Novel Modeling Approaches for the Entrained-Flow Gasification of Bio
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Novel modeling approaches for the entrained-flow gasification of bio-slurries A thesis accepted by the Faculty of Aerospace Engineering and Geodesy of the Universität Stuttgart in partial fulfillment of the requirements for the degree of Doctor of Engineering Sciences (Dr.-Ing.) by Quentin FRADET born in Montivilliers, France Main referee: Prof. Dr. rer. nat. Uwe RIEDEL Co-referee: Prof. Dr.-Ing. Dieter STAPF Date of defense: 30. June 2020 Institute of Combustion Technology for Aerospace Engineering (IVLR) Universität Stuttgart 2020 iii Acknowledgements This work has been carried out at the Institute of Combustion Technology of the German Aerospace Center (DLR) in Stuttgart under the direction of Prof. Dr. Uwe Riedel. I would like to express my deep gratitude to him for the chance that he gave me and for the guidance throughout this research work. I would also like to thank Prof. Dr. Dieter Stapf from the Karlsruhe Institute of Technology (KIT) for having taken over the co-assessment of this thesis. This work would not have been possible without the scientific cooperation between KIT and DLR, and especially the input of Prof. Dr. Thomas Kolb, Prof. Dr. Nicolaus Dahmen and Dr. Sabine Fleck. I would like to thank everyone who supported and accompanied me in many ways during my time at the institute. I would also like to acknowledge Dr. Marina Braun-Unkhoff for her supervision and her always fair advises, Dr. Elke Goos for her personal support and Niranjan Fernando for the mutual help and the company at various conferences. My thanks also to Dr. Markus Köhler for his assistance over the last year. Little would have been possible without all the IT support of Dr. Jan Hendrik Starcke and Dietmar Schmitt. Also, many thanks to my seatmates Aziza Kanz and Dr. Torsten Methling. I truly appreciated the time spent together and the daily liter of coffee. For many memorable times, I must also thank, among others, Dr. Mehdi Abbasi and Astrid Ramirez. Finally, I’m especially grateful towards my family for their understanding and support throughout these years; the visits in Germany were appreciated. And a very special thank to Alice, who provided unwavering encouragement and support. v Contents Acknowledgements iii Résumé xxvii Kurzfassung xxix Abstract xxxi 1 Introduction1 1.1 Synthetic fuels..............................1 1.1.1 Synthesis routes.........................1 1.1.2 Biomass-to-Liquid.......................2 1.2 The bioliq process............................6 1.2.1 Principle.............................6 1.2.2 Entrained-flow gasification of bio-slurry.......... 11 Bio-slurry atomization..................... 13 Bio-oil conversion....................... 15 Solid conversion........................ 19 Slag................................ 22 Gas phase............................ 23 1.3 Modeling the entrained-flow gasification.............. 24 1.3.1 Experimental data from the laboratory gasifier REGA... 24 1.3.2 Traditional models and their limitations........... 25 1.4 Scope of this thesis........................... 26 2 Computational Fluid Dynamics modeling of combustion 29 vi 2.1 Basic flows................................ 29 2.1.1 Governing equations...................... 29 2.1.2 Finite volume method..................... 33 2.2 Simple combustion applications.................... 41 2.2.1 Test case presentation and setup............... 41 2.2.2 Finite Rate chemistry...................... 42 2.3 Turbulence................................ 47 2.3.1 Overview............................ 47 2.3.2 Closure models......................... 50 2.3.3 Limitations of RANS approach................ 51 2.4 Chemistry turbulence interaction................... 52 2.4.1 Combustion model desideratum............... 52 2.4.2 Combustion models...................... 53 2.5 Multiphase flow approaches...................... 55 2.5.1 Lagrangian methods...................... 56 2.5.2 Eulerian methods........................ 56 3 Eulerian-Eulerian approach for liquid spray modeling 59 3.1 Governing equations.......................... 60 3.2 Interphase transfers........................... 66 3.2.1 Evaporation modeling..................... 66 3.2.2 Momentum transfer...................... 69 3.2.3 Validation case......................... 71 4 The sectional approach for char gasification 75 4.1 Concept of the sectional approach.................. 75 4.2 Model construction........................... 76 4.2.1 Particle size distribution.................... 76 4.2.2 Discretization.......................... 77 4.3 Reactions................................. 79 4.3.1 Equations............................ 79 vii 4.3.2 Associated kinetic rates.................... 81 4.4 Thermodynamic properties of bio-char................ 85 4.4.1 Heat capacity.......................... 86 4.4.2 Enthalpy and entropy..................... 87 5 Simulation results on the REGA gasifier 91 5.1 REGA experiments and their numerical representation...... 91 5.1.1 Experimental setup....................... 91 5.1.2 Numerical setup........................ 92 5.2 Gasification of ethylene glycol..................... 95 5.2.1 REGA-glycol-T1........................ 95 5.2.2 Effect of operating conditions on the gasification yield.. 100 5.3 Gasification of ethylene glycol and char............... 104 5.3.1 REGA-slurry1-T2........................ 104 5.3.2 Comparison with a second char............... 110 5.3.3 Higher char content...................... 112 6 Conclusion 115 Bibliography 118 A Gasification cost estimation 139 B Summary of wood and straw char input parameters 141 C CFD contours 143 C.1 REGA-glycol-T1............................. 143 C.2 REGA-slurry1-T2............................ 147 C.3 REGA-slurry2-T2............................ 150 ix List of Figures 1.1 Estimation of the cost of one liter BtL fuel for various plant sizes.5 1.2 Schematic overview of a BtL manufacturing process........7 1.3 Bioliqr high-pressure entrained-flow gasifier............ 12 1.4 SEM images of cenospheres...................... 18 a Cenosphere formed after pyrolysis of a straw oil droplet. 18 b Slurry cenospheres with embedded former primary char. 18 1.5 Gasification regimes of a porous carbon............... 20 2.1 CFD plots of a hydrogen laminar flame............... 46 a Mesh and initial temperature................. 46 b Temperature field........................ 46 c Water mass fraction...................... 46 2.2 Experimental and simulation results of a hydrogen laminar flame 47 a Results along the axis of symmetry.............. 47 b Results along the radius 20 mm above the burner..... 47 3.1 CFD grids used for the Eulerian-Eulerian validation case..... 72 a 2D grid: 3,400 cells....................... 72 b 3D grid: 1,142,400 cells..................... 72 3.2 Eulerian-Eulerian validation test case: liquid and gas evolution. 73 a Liquid evolution for EE 2D, EE 3D and EL 3D....... 73 b Verification of the gas phase continuity for EE 2D..... 73 3.3 Results along the axis of EE 2D, EE 3D, and EL 3D......... 74 a Ethylene glycol mass fraction vs. distance.......... 74 b Temperature vs. distance................... 74 x 4.1 Classes creation of the sectional approach.............. 78 a Volume distribution function vs. particle diameter..... 78 b Mass fraction distribution of the BIN-classes........ 78 c Mass distribution function vs. logarithm of molar weight. 78 d Ratio representative of the intra-class distribution..... 78 4.2 Global char reaction scheme...................... 80 4.3 Specific heat capacity of primary char, secondary char and ash.. 87 5.1 Meshes for the nozzles region of REGA............... 94 a Nozzle with angled gas outlet................ 94 b Nozzle with parallel gas outlet................ 94 5.2 Results regarding the liquid phase for REGA-glycol-T1...... 97 a CFD contour of the liquid volume fraction......... 97 b CFD contour of the evaporation rate............. 97 c Liquid mass and volumetric flow rate along the axis.... 97 5.3 Gas phase CFD contours of REGA-glycol-T1............ 98 a Axial velocity and streamlines in grey............ 98 b Gas phase temperature..................... 98 c Ethylene glycol mole fraction................. 98 d Hydrogen reaction rate.................... 98 e Hydrogen mole fraction.................... 98 5.4 Major gas phase species of REGA-glycol-T1............. 99 a Carbon monoxide mole fraction............... 99 b Water mole fraction....................... 99 c Carbon dioxide mole fraction................. 99 d Nitrogen mole fraction..................... 99 e Oxygen mole fraction..................... 99 f Methane mole fraction..................... 99 5.5 Experimental and simulation results of REGA-glycol-T1..... 100 a Concentration 300 mm below the burner.......... 100 xi b Concentration 680 mm below the burner.......... 100 c Temperature 300 mm below the burner........... 100 d Temperature 680 mm below the burner........... 100 5.6 Experimental and simulation results of REGA-glycol-T2..... 101 a Concentration 300 mm below the burner.......... 101 b Concentration 680 mm below the burner.......... 101 c Temperature 300 mm below the burner........... 101 d Temperature 680 mm below the burner........... 101 5.7 Operating conditions of the 29 simulations tested......... 102 5.8 Simulation results of the 29 simulations tested........... 103 a Methane mole fraction..................... 103 b Cold gas efficiency....................... 103 5.9 Comparison REGA-glycol-T2 and REGA-slurry1-T2........ 105 a REGA-glycol-T2: concentration................ 105 b REGA-slurry1-T2: concentration............... 105 c REGA-glycol-T2: