Exergoeconomic Viewpoints Research Articles

Thermoeconomic analysis of a novel combined cooling, heating and power system based on solar organic Rankine cycle and cascade refrigeration cycle

This paper proposes a solar organic Rankine cycle integrated cascade refrigeration system to meet a hospital’s heating, cooling (each in two temperature levels) and electricity demands. The system is analyzed from energy, exergy and exergoeconomic point of view. Energy and exergy efficiency of the system calculated 89.39% and 8.70%, respectively. Exergy destruction rates of the system components are carried out and results reveal that the solar collector is the main source of irreversibility. The value of exergoeconomic factor for total system shows that the capital investment cost is more than the cost of exergy destruction. Collector is the main component from exergoeconomic point of view. The effect of ORC working fluid change, collector type, solar irradiation and ambient temperature are investigated. Cyclohexane from energy and exergy point of view and octane from exergoeconomic point of view are more efficient. The system with parabolic through collector indicates better results compared to the use of linear Fresnel reflector and parabolic dish collector. Increasing solar irradiation causes reduction in solar field area, energy and exergy efficiencies and total cost of the system. Increasing ambient temperature reduces solar field area and exergy efficiency, and improves thermal efficiency and the total cost of the system.

Thermodynamic and exergoeconomic analysis of two novel tri-generation cycles for power, hydrogen and freshwater production from geothermal energy

Thermodynamic and exergoeconomic analysis of two novel tri-generation systems based on single and double flash are reported to generate power and produce hydrogen and freshwater from geothermal energy. Both proposed cycles use the organic Rankine cycle to generate power, proton exchange membrane electrolyzer to produce hydrogen and reverse osmosis desalination to produce freshwater. The proposed cycles are assessed based on the thermodynamic and exergoeconomic approaches. Different single-objective optimizations are done to maximize produced power and thermal and exergy efficiencies as well as minimize power production cost. Multi-objective optimization is also performed based on weight coefficients. Moreover, the thermodynamic and exergoeconomic parameters of the proposed systems in different conditions are investigated through a comprehensive parametric study. The results showed that the tri-generation system based on the double flash (system 2) has better performance from the exergy and exergoeconomic viewpoints compared to the single flash-based one (system 1) so that the optimum values of 8613 kW, 2.308 kg/hr, 9.502 kg/s, 12.96%, 53.79%, and 5.845 $/GJ are obtained for net power output, hydrogen production rate, desalinated water rate, energy and exergy efficiencies, and power specific cost of this system at the geofluid temperature of 200 ℃.

Parametric analysis of combined power and freshwater producing system for natural gas engine heat recovery

The present paper focuses on exergoeconomic optimization of a proposed system with the goal of cogenerating freshwater and power, simultaneously. The cogeneration system includes Internal Combustion Engine, Organic Rankine Cycle, and Reverse Osmosis desalination unit. The thermodynamic model of the cogeneration system is investigated from energy, exergy, and exergoeconomic viewpoint. In addition, the variation of some key parameters including the engine speed, turbine inlet pressure, the number of the active vessels, freshwater mass flow rate, and the unit cost of freshwater to obtain optimum working condition is analyzed. The results show that the optimum value of the unit cost of power generation and freshwater occurs when the engine speed is 4000 rpm. Based on the optimization, the optimal condition does not occurred at the speed that exergy destruction becomes minimum. Furthermore the optimum value of the turbine inlet pressure was obtained respect to the maximum exergy efficiency and minimum unit cost of fresh water. The result showed that the optimum value of the turbine inlet pressure is 2690 kPa. There is an optimum value for the number of the active vessels that is achieved when 3 pressure vessels exist in the stage. In addition, the multi-objective optimization of the system based on the Pareto method revealed that at the optimum working condition, the exergy efficiency and freshwater mass flow rate are 30.7% and 2.926 kg/s, respectively. As a final result, it can be stated that the optimal values are not achieved in the minimum exergy destruction.

Comparative analysis and multi-criteria optimization of a supercritical recompression CO2 Brayton cycle integrated with thermoelectric modules

Regarding the high expense of the exploiting energy from energy resources, each innovation or modification on the energy systems with the aim of enhancing the efficiency and affordability is so valuable. Along with this fact, in the present work, the effects of employing thermoelectric (TEG) unit in a recompression Brayton cycle ( $${\text{sCO}}_{2}$$ -reB/TEG) are examined. The results of thermodynamic modeling represents that adding the thermoelectric to the system in the s $${\text{CO}}_{2}$$ -reB can improve the net output power about 2.41 kW and increase the first and second law efficiency of s $${\text{CO}}_{2}$$ -reB/TEG system about 1.09% and 1.12% in comparison with s $${\text{CO}}_{2}$$ -reB system. Additionally the exergo-economic analysis for s $${\text{CO}}_{2}$$ -reB/TEG revealed that the reactor and turbine II should be considered more than other elements from exergo-economic point of view since the highest values of $$\dot{Z}_{\rm k} + \dot{C}_{\rm D,k}$$ belong to these components. After identifying the important parameters as well as evaluating system from thermodynamic and economic aspects, a multi-objective optimization is implemented on the $${\text{sCO}}_{2}$$ -reB-TEG system for determining the optimum conditions. Two optimization scenarios are defined using the results of parametric analysis. Multi-objective optimization with first scenario results in total cost rate of 1.6 $ h−1 and total exergy efficiency of 0.5 in minimum temperature, maximum temperature and compression ratio of 36.17 °C, 577.15 °C and 1.6. Furthermore, for optimization based on second scenario results in total exergy destruction cost and exergy destruction rate of 3.04 $ h−1 and 435.85 kW in 48.75 °C, 569.77 °C and 3.44 for minimum temperature, maximum temperature and compression ratio.

Evaluation and optimization of a novel geothermal-driven hydrogen production system using an electrolyser fed by a two-stage organic Rankine cycle with different working fluids

Abstract In this study, a novel system comprising of a two-stage organic Rankine cycle, driven by geothermal energy and coupled with a proton exchange membrane electrolyser, is investigated and optimized from thermodynamic and exergoeconomic viewpoints. Various working fluids are considered so as to ascertain the effects of thermophysical properties on the performance of the system. The electricity output from the two-stage organic Rankine cycle is employed to produce hydrogen through electrochemical reactions in the proton exchange membrane electrolyser. The effects are assessed on key parameters of variations in geothermal water temperature and the pressure ratio of high-pressure organic Rankine cycle turbine. Considering three distinct cases, a thorough optimization is performed utilizing a genetic algorithm. It is concluded that a 2-3 percent-point improvement in energy efficiency, as well as a 35% to 41% increase in hydrogen production and a 9.5% to 12% reduction in cost per unit exergy of hydrogen can be achieved via optimization. R123 is shown in the optimization to perform the best among the considered working fluids, with isopentane performing second best.

Thermo-economic performance evaluation and multi-objective optimization of a screw expander-based cascade Rankine cycle integrated with parabolic trough solar collector

In the present study, a cascade power generation system, consisting of a partial evaporation Rankine cycle (PERC), and an organic Rankine cycle (ORC) with a parabolic trough solar collector (PTSC) as the driver coupled with a storage tank, has been studied and optimized from energy and exergoeconomic viewpoints. Instead of using conventional steam turbine, a screw expander has been utilized in PERC, in order to facilitate coupling the PERC with the PTSC and the storage tank, operating near the recommended temperature of 300 °C, as well as to avoid producing superheated vapor in the upper Rankine cycle. This configuration is appropriate specifically because of the pressure limit at the inlet of expander (4 MPa), corresponding to a saturation temperature of 250 °C for steam. With toluene as the selected organic fluid among 4 candidates, parametric analysis was performed to investigate the effect of variations in solar radiation intensity, collector aperture area, PERC evaporation and condensation temperatures, and expander inlet steam quality on the thermoeconomic performance of the system, followed by a tri-objective optimization using genetic algorithm considering net power output, exergy efficiency and total cost rate as objective functions. The obtained results show that for the optimum design point, the studied solar power plant with aperture area of 5540 m2 and storage tank volume of 184.7 m3 can produce 782 kW of power with exergy efficiency of 18.61% and total cost rate of 228 $·h−1. The optimum design case indicates an improvement in net power output, exergy efficiency, and unit cost of electricity by 65%, 2.9%, and 27.26%, respectively, compared to the base case. Furthermore, at the optimal point, the power output of ORC (440.6 kW) is higher than that of PERC (349.2 kW). However, the unit cost of electricity production is lower for PERC (22.82 $·GJ−1) compared to ORC (37.19 $·GJ−1).

A comparative analysis of novel combined flash-binary cycles for Sabalan geothermal wells: Thermodynamic and exergoeconomic viewpoints

Sabalan geothermal field is one of the most important geothermal fields in Iran. In this study, four novel configurations namely Single Flash-ORC (SF-ORC), Double Flash 1-ORC (DF1-ORC), Double Flash 2-ORC (DF2-ORC) and Triple Flash-ORC (TF-ORC) are proposed to produce power from two wells of the field. The configurations are assessed by thermodynamic and exergoeconomic viewpoints. The exergy and SPECO based exergoeconomic equations are developed for the components of the proposed cycles and thermodynamic as well as exergoeconomic performance parameters are calculated for the components and the cycles. A comprehensive parametric study is also carried out for the proposed configurations considering various working fluids in the ORCs. Moreover, an optimization is performed to maximize the produced power from the wells. The results depicted that the DF1-ORC produces 4.03%, 1.32% and 1.2% more power than the SF-ORC, DF2-ORC and TF-ORC, respectively, in the optimum condition. It can be concluded from the exergoeconomic analysis that the SF-ORC with R123 working fluid has the best exergoeconomic performance with the power specific cost of 3.62 $/GJ. The thermodynamic and exergoeconomic performance of the DF1-ORC is compared with previous similar studies which shows the superiority of the proposed cycle.

Exergoeconomic analysis of a novel trigeneration system containing supercritical CO2 Brayton cycle, organic Rankine cycle and absorption refrigeration cycle for gas turbine waste heat recovery

Poly-generation system is gaining more attentions recently due to its advantages of the effective promotion on energy utilization efficiency and deceleration of environmental pollution, as well as the security and reliable improvement on power supply. In this study, a novel trigeneration system composed of a gas turbine cycle (GTC), a regenerative supercritical carbon dioxide (sCO2) Brayton cycle, an organic Rankine cycle (ORC), and an absorption refrigeration cycle (ARC), is proposed. The waste heat exhausted from the GTC is firstly absorbed by sCO2 cycle and then utilized by ORC to generate power. The bottoming ARC is driven by the remaining heat to provide cooling capacity, while the hot water is provided by an intercooler in the GTC. The thermodynamic and exergoeconomic analyses are conducted to investigate the trigeneration system performance. Comparative study is carried out to evaluate the effects of ORC with different working fluids on the whole system performance. Besides, the performances of the proposed system are optimized and compared from the first law, second law of thermodynamics, and exergoeconomic viewpoints. Results show that the trigeneration system can generate 40.65 MW net power, 6.02 MW cooling capacity, and the 9.93 MW heating loads, with 20.17% overall exergoeconomic factor after the optimization on exergoeconomic aspect. Component combustion chamber presents the highest exergy destruction rate, while the subsystem GTC has the largest total exergy destruction and the highest total capital cost, successively followed by sCO2 cycle, ORC, and ARC. Compared with system using n-butane case, the total product unit costs increase by 0.27%, 1.09%, and 0.20% for fluids i-butane, n-pentane, and i-pentane cases, respectively, and the exergy efficiencies elevate correspondingly. However, the thermal efficiencies of above three cases decrease by 0.48%, 0.71%, and 1.06%, respectively. Moreover, combustion chamber is always the most important component for cost in the proposed trigeneration system optimized on the thermodynamic and exergoeconomic aspects, as well as the absorber being foremost in the bottoming ARC.

Proposal and 3E (energy, exergy, and exergoeconomic) assessment of a cogeneration system using an organic Rankine cycle and an Absorption Refrigeration System in the Northeast Brazil: Thermodynamic investigation of a facility case study

This paper proposes a cogeneration system to achieve the partial electric and thermal demands of a building in the public University. This proposed system comprises an Internal Combustion Engine (ICE), an organic Rankine cycle (ORC), and equipment that will operate as a sink. For the latter, two types of equipment were selected: a cooling tower and an Absorption Refrigeration System (ARS). The building selected to propose the cogeneration system is the Institute of Sustainable Energies (IES), located at the Federal University of Paraíba (UFPB), in the Northeast of Brazil. The performance of the system based on energetic and exergetic points of view operating under two distinct modes; ORC Simple (ORC-S) and ORC Combined (ORC-C), was compared. Both modes are based on the energy availability of the ICE exhaust gases. The thermodynamic models for both modes were developed based on the first and second laws of thermodynamic considering input parameters, such as inlet temperature, pressure ratio, and outlet temperature of the expander and the cold-water storage tank. For the exergoeconomic technique, the SPECO Method (Specific Exergy Costing) was used and implemented along with the Thermodynamic model. The ORC system studied uses a scroll expander and operates with R-134a as the working fluid and water/ammonia pair for the single-effect ARS. The results showed that the ORC-C mode can meet from 18.9% to 37.5% of the IES electricity demand, while the ORC-S mode can meet from 12.4% to 24.5%. The thermodynamic analysis reported that the ORC-C allowed a 33.6% increase in mechanical power production, an increase from approximately 4.5% to 34.5% in energy efficiency as well as exergy efficiencies around 40% and reduction of the total destroyed exergy. From the exergoeconomic point of view, the specific cost of the chilled water has a slight influence on the total cost of the products, while the specific cost of hot water has a strong influence on the total cost of the products (a variation of approximately 46% for a distinct heat source).

Energy, exergy and exergoeconomic analysis of an ultra low-grade heat-driven ammonia-water combined absorption power-cooling cycle for district space cooling, sub-zero refrigeration, power and LNG regasification

An ultra low-grade waste heat (≤100 °C) driven ammonia-water combined absorption power-cooling (APC) cycle-based multi-generation system with liquefied natural gas (LNG) cold exergy recovery is thermodynamically and exergoeconomically investigated for sustainable district cooling (DC) at two different temperature levels, and electricity generation in coastal hot climate regions serviced by LNG regasification terminals. At 70 °C heat source temperature, the system yields a specific net equivalent power output of 51.4 kWh/tonLNG at a cooling-to-power ratio of 7.3, and effective first-law and effective exergy efficiencies of 39% and 36%, respectively. Per million ton per annum (MTPA) LNG regasification capacity, the system would deliver 9.4 MW of space cooling, 6.5 MW of sub-zero refrigeration, and 2.2 MW of electricity for the district, while saving 8.4 ktons of natural gas and 19.3 kt of CO2-equivalent emissions per year, compared with conventional cooling, power and regasified LNG provision systems. The LNG refrigeration heat exchanger and APC absorber-evaporator are the most important components from exergoeconomic viewpoints. In addition to enhancing overall cooling and power generation capacity, the use of LNG as a cold source/sink reduces the minimum APC driving heat source temperature and rectification requirements, relative to an ambient water-cooled absorber sink. Additional benefits include the avoided use of conventional refrigerants, and reduced impact of LNG regasification on marine ecosystems.

Exergoeconomic analysis and multi-objective optimization of a semi-solar greenhouse with experimental validation

Fossil fuels limitation and environmental pollution have justified using renewable energy resources. Utilization of the solar energy as a promising method to supply the heat required for a greenhouse with the aim of endurable agriculture has been an interesting subject for many researchers. In the present work, using MATLAB software, a dynamic model is developed to investigate an innovative semi-solar greenhouse from the thermodynamic and exergoeconomic viewpoints, which, to our knowledge, has not yet been performed for Iran conditions. This simulation is used to estimate the temperature in four different points of the semi-solar greenhouse, considering the crop evapotranspiration. In addition, the total exergy destruction values associated with different processes are inspected. Providing an appropriate thermal condition for the air inside was considered as the aim of the present study. In this regard, the air unit cost of the greenhouse for each time step is analyzed. A multi-objective optimization is conducted considering the total exergy destruction and mean air unit cost as the objective functions.To validate the simulation, the results of the proposed thermodynamic analysis are compared with the measured data recorded every one minute from the constructed typical semi-solar greenhouse. Temperature difference of 19.5 ℃ between the indoor and outdoor air is obtained during the experiment. The mean values of 6.08% and 2.1 ℃ for MAPE (Mean Absolute Percentage Error) and RMSE (Root Mean Squared Error) indicate the accuracy of the thermal simulation. The results show that using double-layer glass separated with air-filled space as the greenhouse cover decreases the overall exergy destruction about 45.36%. The multi-objective optimization results obtained from the Pareto frontier also shows total exergy destruction of 8.8623 MJ and mean air unit cost of 15.9164 $/MJ at the optimum point.

Multi-objective optimization of a tri-generation system based on biomass gasification/digestion combined with S-CO2 cycle and absorption chiller

A novel configuration of biomass-based cooling, heating and power (CCHP) system, consisting of Gas Turbine (GT), Supercritical Carbon dioxide cycle (S-CO2) and double effect LiBr-H2O absorption chiller is proposed and its performance is analyzed and compared for two cases: 1) fueling with syngas from the gasification process and 2) fueling with biogas from the digestion process. Thermodynamic models are developed to evaluate the proposed systems’ performance from energy, exergy and exergoeconomic viewpoints and an environmental assessment is conducted to evaluate the systems’ CO2 emission. Then, a multi-objective optimization is applied for which the exergy efficiency and unit cost of system products are selected as the objective functions. The results revealed that the digestion-based system performs better than the gasification-based one in terms of efficiency, unit product cost and environmental impacts. The former yields a maximum exergy efficiency of 47.8%, while for the latter a maximum efficiency of 42.74% is calculated. For digestion-based system, the values of 47.09% and 5.436 $/GJ are calculated for exergy efficiency and product unit cost at the optimum operating conditions. Also, the results of environmental assessment indicated the values of 2.6×10-2t/MWhand 4.21×10-2t/MWh for CO2 emissions for digestion- and gasification-based systems, respectively.

Exergoeconomic investigation of a multi-generation system with CO2 as the working fluid using waste heat

A combined cycle coupling a supercritical power cycle with a transcritical refrigeration cycle with carbon dioxide as working fluid is evaluated and optimized from the exergoeconomic viewpoint. The system is designed to produce power, refrigeration, and heating simultaneously. If no net power is generated, the system can be described as a cogeneration. First, the cogeneration system working with various evaporation temperatures is optimized for having the lowest average cost of the products, which indicates that the system is preferred to operate at the lower evaporation temperature. Then for tri-generation, by increasing the power output and the pressure merging two sub-systems, the cost of the products (average and individual) reduces and the efficiency of the overall system increases. In addition, the cost of the power is the lowest while the cost of the refrigeration is the highest, and the cost of the heating is sensitive to the operation conditions of the overall system.

On the economics of methanol production from natural gas

Methanol is rated among the top chemical commodities worldwide. Its production via indirect synthesis routes from natural gas is energy intensive and costly regarding the investment and operation. This study addresses the economics of methanol synthesis routes with different reforming technologies. Processes with steam reforming, autothermal reforming, and dry methane reforming are considered for medium capacities below 3000 metric tons per day. The exergetic efficiency of these processes is 34.8%, 56.9% and 39.8%, respectively.Furthermore, combined methane reforming, two-step reforming and a parallel configuration of steam – and dry methane reforming are discussed. Their exergetic efficiency is 48.6%, 57.2% and 46.3%, respectively. The processes with endothermic reforming technology inherently feature a co-production of electricity for high efficiency.The results from an economic case study are reported. Approximately 60–70% of the investment is required for the reforming unit. The fuel cost has a contribution of 50–60% in the specific product cost. Depending on the process, the payback period is 2 to 10 years. The economic uncertainties are addressed by conducting sensitivity analyses.An exergoeconomic analysis is used to calculate the levelized cost of methanol and electricity. The two-step reforming process constitutes the most attractive design from an exergoeconomic point of view, having the lowest levelized cost of methanol and electricity production among all processes.Finally, the plants are assessed by comparing the levelized cost of methanol with the range of historical methanol prices in Europe and North America. A low natural gas price makes an operation economically viable in both continents.

Performance analysis and exergoeconomic evaluation of a TRC system enhanced by a dedicated mechanical subcooling

In the present study, a transcritical refrigeration cycle’s performance with dedicated mechanical subcooling (MS) is investigated from the energy, exergy and exergoeconomic viewpoints. Three different refrigerants containing CO2 (R744), N2O (R744A) and ethane (R170) are considered as the transcritical cycle’s refrigerant. A thorough parametric study is carried out on the system and finally, the effect of dedicated subcooling system is checked out on the energy, exergy and exergoeconomic perimeters. Based on the results, value of the COP and exergy performance for N2O, unlike the CO2, is the highest. In other words, the CO2 refrigerant shows the best economic performance. By comparing the system with and without subcooling cycle, it can be concluded that utilizing subcooler improves performance of the system and increases the unit product cost. However, the unit product cost increment is much lower than COP improvement which makes the subcooling an effective and economical way to improve the refrigeration system’s performance. Application of subcooler leads to an enhancement of 30.74%, 26.48% and 36.1% in COP for CO2, N2O, and ethane, respectively while the unit product cost increment is 9.04%, 8.37% and 10.63% for the mentioned refrigerants, respectively.

Exergoeconomic analysis of a novel trigeneration system based on organic quadrilateral cycle integrated with cascade absorption-compression system for waste heat recovery

The present research proposes a novel trigeneration system for cooling, heating, and power generation which is consisted of organic quadrilateral cycle (QLC) and cascade absorption – compression system. The system is simulated and studied from energy, exergy, and exergoeconomic viewpoints. Cyclohexane, LiBr-H2O, and R410a are respectively used as working fluids for QLC, Absorption refrigeration system (ARS), and Compression refrigeration system (CRS) in the combined system. Using QLC instead of simple organic Rankine cycle (ORC) in the combined system makes it possible to generate electricity besides improvement of total system performance from energy and exergy viewpoints for the same input values. According to the base case results, the unit cost of electricity is 36.9 $/GJ and it has much less value compared with unit cost of heating and cooling which are equal to 101 $/GJ and 84.7 $/GJ, respectively. Therefore, more electricity production by employing QLC instead of ORC is economical. The results of system parametric analysis show that by variation of QLC expander inlet temperature and QLC condensation temperature while cooling rate decreases, the other output parameters such as output electricity, heating rate, exergy efficiency, and total cost rate improve. Selection of these two input parameters depends on demands. On the other hand, less ARS evaporation temperature and higher CRS evaporation temperature in the allowed range lead to better performance of the system.

Optimization strategies for mixing ratio of biogas and natural gas co-firing in a cogeneration of heat and power cycle

The most suitable design parameters of the cogeneration system, from the exergetic and the exergo-economic viewpoints, were determined using the genetic algorithm based on optimization method. In this study, a cogeneration cycle, consisting of a gas turbine cycle with power generation capacity of 30 MW, an anaerobic digester, a steam generator, and a heat exchanger for heating the digester and pretreatment system, has been used. The air compressor pressure ratio, the isentropic efficiencies of gas turbine and air compressor, biogas and natural gas mixing ratio, air preheater outlet temperature, turbine inlet temperature, and evaporator pinch point temperature difference were selected as the decision variables. Multi-objective optimization based on genetic algorithm using MATLAB software is carried out to discover the optimum point with regard to the total cost rate and exergy efficiency as the objective functions. The optimization was conducted according two scenarios. While the fuel mixing ratio was considered as a decision variable in the first scenario, in the second one this mixing ratio was kept constant, 50%. Optimization of the cycle according to the first scenario raised the exergy efficiency from 46.59% to 53.25% and decreased the system total cost rate from 4385$/h to 2935$/h. As well, compared to the base case, the optimal case of the second scenario had more exergy efficiency and less total cost rate, 48.35% versus 50.5% and 4028$/h versus 3665$/h, respectively.

An efficient auxiliary power generation system for exploiting hydrogen boil-off gas (BOG) cold exergy based on PEM fuel cell and two-stage ORC: Thermodynamic and exergoeconomic viewpoints

A heat recovery system is employed for power generation from a PEM fuel cell’s waste heat. The proposed system involves the parallel organic Rankine cycle for utilizing the provided heat and hydrogen boil-off gas (BOG) stream as a heat sink for the cycle. Also, this stream generates power by using an expander and prepares some chilled water that enhances system performance. The PEM fuel cell as the major component of the system is modeled and then the parallel two-stage ORC (PTORC) and BOG streams are analyzed in points of the energy and exergy view. Exergoeconomic concept is applied to evaluate the economic view of the system besides energy and exergy analyses. Also, a sensitivity analysis is performed by system key parameters which provided some valuable information to comprehend the performance of the overall system. The results show that the proposed system can generate 1353 kW power. Exergoeconomic factor, energy efficiency and exergy efficiency of the overall system are computed to be 26.21%, 58.15%, and 36.64%, respectively. Also, it is concluded that the higher current density and lower operating temperature, will raise the total cost rate.

Exergoeconomic analysis of a novel integrated transcritical CO2 and Kalina 11 cycles from Sabalan geothermal power plant

A new integrated cycle based on different real temperatures and pressures on Sabalan geothermal power plant, located in Iran, has been proposed and thermodynamic and exergoeconomic analyses are performed. The Kalina and Transcritical Rankine cycles are used as bottoming cycles and an algorithm are applied to find the exact location of the pinch points in heat exchangers. Also, a parametric study carried out to reveal the effects on the thermodynamic and exergoeconomic performance of the integrated cycle of such important parameters as separator 1 pressure, separator 2 pressure, pinch point temperature difference in the evaporators, higher pressure of the Kalina cycle and the ratio of the Transcritical cycle higher pressure to the critical pressure. Finally, the proposed cycle performance is optimized from the thermodynamic and exergoeconomic viewpoints. The results show that for the integrated geothermal power plant, the power generation, thermal efficiency, exergy efficiency and power specific cost rate are calculated to be 19,448 kW, 16.63%, 63.78%, and 4.521 $/GJ, respectively, which indicate that the proposed cycle has improved thermodynamically and exergoeconomically compared to previous studies.

Enhanced performance and reduced payback period of a low grade geothermal-based ORC through employing two TEGs

In this paper, a novel integrated system is proposed to improve the performance of a conventional low-grade geothermal-based organic Rankine cycle (ORC). The main idea is to utilize two TEG units to recover the waste heat of the condenser and geothermal brine. The proposed model is investigated and compared with simple ORC from the energy, exergy, and exergoeconomic viewpoints through the parametric study. Furthermore, the payback period of the systems is calculated to investigate the economic aspects of the model in more details. Results show that the exergy efficiency of the proposed system would be 56.81% at the base case (4.67% higher than the simple geothermal-based ORC system) and the total product cost of the proposed integrated system is 24.55 $/GJ at the base case (5.5% lower than simple ORC), while the payback period of the suggested system is 2.422 years (15 days lower than the simple ORC cycle). Furthermore, the net power output of the novel proposed system is 75.24 kW (9% higher than the simple ORC cycle). Comprehensive paramedic study and comparison of the exergy and exergoeconomic aspects reveal that the proposed system is a promising method to optimize such systems from exergy/exergoeconomic viewpoints.