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Contents

Preface xvAcknowledgments xviiAbout the Author xix

1. Introduction 1

1.1 Biomass and its Products 21.1.1 Products of Biomass 3

1.2 Biomass Conversion 71.2.1 Biochemical Conversion 81.2.2 Thermochemical Conversion 10

1.3 Motivation for Biomass Conversion 151.3.1 Renewability Benefits 151.3.2 Environmental Benefits 161.3.3 Sociopolitical Benefits 18

1.4 Historical Background 181.5 Commercial Attraction of Gasification 21

1.5.1 Comparison of Gasification and Combustion 221.6 Brief Description of Some Biomass Conversion Processes 25

1.6.1 Torrefaction 251.6.2 Pyrolysis 251.6.3 Combustion of Carbon 251.6.4 Gasification of Carbon 251.6.5 Syngas Production 261.6.6 Methanol Synthesis 261.6.7 Ammonia Synthesis 271.6.8 Fischer!Tropsch Reaction 271.6.9 Methanation Reaction 27

Symbols and Nomenclature 27

2. Economic Issues of Biomass Energy Conversion 29

2.1 Introduction 292.2 Biomass Availability and Products 30

2.2.1 Availability Assessment 302.2.2 Product Revenue from Biomass Conversion 33

2.3 Biomass Conversion Process Plant Equipment and Cost 342.3.1 Biomass Collection System 352.3.2 Preprocessing 352.3.3 Gasifier Cost 36

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2.3.4 Torrefier Cost 382.3.5 Pyrolyzer Cost 392.3.6 Comparison of Capital Costs 39

2.4 Financial Analysis 402.4.1 Capital Cost Adjustment for Size and Time 402.4.2 Capital Requirement 422.4.3 Operation and Maintenance Cost 43

Symbols and Nomenclature 46

3. Biomass Characteristics 47

3.1 Introduction 473.2 What Is Biomass? 47

3.2.1 Biomass Formation 483.2.2 Types of Biomass 49

3.3 Structure of Biomass 543.3.1 Structure of Wood 553.3.2 Constituents of Biomass Cells 56

3.4 General Classification of Fuels 603.4.1 Atomic Ratio 603.4.2 Relative Proportions of Lignocellulosic Components 613.4.3 Ternary Diagram 62

3.5 Properties of Biomass 633.5.1 Physical Properties 633.5.2 Thermodynamic Properties 67

3.6 Composition of Biomass 733.6.1 Ultimate Analysis 733.6.2 Proximate Analysis 753.6.3 Thermogravimetric Analysis 783.6.4 Bases of Expressing Biomass Composition 783.6.5 Heating Value of Fuel 803.6.6 Stoichiometric Calculations for Complete Combustion 823.6.7 Composition of the Product Gas of Gasification 83

Symbols and Nomenclature 84

4. Torrefaction 87

4.1 Introduction 874.2 What Is Torrefaction? 87

4.2.1 Pyrolysis, Carbonization, and Torrefaction 894.3 Carbonization 92

4.3.1 Charcoal Fuel 924.3.2 Activated Charcoal 934.3.3 Biocoke 934.3.4 Biochar 94

4.4 Torrefaction Process 944.4.1 Heating Stages 964.4.2 Mechanism of Torrefaction 994.4.3 Effect of Design Parameters on Torrefaction 101

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4.5 Degree of Torrefaction 1074.5.1 Mass Yield 1084.5.2 Energy Density 1124.5.3 Energy Yield 113

4.6 Physical Properties of Torrefied Biomass 1144.6.1 Density and Volume 1144.6.2 Grindability 1154.6.3 Hydrophobicity of Torrefied Biomass 1164.6.4 Explosion Potential of Torrefied Dust 1184.6.5 Densification or Pelletization 118

4.7 Torrefaction Technologies 1224.7.1 Classification of Torrefaction Reactors 123

4.8 Design Methods 1304.8.1 Design of Torrefaction Plant 130

Symbols and Nomenclature 141Appendix: Mass and Energy Balance of Torrefier 142

Assumptions 142Mass Balance 143

Torrefier 143Oil Burner 143

Energy Balance 144Torrefier: Control Volume of Torrefaction Zone (Figure 4.11) 144Oil Burner: Control Volume of Oil Burner 145

5. Pyrolysis 147

5.1 Introduction 1475.1.1 Historical Background 147

5.2 Pyrolysis 1495.2.1 Pyrolysis Products 1515.2.2 Types of Pyrolysis 153

5.3 Pyrolysis Product Yield 1585.3.1 Effect of Biomass Composition 1585.3.2 Effect of Pyrolysis Temperature 1595.3.3 Effect of Heating Rate 1595.3.4 Effect of Particle Size 160

5.4 Pyrolysis Kinetics 1615.4.1 Physical Aspects 1615.4.2 Chemical Aspects 1625.4.3 Kinetic Models of Pyrolysis 165

5.5 Heat Transfer in a Pyrolyzer 1665.5.1 Mass Transfer Effect 1675.5.2 Is Pyrolysis Autothermal? 167

5.6 Pyrolyzer Types 1685.6.1 Fixed-Bed Pyrolyzer 1695.6.2 Bubbling-Bed Pyrolyzer 1705.6.3 CFB Pyrolyzer 1705.6.4 Ultrarapid Pyrolyzer 171

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5.6.5 Ablative Pyrolyzer 1715.6.6 Rotating-Cone Pyrolyzer 1715.6.7 Vacuum Pyrolyzer 172

5.7 Pyrolyzer Design Considerations 1725.7.1 Production of Liquid Through Pyrolysis 172

5.8 Biochar 1735.8.1 Potential Benefits of Biochar 175

Symbols and Nomenclature 176

6. Tar Production and Destruction 177

6.1 Introduction 1776.2 Tar 177

6.2.1 Acceptable Limits for Tar 1786.2.2 Tar Formation 1806.2.3 Tar Composition 181

6.3 Tar Reduction 1836.3.1 In Situ Tar Primary Reduction 1846.3.2 Postgasification—Secondary Reduction of Tar 193

7. Gasification Theory 199

7.1 Introduction 1997.2 Gasification Reactions and Steps 199

7.2.1 Gasifying Medium 2007.3 The Gasification Process 200

7.3.1 Drying 2017.3.2 Pyrolysis 2037.3.3 Char Gasification Reactions 2037.3.4 Char Combustion Reactions 2087.3.5 Catalytic Gasification 2107.3.6 Gasification Processes in Reactors 212

7.4 Kinetics of Gasification 2187.4.1 Chemical Equilibrium 2187.4.2 Char Reactivity 229

7.5 Gasification Models 2327.5.1 Simulation Versus Experiment 2327.5.2 Gasifier Simulation Models 233

7.6 Kinetic Model Applications 2407.6.1 Moving-Bed Gasifiers 2407.6.2 Fluidized-Bed Gasifiers 2417.6.3 Entrained-Flow Gasifiers 244

Symbols and Nomenclature 246

8. Design of Biomass Gasifiers 249

8.1 Introduction 2498.1.1 Gasifier Types 249

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8.2 Fixed-Bed/Moving-Bed Gasifiers 2518.2.1 Updraft Gasifiers 2528.2.2 Downdraft Gasifiers 2548.2.3 Crossdraft Gasifiers 258

8.3 Fluidized-Bed Gasifiers 2598.3.1 Bubbling Fluidized-Bed Gasifier 2598.3.2 Circulating Fluidized-Bed Gasifier 261

8.4 Entrained-Flow Gasifiers 2688.4.1 Top-Fed Gasifier 2708.4.2 Side-Fed Gasifier 2718.4.3 Advantages of Entrained-Flow Gasifiers 2728.4.4 Entrained-Flow Gasification of Biomass 272

8.5 Plasma Gasification 2738.6 Process Design 274

8.6.1 Design Specification 2758.6.2 Mass Balance 2768.6.3 Energy Balance 282

8.7 Product Gas Prediction 2878.7.1 Equilibrium Approach 287

8.8 Gasifier Sizing 2898.8.1 Moving-Bed Gasifiers 2898.8.2 Fluidized-Bed Gasifiers 292

8.9 Entrained-Flow Gasifier Design 2998.9.1 Gasifier Chamber 300

8.10 Auxiliary Items 3008.10.1 Position of Biomass Feeding Position 3018.10.2 Distributor Plate 3018.10.3 Bed Materials 301

8.11 Design Optimization 3028.11.1 Process Optimization 303

8.12 Performance and Operating Issues 3038.12.1 Gasification Efficiency 3038.12.2 Operational Considerations 310

Symbols and Nomenclature 311

9. Hydrothermal Gasification of Biomass 315

9.1 Introduction 3159.2 Supercritical Water 316

9.2.1 Properties of SCW 3189.2.2 Application of SCW in Chemical Reactions 3219.2.3 Advantages of SCW Gasification over Conventional

Thermal Gasification 3229.3 Biomass Conversion in SCW 323

9.3.1 Gasification 3239.3.2 Hydrolysis 3249.3.3 SCW Oxidation 3259.3.4 Scheme of an SCWG Plant 325

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9.4 Effect of Operating Parameters on SCW Gasification 3279.4.1 Reactor Temperature 3279.4.2 Catalysts 3299.4.3 Residence Time 3309.4.4 Solid Concentration in Feedstock 3309.4.5 Heating Rate 3319.4.6 Feed Particle Size 3319.4.7 Pressure 3339.4.8 Reactor Type 333

9.5 Application of Biomass Conversion in SCWG 3339.5.1 Energy Conversion 3349.5.2 Waste Remediation 3359.5.3 Chemical Production 335

9.6 Reaction Kinetics 3369.7 Reactor Design 337

9.7.1 Reactor Temperature 3379.7.2 Catalyst Selection 3389.7.3 Reactor Size 3389.7.4 Heat-Recovery Heat-Exchanger Design 3399.7.5 Carbon Combustion System 3419.7.6 Design of Gas!Liquid Separator System 3439.7.7 Biomass Feed System 347

9.8 Corrosion 3489.8.1 Mechanism of Corrosion 3489.8.2 Prevention of Corrosion 349

9.9 Energy Conversion Efficiency 3519.10 Major Challenges 351Symbols and Nomenclature 352

10. Biomass Cofiring and Torrefaction 353

10.1 Introduction 35310.2 Benefits and Shortcomings of Biomass Cofiring 35410.3 Emission Reduction Through Biomass Cofiring 355

10.3.1 CO2 Reduction 35710.4 Carbon Capture and Storage (CCS) versus Biomass Firing 35710.5 Cofiring Options 359

10.5.1 Direct Cofiring of Raw or Torrefied Biomass 35910.5.2 Gasification Cofiring 36110.5.3 Parallel Cofiring 361

10.6 Operating Problems of Biomass Cofiring 36210.6.1 Combustion Issues 36310.6.2 Fuel Preparation 36310.6.3 Storage 36410.6.4 Fouling, Agglomeration, and Corrosion 36410.6.5 Biomass Variability 36510.6.6 Capacity Reduction 36610.6.7 Safety Issue 366

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10.7 Cofiring with Torrefied Wood 36710.7.1 Effect of Cofiring on Plant Output 36810.7.2 Feed Preparation 36810.7.3 Effect of Torrefaction Parameters on Grinding 36910.7.4 Explosion and Fire 370

11. Production of Synthetic Fuels and Chemicalsfrom Biomass 375

11.1 Introduction 37511.2 Syngas 376

11.2.1 What Is Syngas? 37611.2.2 Applications of Syngas 37611.2.3 Production of Syngas 37711.2.4 Gasification for Syngas Production 37811.2.5 Cleaning and Conditioning of Syngas 378

11.3 Bio-Oil production 38011.3.1 What Is Bio-Oil? 38011.3.2 Physical Properties of Bio-Oil 38211.3.3 Applications of Bio-Oil 38211.3.4 Production of Bio-Oil 384

11.4 Conversion of Syngas into Chemicals 38511.4.1 Methanol Production 38511.4.2 Fischer!Tropsch Synthesis 38711.4.3 Ammonia Synthesis 39411.4.4 Glycerol Synthesis 395

11.5 Transport Fuels from Biomass 39611.5.1 Biochemical Ethanol Production 39611.5.2 Gasoline 39811.5.3 Diesel 39911.5.4 Transport Fuel Production from

Nonfood Biomass 400

12. Biomass Handling 405

12.1 Introduction 40512.2 Design of a Biomass Energy System 40512.3 Biomass-Handling System 407

12.3.1 Receiving 40712.3.2 Storage 40912.3.3 Conveying 42112.3.4 Feed Preparation 42212.3.5 Feeding 426

12.4 Biomass Feeders 42612.4.1 Feeding Systems for Harvested Fuel 42612.4.2 Feeding Systems for Nonharvested Fuels 42612.4.3 Feeder Types 42812.4.4 Fuel Feed into the Reactor 433

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12.5 Cost of Biomass-Handling System 436Symbols and Nomenclature 438

13. Analytical Techniques 439

13.1 Composition of Biomass 43913.1.1 Ultimate (Elemental) Analysis 43913.1.2 Proximate Analysis 44013.1.3 Analysis of Polymeric Components of Biomass 442

13.2 Heating Value 44713.3 Differential Scanning Calorimetry 44813.4 Reactivity Measurements 450

13.4.1 Thermogravimetric Analysis 45013.4.2 Differential Thermal Analyzer 45113.4.3 Quartz Wool Matrix Apparatus 451

13.5 Pyrolysis-Gas Chromatography/Mass Spectrometry 454

Appendix A: Definition of Biomass 457Appendix B: Physical Constants and Unit Conversions 461Appendix C: Selected Design Data Tables 485Glossary 493References 495Index 515

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