Fused salt coupling sand tank energy storage system

Abstract

The invention discloses a molten salt coupling sand tank energy storage system. The system comprises a salt storage tank, a molten salt pump and a molten salt heater which are sequentially connected. High-temperature molten salt at an outlet of the molten salt heater is communicated with an inlet of the heat exchanger; an outlet of the heat exchanger is circularly communicated with the salt storage tank; a nitrogen cylinder is arranged on the heat exchanger, and nitrogen in the nitrogen cylinder exchanges heat with the molten salt in the heat exchanger and then is input into the sand storage tank for heating the sand storage tank; a high-temperature molten salt outlet of the molten salt heater is connected with the sand storage tank and is used for heating sand in the sand storage tank; and the high-temperature molten salt output end of the heating sand storage tank is communicated with the molten salt storage tank through the heat exchanger. By combining the low-cost and high-stability heat storage characteristics of the sand and the efficient heat transfer advantages of the molten salt, the device has the advantages of high heat storage density, safe operation, good economy and the like, and is suitable for large-scale energy storage application.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and more specifically to a system for energy storage using molten salt coupled with a sand tank. Background Technology

[0002] Currently, there are various energy storage methods, among which molten salt thermal energy storage technology has been widely used in fields such as concentrated solar power (CSP) and industrial thermal energy storage due to its high energy storage density and relatively mature engineering application experience. Traditional molten salt thermal energy storage systems typically rely on solar collectors or electric heaters to heat solid salt to a molten state, utilizing the molten salt to store a large amount of thermal energy at high temperatures. These systems generally have dedicated molten salt storage tanks and require continuous insulation measures to prevent the molten salt from solidifying at low temperatures, causing pipeline blockage and equipment damage.

[0003] However, the overall heat capacity and long-term economic viability of this type of thermal storage system using molten salt as the single medium still face challenges. Molten salt itself is expensive, and the energy consumption required for thermal management to keep the entire system above its freezing point constitutes ongoing operating expenses.

[0004] Sand is widely available, extremely inexpensive, chemically stable, and can withstand temperatures of several hundred degrees Celsius, making it a promising candidate for high-temperature thermal storage. Some research and practical applications have verified the feasibility of using sand as a solid-filled bed thermal storage medium. Its working principle involves direct or indirect heat exchange through the flow of heat transfer oil or other hot fluids through the sand bed.

[0005] However, existing sand thermal energy storage systems are limited by the heat transfer fluids. Common heat transfer gases such as nitrogen have low thermal conductivity compared to sand, which may limit the heat transfer rate during energy storage and release, requiring a large heat exchange area to achieve effective power output. Heat transfer oils have limited maximum temperatures and pose a flammability risk, limiting the system's temperature ceiling and thus its energy storage density.

[0006] Existing technologies include, for example, the Suzhou molten salt thermal power plant flexibility technology research and demonstration application project. This project has two molten salt storage tanks, and the initial costs associated with purchasing molten salt and constructing and maintaining these tanks are substantial. For example, the megawatt-hour "sand thermal battery" pilot plant of my country's first sand-based battery heating project. This project uses an air fluidized bed to exchange heat with sand. The system is large in size and requires the addition of a fluidization device, which generates additional power consumption. Summary of the Invention

[0007] To overcome the shortcomings of the existing technologies mentioned above, this invention provides a molten salt coupled sand tank energy storage system. Molten salt is used as an intermediate heat transfer medium, and sand is used as a heat storage medium. The sand is heated to 500-550℃ for long-term storage. The system features high heat storage and release power, large heat storage capacity, relatively low cost, high energy conversion efficiency, and significantly improved safety.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A system for energy storage of molten salt coupled with sand tanks includes a salt storage tank and a sand storage tank connected in sequence; The salt storage tank is connected in sequence to a molten salt pump and a molten salt heater; The high-temperature molten salt at the outlet of the molten salt heater is connected to the molten salt side inlet of the second heat exchanger, and the molten salt side outlet of the second heat exchanger is circulated and connected to the salt storage tank. A nitrogen cylinder is installed on the heat exchanger 2. The nitrogen in the nitrogen cylinder exchanges heat with the molten salt in the heat exchanger 2 and is then fed into the sand storage tank to heat the sand in the sand storage tank. The high-temperature molten salt outlet of the molten salt heater is connected to a sand storage tank for heating the sand in the sand storage tank. The high-temperature molten salt output end of the heated sand storage tank is connected to the molten salt storage tank through a heat exchanger.

[0009] The sand storage tank is an integrated container for heat storage / exchange with a vertical packed bed inside. It is used to contain quartz sand energy storage material and ensure that molten salt and nitrogen gas can be efficiently and uniformly exchanged in direct contact. Its interior includes, from top to bottom, a liquid / gas distribution zone, a quartz sand packed bed, a porous support distribution plate, and a bottom collection zone. The flow direction of all heat transfer media is designed to be from top to bottom.

[0010] The liquid / gas distribution zone is located at the top of the sand storage tank and is connected to the pipes of the fifth and sixth outlets of the gate valve. This zone is equipped with a fluid dispersion device to evenly distribute the incoming molten salt or nitrogen gas to the entire cross-section of the tank, avoiding direct impact of the fluid on the sand bed surface to form channel flow and ensuring the uniformity of subsequent flow. The quartz sand-filled bed is the core area of ​​the thermal storage, filled with sieved and pretreated quartz sand; the sand particle size is 0.5mm to 3mm; this range ensures a large thermal storage density and heat transfer area while facilitating medium flow and reducing flow resistance. The porous support distribution plate is horizontally set at the bottom of the quartz sand-filled bed and is a key functional component. The distribution plate is made of high-temperature resistant and molten salt corrosion resistant materials (such as special alloys or high-temperature ceramics), and its function is to uniformly guide the flow, support the bed, and trap sand particles. The bottom collection area and outlet are located below the porous support distribution plate. The heat transfer medium after heat exchange with the sand bed collects in this area and flows out of the sand storage tank through the bottom pipe of the tank. The structure of this area is easy to maintain and can be equipped with a flushing interface to prevent and clean possible impurity deposits. A high-temperature filter can be installed on the outlet pipe as an additional safeguard against the escape of trace amounts of fine sand. The outlet of the molten salt storage tank is connected to gate valve one via a pipeline. Gate valve one is connected to the inlet of the molten salt pump via a pipeline. The outlet of the molten salt pump is connected to throttle valve two via a pipeline. Throttle valve two is connected to the inlet of the molten salt heater via a pipeline. The outlet of the molten salt heater is connected to gate valve two via a pipeline. Gate valve two is connected to gate valve five via a pipeline. Gate valve five is connected to the inlet of the sand storage tank via a pipeline. The outlet of the sand storage tank is connected to gate valve seven via a pipeline. Gate valve seven is connected to the molten salt side inlet of heat exchanger one via a pipeline. The molten salt side outlet of heat exchanger one is connected to gate valve ten via a pipeline. Gate valve ten is connected to the inlet of the molten salt storage tank via a pipeline.

[0011] A bypass is installed directly between the outlet of the molten salt storage tank and the outlet of the molten salt pump via a pipeline, and a throttle valve is installed on the bypass. A bypass is installed between the outlet of the molten salt heater and the outlet of heat exchanger one via a pipeline, and gate valve three is installed on the bypass; A bypass is installed between the outlet of gate valve two and the outlet of the sand storage tank via a pipeline, and gate valve four is installed on the bypass. A bypass is installed between the outlet of the sand storage tank and the outlet of heat exchanger 1 via a pipeline, and gate valve 8 is installed on the bypass. A pipe is installed at the outlet of the sand storage tank to directly connect to the ambient atmosphere, and a gate valve is installed on the pipe. A bypass of gate valve 10 is installed through a pipeline, and gate valve 11 and the molten salt side flow channel of heat exchanger 2 are installed in sequence on the bypass. The outlet of the nitrogen cylinder is connected to the nitrogen side inlet of heat exchanger two, and the nitrogen side outlet of heat exchanger two is connected to the inlet of the sand storage tank through a bypass pipeline, with gate valve six installed on the bypass.

[0012] The second heat exchanger is used to supply nitrogen gas for heating preheated sand using molten salt during the preheating stage. One side is high-temperature molten salt, and the other side is low-temperature nitrogen gas.

[0013] The outer wall of the molten salt storage tank is covered with tightly wound electric heating tape, which is wrapped with heat insulation materials such as rock wool to keep the molten salt inside the tank in a molten state. The outer wall of the sand storage tank is wrapped with heat insulation materials such as refractory bricks, rock wool, and aluminum silicate fiber, which is conducive to the long-term storage of heat energy inside the sand storage tank. All pipes in the energy storage system are wrapped with insulation cotton to reduce heat loss of molten salt during pipeline flow and to prevent molten salt from condensing and clogging. Electric heating tape is tightly and evenly wrapped around all gate valves 1, 2, 3, 4, 5, 7, 8, 10, 11, 1 throttle valve 1, and 2 through which the molten salt flows on the pipeline to prevent the molten salt from condensing and blocking it. The molten salt heater is an immersion tubular electric heater, which heats molten salt and converts electrical energy into the heat energy of the molten salt. It has the advantages of extremely high thermal efficiency and rapid and uniform heating. The bypass function of the throttling valve 1 in the energy storage system is to fine-tune the flow rate of molten salt flowing into the molten salt heater. By adjusting the opening of throttling valve 1 and throttling valve 2, a small flow rate of molten salt in the system can be achieved during heat preservation.

[0014] The bypass of the gate valve is a safety bypass designed to prevent molten salt from condensing and clogging the main channel, and it does not open during normal system operation.

[0015] A method of using a molten salt coupled sand tank energy storage system includes the following steps; During the preheating phase at the start of energy storage, close gate valves 2, 4, 5, 7, 8, 10, and throttle valve 1; open gate valves 1, 3, 6, 9, 11, and throttle valve 2; run the molten salt pump and molten salt heater; and open the nitrogen cylinder to start heat exchanger 2. During the preheating stage, molten salt flows from the molten salt storage tank to the molten salt pump, and is then pumped into the molten salt heater, where it is heated to 500-550°C. The high-temperature molten salt from the outlet of the molten salt heater flows into heat exchanger II, where it exchanges heat with low-temperature nitrogen gas, and then flows back to the molten salt storage tank to complete the cycle. During the preheating stage, nitrogen from the nitrogen cylinder flows into heat exchanger two, where it exchanges heat with the molten salt and is heated to 250-300°C. Then, it flows into the sand storage tank to exchange heat with the sand, ultimately heating the sand in the entire sand storage tank to 240-250°C. The nitrogen flowing out of the sand storage tank is directly discharged into the atmosphere. When the temperature of the sand in the sand storage tank is higher than 240℃, the preheating stage ends and the molten salt heat storage stage begins. The nitrogen cylinder is closed, and gate valves three, four, six, seven, nine, eleven, and throttle valve one are closed. Gate valves one, two, five, eight, ten, and throttle valve two are opened, and the molten salt pump and molten salt heater are started. During the molten salt thermal storage stage, molten salt flows from the molten salt storage tank to the molten salt pump, and is then pumped into the molten salt heater, where it is heated to 500-550°C. The high-temperature molten salt from the outlet of the molten salt heater flows into the sand storage tank to exchange heat with the sand, ultimately heating the sand in the entire sand storage tank to 500-550°C. The molten salt flowing out of the sand storage tank flows directly back into the molten salt storage tank, completing the cycle. During the heat preservation stage, close gate valves three, four, six, seven, and eleven, open gate valves one, two, five, eight, and ten, adjust the opening of throttle valve one and throttle valve two, and intermittently run the molten salt pump and molten salt heater at low power to maintain a small flow rate in the pipeline, maintain the salt temperature in the pipeline above 250℃, and keep it in a molten state; During the energy release phase, close gate valves 3, 4, 6, 8, 9, 11, and throttle valve 1; open gate valves 1, 2, 5, 7, 10, and throttle valve 2; start the circulation of the power generation medium to start the heat exchanger and the molten salt pump; and shut down the molten salt heater. During the energy release phase, molten salt flows from the molten salt storage tank to the molten salt pump, then flows through the molten salt heater without heating, and then flows into the sand storage tank to exchange heat with the high-temperature sand. After heat exchange, the high-temperature molten salt flows into the heat exchanger to exchange heat with the power generation working fluid, and then flows back to the molten salt storage tank to complete the cycle.

[0016] The internal fluid of the pipelines that participate in the operation during the molten salt heat storage stage, the heat preservation stage and the energy release stage is molten salt. During the preheating phase before energy storage begins, the internal fluid in the pipeline containing gate valve six, the inlet and outlet pipelines of the sand storage tank, and the pipeline containing gate valve nine is nitrogen, while the fluid in the other operating pipelines is molten salt.

[0017] The energy storage material in the sand storage tank is quartz sand; the heat exchanger is used to transfer the stored energy to the power generation working fluid, with one side being high-temperature molten salt and the other side being the working fluid participating in the power generation cycle, which is low-temperature water vapor or supercritical carbon dioxide. The beneficial effects of this invention are: This invention innovatively combines molten salt as an intermediate heat transfer medium with the thermal storage properties of sand to construct an energy storage system with high safety, high energy efficiency, and high economy. Specifically, this system has the following advantages: This invention uses inexpensive sand as the primary heat storage medium, replacing some or all of the molten salt used in traditional systems, thereby significantly reducing the cost of heat storage materials. Simultaneously, molten salt, as a highly efficient heat transfer fluid, can achieve rapid heat storage and release at high temperatures of 500–550℃, enabling the system to possess both high energy density and good economic efficiency. This invention introduces an independent nitrogen preheating stage before energy storage, preheating the sand to above 240°C, effectively avoiding the risk of condensation and blockage when high-temperature molten salt enters the low-temperature sand bed, and significantly improving the safety and operational stability of the system during startup and operation. This invention incorporates multiple bypasses and valve combinations with different functions, enabling flexible switching between various operating conditions such as preheating, energy storage, heat preservation, and energy release. By adjusting the opening of the throttle valve in the parallel bypass of the molten salt pump and the throttle valve in the main line, a small flow rate of molten salt can be maintained during the heat preservation stage, preventing solidification and reducing energy consumption. Furthermore, the sand tank bypass can serve as an emergency flow path in case of accidental solidification in the main channel, improving system reliability.

[0018] In this invention, all pipes and valves through which the molten salt flows are equipped with electric heat tracing and insulation layers. Combined with an intermittent low-power operation strategy, this ensures that the pipeline remains in a molten state for a long time, further enhancing the system's anti-condensation capability and long-term operational stability.

[0019] This invention achieves efficient coupling of molten salt heat transfer and sand thermal storage through a unique system structure and process design. While ensuring system power density and operating efficiency, it significantly reduces construction and maintenance costs and is suitable for large-scale, long-term energy storage scenarios. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a molten salt coupled sand tank energy storage system. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings.

[0022] A system for molten salt coupled with sand tank energy storage includes a sand tank preheating stage before energy storage, an energy storage cycle stage, and an energy release cycle stage; During the preheating stage of the sand storage tank before energy storage, electrical energy is converted into the heat energy of nitrogen gas. The nitrogen gas is used to preheat the cold sand in sand storage tank 4 to prevent condensation when molten salt is introduced. During the energy storage cycle stage, electrical energy is converted into the thermal energy of molten salt. The molten salt is used to heat the sand in the sand storage tank 4. The insulated sand storage tank 4 stores the hot sand for a long time to achieve the purpose of energy storage. During the energy release cycle, the thermal energy stored in the hot sand in sand storage tank 4 is transferred to the molten salt, and the molten salt transfers heat to the power generation medium, ultimately realizing the conversion of thermal energy into electrical energy.

[0023] This invention uses inexpensive sand as the primary heat storage medium, replacing some or all of the molten salt used in traditional systems, thereby significantly reducing the cost of heat storage materials. Simultaneously, molten salt, as a highly efficient heat transfer fluid, can achieve rapid heat storage and release at high temperatures of 500-550℃, enabling the system to possess both high energy density and good economic efficiency.

[0024] like Figure 1 As shown, the energy storage system includes a molten salt storage tank 1, a molten salt pump 2, a molten salt heater 3, a sand storage tank 4, a heat exchanger 1 5, a heat exchanger 2 6, a nitrogen cylinder 7, a gate valve 1 8, a throttle valve 1 9, a gate valve 2 10, a gate valve 3 11, a gate valve 4 12, a gate valve 5 13, a gate valve 6 14, a gate valve 7 15, a gate valve 8 16, a gate valve 9 17, a gate valve 10 18, a gate valve 11 19, and a throttle valve 2 20. The outlet of the molten salt storage tank 1 is connected to gate valve 8 via a pipe. Gate valve 8 is connected to the inlet of the molten salt pump 2 via a pipe. The outlet of the molten salt pump 2 is connected to throttle valve 20 via a pipe. Throttling valve 20 is connected to the inlet of the molten salt heater 3 via a pipe. The outlet of the molten salt heater 3 is connected to gate valve 10 via a pipe. Gate valve 10 is connected to gate valve 13 via a pipe. Gate valve 13 is connected to the inlet of the sand storage tank 4 via a pipe. The outlet of the sand storage tank 4 is connected to gate valve 15 via a pipe. Gate valve 15 is connected to the molten salt side inlet of heat exchanger 5 via a pipe. The molten salt side outlet of heat exchanger 5 is connected to gate valve 18 via a pipe. Gate valve 18 is connected to the inlet of the molten salt storage tank 1 via a pipe. A bypass is installed directly between the outlet of molten salt storage tank 1 and the outlet of molten salt pump 2 via a pipeline, and a throttle valve 9 is installed on the bypass; a bypass is installed between the outlet of molten salt heater 3 and the outlet of heat exchanger 5 via a pipeline, and a gate valve 11 is installed on the bypass; a bypass is installed between the outlet of gate valve 10 and the outlet of sand storage tank 4 via a pipeline, and a gate valve 12 is installed on the bypass; a bypass is installed between the outlet of sand storage tank 4 and the outlet of heat exchanger 5 via a pipeline. A bypass is provided, with gate valve 816 installed on the bypass; a pipeline is then installed at the outlet of sand storage tank 4 directly to the ambient atmosphere, with gate valve 917 installed on the pipeline; a bypass with gate valve 1018 is installed through the pipeline, with gate valve 1119 and the molten salt side flow channel of heat exchanger 26 installed in sequence on the bypass; the outlet of nitrogen cylinder 7 is connected to the nitrogen side inlet of heat exchanger 26, and the nitrogen side outlet of heat exchanger 26 is connected to the inlet of sand storage tank 4 through the bypass pipeline, with gate valve 614 installed on the bypass; This invention incorporates multiple bypasses and valve combinations with different functions, enabling flexible switching between various operating conditions such as preheating, energy storage, heat preservation, and energy release. For example, by adjusting the opening of the throttle valve in the parallel bypass of the molten salt pump 2 and the throttle valve in the main circuit, a small flow rate of molten salt can be maintained during the heat preservation stage, preventing solidification and reducing energy consumption.

[0025] The pipelines operating during the molten salt heat storage, heat preservation, and energy release stages all contain molten salt as their internal fluid. During the preheating stage before energy storage begins, the internal fluid in the pipeline containing gate valve 614, the inlet and outlet pipelines of sand storage tank 4, and the pipeline containing gate valve 917 is nitrogen; the fluid in the remaining operating pipelines is molten salt. The energy storage material in the sand storage tank 4 is quartz sand. Compared with molten salt, quartz sand has a higher cost. Therefore, quartz sand is more economical and suitable for large-scale, long-term thermal storage applications. The function of the heat exchanger 5 is to transfer the stored energy to the power generation working medium. One side of it is high-temperature molten salt, and the other side is low-temperature water vapor or supercritical carbon dioxide, which can participate in the power generation cycle. Then, the power generation working medium converts the thermal energy stored in the system back into electrical energy. The function of the heat exchanger 6 is to use molten salt to heat the nitrogen gas used for preheating sand during the preheating stage. One side is high-temperature molten salt, and the other side is low-temperature nitrogen gas. The outer wall of the molten salt storage tank 1 is covered with a tightly wound electric heating tape, which is wrapped with heat insulation materials such as rock wool to keep the molten salt inside the tank in a molten state. The outer wall of the sand storage tank 4 is wrapped with heat insulation materials such as refractory bricks, rock wool, and aluminum silicate fiber, which is conducive to the long-term storage of heat energy inside the sand storage tank. All pipes of the energy storage system are wrapped with thermal insulation cotton to reduce heat loss of molten salt during pipeline flow and to prevent molten salt from condensing and clogging. Electric heating tape is tightly and evenly wrapped around all the gate valves 1-8, 2-10, 3-11, 4-12, 5-13, 7-15, 8-16, 10-18, 11-19, 1-9, and 2-20 through which the molten salt flows on the pipeline to prevent the molten salt from condensing and blocking it. The molten salt heater 3 is an immersion tubular electric heater, which heats the molten salt and converts electrical energy into the heat energy of the molten salt. It has the advantages of extremely high thermal efficiency and rapid and uniform heating. The bypass function of the throttle valve 9 in the energy storage system is to finely adjust the flow rate of molten salt flowing into the molten salt heater 3. By adjusting the opening of the throttle valve 9 and the throttle valve 20, a small flow rate of molten salt in the system can be achieved during heat preservation. The bypass of the gate valve 412 is a safety bypass designed to prevent molten salt from condensing and blocking the main channel, and it does not open during normal system operation.

[0026] A method of using a molten salt coupled sand tank energy storage system includes the following steps; During the preheating phase at the start of energy storage, close gate valves 210, 412, 513, 715, 816, 1018, and throttle valve 19; open gate valves 18, 31, 614, 917, 111, and throttle valve 20; start molten salt pump 2 and molten salt heater 3; and open nitrogen cylinder 7 to start heat exchanger 26. During the preheating stage, molten salt flows from molten salt storage tank 1 to molten salt pump 2, and is then pumped into molten salt heater 3, where it is heated to 500-550°C. The high-temperature molten salt at the outlet of molten salt heater 3 flows into heat exchanger 2 6, where it exchanges heat with low-temperature nitrogen gas, and then flows back to molten salt storage tank 1 to complete the cycle. During the preheating stage, nitrogen gas in nitrogen cylinder 7 flows into heat exchanger 6 to exchange heat with molten salt and is heated to 250-300℃. Then it flows into sand storage tank 4 to exchange heat with sand, and finally heats the sand in the entire sand storage tank to 240-250℃. The nitrogen gas flowing out of the sand storage tank is directly discharged into the atmosphere. When the temperature of the sand in sand storage tank 4 is higher than 240℃, the preheating stage ends and the molten salt heat storage stage begins. Nitrogen cylinder 7 is closed, and gate valves 311, 412, 614, 715, 917, 111, and throttle valve 19 are closed. Gate valves 18, 210, 513, 816, 1018, and throttle valve 20 are opened. Molten salt pump 2 and molten salt heater 3 are started. During the molten salt heat storage stage, molten salt flows from molten salt storage tank 1 to molten salt pump 2, and is then pumped into molten salt heater 3, where it is heated to 500-550℃. The high-temperature molten salt at the outlet of molten salt heater 3 flows into sand storage tank 4 to exchange heat with sand, ultimately heating all the sand in sand storage tank 4 to 500-550℃. The molten salt flowing out of sand storage tank flows directly back to molten salt storage tank 1, completing the cycle. During the heat preservation stage, close gate valves 311, 412, 614, 715, and 1119, and open gate valves 18, 210, 513, 816, and 1018. Adjust the opening of throttle valves 19 and 20, and intermittently operate molten salt pump 2 and molten salt heater 3 at low power to maintain a small flow rate in the pipeline and keep the salt temperature in the pipeline above 250℃ to maintain the molten state. During the energy release phase, close gate valves 31, 41, 61, 81, 91, 111, and throttle valve 19; open gate valves 18, 210, 513, 715, 1018, and throttle valve 20; start the circulation of the power generation medium to start heat exchanger 15; start molten salt pump 2; and shut down molten salt heater 3. During the energy release phase, molten salt flows from molten salt storage tank 1 to molten salt pump 2, then flows through molten salt heater 3 without heating, and then flows into sand storage tank 4 to exchange heat with high-temperature sand. After heat exchange, the high-temperature molten salt flows into heat exchanger 5 to exchange heat with the power generation working fluid, and then flows back to molten salt storage tank 1 to complete the cycle.

[0027] Example: Based on this invention, a molten salt coupled sand tank energy storage system with a storage capacity of 10 MW·h is designed. The designed thermal storage temperature is 550℃, the quartz sand filling amount is 50t, the molten salt consumption is 20t, and the maximum flow rate of the molten salt pump 2 is 25m³ / h. 3 / h, the maximum heating power of molten salt heater 3 is 2MW; During the preheating stage, molten salt pump 2 is started to drive the molten salt circulation at a flow rate of 15 m³ / h. At the same time, molten salt heater 3 is started and operates at a power of 1 MW to heat the molten salt to 450℃. The high-temperature molten salt flows through the molten salt side of heat exchanger 2 6, where it transfers heat to nitrogen gas, and its own temperature drops to 350℃ before returning to molten salt storage tank 1.

[0028] Nitrogen gas from nitrogen cylinder 7 is heated to 280°C in heat exchanger 2 6, and then enters sand storage tank 4 through gate valve 6 14. As the hot nitrogen flows through the cold sand bed, it undergoes thorough heat exchange with the sand, transferring its heat to the sand. After heat exchange, the nitrogen temperature drops to approximately 50°C and is directly discharged into the atmosphere through gate valve 9 17. This process continues until the overall temperature of the sand in sand storage tank 4 reaches above 240°C. The total heat input for this stage is approximately 2.8 MW·h, and the total time is approximately 3.5 hours. During the energy storage phase, the nitrogen system molten salt pump 2 is shut down and operated at its rated flow rate of 25 m³ / h. The molten salt heater 3 is switched to full-load operation at 2 MW, heating the flowing molten salt to 550°C. The 550°C high-temperature molten salt flows into the sand storage tank 4 from the top through gate valves 2 (10) and 5 (13). Under gravity, it flows through the high-temperature sand bed, transferring heat to the preheated sand. After its own temperature drops to approximately 300°C, it flows out of the sand tank, passes through gate valve 8 (16), and returns to the molten salt storage tank 1, completing the cycle. During this process, the sand is gradually and uniformly heated from 240°C to the final 550°C. The total electrical energy input to the system in this phase is approximately 9.0 MW·h. At a heating power of 2 MW, the effective charging time is approximately 4.5 hours. During the heat preservation phase, the system switches to a low-power intermittent operation mode. Molten salt pump 2 operates at a low frequency, with an initial flow rate of 5 m³ / h, running for 10 minutes and then stopping for 50 minutes. While the pump is running, molten salt heater 3 starts synchronously at low power (approximately 100 kW) to precisely compensate for heat loss in the circulation pipeline, ensuring that the temperature of the molten salt returning to the storage tank remains above 250°C. The sand storage tank 4, thanks to its outer wall cladding with highly efficient insulation materials such as refractory bricks and rock wool, can control its static heat loss rate to within 1% / h. During the energy release phase, the power generation medium circulation system is activated, and heat exchanger 5 is put into operation. Molten salt pump 2 operates at a flow rate of 22 m³ / h. Molten salt heater 3 is shut off. Molten salt at 400°C flows out of the storage tank and is pumped into sand storage tank 4. It is heated while flowing through a high-temperature sand bed at 550°C, reaching a temperature of 500°C upon exiting the sand tank. This 500°C high-temperature molten salt enters heat exchanger 5, transferring heat to the power generation medium, and then cools itself to 400°C before returning to molten salt storage tank 1. The system continuously releases 1.74 MW of thermal power, and the 10 MW·h of thermal energy stored in the system can supply continuous discharge for approximately 5.75 hours. The power generation medium's power generation cycle efficiency is 30%, and the system can output approximately 0.52 MW of electrical power, providing 3.0 MW·h of electrical energy.

Claims

1. A system for energy storage using molten salt coupled with a sand tank, characterized in that, Including salt storage tanks (1) and sand storage tanks (4); The salt storage tank (1) is connected in sequence to the molten salt pump (2) and the molten salt heater (3); The high-temperature molten salt at the outlet of the molten salt heater (3) is connected to the molten salt side inlet of the heat exchanger (6), and the molten salt side outlet of the heat exchanger (6) is circulated and connected to the salt storage tank (1). A nitrogen cylinder (7) is installed on the heat exchanger (6). The nitrogen in the nitrogen cylinder (7) exchanges heat with the molten salt in the heat exchanger (6) and is then fed into the sand storage tank (4) to heat the sand in the sand storage tank (4). The high-temperature molten salt outlet of the molten salt heater (3) is connected to the sand storage tank (4) for heating the sand in the sand storage tank (4); The high-temperature molten salt output end of the heated sand storage tank (4) is connected to the molten salt storage tank (1) through a heat exchanger (5).

2. The molten salt coupled sand tank energy storage system according to claim 1, characterized in that, The sand storage tank (4) is an integrated container for heat storage / heat exchange with a vertical packed bed inside, used to contain quartz sand energy storage material and ensure that molten salt and nitrogen gas exchange heat directly with the quartz sand energy storage material; Its interior, from top to bottom, includes a liquid / gas distribution zone, a quartz sand-filled bed, a porous support distribution plate, and a bottom collection zone, and the flow direction of all heat transfer media is designed to be from top to bottom.

3. The molten salt coupled sand tank energy storage system according to claim 2, characterized in that, The liquid / gas distribution zone is located at the top of the sand storage tank (4) and is connected to the pipes of the outlet of gate valve five (13) and the outlet of gate valve six (14). The zone is equipped with a fluid dispersion device to evenly distribute the incoming molten salt or nitrogen gas to the entire cross-section of the tank. The quartz sand filling bed is filled with sieved and pretreated quartz sand; the sand particle size is 0.5 mm to 3 mm; The porous support distribution plate is horizontally positioned at the bottom of the quartz sand-filled bed. The bottom collection area and outlet are located below the porous support distribution plate. The heat transfer medium after heat exchange with the sand bed is collected in this area and flows out of the sand storage tank (4) through the bottom pipe of the tank body. A high-temperature filter can be installed on the outlet pipeline.

4. The molten salt coupled sand tank energy storage system according to claim 1, characterized in that, The outlet of the molten salt storage tank (1) is connected to gate valve one (8) through a pipe. Gate valve one (8) is connected to the inlet of the molten salt pump (2) through a pipe. The outlet of the molten salt pump (2) is connected to throttle valve two (20) through a pipe. Throttling valve two (20) is connected to the inlet of the molten salt heater (3) through a pipe. The outlet of the molten salt heater (3) is connected to gate valve two (10) through a pipe. Gate valve two (10) is connected to gate valve five (13) through a pipe. Gate valve five (13) is connected to the inlet of the sand storage tank (4) through a pipe. The outlet of the sand storage tank (4) is connected to gate valve seven (15) through a pipe. Gate valve seven (15) is connected to the molten salt side inlet of heat exchanger one (5) through a pipe. The molten salt side outlet of heat exchanger one (5) is connected to gate valve ten (18) through a pipe. Gate valve ten (18) is connected to the inlet of the molten salt storage tank (1) through a pipe.

5. The molten salt coupled sand tank energy storage system according to claim 4, characterized in that, A bypass is installed directly between the outlet of the molten salt storage tank (1) and the outlet of the molten salt pump (2) via a pipeline, and a throttle valve (9) is installed on the bypass. A bypass is installed between the outlet of the molten salt heater (3) and the outlet of the heat exchanger (5) via a pipeline, and a gate valve (11) is installed on the bypass. A bypass is installed between the outlet of gate valve 2 (10) and the outlet of sand storage tank (4) via a pipeline, and gate valve 4 (12) is installed on the bypass. A bypass is installed between the outlet of the sand storage tank (4) and the outlet of the heat exchanger (5) via a pipeline, and a gate valve (16) is installed on the bypass. A pipe is installed at the outlet of the sand storage tank (4) directly into the ambient atmosphere, and a gate valve (17) is installed on the pipe. A bypass of gate valve 10 (18) is installed through a pipeline, and gate valve 11 (19) and the molten salt side flow channel of heat exchanger 2 (6) are installed in sequence on the bypass. The outlet of the nitrogen cylinder (7) is connected to the nitrogen side inlet of the heat exchanger (6), and the nitrogen side outlet of the heat exchanger (6) is connected to the inlet of the sand storage tank (4) through a bypass pipe. A gate valve (14) is installed on the bypass.

6. The molten salt coupled sand tank energy storage system according to claim 5, characterized in that, The energy storage material in the sand storage tank (4) is quartz sand; the heat exchanger (5) is used to transfer the stored energy to the power generation working medium. One side is high-temperature molten salt, and the other side is the working medium participating in the power generation cycle. The working medium participating in the power generation cycle is low-temperature water vapor or supercritical carbon dioxide. The second heat exchanger (6) is used for the nitrogen gas used to heat the preheated sand with molten salt during the preheating stage. One side is high-temperature molten salt, and the other side is low-temperature nitrogen gas.

7. The molten salt coupled sand tank energy storage system according to claim 5, characterized in that, The outer wall of the molten salt storage tank (1) is covered with a tightly wrapped electric heating tape, and the electric heating tape is wrapped with rock wool to keep the molten salt in the tank in a molten state. The outer wall of the sand storage tank (4) is wrapped with refractory bricks, rock wool and aluminum silicate fiber, which is conducive to the long-term storage of thermal energy in the sand storage tank. All pipes in the energy storage system are wrapped with insulation cotton.

8. The molten salt coupled sand tank energy storage system according to claim 5, characterized in that, Electric heating tape is tightly and evenly wrapped around all the gate valves 1 (8), 2 (10), 3 (11), 4 (12), 5 (13), 7 (15), 8 (16), 10 (18), 11 (19), 1 (9), and 2 (20) through which the molten salt flows in the pipeline. The molten salt heater (3) is an immersion tubular electric heater.

9. A method of using a molten salt coupled sand tank energy storage system according to any one of claims 5-8, characterized in that, Includes the following steps; During the preheating phase at the start of energy storage, close gate valves 2 (10), 4 (12), 5 (13), 7 (15), 8 (16), 10 (18), and throttle valve 1 (9), and open gate valves 1 (8), 3 (11), 6 (14), 9 (17), 11 (19), and throttle valve 2 (20), run molten salt pump (2) and molten salt heater (3), and open nitrogen cylinder (7) to start heat exchanger 2 (6); During the preheating stage, molten salt flows from the molten salt storage tank (1) to the molten salt pump (2), and is then pumped into the molten salt heater (3) and heated to 500-550°C. The high-temperature molten salt at the outlet of the molten salt heater (3) flows into the second heat exchanger (6) to exchange heat with low-temperature nitrogen gas, and then flows back to the molten salt storage tank (1) to complete the cycle. During the preheating stage, nitrogen gas in nitrogen cylinder (7) flows into heat exchanger (6) to exchange heat with molten salt and is heated to 250-300°C. Then it flows into sand storage tank (4) to exchange heat with sand and finally heats the sand in the entire sand storage tank to 240-250°C. The nitrogen gas flowing out of the sand storage tank is directly discharged into the atmosphere. When the temperature of the sand in the sand storage tank (4) is higher than 240℃, the preheating stage ends and the molten salt heat storage stage begins. The nitrogen cylinder (7) is closed, and gate valves three (11), four (12), six (14), seven (15), nine (17), eleven (19), and throttle valve one (9) are closed. Gate valves one (8), two (10), five (13), eight (16), ten (18), and throttle valve two (20) are opened. The molten salt pump (2) and molten salt heater (3) are run. During the molten salt heat storage stage, molten salt flows from the molten salt storage tank (1) to the molten salt pump (2), and is then pumped into the molten salt heater (3) and heated to 500-550°C. The high-temperature molten salt at the outlet of the molten salt heater (3) flows into the sand storage tank (4) to exchange heat with the sand, and finally heats the sand in the entire sand storage tank to 500-550°C. The molten salt flowing out of the sand storage tank flows directly back into the molten salt storage tank (1) to complete the cycle. During the heat preservation stage, close gate valves three (11), four (12), six (14), seven (15), and eleven (19), and open gate valves one (8), two (10), five (13), eight (16), and ten (18). Adjust the opening of throttle valve one (9) and throttle valve two (20), and run the molten salt pump (2) and molten salt heater (3) intermittently at low power to maintain a small flow rate in the pipeline, maintain the salt temperature in the pipeline above 250°C, and maintain the molten state. During the energy release phase, close gate valves 3 (11), 4 (12), 6 (14), 8 (16), 9 (17), 11 (19), and throttle valve 1 (9), and open gate valves 1 (8), 2 (10), 5 (13), 7 (15), 10 (18), and throttle valve 2 (20). Start the circulation of the power generation medium to make heat exchanger 1 (5) start running, molten salt pump (2) run, and shut down molten salt heater (3). During the energy release phase, molten salt flows from the molten salt storage tank (1) to the molten salt pump (2), then flows through the molten salt heater (3) without heating, and then flows into the sand storage tank (4) to exchange heat with the high-temperature sand. After heat exchange, the high-temperature molten salt flows into the heat exchanger (5) to exchange heat with the power generation medium, and then flows back into the molten salt storage tank (1) to complete the cycle.

10. The method of using the molten salt coupled sand tank energy storage system according to claim 9, characterized in that, The internal fluid of the pipelines that participate in the operation during the molten salt heat storage stage, the heat preservation stage and the energy release stage is molten salt. During the preheating stage before energy storage begins, the internal fluid in the pipes containing gate valve six (14), the inlet and outlet pipes of sand storage tank (4), and the pipe containing gate valve nine (17) is nitrogen, while the fluid in the other operating pipes is molten salt.

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