Hybrid Systems Based on Solid Oxide Fuel Cells

Preface xi

Acknowledgements xv

1 Introduction 1

1.1 World Population Growth, Energy Demand and its Future 1

1.2 World Energy Future 3

1.3 Introduction to Fuel Cells and Associated Terms 6

1.3.1 Background for Fuel Cells and Thermodynamic Principles 6

1.3.2 Solid Oxide Fuel Cells (SOFCs) 11

1.3.3 Fuel Cell Reactions 15

1.3.4 Fuel Cell Performance 15

1.3.5 Pressure and Concentration Effects 18

1.3.6 Irreversibilities in Fuel Cells 19

1.3.7 Fuel Cell Applications 23

1.4 Gas Turbines 24

1.4.1 Background of Gas Turbines 24

1.5 Coupling of Microturbines with Fuel Cells to Obtain 'Hybrid Systems' 25

1.5.1 Active Hybrid Systems Research Groups 29

1.6 Conclusions 29

References 29

2 SOFC Technology 33

2.1 Basic Aspects of Solid Oxide Fuel Cells 33

2.2 SOFC Types 35

2.2.1 High-temperature SOFCs 35

2.2.2 Intermediate/Low-temperature SOFCs 35

2.3 Materials for SOFCs 36

2.4 Different SOFC Geometries 38

2.4.1 Tubular SOFCs 39

2.4.2 Planar SOFCs 41

2.5 SOFC Stacks 43

2.6 Effect of Pressurization for SOFCs 44

2.7 Fuel Processing for SOFCs 45

2.7.1 Processing for Gas and Liquid Fuels 46

2.7.2 Processing for Solid Fuels 48

2.8 SOFC Applications in Hybrid Systems 49

2.8.1 Atmospheric SOFC Hybrid Systems 50

2.8.2 Pressurized SOFC Hybrid Systems 51

2.9 Aspects Related to SOFC Reliability, Degradation and Costs 52

2.10 Conclusions 54

2.11 Questions 54

References 55

3 Micro Gas Turbine Technology 59

3.1 Fundamentals of the Brayton Cycle 59

3.1.1 The Simple Cycle 59

3.1.2 The Simple Recuperative Cycle 68

3.1.3 The Intercooled and Reheat Brayton Cycles 74

3.1.4 The Intercooled and Reheat, Recuperative Brayton Cycle 79

3.1.5 Cycle Layouts used by Contemporary Micro Gas Turbines 84

3.2 Turbomachinery 85

3.2.1 General Considerations on the Selection of Turbomachinery for Micro Gas Turbines 85

3.2.2 Fundamentals of Radial Compressor Design and Performance 89

3.2.3 Some Notes on Compressor Surge 101

3.2.4 Fundamentals of Radial Turbine Design and Performance 105

3.2.5 Scaling of Radial Turbomachinery 113

3.3 Recuperative Heat Exchanger 115

3.4 Bearings 124

3.5 Conclusions: Commercial Status and Areas of Research 131

3.6 Questions and Exercises 134

References 135

4 SOFC/mGT Coupling 141

4.1 Basic Aspects of SOFC Hybridization 141

4.2 SOFC Coupling with Traditional Power Plants 143

4.2.1 Coupling with Steam Power Plants 143

4.2.2 Coupling with Gas Turbines 144

4.2.3 Coupling with Combined Cycle-based Plants 146

4.3 Beneficial Attributes Related to SOFC/mGT Coupling 147

4.4 Constraints Related to SOFC/mGT Coupling 150

4.4.1 Turbine System Constraints 152

4.4.2 SOFC System Constraints 156

4.4.3 Control System Constraints 158

4.5 Design and Off-design Aspects 159

4.5.1 Design Aspects 159

4.5.2 Off-design Aspects 161

4.6 Issues Related to Dynamic Aspects 163

4.7 Main Prototypes Developed for SOFC Hybrid Systems 166

4.7.1 Prototype by Siemens-Westinghouse 167

4.7.2 Prototype by Mitsubishi Heavy Industries 169

4.7.3 Prototype by Rolls-Royce Fuel Cell Systems 170

4.8 Conclusions 171

4.9 Questions and Exercises 173

References 174

5 Computational Models for Hybrid Systems 183

5.1 Introduction 183

5.2 Steady-state Models for Hybrid Systems 185

5.3 Computational Models for Hybrid Systems: Modelling Steps 186

5.3.1 Computational Models for Hybrid Systems at the Component Level 190

5.3.2 Prediction of Performance of Gas Turbines 191

5.3.3 Off-design Operation of the Single-shaft Gas Turbine 192

5.3.4 Off-design Calculation with 'Complex' Layout Turbines 196

5.4 System Modelling 200

5.4.1 Reformer 201

5.4.2 SOFC Module 205

5.4.3 Overpotentials 207

5.4.4 Fuel and Air Supply Calculations 208

5.4.5 Combustor 209

5.4.6 Turbine 210

5.5 Compressor 211

5.5.1 Recuperator 211

5.6 Results and Discussion 212

5.7 Dynamic Models 213

5.8 Model Validation 216

5.9 Conclusion 217

5.10 Questions and Exercises 218

References 218

6 Experimental Emulation Facilities 225

6.1 Experimental Emulation Facilities 225

6.2 Reduced-scale Test Facilities 226

6.2.1 Anodic Recirculation Test Rig 227

6.2.2 Cathodic Loop Test Rig 229

6.3 Actual-scale Test Facilities 232

6.3.1 Low-temperature Rigs 233

6.3.2 High-temperature Rigs 236

6.4 Conclusions 247

6.5 Questions and Exercises 247

References 249

7 Problems and Solutions for Future Hybrid Systems 255

7.1 The Future of Micro Power Generation Systems 256

7.2 The Future of Hybrid Systems: Hydrogen as an Energy Carrier 258

7.2.1 Hydro-methane and Hydrogen-rich Fuel Mixtures 259

7.3 Future Hybrid Systems: Design, Optimization and Sizing 260

7.3.1 Hybrid Systems Sizing Techniques 261

7.3.2 Hybrid System Sizing Simulation Tools 262

7.4 Cost Analysis of Hybrid Systems for Power Generation Applications 264

7.5 Performance Degradation Problems in Solid Oxide Fuel Cells 268

7.6 Turbomachinery Problems 269

7.7 Dynamic and Control System Aspects 271

7.8 CO2 Separation Technologies for SOFC Hybrid Plants 272

7.9 Coal and Biofuel for Hybrid Systems 273

7.10 Conclusions 275

References 275

Glossary 285

Index 307