ABSTRACT Title of Document: CHARACTERISTICS AND CHEMICAL KINETICS OF HYDROGEN SULFIDE COMBUSTION IN THERMAL CLAUS REACTOR Hatem Mohamed Mohiy Elden Selim, Doctor of Philosophy, 2012 Directed by: Professor Ashwani K. Gupta, Department of Mechanical Engineering Hydrogen sulfide is a hazardous gas from both environmental safety and human health perspectives. Hydrogen sulfide presence in any combustion application results in the formation of acidic gases that affects ozone layer and causes acidic precipitation. Exposure to H 2S levels at 100 ppm or higher can endanger human life. Hydrogen sulfide is commonly found to exist in crude natural gas and oil wells. With the decrease in fossil fuels reserves around the world, we will have to rely on extracting energy from wells that contain higher amounts of H 2S. In addition, environmental regulations strictly regulate the H2S discharge into the atmosphere. Subsequently, efficient hydrogen sulfide treatment becomes of increasing importance with time. Hydrogen sulfide treatment is typically a chemical reaction process (Claus process) in which hydrogen sulfide is combusted to end-products of sulfur and water. Hydrogen sulfide combustion in thermal Claus reactor has been investigated in this research. A reduced reaction mechanism for H 2S oxidation has been developed using a novel error-propagation-based approach for reduction of detailed reaction mechanisms. The reduced mechanism has been used for detailed investigation of chemical kinetics mechanistic pathways in Claus process. Experimental examination of H 2S combustion in different flames, methane/air and hydrogen/air, is provided. Chemical kinetics pathways and reaction conditions responsible for sulfurous compounds formation (SO 2, CS 2, and COS) are addressed. Hydrogen sulfide flame emissions have been investigated for intermediate species identification using chemiluminescence flame spectroscopy. Effect of acid gas composition (H 2S, CO 2 and N2) on hydrogen sulfide combustion and Claus process efficiency is also provided. Finally, examination of the quality of captured sulfur with respect to reactor conditions is presented. CHARACTERISTICS AND CHEMICAL KINETICS OF HYDROGEN SULFIDE COMBUSTION IN THERMAL CLAUS REACTOR By Hatem Mohamed Mohiy Elden Selim Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2012 Advisory Committee Professor Ashwani K. Gupta, Chair Professor Ahmed S. Al Shoaibi, The Petroleum Institute, Abu Dhabi Professor Nam S. Wang Professor Bao Yang Professor Kenneth H. Yu, Dean’s Representative © Copyright by Hatem Mohamed Mohiy Elden Selim 2012 DEDICATION To my parents, my beloved wife, and my children ii ACKNOWLEDGMENTS My experience as a student in The Combustion Laboratory at The University of Maryland has been very fruitful. One result of this experience is the five-year research effort presented in this dissertation. Throughout these years I have also met so many amazing persons. I would like firstly to thank my advisor, Dr. Ashwani Gupta for his sustained support. I have learned from Dr. Gupta the true meaning of hard work and perseverance. I am also grateful to Dr. Ahmed Al Shoabi for his insightful input on my research. I also will never forget the sincere friendship and great memories I have had with all the Lab. members. I, also, am dearly thankful to my family who gave me nothing but support and belief. I am especially thankful to my father, Dr. Mohiy Selim for his support and inspiration, and my mother, Mrs Hala El Halwagy for all her love. I am also sincerely thankful to my beloved wife, Mai Omar for all the support and all what she sacrificed to company me along in this journey. Also my daughter Farida and my son Malek for all the love and euphoria they filled my life with. Finally, I would like to express my deep gratitude to The Petroleum Institute, Abu Dhabi and ADNOC for their financial support of this project. I am also grateful to Reaction Design for their support to the numerical part of this research by providing a free license of CHEMKIN-PRO software. iv TABLE OF CONTENTS Dedication...........................................................................................................................ii Acknowledgments..............................................................................................................iv Table of Contents………………………………………………………………………...vi List of Tables…………………………………………………………………………......x List of Figures……………………………………………………………………………xi Nomenclature.................................................................................................................xviii Chapter 1: Introduction……………………………………………………………………1 1.1 Hazards of Hydrogen Sulfide……………………………..………………………1 1.2 Hydrogen Sulfide Treatment……………………………………………………...2 1.2.1 Amine Extraction process……………………………………….………….2 1.2.2 Claus Process………………………………………………………………..4 1.3 Motivations and Objectives……………………………………………………….4 1.4 Research Framework……………………………………………………………...6 Chapter 2: Literature Review……………………………………………………………...8 2.1 Development of H 2S Reaction Mechanisms………………………………………8 2.2 Hydrogen Sulfide Flame Chemistry……………………………………………..15 2.3 Hydrogen Sulfide Flame Spectroscopy………………………………………….23 Chapter 3: Reduced Mechanism for Hydrogen Sulfide Oxidation………………………28 3.1 Detailed Mechanism, Temperature Range, and Major Species……………….…29 3.2 Reduction Methodology………………………………………………………….30 3.2.1 Preliminary Reduction Procedure………………………………………….30 3.2.2 Direct Relation Graph and Error Propagation Methodology………………31 vi 3.2.2.1 Direct Relation Graph (DRG) Approach…………………………….31 3.2.2.2 Error Propagation (EP) Approach……………………………………34 3.2.3 Direct Elementary Reaction Error (DERE) Approach……………………..35 3.3 Reduced Mechanism Validation………………………………………………....39 3.4 Mechanistic Pathways of Claus Reactions……………………………………....44 3.5 Summary……………………………………………………………...………….45 Chapter 4: Experimental Setup and Diagnostics………………………………………...48 4.1 Experimental Setup………………………………………………………………48 4.1.1 Burner………………………………………………………………………...48 4.1.2 Quartz Tube Reactor…………………………………………………….……49 4.1.3 Sampling System……………………………………………………………..50 4.1.4 Flow Rates Supply and Control System……………………………………...51 4.2 Diagnostics…………………………………………………………………….…51 4.2.1 Gas Chromatography……………………………………………...……….52 4.2.2 Flame Spectroscopy………………………………………………………..52 4.2.3 X-Ray Powder Diffraction………………………………………...……….52 4.2.4 Laser Induced Breakdown Spectroscopy (LIBS)………………………….53 4.3 Experimental Difficulties……………………………………………...…………54 Chapter 5: Experimental Results and Discussion………………………………………..56 5.1 Hydrogen Sulfide Combustion in Flames………………………………………..56 5.1.1 H2S Combustion in Methane/Air Flames.........................................................57 5.1.1.1 Temperature Measurements.................................................................58 5.1.1.2 Combustion Products Analysis………………………………………59 vii 5.1.1.3 Summary…………………………………………………………..…67 5.1.2 H2S Premixed Combustion in CH 4/Air Flames……………………………....69 5.1.2.1 Reactor Temperature Distribution………………………………...…69 5.1.2.2 Hydrogen Sulfide Combustion Analysis…………………………….71 5.1.2.3 Summary……………………………………………………………..78 5.1.3 Acid Gas (H 2S and CO 2) Combustion in H 2/Air Flames……………………..79 5.1.3.1 Temperature Measurements………………………………………….80 5.1.3.2 Hydrogen/Air Flame……………………………………………...….81 5.1.3.3 Addition of 100% H 2S Acid Gas…………………….………………81 5.1.3.4 Addition of 50% H 2S/50% CO 2 Acid Gas………………………...…84 5.1.3.5 Summary……………………………………………………………..89 5.2 Hydrogen Sulfide Flame Spectroscopy………………………………………….90 5.2.1 H 2S/O 2 Flame Spectroscopy……………………………………….…………90 5.2.2 H 2/Air/H 2S Flame Spectroscopy.......................................................................95 5.2.3 Summary.........................................................................................................103 5.3 Effect of Acid Gas Composition on H 2S Treatment…………………………....103 5.3.1 Temperature Measurements………………………………………………104 5.3.2 Combustion of CO 2-Laden Acid Gas…………………………………….106 5.3.3 Combustion of N 2-Laden Acid Gas………………………………………112 5.3.4 Summary………………………………………………………………….113 5.4 Effect of Reaction Parameters on the Quality (Purity) of Captured Sulfur in Claus Process………………………………………………………………………….114 5.4.1 Effect of Equivalence Ratio………………………………………………115 viii 5.4.2 Effect of Acid Gas Contaminants………………………………………...117 5.4.3 Effect of Hydrocarbon Fuels……………………………………………...118 5.4.4 Summary.....................................................................................................121 Chapter 6: Experimental Error Analysis………………………………………..………123 6.1 Systematic Error…………………………………………………….…………..123 6.2 Random Error……………………………………………...……………………127 Chapter 7: Conclusions and Research Contributions……………………………..…….128 7.1 Conclusions………………………………………………………….………….128 7.1.1 Reduced Mechanism for H 2S Oxidation……………….…………………128 7.1.2 Hydrogen Sulfide Combustion in Flames…………………...……………129 7.1.3 Hydrogen Sulfide Flame Spectroscopy…………………………………..131 7.1.4 Practical issues of H 2S Treatment……………………………………..….131 7.2 Research Contributions………………………………………...……………….132 Chapter 8: Recommendations for Future Work……………………………...…………133 8.1 Effect of BTX on H 2S Treatment…………………………………………….…133 8.2 Near-Isothermal Claus Reactor……………………………………………...….133 8.3 Hydrogen Separation from H 2S stream…………………………...…………….134 8.4 Reforming of Sulfur Compounds in Claus Reactor…………………………….134 Appendix