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.

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.

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.

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 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.

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.

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.

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).