High-temperature long molten salt tank expansion joint rapid salt discharging and emptying system, heat storage system and method

Abstract

The invention relates to a high-temperature long molten salt tank expansion joint rapid salt discharging and emptying system, a heat storage system and a heat storage method, and belongs to the technical field of molten salt heat storage. The salt discharging and emptying system comprises a high-temperature expansion joint residual fused salt emptying device which is provided with salt discharging pipelines connected to salt discharging ports of wave troughs of all expansion joints, purging gas paths introduced into the wave troughs and a control unit. And a heat tracing band and a temperature measuring point are arranged on the salt discharging pipeline. The control unit is configured to start the heat tracing band to melt the solidified molten salt in the pipeline when the machine is stopped to discharge the salt; when the temperatures of all the temperature measuring points reach a preset melting threshold value, a first molten salt valve on a salt discharging pipeline is opened; and then the purging gas path is started to purge and discharge the residual liquid molten salt in the trough. By means of the collaborative process of heat tracing melting, temperature control valve opening and pneumatic purging, the technical problems that molten salt remains in the trough of the expansion joint of the ultra-long molten salt equipment, and a corrugated pipe is solidified and expanded to be cracked are thoroughly solved, and safe and long-term reliable operation of the system is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of molten salt thermal energy storage technology, and particularly to a rapid salt discharge and purification system, thermal energy storage system, and method for high-temperature long molten salt tank expansion joints. Background Technology

[0002] In molten salt thermal storage systems used in solar thermal power generation and industrial waste heat utilization, ultra-long molten salt tanks are often employed as heat absorption or storage units. To absorb the enormous thermal expansion between hot and cold states, metal bellows expansion joints must be installed between the tank sections. However, when the system shuts down, high-temperature molten salt easily accumulates in the troughs (grooves of the corrugated structure) of the expansion joints. As the temperature drops, the residual molten salt solidifies, and its volume expansion exerts significant static pressure on the fragile bellows, easily leading to cracks or plastic deformation at the troughs. Upon the next system startup, the molten salt leaks from these cracks, causing safety accidents and system shutdowns.

[0003] In existing technologies, there is generally a lack of effective active methods for draining residual media from expansion joints. Conventional purging methods can only drain molten salt from the main equipment, and are ineffective in addressing the "dead zone" of the expansion joint's trough. A few solutions attempt to drain liquid through openings at the bottom of the trough, but under normal operating high-temperature conditions, the valves at the drain holes are subject to long-term scouring and immersion in high-temperature molten salt, making them prone to internal leakage, and the valves are also expensive. Therefore, there is an urgent need for a system and method that can quickly, thoroughly, and automatically drain residual molten salt from the expansion joint's trough during shutdown, while ensuring reliable sealing during normal operation and cost control. Summary of the Invention

[0004] The first objective of this invention is to provide a rapid salt removal system for expansion joints in high-temperature long molten salt tanks, which aims to solve the technical problems in the prior art where residual molten salt in the troughs of expansion joints cannot be completely removed and the bellows cracks after solidification, thereby achieving rapid, thorough, and automated removal of residual molten salt when the machine is shut down.

[0005] The technical solution to achieve the first objective of this invention is: a rapid salt discharge system for high-temperature long molten salt tank expansion joints, comprising a high-temperature long molten salt tank; the high-temperature long molten salt tank is an integral heat storage tank formed by connecting multiple heat storage tanks together through one or more expansion joints; characterized in that: it further includes a high-temperature expansion joint residual molten salt discharge device for discharging residual liquid molten salt located at the troughs of each expansion joint; a salt discharge port is provided at the lowest point of each trough in each expansion joint; the high-temperature expansion joint residual molten salt discharge device includes a salt discharge pipeline, a purging air pipeline, and a control unit corresponding to each expansion joint; the salt discharge port on each expansion joint is connected to the corresponding salt discharge pipeline; the outlets of each salt discharge pipeline are connected to a first molten salt valve after convergence; each salt discharge pipeline is provided with a heating tape for melting the solidified molten salt in the salt discharge pipeline; The purging air path includes an air source and a purging pipe connected to the air source and introduced into the high-temperature long molten salt tank; the purging pipe is used to purge the residual liquid molten salt deposited at each trough in each expansion joint so that it flows to the corresponding salt discharge port when the air source is supplying air. The control unit is configured to, during the shutdown and salt discharge process of the thermal storage system, first control the working of the heat tracing cable to melt the solidified molten salt in the salt discharge pipeline, then open the first molten salt valve; then control the opening of the purging air path to purge the residual liquid molten salt located at the trough of each expansion joint to the salt discharge port and discharge it from the salt discharge pipeline.

[0006] Furthermore, the aforementioned air blowing pipeline includes a main air supply pipe connected to the air source, and multiple air blowing branch pipes connected to the main air supply pipe; each trough in each expansion joint is provided with a corresponding air blowing branch pipe; each air blowing branch pipe is laid along the inner wall of the corresponding trough, and its air outlet is set in the direction of the salt discharge port of the corresponding trough.

[0007] Furthermore, each salt discharge pipeline is equipped with a temperature measuring point; each temperature measuring point is equipped with a temperature measuring device for feeding back the detected temperature to the control unit; the control unit controls the start and stop of the heating tape on each salt discharge pipeline based on the temperature feedback from each temperature measuring point.

[0008] Furthermore, the air source for the aforementioned purging air path is an air storage tank, and an air valve is provided on the pipeline connecting the main air supply pipe to the air source; the control unit controls the opening and closing of the air valve to control the opening or closing of the purging air path.

[0009] Furthermore, the aforementioned high-temperature long molten salt tank is equipped with three expansion joints; the three expansion joints are respectively connected to the first salt discharge pipeline, the second salt discharge pipeline, and the third salt discharge pipeline; the first salt discharge pipeline, the second salt discharge pipeline, and the third salt discharge pipeline converge to an upstream salt discharge pipeline; the upstream salt discharge pipeline is connected to the downstream salt discharge pipeline through a first molten salt valve, and the first molten salt valve is used to control the connection or disconnection of the upstream and downstream salt discharge pipelines; The first, second, and third salt discharge pipelines are respectively equipped with a first temperature measuring point, a second temperature measuring point, and a third temperature measuring point; the upstream salt discharge pipeline is equipped with a fourth temperature measuring point, the first molten salt valve is equipped with a fifth temperature measuring point, and the downstream salt discharge pipeline is equipped with a sixth temperature measuring point; Temperature measuring devices for feeding back the detected temperature to the control unit are provided at the first to sixth temperature measuring points.

[0010] Furthermore, the aforementioned expansion joint is a square expansion joint; the air blowing branch pipe includes a vertical section, a rounded corner section, and a horizontal section connected in sequence, and laid along the inner wall of the corresponding trough; wherein, the vertical section extends along the vertical side wall of the corresponding trough, the rounded corner section extends along the arc-shaped corner at the bottom of the corresponding trough, and the horizontal section extends along the bottom horizontal wall of the corresponding trough; and, an air blowing port is provided at the end of the vertical section, the rounded corner section, and the horizontal section.

[0011] Furthermore, the aforementioned expansion joint is a square expansion joint; the air blowing branch pipe includes a vertical section, a rounded corner section, and a horizontal section connected in sequence, and laid along the inner wall of the corresponding trough; wherein, the vertical section extends along the vertical side wall of the corresponding trough, the rounded corner section extends along the arc-shaped corner at the bottom of the corresponding trough, and the horizontal section extends along the bottom horizontal wall of the corresponding trough; and, an air blowing port is provided at the end of the vertical section, the rounded corner section, and the horizontal section.

[0012] The second objective of this invention is to provide a thermal storage system that employs the above-mentioned high-temperature long molten salt tank expansion joint rapid salt discharge system, aiming to construct a molten salt thermal storage system that not only has efficient heat storage and release functions, but also has the self-maintenance capability of key components (expansion joints) and higher overall reliability.

[0013] The technical solution to achieve the second objective of this invention is as follows: The thermal storage system of this invention includes a high-temperature molten salt tank, a heat release unit, and a low-temperature molten salt tank; characterized in that it further includes the rapid salt discharge system of the high-temperature long molten salt tank expansion joint as described in claim 5; the salt outlet of the high-temperature molten salt tank is connected to the inlet of the first molten salt pump via a pipe, the outlet of the first molten salt pump is connected to the salt inlet of the heat release unit via a pipe, and the salt outlet of the heat release unit is connected to the salt inlet of the low-temperature molten salt tank via a pipe; the salt outlet of the low-temperature molten salt tank is connected to the inlet of the second molten salt pump via a pipe, and the outlet of the second molten salt pump is connected to the inlet of the second molten salt pump via a pipe. The inlet of the high-temperature long molten salt tank is connected; the main outlet of the high-temperature long molten salt tank is connected to the first inlet of the high-temperature long molten salt tank via a pipeline; a molten salt valve is provided on the pipeline connecting the outlet of the high-temperature long molten salt tank to the first inlet; the downstream outlet pipe of the rapid salt discharge system of the expansion joint of the high-temperature long molten salt tank is connected to the second inlet of the high-temperature long molten salt tank; the high-temperature long molten salt tank is located above the high-temperature molten salt tank and discharges salt to the first inlet and / or the second inlet by gravity; the control unit is used to control the opening and closing of the lava valve and to control the start and stop of the first molten salt pump and the second molten salt pump.

[0014] The third objective of this invention is to provide a thermal storage method using the aforementioned thermal storage system, which aims to standardize and protect the entire operation process of the thermal storage system, including a special desalination procedure, and to ensure the reproducibility and optimality of the desalination effect of the expansion joint.

[0015] The technical solution to achieve the third objective of this invention is: the thermal storage method of this invention includes a normal working mode and a salt discharge mode. The normal working mode includes the following steps: A. The molten salt in the low-temperature molten salt tank is pumped into the high-temperature long molten salt tank through the second molten salt pump to absorb heat; B. The molten salt, after absorbing heat, is discharged into the high-temperature molten salt tank through the main discharge port of the high-temperature long molten salt tank; at this time, the first molten salt valve is closed. C. The molten salt in the high-temperature molten salt tank is returned to the low-temperature molten salt tank after being heated by the first molten salt pump through the heat release unit, forming a cycle; The salt removal method includes the following steps: a. Stop supplying molten salt to the high-temperature long molten salt tank and drain all molten salt except for the molten salt in the trough through the main salt drain outlet; b. Activate the heat tracing tape to heat and melt the molten salt in the brine drainage pipeline; c. Monitor the temperature at each temperature measuring point. When the temperature at all temperature measuring points reaches a preset melting temperature threshold, open the first molten salt valve. d. Supply air to the air blowing pipes installed in the troughs of each expansion joint, and use the airflow to blow away the residual liquid molten salt in the troughs and discharge it through the salt discharge port and the first molten salt valve.

[0016] The present invention has the following positive effects: (1) The present invention, through the purge air path and salt discharge pipeline specially designed for the trough, can actively purge and discharge the residual liquid molten salt, fundamentally avoiding the physical damage to the expansion joint caused by the solidification and expansion of molten salt, and greatly extending the service life of the equipment. The present invention realizes the automation and programming of the salt discharge process through the preset logic of the control unit (heating first, then opening the valve, and then purging), reducing manual operation and improving reliability. Furthermore, the present invention integrates heating, salt discharge, purging and control into a special device, providing a complete expansion joint maintenance solution for ultra-long molten salt tanks.

[0017] (2) This invention clarifies that the blowing pipeline adopts a "gas supply main pipe + multiple blowing branch pipes" structure, and the blowing branch pipes are laid along the trough and point towards the salt discharge port. The beneficial effects are that the gas delivery and distribution are reasonable, the blowing direction is accurate, the energy is concentrated, and the discharge efficiency is high.

[0018] (3) The present invention adds temperature measuring points and heat tracing control based on their feedback to achieve precise and on-demand control of the heating process, avoid energy waste or insufficient heating, and ensure melting effect.

[0019] (4) The present invention limits the gas source to a gas storage tank and controls it through an air valve, thereby providing a stable and controllable gas source. The gas storage tank can be pre-stored to achieve rapid response, and the air valve is easy to control automatically.

[0020] (5) By defining three expansion joints, this invention provides a clear and feasible solution for the networked layout of the salt drainage pipeline and temperature measurement points, and demonstrates the integrated and modular design concept of the multi-expansion joint system, with all key points having controllable temperatures.

[0021] (6) In this invention, the expansion joint adopts a square shape and the air blowing branch pipe is a three-section multi-air blowing port structure. It is designed to optimize the geometric characteristics of the square trough. Through multiple air blowing ports at the ends of the vertical section, rounded corner section and horizontal section, it can achieve directional and coordinated blowing of dead areas such as corners and bottom surfaces that are prone to salt accumulation. The cleaning effect is far greater than that of a single air blowing port.

[0022] (7) In this invention, the thermal storage system organically integrates an innovative salt drainage and purification system into the main thermal storage process, enabling the system to have preventive maintenance capabilities and significantly reducing the risk of unplanned downtime due to expansion joint failure. The connection between the purification system and the main molten salt tank (high-temperature molten salt tank) is clearly defined. In particular, the use of gravity-driven salt drainage and high-level tank design simplifies the pipeline layout and reduces salt drainage energy consumption. At the same time, the function of the control unit is expanded, enabling it to coordinate and manage the operation of the main system and the purification process, realizing integrated intelligent control of thermal storage and equipment maintenance.

[0023] (8) The heat storage method in this invention clearly defines the strict sequence of steps in the "salt discharge mode": "first, heat-induced melting; then, monitoring valve opening; and finally, pneumatic purging." In particular, temperature monitoring ensures that the entire salt discharge path is unobstructed before purging, effectively preventing local blockage or incomplete purging. After normal operation, the main molten salt is emptied first, followed by fine purging, which improves the purging efficiency and reduces the long-term retention of high-temperature molten salt and heat loss. Attached Figure Description

[0024] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a schematic diagram of the thermal storage system in this invention; Figure 2 This is a schematic diagram of the rapid salt discharge and purification system of the high-temperature long molten salt tank expansion joint in this invention; Figure 3 This is a schematic diagram of the fit between the trough of the expansion joint and the air blowing branch pipe in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the air blowing branch pipe in this invention; Figure 5 This is a schematic diagram of the electrical connections of the control unit in this invention; Figure 6 This is a schematic diagram of the expansion joint and the air blowing branch pipe in Embodiment 3 of the present invention.

[0025] In the diagram, the components are: 1. High-temperature long molten salt tank; 2. Expansion joint; 21. Valley; 3. Salt discharge port; 4. Control unit; 51. First salt discharge pipeline; 52. Second salt discharge pipeline; 53. Third salt discharge pipeline; 54. Upstream salt discharge pipeline; 55. Downstream salt discharge pipeline; 6. First molten salt valve; 81. First temperature measuring point; 82. Second temperature measuring point; 83. Third temperature measuring point; 84. Fourth temperature measuring point; 85. Fifth temperature measuring point; 86. Sixth temperature measuring point; 9. Air source; 10. Electromagnetic air valve; 11. Main air supply pipe; 12. Air blowing branch pipe; 121. Vertical section; 122. Rounded corner section; 123. Horizontal section; 13. High-temperature molten salt tank; 14. Heat release unit; 15. Low-temperature molten salt tank; 16. First molten salt pump; 17. Second molten salt pump; 18. Main salt discharge port; 19. Molten salt valve; 131. First salt inlet; 132. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Example 1:

[0027] like Figures 1 to 5 As shown, the high-temperature long molten salt tank expansion joint rapid salt discharge system in this embodiment includes a high-temperature long molten salt tank 1 and a high-temperature expansion joint residual molten salt discharge device.

[0028] The high-temperature long molten salt tank 1 consists of four tank bodies connected by three expansion joints 2 to form an integral thermal storage tank. The expansion joints 2 are square single-wave metal bellows expansion joints, that is, each square single-wave metal bellows expansion joint has only one trough 21. Each expansion joint 2 has a salt discharge port 3 at the lowest point of its trough 21.

[0029] The residual molten salt removal device for the high-temperature expansion joint mainly includes a salt removal pipeline, a purging gas pipeline, and a control unit 4.

[0030] Each salt discharge port 3 is connected to a connected salt discharge pipeline. In this embodiment, the salt discharge ports 3 of three square single-wave metal corrugated expansion joints are respectively connected to the first salt discharge pipeline 51, the second salt discharge pipeline 52, and the third salt discharge pipeline 53. The outlets of the first salt discharge pipeline 51, the second salt discharge pipeline 52, and the third salt discharge pipeline 53 converge on an upstream salt discharge pipeline 54. The upstream salt discharge pipeline 54 is connected to the downstream salt discharge pipeline 55 through a first molten salt valve 6, and the first molten salt valve 6 is used to control the connection or disconnection of the upstream salt discharge pipeline 54 and the downstream salt discharge pipeline 55. The first salt discharge pipeline 51, the second salt discharge pipeline 52, and the third salt discharge pipeline 53 are all equipped with heat tracing cables for melting the solidified molten salt in the salt discharge pipeline. The heat tracing cables are high-temperature resistant electric heating heat tracing cables.

[0031] The first salt discharge pipeline 51, the second salt discharge pipeline 52, and the third salt discharge pipeline 53 are respectively equipped with a first temperature measuring point 81, a second temperature measuring point 82, and a third temperature measuring point 83; the upstream salt discharge pipeline 54 is equipped with a fourth temperature measuring point 84, the first molten salt valve 6 is equipped with a fifth temperature measuring point 85, and the downstream salt discharge pipeline 55 is equipped with a sixth temperature measuring point 86; each temperature measuring point uses a sheathed thermocouple, and the signal is connected to the control unit 4.

[0032] The purging air path includes an air source 9 and a purging pipe connected to the air source 9 and introduced into the high-temperature long molten salt tank 1; the purging pipe is used to purge the residual liquid molten salt deposited at each trough 21 in each expansion joint 2 when the air source 9 is supplying air, so that it flows to the corresponding salt discharge port 3.

[0033] The air source 9 for the purging air path is a 2m³ air storage tank with a working pressure of 0.8MPa. The outlet of the air storage tank is connected to a solenoid air valve 10 via a pipeline. The solenoid air valve 10 is then connected to the main air supply pipe 11. After extending to the vicinity of the high-temperature long molten salt tank 1, the main air supply pipe 11 branches off into several purging branch pipes 12 that are introduced into the expansion joint 2.

[0034] Regarding the number of troughs 21 in the square single-wave metal bellows expansion joint, this embodiment uses three air-blowing branch pipes 12; each air-blowing branch pipe 12 corresponds to one trough 21, which is formed by welding three sections in sequence and is laid and fixed completely against the inner wall of the corresponding trough 21. Starting from the air inlet end, the sections are as follows: a vertical section 121 extending along the vertical side wall of the trough 21, a rounded corner section 122 extending along the arc-shaped corner connecting the bottom of the trough 21 to the side wall, and a horizontal section 123 extending along the bottom horizontal wall of the trough 21.

[0035] See Figure 4 Air holes are provided at the ends of vertical section 121, rounded section 122, and horizontal section 123.

[0036] The air inlet at the end of the vertical section 121 is tilted downwards and blows towards the vertical sidewall of the trough 21 at an angle between 10° and 30° (preferably 15°). This design allows the airflow to closely adhere to the vertical wall and scour downwards, using the shear force of the airflow to peel off the molten salt film adhering to the vertical wall surface. This eliminates any residue that would otherwise adhere to the vertical wall surface due to the surface tension of the molten salt.

[0037] The central axis of the air inlet at the end of the rounded corner 122 is strictly aligned with the tangent of the arc-shaped corner at the bottom of the trough 21. This design is based on fluid mechanics, where the airflow injected along the tangent will create a strong vortex within the arc-shaped space. This vortex effectively agitates and gathers the molten salt deposited in the arc-shaped dead corner, overcoming the problem of low salt removal efficiency due to gravity at this location.

[0038] The air inlet at the end of the horizontal section 123 impacts the corresponding horizontal bottom surface of the trough 21 at an elevation angle of 5° to 20° (preferably 10°). This design "rolls up" the molten salt deposited at the bottom and imparts a horizontal velocity component towards the salt discharge port 3, which merges with the molten salt blown out by the vertical section 121 and the rounded corner section 122, flowing together towards the salt discharge port 3. The airflow generated by the three air inlets forms a coordinated three-dimensional purging flow field within the space of the trough 21, achieving thorough purging without dead zones.

[0039] In this embodiment, the heat storage system includes a high-temperature molten salt tank 13, a heat release unit 14, and a low-temperature molten salt tank 15; it also includes the aforementioned high-temperature long molten salt tank expansion joint rapid salt discharge system; the salt outlet of the high-temperature molten salt tank 13 is connected to the inlet of the first molten salt pump 16 via a pipe, the outlet of the first molten salt pump 16 is connected to the salt inlet of the heat release unit 14 via a pipe, and the salt outlet of the heat release unit 14 is connected to the salt inlet of the low-temperature molten salt tank 15 via a pipe; the salt outlet of the low-temperature molten salt tank 15 is connected to the inlet of the second molten salt pump 17 via a pipe, and the outlet of the second molten salt pump 17 is connected to the salt inlet of the high-temperature long molten salt tank 15 via a pipe; the high-temperature long molten salt... The main salt discharge port 18 of the tank 1 is connected to the first salt inlet 131 of the high-temperature long molten salt tank 13 via a pipeline; a molten salt valve 19 is provided on the pipeline connecting the salt discharge port of the high-temperature long molten salt tank 1 to the first salt inlet 131; the downstream salt discharge pipe 55 of the rapid salt discharge system of the expansion joint of the high-temperature long molten salt tank is connected to the second salt inlet 132 of the high-temperature long molten salt tank 13; the high-temperature long molten salt tank 13 is located above the high-temperature molten salt tank 13, and discharges salt to the first salt inlet 131 and / or the second salt inlet 132 by gravity; the control unit 4 is used to control the opening and closing of the lava valve 19, and to control the start and stop of the first molten salt pump 16 and the second molten salt pump 17.

[0040] The high-temperature long molten salt tank 1 has main salt outlets 18 at both ends. The two main salt outlets 18 are connected to the first salt inlet 131 through pipelines. Each main salt outlet 18 is equipped with a molten salt valve 19.

[0041] The control unit 4 is a PLC controller configured to execute preset logic. In normal operating mode, the first molten salt valve 6, the temperature measuring devices at each temperature measuring point, and the heating tape are all in the closed state.

[0042] In the thermal storage system, the molten salt valve 19 is opened, and the molten salt circulates between the high-temperature long molten salt tank 1, the high-temperature molten salt tank 13, the heat release unit 14, and the low-temperature molten salt tank 15.

[0043] When the system needs to be shut down, it enters the salt discharge mode, and control unit 4 executes the following steps in sequence: Stop the first molten salt pump 16 and the second molten salt pump 17, open the molten salt valve 19 on the high temperature long molten salt tank 1, and drain the molten salt except for the residual liquid molten salt in the trough 21.

[0044] Turn on all heat tracing cables.

[0045] The system monitors the temperatures at the first temperature measuring point 81 to the sixth temperature measuring point 86 in real time. The PLC only outputs a command to open the first molten salt valve 6 when the temperatures at all measuring points reach or exceed the preset melting temperature threshold (e.g., 300℃, which is approximately 50℃ higher than the freezing point of the molten salt used). This logic ensures that the entire salt discharge path is completely unobstructed, preventing unmelted solidified salt from clogging pipes or valves.

[0046] Open the air valve 10, and compressed air in the air tank 9 is ejected through the main air supply pipe 11, the blowing branch pipe 12, and the blowing ports at various optimized angles to purge the trough 21. The purging pressure and time can be set, for example, purging at 0.5 MPa for 60 seconds.

[0047] After purging is complete, close the air valve 10, the first molten salt valve 6, and the heat tracing cable.

[0048] The control unit 4 not only manages the drainage process, but also coordinates the operation of the thermal storage system.

[0049] In this embodiment, the method for storing heat using the above-mentioned heat storage system includes a normal working mode and a salt discharge mode.

[0050] The normal working mode includes the following steps: A. The molten salt in the low-temperature molten salt tank 15 is pumped into the high-temperature long molten salt tank 1 through the second molten salt pump 17 to absorb heat; B. The molten salt that has absorbed heat is discharged through the main salt outlet 18 of the high-temperature long molten salt tank 1 to the high-temperature molten salt tank 13; at this time, the first molten salt valve 6 and the heat tracing cable are in the closed state. C. The molten salt in the high-temperature molten salt tank 13 is returned to the low-temperature molten salt tank 15 after being heated by the first molten salt pump 16 and the heat release unit 14, forming a cycle; The salt removal method includes the following steps: a. Stop supplying molten salt to the high-temperature long molten salt tank 1, and drain the molten salt in the entire heat storage tank except for the molten salt in the trough 21 through the main salt drain port 18; b. Activate the heating tape to heat and melt the molten salt in the drainage pipeline. The power P of the heating tape must meet the requirements for melting the solidified salt and compensating for heat loss. This can be estimated using a simplified formula: P ≥ [ρVΔH / t] + kAΔT, where ρ is the density of the molten salt, V is the volume of solidified salt in the drainage pipeline, ΔH is the latent heat of molten salt melting, t is the target melting time, k is the comprehensive heat dissipation coefficient of the drainage pipeline, A is the heat dissipation area, and ΔT is the temperature difference between the drainage pipeline and the environment. In practice, constant power heating is used, controlled by temperature feedback.

[0051] c. Monitor the temperature at each measuring point. When the temperature at all measuring points reaches a preset melting temperature threshold, open the first molten salt valve 6. Specifically, the PLC controller of the control unit 4 collects the temperatures of the first measuring point 81 to the sixth measuring point 86 (T1~T6 respectively) in real time. The control logic is: the first molten salt valve 6 is opened only when the conditions (T1≥300℃) and (T2≥300℃) and (T3≥300℃) and (T4≥300℃) and (T5≥300℃) and (T6≥300℃) are met.

[0052] d. Supply air to the air-blowing pipes located in the troughs 21 of each expansion joint 2. Use the airflow to purge the residual liquid molten salt in the troughs 21 and discharge it through the salt discharge port 3 and the first molten salt valve 6. The minimum air volume Q required for purging can be estimated by Q ≥ (V_cavity / η) / t_blow, where V_cavity is the volume of the trough 21, η is the airflow carrying efficiency coefficient, and t_blow is the set purging time. In practice, the purging pressure is stabilized at 0.4-0.6MPa for 60-120 seconds by adjusting the air valve 10.

[0053] e. After purging is complete, close air valve 10, first molten salt valve 6, and heat tracing cable in sequence. The system enters cold standby mode.

[0054] When the molten salt in the salt discharge pipeline solidifies, the molten salt in front of the first molten salt valve 6 is prevented from leaking out of the first molten salt valve 6 under normal operating conditions. Example 2:

[0055] The main difference between this embodiment and Embodiment 1 lies in the cross-sectional shape of the expansion joint 2 and the simplified design of the air blowing branch pipe 12. The high-temperature long molten salt tank 1 is connected using a circular single-wave metal bellows expansion joint.

[0056] Because the circular trough is a smooth U-shape, without any square vertical corners or dead angles, the design of the air blowing branch pipe 12 can be simplified. Each air blowing branch pipe 12 is a straight pipe or a pipe with a gentle curve, laid along the bottom of the inner wall of the trough. One or more air blowing ports are provided at its end, with the direction of the air blowing ports slightly offset from the axial direction of the trough towards the salt discharge port 3. It mainly relies on the thrust of the airflow to drive the molten salt towards the salt discharge port 3. Its salt discharge pipeline, control logic, etc., are the same as in Embodiment 1. This embodiment illustrates that the basic principles of the present invention are also applicable to conventional circular expansion joints. Example 3:

[0057] See Figure 6In this embodiment, the expansion joint 2 adopts a double wave design, that is, one expansion joint has two wave troughs 21. In this embodiment, each wave trough 21 is equipped with an air blowing branch pipe 12, that is, two air blowing branch pipes 12 are correspondingly set on one expansion joint 2. At the same time, each wave trough 21 on one expansion joint 2 is provided with a salt discharge port 3, and the two salt discharge ports 3 on a single expansion joint 2 are connected to a salt discharge pipeline.

[0058] The other technical details are the same as in Example 1.

[0059] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rapid salt discharge system for a high-temperature long molten salt tank using expansion joints, comprising a high-temperature long molten salt tank; wherein the high-temperature long molten salt tank is an integral thermal storage tank formed by connecting multiple thermal storage tanks together through one or more expansion joints; characterized in that: It also includes a high-temperature expansion joint residual molten salt draining device for draining residual liquid molten salt located in the troughs of each expansion joint; a drain port is provided at the lowest point of each trough in each expansion joint; the high-temperature expansion joint residual molten salt draining device includes a drain pipe, a purge air path and a control unit corresponding to each expansion joint; the drain port on each expansion joint is connected to the corresponding drain pipe; the outlets of each drain pipe are connected to the first molten salt valve after being merged; each drain pipe is provided with a heat tracing cable for melting the solidified molten salt in the drain pipe; The purging air path includes an air source and a purging pipe connected to the air source and introduced into the high-temperature long molten salt tank; the purging pipe is used to purge the residual liquid molten salt deposited at each trough in each expansion joint so that it flows to the corresponding salt discharge port when the air source is supplying air. The control unit is configured to, during the shutdown and salt discharge process of the thermal storage system, first control the working of the heat tracing cable to melt the solidified molten salt in the salt discharge pipeline, then open the first molten salt valve; then control the opening of the purging air path to purge the residual liquid molten salt located at the trough of each expansion joint to the salt discharge port and discharge it from the salt discharge pipeline.

2. The rapid salt discharge system for high-temperature long molten salt tank expansion joints according to claim 1, characterized in that: The air blowing pipeline includes a main air supply pipe connected to the air source, and multiple air blowing branch pipes connected to the main air supply pipe; each trough in each expansion joint is provided with an air blowing branch pipe; each air blowing branch pipe is laid along the inner wall of the corresponding trough, and its air outlet is set in the direction of the salt discharge port of the corresponding trough.

3. The rapid salt discharge and purification system for high-temperature long molten salt tank expansion joints according to claim 1, characterized in that: Temperature measuring points are installed on each salt discharge pipeline; each temperature measuring point is equipped with a temperature measuring device for feeding back the detected temperature to the control unit; the control unit controls the start and stop of the heating tape on each salt discharge pipeline based on the temperature feedback from each temperature measuring point.

4. The rapid salt discharge and purification system for high-temperature long molten salt tank expansion joints according to claim 2 or 3, characterized in that: The purge air circuit is powered by an air storage tank, and an air valve is installed on the main air supply pipe connected to the air source. The control unit controls the opening and closing of the air valve to control the opening or closing of the purge air circuit.

5. The rapid salt discharge and purification system for high-temperature long molten salt tank expansion joints according to claim 4, characterized in that: The high-temperature long molten salt tank is equipped with three expansion joints; the three expansion joints are respectively connected to the first salt discharge pipeline, the second salt discharge pipeline, and the third salt discharge pipeline; the first salt discharge pipeline, the second salt discharge pipeline, and the third salt discharge pipeline converge to an upstream salt discharge pipeline; the upstream salt discharge pipeline is connected to the downstream salt discharge pipeline through a first molten salt valve, and the first molten salt valve is used to control the connection or disconnection of the upstream and downstream salt discharge pipelines; The first, second, and third salt discharge pipelines are respectively equipped with a first temperature measuring point, a second temperature measuring point, and a third temperature measuring point; the upstream salt discharge pipeline is equipped with a fourth temperature measuring point, the first molten salt valve is equipped with a fifth temperature measuring point, and the downstream salt discharge pipeline is equipped with a sixth temperature measuring point; Temperature measuring devices for feeding back the detected temperature to the control unit are provided at the first to sixth temperature measuring points.

6. The rapid salt discharge and purification system for high-temperature long molten salt tank expansion joints according to claim 2, characterized in that: The expansion joint is a square expansion joint; the air blowing branch pipe includes a vertical section, a rounded corner section and a horizontal section connected in sequence, and is laid along the inner wall of the corresponding trough; wherein, the vertical section extends along the vertical side wall of the corresponding trough, the rounded corner section extends along the arc-shaped corner at the bottom of the corresponding trough, and the horizontal section extends along the bottom horizontal wall of the corresponding trough; and, an air blowing port is provided at the end of the vertical section, the rounded corner section and the horizontal section.

7. The rapid salt discharge and purification system for high-temperature long molten salt tank expansion joints according to claim 5, characterized in that: The expansion joint is a square expansion joint; the air blowing branch pipe includes a vertical section, a rounded corner section and a horizontal section connected in sequence, and is laid along the inner wall of the corresponding trough; wherein, the vertical section extends along the vertical side wall of the corresponding trough, the rounded corner section extends along the arc-shaped corner at the bottom of the corresponding trough, and the horizontal section extends along the bottom horizontal wall of the corresponding trough; and, an air blowing port is provided at the end of the vertical section, the rounded corner section and the horizontal section.

8. A thermal storage system, comprising a high-temperature molten salt tank, a heat release unit, and a low-temperature molten salt tank; characterized in that: It also includes the rapid salt discharge system for the high-temperature long molten salt tank expansion joint as described in claim 5; the salt outlet of the high-temperature molten salt tank is connected to the inlet of the first molten salt pump via a pipe, the outlet of the first molten salt pump is connected to the salt inlet of the heat release unit via a pipe, and the salt outlet of the heat release unit is connected to the salt inlet of the low-temperature molten salt tank via a pipe; the salt outlet of the low-temperature molten salt tank is connected to the inlet of the second molten salt pump via a pipe, and the outlet of the second molten salt pump is connected to the salt inlet of the high-temperature long molten salt tank via a pipe; the main salt discharge system of the high-temperature long molten salt tank... The outlet is connected to the first salt inlet of the high-temperature long molten salt tank via a pipeline; a molten salt valve is installed on the pipeline connecting the salt outlet of the high-temperature long molten salt tank to the first salt inlet; the downstream salt discharge pipe of the rapid salt discharge system of the expansion joint of the high-temperature long molten salt tank is connected to the second salt inlet of the high-temperature long molten salt tank; the high-temperature long molten salt tank is located above the high-temperature molten salt tank and discharges salt to the first salt inlet and / or the second salt inlet by gravity; the control unit is used to control the opening and closing of the lava valve and to control the start and stop of the first molten salt pump and the second molten salt pump.

9. The thermal storage system according to claim 8, characterized in that: The expansion joint is a square expansion joint; the air blowing branch pipe includes a vertical section, a rounded corner section and a horizontal section connected in sequence, and is laid along the inner wall of the corresponding trough; wherein, the vertical section extends along the vertical side wall of the corresponding trough, the rounded corner section extends along the arc-shaped corner at the bottom of the corresponding trough, and the horizontal section extends along the bottom horizontal wall of the corresponding trough; and, an air blowing port is provided at the end of the vertical section, the rounded corner section and the horizontal section.

10. A method for heat storage using the heat storage system of claim 8, characterized in that: Includes normal working mode and salt excretion mode: The normal working mode includes the following steps: A. The molten salt in the low-temperature molten salt tank is pumped into the high-temperature long molten salt tank through the second molten salt pump to absorb heat; B. The molten salt, after absorbing heat, is discharged into the high-temperature molten salt tank through the main discharge port of the high-temperature long molten salt tank; at this time, the first molten salt valve is closed. C. The molten salt in the high-temperature molten salt tank is returned to the low-temperature molten salt tank after being heated by the first molten salt pump through the heat release unit, forming a cycle; The salt removal method includes the following steps: a. Stop supplying molten salt to the high-temperature long molten salt tank and drain all molten salt except for the molten salt in the trough through the main salt drain outlet; b. Activate the heat tracing tape to heat and melt the molten salt in the brine drainage pipeline; c. Monitor the temperature at each temperature measuring point. When the temperature at all temperature measuring points reaches a preset melting temperature threshold, open the first molten salt valve. d. Supply air to the air blowing pipes installed in the troughs of each expansion joint, and use the airflow to blow away the residual liquid molten salt in the troughs and discharge it through the salt discharge port and the first molten salt valve.

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