Coaxial casing pipe type water body heat storage system and method based on vertical shaft of shut-off and retreat mine

Abstract

The invention discloses a coaxial sleeve type water body heat storage system and method based on a vertical shaft of a shut-off and retreat mine. A coaxial sleeve with a deep inner part and a shallow outer part is mounted in the center of a top sealing well cover of the vertical shaft which is sealed by a sealing and filling section; the outer pipe and a well wall annulus form a cement sheath which is matched with a casing hanger to share the weight of the casing; a one-way valve and a perforated screen pipe are arranged at the specific depth of the inner pipe to form a two-way heat storage adaptive assembly. According to the method, natural rebound underground water serves as a medium, a high-temperature heat source heat storage mode and a low-temperature heat source heat storage mode are switched according to the relation between the heat storage heat source temperature and the original ground temperature of the top face of a shaft sealing and filling section, in the non-heating season, water is pumped through an outer pipe for heating and then recharged for heat storage, in the heating season, reverse circulation heat release heating is conducted, and the low-temperature mode can synchronously provide summer cold loads. The method adapts to the large-diameter and large-depth characteristics of a shaft, large-scale cross-season heat storage is achieved, mine remaining resources are fully utilized, the heat storage cost is reduced, the method adapts to various heat sources, the space-time intermittency of renewable energy sources is relieved, and green and low-carbon transformation of closed and retreated mines is promoted.

Description

Technical Field

[0001] This invention relates to the technical field of the intersection of mining engineering and energy storage science, and in particular to a coaxial casing type water thermal storage system and method based on the shaft of a closed-down mine. Background Technology

[0002] The development of hydrothermal geothermal resources in mines based on heat pump and gravity heat pipe technologies, relying on the early mining operations and supporting shaft facilities of closed mines, has reduced development costs and improved the technical and economic feasibility of geothermal utilization, becoming a research hotspot in the mining and energy sector. However, current geothermal development in closed mines generally adopts a one-way extraction and utilization model, lacking technical design for two-way thermal energy storage and utilization. It is also unable to incorporate energy storage to alleviate the spatiotemporal fluctuations and supply-demand imbalances of renewable energy sources such as wind and solar power. This results in a low degree of integration between geothermal development and multi-energy complementarity, few actual engineering projects, and low resource development and utilization rates, making it difficult to promote the green and low-carbon transformation of closed mines.

[0003] Geothermal energy storage in closed mines utilizes underground space, geological formations, and remaining facilities. Using water as a heat carrier, it enables large-scale, long-term storage of industrial waste heat and off-peak electricity. Compared to traditional underground thermal storage methods such as borehole storage, underground water tank storage, and aquifer storage, it offers advantages such as lower initial construction costs, larger storage capacity, longer storage periods, and less impact on surface space. The vertical shafts, constructed of concrete masonry, boast high support strength and a long service life. Their cylindrical structure resembles that of hot water storage tanks, and the shafts remain intact after mine closure, making them excellent natural carriers for groundwater thermal storage and possessing inherent conditions for large-scale thermal storage. However, there is currently a lack of theoretical research and engineering practice on water thermal storage in vertical shafts of mines in Guantui. Their unique large-diameter and deep structural features have significant dimensional differences from traditional hot water storage tanks and coaxial tube heat exchangers used in medium-deep geothermal development. This makes it difficult to directly apply the process design of traditional hot water storage tanks, such as the inlet and outlet forms and opening positions, as well as the coaxial tube heat exchange technology for medium-deep geothermal development. It is difficult to adapt to the structural characteristics of the shaft to achieve efficient thermal storage.

[0004] Therefore, there is an urgent need to develop a thermal energy storage technology solution that is compatible with the large-diameter and deep structural characteristics of vertical shafts in closed and decommissioned mines, to break through the adaptation bottleneck of existing technologies, so as to realize bidirectional storage and use of thermal energy and large-scale cross-seasonal storage, and provide technical support for the resource utilization and multi-energy complementarity of renewable energy in closed and decommissioned mines. Summary of the Invention

[0005] To address the aforementioned technical issues, this invention provides a coaxial sleeve-type water thermal storage system and method based on the shaft of a closed-down mine. Utilizing the structural advantages of the shaft, it integrates a coaxial sleeve-type heat exchange structure with a dual-mode thermal storage design, breaking through the adaptation bottlenecks of traditional technologies, achieving large-scale cross-seasonal water thermal storage, effectively utilizing legacy mining resources, alleviating the temporal and spatial intermittent nature of renewable energy, and promoting the green and low-carbon transformation of closed-down mines.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a coaxial casing type water thermal storage system based on the shaft of a closed-off mine, including the shaft of the closed-off mine, a coaxial casing and a casing hanger; The bottom of the wellbore is provided with a sealing section, and the top of the wellbore is provided with a sealing cover at the well neck. The coaxial sleeve is vertically installed in the wellbore through the installation hole in the center of the sealing cover. The coaxial sleeve includes an inner tube and an outer tube. The depth of the inner tube is greater than the depth of the outer tube. The lower end of the inner tube extends above the sealing section. The lower end of the outer tube extends below the interface between the loose layer and the bedrock layer. Within the range of the loose layer to the bedrock layer below the sealed well cover, full-section grouting and cementing are carried out in the annular gap formed between the outer pipe and the well wall to form a cement sheath cementing section; the casing hanger is installed at the top of the annular gap and works with the cement sheath cementing section to share the weight of the coaxial casing. The inner tube is equipped with a one-way valve that can open 360° circumferentially. Within the installation height range of the one-way valve, the inner tube is replaced with a perforated screen tube. When the one-way valve is opened, the inner tube and the outer tube are connected through the perforated screen tube.

[0007] Furthermore, the sealing section is composed of a sealed filling body for the shaft well socket, a sidewall sealing body at the connection between the bottom of the shaft and the horizontal roadway, and a bottom plate sealing body for the shaft bottom. The top of the sealing section is bounded by the top surface of the bottom plate sealing body of the shaft bottom, and the bottom extends to the bottom of the well socket. The sidewall covers the entire cross-section of the connection between the shaft bottom and the horizontal roadway. The top surface of the bottom plate sealing body of the shaft bottom is higher than or equal to the top surface of the sealed filling body of the horizontal roadway on the sidewall of the shaft.

[0008] Furthermore, the lower end of the inner pipe extends 3-5m above the top surface of the bottom sealing layer of the wellbore; the lower end of the outer pipe extends 3-5m below the interface between the loose layer and the bedrock layer.

[0009] Furthermore, the area between the top surface of the sealing section and the bottom surface of the cement sheath cementing section inside the wellbore is a heat storage section, which is filled with naturally rebounding groundwater as a heat storage medium.

[0010] This invention also provides a method for coaxial casing water thermal storage based on the shaft of a closed-down mine. The method, based on the aforementioned coaxial casing water thermal storage system, includes the following steps: S1: Inject natural rebound groundwater into the wellbore thermal storage section, so that the natural rebound groundwater fills the entire thermal storage section; S2: Determine the temperature T of the heat storage heat source. R The original ground temperature T at the top surface depth of the wellbore sealing section vir Size relationship: If T R ≥T vir It adopts a high-temperature heat source heat storage mode and controls the one-way valve to keep it closed; If T R <T vir It adopts a low-temperature heat source storage mode and controls the one-way valve to keep it open; In addition, the installation depth h of the check valve meets the following requirements. ; In the formula, T0 is the temperature of the isothermal zone of the formation in the area where the well is located, in °C; G is the geothermal gradient of the warming zone of the formation in the area where the well is located, in °C / hm; h c The depth of the isothermal zone of the formation in the area where the well is located, in meters; S3: Heat storage stage during the non-heating season: In the high-temperature heat source heat storage mode, groundwater is extracted from the well through the outer pipe, and the groundwater is heated to the target temperature by the heat source. Then, it is reinjected to the bottom of the well through the inner pipe to complete the heat storage. In the low-temperature heat source storage mode, groundwater is extracted from the well through the outer pipe, and the groundwater is heated to the target temperature by the heat source. Then, it is reinjected through the inner pipe. Since the one-way valve is open at this time, part of the water is diverted to the annular void at the same level through the perforated screen pipe, and part of the water is reinjected to the bottom of the well to complete the heat storage and provide cooling load for building users. S4: Heating season heat release phase: In the high-temperature heat source storage mode, the water circulation direction of the inner and outer pipes is adjusted. High-temperature hot water in the storage section is extracted through the inner pipe for building heating. The return water with reduced temperature after heat extraction is reinjected back into the well through the outer pipe. In the low-temperature heat source storage mode, the one-way valve is closed first, and then hot water in the heat storage section is extracted through the inner pipe for building heating. The return water with reduced temperature after heat extraction is reinjected into the well through the outer pipe.

[0011] Furthermore, the heat source includes one or more of the following: wind, solar, and thermal renewable energy sources; off-peak electricity from the power grid; industrial waste heat; and waste heat from building air conditioning recovered by shallow ground source heat pumps.

[0012] The beneficial effects of this invention are: This invention fully utilizes the vertical shaft resources of closed and decommissioned mines, solving the resource waste, safety hazards, and ecological environmental problems caused by traditional shutdown treatment. By integrating the coaxial casing structure of medium-deep geothermal development with a fixed-depth thermal storage design, it not only adapts to the unique characteristics of large-diameter and deep mine shafts, overcoming the bottleneck of the inability to directly apply traditional hot water storage tanks and medium-deep geothermal casing technologies, but also enables large-scale cross-seasonal thermal storage in both high-temperature and low-temperature modes. It is particularly suitable for the storage and cooling needs of waste heat from shallow ground source heat pump air conditioning in summer, significantly improving the comprehensive utilization rate of low-grade and intermittent energy. Compared with traditional methods such as borehole thermal storage and underground water tank thermal storage, it has the advantages of low initial construction cost, long thermal storage period, and no occupation of ground space. It can effectively alleviate the spatiotemporal intermittent fluctuations of renewable energy sources such as wind and solar power, provide efficient energy storage support for multi-energy complementarity, and promote the development of resource utilization of closed and decommissioned mines towards large-scale, commercial, and low-carbon directions. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0014] Figure 2 This is a schematic diagram of the structure when the one-way valve is open in the low-temperature heat source storage mode of the present invention.

[0015] Figure 3 This is a schematic diagram of the structure when the one-way valve is closed in the high-temperature heat source heat storage mode of the present invention.

[0016] In the diagram: 1. Outer pipe; 2. Inner pipe; 3. One-way valve; 4. Perforated screen pipe; 5. Sealing section; 6. Thermal storage section; 7. Cementing section; 8. Sealed well cover; 9. Horizontal tunnel; 10. Loose layer; 11. Bedrock layer. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings.

[0018] This invention discloses a coaxial casing type water thermal storage system based on the shaft of a closed-off mine.

[0019] Reference Figure 1 A coaxial casing type water thermal storage system based on the vertical shaft of a closed-off mine includes the vertical shaft of the closed-off mine, coaxial casing, casing hanger, and bidirectional thermal storage adapter; the components work together to form a sealed, stable integrated system with dual-mode thermal storage capabilities.

[0020] The well shaft serves as the core heat storage carrier, and a sealing section 5 is set at its bottom. The sealing section 5 is composed of the sealed filling body of the well shaft well cavity, the side wall sealing body at the connection between the bottom of the well shaft and the horizontal tunnel 9, and the bottom plate sealing body of the well shaft. The top of the sealing section 5 is bounded by the top surface of the bottom plate sealing body of the well shaft, and the bottom extends to the bottom of the well cavity. The side wall completely covers the entire cross section at the connection of the horizontal tunnel 9, forming a comprehensive sealed barrier.

[0021] To further prevent the leakage of stored hot water into the roadway or formation, the design ensures that the top surface of the bottom plate of the wellbore is higher than or equal to the top surface of the sealed backing of the horizontal roadway 9 on the sidewall of the wellbore, forming a seepage-proof gradient through the height difference. A sealing cover 8 is installed at the top of the wellbore neck, and the connection between the sealing cover 8 and the well neck is treated with a sealing structure, with an installation hole in the center matching the outer diameter of the coaxial sleeve.

[0022] It is important to note that the dimensional characteristics of the mine shaft are one of the core bases for the design of this system. In terms of vertical depth, it is much greater than the depth of a typical traditional hot water storage tank and vertical buried pipe, but generally less than the depth of a coaxial casing for medium-deep geothermal development. In terms of radial dimensions, it is much larger than a typical traditional water storage tank, vertical buried pipe, and coaxial casing, by an order of magnitude. This unique dimensional characteristic gives the shaft the spatial advantage of large-volume heat storage, but also makes it impossible to directly apply the technology and processes of traditional hot water storage tanks. It also creates a dimensional difference compared to the coaxial casing heat exchangers for medium-deep geothermal development.

[0023] The coaxial casing is vertically and centrally installed inside the wellbore through the mounting hole. It includes an inner tube 2 and an outer tube 1. The depth of the inner tube 2 is greater than that of the outer tube 1 to accommodate the large depth of the wellbore and the fluid circulation requirements of different heat storage modes. The lower end of the inner tube 2 extends to 3-5m above the top surface of the bottom seal of the wellbore, reaching the bottom area of ​​the heat storage section 6. This ensures that hot water can sink and be stored fully when the high-temperature heat source is stored, reducing heat loss. The lower end of the outer tube 1 extends to 3-5m below the interface between the loose layer 10 and the bedrock layer 11.

[0024] Within the height range of the loose layer 10 to the bedrock layer 11 below the sealed well cover 8, the entire section of the well is grouted and cemented using an eccentric cementing process within the annular gap formed between the outer pipe 1 and the well wall, forming a dense cement annular cemented section 7. In this embodiment, the grouting material is anti-permeability cement grout, and the grouting pressure is controlled at 1.5-2.5 MPa. This ensures that the cement grout can fully fill the tiny cracks in the annular gap, while avoiding excessive pressure that could cause deformation of the well wall or casing, thus achieving complete sealing of the annular area and preventing the hot water from seeping into the layers or leaking at the wellhead.

[0025] The casing hanger is installed at the top of the aforementioned annular gap and adopts a hydraulic structure design. Its load-bearing capacity is no less than 1.2 times the total weight of the coaxial casing. It works together with the cement sheath cementing section 7 to share the weight of the coaxial casing in order to cope with the gravity load of the deep casing, avoid deformation or breakage of the connection due to long-term stress, and ensure the long-term operational stability of the system.

[0026] The area between the top surface of the bottom sealing section 5 and the bottom surface of the cement sheath cementing section 7 is defined as the heat storage section 6. The heat storage section 6 is filled with naturally rebounding groundwater as the heat storage medium. The selection of groundwater is based on its characteristics of large heat capacity, convenient source and good compatibility with the formation environment. It can efficiently carry and store heat energy and is suitable for long-term heat storage needs across seasons.

[0027] The bidirectional thermal storage adapter assembly is the core structure for realizing dual-mode thermal storage. It includes a one-way valve 3 with a 360° circumferential opening and a perforated screen tube 4. The one-way valve 3 is installed at a specific depth in the inner tube 2. Its core function is to control the unidirectional flow of water, allowing water to flow only from the inner tube 2 through the perforated screen tube 4 into the annular gap, thus preventing water backflow and thermal energy disturbance during thermal storage. Within the installation height range of the one-way valve 3, the inner tube 2 is replaced with the perforated screen tube 4. The inner tube 2 and outer tube 1 of the coaxial sleeve are both 10m long. The sections are connected by standard threads and sealed with grease to ensure the sealing and tensile strength in the underwater environment, ensuring that the coaxial sleeve does not leak or detach under deep and high-pressure conditions.

[0028] It is important to emphasize that the reason for the need for low-temperature heat source storage is that traditional coaxial casing technology is mostly used in medium-deep geothermal development, where drilling depths often exceed one kilometer and the bottom formation temperature is high. However, current mine shafts are generally no more than one kilometer deep, resulting in lower bottom formation temperatures. Coaxial casings used in medium-deep geothermal development are generally insufficient for low-temperature heat source storage, especially for the waste heat from building air conditioning recovered by shallow ground source heat pumps in summer. This means the heat pump system struggles to transfer this waste heat to the deep, high-temperature formations, leading to difficulties in condensation heat dissipation and consequently impacting the summer cooling load demand of building users. Therefore, it is sometimes necessary to utilize the relatively shallow depth of mine shafts compared to medium-deep coaxial casings to implement low-temperature heat source storage. The design of bidirectional heat storage adapter components is precisely to meet this need.

[0029] This invention also discloses a coaxial casing-type water thermal storage method for closed-down mine shafts based on the above-mentioned thermal storage system. Its core logic is to switch between dual thermal storage modes according to the matching relationship between the heat source temperature and the original geothermal temperature of the formation, thereby achieving efficient storage and on-demand release of thermal energy. Specifically, it includes the following steps: S1: Inject natural rebound groundwater into the wellbore thermal storage section 6, so that the natural rebound groundwater completely fills the entire thermal storage section 6, providing a basic carrier for thermal energy storage.

[0030] S2: Determine the temperature T of the heat storage heat source. R The original ground temperature T at the top surface depth of section 5 of the wellbore sealing section vir Size relationship; If T R ≥T vir The system adopts a high-temperature heat source heat storage mode and controls the one-way valve 3 to remain closed. At this time, the system forms a full-depth heat storage space, which is suitable for long-term storage of high-temperature heat sources. If T R <T vir A low-temperature heat source storage mode is adopted, and the one-way valve 3 is kept open. At the same time, the installation depth h of the one-way valve 3 must meet the formula. ; In the formula, T0 is the temperature of the isothermal zone of the formation in the area where the well is located, in °C; G is the geothermal gradient of the warming zone of the formation in the area where the well is located, in °C / hm; h c The depth of the isothermal zone of the formation in the area where the well is located, in meters.

[0031] S3: The heat storage stage during the non-heating season. The core of this stage is to convert the heat energy of various heat sources into the heat energy of the water body and store it in the heat storage section 6.

[0032] like Figure 3 As shown, in the high-temperature heat source storage mode, groundwater is drawn from the wellbore by the outer pipe 1 through the circulation pump. The groundwater is heated to the target temperature of 60-90℃ by renewable energy sources such as wind, solar and thermal energy, off-peak electricity from the power grid, and industrial waste heat. Then, it is reinjected to the bottom of the wellbore through the inner pipe 2. The heat energy is stored by sinking, taking advantage of the fact that the density of hot water is less than that of cold water, thus completing the full-depth heat storage.

[0033] like Figure 2 As shown, in the low-temperature heat source storage mode, groundwater is also extracted through the outer pipe 1. The groundwater is heated to the target temperature of 30-45℃ by low-temperature heat sources such as waste heat from building air conditioning recovered by the shallow ground source heat pump. Then, it is reinjected through the inner pipe 2. Since the one-way valve 3 is in the open state, part of the water is evenly distributed to the annular gap in the same layer through the perforated screen pipe 4, and part of the water is reinjected to the bottom of the well. This makes the stored water concentrated in the upper area of ​​the heat storage section 6, realizing low-temperature heat storage at a certain depth. At the same time, the temperature difference between the upper well and the ground surface is used to provide effective cooling load for building users in summer, realizing the dual functions of heat storage and cooling.

[0034] S4: Heating season heat release phase. The core of this phase is to release the stored heat energy as needed for building heating.

[0035] In the high-temperature heat source storage mode, the water circulation direction of the inner and outer pipes 1 is adjusted, and the high-temperature hot water in the heat storage section 6 is extracted through the inner pipe 2 and transported to the building heating system. The return water with reduced temperature after heat extraction is reinjected into the well through the outer pipe 1 to complete the heat energy recycling. In the low-temperature heat source storage mode, it is necessary to first control the one-way valve 3 to close to prevent the water from being diverted to the annular gap through the perforated screen pipe 4 when the inner pipe 2 is drawing hot water, thus causing the heat extraction to be dispersed; then, the hot water in the heat storage section 6 is drawn through the inner pipe 2 for building heating, and the return water after heat extraction is reinjected into the well through the outer pipe 1 to form a stable circulation of the heat storage medium, ensuring the concentrated release of heat energy, improving heating efficiency, and avoiding heat waste or circulation disorder caused by diversion.

[0036] Through structural optimization and mode switching, the entire system and method not only fully leverage the spatial advantages of closed and retreated mine shafts but also solve the adaptation problem of traditional thermal storage technologies, achieving the goal of large-scale, cross-seasonal, and multi-heat source compatible thermal storage, and promoting the development of resource utilization in closed and retreated mines towards large-scale and commercialization.

[0037] Taking the main shaft of a certain coal mine as a specific application scenario: the inner diameter of the main shaft is 7m, the depth of the shaft from the surface to the bottom is 1000m, the surrounding strata have a constant temperature zone depth of 50m and a temperature of 15℃, the geothermal gradient of the warming zone is 3℃ / hm, the bottom sealing height is 50m, and the original geothermal temperature at the top surface of the sealing section 5 is 42℃. Based on the above conditions, a coaxial casing-type water thermal storage system is constructed.

[0038] Assuming the heat source is waste heat from a power plant (>80℃), which can heat the well water to 80℃, determine the temperature T of the heat storage source. R =80℃>Original geothermal temperature at the top surface depth of the wellbore sealing section 5 (T) vir =42℃, using a high-temperature heat source heat storage mode; During the non-heating season, groundwater at 15°C is extracted from the wellbore through outer pipe 1 and heated to 80°C by a waste heat exchanger from the power plant. The hot water is then pumped back to the bottom of the wellbore through inner pipe 2 using a circulating pump. Because the density of hot water is less than that of cold water, the hot water accumulates at the bottom of the wellbore and slowly diffuses upwards, creating a uniform heat storage environment throughout the entire depth. During the heating season, water is extracted from the wellbore through inner pipe 2 to heat the buildings. The cooled return water, after the superheated water is extracted, is then pumped back to the wellbore through outer pipe 1, completing the heat energy cycle.

[0039] Assuming the heat source is waste heat from building air conditioning recovered by a shallow ground source heat pump at 40℃, and the condensing temperature of the heat pump system in summer cooling mode is the standard temperature of 40℃, the extracted well water can be condensed to 35℃. At this point, determine the temperature T of the heat storage source. R =35℃ < Original ground temperature at the top surface depth of the wellbore sealing section 5 (T) vir =42℃, using a low-temperature heat source storage mode. A one-way valve 3 is installed in the inner pipe 2, with a depth h of... That is, a 360° openable circumferential one-way valve 3 is installed at a certain position of the inner pipe 2 at a depth h<717m. Within the installation height range of the one-way valve 3, the inner pipe 2 is replaced with a perforated screen pipe 4.

[0040] During the non-heating season, groundwater at 15°C is extracted through the outer pipe 1, heated to 35°C by the shallow ground source heat pump condenser, and then reinjected into the well shaft through the inner pipe 2. Part of the hot water is diverted to the annular gap at the same level through the perforated screen pipe 4, and part is reinjected into the bottom of the well shaft to achieve relatively low-temperature heat storage, while providing cooling load for building users. Before the heating season, the one-way valve 3 is closed remotely to form a sealed space in the heat storage section 6. Well water is pumped through the inner pipe 2 and transported to the building heating system. The return water with reduced temperature after the superheat is extracted is reinjected into the well through the outer pipe 1.

[0041] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A coaxial casing-type water thermal storage system based on the shaft of a closed-down mine, characterized in that: This includes vertical shafts, coaxial casings, and casing hangers for closed and decommissioned mines; The bottom of the well is provided with a sealing section (5), and the top of the well is provided with a sealing cover (8); the coaxial sleeve is vertically installed in the well through the installation hole in the center of the sealing cover (8), and the coaxial sleeve includes an inner tube (2) and an outer tube (1); the depth of the inner tube (2) is greater than the depth of the outer tube (1), and the lower end of the inner tube (2) extends above the sealing section (5); the lower end of the outer tube (1) extends below the interface between the loose layer (10) and the bedrock layer (11); Within the height range from the loose layer (10) to the bedrock layer (11) below the sealed well cover (8), full-section grouting and cementing are carried out in the annular gap formed between the outer pipe (1) and the well wall to form a cement sheath cementing section (7); the casing hanger is installed at the top of the annular gap and shares the weight of the coaxial casing with the cement sheath cementing section (7); The inner tube (2) is equipped with a one-way valve (3) that can open 360° in all directions. The inner tube (2) within the installation height range of the one-way valve (3) is replaced with a perforated screen tube (4). When the one-way valve (3) is opened, the inner tube (2) and the outer tube (1) are connected through the perforated screen tube (4).

2. The coaxial casing type water thermal storage system based on the shaft of a closed-down mine as described in claim 1, characterized in that: The sealing section (5) is composed of the sealed filling body of the well hole, the side wall sealing body at the connection between the bottom of the well and the horizontal roadway (9), and the bottom plate sealing body of the well. The top of the sealing section (5) is bounded by the top surface of the bottom plate sealing body of the well, and the bottom extends to the bottom of the well hole. The side wall covers the entire cross section at the connection between the horizontal roadway (9). The top surface of the bottom plate sealing body of the well is higher than or equal to the top surface of the sealed filling body of the horizontal roadway (9) on the side wall of the well.

3. A coaxial casing-type water thermal storage system based on a closed-down mine shaft, as described in claim 2, is characterized in that: The lower end of the inner pipe (2) extends 3-5m above the top surface of the bottom sealing of the well; the lower end of the outer pipe (1) extends 3-5m below the interface between the loose layer (10) and the bedrock layer (11).

4. A coaxial casing-type water thermal storage system based on a closed-down mine shaft, as described in claim 3, is characterized in that: The section between the top surface of the sealing section (5) and the bottom surface of the cement sheath cementing section (7) is the heat storage section (6), which is filled with naturally rebounding groundwater as the heat storage medium.

5. A method for water thermal storage based on coaxial casing in the vertical shaft of a closed-down mine, characterized in that: The coaxial sleeve-type water thermal storage system according to claim 4 includes the following steps: S1: Inject natural rebound groundwater into the wellbore heat storage section (6) so that the natural rebound groundwater fills the entire heat storage section (6); S2: Determine the temperature T of the heat storage heat source. R The original ground temperature T at the top surface depth of the wellbore sealing section (5) vir Size relationship: If T R ≥T vir The high-temperature heat source heat storage mode is adopted, and the one-way valve (3) is controlled to remain closed. If T R <T vir The low-temperature heat source storage mode is adopted, and the one-way valve (3) is kept open. In addition, the installation depth h of the one-way valve (3) satisfies ; In the formula, T0 is the temperature of the isothermal zone of the formation in the area where the well is located, in °C; G is the geothermal gradient of the warming zone of the formation in the area where the well is located, in °C / hm; h c The depth of the isothermal zone of the formation in the area where the well is located, in meters; S3: Heat storage stage during the non-heating season: In the high-temperature heat source heat storage mode, groundwater is extracted from the well through the outer pipe (1), and the groundwater is heated to the target temperature by the heat source and then reinjected to the bottom of the well through the inner pipe (2) to complete the heat storage. In the low-temperature heat source heat storage mode, groundwater is extracted from the well through the outer pipe (1), and the groundwater is heated to the target temperature by the heat source and then reinjected through the inner pipe (2). Since the one-way valve (3) is open at this time, part of the water is diverted to the annular gap in the same layer through the perforated screen pipe (4), and part of the water is reinjected to the bottom of the well to complete the heat storage and provide cooling load for building users. S4: Heating season heat release phase: In the high temperature heat source heat storage mode, the water circulation direction of the inner pipe (2) and the outer pipe (1) is adjusted, and the high temperature hot water in the heat storage section (6) is extracted through the inner pipe (2) for building heating. The return water with reduced temperature after heat extraction is injected back into the well through the outer pipe (1). In the low-temperature heat source storage mode, the one-way valve (3) is closed first, and then the hot water in the heat storage section (6) is extracted through the inner pipe (2) for building heating. The return water with reduced temperature after heat extraction is injected back into the well through the outer pipe (1).

6. A method for water thermal storage based on coaxial casing of vertical shaft in closed-down mines according to claim 5, characterized in that: Heat sources include one or more of the following: wind, solar, and thermal renewable energy sources; off-peak electricity from the power grid; industrial waste heat; and waste heat from building air conditioning recovered by shallow ground source heat pumps.

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