University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2013-07-24 Ultraviolet Degradation of H2S in Waste Gas: A Comprehensive First–Principles Model Asili, Vahid Asili, V. (2013). Ultraviolet Degradation of H2S in Waste Gas: A Comprehensive First–Principles Model (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/28548 http://hdl.handle.net/11023/847 master thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY Ultraviolet Degradation of H2S in Waste Gas: A Comprehensive First – Principles Model by Vahid Asili A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF CHEMICAL AND PETROLEUM ENGINEERING CALGARY, ALBERTA JULY, 2013 © Vahid Asili 2013 ABSTRACT In upstream oil and gas operations, a considerable amount of hydrogen sulfide (H2S) is being emitted every year. Health issues associated with H2S that might be very serious vary dependent on the length of exposure. Furthermore, the gas is highly corrosive, which is a concern in the industry. A promising technique that can be used to remove this air pollutant from waste gas is photolysis, which has been successfully used in wastewater treatment processes. However, to the best knowledge of the author, no inclusive model has yet been developed for H2S gas phase photolysis. In this research study, a sophisticated simulation model was developed successfully to describe ultraviolet degradation of H2S from waste gas. The photochemical reactor has been modeled with 19 chemical species and a total of 47 chemical and photochemical reactions which includes a light field model, a chemical model, a flow pattern model and a mass transfer model. Simulation shows that the UV degradation of H2S in waste gas is a highly efficient process. Simulations were run to investigate the process efficiency is a function of initial concentration, gas flow rate, and relative humidity. The model was also validated with some literature experimental data by applying the model to those experimental conditions, and comparing the results. Comparison of simulation results and the experimental data indicates that the model overestimates the removal efficiency to some extent; however, observing the same trends in two different cases of the effect of initial H2S concentration and the effect of gas flow rate validates the model with sufficient accuracy to establish the feasibility of the process. Previously, it was found experimentally that the main photolysis (or photocatalysis) product is 2- SO4 (or H2SO4) at very low concentration of H2S. The model also agrees with this result, and furthermore predicts SO2 as another photolysis product which is predominant at high ii concentration of H2S. Hence altogether, it can be concluded based on the model that the UV degradation technique is effective, and it decomposes H2S to less harmful products which are also easier to be treated. Moreover, the capability of the model for modeling the degradation of multiple pollutants at the same time was tested by model extension with NOx reactions. According to the simulation results, adding H2S in the NOx photolysis system has positive effects on the degradation efficiency for both H2S and NOx. The extended model indicates that the proposed model can be used as the basis of a modular comprehensive model to predict removal efficiency for each species and moreover product analysis when more than one pollutant is present. iii ACKNOWLEDGEMENTS I would like to express my utter gratitude to my supervisor, Dr. Alex De Visscher, for his continuous support throughout the course of my program. His fruitful advices have always helped and encouraged me through different stages of work. He has remarkably been thoughtful of me and encouraged me during my research. In addition, I am thankful to my co-supervisor, Dr. Jalel Azaiez. His support is greatly acknowledged and appreciated. I would like to express my sincere appreciation and love for my parents and siblings, whose support has always been with me in life. Moreover, I would like to specially thank my lovely wife, Behnoosh, for her patience, understanding, and invaluable source of unconditional love and support. Also, I thank my dear friends; Kamran, Ehsan and Hashem for being great sources of motivation and encouragement in many respects during the project and over the project in my day to day life. I am also grateful to my official referees; Dr. Roberts, Dr. Mahinpey, and Dr. Mohamad for their participation in assessment of my thesis. iv DEDICATION To my beloved parents whose love, guidance, and sacrifices have made me the person I am today. To my lovely wife for her constant love, understanding, support and encouragement. v Table of Contents Abstract ............................................................................................................................... ii Acknowledgements ............................................................................................................ iv Dedication ............................................................................................................................v Table of Contents ............................................................................................................... vi List of Tables ................................................................................................................... viii List of Figures .................................................................................................................... ix List of Symbols .................................................................................................................. xi CHAPTER 1 : INTRODUCTION .......................................................................................1 CHAPTER 2 : LITERATURE REVIEW ............................................................................4 2.1. Definition of Photolysis Terms ................................................................................4 2.2. Hydrogen Sulfide (H2S) ...........................................................................................9 2.2.1. General Properties: ....................................................................................9 2.2.2. Health effects of H2S...............................................................................10 2.2.3. H2S in Oil and Gas industries .................................................................12 2.2.4. H2S Emission ..........................................................................................12 2.2.5. Corrosive Effects.....................................................................................14 2.3. Waste Water Photolysis .........................................................................................15 2.4. Waste gas photolysis ..............................................................................................17 2.4.1. Background .............................................................................................17 2.4.2. H2S Removal ...........................................................................................20 CHAPTER 3 : MODEL DEVELOPMENT ......................................................................23 3.1. Flow Pattern Model (Velocity Profile) ..................................................................23 3.2. Material Balance ....................................................................................................26 3.3. Radiation Field .......................................................................................................29 3.4. Chemical Model .....................................................................................................34 3.4.1. Chemical Reactions.................................................................................34 3.4.2. Photochemical Reactions ........................................................................40 3.5. Summary of the Model Equations .........................................................................44 3.6. Model Extension (Adding NOx reactions) .............................................................47 3.6.1. Chemical Reactions Added .....................................................................47 3.6.2. Photochemical Reactions Added ............................................................52 CHAPTER 4 : SIMULATION RESULTS AND DISCUSSIONS ...................................55 4.1. Product Analysis and Mechanisms ........................................................................56 4.2. Parameters of H2S Degradation .............................................................................59 4.2.1. Effect of H2S inlet concentration ............................................................59 4.2.2. Effect of gas flow rate .............................................................................60 4.2.3. Effect of water content (Relative Humidity) ...........................................62 4.2.4. Effect of Temperature .............................................................................65