Development and multi-criteria optimization of a solar thermal power plant integrated with PEM electrolyzer and thermoelectric generator

This study investigates a novel solar-driven energy system for co-generating power, hydrogen, oxygen, and hot water. In the proposed system, parabolic trough collectors (PTCs) are used as the heat source of cascaded power cycles, i.e., steam and organic Rankine cycles (SRC and ORC). While the electricity produced by the SRC is supplied to the grid, the energy output of the ORC is used to drive an electrolyzer for hydrogen production. In addition, the use of a thermoelectric generator (TEG) using heat rejected from the ORC condenser for supplying additional electricity to the electrolyzer is investigated. A multi-objective optimization based on the genetic algorithm approach is carried out to estimate the optimal results for the proposed system. The specific cost of the system product and exergy efficiency are the chosen objective parameters to be minimized and maximized, respectively. The results show that, for the optimal system with the TEG, the specific cost of the system product and the exergy efficiency are 30.2$/GJ and 21.9%, respectively, and the produced hydrogen rate is 2.906 kg/h. The results also show that using a TEG increases efficiency and reduces the specific cost of system product. For having the most realistic interpretation of the investigations, the performance of the proposed system is investigated for four cities in Khuzestan province in Iran.     

4E analysis of efficient waste heat recovery from SOFC using APC: An effort to reach maximum efficiency and minimum emission through an application of grey wolf optimization

This article presents an innovative combined heat and power system comprising a solid oxide fuel cell (SOFC), a heat recovery unit, and a lithium bromide absorption power cycle (APC). The energy, exergy, economic, and environmental perspectives of the proposed system are compared against the same configuration using an organic Rankine cycle (ORC), recovering the waste heat of the SOFC. A multi-criteria optimization based on the Grey Wolf approach is applied to each system to specify the best operation conditions having the exergy efficiency and total cost rate as the objectives. Furthermore, a parametric investigation is conducted to assess the effects of changing the decision variables on the systems proficiencies. The results indicate that although the ORC-based cycle is economically very slightly superior, the integration of the SOFC with the APC offers a much higher exergy efficiency due to the better temperature matching between the working fluid and heat source. Optimization can increase the exergy efficiencies of the SOFC-ORC and the SOFC-APC systems by about 13.8% and 14.7% while reducing the total cost rate by 11.2 $/h and 11.0 $/h, respectively, compared to the base system. Environmental analysis results reveal that APC use leads to a lower emission of 2.8 kg/MWh.     

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.     

Design and analysis of a novel structure for green syngas and power cogeneration based on PEM electrolyzer and Allam cycle

In this study, a new process with the aim of producing green synthesis gas (syngas) with high thermodynamic energy and exergy efficiency is presented. This process consists of four units including a water electrolysis unit (WEU), an Allam power cycle (APC), a Water/Ammonia power cycle (WAPC), and an organic Rankine cycle (ORC). The process was simulated, and the results showed that the overall efficiency of energy and exergy is 60.44% and 63.22%, respectively. It was also found that for this novel process, total exergy destruction is 10.97 MJ/kg_syngas, whereas APC, ORC, WAPC, and WEU units have 66%, 4%, 2%, and 28% share in exergy destruction, respectively. Additionally, the energy analysis results showed that APC, ORC, WAPC, and WEU units have an energy efficiency of 19.07%, 17.76%, 14.48%, and 83.22% respectively. According to the environmental assessment, the direct and indirect emission of carbon dioxide in the proposed process is zero. In this respect, the proposed process has a significant advantage compared to other syngas production methods.     

The first and second law analysis on an organic Rankine cycle with ejector

In consideration of the low efficiency of the organic Rankine cycle (ORC) with low-grade heat source (LGHS), an organic Rankine cycle with ejector (EORC) and a double organic Rankine cycle (DORC) based on the ORC is introduced in this paper. The thermodynamic first law and second law analysis and comparison on the ORC, EORC and DORC cycles are conducted on the cycle’s power output, thermal efficiency, exergy loss and exergy efficiency. Water is chosen as the LGHS fluid, and the same temperature and mass flow rate of the water is the standard condition for the comparative analysis on the cycles. The emphasis is on the thermodynamic performance at the maximum net power output of the cycles. The results show the power output is higher in the EORC and DORC compared to the ORC. And the cycle’s exergy efficiency could be ranked from high to low: DORC > EORC > ORC.     

烟气驱动复叠式非共沸工质有机朗肯循环系统㶲分析

通过构建复叠式非共沸工质有机朗肯循环系统模型,并采用■分析方法,研究了系统■效率随工质摩尔组分的变化规律以及不同摩尔组分下,系统各部件■损失分布情况。研究结果表明:受蒸发器泡点温度与高温级蒸发器夹点位置影响,当高温级循环工质环戊烷摩尔分数为0.8,低温级循环工质异丁烷摩尔分数为0.1时,系统■效率取得最大值48.56%,比采用纯工质时相对提高了3.83%;且采用非共沸工质后,排烟损失、高温级蒸发器■损失、低温级冷凝器■损失均有显著降低。     

Multi-criteria optimization of an integrated energy system with thermoelectric generator,parabolic trough solar collector and electrolysis for hydrogen production

In this research paper, a newly energy system consisting of parabolic trough solar collectors (PTSC) field, a thermoelectric generator (TEG), a Rankine cycle and a proton exchange membrane (PEM) is proposed. The integration is performed by establishing a TEG instead of the condenser as power generation and cooling unit thereafter surplus power output of the TEG is transferred to the PEM electrolyzer for hydrogen production. The integrated renewable energy system is comprehensively modeled and influence of the effective parameters is investigated on exergy and economic indicators through the parametric study to better understand the system performance. Engineering equation solver (EES) as a potential engineering tool is used to simulate the system and obtain the desired results. In order to optimize the system, a developed multi-objective genetic algorithm MATLAB code is applied to determine the optimum operating conditions of the system. Obtained results demonstrate that at optimum working condition from exergy viewpoint, exergy efficiency and total cost are 12.76% and 61.69 $/GJ, respectively. Multi-objective optimization results further show that the final optimal point which is well-balanced between exergy efficiency and total cost, has the maximum exergy efficiency of 13.29% and total cost of 63.96 $/GJ, respectively. The corresponding values for exergy efficiency and total cost are 10.01% and 60.21 $/GJ for optimum working condition from economic standpoint. Furthermore, hydrogen production at well-balanced operating condition would be 2.28 kg/h. Eventually, the results indicate that establishing the TEG unit instead of the condenser is a promising method to optimize the performance of the system and reduce total cost.     

Energy,exergy, and environmental (3E) assessments of an integrated molten carbonate fuel cell (MCFC), Stirling engine and organic Rankine cycle (ORC) cogeneration system fed by a biomass-fueled gasifier

In this paper, a novel syngas-fed combined cogeneration plant, integrating a biomass gasifier, a molten carbonate fuel cell (MCFC), a heat recovery steam generator (HRSG) unit, a Stirling engine, and an organic Rankine cycle (ORC), is introduced and thermodynamically analyzed to recognize its potentials compared to the previous solo/combined systems. For the proposed system, energetic, exergetic as well as environmental evaluations are performed. Based on the results, the gasifier and the fuel cell have a significant contribution to the exergy destruction of the system. Through a parametric study, the current density and the stack temperature difference are known as the main effective factors on the plant performance. Meanwhile, dividing the whole system into three sub-models, i.e., model (1): power production plant including the gasifier and MCFC without including Stirling engine, HRSG, and ORC unit, model (2): the cogeneration system without ORC unit, and model (3): the whole cogeneration system, an environmental impact assessment is carried out regarding CO₂ emission. Considering paper as biomass revealed that maximum value of exergy efficiency is 50.18% with CO₂ emissions of 28.9 × 10⁻² t.MWh⁻¹ which compared to the solo MCFC system indicates 28.40% increase and 13.3 × 10⁻² t.MWh⁻¹ decrease in exergy efficiency and CO₂ emission, respectively.     

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.     

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power is proposed and analyzed in this paper. Unlike a conventional organic Rankine cycle, a supercritical Rankine cycle does not go through the two-phase region during the heating process. By adopting zeotropic mixtures as the working fluids, the condensation process also happens non-isothermally. Both of these features create a potential for reducing the irreversibilities and improving the system efficiency. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle can achieve thermal efficiencies of 10.8-13.4% with the cycle high temperature of 393 K-473 K as compared to 9.7-10.1% for the organic Rankine cycle, which is an improvement of 10-30% over the organic Rankine cycle. When including the heating and condensation processes in the system, the system exergy efficiency is 38.6% for the proposed supercritical Rankine cycle as compared to 24.1% for the organic Rankine cycle.     

Performance comparison and parametric optimization of subcritical Organic Rankine Cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation

Organic Rankine Cycle (ORC) is a promising technology for converting the low-grade energy to electricity. This paper presents an investigation on the parameter optimization and performance comparison of the fluids in subcritical ORC and transcritical power cycle in low-temperature (i.e. 80–100 °C) binary geothermal power system. The optimization procedure was conducted with a simulation program written in Matlab using five indicators: thermal efficiency, exergy efficiency, recovery efficiency, heat exchanger area per unit power output (APR) and the levelized energy cost (LEC). With the given heat source and heat sink conditions, performances of the working fluids were evaluated and compared under their optimized internal operation parameters. The optimum cycle design and the corresponding operation parameters were provided simultaneously. The results indicate that the choice of working fluid varies the objective function and the value of the optimized operation parameters are not all the same for different indicators. R123 in subcritical ORC system yields the highest thermal efficiency and exergy efficiency of 11.1% and 54.1%, respectively. Although the thermal efficiency and exergy efficiency of R125 in transcritical cycle is 46.4% and 20% lower than that of R123 in subcritical ORC, it provides 20.7% larger recovery efficiency. And the LEC value is relatively low. Moreover, 22032L petroleum is saved and 74,019 kg CO₂ is reduced per year when the LEC value is used as the objective function. In conclusion, R125 in transcritical power cycle shows excellent economic and environmental performance and can maximize utilization of the geothermal. It is preferable for the low-temperature geothermal ORC system. R41 also exhibits favorable performance except for its flammability.     

Thermodynamic and economic assessments and multi-criteria optimization of a novel poly-generation plant using geothermal energy and multi heat recovery technique

Smart use of clean energy sources for achieving higher performance and designing cost-effective systems is recognized as an essential solution for reducing fossil fuel consumption. In this regard, this study supports a comprehensive evaluation and multi-criteria optimization of a novel poly-generation plant embracing geothermal energy from thermodynamic and thermoeconomic perspectives. Hence, the utilization of modified subsystems and smart use of multi heat recovery processes are projected and appraised. In this regard, the plant consists of a double-flash binary geothermal subsystem, an organic Rankine cycle in combination with an ejector refrigeration cycle considering a zeotropic working fluid (a mixture of pentane and R142b), a heating production heat exchanger, and a proton exchange membrane electrolyzer with the combined production of cooling, heating, power, and hydrogen. The crucial thermodynamic and thermoeconomic variables are investigated against key parameters and concluded that the sensitivity of outcomes is more evident with the variation in zeotropic working fluid composition and the vapor quality at the heating production heat exchanger's outlet. The attained results at the optimum mode demonstrated, the energy and exergy efficiencies of the plant as well as total unit costs of products are as being 44.5%, 35.8%, and 18.8 $/GJ, respectively.     

Comparison of trilateral cycles and organic Rankine cycles

A comparison of optimized trilateral cycle (TLC) - systems with water as working fluid and optimized organic Rankine cycle (ORC) – systems with pure organic working fluids is presented. The study includes the heat transfer to and from the cycles. The TLC - systems were optimized by the selection of the maximum water temperature, the ORC - systems by the selection of the working fluid and the process parameters. The optimization criterion is the exergy efficiency for power production being the ratio of the net power output to the incoming exergy flow of the heat carrier. Results will be presented for five different cases specified by the inlet temperature of the heat carrier and the inlet temperature of the cooling agent. The inlet temperature pairs are (350 °C, 62 °C), (280 °C, 62 °C), (280 °C, 15 °C), (220 °C, 15 °C) and (150 °C, 15 °C). It is found that the exergy efficiency for power production is larger by 14%–29% for the TLC than for the ORC. On the other hand, the outgoing volume flows from the expander are larger for the TLC than for the ORC by a factor ranging from 2.8 for the first case to 70 for the last case.     

Model for analyzing the energy efficiency of hydrogen liquefaction process considering the variation of hydrogen liquefaction ratio and precooling temperature

The energy efficiency of the hydrogen liquefaction process is studied, and a general model of the hydrogen liquefaction process is built for analyzing the energy efficiency and the influence of multiple parameters. Energy and exergy analysis models of the typical single-pass cycle and multiple-pass cycle are developed. The specific relationships among the parameters and energy efficiency of the total liquefaction system are deduced. A hydrogen liquefaction process with precooling nitrogen and cryogenic helium cycles is studied. For the precooling and cryogenic cycles, the SEC and net power consumption of the cryogenic helium cycle have different variation trends along with the precooling temperature and hydrogen liquefaction ratio. Their optimal values are identified to be ?194 °C and 0.9453, and the corresponding SEC, exergy efficiency, total capital expense, and total annual cost are 3.619 kWh/kg_LH2, 33.44%, 82.58%, 8.263 M$, and 531.62 M$/yr, respectively. The proposed model can be used in the design and operation stages to analyze the variation of energy efficiency along with multiple parameters of the hydrogen liquefaction process.     

Thermodynamic analysis and assessment of novel ORC- DEC integrated PEMFC system for liquid hydrogen fueled ship application

Proton-exchange membrane fuel cell (PEMFC) and liquid hydrogen are gaining attention as a power generation system and alternative fuel of ship. This study proposes a novel PEMFC system, integrated with the organic Rankine cycle–direct expansion cycle (ORC-DEC), which exploits cold exergy from liquid hydrogen and low temperature waste heat generated by the PEMFC for application in a liquid hydrogen fueled ship. A thermodynamic model of each subsystem was established and analyzed from the economic, energy, and exergy viewpoints. Moreover, parametric analysis was performed to identify the effects of certain key parameters, such as the working fluid in the ORC, pressure exerted by the fuel pump, cooling water temperature of the PEMFC, and the stack current density on the system performance. The results showed that the proposed system could generate 221 kW of additional power. The overall system achieved an exergy and energy efficiency of 43.52 and 40.45%, respectively. The PEMFC system had the largest exergy destruction, followed by the cryogenic heat exchanger. Propane showed the best performance among the several investigated ORC working fluids and the system performance improved with the increase in the cooling water temperature of the PEMFC. The economic analysis showed that the average payback time of ORC-DEC was 11.2 years and the average net present value (NPV) was $295,268 at liquid hydrogen costing $3 to $7, showing the potential viability of the system.     

Exergetic analysis of various types of geothermal power plants

Based on available surveys, it has been shown that Iran has substantial geothermal potential in the north and north-western provinces, where in some places the temperature reaches 240 °C. In order to better exploit these renewable resources, it is necessary to study this area. Thus, the aim of this paper is a comparative study of the different geothermal power plant concepts, based on the exergy analysis for high-temperature geothermal resources. The considered cycles for this study are a binary geothermal power plant using a simple organic Rankine cycle (ORC), a binary geothermal power plant using an ORC with an internal heat exchanger (IHE), a binary cycle with a regenerative ORC, a binary cycle with a regenerative ORC with an IHE, a single-flash geothermal power plant, a double-flash geothermal power plant and a combined flash-binary power plant. With respect to each cycle, a thermodynamic model had to be developed. Model validation was undertaken using available data from the literature. Based on the exergy analysis, a comparative study was done to clarify the best cycle configuration. The performance of each cycle has been discussed in terms of the second-law efficiency, exergy destruction rate, and first-law efficiency. Comparisons between the different geothermal power plant concepts as well as many approaches to define efficiencies have been presented. The maximum first-law efficiency was found to be related to the ORC with an IHE with R123 as the working fluid and was calculated to be 7.65%. In contrast, the first-law efficiency based on the energy input into the ORC revealed that the binary cycle with the regenerative ORC with an IHE and R123 as the working fluid has the highest efficiency (15.35%). Also, the maximum first-law efficiency was shown to be given by the flash-binary with R123 as the working fluid and was calculated to be 11.81%.     

Application,comparative study,and multi-objective optimization of a hydrogen liquefaction system utilizing either ORC or an absorption power cycle

Environmental degradation and global warming are presently two of the most pressing global concerns. According to the (IAE), around 80% of global energy demand has been met by fossil fuels in recent years, resulting in an increase in CO₂ emissions as the primary greenhouse gas. Switching to renewable energy sources and using more energy-efficient energy systems are vital for mitigating environmental challenges and reducing our reliance on fossil fuels, among other things. Hydrogen fuels are primary renewable resources because of their reduced cost and ability to produce net-zero CO₂ emissions. In the present study, a system is designed to generate power and liquid hydrogen from geothermal sources. The generated power by employing either the organic Rankin cycle (ORC) or absorption power cycle (APC) is compared to seek the best cycle performance from power generation standpoint. A comprehensive thermodynamic and economic modeling is carried out for the proposed system. In addition, a parametric study is applied to see which parameters affect the performance of the system. Multi-objective optimization is carried out to find the best operating point of the hydrogen liquefaction energy system. The system demonstrates better performance when APC is applied for power generation. The cost of generated liquid hydrogen by ORC and APC is 3.8 $/kg.LH₂ and 3.6 $/kg.LH₂, respectively. Furthermore, 0.014 $/kWh of electricity cost is reached by ORC compared to 0.012 $/kWh of APC. Parametric analysis shows that the higher the temperature and flow rate of the brine of geothermal fluid, the higher the efficiency and the lower cost. Finally, the multi-objective optimization pinpoints that the system's efficiency and unit product cost at the optimal ORC-based design is 33.85% and 0.0121 $/kWh. In comparison, the APC demonstrates better performance by 34.5% and 0.011 $/kWh.     

Energy,exergy and economic analyses and multiobjective optimization of a novel solar multi-generation system for production of green hydrogen and other utilities

Renewable energy based multi-generation systems can help solving energy-related environmental problems. For this purpose, a novel solar tower-based multi-generation system is proposed for the green hydrogen production as the main product. A solar-driven open Brayton cycle with intercooling, regeneration and reheat is coupled with a regenerative Rankine cycle and a Kalina cycle-11 as a unique series of power cycles. Significant portion of the produced electricity is utilized to produce green hydrogen in an electrolyzer. A thermal energy storage, a single-effect absorption refrigeration cycle and two domestic hot water heaters are also integrated. Energy, exergy and economic analyses are performed to examine the performance of the proposed system, and a detailed parametric analysis is conducted. Multiobjective optimization is carried out to determine the optimum performance. Optimum energy and exergy efficiencies, unit exergy product cost and total cost rate are calculated as 39.81%, 34.44%, 0.0798 $/kWh and 182.16 $/h, respectively. Products are 22.48 kg/h hydrogen, 1478 kW power, 225.5 kW cooling and 7.63 kg/s domestic hot water. Electrolyzer power size is found as one of the most critical decision variables. Solar subsystem has the largest exergy destruction. Regenerative Rankine cycle operates at the highest energy and exergy efficiencies among power cycles.     

Investigation of green hydrogen production and development of waste heat recovery system in biogas power plant for sustainable energy applications

In this study, biogas power production and green hydrogen potential as an energy carrier are evaluated from biomass. Integrating an Organic Rankine Cycle (ORC) to benefit from the waste exhaust gases is considered. The power obtained from the ORC is used to produce hydrogen by water electrolysis, eliminate the H₂S generated during the biogas production process and store the excess electricity. Thermodynamic and thermoeconomic analyses and optimization of the designed Combined Heat and Power (CHP) system for this purpose have been performed. The proposed study contains originality about the sustainability and efficiency of renewable energy resources. System design and analysis are performed with Engineering Equation Solver (EES) and Aspen Plus software. According to the results of thermodynamic analysis, the energy and exergy efficiency of the existing power plant is 28.69% and 25.15%. The new integrated system's energy, exergy efficiencies, and power capacity are calculated as 41.55%, 36.42%, and 5792 kW. The total hydrogen production from the system is 0.12412 kg/s. According to the results of the thermoeconomic analysis, the unit cost of the electricity produced in the existing power plant is 0.04323 $/kWh. The cost of electricity and hydrogen produced in the new proposed system is determined as 0.03922 $/kWh and 0.181 $/kg H₂, respectively.     

Analysis of zeotropic mixtures used in low-temperature solar Rankine cycles for power generation

This paper presents the analysis of low-temperature solar Rankine cycles for power generation using zeotropic mixtures. Three typical mass fractions 0.9/0.1 (Ma) 0.65/0.35 (Mb), 0.45/0.55 (Mc) of R245fa/R152a are chosen. In the proposed temperature range from 25 °C to 85 °C, the three zeotropic mixtures are investigated as the working fluids of the low-temperature solar Rankine cycle. Because there is an obvious temperature glide during phase change for zeotropic mixtures, an internal heat exchanger (IHE) is introduced to the Rankine cycle. Investigation shows that different from the pure fluids, among the proposed zeotropic mixtures, the isentropic working fluid Mb possesses the lowest Rankine cycle efficiency. For zeotropic mixtures a significant increase of thermal efficiencies can be gained when superheating is combined with IHE. It is also indicated that utilizing zeotropic mixtures can extend the range of choosing working fluids for low-temperature solar Rankine cycles.