Energy,exergy, and exergoeconomics (3E) analysis and multi-objective optimization of a multi-generation energy system for day and night time power generation - Case study: Dezful city

The present study aimed to investigate a multi-generation energy system for the production of hydrogen, freshwater, electricity, cooling, heating, and hot water. Steam Rankine cycle (SRC), organic Rankine cycle (ORC), absorption chiller, Parabolic trough collectors (PTCs), geothermal well, proton exchange membrane (PEM) electrolyzer, and reverse osmosis (RO) desalination are the main subsystems of the cycle. The amount of exergy destruction is calculated for each component after modeling and thermodynamic analysis. The PTCs, absorption chiller, and PEM electrolyzer had the highest exergy destruction, respectively. According to meteorological data, the system was annually and hourly tested for Dezful City. For instance, it had a production capacity of 13.25 kg/day of hydrogen and 147.42 m³/day of freshwater on 17th September. Five design parameters are considered for multi-objective optimization after investigating objective functions, including cost rate and exergy efficiency. Using a Group method of data handling (GMDH), a mathematical relation is obtained between the input and output of the system. Next, a multi-objective optimization algorithm, a non-dominated sorting genetic algorithm (NSGA-II), was used to optimize the relations. A Pareto frontier with a set of optimal points is obtained after the optimization. In the Pareto frontier, the best point is selected by the decision criterion of TOPSIS. At the TOPSIS point, the exergy efficiency is 31.66%, and the total unit cost rate is 21.9 $/GJ.     

Energy and exergy analyses of hydrogen production via solar-boosted ocean thermal energy conversion and PEM electrolysis

Energy and exergy analyses are reported of hydrogen production via an ocean thermal energy conversion (OTEC) system coupled with a solar-enhanced proton exchange membrane (PEM) electrolyzer. This system is composed of a turbine, an evaporator, a condenser, a pump, a solar collector and a PEM electrolyzer. Electricity is generated in the turbine, which is used by the PEM electrolyzer to produce hydrogen. A simulation program using Matlab software is developed to model the PEM electrolyzer and OTEC system. The simulation model for the PEM electrolyzer used in this study is validated with experimental data from the literature. The amount of hydrogen produced, the exergy destruction of each component and the overall system, and the exergy efficiency of the system are calculated. To better understand the effect of various parameters on system performance, a parametric analysis is carried out. The energy and exergy efficiencies of the integrated OTEC system are 3.6% and 22.7% respectively, and the exergy efficiency of the PEM electrolyzer is about 56.5% while the amount of hydrogen produced by it is 1.2 kg/h.     

Energy,exergy, economic and environmental (4E) analysis of using city gate station (CGS) heater waste for power and hydrogen production: A comparative study

This paper deals with energy, exergy, economic, and environmental (4E) analysis of two new combined systems for simultaneous power and hydrogen production. The combined systems are integrated from a city gate station (CGS) system, a Rankine cycle (RC), an absorption power cycle (APC), and a proton exchange membrane (PEM) electrolyzer. Since the pressure of natural gas (NG) in transmission pipeline is high, this pressure is reduced at CGS to a lower pressure. However, this NG has also ample potential to be recovered for multiple productions, too. In the proposed systems, the outlet energy of NG is used for power and hydrogen production by employing RC/APC and PEM electrolyzer. The power sub-cycles are driven by waste heat of CGS, while PEM electrolyzer is driven by this waste heat along with a portion of CGS-Turbine output power. A comprehensive thermodynamic modeling and parametric study of the proposed combined systems are conducted from the 4E analysis viewpoint. The results of two proposed systems are compared with each other, considering a fixed value of 1 MW for RC- and APC-Turbines power. Under the same external conditions and using steam as working fluid of RC, the thermal efficiency of the combined CGS/PEM-RC and -APC systems are obtained 32.9% and 33.6%, respectively. The overall exergy efficiency of the combined CGS/PEM-RC and -APC systems are also calculated by 47.9% and 48.9%, respectively. Moreover, the total sum unit cost of product (SUCP) and CO₂ emission penalty cost rate are obtained 36.9 $/GJ and 0.033 $/yr for the combined CGS/PEM-RC and 36 $/GJ and 0.211 $/yr for the combined CGS/PEM-APC systems, respectively. The results of exergy analysis also revealed that the vapor generator (in both systems) has the main contribution in the overall exergy destruction.     

Exergy and exergo-economic investigation of a novel hydrogen production and storage system via an integrated energy system

The main purpose of the current research work is to suggest a novel integrated multi-generation energy system and scrutinize 4E evaluation. This system consists of a solid oxide fuel cell, a PEM electrolyzer for hydrogen production, and an ejector-based absorption chiller for the coefficient of performance improvement. All parts of this system are verified with existing reports and papers. Effect of fuel cell current density, SOFC fuel cell temperature, absorption chiller evaporator temperature, and condenser temperature, and outlet turbine pressure has been investigated and reported. The effect of mentioned parameters on the exergy and cost rate has been considered. Data illustrate that the maximum exergy destruction rate belongs to the SOFC contributing 60% of the total exergy destruction rate of the system. Under the given condition of the system, the net produced power is about 200 kW with an exergy efficiency of 30.2% and thermal efficiency of 60.4%. At the considered condition the total cost rate of the system is estimated about 22.29 $/hr. The results of the present work provide a scientific base for designing poly-generation systems with high efficiency and reasonable cost rate.     

An integrated system for ammonia production from renewable hydrogen: A case study

This study presents an analysis and assessment study of an integrated system which consists of cryogenic air separation unit, polymer electrolyte membrane electrolyzer and reactor to produce ammonia for a selected case study application in Istanbul, Turkey. A thermodynamic analysis of the proposed system illustrates that electricity consumption of PEM electrolyzer is 3410 kW while 585.4 kW heat is released from ammonia reactor. The maximum energy and exergy efficiencies of the ammonia production system which are observed at daily average irradiance of 200 W/m² are found as 26.08% and 30.17%, respectively. The parametric works are utilized to find out the impacts of inlet air conditions and solar radiation intensity on system performance. An increase in the solar radiation intensity results in a decrease of the efficiencies due to higher potential of solar influx. Moreover, the mass flow rate of inlet air has a substantial effect on ammonia production concerning the variation of generated nitrogen. The system has a capacity of 0.22 kg/s ammonia production which is synthesized by 0.04 kg/s H₂ from PEM electrolyzer and 0.18 kg/s N₂ from a cryogenic air separation unit. The highest exergy destruction rate belongs to PEM electrolyzer as 736.2 kW while the lowest destruction rate is calculated as 3.4 kW for the separation column.     

Analysis and performance assessment of a combined geothermal power-based hydrogen production and liquefaction system

In this paper, the thermodynamic study of a combined geothermal power-based hydrogen generation and liquefaction system is investigated for performance assessment. Because hydrogen is the energy of future, the purpose of this study is to produce hydrogen in a clear way. The results of study can be helpful for decision makers in terms of the integrated system efficiency. The presented integrated hydrogen production and liquefaction system consists of a combined geothermal power system, a PEM electrolyzer, and a hydrogen liquefaction and storage system. The exergy destruction rates, exergy destruction ratios and exergetic performance values of presented integrated system and its subsystems are determined by using the balance equations for mass, energy, entropy, energy and exergy and evaluated their performances by means of energetic and exergetic efficiencies. In this regard, the impact of some design parameters and operating conditions on the hydrogen production and liquefaction and its exergy destruction rates and exergetic performances are investigated parametrically. According to these parametric analysis results, the most influential parameter affecting system exergy efficiency is found to be geothermal source temperature in such a way that as geothermal fluid temperature increases from 130 °C to 200 °C which results in an increase of exergy efficiency from 38% to 64%. Results also show that, PEM electrolyzer temperature is more effective than reference temperature. As PEM electrolyzer temperature increases from 60 °C to 85 °C, the hydrogen production efficiency increases from nearly 39% to 44%.     

Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber

A hydrogen production unit is successfully integrated with an externally fired combined cycle using biomass fuel. The hydrogen produced in an electrolyzer can be used for other purposes, but when there is temporarily no market for it is injected into the combustion chamber of an externally fired combined cycle. Injecting hydrogen into the combustion chamber was found to reduce fuel consumption by almost 27%. Moreover, hydrogen injection decreased the energy efficiency and exergy efficiency by 45%, and decreased both the exergy loss and exergy destruction rates. Meanwhile, CO₂ emissions decreased by 32%. However, there are some disadvantages to hydrogen injection, especially from the viewpoint of exergoeconomics. The total unit product cost for the externally fired combined cycle with hydrogen injection is almost 27% more than the unit without hydrogen injection, although the exergy loss and destruction costs decreased with hydrogen injection. The value of the relative cost difference with hydrogen injection rises by 40%. Also the exergoeconomic assessment demonstrates that the cost of components (purchase and maintenance) are higher than cost of components' exergy destruction for both cycles, i.e., with and without hydrogen injection. As the compressor pressure ratio increases, optimal points are identified for biomass flow rate, energy and exergy efficiencies, exergy destruction and loss rates, exergy destruction and loss exergy cost rates, total unit product cost and relative cost difference.     

Numerical simulation and exergoeconomic analysis of a high temperature polymer exchange membrane electrolyzer

In this paper, a finite volume numerical method is developed to investigate a high temperature polymer exchange membrane (PEM) electrolyzer cell using a three-dimensional and non-isothermal model. The results that are obtained for the single cell are generalized to a full stack of electrolyzer and an exergoeconomic analysis is performed based on the numerical data. The effects of operating temperature, the pressure of cathode, gas diffusion layer (GDL) thickness, and membrane thickness on the energy and exergy efficiencies and exergy cost of the electrolyzer are examined. This study reveals that by increasing the working temperature from 363 K to 393 K, the exergy cost of hydrogen decreases from 23.16 $/GJ to 22.39 $/GJ, and the exergy efficiency of PEM electrolyzer stack at current density of 10,000 A/m² increases from 0.56 to 0.59. The results indicate that increase of pressure deteriorates the system performance at voltages below 1.4 V. It is concluded that operation of the electrolyzer at higher pressures results in decrease of the exergy cost of hydrogen. Increase of membrane thickness from 50 μm to 183 μm leads to increase of the exergy cost of hydrogen from 23.24 $/GJ to 35.99 $/GJ.     

Exergy,exergoeconomic and multi-objective optimization of a clean hydrogen and electricity production using geothermal-driven energy systems

In this research paper, comprehensive thermodynamic modeling of an integrated energy system consisting of a multi-effect desalination system, geothermal energy system, and hydrogen production unit is considered and the system performance is investigated. The system's primary fuel is a geothermal two-phase flow. The system consists of a single flash steam-based power system, ORC, double effect water–lithium bromide absorption cooling system, PEM electrolyzer, and MED with six effects. The effect of numerous design parameters such as geothermal temperature and pressure on the net power of steam turbine and ORC cycle, the cooling capacity of an absorption chiller, the amount of produced hydrogen in PEM electrolyzer, the mass flow rate of distillate water from MED and the total cost rate of the system are studied. The simulation is carried out by both EES and Matlab software. The results indicate the key role of geothermal temperature and show that both total exergy efficiency and total cost rate of the system elevate with increasing geothermal temperature. Also, the impact of changing absorption chiller parameters like evaporator and absorber temperatures on the COP and GOR of the system is investigated. Since some of these parameters have various effects on cost and efficiency as objective functions, a multi-objective optimization is applied based on a Genetic algorithm for this system and a Pareto-Frontier diagram is presented. The results show that geothermal main temperature has a significant effect on both system exergy efficiency and cost of the system. An increase in this temperature from 260 C to 300 C can increase the exergy efficiency of the system for an average of 12% at various working pressure and also increase the cost of the system by 13%.     

Performance assessment of a solar hydrogen and electricity production plant using high temperature PEM electrolyzer and energy storage

This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants.     

Thermodynamic assessment of modified Organic Rankine Cycle integrated with parabolic trough collector for hydrogen production

Hydrogen is one of the most clean energy carrier and the best alternative for fossil fuels. In this study, thermodynamic analysis of modified Organic Rankine Cycle (ORC) integrated with Parabolic Trough Collector (PTC) for hydrogen production is investigated. The integrated system investigated in this study consists of a parabolic trough collector, a modified ORC, a single effect absorption cooling system and a PEM electrolyzer. By using parabolic trough collector, solar energy is converted heat energy and then produced heat energy is used in modified ORC to produce electricity. Electricity is then used for hydrogen production. The outputs of this integrated system are electricity, cooling and hydrogen. By performing a parametric study, the effects of design parameters of PTC, modified ORC and PEM electrolyzer on hydrogen production is evaluated. According to the analysis results, solar radiation is one of the most important factor affecting system exergy efficiency and hydrogen production rate. As solar radiation increases from 400?W/m² to 1000?W/m², exergy efficiency of the system increases 58%–64% and hydrogen production rate increases from 0.1016?kg/h to 0.1028?kg/h.     

Performance assessment of a direct steam solar power plant with hydrogen energy storage: An exergoeconomic study

Power generation and its storage using solar energy and hydrogen energy systems is a promising approach to overcome serious challenges associated with fossil fuel-based power plants. In this study, an exergoeconomic model is developed to analyze a direct steam solar tower-hydrogen gas turbine power plant under different operating conditions. An on-grid solar power plant integrated with a hydrogen storage system composed of an electrolyser, hydrogen gas turbine and fuel cell is considered. When solar energy is not available, electrical power is generated by the gas turbine and the fuel cell utilizing the hydrogen produced by the electrolyser. The effects of different working parameters on the cycle performance during charging and discharging processes are investigated using thermodynamic analysis. The results indicate that increasing the solar irradiation by 36%, leads to 13% increase in the exergy efficiency of the cycle. Moreover, the mass flow rate of the heat transfer fluid in solar system has a considerable effect on the exergy cost of output power. Solar tower has the highest exergy destruction and capital investment cost. The highest exergoeconomic factor for the integrated cycle is 60.94%. The steam turbine and PEM electrolyser have the highest share of exergoeconomic factor i.e., 80.4% and 50%, respectively.     

Thermoeconomic assessment of an absorption refrigeration and hydrogen-fueled diesel power generator cogeneration system

The thermoeconomic assessment of a cogeneration application that uses a reciprocating diesel engine and an ammonia–water absorption refrigeration system for electrical power and cold production from hydrogen as fuel is presented. The purpose of the assessment is to get both exergetic and exergoeconomic costs of the cogeneration plant products at different load conditions and concentrations of hydrogen–diesel oil blends. The exhaust gas of the reciprocating diesel engine is used as an energy source for an ammonia–water absorption refrigeration system. The reciprocating diesel engine was simulated using the Gate Cycle™ software, and the ammonia–water absorption refrigeration system simulation and the thermoeconomic assessment were carried out using the Engineering Equation Solver software (EES). The results show that engine combustion is the process of higher exergy destruction in the cogeneration system. Increased hydrogen concentration in the fuel increases the system exergetic efficiency for all load conditions. Exergy destruction in the components of the ammonia–water absorption refrigeration system is increased with increasing load due to the rise of heat transfer. At intermediate and high loads energy efficiency is increased in the power system, and low values of unit exergetic cost and competitive specific exergoeconomic costs are noticed. The cogeneration system operation at intermediate and high engine loads was proven to be feasible.     

Exergoeconomic and environmental impact analyses of a renewable energy based hydrogen production system

In this study, exergoeconomic and environmental impact analyses, through energy, exergy, and sustainability assessment methods, are performed to investigate a hybrid version renewable energy (including wind and solar) based hydrogen and electricity production system. The dead state temperatures considered here are 10 °C, 20 °C and 30 °C to undertake a parametric study. An electrolyzer and a metal hydride tank are used for hydrogen production and hydrogen storage, respectively. Also, the Proton Exchange Membrane Fuel Cell (PEMFC) and battery options are utilized for electricity generation and storage, respectively. As a result, the energy and exergy efficiencies and the sustainability index for the wind turbine are found to be higher than the ones for solar photovoltaic (PV) system. Also, the overall exergy efficiency of the system is found to be higher than the corresponding overall energy efficiency. Furthermore, for this system, it can be concluded that wind turbine with 60 gCO₂/month is more environmentally-benign than the solar PV system with 75 gCO₂/month. Finally, the total exergoeconomic parameter is found to be 0.26 W/$, when the energy loss is considered, while it is 0.41 W/$, when the total of exergy loss and destruction rates are taken into account.     

Energy,exergy, exergo-economic and exergo-environmental analyses of solar based hydrogen generation system

The present study focuses on the energy, exergy, exergo-economic, and exergo-environmental analyses of the solar-assisted multi-generation system. The multi-generation system consists of parabolic trough solar collector, regenerative power plant, double-effect absorption chiller system, proton exchange membrane electrolyzer, and multi-stage flash desalination plant. In the regenerative power plant, liquid petroleum gas (LPG) based boiler is implemented. The propane (C₃H₈) is used as the fuel in the boiler combustion chamber. The thermal and exergetic efficiencies of the power cycle are observed to be 41.08% and 23.26%, respectively. The electrical power of 1.384 MW is produced by the low-pressure turbine. Whereas, the thermal COP and exergetic COP are observed and maintained in the range of 1.28 to 0.22, respectively. The liquid hydrogen is produced by the PEM electrolyzer with the thermal and exergetic efficiencies of 60.83% and 64.65%, respectively. Furthermore, the exergo-economics and exergo-environmental analyses have also been conducted and all the parameters have been analyzed and concluded through graphs and tables.     

Development and exergoeconomic evaluation of a SOFC-GT driven multi-generation system to supply residential demands: Electricity,fresh water and hydrogen

In this study, a novel multi-generation system is proposed by integrating a solid oxide fuel cell (SOFC)-gas turbine (GT) with multi-effect desalination (MED), organic flash cycle (OFC) and polymer electrolyte membrane electrolyzer (PEME) for simultaneous production of electricity, fresh water and hydrogen. A comprehensive exergoeconomic analysis and optimization are conducted to find the best design parameters considering exergy efficiency and total unit cost of products as objective functions. The results show that the exergy efficiency and the total unit cost of products in the optimal condition are 59.4% and 23.6 $/GJ, respectively, which offers an increase of 2% compared to exergy efficiency of SOFC-GT system. Moreover, the system is capable of producing 2.5 MW of electricity by the SOFC-GT system, 5.6 m³/h of fresh water by MED unit, and 1.8 kg/h of hydrogen by the PEME. The associated cost for producing electricity, fresh water and hydrogen are 3.4 cent/kWh, 37.8 cent/m³, and 1.7 $/kg, respectively. A comparison between the results of the proposed system and those reported in other related papers are presented. The diagram of the exergy flow is also plotted for the exact determination of the exergy flow rate in each component, and also, location and value of exergy destruction. Finally, the capability of the proposed system for a case study of Iran is examined.     

An innovative compressed air energy storage (CAES) using hydrogen energy integrated with geothermal and solar energy technologies: A comprehensive techno-economic analysis - different climate areas- using artificial intelligent (AI)

The present study evaluates the optimal design of a renewable system based on solar and geothermal energy for power generation and cooling based on a solar cycle with thermal energy storage and an electrolyzer to produce hydrogen fuel for the combustion chamber. The subsystems include solar collectors, gas turbines, an electrolyzer, an absorption chiller, and compressed air energy storage. The solar collector surface area, geothermal source temperature, steam turbine input pressure, and evaporator input temperature were found to be major determinants. The economic analysis of the system showed that the solar subsystem, steam Rankine cycle, and compressed air energy storage accounted for the largest portions of the cost rate. The exergy analysis of the system demonstrated that the solar subsystem and SRC had the highest contributions to total exergy destruction. A comparative case study was conducted on Isfahan, Bandar Abbas, Mashhad, Semnan, and Zanjan in Iran to evaluate the performance of the proposed system at different ambient temperatures and irradiance levels during the year. To optimize the system and find the optimal objective functions, the NSGA-II algorithm was employed. The contradictory objective functions of the system included exergy efficiency maximization and cost rate minimization. The optimal Exergy round trip efficiency and cost rate were found to be 29.25% and 714.25 ($/h), respectively.     

Exergoeconomic analysis of a PEM electrolyser at various operating temperatures and pressures

In this paper, an exergoeconomic analysis of a 12 900 kW PEM electrolyser developed by WE‐NET at various operating temperatures and pressures is conducted. The analysis is performed at electrolyser's operating temperatures (T/T₀) and pressures (P/P₀) ranging from 1 to 1.4 and 1 to 10, respectively. A 40% improvement in the exergy cost of hydrogen could be achieved by operating the PEM electrolyser at a low temperature. However, a 2% decrease in the exergy cost could be achieved if the operating pressure is increased from 1 to 10 atm. Furthermore, a lower annual capital cost, O&M cost, electricity cost and higher year life could contribute greatly in reducing the exergy cost of hydrogen. Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis and evaluation of a new solar energy‐based multigeneration system

In this study, a novel, renewable energy based, multigeneration energy system is introduced, and solar energy is, in this regard, used to produce electricity for a multi‐unit building utilizing a Kalina cycle. For cooling a four‐stage absorption chiller running on excessive or recovered heat is used. An electrolyzer is employed to produce hydrogen from the unused portion of electricity. In addition, domestic hot water is obtained from the system. In the analysis, a comprehensive thermodynamic model of the system is developed; the exergy efficiencies of the overall system and its components are determined; and the effects of varying configurations and operating conditions on the system performance are investigated. The number of suites that the system can satisfactory meet the demands is determined. Finally, an environmental impact assessment is conducted to determine the reductions in the amount of greenhouse gases, which can easily be achieved here by this solar energy based multigeneration system. The highest energy efficiency of the system is 57%, while the maximum exergy efficiency is 36%. It produces a maximum power of 92 kW and has a maximum cooling effect of 128 kW. It saves 1398 t of CO₂ per year compared with a conventional system to produce the same amounts of outputs, which can sufficiently meet the demand of 94 suites, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Design and modeling of a multigeneration system driven by waste heat of a marine diesel engine

In this study, a novel marine diesel engine waste heat recovery layout is designed and thermodynamically analyzed for hydrogen production, electricity generation, water desalination, space heating, and cooling purposes. The integrated system proposed in this study utilizes waste heat from a marine diesel engine to charge an organic Rankine and an absorption refrigeration cycle. The condenser of the Organic Rankine Cycle (ORC) provides the heat for the single stage flash distillation unit (FDU) process, which uses seawater as the feedwater. A portion of the produced freshwater is used to supply the Polymer Electrolyte Membrane (PEM) electrolyzer array. This study aims to store the excess desalinated water in ballast tanks after an Ultraviolet (UV) treatment. Therefore it is expected to preclude the damage of ballast water discharge on marine fauna. The integrated system's thermodynamic analysis is performed using the Engineering Equation Solver software package. All system components are subjected to performance assessments based on their energy and exergy efficiencies. Additionally, the capacities for power generation, freshwater production, hydrogen production, and cooling are determined. A parametric study is conducted to evaluate the impacts of operating conditions on the overall system. The system's overall energy and exergy efficiencies are calculated as 25% and 13%, respectively, where the hydrogen production, power generation, and freshwater production capacities are 306.8 kg/day, 659 kW, and 0.536 kg/s, respectively. Coefficient of Performance (COP) of the absorption refrigeration cycle is calculated as 0.41.