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In the current study, a detailed assessment and multi-objective optimization of a geothermal-driven cogeneration system for producing hydrogen and electricity have been carried out. The system includes two parts; the primary cycle is the geothermal cycle, which extracts geothermal energy. The secondary cycle consists of an organic Rankine cycle (ORC) and a proton exchange membrane (PEM) electrolyzer. In order to enhance ORC performance, zeotropic mixes have been used as working fluids. The concentration on the destructive environmental impacts of the system, which has not been considered in prior studies, is the research’s main novelty. This study mainly focuses on environmental evaluation using Life Cycle Assessment (LCA) to decrease destructive environmental impacts. From the perspectives of energy, exergy, exergoeconomic, and exergoenvironmental (4E), the pentane (0.3)-butane (0.7) working fluid performed better than other working fluids. Energy and exergy efficiency for the cogeneration system increased by 19.34% and 58.67%, respectively. According to the results of the exergoenvironmental analysis, the PEM showed significant product environmental consequences at a speed of 261 mpts/h. The multi-objective optimization findings illustrated that energy efficiency and destruction cost in optimum conditions reach 20.06% and 22.64 $/h. Furthermore, exergy efficiency and destruction environmental impacts will reach 59.81% and 1762.11 mpts/h, respectively.

A novel polygeneration system is designed to provide electricity, heating and cooling capacity on basis of solar energy. Two-stage power cycle of sCO2 Brayton and steam Rankine is propelled to generate electricity with residual heat transferred to drive an efficient heating device and an intercooled absorption cooling system. System performance is comprehensively analyzed from thermal efficiency in terms of energy and exergy, based on the quasi-steady numerical model. Results indicate that built system obtains electricity, heating and cooling capacity of 243.84, 42.05 and 10.746 MW with energy efficiency of 0.5304, 0.0915 and 0.0234 and exergy efficiency of 0.562, 0.0174 and 0.0024, respectively. Mass flows of working fluids and detailed specifications of solar collecting field are also included in this investigation. Parametric analysis exhibits that operating parameters exert remarkable influence on thermal efficiencies. Proposed system can save amounts of energy over three individual systems with identical products by means of a primary energy saving ratio analysis and energy saving performance is more sensitive to turbine inlet temperature of Brayton. Exergoeconomic evaluation reveals that designed system achieves inferior electricity performance and superior heating and cooling performance in comparison with current circumstance. In conclusion, this novel cogeneration system takes full advantage of solar energy to meet various energy consumptions. [ABSTRACT FROM AUTHOR]

In this study, comprehensive energy, exergy, and economic modeling, and optimization of a flash-binary geothermal system, were carried out for power and hydrogen production. The binary system is a combination of a dual-pressure organic Rankine cycle and proton exchange membrane electrolyzer. For performance improvement of dual-pressure organic Rankine cycle, zeotropic mixtures were used as the working fluids. The multi-objective Genetic algorithm was employed to optimize the system performance. According to the obtained results, the highest rate of exergy destruction was obtained for the steam turbine with a value of 16.42 kW. For the base case simulation, the energy and exergy efficiencies of the proposed system were obtained by 16.66 % and 58.03 % , respectively; also, the generated power, overall exergy destruction, and hydrogen production capacity were calculated by 114.53 kW , 82.755 kW , and 0.306 kg · hr − 1 , respectively. For the multi-objective optimization mode, the best performance was calculated for Pentane (0.467)/Butane (0.533) with energy and exergy efficiencies and hydrogen production of 16.67 % , 58.14 % , and 0.37 kg · hr − 1 . Moreover, the optimized payback period and NPV were around 5.52 years and 402600 $ , respectively. • Proposal of a flash-binary geothermal system for power and hydrogen production. • Using zeotropic mixtures for performance improvement of dual-pressure ORC. • Analyzing economic aspects of the proposed system for probable investment. • Energy and exergy efficiencies of 16.67 % and 58.14 % for the optimized mode. • Optimized payback period and total profit of 5.52 years and 402800 $. [ABSTRACT FROM AUTHOR]

The exergoeconomic analysis of an energy conversion system is helpful to decide about topics like the cost of fuel required to produce each unit of energy, electricity sales prices affecting energy production cost amounts and how to allocate R&D funds to develop system equipment. With this aim, exergoeconomic assessment of a binary geothermal power plant (GPP) with organic Rankine cycle (ORC) is researched in detail. Therefore, a parametric study about the effect of well head and ambient temperatures, electricity production, and CO2 release is conducted for the GPP. The study shows that the exergy efficiency, exergy destruction ratio and exergoeconomic factor for the GPP are, respectively, 39.1%, 31.4%, and 58.1%. The highest total operating costs and exergy destruction rate belong to the condenser in the system with values of 186 $/h and 2.49 MW. The costs per unit exergy for the liquid and steam geothermal fluid in the GPP are 1.2 $/GJ and 370 $/GJ, respectively. The total operating cost of the GPP is nearly 1,218.38 $/h, while the cost rate per unit of electricity produced by the GPP is 0.055 $/kWh. As the ambient temperature increased, there is a 10% increase in total operating cost and this results in a 21% increase in cost per electricity produced. With the brine input temperatures of 160°C, 165°C, and 170°C, the costs per unit CO2 output are, respectively, 110 $/h, 167.50 $/h, and 307 $/h. In conclusion, as the amount of steam brine entering the GPP increases, the amount of CO2 released to the atmosphere ascends. [ABSTRACT FROM AUTHOR]

In this paper, the exergoeconomic analysis was conducted to an existing ultra-supercritical coal-fired power plant in China to understand the cost-formation process, to evaluate the economic performance of each component and to find possible solutions for more cost-effective designs. The total revenue requirement (TRR) and the specific exergy costing (SPECO) methods were applied for economic analysis and exergy costing, respectively. Quantitative balances of exergy and exergetic costs as well as necessary auxiliary equations for both individual component and the overall system were established. The results show that the exergoeconomic factors of the furnace and heat exchangers at low temperature levels, including air preheater and low-pressure feedwater preheaters, are rather small; while those of other components are relatively large. Moving more heat absorption into furnace to use the effective radiation heat transfer, increasing the air preheating temperature and adding more low pressure feedwater preheaters can be promising solutions for future design.

Nowadays, solar energy is one of the most promising renewable energy sources that can effectively mitigate the current serious energy crisis and environmental pollution. To efficiently utilize solar energy and positively comply with the carbon neutrality policy, this research developed an efficient and environmentally-friendly improved He-CO 2 cascade Brayton cycle for concentrated solar power, and then implemented a series of studies, including performance prediction, sensitivity analysis, and exergoeconomic optimization. After optimization, the most suitable condition was determined via a decision-making method, and the exergoeconomic performances of each subsystem and component were thoroughly investigated. Finally, the concentrated solar power system was comprehensively evaluated from the perspectives of thermodynamic and exergoeconomic performance. The numerical results imply that the system provides excellent thermodynamic and exergoeconomic performance with power, investment cost rate, and exergoeconomic factor of 697.75 kW, 33.09 $/h, and 77.48%, respectively, representing an exergy efficiency improvement of 3.51%–6.35% compared to similar concentrated solar power configurations. This research complies with the carbon neutrality policy, meets energy conservation and emission reduction requirements, and offers meaningful guidance for scientists who are committed to improving solar energy conversion and implementing exergoeconomic analysis. [Display omitted] • An improved He-CO 2 cascade Brayton cycle is developed for concentrated solar power. • Performance prediction and comparison are implemented under large temperature gradients. • Sensitivity analysis and multi-objective optimization are performed to determine best condition. • Exergoeconomic assessments are conducted to formulate effective improvement plan. [ABSTRACT FROM AUTHOR]

Abstract: This study presents the exergoeconomic analysis and evaluation in order to provide cost based information and suggests possible locations/components in a GDHS (geothermal district heating system) for improving the cost effectiveness. The analysis is based on the SPECO (specific exergy costing) method, and used to calculate exergy-related parameters and display cost flows for all streams and components. As a real case study, the Afyon GDHS in Turkey is considered based on actual operational data. The obtained results show that the unit exergy cost of heat produced by the Afyon GDHS is calculated as average 5624 $/h. The HEX (heat exchanger)-III among all components should be improved quickly due to the high total operating cost rate and relative cost difference. The HEX-I and PM (pump)-V have the highest exergoeconomic factors among all other system components due to the high owning and operating costs of these components. The heat production costs per exergy unit for all the HEXs decrease due to the high exergy destruction cost rate of the system, while the well head temperature and ambient temperature increase. The SPECO method may be used to improve the cost effectiveness according to exergy rates in GDHSs as a thermal system. [Copyright &y& Elsevier]

In this paper, the exergoeconomic analysis was conducted to an existing ultra-supercritical coal-fired power plant in China to understand the cost-formation process, to evaluate the economic performance of each component and to find possible solutions for more cost-effective designs. The total revenue requirement (TRR) and the specific exergy costing (SPECO) methods were applied for economic analysis and exergy costing, respectively. Quantitative balances of exergy and exergetic costs as well as necessary auxiliary equations for both individual component and the overall system were established. The results show that the exergoeconomic factors of the furnace and heat exchangers at low temperature levels, including air preheater and low-pressure feedwater preheaters, are rather small; while those of other components are relatively large. Moving more heat absorption into furnace to use the effective radiation heat transfer, increasing the air preheating temperature and adding more low pressure feedwater preheaters can be promising solutions for future design. [ABSTRACT FROM AUTHOR]

Abstract: Based on the concepts of avoidable/unavoidable exergy destructions and investment costs, this article presents an exergy analysis and an exergoeconomic evaluation to identify the potential energy savings in distillation processes. Methods for calculating the avoidable/unavoidable exergy destructions and investment costs for distillation columns, and hot-utility/cold-utility heat exchangers are proposed. For a distillation column, the unavoidable exergy destruction is estimated through the minimum reflux ratio, and the unavoidable investment cost is determined according to the minimum theoretical stage number obtained under the condition of total reflux. For the utility heat exchangers, the unavoidable exergy destruction is estimated through the minimum possible temperature difference, and the unavoidable investment cost corresponds to the maximum allowed temperature difference that is related to practical applications. A light-ends separation plant is used to demonstrate the performance of the proposed approach. The results indicate that the exergy-savings potential enables comparisons of energy-savings potentials among different system components, and the value of the cost-savings potential points out the cost that could be avoided in today’s technological and economic environment. The modified exergoeconomic factor provides the improvement direction in a more accurate way compared with the conventional one. [Copyright &y& Elsevier]

Thermodynamic and related ‘exergoeconomic’ performance criteria have been used to evaluate natural gas combined cycle (NGCC) power generation systems, with and without carbon dioxide (CO2) removal technologies. These plants were previously studied by the US National Energy Technology Laboratory employing conventional energy and mass balance results, and have now been evaluated using detailed energy, exergy and exergoeconomic analyses. The plant consisted of a gas turbine together with a steam cycle having three pressure levels. Such NGCC plants show the least exergetic improvement potential amongst competing fossil fuel generators going forward, because they are already enhanced by use of a thermodynamic ‘topping’ cycle. Carbon capture was simulated on the basis of CO2 recovery from the flue gas stream that leaves the heat recovery steam generator via a commercial amine process. Ninety per cent of the CO2 was captured in this way, and then compressed into a high-pressure liquid. This was achieved with significant power penalty (some 21%) and increase in generating cost per MWh (44%). Combustion and heat transfer processes are the main sources of exergy degradation within power cycles. Fuel combustion accounted for some 32% of exergy destruction. Even with CO2 sequestration, the NGCC system is still a thermodynamically attractive option compared with modern fossil fuel alternatives. Overall, the exergoeconomic results indicate that significant improvements can be achieved by considering the power generation systems as a whole, rather than concentrating on the improvement in performance of individual components (which is a common practice in exergoeconomic optimization studies). Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The real thermodynamic inefficiencies in a thermal system are related to exergy destruction and exergy loss. An exergy analysis identifies the system components with the highest exergy destruction and the processes that cause them. However, only a part of the exergy destruction in a component can be avoided. A minimum exergy destruction rate for each system component is imposed by physical, technological, and economic constraints. The difference between the total and the unavoidable exergy destruction rate represents the avoidable exergy destruction rate, which provides a realistic measure of the potential for improving the thermodynamic efficiency of a component. The calculation of avoidable cost rates associated with both exergy destruction and capital investment is described in the paper and is applied to the exergoeconomic evaluation of an externally fired combined cycle power plant. For each plant component, avoidable and unavoidable exergy destructions and investment costs are calculated. The assumptions required for these calculations are discussed. Modified exergoeconomic variables assist in identifying the real potential of improving single plant components. In addition, some aspects of the design and improvement of externally fired combined cycles are discussed. The results of this study show that the concepts of avoidable exergy destruction and avoidable investment cost are very useful in designing cost-effective energy conversion systems. [Copyright &y& Elsevier]

Abstract: Evaluation of the efficiency and economic benefit of energy conversion processes and technologies requires a scientifically based analysis. The hierarchically structured exergetic analysis provides a detailed characterization of complex technical systems. By defining corresponding evaluation coefficients, the exergetic efficiency can be assessed for units within the whole system. Based on this exergetic analysis, a thermoeconomic evaluation method is developed. A cost function is defined for all units, subsystems and the total plant, so that the cost flow in the system can be calculated. Three dimensionless coefficients, the Pauer factor, the loss coefficient and the cost factor, enable pinpointing cost intensive process units, allocating cost in cases of co-production and gaining insight for future design improvements. The methodology is demonstrated by a biomass gasification plant producing electricity, heat and cold. [Copyright &y& Elsevier]