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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]

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]

• 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]

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]

• 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]

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]

• A novel combined cooling and power (CCP) system is proposed. • The effective efficiency of the CCP system is up to 0.42. • The heat exchanger has small exergy destruction because of good temperature match. • The CCP system is more stable and efficient than the conventional CCP system. • R1234ze is a good choice for a high thermal efficiency and low environment impact. This paper presents a novel combined cooling and power (CCP) system that integrates a supercritical CO 2 Brayton (sCO 2) cycle and a transcritical ejector refrigeration cycle. The two cycles are combined by a heat exchanger wherein heat is exchanged between CO 2 and the refrigerant at supercritical pressures to reduce exergy destruction and improve system performance. A thermodynamic model was established to simulate the CCP system based on energy and exergy balance equations. The transcritical ejector model was validated with experimental and literature data. The performance of the system was studied for different CO 2 mass flow rates, turbine inlet temperatures, turbine inlet pressures, turbine outlet pressures, and pump outlet pressures. The thermal, exergy, and effective efficiencies of the CCP system were compared with those of a combined cooling and power system (CCP_ab) that uses a single-effect absorption refrigeration cycle. The CCP system maximum thermal efficiencies of four refrigerants— R 32, R134a, R1234yf, and R1234ze—were obtained using a genetic algorithm. The results show that the major components that contribute in exergy destruction are internal heat exchanger, ejector, compressor and turbine, and the heat exchanger has small exergy destruction because of a good variable-temperature match between the supercritical pressure refrigerant and supercritical pressure CO 2. The effective efficiency of the CCP system reaches 0.42 at turbine inlet temperature of 873.15 K. The CCP system is more stable and efficient than the CCP_ab system in varying conditions. The CCP system with R 32 has the highest thermal efficiency. R1234ze with relatively high thermal efficiency and low Global Warming Potential is a good choice in the future as it is environmentally friendly. [ABSTRACT FROM AUTHOR]

The supercritical CO 2 (S–CO 2) Brayton cycle is considered a promising power generation system owing to its high efficiency and compactness. This cycle has numerous layouts which have been extensively investigated for design condition performance, whereas it often operates under part-load conditions, Therefore, it is vital to compare layouts based on part-load performance. Because part-load performance is influenced by control strategies and layout elements such as recompression, reheating, and intercooling processes, the part-load performance of four typical S–CO 2 Brayton cycles including simple recuperated cycle, recompression cycle, reheating cycle, and intercooling cycle with different control strategies are explored using dynamic models. The results indicated that the thermal efficiency of the four layouts was simultaneously influenced by the layouts and control strategies. Safety performance is mainly determined by the control strategies. Moreover, when the turbine bypass valve and inventory are adopted to follow the load, the intercooling cycle overtakes the reheating cycle to attain the maximum thermal efficiency at low and medium loads. There was no overpressure or surge for the four layouts with the necessary controllers. However, when using bypass valves following the load, the four layouts are at risk of operating with overloaded drive motors at low loads. This is beneficial for guiding the selection of layouts and corresponding control strategies in different operation scenarios. • Dynamic models of four SCBC layouts are developed. • Part-load performance of four SCBC layouts are compared. • Thermal efficiency is influenced by layouts and control strategies simultaneously. • Intercooling cycle with inventory control should be preferred at low and medium loads. [ABSTRACT FROM AUTHOR]

[Display omitted] • A method that integrates parametric and graphical analysis of cycles is proposed. • Three basic logical operations in the flexible programming of cycles are identified. • A complex cycle can be decomposed into several simple cycles using this method. • Parametric analyses of complex cycles only need physical models of simple cycles. • The method provides a new perspective to easily understand complex cycles. A growing number of complex thermodynamic cycles, such as different configurations of supercritical carbon dioxide (sCO 2) Brayton cycles, have been recently proposed. However, the understanding and analysis of complex cycles are very arduous and time-consuming, due to the lack of a general theory for cycle analysis and numerous equations included in physical models of cycles. To address these challenges, a novel method named the flexible programming of thermodynamic cycles (FPTC) is developed based on the graphical analysis in the T-s diagram. Within the theoretical framework of the FPTC, the complex cycle can be obtained by performing logical operations of several simple cycles in the T-s diagram. Meanwhile, the type of logical operation also determines the relationship of the thermodynamic performance indexes (heat input, heat output, net-work output, and thermal efficiency) between the synthetic complex cycle and simple cycles. There are three basic types of logical operation (addition, subtraction, and interchange) in the FPTC, and the detailed rules in each logical operation are presented by using the Carnot cycle as the basic simple cycle. In the case study, four different configurations of sCO 2 Brayton cycles are analyzed using the FPTC, and their evolutions from simple Brayton cycles to complex are shown. Meanwhile, the thermal efficiencies of different configurations can be calculated by efficiency formulas obtained from the FPTC. Results show this case analysis is an efficient approach to analyze complex cycles. The FPTC is not only a graphical analysis method to study the evolution of complex cycles, but also provides a simple method to calculate the performance of synthetic complex cycles. It allows researchers to evaluate the performance of synthetic cycles by physical models of simple cycles, instead of building physical models for complex cycles. Furthermore, the FPTC also provides a new perspective for constructing or designing complex thermodynamic cycles. [ABSTRACT FROM AUTHOR]

• A novel waste heat recovery system is proposed based on WTE plant. • A comprehensive thermodynamic analysis of the system is conducted. • Based on NPV, the dynamic payback period of new WTE plant is studied. • Sensitivity analysis as well as multi-objective optimization are employed. • The system levelized cost of electricity and ecological efficiency are studied. Owning to its advantage in waste reuse, waste-to-energy technology, has become the most popular way to deal with the increasingly municipal solid waste. However, the energy efficiency of waste-to-energy plant is limited because of the huge heat loss. In this study, a novel waste heat recovery system, consisting of a supercritical CO 2 cycle, an organic Rankine cycle, and an absorption refrigeration cycle, is proposed to improve both the thermal efficiency and economic performance of the waste-to-energy plant. A comprehensive thermodynamic analysis is performed to study the energy and exergy efficiency of the system by establishing a reliable mathematical model. Net present value analysis is carried out to study the final net profit and dynamic investment payback period. Besides, the levelized cost of electricity and ecological efficiency of the waste-to-energy plant are investigated. Based on the results of parameter sensitivity analysis of the system, multiple objective optimizations is carried out by using non-dominated sorting genetic algorithm-II. The results show that the combined system obtains the highest economic benefit in winter. The energy efficiency of the waste-to-energy plant can be up to 75.07% after adding the waste heat recovery system, with an increment of 54.58%. And the maximum net present value and minimum dynamic payback period are 23.22 M$ and 4.11 years, separately. Compared with the original waste-to-energy plant, the levelized cost of electricity and ecological efficiency are decreased by 68% and increased by 16%, respectively. From the results of sensitivity analysis, the isentropic efficiency of turbine of supercritical CO 2 cycle, the evaporator pressure of organic Rankine cycle, and the generator temperature of absorption refrigeration cycle are the most sensitive factors for the thermal efficiency and economic performance of the system. The exergy destruction analysis shows that the exergy destruction rate of the boiler declines to 48.41% after adding the waste heat recovery system, but the condensers need further improvement for their lowest exergy efficiency. In conclusion, the waste-to-energy plant can provide electricity, heating and cooling simultaneously after adding the waste heat recovery system and the proposed system is theoretically feasible from the results of thermodynamic, economic and environmental analysis. [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]

• S-CO 2 Brayton cycle has the highest efficiency for 500–1000 °C solar temperatures. • The lowest P tur_in of the cycle for ' η max -1%' is much lower than P tur_in for η max. • S-CO 2 Brayton cycle is severely undervalued if P tur_in is restricted to 30 MPa. • Air Brayton cycle does not need high P tur_in but 6% lower than s-CO 2 efficiency. • Sensitivity to η tur is air Brayton cycle > steam Rankine cycle > s-CO 2 Brayton cycle. Concentrated solar power (CSP) is an important way for solar energy utilization, and the efficient solar energy utilization is closely related to a reasonable power cycle. The comparative analysis of the steam Rankine cycle, supercritical CO 2 (s-CO 2) Brayton cycle and air Brayton cycle is always with a particular heat source, working parameter and working condition. However, the solar energy for CSP has a wide temperature range from 250 to 1000 °C and the energy conversion potential of the cycles varies obviously under different heat source temperatures. The maximum pressure of the working condition restricts the cycle energy conversion potential especially for s-CO 2 Brayton cycle. The isentropic efficiency settings severely influence on the cycle comparison results. Therefore, in this work, the energy conversion mechanism and potential of the three types of cycles under a wide solar energy temperature ranges are revealed by optimized with multi-operating conditions. The sensitivity of each cycle to the high working pressure and irreversible processes are analyzed. Results show that, achieving the highest efficiency η max often means an extremely high working pressure. However, the lowest P tur_in to keep relatively high efficiency (higher than ' η max -1%') can be much lower than that of the maximum efficiency. S-CO 2 Brayton cycle has the absolutely highest cycle thermal efficiency when the turbine inlet temperature is higher than 500 °C and the least sensitive to the turbine isentropic efficiency. However, s-CO 2 Brayton cycle is the most dependent on high turbine inlet pressure and the energy conversion potential of s-CO 2 Brayton cycle is severely undervalued if the working pressure is restricted to 20 MPa or 30 MPa. The air Brayton cycle efficiency keeps around 6% lower than the s-CO 2 Brayton cycle at the same turbine inlet temperature and exceed the steam Rankine cycle when the turbine inlet temperature is higher than 750 °C. The air Brayton cycle has the least dependence on high working pressure, however, it is most affected by the non-ideality of expansion and compression processes. [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]