An exergy based method for resource accounting in factories

196 Pages·2016·4.33 MB·English

An exergy based method
for resource accounting in
factories
Sanober Hassan Khattak

Submitted in partial fulfilment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Institute of energy and sustainable development,
De Montfort University, Leicester

January 2016
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Abstract
In the current global climate of declining fossil fuel reserves and due to the impact of industry on the
natural environment, industrial sustainability is becoming ever more important. However,
sustainability is quite a vague concept for many, and there are a range of interpretations of the
word. If the resource efficiency of a factory is taken as a measure of its sustainability, then the
concept becomes better defined and quantifiable. In order to analyse the resource efficiency of a
factory and suggest improvements, all flows through the manufacturing system need to be
modelled. However the factory is a complex environment, there is a wide variation in the quality
levels of energy as well as the composition of material flows in the system. The research presented
in this thesis shows how the thermodynamics-based concept of ‘exergy’ can be used to quantify the
resource efficiency of a factory. The factory is considered an ‘integrated system’, meaning it is
composed of the building and the production processes, both interacting with each other. This is
supported by three case studies in different industries that demonstrate the practical application
of the approach.
A review of literature identified that it was appropriate to develop a novel approach that combined
exergy analysis with the integrated view of the factory. Such an approach would allow a ‘holistic’
assessment of resource efficiency for different technology options possibly employable. The
development of the approach and its illustration through practical case studies is the main
contribution of the work presented.
Three case studies, when viewed together, illustrate all aspects of the novel exergy based resource
accounting approach. The first case study is that of an engine production line, in which the resource
efficiency of this part of the factory is analysed for different energy system options relating to
heating ventilation and air conditioning. Firstly, the baseline is compared with the use of a solar
photovoltaic array to generate electricity, and then a heat recovery unit is considered. Finally, both
of these options were used together, and here it is found that the non-renewable exergy supply and
exergy destruction are reduced by 51.6% and 49.2% respectively.
The second case study is that of a jaggery (a sugar substitute) production line. The exergy efficiency
of the process is calculated based on varying the operating temperature of the jaggery furnace. The
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case study describes the modelling of al flows through the jaggery process in terms of exergy. Since
this is the first example of an exergy analysis of a jaggery process, it can be considered a minor
contribution of the work. An imaginary secondary process that could utilize the waste heat from the
jaggery process is considered in order to illustrate the application of the approach to industrial
symbiosis. The non-renewable exergy supply and exergy destruction are determined for the baseline
and the alternative option. The goal of this case study is not to present a thermally optimized design;
rather it illustrates how the exergy concept can be used to assess the impact of changes to individual
process operations on the overall efficiency in industrial symbiosis.
When considering natural resource consumption in manufacturing, accounting for clean water
consumption is increasingly important. Therefore, a holistic methodology for resource accounting in
factories must be able to account for water efficiency as well. The third case study is that of a food
production facility where the water supply and effluent are modelled in terms of exergy. A review of
relevant literature shows that previously, the exergy content of only natural water bodies and urban
wastewater had been quantified. To the author’s knowledge, this is the first example of applying this
methodology of modelling water flows in a manufacturing context. The results show that due to a
high amount of organic content in food process effluent, there is significant recoverable exergy in it.
Therefore, a hypothetical water treatment process was assumed to estimate the possible savings in
exergy consumption. The results show that at least a net 4.1% savings in terms of exergy could be
possible if anaerobic digestion water treatment was employed. This result can be significant for the
UK since the food sector forms a significant portion of the industry in the country.
Towards the end of the thesis, a qualitative study is also presented that aims to evaluate the
practical utility of the approach for the industry. A mixed method approach was used to acquire data
from experts in the field and analyse their responses. The exergy based resource accounting method
developed in this thesis was first presented to them before acquiring the responses. A unanimous
view emerged that the developed exergy based factory resource accounting methodology has good
potential to benefit industrial sustainability. However, they also agreed that exergy was too complex
a concept to be currently widely applied in practice. To this effect, measures that could help
overcome this barrier to its practical application were presented which form part of future work.
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Dedication
To my late big brother, Rambail Ibrar Khattak, the person I loved and admired the most. His love for
life, beauty in persona and strength in character will always be remembered. May you rest in the
best of places.
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Acknowledgements
Undertaking this PhD has truly been a life changing experience for me and it would not have been
possible to do without the support of many people.
First and foremost, I would like to thank my supervisor Dr. Rick Greenough who made is possible for
me to succeed in this journey. I am sincerely grateful to him for all his support and guidance through
this long and tough period of my life. I greatly appreciate the financial support I received through
the KAP and REEMAIN projects, which also provided invaluable experience. I am also thankful to Neil
Brown, my second supervisor who has helped me when I needed it. Many thanks also to friends and
colleagues at IESD, especially Dr. Ivan Korolija. I must also thank here Dr. Alicia Valero Delgado of the
CIRCE institute at the University of Zaragoza, Spain. My chapter on modelling water flows through
the factory would not have been possible without her support. This section would not be complete
without me expressing my gratitude for my close family; my parents who supported me throughout
and my wife and kids for making the journey a pleasure.
Finally, thanks to almighty Allah, the source of all knowledge, provider of all sustenance and the best
of writers. I hope to be guided by Allah in the future, to progress my career and influence the earth
in a positive way through my profession.
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Table of contents

Chapter 1 Introduction ........................................................................................................................ 1
1.1. Chapter overview .................................................................................................................... 1
1.2. Background ............................................................................................................................. 1
1.3. Resource consumption in the manufacturing sector ............................................................. 3
1.4. Research focus ........................................................................................................................ 4
1.5. Central aim .............................................................................................................................. 4
1.6. Specific objectives ................................................................................................................... 5
1.7. Summary of major contributions ............................................................................................ 6
1.8. List of related peer reviewed publications ............................................................................. 6
1.9. Thesis structure ....................................................................................................................... 7
Chapter 2 Literature review ................................................................................................................. 8
2.1. Chapter overview .................................................................................................................... 8
2.2. Approach to literature review................................................................................................. 8
2.3. Conventional methods for measuring industrial sustainability ............................................ 10
2.4. Analysis methods based on the 2nd law of thermodynamics .............................................. 12
2.4.1. Entransy: ....................................................................................................................... 14
2.4.2. Entropy: ......................................................................................................................... 15
2.5. Exergy: ................................................................................................................................... 15
2.5.1. Limitations of the exergy concept: ............................................................................... 19
2.5.2. Strengths of the exergy concept: .................................................................................. 22
2.6. Application of exergy to environmental science .................................................................. 23
2.6.1. Ecosystems modelling ................................................................................................... 24
2.6.2. Sustainability assessment of societies .......................................................................... 25
2.6.3. Buildings exergy management ...................................................................................... 27
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2.7. Other areas of application: ................................................................................................... 30
2.8. Application of exergy to manufacturing ............................................................................... 31
2.9. Integrated approach to factory analysis ............................................................................... 35
2.10. Refined research question ................................................................................................ 38
Chapter 3 Methodology ..................................................................................................................... 40
3.1. Chapter overview .................................................................................................................. 40
3.2. The general research process: .............................................................................................. 40
3.2.1. Types of research: ......................................................................................................... 40
3.2.2. Research method and methodology: ........................................................................... 41
3.3. Overall research design: ........................................................................................................ 41
3.3.3. Formulation and clarification of research topic: ........................................................... 42
3.3.4. Literature review: .......................................................................................................... 43
3.3.5. Formulation of research approach and design: ............................................................ 43
3.3.6. Data collection: ............................................................................................................. 46
3.3.7. Data analysis: ................................................................................................................ 47
3.3.8. Writing phase: ............................................................................................................... 47
3.3.9. Limitations of the research design: ............................................................................... 47
3.4. Chapter summary: ................................................................................................................ 48
Chapter 4 A novel approach to resource accounting in factories ..................................................... 50
4.1. Chapter overview: ................................................................................................................. 50
4.2. The conceptual approach: .................................................................................................... 50
Chapter 5 Case study 1 – An engine cylinder head production line .................................................. 56
5.1. Introduction: ......................................................................................................................... 56
5.2. Case study description: ......................................................................................................... 56
5.3. Baseline scenario .................................................................................................................. 61
5.4. Option 1 – With renewable exergy supplied from the PV array ........................................... 61
5.5. Option 2 – With heat recovery ............................................................................................. 62
5.6. Option 3 – With heat recovery and solar power .................................................................. 62
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5.7. Results: .................................................................................................................................. 64
5.8. Discussion: ............................................................................................................................ 67
Chapter 6 Case study 2 – A jaggery production process ................................................................... 70
6.1. Introduction: ......................................................................................................................... 70
6.2. Industrial symbiosis, industrial ecology and exergy ............................................................. 71
6.3. Case study methodology ....................................................................................................... 72
6.4. Jaggery production case study .............................................................................................. 73
6.5. System analysis ..................................................................................................................... 74
6.6. Energy analysis ...................................................................................................................... 75
6.7. Exergy balance ...................................................................................................................... 76
6.7.1. Specific exergy of sugar cane juice ............................................................................... 77
6.7.2. Specific exergy of bagasse............................................................................................. 78
6.7.3. Specific exergy of the jaggery produced ....................................................................... 78
6.7.4. Specific exergy of the water vapour ............................................................................. 79
6.7.5. Exergy of the flue gas .................................................................................................... 79
6.7.6. Specific exergy of bagasse ash ...................................................................................... 79
6.7.7. Exergy lost due to wall losses........................................................................................ 80
6.8. Results and discussion .......................................................................................................... 82
6.8.1. Major causes of exergy destruction .............................................................................. 82
6.9. Implications for industrial symbiosis .................................................................................... 83
6.10. Symbiosis with increased furnace temperature ............................................................... 86
6.11. Summary and concluding comments: ............................................................................... 88
Chapter 7 Case study 3 - Exergy modelling of water flows in manufacturing ................................... 89
7.1. Introduction: ......................................................................................................................... 89
7.2. Background to the factory and its resource use: .................................................................. 89
7.3. Methodology: ........................................................................................................................ 90
7.4. Application of exergy analysis for wastewater treatment: ................................................... 91
7.5. Selection of the reference environment (RE): ...................................................................... 92
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7.5.1. Water with high concentrations of impurities: ............................................................. 93
7.5.2. Spring water: ................................................................................................................. 93
7.5.3. Pure water: .................................................................................................................... 93
7.5.4. Seawater with organic matter: ..................................................................................... 93
7.5.5. Seawater without organic matter: ................................................................................ 93
7.5.6. RE water selection:........................................................................................................ 94
7.6. Calculating exergy of water (method): ................................................................................. 95
7.6.1. Thermo-mechanical exergy: ......................................................................................... 95
7.6.2. Kinetic and potential exergy: ........................................................................................ 96
7.6.3. Chemical exergy: ........................................................................................................... 96
7.6.4. Chemical formation exergy (organic portion): .............................................................. 96
7.6.5. Chemical concentration exergy (inorganic part): ......................................................... 98
7.6.6. The total exergy: ........................................................................................................... 98
7.7. Exergy of water flow (results): .............................................................................................. 99
7.7.1. Exergy of supply water: ................................................................................................. 99
7.7.2. Exergy of effluent water: .............................................................................................. 99
7.8. Water treatment: ................................................................................................................ 101
7.9. Results: ................................................................................................................................ 104
7.10. Findings and discussion: .................................................................................................. 104
7.11. Chapter summary: .......................................................................................................... 106
Chapter 8 Qualitative assessment of the developed method ......................................................... 107
8.1. Chapter overview ................................................................................................................ 107
8.2. Method for Data collection: ................................................................................................ 107
8.3. Data Organization: .............................................................................................................. 109
8.4. Analysis: .............................................................................................................................. 111
8.4.1. Understanding and importance of sustainable manufacturing: ................................. 111
8.4.2. Utility of the novel factory analysis approach ............................................................ 113
8.4.3. Barriers to practical implementation: ......................................................................... 116
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8.4.4. Drivers for practical implementation and suggestions: .............................................. 119
8.5. Summary: ............................................................................................................................ 121
Chapter 9 Conclusions and future work .......................................................................................... 123
9.1. Introduction: ....................................................................................................................... 123
9.2. Short summary and conclusions: ........................................................................................ 123
9.2.1. Strengths: .................................................................................................................... 123
9.2.2. Weaknesses: ............................................................................................................... 124
9.2.3. Contribution to knowledge: ........................................................................................ 125
9.3. Recommendations for future work: ................................................................................... 126
9.3.1. A software tool: ........................................................................................................... 126
9.3.2. An exergy audit guide: ................................................................................................ 126
9.3.3. Sustainability in the built environment: ..................................................................... 127
9.3.4. Understanding buildings control systems: .................................................................. 127
9.3.5. Exergy based indicators for resource consumption and impact: ............................... 127
9.3.6. Barriers to the implementation of exergy analysis study: .......................................... 127
9.4. Final conclusion: .................................................................................................................. 127
References .......................................................................................................................................... 129
Appendix 1 .......................................................................................................................................... 143
Appendix 2 .......................................................................................................................................... 145
Appendix 3 .......................................................................................................................................... 146
Appendix 4 .......................................................................................................................................... 170