Flocculation studies in papermaking

211 Pages·2009·2.25 MB·English

FLOCCULATION STUDIES

IN PAPERMAKING

PhD E S A
LISABETE IMÕES NTUNES

Thesis

2009

UNIVERSITY OF COIMBRA
FACULTY OF SCIENCES AND TECHNOLOGY
CHEMICAL ENGINEERING DEPARTMENT
FLOCCULATION STUDIES IN PAPERMAKING

A dissertation submitted to the
University of Coimbra

in fulfilment of the requirements for the degree of

Doctor of Philosophy

by

Elisabete Simões Antunes

University of Coimbra
Chemical Engineering Department
2009

To my parents, Jaime and Benilde and my sister, Célia

ACKNOWLEDGEMENTS

I would like to thank those that helped me to make this thesis possible. First of all, I
would like to express my gratitude to my supervisors.
To Professor Graça Rasteiro for all the help, guidance and support during the
realization of the research work and especially for encouraging me and believing in me
since the day that I became one of her students.
To Professor Carlos Negro for his advice and especially, for his support and help
during my stay in Madrid.
I am also thankful to Prof. Fernando Garcia and to Dr. Paulo Ferreira for their
assistance whenever necessary since the beginning of this work and for their comments
that made valuable inputs to this work.
Then, I would like to acknowledge the collaboration of the Aqua+Tech Specialities,
S.A., Switzerland, for providing flocculants samples with a special thank to Doctor David
Hunkeler for his constant interest in my work.
I also wish to thank the Paper and Forest Research Institute RAIZ (Portugal) that
had kindly provided the Dynamic Drainage Analyser and the Labgran of the “Instituto
Pedro Nunes” (Portugal) that allowed using the microscope for image analysis.
I would like to thank the European Project “Novel Device to Study Pulp
Suspensions Behaviour in order to Move towards Zero Energy Losses in Papermaking”,
(COOP-CT-2004/513117) and the “Fundação para a Ciência e Tecnologia” (Portugal)
(POPH-QREN funding program) for the financial support.
My acknowledgments go also to people from the Chemical Engineering
Department of the Complutense University of Madrid, especially to Professor Angeles
Blanco and to Dr. Elena Fuente for all the help, comments and support.
Finally, my sincere thank to my parents and my sister for all their support and
encouragement over the years and to João for his patience and support, without which none
of this would be possible.

CONTENTS

ABSTRACT 1
RESUMO 3
RÉSUMÉ 5
LIST OF FIGURES 7
LIST OF TABLES 13
NOMENCLATURE 15
CHAPTER 1 – LITERATURE REVIEW 19
1.1 – OVERVIEW OF THE WET-END CHEMISTRY IN PAPERMAKING 19
1.2. – RETENTION AND DRAINAGE IN PAPERMAKING 22
1.2.1 – CHEMICAL ASPECTS OF RETENTION 22
1.2.2 – FLOCCULATION MECHANISMS 25
1.2.3 – FACTORS THAT INFLUENCE RETENTION MECHANISMS 30
1.2.4 – DRAINAGE MECHANISMS 37
1.2.5 – RETENTION AND DRAINAGE MEASUREMENT DEVICES 39
1.3 – FLOCCULATION EVALUATION 46
1.3.1 – AGGREGATES PROPERTIES 46
1.3.2 – MEASUREMENT OF AGGREGATE PROPERTIES 51
1.4 – RHEOLOGICAL PROPERTIES OF FLOCCULATED SUSPENSIONS 56
1.5 – MODELLING OF FLOCCULATION PROCESSES 59
CHAPTER 2 – PROBLEM ANALYSIS AND OBJECTIVES 65
CHAPTER 3 – FLOCCULATION EVALUATION 71
3.1 – INTRODUCTION 71
3.2 – EXPERIMENTAL STRATEGY 73
3.2.1 – MATERIALS 73
3.2.2 – FLOCCULATION MONITORING 75
3.2.3 – FLOCS RESISTANCE AND THEIR REFLOCCULATION CAPACITY 77
3.2.4 – FLOCCULATION IN WHITE WATER 77
3.2.5 – COMPLEX FLOCCULATION WITH A MICROPARTICLE SYSTEM 78
3.3 – RESULTS AND DISCUSSION 79
3.3.1 – FLOCCULATION PROCESS 79
3.3.2 – FLOCS RESISTANCE 101
3.3.3 – REFLOCCULATION CAPACITY 104
3.3.4 – EFFECT OF MICROPARTICLES ON THE REFLOCCULATION PROCESS 105
3.3.5 – EFFECT OF WATER CATIONIC CONTENT ON FLOCCULATION PROCESS 115
3.4 - CONCLUSIONS 121
CHAPTER 4 – RETENTION AND DRAINAGE EVALUATION IN THE
DYNAMIC DRAINAGE ANALYSER 125
4.1 - INTRODUCTION 125
4.2 – EXPERIMENTAL STRATEGY 126
4.2.1 – MATERIALS 126
4.2.2 – DRAINAGE EVALUATION 126
4.2.3 – RETENTION EVALUATION 126
4.3 – RESULTS AND DISCUSSION 127
4.3.1 – RETENTION AND DRAINAGE 127
4.3.2 – CORRELATION WITH FLOCS PROPERTIES 136
4.4 - CONCLUSIONS 138
CHAPTER 5 – RHEOLOGICAL BEHAVIOUR OF FLOCCULATED
SUSPENSIONS 139
5.1 - INTRODUCTION 139
5.2 – EXPERIMENTAL STRATEGY 139
5.2.1 – MATERIALS 139
5.2.3 – RHEOLOGICAL TESTS 139
5.3 – RESULTS AND DISCUSSION 140
5.4 – CONCLUSIONS 143
CHAPTER 6 – FLOCCULATION PROCESS MODELLING 145
6.1 – INTRODUCTION 145
6.2 – POPULATION BALANCE MODEL DESCRIPTION 146
6.2.1 – COLLISION EFFICIENCY 146
6.2.2 – COLLISION FREQUENCY 147
6.2.3 – FRAGMENTATION RATE 148
6.2.4 – BREAKAGE DISTRIBUTION FUNCTION 148
6.2.5 – FLOCS RESTRUCTURING 149
6.2.6 – FLOCS SIZE DETERMINATION 149
6.2.7 – SOLUTION OF THE MODEL EQUATIONS 150
6.3 – RESULTS AND DISCUSSION 151
6.3.1 – COMPARISON WITH EXPERIMENTAL DATA 151
6.3.2 – EFFECT OF POLYMER CHARACTERISTICS 155
6.3.3 – EFFECT OF POLYMER DEGRADATION 159
6.4 – CONCLUSIONS 161
CHAPTER 7 – FINAL CONCLUSIONS AND RECOMMENDATIONS FOR
FUTURE WORK 163
REFERENCES 169
APPENDIX A 181
APPENDIX B 193
APPENDIX C 199