Constant pressure air supply system for compressed air energy storage power generation system and operation method thereof

Abstract

The present invention provides a constant-pressure air supply system for a compressed air energy storage power generation system and an operating method thereof, comprising a first-stage motor, a first-stage compressor, a first-stage air cooler, a second-stage motor, a second-stage compressor, a second-stage air cooler, a third-stage motor, a third-stage compressor, a third-stage air cooler, a fourth-stage motor, a fourth-stage compressor, a fourth-stage air cooler, a heat storage tank, a cold storage tank, a heat storage medium circulation pump, a cold storage medium circulation pump, a generator, a third-stage expander, a second-stage expander, a first-stage expander, a third-stage air heater, a second-stage air heater, a first-stage air heater, an exhaust pipe, a high-pressure gas storage device, a normal-pressure water storage device, a constant-pressure pump, an air inlet shut-off valve, an air outlet shut-off valve, a water inlet shut-off valve, a drain shut-off valve, a constant-pressure pump outlet shut-off valve, a constant-pressure pump inlet shut-off valve, and other pipeline connectors required by the system. The present invention greatly reduces the volume of the high-pressure gas storage device and significantly reduces the system cost.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage systems, and in particular to a constant-pressure air supply system for a compressed air energy storage power generation system and an operating method thereof. Background Art

[0002] Among existing power storage technologies, pumped hydro and compressed air storage offer advantages such as large scale, low cost, and long lifespan, making them widely recognized as the most suitable physical energy storage technologies for large-scale deployment. Due to its relative maturity, pumped hydro is the only energy storage technology currently widely deployed in my country. However, it faces natural geographical limitations, particularly its geographical dislocation from my country's wind and solar energy resources. Furthermore, its capacity and functionality cannot fully meet the country's energy storage development needs (by 2050, installed energy storage capacity in my country is expected to reach 10%-15% of total installed power capacity, more than double the exploitable capacity of pumped hydro). Therefore, the development of other large-scale energy storage technologies beyond pumped hydro is imperative.

[0003] Compressed air energy storage has the advantages of large energy storage capacity, long energy storage cycle, and low specific investment, and is considered to be the most promising large-scale energy storage technology. Currently, most of the compressed air energy storage power stations developed in China are based on non-supplementary combustion and thermal storage compressed air energy storage technology. The system schematic diagram is shown in Figure 1 The energy storage and release process mainly goes through the following two stages:

[0004] First, during the compression and heat storage phase, electrical energy is converted into mechanical energy, using a compressor to compress atmospheric air into high-pressure air. The electric motor drives the compressor, gradually compressing the air. During this process, according to the first law of thermodynamics, the air pressure gradually increases as the compression progresses, accompanied by a significant temperature rise.

[0005] The high-temperature, high-pressure air then enters the thermal storage system, exchanging heat with a heat medium (such as water, thermal oil, or molten salt). During this heat storage process, most of the compressed air's thermal energy is transferred to the heat medium for storage. Simultaneously, the compressed air's temperature drops as its thermal energy is transferred to the heat medium. The cooled compressed air is then stored in the gas storage device, awaiting subsequent energy release.

[0006] Second, during the heat release and expansion phase, the high-temperature, high-pressure air first passes through a heat exchanger to exchange heat with the stored heat medium, releasing thermal energy. Through heat exchange, the stored heat medium cools down, while the compressed air regains some of its thermal energy, raising its temperature.

[0007] Next, the high-temperature, high-pressure air, rich in heat energy, enters the expander. The expansion process releases energy, driving the generator to generate electricity. During this expansion process, the pressure energy of the high-pressure air is converted into mechanical energy, thus achieving energy conversion. Simultaneously, the expansion process reduces the temperature and pressure of the compressed air, achieving both cooling and pressure reduction.

[0008] The heat release and expansion phases occur continuously, with heat exchange and expansion intertwined. The heat release process transfers heat energy to the compressed air through a heat exchanger, raising its temperature. The expansion process, on the other hand, utilizes the energy of the high-temperature, high-pressure air to expand, drive a generator to generate electricity, and reduce the temperature and pressure of the compressed air.

[0009] In this way, the heat release and expansion stages realize the conversion and utilization of energy, converting the stored thermal energy into electrical energy, and completing the energy circulation process in the compression and heat storage system.

[0010] It should be noted that in order to improve system parameters and power generation efficiency, the compression system usually adopts multi-stage series connection to increase the gas storage pressure and density, avoid excessive outlet temperature due to excessive compressor pressure ratio, and adopt staged compression + staged heat exchange method to gradually increase the air pressure and finally reach the maximum design pressure of the high-pressure gas storage device. In the multi-stage series compressor, the last stage compressor adopts full-load variable frequency operation, and the other stages of compressors all adopt the power frequency operation mode;

[0011] The heat storage and release system can be a single-stage or two-stage series system depending on the type of heat storage medium.

[0012] The expansion system generally adopts multi-stage series connection. For example, the exhaust of the previous stage expander is reheated and then enters the next stage expander to continue working.

[0013] Currently, the largest portion of the system cost is primarily comprised of equipment costs for the compression system, expansion power generation system, and heat exchange and storage system, as well as the gas storage system. For projects utilizing natural salt cavern gas storage, these three components account for approximately 45% of the total cost, while the gas storage system accounts for 6% to 9%. The remainder of the investment primarily covers conventional electrical system equipment, construction costs, installation costs, and other expenses. For projects utilizing artificial caverns and compressed air tanks for gas storage, the gas storage system can contribute over 30% of the total cost.

[0014] A comprehensive analysis of the project data of domestic projects that have completed feasibility studies and entered the construction stage, taking into account the average cost levels of three main gas storage methods: for compressed air energy storage projects with a discharge time of 6 hours, the cost of salt cavern gas storage is relatively low, about 600 yuan / kW, and the cost of salt caverns with better conditions can be further reduced, the cost of artificial chambers is about 2,600 yuan / kW; the cost of compressed air storage tanks is about 7,500 yuan / kW. The specific process and construction plan under the same gas storage method also have a certain impact on the cost. Taking artificial chambers as an example, different geological conditions, excavation plans, support plans, and sealing plans will all result in differences in engineering costs. Based on the projects currently under construction and in the early stages of development, the unit cost of chambers is approximately 2,000 to 3,500 yuan / m 3 .

[0015] In the compressed air energy storage power stations currently being developed in China, the pressure at the expander inlet continues to drop during the energy release process, but the drop cannot be too large. This is mainly due to the following reasons:

[0016] (1) Impact on energy conversion efficiency: The efficiency of the expander is closely related to the inlet pressure. A drop in inlet pressure will cause the expander to deviate from its designed high-efficiency range, thereby affecting the efficiency of energy conversion. Expanders are usually optimized for a certain inlet pressure range during design. If this range is exceeded, the efficiency of the expander will be affected, thereby reducing the energy conversion efficiency of the entire system.

[0017] (2) Reliability and stability requirements: The expander is a key energy conversion device in the system. Frequent and excessive fluctuations in intake pressure will impose a greater workload and pressure shock on the expander, increasing its operational instability and the risk of fatigue damage. To ensure the reliability and long-term stable operation of the expander, the fluctuation range of intake pressure needs to be kept as small as possible.

[0018] (3) Stability of control system operation: A compressed air energy storage power station is a complex system. Excessive fluctuations in intake pressure can affect the stability and control performance of the entire system. The control system needs to adjust and respond to changing intake pressure conditions. Excessive fluctuations increase the complexity and accuracy of the system, potentially leading to unstable or uncontrolled system operation.

[0019] For compressed air energy storage power stations using natural salt caverns, the natural volume of the salt caverns is relatively large, and the pressure fluctuation range is generally limited to around 1.5MPa, which can ensure the stability of the expander inlet pressure as much as possible. In projects using artificially excavated underground chambers or above-ground compressed air storage tanks to store gas, the pressure fluctuation range can be increased to 6MPa, allowing more gas to be released in a relatively small volume, minimizing the project cost.

[0020] As the pressure at the expander inlet continues to drop, conventional compressed air energy storage power stations use sliding pressure to generate electricity during the energy release process. When the expander is not equipped with an air supply pipeline, the unit's power generation capacity continues to decrease over time; when the expander is equipped with an air supply pipeline, the unit's power generation capacity remains unchanged, but the intake pressure decreases and the flow rate increases. The gas pressure will continue to deviate from the design value, and the expander's power generation efficiency will decrease accordingly.

[0021] In order to achieve the set pressure fluctuation range during the expansion power generation process, after the energy release is completed and the high-pressure gas storage device releases the compressed air required for power generation, a certain pressure, namely the bottom air pressure, must still be maintained, and the corresponding compressed air volume is the bottom air volume.

[0022] In conventional compressed air energy storage systems, the bottom pressure is usually set higher than the pressure of the second-to-last compressor. This is to ensure that the final variable frequency drive compressor can be put into operation smoothly during the initial stage of energy storage. In other words, all series compressors need to be started during the energy storage process.

[0023] Setting a base pressure higher than the pressure of the penultimate compressor ensures sufficient airflow through the final variable-frequency compressor at the start of energy storage, enabling normal operation. This allows all compressors to participate in the air compression process during energy storage, continuously injecting air into the high-pressure gas storage device until the device reaches its maximum design pressure.

[0024] By reasonably setting the bottom air pressure, the coordinated operation of various parts of the system during the energy storage process can be ensured, and the compressor running at the rated frequency can be prevented from overspeeding and tripping due to the inability to maintain back pressure.

[0025] Taking a 300MW / 1800MWh (6h energy release) compressed air energy storage power station as an example, when using underground artificial chambers or above-ground compressed air storage tanks to store gas, the bottom gas pressure is 10.5MPa. During the energy storage process, the storage gas pressure increases from the bottom gas pressure to 16.5MPa, with a pressure difference of 6MPa; during the energy release process, the pressure in the high-pressure gas storage device continues to drop to 10.5MPa, and the system returns to its initial state, ready for the next cycle.

[0026] According to engineering calculations, the entire energy release process consumes approximately 12,200 tons of gas. After the energy release is completed or before the energy storage begins, the high-pressure gas storage device only stores the bottom gas volume at a pressure of 10.5 MPa. After the energy storage is completed, this gas volume and the bottom gas volume are stored together in the high-pressure gas storage device at a pressure of 16.5 MPa. According to the ideal gas state equation, the volume of the high-pressure gas storage device should be 176,900 m 3 The gas volume before energy storage is 29,800 tons, and the total gas volume after energy storage is 42,000 tons. 3According to calculations, the cost of the gas storage system will reach 531 million yuan.

[0027] While gas storage systems using salt caverns are relatively inexpensive, they require a long time and high electricity costs to build up a base pressure in the caverns for energy storage. Initial operating costs are significantly higher than those using underground man-made chambers or above-ground compressed air storage tanks. Furthermore, my country's natural salt cavern resources are limited. Many high-quality, large-capacity salt caverns have been developed as natural gas storage facilities for strategic reserves or seasonal peak-shaving. Salt caverns suitable for compressed air energy storage power plants are even scarcer. Compressed air energy storage power plants using man-made chambers or above-ground compressed air storage tanks, on the other hand, do not require excessive consideration of location and have more universal construction conditions. However, reducing the cost of the gas storage system has become a key factor restricting the development of compressed air energy storage power plants.

[0028] The excessive volume of the high-pressure gas storage device is mainly caused by the amount of bottom gas, and the amount of bottom gas is necessary to ensure that the pressure fluctuation range is minimized during the sliding pressure power generation process and to improve the power generation efficiency.

[0029] The key to reducing the cost of gas storage systems lies in finding effective ways to reduce storage volume while maintaining high-efficiency power generation. By comprehensively considering factors such as storage volume, technological innovation, and system optimization, a suitable solution to reduce the cost of gas storage systems is needed to promote the development of compressed air energy storage technology and provide an economically viable solution for large-scale energy storage implementation. Summary of the Invention

[0030] This invention aims to address the problem of high-pressure gas storage devices requiring a certain amount of backing gas, resulting in excessive volume and, consequently, increased construction costs. To mitigate the effects of this backing gas, the pressure in the high-pressure gas storage device must be maintained constant during energy release. The expander can then utilize a constant-pressure intake system, maintaining power generation efficiency. This completely eliminates the backing gas requirement, allowing the high-pressure gas storage device to only accommodate the amount of gas required for power generation. This significantly reduces volume and significantly reduces the construction cost of the gas storage system.

[0031] To achieve the above-mentioned object of the invention, the present invention provides a constant-pressure air supply system for a compressed air energy storage power generation system, comprising a first-stage motor, a first-stage compressor, a first-stage air cooler, a second-stage motor, a second-stage compressor, a second-stage air cooler, a third-stage motor, a third-stage compressor, a third-stage air cooler, a fourth-stage motor, a fourth-stage compressor, a fourth-stage air cooler, a heat storage tank, a cold storage tank, a heat storage medium circulation pump, a cold storage medium circulation pump, a generator, a third-stage expander, a second-stage expander, a first-stage expander, a third-stage air heater, a second-stage air heater, a first-stage air heater, an exhaust pipe, a high-pressure air storage device, a normal-pressure water storage device, a constant-pressure pump, an air inlet shut-off valve, an air outlet shut-off valve, a water inlet shut-off valve, a drain shut-off valve, a constant-pressure pump outlet shut-off valve, a constant-pressure pump inlet shut-off valve, and other pipe connectors required by the system;

[0032] The first-stage motor, the first-stage compressor, the first-stage air cooler, the second-stage motor, the second-stage compressor, the second-stage air cooler, the third-stage motor, the third-stage compressor, the third-stage air cooler, the fourth-stage motor, the fourth-stage compressor, the fourth-stage air cooler, and the high-pressure air storage device are connected in sequence, and an air intake shut-off valve is provided between the fourth-stage air cooler and the high-pressure air storage device;

[0033] The high-pressure gas storage device, the first-stage air heater, the first-stage expander, the second-stage air heater, the second-stage expander, the third-stage air heater, the third-stage expander, the generator, and the exhaust pipe are connected in sequence, and a gas outlet shut-off valve is provided between the high-pressure gas storage device and the first-stage air heater;

[0034] The heat storage tank, heat storage medium circulation pump, first-stage air heater, second-stage air heater, third-stage air heater, cold storage tank, cold storage medium circulation pump, first-stage air cooler, second-stage air cooler, third-stage air cooler, and fourth-stage air cooler are connected in sequence to transfer heat through the circulating medium;

[0035] The high-pressure gas storage device is connected to the normal-pressure water storage device through a pipeline. A water inlet shut-off valve is provided near the high-pressure gas storage device. The pipeline near the normal-pressure water storage device is divided into an outlet pipe and a return pipe. A constant-pressure pump is provided on the outlet pipe and a constant-pressure pump inlet shut-off valve and a constant-pressure pump outlet shut-off valve on the inlet and outlet pipes thereof. A drainage shut-off valve is provided on the return pipe.

[0036] The normal pressure water storage device is connected to the atmosphere through a pipeline.

[0037] Furthermore, the effective volume of the normal-pressure water storage device should not be smaller than that of the high-pressure gas storage device.

[0038] Furthermore, the pipeline connecting the high-pressure gas storage device and the first-stage air heater should be connected from the top of the high-pressure gas storage device.

[0039] Furthermore, the pipeline connecting the high-pressure gas storage device and the normal-pressure water storage device should be led out from the bottom of the high-pressure gas storage device, or the pipeline should be extended into the vicinity of the lowest point inside the high-pressure gas storage device.

[0040] The present invention also provides an operating method of the constant pressure air supply system for the compressed air energy storage power generation system:

[0041] Before the system stores energy, the high-pressure gas storage device is filled with normal-pressure liquid water, and the normal-pressure water storage device is filled with normal-pressure air and is connected to the atmosphere;

[0042] When the system stores energy, air from the atmosphere is compressed by the first-stage compressor driven by the first-stage motor and then heated and pressurized. The cold storage medium from the cold storage tank enters the first-stage air cooler to exchange heat with the air, and then enters the heat storage tank for storage after being heated. The low-temperature and high-pressure air is continuously compressed into the high-pressure gas storage device, and water is squeezed into the normal-pressure water storage device through the pipeline until there is no water in the high-pressure gas storage device. The water inlet shut-off valve, the drain shut-off valve, and the constant-pressure pump outlet shut-off valve of the pipeline connecting the high-pressure gas storage device and the normal-pressure water storage device are closed to continuously store compressed air.

[0043] When the pressure in the high-pressure gas storage device reaches the exhaust pressure of the first-stage compressor, the valve between the first-stage compressor and the high-pressure gas storage device is closed, and the second-stage compressor is opened to continue compressing the air and store the heated heat storage medium in the heat storage tank;

[0044] When the pressure in the high-pressure gas storage device reaches the exhaust pressure of the secondary compressor, the valve between the secondary compressor and the high-pressure gas storage device is closed, and at the same time, the valve between the tertiary compressor and its outlet to the high-pressure gas storage device is opened to continue compressing the air and store the heated heat storage medium in the heat storage tank;

[0045] When the pressure in the high-pressure gas storage device reaches the exhaust pressure of the third-stage compressor, the valve between the third-stage compressor and the high-pressure gas storage device is closed, and at the same time, the valve between the fourth-stage compressor and its outlet to the high-pressure gas storage device is opened, and the air is continued to be compressed and the heated heat storage medium is stored in the heat storage tank until the air pressure in the high-pressure gas storage device reaches the maximum design pressure. The air inlet shut-off valve between the fourth-stage compressor and the high-pressure gas storage device is closed to complete the energy storage process;

[0046] When the system releases energy, the gas outlet shut-off valve between the high-pressure gas storage device and the first-stage expander is opened, and the constant pressure pump is simultaneously turned on to continuously pressurize the water in the normal-pressure water storage device into the high-pressure gas storage device to maintain the pressure in the high-pressure gas storage device constant; the high-pressure gas is heated by the first-stage air heater and then enters the first-stage expander to generate power; the exhaust gas pressure and temperature decrease after the expansion and work process in the first-stage expander, and then enters the second-stage air heater, the second-stage expander, the third-stage air heater, and the third-stage expander in sequence. The low-temperature, low-pressure air at the outlet of the third-stage expander cannot be used for work, and is directly discharged into the atmosphere after overcoming the resistance of the exhaust pipe;

[0047] When all the gas in the high-pressure gas storage device is released, the constant pressure pump is turned off, and the water inlet shut-off valve and the drain shut-off valve between the high-pressure gas storage device and the normal-pressure water storage device are opened. The pressurized water in the high-pressure gas storage device is depressurized to normal pressure through the pipeline, and the entire system is restored to its original state ready for storage.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The volume of the high-pressure gas storage device is greatly reduced, and the system cost is significantly reduced;

[0050] (2) The compressor uses multi-stage compression. After energy storage begins, the number of compressor stages in series is gradually increased until the pressure in the high-pressure gas storage device reaches the design value. The power consumption during the compression process gradually increases, and the total power consumption is significantly reduced.

[0051] (3) During the energy release process, the internal pressure of the high-pressure gas storage device and the inlet pressure of the expander remain unchanged. The expander can achieve long-term power generation at rated load without the need to set up an air supply system. The air supply system is eliminated, and the expansion power generation system is greatly simplified.

[0052] (4) The expander inlet pressure always maintains a high pressure state, the gas density is high, the volume flow rate is low, the expander equipment size and the inlet pipe specifications are small, reducing the initial investment;

[0053] (5) The system operating parameters remain unchanged during the expansion power generation process, and the operation control is simple.

[0054] (6) The internal pressure of the gas storage reservoir remains constant, and the temperature will not drop due to the pressure drop caused by the continuous release of gas.

[0055] (7) After the energy release is completed, all equipment and pipelines in the system are at normal pressure, which is convenient for inspection and maintenance, and safety is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The invention provides a constant pressure air supply system for a compressed air energy storage power generation system;

[0057] Figure 2(a) is a schematic diagram of the system state at the start of energy storage;

[0058] FIG2( b ) is a schematic diagram of the system state when the first-stage compressor is operating alone;

[0059] Figure 2(c) is a schematic diagram of the system status in the late stage of the single-stage compressor operation;

[0060] Figure 3 This is a schematic diagram of the system status after the secondary compressor is put into use;

[0061] Figure 4 This is a schematic diagram of the system status after the three-stage compressor is put into use;

[0062] Figure 5 This is a schematic diagram of the system status after the four-stage compressor is put into use;

[0063] Figure 6(a) is a schematic diagram of the system state at the start of energy release;

[0064] Figure 6(b) is a schematic diagram of the system status during the energy release process;

[0065] Figure 6(c) is a schematic diagram of the system state after energy release is completed;

[0066] Among them: 1. First-stage motor; 2. First-stage compressor; 3. First-stage air cooler; 4. Second-stage motor; 5. Second-stage compressor; 6. Second-stage air cooler; 7. Third-stage motor; 8. Third-stage compressor; 9. Third-stage air cooler; 10. Fourth-stage motor; 11. Fourth-stage compressor; 12. Fourth-stage air cooler; 13. Heat storage tank; 14. Cold storage tank; 15. Heat storage medium circulation pump; 16. Cold storage medium circulation pump; 17. Generator; 18. Three-stage expander; 19. Two-stage expander; 20. One-stage expander; 21. Three-stage air heater; 22. Two-stage air heater; 23. One-stage air heater; 24. Exhaust pipe; 25. High-pressure air storage device; 26. Normal-pressure water storage device; 27. Constant-pressure pump; 28. Air inlet shut-off valve; 29. ​​Air outlet shut-off valve; 30. Water inlet shut-off valve; 31. Drain shut-off valve; 32. Constant-pressure pump outlet shut-off valve; 33. Constant-pressure pump inlet shut-off valve. DETAILED DESCRIPTION

[0067] To help those skilled in the art better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the drawings are for illustrative purposes only and are not to be construed as limiting this patent. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and are not to be construed as limiting this patent.

[0068] like Figure 1 As shown, the present invention provides a constant pressure air supply system for a compressed air energy storage power generation system, including a first-stage motor 1, a first-stage compressor 2, a first-stage air cooler 3, a second-stage motor 4, a second-stage compressor 5, a second-stage air cooler 6, a third-stage motor 7, a third-stage compressor 8, a third-stage air cooler 9, a fourth-stage motor 10, a fourth-stage compressor 11, a fourth-stage air cooler 12, a heat storage tank 13, a cold storage tank 14, a heat storage medium circulation pump 15, a cold storage medium circulation pump 16, a generator 17, a third-stage expander 18, a second-stage expander 19, a first-stage expander 20, a third-stage air heater 21, a second-stage air heater 22, a first-stage air heater 23, an exhaust pipe 24, a high-pressure gas storage device 25, a normal-pressure water storage device 26, a constant-pressure pump 27, an air inlet shut-off valve 28, an air outlet shut-off valve 29, a water inlet shut-off valve 30, a drainage shut-off valve 31, a constant-pressure pump outlet shut-off valve 32, a constant-pressure pump inlet shut-off valve 33, and other pipe connectors required by the system.

[0069] The first-stage motor 1, the first-stage compressor 2, the first-stage air cooler 3, the second-stage motor 4, the second-stage compressor 5, the second-stage air cooler 6, the third-stage motor 7, the third-stage compressor 8, the third-stage air cooler 9, the fourth-stage motor 10, the fourth-stage compressor 11, the fourth-stage air cooler 12, and the high-pressure air storage device 13 are connected in sequence, and an air intake shut-off valve 28 is provided between the fourth-stage air cooler 12 and the high-pressure air storage device 26.

[0070] The high-pressure gas storage device 25, the first-stage air heater 23, the first-stage expander 20, the second-stage air heater 22, the second-stage expander 19, the third-stage air heater 21, the third-stage expander 18, the generator 17, and the exhaust pipe 24 are connected in sequence, and a gas outlet shut-off valve 29 is provided between the high-pressure gas storage device 25 and the first-stage air heater 23;

[0071] The heat storage tank 13, the heat storage medium circulation pump 15, the primary air heater 23, the secondary air heater 22, the tertiary air heater 21, the cold storage tank 14, the cold storage medium circulation pump 16, the primary air cooler 3, the secondary air cooler 6, the tertiary air cooler 9, and the quaternary air cooler 12 are connected in sequence to transfer heat through the circulating medium.

[0072] The high-pressure gas storage device 25 is connected to the normal-pressure water storage device 26 through a pipeline. The pipeline should be connected from the top of the high-pressure gas storage device 25 to ensure that all the stored air can be released during the energy release process. A water inlet shut-off valve 30 is set near the high-pressure gas storage device 25. The pipeline near the normal-pressure water storage device 26 is divided into an outlet pipe and a return pipe. The outlet pipe is provided with a constant-pressure pump 27 and a constant-pressure pump inlet shut-off valve 33 and a constant-pressure pump outlet shut-off valve 32 on its inlet and outlet pipes, and a drain shut-off valve 31 is provided on the return pipe. The outlet pipe of the normal-pressure water storage device 26 should be connected from its bottom, and the outlet should be higher than the inlet elevation of the constant-pressure pump 27 to ensure that when the system releases energy, water can smoothly enter the constant-pressure pump 27 to increase the pressure and be injected into the high-pressure gas storage device 26.

[0073] The atmospheric pressure water storage device is connected to the atmosphere through a pipe.

[0074] As shown in Figure 2(a), when the system starts to store energy, the high-pressure gas storage device 25 is filled with normal-pressure liquid water, and the normal-pressure water storage device 26 is filled with normal-pressure air and is connected to the atmosphere;

[0075] As shown in Figure 2(b), the primary motor 1 consumes electricity to drive the primary compressor 2. Atmospheric air is compressed by the primary compressor 2, increasing its temperature and pressure. Cold storage medium from the cold storage tank 14 enters the primary air cooler 3, exchanges heat with the air, and, after heating, enters the heat storage tank 14 for storage. The low-temperature, high-pressure air is continuously compressed into the high-pressure air storage device 25, while water is squeezed through a pipeline to the normal-pressure water storage device 26.

[0076] As shown in Figure 2(c), after all the water in the high-pressure gas storage device 25 is pressed into the normal-pressure water storage device 26, the water inlet shut-off valve 30 and the drain shut-off valve 31 of the pipe connecting the high-pressure gas storage device 25 and the normal-pressure water storage device 26 are closed to continuously store compressed air.

[0077] like Figure 3 As shown, when the pressure in the high-pressure gas storage device 25 reaches the exhaust pressure of the first-stage compressor 2, the valve between the first-stage compressor 2 and the high-pressure gas storage device 25 is closed, and at the same time, the valve between the second-stage compressor 5 and its outlet to the high-pressure gas storage device 25 is opened to continue compressing the air and store the heated heat storage medium in the heat storage tank 13.

[0078] like Figure 4 As shown, when the pressure in the high-pressure gas storage device 25 reaches the exhaust pressure of the secondary compressor 5, the valve between the secondary compressor 5 and the high-pressure gas storage device 25 is closed, and at the same time, the valve between the tertiary compressor 8 and its outlet to the high-pressure gas storage device 25 is opened to continue compressing the air and store the heated heat storage medium in the heat storage tank 13.

[0079] like Figure 5As shown, when the pressure in the high-pressure gas storage device 25 reaches the exhaust pressure of the three-stage compressor 18, the valve between the three-stage compressor 18 and the high-pressure gas storage device 25 is closed, and at the same time, the valve between the four-stage compressor 11 and its outlet to the high-pressure gas storage device 25 is opened to continue compressing the air and store the heated heat storage medium in the heat storage tank 13 until the air pressure in the high-pressure gas storage device 25 reaches the maximum design pressure, completing the energy storage process.

[0080] Heat is transferred between the heat storage tank 13, air heaters at various stages, the cold storage tank 14, and air coolers at various stages through a circulating medium.

[0081] As shown in Figures 6(a) and 6(b), when the system begins to release energy, the outlet shutoff valve 29 at the outlet of the high-pressure gas storage device 25 is opened, and the constant-pressure pump 27 is simultaneously started to continuously pressurize the water in the normal-pressure water storage device 26 into the high-pressure gas storage device 25 to maintain a constant pressure within the high-pressure gas storage device 25. The high-pressure gas is heated by the first-stage air heater 23 and then enters the first-stage expander 20 to generate power. The exhaust gas from the first-stage expander 20 undergoes expansion and power generation, with its pressure and temperature reduced. The exhaust gas then enters the second-stage air heater 22, the second-stage expander 19, the third-stage air heater 21, and the third-stage expander 18 in sequence. The low-temperature, low-pressure air at the outlet of the third-stage expander 18 cannot be used for power generation and is directly discharged into the atmosphere after overcoming the resistance of the exhaust pipe 24.

[0082] As shown in Figure 6(c), after all the gas in the high-pressure gas storage device 25 is released, the constant pressure pump 27 is turned off, and the water inlet shut-off valve 30 and the water discharge shut-off valve 31 between the high-pressure gas storage device 25 and the normal-pressure water outlet device 26 are opened. The pressurized water in the high-pressure gas storage device 25 is depressurized to normal pressure through the pipeline, and the entire system is restored to the initial state ready for storage.

[0083] The technical innovation method proposed in the present invention can ensure that the air intake parameters of the expander remain unchanged, so the expansion power generation system does not need to be equipped with an air supply pipeline and can maintain high-efficiency power generation operating conditions for a long time.

[0084] The present invention utilizes the incompressibility of water and injects water of the same volume as the gas required for power generation into the high-pressure gas storage device during the energy release process, thereby maintaining the pressure in the high-pressure gas storage device constant. There is no need to set a bottom gas pressure in the high-pressure gas storage device, so the volume of the high-pressure gas storage device is determined entirely according to the gas volume required for energy release and the design pressure, and the volume of the high-pressure gas storage device can be greatly reduced. Similarly, taking a 300MW / 1800MWh compressed air energy storage power station as an example, due to the cancellation of the bottom gas volume, the volume of the high-pressure gas storage device is 88,300 m 3 , which is half of the conventional solution. According to the unit cost of underground artificial chamber 3000 yuan / m 3Calculation shows that the cost of the gas storage system is only RMB 265 million. Although the volume of the atmospheric water storage device is basically the same as that of the high-pressure gas storage device, its cost is much lower than that of the underground artificial chamber. 3 It is estimated that the total cost of the gas storage system is 291 million yuan, which is about 55% of the conventional plan.

[0085] At the same time, because the high-pressure gas storage device maintains a constant pressure, this stability allows the expander's inlet pressure to be maintained at the designed value, so the expander does not need to consider the gas replenishment operating conditions. This advantage brings two significant benefits: equipment size and cost reduction.

[0086] First, the expander design can be simplified because no additional air supply system is required. In conventional compressed air power generation systems, if the expander's inlet pressure fluctuates significantly, air supply operation must be considered to ensure stable power generation. Furthermore, low-pressure inlet conditions inevitably increase the gas volume flow rate, which in turn increases the size of the equipment and pipelines. High-pressure gas storage devices utilize a constant-pressure air supply, resulting in a higher inlet density for the expander, allowing for minimal equipment and pipeline design.

[0087] Secondly, since an air supply system is not required, the overall system cost is significantly reduced. Air supply systems require additional piping and valves to introduce excess air, increasing project complexity and investment costs. In contrast, a constant-pressure air supply system eliminates these additional equipment and piping, reducing overall project costs.

[0088] The constant pressure system can ensure that all the gas in the high-pressure gas storage device is used for power generation. Therefore, there is no need to pre-compress the bottom gas into the high-pressure gas storage device before energy storage, which saves a lot of time and electricity. At the same time, since there is no need to set the bottom gas pressure, the pressure in the high-pressure gas storage device is normal pressure when energy storage starts, and gas injection can be achieved by starting the first-stage compressor. During the energy storage process, the second, third, and fourth-stage compressors are successively put into operation, so the power consumption of the system is gradually increased. In conventional compressed air energy storage systems, from the beginning to the end of energy storage, all compressors in series need to be put into operation, and the power consumed by the compressors in the compression process continues to maintain a high level of operation. Therefore, in the system proposed by the present invention, although the energy release process increases the power consumption of the constant pressure pump, since the power consumption during the energy storage process is greatly reduced, the overall efficiency is basically equivalent to that of the conventional solution.

[0089] Taking a 300MW / 1800MWh compressed air energy storage power station (8h energy storage, 6h energy release) as an example, during the energy storage process, the compressors at all levels are gradually put into operation, with a total power consumption of 1965MWh. During the energy release process, the expander is always in a constant pressure power generation state, with a total power generation of 1800MWh. After deducting the 393MWh of power consumption of the constant pressure pump when it is continuously running, the overall storage-power generation conversion efficiency can reach 71.6% (excluding plant power consumption).

Claims

1. A constant pressure air supply system for a compressed air energy storage power generation system, characterized by: The invention comprises a first-stage motor (1), a first-stage compressor (2), a first-stage air cooler (3), a second-stage motor (4), a second-stage compressor (5), a second-stage air cooler (6), a third-stage motor (7), a third-stage compressor (8), a third-stage air cooler (9), a fourth-stage motor (10), a fourth-stage compressor (11), a fourth-stage air cooler (12), a heat storage tank (13), a cold storage tank (14), a heat storage medium circulation pump (15), a cold storage medium circulation pump (16), a generator (17), a third-stage expander (1 8), a secondary expander (19), a primary expander (20), a tertiary air heater (21), a secondary air heater (22), a primary air heater (23), an exhaust pipe (24), a high-pressure gas storage device (25), a normal-pressure water storage device (26), a constant-pressure pump (27), an air inlet shut-off valve (28), an air outlet shut-off valve (29), a water inlet shut-off valve (30), a drainage shut-off valve (31), a constant-pressure pump outlet shut-off valve (32), a constant-pressure pump inlet shut-off valve (33) and other pipe connectors required for the system; The first-stage motor (1), the first-stage compressor (2), the first-stage air cooler (3), the second-stage motor (4), the second-stage compressor (5), the second-stage air cooler (6), the third-stage motor (7), the third-stage compressor (8), the third-stage air cooler (9), the fourth-stage motor (10), the fourth-stage compressor (11), the fourth-stage air cooler (12), and the high-pressure gas storage device (25) are connected in sequence, and an air intake shutoff valve (28) is provided between the fourth-stage air cooler (12) and the high-pressure gas storage device (25); The high-pressure gas storage device (25), the first-stage air heater (23), the first-stage expander (20), the second-stage air heater (22), the second-stage expander (19), the third-stage air heater (21), the third-stage expander (18), the generator (17), and the exhaust pipe (24) are connected in sequence, and an air outlet shut-off valve (29) is provided between the high-pressure gas storage device (25) and the first-stage air heater (23); The heat storage tank (13), the heat storage medium circulation pump (15), the first-stage air heater (23), the second-stage air heater (22), the third-stage air heater (21), the cold storage tank (14), the cold storage medium circulation pump (16), the first-stage air cooler (3), the second-stage air cooler (6), the third-stage air cooler (9), and the fourth-stage air cooler (12) are connected in sequence to transfer heat through the circulating medium; The high-pressure gas storage device (25) is connected to the normal-pressure water storage device (26) through a pipeline. A water inlet shut-off valve (30) is provided near the high-pressure gas storage device (25). The pipeline near the normal-pressure water storage device (26) is divided into an outlet pipe and a return pipe. The outlet pipe is provided with a constant-pressure pump (27) and a constant-pressure pump inlet shut-off valve (33) and a constant-pressure pump outlet shut-off valve (32) on its inlet and outlet pipes. The return pipe is provided with a drainage shut-off valve (31). The normal pressure water storage device (26) is connected to the atmosphere through a pipeline.

2. A constant pressure air supply system for a compressed air energy storage power generation system according to claim 1, characterized in that: The effective volume of the normal-pressure water storage device (26) should not be smaller than that of the high-pressure gas storage device (25).

3. The constant pressure air supply system for a compressed air energy storage power generation system according to claim 1, characterized in that: The pipeline connecting the high-pressure gas storage device (25) and the primary air heater (23) should be connected from the top of the high-pressure gas storage device (25).

4. The constant pressure air supply system for a compressed air energy storage power generation system according to claim 1, characterized in that: The pipeline connecting the high-pressure gas storage device (25) and the normal-pressure water storage device (26) should be led out from the bottom of the high-pressure gas storage device (25), or the pipeline should be extended into the vicinity of the lowest point inside the high-pressure gas storage device (25).

5. A method for operating a constant pressure air supply system for a compressed air energy storage power generation system according to any one of claims 1 to 4, characterized in that: Before the system stores energy, the high-pressure gas storage device (25) is filled with normal-pressure liquid water, and the normal-pressure water storage device (26) is filled with normal-pressure air and is connected to the atmosphere; When the system stores energy, air from the atmosphere is compressed by the first-stage compressor (2) driven by the first-stage motor (1) and then heated and pressurized. The cold storage medium from the cold storage tank (14) enters the first-stage air cooler (3) to exchange heat with the air, and enters the heat storage tank (13) for storage after being heated. The low-temperature high-pressure air is continuously pressed into the high-pressure gas storage device (25), and water is squeezed into the normal-pressure water storage device (26) through the pipeline until there is no water in the high-pressure gas storage device (25). The water inlet shut-off valve (30), the water discharge shut-off valve (31) and the constant-pressure pump outlet shut-off valve (32) of the pipeline connecting the high-pressure gas storage device (25) and the normal-pressure water storage device (26) are closed to continuously store compressed air. When the pressure in the high-pressure gas storage device (25) reaches the exhaust pressure of the first-stage compressor (2), the valve between the first-stage compressor (2) and the high-pressure gas storage device (25) is closed, and the second-stage compressor (5) is opened to continue compressing the air and store the heated heat storage medium in the heat storage tank (13); When the pressure in the high-pressure gas storage device (25) reaches the exhaust pressure of the secondary compressor (5), the valve between the secondary compressor (5) and the high-pressure gas storage device (25) is closed, and at the same time, the valve between the tertiary compressor (8) and its outlet to the high-pressure gas storage device (25) is opened to continue compressing the air and store the heated heat storage medium in the heat storage tank (13); When the pressure in the high-pressure gas storage device (25) reaches the exhaust pressure of the three-stage compressor (8), the valve between the three-stage compressor (8) and the high-pressure gas storage device (25) is closed, and at the same time, the valve between the four-stage compressor (11) and its outlet to the high-pressure gas storage device (25) is opened, and the air is continued to be compressed and the heated heat storage medium is stored in the heat storage tank (13) until the air pressure in the high-pressure gas storage device (25) reaches the maximum design pressure, and the air intake shut-off valve (28) between the four-stage compressor (11) and the high-pressure gas storage device (25) is closed to complete the energy storage process; When the system releases energy, the outlet shut-off valve (29) between the high-pressure gas storage device (25) and the first-stage expander (20) is opened, and the constant pressure pump (27) is simultaneously opened to continuously pressurize the water in the normal-pressure water storage device (26) into the high-pressure gas storage device (25) to maintain the pressure in the high-pressure gas storage device (25) constant; the high-pressure gas is heated by the first-stage air heater (23) and then enters the first-stage expander (20) to generate power; the exhaust pressure and temperature after the expansion and power generation process of the first-stage expander (20) are reduced, and then the exhaust gas enters the second-stage air heater (22), the second-stage expander (19), the third-stage air heater (21), and the third-stage expander (18) in sequence; the low-temperature, low-pressure air at the outlet of the third-stage expander (18) cannot be used for power generation, and is directly discharged into the atmosphere after overcoming the resistance of the exhaust pipe (24); When all the gas in the high-pressure gas storage device (25) is released, the constant pressure pump (27) is turned off, and the water inlet shut-off valve (30) and the water discharge shut-off valve (31) between the high-pressure gas storage device (25) and the normal-pressure water storage device (26) are opened. The pressurized water in the high-pressure gas storage device (25) is depressurized to normal pressure through the pipeline, and the entire system is restored to its original state ready for storage.

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