CN114810238B - Self-pressure enhanced gravity compressed air energy storage system and energy storage method - Google Patents

Abstract

The invention provides a self-pressure enhanced gravity compressed air energy storage system and an energy storage method, wherein the energy storage system comprises a closed air cavity, a communication pipeline, a multistage compressor unit and an air expansion unit which are connected in series, wherein a gravity plunger is movably inserted in the closed air cavity, and the gravity plunger is hermetically connected with the closed air cavity so as to divide the closed air cavity into an upper air cavity and a lower air cavity through the gravity plunger; two ends of the communicating pipeline are respectively connected with the upper air cavity and the lower air cavity, and a valve is arranged on the communicating pipeline; the multistage compressor sets connected in series are connected with the lower air cavity through the energy storage pipeline and used for inflating the lower air cavity, and the middle stage air suction port of the multistage compressor sets connected in series is connected with the upper air cavity; the air expansion unit is connected with the lower air cavity through an energy releasing pipeline. The constant pressure of the air storage device in the air charging and discharging process can be realized, the stability of the outlet pressure of the air compressor and the inlet pressure of the air expander is guaranteed, the operation efficiency of the air compressor and the expander is further improved, and the energy storage efficiency of the system is improved.

Description

A self-pressure-enhanced gravity compressed air energy storage system and energy storage method

technical field

The invention relates to the technical field of electrical energy storage, in particular to a self-pressure-enhanced gravity compressed air energy storage system and an energy storage method.

Background technique

Energy storage, especially the storage of electric energy, is of great significance to the optimization of energy structure and the regulation of power grid operation. The compressed air energy storage system is a new type of large-scale energy storage technology. In the gas storage device; when the electrical load of the power system reaches the peak, the gas storage device releases the stored compressed air, expands in the turboexpander to do work and drives the generator to generate electricity; according to the above principles, the compressed air energy storage system can Complete the conversion of electrical energy-air potential energy-electrical energy.

Conventional compressed air energy storage systems generally use fixed-volume air storage devices for compressed air storage. According to the gas state equation and common sense, the gas storage pressure will change during the charging and discharging process of the fixed volume gas storage device. Specifically, with the progress of the charging process, the air storage pressure in the air storage device will gradually increase, so the air compressor is required to continuously increase the exhaust pressure to meet the intake pressure requirements, which will cause the air compressor to deviate from the design operating condition. , the operating efficiency decreases and the operating power consumption increases, thereby limiting the improvement of the energy storage efficiency of the system; similarly, with the progress of the deflation process, the air storage pressure in the air storage device gradually decreases, so the intake pressure of the air expander gradually decreases. , resulting in the operation of the air expander deviating from the design condition, the operation efficiency and the output power decrease, which in turn limits the improvement of the energy storage efficiency of the system.

SUMMARY OF THE INVENTION

The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

Therefore, the purpose of the present invention is to propose a self-pressure-enhanced gravity compressed air energy storage system, which can realize the constant pressure of the air storage device during the charging and discharging process, and ensure the outlet pressure of the air compressor and the intake pressure of the air expander. In addition, due to the stable pressure conditions, the design difficulty and production cost of the air compressor and air expander can be reduced.

In order to achieve the above purpose, a self-pressure-enhanced gravity compressed air energy storage system proposed by the present invention includes:

A closed air cavity, a gravity plunger is movably inserted into the closed air cavity, and the gravity plunger is sealed with the closed air cavity, so that the closed air cavity is divided into an upper part by the gravity plunger air cavity and lower air cavity;

a communication pipeline, two ends of the communication pipeline are respectively connected to the upper air cavity and the lower air cavity, and a valve is arranged on the communication pipeline;

The series-connected multi-stage compressor units are connected to the lower air cavity through an energy storage pipeline for inflating the lower air chamber, and the middle-stage suction of the series-connected multi-stage compressor units The port is connected to the upper air chamber through the suction pipe;

An air expansion unit, the air expansion unit is connected to the lower air chamber through an energy release pipeline.

Further, the air inlet of the lower air cavity is provided with an air inlet sealing valve, one end of the energy storage pipeline is connected to the air inlet sealing valve, and the other end is connected to the air outlet of the multi-stage compressor unit in series;

The air outlet of the lower air cavity is provided with a first air outlet sealing valve, one end of the energy releasing pipeline is connected to the first air outlet sealing valve, and the other end is connected to the air inlet of the air expansion unit.

Further, an air outlet is provided on the upper air cavity, a second air outlet sealing valve is arranged at the air outlet, and one end of the suction pipeline is connected to the second air outlet sealing valve.

Further, a sealing film is arranged between the outer wall of the gravity plunger and the inner wall of the airtight air cavity, the sealing film is sleeved outside the gravity plunger, and the sealing film is respectively connected with the outer wall of the gravity plunger and the inner wall of the airtight air cavity. The inner wall of the airtight air cavity is sealed and connected.

Further, the airtight air cavity is a cylindrical structure;

A plurality of vertically distributed smooth grooves are arranged on the peripheral side of the outer wall of the gravity plunger;

The sealing film is an annular cylindrical structure sleeved on the outside of the gravity plunger. The outer diameter of the sealing film is equal to the inner diameter of the airtight air cavity. The annular saddle surface structure formed by the ring connection, the inner ring obtained after being folded forms a wrinkled protrusion on the peripheral side, the bottom end of the outer ring is sealed with the inner wall of the airtight air cavity, and the bottom end of the inner ring is connected to The outer walls of the gravity plunger are sealed and connected, and the corrugated protrusions fit with the smooth grooves.

Further, the annular cylindrical structure of the sealing film is a cylindrical surface structure with equal diameters up and down.

Further, the circumferential circumference of the cross section of the gravity plunger at the smooth groove is equal to the outer circumference of the circular section of the cylindrical structure of the sealing film.

Further, a self-pressure-enhanced gravity compressed air energy storage method, comprising the following steps:

Sealing connection between the gravity plunger and the airtight air cavity, so as to divide the airtight air cavity into an upper air cavity and a lower air cavity by the gravity plunger;

When storing energy, open the energy storage pipeline connecting the series-connected multi-stage compressor unit and the lower air chamber and the suction pipeline connecting the middle-stage suction port of the series-connected multi-stage compressor unit and the upper air chamber, and close the connection. The energy release pipeline between the air expansion unit and the lower air cavity and the communication pipeline connecting the upper air cavity and the lower air cavity. The energy pipeline inflates the lower air cavity, and the compressed gas pushes the gravity plunger to move upward, compressing the gas in the upper air cavity, and the compressed gas in the upper air cavity enters the middle-stage suction port of the series-connected multi-stage compressor unit through the suction pipeline. After compression, it is passed into the lower air chamber through the energy storage pipeline, so that the pressure difference between the upper air chamber and the lower air chamber is constant during the inflation process;

When releasing energy, open the energy release pipeline, close the energy storage pipeline, suction pipeline, and communication pipeline, the lower air chamber is released to the air expansion unit, the gravity plunger moves downward, and the valve on the communication pipeline is connected between the upper air chamber and the air expansion unit. When the pressure difference between the lower air chamber reaches a certain value, it is opened, so that the compressed gas in the lower air chamber enters the upper air chamber in a controlled state, so as to keep the pressure difference between the upper air chamber and the lower air chamber constant, and at the same time maintain the pressure of the lower air chamber Constant, the compressed air enters the air expansion unit to do work, and drives the generator to generate electricity.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

1 is a schematic structural diagram of a self-pressure-enhanced gravity compressed air energy storage system proposed by an embodiment of the present invention;

Fig. 2 is the structure schematic diagram of gravity plunger of the present invention;

FIG. 3 is a schematic diagram of a partial structure of FIG. 1 .

In the figure, 1, airtight air chamber; 11, upper air chamber; 12, lower air chamber; 2, connecting pipeline; 3, multi-stage compressor unit in series; 31, energy storage pipeline; 4, air expansion unit; 41, Energy release pipeline; 5, gravity plunger; 51, smooth groove; 6, valve; 7, suction pipeline; 8, sealing membrane; 81, outer ring; 82, inner ring.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, only used to explain the present invention, and should not be construed as a limitation of the present invention. On the contrary, embodiments of the present invention include all changes, modifications and equivalents falling within the spirit and scope of the appended claims.

FIG. 1 is a schematic structural diagram of a self-pressure-enhanced gravity compressed air energy storage system proposed by an embodiment of the present invention.

Referring to FIG. 1, a self-pressure-enhanced gravity compressed air energy storage system includes a closed air chamber 1, a communication pipeline 2, a series-connected multi-stage compressor unit 3 and an air expansion unit 4, wherein the closed air chamber 1 is movably plugged There is a gravity plunger 5, and the gravity plunger 5 is in a sealed connection with the airtight air cavity 1, so that the airtight air cavity 1 is divided into an upper air cavity 11 and a lower air cavity 12 by the gravity plunger 5, that is, the gravity plunger A piston-cylinder structure is formed between 5 and the airtight air chamber 1 , so that the gravity plunger 5 can move up and down in the airtight air chamber 1 .

The two ends of the communication pipeline 2 are respectively connected to the upper air cavity 11 and the lower air cavity 12, and a valve 6 is provided on the communication pipeline 2, that is to say, the upper air cavity 11 and the lower air cavity 12 are communicated through the communication pipeline 2, The two can be ventilated, and at the same time, the communication between the upper air chamber 11 and the lower air chamber 12 can be controlled by controlling the opening and closing of the valve 6 .

In addition, the multi-stage compressor units 3 connected in series are connected to the lower air chamber 12 through the energy storage pipeline 31 for charging the lower air chamber 12, and the intermediate-stage suction ports of the series-connected multi-stage compressor units 3 are connected through the suction pipeline 7. The upper air chamber 11, while the air expansion unit 4 is connected to the lower air chamber 12 through the energy release pipeline 41, and the air expansion unit 4 is connected to the generator. During the compression process, the valve 6 on the communication pipeline 2 is closed. At this time, the upper air chamber 11 and The lower air chamber 12 is separated and does not ventilate, the multi-stage compressor group 3 connected in series inflates the lower air chamber 12, and the gravity plunger 5 moves upward to compress the upper air chamber 11, so that the gas in the upper air chamber 11 has a certain pressure. The gas with a certain pressure in the air cavity 11 is introduced into the middle-stage suction port of the multi-stage compressor unit 3 in series, so that the gas with a certain pressure can be compressed and passed into the lower air cavity 12 for recycling instead of being directly discharged into the atmosphere. , reduce the loss of system energy, and thus keep the pressure difference between the upper air chamber 11 and the lower air chamber 12 constant during the inflation process, and at the same time keep the lower air chamber 12 constant at a higher pressure by the pressure difference + the weight of the gravity plunger 5 Level. During the expansion process, the lower air chamber 12 is deflated to the air expansion unit 4. When the pressure difference between the upper air chamber 11 and the lower air chamber 12 reaches a certain value, the valve 6 on the communication pipeline 2 is controlled to open, so that the lower air chamber 12 is opened. The high-pressure gas in the air chamber 12 enters the upper air chamber 11 in a controlled state to keep the pressure difference between the upper and lower air chambers constant, and at the same time maintain the pressure of the lower air chamber 12 constant, so as to realize the constant pressure of the airtight air chamber 1 during the filling and deflating process. It can ensure the stability of the outlet pressure of the air compressor and the inlet pressure of the air expander, thereby improving the operating efficiency of the air compressor and the expander, and improving the energy storage efficiency of the system. In addition, for the air compressor, the actual operating efficiency under the design conditions The highest (most energy-saving), if the exhaust pressure (pressure in the gas storage device) is unstable, it will cause the compressor to deviate from the design operating conditions, the operating efficiency will decrease, and the energy consumption will increase, which will lead to the system energy storage efficiency (expansion output/compression work). Similarly, for the air expander, the actual operating efficiency under the design condition is the highest. If the intake pressure changes, the operating efficiency will decrease, the air output will decrease, and the energy storage efficiency of the system will decrease; in addition, if the compressor The expansion machine needs to deal with the operating conditions of large pressure fluctuations, and special design is required, which leads to increased design difficulties and production costs, complex equipment structure, and operation that deviates from the operating conditions will also shorten the operating life to a certain extent. In the application, by controlling the pressure condition to be stable, the design difficulty and production cost of the air compressor and the air expander can be reduced. At the same time, applying pressure to the gravity plunger 5 through the upper cavity 11 can reduce the quality and height of the gravity plunger 5 and reduce the cost; by reasonably setting the upper and lower pressure difference of the gravity plunger 5, the gravity plunger 5 and the airtight air cavity 1 can be reduced. In addition, since the system is in a fully sealed state, when the position of the gravity plunger 5 is locked, the high pressure gas in the lower air cavity 12 will pass through the gravity plunger 5 and There is leakage between the walls of the airtight air chamber 1, and the leaked gas will enter the upper air chamber 11, thereby increasing the pressure of the upper air chamber 11, and reducing the pressure difference between the upper air chamber 11 and the lower air chamber 12, further enhancing the sealing effect and reducing air leakage Even if air leakage occurs, the air leaking into the low-pressure upper air chamber remains at a certain pressure and is directly used by the compressor in the next compression process, reducing the total energy loss of the system. In addition, in order to ensure that the gravity plunger 5 is in the initial state, the lower air cavity 12 can have enough space to be filled with compressed gas and can push the gravity plunger 5 to move upward. At this time, a support device can be provided at the bottom of the lower air cavity 12 , The gravity plunger 5 can be supported by the supporting device, so that when the gravity plunger 5 is lowered to the lowest limit, after being supported by the supporting device, there is still a certain space in the lower air cavity 12 at the lower part of the airtight air cavity 1. The pressure of the compressed air introduced into the air cavity 12 is sufficient to push the gravity plunger 5 to move upward, and the supporting device may be an existing device capable of supporting the gravity plunger 5 , which will not be described in detail.

In some embodiments, the air inlet of the lower air chamber 12 is provided with an air inlet sealing valve, one end of the energy storage pipeline 31 is connected to the air inlet sealing valve, and the other end is connected to the air outlet of the series-connected multi-stage compressor unit 3; The air outlet of the lower air chamber 12 is provided with a first air outlet sealing valve, one end of the energy release pipeline 41 is connected to the first air outlet sealing valve, and the other end is connected to the air inlet of the air expansion unit 4, so that when the energy is stored, the first air outlet is sealed. When the outlet sealing valve is closed, the energy storage pipeline 31 is in communication with the lower air chamber 12 .

In addition, the upper air chamber 11 is provided with an air outlet, and the air outlet is provided with a second air outlet sealing valve, and a suction line 7 is connected to the middle-stage suction port of the series-connected multi-stage compressor group 3, and the suction line 7 One end is connected to the second air outlet sealing valve.

In some embodiments, the air expansion unit 4 includes multiple stages of series-connected expanders.

It should be noted that the gravity plunger 5 and the airtight air cavity 1 are in a sealed connection, and there may be various ways of sealing connection.

2 and 3, as a possible situation, a sealing film 8 is provided between the outer wall of the gravity plunger 5 and the inner wall of the airtight air cavity 1, the sealing film 8 is sleeved outside the gravity plunger 5, and the sealing film 8 is The outer wall of the gravity plunger 5 and the inner wall of the airtight air chamber 1 are sealed and connected, so that the airtight air chamber 1 is divided into an upper air chamber 11 and a lower air chamber 12 which are sealed respectively.

In detail, the airtight air cavity 1 is a cylindrical structure, and the outer wall surface of the gravity plunger 5 is provided with a plurality of vertically distributed smooth grooves 51 , wherein the vertical direction is the same as the axial direction of the gravity plunger 5 . Consistently, the sealing film 8 is a ring-shaped cylindrical structure sleeved on the outside of the gravity plunger 5, the outer diameter of the sealing film 8 is equal to the inner diameter of the airtight air cavity 1, and the sealing film 8 is folded from the middle from the upper part to form an outer ring 81. The annular saddle surface structure formed by connecting with the inner ring 82, the inner ring 82 obtained after being folded forms a folded protrusion on the peripheral side, the top end of the outer ring 81 is connected with the top end of the inner ring 82, and the bottom end of the outer ring 81 is connected to the airtight air chamber 1 The inner wall is sealingly connected, the bottom end of the inner ring 82 is sealingly connected with the outer wall of the gravity plunger 5, and the pleated protrusions are fitted with the smooth groove 51. Through the above settings, the sealing film 8 is allowed to be recessed in the smooth groove 51, thereby increasing the The length of the outer wall of the gravity plunger 5 in contact with the sealing film 8 increases the length of the sealing film 8 fixed on the circumference of the gravity plunger 5. During the upward and downward movement of the gravity plunger 5, the outer ring 81 of the sealing film 8 and the The inner ring 82 always maintains a good fit with the inner wall of the airtight air cavity 1 and the outer wall of the gravity plunger 5, which increases the direct bonding site of the gravity plunger 5 and the sealing film 8. The inner diameter of the cavity 1 is the same, so that the outer ring 81 of the sealing film 8 can be completely attached to the inner wall of the airtight air cavity 1. The airtight air cavity 1 and the rigid wall of the gravity plunger 5 provide support for the sealing film 8 to offset the pressure caused by the The hoop tension improves the safety, reliability and life of the sealing film 8.

In detail, since the inner ring 82 formed by the folded sealing film 8 is located inside the outer ring 81 , and the sealing film 8 is a cylindrical structure, the inner ring 82 after folded has a wrinkled protrusion in order to adapt to the size of the annular space. , the wrinkled bulge is not in contact with the side wall of the gravity plunger 5, by setting a plurality of vertically distributed smooth grooves 51 on the peripheral side of the gravity plunger 5, so that the wrinkled bulge can be placed in the smooth concave At the groove 51, it can be ensured that the wrinkled bulge can also fit with the gravity plunger 5, so that the area of the sealing film 8 combined with the gravity plunger 5 in the circumferential direction increases, and the smooth groove 51 in the gravity plunger 5 Supporting the sealing film 8 at the folds and protrusions can improve the supporting stability of the sealing film 8, and then offset the annular tension of the sealing film 8 under pressure through the solid wall surface, and improve the safety, reliability and life of the sealing film 8. , and the corrugated protrusion is fixed in the smooth groove 51 so that the sealing performance of the corrugated protrusion is enhanced.

In some embodiments, the annular cylindrical structure of the sealing film 8 is a cylindrical surface structure with equal diameters up and down, which makes processing easier.

It should be noted that the circumferential circumference of the cross section of the gravity plunger 5 at the smooth groove 51 is equal to the outer circumference of the circular section of the cylindrical structure of the sealing film 8. By controlling the depth and number of the smooth grooves 51, the gravity plunger is 5. The circumferential perimeter of the smooth groove 51 increases (as far as the smooth groove 51 runs through the bottom end of the gravity plunger 5, the circumferential circumference of the gravity plunger 5 at the smooth groove 51 is the gravity plunger 5 The perimeter of the edge of the bottom end face, and the circumferential perimeter of the outer wall of the sealing film 8 is the perimeter of the end face of the outer cylinder of the annular cylindrical structure of the sealing film), and the wrinkled and raised part of the inner ring 82 can fit in the smooth groove. In 51, the gravity plunger 5 can support the sealing film 8, which improves the use safety, reliability and life of the sealing film 8.

In some embodiments, a self-pressure-enhanced gravity compressed air energy storage method, comprising the steps of:

Sealing connection between the gravity plunger 5 and the airtight air cavity 1, so that the airtight air cavity 1 is divided into an upper air cavity 11 and a lower air cavity 12 by the gravity plunger 5;

When storing energy, open the energy storage pipeline 31 connecting the series-connected multi-stage compressor group 3 and the lower air cavity 12 and the suction between the middle-stage suction port connecting the series-connected multi-stage compressor group 3 and the upper air cavity 11 Pipeline 7, close the energy release pipeline 41 connecting the air expansion unit 4 and the lower air cavity 12 and the communication pipeline 2 connecting the upper air cavity 11 and the lower air cavity 12, the motor uses electric energy to drive the multi-stage compression in series The unit 3 compresses the gas to form compressed gas, the compressed gas inflates the lower air cavity 12 through the energy storage pipeline 31, and the compressed gas pushes the gravity plunger 5 to move upward, compressing the gas in the upper air cavity 11, and the compressed air in the upper air cavity 11. The gas enters the middle-stage suction port of the series-connected multi-stage compressor group 3 through the suction line 7 for compression, and then passes into the lower air cavity 12 through the energy storage line 31, so that the upper air cavity 11 and the lower air cavity 12 during the inflation process. The pressure difference is constant;

When releasing energy, open the energy release pipeline 41, close the energy storage pipeline 31, the suction pipeline 7, and the communication pipeline 2, the lower air chamber 12 is released to the air expansion unit 4, the gravity plunger 5 moves down, and the communication pipeline The valve on 2 is opened when the pressure difference between the upper air chamber 11 and the lower air chamber 12 reaches a certain value, that is, the valve is opened under the control of the pressure difference signal, so that the compressed gas in the lower air chamber 12 is in a controlled state. Enter the upper air chamber 11 to keep the pressure difference between the upper air chamber 11 and the lower air chamber 12 constant, and at the same time keep the pressure of the lower air chamber 12 constant, the compressed air enters the air expansion unit 4 to perform work, and drives the generator to generate electricity, in which the gravity plunger 5 The gravitational potential energy is also converted into part of the electrical energy.

It should be noted that, in the description of the present invention, the terms "first", "second", etc. are only used for the purpose of description, and should not be construed as indicating or implying relative importance. Also, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

Any description of a process or method in the flowcharts or otherwise described herein may be understood to represent a module, segment or portion of code comprising one or more executable instructions for implementing a specified logical function or step of the process , and the scope of the preferred embodiments of the invention includes alternative implementations in which the functions may be performed out of the order shown or discussed, including performing the functions substantially concurrently or in the reverse order depending upon the functions involved, which should It is understood by those skilled in the art to which the embodiments of the present invention belong.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Claims (6)

1. a self-pressure enhanced gravity compressed air energy storage system, is characterized in that, comprises: A closed air cavity, a gravity plunger is movably inserted into the closed air cavity, and the gravity plunger is sealed with the closed air cavity, so that the closed air cavity is divided into an upper part by the gravity plunger air cavity and lower air cavity; a communication pipeline, two ends of the communication pipeline are respectively connected to the upper air cavity and the lower air cavity, and a valve is arranged on the communication pipeline; The series-connected multi-stage compressor units are connected to the lower air cavity through an energy storage pipeline for inflating the lower air chamber, and the middle-stage suction of the series-connected multi-stage compressor units The port is connected to the upper air chamber through the suction pipe; Air expansion unit, the air expansion unit is connected to the lower air chamber through an energy release pipeline. During the compression process, the valve on the connecting pipeline is closed, and the upper air chamber and the lower air chamber are separated and blocked. The multi-stage compressor unit in series Inflate the lower air cavity, and the gravity plunger moves upward to compress the upper air cavity, so that the gas in the upper air cavity has a certain pressure. The air port can make the gas with a certain pressure pass into the lower air chamber after being compressed for recycling, and keep the pressure difference between the upper air chamber and the lower air chamber constant during the inflation process. Deflate, when the pressure difference between the upper air chamber and the lower air chamber reaches a certain value, control the valve on the communication pipeline to open, so that the high-pressure gas in the lower air chamber 1 enters the upper air chamber in a controlled state, so as to maintain the upper and lower air chambers. The pressure difference of the air cavity is constant, and the pressure of the lower air cavity is kept constant at the same time, so that the constant pressure of the airtight air cavity during the filling and deflating process can be realized; A sealing film is arranged between the outer wall of the gravity plunger and the inner wall of the airtight air cavity, the sealing film is sleeved outside the gravity plunger, and the sealing film is respectively sealed with the outer wall of the gravity plunger and the airtight cavity. The inner wall of the air cavity is sealed and connected; The airtight air cavity is a cylindrical structure; A plurality of vertically distributed smooth grooves are arranged on the peripheral side of the outer wall of the gravity plunger; The sealing film is an annular cylindrical structure sleeved on the outside of the gravity plunger, the outer diameter of the sealing film is equal to the inner diameter of the airtight air cavity, and the sealing film is folded inward from the middle to form an outer ring The annular saddle surface structure formed by connecting with the inner ring, the inner ring obtained after being folded forms a wrinkled protrusion on the peripheral side, the bottom end of the outer ring is sealed with the inner wall of the airtight air cavity, and the bottom of the inner ring is sealed. The end is sealingly connected with the outer wall of the gravity plunger, and the corrugated protrusion fits with the smooth groove. 2. A self-pressure-enhanced gravity compressed air energy storage system according to claim 1, wherein the air inlet of the lower air cavity is provided with an air inlet sealing valve, and one end of the energy storage pipeline is connected to the air inlet. On the air inlet sealing valve, the other end is connected with the air outlet of the multi-stage compressor unit in series; The air outlet of the lower air cavity is provided with a first air outlet sealing valve, one end of the energy releasing pipeline is connected to the first air outlet sealing valve, and the other end is connected to the air inlet of the air expansion unit. 3. A self-pressure-enhanced gravity compressed air energy storage system according to claim 1, wherein an air outlet is arranged on the upper air cavity, and a second air outlet sealing valve is arranged at the air outlet, One end of the air suction line is connected to the second air outlet sealing valve. 4 . The self-pressure-enhanced gravity compressed air energy storage system according to claim 1 , wherein the annular cylindrical structure of the sealing film is a cylindrical surface structure with equal diameters up and down. 5 . 5 . The self-pressure-enhanced gravity compressed air energy storage system according to claim 4 , wherein the gravity plunger is located at the smooth groove, and the circumferential perimeter of the cross-section is equal to the cylindrical shape of the sealing film. 6 . The outer circumference of the circle of structural cross-section. 6. An energy storage method based on the self-pressure-enhanced gravity compressed air energy storage system described in any one of claims 1-5, characterized in that, comprising the steps: Sealing connection between the gravity plunger and the airtight air cavity, so as to divide the airtight air cavity into an upper air cavity and a lower air cavity by the gravity plunger; When storing energy, open the energy storage pipeline connecting the series-connected multi-stage compressor unit and the lower air chamber and the suction pipeline connecting the middle-stage suction port of the series-connected multi-stage compressor unit and the upper air chamber, and close the connection. The energy release pipeline between the air expansion unit and the lower air cavity and the communication pipeline connecting the upper air cavity and the lower air cavity. The energy pipeline inflates the lower air cavity, and the compressed gas pushes the gravity plunger to move upward, compressing the gas in the upper air cavity, and the compressed gas in the upper air cavity enters the middle-stage suction port of the series-connected multi-stage compressor unit through the suction pipeline. After compression, it is passed into the lower air chamber through the energy storage pipeline, so that the pressure difference between the upper air chamber and the lower air chamber is constant during the inflation process; When releasing energy, open the energy release pipeline, close the energy storage pipeline, suction pipeline, and communication pipeline, the lower air chamber is released to the air expansion unit, the gravity plunger moves downward, and the valve on the communication pipeline is connected between the upper air chamber and the air expansion unit. When the pressure difference between the lower air chamber reaches a certain value, it is opened, so that the compressed gas in the lower air chamber enters the upper air chamber in a controlled state, so as to keep the pressure difference between the upper air chamber and the lower air chamber constant, and at the same time maintain the pressure of the lower air chamber Constant, the compressed air enters the air expansion unit to do work, and drives the generator to generate electricity.

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