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The solar-driven high-temperature steam electrolysis is promising for efficient large-scale H 2 production. In this study, a comprehensive component-to-system model and optimization framework is developed to investigate the performance of a zero-emission H 2 production system based on solar power plant and protonic ceramic electrolysis cell. Compared to previous system studies, the detailed description of cell internal operating characteristics is realized by integrating multi-physics simulation and artificial neural network. After parametric analyses, it is found that the system energy/exergy efficiency and co-generation performance are complicated by each subsystem. And the optimal system performance (η th = 50.63 %, Z = 179.63 $·h−1 and η ex = 33.03 %, Z = 178.94 $·h−1, with LCOE = 0.172 $·kWh−1 and Z H2 = 6.497 $·kg−1) is obtained considering cell operating features and system energy-exergy-economic factors through multi-objective optimizations. Besides, the tradeoff between system maximum H 2 production capacity and cell internal thermal conditions is revealed. This study can facilitate the development of zero-emission green H 2 production driven by renewable energy. • A novel SPT-PCEC based integrated system is proposed for green H 2 production. • Both PCEC state and system energy-exergy-economic performance are considered. • Effects of each subsystem parameters on system performance are analyzed. • Optimal system performance under different constraints is obtained. • The tradeoff between system H 2 capacity and PCEC thermal conditions is revealed. [ABSTRACT FROM AUTHOR]

This paper investigated four different S-CO2 Brayton cycle layouts for nuclear energy conversion: simple recuperation cycle (SR), recompression cycle (RC), re-heating cycle (RH), and intercooling cycle (IC). We compared these S-CO2 Brayton cycle schemes for nuclear energy conversion using the G1+TOPSIS multi-index evaluation method. The evaluation results of different schemes based on their safety, thermodynamics, techno-economic and compactness are given. The results show that for Generation IV reactors with the same designed thermal power, the thermodynamic performance of the S-CO2 system is better for higher reactor exit temperature. Among the schemes, the gas-cooled fast reactor (GFR)+RC scheme has the highest thermal efficiency (47.4%) and exergy efficiency (56.48%). The GFR+IC scheme has the lowest specific cost (1861.3$/W) and the internal rate of return (24.8%). The re-heating cycle (RH) has worse indexes, but it requires the lowest initial investment cost. The intercooling cycle (IC) has the lowest levelized cost of electricity (0.0134 $/KW•h) coupling to GFR. Considering all indexes of four aspects, the reactor's performance ranking is MSR>LFR>SFR>GFR, and the S-CO2 system's performance ranking is RC>SR>IC>RH. For Generation IV nuclear energy conversion technologies, the molten salt reactor (MSR)+RC scheme should be given priority, while GFR+RH schemes should be carefully considered. [ABSTRACT FROM AUTHOR]

The supercritical CO2 (S-CO2) Brayton cycle is expected to replace steam cycle in the application of solar power tower system due to the attractive potential to improve efficiency and reduce costs. Since the concentrated solar power plant with thermal energy storage is usually located in drought area and used to provide a dispatchable power output, the S-CO2 Brayton cycle has to operate under fluctuating ambient temperature and diverse power demand scenarios. In addition, the cycle design condition will directly affect the off-design performance. In this work, the combined effects of design condition, and distributions of ambient temperature and power demand on the cycle operating performance are analyzed, and the off-design performance maps are proposed for the first time. A cycle design method with feedback mechanism of operating performance under varied ambient temperature and power demand is introduced innovatively. Results show that the low design value of compressor inlet temperature is not conductive to efficient operation under low loads and sufficient output under high ambient temperatures. The average yearly efficiency is most affected by the average power demand, while the load cover factor is significantly influenced by the average ambient temperature. With multi-objective optimization, the optimal solution of designed compressor inlet temperature is close to the minimum value of 35°C in Delingha with low ambient temperature, while reaches 44.15°C in Daggett under the scenario of high ambient temperature, low average power demand, long duration and large value of peak load during the peak temperature period. If the cycle designed with compressor inlet temperature of 35°C instead of 44.15°C in Daggett under light industry power demand, the reduction of load cover factor will reach 0.027, but the average yearly efficiency can barely be improved. [ABSTRACT FROM AUTHOR]

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 supercritical CO 2 Brayton cycle (SCO 2 BC) has emerged as a promising next-generation power generation technology due to its potential for high thermal efficiency and compact components design. Dynamic modeling of SCO 2 BC is crucial for understanding and analyzing its performance under design and off-design conditions. Turbomachines are critical components in SCO 2 BC dynamic models. While turbomachinery components are often modeled using their design-point turbomachinery performance maps (TPM), these maps become less accurate during off-design operations. Despite the existence of various TPM correction methods that ensure model validity, the implementation of the accurate ones within dynamic SCO 2 BC models remains scarce in the literature. This is crucial as it potentially compromises the accuracy of the obtained results. Therefore, there is a need to investigate the errors in the existing literature TPM correction models (in dynamic SCO 2 BC simulation) by comparing them against dynamic SCO 2 BC models employing a highly accurate correction method. Thus, in the current work, the common TPM correction methods from the literature are implemented in SCO 2 BC dynamic models and compared against a baseline mode, which uses the highly-accurate Pham method (at both the component and cycle levels). To the authors' knowledge, this is the first work to address this research gap for the SCO 2 BC dynamic simulations and on both component and cycle levels. Additionally, another novelty is the usage of Simcenter Amesim software to dynamically model the SCO 2 BC aided with Pham model. Multible dynamic models for both the turbomachines of SCO 2 BC and the whole cycle are constructed and equipped with the different TPM correction methods found in literature to compare their dynamic behaviour that of Pham model. The Ideal Gas Compressibility factor (IGZ) method demonstrates a better performance than the other tested methods, as it exhibits the lowest discrepancy compared to the Pham model. Many of the other tested methods show significant errors. Furthermore, a popular hybrid correction combining IGZ and Pham (IGZ-Ph) is also investigated. Surprisingly, while seemingly beneficial, this hybrid approach negatively impacts accuracy, even resulting in predictions as if no correction was applied. • Two Supercritical CO 2 Brayton cycle layouts are dynamically modeled in Simcenter Amesim. • Four Turbomachines correction methods are compared to the baseline Pham model. • The comparison is dynamically done on both component- and cycle-levels for the two layouts. • Correction using the IGZ method has good phase predictions but with amplitude errors. • Enhancing the IGZ method by combining it with Pham backfires. [ABSTRACT FROM AUTHOR]

• Detailed model of reversible solid oxide cell-based power-H 2 -power system created. • In-depth parametric analyses and optimizations at two basic modes are conducted. • Larger stack capacity and higher operating temperature of the cell are preferred. • Power-H 2 -power system performance is limited by high power generation fuel cost. • Critical power capacity is obtained considering system capacity and economics. The power-H 2 -power system based on reversible solid oxide cell is a promising pathway for large-scale renewable energy storage but not well understood due to the absence of comprehensive system analyses. In this study, a reversible solid oxide cell-based H 2 energy storage system for a 100 % renewable solar power plant is proposed and analyzed through detailed modeling approach and optimization framework. The detailed parametric analyses and economic evaluations are performed in electrolysis (12:00 pm, sufficient solar energy) and power generation (6:30 am, insufficient solar energy) conditions. Notably, it is found that larger stack capacity (N cell) and higher operating temperature (T ReSOC) of the cell enhances system net H 2 production and system economics despite additional investment cost. Afterwards, the optimal system performance is obtained (V H2,produce = 498.40 Nm3·h−1, Z =263.59 $·h−1 for electrolysis, and V H2,consume = 380.33 Nm3·h−1 for power generation) through multi-objective optimization by fully considering cell internal operating characteristics and system energy-exergy-economic factors. Besides, it is also found that the performance of power-H 2 -power system is still limited by remarkable fuel (H 2) costs for nighttime power generation (daytime H 2 production is smaller than nighttime H 2 consumption when W tot = 1 MW). Therefore, the critical power capacity (P critical) is obtained, offering a convenient approach to determine the maximum output capacity (P critical = 880 kW) to make the power-H 2 -power system profitable at specific solar energy input. This study provides valuable insights between system capacity, economics, and cell operating features in solar power plants, which are useful for the design and optimization of practical power-H 2 -power systems for renewable energy storage. [ABSTRACT FROM AUTHOR]

The multilevel cascade SCO 2 Brayton cycles are developed based on the conventional recompression-reheat cycle to enhance thermodynamic performances using the multilevel cascade scheme. Mathematical models are proposed to characterize their thermal cycle efficiency. The results show that for three typical cases, the proposed multilevel cascade cycle with 3 compressors × 3 reheats × 2 turbines improve cycle efficiency by 2.56 %, 3.17 %, and 3.44 % in absolute change, while the other with 3 compressors × 3 reheats × 3 turbines further enhance by 3.17 %, 4.19 %, and 4.17 % in absolute change over the conventional cycle. The latter cycle as the optimal layout is chosen to perform the key parametric analysis. The cycle efficiency increases with increasing high-pressure turbine inlet temperature, while the main compressor inlet temperature has the opposite effect. It increases and then decreases with the high-pressure turbine inlet pressure, the main compressor inlet pressure, and the split ratio of the recompressor, respectively. Finally, the parametric global optimization is conducted to improve the cycle performance more deeply. It is demonstrated that the absolute efficiency can be further increased by 2.62 %, 1.81 %, and 1.09 % for the responding cases. The integrated configurations are also suggested for power generation systems with different applications. [Display omitted] • Multilevel cascade strategy-based layouts are designed for SCO 2 Brayton power cycle. • A maximum of 4.19 % increase in cycle efficiency can be achieved in the cases studied. • Response of cycle efficiency is addressed to operating parameters. • Key parameters are optimized to further improve cycle efficiency by up to 2.62 %. • Integrated configurations for typical power generation systems are suggested. [ABSTRACT FROM AUTHOR]

• Detailed component-to-system numerical model of SPT-RSOC system is developed. • Comparative analyses of H 2 –/GL-RSOC systems are conducted at typical conditions. • H 2 -RSOC system faces economic challenges from remarkable nighttime fuel costs. • GL-RSOC system exhibits doubled H 2 production and notable lower fuel costs. • Competitive H 2 production cost and LCOE is achieved by using glycerol in RSOC. Reversible solid oxide cells (RSOCs) represent a promising solution for addressing the future challenge of large-scale renewable energy storage. However, the performance and economic viability of current RSOC systems are hindered by the large overpotential losses in electrolysis and apparent fuel (H 2) costs associated with power generation. This study employs a comprehensive numerical modeling approach to analyze the potential of renewable fuel (glycerol) in assisting hydrogen production performance and reducing operating costs within RSOC systems. The detailed comparative analyses and parametric studies are conducted on H 2 -based and glycerol-based RSOC systems at typical operating conditions. Notably, it is found that the economic viability of hydrogen-based RSOC systems is hindered by the remarkable fuel (H 2) costs during nighttime despite of the favorable effects of larger stack capacity and higher temperature. While incorporating glycerol as an alternative fuel in RSOC systems offers significant advantages, including doubling the electrolytic H 2 production (from 585.92 Nm3·h−1 to 1191.24 Nm3·h−1) at a relatively low cost and substantially reducing the fuel expenses (from 594.30 $·h−1 to 30.57 $·h−1) for nighttime power generation, thus leading to competitive electrolytic hydrogen production cost (2.982 $·kg−1) and noteworthy enhancement in economic viability (LCOE of 0.090 $·kWh−1 and 0.304 $·kWh−1 for electrolysis and power generation, respectively). The findings of this study provide valuable insights that contribute to the advancement of RSOC systems, thus facilitating the development of efficient, cost-effective, and sustainable energy storage and conversion technologies. [ABSTRACT FROM AUTHOR]

• A thermodynamic-economic model for supercritical CO 2 directly cooled reactor is developed based on thermal current theory. • PCHE's model incorporating actual channel geometries is established based on ITDB thermal resistance. • Effects of PCHE types and size on cycle's thermo–economic performances are clarified. The supercritical CO 2 Brayton cycle is a potential technology in small modular reactors (SMRs), and the overall system efficiency can be significantly improved by optimizing the PCHE design parameters. This study develops a thermodynamic-economic analysis model for a supercritical CO 2 simple Brayton cycle cooled SMR, with consideration of the detailed parameters of PCHEs. The impact of the length, channel number and channel type for the recuperator and the precooler on system thermal efficiency and levelized cost of electricity (LCOE) are analyzed. A dual-objective optimization study is conducted at the system level to identify the optimal design of size parameters and types for the heat exchangers. The results indicate that the influence of PCHE size parameters variations on system performance varies across different channel types. Additionally, the selection of the recommended recuperator type is influenced by the recuperator inlet Reynolds number. At the optimum design, the recommended channel type for recuperator and precooler are both S-shaped, resulting in a system efficiency of 39.12% and LCOE of 0.0456 $/kW e. The findings are valuable for enhancing energy utilization and reducing the power generation cost of SMRs. [ABSTRACT FROM AUTHOR]

In this paper, the concept of partial discharge shrouded impeller is proposed to enhance the performance of supercritical carbon dioxide (S-CO 2) centrifugal compressor under low flow rates, thereby increasing the overall efficiency of the S-CO 2 Brayton cycle. The influence mechanism of the partial discharge shrouded impeller on the flow behavior inside the impeller domain has been revealed by computational fluid dynamics (CFD) simulation. The results indicate a notable enhancement in the pressure ratio and isentropic efficiency of the S-CO 2 centrifugal compressor utilizing the best partial discharge shrouded impeller, showcasing improvements of 0.9% and 10.2% respectively under designed flow rate condition, while the stability parameter (S P) surpasses 0 at lower flow rates when compared to conventional impeller. With the partial discharge shrouded impeller, the flow separation on the blade pressure surface tends to occur nearer the impeller outlet, restricting the wake secondary flow shedding off to the diffuser, thus the flow loss being weakened. Meanwhile, with the optimized compressor by employing the best partial discharge shrouded impeller, the efficiency of S-CO 2 Brayton cycle has been increased by 5% relative to that with full discharge shrouded impeller. • A partial discharge shrouded impeller for S-CO 2 centrifugal compressor was proposed. • The compressor performance was improved by the partial discharge shrouded impeller. [ABSTRACT FROM AUTHOR]

• "SCTRAN/CO2-SIMULINK, a simulation platform, is developed and validated in this study." • Control systems are designed to regulate S-CO2 Brayton cycle-cooled reactor system during operational transients. • The control system uses integral time absolute error as the performance metric, minimized by a Real Coded Genetic Algorithm. • The control system's performance is tested using linear and abrupt load-following transients. The Supercritical CO 2 (S-CO 2) Brayton cycle-cooled nuclear reactor system is characterized by its high efficiency, small size, and ability to adapt to changes in load swiftly. The use of modern control methods to enhance its stability and efficiency necessitates using a simulation tool that enables their implementation. In this study, an integrated simulation platform, "SCTRAN/CO2-SIMULINK", is developed and verified. Various control systems are designed, and integral time absolute error is adopted as a performance metric for the analysis. A real-coded genetic algorithm is introduced to optimize the performance. The control system's performance is analyzed by applying linear load-following and abrupt load transients. Analysis of simulation results indicates that the developed platform enables the application of control and optimization methods from MATLAB/SIMULINK to S-CO2 Brayton cycle-cooled nuclear reactor system. Regulation of the inlet pressure of the reactor core is proposed in order to prevent it from pressure-induced strains during the transients. [ABSTRACT FROM AUTHOR]

• The dynamic analysis program for PCHE was developed based on the 1-dimensional discrete method. • The program can accurately describe the thermal inertia of the PCHE, the temperature error is less than 2 %, with a temperature error less than 2%. • The nonlinear changes in the physical properties of SCO 2 complicate the transient behavior of PCHE. • When the temperature or flow rate changes, the structural heat storage of PCHE cannot be ignored. • After bypass, PCHE loses nearly 10% of heat storage and experienced significant thermal shock. In order to improve the accuracy of dynamic simulation under limited time cost, the dynamic analysis program for SCO 2 Printed Circuit Heat Exchanger (PCHE) was developed based on the 1-dimensional (1-D) discrete method. The distribution of main thermodynamic parameters and physical properties along the channel are considered, and the calculated results are compared with the 3-D numerical simulation. The results showed that the program can accurately describe the thermal inertia of the heat exchanger, the temperature error is less than 2 %, and the heat transfer power error is only 3.16 %. The thermodynamic parameter field in the channel is complicated, which is attributed to the nonlinear change of the physical properties of SCO 2. The heat capacity of PCHE increases linearly with the increase of the hot side inlet temperature, but when the hot side mass flow rate exceeds 125 % of the rated value, the heat capacity increase rate decreases significantly. The temperature and mass flow fluctuation will lead to the mutual transfer between the PCHE structure heat storage and fluid energy. In addition, after the opening of the bypass valve, the PCHE loses nearly 10 % of its heat storage, and the significant deviation of the temperature field will lead to a large thermal shock. [ABSTRACT FROM AUTHOR]

For realizing efficient utilization of liquified natural gas cold energy and high‐temperature flue gas waste heat, herein, a combined cooling, heating, and power system using Peng–Robinson property package in Aspen HYSYS software, which includes a three‐stage parallel Rankine cycle (RC) in series with single‐stage RC and a supercritical CO2 (S‐CO2) Brayton cycle, is proposed. The system performance is evaluated using the first law of thermodynamics, second law of thermodynamics, specific energy costing method, and exergoenvironment analysis method. The influences of the pump 1 outlet pressure, turbine 3 inlet temperature, working fluid R23 mass flow rate, compressor 1 outlet pressure, CO2 liquefaction pressure, and ambient temperature on system performance are investigated. The nondominated sorting whale optimization algorithm and technique for order preference by similarity to ideal situation are applied to optimize the multiobjective system performance, and the payback periods of system before and after optimization are calculated. The analysis indicates that under the initial conditions, the thermal efficiency, exergy efficiency, total product unit cost, and sustainability index of the system are 41.68%, 48.50%, 112.293 $ GJ−1, and 1.75, respectively. After optimization, exergy efficiency increases by 2.4% and exergoeconomy decreases by 8.277 $ GJ−1. [ABSTRACT FROM AUTHOR]

Summary: The large‐scale penetration of renewable energy leads to some imperative issues to the power grid. Energy storage technology is regarded as an effective method to solve these problems. In this paper, a hybrid cogeneration energy system based on compressed air energy storage system with high temperature thermal energy storage and supercritical CO2 Brayton cycle is proposed. A thermodynamic model of the system is established. Energy and exergy analysis are carried out based on a case study. It was found that under the design condition, the round trip efficiency of 58.66%, the energy storage density of 5.45 kWh/m3, and the overall exergy efficiency of 62.00% can be achieved. At the same time, the hot water about 88°C can be supplied. The influences of some key parameters on the performance are analyzed. It was found that the round trip efficiency is most sensitive to the outlet temperature of high temperature thermal energy storage system, isentropic efficiency of compressors and turbines, followed by the intercoolers effectiveness. [ABSTRACT FROM AUTHOR]

The combination of supercritical carbon dioxide (SCO 2) Brayton cycle and microreactor is a promising technology. SCO 2 direct-cooled microreactor system takes advantages of compact system design and high efficiency, which can be applied in various scenes. Although the design SCO 2 Brayton cycle system is already compact, the control rods in reactor core still results in relatively large design size of the reactor. Considering relatively high negative temperature coefficient of reactor core and fast response characteristics of SCO 2 Brayton cycle, simplified control strategies are proposed in this paper to reduce the number of control rods in the reactor, thus decreasing the diameter of the reactor. Aimed towards the design of SCO 2 cooled floating nuclear power plant (SCFNP),the simplified control strategies are proposed. Then, adjustment ranges of system key parameters with different control strategies are simulated, and comparisons between them in various aspects are performed. According to the results, inventory control, shaft speed control and bypass valve control are proved to be able to adjust reactor power effectively instead of control rods. When applied shaft speed control and bypass valve control, system maximum temperature obviously exceeds the design temperature, which is about 12% and 20% respectively. What's more, inventory control and shaft speed control take about six times longer than bypass control to stabilized the system parameters. Besides, advantages and disadvantages are concluded of the three different control strategies, which can be used as reference of the control system design for SCO 2 direct-cooled microreactor system. • Transient characteristics of SCO 2 -cooled reactor system coupled with Brayton cycle are analyzed, which uses negative reactivity of reactor core to control the reactor power instead of control rods or drums. • The adjustment ranges of system key parameters are studied when applied different control strategies, and comparisons are made between the equipment with different initial parameters. • In transient process, maximum temperature and pressure change are analyzed to show system safety under different control strategies. • Three different control strategies are compared in various aspects, which thoroughly shows their advantages and weaknesses under the condition of PID automatic 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]

Central receiver concentrating solar power (CSP) plants based on particles as heat transfer fluid in solar circuits and supercritical CO 2 (S–CO 2) Brayton cycles can fulfil the requirements for next generation CSP to improve solar-to-electric efficiency and reduce energy storage costs. However, effective incorporation of these two concepts requires an in-depth understanding of their characteristics and an appropriate approach to match them. This paper addresses the importance of the design features and annualized performances of the optical subsystem (heliostat-receiver) and the thermal-to-electricity subsystem (solar receiver-energy storage-power block) on the global optimization of any integrated CSP plant. The analysis lies in a complete model of a particle-based CSP plant, which includes detailed modeling for the solar field, a cavity solar receiver with an up bubbling fluidized bed (UBFB) tubular panel, particles storage tanks and a recompression S–CO 2 Brayton cycle. The design incident irradiance on the receiver aperture (IR) and the particles temperature at the receiver outlet (T p) are identified as key parameters determining the solar-to-electric integration procedure and affecting the overall plant design and annual performance. Regarding subsystems located upstream and downstream of the receiver, the effects of heliostat and power block characteristics on the optimal IR and T p are also evaluated, represented by the heliostat beam quality and main compressor inlet temperature. Results show that IR around 1,200–1,500 W/m2 provides the maximum system design efficiency and annual efficiency. Improvements on heliostat beam quality and power block efficiency help to increase the optimal IR and overall system efficiency. In the optimal range of IR , increasing T p leads to higher system design efficiency, but lower system annual efficiency and annual electricity output. The optimal combination of IR and T p contributes to a minimum heliostat design area, representing the integration trade-off between the system optical and thermal characteristics. [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.

Supercritical CO2 Brayton cycle has high efficiency, compactness, and excellent power generation potential. In the design of the cycle, some parameters, such as recuperator pinch point temperature difference (ΔTrec,pp), turbine inlet temperature (Ttur,in), and maximum cycle pressure (pmax), are often preset without optimization. Furthermore, different preferences on efficiency and cost tradeoff can significantly affect the optimal design of the cycle, and the influence of different parameters on the design condition and the optimum cycle configuration becomes unclear as the preference changes. In this study, different preferences on efficiency and cost tradeoff are considered, and the effects of cycle configuration and optimization parameter addition on the tradeoff are investigated. In addition, four configurations under different preferences on tradeoff are recommended. Results show that the design condition parameters ΔTrec,pp decrease and Ttur,in and pmax increase as the preference of thermal efficiency (Wth) increases. Different optimized parameters affect the results of the design point and cycle performance. In addition, the simple recuperative cycle and reheating cycle are recommended when low cycle initial cost dominates (Wth<0.598), and the recompression cycle and intercooling cycle are recommended when high cycle thermal efficiency dominates (Wth>0.701). The decision maker can select appropriate configuration according to specific preferences. [ABSTRACT FROM AUTHOR]

• Solar thermal energy drives supercritical CO 2 cycle for power generation. • Solar-heated air supplies thermal energy to reduce electric demand of electrolysis. • No thermal energy storage is required. • Energy, exergy, and economic analyses are conducted to evaluate system performance. • Hydrogen is priced at 6.5 $/kg with a payback period of 20 years. Typical solar power tower (SPT) systems employ molten salt as the heat transfer and thermal energy storage medium to facilitate stable energy output. However, these systems are constrained by their limited operating temperature, which is insufficient to supply heat for high-temperature electrolysis. In this paper, a small-scale (2.5 MW) solar-thermal-assisted energy system with a SPT, a supercritical CO 2 (SCO 2) Brayton cycle, and solid oxide electrolysis/fuel cells (SOEC/SOFC) is proposed. With heat supply via air, the SOEC subsystem can operate at 800 ℃ to reach high energy efficiency and reduce electric demand, which replaces conventional waste heat from flue gas produced by fossil fuel combustion. Such a system can convert excess electricity into hydrogen for storage or sale and provides stable electricity 24 h a day. The key factors determining the system performance are investigated, including the turbine inlet parameters, main compressor inlet parameters, the recompression fraction of the SCO 2 subsystem, and the operating temperature and current density of the SOEC/SOFC subsystems. The case study shows that the net hydrogen output can reach 13365.4 kWh/d in summer with the SOEC operating at 800 ℃, which is 86.7 % higher compared to 7157.6 kWh/d when operating at 600 ℃. To recoup the investment costs by the 20th year, hydrogen must be priced at 6.5 $/kg. After multi-objective optimization, the optimal exergy efficiency and capital investment for the SPT-SCO 2 -SOEC subsystem are determined to be 29.6 % and 3.65 M$, respectively. For the SOFC subsystem, the corresponding figures are 56.1 % for exergy efficiency and 0.23 M$ for capital investment. This study benefits the solar power generation and hydrogen production by high-temperature electrolysis. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle (ORC) and supercritical CO 2 (sCO 2) Brayton cycle are two key and competition technology routes as the power cycle of Lead–Bismuth micro-reactor (LBMR). However, few studies focus on the comparison of thermodynamic and economic performance between ORCs and sCO 2 cycles in nuclear micro-reactor. The objectives in this study are to perform parameters analysis and techno-economic comparison in ORCs and sCO 2 cycles with various configurations as the power cycle of LBMR, so as to provide the technical support for the selection of power cycle and its operating conditions in different scenarios. Several high/low-temperature working fluids are screened for ORCs in view to achieve high net efficiency (η th) and low electricity production cost (EPC). Multi-objective optimization is performed to solve the trade-off between η th and EPC , and then to compare the comprehensive performance of various cycles from thermodynamic, compact and economic aspects. Results show that, the η th and EPC of ORCs are comparable or superior to that in sCO 2 cycles when the two cycles have similar structures (simple/regenerative). Among the ORCs, the cascade ORC with two-side regeneration using N -Dodecane/Pentane as working fluid pair has the best performance. In all cycles, recompression sCO 2 cycle performs best, but only when the heat source temperature is higher than 460 °C, the performance of the recompression sCO 2 cycle are overall better than the cascade ORC. • Techno-economic comparison of various power cycles for LBR are conducted. • Several high/low-temperature fluids are screened in different configurations of ORC. • N -Dodecane/Pentane is the best working fluid pair for the cascade ORC2. • The η net and EPC of ORCs are slight superior to sCO 2 cycles with similar structures. • The η net and EPC of recompression sCO 2 cycle are both better than ORC when t s > 460 °C. [ABSTRACT FROM AUTHOR]

• To analyze system level performances of Thermal Energy Storage and Hydrogen Energy Storage Systems. • To quantitatively study the energy storage systems coupled with applicable energy sources. • To objectively compare energy storage system performances for reliable and dispatchable renewable power supply. Utility scale energy storage is an integral part of renewable energy installations to achieve sustainable and reliable transition to a net zero energy economy. There exists a myriad of such storage solutions each having unique characteristics. This paper attempts at a systems level quantitative study and comparison between two different energy storage technologies, Thermal Energy Storage System (TESS) which is already mature, and Hydrogen Energy Storage System (HESS) which gained a lot of momentum recently, with the former coupled with a concentrated parabolic trough solar field using molten salt as heat transfer fluid and a power block running on high efficiency sCO 2 Brayton cycle while the latter is coupled with a solar photovoltaic (PV) field. So that comparisons can be made on similar scale, both the systems are normalized on the total equipment area used for capturing incident solar irradiation, i.e., total aperture area for the PTC field and total flat surface area of PV modules. Both the systems are subjected to year-long variations of ambient conditions and solar irradiance and off-design performances are simulated over various seasons. The results show superior performance of TESS in terms of roundtrip efficiency (96% as opposed to 32% with HESS) which also results in superior capacity utilization factor (CUF of 64.5% and 48% for TESS and HESS respectively) and better specific energy and energy density. However, HESS offers virtually infinite idling time where TESS has a shorter self-discharge time (17 h), and better power performance (specific power and power density) in 10MW e output range. [ABSTRACT FROM AUTHOR]

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]

• Introducing D-ARC and MED-TVC technologies to recover SOFC-GT unit waste heat. • Employing SCBC to facilitate the reliable operation of D-ARC and MED-TVC. • Achieving large-capacity cooling and freshwater supply while enabling power output. • Showing excellent thermodynamic performance compared to similar systems. • Evaluating its feasibility from energy, exergy, economic and environmental views. This study introduces the double-effect absorption refrigeration cycle (D-ARC) and multi-effect distillation with thermal vapor compression unit (MED-TVC) technologies to recover exhaust heat from the SOFC-GT system. This scheme can efficiently utilize waste heat at various temperature levels while enabling large-capacity cooling and freshwater production. The supercritical CO 2 Brayton cycle is employed to facilitate the reliable operation of D-ARC and MED-TVC within their preferred temperature zones while enhancing the power output of the entire system. The techno-economic-environmental evaluation, comparative analysis and sensitivity analysis are performed to explore the feasibility of its engineering implementation. The proposed system obtains thermal, exergic and electrical efficiencies of 78.56 %, 65.41 % and 65.77 % with the total cost rate being 18.53 $/h and freshwater production 829.30 ton/year under design conditions, respectively. Exergy analysis indicates that SOFC and afterburner exhibit the highest irreversibility with values of 21.60 kW and 26.02 kW among all the components. Comparative analysis reveals that the system has exceptional thermal efficiency while exhibiting competitive advantages in electrical and exergic efficiencies compared to similar systems. Sensitivity analysis demonstrates that the electrical efficiency and net power output stabilize at their respective maximum values within the SOFC inlet temperature range of 514.3℃-528.6℃. Moreover, it is a promising option by increasing SOFC operating pressure and GT isentropic efficiency to enhance system efficiency and reduce CO 2 emission. This work contributes to the development and waste heat recovery of the SOFC-GT system and other prime power units with similar exhaust gas temperature levels. [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.

Summary: A reheating process is generally incorporated in a supercritical CO2 (S‐CO2) Brayton cycle to enhance its efficiency. The heat transfer process from the reactor coolant to the working fluid of the power cycle is a key issue encountered when designing reheating power systems for the lead‐based reactor. The traditional reheating system, called RH‐1, utilizes an intermediate coolant circuit. In this paper, a novel reheating system, called RH‐2, is proposed. It eliminates the intermediate coolant circuit and combines the processes of the primary heating and reheating in a single heat exchanger. A thermodynamic analysis of three different systems for the lead‐based reactor integrated with the S‐CO2 power cycle with or without reheating was conducted to evaluate the performance of the proposed system. The results confirmed that the performance of RH‐2 was the best of all the three systems. Under the same reactor conditions, the system efficiency of RH‐2 was greater than those of RH‐1 and the recompression (no reheating) system by 1.2% and 1.7%, respectively. RH‐2 could also maintain higher efficiency when the main operating parameters varied. The efficiency of RH‐2 was higher at different core outlet temperatures and split ratios. The maximum efficiency at optimal maximum pressure of RH‐2 was greater than those of the other two systems. RH‐2 was less sensitive to the variations in the isentropic efficiencies of the components than the other two systems, while the turbine isentropic efficiency demonstrated a significantly higher impact on the system efficiency than the two compressors (approximately 3.8 times). [ABSTRACT FROM AUTHOR]

• A solar receiver for heating supercritical CO 2 is proposed. • The receiver possesses the advantages of both volumetric and tubular receivers. • The solar-thermal efficiency of ˜86.64% can be reached in the proposed receiver. • Volumetric absorption with active temperature regulation via circulating airflow is incorporated. In recent years, a great amount of attention has been focused on the study of combining the concentrating solar power (CSP) and supercritical CO 2 (s-CO 2) Brayton cycle, for it is a very promising way for clean energy utilization in the future. But its development is somewhat hindered by the lack of efficient solar receiver for s-CO 2 heating. The surface absorption of solar energy in current miniature tube receiver is becoming the main obstacle to further improve solar-thermal efficiency. In this work, efforts have been made to design a composite solar receiver by elaborating the advantages of high solar absorption of a volumetric receiver and the ability of withstanding high pressure of a miniature surface receiver. Meanwhile, the circulating air flow is used for regulating temperature of the whole absorber. This proposed receiver is constructed by porous media blocks and plate fin tubes layer by layer like a sandwich. Thus, the proposed solar receiver possesses the ability to accommodate high temperature, pressure, and solar flux. The calculated solar-thermal efficiency amounts to 93.7%, which is mainly attributed to the highly efficient capture of solar energy via volumetric absorption and reasonable temperature regulation by circulating airflow. This proposed receiver is expected to achieve high-efficiency heating of s-CO 2 and greatly boost the development of CSP and s-CO 2 Brayton cycle. [ABSTRACT FROM AUTHOR]

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]

Abstract Power generation from coal-fired power plants represents a major source of CO 2 emission into the atmosphere. Efficiency improvement and integration of carbon capture and storage (CCS) facilities have been recommended for reducing the amount of CO 2 emissions. The focus of this work was to evaluate the thermodynamic performance of s-CO 2 Brayton cycles coupled to coal-fired furnace and integrated with 90% post-combustion CO 2 capture. The modification of the s-CO 2 power plant for effective utilisation of the sensible heat in the flue gas was examined. Three bottoming s-CO 2 cycle layouts were investigated, which included a newly proposed single recuperator recompression cycle. The performances of the coal-fired s-CO 2 power plant with and without carbon capture were compared. Results for a 290 bar and 593 °C power cycle without CO 2 capture showed that the configuration with single recuperator recompression cycle as bottoming cycle has the highest plant net efficiency of 42.96% (Higher Heating Value). Without CO 2 capture, the efficiencies of the coal-fired s-CO 2 cycle plants were about 3.34–3.86% higher than the steam plant and about 0.68–1.31% higher with CO 2 capture. The findings so far underscored the promising potential of cascaded s-CO 2 power cycles for coal-fired power plant application. Graphical abstract Image Highlights • Supercritical CO 2 cycle was investigated for coal-fired power plant application. • Three s-CO 2 cycles were investigated as possible bottoming cycle options. • Integration of coal-fired plant with post-combustion CO 2 capture was studied. • Thermodynamic analysis and performance comparison were performed. [ABSTRACT FROM AUTHOR]

Turbine-based combined cycle (TBCC) engines are a promising system of hypersonic vehicles, the main problem being the thrust gap during propulsion. To solve this problem, we proposed a pre-cooling system of turbofan based on the supercritical carbon dioxide (sCO 2) Brayton cycle for TBCC engines fueled by hydrocarbon. A pre-cooler was set in the intake of the turbofan engine to achieve coupling between the Brayton cycle and the turbofan engine. The turbofan and Brayton cycle models were established, and several weight and limited cold source parameters were used to evaluate the system's performance. The effects of the inlet air temperature drop and pressure drop caused by the pre-cooler on the engine performance were obtained. The relationship between thermal performance and system weight of the sCO 2 Brayton cycle under different pre-cooling target temperatures and recuperated heat loads was also analyzed. The results showed that it is feasible to use sCO 2 to pre-cool the inlet air and generate power. When the pre-cooling target was set to Ma 2.2, the simple cycle could output 347 kW power with a power-to-weight ratio of 0.39 kW/kg. This study provides a new scheme for the pre-cooling and power generation technology of hydrocarbon-fueled TBCC engines. • A new scheme for the precooling and power generation of TBCC engines is provided. • Brayton cycle is proposed to address the thrust gap during propulsion. • The pre-cooling of the inlet air can maintain the gross thrust at the normal level • The Brayton cycle can output power to the aircraft while precooling the air. [ABSTRACT FROM AUTHOR]

• CO 2 seal experiments were conducted under super/trans-critical conditions. • Traditional theoretical models of seal were collected, derived and examined. • Temperature and specific heat ratio can result in large errors in calculation. • 3 models were recommended for CO 2 seal under super/trans-critical conditions. In the supercritical CO 2 Brayton cycle, dynamic sealing of rotating machines is one of the critical technologies. Under drastic variations of physical properties, the flow characteristics, sensitivity of parameters to leakage, and feasibility of theoretical models are not well understood. Experimental parameters of labyrinth seals include upstream parameters (302.15 K to 379.15 K, 7 MPa to 14 MPa) and pressure ratios (1.05 to 1.60, below the critical flow) covering trans-critical and pseudo-critical conditions. A comparison between experiments and traditional models leads to the following conclusions: In terms of linear correlation with the leakage, the upstream parameters in the density form are significantly superior to those in the temperature form. For the expansion factor part, the isentropic form can lead to errors ranging from -25% to 45%. In model prediction, the use of both temperature-based and isentropic-based parameters can result in significant prediction errors ranging from -41% to 67%. This paper recommends Martin's model with the density-based upstream parameters, the iterative isentropic model, and the Childs model, each with an error of ±10% or less. [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.

• Integrate solid oxide fuel cell with supercritical carbon dioxide Brayton cycle and CO 2 capture. • 60.96% of net electrical efficiency and 0.342 kg/kWh reducing CO 2 emission are achievable. • Develop detailed off-design models of components and system. • Investigate three key operating parameters' effects on system performance. • Propose system control strategy to investigate part-load system performance. Solid oxide fuel cell (SOFC) and supercritical carbon dioxide (sCO 2) Brayton cycle are both clean and efficient technologies for energy supply. The present study proposes an innovative SOFC-based system combined with sCO 2 Brayton cycle and CO 2 capture system. The bottoming sCO 2 cycle can improve efficiency of the integrated system by recovering waste heat from the combustion chamber while using oxy-fuel combustor to achieve low-energy CO 2 capture. And the quasi-steady model of the system is developed to evaluate the system design and off-design performances. The simulated results indicate that the net electrical efficiency and reducing CO 2 emission of the system are 60.96% and 0.342 kg/kWh, respectively. The system parametric analysis indicates that the reasonable recirculation ratio, fuel utilization and fuel flow rate are prerequisites for the safe and efficient operation of the integrated system. Based on the analysis, a system control strategy is proposed to satisfy the demand for wide-range load adjustment (30%-100%), while the efficiency of the integrated system is decreased from 60.96% to 50.33% during the load reduction process. [ABSTRACT FROM AUTHOR]

Combined system based on supercritical CO 2 Brayton cycle exhibits great potential to recover waste heat from engine. However, the effective utilization of waste heat from jacket water along with that from engine exhaust still remains a challenge, owing to the heat load mismatching of different heat sources. In this paper, a novel combined cooling and power (CCP) system, comprised of a topping supercritical CO 2 Brayton cycle and a bottoming transcritical CCP cycle using CO 2 -based mixture, is proposed to realize the heat recovery of both engine exhaust and jacket water. Detailed parametric analysis is conducted to study the effect of seven key parameters on system performance from thermodynamic, economic and environmental viewpoints. Thereafter, a multi-objective optimization is performed to explore the performance improvement potential. The results show that the increasing turbine Ⅰ inlet pressure and the decreasing compressor inlet temperature are conductive to all performances. Through multi-objective optimization, the optimal thermal efficiency, cost rate per unit of exergy output and environment impact per unit of exergy output are 38.42%, 0.0529$/kWh and 0.0762mPts/kWh, respectively. Under optimal conditions, the maximum net power output of the system could achieve 384.64 kW, accounting for 13.14% of the engine output, with a cooling capacity output of 268.35 kW. • A combined cooling and power system was proposed for engine waste heat recovery. • Thermodynamic, economic and environmental analysis was conducted. • Multi-objective optimization by means of NSGA-Ⅱ was carried out. [ABSTRACT FROM AUTHOR]

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.

CO 2 capture from coal-fired power plants (CFPP) with low cost is crucial for China to achieve carbon peaks in 2030. The manuscript proposes a novel combined cycle of supercritical CO 2 Brayton cycle (SCBC) and organic Rankine cycle (ORC) in CFPP with CO 2 capture. The novelty of the proposed scheme lies on its high-level thermal integration which can efficiently complete the conversion of heat to electricity, waste heat recovery, and CO 2 capture. Exergy analysis and levelized cost of electricity (LCOE) are employed to respectively evaluate the thermodynamic and economic performance. The simulation results show that the exergy efficiency of the combined cycle is 39.74% as considering CO 2 capture, resulting in a 3.41% of efficiency penalty. The introduction of ORC improves the exergy efficiency by 1.05%. The LCOE of the combined cycle is 79.03$/MWh, almost 19.3$/MWh (32.29%) more expensive than the base plant, and the costs of CO 2 captured and avoided are respectively 21.81$/tCO 2 and 26.25$/tCO 2. The results indicate that the proposed combined cycle has the potential to compete with other carbon capture technologies from the views of exergy efficiency and cost. Coal combustion in the S–CO 2 boiler and the calciner is responsible for the maximum internal exergy destructions, and increasing the cycle maximum temperature may reduce the exergy destruction. The largest cost contributor to LCOE is associated with capital expenditures (41.55%), and the cost reduction efforts should be aimed at capital expenditures. • The highly integrated combined cycle of SCBC and ORC is proposed for power generation with CO 2 capture. • The exergy efficiency penalty arising from CO 2 capture is 3.41% for the proposed scheme. • The introduction of ORC for heat recovery improves exergy efficiency by 1.05%. • The CO 2 capture cost of the proposed combined cycle is 21.81$/t. • The largest cost contributor to LCOE is associated with capital expenditures (41.55%). [ABSTRACT FROM AUTHOR]