Preface xi
List of Contributors xv
Acknowledgments xvii
Recommended Reading xix
Coal Gasification: Basic Terminology xxi
1 Modeling of Gasifiers: Overview of Current Developments 1
Petr A. Nikrityuk, Thomas F¶rster, and Bernd Meyer
1.1 Numerical Modeling in Engineering 1
1.1.1 The Role of Direct Numerical Simulation (DNS) in Particulate-Flow Modeling 3
Summary 6
1.2 CFD-based Modeling of Entrained-Flow Gasifiers 6
1.2.1 Mainstream Computational Submodels 8
1.2.1.1 Particle Conversion 9
1.2.1.2 Turbulenceâ"Chemistry Interaction 12
1.2.2 Review of CFD-related Works 13
1.2.2.1 Noncommercial Software 13
1.2.2.2 Commercial Software 14
Summary 17
1.3 Benchmark Tests for CFD Modeling 17
1.3.1 British Coal Utilization Research Association Reactor (bcura) 18
1.3.2 Brigham Young University Reactor (BYU) 19
1.3.3 Pressurized Entrained-Flow Reactor (PEFR) 22
References 24
2 Gasification of Solids: Past, Present, and Future 29
Martin Gr¤bner
2.1 Introduction 29
2.2 Historical Background 30
2.3 Types of Gasification Reactors 33
2.4 Trends in Gasifier Development 36
2.5 Derived Challenges for Research 40
References 40
3 Modeling of Moving Particles: Review of Basic Concepts and Models 43
Sebastian Schulze, Robin Schmidt, and Petr A. Nikrityuk
3.1 Introduction 43
3.2 Soft-Sphere Model 47
3.2.1 Numerical Implementation 48
3.2.1.1 Contact Forces 48
3.2.1.2 Collision Parameters 49
3.2.1.3 Contact Detection 50
3.2.1.4 Time Integration 52
3.2.2 Validation Cases 53
3.2.2.1 Free-Falling Particle 53
3.2.2.2 Analytic Solution for the Free-falling Particle 54
3.2.2.3 Slipping Sphere on a Rough Surface 55
3.2.3 Illustrative Examples 56
3.2.3.1 Breaking Dam Problem 56
3.2.3.2 Rotating Drum 57
3.2.3.3 Generation of Fixed Beds 58
3.3 Hard-Sphere Model 59
3.3.1 Governing Equations 60
3.3.2 Collision Treatment in Dense Particulate Systems 62
3.3.3 2D Formulation of Hard-Sphere Collisions 63
3.3.4 Illustration of Hard-Sphere Models 65
3.3.5 Conclusions 68
Nomenclature 68
References 70
4 c d and Nu closure Relations for Spherical and NonSpherical Particles 73
Kay Wittig, Andreas Richter, and Aakash Golia
4.1 Literature Review 73
4.2 Model Description 74
4.2.1 Numerical Scheme and Discretization 75
4.3 Code and Software Validation 78
4.4 Porous Particles 81
4.4.1 Geometry Assumptions 81
4.4.2 Heat and Fluid Flow Past Porous Particles 82
4.4.3 Drag and Nusselt Numbers for Porous Particles 85
4.5 Nonspherical Particles 88
4.5.1 Heat and Fluid Flow of Particles Oriented in the Flow Direction 88
4.5.2 Flow Characteristics of Particles at Different Angles of Attack 91
4.5.3 Influence of Particle Orientation on Drag Forces and Heat Transfer 95
4.5.3.1 Drag Forces 95
4.5.3.2 Heat Transfer 96
4.5.3.3 Drag Forces and Nusselt Relations for Two Rotations 97
4.5.4 Discussion 100
4.5.5 Conclusion 100
References 101
5 Single Particle Heating and Drying 105
Robin Schmidt, Kay Wittig, and Petr A. Nikrityuk
5.1 Nonporous Spherical Particle Heating in a Stream of Hot Air 105
5.1.1 State of the Art 105
5.1.2 Problem and Model Formulation 107
5.1.2.1 Linear Model 108
5.1.3 Illustration of Results and Subgrid Model 109
5.1.4 Semiempirical Two-Temperature Subgrid Model 114
5.2 Heating of a Porous Particle 116
5.2.1 Problem and Model Formulation 117
5.2.2 Porosity 118
5.2.3 Results of Simulations 119
5.2.3.1 Conclusion 123
5.2.4 Appendix: Analytical Model 123
5.3 Spherical Particle Drying in a Stream of Hot Air 124
5.3.1 CFD-based Drying Model 125
5.3.2 Subgrid Models 127
5.3.2.1 Standard Model 127
5.3.2.2 New Model 127
5.3.3 Illustration and Validation of Models 131
5.3.3.1 Results: CFD-Based Model 131
5.3.3.2 Validation of Subgrid Model 135
5.4 Conclusions 138
References 139
6 Unsteady Char Gasification/Combustion 143
Dmitry Safronov
6.1 Introduction 143
6.2 Modeling Approach 145
6.2.1 Governing Equations 146
6.2.2 Initial Conditions and Boundary Conditions 148
6.2.3 Reaction Kinetics and Transport Properties 151
6.2.4 Evolution of Pore Structure and Interface Tracking 152
6.3 Numerics and Code Validation 153
6.3.1 Results and Discussion 155
6.3.1.1 Oxidation Behavior of Porous Particles 156
6.3.1.2 Details Inside the Particle 157
6.3.1.3 Effect of Ambient Gas Composition 157
6.3.1.4 Effect of Initial Particle Size and Ambient Gas Temperature on the Oxidation Regime 158
6.4 Advice for Beginners 160
6.5 Analytical Models 162
6.5.1 One-Film Model 162
6.5.2 Two-Film Model 165
6.5.3 Chemically Reacting Porous Particle 166
Nomenclature 167
References 168
7 Interface Tracking During Char Particle Gasification 171
Frank Dierich and Kay Wittig
7.1 Interface and Porosity Tracking for a Moving Char Particle 171
7.1.1 Introduction 171
7.1.2 Model and Governing Equations 172
7.1.2.1 Setup 172
7.1.2.2 Governing Equations in the Gas Phase 173
7.1.2.3 Governing Equations in Porous Particles 174
7.1.2.4 Boundary Conditions at the Particle Surface 175
7.1.2.5 Reaction Kinetics 175
7.1.2.6 Change of Porous Structure and Particle Shape 176
7.1.2.7 Transport Properties 177
7.1.3 Numerics 178
7.1.4 Results and Discussion 180
7.2 3D Interface Tracking for a Porous Char Particle in the Kinetic Regime 192
7.2.1 Problem Description 192
7.2.2 Porous Particle Description 194
7.2.3 Internal Surface Reconstruction 196
7.2.4 Results 197
7.3 Conclusions 200
References 201
8 Pseudo-Steady-State Approach for Carbon Particle Combustion/Gasification 205
Matthias Kestel, Dmitry Safronov, Andreas Richter, and Petr A. Nikrityuk
8.1 Particle-Resolved CFD Simulations: Spherical Particles 205
8.1.1 Review of the Literature 205
8.1.2 Setup and Model Formulation 207
8.1.3 Governing Equations 210
8.1.4 Boundary Conditions 211
8.1.5 Numerics and Software Validation 212
8.1.5.1 Validation against Analytical Solution 213
8.1.5.2 Validation against Experiments I: Laminar and Turbulent Regimes 214
8.1.5.3 Validation against Experiments II: The impact of Particle Porosity 217
8.1.6 Results: The Impact of Re on the Oxidation Regimes 219
8.2 Particle-Resolved CFD Simulations: Nonspherical Particles 225
8.2.1 Introduction 225
8.2.2 Shapes of Particles 227
8.2.3 Results 228
8.2.3.1 Integral Characteristics 231
8.3 Conclusions 235
8.4 Setup of Heterogeneous Reactions in ANSYS FLUENT 235
8.4.1 Step 1: Species Transport Settings 235
8.4.2 Step 2: Define Species and Mixtures 236
8.4.3 Step 3: Define Reactions 237
8.4.4 Step 4: Boundary Settings 238
Nomenclature 239
References 240
9 Pore-Resolved Simulation of Char Particle Combustion/Gasification 243
Andreas Richter, Matthias Kestel, and Petr A. Nikrityuk
9.1 Introduction 243
9.2 Model Assumptions and Chemistry 245
9.2.1 Numerical scheme, discretization, and software validation 248
9.3 Small Porous Particle: 90 μm 249
9.3.1 Influence of Gas Temperature 256
9.4 Large Porous Particle: 2 mm 257
9.4.1 Small Reynolds Numbers 257
9.4.2 Large Reynolds Numbers 259
9.5 3D Simulations under Gasification Conditions 264
9.6 Conclusions 267
Nomenclature 267
References 268
10 Subgrid Models for Particle Devolatilization-Combustion-Gasification 271
Sebastian Schulze, Robin Schmidt, and Petr A. Nikrityuk
10.1 Subgrid Model for the Devolatilization/Combustion of a Moving Coal Particle 271
10.1.1 State of the Art 271
10.1.2 Model Formulation 276
10.1.2.1 Semiglobal Chemical Reactions 280
10.1.3 CFD-based Model 281
10.1.4 Model Validation 282
10.2 Novel Intrinsic Submodel for Gasification of a Moving Char Particle 290
10.2.1 Model Formulation 291
10.2.1.1 Total Carbon Consumption Rate 292
10.2.1.2 Basic Equations 293
10.2.2 CFD-based Model 295
10.2.2.1 Numerics and Validation 297
10.2.3 Model Performance 297
Nomenclature 300
References 301
11 New Frontiers and Challenges in Gasification Technologies 305
Alexander Laugwitz and Bernd Meyer
11.1 Introduction 305
11.2 Trends in Gasifier Design 307
11.2.1 Advanced Fluidized-Bed Coal Gasifiers 308
11.2.1.1 Fluidized Bed with Slag Bath 309
11.2.1.2 Multistaged Spouted Bed with Slag Bath 310
11.2.1.3 Internal Circulating Fast Fluidized-Bed Gasifier (INCI) 311
11.2.1.4 Agglomerating Fluidized Bed with Internal Post Gasification 314
11.2.2 Highly Loaded Compact Gasifiers 315
11.2.2.1 Hybrid Wall Gasifier 316
11.3 Future Gasifier Simulations 319
11.3.1 Requirements of Proposed Future Gasifiers 319
11.3.2 Additional Fundamental Aspects of Future Numerical Simulations 322
References 325
Index 329
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