Table Of ContentZoltán Kocsis · Etele Csanády
Theory and
Practice of
Wood Pellet
Production
Theory and Practice of Wood Pellet Production
á á
Zolt n Kocsis Etele Csan dy
(cid:129)
Theory and Practice of Wood
Pellet Production
123
Zoltán Kocsis EteleCsanády
Sopron, Hungary Sopron, Hungary
ISBN978-3-030-26178-8 ISBN978-3-030-26179-5 (eBook)
https://doi.org/10.1007/978-3-030-26179-5
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Foreword
Theproductionofpellets,asarenewableenergysource,iscontinuouslyincreasing
worldwide. Industrial and agricultural wastes, by-products, and residues are
availableinallcountriesoftheworld,andoneoftherationalusesofthesematerials
is the pellet making supply energy. Furthermore, a major advantage, using these
by-productsforenergyproduction,contributestothereductionofCO emissionto
2
the environment.
This book is the first attempt to provide a comprehensive theoretical approach
for the compaction process of various bulk materials prepared from wood wastes
and by-products. A nonlinear rheological compaction model is developed and
demonstratedwithexperimentalresults.Anewsimilarityrelationshipisdeveloped
for the quick estimate of compaction energy as a function of the influencing
variables. Furthermore, for the proper selection of channel length of the die ring a
new approach is developed based on experimental measurements.
The practice of pellet making is equally treated in detail. There are many
practical problems which fundamentally influence the production process. The
preparation of the raw material, a continuous and accurate material flow to the
press, the post-processing of pellets, and the economic analysis of the pellet pro-
duction are important features needed to produce quality product at competitive
price.
This new textbook on Theory and Practice of Wood Pellet Production may
contribute tothe better understanding ofphysical–mechanical processes associated
with the compaction of bulk materials. The material is designed for undergraduate
and postgraduate students, special courses at universities, research workers and
application engineers working in the field of biomass utilization.
Sopron, Hungary György Sitkei
June 2019
v
Preface
Biomass as a renewable energy source is available in many countries worldwide,
and it is important to utilize it economically and efficiently. The main sources are
the wood industry, thinning and residues from forests, and agriculture with quite
different material properties. Depending on their initial size or size distribution,
moisture content, and plant origin, they require very different preprocessing and
treatments to transform them into an appropriate final product. The most common
practice is to produce pellets or briquettes and to utilize them for energy supply in
households and power plants.
The whole production process for biomass conversion requires capital and
energy investments, material and labor costs, transport and marketing activities
which determine the production cost and the competitiveness of the product
comparedtootherenergysources.Inordertobecompetitive,adeepunderstanding
of all processes associated with the whole production system is necessary.
Especially, the utilization of agricultural by-products requires careful planning
where a lot of problems are not fully solved yet.
Thistextbook isafirst attempt toprovidea systematic approachconcerningthe
main processes of pellet production in theory and practice. The theoretical back-
ground of viscoelastic materials, their modeling, and calculation methods are dis-
cussed in detail. The general regularities of the compaction process, including a
new nonlinear approach, are described and illustrated with measurement results.
New measurement results for the energy consumption of pelletizing are provided,
and also a generally valid similarity relationship is developed. Further new
developmentsarethepressure—channellengthrelationshipandtheroleofmoisture
in the development of bonding forces in the pellet.
The practice of pellet making has many technical and economic problems. The
mainworkingphasesofpelletproductionincludingchipping,drying,post-chipping,
andcompactionarediscussed.Furtherimportantquestionsaretheenergybalanceof
pellet production, the energetic utilization of pellets and the overall economy of
pellet production.
vii
viii Preface
The authors are indebted to Prof. György Sitkei for reading the manuscript and
offering many useful suggestions, especially about the nonlinear treatment of the
compaction process, to the development of similarity relations and the economic
analysis of pellet production. The authors are also sincerely grateful to the staff of
Springer Verlag for their excellent cooperation.
Sopron, Hungary Zoltán Kocsis
Etele Csanády
Contents
1 General Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 History of Pellet Making. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Importance of Pellet Making . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Resources of Raw Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Theory of Compaction of Bulk Materials . . . . . . . . . . . . . . . . . . . . . 5
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Wood as Rheological Material. . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Modeling of Rheological Materials . . . . . . . . . . . . . . . . . . . . . . 12
2.3.1 Rheological Models . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.2 Rheological Equations . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4 Non-linear Compaction with Plastic Deformation . . . . . . . . . . . . 21
2.5 General Regularities of Compaction Processes . . . . . . . . . . . . . . 31
2.5.1 Energy Requirements of Compaction. . . . . . . . . . . . . . . 34
2.5.2 Rebound of Material After Compaction. . . . . . . . . . . . . 37
2.6 Pressure Distribution in a Compaction Chamber . . . . . . . . . . . . . 39
2.7 Pressure Relation of the Pellet Production . . . . . . . . . . . . . . . . . 41
2.8 Operational Characteristics of Die Ring Presses . . . . . . . . . . . . . 46
2.9 Effects of Various Parameters on the Pelleting Process . . . . . . . . 48
2.10 Similarity Equation of the Energy of Compaction. . . . . . . . . . . . 51
2.10.1 Theoretical Considerations . . . . . . . . . . . . . . . . . . . . . . 52
2.10.2 Experimental Results and Similarity Equation . . . . . . . . 54
2.11 Wall Friction and Channel Length . . . . . . . . . . . . . . . . . . . . . . . 58
2.11.1 Theoretical Considerations . . . . . . . . . . . . . . . . . . . . . . 62
2.11.2 An Approximate Modeling of the Pushing Force . . . . . . 63
2.11.3 Determination of Channel Length
for a Given Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.12 Optimum Selection of Operational Parameters . . . . . . . . . . . . . . 69
2.13 Influence of Moisture Content . . . . . . . . . . . . . . . . . . . . . . . . . . 70
ix
x Contents
3 The Practice of Pellet Making. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2 Working Phases of Pellet Production . . . . . . . . . . . . . . . . . . . . . 78
3.2.1 Basic Material Properties . . . . . . . . . . . . . . . . . . . . . . . 78
3.2.2 Primary Chipping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.2.3 Drying of Chips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.2.4 Rechipping and Screening. . . . . . . . . . . . . . . . . . . . . . . 81
3.2.5 Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.2.6 Pressing Technologies . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.3 Problems Encountered at Pressing . . . . . . . . . . . . . . . . . . . . . . . 84
3.4 Post Treatments and Packing. . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.5 Technology of Pellet Production . . . . . . . . . . . . . . . . . . . . . . . . 91
3.6 Characteristics of Wood Pellets . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.7 Energy Balance of Pellet Production . . . . . . . . . . . . . . . . . . . . . 93
3.8 Quality Requirements, Standardization . . . . . . . . . . . . . . . . . . . . 94
3.9 Energetic Utilization of Pellets. . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.10 Competitiveness and Market Conditions. . . . . . . . . . . . . . . . . . . 101
3.11 Some Practical Observations on Energy Requirements . . . . . . . . 103
3.12 Economy of Pellet Production . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Concluding Remarks ... .... ..... .... .... .... .... .... ..... .... 111
Literature .... .... .... .... ..... .... .... .... .... .... ..... .... 113
Index .... .... .... .... .... ..... .... .... .... .... .... ..... .... 117
Chapter 1
General Remarks
1.1 Introduction
Thefirstintroductorychaptercoversthehistoryofpelletmaking,firstusedforthe
stabilizationofingredientsdistributioninanimalfodders.Inourdaystheimportance
ofpelletmakingishighlyexpandedtothefieldofbiomassutilizationforsupplying
energy.
Theresourcesofbiomassrawmaterialsareabundantinallcountriesoftheworld
which can economically be used either in households or industrial plants and for
powergeneration.Atthesametime,biomassesmayhavequitedifferentproperties
which require dissimilar preparation, compaction techniques and, mainly burning
equipment.
1.2 HistoryofPelletMaking
Thehistoryofpelletsbeganinthe1870s.Bothindustrializationandanimalhusbandry
atthattimehadundergoneseriousdevelopment.Thegrowingfeedrequirementsand
thedevelopmentoftheindustry,therewasaneedtoproducefeedcontainingacertain
proportionofingredients.Thefirstmachinewasbuiltin1906,whichwaslinkedto
theLouisSmulder&Co.machinefactoryinUtrecht,andofferedasolutiontothe
problem as compression kept mixing rates constant in the product. The pellet is
actuallyadenserbiomass.
In the 1920s, fuel pellets were first produced for fuel in North America. In the
firstperiod,sawdustfromsawmillswasusedasrawmaterialformakingfuelpellets.
Thesimpleexplanationforthisisthatsawdustcanbedirectlyconvertedintopellets
withoutpreparation.Thecompaction generated bythepressureisstrengthenedby
fibrouscellulosicfibers.Ifthewoodcontainslargeramountsofresinsandoils,the
product is less crumbly and less pressure is needed. Thus, with the use of simple
technology,theywereabletoproducepelletsfromwoodwaste.Theproductionof
©SpringerNatureSwitzerlandAG2019 1
Z.KocsisandE.Csanády,TheoryandPracticeofWoodPelletProduction,
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