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

Abstract

The invention discloses a hydrothermal type heat storage CO2 circulating heat extraction-power generation integrated system and method.The system comprises a heat extraction subsystem used for underground heat extraction and CO2 geological storage, a transcritical CO2-flash evaporation-ORC combined power generation subsystem and a cooling water subsystem, and the heat extraction subsystem is used for extracting geothermal fluid; the transcritical CO2-flash evaporation-ORC combined power generation subsystem is used for generating power by utilizing geothermal fluid, and the cooling water subsystem is used for condensing a working medium of the transcritical CO2-flash evaporation-ORC combined power generation subsystem. According to the invention, hydrothermal heat storage is used as a heat extraction and CO2 storage space, so that the purpose of integration of storage, extraction and use is realized, an underground heat storage space does not need to be constructed manually, and the construction cost is saved. The CO2 is adopted as a heat extraction working medium, the CO2 generates an obvious gravity difference between the injection well and the production well, the outlet pressure of the production well is increased, the working medium power capability of a turbine inlet is improved, and meanwhile, the power consumption of CO2 injection is reduced.

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-power generation integrated system and method. Background Art

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

[0003] Patents CN114046230A and CN114016986A disclose respectively compressed gas energy storage and geothermal extraction coupling systems for aquifers and enhanced geothermal systems. Both heat extraction and energy storage media use compressed air. 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 heat extraction are called plume geothermal systems; systems that apply CO2 to hot dry rocks / enhanced geothermal systems (Enhanced Geothermal System, EGS) are called CO2-EGS systems. Both are geothermal systems that integrate geothermal energy extraction and CO2 storage.

[0004] Commonly used geothermal power generation methods include ORC (Organic Rankine Cycle) and flash evaporation power generation system. At present, the research on power generation system mainly focuses on the optimization of operating parameters under fixed input conditions, and the operation mode of ground power generation system is relatively fixed, and the coupling with the dynamic heat extraction characteristics of underground system is rarely considered. Therefore, for the hydrothermal heat storage CO2 heat extraction system, it is particularly important to develop a new high-efficiency composite power generation technology that matches it and build an integrated heat extraction-power generation system, and at the same time conduct research on the dynamic matching characteristics of heat extraction-power generation to improve the utilization efficiency of geothermal energy and promote the implementation of the national "dual carbon" goals. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the hydrothermal heat storage CO2 cycle heat extraction-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 system and CO2-EGS system, the power generation system is usually a simple configuration, which cannot fully utilize the heat extracted by the heat extracting medium, and the system power generation efficiency is low. At present, there is still a lack of composite power generation technology solutions based on CO2 cycle coupling ORC and flash evaporation system.

[0008] (3) Research on ground-based power generation systems focuses on optimizing operating parameters under fixed input conditions, and rarely considers the coupling with the dynamic heat extraction characteristics of underground systems. The ground-based 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 invention object, the technical solution adopted by the present invention is: a hydrothermal heat storage CO2 cycle heat extraction-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-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-ORC composite power generation subsystem.

[0011] Further: 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] Wherein, 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 through 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 reservoir includes a cap layer, a hydrothermal heat reservoir and a bottom impermeable layer 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 reservoir.

[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, the flash evaporation power generation unit and the 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 respectively connected to one end of the sixth valve, one end of the seventh valve and the other end of the eighth valve, the other end of the seventh valve is respectively connected to the other end of the sixth valve and one end of the fifth valve 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, and 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 turn.

[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 circulating 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-power generation integrated method, the method comprising the following steps:

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

[0031] S2, using geothermal fluids to generate electricity through a transcritical CO2-flash-ORC composite power generation subsystem;

[0032] Further: S1 specifically includes:

[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 CO2 from the injection well into the hydrothermal heat storage. The CO2 in the hydrothermal heat storage continuously displaces the geothermal water to flow to the bottom of the production well, and the geothermal fluid is extracted from the production well. The geothermal fluid undergoes a component transformation process of geothermal water, a mixture of water and CO2, and CO2 in sequence;

[0034] The S2 is specifically:

[0035] S21. Operate the evaporation power unit and the 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 into a vapor-liquid mixture in the flash evaporator by reducing the pressure;

[0037] The saturated steam separated from the steam-liquid mixture is input into the steam turbine through the tenth valve to do work, driving the third generator to generate electricity, and 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, and the condensed water is sent into the water storage tank through the eleventh valve;

[0038] The saturated water separated from the vapor-liquid mixture is input into the evaporator through the seventh valve, and the heat is transferred to the organic working medium. After absorbing the heat, the organic working medium is sent to the ORC turbine to do work, driving the second generator to generate electricity. During the power generation process, the exhaust steam at the outlet of the ORC turbine is condensed into liquid in the second condenser, and then pressurized to the evaporation pressure by the working medium pump and sent to the evaporator;

[0039] S22. Keep the flash evaporation unit and the ORC power generation unit open during the mid-stage of the combined power generation, and operate the transcritical CO2 power generation unit at the same time:

[0040] The third valve is opened, 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, and then pressurized to the specified pressure by the second booster pump. The fourth valve is opened to inject it into the ground together with the supercritical CO2 from the CO2 storage tank;

[0041] S23. In the later stage of compound 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 heat storage and CO2 storage space to achieve the purpose of "storage-extraction-use" integration, does not require artificial underground heat storage space, and saves construction costs.

[0044] (2) 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 and the production well. The working fluid pressure at the production well outlet increases, which enhances the working capacity of the turbine inlet working fluid, 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, help achieve the dual carbon goals, and avoid problems such as ground subsidence and collapse caused by groundwater exploitation.

[0046] (4) The present invention has developed a variety of 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 the 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] Among them: 1-CO2 storage tank; 2-first booster pump; 3-first valve; 4-injection well; 5-injection well wall; 6-bottom water-proof layer; 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 implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept 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-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-ORC composite power generation subsystem, with each other providing input and output, and the cooling water subsystem exchanges heat with the composite power generation subsystem through a 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] Wherein, 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 impermeable layer 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, the flash evaporation power generation unit and the 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 respectively connected to one end of the eighth valve 26 and one end of the ninth valve 27, 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 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, 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;

[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 turn.

[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-power generation integrated method comprises the following steps:

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

[0078] S2, using geothermal fluids to generate electricity 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 to the hydrothermal heat storage 7. The CO2 continuously displaces the geothermal water in the hydrothermal heat storage 7 to move to the bottom of the production well 10, and at the same time replaces the geothermal water in the pores, completing the geological storage of CO2, and extracting the geothermal fluid 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.

[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. Operation of 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 send the geothermal water into the separator 12, the ninth valve 27 is opened, the third valve 13 and the eighth valve 26 are closed, and the geothermal water is sent into the flash evaporator 28 after removing impurities, and is flash-evaporated into a vapor-liquid mixture in the flash evaporator 28 by reducing the pressure;

[0085] The saturated steam separated from the steam-liquid mixture is sent to the steam turbine 33 through the tenth valve 32 to perform work, driving the third generator 34 to generate electricity, and the 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;

[0086] The saturated water separated from the vapor-liquid mixture is sent to the evaporator 23 through the seventh valve 25 to transfer heat to the organic working medium. The organic working medium absorbs heat and is sent to the ORC turbine 29 to do 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 liquid in the second condenser 31, and then pressurized to the evaporation pressure by the working medium pump 24 and sent to the evaporator 23.

[0087] When the local hot water temperature is low, the seventh valve 25 is closed, the sixth valve 22 is opened, and the saturated water separated by the flash evaporator 28 is directly sent to the water storage tank 41 through the bypass. 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. Keep the flash evaporation unit and the ORC power generation unit open during the mid-stage of the combined power generation, and operate the transcritical CO2 power generation unit at the same time:

[0089] 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, 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 be injected into the ground together with the supercritical CO2 from the CO2 storage tank 1;

[0090] S23, in the later stage of compound 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 spaces of the hydrothermal heat storage 7 has been displaced by CO2, and the water content in the geothermal fluid at the outlet of the production well 10 has been reduced to the point where the flash evaporation and ORC power generation unit cannot be kept running stably. The eighth valve 26 and the ninth valve 27 are closed, and the third valve 13 is opened, leaving only the transcritical CO2 power generation unit running. When the CO2 flow rates in the injection well 4 and the production well 10 are consistent, the first valve 3 is closed to stop the operation of 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 heat storage and CO2 storage space to achieve the purpose of "storage-extraction-use" integration, without the need to artificially create underground heat storage space, saving construction costs.

[0093] The present invention adopts CO2 as the 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 an obvious 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 turbine inlet working fluid, improves the power generation performance of the system, and reduces the power consumption of the injected CO2, further reducing the operating cost.

[0094] The present invention can achieve geological storage of CO2, help achieve the dual carbon goals as soon as possible, and avoid problems such as ground subsidence and collapse caused by groundwater exploitation.

[0095] The present invention develops multiple operating modes of the ground composite power generation system, which can adjust the operating mode and structure according to the state of 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 fluid.

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

Claims

1. Hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system, characterized in that: It 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; Among them, 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 for working fluid condensation of the transcritical CO2-flash-ORC composite power generation subsystem.

2. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system according to claim 1 is characterized in that: The heat extraction subsystem comprises a CO2 injection unit, an underground heat storage and a geothermal well, wherein the geothermal well comprises an injection well (4) and a production well (10); The CO2 injection unit comprises 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); an injection well (4) and a 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-power generation integrated system according to claim 2 is characterized in that: The material of the injection well wall (5) of the injection well (4) is a high thermal conductivity material, and the material of the production well wall (9) of the production well (10) is a thermal insulation material.

4. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system according to claim 1 is characterized in that: 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, the flash evaporation power generation unit and the 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.

5. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system according to claim 4 is characterized in that: The transcritical CO2 power generation unit comprises 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 respectively connected to one end of the eighth valve (26) and one end of the ninth valve (27), 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).

6. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system according to claim 5 is characterized in that: The flash evaporation power generation unit comprises 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.

7. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system according to claim 6 is characterized in that: The ORC power generation unit comprises 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.

8. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system according to claim 7 is characterized in that: The cooling water subsystem comprises 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 a second circulating 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).

9. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated method according to claim 8 is applied to the hydrothermal heat storage CO2 cycle heat extraction-power generation integrated system according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: S1. Collecting geothermal fluid through the heat extraction subsystem; S2. Use geothermal fluid to generate electricity through a transcritical CO2-flash-ORC composite power generation subsystem.

10. The hydrothermal heat storage CO2 cycle heat extraction-power generation integrated method according to claim 9, 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 a 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). A 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. Operation of 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 cooling water in the third condenser (35), and the condensed water is sent into the water storage tank (41) through the eleventh valve (38); The saturated water separated from the vapor-liquid mixture is sent to the evaporator (23) through the seventh valve (25) to transfer heat to the organic working fluid. The organic working fluid absorbs heat and is then input 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 fluid pump (24) and sent to the evaporator (23). S22. Keep the flash evaporation unit and the ORC power generation unit open during the mid-stage of the combined power generation, and operate the transcritical CO2 power generation unit 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 compound 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.

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