Geothermal energy extraction device and extraction method

Abstract

The present invention discloses a geothermal energy extraction device and extraction method. The gravity heat pipe of the device of the present invention includes an evaporation section, an insulation section, a condensation section and a reflux section. The evaporation section is sealed at the end away from the insulation section, and the evaporation section, insulation section, condensation section, plate heat exchanger, reflux section, and gas-liquid separator are connected end to end in sequence. The gas-liquid separator is sleeved on a section of the tube wall of the insulation section, and the gas-liquid separator is fixed on the tube wall of the insulation section by seamless welding. An independent space is formed between the inside of the gas-liquid separator and the tube wall of the section, and the liquid outlet end of the space is a guide hole arranged on the tube wall of the section; the heat transfer pipe includes a liquid inlet section and a liquid outlet section, and the liquid outlet end of the liquid inlet section and the liquid inlet end of the liquid outlet section are respectively connected to the inside of the plate heat exchanger. The method of the present invention is realized by operating the device. The present invention is both environmentally friendly and economical, does not require the consumption of pump power, and at the same time, the heat transfer speed of the heat pipe is fast and the heat transfer is stable, which can improve the efficiency of thermal energy extraction.

Description

Technical Field

[0001] The present invention belongs to the field of geothermal energy exploitation, and in particular relates to a two-phase closed thermosyphon geothermal energy extraction device and a geothermal energy extraction method. Background Art

[0002] Geothermal resources currently include shallow geothermal energy and deep underground geothermal energy. Shallow geothermal energy, or ground source heat pump, refers to a location hundreds to thousands of meters below the ground, where the temperature generally does not exceed 25°C. This part of heat energy is currently mainly used for household heating; the other part is deep underground geothermal energy, which is buried in hot dry rocks 3 to 10 kilometers from the surface. The rock layer temperature is 150 to 650°C, and there is almost no water or steam in the layer. It exists in rocks with a certain porosity and a relatively small permeability. Geothermal resources with a temperature gradient greater than 50°C / km are considered to have development and utilization value. Currently, this heat energy is mainly used for heat generation.

[0003] According to investigations by relevant departments, the total geothermal energy currently stored in the earth's interior exceeds 170 million times the total coal resources on earth. The total reserves of hot dry rocks in my country can reach 100 trillion tons of standard coal. According to statistics, the apparent energy consumption in 2016 was 4.18 billion tons of standard coal. If a small amount of hot dry rock resources can be developed and utilized to replace disposable fossil energy, it can greatly alleviate energy pressure, while reducing environmental pollution caused by fossil energy and promoting stable and sustainable development of social economy. my country has huge reserves of hot dry rock resources. If calculated based on the amount of available resources as a percentage of total resources, it is 168 times that of traditional hydrothermal geothermal resources. my country's hot dry rock geothermal systems are widely distributed and diverse in types. There are uplift mountain types, mainly distributed in southern Tibet and western Yunnan in the southwest; there are sedimentary basin types, mainly distributed in the Mesozoic and Cenozoic rifts and fault basins in the central and eastern parts.

[0004] The traditional hot dry rock thermal energy mining system artificially fractures the high-temperature rocks deep underground, connecting these fractures into systematic channels to form artificial heat storage. In this mining system, the cold fluid exchanges heat with the high-temperature rocks through the channel entrance to the fractures, and the heated fluid removes the heat through the outlet. After the ground equipment uses the heat, the high-temperature fluid is converted back into a low-temperature fluid for heat extraction circulation, thereby realizing the mining and utilization of deep geothermal energy. This method of thermal energy mining means that a large amount of pumping power is required to inject and discharge the fluid. At the same time, due to the irregularity of the fractures, a large amount of heat medium fluid will be lost during the underground circulation process, and water will inevitably come into contact with the rock to produce some non-thermal reactions, affecting the entire heat extraction process. Summary of the invention

[0005] The primary purpose of the present invention is to provide a two-phase closed thermosyphon geothermal energy extraction device, which aims to solve the problems of large-scale loss of heat medium fluid during underground circulation and low heat extraction efficiency during the operation of existing dry hot rock thermal energy extraction systems.

[0006] Another object of the present invention is to provide a method for extracting geothermal energy using the above-mentioned two-phase closed thermosiphon geothermal energy extraction device.

[0007] The present invention is implemented as follows: a geothermal energy extraction device, the device comprising a gravity heat pipe, a heat transfer pipe, a plate heat exchanger, and a gas-liquid separator;

[0008] The gravity heat pipe comprises an evaporation section, an insulation section, a condensation section and a reflux section, the evaporation section is sealed at the end away from the insulation section, and the evaporation section, insulation section, condensation section, plate heat exchanger, reflux section and gas-liquid separator are connected end to end in sequence, the gas-liquid separator is sleeved on a section of the tube wall of the insulation section, and the gas-liquid separator is fixed to the section of the tube wall of the insulation section by seamless welding, an independent space is formed between the inside of the gas-liquid separator and the section of the tube wall, and the liquid outlet end of the space is a guide hole arranged on the section of the tube wall;

[0009] The heat transfer pipe comprises a liquid inlet section and a liquid outlet section, and the liquid outlet end of the liquid inlet section and the liquid inlet end of the liquid outlet section are respectively connected to the inside of the plate heat exchanger.

[0010] Preferably, the device further comprises a guide tube, wherein the reflux section, the guide tube and the gas-liquid separator are connected end to end in sequence.

[0011] Preferably, a liquid distributor is provided on the tube body in the reflux section and located between the guide tube and the heat exchanger.

[0012] Preferably, a valve and a flow meter are provided on the pipe body in the reflux section and between the liquid distributor and the heat exchanger.

[0013] The present invention further discloses a method for extracting geothermal energy using the geothermal energy extraction device, which specifically comprises:

[0014] (1) CO2 is injected into the underground hot dry rock heat storage area, and the CO2 gas forms a supercritical form of CO2 with low viscosity, high density and high permeability in the area, and the CO2 in this form is used to perform convection heat exchange with the hot dry rock heat storage area;

[0015] (2) inserting the evaporation section of the gravity heat pipe into the underground hot dry rock heat storage area, the working medium in the evaporation section absorbs the heat of the supercritical CO2 through the pipe wall and forms an ascending gaseous working medium, the gaseous working medium passes through the insulation section and the condensation section in turn and releases heat with the plate heat exchanger to form a cold liquid working medium, the cold liquid working medium passes through the reflux section in turn and enters the gas-liquid separator, after the gaseous working medium and the liquid working medium are separated by the gas-liquid separator, the cold liquid working medium enters the independent space and flows into the evaporation section through the guide hole along the inner side of the pipe wall; wherein, inside the evaporation section, the cold liquid working medium and the gaseous working medium form a density difference and drive the working medium to circulate in the gravity heat pipe;

[0016] (3) The heat absorbed by the plate heat exchanger is transferred to the heat transfer tube. The liquid inlet end of the heat transfer tube and the liquid outlet end of the heat transfer tube are inserted into the container below the liquid surface of the heat exchange medium to complete the heat transfer.

[0017] Compared with the shortcomings and deficiencies of the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention injects carbon dioxide into underground heat storage through artificial fracturing. Carbon dioxide has supercritical properties under high temperature and high pressure. Supercritical carbon dioxide forms convection in the heat storage, continuously transferring geothermal energy to the working medium in the gravity heat pipe. The working medium in the heat pipe evaporates under heat and transfers heat to the ground plate heat exchanger. The working medium after heat exchange forms condensate and flows back to the evaporation section of the gravity heat pipe. At the junction of the rising gaseous working medium and the returning condensate working medium, the gas-liquid separator can separate the steam and condensate channels, avoiding the occurrence of carrying limit at the gas-liquid junction that causes the evaporation section to dry up, thereby improving the heat recovery efficiency;

[0019] (2) In the heat recovery process of the present invention, the supercritical carbon dioxide stored in the hot dry rock geothermal heat storage can encapsulate carbon dioxide underground, which is both environmentally friendly and economical;

[0020] (3) The working principle of the heat pipe of the present invention is to transfer heat through evaporation and condensation of the working medium in a closed space, absorbing and releasing the latent heat of vaporization, without consuming pump work. At the same time, the heat pipe has a fast heat transfer speed and stable heat transfer, which can improve the efficiency of thermal energy extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the geothermal energy extraction device of the present invention;

[0022] Figure 2 It is a front view structural diagram of the vapor-liquid separator in the device of the present invention after being installed on the gravity heat pipe;

[0023] Figure 3 for Figure 2 The cross-sectional structure diagram of AA in the middle;

[0024] Figure 4 yes Figure 2 The cross-sectional structure diagram of the middle BB;

[0025] Figure 5 It is a structural schematic diagram of the guide tube in the device of the present invention;

[0026] Figure 6 It is a schematic diagram of the structure of the condensed liquid uniform distributor in the device of the present invention;

[0027] Figure 7 yes Figure 6 Cross-sectional structural diagram of CC. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] like Figures 1 to 7 As shown, Figure 1 It is a schematic diagram of the overall structure of the geothermal energy extraction device of the present invention; Figure 2 It is a front view structural diagram of the vapor-liquid separator in the device of the present invention after being installed on the gravity heat pipe; Figure 3 for Figure 2 The cross-sectional structure diagram of AA in the middle; Figure 4 yes Figure 2 The cross-sectional structure diagram of the middle BB; Figure 5 It is a structural schematic diagram of the guide tube in the device of the present invention; Figure 6 It is a schematic diagram of the structure of the condensed liquid uniform distributor in the device of the present invention; Figure 7 yes Figure 6 Cross-sectional structural diagram of CC.

[0030] The present invention discloses a two-phase closed thermosyphon geothermal energy extraction device, which includes a gravity heat pipe 1, a heat transfer pipe 2, a plate heat exchanger 3, and a gas-liquid separator 4; the gravity heat pipe 1 includes an evaporation section 1A, an insulation section 1B, a condensation section 1C, and a reflux section 1D, the evaporation section 1A is sealed at the end away from the insulation section 1B, and the evaporation section 1A, the insulation section 1B, the condensation section 1C, the plate heat exchanger 3, the reflux section 1D, and the gas-liquid separator 4 are sequentially butt-jointed end to end, the gas-liquid separator 4 is sleeved on a section of the tube wall of the insulation section 1B, and the gas-liquid separator 4 is fixed to the section of the tube wall of the insulation section 1B by seamless welding, an independent space 5 is formed between the inside of the gas-liquid separator 4 and the section of the tube wall, and the liquid outlet end of the space is a guide hole 6 arranged on the section of the tube wall;

[0031] The heat transfer tube 2 includes a liquid inlet section 2A and a liquid outlet section 2B. The liquid outlet end of the liquid inlet section 2A and the liquid inlet end of the liquid outlet section 2B are respectively connected to the inside of the plate heat exchanger 3 .

[0032] In the embodiment of the present invention, specifically, the gas-liquid separator 4 is cylindrical, and the gas-liquid separator 4 is sleeved on a section of the tube wall of the insulating section 1B, and the two ends of the gas-liquid separator 4 are seamlessly welded to the tube wall of the insulating section 1B, thereby forming the above-mentioned independent space 5 between the gas-liquid separator 4 and the section of the tube wall, and a plurality of guide holes 6 are provided at the bottom of the independent space 5 and located on the tube wall, and the guide holes 6 constitute the liquid outlet end of the gas-liquid separator 4; wherein, the independent space 5 not only plays the role of buffering and storing the liquid working medium, but also can effectively separate the rising gaseous working medium channel in the gravity heat pipe 1 and the reflux cold liquid working medium channel in the reflux pipe, so as to avoid the carrying limit at the gas-liquid junction causing the evaporation section 1A to dry up, and the gas-liquid separation is also used to separate the gaseous components in the liquid working medium to avoid directly entering the insulating section 1B and the evaporation section 1A. In addition, an important advantage of the structural relationship formed by the insulation section 1B, the condensation section 1C and the gas-liquid separator 4 is that a density difference is formed between the cold liquid working medium flowing downward into the evaporation section 1A in the independent space 5 and the heat-carrying gaseous working medium rising in the evaporation end. Without the aid of an external pump, this density difference can drive the working medium to circulate in the gravity heat pipe 1 on its own.

[0033] In the further implementation process, in order to extend the service life of the gas-liquid separator, specifically, the device further includes a guide tube 7, wherein the reflux section 1D, the guide tube 7, and the gas-liquid separator 4 are sequentially butted end to end. The guide tube 7 can effectively prevent the condensate in the independent section of the reflux pipe from directly scouring the gas-liquid separator.

[0034] In the further implementation process, in order to facilitate the uniform distribution of the refluxed condensate, in the embodiment of the present invention, specifically, the reflux section 1D and the tube body located between the guide tube 7 and the heat exchanger are provided with a liquid uniform distributor 8. The liquid uniform distributor 8 in the present invention can distribute the refluxed condensate with the umbrella surface of the uniform distributor, and flow out from the annular gap between the bottom of the uniform distributor and the reflux pipe.

[0035] In the further implementation process, in order to ensure the monitoring and control of the pressure and flow in the pipeline, specifically, a valve 9 and a flow meter 10 are provided on the independent section of the reflux pipe and the pipe body located between the liquid distributor 8 and the heat exchanger.

[0036] In addition, as a conventional setting of internal circulation, the device of the present invention should also include a container 11 for containing heat exchange medium, wherein the liquid inlet end 2A of the heat transfer tube 2 and the liquid outlet end 2B of the liquid outlet section 2 are both located below the liquid level of the heat exchange medium in the container.

[0037] In the actual application of the device of the present invention, the evaporation section 1A of the gravity heat pipe 1 is 300 meters long and the insulation section 1B is 3700 meters long; in addition, unlike the traditional gravity heat pipe, the condensation section 1C of the gravity heat pipe 1 in the present invention is not on the same vertical pipe as the evaporation section 1A and the insulation section 1B, wherein the condensation section 1C and the reflux pipe of the gravity heat pipe 1 at the position of the plate heat exchanger 3 are both horizontally arranged pipes. In the embodiment of the present invention, the bottom end of the evaporation section 1A of the gravity heat pipe 1 is sealed, and the evaporation section 1A and the insulation section 1B are integrally inserted into the ground by filling the evaporation section 1A with a working medium. When the evaporation section 1A is heated, the working medium becomes gaseous, and the gaseous working medium passes through the insulation section 1B and the condensation section 1C in sequence and enters the plate heat exchanger 3 to complete heat release. After releasing the heat, the working medium condenses into a liquid state, and the liquid working medium enters the gas-liquid separator 4 through the reflux section 1D. The liquid working medium enters the independent space 5 after passing through the gas-liquid separator 4. Under the action of gravity, the liquid working medium in the independent space 5 enters the insulation section 1B through the guide hole 6 and flows back to the evaporation section 1A along the pipe wall; at the same time, a heat exchange medium circulates in the heat transfer tube 2, and the heat absorbed by the plate heat exchanger 3 is transferred through the heat exchange medium.

[0038] The present invention further provides a method for extracting geothermal energy using the geothermal energy extraction device, and is used to further illustrate the actual application and operation process of the geothermal energy extraction device of the present invention. The method is specifically as follows:

[0039] (1) CO2 is injected into the underground hot dry rock heat storage area, and the CO2 gas forms a supercritical form of CO2 with low viscosity, high density and high permeability in the area, and the CO2 in this form is used to perform convection heat exchange with the hot dry rock heat storage area;

[0040] (2) The evaporation section 1A of the gravity heat pipe 1 is inserted into the underground hot dry rock heat storage area. The working medium in the evaporation section 1A absorbs the heat of the supercritical CO2 through the pipe wall and forms an ascending gaseous working medium. The gaseous working medium passes through the insulation section 1B and the condensation section 1C in turn and releases heat with the plate heat exchanger 3 to form a cold liquid working medium. The cold liquid working medium passes through the reflux section 1D and enters the gas-liquid separator 4 in turn. After the gaseous working medium and the liquid working medium are separated by the gas-liquid separator 4, the cold liquid working medium enters the independent space 5 and flows into the evaporation section 1A along the inner side of the pipe wall through the guide hole 6. In the evaporation section 1A, the cold liquid working medium and the gaseous working medium form a density difference and drive the working medium to circulate in the gravity heat pipe 1.

[0041] (3) The heat absorbed by the plate heat exchanger 3 is transferred to the heat transfer tube 2. The liquid inlet end 2A of the heat transfer tube 2 and the liquid outlet end 2B of the liquid outlet section 2 are inserted under the liquid surface of the container containing the heat exchange medium to complete the heat transfer.

[0042] The present invention injects carbon dioxide into underground heat storage by artificial fracturing. Carbon dioxide has supercriticality under high temperature and high pressure. Supercritical carbon dioxide forms convection in the heat storage, continuously transfers geothermal energy to the working medium in the gravity heat pipe 1, and the working medium in the heat pipe evaporates by heat, and transmits heat to the ground plate type heat exchanger 3. The working medium after heat exchange forms condensate and flows back to the evaporation section 1A of the gravity heat pipe 1. At the junction of the rising gaseous working medium and the refluxed condensate working medium, the gas-liquid separator 4 can separate the steam and condensate channels to avoid the carrying limit at the gas-liquid junction causing the evaporation section 1A to dry up, thereby improving the heat extraction efficiency. In addition, in the heat extraction process of the present invention, supercritical carbon dioxide in the dry hot rock geothermal heat storage can encapsulate carbon dioxide underground, which is both environmentally friendly and economical. Finally, the working principle of the heat pipe of the present invention is to transfer heat by evaporating and condensing the working medium in a closed space, absorbing and releasing the latent heat of vaporization, without consuming pump work. At the same time, the heat transfer speed of the heat pipe is fast and the heat transfer is stable, which can improve the efficiency of heat energy extraction.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A geothermal energy extraction device, characterized in that: The device includes a gravity heat pipe, a heat transfer pipe, a plate heat exchanger, and a gas-liquid separator; The gravity heat pipe comprises an evaporation section, an insulation section, a condensation section and a reflux section. The evaporation section is sealed at the end away from the insulation section, and the evaporation section, insulation section, condensation section, plate heat exchanger, reflux section and gas-liquid separator are connected end to end in sequence. The gas-liquid separator is sleeved on a section of the tube wall of the insulation section, and the gas-liquid separator is fixed to the section of the tube wall of the insulation section by seamless welding. An independent space is formed between the inside of the gas-liquid separator and the section of the tube wall to avoid the problem of carrying limit at the gas-liquid junction causing the evaporation section to dry up. The liquid outlet end of the space is a guide hole arranged on the section of the tube wall. The heat transfer pipe comprises a liquid inlet section and a liquid outlet section, and the liquid outlet end of the liquid inlet section and the liquid inlet end of the liquid outlet section are respectively connected to the inside of the plate heat exchanger; The device also includes a container for containing heat exchange medium, wherein the liquid inlet end of the liquid inlet section and the liquid outlet end of the liquid outlet section of the heat transfer tube are both located below the liquid level of the heat exchange medium in the container.

2. The geothermal energy extraction device according to claim 1, characterized in that: The device also includes a guide tube, wherein the reflux section, the guide tube, and the gas-liquid separator are connected end to end in sequence.

3. The geothermal energy extraction device according to claim 2, characterized in that: A liquid distributor is arranged on the tube body of the reflux section and located between the guide tube and the heat exchanger.

4. The geothermal energy extraction device according to claim 3, characterized in that: A valve and a flow meter are arranged on the pipe body of the reflux section and located between the liquid distributor and the heat exchanger.

5. The method for extracting geothermal energy by the geothermal energy extraction device according to any one of claims 1 to 4, characterized in that: The method is as follows: (1) CO2 is injected into the underground hot dry rock thermal reservoir area, and the CO2 gas forms a supercritical form of CO2 with low viscosity, high density and high permeability in the area, and heat exchange with the hot dry rock thermal reservoir area is carried out in the form of convection through this form of CO2; (2) inserting the evaporation section of the gravity heat pipe into the underground hot dry rock heat storage area, the working medium in the evaporation section absorbs the heat of the supercritical CO2 through the pipe wall and forms an ascending gaseous working medium, the gaseous working medium passes through the insulation section and the condensation section in turn and releases heat with the plate heat exchanger to form a cold liquid working medium, the cold liquid working medium passes through the reflux section in turn and enters the gas-liquid separator, after the gaseous working medium and the liquid working medium are separated by the gas-liquid separator, the cold liquid working medium enters the independent space and flows into the evaporation section through the guide hole along the inner side of the pipe wall; wherein, inside the evaporation section, the cold liquid working medium and the gaseous working medium form a density difference and drive the working medium to circulate in the gravity heat pipe; (3) The heat absorbed by the plate heat exchanger is transferred to the heat transfer tube. The inlet end of the heat transfer tube and the outlet end of the heat transfer tube are inserted into the liquid surface of the container containing the heat exchange medium to complete the heat transfer.

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