Page 10 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Contents ix

4.5 Degree of Torrefaction 107
4.5.1 Mass Yield 108
4.5.2 Energy Density 112
4.5.3 Energy Yield 113
4.6 Physical Properties of Torrefied Biomass 114
4.6.1 Density and Volume 114
4.6.2 Grindability 115
4.6.3 Hydrophobicity of Torrefied Biomass 116
4.6.4 Explosion Potential of Torrefied Dust 118
4.6.5 Densification or Pelletization 118
4.7 Torrefaction Technologies 122
4.7.1 Classification of Torrefaction Reactors 123
4.8 Design Methods 130
4.8.1 Design of Torrefaction Plant 130
Symbols and Nomenclature 141
Appendix: Mass and Energy Balance of Torrefier 142
Assumptions 142
Mass Balance 143
Torrefier 143
Oil Burner 143
Energy Balance 144
Torrefier: Control Volume of Torrefaction Zone (Figure 4.11) 144
Oil Burner: Control Volume of Oil Burner 145

5. Pyrolysis 147
5.1 Introduction 147
5.1.1 Historical Background 147
5.2 Pyrolysis 149
5.2.1 Pyrolysis Products 151
5.2.2 Types of Pyrolysis 153
5.3 Pyrolysis Product Yield 158
5.3.1 Effect of Biomass Composition 158
5.3.2 Effect of Pyrolysis Temperature 159
5.3.3 Effect of Heating Rate 159
5.3.4 Effect of Particle Size 160
5.4 Pyrolysis Kinetics 161
5.4.1 Physical Aspects 161
5.4.2 Chemical Aspects 162
5.4.3 Kinetic Models of Pyrolysis 165
5.5 Heat Transfer in a Pyrolyzer 166
5.5.1 Mass Transfer Effect 167
5.5.2 Is Pyrolysis Autothermal? 167
5.6 Pyrolyzer Types 168
5.6.1 Fixed-Bed Pyrolyzer 169
5.6.2 Bubbling-Bed Pyrolyzer 170
5.6.3 CFB Pyrolyzer 170
5.6.4 Ultrarapid Pyrolyzer 171