Latest ArticlesCurrent researches on advanced adiabatic compressed air energy storage (AA-CAES) systems primarily focus on optimizing designs and analyzing performance under off-design conditions based on fixed system structures, with limited attention to system-level optimization involving predefined operational modes. By taking a 300 MW-class asymmetric AA-CAES system featuring four-stage compression and three-stage expansion as the object, a novel variable-pressure (sliding-pressure) operation strategy is proposed, along with a matching design between compression and expansion stages. A quasi-dynamic thermodynamic model is developed to analyze and optimize the full charge-discharge cycle performance under fixed time constraints with sliding-pressure control. The results show that the optimized sliding-pressure mode improves the system’s round-trip efficiency to 73.32%, increases the energy density to 3.404 kW·h/m³, and reduces the required air storage volume to 440 000 m³ (only one-fourth of that under constant-pressure operation). Exergy losses are mainly concentrated in the compressors and turbines, accounting for 40.7% and 29.3% respectively. The isentropic efficiency and heat recovery capability of these components has significant influence on overall performance of the system.
Using molten salt as a heat medium to form a high-temperature molten salt heat exchange system, a set of molten salt heat storage and carbonization device was designed. The structure and rated working conditions of the molten salt-carbonization furnace were designed, and the Nu empirical formula was applied to calculate the composite surface heat transfer coefficient of the molten salt-cylinder wall, and the relevant small-scale carbonization tests were carried out. The results showed that the convective heat transfer coefficient hti of the molten salt in the pipeline was much greater than the convective heat transfer coefficient ho1 of the molten salt heating layer of the carbonization furnace. The theoretical thermal efficiency and the measured thermal efficiency of the biomass carbonization device increased with the carbonization temperature. With the increase in carbonization temperature, decrease in material handling capacity, and extension of carbonization time, the calorific value of the products increased, but the solid energy yield decreased. Compared with rice husks, the organic components of pine wood shavings were more likely to escape into tar and even the vapor phase during the carbonization process. The designed experimental device can realize the carbonization of biomass under the condition of storing molten salt as a heat medium, which achieves the purpose of energy saving and carbon dioxide emission reduction.
A stand-alone liquid air energy storage (LAES) system with a water-oil combined heat storage system was constructed, and the effects of compression stages, expansion stages, and heat-storage water temperature on the system’s round-trip efficiency and compression heat utilization were analyzed. The results indicate that increasing the number of compression stages will reduce the round-trip efficiency, and the optimal number of compression stages is two. The optimal number of expansion stages is one more than the number of compression stages. Within the temperature range of 25~65 ℃, increasing the heat-storage water temperature can improve the system’s round-trip efficiency and the utilization degree of compression heat. However, the system efficiency will no longer increase when the temperature of the heat-storage water exceeds 65 ℃. Under optimal conditions, the system with two compression stages, three expansion stages, and a heat-storage water temperature of 65 ℃ has a compression heat surplus ratio of 0.349 and a round-trip efficiency of 0.622. The study provides a theoretical reference for optimizing the compression heat utilization process in LAES systems.
The high-temperature and high-pressure steam control valves in steam-heated molten salt thermal energy storage systems have to withstand high temperature, high pressure, and high pressure difference, and require frequent and high-precision adjustments. In view of these design and manufacturing challenges, a steam-heated molten salt thermal energy storage demonstration project was taken as the research object. Focusing on the actual application requirements of high-temperature and high-pressure steam control valves, systematic calculation and analysis were conducted on their flow capacity under different selection working conditions. An innovative technical scheme was proposed, which involves designing different stages of throttling and pressure reduction for different opening ranges of the control valve. This scheme effectively achieves good adaptability of the valve under full working conditions. It can accurately match the regulation requirements of the system in different operation stages, and significantly improves the adjustment accuracy. When the upstream steam flow rate is low, the use of steam-assisted atomizing nozzles is recommended, as they can make the atomized water particles finer, achieve a better atomization effect, reduce thermal shock and thermal stress on the pipeline, and ensure the safety of the device after desuperheating. This study sorts out the key considerations in the selection process of high-temperature and high-pressure steam control valves, which can provide important reference for the selection and design of high-temperature and high-pressure steam control valves in subsequent similar steam-heated molten salt heat storage projects.
Against the source-load imbalance caused by daily-scale periodic fluctuations in grid loads, this study investigates performance optimization methods for ejectors within compressed air energy storage (CAES) systems. The aim is to improve the overall efficiency of CAES systems in terms of power generation during energy release, as well as enhance their operational control capabilities during actual operation. In CAES systems, the ejector performs the dual functions of regulating the state parameters of the working gas and introducing low-pressure exhaust gas. This critically affects the system efficiency.
By taking a 10 MW-class CAES demonstration system under construction as the research subject, this study combines response surface methodology with Computational Fluid Dynamics (CFD) numerical simulation to analyze the ejector’s entrainment performance under varying working gas pressures, entrainment exhaust gas pressures, and outlet backpressure conditions. This determines the ejector’s efficient operating range. Subsequently, the volume of the storage tank is designed based on the entrainment performance results of the ejector and the variable pressure operating conditions during the energy release process of the CAES system. The power generation capacity of the CAES system is then predicted using a theoretical model.
The entrainment performance of the ejector is sensitive to variations in the working gas pressure and the entrainment exhaust gas pressure. Optimal entrainment characteristics are achieved when the working gas pressure is between 10.0 and 11.75 MPa, and the entrainment exhaust gas pressure is 5.6 MPa. The outlet back pressure of the ejector significantly affects the structure of the internal flow field and the operational window of the CAES system. Higher back pressure results in a narrower operating pressure range, necessitating larger storage tank volumes and reducing energy release efficiency. When the back pressure is 8.0 MPa, the ejector operates efficiently within a working pressure range of 10.00~12.00 MPa, achieving an energy utilization efficiency rate of 10.46%. A CAES system with a 2.2×103 m3 storage tank can sustain continuous operation at design power for 4.0 hours under a back pressure of 8.0 MPa. Its energy conversion efficiency is 16.67%, with cumulative energy released for power generation reaching 5.01×104 kW·h. This represents a 2.04% improvement on systems without an ejector.
Defining the high-efficiency operating range of the ejector and rationally configuring the air storage tank volume can effectively enhance the power generation capabilities of the CAES system, providing a foundation for optimizing the system and formulating operational strategies in engineering practice.
In order to better cope with the impact of the rapid development of new energy on the existing power grid structure and improve the stability and economy of thermal power unit operation, this paper proposes to construct a dual-layer optimization model of fire storage frequency regulation based on real-time power prediction of thermal power units and fuzzy control allocation of energy storage power.
The upper layer of the model utilizes frequency deviation decomposition and real-time power prediction of thermal power to optimize the power benchmark, effectively overcoming the response delay of the unit. The lower layer introduces a fuzzy logic control strategy to achieve adaptive and precise power allocation between the thermal unit and the energy storage system. On this basis, multi-objective genetic algorithm is used to optimize the energy storage capacity configuration scheme, and the frequency modulation performance under different control strategies is quantitatively evaluated based on indicators such as system frequency fluctuation. Taking a 600 MW thermal power unit as the research object, the optimal energy storage configuration was obtained through algorithm as follows: flywheel energy storage power of 8.5 MW and capacity of 1.3 MW·h, and lithium battery energy storage power of 3.6 MW and capacity of 14.6 MW·h. The total investment cost corresponding to this configuration is 2.027 7×109 yuan, and the actual income during the 400 s frequency modulation cycle is 850.95 yuan.
After simulation verification using MATLAB/Simulink, it was found that under step disturbance, the dual layer optimization strategy of fire storage coordination reduces the frequency fluctuation of the system to 4.826×10–2 Hz, which is 38.53% lower than the independent frequency regulation of the fire power unit. The average absolute deviation of power fluctuation is reduced to 4.224 MW, which is 32.57% lower than the independent operation. Under continuous disturbance, the frequency fluctuation of the system decreased by 19.31%, the average absolute deviation of power fluctuation decreased by 78.71%, and the actual contribution of electricity increased by 0.527 MW·h. The results show that the thermal-storage coordinated dual layer optimization control strategy presented in this paper effectively mitigates system frequency and power fluctuations, thereby alleviating the frequency regulation pressure on thermal power units. Concurrently, it enhances the utilization efficiency of the energy storage system and improves the economic viability of frequency regulation services.
This research thus provides a novel technical direction for the flexible transformation of thermal power plants, enabling them to play a more supportive and complementary role in future power systems dominated by renewable energy sources.
To address the pressing demand for grid frequency stability under high-proportion renewable energy integration and mitigate the slow frequency regulation response of thermal power units, aqueous organic redox flow batteries (AORFBs) have emerged as a viable technical solution for frequency regulation scenarios due to their advantages of long cycle life and low self-discharge rate.
A thermal-storage combined AGC frequency regulation technology utilizing AORFBs for energy storage is presented. The fundamental principles of coordinated thermal-storage technology and AORFBs are elaborated, the core performance parameters of flow batteries are tested, a frequency regulation control strategy for AORFBs-assisted thermal power units is proposed, and this approach is applied to the 200 kW/400 kW·h thermal-storage combined frequency regulation demonstration project at Luoyuan Power Plant.
Operational data and analytical testing demonstrate that AORFBs exhibit rapid regulation and precise output response characteristics, thereby enhancing the frequency regulation capability of the combined system.
Applying AORFBs to thermal power frequency regulation is feasible.
The large-scale integration of renewable energy poses significant challenges to the peak-shaving capacity of coal-fired units. To enhance operational flexibility and address energy flow conflicts in typical coal-fired systems coupled with compressed air energy storage systems during peak shaving, this study investigates a 660 MW coal-fired unit using EBSILON software. Three energy storage schemes and two energy release schemes are proposed and evaluated through thermo-economic analysis, focusing on thermal-time decoupling capability, peak-shaving paradox elimination, and system performance. The results show that during energy storage, the scheme utilizing intermediate-pressure cylinder exhaust for thermal oil heating achieves the highest thermal storage gain ratio (1.370) and the lowest heat rate (8 814.976 kJ/(kW·h)). During energy release, the scheme absorbing heat from No.3 high-pressure heater drain outlet yields the minimum heat rate (7 547.945 kJ/(kW·h)). After 8 hours of operation, the system retains 38.503 MW·h of utilizable thermal energy and reduces the peak-shaving paradox index to –0.041. Parameter optimization improves the round-trip efficiency of the compressed air energy storage system by 2.702 percentage points and increases the unit’s peak-shaving depth by 2.481%. This study provides a viable solution for synergistic optimization of coal-fired units and energy storage systems.
Driven by the global energy transition and the “dual-carbon” goals, enhancing the operational flexibility of coal-fired units has become pivotal for improving the grid’s renewable energy accommodation capacity. To enhance the frequency-regulation flexibility of coal-fired units and address the pinch-point bottleneck in molten-salt/steam heat exchange, this study proposes a three-tank cascaded thermal energy storage (TES) system integrated with a subcritical unit.
A steady-state model of a 330 MW unit was developed in EBSILON. It incorporated high-, intermediate-, and low-temperature molten-salt loops, and achieved partial boiler-turbine decoupling via main-steam and feedwater bypass circuits.
The simulation results indicate that the cycle electric efficiency reached 63.51% at 100% THA; the heat rate increase of the integrated system was about 1% in hot standby working state of each working condition, and 13.2% at 40% THA with a 5%Pe regulation depth; the coal consumption penalty grew exponentially with regulation depth, providing a basis for defining an economic dead band.
The cascaded TES structure preserves steam exergy while significantly improving load-response rate and frequency-regulation capability, offering both theoretical insights and a practical design paradigm for flexibility retrofits of coal-fired units in power systems with high renewable penetration.
This paper aims to reduce carbon emissions and enhance the operational flexibility of coal-fired power units.
A coupled system integrating compressed air energy storage (CAES) with oxygen-enriched coal-fired units was proposed based on energy complementary utilization principles. Various coupling schemes were proposed, and the thermodynamic performance and economic feasibility of the integrated system were analyzed.
The results show that by replacing steam turbine extraction with flue gas waste heat to preheat the turbine inlet air, when the heat exchange efficiency of HE1–HE3 is 89% and turbine inlet temperature is raised to 115 ℃, the round-trip efficiency of the CAES system can reach a maximum of 74.33%, representing a 24.25% improvement over the standalone CAES system. When carbon allowances, CO2 revenue, and carbon taxes are considered, the coupled system achieves a static payback period of 11.256 years, shorter than that of the conventional unit. In this case, the net present value (NPV) and internal rate of return (IRR) reach 801.73 million yuan and 9.63%, respectively, both exceeding those of the conventional system, indicating better economic performance. Carbon taxes increase the levelized cost of electricity (βLCOE) of the coupled unit, while carbon allowance trading and CO2 sales significantly reduce the βLCOE. The βLCOE of the coupled unit becomes lower than that of the conventional unit when the carbon tax, carbon allowance price, and CO2 price exceed 6.4 yuan/t, 73.9 yuan/t, and 14.68 yuan/t, respectively. Sensitivity analysis reveals that coal price has the greatest impact on the economic performance of the coupled unit, followed by the carbon allowance price, CO2 price, and carbon tax.
The proposed low-carbon pathway for the deep integration of thermal power and energy storage offers theoretical and engineering guidance for promoting low-carbon emissions from coal-fired power units and accelerating their transition into flexible, dispatchable power sources under the framework of a new power system.
No. 86 Xueyuan South Road, Haidian District, Beijing
010-62662699(Operation and Technical Support)
qkjq@cast.org.cn
Copyright © 2025 China Association for Science and Technology. All rights reserved. For all open access content, the relevant licensing terms apply.
Sponsored by the Office of the Leading Group for Cybersecurity and Informatization of CAST, and supported by Science and Technology Review Publishing House
