Underground high-temperature molten salt heat storage system and construction and operation method

Abstract

The invention relates to the technical field of heat energy storage, in particular to an underground high-temperature molten salt heat storage system and a construction and operation method. The system comprises an underground storage tank unit, a heat management unit, a structural unit and an anti-seepage unit, the underground storage tank unit is used for containing high-temperature molten salt and arranged in an underground foundation pit, and the outer side of the underground storage tank unit is coated with the heat management unit; the structural unit comprises an inner heat-resisting structural layer and an outer structural layer which are sequentially arranged on the outer side of the heat management unit from inside to outside, and the anti-seepage unit comprises a lining coating arranged in the underground storage tank unit, a geomembrane layer and a backfill anti-seepage layer, wherein the geomembrane layer and the backfill anti-seepage layer are sequentially arranged on the outer side of the outer structural layer from inside to outside. According to the integrated structure, the limitation of the size and materials of a traditional steel tank can be broken through, the capacity of a single tank is remarkably improved, dependence on parallel connection of multiple tanks is reduced, system complexity and construction cost are reduced, and meanwhile safety and environmental friendliness of long-term operation are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal energy storage, in particular to an underground high-temperature molten salt thermal energy storage system and a construction and operation method. BACKGROUND

[0002] Thermal energy storage can realize multi-energy grade cold, heat, electricity and steam combined supply according to user demand, and has broad application prospects in the fields of coal power steam storage, photo-thermal power generation, new energy consumption, industrial steam supply and cross-season heating. Molten salt energy storage is one of the most common forms of large-scale energy storage at present. The existing molten salt storage tanks are all steel storage tanks, and the design service life is usually about 20 years, which is designed according to the Design Specification for Vertical Cylindrical Steel Welded Oil Tanks (GB 50341-2014). Among them, the operating environment of high-temperature molten salt storage tank is relatively harsh, and the molten salt in the hot tank must be continuously maintained at a temperature of 500 ℃ or above, and the molten salt itself has certain corrosion characteristics.

[0003] At present, 347H stainless steel is generally used as the main construction material of high-temperature storage tanks in the industry, which has high cost and will creep deformation at 538 ℃. It is easy to produce creep damage under long-term high-temperature environment, which poses a serious hidden danger to the safe operation of the storage tank. From the structure design, the existing large storage tanks generally adopt vertical cylindrical steel welded structure. This structure has a obvious defect: the connection part of the tank wall and the tank bottom often produces stress concentration due to the structure mutation. Under the action of long-term alternating load, these stress concentration areas are prone to cracking damage, which may eventually lead to the rupture of the storage tank and the leakage of molten salt. Such leakage accidents not only cause serious environmental pollution, but also force the entire energy storage system to be shut down, and the repair period is often several months, and the repair cost is very high.

[0004] Under high-temperature operating conditions, thermal stress and material expansion effect seriously restrict the large-scale development of traditional storage tanks. At present, the typical design parameters of a single storage tank are usually controlled within a diameter of 40 meters and a height of about 15 meters, which is difficult to meet the demand of larger scale energy storage. In order to achieve the required energy storage capacity, multiple tanks in parallel solution is often used in engineering practice, but this configuration will bring significant negative effects: (1) multiple tank parallel system needs to repeat the configuration of various auxiliary equipment, including but not limited to circulating pump group and pipeline of molten salt heat storage medium and electric control system, which not only greatly increases the initial investment cost, but also significantly improves the system complexity; (2) the coordinated operation of multiple storage tanks requires more complex control strategies, and any single tank failure may affect the reliability of the overall system; (3) multiple tank arrangement also occupies more site area, increases land cost, and causes the heat loss surface area to increase by several times, reducing the overall energy efficiency of the system.

[0005] The above technical limitations have become an important bottleneck restricting the technical economy and large-scale application of molten salt energy storage in the fields of photo-thermal power generation, flexible modification of thermal power, and independent electric heat energy storage power generation. Therefore, there is an urgent need to develop a new type of thermal storage system to greatly improve the energy storage capacity of a single tank while ensuring safety, thereby reducing the dependence on multiple tanks in parallel, reducing system complexity and overall cost. SUMMARY

[0006] The technical problem to be solved by the embodiments of the present application is to provide an underground high-temperature molten salt thermal storage system and a construction and operation method to solve the problems of stress concentration, material creep and single tank capacity limitation of large high-temperature molten salt storage tanks in the prior art.

[0007] The present application discloses an underground high-temperature molten salt thermal storage system, comprising an underground storage tank unit, a thermal management unit, a structural unit and a seepage prevention unit. The underground storage tank unit is used to contain high-temperature molten salt, and the underground storage tank unit is arranged in an underground pit. The thermal management unit is wrapped on the outside of the underground storage tank unit, and is used to absorb the heat of the underground storage tank unit and the radial displacement caused by thermal expansion. The structural unit comprises an inner heat-resistant structural layer and an outer structural layer arranged in sequence from inside to outside of the thermal management unit, and is used to form a support structure that jointly bears the static pressure of the molten salt. The seepage prevention unit comprises an inner lining coating arranged inside the underground storage tank unit, and a geomembrane layer and a backfill seepage prevention layer arranged in sequence from inside to outside of the outer structural layer, and is used to jointly form a multi-layer composite seepage prevention structure.

[0008] Optionally, the underground storage tank unit comprises a tank body, the tank body is a rounded table type structure formed by a variable cross-section stainless steel plate, the thermal management unit comprises a side wall heat preservation layer made of flexible heat preservation material and arranged on the outer wall of the tank body in a circumferential direction, and the inner lining coating is arranged on the inner wall of the tank body.

[0009] Optionally, the junction between the side wall and the bottom wall of the tank body is a circular arc chamfer structure, and a drainage layer is arranged between the bottom wall of the tank body and the bottom pit wall of the underground pit.

[0010] Optionally, the inner heat-resistant structural layer is a layered structure formed by pouring heat-resistant concrete in a circumferential direction outside the side wall heat preservation layer, and the outer structural layer is a layered structure formed by pouring prestressed reinforced concrete containing steel fibers in a circumferential direction outside the inner heat-resistant structural layer.

[0011] Optionally, the geomembrane layer is laid on the sidewall of the underground foundation pit in the circumferential direction, and the geomembrane layer and the outer structure layer have a space therebetween, and the backfill impermeable layer is filled with backfill soil in the space between the geomembrane layer and the outer structure layer.

[0012] Optionally, the top of the tank body is provided with an opening, and the underground storage tank unit further comprises a top cover plate covering the opening of the top of the tank body, the outer diameter of the top cover plate corresponds to the outer diameter of the outer structure layer, and the outer side of the outer structure layer is at an ambient temperature.

[0013] Optionally, the top of the tank body is a metal structure, and the inner and outer sides of the top of the tank body are coated with a rust-proof coating.

[0014] Optionally, the underground storage tank unit further comprises a cover top arranged above the top cover plate, the cover top is a hollow hemispherical structure with a downward opening, and the bottom opening of the cover top is matched to cover the top cover plate; A plurality of hangers are arranged between the cover top and the top cover plate, one end of the hanger is vertically downwardly fixed to the top plate surface of the top cover plate, and the other end of the hanger is vertically upwardly fixed to the inner top wall surface of the cover top. The heat management unit further comprises a top plate heat preservation layer made of flexible heat preservation material and horizontally arranged on the top plate surface of the top cover plate.

[0015] Optionally, the underground high-temperature molten salt heat storage system further comprises a monitoring and control unit, the monitoring and control unit comprises a displacement sensor, a liquid level monitor, and a plurality of point-distributed thermocouples and osmometers, the displacement sensor is arranged on the outer sidewall of the tank body, the liquid level monitor is arranged inside the tank body at the top opening, and the side surfaces of the inner lining coating, the sidewall heat preservation layer, the inner layer heat-resistant structure layer, and the outer structure layer are respectively arranged with a group of the thermocouples and the osmometers.

[0016] The application also discloses a construction and operation method, which adopts the underground high-temperature molten salt heat storage system, and the construction and operation method comprises the following steps: S1, excavating the underground foundation pit in a reverse circular table shape, and laying a gravel drainage layer on the bottom sidewall of the underground foundation pit after tamping and leveling the bottom sidewall; S2, pouring and forming the outer structure layer in the circumferential direction in the underground foundation pit by using a prestressed reinforced concrete containing steel fibers, and laying the geomembrane layer on the sidewall of the underground foundation pit in the circumferential direction to form the outermost impermeable barrier; S3, backfilling backfill soil between the geomembrane layer and the outer structure layer to form the backfill impermeable layer; S4, pouring the inner layer heat-resistant structure layer along the circumference of the inner side of the outer layer structure layer by using heat-resistant concrete; S5, welding the tank body of the underground storage tank unit in the underground foundation pit, fixing the side wall heat preservation layer composed of flexible heat preservation material on the outer side wall of the tank body along the circumference, and fixing the inner lining coating on the inner side wall of the tank body; S6, installing the top cover plate on the top of the tank body, laying the top plate heat preservation layer on the top cover plate, connecting the cover top with the top cover plate through the hanger, and fixing the cover top with the top of the outer layer structure layer through the embedded part; S7, after the underground high-temperature molten salt heat storage system is put into operation, the state data of each layer are obtained in real time through the monitoring instruments embedded synchronously in the construction process, and a storage tank health state model is established according to the obtained state data to carry out predictive maintenance.

[0017] Compared with the prior art, the underground high-temperature molten salt heat storage system and the construction and operation method provided by the embodiment of the present application have the beneficial effects that: By embedding the underground storage tank unit as a whole and effectively absorbing the radial displacement and thermal stress caused by high-temperature molten salt by using the heat management unit, the local stress concentration and creep risk of the underground storage tank unit are significantly reduced. The structure unit bears the static pressure of the molten salt together through the inner and outer layered design, which enhances the overall stability. The anti-seepage unit blocks the leakage of the molten salt through the multi-layer composite structure, which greatly improves the safety. The integrated structure can break through the size and material limitations of traditional steel tanks, significantly increase the single-tank capacity, reduce the dependence on multiple-tank parallel connection, reduce the system complexity and construction cost, and at the same time ensure the safety and environmental protection of long-term operation. BRIEF DESCRIPTION OF DRAWINGS

[0018] The technical solutions of the present application will be further described in detail below with reference to the drawings and embodiments, and the drawings are as follows: Figure 1 The structure schematic diagram of the side section of the underground high-temperature molten salt heat storage system provided by the embodiment of the present application is shown in the figure. Figure 2 The plan view of the cooperation of each layer in the underground high-temperature molten salt heat storage system provided by the embodiment of the present application is shown in the figure.

[0019] The marks in the drawings represent as follows: 1, underground storage tank unit; 11, tank body; 12, top cover plate; 13, cover top; 14, hanger; 2, heat management unit; 21, side wall heat preservation layer; 22, top plate heat preservation layer; 3, structure unit; 31, inner layer heat-resistant structure layer; 32, outer layer structure layer; 4, anti-seepage unit; 41, inner lining coating; 42, geomembrane layer; 43, backfill anti-seepage layer. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The preferred embodiments of the present application will be described in detail with reference to the drawings.

[0021] The present application discloses an underground high-temperature molten salt thermal storage system, as shown in Figure 1 and Figure 2 , comprising an underground storage tank unit 1, a thermal management unit 2, a structural unit 3, and an anti-seepage unit 4. The underground storage tank unit 1 is used to contain high-temperature molten salt, and the underground storage tank unit 1 is arranged in a underground foundation pit; The thermal management unit 2 is wrapped on the outside of the underground storage tank unit 1, and is used to absorb the heat of the underground storage tank unit 1 and the radial displacement caused by thermal expansion; The structural unit 3 comprises an inner heat-resistant structural layer 31 and an outer structural layer 32 arranged in turn on the outside of the thermal management unit 2 in the inner-to-outer direction, and is used to form a support structure that jointly bears the static pressure of the molten salt; The anti-seepage unit 4 comprises an inner lining coating 41 arranged inside the underground storage tank unit 1, and a geomembrane layer 42 and a backfill anti-seepage layer 43 arranged in turn on the outside of the outer structural layer 32 in the inner-to-outer direction, and is used to jointly form a multi-layer composite anti-seepage structure.

[0022] Through the implementation of the above-mentioned underground high-temperature molten salt thermal storage system embodiment, the underground storage tank unit 1 is buried as a whole in the ground, and the natural confining pressure and heat preservation characteristics of the surrounding rock-soil mass are utilized to provide an extremely stable and low-heat-loss environment for the storage of high-temperature molten salt. Based on this, the thermal management unit 2 is closely wrapped on the outside of the underground storage tank unit 1, and its core role is to actively absorb and dissipate the huge heat transferred by the high-temperature molten salt, and can effectively accommodate and absorb the radial displacement caused by the thermal expansion of the underground storage tank unit 1 through its flexibility or compressibility, thereby minimizing the fatal thermal stress concentration problem existing in traditional ground steel tanks to avoid the risk of tank body 11 cracking caused by creep fatigue and structural mutation.

[0023] At the same time, the structural unit 3 adopts a composite design of the inner heat-resistant structural layer 31 and the outer structural layer 32, which work together to jointly bear the huge static pressure load of the molten salt: the inner heat-resistant structural layer 31 directly faces the high temperature to ensure the stability of the structural strength in the thermal environment, while the outer structural layer 32 provides the main mechanical support and combines with the surrounding stratum to form a solid load-bearing body. This division of labor and cooperation of the structural form breaks through the limitations of materials and sizes of traditional steel tanks, making it possible to build a giant tank with a single-tank capacity far exceeding the current ground tank scale.

[0024] In addition, the anti-seepage unit 4 sets multiple redundant barriers on each path where the underground storage tank unit 1 can leak by the multilayer composite anti-seepage structure composed of the inner lining coating 41, the geomembrane layer 42 and the backfill anti-seepage layer 43, greatly improves the safety and reliability of the system, and completely eliminates the environmental risk of molten salt leakage polluting the soil and groundwater. Thus, the underground high-temperature molten salt heat storage system of the embodiment of the application improves the energy storage capacity of a single tank by an order of magnitude through the organic integration and functional synergy of each unit, reduces the dependence on a multi-tank parallel system and its complex auxiliary facilities, significantly reduces the initial investment and operation and maintenance costs, and further clears the key technical obstacles for the large-scale application of molten salt energy storage technology in the fields of solar thermal power generation and thermal power flexibility reconstruction.

[0025] Further, the underground storage tank unit 1 comprises a tank body 11 which is a rounded table type structure formed by a variable cross-section stainless steel plate, the heat management unit 2 comprises a side wall insulation layer 21 made of flexible insulation material and arranged on the outer wall of the tank body 11 in the circumferential direction, and the inner lining coating 41 is arranged on the inner wall of the tank body 11.

[0026] Further, the side wall and the bottom wall of the tank body 11 are connected by a circular arc chamfer structure, and a drainage layer is arranged between the bottom wall of the tank body 11 and the bottom pit wall of the underground pit.

[0027] Through the implementation of the above-mentioned underground high-temperature molten salt heat storage system embodiment, the rounded table type structure formed by the variable cross-section stainless steel plate is used as the tank body 11, which can effectively avoid the weak link and stress concentration risk caused by the welding joint, and the variable cross-section design can be optimized according to the distribution law of the molten salt static pressure, thereby realizing the reasonable use of materials while ensuring the structural safety. For example, thicker plate walls are used in the bottom and lower area of the tank body 11 which bears the maximum pressure to provide sufficient strength support, while the material thickness is appropriately reduced in the upper area with smaller pressure, so as to optimize the material usage and reduce the manufacturing cost on the premise of ensuring the structural safety. In addition, the rounded table type structure can uniformly transmit the molten salt load to the surrounding structural unit 3, thereby improving the structural integrity and bearing performance of the tank body 11.

[0028] As described above, the inner lining coating 41 arranged on the inner wall of the tank body 11, such as a ceramic matrix composite material or a special alloy coating with excellent high-temperature stability, directly faces the high-temperature molten salt medium, effectively preventing corrosion and erosion of the molten salt on the stainless steel tank body 11, and provides the first anti-seepage protection barrier for the underground storage tank unit 1. The side wall insulation layer 21 is made of a flexible insulation material, such as a high-temperature resistant ceramic fiber module or a nano-porous super-insulation material, which tightly covers the outer wall of the tank body 11 in the circumferential direction. Not only does it greatly reduce heat loss through the tank wall and improve system energy efficiency, but more importantly, its flexible properties can fully accommodate and absorb the radial displacement caused by the thermal expansion of the tank body 11, effectively releasing thermal stress through its own compression deformation, avoiding structural damage caused by rigid constraints.

[0029] The side wall and bottom wall of the tank body 11 adopt a circular arc chamfer structure, which can eliminate the stress concentration phenomenon of the traditional right-angle connection form, making the stress distribution more smooth and continuous, and greatly improving the fatigue resistance of the structure under long-term alternating loads. At the same time, the large underground high-temperature molten salt storage tank has a large volume, and the foundation part must have the same heat preservation and anti-seepage structure as the side wall. The bottom foundation should also use the strong compaction method to compact the in-situ soil, and the drainage layer should be arranged around the tank to provide important safety protection for system operation, thereby enhancing the reliability, safety and durability of the storage tank.

[0030] Further, the inner heat-resistant structural layer 31 is a heat-resistant concrete layer cast in the circumferential direction on the outer side of the side wall insulation layer 21 to form a layered structure, and the outer structural layer 32 is a steel fiber-containing prestressed reinforced concrete layer cast in the circumferential direction on the outer side of the inner heat-resistant structural layer 31 to form a layered structure.

[0031] Further, the geomembrane layer 42 is laid in the circumferential direction on the side wall of the underground pit, and the geomembrane layer 42 and the outer structural layer 32 have a gap therebetween, and the backfill anti-seepage layer 43 is filled with backfill soil to fill the gap between the geomembrane layer 42 and the outer structural layer 32.

[0032] Through the implementation of the above underground high-temperature molten salt heat storage system embodiment, the inner heat-resistant structural layer 31 is made of heat-resistant concrete (such as concrete prepared by selecting high-aluminum cement or phosphate combined with bauxite aggregate), which is circumferentially cast and formed, directly contacts the side wall heat preservation layer 21, and can long-term resist the high-temperature environment transmitted from the inside, provides stable high-temperature protection for the entire structural unit 3 and bears part of the load. The outer structural layer 32 is made of prestressed reinforced concrete containing steel fibers (the concrete can be preferably C50 and above strength grade, mixed with end-hook type steel fibers, and ring prestress is applied) poured outside the heat-resistant layer. The incorporation of steel fibers can significantly enhance the crack resistance and toughness of the concrete, and the application of prestress effectively offsets most of the tensile stress generated by the static pressure of the molten salt, greatly improving the load-bearing efficiency and durability of the structure, and the two together form a solid support that finally transmits the load to the surrounding rock-soil.

[0033] The geomembrane layer 42 (such as HDPE high-density polyethylene geomembrane) is laid along the side wall of the pit, and an annular gap is formed between the outer structural layer 32, which constitutes an independent anti-seepage isolation area. The backfill anti-seepage layer 43 filled in the gap is made of low-permeability backfill soil (such as mixed with bentonite or using a mixture of sand and clay), which not only plays a role in stabilizing the outer structural layer 32, but also forms a physical and material double anti-seepage barrier with the geomembrane layer 42. This structure ensures that even if the outer structural layer 32 has a small amount of leakage, it will be confined in this gap and completely blocked by the geomembrane layer 42, ensuring that under any circumstances, the molten salt will not seep into the soil environment outside the underground pit, achieving a redundant backup of anti-seepage efficiency and greatly improving the safety and environmental reliability of the system as a whole.

[0034] Further, the top of the tank body 11 is provided with an opening, and the underground storage tank unit 1 further comprises a top cover plate 12 covering the opening at the top of the tank body 11. The outer diameter of the top cover plate 12 corresponds to the outer diameter of the outer structural layer 32, and the outer side of the outer structural layer 32 is at ambient temperature.

[0035] Further, the top of the tank body 11 is a metal structure, and the inner and outer sides of the top of the tank body 11 are coated with a rust-proof coating.

[0036] Through the implementation of the above underground high-temperature molten salt heat storage system embodiment, the top cover plate 12 is covered at the top opening of the tank body 11, and the outer diameter thereof is accurately matched with the outer diameter of the outer structural layer 32, thereby forming a complete top closed structure, which not only prevents the loss of a large amount of heat and the entry of external pollutants, but more importantly, can limit the high-temperature region inside the storage tank main body. Since the outer side of the outer structural layer 32 is at the ambient temperature, the main force structure can avoid being directly exposed to the high-temperature environment, thereby completely eliminating the adverse effects of high temperature on the material properties (such as strength decay and creep) thereof, ensuring that the prestressed reinforced concrete and other materials can exert their best mechanical properties at room temperature, and greatly improving the long-term stability and safety of the structural unit 3.

[0037] The top of the tank body 11 is a key interface that forms a seal with the top cover plate 12, and the metal structure thereof guarantees the necessary structural strength and rigidity. The inner and outer sides of the metal substrate are fully coated with a rust-proof coating (such as an aluminum-based metal coating or a special high-temperature corrosion-resistant paint with good adhesion), which provides all-round corrosion protection for the component. The inner side coating can effectively resist the corrosive erosion of high-temperature molten salt volatile substances to the lower surface of the top plate, and the outer side coating can resist the electrochemical corrosion of moisture and oxygen in the environment to the upper surface of the top plate. This double protection strategy ensures the integrity of the metal structure of the top of the tank body 11 under severe working conditions, prevents seal failure or structural strength reduction due to local corrosion, thereby ensuring the long-term air tightness and overall structural safety of the top of the underground storage tank unit, reducing maintenance requirements and prolonging the service life of the system.

[0038] Further, the underground storage tank unit 1 further comprises a cover top 13 arranged above the top cover plate 12, the cover top 13 being a hollow hemispherical structure with an opening facing downward, and the bottom opening of the cover top 13 being matched and covered on the top cover plate 12; A plurality of hangers 14 are arranged between the cover top 13 and the top cover plate 12, one end of each hanger 14 being vertically downwardly fixed to the top plate surface of the top cover plate 12, and the other end of each hanger 14 being vertically upwardly fixed to the inner top wall surface of the cover top 13; The heat management unit 2 further comprises a top plate thermal insulation layer 22 made of a flexible thermal insulation material and horizontally arranged on the top plate surface of the top cover plate 12.

[0039] Through the implementation of the above underground high-temperature molten salt thermal storage system embodiment, the hollow hemispherical structure with the opening facing downward is arranged as the cover top 13, and the bottom opening thereof is covered on the top cover plate 12 to form an effective secondary protection and heat buffer space. The hemispherical structure not only has good mechanical properties and can disperse external loads, but also the air layer between the hemispherical structure and the top cover plate 12 constitutes an additional static air heat insulation layer, which further blocks the heat loss to the atmosphere. The cover top 13 and the top cover plate 12 are connected through a plurality of vertically arranged hangers 14 (the hangers 14 can preferably be made of heat-resistant alloy steel, such as 310S stainless steel), and the suspended connection structure can transmit the gravity load of the cover top 13 to the solid top cover plate 12, and allow the thermal displacement between the cover top 13 and the top cover plate 12, so as to avoid the structural constraint stress caused by the different thermal expansion coefficients.

[0040] The top plate heat preservation layer 22 (for example, a flexible heat preservation material such as a ceramic fiber blanket or a module) horizontally arranged on the top plate surface of the top cover plate 12 directly covers the high-temperature area, which can effectively absorb the expansion displacement of the top cover plate 12 caused by heating, greatly reduce the heat loss through the tank top, and maintain the temperature of the top cover plate 12 at a relatively low level, thereby protecting the structure and sealing material below from high temperature. These structures jointly construct a multi-level and high-performance heat management and structural protection system in the top region of the tank body 11, which significantly improves the heat preservation efficiency, structural safety and long-term operation reliability of the overall system.

[0041] Further, the underground high-temperature molten salt thermal storage system further comprises a monitoring and control unit, which comprises a displacement sensor, a liquid level monitor, and a plurality of point-distributed thermocouples and osmometers. The displacement sensor is arranged on the outer side wall of the tank body 11, the liquid level monitor is arranged inside the tank body 11 at the top opening, and a group of thermocouples and osmometers are arranged on the side surfaces of the inner lining coating 41, the side wall heat preservation layer 21, the inner layer heat-resistant structure layer 31 and the outer layer structure layer 32.

[0042] Through the implementation of the above underground high-temperature molten salt heat storage system embodiment, a multi-level and full-cycle intelligent health diagnosis and safety warning system can be constructed. A displacement sensor (such as a high-precision LVDT (Linear Variable Differential Transformer)) is arranged on the outer sidewall of the tank 11, which can monitor the radial displacement change of the tank 11 under the action of thermal expansion and molten salt static pressure in real time, and provide key data for evaluating the working state of the heat management unit 2 and the structural stability of the tank 11. The liquid level monitor (such as a radar liquid level meter) located at the top opening continuously tracks the molten salt liquid level in the tank, which is the basis for ensuring the normal operation and capacity management of the system. A group of thermocouples (such as K-type nickel-chromium-nickel silicon thermocouples) and osmometers (such as vibrating wire osmometers) are arranged on the side surfaces of the inner lining coating 41, the sidewall insulation layer 21, the inner layer heat-resistant structural layer 31 and the outer layer structural layer 32, which constitutes a key sensing network deep into the system. The thermocouples distributed in each layer can accurately measure the temperature gradient distribution from the tank to the external environment, so as to evaluate whether the heat insulation efficiency of the heat management unit 2 is normal in real time, and effectively monitor any abnormal overheating phenomenon. The corresponding arranged osmometers are used to monitor the subtle changes of the pore water pressure between each layer, and the corresponding arrangement of the measuring points of the thermocouples enables the system to accurately locate the potential molten salt leakage position and path. Therefore, the warning can be given at the initial stage of leakage before the molten salt reaches the outer layer structural layer 32, so as to realize real-time verification and advanced monitoring of the performance of the multi-layer composite anti-seepage structure.

[0043] Preferably, all these monitoring data can be collected to the control system, so as to realize subsequent all-weather, digital intelligent management of the tank structure response, thermal state and anti-seepage safety, and provide solid data support and decision basis for long-term safe operation, preventive maintenance and risk intervention of the system, which greatly improves the observability, controllability and intrinsic safety level of the whole underground high-temperature molten salt heat storage system.

[0044] The application also discloses a construction and operation method, which adopts the above underground high-temperature molten salt heat storage system, and the construction and operation method comprises the following steps: S1, excavating a reverse circular table type underground foundation pit, tamping and leveling the bottom pit wall of the underground foundation pit, and then laying a gravel drainage layer; S2, pouring a prestressed reinforced concrete containing steel fibers in the underground foundation pit to form the outer layer structural layer 32 in the circumferential direction, and laying a geomembrane layer 42 on the side pit wall of the underground foundation pit to form the outermost anti-seepage barrier; S3, backfilling soil between the geomembrane layer 42 and the outer layer structural layer 32 to form a backfill anti-seepage layer 43; S4, pouring heat-resistant concrete close to the inner side of the outer layer structural layer 32 to form the inner layer heat-resistant structural layer 31 in the circumferential direction; S5, welding the tank body 11 included in the underground storage tank unit 1 in the underground foundation pit, fixing the side wall thermal insulation layer 21 composed of flexible thermal insulation material on the outer side wall of the tank body 11 in the circumferential direction, and fixing the inner lining coating 41 on the inner side wall of the tank body 11; S6, installing the top cover plate 12 on the top of the tank body 11, laying the top plate thermal insulation layer 22 on the top cover plate 12, connecting the cover top 13 with the top cover plate 12 through the suspender 14, and fixing the cover top 13 with the top of the outer layer structure layer 32 through the embedded part; S7, after the underground high-temperature molten salt heat storage system is put into operation, the state data of each layer are obtained in real time through the monitoring instruments pre-embedded in the construction process, and a storage tank health state model is established based on the obtained state data to realize predictive maintenance.

[0045] Through the implementation of the above construction and operation method embodiment, first, the circular inverted truncated cone type underground foundation pit is excavated and the gravel drainage layer is laid, thereby establishing good foundation drainage conditions for the entire project, preventing the accumulation of underground water from adversely affecting the structure. Then, the outer layer structure layer 32 is poured to form the main load-bearing structure, which can be formed early, providing a stable operation reference and safety support for subsequent construction. At the same time, the geomembrane layer 42 is laid on the side wall of the foundation pit to form the outermost anti-seepage barrier, thereby blocking the influence of the external environment from the source. Then, the backfill soil is used to backfill between the geomembrane layer 42 and the outer layer structure layer 32 to form the backfill anti-seepage layer 43, which not only plays a role in stabilizing the outer layer structure layer 32, but more importantly, together with the geomembrane layer 42, forms the first composite anti-seepage system, greatly improving the reliability of anti-seepage.

[0046] The inner layer heat-resistant structure layer 31 is poured close to the inner side of the outer layer structure layer 32 to complete the construction of the main support structure, and the two layers work together to effectively share the load. The process of welding and forming the tank body 11 in the foundation pit ensures the integrity of the large structure, avoiding potential damage risks during transportation; at the same time, the fixation of the side wall thermal insulation layer 21 and the construction of the inner lining coating 41 are completed synchronously under ground conditions, ensuring the uniformity of the flexible thermal insulation material and the quality of the inner lining coating 41, significantly improving the construction precision and protection effect.

[0047] The installation of the top cover plate 12 and the laying of the top plate thermal insulation layer 22, combined with the cover top 13 connected through the suspender 14, together form a complete top sealing and thermal insulation system, effectively reducing heat loss. The monitoring instruments pre-embedded in the construction process provide conditions for obtaining real-time state data of each layer after the system is put into operation, and the storage tank health state model established based on these data can realize predictive maintenance, changing the traditional passive maintenance to an active and intelligent operation and maintenance mode. Not only does it improve construction efficiency, but it also lays a solid foundation for safe and efficient operation of the system throughout its life cycle, effectively solving the technical problems of stress concentration, material creep and single tank capacity limitation of traditional ground storage tanks.

[0048] It should be understood that the above examples are only used to illustrate the technical solutions of the present application, but not limit the technical solutions of the present application. Those skilled in the art can make modifications to the technical solutions described in the above examples, or make equivalent replacements to some of the technical features. All these modifications and replacements shall belong to the protection scope of the present application.

Claims

1. An underground high temperature molten salt thermal storage system characterized by, The underground high-temperature molten salt heat storage system comprises an underground storage tank unit, a heat management unit, a structure unit and an anti-seepage unit; The underground storage tank unit is used for containing high-temperature molten salt, and is arranged in an underground foundation pit; The heat management unit is arranged outside the underground storage tank unit, and is used for absorbing heat of the underground storage tank unit and radial displacement caused by thermal expansion; The structure unit comprises an inner heat-resistant structure layer and an outer structure layer arranged outside the heat management unit in sequence from inside to outside, and is used for forming a support structure which jointly bears static pressure of the molten salt; The anti-seepage unit comprises an inner lining layer arranged inside the underground storage tank unit, and a geomembrane layer and a backfill anti-seepage layer arranged outside the outer structure layer in sequence from inside to outside, and is used for jointly forming a multilayer composite anti-seepage structure.

2. The underground high temperature molten salt thermal storage system of claim 1, wherein: The underground storage tank unit comprises a tank body, the tank body is a rounded table type structure formed by a variable cross-section stainless steel plate, the heat management unit comprises a side wall heat preservation layer made of flexible heat preservation material and arranged on an outer wall of the tank body in a circumferential direction, and the inner lining layer is arranged on an inner wall of the tank body.

3. The underground high temperature molten salt thermal storage system of claim 2, wherein: A junction between a side wall and a bottom wall of the tank body is a circular arc chamfer structure, and a drainage layer is arranged between the bottom wall of the tank body and a bottom pit wall of the underground foundation pit.

4. The underground high temperature molten salt thermal storage system of claim 2, wherein: The inner heat-resistant structure layer is a layered structure formed by pouring heat-resistant concrete in a circumferential direction outside the side wall heat preservation layer, and the outer structure layer is a layered structure formed by pouring prestressed reinforced concrete containing steel fibers in a circumferential direction outside the inner heat-resistant structure layer.

5. The underground high temperature molten salt thermal storage system of claim 4, wherein: The geomembrane layer is laid on a pit side wall of the underground foundation pit in a circumferential direction, and has a spacing with the outer structure layer, and the backfill anti-seepage layer is filled with backfill soil filled in the spacing between the geomembrane layer and the outer structure layer.

6. The underground molten salt thermal storage system of claim 2, wherein: A top of the tank body is provided with an opening, the underground storage tank unit further comprises a top cover plate covering the opening of the top of the tank body, an outer diameter of the top cover plate corresponds to an outer diameter of the outer structure layer, and an outer side of the outer structure layer is at an ambient temperature.

7. The underground molten salt thermal storage system of claim 6, wherein: The top of the tank body is a metal structure, and an inner side and an outer side of the top of the tank body are coated with an anti-rust coating.

8. The underground molten salt thermal storage system of claim 6, wherein: The underground storage tank unit further comprises a cover top arranged above the top cover plate, the cover top is a hollow hemispherical structure with a downward opening, and the bottom opening of the cover top is matched to cover the top cover plate; A plurality of hangers are arranged between the cover top and the top cover plate, one end of each of the hangers is fixed to a top plate surface of the top cover plate in a vertical downward direction, and the other end of each of the hangers is fixed to a top inner wall surface of the cover top in a vertical upward direction; The heat management unit further comprises a top plate heat preservation layer made of flexible heat preservation material and arranged on the top plate surface of the top cover plate in a horizontal direction.

9. The underground molten salt thermal storage system of any of claims 2-8, wherein: The underground high-temperature molten salt heat storage system further comprises a monitoring control unit, the monitoring control unit comprises a displacement sensor, a liquid level monitor, and a plurality of thermocouples and osmometers distributed in multiple positions, the displacement sensor is arranged on the outer sidewall of the tank body, the liquid level monitor is arranged inside the tank body at the top opening, and the side surfaces of the inner lining coating, the sidewall thermal insulation layer, the inner layer heat-resistant structural layer, and the outer layer structural layer are respectively provided with a group of the thermocouples and the osmometers.

10. A method of building and operating a high temperature molten salt thermal storage system according to any one of claims 1 to 9, wherein, The construction operation method comprises: S1, excavating the underground foundation pit in the shape of an inverted circular table, and paving a gravel drainage layer after tamping and leveling the bottom pit wall of the underground foundation pit; S2, pouring a prestressed reinforced concrete containing steel fibers to form the outer layer structural layer in the circumferential direction in the underground foundation pit, and laying the geomembrane layer on the side pit wall of the underground foundation pit in the circumferential direction to form the outermost impermeable barrier; S3, backfilling soil between the geomembrane layer and the outer layer structural layer to form a backfill impermeable layer; S4, pouring heat-resistant concrete close to the inner side of the outer layer structural layer in the circumferential direction to form the inner layer heat-resistant structural layer; S5, welding the tank body included in the underground storage tank unit in the underground foundation pit, fixedly arranging a sidewall thermal insulation layer composed of a flexible thermal insulation material on the outer sidewall of the tank body in the circumferential direction, and fixedly arranging the inner lining coating on the inner sidewall of the tank body; S6, installing a top cover plate on the top of the tank body, laying a top cover plate thermal insulation layer on the top cover plate, connecting the top cover plate with the top cover through a suspender, and fixing the top cover to the top of the outer layer structural layer through a pre-embedded part; S7, after the underground high-temperature molten salt heat storage system is put into operation, the state data of each layer are obtained in real time through the monitoring instruments pre-embedded synchronously in the construction process, and a storage tank health state model is established according to the obtained state data to perform predictive maintenance.

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