Compressed air energy storage system based on underground cavern of hydropower station and efficiency improving method

Abstract

The invention discloses a compressed air energy storage system based on an underground cavity of a hydropower station and an efficiency improving method. The system comprises an air compression part, a gas storage part, an air expansion part and a cold and heat storage part. The gas storage part is mainly composed of various throttling control valves, a construction adit series and an ejector. According to the compressed air energy storage system, the ejector is introduced to adjust the output capacity of the construction adit series, the amount of cushion air in the construction adit series is reduced, and the circulation efficiency and the energy storage density of the compressed air energy storage system based on the underground cavern of the hydropower station are improved. The system can be used for assisting a power system to realize peak load shifting of a power grid, and can also be coupled with renewable energy heating to improve the permeability of renewable energy.

Description

Technical Field

[0001] The present invention relates to the technical field of physical energy storage, and in particular to a compressed air energy storage system based on an underground cavern of a hydropower station and an efficiency improvement method. Background Art

[0002] With the rapid development of the global economy, human demand for energy is growing. However, long-term over-reliance on traditional fossil energy such as coal, oil, and natural gas has led to a large amount of greenhouse gas emissions, and the problem of global warming is becoming increasingly serious. In recent years, extreme climate events have occurred frequently, the ecological environment has deteriorated, and human survival and development are facing unprecedented challenges. In order to cope with global warming and seek a path for sustainable development, the alternative role of new energy has become increasingly prominent. The development and utilization of new energy such as wind energy and solar energy has provided a solution to energy and environmental problems. However, wind energy and solar energy are intermittent and volatile, and have great uncertainty. In order to improve the absorption capacity of new energy, it is particularly urgent to build large-scale energy storage facilities. Compressed air energy storage has the advantages of large energy storage capacity, long energy storage time, environmental friendliness, high safety factor, short construction period, and high cycle efficiency. Compressed air energy storage is regarded as one of the new energy storage technologies with great development potential due to these advantages.

[0003] Compressed air energy storage technology is mainly derived from gas turbine technology. Early compressed air energy storage systems directly added a gas storage reservoir to the gas turbine to achieve the temporal separation of the energy storage and release processes. This system, like a gas turbine, requires the combustion of fossil fuels to supplement heat. This type of compressed air energy storage system is called a traditional supplementary combustion compressed air energy storage system. This system not only has low system efficiency, but the burning of fuel will cause pollution and increase the system operating costs. An alternative to the traditional supplementary combustion compressed air energy storage system is the advanced adiabatic compressed air energy storage system, which stores the compression heat and heats the air during the expansion stage. This system has a high conversion efficiency and is the mainstream compressed air energy storage method today. The advanced adiabatic compressed air energy storage system mainly relies on the throttle valve to maintain the stability of the expander inlet pressure. This system requires the gas storage reservoir to retain a portion of unusable gas as cushion gas. Due to the low density of high-pressure air and the presence of cushion gas, this system requires a larger volume of gas storage reservoir to store high-pressure air. Therefore, the energy storage density of the system is relatively low. At present, an effective solution is the liquid air energy storage system. Liquid air energy storage further cools the high-pressure air to liquid and stores it as liquid air, which significantly reduces the volume of the gas storage reservoir. However, the system efficiency of the liquid air energy storage system is low, and the low-temperature storage of liquid air is difficult, so it has not been widely used.

[0004] An ejector is a device that uses high-pressure fluid to eject low-pressure fluid to mix and generate a medium-pressure fluid. It has a variety of applications in compressed air energy storage systems with multiple streams. In a compressed air energy storage system with multiple gas storage reservoirs, the ejector can increase the energy storage volume of the compressed air energy storage system through the ejection effect, thereby improving the system cycle efficiency and increasing the energy storage density of the gas storage reservoir. Summary of the invention

[0005] The purpose of the present invention is to provide a compressed air energy storage system and efficiency improvement method based on the underground caverns of hydropower stations, so as to improve the performance of advanced adiabatic compressed air energy storage systems. The underground caverns of hydropower stations are generally large in scale, high in strength, and large in number. The volume of each underground cavern of a hydropower station is generally different. In this system, the ejector is used to reduce the amount of cushioning air in the construction branch cavern group in the underground cavern of the hydropower station, thereby improving the system circulation efficiency and energy storage density. The present invention has the advantages of flexibility, high efficiency, stable output power and high energy storage density. It can be applied to the power generation and grid-connected occasions of hydropower stations, effectively increase the energy storage density of the construction branch cavern group, and increase the peak shaving and valley filling capacity of the hydropower station.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] According to a first aspect of the present invention, there is provided a compressed air energy storage system based on an underground cavern of a hydropower station, comprising an air compressor unit, the air compressor unit being driven by an electric motor unit, the outlet of the air compressor unit being connected to an inlet of a cooler via a pipeline, the outlet of the cooler being connected to an inlet of a main control valve via a pipeline, the outlet of the main control valve being connected to an inlet of a construction branch tunnel opening control valve series via a pipeline, the outlet of the construction branch tunnel opening control valve series being connected to an inlet of a construction branch tunnel opening control valve series via a pipeline, the inlet of the construction branch tunnel opening control valve series and the outlet of the main control valve being connected to an inlet of a bypass throttling valve via a pipeline, the inlet of the construction branch tunnel opening control valve series and the outlet of the main control valve being connected to an inlet of a bypass control valve via a pipeline, The outlet of the branch tunnel series is connected to the second fluid inlet of the ejector through the construction branch tunnel outlet control valve series, the bypass control valve outlet is connected to the first fluid inlet of the ejector through a pipeline, the ejector outlet is connected to the ejector control valve inlet through a pipeline, the bypass throttling valve outlet and the ejector control valve outlet are commonly connected to the preheater inlet, the preheater outlet is connected to the air expansion unit inlet through a pipeline, the air expansion unit is connected to a generator set, and also includes a hot water tank, the hot water tank outlet is connected to the No. 2 pressure pump inlet through a pipeline, the No. 2 pressure pump outlet is connected to the cold water tank inlet through an interstage heater, the cold water tank outlet is connected to the No. 1 pressure pump inlet through a pipeline, and the No. 1 pressure pump outlet is connected to the hot water tank inlet through an interstage cooler.

[0008] Furthermore, the air compressor unit includes a No. 1 compressor, a No. 2 compressor, and a No. 3 compressor connected in series in sequence, and an interstage cooler is connected in series between the No. 1 compressor, the No. 2 compressor, and the No. 3 compressor.

[0009] Furthermore, the air compressor unit compresses the air into high-temperature and high-pressure gas, which is stored in the construction branch tunnel series after passing through the interstage cooler and the cooler releases heat, and the released heat is stored in the hot water tank.

[0010] Furthermore, the air expansion unit includes a No. 1 expander, a No. 2 expander, and a No. 3 expander connected in series in sequence, and an interstage heater is connected in series between the No. 1 expander, the No. 2 expander, and the No. 3 expander.

[0011] Furthermore, the air expansion unit generates electricity by expanding high-pressure air, and the exhaust gas is discharged into the environment. At the same time, the preheater and the interstage heater are used to heat the air between the expander stages, and the water cooled by the preheater and the interstage heater is stored in a cold water tank.

[0012] Furthermore, the number of the series of construction branch holes is at least two, and the volume of each construction branch hole in the series of construction branch holes is generally different.

[0013] Furthermore, each construction branch tunnel entrance of the construction branch tunnel series is connected to a construction branch tunnel entrance control valve, and each construction branch tunnel outlet of the construction branch tunnel series is connected to a construction branch tunnel outlet control valve.

[0014] Furthermore, the construction branch tunnel outlet control valve series is connected to the first fluid inlet of the ejector, and the construction branch tunnel entrance control valve series is connected to the second fluid inlet of the ejector via a bypass control valve.

[0015] Furthermore, the ejector is a variable-size ejector, which can change the size of its throat area in real time according to demand. The ejector can eject the first fluid in a high-pressure state and the second fluid in a low-pressure state into a medium-pressure fluid at the outlet, so that the air of the rated cushion pressure in the construction branch hole can be fully deflated to the minimum cushion pressure.

[0016] According to a second aspect of the present invention, there is also provided a method for improving the efficiency of a compressed air energy storage system based on an underground cavern of a hydropower station, comprising:

[0017] In the energy storage process, the inflation of the construction branch tunnel series is divided into two steps. In the first step, the first three compressors work in series, and the fourth compressor is set not to work. The ambient air undergoes three-stage compression and interstage cooling to be compressed to above 10MPa. The high-pressure air passes through the main control valve and the valves of the construction branch tunnel opening control valve series, and the pressure of each construction branch tunnel in the construction branch tunnel series is inflated to above 10MPa in turn; in the second step, the four-stage compressor is set to work in series to compress the air to the rated energy storage pressure. The rated energy storage pressure air passes through the main control valve and the valves of the construction branch tunnel opening control valve series, and the pressure of each construction branch tunnel in the construction branch tunnel series is inflated to the rated energy storage pressure in turn. This inflation method can reduce the energy loss caused by the mixing of high and low pressure gases when the construction branch tunnel series is inflated, thereby reducing the total power consumption of the air compressor unit during the energy storage process and improving the system cycle efficiency.

[0018] During the energy release process, the high-pressure air in the smallest construction branch tunnel in the construction branch tunnel series is first throttled to the rated cushion gas pressure through the bypass throttle valve until the bypass throttle valve opening reaches the maximum, at which time the bypass throttle valve is closed, and then the high-pressure gas in the second smallest construction branch tunnel in the construction branch tunnel series passes through the construction branch tunnel port control valve and the bypass control valve of the corresponding construction branch tunnel port control valve series as the first fluid of the ejector, while the low-pressure gas in the smallest construction branch tunnel in the construction branch tunnel series passes through the fully opened construction branch tunnel outlet control valve of the corresponding construction branch tunnel outlet control valve series as the second fluid of the ejector. The ejector is sized to maintain the ejector outlet pressure at the rated energy release pressure until the high-pressure gas in the smallest construction branch tunnel in the construction branch tunnel series is released to the lowest cushion gas pressure, and then the air in the second smallest construction branch tunnel in the construction branch tunnel series is first throttled to the rated cushion gas pressure through the bypass throttle valve, and then the air in the third smallest construction branch tunnel in the construction branch tunnel series is throttled to the rated cushion gas pressure. The air in the construction branch tunnel draws out the air in the second smallest construction branch tunnel, and so on, until the largest construction branch tunnel in the construction branch tunnel series is directly throttled to the rated air cushion pressure through the bypass throttling valve, and the air at the rated energy release pressure expands in the air expansion unit, and the air expansion unit drives the generator set to generate electricity. The low-temperature air generated in the expansion process absorbs heat through the interstage heater and preheater to generate electricity, and is then discharged into the environment. The working fluid water cooled during the expansion process is stored in the cold water tank, completing the conversion of air pressure heat and thermal energy into electrical energy. This deflation process can reduce the amount of air cushion in each construction branch tunnel when the construction branch tunnel series is deflated, so as to achieve the following beneficial effects: First, the reduction in the amount of air cushion in the construction branch tunnel series increases the output gas volume entering the air expansion unit, thereby extending the system energy release time and improving the system efficiency; Second, when the volume of the construction branch tunnel series is constant, the reduction in the amount of air cushion increases the total amount of gas charged and discharged, and the system energy storage density is improved.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] Firstly, the present invention sets up a two-step inflation process to slide the air pressure in the construction branch tunnel series to the rated energy storage pressure, thereby reducing the energy loss caused by the mixing of high and low pressure gases when the construction branch tunnel series is inflated, thereby reducing the total power consumption of the air compressor unit in the energy storage process and improving the system circulation efficiency.

[0021] Secondly, the system of the present invention utilizes the characteristics of large scale and large number of underground caverns in hydropower stations, and introduces an ejector to adjust the output pressure of the construction branch cavern series of the hydropower station underground caverns. The application of the ejector reduces the amount of cushioning air in the construction branch cavern series, which increases the output gas volume entering the air expansion unit, thereby extending the energy release time of the system, increasing the total amount of air for charging and discharging, and improving the system circulation efficiency and energy storage density. The system has the advantages of high energy storage density and stable power output, which can effectively improve the energy storage capacity of the hydropower station and has important engineering application value and scientific significance for accelerating the transformation of my country's energy structure.

[0022] Furthermore, the present invention introduces an ejector into the energy storage system. Compared with the traditional single throttle valve method of controlling pressure, the ejector uses the gas in the high-pressure gas storage reservoir to eject the gas in the low-pressure gas storage reservoir during the application stage, thus avoiding throttling losses. The efficiency of this system will be higher than that of the traditional compressed air energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art; obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 The present invention is a schematic structural diagram of a compressed air energy storage system based on an underground cavern of a hydropower station according to an embodiment of the present invention.

[0025] Figure 1 In: 1. Electric motor unit; 2. Air compressor unit; 3. Interstage cooler; 4. Cooler; 5. Main control valve; 6. Bypass throttle valve; 7. Construction branch tunnel entrance control valve series; 8. Bypass control valve; 9. Construction branch tunnel series; 10. Construction branch tunnel outlet control valve series; 11. Ejector; 12. Ejector control valve; 13. Preheater; 14. Air expansion unit; 15. Interstage heater; 16. Generator unit; 17. No. 2 pressure pump; 18. Hot water tank; 19. Cold water tank; 20. No. 1 pressure pump. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0027] It should be noted that the technical terms used in the specification and claims of the present invention should be understood by persons with ordinary skills in the technical field to which the present invention belongs. The terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. "Connected" or "connected" and similar words are not limited to physical or mechanical connections, nor are they limited to direct or indirect connections.

[0028] A compressed air energy storage system based on the underground cavern of a hydropower station, such as Figure 1 As shown, the system is mainly composed of an air compression part, a gas storage part, an air expansion part, and a cold and heat storage part. The gas storage part is mainly composed of various throttling control valves, a construction branch tunnel system, and an ejector.

[0029] The invention comprises an air compressor unit 2, wherein the air compressor unit 2 is driven by an electric motor unit 1, the outlet of the air compressor unit 2 is connected to the inlet of a cooler 4 through a pipeline, the outlet of the cooler 4 is connected to the inlet of a main control valve 5 through a pipeline, the outlet of the main control valve 5 is connected to the inlet of a construction branch hole opening control valve series 7 through a pipeline, the outlet of the construction branch hole opening control valve series 7 is connected to the inlet of a construction branch hole series 9 through a pipeline, the inlet of the construction branch hole opening control valve series 7 and the outlet of the main control valve 5 are connected to the inlet of a bypass throttle valve 6 through a pipeline, the inlet of the construction branch hole opening control valve series 7 and the outlet of the main control valve 5 are connected to the inlet of a bypass control valve 8 through a pipeline, and the outlet of the construction branch hole series 9 is connected to an ejector 11 through a construction branch hole outlet control valve series 10. The second fluid inlet, the outlet of the bypass control valve 8 is connected to the first fluid inlet of the ejector 11 through a pipeline, the outlet of the ejector 11 is connected to the inlet of the ejector control valve 12 through a pipeline, the outlet of the bypass throttling valve 6 and the outlet of the ejector control valve 12 are commonly connected to the inlet of the preheater 13, the outlet of the preheater 13 is connected to the inlet of the air expansion unit 14 through a pipeline, the air expansion unit 14 is connected to a generator set 16, and also includes a hot water tank 18, the outlet of the hot water tank 18 is connected to the inlet of the No. 2 pressure pump 17 through a pipeline, the outlet of the No. 2 pressure pump 17 is connected to the inlet of the cold water tank 19 through the interstage heater 15, the outlet of the cold water tank 19 is connected to the inlet of the No. 1 pressure pump 20 through a pipeline, and the outlet of the No. 1 pressure pump 20 is connected to the inlet of the hot water tank 18 through the interstage cooler 3.

[0030] Each construction branch hole entrance of the construction branch hole series 9 is connected to a construction branch hole entrance control valve, and each construction branch hole outlet of the construction branch hole series 9 is connected to a construction branch hole outlet control valve.

[0031] The present invention is based on advanced adiabatic compressed air energy storage technology. During the low electricity consumption period, the electric energy is converted into the pressure potential energy and internal energy of the air through a compressor and stored in the construction branch tunnel of the underground cavern of the hydropower station. During the peak electricity consumption period, the stored energy is converted into electric energy and released through an expander. The main advantages include two aspects: 1. The two-step inflation process is set up to reduce the total power consumption of the air compressor unit during the energy storage process and improve the system circulation efficiency; 2. The ejector reduces the amount of cushioning air in the construction branch tunnel series in the underground cavern of the hydropower station, further improving the system circulation efficiency and energy storage density. In the ejector application stage, the gas in the high-pressure gas storage reservoir is used to eject the gas in the low-pressure gas storage reservoir, which also avoids throttling losses.

[0032] According to a second aspect of the present invention, there is also provided a method for improving the efficiency of a compressed air energy storage system based on an underground cavern of a hydropower station, comprising:

[0033] In the energy storage process, the inflation of the construction branch tunnel series 9 is divided into two steps. In the first step, the first three compressors work in series, and the fourth compressor is set not to work. The ambient air undergoes three-stage compression and interstage cooling processes to be compressed to above 10MPa. The high-pressure air passes through the main control valve 5 and the valves of the construction branch tunnel opening control valve series 7, and the pressure of each construction branch tunnel in the construction branch tunnel series 9 is inflated to above 10MPa in turn; in the second step, the four-stage compressor is set to work in series to compress the air to the rated energy storage pressure. The rated energy storage pressure air passes through the main control valve 5 and the valves of the construction branch tunnel opening control valve series 7, and the pressure of each construction branch tunnel in the construction branch tunnel series 9 is inflated to the rated energy storage pressure in turn. This inflation method can reduce the energy loss caused by the mixing of high and low pressure gases when the construction branch tunnel series 9 is inflated, thereby reducing the total power consumption of the air compressor unit 2 during the energy storage process and improving the system cycle efficiency.

[0034] During the energy release process, the high-pressure air in the smallest construction branch hole in the construction branch hole series 9 is first throttled to the rated cushion gas pressure through the bypass throttle valve, until the bypass throttle valve 6 reaches the maximum opening, at which time the bypass throttle valve 6 is closed, and then the high-pressure gas in the second smallest construction branch hole in the construction branch hole series 9 passes through the construction branch hole port control valve of the corresponding construction branch hole port control valve series 7 and the bypass control valve 6 as the first fluid of the ejector 11, and the low-pressure gas in the smallest construction branch hole in the construction branch hole series 9 passes through the construction branch hole outlet control valve of the corresponding construction branch hole outlet control valve series 10 which is fully opened as the second fluid of the ejector 11. The ejector 11 is sized so that the outlet pressure of the ejector 11 is maintained at the rated energy release pressure, until the high-pressure gas in the smallest construction branch hole in the construction branch hole series 9 is released to the lowest cushion gas pressure, and then the air in the second smallest construction branch hole in the construction branch hole series 9 is first throttled to the rated cushion gas pressure through the bypass throttle valve 6, and then the air in the third smallest construction branch hole in the construction branch hole series 9 is throttled to the rated cushion gas pressure. The air in the construction branch tunnel is ejected to the air in the second smallest construction branch tunnel, and so on, until the largest construction branch tunnel in the construction branch tunnel series 9 is directly throttled to the rated cushion air pressure through the bypass throttling valve 6, and the air under the rated energy release pressure is expanded in the air expansion unit 14, and the air expansion unit 14 drives the generator set 16 to generate electricity. The low-temperature air generated in the expansion process absorbs heat through the interstage heater 15 and the preheater 13 to generate electricity, and is then discharged into the environment. The working fluid water cooled during the expansion process is stored in the cold water tank 19, completing the conversion of air pressure heat and thermal energy into electrical energy. The deflation process can reduce the amount of cushion air in each construction branch tunnel when the construction branch tunnel series 9 is deflated, so as to achieve the following beneficial effects: First, the reduction in the amount of cushion air in the construction branch tunnel series 9 increases the output gas volume entering the air expansion unit 14, thereby extending the system energy release time and improving the system efficiency; Second, when the volume of the construction branch tunnel series 9 is constant, the reduction in the amount of cushion air increases the total amount of gas charged and discharged, and the system energy storage density is improved.

[0035] The present invention is further described in detail below in conjunction with specific implementation cases, which are intended to explain the present invention rather than to limit it.

[0036] Reference Figure 1 , a schematic diagram of a compressed air energy storage system based on the underground cavern of a hydropower station is used to describe its working principle in detail. The main working principle is described as follows:

[0037] During the energy storage process, the air in the environment is compressed into high-temperature and high-pressure gas by the air compressor unit 2, and is cooled and released into high-pressure gas in the interstage heat exchanger 3 of the air compressor unit 2 and the cooler 4 after the final compressor. In this process, the electric energy drives the motor unit 1 to drive the air compressor unit 2 to compress the air, realizing the conversion of electric energy into air pressure energy and thermal energy. The compressed and cooled high-pressure air enters the construction branch tunnels in the construction branch tunnel series 9 in sequence for storage. Preferably, the energy storage and inflation process is divided into two steps. The cold water in the cold water tank 19 is pressurized by the No. 1 pressure pump 20, and then absorbs the compression heat generated by the compression process through the cooler 4 and the interstage heater 3, and is stored in the hot water tank 18. The energy storage process is completed;

[0038] During the energy release process, the high-pressure air in the smallest construction branch tunnel in the construction branch tunnel series 9 is throttled to the design pressure through the bypass throttle valve 6, and then absorbs the compression heat stored in the hot water tank 18 in the preheater 13 to enter the air expansion unit 14, and further absorbs the compression heat in the hot water tank 18 through the interstage heater 15 in the air expansion unit 14. The air expansion machine drives the generator set 16 to generate electricity and send the electricity to the power grid. This process continues until the bypass throttle valve 6 opens to the maximum. At this time, the bypass throttle valve 6 is no longer available. The bypass throttle valve 6 is completely closed, and the high-pressure gas in the second smallest construction branch tunnel in the construction branch tunnel series 9 flows through the construction branch tunnel opening control valve of the corresponding construction branch tunnel opening control valve series 7 and the bypass control valve 8 as the first fluid of the ejector 11. The low-pressure gas in the smallest construction branch tunnel in the construction branch tunnel series 9 that has undergone a round of power generation flows through the construction branch tunnel outlet control valve of the corresponding construction branch tunnel outlet control valve series 10 that is fully opened as the second fluid of the ejector 11 The ejector mixes the fluids at the two inlets in the ejector and adjusts the size so that the outlet maintains a stable design pressure. This process continues until the ejector 11 is no longer available. Next, the second smallest construction branch hole in the construction branch hole series 9 is throttled to the design pressure through the bypass throttling valve 6 and enters the inlet of the preheater 13, and undergoes the same process as the high-pressure gas in the smallest construction branch hole, and so on, until the largest construction branch hole in the construction branch hole series 9 is directly throttled to the design pressure through the bypass throttling valve 6. The air at the design pressure is heated by the preheater 13 and then expanded in the air expansion unit 14 to generate electricity. During the entire expansion process, the air before the inlet of the preheater 13 remains stable. During the expansion process, the stable output electric energy is sent to the power grid. The low-temperature air generated in the expansion process absorbs heat through the interstage heater 15 and the preheater 13 to generate electricity, and is then directly discharged into the environment. The working medium water after cooling during the expansion process is stored in the cold water tank 19, completing the conversion of air pressure heat and thermal energy into electrical energy, and the energy release process is completed.

[0039] The ejector 11 can adjust its size by itself to maintain the pressure of the mixed fluid at the ejector 11 outlet stable when the pressure of the gas storage reservoir is constantly changing.

[0040] In addition, heat sources such as solar heat and geothermal heat can be used to heat the high-pressure air through the preheater 13 and the interstage heater 15 to increase the inlet temperature before the expander and the power generation capacity of the expander.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A compressed air energy storage system based on an underground cavern of a hydropower station and an efficiency improvement method, characterized in that: The invention comprises an air compressor unit, which is driven by an electric motor unit, wherein the outlet of the air compressor unit is connected to the inlet of a cooler through a pipeline, the outlet of the cooler is connected to the inlet of a main control valve through a pipeline, the outlet of the main control valve is connected to the inlet of a construction branch hole opening control valve series through a pipeline, the outlet of the construction branch hole opening control valve series is connected to the inlet of a construction branch hole series through a pipeline, the inlet of the construction branch hole opening control valve series and the outlet of the main control valve are connected to the inlet of a bypass throttling valve through a pipeline, the inlet of the construction branch hole opening control valve series and the outlet of the main control valve are connected to the inlet of a bypass control valve through a pipeline, and the outlet of the construction branch hole series passes through a construction branch hole outlet control valve The gate series is connected to the second fluid inlet of the ejector, the bypass control valve outlet is connected to the first fluid inlet of the ejector through a pipeline, the ejector outlet is connected to the ejector control valve inlet through a pipeline, the bypass throttling valve outlet and the ejector control valve outlet are commonly connected to the preheater inlet, the preheater outlet is connected to the air expansion unit inlet through a pipeline, the air expansion unit is connected to a generator set, and also includes a hot water tank, the hot water tank outlet is connected to the No. 2 pressure pump inlet through a pipeline, the No. 2 pressure pump outlet is connected to the cold water tank inlet through an interstage heater, the cold water tank outlet is connected to the No. 1 pressure pump inlet through a pipeline, and the No. 1 pressure pump outlet is connected to the hot water tank inlet through an interstage cooler; A method for improving the efficiency of a compressed air energy storage system based on an underground cavern of a hydropower station is also provided. In the energy storage process, the inflation of the construction branch tunnel series is carried out in two steps. In the first step, the first three compressors work in series, and the fourth compressor is set not to work. The ambient air undergoes three-stage compression and interstage cooling to be compressed to an initial inflation pressure. The high-pressure air passes through the main control valve and each valve of the construction branch tunnel opening control valve series, and the pressure of each construction branch tunnel series is inflated to the initial inflation pressure in turn. In the second step, four compressors are set to work in series to compress the air to the rated energy storage pressure. The rated energy storage pressure air passes through the main control valve and each valve of the construction branch tunnel opening control valve series, and the pressure of each construction branch tunnel series is inflated to the rated energy storage pressure in turn. This inflation method can reduce the energy loss caused by the mixing of high and low pressure gases when the construction branch tunnel series is inflated, thereby reducing the total power consumption of the air compressor unit during the energy storage process and improving the system circulation efficiency. During the energy release process, the high-pressure air in the smallest construction branch tunnel in the construction branch tunnel series is first throttled to the rated cushion gas pressure through the bypass throttle valve until the bypass throttle valve opening reaches the maximum, at which time the bypass throttle valve is closed, and then the high-pressure gas in the second smallest construction branch tunnel in the construction branch tunnel series passes through the construction branch tunnel port control valve and the bypass control valve of the corresponding construction branch tunnel port control valve series as the first fluid of the ejector, while the low-pressure gas in the smallest construction branch tunnel in the construction branch tunnel series passes through the fully opened construction branch tunnel outlet control valve of the corresponding construction branch tunnel outlet control valve series as the second fluid of the ejector. The ejector is sized to maintain the ejector outlet pressure at the rated energy release pressure until the high-pressure gas in the smallest construction branch tunnel in the construction branch tunnel series is released to the lowest cushion gas pressure, and then the air in the second smallest construction branch tunnel in the construction branch tunnel series is first throttled to the rated cushion gas pressure through the bypass throttle valve, and then the air in the third smallest construction branch tunnel in the construction branch tunnel series is throttled to the rated cushion gas pressure. The air in the largest construction branch tunnel is ejected to the air in the second smallest construction branch tunnel, and so on, until the largest construction branch tunnel in the construction branch tunnel series is directly throttled to the rated cushion air pressure through the bypass throttling valve, and the air under the rated energy release pressure is expanded in the air expansion unit, and the air expansion unit drives the generator set to generate electricity. The low-temperature air generated in the expansion process absorbs heat through the interstage heater and preheater to generate electricity and is then discharged into the environment. The working fluid water cooled in the expansion process is stored in the cold water tank to complete the conversion of air pressure heat and thermal energy into electrical energy. This deflation process can reduce the amount of cushion air in each construction branch tunnel when the construction branch tunnel series is deflated, so as to achieve the following beneficial effects: First, the reduction in the amount of cushion air in the construction branch tunnel series increases the output gas volume entering the expansion unit, thereby extending the system energy release time and improving the system efficiency; Second, when the volume of the construction branch tunnel series is constant, the reduction in the amount of cushion air increases the total amount of gas charged and discharged, and the system energy storage density is improved.

2. A compressed air energy storage system and efficiency improvement method based on an underground cavern of a hydropower station according to claim 1, characterized in that: The number of the series of construction branch holes is at least two, and the volume of each construction branch hole in the series of construction branch holes is generally different.

3. A compressed air energy storage system and efficiency improvement method based on an underground cavern of a hydropower station according to claim 1, characterized in that: Each construction branch hole entrance of the construction branch hole series is connected to a construction branch hole entrance control valve, and each construction branch hole outlet of the construction branch hole series is connected to a construction branch hole outlet control valve.

4. A compressed air energy storage system and efficiency improvement method based on an underground cavern of a hydropower station according to claim 1, characterized in that: The construction branch tunnel outlet control valve series is connected to the first fluid inlet of the ejector, and the construction branch tunnel entrance control valve series is connected to the second fluid inlet of the ejector through a bypass control valve.

5. A compressed air energy storage system and efficiency improvement method based on an underground cavern of a hydropower station according to claim 1, characterized in that: The ejector is a variable-size ejector that can change the size of its throat area in real time according to demand. The ejector can eject the first fluid in a high-pressure state and the second fluid in a low-pressure state into a medium-pressure fluid at the outlet, so that the air with the rated cushion pressure in the construction branch tunnel can be fully deflated to the minimum cushion pressure.

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