Mechanical supercharging type constant-pressure compressed air energy storage system

Abstract

The invention discloses a mechanical supercharging type constant-pressure compressed air energy storage system which comprises an earth surface equipment system, an underground cavern and an underground pipeline, the earth surface equipment system comprises a water storage reservoir, mechanical or hydraulic supercharging equipment, an air compressor and a power generation expansion machine, and the height difference between the underground cavern and the water storage reservoir forms a natural water head. The bottom of the underground cavern is provided with a sump, the underground pipeline comprises a water conveying pipeline and a gas conveying pipeline, the upper end of the water conveying pipeline is communicated with the reservoir, the lower end of the water conveying pipeline is communicated with the sump, a first control valve, a second control valve and supercharging equipment are installed on the water conveying pipeline, and the upper end of the gas conveying pipeline is communicated with an air compressor through a third control valve. And the lower end of the gas pipeline is communicated with the top space of the underground cavern through the fourth control valve. According to the system, through dual control of natural water head and mechanical supercharging, the working pressure of the underground cavern during operation is always maintained at the target pressure, so that the lining and the surrounding rock are in a constant pressure working condition.

Description

Technical Field

[0001] This invention belongs to the field of compressed air energy storage (CAES), specifically relating to a mechanically boosted constant pressure compressed air energy storage system. Background Technology

[0002] With the increasing proportion of renewable energy in the power system, compressed air energy storage (CAES), as a large-scale, long-term energy storage technology, has shown promising application prospects in new power systems and has therefore attracted widespread attention. In current engineering practice and research, transformer-type CAES systems commonly use underground spaces such as salt caverns, artificial caverns, or abandoned mines as storage chambers, where the internal pressure exhibits typical periodic changes with charge-discharge cycles. Although these pressure changes can be controlled through reasonable design and support under suitable engineering geological conditions, they inevitably cause periodic loading and unloading of the surrounding rock and lining structure. This leads to a continuous shift in the stress path as operating conditions change, making it difficult to equate the long-term mechanical behavior of the underground storage cavern to static conditions, resulting in more complex cavern stability. Simultaneously, the periodic pressure changes also trigger temperature fluctuations, further complicating the system's thermal management design and adversely affecting overall energy efficiency.

[0003] To reduce the structural and thermodynamic control difficulties caused by pressure changes with air energy state, some research and engineering practices have explored the use of "water seals" or "water column compensation" to maintain relatively stable gas storage pressure. These systems utilize the hydrostatic properties of water to keep the pressure within the gas storage cavity relatively constant within a certain range. However, water-sealed constant pressure methods typically rely on natural head or the height difference of available water bodies, and their pressure level and stability are limited by natural conditions. In areas with significant topographic variations, such as marine areas, deep wells, or onshore regions, it is often difficult to obtain a head that matches the target gas storage pressure. Furthermore, during high-power energy release phases, the water compensation flow rate needs to be coordinated with the air discharge rate; otherwise, pressure deviations may still occur, and large-scale rapid water flow also places higher demands on control equipment. These factors mean that while existing water-sealed constant pressure solutions have engineering potential, there is still room for improvement in terms of controllability, applicability, and operational stability.

[0004] Against this backdrop, it is necessary to explore an energy storage method that can maintain the safety and stability of underground gas storage chambers while effectively reducing pressure fluctuations caused by changes in operating conditions. Summary of the Invention

[0005] To address the need for improved pressure regulation capabilities and expanded applicability of gas storage caverns, this invention proposes a constant-pressure compressed air energy storage concept combining natural water head and mechanical pressurization. This leads to a mechanically pressurized constant-pressure compressed air energy storage system. Its core objective is to achieve constant-pressure charging and discharging cycles of high-pressure air within underground caverns. Through dual control of natural water head and mechanical pressurization, this system maintains the operating pressure of the underground cavern at the target pressure during operation. P set This results in a constant pressure condition for the lining and surrounding rock.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a mechanically boosted constant-pressure compressed air energy storage system, including a surface equipment system, an underground cavern, and underground pipelines. The surface equipment system includes a reservoir, a mechanical or hydraulic booster, an air compressor, and a generator expander. The underground cavern is constructed in the rock mass below the reservoir. The structural stability of the underground cavern is supported by the lining and the surrounding rock. The height difference between the underground cavern and the reservoir constitutes a natural water head. A sump is provided at the bottom of the underground cavern. The underground pipeline includes a water supply pipeline and an air supply pipeline. The upper end of the water supply pipeline is connected to the reservoir, and the lower end is connected to the sump. A first control valve and a second control valve are respectively installed on the upper and lower parts of the water supply pipeline. The booster is connected to the pipeline of the water supply pipeline located between the first and second control valves. The upper end of the air supply pipeline is connected to the outlet of the air compressor through a third control valve and to the inlet of the generator expander through a fourth control valve. The lower end of the air supply pipeline is connected to the top space of the underground cavern.

[0007] This invention relates to a mechanically pressurized constant-pressure compressed air energy storage system. This system utilizes the combined effects of natural water head and mechanical pressurization to achieve constant-pressure operation. Its basic principle is to maintain a constant pressure within the underground cavern through natural water head, mechanical pressurization, and internal air pressure, avoiding frequent pressure fluctuations and achieving constant pressure on the lining and surrounding rock. This reduces long-term cyclic fatigue damage to the lining and surrounding rock structures, significantly improving the system's long-term operational safety. Natural water head can be provided by lakes, reservoirs, or the sea, and the underground cavern can be artificially excavated or converted from existing mine pits, salt caverns, etc.

[0008] In this invention's mechanically pressurized constant-pressure compressed air energy storage system, natural water head provides a stable static pressure for the underground cavern, ensuring a favorable pressure environment during static and low-power phases. Mechanical pressurization further pressurizes the compensating water during the energy release phase, maintaining the target pressure level throughout the entire charge / discharge cycle. By combining natural pressure with active regulation, this invention aims to improve the pressure fluctuations of traditional cavity-type CAES during the charge / discharge process. It also overcomes the limitations of insufficient control capabilities when relying solely on natural water head, resulting in a more balanced performance in terms of surrounding rock stress, thermal management, and operational controllability. Consequently, it offers greater engineering adaptability in various scenarios, including seabed, underground mines, and others.

[0009] Specifically, the water pipeline is installed in a first vertical shaft or a first inclined shaft excavated below the ground surface, the water collection pit is located at the bottom of the first vertical shaft or the first inclined shaft, and the gas pipeline is installed in a second vertical shaft or a second inclined shaft excavated below the ground surface.

[0010] Specifically, the reservoir can be a surface water body such as a lake, reservoir, or ocean.

[0011] The operation of the mechanically boosted constant-pressure compressed air energy storage system of this invention is divided into the following four stages: S1. Initial water filling: Open the first control valve and the second control valve to fill the water pit with water using natural water head. When the water fills the water delivery pipe and the bottom of the water pit, close the first control valve and the second control valve. S2. Air-filled energy storage: Turn on the air compressor and the third control valve to fill the underground cavern with air until the air pressure is slightly higher than the natural water head. Then, turn on the second control valve to continue filling the underground cavern with air until the set target pressure is reached. P set At this time, both the air pressure inside the underground cavern and the water pressure in the water pipes are... P set The air compressor and the third control valve are shut off, and the energy storage process is complete. S3. Energy Release and Constant Pressure Operation: The generator expander and the fourth control valve are activated. High-pressure air in the underground cavern drives the generator expander to generate electricity via the gas pipeline. Simultaneously, the pressurization equipment and the first control valve are activated. The pressurization equipment pressurizes the water in the reservoir to... P set Subsequently, water is injected into the underground cavern through pipelines to displace the discharged air volume. At this point, by precisely controlling the dynamic matching of the water injection flow rate and the energy release rate, the air pressure within the underground cavern is ensured to remain constant throughout the entire energy release process. P set To achieve stable and efficient power output, when the gas in the underground cavern is exhausted, the generator expander and the fourth control valve are shut off, power generation ends, and the "mechanical booster water injection and energy release power generation" is completed. S4. Subsequent Cycle Start-up: Restart the air compressor and the third control valve to refill the underground cavern with air. The water in the underground cavern is discharged back to the reservoir through the water pipeline. When the water level in the sump returns to the predetermined position, stop the air filling, shut off the air compressor and the third control valve, and the system enters the state at the completion of stage S2, ready for the next "mechanical pressurization water injection and energy release power generation". This process is repeated to achieve multiple energy release and constant pressure operation cycles.

[0012] Compared with the prior art, the present invention has the following advantages: 1. Constant pressure operation significantly reduces the risk of surrounding rock damage: The system, through the coordinated use of natural water head and mechanical pressurization water compensation, controls the operating pressure of the underground cavern at a constant pressure. P set This invention achieves constant pressure operation in an engineering sense. Compared with conventional compressed air energy storage systems where "charging and discharging cause large-scale periodic fluctuations in storage pressure," the system of this invention effectively avoids repeated rises and falls in internal pressure within underground caverns over a wide range, significantly reducing the stress cycle amplitude and rate of change borne by the surrounding rock. This constant pressure characteristic of the system of this invention has three advantages: 1) Suppress crack propagation and fatigue failure: The pressure fluctuates slowly within a small range, and the surrounding rock is in a relatively stable high-pressure stress field. The degree of repeated opening and closing of microcracks is greatly weakened, which can significantly slow down crack propagation and fatigue accumulation, and help maintain the long-term integrity of the cavern. 2) Reduce the uncertainty of “uncontrollable damage”: Under conventional large pressure cycling, joints, faults and weak interlayers in natural rock masses are prone to local instability during multiple loading-unloading processes, and the evolution path is difficult to predict; while near constant pressure operation makes the stress path more singular and mild, which is convenient for assessment and early warning through numerical simulation and monitoring methods, transforming the surrounding rock damage from “uncontrollable” to “assessable and manageable”. 3) Facilitates long-term safe life design: Under small-amplitude stress fluctuation conditions, the surrounding rock and lining structure can be designed for life under conditions close to "quasi-static load", which greatly reduces the risk of structural fatigue and leakage caused by high-frequency and large-amplitude pressure cycles, and provides a higher safety margin for the long-term high-pressure operation of the gas storage cavern. 2. Since the water seal characteristics of water are not affected by temperature and pressure changes, compared with traditional air compression energy storage systems, the mechanical booster constant pressure compressed air energy storage system of this invention exhibits higher reliability and durability in long-term operation, which makes the system have lower maintenance costs and can operate stably for a long time. 3. The system of the present invention effectively combines water potential energy with constant pressure regulation, which enables the system to store and release energy more efficiently, ensuring stable power generation quality. The system makes full use of energy storage space and takes into account multiple scenarios such as seawater / freshwater and seabed / land, and has an scalable and industrializable engineering path. 4. The system of this invention "decouples" the energy storage pressure from the natural water head depth, eliminating the requirement for strict matching between the two. This breaks the harsh geographical limitations of traditional water-sealed constant pressure energy storage, making the technology applicable to a wider range of regions and greatly increasing site selection flexibility. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the post-construction effect of the mechanically boosted constant-pressure compressed air energy storage system in the embodiment. The specific reference numerals in the figure are as follows: 1-Reservoir, 2-First control valve, 3-Boosting equipment, 4-Water pipeline, 5-First shaft, 6-Lined, 7-Underground cavern, 8-Sump pit, 9-Second control valve, 10-Gas pipeline, 11-Second shaft, 12-Fourth control valve, 13-Third control valve, 14-Air compressor, 15-Power generator expander, 16-Surrounding rock. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Components or structures not limited in this invention are all constructed using conventional techniques in the art.

[0015] Example: A mechanically boosted constant-pressure compressed air energy storage system, such as Figure 1 As shown, the structure includes a surface equipment system, an underground cavern 7, and underground pipelines. The surface equipment system includes a reservoir 1, a mechanical or hydraulic booster 3, an air compressor 14, and a generator expander 15. The reservoir 1 can be a lake, reservoir, or ocean. The underground cavern 7 is constructed within the rock mass below the reservoir 1. The structural stability of the underground cavern 7 is jointly supported by the lining 6 and the surrounding rock 16. The height difference between the underground cavern 7 and the reservoir 1 constitutes the natural water head. A sump pit 8 is provided at the bottom of the underground cavern 7. The underground pipelines include a water pipeline 4 and a gas pipeline 5. Pipeline 10, the upper end of water pipeline 4 is connected to reservoir 1 and the lower end is connected to sump 8. The upper and lower parts of water pipeline 4 are respectively equipped with first control valve 2 and second control valve 9. The booster device 3 is connected to the pipeline of water pipeline 4 located between the first control valve 2 and the second control valve 9. The upper end of gas pipeline 10 is connected to the outlet of air compressor 14 through third control valve 13 and to the inlet of generator expander 15 through fourth control valve 12. The lower end of gas pipeline 10 is connected to the top space of underground cavern 7.

[0016] The water pipeline 4 is installed in the first vertical shaft 5 (or the first inclined shaft) excavated below the ground surface, the water collection pit 8 is located at the bottom of the first vertical shaft 5, and the gas pipeline 10 is installed in the second vertical shaft 11 (or the second inclined shaft) excavated below the ground surface.

[0017] The operation of the above-mentioned mechanically boosted constant-pressure compressed air energy storage system is divided into the following four stages: S1. Initial water filling: Open the first control valve 2 and the second control valve 9 to fill the water collection pit 8 with water using natural water head. When the water fills the bottom of the water supply pipe 4 and the water collection pit 8, close the first control valve 2 and the second control valve 9. S2. Air Inflation and Energy Storage: Turn on the air compressor 14 and the third control valve 13 to inflate the underground cavern 7 until the air pressure is slightly higher than the natural water head. Then, turn on the second control valve 9 to continue inflating the underground cavern 7 until the set target pressure is reached. P set At this time, the air pressure in underground chamber 7 and the water pressure in water pipe 4 are both... P set The air compressor 14 and the third control valve 13 are turned off, and the energy storage process is completed. S3. Energy Release and Constant Pressure Operation: The generator expander 15 and the fourth control valve 12 are activated. High-pressure air in the underground cavern 7 drives the generator expander 15 to generate electricity via the gas pipeline 10. Simultaneously, the booster device 3 and the first control valve 2 are activated. The booster device 3 pressurizes the water in the reservoir 1 to... P set Subsequently, water is injected into underground chamber 7 via pipeline 4, displacing the discharged air volume. At this point, by precisely controlling the dynamic matching of the water injection flow rate and the energy release rate, the air pressure inside underground chamber 7 is ensured to remain constant throughout the entire energy release process. P set When the gas in underground chamber 7 is exhausted, the generator expander 15 and the fourth control valve 12 are closed, the power generation ends, and the "mechanical booster water injection and energy release power generation" is completed. S4. Subsequent cycle start-up: Restart the air compressor 14 and the third control valve 13 to refill the underground cavern 7 with air. The water in the underground cavern 7 is discharged back to the reservoir 1 through the water pipe 4. When the water level in the sump 8 returns to the predetermined position, stop the air filling, shut off the air compressor 14 and the third control valve 13, and the system enters the state at the completion of stage S2, ready for the next "mechanical pressurization water injection and energy release power generation". This process is repeated to achieve multiple energy release and constant pressure operation cycles.

[0018] Through the above-mentioned "charging-releasing-standby" working condition switching, this system achieves safe and efficient energy storage under high pressure and constant pressure conditions, and achieves constant pressure on lining 6 and surrounding rock 16, thereby reducing damage to the structure of lining 6 and surrounding rock 16 and significantly improving the long-term operational safety of the system.

Claims

1. A mechanically boosted constant-pressure compressed air energy storage system, characterized in that, The system includes a surface equipment system, an underground cavern, and underground pipelines. The surface equipment system includes a reservoir, a mechanical or hydraulic booster, an air compressor, and a generator expander. The underground cavern is constructed within the rock mass below the reservoir. The structural stability of the underground cavern is supported by the lining and surrounding rock. The height difference between the underground cavern and the reservoir constitutes a natural water head. A sump pit is provided at the bottom of the underground cavern. The underground pipelines include a water pipeline and an air pipeline. The upper end of the water pipeline is connected to the reservoir, and the lower end is connected to the sump pit. A first control valve and a second control valve are installed at the upper and lower parts of the water pipeline, respectively. The booster is connected to the water pipeline between the first and second control valves. The upper end of the air pipeline is connected to the outlet of the air compressor through a third control valve and to the inlet of the generator expander through a fourth control valve. The lower end of the air pipeline is connected to the top space of the underground cavern.

2. The mechanically boosted constant-pressure compressed air energy storage system according to claim 1, characterized in that, The water pipeline is installed in the first vertical shaft or the first inclined shaft excavated below the ground surface, the water collection pit is located at the bottom of the first vertical shaft or the first inclined shaft, and the gas pipeline is installed in the second vertical shaft or the second inclined shaft excavated below the ground surface.

3. The mechanically boosted constant-pressure compressed air energy storage system according to claim 1, characterized in that, The reservoir can be a lake, a water reservoir, or an ocean.

4. A mechanically boosted constant-pressure compressed air energy storage system according to claim 1, 2, or 3, characterized in that, Its operation is divided into the following four stages: S1. Initial water filling: Open the first control valve and the second control valve to fill the water pit with water using natural water head. When the water fills the water delivery pipe and the bottom of the water pit, close the first control valve and the second control valve. S2. Air-filled energy storage: Turn on the air compressor and the third control valve to fill the underground cavern with air until the air pressure is slightly higher than the natural water head. Then, turn on the second control valve to continue filling the underground cavern with air until the set target pressure is reached. P set At this time, both the air pressure inside the underground cavern and the water pressure in the water pipes are... P set The air compressor and the third control valve are shut off, and the energy storage process is complete. S3. Energy Release and Constant Pressure Operation: The generator expander and the fourth control valve are activated. High-pressure air in the underground cavern drives the generator expander to generate electricity via the gas pipeline. Simultaneously, the pressurization equipment and the first control valve are activated. The pressurization equipment pressurizes the water in the reservoir to... P set Subsequently, water is injected into the underground cavern through pipelines to displace the discharged air volume. At this point, by precisely controlling the dynamic matching of the water injection flow rate and the energy release rate, the air pressure within the underground cavern is ensured to remain constant throughout the entire energy release process. P set When the gas in the underground cavern is exhausted, the generator expander and the fourth control valve are shut off, power generation ends, and the "mechanical pressurization water injection and energy release power generation" is completed. S4. Subsequent Cycle Start-up: The air compressor and the third control valve are turned on again to refill the underground cavern with air. The water in the underground cavern is discharged back to the reservoir through the water pipeline. When the water level in the sump returns to the predetermined position, the air filling is stopped, the air compressor and the third control valve are turned off, and the system enters the state at the completion of stage S2, ready for the next "mechanical booster water injection and energy release power generation". This process is repeated to achieve multiple energy release and constant pressure operation cycles.

Images