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Investigation of Compressible Fluid Behaviour in a Vent Pipe During Blowdown

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Investigation of Compressible Fluid Behaviour in a Vent Pipe During Blowdown Department of Chemical Engineering Investigation of Compressible Fluid Behaviour in a Vent Pipe during Blowdown Farhan Liyakat Husain Rajiwate This thesis is presented for the Degree of Master of Philosophy (Chemical Engineering) of Curtin University August 2011 Declaration To the best of my knowledge and belief this thesis contains no material previously published by any other person except where due acknowledgment has been made. This thesis contains no material which has been accepted for the award of any other degree or diploma in any university. Signature: …………………………………………. Date: ………………………... Dedications To Mum and Dad “Never regard study as a duty, but as the enviable opportunity to learn to know the liberating influence of beauty in the realm of the spirit for your personal joy and to the profit of the community to which your later work belongs” Albert Einstein I Abstract In the process industry, upset conditions can result in the release of fluids to the atmosphere. Such a release process is known as ‘Blowdown’. Accurate modeling and prediction of the blowdown process is important in determining the consequences of venting operations and the design conditions required for vent and flare systems. The predicted information such as the rate at which the fluids are released, the total quantity of fluids released and the physical state of the fluid is valuable and helps in evaluating the new process designs, process improvements and improves the safety of the existing processes. Blowdown events, amongst other transient processes, are the subject of particular interest to the chemical, oil/gas, and power industries. In the process plants, particularly in the hydrocarbon industry, there are many large vessels and pipelines operating under pressure and containing hydrocarbon mixture. Depressurization of such equipment’s is frequently necessary during maintenance, and in an emergency it may have to be rapid. Hazards arise because of the very low temperatures generated within the fluid during the process and also from the large total efflux and high efflux rates that arise from the large inventory of the long pipelines and high pressure vessels. This inevitably leads to a reduction in the temperature of the vessel / pipeline and associated vent system, possibly to a temperature below the ductile-brittle transition temperature of the material from which the vessel, pipeline or piping is fabricated. To date, a number of blowdown models and simulation codes related to pressure vessels and pipelines have been developed to estimate the blowdown conditions in pressure vessels and pipelines. There is no general model developed specifically for analyzing the conditions developed in a vent pipe. The scope of this work encompasses investigating the behavior of compressible gas in a vent pipe, during venting, by developing a vent pipe model. A fluid dynamic and thermodynamic approach is used in developing the model. The investigation is focused on the pressure, temperature and flow rates of flowing gas and pipe wall temperatures. The model is validated with experimental data generated by performing steady-state venting runs using compressed air. The model is also validated by comparing the simulations performed in Aspen Hysys for single component gases such as air, carbon dioxide, methane and multicomponent gases which are in very close agreement. II Acknowledgement It is great pleasure for me to acknowledge all the people who helped me to accomplish this dissertation. First of all I would like to express my deepest gratitude to my supervisor Dr. Hari B. Vuthaluru for giving me the opportunity to pursue my Master’s Degree and the incredible support provided during this study. I would like to thank my co-supervisor’s Mr. Clinton Smith, Principal Process Engineer at Atkins Global and Mr. Dennis Kirk-Burnnand, Principal Consultant at GHD Pty Ltd, for their timely support. Their in-depth advice, encouragement, easy accessibility and freedom for work helped me to explore new ideas and to complete the work in time. I would also like to thank Professor Moses Tadé, Dean of Engineering and Professor Ming H. Ang, Chairman of thesis committee, for evaluating my work. I would like to thank all members of the administrations at Chemical Engineering Department as well as library staff for their help during this course. Timely help from the secretarial staff, Mrs. Naomi Mockford is highly appreciated. The support given by the technical staff, notably Mr. John Murray, Ms. Karen Haynes, Mr. Jason Wright, Mr. Carl Lewis, Mr. Ashley Hughes and Mr. Pierre Bastouil is worth mentioning. I am also thankful to my colleagues at Independent Metallurgical Operations Pty Ltd, especially Mr. David Symons, Managing Director, Mr. Steve McGhee, Director, Mr. Dennis Boska, Project Development Manager and Mrs. Sharon O’Reilly, Recruitment Consultant for all the support they have provided during this thesis. I would also like to thank my friends Faizaan, Jawad and Riyadh for all their help in non- technical matters. Finally, all the credentials of this degree go to my beloved parents. This course would not have been possible without the financial support given by my father Mr. Liyakat Husain Gulmohamad Rajiwate. I am deeply indebted to my parents, my brother Fahim and sister Faiza, who have been with me at every step before and during this project completion. Last but not the least my wife, Simin’s support before and during this thesis writing cannot be expressed in words. I also acknowledge everyone who has assisted me directly or indirectly in the completion of this work. Their assistance is invaluable and shall always be held in high regards. III Brief Biography of Author Author of this thesis Mr. Farhan Rajiwate has completed Bachelor of Chemical Engineering in year 2007 from Thadomal Shahani Engineering College, Mumbai, India, standing with First Class Distinction. He worked as a graduate for Bharat Petroleum Corporation Ltd, India where he was responsible for simulation of MTBE plant. He joined Curtin University, Perth, Australia in February 2008 with the enrolment in Postgraduate Diploma in Chemical Engineering. On successfully completing PG Diploma, he enrolled in Master of Philosophy (Chemical Engineering) to work on the industry related research offered to him by GHD Pty Ltd. During his time as a researcher, he was employed as a Process Engineer for Independent Metallurgical Operations Pty Ltd (IMO) and has worked on a number of mineral processing projects related to copper, gold, iron-ore and manganese with experience in plant commissioning, plant operation, and designing. Prior to joining IMO, he worked for Nuplex Industries, a polyester resin company, Perth and SGS Australia, Perth as a vacation-work student. Farhan holds interest in process engineering related to oil & gas as well as mineral processing, specifically in the field of process modeling / simulations, process control and plant operations. He has written the following paper in the support of this thesis: • “Investigations into Compressible Gas Behavior in a Vent Pipe during Blowdown”, a paper to be submitted for PSE-2012 conference, Singapore. IV Thesis Contents Dedications……………………………………………………………………………………….I Abstract………………………………………………………………………………………….II Acknowledgement……………………………………………………………………………...III Brief Biography of Author…………………………………………………………………….IV List of Figures………………………………………………………………………………...VIII List of Tables…………………………………………………………………………………..XV Nomenclature………………………………………………………………………………....XVI Chapter 1 Introduction and Objectives ................................................................................................... 1 1.1 Objectives ...................................................................................................................... 2 1.2 Thesis Outline ................................................................................................................ 4 Chapter 2 Literature Review .................................................................................................................... 5 2.1 Blowdown ...................................................................................................................... 5 2.2 Blowdown Process ......................................................................................................... 6 2.2.1 Blowdown of Pressure Vessel ................................................................................ 7 2.2.2 Blowdown of Pipeline ............................................................................................ 8 2.3 Blowdown or Emergency Depressurising Systems ....................................................... 9 V 2.3.1 Pressure Safety Valve .......................................................................................... 10 2.4 Thermophysical Property ............................................................................................. 11 2.5 Blowdown Effects ........................................................................................................ 12 2.6 Investigations into Developed Simulation Codes and Models..................................... 13 2.7 Summary of Literature Review .................................................................................... 24 Chapter 3 Model Development ............................................................................................................... 26 3.1 Development of Mathematical Models .......................................................................
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