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Abstract The potential to improve the performance of molten salt solar power tower system (SPT) is explored through the proposal of CO 2 -based binary mixture cycle in the present study. The feasibility of using xenon and butane as the additives to the S-CO 2 cycle are discussed from the perspective of thermodynamic analysis. The detail parametric study is performed to reveal the effects of crucial parameters on the performance of 4 system configurations. Furthermore, the systematic comparison is conducted for 4 cycle layouts adopting CO 2 /xenon, CO 2 and CO 2 /butane separately to illustrate the mechanism of performance improvement of SPT system coupled to CO 2 -based binary mixture cycle. The optimal performance of the SPT system is also demonstrated. Finally, the best performance system layout and suitable additives are recommended. The results indicate the following issues. Adding xenon into S-CO 2 cycle can obviously improve the overall thermal efficiency and exergy efficiency. While the effects of butane as an additive are converse. The inter-cooling CO 2 /xenon cycle is recommended as the most suitable layout coupled to the SPT system, and the exergy efficiency is 1.18%∼1.32% higher than that of the SPT system with S-CO 2 inter-cooling cycle. Detail exergy loss fraction distribution illustrates that the receiver is the highest exergy loss part and followed by the heliostat field, and butane as an additive is beneficial to reduce the receiver exergy loss for its smaller temperature difference. The study can provide a novel way to improve the SPT system performance and give a clue to the addition of CO 2 -based binary mixture in power cycles particularly for the application of SPT system. Highlights • Improvement on SPT performance is explored via using CO 2 -based mixture cycle. • Effects of key parameters on SPT with various CO 2 -based mixture cycle are analyzed. • Systematic comparison of different system layouts is performed. • Optimal additive and cycle configuration are recommended for SPT. [ABSTRACT FROM AUTHOR]

• The energy-exergy-economic (3E) model is developed for S-CO 2 coal-fired system. • The layout of water-cooling wall is optimized for large scale S-CO 2 power plant. • The effect of inter-cooling process on performance of component is revealed. • Preliminarily conceptual design of the crucial components is proposed. The conceptual design and systematic comparison of S-CO 2 coal-fired power generation systems are performed in the viewpoint of the thermodynamic analysis and economic assessment to promote the practical application in the industry. First, the differences between the conventional steam boiler and S-CO 2 boiler are pointed out. 3 layouts of the water-cooling wall are compared in the aspect of the hydrodynamic characteristic and structural parameters to select the suitable one coupled to the S-CO 2 cycles. Based on the optimized water-cooling wall layout, the energy, exergy and economic analysis models of the integrated S-CO 2 coal-fired power systems are further developed. Finally, the mechanism of the inter-cooling thermodynamic process to improve the system performance is investigated and the distribution of the individual irreversibility is given. The systematic comparison is performed among 3 configurations of S-CO 2 coal-fired power plants with consideration of the thermo-economic performance. The conceptual design of key components is also provided. The results demonstrate that the S-CO 2 boiler is fatter due to 8 times larger mass flow rate of working fluid than the conventional steam boiler. The layout of water-cooling wall with the split flow strategy and vertical tubes is helpful in compacting the scale of the boiler for its less diameter and number of tubes, and its thermal efficiency is higher than that of other layouts. Among the 3 S-CO 2 cycle layouts studied, the S-CO 2 coal-fired power system with the inter-cooling cycle yields highest efficiency and is the most economic configuration. The thermal efficiency of the S-CO 2 coal-fired power plant composing the inter-cooling cycle is 47.69–49.09% with total thermal conductance of recuperators changed from 120 MW·K−1 to 180 MW·K−1 when the turbine inlet parameters are 620 °C/620 °C/30 MPa, and displays an advantage over the ultra-supercritical steam Rankine power plant. The system levelized cost of electricity is 0.0397 $·(kW·h)−1 and shows great commercial potential. The detailed discussion of this study is beneficial to a comprehensive understanding of various S-CO 2 coal-fired power systems and provide a clue to establish a practical power plant for the application of coal-fired industry. [ABSTRACT FROM AUTHOR]

• Effects of key parameters on performance of CO 2 -based mixture cycles are revealed. • Comprehensive performance evaluation method is proposed based on η exe, SPT - w -Δ T MH. • Trade-off relations for 3 performance metrics are found based on Pareto fronts. • Optimal cycle configuration, operating parameters and additive are recommended. This study provides an exploration on improving the performance of solar power tower (SPT) plant via integrating with the CO 2 -based mixture Brayton cycle, and proposes a comprehensive comparison method. The effects of the crucial parameters on the SPT system are firstly revealed. Then, a comprehensive evaluation method is proposed based on 3 performance metrics including exergy efficiency, specific work and temperature difference of the main-heater, which are used to assess the thermodynamic performance and the compatibility between the thermal storage system and power cycle. Finally, the trade-off relationships of these metrics are found. The optimal layout, additive and operating parameters are also pointed out based on the comparative results to meet different design requirements. The findings show that the effects of crucial parameters on the performance of SPT system are not monotonous and individual criterion cannot comprehensively evaluate the system performance. Using xenon as an additive can yield excellent performance with higher exergy efficiency and better compatibility between cycle and thermal storage system than the CO 2 alone. While the ability to generate specific work is decreased to 105–112 kW·kg−1 with xenon-added that compares to the inter-cooling S-CO 2 cycle (121–130 kW·kg−1). When the exergy efficiency is required higher than 33%, the inter-cooling CO 2 /xenon cycle is the primarily recommended layout for its large specific work and good compatibility between the thermal storage system and cycle. The findings provide a novel way to improve the efficiency of SPT system as well as the compatibility between the cycle and thermal storage system. [ABSTRACT FROM AUTHOR]

Supercritical CO 2 (S-CO 2 ) Brayton cycles are recently proposed to be integrated into the solar power tower (SPT) due to their high efficiency and compactness. Comparison of different S-CO 2 Brayton cycle layouts is of great significance for selecting a suitable one in the SPT plant. Both of the efficiency and specific work are important performance criteria for the SPT plant. However, previous studies compared only one individual criterion, or both of them just separately. This paper puts forward a systematic comparison of different S-CO 2 Brayton cycle layouts based on multi-objective optimizations. The two performance criteria are compared simultaneously between different S-CO 2 cycle layouts by comparing the Pareto optimal fronts obtained from multi-objective optimizations. The results suggest that the inter-cooling cycle layout and the partial-cooling cycle layout can generally yield the most excellent performances, and followed by the recompression cycle layout and the pre-compression cycle layout, while the simple recuperation cycle layout has the worst performances. The advantages of the partial-cooling cycle layout and the inter-cooling cycle layout are more prominent compared with the other cycle layouts in the case of high compressor inlet temperature. The provided systematic comparison can be helpful in selecting the most suitable cycle layout for the application in SPT when there are specified requirements for the efficiency and the specific work. In addition, novel salts with high upper limit temperature (higher than 650 °C) are recommended to be developed as the heat transfer fluid for improving system performances. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive study of thermo-economic analysis and practical conceptual design of miniaturized lead-cooled fast reactor (LFR) composing supercritical CO 2 power cycle is proposed in order to promote the real application in the market. The thermodynamic model and economic model are established based on the following five supercritical CO 2 (S-CO 2) Brayton cycles integrating with the miniaturized LFR, separately. Moreover, the optimization algorithm is adopted to optimize the key parameters of five power cycles with the objectives of maximizing the system thermoelectric conversion efficiency and electricity production costs (EPC) simultaneously. The optimal cycle and optimum parameters are obtained for the integrated system. Furthermore, the structural parameters of key components are confirmed based on the above results. The main subsidiary systems are designed. Finally, the practical design of LFR composing S-CO 2 power cycle is carried out. The results shown that various parameters have different effects on the thermodynamic-economic performance of the system. The higher inlet temperature of turbine is beneficial to improve both thermodynamic and economic performance of the system. With the ƞ t,sys -EPC analyzed simultaneously, the recompression cycle is the optimal to operate with more working conditions. Its ƞ t,sys is from 36.68% to 44.46%, and EPC is from 0.050 $·kW−1·h−1 to 0.055 $·kW−1·h−1). [ABSTRACT FROM AUTHOR]

In this perspective paper, the present status and development tendency of concentrating solar power (CSP) are analyzed from two aspects: (1) Potential pathways to efficient CSP through improving operation temperature to above 700 °C; (2) Technologies for efficient solar collection, thermal storage, and power generation at >700 °C. Based on the analyses, barriers on the way to the high-temperature CSP are summarized. They are: (1) the lack of methodology for heliostat design and field layout optimization, (2) significant performance degradations of solar-thermal conversion, heat storage and transfer in receiver and thermal energy storage due to high temperature, (3) the lack of suitable supercritical CO 2 (S–CO 2) Brayton cycle for CSP and mature design methods for S–CO 2 components. To overcome these issues, perspectives on following three aspects are proposed. Firstly, optimization approaches for optimal heliostat size and layout, and game-changing techniques for heliostat structure design should be brainstormed. Secondly, receivers and thermal storage devices designed through efficiency-improving approaches and fabricated by durable materials should be developed to maintain efficient and reliable operation. Thirdly, the developments of novel S–CO 2 cycle and corresponding key components are eagerly desired to achieve efficient thermal-electric conversion. Perspectives from this paper would present possible approaches to efficient CSP. • Present status and perspectives of concentrating solar power are analyzed. • Approaches to optimal heliostat size, structure, and layout shall be brainstormed. • Efficient high-temperature receivers and heat storage devices shall be developed. • Developments of novel S–CO 2 cycle and its key components are eagerly desired. [ABSTRACT FROM AUTHOR]