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In this study, the partial heating supercritical CO2 power cycle for waste heat recovery is investigated to understand more about the true potential of thermodynamic and economic performance improvement of each system component, as well as a more profound comprehension of the simultaneous interactions between the system components using advanced exergy and advanced exergoeconomics analysis. In addition, the affirmative or nugatory impact of the inefficiency of each component on the exogenous exergy destruction and exogenous costs in other system components separately, as well as the effect of the inefficiency combination of other components on the desired component (mexogenous effect) have been determined. The results demonstrated that according to the technological constraints in the system, the maximum exergy efficiency that can be achieved is 59.8%, and 38.4% (926.9 kW) of the total exergy destruction and 46.18% (32.52 $ h - 1 ) of the total exergy destruction cost of the system is avoidable. According to the mexogenous exergy destruction, the simultaneous interplay among other system components affects the turbine performance most. The priority of improving the components based on the highest avoidable endogenous exergy destruction cost is related to the turbine, cooler, and compressor. The results of this study revealed that 97.8% (79.73 $ h - 1 ) of the system's total cost is relevant to the endogenous part, which shows that the cost caused by the interaction among the components is very small. The turbine and compressor have the most significant cost-saving potential, while the heaters have the lowest. [ABSTRACT FROM AUTHOR]

Gas–steam combined cycle power plants are the most efficient electricity‐generation units based on fossil fuels. However, these power plants are prone to efficiency decrease in hot climates as high ambient temperatures adversely influence the gas turbine's output. The present study investigated the effect of incorporating a solar absorption refrigeration (SAR) system into an actual combined cycle power plant for the first time. First, the energy and exergy analyses were performed using THERMOFLOW software. Then, the influence of the ambient temperature (10°C–52.5°C) on the power plant's performance and its components was investigated. The SAR system was then used to cool the compressor's input air and improve the power generation capacity by employing TRNSYS software. The results showed that the power plant reached its maximum efficiency at an ambient temperature of 26.6°C. However, its overall efficiency and net power generation were dropped with a further increase in the ambient temperature. Employing the SAR system for each gas turbine in the power plant on a sunny day until 2 p.m. would decrease the compressor's input air temperature. For example, for the refrigeration capacities of 450, 700, and 1000 tons for each gas turbine, the temperature was reduced by nearly 3°C, 5°C, and 7°C, respectively. Under the same condition, power generation capacity improved by 12.5, 24, and 32.5 MW, and the overall efficiency rose by 0.6%, 1.4%, and 2%. Such an increase in power and efficiency occurred during peak demand, which was significant. [ABSTRACT FROM AUTHOR]

A novel hybrid system, including photovoltaic, wind turbine, diesel generator, battery, electrolyzer, gas turbine cycle, Rankine cycle, absorption chiller, and hot water line, is introduced in order to supply electricity, cooling, and heating simultaneously for a town in Istanbul. The dynamic method is employed for different parts of the system dependent on meteorological information, and the steady-state situation is considered for the other parts, such as the gas turbine cycle, Rankine cycle, absorption chiller, and hot water line. Therefore, every operational parameter of the proposed system is evaluated monthly based on the meteorological information of 2019 in Istanbul. Also, the combination of the non-dominated sorting algorithm and multi-criteria decision-making of TOPSIS is employed in order to obtain the optimum rates of monthly operational parameters. Accordingly, the maximum rates of energy and exergy efficiencies can be acquired, which belong to September, October, and November, approximately 54–60%. Furthermore, exergy destruction can be achieved at the lowest rate. The highest exergy destruction is dedicated to December, with 1925.7 MW and the combustion chamber in the gas turbine cycle has the highest contribution (48%) in the exergy destruction related to this month. At the end, the COE and NPC of the system based on the optimum operational parameters are obtained 0.05147 $kW h−1 and 579.3 M$, respectively. [ABSTRACT FROM AUTHOR]

A parametric study has been carried out based on advanced exergy assessment for a parallel double‐effect LiBr–water absorption chiller. The advanced exergy method provides the real potential of the equipment for improvement in the system by recognizing the avoidable irreversibilities. The sensitivity analysis of various parts of the exergy destruction (endogenous avoidable, endogenous unavoidable, exogenous avoidable, and exogenous unavoidable) in system components and the overall performance (coefficient of performance, exergy efficiency, and modified exergy efficiency) of the system has been done to identify the actual potential of different components of the system to improve the overall performance of the system relative to operational parameters. Operational parameters include the heat source temperature, heat sink temperature, and the difference between the absorption and condensation temperature. The results showed that by modifying and improving the performance of components, 18.5% of the total exergy destruction of the system could be reduced. The modified exergy efficiency reduces sharply (nearly 40%) with the rising heat sink temperature. The endogenous exergy destruction increases in all system components except the condenser and evaporator by the heat source temperature increase. With the increase in the heat sink temperature, the avoidable part of the total exergy destruction in the system increases due to the significant rise in the avoidable exogenous exergy destruction in the components, and the unavoidable endogenous exergy destruction decreases (more than 200%) in the absorber. Increasing the condensation temperature reduces the unavoidable endogenous exergy destruction in the components except for the low‐temperature heat exchanger. [ABSTRACT FROM AUTHOR]

Solar chimney is one of the attractive approaches to produce power from a clean source of renewable energy. In this investigation, a potentiometric study is carried out to find out a best location for construction of a solar chimney in different climates of Iran, in the Middle East. With this objective, three locations with different weather climates were chosen, i.e. Tehran, Semnan, and Bandar Abbas. These locations were chosen due to their different climatic conditions and solar irradiation. The used weather conditions are extracted for the middle day of summer, 6th August. The output power of the solar chimney plant was assessed as a function of various thermo-physical properties such as ambient pressure, ambient temperature, and local average solar irradiation. Three different typical geometry size were designed to assess the effect of ambient pressure on the output power meanwhile ambient temperature and solar irradiation is supposed to be the same for all cases. It is concluded that the output power is not significantly changed for different selected cities. In addition, Genetic algorithm (GA) is used to optimize the geometry size, performance, and economic factors of the solar chimney in three different cities. It is obtained from GA algorithm that Bandar-Abbas is the best location to construct a solar chimney. The collector diameter of 1544.82m and chimney height of 823.35m is calculated as the optimized geometry of the solar chimney for constructing in Bandar-Abbas city. Moreover, performance and economic considerations resulted that the solar chimney in Bandar-Abbas is able to produce 167.18 MW output work and the net present value after a 25 years of 6350.3x 1012$. Exergy assessment resulted that the solar chimney in Bandar-Abbas is the most destructive exergy condition since the input ambient temperature and the bigger geometry size of this solar chimney. After Bandar-Abbas, Semnan and Tehran were ranked, respectively. [ABSTRACT FROM AUTHOR]

Abstract In this study, the sulfur recovery unit based on the modified Claus process with the split flow is simulated and the results are validated with South Pars gas refinery data. Since optimum energy consumption is essential for community development, exergoeconomic and sensitivity analyses are conducted to prevent waste production and increase energy efficiency in this unit. Energy and exergy analyses are performed to identify the equipment with low exergy efficiency and calculate their exergy destruction extent. Reaction furnace with 4178.8 kW exergy destruction has the highest rate, and then waste heat boiler and P-7 pump are placed. After the pumps, the heat exchangers have the lowest exergy efficiency so that the acid gas preheater with the value of 60% has the lowest one. All equipment investment and operating and maintenance cost calculations are carried out so that the largest cost is related to the hydrolyzing Claus bed that followed by waste heat boiler and P-7 pump. Then equipment exergoeconomic parameters such as exergoeconomic factor, cost rate of exergy destruction and relative cost difference are obtained. The lowest exergoeconomic factor among the process equipment is related to reaction furnace and second condenser with the values of 0.26% and 0.86%, respectively. The maximum exergoeconomic factor is 94% which is attributed to compressors. The reaction furnace with 4706.16 ($/h) and waste heat boiler with 4629.89 ($/h) have the highest cost rate of exergy destruction and CMPR-5 compressor with 0.2451 ($/h) has the lowest cost rate. Finally, considering some of the functional and economic parameters in the sensitivity analysis procedure, the influence of changing these variables on exergoeconomic parameters have been investigated. Highlights • The gas refinery sulfur recovery unit is simulated. • The exergoeconomic analysis is performed on a sulfur recovery unit. • Products cost rates including sulfur streams, LP and MP steams are calculated. • All equipments in terms of exergoeconomic variables are ranked. • Sensitivity analyses on the operational and economic parameters are conducted. [ABSTRACT FROM AUTHOR]

Highlights • A hybrid system including high-temperature fuel cell and absorption chiller is developed. • Nanofluids are employed as absorbent for increasing of COP in the refrigeration system. • Exergy analysis has been conducted for the hybrid fuel cell refrigeration system. • Sensitivity analysis is employed for assessing of main parameters on the system performance. Abstract A hybrid system including high-temperature polymer fuel cell with capacity of 5 kW along with fuel processing unit for producing rich hydrogen from natural gas integrated by a 3 kW absorption chiller has been developed. The waste heat of flue gas from the burners is utilized in the ammonia-water absorption chiller for refrigerating purposes. The hybrid refrigeration system is simulated by Aspen HYSYS software in a steady state condition. After defining the properties of nanoparticles in HYSYS software, the water-based nanofluids are employed as absorbent liquid for increasing of COP in the refrigeration system, and their effects have been evaluated on overall system performance. The electrochemical model of the fuel cell as well as the main parameters of refrigeration system have been validated with experimental results and similar works. Electrical efficiency and overall efficiency of the hybrid system are equal to 36% and 77.3%, respectively. The overall efficiency in the presence of silver nanofluid can be increased up to 81%. Exergy analysis has been conducted for the hybrid system, and the obtained exergy efficiency of the system is equal to 29%. Sensitivity analysis has been employed for evaluating of significant parameters on the hybrid system performance. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the advanced exergy analysis was used to determine the avoidable and unavoidable exergy destructions of the heat exchanger networks (HENs) in a complex natural gas refinery in the South Pars gas field, focusing only on the improvement of the avoidable part. Exergy balances were evaluated for the HENs and the equations of advanced exergy destruction and exergetic efficiency for the HENs were developed. The total exergetic efficiency of the HEN in the plant was determined to be 62.8% that could be increased up to 84.2%, suggesting a high potential for improvement. Also, it was shown that the HEN1 had the most severe condition in the plant with the highest inefficiencies among the other networks. The avoidable and inevitable irreversibilities were calculated for all the heat exchangers running in the plant network. The advanced exergy analysis revealed that the exergy destruction had two major contributors. First, about 59% of the total irreversibility of the system was avoidable and could be eliminated by the well-known optimization techniques. Secondly, only 18 most inefficient heat exchangers (17% in numbers) contributed to more than 61% of the total exergy destruction in the plant network. Hence, there was a high potential for improvement of the operational cost in such a huge consuming energy system. Graphical abstract Image 1 Highlights • The HEN of a complex gas refinery has been analyzed by Advanced Exergy Analysis (AEA). • By AEA, exergy efficiency of the HEN was increased about 34% relative to the old one. • By AEA, the most inefficient heat exchangers in the network were found. • About 61% of total irreversibility of HEN corresponded to only 17% of the heat exchangers. • About 59% of the irreversibility of the HEN was avoidable and can be eliminated. [ABSTRACT FROM AUTHOR]

This paper aims to investigate a hybrid cycle consisting of a molten carbonate fuel cell (FC) and a Stirling engine which, by connecting to a seawater reverse osmosis desalination unit, provides fresh water. First, a parametric evaluation is performed to study the effect of some key parameters, including the current density and the working temperature of the FC and the thermal conductance between the working substance and the heat reservoirs in the Stirling engine, on the objective functions. The objective functions include the energy efficiency, the exergy destruction rate density, the fresh water production rate, and the ecological function density. After investigating each double combination of these objective functions, two scenarios are defined in quest to concurrently optimize three functions together. The first scenario aims to optimize the energy efficiency, the exergy destruction rate density, and the fresh water production rate; and the second scenario attempts to optimize the energy efficiency, the fresh water production rate, and the ecological function density. A multi‐objective evolutionary algorithm joined with the nondominated sorting genetic algorithm (NSGA‐II) approach is employed to obtain Pareto fronts in each case scenario. In order to ascertain final solutions between Pareto fronts, three fast and robust decision‐making methods are employed including TOPSIS, LINMAP, and Fuzzy. Finally, a sensitivity analysis is conducted to critically analyze the performance of the system. Thermodynamic analysis of irreversible molten carbonate fuel cell–Stirling heat engine–reverse osmosis hybrid system is studied. A multi‐objective optimization approach is carried out for performance optimization. Three decision‐making methods are employed to select final answers. [ABSTRACT FROM AUTHOR]

This article presented a simplified method for quick estimating exergy destruction and irreversibility distribution ratio (φ) in a complex Heat Exchanger Network (HEN) of a large natural gas refinery in South Pars Gas Field located in the Persian Gulf. By the presented method, the designing of the HEN isn't required and the only necessary data are the temperatures and thermo-physical properties of the fluids at the inlets and outlets of the HEN. The equation of exergy destruction for the HEN was developed and the model was adapted to estimate the contributions of heat transfer and pressure drops due to fluid friction, as the two major causes of irreversibility in the HEN. The irreversibility factors were compared with the results obtained by conventional irreversibility analysis, i.e. considering irreversibility analysis of all individual heat exchangers running in the HEN. By comparison of the results of the two methods, it was shown that the values and trends of the irreversibility factors estimated by the two methods were approximately the same. By this procedure, it is possible to estimate the irreversibility distribution ratio in any HEN very quickly, especially in early stages of the thermal system designs, without solving very complex mathematical relations. [ABSTRACT FROM AUTHOR]

Fuel cell-heat engine hybrid system is a relatively new discipline which proposes to utilize the excess high-temperature heat of the fuel cell as the heat source for the heat engine. This paper is concerned with a thermodynamic analysis of a molten carbonate fuel cell-SCO 2 Brayton hybrid system to optimize its performance based on a list of criteria. Four objective functions are considered, including energy efficiency, power density, exergy destruction rate density and ecological function density, to study the influence of four main parameters, including compressor inlet temperature and turbine inlet temperature of the Brayton cycle, and interconnect plate area and current density of the fuel cell, on the performance of the hybrid cycle. The strong conflict between the objective functions necessitates a multi-objective optimization procedure and, therefore, three scenarios are proposed, each takes into account a combination of three of these objective functions. The multi-objective evolutionary method integrated with non-dominated sorting genetic algorithm is used to obtain Pareto optimal frontiers. Finally, three efficient decision-making tools including TOPSIS, LINMAP and Fuzzy are employed by means of which the best answers in each case scenario are selected. Examining the Fuzzy method results for example, in the first scenario, which doesn’t consider power density, ecological function density and exergy destruction rate density meet their optimum values, 1.314 and 0.3864 kW/m 2 , respectively. However, energy efficiency falls by 10% compared to its maximum, which occurs in the third scenario (0.6676), where ecological function density isn’t included, and power density drops by 25% compared to its own in the second scenario (2.2783 kW/m 2 ), where energy efficiency is not. This indicates the strong confliction between the objective functions and also the necessity of this kind of analysis. However, the first scenario would roughly provide the best condition for the system if one wanted all the objective functions to be optimum all together. [ABSTRACT FROM AUTHOR]

In recent years, many studies have been conducted on hybrid solid oxide fuel cell and gas turbine which fed by renewable fuels to reach the high-efficiency power and the low pollution. In this paper, a thermodynamic study based on energy and exergy analyses of a hybrid solid oxide fuel cell and gas turbine hybrid system has been conducted in the presence of reforming with steam, in which the effects of using natural gas and other biofuels including Sewage biogas, Agricultural and Industrial waste biogas, Syngas, Biofuel and Gasified biomass, have been compared to this system. The purpose of this paper is to investigate the effect of each of the mentioned fuels on the performance of individual equipment and the entire system from the thermodynamic perspective. Initially, the modeling and energy balance of all components in the system were carried out in detail. Further, calculating the exergy destruction of all components of the system and the effects of applying different biofuels on the key parameters of the system, including total production power, operating pressure and temperature, compression ratio, the water-to-fuel ratio in the reforming, energy and exergy efficiency, and the amount of irreversibility of each component in the system have been analyzed. To compare more accurately between different fuels, an equal amount of each fuel is considered, and the effect of each fuel system on the hybrid system is analyzed by calculating the operating parameters of the system. By studying the results of modeling, it was determined that natural gas with 879.03 kW produced the highest production capacity and Gasified biomass with 45.44 kW has the least amount of power generation. By studying the thermodynamics of the system, if it is fed with Natural gas, the highest exergy destruction (687.45 kW) occurs and the lowest total exergy destruction rate is related to the system fed by gasified biomass (101.12 kW). Comparing the fuels, it was concluded that the electrical efficiency of the system fed with natural gas has the highest efficiency (72.71%) and Biofuel has the lowest total electrical efficiency (56.6%). Furthermore, by examining the exergy efficiency of the whole system, it was found that Natural gas with the highest efficiency of 61.29% and Gasified biomass with 46.06% the lowest exergy efficiency can be detected. Finally, the effect of the percentage combination of each fuel on the performance of all equipment from the perspective of energy and exergy has been studied. • SOFC-GT hybrid systems fed by natural gas & various biofuels were modeled and studied. • Energetic & exergetic performances of the hybrid systems were analyzed compared with together. • The systems fed with natural gas and Biofuel had the highest and lowest electrical efficiencies, respectively. • The systems fed with natural gas and Gasified biomass had the highest and lowest exergy efficiencies, respectively. [ABSTRACT FROM AUTHOR]

An exergy analysis of a novel integrated power system is represented in this study. A Solid Oxide Fuel Cell (SOFC), which has been assisted with a Gas Turbine (GT) and Organic Rankine Cycle (ORC) by employing liquefied natural gas (LNG) as a heat sink in a combined power system is simulated and investigated. Initially in this paper, the integrated power system and the primary concepts of the simulation are described. Subsequently, results of the simulation, exergy analysis, and composite curves of heat exchangers are represented and discussed. The equations of the exergy efficiency and destruction for the main cycle’s units such as compressors, expanders, pumps, evaporators, condensers, reformers, and reactors are presented. According to the results, the highest exergy destruction is contributed to the SOFC reactor, despite its acceptable exergy efficiency which is equal to 75.7%. Moreover, the exergy efficiencies of the ORC cycle and the whole plant are determined to be 64.9% and 39.9%, respectively. It is worth noting that the rational efficiency of the integrated power system is 53.5%. Among all units, the exergy efficiency of the LNG pump is determined to be 11.7% the lowest exergy efficiency among the other investigated components, indicating a great potential for improvements. [ABSTRACT FROM AUTHOR]

Today, the increase in the production and consumption of biofuels such as biodiesel in the transportation sector is considered an appropriate solution to decrease the consumption of fossil fuels and their consequent pollutions. However, in order to increase energy efficiency and minimize energy losses and waste materials, the biodiesel production processes require the particular revisions and modifications. In the present study, the exergy analyses of the mechanical stirrer (MS), ultrasonic cavitation (UC) and hydrodynamic cavitation (HC)-based biodiesel production processes were performed and the results were compared together, in order to improve the efficiency of the biodiesel production process. To compare the results, three parameters of the exergy waste emission, the exergy destruction, and the exergy efficiency were used. The results indicated that both the cavitation processes lead to improved exergy efficiency in the biodiesel production. However, the HC process proved to be a more appropriate option to replace the conventional biodiesel production process equipped with stirred-rank reactors (the MS process) due to eliminating the main waste streams, decreasing exergy destruction to half, and increasing exergy efficiency by 6.2%. [ABSTRACT FROM AUTHOR]

Introducing nanotechnology made a revolution in various industries such as upstream, downstream and energy industries. As a result, developing new types of nanoscale thermal cycles can develop the future of energy systems. The present work investigated a nanoscale irreversible Stirling refrigeration cycle thermodynamically in order to optimize the performance of the aforesaid cycle. In the above-mentioned cycle, an Ideal Maxwell–Boltzmann gas plays a role of a working fluid. Ideal Maxwell–Boltzmann gas was employed for working fluid in the cycle. Owing to the quantum limit influence on the gas particles restricted in the finite area, the cycle no longer retains the circumstance of perfect regeneration. He 4 is chosen as working fluid. This paper demonstrates two different plans in the process of multi-objective optimization; though, the results of each plan are assessed individually. The first scenario constructed with the purpose of maximizing the ecological coefficient of performance (ECOP) , the coefficient of performance ( C O P ) and the dimensionless Ecological function ( e c f ). Furthermore, the second scenario planned with the purpose of maximizing the exergy efficiency ( η e x ) , the coefficient of performance ( C O P ) and the dimensionless Ecological function ( e c f ). All the scenarios in this paper are performed through the multi-objective evolutionary algorithms (MOEA) joined with NSGA II approach. Moreover, to determine the final solution in each scenario three effective decision makers are employed. Deviation of the results obtained in each scenario and each decision maker are calculated individually. Finally, the results of the suggested scenarios were compared to each other, and it reveals that when the exergy efficiency achieved the maximum value, the values of COP, ECOP, and ecf also maximized. [ABSTRACT FROM AUTHOR]

This research presents the optimization and performance analysis for irreversible heat pumps operating with reversed Brayton cycle with constant-temperature heat reservoirs via finite-time thermodynamics (FTT) by considering exergetic efficiency as the optimization objective combining exergy model. Moreover, two different strategies in the process of multi-objective optimization are proposed, and the outcomes of each strategy are evaluated separately. The first strategy is proposed to maximize the coefficient of performance (COP), the ecological coefficient of performance (ECOP) and the exergetic efficiency. Furthermore, the second strategy is suggested to maximize the COP, ECOP and Ecological function. All the strategies in the present work are executed via the multi objective evolutionary algorithms based on NSGA|| method. Finally, to govern the final answer in each strategy, three efficient decision makers were executed. [ABSTRACT FROM AUTHOR]

A novel integrated structure is introduced in order to produce power and heat through biomass fuel simultaneously. This cycle has different sections including the gasification process, solid oxide fuel cell, gas turbine cycle, Rankine cycle, ORC, and hot air and water line. The heat required for the gasifier agent and the air is supplied through heat recovery in this system. In this article, wood chips are employed to supply the required fuel for a solid oxide fuel cell by gasification process. Also, the heat of the SOFC outlet stream is employed for heating the inlet streams of the Rankine cycle, gas turbine, and ORC. Both energetic and exergetic analyses are considered in order to evaluate the performance of the proposed cycle. A sensitivity analysis is performed for observing the effects of the operational parameters on the output power and overall efficiency of the system. The results illustrate that the output power of the cycle is 152.8 MW, and the electrical and overall efficiencies are 51.43% and 81.13%, respectively. Also, the highest portion of exergy destruction is allocated to the fuel cell, which is about 65 MW. [ABSTRACT FROM AUTHOR]

It is expected that fossil fuels will be replaced by renewable energy sources to reduce environmental pollution. Multigenerational integrated plants which generate various useful outputs from the same input are required to utilize these sources more efficiently. An innovative multigeneration system based on biomass for useful outputs including district cooling and heating, bioethanol, biogas, and electricity is proposed in this study. The system includes a biomass combustion unit, Rankine cycle, biofuel production unit, and absorption cooling cycle. 15 types of biomass sources are considered for the combined system and a thermodynamic and environmental analyses are carried out to assess the effects of biomass sources on the multigeneration system. According to the modeling results, using cotton stem leads to the highest CO 2 emission (195.3 kg/MWh) while switchgrass produces the lowest (147.0 kg/MWh). The thermodynamic analysis reveals that, for all considered cases, the burner has the maximum exergy destruction rate among all the stages. Moreover, the exergy and energy efficiencies of the plant for different fuels were assessed, and show that the use of rice straw and rice husk exhibit the highest (68.30%) and lowest (62.72%) overall energy efficiencies, respectively. It is also observed that the system using rice straw and larch wood has the highest (45.29%) and lowest (42.86%) overall exergy efficiencies, respectively. The effects of significant input factors are examined on the system performance and emission indicants. • A new multigeneration system fed by various biomass sources was investigated. • Exergy, energy and environmental performances were analyzed for 15 biomass types. • The system fed by rice straw exhibited the highest energy efficiency. • The system fed by rice straw had the highest exergy efficiency. • The system fed by switchgrass had the lowest CO 2 emission. [ABSTRACT FROM AUTHOR]