PRESSURE EXCHANGE BASED THERMAL DESALINATION By Kaustubh Anil Chabukswar B.E. in Mechanical Engineering, 2006, University of Mumbai, India A Thesis submitted to the Faculty of The School of Engineering and Applied Science of The George Washington University in partial fulfillment of the requirements for the degree of Master of Science August 31 st , 2009 Thesis directed by Charles Alexander Garris Jr. Professor of Mechanical and Aerospace Engineering Dedication I would like to dedicate this thesis to my fellow countrymen and hope that the revolutionary technology that we are trying to develop and implement would help them get safe and healthy drinking water. ii Acknowledgement It gives me a great pleasure to present you this thesis on application of pressure exchange device, in single effect thermal vapor compression desalination system. It’s been a long journey from the day I started working on the topic until the day I finished writing the last line in my thesis. This thesis is a cumulative product of backing of a number of important people, whom I would like to thank today. Let me begin with thanking my parents and my elder sister for supporting my dream of coming here for my masters. Without their support and continuous backing through all the tough times this day would have never come to its fullest realization. I am deeply obliged to Prof. Charles A. Garris, who had been kind enough to accept me in his research group and guide me through my Master’s education. He has been a constant source of encouragement and it’s only because of his kind words and motivation that I have successfully completed my thesis. At the same time I would like to thank my committee members for taking time to read through and critique this document. I would like to express my gratitude to the Department of Mechanical and Aerospace Engineering and Department of Finance, Business School at the George Washington University for supporting my Masters study and helping to make this thesis possible. I also would like to thank my senior research colleague Kartik Bulusu, for his timely advice and to all my friends at GWU, for making my stay here a memorable one. Last but not the least special big thanks to my fellow graduate research assistant David Gould for the innumerable precise advices. iii Abstract PRESSURE EXCHANGE BASED THERMAL DESALINATION The use of ejectors in distillation type water desalination systems is well known. However the energy efficiency of such systems is limited by the mechanical energy dissipation in the ejector. Conventional ejectors have been limited in their performance due to the dissipative mechanism of turbulent mixing upon which they rely. Recent advances in direct fluid-fluid flow induction provide potential for major improvement in the performance of ejectors based on the pressure exchange phenomenon compared to the conventional turbulent mixing controlled ejectors. Pressure exchange devices utilize the work of non-steady pressure forces acting across moving interfaces. The limits in performance of such devices can be determined through the use of the ideal turbomachinery analog. The analog is configured as a turbine-compressor unit, where the high energy primary fluid expands through the turbine that drives a compressor which compresses the low energy secondary fluid and the two then discharge in a common mixing chamber at a common intermediate pressure. The system implementation of the turbomachinery analog is similar to the conventional ejector. Thus the analog provides the highest possible performance that an ejector can achieve ideally. The analog defines the ejector efficiency as the product of adiabatic turbine and compressor efficiencies. An analytical single effect thermal vapor compression desalination model for 5m 3/day capacity is developed. The turbomachinery analog which is the conceptually simplest kind of pressure exchange device, replaces the conventional ejector. The objective of the research is to iv investigate the improvement in performance of the system by employing pressure-exchange technology. Critical parameters that directly affect the cost of the distillate produced will be analyzed. The indicators will be compression ratio, top brine temperature, primary pressure, primary temperature and ejector efficiency. The system performance is expressed in the form of thermal performance ratio (TPR), energy performance ratio (EPR), entrainment ratio (Er) and specific mass flow rate of cooling seawater (sMcw). Results show that the use of pressure exchange technology results in three fold rise in energy efficiency. v TABLE OF CONTENTS Dedication …………...…………………………………………………….……………..……… ii Acknowledgments …...…………………………………………………………………………...iii Abstract ……………………………………………………………..…………………………….iv Table of Contents ………………………………………………….……………………………..vi List of Figures ………………………………………………………………………………….....x List of Tables ………….…………………………………………..……………………………..xv Nomenclature ………...…………………………………………..………………………….….xvi List of Acronyms ……………………………………………..………………………...xvi List of Symbols ………………………………………………..……………………….xvii List of Subscripts ………………………………………………..………………..…....xix Chapter 1- Introduction………………………………………………………………………….1 Chapter 2- Literature Review of Various Desalination Processes …………………………….6 2.1 Desalination without Vapor Compression………………………………………..6 2.1.1 Membrane Separation- Reverse Osmosis………………………………..7 2.1.2 Multistage Flash Desalination………………………………………….13 2.1.3 Multiple-Effect Evaporation Desalination……………………………...16 2.2 Desalination Combined with Vapor Compression System………………. ……21 2.2.1 Mechanical Vapor Compression ……………………………………...22 2.2.2 Absorption Vapor Compression………………………………………..24 2.2.3 Thermal Vapor Compression…………………………………………...27 Chapter 3- Steam Jet Ejectors ………………………….………………………………………32 3.1 Introduction…………………………...…………………………………………32 3.2 Basic Principles of Ejectors…………………………………………………......33 vi 3.3 Performance Evaluation Parameters…………………………………………….36 3.3.1 Entrainment Ratio………………………………………………………36 3.3.2 Expansion Ratio………………………………………………………...36 3.3.3 Compression Ratio……………………………………………………...37 3.4 Application of Steam-jet Ejectors……………………………………………….37 3.4.1 Refrigeration……………………………………………………………37 3.4.2 Thrust Augmentation…………………………………………………...39 3.4.3 Air and Gas Burner Injectors…………………………………………...40 3.4.4 Gas-Vapor Recovery…………………………………………………...40 3.4.5 Improving Turbine Performance……………………………………….41 3.5 Limitations……………………………………………………………………....42 Chapter 4- Turbomachinery Analog …………………………………………………………...43 4.1 Introduction……………………………………………………………………...43 4.2 Model Description and Basic Principle…………………………………………43 4.3 Fundamental Assumptions………………………………………………………45 4.4 Ejector Performance…………………………………………………………….46 4.4.1 Turbine Efficiency……………………………………………………...46 4.4.2 Compressor Efficiency…………………………………………………47 4.4.3 Ejector Efficiency………………………………………………………48 4.5 Proposed Simulation…………………………………………………………….49 Chapter 5- Supersonic Pressure Exchange Ejector ………………………………………51 5.1 Introduction to Pressure Exchange……………………………………………...51 5.2 Axial Supersonic Flow Pressure Exchange Ejector……………………………..52 5.2.1 Model Description and Working principle……………………………..52 vii Chapter 6- Analysis of Single Effect Thermal Vapor Compression System ………………..58 6.1 Hypothesis………………………………………………………………………58 6.2 Setup Overview..............................................................................................…...59 6.3 Process Description……………………………………………………………...61 6.4 Assumptions……………………………………………………………………..63 6.5 System Performance Parameters………………………………………..………64 6.6 Methodology of Systemic Evaluation…………………………………………...65 6.6.1 Method- Temperature of Primary Specified……………………….…...65 Chapter 7- Results and Discussions …………………………………………………………….70 7.1 Effect of Seawater Boiling Temperature on System Performance……………...70 7.1 .1 Effect on Flow Rates……...……………………………………………71 7.1.2 Effect on Thermal Performance Ratio………………………………….72 7.1.3 Effect on Energy Performance Ratio…………………………………...73 7.1.4 Effect of Mass Flow Rate of Cooling Seawater………………………..74 7.2 Effect of Compression Ratio on System Performance…………………………..75 7.2 .1 Effect on Flow Rates……...…………………...……………………….76 7.2.2 Effect on Thermal Performance Ratio……………………………...…..77 7.2.3 Effect on Energy Performance ratio………………………………........79 7.2.4 Effect on Mass Flow Rate of Cooling Seawater……………………….79 7.2.5 Effect on Evaporator Tube Wall Temperature……………………...….81 7.3 Effect of Primary Temperature on System Performance………………………..82 7.3.1 H-S Diagram of the System…………………………………………….82 7.3.2 Effect on Flow Rates……...……………………………………………83 7.3.3 Effect on Thermal Performance Ratio………………………………….85 7.3.4 Effect on Energy Performance Ratio…………………………………...85 viii 7.3.5 Effect on Evaporator Tube Wall Temperature…………………………86 7.3.6 Effect on Mass Flow Rate of Cooling Seawater………………..............87 7.4 Effect of Analog Efficiency on System Performance ………………………….88 7.4.1 Effect of Boiling Temperature As A Function of Ejector Efficiency….………………………………………………………..89 7.4.2 Effect of Evaporation Ratio on System Performance …………………93 7.4.3 Effect of Compression Ratio As A Function of Ejector Efficiency…….……………………………………………………..94 7.5 Validation and Error Analysis…………………………………………………..95 7.5.1 Validation of Thermal Performance Ratio……………………………..95 7.5.2 Validation of Ideal Operating Temperature……………………………97 7.5.3 Validation of Conventional Ejector Efficiency………………………...99 7.5.4 Error Analysis…………………………………………………………102 7.5.5 Sample Calculations……………………………………………………..102 CHAPTER