DESIGN AND ANALYSIS OF TRI-GENERATION PLANT FOR HEATING, COOLING AND POWER A Thesis Presented By Dongchuan You to The Department of Mechanical and Industrial Engineering in partial fulfillment of the requirements for the degree of Master of Science in the field of Mechanical Engineering Northeastern University Boston, Massachusetts April 2021 i ACKNOWLEDGEMENTS It is my extreme pleasure to thank Professor Metghalchi for his guidance, patience, encouragement, and inspiration that he provided generously during my whole master studies, not only throughout the thesis but also in his class. It has been my honor to be his student and learning under his instruction. The author also would like to say thanks to his friends, Aobo Liu, Zhenyu Lu, Ziyu Wang and others who give me a helping hand on my way of studying abroad. It is really an unforgettable happy time to study, communicating with each other and I will never forget the encouragement when I am confusing and frustrating. Next, I must thank my parents sincerely, not only because of the financial support for my tuition and daily expenses, but also for their constant understanding, patience, encouragement during my whole master studies. I also want to thank the department, the college of engineering, for their assistance for my study for the past two years. I would like to say thank you to all professors who taught me with their kindness and try their best effort to guide me. Finally, please allow me to show my appreciation to all the people who have helped me in my master studies. It builds an impressive memory of my past time, an unforgettable journey on my learning road. ii ABSTRACT A new tri-generation plant for heating, cooling and power has been designed and analyzed. Tri-generation system has been studied in recent years and its advantages like energy saving and environmental safety has been proved. Research on improving their performance has been increasing lately. In this thesis, a new tri-generation plant, consisted of a supercritical carbon dioxide (sCO2) recompression Brayton cycle and aqueous lithium bromide absorption refrigeration cycle, has been designed and its performance has been determined. Mass, energy, entropy and exergy balances have been used to model sCO2 recompression Brayton cycle, aqueous lithium bromide absorption refrigeration cycle and the tri-generation power plant. Parametric studies have been done in all three cycles to investigate effects of operating conditions on the performance of the system. Results show efficiency of sCO2 recompression Brayton cycle increases when pressure ratio and maximum temperature increase; the coefficient of performance of the absorption refrigeration system increases when generator exit temperature increases; the exergetic efficiency of the tri-generation plant increase when pressure ratio increases. iii TABLE OF CONTENTS 1 Introduction……………………………………………………………………….…….1 2 Supercritical Carbon Dioxide Recompression Cycle……………………………………3 2.1 Background………………………………………………………………………...3 2.2 Description of Recompression Cycle………………………………………………4 2.3 Method and Assumptions……………………………………………………….….6 2.4 Thermodynamic Model…………………………………………………………….7 2.5 Results…………………………………………………………………………….10 2.5.1 Model 1………………………………………………………………….….10 2.5.1.1 Effects of Pressure Ratio……………………………………...….…10 2.5.1.2 Effects of Split Fraction…………………………………………….13 2.5.1.3 Effects of Maximum Temperature……………………………….....14 2.5.2 Model 2……………………………………………………...……………...16 2.5.3 Model Comparison…………………………………………………….…...19 2.6 Conclusion………………………………………………………………………..20 3 Aqueous Lithium Bromide Absorption Refrigeration System………………………....22 3.1 Background………………………………………………….……………………22 3.2 Refrigerators Description…………………………………………………………24 3.3 Mathematical Model………………...……………………………………………27 3.3.1 Working Fluid Property Calculation……………………………………….27 3.3.2 Analysis of Single-effect Cycle…………………………………………….28 3.3.3 Analysis of Double-effect Cycle…………………………………………...31 3.3.4 Assumptions and Parameters…………………………………………….…35 3.4 Results and Discussion……………………………………………………………36 3.4.1 Single-effect Cycle…………………………………………………...…….36 iv 3.4.1.1 Effect of Cooling Loads………………………………….……….…36 3.4.1.2 Effect of Evaporator Exit Temperature………………….….………37 3.4.1.3 Effect of Condenser Exit Temperature…………………..……….…38 3.4.1.4 Effect of Absorber Exit Temperature…………………….…………39 3.4.1.5 Effect of Generator Exit Temperature………………….…….……..39 3.4.1.6 Effect of Solution Energy Exchanger Effectiveness…….…….……41 3.4.2 Double-effect Cycle……………………………….………………….…….42 3.4.2.1 Effect of Cooling Loads……………………………………….……42 3.4.2.2 Effect of Evaporator Exit Temperature……………………….…….42 3.4.2.3 Effect of Upper Condenser Exit Temperature………………..…….43 3.4.2.4 Effect of Absorber Exit Temperature……………………….….…..43 3.4.2.5 Effect of Upper Generator Exit Temperature……………….….…..45 3.4.2.6 Effect of Solution Energy Exchanger Effectiveness……….….……46 3.4.2.7 Effect of Lower Condenser Exit Temperature……………….….….47 3.5 Conclusion………………………………………………………………………..48 4 Tri-Generation System Analysis……………………………………………………….50 4.1 Model description………………………………………………………………...50 4.2 Thermodynamic Model…………………………………………………………..52 4.3 Assumptions and Parameters…………………………………………………….54 4.4 Results……………………………………………………………………………55 5 Conclusion and Recommendation………………………………………………….…61 5.1 Conclusion……………………………………………………………………..…61 5.2 Recommendation…………………………………………………………………62 References……………………………………………………………..…………………63 Appendices..…...…………………………………………………………………..……..72 v Appendix Ⅰ MATLAB Code for sCO2 Recompression Cycle (Trial and Error)……..72 Appendix Ⅱ MATLAB Code for sCO2 Recompression Cycle (Newton-Raphson Iteration)………………………...………………………………………………….…75 Appendix Ⅲ MATLAB Code for Single-Effect Absorption Refrigeration System.....79 Appendix Ⅳ MATLAB Code for Double-Effect Absorption Refrigeration System…………...……………………………………………………………………81 Appendix Ⅴ MATLAB Code for Tri-Generation Plant………………………….…....83 1 CHAPTER 1 INTRODUCTION Tri-generation systems also known as combined cooling, heating and power (CCHP) systems, is becoming a major subject of research in order to improve energy efficiency of power generation, thermal energy needs of plants and refrigeration systems. Tri-generation systems include various new technologies, provide an alternative for the world to meet and solve energy-related problems such as energy shortages, energy supply security, emission control, conservation of energy, and energy economy [1]. Tri-generation systems mostly produce both electric and usable thermal energy on-site or near site and converts 75–80% of the fuel source into useful energy [2-3]. The research of tri-generation system has been heated up in recent years [4-8], covering analysis based on different energy source like solar power plant [9], geothermal energy [10-11], fuel cell [12-13]. Also, studies based on different types of cycles in the system, such as organic Rankine cycle [14], Kalina cycle [15], have been reported. The purpose of this thesis is to perform analysis of a given tri-generation consisted of supercritical carbon dioxide (sCO2) recompression cycle and aqueous lithium bromide refrigeration cycle. The effects of some operating variables, such us pressure ratio, generator exit temperature on energy effectiveness as well as exergetic efficiency have been evaluated. Chapter 2 covers complete design and analysis of a recompression super critical Brayton cycle based. Results of this chapter will be published in American Society of Mechanical Engineers (ASME) Journal of Energy Resources Technology (JERT). Chapter 3 is the design and analysis of both single effect as well as double effect water 2 lithium bromide absorption refrigerator system. A paper based on the results of chapter 3 will be published in JERT too. Chapter 4 is a complete Tri-generation system combing results of chapters 2 and 3 and also developing thermal energy for use as needed. Chapter 5 is the conclusion and recommendation of this study. 3 CHAPTER 2 SUPERCRITICAL CARBON DIOXIDE RECOMPRESSION CYCLE In this chapter, parametric analysis of different variables such as pressure ratio, split fraction and maximum temperature of the sCO2 recompression cycle have been performed. The effects of these variables on thermal efficiency as well as exergetic efficiency have been evaluated. 2.1 Background Carbon dioxide has been studied as a working fluid in power plants for years due to favorable high efficiency of the plant using carbon dioxide [16] and environmental safety [17]. Supercritical carbon dioxide can be used in different types of energy sources, such us nuclear [18], solar [19], coal fired [20,21] in topping cycles [22], bottom cycles [23] and power cycles [24]. Also, additional attributes of sCO2 Brayton cycle, such us impurities [25], pinch point analysis [26], convective energy transfer coefficient [27] have been reported. Ahn [28] wrote a review paper on the thermal efficiencies of sCO2 power conversion systems and applications with respect to the turbine inlet temperature. Geothermal, nuclear and solar power plants have excellent environmental attributes, but their most common efficiencies are less than 45% [29] because their turbine inlet temperature are mostly between 400-700 ℃, which are much lower than gas or steam turbine system. The sCO2 Brayton cycles, which have been studied in recent decades, can have higher thermal efficiency, about 5% higher while having lower turbine inlet temperature [28]. The main 4 advantage for the sCO2 Brayton cycle is that the