who face challenges and wish to find

opportunities for improved processing energy efficiency and are searching for tools

for better energy management.

It is my hope that readers are able to take away methods and techniques for

analysis, optimization, engineering design, and monitoring, which are required to

identify, assess, implement, and sustain energy improvement opportunities. The

4 OVERVIEW OF THIS BOOK

analysis methods are used for energy benchmarking and gap assessment, while

optimization methods are used for operation improvement, heat integration, process

changes, and utility system optimization. Engineering methods are applied for

developing energy revamp projects, while monitoringmethods are used for establish-

ing energy management systems. More importantly, I would like to help readers to

build mental models for critical equipment and processes in terms of key parameters

and their limits and interactions. You can then revisit these models whenever you

need them.

1.3 FIVE WAYS TO IMPROVE ENERGY EFFICIENCY

The five ways in which improved energy efficiency can be achieved within plant

processes are highlighted below and will be discussed in detail in this book:

� Minimizing wastes and losses

� Optimizing process operation

� Achieving better heat recovery

� Determining process changes

� Optimizing energy supply system

1.3.1 Minimize Waste and Losses

In reality, steam generated in the boiler house is distributed through an extensive

network of steam pipelines to end users. The losses in steam distribution can be

10–20% of fuel fired in boilers. Hence, the net boiler efficiency could be 10–20%

lower from the user’s point of view.

The losses do not necessarily attribute to a single cause but are the result of a

combination of various causes. It is common to observe the major steam loss caused

by steam trap failure and condensate discharge problems. Steam loss could also

occur due to poor insulation of steam pipes, leaks through flanges and valve seals,

opened bypass and/or bleeder valves, and so on. Simple measures such as mainte-

nance of steam traps and monitoring of steam distribution to determine if steam

generated is in accordance with steam consumed can lead to significant cost-saving

benefits.

Apart from distribution losses, other forms of energy losses could occur due to

poor insulation, condensate loss to drainage, pressure loss from steam letdown

through valves, pump spill backs, and so on. To detect losses, you must know how

much energy is generated versus how much is used in individual processes. The

benchmarking method in Chapter 3 could be used to determine the overall gap of the

energy performance, and individual losses are identified using different methods.

Process energy losses can be detected using the energy loss assessment methods

discussed in Chapter 8, while identification of steam losses and theways to overcome

the losses in the steam system are discussed in Chapter 18.

FIVEWAYS TO IMPROVE ENERGY EFFICIENCY 5

1.3.2 Optimizing Process Operation

The most important step in developing an energy management solution to optimize a

process is to be able to measure what process performance looks like against a

reasonable set of benchmarks. This involves capturing energy data related to the

process and organizing it in a way that allows operations to quickly identify where the

big energy consumers are and how well they are doing against a consumption target

that reflects the current operations. Only then is it possible to do some analysis to

determine the cause of deviations from target and take appropriate remedial action. For

this purpose, the concept of key energy indicators is introduced in Chapter 4.

The operation performance gaps are mainly caused by operation variability. Two

kinds of operation variability are common in the industry. The first is the so-called

operation inconsistency, which is mainly caused by different operation policy and

practices applied due to different experience from operators. The second operation

inefficiency refers to thekindofoperation that is consistent but nonoptimal.This occurs

when there are no tools available to indicate to the shift operators the optimalmethod to

run the process and equipment when conditions of feeds and product yields vary.

Once operational gaps are identified, assessment methods (Chapters 5–8 for

energy operation, Chapters 12 and 13 for process operation, and Chapter 16 for

utility system operation) are then applied to identify root causes—potential causes

include inefficient process operation, insufficient maintenance, inadequate operating

practices, procedures, and control, inefficient energy system design, and outdated

technology. Assessment results are translated into specific corrective actions to

achieve targets via either manual adjustments, the best practices, or by automatic

control systems. Finally, the results are tracked to measure the improvements and

benefits achieved.

1.3.3 Achieving Better Heat Recovery

Using monitoring and optimization tools to improve energy efficiency usually results

in pushing the process up against multiple physical constraints. To reach the next level

of energy efficiency requires capital costmodifications to increase heat recoverywithin

and across process units. One of the key values of implementing operational solutions

first is that it can clearly highlight where the physical constraints exist to the process.

Once specific process units have been identified for improved heat integration,

pinch technology can be applied to efficiently screen potential modification options,

which is explained in Chapter 9. Practical assessment (Chapter 10) is required, which

considers not only the value and cost of improved heat recovery but also the impact in

terms of operating flexibility, especially with respect to start-up, shutdown, mainte-

nance, control, and safety.

1.3.4 Determining Process Changes

Improved heat recovery is the most common type of capital projects implemented to

improve energy efficiency. However, the use of advanced process/equipment


technology may provide significant opportunities. Many of these areas make use of

advanced process technology, such as enhanced heat exchangers, high-capacity

fractionator internals, dividing wall columns, new reactor internals, power recovery

turbines, improved catalysts, and other design features.

There are a variety of advanced technologies that can be applied, all of which vary

in terms of implementation cost and return on investment. Careful evaluation of each

of these solutions is required to select only the best opportunities that provide the

highest return on the capital employed. Chapter 11 provides directions and principles

for making process changes.

1.3.5 Optimizing Energy Supply System

In addition to using energy more efficiently in the process, another common strategy

is to produce energy more efficiently. Many plants have their own on-site power

plants that primarily exist to provide steam and power to the process units, but may

also supply electricity to the grid when electricity price is high.

Energy supply optimization is achieved by optimizing the configuration and

operating profiles of the boilers and turbines to meet energy demand while taking

into account tiered pricing for power and natural gas, power contracts to the grid

while meeting environmental limits on NOx and CO2 emissions. Energy supply

optimization is discussed in Chapter 19.

1.4 FOUR KEY ELEMENTS FOR CONTINUOUS IMPROVEMENT

An effective energy optimization consists of four key elements: target setting,

measuring, gap identification, and implementation. Achieving continuous energy

improvement occurs only when all these four elements are working in good order as

shown in Figure 1.1.

Define key energy indicators and set

up realistic targets

Measure actual energy performance

Identify gaps and root

causes

Determine actions for closing the gaps

FIGURE 1.1. Four elements of energy management system.

FOUR KEY ELEMENTS FOR CONTINUOUS IMPROVEMENT 7

The energy targeting implies setting up a base line energy performance against which

actual energy performance can be compared. The base line energy performance should

take into account the production rate and processing severity. The ratio of actual

performance and base line performance is the energy performance indicator for a process

area andanoverall plant.The base line energyperformancebecomes the energyguideline

or target for operation. For the energy target to be practical, itmust be achievable based on

equipment integrity, technology capability, availability of required tools, and skills.

1.5 PROMOTING IMPROVEMENT IDEAS IN THE ORGANIZATION

As a technicalmanager or process engineer or operator, youmayhave already acquired

some good ideas for improving your plant and process unit. However, it is not an easy

feat to persuade the technical committee to consider your ideas and then proceed to

accept and eventually implement them. I have observedmanygood ideas that have died

in the infancy stage because they could not pass the evaluation gates. Such failure is

commonly due to a lack of techno-economic assessment and communications.

Remember, it is always necessary to sell your ideas to key stakeholders.

First, you need to develop technical and economic merits to build a business case.

Therefore, it is imperative that you determine the benefit of your ideas, that is, what is

the value to the stakeholders, in the very early stages. Next, you should identify, with

the help of process specialists, what it takes to implement the idea. You need to do the

necessary homework to come up with rough estimates of the capital cost required to

deliver the benefit for your ideas.

If the benefit outweighs the cost significantly, it is then necessary to elicit

comments and feedback from technical specialists in the areas of operation,

engineering, maintenance, and control. Their feedback will provide additional

insights for the feasibility of implementing your ideas. Several review meetings

may be required during idea development and assessment. Try to limit the scope of

these meetings with highly selective attendees because a focused meeting could

allow in-depth discussions leading to idea expansion and improvements. In the end,

a thorough safety review is essential.

Once you pass reviews based on technical merits, you need to sell your ideas to get

buy-in from management. Although management expresses a strong voice for

supporting energy efficiency improvement, management will not provide a blank

check. You should remember the fact that the business objective of your plant is to

produce desirable products and realize targeted economic margins. To successfully

convince management, you need to connect your ideas with key business drivers.

In the chapters that follow, all the essential tools will be provided in a clear, step-

by-step manner together with application examples. My hope is that by applying the

methods in your work—one step at a time, whether you are a manager, an engineer,

or an operator—it will enable you to discover improvement ideas, to asses them, and

then finally to prioritize them in a good order. Once all these boxes are checked, you

will have a good chance to communicate and implement your ideas successfully

within your organization.


2THEORY OF ENERGY INTENSITY

Management’s vision and intent is not good enough to achieve energy improve-

ments. Technical concepts and targets must be used as the basis for measuring and

improving process energy efficiency. Energy intensity is one of the key technical

concepts as it lays down the foundation for process energy benchmarking.

2.1 INTRODUCTION

In some industrial plants, energy optimization work falls into no-man’s land. If you

ask process engineers, supervisors, and operators, they will tell you that they have

done everything they can in making their process units energy efficient. It is

understandable that technical people feel proud of themselves in trying to do their

job right. If you ask plant managers, they may tell you everything is in good order.

The truth of the matter is that there is large room for energy efficiency improve-

ment. To find out the truth, you may ask a few questions: What metrics are applied to

measure the process energy efficiency? What energy indicators are defined for the

key equipment? How do you set up targets for these indicators?

The answers to these three questions will show if the plant management only stays

in good intention but without proper measures in place. If no energy metrics are used

to measure performance level and no indicators are applied for major equipment and

no targets are employed for identifying improvements, the energy management

program is only on the basis of good intent. It is possible to get people motivated with

9

Energy and Process Optimization for the Process Industries, First Edition. Frank (Xin X.) Zhu.� 2014 by the American Institute of Chemical Engineers, Inc. Published 2014 by JohnWiley & Sons, Inc.

good intention. However, the motivation will decline gradually if people do not know

what to do and have no directions.

To overcome this shortfall, two key concepts are introduced, namely, energy

intensity and key energy indicators. The concept of energy intensity sets the basis

formeasuring energy performance,while the concept of key energy indicators provides

guidance for what to do and how. Both energy intensity and key indicators are the

cornerstones of an effective and sustainable energy management system. Energy

intensity is introduced in this chapter, while example calculations for energy intensity

are given in Chapter 3. The concept of key indicators will be discussed in Chapter 4.

2.2 DEFINITION OF PROCESS ENERGY INTENSITY

Meaning must transfer to correct concepts and then concepts must be expressed in

mathematical forms for the meaning to be precise and measurable for industrial

applications. Adjectives like excellent, good, and bad, have no quantifiable values for

technicalapplicationsbecause theycannotbemeasured.Thus,weneedacleardefinition

of mere linguistic terms frommanagement intent to make sustainable energy perform-

ance improvement. In other words, we need to have an operational definition of process

energy performance that everyone can agree on and relate to and act upon.

Let us start with the specific question: how to define energy performance for a

process? People might think of energy efficiency first. Although energy efficiency is

a good measure as everyone knows what it is about, it does not relate energy use to

process feed rate and yields, and thus it is hard to connect the concept of energy

efficiency to plant managers and engineers.

To overcome this shortcoming, the concept of energy intensity is adopted, which

connects process energy use and production activity. The energy intensity originated

from Schipper et al. (1992a, 1992b), who attempted to address the intensity of energy

use by coupling energy use and economic activity through the energy use history in

five nations: the United States, Norway, Denmark, Germany, and Japan. The concept

of energy intensity allows them to better examine the trends that prevailed during

both increasing and decreasing energy prices.

By definition, energy intensity (I) is described by

I ¼ Energy use

Activity¼ E

A: (2.1)

Total energy use (E) becomes the numerator, while common measure of activity (A)

is the denominator. For example, commonly used measures of activity are vehicle

miles for passenger cars in transportation, kWh of electricity produced in the power

industry, and unit of production for the process industry, respectively.

Physical unit of production can be t/h or m3/h of total feed (or product). Thus,

industrial energy intensity can be defined as

I ¼ Quantity of energy

Quantity of feed or product: (2.2)

10 THEORY OF ENERGY INTENSITY

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