A multi-segment independent ultra-long gravity heat pipe system and a geothermal extraction method

Abstract

This invention provides a multi-segment independent ultra-long gravity heat pipe system, comprising several composite segments arranged sequentially along a depth direction and a ground-based heat pump unit installed on the ground. The length of the bottom composite segment along the depth direction is shorter than the length of the top composite segment. The top composite segment is connected to the ground-based heat pump unit through a steam outlet and a liquid return outlet at its top. Each composite segment consists of several heat pipes, including evaporator heat pipes, adiabatic heat pipes, and heat exchanger heat pipes. The bottom of each composite segment has one heat exchanger heat pipe, and the top of each heat exchanger heat pipe has multiple evaporator heat pipes or adiabatic heat pipes. The bottommost composite segment has no heat exchanger heat pipe. This invention also provides a geothermal extraction method using the aforementioned multi-segment independent ultra-long gravity heat pipe system.

Description

Technical Field

[0001] This invention relates to the technical field of geothermal energy extraction, specifically to a multi-segment independent ultra-long gravity heat pipe system and a geothermal extraction method. Background Technology

[0002] Geothermal energy is a clean and reliable renewable energy source with abundant reserves. In recent years, the technology for the extraction and utilization of geothermal energy has been continuously developing. Ultra-long gravity heat pipe technology is a single-well extraction technology for medium-deep geothermal energy that has been developed in recent years. Ultra-long gravity heat pipe technology utilizes the working fluid to absorb heat underground and vaporize into saturated steam for heat extraction. It can efficiently transfer heat energy from thousands of meters underground to the surface, and has the unique advantages of extracting heat without extracting water and being self-driven without pump power.

[0003] However, existing ultra-long gravity heat pipe solutions face several core technical bottlenecks in practical applications:

[0004] 1. Hydraulic Effect: To ensure sufficient wetting of the evaporation section, a liquid column of a certain height must be maintained at the bottom of the heat pipe. When the heat pipe length reaches several kilometers, the liquid column height can reach hundreds of meters, and the static pressure can reach tens of bar. According to the Clausius-Clapeyron equation, static pressure significantly increases the boiling point of the working fluid, making it difficult for the working fluid at deep depths to evaporate under external geothermal temperatures, severely reducing heat transfer efficiency.

[0005] 2. Gas-liquid entrainment: Studies have shown that the vapor velocity of ordinary ultra-long gravity heat pipes reaches its maximum value at the top of the evaporation section. When the vapor velocity exceeds the critical value, severe droplet entrainment occurs in the gas-liquid two-phase flow, leading to liquid film rupture and a sharp deterioration in heat transfer performance.

[0006] 3. Wide range of impact from failure: If a single heat pipe leaks, the working fluid in the entire pipe will be lost, causing the entire well to fail. Repair requires removing the entire pipe, which is very costly.

[0007] To address the aforementioned issues, Chinese patent CN103015954A discloses a combined gravity heat pipe for oil wellbore construction. This design employs multiple independent, enclosed heat pipe units mechanically connected by solid connectors, relying on metal conduction for heat transfer. While this solution achieves working fluid isolation, it suffers from low heat transfer efficiency and lacks a dedicated gas-liquid separation structure, making it unsuitable for high-power geothermal extraction.

[0008] In summary, there is a need in this field to improve existing ultra-long gravity heat pipe solutions in order to enhance heat transfer efficiency and operational stability. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a multi-segment independent ultra-long gravity heat pipe system, which achieves working fluid isolation and non-accumulation of static pressure by dividing the heat pipe into multiple functional segments, and achieves passive gas-liquid separation through annular metal mesh.

[0010] Another objective of this invention is to provide a geothermal extraction method employing the aforementioned multi-segment independent ultra-long gravity heat pipe system.

[0011] To achieve the above objectives, the present invention provides a multi-segment independent ultra-long gravity heat pipe system, characterized in that it comprises several composite segments arranged sequentially along the depth direction and a ground heat pump unit installed on the ground. The length of the composite segment at the bottom along the depth direction is shorter than the length of the composite segment at the top. The top composite segment is connected to the ground heat pump unit through a steam outlet and a liquid return outlet at its top. Each composite segment consists of several heat pipes. The heat pipes include evaporation section heat pipes, insulation section heat pipes, and heat exchanger section heat pipes. The bottom of each composite segment has one heat exchanger section heat pipe, and the top of each heat exchanger section heat pipe has multiple evaporation section heat pipes or insulation section heat pipes. The bottommost composite segment has no heat exchanger section heat pipe.

[0012] Preferably, all heat pipes use oil casing as outer tubes, and adjacent oil casings are connected and fixed by oil casing couplings; the outer side of the end of each oil casing has oil casing threads, and the oil casing couplings are threadedly connected to the oil casing threads of two adjacent oil casings.

[0013] Preferably, the number of heat pipes in the evaporation section or the heat pipes in the insulation section increases with the increase of the height of the composite section.

[0014] Preferably, the evaporation section heat pipe includes an oil casing, an inner tube coaxially arranged inside the oil casing, and an annular metal mesh disposed between the outer wall of the inner tube and the inner wall of the oil casing, wherein the annular metal mesh is located at the bottom of the evaporation section heat pipe and is disposed adjacent to the bottom opening of the inner tube.

[0015] Preferably, the annular metal mesh is a stainless steel wire mesh with a mesh count of 80-200 and a thickness of 5-20 mm.

[0016] Preferably, the heat pipe in the insulating section includes an oil jacket, an inner tube coaxially disposed inside the oil jacket of the heat pipe in the insulating section, and an insulation layer covering the inside of the oil jacket, wherein an annular gap is formed between the inner tube of the heat pipe in the insulating section and the oil jacket of the heat pipe in the insulating section.

[0017] Preferably, the heat exchanger section heat pipe includes an oil sheath, a gas collecting chamber, a heat exchange tube bundle, a gas short pipe, an upper tube sheet, and a lower tube sheet. The gas collecting chamber is located above the heat exchanger heat pipe and is a central cylinder with a diameter smaller than the inner diameter of the oil sheath of the heat exchanger section heat pipe. The upper tube sheet is located below the gas collecting chamber and is used to fix the heat exchange tube bundle. The heat exchange tube bundle is arranged vertically, and its tube-side inlet communicates with the gas collecting chamber. The gas short pipe connects the gas collecting chamber to the inner tube of an adjacent heat pipe. The lower tube sheet is located below the heat exchange tube bundle and is fixedly connected to the oil sheath to fix the lower end of the heat exchange tube bundle.

[0018] Preferably, each section of the heat pipe is filled with the same or different working fluid, which is one of ammonia (NH3), water (H2O) or an organic working fluid.

[0019] This application also provides a geothermal extraction method, employing the aforementioned multi-segment independent ultra-long gravity heat pipe system, including the following steps:

[0020] (S1) Determine the number of composite sections and the length of each composite section based on the depth of the geothermal well, so that the static pressure generated by the working fluid column in a single heat pipe section is ≤3 bar, and determine the number of heat pipes in the evaporation section based on the cumulative heat load borne by each composite section.

[0021] (S2) Connect each section of the heat pipe sequentially through the oil casing coupling and lower it into the geothermal well. Fill each section of the heat pipe with working fluid, with the filling rate being 30%-40% of the volume of the evaporation section.

[0022] (S3) The system is in operation, with each heat pipe section forming an independent closed loop:

[0023] (S4) Heat is transferred upwards through the heat pipes of each heat exchanger section, and finally delivered to the ground heat pump unit through the steam outlet of the top composite section. The condensed working fluid returns to the top composite section through the liquid return port.

[0024] Preferably, step (S3) specifically includes:

[0025] (S31) The steam generated in the annular gap of the heat pipe in the evaporation section enters the inner tube preferentially under the action of the annular metal mesh, and gathers upward along the connected inner tube to the top of the composite section, and enters the gas collection chamber of the heat pipe in the heat exchanger section of the previous composite section through the gas short pipe.

[0026] (S32) Steam condenses and releases heat inside the heat exchange tube bundle, and the condensate drips from the lower end of the heat exchange tube bundle and enters the annulus of the next composite section;

[0027] (S33) The liquid working fluid of the previous composite section enters the shell side of the heat exchanger through the annular space, absorbs the heat transferred by the tube wall of the heat exchange tube bundle and evaporates, and the steam enters the inner tube of this composite section and rises.

[0028] Compared with existing technologies, the advantages of the multi-segment independent ultra-long gravity heat pipe system and geothermal extraction method disclosed in this invention are as follows: Each segment of the multi-segment independent ultra-long gravity heat pipe system is independently sealed, and the static pressure of each segment is determined only by the height of the liquid column in that segment, without accumulation or transfer. This makes it suitable for geothermal extraction in ultra-deep wells exceeding 5000 meters, and it also has high heat transfer efficiency. Each segment of the multi-segment independent ultra-long gravity heat pipe system is independently sealed, and the top high-load segment can be independently designed with a large-diameter inner pipe to control the steam velocity below the critical value, avoiding liquid film rupture and a sharp deterioration in heat transfer performance caused by droplet entrainment. The annular metal mesh utilizes the porous medium characteristics to guide steam preferentially into the... The inner tube further enhances gas-liquid separation, ensuring stable operation of the heat pipe across the full load range. The multi-segment independent ultra-long gravity heat pipe system uses standard oil casing as the basic unit, with each segment independently sealed. The inner tube diameter, filling rate, filling medium, and composite segment length can be independently designed according to the depth, geothermal conditions, and steam flow rate of each segment, achieving targeted optimization across the entire well without interference. Each segment of the multi-segment independent ultra-long gravity heat pipe system is independently sealed; if a segment leaks or malfunctions, only that segment fails, while the remaining segments can still operate independently. The geothermal extraction method using this multi-segment independent ultra-long gravity heat pipe system boasts high thermal conductivity and stable operation. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the overall structure of a multi-segment independent ultra-long gravity heat pipe system according to this application.

[0031] Figure 2 This is a schematic diagram of the internal structure of the heat pipe in the evaporation section.

[0032] Figure 3 This is a schematic diagram of the internal structure of the heat pipe in the adiabatic section.

[0033] Figure 4 This is a schematic diagram of the internal structure of the heat pipe in the heat exchanger section.

[0034] Figure 5 This is a schematic diagram of the structure of the ring-shaped metal mesh.

[0035] Figure 6 This is a schematic diagram of the upper tube sheet of the heat exchanger.

[0036] Figure 7This is a schematic diagram of the lower tube sheet of the heat exchanger. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] like Figure 1 As shown, this application discloses a multi-segment independent ultra-long gravity heat pipe system, which includes several composite segments arranged sequentially along the depth direction and a ground heat pump unit 6 installed on the ground. The length of each composite segment is independently designed according to its cumulative heat load. Since the cumulative heat load of the bottom composite segment is lower than that of the upper segment, the length of the bottom composite segment along the depth direction is shorter than that of the top composite segment. The top composite segment is connected to the ground heat pump unit 6 through its top steam outlet 4 and liquid return port 5.

[0039] join Figures 1 to 4 Each composite section consists of several heat pipes, and each heat pipe uses an oil casing 14 as its outer tube. Adjacent oil casings 14 are connected and fixed together by oil casing couplings 11. Specifically, the outer side of the end of the oil casing 14 has an oil casing thread 12, and the oil casing coupling 11 is threadedly connected to the oil casing threads 12 of two adjacent oil casings 14 to achieve a fixed connection between adjacent oil casings 14.

[0040] The heat pipes consist of an evaporator heat pipe 1, an adiabatic heat pipe 2, and a heat exchanger heat pipe 3. The bottom of the composite section has one heat exchanger heat pipe 3, and the top of the heat exchanger heat pipe 3 has multiple evaporator heat pipes 1 or adiabatic heat pipes 2, with the number of evaporator heat pipes 1 or adiabatic heat pipes 2 increasing with the height of the composite section. Notably, the bottommost composite section has no heat exchanger heat pipe 3. The working fluids inside adjacent heat pipes are not interconnected; heat exchange between other heat pipes is achieved through the heat exchanger heat pipes 3, ensuring working fluid isolation and preventing static pressure accumulation.

[0041] The evaporation section heat pipe 1 includes an oil sheath 14, an inner tube 15 coaxially arranged inside the oil sheath 14, and an annular metal mesh 16 disposed between the outer wall of the inner tube 15 and the inner wall of the oil sheath 14. The annular metal mesh 16 is located at the bottom of the evaporation section heat pipe 1 and is adjacent to the bottom opening of the inner tube 15. The inner tube 15 and the oil sheath 14 are fixedly connected by an annular fixing plate 13.

[0042] See Figure 5The annular metal mesh 16 is made of stainless steel wire mesh with a mesh count of 80-200 and a thickness of 5-20 mm. It is used to guide the liquid working fluid downwards using capillary force, while simultaneously forming a barrier against rising steam, forcing the steam to rise from the inner tube's internal channel, thus achieving passive gas-liquid separation. The annular metal mesh 16 guides the steam generated within the annular gap to preferentially enter the inner tube 15 of the evaporation section heat pipe 1, reducing steam retention in the annular gap.

[0043] The heat pipe 2 with insulation section includes an oil jacket 14, an inner tube 15 coaxially arranged inside the oil jacket 14, and an insulation layer 21 covering the inside of the oil jacket 14. An annular gap 22 is formed between the inner tube 15 and the oil jacket 14. The inner tube 15 and the oil jacket 14 are fixedly connected by an annular fixing plate 13.

[0044] See Figures 6 to 7 The heat exchanger section heat pipe 3 includes an oil casing 14, a gas collecting chamber 31, a heat exchanger tube bundle 32, a gas short pipe 33, an upper tube sheet 34, and a lower tube sheet 35. The gas collecting chamber 31 is located above the heat exchanger heat pipe 3 and is a central cylinder with a diameter smaller than the inner diameter of the oil casing 14. The upper tube sheet 34 is located below the gas collecting chamber 31 and is used to fix the heat exchanger tube bundle 32. The heat exchanger tube bundle 32 is arranged vertically, and its tube-side inlet is connected to the gas collecting chamber 31. The gas short pipe 33 connects the gas collecting chamber 31 to the inner tube 15 of the adjacent heat pipe. The lower tube sheet 35 is located below the heat exchanger tube bundle 32 and is fixedly connected to the oil casing 14 to fix the lower end of the heat exchanger tube bundle 32. The oil casing 14 is the heat exchanger shell, and an annular space is formed between the gas collecting chamber 31 and the oil casing 14, serving as a channel for the liquid working fluid of the previous composite section to enter the shell side.

[0045] Each heat pipe section can be filled with the same or different working fluids, wherein the working fluid is one of ammonia (NH3), water (H2O), or an organic working fluid. Preferably, the inner tube diameter of the top composite section is larger than that of the lower composite section, in order to control the steam flow rate of the top high-load section below a critical value.

[0046] This application also discloses a geothermal extraction method, employing the aforementioned multi-segment independent ultra-long gravity heat pipe system, including the following steps:

[0047] (S1) Determine the number of composite sections and the length of each composite section based on the depth of the geothermal well, so that the static pressure generated by the working fluid column in a single heat pipe section is ≤3 bar, and determine the number of heat pipes in the evaporation section based on the cumulative heat load borne by each composite section.

[0048] (S2) Connect each section of the heat pipe sequentially through the oil casing coupling and lower it into the geothermal well. Fill each section of the heat pipe with working fluid, with the filling rate being 30%-40% of the volume of the evaporation section.

[0049] (S3) The system is in operation, with each heat pipe section forming an independent closed loop:

[0050] (S4) Heat is transferred upwards through the heat pipes of each heat exchanger section, and finally delivered to the ground heat pump unit through the steam outlet of the top composite section. The condensed working fluid returns to the top composite section through the liquid return port.

[0051] Specifically, step (S3) includes:

[0052] (S31) The steam generated in the annular gap of the heat pipe in the evaporation section enters the inner tube preferentially under the action of the annular metal mesh, and gathers upward along the connected inner tube to the top of the composite section, and enters the gas collection chamber of the heat pipe in the heat exchanger section of the previous composite section through the gas short pipe.

[0053] (S32) Steam condenses and releases heat inside the heat exchange tube bundle, and the condensate drips from the lower end of the heat exchange tube bundle and enters the annulus of the next composite section;

[0054] (S33) The liquid working fluid of the previous composite section enters the shell side of the heat exchanger through the annular space, absorbs the heat transferred by the tube wall of the heat exchange tube bundle and evaporates, and the steam enters the inner tube of this composite section and rises.

[0055] Taking a total well depth of 3000 meters and a single oil casing length of 11 meters as an example, firstly, based on the geothermal gradient (3.5℃ / 100m), the heat output of each composite section increases with depth: approximately 30kW for the bottom section, approximately 20kW for the middle section, and approximately 10kW for the top section. However, the total heat to be transferred within the section (cumulative heat load) increases with increasing location.

[0056] Each evaporation section heat pipe 1 is designed to consist of an oil jacket 14 (Φ177.8 mm) and an inner tube 15. The inner tube 15 is fixed by an annular fixing plate 13. A ring-shaped metal mesh 16, made of 100-mesh stainless steel wire, 10 mm thick and 200 mm high, is installed at the bottom of each evaporation section heat pipe 1, adjacent to the bottom opening of the inner tube 15. Steam generated within the annular gap, under the action of the porous medium of the ring-shaped metal mesh 16, preferentially enters the inner tube 15 from the bottom opening and flows upwards along the inner tube 15. The inner tubes of multiple evaporation section heat pipes within the same composite section are interconnected, ensuring smooth steam collection at the top of the composite section. The structure of the insulation section heat pipe 2 is similar to that of the evaporation section, but the outer wall of the oil jacket 14 is wrapped with a 20 mm thick aerogel insulation layer 21, making it only a heat transfer channel and not absorbing heat from the rock. The heat pipe 3 of the heat exchanger section is 11 meters long (the same length as a single oil casing). The oil casing 14 is Φ177.8 mm with an inner diameter of approximately 159 mm. The gas collecting chamber 31 is a central cylinder with a diameter of 100 mm and a height of 250 mm, forming an annular space of approximately 30 mm between it and the shell. The upper tube sheet 34 of the heat exchanger is 30 mm thick and has openings for installing the heat exchange tube bundle 32. The heat exchange tube bundle 32 consists of 16 vertical stainless steel tubes with a diameter of Φ16×1.5 mm and a length of 4000 mm. The upper end is welded to the upper tube sheet, and the lower end passes through the lower tube sheet. The gas short tube 33 has an inner diameter of 80 mm and connects the gas collecting chamber 31 to the inner tube of the previous composite section. The lower tube sheet 35 of the heat exchanger is 30 mm thick and fixes the lower end of the heat exchange tubes.

[0057] The heat transfer path is as follows: The bottom is the first composite section. In the evaporation section of the first composite section, the liquid absorbs heat and evaporates in the annular gap of the heat pipe → the steam enters the inner pipe through the annular metal mesh → it flows upward along the inner pipe → it enters the gas collection chamber 31 of the heat pipe 3 at the bottom of the heat exchanger section of the second composite section through the gas short pipe 33; the middle includes the second to 29th composite sections connected in sequence. The steam from below enters the heat exchanger tube and condenses, and the heat is transferred to the liquid in this composite section; the steam generated in the evaporation section of this composite section merges with the steam from below and continues to be transferred upward; the top is the 30th composite section. The 30th composite section receives the steam from the 29th composite section, condenses and releases heat in the heat exchanger tube of this section, and the heat is transferred to the liquid in the insulation section of this section (it does not absorb heat from the rock). The generated steam enters the ground heat pump unit 6; the liquid condensed by the ground heat pump unit 6 returns to the annular gap of the 30th composite section through the liquid return port 5, and flows back down the annular gap step by step to complete the cycle.

[0058] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-segment independent ultra-long gravity heat pipe system, characterized in that, The system comprises several composite sections arranged sequentially along a depth direction and a ground-mounted heat pump unit. The length of the bottom composite section along the depth direction is shorter than that of the top composite section. The top composite section is connected to the ground-mounted heat pump unit through its top steam outlet and liquid return outlet. Each composite section consists of several heat pipes, including evaporation section heat pipes, insulation section heat pipes, and heat exchanger section heat pipes. The bottom of each composite section has one heat exchanger section heat pipe, and the top of each heat exchanger section heat pipe has multiple evaporation section heat pipes or insulation section heat pipes. The bottommost composite section has no heat exchanger section heat pipes.

2. The multi-segment independent ultra-long gravity heat pipe system as described in claim 1, characterized in that, All heat pipes use oil casing as the outer tube, and adjacent oil casings are connected and fixed by oil casing couplings; the outer side of the end of each oil casing has oil casing threads, and the oil casing couplings are threadedly connected to the oil casing threads of two adjacent oil casings.

3. The multi-segment independent ultra-long gravity heat pipe system as described in claim 1, characterized in that, The number of heat pipes in the evaporation section or the heat pipes in the insulation section increases with the increase of the composite section height.

4. The multi-segment independent ultra-long gravity heat pipe system as described in claim 1, characterized in that, The evaporation section heat pipe includes an oil casing, an inner tube coaxially arranged inside the oil casing, and an annular metal mesh disposed between the outer wall of the inner tube and the inner wall of the oil casing. The annular metal mesh is located at the bottom of the evaporation section heat pipe and is disposed adjacent to the bottom opening of the inner tube.

5. The multi-segment independent ultra-long gravity heat pipe system as described in claim 4, characterized in that, The annular metal mesh is made of stainless steel wire mesh with a mesh count of 80-200 and a thickness of 5-20 mm.

6. The multi-segment independent ultra-long gravity heat pipe system as described in claim 4, characterized in that, The heat pipe with insulation section includes an oil casing, an inner tube coaxially arranged inside the oil casing of the heat pipe with insulation section, and an insulation layer covering the inside of the oil casing. An annular gap is formed between the inner tube of the heat pipe with insulation section and the oil casing of the heat pipe with insulation section.

7. The multi-segment independent ultra-long gravity heat pipe system as described in claim 6, characterized in that, The heat exchanger section includes an oil sheath, a gas collecting chamber, a heat exchange tube bundle, a gas short pipe, an upper tube sheet, and a lower tube sheet. The gas collecting chamber is located above the heat exchanger heat pipes and is a central cylinder with a diameter smaller than the inner diameter of the oil sheath of the heat exchanger section heat pipes. The upper tube sheet is located below the gas collecting chamber and is used to fix the heat exchange tube bundle. The heat exchange tube bundle is arranged vertically, and its tube-side inlet communicates with the gas collecting chamber. The gas short pipe connects the gas collecting chamber to the inner tube of an adjacent heat pipe. The lower tube sheet is located below the heat exchange tube bundle and is fixedly connected to the oil sheath, used to fix the lower end of the heat exchange tube bundle.

8. The multi-segment independent ultra-long gravity heat pipe system as described in claim 1, characterized in that, Each heat pipe segment is filled with the same or different working fluid, which is one of ammonia (NH3), water (H2O) or an organic working fluid.

9. A method for geothermal extraction, characterized in that, The multi-segment independent ultra-long gravity heat pipe system as described in claim 7 includes the following steps: (S1) Determine the number of composite sections and the length of each composite section based on the depth of the geothermal well, so that the static pressure generated by the working fluid column in a single heat pipe section is ≤3 bar, and determine the number of heat pipes in the evaporation section based on the cumulative heat load borne by each composite section. (S2) Connect each section of the heat pipe sequentially through the oil casing coupling and lower it into the geothermal well. Fill each section of the heat pipe with working fluid, with the filling rate being 30%-40% of the volume of the evaporation section. (S3) The system is in operation, with each heat pipe section forming an independent closed loop: (S4) Heat is transferred upwards through the heat pipes of each heat exchanger section, and finally delivered to the ground heat pump unit through the steam outlet of the top composite section. The condensed working fluid returns to the top composite section through the liquid return port.

10. The geothermal extraction method as described in claim 9, characterized in that, The specific steps (S3) include: (S31) The steam generated in the annular gap of the heat pipe in the evaporation section enters the inner tube preferentially under the action of the annular metal mesh, and gathers upward along the connected inner tube to the top of the composite section, and enters the gas collection chamber of the heat pipe in the heat exchanger section of the previous composite section through the gas short pipe. (S32) Steam condenses and releases heat inside the heat exchange tube bundle, and the condensate drips from the lower end of the heat exchange tube bundle and enters the annulus of the next composite section; (S33) The liquid working fluid of the previous composite section enters the shell side of the heat exchanger through the annular space, absorbs the heat transferred by the tube wall of the heat exchange tube bundle and evaporates, and the steam enters the inner tube of this composite section and rises.

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