Partial Oxidation and Autothermal Reforming of Heavy Hydrocarbon Fuels with Non- Equilibrium Gliding Arc Plasma for Fuel Cell Applications A Thesis Submitted to the Faculty of Drexel University by Michael J. Gallagher, Jr. in partial fulfillment of the requirement for the degree of Doctor of Philosophy February 2010 © Copyright 2010 Michael J. Gallagher, Jr. All Rights Reserved. ii Acknowledgements I would like to express my sincerest gratitude to my Ph.D. advisors Dr. Alexander Fridman and Dr. Alexander Gutsol for all of their help and guidance over these past years. Working with them was a rewarding challenge and I had the privilege to participate in interesting research projects, travel to many interesting places, and be introduced to many of their friends and colleagues in the plasma community. I would like to especially thank my Ph.D. Committee: Dr. Alex Fridman, Dr. Nick Cernansky, Dr. Alex Rabinovich, Dr. Gary Friedman, and Dr. Alex Dolgopolsky. All of them have contributed greatly to my development at Drexel in many ways from teaching interesting courses, providing excellent research advice, and giving important career advice. I would also like to thank my fellow graduate students in the Mechanical Engineering Department and within the Drexel Plasma Institute. They are too numerous to name here, so I will just say thank you for your support, creative ideas, and encouragement. I also would like to thank my family who has supported and guided me throughout my lifetime and especially my parents, for without their hardwork and dedication to their children, I would never have made it this far. Finally, I would like to thank my wife Angela. You are everything to me and if it weren’t for your constant love and encouragement, I never would have finished this doctoral thesis. iii Table of Contents List of Tables ................................................................................................................................. vii List of Figures ............................................................................................................................... viii Abstract ..........................................................................................................................................xiii 1. Introduction to Plasma-assisted Synthesis Gas Production for Fuel Cell Applications .............. 1 1.1 Introduction ...................................................................................................................... 1 1.2 What is Plasma? ............................................................................................................... 4 1.3 Types and Classifications of Plasmas .............................................................................. 6 1.3.1 Arc Plasmas ............................................................................................................. 6 1.3.2 Non-Thermal Gliding Arc Plasmas .......................................................................... 7 1.3.3 Microwave and Radio-Frequency Plasma Discharges ............................................. 8 1.3.4 Dielectric Barrier Discharge Plasmas ...................................................................... 9 1.3.5 Continuous & Pulsed Corona Discharges .............................................................. 10 1.4 Chemical Reactions in Fuel Processing ......................................................................... 11 1.4.1 Combustion of Hydrocarbons ................................................................................ 11 1.4.2 Partial Oxidation of Hydrocarbons ........................................................................ 11 1.4.3 Steam Reforming of Hydrocarbons ....................................................................... 12 1.4.4 Oxidative Steam Reforming of Hydrocarbons ....................................................... 12 1.4.5 Dry (CO2) Reforming of Hydrocarbons ................................................................. 13 1.4.6 Water gas shift reaction.......................................................................................... 13 1.4.7 Oxygen-to-Carbon Ratio ........................................................................................ 14 1.4.8 Steam-to-Carbon Ratio .......................................................................................... 14 1.5 Important Equations to Measure Reforming Performance ................................................. 15 1.5.1 Specific Energy Requirement ...................................................................................... 15 1.5.2 Product yield ................................................................................................................ 16 1.5.3 Product Selectivity ....................................................................................................... 16 1.5.4 Energy conversion efficiency ....................................................................................... 16 1.6 Plasma as an alternative to traditional catalyst in fuel reforming .................................. 17 1.6.1 Thermal versus non-thermal mechanisms of plasma catalysis .............................. 19 1.6.2 Non-thermal plasma-induced mechanisms of ignition and stabilization of flames 20 iv 1.6.3 Effect of excited species on subthreshold ignition in H2-O2 mixtures ................... 21 1.6.4 Effect of ions on subthreshold ignition in H2-O2 mixtures .................................... 22 1.6.5 Effect of radicals and other long-lived species on subthreshold ignition .............. 23 1.6.6 Effect of plasma active species on hydrogen-rich syngas production systems ...... 24 1.6.7 Plasma catalysis of direct decomposition (pyrolysis) of methane ......................... 24 1.6.8 Plasma Catalysis of Partial Oxidation (POX) of methane ..................................... 25 1.7 Other Advantages of Plasma Catalysis in Fuel Reforming Systems ............................. 27 1.7.1 No Inertia (Preheating) Required ........................................................................... 28 1.7.2 No Sensitivity to Sulfur or Other Contaminates .................................................... 28 1.7.3 No Soot Formation ................................................................................................. 28 1.7.4 Plasma Reformers are Small and Compact ............................................................ 29 1.7.5 Possibility of Combining Desulfurization and Reforming ..................................... 30 1.8 Plasma Reforming of C1-C6 Hydrocarbons .................................................................... 30 1.8.1 Non-thermal plasma-assisted partial oxidation of methane ................................... 31 1.8.2 Non-Thermal Plasma-Assisted Steam-Reforming of Methane .............................. 32 1.8.3 Non-Thermal Plasma-Assisted Carbon Dioxide (Dry) Reforming of Methane .... 33 1.8.4 Non-thermal Plasma-Assisted Pyrolysis of Methane ............................................. 34 1.9 Plasma Reforming of Liquid Hydrocarbons .................................................................. 35 1.9.1 Plasma-Assisted Partial Oxidation of Diesel Fuel and its Surrogates into Synthesis Gas 37 1.9.2 Plasma-Assisted Steam-Oxidative Reforming (SOR) of Various Hydrocarbons Fuels into Synthesis Gas ........................................................................................................ 38 1.10 Combined plasma-catalytic reforming of hydrocarbons fuels into hydrogen-rich synthesis gas .............................................................................................................................. 39 1.10.1 Plasma-catalytic two-stage configuration for hydrocarbon reforming .................. 41 1.10.2 Plasma-catalytic single-stage configuration for hydrocarbon reforming ............... 42 2. Design, Testing, and Evaluation of Gliding Arc Plasma Reformers for Partial Oxidation of n- Tetradecane and Diesel Fuel to Synthesis Gas .............................................................................. 56 2.1 Introduction ......................................................................................................................... 56 2.2 Materials and Methods ......................................................................................................... 56 2.2.1 General System Scheme .............................................................................................. 56 2.2.2 Gas Chromatography and Detection of Products ......................................................... 57 v 2.2.3 Plasma power supplies ................................................................................................. 58 2.3 Concept and design of the Reverse Vortex Gliding Arc Reformer..................................... 59 2.3.1 The Concept of Reverse Vortex Flow .......................................................................... 59 2.3.2 System Design Constraints for the RVF-GA Reformer ............................................... 60 2.3.3 RVF-GA Reactor Design Scheme ............................................................................... 61 2.4 Thermodynamic Analysis of Partial Oxidation of n-Tetradecane .................................. 62 2.5 Experimental investigation of Partial Oxidation of n-Tetradecane using the RVF-GA Reformer .................................................................................................................................... 63 2.5.1 Effect of Increasing O/C