Annual performance of a calcium looping thermochemical energy storage with sCO2 Brayton cycle in a solar power tower

The aim of this study was to conduct thermodynamic and economic analyses of a concentrated solar power (CSP) plant to drive a supercritical CO2 recompression Brayton cycle. The objectives were to assess the system viability in a location of moderate-to-high-temperature solar availability to sCO2 power block during the day and to investigate the role of thermal energy storage with 4, 8, 12, and 16 h of storage to increase the solar share and the yearly energy generating capacity. A case study of system optimization and evaluation is presented in a city in Saudi Arabia (Riyadh). To achieve the highest energy production per unit cost, the heliostat geometry field design integrated with a sCO2 Brayton cycle with a molten-salt thermal energy storage (TES) dispatch system and the corresponding operating parameters are optimized. A solar power tower (SPT) is a type of CSP system that is of particular interest in this research because it can operate at relatively high temperatures. The present SPT-TES field comprises of heliostat field mirrors, a solar tower, a receiver, heat exchangers, and two molten-salt TES tanks. The main thermoeconomic indicators are the capacity factor and the levelized cost of electricity (LCOE). The research findings indicate that SPT-TES with a supercritical CO2 power cycle is economically viable with 12 h thermal storage using molten salt. The results also show that integrating 12 h-TES with an SPT has a high positive impact on the capacity factor of 60% at the optimum LCOE of $0.1078/kW h.

Supercritical carbon dioxide (sCO2) Brayton cycle is a promising technology for concentrating solar power systems. However, existing studies predominantly rely on steady-state or quasi-steady-state assumptions, thereby neglecting transient characteristics of fluid flow and heat transfer. This study develops a transient analysis program for solar power tower systems integrated with sCO2 Brayton cycles using the finite difference method. The program comprises two interactive modules—a molten salt loop and a Brayton cycle module—coupled through an intermediate heat exchanger. For the Brayton cycle module, a fluid network model enabling a unified framework for the simultaneous solution of all governing equations is adopted. The SIMPLE algorithm and Gauss–Seidel iteration method are employed to solve the conservation equations. Following validation of key components and system performance, dynamic simulations under load and solar irradiance step disturbances are conducted. The results demonstrate that the program accurately captures transient behaviors and supports control strategy design and safety analysis for solar power tower systems with arbitrary sCO2 Brayton cycle layouts.

Although a number of power conversion applications have been identified or have even been developed (e.g., waste heat recovery) for supercritical carbon dioxide (S-CO2) cycles including fossil fuel combustors, concentrated solar power (i.e., solar power towers), and marine propulsion, the benefits of S-CO2 Brayton cycle power conversion are especially prominent for applications to nuclear power reactors. In particular, the S-CO2 Brayton cycle is well matched to the Sodium-Cooled Fast Reactor (SFR) nuclear power reactor system and offers significant benefits for SFRs. The recompression closed Brayton cycle is highly recuperated and wants to operate with an approximate optimal S-CO2 temperature rise in the sodium-to-CO2 heat exchangers of about 150 °C which is well matched to the sodium temperature rise through the core that is also about 150 °C. Use of the S-CO2 Brayton cycle eliminates sodium-water reactions and can reduce the nuclear power plant cost per unit electrical power. A conceptual design of an optimized S-CO2 Brayton cycle power converter and supporting systems has been developed for the Advanced Fast Reactor – 100 (AFR-100) 100 MWe-class (250 MWt) SFR Small Modular Reactor (SMR). The AFR-100 is under ongoing development at Argonne National Laboratory (ANL) to target emerging markets where a clean, secure, and stable source of electricity is required but a large-scale power plant cannot be accommodated. The S-CO2 Brayton cycle components and cycle conditions were optimized to minimize the power plant cost per unit electrical power (i.e., $/kWe). For a core outlet temperature of 550 °C and turbine inlet temperature of 517 °C, a cycle efficiency of 42.3 % is calculated that exceeds that obtained with a traditional superheated steam cycle by one percentage point or more. A normal shutdown heat removal system incorporating a pressurized pumped S-CO2 loop slightly above the critical pressure on each of the two intermediate sodium loops has been developed to remove heat from the reactor when the power converter is shut down. Three-dimensional layouts of S-CO2 Brayton cycle power converter and shutdown heat removal components and piping have been determined and three-dimensional CAD drawings prepared. The S-CO2 Brayton cycle power converter is found to have a small footprint reducing the space requirements for components and systems inside of both the turbine generator building and reactor building. The results continue to validate earlier notions about the benefits of S-CO2 Brayton cycle power conversion for SFRs including higher efficiency, improved economics, elimination of sodium-water reactions, load following, and smaller footprint.

Novel design optimization of concentrated solar power plant with S-CO2 Brayton cycle based on annual off-design performance

Thermodynamic analysis and comparison for different direct-heated supercritical CO2 Brayton cycles integrated into a solar thermal power tower system

Cogeneration using multi-effect distillation and a solar-powered supercritical carbon dioxide Brayton cycle

Concentrating solar power (CSP) technology, possessing an inherent capacity to couple with energy storage ideally, attracts a great deal of attention nowadays. However, these power plants with various types of CSP system still cannot compete with the traditional thermal power plants in terms of levelized cost of electricity (LCOE), and their potential for utilizing clear and renewable solar energy cannot be overestimated. To improve the total efficiency of the solar power tower (SPT) plant is the key factor for its development. In this present paper, a SPT plant based on an S-CO2 Brayton cycle (with S-CO2 serving as heat transfer and working fluid) is proposed. A numerical simulation is carried out to calculate the effects of key operating parameters, including power cycle and subsystem parameters, on the overall performance of the SPT plant. The results show that there is an optimum value for the compression ratio for the SPT plant. For the heat receiver, the trends of exergy and thermal efficiency varying with turbine inlet temperature are reversed, because of the significant energy loss caused by high temperature of the surface of the heat receiver. As for the overall performance, the SPT plant proposed in this paper is better than other SPT plants based on a steam Rankine system and an S-CO2 Brayton system with molten salt serving as heat transfer fluid (HTF) operating under the similar condition. Its overall thermal efficiency is 1.04% and 3.42% higher than that of two other SPT plants, respectively.

Performance and parameter sensitivity comparison of CSP power cycles under wide solar energy temperature ranges and multiple working conditions

Performance evaluation of a co-production system of solar thermal power generation and seawater desalination

Increasing global energy consumption and greater market penetration of intermittent energy sources require a baseline power source to enable renewable energies. Here, a case is made for pairing supercritical CO2 Brayton cycles with carbon capture to create low-emission, high-efficiency, combustion-based power generation systems. Pairing carbon capture and storage (CCS) systems with supercritical carbon dioxide (sCO2) Brayton cycles enables the reduction of greenhouse gas emissions in combustion systems, but with an associated energy cost. Three different representative models of CCS systems (oxyfuel combustion, amine scrubbing, and cryogenic carbon capture) are considered for pairing with an sCO2 Brayton cycle, each with assumed capture efficiency between 87% and 90%. Integrated models of supercritical CO2 Brayton cycles with CCS are used to predict the thermal efficiency of each combined system utilizing the process modeling software steamgen expert. The recompression sCO2 Brayton cycle exhibits thermal efficiencies in the range of 44–52%. When integrated with a cryogenic CCS system, the combined system demonstrated a nominal thermal efficiency of 39.1% with the potential to achieve 34–46%. Similarly, for oxyfuel combustion or amine scrubbing, the range of expected thermal efficiencies is 26–39% and 28–40%, respectively. The upper limits for these ranges represent a best-case scenario for aggressive operating conditions of the sCO2 Brayton cycle. CCS systems provide a CO2 source stream for operating the sCO2 Brayton cycle with other energy sources, including nuclear and solar. Additionally, the combined system has the potential to reach carbon negativity when paired with biomass combustion.

In 2005, Hohai university and Nanjing Chunhui science & technology Ltd. of China, cooperating with Weizmann Instituted of Science and EDIG Ltd. of Israel, built up a 70kWe solar power tower test plant in Nanjing, Jiangsu province, China, which was regarded as the first demonstration project to demonstrate the feasibility of solar power tower system in China. The system consists of heliostats field providing concentrated sunlight, a solar tower with a height of 33 meter, a pressured cavity-air-receiver transforming solar energy to thermal energy, a modified gas turbine adapting to solar power system, natural gas subsystem for solar-hybrid generation, cooling water subsystem for receiver and CPC, controlling subsystem for whole plant, et al.. In this system, air acts as actuating medium and the system works in Brayton cycle. Testing results show that solar power tower system is feasible in China. To promote the development of solar powered gas turbine system and the pressured cavity-air-receiver technology in China, it is necessary to study the mechanical design for pressured Cavity-air-receiver. Mechanical design of pressured cavity-air-receiver is underway and some tentative principles for pressured cavity-air-receiver design, involving in power matching, thermal efficiency, material choosing, and equipment security and machining ability, are presented. At the same time, simplified method and process adapted to engineering application for the mechanical design of pressured cavity-air-receiver are discussed too. Furthermore, some design parameters and appearance of a test sample of pressured cavity-air-receiver designed in this way is shown. It is appealed that, in China, the research in this field should be intensified and independent knowledge patents for pivotal technological equipments such as receiver in solar power tower system should be formed.

The supercritical carbon dioxide (sCO2) Brayton cycle is a promising candidate for future nuclear reactors due to its ability to improve power cycle energy conversion efficiency. The sCO2 Brayton cycle can operate with an efficiency of 45-50% at operating temperatures of 550-700 C. One of the greatest hurdles currently faced by sCO2 Brayton cycles is the corrosivity of sCO2 and the lack of long-term alloy corrosion and mechanical performance data, as these will be key to enhancing the longevity of the system, and thus the levelized cost of electricity. Past studies have shown that sCO2 corrosion occurs through the formation of metal carbonates, oxide layers, and carburization, and alloys with Cr, Mo and Ni generally exhibit less corrosion. While stainless steels may offer sufficient corrosion resistance at the lower range of temperatures seen by the sCO2 Brayton cycles, more expensive nickel-based alloys are typically needed for the higher temperature regions. This study investigates the effects of corrosion on the Haynes 230 alloy, with a preliminary view on changes in the mechanical properties. High temperature CO2 is used for this study as the corrosion products are similar to that of supercritical CO2, allowing for an estimation of the susceptibility towards corrosion without the need for high pressure experimentation.

Techno-economic assessment and optimization of the performance of solar power tower plant in Egypt's climate conditions

Thermal desalination via supercritical CO2 Brayton cycle: Optimal system design and techno-economic analysis without reduction in cycle efficiency

Thermodynamic and economic assessment of a new generation of subcritical and supercritical solar power towers