Hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system and method

Abstract

The present invention discloses a hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system and method. The system includes a heat extraction subsystem for underground heat extraction and CO2 geological storage, a transcritical CO2-flash-ORC composite power generation subsystem and a cooling water subsystem. The heat extraction subsystem is used to extract geothermal fluid, the transcritical CO2-flash-ORC composite power generation subsystem uses geothermal fluid to generate electricity, and the cooling water subsystem is used to condense the working fluid of the transcritical CO2-flash-ORC composite power generation subsystem. The present invention utilizes hydrothermal heat storage as a heat extraction and CO2 storage space to achieve the purpose of "storage, extraction and use" integration, does not require the artificial construction of underground heat storage space, and saves construction costs. The present invention uses CO2 as a heat extraction working fluid. CO2 produces a significant gravity difference between the injection well and the production well, the pressure at the outlet of the production well increases, and the working capacity of the turbine inlet working fluid is improved, while reducing the power consumption of the injected CO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal energy development and utilization, and specifically relates to a hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system and method. Background Art

[0002] Large-scale development and utilization of geothermal energy can play a key role in meeting growing global energy demand and achieving decarbonization goals. In this context, maximizing geothermal energy efficiency is crucial to fully realizing its decarbonization potential. Geothermal power generation systems typically consist of two main components: underground heat extraction and surface power generation. Improving overall system efficiency requires maximizing heat extraction performance and establishing an optimal match between underground and surface processes.

[0003] Patents CN114046230A and CN114016986A disclose compressed gas energy storage and geothermal extraction coupling systems for aquifers and enhanced geothermal systems, respectively. Compressed air is used as the heat extraction and energy storage medium. In terms of heat extraction working fluid research, in addition to compressed air, CO2 is gradually being used in underground heat extraction processes. Existing CO2 heat extraction systems are mainly divided into two categories: systems that apply CO2 to natural permeable formations / hydrothermal heat storage and extraction are called plume geothermal systems; systems that apply CO2 to hot dry rocks / enhanced geothermal systems (EGS) are called CO2-EGS systems. Both are geothermal systems that integrate geothermal energy extraction and CO2 storage.

[0004] Common geothermal power generation methods include the ORC (Organic Rankine Cycle) and flash evaporation systems. Current research on power generation systems focuses primarily on optimizing operating parameters under fixed input conditions. Furthermore, the operating mode of surface power generation systems is relatively fixed, with little consideration given to coupling with the dynamic heat extraction characteristics of underground systems. Therefore, developing new, highly efficient, hybrid power generation technologies to match hydrothermal CO2 heat storage systems and constructing integrated heat extraction and power generation systems, while also conducting research on the dynamic matching characteristics of heat extraction and power generation, is crucial for improving geothermal energy utilization efficiency and promoting the implementation of the nation's "dual carbon" goals. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system and method provided by the present invention solve the following technical problems:

[0006] (1) In patents CN114046230A and CN114016986A, the compressed air heat extraction performance is poor, and the density change is less affected by temperature, which makes it impossible to fully utilize the thermal siphon effect, and the system's own pump power consumption is large.

[0007] (2) CO2 plume geothermal systems and CO2-EGS systems. The power generation system is usually a simple configuration and cannot fully utilize the heat extracted by the heat extracting medium, resulting in low power generation efficiency. Currently, there is a lack of a hybrid power generation technology solution based on a CO2 cycle coupled with an ORC and flash evaporation system.

[0008] (3) Research on ground power generation systems focuses on the optimization of operating parameters under fixed input conditions, and rarely considers the coupling with the dynamic heat extraction characteristics of the underground system. The ground power generation system does not make corresponding operating strategy adjustments based on the dynamic changes in the long-term operation of the underground heat extraction system.

[0009] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system, including a heat extraction subsystem for underground heat extraction and CO2 geological storage, a transcritical CO2-flash evaporation-ORC composite power generation subsystem and a cooling water subsystem;

[0010] Among them, the heat extraction subsystem is used to extract geothermal energy, the transcritical CO2-flash evaporation-ORC composite power generation subsystem is used for geothermal power generation, and the cooling water subsystem is used for the working fluid condensation process of the transcritical CO2-flash evaporation-ORC composite power generation subsystem.

[0011] Furthermore: the heat extraction subsystem includes a CO2 injection unit, an underground heat storage and a geothermal well, and the geothermal well includes an injection well and a production well;

[0012] The CO2 injection unit includes a CO2 storage tank, a first booster pump and a first valve;

[0013] The CO2 storage tank is connected to one end of the first valve via a first booster pump, and the other end of the first valve is connected to the wellhead of the injection well;

[0014] The underground heat storage includes a cap layer, a hydrothermal heat storage and a bottom aquiclude from top to bottom. The injection well and the production well both penetrate the cap layer, and the bottom of the well is set inside the hydrothermal heat storage.

[0015] Furthermore: the material of the injection well wall of the injection well is a high thermal conductivity material, and the material of the production well wall of the production well is a thermal insulation material.

[0016] Further: the transcritical CO2-flash evaporation-ORC composite power generation subsystem includes a transcritical CO2 power generation unit, a flash evaporation power generation unit and an ORC power generation unit;

[0017] Among them, the transcritical CO2 power generation unit, flash evaporation power generation unit and ORC power generation unit all exchange heat with the cooling water subsystem in the condenser. The transcritical CO2 power generation unit and the flash evaporation power generation unit are arranged in parallel, and the flash evaporation power generation unit and the ORC power generation unit are arranged in series.

[0018] Further: the transcritical CO2 power generation unit includes a second valve, a separator, a CO2 turbine, a first generator, a second booster pump, a fourth valve, an eighth valve, and a ninth valve;

[0019] Among them, one end of the second valve is connected to the wellhead of the production well, the other end of the second valve is connected to the inlet of the separator, the liquid outlet of the separator is connected to one end of the eighth valve and one end of the ninth valve respectively, the gas outlet of the separator is connected to the inlet of the CO2 turbine through the third valve, the first generator is coaxially connected to the CO2 turbine, the CO2 turbine outlet is connected to the inlet of the second booster pump through the first condenser, and the outlet of the second booster pump is connected to the wellhead of the injection well through the fourth valve.

[0020] Further: the flash evaporation power unit includes a fifth valve, a sixth valve, an evaporator, a seventh valve, a flash evaporator, a steam turbine, a third generator, an eleventh valve and a water storage tank;

[0021] The inlet of the flash evaporator is connected to the other end of the ninth valve, the liquid outlet of the flash evaporator is connected to one end of the sixth valve, one end of the seventh valve and the other end of the eighth valve respectively, the other end of the seventh valve is connected to the other end of the sixth valve and one end of the fifth valve respectively through the evaporator, and the other end of the fifth valve is connected to the water storage tank;

[0022] The steam outlet of the flash evaporator is connected to the inlet of the steam turbine through the tenth valve. The steam turbine is coaxially connected to the third generator. The outlet of the steam turbine is connected to the water tank through the third condenser and the eleventh valve in turn.

[0023] Further: the ORC power generation unit includes a working fluid pump, an ORC turbine and a second generator;

[0024] The working fluid outlet of the evaporator is connected to the inlet of the ORC turbine, the ORC turbine is coaxially connected to the second generator, and the outlet of the ORC turbine is connected to the working fluid inlet of the evaporator through the second condenser and the working fluid pump in sequence.

[0025] Further: the cooling water subsystem includes a first condenser, a second condenser, a third condenser, a first cooling tower, a second cooling tower, a third cooling tower, a first circulating pump, a second circulating pump and a third circulating pump;

[0026] The inlet of the first condenser is connected to the outlet of the CO2 turbine, the outlet of the first condenser is connected to the inlet of the second booster pump, the cooling water outlet of the first condenser is connected to the inlet of the first cooling tower, and the outlet of the first cooling tower is connected to the cooling water inlet of the first condenser through the first circulating pump;

[0027] The inlet of the second condenser is connected to the outlet of the ORC turbine, the outlet of the second condenser is connected to the inlet of the working fluid pump, the cooling water outlet of the second condenser is connected to the inlet of the second cooling tower, and the outlet of the second cooling tower is connected to the cooling water inlet of the second condenser through the second circulation pump;

[0028] The inlet of the third condenser is connected to the outlet of the steam turbine, the outlet of the third condenser is connected to the inlet of the eleventh valve, the cooling water outlet of the third condenser is connected to the inlet of the third cooling tower, and the outlet of the third cooling tower is connected to the cooling water inlet of the third condenser through the third circulating pump.

[0029] A hydrothermal heat storage CO2 cycle heat extraction and power generation integrated method, the method comprising the following steps:

[0030] S1. Collect geothermal fluid through the heat extraction subsystem;

[0031] S2. Power generation using geothermal fluids through a transcritical CO2-flash-ORC composite power generation subsystem;

[0032] Furthermore: the S1 is specifically:

[0033] The liquid CO2 in the CO2 storage tank is pressurized to above the critical pressure by the first booster pump, and the first valve is opened to inject the CO2 from the injection well into the hydrothermal heat storage. The CO2 continuously displaces the geothermal water in the hydrothermal heat storage and flows toward the bottom of the production well. The geothermal fluid is extracted from the production well. The geothermal fluid undergoes a composition transformation process in sequence: geothermal water, a mixture of water and CO2, and CO2.

[0034] The S2 is specifically:

[0035] S21. Operate the evaporation power unit and ORC power generation unit in the initial stage of combined power generation:

[0036] Open the second valve at the wellhead of the production well to send the geothermal water into the separator, open the ninth valve, close the third valve and the eighth valve, and send the geothermal water into the flash evaporator after removing impurities, and flash evaporate it into a vapor-liquid mixture in the flash evaporator by reducing the pressure;

[0037] The saturated steam separated from the vapor-liquid mixture is fed through the tenth valve into the steam turbine to perform work, driving the third generator to generate electricity. The heat energy is converted into electrical energy. During the power generation process, the exhaust steam at the steam turbine outlet transfers heat to the cooling water in the third condenser. The condensed water is then fed into the water storage tank through the eleventh valve.

[0038] The saturated water separated from the vapor-liquid mixture is fed into the evaporator through the seventh valve, transferring heat to the organic working fluid. The organic working fluid absorbs the heat and is fed into the ORC turbine to perform work, driving the second generator to generate electricity. During the power generation process, the exhaust steam at the ORC turbine outlet is condensed into liquid in the second condenser, then pressurized to the evaporation pressure by the working fluid pump and fed into the evaporator.

[0039] S22. In the middle stage of the combined power generation, the flash evaporation unit and the ORC power generation unit are kept open, and the transcritical CO2 power generation unit is operated at the same time:

[0040] Open the third valve, and the CO2 separated from the geothermal water containing CO2 is sent to the CO2 turbine to perform work, driving the first generator to generate electricity. During the power generation process, the exhaust steam at the outlet of the CO2 turbine is sent to the first condenser to be condensed into liquid. The exhaust steam is then pressurized to the specified pressure by the second booster pump. The fourth valve is opened and the exhaust steam is injected into the ground together with the supercritical CO2 from the CO2 storage tank.

[0041] S23. In the later stage of the combined power generation, the eighth valve and the ninth valve are closed, the third valve is opened, and only the transcritical CO2 power generation unit is kept in operation.

[0042] The beneficial effects of the present invention are:

[0043] (1) The present invention provides a hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system and method, which utilizes hydrothermal heat storage as heat extraction storage and CO2 storage space to achieve the purpose of "storage-extraction-use" integration, without the need for artificial underground heat storage space, saving construction costs.

[0044] (2) The present invention uses CO2 as a circulating heat extracting medium, which has the characteristics of being environmentally friendly, economical, and easy to obtain. At the same time, its density is greatly affected by temperature. CO2 produces a significant gravity difference between the injection well and the production well. The pressure of the working fluid at the outlet of the production well increases, which enhances the working capacity of the working fluid at the turbine inlet, improves the power generation performance of the system, and reduces the power consumption of the injected CO2, further reducing the operating cost.

[0045] (3) The present invention can achieve geological storage of CO2, helping to achieve the dual carbon goals, while avoiding problems such as ground subsidence and collapse caused by groundwater extraction.

[0046] (4) The present invention has developed multiple operating modes for the ground composite power generation system, which can adjust the operating mode and structure according to the state of the underground fluid, cope with the changes in the heat extraction performance of the hydrothermal heat storage CO2 cycle under long-term operating conditions, and maximize the utilization efficiency of geothermal fluids. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of a hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system.

[0048] Figure 2 This is a flow chart of the integrated method of hydrothermal thermal storage CO2 cycle heat extraction and power generation.

[0049] Figure 3 Schematic diagram of a hydrothermal heat storage transcritical CO2-flash composite power generation system.

[0050] Figure 4 Schematic diagram of a hydrothermal heat storage transcritical CO2-ORC composite power generation system.

[0051] Figure 5 Schematic diagram of a hydrothermal heat storage transcritical CO2 cycle power generation system.

[0052] 1-CO2 storage tank; 2-first booster pump; 3-first valve; 4-injection well; 5-injection well wall; 6-bottom aquiclude; 7-hydrothermal heat storage; 8-cap layer; 9-production well wall; 10-production well; 11-second valve; 12-separator; 13-third valve; 14-CO2 turbine; 15-first generator; 16-first condenser; 17-second booster pump; 18-fourth valve; 19-first cooling tower; 20-first circulation pump; 21-fifth valve Door; 22-sixth valve; 23-evaporator; 24-working fluid pump; 25-seventh valve; 26-eighth valve; 27-ninth valve; 28-flash evaporator; 29-ORC turbine; 30-second generator; 31-second condenser; 32-tenth valve; 33-steam turbine; 34-third generator; 35-third condenser; 36-third circulating pump; 37-third cooling tower; 38-eleventh valve; 39-second circulating pump; 40-second cooling tower; 41-water tank. DETAILED DESCRIPTION

[0053] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0054] like Figure 1 As shown, in one embodiment of the present invention, a hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system includes a heat extraction subsystem for underground heat extraction and CO2 geological storage, a transcritical CO2-flash evaporation-ORC composite power generation subsystem, and a cooling water subsystem;

[0055] Among them, the heat extraction subsystem is used to extract geothermal fluid, the transcritical CO2-flash-ORC composite power generation subsystem is used to generate electricity using geothermal fluid, and the cooling water subsystem is used for the working fluid condensation process of the transcritical CO2-flash-ORC composite power generation subsystem.

[0056] In this embodiment, the heat extraction subsystem is connected to the transcritical CO2-flash evaporation-ORC composite power generation subsystem, serving as input and output to each other, and the cooling water subsystem exchanges heat with the composite power generation subsystem through the condenser.

[0057] The heat extraction subsystem includes a CO2 injection unit, an underground heat storage and a geothermal well, wherein the geothermal well includes an injection well 4 and a production well 10;

[0058] The CO2 injection unit includes a CO2 storage tank 1, a first booster pump 2 and a first valve 3;

[0059] The CO2 storage tank 1 is connected to one end of the first valve 3 through the first booster pump 2, and the other end of the first valve 3 is connected to the wellhead of the injection well 4;

[0060] The underground heat storage includes a cap layer 8, a hydrothermal heat storage 7 and a bottom aquiclude 6 from top to bottom. The injection well 4 and the production well 10 both penetrate the cap layer 8, and the well bottom is set inside the hydrothermal heat storage 7.

[0061] The injection well wall 5 of the injection well 4 is made of a high thermal conductivity material, and the production well wall 9 of the production well 10 is made of a thermal insulation material.

[0062] The transcritical CO2-flash evaporation-ORC composite power generation subsystem includes a transcritical CO2 power generation unit, a flash evaporation power generation unit and an ORC power generation unit;

[0063] Among them, the transcritical CO2 power generation unit, flash evaporation power generation unit and ORC power generation unit all exchange heat with the cooling water subsystem in the condenser. The transcritical CO2 power generation unit and the flash evaporation power generation unit are arranged in parallel, and the flash evaporation power generation unit and the ORC power generation unit are arranged in series.

[0064] The transcritical CO2 power generation unit includes a second valve 11, a separator 12, a CO2 turbine 14, a first generator 15, a second booster pump 17, a fourth valve 18, an eighth valve 26, and a ninth valve 27;

[0065] Among them, one end of the second valve 11 is connected to the wellhead of the production well 10, the other end of the second valve 11 is connected to the inlet of the separator 12, the liquid outlet of the separator 12 is connected to one end of the eighth valve 26 and one end of the ninth valve 27 respectively, the gas outlet of the separator 12 is connected to the inlet of the CO2 turbine 14 through the third valve 13, the first generator 15 is coaxially connected to the CO2 turbine 14, the outlet of the CO2 turbine 14 is connected to the inlet of the second booster pump 17 through the first condenser 16, and the outlet of the second booster pump 17 is connected to the wellhead of the injection well 4 through the fourth valve 18.

[0066] The flash evaporation power unit includes a fifth valve 21, a sixth valve 22, an evaporator 23, a seventh valve 25, a flash evaporator 28, a steam turbine 33, a third generator 34, an eleventh valve 38 and a water storage tank 41;

[0067] The inlet of the flash evaporator 28 is connected to the other end of the ninth valve 27, and the liquid outlet of the flash evaporator 28 is respectively connected to one end of the sixth valve 22, one end of the seventh valve 25, and the other end of the eighth valve 26. The other end of the seventh valve 25 is respectively connected to the other end of the sixth valve 22 and one end of the fifth valve 21 through the evaporator 23. The other end of the fifth valve 21 is connected to the water storage tank 41.

[0068] The steam outlet of the flash evaporator 28 is connected to the inlet of the steam turbine 33 through the tenth valve 32. The steam turbine 33 is coaxially connected to the third generator 34. The outlet of the steam turbine 33 is connected to the water tank 41 through the third condenser 35 and the eleventh valve 38 in turn.

[0069] The ORC power generation unit includes a working fluid pump 24, an ORC turbine 29 and a second generator 30;

[0070] The working fluid outlet of the evaporator 23 is connected to the inlet of the ORC turbine 29 , the ORC turbine 29 is coaxially connected to the second generator 30 , and the outlet of the ORC turbine 29 is connected to the working fluid inlet of the evaporator 23 through the second condenser 31 and the working fluid pump 24 in sequence.

[0071] The cooling water subsystem includes a first condenser 16, a second condenser 31, a third condenser 35, a first cooling tower 19, a second cooling tower 40, a third cooling tower 37, a first circulating pump 20, a second circulating pump 39 and a third circulating pump 36;

[0072] The inlet of the first condenser 16 is connected to the outlet of the CO2 turbine 14, the outlet of the first condenser 16 is connected to the inlet of the second booster pump 17, the cooling water outlet of the first condenser 16 is connected to the inlet of the first cooling tower 19, and the outlet of the first cooling tower 19 is connected to the cooling water inlet of the first condenser 16 through the first circulating pump 20;

[0073] The inlet of the second condenser 31 is connected to the outlet of the ORC turbine 29, the outlet of the second condenser 31 is connected to the inlet of the working fluid pump 24, the cooling water outlet of the second condenser 31 is connected to the inlet of the second cooling tower 40, and the outlet of the second cooling tower 40 is connected to the cooling water inlet of the second condenser 31 through the second circulation pump 39;

[0074] The inlet of the third condenser 35 is connected to the outlet of the steam turbine 33, the outlet of the third condenser 35 is connected to the inlet of the eleventh valve 38, the cooling water outlet of the third condenser 35 is connected to the inlet of the third cooling tower 37, and the outlet of the third cooling tower 37 is connected to the cooling water inlet of the third condenser 35 through the third circulating pump 36.

[0075] In this embodiment, three cooling water subsystems are provided, which are used for the working fluid condensation process of the transcritical CO2 power generation unit, the flash evaporation power generation unit and the ORC power generation unit respectively;

[0076] like Figure 2 As shown, a hydrothermal heat storage CO2 cycle heat extraction and power generation integrated method includes the following steps:

[0077] S1. Collect geothermal fluid through the heat extraction subsystem;

[0078] S2. Power generation using geothermal fluids through a transcritical CO2-flash-ORC composite power generation subsystem;

[0079] The S1 is specifically:

[0080] The liquid CO2 in the CO2 storage tank 1 is pressurized to above the critical pressure by the first booster pump 2, and the first valve 3 is opened to send the CO2 from the injection well 4 into the hydrothermal heat storage 7. The CO2 continuously displaces the geothermal water in the hydrothermal heat storage 7 and moves to the bottom of the production well 10, while replacing the geothermal water in the pores, completing the geological storage of CO2. The geothermal fluid is extracted from the production well 10, and the geothermal fluid undergoes a component transformation process of geothermal water, a mixture of water and CO2, and CO2 in sequence.

[0081] In this embodiment, at the initial stage of operation of the heat extraction subsystem, the geothermal fluid extracted from the production well 10 is geothermal water. After a period of time, when CO2 migrates to the bottom of the production well 10, the extracted geothermal fluid begins to transform into a mixture of water and CO2. As the operating time increases, the CO2 content in the mixture increases and the water content continues to decrease.

[0082] The S2 is specifically:

[0083] S21. Operate the flash evaporation unit and ORC power generation unit in the initial stage of combined power generation:

[0084] The second valve 11 at the wellhead of the production well 10 is opened to feed the geothermal water into the separator 12. The ninth valve 27 is opened, and the third valve 13 and the eighth valve 26 are closed. After removing impurities from the geothermal water, the water is fed into the flash evaporator 28, where it is flash-evaporated into a vapor-liquid mixture by reducing the pressure.

[0085] The saturated steam separated from the vapor-liquid mixture is fed through the tenth valve 32 into the steam turbine 33 to perform work, driving the third generator 34 to generate electricity, converting heat energy into electrical energy. During the power generation process, the exhaust steam at the outlet of the steam turbine 33 transfers heat to cooling water in the third condenser 35. The condensed water is then fed through the eleventh valve 38 into the water storage tank 41.

[0086] The saturated water separated from the vapor-liquid mixture is fed into the evaporator 23 through the seventh valve 25, where it transfers heat to the organic working fluid. The organic working fluid absorbs the heat and is fed into the ORC turbine 29 to perform work, driving the second generator 30 to generate electricity. During the power generation process, the exhaust steam at the outlet of the ORC turbine 29 is condensed into a liquid in the second condenser 31, then pressurized to the evaporation pressure by the working fluid pump 24 and fed into the evaporator 23.

[0087] When the local hot water temperature is low, close the seventh valve 25 and open the sixth valve 22. The saturated water separated by the flash evaporator 28 is directly sent to the water storage tank 41 through the bypass. The system path is as follows: Figure 3 As shown, when the pressure in the geothermal water is low, the efficiency of the flash evaporation system is low. The ninth valve 27 is closed and the eighth valve 26 is opened. The geothermal water is directly sent to the ORC evaporator 23 to provide heat to the ORC system. The system path is as follows Figure 4 shown.

[0088] S22. In the middle stage of the combined power generation, the flash evaporation unit and the ORC power generation unit are kept open, and the transcritical CO2 power generation unit is operated at the same time:

[0089] Open the third valve 13, and the CO2 separated from the geothermal water containing CO2 is sent to the CO2 turbine 14 to perform work, driving the first generator 15 to generate electricity. During the power generation process, the exhaust steam at the outlet of the CO2 turbine 14 is sent to the first condenser 16 to be condensed into liquid. The exhaust steam is then pressurized to a specified pressure by the second booster pump 17, and then the fourth valve 18 is opened to inject it into the ground together with the supercritical CO2 from the CO2 storage tank 1.

[0090] S23, in the later stage of combined power generation, the eighth valve 26 and the ninth valve 27 are closed, the third valve 13 is opened, and only the transcritical CO2 power generation unit is kept in operation.

[0091] In the later stage of compound power generation, the system pathways are as follows Figure 5As shown, the geothermal water in most of the pore space of hydrothermal heat reservoir 7 has been displaced by CO2. The water content of the geothermal fluid at the outlet of production well 10 has decreased to the point where it is no longer possible to maintain stable operation of the flash evaporation and ORC power generation units. Therefore, valves 8 and 9, 27, are closed, and valve 13 is opened, leaving only the transcritical CO2 power generation unit operational. When the CO2 flow rates in injection well 4 and production well 10 are consistent, valve 3 is closed, halting the CO2 injection unit.

[0092] The beneficial effects of the present invention are as follows: the present invention provides a hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system and method, using hydrothermal heat storage as heat extraction storage and CO2 storage space to achieve the purpose of "storage-extraction-use" integration, without the need for artificial creation of underground heat storage space, saving construction costs.

[0093] The present invention uses CO2 as a circulating heat extracting working fluid, which has the characteristics of being environmentally friendly, economical, and easy to obtain. At the same time, its density is greatly affected by temperature. CO2 produces a significant gravity difference between the injection well 4 and the production well 10. The working fluid pressure at the outlet of the production well 10 increases, which enhances the working capacity of the working fluid at the turbine inlet, improves the power generation performance of the system, and reduces the power consumption of the injected CO2, further reducing operating costs.

[0094] This invention can achieve geological storage of CO2, helping to achieve the dual carbon goals as soon as possible, while avoiding problems such as ground subsidence and collapse caused by groundwater exploitation.

[0095] The present invention develops multiple operating modes for the ground composite power generation system, which can adjust the operating mode and structure according to the state of the underground fluid, cope with the changes in the heat extraction performance of the hydrothermal heat storage CO2 cycle under long-term operating conditions, and maximize the utilization efficiency of geothermal fluids.

[0096] In the description of the present invention, it should be understood that the terms "center", "thickness", "upper", "lower", "horizontal", "top", "bottom", "inner", "outer", "radial", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying the relative importance or the number of technical features implicitly specified. Therefore, the features defined by "first", "second", and "third" may explicitly or implicitly include one or more of such features.

Claims

1. Hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system, characterized by: It includes a heat extraction subsystem for underground heat extraction and CO2 geological storage, a transcritical CO2-flash evaporation-ORC composite power generation subsystem, and a cooling water subsystem; Among them, the heat extraction subsystem is used to extract geothermal fluid, the transcritical CO2-flash evaporation-ORC composite power generation subsystem uses geothermal fluid to generate electricity, and the cooling water subsystem is used to condense the working fluid of the transcritical CO2-flash evaporation-ORC composite power generation subsystem; The transcritical CO2-flash evaporation-ORC composite power generation subsystem includes a transcritical CO2 power generation unit, a flash evaporation power generation unit and an ORC power generation unit; Among them, the transcritical CO2 power generation unit, flash evaporation power generation unit and ORC power generation unit all exchange heat with the cooling water subsystem in the condenser. The transcritical CO2 power generation unit and the flash evaporation power generation unit are arranged in parallel, and the flash evaporation power generation unit and the ORC power generation unit are arranged in series. The transcritical CO2 power generation unit includes a second valve (11), a separator (12), a CO2 turbine (14), a first generator (15), a second booster pump (17), a fourth valve (18), an eighth valve (26), and a ninth valve (27); One end of the second valve (11) is connected to the wellhead of the production well (10), the other end of the second valve (11) is connected to the inlet of the separator (12), the liquid outlet of the separator (12) is connected to one end of the eighth valve (26) and one end of the ninth valve (27), respectively, the gas outlet of the separator (12) is connected to the inlet of the CO2 turbine (14) through the third valve (13), the first generator (15) is coaxially connected to the CO2 turbine (14), the outlet of the CO2 turbine (14) is connected to the inlet of the second booster pump (17) through the first condenser (16), and the outlet of the second booster pump (17) is connected to the wellhead of the injection well (4) through the fourth valve (18).

2. The hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system according to claim 1 is characterized in that: The heat extraction subsystem includes a CO2 injection unit, an underground heat storage and a geothermal well, wherein the geothermal well includes an injection well (4) and a production well (10); The CO2 injection unit includes a CO2 storage tank (1), a first booster pump (2) and a first valve (3); The CO2 storage tank (1) is connected to one end of a first valve (3) via a first booster pump (2), and the other end of the first valve (3) is connected to the wellhead of an injection well (4); The underground heat storage comprises, from top to bottom, a cap layer (8), a hydrothermal heat storage (7) and a bottom aquiclude (6); the injection well (4) and the production well (10) both penetrate the cap layer (8), and the well bottom is arranged inside the hydrothermal heat storage (7).

3. The hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system according to claim 2 is characterized in that: The injection well wall (5) of the injection well (4) is made of a high thermal conductivity material, and the production well wall (9) of the production well (10) is made of a thermal insulation material.

4. The hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system according to claim 2 is characterized in that: The flash evaporation power generation unit includes a fifth valve (21), a sixth valve (22), an evaporator (23), a seventh valve (25), a flash evaporator (28), a steam turbine (33), a third generator (34), an eleventh valve (38) and a water storage tank (41); The inlet of the flash evaporator (28) is connected to the other end of the ninth valve (27), the liquid outlet of the flash evaporator (28) is respectively connected to one end of the sixth valve (22), one end of the seventh valve (25), and the other end of the eighth valve (26), the other end of the seventh valve (25) is respectively connected to the other end of the sixth valve (22) and one end of the fifth valve (21) through the evaporator (23), and the other end of the fifth valve (21) is connected to the water storage tank (41); The steam outlet of the flash evaporator (28) is connected to the inlet of the steam turbine (33) through the tenth valve (32), the steam turbine (33) is coaxially connected to the third generator (34), and the outlet of the steam turbine (33) is connected to the water storage tank (41) through the third condenser (35) and the eleventh valve (38) in sequence.

5. The hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system according to claim 4 is characterized in that: The ORC power generation unit includes a working fluid pump (24), an ORC turbine (29) and a second generator (30); The working fluid outlet of the evaporator (23) is connected to the inlet of the ORC turbine (29), the ORC turbine (29) is coaxially connected to the second generator (30), and the outlet of the ORC turbine (29) is connected to the working fluid inlet of the evaporator (23) through the second condenser (31) and the working fluid pump (24) in sequence.

6. The hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system according to claim 5 is characterized in that: The cooling water subsystem includes a first condenser (16), a second condenser (31), a third condenser (35), a first cooling tower (19), a second cooling tower (40), a third cooling tower (37), a first circulating pump (20), a second circulating pump (39) and a third circulating pump (36); The inlet of the first condenser (16) is connected to the outlet of the CO2 turbine (14), the outlet of the first condenser (16) is connected to the inlet of the second booster pump (17), the cooling water outlet of the first condenser (16) is connected to the inlet of the first cooling tower (19), and the outlet of the first cooling tower (19) is connected to the cooling water inlet of the first condenser (16) through the first circulating pump (20); The inlet of the second condenser (31) is connected to the outlet of the ORC turbine (29), the outlet of the second condenser (31) is connected to the inlet of the working fluid pump (24), the cooling water outlet of the second condenser (31) is connected to the inlet of the second cooling tower (40), and the outlet of the second cooling tower (40) is connected to the cooling water inlet of the second condenser (31) through the second circulation pump (39); The inlet of the third condenser (35) is connected to the outlet of the steam turbine (33), the outlet of the third condenser (35) is connected to the inlet of the eleventh valve (38), the cooling water outlet of the third condenser (35) is connected to the inlet of the third cooling tower (37), and the outlet of the third cooling tower (37) is connected to the cooling water inlet of the third condenser (35) through the third circulating pump (36).

7. A hydrothermal heat storage CO2 cycle heat extraction and power generation integrated method, applied to the hydrothermal heat storage CO2 cycle heat extraction and power generation integrated system according to any one of claims 4 to 6, characterized in that: The method comprises the following steps: S1. Collect geothermal fluid through the heat extraction subsystem; S2. Use geothermal fluid to generate electricity through a transcritical CO2-flash-ORC composite power generation system.

8. The hydrothermal heat storage CO2 cycle heat extraction and power generation integrated method according to claim 7, characterized in that: The S1 is specifically: The liquid CO2 in the CO2 storage tank (1) is pressurized to a pressure above the critical pressure by the first booster pump (2), and the first valve (3) is opened to inject the CO2 from the injection well (4) into the hydrothermal heat storage (7). The CO2 in the hydrothermal heat storage (7) continuously displaces the geothermal water and moves toward the bottom of the production well (10). High-temperature geothermal fluid is extracted from the production well (10). The geothermal fluid sequentially undergoes a component transformation process of geothermal water, a mixture of water and CO2, and CO2; The S2 is specifically: S21. Operate the flash evaporation unit and ORC power generation unit in the initial stage of combined power generation: Open the second valve (11) at the wellhead of the production well (10), send the geothermal water into the separator (12), open the ninth valve (27), close the third valve (13) and the eighth valve (26), and send the geothermal water into the flash evaporator (28) after removing impurities, and flash evaporate the geothermal water into a vapor-liquid mixture by reducing the pressure in the flash evaporator (28); The saturated steam separated from the steam-liquid mixture is input into the steam turbine (33) through the tenth valve (32) to perform work, thereby driving the third generator (34) to generate electricity, and heat energy is converted into electrical energy. During the power generation process, the exhaust steam at the outlet of the steam turbine (33) transfers heat to the cooling water in the third condenser (35), and the condensed water is sent to the water storage tank (41) through the eleventh valve (38); The saturated water separated from the vapor-liquid mixture is fed into the evaporator (23) through the seventh valve (25) to transfer heat to the organic working medium. The organic working medium absorbs heat and is fed into the ORC turbine (29) to perform work, thereby driving the second generator (30) to generate electricity. During the power generation process, the exhaust steam at the outlet of the ORC turbine (29) is condensed into liquid in the second condenser (31), and then pressurized to the evaporation pressure by the working medium pump (24) and fed into the evaporator (23). S22. In the middle stage of the combined power generation, the flash evaporation unit and the ORC power generation unit are kept open, and the transcritical CO2 power generation unit is operated at the same time: The third valve (13) is opened, and the CO2 separated from the geothermal water containing CO2 is sent to the CO2 turbine (14) to perform work, thereby driving the first generator (15) to generate electricity. During the power generation process, the exhaust steam at the outlet of the CO2 turbine (14) is sent to the first condenser (16) to be condensed into liquid, and then pressurized to a specified pressure by the second booster pump (17). The fourth valve (18) is opened to inject the exhaust steam into the ground together with the supercritical CO2 from the CO2 storage tank (1); S23. In the later stage of the combined power generation, the eighth valve (26) and the ninth valve (27) are closed, and the third valve (13) is opened, so that only the transcritical CO2 power generation unit is kept in operation.

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