There is an increasing participation of thermal power units in peak shaving of power grid due to the national "double carbon" target and the strategic demand of energy transformation in China. The molten salt heat storage system can substantially improve the peak shaving capacity of thermal power system by absorbing or releasing heat efficiently from or into the thermal system. The key technologies of thermal power units coupled with molten salt heat storage system and the research progress of the heat storage system process flow design are combed in detail. Firstly, the formulas and physicochemical properties of commonly used molten salts are summarized. Great attention is paid to the characteristics and application prospects of the currently widely used binary and ternary nitric acid molten salts. Secondly, the critical equipment components including the thermal storage tank as well as heat exchangers used in the heat storage system are elaborated. The heat storage principle and characteristics of single-tank and double-tank molten salt heat storage methods are summarized, and the applicability of the former two methods to thermal power units' heat storage and peak shaving system is analyzed from the perspectives of system safety, cost, technology maturity and peak shaving response speed. Then, the current research status of molten salt heat exchanger is summarized, and the research achievements and shortcomings of molten salt-steam-water tube shell heat exchanger are emphatically analyzed from multiple perspectives. Moreover, the design schemes of molten salt heat storage system are sorted out emphatically for the process of heat storage system. The different design features of thermal storage systems are compared. Furthermore, some of the future work on the design of flexible-peak-shaving thermal storage system is also figured out. Finally, the design and practical application of molten salt heat storage system are prospected.

Phase change energy storage technology has the advantages of high heat storage density and constant temperature, so it has great potential for large-scale commercialization. The development of phase change materials is very important to the application of phase change energy storage technology. To solve the problems of poor heat transfer performance and easy leakage of phase change materials, extensive research has been conducted based on the heat transfer enhancement and packaging of phase change materials. The characteristics of thermal energy storage technologies are firstly compared. Then, the classification and properties of phase change materials are summarized. The progress of heat transfer and storge enhancement is discussed from the aspects of increasing heat transfer area, thermal conductivity, melting latent heat and specific heat capacity. The packaging of phase change materials is also discussed. Finally, a prospect for the future development direction of phase change energy storage is made.

In order to solve the problems of high supercooling degree, low thermal conductivity and poor cycle stability of single hydrated salt phase change material, ammonium aluminum sulfate dodecahydrate was used as phase change material, Al₂O₃ and xanthan gum were used as additives to modify ammonium aluminum sulfate dodecahydrate by melt blending, and a new composite phase change material was prepared by using porous adsorption method to composite modified expanded graphite and modified ammonium aluminum sulfate dodecahydrate. The thermophysical properties, supercooling degree, cycle stability and material compatibility were analyzed. The results show that, the melting point, latent heat and thermal conductivity of the composite phase change material were 93.23 ℃, 235.40 kJ/kg and 4.086 W/(m·K), respectively. After 50 cycles, the supercooling degree was stable at 24 ℃, and after 300 cycles, the latent heat only decreased by 5.9%, with good stability. The 316L stainless steel and composite phase change materials have good compatibility, and can be used as packaging container materials. The composite phase change material has good performance and great application potential in building heating.

Heat transfer fins can be used to improve the operation performance of heat storage tanks using phase change filling material (PCM). Based on the COMSOL software, the effects of annular heat transfer fin's parameters (fin length, fin thickness and fin angle) on charging performance of a double-tube PCM heat storage tank is preliminarily evaluated. The results show that, when the fin length increases from 1.0 m to 1.2 m, the total melting time of the filling material shortens from 8 h to 5 h. When the fin thickness increases from 40 mm to 60 mm, the total melting time of the filling material decreases from 10 h to about 6 h, and the average charging rate increases from 11.3×10⁸ kJ/h to 14.8×10⁸ kJ/h. When the fin angle is –15°, the tank has the shortest total melting time and the maximum average charging rate, which is 14.3×10⁸ kJ/h. For the double-tube PCM tank investigated in this study, the optimal fin angle is -15°. The results can provide basis for the design of double-tube PCM heat storage tanks for CSP plants.

Electric-heat conversion is an effective way to realize local consumption of new energy and help build a clean and low-carbon heating system. To this end, a new heating substation system with new energy consumption capability is designed. The system is based on the traditional heating substation, and the adjustment equipment such as the electric boiler and heat storage tank is added. At the same time, a heating substation dispatch strategy based on the coordinated regulation of flexible resources such as the primary heat source and heat storage tank is proposed to achieve complete consumption of new energy, meet the heat load demand, and obtain the required energy capacity of the heat storage tank. Furthermore, the configuration method of the volume of the heat storage tank and its structural parameters considering the dynamic characteristics of charging is proposed to calculate the volume of hot water injected into the heat storage tank and the volume considering the thickness of the thermocline layer. The inlet and outlet pipe diameters of the heat storage tank determine through the maximum heat charging flow. Appropriate ratio of diameter to height is selected to ensure the ideal temperature stratification characteristics of the heat storage tank. The effectiveness of the proposed method is verified by a simulation example. This method can provide a reference for the local consumption of new energy and the construction of heating substations.

The coaxial casing heat exchanger is one of the technologies to realize high efficient heat extraction in the middle and deep geothermal energy wells, and its heat transfer capacity is crucial to the sustainable development of geothermal system. Taking Guanzhong area as an example, the heat transfer model of coaxial casing heat exchanger in middle-deep geothermal wells is established considering the formation inhomogeneity, and the effects of injection temperature, injection flow rate, buried depth and other factors on its heat extraction performance are studied. The influences of injection temperature and injection flow rate on thermal reservoir temperature recovery under intermittent production condition are discussed. The results show that, the outlet fluid temperature decreases with the increasing of injection flow rate, but the heat extraction power of the whole system increases. Increasing the injection temperature can improve the outlet fluid temperature, but the system heat extraction power decreases greatly. With the increasing of formation depth, the temperature of outlet fluid and heat extraction power increase gradually. Reducing the inner pipe diameter and enlarging the outer pipe diameter can effectively improve the temperature of outlet fluid and heat extraction power. The temperature recovery ability of the thermal reservoir increases with the injection flow and injection temperature. Reducing the thermal conductivity of inner pipe or choosing double-layer inner pipe structure can reduce the fluid temperature loss along the inner tube and increase the outlet fluid temperature.

Sensible heat storage is an effective way to solve the instability and fluctuation of solar thermal utilization. The common water medium was used as the medium material of sensible heat energy storage, and the heat storage tank device was used to realize the application of solar energy heat storage and release. The basic shape of the initially selected water tank was cylindrical. The conical structure of the tank bottom was optimized, and the respective heat storage change characteristics of the heat storage water tank under the three working conditions of 40°, 45° and 50° cone bottom angles were explored. Based on the unsteady laminar heat transfer model, the volume average temperature change and the maximum volume temperature change of the heat storage device were simulated by using the Fluent numerical software. The results showed that, when the cone bottom angle was 50°, the overall heat charging and discharging performance of the heat storage tank was better. When the average temperature of the heat storage tank body was 308.612 K under this parameter, the average temperature of the heat storage tank body was 0.202% and 0.053% higher than that of the heat storage tank body with a cone bottom angle of 40°and 45°, respectively. On this basis, the dynamic change law of heat storage and heat release of 50°tank was further analyzed, and the distribution characteristics of key indicators such as volume fraction and velocity field in the process of water storage and drainage inside the tank were studied. This research can provide some reference for the optimal design and engineering application of solar energy thermal storage system.

Electric heat storage technology is an important approach to promote the utilization of electric energy, which has a broad prospect in the aspects of deep peak shaving, improving the utilization rate of new energy and protecting environment. In order to explore the adaptability of heat storage in steam heating, molten salt heat storage system and solid heat storage system are designed and compared based on specific engineering project. An optimal design scheme of molten salt heat storage system is put forward, and comparison is conducted from the aspects of system performance, economy and reliability. The result shows that, the proposed optimization scheme is beneficial to save investment, save space and simplify the system. For the electric energy storage heat supply station with simutaneous heat storage and heat discharge working conditions, the molten salt heat storage mode it is recommended, which is more stable for steam generation. Although the molten salt heat storage system is more complex and the total investment is slightly higher, it has higher heat exchange efficiency, lower power consumption, lower operating cost and higher income. If the total investment can be further reduced, molten salt heat storage technology will become the most competitive clean heating method in heat storage.

In order to reduce the phenomenon of "wind and solar energy power abandonment" caused by the mismatch between the on-grid electricity generated by renewable energy power and coal-fired power unit, the coal-fired power unit needs to achieve the deep peak shaving to provide the grid space for renewable energy power with the continuous increase of the installed capacity of renewable energy. At the same time, the coal-fired power unit provides the ability to further consume renewable energy power. The utilization of coupling reheated steam extraction with thermal energy storage and molten salt thermal energy storage heated by renewable energy power in deep peak shaving system of coal- fired power unit is proposed. The research on large-scale renewable energy power consumption by peak shaving system of coal-fired power unit integrated with thermal energy storage is discussed. Moreover, the comprehensive coal consumption for power generation and the CO₂ emission is analyzed. The results show that, the power output of the coal-fired unit decreases from 300.03 MW to 210.07 MW when the reheated steam extraction mass flowrate is 270.70 t/h, and the maximum power of renewable energy power consumption by thermal energy storage system is 187.26 MW. When the stored heat is released, the power output of coal-fired unit increases from 300.03 MW to 348.68 MW. When the renewable energy power consumption per unit time is 187.26 MWh, the comprehensive coal consumption for power generation is reduced by 8.49 g/kWh and the CO₂ emission is reduced by 28.23 t. This study provides a guiding idea for the absorption of high-proportion renewable energy power.

Flexible transformation of thermal power units is the key to build a new power system and achieve the goal of "carbon peak" and "carbon neutrality". In order to promote the flexibility of thermal power units, the coupling scheme for small steam turbine drive and motor drive liquid compressed carbon dioxide energy storage system and thermal power unit is put forward, and the thermodynamic system model is established. Moreover, the heat consumption rate and energy utilization coefficient are used to evaluate the system, the thermodynamic performance of the system is compared and analyzed, and the optimal coupling scheme of energy storage is established. The researches show that, in the energy storage stage, condensate water is extracted from the outlet of the condensate pump, and the compressed heat is absorbed and returned to the outlet of No.7 low-pressure heater. In the energy release stage, steam is extracted from the exhaust of the middle pressure cylinder, and the expanded CO₂ is heated and returned to the No.5 low-added hydrophobic cooler, the coupling system has the best performance. The heat consumption rate is 48.308 kJ/(kW·h) lower than that of the original system, and the energy utilization coefficient increases by 0.52 percentage point. Changing the inlet temperature and the mass flow rate of CO₂ expander can quickly change the load. After coupling with the energy storage system, the peak regulation capacity of thermal power unit increases by 17.1%, when the hot water tank is configured and the maximum heat is released, the peak regulation capacity of the unit increases by 37.4%, indicating the flexibility of thermal power unit is improved.