Thermoeconomic Optimization Research Articles

Comprehensive analysis and thermo-economic optimization of the dry cooling system for supercritical CO2 power cycle

This paper presents a comprehensive analysis and optimization of the dry cooling system for the supercritical CO2 (sCO2) power cycle, a promising technology for generating electricity from renewable heat sources. Unlike prior studies that concentrated solely on specific cooling system components, this paper examines thermoeconomic factors and employs mathematical models to analyze how various operational parameters impact both the cooling system's performance and cost, as well as the overall power cycle. Additionally, the paper employs a multi-objective optimization method to determine the optimal parameter values across varying cooling capacities and ambient temperatures. The results show that the thermal efficiency of the power cycle does not increase linearly with the cooling capacity, due to the change in CO2's physical properties near the temperature and pressure where it behaves like both a liquid and a gas (the pseudo-critical point). Furthermore, optimal cooling system area varies based on cooling capacity and ambient temperature, leading to cost reduction and improved power system efficiency. This paper provides a useful tool and guidance for designing and operating the dry cooling system for the sCO2 power cycle.

Thermo-economic optimization on a combined heat and power system with supercritical Rankine cycle for power-to-heat batteries

The global energy structure is transforming to low-carbon, and it is urgent to construct a sustainable energy system mainly based on renewables. The power-to-heat batteries (P2HBs) show great potential for large-scale energy storage by converting low-cost renewable power to heat. This paper aims to study the thermodynamic and economic advantages of the P2HB integrated with a supercritical steam Rankine cycle (RC) to achieve combined heat and power (CHP) generation. Firstly, a system model of P2HB-CHP consuming grid valley power is developed. The system includes three sub-systems: P2HB, steam generator, and CHP. Thermodynamic and economic analysis models are developed, and the average exergy efficiency (ηav) and net present value (NPV) are formulated as performance evaluation targets, respectively. The genetic algorithm is used to perform multi-parameter optimization of the system. The thermodynamic optimization results show that the maximum ηav of supercritical P2HB-CHP is 0.47 %, 1.16 %, and 1.44 % higher than that of subcritical P2HB-CHP when the high working temperature of the molten salt reaches 505 °C, 570 °C, and 640 °C, respectively. The largest proportion of anergy is generated by electric heaters, over 72 %. The next largest proportion is heat exchangers, which is related to the heat transfer temperature differences. The results of the economic analysis show that the maximum NPV of supercritical P2HB-CHP is lower by 158 M$, lower by 74 M$, and higher by 55 M$ than that of subcritical P2HB-CHP when the high working temperature of the molten salt is reached 505 °C, 570 °C, and 640 °C, respectively. The high efficiency of supercritical RC reduces the costs of electric heaters and molten salts, but sets high demands on the heat exchangers. Although high-temperature molten salt results in high energy efficiency, the increased cost of molten salt reduces the profitability of the system.

Thermoeconomic optimization with a dissipation cost

Abstract From a finite-time thermodynamics perspective, a thermoeconomic analysis of a Novikov model employing a linear heat transfer law is carried out. A new component in the cost function is proposed to examine its relationship with waste management while operating in the maximum power, ecological, and efficient power regimes. The methodology consists of optimizing the profit function by including our new waste management cost function, leveraging the same method used by DeVos (“Endoreversible thermoeconomics,” Energy Convers. Manage., vol. 36, pp. 1–5, 1995) and Pacheco et al. (“Thermoeconomic optimization of an irreversible novikov plant model under different regimes of performance,” Entropy, vol. 19, p. 118, 2017). Searching for the optimal thermoeconomic efficiencies for the ecological case a novel numerical method developed by the corresponding author (A. M. Ares de Parga-Regalado, “Analytical approximation of optimal thermoeconomic efficiencies for a novikov engine with a Stefan–Boltzmann heat transfer law,” Results Phys., 2023) is used. Analytical expressions for the optimal efficiencies are obtained, and the impact of the proposed term on these values is investigated.

Thermo-economic optimization of hybrid solar-biomass driven organic rankine cycle integrated heat pump and PEM electrolyser for combined power, heating, and green hydrogen applications

The energy sector prioritizes innovative clean energy production. This research explores a versatile hybrid solar-biomass trigeneration system, integrating organic Rankine cycle (ORC), a heat pump, and a proton exchange membrane electrolyser. Sustainable and adaptable, it produces electricity, heating, and hydrogen for Indian paper and pulp industries. The study assesses the system's thermodynamic, economic, and environmental feasibility. Initially, parametric analysis and first layer multi-objective optimization (MOO) are performed to select the efficient working fluid and operating temperatures. Benzene outperforms other fluids, achieving an energy utilization ratio (EUR) of 0.27 and exergy efficiency of 75 %. A typical heat requirement of 250 kW for processing 150 kg of paper necessitates collector areas of 3500 m2 and 4500 m2 in Aurangabad and Tiruchirappalli, respectively, and biomass waste of 0.05 kg/s. The combined system performance during day time and night time operation was studied by altering the critical solar radiation, ambient temperature and biomass waste flow rate. The second layer MOO revealed an optimum EUR of 0.25 and exergy efficiency of 9 % at the lowest cost of 33 $/h for biomass waste operation. In comparison to the conventional electricity-powered system, the proposed system would reduce CO2 emissions by 90 kg/h to 270 kg/h.

Thermo-economic optimization of an innovative integration of thermal energy storage and supercritical CO2 cycle using artificial intelligence techniques

This research delves into the integration of Thermal Energy Storage (TES) and Supercritical Carbon Dioxide (s-CO2) in an innovative Energy Recycling System (ERS) that aims to improve overall system efficiency. The combination of TES and s-CO2 is a promising solution to address modern energy challenges and promote a sustainable and efficient energy future. For this research, the TES system is based on a packed bed of stones (PBS). This approach has several benefits, such as the use of inexpensive and readily available materials for storage, a broad range of operating temperatures, allowing for direct heat transfer, and the ability to achieve high maximum temperatures. The simulation methodology for TES is based on Schumann's approach, and energy and exergy analysis are used for thermodynamic modeling. Additionally, levelized costs are employed for the economic modeling of the system. Through rigorous thermos-economic modeling and simulation, operational parameters are optimized using genetic algorithms and neural network techniques to balance thermodynamic efficiency, energy storage, and economic feasibility. The findings reveal exceptional energy and exergy efficiencies, exceeding expectations, and suggest the ERS, with grid-scale energy storage, as a cost-effective solution. The simulations demonstrate remarkable energy and exergy efficiencies of 92.15% and 49.66%, respectively, with levelized costs of 104.69 €/MWh for heat, 135.20 €/MWh for electricity, and 65.7€/MWh for storage.

Thermo-economic optimization of an artificial cavern compressed air energy storage with CO2 pressure stabilizing unit

In recent years, the attention of engineers has been increasingly attracted to the compressed air energy storage with artificial cavern as it frees the conventional system from the dependence of salt cavern, greatly reducing the limiting factors of project location. However, the current issues are how to enhance the reliability and safety of the artificial cavern due to the cyclical pressure loading and to cut down the cost of cavern construction. The present study overtures an isobaric system for doing this via designing pressure stabilizing unit utilizing the CO2 phase change process. The specific volume of saturated liquid is an order of magnitude lower than that of the saturated gas and this characteristic contributes much to reduce the cavern size. The system thermodynamics and economics are calculated numerically and the findings are discussed to identify whether the additional complexity of isobaric gas storage are worth to do. It is recommended that the air storage pressure, CO2 storage pressure and CO2 liquefaction pressure should be positioned in sequence at 6.5 MPa, 6 MPa and 9 MPa as the optimal design conditions. In this case, the system efficiency is 69.92 %, the levelized cost of storage is 0.1332 $/kWh, the dynamic payback period is 7.26 years and the investment return ratio is 1.58. Compared to the isochoric system with equivalent efficiency, the air storage pressure in proposed system is highly reduced with just 0.65 times of original value. More importantly, the constant pressure in the cavern operation process significantly upgrades its reliability and safety. The size of cavern volume is narrowed with a decline rate of 31.86 % and the system levelized cost of storage scales back with an amplitude of 0.0138 $/kWh. To be matched with, the investment return ratio is increased by 54.9 %.

Thermo-economic multi-objective optimization of the liquid air energy storage system

Liquid Air Energy Storage (LAES) is a promising energy storage technology for large-scale application in future energy systems with a higher renewable penetration. However, most studies focused on the thermodynamic analysis of LAES, few studies on thermo-economic optimization of LAES have been reported so far. Thus, this work focuses on the multi-objective optimization of LAES by using non-dominated sorting genetic algorithm (NSGA-II), taking the round trip efficiency (RTE) and economic indicators as the optimization objectives. Three major results were obtained from this work. First, the NSGA-II-based optimization framework is able to determine the optimal design and operational parameters of LAES under different configurations and scenarios, including the optimal charging and discharging pressure, heat transfer areas, and mass flow rates of hot and cold storage media etc. It is shown that the increase of energy efficiency by 9 % ~ 14 % and a decrease of exergy destruction by 16 % were seen. Secondly, the design and operational guidelines of LAES can be derived from the optimization. The optimal charging pressure was found to vary between 13 and 15 MPa, and the optimal discharging pressure is between 9 and 12 MPa, depending on the machines' efficiencies and pinch points of heat exchangers of a LAES system. Finally, the Pareto Fronts of capital expenditure, energy efficiency and the occupied space energy density of a LAES system provide system operators good operational and investment advice. Specifically, the RTE of the LAES increasing by 1 % is at the cost of increasing the capital cost by 0.5–1 %. In this study, if the investment budget is over 48 M£, a LAES system with three-stage compressors and four-stage turbines presents better trade-off between RTE and investment cost than the three-stage and four-stage systems. Overall, this work provides, for the first time, an NSGA-II-based optimization framework capable of determining the optimal design and operational parameters of LAES, informing the stakeholders of the design guidelines and investment guidance under different scenarios.

Energy integration of light hydrocarbon separation, LNG cold energy power generation, and BOG combustion: Thermo-economic optimization and analysis

To recover boil-off gas (BOG) and liquefied natural gas (LNG) cold energy, this paper proposes three systems integrating light hydrocarbon separation (LHS), BOG combustion, organic Rankine cycle (ORC) with different structures and natural gas (NG) direct expansion. Both single and multi-objective optimizations are implemented to find the best system performance. Meanwhile, two multi-objective decision methods are also used to refine this work. Single objective optimization depicts that the system with parallel ORC has the highest net electric power (NEP), exergy efficiency, and net present value (NPV) of 6.85 MW, 29.07%, and 31.08 × 107 $ respectively. Multi-objective optimization results indicate the NEP, exergy efficiency, and NPV of the system with parallel ORC still outperform the other two systems. From the energy analysis, it is found that the system with parallel ORC achieves 81.07% utilization of LNG cold energy, which is the highest among the three systems. The exergy analysis indicates that the combustion chamber and heat exchanger (HX) with the highest exergy destruction in any system. Moreover, economic analysis demonstrates that the three systems are more sensitive to fluctuations in interest rates than in electricity prices.

Thermo-economic optimization of a 100 kW air-to-water heat pump for heating purposes in residential units

In order to reach the ambitious objectives of carbon neutrality by 2050 and the limitation of the ambient temperature rise at 1.5 °C, several intensive energy fields such as heating and cooling appliances should be decarbonized. On this regard, electric heat pumps represent the most promising solutions to replace old and inefficient conventional boilers and comply with the ecological transition through the increase of electric energy production by means of renewable sources. In this paper, a thermo-economic optimization analysis of a 100 kW air-to-water electric heat pump is proposed. The appliance is designed to produce hot water at 55 °C. The developed model employs phenomenological equations calibrated on real data and manufacturer datasheets for compressor, heat exchangers, and costs. Different design options, including the heat exchangers size and the choice of the working fluid (among R32, propane R290, ammonia R717, R454C), are presented and discussed. The Pareto analysis is then employed to find the best possible configurations in terms of costs and performance.

Ammonia heat pumps for district heating: thermo-economic optimization analysis based on evaporator geometry for either direct expansion or chilled water configurations

Electric heat pumps are recognized as a key technology for decarbonization and have received increasing policy support in several countries over the last few years. These devices offer a highly efficient form of electric heating and could make an important contribution to the transition to a low carbon future, especially in case of district heating systems. Within this context, this paper presents a thermo-economic optimization analysis of a 7.35 MW electric heat pump system employed for district heating purposes and using ammonia as working fluid. The implemented code gathers multiple sub-models calibrated ad-hoc from real data or manufacturers’ datasheets. The heat exchangers are simulated by considering phenomenological equations and well-known heat transfer coefficient and pressure drop prediction methods. The optimization analysis is performed at constant condensation temperature that guarantees in/out hot water temperatures of 30/62 °C and is focused on the matching between compressor and evaporator heat exchanger, by considering either a direct expansion system or a chilled water heat pump. Both the coefficient of performance (COP) and the set-up costs are considered as optimization performance indicators for the construction of the Pareto front.

Thermo-economic assessment of air conditioner utilizing direct evaporative cooling: A comprehensive analysis

As concerns regarding energy consumption and environmental impact continue to grow, the need for efficient and sustainable cooling technologies becomes increasingly significant. Among various alternatives, direct evaporative cooling (DEC) has emerged as a promising solution due to its energy-efficient operation and low environmental footprint. This paper aims to provide a comprehensive thermo-economic assessment of a 5.25 kW capacity split air conditioner (SAC) integrated with direct evaporative cooling, focusing on evaluating its performance, energy consumption, coefficient of performance(COP), and economic viability. A numerical model is developed to determine the reduction in the condenser inlet air temperature due to direct evaporative cooling. The ambient temperature (30–45 ⁰C), relative humidity (20–80 %), and evaporator temperature (3–12 ⁰C) are taken as the design variables. Box–Behnken design (BBD) technique of response surface methodology is applied for multi-objective optimization. The COP, total cost rate (TCR), and total exergy destruction (E˙D,t) are set as the objective functions. Cooling capacity, life period, operation time, interest rate, maintenance factor, and electricity cost are taken as constants. The thermoeconomic optimization evolved maximized COP enhancement of 68.94 %, and reduction in TCR and ED,t by 26.12 % and 57.23 %, respectively. The water consumption to energy saving ratio varies from 5.5 to 9.8 L/kWh for different months of the cooling season. The thermoeconomic performance and sustainability of DECSAC is observed to significantly improve compared to conventional SAC specifically in hot-dry climates. The simple payback of the proposed system ranges between 1.21 to 2.99 years depending upon the operating conditions.

Multi-criteria thermoeconomic optimization of a geothermal energy-driven green hydrogen production plant coupled to an alkaline electrolyzer

Among the various technologies for hydrogen production, the renewable energy driven water electrolysis has emerged as a favorable method. In this respect, the present research proposes and analyses a novel and efficient medium-temperature driven geothermal system for green hydrogen production. An alkaline electrolyzer is deployed for hydrogen production which is powered by a double flash steam geothermal power cycle. To boost the power generation (and hence the hydrogen production amount) the double flash cycle is equipped with a self-superheating process, which superheats the saturated vapor at turbine inlet without using another external heat source. Thermodynamic evaluations, based on exergy concept, along with economic analysis are carried out to assess the hydrogen production amount, plant exergy efficiency and total cost rate, and the unit hydrogen price. In order to represent a comprehensive investigation of the plant performance, parametric analyses along with single- and multi-criteria optimizations were conducted. The results revealed that, for 1kg/s of geothermal brine, the capacity of hydrogen production of the proposed plant is ∼1.5−3kg/h under various operating conditions. It is found that, under multi-objective optimum operating conditions, the plant yields 12.63% exergy efficiency and its total cost rate is calculated to be 10.42 $/h. However, if the plant is to be optimized for maximum exergy efficiency, the value of 14.25% is achievable which will result in increment of total cost rate to 11.97 $/h.

Thermo-economic optimization of an ORC system for a dual-fuel marine engine

The Organic Rankine Cycle (ORC) is one of the most promising systems to recover the waste heat sourced from internal combustion engines. In this study, thermodynamic, economic and environmental analyses of the scavenge air cooling water-driven Waste Heat Recovery System (WHRS) based on the organic Rankine cycle are conducted for a dual-fuel marine engine integrated with exhaust gas recirculation (EGR) system. Zero ozone-depleting and low global warming potential working fluids; R245fa, R236ea from hydrofluorocarbons, R600a, R601a from hydrocarbons, R1234ze and R1234yf from hydrofluoroolefins are selected for the low-grade WHRS. In addition to the thermal analyses, the mass and volume of the system along with the safety factors of the working fluids are evaluated to judge the physical applicability of the system for ships. Thermo-economic performances of the fluids are analyzed, optimized and compared under various engine loads, Tier II and Tier III modes to reveal the effects of different engine operating conditions on the parameters. According to the results, scavenge air has a significant amount of waste heat at medium and heavy loads and switching the engine mode remarkably affects the performance of the WHRS. R601a shows the best thermo-economic performance, however, considering the applicability of the system R236ea is the most suitable working fluid for the ORC WHRS. The overall thermal efficiency of the power generation system can be increased by about 2.8%.

Thermal energy recovery from a Brayton cycle nuclear power plant for efficiency improvement via compressor inlet cooling: Thermoeconomic optimization

Due to the well-known limitations of renewable energy resources, nuclear power is considered as another alternative for carbon-free electricity generation. A great deal of interest has been paid to developing gas-cooled reactors due to their efficient and cost effective electricity generation ability. Among these systems, the GT-MHR is a promising one which employs the Brayton closed cycle for power generation with an energy efficiency of around 47% and a waste heat of around 300 MWth. The present work aims at utilizing this waste heat to produce additional power (via an ORC) and inlet gas cooling of compressor via employing absorption chiller. In this respect a combined GT-MHR/ORC/ARC structure is designed and assessed thermodynamically and economically and is compared with the standalone GT-MHR performance. A sensitivity analysis is implemented to inspect the influences of design variables, and then optimizations are conducted based on cost and exergy. Results revealed better performance for combined system in comparison to the GT-MHR. Under the optimal working conditions obtained for cost optimal design case, the combined cycle yields 12.4% higher efficiency and 9.7% lower LCOE compered to GT-MHR power plant. Another interesting outcome is obtained, as under the optimal operation, the total levelized investment cost for the novel combined cycle (9065 $/h) is less than the GT-MHR system (9285 $/h). This is due to the larger optimal pressure ratio for compressor in combined cycle which causes less helium flow rate, as a result of which the components sizes and costs are decreased.

Thermoeconomic and environmental analyses based single objective optimization of subcooled compression-absorption cascaded refrigeration system using evolutionary techniques

ABSTRACT This article analyses a subcooled compression-absorption cascaded refrigeration system (SCRS) in comparison with a standalone compression-absorption cascaded refrigeration system (CRS) based on thermoeconomic optimization. Three different absorbent solution/solution mixture-refrigerant combinations have been tested as working pairs in vapor absorption refrigeration system (VARS), whereas four environmentally friendly refrigerants have been utilized in vapor compression refrigeration system (VCRS). The total annual cost of the system is formulated using energy, exergy, and economic performance of the system and is minimized for optimal operational parameters by implementing five recent evolutionary optimization techniques. The effect of compression subcooling on various operational parameters of the cascaded system is reported. Amid all absorbent solution/solution mixture-refrigerant-refrigerant combinations, R290 combined with (CaCl2-LiBr-LiNO3)-H2O provides the minimum total annual cost of 13,164.8 US$ yr−1 and 15,401.9 US$ yr−1 for CRS and SCRS, respectively. Sanitized Teaching Learning Based Optimization (sTLBO) and Coyote Optimization Algorithm (COA) obtain the optimal total annual cost for most VARS-VCRS absorbent solution/solution mixture-refrigerant-refrigerant combinations. Though the coefficient of performance (COP) of an optimal SCRS is about 250% higher than its optimal CRS, higher compressor work results in a higher penalty cost for the optimal SCRS, which is almost 190% higher than the optimal CRS. A quick convergence is observed for sTLBO and COA.

Thermoeconomic optimization for a solar power generating system capable of storing energy by using calcium looping process

Energy storage facilities play a crucial role in mitigating the fluctuations of renewable energy sources such as solar and wind. These facilities can be used in solar-driven power plants to store solar energy during the day for use during periods of low or no sunlight to increase the plant’s capacity factor. This study evaluates the application of calcium looping reaction as a thermochemical energy storage unit in solar power plants to produce renewable electricity 24 h per day. Supercritical and trans-critical CO2 cycles are employed as upper and bottoming cycles, respectively, to produce power from solar energy. The energy storage unit absorbs energy during the day through a chemical reaction and releases it at night via a reverse chemical reaction. The proposed system is evaluated from both thermodynamic and economic points of view. A genetic algorithm-based multi-objective optimization is also carried out considering different scenarios. Energy and exergy efficiencies of the power generation cycle and levelized cost of electricity are found to be 46.4%, 50%, and 132.5 $/MWh, respectively, under the base case operating conditions. The obtained energy efficiency is 2% higher than a similar design operating with subcritical CO2 Brayton and steam cycles. Furthermore, under the optimization conditions, the power cycle exergy efficiency is improved by 1.2%, and the levelized cost of electricity is decreased by 5.1% compared with the base case conditions.

Part-Load Energy Performance Assessment of a Pumped Thermal Energy Storage System for an Energy Community

Research on pumped thermal energy storage (PTES) has gained considerable attention from the scientific community. Its better suitability for specific applications and the increasing need for the development of innovative energy storage technologies are among the main reasons for that interest. The name Carnot Battery (CB) has been used in the literature to refer to PTES systems. The present paper aims to develop an energy analysis of a CB comprising a high-temperature two-stage heat pump (2sHP), an intermediate thermal storage (latent heat), and an organic Rankine cycle (ORC). From a broad perspective, the CB is modeled considering two types of heat inputs for the HP: a cold reservoir in the ground (at a constant temperature of 12 °C throughout the entire year) and a heat storage at 80 °C (thermally-integrated PTES—TI-PTES). The first part defines simple models for the HP and ORC, where only the cycles’ efficiencies are considered. On this basis, the storage temperature and the kind of fluids are identified. Then, the expected power-to-power (round-trip) efficiency is calculated, considering a more realistic model, the constant size of the heat exchangers, and the off-design operation of expanders and compressors. The model is simulated using Engineering Equation Solver (EES) software (Academic Professional V10.998-3D) for several working fluids and different temperature levels for the intermediate CB heat storage. The results demonstrate that the scenario based on TI-PTES operation mode (toluene as the HP working fluid) achieved the highest round-trip efficiency of 80.2% at full load and 50.6% round-trip efficiency with the CB operating at part-load (25% of its full load). Furthermore, when the HP working fluid was changed (under the same scenario) to R1336mzz(Z), the round-trip full-load and part-load efficiencies dropped to 72.4% and 46.2%, respectively. The findings of this study provide the HP and ORC characteristic curves that could be linearized and used in a thermo-economic optimization model based on a Mixed-Integer Linear Programming (MILP) algorithm.

Proposing and thermo-economic optimization of an annular-thermoelectric gas heat recovery unit with a novel hybrid fin-pin vane and porous insert

Heat recovery from the cylindrical surface of the exhaust gas pipes is one of the promising applications of annular thermometric generators (ATEG). A pipe-shape based heat exchanger can be attached to the inner surface of the annular-thermoelectric generator to recover the hot exhaust gas in the form of electricity generation. In this paper, a novel grid annular fin-based heat exchanger with porous inserts is proposed which can boost the output power of the ATEG up to 1.45 and 2.12 times compared to the conventional common pipe-based heat exchangers. A comprehensive parametric analysis is carried out to investigate the impact of various geometric and operational parameters such as porous insert height, porous insert angle, porous inserts length, Re number, number of thermocouples, and so on thermal, exergetic, and economic factors. An optimized value of height, length, and angle of the porous insert can maximize the output power of the proposed system. Economic analysis is also provided to identify the corresponding costs of the grid annular fin-based heat exchanger with porous inserts for the heat recovery aim.

Thermo-economic optimization and comparative analysis of different organic flash cycles for the supercritical CO2 recompression Brayton cycle waste heat recovery

It is well known that the energy efficiency of the supercritical carbon dioxide recompression Brayton cycle (sCO2RBC) can be improved by employing the bottoming cycles to recover its large waste heat. To achieve better performance, three bottoming cycles with a good temperature matching with the sCO2 stream, namely the basic organic flash cycle (BOFC), the regenerative organic flash cycle (ROFC), and the organic flash Rankine cycle (OFRC), are employed to combine with the sCO2RBC in this work. The parametric analysis is performed to determine the variation trends of systems’ thermodynamic and exergoeconomic performance with five important parameters. The single-objective optimization is conducted for the sCO2RBC/BOFC, sCO2RBC/ROFC and sCO2RBC/OFRC systems with six organic fluids. The single-objective optimization results show that the highest exergy efficiency of the sCO2RBC/OFRC is higher than that of the rest combined sCO2RBC/OFCs by up to 1.95%. And the lowest total product unit cost for the sCO2RBC/OFRC is up to 0.93% lower than that of the rest combined sCO2RBC/OFCs. Finally, a comparative analysis is performed for the three combined sCO2RBC/OFCs, sCO2RBC/ORC and stand-alone sCO2RBC systems under the multi-objective optimization conditions. Results show that the integrated systems can improve the ηex by 4.62–6.06% and reduce the cp,tot by 2.68–3.14% when taking the sCO2RBC system as the baseline system. The sCO2RBC/OFCs and sCO2RBC/ORC are recommended to use R1336mzz(Z) and R245fa as working fluids, respectively. Moreover, the sCO2RBC/OFRC system achieves an improvement of 0.41%–1.37% in exergy efficiency with a comparable total product unit cost, compared to other aforementioned integrated systems.

Thermo-economic optimization design of steam-water organic Rankine cycle with splitting flow

Aiming to address the potential scenario of waste heat recovery from a steam-water dual heat source, this paper proposes the thermo-economic models of split-flow dual-loop organic Rankine cycle (SFD-ORC) and split-flow triple-loop organic Rankine cycle (SFT-ORC) systems. The particle swarm optimization (PSO) algorithm is employed for single-objective optimization of the systems, with the goal of maximizing the net power output. The non-dominated sorting genetic algorithm-II (NSGA-II) algorithm is used to find the Pareto frontier by considering both the maximum net power output and the lowest cost of electricity production. The multi-objective optimization parameters are evaluated using the entropy weight method and TOPSIS method. The results show that the hot water split ratio and hot water outlet temperature of the high-pressure loop are higher in multi-objective optimization compared to single-objective optimization. The net output power of the SFT-ORC system after single-objective optimization can be up to 7.9% higher than that of the SFD-ORC system. From an economic perspective, it is recommended to use the SFD-ORC system at a hot water temperature of 85 °C–90 °C. In order to enhance the economic performance of the system, the steam outlet pressure should be as low as possible within the allowable range.