Wide-temperature-range molten salt driven step-change phase change thermal storage system and operating method

Abstract

The application provides a wide-temperature-range molten salt driven step-by-step phase change heat storage system and an operation method, relates to the technical field of phase change heat storage, and comprises a step-by-step phase change heat storage unit, a molten salt buffer tank, an electric heater and a heat exchanger. The step-by-step phase change heat storage unit comprises high-temperature phase change tanks, medium-temperature phase change tanks and low-temperature phase change tanks which are connected in series through heat exchange channels. The molten salt buffer tank is used for storing wide-temperature-range molten salt. The outlet of the molten salt buffer tank is connected with a high-temperature heat exchange port and a low-temperature heat exchange port. An electric heater is arranged between the outlet of the molten salt buffer tank and the high-temperature heat exchange port. The hot side of the heat exchanger is connected in series between the high-temperature heat exchange port and the inlet of the molten salt buffer tank. The cold side inlet of the heat exchanger is connected with a water source. The cold side outlet of the heat exchanger is connected with a steam user. The application adopts the form of wide-temperature-range molten salt reinforced heat exchange, step-by-step series connection of phase change heat storage modules and high-density heat storage, can fully utilize the latent heat part of the heat storage medium, and realizes more efficient heat transfer through different temperature step-by-step heat exchange.

Description

Technical Field

[0001] This invention relates to the field of phase change thermal energy storage technology, and in particular to a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system and its operation method. Background Technology

[0002] Under the "dual carbon" goal, the installed capacity of new energy power generation continues to expand, while the phenomena of wind and solar curtailment and the demand for peak shaving of thermal power are becoming increasingly prominent. Converting intermittent and fluctuating new energy power or surplus thermal power for peak shaving into thermal energy storage, and then converting it into energy output in the form of industrial steam according to demand, has become a key technological direction for improving energy utilization efficiency and ensuring the stable operation of the energy system. Phase change thermal energy storage technology can achieve efficient storage and release of thermal energy through the solid-liquid-gas phase transition of phase change media. It has significant advantages such as high thermal energy storage density, stable heat release temperature, and compact system structure. At the same time, it has excellent thermal cycle performance, stable and controllable operation, and the phase change temperature of different phase change materials can cover the low to medium-high temperature range, with a wide temperature selection range, which can be adapted to the thermal energy supply and demand characteristics of multiple scenarios.

[0003] Therefore, related technologies use a combination of phase change thermal energy storage and new energy power generation or thermal power peak shaving to achieve thermal energy storage and reuse. However, in actual use, there are often problems such as complex system structure, high initial investment, and large consumption of molten salt. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, one embodiment of the present invention proposes a wide-temperature-range molten salt driven cascade phase change thermal storage system. This wide-temperature-range molten salt driven cascade phase change thermal storage system adopts a form of wide-temperature-range molten salt enhanced heat exchange and high-density heat storage in the form of cascade series connection of phase change thermal storage modules. It can make full use of the latent heat of the thermal storage medium, and can significantly reduce the consumption of molten salt compared with traditional molten salt thermal storage. At the same time, the cascade heat exchange at different temperatures achieves more efficient heat transfer.

[0006] Another embodiment of the present invention proposes an operation method for a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system.

[0007] According to an embodiment of the present invention, a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system includes a cascade phase change thermal energy storage unit, a molten salt buffer tank, an electric heater, and a heat exchanger. The cascade phase change thermal energy storage unit includes a high-temperature phase change tank, a medium-temperature phase change tank, and a low-temperature phase change tank connected in series via heat exchange channels. The heat exchange channels are in contact with the phase change media within the corresponding phase change tanks and can transfer heat. The high-temperature phase change tank is provided with a high-temperature heat exchange port communicating with the heat exchange channels, and the low-temperature phase change tank is provided with a low-temperature heat exchange port communicating with the heat exchange channels. The molten salt buffer tank is used to store a wide-temperature-range... Molten salt, the outlet of the molten salt buffer tank is connected to the high-temperature heat exchange port and the low-temperature heat exchange port, and an electric heater is provided between the outlet of the molten salt buffer tank and the high-temperature heat exchange port. The electric heater is capable of heating the wide-temperature-range molten salt flowing out of the molten salt buffer tank. The inlet of the molten salt buffer tank is also connected to the high-temperature heat exchange port and the low-temperature heat exchange port. The hot side of the heat exchanger is connected in series between the high-temperature heat exchange port and the inlet of the molten salt buffer tank. The cold side inlet of the heat exchanger is connected to a water source, and the cold side outlet of the heat exchanger is connected to a steam user.

[0008] According to an embodiment of the present invention, in a wide-temperature-range molten salt-driven cascade phase change thermal storage system, during thermal storage, wide-temperature-range molten salt in a molten salt buffer tank is transported to an electric heater. The electric heater heats the molten salt to a set temperature (i.e., a temperature matching the phase change temperature of the phase change medium in the high-temperature phase change tank), resulting in high-temperature molten salt. The high-temperature molten salt enters the heat exchange channel through a high-temperature heat exchange port, and then flows sequentially through a high-temperature phase change tank, a medium-temperature phase change tank, and a low-temperature phase change tank to exchange heat with the phase change medium in the corresponding tanks step by step. The phase change medium absorbs heat and stores it, while the high-temperature molten salt cools down to low-temperature molten salt and returns to the molten salt buffer tank. During heat release, the wide-temperature-range molten salt in the molten salt buffer tank enters the heat exchange channel through a low-temperature heat exchange port, and then flows sequentially through a low-temperature phase change tank, a medium-temperature phase change tank, and a high-temperature phase change tank to exchange heat with the phase change medium in the corresponding tanks step by step. The phase change medium releases latent heat. Molten salt is heated to a high-temperature molten salt. The counter-current cascade coupling design minimizes the heat exchange temperature difference and improves thermodynamic efficiency. Finally, the high-temperature molten salt enters the hot side of the heat exchanger to heat the water entering the cold side of the heat exchanger from the water source, producing steam and low-temperature molten salt. The steam is delivered to the steam user, while the low-temperature molten salt is returned to the molten salt buffer tank. The aforementioned process fully utilizes the advantages of the solid-liquid phase change latent heat of phase change materials at each temperature level, the good heat transfer performance of wide-temperature-range molten salt, and the high phase change heat storage density. Therefore, compared with related technologies, this invention adopts a wide-temperature-range molten salt enhanced heat exchange and a cascade series high-density heat storage form of phase change heat storage modules. It can fully utilize the latent heat of the heat storage medium and significantly reduce the molten salt consumption compared with traditional molten salt heat storage. At the same time, the cascade heat exchange at different temperatures achieves more efficient heat transfer.

[0009] In some embodiments, the wide-temperature-range molten salt is a ternary Hitec XL salt, wherein the melting point of the wide-temperature-range molten salt is below 150°C and the decomposition temperature is above 500°C.

[0010] In some embodiments, the temperature of the phase change medium after heat storage in each of the high-temperature phase change tank, the medium-temperature phase change tank, and the low-temperature phase change tank is higher than the solid-liquid phase change temperature of the corresponding phase change medium, and lower than the liquid-gas phase change temperature of the corresponding phase change medium.

[0011] In some embodiments, the outlet of the molten salt buffer tank is provided with a molten salt pump, which can provide pumping power for the molten salt flowing out of the molten salt buffer tank and regulate the flow rate of the molten salt so that the molten salt enters the electric heater or the low-temperature heat exchange port.

[0012] In some embodiments, the heat exchange channel includes a high-temperature section, a medium-temperature section, and a low-temperature section connected in sequence, wherein the high-temperature section is connected to the high-temperature heat exchange port, and the low-temperature section is connected to the low-temperature heat exchange port;

[0013] The high-temperature section is located inside the high-temperature phase change tank, the medium-temperature section is located inside the medium-temperature phase change tank, and the low-temperature section is located inside the low-temperature phase change tank. At least one of the high-temperature section, the medium-temperature section, and the low-temperature section includes an upper heat exchange section and a lower heat exchange section arranged in a vertical direction.

[0014] In some embodiments, each of the upper heat exchange section and the lower heat exchange section includes a first main pipe, a branch pipe and a second main pipe connected in sequence, the first main pipe and the second main pipe are arranged at intervals along the vertical direction, the branch pipe is located between the first main pipe and the second main pipe, and there are multiple branch pipes arranged at intervals.

[0015] In some embodiments, the first main pipe and the second main pipe both extend in a horizontal direction, and the plurality of branch pipes extend in the vertical direction and are spaced apart in the horizontal direction.

[0016] In some embodiments, the electric heater is adapted to be powered by curtailed wind and solar power or peak-shaving power from thermal power plants.

[0017] In some embodiments, the cascade phase change thermal storage unit is a single unit; or, there are multiple cascade phase change thermal storage units, all of which are connected in parallel.

[0018] According to an embodiment of the present invention, an operation method for a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system, based on any of the above embodiments, includes the following operating modes: In the heat storage mode, the molten salt with a wide temperature range in the molten salt buffer tank is heated by an electric heater to obtain high-temperature molten salt. The high-temperature molten salt enters the high-temperature phase change tank, the medium-temperature phase change tank and the low-temperature phase change tank in sequence to exchange heat with the phase change medium in the corresponding phase change tank step by step. The phase change medium absorbs heat to realize latent heat storage. The high-temperature molten salt is cooled to low-temperature molten salt and then flows back to the molten salt buffer tank. In the exothermic mode, the molten salt with a wide temperature range in the molten salt buffer tank sequentially enters the low-temperature phase change tank, the medium-temperature phase change tank, and the high-temperature phase change tank to exchange heat with the phase change medium in the corresponding phase change tanks in stages. The phase change medium releases latent heat, and the molten salt is heated into high-temperature molten salt. The high-temperature molten salt enters the hot side of the heat exchanger to heat the water entering the cold side of the heat exchanger from the water source, thereby obtaining steam and low-temperature molten salt. The steam is delivered to the steam user, and the low-temperature molten salt is returned to the molten salt buffer tank.

[0019] The technical advantages of the operation method of the wide-temperature-range molten salt driven cascade phase change thermal energy storage system according to the embodiments of the present invention are the same as those of the wide-temperature-range molten salt driven cascade phase change thermal energy storage system described above, and will not be repeated here.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of the thermal storage mode of a wide-temperature-range molten salt-driven cascade phase change thermal storage system according to an embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram of the heat release mode of a wide-temperature-range molten salt-driven cascade phase change thermal storage system according to an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the parallel connection between the cascade phase change thermal storage units in a wide-temperature-range molten salt driven cascade phase change thermal storage system according to an embodiment of the present invention.

[0025] Figure label: A. Low-temperature phase change tank; A1. Low-temperature tank body; A2. Low-temperature phase change medium; A3. Low-temperature section; A4. Low-temperature heat exchange port; B. Medium-temperature phase change tank; B1. Medium-temperature tank body; B2. Medium-temperature phase change medium; B3. Medium-temperature section; C. High-temperature phase change tank; C1. High-temperature tank body; C2. High-temperature phase change medium; C3. High-temperature section; C4. High-temperature heat exchange port; 1. Molten salt buffer tank; 2. Molten salt pump; 3. Electric heater; 4. Water source; 5. Heat exchanger; 6. Steam user. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] like Figures 1 to 3 As shown in the figure, a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to an embodiment of the present invention includes a cascade phase change thermal energy storage unit, a molten salt buffer tank 1, an electric heater 3, and a heat exchanger 5. The cascade phase change thermal energy storage unit includes a high-temperature phase change tank C, a medium-temperature phase change tank B, and a low-temperature phase change tank A connected in series via heat exchange channels. The heat exchange channels are in contact with the phase change medium in the corresponding phase change tanks and can transfer heat. The high-temperature phase change tank C is provided with a high-temperature heat exchange port C4 connected to the heat exchange channels, and the low-temperature phase change tank A is provided with a low-temperature heat exchange port A4 connected to the heat exchange channels. The molten salt buffer tank 1 is used for storing... A wide-temperature-range molten salt is stored in a buffer tank 1. The outlet of the molten salt buffer tank 1 is connected to the high-temperature heat exchange port C4 and the low-temperature heat exchange port A4. An electric heater 3 is installed between the outlet of the molten salt buffer tank 1 and the high-temperature heat exchange port C4. The electric heater 3 can heat the wide-temperature-range molten salt flowing out of the molten salt buffer tank 1. The inlet of the molten salt buffer tank 1 is also connected to the high-temperature heat exchange port C4 and the low-temperature heat exchange port A4. The hot side of the heat exchanger 5 is connected in series between the high-temperature heat exchange port C4 and the inlet of the molten salt buffer tank 1. The cold side inlet of the heat exchanger 5 is connected to the water source 4, and the cold side outlet of the heat exchanger 5 is connected to the steam user 6.

[0028] According to an embodiment of the present invention, in a wide-temperature-range molten salt driven cascade phase change thermal storage system, during thermal storage, wide-temperature-range molten salt in molten salt buffer tank 1 is transported to electric heater 3. Electric heater 3 heats the molten salt to a set temperature (i.e., a temperature matching the phase change temperature of the phase change medium in high-temperature phase change tank C), resulting in high-temperature molten salt. The high-temperature molten salt enters the heat exchange channel through high-temperature heat exchange port C4, and then flows sequentially through high-temperature phase change tank C, medium-temperature phase change tank B, and low-temperature phase change tank A to exchange heat with the phase change medium in the corresponding phase change tanks step by step. The phase change medium absorbs heat and stores it, while the high-temperature molten salt cools down to low-temperature molten salt and returns to molten salt buffer tank 1. During heat release, wide-temperature-range molten salt in molten salt buffer tank 1 enters the heat exchange channel through low-temperature heat exchange port A4, and then flows sequentially through low-temperature phase change tank A, medium-temperature phase change tank B, and high-temperature phase change tank C to exchange heat with the phase change medium in the corresponding phase change tanks step by step. The latent heat of the molten salt is released, and the molten salt is heated to a high-temperature molten salt. The counter-current cascade coupling design can minimize the heat exchange temperature difference and improve thermodynamic efficiency. Finally, the high-temperature molten salt enters the hot side of the heat exchanger 5 to heat the water entering the cold side of the heat exchanger 5 from the water source 4, resulting in steam and low-temperature molten salt. The steam is delivered to the steam user 6, and the low-temperature molten salt is returned to the molten salt buffer tank 1. The aforementioned process fully utilizes the advantages of the solid-liquid phase change latent heat of phase change materials at each temperature level, the good heat transfer performance of wide-temperature-range molten salt, and the high phase change heat storage density. Therefore, compared with related technologies, the present invention adopts the form of wide-temperature-range molten salt enhanced heat exchange and high-density heat storage in a cascade series of phase change heat storage modules, which can make full use of the latent heat of the heat storage medium. Compared with traditional molten salt heat storage, it can significantly reduce the molten salt consumption. At the same time, the cascade heat exchange at different temperatures achieves more efficient heat transfer.

[0029] Specifically, the molten salt buffer tank 1 serves to buffer the molten salt flow rate and homogenize the temperature, preventing local solidification of the molten salt and ensuring the stability of the molten salt circulation. The phase change temperatures of the phase change media in the high-temperature phase change tank C, the medium-temperature phase change tank B, and the low-temperature phase change tank A decrease sequentially. In other words, the phase change media in the high-temperature phase change tank C is high-temperature phase change media C2, the phase change media in the medium-temperature phase change tank B is medium-temperature phase change media B2, and the phase change media in the low-temperature phase change tank A is low-temperature phase change media A2. This allows for the storage and release of thermal energy through the solid-liquid phase change of the phase change media in each tank, while the heat exchange channel enables efficient heat exchange between the molten salt and the phase change media. The heat exchanger 5 is a molten salt-water heat exchanger, which enables heat exchange between the molten salt and softened water, transferring the thermal energy of the molten salt to the softened water to generate industrial steam.

[0030] In some specific embodiments, taking the supply of 300℃ industrial steam as an example, the following selection of phase change media in high-temperature phase change tank C, medium-temperature phase change tank B, and low-temperature phase change tank A can meet the requirements:

[0031] In some embodiments, the wide-temperature-range molten salt is a ternary Hitec XL salt, wherein the composition of the ternary Hitec XL salt is 48% Ca(NO3)2-45% KNO3-7% NaNO3. The melting point of the wide-temperature-range molten salt is below 150°C and the decomposition temperature is above 500°C, so that when the wide-temperature-range molten salt is used as a heat transfer medium, it can remain liquid in a wide temperature range of 150°C to 500°C, and has good fluidity and thermal stability.

[0032] In some embodiments, the temperature of the phase change medium after heat storage in each of the high-temperature phase change tank C, the medium-temperature phase change tank B, and the low-temperature phase change tank A is higher than the solid-liquid phase change temperature of the corresponding phase change medium and lower than the liquid-gas phase change temperature of the corresponding phase change medium. That is, the temperature of each of the high-temperature phase change medium C2, the medium-temperature phase change medium B2, and the low-temperature phase change medium A2 after heat storage is higher than the solid-liquid phase change temperature of the corresponding phase change medium and lower than the liquid-gas phase change temperature of the corresponding phase change medium, so as to effectively avoid the problem of pressure surge caused by internal vaporization.

[0033] Among them, the temperature of each of the high-temperature phase change medium C2, the medium-temperature phase change medium B2, and the low-temperature phase change medium A2 after heat storage is higher than the solid-liquid phase change temperature of the corresponding phase change medium. At this time, the heat output includes the latent heat of phase change and part of the sensible heat of the liquid medium.

[0034] It should be noted that the "solid-liquid phase transition temperature" refers to the temperature at which a substance reaches phase equilibrium between its solid and liquid states. The most commonly used names are melting point (solid → liquid) and freezing point (liquid → solid). The melting point and freezing point of a pure substance are equal. Similarly, the "liquid-gas phase transition temperature" refers to the temperature at which a substance reaches equilibrium between its liquid and gaseous states. The commonly used names are boiling point (liquid → gas) and condensation point / dew point (gas → liquid). The values ​​of both are the same for pure substances.

[0035] like Figures 1 to 3 As shown, in some embodiments, the outlet of the molten salt buffer tank 1 is equipped with a molten salt pump 2. The molten salt pump 2 can provide pumping power for the molten salt flowing out of the molten salt buffer tank 1 and adjust the molten salt flow rate so that the molten salt can enter the electric heater 3 or the low-temperature heat exchange port A4. The flow rate of the molten salt pump 2 can be adjusted according to the working conditions to match the heat storage and release capacity.

[0036] Specifically, the inlet of molten salt pump 2 is connected to the outlet of molten salt buffer tank 1, the outlet of molten salt pump 2 is connected to the inlet of electric heater 3 and low-temperature heat exchange port A4, and the outlet of electric heater 3 is connected to high-temperature heat exchange port C4.

[0037] like Figures 1 to 3 As shown, in some embodiments, the heat exchange channel includes a high-temperature section C3, a medium-temperature section B3, and a low-temperature section A3 connected in sequence. The high-temperature section C3 is connected to the high-temperature heat exchange port C4, and the low-temperature section A3 is connected to the low-temperature heat exchange port A4.

[0038] The high-temperature section C3 is located inside the high-temperature phase change tank C, the medium-temperature section B3 is located inside the medium-temperature phase change tank B, and the low-temperature section A3 is located inside the low-temperature phase change tank A. At least one of the high-temperature section C3, the medium-temperature section B3, and the low-temperature section A3 includes an upper heat exchange section and a lower heat exchange section arranged in a vertical direction; that is, the high-temperature section C3 includes an upper heat exchange section and a lower heat exchange section arranged in a vertical direction; or, the medium-temperature section B3 includes an upper heat exchange section and a lower heat exchange section arranged in a vertical direction; or, the low-temperature section A3 includes an upper heat exchange section and a lower heat exchange section arranged in a vertical direction; or, both the high-temperature section C3 and the medium-temperature section B3 include an upper heat exchange section and a lower heat exchange section arranged in a vertical direction; or, both the high-temperature section C3 and the low-temperature section A3 include an upper heat exchange section and a lower heat exchange section arranged in a vertical direction; or, both the medium-temperature section B3 and the low-temperature section A3 include an upper heat exchange section and a lower heat exchange section arranged in a vertical direction; or, each of the high-temperature section C3, the medium-temperature section B3, and the low-temperature section A3 includes an upper heat exchange section and a lower heat exchange section arranged in a vertical direction.

[0039] It is understandable that the high-temperature phase change tank C, the medium-temperature phase change tank B, and the low-temperature phase change tank A are equipped with upper and lower heat exchange sections, that is, upper and lower dual heat exchange channels. During the heat storage / release process, the molten salt can simultaneously pass through the upper and lower heat exchange sections to achieve uniform heat exchange in the corresponding phase change tank. This breaks the problem of temperature stratification in the corresponding phase change tank caused by traditional single-channel heat exchange, making the phase change medium in the tank more uniformly heated / released, avoiding local overheating or insufficient phase change in some areas, and improving the overall heat storage and release efficiency of the phase change medium.

[0040] Specifically, the high-temperature phase change tank C, the medium-temperature phase change tank B, and the low-temperature phase change tank A all extend vertically. The high-temperature phase change tank C includes a high-temperature tank body C1, which contains a high-temperature phase change medium C2 and a high-temperature section C3 (or a high-temperature heat exchange channel). The medium-temperature phase change tank B includes a medium-temperature tank body B1, which contains a medium-temperature phase change medium B2 and a medium-temperature section B3 (or a medium-temperature heat exchange channel). The low-temperature phase change tank A includes a low-temperature tank body A1, which contains a low-temperature phase change medium A2 and a low-temperature section A3 (or a low-temperature heat exchange channel).

[0041] like Figures 1 to 3 As shown, in some embodiments, each of the upper heat exchange section and the lower heat exchange section includes a first main pipe, a branch pipe and a second main pipe connected in sequence. The first main pipe and the second main pipe are arranged at intervals in the vertical direction. The branch pipe is located between the first main pipe and the second main pipe. There are multiple branch pipes arranged at intervals to simplify the overall structure of the upper heat exchange section and the lower heat exchange section and further ensure heat exchange uniformity.

[0042] like Figures 1 to 3 As shown, in some embodiments, both the first main pipe and the second main pipe extend horizontally, and multiple branch pipes extend vertically and are spaced apart horizontally.

[0043] like Figures 1 to 3 As shown, in some specific embodiments, the inlet of the molten salt buffer tank 1 is connected to the hot side outlet of the heat exchanger 5 and the three-way valve V2 via a three-way valve V1. The three-way valve V2 is connected to the first inlet and outlet of the upper heat exchange section and the first inlet and outlet of the lower heat exchange section of the low-temperature section A3 via a low-temperature heat exchange port A4. The second inlet and outlet of the upper heat exchange section and the second inlet and outlet of the lower heat exchange section of the low-temperature section A3 are connected to a three-way valve V4 via a three-way valve V3. The three-way valve V4 is also connected to the first inlet and outlet of the upper heat exchange section and the first inlet and outlet of the lower heat exchange section of the intermediate-temperature section B3. The second inlet and outlet of the upper heat exchange section and the second inlet and outlet of the lower heat exchange section of the intermediate-temperature section B3 are connected to the first inlet and outlet of the upper heat exchange section and the first inlet and outlet of the lower heat exchange section of the intermediate-temperature section B3. The second inlet and outlet are connected to the three-way valve V6 via three-way valve V5. The three-way valve V6 is also connected to the first inlet and outlet of the upper heat exchange section and the first inlet and outlet of the lower heat exchange section of the high-temperature section C3. The second inlet and outlet of the upper heat exchange section and the second inlet and outlet of the lower heat exchange section of the high-temperature section C3 are connected to the three-way valve V7 via the high-temperature heat exchange port C4. The three-way valve V7 is connected to the hot side inlet of the heat exchanger 5 and the outlet of the electric heater 3 via three-way valve V8. The outlet of the molten salt pump 2 is connected to the inlet of the electric heater 3 and the three-way valve V2 via three-way valve V9. The inlet of the molten salt pump 2 is connected to the outlet of the molten salt buffer tank 1.

[0044] An electric valve F1 is installed between three-way valve V1 and the hot-side outlet of heat exchanger 5; an electric valve F2 is installed between three-way valve V1 and three-way valve V2; an electric valve F3 is installed between three-way valve V2 and three-way valve V9; an electric valve F4 is installed between three-way valve V9 and the inlet of electric heater 3; an electric valve F5 is installed between the outlet of electric heater 3 and three-way valve V8; an electric valve F6 is installed between three-way valve V8 and three-way valve V7; an electric valve F7 is installed between three-way valve V8 and the hot-side inlet of heat exchanger 5; an electric valve F8 is installed between the cold-side inlet of heat exchanger 5 and water source 4; and an electric valve F9 is installed between the cold-side outlet of heat exchanger 5 and steam user 6.

[0045] like Figures 1 to 3 As shown, in some embodiments, the electric heater 3 is adapted to be powered by curtailed wind and solar power or peak-shaving power from thermal power, so as to use the curtailed wind and solar power or peak-shaving power from thermal power to heat the molten salt and provide a heat source for the system.

[0046] like Figure 4 As shown, in some embodiments, the cascade phase change thermal storage unit is a single unit; or, there are multiple cascade phase change thermal storage units connected in parallel. In other words, the specific number of cascade phase change thermal storage units can be replicated according to capacity requirements.

[0047] It is understood that the core of the flexible capacity adjustment function of this invention relies on the modular parallel design of the cascade phase change thermal storage unit. For the thermal storage needs of different scenarios, multiple standardized high, medium and low temperature phase change tanks A can be arranged in parallel at the same temperature level. Molten salt is diverted through pipelines and enters each group of phase change tanks at the same temperature level to complete the cascade thermal storage and release. The thermal storage capacity increases linearly with the number of parallel modules. Therefore, system expansion only requires upgrading the molten salt buffer tank 1 and the electric heater 3 in the same proportion according to the parallel scale to achieve flexible expansion of thermal storage capacity. The modification adaptability is strong, which greatly reduces the construction cost and cycle of expansion.

[0048] Therefore, compared with related technologies, the present invention has the following technical advantages: 1) The present invention has made innovations in the system, adopting a wide temperature range molten salt enhanced heat exchange and phase change heat storage module series high-density heat storage. Compared with traditional molten salt heat storage, it makes full use of the latent heat of the heat storage medium. Phase change traditional molten salt heat storage can significantly reduce the amount of molten salt consumed. Different temperature series heat exchange realizes more efficient heat transfer. 2) The invention innovates the process. During heat storage, the high-temperature molten salt flows through the high-temperature → medium-temperature → low-temperature phase change module in sequence to realize the stepwise "storage" of heat. During heat release, the low-temperature molten salt flows through the low-temperature → medium-temperature → high-temperature phase change module in sequence to realize the stepwise "removal" and "quality improvement" of heat. This counter-current stepwise coupling process design minimizes the heat exchange temperature difference and improves thermodynamic efficiency. 3) This invention innovates in capacity regulation. By connecting multiple phase change thermal storage modules with the same temperature layer in parallel, it realizes flexible expansion of thermal storage capacity in a "building block" manner. This regulation method is far more direct, more economical and easier to achieve large-scale and standardized systems than "mode" switching achieved through complex valve switching. 4) The invention innovates in functional synergy. The system cleverly uses wide-temperature-range molten salt as a "heat exchange medium" to convert the unstable heat energy of abandoned electricity into stable latent heat storage of phase change. The latent heat is then efficiently released through the molten salt stepped heating method, and finally produces high-quality steam with stable parameters. The entire process has a short energy transfer path, low heat loss, and fast system response.

[0049] An operating method for a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to an embodiment of the present invention, based on any of the above embodiments of the wide-temperature-range molten salt-driven cascade phase change thermal energy storage system, includes the following operating modes: like Figure 2As shown, in the heat storage mode, the molten salt with a wide temperature range in the molten salt buffer tank 1 is heated by the electric heater 3 to obtain high temperature molten salt. The high temperature molten salt enters the high temperature phase change tank C, the medium temperature phase change tank B and the low temperature phase change tank A in sequence to exchange heat with the phase change medium in the corresponding phase change tank step by step. The phase change medium absorbs heat to realize latent heat storage. The high temperature molten salt is cooled to low temperature molten salt and the low temperature molten salt flows back to the molten salt buffer tank 1. like Figure 3 As shown, in the exothermic mode, the molten salt with a wide temperature range in the molten salt buffer tank 1 enters the low-temperature phase change tank A, the medium-temperature phase change tank B, and the high-temperature phase change tank C in sequence to exchange heat with the phase change medium in the corresponding phase change tanks step by step. The phase change medium releases latent heat, and the molten salt is heated into high-temperature molten salt. The high-temperature molten salt enters the hot side of the heat exchanger 5 to heat the water entering the cold side of the heat exchanger 5 from the water source 4, and steam and low-temperature molten salt are obtained. The steam is delivered to the steam user 6, and the low-temperature molten salt is returned to the molten salt buffer tank 1.

[0050] The technical advantages of the operation method of the wide-temperature-range molten salt driven cascade phase change thermal energy storage system according to the embodiments of the present invention are the same as those of the wide-temperature-range molten salt driven cascade phase change thermal energy storage system described above, and will not be repeated here.

[0051] It is understandable that, based on the above description of the wide-temperature-range molten salt-driven cascade phase change thermal energy storage system, the specific operation method is as follows: I. Operation Method - Thermal Storage The core of thermal storage is to transfer the heat from the high-temperature molten salt heated by the electric heater to the high-temperature, medium-temperature, and low-temperature phase change medium in sequence according to the temperature gradient, thus realizing solid-liquid phase change thermal storage. Specific steps include: 1) Molten salt heating: Low-temperature molten salt in the molten salt buffer tank is transported to the electric heater by the molten salt pump. The electric heater uses the power curtailed wind and solar power / thermal power peak-shaving power to heat the molten salt to the target high temperature (matching the phase change temperature of the high-temperature phase change medium). 2) High-temperature heat storage: High-temperature molten salt enters the high-temperature section of the high-temperature phase change tank through pipelines and exchanges heat with the high-temperature phase change medium. The high-temperature phase change medium absorbs heat and changes from solid to liquid, realizing latent heat storage. After the molten salt releases some heat, its temperature drops to the medium temperature range, completing the high-temperature heat storage process. 3) Medium-temperature thermal storage: The medium-temperature molten salt flowing out of the high-temperature phase change tank enters the medium-temperature section of the medium-temperature phase change tank through pipelines, and exchanges heat with the medium-temperature phase change medium. The medium-temperature phase change medium absorbs heat and changes from solid to liquid, realizing latent heat storage. The molten salt continues to release heat and its temperature drops to the low-temperature range, completing the medium-temperature thermal storage process. 4) Low-temperature thermal storage: The low-temperature molten salt flowing out of the medium-temperature phase change tank enters the low-temperature section of the low-temperature phase change tank through pipelines, where it exchanges heat with the low-temperature phase change medium. The low-temperature phase change medium absorbs heat and changes from solid to liquid, realizing latent heat storage. After the molten salt releases the remaining heat, its temperature drops to a low temperature and flows back to the molten salt buffer tank, completing the thermal storage cycle.

[0052] II. Operating Method - Heat Release The core of the exothermic operation is to feed molten salt into the phase change tank in a reverse temperature gradient from low temperature to medium temperature to high temperature, absorbing the latent heat (and sensible heat) released by the phase change medium. Then, the softened water is heated through a molten salt-water heat exchanger to generate industrial steam. Specific steps are as follows: 1) Molten salt start-up: Molten salt in the molten salt buffer tank is transported by the molten salt pump and first enters the low-temperature section of the low-temperature phase change tank; 2) Low-temperature heat absorption: Molten salt exchanges heat with low-temperature phase change medium in the low-temperature section. The low-temperature phase change medium releases latent heat and changes from liquid to solid. Molten salt absorbs heat and its temperature rises, completing the low-temperature heat absorption process. 3) Intermediate-temperature heat absorption: Molten salt flowing out of the low-temperature phase change tank enters the intermediate-temperature section of the intermediate-temperature phase change tank and exchanges heat with the intermediate-temperature phase change medium. The intermediate-temperature phase change medium releases latent heat and changes from liquid to solid, and the temperature of the molten salt further rises to the intermediate-high temperature range, completing the intermediate-temperature heat absorption process. 4) High-temperature heat absorption: Molten salt flowing out of the medium-temperature phase change tank enters the high-temperature section of the high-temperature phase change tank and exchanges heat with the high-temperature phase change medium. The high-temperature phase change medium releases latent heat and changes from liquid to solid. The temperature of the molten salt rises to the target heat release temperature (to meet the 300℃ steam requirement), completing the high-temperature heat absorption process. 5) Steam generation: High-temperature molten salt enters the molten salt-water heat exchanger through pipelines. Water from the water source continuously enters the heat exchanger and undergoes efficient heat exchange with the high-temperature molten salt. The water is heated to 300°C to form industrial steam. The steam is delivered to steam users to meet industrial load requirements. The temperature of the molten salt decreases after releasing heat and flows back to the molten salt buffer tank, completing the heat release cycle.

[0053] In addition, the above process is achieved by switching valves.

[0054] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0055] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0056] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0058] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0059] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A wide-temperature-range molten salt-driven cascade phase change thermal energy storage system, characterized in that, include: A cascaded phase change thermal energy storage unit includes a high-temperature phase change tank, a medium-temperature phase change tank, and a low-temperature phase change tank connected in series via heat exchange channels. The heat exchange channels are in contact with the phase change media in the corresponding phase change tanks and can transfer heat. The high-temperature phase change tank is provided with a high-temperature heat exchange port connected to the heat exchange channels, and the low-temperature phase change tank is provided with a low-temperature heat exchange port connected to the heat exchange channels. A molten salt buffer tank and an electric heater are provided. The molten salt buffer tank is used to store molten salt with a wide temperature range. The outlet of the molten salt buffer tank is connected to the high-temperature heat exchange port and the low-temperature heat exchange port. The electric heater is provided between the outlet of the molten salt buffer tank and the high-temperature heat exchange port. The electric heater is capable of heating the molten salt with a wide temperature range flowing out of the molten salt buffer tank. The inlet of the molten salt buffer tank is also connected to the high-temperature heat exchange port and the low-temperature heat exchange port. A heat exchanger, wherein the hot side of the heat exchanger is connected in series between the high-temperature heat exchange port and the inlet of the molten salt buffer tank, the cold side inlet of the heat exchanger is connected to a water source, and the cold side outlet of the heat exchanger is connected to a steam user.

2. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to claim 1, characterized in that, The wide-temperature-range molten salt is a ternary Hitec XL salt, with a melting point below 150°C and a decomposition temperature above 500°C.

3. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to claim 1, characterized in that, The temperature of the phase change medium after heat storage in each of the high-temperature phase change tank, the medium-temperature phase change tank, and the low-temperature phase change tank is higher than the solid-liquid phase change temperature of the corresponding phase change medium, but lower than the liquid-gas phase change temperature of the corresponding phase change medium.

4. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to claim 1, characterized in that, The outlet of the molten salt buffer tank is equipped with a molten salt pump, which can provide pumping power for the molten salt flowing out of the molten salt buffer tank and regulate the flow rate of the molten salt so that the molten salt can enter the electric heater or the low-temperature heat exchange port.

5. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to claim 1, characterized in that, The heat exchange channel includes a high-temperature section, a medium-temperature section, and a low-temperature section connected in sequence. The high-temperature section is connected to the high-temperature heat exchange port, and the low-temperature section is connected to the low-temperature heat exchange port. The high-temperature section is located inside the high-temperature phase change tank, the medium-temperature section is located inside the medium-temperature phase change tank, and the low-temperature section is located inside the low-temperature phase change tank. At least one of the high-temperature section, the medium-temperature section, and the low-temperature section includes an upper heat exchange section and a lower heat exchange section arranged in a vertical direction.

6. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to claim 5, characterized in that, Each of the upper heat exchange section and the lower heat exchange section includes a first main pipe, a branch pipe and a second main pipe connected in sequence. The first main pipe and the second main pipe are arranged at intervals along the vertical direction. The branch pipe is located between the first main pipe and the second main pipe, and there are multiple branch pipes arranged at intervals.

7. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to claim 6, characterized in that, Both the first main pipe and the second main pipe extend horizontally, and the multiple branch pipes extend vertically and are spaced apart horizontally.

8. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to any one of claims 1-6, characterized in that, The electric heater is suitable for use with power from curtailed wind and solar power or peak-shaving power from thermal power plants.

9. The wide-temperature-range molten salt-driven cascade phase change thermal energy storage system according to claim 1, characterized in that, The cascade phase change thermal storage unit is a single unit; or... There are multiple cascade phase change thermal storage units, and all of the cascade phase change thermal storage units are connected in parallel.

10. An operation method for a wide-temperature-range molten salt-driven cascade phase change thermal energy storage system, based on the wide-temperature-range molten salt-driven cascade phase change thermal energy storage system as described in any one of claims 1-9, characterized in that, The operation method of the wide-temperature-range molten salt-driven cascade phase change thermal energy storage system includes the following working modes: In the heat storage mode, the molten salt with a wide temperature range in the molten salt buffer tank is heated by an electric heater to obtain high-temperature molten salt. The high-temperature molten salt enters the high-temperature phase change tank, the medium-temperature phase change tank and the low-temperature phase change tank in sequence to exchange heat with the phase change medium in the corresponding phase change tank step by step. The phase change medium absorbs heat to realize latent heat storage. The high-temperature molten salt is cooled to low-temperature molten salt and then flows back to the molten salt buffer tank. In the exothermic mode, the molten salt with a wide temperature range in the molten salt buffer tank sequentially enters the low-temperature phase change tank, the medium-temperature phase change tank, and the high-temperature phase change tank to exchange heat with the phase change medium in the corresponding phase change tanks in stages. The phase change medium releases latent heat, and the molten salt is heated into high-temperature molten salt. The high-temperature molten salt enters the hot side of the heat exchanger to heat the water entering the cold side of the heat exchanger from the water source, thereby obtaining steam and low-temperature molten salt. The steam is delivered to the steam user, and the low-temperature molten salt is returned to the molten salt buffer tank.

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