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.

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.

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.

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.

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.

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.

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.

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).

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.

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.