JP2020148200A - Geothermal heat recovery device - Google Patents

Abstract

To provide a geothermal heat recovery device which can suppress temperature drop of a fluid heated by geothermal heat to efficiently recover the heated fluid.SOLUTION: A geothermal heat recovery device 10 includes an outer pipe 12 and an inner pipe 14 buried in the ground and communicating with each other at lower parts thereof, and recovers geothermal heat by heating fluid flowing from above the ground while the fluid passes through the outer pipe 12 and the inner pipe 14, and making the heated fluid flow out again to above the ground. The inner pipe 14 has a heat insulation part 22 in a part thereof except the lower part.SELECTED DRAWING: Figure 1

Description

The present invention relates to a geothermal recovery device, for example, a geothermal recovery device used for geothermal power generation.

Geothermal power generation, which uses geothermal fluid that has become a high-temperature fluid that has penetrated deep underground into the ground surface, does not require fossil fuels and has little impact on the environment, so it can be used as renewable energy. Expectations are rising. Geothermal power generation is also attracting attention because it can utilize many volcanic belts that exist in Japan and is not affected by the weather.

This geothermal power generation includes the so-called flash method and dry steam method, in which hot water and steam pumped from the underground geothermal fluid reservoir are used to generate electricity by turning a turbine, and the heat pumped from the underground geothermal fluid reservoir. There is a so-called binary method in which steam is produced by heating an organic medium having a low boiling point with water or steam, and the turbine is rotated by the steam to generate power.

On the other hand, as a method of recovering geothermal heat, instead of using hot water or steam pumped from the underground reservoir as it is, the fluid that has flowed in from the ground is heated by the geothermal heat and flows out to the ground again to recover the geothermal heat. A method has also been proposed.

As a device for recovering such geothermal heat, for example, an outer pipe placed in the ground is closed except for an opening on the ground side or its vicinity, and is tens to several tens to the bottom and upward from the bottom. An outer pipe in which a fluid can exchange heat with external geothermal heat in a region of several hundred meters, and an inner pipe arranged inside the outer pipe, at least the bottom or a vicinity thereof is open, and the bottom is the outer pipe. A device including an inner tube located within a range of several tens to several hundreds of meters upward from the bottom of the device has been proposed (see Patent Document 1).

JP-A-2016-098806

The device for recovering geothermal heat described in Patent Document 1 is a device in which a fluid (hereinafter, may be referred to as a heating fluid) flows in from an outer pipe and flows out from an inner pipe, but the inner pipe has high thermal conductivity. Since it is made of stainless steel, there is a problem that the heated fluid cools while flowing out to the ground through the inner pipe (relatively low temperature range in the upper part).

An object of the present invention is to provide a geothermal recovery device capable of efficiently recovering geothermal heat by suppressing a temperature drop of a fluid heated by geothermal heat.

The present inventors are studying a means for efficiently recovering geothermal heat by suppressing a temperature drop of the heating fluid, and by providing a heat insulating portion in a part of the inner pipe (a part excluding the lower part), the geothermal heat is obtained. It has been found that the temperature drop of the fluid heated by the above can be suppressed and the geothermal heat can be efficiently recovered, and the present invention has been completed.

That is, the present invention is as follows.
[1] An outer pipe and an inner pipe that are buried in the ground and communicate with each other at the lower part are provided, and the fluid flowing from the ground is heated by geothermal heat while passing through the outer pipe and the inner pipe, and the heated fluid is heated again on the ground. It is a geothermal recovery device that recovers geothermal heat by flowing it out to
A geothermal recovery device characterized in that the inner pipe has a heat insulating portion in a portion other than the lower portion thereof.
[2] The geothermal recovery device according to the above [1], wherein the inner pipe has a heat insulating portion in a range where the underground temperature is 100 ° C. or lower.
[3] The geothermal recovery device according to the above [1] or [2], wherein the inner pipe has a communication opening for communicating with the outer pipe on the lower side portion thereof.
[4] The geothermal recovery device according to the above [3], wherein the bottom of the inner pipe is closed.
[5] The geothermal recovery device according to the above [3] or [4], wherein the communication opening on the lower side portion is provided within a range of 0.5 to 5 m from the lower end of the inner pipe.
[6] The geothermal recovery device according to any one of the above [1] to [5], wherein the lower end of the inner pipe is located in a range of 0 to 10 m from the inner bottom surface of the outer pipe.
[7] The geothermal recovery device according to the above [6], wherein the lower end of the inner pipe is located in a range of more than 0 and 30 cm or less from the inner bottom surface of the outer pipe.

[8] A geothermal recovery device in which a fluid flowing in from the ground flows out from an outer pipe to the ground through an inner pipe.
The geothermal recovery device according to any one of the above [1] to [7], wherein the outer pipe has a heat insulating portion in a range where the underground temperature is 100 ° C. or less.
[9] The geothermal recovery device according to any one of the above [1] to [8] and
A generator that uses the fluid flowing out of the geothermal recovery device to generate electricity,
A geothermal power generation system characterized by being equipped with.
[10] The geothermal power generation system according to the above [9], wherein the generator rotates a turbine with a fluid flowing out of the geothermal recovery device to generate electricity.
[11] The geothermal power generation system according to the above [9], wherein the generator rotates a turbine with an operating fluid heated by a fluid flowing out of the geothermal recovery device to generate electricity.

According to the geothermal recovery device of the present invention, it is possible to suppress the temperature drop of the fluid heated by the geothermal heat and efficiently recover the geothermal heat.

It is schematic cross-sectional view for demonstrating the geothermal recovery apparatus which concerns on 1st Embodiment of this invention. It is schematic cross-sectional view for demonstrating the geothermal recovery apparatus which concerns on 2nd Embodiment of this invention. It is schematic cross-sectional view for demonstrating the geothermal recovery apparatus which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows the outline of the structure of the geothermal power generation system of the system which directly uses the heating fluid provided with the geothermal recovery device of this invention for power generation. It is explanatory drawing which shows the outline of the structure of the binary type geothermal power generation system which includes the geothermal recovery device of this invention.

The geothermal recovery device of the present invention includes an outer pipe and an inner pipe that are buried in the ground and communicate with each other at the lower part, and the fluid flowing in from the ground is heated by geothermal heat while passing through the outer pipe and the inner pipe. It is a geothermal recovery device that recovers geothermal heat by letting the fluid flow out to the ground again, and is characterized in that the inner pipe has a heat insulating portion in a portion other than the lower portion thereof.

In the geothermal recovery device of the present invention, it is possible to suppress a temperature drop when the fluid heated by the geothermal heat flows out to the ground, and the geothermal heat can be efficiently recovered. Further, since the geothermal recovery device of the present invention does not directly recover hot water or steam in the ground, resources such as hot springs are not depleted, and scales such as sulfur adhere to the device. Since there is no such thing, maintenance costs are low and it can be used for a long time.

The geothermal recovery device of the present invention allows a heating fluid to flow in from an inner pipe or an outer pipe buried in the ground, and the heating fluid is at least in a reservoir (high temperature portion) of an underground geothermal fluid having an underground temperature of 100 ° C. or higher. Is heated and discharged to the ground again through the outer pipe or the inner pipe to recover the geothermal heat. That is, at least the outer pipe has a structure that reaches the storage layer of the geothermal fluid. As the storage layer of the geothermal fluid, for example, the underground temperature is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and further preferably 150 ° C. or higher. preferable. As the heating fluid used in the geothermal recovery device of the present invention, water, an organic medium having a boiling point of 100 ° C. or lower, and the like can be preferably exemplified.

(Outer pipe)
The outer pipe in the geothermal recovery device of the present invention is buried in the ground and communicates with the inner pipe at the lower part. Examples of the cross-sectional shape of the outer tube include various shapes such as a square, a rectangle, and a circle, but a circular shape is preferable. The bottom and sides of this outer tube are closed.

Further, the outer pipe may be entirely buried in the ground, but may be partially provided on the ground. That is, the outer pipe may be provided from the ground to the ground.

The material of the outer tube is not particularly limited as long as it is a material having thermal conductivity, and examples thereof include iron, stainless steel, and carbon steel in terms of thermal conductivity, durability, cost, and the like. Therefore, stainless steel is preferable. Further, the periphery of the outer pipe may be partially or wholly covered with concrete or the like, whereby durability can be enhanced.

Further, the length of the outer pipe may be at least as long as it reaches the storage layer (high temperature portion) of the geothermal fluid, and can be appropriately determined depending on the installation location and the like. The length of the outer pipe is, for example, preferably 100 m or more in the range of the underground temperature of 100 ° C. or higher, and 100 m or more in the range of the underground temperature of 120 ° C. or higher. More preferably, the length is 100 m or more in the range of the underground temperature of 150 ° C. or more.

The diameter of the outer pipe can accommodate at least the inner pipe, and can be appropriately set depending on the installation location and the like. The inner diameter of the outer tube is, for example, 50 to 500 mm, preferably 80 to 300 mm, more preferably 100 to 300 mm, and even more preferably 150 to 300 mm. When the inner diameter of the outer pipe is in this range, the heating fluid is sufficiently retained in the high temperature portion in the ground, and the heating fluid can be sufficiently heated.

The upper end of the outer pipe has an inflow port through which fluid can flow in or out on the ground. This inflow port is connected to a circulation pump for circulating a fluid, a part of a geothermal power generation system such as a heat exchanger, or the like.

(Inner tube)
The inner pipe in the geothermal recovery device of the present invention is provided inside the outer pipe buried in the ground, and communicates with the outer pipe at the lower portion thereof. Examples of the cross-sectional shape of the inner tube include various shapes such as a square, a rectangle, and a circle, but a circular shape is preferable.

The diameter of the inner tube is, for example, 10 to 400 mm, preferably 10 to 200 mm, more preferably 12 to 150 mm, still more preferably 15 to 50 mm. The ratio of the volume of the inner pipe to the volume of the outer pipe excluding the inner pipe is preferably 1: 1.5 to 100, more preferably 1: 2 to 80, from the viewpoint of efficiently heating the heating fluid. , 1: 20-50 is even more preferred.

Further, the inner pipe may be entirely buried in the ground, but may be partially provided on the ground. That is, the inner pipe may be provided from the ground to the ground.

As described above, the inner pipe communicates with the outer pipe at the lower portion thereof, and the communication form thereof includes, for example, an inner pipe having an open bottom surface or an outer pipe at the lower portion of the inner pipe. Examples thereof include a form having a communication opening for communication. Communication openings can be provided at the bottom and / or sides of the inner tube. Specifically, for example, a form having a hole and / or a slit in the closed bottom of the inner tube, a form having a hole and / or a slit in the lower side of the inner tube (the bottom is closed or open), or an inner tube. The form having a hole and / or a slit in the closed bottom and the lower side of the inner pipe can be mentioned, and the form having a hole and / or a slit in the lower side of the inner pipe while the bottom of the inner pipe is closed can be mentioned. preferable. By closing the bottom of the inner pipe and forming a hole and / or a slit in the lower side to allow the fluid to flow, it is possible to prevent filth from flowing into the inner pipe. In the case of a form having a hole and / or a slit in the lower side portion of the inner pipe, the hole and / or the slit is preferably provided within a range of 0.5 to 5 m from the lower end of the inner pipe, for example, 0. It is more preferable that it is provided within the range of .8 to 3 m. As a result, the heating fluid in the deepest part (inside the lower end of the outer pipe), which has the highest temperature, can be recovered. In addition, the durability of the lower part of high heat can be enhanced, and the deformation of the inner pipe can be prevented. Further, it is possible to further prevent the inflow of the filth accumulated at the bottom of the outer pipe into the inner pipe.

Further, the lower end of the inner pipe is preferably located in the storage layer (high temperature portion) of the geothermal fluid, and although it depends on the installation location, for example, it is preferably located in the range of 0 to 150 m from the inner bottom surface of the outer pipe. , It is more preferably located in the range of 0 to 80 m from the inner bottom surface of the outer pipe, further preferably located in the range of 0 to 10 m, particularly preferably located in the range of 0 to 5 m, and exceed 0. Most preferably, it is located in a range of 30 cm or less. As a result, the heating fluid in the deepest part (inside the lower end of the outer pipe), which has the highest temperature, can be recovered. Further, by providing the lower end of the inner pipe slightly away from the inner bottom surface of the outer pipe, it is possible to prevent the inner pipe from being damaged even when the inner pipe is stretched at a high temperature, and in particular, the diameter of the inner pipe is increased. It is effective when it is small.

The inner pipe of the present invention has a heat insulating portion except for the lower portion thereof. The heat insulating portion may have a structure in which a part of the inner pipe itself has a heat insulating structure, or may have a structure in which a heat insulating member is provided around the inner pipe. Examples of the structure in which a part of the inner pipe itself has a heat insulating structure include a structure in which a part of the pipe has a heat insulating double structure and a structure in which a part of the pipe is made of a heat insulating material. it can. In addition, examples of the heat insulating member provided around the inner pipe include glass wool, heat-resistant expanded polystyrene, and heat-resistant urethane foam.

The heat insulating portion of the inner pipe is preferably provided in a range where the underground temperature is 100 ° C. or lower, and more preferably 120 ° C. or lower. As a result, in the case of a method in which the heating fluid flows in from the outer pipe and flows out from the inner pipe to the ground, heat transfer from a lower temperature fluid flowing through the surrounding outer pipe is blocked, and the temperature of the fluid flowing through the inner pipe is lowered. Can be suppressed. In addition, in the case of the method in which the heating fluid flows in from the inner pipe and flows out from the outer pipe to the ground, heat transfer from the lower temperature fluid flowing through the inner pipe is blocked, and the temperature drop of the fluid flowing through the outer pipe is suppressed. be able to. For example, since the heating fluid can be maintained at 100 ° C. or higher, it can be recovered in a gas state suitable for a heat medium.

The material other than the heat insulating portion of the inner pipe is not particularly limited as long as it has thermal conductivity, and examples thereof include iron, stainless steel, and carbon steel, which have thermal conductivity and durability. Stainless steel is preferable from the viewpoint of cost and the like.

The length of the lower part of the inner pipe (the part that does not have a heat insulating part) is a reservoir of geothermal fluid (high temperature part) with an underground temperature of 100 ° C or higher (preferably 120 ° C or higher, more preferably 150 ° C or higher). ) Can be determined as appropriate. The length is, for example, 1 to 200 m. The upper limit of length depends on the length of the outer tube present in the geothermal fluid reservoir. On the other hand, the lower limit of the length may be a length that secures an area for providing a communication opening on the lower side portion. The longer the length of the lower part of the inner pipe, the more the heating fluid can absorb the heat from the geothermal fluid reservoir of the heating fluid, so the higher temperature heating fluid tends to be recovered. There is a tendency to be able to recover a heating fluid with a stable temperature. Therefore, the length of the lower part of the inner pipe is preferably about 5 to 70 m, more preferably about 10 to 60 m.

The upper end of the inner pipe has an inflow port through which a fluid can flow in or out on the ground. This inflow port is connected to a circulation pump for circulating a fluid, a part of a geothermal power generation system such as a heat exchanger, or the like.

Further, in the geothermal recovery device of the present invention, in the case of the method in which the heating fluid flows in from the inner pipe and flows out from the outer pipe to the ground, the outer pipe has a heat insulating portion in the range where the underground temperature is 100 ° C. or less. It is preferable to do so. As a result, when the heated fluid passes through the outer pipe (flows out to the ground), it is possible to suppress a temperature drop due to heat transfer from the low temperature underground. The structure of the heat insulating portion of the outer pipe is the same as that of the heat insulating portion of the inner pipe.

Subsequently, a geothermal power generation system using the above-mentioned geothermal recovery device of the present invention will be described.
The geothermal power generation system of the present invention includes the above-mentioned geothermal recovery device and a generator that generates power by using the fluid flowing out from the geothermal recovery device.

The geothermal power generation system of the present invention can be adopted for various geothermal power generation methods such as a method in which a heating fluid is directly used for power generation and a so-called binary method in which a heating fluid is indirectly used for power generation. Specifically, for example, when adopting a method in which a heating fluid is directly used for power generation, the geothermal power generation system of the present invention generates electricity by rotating a turbine with the above-mentioned geothermal recovery device and the fluid flowing out of the geothermal recovery device. It is a power generation system equipped with a generator. Further, when the binary method is adopted, the geothermal power generation system of the present invention comprises the above-mentioned geothermal power recovery device and a generator that rotates a turbine by a working fluid heated by a fluid flowing out from the geothermal recovery device to generate electricity. It is a power generation system equipped.

Hereinafter, embodiments of the geothermal recovery device of the present invention will be specifically described with reference to the drawings, but the present invention is not limited to these embodiments.

Here, FIG. 1 is a schematic cross-sectional view for explaining the geothermal recovery device according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view for explaining the geothermal recovery device according to the second embodiment of the present invention. FIG. 3 is a schematic cross-sectional view for explaining the geothermal recovery device according to the third embodiment of the present invention.

As shown in FIG. 1, the geothermal recovery device 10 according to the first embodiment of the present invention includes an outer pipe 12 and an inner pipe 14 which are buried in the ground and communicate with each other at the lower part. The geothermal recovery device 10 is a device in which a heating fluid flows from the outer pipe 12 to the inner pipe 14.

The outer pipe 12 is, for example, a stainless steel cylinder extending from the ground to the tropics (high temperature part) having an inner diameter of about 200 mm and a length (depth) of about 450 m from the above-ground part. The outer pipe 12 has a bottom and a side closed, and has an inflow port 16 at the upper end. The inflow port 16 is connected to a circulation pump 18 or the like for circulating a fluid in the geothermal recovery device 10. Further, the periphery of the outer pipe 12 in the ground is covered with the concrete material 20.

The inner pipe 14 is provided inside the outer pipe 12 and is a cylindrical body extending from the ground to the tropics (high temperature portion). The inner pipe 14 has an inner diameter of about 35 mm, and a central portion (for example, about 400 m) from the upper portion thereof is composed of a heat insulating double pipe 22 (heat insulating portion). Further, about 50 m to the bottom of the lower portion following this is composed of a steel pipe 24 made of stainless steel.

The heat insulating double pipe 22 is provided at least in a range (low temperature part, medium temperature part) where the underground temperature is 100 ° C. or less from the ground, and can block heat transfer inside and outside the inner pipe 14 in this range. Since the steel pipe 24 is provided in a range where the underground temperature is 100 ° C. or higher (high temperature portion) and has high thermal conductivity, the inner pipe 14 in this range can easily transfer heat from the outside.

The bottom surface of the lower end of the inner pipe 14 is closed, and is provided about 10 to 20 cm above the inner bottom surface 26 of the outer pipe 12. Further, the inner pipe 14 has a plurality of holes 28 communicating with the outer pipe 12 in a range of about 1 m (a range of 0.5 to 1.5 m from the lower end) on the lower side thereof. Further, the inner pipe 14 has an outlet 30 at its upper end. The outlet 30 is connected to a power generation system such as a generator 32 outside the geothermal recovery device 10.

Next, the geothermal recovery device 34 according to the second embodiment will be described. The members having the same configuration as the geothermal recovery device 10 according to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. The present embodiment is different from the above embodiment in that the bottom surface of the lower end of the inner pipe 36 is opened and the lower end of the inner pipe 36 is not close to the inner bottom surface of the outer pipe 38.

As shown in FIG. 2, the geothermal recovery device 34 according to the second embodiment of the present invention includes an inner pipe 36. The lower portion of the inner pipe 36 (a portion other than the heat insulating double pipe) is composed of, for example, a stainless steel pipe 40 having a length of about 11 m. The lower end of the inner pipe 36 has an open bottom surface, and is provided at a position separated from the inner bottom surface 42 of the outer pipe 38 by, for example, about 40 m.

Next, the geothermal recovery device 44 according to the third embodiment will be described. The members having the same configuration as the geothermal recovery device 10 according to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. In the present embodiment, the outer pipe 46 has a heat insulating portion 48 in a range where the underground temperature is 100 ° C. or less, and the heating fluid flows in from the inner pipe 14 and flows out from the outer pipe 46 to the ground. This is different from the first embodiment.

As shown in FIG. 3, the geothermal recovery device 44 according to the third embodiment of the present invention includes an outer pipe 46. The outer pipe 46 has a heat insulating double pipe 48 at the center (for example, about 400 m) from the upper part (heat insulating part). Further, about 50 m to the bottom of the lower portion following this is composed of a steel pipe 50 made of stainless steel. As a result, it is possible to suppress the temperature drop of the fluid heated by the geothermal heat flowing through the outer pipe from the low temperature underground portion and efficiently recover the fluid.

The geothermal power generation system provided with the geothermal recovery device of the present invention described above will be specifically described with reference to the drawings. FIG. 4 is an explanatory diagram showing an outline of a configuration of a geothermal power generation system in which a heating fluid provided with the geothermal recovery device of the present invention is directly used for power generation. FIG. 5 is an explanatory diagram showing an outline of the configuration of a so-called binary type geothermal power generation system including the geothermal recovery device of the present invention.

As shown in FIG. 4, the geothermal power generation system 100 of the present invention includes a geothermal power recovery device 10, a separator, a turbine, a generator, a condenser, a water storage tank, and a circulation pump. The geothermal power generation system 100 of the present invention generates electricity by rotating a turbine with a heating fluid heated by the geothermal heat recovered by the geothermal recovery device 10.

As shown in FIG. 5, the geothermal power generation system 200 of the present invention is a so-called binary system, and is heated by a heating fluid circuit in which the heating fluid of the geothermal recovery device 10 circulates and a turbine heated by the heating fluid. It is equipped with a working fluid circuit in which the working fluid that rotates is circulated. In the geothermal power generation system 200 of the present invention, heat exchange is performed by an evaporator. For example, an operating fluid having a boiling point lower than that of a heating fluid is used as steam, and a turbine is rotated to generate power.

Next, a geothermal recovery test was conducted using the geothermal recovery device of the present invention.
In the test, as the device of the present invention, an inner pipe (steel pipe) having a length of 18 m with the bottom closed is placed below the heat insulating portion (heat insulating double pipe) so that the lower end thereof is separated from the inner bottom surface of the outer pipe by about 15 cm. A device was used in which a communication opening was provided within a range of 0.5 to 5 m from the lower end of the side portion of the inner pipe. In addition, a similar device (the lower end of the inner pipe is located at a height of 9 m from the bottom surface of the outer pipe) was used in which an inner pipe (steel pipe) having an open bottom and a length of 9 m was arranged below the heat insulating portion. ..

In the former geothermal recovery device, the outlet temperature of the recovered heating fluid (water) was 87 to 90 ° C, whereas in the latter device, the outlet temperature of the recovered heating fluid (water) was 83 to Although the temperature was 84 ° C. and both were able to recover the high-temperature fluid, the recovery efficiency of the former device was much better.

Since the geothermal recovery device of the present invention can be used for geothermal recovery of geothermal power generation, it is industrially useful.

10 Geothermal recovery device 12 Outer pipe 14 Inner pipe 16 Inflow port 18 Circulation pump 20 Concrete material 22 Insulated double pipe (insulated part)
24 Steel pipe 26 Inner bottom surface 28 Hole 30 Outlet 32 Generator 34 Geothermal recovery device 36 Inner pipe 38 Outer pipe 40 Steel pipe 42 Inner bottom surface 44 Geothermal recovery device 46 Outer pipe 48 Insulated double pipe (insulation part)
50 Steel pipe 100 Geothermal power generation system 200 Geothermal power generation system

Claims (11)

It is equipped with an outer pipe and an inner pipe that are buried in the ground and communicate with each other at the bottom, and the fluid flowing in from the ground is heated by geothermal heat while passing through the outer pipe and the inner pipe, and the heated fluid is discharged to the ground again. It is a geothermal recovery device that recovers geothermal heat.
A geothermal recovery device characterized in that the inner pipe has a heat insulating portion in a portion other than the lower portion thereof. The geothermal recovery device according to claim 1, wherein the inner pipe has a heat insulating portion in a range where the underground temperature is 100 ° C. or lower. The geothermal recovery device according to claim 1 or 2, wherein the inner pipe has a communication opening for communicating with the outer pipe on the lower side portion thereof. The geothermal recovery device according to claim 3, wherein the bottom of the inner pipe is closed. The geothermal recovery device according to claim 3 or 4, wherein a communication opening on the lower side is provided within a range of 0.5 to 5 m from the lower end of the inner pipe. The geothermal recovery device according to any one of claims 1 to 5, wherein the lower end of the inner pipe is located in a range of 0 to 10 m from the inner bottom surface of the outer pipe. The geothermal recovery device according to claim 6, wherein the lower end of the inner pipe is located in a range of more than 0 and 30 cm or less from the inner bottom surface of the outer pipe. A geothermal recovery device in which fluid flowing in from the ground flows out from the outer pipe to the ground through the inner pipe.
The geothermal recovery device according to any one of claims 1 to 7, wherein the outer pipe has a heat insulating portion in a range where the underground temperature is 100 ° C. or less. The geothermal recovery device according to any one of claims 1 to 8.
A generator that uses the fluid flowing out of the geothermal recovery device to generate electricity,
A geothermal power generation system characterized by being equipped with. The geothermal power generation system according to claim 9, wherein the generator rotates a turbine with a fluid flowing out of the geothermal recovery device to generate electricity. The geothermal power generation system according to claim 9, wherein the generator rotates a turbine with an operating fluid heated by a fluid flowing out of the geothermal recovery device to generate electricity.