WO2026056324A1 - Integrated solid electric heat storage device based on molten salt heat storage and use method - Google Patents

Abstract

Provided in the present application are an integrated solid electric heat storage device based on molten salt heat storage and a use method. The device comprises flow channels, a circulation pipe, solid heat storage blocks, a heat exchanger and a molten salt pump; the plurality of flow channels are arranged in parallel, each of the flow channels containing molten salt; output ends of the flow channels are all connected to a first end of the circulation pipe, and input ends of the flow channels are all connected to a second end of the circulation pipe; the plurality of solid heat storage blocks are arranged in the molten salt in each of the flow channels; the heat exchanger and the molten salt pump are arranged on the circulation pipe; the molten salt pump is located on the side of the heat exchanger away from the output ends of the flow channels, and is used for providing power for the circulation of the liquid molten salt between the flow channels and the circulation pipe, wherein the liquid molten salt releases heat in the heat exchanger. The present application has one technical effect of reasonable design, thus improving heat transfer efficiency while significantly reducing investment costs.

Description

An integrated solid-state electric thermal storage device based on molten salt thermal storage and its usage method

Cross-reference to related applications

This application claims priority to Chinese Patent Application No. 202411290820.9, filed on September 14, 2024, entitled "An Integrated Solid Electric Thermal Storage Device Based on Molten Salt Thermal Storage and Its Usage Method", the entire contents of which are incorporated herein by reference.

Technical Field

This application belongs to the field of energy storage technology, specifically relating to an integrated solid-state electric thermal storage device based on molten salt thermal storage and its usage method.

Background Technology

The significance of energy storage technology lies in its ability to change the synchronous model of electricity production, transmission, and use, enabling staggered energy utilization across time. Energy storage systems can smooth energy fluctuations and perform peak shaving and valley filling, mitigating grid frequency fluctuations by instantaneously balancing differences in load and power generation. Solid-state electric thermal storage boilers and molten salt thermal storage technology are conventional large-scale energy storage technologies that have been widely applied in engineering projects. Solid-state electric thermal storage boilers convert electrical energy into sensible heat stored in solid thermal storage blocks. During heat release, air carries away the heat to heat feedwater, allowing direct operation at voltage levels such as 66kV/35kV/10kV. Although the storage temperature of solid thermal storage blocks can reach over 600℃, the heat release temperature is limited to only 80℃～130℃ due to the low thermal conductivity of air, resulting in significant energy loss.

Therefore, there is an urgent need for an integrated solid-state electric thermal storage device and its application method based on molten salt thermal storage, in order to improve heat transfer efficiency while reducing investment costs.

Summary of the Invention

This application aims to at least solve one of the technical problems existing in the prior art, and to provide a new technical solution for an integrated solid-state electric thermal storage device based on molten salt thermal storage and its usage method.

According to a first aspect of this application, an integrated solid-state electric thermal storage device based on molten salt thermal storage is provided, comprising:

The system includes flow channels and circulation pipes, with multiple flow channels connected in parallel and each flow channel filled with molten salt; the output end of each flow channel is connected to the first end of the circulation pipe, and the input end of each flow channel is connected to the second end of the circulation pipe.

Solid heat storage blocks are provided in the molten salt of each flow channel, and each solid heat storage block is used to convert electrical energy into heat energy and store it in the molten salt.

A heat exchanger and a molten salt pump are provided in the circulation pipeline, with the molten salt pump located on the side of the heat exchanger away from the output end of the flow channel. The molten salt pump is used to provide power for the circulation of liquid molten salt between the flow channel and the circulation pipeline; wherein the liquid molten salt releases heat in the heat exchanger.

Optionally, the solid heat storage block includes a metal shell, heat storage filler, and resistance wire;

The interior of the metal shell is filled with heat storage filler, and the interior of the heat storage filler is provided with resistance wire;

The resistance wire is energized to convert electrical energy into heat energy and deliver it to the heat storage filler, which is used for heat storage and can transfer the heat energy through the metal shell to the molten salt outside the metal shell.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a power regulator and a power grid;

Each of the solid thermal storage blocks is electrically connected to the power grid via the power regulator.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes an output pipe, an input pipe, an outlet isolation valve, and an inlet isolation valve;

The output end of each flow channel is connected to the first end of the circulation pipe through an output pipe, and the outlet isolation valve is located in the output pipe;

The input end of each flow channel is connected to the second end of the circulation pipe through an input pipe, and the inlet isolation valve is located in the input pipe.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a first temperature sensing element;

Each of the output pipes is equipped with a first temperature sensing element, which is used to measure the temperature of the molten salt at the output end of the flow channel.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a second temperature sensing element;

The second temperature sensing element is disposed on the metal casing and is used to measure the temperature of the solid heat storage block.

Optionally, each of the flow channels is located at the lowest point of the integrated solid-state electric thermal storage device.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a first branch pipe, a second branch pipe, a bypass valve, and a regulating valve;

The second end of the circulation pipe has two ports, one port is connected to the input pipe through the first branch pipe, and the other port is connected to the input pipe through the second branch pipe;

The regulating valve is located in the first branch pipe, and the bypass valve is located in the second branch pipe.

According to a second aspect of this application, a method of using an integrated solid-state electric thermal storage device based on molten salt thermal storage is provided, comprising:

During periods of low electricity demand, the power load is increased by a power regulator to convert surplus electricity from the grid into sensible heat from solid thermal storage blocks and molten salt. The surplus electricity from the grid flows through the solid thermal storage blocks via cables and is converted into heat. As the temperature of the solid thermal storage blocks gradually increases, the temperature of the molten salt inside the flow channels also increases and forms high-temperature molten salt.

During peak electricity demand, the power load is reduced or power is stopped by the power regulator. The stored high-temperature molten salt is used to heat the feedwater and generate steam through the heat exchanger. The steam is then used for external work or steam supply. First, all inlet isolation valves, outlet isolation valves, and regulating valves are opened, and the bypass valve is closed. The molten salt pump is then started to pump the high-temperature molten salt out of the flow channel. Second, the high-temperature molten salt enters the heat exchanger and releases heat to form low-temperature molten salt. The low-temperature molten salt then passes through the regulating valve and inlet isolation valve in sequence and circulates back into the flow channel.

Alternatively, the method of using the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes:

During system shutdown, each inlet isolation valve and each outlet isolation valve is opened, and the regulating valve is closed. The molten salt in the circulation pipeline and the heat exchanger flows back into the flow channel under the action of gravity.

One technical advantage of this application is:

In this embodiment, solid thermal storage blocks are used as the main thermal storage medium, and molten salt is used as the heat exchange medium. This not only leverages the low-cost advantage of solid thermal storage but also significantly improves heat transfer efficiency compared to air as the heat exchange medium. Furthermore, this integrated solid-state electric thermal storage device based on molten salt thermal storage can reduce the amount of molten salt used and avoid the need for anti-condensation equipment (electric heat tracing, electric heaters, etc.), thus helping to reduce operating costs.

In addition, this integrated solid-state electric thermal storage device based on molten salt thermal storage has significant advantages such as large scale, long duration, low cost, and modularity, which can assist the power grid in peak shaving and valley filling and improve the level of new energy consumption.

Attached Figure Description

Figure 1 is a schematic diagram of the structure of an integrated solid-state electric thermal storage device based on molten salt thermal storage according to an embodiment of this application;

Figure 2 is a schematic diagram of the solid heat storage block of an integrated solid electric heat storage device based on molten salt heat storage according to an embodiment of this application;

Figure 3 is a cross-sectional schematic diagram of the solid heat storage block of an integrated solid electric heat storage device based on molten salt heat storage according to an embodiment of this application.

In the diagram: 1. Flow channel; 2. Circulation pipe; 3. Molten salt; 4. Solid heat storage block; 41. Metal shell; 42. Heat storage packing; 43. Resistance wire; 5. Heat exchanger; 6. Molten salt pump; 7. Power regulator; 8. Power grid; 9. Output pipe; 10. Input pipe; 11. Outlet isolation valve; 12. Inlet isolation valve; 13. First temperature sensing element; 14. Second temperature sensing element; 15. First branch pipe; 16. Second branch pipe; 17. Bypass valve; 18. Regulating valve.

Detailed Implementation

Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values of the components and steps set forth in these embodiments do not limit the scope of the present application.

The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and/or" in the specification and claims indicates at least one of the connected objects, and the character "/" generally indicates that the preceding and following objects are in an "or" relationship.

In the description of this application, 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", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

According to a first aspect of this application, referring to Figures 1 to 3, an integrated solid-state electric thermal storage device based on molten salt thermal storage is provided, comprising:

The system includes a flow channel 1 and a circulation pipe 2. Multiple flow channels 1 are connected in parallel, and each flow channel 1 is filled with molten salt 3, meaning that the molten salt 3 remains in the flow channel 1 for a long time. The output end of each flow channel 1 is connected to the first end of the circulation pipe 2, and the input end of each flow channel 1 is connected to the second end of the circulation pipe 2.

Solid heat storage block 4, multiple solid heat storage blocks 4 are provided in the molten salt 3 in each flow channel 1. Each solid heat storage block 4 is used to convert electrical energy into heat energy and store it in the molten salt. That is, when the temperature of the solid heat storage block 4 rises, the molten salt 3 absorbs the heat of the solid heat storage block 4 and its temperature rises.

A heat exchanger 5 and a molten salt pump 6 are provided in the circulation pipe 2, and the molten salt pump 6 is located on the side of the heat exchanger 5 away from the output end of the flow channel 1. The molten salt pump 6 is used to provide power for the circulation of liquid molten salt 3 between the flow channel 1 and the circulation pipe 2; wherein, the liquid molten salt 3 releases heat in the heat exchanger 5.

In this embodiment, solid heat storage block 4 is used as the main heat storage medium and molten salt 3 as the heat exchange medium. This not only leverages the low-cost advantage of solid heat storage but also significantly improves heat transfer efficiency compared to air as the heat exchange medium. Furthermore, this integrated solid-state electric heat storage device based on molten salt heat storage can reduce the amount of molten salt 3 used and avoid the need for anti-condensation equipment (electric heat tracing, electric heaters, etc.), thus helping to reduce operating costs.

In addition, this integrated solid-state electric thermal storage device based on molten salt thermal storage has significant advantages such as large scale, long duration, low cost, and modularity, which can assist the power grid in peak shaving and valley filling and improve the level of new energy consumption.

Optionally, the solid heat storage block 4 includes a metal shell 41, a heat storage filler 42, and a resistance wire 43; for example, the heat storage filler 42 can be an insulating-heat storage filler made of magnesium oxide.

The interior of the metal shell 41 is filled with heat storage filler 42, and the interior of the heat storage filler 42 is provided with resistance wire 43;

The resistance wire 43 is energized to convert electrical energy into heat energy and deliver it to the heat storage filler 42, which is used for heat storage and can transfer the heat energy through the metal shell 41 to the molten salt outside the metal shell 41.

In the above embodiments, the solid heat storage block 4 has a reasonable structural design, which can effectively store the heat energy converted from electrical energy, and can transfer the heat energy to the soluble salt to achieve heat exchange.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a power regulator 7 and a power grid 8;

Each of the solid thermal storage blocks 4 is electrically connected to the power grid 8 via the power regulator 7.

In the above embodiment, the internal resistance of the solid heat storage block 4 is electrically connected to the power regulator 7 via a cable, and the power regulator 7 is connected to the power grid 8. The excess power of the power grid 8 flows through the resistance wire 43 through the power regulator 7. The current flowing through the resistance wire 43 can generate heat, which is stored in the heat storage filler 42.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes an output pipe 9, an input pipe 10, an outlet isolation valve 11, and an inlet isolation valve 12;

The output ends of each flow channel 1 are connected to the first end of the circulation pipe 2 through the output pipe 9, and the outlet isolation valve 11 is provided in the output pipe 9;

The input end of each flow channel 1 is connected to the second end of the circulation pipe 2 through the input pipe 10, and the inlet isolation valve 12 is disposed on the input pipe 10.

In the above embodiment, the output end of each flow channel 1 is connected to the first end of the circulation pipe 2 through the output pipe 9, and the input end of each flow channel 1 is connected to the second end of the circulation pipe 2 through the input pipe 10, making the connection between each flow channel 1 and the circulation pipe 2 relatively simple.

In addition, the soluble salt in the flow channel 1 can be effectively isolated by the outlet isolation valve 11 and the inlet isolation valve 12.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a first temperature sensing element 13;

Each of the output pipes 9 is provided with a first temperature sensing element 13, which is used to measure the temperature of the dissolved salt at the output end of the flow channel 1.

In the above embodiment, the temperature of the molten salt at the output end of the flow channel 1 can be measured in real time by the first temperature measuring element 13 to avoid the molten salt from overheating, thereby ensuring the safe and stable operation of the integrated solid electric thermal storage device based on molten salt thermal storage.

For example, by observing the temperature of the molten salt at the output end of the flow channel 1 measured by each of the first temperature measuring elements 13, the rotation speed of the molten salt pump 6 is adjusted in a timely manner to change the flow rate of the molten salt 3, thereby ensuring that the temperature of the molten salt 3 at the output end of the flow channel 1 is stable.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a second temperature sensing element 14;

The second temperature sensing element 14 is disposed on the metal casing 41, and the second temperature sensing element 14 is used to measure the temperature of the solid heat storage block 4. For example, the second temperature sensing element 14 is used to measure whether the temperature of the solid heat storage block 4 exceeds the limit.

In the above embodiment, the temperature of the solid heat storage block 4 can be measured in real time by the second temperature sensing element 14 to avoid the solid heat storage block 4 from overheating, thereby ensuring the safe and stable operation of the solid heat storage block 4.

Optionally, each of the flow channels 1 is located at the lowest point of the integrated solid-state electric thermal energy storage device. This allows the liquid soluble salt in the heat exchanger 5 and the circulation pipe 2 to flow smoothly back into the flow channel 1 under the action of gravity.

Optionally, the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes a first branch pipe 15, a second branch pipe 16, a bypass valve 17, and a regulating valve 18;

The second end of the circulation pipe 2 has two ports. One port is connected to the input pipe 10 through the first branch pipe 15, and the other port is connected to the input pipe 10 through the second branch pipe 16.

The regulating valve 18 is located on the first branch pipe 15, and the bypass valve 17 is located on the second branch pipe 16.

In the above embodiment, under shutdown conditions, the liquid molten salt in the heat exchanger 5 and the circulation pipe 2 can smoothly flow back to the flow channel 1 through the second branch pipe 16. During the pumping of the molten salt pump 6, the bypass valve 17 is in the closed state, and the flow rate of the liquid molten salt in the first branch pipe 15 is adjusted by the regulating valve 18.

It should be noted that the molten salt remains in a liquid state within this integrated solid-state electric thermal storage device based on molten salt heat storage. For example, each flow channel 1 is located at the lowest point of the integrated solid-state electric thermal storage device. When the integrated solid-state electric thermal storage device is shut down, the stored salt within it flows by gravity into the flow channel 1. Simultaneously, the flow channel 1 is equipped with an insulation and heating layer on its exterior, allowing for heating and insulation of the molten salt inside when its temperature decreases.

In one specific implementation, the solid thermal storage block converts electrical energy into heat energy in real time, and also has a heat storage function. When the integrated solid electric thermal storage device only heats and does not release heat, the molten salt does not flow, and the main function of the solid thermal storage block and the molten salt in the flow channel 1 is heat storage.

According to a second aspect of this application, a method of using an integrated solid-state electric thermal storage device based on molten salt thermal storage is provided, comprising:

During periods of low electricity demand, the power load is increased by the power regulator 7 to convert the surplus electrical energy of the grid 8 into sensible heat stored in the solid heat storage block 4 and molten salt 3. The surplus electrical energy of the grid 8 flows through the solid heat storage block 4 via the cable and is converted into heat. As the temperature of the solid heat storage block 4 gradually increases, the temperature of the molten salt 3 inside the flow channel 1 also continuously increases and forms high-temperature molten salt.

During peak electricity demand, the power load is reduced or power is stopped by the power regulator 7. The stored high-temperature molten salt 3 is used to heat the feedwater and generate steam by passing it through the heat exchanger 5. The steam is used to perform external work or supply steam. First, the inlet isolation valves 12, outlet isolation valves 11, and regulating valve 18 are opened, and the bypass valve 17 is closed. The molten salt pump 6 is started to pump the high-temperature molten salt out of the flow channel 1. Second, the high-temperature molten salt 3 enters the heat exchanger 5 and releases heat to form low-temperature molten salt. The low-temperature molten salt passes through the regulating valve 18 and the inlet isolation valve 12 in sequence and circulates into the flow channel 1.

In the above embodiment, the integrated solid-state electric thermal storage device based on molten salt thermal storage is rationally designed. Utilizing solid thermal storage block 4 as the main thermal storage medium and molten salt 3 as the heat exchange medium, it not only leverages the low-cost advantage of solid thermal storage but also significantly improves heat transfer efficiency compared to air as the heat exchange medium. Furthermore, this integrated solid-state electric thermal storage device based on molten salt thermal storage can reduce the amount of molten salt 3 used and avoid the need for anti-condensation equipment (electric heat tracing, electric heaters, etc.), thus helping to reduce operating costs.

Alternatively, the method of using the integrated solid-state electric thermal storage device based on molten salt thermal storage also includes:

During system shutdown, i.e. when neither heat is stored nor released, the inlet isolation valves 12 and outlet isolation valves 11 are opened, and the regulating valve 18 is closed. The molten salt 3 in the circulation pipe 2 and the heat exchanger 5 flows back to the flow channel 1 under the action of gravity to prevent the molten salt 3 from staying in the circulation pipe 2 and the heat exchanger 5 for a long time and solidifying.

In the above embodiment, during system shutdown, the molten salt 3 in the circulation pipe 2 and heat exchanger 5 flows back to the flow channel 1 under the action of gravity, which better ensures the safety of system use.

It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to be within the scope of protection of this application.

Claims (10)

An integrated solid-state electric thermal storage device based on molten salt thermal storage, characterized in that it comprises: The system includes flow channels and circulation pipes, with multiple flow channels connected in parallel and each flow channel filled with molten salt; the output end of each flow channel is connected to the first end of the circulation pipe, and the input end of each flow channel is connected to the second end of the circulation pipe. Solid heat storage blocks are provided in the molten salt of each flow channel, and each solid heat storage block is used to convert electrical energy into heat energy and store it in the molten salt. A heat exchanger and a molten salt pump are provided in the circulation pipeline, with the molten salt pump located on the side of the heat exchanger away from the output end of the flow channel. The molten salt pump is used to provide power for the circulation of liquid molten salt between the flow channel and the circulation pipeline; wherein the liquid molten salt releases heat in the heat exchanger. The integrated solid-state electric thermal storage device based on molten salt thermal storage according to claim 1 is characterized in that the solid thermal storage block includes a metal shell, thermal storage filler and resistance wire; The interior of the metal shell is filled with heat storage filler, and the interior of the heat storage filler is provided with resistance wire; The resistance wire is energized to convert electrical energy into heat energy and deliver it to the heat storage filler, which is used for heat storage and can transfer the heat energy through the metal shell to the molten salt outside the metal shell. The integrated solid-state electric thermal storage device based on molten salt thermal storage according to claim 2 is characterized in that it further includes a power regulator and a power grid; Each of the solid thermal storage blocks is electrically connected to the power grid via the power regulator. The integrated solid-state electric thermal energy storage device based on molten salt thermal energy storage according to claim 3 is characterized in that it further includes an output pipe, an input pipe, an outlet isolation valve, and an inlet isolation valve; The output end of each flow channel is connected to the first end of the circulation pipe through an output pipe, and the outlet isolation valve is located in the output pipe; The input end of each flow channel is connected to the second end of the circulation pipe through an input pipe, and the inlet isolation valve is located in the input pipe. The integrated solid-state electric thermal storage device based on molten salt thermal storage according to claim 4 is characterized in that it further includes a first temperature sensing element; Each of the output pipes is equipped with a first temperature sensing element, which is used to measure the temperature of the molten salt at the output end of the flow channel. The integrated solid-state electric thermal storage device based on molten salt thermal storage according to claim 5 is characterized in that it further includes a second temperature sensing element; The second temperature sensing element is disposed on the metal casing and is used to measure the temperature of the solid heat storage block. The integrated solid-state electric thermal storage device based on molten salt thermal storage according to claim 6 is characterized in that each of the flow channels is located at the lowest point of the integrated solid-state electric thermal storage device. The integrated solid-state electric thermal storage device based on molten salt thermal storage according to claim 7 is characterized in that it further includes a first branch pipe, a second branch pipe, a bypass valve, and a regulating valve; The second end of the circulation pipe has two ports, one port is connected to the input pipe through the first branch pipe, and the other port is connected to the input pipe through the second branch pipe; The regulating valve is located in the first branch pipe, and the bypass valve is located in the second branch pipe. A method of using an integrated solid-state electric thermal storage device based on molten salt thermal storage, characterized in that the integrated solid-state electric thermal storage device based on molten salt thermal storage as described in claim 8 includes: During periods of low electricity demand, the power load is increased by a power regulator to convert surplus electricity from the grid into sensible heat from solid thermal storage blocks and molten salt. The surplus electricity from the grid flows through the solid thermal storage blocks via cables and is converted into heat. As the temperature of the solid thermal storage blocks gradually increases, the temperature of the molten salt inside the flow channels also increases and forms high-temperature molten salt. During peak electricity demand, the power load is reduced or power is stopped by the power regulator. The stored high-temperature molten salt is used to heat the feedwater and generate steam through the heat exchanger. The steam is then used for external work or steam supply. First, all inlet isolation valves, outlet isolation valves, and regulating valves are opened, and the bypass valve is closed. The molten salt pump is then started to pump the high-temperature molten salt out of the flow channel. Second, the high-temperature molten salt enters the heat exchanger and releases heat to form low-temperature molten salt. The low-temperature molten salt then passes through the regulating valve and inlet isolation valve in sequence and circulates back into the flow channel. The method of using the integrated solid-state electric thermal storage device based on molten salt thermal storage according to claim 9 is characterized in that it further includes: During system shutdown, each inlet isolation valve and each outlet isolation valve is opened, and the regulating valve is closed. The molten salt in the circulation pipeline and the heat exchanger flows back into the flow channel under the action of gravity.