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  • Atlanta University CenterDigitalCommons@Robert W. Woodruff Library, AtlantaUniversity Center

    ETD Collection for AUC Robert W. Woodruff Library

    5-1-1999

    Reaction mechanism of N0x destruction by non-thermal plasma dischargeZhicheng WangClark Atlanta University

    Follow this and additional works at: http://digitalcommons.auctr.edu/dissertations

    Part of the Chemistry Commons

    This Thesis is brought to you for free and open access by DigitalCommons@Robert W. Woodruff Library, Atlanta University Center. It has beenaccepted for inclusion in ETD Collection for AUC Robert W. Woodruff Library by an authorized administrator of DigitalCommons@Robert W.Woodruff Library, Atlanta University Center. For more information, please contact cwiseman@auctr.edu.

    Recommended CitationWang, Zhicheng, "Reaction mechanism of N0x destruction by non-thermal plasma discharge" (1999). ETD Collection for AUC RobertW. Woodruff Library. Paper 980.

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  • ABSTRACT

    CHEMISTRY

    WANG, ZHICHENG B.A. SICHUAN UNIVERSITY,1986

    M.S. RIPP, 1991

    REACTION MECHANISM OF NOx DESTRUCTION

    BY NON-THERMAL PLASMA DISCHARGE

    Advisors: Professors Kofi B. Bota and Yaw D. Yeboah

    Dissertation dated May, 1999

    Nitrogen oxides (NOx) contribute to the formation of acid rain and ground-level

    ozone. Cost-effective technologies that destroy NOx from gas streams are needed. Of

    particular interest are Non-thermal plasma technologies that offer an innovative approach

    to the solution ofNOx emission control.

    This study investigates the use of a particular electrical discharge technique, the

    barrier discharge. Experiments were conducted in double dielectric barrier discharge

    (DDBD) reactors to elucidate the effects of physical and chemical variables on the NOx

    removal efficiencies. Analysis instruments included a FT-IR with a length adjustable gas

    cell, a GC-MS, several gas analyzers and an emission spectrometer.

    The variables investigated include input power, chemical composition, residence

    time, and gap spacing. Through this investigation, an overall optimization of DDBD

    performance was obtained. Of these, we primarily investigated the effect of discharge gap

    spacing on the electrical and chemical processes that occur in non-thermal plasma

    discharge (NTPD). A numerical model was developed to simulate the physical and

    chemical processes during the oxidation and reduction of NOx. Experiments and

    1

  • calculations were performed to investigate the effects of the above-mentioned variables

    on breakdown electric field, free electron energy distribution, electron impact kinetic

    rates, and chemical reactions. Results from the calculations and experiments

    demonstrated the complex relations between NOx removal efficiency and the tested

    variables. A mechanism ofNOx destruction in a NTPD was proposed.

    This study revealed that the characteristics of microdischarges are the key to

    understanding the NTPD process. Optical measurements, by means of a high speed

    intensified imager, provided important information on the microdischarge. This

    information helped to develop the numerical model, which established the relation

    between surface charge and charge density within a microdischarge. Results of this study

    should provide a basis for developing a potential solution for the reduction of NOx

    emission from off-gas sources, such as diesel-powered aerospace ground equipment used

    on the Air Force.

  • REACTION MECHANISM OF NOx DESTRUCTION

    BY NON-THERMAL PLASMA DISCHARGE

    A DISSERTATION

    SUBMITTED TO THE FACULTY OF CLARK ATLANTA UNIVERSITY

    IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR

    THE DEGREE OF DOCTOR OF PHILOSOPHY

    IN CHEMISTRY

    BY

    ZHICHENG WANG

    DEPARTMENT OF CHEMISTRY

    ATLANTA, GEORGIA

    MAY 1999

  • 1999

    ZHICHENG WANG

    All Right Reserved

  • ACKNOWLEDGEMENT

    I am extremely grateful to Professor Kofi B. Bota, Professor Yaw D. Yeboah and

    Professor T.J Bai for their guidance, experience and encouragement in directing the

    research presented in this thesis. Also thanks to Mr. Steven Federle, Dr. John Rogers and

    Dr. Glenn Rolader for providing technical insights. Additionally, thanks to Professor

    Reynolds Verrett for his input as my thesis committee member.

    I would like to thank the following people for their assistance and advise: Dr. Jad

    Batteh and Dr. Xiansheng Nie.

    I also would like to thank Professor Cass Parker for his help in the Graduate

    program and Dr. Yi Pang for his advises and support.

    This project was supported by the US Air Force under grant number

    F08630-96-K-0015.

    Finally, I wish to express my thanks and appreciation to my wife, Liqin, for all

    her love and support.

  • TABLE OF CONTENTS

    ACKNOWLEDGEMENT ii

    LIST OF FIGURES ""viLIST OF TABLES viii

    I. INTRODUCTION

    LIBackground 1

    1.2 Conventional Techniques for NOx Control 2

    1.3 Non-thermal Plasma Discharge Technologies 3

    1.4 Literature Reviews 5

    II. NON-THERMAL PLASMA DISCHARGE

    2.1 Theory and Apparatus 19

    2.1.1 The Electrical Breakdown 19

    2.1.2 The Boltzmann Equation 22

    2.1.3 Poisson's Equation 24

    2.1.4 Particle and Charge Density 24

    2.1.5 Reaction Rate Coefficients 25

    2.1.6 Manley's Equation 27

    2.2 Method Development 28

    2.3 Chemical Reactions 30

    III. EXPERIMENTS AND PROCEDURE

    3.1 Experimental Setup 32

    iii

  • 3.2 Physical Characteristics 35

    3.2.1 Power Measurement 35

    3.2.2 Breakdown Voltage, Current and Charge 36

    3.3 Optical Measurement 40

    3.4 Spectrum Analysis 42

    IV. RESULTS AND DISCUSSION

    4.1.1 The effect of Gas Composition 46

    4.1.1.1 Water 47

    4.1.1.2 Oxygen 49

    4.1.1.3 Hydrogen 52

    4.1.1.4 NOx 55

    4.1.2 Gap Spacing 57

    4.1.2.1 Breakdown Voltage 58

    4.1.2.2 NOx Removal 61

    4.1.2.3 Microdischarge Characteristics 64

    4.1.3 Photo Chemistry 72

    4.1.4 Power Input 75

    4.2 System Optimization 80

    4.3 Reaction Mechanisms and Modeling 83

    V. CONCLUSIONS AND RECOMMENDATIONS

    5.1 Conclusions 92

    5.2 Recommendations 97

    APPENDIX A 98

    IV

  • APPENDIXB 100

    APPENDIX C 113

    REFERENCES 134

  • LIST OF FIGURES

    No. Page

    3.1 The Experimental Set-up 34

    3.2 Voltage Waveforms for DDBD Cell 37

    3.3 Current Waveform 37

    3.4 Charge Waveform 38

    3.5 Comparison of Voltage, Current and Charge During Spikes 38

    3.6 Q-V Plot for Calculation ofBreakdown Voltage and Power 39

    3.7 Sketch of Simplified Microdischarge and Arrangement ofDDBD 41

    3.8 Picture ofA Microdischarge 42

    3.9 Spectrum ofFT-IR 43

    3.10 Emission Spectrum 44

    4.1 The Effect ofWater Concentration on NOx Removal Efficiency 47

    4.2 Picture ofA Single Microdischarge 49

    4.3 Dependence ofNOx Removal Efficiency on [02] 50

    4.4 Picture of Microdischarge 52

    4.5 NOx Removal Efficiency versus Power 53

    4.6 Gas Composition versus Power 54

    4.7 NO Concentration Effect on NO Removal 56

    4.8 Relationship Between Breakdown Voltage and Gap width 61

    4.9 NO Removal versus Energy Deposition 62

    vi

  • 4.10 NO Removal versus Gap Width 63

    4.11 Images ofMicrodischarges at Different Gap Widths 65

    4.12 Plot ofDischarge Radius versus Gap Width 68

    4.13 Plot ofFootprint Radius versus Gap Width 69

    4.14 Plot of the Footprint Radius, RO, versus the Microdischarge Radius, r 70

    4.15 Spectra ofProcessing Gases in NTPD 73

    4.16 Lissajous Figures with Input Powers 75

    4.17 Dependence of the Total Charges Transferred on Power Input 76

    4.18 NOx/NO Removal Efficiency versus Power Input 77

    4.19 FT-IR Spectra with Power Increasing 78

    4.20 Effects ofPower on the Photo Emission in the Discharge 79

    4.21 Dependence ofNOx Removal Efficiency on Residence Time 79

    4.22 NOx Removal versus Power Input at Optimized Conditions 82

    4.23 Results ofBOLSIG Running 88

    4.24 Simulation Results from Model 91

    vu

  • LIST OF TABLES

    No. Page

    4.1 NO Removal Efficiency at Various Gap Widths and Energy Depositions 65

    4.2 Summary ofMicrodischarge Properties Derived

    from Optical Measurements 68

    4.3 Estimates of the Volume Charge Density and Electron Density

    Using Equation (4.23) and Calculation of Reduced Electric Field 73

    4.5 Parameters Used in the One Run ofBOLSIG Modeling 88

    Vlll

  • CHAPTER I

    INTRODUCTION

    1.1 Background

    Nitrogen oxides have contributed to several air pollution problems including acid

    rain, ozone deplet

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