PEMFC heat recovery for preheating inlet air in standalone solar hydrogen systems for remote telecommunication applications (tt)

PEMFC HEAT RECOVERY FOR PREHEATING INLET AIR IN STANDALONE SOLAR-HYDROGEN SYSTEMS FOR REMOTE TELECOMMUNICATION APPLICATIONS A thesis submitted in fulfilment of the requirements for the degree of Master (by Course work) Student name: HUY QUOC NGUYEN Student number: 3463748 Supervisor: Dr Bahman Shabani SCHOOL OF AEROSPACE, MECHANICAL & MANUFACTURING ENGINEERING RMIT UNIVERSITY Melbourne, 2015 i To my wife, Huong Thao and my son, Gia Hung ii ACKNOWLEGMENT First and foremost, I would like to express my sincere gratitude to my supervisor, Dr Bahman Shabani, for his patience, motivation, enthusiasm and support of my study and research I appreciate his vast knowledge and skills in sustainable energy areas, and his assistance in writing papers and valuable comments My sincere thanks go to Asma Mohamed Aris, a PhD student in RMIT, for her advice, support and sharing knowledge about solar-hydrogen system with me I want to express my gratitude to my parents for their motivation, encouragement and support me I would also express my loving appreciation to my wife, Huong Thao for her unconditional support, patience, understanding, and self-abnegation during my study iii DECLARATION I, Huy Quoc Nguyen, hereby submit the thesis entitled “PEMFC Heat Recovery for Preheating Inlet Air in Standalone Solar-Hydrogen Systems for Telecommunication Applications” in fulfilment of the requirements for the degree of Master degree by Course work, and certify that except where due acknowledgement has been made, the work is that of the author alone; the work has not been submitted previously, in whole or in part, to qualify for any other academic award, and the content of the thesis is the result of work that has been carried out since the official commencement date of the approved research program Melbourne, Nov 2015 Huy Quoc Nguyen iv TABLE OF CONTENT ACKNOWLEGMENT iii DECLARATION iv TABLE OF CONTENT v LIST OF FIGURES vii LIST OF TABLES ix EXECUTIVE SUMMARY .x Introduction 1.1 Background 1.2 Aim and objectives 1.3 Research questions .4 1.4 Methodologies 1.5 Scope 1.6 Hypotheses 1.7 Structure of the report Literature review 2.1 Issues of PEMFC’s operation in extreme cold environment 2.1.1 Impacts on the components of fuel cell 2.1.2 Cold start issues 11 2.1.3 Issues of operating process 12 2.2 PEMFC Thermal Management Opportunities in Cold Climate Conditions 14 2.3 An Exergy Analysis Approach 17 2.4 Solar-Hydrogen Systems for Telecom Applications .18 Exergy analysis for Theoretical Modeling 20 3.1 Structure of Theoretical Modeling 20 3.2 Overall Approach .21 3.3 Exergy Mathematical Modeling in MATLAB .23 3.3.1 Mathematical modeling 23 3.3.2 Model Validation 32 3.4 A Case Study 34 3.4.1 Description of the Case 34 3.4.2 Results and Discussion 38 1) Effects of Heat Exchanger Effectiveness and Ambient Temperature 38 2) Exergetic Efficiencies of PEMFC-HR and PEMFC-EH arrangements 41 3) Exergetic Efficiency of a PEMFC in the Context of Telecommunication Application 44 experimentally setting up pemfc with heat recovery for preheating inlet air 48 4.1 Introduction 48 v 4.2 Experimental setup 49 4.2.1 Description of overall system .49 4.2.2 Hydrogen line .50 1) Properties of hydrogen 50 2) Measurement equipment 50 4.2.3 Fuel cell 51 1) General information about the fuel cell stack .51 2) Blowers 53 3) Air flow rates 53 4.2.4 Air line 54 1) Overall plan 54 2) Manifolds 55 3) Heat exchanger 55 4) Additional blower 56 5) Vortex Tube 57 6) Measurements .58 7) Tubing, Valves and connectors 58 8) Climate chamber 59 9) Insulation 59 4.2.5 Electronic load 60 4.3 Planning for future work 60 Conclusion 62 1) A reference environment model (Dincer & Rosen 2012) 70 2) Partial pressure and molar fraction of substances in the air (Dincer & Rosen 2012) 70 3) Standard chemical exergy value of substance of the air at T and P0 (Dincer & Rosen 2012) 70 1) Technical Specification 71 2) Performance Characteristics 71 1) Hydrogen Pressure Gauge 74 2) Hydrogen mass flow rate 74 3) K type thermocouple 75 4) Data Taker DT80 75 5) Vortex flow meter 75 vi LIST OF FIGURES Figure Sankey diagram show energy flow of a PEMFC with heat recovery system Figure 2: Effects of ice formation on the membrane (Yan et al 2006); (a) – fresh PEM; (b) – Membrane after operate at 25 °C; (c) – Membrane after operate at -15 °C; (d) – damage at pinhole when operate at -15 °C .9 Figure 3: (a) Effect of thermal cycles on pore size of GDL; (b) Effect of thermal cycles on the performance curve of fuel cell (Cho et al 2003) 10 Figure 4: (a) Performance curves of a fuel cell as a function of temperature; (b) Temperature of the cathode cell operation at various ambient temperatures (Yan et al 2006) 14 Figure 5: PEMFC combined heat and power schematic (Briguglio et al 2011) 16 Figure 6: Schematic of a hybrid solar-hydrogen (hybridized with a battery system) used as power supply system for remote telecommunication applications 19 Figure 7: Schematic of a PEMFC, with heat recovery arrangement for preheating inlet air (PEMFC-HR), to be operated under extreme cold climate condition 20 Figure 8: TRNSYS modelling arrangement of a hybrid solar-hydrogen/battery system 22 Figure 9: Schematic exergy balance diagram of a PEMFC-HR system; ࡱࡴ૛ǡ ࢏࢔, ࡱࢇ࢏࢘ǡ ࢏࢔ and ࡱࢉ࢕࢕࢒ࢇ࢔࢚ǡ ࢏࢔ are inlet exergy transfer of hydrogen, air and coolant air respectively; ࡱࡴ૛ǡ ࢕࢛࢚, ࡱࡴ૛ࡻǡ ࢕࢛࢚, ࡱࢇ࢏࢘ǡ ࢕࢛࢚ and ࡱࢉ࢕࢕࢒ࢇ࢔࢚ǡ ࢕࢛࢚ are outlet exergy of hydrogen, product water, air and coolant air; ࢃࡱࡴ and ࢃࡲ࡯ are exergy of electric heater and electrical output power 24 Figure 10: A comparison between the cooling loads of a 500 W PEMFC obtained from the model and those measured experimentally (Shabani & Andrews 2011) at 60-65 °C of operating temperature 33 Figure 11: (a) Daily load profile of a typical BS site in Eureka, Canada (Bruni et al 2014); (b) Annual temperature and horizontal solar radiation profiles of Eureka, Canada 34 Figure 12: PEMFC load profile obtained from TRNSYS simulation for the case study described in section 3.4.2.3 .36 Figure 13: The characteristic curves of kW PEMFC (H-2000) manufactured by Horizon Fuel Cell Technologies (Horizon Fuel Cell Technologies 2013) 37 vii Figure 14: The effect of heat exchanger effectiveness on the fuel cell (with heat recovery to preheat the inlet air) inlet air temperature at various ambient temperatures; the fuel cell operating temperature was assumed to be 65 °C 39 Figure 15: Exergy destruction of main components of a 2-kW PEMFC-HR 40 Figure 16: Exergetic efficiency of the kW PEMFC-HR suggested by the model at various ambient temperatures, and 65 °C fuel cell operating temperatures 41 Figure 17: Variations of exergetic efficiency of PEMFC-HR and PEMFC-EH with ambient temperature at operating temperature of 65 °C and kW operating point based on different desired inlet air temperature at cathode (ࢀࢉࢇሻ: °C, 15 °C and 25 °C 43 Figure 18: Exergetic efficiency of PEMFC-HR and PEMFC-EH arrangements over a range of operating power at constant ambient and operating temperature (- 40 °C and 65 °C, respectively) based on the °C required inlet air temperature at the cathode 44 Figure 19: Exergetic efficiency of PEMFC-HR and PEMFC-EH based on the fuel cell load and ambient temperature over a year period 45 Figure 20: Percentage improvement between PEMFC-HR and PEMFC-EH systems The desired inlet air temperatures at cathode: °C, 15 °C and 25 °C .46 Figure 21: Energy saving by using PEMFC-HR replaced for PEMFC-EH over a year period; desired inlet air temperature at cathode: °C, 15 °C and 25 °C 47 Figure 22: General schematic diagram of experiment rigs 49 Figure 23: The 300 W PEMFC used for experimental setup .52 Figure 24: The fuel cell controller 52 Figure 25: Statistic – pressure characteristics of the 300 W PEMFC blowers 53 Figure 26: Schematic of supplied air line 54 Figure 27: Plate and Fin heat exchanger customized for experiment 56 Figure 28: Rule 3” Inline Bilge bower and its characteristic curve 56 Figure 29: Vortex tube for cold air supply (EXAIR, 2014) 57 Figure 30: Kikusui PLZ1004W electronic load 60 viii LIST OF TABLES Table 1: Description of the components used in TRNSYS modelling 22 Table 2: Cost and economic assumptions for HOMER input (Shabani & Andrews 2015b) 35 Table 3: Optimal sizing of the solar-hydrogen/battery system for the case study and fed into the TRNSYS model .35 Table 4: Operating condition of PEMFC-HR system 37 Table 5: Air flow rates of 300 W PEMFC at different power and air stoichiometry 54 Table 6: Velocity of air at each pipe diameters 59 ix EXECUTIVE SUMMARY Water and thermal management in the polymer exchange membrane (PEM) fuel cell is considered as technical challenges not only in normal condition but also in sub-freezing temperature The present of water in pore of fuel PEMFC components like membrane assembly (MEA), catalyst layer (CL) and gas diffusion layer (GDL) may freeze once the cell temperature reduces to below the freezing point Unbalance stress due to ice formation within the cell may cause severe physical damage for components that results in impact on durability and performance degradation of the fuel cell An overview of the effects of water phase change on the performance of the cell when it operates in subfreezing environment was presented In addition, mitigation strategies for rapid up and preventing fuel cell performance degradation is summarized It is found from the literature review that mitigation strategies only focus on integration an additional heat source for warming the cell before the start Furthermore, the higher inlet reactants temperature can lead to the higher performance of fuel cell Using PEMFC for base stations (BSs) back-up power for remote telecommunication application has been taken into consideration However, in cold regions like Canada, Alaska the PEMFC in the system is often experiencing extreme cold temperature conditions (-50 °C of peak temperature during winter) that can lead to significant performance degradation In this case, an electric heater is normally used to preheat the inlet air fed into the fuel cell for maintaining stable operation as well as mitigation performance degradation of fuel cell However, this strategy requires an additional energy resulting in decrease in overall efficiency of system At steady operating condition about half of energy content of hydrogen reacted inside the fuel cell is converted to heat x In this study, a theoretical model of a PEM fuel cell with heat recovery system that is used to recover the generated heat from the cell stack for preheating the inlet air used in the extreme cold environment was proposed A mathematical model of the PEMFC with heat recovery system was generated in MATLAB to dynamically simulate the performance of the system The model was then used to conduct an exergy analysis for a case study of a kW PEMFC to meet the load demand of a telecom base station in Eureka, Canada where usually extreme cold climate condition are experienced The HOMER and TRNSYS are used to obtain the load profile of the PEMFC system over a year operation of the case study This is because, the yearly load profile is a key input into the MATLAB model to conduct the exergy analysis on both PEMFC heat recovery system and PEMFC with external heat system The results showed that the exergy destruction of the fuel cell stack is dominant in the PEMFC-HR system, so by reducing the irreversibilities, the efficiency of the system can be improved quite considerably It was also found that the exergetic efficiency of the PEMFC-HR system is not greatly affected (only about ~ 0.5%) by the ambient temperature (over the range of -50°C to 30 °C) This analysis also suggested that performing fuel cell heat recovery at higher power operating point can lead to better improvement in the exergetic efficiency of the system as compared to the improvements that can be achieved at lower power operating points (~40% improvement at maximum power point compared to 25% at 100 W power point shown in section 3.4.2.3) This is consistent with the fact that more heat is generated at operating points closer to fuel cell rated power that is normally wasted if the fuel cell heat is not recovered for this purpose xi According to the results of the case study, using the PEMFC-HR system for preheating the inlet air is more effective, in terms of improving the exergy efficiency, at higher power outputs, lower ambient temperatures, and higher desired inlet air temperatures It was also found that through the recovery and deployment of fuel cell’s generated heat, the energy that is normally consumed (i.e the parasitic energy) by using an external electric heater, can be fully avoided if the heat exchanger used for this heat recover is of high effectiveness (i.e above 65%) By the account of the results of this case study, implementing fuel cell heat recovery can lead to saving 1500 kWh to 3700 kWh (over the – 25 °C range of set inlet air temperature) of energy These savings are equivalent to about 30-72% of the total yearly energy generated by the fuel cell stack An experimental system of PEMFC heat recovery working in simulated extreme cold climate was designed and planned for future work The main purpose of this experimental study is to investigate experimentally the impacts of the heat recovery system for preheating inlet air in such climate on the performance of the fuel cell xii ... entitled PEMFC Heat Recovery for Preheating Inlet Air in Standalone Solar- Hydrogen Systems for Telecommunication Applications in fulfilment of the requirements for the degree of Master degree by... temperature during winter) that can lead to significant performance degradation In this case, an electric heater is normally used to preheat the inlet air fed into the fuel cell for maintaining stable... fuel cell heat is not recovered for this purpose xi According to the results of the case study, using the PEMFC- HR system for preheating the inlet air is more effective, in terms of improving the