A geothermal energy cascade utilization heat exchange system and a geothermal energy cascade utilization method

Abstract

The present application belongs to the technical field of geothermal energy development, and particularly relates to a geothermal energy cascade utilization heat exchange system and a geothermal energy cascade utilization method. The telescopic outer pipe is vertically arranged in the well, and the telescopic inner pipe is vertically arranged in the telescopic outer pipe. The telescopic outer pipe is composed of the first outer pipe and the second outer pipe which is slidably sleeved on the outer side of the lower end of the first outer pipe. The telescopic inner pipe is composed of the first inner pipe and the second inner pipe which is slidably sleeved on the outer side of the lower end of the first inner pipe. The second inner pipe is fixedly connected with the second outer pipe. Therefore, the lifting of the second outer pipe is controlled by the traction device, the positions of the lower ends of the telescopic inner pipe and the telescopic outer pipe in the well are simultaneously adjusted, the utilization of geothermal energy at different depths is realized, the heat extraction position of the heat exchange system in the well can be timely planned according to the heating demand, the heat extraction position can be timely adjusted, the utilization rate of geothermal energy is improved, and the heat exchange efficiency between the circulating fluid and the heat storage layer is improved.

Description

Technical Field

[0001] This invention belongs to the field of geothermal energy development technology, specifically relating to a geothermal energy cascade utilization heat exchange system and a geothermal energy cascade utilization method. Background Technology

[0002] Traditional geothermal heating methods utilize geothermal water systems, which directly feed the treated water into the heating network. However, this often faces challenges such as reinjection and blockage due to factors like formation pressure and sediment. Furthermore, large-scale groundwater extraction can cause groundwater imbalance, land subsidence, and environmental pollution. In contrast, coaxial tube heat exchangers indirectly extract heat from high-temperature groundwater / soil through a closed-loop circulation of the working fluid, achieving "heat extraction without water extraction" and avoiding geothermal tailwater reinjection. This is a simple and clean way to utilize geothermal energy. It can be widely applied in various geological conditions, and the single-well (hole) operation reduces drilling costs, optimizes economic efficiency, and has a very broad application prospect.

[0003] Conventional coaxial tube heat exchangers have fixed inner and outer tube structures, and are placed at the bottom of a well to extract heat from the high-temperature rock formations or groundwater for heating. However, the heating load is constantly changing throughout the heating season, with peak and trough periods, each with different heat demands. The relatively fixed position of mid-deep coaxial tube heat exchangers prevents dynamic adjustment of heat extraction based on load requirements. During trough periods, excessive heat is extracted, resulting in wasted heat beyond heating needs; conversely, during peak periods, insufficient heat supply occurs because the previous over-extraction prevents timely recovery. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems and provide a geothermal energy cascade utilization heat exchange system and a geothermal energy cascade utilization method. This invention installs a telescopic coaxial sleeve heat exchanger in the well, and uses a traction device to control the raising and lowering of the second outer tube to adjust the length of the telescopic inner tube and the telescopic outer tube, thereby adjusting the heat exchange position of the telescopic coaxial sleeve heat exchanger in the well. The heat absorbed by the heat exchanger is reasonably adjusted according to the dynamic changes of the heating load, thereby improving the utilization rate of geothermal energy.

[0005] The technical problem to be solved by the present invention is achieved by the following technical solution: a geothermal energy cascade utilization heat exchange system, including drilling, a telescopic coaxial sleeve heat exchanger and a traction device, wherein the telescopic coaxial sleeve heat exchanger includes a telescopic inner tube and a telescopic outer tube, and the telescopic outer tube is a heat-conducting tube;

[0006] The retractable outer tube is vertically installed inside the well, and the retractable inner tube is vertically installed inside the retractable outer tube. The upper end of the retractable outer tube is provided with a water inlet, the bottom opening of the retractable inner tube is connected to the retractable outer tube, the upper end of the retractable inner tube is provided with a water outlet, and the lower end of the retractable outer tube is closed.

[0007] The retractable inner tube includes a first inner tube and a second inner tube. The first inner tube is fixedly installed inside the well, and the second inner tube is slidably sleeved on the outside of the lower end of the first inner tube. A first sealing ring is provided between the first inner tube and the second inner tube, and the first sealing ring is located at the lower end of the first inner tube or the upper end of the second inner tube.

[0008] The retractable outer tube includes a first outer tube and a second outer tube. The first outer tube is fixedly installed inside the well, and the second outer tube is slidably sleeved on the outside of the lower end of the first outer tube. A second sealing ring is provided between the first outer tube and the second outer tube, and the second sealing ring is located at the lower end of the first outer tube or the upper end of the second outer tube.

[0009] The second inner tube is fixedly connected to the second outer tube;

[0010] The traction device is used to control the raising and lowering of the second outer tube.

[0011] The technical solution of the present invention also includes: a press-type spring heat-conducting pin distributed on the outer wall of the first outer tube, the second sealing ring being disposed at the lower end of the first outer tube, and the press-type spring heat-conducting pin being located above the second sealing ring;

[0012] The press-type spring heat-conducting pin is arranged radially along the first outer tube;

[0013] When the press-type spring heat-conducting pin is located between the outer wall of the first outer tube and the inner wall of the second outer tube, it is in a compressed state, and the top of the press-type spring heat-conducting pin is in contact with the inner wall of the second outer tube.

[0014] When the press-type spring heat-conducting pin is located between the outer wall of the first outer tube and the inner wall of the well, it is in an extended state, with the tip of the press-type spring heat-conducting pin in contact with the inner wall of the well. By setting the press-type spring heat-conducting pin on the outer wall of the first outer tube, since the press-type spring heat-conducting pin is radially arranged along the first outer tube, when the outer wall of the first outer tube rises, it will compress the press-type spring heat-conducting pin, causing it to contract. When the press-type spring heat-conducting pin is located between the outer wall of the first outer tube and the inner wall of the second outer tube, it is in a compressed state. Since the tip of the press-type spring heat-conducting pin is in contact with the inner wall of the second outer tube, it plays a heat-conducting role between the outer wall of the first outer tube and the inner wall of the second outer tube, thereby improving heat transfer efficiency. When the press-type spring heat-conducting pin is located between the outer wall of the first outer tube and the inner wall of the well, it is in an extended state. Since the tip of the press-type spring heat-conducting pin is in contact with the inner wall of the well, it quickly conducts heat from the well sidewall to the inner wall of the second outer tube, improving heat transfer efficiency.

[0015] The technical solution of the present invention also includes: the press-type spring heat-conducting pin includes a fixed sleeve, a sliding top rod, and a telescopic spring;

[0016] The fixed sleeve is radially disposed on the outer wall of the first outer tube, and the sliding push rod is slidably disposed inside the fixed sleeve along the axial direction of the fixed sleeve. A telescopic spring is provided between the sliding push rod and the fixed sleeve.

[0017] The top of the sliding push rod is conical or arc-shaped. Under the action of the telescopic spring, the sliding push rod can slide axially along the fixed sleeve. Because the top of the sliding push rod is conical or arc-shaped, when the second outer tube rises, the side wall of the second outer tube squeezes the top of the sliding push rod, causing the sliding push rod to compress the telescopic spring and enter the fixed sleeve. When the top of the sliding push rod is not compressed, under the action of the telescopic spring, the sliding push rod extends out from the fixed sleeve.

[0018] The technical solution of the present invention also includes: the traction device comprising a traction rope and a winding mechanism;

[0019] The lower end of the traction rope is connected to the second outer tube, and the upper end of the traction rope is connected to the winding mechanism. Connecting the lower end of the traction rope to the second outer tube and the upper end of the traction rope to the winding mechanism increases the upward traction force of the winding mechanism on the traction rope, i.e., when the winding mechanism winds the traction rope upward, it can drive the second outer tube and the second inner tube to slide upward along the well. When the upward traction force of the winding mechanism on the traction rope is reduced, i.e., when the winding mechanism lowers the traction rope, the second outer tube and the second inner tube will slide downward along the well under the action of gravity, thereby adjusting the heat exchange position of the heat exchange system.

[0020] The technical solution of the present invention also includes: the expandable inner tube is an insulated tube. The expandable inner tube being an insulated tube provides excellent thermal insulation performance, preventing heat exchange between the high-temperature circulating fluid inside the expandable inner tube and the low-temperature circulating fluid between the expandable inner tube and the expandable outer tube. Specifically, plastic pipes made of materials such as PE, PP, and PVC can be selected, or a composite structure of a metal inner tube nested and coated with thermal insulation material can be used.

[0021] The technical solution of the present invention also includes: a temperature sensor disposed on the drilling sidewall along the drilling axis;

[0022] The temperature sensor is used to monitor the temperature at different drilling depths. By installing temperature sensors on the borehole sidewall, the temperature at different drilling depths can be monitored in real time, thereby allowing for reasonable adjustment of the lengths of the telescopic inner and outer pipes and improving the utilization rate of geothermal energy.

[0023] The technical solution of the present invention also includes: a heat insulation layer disposed in the shallow layer of the well, wherein the heat insulation layer is located between the inner wall of the well and the outer wall of the first inner pipe. By setting the heat insulation layer in the shallow surface, between the inner wall of the well and the outer wall of the first inner pipe, heat exchange between the circulating fluid and the low-temperature surface is avoided, thus preventing heat loss.

[0024] The technical solution of the present invention also includes: a slide rail vertically disposed on the drilling sidewall;

[0025] The outer wall of the second outer tube is provided with a slide rail that matches the slide channel. The slide rail of the second outer tube is slidably installed in the slide channel. By setting a vertical slide channel on the drilling sidewall and matching the slide rail with the slide channel, the second outer tube is guided, reducing the friction between the outer wall of the second outer tube and the drilling sidewall. When the upward traction force is less than the gravity, it ensures that the second outer tube can slide downward under the action of gravity.

[0026] The technical solution of the present invention also includes a connecting rod, which is disposed between the outer wall of the second inner tube and the inner wall of the second outer tube, and both ends of the connecting rod are respectively connected to the second inner tube and the second outer tube. The connecting rod, disposed between the outer wall of the second inner tube and the inner wall of the second outer tube, allows the second inner tube to rise and fall synchronously with the second outer tube. Because the connecting rod is small in size, the impact on the flow of the circulating fluid is reduced.

[0027] This invention also discloses a method for cascade utilization of geothermal energy, employing the aforementioned geothermal energy cascade utilization heat exchange system, comprising the following steps:

[0028] S1. Determine the heat extraction location of the telescopic coaxial sleeve heat exchanger based on the heat load demand, temperature, time of day, and temperature distribution of the rock and soil layer in the well.

[0029] S2. Use the traction device to control the raising and lowering of the second outer tube, and adjust the length of the telescopic inner tube and the telescopic outer tube to the heat extraction position set in the drilling for heat extraction.

[0030] S3. Real-time monitoring of dynamic changes in heat load demand, air temperature, and water temperature at the outlet, and timely adjustment of the heat extraction position of the telescopic coaxial sleeve heat exchanger to achieve cascade utilization of geothermal energy.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention vertically installs a telescopic outer tube inside the well and a telescopic inner tube vertically installs inside the telescopic outer tube. Since the telescopic outer tube is composed of a second outer tube that can slide up and down on the outer side of the lower end of the first outer tube, and the telescopic inner tube is composed of a second inner tube that can slide up and down on the outer side of the lower end of the first inner tube, and the second inner tube is fixedly connected to the second outer tube, the position of both the telescopic inner tube and the lower end of the telescopic outer tube within the well can be simultaneously adjusted by controlling the raising and lowering of the second outer tube using a traction device. This allows for the utilization of geothermal energy at different depths, enabling the timely planning of the heat extraction location of the heat exchange system within the well according to heating needs, and timely adjustment of the heat extraction location, thereby improving the utilization rate of geothermal energy and the heat exchange efficiency between the circulating fluid and the storage layer. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the geothermal energy cascade utilization heat exchange system described in this invention;

[0034] Figure 2 This is a partially enlarged view of the geothermal energy cascade utilization heat exchange system described in this invention;

[0035] Figure 3 This is a schematic diagram of the structure of the press-type spring heat-conducting pin in a compressed state according to the present invention;

[0036] Figure 4 This is a schematic diagram of the structure of the press-type spring heat-conducting pin in the extended state according to the present invention;

[0037] Figure 5 This is a schematic diagram illustrating the fit between the second outer tube and the drilling well according to the present invention;

[0038] Figure 6 This is a schematic diagram of the structure of the retractable outer tube described in this invention;

[0039] Figure 7 This is a schematic diagram illustrating the working principle of the geothermal energy cascade utilization heat exchange system described in this invention.

[0040] In the image, 100 represents drilling and 101 represents slipway.

[0041] 200 inlet, 300 outlet, 400 filler layer;

[0042] 1. Traction device; 11. Traction rope; 12. Winding mechanism;

[0043] 2. Retractable inner tube; 21. First inner tube; 22. Second inner tube;

[0044] 3. Telescopic outer tube, 31. First outer tube, 32. Second outer tube, 321. Slide rail, 322. End cap;

[0045] 4 First sealing ring, 5 Second sealing ring, 6 Press-type spring heat-conducting pin;

[0046] 61 Fixed sleeve, 62 Sliding top rod, 63 Telescopic spring;

[0047] 7. Insulation layer; 8. Connecting rod. Detailed Implementation

[0048] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0049] like Figure 1 and Figure 2 As shown, a geothermal energy cascade utilization heat exchange system includes a drilling well 100, a telescopic coaxial shell heat exchanger, and a traction device 1. The telescopic coaxial shell heat exchanger includes a telescopic inner tube 2 and a telescopic outer tube 3, the telescopic outer tube 3 being a heat-conducting tube. The telescopic outer tube 3 is made of a superior metal material, giving it excellent thermal conductivity, compressive strength, and tensile strength; specifically, stainless steel, high-quality iron, or copper can be selected.

[0050] The retractable outer tube 3 is vertically installed inside the drilling rig 100. A filling layer 400 is provided between the outer wall of the retractable outer tube 3 and the inner wall of the drilling rig 100 to ensure close contact between the retractable outer tube 3 and the well wall of the drilling rig 100, thereby improving heat transfer efficiency. The retractable inner tube 2 is vertically installed inside the retractable outer tube 3. The upper end of the retractable outer tube 3 is provided with a water inlet 200. The bottom opening of the retractable inner tube 2 is connected to the retractable outer tube 3. The upper end of the retractable inner tube 2 is provided with a water outlet 300. The lower end of the retractable outer tube 3 is closed.

[0051] The retractable inner tube 2 includes a first inner tube 21 and a second inner tube 22. The first inner tube 21 is fixedly installed inside the drilling rig 100. The second inner tube 22 is slidably fitted onto the outer side of the lower end of the first inner tube 21. A first sealing ring 4 is provided between the first inner tube 21 and the second inner tube 22, and the first sealing ring 4 is located at the lower end of the first inner tube 21. The first sealing ring 4 serves a sealing function to prevent heat exchange between the high-temperature circulating fluid in the retractable inner tube 2 and the low-temperature circulating fluid in the retractable outer tube 3.

[0052] The retractable outer tube 3 includes a first outer tube 31 and a second outer tube 32. The first outer tube 31 is fixedly installed inside the drilling rig 100. The second outer tube 32 is slidably fitted onto the lower outer side of the first outer tube 31. The outer wall of the second outer tube 32 is tightly fitted with the high-temperature rock stratum on the side wall of the drilling rig 100 to ensure that the circulating fluid can fully exchange heat with the high-temperature rock stratum / groundwater. An elliptical end cap 332 is provided at the lower end of the second outer tube 32. A second sealing ring 5 is provided between the first outer tube 31 and the second outer tube 32. The second sealing ring 5 is located at the lower end of the first outer tube 31. The second sealing ring 5 serves a sealing function to prevent the low-temperature circulating fluid in the retractable outer tube 3 from flowing out and affecting the heat exchange process of the circulating fluid.

[0053] Specifically, both the first inner tube 21 and the second inner tube 22 are made of PVC, which has good thermal insulation properties. The first outer tube 31 and the second outer tube 32 are made of stainless steel, which has excellent thermal conductivity as well as compressive and tensile strength.

[0054] The second inner pipe 22 is fixedly connected to the second outer pipe 32. The circulating fluid is degassed pure water, which flows in through the inlet 200, flows along the inner wall of the retractable outer pipe 3, and after exchanging heat with the high-temperature rock strata / groundwater on the side wall of the well 100, it becomes a high-temperature circulating fluid that enters the retractable inner pipe 2 along the elliptical end cap 332, flows along the retractable inner pipe 2 to the ground, and then exchanges heat with the heat exchange network before returning to the retractable outer pipe 3, completing one cycle.

[0055] The traction device 1 is used to control the lifting and lowering of the second outer tube 32.

[0056] Among them, the traction force of the traction device 1 on the second outer tube 32 is F, the weight of the second outer tube 32 is G1, the weight of the second inner tube 22 is G2, the maximum static friction force on the second outer tube 32 is f1, and the maximum static friction force on the second inner tube 22 is f2.

[0057] When F > G1 + G2 + f1 + f2, the second outer tube 32 and the second inner tube 22 will rise together.

[0058] When F < G1 + G2 - f1 - f2, the second outer tube 32 and the second inner tube 22 will descend synchronously.

[0059] When G1+G2-f1-f2≤F≤G1+G2+f1+f2, the second outer tube 32 and the second inner tube 22 will remain stationary.

[0060] The geothermal energy cascade utilization heat exchange system also includes a press-type spring heat-conducting pin 6 distributed on the outer wall of the first outer pipe 31, the press-type spring heat-conducting pin 6 being located above the second sealing ring 5.

[0061] The press-type spring heat-conducting pin 6 is arranged radially along the first outer tube 31. The press-type spring heat-conducting pin 6 is made of the same material as the first outer tube 31 and is reliably connected by welding.

[0062] like Figure 2 and Figure 3 As shown, when the press-type spring heat-conducting pin 6 is located between the outer wall of the first outer tube 31 and the inner wall of the second outer tube 32, it is in a compressed state. The top of the press-type spring heat-conducting pin 6 contacts the inner wall of the second outer tube 32 to fill the gap between the outer wall of the first outer tube 31 and the inner wall of the second outer tube 32.

[0063] like Figure 2 and Figure 4 As shown, when the press-type spring heat-conducting pin 6 is located between the outer wall of the first outer tube 31 and the inner wall of the drilling 100, it is in an extended state, and the top of the press-type spring heat-conducting pin 6 is in contact with the inner wall of the drilling 100. The press-type spring heat-conducting pin 6 is arranged in an array only in the non-insulation layer area of ​​the first outer tube 31 for a tight connection between the first outer tube 31 and the second outer tube 32 or the high-temperature rock layer, so as to effectively transfer heat.

[0064] Specifically, such as Figure 3 and Figure 4 As shown, the press-type spring heat-conducting pin 6 includes a fixed sleeve 61, a sliding top rod 62, and a telescopic spring 63.

[0065] The fixed sleeve 61 is radially disposed on the outer wall of the first outer tube 31. The sliding push rod 62 is slidably disposed inside the fixed sleeve 61 along the axial direction of the fixed sleeve 61. A telescopic spring 63 is disposed between the sliding push rod 62 and the fixed sleeve 61. The telescopic spring 63 is located between the bottom of the sliding push rod 62 and the bottom of the inner cavity of the fixed sleeve 61.

[0066] The top of the sliding top rod 62 is arc-shaped.

[0067] Specifically, such as Figure 1 and Figure 2 As shown, the traction device 1 includes a traction rope 11 and a winding mechanism 12.

[0068] The lower end of the traction rope 11 is connected to the second outer tube 32, and the upper end of the traction rope 11 is connected to the winding mechanism 12.

[0069] The retractable inner tube 2 is an insulated tube.

[0070] The geothermal energy cascade utilization heat exchange system also includes a temperature sensor installed along the axial direction of the well 100 on the side wall of the well 100.

[0071] The temperature sensor is used to monitor the temperature at different depths in the well.

[0072] like Figure 1 and Figure 2 As shown, the geothermal energy cascade utilization heat exchange system also includes an insulation layer 7 disposed in the shallow layer of the well 100, the insulation layer 7 being located between the inner wall of the well 100 and the outer wall of the first inner pipe 21.

[0073] like Figure 5 As shown, the geothermal energy cascade utilization heat exchange system also includes a slide 101 vertically installed on the side wall of the well 100.

[0074] like Figure 5 and Figure 6 As shown, the outer wall of the second outer tube 32 is provided with a slide rail 321 that matches the slide rail 101, and the slide rail 321 of the second outer tube 32 is slidably disposed in the slide rail 101.

[0075] like Figure 2 As shown, the geothermal energy cascade utilization heat exchange system also includes a connecting rod 8, which is disposed between the outer wall of the second inner pipe 22 and the inner wall of the second outer pipe 32, and the two ends of the connecting rod 8 are respectively connected to the second inner pipe 22 and the second outer pipe 32.

[0076] A method for cascade utilization of geothermal energy, employing the aforementioned cascade utilization heat exchange system, includes the following steps:

[0077] S1. Determine the heat extraction location of the telescopic coaxial sleeve heat exchanger based on the heat load demand, temperature, time of day, and temperature distribution of the soil and rock layers within 100 meters of the well. For example... Figure 7 As shown, during drilling, the temperature distribution of the soil and rock layers within the wellbore (100mm diameter) is collected to provide data reference for determining the heat extraction location later. Since the temperature of the soil and rock layers varies with different seasons and time periods, temperature sensors can be installed within the wellbore to monitor and collect the temperature of the soil layers at different depths in real time during later use. The specific method for determining the heat extraction location of the telescopic coaxial sleeve heat exchanger is not covered by this invention and will not be elaborated here.

[0078] S2. Use the traction device 1 to control the lifting and lowering of the second outer pipe 32, and adjust the length of the telescopic inner pipe 2 and the telescopic outer pipe 3 to the heat extraction position set by the drilling 100 for heat extraction.

[0079] S3. Real-time monitoring of heat load demand, air temperature, and dynamic changes in water temperature at 300 outlets allows for timely adjustment of the heat extraction position of the telescopic coaxial tube heat exchanger, enabling cascade utilization of geothermal energy.

[0080] Specifically, during the initial and later stages of the heating season when temperatures are higher, the thermal energy from the shallower formations of Well 100 can be used; during the middle stages of the heating season when temperatures are lower, the thermal energy from the deeper formations of Well 100 can be used.

[0081] Specifically, during the daytime of heating season, the heat energy from the shallower formation of well 100 can be used for heating, while at night the heat energy from the deeper formation of well 100 can be used for heating.

[0082] Specifically, intermittent utilization of shallow and deep geothermal energy from drilling 100 wells helps avoid the "cold accumulation" phenomenon and improves the utilization rate of geothermal energy.

[0083] The advantages of this invention are:

[0084] 1) The telescopic coaxial tube heat exchanger has a telescopic structure, which can reasonably adjust the heat extraction position of the telescopic coaxial tube heat exchanger within the well 100 according to the heat load demand, so as to realize the cascade utilization of geothermal energy and improve the geothermal energy utilization rate.

[0085] 2) By intermittently utilizing the geothermal energy at different depths, the shallow and deep geothermal energy of the well can be extracted intermittently, which helps to avoid the phenomenon of "cold accumulation" and improve the heat exchange capacity of the heat exchanger.

[0086] 3) The heat exchange structure and insulation arrangement of the heat exchange system are reasonably distributed. The insulation layer 7 is set on the shallow surface where the temperature is low to reduce the heat loss of the circulating fluid on the shallow surface. The press-type spring heat conduction pin 6 is set on the outer wall of the first outer pipe 31 at a higher depth to help enhance the heat exchange effect.

Claims

1. A geothermal energy cascade utilization heat exchange system, characterized in that: It includes a drilling (100), a telescopic coaxial sleeve heat exchanger and a traction device (1), wherein the telescopic coaxial sleeve heat exchanger includes a telescopic inner tube (2) and a telescopic outer tube (3), wherein the telescopic outer tube (3) is a heat-conducting tube; The retractable outer tube (3) is vertically installed inside the drilling (100), the retractable inner tube (2) is vertically installed inside the retractable outer tube (3), the upper end of the retractable outer tube (3) is provided with a water inlet (200), the bottom opening of the retractable inner tube (2) is connected to the retractable outer tube (3), the upper end of the retractable inner tube (2) is provided with a water outlet (300), and the lower end of the retractable outer tube (3) is closed. The retractable inner tube (2) includes a first inner tube (21) and a second inner tube (22). The first inner tube (21) is fixedly installed inside the drilling (100). The second inner tube (22) is slidably sleeved on the outside of the lower end of the first inner tube (21). A first sealing ring (4) is provided between the first inner tube (21) and the second inner tube (22). The first sealing ring (4) is located at the lower end of the first inner tube (21) or the upper end of the second inner tube (22). The retractable outer tube (3) includes a first outer tube (31) and a second outer tube (32). The first outer tube (31) is fixedly installed inside the drilling (100). The second outer tube (32) is slidably sleeved on the outer side of the lower end of the first outer tube (31). A second sealing ring (5) is provided between the first outer tube (31) and the second outer tube (32). The second sealing ring (5) is located at the lower end of the first outer tube (31) or the upper end of the second outer tube (32). The second inner tube (22) is fixedly connected to the second outer tube (32); The traction device (1) is used to control the lifting and lowering of the second outer tube (32); It also includes a press-type spring heat-conducting pin (6) distributed on the outer wall of the first outer tube (31), the second sealing ring (5) is located at the lower end of the first outer tube (31), and the press-type spring heat-conducting pin (6) is located above the second sealing ring (5); The press-type spring heat-conducting pin (6) is arranged radially along the first outer tube (31); When the press-type spring heat-conducting pin (6) is located between the outer wall of the first outer tube (31) and the inner wall of the second outer tube (32), it is in a compressed state, and the top of the press-type spring heat-conducting pin (6) is in contact with the inner wall of the second outer tube (32); When the press-type spring heat-conducting pin (6) is located between the outer wall of the first outer tube (31) and the inner wall of the well (100), it is in an extended state, and the top of the press-type spring heat-conducting pin (6) is in contact with the inner wall of the well (100); The press-type spring heat-conducting pin (6) includes a fixed sleeve (61), a sliding top rod (62), and a telescopic spring (63); The fixed sleeve (61) is radially arranged on the outer wall of the first outer tube (31) along the first outer tube (31), and the sliding top rod (62) is slidably arranged in the fixed sleeve (61) along the fixed sleeve (61) axis. A telescopic spring (63) is provided between the sliding top rod (62) and the fixed sleeve (61). The top of the sliding top rod (62) is conical or arc-shaped.

2. The geothermal energy cascade utilization heat exchange system according to claim 1, characterized in that: The traction device (1) includes a traction rope (11) and a winding mechanism (12); The lower end of the traction rope (11) is connected to the second outer tube (32), and the upper end of the traction rope (11) is connected to the winding mechanism (12).

3. The geothermal energy cascade utilization heat exchange system according to claim 1, characterized in that: The retractable inner tube (2) is an insulated tube.

4. The geothermal energy cascade utilization heat exchange system according to claim 1, characterized in that: It also includes a temperature sensor disposed on the sidewall of the well (100) along the drilling (100) axis; The temperature sensor is used to monitor the temperature at different depths of the well (100).

5. The geothermal energy cascade utilization heat exchange system according to claim 1, characterized in that: It also includes a thermal insulation layer (7) disposed in the shallow layer of the well (100), the thermal insulation layer (7) being located between the inner wall of the well (100) and the outer wall of the first inner tube (21).

6. The geothermal energy cascade utilization heat exchange system according to claim 1, characterized in that: It also includes a slide (101) vertically installed on the side wall of the well (100); The outer wall of the second outer tube (32) is provided with a slide rail (321) that matches the slide rail (101). The slide rail (321) of the second outer tube (32) is slidably arranged in the slide rail (101).

7. The geothermal energy cascade utilization heat exchange system according to claim 1, characterized in that: It also includes a connecting rod (8), which is disposed between the outer wall of the second inner tube (22) and the inner wall of the second outer tube (32), and the two ends of the connecting rod (8) are respectively connected to the second inner tube (22) and the second outer tube (32).

8. A method for cascade utilization of geothermal energy, employing the geothermal energy cascade utilization heat exchange system as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Determine the heat extraction location of the telescopic coaxial sleeve heat exchanger based on the heat load demand on the heating day, the temperature on the day, the time period, and the temperature distribution of the rock and soil layer in the well (100). S2. Use the traction device (1) to control the lifting and lowering of the second outer tube (32), and adjust the length of the telescopic inner tube (2) and the telescopic outer tube (3) to the heat extraction position set by the drilling (100) for heat extraction. S3. Real-time monitoring of heat load demand, air temperature, and water temperature at the outlet (300) dynamically changes the heat extraction position of the telescopic coaxial sleeve heat exchanger in a timely manner, and intermittently extracting heat from the shallow and deep geothermal energy of the well (100) to realize the cascade utilization of geothermal energy.

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