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Using energy storage technologies in combination with renewable energy sources can improve power generation efficiency and reliability. Here, we predict the performance of a wind farm-based molten salt energy storage system combined with a supercritical CO2 Brayton cycle (s-CO2BC) with the aid of artificial intelligence (AI). For this purpose, the Grasshopper Optimization Algorithm (GOA) and Particle Swarm Optimization (PSO) are applied to train a Multilayer Perceptron Artificial Neural Network (MLP-ANN). The proposed AI approaches model the complex interactions between the wind farm, the molten salt energy storage, and the s-CO2BC components. Integrated system simulations under various operating conditions are used for training the performance prediction model. Power generation, energy storage, and system efficiency can all be accurately predicted by a trained AI model. In addition to providing valuable insight into the optimal operation and control strategies of the integrated system, the proposed approach enables the efficient utilization of renewable energy resources and energy storage to generate sustainable power. This study contributes to the development of AI-based optimization approaches and predicts the performance of integrated renewable energy systems, resulting in improved grid integration and stability. According to the results, the PSO method yields average absolute percentage deviations (AAPDs) between 0.47% and 0.51% across different parameters, while GOA yields AAPDs between 0.05% and 0.27%.

Membrane distillation is a new desalination process that uses low-grade heat to produce clean water. Membrane distillation (MD), in contrast to energy conversion with reverse osmosis, uses the excess heat produced by the Brayton cycle for desalination processes without the need for great energy. The Brayton cycle of sCO2 is viewed as a viable key motivator of the integrated power system, heating, and cooling, with the potential to boost efficacy. Because of its compact construction and great efficiency, in recent decades, it has been used forseveral heat sources. In this study, a literature study was conducted related to membrane distillation with a direct-contact process and a closed Brayton cycle of supercritical CO2 for the cogeneration of water.

This paper presents an investigation of a supercritical CO2 Brayton and organic Rankine (sCO 2-ORC) combined cycle for solar energy utilization. This combined cycle uses typical geothermal as auxiliary heat source to enhance its thermodynamic performance. Organic working fluid is preheated by supercritical carbon dioxide, which absorbs heat from solar power tower and then expands in a turbomachinery. Then geothermal source enhances the grade of organic working fluid before it expanded. A solution procedure is proposed to estimate the thermodynamic performance of this combined cycle. Results show that the recompression sCO 2-ORC combined cycle has the best thermodynamic performance when using CO2- enhanced geothermal system (EGS) as auxiliary heat source. The most suitable organic working fluid for CO2-EGS is R245ca. Genetic algorithm optimization indicates that the optimal thermal efficiency and net power of the combined cycle is 35.07% and 16.63 MW, respectively, whose decision variable of split ratio is 0.559. Findings suggest that the sCO 2-ORC combined cycle has a thermodynamic advantage utilizing the solar energy and auxiliary geothermal energy.

The startup process is the crucial transition phase of the supercritical carbon-dioxide Brayton cycle, so it is essential to focus on and investigate the transient performance for the system's safety and stability. The pressure in the buffer tank approaches the safety upper limit with different startup schemes during the joint commissioning of the compressor and heater in a MWe-scale experiment system, while the maximum temperature is 309 °C. Hence, dynamic simulations are carried out to explore the dynamic startup characteristics from a cold state or a warm state to the turbine pre-start condition, in which 60% of the rated mass flow rate and 67% of the rated compressor speed are reached in the end. The results show that, when starting from a cold state, the startup scheme of simultaneously heating and speeding up has a limited effective application scope. Two venting operations during the above process help the system establish heat regeneration and promote temperature uniformity in the system. Furthermore, when starting from a warm state with an existing temperature gradient in the system, the startup scheme of simultaneously heating and speeding up is more effective and has a more extensive range of control. [ABSTRACT FROM AUTHOR]

The system performance of the supercritical CO2 Brayton cycle for the Sodium Fast Reactor with a partial-cooling layout was studied, and an economic analysis was carried out. The energetic, exergetic, and exergoeconomic analyses are presented, and the optimized results were compared with the recompression cycle. The sensitivity analyses were conducted by considering the variations in the pressure ratios and inlet temperatures of the main compressor and the turbine. The exergy efficiency of the partial-cooling cycle reached 63.65% with a net power output of 34.39 MW via optimization. The partial-cooling cycle obtained a minimum total cost rate of 2230.36 USD/h and exergy efficiency of 63.65% when the pressure ratio was equal to 3.50. The inlet temperature of the main compressor was equal to 35 °C, and the inlet temperature of the turbine was equal to 480 °C. The total cost of recuperators decreased with the increase in the pressure ratio and the inlet temperatures of the main compressor. In addition, the total cost of recuperator could be reduced by increasing the outlet temperature of the turbine. The change in cost from exergy loss and destruction with the pressure ratio was substantially larger than with the inlet temperature of the turbine or the main compressor. Manipulating the pressure ratio is an essential method to guarantee good economy of the system. Moreover, capital investment, operation, and maintenance costs normally accounted for large proportions of the total cost rate, being almost double the cost from the exergy loss and destruction occurring in each condition. [ABSTRACT FROM AUTHOR]

The startup process is the crucial transition phase of the supercritical carbon-dioxide Brayton cycle, so it is essential to focus on and investigate the transient performance for the system’s safety and stability. The pressure in the buffer tank approaches the safety upper limit with different startup schemes during the joint commissioning of the compressor and heater in a MWe-scale experiment system, while the maximum temperature is 309 °C. Hence, dynamic simulations are carried out to explore the dynamic startup characteristics from a cold state or a warm state to the turbine pre-start condition, in which 60% of the rated mass flow rate and 67% of the rated compressor speed are reached in the end. The results show that, when starting from a cold state, the startup scheme of simultaneously heating and speeding up has a limited effective application scope. Two venting operations during the above process help the system establish heat regeneration and promote temperature uniformity in the system. Furthermore, when starting from a warm state with an existing temperature gradient in the system, the startup scheme of simultaneously heating and speeding up is more effective and has a more extensive range of control.

In this paper, the Chinese Fusion Engineering Testing Reactor (CFETR) power conversion system, with a supercritical CO _2 (SCO _2 ) Brayton cycle, is designed, analyzed and optimized. Considering the pulse operation of the reactor, a heat storage loop with high temperature molten salt and low temperature concrete is introduced. Based on the parameters of the first cooling loop, the CFETR power conversion loop is designed and studied. A new SCO _2 Brayton cycle for the CFETR dual heat sources, blanket and divertor, is developed and optimized using a genetic algorithm. Compared to other simple and recompression cycles, it is shown that the new SCO _2 Brayton cycle combines maximum thermal efficiency with simplicity. Exergy analyses are carried out and show that the exergy destruction rates of turbine and heat exchangers between different loops are the largest due to the large turbine power and the large temperature difference. The exergoeconomic analyses show that the fusion reactor accounts for the main cost, which is the key to the economy of fusion power generation. The following sensitivity analyses show that the hot molten salt temperature has a major influence on the system performance. Finally, several multi-criteria optimization algorithms are introduced to simultaneously optimize the three fitness functions, the cycle thermal efficiency, the system exergy efficiency and the total system product unit cost. It is found that the maximum thermal efficiency, the maximum exergy efficiency and the lowest total system product unit cost can be obtained almost simultaneously for the new CFETR power conversion system, and this optimal operation scheme is presented.

In this study, an integrated adiabatic operated chemical looping combustion and supercritical CO2 Brayton cycle using biomass as feedstock was studied based on the thermodynamic analysis. Based on comparisons of species and adiabatic flame temperature in the product gas, it was found that high air and oxygen carrier flow rates are required in adiabatic chemical looping combustion for obtaining the results from the conventional combustion under adiabatic operation. Using the product gas from the fuel reactor and flue gas from the air reactor as heat sources for the simple recuperated supercritical CO2 Brayton cycle, it is found that the cycle efficiency increases with increased turbine inlet temperature and decreased condenser exit temperature under various compressor discharge pressures. The overall thermal efficiency of the integrated system, defined as the ratio of total net work of the power cycle to the higher heating value of biomass, depends on the CO2 mass flow rates in the power cycles and also increases with increased compressor discharged pressures. The maximum cycle and overall thermal efficiencies are found to be 51% and 21%, respectively.

The system performance of the supercritical CO2 Brayton cycle for the Sodium Fast Reactor with a partial-cooling layout was studied, and an economic analysis was carried out. The energetic, exergetic, and exergoeconomic analyses are presented, and the optimized results were compared with the recompression cycle. The sensitivity analyses were conducted by considering the variations in the pressure ratios and inlet temperatures of the main compressor and the turbine. The exergy efficiency of the partial-cooling cycle reached 63.65% with a net power output of 34.39 MW via optimization. The partial-cooling cycle obtained a minimum total cost rate of 2230.36 USD/h and exergy efficiency of 63.65% when the pressure ratio was equal to 3.50. The inlet temperature of the main compressor was equal to 35 °C, and the inlet temperature of the turbine was equal to 480 °C. The total cost of recuperators decreased with the increase in the pressure ratio and the inlet temperatures of the main compressor. In addition, the total cost of recuperator could be reduced by increasing the outlet temperature of the turbine. The change in cost from exergy loss and destruction with the pressure ratio was substantially larger than with the inlet temperature of the turbine or the main compressor. Manipulating the pressure ratio is an essential method to guarantee good economy of the system. Moreover, capital investment, operation, and maintenance costs normally accounted for large proportions of the total cost rate, being almost double the cost from the exergy loss and destruction occurring in each condition.

The carbon dioxide (CO2), which is an environmental friendly working fluid, has good thermal physical properties under the supercritical condition. The heat transfer mechanism and the enhanced heat transfer method of the supercritical CO2 Brayton cycle (SCO2-BC) have been studied by many researchers, which can be used in the new generation of Fast Cooling Reactor (FCR), solar power system, extraction progress and heat pump system. With the development of engineering technology, the system miniaturization is the most important characteristics in application, which the SCO2-BC can satisfy the requirements with high efficiency and high compactness. In the present paper, the research progress of SCO2-BC including the performance evaluation, system optimization and economic evaluation are reviewed based on the references in recent years. Then, the analysis of the key components including the compressor, turbine and heat exchanger are introduced with the special thermal properties of supercritical CO2, which are different from the conventional devices in the traditional steam cycle. Finally, some recommendations for future work are primarily proposed towards the development of SCO2-BC system.

Supercritical CO2 (S-CO2) Brayton cycles have become an effective way in utilizing solar energy, considering their advantages. The presented research discusses a parametrized analysis and systematic comparison of three S-CO2 power cycles coupled with parabolic trough collectors. The effects of turbine inlet temperature and pressure, compressor inlet temperature, and pressure on specific work, overall efficiency, and cost of core equipment of different S-CO2 Brayton cycles are discussed. Then, the two performance criteria, including specific work and cost of core equipment, are compared, simultaneously, between different S-CO2 cycle layouts after gaining the Pareto sets from multi-objective optimizations using genetic algorithm. The results suggest that the simple recuperation cycle layout shows more excellent performance than the intercooling cycle layout and the recompression cycle layout in terms of cost, while the advantage in specific work of the intercooling cycle layout and the recompression cycle layout is not obvious. This study can be useful in selecting cycle layout using solar energy by the parabolic trough solar collector when there are requirements for the specific work and the cost of core equipment. Moreover, high turbine inlet temperature is recommended for the S-CO2 Brayton cycle using solar energy. [ABSTRACT FROM AUTHOR]

Printed circuit heat exchangers (PCHEs) have the characteristics of high temperature and high pressure resistance, as well as compact structure, so they are widely used in the supercritical carbon dioxide (S-CO2) Brayton cycle. In order to fully study the heat transfer process of the Z-type PCHE, a numerical model of traditional Z-type PCHE was established and the accuracy of the model was verified. On this basis, a new type of spiral PCHE (S-ZPCHE) is proposed in this paper. The segmental design method was used to compare the pressure changes under 5 different spiral angles, and it was found that increasing the spiral angle θ of the spiral structure will reduce the pressure drop of the fluid. The effects of different spiral angles on the thermal-hydraulic performance of S-ZPCHE were compared. The results show that the pressure loss of fluid is greatly reduced, while the heat transfer performance is slightly reduced, and it was concluded that the spiral angle of 20° is optimal. The local fluid flow states of the original structure and the optimal structure were compared to analyze the reason for the pressure drop reduction effect of the optimal structure. Finally, the performance of the optimal structure was analyzed under variable working conditions. The results show that the effect of reducing pressure loss of the new S-ZPCHE is more obvious in the low Reynolds number region.

Abstract The printed circuit heat exchanger is currently the preferred type of recuperative heat exchanger for the supercritical CO 2 Brayton cycle due to its highly compact construction, high heat transfer coefficients and its ability to withstand high pressures and temperatures. This paper employs a three-dimensional numerical model to investigate the thermohydraulic performance of supercritical CO 2 flow in a printed circuit heat exchanger. This numerical model considers entrance effects, conjugate heat transfer, real gas thermophysical properties and buoyancy effects. The inlet temperature and pressure are 100 °C/150 bar on the cold side and 400 °C/75 bar on the hot side while the mass flux is varied from 254.6 to 1273.2 kg/(m2·s). The overall performance of the heat exchanger and comparisons of local heat transfer and friction pressure drop with predictions from the empirical correlations are presented and discussed. Overall, this paper provides useful information that can be employed in the design of recuperators for supercritical CO 2 Brayton cycle applications. [ABSTRACT FROM AUTHOR]

Abstract In recent years, supercritical CO 2 (s-CO 2) Brayton-cycle engines attract more and more attention for its advantages of simple structure, compact layout, high efficiency and energy saving. Plenty efforts are made to apply them in many areas of power generation including concentrated solar power (CSP) plants. In the application of CSP plants, s-CO 2 Brayton cycle has an extra advantage of low water consumption versus Rankin cycle, which is very helpful for its spreading in water shortage area. For an efficient collaboration of this thermodynamic cycle and concentrated solar thermal system, a new s-CO 2 tubular receiver applying porous media and circulating air flow is proposed in this study. The heat transfer area is ~13 times larger than the heat loss area, which enables the proposed receiver to obtain the efficiency of ~95%. With the volumetric absorption concept applied, this receiver can absorb the sunlight volumetrically and has smaller heat loss area, which also enables it to operate at high solar flux. The proposed receiver is the suitable combination of the air based volumetric receivers and tubular receivers, which may provide a new approach for receiver design. [ABSTRACT FROM AUTHOR]

Supercritical CO2 (S-CO2) Brayton cycles have become an effective way in utilizing solar energy, considering their advantages. The presented research discusses a parametrized analysis and systematic comparison of three S-CO2 power cycles coupled with parabolic trough collectors. The effects of turbine inlet temperature and pressure, compressor inlet temperature, and pressure on specific work, overall efficiency, and cost of core equipment of different S-CO2 Brayton cycles are discussed. Then, the two performance criteria, including specific work and cost of core equipment, are compared, simultaneously, between different S-CO2 cycle layouts after gaining the Pareto sets from multi-objective optimizations using genetic algorithm. The results suggest that the simple recuperation cycle layout shows more excellent performance than the intercooling cycle layout and the recompression cycle layout in terms of cost, while the advantage in specific work of the intercooling cycle layout and the recompression cycle layout is not obvious. This study can be useful in selecting cycle layout using solar energy by the parabolic trough solar collector when there are requirements for the specific work and the cost of core equipment. Moreover, high turbine inlet temperature is recommended for the S-CO2 Brayton cycle using solar energy.

In this study, a direct recompression supercritical CO2 Brayton cycle, using parabolic trough solar concentrators (PTC), is developed and analyzed employing a new simulation model. The effects of variations in operating conditions and parameters on the performance of the s-CO2 Brayton cycle are investigated, also under varying weather conditions. The results indicate that the efficiency of the s-CO2 Brayton cycle is mainly affected by the compressor outlet pressure, turbine inlet temperature and cooling temperature: Increasing the turbine inlet pressure reduces the efficiency of the cycle and also requires changing the split fraction, where increasing the turbine inlet temperature increases the efficiency, but has a very small effect on the split fraction. At the critical cooling temperature point (31.25 °C), the cycle efficiency reaches a maximum value of 0.4, but drops after this point. In optimal conditions, a cycle efficiency well above 0.4 is possible. The maximum system efficiency with the PTCs remains slightly below this value as the performance of the whole system is also affected by the solar tracking method used, the season and the incidence angle of the solar beam radiation which directly affects the efficiency of the concentrator. The choice of the tracking mode causes major temporal variations in the output of the cycle, which emphasis the role of an integrated TES with the s-CO2 Brayton cycle to provide dispatchable power.

Abstract: Power generation efficiency penalty is the main concern about carbon capture technologies. Improvement of power plant efficiency due to higher steam condition is frequently foreseen to outbalance the carbon capture penalty. This work focuses on the conceptual design of two coal-fired power plants using CO2 as working fluid: one with post- combustion MEA-based CO2 capture and one with oxy-combustion CO2 capture with cryogenic air separation. Two maximal supercritical CO2 temperatures are investigated (620 and 700°C). The combination of a Brayton supercritical CO2 power cycle, a coal boiler and a capture process allows significant increase of the overall plant efficiency. Both post-combustion and oxy-combustion capture processes lead to a very high overall plant efficiency: approximately 41.5% for a 620°C power cycle and 44.5% for a 700°C power cycle. Oxy-combustion seems best fitted for supercritical CO2 Brayton cycle due to a simpler thermal integration and the CO2 purification devices already integrated in the CO2 processing unit. Main resulting technological challenges are the very large heat exchanger needed in the CO2 cycle in order to achieve high power cycle efficiency and the development of supercritical CO2 turbine significantly different than steam or gas turbine especially because of the very large effort on wheel and the small size of the equipment. Numerous technological developments on process component will be necessary and a representative CO2 cycle pilot plant will be needed to assess CO2 leakage, corrosion and flexibility issues. [Copyright &y& Elsevier]

Under the severe situation of low energy efficiency and strict emission standards, waste heat recovery, is considered to be a feasible technology, to achieve fuel economic in automobile industry. Among them, supercritical CO 2 Brayton cycle has become one of the most promising technology owing to its high efficiency and compactness. Besides, the exhaust temperature and flow of automobile engine change dramatically in practice, resulting in a negative impact on the thermodynamic performance of the power cycle. Therefore, this paper develops a dynamic model of waste heat recovery system, carries out operating parameters analysis, transient response characteristics research and performance optimization, and finally proposes an improved method to adjust turbine inlet temperature to obtain higher output power. The change trend displays that the influence of turbine inlet pressure on thermodynamic performance is opposite to the dynamic response characteristics, and similar results also occur under engine start-up conditions. The numerical results indicate that the optimized output power and electric production cost reach 2.97 kW and 0.38 USD/kW·h, compared with the previous method, an improvement of 3.48% and 5.00% are achieved, respectively, reflecting the significance of energy conservation and emission reduction. [Display omitted] • A dynamic model for a recuperator supercritical CO 2 Brayton cycle is proposed. • Transient response characteristics in different operating conditions are considered. • To propose a new method to adjust turbine inlet temperature for higher output work. • Optimization gets improvements of 3.48% and 5.00% in output and economic performance. [ABSTRACT FROM AUTHOR]

Membrane distillation is an emerging desalination technology using low-grade heat for sustainable water production. This paper proposes a novel integrated design of direct-contact membrane distillation process and a closed supercritical CO 2 Brayton cycle for water cogeneration. The membrane distillation uses the waste heat rejected by the Brayton cycle for seawater desalination without consuming high grade energy, as compared to the cogeneration with reverse osmosis. The design includes a "split flow" coupling of Brayton cycle's cooling water to fully utilize the temperature gradient of the waste heat for membrane distillation. A mathematical model is also developed to evaluate and optimize the thermo-economic performance of the systems. The proposed integrated design is applied to a 50 MWe supercritical CO 2 recompression Brayton cycle power plant combined with membrane distillation to demonstrate its efficacy. Results show that the proposed design can achieve a levelized water production cost of 1.39 $/m3 with a water production capacity of 2.06 × 105 m3/year, outperforming the design without the "split flow". [Display omitted] • A novel integrated design of MD-sCO 2 Brayton cycle system for water cogeneration. • Exploitation of waste heat temperature gradient without adding load on power cycle. • 1.39 $/m3 of water desalination cost is achieved for the optimal design. • Up to 2.40 × 105 m3/year of water can be produced for a 50 MWe sCO 2 Brayton cycle. [ABSTRACT FROM AUTHOR]

• Dynamic models of nuclear fusion plant can help optimize their performance. • A model of a supercritical CO 2 power cycle developed using Modelica language. • Adequate controls have been implemented in the model aiming at real control design. • When simulating a variable load operation, the modelled system has performed well. • Modelica is a convenient tool to design control algorithms of dynamic systems. Nuclear fusion technology is one of the main valuable candidates for providing a trustable base load in low-carbon future energy scenarios, thanks to its power density, low emissions and flexibility, together with innovative power conversion systems that could improve its performance, as the supercritical CO 2 Brayton cycle. Since the nuclear plant will be required to provide variable loads, due to the fluctuating nature of renewable energies, a powerful modelling tool will be necessary to simulate different power outputs. The present paper presents a dynamic model of a supercritical CO 2 power cycle developed with Modelica, aimed at the design of control systems to adjust the power production according to the load required. Thanks to the activity of three PI controllers, the system is able to follow a variable load profile while preserving the turbomachinery inlet temperature, to avoid any possible damage of the devices. The work has shown the adequacy and potential interest of the use of Modelica in this kind of analyses. [ABSTRACT FROM AUTHOR]

Printed circuit heat exchangers (PCHEs) have the characteristics of high temperature and high pressure resistance, as well as compact structure, so they are widely used in the supercritical carbon dioxide (S-CO2) Brayton cycle. In order to fully study the heat transfer process of the Z-type PCHE, a numerical model of traditional Z-type PCHE was established and the accuracy of the model was verified. On this basis, a new type of spiral PCHE (S-ZPCHE) is proposed in this paper. The segmental design method was used to compare the pressure changes under 5 different spiral angles, and it was found that increasing the spiral angle θ of the spiral structure will reduce the pressure drop of the fluid. The effects of different spiral angles on the thermal-hydraulic performance of S-ZPCHE were compared. The results show that the pressure loss of fluid is greatly reduced, while the heat transfer performance is slightly reduced, and it was concluded that the spiral angle of 20° is optimal. The local fluid flow states of the original structure and the optimal structure were compared to analyze the reason for the pressure drop reduction effect of the optimal structure. Finally, the performance of the optimal structure was analyzed under variable working conditions. The results show that the effect of reducing pressure loss of the new S-ZPCHE is more obvious in the low Reynolds number region. [ABSTRACT FROM AUTHOR]

Heat transfer fluids play a crucial role in solar thermal power plants. Several novel salt formulas with higher temperature limit, such as MgCl 2 -KCl, have been proposed to serve as heat transfer fluids in a solar power tower system with S-CO 2 cycles. Although the thermophysical properties of these novel salt formulas have been obtained in previous studies, it is necessary to evaluate their performances from the viewpoint of system-level analysis. This paper develops an integrated model for the solar power tower plants with a recompression S-CO 2 Brayton cycle, and the performances of the MgCl 2 -KCl salt are evaluated based on the thermodynamic analyses and multi-objective optimizations about the system. The results indicate that: (1) Attributed to the higher heat source temperature, the system with MgCl 2 -KCl can achieve a slightly higher system efficiency and a significantly larger specific work than the conventional solar salt; (2) Reheating is not recommended for solar power tower plant with supercritical CO 2 Brayton cycles when high-temperature MgCl 2 -KCl serves as heat transfer fluid; (3) The MgCl 2 -KCl solar power tower system without reheating enlarges the temperature difference between hot salt and cold salt and thus needs less molten salt for the thermal storage than the solar salt system; (4) The novel MgCl 2 -KCl salt has no advantages under the conditions with the operating temperature lower than 565 °C, which yields lower system efficiency and smaller specific work than the conventional solar salt due to the higher pump consumption associated with its higher viscosity. • Novel eutectic salt is evaluated as HTF in SPT from view of system-level analysis. • High-temperature MgCl 2 -KCl yields a larger specific work and a higher efficiency. • Reheating is not recommended for SPT with S-CO 2 cycles when high-temperature MgCl 2 -KCl serves as HTF. • MgCl 2 -KCl SPT without reheating needs less salt for thermal storage in spite of its smaller specific heat capacity. [ABSTRACT FROM AUTHOR]

This paper addresses the simultaneous optimization of a novel combined supercritical CO 2 Brayton cycle-organic Rankine cycle integrated with molten salt solar power tower plant. The supercritical CO 2 Brayton cycle adopts a two-stage compression intercooling design. The organic Rankine cycle is added as a bottoming cycle to recover the waste heat of the Brayton cycle to generate extra power. Due to its complexity, the integrated system involves many degrees of freedom, which make it challenging to optimize using metaheuristic methods. To tackle this issue, we develop an equation-based model that simultaneously optimizes stream thermodynamic properties and flowsheet mass/heat equilibrium of the integrated system. The problem is formulated as a nonlinear programming model, and a tailored two-step solution strategy is developed to improve its solution efficiency. Several numerical studies are carried out to demonstrate the effectiveness of the proposed optimization method, as well as the efficiency of the integrated system. Solution time of the model is less than 224 CPU seconds. Results show that the method obtains an increase up to 3.6% in thermal efficiency compared with literature results; the optimal intercooling design increases net power output by 2.7% comparing with recompression cycle; the recompression cycle-organic Rankine cycle design obtains a 3.5% increase; and the combined intercooling cycle-organic Rankine cycle design achieves a total 4.4% increase. • A novel concentrated solar power-sCO 2 Brayton cycle-ORC integrated system is proposed. • An NLP model is formulated for simultaneous optimization of the integrated system. • High accuracy thermodynamics module is embedded to estimate physical properties. • Four types of system design are optimized and compared for energy performance. [ABSTRACT FROM AUTHOR]

This study presents an investigation of a CO 2 plume geothermal and supercritical CO 2 Brayton (CPG-sCO 2) combined cycle using solar energy as auxiliary heat source. This combined cycle may help solve the problems of CO 2 sequestration and geothermal energy utilization simultaneously. The CPG production is heated by a solar power generation system with solar tower and molten salt. Then a recompression sCO 2 cycle utilizes geothermal energy and solar energy directly. A solution procedure is performed to analyze the thermoeconomic performance of the CPG-sCO 2 combined cycle. Results show that the combined cycle has an optimal main compressor inlet pressure and split ratio for maximum combined cycle efficiency. It can achieve 19.57% by genetic algorithm (GA) optimization, which is 5.65% and 4.07% higher than CPG systems with indirect sCO 2 cycle and organic Rankine cycle, respectively. Moreover, it indicates that the combined cycle efficiency and total capital cost have opposite variation trends with the increase of parameters, including main compressor inlet pressure (p 5), split ratio (sr), well distance (d 8,11) and injection temperature (T 8). Based on multi-objective GA optimization and optimal solution selection, it is concluded that the most thermoeconomic CPG-sCO 2 combined cycle has a combined cycle efficiency of 18.09% and a total capital cost of $5.959 × 107, respectively. Findings suggest that the CPG-sCO 2 combined cycle has potential to combine CO 2 sequestration with geothermal energy utilization. • A CPG-sCO 2 combined cycle with auxiliary solar energy source was studied. • This combined cycle coupled CO 2 sequestration with geothermal energy utilization. • The CPG-sCO 2 combined cycle had a maximum efficiency of 19.57%. • Its efficiency is 5.65% and 4.07% higher than CPG with indirect sCO 2 cycle and ORC. • Most thermoeconomic combined cycle had η cc of 18.09% and C cur,cc of $5.959 × 107. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study on the energy, exergetic and thermo-economic performance of a novelty thermal power system integrated by a supercritical CO 2 Brayton cycle, and a recuperative organic Rankine cycle (RORC) or a simple organic Rankine cycle (SORC). A thermodynamic model was developed applying the mass, energy and exergy balances to all the equipment, allowing to calculate the exergy destruction in the components. In addition, a sensitivity analysis allowed studying the effect of the primary turbine inlet temperature (T IT, P HIGH , r P and T C ) on the net power generated, the thermal and exergy efficiency, and some thermo-economic indicators such as the payback period (PBP), the specific investment cost (SIC), and the levelized cost of energy (LCOE), when cyclohexane, acetone and toluene are used as working fluids in the bottoming organic Rankine cycle. The parametric study results show that cyclohexane is the organic fluid that presents the best thermo-economic performance, and the optimization with the PSO method conclude a 2308.91 USD/kWh in the SIC, 0.22 USD/kWh in the LCOE, and 9.89 year in the PBP for the RORC system. Therefore, to obtain technical and economic viability, and increase the industrial applications of these thermal systems, thermo-economic optimizations must be proposed to obtain lower values of the evaluated performance indicators., (© 2020 Published by Elsevier Ltd.)

In this study, a direct recompression supercritical CO2 Brayton cycle, using parabolic trough solar concentrators (PTC), is developed and analyzed employing a new simulation model. The effects of variations in operating conditions and parameters on the performance of the s-CO2 Brayton cycle are investigated, also under varying weather conditions. The results indicate that the efficiency of the s-CO2 Brayton cycle is mainly affected by the compressor outlet pressure, turbine inlet temperature and cooling temperature: Increasing the turbine inlet pressure reduces the efficiency of the cycle and also requires changing the split fraction, where increasing the turbine inlet temperature increases the efficiency, but has a very small effect on the split fraction. At the critical cooling temperature point (31.25 °C), the cycle efficiency reaches a maximum value of 0.4, but drops after this point. In optimal conditions, a cycle efficiency well above 0.4 is possible. The maximum system efficiency with the PTCs remains slightly below this value as the performance of the whole system is also affected by the solar tracking method used, the season and the incidence angle of the solar beam radiation which directly affects the efficiency of the concentrator. The choice of the tracking mode causes major temporal variations in the output of the cycle, which emphasis the role of an integrated TES with the s-CO2 Brayton cycle to provide dispatchable power. [ABSTRACT FROM AUTHOR]

• The novel CO 2 transcritical power cycle operates with conventional water cooling. • Theoretical study was executed on the relationships among the cycle's parameters. • The novel cycle simplifies the development of the pressurizing component. Compared with the conventional Rankine cycle, the CO 2 transcritical power cycle gives a higher thermal efficiency because of its high average heat absorbing temperature and is suitable for driving a compact system. The self-condensing CO 2 transcritical power cycle can solve the problem that CO 2 is difficult to condense in a conventional CO 2 transcritical power cycle using conventional water cooling. Based on solar thermal energy, a theoretical analysis model was established to study the relationship between the cycle performance and the operating parameters. The results showed that the thermal efficiency increases with increasing the cooled pressure with a low final cooled temperature. By increasing the final cooled temperature, a peak appears on the thermal efficiency curve. The outlet temperature of the cooling water is affected by a shift of the pinch point position in the cooler. According to the variation of the outlet temperature of the cooling water and the proportion of the mass flow rate of CO 2 in the power sub-cycle and that in the whole cycle, it can be concluded that conditions with a very low cooled pressure are uncontrollable. In these conditions, the maximum thermal efficiency of the self-condensing CO 2 transcritical cycle is 0.3463, which is 0.0313 a little lower than that of the supercritical CO 2 Brayton cycle. However, the novel cycle simplifies the development of the pressurizing component and avoids the liquid hammer in the pressurizing process. [ABSTRACT FROM AUTHOR]

• Experimentally tested spray cooling system to enhance the performance of NDDCT. • Modelled the sCO 2 Brayton circle for solar power plants with spray-assisted towers. • Identified optimal circulating water flowrate based on circle thermal efficiency. Supercritical carbon dioxide (sCO 2) based Brayton cycle integrated with concentrated solar power applications is a promising technology to exploit solar energy for electricity production. To reduce the energy cost of this solar power plant, spray-assisted dry cooling technology is developed, which makes electricity more affordable for isolated and arid regions. However, pure dry cooling technology suffers from low efficiency under high ambient conditions and a spray cooling system has been proposed to address this problem. Due to the high cost and great complexity, experimental test of a designed spray cooling system on a natural draft dry cooling tower is never reported. Here a spray cooling system consisted of multiple nozzles was tested on a 20 m high experimental tower. This is, to our knowledge, the world's first attempt to practice spray enhancement of NDDCT at full scale. It is found that the introduced spray cooling can effectively precool the inlet hot air and consequently reduce the circulating water exit temperature. The promising application of this new technology in solar power plants was firstly revealed by integrating the tower into a 1 MW concentrated solar thermal sCO 2 Brayton cycle. As spraying water flowrate increases, cooling tower dissipates more waste heat, lowering the compressor inlet temperature and consequently improving the efficiency of thermal cycle. Power cycle simulations also show that cycle efficiency can be higher than 40.5% at the optimal circulating water flow rate, i.e., 4–5 kg/s, depending on the sCO 2 flow rate. [ABSTRACT FROM AUTHOR]