Clean Energy from Waste: Fundamental Investigations on Ashes and Tar Behaviours in a Two Stage Fluid Bed-Plasma Process for Waste Gasification (Springer Theses)

This book explores the use of recent advanced multiple stage conversion technologies. These applications combine conventional fluidised bed systems with new plasma technologies to efficiently generate different energy outputs from waste materials with minimum cleaning effort. Using a mix of modelling and experimental approaches, the author provides fundamental insights into how the key operating variables of the two-stage process may impact the final quality of syngas. This thesis serves as a useful reference guide on the modelling and design of single and multiple-stage systems for thermal waste treatment. Its extended section on plant configuration and operation of waste gasification plants identifies the main technical challenges, and is of use to researchers entering the field. Supervisor’s Foreword 6 Abstract 8 Parts of this thesis have been published in the following journal articles:Massimiliano Materazzi, Paola Lettieri, Luca Mazzei, Richard Taylor, Chris Chapman, Tar evolution in a two stage fluid bed–plasma gasification process for waste valorization, Fuel Processing Technology, Volume 128, December 2014, Pages 146–157Massimiliano Materazzi, Paola Lettieri, Luca Mazzei, Richard Taylor, Chris Chapman, Reforming of tars and organic sulphur compounds in a plasma-assisted process for waste gasification, Fuel Processing Technology, Volume 137, September 2015, Pages 259–268Massimiliano Materazzi, Paola Lettieri, Luca Mazzei, Richard Taylor, Chris Chapman, Fate and behavior of inorganic constituents of RDF in a two stage fluid bed-plasma gasification plant, Fuel, Volume 150, 15 June 2015, Pages 473–485Massimiliano Materazzi, Paola Lettieri, Luca Mazzei, Richard Taylor, Chris Chapman, Thermodynamic modelling and evaluation of a two-stage thermal process for waste gasification, Fuel, Volume 108, June 2013, Pages 356–369M. Materazzi, P. Lettieri, R. Taylor, C. Chapman, Performance analysis of RDF gasification in a two stage fluidized bed–plasma process, Waste Management, Volume 47, Part B, January 2016, Pages 256–266 10 Acknowledgements 11 Contents 13 Nomenclature 18 List of Figures 20 List of Tables 25 1 Introduction 27 1.1 World Energy Outlook 27 1.2 The Waste Debate 30 1.3 Waste as a Resource of Energy 31 1.4 Basics of Thermochemical Waste-to-Energy Technologies 33 1.4.1 Pyrolysis 34 1.4.2 Gasification 34 1.4.3 Plasma Arc Gasification 35 1.4.4 Hydrothermal Liquefaction 35 1.5 Current Obstacles to WtE Plants Deployment 36 1.6 Aims of the Thesis 38 1.7 Methodology 39 1.7.1 Operation of Fluidised Bed Reactors on Waste Fuels 40 1.7.2 Plasma for Treatment of Ashes and Gases 40 1.7.3 Performance Analysis of Two-Stage Versus Single Stage Processes 40 1.7.4 Reforming Mechanisms of Tars and Organic Sulphur Compounds in Plasma Environment 41 1.7.5 Partitioning and Chemistry of Inorganic Components in the Solid Phase 41 1.8 Thesis Outline 41 References 43 2 Gasification of Waste Derived Fuels in Fluidized Beds: Fundamental Aspects and Industrial Challenges 44 2.1 Fuel Characterization 45 2.1.1 Fuel Preparation 45 2.1.2 Component Materials 47 2.1.3 Organic Content 47 2.1.4 Ash Content and Composition 51 2.1.5 Moisture Content 52 2.1.6 Element Content 53 2.1.6.1 Ultimate Analysis 53 2.1.6.2 Proximate Analysis 53 2.1.7 The Energy Value of RDF 55 2.1.8 Preliminary Considerations Based on Fuel Characterization 56 2.2 Fluidized Bed Gasification: Process Overview 58 2.2.1 Material in-Feeding 60 2.2.2 Heating and Drying 61 2.2.3 Devolatilization and Volatile Conversion 61 2.2.4 Fixed Carbon Conversion 62 2.2.5 Particle Attrition and Elutriation 63 2.2.6 Comparison Between Conventional and Waste Fuels 64 2.3 Ash Behaviour and Agglomeration Issues 65 2.3.1 Mechanism 66 2.3.2 Effect of Temperature and Segregation Profiles 66 2.3.3 Effect of RDF Ash Composition 67 2.3.4 Entrainment, Slagging and Fouling 69 2.3.5 Use and Disposal of Solid Residues 70 2.4 Tar Formation and Reduction Measures 72 2.4.1 Tar Definition and Formation 73 2.4.2 Effect of Temperature 75 2.4.3 Effect of Equivalent Ratio and Steam 76 2.4.4 Effects of Residence Time 77 2.4.5 Effect of Active Materials 78 2.4.6 Physical Tar Reduction Measures 79 2.4.6.1 Wet ESP’s for Tar Removal 80 2.4.6.2 Wet Scrubbers 80 2.4.6.3 Use and Disposal of Collected Tars 81 2.4.7 Thermal and Plasma Cracking 82 2.5 Remarks and Conclusions 83 References 85 3 Plasma as an Alternative Way to Gas Reforming and Ash Disposal 89 3.1 Plasma Principles 89 3.2 Plasma in Hydrocarbon Processing Applications 90 3.2.1 Non-thermal Plasmas 91 3.2.1.1 Continuous and Pulsed Corona 91 3.2.1.2 Dielectric Barrier Discharge 92 3.2.1.3 Microwave Discharge 92 3.2.1.4 Gliding Arc Discharge 93 3.2.1.5 Combined Plasma-Catalytic Beds 94 3.2.2 Thermal Plasmas 95 3.3 Plasma-Chemical Conversion of Tars into Syngas (CO2–H2) and Other Hydrogen Rich Mixtures 96 3.3.1 Kinetics in Plasma Chemistry 98 3.3.2 Reactions in CO2, H2O, H2 100 3.3.3 Cooling and Quenching 101 3.4 Ash Vitrification and Material Recovery 101 3.5 Coupling the Plasma with the FBG: The Gasplasma Process 104 3.5.1 Process Overview 105 3.5.2 Comparison of Wet Gas Cleaning and Plasma Gas Processing Systems 108 3.6 Remarks and Conclusions 112 3.7 Current Issues and Refined Objectives of the Thesis 112 References 114 4 Apparatus and Investigative Approach 117 4.1 Plant Overview 118 4.2 The Experimental Set-up 119 4.2.1 The Fluidized Bed Gasifier 119 4.2.1.1 Fuel Addition System 120 4.2.1.2 Steam and Oxygen 121 4.2.2 The Plasma Converter 123 4.2.3 Containment and Tapping of Molten Products 125 4.2.4 Gas Cooling System 126 4.2.5 Dry Gas Cleaning 128 4.2.6 Wet Gas Cleaning 128 4.2.7 Syngas Utilization 128 4.3 Sampling and Analysis 129 4.3.1 Off-Gas Continuous Emissions Monitoring 130 4.3.2 Syngas Calorific Value 133 4.3.3 Tar and Organic Sulphur Sampling and Analysis 133 4.3.4 Solid Analysis and Residues Characterization 134 4.3.4.1 Compositional Analyses 134 4.3.4.2 Leachate Tests 137 4.3.4.3 XRD Analysis 137 4.3.4.4 Morphological Analysis 137 4.4 Plant Operation 138 4.4.1 Start up 139 4.4.2 Normal Operation 139 4.4.3 Shut Down 140 4.4.4 Test Materials and Conditions 141 5 Modelling of a Two-Stage Process: Comparison of Different Approaches and Performance Analysis 144 5.1 Introduction 144 5.2 Single Versus Two-Stage Process 146 5.3 Process Modelling 148 5.3.1 Kinetic Models 148 5.3.2 Kinetic Model Formulation 149 5.3.3 CFD Integration 154 5.3.4 Thermodynamic Models 155 5.3.5 Thermodynamic Equilibrium Formulation 156 5.3.5.1 Energy Balance 158 5.3.5.2 The Preliminary Conversion Process and the Input Data 159 5.3.5.3 The Solver 160 5.4 Results and Discussion 161 5.4.1 Experimental Validation of Kinetic Model Data: Single Versus Two-Stage Process 162 5.4.2 Experimental Validation of Thermodynamic Model Data: Single Versus Two-Stage Process 166 5.4.2.1 Carbon Conversion Efficiency 168 5.4.2.2 Energy Conversion Efficiency 170 5.5 Performance Analysis 171 5.5.1 First Law Efficiency 173 5.5.2 Plasma Versus Secondary Oxygen 174 5.5.3 Second Law Efficiency 178 5.6 Conclusion 180 References 181 6 Tar Evolution in the Two Stage Fluid Bed-Plasma Gasification Process 184 6.1 Introduction 184 6.2 Thermal-Activated Model for Tar Reforming 187 6.2.1 Model Formulation 188 6.3 Experimental Description 190 6.3.1 Test Conditions 190 6.3.2 Materials 191 6.3.3 System Monitoring and Analysis 191 6.4 Results and Discussion 192 6.4.1 Kinetic Model Validation 192 6.4.2 Organics in the Slag Phase 195 6.4.3 Effects on Sulphur Species 196 6.4.4 The Role of Plasma in the Reforming of Tars 198 6.4.5 Effects on CO and CO2 Distribution and Soot Formation 201 6.4.5.1 Soot Characterization 202 6.4.5.2 Soot Quantification 204 6.5 Evaluation of the Reforming Mechanism 206 6.5.1 Destabilization of the Aromatic System 207 6.5.2 Oxidation of Soot Precursors and CO Formation 207 6.5.3 Further Evidence of the Effect of Plasma 209 6.6 Conclusions 210 References 211 7 Fate and Behaviour of Inorganic Constituents 214 7.1 Introduction 214 7.2 Experiments and Methods 217 7.2.1 Materials 217 7.2.2 Test Conditions 218 7.2.3 Sampling and Analysis 220 7.3 Results and Discussion 222 7.3.1 Plant Operation 222 7.3.1.1 Process Stability 222 7.3.1.2 Gasification Operation Analysis 224 7.3.1.3 Mass Balance 225 7.3.2 Analysis Data and Evaluation of Solid Samples 226 7.3.2.1 Partitioning of Major and Trace Elements 226 7.3.2.2 Chlorine and Sulphur Self-retention in the Fluid-Bed 229 7.3.2.3 Mineralogical-Chemical Characterisation of Residues 231 7.3.2.4 FBG Bed 232 PC Slag 233 7.4 Conclusions 236 References 236 8 Conclusions and Future Work 238 8.1 Further Discussion and Recommendations 240 8.1.1 Operation of Fluidised Bed Reactors on Waste Fuels 240 8.1.2 Plasma for Treatment of Ashes and Gases 241 8.1.3 Fuel Flexibility 242 8.1.4 Correlation Between Theoretical and Observed Behaviour 242 8.1.5 New Reforming Mechanisms of Tars and Organic Sulphur Compounds in Plasma Environment 243 8.1.6 Partitioning and Chemistry of Inorganic Components in the Solid Phase 243 8.1.7 Accuracy and Consequences for Scale up 244 8.2 Future Work 244 8.2.1 Modelling 244 8.2.2 Experimental 245 Appendix 246 A.1 FTIR Spectrometer Calibration Testing 246 Outline placeholder 0 A.1.1 General Background 246 A.1.2 Report on Testing Undertaken 246 A.2 SCADA Screen 248 A.3 Run Operating Logs 248 A.4 Error Assessment 249 Front Matter....Pages i-xxviii Introduction....Pages 1-17 Gasification of Waste Derived Fuels in Fluidized Beds: Fundamental Aspects and Industrial Challenges....Pages 19-63 Plasma as an Alternative Way to Gas Reforming and Ash Disposal....Pages 65-92 Apparatus and Investigative Approach....Pages 93-119 Modelling of a Two-Stage Process: Comparison of Different Approaches and Performance Analysis....Pages 121-160 Tar Evolution in the Two Stage Fluid Bed-Plasma Gasification Process....Pages 161-190 Fate and Behaviour of Inorganic Constituents....Pages 191-214 Conclusions and Future Work....Pages 215-222 Back Matter....Pages 223-231