cellulosic ethanol from sugarcane bagasse in australia...
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Queensland University of Technology
Cellulosic ethanol from sugarcane bagasse in Australia: exploring industry
feasibility through systems analysis, techno-economic assessment and pilot
plant development
Ian O’Hara BE (Chem), MBA
Principal Supervisor: Dr Les A Edye
Associate Supervisor: Dr Geoff A Kent
A thesis submitted for the degree of
Doctor of Philosophy
in the Faculty of Science and Technology
Queensland University of Technology
according to QUT requirements
2011
ii
Keywords
sugarcane, bagasse, lignocellulose, fibre, biofuels, biorefinery, ethanol,
pretreatment, systems analysis, uncertainty, risk, techno-economic
assessment, feasibility, plant expressed enzymes, pilot plant
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Abstract
Overcoming many of the constraints to early stage investment in biofuels
production from sugarcane bagasse in Australia requires an understanding of the
complex technical, economic and systemic challenges associated with the transition
of established sugar industry structures from single product agri-businesses to new
diversified multi-product biorefineries.
While positive investment decisions in new infrastructure requires technically
feasible solutions and the attainment of project economic investment thresholds,
many other systemic factors will influence the investment decision. These factors
include the interrelationships between feedstock availability and energy use,
competing product alternatives, technology acceptance and perceptions of project
uncertainty and risk.
This thesis explores the feasibility of a new cellulosic ethanol industry in Australia
based on the large sugarcane fibre (bagasse) resource available. The research
explores industry feasibility from multiple angles including the challenges of
integrating ethanol production into an established sugarcane processing system,
scoping the economic drivers and key variables relating to bioethanol projects and
considering the impact of emerging technologies in improving industry feasibility.
The opportunities available from pilot scale technology demonstration are also
addressed.
Systems analysis techniques are used to explore the interrelationships between the
existing sugarcane industry and the developing cellulosic biofuels industry. This
analysis has resulted in the development of a conceptual framework for a bagasse-
based cellulosic ethanol industry in Australia and uses this framework to assess the
uncertainty in key project factors and investment risk. The analysis showed that the
fundamental issue affecting investment in a cellulosic ethanol industry from
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sugarcane in Australia is the uncertainty in the future price of ethanol and
government support that reduces the risks associated with early stage investment is
likely to be necessary to promote commercialisation of this novel technology.
Comprehensive techno-economic models have been developed and used to assess
the potential quantum of ethanol production from sugarcane in Australia, to assess
the feasibility of a soda-based biorefinery at the Racecourse Sugar Mill in Mackay,
Queensland and to assess the feasibility of reducing the cost of production of
fermentable sugars from the in-planta expression of cellulases in sugarcane in
Australia. These assessments show that ethanol from sugarcane in Australia has the
potential to make a significant contribution to reducing Australia’s transportation
fuel requirements from fossil fuels and that economically viable projects exist
depending upon assumptions relating to product price, ethanol taxation
arrangements and greenhouse gas emission reduction incentives.
The conceptual design and development of a novel pilot scale cellulosic ethanol
research and development facility is also reported in this thesis. The establishment
of this facility enables the technical and economic feasibility of new technologies to
be assessed in a multi-partner, collaborative environment. As a key outcome of this
work, this study has delivered a facility that will enable novel cellulosic ethanol
technologies to be assessed in a low investment risk environment, reducing the
potential risks associated with early stage investment in commercial projects and
hence promoting more rapid technology uptake.
While the study has focussed on an exploration of the feasibility of a commercial
cellulosic ethanol industry from sugarcane in Australia, many of the same key issues
will be of relevance to other sugarcane industries throughout the world seeking
diversification of revenue through the implementation of novel cellulosic ethanol
technologies.
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Contents
Keywords ii Abstract iii Contents v
Figures ix
Tables x
Authorship xi Acknowledgements xii
Chapter 1
Introduction 1
1.1 Introduction 1
1.2 Aims and objectives of the research 2
1.3 Research and communication methodology 3
1.4 Thesis outline 4
1.5 Original contributions 7
1.6 Conclusion 8
Systems analysis
Chapter 2
Introduction to biofuels and the Australian sugar industry 11
2.1 Transportation fuels in the early 21st century 11
2.1.1 The use of crude oil as a transportation fuel 11
2.1.2 The contribution of transport fuels to climate change 12
2.1.3 Peak oil and future oil price 13
2.1.4 Energy security and development 14
2.2 Bioethanol – a renewable transport fuel 14
2.2.1 Ethanol as a transportation fuel 14
2.2.2 First-generation ethanol 15
2.2.3 Second-generation bioethanol 16
2.2.4 The global biomass resource 17
2.3 Sugarcane as a bio-energy resource 18
2.3.1 The global sugar industry 18
2.3.2 The sugarcane biomass resource 19
2.3.3 The Australian sugar industry 20
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2.3.4 Current uses of sugarcane bagasse in Australia 22
2.3.5 The sugarcane biorefinery 23
2.4 The composition and structure of sugarcane bagasse 24
2.4.1 Cellulose 26
2.4.2 Hemicelluloses 27
2.4.3 Lignin 28
2.5 Overview of the process for ethanol production from sugarcane bagasse 28
2.6 Conclusion 30
Chapter 3
Pretreatment technologies for ethanol production from sugarcane bagasse 31
3.1 Introduction 31
3.2 The objectives of the pretreatment process 31
3.3 Chemical pretreatments 34
3.3.1 Concentrated acid hydrolysis 34
3.3.2 Dilute acid hydrolysis and pretreatment 34
3.3.3 Alkaline pretreatments 38
3.3.4 Oxidative pretreatments 40
3.3.5 Solvent pretreatments 41
3.3.6 Ionic liquid pretreatments 43
3.4 Physical pretreatments 43
3.4.1 Steam explosion pretreatment 43
3.4.2 Other explosive pretreatments 44
3.4.3 Liquid hot water pretreatments 45
3.4.4 Mechanical pretreatments 46
3.4.5 Ultrasonic and radiation pretreatments 47
3.5 Biological pretreatments 47
3.5.1 Microbiological degradation 47
3.6 Conclusion 49
Chapter 4
Commercialising cellulosic ethanol from sugarcane bagasse: use of systems analysis to reduce the risk and uncertainty associated with early stage investment 51
4.1 Introduction 51
4.2 Systems analysis 52
4.3 Scoping and exploring the problem space 54
4.4 Defining the system purpose and CONOPS 58
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4.5 Scoping the solution space through techno-economic modelling 64
4.6 Manifesting the optimum solution 70
4.6.1 Ethanol price and production incentives 70
4.6.2 Bagasse price 71
4.6.3 Cellulase price 73
4.6.4 Bioethanol plant capital cost 73
4.7 Creating the solution and deep learning 73
Techno-economic assessment
Chapter 5
The potential for ethanol production from sugarcane in Australia 77
5.1 Introduction 77
5.2 Transport fuel use in Australia 77
5.3 The capacity of the Australian sugarcane industry 78
5.4 Ethanol production from sugarcane juice and molasses 79
5.5 Ethanol production from bagasse and sugarcane trash 80
5.6 Scenario analysis 83
5.7 Discussion 86
5.8 Conclusion 89
Chapter 6
Economic feasibility of a soda-based biorefinery at Racecourse Mill 91
Chapter 7
Feasibility assessment of in-planta cellulolytic enzyme expression for the production of biofuels from sugarcane bagasse in Australia 93
Pilot plant development
Chapter 8
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Towards a commercial lignocellulosic ethanol industry in Australia: the Mackay Renewable Biocommodities Pilot Plant 97
8.1 Introduction 97
8.2 Pilot plants – facilitating commercial development 98
8.3 MRBPP funding 98
8.4 Design and construction of the MRBPP 100
8.5 Site services 101
8.6 Plant and equipment 102
8.7 Lignin product recovery 105
8.8 Future developments 105
Discussion
Chapter 9
Discussion 109
9.1 Introduction 109
9.2 Achievement of research objectives and key findings 109
9.3 Importance of research 112
9.4 Recommendations for future work 112
Bibliography 115
Appendices
APPENDIX A
Supplementary data for Chapter 6 145
APPENDIX B
The Mackay Renewable Biocommodities Pilot Plant – photographic record of construction and equipment installation 147
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Figures Figure 2.1 Leading sugarcane producing countries 2006 [32] ................................. 18
Figure 2.2 Map of the Australian sugar industry [39] .............................................. 21
Figure 2.3 Australian No.1 sugar pool price 1990-91 to 2005-06 and QSL seasonal pool price 2006-07 to 2010-11 (AU$/t) [38, 41] ..................... 22
Figure 2.4 An overview of current and potential products from sugarcane in Australia – current products shown in black and potential products shown in red ........................................................................................ 24
Figure 2.5 Simple schematic of the key processes required for the ethanol from sugarcane bagasse ...................................................................... 30
Figure 4.1 Issues impacting the commercialisation of bioethanol technologies viewed through economic, technical, sustainability and public policy lenses ........................................................................................ 53
Figure 4.2 Conceptual map of a sugarcane processing system in Australia ............. 55
Figure 4.3 Objectives tree for the sugarcane bioethanol system ............................ 60
Figure 4.4 Schematic representation of the sugarcane bioethanol system ............. 61
Figure 4.5 Techno-economic model of the sugarcane bioethanol system (the sugarcane bioethanol model) based upon the common methodological framework [194] ......................................................... 64
Figure 4.6 Sensitivity of the key factors in bagasse based ethanol project viability (net present value) to the project assumptions....................... 68
Figure 4.7 Sensitivity of the major factors in bagasse based ethanol project viability (net present value) to the assumptions in the techno-economic model .................................................................................. 69
Figure 5.1 Schematic representation of the QUT techno-economic model of an integrated sugar factory, juice and molasses distillery and cellulosic ethanol production facility .................................................... 83
Figure 8.1 Typical biorefinery process diagram .....................................................102
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Tables Table 2.1 Typical constitutive analysis of Australian sugarcane bagasse ................. 26
Table 4.1 Summary of the key issues relating to bagasse-based bioethanol commercialisation in the sugarcane industry in Australia..................... 57
Table 4.2 Summary purpose, concept of operations (CONOPS) and key measures of effectiveness of the integrated sugar – ethanol system ................................................................................................. 63
Table 4.3 Key variable inputs to the sugarcane bioethanol model .......................... 66
Table 4.4 Key fixed inputs to the sugarcane bioethanol model ............................... 67
Table 5.1 Consumption of petroleum products in Australia, Queensland and NSW 2007-08 [198] .............................................................................. 78
Table 5.2 Approximate ethanol yields per tonne of product................................... 80
Table 5.3 Common input data for scenario analysis ............................................... 87
Table 5.4 Input data for the scenario analysis ........................................................ 87
Table 5.5 Results from scenario analysis ................................................................ 88
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Authorship
The work contained in this thesis has not been previously submitted to meet the requirements for an award at this or any other higher education institution. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made. Signature
Name Ian Mark O’Hara
Date
xii
Acknowledgements I would like to thank my Supervisors Dr Les Edye and Dr Geoff Kent for their support
throughout the research program and their invaluable advice and feedback on the
various aspects of the work.
I would like to especially acknowledge receipt of scholarship
funding from the Australian Government and the Australian
Sugarcane Industry as provided by the Sugar Research and
Development Corporation.
The author of this thesis is not a partner, joint venturer, employee or agent of SRDC
and has no authority to legally bind SRDC, in any publication of substantive details
or results of this Project.
I would also like to acknowledge and thank the QUT Centre for Tropical Crops and
Biocommodities for financial support in this project.
This research program would not have been possible without the strong support of
several research partner organisations. I would like to acknowledge the support of
the partners of the Biorefinery Development Project including the Queensland
Government through the Research Industries Partnership Program (RIPP), Mackay
Sugar Ltd, Sugar Research Ltd, Veridian Chemicals Pty Ltd and Hexion Specialty
Chemicals Inc. I would also like to acknowledge the partners of the Syngenta Centre
for Sugarcane Biofuels Development including the Queensland Government
through the National and International Research Alliances Program (NIRAP),
Syngenta Biotechnology Inc, and Farmacule Bioindustries Pty Ltd.
I would like to thank funding partners of the Mackay Renewable Biocommodities
Pilot Plant for the opportunity to be involved in such an exciting and visionary
project. The funding for the design and construction of the pilot plant was provided
by the Australian Government through the National Collaborative Research
Infrastructure Strategy (NCRIS) and the Education Investment Fund (EIF), the
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Queensland Government through the Innovation Building Fund (IBF) and QUT. The
strong support of Mackay Sugar Ltd in the development of the facility has again
been invaluable.
There are many individuals who have contributed to the research program or this
thesis in many ways and your contributions are very much appreciated. In
particular, I would like to acknowledge the contributions and support of Professor
James Dale, Dr William Doherty, Dr Zhanying Zhang, Dr Heng-Ho Wong and Mr
Peter Albertson from the QUT Centre for Tropical Crops and Biocommodities and Dr
Bryan Lavarack from Mackay Sugar Ltd for your support in various aspects of the
work.
Finally I would like to thank my family and in particular my wife Penny for your on-
going patience and support.
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1
Chapter 1
Introduction
1.1 Introduction
This thesis reports the results of a research program exploring the feasibility of
ethanol production from sugarcane bagasse in Australia. The nature of the research
undertaken in this research program acknowledges that overcoming many of the
constraints to early stage investment in biofuels production from sugarcane bagasse
requires a multi-disciplinary approach to the technical, economic and systemic
challenges associated with the transition of established sugar industry structures
from single product agri-businesses to new multi-product, diversified, integrated
biorefineries. These challenges include not only the technical challenges associated
with the novel biofuel technology, but also the integration of new and existing
facilities (site integration), the requirement to produce surplus bagasse (energy
efficiency), changed imperatives for sugarcane variety selection (higher fibre) and
the need to balance agronomic and industrial value-adds (trash collection or field
retention of trash).
Some of the work reported in this thesis was undertaken within research projects at
QUT and funded by several project partners. Of particular note are:
- The work undertaken for Chapter 6 was funded by the partners of the
Biorefinery Development Project including the Queensland Government
through the Research Industries Partnership Program (RIPP), Mackay Sugar
Ltd, Sugar Research Ltd, Veridian Chemicals Pty Ltd and Hexion Specialty
Chemicals Inc.
- The work undertaken for Chapter 7 was funded by the partners of the
Syngenta Centre for Sugarcane Biofuels Development including the
Queensland Government through the National and International Research
2
Alliances Program (NIRAP), Syngenta Biotechnology Inc, and Farmacule
Bioindustries Pty Ltd.
- The work undertaken for Chapter 8 was funded by the partners of the
Mackay Renewable Biocommodities Pilot Plant (MRBPP) project including
the Australian Government through the National Collaborative Research
Infrastructure Strategy (NCRIS) and Education Investment Fund (EIF), the
Queensland Government through the Innovation Building Fund (IBF),
Mackay Sugar Ltd and QUT.
- Scholarship funding for the overall PhD project was provided by the Sugar
Research and Development Corporation (SRDC).
1.2 Aims and objectives of the research
The research program aimed to answer key questions relating to the technical and
economic feasibility of ethanol production from sugarcane bagasse in Australia and
the systemic impediments to commercialisation of the technology in Australia.
The research program aimed to:
- Identify the key technical, economic and systemic factors impacting upon
investment in commercial scale facilities for the production of ethanol from
sugarcane bagasse in Australia;
- Explore leading technologies for the biochemical production of ethanol from
sugarcane bagasse to determine the conceptual feasibility of the technology;
- Conceptualise and develop a framework for assessing the interrelationships
between energy use, feedstock availability and potential cellulosic ethanol
production of integrated sugar and bagasse-based ethanol production
facilities;
- Model the use of the framework through its application to the design and
construction of a pilot scale facility for demonstration of technology for the
production of ethanol from bagasse; and
3
- Communicate key outcomes to the Australian sugar industry to develop a
deeper understanding within the industry of the potential opportunities and
economic feasibility of the technology.
1.3 Research and communication methodology
The research program was based on developing a comprehensive understanding of
the issues impacting on the feasibility of ethanol production from sugarcane
bagasse in Australia. This understanding was formed through both literature
reviews and the use of systems analysis techniques to explore the complex
interrelationships between the existing sugarcane industry and the developing
cellulosic biofuels industry.
The systems analysis led to the development of new technical and economic models
of integrated sugarcane processing, sugar production and cellulosic ethanol
production facilities. These models were then used to undertake comprehensive
assessments of technology options that impact on the feasibility of the system.
These models were applied to the development of a pilot plant for research and
demonstration of ethanol production from sugarcane bagasse. Many of the
elements associated with the design and construction of the facility resulted from
the modelling framework developed in the systems analysis and techno-economic
assessments.
Information contained in two of the chapters in this thesis (Chapter 5 and Chapter
8) were presented as peer-reviewed conference papers to the Australian Society of
Sugar Cane Technologists (ASSCT) in 2009 and 2010. Two further papers have been
submitted to the ASSCT conference in 2011. The decision to address aspects of the
reporting for this research project to the ASSCT conference was made on the basis
that:
- ASSCT is the preeminent research forum of the Australian sugarcane
industry and globally recognised for leading industry-specific research;
4
- ASSCT attracts many of the Australian sugar industry leaders,
researchers and industry practitioners to discuss innovation and the
future directions of the industry;
- The Australian sugar industry is actively seeking diversification options
for bagasse, however, most industry participants have only a limited
understanding of the technology and the economics of ethanol
production from bagasse;
- The papers addressed to the ASSCT conference will serve to inform and
educate participants in the Australian sugar industry on the technology
and economics of ethanol production from bagasse and, through
engaging in on-going dialogue in the ASSCT forum, promote
consideration of sugar industry investment in this technology; and
- Presenting work at the ASSCT forum was encouraged by the scholarship
provider for the research project (SRDC).
1.4 Thesis outline
This thesis explores the progress toward the feasibility of ethanol from cellulosic
biomass feedstock through three different approaches to understanding and
analysing the biofuels system.
Section 1 contains three chapters that provide an analysis of the sugarcane and
bioethanol systems. These chapters provide an introduction to the national and
global drivers impacting upon ethanol production from cellulosic biomass, describe
the literature underpinning the research and address strategies that promote
investment in the technology.
Chapter 2 is an introduction to transportation fuels, the global and national
challenges impacting upon future transportation fuel use and the drivers for
the development of biofuels from cellulosic feedstocks. In addition, this
chapter describes the sugarcane industry in Australia and the factors
5
impacting upon the production of biofuels (and in particular) ethanol from
sugarcane fibre (bagasse).
Chapter 3 provides a brief review of the leading pretreatment technologies
for ethanol production from sugarcane bagasse and the strategies for
producing a fibre that is more amenable to enzymatic hydrolysis.
Chapter 4 reports on a comprehensive analysis of the sugarcane bioethanol
system and uses complex decision making tools to analyse the risks and
uncertainties associated with early stage investment in cellulosic ethanol
production facilities. From this analysis, the chapter draws conclusions about
the relative magnitude of the key investment risks and proposes strategies
that seek to minimise risk and hence promote the likelihood of positive early
stage investment decisions in cellulosic ethanol production from bagasse.
Section 2 contains three chapters that provide techno-economic assessments of
various cellulosic ethanol systems. These assessments reflect different model
systems and focus upon increasing the understanding of the technical and
economic feasibility of each system.
Chapter 5 reports on an assessment of the potential quantum of ethanol
production from sugarcane in Australia and analyses several case studies of
integrated sugarcane processing, juice and molasses-based ethanol
production and bagasse-based ethanol production facilities. This chapter
was presented as a peer-reviewed conference paper at the Australian
Society of Sugar Cane Technologists annual conference in Bundaberg,
Queensland in May 2010.
Chapter 6 is an assessment of the conceptual feasibility of a soda-based
biorefinery at a specific site in Australia, namely the Mackay Sugar Ltd
Racecourse Mill in Mackay, Queensland. The chapter details the results of a
comprehensive techno-economic assessment of the proposed project,
reports on one and two-component sensitivity analyses and assesses several
project alternatives. This chapter was provided as a confidential research
6
report to the partners of the Queensland Government Research Industry
Partnerships Program (RIPP) and multi-partner funded Biorefinery
Development Project.
Chapter 7 is an assessment of the conceptual economic feasibility of the in-
planta expression of cellulase enzymes in the sugarcane production and
processing system, exploring several processing strategies. This chapter was
provided as a confidential research report to the partners of the Syngenta
Centre for Sugarcane Biofuels Development (SCSBD).
Section 3 reports on the development of the Mackay Renewable Biocommodities
Pilot Plant (MRBPP). The author of this thesis was responsible for the conceptual
and detailed process design of the MRBPP, was responsible for the selection and
purchasing of equipment and was the key client representative during the design,
construction and installation phases. The development of this novel facility has
provided significant capability in Australia for the development and demonstration
of innovative technologies for ethanol production from bagasse and other cellulosic
feedstocks and is one of the only flexible and publicly accessible cellulosic ethanol
pilot scale development facilities in the world.
Chapter 8 reports on the development of the MRBPP and discusses the
funding of the facility, the value of pilot plants to commercial development
and provides an overview of the sugarcane biorefinery. Information
contained in this chapter was presented as a peer-reviewed conference
paper at the opening general session of the Australian Society of Sugar Cane
Technologists annual conference in Ballina, NSW in May 2009.
Section 4 is a critical evaluation of the key themes of the thesis and highlights the
fundamental contributions and key outcomes that have resulted from the overall
research project.
Chapter 9 presents the discussion of the key themes of the thesis and draws
conclusions on the value of this work to the development of a sustainable
cellulosic ethanol industry in Australia.
7
Throughout this thesis, the terms ‘cellulosic ethanol’ and ‘bioethanol’ have been
used to refer to ethanol produced from cellulosic feedstocks. While a purified
ethanol product from cellulosic feedstocks is indistinguishable from ethanol
produced from other feedstocks and processes, the terms are convenient ones to
imply an ethanol product manufactured from a cellulosic feedstock.
1.5 Original contributions
This thesis is the first comprehensive assessment of the integration of bagasse-
based ethanol production facilities into established sugar processing systems and
the first to take an integrated approach to systems analysis, feasibility assessment
and pilot plant development. This thesis describes the following original
contributions to the fields of sugar and biofuels research:
- A detailed analysis of the Australian sugarcane processing system with
reference to the integration of ethanol from bagasse into the system;
- The development of a new framework and comprehensive techno-
economic models for assessing the feasibility of ethanol production from
sugarcane in integrated processing facilities;
- An assessment of the economic and systemic uncertainties that will
impact upon early stage investment in cellulosic ethanol technology in
Australia and the identification of strategies for reducing investment risk.
This assessment used Monte Carlo analysis to identify the key variables
and to simulate the impact of uncertainty on the economic indicators of
investment;
- A comprehensive assessment of the technical and economic feasibility of
a soda-based biorefinery in Australia, including a one and two-
component sensitivity analysis of the key variables affecting feasibility;
- An assessment of the economic and technical impact of energy systems
integration for co-located sugar and bagasse-based ethanol production
8
facilities including the impact of energy demand on feedstock
availability, electricity use and ancillary fuel requirements; and
- The conceptual design and development of a novel pilot scale facility for
demonstrating the technical and economic feasibility of processes for
the ethanol production from sugarcane bagasse.
Despite sugarcane being perhaps the best biomass feedstock for early stage
cellulosic ethanol production, such an integrated and multi-dimensional analysis for
cellulosic ethanol production from sugarcane has not previously been undertaken in
Australia, and an extensive literature review has not revealed a similar study
elsewhere in the world.
1.6 Conclusion
This chapter has reviewed the key research question, the aims and outcomes of the
research and provided an outline of the thesis. The next section of the thesis
provides a more detailed introduction to the sugarcane and biofuels systems and
analyses the key factors impacting upon early stage investment in cellulosic ethanol
technologies.
9
Systems analysis
11
Chapter 2
Introduction to biofuels and the Australian sugar industry
2.1 Transportation fuels in the early 21st century
2.1.1 The use of crude oil as a transportation fuel
Although some of the earliest combustion powered transportation vehicles were
fuelled with ethanol, crude oil derivatives have provided the vast majority of
transportation fuels throughout the 20th and early 21st centuries. The overwhelming
reliance on crude oil derivatives as the source of virtually all transportation fuels
throughout this period has been the result of abundant crude oil deposits that have
been inexpensive to extract, refine and distribute to the consumer. The high energy
density of crude oil and its derivatives (including automotive gasoline, diesel and
aviation fuels) has also contributed to the popularity of these products as
transportation fuels.
In 2006, global demand for petroleum and other liquid fuels was 85.0 million barrels
oil equivalent per day (Mb/d) and this is forecast to grow to 106.6 Mb/d in 2030,
with the growth in transportation fuel use being responsible for 80 % of the higher
total crude oil use [1]. Despite improvements in energy efficiency standards in many
countries and the dampened demand resulting from the global economic recession
experienced in 2008-09, global crude oil consumption continues to increase by over
1 % annually, driven primarily by the increased demand for fuel in developing
countries [2], and particularly by the growth in demand in India and China [2, 3].
The only non-fossil liquid transport fuels currently of significance on a global scale
are biofuels, including bioethanol and biodiesel. World production of biofuels
12
exceeded 0.7 Mb/d in 2007, an increase of 35 % from 2006 and accounting for 1.5 %
of total road transport fuel use [4]. Biofuels production is forecast to grow by about
8.6 % annually to approximately 5.9 Mb/d in 2030, increasing to 5.5 % of total liquid
fuel consumption [2].
2.1.2 The contribution of transport fuels to climate change
The Stern Review on the Economics of Climate Change [5] concluded that the
scientific evidence on climate change is now overwhelming, a serious and urgent
issue and that the benefits of strong, early action considerably outweigh the costs
of action. Independent reviews from many sources now recognise the majority
scientific opinion that the climate is changing as a result of anthropogenic
greenhouse gas emissions [5-8] and that the energy future we are creating is
unsustainable [9]. In general, these reports conclude that it is economically
advantageous to undertake early action, and that the introduction of deep cuts in
carbon emissions in the first half of the 21st century is not only essential but
achievable and affordable. Emissions reduction actions, however, are likely to
require a high carbon price in an emissions trading scheme depending upon the
stabilisation goal and emissions target trajectory to achieve the goal [10].
Transport fuels account for 14 % (6.5 GtCO2-e) of global greenhouse gas emissions,
with the majority of these from road transport (76 %) and aviation (12 %), without
accounting for non-CO2 effects of aviation or upstream CO2 emissions from fuel
production. These percentages are expected to remain stable although the total
greenhouse gas emissions from the transport sector are projected to grow to 9
GtCO2-e by 2030 and 12 GtCO2-e by 2050 [5].
It is generally recognised that there is no single solution for the challenges that
climate change will bring through the 21st century and beyond, and that multiple
strategies are required to both reduce carbon emissions and to adapt to the climate
change effects that will inevitably occur. Cost effective greenhouse gas emissions
savings in transportation are expected to result from improvements to fuel
efficiency, behavioural change and the increased use of biofuels. A combination of
13
energy efficiency measures in transport fuel use and increased biofuel use are
estimated to have the potential to result in greenhouse gas savings of 7 GtCO2-e
per annum by 2050 at a cost of $25 /tCO2-e [5, 11].
2.1.3 Peak oil and future oil price
In 1956, M. King Hubbert [12] proposed a state where the production rate of crude
oil in the USA would peak, which would be followed by rapid depletion of the
remaining reserves. He later proposed a similar global state and this point became
known as Hubberts’ peak. Many commentators have since attempted to estimate
the date of this peak, although some commentators doubt the existence of a near
term peak [13].
One of the difficulties in estimating the peak is whether or not to include in the
analysis non-conventional oil deposits such as oil shale and tar sand deposits. While
these deposits are significant, the cost of extraction and environmental concerns
may limit the future viability of these deposits for large scale oil production. The use
of synfuels (liquid fuels produced from coal or gas) also affects the date of the peak.
Synfuels, oil shale and tar sand based fuels have much higher carbon emissions than
conventional crude oil based fuels as a result of emissions released in the
production process [5, 9].
It appears certain, however, that increasing scarcity of economically recoverable
conventional oil deposits will lead to higher costs of crude oil and its fuel
derivatives. Estimates of the future cost of crude oil are highly variable, but it is very
likely that crude oil prices will increase as conventional crude oil deposits deplete
and become more geographically concentrated.
The US Energy Information Agency reference case in 2009 [2] shows the crude oil
price being greater than US$100 /barrel in 2013 and rising to US$130 /barrel in
2030 (2007 dollars). Uncertainty in the projections is evident from the range of
alternative oil price scenarios between US$50 /barrel and US$200 /barrel [2].
14
In their 2009 study, the International Energy Agency [4] reports a reference case
import crude oil price of US$115 per barrel in 2030 (2008 dollars), and also
acknowledge considerable uncertainty in attempting to estimate future oil prices
[9].
2.1.4 Energy security and development
Conventional crude oil reserves are becoming increasingly geographically
concentrated with 62 % of known reserves in Middle Eastern and North African
countries [9]. As conventional reserves diminish, supply pressures are likely to
increase and continuing supply may become politically prejudiced.
Many nations are increasingly concerned with ensuring the security of their future
energy resource and seek to ensure that a sizable portion is able to be produced
domestically. Renewable energy technologies (including renewable transport fuels),
have been reported to have the potential to play a significant role in enhancing
energy security [14] through diversifying energy sources.
In addition to the potential environmental benefits, many developing countries
have a particular interest in developing biofuel industries with the aim of
diversifying energy sources, reducing exposure to price volatility in the international
oil market, stimulating rural development, creating jobs and saving foreign
exchange [15].
2.2 Bioethanol – a renewable transport fuel
2.2.1 Ethanol as a transportation fuel
Ethanol has been used as an alternate transportation fuel since the introduction of
the very first combustion engines. Although crude oil fuel derivatives became the
primary fuel for transportation, ethanol production spikes occurred during the
1920s and 1930s (following the first world war), and during the 1970s and early
1980s as a result of high petroleum prices [16].
15
Ethanol has been used in combustion engines as a standalone fuel, fuel extender in
petroleum blends and as an additive. As an additive, ethanol increases the octane
rating of the fuel, reducing or eliminating the need for toxic octane enhancing
additives such as benzene [17]. While ethanol has a volumetric energy content
about two-thirds that of petroleum, the higher efficiency of combustion of ethanol
leads to an ethanol volumetric fuel efficiency about 75 - 80 % that of petroleum
[17].
Ethanol burned as a standalone fuel, or in blends with petroleum products,
produces fewer tailpipe particulate emissions, fewer oxides of nitrogen emissions
(NOx) and fewer emissions of aromatics, although produces higher volatile organic
carbons (VOCs) [17]. A recent Australian study [18] reported significant health cost
savings in urban Australia from a move to 10 % ethanol substitution in spark-
ignition engines from both a 50 % and 100 % uptake of E10 use in these vehicles.
The majority of post-1986 vehicles operating on Australian roads are suitable for
use with ethanol in blends up to 10 % ethanol [19]. In Brazil, vehicles with an
ethanol - petroleum fuel management system, known as flex-fuel vehicles are
capable of using a wide range of ethanol fuel blends. Eighty-five percent of all new
cars sold in Brazil are flex-fuel, capable of utilising any blend of petrol and ethanol
up to ethanol concentrations of 100 % [20].
2.2.2 First-generation ethanol
First generation ethanol has been produced primarily from starch based feedstocks
(grains such as wheat and corn) or sugar based feedstocks including sugarcane juice
and molasses. Both starch and sucrose are readily hydrolysed into simple hexose
sugars that can be fermented at high efficiency using conventional fermentation
organisms [21].
Starch and sucrose based feedstocks, however, are also used for both human
consumption and for livestock feed, and as a result, the price of these feedstocks
may be impacted by their relative value as a food. The impact of the diversion of
food crops such as corn into ethanol has already been linked to higher food prices in
16
some countries including Mexico and the United States of America [22] although
other reports suggest that the increased use of biofuels accounted for only 10 –
30 % of the food price increase evident during 2007 and 2008 [23, 24]. Other factors
such as the effects of drought, higher oil prices and economic growth increasing
global demand for wheat, dairy and protein in Asia and Africa, along with market
speculation and trade barriers, also impacted on the price of grain [24]. As the cost
of first generation feedstocks is typically 60 – 80 % of the ethanol production cost,
factors that act to increase the price of feedstocks used for both ethanol and food
production will have a significant impact on first generation bioethanol viability
during these periods of high feedstock prices.
2.2.3 Second-generation bioethanol
In contrast, second generation biofuels utilise lower value lignocellulosic materials
from forestry, agricultural residues or dedicated energy crops for ethanol
production. Materials considered for second generation biofuel production are
generally low value feedstocks that are often excess to that required in the farming
system.
Lignocellulosic biomass consists principally of the biopolymers cellulose,
hemicellulose and lignin. Both the cellulose and hemicellulose can be pretreated,
hydrolysed and fermented with varying efficiencies into ethanol [21, 25].
While considerable research has been undertaken on lignocellulosic ethanol since
the early 20th century, there remain some significant challenges to the economic
commercialisation of the technology. Apart from the financial challenges of
developing a cost-effective process, one of the major issues for any biomass
processing system is developing an efficient collection and transportation system
for the high volume, low density biomass feedstock to the ethanol processing
facility [22].
17
2.2.4 The global biomass resource
Cellulose is the most abundant organic material on the earth with natural processes
producing biomass from carbon dioxide and water. As the biomass resource can be
replenished in a short timeframe, the resource is both renewable and carbon
neutral. The continental biomass resource resulting from the growth of plants is
estimated to be 117.5 billion t/y, with 62 % of this resource in tropical rainforests
and other woods [26]. Agricultural crops contribute currently about 9.1 billion t/y
[26], with biomass typically yielding an ethanol volume of 275 - 309 L/t feedstock
(dry basis) [27].
Biomass contributes about 45 EJ/y of the current 467 EJ/y (2004 data) of global
energy demand, supplying up to 10 % of the energy in developed countries and 20 –
30 % in developing countries. Average estimates of global biomass energy farming
potential on current agricultural land are reported typically in the range of 100 - 300
EJ/y, without jeopardising future food supply. The use of organic wastes and
residues are reported to offer the potential of an additional 40 - 170 EJ/y, making
the total potential contribution from biomass this century up to 400 EJ/y [28]. A
review of 17 previous biomass energy studies reported estimates from less than
100 EJ/y to greater than 400 EJ/y [29].
Biofuels currently contribute about 1.5 EJ/y or about 1.5 % of global transportation
fuel use [28]. Production of ethanol in 2006 was 39 billion litres, increasing 18 %
from 2005 [30]. Estimates of the long-term world liquid biofuel production potential
range from 12 - 455 EJ/y, with most studies in the range of 48 - 158 EJ/y [21],
although the economically viable production potential may be significantly lower
than the technical production potential frequently reported. In Australia, up to
140 % of existing transport fuel use could be supplied by biofuels if the industry
develops around second generation biofuel technologies [31].
18
2.3 Sugarcane as a bio-energy resource
2.3.1 The global sugar industry
Sugar is one of the major food carbohydrate energy sources in the world. It is
principally produced from two major crops – sugarcane, grown in tropical and sub-
tropical regions of the world, and sugar beet grown in more temperate climates.
In 2006, 1.392 billion tonnes of sugarcane were grown globally at an average yield
of 68.3 t/ha dominated by production in Brazil and India. Sugar beet production in
2006 was 256 million tonnes at an average yield of 47.1 t/ha [32]. The leading
sugarcane producing countries are shown in Figure 2.1.
Figure 2.1 Leading sugarcane producing countries 2006 [32]
The principal use of sugarcane throughout the world is for crystal sugar production
for human consumption. In several countries including Brazil, a sizable portion of
the crop is also used for ethanol production from both sugarcane juice and
molasses. Many other countries including Australia produce lesser quantities of
ethanol from molasses.
0
100
200
300
400
500
Brazil
India
China
Mexico
Thaila
nd
Pakist
an
Colombia
Austra
lia
Indon
esia
USA
Philipp
ines
South
Africa
2006
sug
ar c
ane
prod
uctio
n (m
illio
n to
nnes
)
19
Over the past decade, global sugarcane production has increased by 8 %, driven by
a 37 % increase in sugarcane production in Brazil [32]. This increased sugarcane
production has resulted in both increased crystal sugar production and increased
ethanol production, and has had a significant impact on the world price of raw
sugar. Land use change enabling this global expansion of sugarcane production has
both direct and indirect sustainability implications and the factors relating to these
implications are diverse and complex [33-35].
2.3.2 The sugarcane biomass resource
Sugarcane is a C4 monocotyledonous perennial grass grown principally in tropical
and subtropical regions of the world. Modern sugarcane varieties cultivated in
Australia are complex hybrids derived through intensive selective breeding between
the species Saccharum officinarum and Saccharum spontaneum [36].
Globally, the 1.4 billion tonnes of sugarcane produced annually is grown on about
20.4 million hectares [32] in tropical and sub-tropical regions of the world. In
Australia, modern sugarcane varieties are capable of producing in excess of 55 t/ha
of biomass (dry weight). The development of high biomass sugarcane (often
referred to as ‘energy cane’) has the potential to significantly increase the amount
of biomass available.
Traditional sugarcane harvesting processes remove the top of the stalk (tops) and
leaf material, and only the stalk is transported into the factory for extraction and
production of sugar. Tops and leaf material remaining after harvesting are either
left in the field to decompose, acting as mulch and providing organic matter and
nutrient for the soil, or burnt depending upon farming practices. It is likely that only
a portion of this leaf material is of value in the agricultural system, and for
improving soil condition. The remainder of this extraneous matter is potentially
available as a feedstock for biomass value adding processes such as bioethanol
production. The impacts of harvesting and transporting extraneous matter on the
sugar milling process and the economics of the industry are complex and an
integrated modelling approach has been developed to analyse these effects [37].
20
2.3.3 The Australian sugar industry
Over the past decade, the Australian sugar industry has harvested approximately 28
– 38 million t/y of sugarcane from approximately 400,000 hectares [38] along the
eastern coast of Australia (Figure 2.2). Approximately 95 % of the sugarcane is
grown in Queensland with the remainder of the industry operating in Northern New
South Wales (NSW). Sugarcane is Queensland’s highest value agricultural crop with
an annual value of approximately $1.5 - $2.5 billion [39].
Sugarcane in Australia is crushed at one of 25 sugar factories and processed into key
products including crystal sugar and molasses. Typically, 4.5 – 5 million tonnes of
raw sugar is produced [39] and 75 % of the sugar produced is exported. While
Australia is only the eighth largest producer of sugarcane [32], Australia is typically
the second or third largest exporter of sugar after Brazil and (in some years)
Thailand.
The average area of sugarcane harvested in Queensland has decreased over the
past decade as a result of economic challenges posed by drought and disease,
extended periods of poor sugar prices and industry restructuring programs. In
particular, low sugar prices during the early 21st century resulted in an industry
restructuring program that led to up to a quarter of the growers in Australia exiting
the industry. A survey of the financial performance of sugarcane growers in 2007-08
[40] determined that the volume of production is relatively stable with a trend
toward a smaller number of larger farms improving the viability of sugarcane
producers. In the period since 2008, higher prices have provided improved financial
conditions for sugarcane growers (Figure 2.3).
For domestic sugar consumption, raw sugar is processed into refined sugar at
refineries in Mackay and Bundaberg (Queensland), Yarraville (Victoria), and
Harwood (NSW).
The only distillery of significant capacity currently producing ethanol from
sugarcane products in Australia is the Sucrogen 60 ML/y molasses-based distillery
located on the site of the Plane Creek sugar factory in Sarina, Queensland. Small
21
quantities of ethanol are also produced in boutique distilleries in Bundaberg and
Beenleigh, Queensland, producing rum and other consumer products from
molasses.
Figure 2.2 Map of the Australian sugar industry [39]
22
Figure 2.3 Australian No.1 sugar pool price 1990-91 to 2005-06 and QSL seasonal pool price 2006-07 to 2010-11 (AU$/t) [38, 41]
2.3.4 Current uses of sugarcane bagasse in Australia
In most sugar factories, bagasse from the crushing or diffuser station is burnt in
suspension fired boilers to generate steam for electricity, mechanical power and
process heat requirements for the factory. Historically, sugar factory boilers and
factory production technologies have been designed to be energy inefficient to
ensure that the energy requirements of the factory match the availability of bagasse
from the sugarcane. This approach has ensured that the factories required little if
any supplementary fuels (such as coal or oil) for process energy, while ensuring that
the factories were not left with an expensive bagasse disposal problem. Small
quantities of surplus electricity have been sold to the electricity transmission or
distribution networks.
With increasing value in the market for energy products, sugar factories are
investing in higher efficiency boilers and more efficient process technologies to
2010-11 Estimated pool price range
200
250
300
350
400
450
500
550
Seas
onal
poo
l pri
ce
(AU
$/t)
Year
23
enable a significantly greater quantity of electrical export and hence capture
additional value from the sugarcane resource [42, 43].
Around the world, sugarcane bagasse is used for many applications including animal
feed, pulp and paper production, particle and fibre board production and furfural
production. Other potential uses of bagasse include xylitol production, speciality
building products, microcrystalline cellulose production and the production of
furfural and lignin derivatives [44, 45].
Sugarcane has some major advantages as a feedstock for lignocellulosic ethanol
production compared to other feedstocks. One of the most significant advantages is
that the sugarcane bagasse is an existing centrally located resource supported by a
harvesting and transport infrastructure that supplies the sugarcane to the sugar
factory.
2.3.5 The sugarcane biorefinery
Several studies have commented on the need to improve the economics of the
bioethanol production process through the integrated production of multiple co-
products in a biomass biorefinery [46-54]. In a biorefinery, bagasse is typically
fractionated into its components and value is added to each component through
the production of multiple high value co-products. Bioethanol is generally
considered to be a significant (but not the only) revenue stream for a biorefinery.
Products that are able to be produced in a biorefinery include ethanol, compounds
derived from lignin, specialty sugars, organic acids, fermentation products, and
other energy products including biodiesel, hydrogen and methane.
Typical products able to be produced in a sugarcane biorefinery are shown in Figure
2.4.
24
2.4 The composition and structure of sugarcane bagasse
Bagasse from the sugarcane diffusion and milling processes generally contains 44 –
53 % moisture, 1 – 2 % soluble solids, 1 – 5 % insoluble solids (ash) and the
remainder lignocellulosic fibre [45]. The fibre analysis of bagasse by standard sugar
factory methods [55] includes dirt and other insoluble impurities and these
impurities can vary from quite small quantities to very significant quantities
depending upon the sugarcane supply and processing technologies.
Lignocellulosic materials such as sugarcane bagasse are complex mixtures of
cellulose, hemicellulose and lignin with minor amounts of ash, proteins, lipids and
extractives. The actual composition of the lignocellulosic material depends upon the
growth conditions of the plant, the plant tissue and the age at harvesting [16].
Reports of bagasse fibre composition in the literature vary with cellulose typically
34 – 47 %, hemicellulose 24 – 29 % and lignin 18 – 28 % on a dry basis [27, 44, 45,
56-58].
Figure 2.4 An overview of current and potential products from sugarcane in Australia –current products shown in black and potential products shown in red
Sugar cane
Renewable electricity
Crystal sugar
Ethanol, Bio-crude Chemicals
Filter mudBagasse
Export
Juice
Fertiliser
High value chemicals
Molasses
Pulp
ChemicalsBio-plastics
Ethanol
WaxesProteinsPlant made products
BiofuelsPharmaceuticalsIndustrial products
Ethanol Animal feed
25
Sugarcane is a non-homogenous material and can be thought of as consisting of
peripheral fibres (rind) enclosing a soft central pith [58]. The rind is covered by a
waxy coating. The sugarcane stalk transports water and nutrients from the soil to
the growing portion of the plant and stores sugar that has been synthesised in the
plant leaves. Vascular bundles in the stalk account for a large proportion of the stalk
fibre and the sugar is stored in parenchyma tissue surrounding the vascular bundles
[45].
In sugar extraction operations, the structural order of the fibres in the sugarcane
plant is lost [44] and the resultant bagasse is a mixture of fibre components of
varying length and composition. Pith cells are broken into fine particles generally
much less than 1 mm in length, while other fibres may retain a length of up to
25 mm. For the practical measurement of pith, all of the fibres passing through a
fine screen of approximately 1.5 mm aperture are generally considered to be pith
fibres. By this definition, pith constitutes approximately 40 % of the total bagasse
fibres by weight. Pith is chemically similar to the non-pith fibre, although the non-
pith fibre has been reported to have lower hemicellulose concentrations [59] and
higher α-cellulose concentrations [45]. For bagasse fibre pulping operations, the
pith is generally removed prior to digestion as the presence of pith increases
chemical usage and adversely affects fibre drainage.
A typical constitutive analysis of Australian bagasse fibre on a dry basis is shown in
Table 2.1.
In lignocellulosic materials such as bagasse, cellulose is ordered into fibrils which are
surrounded by lignin and hemicellulose [60]. The hemicellulose provides an
interpenetrating matrix for the cellulose microfibrils with molecular interactions
including hydrogen bonds and Van der Waals forces, while lignin is incorporated
into the spaces around the fibrillar elements, forming lignin polysaccharide
complexes [61].
26
Table 2.1 Typical constitutive analysis of Australian sugarcane bagasse
Weight
percent
Cellulose 43
Hemicellulose
– xylose
– arabinose
27
4
Lignin 23
Extractives 1
Ash 2
2.4.1 Cellulose
To describe the structure of native celluloses, it is necessary to consider three levels
of structure, including at the molecular scale of the macromolecule, the
supramolecular level of packing and ordering and the morphological architecture
[62].
At the molecular level, cellulose is a linear homopolymer of D-glucopyranose units
linked at the 1 and 4 carbon atoms by b-glycosidic bonds, with hydroxy groups at C-
2, C-3 and C-6. The hydroxy group at the C-1 end of the glucose chain has reducing
properties and the hydroxy group at C-6 is non-reducing [62]. The solubility of the
anhydroglucose polymer in water decreases above a degree of polymerisation (DP)
of 6, due to strong intermolecular hydrogen bonds. Sugarcane bagasse celluloses
typically have a molecular weight between 150,000 and 350,000 [44] which equates
to a DP between 800 and 1900.
At the supramolecular level, the chemical composition and spatial conformation of
cellulose molecules results in cellulose having the tendency to aggregate into highly
ordered structural entities through an extensive network of hydrogen bonds. This
27
structural aggregation is not uniform throughout the structure with regions of high
crystalline order and regions of relatively low crystallinity (amorphous) [62].
Native cellulose morphology is characterised by the well-ordered aggregation of
microfibrils into macrofibrils. The macrofibrils contain a non-uniform system of
pores, capillaries, voids and interstices that increase the surface area of the
cellulose fibrils [62].
2.4.2 Hemicelluloses
Hemicelluloses are heterogeneous polymers of pentoses (xylose, arabinose),
hexoses (mannose, glucose and galactose), and uronic acids [54]. Hemicelluloses
are typically branched with much lower degrees of polymerisation than cellulose
(typically 80 - 200) [63]. Hemicelluloses are not crystalline and as a result are more
readily accessible for hydrolysis than cellulose [64]. The structure of hemicelluloses
is generally considered to be rod-shaped with branches and side chains folded back
to the main chain through hydrogen bonding [65].
In cell walls, hemicellulose molecules hydrogen bond to the cellulose microfibrils.
While they act to coat the microfibrils, restricting the enzyme pathway to the
cellulose, they are also long enough to span the microfibrils and link them together
[66].
In sugarcane bagasse, the principle hemicelluloses are heteropolymers based on a
D-xylose polymer backbone with side groups containing mainly glucuronic acid and
arabinose. The average viscometric molecular weight of sugarcane bagasse
hemicelluloses is between 10,000 and 20,000 [44]. A review of previous research
has found considerable variation in the proportions of the relative constituents of
hemicellulose, with a mole ratio of xylose to arabinose of 4.0 - 52.6 and a mole ratio
of xylose to glucuronic acid of 7.4 - 100 [67].
Hemicellulose extraction from bagasse with water at temperatures between 150 oC
and 170 oC resulted in xylose yields of 60 %, with 80 % of the extracted xylose in the
oligo- or polysaccharide form [68].
28
2.4.3 Lignin
Lignin is a natural amorphous polymer composed of phenylpropane olignol units
with hydroxyl and carbonyl substitutions. There are three major phenylpropane
units, p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) which differ in the O-
methyl substitution of the aromatic ring. The structure of lignin that has been
isolated from biomass is dependent upon both the plant and the process used for
delignification [69, 70].
In a lignocellulosic material, lignin is covalently linked to both cellulose and
hemicellulose. Cross-linking possibilities exist through hydrogen bonds, ionic
interactions, ester and ether linkages and Van der Waals interactions. Lignin –
carbohydrate interactions have been shown to strongly affect ruminant and
enzymatic digestibility [66].
Both the total quantity and structure of the lignin within the plant varies with cell
tissue and these have been shown to affect the recalcitrance of the tissue to
biodegradation. Warm season grasses such as sugarcane are reported to have both
lignified cell walls as well as high levels of phenolic acid esters linked to arabinose
[71]. In addition, warm season grasses contain ferulic acid esterified with
hemicelluloses and etherified with lignin while p-coumaric acid is esterified with
lignin [72]. Each of these linkages, in addition to the structure and quantity of lignin
present, has a substantial effect on digestibility for bioethanol production through
both the covalent linkages themselves and the effect they have of physically
reducing access to the carbohydrate polymers [73].
Sugarcane bagasse lignin has a higher content of p-hydroxyphenyl lignin, and as a
result, a lower methoxy content than lignin from other hardwood and softwood
lignins [69]. The importance of delignifying bagasse to produce a residue that is
readily hydrolysed by enzyme has been highlighted [74].
2.5 Overview of the process for ethanol production from sugarcane bagasse
Unlike the starch or sugar feedstocks upon which first generation bioethanol has
been based, the structural rigidity of lignocellulosic materials results in a material
29
that is extremely resistant to hydrolysis (depolymerisation). As a result, the ethanol
production process from biomass such as sugarcane bagasse requires aggressive
thermochemical or physical pretreatments, or combinations of both to generate a
material more amenable to hydrolysis. These pretreatment processes add to the
cost of bioethanol production from biomass feedstocks and, depending upon the
process used, generate significant degradation products that can detrimentally
affect the fermentation productivity and product yield [75].
Due to the formation of degradation products in the acid hydrolysis of cellulose and
hemicellulose, considerable attention is being given to the development of efficient
enzymatic hydrolysis processes for the conversion of cellulose and hemicellulose
into fermentable sugars. Significant quantities of cellulolytic and hemicellulolytic
enzymes are required for this conversion process to ensure both high yields and
rapid hydrolysis rates.
Despite significant research investment into improved enzyme efficacy, the cost of
the enzymes and the capital required to produce them in the quantities required for
commercial bioethanol facilities remain major cost impediments to the
commercialisation of the technology. In the landmark 2002 study by Aden, et al [76]
on ethanol production from corn stover, cellulase enzyme cost was assessed to be
9 % of the total cost contribution to the process, with pretreatment and
conditioning accounting for 19 % of the total cost contribution (including feedstock
and capital depreciation costs). A later study by Tao and Aden [77] showed an
enzyme cost of 7 % of total operating costs (including feedstock and capital
depreciation costs).
Effective pretreatment strategies reduce the quantity and cost of enzymes required
for hydrolysis of cellulose and hemicellulose. These strategies include hydrolysing
the hemicellulose fraction of the fibre, decreasing the lignin content of the material,
reducing the crystallinity of the cellulose fibrils or modifying the fibre architecture
to enable more rapid transport of the enzyme into the fibre.
A simple schematic of the key processes required for ethanol production from
sugarcane bagasse via a biochemical pathway is shown in Figure 2.5.
30
Figure 2.5 Simple schematic of the key processes required for the ethanol from sugarcane bagasse
2.6 Conclusion
This chapter has provided an introduction to transportation fuel use and the
challenges associated with commercialising biofuels production from cellulosic
feedstocks. An overview of the global and Australian sugar industries and the
structure of sugarcane bagasse as a bioenergy feedstock have also been provided.
Chapter 3 provides more detail on the technologies for pretreatment of fibre from
sugarcane bagasse.
31
Chapter 3
Pretreatment technologies for ethanol production from sugarcane bagasse
3.1 Introduction
Chapter 2 provided an introduction to the sugarcane system and to the drivers
affecting biofuel production from sugarcane. This chapter builds upon the
information in the previous chapter discussing in more detail the objectives of
the pretreatment processing of sugarcane bagasse and reviews the key research
work that has been reported for the pretreatment of sugarcane bagasse.
3.2 The objectives of the pretreatment process
The economic production of ethanol from lignocellulosic fibre requires a
feedstock to the hydrolysis process that is readily amenable to enzymatic attack
and subsequent fermentation at high yields. Native lignocellulosic materials are
extremely resistant to enzymatic hydrolysis and require an effective
pretreatment process prior to hydrolysis.
The pretreatment process in a lignocellulosic ethanol facility can be considered
to have the following key objectives [16, 78]:
- To improve the structure and accessibility of the carbohydrate
compounds to enable rapid and cost-effective enzymatic hydrolysis;
- To avoid the degradation of carbohydrates, ensuring maximum
fermentable sugar and ethanol yield;
- To avoid the production of degradation products inhibitory to
hydrolysis or fermentation; and
32
- To be a cost-effective process within the context of an economically
viable facility.
To achieve these objectives, the following specific attributes are desirable in a
pretreatment process [79, 80]:
- Low cost of chemicals for both the pretreatment and neutralisation or
chemical recovery stages;
- Minimal generation of wastes;
- Minimal requirement for energy-intensive biomass particle size
reduction prior to pretreatment;
- Preservation of hemicelluloses and enhancement of the accessibility
of hemicelluloses for fermentation;
- Short reaction times with non-corrosive chemicals to minimise
reactor costs;
- High fermentable sugars concentration to minimise fermentation
reactor sizes and energy costs in ethanol recovery;
- High product yields in hydrolysis and fermentation with minimal
hydrolysate conditioning (for removal of fermentation inhibitory
compounds) required;
- Hydrolysate conditioning should not form products that present
processing or waste disposal challenges;
- The pretreated cellulose and hemicellulose should require minimal
enzyme loadings to obtain greater than 90 % digestibility in less than
three days; and
- Facilitate recovery of lignin and other products for conversion to
valuable co-products.
33
Several reviews have been undertaken relating to the pretreatment processing
of lignocellulosic materials and the technology involved [16, 25, 27, 78, 79, 81-
85]. In general, most pretreatment strategies improve the digestibility of the
fibre through one or more of the following strategies:
- Reducing the lignin content or modifying or redistributing the lignin
component;
- Reducing the hemicellulose content;
- Reducing the crystallinity or degree of polymerisation of the cellulose
component; and
- Influencing the fibre particle size, porosity, cell wall thickness or fibre
surface area.
The lignin concentration of the fibre and the degree of cellulose crystallinity have
been shown to have the most significant effect on biomass digestibility by
enzyme and this has been shown to hold true for bagasse [86]. Reducing the
acetyl content has been shown to have a lesser impact on biomass digestibility
although this remains an effective strategy [86]. While effective pretreatment is
critical to bagasse digestion by enzymes, the hydrolytic effectiveness is also
dependent upon digestion conditions including pH, temperature, solids content
and enzyme loading [87].
Bagasse pretreatment technologies can be categorised as chemical, physical and
biological treatments and have been used either singly or in combinations of
treatments. The following sections review some of the key work that has been
undertaken.
34
3.3 Chemical pretreatments
3.3.1 Concentrated acid hydrolysis
Concentrated acid hydrolysis has been used commercially (during the Second
World War) for hydrolysing biomass. In the concentrated acid process, sulphuric
acid is typically used at concentrations greater than 40 % at room temperature
for periods of approximately 1 hour [25]. The use of concentrated acids for
hydrolysis at low temperatures results in high yields of both pentoses and
hexoses, with reported yields of 85 – 95 % of theoretical yields and with minimal
production of degradation products [25].
Commercialisation of the concentrated acid process has been hindered by the
high cost of acid, necessitating expensive acid recovery processes (such as
chromatographic techniques for separating the acid and sugars) and the
requirement for expensive alloys in plant construction [25].
3.3.2 Dilute acid hydrolysis and pretreatment
Dilute acid hydrolysis of biomass for ethanol production is favoured by many
researchers as the process is simple, rapid and requires no solvent recovery
process. In dilute acid hydrolysis, both the cellulose and the hemicellulose
fractions are substantially hydrolysed.
In general, the dilute acid hydrolysis process is a single or double stage process
using sulphuric acid in concentrations of up to 1.5 % acid, with reaction times of
several minutes and temperatures between 180 oC and 230 oC. Higher
temperatures are mostly used to ensure rapid hydrolysis rates and high glucose
yields during saccharification. The higher temperatures, however, also increase
the rate of generation of pentose degradation products, primarily furfural, and
hexose degradation products, primarily 5-hydroxymethyl furfural (HMF) [56, 79].
Furfural and HMF can further degrade to other products including furan, levulinic
acid and formic acid. Several phenolic compounds resulting from lignin
degradation can also be formed under these conditions [25].
35
Glucose yields from the dilute acid hydrolysis process have been mostly reported
between 50 % and 60 % of theoretical glucose yield, however, more recent
studies have reported glucose yields over 80 % and xylose yields above 90 % with
new reactor designs [25]. Despite the improvements in glucose and xylose
yields, significant quantities of inhibitory degradation products are formed and
low hydrolysate sugar concentrations have been achieved [25].
Acetic acid is also formed from the hydrolysis of acetyl groups in the
hemicellulose fraction and can be a further inhibitor to microbial growth in
concentrations as low as 4 g/L [88]. HMF and furfural concentrations as low as
0.5 g/L have been shown to reduce microbial growth substantially in
lignocellulosic materials [88] and in sugarcane bagasse hydrolysates at
concentrations greater than 0.9 g/L [89].
Mild acid pretreatment processes utilise lower process temperatures, shorter
reaction times and lower acid concentrations than dilute acid hydrolysis to
substantially hydrolyse the hemicellulose with a resultant 80 – 90 % yield of
monomer sugars. The cellulose and lignin remain in the solid residue following
pretreatment, and the cellulose can be subsequently enzymatically hydrolysed
[79].
Mild acid pretreatments on bagasse attack the lignocellulosic structure through
hydrolysing hemicellulose chains attached to the lignin, as well as degrading
some of the lignin. The degree of cellulose crystallinity of the fibre can increase
during mild acid pretreatment as a portion of the amorphous cellulose is
solubilised, resulting in a residual solid with a higher proportion of more resistant
crystalline cellulose [90].
One approach to reducing the formation of degradation products in mild acid
pretreatment processes is to utilise a two stage pretreatment process, with a
moderate temperature first stage solubilising the most readily available
hemicellulose and separating the hydrolysate from the solid residue prior to a
second stage higher temperature process. Following the second stage hydrolysis,
36
the fibre undergoes rapid decompression in a process known as steam explosion
(Section 3.4.1) to affect fibre morphology.
One of the major challenges with mild acid hydrolysis or pretreatment is the
corrosive nature of the process conditions (low pH, elevated temperature and
pressure) resulting in a requirement for pressurised reactors manufactured from
exotic and expensive alloys. Other concerns include the need for neutralisation
chemicals for hydrolysate conditioning and the disposal costs associated with the
salts formed (typically gypsum). The continuing presence of lignin in the solid
residue results in non-productive adsorption of a portion of the enzymes on the
lignin, requiring a higher enzyme usage rate [79].
Studies with sugarcane bagasse have looked at the kinetics of hydrolysis with a
range of mineral acids. A kinetic study [56] of sulphuric acid hydrolysis of bagasse
modelled xylose, glucose, acetic acid and furfural concentrations at
temperatures of 100 - 128 oC and acid concentrations of 2 – 6 %. Up to 90 % of
the hemicelluloses were hydrolysed under these conditions with minimal
hydrolysis of cellulose. Further detailed studies [59, 67] looked at the kinetics of
xylose, arabinose, glucose and furfural production under a large range of
temperature conditions, solid to liquid ratios and bagasse type, comparing both
sulphuric and hydrochloric acids. About 80 % of theoretical xylose yields were
achieved. Bagasse particle size was found to have a negligible effect on the rate
of hydrolysis.
Further studies with sugarcane bagasse have also investigated the kinetics of
hemicellulose hydrolysis in dilute sulphuric acid [91], hydrochloric acid [92],
phosphoric acid [93-96] and nitric acid [97]. The use of sulphur dioxide
impregnated bagasse with steam treatment has been studied and resulted in
sugar yields of 87 % [98].
A study [99] on dilute acid pretreatment of sugarcane bagasse and other biomass
sources (rice hulls, peanut shells and cassava stalks) using dilute sulphuric acid at
122 oC and times up to 1 hour showed that bagasse was the most susceptible of
these materials to hemicellulose hydrolysis, with conversion of the xylan of 73 –
37
81 %. Cellulose was only marginally hydrolysed (less than 10 %) under these
conditions. Minor inhibition of the fermentability of the prehydrolysate was
reported as a result of inhibitory compound formation, but the yield of glucose
from cellulose from enzymatic hydrolysis of the solid residue was only 40 %
taking into account losses from the dilute acid prehydrolysis [99].
Another study of sugarcane bagasse with sulphuric acid pretreatment has shown
that hemicellulose monomer sugar yield is most influenced by acid concentration
and that higher temperatures increase degradation product formation, favouring
the selection of reaction conditions with higher acid concentrations, longer
reaction times and lower reaction temperatures [91]. Despite the hydrolysis and
removal of hemicellulose from the residual solid, the relative increase in lignin in
the solid residue has been shown to restrict the potential gains in susceptibility
of the solid residue to enzymatic hydrolysis [100].
Reprecipitated cellulose from sugarcane bagasse pretreated with zinc chloride
and dilute hydrochloric acid was found to have a significantly greater rate and
extent of hydrolysis than untreated bagasse cellulose [101].
Acid pretreatments under very mild concentrations have also been trialled for
enhancing the digestion characteristics of bagasse feeds for ruminant animals
[102].
Strategies for minimising the impact of fermentation inhibitors on ethanol
production from acidic treatments of bagasse include control of process
conditions to minimise the production of inhibitory compounds, detoxification
prior to fermentation and the selection and adaptation of inhibitor tolerant
fermentation organisms [103]. Strategies for detoxification of hydrolysates from
bagasse include overliming [89, 103], laccase treatment [103], pH adjustment
[104], activated carbon adsorption [105] and electrodialysis [106]. Mechanisms
of inhibition and detoxification have been reviewed generally for lignocellulosic
materials [88, 107, 108].
38
3.3.3 Alkaline pretreatments
Alkaline pretreatments are extensively used in the pulping industry for both
wood and non-wood feedstocks. The pulping industry principally uses the Kraft
process for pulping of wood fibres which combines the use of caustic soda and
sodium sulphite for effective delignification. Non-wood fibres such as bagasse
more readily delignify than fibres from woody plants and as a consequence, for
bagasse, caustic soda is a satisfactory delignifying agent. In the bagasse pulping
soda process, caustic soda is typically used at a concentration of 18 - 26 % NaOH
on dry fibre at temperatures up to 160 oC.
Alkaline pretreatments aim to dissolve a large proportion of the lignin from the
biomass with the rate and extent of dissolution varying with the alkali
concentration, reaction time and reaction temperature [109]. The removal of
lignin from lignocellulosic materials is a key strategy in improving cellulose
digestibility [75, 79, 100]. Pulping processes aim to delignify bagasse to a target
lignin concentration (known in the pulping industry as the Kappa number [110]).
Some dissolution of hemicellulose also occurs in alkaline pretreatments but this
is generally undesirable as this leads to a reduction in pulp yield.
Alkali pretreatments of sugarcane bagasse have been shown to remove lignin
and hemicellulose through both solubilisation and hydrolysis from the fibre,
resulting in a more open structure that is more readily accessible to cellulosic
enzymes than untreated bagasse [90]. Delignification of bagasse fibre in alkali
pretreatment is rapid to about 75 % delignification with the preferential removal
of p-hydroxyphenol lignin [111]. The major degradation products from alkali
bagasse pretreatments are formic acid, acetic acid and hydroxymonocarboxylic
acids [112], although the inhibitory impact of these on fermentation are much
less significant than the degradation products that result from acidic
pretreatments.
Due to the less corrosive environment, the cost of materials for the fabrication of
pretreatment reactors for alkaline pulping is significantly lower than the cost of
materials required for acidic pretreatments, however, it is reported that the cost
39
of chemicals is likely to be significantly higher with caustic soda being four times
as expensive as sulphuric acid. As the processes operate in aqueous
environments above 100 oC, pressure vessels are required for pretreatment
processing. Little testing of alkaline processes at pilot scale has been reported in
the literature and little information is available on the process economics [80].
Low temperature, low concentration NaOH treatment of bagasse has been
trialled with long residence times (1 - 6 days) although improved results were
obtained with bagasse pretreatment by sodium chlorite prior to NaOH
pretreatment [113].
Lime pretreatment has been studied for its effectiveness in enhancing enzymatic
digestibility of bagasse and wheat straw [114]. Short pretreatment times (1 - 3
hours) at high temperatures (85 – 135 oC) were effective in achieving high sugar
yields, while lower temperatures (50 – 65 oC) required much longer pretreatment
times (24 hours). Glucans and xylans were not removed in the pretreatment and
a maximum of only 14 % of the lignin was solubilised. Enzymatic hydrolysis of the
lime pretreated bagasse produced 75 % of theoretical sugar yield after 72 hours
[114]. A comparison of lime and alkaline hydrogen peroxide pretreatments
achieved glucose yields of up to 87.5 % for lime and 62.4 % for alkaline hydrogen
peroxide with longer reaction times, higher temperatures and higher lime
loadings all favoured in producing a higher glucose yield [115].
Aqueous ammonia has been trialled for its effectiveness as a pretreatment agent
for enzymatic hydrolysis of bagasse, corn husk and switchgrass [116]. Bagasse
was treated with aqueous ammonia at 120 oC for 20 minutes and glucan and
xylan yields of 72.9 % and 82.4 % respectively were reported. The residual
ammonia was separated from the bagasse by vacuum drying and no washing of
the biomass prior to hydrolysis was required. The enzymatic effectiveness of
various cellulase and hemicellulase preparations and mixtures have also been
studied on aqueous ammonia and ammonia freeze explosion pretreated bagasse
[117].
40
The addition of potassium hydroxide has been used to significantly improve
delignification of aqueous ammonia bagasse pulps for paper applications. The
use of aqueous ammonia and potash offers an alternative alkaline pretreatment
strategy as the black liquor from the process can be converted into a valuable
fertiliser, reducing the necessity for expensive alkali recovery processes. Eighty
percent delignification was achieved using 35 % NH4OH and 5 % KOH and minor
amounts of anthroquinone at temperatures of 165 oC for 1 hour [118].
Alkaline pretreatments have been conducted in conjunction with oxidative
pretreatments and these are discussed in the following section.
3.3.4 Oxidative pretreatments
Wet oxidation involves the reaction of a lignocellulosic material with water
(under alkaline conditions) and oxygen or air at temperatures greater than
120 oC, more typically at 170 - 200 oC and pressures of 10 - 12 bar [25]. Sodium
carbonate is often added to the process to prevent the formation of degradation
products that would occur under acidic conditions.
During wet oxidation, both a low temperature hydrolytic reaction and a high
temperature oxidative reaction occur. Wet oxidation of sugarcane bagasse under
alkali conditions has been shown to reduce the formation of toxic formaldehydes
and phenol aldehydes compared to wet oxidation alone [119-121].
Alkaline wet oxidation is reported to enhance the susceptibility of bagasse to
enzymatic hydrolysis. In the studies, alkaline wet oxidation at 195 oC for 15
minutes produced a solid product with 70 % cellulose content, and solubilised
93 % of the hemicellulose and 50 % of the lignin [119-121].
Oxidising agents including peracetic acid [94, 122-127], acetic acid and ozone
[128], peroxyacetic acid [129], alkaline hydrogen peroxide [130] and sodium
hypochlorite and hydrogen peroxide [131] have also been used to reduce the
lignin content of lignocellulosic pulps.
41
Peracetic acid is known to selectively oxidise aromatic compounds such as lignin,
resulting in delignification of the fibre, increasing surface area and exposure of
cellulose fibres [127]. The effectiveness of the peracetic acid pretreatment on
bagasse was studied for its effect on simultaneous saccharification and
fermentation and ethanol yields greater than 90 % of theoretical were achieved
[126]. Peracetic acid charge, reaction temperature and reaction time have been
found to have a significant effect on the yield of glucose from peracetic acid
pretreatments [125]. Although the process provides high yields of sugars, the
high cost of chemicals is likely to make the process too expensive for commercial
application [127].
Peracetic acid pretreatment of bagasse at room temperature has also been
studied [123] with pretreatment reaction periods of 7 days, delivering high
glucan, xylan and ethanol yields. The treatment of bagasse with 6 % NaOH prior
to peracetic acid pretreatment was found to enable a significant reduction in the
concentration of peracetic acid used.
3.3.5 Solvent pretreatments
The organosolv process utilises aqueous ethanol at temperatures of between
150 oC and 200 oC to dissolve lignin from lignocellulosic fibre. The organosolv
process is reported to require less capital than conventional pulping technologies
as the organic solvent used (ethanol) is readily recovered through flashing and
distillation [132]. Using aqueous ethanol as a fractionating medium is attractive
in an ethanol based biorefinery as large quantities of ethanol are produced as a
major product in the plant which reduces chemical costs for the fractionation
stage.
A number of organosolv pulping studies using sugarcane bagasse and aqueous
ethanol [132-136] or butanol [137] have been reported. Studies at the Sugar
Research Institute in Australia on the organosolv process on bagasse, utilising
technology supplied by Ecopulp, produced bleachable pulps with a moderate
reduction in lignin content and cellulose viscosity. Lower lignin contents were
42
achieved using bagasse that had been stored for a period prior to treatment
[132].
The DHR – Dedini rapid hydrolysis process uses an organsolv process to delignify
bagasse under mild acid conditions for the subsequent acid hydrolysis of
polysaccharides. Saccharification yields of 82 % and hexose fermentation yields
of 90 % have been reported at the pilot scale [138].
In the search for more environmentally benign pulping chemicals in the paper
industry, acetic acid has been used for delignification [128, 139, 140]. While
acetic acid is an effective solvent of lignin, a variety of catalysts have been used
to enhance the lignin removal characteristics of acetic acid including magnesium
chloride, sulphuric acid, hydrochloric acid, acetone and oxygen [128]. The
acetosolv process uses a combination of 93 % acetic acid and 0.1 % hydrochloric
acid [139].
Both the kappa number and viscosity of acetosolv and organosolv bagasse pulps
have been shown to decrease following subsequent treatments of both pulps
with commercial xylanase enzymes [141].
Studies of bagasse delignification using upper critical temperature binary
mixtures of cyclohexane and water enabled good sugar recovery and
delignification [142], and delignification was shown to improve further with the
use of non-ionic surfactants [143].
N-methylmorpholine-N-oxide (NMMO) is used as a cellulose solvent in the
commercial Lyocell process for the manufacture of textile fibres and has been
investigated for the pretreatment of sugarcane bagasse [144]. NMMO is both a
solvent and a strong oxidant. The components of bagasse reprecipitated from an
NMMO – bagasse solution (with the addition of water) formed a porous and
amorphous mixture of the original components which could be readily
hydrolysed and fermented [144].
43
3.3.6 Ionic liquid pretreatments
Ionic liquids are a class of organic salts that have the ability to either completely
or selectively dissolve the fractional components of bagasse. Little work has been
published to date on the pretreatment of sugarcane bagasse with ionic liquids
for ethanol production although some work has occurred for the production of
bagasse pulp [145]. Most of the work reported has focussed on compounds
based on the imidazolium cation [146].
3.4 Physical pretreatments
3.4.1 Steam explosion pretreatment
Steam explosion is a process that involves heating a wet biomass under pressure
to maintain the water in the biomass in a liquid phase and then rapidly
depressurising the fibre to atmospheric pressure. This process improves enzyme
hydrolysis rates by increasing available surface area for enzyme activity, partially
removing hemicellulose and through a minor impact on lignin structure [75].
Typically, the process involves heating the bagasse to a temperature around
200 oC under pressure, holding the biomass under these conditions for a short
period of time and then expelling the material through a valve to a blow tank at
atmospheric pressure. The high temperature steam impregnation into the fibre
solubilises hemicellulose and some lignin, while the rapid depressurisation
dramatically affects the cell integrity and fibre dimensions. A dye may be used at
the exit of the chamber to assist in fibre disruption.
Steam explosion can be carried out in the presence of an acid catalyst (acid
catalysed steam explosion) or without an acid catalyst (autohydrolysed steam
explosion). When no acid catalyst is present, the acid catalysed cleavage of
glycosidic linkages results from acids released from the biomass itself [65]. Steam
exploded sugarcane bagasse without an acid catalyst has been compared to
steam exploded bagasse that was impregnated with sulphur dioxide or sulphuric
acid prior to steaming [147]. The highest hydrolysis glucose yields were achieved
with sulphuric acid impregnated bagasse, however, the hydrolysate from this
44
bagasse also contained the highest levels of fermentation inhibitory furan
aldehydes and levulinic acid [148]. The impregnation of bagasse and trash with
carbon dioxide prior to steam explosion has also been investigated [148].
Steam explosion with bagasse was trialled by steaming for 10 minutes at 205 oC
[121, 149]. A 66.5 % yield of dry matter was achieved with a significant
reduction in hemicellulose content and lignin content. Significant inhibition of
hydrolysis and fermentation of the product was reported, resulting from the
presence of furan aldehydes. Furan aldehydes were reported to be more
significant inhibitory compounds than acetic acid. Hydrolysis and fermentation
rates in the washed residual solid were significantly higher than in the unwashed
slurry [121].
In another study, steam exploded sugarcane bagasse achieved solubilisation of
90 % of the hemicelluloses. Shorter reaction times were shown to result in a
pulp more amenable to hydrolysis [150]. A number of other studies of steam
explosion for both ethanol and pulp production have been reported [150-159].
Steam explosion was trialled on bagasse in combination with a variety of alkali
treatments to determine its effectiveness for production of volatile fatty acids by
fermentation. The digestibility of steam exploded bagasse under alkaline
conditions was found to increase with no inhibitory effect on degradation by
cellulolytic enzymes or rumen microorganisms [160].
3.4.2 Other explosive pretreatments
Ammonia fibre explosion (AFEX) is a rapid decompression treatment that occurs
in an alkaline environment. In this pretreatment process, lignocellulosic fibre is
treated with liquid ammonia and heated to 50 - 90 oC under a pressure of 10 - 20
atmospheres. After 15 - 30 minutes the material is rapidly depressurised. The
treatment with ammonia results in some decrystallisation of the cellulose and
the rapid depressurisation disrupts fibre structure. AFEX does not significantly
hydrolyse hemicellulose or solubilise lignin, but does cause alterations in the
structure of cellulose and lignin and an increase in fibre surface area [25].
45
AFEX pretreated sugarcane bagasse has been shown to have higher cellulase and
xylanase hydrolysis rates than aqueous ammonia treated bagasse with a variety
of commercial enzymes [117]. AFEX pretreatment of moist sugarcane bagasse
and trash have been studied with a maximum glucan conversion in hydrolysis of
about 85 % [161].
Carbon dioxide explosion has also been trialled as a pretreatment process with
bagasse [162, 163]. In this process, supercritical carbon dioxide is injected into a
reactor at pressures of 68 - 279 atmospheres and temperatures of 35 – 80 oC and
subsequently depressurised. Cellulolytic enzyme hydrolysis rates and yields
increased as a result of the treatment.
3.4.3 Liquid hot water pretreatments
Sugarcane bagasse and leaves have been fractionated in hot compressed liquid
water at 190 – 230 oC in less than 4 minutes at pressures greater than the
saturation pressure of the liquid [164]. Under these conditions, over 50 % of the
biomass was solubilised. This included all of the hemicellulose and greater than
60 % of the acid-insoluble lignin, with less than 10 % of the cellulose solubilised.
Complete recovery of the hemicellulose as monomeric sugars following the
liquid hot water pretreatment at a reaction temperature of 190 oC and a mild
acid hydrolysis is possible. Greater than 90 % recovery of hemicellulose is
possible at a temperature of 220 oC with about 5 % of the hemicellulose
converted into furfural [164].
Significant quantities of lignin are also solubilised in the liquid hot water
pretreatment process. Sugarcane bagasse and leaves showed similar solubility
outcomes [164]. Hemicellulose from liquid hot water pretreated bagasse has
been shown to be readily enzymatically hydrolysed [165].
Further studies on liquid hot water pretreatment and steam pretreatment of
sugarcane bagasse investigated the effect of the pretreatments on fibre
reactivity, xylan recovery and the extent of fermentation inhibition [166]. Both
pretreatments increased the reactivity of the fibre for simultaneous
46
saccharification and fermentation (SSF), although liquid hot water treatment
resulted in higher xylan recovery. Fermentation inhibition was significant at
increasing solids concentration. SSF conversion was favoured under the
conditions of high temperature (220 oC) and short residence time (2 minutes)
[166].
Hydrotreating bagasse at increasing temperatures up to 330 oC, showed that
organic compounds from hemicellulose and lignin (equivalent to 60 % of the
initial bagasse) are extracted into the liquid phase at temperatures of 200 –
230 oC as measured by the organic constituents of the filtrate. At temperatures
between 230 oC and 280 oC, glucose and cellobiose (and some additional
aromatic compounds) are extracted equivalent to 30 % of the initial bagasse. The
residue remaining after the hydrothermal treatment had a crystal structure and
composition similar to crystalline cellulose [167].
Liquid hot water pretreated bagasse has been used as a substrate for the
production of cellulases from Trichoderma reesei [168]. The kinetics of
hemicellulose removal from bagasse under hydrothermal conditions at varying
solids concentration identified a trend toward lower xylose yield at higher solids
concentrations [169].
3.4.4 Mechanical pretreatments
In the pulping industry, semi-chemical, mechanical or thermo-mechanical
pulping techniques may be used to reduce or eliminate the pulping chemicals
used in the process. Mechanical pulping produces higher pulp yields and is less
capital intensive than chemical pulping. Mechanical pulping, however, requires
extensive input of electrical energy [170]. In semi-chemical pulping, mild
chemical treatments are applied to soften and swell the fibres and then
mechanical work is applied to shear the lignin – fibre bonds. In mechanical
pulping, all of the work required to break the lignin – fibre bonds is applied
mechanically [45].
47
A study with sugarcane bagasse used a high pressure homogenisation process to
investigate the digestibility of bagasse pretreated by this process. Significant
changes in fibre microstructure were noted, crystallinity of the fibre decreased
and hydrolysis rate increased [171].
The impacts of ball milling and wet disc milling of sugarcane bagasse were
investigated with ball milled bagasse at optimum conditions achieving a glucose
hydrolysis yield of 78 % and wet disc milled bagasse achieving a glucose
hydrolysis yield of 49 % [172]. The ball milling process was reported to
significantly decrease bagasse crystallinity and particle size, while wet disc milling
was shown to result in defibrillation of the bagasse and reduced particle size
[172]. Other ball milling studies of sugarcane bagasse have also been reported
recently [173].
3.4.5 Ultrasonic and radiation pretreatments
Small scale trials of ultrasonic and radiation pretreatments of sugarcane bagasse
have been conducted to improve pretreatment outcomes in the laboratory.
Ultrasonic irradiation is well established as a method for separating plant
materials [72, 174].
Gamma and microwave irradiation pretreatments on sugarcane bagasse have
been shown to improve glucose yield for both acid and enzyme hydrolysis [175-
179]. At radiation doses above 10 MR, bagasse was extensively degraded and
became fragile. It was proposed that at this level irradiation may cleave b-1-4-
glucosidic bonds. Higher radiation levels (above 100 MR) appear to lead to
decomposition of oligosaccharides and the glucose ring structure [176].
3.5 Biological pretreatments
3.5.1 Microbiological degradation
Fungal or enzymatic pretreatments have been principally studied to analyse their
effect on both mechanical and chemical pulping treatments. While unlikely to be
48
effective enough as a standalone pretreatment, microbial pretreatments may be
able to be used to reduce the severity of subsequent chemical and physical
pretreatments, reducing energy and chemical use in processing.
Fungal pretreatments of bagasse prior to chemical pulping have been trialled
using Ceriporiopsis subvermispora. Pretreatment with the fungus for two weeks
has been shown to increase the amount of delignification of chemical pulps and
produce biopulps with higher final brightness although a yield loss of 1.5 – 2.0 %
was noted [180, 181] The yield loss was principally the result of decreased
hemicellulose, lignin and extractives [180].
In another trial [182], the use of C. subvermispora prior to chemi-thermo-
mechanical pulping (CMTP) resulted in a reduction in energy consumption of
28 % and a reduced lignin content of the pulp. Xylanase enzyme pretreatment in
addition to the C. subvermispora pretreatment resulted in a 33 % reduction in
refining energy consumption, and a similar lignin reduction. Significant
mechanical pulping energy consumption savings have also been found for wood,
kenaf and jute using similar fungal treatments.
C. subvermispora pretreatment of sugarcane trash resulted in degradation of
both cellulose and lignin, with lignin degradation rates exceeding cellulose
degradation rates 2.4 fold [183]. Biopulps with reduced lignin content required
40 % reduced pulping time and generated less acetic acid during the subsequent
organosolv pretreatment [183].
The use of crude ligninolytic enzymes extracted from Phanerochaete
chrysosporium fungi as a pretreatment for thermomechanical pulping (TMP) and
CTMP reduced energy consumption by 29.2 % and 17.3 % respectively in 36
hours of enzyme treatment [170]. P chrysosporium has also been used for the
biodegradation of effluent from wet storage of sugarcane bagasse [184].
The effects of various microorganisms on the biological pretreatment of
sugarcane trash have also been studied [185].
49
3.6 Conclusion
This chapter has reviewed the work that has been undertaken on sugarcane
bagasse pretreatment which is a critical process stage in the manufacture of
ethanol from bagasse. The choice of pretreatment technology determines many
of the following process requirements and has the largest impact on overall
process efficiency, capital cost and operating cost.
The next chapter undertakes a systems assessment of bioethanol production in
the sugar industry and assesses key uncertainties and risks associated with early
stage investment.
51
Chapter 4
Commercialising cellulosic ethanol from sugarcane bagasse: use of systems analysis to reduce the risk and uncertainty associated with early stage investment
4.1 Introduction
Globally, sugarcane is one of the major crop feedstocks for ethanol production via
first generation molasses and juice fermentation technologies. The ready availability
of the fibrous residue from sugarcane processing (bagasse) at existing industrial
facilities, the scale of the sugarcane resource and the existence of established
infrastructure for research, breeding, harvesting, transport and crop processing,
makes sugarcane perhaps the best feedstock for early commercialisation of
cellulosic ethanol technologies.
Some significant challenges, however, do exist in developing early stage investment
in cellulosic ethanol technologies within the global sugarcane industry. These
challenges relate not only to the technical and economic imperatives, but to the
broader industry structures within which the sugarcane industries operate.
Through a detailed understanding of the complex sugarcane processing, sugar
production and bioethanol production systems, opportunities for lower cost
synergistic integration of bagasse-based bioethanol processing into the existing
production systems can be developed. In this chapter, systems analysis and techno-
economic modelling are used to develop an understanding of the risks and
uncertainties that affect the viability of early stage investment in cellulosic ethanol
production within the sugarcane agro-industrial system.
52
4.2 Systems analysis
The science of systems, which includes complex systems theory, the study of
complexity and non-linearity, arose from the recognition that not every problem
could be resolved by taking the more traditional reductionist approach to problem
solving. Many systems, while constituted of separate elements, operate as an
interdependent whole and an analysis of the individual elements in isolation can
lead to incorrect or incomplete understandings of the behaviour of the whole
system.
A system is typically considered to consist of a number of interacting, interrelating
or interdependent elements that form a complex whole [186]. Many definitions of a
system add that the system works toward some common goal or purpose, and use
analogies based upon functioning organisms or social organisations. Systems theory
seeks to understand the interactions between the system elements and between
the system whole and its environment [187].
A complex system is a system that is recognised as exhibiting degrees of non-
linearity, emergence and self-organisation [187]. Complex systems approaches are
useful when accurate predictions of the whole system cannot be inferred by
studying the system components in isolation [188], when the system cannot be
truly understood by reducing it into smaller manageable units and when the
emergence of different properties at different scales is evident [189]. Increasingly,
complex systems theory is being used for studying manufacturing environments
[188].
Complex adaptive systems can be further considered as a subset of complex
systems where the system consists of individually acting elements that learn and
adapt to their environment [188]. Complex adaptive systems typically make
predictions based upon internal models of the environment and the assumptions of
the agents, and then act, learn and adapt to the outcomes.
The challenges of commercialising cellulosic ethanol present a problem significantly
broader than the technical challenges alone. Different conclusions on the most
53
significant commercialisation challenges will be reached depending upon the lens
through which the viewer sees the system (Figure 4.1).
Figure 4.1 Issues impacting the commercialisation of bioethanol technologies viewed through economic, technical, sustainability and public policy lenses
It is proposed that the system encompassing the commercialisation of cellulosic
ethanol from sugarcane, the sugarcane bioethanol system, can be considered as a
complex system within a dynamic economic, technical, policy and social
environment, and further that the system can be considered to act like a complex
adaptive system. In this system, multiple agents contribute and compete to deliver
components of the technology, with each of these agents learning and adapting to
the rapidly changing environment. The success of any component technology is
dependent perhaps to only a minor extent on its technical superiority, but to a
significantly greater extent on its proponent’s entrepreneurial aptitude, financial
backing and ability to establish collaborative relationships with other key
technology partners, feedstock providers and customers.
TechnicalBiomass collection
Biomass storageChemical usage & recovery
Pretreatment strategyCo-product options
Reactor designs
Enzyme productionHydrolysis strategyFermentation organismProcess integrationWaste processingEnergy use
EconomicProduction costs
Capital costsBiomass transport costs
Feedstock priceOff-take agreements
Product price
Project hurdle ratesRevenue diversificationCash flowPrice risk and sensitivityLiquidityFunding models
SustainabilityLife cycle analysisCarbon efficiency
Future energy technologiesFate of process wastes
Embedded energyFertiliser inputs
Land use changeImpact on food productionGreenhouse gas reductionFarming practicesWater useFossil fuel use
Public policyCarbon tax
Emissions trading Post-Kyoto agreements
Uni/multi-lateral actionCommunity support
Support for R&D
Energy securityBiofuel mandatesRural supportRenewable energy policyTax incentivesHealth benefits
54
Systems engineering offers a framework for the analysis of complex engineering
systems. Systems engineering is generally considered to be multi-disciplinary, to
deal with systems that are open (interacting with their environment) and to take a
top-down approach to generating a solution; starting with the high level intent or
purpose of the system and successively elaborating increasing functional detail
[190]. Systems engineering aims to produce whole-of-system solutions through a
process which includes:
1. Scoping the problem space;
2. Exploring the problem space;
3. Characterising the whole problem;
4. Conceiving potential remedies;
5. Formulating and manifesting the optimum solution (best solution achievable
given constraints and circumstance); and hence
6. Solving, resolving or dissolving the problem [190].
In this study, systems engineering tools have been used for analysing the challenges
associated with developing commercially feasible cellulosic ethanol from sugarcane.
4.3 Scoping and exploring the problem space
A conceptual map of the Australian sugarcane processing system is shown in Figure
4.2. This map views the system with a simplified value chain at its core, highlights
the key factors impacting upon profitability and sustainability of the system and
identifies the broader environmental influences.
55
Figure 4.2 Conceptual map of a sugarcane processing system in Australia
An analysis of the factors affecting the sugarcane bioethanol system has been
undertaken using a systems analysis method [191]. This approach has identified
core understandings related to Identity, Information and Relationships, and the key
issues in the pathway to developing a new sugarcane bioethanol system, from
Intention through to the development of New Contexts, Structures and Strategies
for the industry. A summary of some of the key issues identified in this analysis is
shown in Table 4.1.
The key issues relating to Identity, Information and Relationships reflect existing
states, both real and perceived. For example, while the sugar industry in Australia
has very efficient sugarcane farming and sugar production systems, there has been
56
some change over the past decade towards increased renewable energy production
as a co-product of the sugar production process. That this shift has not been more
pronounced has been the result of challenging investment conditions including low
industry returns, declining sugarcane production, sunk capital in sugar manufacture
and the high capital cost of plant and equipment in Australia.
The issues relating to Intention, Principles and Tensions reflect the opportunities
(and challenges) in the industry that have been presented by the increasing cost of
energy and the community desire for access to low greenhouse gas emission
renewable energy. Assessing financial viability and sustainability is a fundamental
component in the further technology development and investment in renewable
energy.
The imperative for revenue diversification in the sugar industry requires a paradigm
shift for the industry from being primarily a sugar producer to a new context as a
renewable energy provider, producing larger scale electrical energy generation from
biomass combustion (cogeneration) and the production of liquid transport fuels and
co-products. An understanding of this new context is required not just by the
industry where new revenue opportunities emerge, but also by the government and
community to whom many of the environmental and social benefits of this new
investment will flow.
Within this new context, the production of ethanol from bagasse is a
complementary measure to both higher efficiency cogeneration infrastructure and
infrastructure for the production of ethanol from sugarcane juice or molasses.
Enabling projects to meet investment thresholds will require the integration of
existing plant and new capital equipment in innovative ways and will challenge
many of the traditional practices at the farm – factory interface.
57
Table 4.1 Summary of the key issues relating to bagasse-based bioethanol commercialisation in the sugarcane industry in Australia
Identity Sugarcane industry – growing, harvesting, transport,
milling, storage and marketing Commodity based agribusinesses Support services – government, research, extension,
financial Conventional ethanol industry from molasses is
established technology Industry exposed to world market and rapidly
restructuring Information
Well developed understanding of conventional sugar milling technology
1st generation ethanol well understood 2nd generation bioethanol technically more complex
and not well developed Future price of crude oil and ethanol difficult to predict Uncertain value for co-products but overall important
for economics Government support needed for the establishment of
industry – what form of assistance? Various technical processes for bioethanol – no clear
technology winner Relationships
Existing contractual and supply chain integration between growers, millers and harvesters
Well developed connections between industry and industry-based researchers
Trend from government regulation of industry to support for innovation
Existing relationships with green energy providers through electricity products
Intention
Enhance industry sustainability and profitability Create increased value from fibre Bioethanol production from lower value biomass Value add through co-products Develop new IP where possible and facilitate
introduction of leading technologies into industry Reduce greenhouse gas emissions and impact on climate
change Reduce dependence on imported crude oil
Principles, standards
Accurately measure and optimise sustainability No impact on food supply Measure and report on financial viability Minimise risk of the new technology for early
adopters Tensions, issues
Food v fuel Resistance from fossil fuel industry Concern with misleading sustainability measures Technology risk for early adopters Existing sunk capital in sugar production Perceived slow rate of technology adoption in
industry Access to finance for industry investment New contexts, structures, strategies
Sugarcane is a renewable bio-energy crop Biofuels and energy efficiency measures together
significantly reduce greenhouse emissions from transport
Sugar mills are integrated sugar and bio-energy factories
Integrated industry vision for bio-energy future Viable industry future independent of any
government support or assistance Industry delivers positive environmental and
financial benefits for community The work
Develop technology for bioethanol from bagasse Key issues of pretreatment, enzymatic hydrolysis
and fermentation technologies Integrate technologies into sugarcane milling system Develop complimentary co-products in biorefinery Market test co-products Deep learning, sustainability
Measurement of sustainability through embodied energy, LCA and other indicators
Assessment of economic viability First bioethanol facilities may look quite different to
later facilities Technology will develop rapidly following early
stage commercialisation
58
Through challenging traditional practices, new opportunities will emerge such as
the development of sugarcane varieties with higher fibre content, harvesting and
collection of sugarcane leaf residue (trash) for increased bioenergy production,
development of new sugarcane payment systems that promote whole of system
profitability and extensions to the traditional annual harvesting season length for
improved utilisation of new processing infrastructure.
4.4 Defining the system purpose and CONOPS
One of the critical steps in systems analysis is to develop a deep understanding of
the ultimate purpose (or prime directive) of the system and to develop a high level
concept of operations (CONOPS). While the purpose clearly articulates objectively
what is to be achieved, the CONOPS describes the way the system is to work or
operate. Competing CONOPS can be assessed using comparative measures of
effectiveness [190].
In the sugarcane bioethanol system, the declaration of the purpose of the system
would reference the requirement for both commercial profitability at the business
level and the delivery of significant societal environmental sustainability benefits.
The following is proposed as a possible definition of the purpose of the sugarcane
bioethanol system:
To deliver long-term profitable return on investment and a high level of
sustainability including greenhouse gas emission reduction from the production of
ethanol from sugarcane fibre in an integrated sugar – bioethanol production facility.
This statement not only defines the purpose of the system, but also infers some of
the key measures of effectiveness of the conceptual system solution. An
understanding of the system purpose can be further developed using an objectives
tree as shown in Figure 4.3.
The objectives tree highlights some of the complexity in understanding the ultimate
purpose of the system, and in particular identifying at which level the ultimate
purpose should be formulated. In the objectives tree, the decision was made to
59
focus the prime directive at the business level, which is ultimately the level at which
investment decisions in new bioethanol facilities will be made.
Within the objectives tree, the sub-objectives provide ever increasing detail on the
means by which the higher level objectives will be met. At the lowest level shown,
the sub-objectives highlight the fundamental drivers of project value, including
maximising economies of scale, minimising capital costs, maximising the revenue
through co-product value adding and integration of the bioethanol system within
existing sugarcane industry structures.
Several public policy objectives were identified that flow from attainment of the
prime directive but which do not necessarily directly relate to the investment
decision at the business level.
As previously stated, the CONOPS describes the way the system is to work, or how
the prime directive is to be achieved. The CONOPS typically addresses strategies,
policies and constraints of the system and the full CONOPS should be demonstrably
realised in the final solution [192].
The proposed CONOPS of the sugarcane bioethanol system is for a system that
identifies as a multi-product renewable energy hub, utilising the existing industry
value chain to produce sugar, ethanol and value-added co-products in a fully
integrated processing environment (Figure 4.4).
Within this environment, process streams flow seamlessly between facilities and
waste or co-product streams are utilised across individual facility boundaries to
maximise overall profitability. The facilities share common utilities and services
including steam and electrical generation infrastructure. Other site services such as
transport infrastructure, waste water and co-product recycling are shared where
possible to minimise capital investment and reduce overall production costs.
60
Figure 4.3 Objectives tree for the sugarcane bioethanol system
61
Figure 4.4 Schematic representation of the sugarcane bioethanol system
The integrated facilities continue to utilise the previously existing processing
facilities, maximising the value from sunk capital and optimising the value from
existing supply and value chains. Opportunities are sought to partner with
technology leaders to produce co-products that add value to the overall profitability
of the system, including promoting value from permit trading in an emissions
trading scheme.
62
The profitability of the whole system is enhanced by harvesting of a proportion of
the sugarcane leaf material (trash) to maximise bioenergy production, but ensuring
that sufficient trash remains in the field crop to enhance soil health and enhance
the future productivity of the farming system. By-products from the process are
recycled to the farming system as required and where this enhances the
productivity of the farming system.
The harvesting and sugarcane processing season length is optimised to produce the
highest overall system profitability. Intermediate product storage for concentrated
liquor, molasses and bagasse enhance the efficient use of capital in the integrated
facilities by extending the ethanol production processes period beyond the
sugarcane harvesting season.
Key measures of effectiveness are required to be able to comparatively assess
alternate viable solutions in order to select the optimum solution and can include
both economic measures and non-economic measures. The key economic measure
used for project investment is typically Net Present Value (NPV) as this measure
allows ranking of alternate solutions. NPV is a measure of the present worth of
project future cashflows and can be represented by the following equation [193]:
∑= +
=N
ott
t
rCFNPV
)1(
where t = time of the cashflow in years;
CFt = net cashflow at time t;
r = the opportunity cost of capital (discount rate); and
N = period (years) over which the NPV is calculated.
Environmental sustainability is principally measured via life cycle assessment to
understand criteria such as greenhouse gas (GHG) emission reduction potential,
allowing comparison between alternate solutions on a consistent basis. A summary
of the purpose, CONOPS and key measures of effectiveness is shown in Table 4.2.
63
Table 4.2 Summary purpose, concept of operations (CONOPS) and key measures of effectiveness of the integrated sugar – ethanol system
The sugarcane bioethanol system
Purpose:
To deliver long-term profitable return on investment and a high level of sustainability performance including greenhouse gas emission reduction from the production of ethanol from sugarcane fibre in an integrated sugar – ethanol production facility
Concept of Operations:
Integrate new bioethanol facilities with sugar processing and juice/molasses processing facilities to reduce capital and operating costs
Utilise shared services, infrastructure and administration
Utilise sugarcane extraneous matter (trash) for extra fibre availability and to improve economies of scale
Enhance the sustainability of the agricultural system through encouraging and enabling good agricultural practice including sufficient trash for green sugarcane trash blanketing and recycling of co-products
Consider the transfer of process streams between sugar and ethanol processing facilities where this enhances overall profitability
Utilise energy transfers between processes to optimise process energy efficiency
Utilise shared liquid and solid waste treatment facilities
Consider storage of bagasse and molasses for effective use of capital
Generate new revenue streams for revenue diversification
Maximise sustainability outcomes for community benefit
Maximise revenue opportunities from carbon trading
Minimise technology risks for early adopters
Have minimal negative impact on global food availability
Create value from co-products for higher economic viability and resilience
Utilise the value from existing sunk capital in sugar and ethanol production facilities
Utilise existing value and supply chains
Utilise existing industry research and extension infrastructure – plant breeding, processing, etc
Focus efforts by working with technology leaders
Continually reinforce the paradigm that sugarcane industry is a renewable energy industry
Key measures of effectiveness:
Net present value of the project
Greenhouse gas emission reduction by life cycle analysis
64
4.5 Scoping the solution space through techno-economic modelling
To understand and explore the solution space, a techno-economic model of a
sugarcane bioethanol system was constructed, the sugarcane bioethanol model.
Conceptually, the sugarcane bioethanol model is based upon the common
methodological framework as described by de Rocquigny et al [194] and links both
fixed inputs (d) and uncertain inputs (x) to the model outputs (z), based upon which
decision criteria are assessed (Figure 4.5). The sugarcane bioethanol model
(constructed in MS Excel) uses Monte Carlo techniques within Oracle Crystal Ball to
analyse model outputs and uncertainty.
Figure 4.5 Techno-economic model of the sugarcane bioethanol system (the sugarcane bioethanol model) based upon the common methodological framework [194]
Other materials usagesOther materials pricesBagasse storage and
handling costsMaintenance costs
Fixed inputs (d)
Quantity of fibre availableFactory availabilityProduct lignin quality Calorific value of ancillary
fuelsBoiler operating conditionsSteam lossesCapital on-costs and
location factorsTransport distancesTransport cost ratesIP and insurance costsInflationDiscount rateTax ratePlant depreciation life
System model
Model outputs (z)
Forecast variables
Net present valueInternal rate of returnPaybackReturn on funds
employedf (x , d)
Decision criteria
Maximise net present value
NPV > 0Certainty > 95%
Feedback process
Take action to reduce uncertainty in model
Input experimental dataConvert less sensitive
variables to fixed
Input uncertainty
Measure of uncertainty
Probability / cumulative distribution function of the uncertain variables
Parameters of the uncertainty model
Correlation coefficients
Output uncertainty
Measure of uncertainty
Probability / cumulative distribution function of the forecast variable
Quantity of interest
Coefficient of variation (=stdev/mean)
Uncertainty propagation
Output presentation
Forecast chartsSensitivity chartsCorrelation dataOptimum results
Uncertainty propagation
Sensitivity analysis
Monte Carlo analysis
Uncertain inputs (x)
Sugarcane constituentsFibre constituents Pretreatment yieldsHydrolysis efficiencyFermentation efficiencyCo-product yieldsCapital costsLabour ratesLabour requirementsHydrolysis solids loadingElectrical requirementsSteam requirementsBagasse priceEthanol priceEthanol production tax
rebateLignin priceElectricity priceRenewable energy
incentivesAncillary fuel pricesEnzyme usage & price
Summary of model inputs
Rank correlation coefficients
65
Unlike the traditional sugarcane production system which utilises well understood
technology and operates in established markets, the sugarcane bioethanol system is
subject to large degrees of uncertainty both in technology outcomes and in the
markets for the products of the process. There is a high degree of uncertainty in the
policy arena with regard to the future price of carbon, emission reduction programs
and renewable fuel production incentives. The common methodological framework
provides a basis for both defining and assessing the impact of this uncertainty on
the model inputs and measuring the effect of this uncertainty on the output of
interest.
The uncertainty in the inputs is caused by the variables being subject to
randomness, lack of knowledge, measurement errors, predictions of future states,
technology assumptions and others sources of uncertainty.
Uncertainty in the sugarcane bioethanol model input assumptions is represented as
probability distribution functions for each of the uncertain inputs. For each of the
variables, a triangular distribution function is applied to each variable using
estimates of the minimum, maximum and most likely states of the variable. Key
uncertain and fixed inputs for the model are shown in Table 4.3 and Table 4.4. Note
that the simulations undertaken in this example refer to a fixed quantity of fibre
available and it is assumed that the sugar factory has the capacity to vary the sugar
production process to enable the fibre to be available as required.
Uncertainty is propagated in the model from the input to the output variables. The
key output variable (forecast variable) of the model is the net present value of the
process. Uncertainty in the net present value is represented as a normalised
probability distribution of the forecast variable and the probability of achieving a
predetermined target or range is termed the ‘certainty’. The decision criteria can
then apply a benchmark to the certainty of the forecast variable distribution
function to determine the acceptability of the result. The certainty can be increased
by analysing the sensitivity of the results to the uncertain assumptions and
focussing on reducing assumption uncertainty.
66
Table 4.3 Key variable inputs to the sugarcane bioethanol model
Key model input variables Units 1 Minimum Likeliest Maximum
Cellulose content of bagasse % odf 2 32 38 52
Hemicellulose content of
bagasse
% odf 2 20 26 30
Lignin content of bagasse % odf 2 17 20 24
Hexose yield (from
pretreatment
kg / kg cellulose 0.70 0.85 0.98
Pentose yield (from
pretreatment)
kg / kg pentan 0.75 0.90 0.98
Ethanol yield from hexose
fermentation
% theoretical 80 88 94
Ethanol yield from pentose
fermentation
% theoretical 40 65 90
Bioethanol plant capital cost
factor 3
6 8 10
Cellulase price $ / t enzyme 120 160 420
Bagasse price $ / t odf 2 10 60 90
Ethanol factory gate price $ / L 0.4 0.7 1.0
Ethanol production incentive
value
$ / L 0 0.26 0.38
Export electricity price $ / MWh 20 30 60
Renewable electricity
incentive value
$/ MWh 0 30 40
Coal price $ / t 40 90 200
Bagasse storage and handling
cost
$ / t bagasse 8 12 20
1All prices in 2009 Australian dollars 2Oven dry fibre 3Capital cost (AUD m) = Cost factor x (Plant capacity ML ^ 0.7)
67
Table 4.4 Key fixed inputs to the sugarcane bioethanol model
Key model fixed inputs Units Value
Annual throughput t odf 1 / annum 1,000,000
Maintenance cost rate % capital cost 2.2
Administration and overheads cost rate % capital cost 2.0
Capital expenditure year 1 / year 2 % 60/40
Inflation rate % / annum 3.0
Discount rate % 12.0
Tax rate % 30.0
1Oven dry fibre
Model simulations were based on 10,000 trials using the Monte Carlo simulation
tool in Oracle Crystal Ball. A typical analysis of the sensitivity of the key input
variables to the net present value of the ethanol production process is shown in the
tornado chart in Figure 4.6. The tornado chart represents in descending order the
factors with the greatest sensitivity to project net present value. Sensitivity is
calculated by computing the rank correlation coefficients between every
assumption and forecast variable using the data generated from all of the 10,000
simulations. In calculating sensitivities, data for the assumption variables were
selected according to a triangular probability distribution generated from the
Minimum, Likeliest and Maximum values shown in Table 4.3.
As can be seen from Figure 4.6, the key variables impacting upon the net present
value include:
1. ethanol price and ethanol producer subsidy;
2. bagasse price;
3. cellulase price; and
4. bioethanol plant capital cost.
Other variables including the constituents of the bagasse, hydrolysis yields and
fermentation yields have a much lower impact on net present value. It is worth
noting that much of the on-going technology development is focussing on
incremental gains in these criteria.
68
The results of an analysis of the relationship between assumption uncertainty and
the net present value sensitivity are shown in Figure 4.7. Assumption uncertainty is
calculated as the coefficient of variation of the probability distribution of the model
uncertain assumption variables and sensitivity is the normalised correlation
coefficients of the forecast variables.
Figure 4.6 Sensitivity of the key factors in bagasse based ethanol project viability (net present value) to the project assumptions
From this figure it can be clearly seen that both the ethanol price and feedstock
price present the most risk to any commercial project as these variables have a high
assumption uncertainty and a high impact on the net present value of the project.
35.7%-16.3%
14.0%
9.2%
-6.6%
-6.0%
4.3%
3.7%
1.5%
1.2%
0.3%
0.3%
0.1%
0.8%
-20% -10% 0% 10% 20% 30% 40%
Ethanol price
Bagasse price
Ethanol producer subsidy
Renewable electricity incentive price
Cellulase price
Plant capital cost factor
Cellulose % fibre
Export electricity price
Hemicellulose % fibre
Lignin % fibre
Pentose fermentation efficiency
Bagasse storage and handling costs
Hexose fermentation efficiency
Other
Sensitivity: Net present value
69
Managing the uncertainty associated with these variables is the most significant
issue in establishing viable commercial projects. While lignin price, capital cost and
enzyme cost have similarly high assumption uncertainties, the impact on the net
present value of the project is less dependent upon variations in the future price of
these factors, although these factors are still significant.
Figure 4.7 Sensitivity of the major factors in bagasse based ethanol project viability (net present value) to the assumptions in the techno-economic model
1 Ethanol price 2 Feedstock (bagasse) price 3 Ethanol producer subsidy 4 Renewable electricity incentive price 5 Cellulase price 6 Bioethanol plant capital cost factor
8 Bagasse storage and handling costs 9 Pentose fermentation efficiency 10 Cellulose % fibre 11 Hemicellulose % fibre 12 Lignin % fibre 13 Hexose fermentation efficiency
7 Export electricity price
1
2
4
3
5 6
10
11
7
912
13 8
Sens
itivi
ty: N
et p
rese
nt v
alue
Assumption uncertaintyLow High
Low
High
Low High
Low
High
70
4.6 Manifesting the optimum solution
To increase the likelihood of early stage investment in bioethanol production from
sugarcane, it is critical to ensure that the key factors identified above are optimised
to provide a positive return for the facility over the life of the project, the risk
associated with these factors is managed and that the uncertainty in the future
value of these factors is reduced to the greatest extent possible. By optimising these
variables and minimising uncertainty, the technological and financial risks are
minimised for early adopters of the technology.
4.6.1 Ethanol price and production incentives
There is a high degree of uncertainty in the future price of fuel grade ethanol and
this uncertainty is the major contributor to investment risk. Future ethanol prices
will be influenced by the complex behaviour of the crude oil market, public demand
for renewable fuels and the presence or absence of national policies promoting the
use of alternate fuels. It is likely though that ethanol prices will be significantly
correlated to traded global crude oil and petroleum prices. For most early stage
commercialisation projects, however, the establishment of long term off-take
agreements will be essential in mitigating the ethanol product demand and price
risks.
Unlike many globally traded commodities there is no accepted international
benchmark price for ethanol, although such a benchmark may develop as the
market matures. Currently, the reference price of ethanol is dependent upon the
market in which it is traded. In the USA, the domestic price of ethanol is largely
determined by trade in the spot and longer term physical markets but, while trading
volumes are still reasonably light, ethanol futures prices on the Chicago Board of
Trade (CBOT) are highly correlated with physical values [195] and can be effectively
used as a reference price for physical market values. The existence of derivatives
markets such as the CBOT for ethanol allows some management of product price
risk through forward pricing in futures contracts, options and other commodity
price management strategies.
71
The technology risk associated with second generation ethanol facilities increases
the risk associated with the commercialisation of early stage second generation
facilities. Many countries currently have in place ethanol incentive schemes to
encourage the uptake of ethanol technologies. Around the world, and particularly in
Brazil and the USA, biofuel production incentive schemes and mandates have
assisted in underpinning an ethanol price either directly or indirectly at a level that
has encouraged early stage investment in first generation biofuels.
For a government subsidy or production rebate to enhance commercialisation of
biofuel processing infrastructure, there needs to be sufficient certainty in the policy
position for an extended period of time. As with the market price of ethanol, the
value of biofuel production incentive schemes for renewable or low emission
transport fuel production has a significant impact on investment indicators, and is a
key factor in promoting early stage investment.
Further government policy support is likely to be necessary to promote this
investment in early stage second generation ethanol technologies in Australia.
4.6.2 Bagasse price
Like other fibrous residues, sugarcane bagasse is a high volume, low value material
and as such is generally considered to only find economic utility within a small
distance of the sugar factory in which it is generated. As a result, there is no
significant national or global market for bagasse, and no commonly traded market
price. The value of bagasse as a feedstock for a bioethanol plant is therefore
dependent upon the region in which it is generated including any local alternative
uses for excess bagasse, such as cogeneration or paper products manufacture.
Historically, bagasse has been combusted in the sugar factory boilers to provide
steam and energy for the process, but as there is significantly more energy in
bagasse than is required for the process, both the boilers and sugar production
processes have been designed to utilise this energy inefficiently to ensure complete
disposal of the bagasse. Increasingly, excess energy from the process is being
72
converted to electricity which is exported to generate additional revenue for the
sugar factory.
The value of bagasse to the factory for site energy generation is dependent upon
the energy balance of the factory and the capacity of the factory to generate and
economically utilise additional steam and electricity. In a factory with surplus
bagasse and limited electricity generation infrastructure, the value of bagasse could
be negative as excess bagasse represents a disposal cost to the factory. In a factory
with both surplus bagasse and surplus capacity to generate and export electricity,
the bagasse value is dependent upon the electricity export price including any value
for renewable or low emission energy generation. Where the factory regularly
imports extraneous fuels to supplement bagasse combustion for energy generation,
the bagasse value may be considered to have the value of the extraneous fuel on an
energy equivalent basis [196].
The farming decision to cultivate sugarcane is (in most of the world) a decision
made on the projected revenue from sugar, or as in Brazil, on the revenue from
sugar and ethanol from juice fermentation. A shortage of fibre from bagasse and
sugarcane trash, leading to an increase in fibre price, is unlikely to result in a
significant supply response from sugarcane growers (in the absence of a sugar price
driver). An increase in fibre price, however, may make the import of alternative
sources of fibre into the process more economic such as through the harvesting of
sugarcane trash or the utilisation of complementary feedstocks (green waste or
fibre crops).
To minimise the risks associated with feedstock price, it is necessary to consider
locating bagasse based bioethanol facilities where there is long term certainty of
bagasse availability and where the bagasse has limited alternate economic value. It
may also be possible to reduce risk by considering in the location of a facility the
availability of cost-effective supplementary feedstocks.
73
4.6.3 Cellulase price
This analysis shows that the cost of cellulase for the cellulose hydrolysis stage is the
key operating cost in a bioethanol facility. Cellulase may be supplied to the facility
as an imported product, but given the large quantity of enzyme required for a
commercial process, is likely to be manufactured on-site in many cases. The future
price of cellulase is uncertain at the scale required for commercial facilities but
there exists a high likelihood of significant cost reductions over the next decade.
The risks associated with enzyme supply cost may be mitigated through innovative
plant design and operation to minimise enzyme requirements and through
contractual supply arrangements with enzyme producers. Research toward plant
made cellulases in sugarcane offers opportunities for significantly reducing the cost
of enzymes in the sugarcane bioethanol system [197].
4.6.4 Bioethanol plant capital cost
The capital cost of the bioethanol facility is dependent upon many factors including
facility location, scale and process technology choices. The uncertainty in bioethanol
plant capital cost has a significant impact on the uncertainty in net present value of
the facility although for any one project may be defined with greater certainty
through detailed engineering design. Integrating processing operations in co-
located sugar processing and ethanol production facilities offers significant
opportunities for reducing the capital cost of new bioethanol facilities.
4.7 Creating the solution and deep learning
A long-term profitable return on investment is the key objective (purpose) of an
integrated sugarcane bioethanol facility. Such a facility, however, must also
demonstrate that there are significant sustainability benefits from the production
system, including in particular a significant greenhouse gas emission reduction
benefit. An analysis of this greenhouse gas reduction benefit is beyond the scope of
this paper.
74
Minimising the commercial and technical risk associated with investment in
sugarcane bioethanol facilities will enhance early stage uptake of the technology.
This process requires solutions at the science, engineering design, marketing and
government policy levels to address the key variables impacting on project
assumption uncertainty and sensitivity to project investment indicators such as net
present value.
This study has analysed the sugarcane bioethanol system as a complex system and
considered the integration of bioethanol production from bagasse into the
sugarcane processing system. The techno-economic analysis of the system
concludes that the key factors which need to be addressed to enable early stage
uptake of the technology and minimise risk for investors in Australia include ethanol
price, bagasse price, ethanol producer subsidy, cellulase price and biorefinery
capital cost.
While to some extent these conclusions appear self-evident, this analysis provides
an assessment of the scale of influence and relative magnitude of importance of
these factors to early stage commercial success. The analysis results in a deeper
understanding of the influence of uncertainty in early stage project investment and
highlights the importance of reducing the uncertainty in these key factors to
encourage project investment.
Uncertainty in the future price of ethanol is the major impediment to early stage
investment in second generation ethanol production from bagasse. Government
policy support which underpins the ethanol price and reduces investment risk
through renewable fuels incentives such as the ethanol producer subsidy in
Australia or through the establishment of a carbon price under an emissions trading
scheme is likely to be necessary to promote early stage commercial investment in
this technology and hence deliver the significant greenhouse gas reduction, health
and community benefits possible from second generation biofuel use.
75
Techno-economic assessment
77
Chapter 5
The potential for ethanol production from sugarcane in Australia
5.1 Introduction
The information in this chapter was presented at the Australian Society of Sugar
Cane Technologists annual conference in Bundaberg, Queensland from the 11th
– 14th May 2010. The paper was peer-reviewed and included in the published
proceedings of the conference cited as the Proceedings of the Australian Society
of Sugar Cane Technologists, Volume 32, 2010.
This chapter identifies the current quantum of transport fuel used in Australia
and assesses the options for substituting a portion of this fuel usage by ethanol
produced from components of the sugarcane crop (juice, molasses, bagasse and
trash). The chapter describes the development of a comprehensive and
integrated techno-economic model of a sugarcane processing facility, juice and
molasses-based ethanol distillery and cellulosic ethanol facility, including an
assessment of the energy requirements of the integrated facility. The chapter
compares the potential industry revenues for five scenarios including a base
case, cogeneration scenario and three ethanol options of varying scales.
5.2 Transport fuel use in Australia
Transport fuel consumption in Australia is dominated by the four key fuels –
automotive gasoline, diesel, aviation fuel and LPG. Statistics on transport fuel
consumption in Australia and in the individual states are reported annually by
the Australian Bureau of Agricultural Resource Economics (ABARE) in the series
entitled Consumption of Petroleum Products [198]. The most recent ABARE data
on petroleum product use in Australia and the key sugarcane growing states of
Queensland and NSW are shown in Table 5.1.
78
The major growth in transport fuel use in Australia is in the consumption of
diesel and to a lesser extent aviation fuels. Over the past 10 years in Australia,
diesel fuel use has increased by 42 % and aviation fuel use has increased 26 %
while automotive gasoline use has only increased by 6 %.
Table 5.1 Consumption of petroleum products in Australia, Queensland and NSW 2007-08 [198]
Australia
(ML)
Queensland
(ML)
NSW
(ML)
Automotive gasoline 19 234 4475 6072
Diesel 18 256 5164 3776
Aviation fuel 6158 1313 2738
LPG 4024 613 1139
Other 3116 573 913
TOTAL 50 788 12 138 14 638
5.3 The capacity of the Australian sugarcane industry
The Australian sugarcane industry extends across 2200 km of coastal Queensland
and NSW. Over the past decade, the industry has contracted as a result of a
sustained period of poor world sugar prices, drought, disease and industry
rationalisation. The Australian sugarcane crop has dropped from a peak of 39.5
Mt in 1998 to 30.3 Mt in the 2008 season. Area harvested has decreased from a
peak of 450 000 ha to about 370 000 ha [38]. The average Australian sugarcane
productivity over the previous ten year period was 85.8 t/ha, varying on a
seasonal basis between 69.8 t/ha and 99.1 t/ha. With the reduction in milling
capacity in some areas, a proportion of the area lost to sugarcane cultivation is
unlikely to be readily returned to production. Higher world sugar prices in 2008
and 2009 are likely to result in the stabilisation of sugarcane production and
perhaps some increases in sugarcane cultivation in several areas in the short
term.
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It seems likely that, unless there is a sustained step change in the world sugar
price or a significant move to high biomass sugarcane cultivation, sugarcane
production in Australia in the short to medium term will continue to average
between 30 and 35 Mt from approximately 400,000 ha. It is recognised that, in
the right business environment, further significant expansion of the sugarcane
industry in Australia is possible particularly through tropical Queensland,
Western Australia and the Northern Territory, however, significant infrastructure
and investment capital is required to support this expansion and as a result this
possible future expansion scenario has not been assessed in this study.
5.4 Ethanol production from sugarcane juice and molasses
Ethanol can be produced from a variety of sugarcane feedstocks, including juice,
molasses and crystal sugar. The conversion of sucrose to reducing sugars and
ethanol through yeast fermentation of juice and molasses has been previously
reported [199].
In the fermentation of sugarcane juice or molasses, sucrose is hydrolysed to
hexoses (glucose and fructose) which are fermented to ethanol as shown in
Equations 1 and 2.
C12H22O11 + H2O 2C6H12O6 (Equation 1)
C6H12O6 2C2H5OH + 2CO2 (Equation 2)
As reported [199], the production of significant quantities of carbon dioxide as a
by-product of the fermentation process limits the maximum theoretical
fermentation yield of ethanol from hexose to 51.14 % (w/w) but the maximum
practical yield using conventional fermentation organisms is around 48.40 %
(w/w) as a result of hexose consumption in side reactions.
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The maximum theoretical yield of ethanol from sucrose is 105.3 % of the ethanol
yield from an equivalent weight of glucose, as a result of a mass increase in the
initial sucrose hydrolysis reaction. Approximate ethanol yields per tonne of
product are shown in Table 5.2.
Table 5.2 Approximate ethanol yields per tonne of product
Typical sucrose concentration1
(%)
Typical reducing sugars
concentration1
(%)
Approximate ethanol yield2
(L/t)
Final molasses 35.0 13.0 280
B molasses 46.5 8.7 324
A molasses 53.5 5.2 345
Evaporator supply juice (ESJ)
13.5 0.4 82
Raw sugar 98.9 0.3 590 1SRI data 2Based on fermentation yield of 88.0 %, distillation efficiency of 99.0 % and ethanol density of 0.789 kg/L
5.5 Ethanol production from bagasse and sugarcane trash
The production of ethanol from the fibre component of tops and leaf (trash) and
bagasse is significantly more complex than the production of ethanol from
sugarcane juice or molasses as a result of the resilience of the carbohydrates in
the fibre to undergo hydrolysis to their monomer sugars. Pretreatment of the
fibre through physical or chemical processing is required to make the
carbohydrates in the fibre more susceptible to hydrolysis. Hydrolysis is achieved
through the application of hydrolytic enzymes or acids.
In general, the hydrolysis reactions can be described as shown in Equation 3 for
cellulose and in Equation 4 for hemicellulose [79]. The hydrolysis of cellulose
results in the production of the glucose monomer and from sugarcane bagasse
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the primary monomers from hemicellulose hydrolysis are the pentoses xylose
and arabinose.
(C6H10O5)n + nH2O nC6H12O6 (Equation 3)
(C5H8O4)n + nH2O nC5H10O5 (Equation 4)
In the cellulose hydrolysis reaction, the molecular weight of the carbohydrates
increases by 11.1 %, and for hemicelluloses the molecular weight increases by
13.6 %.
Due to the harsh nature of the leading pretreatment processes, a number of
degradation products may be formed which not only reduce hexose and pentose
yields but can be inhibitory to the organisms involved in fermentation of the
sugars to ethanol. These degradation products include furfural, 5-
hydroxymethylfurfural, levulinic acid, formic acid and acetic acid. Minimising the
formation of these degradation products is a critical challenge for any biomass
pretreatment strategy.
The crystalline nature of the cellulose in plant fibres typically restricts the
economically achievable glucose yield from cellulose hydrolysis, although the
glucose released can be readily fermented at very high efficiencies using
conventional fermentation organisms.
While hemicellulose can be readily hydrolysed to pentoses using mild acid
processes, the slow rate of fermentation of pentoses by yeasts and other
organisms restricts the economically achievable ethanol yield from pentoses. A
large global research effort is focussing on increasing the economic yield of
ethanol from cellulose and hemicellulose by improving enzyme and fermentation
organism effectiveness. Currently, however, pentose fermentation remains a key
challenge for the development of a commercial cellulosic ethanol industry.
When estimating the potential yield of ethanol from bagasse, it is necessary to
account for the efficiency of the whole production process. The overall yield of
ethanol will be a product of the yields from each of the pretreatment, hydrolysis,
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fermentation and distillation stages and will account for the different yields from
the cellulose and hemicellulose components of the biomass.
For an ethanol conversion efficiency of approximately 80 % from cellulose and a
moderate 50 % from hemicellulose, an ethanol product yield of around 340 L/t
dry fibre can be achieved. This consists of about 260 L/t dry fibre from the
cellulose component and 80 L /t dry fibre from the hemicellulose component of
the fibre.
In most sugarcane factories, bagasse is the primary energy source, where it is
combusted to produce steam and electricity for the process and export.
Historically, the bagasse has been burnt inefficiently in low pressure boilers and
with energy inefficient sugar processing techniques to ensure complete disposal
of the bagasse. With increasing prices for sales of export electricity to the
electricity distribution network, and for green incentives such as renewable
energy certificates generated under the Mandatory Renewable Energy Target
(MRET) scheme, there is now a significant focus on energy efficiency
improvements of sugarcane factories to maximise electricity generation and
export.
In an integrated crystal sugar factory and bagasse ethanol facility, it is envisaged
that the energy requirements for the process will still principally derive from
bagasse combustion, and it is only the surplus bagasse (the bagasse in excess of
that required for process energy) that is made available for cellulosic ethanol
production. This bagasse can be supplemented with a portion of the available
trash to provide extra fibre for both combustion and ethanol production, while
still ensuring sufficient trash remains in the field for its mulch and soil
conditioning value. The availability of trash for value-adding applications in a
region will depend upon both the economics of trash collection and transport,
and the value of the trash to the farming system. A previous biomass availability
model has assessed utilisation options based upon additional trash availability of
12.3 % for whole of crop harvesting compared to a typical sugarcane supply
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[200]. The following scenario analyses assume a maximum trash availability
equivalent to 10 % of the existing sugarcane supply.
5.6 Scenario analysis
A comprehensive technical and economic model of an integrated sugar factory,
juice and molasses-based ethanol distillery and cellulosic ethanol facility has
been developed in this research program (shown schematically in Figure 5.1).
This model enables the evaluation of possible scenarios for integrated sugar and
ethanol production facilities, including integrated options for energy generation
and export.
Simulations have been undertaken for several whole-of-industry scenarios to
estimate the potential for ethanol production from the Australian sugar industry
and the results of five of these scenarios are summarised in this report.
Figure 5.1 Schematic representation of the QUT techno-economic model of an integrated sugar factory, juice and molasses distillery and cellulosic ethanol production facility
Supplementary fuel
Cane preparation
and juice extraction
Juice and molasses distillation
Cellulosic ethanol
facility and biorefinery
Cogeneration boiler
Bagasse
Sugar cane
Crystal sugar
production
Electricity generation
Juice
Molasses storage
Bagasse storage
Sugar
Export molasses
Export bagasse
Ethanol
CO2
Vinasse
Ethanol
CO2
Lignin
Solid residue
Waste water treatment
Water
Import trash
Import bagasse
Import molasses
Export electricity
Import electricity
Filter mud
Boiler ash
ElectricitySteam
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In all of the scenarios reported, the average Australian sugarcane crop is
assumed to be 35 million tonnes. Additionally, it is assumed that a portion of the
trash from the field is collected and transported to the factory for processing.
The sugarcane processing period is assumed to be 23 weeks/y with the ethanol
facilities operating 48 weeks/y, requiring significant bagasse and molasses
storage. The bagasse is assumed to be composed of 45 % cellulose, 22 %
hemicellulose and 19 % lignin, the remainder being minor amounts of ash,
extractives and protein.
Although the model allows for their inclusion, in these scenarios, no value has
been included for renewable energy certificates, carbon credits or ethanol
production incentives. The analysis excludes rum production at the Bundaberg
distillery and other minor ethanol production in small distilleries. It is noted that
there is a considerable market for molasses as an animal feed which is likely to
limit the availability of molasses for ethanol production, but this is not
considered in these scenarios. Likewise, other markets for bagasse or trash
products are not assessed.
The five scenarios presented in this paper are:
Base scenario
This scenario models the approximate sugar, ethanol and electricity production
in the Australian sugar industry using currently installed infrastructure. In this
scenario, no sugarcane juice is utilised for ethanol production and a total of 60
ML of ethanol is produced from final molasses. All of the bagasse is used for
cogeneration and the production of export electricity. Bagasse is assumed to be
combusted in low pressure inefficient boilers and no bagasse is used for
cellulosic ethanol production. No trash is processed in this scenario.
Cogeneration scenario
In this scenario, no sugarcane juice is utilised for ethanol production. A total of
60 ML of ethanol is produced from final molasses. All of the bagasse and a
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proportion of the available trash are used for cogeneration and the production of
export electricity. Bagasse is assumed to be combusted in high pressure efficient
boilers and energy efficient process technologies are implemented to maximise
electricity generation and export.
Low ethanol scenario
In the low ethanol scenario, no sugarcane juice is utilised for ethanol production.
Ethanol is produced from all of the final molasses generated from the sugar
production process. Bagasse and trash surplus to the energy requirements of the
process are used for cellulosic ethanol production. Bagasse and trash used for
energy production are combusted in high pressure efficient boilers and energy
efficient sugar production process technologies are implemented.
Moderate ethanol scenario
In the moderate ethanol scenario, 70 % of the sugarcane juice is utilised for
crystal sugar production with the remaining sugarcane juice utilised for ethanol
production. All of the A molasses from the crystal sugar production process is
utilised for ethanol production. Bagasse and trash surplus to the energy
requirements of the process are used for cellulosic ethanol production. Bagasse
and trash used for energy production are combusted in high pressure efficient
boilers and energy efficient sugar production process technologies are
implemented.
High ethanol scenario
In the high ethanol scenario, no crystal sugar is produced and all of the
sugarcane juice is used for ethanol production. Bagasse and trash surplus to the
energy requirements of the process are used for cellulosic ethanol production.
Bagasse and trash used for energy production are combusted in high pressure
efficient boilers. Key input data for the scenario analyses are shown in Table 5.3
and Table 5.4 and the results are shown in Table 5.5.
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5.7 Discussion
Based on the assumptions used, the scenario analysis detailed in this report
shows that in a high ethanol scenario, a maximum of 4657 ML of ethanol is able
to be produced which equates to 24 % of Australia’s automotive gasoline
requirement or 104 % of Queensland’s automotive gasoline requirement on a
volumetric basis1. With the quantity of existing crystal sugar production
infrastructure in Australia, however, it is very unlikely at any stage in the future
that this quantity of sugarcane juice will be diverted from crystal sugar
manufacture to ethanol production.
The moderate scenario is a more achievable long-term ethanol production
estimate from sugarcane in Australia that may be possible in the right
commercial and policy environment. In this scenario, 30 % of the current
sugarcane juice is diverted from crystal sugar production to ethanol production
and, with the production of cellulosic ethanol from surplus bagasse and trash,
results in the production of 2622 ML of ethanol, equivalent to 14 % of Australia’s
(or 61 % of Queensland’s) automotive gasoline requirement on a volumetric
basis. It must be noted, however, that several significant economic and technical
challenges need to be overcome particularly with respect to aspects of the
cellulosic ethanol production process and the collection, transport and
processing of sugarcane trash before ethanol production at these levels could be
realised.
Even in the low ethanol production scenario, over 28 % of Queensland’s
automotive gasoline requirement on a volumetric basis can be met using ethanol
produced from sugarcane resources alone. In all of the scenarios analysed, the
process is energy self-sufficient, requiring no significant quantities of coal or
other ancillary fuels for energy generation and no significant electricity import
during operation.
1 Throughout this chapter, ethanol substitution in automotive gasoline is referenced on a volumetric basis. Reporting on a volumetric basis does not account for the lower energy content of ethanol compared to gasoline. Ethanol substitution results on an energy content basis can be calculated by multiplying the result on a volumetric basis by 0.67.
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Table 5.3 Common input data for scenario analysis
Common input data
Cane crushed (t) 35 000 000
Crushing season length (weeks/y) 23
Ethanol production period (weeks/y) 48
Commercial cane sugar content (CCS) 13.72
Cane purity (%) 85.9
Fibre % sugarcane 14.70
Fibre % trash 51.06
Cellulose % dry fibre 45.0
Hemicellulose % dry fibre 22.0
Lignin % dry fibre 19.0
Overall ethanol yield from fibre (L/t dry fibre) 340
Sugar price ($ /t IPS) 350
Ethanol price ($ /L) 0.70
Molasses price ($ /t) 90
Export electricity price ($ /MWh) 40
Table 5.4 Input data for the scenario analysis
Base scenario
Cogeneration scenario
Low ethanol scenario
Moderate ethanol scenario
High ethanol scenario
Trash collected (% cane) 0 10 10 10 10
Mixed juice to ethanol production (%)
0 0 0 30 100
Final molasses purity (molasses distillery feed purity; %)
45 45 45 72 -
Average boiler pressure (bar)
18 65 65 65 65
Average boiler efficiency (%)
60 72 72 72 72
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Table 5.5 Results from scenario analysis
Base scenario
Cogeneration scenario
Low ethanol scenario
Moderate ethanol scenario
High ethanol scenario
Sugar produced (t IPS) 4 850 000 4 850 000 4 850 000 2 770 000 0
Molasses produced (t) 1 002 000 1 002 000 0 0 0
Ethanol produced from juice or molasses fermentation (ML)
60 60 316 1574 3248
Ethanol produced from cellulosic biomass (ML)
0 0 973 1159 1409
Total ethanol produced (ML)
60 60 1289 2733 4657
Export electricity produced (GWh)
1156 12 784 3122 2425 1493
% fibre required for combustion
100 100 61.8 54.4 44.6
Sugar revenue ($ M) 1698 1698 1698 970 0
Molasses revenue ($ M) 90 90 0 0 0
Electricity revenue ($ M) 46 511 125 97 60
Ethanol revenue ($ M) 42 42 902 1913 3260
Total revenue ($ M) 1876 2341 2725 2980 3320
Sugar revenue (%) 90 72 62 33 0
Molasses revenue (%) 5 4 0 0 0
Electricity revenue (%) 3 22 5 3 2
Ethanol revenue (%) 2 2 33 64 98
% Australian automotive gasoline substitution1
0.3 % 0.3 % 6.7 % 14.2 % 24.2 %
% Queensland automotive gasoline substitution1
1.3 % 1.3 % 28.8 % 61.1 % 104.1 %
12007-08 automotive gasoline usage on a volumetric basis for ethanol substitution
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The proportion of fibre required for energy generation decreases with a decrease
in the amount of crystal sugar produced, as a result of the lower energy
requirements for ethanol production, increasing the amount of fibre available for
cellulosic ethanol production. An increase in the production of export electricity
is expected even in the high ethanol production scenario as excess high pressure
steam is utilised for electricity generation.
Compared to the base scenario with revenue of $1876 million, the cogeneration
scenario shows that an additional $465 million is able to be generated from
increased electricity production with the installation of efficient high pressure
boilers and generation equipment, energy efficient processing technologies and
the combustion of additional trash. Significantly more income is able to be
generated from the combined use of molasses, juice and bagasse for ethanol
production with an additional $849 million possible in the low ethanol scenario,
$1104 million possible in the moderate ethanol scenario and an additional $1444
million possible in the high ethanol scenario.
Further income is possible from the cellulosic ethanol production process if a
valuable co-product is able to be made from the lignin component of the fibre.
5.8 Conclusion
With a sugarcane crop of 35 Mt, ethanol produced from sugarcane has the
potential to meet a very significant proportion of Australia’s current automotive
gasoline requirements. In a possible moderate ethanol production scenario that
includes trash collection and cellulosic ethanol production, sugarcane has the
potential to provide sufficient ethanol to meet 14 % of Australia’s (or 61 % of
Queensland’s) automotive gasoline requirement on a volumetric basis while not
consuming any additional coal or other supplementary fuels.
Through crop expansion or the co-processing of other renewable fibres (such as
sweet sorghum or green waste), further ethanol production may even be
possible. Higher ethanol production quantities are also possible with the
90
cultivation of higher biomass sugarcane varieties and the cultivation of varieties
with a higher proportion of total fermentable sugars.
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Chapter 6
Economic feasibility of a soda-based biorefinery at Racecourse Mill
This chapter was written as a confidential research report in 2010 for the
partners in the Biorefinery Development Project including Mackay Sugar Ltd,
Sugar Research Ltd, Viridian Chemicals Pty Ltd and Hexion Specialty Chemicals
Inc. Funding for this project was also provided by the Queensland Government
through the Research Industry Partnerships Program (RIPP).
This chapter assesses the technology options for a biorefinery that utilises
caustic soda pulping technology for pretreatment of sugarcane bagasse to
produce ethanol, lignin and co-products. The chapter develops a process for
feasibility analysis, and utilises a comprehensive technical and economic model
to assess the likely revenue, capital and operating costs for a potential facility
located at a sugar factory in the Mackay region of Queensland. The chapter
assesses the feasibility of the proposed facility against benchmark project
indicators, and undertakes a one and two component sensitivity analysis of the
key factors impacting project viability. The chapter also analyses the feasibility of
several process alternatives.
This chapter will not be made publicly available without the consent of the
project partners. Any requests for information relating to this chapter should be
directed to the author of this thesis.
92
.
93
Chapter 7
Feasibility assessment of in-planta cellulolytic enzyme expression for the production of biofuels from sugarcane bagasse in Australia
This chapter includes information confidential to the partners of the Syngenta
Centre for Sugarcane Biofuels Development (SCSBD) including QUT, Syngenta
Biotechnology Inc and Farmacule Bioindustries Pty Ltd. This research project was
funded by both Syngenta and the Queensland Government through the National
and International Research Alliances Program (NIRAP).
This chapter explores the feasibility of a novel technology for reducing the cost
of cellulolytic enzymes for the production of ethanol from sugarcane bagasse.
The chapter explores the advantages and disadvantages of several concepts for
in-plant expression of cellulases in sugarcane and investigates the economic
benefits of the two leading concepts.
The analysis of concept feasibility reported in this chapter was undertaken by the
author of this thesis. Dr Zhanying Zhang undertook the protein analysis reported
in this chapter, assisted with the analysis of the project concepts and co-
authored the reports on this work to the project partners.
This chapter will not be made publicly available without the consent of the
project partners. Any requests for information relating to this chapter should be
directed to the author of this thesis.
94
95
Pilot plant development
97
Chapter 8
Towards a commercial lignocellulosic ethanol industry in Australia: the Mackay Renewable Biocommodities Pilot Plant
8.1 Introduction
This chapter describes the value of pilot-scale production facilities in the context of
the development of a cellulosic ethanol industry in Australia. The chapter details the
funding, design and construction of a new pilot scale biorefinery facility, the Mackay
Renewable Biocommodities Pilot Plant (MRBPP), the unique capabilities of the
facility and the future opportunities that the facility generates for the Australian
sugar industry.
The author of this thesis was responsible for the conceptual and detailed process
design of the MRBPP, was responsible for the selection and purchasing of
equipment and was the key client representative during the design, construction
and installation phases. The MRBPP is the only facility of its kind in Australia and
one of the only publicly available, flexible pilot scale cellulosic ethanol facilities in
the world, requiring a novel approach to the facility design and the development of
collaborative industry partnerships.
The pilot plant will be utilised for demonstrating the technologies described in
Chapter 6 and Chapter 7 of this thesis and has been designed to be flexible enough
to demonstrate many of the pretreatment processes described in Chapter 3. The
demonstration to be undertaken includes both the technical feasibility and the
economic feasibility of the biofuel production processes.
98
8.2 Pilot plants – facilitating commercial development
Pilot plants are an essential tool for the development of new technologies, bridging
the gap between laboratory research and commercial application of the technology.
Pilot plants are used to optimise key process parameters such as yield, rate and
efficiency at a scale much larger than that used for laboratory development and in
equipment that mimics large scale industrial facilities. This allows key process
economics to be evaluated and provides information on both the robustness of the
process and scale-up data for the design of the commercial facility. Additionally,
pilot plants also allow production of a significant amount of product for pre-
commercial testing.
Several pilot scale research facilities exist around the world for the production of
ethanol in a biorefinery. Most pilot and demonstration facilities are focussed on a
particular process technology, with only a few facilities capable of demonstrating a
broader range of technologies.
8.3 MRBPP funding
The Mackay Renewable Biocommodities Pilot Plant (MRBPP) was funded jointly by
the Queensland Government through a $3.1 million loan agreement and by the
Australian Government through a $3.4 million grant under the National
Collaborative Research Infrastructure Scheme (NCRIS) and a $1.765 million grant
under the Education Investment Fund (EIF). Further funding of about $1.7 million
was provided by QUT to ensure that the facility meets its objectives and to underpin
the pilot plant as a world class facility.
Queensland Government funding was provided through the then Department of
State Development through the Innovation Building Fund. The Innovation Building
Fund was established to promote the development of research infrastructure for
science and technology in Queensland. The funding under this program was to
provide the MRBPP building (factory building, laboratory, offices and hazardous
goods containment facilities) and plant and equipment for the pretreatment /
fractionation stages and for the separation and concentration of the lignin product.
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The NCRIS program was initiated by the Australian Government in 2004-05 to
implement “a strategic and collaborative approach to investment in world-class
facilities, networks and infrastructure that are accessible to researchers and meet
their long term needs” [201]. In the initial round, $542 million was provided to
2010-11, with an initial nine high priority areas identified in the 2006 Strategic
Roadmap.
Funding for the MRBPP was awarded to QUT under NCRIS Capability 5.5
Biotechnology Products. The aim of this program was to “develop research
infrastructure to assist in the production of pre-commercial quantities of
recombinant proteins and biofuels”. A total of $23.5 million of Australian
Government funding was awarded under this capability at 11 sites around Australia.
The overall project value (including other funding sources) totalled $62 million
[202]. NCRIS Capability 5.5 is being managed by AusBiotech Ltd.
Under the NCRIS funding rules, it is a requirement that facilities be substantially
available for both public and private sector research. The priority and cost of access
to any of the NCRIS Capability 5.5 facilities including MRBPP is determined in
accordance with an Access and Pricing Code, a copy of which is available on the
program website http://www.ncrisbiofuels.org/. Access to the facility for eligible
researchers is at a subsidised rate.
The NCRIS funding for the MRBPP facility included $2.85 million for hard
infrastructure (plant and equipment) and an additional $0.6 million for soft
infrastructure (facility labour). Plant and equipment funding under the NCRIS
program includes funding for equipment for the saccharification and fermentation
facilities and for ethanol product purification and concentration. A Mettler Toledo
RCe1 reaction calorimeter with on-line infra-red detection was funded to enable the
development of comprehensive chemical reaction kinetic and thermodynamic
information.
Soft infrastructure funding included salaries for 2 facility employees through to July
2011. The inclusion of the soft infrastructure is a valuable component of the NCRIS
program in ensuring that core skills are developed and maintained in operation of
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the infrastructure and in ensuring that the access cost is minimised for users of the
facility.
8.4 Design and construction of the MRBPP
The MRBPP is located at the Mackay Sugar Limited (MSL) Racecourse Mill to the
north-west of the factory boiler station. The facility is built on land leased from MSL
to QUT. Co-location of the facility at the site of a raw sugar factory offers a number
of advantages, with the most significant advantage being the development of the
facility to industrial standards.
Co-location also allowed the facility ready access to large amounts of bagasse and
to utilise essential services from the Racecourse Mill site, reducing the cost of
construction. Services provided by the site include electrical supply, potable and
raw water supply and waste water treatment. The initiative shown by MSL in
supporting the establishment of a long term research facility on-site and in
providing services and personnel support during the design and construction phase
has been invaluable. This support has also ensured that the development of the
facility was undertaken according to industrial standards, including rigorous
consideration of environmental and health and safety requirements.
A design contract was awarded to Champion Engineers of Mackay in February 2008
to design the ‘site infrastructure’, including the provision of site services, factory
building, laboratory and office facilities, bagasse feeding arrangements, hazardous
chemical and waste management facilities for the site. Conceptual and process
design, including the mass and energy balances and the specification and selection
of plant and equipment, was undertaken by the author of this thesis. Electrical and
control system design was undertaken by Logicamms Pty Ptd.
Separate tenders were issued for the construction of the site infrastructure and the
installation of facility plant and equipment. The tender for the construction of the
site infrastructure was issued in October 2008 and the tender awarded to FK
Gardner and Sons in December 2008. Construction of the MRBPP factory building
commenced in January 2009, and the majority of the site infrastructure including
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factory building, hazardous chemicals storage, waste capture and storage and truck
loading facilities were completed by July 2009.
The construction of the office, laboratory and amenity areas, which had been
delayed pending the finalisation of costs from the main building contract, was
commenced in July 2009. The office, laboratory and amenity buildings were
supplied as modular buildings from ATCO Structures and Logistics Pty Ltd and
transported to site for installation by FK Gardener & Sons. Practical completion was
achieved on 11th December 2009.
The mechanical installation of plant and equipment commenced in May 2010 and
was undertaken by J&T Mechanical Installation Pty Ltd. Electrical installation of
plant and equipment commenced in September 2010 and was undertaken by MIE
Pty Ltd. Installation of the plant and equipment was completed in November 2010.
Commissioning of the facility was undertaken throughout November and December
2010 and the facility became fully operational in December 2010.
A photographic record of the construction of the MRBPP facility is contained in
Appendix B.
8.5 Site services
Electrical supply for the facility is fed from a switch room located within Racecourse
Mill which feeds a distribution board located within the MRBPP electrical switch
room. Potable water, raw water and fire water are also provided through a
common services trench from the Racecourse Mill to the MRBPP site. This trench
also returns waste water from the MRBPP site to connect to the mill waste water
treatment system.
Steam for the facility is provided by an on-site LPG steam generator. The steam
generator is a TSG Thermic HPTS30 package water tube boiler capable of providing
470 kg/h steam at a pressure of 27 bar. Compressed air (Champion CSF11 11kW
rotary screw compressor with a capacity of 31 L/s at 7.8 bar) and chilled water are
also provided from on-site units located within the services room of the MRBPP. A
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control room inside the MRBPP contains the PLC and operator interface stations.
Other services for the facility are either produced on-site or supplied under a supply
of services agreement with Mackay Sugar Ltd.
The facility has designated storage areas for both Class 3 and Class 8 hazardous
goods. The site contains a first flush waste water collection system and a dedicated
truck unloading area with spill containment. Waste water is able to collected and
stored in on-site storage tanks for collection and off-site disposal if required. Solid
wastes are also collected for off-site disposal.
8.6 Plant and equipment
Plant and equipment for the MRBPP facility has been selected to simulate a range
of processes typical of biochemical biorefineries and in particular to demonstrate
the processes required for soda based pretreatments and lignin recovery processes.
A typical biorefinery process is shown in Figure 8.1, in which the major products are
ethanol and lignin.
Figure 8.1 Typical biorefinery process diagram
One of the major considerations in the conceptual design and selection of plant and
equipment for the facility was the need to provide sufficient flexibility to
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demonstrate several of the pretreatment processes described in Chapter 3 of this
thesis. While sugarcane bagasse was the feedstock of most interest, the facility had
to also be capable of processing a variety of other woody and fibrous feedstocks.
Providing the flexibility to simulate a range of pretreatment processes, feedstocks
and product options maximises the value of the facility both to the Australian
research community and to potential industry partners.
The requirement for flexible processing options and multiple product options
presented challenges in designing a fully integrated process. In particular, the
requirement to be able to undertake a variety of pretreatment processing options
required a novel approach to the design of the pretreatment reactor, as it was
clearly identified that no reactors were currently available on the market with the
capabilities required of the facility.
The techno-economic model described in Chapter 6 of this thesis was used to
provide detailed mass and energy balances of biorefinery processes (in particular
for caustic soda and mild acid processes). This provided data on the flowrates of
process streams and allowed selection of equipment size including pumping energy
requirements. Energy balance data were used to calculate the heat and power
requirements for processing heating, cooling and evaporation.
Results from the uncertainty assessment in the systems analysis and the analysis of
soda-based biorefinery processes clearly identified that the major focus of pilot
scale work needed to be in the areas of pretreatment, enzymatic hydrolysis and
fermentation. The high energy costs identified in the soda-based biorefinery
assessment highlighted the requirement for high solids concentration processing of
biomass and the need for minimal energy input in mechanical biomass size
reduction prior to pretreatment.
The biomass storage, preparation and weighing systems were constructed by Paxon
Packaging Pty Ltd from Melbourne. The integrated feeding system includes a feed
hopper, clump breaker to loosen large clumps of bagasse, vibrating table and sieve
tray for separating pith and ash if required, conveyor and linear weighing machine.
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The main pretreatment reactor for the facility was constructed by Andritz Inc in
Glens Falls, NY. The batch pretreatment reactor is constructed mostly from
corrosion resistant Hastelloy C-2000 enabling simulation of many of the leading
pretreatment technologies with up to 25 kg of fibre per batch. The pretreatment
reactor consists of a horizontal pre-hydrolysis reactor with an integrated hydraulic
ram, vertical reactor for steam explosion, blow tank for collecting solid material
expelled from the reactor and a hydrolysate collection vessel. Chemicals and wash
water for the reactor are fed from two purpose built tanks constructed by TSG
Thermic.
The majority of the fermentation equipment and bioseparations equipment was
purchased from the Tridan Pty Ltd – Albright & Wilson Australia CRC fermentation
facility located at the Albright & Wilson Australia manufacturing plant in Yarraville,
Melbourne. Key equipment purchased from this facility included:
- Stirred fermenters – 10 L, 100 L, 1000 L, 10 000 L;
- Airlift fermenters – 10 L, 100 L, 1000 L;
- Westfalia SB-7 disc stack centrifuge;
- Rotary drum vacuum filter;
- NIRO production minor spray drier;
- Fluidised bed drier;
- Steriliser; and
- Assorted feed tanks and pumps.
The continuous packed bed distillation column was also purchased second hand and
was a Davy McKee design.
A Mettler Toledo RCe1 reaction calorimeter with an integrated infra-red probe was
purchased for use in process development from Mettler Toledo Australia. While an
105
asset of the MRBPP facility, this item is permanently housed at the QUT Gardens
Point Campus in Brisbane.
The control system is a Schneider Electric Modicon TSX Micro PLC processor.
Supervisory control and data acquisition is undertaken using Citect software.
8.7 Lignin product recovery
One of the key co-products from the biorefinery is lignin. The economic assessment
of the soda-based biorefinery process highlighted the necessity of producing a
valuable product from the lignin component of the fibre in developing an
economically feasible process. As a result, the extraction, recovery and purification
of lignin became a key focus of the pilot plant design.
The pilot plant includes equipment for both the delignification of biomass
(pretreatment) and the subsequent recovery of lignin from chemical solvents. The
purified lignin can be manufactured and dried in significant quantities to enable
product development and testing and this work aims to reduce the uncertainty in
the future marketability and market value of soda-lignin.
8.8 Future developments
Commissioning of the MRBPP was completed in December 2010. Preliminary trials
of pretreatment, hydrolysis and fermentation have laid the foundation for further
validation of the techno-economic assessments undertaken in Chapter 6 and
Chapter 7 of this thesis. While the conceptual design of the pilot plant was a key
outcome of this research program, the conduct of pilot trials was not a component
of the work of this thesis but will be undertaken in on-going research with the
project partners.
The MRBPP is valuable research and development infrastructure for both the
Australian research community, future biomass-based industries and in particular
the Australian sugar industry. This facility provides unique subsidised infrastructure
106
for biomass utilisation, particularly focussed upon the enzymatic conversion of
cellulose into ethanol in an integrated biorefinery.
Additionally, the ability to produce novel co-products such as lignin allows
opportunities for large scale product development and testing.
The infrastructure will provide even greater value over time as it evolves to meet
the product diversification challenges of the next decade. This evolution will be
essential if the facility is to remain relevant to future research challenges. It is
expected that the MRBPP will have sufficient flexibility to undertake pilot trials on
fermentation technologies based on sugar, molasses and bioethanol process
streams to manufacture organic acids and other products.
It is envisaged that the MRBPP will in the future need to incorporate additional
technologies, including thermochemical processing technologies such as gasification
and pyrolysis including downstream catalytic processing. This will assist in ensuring
that the MRBPP remains at the forefront of bioenergy research and one of the
leading tools for facilitating the introduction of new products into Australian
industries.
107
Discussion
109
Chapter 9
Discussion
9.1 Introduction
This chapter provides an analysis of the work undertaken in the research
program and highlights the key findings of the research, the importance of this
research and recommendations for future work.
9.2 Achievement of research objectives and key findings
This section reviews the achievement of the research objectives outlined for this
research project in Chapter 1.
Objective 1 - Identify the key technical, economic and systemic factors
impacting upon investment in commercial scale facilities for the production of
ethanol from sugarcane bagasse in Australia
Chapter 2 provides an introductory analysis of the role of crude oil in transport
fuel use, the growing impact of biofuel use and an overview of the sugarcane
industry in Australia. Chapter 3 reviews the scientific research that has occurred
globally on the pretreatment of sugarcane bagasse. Chapter 4 provides an
analysis of the systemic factors influencing investment in commercial cellulosic
ethanol facilities and, through the use of Monte Carlo analysis, provides a
probabilistic analysis of the relative impact of assumption uncertainty on
investment risk for investment in cellulosic ethanol production. Chapter 6
provides a comprehensive assessment of a specific potential cellulosic ethanol
project in Australia and identifies through one and two component sensitivity
analyses the key impacts on project viability.
110
In general, these analyses conclude ethanol price, government production
incentives, feedstock price, capital cost, co-product revenue, cellulase cost and
energy cost have the major impact on project investment and a number of
strategies are proposed in Chapters 1 – 4 and Chapter 6 for reducing investment
risk and increasing the viability of cellulosic ethanol production in Australia.
Objective 2 - Explore leading technologies for the biochemical production
of ethanol from sugarcane bagasse to determine the conceptual
feasibility of the technology
Chapter 3 reviews the leading pretreatment technologies and the scientific work
that has been undertaken globally on sugarcane bagasse pretreatment. The
choice of pretreatment technology is the critical determinant of the style of
facility and determines many of the other technological requirements of the
facility. Chapter 6 analyses the technical and economic feasibility of a soda-based
biorefinery in Australia, producing ethanol and lignin in an integrated facility.
Chapter 7 analyses the economic feasibility of a leading but early stage
technology for reducing the cost of cellulase enzymes through the expression of
cellulase in sugarcane.
These chapters highlight the potential feasibility of this technology and the
conditions under which the technology becomes commercially viable, providing
recommendations relating to the choice of technology for managing project risk.
Objective 3 - Conceptualise and develop a framework for assessing the
interrelationships between energy use, feedstock availability and
potential cellulosic ethanol production of integrated sugar and bagasse-
based ethanol production facilities
In the systems analysis undertaken in Chapter 4, the interrelationships between
energy use and feedstock availability are clearly identified as a major factor in
understanding the feasibility of the cellulosic ethanol system. Chapter 5 identifies
the potential quantum of ethanol production from sugarcane in Australia and
explores the relationship between energy consumption, energy production
111
(cogeneration and ethanol production) and feedstock availability. Chapter 6
analyses through comprehensive technical and economic modelling the
relationship between energy use and project viability.
These chapters identify that ethanol from sugarcane has the potential to
contribute significantly to the transport fuel mix in Australia and that both
cogenerated electricity and ethanol production are complementary products
from integrated facilities. Technology choices that minimise overall energy use
are critical in maximising revenue and minimising process costs.
Objective 4 - Model the use of the framework through its application to
the design and construction of a pilot scale facility for demonstration of
technology for the production of ethanol from bagasse
Chapter 8 relates the details of the design and construction of the Mackay
Renewable Biocommodities Pilot Plant (MRBPP) through to the commencement
of facility commissioning. The process design of this facility, undertaken by the
author and supported by the work of this research program is a key outcome of
this research program and provides an on-going contribution to the further
research, development and techno-economic assessment of this important
technology in Australia.
Objective 5 - Communicate key outcomes to the Australian sugar industry
to develop a deeper understanding within the industry of the potential
opportunities and economic feasibility of the technology
Information reported in Chapter 3 and Chapter 8 of this thesis have been
presented as peer-reviewed conference papers to the Australian Society of Sugar
Cane Technologists (ASSCT) which is the leading research forum for the
Australian sugar industry. Two further papers will be presented to the same
forum in 2011. Chapter 6 has been presented to Australian sugar company
Mackay Sugar Ltd as a confidential research report for consideration at a senior
level in their organisation.
112
The construction of the MRBPP has been widely anticipated across the sugar
industry and the author has spoken to many conferences and groups within the
industry about the facility. This engagement has provoked considerable interest
and engagement in cellulosic ethanol technologies across the industry and
further reporting will occur as the MRBPP facility commences operations and
generates research outcomes.
9.3 Importance of research
This research program has provided a multi-dimensional analysis of the feasibility
of cellulosic ethanol from sugarcane in Australia, assessing the key factors
affecting industry viability and the likely impacts of these on investment.
Through engagement with project partners and the sugar industry research
community, the research outcomes have provided a deeper understanding of
cellulosic ethanol production at both a conceptual and project specific level.
Despite sugarcane being perhaps the best biomass feedstock for early stage
cellulosic ethanol production, such an integrated and multi-dimensional analysis
has not previously been undertaken in Australia, or to the author’s knowledge
anywhere around the world for cellulosic ethanol production from sugarcane.
9.4 Recommendations for future work
The following recommendations are made for future work in understanding and
promoting the establishment of a viable cellulosic ethanol industry in Australia.
1. Explore the opportunities for energy reduction in integrated sugarcane –
cellulosic ethanol facilities through the modelling of energy efficiency
measures and pinch analysis;
2. Explore the opportunities in sugarcane production regions for
supplementing the availability of fibre for cogeneration or ethanol
production with other new or existing fibre sources;
113
3. Explore the economic case for regional clustering of sugarcane processing
facilities for ethanol production;
4. Explore the business case for modified sugar milling operations for
integrated ethanol facilities from sugarcane juice and bagasse;
5. Explore the impact of possible government policy incentive measures on
promoting investment in cellulosic ethanol production from sugarcane,
and particularly measures relating to a carbon price or emissions trading
scheme; and
6. Explore the impact of higher fibre sugarcane on fibre availability for
cellulosic ethanol production and in particular, explore models for the
industry transition from processing current sugarcane varieties to
processing higher fibre varieties.
115
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Appendices
145
APPENDIX A
Supplementary data for Chapter 6
The supplementary data for Chapter 6 is not available in this version of the
thesis.
147
APPENDIX B
The Mackay Renewable Biocommodities Pilot Plant – photographic record of construction and equipment installation
This appendix provides a photographic record of the construction and equipment
installation for the Mackay Renewable Biocommodities Pilot Plant (MRBPP) from
the commencement of facility construction to the completion of equipment,
electrical and instrumentation installation.
149
Site infrastructure
The infrastructure for the MRBPP site consists of a three story factory building,
office and laboratory. To the west of the factory building is an outdoor pad
consisting of truck unloading area, Class 3 and Class 8 chemical storage facility, LPG
storage tank and waste water storage tanks.
Appendix Figure B.1 contains a photographic record of the construction of the site
infrastructure.
A Construction signage
B Preparation and levelling of site
C Laying of building foundations
D Concrete base of factory building
E Concrete base of factory building looking west toward Racecourse Mill
F Installation of block work for fermentation room and services rooms
G Framing for the concrete slab and factory building
H Pouring of the concrete slab
I Installation of the ATCO modular laboratory and office buildings
J Factory building looking toward the Racecourse Mill bagasse stockpile
K Factory building looking north-west
L Site photo looking east
M Internal photo of factory building (west)
N Internal photo of factory building (north)
O Top floor of factory building
P Office area during construction
Q Laboratory area during construction
R Completed exterior of factory building
S Site photo looking west
T Site photo looking east toward Racecourse Mill
150
G H
F E
C D
B A
151
K L
N M
J I
152
Appendix Figure B.1 Photographic record of the construction of site infrastructure
T S
Q R
P O
153
Plant and equipment
The first stage of plant and equipment in the facility includes a biomass feeding and
weighing system supplied by Paxon Packaging Pty Ltd, a two-stage pretreatment
reactor supplied by Andritz Inc and chemical and wash water tanks supplied by
Thermic TSG.
Appendix Figure B.2 contains a photographic record of the plant and equipment
installed in the biomass feeding and pretreatment stages of the MRBPP facility.
A Biomass feeding system, conveyor and weighing machine
B Schematic of the Andritz two-stage pretreatment reactor
C Chemical and wash water feed tank for pretreatment reactor
D Pre-hydrolysis reactor
E Front view of the pre-hydrolysis reactor
F Vertical pressure reactor (steam explosion reactor)
G Reactor blow tank and hydrolysate tank
154
Appendix Figure B.2 Photographic record of the biomass feeding and pretreatment stage equipment
A
B C
E D
F G
155
The saccharification, fermentation, distillation and co-product recovery stages
contain a variety of equipment which can be configured in a flexible manner.
Appendix Figure B.3 contains a photographic record of the fermentation,
bioseparations and other equipment installed in the MRBPP facility.
A 100 L stirred fermenter
B 1000 L stirred fermenter
C 10 000 L stirred fermenter
D 10 L airlift fermenter
E 100 L airlift fermenter
F 1000 L airlift fermenter
G Fermenter feed tank
H Membrane filter
I Westfalia centrifuge
J Steriliser
K Rotary drum vacuum filter
L Spray drier
M Hydrolysis reactor
N Mettler Toledo RCe1 reaction calorimeter
156
E F
D C
B A
157
L K
J I
H G
158
Appendix Figure B.3 Photographic record of the plant and equipment installed in the MRBPP facility
M
N
159
Opening of the MRBPP facility
The official opening of the MRBPP facility was held on the 9th July 2010. The facility
was opened by The Hon Anna Bligh MP, Premier of Queensland and Minister for the
Arts and Senator Kim Carr MP, Minister for Innovation, Industry, Science and
Research and supported by The Hon Tim Mulherin MP, Minister for Primary
Industries, Fisheries and Rural and Regional Queensland and Member for Mackay.
Appendix Figure B.4 contains a photographic record of the MRBPP opening.
A Opening ceremony
B Mr Andrew Cappello, Chairman, Mackay Sugar Ltd
C The Hon Anna Bligh MP
D Official party with the opening plaque (l – r) – Professor Peter Coaldrake, Senator Kim Carr MP, The Hon Anna Bligh MP, Distinguished Professor James Dale, Mr Andrew Cappello
E Senator Kim Carr MP, The Hon Anna Bligh MP and the author during the official tour of the MRBPP facility
F The Hon Anna Bligh MP, Distinguished Professor James Dale, Senator Kim Carr MP and the author in front of the Andritz pretreatment reactor during the official tour of the facility
G Dr William Doherty discusses biorefinery value added products with guests at the opening
H The MRBPP opening official plaque
160
Appendix Figure B.4 Photographic record of the opening of the MRBPP facility
B A
C D
F E
G H
161
Image credits Photographs used in this appendix were provided by the author, Erika Fish, Jan
Zhang, Bernard Milford, John Bankie, Barry George, Heng-Ho Wong and Peter
Albertson.