A Study Into the Permeability and Compressibility Properties of Australian Bagasse Pulp

Queensland University of Technology

A study into the permeability and compressibility properties of Australian bagasse pulp

By Thomas J. Rainey B.Eng (Chem), Hons I

A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

School of Engineering Systems Queensland University of Technology

2009

IMPORTANT NOTICE

The information in this thesis is confidential and should not be disclosed for any reason nor relied on for a particular use or application. Any invention or other intellectual property described in this document remains the property of Queensland University of Technology.

i Thomas J. Rainey, A study of bagasse pulp filtration

© Copyright 2009 by Thomas J. Rainey

ii Thomas J. Rainey – A study of bagasse pulp filtration

Keywords

Sugarcane; bagasse; pulp; paper; permeability; compressibility; filtration; Kozeny-Carman; drainage; forming; steady-state; dynamic; chemical additives; flocculants.

iii Thomas J. Rainey, A study of bagasse pulp filtration

Executive Summary

This is an experimental study into the permeability and compressibility properties of bagasse pulp pads. Three experimental rigs were custom-built for this project. The experimental work is complemented by modelling work. Both the steady-state and dynamic behaviour of pulp pads are evaluated in the experimental and modelling components of this project.

Bagasse, the fibrous residue that remains after sugar is extracted from sugarcane, is normally burnt in Australia to generate steam and electricity for the sugar factory. A study into bagasse pulp was motivated by the possibility of making highly value-added pulp products from bagasse for the financial benefit of sugarcane millers and growers. The bagasse pulp and paper industry is a multibillion dollar industry (1). Bagasse pulp could replace eucalypt pulp which is more widely used in the local production of paper products. An opportunity exists for replacing the large quantity of mainly generic paper products imported to Australia. This includes 949,000 tonnes of generic photocopier papers (2). The use of bagasse pulp for paper manufacture is the main application area of interest for this study.

Bagasse contains a large quantity of short parenchyma cells called ‘pith’. Around 30% of the shortest fibres are removed from bagasse prior to pulping. Despite the ‘depithing’ operations in conventional bagasse pulp mills, a large amount of pith remains in the pulp. Amongst Australian paper producers there is a perception that the high quantity of short fibres in bagasse pulp leads to poor filtration behaviour at the wet-end of a paper machine. Bagasse pulp’s poor filtration behaviour reduces paper production rates and consequently revenue when compared to paper production using locally made eucalypt pulp.

Pulp filtration can be characterised by two interacting factors; permeability and compressibility. Surprisingly, there has previously been very little rigorous investigation into neither bagasse pulp permeability nor

iv Thomas J. Rainey – A study of bagasse pulp filtration compressibility. Only freeness testing of bagasse pulp has been published in the open literature. As a result, this study has focussed on a detailed investigation of the filtration properties of bagasse pulp pads.

As part of this investigation, this study investigated three options for improving the permeability and compressibility properties of Australian bagasse pulp pads. Two options for further pre-treating depithed bagasse prior to pulping were considered. Firstly, bagasse was fractionated based on size. Two bagasse fractions were produced, ‘coarse’ and ‘medium’ bagasse fractions. Secondly, bagasse was collected after being processed on two types of juice extraction technology, i.e. from a sugar mill and from a sugar diffuser. Finally one method of post-treating the bagasse pulp was investigated. The effects of chemical additives, which are known to improve freeness, were also assessed for their effect on pulp pad permeability and compressibility.

Pre-treated Australian bagasse pulp samples were compared with several benchmark pulp samples. A sample of commonly used kraft Eucalyptus globulus pulp was obtained. A sample of depithed Argentinean bagasse, which is used for commercial paper production, was also obtained. A sample of Australian bagasse which was depithed as per typical factory operations was also produced for benchmarking purposes.

The steady-state pulp pad permeability and compressibility parameters were determined experimentally using two purpose-built experimental rigs. In reality, steady-state conditions do not exist on a paper machine. The permeability changes as the sheet compresses over time. Hence, a dynamic model was developed which uses the experimentally determined steady-state permeability and compressibility parameters as inputs. The filtration model was developed with a view to designing pulp processing equipment that is suitable specifically for bagasse pulp. The predicted results of the dynamic model were compared to experimental data.

The effectiveness of a polymeric and microparticle chemical additives for improving the retention of short fibres and increasing the drainage rate of a bagasse pulp slurry was determined in a third purpose-built rig; a modified

v Thomas J. Rainey, A study of bagasse pulp filtration

Dynamic Drainage Jar (DDJ). These chemical additives were then used in the making of a pulp pad, and their effect on the steady-state and dynamic permeability and compressibility of bagasse pulp pads was determined.

The most important finding from this investigation was that Australian bagasse pulp was produced with higher permeability than eucalypt pulp, despite a higher overall content of short fibres. It is thought this research outcome could enable Australian paper producers to switch from eucalypt pulp to bagasse pulp without sacrificing paper machine productivity. It is thought that two factors contributed to the high permeability of the bagasse pulp pad. Firstly, thicker cell walls of the bagasse pulp fibres resulted in high fibre stiffness. Secondly, the bagasse pulp had a large proportion of fibres longer than 1.3 mm. These attributes helped to reinforce the pulp pad matrix.

The steady-state permeability and compressibility parameters for the eucalypt pulp were consistent with those found by previous workers.

It was also found that Australian pulp derived from the ‘coarse’ bagasse fraction had higher steady-state permeability than the ‘medium’ fraction. However, there was no difference between bagasse pulp originating from a diffuser or a mill.

The bagasse pre-treatment options investigated in this study were not found to affect the steady-state compressibility parameters of a pulp pad.

The dynamic filtration model was found to give predictions that were in good agreement with experimental data for pads made from samples of pre- treated bagasse pulp, provided at least some pith was removed prior to pulping.

Applying vacuum to a pulp slurry in the modified DDJ dramatically reduced the drainage time. At any level of vacuum, bagasse pulp benefitted from chemical additives as quantified by reduced drainage time and increased retention of short fibres. Using the modified DDJ, it was observed that under specific conditions, a benchmark depithed bagasse pulp drained more rapidly than the ‘coarse’ bagasse pulp.

vi Thomas J. Rainey – A study of bagasse pulp filtration

In steady-state permeability and compressibility experiments, the addition of chemical additives improved the pad permeability and compressibility of a benchmark bagasse pulp with a high quantity of short fibres. Importantly, this effect was not observed for the ‘coarse’ bagasse pulp. However, dynamic filtration experiments showed that there was also a small observable improvement in filtration for the ‘medium’ bagasse pulp. The mechanism of bagasse pulp pad consolidation appears to be by fibre realignment. Chemical additives assist to lubricate the consolidation process.

This study was complemented by pulp physical and chemical property testing and a microscopy study. In addition to its high pulp pad permeability, ‘coarse’ bagasse pulp often (but not always) had superior physical properties than a benchmark depithed bagasse pulp.

vii Thomas J. Rainey, A study of bagasse pulp filtration

List of publications

Journal articles

Rainey, T.J., Doherty, W.O.S., Brown, R.J., Martinez, D.M., and Kelson, N.A. – Pressure Filtration of Australian bagasse pulp, Appita J. (2009) submitted to Transport Porous Med .

Rainey, T.J., Doherty, W.O.S., Brown, R.J., Martinez, D.M., and Kelson, N.A. - An Experimental Study of Australian Sugarcane Bagasse Pulp Permeability, Appita J. (2009) accepted for publication .

Peer-reviewed conference papers

Doherty, B. and Rainey, T. - Bagasse fractionation by the soda process, Proc. Aust. Soc. Sugar Cane Technol., Mackay. (2006). 545-554.

Conference papers

Rainey, T.J., Doherty, W.O.S., Brown, R.J., Kelson, N.A. and Martinez, D.M. - Determination of the Permeability Parameters of Bagasse Pulp from Two Different Sugar Extraction Methods. In Proceedings Tappi Engineering Pulping and Environmental Conference , Session 4.1, Portland, Oregon, USA. (2008).

Rainey, T., Brown, R., Martinez, D.M., and Doherty, B. - The use of CFD to simulate the behaviour of bagasse pulp suspensions during the dewatering process, Appita conference, Melbourne. (2006). Available online at QUT e-prints .

Several of the above papers are available online at the following site: http://eprints.qut.edu.au/

viii Thomas J. Rainey – A study of bagasse pulp filtration

Acknowledgements

I would like to thank all of my supervisors, without whom this thesis would not be possible. I would like to thank Bill Doherty for helping me cope with much of the structure and direction of my work – your door was always open to me; Richard Brown - you always helped me with resource issues and smooth progression through the milestones; Mark Martinez at UBC for assistance with developing the dynamic filtration model and the long discussions interpreting my data; and Neil Kelson for helping me with the coding and article writing. All of you helped me in many ways.

This work would not have been possible without the financial contribution of the Federal Government’s Sugar Research and Development Corporation PhD scholarship fund, and income support from QUT’s Sugar Research and Innovation. I would like to thank the Queensland Government’s financial contribution through the PhD Smart State Fund. I also acknowledge the financial contribution of the Faculty of Built Environment and Engineering and the Engineering Systems theme. Your significant financial contributions are deeply appreciated.

I would like to thank my family, particularly Jenni for her unending patience through all those sleepless nights. Thank you Mum and Dad for your support. Thank you Anna for entertaining me through my final year.

I would like to acknowledge the generous in-kind contribution of the following organisations: the Australian Pulp and Paper Institute, particularly Loi Nguyen, for use of their facilities; CSR Sugar and Mr. Paul Turnbull for assistance with collection of the bagasse; Covey Consulting (Geoff Covey); Appita (Ralph Coghill); Scion (Alan Dickson); Visy (Darren Ralston); Amcor (Karl Osswald); Central Pulp and Paper Research Institute (Dr Roy and Dr Sood); and HurterConsult (Bob Hurter).

Thank you Neil McKenzie for helping build the experimental equipment.

Thank you also to the countless others that contributed to this thesis.

ix Thomas J. Rainey, A study of bagasse pulp filtration

Formal supervisory team

Dr. Richard J. Brown, QUT, Built Environment and Engineering Dr. William O.S. Doherty, QUT, Sugar Research and Innovation Dr. Neil A. Kelson, QUT, High Performance Computing

Informal supervisor Prof. D. Mark Martinez, University of British Columbia, Department of Chemical and Biological Engineering

The project participants wish to acknowledge receipt of project funding from the Australian Government and the Australian Sugarcane Industry as provided by the Sugar Research and Development Corporation

This research is proudly supported by the Queensland Government’s Growing the Smart State PhD Funding Program and may be used to assist public policy development. However, the opinions and information contained in the research do not necessarily represent the opinions of the Queensland Government or carry any endorsement by the Queensland Government. The Queensland Government accepts no responsibility for decisions or actions resulting from any opinions or information supplied.

x Thomas J. Rainey – A study of bagasse pulp filtration

This thesis is dedicated to my Dad, thank you for enriching my life, and to my daughter Anna, welcome to the world.

“Even though I walk through the valley of the shadow of death, I will fear no evil, for you are with me; your rod and your staff, they comfort me.” – Ps 23:4

xi Thomas J. Rainey, A study of bagasse pulp filtration

The work contained in this thesis has not been previously submitted to meet requirements for an award at this or any other higher education institution. To the best of my knowledge and belief, the thesis contains no materials previously published or written by another person except where due reference is made.

Signature ______

Date ______

xii Thomas J. Rainey – A study of bagasse pulp filtration

Contents

Executive Summary ------iv

Abbreviations and nomenclature ------xvii

Terminology------xx

Chapter 1 Introduction ------1 1.1. Background and motivation 2 1.1.1. The production of sugar and bagasse from sugarcane 3 1.1.2. Potential uses of bagasse 6 1.1.3. Paper manufacture 7 1.1.4. Issues with bagasse paper manufacture in the Australian context 10 1.1.5. The benefits of flocculants to assist paper formation 12 1.2. Research aim 12 1.3. Statement of objectives 12 1.4. Statement of novelty 14 1.5. Summary of thesis chapters 16

Chapter 2 Theory and Literature Review ------19 2.1. Background 19 2.2. Bagasse pulp properties 21 2.2.1. Bagasse pulp yield 21 2.2.2. Bagasse pulp fibre morphology 22 2.2.3. Chemical character of bagasse pulp fibres 23 2.2.4. Bagasse pulp physical properties 24 2.3. Pulp permeability and compressibility parameters 26 2.3.1. Steady-state permeability theory 26 2.3.2. Steady-state compressibility theory 35 2.3.3. Dynamic filtration theory 36 2.3.4. Non-Darcy flow 39 2.3.5. Equipment used in filtration studies 40 2.3.6. Additional filtration theory of particular importance to this study 48 2.4. Chemical additives 52 2.4.1. The mechanism of CPAM and microparticle dual polymer systems for pulp flocculation 52 2.4.2. Flocculant systems 53 2.4.3. Literature on flocculants used for bagasse pulp 55

xiii Thomas J. Rainey, A study of bagasse pulp filtration

2.4.4. Using the Dynamic Drainage Jar as a tool for comparing flocculants 56 2.4.5. Summary of chemical additives literature and theory 57 2.5. Summary of theory and literature review 58

Chapter 3 Experimental procedure and modelling------60 3.1. Overview of experimental and modelling methodology 61 3.1.1. Preparation of Australian bagasse pulp 62 3.1.2. Physical and chemical property testing 63 3.1.3. Steady-state permeability property testing 63 3.1.4. Steady-state compression testing 64 3.1.5. Dynamic filtration modelling and verification 64 3.1.6. Effect of chemical additives on the drainage and retention properties 65 3.1.7. Flow diagram of the experimental and modelling methodology 65 3.2. Bagasse pulp preparation 67 3.2.1. Collection of raw materials 67 3.2.2. Pulp sample preparation 71 3.2.3. Test for statistical significance between two populations of pulp samples 76 3.3. Physical and chemical property testing procedure 78 3.3.1. Chemical characterisation of pulp and bagasse 78 3.3.2. Pulp physical property testing 79 3.3.3. Fibre length analysis 80 3.3.4. Microscopy investigation 81 3.4. Steady-state permeability testing equipment and experimental procedure 83 3.5. Quasi steady-state compressibility experimental procedure 88 3.6. Dynamic filtration modelling and experimental verification procedure 90 3.6.1. Dynamic filtration modelling procedure 91 3.6.2. Verification of the dynamic model 91 3.7. Equipment and procedure for testing the effect of chemical additives 92 3.7.1. Methodology – Effect of shear 94 3.7.2. Methodology – Effect of vacuum 95 3.7.3. Methodology – Effect of chemical additives on permeability and compressibility. 97 3.8. Summary of the experimental investigation 97

Chapter 4 Results and discussion ------99 xiv Thomas J. Rainey – A study of bagasse pulp filtration

4.1. Results of bagasse chemical pulping 100 4.1.1. Bagasse pulping kinetics 100 4.1.2. Effect of bagasse pre-treatment on Australian bagasse pulp yield 101 4.1.3. Effect of bagasse pre-treatment on bagasse pulp kappa number 103 4.1.4. Summary of bagasse pulping analyses 103 4.2. Results of physical and chemical property testing 104 4.2.1. Pulp chemical analysis results 104 4.2.2. Pulp physical property results 107 4.2.3. Fibre length distribution analysis 112 4.2.4. Microscopic analysis 115 4.2.5. Summary of pulp physical and chemical property testing 116 4.3. Results of steady-state permeability testing 117 4.3.1. Data from steady-state permeability testing 117 4.3.2. Effect of bagasse pre-treatment on pulp permeability properties 121 4.3.3. Review of bagasse pulp steady-state permeability model 122 4.3.4. Comparison of steady-state permeability data with previous work 123 4.3.5. Summary of steady-state permeability experiments 125 4.4. Results of quasi steady-state compressibility testing 126 4.4.1. Suitability of the power law steady-state compressibility model 127 4.4.2. Pulp steady-state compressibility data and comparison with the findings of previous workers 128 4.4.3. The effect of pre-treament on bagasse compressibility 129 4.4.4. Summary of steady-state compressibility testing 131 4.5. Results of dynamic filtration modelling and validation 131 4.5.1. Predictions of the dynamic model 131 4.5.2. Dynamic filtration experiments and comparison with predicted values 136 4.5.3. Summary of dynamic filtration modelling 137 4.6. Results of chemical additives testing 139 4.6.1. The effect of shear and additives on pulp retention 140 4.6.2. The effect of chemical additives and vacuum 146 4.6.3. The effects of chemical additives on permeability and compressibility parameters 151 4.6.4. The effect of chemical additives on bagasse pulp’s dynamic filtration behaviour 158

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4.6.5. Summary of the effect of chemical additives on pulp permeability and compressibility 161

Chapter 5 Conclusions ------163 5.1. Findings of this thesis 164 5.2. Recommendations for future work 167

References------169

Appendix A Supplementary material for dynamic filtration modeling ------183 A.1 Derivation of the dimensional governing equation for the dynamic filtration model 184 A.2 Non-dimensionalising of dynamic model for FORTRAN 188 A.3 FORTRAN 77 program for the dynamic filtration model 191 A.4 Graphs comparing predictions of dynamic filtration model with experimental data 197

Appendix B Summary of pulp samples ------203

Appendix C Supplementary photographs of experimental work ------207

Appendix D Table of Students t distribution------211

Appendix E Fibre length data of pulp sample ------213

Appendix F Engineering drawings of compression cell--- 215

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Abbreviations and nomenclature

Abbreviations APPI Australian Pulp and Paper Institute CPAM Cationic polyacrylamide CPPRI Central Pulp and Paper Research Institute CSF Canadian Standard Freeness DCM Dichloromethane DDJ Dynamic Drainage Jar FQA Fibre Quality Analyser OD Oven dry LSD Least Significant Difference used by Scion for comparing populations of pulp fibres PAM Polyacrylamide PPJ Positive Pulse Jar QUT Queensland University of Technology SRI A QUT institute; Sugar Research and Innovation UBC University of British Columbia WRV Water retention value

xvii Thomas J. Rainey, A study of bagasse pulp filtration

Nomenclature A cm 2 the cross sectional area of a porous bed for use with Darcy’s Law a - an experimental constant for use in the Davies Kozeny factor correction b - an experimental constant for use in the Davies Kozeny factor correction c g/cm 3 pulp concentration D the flexural term in for the filtration governing equation; used in Appendix A. D* - the dimensionless form of D used for coding the dynamic filtration model in FORTRAN (Appendix A) g cm/s 2 acceleration due to gravity h cm the height of the pulp mat in the compressibility cell K cm 2 Darcy’s permeability constant k - the Kozeny factor k’ cm 2 a permeability constant used by El-Sharkawy and co-workers for measuring an Indian bagasse pulp L cm the height of a bed of porous material for use with Darcy’s Law l cm the distance between the two manometers L mm the length of a fibre or capillary N M kPa a compressibility constant, used in the expression P s=Mc n m kPa a compressibility constant, , used in the expression P s=m Ф m* cm -1 the ratio of surface area to volume of a capillary N N - a compressibility constant, used in the expression P s=Mc n n - a compressibility constant, used in the expression P s=m Ф ni - the number of fibres with length L i P mPa the pressure drop across a bed of porous material for use with Darcy’s Law, p mPa the pressure drop between two manometers Q cm 3/s the flow rate through a porous material for use with Darcy’s Law 2 3 Sv cm /cm the specific surface area of pulp fibre t min time xviii Thomas J. Rainey – A study of bagasse pulp filtration

T - the dimensionless time used for coding the dynamic filtration model in FORTRAN u m/min the compression rate of the platen during experiments with the compressibility cell r v cm/s velocity x cm the distance from the top platen of the compressibility cell

X - the dimensionless distance from the top platen of the compressibility cell used for coding the dynamic filtration model in FORTRAN

Greek letters α cm 3/g pulp swelling factor, ε - pulp porosity (between 0 and 1) mPa.s liquid viscosity Φ - solidity (i.e. volume solids fraction) ρ g/cm 3 density σ standard deviation τ Student’s t- statistic

τs viscous stress tensor

Subscripts e equivalent length, as distance through a capillary, L e, or velocity

through a capillary, u e. f the fluid phase i the number of a fibre or population, as in fibre length L i PE pooled estimate s the solid phase w weighted basis, as in L w. 0 initial

xix Thomas J. Rainey, A study of bagasse pulp filtration

Terminology

Chemical additives includes microparticle and polymeric additives that increase fibre flocculation (see ‘fibre’).

‘Coarse’ bagasse bagasse that is retained on a 12.5 mm screen.

Compressibility the compression behaviour of a pulp mat or pad (see ‘pulp mat’ and ‘pulp pad’).

Digester a pulp and paper reactor (see Reactor) for the digestion of lignocellulosic material by delignification to produce pulp.

Dynamic varies with time. For some experiments in this study the dynamic effect is the varying compressive load which changes the filtration properties and shape of a pulp pad over time.

Fibre normally refers to pulp fibre. Composed of mainly liberated schlerenchyma cells and some parenchyma material. This term is conventionally used in the pulp and paper industry. Bagasse is often described as ‘material’ rather than ‘fibre’ in this thesis to assist with clarity on whether the parent material or the pulp is being discussed.

Filtration in this study includes the combined effects of permeability and compressibility behaviour in a pulp mat or pad. In this thesis, this term is reserved to describe dynamic behaviour.

xx Thomas J. Rainey – A study of bagasse pulp filtration

‘Fine’ bagasse very short fibre that passes through a 4 mm screen. Contains mainly pith (see ‘pith’).

Fines very short material which includes fibres.

Freeness an experimental measure of the ability of pulp to drain freely.

Forming the process of producing a pulp mat from a pulp slurry.

Hardwood a wood species containing short fibres, such as eucalypt.

Kappa number a measure of the residual lignin content.

‘Medium’ bagasse bagasse which passes a 12.5 mm screen but is retained on a 4 mm screen.

Non-wood a fibre resource not derived from wood, such as sugarcane bagasse, wheat straw, kenaf, sorghum, bananas or hemp.

Permeability the ability of a fluid to permeate a porous material.

Pith very short parenchyma cells which exists in sugarcane and which do not have the characteristics of fibres.

Porosity the void fraction of a porous material on a volume basis (see also ‘solidity’).

Pre-treatment describes how the fibrous material is treated prior to or preparation pulping.

Pulp mat used in this thesis to mean a thin sheet of fibres less than a few millimetres produced from a dilute pulp slurry, as at the wet end of a paper machine.

Pulp pad is used for very thick pulp mats, such as those used for experiments in this thesis. Applies to mats more than a few millimetres and up to 300 mm in depth.

xxi Thomas J. Rainey, A study of bagasse pulp filtration

Quasi steady-state an approximation of steady-state conditions (see ‘steady-state’).

Reactor equipment for carrying out a chemical reaction. In this thesis it has the same meaning as a digester (see digester).

Solidity the solids fraction of a porous material on a volume basis (see ‘porosity).

Steady-state invariant with time. For some experiments in this study the level of compression of a pulp pad is constant (or almost constant, i.e. ‘quasi steady-state’) meaning the filtration properties are not changing with time.

xxii Chapter 1 - Introduction

Chapter 1 Introduction

The study presented in this thesis investigates the permeability and compressibility properties of Australian bagasse pulp pads 1. Three options are assessed for improving these properties of pulp pads. Firstly, the permeability and compressibility properties of pulp prepared from ‘coarse’ and ‘medium’ size fractions of bagasse are compared. Secondly, bagasse produced from two different modes of cane juice extraction, i.e. a mill and a diffuser, are considered. Finally, the effect of flocculating chemical additives, namely cationic polyacrylamide and bentonite, are examined. The steady-state permeability and compressibility parameters for bagasse pulp are determined experimentally using purpose built experimental equipment and are used as inputs for a dynamic filtration model. The permeability and compressibility properties of Australian bagasse pulp are compared with numerous benchmarks including eucalypt pulp and bagasse pulp from Argentina.

In this chapter, the background and motivation for the work is presented in section 1.1. Also, the aims (section 1.2) and the objectives (section 1.3) are provided. A statement on the novel aspects of this study is in section 1.4 and the chapter concludes with a summary of the thesis structure (section 1.5).

1 The ‘Terminology’ section in the preamble to this thesis should be read in order to assist the reader’s understanding of key concepts.

1 Thomas J. Rainey, A study of bagasse pulp filtration

1.1. Background and motivation

The Australian sugar industry is mainly a single commodity producer with raw sugar as the primary product. It consists of 25 raw sugar factories producing $1.5 billion worth of raw sugar. Australia exports 80-85% of its raw sugar product and so the industry is exposed to fluctuations in the world sugar price (e.g. 3). Recently the Australian sugar industry was faced with a near financial collapse because of the low sugar price, a series of poor crops and a strengthening Australian dollar. As such the sugar industry is seeking to diversify its product stream to increase revenue and reduce its dependence on sugar. To achieve this, the industry is investigating new products that can be made from the fibrous sugarcane residue, that is, bagasse. Of particular interest to the sugar industry is the use of bagasse in paper manufacture.

Figure 1.1 shows a sketch of a billet of cane. The ‘bast’ is the external part of the plant and the ‘pith’ is the internal part of the plant. The bast and the pith are particularly important in the context of this thesis. The good papermaking fibre from bagasse is mainly derived from the bast portion of the sugarcane plant. Bagasse pulp quality is believed to be detrimentally affected by short ‘pith’ material (length < 0.3 mm). This material is liberated by the sugar extraction process and constitutes 30% of the bagasse. The short material can block the holes in the paper mat, preventing water from draining through it, reducing the production rate and various quality characteristics of the final paper product (4-6). It is thought that ‘depithing’ of the bagasse by removing 30% of the shortest bagasse material is essential to make pulp of acceptable quality (e.g. (7), (8)).

2 Chapter 1 - Introduction

Figure 1.1 Sketch of a billet of sugarcane showing the bast and pith regions of the plant (adapted from 9).

Paper machines making fine papers (e.g. tissues, photocopier papers) use short pulp fibres, such as bagasse and eucalypt, and are generally faster than machines making paper products from longer fibres. Consequently these machines require fibres with good filtration properties (i.e. better web drainage) to generate a homogeneous sheet.

Industry experts have observed that replacing hardwood pulp with bagasse pulp reduces paper machine production rates by 25-30% (10, 11). For a small 70 t/d tissue machine, using bagasse would result in a loss of revenue of $8 million per year. Improving the drainage properties of bagasse pulp would allow higher production rates, reducing the competitive advantage of eucalypt pulp over bagasse pulp in terms of production rate.

1.1.1. The production of sugar and bagasse from sugarcane In Australia, sugarcane is typically harvested and brought to the sugar factory as short lengths of cane called ‘billets’.

The billets are crushed in a sugar factory to extract the juice which contains the sugar (13% - 15% of the plant). The juice is concentrated and sugar crystals are produced. The fluid surrounding the sugar crystals, (i.e.

3 Thomas J. Rainey, A study of bagasse pulp filtration molasses), has a high sugar content (around 40%) which is sold for cattle feed or converted into fuel ethanol. In Australia, revenue from molasses and its products is very small compared to the revenue from sugar. The fibre left over from the crushing process, i.e. bagasse, constitutes around 14% of the plant. Australia produces 10 million tonnes of bagasse annually. The production of sugar and bagasse is shown in Figure 1.2.

Crushing Sugarcane Juice Sugar

Molasses Bagasse

Conventional ethanol

Figure 1.2 Schematic of sugarcane processing and bagasse utilisation options.

There are two main methods of extracting juice from cane. Sugar ‘mills’ are used almost exclusively in Australian raw sugar factories. Sugar ‘diffusers’ are not common in Australia but are commonly used overseas.

Bagasse fibres are severely damaged by sugar milling. A typical sugar milling roller unit is shown in Figure 1.3. Sucrose is extracted after opening up the parenchyma cells (mainly in the pith). The opening up of the pith occurs when the sugarcane is initially shredded in the hammermills, when it is processed in the subsequent roller mills (typically, six roller mills) and also in the final dewatering mill. However, some shear forces are also exerted in the roller mills in between the hammermills and the dewatering mill in a sugar mill that uses only a milling train.

4 Chapter 1 - Introduction

Rollers Feed Pressure feeder rolls chute

Pressure feeder chute

Delivery nip

Feed nip

Figure 1.3 Sketch of a six roller unit where juice is extracted. Several of these units follow the shredder and precede the final dewatering roller mill (12).

The other form of juice extraction technology is a sugar ‘diffuser’ (see Figure 1.4). For a diffuser, after cane preparation in a hammermill, and possibly a first roller mill, the cane passes over a perforated plate, and juice or press water is sprayed onto the fibrous bed to extract more sucrose. Along the diffuser the juice is heated and lime is added to maintain a pH of 7. Subsequent to the diffuser, the cane is passed through one or two drying roller mills.

Perforated plate

Figure 1.4 Sketch of a sugar diffuser (13).

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The subtle differences between mill bagasse and diffuser bagasse may affect pulp quality. Thus, this project examined the impact of the extraction process on pulp fibres.

1.1.2. Potential uses of bagasse In Australia, bagasse is normally burnt for its fuel value to produce steam and renewable electricity. Despite its 50% moisture content, bagasse has a high calorific value, 9.9 MJ/kg (14). Bagasse’s opportunity cost, based on its fuel value, is low ($30-$60 per tonne) because of the availability of high quality local coal.

Bagasse has properties suitable for a range of highly value-added renewable products such as pulp and paper products, polymers, building materials and renewable fuels (Figure 1.5).

Polymers Steam & electricity Pulp and paper

Fibreboard and Hydrothermal building materials liquefaction Bagasse biofuels Animal feed

Cellulosic ethanol Dietary fibre Waxes and resins

Figure 1.5 Potential uses of bagasse.

One of the main uses of bagasse internationally, which is overlooked in Australia, is pulp and paper manufacture, which is the topic of this thesis. Dozens of countries (e.g. China, India, Argentina and Mexico) make bagasse pulp and paper products estimated to be worth between $4 billion and $10 billion annually. This estimate is based on bagasse pulp accounting for around 3% of the pulp and paper industry (15). Imported bagasse paper products from South Africa, India and China are available in Australian supermarkets and could be displaced by local production, generating revenue for sugarcane millers and growers.

6 Chapter 1 - Introduction

Bagasse fibre is also used in building products. It is often used as a cheap raw material in fibreboard or used as a filler in other products including composite materials. Sometimes it is combined with cement and sand to make reinforced concrete (16). These building products are common in India.

Recently, Australian researchers have investigated bagasse lignin and cellulose as resources for renewable polymeric materials (17, 18). Revenue from bagasse based polymers may grow substantially in the medium-term because consumer demand for plastics produced from renewable and sustainable resources is likely to increase.

There has been considerable interest for using lignocellulosic material, including bagasse, for the production of fuel ethanol (19). However, at this point in time, there is very little fuel ethanol commercially produced from lignocellulosics, although a significant research effort is being undertaken in Australia and overseas to realise this long-term goal that would reduce society’s dependence on fossil fuels.

1.1.3. Paper manufacture Modern paper manufacture is a highly capital intensive industry with many stages of value adding being required until the paper finally reaches the consumer.

The raw fibrous material is sourced from the forestry or agricultural sector and usually stored in a large stockpile. Some pre-treatment often occurs, such as the removal of pith in the case of bagasse, or fungal treatment in the case of woodchips. In the case of bagasse, two stage depithing usually occurs. The first stage is a ‘moist depithing’ where the bagasse from the mill is separated into two fractions using a hammermill and a screen. The second stage is ‘wet depithing’ which brings the total amount of pith that is removed to 30%.

The fibrous material is then broken down by mechanical or chemical means into individual pulp ‘fibres’. The ‘fibres’ are often the tracheids (softwood) or schlerenchyma cells (for bagasse), which are typically 1.0- 3.0 mm in length. For bagasse chemical pulp, which is investigated in this

7 Thomas J. Rainey, A study of bagasse pulp filtration study, the bagasse is normally loaded into a twin-screw horizontal ‘digester’ and the fibres are exposed to chemicals, such as caustic soda, elevated temperature and pressure. Soda and soda AQ pulping, as used in this study, is commonly used for bagasse chemical pulp. Bagasse lignin is much more reactive than wood lignin, so the pulping conditions are very mild. Industrially, the chemical charge is 12%-16% of sodium hydroxide (as NaOH on dry fibre), at 170 °C but the pulping time is only 10 min to 12 min (20).

The formation of a fibre mat is a filtration process whereby a suspension of fibres are deposited one layer at a time and water drains through the formed mat (21). The result is that the flexible fibres overlay one another forming a sheet of paper (see Figure 1.6).

Forming fabric

(i) (ii)

Figure 1.6 Fibre orientation during paper formation at the microscopic level shown in: (i) plan view (22); and (ii) elevation view (21)

It is thought that for bagasse pulp, the high content of short pith fibres impede drainage which consequently reduces paper production rate.

There are two types of equipment commonly used to form a pulp mat from a pulp slurry. These are the traditional ‘Fourdrinier former’ and the modern ‘Twin-wire former’ which are normally designed for processing wood pulp. Pulp fibres are suspended in water at 0.01% to 1% and are pumped into a headbox.

The Fourdrinier former consists of continuous moving fabric. The pulp is distributed along the width of the fabric and passes over a series of hydrofoils

8 Chapter 1 - Introduction which creates a pulsating vacuum underneath, promoting the drainage of the pulp (Figure 1.7). At high speeds, instability of the free surface of the pulp suspension on the polymer fabric can occur because of the pulsating vacuum (23). The desire to increase the manufacturing speed ultimately resulted in the development of the Twin-wire former.

B headbox C slice G hydrofoils

Figure 1.7 Elevation view of a Fourdrinier former (24)

Twin-wire forming involves pulp leaving a headbox slice and impinging on a converging gap between two polymer fabrics (24). The dewatering rate is higher in twin-wire forming than on a Fourdrinier former. The dewatering occurs at both surfaces of the pulp/paper mat and a large mechanical force is applied.

Fabric 2

Fabric 1

Figure 1.8 Elevation sketch of a roll former adapted from Parker (25)

9 Thomas J. Rainey, A study of bagasse pulp filtration

Following paper formation, the moist wet sheet is mechanically pressed, dried and reeled. Once a continuous dry paper sheet is produced, it is slit, cut and packaged ready for the public.

1.1.4. Issues with bagasse paper manufacture in the Australian context Eucalypt (a hardwood) is the material of choice for most Australian pulp and paper manufacturers making fine papers, such as tissue and photocopier paper, due to its ready local availability and its good pulp properties, such as high tensile strength and printability. The average fibre length of bagasse pulp is short, around 1.2 mm, and so it is a potential alternative to eucalypt (which has an average fibre length of 0.8 mm to 1.0 mm) for paper production in Australia. Despite the cost advantage of using bagasse ($30-$60 per tonne) when compared to eucalypt ($150 per tonne) and the large existing sugar industry, no bagasse-based products are made in Australia. The reasons for the preferred use of eucalypt pulp include (26):

Processing issues due to the poor filtration properties of bagasse pulp;

Bagasse pulp has inferior strength properties relative to eucalypt pulp;

High capital cost, given the enormous economies of scale achieved by many modern wood pulp mills; and

The remoteness of cane farms relative to Australian wood pulp mills (see Figure 1.9).

An important focus of the work described in this thesis is the investigation of options to improve bagasse pulp filtration properties. As will be shown, the filtration characteristics can be improved by carefully preparing bagasse prior to pulping.

10 Chapter 1 - Introduction

(i) (ii)

Figure 1.9 Sketch of Australia showing (i) the paper industry concentrated in south-eastern Australia (only three relatively modern mills in Brisbane) (15) and (ii) the sugar industry concentrated in north-eastern Australia (coloured yellow 27).

Additionally, the question of whether bagasse pulp could be produced with permeability and strength properties similar to eucalypt is also addressed as part of this investigation. If comparable properties for bagasse pulp and eucalypt pulp can be achieved then there would be numerous benefits of switching to bagasse pulp. As well as the lower cost of the raw material, current consumer attitudes are favourable towards products with a perceived environmental benefit. ‘Tree-free’ paper that is made without wood fibre reduces deforestation. This is a particularly sensitive topic in southern Australia where the current pulp and paper industry in concentrated.

The sugar extraction process also reduces the quality of the bagasse fibres, reducing the pulp strength characteristics, including tensile strength, tear strength and burst strength (28).

Bagasse pulp is normally processed on equipment designed for wood pulp. To this end, if the filtration properties of bagasse pulp could be characterised, this would provide valuable information to assist the design of specialised bagasse pulp processing equipment using Computational Fluid Dynamics, such as pulp washers and paper machine sheet forming fabrics.

11 Thomas J. Rainey, A study of bagasse pulp filtration

Hence, complementary modelling of the bagasse filtration properties is investigated in this study. However, equipment design using the model is outside the scope of this investigation.

1.1.5. The benefits of flocculants to assist paper formation Apart from improving the preparation of bagasse prior to pulping, chemical additives, i.e. flocculants, also improve the production rate of a paper/board machine. Pietschker and co-workers (29) for example reported 30 m/min increase in machine speed when a good drainage aid program was employed at a corrugated medium mill and the increased fibre retention resulted in $5-$20 per tonne reduction in fibre requirements. If similar results were achieved say in a tissue mill with a production capacity of 70 t/d using Australian bagasse, the increase in revenue resulting from the increased production rate would be around $2-3 million per year and fibre savings of up to $500,000 per year. The use of effective flocculants improves the quality of formed bagasse sheets. For example, wire-marks are common in bagasse photocopier paper.

1.2. Research aim

The aim of this project is to experimentally investigate three options to improve the permeability and compressibility parameters of Australian bagasse pulp pads with a view to making bagasse pulp competitive with local eucalypt pulp. The experimental investigation is complemented by modelling of the filtration behaviour of bagasse pulp pads.

1.3. Statement of objectives

The objectives of this project are:

1. To investigate three options to improve permeability and compressibility properties of Australian bagasse pulp pads. The options considered were:

1a: To use pulp derived from two selected fractions of non-pith bagasse material.

12 Chapter 1 - Introduction

1b: To use bagasse obtained from two different sugar extraction methods.

1c: To select and add flocculants to the pulp slurry prior to pad formation.

The effect of each option on the steady-state permeability and compressibility constants is quantified. The bagasse pulp from this study is compared to bagasse pulp produced industrially and also eucalypt pulp.

2. To develop a dynamic filtration model that is well suited for Australian bagasse pulp using the steady-state permeability and compressibility parameter data experimentally obtained in (1).

3. To validate the dynamic model obtained in (2) by performing dynamic filtration experiments with the pulp samples derived in (1).

The outcomes of the experimental and modelling filtration study, along with supplementary pulp physical and chemical property testing, provided guidance on the suitability of Australian bagasse pulp for various paper products.

The relationship between objectives 1, 2 and 3 are shown in Figure 1.10.

13 Thomas J. Rainey, A study of bagasse pulp filtration

Australian bagasse pulp preparation Commercial Australian Pulp from fractioned bagasse from bagasse pulp eucalypt a mill or diffuser with and without from Argentina pulp flocculants added

Objective 1: Steady-state experiments Experimentally obtain the steady-state compressibility and permeability parameters for each pulp and statistically compare the pulp samples.

Objective 2: Dynamic filtration modelling Use steady-state permeability and compressibility data in a dynamic filtration model to predict the dynamic filtration behaviour

Objective 3: Dynamic model validation

Dynamic Verification of filtration dynamic filtration experiments model

Figure 1.10 Flow diagram of the relationship between the project objectives.

1.4. Statement of novelty

To the author’s knowledge, there is no information on bagasse pulp pad compressibility and permeability in the open literature. The study reported in this thesis is a first attempt at investigating the permeability and compressibility properties of bagasse pulp.

A bagasse pulp filtration study was performed as this has not been studied extensively as will be shown in the literature review. Experimental work and complementary mathematical modelling were used.

In this section, the novel aspects of the experimental study and complementary theoretical modelling work are reported in light of the existing body of knowledge described shortly in the literature review (Chapter 2).

14 Chapter 1 - Introduction

The novelty of the experimental work

This study includes an investigation into whether three treatment options have any influence on the steady-state permeability and compressibility of a bagasse pulp pad. These options are the choice of mill or diffuser bagasse, fractionation of the depithed bagasse stock prior to pulping and the addition of flocculants to bagasse pulp slurry.

Several experimental rigs were specially designed and fabricated during the course of this project in order to investigate the material properties of pulp pads.

The first experimental rig, a ‘permeability cell’, tested the steady-state permeability parameters of bagasse and eucalypt pulp pads. The collected data were verified in dynamic filtration experiments using a second purpose built experimental rig, namely a ‘compressibility cell’. This approach is different from that used by previous authors. The approach in this study is believed to be unique because the steady-state permeability data is measured using one rig and verified using a dynamic filtration model in a second rig. In recent studies by other workers, the steady-state permeability and compressibility parameters are inferred directly from dynamic filtration experiments alone.

A third piece of experimental equipment, a ‘modified Dynamic Drainage Jar’ was purpose built to optimise a flocculant system that is suitable for bagasse pulp. The equipment was used to vary the flocculant addition rate, shear and the level of vacuum. Their effect on the fines retention and the drainage time of a pulp slurry was measured. This flocculant system that was optimised for use with a pulp slurry was then used to make pulp pads.

Quantifying the effect of microparticle and polymeric additives (i.e. flocculants) on bagasse and wood pulp pad steady-state compressibility and permeability parameters has not been performed before. Normally, the effectiveness of flocculants as drainage aids is almost always measured by the ‘freeness’ of a pulp slurry rather than by pad permeability. This is because measuring freeness is a simple experimental procedure compared to measuring pad permeability and compressibility. Pad permeability more accurately

15 Thomas J. Rainey, A study of bagasse pulp filtration represents paper mat filtration than the freeness test. The effect of these additives on the dynamic filtration behaviour is also studied for the first time.

In addition to the novelty resulting from the filtration study, the type of laboratory reactor used to produce the majority of the pulp samples (i.e. a ‘flow-through’ reactor) has not previously been used for processing bagasse.

The novelty of the modelling work

Regarding the mathematical modelling work, a review of the open literature indicated that a dynamic filtration model has not previously been developed and verified using a non-wood pulp, such as bagasse pulp. The values for the various permeability and compressibility factors which are required in the dynamic model presented in this thesis are determined, both for bagasse pulp and wood pulp. It is believed that the model developed in this study is valid over a wider range of compression rates than many existing models. The range of compression rates for which other models are valid is a potential contribution for a further study, but this is outside the scope of this study.

1.5. Summary of thesis chapters

Chapter 2 presents theory and a literature review for a study into bagasse pulp filtration, setting this project in the context of the wider body of knowledge. Areas covered include bagasse pulping, chemical additives, filtration theory and experimental equipment used by other workers for studying paper formation. The gaps in the body of knowledge are identified.

Chapter 3 presents the experimental equipment and procedure for the project. The chapter describes how the bagasse pulp samples were prepared, the chemical and physical properties of the pulp samples and the equipment and procedure for the steady-state permeability and compressibility testing. The method used for coding and verifying the dynamic filtration model is explained. Finally the approach for the chemical additives testing is described.

Chapter 4 gives detailed results and discussion from this experimental and modelling investigation. The pulp characteristics are provided and

16 Chapter 1 - Introduction compared to previous workers. Data is collected to test for differences between pulp samples and for use in verifying a dynamic filtration model. The findings of a chemical additives study are presented.

Chapter 5 summarises the main conclusions resulting from the work, and areas of further research are suggested.

Appendices are attached with supplementary material. The material relating to the filtration modelling is in Appendix A. Information on the pulp samples prepared in this study is in Appendix B. Numerous supplementary photographs were taken during the experimental investigations to further illustrate the experiments (Appendix C). Student’s t test is most commonly used for statistically comparing populations of pulp samples, the table of t values is provided in Appendix D. Data on the pulp fibre length distributions are provided in Appendix E. Appendix F is the engineering drawings of the equipment used for measuring pulp pad compression.

17 Thomas J. Rainey, A study of bagasse pulp filtration

This page is deliberately blank.

18 Chapter 2 - Theory and Literature Review

Chapter 2 Theory and Literature Review

This chapter describes the theory and literature that is relevant to a study on bagasse pulp filtration.

This chapter proceeds by describing the background literature related to bagasse pulp (section 2.1), and bagasse pulp’s properties (section 2.2). Pulp permeability and compressibility theory is discussed (section 2.3). The use of chemical additives for improving flocculation and drainage of pulp suspensions is reviewed (section 2.4). A summary of the theory and literature review is presented (section 2.5).

2.1. Background

Bagasse can be used to manufacture various pulp types including mechanical pulp (6), semichemical pulp (30), and chemical pulp (31). It is used to manufacture various paper grades including newsprint (32-36), fine papers (36, 37), tissue and packaging grades (38).

Due to the wide range of applications, the body of literature on bagasse pulping is large (4-8, 26, 28, 30, 32-63). The consensus is that pith detrimentally affects most properties of the pulp, particularly the filtration properties and that good depithing is essential for high quality bagasse pulp. The strength properties of paper sheets made from bagasse pulp are generally weaker than for those made from equivalent hardwood fibres. The body of literature pertaining to bagasse paper formation is much smaller (39-41, 50, 53,

19 Thomas J. Rainey, A study of bagasse pulp filtration

64) and is focussed on the use of chemical additives that can be used to improve the filtration properties. It is the authors view that despite the consensus that pith adversely affects the filtration properties of bagasse pulp, there is a significant gap in the literature when it comes to scientifically quantifying its effect. This was one of the main objectives of this study.

A review of bagasse utilisation for the manufacture of paper, board and composite materials reveals that the groundwork for bagasse paper manufacture was laid between 1960 and 1980. Josef E. Atchison stands widely recognised as the authority on bagasse paper manufacture having provided a significant contribution to the literature over an extended period (see for example 8, 32, 33, 43, 44). His work is very well known amongst the non-wood pulp researcher community.

Until recently, the focus of research into bagasse papermaking in Australia has been on maximising pulp strength properties. The most comprehensive work on Australian bagasse paper manufacture was published in the early 1980s by Gartside and co-workers (28, 51, 65). The work by Gartside and his group focussed on the relatively poor strength of bagasse pulp caused by the milling process. These workers concluded that a change to the milling process is required for Australian bagasse to be used as feedstock in paper manufacture. This conclusion was misleading and incorrect. The following important factors were not considered in the work of Gartside and his group:

Pulp strength, although usually important, is not critical to meet the specific demands of many pulp and paper products. For example water absorption is critical in fluff pulp products. High pulp strength is detrimental to tissue softness and a balance between softness and strength is required. Bagasse pulp is usually well suited to both of these applications;

The drainage and retention properties of the pulp. In the opinion of this author, these properties are considered to be of more importance for the economics of a bagasse paper mill than pulp strength;

20 Chapter 2 - Theory and Literature Review

The mode of sugar/juice extraction from sugarcane;

The pulping process employed; and

The availability of specialised cane varieties, with stronger fibre strength.

In addition to the above list, some technical developments within the sugar and pulp & paper industries have emerged since Gartside’s work, such as the advent of anthraquinone as a soda pulping additive, used in this study, and the development of cane varieties that are better suited to paper manufacture.

Following chronologically on from the work of Gartside and co-workers, Edwards in 1990 (66), investigated alternative juice extraction technology in an attempt to improve pulp strength properties. Although this approach improved pulp strength, it resulted in poor juice extraction.

There is a gap in the literature of Australian bagasse paper research between Edward’s work in 1990 until other works by the author of this thesis, i.e. Rainey, and his colleagues, Doherty and Lavarack commencing 2003 and continuing until today (55, 67-69). These researchers investigated multiple by- products from the pulping of bagasse such as organosolv lignin and soda lignin and ethanol in addition to paper pulp. These studies were mainly focussed on making co-products and bagasse pulp rather than converting bagasse pulp into paper.

2.2. Bagasse pulp properties

Apart from the work by Gartside and co-workers, pulp property data used in this thesis is largely drawn from three excellent articles; Giertz and Varma (4), Paul and Kasiviswanathan (70) and Triana and co-workers (71).

2.2.1. Bagasse pulp yield The unbleached pulp yield for soda bagasse pulp after screening is reported by numerous authors (4, 28, 70, 71) in Table 2.1. There is variability in the reported pulp yield, from 50% (71) to 61.4% (28). The yield reported by Gartside (28) is significantly higher than found by most other researchers. The

21 Thomas J. Rainey, A study of bagasse pulp filtration fibres used by Gartside have different morphology which is discussed later in this chapter.

Table 2.1 Soda bagasse pulp yield reported by various workers.

Kappa Screened Rejects, % number, - yield, %

Paul (3.8:1 fibre to pith) (70) 14 54.4 0 Giertz and Varma (4) (14% NaOH, soda pulp, 30 min) 20 51 7.6 (14% NaOH, 60 min) 18.5 56.9 2 Gartside (Cane variety NCo310) 21.7 61.4 Not reported (28) Triana (71) 29 50 Not reported

2.2.2. Bagasse pulp fibre morphology Useful chemical characterisation and fibre morphology data are provided by Triana and co-workers (71). The data is for pulp derived from both conventional cane and ‘energy cane’ varieties. Energy cane is bred for its high fibre content rather than its sugar content. Selected data is reproduced in Table 2.2 along with some fibre morphology data reported by Gartside and his group for Australian bagasse pulp (28). The narrower width of the fibres reported by Gartside and co-workers is due to a smaller lumen rather than due to a thinner cell wall.

The bagasse pulp fibres measured in the detailed morphology studies by Gartside and co-workers (28) and Triana and co-workers (71) were substantially longer and narrower than reported in a number of other works, such as (50, 64, 65). It is presumed that the average fibre lengths reported in (28) and (71) were obtained from pulp containing mainly sclerenchyma material and that the lengths of a limited number of fibres (typically only 1000 fibres) were measured manually with a projection microscope. However, other authors reported the average fibre length as measured by an automated image capture and analysis (e.g. Kajaani Fibrelab apparatus (50, 64)).

22 Chapter 2 - Theory and Literature Review

Table 2.2 Fibre morphology data of washed conventional cane and energy cane by previous workers.

Fibre Fibre Lumen Wall length diameter diameter thickness (mm) ()m) ()m) ()m) Ja 60-5 and Ba. 43-26 (71) 1.1-1.3 22-23 10.8-13.1 4.9-5.6 CSR6-81 (71) 1.4 22 12 5 Triton (28) 1.43 17.6 8.1 4.8 NCo310 (28) 1.33 13.6 4.1 4.8 (65) 1.11

Conventional cane Conventional cane varieties (50, 64) 0.73 Energy C90-176 and Cane C90-178 (71) 2.0-2.1 23 13 5

2.2.3. Chemical character of bagasse pulp fibres The chemical composition of bagasse pulp and the parent bagasse has been reported by several authors. The characterisation method used by Triana and co-workers (71) is the most similar to that used in this thesis. Their results are reproduced below (Table 2.3). The cellulose component of the bagasse is around 47% for conventional cane and increases to 73% for bagasse pulp. Giertz and Varma (4) noted that the ash content decreased with increased depithing.

Table 2.3 Chemical characterisation of washed cane and unbleached bagasse pulp (71).

Conventional cane Energy cane Bagasse pulp Parent bagasse Bagasse pulp Parent bagasse Cellulose (%) 73 47 72-73 45-46 Hemicellulose (%) 23 27 23-24 28 Lignin (%) 2.4 23 2.3 22 Ash (%) 1.7 1 1.5 1

23 Thomas J. Rainey, A study of bagasse pulp filtration

2.2.4. Bagasse pulp physical properties The physical properties of bagasse pulp are highly dependent on the level of depithing. Both Paul and Kasiviswanathan (70) and Giertz and Varma (4) studied the effect of pith level and pulping conditions on the strength of bagasse pulp. Paul and Kasiviswanathan focussed specifically on the effect of pith levels on soda bagasse pulp, which was similar to the chemical process used in this study (i.e. soda AQ). The study by Giertz and Varma looked at the effect of pith level incidentally to the focus of their research and had similar findings. The physical properties of unbleached pulp reported by various authors are presented in Table 2.4. The results in the table published by Paul and Kasiviswanathan are for pulps with a fibre to pith ratio similar to that used in this study (i.e. 3.43:1).

24 Chapter 2 - Theory and Literature Review

Table 2.4 Physical properties of unbleached bagasse pulp reported by previous workers.

Gartside Paul Giertz Triana et al. (28) et al. (70) et al. (4) et al. (71) Freeness CSF (mL) 540 250 313 558 558 313 Tensile Index (Nm.g) 85 112 70 62.9 28 40 Tear Index (mN.m 2/g) 6.2 5.55 5.5 6.1 5.2 5.1 Burst Index (kPa.m 2/g) 6.1 3.6 1.4 2.4 Apparent Density (g/cm 3) 0.664

Paul and Kasiviswanathan (70) varied the level of depithing and report the response of the bagasse pulp physical properties. In their study, the ‘fibre to pith’ ratio is reported. The fibre to pith ratio is 1.8:1 to 2.0:1 for ‘whole bagasse’, 2.6:1 to 2.8:1 for moist depithed bagasse, 3.0:1 to 3.8:1 for wet depithed bagasse. The pulp samples were refined to 40 Schopper-Riegler freeness. Some results from their study are reproduced in Table 2.5. In their study, as the level of depithing increased (i.e. higher fibre to pith ratio), the initial pulp freeness increased and the strength properties increased.

Table 2.5 Effect of depithing on unbleached bagasse pulp properties (70).

Fibre to pith ratio 0.86:1 1.84:1 2.25:1 2.79:1 3.43:1 3.8:1 5.2:1

Initial pulp freeness (SR) 53 40 35 32 29 26 24

Final pulp freeness (SR) 53 40 40 41 39 40 40

Burst ‘factor’ (-) 33 31 32 34 36 36 41

Tear ‘factor’ (-) 36 43 49 51 55 58 68

Breaking length (km) 6.2 6.5 6.7 6.8 7.0 7.2 7.7

25 Thomas J. Rainey, A study of bagasse pulp filtration

2.3. Pulp permeability and compressibility parameters

There is a significant body of literature where the compression of bagasse was investigated by Australian workers, such as by Kent (72-74). This work was performed with the intent of increasing sugar extraction from the sugar milling process. The compression properties of bagasse are similar to that of soil (75). The mechanisms involved in dynamic pulp pad filtration, particularly particle collapse and flexural stiffness, are quite different to those that occur during soil consolidation. To this end, the literature review focussed on permeability theory generally, and also on pulp pad filtration more specifically.

The discussion of pulp pad permeability and compressibility that follows has been divided into general steady-state permeability theory (section 2.3.1) and steady-state compressibility theory (section 2.3.2), dynamic filtration where permeability and compressibility are interdependent and are a function of time (section 2.3.3) and the special case of non-Darcy flow (section 2.3.4). Equipment which has been used previously for measuring the permeability and compressibility of pulp pads is outlined (2.3.5). Additional theory which is relevant to this study is presented (section 2.3.6).

2.3.1. Steady-state permeability theory

2.3.1.1. Darcy’s Law

The theory of steady-state laminar flow through a homogeneous porous media is based on Darcy’s Law.

In 1856, Henry Darcy, developed an empirical law for the design and construction of water distribution systems in Dijon, France. In his simple experiment sand was packed into a column (see Figure 2.1) and water was pumped through it.

26 Chapter 2 - Theory and Literature Review

Q (cm 3/s) p2 (mPa)

L (cm) Rigid porous  (mPa) material

3 Q (cm /s) p1 (mPa)

Figure 2.1 Sketch defining the parameters used in Darcy’s law for flow through a homogeneous rigid porous media.

Darcy measured the flow rate through the packed bed and measured the pressure drop between the top of the bed and the bottom of the bed, P, with manometers. The resulting equation, Darcy’s original correlation is

Q 'K (∆P) = A ∆L

Equation 2.1 where Q is the volumetric flow rate through a bed of porous material with cross-sectional area A, P is the frictional pressure drop across the length ( L) of the porous media bed, and K’ is a permeability constant which is dependent on viscosity.

Although Darcy’s law is useful in this form for water, K’ is dependent on the viscosity as well as geometric factors. In order to separate the dependence of the permeability constant on viscosity, ), K’=K/ ) is substituted where K is a permeability constant that is independent of water viscosity (76, 77). K is dependent on the shape, arrangement and porosity of the rigid material. This amendment to Darcy’s correlation (Equation 2.1) became known as Darcy’s Law (Equation 2.2) (77).

Q K∆P = A µ∆L

Equation 2.2

27 Thomas J. Rainey, A study of bagasse pulp filtration

2.3.1.2. Relating K to porosity, ; the Kozeny-Carman equation and its derivation from Poiseuille’s Law

In paper manufacture, the permeability of a pulp mat is affected by the varying concentration and hence porosity of the developing pulp mat as well as by the structural arrangement of the mat. There are a wide range of steady-state permeability models relating Darcy’s permeability to the porosity. Scheidegger (77) gives an exhaustive discourse on the various models that have been derived. These correlations are broadly classified into (i) empirical correlations; (ii) capillaric models; and (iii) hydraulic radius theories.

By far the most commonly used correlation between Darcy’s permeability constant, K, and porosity for pulp and paper research is the Kozeny-Carman equation (78-80).

The Kozeny-Carman equation is based on hydraulic radius theory. Kozeny originally proposed the basic theory in 1927 which was significantly modified by Carman in 1937 and 1956. The original form of the equation is usually attributed to Kozeny due to his experimental work, although Blake (as reported in 77) had previously derived a similar form of the equation from Darcy’s law. The assumptions of all hydraulic theories include (77): • Fluid motion occurs like motion through capillaries • No tangential component of the fluid velocity • No pores are sealed off • The pores are randomly distributed • The pores are uniform in size • The porosity is not too high • Diffusion phenomena are absent

The derivation of the Kozeny-Carmen equation starts by assuming that flow through porous media can be approximated by assuming that the liquid

28 Chapter 2 - Theory and Literature Review flows under laminar conditions through a series of parallel circular capillaries (i.e. fixed parallel cylindrical tubes) as shown in Figure 2.2.

Hollow capillaries Solid material

Figure 2.2 Sketch to illustrate the derivation of the Kozeny-Carman equation.

Using Poiseuille’s law for a single capillary where u e is the actual velocity through the capillary, L e is the length of the capillary, P is the pressure drop across the capillary and d is the diameter of the capillary

d 2 ∆P u e = 32 µ L e

Equation 2.3 By definition, the ratio of surface area to volume (m*) of a capillary is

π 2 d L e d m* = 4 = πdL e 4

Equation 2.4 So d=4m* and substituting into Equation 2.3 gives

29 Thomas J. Rainey, A study of bagasse pulp filtration

m *2 ∆P u e = k 0µ L e

Equation 2.5

Where k 0 is a constant.

The average (i.e. superstitial) velocity across the bed of porous material, u, is lower than the velocity in the capillary. Also the length of the capillary,

Le, is longer and more tortuous than the actual length of the pulp pad, L. i.e.

u L u = e e ε L

Equation 2.6 Substituting Equation 2.6 into Equation 2.5 yields

2 C L S m *2 ε ∆P u = D T E L e U k 0µ L

Equation 2.7 Defining a new constant, k

C L S2 k = k D e T 0 E L U

Equation 2.8 And now applying the definition of m* over the whole of the porous material,

pore volume ε m* = = surface area of particles (1− ε ) Sv

Equation 2.9 1 ε3 ∆P u = 2 2 kS v (1− ε ) µL

Equation 2.10

30 Chapter 2 - Theory and Literature Review

This on comparison with Darcy’s Law implies the Kozeny-Carman equation which is Equation 2.11.

1 ε3 K = 2 2 kS v (1− ε )

Equation 2.11 where the porosity (i.e. the void fraction) of the material is , the specific surface area of the material (i.e. surface area per unit volume of porous material) is S v, and k is known as the ‘Kozeny factor’. The Kozeny factor, k, is often referred to as a shape factor because it depends on the orientation and interconnectivity of the channels. Unlike K, S v is independent of concentration.

For this reason, S v is more useful than K to compare the permeability of pulp samples over a wide concentration range. S v is used extensively in this thesis to compare the steady-state permeability properties of pulp samples.

Values for S v are widely reported in the literature for wood pulp (81-86). The earliest reported values were by Robertson and Mason (86) for a sulfite -1 wood pulp. S v was reported to be 2300 cm for pulp that has never been dried and 4100 cm -1 for pulp that has previously been dried. Gren (84) investigated

Sv as a function of kappa number for a sulphate wood pulp. Values of S v were reported to be between 2000 cm -1 and 3000 cm -1 . These previous findings are discussed in more detail when they are compared to the bagasse pulp measured in this study (Chapter 4).

The most common variants of the Kozeny-Carman equation as presented in Equation 2.11 include: using the solidity of the porous material
instead of the porosity (
= 1 - ); separating the generalised specific surface area S v into 2 2 a specific surface area multiplied by a tortuosity factor , S v  ; and simplifying 2 the kS v expression into a single term. The Kozeny-Carmen factor, k is often applied as a constant for pulp fibres, 5.55, which was measured by Brown (87).

Despite its age this permeability model is still used today because of its simplicity and accuracy. The Kozeny-Carman model is still being tailored today for applications in a wide range of industries, such as in the coal industry (88) and for groundwater management (89).

31 Thomas J. Rainey, A study of bagasse pulp filtration

A common criticism of the Kozeny-Carman model is that k is actually a function of porosity, and hence is variable. Soon after its inception, it was found by Davies (90) and experimentally verified by Ingmanson and co- workers (81), that for fibrous materials it can be represented by:

aε3 k = [1+ b(1− ε ) 3 ] (1− ε ) 2/1

Equation 2.12 where a = 3.5 and b = 57 for fibrous materials. Other authors use a=4.0, b=57 (81, 91) for rigid materials.

Notably, the value of S v was found to vary depending on whether k was fixed (at 5.55) or whether it varied according to Equation 2.12. Ingmanson (81) -1 found that for a wood pulp, for a fixed value for k, S v was 4200 cm but for a -1 variable k, S v was 2900 cm .

Other criticisms of Kozeny’s approach include the use of arbitrary correlations by many authors to reproduce results experimentally as well as failure of the model under conditions of turbulence, high porosity or tangential flow. Many modifications to the Kozeny model exist including those concisely reported by Mauret and Renaud (92) which are all adaptations of the Kozeny- Carman equation (Equation 2.11), mostly incorporating corrections for k (such as Davies’s Equation 2.12).

32 Chapter 2 - Theory and Literature Review

Table 2.6 Reproduction of Kozeny constant correlations (92).

2.3.1.3. Alternatives to the Kozeny-Carman equation for steady-state permeability Dullien (93) provides a good summary of the relationship between permeability and porosity proposed by various investigators, part of which is reproduced below. These correlations are all of a similar form to Kozeny’s correlation. Kozeny compared his experimental data and his correlation with that of Zunker and Terzaghi. Carman (1937) acknowledges Slichter as having made a major contribution to the development of steady-state permeability correlations.

Table 2.7 The form of the relation between Darcy’s permeability factor and porosity developed by various workers (93)

Relation Author 3.3 Slichter (1898) /(1- )2 Zunker (1920) [( -0.13)/(1- )1.3 ]2 Terzaghi (1925) 3/(1- )2 Blake (1922), Kozeny (1927), Carman (1937, 1948)

The only known work into measuring the permeability constant of bagasse pulp was undertaken recently by El-Sharkawy and co-workers (50, 64) for a commercial Indian pulp. In this work, an axial feed pressure screen was used to process the pulp and the improvement in pad permeability was measured using a pulsed ultrasound Doppler anemometer.

33 Thomas J. Rainey, A study of bagasse pulp filtration

The form of the permeability model used by these authors is not commonly used; the permeability constant is proportional to the first power of the porosity in the numerator. This is the form first developed by Zunker viz

ε K = 'k (1− ε ) 2

Equation 2.13 where k ' is a permeability constant.

El-Sharkawy and co-workers found the permeability constant for their commercial bagasse pulp was 2.36×10 -9 cm 2. The work of El-Sharkawy and co-workers is discussed further when their data is compared with the data generated in this study (i.e. in Chapter 4).

There are a number of equations relating porosity to Darcy’s permeability constant that are quite different to those discussed so far. One such correlation is the Happel equations. Happel derived his equations directly from the Navier Stokes equations for flow over an array of parallel cylinders both parallel and perpendicular to flow (94). There is a fundamental difference to the approach of Happel and Kozeny-Carman in that Happel derived the equations for flow over an array of cylinders whereas the Kozeny-Carman model is derived from Poiseulle’s law for flow through capillaries .

For flow parallel to an array of cylinders, Happel’s equation is (95)

D 2 K = (− 2 ln()1− ε − 3 + 4 ()()1− ε − 1− ε 2 ) 32 (1− ε )

Equation 2.14 For flow perpendicular to an array of cylinders, Happel’s equation is

D 2 F C 1 S (1− ε)2 −1V K = Gln D T + W 32 (1− ε ) H E1− ε U (1− ε ) 2 +1X

Equation 2.15

34 Chapter 2 - Theory and Literature Review

Happel’s approach was further developed by Jackson and James (96). In reality, assuming all the pulp fibres are cylindrically shaped, most pulp fibres are aligned roughly perpendicular to flow and there is some component of the fibre being aligned parallel to flow. Jackson and James used Happel’s equations to determine the permeability of cylinders arranged in a three dimensional cubical lattice (96). If flow passes axially to a perfect cubical lattice, exactly two thirds of the cylinders are perpendicular to flow and exactly one third of the cylinders are parallel to flow (see Figure 2.3). Thus

D 2 K = (2 F (φ ) + 1 F (φ ) ) 32 φ 3 1 3 2 Equation 2.16 where

2 F1 (φ) = −2 ln(φ)− 3 + 4(φ)− (φ) from Equation 2.14 (φ2 −1) F (φ ) = −ln φ + from Equation 2.15 2 (φ2 +1 )

Figure 2.3 Sketch illustrating Jackson and James (91) approach to developing their steady-state permeability model.

2.3.2. Steady-state compressibility theory Only one compressibility model for pulp pads was observed in the literature. The various authors use variants on the following model

35 Thomas J. Rainey, A study of bagasse pulp filtration

N Ps = M c

Equation 2.17 where c is the pulp concentration and M and N are experimental constants.

This compressibility model is used universally for steady-state conditions by the authorities in the field, such as Ingmanson in particular and also Gren (81, 82, 84, 85). For comparative purposes, it is normally essential to rearrange the compressibility factors used by each author into M and N.

2.3.3. Dynamic filtration theory Dynamic filtration modelling was performed in this study so that pulp processing equipment can be designed specifically for bagasse pulp, although this is beyond the scope of this study. Also, for this study, steady-state approximations are adequate for the initial phases of the investigation, but to increase similitude with industrial paper making dynamic modelling is considered. Dynamic filtration modelling is currently in vogue in the modern pulp and paper literature.

2.3.3.1. The continuity and Navier-Stokes equations A brief background on the origins of the fluid mechanics equations is provided below. This thesis uses a filtration model built from these equations.

In summary both the equations describing the conservation of mass, the continuity equations, and the conservation of momentum, the Navier-Stokes equations, are required to fully describe the fluid kinematics and interaction between pulp permeability and compressibility.

The equations of continuity are:

∂ρ + ρ∇ • v = 0 ∂t

Equation 2.18 recalling that divergence is defined as

36 Chapter 2 - Theory and Literature Review

∂v ∂v ∂v ∇ • v = + + ∂x ∂y ∂z

The form of the Navier Stokes equations for incompressible flow is

DV ρ = −∇ P + µ∇ 2 V + ρg s Dt

Equation 2.19 The derivation of the equations of momentum start with Cauchy’s equation which was improved first by Navier in 1822 (97) and further refined by Stokes in 1845.

The left hand term in Equation 2.19 is the acceleration term (or inertial term), the right hand side of Equation 2.19 consists of the pressure gradient term (∇ P ), the viscous force term ( µ∇2 V ) and the gravity term ( ρg ).

Assuming incompressible laminar flow through a cylindrical pipe, Poiseuille’s Law can be derived from the Navier Stokes equations. For this derivation, see (98)

Equation 2.19 is for incompressible flow of a single phase media. Pulp mats are compressible two phase porous media so a number of amendments are made. The momentum balance on the fibres and the fluid must be considered separately and take into account the porosity of the structure. There exists momentum transfer between the phases and the generalised viscous stress tensor is used (i.e. s instead of )). In summary, for a porous media such as a pulp pad, the momentum equations are applied to both the fibres and the fluid.

The general formula for momentum balance on the fibres is

Du ρsφ = −φ∇Pf − ∇Ps + ∇ (τφ• s ) + ρsφg + mi Dt

Equation 2.20

37 Thomas J. Rainey, A study of bagasse pulp filtration

Where u is the velocity of the fibres, s is the viscous stress tensor. The subscript f refers to the fluid phase and the subscript s refers to the solid phase

(i.e. the fibre). m i is the interphase momentum transfer

The general formula for momentum balance on the fluid is

Dv ρf 1( − φ) = − 1( − φ)∇Pf + ∇ • (1( − φ)τs ) + ρsφg − mi Dt

Equation 2.21

Where v is the velocity of the fluid.

These equations are used to develop the governing equation used in this thesis (section 2.4).

2.3.3.2. Filtration through compressible pulp mats and pads

There are a number of papers that have derived equations to calculate the mechanics of fluid flow through compressible pulp media including porosity, permeability and compressibility for various conditions (81, 95, 99-102). Landman and co-workers (100) provide the governing equations for the basic fluid mechanics of 1-D compressible porous media that can be determined experimentally in a 1-D flow cell (Figure 2.4). The governing equations are derived from the continuity equations, Navier-Stokes equations, Darcy’s Law and the compressibility relation above. Landman and co-workers consider the cases where (i) the initial pulp slurry is initially networked, as in a pulp pad, or unnetworked, as in a pulp slurry, and (ii) the equipment used is a constant pressure device (i.e. the piston exerts a constant force at variable rate as the pad forms) or constant rate device (i.e. the piston exerts a constant rate despite the increasing resistance as the pad forms). The four practical cases for which she derives the solidity are:

• initially unnetworked fibre suspension & constant pressure apparatus; • initially unnetworked fibre suspension & constant rate apparatus;

38 Chapter 2 - Theory and Literature Review

• initially networked fibre suspension & constant pressure apparatus; and • initially networked fibre suspension & constant rate apparatus.

Figure 2.4 Schematic of a 1-D flow cell where a piston is expressing liquid through an initially un-networked suspension.

This thesis considers the permeability and compressibility of a pulp pad using an initially networked model.

2.3.4. Non-Darcy flow The above equations all assume laminar flow. For flow at a sufficiently high velocity, turbulence occurs and the more complex Forcheimer equation can be used instead of Darcy’s Law (103).

µ 2 − ∇P = v + βρ v K *

Equation 2.22 Where ! is an experimental constant and K* is a permeability constant that is analogous to that used in Darcy’s Law.

39 Thomas J. Rainey, A study of bagasse pulp filtration

2.3.5. Equipment used in filtration studies

This thesis uses an initially networked model for the permeability and compressibility study since the steady-state permeability and compressibility parameters. These parameters can be measured using simple equipment (see sections 2.3.5.1). However, optimisation of a good chemical additives system must be performed using equipment where a slurry is used rather than a pulp pad, i.e. the pulp is initially un-networked. The equipment used for these studies is described in section 2.3.5.2.

2.3.5.1.Equipment used for permeability and compressibility testing of pulp pads The equipment used by various workers into the permeability and compressibility testing of pulp pads are fairly simple (81-86). Sometimes, the focus of the investigation is on pad permeability only (86). Some investigations attempt to measure the compressibility and permeability properties simultaneously (81-85). The equipment in all of these investigations involves loading a pulp slurry into a (most commonly) transparent vessel. For permeability studies, the pressure gradient is measured by manometers as well as the water flow rate. For compressibility studies, the response of a hydraulic or mechanical load to the height of the pulp pad is measured.

Figure 2.5 shows the cell used by Robertson and Mason which is fairly typical of permeability and compressibility studies. In this particular arrangement, the pulp is loaded into a 40 mm cylinder which is bounded by a plunger with a reinforced 100 mesh screen at the top of the pad. The flow rate is measured by timing the drop in level of a measuring cylinder, and the pressure head is measured by the difference in fluid height between the cylinder and a side arm.

40 Chapter 2 - Theory and Literature Review

Figure 2.5 Sketch of a permeability cell used by Robertson and Mason (86).

For the case of measuring compressibility simultaneously, the plunger compresses the pulp pad in the experiment and there is continuous monitoring of the flow rate and pressure.

In previous permeability and compressibility studies, the temperature of the water was not reported, so it is assumed the experiments were carried out at ambient temperature. The author acknowledges that industrial paper forming occurs at elevated temperature which affects pulp pad permeability and compressibility. Ambient temperature was used in this study in order to be consistent with that used by previous workers for comparative purposes.

In reality, paper manufacture involves thin pulp mats rather than thick pulp pads. Experimentally measuring the permeability and compressibility of thin pulp mats is difficult, and beyond the scope of this study. For this reason, previous authors, as well as this author, measured the permeability and compressibility of pulp pads because it only requires very simple equipment. It is common practice to use the results from experiments with pulp pads to represent the behaviour of pulp mats.

41 Thomas J. Rainey, A study of bagasse pulp filtration

2.3.5.2.Equipment for filtration studies of fibre suspensions

A review of equipment used previously for accurately simulating sheet formation on a paper machine, from pulp slurry, was conducted. For this study, equipment that was well suited to testing the effects of chemical additives under shear conditions and vacuum was investigated.

A Dynamic Drainage Jar (DDJ) is a simple stirred vessel into which a dilute pulp slurry and flocculants are added. The water and fine fibrous material passes through a permeable screen with 75 )m holes and the fraction of fines retained above the screen is measured. By increasing the stirrer speed (i.e. shear), the effectiveness of flocculants under high shear conditions can be determined. Flocculation effectiveness is measured by the retention of fine fibrous material. A higher level of retained fines over a wide range of stirrer speeds means that flocculation has improved. The DDJ is most commonly used to test the effectiveness of various flocculants and so it is discussed in more detail in section 2.4. A DDJ was used in this study.

Figure 2.6 Sketch of a Dynamic Drainage Jar.

42 Chapter 2 - Theory and Literature Review

Many modifications of the DDJ exist for simulating the industrial forming process. Modifications of the DDJ are the subject of a number of papers (for example 104, 105). Modifications of the DDJ usually permit pad formation to look at the combined effect of mechanical entrapment and colloidal interaction.

The DDJ was modified by Britt and Unbehend in 1980 (106) to measure the dryness of a sheet after exposure to a controlled vacuum. The vacuum was applied to simulate the suction created on the Fourdrinier former; however, it was not a pulsed vacuum. Britt and Unbehend (106) describe a method for testing a dynamic drainage rate. An observation was that over-flocculation created channels in the fibre pad, improving the initial drainage rate but once the water was removed from the interstices of the pad air was sucked through the sheet when vacuum was applied, resulting in higher final sheet moisture content. Pulp suspensions of lower initial drainage rate tended to form more consolidated and uniform sheets which when subjected to vacuum resulted in a sheet of lower moisture content.

In 1982, the application of vacuum to a modified DDJ was automated (107). In trials, Britt applied vacuum for 5 s and measured the final consistency of the pad. In 1985, Britt further illustrated that pulp which drained quickly had poor final dryness when vacuum was applied and that a certain level of fines can improve the final sheet dryness (108). The following mechanism was suggested: when the shortest fibres are mobile with respect to the fibre pad, the fines migrate to the interstices of the forming web, sealing or plugging some of the openings and slowing drainage but when the fines are flocculated and attached to fibres, they are no longer free to migrate to the interstices and drainage is not impeded.

The modification by Forsberg, called the “Dynamic Drainage Analyser” (DDA) in (104) involved a microprocessor which served two functions; to control (i) the duration of chemical addition in order to investigate contact time between retention chemicals and fibres and (ii) the duration of stirring in order to investigate different shear conditions. In this arrangement, it was intended to form a pad to investigate mechanical entrapment of fibres as well as the

43 Thomas J. Rainey, A study of bagasse pulp filtration colloidal interaction. See Figure 2.7, for an illustration of the arrangement. The DDA provided information on retention, drainage, porosity and wet web dryness. The DDA recorded the vacuum level as a function of time. Figure 2.8 shows that the graphical output provided information on the drainage rate under vacuum (time from point a to point c) and the final porosity of the dry sheet (magnitude of vacuum at point d). The modified DDJ used in this study most closely resembles Forsberg’s DDA.

Figure 2.7 Diagram of Forsberg’s Dynamic Drainage Analyser (104).

Figure 2.8 Graphical output of the DDA(104).

Although laboratory equipment that more accurately simulates the industrial forming process exists, they came with increasing cost. In order to

44 Chapter 2 - Theory and Literature Review improve the behaviour of bagasse pulp, a reasonably accurate and affordable method of simulating the pulp dewatering process must be achieved in the laboratory.

In order to further improve the similarity between laboratory equipment and a Fourdrinier paper former, it was necessary to introduce pressure pulses into the equipment. Various modifications of the DDJ attempted to incorporate pulsed vacuum such as that described by Hubbe (105).

The modification by Hubbe, the “Positive Pulse Jar” (PPJ) (105) as shown in Figure 2.9, introduced pressure pulses by a Bellows pump, pumping dilutant under the jar. Previous versions had introduced pulses by vacuum pump. The advantage of this method was that it more accurately simulated the refluidising of the fibre mat facing the fabric, resulting in reduced fines content in this region. The PPJ also investigated the use of a specialised rotor to simulate uniform shear, as opposed to the random turbulence obtained in a standard DDJ. The pressure pulses reduced retention. Importantly, the use of the specialised rotor also resulted in reduced retention compared to the standard impeller used by Britt.

Figure 2.9 Diagram of the PPJ and specialised rotor (105).

The Australian Pulp and Paper Institute (APPI) have pilot laboratory equipment that more accurately simulates a Fourdrinier style paper machine; see Figure 2.10 taken from Xu and Parker (109). It contains a moving belt with hydrofoils attached in order to simulate the pressure pulses of a Fourdrinier former. The equipment does not take into account the velocity profile of the stock leaving the headbox slice.

45 Thomas J. Rainey, A study of bagasse pulp filtration

Figure 2.10 Moving Belt Drainage Former (109).

Melbourne University in conjunction with CSIRO Forestry and Forest Products (now called Ensis) also developed laboratory forming equipment that simulates the velocity profile of the stock leaving the slice of an industrial paper machine (110-112). This configuration is shown in Figure 2.11. Importantly, this equipment is capable of aligning the fibres, approximating fibre alignment on a paper machine. It does not take into account pressure pulses characteristic of a Fourdrinier former.

Figure 2.11 Setup of the laboratory former by Helmer (110-112).

Another sophisticated piece of laboratory equipment outlined by Kataja and Hirsila (113) should be mentioned here. Although it does not simulate the forming process as accurately as the laboratory formers, it can be used to obtain very detailed data about pulp pad formation; more than any other laboratory equipment encountered. The equipment used by Kataja and Hirsila can be used to measure the velocity of fibres at various heights in a dewatering fluid flow,

46 Chapter 2 - Theory and Literature Review see Figure 2.12. This equipment is particularly useful for developing numerical models of pulp suspension behaviour. The unit consists of a sealed tank with a riser tube. Inside the riser tube is a wire and support grid. The suspension of fibre is allowed to drain through the wire. The fibre is retained on the wire and forms a fibre mat. The water level inside the riser is measured with an ultrasonic surface detector. The vertical velocity of the fibres is measured through the wire by four pulsed ultrasound Doppler anemometers. The signal sent from the surface detector and the anemometers are processed and the data is captured. The probes can measure the vertical velocity of the fibres up to 70 mm above the wire. The water level in the riser tube is adjusted by valves V1, V2 and V3. Assuming valves V1 and V3 have adequate accuracy and response time, the programmable logic could be modified to allow a time- varying pressure pulse, simulating the effect of foils in Fourdrinier forming.

El-Sharkawy (50) used the equipment outlined by Kataja and Hirsila to control bagasse pulp quality through fractionation and refining (50). This work is the only published work with data presented on the drainage properties of bagasse pulp.

Figure 2.12 Ultrasound anemometry for measuring filtration of fibre suspension (113).

47 Thomas J. Rainey, A study of bagasse pulp filtration

To measure the efficacy of chemical additives under both vacuum and shear, a modified DDJ that most closely resembles that developed by Forsberg was used for this project. It was simple to construct and gives an indication of how chemical additives would perform under the dual effects of shear and vacuum. The main differences are that it will involve a laptop computer to log the data, the vacuum will be controlled by actuating a bleed valve on the vacuum vessel and flow rate will be measured with digital scales. The modified DDJ more closely resembles a Fourdrinier former than a Twin-wire former.

2.3.6. Additional filtration theory of particular importance to this study

2.3.6.1.Steady state permeability theory In the case of pulp fibres in the swollen state, a considerable amount of water occupies the pores of the fibres. Incorporating  into the Kozeny-Carman model (Equation 2.11) allows this study to obtain information on potential strength generation during refining as well as permeability data. If the swelling factor of the fibres is  cm 3/g, then the porosity is related to the concentration, c g/cm 3, by  = 1 – c.

Inserting into (Equation 2.11) and rearranging obtains

C S 3/1 2 3/1 D 1 T (Kc ) = D 2 2 T (1− αc ) E kα Sv U

Equation 2.23 Plotting (Kc 2)1/3 against concentration, c, will give a linear relation. Darcy’s permeability, K, is determined from permeability experiments using equation (1) and c is calculated from the height and diameter of the pulp pad for a known mass of pulp. The specific surface area, S v, and the swelling factor, , are calculated from the slope and the intercept of the graph. This method was first used by Robertson and Mason (86). S v and  are then inserted back into equation (2) to test the agreement of the experimental data with the Kozeny- Carman model. The Kozeny factor, k, is frequently assumed to be constant. For randomly packed fibrous beds, k was determined to be 5.55 (114).

48 Chapter 2 - Theory and Literature Review

Values for  are reported in the same literature in which S v is reported

(81-86). Reported values of  vary more than the reported values of S v. Ingmanson and co-workers report values as low as 1.65 cm 3/g for wood pulp whilst Robertson and Mason report  as high as 4.5 cm 3/g for a sample of never dried wood pulp.

The advantage of this method for quantifying the steady-state permeability of pulp samples is that it requires a very simple experimental method and also the equipment required is extremely simple. A pulp pad is created by draining pulp slurry into a transparent vessel which is reinforced at the bottom by a mesh. The flow rate is measured using a collection vessel and stopwatch. The pressure drop per unit length can be measured by manometers. The height of the pulp pad is measured to determine the pulp concentration, assuming that the pulp concentration is approximately uniform in the absence of significant hydraulic pressure. Darcy’s permeability constant, K, can be determined from this data.

2.3.6.2.Steady-state compressibility theory The compressibility equipment was designed so that the pulp could be loaded into a cell and compressed with a permeable top platen which expresses water. This is shown diagrammatically in Figure 2.13, indicating the pressure on the solid phase, P s, at the platen. The distance, x, is defined from the top platen.

The hydraulic pressure at the top surface of the pulp pad is negligible so the force on the fibres equals the force exerted on the platen.

N The compression model used is the power law model viz P s = M c

49 Thomas J. Rainey, A study of bagasse pulp filtration

Expressed water Applied pressure Permeable Ps top platen

x Loaded Depth into pulp Height, h the pulp mat Impermeable base

Figure 2.13 Sketch of the compressibility cell.

The pulp concentration can be related to the solidity (that is, the volume solids fraction), which is used in the dynamic model, by
= c. Values for  are in the range of 3.2-3.8 cm 3/g.

For this geometry,

n Ps=m

Equation 2.24 where m and n are experimental constants analogous to, and calculated from, M and N.

2.3.6.3.The dynamic filtration model This study follows the analysis of Landman and co-workers (100) for a one dimensional constant rate filtration (i.e. platen moves with constant speed) using an initially networked suspension. Martinez has built on this work for pulp and paper applications (115, 116). The modifications include the incorporation of the Kozeny-Carman steady-state permeability model (Equation 2.11) and the power law steady-state compressibility model (Equation 2.24). The derivation of the governing equations for the filtration of a pulp pad is provided in Appendix A.

Using the definitions presented in Figure 2.13, the dimensional form of the governing equation for constant rate filtration is

50 Chapter 2 - Theory and Literature Review

dφ d F dφV dh dφ = GD(φ ) W − dt dx H dx X dt dx Equation 2.25

Where φ(1− φ) K (φ)mn φn−1 D(φ ) = ) Equation 2.26 K(Z) is the permeability as predicted by the Kozeny Carman model (Equation 2.11). This governing equation is subjected to the initial condition

(x,0) =
0 as the solidity is uniform throughout the cell, as well as the following boundary conditions:

Boundary condition at the top platen dh x = 0, u = − dt dφ = 0 dx Equation 2.27

Boundary condition at the base x = 0, u = 0 dφ dh µ = dx dt K(φ )(1− φ ) mn φn−1 Equation 2.28

Solution of the dynamic model requires the factors m and n calculated from steady state compression experiments, S v and  from permeability experiments. These equations are non-dimensionalised before being solved (see Appendix A for the non-dimensional equations). The solution of these equations provides values for
over the ranges of x and t.

For comparative purposes, the model predictions for
are determined at x=0 for all t and consequently P s is calculated (Equation 2.24). In the experimental setup, the Instron measures the load on the top platen which is converted to pressure. Validation of the model occurs if the experimental pressure data matches the model predictions for solids pressure at the surface of the pulp pad.

51 Thomas J. Rainey, A study of bagasse pulp filtration

Both a constant k (k = 5.55), and variable k (Equation 2.12) with the relevant values of S v and , are investigated for use in the dynamic model.

The dynamic model assumes that 100% of the fibre is retained by the platen and also neglects friction between the platen and the side wall.

The effect of applying vacuum at the bottom boundary, which occurs in a Fourdrinier former has the same effect as increasing the pressure at the top boundary.

2.4. Chemical additives

As mentioned in Chapter 1, the use of an effective flocculant system in paper manufacture increases production rates, improves paper quality and reduces raw material requirements. A reduction in the quantity of organic material in the effluent also improves environmental performance. In this thesis, cationic polyacrylamide (CPAM) is combined with microparticles.

2.4.1. The mechanism of CPAM and microparticle dual polymer systems for pulp flocculation Cationic polyacrylamide (CPAM) is used widely as a drainage aid for all types of chemical pulp but has been shown to be suitable for applications with a high amount of fine fibres, such as in mechanical pulp (117). Bagasse pulp similarly has a very high quantity of fine fibre and so CPAM was the polymer selected for this study. CPAM’s mode of action is straightforward. The cationic polymer attaches to the negatively charged surface of the fibres resulting in neutralisation and flocculation.

The addition of anionic microparticles, such as bentonite or colloidal silica can further improve flocculation by bridging the cationic flocculant chains (see Figure 2.14).

52 Chapter 2 - Theory and Literature Review

Figure 2.14 Mechanism of silica microparticles (118).

The important difference between conventional polymer flocculation and microparticle systems is that under conditions of high shear, such as those in a papermachine headbox, the bonds formed with polymers are destroyed, but microparticle systems have the ability to reflocculate the fibres after being subjected to high shear.

2.4.2. Flocculant systems

A large volume of work has been undertaken in developing and comparing chemical additives for various types of pulp (mainly wood grades) (e.g. 107, 119, 120-126). The progression of additive chemistry has been from the single polymer systems (pre 1970s) to dual polymer systems (1970s, 1980s) to polymer and microparticle systems (1990s to present). The following articles on flocculant research are all for wood pulp grades, often with high amounts of very short fibre.

Hubbe (124) and Rojas & Hubbe (127) define three forms of chemicals widely used as drainage additives: coagulants; flocculants; and microparticles. Hubbe defines coagulants as compounds of high positive charge density which act to neutralise the negative charge on fibres and ‘ionic trash’. Ionic trash is undesirable very small fibres that are generated in mechanical pulping and has very high surface area; bagasse pith may be considered ionic trash. Examples of coagulants include aluminium sulphate (or alum), polyamines and polyethyleneimine (PEI). Flocculants are polymers that link fine particles together. Flocculants are often very high molecular weight copolymers of acrylamide (PAM). Microparticles are very small negatively charged particles, such as colloidal silica and bentonite, that interact with cationic flocculants (e.g.

53 Thomas J. Rainey, A study of bagasse pulp filtration

CPAM) or cationic starch and further improve flocculation. Brouillette and co- workers (128), Sherman and Keiser (129) and Ledda et al. (130) all describe various microparticle systems.

Flocculant systems often consist of various combinations of coagulants, flocculants and microparticles. These studies tend to focus on fibre retention rather than drainage . This point is noted by Allen and Yaraskavitch (119). This study gives an excellent review of the dewatering potential of a large number of systems. They make the following pertinent observations: microparticle systems improve dewatering in alkaline systems; CPAM’s give a small improvement in dewatering; and several other systems (e.g. PEI, polyDADMAC and dual polymer) improve drainage at the expense of final sheet moisture in vacuum dewatering. Britt and Unbehend (108) also observed this effect.

Recently Carr (123, 131-133) has strongly advocated silica nanoparticles rather than microparticles. Carr claims that the shear resistance of a particle attached to a surface is inversely proportional to its size i.e. the smaller the particle, the greater the shear resistance (131). Carr claims inventorship of nanoparticles as a flocculant. However, Duffy (from Nalco Chemicals), in 1993, had previously noted that nanometer sized silica particles were extremely efficient (118).

Miyanishi and Shigeru (134, 135) optimised flocculation and drainage by comparing various microparticle systems and controlling the zeta potential (i.e. the streaming potential which is an indication of the charge of the “white” water). Miyanishi and Shigeru looked at the effect of adding various chemicals, (alum, anionic polyacylamide, DADMAC, bentonite and CPAM), in various sequences on both types of pulp containing and free from ionic trash. It was found that alum, CPAM and then bentonite was the best sequence for acid papermaking in the presence of ionic trash, with a 6% increase in flocculation (as measured by improved turbidity) and 65% improvement in their defined measure of “drainage”. DADMAC, anionic polyacrylamide and then bentonite was found to be the best sequence for alkaline papermaking, with a 7% improvement in flocculation and 50% improvement in “drainage”.

54 Chapter 2 - Theory and Literature Review

Kumar also used zeta potential to improve the retention of bagasse pulp in a less thorough study (54). Using a DDJ, the bagasse pulp was fractionated. The best order for retention aids was found to be rosin-starch-alum-filler. The best zeta potential for retention was found to be -5 mV.

In contrast to the studies by Miyanishi and Shigeru (134, 135) and Kumar (54), Britt (121) found that in dynamic systems, although zeta potential provides additional information, flocculation can be improved without any change in the zeta potential.

As can be observed from the variability in optimised flocculant systems, the optimum chemical additives system is dependent on the pulp and needs to be determined on a case-by-case basis. It appears from the literature that CPAM and bentonite should give reasonable improvements in pulp drainage.

It is noted that most articles tend to focus on the fibre retention properties of chemical additives rather than the drainage properties, which is the focus of this thesis.

2.4.3. Literature on flocculants used for bagasse pulp The literature on flocculants used for bagasse pulp is limited.

Abril’s work during the 1980s is the best reported literature with regards to developing flocculant systems for improving the drainage behaviour of bagasse pulp (39-41). Abril’s work was published in Spanish which was translated into English because of its relevance to this study. Abril investigated the effect of polymer drainage and retention aids on bagasse pulp (41). In this laboratory study Abril used a DDJ to assess a range of drainage and retention aids namely dextran, polyethyleneimine, anionic PAM and polyamideamine. The polyethyleneimine and polyamideamine showed the biggest improvement in retention and the best improvement in freeness.

In a further study (40), Abril tested modified polyamideamines, modified polyethyleneimines (PEI’s) and CPAM in the laboratory. One of the modified PEI’s gave the best drainage properties and was tested industrially. In the industrial trial, the headbox freeness and retention (as measured by whitewater

55 Thomas J. Rainey, A study of bagasse pulp filtration consistency) both improved, permitting the machine speed to be increased from 245-270 m/min to 300 m/min.

Ibrahem and co-workers (53) looked at PAM as a filler retention aid for bagasse paper. The fillers investigated were titanium dioxide, silica and kaolin. Strength data is provided for pulp containing each filler over a range of PAM addition. PAM can improve filler retention by between 63% and 86%. It does not contain information about the effect of PAM addition on drainage.

There is no known literature on the use of microparticles as a drainage aid for bagasse pulp.

2.4.4. Using the Dynamic Drainage Jar as a tool for comparing flocculants The DDJ has been described in section 2.3.5.2. It was developed by Britt and Unbehend in the early 1970s for comparing the effectiveness of flocculants under the high shear conditions that exist in a paper machine. Pulp flocculants can be tested very quickly in the laboratory using this equipment. The DDJ has become the standard test method used by the paper industry to test the suitability of pulp flocculants under high shear. Several TAPPI test methods have been written that use this device.

In 1977, Unbehend, Britt’s colleague and frequent co-author, describes the equipments use for measuring fines and colloidal retention. This paper forms the basis of Tappi (the Technical Association of the Pulp and Paper Industry) Test method T261 “Fines fraction by weight of paper stock by wet screening”, making the equipment part of a standard test procedure.

In the standard test method, turbulence of the stock is maintained to prevent pad formation (122). As shown in Figure 2.15, a stock is processed through the DDJ giving the fines retention as a function of stirrer speed (line A). When the same stock is processed with a strong dispersant, 50 ppm of TAMOL 850 and the pH adjusted to 10.5 with sodium carbonate in the presence of ultrasonic dispersion forces, a minimum fines retention line (line B) is obtained, which is a characteristic of the stock. Britt proposed that the

56 Chapter 2 - Theory and Literature Review colloidal forces are measured by the difference between line A and line B. Flocculants raise the A line and dispersants lower it. Fines retention, % Fines % retention,

Stirrer speed, rpm

Figure 2.15 Retention in Dynamic Drainage Jar as a function of stirrer speed (122).

From the literature, the DDJ is a reasonable approach to optimising a chemical additives system.

2.4.5. Summary of chemical additives literature and theory There is a large body of literature for pulp chemical additives. The literature on bagasse pulp chemical additives is small and not recent. Although microparticle systems are not very new, the effectiveness of these flocculant systems are not reported for bagasse pulp.

The literature on the effect of chemical additives to improve the drainage properties is not large as many studies focus solely on fines retention. Miyanishi and Shigeru (134, 135), and Abril are the best works in measuring the improvements in drainage caused by chemical additives. In every case, these workers measure freeness rather than permeability which is a more vigorous measure of drainage. As will be discussed, this thesis investigates the compressibility and permeability of bagasse pulp. Quantifying the effect of microparticle systems on the compressibility and permeability parameters of a bagasse pulp has not been published before.

57 Thomas J. Rainey, A study of bagasse pulp filtration

No work exists quantifying the effects of flocculants on the permeability and compressibility parameters required for modelling dynamic pulp filtration/formation behaviour.

2.5. Summary of theory and literature review

The background literature for bagasse pulping has been discussed. The work of Gartside and co-workers (28, 51, 65) stands out as the most thorough work performed in Australia. However previous published work with bagasse in Australia has traditionally focussed strongly on improving the pulp strength properties and did not consider pulp filtration properties.

The properties of bagasse pulp have been reported by numerous workers apart from Gartside and co-workers (e.g. 71). The fibre morphology and chemical character have been described. The pulp physical properties depend on the level of depithing.

The pulp permeability and compressibility theory has been described for both steady-state filtration and dynamic filtration under compression. The Kozeny-Carman equation is the most common steady-state permeability correlation linking Darcy’s permeability factor, K, to porosity. The power-law compression model is the most common steady-state model for pulp pads. The dynamic filtration model developed in this thesis is based on an initially networked filtration model (100). The equipment designs most commonly used in pulp filtration studies have been discussed.

The method of testing the effectiveness of flocculants using a DDJ has been presented, along with the mechanism of pulp fibre flocculation.

This study investigates the permeability and compressibility of bagasse pulp which has not been performed extensively. The gaps in the literature have been identified as foreshadowed in section 1.4. Particularly, this thesis adds to the existing literature.

The two options for treating bagasse prior to pulping (fractionation and the mode of juice extraction) have not

58 Chapter 2 - Theory and Literature Review

previously been considered with a view to improving their permeability and compressibility properties.

Obtaining steady-state permeability data on steady-state equipment and confirming the data with a second piece of equipment is a unique approach .

Quantifying the effect of flocculants on pulp pad steady-state and dynamic permeability and compressibility has not been previously studied.

Finally, a dynamic filtration model has not been previously investigated for a non-wood pulp such as bagasse pulp.

This study is the first time that the filtration of bagasse pulp has been directly compared to wood pulp.

59 Thomas J. Rainey – A study of bagasse pulp filtration

Chapter 3 Experimental procedure and modelling

The experimental component of the research plan was substantial. For the filtration study three pieces of experimental equipment were constructed specifically for the study, namely the ‘permeability cell’, the ‘compressibility cell’ and the modified DDJ (all terms are defined later in this chapter). This was in addition to the three styles of digestion equipment used to produce the pulp samples.

The research plan was implemented in six stages of experimentation and modelling. This chapter proceeds in the order described by the experimental and modelling methodology (section 3.1). The bagasse was treated and pulped using the three types of digestion equipment, a ‘flow-through’ reactor, a ‘Parr’ reactor and an ‘air-bath’ reactor (section 3.2). The chemical and physical properties of the pulp were analysed as well as the fibre morphology (section 3.3). The steady- state permeability of a pulp pad was measured using a custom built ‘permeability cell’ (section 3.4). The steady-state compressibility of a bagasse pulp pad was measured using a custom built ‘compressibility cell’ (section 3.5). The steady- state permeability and compressibility of bagasse pulp was compared to numerous benchmark pulp samples and the findings of previous workers for wood pulp. The steady-state permeability and compressibility parameters for bagasse pulp pads were used in a dynamic model which was coded in FORTRAN and compared to experimental data obtained under dynamic filtration conditions

60 Chapter 3- Experimental procedure and modelling

(section 3.6). A suitable chemical additive system was optimised with a modified Dynamic Drainage Jar (DDJ) using a bagasse pulp slurry, and the effect of vacuum on drainage time was examined. The modified DDJ was also used to obtain complementary information about the drainage behaviour through thin pulp mats rather than thick pulp pads. The effect of chemical additives on the steady- state permeability and compressibility constants of a bagasse pulp pad was quantified (section 3.7). Finally a summary of the experimental procedure is presented (section 3.8).

3.1. Overview of experimental and modelling methodology

The aims and objectives were achieved in six phases using the following program of work.

Phase 1 Fractionated bagasse pulp from milled and diffuser bagasse was prepared. A benchmark Australian eucalypt pulp and a commercial bagasse pulp were obtained (section 3.2);

Phase 2 The physical and chemical properties of the bagasse pulp were determined (section 3.3);

Phase 3 The steady-state permeability parameters of a bagasse pulp pad were determined using simple permeability experimental equipment. The effect of bagasse fraction and the mode of juice extraction on pulp pad permeability was examined without the addition of flocculants (section 3.4);

Phase 4 The steady-state compressibility parameters of a bagasse pulp pad were determined using simple compression equipment. The effect of bagasse fraction and the mode of juice extraction on pulp pad compressibility was examined, also without flocculants added (section 3.5);

Phase 5 The values of the steady-state permeability and compressibility parameters were used by a dynamic model for predicting the solidity and consequently load pressure of

61 Thomas J. Rainey – A study of bagasse pulp filtration

a pulp pad compressed under dynamic conditions. The model values are compared to data from dynamic filtration experiments (section 3.6);

Phase 6 A suitable chemical additives system is optimised using a modified DDJ using a pulp slurry rather than a pulp pad as used in phases 3-5. The effect of additives on fines retention and drainage time is determined. The effect of chemical additives on the steady-state parameters of a bagasse pulp pad is determined by repeating phases 3, 4 and 5 above (section 3.7).

The above order of research is used in the experimental procedure section (Chapter 3) and the results section (Chapter 4).

3.1.1. Preparation of Australian bagasse pulp Bagasse was prepared in a manner to maximise its permeability properties and permit its long term storage for this study.

For Objective 1a , bagasse was separated into three fractions prior to pulping using two wire mesh sieves of different aperture sizes (12.5 mm and 4 mm). The three bagasse sizes produced were nominated: ‘coarse’, ‘medium’ and ‘fine’ pith material. The terms ‘coarse’ bagasse pulp and ‘medium’ bagasse pulp are used extensively in this thesis and refer to pulp which originated from the coarse and medium fractions of bagasse respectively. Pulp from the ‘fine’ material blocks the pores of the paper mat as it forms, reducing the drainage rate and sheet quality (e.g. poor formation and wire-marks). Removing as much ‘fine’ material as possible prior to pulping improves the drainage properties of the mat.

For Objective 1b , samples of bagasse from the different modes of juice extraction were collected (i.e. milled and diffuser bagasse) from the same factory.

Several other pulp samples were prepared or obtained for comparative purposes. The most important comparative pulp samples are: Eucalyptus globulus pulp; pulp produced from Argentinean depithed bagasse used at a commercial pulp mill; and a conventionally depithed Australian bagasse pulp.

62 Chapter 3- Experimental procedure and modelling

3.1.2. Physical and chemical property testing The Australian bagasse pulp samples were evaluated for their chemical properties. The chemical analyses of the pulp samples included carbohydrate composition by High Performance Liquid Chromatography, Klasson and acid soluble lignin, ash, extractives and pulp yield.

Bagasse is commonly used for the production of linerboard, writing paper and tissues amongst other products. The pulp samples were evaluated for strength properties (tensile, tear, burst and short-span compression) over a range of refining levels, fibre length distribution and optical properties amongst other properties. The suitability of the bagasse pulp produced in this study for these grades were assessed.

The pulp fibres were thoroughly measured for their morphology including the distributions of fibre length, using a Kajaani fibre length analyser, as well as other parameters including wall thickness and collapse ratio using a confocal laser microscope.

3.1.3. Steady-state permeability property testing The effect of bagasse preparation on the steady-state permeability properties of pulp pads was studied. Objective 1a and Objective 1b (section 1.3) were investigated with respect to the steady-state permeability properties.

Pulp permeability was measured in a simple experimental apparatus referred to as a ‘permeability cell’. A transparent Perspex tube filled with pulp and attached to a constant head tank was used to achieve steady-state flow.

Using this simple equipment, the suitability of the Kozeny-Carman permeability model could be quickly determined.

The variables measured in the steady-state testing are the pulp specific surface area, S v, and the swelling factor, . These parameters were determined for use in the Kozeny-Carman permeability model (78, 79). These steady-state variables are required for the dynamic filtration model. The findings of this permeability study are compared to that of previous workers for wood pulp, as

63 Thomas J. Rainey – A study of bagasse pulp filtration

well as to the only known previous work on bagasse permeability which was performed recently (64).

The optimum values of S v and  depend on whether a constant or a variable Kozeny factor, ‘k’ is used. For this study, both constant and variable k was used. Ingmanson and co-workers (81) found that using a variable Kozeny factor resulted in an increase in the prediction for  of around 25% and a decrease in the

prediction for S v of around 7% for wood pulp. The variation in S v and  is measured for non-wood pulp.

Objective 1a and Objective 1b were investigated using Student’s t-test with

respect to their effect on the compressibility properties S v and .

The steady-state permeability of eucalypt pulp, pine pulp and Argentinean bagasse pulp was also measured.

3.1.4. Steady-state compression testing The steady-state compressibility behaviour of pulp pads was measured using simple compression equipment, i.e. a ‘compressibility cell’, using a simple Power- N Law correlation between load pressure and pulp concentration, P s = M C (see Chapter 2 for definitions).

The pulp pad was initially compressed over a very long time-period to measure the quasi steady-state compressibility parameters. The steady-state factors M and N are necessary for the dynamic filtration modelling. Objective 1a and Objective 1b were investigated using Student’s t-test with respect to their effect on the compressibility properties M and N.

The same samples tested for their steady-state permeability were also measured for their steady-state compressibility and compared to the numerous benchmark pulp samples used in this study, including eucalypt, as well as previous workers.

3.1.5. Dynamic filtration modelling and verification In dynamic filtration, the permeability properties change as the pulp pad compresses. Once the steady state compressibility and permeability parameters

64 Chapter 3- Experimental procedure and modelling are determined, the dynamic filtration of bagasse pulp can be predicted using a filtration model similar to that used for wood pulp (100) . This model requires the steady-state permeability parameters, S v and , and the compressibility parameters, M and N, for bagasse pulp previously determined experimentally.

The model was non-dimensionalised and coded in FORTRAN. The model predicts the dynamic filtration behaviour using the experimentally determined steady-state permeability and compressibility parameters. The actual dynamic filtration behaviour of the pulp is then measured experimentally in the compressibility cell. The experimental data is compared with the predictions of the dynamic model in order to verify the model.

3.1.6. Effect of chemical additives on the drainage and retention properties A chemical additives system is optimised using a Dynamic Drainage Jar. This was performed using a pulp slurry. The equipment was modified to also investigate the effect of vacuum on fine fibre retention and drainage time.

In previous phases of this study, thick pulp pads were investigated because the permeability and compressibility can be determined with simple equipment. The behaviour of pulp pads is frequently used by numerous workers to represent the behaviour of thin pulp mats (e.g. 81, 82, 83, 84-86). In this phase, the modified DDJ was also used to obtain additional information on the behaviour of thin bagasse pulp mats, which more closely resembles a Fourdrinier former than a Twin-wire former.

Finally, the effect of chemical additives on pulp pad steady-state and dynamic permeability and compressibility is quantified.

3.1.7. Flow diagram of the experimental and modelling methodology The relationship between sections of the experimental and modelling methodology is shown in Figure 3.1. The numbers in the figure are the phases of the methodology described at the start of section 3.1. This is a theme of this thesis. Chapter 3, the experimental and modelling procedure, and Chapter 4, the results and discussion, proceed in the same order as the methodology.

65 Thomas J. Rainey – A study of bagasse pulp filtration

Phase 1. Bagasse pulp preparation Bagasse preparation Fractionated bagasse (Chemical ‘coarse’ vs ‘medium’ pulp characterisation Phase 2. Physical from mill or diffuser only) and chemical property testing Bagasse pulp

Phase 6. Development of a Bagasse pulp slurry chemical additives With and without flocculants system using a pulp slurry Bagasse pulp pad

Steady-state experiments with bagasse pulp pads Phase 3. Steady-state Phase 4. Steady-state permeability compressibility experiments experiments Obtain S v and  Obtain M and N

Phase 5. Dynamic filtration modeling and experiments with bagasse pulp pads Dynamic Dynamic filtration model compression Use steady-state experiments parameters, S v, , M and N

Model verification

Figure 3.1 Flow diagram of the experimental and modelling methodology for bagasse pulp.

66 Chapter 3- Experimental procedure and modelling

3.2. Bagasse pulp preparation

The preparation and storage of bagasse and pulp created some challenges since bagasse is extremely bulky with a specific mass of 150 kg/m 3. Bagasse also degrades quickly due to the presence of a residual sugar. It was necessary to wash it and dry it as quickly as possible for long-term storage in a large walk in refrigerator at 4 °C. The large number of pulp samples generated in this report are summarised in Appendix B.

The treatment of the bagasse prior to pulping is presented in section 3.2.1. The pulp samples were prepared in Melbourne and QUT using three types of reaction equipment as described in section 3.2.2. The statistical methods used to determine whether there is a difference between populations of pulp samples are provided in section 3.2.3. The effect of bagasse pre-treatment on yield and kappa number is provided in section 4.1. The physical and chemical properties of the pulp are provided in section 4.2.

3.2.1. Collection of raw materials

3.2.1.1. Australian bagasse

As previously mentioned, bagasse was collected from both a sugar diffuser and a sugar mill and fractionated into three fractions ‘coarse’, ‘medium’ and ‘fine’ fractions.

The pre-treatment procedure used in this study is intended to maximise the permeability of Australian bagasse pulp pads and also to minimise degradation of the bagasse for long term storage. The total amount of pith removed (around 43%) was higher than normally used by industry to achieve acceptable bagasse pulp permeability (typically 30%).

Bagasse was collected from CSR Invicta sugar factory. The Invicta milling train consisted of a shredder and five milling units including the final dewatering mill. The Invicta diffuser consisted of a separate shredder, a preliminary milling unit, the diffuser and a final dewatering mill.

67 Thomas J. Rainey – A study of bagasse pulp filtration

On 28 th September 2006 ten 75 L bins were lined with garbage bags. Six bins were filled with bagasse from the final dewatering mill of the milling train. Four were filled with bagasse from the final dewatering mill following the diffuser. Each bin was filled with 10 kg of bagasse. The bagasse in these bins were turned over several times in order to reduce the temperature and moisture content and hence degradation during transport. The bins arrived at QUT, Carseldine Campus on 4 th October 2006.

The bagasse obtained from the sugar mill was from cane species Q208B (B for burnt). The bagasse collected from the diffuser was TellB. It was not possible to collect bagasse of the same variety of cane from both the mill and the diffuser during the visit. As will be shown in Chapter 4, the difference in cane varieties was inconsequential. No difference was found in the pulping kinetics (section 4.1.1) or the permeability and compressibility characteristics (sections 4.3 and 4.4).

The fibre content of the parent cane was measured by factory staff and determined to be 15.6% (wet basis) for both varieties of cane. The fibre content of Australian cane is typically 10% to 17%. The fibre content of the cane was towards the higher end of this range.

The bagasse was washed in copious amounts of water to remove sugar using a cement mixer. The bagasse mixture was drained through a 4 mm wire mesh. The fines in the filtrate were recovered by refiltering the filtrate through the bagasse bed several times. Only 3% of the fines were lost through this washing process.

The bagasse was allowed to dry to 10% moisture, see Figure 3.2. The bagasse piles were rotated with one another for even exposure to the sun.

68 Chapter 3- Experimental procedure and modelling

Bin 1 Bin 2

Bin 3 Bin 4 Bin 5 Bin 6

Bin 7 Bin 8

Bin 9 Bin 10

Figure 3.2 Photograph of bagasse drying outside on tarpaulins.

The washed milled and diffuser bagasse was separated into three fractions prior to pulping using two wire mesh sieves of different aperture sizes, 12.5 mm and 4 mm respectively. Subsamples of around 50 g of bagasse were manually sieved for approximately 3 min to achieve the separation. The three bagasse sizes produced were nominated: ‘coarse’ which accounts for the 25 % of the bagasse that is retained on the 12.5 mm sieve (i.e. +2 mesh); ‘medium’ (i.e. 4.0 mm to 12.5 mm) which accounts for the 35% of the bagasse that passes the 12.5 mm sieve but is retained on the 4.0 mm sieve (i.e. +6 mesh); and ‘fine’ which accounts for around 40 % of the bagasse and passes through the 4.0 mm sieve (i.e. -6 mesh).

The fractionated bagasse samples are shown in Figure 3.3 (a), (b) and (c) together with samples of ‘whole’ (unfractionated) Australian bagasse (d). The ‘coarse’ bagasse (a) contains a much higher content of large chip-like material compared to the ‘medium’ bagasse (b). These definitions of ‘coarse’, ‘medium’,

69 Thomas J. Rainey – A study of bagasse pulp filtration

‘fine’ and ‘whole’ bagasse pulp are used throughout this thesis. The ‘fine’ fraction is assumed to be mainly pith material so this terminology is used interchangeably.

(a) (b)

50 mm 50 mm

(c) (d)

50 mm 50 mm

Figure 3.3 Photographs of (a) ‘coarse’, (b) ‘medium’ and (c) ‘fine’ fractions of Australian bagasse, and (d) Australian ‘whole’ bagasse.

A sample of Australian bagasse was sieved in order to remove 30% of its shortest material. This is typical of overseas industrial depithing operations. The pulp produced from this Australian bagasse is herein referred to as ‘30% depithed’ bagasse pulp.

After washing and fractionating, the bagasse was then stored in a walk-in fridge (4 °C) until it was ready to be pulped.

3.2.1.2. Argentinean bagasse A depithed Argentinean bagasse sample that is used by the company Ledesma Paper Mill to make writing papers was included in the evaluation. Their depithing process removed 30% of the finest material (i.e. the pith). This sample

70 Chapter 3- Experimental procedure and modelling was stored in the fridge but not washed so as not to alter its preparation conditions prior to pulping. The pulp produced from this sample is referred to as ‘Argentinean’ bagasse pulp.

3.2.1.3. Wood material

Samples of Eucalyptus globulus and Pinus radiata wood material were supplied in pulp form by Ensis and the Australian Pulp and Paper Research Institute (APPI) respectively. These organisations are two of Australia’s leading pulp and paper research and development companies. No pre-treatment was performed on these samples. The pulping conditions are provided in section 3.2.2.3.

3.2.2. Pulp sample preparation A large number of pulp samples were required to (i) investigate permeability and compressibility differences between pulp samples originating from different size fractions of bagasse 2 as well as differences in milled and diffuser bagasse pulp, (ii) undertake the required physical property testing and (iii) investigate the effect of chemical additives on the flocculation of pulp fibres.

The large number of pulp samples was particularly important to achieve Objective 1. If the populations were compared with a small number of large cooks, then subtle changes in cooking conditions between the cooks could potentially affect the outcome. To test whether there is a difference between fractionated milled and diffuser bagasse, samples were pulped in an APPI digester containing six 1.5 L cells (discussed in more detail in section 3.2.2.1). This reactor is called a ‘flow-through’ digester herein. Samples of bagasse were cooked in a randomised order.

Several pulp samples were produced in a much larger batch 18.5 L reactor for a number of reasons. The size of the samples produced in the APPI ‘flow- through’ digester were not sufficient for destructive physical property testing (section 3.3). Also, for experiments involving chemical additives (section 3.7),

2 For bagasse with a very high proportion of short fibres, it was not possible to pulp the material because it was difficult to circulate the liquor in the APPI ‘flow-through’ digester.

71 Thomas J. Rainey – A study of bagasse pulp filtration the pulp had to be disposed after each experiment. As such, a much larger batch of pulp was prepared so that subtle differences that may affect pulping experiments could be eliminated as a potential source of error.

Over 60 pulp samples were produced in the course of the project. Each bagasse pulp sample produced was labelled with a unique number which is referred to hereafter in this thesis. The pulping conditions, origin of the bagasse, yield and kappa number for each pulp sample are provided in Appendix B.

Supplementary photographs of the pulping equipment are provided in Appendix C.

3.2.2.1. Bagasse pulping in the ‘flow-through’ digester

The APPI ‘flow-through’ digester consists of six cells into which bagasse is packed. Each cell is 1.5 L. Hot cooking liquor is pumped from a 50 L tank through each of the cells and drains back into the tank. The flow diagram of the equipment is reproduced in Figure 3.4 (136) and a photograph of the equipment is provided in Figure 3.5.

Liquor inlet lines

Digestion cells

Figure 3.4 Sketch of the 6 cell ‘flow-through’ digester at APPI (136).

72 Chapter 3- Experimental procedure and modelling

Inlet liquor lines from common header (valve on each)

Cells

Outlet liquor lines

Figure 3.5 Photograph of the APPI ‘flow-through’ digester showing the 6 digestion cells.

Bagasse was soaked in warm water for 20 min to soften it so that each 180 g sample of ‘medium’ bagasse and 210 g of ‘coarse’ bagasse could be packed into the digester cells. The increase in flexibility is due to the plasticisation of the lignin rather than bending of the sclerenchyma pulp fibres.

Fifty litres of cooking liquor was recirculated through six cells containing 100-200 g of fractionated bagasse (air dry basis). The pulping conditions were 0.4

M sodium hydroxide (approx. 13.8% Na 2O on oven dry fibre) and 0.1%, anthraquinone, AQ, (on oven dry fibre) at 145 °C.

In this reactor, the cells can be independently isolated from the cooking liquor by manual valves. The liquor is heated indirectly by steam. When the liquor reaches temperature, the liquor can be circulated immediately through the material in the cell.

An initial kinetics study was performed to determine the cooking time required to achieve a pulp with a kappa number (i.e. residual lignin content) of 20. A pulp screen was not available during the trials with the APPI digester, so the kappa number was measured on unscreened pulp. The cooking length was varied between 5 min and 70 min. It was found that only 30 min of cooking time was

73 Thomas J. Rainey – A study of bagasse pulp filtration

required. Normally several hours is required to produce wood pulp using this equipment (136). Bagasse pulp is well known to delignify much more quickly than wood chips due to the high reactivity of grass lignins.

The depithed bagasse obtained from Argentina’s Ledesma Mill was also pulped under these conditions for 30 min using the ‘flow-through’ reactor.

At the end of a cook, the pulp was transferred to a standard disintegrator. The pulp was disintegrated for 10,000 rev. The pulp was thoroughly washed with water and dewatered using a very large steel Buchner funnel.

A total of 30 pulp samples were generated in the ‘flow-through’ digester.

3.2.2.2. Bagasse pulping in a batch ‘Parr reactor’ It was not possible to pulp whole (unfractionated) bagasse or the ‘fine’ fractionated material in the APPI ‘flow-through’ digester because the liquor would pool on top of the bagasse and not permeate through the bed of bagasse. Consequently, samples of whole and fine Australian bagasse were pulped to a target kappa number of 20 in the 18.5 L batch reactor at 170 °C for 105 min at a liquor to fibre ratio of 14:1 with a concentration of approximately 0.4 M sodium hydroxide and 0.1% AQ. The Parr reactor is shown in Figure 3.6. The reactor is electrically heated. The time to temperature for the majority of the experiments was typically 45 min - 60 min. 1 kg of bagasse (10%-15% moisture) was loaded into the Parr reactor in each cook. The ‘Parr reactor’ is cooled by ambient water flowing through serpentine cooling coils and takes 60 min to reach a temperature at which the vessel can be safely handled.

74 Chapter 3- Experimental procedure and modelling

Vessel head

Crane for moving vessel head

Temperature controller Heating jacket

Figure 3.6 The QUT 18.5 L Parr reactor.

In addition to the ‘whole’ and ‘fine’ bagasse pulp samples, large quantities of bagasse pulp originating from ‘coarse’ and ‘medium’ fractions of bagasse were produced in this reactor for physical property testing and the tests involving chemical additives.

Pulp produced from ‘30% depithed’ bagasse was also produced in this reactor under these cooking conditions. This pulp is used for benchmarking purposes as it has been depithed to a similar level to that used by overseas commercial operations. This benchmark pulp was cooked in this reactor so as to prevent any pith material from being washed into the liquor. It is acknowledged that this benchmark pulp sample was cooked at a higher temperature than the majority of the pulp samples cooked using the ‘flow-through’ reactor. It was decided that preserving the pith in this benchmark bagasse pulp sample, as could be achieved using the Parr reactor, was very important.

In order to determine whether bleaching had any effect on the permeability and compressibility properties, one of the pulp samples produced using the ‘Parr reactor’ (Sample 56) was bleached using calcium hypochlorite according to Tappi test method UM-206 from 28 brightness to 54 brightness (137).

75 Thomas J. Rainey – A study of bagasse pulp filtration

3.2.2.3. Benchmark wood pulp The two wood pulp samples were supplied by Australian pulp and paper research and development organisations.

Eucalypt pulp was prepared at Ensis, Melbourne, Australia, using an ‘air- bath’ reactor. The wood is loaded into a sealed cell with 2 L volume and the cell is loaded into a pressure vessel and heated with steam. The cooking conditions used to produce the pulp were 11.75% Na 2O on oven dry fibre, sulphidity of 25%, cooking temperature of 165 oC for 2 h. The eucalypt was pulped to a target of 20 kappa.

A sample of kraft pine pulp was obtained from APPI, also in Melbourne. The sample was similarly prepared in an air-bath reactor and pulped to a kappa number of 20 using kraft pulping chemicals. The concentration of the cooking chemicals that were used is not known.

3.2.2.4. Pulp screening Each pulp sample was screened through a 200 )m slotted Packer screen with water recirculation. The pulp samples were not allowed to dry at any stage. The pulp was placed in a dough mixer to break up the pulp in order to make the moisture content homogeneous enabling consistent dry substance measurements to be obtained. The pulp was stored at 25% consistency in a 4 °C refrigerator for the duration of the project.

3.2.3. Test for statistical significance between two populations of pulp samples In some experiments, it was necessary to test whether a sample group was from a single population or two independent populations. For these tests of statistical significance, the mean value of a parameter is compared using Student’s ‘two-sample test’ (e.g. reference 138). Also known as Student’s t test, it is particularly suitable for comparing populations when the sample size is small, such as in this study (139). The test determines whether independently obtained samples are consistent with the null hypothesis that they are from populations with equal means.

76 Chapter 3- Experimental procedure and modelling

Suppose we have two independent populations (x i , i = 1,2,…,n x) and (y j j=1,2,…n j). The pooled estimate of standard deviation between the two samples is

2 2 2 (n x −1)s x + (n y −1)s y s PE = n x + n y − 2

Equation 3.1

Where sPE is the pooled estimate of standard deviation

nx is the number of samples in the first population

ny is the number of samples in the second population

sx is the estimated standard deviation of the first population

sy is the estimated standard deviation of the second population

Equation 2.26 assumes that the values are obtained from one experiment. When an experiment has a limited sample size, repeating the experiment for each sample improves confidence of each datum. Determining the pooled estimate from the average values for each sample over a number of tests, improves confidence in the accuracy of the values for each sample, x i and y i. The estimate of standard deviation for each population is now

' s x ' s y s x = s; y = rx ry

Equation 3.2

where s x’ is the standard deviation of a population of averaged values r is the number of times the experiment is performed. Substituting this value into Equation 3.1 gives

2 2 s x s y (n x −1 ) + (n y −1 ) r r 2 x y s* = n x + n y − 2 Equation 3.3

77 Thomas J. Rainey – A study of bagasse pulp filtration

For determining whether the sample group is from a single or two populations, Student’s Test Statistic,  is:

x − y τ = 1 1 s* + n x n y

Equation 3.4 Where x and y are the average values for the two hypothetical populations. The observed value of  is compared to tables of Student’s Test Statistic to determine statistical significance provided in Appendix D. The tables provide threshold values of  for each degree of freedom and confidence interval. Values of  greater than those in the table mean that the sample group is from two populations for the number of degrees of freedom and desired confidence interval.

3.3. Physical and chemical property testing procedure

The physical and chemical properties of selected bagasse pulp samples were characterised. The chemical composition of several bagasse and bagasse pulp samples was determined as well as eucalypt pulp (section 3.3.1). The pulp physical properties of a ‘coarse’ bagasse pulp (Sample 56) and a benchmark Australian bagasse pulp (Sample 58) were studied at various levels of refining (section 3.3.2) and the results were compared to the findings of other researchers. The fibre length distribution of all pulp samples was determined by a Kajaani Fibre Length Analyser and by a Fibre Quality Analysis unit (section 3.3.3). A microscopy study was undertaken to determine the fibre dimensions including cell wall thickness, lumen diameter and collapse of the fibres (section 3.3.4).

3.3.1. Chemical characterisation of pulp and bagasse The following chemical analyses of bagasse and pulp samples were undertaken using the methods of the National Renewable Energy Laboratory for biomass characterisation (140).

78 Chapter 3- Experimental procedure and modelling

o Total solids in biomass; o Carbohydrates in biomass by High Performance Liquid Chromatography; o Acid-soluble lignin in biomass; o Ash; o Extractives; o Kappa number; and o Pulp yield. The chemical composition of six bagasse pulp samples was analysed as well as a sample of eucalypt pulp. The bagasse pulp samples analysed included ‘coarse’ and ‘medium’ fractions of milled and diffuser bagasse pulp (four samples; 26, 27, 20 and 39), whole bagasse pulp (Sample 53) and pulp from Argentinean depithed bagasse (Sample 32). The parent bagasse material of each of the bagasse pulp samples was also analysed.

The cellulose content is related to the quantities of glucan and xylan in the pulp/bagasse hydrolysate and the hemicellulose content is related to the quantity of arabinan.

3.3.2. Pulp physical property testing Two samples of Australian bagasse pulp were tested at the Central Pulp and Paper Research Institute (CPPRI), in India. CPPRI have significant experience with bagasse pulp and paper testing.

The samples analysed were a ‘coarse’ bagasse pulp (Sample 56) and the ‘30% depithed’ bagasse pulp (Sample 58). Sample 58 is the benchmark sample and Sample 56 is a sample with high permeability (refer Chapter 5). Both samples were produced from Australian bagasse.

The pulp samples were analysed for strength properties that are typically required for photocopier paper, tissue and boxes. The strength properties analysed were tensile, tear, short-span compression and burst strength properties. For these tests, handsheets of 60 g/m 2 were formed. The handsheets were tested after conditioning at temperature 27 ± 1 ºC and a relative humidity of 65 ± 2% according to ISO 5269/1. Test specimens were cut from the handsheets. The

79 Thomas J. Rainey – A study of bagasse pulp filtration tensile and tear tests involve measuring the force required in the direction of the sheet and perpendicular to the sheet respectively before the specimen fails. The compression test involves compressing the specimen until it buckles. The burst test involves clamping a specimen and applying a hydrostatic force, allowing the specimen to bulge, until the specimen fails.

The water retention value (WRV) was also measured. WRV is an important parameter for non-wood pulp as it provides an indication of the ability to dry a sheet of paper. The apparent density of the pulp samples was also determined.

The effect of refining was determined. Pulps were beaten in the laboratory PFI mill to three freeness levels according to the ISO 5264/2 method. Again, handsheets of 60 gsm were prepared according to the ISO 5269/1 method.

3.3.3. Fibre length analysis The fibre length analysis for the majority of the pulp samples as performed on a Kajaani Fibre Analyser FS100 at Petrie Mill, Brisbane, Australia. The results for fibre length produced from this unit are a length weighted basis, i.e.

2 B n i Li Lw = B n i Li

Equation 3.5

th Where L w is the length weighted fibre length, L i is the length of the i fibre, ni is the number of fibres with length L i.

For curl and kink properties, three samples (Sample 56, Sample 58 and Sample 60) were analysed on a Fibre Quality Analyser LDA 96, supplied by Optest Equipment, at the University of British Columbia, UBC. 5000 fibres were analysed for each sample.

The curl index is calculated using the formula

L Curl index = −1 Equation 3.6 ll

80 Chapter 3- Experimental procedure and modelling

where L is the true length of the fibre and l is the apparent length of the fibre (see Figure 3.7).

L l

Figure 3.7 Sketch of a longitudinal section of a pulp fibre.

The kink index is related to the number and magnitude of bends in the fibre.

Apart from the discussion in Chapter 4, some additional fibre length distribution data is provided in Appendix E.

3.3.4. Microscopy investigation The microscopy investigation on the morphology of the pulp fibres was performed by Scion, New Zealand, using a confocal laser microscope. This investigation was performed to gain insight into the shape of both bagasse pulp fibres and eucalypt pulp fibres and how they might behave during pad formation.

Three samples were analysed, a milled ‘coarse’ Australian bagasse pulp (Sample 26), a milled ‘medium’ bagasse pulp (Sample 27) and the eucalyptus pulp. 500 fibres from each pulp sample were chemically dehydrated by solvent exchange through a graded series of water/acetone solutions. Fibres were then mounted in a Spurr’s resin and the resin was allowed to cure before the surface was sectioned and polished for image analysis. The images were analysed using Scion’s image analysis software. A small quantity of chipped and broken fibres as well as contaminants is removed during the image analysis.

Figure 3.8 shows a typical fibre section with the fibre width and thickness dimensions determined in the image analysis. The orientation of the fibre was optimised so as to minimise the fibre area, according to the definitions listed below.

81 Thomas J. Rainey – A study of bagasse pulp filtration

Fibre area (bounded by rectangle) Fibre perimeter

Fibre thickness

Fibre width

Figure 3.8 An image of a bagasse fibre cross section showing fibre width and thickness for the microscopy investigation.

The following measurements were calculated for each fibre, amongst others:

• Fibre width. This is the longest cross-sectional dimension as shown in Figure 3.8.

• Fibre thickness. This is the shortest cross-sectional dimension as shown in Figure 3.8.

• Wall area. The area of the black portion in Figure 3.8.

• Centreline perimeter. The perimeter of a line drawn between the inside and outside walls of the fibre as shown in Figure 3.8.

• Wall thickness. The wall area divided by the centreline perimeter.

• Fibre area. This is the area bounded by a rectangle around the fibre.

• Fibre perimeter. The perimeter of the outside wall of the fibre.

• Lumen area. The area of the lumen inside the inner fibre wall.

• Lumen perimeter. The perimeter of the inside wall of the fibre.

• Collapse ratio. The fibre width divided by the fibre thickness.

• Maximum and minimum wall thicknesses.

82 Chapter 3- Experimental procedure and modelling

These measurements were compiled for each sample of 500 fibre sections. The distributions of these parameters were collected.

Elsewhere in this thesis, Student’s t test is used for statistical comparisons of populations. For the microscopy investigation, a different statistical test was used. For this analysis the variability data were supplied by an external organisation and their statistical test was employed. The results of the image analysis provide the mean of each parameter as well as a ‘Least Significant Difference’ (LSD) between means. If the difference in means of two pulp samples is greater than the LSD, then the samples are significantly different using a 95% confidence interval.

3.4. Steady-state permeability testing equipment and experimental procedure

The primary objective of the steady-state permeability study was to examine the effect of bagasse preparation and processing on pulp permeability properties and to compare the permeability data with the findings of previous workers for wood pulp (e.g. 81) and bagasse pulp (64) .

Australian bagasse from a sugar mill and a diffuser was separated into three size fractions (i.e. ‘coarse’, ‘medium’ and ‘fine’ fractions) prior to chemical pulping. For comparative purposes, the permeability properties of kraft eucalypt pulp, a hardwood pulp with short fibres typically around 0.8 mm in length, were determined as the benchmark for this study. The permeability of several other pulp samples was also measured including pulp made from milled bagasse that has had 30% of the finest material removed (Sample 58), unfractionated milled Australian bagasse (i.e. ‘whole’ bagasse) pulp (Sample 53), and depithed bagasse pulp from Ledesma Sugar, Pulp and Paper Mill in Argentina (Sample 32). Finally, the permeability of a kraft pine pulp, a long fibre pulp typically 3 mm in length, was measured.

The pressure drop and flow rate data from the experiments were used to determine Darcy’s permeability, K, and consequently the specific surface area, S v, and the swelling factor, , an indicator of the strength generation potential during refining, were determined for use in the Kozeny-Carman permeability model (78, 79).

83 Thomas J. Rainey – A study of bagasse pulp filtration

The ‘Kozeny factor’, k, is actually a function of pulp porosity, although a

constant is often used. The optimum values of S v and  depend on whether a constant or a variable k is used. For this study, both constant and variable k was used. Ingmanson and co-workers (81) found that using a variable Kozeny factor resulted in an increase in the prediction for  of around 25% and a decrease in the

prediction for S v of around 7% for wood pulp.

The secondary objective of the permeability experiments was to obtain data for the dynamic filtration model examined.

Pulp permeability was measured in a simple, custom built, experimental cell, hereafter referred to as the ‘permeability cell’.

Figure 3.9 shows the schematic diagram of the experimental equipment assembly which was custom built to obtain the permeability data. A photograph is also provided (Figure 3.10) with the permeability cell highlighted in the bottom right hand corner of the figure. The main feature of the permeability apparatus is a permeability cell made from a Perspex tube with an internal diameter of 41 mm and height of 300 mm. The cell has an airtight seal at the top - a rubber bung that is connected to a manual valve. The bottom is supported by reinforced screen of 100 mesh. The cell is connected to two manometers to measure the pressure drop (p) across two positions of the pulp pad ( l).

30 g of equivalent dry pulp and 3 L of distilled water were added to a disintegrator to make a pulp slurry of 0.9 % consistency. Two litres of this slurry was slowly poured into the permeability cell to form a saturated pad. The slurry was vigorously agitated as it was added to the cell to ensure uniform layering of the pulp fibres in the cell. Although the water supply was not de-aerated, it was consistent in every experiment. The data is similar to that obtained by other workers using de-aerated water (86).

84 Chapter 3- Experimental procedure and modelling

Water level

Constant head tank

Town water supply Overflow

p

Manual valve Cell ID 41 mm

Water layer

Pulp mat l L, P

Q

Figure 3.9 Schematic diagram of the apparatus used for permeability measurements.

85 Thomas J. Rainey – A study of bagasse pulp filtration

Constant head tank

Manometer level

Rubber bung Manual valve

Manometer Permeability offtakes cell Mesh screen

Figure 3.10 Photograph of permeability cell.

The town water supply valve to the constant head tank was opened until the tank overflowed and a constant head was maintained above the manual water valve to the cell. The manual valve was opened and water flowed from the constant head tank through the cell. The manual valve was adjusted until the height in the manometer was constant (typically 5-15 min). The pulp pad height (L) was recorded to determine the pulp concentration for a known pulp mass. The flow rate of the water through the cell was measured (Q) with a measuring cylinder and a stopwatch and the difference in water height between the two

86 Chapter 3- Experimental procedure and modelling manometers was recorded ( p). The pressure drop p applies over the distance between the two manometers, l. The hydraulic compression is negligible so p/ l is extrapolated over the full height of the pulp pad to determine P/ L that is required for the calculation of K using Darcy’s Law (Equation 2.2).

The town water supply temperature was 23 °C. The temperature of the water supply varied only 2 °C during the period of the experiments. The variation of the town water supply temperature did not significantly affect the pulp pad permeability.

Great care was taken to ensure that the pulp pad was constantly saturated with water by maintaining a pool of water above the pulp pad at all times. If the pulp pad dries out, the fibres contract and the pulp pad could become unevenly distributed across the cross section of the cell and channelling of water could occur.

After these measurements at the lowest flow rate were recorded, the flow rate of water through the cell was increased incrementally and the values for p, L and Q were recorded.

Once these measurements were completed the supply of water to the cell was turned off and another 500 mL of pulp slurry was then added to the permeability cell. Values for L, Q, and p were again recorded over a range of flow rates. Finally the remaining pulp slurry was added.

When fully loaded with pulp, the pad was compressed to heights of 210 mm, 180 mm and 150 mm using compressed air. In order to compress the pulp pad, the permeability cell, including the rubber bung was detached from the constant head tank. A compressed air line was attached to the rubber bung (and hence the permeability cell) by a barbed nipple. At this point, the pulp pad is very compressed (>0.1 g/cm 3) and a pool of water above the pulp pad was easily maintained as the compressed air was applied. Obtaining pressure drop and flow rate data over a wide concentration range was important for accurate calculation of S v and .

87 Thomas J. Rainey – A study of bagasse pulp filtration

Sv and  were calculated from the intercept and slope of a graph of concentration against (Kc 2)1/3 as per Equation 2.23.

It was observed during the permeability experiments that at high pulp concentrations (i.e. >0.1 g/cm 3) repeatable results were readily obtained since it was easier to avoid channelling than at low concentrations. Obtaining repeatable results was more challenging in the low concentration range between 0.06 g/cm 3- 0.08 g/cm 3. At these low concentrations, the following problems were occasionally encountered: (i) channelling. This problem could often, but not always, be observed by water ‘fast-tracking’ down the inner walls of the Perspex cell. At lower concentrations, the calculated permeability data obtained was continuously checked by plotting (Kc 2)1/3 against concentration, c. When channelling occurred, the datum was obviously far too high (typically an order of magnitude higher) and the datum was subsequently rejected; and (ii) pulp slurry entrained in the manometer lines. This was overcome by purging the lines.

For the Australian bagasse pulp samples, the permeability experiment was

performed at least twice and the average S v and  are presented in the results section. For the other pulp samples, the permeability experiments were performed

typically five times and the average for S v and  are presented in the results section.

3.5. Quasi steady-state compressibility experimental procedure

The primary objective of the steady-state compressibility study was to examine the effect of bagasse preparation on pulp steady-state compressibility properties and to compare the findings with those for wood pulp (21, 6,7, 8).

The secondary objective of the compressibility study is to verify the steady- state compression model and obtain steady-state compressibility data required for the dynamic filtration model in section 3.6.

A simple, custom made, ‘compression cell’ (this term is used hereafter) was designed, fabricated and mounted to an Instron 5500R capable of a maximum load of 100 kN although for this study the load applied did not exceed 5 kN. Photographs of the cell assembly are shown in Figure 3.11. The engineering

88 Chapter 3- Experimental procedure and modelling drawings are available in Appendix F. The cell is 100 mm in height, the platen is 10 mm thick, resulting in a total possible working height of 90 mm. The platen is fitted with a shamband and Teflon ring to prevent water flowing around the platen, and the platen is drilled with thirty 6 mm holes for the water to evacuate (see Figure 3.11).

Pulp samples were disintegrated to 0.9% consistency. The barrel of the compressibility cell was removed from the base and suspended on a screen of 100 mesh. The disintegrated pulp was added to the barrel of the compressibility cell and the bulk of the water was allowed to drain through the mesh. Once the desired height of pulp in the barrel was reached, the barrel, the supporting screen and the loaded pulp could be transferred to the base and bolted in. The pulp pad remained saturated during the transfer; in practice, this was easy to achieve. The platen of the compressibility cell is then connected to the Instron, ready to commence the compression experiment (see Figure 3.11).

    

 

      
  

(a) (b)

Figure 3.11 Photographs of (a) the loaded compressibility cell with the barrel fixed onto the base and (b) the top platen and the base of the cell when the cell is dismantled.

‘Quasi steady-state’ behaviour is the experimental approximation to the actual steady-state behaviour. This is reached by compressing the pulp pad over a very long time period. During steady-state compression, the permeability effects are insignificant. The hydraulic load (i.e. the head of water above the platen) is

89 Thomas J. Rainey – A study of bagasse pulp filtration

negligible compared to the applied mechanical load, and so the concentration

distribution is uniform throughout the bed. The graph of log(P s) against log(c) is linear. Values of M and N are obtained from the slope and intercept of the graph.

For all of the quasi steady-state compressibility tests, the platen finished compressing the pulp pad 15 mm above the base of the cell. The platen was lowered very slowly over 300 min at a constant rate of 0.25 mm/min (that is, 75 mm over 300 min). The wood pulp samples and the Argentinean bagasse pulp (Sample 32) were compressed several times to obtain average values of M and N. The Instron load and time were logged. The load on the platen was recorded by the Instron and the applied pressure was calculated. The measured load was reduced by the frictional resistance between the Teflon seal and the barrel. This was typically equivalent to 2.5 – 4.5 kPa. This was measured by compressing the cell when loaded with water.

3.6. Dynamic filtration modelling and experimental verification procedure

This development of a dynamic filtration model was performed to assist with the future development of specialised equipment for the processing of bagasse pulp and also because a dynamic model more closely resembles the industrial paper manufacturing process.

Two pulp parameters affect the drainage properties of fibre beds; compressibility and permeability under dynamic conditions (84).

The steady-state permeability and compressibility parameters required for the dynamic filtration model were previously collected (sections 3.4 and 3.5). The model was coded (section 3.6.1) and pulp pad experimental data was obtained under dynamic conditions for comparison and verification of the bagasse pulp dynamic filtration model (section 3.6.2). The verification of the dynamic model followed the sequence,

1. Steady-state permeability tests of depithed bagasse pulp to calculate the

permeability constants (the specific surface area, Sv and swelling factor, ) (section 3.4).

90 Chapter 3- Experimental procedure and modelling

2. Compression tests of depithed bagasse pulp to calculate the steady state compressibility constants, M and N (section 3.5). 3. Calculation of the fibre pressure at the top surface of the pulp pad at higher compression rates using the dynamic model (section 3.6.1). The model uses the physical constants obtained from section 3.4 and 3.5. 4. Dynamic filtration of depithed bagasse pulp for comparison with the predictions of the dynamic model (section 3.6.2).

3.6.1. Dynamic filtration modelling procedure The governing equations (Equation 2.25 to Equation 2.28) were non- dimensionalised, programmed in the language FORTRAN 77 and compiled. FORTRAN 77 was chosen for its compatibility with the library subroutines used to solve the non-dimensionalised governing equation. The derivation of the non- dimensional governing equation from the dimensional governing equation is available in the supplementary modelling material in Appendix A, as is the FORTRAN code. The resolution of the output was 100 increments in height, h, and time, t. The experimental compressibility constants M and N for each pulp sample were converted to m and n for use in the dynamic model. The four physical constants, m, n, S v and  are inputs for the program. Other inputs into the model include the initial pulp concentration and the platen speed.

The program outputs the solidity throughout the height of the cell for many discreet time intervals. For comparison with the experimental data, the predicted solidity at the top platen is determined and converted to fibre pressure (using Equation 2.24). The model predictions using both a constant k (k = 5.55) and a variable k (Equation 2.12) can then be compared with experimental data.

3.6.2. Verification of the dynamic model

The same pulp samples which were tested for their steady-state permeability and compressibility properties were also tested under dynamic conditions. The model was verified with over 20 pulp samples.

The experimental procedure for the dynamic filtration experiments used the equipment and procedure used for the steady-state compression experiments

91 Thomas J. Rainey – A study of bagasse pulp filtration outlined in section 3.5, but with a higher compression rate so that the dynamic effects can be observed. In the dynamic filtration experimental phase, the compression speed was increased by 100 times in most instances to 25 mm/min (that is 75 mm over 3 min) and the load on the platen was recorded and converted to average pressure over the platen.

For the dynamic filtration experiments, the compression cell was loaded to 75 mm in depth, leaving 15 mm clearance to the platen, and compressed to 15 mm. The lower initial height of the pad is required for the dynamic testing because the calculated values of the compressibility constants are valid over the limited range of pressures used in the quasi steady state testing.

The repeatability of the dynamic filtration experiments was investigated using two samples of ‘medium’ diffuser bagasse pulp. The pulp samples were made into pulp pads, compressed under dynamic conditions, slurried again and the experiment was repeated.

A sample was also tested under dynamic conditions before and after bleaching.

3.7. Equipment and procedure for testing the effect of chemical additives

The chemical additives experiments were conducted in three phases. A suitable shear stable chemical additives system was optimised using a DDJ and bagasse pulp slurry. Section 3.7.1 provides the methodology used for optimising a flocculant system for a bagasse pulp slurry with a DDJ (DDJ equipment has already been described in length in section 2.4.4). The DDJ was then modified to investigate the performance of the chemical additive under vacuum. The modified DDJ was used to obtain additional information on the behaviour of thin pulp mats, without chemical additives (section 3.7.2). Finally, the chemical additives were used to make pulp pads. The steady-state permeability and compressibility experiments and dynamic filtration experiments were repeated (section 3.7.3). Data obtained using the DDJ was collected in duplicate. The work program for this section of work is outlined in Figure 3.12. Up until this point, all the

92 Chapter 3- Experimental procedure and modelling permeability and compressibility testing was performed without chemical additives.

1. Develop a shear stable flocculant system for a bagasse pulp slurry Use a DDJ looking at shear only on pulp slurry (Section 3.7.1)

2. The effect of vacuum on bagasse pulp slurry flocculation with and without the flocculant system developed in (1) using a modified DDJ (Section 3.7.2)

3. The effect of the flocculants on pulp pad steady-state and dynamic permeability and compressibility Pulp pads made using the flocculant system developed in (1) and measured in the permeability and compressibility cells (Section 3.7.3)

Figure 3.12 Flow diagram of the experimental program for chemical additives.

Four types of bagasse pulp produced in the 18.5 L batch Parr reactor were investigated; a ‘whole’ bagasse pulp (Sample 53); a depithed Australian bagasse pulp (30% of shortest material removed as “pith” prior to pulping, Sample 58); a ‘coarse’ bagasse pulp (Sample 56); and a ‘medium’ bagasse pulp (Sample 60).

The pulping conditions were 90 min, 15% Na 2O, 0.1% AQ, at 170 °C.

A range of additives used for pulp and paper manufacture were obtained from Ciba Specialty Chemicals. Ciba recommended Percol 182, a high molecular weight cationic polyacrylamide (CPAM) in conjunction with Hydracol ONZ, a modified bentonite microparticle, as the most effective chemical additives based on their own work. Hence, this study only optimised one chemical additives system.

93 Thomas J. Rainey – A study of bagasse pulp filtration

Up until this point in the study, the permeability and compressibility of thick pulp pads was studied. In reality, industrial paper manufacture actually involves water draining through thin pulp mats. Thin pulp mats were produced, without using chemical additives, in the modified DDJ. The drainage of pulp slurry through thin pulp mats provided complementary information to the pulp pad filtration data collected in the previous phases.

3.7.1. Methodology – Effect of shear The efficacy of the flocculants was tested using a DDJ (Figure 2.6) for their suitability in bagasse paper manufacture. Their efficacy was quantified using fines retention in this part of the study. CPAM was tested in the range 0.01% to 0.5% (on dry fibre) and the bentonite was tested from 0% to 1.6% (on dry fibre). Tappi test method T 261 cm-00 was followed for measuring the retention of fines (141). A standard 76 )m screen was used.

500 mL of pulp slurry was made up to 0.1% consistency. The pinch valve at the base of the vessel, below the screen, was opened for 30 s and the fines in the filtrate (typically 120 mL) were collected and measured by filtering the filtrate through a GP-C glass microfiber filter paper. The experiments were conducted over a range of stirrer speeds from 500 rpm to 1500 rpm as recommended by the test method.

To measure the total quantity of fines, 500 mL of pulp slurry at 0.1% consistency was washed with several quantities of wash water containing Tamol 182 dispersant until the filtrate was transparent. This is in accordance with the test method. The determination of the total quantity of fines using this method is required for calculating the percentage of fines retained during experiments with CPAM and bentonite.

The addition rate of the chemical additives were optimised on a sample of ‘whole’ bagasse pulp. The optimum addition rate for the ‘whole’ bagasse pulp was then used for the other pulp samples investigated, i.e. ‘coarse’ bagasse pulp, ‘medium’ bagasse pulp and the benchmark ‘30% depithed bagasse pulp.

94 Chapter 3- Experimental procedure and modelling

3.7.2. Methodology – Effect of vacuum Industrially, not only is shear applied during paper manufacture but vacuum is also applied. There are no standard test methods although numerous attempts have been made to simulate both shear and vacuum in the laboratory (Chapter 2).

The DDJ was modified to allow the pulp suspension to dewater under a controlled vacuum. The DDJ was connected to a small filtrate vessel which is under vacuum, supplied by a small vacuum pump. The vacuum level was measured using a pressure transducer that sent a signal back to the PLC. The PLC regulates the position of a bleed valve to control the vacuum level. The flow rate was measured by a 2000 g set of scales with an analogue output. The data output from the scales and the pressure transducer were logged. A diagram of the setup is shown in Figure 3.13 and a photograph is provided in Figure 3.14. The experimental setup closely resembles that described by Forsberg (104).

Data logger Bleed line

DDJ PLC

Vacuum Receiver PT Pump

Scales

Figure 3.13 Diagram of modified Dynamic Drainage Jar to measure the drainage properties of pulps.

95 Thomas J. Rainey – A study of bagasse pulp filtration

Stirrer Vacuum line Controllers and data logging equipment Pressure transducer

Filtrate r eceiver vessel Vacuum controller solenoid

DDJ

Filtrate line Vacuum bleed line Digital weigh scales Flowmeter (logged)

Figure 3.14 Photograph of the modified dynamic drainage jar with vacuum control and data logging.

The vacuum was varied between 0 kPa and 40 kPa. Applying even a small vacuum to the DDJ resulted in the entire amount of water in the slurry (i.e. almost all of the 500 mL) passing through the screen in well under the 30 s required by the Tappi test method. Tappi test method T 261 cm-00 was modified so that the experiment ended when there was no water level in the DDJ (i.e. it had all passed through the screen to become filtrate). The time for the water to pass through the screen was recorded and the fines retention was calculated.

The effect of vacuum on the bagasse pulp fines retention and drainage time was studied both with and without CPAM and bentonite drainage aids.

The fines retention data obtained using this method are not comparable with the fines retention data presented in the previous section. The formation of a pulp pad using the modified method increases the fines retention when compared to the standard Tappi method.

96 Chapter 3- Experimental procedure and modelling

3.7.3. Methodology – Effect of chemical additives on permeability and compressibility. The procedure for measuring the steady-state and dynamic permeability and compressibility in sections 3.4, 3.5 and 3.6 were repeated using the four types of bagasse pulp used in the study of chemical additives (i.e. samples 53, 56, 58 and 60) but with the addition of the CPAM and bentonite dual additive system optimised in section 3.7.1. The required concentrations of flocculants were determined (see section 4.6).

For both the permeability and compressibility experiments, the chemical additives were added to the pulp slurry immediately prior to loading into the respective equipment. The CPAM was added first and the slurry was stirred with a large spatula for 30 s, followed by the addition of bentonite.

3.8. Summary of the experimental investigation

The washing, drying and cold storage of bagasse were necessary to minimise degradation of the bagasse. This was undertaken as quickly as possible once the bagasse was delivered from the sugar factory. Turning the bagasse over at the factory in order to cool it quickly from the processing temperature of the milling train is also thought to reduce degradation. The large volume of bagasse required for this thesis also presented logistical challenges.

A large number of bagasse pulp samples were produced in a ‘flow-through’ reactor in Melbourne. In order to pack the maximum amount of material into the digester, it was necessary to impregnate bagasse with hot water to make the bagasse more flexible. This made it easier to pack bagasse into the cells.

The chemical characterisation and the majority of the fibre length distribution analysis was conducted in Brisbane. The response of the pulp to beating was undertaken in India as the pulp refining equipment was not available in Queensland. The microscopy work was conducted in New Zealand by Scion as the expertise in pulp fibre analysis was not available here.

97 Thomas J. Rainey – A study of bagasse pulp filtration

Three types of reactor were necessary to undertake the work program. The ‘flow-through’ digester was used mainly for comparing populations of pulp samples in compressibility and permeability experiments. The 18.5 L ‘Parr reactor’ was used for preparing large quantities of stock pulp. Pulp prepared in this reactor was used for destructive testing such as physical property testing and testing with chemical additives. The benchmark wood species supplied were produced with an ‘air-bath reactor’.

Three types of experimental equipment were constructed for this thesis, namely a simple ‘permeability cell’, a simple ‘compressibility cell’ and a ‘modified DDJ’.

The ‘permeability cell’ was used for measuring the steady-state permeability parameters, S v and , of bagasse and wood pulp pads.

The compressibility cell was used initially to measure the steady-state compressibility parameters M and N of a bagasse and wood pulp pads. Quasi steady-state conditions were reached by compressing the pulp pad over a very long time. The compressibility cell was then used to measure the dynamic filtration properties of a pulp pad under a constant rate of compression. The load on the pulp pad was compared to the predictions of the dynamic filtration model generated in FORTRAN 77 using the steady-state permeability and compressibility parameters.

Finally, the modified DDJ was used to optimise a suitable shear-stable chemical additives system for a bagasse pulp slurry. The chemical additives were added to the slurry used to make pulp pads in the permeability and compressibility experiments and the effect of chemical additives on the steady-state permeability and compressibility parameters were measured. The effect on the dynamic filtration was also measured in the compressibility cell. The modified DDJ allowed for complementary information to be collected using thin pulp mats.

98 Chapter 4- Results and discussion

Chapter 4 Results and discussion

This chapter presents the findings of the investigation into bagasse pulp filtration, comparing the permeability and compressibility data of Australian bagasse pulp with numerous benchmark pulp samples and the findings of previous workers, such as El-Sharkawy and co-workers for bagasse pulp (64), and Ingmanson for wood pulp (82). The effect of bagasse preparation and flocculants affects the permeability and compressibility properties of a bagasse pulp pad. Of particular importance are the steady-state permeability parameters, the specific surface area (S v) and the swelling factor ( ) and the compressibility factors M and N. These parameters are independent of pulp concentration.

The dynamic filtration model developed in Chapter 3 is validated. Supplementary information is provided to assist with identifying potential bagasse paper products.

Similarly to Chapter 3, this chapter proceeds in the same order as the research methodology outlined in section 3.1. An analysis of the kappa number and yield data obtained during the pulping experiments with the ‘flow-through’ reactor is provided (section 4.1). The chemical character of the bagasse pulp was determined and compared to the parent bagasse. The physical properties of the

99 Thomas J. Rainey – A study of bagasse pulp filtration bagasse pulp are compared to the findings of previous workers. The fibre morphology is also measured (section 4.2). The steady-state permeability (section 4.3) and compressibility (section 4.4) of bagasse pulp pads was investigated. This information was used to determine whether the fraction of bagasse or the mode of juice extraction has a measurable effect on permeability and/or compressibility. The steady-state permeability and compressibility parameters for bagasse pulp were used in the dynamic model developed in this study. The output of the model is compared to experimental data obtained under dynamic filtration conditions (section 4.5). A suitable flocculant system was optimised with a DDJ using a pulp slurry. The effect of vacuum on the drainage time of a bagasse pulp slurry was examined. The effect of chemical additives on the permeability and compressibility constants of a pulp pad was quantified (section 4.6).

4.1. Results of bagasse chemical pulping

In order to achieve a pulp with a kappa number of 20, kinetics experiments were undertaken using the ‘flow-through’ reactor to determine the required cooking time (section 4.1.1). The effect of pre-treatment conditions on the yield (section 4.1.2) and kappa number (section 4.1.3) were examined. A summary of the findings of the bagasse chemical pulping study is provided in section 4.1.4.

4.1.1. Bagasse pulping kinetics The cooking conditions for the kinetics experiments were 0.4 M caustic soda and 0.1% AQ on dry fibre at 145 °C. The pulping time was varied between 6 min and 70 min. Screening of the pulp was not possible at APPI. Figure 4.1 shows the effect of cooking time on the unscreened kappa number of the ‘medium’ milled Q208B bagasse pulp produced in the flow-through reactor. The kappa number decreased linearly with increasing cooking time. This chemical concentration had been previously successful for cooking bagasse in a previous study (68). Previous work had established that the cooking time for eucalypt using the flow-through reactor is 3 h - 5 h (136) indicating that bagasse is far more easy to pulp compared to eucalypt.

100 Chapter 4- Results and discussion

30.0

25.0

20.0

15.0

10.0 Kappanumber, -

5.0

0.0 0 10 20 30 40 50 60 70 80 Pulping time, min

Figure 4.1 Effect of cooking time on the kappa number of ‘medium’ milled Q208B unscreened bagasse pulp.

The milled and diffuser bagasse required similar cooking conditions to achieve a kappa number of 20 on unscreened material3. From the kinetics study it was established that a cooking time of 30 min was adequate to achieve a kappa number of 20.

When the pulped samples were later screened with a Packer screen (200 )m slots), the rejects was in the range 3% to 7% of total pulp weight.

Data on screen rejects are available in the summary of the pulp samples produced for this study (i.e. Appendix B).

4.1.2. Effect of bagasse pre-treatment on Australian bagasse pulp yield The effect of the two pre-treatment variables on the pulp yield, i.e. the fraction of bagasse (coarse or medium fractions) and the method used to obtain the bagasse (i.e. milled or diffuser extraction process) is presented in Table 4.1. These pulp samples were prepared under identical conditions in the ‘flow-through reactor’, 30 min at 145 °C. The average values presented are for Samples 20-43 (excluding the bagasse from Argentina, Samples 32 and 37). Each of these

3 The kappa number of the screened samples were 3-5 units higher than the unscreened samples.

101 Thomas J. Rainey – A study of bagasse pulp filtration

samples is classified as being derived from four categories, ‘coarse’ bagasse from a mill, ‘medium’ bagasse from a mill, ‘coarse’ bagasse from a diffuser and ‘medium’ bagasse from a diffuser. The variables were tested for statistical significance using Student’s pooled t-test at a 95% confidence interval.

The fraction of bagasse used (‘coarse’ or ‘medium’) had a significant effect on pulp yield for both the milled and diffuser bagasse, as shown by the high  (i.e. Student’s test statistic) values. The pulp yield of ‘coarse’ bagasse was higher than

that for ‘medium’ bagasse. The value of PE for pulp yield is very small (1.3% for milled bagasse population and 1.8% for diffuser bagasse population).

Although ‘coarse’ diffuser bagasse had 1.5% higher pulp yield than ‘coarse’ milled bagasse, this was found not to be statistically significant implying that the method of bagasse preparation was not a factor.

Table 4.1 Summary of average bagasse pulp yield fraction obtained in the ‘flow-through’ reactor.

Milled, % Diffuser, % (number of (number of samples) samples)

Coarse 54.04 (6) 55.71 (3) Medium 50.15 (5) 50.66 (4)  PE 1.31 1.83  4.909 3.614

The overall average pulp yield for Australian bagasse samples was 52.5%. The screened rejects were 3% - 7%. However, the screened yield for the Argentinean sample was much higher, 61.8%. The difference between the Australian pulp and Argentinean pulp may be related to differences in cane variety.

The average pulp yield for Australian bagasse obtained is slightly lower than found by previous workers, perhaps due to the reasonably high level of screened rejects or simply due to the type of digester used in pulping. Paul and

102 Chapter 4- Results and discussion

Kasiviswanathan (70) reported screened pulp yield of 54.4% with 0% screen rejects for a highly depithed soda pulp. Giertz and Varma (4) reported 51% pulp yield with screen rejects of 7.6%. This was increased to 56.9% when increased cooking time to reduce the screened rejects to 2%.

4.1.3. Effect of bagasse pre-treatment on bagasse pulp kappa number Student’s t test, as in the previous section, was used to analyse the kappa number of pulp samples originating from different bagasse preparation methods. The average kappa number of ‘coarse’ bagasse pulp was 2 units higher than that for ‘medium’ bagasse pulp (Table 4.2). As PE for the kappa number was very low there was a statistically significant difference in kappa number at a 95% confidence interval between the ‘coarse’ and ‘medium’ bagasse pulp. This is supported by the high  value. The increase in residual lignin content for ‘coarse’ bagasse pulp accounted for a small part (0.3%) of the 4% increase in the pulp yield between the bagasse fractions. No statistically significant difference in kappa number was observed between the pulp obtained from the diffuser bagasse and the pulp obtained from milled bagasse for either the ‘coarse’ or ‘medium’ fractions.

Table 4.2 Summary of average bagasse pulp kappa number in the ‘flow- through’ reactor.

Milled, - Diffuser, - (number of samples) (number of samples)

Coarse 25.2 (6) 25.8 (3) Medium 23.3 (5) 23.5 (4)  PE 1.01 1.00  2.97 3.00

4.1.4. Summary of bagasse pulping analyses A brief kinetics study that only considered time as a variable was performed on the delignification of Australian bagasse in the ‘flow-through’ reactor. The chemical concentration was 0.4 M caustic and 0.1% AQ and the temperature was

103 Thomas J. Rainey – A study of bagasse pulp filtration

145 °C. It was found that a cooking time of 30 min was required to make bagasse pulp with an unscreened kappa number of 20.

Fractionation of bagasse had a significant effect on pulp yield and kappa number.

The bagasse pulp yield and the pulp’s kappa number were not affected by whether the pulp originated from bagasse was processed by a mill or a diffuser.

4.2. Results of physical and chemical property testing

In this section, the results of the pulp chemical and physical properties are presented and discussed (section 4.2.1 and section 4.2.2). The fibre length distribution data is provided in section 4.2.3. The findings of the microscopy investigation are shown in section 4.2.4. The chemical and physical property testing are summarised in section 4.2.5.

4.2.1. Pulp chemical analysis results The results from the chemical analysis of the bagasse and pulp samples are presented in Table 4.3 along with those of eucalypt pulp. All samples had negligible quantities of Dichloromethane (DCM) extractives. The acid insoluble lignin content was typically 21% in bagasse and less than 3% for the pulp. Both the pulp and bagasse had around 1% acid soluble lignin. The lignin content is consistent with the pulp kappa number (Appendix B).

The ash content of the whole bagasse (6.9%) was significantly higher than for the ‘coarse’ and ‘medium’ fractions of the bagasse (1.8%-2.5%). Depithing the bagasse has the added effect of reducing the ash content. Depithing removed some fine dirt that was entrained in the whole bagasse. This effect has been noted by previous workers, for example, Paul and Kasiviswanathan (70). For the fractionated bagasse samples that were generated using the ‘flow-through’ reactor, around 75% of the ash was removed during pulping. Less than 20% of the ash from the whole bagasse produced in the ‘Parr’ reactor was removed during pulping. This is believed to occur in the ‘flow-through’ reactor by liquor washing the ash out of the pulp. The geometry of the ‘flow-through’ reactor is more conducive to circulation of liquor through the bed of bagasse.

104 Chapter 4- Results and discussion

The glucan content of the bagasse pulp hydrolysate was increased slightly by fractionating the bagasse prior to pulping from 65.7% for the whole bagasse pulp up to 75% for ‘coarse’ diffuser pulp. The diffuser pulp had slightly higher glucan content than the milled bagasse pulp (around 69%).

The arabinan content of all the bagasse pulp samples was similar (mainly 4- 5%).

The depithed Argentinean bagasse had a lower glucan content and higher arabinan content than the fractionated Australian bagasse pulp. However this did not translate to any difference in the pulp composition.

The chemical composition of the eucalypt pulp hydrolysate is unremarkable except to note that it has a higher glucan content and lower arabinan content than any of the bagasse pulp samples. This result was expected because eucalypt is grown primarily for its fibre content, unlike Australian sugarcane.

105 Thomas Rainey J. – A of study bagasse filtrati pulp 106

Table 4.3 Chemical analysis of bagasse, bagasse pulp and eucalypt pulp.

%DCM %Acid %Acid %Ash on Sample extractives Insoluble soluble OD %Glucan %Xylan %Arabinan on air dry wt Residue lignin bagasse

Milled coarse bagasse (parent of Sample 26) 0.42% 21.05 1.02 2.245 45.6 27.2 2.2 Milled medium bagasse (parent of Sample 27) 0.49% 21.45 1.03 2.588 40.5 24.3 3.4 Diffuser coarse bagasse (parent of Sample 20) 0.45% 21.44 1.01 1.784 42.4 24.2 3.8 Diffuser medium bagasse (parent of Sample 39) 0.34% 21.69 0.99 2.477 40.9 24.3 5.8 Bagasse Bagasse Argentinean depithed bagasse (parent of Sample 32) 0.79% 21.29 0.99 2.330 37.0 23.7 7.1 Whole bagasse (parent of Sample 53) 0.48% 24.16 0.96 6.869 38.9 22.4 6.9

Milled coarse pulp (Sample 26) 0.17% 3.00 0.93 0.484 68.4 23.3 4.1 on Milled medium pulp (Sample 27) 0.19% 2.42 0.94 0.659 69.2 23.6 2.7 Diffuser coarse pulp (Sample 20) 0.18% 2.32 0.97 0.378 73.3 25.3 4.6 Diffuser medium pulp (Sample 39) 0.32% 2.60 0.96 0.551 75.3 25.4 5.9 Argentinean bagasse pulp (Sample 32) 0.46% 3.42 0.90 0.862 71.8 26.9 4.2 Bagasse pulp Bagasse Whole bagasse pulp (Sample 53) 0.15% 1.43 0.95 5.704 65.7 23.9 4.1

Eucalypt pulp 0.24% 2.60 1.04 0.799 77.7 23.2 1.0

106 Chapter 4 - Results and discussion

4.2.2. Pulp physical property results For this study, only one bagasse pulp (‘coarse’ pulp, Sample 56) was evaluated for its physical properties. The results presented in Table 4.4 are compared to the benchmark “30% depithed” Australian bagasse pulp (Sample 58). Additional comparisons were also conducted with the findings of previous workers.

Table 4.4 Physical properties of a ‘coarse’ bagasse pulp with a benchmark Australian bagasse pulp (142).

Benchmark bagasse ‘Coarse’ bagasse pulp Property pulp; ‘30% depithed’ (Sample 56) pulp (Sample 58) 0 1000 2000 0 500 1000 Amount of PFI refining (rev) (rev) (rev) (rev) (rev (rev)

Freeness CSF (mL) 615 410 290 485 250 200

Tensile Index (Nm.g) 70.2 73.4 76.0 74.0 81.5 82.5

Tear Index (mN.m 2/g) 7.05 6.20 5.60 5.60 4.35 4.30

Burst Index (kPa.m 2/g) 3.50 3.80 4.25 3.60 4.50 5.35

Short Span Compression 31.2 32.1 34.0 32.6 35.0 37.7 Index (kNm/kg)

Water Retention Value (%) 255 262 281 274 287 292

Apparent Density (g/cm 3) 0.67 0.72 0.75 0.60 0.72 0.81

Fibre Strength Index 10.5 - - 9.0 - -

The ‘coarse’ bagasse pulp (Sample 56) starts with a much higher freeness than the benchmark pulp (Sample 58, Table 4.4) as would be expected from its higher permeability (see section 4.3).

107 Thomas J. Rainey – A study of bagasse pulp filtration

In comparison to the benchmark Australian bagasse pulp, the ‘coarse’ bagasse pulp has similar tensile strength for a given freeness. For both pulp samples, refining, as shown in Figure 4.2, only made a modest improvement in tensile strength (+10%). The Australian benchmark pulp had slightly higher tensile strength than reported by most previous workers (4, 70). The pulp had lower tensile strength than reported by Gartside and co-workers (28).

The ‘coarse’ bagasse pulp had much higher tear strength than the benchmark pulp but for both samples, as shown in Figure 4.3, refining had a significant detrimental effect on its tear index (-20%). The Australian bagasse pulp had tear strength similar to those reported by previous workers (4, 70).

As shown in Figure 4.4, ‘coarse’ bagasse pulp had similar burst strength to the benchmark pulp, but higher than the findings of other workers (4). Refining was moderately effective for the burst index of ‘coarse’ bagasse pulp (+21%) but was extremely effective for the benchmark pulp (+49%). The datum from Gartside and co-workers (28) are unusually high and may be as a consequence of the much longer fibre length of their pulp. It is noted that the bagasse pulp used by Gartside and co-workers had a longer fibre length, typically 1.38 mm for most species of cane (although one variety is reported to be as long as 1.55 mm) than the bagasse pulp in this study (~1 mm).

In this study, tensile and burst strengths did not improve by changing the treatment conditions which is a different finding to that reported by Paul and Kasiviswanathan (70). In this study, tear improved dramatically by changing the pre-treatment conditions.

108 Chapter 4 - Results and discussion

120

100

80

60

Sample 56 - 'Coarse' bagasse pulp 40 Sample 58 - 'benchmark bagasse pulp

Tensile (Nm/g) Index Tensile Gartside and coworkers Giertz and Varma 20 Paul and Kasiviswanathan Linear (Sample 56 - 'Coarse' bagasse pulp) 0 0 100 200 300 400 500 600 700 Canadian Standard Freeness (ml)

Figure 4.2 Tensile index as a function of freeness.

8

7

/g) 6 2 5

4

3 Sample 56 - 'Coarse' bagasse pulp Sample 58 - benchmark bagasse pulp Gartside and coworkers Tear Index (mN.m 2 Giertz and Varma Paul and Kasiviswanathan 1 Linear (Sample 56 - 'Coarse' bagasse pulp) 0 0 100 200 300 400 500 600 700 Canadian Standard Freeness (ml)

Figure 4.3 Tear index as a function of freeness.

109 Thomas J. Rainey – A study of bagasse pulp filtration

7

6 /g) 2 5

4

3

2 Sample 56 - 'Coarse' bagasse pulp

Burst Index (kPa.m Sample 58 - benchmark bagasse pulp Gartside and coworkers 1 Paul and Kasiviswanathan Linear (Sample 56 - 'Coarse' bagasse pulp) 0 0 100 200 300 400 500 600 700 Canadian Standard Freeness (ml)

Figure 4.4 Burst index as a function of freeness.

The benchmark pulp had slightly better compression properties than the ‘coarse’ bagasse pulp (Figure 4.5). Refining provided a minor improvement to compressive strength. The ‘coarse’ bagasse pulp had better WRV than the benchmark pulp (Figure 4.6). Refining was slightly detrimental to WRV. The density of the benchmark pulp was initially better than the ‘coarse’ bagasse pulp but deteriorated rapidly when refined (Figure 4.7).

The short-span compression, WRV and density of the bagasse pulp in this study were not compared with previous workers as the associated pulp freeness is not reported in other literature.

110 Chapter 4 - Results and discussion

40 38 36 34 32 30 28 26 Sample 56 - 'Coarse' bagasse pulp 24 Sample 58 - benchmark bagasse pulp 22 20 Short span compression index(kN.m/g) 0 100 200 300 400 500 600 700 Canadian Standard Freeness (ml)

Figure 4.5 Short span compression as a function of freeness.

300

280

260

240

Sample 56 - 'Coarse' bagasse pulp

Water retention value, % 220 Sample 58 - benchmark bagasse pulp

200 0 100 200 300 400 500 600 700 Canadian Standard Freeness (ml)

Figure 4.6 Water Retention Value as a function of freeness.

111 Thomas J. Rainey – A study of bagasse pulp filtration

0.9 0.8 ) 3 0.7 0.6 0.5 0.4 0.3 Sample 56 - 'Coarse bagasse pulp 0.2 Apparent density (g/cm Sample 58 - benchmark bagasse pulp 0.1 0 0 100 200 300 400 500 600 700 Canadian Standard Freeness (ml)

Figure 4.7 Density of bagasse pulp as a function of freeness.

4.2.3. Fibre length distribution analysis Table 4.5 provides a summary of the average fibre length of the samples analysed mainly using the FS100 unit. The order of decreasing average fibre length is ‘coarse’ (1.09 mm) > ‘medium’ (0.95 mm) > ‘fine’ (0.52 mm). The presence of short pith fibres reduced the average fibre length of the ‘whole’ bagasse pulp (Sample 53) and the ‘30% depithed’ bagasse pulp (Sample 58). The Argentinean bagasse pulp (Sample 32) has the same average fibre length as the ‘30% depithed’ Australian bagasse pulp (Sample 58). All bagasse pulp samples have a longer fibre length than the eucalypt pulp (0.77 mm), apart from the ‘fine’ bagasse pulp. Pine pulp has the longest fibre length (2.65 mm). There was no difference between diffuser and mill bagasse pulp.

Table 4.5 also presents a summary of the fines content. The FS100 unit reported this information as the length of the first decile of the population, i.e. the more fines, the shorter the length of the smallest 10% of fibres. It is noted that every bagasse pulp sample have a higher proportion of short fibres than the eucalypt pulp.

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Table 4.5 Summary of fibre length analyses using a Kajaani FS100 on a length weighted basis.

Average Maximum length of Pulp sample fibre the shortest 10% of length, mm fibres, mm 'coarse' (average for 1.09 0.31 all samples) 'medium' (average for 0.95 0.27 all samples) 'fine' (Sample 51) 0.52 0.11 ‘whole' (Sample 53) 0.8 0.21 Bagasse pulp with 30% fibre removal 0.965 Not available (Sample 58) * 'Argentinean bagasse' 0.96 0.23 (Sample 32) Eucalypt 0.77 0.39 Pine pulp 2.65 0.65 *sample analysed on FQA at UBC. The maximum length of the smallest 10% of fibres is not available on this unit.

Figure 4.8 shows the fibre length distribution of Australian pulps derived from fractionated bagasse, with those of Argentinean and eucalypt pulps. The figure shows that the fraction of fibres shorter than 0.3 mm in length for bagasse pulp is far higher than that for the eucalypt pulp. However, the bagasse pulp samples have more fibres greater than 1.3 mm in length. The ‘coarse’ and ‘medium’ bagasse pulp samples often have a bimodal distribution which is more pronounced in the ‘coarse’ bagasse samples than the ‘medium’ bagasse samples; a curious observation. More data is available in Appendix E.

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20

15

10

5

Percentlength fraction (%) 0 0 0.5 1 1.5 2 2.5 Fibre length (mm) Eucalypt Argentinean bagasse pulp (Sample 32) Pulp from coarse bagasse material (Sample 20) Pulp from medium bagasse material (Sample 30) Pulp from fine material (Sample 51)

Figure 4.8 Fibre length distribution of pulp samples including ‘coarse’ ‘medium’ and ‘fine’ bagasse pulp, bagasse pulp from Argentina and eucalypt pulp.

The results for curl and kink index are presented in Table 4.6 as they were produced on a FQA. The curl and kink index for the ‘medium’ bagasse pulp was slightly lower than the ‘coarse’ bagasse pulp. It is presumed that the higher level of mechanical damage may give appreciably higher curl and kink index for the ‘medium’ bagasse pulp fibres. Both the coarse and medium bagasse pulp fibres were found to have a lower kink index than the 30% depithed bagasse pulp and slightly lower curl.

Table 4.6 Curl and kink index measurements for bagasse pulp samples

Curl, length Kink index (mm -1 ) weighted basis (-)

Coarse bagasse pulp (Sample 56) 0.055 0.78

Medium bagasse pulp (Sample 60) 0.045 0.65

30% depithed bagasse pulp (Sample 58) 0.079 1.24

114 Chapter 4 - Results and discussion

4.2.4. Microscopic analysis

Confocal laser microscope and image analyses were used to obtain additional information about fibre morphology. Over 500 fibre sections were analysed for each of three pulp samples, ‘coarse’ milled bagasse (Sample 26), ‘medium’ milled bagasse (Sample 27) and the eucalypt pulp. Some of the key results of the microscopy investigation are reported in Table 4.7.

Table 4.7 Results of microscopy study using a confocal laser microscope and image analysis (143).

Bagasse pulp Bagasse pulp derived from derived from Least Significant Eucalypt the coarse the medium Difference (LSD) pulp fraction of fraction of between means milled bagasse milled bagasse Fibre width ( )m) 20.2 20.7 18.6 0.820 Fibre thickness ( )m) 13.9 12.7 11.6 0.365 Wall thickness ( )m) 5.13 4.72 4.19 0.151 Fibre area ( )m2) 214 200 159 12.4 Fibre perimeter ( )m) 68.5 67.6 60.9 2.26 Wall area ( )m2) 186 169 132 9.65 Lumen area ( )m2) 31.0 27.9 26.3 4.41 Collapse ratio (-) 1.48 1.66 1.63 0.0591 Minimum wall thickness 3.46 3.18 2.75 0.126 ()m) Maximum wall 7.03 6.70 6.09 0.243 thickness ( )m)

The fibre widths of the ‘coarse’ and ‘medium’ pulp samples were around 20.5 )m. The difference between the means of the two samples was less than the Least Significant Difference, so there is no statistically significant difference in fibre width between the ‘coarse’ and ‘medium’ bagasse pulp samples. The bagasse pulp width was slightly wider than the eucalypt pulp, 18.55 )m.

The ‘coarse’ bagasse pulp fibres were significantly thicker (13.86 )m) than the ‘medium’ bagasse pulp fibres (12.67 )m). Fibres from both bagasse pulp

115 Thomas J. Rainey – A study of bagasse pulp filtration

samples were thicker than those from the eucalypt pulp sample, 11.63 )m. Similarly, the fibre walls of the ‘coarse’ bagasse pulp fibres (5.13 )m) were significantly thicker than for the ‘medium’ bagasse pulp fibres (4.72 )m) and the eucalypt pulp fibres (4.19 )m).

The ‘coarse’ bagasse pulp fibres had a higher wall area (186 )m2) than the ‘medium’ bagasse fibres (169 )m2). The fibres from both bagasse pulp samples had much higher wall area than the eucalypt pulp sample (132 )m2). The lumen area for the ‘coarse’ bagasse pulp res (31.0 )m2) was found to be slightly larger than the eucalypt pulp fibres (26.3 )m2). The mean lumen area of the ‘medium’ bagasse pulp fibres could not be differentiated statistically from either the ‘coarse’ or eucalypt pulp fibres.

The collapse ratio for the ‘coarse’ bagasse pulp (1.48) was substantially greater than for the ‘medium’ bagasse pulp and the eucalypt bagasse pulp. This is potentially due to the higher mechanical damage to the ‘medium’ bagasse material in the milling train.

The morphological data suggests that the bagasse pulp fibres have thicker cell walls and are less likely to collapse than the eucalypt pulp fibres.

4.2.5. Summary of pulp physical and chemical property testing The ash content of the bagasse is significantly reduced by the pre-treatment. More ash is washed away by the ‘flow-through’ reactor than by the ‘Parr’ reactor. However, there was little difference in composition between the fractionated Australian bagasse and the Argentinean bagasse.

The ‘coarse’ fraction of bagasse significantly improved the initial freeness, tear properties and WRV of the pulp compared to the benchmark Australian pulp. The pre-treament did not improve tensile or burst properties and had a slightly negative impact on apparent density and compressive strength. Refining did not significantly improve any strength properties and reduced the tear strength. Fractionating the bagasse makes the bagasse pulp more suitable for products where tear strength is important. As shall be shown in more detail in the next

116 Chapter 4 - Results and discussion section, the increase in freeness with pre-treatment improves permeability and improves the prospects for increasing production rates.

The fibre length of the ‘coarse’ bagasse pulp is longer than the ‘medium’ bagasse pulp. The Argentinean bagasse pulp has similar fibre length to Australian bagasse pulp prepared under the same conditions. All bagasse pulps had a much wider fibre length distribution than the eucalypt pulp. They also had far more short fibres than the eucalypt pulp.

The bagasse pulp fibres have thicker walls than the eucalypt fibres. This suggests that they may be more rigid.

4.3. Results of steady-state permeability testing

This section gives data for K (for two fixed concentrations), S v and . The effect of using a constant and variable k on the optimum values for S v and  is reported (section 4.3.1). A statistical analysis to determine the effect of pre- treatment conditions on pulp pad permeability is shown in section 4.3.2. A discussion of the suitability of the Kozeny-Carman steady-state permeability model for bagasse pulp is provided in section 4.3.3. The results are compared with the findings of previous workers (section 4.3.4). The findings of the permeability study given the high proportion of short material are surprising. Finally a summary of the steady-state permeability results is given in section 4.3.5.

4.3.1. Data from steady-state permeability testing For each pulp sample tested, K was determined from Darcy’s Law over a wide concentration range. Table 4.8 shows K, at only two concentrations, 3 3 0.08 g/cm and 0.12 g/cm . S v and  values were determined from the intercept and slope of graphs of (Kc 2)1/3 against concentration, such as those shown in Figure 4.9.

117 118 Thomas Rainey J. – A of study bagasse filtrati pulp

Table 4.8 Comparison of permeability parameters obtained from the Kozeny-Carman model with both a constant and variable Kozeny factor.

Permeability Permeability Swelling Swelling K K Specific surface area Specific surface factor  factor  Sample Fraction (×10 8 cm 2) (×10 8 cm 2) S (cm -1 ) area S (cm -1 ), (cm 3/g), (cm 3/g), name v v at - = at - = constant k factor variable k factor constant k variable k 0.08 g/cm 3 0.12 g/cm 3 factor factor 43 Coarse Milled 37.3 9.31 1540 1160 3.44 4.03 26 Coarse Milled 51.7 13.3 1420 1010 3.27 3.96 38 Coarse Milled 26.9 5.19 1570 1180 3.84 4.50 20 Coarse Diffuser 37.5 8.56 1520 1120 3.52 4.19 21 Coarse Diffuser 40.9 6.15 1390 980 3.61 4.39 Crude average for Coarse fraction 38.8 8.51 1490 1090 3.54 4.21 18 Medium Milled 30.6 7.47 1820 1290 3.33 4.04

27 Medium Milled 26.6 6.95 1830 1290 3.38 4.10 on 42 Medium Milled 23.1 6.45 2260 1610 3.10 3.75 39 Medium Diffuser 24.1 6.15 2170 1630 3.20 3.76 35 Medium Diffuser 18.2 4.81 2760 1970 3.00 3.64 Crude average Medium fraction 24.5 6.37 2170 1560 3.20 3.94 58 30% depithed Milled 6.80 1.77 4640 4020 2.97 3.19 51 Fine 2.2 0.58 14100 9880 2.01 2.52 53 Whole 4.40 1.73 20200 11200 1.11 1.67 32; Argentinean depithed bagasse 17.8 4.16 2100 1510 3.58 4.29 Eucalypt 15.4 3.88 2480 1920 3.38 3.93 Pine 36.4 1.59 327 319 7.17 7.60

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0.002 Coarse bagasse pulp Medium bagasse pulp Unfractionated bagasse pulp Fine bagasse pulp 0.0015 -4/3 cm

2/3 0.001 , g 1/3 ) 2 (Kc 0.0005

0 0.00 0.05 0.10 0.15 0.20 c (g/cm 3)

Figure 4.9 Graphs of (Kc 2)1/3 against concentration

A statistical analysis of K would only provide a comparison for a specific pulp concentration. A statistical analysis was performed on S v and  rather than K as they are independent of concentration. Optimum values for S v and  were determined for both constant and variable k using a least squares regression method. The following analysis between pulp samples compares the results for S v and  using a constant k.

Table 4.8 shows that fractionating the bagasse prior to pulping has a significant effect on S v. For Australian bagasse pulp samples, the samples obtained from the ‘coarse’ bagasse fraction has the lowest S v value whilst the pulp obtained from ‘whole’ bagasse has the highest S v value. The average S v was 1490 cm -1 for Australian bagasse pulp obtained from the coarse bagasse fraction and 2170 cm -1 for Australian bagasse pulp obtained from the medium bagasse fraction.

-1 The benchmark ‘30% depithed’ bagasse pulp also had higher S v, 4640 cm (Sample 58) than the pulp samples obtained from coarse and medium fractions of bagasse. The very high values for S v obtained for the fine bagasse pulp (Sample

119 Thomas J. Rainey – A study of bagasse pulp filtration

51) and the whole bagasse pulp (Sample 53) was associated with the very high proportion of pith material. Pith has a very high surface area to volume ratio and consequently increases S v.

-1 The S v of Argentinean bagasse pulp (Sample 32), 2100 cm , was higher than the Australian pulps derived from the ‘coarse’ and ‘medium’ bagasse fractions.

Although both the Australian ‘30% depithed’ bagasse pulp (Sample 58) and the Argentinean bagasse pulp both had 30% of the shortest material removed, they have quite different values for S v. The difference between the S v values was possibly due to the difference between the APPI ‘flow-through’ reactor and the batch Parr reactor. Alternatively the difference may have been related to the cane variety. Argentinean sugarcane is bred specifically to produce fibre for paper manufacture (144).

Significantly, the Australian bagasse pulp had a lower S v than the eucalypt pulp, 2480 cm -1 , meaning that it has higher permeability. This is the most important finding of this bagasse pulp study. The thicker fibre walls and the higher proportion of longer fibres contributed to a more open pulp pad matrix, despite the higher fraction of short fibres (section 4.2.3). A significant proportion of pith was removed by the pre-treatment and possibly also by the cooking process in the ‘flow-through’ digester, reducing the influence of pith on bagasse pulp permeability.

The S v for eucalypt pulp was much less than the benchmark ‘30% depithed’ bagasse pulp as expected.

The S v for pine pulp was much lower than the pulp obtained from Australian bagasse pulp because of its longer fibre length.

For the Australian bagasse pulp samples, when a variable k is used in the -1 calculation of S v the value of S v is about 400 cm (~25%) on average lower than when it is calculated with constant k. As mentioned previously, the factor k gives an indication of the tortuosity for the capillaries through the pulp pad.

120 Chapter 4 - Results and discussion

The  values of the pulps derived from coarse and medium Australian bagasse fractions were not very different from Argentinean bagasse (Sample 32) and eucalypt pulp (see Table 4.8). The benchmark ‘30% depithed’ bagasse pulp (Sample 58), also had a slightly lower  value.  affects the permeability properties as well as S v.  values obtained with a variable k were about 25% higher than the values obtained with a constant k. High  values should also indicate the potential for strength generation during refining. However, pulp samples with higher values of  were not observed to have better strength generation properties during refining.

4.3.2. Effect of bagasse pre-treatment on pulp permeability properties

The breakdown of S v and  values for pulp samples originating from different bagasse fractions and different sugar extraction processes are shown in Table 4.9.

Table 4.9 Average S v and  values for pulp samples originating from Australian bagasse.

-1 3 S v (cm )  (cm /g) Coarse Medium Coarse Medium Milled 1510 1970 3.52 3.27 Diffuser 1460 2470 3.57 3.10

The S v and  values for each type of bagasse pulp were compared using Student’s pooled t-test with a 95% confidence interval. The test statistic, , used to compare ‘coarse’ and ‘medium’ bagasse pulp is shown in Table 4.10 The  value indicates that there is a difference in S v between coarse and medium bagasse pulp for either milled and diffuser bagasse pulp. The test statistic for  is less clear. There is very strong evidence that there is a difference in  between pulp derived from coarse and medium bagasse from the diffuser (high  = 6.07) but not from the mill (low  = 1.83).

121 Thomas J. Rainey – A study of bagasse pulp filtration

Table 4.10  values for S v and  for pulp samples obtained from different bagasse fractions.

 for S v values  for  values (-) (-)

 within milled bagasse population 4.24 1.83

 within diffuser bagasse population 4.69 6.07

The low values for the test statistic, , show that there is no difference between the pulp samples obtained from the two sugar extraction methods for either S v nor  (Table 4.11).

Table 4.11  values for S v and  test statistic for pulp samples obtained from different sugar extraction methods.

 for S v values  for  values (-) (-)

 within coarse bagasse population 0.87 0.25

 within medium bagasse population 2.41 1.78

4.3.3. Review of bagasse pulp steady-state permeability model

The values of S v and  presented in Table 4.8 obtained using a constant and variable Kozeny factor were inserted back into the Kozeny-Carman model and compared with the original experimental data (shown in Figure 4.10). The Kozeny-Carman model with either a constant k (the solid line) or a variable k (the dashed line) reasonably predicts the experimental permeability data over the concentration range used in this study.

A dynamic permeability and compressibility model is developed and verified later in this chapter. The dynamic model uses data extrapolated beyond the concentration range considered here. Extrapolating the permeability model slightly above the concentration range used in the cell shows that the model predicts higher permeability with a variable Kozeny factor than with a constant factor. This suggests that the tortuosity of the capillaries in the pulp pad decrease

122 Chapter 4 - Results and discussion as the pulp concentration increases. It will be shown later in this chapter that extrapolating the Kozeny-Carman model with a variable Kozeny factor beyond this concentration range allows the dynamic model to give good predictions.

1.00E-06 Experimental results, coarse bagasse pulp Experimental results, medium bagasse pulp

Experimental results, fine bagasse pulp

Kozeny prediction ) 2 Kozeny prediction with Davies Kozeny factor correction Kozeny prediction (medium)

1.00E-07 Permeability, K K (cm Permeability,

1.00E-08 0.05 0.10 0.15 0.20 Concentration, c (g/cm 3)

Figure 4.10 Comparison of the Kozeny-Carman model with experiment data with both a constant and variable Kozeny factor.

4.3.4. Comparison of steady-state permeability data with previous work The only published bagasse pulp permeability data is by El-Sharkawy and co-workers who examine a commercial bagasse pulp from India (50, 64).

Unfortunately, it was not possible to determine values of S v from their study as the variation of K with concentration was not provided. This work reported a “Kozeny-Carman permeability constant”. The paper contained unusual units for the constant (cm 2) when k is normally unitless. Upon discussion with the authors, this paper used an obscure permeability model and not the Kozeny-Carman model, viz

ε K = 'k Equation 4.1 (1− ε ) 2 where k’ is a permeability constant

123 Thomas J. Rainey – A study of bagasse pulp filtration

In their study, bagasse pulp was fractionated using an axial feed pressure screen with 0.06 mm slots to reduce the fines content and improve steady-state permeability. Their data is presented in Table 4.12. They were able to improve permeability by 30% by pressure screening increasing k’ from 2.36×10 -9 cm 2 to 3.08×10 -9 cm 2.

Table 4.12 Values for bagasse pulp “Permeability constant” reported by El-Sharkawy and co-workers (50, 64)

Permeability constant Canadian Standard of original pulp (cm 2) Freeness (ml)

Original pulp 2.36×10 -9 290

Screened pulp 3.08×10 -9 459

Rejected 5.61×10 -10 200 material

The results of this work have been recalculated into the form of their ‘permeability constant’. It was found that the ‘permeability constant’ for ‘coarse’ and ‘medium’ Australian bagasse pulp was between 2×10 -8 cm 2 and 4×10 -8 cm 2. This is compared to 2.36×10 -9 cm 2 for El-Sharkawy and co-worker’s original Indian bagasse pulp, and 3.08×10 -9 for their most permeable screened pulp, a ten- fold improvement.

For data collected in this study, the form of the conventional Kozeny- Carman model was found to have better agreement with the experimental data than the permeability model used by El-Shakawy and co-workers.

Table 4.13 shows a comparison of the S v and  values from this study with those of previous workers that investigated wood pulp. Most of these workers did not specify the wood species used. The specific surface area, S v, for the bagasse pulp samples was lower than that found by previous workers for wood pulp. Previous workers have reported a wide range for , from 1.65 cm 3/g up to

124 Chapter 4 - Results and discussion

3 4.5 cm /g. The values of  for bagasse pulp were in this range. S v and  for the benchmark eucalypt pulp sample measured in this study was very similar to that of Robertson and Mason for a kraft wood pulp (86).

Table 4.13 Comparison of S v and  measured by various workers.

Pulp source Investigator Kozeny Other details Specific Swelling factor surface area, factor,  -1 3 Sv (cm ) (cm /g) Soda AQ ‘Coarse’ This study Constant, Not dried 1490-2170 3.20-3.54 and ‘Medium’ 5.55 Australian Bagasse Soda AQ ‘Coarse’ This study Variable Not dried 1100-1600 3.94-4.21 and ‘Medium’ Australian Bagasse Eucalypt pulp This study Constant Not dried 2480 3.38 Soda AQ bagasse This study Constant, Not dried 4644 2.97 with 30% of pith 5.55 removed Sulfite wood pulp Robertson and Constant, Previously dried ~4100 2.80-3.08 Mason (86) 5.55 Not dried ~2300 4.4-4.5 Kraft wood pulp Robertson and Constant, Not dried ~2300 3.66-4.27 Mason (86) 5.55 Wood pulp Ingmanson Constant 4200 1.65 and co- workers (81) Variable ~2900 ~2.07 Sulphate wood pulp Gren (84) Constant, 2000-3000 4.8 5.55

The relative changes in bagasse pulp S v values (~25%) between a variable and constant k were more than the 7% previously reported by Ingmanson and co- workers (81) for wood pulp. The change in  values was the same as previously reported for wood pulp, 25%.

4.3.5. Summary of steady-state permeability experiments The steady-state permeability properties of Australian bagasse pulp have been measured in a simple custom built cell and reported. The steady-state permeability data are needed for the dynamic filtration model.

125 Thomas J. Rainey – A study of bagasse pulp filtration

Pulp derived from fractionated Australian bagasse was produced in the laboratory with permeability that compares favourably with eucalypt pulp, despite a higher overall fine fibre content. It is thought the fibre stiffness and the high proportion of fibres greater than 1.3 mm in length creates a highly permeable bagasse pulp pad.

Australian pulp derived from the ‘coarse’ bagasse fraction has better steady- state permeability than the ‘medium’ fraction, as measured by lower S v. The ‘coarse’ bagasse pulp from a diffuser has a higher  value. This confirms that there is a difference between the fractions of bagasse (Objective 1a) with respect to pulp permeability.

There was not found to be a difference in bagasse pulp permeability between bagasse pulp from a diffuser and a mill (Objective 1b) .

For bagasse pulp, a variable k gives a 25% higher value for  and a 25% lower value of S v compared with a constant k. This is similar to the findings obtained for wood pulps.

The findings from the steady-state permeability study are consistent with the findings of previous workers. A standard Australian bagasse pulp (Sample 58) had worse S v than wood pulp but was improved dramatically by the pre-treatment and pulping procedure. The values of  for bagasse pulp are within the range of findings for other workers using wood pulp.

Good agreement was found to exist between the experimental data and the theoretical predictions for the permeability properties of Australian bagasse pulp using the Kozeny-Carman model with a constant or variable k.

4.4. Results of quasi steady-state compressibility testing

In this section, the steady-state compressibility parameters of pulp pads, M and N, are determined from experiments using the compressibility cell. The steady-state power law compressibility model was found to be suitable (section 4.4.1). The values of M and N are presented and compared to the findings of previous workers (section 4.4.2). These values for M and N are used in the

126 Chapter 4 - Results and discussion dynamic model later in this chapter. The effect of pre-treatment conditions on the compressibility parameters is compared statistically (section 4.4.3). A summary of the quasi steady-state compressibility tests is presented in section 4.4.4.

4.4.1. Suitability of the power law steady-state compressibility model The pressure of the platen was calculated from the load recorded by the Instron. For each pulp sample, the platen pressure was plotted as a function of concentration on a log-log scale. The compressibility factor, N was determined from the slope of the linear approximation and the compressibility factor, M was determined as the exponent of the abscissa intercept. Figure 4.11 is an example of this graph for experimental data.

2.5

2 log(P) = 2.65*log(c) + 3.50

1.5

1 log(pressure) (kPa) 0.5

0 -1.3 -1.2 -1.1 -1 -0.9 -0.8 -0.7 -0.6 -0.5 log (concentration) (g/cm 3)

Figure 4.11 Plot of the log of the platen pressure against the log of the pulp concentration for a sample of bagasse pulp compressed under quasi steady-state conditions (Sample 39; experimental data is shown as the thin solid line and the linear approximation is shown as the thick dashed line).

The figure demonstrates that the power law steady-state compressibility N relationship, P s = M Z is suitable.

127 Thomas J. Rainey – A study of bagasse pulp filtration

4.4.2. Pulp steady-state compressibility data and comparison with the findings of previous workers Table 4.14 is a summary of the compressibility constants M and N obtained from quasi steady state compressibility experiments using a range of pulp samples. These values were used as inputs to the dynamic model presented later in this chapter.

Table 4.14 Table of values for the compressibility factors N and M found in this study.

This study Sample number Fraction Source N M (kPa) Sample 26 Coarse Mill 2.83 7650 Sample 38 Coarse Mill 2.60 3320 Sample 43 Coarse Mill 2.94 8040 Sample 20 Coarse Diffuser 2.66 4990 Sample 21 Coarse Diffuser 2.68 3960 Sample 18 Medium Mill 2.72 6090 Sample 27 Medium Mill 2.61 3730 Sample 42 Medium Mill 2.56 3780 Sample 35 Medium Diffuser 2.72 4490 Sample 39 Medium Diffuser 2.65 3190 Average 2.70 4920 Whole bagasse pulp Whole Mill 2.74 4960 Fine bagasse pulp Fine Mill 3.23 25900 Argentinean bagasse pulp 2.82 8450 Eucalypt pulp 2.43 4780 Pine pulp 2.47 6010

The compressibility parameters for wood pulp determined by previous workers were recalculated in terms of M and N. The results for eucalypt and pine from this study are similar to the findings by previous workers for wood pulp (Table 4.15).

Gren and Hedstrom (85) report N over the full range of kappa numbers for chemical pulps, from 2.22 for a fully bleached pulp to 2.37 for a 100 kappa pulp whilst Ingmanson reports N to be between 2.66 and 3.17 (81-83). Gren and Hedstrom (85) noted that the difference in their results compared to Ingmanson’s (81) is due to the different compression range used in their experiments. Our results for N were all within the range reported by these authors.

128 Chapter 4 - Results and discussion

Table 4.15 Table of values for the compressibility factors N and M found by other workers.

Previous studies Sample description N M (kPa) Unclassified wood pulp at moderate Not 2.22-2.37 levels of compression (85) provided Wood pulp (81) 2.66 1450 Beaten wood pulp (82, 83) 3.12 2950 Beaten wood pulp (82, 83) 3.14 3160 Unbeaten wood pulp (82, 83) 3.17 3480 Unbeaten wood pulp (82, 83) 3.14 3190

M was found to vary significantly between samples, however N was less variable. The values of M reported in this study (generally 3000 kPa to 8000 kPa) were often slightly higher than previously reported (1450 kPa to 3480 kPa). This is possibly due to the concentration range which was selected as being suitable for the dynamic filtration study in the next phase of the project.

The bagasse pulp was not statistically different from the eucalypt pulp in terms of M and N (determined using Student’s t-test with a 95% confidence interval). This is despite the significant difference in the fibre morphology. Bagasse pulp has a longer fibre length and thicker cell walls than the eucalypt pulp.

4.4.3. The effect of pre-treament on bagasse compressibility The pulp compressibility parameters were again statistically compared using Student’s t test. The pulp samples analysed were subdivided into four categories. These categories are pulp produced from ‘coarse’ and ‘medium’ fractions of milled and diffuser bagasse.

The average values for N and M within each of the milled and diffuser bagasse pulp populations are provided in Table 4.16

129 Thomas J. Rainey – A study of bagasse pulp filtration

Table 4.16 Table of average N and M values for milled and diffuser, coarse and medium bagasse.

N (-) M (kPa) Coarse Medium Coarse Medium Milled 2.79 2.63 5890 4410 Diffuser 2.67 2.57 4440 3030

Firstly the effect of the bagasse fraction on N and M will be determined followed by the effect of the method of juice extraction

4.4.3.1. The effect of bagasse fraction on N and M

The values of  comparing the difference between coarse and medium bagasse pulp is presented for each of the milled and diffuser bagasse pulp samples. The low values of  in Table 4.17 indicates that the bagasse fraction did not affect the value of N within either the milled or diffuser bagasse pulp populations. Similarly, the bagasse fraction was not found to affect the value of M.

Table 4.17  values for N and M comparing ‘coarse’ and ‘medium’ bagasse pulp.

Value of  for Value of  for comparing N comparing M values (-) values (-)

 within milled bagasse population 1.46 0.866

 within diffuser bagasse population 1.30 2.64

4.4.3.2. The effect of the mode of juice extraction on N and M

The effect of the mode of juice extraction on N and M is now determined within each of the milled and diffuser bagasse pulp populations. Table 4.18 shows the test statistic, , calculated to determine whether there is an effect of the

130 Chapter 4 - Results and discussion mode of juice extraction on M and N firstly within the ‘coarse’ bagasse population and then the ‘medium’ bagasse population.

Table 4.18  values for N and M comparing pulp from two methods of juice extraction.

 values comparing  values comparing mean N values (-) mean M values (-)

within coarse bagasse population 0.940 0.724

within medium bagasse population 0.709 1.36

4.4.4. Summary of steady-state compressibility testing The power law compressibility model is suitable for bagasse pulp and wood pulp samples. The values for M and N were measured for use in the dynamic model. The values for N were consistent with the findings of previous workers for wood pulp, but the values of M were slightly higher than previously reported.

Bagasse pre-treatment was not found to affect the compressibility parameters, rejecting the notion that either fractionated bagasse or the mode of juice extraction (i.e. Objective 1a and Objective 1b) affects the steady-state compressibility.

4.5. Results of dynamic filtration modelling and validation

The output of the dynamic model was tested using a sensitivity analysis of the key permeability and compressibility variables, S v, , M and N (section 4.5.1). The output of the dynamic model was compared with experimental data obtained under dynamic filtration conditions (section 4.5.2) and a summary is provided (section 4.5.3).

4.5.1. Predictions of the dynamic model The output from the dynamic model (Equation 2.25 to Equation 2.28) calculated by the FORTRAN program provides the solidity as a function of both the position within the cell as well as time. The dimensionless output of the model is easily converted back to dimensional form. An example of the output for

131 Thomas J. Rainey – A study of bagasse pulp filtration

Australian bagasse pulp is shown in Figure 4.12 and Figure 4.13 where the time axis was scaled to 3 min. The data presented used typical values for the permeability and compressibility parameters obtained in this study. The solidity,
= c is initially constant through the cell (in Figure 4.12 as t  0 min) but during the experiment, the solidity at the top platen is higher than lower in the cell (Figure 4.13). The concentration gradient throughout the cell is roughly uniform and small.

0.9 0.8 t = 0 min 0.7 t = 1 min 0.6 t = 2 min 0.5 t = 2.5 min (-) 0.4
t = 3 min 0.3 0.2 0.1 0 0 20 40 60 80 x (mm) Figure 4.12 Output from the dynamic model for Sample A; graph of
as a function of depth below the platen.

0.8 at the top platen 0.7 at the base 0.6 0.5

(-) 0.4
0.3 0.2 0.1 0 0 1 2 3 t (min)

Figure 4.13 Output from the dynamic model for Sample A; graph of
as a function of time.

132 Chapter 4 - Results and discussion

Sv and  were determined from the permeability experiments in the concentration range 0.05 g/cm 3 to 0.2 g/cm 3. The dynamic filtration model governing equation used these factors beyond this concentration range in the dynamic filtration experiments, as mentioned in section 4.3.3. It will be shown in section 4.5.2 that this is a valid assumption provided a variable Kozeny factor, k, is used.

A sensitivity analysis of the effect of compression rate, M, N and S v on the calculated P s was performed. Each of these parameters were varied one at a time and compared to a ‘base-case’ where all other parameters were fixed. The solidity predicted from the FORTRAN model was converted to platen pressure, P s using Equation 2.24.

The effect of  was not studied explicitly.  is assumed to be invariant with concentration for a given pulp sample. Increasing  has the same effect as increasing concentration viz

n Ps = m(αc)

Equation 4.2 recalling that m and n are calculated from M and N. Hence  has a considerable effect on the dynamic model.

Firstly, it was necessary to determine the compression rate required to observe dynamic effects for use in the ‘base-case’ conditions. Figure 4.14 shows the dynamic filtration effects where the compressibility and permeability parameters were held constant. There was only a small increase in solids pressure when the compression (75 mm) was undertaken over 20 min compared to 5 hr. From the modelling, steady-state compression behaviour appears to occur when the pulp pad is compressed for around 20 minutes. Compressing the pulp pad over 5 hr in the previous experimental phase appears to be a valid timescale that achieves quasi steady-state conditions. The data in Figure 4.14 was obtained -1 using Z0 = 0.04 and S v =1740 cm which is the crude average for the milled bagasse samples in Table 4.9, N=2.71 and M=5100 are the crude averages for milled bagasse samples in Table 4.16. A compression time of 3 min for the

133 Thomas J. Rainey – A study of bagasse pulp filtration experiments was selected based on the observation in the figure that this compression rate is fast enough for the model to exhibit the effects of dynamic filtration.

300 75 mm compression over 5 hr 75 mm compression over 20 min 250 75 mm compression over 3 min 75 mm compression over 1 min

200 Sv=1740; N=2.71

150 (kPa) s P 100

50

0 0 0.2 0.4 0.6 0.8 1 C/Cmax Figure 4.14 Effect of compression rate on the fibre pressure; dynamic -1 model predictions; Z0 = 0.04, S v = 1740 cm ; N = 2.71 kPa; M = 5100.

The effect of M, N and S v were compared by changing one variable at a time and comparing it to the ‘base case’. The ‘base case’ uses the same values for the permeability and compressibility parameters in Figure 4.14, at a compression -1 rate of 75 mm in 3 min, i.e. Z0 = 0.04, S v =1740 cm , N=2.71 and M=5100. The results are shown in Figure 4.17 to Figure 4.19. Figure 4.17 shows the effect of -1 -1 increasing S v from 1740 cm to 2000 cm , Figure 4.18 shows the effect of increasing N from 2.71 to 3.2, and Figure 4.19 shows the effect of increasing M from 5100 kPa to 7000 kPa. S v and N have quite a significant affect on P s but M only has a minor effect.

134 Chapter 4 - Results and discussion

300

250 Sv=1740 - Base case Sv=2000 200

150 Ps (kPa) Ps 100

50

0 0 0.25 0.5 0.75 1 C/Cmax

Figure 4.15 Effect of S v on the dynamic model predictions compared to the -1 base case; Z0 = 0.04, S v = 1740 cm ; N = 2.71 kPa; M = 5100, compression time = 3min.

300

250 N=3.2

N=2.71 - Base case 200

150 Ps (kPa) Ps 100

50

0 0 C/Cmax Figure 4.16 Effect of N on the dynamic model predictions compared to the -1 base case; Z0 = 0.04, S v = 1740 cm ; N = 2.71 kPa; M = 5100, compression time = 3min.

135 Thomas J. Rainey – A study of bagasse pulp filtration

300

250 M=5100 - Base case M=7000

200

150 Ps(kPa) 100

50

0 0 0.25 0.5 0.75 1 C/Cmax

Figure 4.17 Effect of M on the dynamic model predictions compared to the -1 base case; Z0 = 0.04, S v = 1740 cm ; N = 2.71 kPa; M = 5100, compression time = 3min.

4.5.2. Dynamic filtration experiments and comparison with predicted values

In order to verify the dynamic model, the fibre pressure P s at the top platen was calculated from
at the top platen using Equation 2.24 and compared to experimentally derived data.

Figure 4.18 and Figure 4.19 show the experimentally determined pressure at the top platen compared to P s calculated from the dynamic model. It was found that for all pulp samples, the best agreement with experimental data occurs when using a variable Kozeny factor (Equation 2.12) rather than a constant Kozeny factor (i.e. k = 5.55). This means that the tortuosity of the capillaries through the pulp pad is changing as the pad compresses. The bagasse pulp samples and the pine pulp sample had very good agreement between the experimental data and the model predictions. The eucalypt pulp had only fair agreement. The reason for the poorer performance in predicting the behaviour of eucalypt pulp is not known.

Two pulp samples had poor agreement between the dynamic model and experimental data; the pulp made from whole bagasse (Sample 53) and fine bagasse (Sample 51). These pulp samples have the highest fine fibre content and

136 Chapter 4 - Results and discussion deviation from the dynamic model is thought to have been caused by incomplete retention of fine fibre by the platen. The comparison between the predictions of the dynamic model and the experimental data for other pulp samples are presented in the supplementary material (Appendix A).

The repeatability of the dynamic filtration experiments was studied using two medium fractions of bagasse pulp. Each pulp pad was compressed twice under identical conditions. The experiments were repeatable. The data from these experiments is attached in Appendix A.

During the dynamic filtration testing, the compression of a sample of pulp was measured both before and after bleaching. Bleaching the pulp did not affect the dynamic filtration behaviour of the pulp.

4.5.3. Summary of dynamic filtration modelling

Two purpose built pieces of laboratory equipment were used to determine the steady-state permeability and compressibility parameters of bagasse pulp pads. These steady-state parameters were used in a dynamic filtration model to accurately predict the compressive load during dynamic filtration of a bagasse pulp pad. The sensitivity of the variables M, N and S v on the platen load pressure was determined.

The dynamic filtration model provided good prediction of the fibre pressure of a compressed bagasse pulp pad at high compression rates when significant dynamic effects occur. It is particularly accurate for bagasse pulp, provided some pith is removed, and pine pulp. The model only provides qualitative predictions for eucalypt pulp at high compression rates. The Kozeny-Carman permeability model allows the dynamic model to give excellent predictions, particularly when a variable Kozeny factor is used (Equation 2.12), rather than a constant Kozeny factor (i.e. k = 5.55).

137 Thomas J. Rainey – A study of bagasse pulp filtration

100 Experimental 100 Experimental 80 Theoretical; constant k 80 Theoretical; constant k 60 Theoretical; variable k Theoretical; variable k 60 40 40 20 Pressure (kPa) 20 Pressure (kPa) 0 0 0 1 2 3 0 1 2 3 Time (min) Time (min) (a) (b)

100 100 Experimental Experimental 80 Theoretical; constant k 80 Theoretical; constant k 60 Theoretical; variable k 60 Theoretical; variable k 40 40

20 20 Pressure (kPa) Pressure (kPa) 0 0 0 1 2 3 0 1 2 3 Time (min) Time (min)

(c) (d)

Figure 4.18 Comparison of the dynamic model with experimental data for bagasse pulp (constant and variable k) (a) Medium milled bagasse pulp (Sample 20); (b) Coarse milled bagasse pulp (Sample 26); (c) Medium diffuser bagasse pulp (Sample 18); (d) Coarse diffuser bagasse pulp (Sample 39).

138 Chapter 4 - Results and discussion

100 100 Experimental Experimental 80 80 Theoretical; constant k Theoretical; constant k Theoretical; variable k 60 Theoretical; variable k 60 40 40 20 20 Pressure (kPa) Pressure (kPa) 0 0 0 1 2 3 0 1 2 3 Time (min) Time (min)

(a) (b)

100 Experimental 80 Theoretical; constant k 60 Theoretical; variable k 40

20 Pressure (kPa) 0 0 1 2 3 Time (min)

(c) Figure 4.19 Comparison of the dynamic model with experimental data for (a) Argentinean bagasse pulp, (b) eucalypt pulp and (c) pine pulp (constant and variable k).

4.6. Results of chemical additives testing

A chemical additive system which is stable under shear conditions was optimised for use with a bagasse pulp slurry using a DDJ. Pulp retention was the principal measure of efficacy for determining the addition rate for the chemical additives (section 4.6.1). The DDJ was modified to investigate the effect of vacuum on the drainage time and retention of bagasse pulp slurries both with and without flocculants (section 4.6.2). The modified DDJ simulates the Fourdrinier forming process. The effect of chemical additives on the steady-state and dynamic permeability and compressibility behaviour of bagasse pulp pads was

139 Thomas J. Rainey – A study of bagasse pulp filtration determined (sections 4.6.3 and 4.6.4). A summary of the effect of chemical additives is presented (section 4.6.5).

4.6.1. The effect of shear and additives on pulp retention A high molecular weight cationic polyacrylamide (CPAM), a flocculant commonly used for wood-based paper manufacture, was investigated at varying concentrations. The supplier recommended applying CPAM in the range of 0.02%-0.08% (on dry fibre) which is typical for mechanical wood pulp with a high quantity of short fibre. The product is sold commercially as Ciba Percol 182.

The effectiveness of various concentrations of CPAM was measured on ‘whole’ bagasse pulp (Sample 53) beyond the ranges suggested by the supplier using a DDJ. The effectiveness of flocculants was quantified by measuring the retention of short fibres (i.e. ‘fines retention’). The flocculation improved with increasing levels of CPAM as shown in Figure 4.20. Even a very small quantity of CPAM improved flocculation. At 0.5% CPAM, over-flocculation was observed which would lead to a ‘patchy’ paper sheet appearance and poor sheet strength properties. An addition rate of 0.05% CPAM, which is the mid-point recommended by the supplier for a mechanical pulp heavily laden with fine fibre was used as a basis for further experiments with flocculants. This concentration is known to be economical for wood-based paper production, improving fibre distribution, whilst also improving drainage and retention.

140 Chapter 4 - Results and discussion

100 90 80 70 60 50 40 Whole bagasse pulp Fines retention, % 30 Whole bagasse pulp + 0.01% CPAM 20 Whole bagasse + 0.05% CPAM 10 Whole bagasse pulp + 0.5% CPAM 0 0 200 400 600 800 1000 1200 1400 1600 Shear (rpm)

Figure 4.20 The effect of CPAM concentration and shear on fines retention on a whole bagasse pulp (Sample 53).

The effect of bentonite addition to a pulp slurry containing 0.1% fibre and 0.05% CPAM (on dry fibre) was investigated. Ciba recommended that their modified bentonite, Hydracol ONZ, should be added at a rate of 0.3% after the CPAM is added to the pulp slurry. Bentonite was added 1 min after CPAM was added to the pulp slurry in the DDJ.

It was found that the addition of CPAM and bentonite, at this rate, actually reduced the fines retention. A high level of bentonite was observed in the filtrate. Consequently, the effect of bentonite addition rate on a bagasse fibre-CPAM system was explored. Figure 4.21 shows that for a pulp slurry containing 0.1% fibre and 0.05% CPAM, the optimum addition rate of bentonite was around 0.06%. A high level of shear (1500 rpm) was used to compare the effect of the level of bentonite. Above this addition level, bentonite is in excess and not attached to the fibre flocs.

141 Thomas J. Rainey – A study of bagasse pulp filtration

100% 90%

80% 0.05% Percol 182 (CPAM) in all samples 70% 60% 50% 40%

Fines Retention 30% 20% 10% Whole bagasse pulp, 1500 rpm 0% 0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 1.2% 1.4% 1.6% Bentonite addition (on dry fibre)

Figure 4.21 The effect of bentonite addition rate on the fines retention of a whole bagasse pulp (Sample 53) with 0.05% CPAM added.

The effect of both CPAM and bentonite on the flocculation of a whole bagasse pulp is shown in Figure 4.22 over a wide range of shear conditions. Using 0.05% CPAM, the best fines retention was achieved with 0.06% of bentonite. This was the most effective rate for whole bagasse pulp over the full range of shear conditions. These addition rates of CPAM and bentonite were then applied to other pulp samples, including ‘coarse’, ‘medium’ and the benchmark ‘30% depithed’ bagasse pulp.

142 Chapter 4 - Results and discussion

100%

80%

60%

40% Whole bagasse pulp Fines retention Fines Whole bagasse pulp + 0.05% CPAM 20% Whole bagasse pulp + 0.05%CPAM +0.06% bentonite Whole bagasse pulp + 0.05%CPAM + 0.3% bentonite 0% 0 200 400 600 800 1000 1200 1400 1600 Shear (rpm)

Figure 4.22 The effect of shear, CPAM and bentonite addition rate on the fines retention of a whole bagasse pulp.

The addition of (i) 0.05% CPAM and (ii) 0.05% CPAM + 0.06% bentonite was then tested on the benchmark ‘30% depithed’ bagasse pulp (Sample 58). Depithed bagasse pulp has better drainage properties than whole bagasse pulp as shown in (section 4.3). Figure 4.23 shows that depithed bagasse pulp had the same response to chemical additives as the whole bagasse pulp. The addition of 0.05% CPAM improved fines retention and was enhanced by the addition of 0.06% of bentonite.

143 Thomas J. Rainey – A study of bagasse pulp filtration

100%

80%

60%

40% Depithed bagasse pulp Fines retention Fines Depithed bagasse pulp + 0.05% CPAM

20% Depithed bagasse pulp + 0.05% CPAM + 0.06% bentonite

0% 0 200 400 600 800 1000 1200 1400 1600 Shear (rpm)

Figure 4.23 The effect of shear, CPAM and bentonite addition rate on the fines retention of a ‘30% depithed’ bagasse pulp (Sample 58).

The effect of CPAM and bentonite on bagasse pulp derived from the ‘coarse’ bagasse pulp (Sample 56), which has high permeability, was performed (Figure 4.24). The addition of CPAM and CPAM & bentonite on the ‘coarse’ bagasse pulp mirrored the results for the ‘30% depithed’ bagasse pulp and the whole bagasse pulp.

144 Chapter 4 - Results and discussion

100%

80%

60%

40% Fines retention Fines 'Coarse' bagasse pulp

20% 'Coarse' bagasse pulp + 0.05% CPAM 'Coarse' bagasse pulp + 0.05% CPAM +0.6kg/t bentonite

0% 0 200 400 600 800 1000 1200 1400 1600 Shear (rpm)

Figure 4.24 The effect of shear CPAM and bentonite addition rate on the fines retention of a ‘coarse’ bagasse pulp.

Finally, the CPAM/bentonite system was tested on ‘medium’ bagasse pulp (Sample 60, Figure 4.25), again with good performance.

100%

80%

60%

40% Fines retention Fines Medium bagasse pulp

20% Medium bagasse pulp + 0.05% CPAM

Medium bagasse pulp +0.05%CPAM + 0.06% bentonite 0% 0 200 400 600 800 1000 1200 1400 1600 Shear (rpm)

Figure 4.25 The effect of shear, CPAM and bentonite addition rate on the fines retention of a ‘medium’ bagasse pulp.

145 Thomas J. Rainey – A study of bagasse pulp filtration

In summary, the combination of 0.05% CPAM + 0.06% bentonite chemicals for improving the retention of all types of bagasse pulp was effective under all shear rates. This two chemical system gives good fines retention, typically 80%- 100%, under a range of shear conditions for every bagasse pulp except ‘whole’ bagasse pulp.

4.6.2. The effect of chemical additives and vacuum The effect of vacuum and shear on the fines retention of a whole bagasse pulp, without any flocculants added, was studied to look into the effect of vacuum. During this process, a pulp mat was formed through which the pulp slurry was filtered. This did not occur in the previous experiments with the DDJ. The data is shown in Figure 4.26. Vacuum clearly had a profound effect on fines retention.

100% 90% 80% 70% 60% 50% 40%

Fines retention 30% Whole bagasse pulp Not Tappi method- 20% 0kPa vacuum 100% of water is 20kPa vacuum removed 10% 40kPa vacuum 0% 0 500 1000 1500 2000 Shear (rpm)

Figure 4.26 The effect of vacuum and shear on the fines retention of a whole bagasse pulp (Sample 53), no chemical additives.

The time taken for the DDJ to drain was measured as a function of vacuum. The drainage time decreased quickly as the first 10 kPa of vacuum were applied (Figure 4.27). The data in Figure 4.27 was collected at a single moderate level of shear. The stirrer speed was set to 1000 rpm.

146 Chapter 4 - Results and discussion

100% 200 Read from left hand axis 90% 180 80% 160 70% 140 Whole bagasse pulp 60% Read from right hand axis 120 Stirrer speed 1000rpm 50% 100 40% 80

Fines retention 30% 60 Drainage time (s) time Drainage 20% 40 10% 20 0% 0 0 10 20 30 40 50 Vacuum kPa Fines retention Drainage time

Figure 4.27 The effect of vacuum on the fines retention and drainage time of a whole bagasse pulp (Sample 53), 1000 rpm shear, no chemical additives.

The experiment was repeated for ‘30% depithed’ bagasse pulp (Sample 58, Figure 4.28), ‘coarse’ bagasse pulp (Sample 56, Figure 4.29) and ‘medium’ bagasse pulp (Sample 60, Figure 4.30). In these experiments, the effect of chemical additives was also investigated as a function of vacuum. The chemicals added were 0.05% CPAM and 0.06% bentonite.

147 Thomas J. Rainey – A study of bagasse pulp filtration

100% 100

90% Read from left hand axis 90 80% 80 70% 70

60% Read from right hand axis 60 50% 50 40% 40

Fines retention 30% 30 Drainage time (s) Drainage 20% 20 10% 10 0% 0 0 10 20 30 40 50 Vacuum kPa Fines retention 'depithed' bagasse pulp no additives Fines retention 'depithed' bagasse pulp 0.05% CPAM + 0.06% bentonite Drainage time 'depithed' bagasse pulp no additives Drainage time 'depithed' bagasse pulp 0.05% CPAM + 0.06% bentonite

Figure 4.28 The effect of vacuum and chemical additives on the fines retention and drainage time of a ‘30% depithed’ bagasse pulp (Sample 58), 1000 rpm shear.

100% 100

90% Read from left hand axis 90 80% 80 70% 70 60% 60 50% 50 40% Read from right hand axis 40

Fines retention 30% 30 Drainage time (s) Drainage 20% 20 10% 10 0% 0 0 10 20 30 40 50 60 70 Vacuum kPa

Fines retention no additives Fines retention 0.05% CPAM + 0.06% bentonite

Drainage time no additives Drainage time 0.05% CPAM + 0.06% bentonite

Figure 4.29 The effect of vacuum and chemical additives on the fines retention and drainage time of a ‘coarse’ bagasse pulp (Sample 56), 1000 rpm shear.

148 Chapter 4 - Results and discussion

100% 100 90% 90 Read left right hand axis 80% 80 70% 70 60% 60 50% 50 40% 40 Read from right hand

Fines retention 30% axis 30 Drainage time (s) Drainage 20% 20 10% 10 0% 0 0 10 20 30 40 50 Vacuum kPa

Fines retention no additives Fines retention 0.05% CPAM + 0.06% bentonite

Drainage time no additives Drainage time 0.05% CPAM + 0.06% bentonite

Figure 4.30 The effect of vacuum and chemical additives on the fines retention and drainage time of a ‘medium’ bagasse pulp (Sample 60), 1000 rpm shear.

For each bagasse pulp examined, the CPAM/bentonite system improved the retention of fines and the drainage time.

These data provided an unexpected result. When no chemical additives were used, the ‘30% depithed’ bagasse pulp (Sample 58) initially had a longer drainage time than the ‘coarse’ bagasse pulp (Sample 56) but as the vacuum increased, the drainage time of the ‘depithed’ bagasse pulp improved and the drainage time became quicker than the ‘coarse’ bagasse pulp. This effect is shown in Figure 4.31. At a vacuum level greater than 10 kPa, the ‘30% depithed’ bagasse pulp drained more quickly than the ‘coarse’ bagasse pulp.

149 Thomas J. Rainey – A study of bagasse pulp filtration

100% 100 90% 90 Read from left hand axis 80% 80 70% 70 60% 60 No additives 50% 50 40% 40 Read from right hand axis

Fines retention 30% 30 Drainage time (s) Drainage 20% 20 10% 10 0% 0 0 10 20 30 40 50 60 70 Vacuum kPa

Fines retention 'Coarse bagasse' Test 56 no additives Fines retention 'Depithed bagasse' Test 58 no additives

Drainage time 'Coarse bagasse' Test 56 no additives Drainage time 'Depithed bagasse' Test 58 no additives

Figure 4.31 The effect of vacuum on the fines retention and drainage time of ‘coarse’ (Sample 56) and ‘30% depithed’ (Sample 58) bagasse pulp, 1000 rpm shear, no flocculants added.

This effect was exacerbated when chemical additives were used (0.05% CPAM and 0.06% bentonite). At 5 kPa, the ‘30% depithed’ bagasse pulp had faster drainage than the ‘coarse’ bagasse pulp.

150 Chapter 4 - Results and discussion

100% 100 95% 90 Read from left hand axis 90% 80 85% 70 80% 60 With additives 75% 50 70% 40 Read from right hand axis

Fines retention 65% 30 Drainage timeDrainage (s) 60% 20 55% 10 50% 0 0 10 20 30 40 50 Vacuum kPa

Fines retention 'Coarse bagasse' with additives Fines retention 'Depithed bagasse' with additives

Drainage time 'Coarse bagasse' with additives Drainage time 'Depithed bagasse' with additives

Figure 4.32 The effect of vacuum on the fines retention and drainage time of ‘coarse’ (Sample 56) and ‘30% depithed’ (Sample 58) bagasse pulp, 1000 rpm shear, with flocculants added.

It was anticipated that the drainage time of the ‘coarse’ bagasse pulp under vacuum and shear conditions would be quicker than the ‘depithed’ bagasse pulp -1 based on its substantially lower S v alone (~4600 cm for ‘30% depithed’ bagasse pulp compared to ~1500 cm -1 for ‘coarse’ bagasse pulp). This affect was also observed for ‘medium’ bagasse pulp. Fibre to fibre interactions during compression evidently plays an important role during bagasse pulp pad formation in the DDJ. This is explored further in the next section.

4.6.3. The effects of chemical additives on permeability and compressibility parameters

4.6.3.1. The effect of chemical additives on bagasse pulp permeability parameters

The study into the permeability properties of bagasse pulp was revisited using the CPAM/bentonite additive system. The experimental procedure used in section 3.4 was repeated with the exception that the chemical additives were added to the pulp slurry prior to loading into the cell. Figure 4.33 and Figure 4.34 show the graph of (Kc 2)1/3 against c for a ‘coarse’ and ‘medium’ bagasse pulp respectively. As can be observed from the figures, there was not found to be a

151 Thomas J. Rainey – A study of bagasse pulp filtration statistically significant difference in the slope or intercept of these plots and consequently no difference in S v or . This was confirmed using Student’s t-test with a 95% confidence interval, using the pooled estimate of standard deviation from section 4.3.

0.0018 0.0016 0.0014 0.0012

1/3 0.001 ) 2 0.0008 (Kc 0.0006 0.0004 Sample 43 no additives 0.0002 Sample 43 with additives 0 0.00 0.05 0.10 0.15 0.20 Concentration, c (g/cm3)

Figure 4.33 The effect of chemical additives on the permeability of a ‘coarse’ bagasse pulp (Sample 43).

152 Chapter 4 - Results and discussion

0.0016

0.0014

0.0012

0.001 1/3 )

2 0.0008

(Kc 0.0006

0.0004 Sample 18 no additives 0.0002 Sample 18 with additives Linear (Sample 18 no additives) 0 0.00 0.05 0.10 0.15 0.20 Concentration, c (g/cm3)

Figure 4.34 The effect of chemical additives on the permeability of a ‘medium’ bagasse pulp (Sample 18).

The effect of additives was significant for a ‘30% depithed’ bagasse pulp (Sample 58), see Figure 4.35. ‘30% depithed’ bagasse pulp had higher permeability when chemical additives were used, although the permeability was still lower than that of eucalypt (without additives). This was confirmed at a 95% confidence interval.

153 Thomas J. Rainey – A study of bagasse pulp filtration

0.0014

0.0012

0.001

0.0008 1/3 ) 2

(Kc 0.0006

0.0004

Eucalypt pulp, no additives 0.0002 Whole bagasse pulp, no additives 'Depithed' bagasse pulp, no additives 'Depithed' bagasse pulp, with additives 0 Linear (Eucalypt pulp, no additives) 0.000 0.050 0.100 0.150 0.200 Concentration, c (g/cm 3)

Figure 4.35 The effect of chemical additives on the permeability of a ‘30% depithed’ bagasse pulp (Sample 58).

The results for S v and  are shown in Table 4.19. The chemical additives had a strong affect on the ‘30% depithed’ bagasse pulp, greatly reducing its S v but not on the ‘coarse’ or ‘medium’ bagasse pulp. There was not found to be any statistically significant difference in  for any bagasse pulp sample using a 95% confidence interval.

Table 4.19 Effect of additives on the permeability parameters S v and .

Parameter Bagasse pulp type No additives With additives

 (-) Coarse (Sample 43) 3.44 3.45 PESD, =0.216 Medium (Sample 18) 3.33 2.98 30% depithed (Sample 58) 2.97 3.26 -1 Sv (cm ) Coarse (Sample 43) 1540 1580 -1 PESD, Sv =211 cm Medium (Sample 18) 1820 2080 30% depithed (Sample 58) 4640 3060

154 Chapter 4 - Results and discussion

4.6.3.2. Effect of chemical additives on bagasse pulp compressibility parameters The investigation into the steady state compressibility of bagasse pulp in section 4.4 was revisited using the CPAM/bentonite system. Figure 4.36 and Figure 4.37 shows typical results for a ‘coarse’ and ‘medium’ bagasse pulp respectively. In both figures, the data is shown prior to chemical additives and after the addition of chemical additives. There was no difference in the steady- state compression factors M and N.

Figure 4.36 The effect of chemical additives on the quasi steady-state compression of ‘coarse’ bagasse pulp (Sample 20).

155 Thomas J. Rainey – A study of bagasse pulp filtration

Figure 4.37 The effect of chemical additives on the steady-state compression of ‘medium’ bagasse pulp (Sample 18).

The effect of chemical additives is more pronounced on the steady state compressibility of a ‘30% depithed’ bagasse pulp (Figure 4.38). This mirrors the observation that chemical additives only affect the permeability parameters of a ‘depithed’ bagasse pulp.

156 Chapter 4 - Results and discussion

Figure 4.38 The effect of chemical additives on the steady-state compression of ‘depithed’ bagasse pulp.

Typical results for the steady-state compressibility test are shown in Table 4.20. The results were duplicated using other pulp samples (Sample 26, a ‘coarse’ bagasse pulp and Sample 42, a ‘medium’ bagasse pulp). The only statistically significant result is that the chemical additives system affected the ‘depithed’ bagasse pulp compressibility parameters by increasing both M and N.

Table 4.20 Typical effect of chemical additives on bagasse pulp compressibility parameters.

Parameter Bagasse pulp type No additives With additives

Log M (kPa) Coarse (Sample 20) 3.77 3.93 PESD, m =0.15 Medium (Sample 18) 3.79 3.79 30% depithed (Sample 58) 3.14 3.74 N, - Coarse (Sample 20) 2.76 2.98 PESD, n =0.12 Medium (Sample 18) 2.73 2.73 30% depithed (Sample 58) 1.89 2.65

157 Thomas J. Rainey – A study of bagasse pulp filtration

4.6.4. The effect of chemical additives on bagasse pulp’s dynamic filtration behaviour

In section 4.6.3, it was found that chemical additives affected the S v, M and N of only the ‘30% depithed’ pulp. The ‘coarse’ and ‘medium’ bagasse pulp could not be shown, statistically speaking, to be affected by chemical additives.

The dynamic filtration tests in section 3.6 were revisited to look at the effect of chemical additives. The results for ‘coarse’ pulp (Sample 43), ‘medium’ pulp (Sample 18) and ‘30% depithed’ pulp (Sample 58) are shown in Figure 4.39. Similar results for the ‘coarse’ and ‘medium’ pulps were obtained using Sample 26 (a ‘coarse’ pulp) and Sample 42 (a ‘medium’ pulp).

Under dynamic conditions, the governing equation (Equation 2.25) is dominated by the flexural term D(
), reproduced below. In the case of the ‘30% depithed’ bagasse pulp, the reduced load has been caused by an increase in the n-1 permeability term (K(
)) and compression term (mn
).

φ(1− φ) K (φ)mn φn−1 D(φ ) = ) Although it could not be determined experimentally using a 95% confidence interval that the chemical additives affect either the steady-state permeability or compressibility properties of ‘coarse’ or ‘medium’ bagasse pulp, there was some anecdotal evidence of their effect demonstrated in the dynamic experiment, Figure 4.39. The figure shows that there is a small reduction in load pressure when chemicals are added to the ‘medium’ pulp.

158 100

90 '30% Depithed' pulp

80

70 'Medium' pulp 60

50 'Coarse' pulp

40 Pressure(kPa)

30

20

10 Chapter and 4 – Results discussion

0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Concentration (g/cm 3)

'Coarse' bagasse pulp (Sample 43) no additives 'Coarse' bagasse pulp (Sample 43) with additives 'Medium' bagasse pulp (Sample 18) no additives 'Medium' bagasse pulp (Sample 18) with additives 'Depithed' bagasse pulp, (Sample 58) no additives 'Depithed' bagasse pulp (Sample 58) with additives

Figure 4.39 The effect of chemical additives on the dynamic filtration of ‘depithed’, ‘coarse’ and ‘medium’ bagasse pulp. 159

159 Thomas J. Rainey – A study of bagasse pulp filtration

Let us now re-examine the finding in section 4.6.2 where the ‘30% depithed’ bagasse pulp had faster drainage under vacuum in the modified DDJ than the ‘coarse’ bagasse pulp, particularly when chemical additives were used. The possible mechanisms for consolidation of compressible fibrous media are (from 102):

1. Fibre collapse 2. Bending of fibres & fibre realignment 3. Breaking of fibres The Australian bagasse fibres are very rigid and significant fibre collapse was not observed in the microscopy study. Fibre breakage is not occurring due to the high repeatability of the permeability and compressibility experiments. This leaves the bending of fibres and fibre realignment.

Further insight is gained by considering the larger improvement in drainage rate for the ‘depithed’ bagasse when chemicals are added compared to the ‘coarse’ and ‘medium’ pulp samples. It seems unlikely that the chemical additives cause the Australian bagasse pulp fibres to become more flexible. If there was a significant bending effect brought about by chemical additives, one would expect the three different types of pulp (i.e. ‘coarse’, ‘medium’ and ‘depithed’ pulp) to exhibit a similar change in M and N. This was not observed. Although the ‘30% depithed’ bagasse pulp had a higher load during steady-state compression when chemical additives were used, it seems unlikely that it is more rigid than the ‘coarse’ and ‘medium’ pulp samples.

By a process of elimination, it seems the most likely mechanism of Australian bagasse pulp consolidation is fibre realignment. The use of chemical additives with bagasse pulp improves fibre realignment by creating a lubricating effect, binding the “pith” fibres to the larger fibres. When using chemical additives, the higher the level of pith, the greater the improvement in dynamic filtration properties (see Figure 4.39).

In the initial stages of pad formation, without chemical additives, the pith fibres roam freely and block pores in the pulp pad. With chemical additives, the pith is attached to the longer fibres and are held back in suspension slightly

160 Chapter 4 - Results and discussion allowing a more porous pad during pad formation. Under the dynamic conditions in the DDJ, as vacuum increased, the ‘30% depithed’ bagasse pulp pad consolidated better than the ‘coarse’ and ‘medium’ pulp samples. Under the dynamic conditions in the compression cell, the ‘coarse’ and ‘medium’ pulp samples filtered more easily.

For processing low consistency pulp suspensions in conditions similar to a DDJ, the pulp drains fastest when ‘30% depithed’ bagasse is used in conjunction with a chemical additives system, but significant vacuum must be applied. The difficulty with this approach is that the ‘30% depithed’ had a lower water retention value (255% for ‘coarse’ bagasse pulp and 274% for ‘30% depithed’ bagasse pulp) which makes the sheet harder to dry. Also, the modified DDJ more closely resembles the Fourdrinier former. It is not known how the filtration of the pulp samples would compare in a Twin-wire former.

For processing initially networked fibre pads under dynamic conditions, ‘coarse’ bagasse pulp was the most easily dewatered bagasse pulp which improved when chemical additives are used. The ‘coarse’ bagasse pulp performed better when either flocculants were not used or when the vacuum level was low.

4.6.5. Summary of the effect of chemical additives on pulp permeability and compressibility

It was found that addition of 0.05% CPAM (as Ciba Percol 182) and 0.06% modified bentonite (as Ciba Hydracol ONZ) improved the retention of bagasse pulp fines over a wide range of shear using a DDJ.

Applying vacuum to the DDJ had the effect of dramatically reducing the drainage time. Every bagasse pulp benefitted from the addition of the flocculants in the DDJ, as measured by reduced drainage time and increased fines retention, at any level of vacuum.

In steady-state permeability and compressibility experiments, the addition of flocculants could only be determined to improve S v for one type of pulp; the ‘30%

161 Thomas J. Rainey – A study of bagasse pulp filtration depithed’ pulp. However, dynamic filtration experiments showed that there is also a significant improvement for the ‘medium’ bagasse pulp.

The mechanism of bagasse pulp consolidation is by fibre realignment which is assisted by chemical additives.

For initially unnetworked suspensions, and the conditions that occur in the DDJ, the fastest drainage rate was achieved by a standard depithing regime practiced by industry (i.e. removal of 30% of the shortest fibres) using high levels of vacuum and chemical additives. These conditions most closely resemble those of a Fourdrinier former rather than a Twin-wire former. The lower WRV of the ‘coarse’ bagasse pulp indicates that it would dry more quickly.

For initially networked fibre pads, as in the compression cell and permeability cell, the ‘coarse’ bagasse pulp was the easiest to filter.

162 Chapter 5 - Conclusions

Chapter 5 Conclusions

A study of bagasse pulp was motivated by the possibility of making highly value-added products from bagasse for the financial benefit of sugarcane millers and growers. In Australia, there is a perception that bagasse pulp always has poor filtration characteristics which results in slower paper production compared to local eucalypt pulp. Surprisingly, there has previously been very little rigorous investigation into bagasse pulp permeability and compressibility. Only freeness testing of bagasse pulp has been published in the open literature. Consequently, this study focussed on improving the filtration properties of bagasse pulp pads.

This study investigated three options for improving the permeability and compressibility properties of Australian bagasse pulp pads. Firstly, the effect of the bagasse size, whether ‘coarse’ or ‘medium’ fractions, was considered. The effect of the mode of juice extraction, whether from a mill or a diffuser, was determined. Finally the effectiveness of chemical additives, which are known to improve freeness of pulp slurries, was assessed.

The pre-treated Australian bagasse pulp samples were compared with samples of eucalypt pulp, depithed Argentinean bagasse pulp that is used industrially, and a benchmark Australian bagasse pulp that also had 30% of its shortest fibres removed.

The steady-state permeability and compressibility parameters of bagasse pulp pads were determined experimentally using two purpose-built experimental

163 Thomas J. Rainey – A study of bagasse pulp filtration rigs. These parameters were used as inputs for a dynamic filtration model which more accurately represents industrial paper manufacture. The filtration model was developed with a view to assist with the development of specialised bagasse pulp processing equipment. The predicted results of the dynamic model were compared to experimental data.

The effectiveness of a CPAM and bentonite chemical additives for improving the retention of fines and increasing the drainage rate of bagasse pulp slurry was determined in a modified Dynamic Drainage Jar. These chemical additives were then used to make a pulp pad and their effect on the steady-state and dynamic permeability and compressibility were determined.

5.1. Findings of this thesis

The most important finding presented in this thesis is that Australian bagasse pulp was produced with permeability higher than eucalypt pulp, despite a higher overall fine fibre content. It is hoped that this higher permeability will enable Australian paper producers to switch from using Australian eucalypt pulp to bagasse pulp without sacrificing paper machine productivity. The high fibre stiffness, resulting from thicker fibre walls, and the high proportion of fibres greater than 1.3 mm in length created a highly permeable bagasse pulp pad. By fractionating the bagasse and using the ‘flow-through’ reactor appears to have mitigated the negative influence of the pith particles.

The specific surface area, S v, for eucalypt pulp was consistent with the findings of previous workers. The benchmark Australian bagasse pulp had worse permeability than the eucalypt pulp which is in harmony with the conventional wisdom which holds that bagasse pulp normally has poor permeability properties.

Australian pulp derived from the ‘coarse’ bagasse fraction had higher steady-state permeability than the ‘medium’ fraction as measured by the specific surface area, S v. However, there was not found to be a difference in bagasse pulp steady-state permeability between bagasse pulp from a diffuser or a mill.

164 Chapter 5 - Conclusions

The values for the swelling factor, , were similar for the bagasse pulp samples and the eucalypt pulp which were all within the ranges reported by previous workers for wood pulp.

For bagasse pulp, a variable Kozeny factor, k, resulted in a higher value for

 and a lower value for S v compared with a constant k. This was similar to the findings obtained for wood pulps reported by Ingmanson (81).

The values for the steady-state compressibility constants M and N were measured for a wide range of pulp samples. The values for N were generally consistent with the findings of previous workers for wood pulp, although the values of M were slightly higher. The bagasse pre-treatment options were not found to affect the steady-state compressibility parameters of a pulp pad.

The steady-state permeability and compressibility parameters, S v, , M and N, were used in a dynamic filtration model to accurately predict the compressive load in dynamic filtration of a bagasse pulp pad. The model was particularly sensitive to S v,  and N but less sensitive to M.

The dynamic model was particularly accurate for bagasse pulp, provided at least some pith was removed. The Kozeny-Carman permeability model allowed the dynamic model to give excellent predictions when a variable Kozeny factor was used (Equation 2.12), rather than a constant Kozeny factor.

A microparticle chemical additive system, 0.05% CPAM and 0.06% modified bentonite, improved the retention of bagasse pulp fines over a wide range of shear using a DDJ. Applying vacuum dramatically reduced the drainage time. At any level of vacuum, bagasse pulp benefitted from the chemical additives as measured by reduced drainage time and increased fines retention. The DDJ was also used to obtain additional information about the behaviour of thin bagasse pulp mats without flocculants being added.

In steady-state permeability and compressibility experiments involving pulp pads, the addition of chemical additives could only be determined to improve S v for one type of pulp; the ‘30% depithed’ pulp. However, dynamic filtration

165 Thomas J. Rainey – A study of bagasse pulp filtration experiments showed that there was a small improvement in permeability for the ‘medium’ bagasse pulp.

The mechanism of bagasse pulp consolidation appears to be by fibre realignment. Chemical additives assist by lubricating the fibres during the consolidation process.

For initially unnetworked suspensions, and the conditions found in the DDJ which is similar to Fourdrinier forming, the fastest drainage rate was achieved by a standard depithing regime practiced by industry (i.e. removal of 30% of the shortest fibres) using a significant level of vacuum and chemical additives. However, the lower WRV of the ‘coarse’ bagasse pulp indicates that it would dry more quickly.

For initially networked fibre pads, as in the compression cell and permeability cell, the ‘coarse’ bagasse pulp was the easiest to filter.

The physical properties of the ‘coarse’ bagasse pulp were compared to the benchmark Australian bagasse pulp. The ‘coarse’ bagasse pulp had significantly improved initial freeness, tear properties and WRV of the pulp. However, the ‘coarse’ bagasse pulp did not have higher tensile strength or burst properties and had slightly worse apparent density and compressive strength. Also, refining did not significantly improve any strength property. The bagasse pulp had acceptable physical properties for the production of generic versions of each paper grade considered (i.e. photocopier papers, tissues and packaging), by comparison with Indian bagasse pulp.

In summary, this study has shown that bagasse pulp can be produced with pulp pad permeability properties that are superior to eucalypt pulp, contrary to conventional wisdom. The high permeability arises from the stiff pulp fibres and the high proportion of longer fibres creating an open matrix. Given its higher pulp pad permeability, ‘coarse’ bagasse pulp could be used for a range of applications where its properties are superior to conventional bagasse pulp.

166 Chapter 5 - Conclusions

5.2. Recommendations for future work

No optimisation of the cane varieties was performed in the study presented in this thesis. High fibre energy canes should be developed in Australia and evaluated for their permeability, compressibility and strength properties. Increasing the fibre content has the benefits of improving the economy of scale for a bagasse pulp and paper mill and it also increases the amount of renewable energy available. Energy canes have the potential to significantly improve the economics of a bagasse paper industry in Australia. The opinion of the author is that should a bagasse pulp mill be built in Australia, development of energy canes would be inevitable.

A dynamic filtration model was developed and verified for bagasse pulp at ambient conditions. This model will be a valuable tool for assisting the development of pulp processing equipment that is specially designed for processing bagasse pulp. This work could be conducted as a further study.

This thesis has outlined methods to improve the filtration properties of bagasse pulp. Using these methods, the sheet drying performance may now become the processing step limiting machine production rate. Improving the sheet drying performance was beyond the scope of this study. Only a few measurements of WRV were taken. A further study on improving the sheet drying properties of bagasse pulp would be interesting.

This study recommends careful treatment of bagasse prior to pulping and the use of chemical additives to improve the filtration properties of bagasse pulp pads. An investigation into the pulp properties of heavily depithed bagasse pulp that has been post-processed by pressure screening (as recommended in 50, 64) may reveal further improvements in bagasse pulp pad permeability.

The issues which are preventing the development of a bagasse pulp industry in Australia (outlined in section 1.1.3) are (i) the poor filtration properties of bagasse pulp, (ii) the poor physical strength properties, (iii) high capital cost and

167 Thomas J. Rainey – A study of bagasse pulp filtration

(iv) the remoteness of cane farms to existing pulp mills. For the first issue, there has recently been significant progress made to improve the filtration properties of bagasse pulp as outlined in this thesis and also by El-Sharkawy and co-workers (50, 64). For the second issue, hopefully pulp strength will be improved by breeding more appropriate cane varieties and changing the juice extraction method in alignment with the work by Gartside and coworkers (28, 51, 65). For the third issue, technologies that reduce the capital cost of a bagasse pulp mill should be explored.

Targeted research into replacing the expensive liquor chemical recovery plant appears to have great potential for dramatically reducing the capital cost of a bagasse pulp mill. The ease with which bagasse is pulped makes it a prime candidate for researching alternative processes which don’t require conventional chemical recovery technology. Three such alternative processes are: using the liquor to make fertiliser (50, 64, 145, 146); using electrostatic membranes to recover pulping chemicals (20); and using organic solvents, such as formic acid, that can be recovered by distillation (147-150).

168 References

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181 Appendix A-Supplementary material for dynamic filtration modeling

Appendix A Supplementary material for dynamic filtration modeling

183 Thomas J. Rainey – A study of bagasse pulp filtration

A.1 Derivation of the dimensional governing equation for the dynamic filtration model

This is the derivation of the governing equations for a constant rate filtration apparatus. The mass and momentum balance equations are provided in Chapter 2.

dh 1D assumption; u (velocity of fibres) = v (velocity of water) = dt at the top platen

Mass balance on the fibres dh + ( u)=0 dt ∇⋅ φ dφ δφ u − =0 (C.1.1) dt δx

Similarly, mass balance for the water d(1 −φ ) + (1 )v=0 dt ∇⋅ −φ

dφ d(1 −φ )v − dt − dx =0 (C.1.2)

(C.1.1)+(C.1.2)

δ(φu) d(1 −φ )v + =0 δx dx

δ[φu+(1 −φ )v] =0 δx

→φ u+(1 −φ )v=c(t) where c(t) is a constant.

dh sub in Boundary Condition: at x=h(t), u=v=− dt

dh dh (1 ) =c(t) →−φ dt − −φ dt

dh c(t)= − dt

184 Appendix A-Supplementary material for dynamic filtration modeling

dh →φ u+(1 −φ )v=− dt Momentum balance

Fibres: Du ρ φ =−φ∇ P −∇ P +∇⋅ (φτ )+ ρ φg+m (C.1.3) s Dt f s s s

Du Dt =0 as inertia not significant

g→0 as gravity effects insignificant

τ =0 s as shear effects insignificant Fluid:

Dv ρ φ =−(1 −φ )∇P +∇⋅ [(1 −φ )τ ]+ ρ φg−m (C.1.4) f Dt f f f

(C.1.3)+(C.1.4)

0= −φ∇ P +∇P f s in 1-D

dP dP f s dx + dx =0 which is Terzaghi’s principle.

d(P +P ) f s dx =0

P +P =c(t) f s At bottom P =σ(t) since P =0 at x=0 recall s f

m=(1 −φ )α(φ)( u−v) back to equation (C.1.4)

−(1 −φ )∇P −m=0 f

dP f = ( )( u v) (C.1.5) dx α φ − sub (C.1.5) into (C.1.3)

185 Thomas J. Rainey – A study of bagasse pulp filtration

dP s 0= −φα (φ)( u−v)− dx +(1 −φ )α(φ)( u−v)

dP s 0= −(1 −φ ) dx +α(φ)[(1 −φ )u−(1 −φ )v] recall

dh u+(1 )v= φ −φ − dt so

dP s dh 0= (1 ) + ( )[(1 )u+ + u] − −φ dx α φ −φ dt φ

dP s dh (1 ) = ( )[ u+ ] → −φ dx α φ dt

dP (1 −φ ) s dh − =u α(φ) dx dt recall (C.1.1) is

dφ δφ u − =0 dt δx eliminate u

dP 1−φ s dh dφ[ − ] dφ α(φ) dx dt dt − dx =0

F dP V dφ d φ(1 −φ ) s dh dφ = G W+ dt dx H α(φ) dx X dt dx µ use fitting model α(φ)= K(φ) and recall

P =MφN s

dP s f'( φ)= dφ

dP dP s s dφ = dx dφ dx

186 Appendix A-Supplementary material for dynamic filtration modeling

dP s dφ → dx =f'( φ) dx so

dφ d F φ(1 −φ )K(φ)f'( φ) dφV dh dφ = G W+ dt dx H µ dx X dt dx let

φ(1 −φ )K(φ)f'( φ) D(φ)= µ

dφ d F dφV dh dφ = GD( ) W (C.1.6) dt dx H φ dx X− dt dt (C.1.6) is the governing equation recall

dP (1 −φ ) s dh u= − α(φ) dx dt

(1 −φ ) dφ dh = f'( φ) − α(φ) dx dt Boundary condition 1 dh x=h(t), u= − dt

dh (1 −φ ) dφ dh − = f'( φ) − dt α(φ) dx dt

dφ → dx =0 Boundary condition 2 x=0, u=0

(1 −φ ) dφ dh 0= f'( φ) − α(φ) dx dt

dφ dh α(φ) → = dx dt (1 −φ )f'( φ)

187 Thomas J. Rainey – A study of bagasse pulp filtration

A.2 Non-dimensionalising of dynamic model for FORTRAN

The dimensional governing equations need to be non-dimensionalised for use with the FORTRAN function libraries.

Dimension Dimensional variable Dimensionless variable Distance from platen x (m) x X (-) = h −u t 0 0 Time t (min) u 0 t* (-) = t h 0

Flexural term D( φ) D(φ)1 D*( φ) (-) = u h 0 0 1 by definition, the reason will be demonstrated shortly

Where h is defined as the initial height of the platen above the base and u 0 0 dh is the speed of the platen ( u = ) 0 dt recall the governing equation in dimensional form

dφ d F dφV dh dφ G W dt = dx HD(φ) dx X− dt dx we can immediately transform the spatial co-ordinates

u dφ d F D(φ) dφV 0 dφ = G W− (C.2.1) dt dX (h −u t)2 dX h −u t dX H 0 0 X 0 0 Firstly, we need to establish a couple of simple relations, by the chain rule

dφ δφ δX δφ δt = + dx δX δx δt δx δt but at a constant rate =0 so δx

δφ 1 δφ = (C.2.2) δx h −u t δX 0 0 also

δx x=X(h −u t)→ =−u X (C.2.3) 0 0 δt 0 By the chain rule, the LHS of (1) becomes

188 Appendix A-Supplementary material for dynamic filtration modeling

δφ δφ δt* δφ δx = + δt δt* dt δx δt substitute (C.2.2) and (C.2.3) and rearranging, the LHS of (C.2.1) reduces to

u u δφ 0 δφ 0 X δφ = h *+ h * (C.2.4) δt 0 δt 0 1−t δX substituting (4) into (3) and rearranging

u u 0 δφ d F D(φ) dφV 0 1−X δφ = G W− h * dX 2 * 2 dX h * δX 0 δt H h0(1 −t ) X 0 1−t h 0 Multiplying all terms by (1 t*)2 we get − u 0

* 2 δφ δ F D(φ) dφV * δφ (1 −t ) *= G u h dX W−(1 −X)(1 −t ) δt δX H 0 0 X δX φ(1 −φ )K(φ)f'( φ) by definition D(φ)= substituting the definitions of µ 3 1 (1 −φ ) N−1 K(φ)= 2 2 and f'( φ)= MN φ we get kS v φ

NM 4 N−2 D(φ)= 2 (1 −φ ) φ µkS u h v o 0 applying the definition of D*(φ) we end up with the non-dimensional form of the governing equation

δφ δ F dφV δφ (1 −t*)2 = GD*(φ) W−(1 −X)(1 −t*) (C.2.5) δt* δX H dX X δX

This is the form of the Governing equation required by the FORTRAN NAB library functions D03PCF and D03PZF

(C.2.5) is subject to the boundary conditions

Boundary condition (1) at X = 1

δφ =0 δX Boundary condition (2) at X = 0

δφ δh φ = δx δt D(φ)

189 Thomas J. Rainey – A study of bagasse pulp filtration substituting (C.2.2) and the definition of D(φ) we get

u φ 1 δφ 0 = h −u t δX u h D*(φ) 0 0 0 0 substituting the definition of t* and rearranging

δφ φ(1 −t*) = δX D*(φ)

190 Appendix A-Supplementary material for dynamic filtration modeling

A.3 FORTRAN 77 program for the dynamic filtration model

**************************************************************** * * Tom Raineys pulp compression modelling program * adapted from * D03PCF Example Program Text * * VERSION 6: FINAL * * Assisted by Neil Kelson * * This version is used for bagasse pulp compression modelling * by adjusting the parameters below * * * To compare with experimental data need to specify PhiInit; Hinit; MPHI; * NPHI; Sv; and DHDT. * Generates two files: fort.21 (output for Ps) and fort.22 (output for phi) * ****************************************************************

* .. Parameters ..

INTEGER NOUT PARAMETER (NOUT=21) INTEGER NPDE, NPTS, INTPTS, ITYPE, NEQN, NIW, NWK, NW * PARAMETER (NPDE=2,NPTS=20,INTPTS=6,ITYPE=1,NEQN=NPDE*NPTS, * + NIW=NEQN+24,NWK=(10+6*NPDE)*NEQN, * + NW=NWK+(21+3*NPDE)*NPDE+7*NPTS+54) PARAMETER (NPDE=1,NPTS=50,INTPTS=50,ITYPE=1,NEQN=NPDE*NPTS, + NIW=NEQN+24,NWK=(10+6*NPDE)*NEQN, + NW=NWK+(21+3*NPDE)*NPDE+7*NPTS+54)

* INTPTS changed from 6 to 50 to increase resolution of X in output * .. Scalars in Common .. * DOUBLE PRECISION DPHI DOUBLE PRECISION PHIINIT, MPHI, NPHI * .. Local Scalars .. DOUBLE PRECISION ACC, HX, PI, PIBY2, TOUT, TS INTEGER I, IFAIL, IND, IT, ITASK, ITRACE, M * .. Local Arrays .. DOUBLE PRECISION U(NPDE,NPTS), UOUT(NPDE,INTPTS,ITYPE), W(NW), + X(NPTS), XOUT(INTPTS) INTEGER IW(NIW) * .. External Functions ..

191 Thomas J. Rainey – A study of bagasse pulp filtration

DOUBLE PRECISION X01AAF EXTERNAL X01AAF * .. External Subroutines .. EXTERNAL BNDARY, D03PCF, D03PZF, PDEDEF, UINIT * .. Intrinsic Functions .. INTRINSIC SIN * .. Common blocks .. COMMON /VBLE/PHIINIT,MPHI,NPHI

* .. Data statements .. XOUT(1) = 1.0D-6

DO 60 I = 2, 51 XOUT(I) = 0.02+XOUT(I-1)

60 CONTINUE

* .. Executable Statements .. WRITE (NOUT,*) 'Raineys compression testing results - Ps' WRITE (NOUT+1,*) 'Raineys compression testing results - PHI only' ACC = 1.0D-6 M = 0 ITRACE = 0 MPHI = 4774D+0 * MPHI unitless NPHI = 2.4333D+0 * NPHI in Pa PHIINIT = 0.025429D+0 * Typical value in compression experiments

IND = 0 ITASK = 1 * * Set spatial mesh points * PIBY2 = 0.5D0*X01AAF(PI) HX = PIBY2/(NPTS-1) X(1) = 0.0D0 X(NPTS) = 1.0D+0 DO 20 I = 2, NPTS - 1 X(I) = SIN(HX*(I-1))

20 CONTINUE * * Set initial conditions * TS = 0.0D0 TOUT = 0.1D-5 * for testing - reduce TOUT step

192 Appendix A-Supplementary material for dynamic filtration modeling

* TOUT = 0.05D0 * Tom:

WRITE (NOUT,99999) ACC, PHIINIT, MPHI, NPHI WRITE (NOUT,99998) (XOUT(I),I=1,50) * Tom: Change from I=1,6 to I=1,50 to accommodate new X columns * Set the initial values CALL UINIT(U,NPTS)

ILOOPS = 87 * Tom: Changed above line from 5 to 83 to get values of TOUT 0 to * 0.83(=75mm/90mm at constant rate)

DO 40 IT = 1, ILOOPS

IFAIL = -1 TOUT = 0.01D0+TOUT * Tom: Introduce a linear timestep * * Call the solver CALL D03PCF(NPDE,M,TS,TOUT,PDEDEF,BNDARY,U,NPTS,X,ACC,W,NW,IW , + NIW,ITASK,ITRACE,IND,IFAIL) * * Interpolate solution at required spatial points CALL D03PZF(NPDE,M,U,NPTS,X,XOUT,INTPTS,ITYPE,UOUT,IFAIL)

WRITE (NOUT+1,99996) TOUT, (UOUT(1,I,1),I=1,INTPTS) WRITE (NOUT,99995) TOUT, ((MPHI*(UOUT(1,I,1))**NPHI),I=1,INTPTS) * Tom: to alternate between PS output and PHI output make active the correct * line here and also make active the appropriate FORMAT line (i.e. * either 99996 or 99995).

40 CONTINUE

* * Print integration statistics * WRITE (NOUT,99997) IW(1), IW(2), IW(3), IW(5) STOP * 99999 FORMAT (//' Accuracy requirement = ',D12.5,/ + ' PHIINIT = ',D12.5,/

193 Thomas J. Rainey – A study of bagasse pulp filtration

+ ' MPHI = ',D12.5,/ + ' NPHI = ',D12.5,/) 99998 FORMAT (' T/ X ',50F8.4,/) 99997 FORMAT (' Number of integration steps in time ', + I4,/' Number of residual evaluations of resulting ODE ' + 'sys', + 'tem',I4,/' Number of Jacobian evaluations ', + ' ',I4,/' Number of iterations of nonlinear solve', + 'r ',I4,/) 99996 FORMAT (1X,F8.4,' PHI',50F8.4) * Tom: Change above format from 6F8.4 to 50F8.4 to display new columns * Tom: for X in output as governed by INTPTS 99995 FORMAT (1X,F8.4,' PS',50F8.3) * Switch between 99996 and 99995 END **************************************************************** ************ SUBROUTINE UINIT(U,NPTS) * Routine for PDE initial conditon

* .. declarations .. INTEGER I, NPTS DOUBLE PRECISION PHIINIT, MPHI, NPHI DOUBLE PRECISION U(1,NPTS)

* .. common blocks.. COMMON /VBLE/PHIINIT,MPHI,NPHI

* .. Executable Statements .. DO 20 I = 1, NPTS U(1,I) = PHIINIT 20 CONTINUE

RETURN END **************************************************************** ************ SUBROUTINE PDEDEF(NPDE,T,X,U,DUDX,P,Q,R,IRES) * .. Scalar Arguments .. DOUBLE PRECISION T, X INTEGER IRES, NPDE * .. Array Arguments .. DOUBLE PRECISION DUDX(NPDE), P(NPDE,NPDE), Q(NPDE), R(NPDE), + U(NPDE) * .. Scalars in Common .. DOUBLE PRECISION DPHI DOUBLE PRECISION PHIINIT,MPHI, NPHI DOUBLE PRECISION MU, KOZ, SV, DHDT, HINITIAL * .. Common blocks ..

194 Appendix A-Supplementary material for dynamic filtration modeling

COMMON /VBLE/PHIINIT,MPHI,NPHI

* NPHI (-) and MPHI (Pa) are the exponent and pre-exponent for the * compression correlation * mu is the viscosity (Pa.s) * koz is the variable kozeny factor (or set to 5.55) * Sv is the specific surface area (m^-1) * DHDT is the rate of the piston (m/s) * HINITIAL is the initial height (m) * Average Milled bagasse pulp MPHI * Average Milled bagasse pulp NPHI

MU = 0.001D0 * Viscosity of water in Pa.s KOZ = 3.5*((1-3.5*U(1))**3)*(1+(57*((3.5*U(1))**3)))/ + ((3.5*U(1))**0.5) * Koz can be set as constant k=5.55 if desired SV = 191700D0 * SV as m-1; this value is for optimum for variable koz factor

DHDT = 4.1667D-4 * in m/s - 75 mm displacement over 3 MINS HINITIAL = 0.073D0 * Initial height of the platen is 90mm, height in metres

* .. Executable Statements ..

DPHI = MPHI*NPHI*((1-U(1))**4)*((U(1))**(NPHI-2)) + /(MU*KOZ*SV*SV*DHDT*HINITIAL) Q(1) = -(1-X)*(1-T)*DUDX(1) R(1) = DPHI*DUDX(1) P(1,1) = (1-T)*(1-T)

RETURN END **************************************************************** ************ SUBROUTINE BNDARY(NPDE,T,U,UX,IBND,BETA,GAMMA,IRES) * .. Scalar Arguments .. DOUBLE PRECISION T INTEGER IBND, IRES, NPDE * .. Array Arguments .. DOUBLE PRECISION BETA(NPDE), GAMMA(NPDE), U(NPDE), UX(NPDE)

* .. Executable Statements ..

IF (IBND.EQ.0) THEN BETA(1) = 1.0D+0 GAMMA(1) = -U(1)*(1-T)

195 Thomas J. Rainey – A study of bagasse pulp filtration

ELSE BETA(1) = 1.0D+0 GAMMA(1) = 0.0D+0 END IF

RETURN END

196 Appendix A-Supplementary material for dynamic filtration modeling

A.4 Graphs comparing predictions of dynamic filtration model with experimental data

Commencing next page

197 Thomas Rainey, J. A of study bagasse filtratio pulp 198 n

198 Appendix A - material Supplementary fil dynamic for tration modeling 199

199 Thomas Rainey, J. A of study bagasse filtratio pulp 200 n

200 Appendix A - material Supplementary fil dynamic for tration modeling 201

201 Thomas Rainey, J. A of study bagasse filtratio pulp 202 n

202 Appendix B Summary of pulp samples

203 204 Thomas Rainey, J. A of study bagasse filtratio pulp Table B.1 Summary of bagasse pulping conditions for all pulp samples presented in this thesis.

Cooking Screened Screened kappa Sample name Cook date Origin Fraction Reactor type Cooking conditions time yield number % rejects Bagasse pulps (min) (-) (-) (%) Sample 8 14/11/2006 Diffuser Medium Flow-through digester 0.4M NaOH & 0.1%AQ 40 0.5086 5.58% Sample 9 14/11/2006 Diffuser Medium Flow-through digester 0.4M NaOH & 0.1%AQ 55 Sample 10 14/11/2006 Diffuser Medium Flow-through digester 0.4M NaOH & 0.1%AQ 70 0.4965 19.4 4.40% Sample 11 14/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 40 0.4436 21.9 4.68% Sample 12 14/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 55 0.4783 19.6 4.58% Sample 13 14/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 70 0.4644 16.1 2.31% Sample 14 16/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 6 0.5031 23.7 7.48% Kinetics study study Kinetics Sample 15 16/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 12 0.4953 27.7 7.60% Sample 16 16/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 18 0.4953 26.6 5.41% Sample 17 16/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 24 0.4837 25.1 7.45% Sample 18 16/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 30 0.4698 23.7 5.71% Sample 19 16/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ 30 0.4896 21.7 3.47% Sample 20 17/11/2006 Diffuser Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5678 26.7 2.98% Sample 21 17/11/2006 Diffuser Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5615 26 3.62% Sample 23 17/11/2006 Diffuser Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5201 22.7 5.93%

Sample 24 17/11/2006 Diffuser Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5419 24.6 5.38% n Sample 26 20/11/2006 Mill Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5467 26.2 3.70% Sample 27 20/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5098 24.3 6.07% Sample 29 20/11/2006 Mill Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5354 26 5.57% Sample 30 20/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5117 24.1 6.38% Sample 31 20/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5061 22.9 6.13% Sample 32 21/11/2006 Ledesma Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.6180* 22.5 4.47% Sample 33 21/11/2006 Mill Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5440 25.1 4.22% Sample 34 21/11/2006 Mill Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5469 25.4 5.31% Sample 35 21/11/2006 Diffuser Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5075 23.9 6.36% Sample 36 21/11/2006 Diffuser Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.4843 23.9 9.58% Sample 37 21/11/2006 Ledesma Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 *Combined with Sample 32 Sample 38 22/11/2006 Mill Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5456 23.6 3.76% Sample 39 22/11/2006 Diffuser Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5145 22.3 4.49% Sample 40 22/11/2006 Diffuser Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 Not recorded Sample 41 22/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.4718 12.08% Sample 42 22/11/2006 Mill Medium Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5082 22 3.98% Sample 43 22/11/2006 Mill Coarse Flow-through digester 0.4M NaOH & 0.1%AQ, 145 deg 30 0.5238 24.6 4.21%

204 Screened Cooking Screened kappa % Sample name Cook date Origin Fraction Reactor type Cooking conditions time yield number rejects (min) (-) (-) (%) 12.5% Na2O, 14:1 liq fibre, 170 deg, 105 minutes, no Sample 52 17/07/2007 Mill Whole bagasse Large Parr Reactor AQ 105 0.5260 40 0.24% 15% Na2O, 0.1% AQ, 12:1 liq fibre, 105 mins, 170 Sample 53 19/07/2007 Mill Whole bagasse Large Parr Reactor deg 105 9.2 Sample 55 9/04/2008 Mill Medium Large Parr Reactor 15% Na2O, 0.1% AQ, 12:1 liq fibre, 90 mins, 170 deg 90 0.4066 9.2 1.09% Sample 56 14/04/2008 Mill Coarse Large Parr Reactor 15% Na2O, 0.1% AQ, 12:1 liq fibre, 60 mins, 170 deg 60 0.4924 16.2 5.09% Sample 57 16/04/2008 Mill Coarse Large Parr Reactor 15% Na2O, 0.1% AQ, 12:1 liq fibre, 90 mins, 170 deg 90 0.4910 10.3 2.80%

Sample 58 23/04/2008 Mill 30% depithed Large Parr Reactor 15% Na2O, 0.1% AQ, 12:1 liq fibre, 60 mins, 170 deg 60 0.4068 14.3 8.07% Appendix - B Summary of samples pulp Sample 59 28/04/2008 Mill Fine Large Parr Reactor 15% Na2O, 0.1% AQ, 12:1 liq fibre, 90 mins, 170 deg 90 0.2868 8.1 8.61% Sample 60 21/07/2008 Mill Medium Large Parr Reactor 15% Na2O, 0.1% AQ, 12:1 liq fibre, 60 mins, 170 deg 60 0.4902 15.7 5.74%

Wood pulps Eucalyptus Globulus Ensis Air-bath reactor 11.75% Na2O, 25% sulfidity, 165 deg 120 19 Pinus Radiata APPI Air-bath reactor 20 205

205 This page is deliberately blank.

206 Appendix C-Supplementary photographs of experimental work

Appendix C Supplementary photographs of experimental work

207 Thomas J. Rainey – A study of bagasse pulp filtration

Figure C.1 Photograph of bagasse packed into a cage ready for insertion into a ‘flow-through’ reactor cell.

Inlet liquor line

Top flange

Packed bagasse

Outlet liquor line

Figure C.2 Photograph of a loaded ‘flow-through’ reactor cell.

208 Appendix C-Supplementary photographs of experimental work

Serpentine cooling coils

Figure C.3 Photograph of the inside of the unloaded 18.5 L Parr reactor.

  
  

   

       

Figure C.4 Photograph of the 18.5 L Parr reactor vessel head.

209 Thomas J. Rainey – A study of bagasse pulp filtration

 

 

      

   

Figure C.5 Barrel of compressibility cell immediately prior to loading with pulp slurry.

  

    

Figure C.6 Compressibility cell mid-way through a compressibility experiment.

Figure C.7 Relaxed pulp pad after compression experiment showing layering of pulp.

210 Appendix D Table of Students t distribution

211 Thomas J. Rainey – A study of bagasse pulp filtration

The point tabulated is t, where P(t v>t)=p and t v has Student’s t-distribution with v degrees of freedom.

Table D.1 Table of Student’s t statistic p 0.25 0.1 0.05 0.025 0.01 0.005 0.0025 0.001 0.0005 v 1 1.000 3.078 6.314 12.71 31.82 63.66 127.3 318.3 636.6 2 0.816 1.886 2.920 4.303 6.965 9.925 14.09 22.33 31.60 3 0.765 1.638 2.353 3.182 4.541 5.841 7.453 10.21 12.92 4 0.741 1.533 2.132 2.776 3.747 4.604 5.598 7.173 8.610 5 0.727 1.476 2.015 2.571 3.365 4.032 4.773 5.893 6.869 6 0.718 1.440 1.943 2.447 3.143 3.707 4.317 5.208 5.959 7 0.711 1.415 1.895 2.365 2.998 3.499 4.029 4.785 5.408 8 0.706 1.397 1.860 2.306 2.896 3.355 3.833 4.501 5.041 9 0.703 1.383 1.833 2.262 2.821 3.250 3.690 4.297 4.781 10 0.700 1.372 1.812 2.228 2.764 3.169 3.581 4.144 4.587 11 0.697 1.363 1.796 2.201 2.718 3.106 3.497 4.025 4.437 12 0.695 1.356 1.782 2.179 2.681 3.055 3.428 3.930 4.318 13 0.694 1.350 1.771 2.160 2.650 3.012 3.372 3.852 4.221 14 0.692 1.345 1.761 2.145 2.624 2.977 3.326 3.787 4.140 15 0.691 1.341 1.753 2.131 2.602 2.947 3.286 3.733 4.073 16 0.690 1.337 1.746 2.120 2.583 2.921 3.252 3.686 4.015 17 0.689 1.333 1.740 2.110 2.567 2.898 3.222 3.646 3.965 18 0.688 1.330 1.734 2.101 2.552 2.878 3.197 3.610 3.922 19 0.688 1.328 1.729 2.093 2.539 2.861 3.174 3.579 3.883 20 0.687 1.325 1.725 2.086 2.528 2.845 3.153 3.552 3.850 21 0.686 1.323 1.721 2.080 2.518 2.831 3.135 3.527 3.819 22 0.686 1.321 1. 717 2.074 2.508 2.819 3.119 3.505 3.792 23 0.685 1.319 1.714 2.069 2.500 2.807 3.104 3.485 3.767 24 0.685 1.318 1.711 2.064 2.492 2.797 3.091 3.467 3.745 25 0.684 1.316 1.708 2.060 2.485 2.787 3.078 3.450 3.725 30 0.683 1.310 1.697 2.042 2.457 2.750 3. 030 3.385 3.646 40 0.681 1.303 1.684 2.021 2.423 2.704 2.971 3.307 3.551 50 0.679 1.299 1.676 2.009 2.403 2.678 2.937 3.261 3.496 60 0.679 1.296 1.671 2.000 2.390 2.660 2.915 3.232 3.460 120 0.677 1.289 1.658 1.980 2.358 2.617 2.860 3.160 3.373 . 0.674 1.282 1.645 1.960 2.326 2.576 2.807 3.090 3.291

212 Appendix E Fibre length data of pulp sample

213 214 Thomas Rainey, J. A of study bagasse filtratio pulp

Table E.1 Results of fibre length distribution analysis for all pulp samples measured in this thesis.

Instumentation Diffuser First First Second Third Ninth Sample Coarse or Number % fines and or decile quartile quartile quartile decile Average name Medium of fibres (<0.2mm) location Milled 10% 25% 50% 75% 90% 18 Milled Medium 4999 0.29 0.51 0.87 1.37 1.89 1.01 20 Diffuser Coarse 3013 0.29 0.51 0.91 1.39 1.93 1.03 21 Diffuser Coarse 5016 0.4 0.72 1.2 1.7 2.23 1.27 26 Milled Coarse 5035 0.32 0.55 0.99 1.51 2.08 1.11 27 Milled Medium 5016 0.3 0.53 0.9 1.41 2.02 1.04 30 Milled Medium 5048 0.24 0.44 0.78 1.24 1.71 0.9 32 N/A N/A 5034 0.23 0.42 0.75 1.28 1.94 0.96 34 Milled Coarse 5027 0.28 0.51 0.94 1.45 2.12 1.09 35 Diffuser Medium 5023 0.26 0.49 0.87 1.31 1.79 0.98 38 Milled Coarse 5024 0.31 0.54 0.91 1.47 2.08 1.07 n 39 Diffuser Medium 5031 0.27 0.47 0.8 1.23 1.76 0.92 42 Milled Medium 5004 0.24 0.42 0.72 1.14 1.6 0.84 43 Milled Coarse 5020 0.26 0.45 0.82 1.37 2 0.99 Kajaani FS100 Mill Amcor, Petrie at Kajaani 51 Milled Fine 5066 0.11 0.21 0.39 0.67 1.09 0.52 53 Milled Unfrac. 4980 0.21 0.38 0.66 1.07 1.56 0.8 Eucalypt 5036 0.39 0.57 0.77 0.98 1.15 0.77 56 Milled Coarse 8097 1.148 10.1 30%

UBC 58 Milled depithed 5857 0.965 17.45 FQA at at FQA 60 Milled Medium 4573 1.149 11.1

214 Appendix F Engineering drawings of compression cell

215 Thomas of Rainey J. bagasse - A study filtrati pulp 216 on

216 Appendix - Engineering F drawings of ce compression

First angle projection ll ll 217

217 218 Thomas of Rainey J. bagasse - A study filtrati pulp on

Third angle projection

218 Appendix - Engineering F drawings of ce compression ll ll 219

219 Thomas of Rainey J. bagasse - A study filtrati pulp 220 on

Third angle projection

220 Appendix - Engineering F drawings of ce compression

Third angle projection ll ll 221

221