Pump-free ultra-long gravity assisted heat pipe steam direct-drive geothermal energy power generation system

Abstract

The invention discloses a pump-free ultra-long gravity heat pipe steam direct-drive geothermal energy power generation system which comprises an ultra-long gravity heat pipe, a power generation device, a condenser and a working medium reinjection device. The super-long gravity heat pipe is buried in a selected geothermal well, the bottom of the super-long gravity heat pipe goes deep into underground heat storage, and a working medium outlet is formed in the top of the super-long gravity heat A working medium outlet of the super-long gravity heat pipe is connected with the power generation device, the power generation device is connected with the condenser, the condenser is connected with an inlet of the working medium reinjection device, and an outlet of the working medium reinjection device is arranged in the super-long gravity heat pipe. According to the system, the pump-free operation of the ultra-long gravity heat pipe steam direct-drive power generation system is realized, the system structure is simplified, the pump work and the maintenance cost of the pump are saved, and the use cost is reduced; and working medium leakage can be avoided, the technical safety of the system is improved, and finally the market competitiveness of the technology is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal power generation, and particularly to a pump-free ultra-long gravity heat pipe steam direct drive geothermal power generation system. Background Art

[0002] To achieve the "dual carbon" goal, the key lies in the development of renewable energy. Geothermal energy has significant advantages of wide distribution and huge reserves. Its output is stable and not easily affected by the environment, and it is considered to have the potential to become a base load. However, the current development of geothermal power generation in China is progressing slowly, significantly lagging behind the world's advanced level. If geothermal power generation is to develop, urgent technological innovation is needed.

[0003] The existing ultra-long gravity heat pipe steam direct drive power generation system operates at a relatively high pressure. Its commonly used booster pump is a plunger type booster pump, which not only has low efficiency and high maintenance costs, but also has relatively serious working medium leakage problems. Summary of the Invention

[0004] The object of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a pump-free ultra-long gravity heat pipe steam direct drive geothermal power generation system.

[0005] The present invention is realized through the following technical solutions: A pump-free ultra-long gravity heat pipe steam direct drive geothermal power generation system includes an ultra-long gravity heat pipe, a power generation device, a condenser, and a working medium reinjection device; the ultra-long gravity heat pipe is buried in a selected geothermal well, its bottom extends deep into the underground heat reservoir, and its top is provided with a working medium outlet; the working medium outlet of the ultra-long gravity heat pipe is connected to the power generation device, the power generation device is connected to the condenser, the condenser is connected to the inlet of the working medium reinjection device, and the outlet of the working medium reinjection device is arranged in the ultra-long gravity heat pipe.

[0006] This system selects a geothermal well according to power demand and resource distribution and buries an ultra-long gravity heat pipe. The overall structure of the system is similar to the Rankine cycle. The heat pipe plays the role of a boiler in it, and it can be used for the development of hydrothermal geothermal sources as well as for the development of hot dry rock geothermal resources. The working medium reinjection device uses gravity to boost the liquid flow after condensation in the condenser, playing the role of a booster pump in the traditional Rankine cycle. This system realizes the pump-free operation of the ultra-long gravity heat pipe steam direct drive power generation system, with high efficiency and reduced maintenance costs.

[0007] In the pump-free ultra-long gravity heat pipe steam direct drive geothermal power generation system, at least one geothermal well is provided. When a multi-well system is adopted, one such ultra-long gravity heat pipe is arranged in each geothermal well.

[0008] The working fluid of the ultra-long gravity heat pipe absorbs heat from the underground heat source and evaporates into saturated vapor; the ultra-long gravity heat pipe extracts heat from an unmodified geothermal well, or the ultra-long gravity heat pipe extracts heat from a geothermal well with an artificial heat storage built underground for enhancing the heat extraction performance. The main function of the ultra-long gravity heat pipe is to extract heat from the underground heat storage: the working fluid of the ultra-long gravity heat pipe absorbs heat from the underground heat source and evaporates into saturated vapor, and then spontaneously rises from the underground to the wellhead under the drive of the saturated pressure difference, and outputs vapor externally to drive the power generation device.

[0009] The power generation device includes a steam turbine and a generator. The working fluid outlet of the ultra-long gravity heat pipe is connected to the steam inlet of the steam turbine. The steam turbine is connected to the generator through a mechanical transmission structure. The steam outlet of the steam turbine is connected to the condenser. In the system, the steam generated by the ultra-long gravity heat pipe directly enters the steam turbine to expand and do work; when necessary, it can also be heat-exchanged through a heat exchanger to a general organic Rankine cycle system or other forms of power generation systems for power generation. In actual operation, the power generation system should be selected according to engineering needs, and the selection of different power generation systems is within the scope of consideration of the present invention.

[0010] The condenser is externally connected with a heat dissipation device; or the condenser is externally connected with a refrigeration system, a heating system or a new power generation system. The hot water exchanged by the condenser can be directly cooled through heat dissipation devices such as cooling towers to enter a new cycle, or can drive or partially drive new power generation systems, refrigeration systems or heating systems and other energy utilization devices according to needs, so as to achieve the purpose of cascaded utilization of energy. All these structural changes are within the scope of consideration of the present invention.

[0011] The working fluid reinjection device includes a working fluid reinjection pipe. The upper end of the working fluid reinjection pipe is connected to the condenser. The lower end of the working fluid reinjection pipe extends deep into the ultra-long gravity heat pipe. The gravitational static pressure of the liquid column in the working fluid reinjection pipe is equal to or greater than the pressure difference between the working fluid outlet of the ultra-long gravity heat pipe and the liquid after condensation in the condenser.

[0012] Alternatively, the working fluid reinjection device includes a working fluid reinjection pipe and a reinjection buffer tank. The reinjection buffer tank is located at the upper part of the working fluid reinjection device and is connected to the working fluid reinjection pipe. The reinjection buffer tank is connected to the condenser, and the lower end of the working fluid reinjection pipe extends deep into the ultra-long gravity heat pipe. The working fluid reinjection pipe is filled with the liquid working fluid to be reinjected, and the gravitational static pressure of the liquid column in the working fluid reinjection pipe is equal to or greater than the pressure difference between the working fluid outlet of the ultra-long gravity heat pipe and the liquid after condensation in the condenser. The purpose of setting the reinjection buffer tank is to temporarily store the working fluid that has not been reinjected, which plays a role in buffering system fluctuations, and it can ensure that the working fluid reinjection pipe is always filled with the working fluid. The working fluid reinjection pipe is a pipe with sufficient length, which extends deep into the ultra-long gravity heat pipe. The working fluid reinjection pipe is filled with the liquid working fluid to be reinjected, and the gravitational static pressure of the liquid column in it can be equal to or greater than the pressure difference between the working fluid outlet of the ultra-long gravity heat pipe and the liquid flow after condensation in the condenser, so as to achieve pump-free working fluid reinjection. The length of the working fluid reinjection pipe is adjusted according to the design requirements, and a valve can be set between it and the previous pipeline according to needs.

[0013] The working fluid reinjection pipe is a pipe made of heat-insulating material, or a heat-insulating layer is provided on the outer periphery of the working fluid reinjection pipe.

[0014] Compared with the prior art, the advantages of the present invention are as follows: This system realizes the pump-free operation of the ultra-long gravity heat pipe steam direct-drive power generation system. By utilizing the characteristic that the ultra-long gravity heat pipe extends deep underground for thousands of meters, the present invention creatively forms sufficient gravitational static pressure through a working fluid reinjection pipe hundreds of meters long, so as to offset the pressure difference, which is equivalent to using the gravitational potential energy of this section to complete the pressurization of the working fluid. This new design can not only simplify the system structure and save the upfront investment, but also save the pump power and the maintenance cost of the pump, reduce the usage cost, and avoid the leakage of the working fluid, improve the technical safety of the system, and ultimately enhance the market competitiveness of the technology. The working fluid reinjection pipe of this system extends dozens to hundreds of meters deep into the ultra-long gravity heat pipe, which can effectively avoid the situation that the reinjected liquid is carried by the rising air flow and re-enters the steam turbine. At this time, the dryness of the steam at the inlet of the steam turbine will be greatly improved, which can not only improve the operation efficiency of the steam turbine, but also extend the service life of the steam turbine and reduce the maintenance frequency. Brief Description of the Drawings

[0015] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0016] The meanings of the reference numerals in the drawings: 1. Ultra-long gravity heat pipe; 11. Underground heat storage; 12. Working fluid outlet; 2. Power generation device; 21. Steam turbine; 22. Generator; 3. Condenser; 4. Working fluid reinjection device; 41. Reinjection buffer tank; 42. Working fluid reinjection pipe. Detailed Embodiments

[0017] The content of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] Embodiment

[0019] The ultra-long gravity heat pipe 1 technology is a new type of (medium)-deep geothermal energy single-well extraction technology proposed and developed by Chinese scientific research personnel, with the significant advantages of full set of self-owned technology and leading international technology. In this technology, the working fluid absorbs heat and evaporates into saturated vapor underground, and automatically rises to the ground under the drive of the saturated pressure difference, and then releases heat and condenses into liquid in the ground equipment and then falls back to the bottom of the heat pipe under the action of gravity for the next cycle. This technology has the unique advantages of only extracting heat without taking water and self-driving without pump work, and the absorbed heat is stored in the form of latent heat, with good temperature uniformity, and can maintain a larger heat exchange temperature difference with the underground heat storage 11. Compared with other geothermal technologies that only extract heat without taking water, it has a larger single-well heat extraction. The ultra-long gravity heat pipe 1 produces steam, which can directly drive the steam turbine 21 to generate electricity. Compared with other technologies, it has a simpler structure and higher efficiency, and is very suitable for geothermal power generation. However, the current technology is still in the basic stage and urgently needs further research and development.

[0020] ① The ultra-long gravity heat pipe 1 technology outputs steam, which can directly drive the steam turbine 21 to do work without heat exchange or flash evaporation equipment. The heat exchange or flash evaporation process not only requires additional equipment, but also causes the temperature of the heat source to drop, resulting in additional losses. Therefore, under the condition of the same heat production, the steam direct drive power generation system of the ultra-long gravity heat pipe 1 has higher power generation efficiency and thus better economic performance.

[0021] ② The ultra-long gravity heat pipe 1 produces saturated steam, and the steam state in each link of its direct drive power generation system is in a saturated state, and the saturated pressure is everywhere related to the temperature. After the steam drives the steam turbine 21, its temperature will drop. In fact, power equipment such as the steam turbine 21 generates electricity relying on this temperature difference. Therefore, the temperature of the saturated liquid working fluid after condensation after power generation is lower than the temperature at the working fluid outlet 12 of the ultra-long gravity heat pipe 1, and its pressure is also correspondingly lower. If the working fluid is to be smoothly reinjected, the previous technology must rely on a booster pump to increase the pressure of the working fluid here so that it is equal to or slightly greater than the pressure at the working fluid outlet 12 of the ultra-long gravity heat pipe 1.

[0022] ③ For the ultra-long gravity heat pipe 1, the flow velocity of the rising saturated gaseous working fluid can reach more than ten or even dozens of meters per second. After the cold liquid working fluid is reinjected into the heat pipe, it is very likely to be carried by the rising gaseous working fluid, resulting in part of the liquid working fluid not reaching the bottom of the pipe to absorb heat and directly discharging from the working fluid outlet 12 of the ultra-long gravity heat pipe 1 along with the gaseous working fluid. These liquid working fluids mixed into the steam turbine 21 will not be able to expand and do work, and will have an adverse impact on the steam turbine 21; moreover, the mixing of these liquid working fluids increases the system mass flow rate, thus increasing the pump work consumption of the booster pump.

[0023] ④Geothermal energy is a low-grade heat source. The enthalpy value of the working fluid per unit mass is relatively low, and the power generation is small. Therefore, the ratio of the pump work required for pressurizing the working fluid to the total power generation is often significantly greater than that of ordinary thermal power plants. Reducing the pump work of the geothermal power generation system will be an effective means to increase the output of the geothermal power generation system and enhance its technical competitiveness.

[0024] ⑤Under the current technical conditions, the gravitational potential energy of the working fluid injected back into the ultra-long gravity heat pipe 1 and falling back to the heat absorption section of the heat pipe cannot be utilized. The recovery and utilization of this part of the gravitational potential energy will improve the operating efficiency of the heat pipe.

[0025] ⑥At present, the operating pressure of the ultra-long gravity heat pipe 1 is often relatively high. Its commonly used booster pump is a plunger type booster pump, which not only has low efficiency and high maintenance costs, but also has relatively serious working fluid leakage problems.

[0026] Refer to Figure 1 , which is a pump-free ultra-long gravity heat pipe 1 steam direct-driven geothermal power generation system, including an ultra-long gravity heat pipe 1, a power generation device 2, a condenser 3 and a working fluid reinjection device 4; the ultra-long gravity heat pipe 1 is buried in a selected geothermal well, its bottom extends deep into the underground heat storage 11, and its top is provided with a working fluid outlet 12; the working fluid outlet 12 of the ultra-long gravity heat pipe 1 is connected to the power generation device 2, the power generation device 2 is connected to the condenser 3, the condenser 3 is connected to the inlet of the working fluid reinjection device 4, and the outlet of the working fluid reinjection device 4 is arranged in the ultra-long gravity heat pipe 1.

[0027] This system selects a geothermal well according to power demand and resource distribution and buries the ultra-long gravity heat pipe 1. The overall structure of the system is similar to the Rankine cycle. The heat pipe plays the role of a boiler in it, and can be used for the development of hydrothermal heat sources and the development of hot dry rock geothermal resources. The working fluid reinjection device 4 uses gravity to boost the liquid flow after condensation of the condenser 3, playing the role of a booster pump in the traditional Rankine cycle. This system realizes the pump-free operation of the ultra-long gravity heat pipe 1 steam direct-driven power generation system, with high efficiency and reduced maintenance costs.

[0028] In the pump-free ultra-long gravity heat pipe 1 steam direct-driven geothermal power generation system, at least one geothermal well is provided. When a multi-well system is adopted, one ultra-long gravity heat pipe 1 is arranged in each geothermal well, and a working fluid reinjection device 4 is arranged in each ultra-long gravity heat pipe 1. Each working fluid reinjection device 4 is different according to the requirements of its matching ultra-long gravity heat pipe 1, such as having different lengths of the working fluid reinjection pipe 42. The production temperature of the ultra-long gravity heat pipe 1 is related to local geothermal conditions, heat pipe length, heat pipe diameter, working fluid selection, etc., and can be changed at any time to meet the needs.

[0029] The working fluid of the ultra-long gravity heat pipe 1 absorbs heat from the underground heat source and evaporates into saturated vapor; the ultra-long gravity heat pipe 1 extracts heat from an unmodified geothermal well, or the ultra-long gravity heat pipe 1 extracts heat from a geothermal well with an artificial heat storage built underground for enhancing the heat extraction performance. The main function of the ultra-long gravity heat pipe 1 is to extract heat from the underground heat storage 11: the working fluid of the ultra-long gravity heat pipe 1 absorbs heat from the underground heat source and evaporates into saturated vapor, and then spontaneously rises from the underground to the wellhead under the drive of the saturated pressure difference, and outputs vapor externally to drive the power generation device 2.

[0030] The power generation device 2 includes a steam turbine 21 and a generator 22. The working fluid outlet 12 of the ultra-long gravity heat pipe 1 is connected to the steam inlet of the steam turbine 21. The steam turbine 21 is connected to the engine through a mechanical transmission structure, and the steam outlet of the steam turbine 21 is connected to the condenser 3. In the system, the steam generated by the ultra-long gravity heat pipe 1 directly enters the steam turbine 21 to expand and do work; when necessary, it can also be heat-exchanged through a heat exchanger to a general organic Rankine cycle system or other forms of power generation systems for power generation. In actual operation, the power generation system should be selected according to the engineering needs, and the selection of different power generation systems is within the scope of consideration of this embodiment.

[0031] The condenser 3 is externally connected with a heat dissipation device; or, the condenser 3 is externally connected with a refrigeration system, a heating system or a new power generation system. The hot water exchanged by the condenser 3 can be directly cooled through a heat dissipation device such as a cooling tower to enter a new cycle, or can drive or partially drive new power generation systems, refrigeration systems or heating systems and other energy utilization devices according to needs to achieve the purpose of cascaded energy utilization. All these structural changes are within the scope of consideration of this embodiment.

[0032] The working fluid reinjection device 4 includes a working fluid reinjection pipe 42. The upper end of the working fluid reinjection pipe 42 is connected to the condenser 3, the lower end of the working fluid reinjection pipe 42 extends deep into the ultra-long gravity heat pipe 1, and the gravitational static pressure of the liquid column in the working fluid reinjection pipe 42 is equal to or greater than the pressure difference between the working fluid outlet 12 of the ultra-long gravity heat pipe 1 and the liquid after condensation in the condenser 3.

[0033] Alternatively, the working fluid reinjection device 4 includes a working fluid reinjection pipe 42 and a reinjection buffer tank 41. The reinjection buffer tank 41 is located at the upper part of the working fluid reinjection device 4 and is communicated with the working fluid reinjection pipe 42. The reinjection buffer tank 41 is connected to the condenser 3, and the lower end of the working fluid reinjection pipe 42 extends deep into the ultra-long gravity heat pipe 1. The working fluid reinjection pipe 42 is filled with the liquid working fluid to be reinjected, and the gravitational static pressure of the liquid column in the working fluid reinjection pipe 42 is equal to or greater than the pressure difference between the working fluid outlet 12 of the ultra-long gravity heat pipe 1 and the liquid after condensation in the condenser 3. The purpose of setting the reinjection buffer tank 41 is to temporarily store the working fluid that has not been reinjected, play a role in buffering system fluctuations, and ensure that the working fluid reinjection pipe 42 is always filled with the working fluid. The working fluid reinjection pipe 42 is a pipe with sufficient length, which extends deep into the ultra-long gravity heat pipe 1. The working fluid reinjection pipe 42 is filled with the liquid working fluid to be reinjected, and the gravitational static pressure of the liquid column in it can be equal to or greater than the pressure difference between the working fluid outlet 12 of the ultra-long gravity heat pipe 1 and the liquid flow after condensation in the condenser 3, so as to realize pump-free working fluid reinjection. The length of the working fluid reinjection pipe 42 is adjusted according to design requirements, and valves can be set between it and the previous pipeline as needed.

[0034] The working fluid reinjection device 4 can be provided with or without the reinjection buffer tank 41 according to needs. The diameter and length of the working fluid reinjection pipe 42 are determined according to the design parameters of the entire power generation system. The design requirement is that during the normal operation of the system, the diameter of the working fluid reinjection pipe 42 meets the flow requirement of the reinjected working fluid, and its length needs to meet the design requirement of eliminating the pressure difference between the working fluid outlet 12 of the ultra-long gravity heat pipe 1 and the liquid flow after condensation in the condenser 3.

[0035] The working fluid reinjection pipe 42 is a pipe made of heat-insulating material, or a heat-insulating layer is provided on the outer periphery of the working fluid reinjection pipe 42. The inner wall surface of the working fluid reinjection pipe 42 can be processed with different internal structures or polished (such as setting a polishing layer) according to different situations to achieve a better reinjection effect.

[0036] Ordinary valves or check valves can be installed on the working fluid reinjection pipe 42 and the previous pipelines as needed to facilitate control and prevent the saturated vapor from flowing back into the working fluid reinjection pipe 42 when shutting down.

[0037] In this embodiment, the ultra-long gravity heat pipe 1 is similar to the boiler in a thermal power plant, producing steam. The steam directly enters the steam turbine 21 to expand and do work, thereby driving the generator 22 to generate electricity. After the exhaust gas is discharged from the steam turbine 21, like in a thermal power plant, it enters the condenser 3 to release heat and condense into saturated liquid. The temperature and pressure of the condensed saturated liquid working medium are both lower than those at the working medium outlet 12 of the ultra-long gravity heat pipe 1, and it flows into the working medium reinjection device 4. The saturated liquid working medium flows into the working medium reinjection pipe 42 in the working medium reinjection device 4, and a liquid column dozens to hundreds of meters high is formed in the working medium reinjection pipe 42. The gravity is used to offset the pressure difference between it and the gaseous working medium in the heat pipe, so as to realize the smooth reinjection of the working medium.

[0038] The working principle of this embodiment is as follows:

[0039] In this embodiment, the ultra-long gravity heat pipe 1 is used to extract (medium)-deep geothermal energy, generating saturated steam to directly drive the steam turbine 21 to generate electricity. Then the working medium condenses into saturated liquid in the condenser 3 and enters the working medium reinjection device 4 to be pressurized by gravity, so as to realize the pump-free operation of the whole system. The whole system has a simple structure and strong operability.

[0040] From the perspective of the working medium: The working medium absorbs heat and evaporates into saturated gas at the bottom heat absorption section of the ultra-long gravity heat pipe 1, and then automatically rises to the working medium outlet 12 of the ultra-long gravity heat pipe 1 under the drive of the saturated pressure difference. This heat extraction process is completely spontaneous and does not require pump drive. The extracted saturated steam successively enters the steam turbine 21 and the condenser 3, and the process is similar to that of a thermal power plant. Different from an ordinary thermal power plant, the "boiler" ultra-long gravity heat pipe 1 of this thermal system has the characteristic of extending thousands of meters underground. Therefore, in this embodiment, it is considered to omit the booster pump, but use the downward gravitational potential energy when the working medium is reinjected into the bottom heat absorption section of the heat pipe to supplement the pressure energy between the condensate and the rising saturated steam. For this reason, a working medium reinjection device 4 is arranged at the top of the ultra-long gravity heat pipe 1. This device is composed of a reinjection buffer tank 41 and a working medium reinjection pipe 42. The former plays the role of stabilizing the working medium fluctuation and ensuring that the latter is filled with liquid working medium. The latter uses the gravitational static pressure formed by the hundreds of meters elevation when it is filled with liquid working medium to overcome the pressure difference between the liquid and gaseous working media.

[0041] In order to prevent the gaseous working medium from flowing back from the working medium reinjection pipe 42 during improper operation or shutdown, a check valve is arranged on the working medium reinjection pipe 42 or the pipeline connected to the condenser 3. In order to ensure the smooth reinjection of the working medium, the wall surface of the working medium reinjection pipe 42 can be heat-insulated as required, and its inner surface can be polished or processed with internal structures.

[0042] The above detailed description is a specific description of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification without departing from the present invention should be included in the patent scope of this case.

Claims

1. A pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system, Characterized in that: It includes an ultra - long gravity heat pipe, a power generation device, a condenser and a working fluid reinjection device; the ultra - long gravity heat pipe is buried in a selected geothermal well, its bottom extends deep into the underground heat reservoir, and its top is provided with a working fluid outlet; the working fluid outlet of the ultra - long gravity heat pipe is connected to the power generation device, the power generation device is connected to the condenser, the condenser is connected to the inlet of the working fluid reinjection device, and the outlet of the working fluid reinjection device is arranged in the ultra - long gravity heat pipe.

2. The pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system according to claim 1, Characterized in that: In the pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system, there is at least one geothermal well. When a multi - well system is adopted, one such ultra - long gravity heat pipe is arranged in each geothermal well.

3. The pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system according to claim 1, Characterized in that: The working fluid of the ultra - long gravity heat pipe absorbs heat and evaporates into saturated vapor in the underground heat source; the ultra - long gravity heat pipe extracts heat from an unmodified geothermal well, or the ultra - long gravity heat pipe extracts heat from a geothermal well with an artificial heat reservoir built underground for enhancing the heat extraction performance.

4. The pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system according to claim 1, Characterized in that: The power generation device includes a steam turbine and a generator. The working fluid outlet of the ultra - long gravity heat pipe is connected to the steam inlet of the steam turbine. The steam turbine is connected to the generator through a mechanical transmission structure, and the steam outlet of the steam turbine is connected to the condenser.

5. The pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system according to claim 1, Characterized in that: The condenser is externally connected with a heat dissipation device; or the condenser is externally connected with a refrigeration system, a heating system or a new power generation system.

6. The pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system according to claim 1, Characterized in that: The working fluid reinjection device includes a working fluid reinjection pipe. The upper end of the working fluid reinjection pipe is connected to the condenser, the lower end of the working fluid reinjection pipe extends deep into the ultra - long gravity heat pipe, and the gravitational static pressure of the liquid column in the working fluid reinjection pipe is equal to or greater than the pressure difference between the working fluid outlet of the ultra - long gravity heat pipe and the liquid after condensation in the condenser.

7. The pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system according to claim 1, Characterized in that: The working fluid reinjection device includes a working fluid reinjection pipe and a reinjection buffer tank. The reinjection buffer tank is located at the upper part of the working fluid reinjection device and is communicated with the working fluid reinjection pipe; the reinjection buffer tank is connected to the condenser, the lower end of the working fluid reinjection pipe extends deep into the ultra - long gravity heat pipe; the working fluid reinjection pipe is filled with the liquid working fluid to be reinjected, and the gravitational static pressure of the liquid column in the working fluid reinjection pipe is equal to or greater than the pressure difference between the working fluid outlet of the ultra - long gravity heat pipe and the liquid after condensation in the condenser.

8. The pump - less ultra - long gravity heat pipe vapor direct - drive geothermal power generation system according to claim 6 or 7, Characterized in that: The working fluid reinjection pipe is a pipe made of heat-insulating material, or a heat-insulating layer is provided on the outer periphery of the working fluid reinjection pipe.

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