torrefaction and pelletization of different forms of
TRANSCRIPT
Torrefaction and Pelletization of Different Forms of Biomass
of Ontario
by
Bimal Acharya
A Thesis
Presented to
The University of Guelph
In partial fulfillment of requirements
for the degree of
Master of Applied Science
in
Engineering
© Bimal Acharya, March, 2013
ii
ABSTRACT
Torrefaction and Pelletization of Different Forms of Biomass of Ontario
Bimal Acharya Advisor
University of Guelph, 2013 Dr. Animesh Dutta
The purpose of this study is to investigate the torrefaction and pelletization
behavior, hydrophobicity, storage behavior, ash analysis on three different biomasses:
one (willow pellets) from wood products, one (oat pellets) from agricultural products and
one (poultry litter) from the non-lignocellulosic biomass products during the processes.
Four different torrefaction temperatures from 200°C-300°C, at 10-60 minute residence
times, 0%-2.4% oxygen concentration, were considered. Of these, 285°C for willow
pellets, 270°C for oat pellets and 275°C for poultry litter were found to be optimum for
hydrophobicity. Studies of XRD and SEM of biomass ash at 800°C, 900°C and 1000°C
were also carried out. The aforementioned results indicate that torrefaction is a feasible
alternative to improve energy properties of ordinary biomass and prevent moisture re-
absorption during storage.
iii
ACKNOWLEDGEMENTS
I would firstly like to acknowledge my graduate advisor Dr. Animesh Dutta P.Eng., for
his thoughtful insight and support throughout my graduate career. His mentorship
extended beyond the walls of the University and his support allowed me to obtain several
prestigious awards and compete in Biological Engineering. I would also like to extend
my appreciation towards Dr. Shohel Mohmud who provided insight throughout the
duration of my research.
These acknowledgements would not be complete without naming the following
individuals for their supports: Dr. Mathias Leon: thanks for English correction and
guidance in the lab setup; John Whiteside, Joanne Ryks(School of Engineering): thanks
for providing lab support; and to my colleagues: Idris Sule, Dr Poritosh Roy, Maxime
Moisan, and Mohammad Tushar. I am glad our journeys have crossed paths and I hope
this is just the beginning of a lasting friendship.
I would lastly like to make personal acknowledgements to my family and friends. To my
mother, father, brother and sister who throughout my life always encouraged higher
education and a quest for knowledge. Special gratitude to my employer Nepal Telecom
for granting me study leave to pursue graduate study from a Canadian University.
Finally, to my wife and best friend Sushma Acharya, son Bibhu and daughter Suyasha,
who has always wholeheartedly supported me throughout my scholarly achievements.
iv
TABLE OF CONTENTS
ABSTRACT ....................................................................................................................... ii
ACKNOWLEDGEMENTS ............................................................................................... iii
TABLE OF CONTENTS .................................................................................................. iv
LIST OF TABLES ............................................................................................................. ix
LIST OF FIGURES .............................................................................................................x
NOMECLATURE .............................................................................................................xv
Chapter I: Introduction ........................................................................................................1
1.1 Introduction ...................................................................................................... 1
1.2 Objectives ......................................................................................................... 4
1.3 Organization of the Thesis ................................................................................ 5
Chapter II: Literature Review ..............................................................................................6
2.1 Overview .......................................................................................................... 6
2.1.1 Fuel Characteristics of Biomass.................................................................... 7
2.1.2 Biomass Components.................................................................................... 8
2.2 Concept of Torrefaction .................................................................................. 11
2.3 Torrefaction Process Methods ........................................................................ 18
2.4 Classification of Reactors ............................................................................... 20
2.5 Commercial Application of Torrefaction in Canada ...................................... 26
2.6 Available Technologies for Torrefaction ....................................................... 29
2.7 Pelletization .................................................................................................... 31
2.8 Gasification ..................................................................................................... 36
v
2.9 Emission ......................................................................................................... 38
2.10 Storage Behavior ............................................................................................ 38
2.11 Economic Potential ......................................................................................... 40
2.12 Scanning Electron Microscopy (SEM) ........................................................... 43
2.13 X-ray Diffraction (XRD) ................................................................................ 45
2.14 Summary from Literature ............................................................................... 46
Chapter III: Methodology ..................................................................................................49
3.0 Problem Statement .......................................................................................... 49
3.1 Research Scope and Objectives ...................................................................... 50
3.2 Methodology ................................................................................................... 52
Chapter IV: Experiment Setup ...........................................................................................54
4.1 Biomass Characterization ............................................................................... 54
4.1.1 Proximate Analysis ......................................................................................... 54
4.1.2 Ultimate Analysis ........................................................................................... 54
4.1.3 Heating Value ................................................................................................. 54
4.2 Torrefaction .................................................................................................... 55
4.3 Hydrophobicity ............................................................................................... 58
4.4 Pelletization .................................................................................................... 58
4.5 Storage Behaviour .......................................................................................... 60
4.6 Scanning Electron Microscopy (SEM) ........................................................... 60
4.7 X-ray Diffraction (XRD) ................................................................................ 62
Chapter V: Results and Analysis .......................................................................................63
5.1 Poultry Litter Biomass .................................................................................... 63
vi
5.1.1 Biomass Characterization ........................................................................... 63
5.1.2 Torrefaction................................................................................................. 65
5.1.3 Hydrophobicity ........................................................................................... 68
5.1.4 Storage Behavior ......................................................................................... 69
5.1.5 Optimization by Box Behnken Model ........................................................ 70
5.1.6 Scanning Electron Microscopy (SEM) ....................................................... 74
5.1.8 Summary ..................................................................................................... 77
5.2 Willow Pellets................................................................................................. 78
5.2.1 Biomass Characterization ........................................................................... 78
5.2.2 Torrefaction................................................................................................. 81
5.2.4 Hydrophobicity ........................................................................................... 84
5.2.5 Storage Behavior ......................................................................................... 86
5.2.6 Pelletization................................................................................................. 88
5.2.7 Scanning Electron Microscope (SEM) ....................................................... 91
5.2.9 Summary ..................................................................................................... 95
5.3 Oat Pellets ....................................................................................................... 96
5.3.1 Biomass Characterization ........................................................................... 97
5.3.2 Torrefaction................................................................................................. 99
5.3.4 Hydrophobicity ......................................................................................... 102
5.3.5 Storage Behavior ....................................................................................... 104
vii
5.3.6 Pelletization............................................................................................... 105
5.3.7 Scanning Electron Microscope (SEM) ..................................................... 107
5.3.9 Summary ................................................................................................... 111
5.4 Comparative Analysis................................................................................... 112
5.4.1 Biomass Characterization ......................................................................... 112
5.4.2 Torrefaction............................................................................................... 116
5.4.3 Hydrophobicity ......................................................................................... 119
5.4.4 Storage Behavior and Moisture Uptake .................................................... 120
5.4.5 Ash Analysis ............................................................................................. 121
5.4.6 Summary ................................................................................................... 123
5.5 Errors and Repeatability Test ....................................................................... 124
Chapter VI: Conclusions and Recommendations ............................................................125
6.1 Conclusions .................................................................................................. 125
6.2 Recommendations ........................................................................................ 127
Chapter VII: References ..................................................................................................129
Chapter VIII: Appendix ...................................................................................................141
Appendix A: Photographs of Willow Pellets .............................................................. 141
Appendix B: Photographs of Oats Pellets ................................................................... 142
Appendix C: Methods and Equipment used in Characterizing Biomass .................... 143
Appendix D: Photograph of Experimental Setup for Torrefaction ............................. 144
Appendix E: Gas Analyzer ......................................................................................... 145
viii
Appendix F: Ultimate Analysis, Ash Fusion Temp and Ash Elemental Analysis ..... 146
Appendix G: Error and Repeatibility Tests ................................................................ 148
ix
LIST OF TABLES
Table 5-2 Ultimate Analysis and Heating Value of Raw Biomass 113
Table Page No.
Table 2-1 Summary of Torrefied pellets Properties versus Coal 18
Table 2-2 Comparison of Potential Torrefaction Reactor Technologies 26
Table 2-3 Overview of Torrefaction Projects 30
Table 2-4 Summary of Specifications for Four Different Pelleting
Equipment
33
Table 2-5 Comparison of BO2 Pellet Properties 36
Table 5-1 Proximate Analysis of Raw Biomass 112
x
LIST OF FIGURES
Figures Page No.
Figure1.1 Energy Density vs. Time and Temperature 3
Figure 2-1 Structure and Pretreatment effect on Biomass 9
Figure 2-2 Carbohydrate in the presence of Carbon Monoxide 10
Figure 2-3 Decomposition regimes of lignocellulosic material during
thermal treatment
13
Figure 2-4 Basic principle of torrefaction Process 20
Figure 2-5 Pictures of raw and pelletized materials 34
Figure 2-6 Schematic Process Flow of the BO2-Technology 35
Figure 2-7 Delivery costs of pelletized biomass. (Numbers indicate
nominal capacity of system dry kilotons of raw biomass feedstock per
year)
40
Figure 2-8 SEM of Wood Ash from Gasifier 45
Figure 3-1 Schematic Block Diagram of Research Procedures 51
Figure 3-2 Flow chart of the methodology 53
Figure 4-1 Experimental Setup for Torrefaction and Weight loss 57
Figure 4-2 Experimental Setup for Pelletization 59
Figure 4-3 SEM Experimental Setup 62
Figure 5-1 Volatile Matter vs. Residence Time for Poultry Litter 64
Figure 5-2 Fixed Carbon vs. Residence Time for Poultry Litter 64
Figure 5-3 Ash Contents vs. Residence Time for Poultry Litter 65
xi
Figure 5-4 % of Mass Yield and Energy Yield vs. Temperature Poultry
Litter (0% Oxygen with 45 minutes residence time)
66
Figure 5-5 % of Mass Yield and Energy Yield vs. Temperature for
Poultry Litter (2.4% Oxygen with 45 minutes residence time)
67
Figure 5-6 Heating Value vs. Residence Time for Poultry Litter 67
Figure 5-7 Heating Value vs. Residence Time for Poultry Litter 68
Figure 5-8 Hydrophobic behavior of Poultry Litter 69
Figure 5-9 % of Moisture uptake vs. temperature of torrefied biomass 70
Figure 5-10 Cube of Temperature, Moisture and Residence Time Vs.
Mass Yield
71
Figure 5-11 Surface Plots of Temperature, Moisture and Residence
Time Vs. Mass Yield
72
Figure 5-12 Cube of Temperature, Moisture and Residence Time Vs.
Energy Yield
73
Figure 5-13 Surface Plot of Temperature, Moisture and Residence
Time Vs. Energy Yield
73
Figure 5-14(a) SEM for poultry litter ash at 800C 74
Figure 5-14(b) SEM for poultry litter ash at 900C 75
Figure 5-14(c) SEM for poultry litter ash at 1000C 75
Figure 5-15 XRD pattern for poultry litter ash at different temperature 77
Figure 5-16 Volatile Matter vs. Residence Time for Willow 79
Figure 5-17 Fixed Carbon vs. Residence Time for Willow 80
Figure 5-18 Ash Contents vs. Residence Time for Willow 80
xii
Figure 5-19 % of Mass Yield and Energy Yield vs. Temperature for
Willow(Different Oxygen % and 45 minutes residence time)
82
Figure 5-20 Energy Density variations with Temperature and residence
time
82
Figure 5-21 Heating Value vs. Residence Time for Willow at 0%
Oxygen
83
Figure 5-22 Heating Value vs. Residence Time for Willow with 2.4%
Oxygen
84
Figure 5-23 % of Moisture absorption vs. temperature of torrefied
biomass
86
Figure 5-24 % of Moisture uptake vs. temperature of Willow Pellets 87
Figure 5-25 Pressure for making Pelletization and Force for Breaking
Pellets
90
Figure 5-26 SEM for Willow at 800°C, 900°C and 1000°C Ash 93
Figure 5-27 XRD pattern for Willow ash at different temperature 95
Figure 5-28 Volatile Matters vs. Residence Time for Oats 97
Figure 5-29 Fixed Carbons vs. Residence Time for Oats 98
Figure 5-30 Ash Contents vs. Residence Time for Oats 98
Figure 5-31 % of Mass Yield and Energy Yield vs. Temperature for
Oats (Different Oxygen % and 45 minutes residence time)
100
Figure 5-32 Energy Density variations with Temperature and residence
time
100
Figure 5-33 Heating Value vs. Residence Time for Oats at 0% Oxygen 101
xiii
Figure 5-34 Heating Value vs. Residence Time for Oats with 2.4%
Oxygen
102
Figure 5-35 % of Moisture absorption vs. temperature of torrefied
biomass
103
Figure 5-36 % of Moisture uptake vs. temperature of Oats Pellets 105
Figure 5-37 Pressure for making Pelletization and Force for Breaking
Pellets
106
Figure 5-38 SEM for Oats at 800°C, 900°C and 1000°C Ash 109
Figure 5-39 XRD pattern for Oats ash at different temperature 110
Figure 5-40 Comparative Study of Ultimate Analysis of different
Biomass
114
Figure 5-41 Comparative Study of Ash Fusion Temperature of different
Biomass
115
Figure 5-42 Comparative Study of Elemental Analysis of different
Biomass
116
Figure 5-43 Comparative Study of Mass Yield of Poultry Litter,
Willow and Oat Pellets at different temp with 45 minutes residence
time
117
Figure 5-44 Comparative Study of Energy Yield of Poultry Litter,
Willow and Oat Pellets at different temp with 45 minutes residence
time
118
Figure 5-45 Comparative Study of Heating Values of different Biomass
with temp
119
xiv
Figure 5-46 Comparative Study of Hydrophobicity of Poultry Litter,
Willow and Oat at different temp with 45 minutes residence time
120
Figure 5-47 Comparative Study of Storage Behavior of Poultry Litter,
Willow and Oat Pellets at different temp with 45 minutes residence
time
121
Figure 5-48 Comparative Study of Elemental Analysis of Poultry
Litter, Willow and Oat Pellets at different temp with 45 minutes
residence time
122
Figure 5-49 Comparative Study of Ash Fusion Temperature of Poultry
Litter, Willow and Oat Pellets at different temp with 45 minutes
residence time
123
xv
NOMECLATURE
Mass (daf) of torrefied biomass
Mass (daf) of raw biomass
Higher Heating Value of torrefied biomass
Higher Heating Value of raw biomass
EY Energy Yield
ME Mass Yield
EDR Energy Density Ratio
MC Moisture Contents in %
TT Torrefaction Temperature in ᴼC
RT Residence Time in min
1
Chapter I: Introduction
1.1 Introduction
Secure supply of sustainable and environmentally friendly energy for future
generations is a global concern these days. “Climate change”, "Global Warming" and
“Ice melting from Artic” are some of the familiar terms we hear on a daily basis. World
events such as the delay in building an oil pipeline between Canada and the United States
of America and the continuing uncertainty in the Middle East remind us of the fragile
supply of energy. Our present world is still so much dependent on fossil fuels,
while looking for other energy options. Processed-biomass has been identified as one of
many options that can significantly contribute to the present global energy requirements.
During photosynthesis, plants convert light (solar radiation) into chemical energy, which
is stored in the form of biomass. Although biomass comes in many forms, wood and
herbaceous biomasses are the main forms of biomass for energy production. Biomass,
traditionally used by mankind in the form of firewood, was the only source of energy that
fulfilled all the energy needs of early man. Of late, global warming concerns and politics
over fossil fuels have again fuelled global interest on our traditional energy source,
“biomass”. New technologies like torrefaction and densification can help in efficient
utilization of biomass, and in reducing the emission of greenhouse gases from burning
fossil fuels. Still, almost 1.5 billion people from the developing world rely on
unprocessed biomass to meet their present energy needs. Processed or treated biomass, in
solid or liquid form, possesses combustion characteristics similar to fossil fuels, and
hence can be used for electricity generation, steam generation or thermal energy
generation by direct combustion, gasification or co-firing. Gasification of biomass
2
generates high-grade combustible gases such as CO, H2 and methane. Anaerobic
digestion produces biogas from biomass.
Canada has access to abundant forest and agricultural land that serve as great
sources for biomass feedstock to generate sustainable energy production. Biomass can be
converted into heat and electricity by means of thermo-chemical (combustion,
gasification, pyrolysis, and liquefaction) and bio-chemical (anaerobic digestion)
processes (Linghong et al., 2010). The most common forms of conversions are the
thermal processes. Helwig et al.(2002) evaluated the biomass inventory in Canada and
reported that approximately one million oven dry tons per year (odt/y) of cereal straw and
three million odt/y of corn stover are available in eastern Canada and in addition, the
gross energy potentials of these residues is approximately 92 million gigajoules per year.
In Canada, approximately 4.7% of national primary energy for 2006 was derived from
the conversion of renewable biomass and wastes. This fraction is projected to increase to
6–9% over the next 20 years (Douglas, 2009). This projection is low compared to other
industrial nations but it is encouraging.
Despite the tremendous popularity gained by biomass energy in recent
years, the fraction of its utilization in producing energy remains insignificant in the
overall source of energy production in Canada (Douglas, 2009). This can be due to
several factors, including the limitation associated with its properties (Bridgeman et. al.,
2008). The variations in biomass feedstock properties cause several challenges during the
conversion process; these include: low heating value, high moisture content, hygroscopic
nature, excess smoke during combustion, low energy density, low combustion efficiency,
and high ash contents. Torrefaction, a thermal pretreatment process of biomass, has been
3
proved to improve the combustion properties of biomass (Pimchuai et al., 2010;
Bridgeman et. al., 2008; Bergman, 2005, Deng et al, 2009). Torrefaction is the
thermochemical treatment of biomass at 200 to 300°C, under atmospheric conditions, but
in the absence of oxygen. During the process the biomass partly decomposes, giving off
various types of volatiles. The final product is the remaining solid, which is often referred
to as torrefied biomass, or torrefied product when produced from agricultural or forest
biomass product. Typically, 70% of the mass is retained as a solid product, containing
approximately 90% of the initial energy content. The remaining 30% of the mass is
converted into torrefaction gases, but contain only approximately 10% of the energy
content of the original biomass. Hence a considerable energy densification can be
achieved, typically by a factor of 1.3 on mass basis. This study points out one of the
fundamental advantages of the process, which is the high transition of the chemical
energy from the feedstock to the torrefied product, while concurrently the fuel properties
are improved.
Figure1.1 Mass and Energy and Energy Balance of a Typical Torrefaction Process
(Acharya et al., 2012)
Torrefaction
(200-300°C)
Mild
Pyrolysis
Torrefied Gas as
Loss
30% Mass+
10% Energy
Biomass Feed Stock
input
100% Mass+
100% Energy
Torrefied
Biomass
70% Mass+
90% Energy
4
1.2 Objectives
It is well known that biomass can be one of the many sources of renewable
energy, and the torrefaction process improves their combustion properties significantly.
Large reduction in the consumption of fossil fuels and development of a sustainable
energy system will require commercial scale production of renewable fuels like torrefied
biomass. However, no commercial operation of torrefaction exists yet. Furthermore only
limited studies are available on agricultural based biomass (Pimchuai et al.,2010;
Tumuluru et al., 2011) and only a few works assessed the commercial applicability of
torrefaction in power plants and the logistics of its impacts on the entire bioenergy supply
chain (Uslu et al., 2008). Hence, this work will expand the torrefaction studies of
different Ontario based biomass feedstock and complete the following objectives by
conducting different experiments and result analysis:
i) Physio-chemical characterization of biomass samples before and after
torrefaction.
ii) Optimization of torrefied conditions based on hydrophobicity
iii) Investigation of pelletization potential before and after torrefaction
iv) Ash analysis of biomass at different combustion temperature.
To achieve the above objectives, the following actions are undertaken: a)
Proximate, Ultimate and Elemental Analysis, and Ash fusion temperature analysis to
characterize the chemical composition of the agricultural based biomass samples with
determination of their respective calorific values prior to and after torrefaction; b) study
of the hydrophobic behavior of torrefied biomass with respect to treatment conditions
5
(torrefaction temperature and residence time); c) study of the Higher Heating Value of
biomass at different temperature, residence time and Oxygen concentration d) study of
the stress analysis during and after pelletization of torrefied biomass; e) SEM and XRD
analyses of ash formed at different temperatures.
1.3 Organization of the Thesis
The summary of the organization of this thesis is as follows:
Chapter II presents a review of literature on biomass, torrefaction, pelletization, moisture
uptake, ash analysis. It also discusses the available technologies of different torrefiers,
economic and environmental impacts in Canada. At the end of the chapter, it explains in
brief about the scanning electromagnetic microscopy and X-ray diffraction.
Chapter III explains the methodology used to achieve the objectives of the study and
explain in tabular and flow chart form about the flow of experimental procedures.
Chapter IV presents the experimental setup for torrefaction, pelletization, moisture
uptake, hydrophobicity. It also explains the procedures which are taken for proximate,
ultimate, ash analysis. Ash analyses are carried out by SEM and XRD.
Chapter V presents the results and analysis observed during the conduction of different
experiment on torrefaction, pelletization, hydrophobicity, moisture uptake and ash
analysis. Detail comparative study of all the studied results are also presented in this
chapter.
Chapter VI presents conclusions found from this study and recommendation for further
study.
At the end, list of the references and appendixes are appended in the thesis.
6
Chapter II: Literature Review
2.1 Overview
The world economy is slowly but steadily transitioning from non-renewable fossil
fuel energy to renewable and sustainable energy. Energy from biomass can be considered
carbon-neutral because of the carbon cycle. Unlike fossil fuels, biomass is a renewable
source of energy that can be replenished; utilizing biomass for energy production does
not result in net greenhouse gas emission to the atmosphere. A good illustration is wood,
which is obtained from trees. Trees absorb sunlight and CO2 from the atmosphere during
photosynthesis to make cellulose from sugars; consequently, the cellulose, which
contains stored chemical energy, releases this energy as heat when combusted, and the
CO2 liberated as off-gas is equivalent to the amount absorbed during photosynthesis
process. Hence, biomass can be greenhouse gas emission-neutral. Increasing the use of
biomass for energy application thus helps to reduce greenhouse gas (GHG) emission. The
word “biomass” originally meant the total mass of living matter within a specified
environmental area, but more recently, it also describes plants products, vegetation, or
agricultural residues used as an energy source. Tumuluru et al. (2010) also defined
biomass materials as a composite of carbohydrate polymers with a small amount of
inorganic substance and low molecular weight extractable organic elements. Others
defined biomass as a biological or organic material, which can be used as source of
renewable energy after performing certain processes. It can also be classified as carbon-
based material, consisting of organic molecules containing hydrogen, oxygen, nitrogen
and small quantities of atoms containing alkali, alkaline earth and heavy metals (Biomass
Energy Centre, UK). Energy contents of biomass are collected from the sunlight and
7
stored in the form of chemical energy. Stored energy from the biomass can be converted
in to heat energy at any suitable time with certain transformation processes.
Biomass feedstock can be from agricultural crops, trees or crops grown for energy
production, wood residues, wood wastes, agricultural residues, animal and human wastes,
and municipal wastes.
2.1.1 Fuel Characteristics of Biomass
Fuel characteristics of biomass depend on the origin and types of biomass which
are categorized by their physical and chemical properties. Sizes, shapes, specific
capacity, thermal conductivity, moisture content, bulk density, grindability and porosity
characterize the physical properties of biomass. The chemical properties are determined
by proximate and ultimate analyses and thermal decomposition. The ultimate analysis of
biomass delivers the elemental structures of biomass by weight percentage in the form of
carbon (C), hydrogen (H), Oxygen (O), nitrogen (N), sulfur (S), chlorine (Cl), and ash
elements such as Sodium (Na) and Potassium (K) compounds etc. However, the
proximate analysis provides the percentage weight of fixed carbon (FC), moisture
contents (MC), ash contents (AC), and volatile matter (VM) in biomass. The methods of
performing these analyses are dependent on the standards in ASTM, ISO etc. These
chemical compositions change with oxygen concentration during torrefaction,
temperature and residence time for all types of biomass fuels. Cellulose, hemicelluloses,
lignin, lipids, proteins, simple sugars, starches also influence the combustion process of
biomass. The concentration of each class of compound differs depending on species,
8
nature of plant tissue, phase of development, and growing environments (Jenkins et al.,
1998).
2.1.2 Biomass Components
The plant cell wall is the strong, usually flexible but sometimes rigid layer that
gives structural support and protection from external mechanical and physical forces. The
major constituents of the primary cell wall are cellulose, carbohydrates, hemicelluloses
and pectin (Tumuluru at el., 2011). Biomass consists of three main polymeric
constituents: Hemicellulose, cellulose, and lignin and generally they cover respectively
20–40, 40–60, and 10-25 wt% for lignocellulosic biomass (McKendry, 2002; Yang et al.,
2005). Pretreatment of biomass changes its physical and chemical structure which makes
more suitable to use for energy application. Figure 2-1 shows the biomass structure and
pretreatment effect on lignocellulosic components.
Cellulose is a linear polymer of biomass that makes up about 45% of the dry weight of
wood, is composed of D-glucose subunits linked together to form long chains (elemental
fibrils), which are further linked together by hydrogen bonds and Van der Waals forces.
The cellular fiber formed by several micro-fibrils coming together can either be
crystalline or amorphous (Pe´rez et al., 2002). Furthermore, cellulose is a high molecular
weight polymer that makes up the fibers in lignocellulosic materials and its degradation
starts anywhere from 240°–350°C because of high resistance of its crystalline structure to
thermal depolymerization owns to its strength (Mohan et al., 2006; Tumuluru et al.,
2010). The waters held in the amorphous regions of the cellulosic wall rupture the
9
structure when converted into steam as a result of thermal treatment (Tumuluru et al.,
2010).
Figure 2-1: Structure and Pretreatment effect on Biomass (Source: Tumuluru at el.,
2011)
Hemicellulose is a complex carbohydrate polymer with a lower molecular weight
than cellulose and makes up 25–30% of total dry weight of wood. It consists of D-xylose,
D-mannose, D-galactose, D-glucose, L-arabinose, 4-O-methyl-glucuronic, D-
galacturonic and D-glucuronic acids (Pe´rez et al., 2002). The principal component of
hardwood hemicellulose is glucuronoxylan whereas glucomannan is predominant in
softwood (Pe´rez et al., 2002). In contrast to cellulose, hemicelluloses are easily
hydrolysable polymers and do not form aggregates. It consists of shorter polymer chains
with 500–3000 sugar units as compared to the 7,000–15,000 glucose molecules per
polymer seen in cellulose (Tumuluru et al., 2010). Thermal degradation of hemicellulose
occurs between 130° – 260°C, with the majority of weight loss occurring above 180°C
10
(Mohan et al., 2006; Tumuluru et al., 2010). Hemicellulose produces less tars and char
due to its low degradation temperature range compared to that of the cellulose (Tumuluru
et al., 2010).
Lignin along with cellulose is the most abundant polymer in nature (Pe´rez et al.,
2002). Lignin is an unstructured and highly branched polymer that fills the spaces in the
cell wall between cellulose, hemicellulose, and pectin components (Tumuluru et al.,
2010). It is covalently bonded to hemicellulose and thereby exhibits mechanical strength
on the cell wall. It is relatively hydrophobic and aromatic in nature and decomposes
between 280 and 500°C when subjected to a thermal treatment (Tumuluru et al., 2010;
Mohan et al., 2006). Lignin is difficult to dehydrate and thus converts to more char than
cellulose or hemicelluloses.
Figure 2-2 Carbon Cycle in Biomass (Source: Uslu et al., 2005)
Plants
(Biomass)
Photosynthesis
Sun
Light
Atmo
spher
e
Soil
Biofuel
Energy
Production
(Combustion)
Water +
Minerals
CO2
Processing
11
2.2 Concept of Torrefaction
Different literatures have defined torrefaction in different terms. Acharya et al.
(2012) has defined torrefaction as a thermal pretreatment process in which isothermal
pyrolysis of biomass takes place at a temperature range of 200°C to 300 °C for a
reasonable residence time, with minimum oxygen concentration. Although almost all the
definitions reveal similarities in terms of processes, the operating temperature range
differs from research to research depending on the types and categories of biomass that
were studied. Sadaka and Negi (2009); Bergman et al.(2005); Rousset et al.(2011) and
Mani (2009) stated the torrefaction temperature range from 200°C - 300°C; Prins et al.
(2006a); Pimchuai et al.(2010) gave temperature between 230°C - 300°C; meanwhile,
Arias et al.(2008) stated temperature range between 220°C - 300°C, and Chen and Kuo
(2011); Zwart et al.(2006) stated temperature range between 225°C - 300°C. Most of the
research has shown that biomass reveal different performance to thermal treatment owing
to their varieties, origin and properties (Bridgeman et al., 2008); hence, the
commencement of biomass decomposition hangs on the biomass types.
According to Bergman et al.(2005), torrefaction is the thermal pretreatment
technique conducted at temperature range of 200°C and 300°C under an inert
environment and reasonably small residence time and slow heating rate less than
50°C/min (Berman et al., 2005, Walton and Van, 2011). The torrefaction process
encompasses the fragmentation of biomass during which various forms of volatiles are
formed and the resulting output is in the form of a solid fuel usually known as torrefied
product or torrefied fuel (Bergman et al., 2005; Pimchuai et al., 2010; Bridgeman et al.,
2008, Tumuluru at el., 2011).
12
Usually, almost all types of biomass contain hemicellulose, lignin and cellulose,
or lignocellulose in general. The thermal disintegration of biomass during torrefaction
causes various reactions to occur through their lignocellulosic configuration (Mosier et
al., 2005). The disintegration process was well studied by Bergman et al. (2005) as shown
in figure 2-3. At lower torrefaction temperatures, disintegration takes place in the
hemicellulose structure by means of a limited devolatilisation and carbonization;
meanwhile, in the lignin and cellulose structure a minor disintegration is observed. Figure
2-4 shows that hemicellulose undergoes extensive thermal disintegration in the
temperature range of 200°C to 300°C while only partial devolatilisation and
carbonization occurs in the lignin and cellulose structure (Bergman et al., 2005). It can
also be noted that the conversion from one decomposition regime occurs at a narrow
temperature range for hemicellulose while the conversion for lignin and cellulose occurs
over a wider temperature range. Hence, it can be concluded that hemicellulose is the most
reactive polymer constituent of biomass and is attributed to the substantial mass loss in
biomass during torrefaction (Bergman et al., 2005; Chen and Kuo, 2011; Sadaka and
Negi, 2009; Acharjee et al., 2011).
After the maximum moisture loss at temperature 100°C to 120°C, the significance
weight loss of biomass is achieved because of depolymerization and partial
devolatilisation of the hemicellulose during torrefaction process at a temperature range of
200°C to 300°C. However, due to minimum depolymerization and devolatilisation
reactions occurring in lignin and cellulose at this temperature range, maximum energy
content is retained in the torrefied biomass.
13
Figure 2.3: Decomposition regimes of lignocellulosic material during thermal
treatment (Source: Uslu et al., 2005)
Physical and Chemical properties of biomass are improved significantly after the
thermal treatment torrefaction, resulting in improve combustible properties. The
combustion properties including physical and chemical properties of torrefied biomass
also rely on the biomass properties, torrefaction temperature and residence time.
Following are the major characteristics of the torrefied products for biofuel application:
a. Hydrophobic behavior: Torrefied biomass has hydrophobic properties, i.e.
repels water, and when combined with densification makes bulk storage in
14
open air feasible. Torrefied Biomass has hydrophobic characteristics owning
to the destruction of is O-H bond structure, hence making it incapable to retain
or absorb moisture. Although standardized test exists yet to come on testing of
hydrophobic strength of Biomass, Pimchuai et al. (2010) demonstrated
hydrophobic test of torrefied biomass in comparison with raw biomass and
confirmed that torrefied biomass is hydrophobic in nature.
b. Elimination of biological activity: All biological activity is stopped, resulting
in total elimination of biological decomposition like rotting and reduced risk
of fire (Kung et al., 2009).
c. Improved grindability: Torrefaction leads to improved grindability of
biomass. This leads to more efficient co-firing in existing coal fired power
stations or entrained-flow gasifier for the production of chemicals and
transportation fuels. TB is more brittle owing to its higher C/H and C/O ratios,
hence provides enhanced pulverization characteristics and requires far less
energy for grinding compared to that of raw biomass (Bergman et al., 2005).
d. Markets for torrefied biomass: Torrefied biomass has added value for different
markets. Biomass in general provides a low-cost, low-risk route to lower CO2-
emissions. When high volumes are needed, torrefaction can make biomass
from distant sources price-competitive as the denser material is easier to
transport and store.
e. Large scale co-firing in coal fired power plants: Torrefied biomass results in
lower handling costs. Torrefied biomass enables higher co-firing rates;
Product can be delivered in a range of LHVs (20 – 25 GJ/ton) and sizes
15
(briquette, pellet). Co-firing by torrefied biomass with coal leads to reduction
in net power plant emissions.
f. Residential/decentralized heating: Relatively long distance transport of
biomass in the supply chain on wheels makes biomass expensive. Increasing
volumetric energy density decreases cost; Limited storage space increases the
need for higher volumetric density; Moisture content is important as moisture
leads to smoke and smell.
g. Higher heating value: The calorific value of torrefied biomass (TB) increases
with increase in treatment temperature and residence time (Bergman et al.,
2005) and this can be explained by the fact that TB has lost its moisture
content and its oxygen-carbon or hydrogen-carbon ratio reduces with
increasing temperature. The energy density increases with incremental
treatment temperature, which in turn increases the calorific value of TB
(Bergman et al., 2005).
h. Densification: Densification increases the bulk and volumetric density of
biomass. Hence, a combination of torrefaction and pelletization processes
produce torrefied pellets, which through pilot-scale experiments have shown
to have better storage properties than biomass pellets due to their
hydrophobicity. Torrefaction process causes dehydration that initiates and
propagates cracks in the lignocellulosic structure (e.g. wood), as result,
induces porosity and density changes. Increased porosity, due to more particle
voids, decreases particle size but inevitably increases the particle density and
bulk density. Generally, density varies in a different way depending on wood
16
species during temperature treatment and the changes with respect to
torrefaction might not be very significant (Repellin et al., 2010).
i. Particle Sizes and Distribution of Torrefied Wood: Torrefied biomass produce
more uniform and smooth particle sizes compared to untreated biomass
because of their brittleness, which is similar to that of coal. This behavior is
supported by their lower energy consumption during grinding. In their
experiment to examine the particle size and particle size distribution of a
torrefied pine chips and logging residues, Phanphanich and Mani (2010)
found out that the mean particle size of ground torrefied biomass decreased
with increase in torrefaction temperature. Consequently, torrefaction of
biomass not only decreased the specific energy required for grinding but also
decreased the average particle size of ground biomass. Furthermore, they
concluded that the particle size distribution curves of torrefied biomass
produces smaller particles than that of untreated biomass and their results
were comparable to the studies by Mani et al.(2009),. Cumulative percent
passing curve also showed similar behavior for torrefied biomass.
j. Explosibility of Torrefied Wood: Generally, a process that involves the
handling of dust poses an explosion hazard and the severity increases when
the process operating pressure rises over the atmospheric conditions (Repellin
et al., 2010). Just like pulverized coal, fine particle biomass such as sawdust
generate carbon dust that is combustible; hence, increase in the concentration
of suspended particles that exist in a confined space of a processing equipment
(e.g. boiler) pose a high risk of explosion when exposed to an ignition source.
17
Consequently, the intensity of explosion of dust particles increases with
increase in the combustible properties of the particles. Hence, torrefied
biomass has a higher dust explosibility than raw biomass and should be
handled with extreme care during plant operation. Although no study exists
that has compared the dust explosibility test of raw biomass to that of torrefied
biomass, it is reasonable to assume that a power plant, for example, should
incorporate dust explosion control measures when designing a plant that
processes pulverized torrefied biomass (wood) for energy supply etc.(Govin et
al., 1988, Ciolkosz and Wallace, 20011)
Additionally, a number of researchers have found that pelletization improves the
biomass bulk and volumetric density. Hence, a combination of torrefaction and
pelletization techniques yield torrefied pellets resulting in easier handling and storage
than raw biomass pellets due to their hydrophobicity and resistance to biodegradability
(Uslu et al., 2008; Kiel et al., 2008). The comparison in fuel characteristics and handling
behaviors of raw wood, wood pellets, torrefied wood pellets, coal and charcoal is
presented in table 2-1.
18
Table 2-1: Summary of Torrefied pellets Properties versus Coal (Source:
Kleinschmidt, 2011)
Parameters Wood
Wood
pellet
Torrefied
Pellets
Coal
Moisture content (% wt) 30-40 7-10 1-5 10-15
Calorific Value (MJ/kg) 9-12 15-16 20-24 23-28
Volatiles (% db) 70-75 70-75 55-65 15-30
Fixed carbon (% db) 20-25 20-25 28-35 50-55
Bulk density (kg/m3) 200-250 550-750 750-850 800-850
Volumetric energy density
(GJ/m3)
2.0-3.0
7.5-10.4 15.0-18.7 18.4-23.8
Dust explosibility Average Limited Limited Limited
Hydroscopic properties Hydrophilic Hydrophilic Hydrophobic Hydrophobic
Biological degradation Yes Yes No No
Milling requirements Special Special Classic Classic
Handling properties Special Easy Easy Easy
Transport cost High Average Low Low
2.3 Torrefaction Process Methods
Technical steps of the torrefaction can be explained in four steps which are
chopping, drying, mild roasting or pyrolysis at 200ᴼC-300ᴼC and cooling. From the field,
biomass is collected and fed into the chopper, which cuts them into small and more
uniform particles. The chopped biomass then passes via the drying segment to eliminate
the moisture and then into the torrefaction reactor. The output from the torrefaction
19
reactor is cooled down to room temperature. The moisture gas mixture released during
the drying process is composed of both condensable and non-condensable gases and
volatiles like CO2, CO, H2O, H2 and other organic elements (Kundra and Mujumdar,
2002). The greater the torrefaction temperature, the greater will be the incineration heat
of the volatile gas liberated during the process. The combustion heat of volatiles can be
reused as a supplement for the drying process. The resulting solid product, after the
complete devolatilisation of the biomass, is known as torrefied biomass or char (Bergman
et al., 2005). Careful regulation of torrefaction temperature and residence time is
necessary to the energy density and heating value of the product. The improved
combustion properties of torrefied biomass result in an attractive solid fuel for
combustion and gasification in thermal power plants.
Furthermore, the enhanced grindability of torrefied biomass makes it more
beneficial for pelletization, which enables storage, transportation, and co-combustion of
biomass with coal in existing coal power plants with no additional investment (Bergman
et al., 2005). The output product of the torrefaction process has high energy density and
enhanced overall fuel characteristics. This process involves high temperature treatment
i.e. overall efficiency of the process solely depends on the use of the heat supplied during
the treatment. The overall efficiency can be enhanced by reprocessing the excess heat
liberated from the process.
20
Figure 2-4: Basic principle of torrefaction Process (Source: Tumuluru et al., 2011)
During the torrefaction process, biomass experiences a series of disintegration
reactions that cause the discharge of gaseous products such as volatile organic
compounds (VOC’s) such as CO, CO2, H2O, H2, and organic volatiles. As a result C, H,
O composition of the biomass is changed, and the ratio of H/C or O/C is decreased as
torrefied biomass loses its hydrogen and oxygen in higher proportion compared to carbon
(Prins et al., 2006; Bergman et al., 2005). The breakdown of biomass polymer structure
throughout torrefaction results in the destruction of its hydroxyl (OH) group and making
it incapable to form hydrogen bond with water and hence, fails in its tendency to absorb
water (Bergman et al. 2005; Sadaka and Negi, 2009).
2.4 Classification of Reactors
Current torrefaction technologies are categorized by their reactor designs. Table
2.2 is a list of some main technology providers with different types of torrefaction
21
reactors. Each of the torrefaction technologies has its distinct style of heat transfer and
gas-solid or solid-solid mixing pattern in the reactor. These reactors could be generally
categorized into two major classes: a) Directly heated and b) Indirectly heated. In directly
heated reactors, biomass is heated by direct contact with the heating media like hot gas,
hot solids, superheated steam or electromagnetic radiation, either inert or minimum
oxygen environment. In indirectly heated reactors biomass is heated across the wall of the
reactor without contacting the heat transporting medium with the biomass. Therefore, it is
comparatively easier to avoid the presence of oxygen in the reactor during torrefaction.
Based on the mode of gas-solid contacts, the torrefaction reactors can also be
classified into the following four types. a) Plug flow (unidirectional motion of gas and
solids), b) Partial back-mixed (gas is unidirectional but solids are back mixed) c)
Tumbling (solids tumbles or moves around in a rotating drum or cylindrical tunnel) and
d) Entrained (solids are transported by gas). The entrained flow reactor (Topell
technology for example) involves the transport of biomass particles at high velocity (50-
80 m/s) through stationery angled blades at temperatures up to 280ºC which gives a
reactor residence time of less than 5 minutes. In both ‘Belt conveyor’ and ‘Multiple plate’
technologies, biomass moves on surfaces at a defined rate while the heating medium (hot
flue gas, hot nitrogen or superheated steam) sweeps over them, providing heat to the
biomass by convection. The heating is therefore mixed convective type. Heating of
biomass particles is the key part of the torrefaction process. The transfer of heat to the
biomass particles could take place through one of the following means: Gas-particle
convection, Wall particle conduction, Electromagnetic heating, Particle-particle heating
and Liquid-particle heating (FGC, 2010).
22
Using the above characteristics, torrefaction reactors can be broadly represented
by six generic types though some reactors could use combination of the basic features of
several generic reactors: i) Directly heated: Convective reactor, fluidized bed reactor,
hydrothermal reactor, microwave reactor, and ii) Indirectly heated: Rotating drum type
reactor, screw in stationery shaft type reactor. It may, however, be noted that some
reactors have a combination of these basic features but they are not listed separately.
Commonly used torrefaction reactors are described below:
a) Convective reactor: This is the most common generic type of reactor used for
torrefaction. Here hot gas flows past the biomass particles. The relative velocity between
the particles and gas drives the convective heating of biomass. The hot gas may be
completely inert or with a small amount of oxygen. In a fixed bed the particles remain
stationary while in a moving bed the particles move with respect to the reactor wall
(Marb and Vortmeyer, 1988). The wall of the reactor can be horizontal, vertical or
inclined. The particles may be moved either by gravity or by the force of a mechanical
device like augur. Particle flow through the reactor is unidirectional without back mixing.
The heat transfer is primarily through gas solid convection. Bergman et al. (2005)
estimates the biomass-to-gas heat transfer to be high in the range of 200 W/m2.K. Their
estimation of heating time (1 minute to heat 10x30x50 mm3 wood chips to 280ᴼC),
however, is much less than the 20 minutes measured in the present work for a wood
cylinder (25 diax75mm to 280ᴼC) in a convective reactor. Some convective type directly
heated torrefier uses a rotating drum where the biomass is heated directly by hot gases
passing through the rotating drum. In this case, the drum simply serves as a mixing
device while heat transfer takes place through gas-particle convection. Bergman et al.
23
(2005) estimates heat transfer coefficient in such reactors to be low, in the range of 40
W/m2K.
b) Fluidized Bed: In this type of torrefier, inert gas is blown through a bed of
granular heat carrier solids in a way that the solids behave like a fluid. These hot
particles, in vigorously mixed and agitated state, easily heat up any fresh biomass
particles dropped amongst them (Basu P., 2006, Pipatmanomai S., 2011). The biomass
particles undergo torrefaction in a well-mixed state with uniform temperature
distribution. This system, therefore, ensures uniform product quality that is a problem
with many other reactors. Separation of heat carrier solids from torrefaction product and
entrainment of fine particles are some of the limitations of this technology. Here the
dominant mode of heat transfer is particle-to-particle heat transfer. Because of the high
degree of particle-particle mixing, the heat transfer in this reactor is very high. This work
measured a heating period of less than14 minutes for heating a wood cylinder (25 mm dia
x 75 mm long) to 280ᴼC. Though this type is not in common use, it can provide very
uniform quality of the torrefaction product. Rapid heating to the torrefaction temperature
could potentially increase the throughput of the reactor without affecting product quality.
c) Hydrothermal Reactor: Here the biomass is subjected to heating in high-
pressure water and thus it obviates the need for drying (Yan et al., 2009). The dominant
mode of heat transfer in hydrothermal reactor is that between hot water (fluid) and solid.
While this process has several potential advantages, the energy required for
pressurization and movement of large volume of biomass across pressure barrier poses
major practical difficulties. No commercial application of this torrefaction is in use at the
moment.
24
d) Microwave: Microwave irradiation involves electromagnetic waves of
frequency in the range of 300 MHz to 300 GHz. Typical microwave ovens or microwave
reactors usually work at 2.45 GHz. The microwave irradiation produces efficient internal
heating by direct coupling of microwave energy with the molecules of biomass. The
electric component of electromagnetic microwave radiation causes heating by two main
mechanisms: dipolar polarization and ionic conduction (Leoneli and Mason, 2010). The
heating depends on the ability of the materials being heated to absorb microwaves and
convert it into heat. Metals for example reflect microwave, while biomass absorbs it
(Miura et al., 2004). This type of reactor is thus different from other directly heated
reactors, where biomass particles are heated externally, which means heat from the heat
carrier (gas, solid, liquid or reactor wall) first arrives at the surface of the biomass particle
and then it is conducted into the interior of the biomass. In a microwave reactor, the
biomass particles are heated from within (Salem and Ani, 2011). Other reactors heat
biomass through conductive heating by an external source, where heat received on the
biomass surface is conducted inside (De la Hoz et al., 2005). Biomass being poor thermal
conductor such heating is less efficient. In microwave processing, heating is internal. The
heating is, thus, volumetric rather than surface heating. Here no other heat transfer
medium, hot wall, particle or gas is needed.
e) Entrained flow reactor: Here ground biomass particles are entrained in high
velocity jet of hot gases. The Torbed process is an example of entrained reactor. Torbed
reactor heats the biomass particles to a temperature of up to 350ᴼC within a relatively
very short time of 90 sec (Michel et al., 2011) that greatly increases the throughput of the
reactor. A major characteristic of such reactor is high heat and mass transfer rates and the
25
absence of moving parts in the reactor. This process is similar to low temperature flash
pyrolysis. Fast heating and short residence time increases the volatile yield and reduces
char production during heating in the absence of oxygen (Michel et al., 2011).
Torrefaction process attempts to maximize char production while minimizing volatiles to
retain higher fraction of the biomass energy in the torrefied solids. From this standpoint
this type of reactor may have lower energy yield. This inference however cannot be
verified due to the absence of any research paper in the open literature with relevant
details on this process.
f) Rotating drum: The indirectly heated rotating drum tumbles the biomass in an
environment of inert gaseous medium. Here, heat is transferred from the hotter drum wall
to the biomass particles. This type of reactor has two major advantages: first the heating
medium does not have to be oxygen free and then the volatiles released are not diluted by
the gas passing through it, so it can be combusted to supplement the thermal load of the
reactor. Heat transfer from the wall to the biomass particles is the controlling factor in
such reactors.
g) Screw or stationary shaft: Here the torrefaction reactor (circular or rectangular
cross-section) is stationary, and it could be vertical, horizontal or inclined. A rotating
screw churns and moves the biomass through the reactor to enhance the heat transfer
between the wall and the bulk of the biomass and at the same time moving the biomass
along its length (Shu-de et al., 1996). To avoid direct contact with oxygen carrying hot
gases, the biomass is heated indirectly by the outer heated wall. Some designs may,
however, have holes for the products of torrefaction to escape. Biomass may also be
heated by the screw heated from inside the reactor (Waje et al., 2007).
26
Table 2.2: Comparison of Potential Torrefaction Reactor Technologies
(Kleinschmidt CP, 2011)
Torrefiers
Technology
Mode of
Heading
Status Criteria
Rotary drum
reactor
Direct Proven Technology, Minimum Heat
Transfer, High heating rate, medium
temperature control, good residence time
control, excellent heating integration,
enhanced mixing, large size tolerance, high
moving parts, good fouling,, little scaling
problem
Fluidized Bed
Reactor
Proven Technology, Enhanced Heat
Transfer, High heating rate, medium
temperature control, medium residence
time control, excellent scalability, excellent
heating integration, excellent uniform
heating materials, enhanced mixing
Moving Bed
Reactor
Direct Under development, Enhanced Heat and
Transfer, High heating rate, medium
temperature control, good residence time
control, excellent heating integration,
enhanced mixing, Good fouling
Screw conveyor Direct Indirect Proven technology, Enhanced Heat and
Transfer, High heating rate, medium
temperature control, good residence time
control, excellent heating integration,
enhanced mixing, large size tolerance, high
moving parts, best fouling and scaling.
Microwave Direct Indirect Under R&D, Enhanced Heat and Transfer,
High heating rate, Good temperature
control, good residence time control
Multiple Hearths
Furnace
Direct Proven Technology, Enhanced Heat and
Transfer, High heating rate, medium
temperature control, good residence time
control, excellent heating integration,
enhanced mixing, large size tolerance, high
moving parts, perfect scaling and best
scalability
2.5 Commercial Application of Torrefaction in Canada
The first and only commercially operated torrefaction plant was built in the 1980s
by the French company, Pechiney, to yield 12000-ton/acre of torrefied wood as a coke
27
substitute for the metallurgical industry. The plant was dismantled in the 1990s for
economic reasons (Bergman et al., 2005). Although the Pechiney demonstration plant
was considered state-of-the-art technology, Bergman et al.(2005) questioned its
feasibility for large-scale production; hence, they recognized its commercial failure partly
to its small scale pilot plant and large residence time during torrefaction, leading to loss
of energy efficiency. As a result, it drove the operating costs to an unmaintainable level.
However, the failure of Pechiney plant still played a positive role in thoughtfully
evaluating the technologies that will deliver an optimized torrefaction process at
minimum costs, while fulfilling the feedstock variability and the end user quality
requirements.
Several technology developers from the EU and the United States have invested
significantly in torrefaction technology. Canada still lags behind in its efforts and
commitment in bringing the technology to the market. The ECN (Energy Centre of the
Netherlands) is currently working on assessing the viability of commercial application of
torrefaction by up-scaling the concept of the Pechiney practice to enhance the efficiency
and sustainability of the operation (ECN, 2010). In June 2010, ECN commissioned a pilot
installation of a torrefaction plant in 2008 with a capacity of 50 kg of biomass per hour.
The plant reportedly achieved a stable process operation for 100 hours. This indicates a
prospect in the installation of a commercial scale torrefaction. Currently, ECN is
developing a demonstration installation with a capacity of nearly 5 tons of biomass per
hour.
Canada has approximately 979.1 million hectares of land. Out of the 397.2
million hectares of treed land, forested land covers 347.7 million hectares with 7.8
28
million and 41.8 million hectares classified as “other land with tree cover” and “other
wooded land” respectively. In 2004, Canadian sawmills produced 83.5 million cubic
meter of lumber, 47% of which was from British Columbia followed by 24% from
Quebec, and 10% from Ontario. Although Lumber production has slowed down in recent
years due to the US-led recession (Douglas, 2009), two main sources of bioenergy
feedstock in Canada are agriculture residues and wood-based products. Wood waste from
mills, residual biomass after harvest, or from stands grown specifically for biomass
production are the sources for wood biomass (Wood and Layzell, 2003). The wood
waste from mills is widely used among the three categories for pellet production and
other biofuel applications.
BIOCAP Canada published results of the analysis of mainly agriculture and
forestry based resources to evaluate the availability of bio-resources obtainable in Canada
(Wood and Layzell, 2003). On the basis of bioenergy stock, 245 million hectares of
timber forest in Canada have a biomass carbon stock of about 15.8 billion tons of carbon,
totaling 566 exajoules or 69 times Canada’s annual energy demand met by fossil fuel; on
the basis of annual harvest, the annual energy content of the biomass crop in Canada
amounts to 5.1 exajoules, which is 62% of the energy recovered from fossil fuel ignition;
and on the basis of biomass residue, about 60 million tons of carbon streams may be
considered “available” feedstock for a bio-based economy and this is conservatively
expected between 1.5-2.2 exajoules of energy contents per year, which is 18 – 27% of the
energy that Canada received from fossil fuels in 2000 (Wood and Layzell, 2003).
Canada retains substantial benefits in bioenergy from its arable land and forested
areas. About 1,866 megawatts of biomass power capacity is currently available in Canada
29
(Center for Energy, 2011). In 2007, 11.856 million tons of Municipal solid waste (MSW)
amounting to about 211-187 MW electricity generating capacity was available in Canada
without considering the thousands of MW of potential energy lost in the sewage. Biomass
feedstock extends from forest and agricultural residues to poultry litters and MSW. So, an
effective implementation commercially operable torrefaction plants can revolutionize the
green energy business potential leading the economy towards sustainable energy systems
and helping in minimizing the utilization of fossil fuels. Processed or unprocessed
biomass can be used for the replacement of coal in future.
2.6 Available Technologies for Torrefaction
Many researchers from the universities and government sectors are involved in
the torrefaction research, but a commercial scale torrefier has still not been developed. In
parallel, a number of private institutions are also involved in the commercial
development of the technology. In fact, majority have either given up their efforts or
delayed the development due to a lack of investment, while others are far behind their
forecasted operation date. On the other hand, the investors are not enthusiastic to invest
into torrefaction technology for fear of financial risk due to technological uncertainty.
Table 2-3 illustrates a number of torrefaction developments, including the companies,
suppliers and projected date of execution. Further studies have shown that a majority of
these projects is either being delayed, cancelled, or status not known.
30
Table 2-3: Overview of Torrefaction Projects (Source: Kleinschmidt CP, 2011)
Company Demo
Technology Supplier Locations
Prod.
Capacit
y (t/a)
ESD1 of
Operation
3RAgrocarbon,
Hungary
Rotary Kiln
(3R Pyrolysis
Biochar)
Unknown Unknown Unknow
n Unknown
4Energy Invest.
(BE) Unknown
Stramproy
Green Tech.
(NL)
Amel (BE) 40,000 Q4 2010
Agri-Tech
Producers LLC
(US/SC)
Belt
Conveyor
Kuster
Zima
Corporation
(US/SC)
Unknown Unknow
n 2010
Andritz
(Austria) Unknown Unknown Unknown 50,000 Unknown
Atmosclear
(CH) Rotary Drum CDS (UK)
Latvia,
New
Zealand,
US
50,000 Q4 2010
BioEnergy
Development
(SWE)
Rotary Drum
Unknown
Ö-vik
(SWE)
25,000 –
30,000
2011/2012
Biogreen
Energy (FR)
Screw
Conveyor ETIA (FR) Unknown
Unknow
n Unknown
Biolake BV
(NL)
Screw
Conveyor Unknown
Eastern
Europe
5,000 –
10,000 Q4 2010
CDS (UK) Rotary Kiln Unknown Unknown Unknow
n Unknown
CMI (NESA)
Multiple
Heath
Furnace
Unknown Unknown Unknow
n Unknown
EBES AG (AT) Rotary Drum Andritz (T) Frohnleite
n (AU) 10,000 2011
ECN (NL) Moving Bed Unknown Unknown Unknow
n Unknown
FoxCoal B.V.
(NL)
Screw
Conveyor Unknown
Winschote
n (NL) 35,000 2012
Integro Earth
Fuels, LLC
(US/NC)
TurboDryer Wyssmont
(US/NC)
Roxboro,
NC 50,000 2010
New Earth
Renewable
Energy Fuels,
Fixed
Bed/Pyrovac
Pyrovac
Group
(CA/QU)
Unknown Unknow
n Unknown
31
Inc. (US/WA)
Rotawave Ltd.
(UK)
Microwave
Heating
Group’s
Vikoma
Terrace ,
B.C,
Canada
110,000 Q4 2011
Stramproy
Green
Investment B.V.
(NL)
Oscillating
belt Conveyor
Stramproy
Green Tech.
(NL)
Sreenwijk
(NL) 45,000 Q3 2010
Thermya (FR) Moving Bed Lantec
Group (SP)
San
Sebastian
(SP)
20, 000 2011
Topell Energy
B.V. NL Torbed
Torftech Inc
(UK)
Duiven
(NL) 60,000 Q4 2010
Torr-Coal B.V. Rotary Drum Unknown
Dilsen-
Stokkem
(BE)
35,000 Q3 2010
Torrefaction
System Inc.
(US)
Unknown
Bepex
Internationa
l (US/MN)
Unknown Unknow
n 2013
Vattenfall
(SWE) Moving Bed Unknown Unknown
Unknow
n Unknown
WPAC (CA) Unknown Unknown Unknown 35, 000 2011
Zilkha Biomass
Energy (US) Unknown Unknown
Crockett,
Texas
(US)
40,000 Q4 2010
2.7 Pelletization
Pelletization is a densification process of biomass that increases the energy
density and bulk density, minimizes the moisture content, resulting in significant savings
in transportation costs (Holley, 1983; Mani et al., 2003; Obernberger et al., 2004;
McMullen et al., 2005). Kumar et al. (2003) showed a detailed study in Western Canada
on the cost to produce biomass electricity by direct combustion and determined that
transportation was the second most important factor that influences the net cost of
operation. This can be addressed by densifying the biomass in the form of pellets or
briquettes or cubes (Kaliyan and Vance, 2009). . Because of uniform shape and sizes,
densified products can be easily handled using the standard handling and storage
32
equipment, and can be easily implemented in direct-combustion or co-firing (Kaliyan and
Vance, 2009).
There are a number of pellet producers around the world, producing tons of
pellets for domestic as well as commercial applications. Pellet plant consists of the
following parts: a) chopper: to break down the feedstock into small and uniform particles;
b) crusher/hammer mill: to convert the small particles into fine powder with diameter less
than 3 mm; d) dryer: to decrease the moisture content to less than 15%; and e) pellet mill:
to densify the material into pellets. The capacity of a pellet mill is generally in the range
of 0.30 tons/h to 10 tons/h.
A German-based company AMANDUS KAHL is one of the leading producers of
pellet equipment from small to industrial scale. KAHL pelleting plants have been applied
successfully for compacting organic products of different particle sizes, moisture
contents, and bulk densities. Their pelleting presses are designed for array of feedstock
characteristics as seen in figure 2-5 below. Available pelleting presses consist of a drive
power of 3 kW to 500 kW and a throughput between 0.3 tons/h and 8 tons/h. KAHL
recently developed pellet press equipment with 15 to 20 tons/h capacity. Table 2-4 below
shows the summary of specifications of different pelletizing equipment from four
different manufacturers.
33
Table 2-4: Summary of Specifications for Four Different Pelleting Equipment
Company La Meccanica NOVA Pellet Kerry Die Amandus Kahl
Model CLM 800 P
LG
N-Plus B-Mass 800 60-1250
Roller Quantity 2 Unknown 6 4 – 5
Drive Power (KW) Up to 280 160 450 3 - 500
Energy Consumption Unknown Unknown Unknown 40 – 60 KWh/t
Capacity (T/H) 2.3 – 3 Up to 2.5 10 15 – 20
Operation Mode Continuous Continuous Continuous Continuous
Weight (kg) 10800 7500 Unknown 9370
Roll Diameter (mm) Unknown 245 250 450
Motor speed (rpm) 750 Unknown 1490 Unknown
Roller Speed (m/s) 6.5 – 7.5 Variable variable 2.5
Die Diameter (mm) Unknown 580 840 175 – 1250
Input Density Unknown Unknown Unknown 150
Output Density (kg/m3) Unknown Unknown Unknown 550 – 650
Feedstock Moisture Unknown 8 – 12% Unknown 12 – 15 wt%
Feedstock Size Unknown 0.5 – 1.5 mm Unknown 4 mm
Pellet Moisture 9 – 12 wt% Unknown Unknown 12 wt%
Pellet diameter (mm) 6 6 8 2 – 30
34
Figure 2-5: Pictures of raw and pelletized materials (Source:
http://www.akahl.de/akahl/files/Prospekte/Prospekte_englisch/1322_Strohpell_10e.pdf)
More recently, research has found a biomass treatment process that combines the
densification (pelletization) and torrefaction to increase the bulk density and the calorific
value of biomass. Kiel et al., (2008) presented BO2-technology under the umbrella of
Energy-research Centre of The Netherlands (ECN) for biomass improvement into
commodity fuel; a technology that combines torrefaction and pelletization methods to
develop products named as torrefied pellets (BO2 pellets ). BO2 pellets possess the
35
benefits of both process but with higher bulk density and calorific values developed from
wide range of biomass such as woodchips, agricultural residues and different residues
from the food and feed processing industry (Kiel et al., 2008). A schematic course flow
of the BO2-technology is shown figure 2-6 below and table 2-5 displays the comparison
of “BO2 Pellets ” characteristics from raw wood chips, wood pellets, and torrefied
woods.
Figure 2-6: Schematic Process Flow of the BO2-Technology (Kiel et al., 2008)
36
Table 2-5: Comparison of BO2 Pellet Properties (Source: Kiel et al., 2008)
Properties
(Typical Values) Wood Chips
Torrefied
Wood Wood Pellets
BO2
Pellet
Moisture wt% 35 0 10 3
LHV KJ/Kg
Dry
As received
17.7
10.5
20.4
20.4
17.7
15.6
20.4
19.9
Bulk Density
Kg/m3
MJ/m3
475
5.0
230
4.7
650
10.1
750
14.9
2.8 Gasification
Gasification is a process that converts biomass into carbon monoxide, hydrogen
and carbon dioxide. This is achieved by reacting the material at high temperatures
(>700°C), without combustion, with a controlled amount of oxygen and/or steam. The
resulting gas mixture is called syngas (from synthesis gas or synthetic gas) or producer
gas and is itself a fuel. The power derived from gasification of biomass and combustion
of the resultant gas is considered to be a source of renewable energy; the gasification of
fossil fuel derived materials such as plastic is not considered to be renewable energy.
The main application of torrefied biomass (wood) is as a renewable fuel for
combustion or gasification. Prins et al. (2006b) studied the possibility of more efficient
biomass gasification via torrefaction in different systems; air-blown circulating fluidized
bed gasification of wood, wood torrefaction and circulating fluidized bed gasification of
torrefied wood, and wood torrefaction integrated with entrained flow gasification of
torrefied wood (Dangtran et al., 2000, Svoboda et al., 2009).
The advantage of gasification is that using the syngas is potentially more
efficient than direct combustion of the original biomass because it can be combusted at
37
higher temperatures or even in fuel cells, so that the thermodynamic upper limit to the
efficiency defined by Carnot's rule is higher or not applicable. Syngas may be burned
directly in gas engines, used to produce methanol and hydrogen, or converted via the
Fischer-Tropsch process into synthetic fuel. Gasification can also begin with material
which would otherwise have been disposed of such as biodegradable waste. In addition,
the high-temperature process refines out corrosive ash elements such as chloride and
potassium, allowing clean gas production from otherwise problematic fuels. Gasification
of fossil fuels is currently widely used in industrial scale to generate electricity.
Gasification of biomass, which in many ways is a more efficient use of the
feedstock, is nowadays an interesting alternative to combustion for many industries but is
still limited. Tar in product gas is a major drawback of wood gasification in any
conventional gasifier. This can be addressed by using torrefied biomass instead of un-
torrefied biomass. Other disadvantages of un-torrefied biomass are their relatively low
energy content and hydroscopic character. Prins et al.(2006) have shown that higher
gasification efficiency can be achieved by fuels with lower O/C ratio by thermo-chemical
process. Torrefaction is a process that effectively lowers the O/C ratio of biomass in a
simple way and lowers the energy consumption during milling and transportation. The
output product in the form of powder greatly enhances the feeding properties (Kiel et al.,
2007). Although extensive studies have been carried out on the solid product and its
application in gasification, only limited publications have been made on the utilization of
torrefied product in existing thermochemical processes.
38
2.9 Emission
Burning biomass is known to be carbon neutral; net carbon emissions would be
zero, which is helpful in the fight against global warming. Many industrialized countries
are planning to replace coal as a fuel in power plants with biomass to minimize the
greenhouse gas emission. Torrefied biomass will be an environmentally friendly fuel
compared to fossil fuels.
However, from the torrefaction process, the output product contains gaseous
volatiles, organic acids and primary tars. After capturing the gaseous and liquid products
of the process, the remaining emissions consists only CO2, H2O, NOx and SOx. NOx
emissions can be negligible due to low temperature and SOx emissions can also be
considered as zero due to negligible sulfur content in lignocellulosic biomass. Condensed
tars are a major concern in the application of torrefied biomass. As the temperature
increases during torrefaction, the tar formation also increases exponentially. This issue
needs to be addressed very carefully. According to Kleinschmidt C.P. (2011), test results
have shown that even after combustion, the flue gas contains some organic compounds
like hydrogen fluorides, sulfides and nitrates that need to be removed before collecting
the flue gas. Bag filters and ceramic filters with an absorbent are suggested to minimize
these emissions. The emission from biomass torrefaction is not a major technical
challenge, but the ash, chlorine, sulfur and alkaline production should be minimized.
2.10 Storage Behavior
There is always chance of off-gassing and self-heating in any kinds of solid
biomass because of presence of moisture and pores by chemical oxidation and
microbiological contamination. Throughout storing of such biomass, there is always
39
chance of occurring chemical-microbial reactions. According to Tumuluru et al.(2011),
high storage temperatures of about 50°C may generate high CO and CO2 emissions, and
the concentrations of these off-gases can range up to 1.7 and 6% during the storage
period of sixty days. Emitted products are also sensitive to relative humidity and moisture
content. Torrefied biomass either pelletized or raw products show superior performance
than the raw biomass or raw pellets because of its hydrophobic nature and low moisture
uptake even under severe storage circumstances. Off gassing and self-heating are at
minimum level in torrefied biomass as most of the solid, liquid, and gaseous products,
because chemically and microbiologically active components are eliminated in the
torrefaction procedure. Studied at University of British Columbia, Vancouver, Canada on
off gassing from torrefied wood chips showed minimum emission of CO and CO2; nearly
one third of the emissions from regular wood chips (Van der at el., 2011). Delivery cost
of pelletized biomass including shipping, trucking, storage, pre-treatment, chopping and
others is presented in figure 2-7 (Van der at el., 2011 and Zwart R. et al., 2006).
40
Fig. 2-7 Delivery costs of pelletized biomass. (Numbers indicate nominal
capacity of system in dry kilotons of raw biomass feedstock per year) (Source: Van
der et al, 2011)
2.11 Economic Potential
To analyze the details of net profit of torrefaction, the impact of the process on the
all steps of the value chain is to be discussed. The segments of benefits are transport,
storage, carbon neutral and production. Higher energy density, condensation,
pelletization and dried mass of the torrefied products make economic benefit on the
transportation. Hydrophobic behavior of torrefied biomass can be successfully stored
outdoors, thus obviating the need for an enclosed storage bin or building but further
studied is required on this issue. However, it should be noted that, in dry climates, wood
chips have been successfully stored in large outdoor piles. The relative fuel losses
(shrinkage) during storage are not well known, but can be expected to be higher for
41
outdoor storage. Comparisons of shrinkage losses of torrefied vs. raw biomass are needed
for different storage conditions and climates. Utilization benefits are related to the higher
energy content, lower oxygen content, and (probable) lower moisture content, relative to
unprocessed biomass. Torrefied biomass is expected to perform as well or better than raw
biomass for many bioenergy applications, including combustion, gasification, and fuel
production applications (Svoboda et al., 2009). Enhanced conversion and utilization,
when compared to the other steps in the supply chain, probably provide the most
significant opportunity for cost savings (followed by transport costs). Torrefied biomass
is believed to be a superior solid fuel for combustion, especially when co-fired with coal
due to its higher energy density and coal-like handling properties. Torrefied biomass is
also expected to provide advantages as a fuel for thermochemical processing, due to the
removal of acids and oxygen. Gasification using torrefied biomass allows for improved
flow properties of the feedstock, increased levels of H2 and CO in the resulting syngas,
and improved overall process efficiencies (Svoboda et al., 2009, IEA, 2010). Torrefaction
combined with pelletization provides a lower cost fuel for power or fuel production when
compared to pelletizing alone, with cost savings ranging from 4% to 16%, depending on
the end use of the biomass. Fig 2-7 shows supply chain costs for several scales and
processing options for biomass, indicating that pelletizing of torrefied biomass
significantly reduces costs, that larger-scale operations are more cost efficient, and that
integrated torrefaction and pelletizing is less costly than pelletizing alone. Zwart et
al.(2006) conclude that, while torrefaction is one of the most cost-effective options for
supply of overseas biomass, modifications to the supply chain, such as the centralized
processing of raw feedstock, can result in similar reductions in overall costs.
42
According to Van der Stelt et al.(2011), the torrefaction step represents an
additional unit operation in the biomass utilization chain. The attendant capital and
operating costs, as well as conversion losses are, however, offset by savings elsewhere.
Recent cost estimates for the ECN torrefaction technology indicate that the total capital
investment of a standalone 75 kton/a plant will be in the range 6.1 to 7.3 MV. The
assumed feedstock is wet softwood chips. The plant consists of a conventional rotary
drum for drying the biomass, ECN torrefaction technology and conventional grinding
equipment and pellet mill. No feedstock preparation (e.g. chipping) before drying was
included. At 75 ktons/a production rate (design), the total production costs are calculated
at 37 V/ton product (2.0 V/GJ), produced from a feedstock with 35% moisture content.
At 50% and 25% moisture content this is 50 V/ton (2.6 V/GJ) and 34 V/ton (1.9 V/GJ) of
product, respectively. The moisture content is one of the most influential parameters of
the torrefaction process as it predominantly determines the energy input of the process.
These data represent the added cost for the torrefaction process without preprocessing of
pre-drying process of biomass.
There is always a cost for any processing so torrefaction also adds some cost in
the processing than raw biomass (Magalhaes et al., 2009). Because of low moisture
contents, it also reduces cost of transportation and grinding. Torrefied biomass acts as
good fuel for any gasification process. Gasification with torrefied biomass enhances flow
properties of the feedstock, improves contents of H2 and CO in the syngas, and enriched
process efficiency resulting with cost savings from 4% to 16%. Zwart et al.(2006)
concluded that torrefaction is one of the best cost-effective alternatives for delivery at
overseas destination with optimum overall costs.
43
ECN, Netherland estimated that torrefaction technology capital investment of a
standalone 75 kton/a plant will be in the range 6.1 to 7.3 M€. The plant comprises of
drying unit (rotary drum), torrefier unit, grinding unit and pellet mill. No feedstock
preparation (e.g. chipping) before drying was counted in for the estimation. For 75
ktons/year manufacturing of torrefied products, the total production costs are estimated as
37 €/ton, with 35% moisture content, 50 €/ton with 50% moisture contents and 34 €/ton
with 25% moisture content.
2.12 Scanning Electron Microscopy (SEM)
A scanning electron microscope (SEM) is used to project the images of a sample
by scanning over it with a high energy focused electron beam. The electrons interact with
electrons in the sample, generating secondary electrons, back-scattered electrons, and
characteristic x-rays that can be detected and that comprise data about the sample's
superficial structure and configuration. The electron beam is generally scanned in a raster
scan pattern, and the beam's position is combined with the detected signal to produce an
image. The electron beam can be concentrated to a spot approximately 1 nanometer in
diameter, and microscopes are able to resolve details ranging from 1–20 nm in size. To
avoid accumulating charge on the surface, samples must be electronically conductive;
non-conducting samples are often coated with an ultrathin coating of metal. Conventional
SEM requires samples to be imaged under vacuum, but methods have been developed
that allow imaging biological samples (Suramya DFM, 2012).
The large content of Silica, Potassium and Chlorine in biomass significantly
increases the deposit formation and corrosion of the thermal power plants, compared to
boilers firing with coal (Basu, 2006; Beatrice et al., 2007). It has been verified that the
44
alkali species which cause the bed agglomeration originate from the biomass ash. So,
study on the behaviors of alkali species in biomass ash is crucial for understanding the
mechanisms of agglomerates and coating layers formation. The ash block can maintain a
fixed shape and presents a little compression strength due to the sintering. Skrifvars et al.
(1997) characterized the sintering tendency of ten biomass ashes and classified the ash
components into three groups: simple alkali salts, silicates and the rest non-melt. We can
see that the fusible compounds melt and coat the surface of ash particles during
combustion. According to the experimental data and plenty of study results by other
investigators (Skrifvars et al., 1997), these melts should be the alkali silicates. Based on
the K2O–CaO–SiO2 phase diagram and the Na2O–SiO2 and K2O–SiO2 phase systems
(Jenkins et al.,1995) the melting point of these alkali silicates should be in the range 800–
1200°C. At the same time, these silicon dioxide grains are coated by the molten alkali
silicates which can freely flow through the gaps between the silicon dioxide grains. From
above findings we see that the alkali metals such as K and Na are mainly found in the
outer layer of biomass ash. The alkali silicates formed during combustion can melt and
coat the surface of ash particles at high temperature. Further, it can be imagined that the
sizes of ash particles must vary in a wider range due to the fragmentation and attrition in
the bed. When the small-sized ash particles collide with bed particles, the molten alkali
species on them will be transferred to surfaces of bed particles. In addition, the large-
sized ash particles may increase the amount of melts on local surface of bed particle and
may act as the necks for the agglomerate formation. So, the large- and small-sized ash
particles may play the different roles in the bed agglomeration. There is no article found
45
in the open literature on SEM analysis of poultry litter ash and this kind of analysis is of
its first kind. The SEM of wood mixture from gasifier is shown in figure 2-8.
2-8. SEM of Wood Ash from Gasifier (Beatrice et al., 2007)
2.13 X-ray Diffraction (XRD)
According to online definition, the scattering of x-rays by crystal atoms,
producing a diffraction pattern that yields information about the structure of the crystal is
defined as XRD. The wavelengths of X-rays are of the same order of magnitude as the
distances between atoms or ions in a molecule or crystal having less than Nano meter in
size. A crystal diffracts an X-ray beam passing through it to produce beams at specific
angles depending on the X-ray wavelength, the crystal orientation, and the structure of
the crystal. X-rays are mainly diffracted by electron density and analysis of the
diffraction angles creates an electron density map of any types of crystal (Cheng et al.,
2011). XRD instrument consists of an X-ray generator, a goniometer and sample holder,
and an X-ray detector such as photographic film or a movable proportional counter. X-
46
ray tubes generate X-rays by bombarding a metal target with high-energy (10 - 100 keV)
electrons that knock out core electrons. An electron in an outer shell fills the hole in the
inner shell and emits an X-ray photon. Two common targets are Mg and Cu, which have
strong K(alpha) X-ray emission at 0.71073 and 1.5418, respectively. X-rays can also be
generated by decelerating electrons in a target or a synchrotron ring. These sources
produce a continuous spectrum of X-rays and require a crystal monochomator to select a
single wavelength.
Powder X-ray Diffraction (XRD) is one of the primary techniques used by
mineralogists and solid state chemists to examine the physic-chemical make-up of
unknown solids. This technique provides information that cannot be obtained any other
way. The information obtained includes types and nature of crystalline phases
present, structural make-up of phases, degree of crystal formation, amount of
amorphous content, micro-strain & size and orientation of crystallites.
2.14 Summary from Literature
From the analysis of above literature review, following conclusions can be made:
a) Biomass can play important role as a carbon neutral fuel in the future.
b) Torrefaction process includes chopping, drying, roasting and cooling of any kinds
of biomass samples which leads polymerization and carbonization phenomenon.
Study on torrefaction gets more and more important for making solid fuels from
biomass even though research on it is still at the primitive stage of commercial
development. Torrefaction process depends on many parameters which are still
47
needs to be studied. Although, researches on the technology and science of
torrefaction have been carried out, further investigations are still required.
c) Torrefaction results are different for different biomasses so it is important to
investigate the different biomass sample separately. None of the published
materials shows the studies on torrefaction characterization of lignocellulosic and
non-lignocellulosic biomasses from Ontario.
d) Different types of torrefaction reactors are now available in the market but still
further research is essential to improve the reactor efficiency.
e) Torrefaction improves the hydrophobicity, grindability, non-degradability,
storability. However, the findings of the optimization of torrefaction temperature
and residence time are still under the investigation which best fit the long storage
capability without bio-degradation.
f) Pelletization is a compressing techniques which reduces the volume of the
biomass drastically and improves the energy density. It will reduce transportation
cost of biomass pellets. Pelletization techniques for raw and torrefied biomass
needs further investigation as limited studies are only available.
g) Safety process during the torrefaction techniques are still under study like dust
explosibility, emissions, health hazard, environmental impact on the surroundings
etc.
h) Major researches on torrefaction are basically based on the lignocellulosic
biomass having cellulose, hemicellulose and lignin but there is lack of in-depth
study on the non-lignocellulosic biomasses like animal wastes, municipal waste
and waste from agro-based plants.
48
i) Torrefied bio-fuels are the potential input for the electrical or thermal power
plants. Biomass creates slagging and fouling at the tubes of boilers. Biomass ash
management is very important issues for designing future bio-fuel boilers. None
of the papers are available on the detail ash analysis of lignocellulosic and non-
lignocellulosic biomass
Hence, this study tries to fill the small gap on torrefaction characterization,
pelletization techniques, optimum temperature for hydrophobicity, storage behaviors and
ash analysis using SEM and XRD. Finally, comparative studies on above mentioned
studies are presented.
49
Chapter III: Methodology
3.0 Problem Statement
The Ontario government is on track to phase out coal-fired electricity plants by
2014. According to Ontario Ministry of Energy, the power demand will increase by
about 15% between 2010 and 2030. Ontario should take timely initiative for the
production of the clean energy as per its’ future demand. The development of clean and
economically viable biomass to bioenergy conversion technologies for a domestic market
is thus imperative to promote the local utilization of biomass in Canada. Certain portion
of the energy demand can be fulfilled by the biomass energy after the successful up
gradation of its quality. One of the methods to upgrade the quality of biomass is the
torrefaction, densification and gasification.
Hence, more interest for research in the area of torrefaction and pelletization has
grown. There is potential to improve the quality of agricultural and woody biomass and
its residues as energy fuel which can be used for many energy applications. Agricultural
products, woody biomass and non-lignocellulosic bio-residues are attractive sources of
energy that can be greenhouse gas emission neutral and can provide sustainable energy
sources to meet the energy economy. Although biomass is abundant and renewable, its
properties pose several challenges during thermal conversion process; hence, limits its
applications in power plant operations even though it has been successfully used as an
upgraded solid fuel in electric power plants and gasification plants. Many studies are
available on torrefaction process; up to date however, majority of them have focused
mainly on lab-scale analysis of biomass compositions and characterization of torrefied
biomass in terms of grindability and energy value while only few have examined its
50
feasibility on commercial applications. These torrefied fuels can be used for high quality
smokeless solid fuels for industrial, commercial and domestic applications, solid fuel for
cofiring directly with pulverized coal at electric power plants, an upgraded feed stock for
fuel pellets, briquettes and densified other biofuels. Not all aspects of torrefaction and its
influence on other processing operations have been explored (Tumuluru et al., 2011;
Khodier, 2011).
There exists several gaps in the development of torrefaction technologies and its
maturities and there is need for continued research and development to characterize and
optimize this promising option for bioenergy feedstock processing for the application of
next generation fuel prior to the depletion of fossil fuels. Governments, private parties
and universities are investing a lot in the field of biomass applications. Several
achievements are still under the scope of laboratory. The most challenging is to see the
laboratory experiment in the commercial applications. For this, in depth study on
composition and application of tar, char, ash has yet to be established, in part due to the
complex chemical nature of the feedstock. Environmental effect, storage behavior of
torrefied biomass, energy analysis of the torrefied products, temperature effect, heating
values due to different temperature, practical reactors, residue management, effective
transportation possibilities are few areas of research on the torrefaction process.
3.1 Research Scope and Objectives
Current research has wide range of scope in the era of global warming reduction
by maximizing the utilization of green fuels. There are number of challenges to minimize
the dependency on fossil fuels and accomplish a sustainable, renewable energy source.
Energy from biomass can be produced from different thermochemical combustion,
51
gasification, and pyrolysis, where direct combustion can provide an energy solution. The
increasing attention in the use of biomass is considered as a solid fuel. This consists of
combustion to produce steam for electrical power and commercial plants. Still, the use of
either producer gas or gas turbines, or to produce higher value chemicals and fuels, is
limited due to biomass feedstock preparation, storage, transportation, logistics, ash
management and economics. This study will add new scope on these aspects so that
biomass can be used as bio fuel in the future.
Figure 3.1 Schematic Block Diagram of Research Procedures
Hence, this work will expand the torrefaction studies on the different lignocellulosic
and non-lignocellulosic biomass of Ontario and complete the following objectives by
conducting different experiments and result analysis:
i) Physio-chemical characterization of biomass samples before and after
torrefaction.
ii) Optimization of torrefied conditions based on hydrophobicity
iii) Investigation of pelletization potential before and after torrefaction
Biomass Product
Input: Willow,
Oats and Poultry
Litter
Energy Input
Torrefier,
Reactor,
Pelletizer, Bomb
Calorie meter Pelletization
Strength,
Heating values
and Ash analysis
Output products
analysis,
Torrefaction,
Hydrophobicity
52
iv) Ash analysis of biomass at different combustion temperature.
3.2 Methodology
The proposed research will focus biomass analyses before and after torrefaction
and will be represented on a dry-ash-free basis. A laboratory setup is prepared and
intensive lab test will be carried out to find the performance on selected biomass samples,
Poultry litter, willow and oat pallet samples to characterize their properties in terms of
moisture content, volatile matter, ash content, and fixed carbon. The proximate analysis,
elemental analysis, ash analysis will be performed on all samples.
The methodology will be based on the following flow chart as mentioned in figure 3.2.
53
Figure 3.2: Flow Chart of Methodology
Biomass Sample: Willow, Oats and
Poultry Litter
Characterization:
Proximate, Ultimate,
Energy Density and
HHV
Torrefaction
-Varied O2
-Temperature (200°C -300ᴼC)
-Residence Time (15-60min)
Comparative Study of
Torrefied and Raw
Biomass:
Characterizations,
Hydrophobicity
Pelletization, Ash
Ash Analysis at
800°C, 900°C,
1000ᴼC
-SEM
-XRD
- Fusion Temp
Hydrophobicity
-Optimum
Torrefaction
Temperature
-Moisture Uptake
Investigation of
Pelletization Potential
-Making Force
-Breaking Force
54
Chapter IV: Experiment Setup
4.1 Biomass Characterization
Biomass samples of poultry litter, willow pellets and oats pellets were collected
from the different locations of Ontario. Drying process of all biomass samples were
conducted at 105°C according to ASTM standard D1762-84 procedure. Muffle furnace
was used to determine the moisture content of the biomass. Different samples of biomass
weighing from 1-2 gram were placed in the muffle furnace for two hours at 105°C and
allowed them to cool at desiccator and weight were taken. The experiments were repeated
till the constant weight reached. The change in weight of biomass was considered as the
total moisture present in biomass and its percentage determined.
4.1.1 Proximate Analysis
Proximate analysis was conducted to determine the moisture, volatile matter, ash
and fixed carbon contents according to the procedure as specified on a modified ASTM D
5142-04 method on a muffle furnace of Thermo Scientific.
4.1.2 Ultimate Analysis
Ultimate analysis of the samples was carried out according to ASTM D 5373-08
method. All samples were dried at 105°C for 24 hours prior to the experiment for
Ultimate analysis. During the experiment, the combustion was carried out at 925°C under
Helium atmosphere while the reduction was carried out at 650°C.
4.1.3 Heating Value
After the specified residence time, crucible were removed from the reactor and
placed for in a vacuum desiccator to cool. The samples were grinded in a coffee grinder
to prepare sample for Bomb Calorimeter (Model IKA C-200) by IKA. The complete
55
basses of calculation for the calorific value were based on ASTM D 240 and ASTM D
5865. Combustion was carried out in a calorimeter in the presence of Oxygen. The
decomposition vessel was filled with a fuel sample of less than 1 gram and pure Oxygen
of maximum of 30 bar, the fuel sample was ignited and the temperature increase in the
calorimeter system measured. The heat quantity required to raise the temperature of the
calorimeter system by one Kelvin was used to determine the C-Value of the system. The
specific calorific values of the sample were calculated as follows:
Where
m = weight of fuel of the sample
C = Heat capacity (C-value) of the calorimeter system.
DT =Calculated temperature increase of water in inner vessel of measuring cell
Correction value for the heat energy generated by the cotton thread as
ignition aid
Correction value for the heat energy generated from other burning aid
4.2 Torrefaction
A novel reactor (Fig. 4.1), similar to Quartz Wool matrix (QWM) reactor (Bashu
P., 2010), was designed, developed and fabricated in the machine lab at University of
Guelph for the purpose of continuous torrefaction to produce a torrefied product, which
is. The reactor consists of a Stainless Steel (SS) tube heated by four electric heaters of
1.25KW capacity in close contact with the reactor wall and separately controlled by two
PID controllers. The SS tube has an inner diameter of 75 mm and height of 600 mm. The
56
percentages of different composition of gaseous particles inside the reactor were
observed using gas analyzer (Testo-350). Experiment were conducted for different
samples at different temperature 210°C, 250°C, 275°C and 300°C and at different
residence time up to 60 minutes. This reactor allows simulation of any gas-solid relative
velocity; gas composition and gas temperature in a reactor while a precision electronic
balance continuously measures the mass change of a reaction. Such reactor could thus
accurately simulate conditions one would expect in a fixed, moving or entrained flow
reactor. Before starting an experiment, the reactor was heated until an equilibrium
temperature or steady state was attained. A stream of inter gas (N2) of flow rate of 1-16
liters per minutes was flushed through flow meter (FMA 5400/5500, Mass Flow
Controller, Omega, USA) to maintain an inert environment inside the reactor.
Temperatures were measured at two different locations one from upper mid portion of
reactor and another from lower mid portion of the reactor by two separate thermocouples
through the temperature controller (CNi16D, Temperature and Process Controller,
Omega, USA). Then the sample of biomass of known mass and moisture content were
placed into the reactor. The residence time was recorded from that instant. During
torrefaction, temperatures of the gas passing through the biomass are continuously
recorded. The electronic balance (Model: MS204S, Mettler Toledo, Switzerland)
continuously measured the mass of the biomass. After a specified time, the biomass is
taken out. Thereafter, the sample is cooled down in desiccator and weighed. Its
composition is analyzed by proximate analysis (ASTM E870-82) and energy density by a
bomb calorimeter (model C-200 by IKA). Similar experiments are repeated for separate
temperature and residence time for individual biomass samples.
57
Percentage of mass yield (MY), percentage of energy yield (EY) and energy
density radio (EDR) are determined by using following formula:
Where,
= Mass (daf) of torrefied biomass
= Mass (daf) of raw biomass
= Higher Heating Value of torrefied biomass
= Higher Heating Value of raw biomass
Figure 4.1 Experimental Setup for Torrefaction and Weight loss
To chimney
Electric tubular
furnace
Analytical balance
N2
SS porous
basket
Gas
analyzer
Temperature
Controller
Pre-heater
Data
Logger
Reactor tube
Mass flow controller
Gas
sample
Thermocouple tube
58
4.3 Hydrophobicity
Very few papers have stated the experimental setup of the hydrophobicity test for
torrefied samples. Pimchaui et al. (2010) demonstrated hydrophobic test by immersing
raw and torrefied biomass in water for two hours, allowed to dry and determined the
weight change as a measure of moisture absorption. This approach was similar to Felfli et
al. (2005) in investigating the hydrophobic characteristics of briquettes where briquettes
were immersed for 70 minutes in water.
Here, Raw and Torrefied Samples were immersed in water for 2 hours at room
temperature of 22°C-25°C and relative humidity of 40%-50% and the hydrophobic
characteristics of torrefied and raw samples were investigated. The contents of the
moisture is determined after drying the immersed samples at the interval of 1 hours till
the nearly constant weight of the sample were achieved. In addition, hydrophobic test
were conducted in controlled environment pressure by using humidifier. The humidity
level was from 88%.
4.4 Pelletization
According to Wolfgang et al. (2011), the pellets were prepared using a single
2812 pellet press from Parr which was modified at the workshop of University of Guelph
as shown in figure 4-2, such that it can connect with Omega LC1001-500 and
CNiS8DH33 to measure the force in Newton maximum of 2224N. The press consisted of
a cylindrical die 6.4 mm in diameter, made of hardened steel. The end of the die was
closed using a removable backstop. Pressure was applied and the force could be
measured using an Omega Process Gauge controller (CNiS6DH33), USA. The die was
rinsed with acetone, and wiped clean using a paper towel before each use, and when
59
changing raw materials. The pressure was released after five seconds, the piston
removed, and more biomass was loaded and compressed until the pellet had a length of
about 16 mm. This results in a layered structure, similar to pellets obtained by
commercial units, although there are some differences. The most significant difference is
that the lower part of the pellet is pressed repeatedly, and the upper layers are pressed
fewer times, with the top layer being pressed only once. For determination of pelletizing
pressure in the press channel of the pellet mill, FN, the pellets were removed from the die
by removing the backstop and pushing out the pellet at a rate of 2mm/s. The applied
maximum force was logged and FN was calculated based on the pellet surface area.
Figure 4-2 Experimental Setup for Pelletization
Modified Parr Pellet Press 2812 pellet press
Strength Meter Omega LC1001-500
Handle of Pellet Press
Heating Tape over die
Temperature Controller CNiS8DH33
Omega Process Gauge controller (CNiS6DH33)
60
The internal strength of the manufactured pellets was analyzed by compression
testing and determined as the force at break. Pellets 15-17 mm in length and between 6-7
mm in diameter were produced in the single pellet press, stored at a relative humidity of
50% and 20°C for three weeks, and tested under the same conditions. The pellets were
placed on their side in the same material tester as was used for pellet preparation.
Breaking test was also carried out in similar setup. The average force at break was
calculated based on 3 replications per test.
4.5 Storage Behaviour
Here, real environmental effects during the storage of the torrefied products were
monitored. Raw and torrefied biomass samples were kept in particular controlled
environmental conditions. Indoor storage behaviors was monitored by placing samples in
a room and see the weight loss or biodegradable behavior for 48 hours. Humidity of test
room was maintained by humidifier and measured the percentage of moisture uptake by
each biomass.
4.6 Scanning Electron Microscopy (SEM)
In this study, ash samples of 800°C, 900°C and 1000°C were prepared and SEM
images analyses were performed on the ash samples. Morphology of the biomass samples
61
were analyzed using SEM. Samples were coated with gold (20 nm) with a sputter coater
(Model K550; Emitech, Ashford, Kent, England) prior to SEM analysis. SEM
micrographs were taken by using a model S-570 (Hitachi High 115, Technologies Corp.,
Tokyo, Japan) at 10 kV accelerating voltage. Many images were captured by extracting
electrons from a sharp tungsten tip, and formed into a fine beam by a series of
electromagnetic lenses. The beam was directed over the surface of the sample, and the
signals were collected point by point to produce a grayscale image. Resolutions of up to
one nanometer could be produced using the SEM as shown in figure 4.3.
(a) Photograph of SEM Setup
62
(b) Schematic Diagram of Setup
Figure 4.3: SEM Experimental Setup (Hitachi S-570)
4.7 X-ray Diffraction (XRD)
XRD patterns were measured in Bragg-Mrentano geometry in a STOE two
circle goniometer using Cu Kalfa characteristic radiation (Lambda = 1.54178 A)
produced by an ENRAF NONIUS FR 571 rotating anode generator. The x-rays were
detected with a MOXTEK energy sensitive Si detector connected to a single channel
analyzer that was set to accept only the Cu Kalfa photons.
The samples were grounded in an agate mortar and the loose powder was packed into an
aluminum sample holder and then X-Ray diffraction tests were carried out on the ash
samples of the biomass. The XRD test gave the structure of constituent elements,
minerals and ores present in the ash. The patterns were measured in the 2θ interval from
5° to 70°, with a step size of 0.02° and 24 s counting time per step.
63
Chapter V: Results and Analysis
5.1 Poultry Litter Biomass
For the study of non-lignocellulose, poultry litter from a poultry farm located
inside the Ontario was collected. Collected poultry litter was dry, mixture of pellets and
powder form. It also contains small feathers of poultry and bed materials of the poultry
farm. Collected samples were dried as per ASTM standard D1762-84 until samples were
dried on the Thermo Scientific muffle furnace with 2416 controller (model: F48055-60)
for two hours at 105°C and conducted different types of experiments and the following
results were obtained.
5.1.1 Biomass Characterization
Proximate analysis of biomass was carried out in the muffle furnace manufactured
by Thermo Scientific muffle furnace with 2416 controller (model: F48055-60) on raw
and torrefied samples and result obtained were listed in figure 5-1 to 5-3. From the
results, volatile matter decreases as the residence time and torrefaction temperature
increases whereas ash contents and amount of fixed carbon slightly increases as the
residence time and torrefaction temperature increases. The cause of variation is due to the
loss of moisture contents of the biomass as the temperature and residence time increases.
The moisture content of the raw sample was 20.1% and the heating value of it was 10.088
MJ/Kg. Other details of biomass characteristics are listed in section 5.4 of this report.
Variation of volatile matter from 55% to 38%, carbon from 3% to 22% and ash contents
from 22% to 38% is observed as the temperature and residence time increases.
64
Figure 5-1 Volatile Matter vs. Residence Time for Poultry Litter
Figure 5-2 Fixed Carbon vs. Residence Time for Poultry Litter
65
Figure 5-3 Ash Contents vs. Residence Time for Poultry Litter
5.1.2 Torrefaction
The torrefaction of biomass samples at 210°C, 250°C, 275°C and 300°C resulted
in four products of very light brown, light brown, dark brown and black color as shown in
appendix. The color change is mainly attributed to chemical changes of the biomass (Lam
et al., 2011). The loss of dry matter through volatilization during torrefaction was within
5% at 210°C, about 20% at 250°C and above 30% at 280°C and more than 50% at 300
°C. Mass yield and energy yield at 210°C, 250°C, 275°C and 300°C are shown in figure
5-4 to 5-7. From the result, it is observed that lower oxygen concentration has more
energy yield and more mass loss than the torrefaction environment with higher
concentration of oxygen. Higher Heating Value of the torrefied samples with lower
oxygen concentration has higher than the torrefied sample of higher oxygen
66
concentration. HHV varies from 10.00 to 12.40 MJ/Kg with 0-0.6% Oxygen
concentration whereas 10.00-11.90 MJ/Kg with 2.4% oxygen concentration. During the
torrefaction process, sample flue gases were measured by the gas analyzer which shows
percentage contents of different gases like CO, NO, SO2. At temperature 275°C, the
highest CO of 101 ppm and 29 ppm of SO2 were observed. Mass yield and energy yield
figures also displayed error bars with 3.5-4.5% standard deviation.
Figure 5-4 Mass Yield and Energy Yield (%) vs. Temp. (45min residence time)
67
Figure 5-5 % of Mass Yield and Energy Yield vs. Temperature for Poultry Litter
(2.4% Oxygen with 45 minutes residence time)
Figure 5-6 Heating Value vs. Residence Time for Poultry Litter (0% O2)
68
Figure 5-7 Heating Value vs. Residence Time for Poultry Litter (2.4% O2)
5.1.3 Hydrophobicity
Figure 5-8 shows that percentage of moisture absorption decreased by multiple
folds after torrefaction and displayed error bars with 2.5-4.0% standard deviation. The
more the torrefaction temperature and residence time the more the decrease in the
percentage of moisture absorption. Similarly, the moisture increases as the torrefaction
parameters are increased which is caused by the emission of volatiles. The emission of
volatiles becomes more intensive as torrefied temperature and residence time is raised
which lead to increase the porosity and hygroscopic characteristics of biomass. For
testing the hydrophobicity behavior, torrefaction at 275°C for any residence time from 30
to 60 minutes shows the best result among tested results.
69
Figure 5-8 Hydrophobic behavior of Poultry Litter
5.1.4 Storage Behavior
Figure 5-9 shows the moisture uptake behavior of the torrefied poultry
litter at different temperature of 30 minutes residence time at 88% relative humidity of a
storage room and displayed error bars with 3.75-4.75% standard deviation. It shows that
maximum absorption of moisture from the humid environment of the dried raw biomass
was about 16% maximum whereas minimum absorption of moisture from the atmosphere
was performed by the torrefied poultry litter at 250°C and 275°C. But, the moisture
absorption increased when the temperature of torrefaction increases to 300°C because of
high porosity and hygroscopic characteristics of biomass at higher temperature. Hence,
70
for storing purpose, torrefied biomass at temperature of 275°C was found as optimum
option for poultry litter.
Figure 5-9 % of Moisture uptake vs. temperature of torrefied biomass
5.1.5 Optimization by Box Behnken Model
A Box Behnken design was used to analyze the data and model the torrefaction process
in term of mass and energy yields and evaluate the significance of temperature, residence
time and moisture content on mass yield and energy yield were observed. From the result
using response surface model, the optimization of Mass Yield and Energy Yield were
found as:
Where
MC =Moisture Contents in %
TT =Torrefaction Temperature in C
RT =Residence Time in Minutes
71
The strength of effect of three significant process parameters on mass yield was better
revealed by surface plot as shown in figure 5-10 and 5-11 which showed the result of
mass yield varies from 55% to 97% as the moisture varies from 3% to 30% and
temperature varies from 250ᴼC to 300ᴼC according to the residence time variation from
15 minutes to 45 minutes.
Figure 5-10 Cubes of Temperature, Moisture and Residence Time Vs. Mass Yield
72
Figure 5-11 Surface Plots of Temperature, Moisture and Residence Time Vs. Mass
Yield
The strength of effect of three significant process parameters on energy yield was
also better revealed by surface plot as shown in figure 5-11 and 5-12 which showed the
result of mass yield varied from 70% to 98% as the moisture varies from 3% to 30% and
temperature varied from 250°C to 300°C according to the residence time variation from
15 minutes to 45 minutes.
73
Figure 5-12 Cubes of Temperature, Moisture and Residence Time Vs. Energy Yield
Figure 5-13 Surface Plots of Temperature, Moisture and Residence Time Vs.
Energy Yield
74
5.1.6 Scanning Electron Microscopy (SEM)
Figure 5-14 (a), (b) and (c) show the images of the poultry litter ash samples at
800°C, 900°C and 1000°C respectively. At low temperature, the sample contains some
wool like structures which gradually disappears with the increase in combustion
temperature. This may be due to the presence of combustible particles. This wool like
structures are not combustible at low temperature and can only be combusted at high
temperature. Also at high temperature, particles become more brittle as the minerals
matters in the form of crystal increases. Hence the particles become smaller and many
cracks start to show up as the combustion temperature increases. The increase in smooth
surfaces in the samples with the increase in combustion temperature also supports the
relative increase in mineral matters in the samples which is obtained in XRD analysis.
a) 800ᴼC
75
b) 900ᴼC
c) 1000ᴼC
Figure 5-14: SEM for poultry litter ash at 800°C, 900°C and 1000ᴼ C
76
5.1.7 X-Ray Diffraction (XRD)
Figure 5-15 shows the XRD patterns for poultry litter ash prepared at
temperatures 800°C, 900°C and 1000°C. As it is well known that calcium is an important
diet for the poultry and hence it is expected to have some kind of crystalline structure of
calcium compound in the litter samples. The XRD analysis confirm that the basic forms
in poultry litter ash were CaCO3, SiO2 and K2Ca(CO3)2, which determined the nature of
the alkaline extracts in water. Poultry litter ash could be considered as an attractive
material for neutralizing acidic soil and could be a good source of material for cement
production because of the availability of high calcium components. It was also observed
that with the increased in temperature, the intensity of peaks increased.
77
Figure 5-15: XRD pattern for poultry litter ash at different temperature
5.1.8 Summary
The non-lignocellulosic biomass of poultry litter showed that the decrease in the
moisture contents increases in the energy yield and mass yield as the temperature and
residence time increases. Increase in temperature and residence time also makes
hydrophobic to the non-lignocellulosic biomass of poultry litter. From the HHV and
hydrophobicity point of view, torrefaction at 260°C-280°C for residence time of 20-40
minutes was found as the optimum region for poultry litter. Dried and torrefied particles
do not bind well which can be solved by adding small quantities of water. The severity of
INT
EN
SIT
Y
78
torrefaction improves the degree of hydrophobicity. Torrefied poultry litter at 275°C
performs considerable resistance to moisture admission.
SEM confirms the brittleness and smoothness of the surface of the ash at 1000°C
than 800°C and 900°C. The XRD analysis confirmed that the basic forms in poultry litter
ash were CaCO3, SiO2 and K2Ca(CO3)2, which determine the nature of the alkaline
extracts in water and poultry litter ash could be an attractive material for neutralizing
acidic soil and be a good source of material for cement production because of the
availability of high calcium components.
5.2 Willow Pellets
For the study of wood family of lignocellulosic biomass, willow samples, in the
form of mixture of powder and pellets from Ontario, were collected. Collected samples
were dried as per ASTM standard D1762-84 until samples were dried on the Thermo
Scientific muffle furnace with 2416 controller (model: F48055-60) for two hours at
105°C and conducted different types of experiments and the following results were
obtained.
5.2.1 Biomass Characterization
From the results as shown in figures 5-16 to 5-18, volatile matter decreases as the
residence time and torrefaction temperature increases whereas ash contents and amount
of fixed carbon slightly increases as the residence time and torrefaction temperature
increases. The cause of variation is due to the loss of moisture contents of the biomass as
the temperature and residence time increases. The moisture content of the raw sample
was 5.15% and the heating value of it was 16.121 MJ/Kg. Other details of biomass
79
characteristics are listed in section 5.4 of this report. It was also observed that an increase
in the temperature resulted to decrease in solid product and an increase in the volatile
portion. During the torrefaction, mostly water is produced and the energy content of the
volatiles is mainly preserved in the lipids and organics. Torrefaction testing condition,
environment and properties of samples have a substantial effect on the amount of solid
residue and the volatile and gaseous outputs generated during the process of torrefaction.
Figure 5-16 Volatile Matter vs. Residence Time for Willow
80
Figure 5-17 Fixed Carbon vs. Residence Time for Willow
Figure 5-18 Ash Contents vs. Residence Time for Willow
81
5.2.2 Torrefaction
The torrefaction of biomass samples at 210°C, 250°C, 280°C and 300°C resulted
in four products of very light brown, light brown, dark brown and black color. The color
change is mainly attributed to chemical changes of the lignin, i.e. the formation of
chromaphoric groups, mainly the increase of carbonyl groups. The loss of dry matter
(anhydrous weight loss) through volatilization during torrefaction was within 5% at
210°C, about 25% at 250°C and above 35% at 280°C and more than 50% at 300°C. Mass
yield, energy yield and energy density at 210°C, 250°C, 275°C and 300°C are shown in
figure 19 and 20. From the result, it is observed that less Oxygen concentration has more
energy yield and more mass loss than the torrefaction environment with higher
concentration of oxygen. During an inert environment at 250°C, energy yield was near
90% and the mass yield was near 75% which is matching with other finding (Bergman et
al., 2005 and Pimchuai et al., 2010) . At 250°C, maximum energy yield was observed.
Temperature range from 250°C to 285°C is found the optimum temperature range for
perfect torrefaction. Figure 5-20 shows that the energy density continues to increase with
the increase in temperature and residence time. The residence time has insignificant
impact up to 250°C. However, more influence of residence time was seen above 250°C to
300°C. The largest increment ratio of energy density is found to be 1.31 at 300°C for 45
minutes residence time and the lowest ratio is found as 1.02 at 210°C of 15 minutes
residence time. Mainly, moisture and hemicellulose are lost during torrefaction process,
which results in a significant mass loss of raw feedstock without compromising much of
its energy value. Mass yield and energy yield figures also displayed error bars with 4.0-
5.0% standard deviation.
82
Figure 5-19 % of Mass Yield and Energy Yield vs. Temperature for Willow
(Different Oxygen % and 45 minutes residence time)
Figure 5-20 Energy Density variations with Temperature and residence time
83
5.2.3 Higher Heating Value
After the specified residence time, samples were removed from the reactor and
placed in a vacuum desiccator to cool. The samples were grinded in a coffee grinder to
prepare sample for Bomb Calorimeter (Model IKA C-200) by IKA, USA. The basis of
complete calculation for the calorific value was based on ASTM D 240 and ASTM D
5865. From the figure 5-21 and 5-22, there is no significance difference on heating value
at an inert environment and 2.4% oxygen concentration. HHV varies from 16 to 21
MJ/Kg with an inert environment which is increase of about 31% more than raw biomass
whereas increase of about 29% observed with 2.4% oxygen concentration. Results show
that torrefaction temperature has more impact on the increase of HHV than residence
time. Moisture reduction and increase in the carbon concentration could be the main
factor contributing to the increase in the heating value.
Figure 5-21 Heating Value vs. Residence Time for Willow at 0% Oxygen
84
Figure 5-22 Heating Value vs. Residence Time for Willow with 2.4% Oxygen
5.2.4 Hydrophobicity
Figure 5-23 shows that percentage of moisture absorption decreased by multiple
folds after torrefaction and displayed error bars with 2.0 - 3.5% of standard deviation.
The more the torrefaction temperature from 200°C to 300°C and residence time up to 60
minutes, the more the decrease in the percentage of moisture absorption. The lower
moisture could be the result of the tar condensation inside the pores, obstructing the
passage of moist air through the solid, and then avoiding the condensation of water vapor.
Another reason for this could be the polar character of condensed tar on the solid, also
preventing the condensation of water vapor inside the pores. Similarly, the moisture
increases as the torrefaction parameters are increased which is caused by the emission of
volatiles. The emission of volatiles becomes more intensive as torrefied temperature and
residence time is raised which lead to increase the porosity and hygroscopic
85
characteristics of biomass. For the hydrophobicity behavior, torrefaction at 275°C to 285
°C for any residence time from 30 to 60 minutes shows the best result among tested
results at 0 to 2.4% of oxygen concentration. During torrefaction, depolymerization of the
polymers occurs. The hemicellulose is largely destroyed, disabling the greatest moisture
absorption capacity. According to Verhoeff F.(2011), many oxygen groups such as
hydroxyl, carbonyl and carboxyl are removed from the cell wall polymers during
torrefaction, making room for furan-aromatic, aliphatic structures. With this change in
structure, the hydrophilic groups are replaced by hydrophobic groups, so water is rather
rejected from than attracted to the torrefied biomass. Slight increment of moisture uptake
can be observed above 285°C because of high porosity and hygroscopic characteristics of
biomass at higher temperature. From the experiment, it is seen that torrefied willow at
275°C-285°C acts as good storage behavior and most water repellent so can be good for
storage. It becomes quickly dry even if it is immersed in water. The optimum temperature
for the hydrophobicity is found at 275°C.
86
Figure 5-23 % of Moisture absorption vs. temperature of torrefied biomass
5.2.5 Storage Behavior
One of the major concerns of raw biomass handling is the storage and
biodegradability by absorbing water from the atmosphere. It is hydrophilic and easily
decomposed with damp during storage. This can be improved by torrefaction converting
hydrophilic characteristic to hydrophobic character. Figure 5-24 shows the moisture
uptake behavior of the torrefied willow with 3.0-4.5% standard deviation of error bars at
different temperature of 30 minutes residence time at 88% relative humidity of a storage
87
room. It shows that maximum absorption of moisture from the humid environment of the
dried raw biomass is about 4% whereas minimum uptake of moisture from the
atmosphere is performed by the torrefied Willow at 275°C and 300°C. Slight increment
of moisture uptake can be observed above 285°C because of high porosity and
hygroscopic characteristics of biomass at higher temperature. Hence, for indoor or under
the shade storing purpose, torrefied biomass at temperature of 275°C -285°C is found as
optimum temperature for Willow. It absorbs minimum moisture even if it exposes to the
higher atmospheric/surrounding humidity. This is because of hydrophobic nature of
torrefied willow. The samples were stored for one week to observe the biodegradability
of the biomass by placing them in separate plastic bags. After three days, raw biomass is
seen with some biodegradation whereas torrefied at 210°C for 45 minutes was affected
after seven days whereas torrefied biomass above 250°C has not any sign of
biodegradation even after 7 days of storage.
Figure 5-24 % of Moisture uptake vs. temperature of Willow Pellets
88
5.2.6 Pelletization
Torrefaction could have a strong effect on the mechanical stability and
combustion behavior of any types of biomass (Prins et al., 2006). During torrefaction, the
hydrogen bonding hydroxyl groups are removed which causes reduction in the moisture
uptake of the torrefied biomass as the temperature of torrefaction increases. The
differences in composition and water content have also a strong effect on the pelletizing
properties of biomass. The pelletizing pressure in the press is a crucial parameter in
pelletizing processes in terms of process energy consumption and pellet quality (Gilbert
et al., 2009). Pellet pressure increases drastically when comparing raw biomass and
torrefied biomass. This increase is mostly likely attributed to the lack of water and low
hemicelluloses content in the torrefied biomass. Water acts as a plasticizer, lowering the
softening temperature of biomass. At raw stage, the hemicellulose binds lignin and
cellulose and provides flexibility in the plant cell wall. Their degradation in binding
forces makes easier to break into small particles (Arias et at., 2008). The degradation of
hemicellulose, lignin and cellulose can affect pelletizing properties like friction
coefficient and Poisson ratio (Gilbert et al., 2009). During the pelletization, cumulative
pressure in MN/m2
is calculated and plotted in figure 5-25. This shows pressure to
prepare pellets of 6.4mm size of length of 16mm from raw Willow is about 14 MN/m2
which is much less than the pellet prepared from torrefied willow at 275°C for 30
minutes residence time of 81MN/m2. As the torrefaction temperature increases, the
pressure increases sharply.
During the testing of breaking force of the pellets, it is observed that a rapid
decrease in the pellet compression strength of torrefied pellet as the torrefied temperature
89
increased. Minimum force is required to break the torrefied pellets of 275°C and 300°C.
Wolfgang et al.(2011) have tested the compression strength and observed similar
behavior to this result for spruce. They found that the breaking force of their samples
decreased both with treatment temperature and residence time and concluded that
strength loss degradation is connected with the degradation of hemicelluloses for the
biomass. For the Willow, decrease in the water contents and above similar reasons could
be the result for the degradation of strength loss. Both plots (b) and (c) also displayed
error bars with 3.5-5.5% of standard deviation.
(a) 3D plot of Pelletization Pressure (MN/m2) and Breaking Force (N)
90
(b) Pelletization Pressure (MN/m2) vs. Torrefaction Temp at 45 min residence time
(c) Breaking Force (N) vs. Torrefaction Temperature at 45 minutes residence time
Figure 5-25 Pressure for making Pelletization and Force for Breaking Pellets
91
5.2.7 Scanning Electron Microscope (SEM)
The large content of potassium and chlorine in biomass greatly increases the
deposit formation and corrosion of the thermal power plants, compared to coal fired
boilers. It has been verified that the alkali species which cause the bed agglomeration
come from the biomass ash. So, study on the behaviors of alkali species in biomass ash is
crucial for understanding the formation mechanisms of agglomerates and coating layers.
The ash block can maintain a fixed shape and presents a little compression strength due
to the sintering. Figure 5-26(a), (b) and (c) show the images of the Willow ash samples at
800°C, 900°C and 1000°C respectively. At low temperature, the sample contains some
wool like structures which gradually disappears with the increase in combustion
temperature. This may be due to the presence of combustible particles. This wool like
structures are not combustible at low temperature and can only be combusted at high
temperature. The surface has irregular structure which signifies the process has not been
enough for complete coalescence of the ash into spherical particles. Some of the particles
were long, fiber like agglomerates still resembling the original wood fiber structure. The
surfaces of the particles were usually formed in small sizes which had often sintered
together forming chain-like agglomerate structures. The primary particles were mainly
cotton shaped but also cornered ones were seen like crystalline structure. This signifies,
the ash particles does not contain significant amount of unburned samples. Also at high
temperature, particles become more brittle as the minerals matters in the form of crystal.
Hence the particles become smaller and many cracks start to show up as the combustion
temperature increases. Because of the presence of high Silicon dioxide, Magnesium
dioxide and other alkalis, the structure contains smooth surface which represents the
92
presence of metallic components in the ash sample. The increase in smooth surfaces in
the samples with the increase in combustion temperature also supports the relative
increase in mineral matters in the samples which is also obtained in XRD analysis and
ash analysis.
(a) SEM for Willow ash at 800C
93
(b) SEM for Willow ash at 900C
(C) SEM for Willow ash at 1000C
Figure 5-26 SEM for Willow at 800°C, 900°C and 1000°C Ash
94
5.2.8 X-ray Diffraction (XRD)
X-Ray diffraction tests were carried out on the ash samples of willow as
mentioned in 5.1. The major components of the Biomass are quartz (SiO2), anhydrite
(CaSO4), iron sulfite (FeSO3), Potassium Aluminum Silicate (KAlSiO4), Calcium
Aluminum Silicate (CaAl2SiO6) and hematite (Fe2O3) (Suramya DFM, 2012) . The ashes
were analyzed with X-Ray Diffraction to determine the crystalline components. Figure 5-
27 shows the XRD patterns for willow ash prepared at temperatures 800, 900 and
1000°C. The peaks at 21, 28, 32 and 36 of 2θ represent the crystalline structure of quartz,
which shows the height of the peak increases with the increase in the temperature. This
can be attributing to the increase in relative amount of crystalline structure in the sample
with the increase in combustion temperature. The XRD analysis confirm that the basic
forms in Willow ash are SiO2, CaSO4 and K2Ca(CO3)2, which determine the nature of the
alkaline extracts in water and Willow ash. The ash fusion temperature of willow is about
1100°C -1300°C which is caused due to the presence of alkalis. This obviously limits the
temperature of the practical furnace of a boiler.
95
Figure 5-27: XRD pattern for Willow ash at different temperature
5.2.9 Summary
The optimum torrefaction treatment temperature was found at 275°C for
hydrophobic characteristics and storage behavior of willow. Because of depolymerization
of the polymers during torrefaction, the hemicellulose is largely ruined leading towards
disabling the largest moisture absorption capacity. The results showed that torrefaction at
higher temperature and residence time had a positive effect on the hydrophobic behavior
by showing smaller amount of water assimilation by the torrefied willow. Pellet pressure
increased by 3-7 folds to prepare pellet from the torrefied products above 250°C. It is not
96
preferable to have pelletization of willow after the treatment at 285°C. Torrefied willow
pellets are brittle in nature which reduces the grinding energy and make efficient burning
during the combustion process at the thermal plant. Pellets made from torrefied material
have a lower density than pellets made from raw samples. It takes more energy to make
pellets from torrefied than from raw willow. Dried and torrefied particles do not bind
well which can be solved by adding small quantities of water or binders. The severity of
torrefaction increases the degree of hydrophobicity. Torrefied willow at 250°C-285°C
performs considerable resistance to moisture admission. It was observed that HHV
increased by about 31% as the temperature and residence time increases whereas there is
insignificance effect on HHV observed by increasing Oxygen concentration by 2.4%.
SEM confirmed the brittleness and smoothness of the surface of the ash at 1000°C than
800°C and 900°C. The ash fusion started from 1115°C temperature for willow because of
presence of alkalis. The XRD analysis confirmed that the basic forms in willow ash were
SiO2, CaCO4 and K2Ca(CO3)2, which determined the nature of the alkaline extracts in
water and willow ash could be an attractive material for neutralizing acidic for soil and
could be a good source of material for farming and cement production because of the
availability of high silica and magnesium components.
5.3 Oat Pellets
For the study of agricultural lignocellulosic biomass, oat samples from Ontario
were collected. Collected oat was dry and in the form of mixture of powder and raw
pellets form. Collected samples were dried as per ASTM standard and conducted
different types of experiments and the following results were obtained.
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5.3.1 Biomass Characterization
From figures 5-28 to 5-30, the moisture content of the raw sample was 7.74%. It
was also observed that an increase in the temperature resulted to decrease in carbon
products and decrease in volatile portion. The product of volatile matter was found from
68-74% which may be due to the limited devolatization and carbonization of
hemicellulose component till the temperature reaches 250°C whereas as the temperature
above 250°C started the decomposition of lignin and cellulose so decrease in volatile
matter was seen between 250°C-300°C. Volatile matter variation was in the range of 1-
10% with the variation of temperature and residence time. This was also the reason for
the poor moisture contents above 250°C. These results are in agreement with other
researchers (Rosillo-Cakke F, 2007; Rousset et al.,2011; Chen and Kuo, 2011; Tumuluru
et al., 2011).
Figure 5-28 Volatile Matters vs. Residence Time for Oats
98
Figure 5-29 Fixed Carbons vs. Residence Time for Oats
Figure 5-30 Ash Contents vs. Residence Time for Oats
99
5.3.2 Torrefaction
The torrefaction of biomass samples at 210°C, 250°C, 275°C and 300°C resulted
in four products of very light brown, light brown, dark brown and black color as shown in
Appendix B. The color change may be mainly attributed to chemical changes of the
lignin, i.e. the formation of chromaphoric groups, mainly the increase of carbonyl groups.
The weight loss of dry matter through volatilization during torrefaction was within 3% at
210°C, about 40% at 250°C and above 55% at 275°C and more than 55% at 300°C. Mass
yield, energy yield and energy density at 210°C, 250°C, 275°C and 300°C are shown in
figure 5-31 and 5-32. From the result, it was observed that less Oxygen concentration had
more energy yield and less mass loss than the torrefaction environment with higher
concentration of oxygen. During an inert environment at 250°C, energy yield was near
87% and the mass yield was near 71% at 30 minutes residence time which is matching
with results of other researchers (Woolf et al., 2010; Aries et al., 2008; Rousset et al.,
2006). At 250°C, maximum energy yield was observed. Temperature range from 250°C
to 275°C is found the optimum temperature range for perfect torrefaction. Figure 5-32
showed that the energy density continued to increase with the increase in temperature and
residence time and error bars of positive standard deviation up to 4.5%. The residence
time has insignificant impact up to 250°C. However, more influence of residence time
was seen above 250°C to 300°C. The largest increment ratio of energy density was found
to be 1.44 at 300°C for 45 minutes residence time and the lowest ratio was found as 1.00
at 210°C of 15 minutes residence time. Mainly, moisture and hemicellulose are lost
during torrefaction process, which results in a significant mass loss of raw feedstock
without compromising much of its energy value.
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Figure 5-31 % of Mass Yield and Energy Yield vs. Temperature for Oats
(Different Oxygen % and 45 minutes residence time)
Figure 5-32 Energy Density variations with Temperature and residence time
101
5.3.3 Higher Heating Value (HHV)
From the figure 5-33 and 5-34, there was no significance difference on heating
value at an inert environment and 2.4% oxygen concentration. HHV varies from 16 to 24
MJ/Kg with an inert environment which was increase of about 44% more than raw
biomass whereas increase of about 42% observed with 2.4% oxygen concentration.
Results showed that torrefaction temperature had more impact on the increase of HHV
than residence time. Moisture reduction and increase in the carbon concentration could be
the main factor contributing to the increase in the heating value.
Figure 5-33 Heating Value vs. Residence Time for Oats at 0% Oxygen
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Figure 5-34 Heating Value vs. Residence Time for Oats with 2.4% Oxygen
5.3.4 Hydrophobicity
Figure 5-35 showed that percentage of moisture absorption decreased by multiple
folds after torrefaction and displayed error bars with 2.75-4.0% standard deviation. The
more the torrefaction temperature from 200°C to 300°C and residence time up to 60
minutes, the more the decrease in the percentage of moisture absorption. The lower
moisture could be the result of the tar condensation inside the pores, obstructing the
passage of moist air through the solid, and then avoiding the condensation of water vapor.
Similarly, it was observed that the moisture absorption increases as the torrefaction
parameters were increased. For the hydrophobicity behavior, torrefaction at 270°C to 285
°C for any residence time from 30 to 60 minutes showed the optimum result among
tested data. The optimum temperature for the hydrophobic behavior for oats was found at
270°C. Raw oats absorbed more than 70% of moisture whereas torrefied oats at 270°C
103
absorbs only about 2% of moisture. According to Verhoeff F.(2011), many oxygen
groups such as hydroxyl, carbonyl and carboxyl are removed from the cell wall polymers
during torrefaction, making room for furan-aromatic, aliphatic structures. With this
change in structure, the hydrophilic groups are replaced by hydrophobic groups, so water
is rather rejected from than attracted to the torrefied biomass. Slight increment of
moisture uptake could be observed above 285°C because of high porosity and
hygroscopic characteristics of biomass at higher temperature. From the experiment, it is
seen that torrefied oats at 270°C-285°C acts as optimum storage behavior and most water
repellent so can be good for storage. It became quickly dry even if it was immersed in
water.
Figure 5-35 Moisture absorption vs. temperature of torrefied biomass
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5.3.5 Storage Behavior
One of the major concerns of raw biomass handling is the storage and
biodegradability by absorbing water from the atmosphere. It is hydrophilic and easily
decomposed with damp during storage. This can be improved by torrefaction converting
hydrophilic characteristic to hydrophobic character. Figure 5-36 showed the moisture
uptake behavior of the torrefied oats with 2.5-5.0% of standard deviation of error values
at different temperature of 30 minutes residence time at 88% relative humidity of a
storage room. It showed that maximum absorption of moisture from the humid
environment of the dried raw biomass was about 10% whereas minimum about 2%
uptake of moisture from the atmosphere was performed by the torrefied oats at 275°C and
300°C. Slight increment of moisture uptake could be observed above 285°C because of
high porosity and hygroscopic characteristics of biomass at higher temperature. Hence,
for indoor or under the shade storing purpose, torrefied biomass at temperature of 275°C
-285°C was found as optimum temperature for oats. It absorbed minimum moisture even
if it was exposed to the higher atmospheric/surrounding humidity. This may be because
of hydrophobic nature of torrefied products. The samples were stored for one week to
observe the biodegradability of the biomass by placing them in separate plastic bags.
After three days, raw biomass was seen with some biodegradation whereas torrefied at
210°C for 45 minutes was affected after seven days whereas torrefied biomass above
250°C had not any sign of biodegradation even after 7 days of storage.
105
Figure 5-36 % of Moisture uptake vs. temperature of Oats Pellets
5.3.6 Pelletization
During the pelletization, cumulative pressure in MN/m2
was calculated and
plotted in figure 5-37. This showed pressure to prepare pellets of 6.4 mm size of length of
8-16 mm from raw oat was about 9 MN/m2
which was much less than the pellet prepared
from torrefied oats at 275°C for 45 minutes residence time of 65 MN/m2.
During the testing of breaking strength of the pellets, it was observed that a rapid
decrease in the pellet compression strength of torrefied pellet as the torrefied temperature
increased. Minimum force 51N and 7N were required to break the torrefied pellets of
275°C and 300°C respectively whereas 1101N was required to break the raw pellets. For
the oats, decrease in the water contents and degradation of lignin and hemicellulose could
be the reasons for getting such result for the degradation of strength loss. Both figures
displayed error bars up to 5% standard deviation.
106
(a) Pelletization Pressure vs. Torrefaction Temperature at 45 min residence time
(b) Breaking Force vs. Torrefaction Temperature at 45 minutes residence time
Figure 5-37 Pressure for making Pelletization and Force for Breaking Pellets
107
5.3.7 Scanning Electron Microscope (SEM)
Fig. 5-38 showed a close-up view of ash sample. The ash block can maintain a
fixed shape and presents a little compression strength due to the sintering. Researcher
(Skrifvars et al., 1997) characterized the sintering tendency of ten biomass ashes and
classified the ash components into three groups: simple alkali salts, silicates and the rest
non-melt. We could see that the fusible compounds melt and coat the surface of ash
particles during combustion. The spot analyses indicated that these melts were rich in K
or Na. From the result of ash fusion analysis, the ash fusion temperature of oats started
from 1279°C. The alkali silicates formed during combustion can melt and coat the
surface of ash particles at high temperature. In addition, the large-sized ash particles may
increase the amount of melts on local surface of bed particle and may act as the necks for
the agglomerate formation. So, the large- and small-sized ash particles may play the
different roles in the bed agglomeration.
Figure 5-38 (a), (b) and (c) showed the images of the oats ash samples at 800°C,
900°C and 1000°C respectively. At low temperature, the sample contained some wool
like structures which gradually disappears with the increase in combustion temperature.
This may be due to the presence of combustible particles. This broken wood like
structures was not combustible at low temperature and can only be combusted at high
temperature. The surface had irregular structure which signified the process had not been
enough for complete coalescence of the ash into spherical particles. Some of the particles
were long, fiber like agglomerates still resembling the original oats fiber structure. At
900°C, the ash metallic components were formed and hole like spots were observed. The
primary particles were mainly cotton shaped but also cornered ones were seen like
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crystalline structure. This signified, the ash particles did not contain significant amount of
unburned samples. Also at high temperature, particles became more brittle as the
minerals matters in the form of crystal. Hence the particles became smaller and many
cracks start to show up as the combustion temperature increases. Because of the presence
of high Silicon dioxide, Magnesium dioxide and other alkalis, the structure contained
smooth surface which represented the presence of metallic components in the ash sample.
The increase in smooth surfaces in the samples with the increase in combustion
temperature supported the relative increase in mineral matters in the samples which was
also obtained from ash analysis.
(a) SEM for Oats ash at 800°C
109
(b) SEM for Oats ash at 900°C
(c) SEM for Oats ash at 1000°C
Figure 5-38 SEM for Oats at 800°C, 900°C and 1000°C Ash
110
5.3.8 X-ray Diffraction (XRD)
Figure 5-39 shows the XRD patterns for oats ash prepared at temperatures 800°C,
900°C and 1000°C. The peaks at 25 and 45 of 2θ represent the crystalline structure of
quartz, which shows the highest peak is observed at 900°C and then followed by 800°C
and 1000°C. The XRD analysis confirm that the basic forms in oats ash are SiO2, CaSO4
and K2Ca(CO3)2, which determine the nature of the alkaline extracts in water and oats
ash. The ash fusion temperature of oats is about 1250°C -1350°C which is caused due to
the presence of alkalis. This obviously limits the temperature of the practical furnace of a
boiler.
Figure 5-39: XRD pattern for Oats ash at different temperature
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5.3.9 Summary
Torrefied products produced from oat were characterized in the view of
combustion applications. The optimum treatment temperature was found at 270°C for
hydrophobic characteristics and storage behavior of oats. Because of depolymerization of
the polymers during torrefaction, the hemicellulose was largely ruined leading towards
disabling the largest moisture absorption capacity. The results showed that torrefaction at
higher temperature and residence time had a positive effect on the hydrophobic behavior
by showing smaller amount of water assimilation by the torrefied oats. Pellet pressure
increased by 4-7 folds to prepare pellet from the torrefied products above 250°C. It is not
preferable to have pelletization of biomass after the treatment at 285°C. Torrefied pellets
were brittle in nature which could reduce the grinding energy and make efficient burning
during the combustion process at the thermal plant. Pellets made from torrefied material
had a lower density than pellets made from raw samples. It took more energy to make
pellets from torrefied than from raw oats. Dried and torrefied particles did not bind well
which could be solved by adding small quantities of water or binders. The severity of
torrefaction increases the degree of hydrophobicity. Fuels made from torrefied oats at
250°C-285°C perform considerable resistance to moisture admission. It was observed
that HHV increased by about 43% as the temperature and residence time increases
whereas there was insignificant effect on HHV observed by increasing oxygen
concentration by 2.4%. SEM confirmed the brittleness and smoothness of the surface of
the ash at 1000°C than 800°C and 900°C. The ash fusion started from 1279°C
temperature for oats because of presence of alkalis. The XRD analysis confirmed that the
basic forms in oats ash are SiO2, Al2O3 and K2O which determine the nature of the
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alkaline extracts in water and oats ash could also be an attractive material for neutralizing
acidic for soil and could be a good source of material for farming and cement production
because of the availability of high silica and magnesium components like other
lignocellulosic biomass.
5.4 Comparative Analysis
5.4.1 Biomass Characterization
a) Proximate Analysis of Raw Biomass
The results of the proximate analysis are listed in the following Table 5-1 which indicated
that poultry litter had the highest moisture contents and willow pellets had the lowest.
The ash contents on the poultry litter had more than 20% with minimum carbon contents
which consequently made the lowest heating value of it.
Table 5-1 Proximate Analysis of Raw Biomass
Sample
Moisture
(%)
Volatile Matter
(%) Ash Contents (%) Fixed Carbon (%)
Poultry
litter 20.1 54.29 22.28 3.33
Willow
Pallets 5.15 73.18 11.45 10.22
Oat Pallets 7.74 74.28 5.64 12.34
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b) Ultimate Analysis:
Results of the ultimate analysis of the raw biomass were given in the Table 5-2.
All of raw biomass contained more than 40% of carbon, more than 5% of hydrogen but
poultry litter had the lowest oxygen less than 6% and the highest sulfur with more than
1%.
Table 5-2 Ultimate Analysis and Heating Value of Raw Biomass
Components
Poultry
Litter Willow Pallets Oat Pallets
Carbon 43.30% 50.65% 52.23%
Hydrogen 6.62% 5.86% 6.59%
Nitrogen 5.72% 0.52% 0.62%
Sulphur 1.15% 0.44% 0.29%
Oxygen 5.95% 24.07% 33.98%
Heating Value
MJ/Kg 10.88 16.12 16.41
From the figure 5-40, the highest components in all biomass were observed as
carbon with more than 40% whereas minimum component was Sulfur with less than 1%.
Lignocellulosic biomass contained more carbon than non-lignocellulosic which could be
because of photosynthesis (carbon capture nature) of biomass. Poultry litter has more
sulfur and nitrogen whereas it contained minimum oxygen. Oats contained maximum
carbon and oxygen among all. All biomass has almost similar percentage of hydrogen.
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Figure 5-40. Comparative Study of Ultimate Analysis of different Biomass
c) Ash Fusion Temperature
From figure 5-41, Poultry litter had highest initial deformation temperature of
about 1400°C whereas willow had the lowest at 1150°C. Oats had about 1300°C. This
could be because of higher alkali contents in the lignocellulosic biomass and high amount
of calcium components in the poultry litter.
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Figure 5-41. Comparative Study of Ash Fusion Temperature of different Biomass
d) Elemental Analysis
From figure 5-42, it was observed that Poultry Litter contained CaO of about 65%
(daf) whereas willow and oats contained more than 60% (daf) of SiO2. This may be due
to high calcium contents in the food of poultry and high silica contents in the soil of
Ontario for the lignocellulosic biomass. In the second components, poultry litter contains
more than 18 % of P2O5, Willow contains 20% of MgO and 15% of AlO3 which
symbolized that woody biomass had more magnesium components and agricultural
biomass contained more aluminum. Similarly, all biomass contained alkalis K2O and
Na2O.
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Figure 5-42. Comparative Study of Elemental Analysis of different Biomass
5.4.2 Torrefaction
a) Mass Yield
From figure 5-43, poultry litter lost less weight than other two lignocellulosic
biomasses with the increase in temperature and residence time and error bars showed 3.0-
4.5% variation on standard deviation. This was due to moisture loss of all the biomasses
and fast devolatilisation of hemicellulose of lignocellulosic of biomasses. Most severe
was the agricultural residue oats because of the loose bonding of the hemicellulose
components than willow.
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Figure 5-43. Comparative Study of Mass Yield of Poultry Litter, Willow and Oat
Pellets at different temp with 45 minutes residence time
b) Energy Yield
From figure 5-44, maximum energy yield was seen on the sample of poultry litter
with more than 80% because of its high mass contents and low heating values whereas
the oats had the lowest energy yield with about 60%. Mass decomposition of agricultural
residue was found the fastest than willow and poultry litter. This is due to lower contents
of calcium and silica in oats than other biomass. Oats has the weak bonding of
hemicellulose than willow so faster evaporation and devolatilisation occurs than other
biomasses. Error bars showed 3.5-5.5% of standard deviation.
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Figure 5-44. Comparative Study of Energy Yield of Poultry Litter, Willow and Oat
Pellets at different temp with 45 minutes residence time
c) Higher Heating Value
From figure 5-45, oats had highest heating value of about 24 MJ/Kg and poultry
litter had the lowest with 12 MJ/Kg while willow had about 22 MJ/Kg. It was seen that
higher heating values increased with temperature. The highest heating value of all the
samples were achieved at 300°C because of the removal of moisture and devolatization
of hemicellulose of woody biomass. However, no significant variation of heating values
was observed after the 275°C. This signifies higher heating value with torrefaction
temperature at 250°C -275°C can be justified. Error bars showed 3.0-5.0% of standard
deviation.
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Figure 5-45. Comparative Study of Heating Values of different Biomass with temp
5.4.3 Hydrophobicity
From figure 5-46, it was observed that oats had the highest moisture absorption
capacity than other two samples. Torrefied oats at 250°C absorbed about 35% whereas
other two samples absorbed only about 7%. All samples performed the minimum
absorption at torrefaction temperature 275°C out of which poultry litter showed the best
performance of hydrophobicity. With the increase of temperature beyond 285°C,
devolatization of hemicellulose and lignin occurred which consequently increased the
porosity of the torrefied biomass and resulted little more absorption of moisture. Hence,
270-285°C was found optimum temperature range for torrefaction for poultry litter, oats
and willow. It also displayed error bars with 2.5-4.5% of standard deviation.
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Figure 5-46. Comparative Study of Hydrophobicity of Poultry Litter, Willow and
Oat at different temp with 45 minutes residence time
5.4.4 Storage Behavior and Moisture Uptake
From the figure 5-47, the optimum moisture uptake was observed on all of the
samples with 4.25-5.0% standard deviation on error bars. Willow and oats performed the
optimum moisture uptake at 275°C. Storing of torrefied biomass at 275°C was found as
optimum. Torrefaction decomposes the hydro-oxy components from the biomass and
make more hydrophobic in nature. This effect could be more severe in the lignocellulosic
biomass than non-lignocellulosic biomass.
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Figure 5-47. Comparative Study of Storage Behavior of Poultry Litter, Willow and
Oat Pellets at different temp with 45 minutes residence time
5.4.5 Ash Analysis
Elemental ash analysis was done based on the ASTM standard and find from
figure 5-48 that Poultry litter contained excessive amounts 65.17% of MgO and 17.46%
of P2O5 whereas only 9.4% and 5.59% of MgO and 1.74% and 4.54% of P2O5 in willow
and oats respectively. Lignocellulosic biomass willow and oats contains more than 60%
of SiO2. Willow contains 20.7% of MgO and 9.47% of Al2O3 whereas oats contains
15.62% of Al2O3 and 9.85% of K2O. The major compounds in poultry litter identified in
the ash are CaO (65%), P2O5 (17.5%) and K2O (6.4%), which falls into the category of
biomass ash with rich in calcium, phosphorous. The concentration of alkali metals
sodium oxide/Na2O, and potassium oxide/K2O were higher in poultry litter than in
willow and oats, indicating that poultry litter is a more challenging fuel than
lignocellulosic biomass for combustion applications. High alkali content, especially in
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conjunction high chloride levels, results in a high potential for slagging, fouling,
particulate emissions, and corrosion. Silica salts formed by K and Na show strong
tendencies to become sticky and form slag on the hot surfaces of the combustion
equipment and the boiler. Maintaining low combustion temperatures will also help in
controlling alkali-related slagging and fouling problems.
Figure 5-48. Comparative Study of Elemental Analysis of Poultry Litter, Willow
and Oat Pellets at different temp with 45 minutes residence time
From figure 5-49, it is observed that out of tested three samples, only poultry litter
contained very small amount of sulfur. Lignocellulosic biomass samples of willow and
oats had lower ash initial deformation temperature 1115°C and 1279°C respectively than
non-lignocellulosic biomass poultry litter at 1421.67°C. This may be due to higher
contents of alkalis in the lignocellulosic biomass than non lignocellulosic biomass. The
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high ash content in poultry litter may require high-volume ash-handling equipment and
more attention to particulate removal, slagging, and fouling while used in a
combustor/boiler.
Figure 5-49. Comparative Study of Ash Fusion Temperature of Poultry Litter,
Willow and Oat Pellets at different temp with 45 minutes residence time
5.4.6 Summary
After torrefaction, the maximum heating value of 24 MJ/Kg for oats, 22 MJ/Kg
for willow and 12 MJ/Kg for poultry litter were found. Mass yield varied from 42%-91%
whereas energy yield varied from 61%-89% with operating temperature and residence
time. Oats showed the fastest mass and energy yield whereas poultry litter showed the
least. For hydrophobicity and moisture uptake, the optimum temperature were found at
285°C for willow, 270°C for oat and 275°C for poultry litter at 45 minutes of residence
time. It was observed that all torrefied products showed hydrophobic character and
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remain unaffected from biodegradation when they were immersed in water after
torrefaction.
5.5 Errors and Repeatability Test
Each test was carried out at least for three times in each experiment. During the
torrefaction, the oxygen inert environment was measured by gas analyzer. The accuracy
of the analyzer was 0.5% of full scale volume and the resolution was 0.01% of volume.
During the control of the oxygen concentration of the torrefaction environment, the
nitrogen gas was released using flow meter which had the accuracy of 0.5% in the flow
volume. The measurement of repeatability was carried out during the 2.4% oxygen two
times and measured 2.4%±0.0069 and 2.39%±0.018 at two different dates of test. This
may be due the environmental condition, human activities (opening and closing moment)
and technical variation of the equipment itself.
During the hydrophobicity and moisture uptake, two similar experiments were
performed for different sample in similar condition and the results are presented in the
appendix G.
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Chapter VI: Conclusions and Recommendations
6.1 Conclusions
Poultry litter (non-lignocellulosic biomass), oat and willow wood (lignocellulosic
biomass) samples from Ontario were collected and torrefied in a locally designed and
fabricated lab-scale reactor. A number of torrefaction experiments were conducted to
characterize different samples at different torrefaction temperatures, ranging from 200°C
to 300°C, residence time ranging from 15 minutes to 60 minutes, and different oxygen
concentrations (from about 0% up to 2.4%) in the torrefaction chamber. Results indicated
that the effect of oxygen concentration on the mass loss, energy loss and higher heating
value were not significant.
During torrefaction, both lignocellulosic and non-lignocellulosic biomass showed
a decrease in moisture content, increase in HHV and decrease in weight as the
temperature and residence time increased. Increase in temperature and residence time
also improved the hydrophobic characteristics of both biomasses. From the HHV and
hydrophobicity point of view, torrefaction at a temperature of 260°C-285°C for a
residence time of 20-40 minutes is found to be the optimum condition for all three
biomasses tested.
After torrefaction, a maximum higher heating value of 24 MJ/Kg for oats, 22
MJ/Kg for willow and 12 MJ/Kg for poultry litter were obtained. Mass yield varied from
42- 91% while energy yield varied from 61- 89% at different operating temperatures and
residence times. Oats showed the fastest mass and energy yields whereas poultry litter
showed the least. For hydrophobicity and moisture uptake, the optimum temperatures
found were 285°C for willow, 270°C for oat and 275°C for poultry litter at 45 minutes of
126
residence time. It was observed that all torrefied products showed hydrophobic
characteristics and remained resistant to moisture re-absorption when they were
immersed in water after torrefaction.
Due to the depolymerization of the polymers during torrefaction, the
hemicellulose was largely removed from the biomass, causing the loss of moisture
absorption capacity. The results showed that torrefaction at higher temperatures and
residence times had a positive effect on the hydrophobic behavior by showing smaller
amount of water assimilation by the torrefied lignocellulosic products. Pelletizing
pressure increased by multiple folds to make pellets from the torrefied willow and oats at
about 250°C. Hence, it took more energy to make pellets from torrefied lignocellulosic
biomass than from raw biomass. It was not preferable to have pelletization of willow and
oats after the treatment at 285°C. Dried and torrefied particles do not bind well, which
can be solved by adding small quantities of water or binders. Torrefied pellets are brittle
in nature which reduces the grinding energy and makes efficient burning during the
combustion process at the thermal plant. Pellets made from torrefied material had a lower
density than pellets made from the raw samples. The level of hydrophobicity was found
to increase with the degree of torrefaction.
SEM analysis of the biomass ash confirmed the brittleness and smoothness of the
surface of the ash at 1000°C rather than at 800°C or 900°C. The XRD analysis indicated
that the basic constituents in poultry litter ash were CaCO3, SiO2 and K2Ca(CO3)2,
whereas SiO2, Al2O3 and K2O in oats and willow ash. These determine the nature of the
alkaline extracts in water. Biomass ash is an attractive material for neutralizing acidic soil
and could be a good source of material for cement production because of the availability
127
of high calcium components. The ash fusion starts from 1115°C temperature for willow,
1279°C for oats, because of the presence of alkalis, and 1421°C for poultry litter.
6.2 Recommendations
Torrefaction has been identified as a key biomass pretreatment/upgrading process
that can offer significant advantages in terms of improvements in storage stability,
hydrophobicity and chemical properties important for thermochemical processes such as
co-firing with coals and gasification. However, more advanced design of commercial
torrefiers are yet to be developed. Multipurpose torrefier and gasifier appears to offer
promise for optimized processing of biomass. From the literature review, followings are
the gaps still available in the torrefaction research:
1) Optimization on the degradation of hemicellulose, lignin and cellulose during the
process of torrefaction.
2) Molecular level understanding during the process of torrefaction like molecular
breaking energy.
3) Study on the changing of colors during torrefaction using advanced device like
colorimeter.
4) Design and development of integrated processes of torrefier, combustion and
gasification for potential applications.
5) Study of the storage behavior of torrefied products in terms of off-gassing and
spontaneous combustion at different temperature.
6) Life cycle assessment of the torrefied biomass in the application of electrical
power generation.
128
7) Study on the explosibility of torrefied biomass and its measures to rectify it.
8) Study of torrefaction and pelletization integrated process
9) Design of economical commercial torrefier and its challenges
10) Economic analysis on the use of torrefied biomass for co-firing with coal or
replacing coal from the electrical power plants.
129
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Chapter VIII: Appendix
Appendix A: Photographs of Willow Pellets
Raw Pellets:
Pellets at 200°C Pellets at 250°C
Pellets at 275°C
Pellets at 300°C
142
Appendix B: Photographs of Oats Pellets
Raw Pellets:
Pellets at 200°C
Pellets at 250°C
Pellets at 275°C
Pellets at 300°C
Biodegradable Raw Oats
Appendix C: Methods and Equipment used in Characterizing Biomass
Proximate Analysis Ultimate Analysis
Higher Heating Value
(HHV) and Ash analysis
Parameter MC AC VM FC C, H, N S O HHV Ash Analysis
Method ASTM
E871
ASTM
E1755
ASTM
D3175
ASTM
E872
ASTM
D5375
ASTM
D4239
ASTM
E870
ASTM
E711
ASTM
D6349
Equipment
Used
Muffle
furnace
Muffle
Furnace
Muffle
Furnace
calculate
d value
Leco
CHN-
1000
Elemental
Analyser
Leco SC-
432
Elemental
Analyser
calculated
value
C-200
Bomb
Calorimeter
Muffle
furnace,
SEM (S-570-
Hitachi High
115) and
XRD (Bragg-
Mrentano
geometry )
Results from
experiment
C=52.2%
H=6.59%
N=0.62%
0.29% 33.98% See: Table 2
Appendix D: Photograph of Experimental Setup for Torrefaction
145
Appendix E: Gas Analyzer
146
Appendix F: Ultimate Analysis, Ash Fusion Temp and Ash Elemental Analysis
Table F.1: Ultimate Analysis of different biomass samples
Components Poultry Litter Willow Pallets Oat Pallets
Carbon 43.30% 50.65% 52.23%
Hydrogen 6.62% 5.86% 6.59%
Nitrogen 5.72% 0.52% 0.62%
Sulphur 1.15% 0.44% 0.29%
Oxygen 5.95% 24.07% 33.98%
Table F.2: Chlorine, Ash Content and Ash Fusion temperatures of different
Biomasses in dry basis
Particular
Poultry
Litter Willow Pellets Oat Pellets
Chlorine (%) 0.07 0 0
Ash Fusion Temperature (°C)
Initial Deformation (IT) (°C) 1421.67 1115 1279
Softening Temperature (ST)
(°C) 1433.89 1171 1303
Hemispherical Temperature
(HT) (°C) 1437.78 1258 1338
Fluid Temperature (FT) (°C) 1440 1292 1354
147
Table F.3. Elemental Analysis of Poultry Litter in % Ash Basis
Components Poultry Litter Willow Pellets Oat Pellets
SiO2 2.69 67.77 60.68
TiO2 0.02 0.44 0.61
Al2O3 0.31 9.47 15.62
Fe2O3 0.57 2.89 0.4
MnO 0.33 0.11 0.09
MgO 4.53 20.7 2.06
CaO 65.17 9.4 5.59
K2O 6.36 3.53 9.85
Na2O 2.48 2.44 0.47
P2O5 17.46 1.74 4.54
Cr2O3 0.03 0.03 0.07
148
Appendix G: Error and Repeatibility Tests
G.1 Error
Errors observed during the testing of characterization of biomasses are listed
which are due to the use of high precision instruments.
Table G-1 Systematic errors
S/N Name of the instrument Accuracy from
manufacturer
Unit
1 Weighing Machine 0.0001 g
2 Temperature and Process Controller ±0.5 ᴼC
3 Flue Gas Analyzer for Oxygen 0.01 Vol %
4 Mass Flow Controller ±1.0 %
5 Water volumetric flask 1 ml
6 Humidity meter ±0.75 %
For the systematic error calculation, procedures with following equations were
taken from http://teacher.pas.rochester.edu/PHY_LABS/AppendixB/AppendixB.html
link and used for the error calculations.
(G.1)
(G.2)
(G.3)
(G.4)
(G.5)
(G.6)
149
(G.7)
Table G-2 Maximum Systematic error
S/N Particular Systematic Error Unit
1 Mass Yield 0.15 %
2 Energy Yield 0.10 %
3 Fixed Carbon 0.1 %
4 Volatile Matter 0.05 %
5 Ash 2.0 %
G.2 Repeatability Test
The accuracy of any lab tests are basically depended on the variability of the data
recorded equipment setup and measuring instruments. The characterizations,
hydrophobicity and moisture uptake experiments involve lots of uncertainty because of
the manual operation for running the experiment and taking the readings using weighing
machine. Here three tests were repeated and presented in the figure G1-G3 for
hydrophobicity and G4-G6 for moisture uptake. All graphs in each categories showed
that results are consistent with insignificant variation from the test results. Repeatability
tests were carried out by using practical tests repetitions rather than some statistical
software.
150
Table G-3 Proximate Analysis:
Repeated Twice for Proximate Analysis
Sample A1 A2 Error A1 A2 Error A1 A2 Error
Volatile Matter (%) Ash Contents (%) Fixed Carbon (%)
I 54.91 53.98 0.93 19.54 21.01 1.47 3.12 3.96 0.84
II 73.88 74.25 0.37 10.91 10.36 0.55 11.05 10.57 0.48
III 73.97 75.01 1.04 4.77 5.22 0.45 13.12 12.58 0.54
Because of the accuracy of the bomb calorimeter, the results are pretty close with the
repetition of the experiment on three different samples.
Table G-4 Heating Value:
a) Repeatability test on Hydrophobicity
Some variations were found during 2.4% oxygen sample which are acceptable
because of the dependability of the results in the environmental conditions.
Repeated Twice for Heating Values
Sample A1 A2 Error A1 A2 Error A1 A2 Error
Heating Value of Raw
(MJ/Kg)
Heating Value of
Torrefied at 250C for 30
min (MJ/Kg)
Heating Value of
Torrefied at 275C for 30
min (MJ/Kg)
I 9.89 10.55 0.66 11.34 12.85 1.51 11.85 12.86 1.01
II 73.88 74.25 0.37 16.86 18.57 1.71 19.89 20.58 0.69
III 73.97 75.01 1.04 20.01 21.22 1.21 22.48 23.97 1.49
151
Figure G- 1: Repeatability test on the Hydrophobicity of a Sample with 0% O2
(30min)
Figure G- 2: Repeatability test on the Hydrophobicity of a Sample with 2.4% O2
(30min)
152
b) Repeatability test on Moisture Uptake
Satisfactory results were obtained during the experimental repetitions.
Figure G- 3: Repeatability test on the Moisture Uptake for a sample 0% O2
Figure G- 4: Repeatability test on the Moisture Uptake for a sample 2.4% O2
In order to test the significance variation on the data of these experiments, ANOVA, a
statistical model was used to see the hydrophobicity and moisture uptake with inert and
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 25 30
Mo
istu
re U
pta
ke (
%)
Exposure Time in hours
275C with 30 min 275C with 30min
153
2.4% oxygen concentration. The null hypothesis states that there is no difference on the
results collected with the oxygen variations.
MS Excel based ANOVA was run with 95% confidence level and the result
obtained for the biomass torrefied at 275ᴼC for 30 minutes are presented in the table G-5.
The P-value obtained was greater than 0.03, which means that the hydrophobicity tested
at different oxygen concentration has no significance variations on the results.
G-5: ANOVA between the hydrophobicity tests of Willow for 30 min residence time
Mean Square
(MS)
Temperature SS df MS F P-Value
Between ground 275ᴼC 3.6112 1 3.6112 42.0746 0.02377
Within Group 0.1716 2 0.0858
Total 3.7828 3
According to Measey et al (2002),
G-8
Where, n= numbers of repeated measurements (2)
Once above data are substituted in the equation G-8, which shows the good
repeatability because ri within range of 70% to 90% are considered as very high
repeatability (Measey et al, 2002).