Unit Exergy Cost Research Articles

Energy and exergoeconomic assessments of a renewable hybrid ERC/ORC integrated with solar dryer unit, PEM electrolyzer, and RO desalination subsystem

In this investigation, a zero-dimensional model of a renewable generation system encompassing a solar-geothermal driven Proton Exchange Membrane (PEM) electrolyzer integrated with Organic Rankine Cycle (ORC), Ejector Refrigeration Cycle (ERC) and Reverse osmosis (RO) unit is expressed with respect to energetic, exergetic, economic, and exergoeconomic points of view. Cooling and heating energies, electricity, distilled water, Hydrogen (H2), Oxygen (O2) are the key products of the mentioned system. In order to acquire the influences of the solar collector numbers, area ratio, and pressure drop of the ejector and working fluid of solar collectors on the efficiency of the hybrid unit, a set of equations were coded in MATLAB and Engineering Equation Solver (EES). The exergy destruction rate, exergy efficiency, and exergy destruction ratio of each subsystem and exergy flow diagram of all subsystems were evaluated in this study. Afterward, the results of the sensitivity analysis were used for multi-criteria optimization in three various layouts that the LINMAP as well as the fuzzy TOPSIS decision makings and Gray Wolf Optimizer (GWO), are considered to get the optimal result. The results have indicated that the main variables analyzed are more affected by the variation in the number of the flat plate solar collector. Besides, in the second optimization scenario, the TOPSIS selects the optimal solution of exergy efficiency and unit exergy cost of the product of 3% and 19.77 $/Gj, while the LINMAP selects 3.001% and 19.80 $/Gj point.

A new solar, natural gas, and biomass-driven polygeneration cycle to produce electrical power and hydrogen fuel; thermoeconomic and prediction approaches

Nowadays, due to the limitations of fossil fuels utilization, renewable energies-driven polygeneration systems (PGSs) are becoming popular. In this article, the simulation and conceptual design of a PGS based on biomass and natural gas fuels to produce products such as electricity, hydrogen fuel, hot water (HW) and chilled water (CHW) is presented and discussed. The introduced PGS is integrated with units and cycles such as water electrolysis (based on polymer electrolyte membrane (PEM) electrolyzer), a ground source heat pump (based on geothermal well), and an absorption chiller. Additionally, in order to supply a fraction of the heat required for the cycle, a solar thermal unit (based on parabolic trough solar collectors, PTSCs) has been embedded. The proposed PGS is evaluated and analyzed from thermodynamic and exergoeconomic points of view. Moreover, as an innovative approach, a prediction on machine learning (ML) model is developed to predict and evaluate hydrogen production rate through biomass gasification. Besides, a state-of-art structure and configuration is considered for the proposed PGS, which had not been reported in the literature. The outcomes indicated that the considered PGS is capable of generating nearly 3.71 MW of electricity, 11.42 kg/h of hydrogen fuel, 5.7 kg/h of oxygen gas, 5.9 MW of CHW, and 2.95 MW of HW. In such a context, the energy and exergy efficiencies of PGS are yielded 74.2 % and 32.3 %, respectively. It is estimated that the implementation of such a system will require an investment cost of almost $ 3.9 million. It was also found that the HW unit exergy cost is approximately 37.8 % higher than that of CHW. Besides, the unit exergy cost of hydrogen fuel is almost 4.4-fold higher than that of electricity. In addition, a detailed parametric research is conducted to analyses the influence of the costing metrics on the PGS behavior under consideration. Finally, the results demonstrated that ML model had acceptable accuracy and could predict the hydrogen production rate through biomass gasification.

Multi-objective optimization of a small-scale solar-hot-spring-geothermal brackish water direct contact membrane distillation system

A small-scale solar-hot-spring-geothermal brackish water membrane distillation (MD) system is proposed by combining hot-spring and solar components to reduce fossil energy consumptions. A performance parameter framework and carbon footprint model is developed to perform an analysis on whole life cycle of the proposed system. The results show that the solar subsystem improved heat recovery with the water generation ratio increased by 22–42 %. As the feed-side inlet temperature increases, the total Specific Energy Consumption (SEC) contribution rate of renewable geothermal and solar energies increases from 12.34 % to 20.45 %. The cold and hot sources are responsible for the largest exergic losses at 1.79 kJ/S and 0.48 kJ/S. The unit exergy cost of the solar subsystem is the highest of 0.037 $/h in terms of economic benefits. One of effective ways to improve the carbon emission reduction rate is to develop a cogeneration process for the water purification. A multi-software co-simulation methodology is proposed to explore innovative MD systems of optimal configurations, improve desalination efficiency and reduce the energy consumptions. The Non-dominated Sorting Genetic Algorithm (NSGAII) and improved NSGAII genetic algorithms (NSGAII-A and NSGAII-B) are utilized for multi-objective optimization of the MD system. Finally, the Technique for Order Preference by Similarity to Ideal Situation (TOPSIS) method based on entropy weight is employed to obtain the Pareto frontier solution set. It is indicated that NSGAII-B based on the four objective-optimal scheme is the best for the Multi-objective optimization of the MD system.

Exergoeconomic assessment of a biomass-based hydrogen, electricity and freshwater production cycle combined with an electrolyzer, steam turbine and a thermal desalination process

Since biomass resources can be found with different contents in most regions of the world, biomass/gasification (Biog) coupling processes can be considered as an attractive and useful technology for integrating in polygeneration configurations. In this regard, a new polygeneration energy configuration based on Biog process is proposed and its conceptual analysis is presented. In the new energy process, a Rankine cycle, a water electrolysis cycle (based on solid oxide electrolyzer, SOE), and a multi-effect desalination (MED) unit are embedded to generate electricity, hydrogen fuel, and freshwater, respectively. The considered polygeneration configuration is comprehensively investigated and discussed utilizing a parametric evaluation and from thermodynamic, energetic and exergoeconomic points of view. Relying on the proposed system can provide a new approach to produce carbon-free hydrogen fuel and freshwater in order to achieve an efficient, modern and green polygeneration configuration. The results indicated that the electrical power generated by the considered polygeneration configuration is close to 1735 kW. In addition, the system is capable of producing almost 9880 kg/h of freshwater and 12.3 kg/h of hydrogen. In such a context, the energy efficiency and total products unit exergy cost were 36.4% and 16.6 USD/GJ, respectively. Also, the system could achieve an exergy efficiency of nearly 17.1%. Moreover, about 8.9 MW of process's exergy is destroyed. The performance of the proposed polygeneration configuration using four different biomass fuels is compared. It was determined that the total products unit exergy costs under paddy husk and paper biomass are approximately 14.8% and 8.6% higher than MSW, respectively.

Exergo-economic analysis of a CFM56-7B turbofan engine

This paper deals with the exergoeconomic cost analysis of a high bypass turbofan engine and its components based on exergy analysis and selected economical parameters. CFM56-7B is selected for this analysis which powers Boeing 737 medium range transportation aircraft widely utilized all over the world. It has accumulated more than 105 million flight hours. Exergoeconomic analysis of engine is conducted in component level and can be performed by integration of exergy analysis and engine economic parameters. Thanks to exergoeconomic analysis, the system costs as well as exergy destructions costs within each engine components can be calculated. The study reveals out that maximum exergy cost of CFM56-7B occurs at HPT inlet as 5365.65 US$/h, however the lowest exergy cost rate as belongs to low pressure compressor work as 112.57 US$/h. Fuel cost is 2202 US$/h with unit exergy cost value of 10.33 US$/GJ based on selected fuel and economic parameters. Although unit exergy costs are around 18.5 US$/GJ value for LPT and HPT, it's calculated to be around 24–25 US$/GJ for HPC and LPC. It is thought that the cost results can be beneficial for airline customer as well as engine designer.

Techno-Economic and Environmental Assessment of Ammonia Production From Residual Bagasse Gasification: A Decarbonization Pathway for Nitrogen Fertilizers

This work evaluates the potential to produce synthetic nitrogen fertilizers by using sugarcane bagasse gasification in the São Paulo state, Brazil, aiming to increase the economic revenues and to decarbonize a chemical sector traditionally based on natural gas. The partial or total substitution of natural gas by consuming bagasse and enabling an intensive import of electricity from the Brazilian electricity mix is studied. The comparative assessment of the alternative production routes considers a reference case in which the residual bagasse is used only to generate surplus power at the cogeneration unit of the sugarcane mill, whereas ammonia is typically produced by consuming only natural gas. Unlike the conventional scenario, the proposed alternative routes employ surplus bagasse to produce ammonia. Regarding the unit exergy cost of ammonia, an increase between 50% and 100% is expected for the biomass-based routes (2.4498–3.1780 kJ/kJNH3) when compared to the conventional case (1.5866 kJ/kJNH3). In contrast, the net CO2 emissions balance of the alternative scenario achieve negative values (−2.5017 tCO2/tNH3), in comparison to the net CO2 positive emissions (1.75 tCO2/tNH3) of the conventional scenario. Additionally, the best location of the ammonia plant is nearby a sugarcane mill with a milling capacity of 10 Mt/y and 20 km far from another smaller sugarcane mill, in order to achieve an ammonia production potential of 1,200 tNH3/day. Concerning the economic analysis, if no carbon taxes are considered, the net present value (NPV) of the alternative scenarios drops up to 52%, compared to the conventional scenario. Finally, since 1.6 MtCO2/y can be avoided by using the residual bagasse as feedstock in the ammonia plant, the alternative scenarios become competitive vis-à-vis the conventional scenario in terms of NPV when carbon taxes of 40–50 USD/tCO2 are adopted. In the absence of carbon taxes, the drawback of the seasonality of the sugarcane crops (240 days of operation compared to 340 days for the conventional scenario) contributes to the decrease (39%–51%) of the NPV for the alternative scenarios.

An Exergoeconomic Analysis of a Gas-Type Industrial Drying System of Black Tea.

The performance evaluation and optimization of an energy conversion system design of an energy intensive drying system applied the method of combining exergy and economy is a theme of global concern. In this study, a gas-type industrial drying system of black tea with a capacity of 100 kg/h is used to investigate the exergetic and economic performance through the exergy and exergoeconomic methodology. The result shows that the drying rate of tea varies from the maximum value of 3.48 gwater/gdry matter h to the minimum 0.18 gwater/gdry matter h. The highest exergy destruction rate is found for the drying chamber (74.92 kW), followed by the combustion chamber (20.42 kW) in the initial drying system, and 51.83 kW and 21.15 kW in the redrying system. Similarly, the highest cost of the exergy destruction rate is found for the drying chamber (18.497 USD/h), followed by the combustion chamber (5.041 USD/h) in the initial drying system, and 12.796 USD/h and 5.222 USD/h in the redrying system. Furthermore, we analyzed the unit exergy rate consumed and the unit exergy cost of water removal in different drying sections of the drying system, and determined the optimal ordering of each component. These results mentioned above indicate that, whether from an energy or economic perspective, the component improvements should prioritize the drying chamber. Accordingly, minimizing exergy destruction and the cost of the exergy destruction rate can be considered as a strategy for improving the performance of energy and economy. Overall, the main results provide a more intuitive judgment for system improvement and optimization, and the exergy and exergoeconomic methodology can be commended as a method for agricultural product industrial drying from the perspective of exergoeconomics.

Energy, exergy, economic, environmental, energy based economic, exergoeconomic and enviroeconomic (7E) analyses of a jet fueled turbofan type of aircraft engine

In this study, energy, exergy, economic, environmental, energy based economic, exergoeconomic and enviroeconomic analyses (namely the 7E analysis) are performed to the gas turbine type of aero engines used in the civil and military aviation industries. The energy efficiency of the system is determined as 19.37%, and the exergy efficiency of the system is computed as 18.25%, whereas the exergetic improvement potential rate, fuel waste exergy rate, productivity lack ratio, improved exergetic efficiency and the improvement percentage of exergetic efficiency of the system are calculated as 36.456 GJ/h, 81.75%, 447.91%, 55.02% and 201.47%, respectively. Also, the exergy efficiencies of the components of the fan, fan duct nozzle, air compressor, combustion chamber, high pressure turbine, low pressure turbine and exhaust duct nozzle are estimated as 88.11%, 96.19%, 89.62%, 49.75%, 98.76% 98.42%, and 98.61%, respectively. The annual loss energy rate of the overall system is estimated to be 16010909.67 kWh/year, while the present worth of the system is 2478509.293 US$ and the energy based economic parameter is obtained to be 6.46 kWh/US$-year. The unit exergy cost rate of the overall engine’s product is calculated as 98.441 US$/GJ and the exergy cost rate of the engine is computed to be 980.111 US$/h.

Energy, exergy and economic investigation of operating temperature impacts on district heating systems: Transition from high to low-temperature networks

District Heating (DH) systems, owing to their remarkable techno-economic benefits compared to decentral heat production methods, are getting more and more popular worldwide. Today, DH systems are much more efficient than in the past but investigations show that there is still much to explore for more benefits and higher efficiencies considering such systems, where lowering the operating temperature is one of the points with the highest potential advantages. This study evaluates the effects of using different levels of operation temperatures of DH systems. For making the assessments quantifiable, specific case study DH network with a CHP plant as the main tool of supply is considered for the analyses. Three different design scenarios for the system are considered for all of which the results of the energy, exergy, and economic analyses are presented for the subsystems and the whole heat grid. Through thermoeconomic analysis, the unit exergy costs of electricity and heat and unit exergy costs of Space Heating (SH) and Domestic Hot Water (DHW) are determined. The results showed that lowering the operating temperatures increased the overall energetic and exergetic efficiencies of the CHP-supplied DH system, while reduced the cost per exergy unit associated with the SH and DHW supply.

4E analysis of an underfloor heating system integrated to the geothermal heat pump for greenhouse heating

In this study, 4E (energy, exergy, exergoeconomic, and exergoenvironmental) analysis of an underfloor heating system integrated with the geothermal heat pump of a greenhouse with a usage area of 90 m2 has been made. When the results of the 4E analysis applied to the system and its elements were examined, the energy efficiency of the heating system in the winter months has been determined to be 77.85% and the exergy efficiency 30.61%. According to the results of exergoeconomic analysis, the levelized energy cost of the system has been determined as 0.894 dollar/h, the unit exergy cost as 0.826 dollar/h, and the exergoeconomic factor value as 51.12%. According to the results of the exergoenvironmental analysis, the part-based environmental impact of the system was 0.0910 mPts/s, the environmental impact value due to exergy was 0.1823 mPts/s, and the exergoenvironmental factor value was 37.77%. In addition, the equivalent CO2 emission value that will occur if the heating requirement of the greenhouse is met with a natural gas boiler instead of a geothermal heat pump was investigated and a comparison was made between the two systems. Accordingly, it has been determined that the emission of 909.75 kg equivalent carbon dioxide to the environment will be prevented in the 4-month period, which is considered the heating season, by using the heat pump. As a result, the examined heating system has been evaluated as the effective system for heating the greenhouse, reducing energy consumption, and reducing emissions that cause environmental pollution.

Exergoeconomic analysis and parametric investigation of a gas turbine power plant

Thermoeconomic models, combining the concept of cost in economics and the concept of exergy in thermodynamics, provide the ability to optimize complex power generation systems to achieve the best balance between thermodynamic efficiency and economic cost. In this paper, a parametric analysis was carried out based on the method of calculating the unit exergy cost, as well as exergo-economic studies and cost sensitivity studies on the exergy of the cycle of a gas turbine power plant. The mathematical models of mass, energy, effort, and economy were created and presented. Thermodynamic properties and research analysis are performed using the MINI- REFerence fluid PROPerties (MINI-REFPROP) and matrix laboratory (MATLAB) SIMULINK software packages. The analysis leads to valuable benchmarks of the economic situation. The exergo-economic coefficient, the total cost of exergy loss, exergy destruction for the combustion chamber, and labor productivity are determined. When conducting parametric studies, the influence of the temperature at the inlet to the gas turbine, the temperature at the inlet to the air compressor, and the degree of pressure increase in the compressor were taken into account. The combustion chamber at the plant was found to have the highest energy destruction rate of 80%, indicating that boilers need to be given more attention in terms of design, selection, operation, and maintenance. However, in percentage terms, the combustion chamber has a high improvement potential of 94%. Sensitivity and parametric analysis show that while the exergy factor, the total cost of exergy loss, exergy destruction for the combustion chamber, and power output fall with increasing air compressor inlet temperature, it can be increased with increasing compressor pressure ratio. The total energy loss cost, combustor energy loss, and power output decrease as the gas turbine inlet temperature rises, while the cycle network and overall exergy destruction rate increase. The rates of the exergy destruction of the Venture Capital (VC), the combustion chamber of the combustion chamber, and the total exergy destruction are 25.2, 122.3, and 153.2 MW, respectively, for the proposed conditions. In addition, the results showed that it was $2,272 per hour, while the cost of work performed in energy terms is $1,769 per hour with a fuel cost of $0.003 per MJ. A valuable achievement is the availability of defined values and clear parametric influences, which can be of great help to engineers and site operators in the efficient execution of unique tasks, playing with the conflicts of energy use, exergy, and cost.

Multi-objective optimisation of supercritical CO<SUB align=right>2 combined cycles based on energy-exergy-economy balanced analysis

In this paper, the supercritical CO2 (sCO2) recompression cycle combined cycles are analysed, where the bottom cycles include transcritical CO2 (tCO2), organic Rankine cycle (ORC) or trilateral flash cycle (TFC). The working fluid for the ORC and the TFC can be R123, R245fa, or n-Pentane. We implemented four sub-models in our calculation: 1) thermodynamic model; 2) heat transfer model; 3) economic model; 4) exergoeconomic model. The specific exergy costing (SPECO) method is utilised in the exergoeconomic model, and the multi-objective genetic algorithm is adopted to give the Pareto front of total unit exergy cost of the product (cPtot) and the thermal efficiency. Our model has been validated with the existing literature. The results show that the thermal efficiency standalone CO2 achieved 41.66% while attaching the tCO2, ORC, or TFC bottom cycle could improve the thermal efficiency by 1.1%, 1.68%, or 0.05%, respectively. In the meantime, the (cPtot, which is the representation of the cost, decreased by 0.2$/GJ for ORC and increased by 0.06$/GJ and 1.05$/GJ for tCO2 and TFC respectively. The influence of different working fluids for ORC and TFC is not obvious. Therefore, attaching the ORC as the bottom cycle will bring about the best performance and lowest cost.

Exergy and exergoeconomic analyses of an ORC-assisted vapour compression refrigeration cycle

In this study, the thermodynamic performance of a vapour compression refrigeration cycle (VCRC) in which an organic Rankine cycle (ORC) has integrated and that generates electricity by utilising a geothermal source is investigated. The system's energy and exergy performance has evaluated by using various refrigerants used in the ORC system, depending on the evaporator (ORC) temperature (70°C-120°C), and an exergoeconomic analysis has performed to determine optimum operating conditions. As a function of the refrigerant and evaporator temperature, the coefficient of performance (COPsys) of the integrated system has varied between 0.55 and 1.01, whereas the exergy efficiency has varied between 14.20% and 20.16%. The unit exergy cost of the cooled air has been determined as 27.22 USD/GJ under the optimum operating conditions.

Energy, Exergy and Exergo-Economic Analysis of an OTEC Power Plant Utilizing Kalina Cycle

This study aims to analyse an Ocean Thermal Energy Conversion (OTEC) system through the use of a Kalina Cycle (KC), having a water-ammonia mixture as a working fluid. KC represents a technology capable of exploiting the thermal gap of ocean water. This system was then compared with OTEC systems, which exploit ammonia, R134A and butane-pentane mixture as working fluid. The comparison was carried on through energy analysis, exergetic analysis, and exergo-economic analysis using the EES (Engineering Equation Solver) software. For each case study, cost rates and auxiliary equations were evaluated for all components and the mass flow rate and unit exergy cost for each stream. The results showed that the KC with water-ammonia as working fluid achieves the best exergo-economic performance among the examined cycles. The cost of electricity produced through KC using water - ammonia mixture was found to be 26,66 c€/kWh. The thermal efficiency and the exergetic efficiency were calculated and the withdrawal depth of ocean water was considered. The efficiencies resulted to be 3.68% for the thermal efficiency and 95.96% for the exergetic efficiency.

Optimization of a biomass-driven Rankine cycle integrated with multi-effect desalination, and solid oxide electrolyzer for power, hydrogen, and freshwater production

The current work is a study of electricity, hydrogen, and freshwater polygeneration system fueled by biomass fuel. Accordingly, innovative integration of a Rankine cycle, a multi-effect desalination, and a solid oxide electrolyzer cell has been considered utilizing a syngas production biomass combustion chamber. The waste heat and a part of the output electricity of the Rankine cycle have been employed to launch the desalination and electrolyzer units, respectively. The suggested polygeneration is analyzed from the thermodynamic and exergoeconomic viewpoints through developing a code in engineering equation solver software and a multi-criteria optimization via MATLAB software. Hence, the NSGA-II optimization method and decision-making TOPSIS technique have been implemented. The parametric study has been conducted based on the effect of biomass fuel mass flow rate, turbine inlet pressure, combustion chamber outlet temperature, and pinch point temperature difference of the steam generator on the thermodynamic and exergoeconomic variables of the whole system. Considering the total exergy destruction rate, exergy efficiency, and total unit exergy cost of products as objective functions, the suggested system achieved the optimum values of 17.64%, 7658.5 kW, and 26 $/GJ corresponding for these variables.

Design and 3E analysis of a hybrid power plant integrated with a single-effect absorption chiller driven by a heliostat field: A case study for Doha, Qatar

This study suggests a novel zero-emission combined cooling and power (CCP) system using a high-temperature solar field, i.e., heliostat reflectors and a central receiver as the heat supplier of the whole system. In addition to the solar field, the proposed system consists of a hybrid power plant comprising a closed Brayton cycle using helium gas and a Kalina cycle, and a cooling production unit through a single-effect absorption chiller. To ameliorate the technical contribution of the current research work, the system suggested here was considered for a case study in Doha, Qatar. Hence, a comprehensive parametric analysis taking into account the energy, exergy, and exergoeconomic (3E analysis) performance criteria based on crucial design parameters is conducted. Furthermore, the economic feasibility analysis of the system is carried out through appraising the net present value. Regarding the parametric analysis, the 3E criteria evaluated here exhibited more sensitivity to variation in heliostat field efficiency and helium turbine inlet temperature, respectively. Moreover, the baseline design mode demonstrated that the electricity was produced by 15.29 MW, the coefficient of performance (COP) of the cooling production unit was 0.812, and also the overall exergy efficiency and sum unit cost of products were obtained as 29.87% and 4.34 $/GJ, respectively. Likewise, for the electrical unit exergy cost of 0.05 $/kWh and cooling unit exergy cost of 0.08 $/kWh, the calculated net present value and payback period of the suggested system were correspondingly equal to 1.605×107 and 3.1 years.

Exergetic and financial parametric analyses and multi-objective optimization of a novel geothermal-driven cogeneration plant; adopting a modified dual binary technique

The use of flash-binary geothermal power plants is recognized as an appropriate concept for preparing a sustainable energy production facility. Hence, the target of the current research is to specify the exergetic and economic aspects of an innovative electricity and cooling cogeneration system comprising a dual-flash binary geothermal power plant and an ejector refrigeration unit. The essential point of this study is the smart use of the total capacity of a medium-temperature geothermal source to produce energy-based products and eliminate the weakness of the conventional setups, increasing the exergy and exergoeconomic performances. A parametric study has been implemented to analyze the effect of several main parameters on the vital variables including efficiencies, exergy destruction rate, sum unit exergy cost, investment cost rate, and exergoeconomic factor. Besides, a multi-objective optimization in different cases has been applied to the calculations through a non-dominated sorting genetic algorithm II (NSGA-II) to achieve an optimal design. The results showed that the performance of the system was more sensitive to changing the separators’ operating pressure of the plant. Likewise, the optimum exergy efficiency and optimum unit exergy cost of the system were found to be 12% and 0.0043 $/kWh through the exergy/cost multi-objective optimization case, correspondingly.

Multi-objective optimization and exergoeconomic analysis for a novel full-spectrum solar-assisted methanol combined cooling, heating, and power system

A novel full-spectrum solar-assisted methanol combined cooling, heating, and power system was proposed. This system realizes the solar energy full-spectrum utilization in the hybrid solar energy device. A multi-objective optimization model with exergoeconomic analysis using energy-level based cost allocation was proposed to improve the comprehensive performance of the system. The heat storage ratio and supplemental heat ratio are defined to transfer the off-design annual operation conditions to the design parameters. The solar water heating area ratio as a structure variable of the hybrid solar energy device is optimized to improve the integrated performance of energy, economy and environment. The optimization results indicate that the comprehensive performance is best when the solar water heating area ratio is 0.5. Compared to the reference system, the unit exergy cost of total products increased by 49.0 %, whereas the primary energy is saved by 22.6 %, and the carbon dioxide is reduced by 70.6 %. The annual energy and exergy efficiencies are improved by 15.9 % and 17.3 %, respectively, and the collected solar energy is increased by 37.6 %. The sensitivity analysis demonstrates that the carbon dioxide emission, primary energy consumption, and unit exergy cost of total products are positively correlated with supplemental heat ratio and heat storage ratio.

Effect of working fluids in a novel geothermal-based integration of organic-flash and power/cooling generation cycles with hydrogen and freshwater production units

One of the essential steps to design energy conversion-based systems is choosing an efficient working fluid under the design goals to access stable products with high efficiency and overcome environmental issues. In this regard, the current paper is motivated to devise and evaluate a novel geothermal-driven multigeneration system under the effect of various working fluids. The proposed system consists of a flash-binary geothermal power plant, an organic flash cycle (OFC), a power/cooling subsystem (an organic Rankine cycle (ORC) and a thermoelectric generator incorporated with a compression refrigeration cycle), and freshwater and hydrogen production units utilizing a humidification-dehumidification desalination unit and a low-temperature electrolyzer. Considering the design potential of the OFC and ORC, four different environmentally-friendly working fluids, i.e., R123 and R600 in the OFC and R1234yf and R1234ze(e) in the ORC are selected and classified in four groups to introduce the best one, under the energy, exergy, and economic (3E analysis) approaches. Also, the whole system is optimized through a genetic algorithm, respecting the optimal solution for the energy efficiency and unit exergy cost of the products. According to the results, R123/R1234ze(e) shows the highest cooling, hydrogen, freshwater production rates, and energy efficiency. Likewise, the maximum power generation and exergy efficiency belong to R600/R1234ze(e). Moreover, R600/R1234yf has the lowest unit exergy cost of products.

Exergoeconomic perspective to evaluate and optimize supercritical carbon dioxide coal-fired power generation system

The application of supercritical carbon dioxide (SCO2) Brayton cycle to coal-fired power generation system has attracted increasing attention since 2018. In this study, the SCO2 coal-fired power generation system is evaluated and optimized from the exergoeconomic perspective. The purpose is to conduct comprehensive and in-depth analysis of this system. The simulated model of the studied system and corresponding exergoeconomic model are initially established. Subsequently, the cost formation process of system is revealed and the exergoeconomic performances of components and overall system are evaluated. The effects of five crucial operation parameters on exergoeconomic performance evaluation parameters are explored. Finally, the exergoeconomic performance of the studied system is optimized and compared with the preliminary design case. The results show that the unit exergy cost of coal, flue gas, SCO2, shaft work, and electricity are 4.705 $/GJ, 6.586 $/GJ, 9.329 $/GJ, 10.175 $/GJ, and 10.331 $/GJ respectively. Design changes should firstly be targeted to superheat cooling wall and high temperature recuperator due to its higher expense cost rate. Moreover, for the overall system, the exergy decrease cost rate is dominant and the total product unit cost is 15.988 $/GJ under preliminary design case. In parametric analysis, importantly, the method of increasing maximum operation temperature/pressure to reduce total product unit cost is limited. From exergoeconomic optimization results, for the system with high facility cost, a moderate decrease of maximum operation temperature/pressure can achieve the reduction of total product unit cost. The ultimate conclusion indicates that the selection criterion of operation parameters is to maintain the balance of exergy efficiency and total facility cost of the overall system. In conclusion, this study could provide reference to the construction of real SCO2 coal-fired power generation system.