Energy storage is the key technology of novel power system. As a medium and high temperature heat transfer and heat storage fluid, molten salt has the advantages of high heat capacity and good stability. It has been widely used in concentrated solar power (CSP) system, peak and frequency modification, green electricity consumption and other new energy fields. However, at present, the core components of molten salt energy storage system, such as the tanks, the electric heaters, the heat exchangers, and so on, are studied and developed based on the demand of CSP technology. The other application scenarios are not sufficiently considered. However, in different application scenarios, the working temperature range, heating and heat exchange methods have different requirements on molten salt. Therefore, the research status and technical achievements of the key technologies of molten salt heat storage are summarized. The development path of molten salt energy storage technology and its application in novel power systems are studied. According to the different application scenarios, the requirements on molten salt parameters and the suitable types of storage tanks and heat exchangers are illustrated.

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.

The spot market of electricity makes electricity return to the commodity attribute, which makes the market play an increasingly prominent role in the allocation of power resources. The electricity-trading mode has become an important part of the power market construction and power reform because it is conducive to promoting the consumption of new energy power generation and realizing the optimal allocation of power resources. This paper constructs technical routes for a thermal power unit in Shandong Province. The first is waste heat recovery, refrigeration scheme based on the voltage shrink heat pump and the second is deep peak shaving scheme based on the electric boiler and energy storage tank. The technical transformation scheme is providefor the thermal power unit to participating in the spot power market. The result show that energy supply capacity of the system increased by 48 MW, the cooling capacity increased by 32 MW, and the peak shaving capacity of the unit increased by 9%. In addition, the financial internal rate of return (before tax) of the project is 30.25%, and the payback period (before tax) is 4.1 years, with good profitability.

The transformation of energy production to renewable energy is the only way to achieve the dual-carbon goal. At present, the lack of peak shaving capacity and flexibility of coal-fired units hinders the large-scale consumption of renewable energy. In this paper, taking a 600 MW coal-fired unit as the research object, eight schemes for peak shaving system aided by molten salt heat storage are proposed, and the peak shaving capacity and thermal performance of each scheme are compared and analyzed through simulation calculation. The results show that, the peak shaving system can improve the flexibility of coal-fired unit, effectively regulate the output, and greatly expand the operating range. Heating by electricity causes a large amount of exergy loss, while extracted exhaust of intermediate pressure cylinder causes a small amount of exergy loss. The maximum peak shaving capacity can be obtained by the scheme of heating the molten salt directly by electric energy output by generator when charging, and heating the bypass feedwater by high-temperature molten salt when discharging, whose peak shaving depth can reach 17.83%. Moreover, the highest system efficiency and economy can be obtained by the scheme of heating the molten salt with extracted exhaust of intermediate-pressure cylinder when charging, and heating the bypass feedwater with high-temperature molten salt when discharging, of which the system thermal efficiency and exergy efficiency are 40.95% and 40.29% respectively, and the coal consumption rate is 350.01 g/(kW·h).

A sludge pyrolysis system coupled with molten salt storage is an emerging novel thermal treatment technique for sludge disposal, which can simultaneously realize reduction and tar recovery by constructing rapid and homogeneous pyrolysis conditions. The effects of heating rate and calcium oxide (CaO) addition on the production characteristics of tar during sludge pyrolysis coupled with molten salt storage system were investigated via a high-precision optical wide heating rate pyrolysis apparatus. The results show that, the heating rate affected the tar yield at low pyrolysis temperatures. The tar yield increased by 14% at 350 ℃ when the heating rate increased from 60 ℃/min to 6 000 ℃/min. Meanwhile, the CaO addition could result in a sharp decrease in tar yield, an 39%~43% decrease could be observed with 10% CaO addition. Also, the CaO addition significantly affected the relative content of the compounds in tar, which was attributed to the fact that CaO could act as a catalyst and heat transfer retardant. The results are helpful to the pyrolysis condition regulation and high value-added tar obtain for the sludge pyrolysis system coupled with molten salt storage.

With the structural upgrading of China's energy industry and the transformation of economic growth mode, clean energy power generation technology has been continuously and rapidly developed. As a high-power electric heating conversion device, electric boiler has become one of the effective technical solutions to enhance the operational flexibility of thermal power units and promote the reliable consumption of new energy power. In this paper, the allocation and accounting principles of electric boiler capacity and heat storage capacity in such projects are proposed. The calculation model of system optimization operation parameters and operation economy evaluation is established based on the principle of maximizing the economic benefits of enterprises, taking into account the factors of grid peak shaving depth dispatching limits. Combined with the actual situation of the multi-unit system of a thermal power plant in Northeast China, the optimal configuration capacity of the electric boiler of the project is 300 MW, and the heat storage capacity is 17 MW·h. At the same time, the optimal operation scheme of the whole plant is proposed. The results show that, under the condition of 30% peak shaving depth limit, the case power plant can add about 139.53 million Yuan in each heating season, and the project investment payback period is about 5 years. In the foreseeable future, the project will have long-term profitability.

Based on the control difficulties in the operation process of the unit after the bypass heating alteration, a complete control strategy was proposed under the bypass heating condition, which realizes the bypass automatic control under the heating condition and meets the needs of the unit heating regulation at the same time. Aiming at the influence of bypass switching on and off and working condition disturbance on the operation stability of steam turbine under the heating condition, as well as the change of unit safety boundary, a set of logic design scheme including bypass blocking and overriding was proposed, which effectively guarantees the unit's safety and stability. Aiming at the changing characteristics of the steam turbine flow characteristics and the boiler's response to temperature and pressure characteristics in the state of bypass heating, an optimization strategy for coordination correction was proposed, which improved the quality of network-related control of the unit. The control scheme proposed in this paper has been applied in the supercritical once-through furnace unit. It has been verified the control strategy can realize the automatic control of the bypass system, and the control effect of the coordinated variable load is good. After the bypass RB acts, the unit can transition smoothly, realizing the bypass supply Automatic and safe control of the unit under thermal conditions.

In order to improve the flexibility of thermal power units, enhance the peak shaving capability of thermal power units coupled with molten salt heat storage system, and reduce project investment, a variety of electric heating molten salt energy storage systems coupled with thermal power plant were proposed. The thermal performance, peak shaving capacity and molten salt consumption of a 350 MW unit were analyzed with EBSILON software. An optimal system for deep peak shaving was proposed. The results show that, during the heat charging process, the electric heating system demonstrates a higher cycling efficiency as 33.2%, which enables the lowest power generation load to be reduced to below 25%. The flow rate of molten salt in this system is only 6.6%~31.2% to that of a steam heating system. During the heat discharging process, the water is drawn from the inlets of No.1 and No.2 high pressure heater. The water temperature is 182.4~242.7 ℃. The molten salt-condensed water heat exchanger is self-anti-condensation. The cycling efficiency during the heat discharging process is 32.7%~33.9% at different unit loads, indicating unit load has little effect on the cycling efficiency of the peaking shaving system. The research results can guide the engineering application of the deep peak shaving technology of thermal power units coupled with molten salt heat storage.

With the continuous progress of the work of "carbon neutrality and carbon peak", the installed scale of photovoltaic, wind power and other new energy is expanding, energy saving and consumption reduction as well as flexibility improvement become the two key tasks the thermal power units faced. Through mathematical modeling and hourly calculation analysis for the hybrid system, performance and economic characters for solar-thermal systems replacing high pressure heaters are obtained. The calculation results indicate that, using solar thermal and coal fired hybrid system can realize sharp decline of the unit coal consumption, which is a most direct and effective method for coal saving and reducing consumption, it has great significance for life prolonging of the units to be retired from active service because of high coal consumption indexes. However, the economic benefit of the system itself is insufficient. So it can be supplemented with molten salt electric heater to improve the system's frequency modulation ability and enhance the project's profitability. According to the calculation, when the frequency modulation income is not considered, the system's yield is only 6.0%, but it can be increased to 8.0% after considering the frequency modulation income. Therefore, the hybrid system has double effects in improvement of both coal saving transformation and flexibility transformation.