A STUDY OF PYROLYSIS OF CHARRING MATERIALS AND ITS APPLICATION TO FIRE SAFETY AND BIOMASS UTILIZATION by Won Chan Park A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Mechanical Engineering) in The University of Michigan 2008 Doctoral Committee: Professor Arvind Atreya, Chair Professor James F. Driscoll Professor Margaret S. Wooldridge Associate Professor Hong G. Im © Won Chan Park 2008 To My Family ii Acknowledgements I would like to express my deepest gratitude to my advisor, Dr. Arvind Atreya for his excellent guidance. This work would not have been possible without his consideration, encouragement, inspiration and insightful suggestions. I would also like to express my appreciation to my doctoral committee, Professor James F. Driscoll, Professor Hong G. Im and Professor Margaret S. Wooldridge for their thoughtful advice. I am grateful to Dr. Howard R. Baum for his helpful suggestions. I would like to thank Professor Michael M. Chen for his advice on numerical techniques. I wish to thank my colleagues, Sung-Joon Hwang, Seung Jun Shin, Paul Teini and former lab members, Dr. Tershia Pinder, Dr. Hyoseok Lee, Dr. Melissa Chernovsky and Dr. Xin He for their collaboration on my research. I also wish to thank Brad Hartwell for his help on my experimental apparatus. I am thankful to Sean Berhan for editing my writing for grammar. I owe my loving thanks to my wife Kyung Hee Lee, my daughter Sejeong Park and my son Bradley Jin Park for their encouragement and understanding. My special gratitude is due to my parents and my brother and his family for their loving support. Financial support for this work was provided, in part, by National Institute of Standard and Technology and Industrial Assessment Center at the University of Michigan. iii Table of Contents Dedication .................................................................................................................... ii Acknowledgements ............................................................................................... iii List of Figures ......................................................................................................... vii List of Tables ........................................................................................................... xii List of Appendices ............................................................................................... xiii List of Abbreviations ......................................................................................... xiv Abstract ..................................................................................................................... xvii 1. Introduction .......................................................................................................... 1 1.1 Background ........................................................................................................ 1 1.2 General features of wood pyrolysis .................................................................... 2 1.3 Pyrolysis modeling ............................................................................................. 4 1.4 Kinetics ............................................................................................................... 6 1.5 Outline of this thesis ........................................................................................... 7 1.5.1 Charring solids undergoing opposed flow flame spread ............................ 8 1.5.2 Determination of pyrolysis temperature ..................................................... 9 1.5.3 Experimental and theoretical investigation of wood pyrolysis ................... 9 1.5.4 Three dimensional pyrolysis model for arbitrary geometry charring material .............................................................................................................. 10 2. Charring Solids Undergoing Opposed-flow Flame Spread ............... 11 2.1 Introduction ...................................................................................................... 11 2.2 Mathematical modeling .................................................................................... 13 2.2.1 Reaction mechanism ................................................................................. 14 2.2.2 Conservation of mass and energy ............................................................. 15 iv 2.2.3 Numerical analysis .................................................................................... 18 2.2.3.1 Discretization of governing equations .............................................. 19 2.2.3.2 Curved interface ................................................................................ 25 2.2.3.3 Tracking interface ............................................................................. 27 2.3 Numerical analysis ........................................................................................... 30 2.3.1 Temperature and pressure ......................................................................... 32 2.3.2 Product yields ........................................................................................... 34 2.3.3 Pyrolysis temperature ............................................................................... 37 2.3.4 Simplified models: Char layer thickness .................................................. 38 2.3.5 Simplified models: Pressure ..................................................................... 39 2.3.6 Comparison with the analytical model ..................................................... 40 2.3.7 Computational time ................................................................................... 40 2.4 Summary .......................................................................................................... 41 3. Determination of Pyrolysis Temperature for Charring Materials 42 3.1 Introduction ...................................................................................................... 43 3.2 Energy and mass balanced pyrolysis temperature concept .............................. 44 3.3 Pyrolysis models .............................................................................................. 45 3.3.1 Finite-rate kinetics model ......................................................................... 45 3.3.2 Infinite-rate kinetics (pyrolysis-front) model ........................................... 47 3.3.3 Determination of the pyrolysis temperature ............................................. 48 3.4 Results and discussion ...................................................................................... 49 3.4.1 Effect of boundary conditions ................................................................... 50 3.4.2 Effect of geometry .................................................................................... 51 3.4.3 Effects of various parameters on the pyrolysis temperature ..................... 53 3.4.4 Kinetic parameters .................................................................................... 59 3.4.5 Estimation of mass and energy balanced pyrolysis temperature .............. 61 3.4.6 Comparison with experiments on wood ................................................... 63 3.5 Summary .......................................................................................................... 64 4. Experimental and Theoretical Investigation of Wood Pyrolysis ..... 66 4.1 Introduction ...................................................................................................... 66 4.1.1 Problem description and literature review ................................................ 67 v 4.2 Experiment setup .............................................................................................. 69 4.3 Experimental result .......................................................................................... 74 4.4 Thermal mechanism of wood pyrolysis ........................................................... 79 4.4.1 Model description ..................................................................................... 79 4.4.1.1 Kinetics model .................................................................................. 79 4.4.1.2 Mass conservation ............................................................................. 83 4.4.1.3 Energy conservation .......................................................................... 87 4.4.2 Results ....................................................................................................... 90 4.4.2.1 Heat of pyrolysis and pyrolysis rate .................................................. 90 4.4.2.2 Exothermic reactions ......................................................................... 91 4.5 Modeling of endo-/exothermic wood pyrolysis ............................................... 99 4.6 Summary ........................................................................................................ 106 5. Three Dimensional Arbitrary Geometry Pyrolysis Model .............. 107 6. Conclusions and Future Work ................................................................... 111 6.1 Summary ........................................................................................................ 111 6.2 Conclusions .................................................................................................... 112 6.3 Contributions .................................................................................................. 114 6.4 Future work ...................................................................................................