A coupled liquid piston heat pump electrical storage system and method of operation thereof

Abstract

The application discloses a kind of heat pump energy storage systems and methods coupled liquid piston, including sequentially connected energy storage compressor, hot storage tank, first heat exchanger, first double-tank liquid piston, second heat exchanger, energy storage expander, cold storage tank and third heat exchanger;Third heat exchanger connects energy storage compressor;It further includes sequentially connected cold storage tank, energy release compressor, first buffer heat exchanger, hot storage tank, energy release expander, second buffer heat exchanger, second double-tank liquid piston and fourth heat exchanger, and the outlet of fourth heat exchanger is connected to cold storage tank;First double-tank liquid piston and second double-tank liquid piston are the same structure;Further compression is carried out to hot storage tank outlet normal temperature high pressure gas using liquid piston, the expansion ratio of energy storage expander is improved, the outlet temperature of energy storage expander is reduced, not only the quality of cold storage tank storage cold energy is improved, but also the round trip efficiency of system is improved, by compressing the gas at the outlet of energy release expander, the expansion ratio of energy release expander can be improved.

Description

Technical Field

[0001] This invention belongs to the field of physical energy storage technology, specifically relating to a heat pump energy storage system coupled with a liquid piston and its operation method. Background Technology

[0002] Against the backdrop of vigorous promotion of energy conservation and emission reduction, renewable energy sources such as solar and wind power have experienced rapid development. However, the utilization of renewable energy is subject to problems such as instability and intermittency, which poses a significant challenge to the grid connection of new energy power generation. Therefore, it is necessary to develop energy storage technology to solve these problems.

[0003] Heat pump energy storage technology is a novel energy storage technology developed based on power cycle and thermal energy storage. During energy storage, excess electrical energy generated from new energy sources is converted into heat and cold energy and stored in high-temperature and low-temperature tanks through a reverse power cycle. During energy release, the energy in the tanks is released using a heat engine cycle to drive an expander to generate electricity. Compared to pumped hydro storage and compressed air energy storage, it has lower costs, higher energy density, and is unaffected by geographical environment, making it a highly competitive large-scale energy storage technology.

[0004] Among numerous heat pump energy storage systems, Brayton cycle-based systems are characterized by high efficiency and high energy density, making them the closest to engineering applications. However, the round-trip efficiency of current Brayton cycle-based heat pump energy storage systems is affected by the compressor temperature ratio. With a constant working fluid, improving the round-trip efficiency requires a higher compression ratio, which places high demands on compressor performance and increases costs. Existing compressor technology makes it difficult to further improve the round-trip efficiency of traditional heat pump energy storage systems. Summary of the Invention

[0005] To address the aforementioned problems and explore new solutions for improving the round-trip efficiency of heat pump energy storage systems, this invention aims to provide a heat pump energy storage system coupled with a liquid piston and its operating method. During energy storage, the liquid piston further compresses the ambient temperature, high-pressure gas at the outlet of the heat storage tank, thereby increasing the expansion ratio of the expander and further reducing the outlet temperature of the expander. This not only improves the quality of the cold energy but also increases the energy storage density of the cold storage tank, thus improving the round-trip efficiency of the system. During energy release, by compressing the gas at the outlet of the expander, the expansion ratio of the energy release expander can be increased, allowing the stored thermal energy to be utilized to a greater extent, avoiding the waste of residual heat after expansion, and further improving the round-trip efficiency of the system.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a heat pump energy storage system with coupled liquid pistons, comprising a reverse Brayton energy storage cycle unit and a forward Brayton energy release cycle unit. The reverse Brayton energy storage cycle unit includes an energy storage compressor, a hot storage tank, a first heat exchanger, a first dual-tank liquid piston, a second heat exchanger, an energy storage expander, a cold storage tank, and a third heat exchanger connected in sequence; the third heat exchanger is connected to the energy storage compressor. The forward Brayton energy release cycle unit includes a cold storage tank, an energy release compressor, a first buffer heat exchanger, a hot storage tank, an energy release expander, a second buffer heat exchanger, a second dual-tank liquid piston, and a fourth heat exchanger connected in sequence; the outlet of the fourth heat exchanger is connected to the cold storage tank; the first dual-tank liquid piston and the second dual-tank liquid piston have the same structure; the energy storage compressor and the energy release compressor are connected to an electric motor, and the energy storage expander and the energy release expander are connected to a generator.

[0007] Furthermore, the outlet of the energy release compressor is connected to the air inlet of the first buffer heat exchanger, the air outlet of the first buffer heat exchanger is connected to the energy release inlet of the hot storage tank, the energy release outlet of the hot storage tank is connected to the air inlet of the energy release expander, the air outlet of the energy release expander is connected to the air inlet of the second buffer heat exchanger, the air outlet of the second buffer heat exchanger is connected to the air inlet of the second dual-tank liquid piston, and the air outlet of the second dual-tank liquid piston is connected to the energy release inlet of the cold storage tank via the fourth heat exchanger. The fourth heat exchanger is used to reduce the air temperature from the air outlet of the second dual-tank liquid piston to room temperature, and the energy release outlet of the cold storage tank is connected to the energy release compressor to form a cycle.

[0008] Furthermore, the first and second buffer heat exchangers are identical in structure, with the buffer heat exchangers being cylindrical in shape. Each buffer heat exchanger includes a buffer air heat exchange space and a gas-liquid heat exchange space. The inner wall of the buffer air heat exchange space is welded with spiral fins. Several parallel air heat exchanger pipes are arranged in the gas-liquid heat exchange space, which connects to the buffer air heat exchange space. A heat exchange liquid inlet and a heat exchange liquid outlet are opened on the side wall of the gas-liquid heat exchange space. The gas-liquid heat exchange space contains equidistant semi-circular baffles, with through holes on the semi-circular baffles for the air heat exchange pipes to pass through.

[0009] Furthermore, the number of through holes in the three rows near the middle surface of the buffer heat exchanger is the same, while the number of through holes in the remaining rows gradually decreases as they are further away from the diameter. The width of the spiral fins is 25-45cm, the pitch is equal, the pitch is 20-30cm, and the radius of the semi-circular baffle is 40-60cm.

[0010] Furthermore, the angle between the semicircular baffle and the buffer heat exchanger cross section increases with the increase of the horizontal distance from the heat exchange liquid inlet. The angle between the semicircular baffle closest to the heat exchange liquid inlet and the buffer heat exchanger cross section is 0°, and the angle between each semicircular baffle and the buffer heat exchanger cross section increases by 2-5° along the liquid flow direction.

[0011] Furthermore, the entire buffer air heat exchange space is made of thermally conductive materials, the outer shell and semi-circular baffle of the gas-liquid heat exchange space are made of thermally insulating materials, and the air heat exchange pipes are made of thermally conductive materials and coated with an anti-corrosion coating on the outer wall.

[0012] Furthermore, the first dual-tank liquid piston includes a first water-gas tank, a second water-gas tank, and a first water pump. The first and second water-gas tanks are connected in parallel. The top air inlets of the first and second water-gas tanks are connected to the energy storage outlet of the heat storage tank. The top air outlets of the first and second water-gas tanks are connected to the air inlet of the energy storage expander. The bottoms of the first and second water-gas tanks are connected by the water pump and a liquid delivery pipeline. The second dual-tank liquid piston includes a third water-gas tank, a fourth water-gas tank, and a second water pump. The third and fourth water-gas tanks are connected in parallel. The top air inlets of the third and fourth water-gas tanks are connected to the air outlet of the second buffer heat exchanger. The top air outlets of the third and fourth water-gas tanks are connected to the air inlet of the fourth heat exchanger. The bottoms of the third and fourth water-gas tanks are connected by the second water pump and a liquid delivery pipeline.

[0013] This invention also provides a heat pump energy storage method with coupled liquid piston. In the energy storage stage, the energy storage compressor compresses air and stores the heat of compression through a hot storage tank. The air is then cooled to room temperature and becomes high-pressure air, which then enters the first dual-tank liquid piston to complete near-isothermal compression. The room-temperature high-pressure air from the first dual-tank liquid piston is then fed into the energy storage expander to expand and do work, thereby driving the generator to generate electricity. After that, the low-temperature atmospheric-pressure air from the outlet of the energy storage expander is fed into a cold storage tank to store its cooling capacity. Finally, the room-temperature atmospheric-pressure air from the outlet of the cold storage tank is fed into the energy storage compressor to start a new cycle.

[0014] During the energy release phase, the low-temperature air from the cold storage tank outlet enters the energy release compressor for compression, and then enters the first buffer heat exchanger for heat exchange. After the compressed air temperature is reduced to room temperature, it is passed into the hot storage tank for heat exchange to absorb the heat energy stored therein. The high-temperature air from the hot storage tank is then passed into the energy release expander for expansion and to drive the generator to generate electricity. After that, the air from the outlet of the energy release expander is passed into the second buffer heat exchanger for heat exchange to reduce the air temperature to room temperature. Then, it is passed into the second dual-tank liquid piston for near-isothermal compression to increase its pressure energy. Finally, the high-pressure air from the outlet of the second dual-tank liquid piston is passed into the cold storage tank for heat exchange to absorb the cold energy therein. After that, the low-temperature air is passed into the energy release compressor to start a new cycle.

[0015] The high-pressure air at the outlet of the liquid piston of the second double tank is cooled using the fourth heat exchanger.

[0016] First, air is introduced into the first water-gas tank. The first water pump then pumps water from the bottom of the first water-gas tank into the second water-gas tank. Once the air in the second water-gas tank is compressed to the set pressure, the compressed air is passed through the second heat exchanger to cool to room temperature before being passed through the energy storage expander to generate electricity. Once the gas level in the second water-gas tank equals the clearance height, the first water pump pumps water from the bottom of the second water-gas tank into the first water-gas tank. Once the air in the first water-gas tank is compressed to the set pressure, the compressed air is passed through the second heat exchanger to cool to room temperature before being passed through the energy storage expander to generate electricity. Once the gas level in the first water-gas tank equals the clearance height, the inlet of the second water-gas tank and the outlet of the first water-gas tank are closed, and the inlet of the first water-gas tank is opened. This cycle is repeated to perform near-isothermal compression in both tanks. The working process of the liquid piston in the second dual-tank tank is the same as that in the first dual-tank tank.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects:

[0018] This invention couples a liquid piston with a heat pump energy storage system. During energy storage, the dual-tank liquid piston further compresses air, enhancing the quality of cold energy stored in the cold tank. During energy release, the dual-tank liquid piston increases the pressure energy of the compressed air, allowing for a greater release of heat energy absorbed from the hot tank and reducing waste heat. This further improves the system's round-trip efficiency without changing the compressor pressure ratio, providing a new solution for improving the round-trip efficiency of heat pump energy storage. Furthermore, the buffer air heat exchange space of the buffer heat exchanger effectively solves the fluctuations in outlet temperature and flow rate of the energy release expander and compressor caused by unstable outlet temperatures of the hot and cold tanks, thus improving system stability. The spiral fins welded into the buffer air heat exchange space enhance heat exchange between air and the surrounding environment during buffering.

[0019] Furthermore, by changing the inclination angle of the semicircular baffle in the gas-liquid heat exchange space, the disadvantages of vertical baffles, such as high flow resistance and easy fouling, can be effectively solved. Moreover, the greater the horizontal distance from the heat exchange liquid inlet, the smaller the gas-liquid heat exchange temperature difference. By increasing the angle between the semicircular baffle and the vertical line, the liquid flow velocity can be increased, thereby increasing the heat transfer coefficient and enhancing heat transfer. Attached Figure Description

[0020] Figure 1 This is a diagram of a heat pump energy storage system coupled with a liquid piston according to the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of a buffer heat exchanger according to the present invention.

[0022] Figure 3 This is a front view of a buffer heat exchanger according to the present invention.

[0023] Figure 4This is a schematic diagram of a semi-circular baffle according to the present invention.

[0024] Wherein: 1-Energy storage compressor, 2-Heat storage tank, 3-First heat exchanger, 4-First inlet valve, 5-Second inlet valve, 6-First water-gas tank, 7-Second water-gas tank, 8-First water pump, 9-First exhaust valve, 10-Second exhaust valve, 11-Second heat exchanger, 12-Energy storage expander, 13-Cold storage tank, 14-Third heat exchanger, 15-Energy release compressor, 16-First buffer heat exchanger, 17-Energy release expander, 18-Second buffer heat exchanger, 19-Third inlet valve, 20-Fourth inlet valve. 21-Third water-gas tank, 22-Fourth water-gas tank, 23-Second water pump, 24-Third exhaust valve, 25-Fourth exhaust valve, 26-Fourth heat exchanger, 27-Electric motor, 28-Generator, 29-First double-tank liquid piston, 30-Second double-tank liquid piston, 31-Heat exchange liquid inlet, 32-Heat exchange liquid outlet, 33-Heat exchange air inlet, 34-Heat exchange air outlet, 35-Helical fins, 36-Semi-circular baffle, 37-Air heat exchange pipe, 38-Buffer air heat exchange space, 39-Gas-liquid heat exchange space. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings:

[0026] Please see Figure 1 A heat pump energy storage system coupled with a liquid piston includes a reverse Brayton energy storage cycle unit for converting and storing excess electrical energy into heat and cold energy, and a forward Brayton energy release cycle unit for absorbing and storing the heat and cold energy for power generation. The reverse Brayton energy storage cycle unit includes an energy storage compressor 1, a hot storage tank 2, a first heat exchanger 3, a first dual-tank liquid piston 29, a second heat exchanger 11, an energy storage expander 12, a cold storage tank 13, and a third heat exchanger 14. The outlet of the energy storage compressor 1 is connected to the energy storage inlet of the hot storage tank 2, and the energy storage outlet of the hot storage tank 2 is connected to the inlet of the first dual-tank liquid piston 29. A first heat exchanger 3 is installed between the two to reduce the air temperature from the energy storage outlet of the hot storage tank 2 to ambient temperature. The outlet of the first dual-tank liquid piston 29 is connected to the inlet of the energy storage expander 12. The air inlets are connected, and a second heat exchanger 11 is installed between them to reduce the air temperature from the outlet of the first dual-tank liquid piston 29 to room temperature. The outlet of the energy storage expander 12 is connected to the energy storage inlet of the cold storage tank 13, and the energy storage outlet of the cold storage tank 13 is connected to the inlet of the energy storage compressor 1. A third heat exchanger 14 is installed between them to raise the air temperature from the energy storage outlet of the cold storage tank 13 to room temperature, thereby forming a cycle. The energy storage compressor and the energy release compressor are connected to an electric motor, and the energy storage expander and the energy release expander are connected to a generator.

[0027] The reverse Brayton energy storage cycle unit and the forward Brayton energy release cycle unit are combined into a complete energy storage system through a hot storage tank and a cold storage tank. The two cycle units do not operate simultaneously. When there is a surplus of electricity generated by new energy sources, the reverse Brayton energy storage cycle unit is used to convert the excess electricity into heat energy and cold energy, which are stored in the hot storage tank and the cold storage tank respectively. When there is a shortage of electricity generated by new energy sources, the forward Brayton energy release cycle unit is used to release the heat energy and cold energy stored in the hot storage tank and the cold storage tank to generate electricity.

[0028] Please see Figure 1 The first dual-tank liquid piston 29 includes a first water-air tank 6, a second water-air tank 7, a first water pump 8, and corresponding inlet and outlet pipes and water pump circulation pipes; such as Figure 1 As shown, the intake and exhaust pipelines include an intake pipeline and an exhaust pipeline that connect the two water-gas tanks in parallel. The intake and exhaust pipelines are connected to the top of the first water-gas tank 6 and the second water-gas tank 7. The intake pipelines corresponding to the first water-gas tank 6 and the second water-gas tank 7 are respectively equipped with a first intake valve 4 and a second intake valve 5. The exhaust pipelines corresponding to the first water-gas tank 6 and the second water-gas tank 7 are respectively equipped with a first exhaust valve 9 and a second exhaust valve 10. The exhaust pipeline is connected to the intake port of the energy storage expander 12. The first water pump 8 and its circulation pipeline are connected to the bottom of the first water-gas tank 6 and the second water-gas tank 7.

[0029] Please see Figure 1 The forward Brayton energy release cycle unit includes an energy release compressor 15, a first buffer heat exchanger 16, a hot storage tank 2, an energy release expander 17, a second buffer heat exchanger 18, a second dual-tank liquid piston 30, a fourth heat exchanger 26, and a cold storage tank 13. The outlet of the energy release compressor 15 is connected to the air inlet of the first buffer heat exchanger 16. The air outlet of the first buffer heat exchanger is connected to the energy release inlet of the hot storage tank 2. The energy release outlet of the hot storage tank 2 is connected to the air inlet of the energy release expander 17. The outlet of the energy release expander 17 is connected to the air inlet of the second buffer heat exchanger 18. The air outlet of the second buffer heat exchanger 18 is connected to the air inlet of the second dual-tank liquid piston 30. The outlet of the second dual-tank liquid piston 30 is connected to the energy release inlet of the cold storage tank 13. A fourth heat exchanger 26 is set between the two to reduce the air temperature from the outlet of the second dual-tank liquid piston 30 to room temperature. The energy release outlet of the cold storage tank 13 is connected to the energy release compressor 15 to form a cycle.

[0030] Please see Figure 1 The second dual-tank liquid piston 30 includes a third water-air tank 21, a fourth water-air tank 22, a second water pump 23, and corresponding inlet and outlet pipes and water pump circulation pipes; such as Figure 1As shown, the intake and exhaust pipes include an intake pipe and an exhaust pipe that connect the two water-gas tanks in parallel. The intake and exhaust pipes are connected to the top of the third water-gas tank 21 and the fourth water-gas tank 22. The intake pipes of the third water-gas tank 21 and the fourth water-gas tank 22 are respectively equipped with a third intake valve 19 and a fourth intake valve 20. The exhaust pipes of the third water-gas tank 21 and the fourth water-gas tank 22 are respectively equipped with a third exhaust valve 24 and a fourth exhaust valve 25. The exhaust pipe is connected to the energy release inlet of the cold storage tank 13. The second water pump 23 and its circulation pipe are connected to the bottom of the third water-gas tank 21 and the fourth water-gas tank 22.

[0031] Please see Figure 2 and Figure 3 The buffer heat exchanger mainly includes a buffer air heat exchange space 38 and a gas-liquid heat exchange space 39. The inner wall of the cylindrical buffer air heat exchange space 38 is welded with spiral fins, the width of which is 25-45cm and the pitch of which is equal at 20-30cm. The buffer air heat exchange space 38 can keep the circulation flow of the system stable, thereby improving the stability of the system. In addition, the welded spiral fins 35 can enhance the heat exchange between air and air or the outside environment.

[0032] Please see Figure 2 , Figure 3 and Figure 4 The gas-liquid heat exchange space 39 of the buffer heat exchanger is equipped with equidistantly placed semicircular baffles 36, each with a radius of 40-60 cm. These baffles have small holes through which air heat exchange pipes 37 can pass. The three rows closest to the diameter have the same number of holes, while the number of holes in the remaining rows gradually decreases with increasing distance from the diameter. The angle between the semicircular baffles 36 and the vertical line increases with increasing horizontal distance from the heat exchange liquid inlet 31. The angle between the closest semicircular baffle and the vertical line is 0°, and the angle between each subsequent semicircular baffle and the vertical line increases by 2-5°. By changing the inclination angle of the semicircular baffles in the gas-liquid heat exchange space 39, the drawbacks of vertical baffles, such as high flow resistance and easy scaling, can be effectively solved. Furthermore, as the horizontal distance from the heat exchange liquid inlet 31 increases, the gas-liquid heat exchange temperature difference decreases. Increasing the angle between the semicircular baffles and the vertical line can increase the liquid flow velocity, thereby increasing the heat transfer coefficient and enhancing heat transfer.

[0033] Based on the above system, the operation of the heat pump energy storage system with coupled liquid piston of the present invention includes the following steps:

[0034] During the energy storage phase, the air compressed by the energy storage compressor 1 is introduced into the heat storage tank 2 to absorb and store the heat of compression. The compressed air exits from the energy storage outlet of the heat storage tank 2 and, after heat exchange in the first heat exchanger 3, its temperature drops to room temperature, becoming high-pressure air. It is then introduced into the first dual-tank liquid piston 29 to complete near-isothermal compression. First, the first inlet valve 4 is opened, and the second inlet valve 5, the first exhaust valve 9, and the second exhaust valve 10 are closed, allowing air to enter the first water-air tank 6. The first water pump 8 pumps water from the bottom of the first water-air tank 6 into the second water-air tank 7. After the air in the second water-air tank 7 is compressed to the set pressure, the second exhaust valve 10 is opened, allowing the compressed air to be introduced into the second heat exchanger 11 to cool to room temperature before being introduced into the energy storage expander 12 to generate electricity. Once the gas level in the second water-air tank 7 is equal to the clearance height, the first inlet valve 4 and the first exhaust valve 5 are closed. The second exhaust valve 10 is opened, and then the second intake valve 5 is opened. The first water pump 8 pumps water from the bottom of the second water-air tank 7 into the first water-air tank 6. After the air in the first water-air tank 6 is compressed to the set pressure, the first exhaust valve 9 is opened, allowing the compressed air to enter the second heat exchanger 11 to cool to room temperature before entering the energy storage expander 12 to generate electricity. Once the gas level in the first water-air tank 6 is equal to the clearance height, the second intake valve 5 and the first exhaust valve 9 are closed, and then the first intake valve 4 is opened. This cycle repeats for near-isothermal compression of the two tanks. The low-temperature air that has completed its work is passed from the outlet of the energy storage expander 12 into the cold storage tank 13 to store its cooling capacity. Finally, the air from the energy storage outlet of the cold storage tank 13, after being cooled to room temperature by the third heat exchanger 14, is passed into the energy storage compressor 1 to begin a new cycle.

[0035] During the energy release phase, the low-temperature air from the energy release outlet of the cold storage tank 13 is compressed by the energy release compressor 15, and then passed to the first buffer heat exchanger 16 for heat exchange. After the compressed air temperature is reduced to room temperature, it is passed to the hot storage tank 2 for heat exchange to absorb the heat energy stored therein. The high-temperature air from the hot storage tank 2 is passed to the energy release expander 17 for expansion and work to drive the generator 28 to generate electricity. Afterward, the air from the outlet of the energy release expander 17 is passed to the second buffer heat exchanger 18 for heat exchange. After the air temperature is reduced to room temperature, it is passed to the second dual-tank liquid piston 30 for near-isothermal compression to increase its pressure energy. First, open the third intake valve 19 and close the fourth intake valve 20, the third exhaust valve 24, and the second exhaust valve 25. Air enters the third water-air tank 21. The second water pump 23 pumps water from the bottom of the third water-air tank 21 into the fourth water-air tank 22. After the air in the fourth water-air tank 22 is compressed to the set pressure, open the fourth exhaust valve 25 to allow the compressed air to pass through the fourth heat exchanger 26 to cool to room temperature before passing it through the cold storage tank 13 to absorb the stored cold energy. Once the gas level in the fourth water-air tank 22 is equal to the clearance height, close the third intake valve 19 and the second exhaust valve 25. The fourth exhaust valve 25 is opened, followed by the fourth intake valve 20. The second water pump 23 pumps water from the bottom of the fourth water-air tank 22 into the third water-air tank 21. After the air in the third water-air tank 21 is compressed to the set pressure, the third exhaust valve 24 is opened, allowing the compressed air to enter the fourth heat exchanger 26 and cool to room temperature before entering the cold storage tank 13 to absorb the stored cold energy. Once the gas level in the third water-air tank 21 equals the clearance height, the fourth intake valve 20 and the third exhaust valve 24 are closed, and then the third intake valve 19 is opened. This cycle repeats, performing near-isothermal compression in both tanks. Finally, the low-temperature air, after absorbing the cold energy stored in the cold tank 13, is introduced into the energy release compressor 15 to begin a new cycle.

[0036]

[0037] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A heat pump energy storage system coupled with a liquid piston, characterized in that, The system includes a reverse Brayton energy storage cycle unit and a forward Brayton energy release cycle unit. The reverse Brayton energy storage cycle unit includes, in sequence, an energy storage compressor (1), a hot storage tank (2), a first heat exchanger (3), a first dual-tank liquid piston (29), a second heat exchanger (11), an energy storage expander (12), a cold storage tank (13), and a third heat exchanger (14); the third heat exchanger (14) is connected to the energy storage compressor (1). The forward Brayton energy release cycle unit includes, in sequence, a cold storage tank (13), an energy release compressor, and a... (15) First buffer heat exchanger (16), thermal storage tank (2), energy release expander (17), second buffer heat exchanger (18), second double-tank liquid piston (30) and fourth heat exchanger (26), the outlet of the fourth heat exchanger (26) is connected to the cold storage tank; the first double-tank liquid piston (29) and the second double-tank liquid piston (30) have the same structure; the energy storage compressor and the energy release compressor are connected to the electric motor, and the energy storage expander and the energy release expander are connected to the generator; the first double-tank liquid piston (29) includes a first water-gas tank (6 The first water-gas tank (6) and the second water-gas tank (7) are connected in parallel. The air inlets at the top of the first water-gas tank (6) and the second water-gas tank (7) are connected to the energy storage outlet of the thermal storage tank (2). The air outlets at the top of the first water-gas tank (6) and the second water-gas tank (7) are connected to the air inlet of the energy storage expander (12). The bottoms of the first water-gas tank (6) and the second water-gas tank (7) are connected by the water pump (8) and the liquid conveying pipeline. The second double-tank liquid piston (30) includes a third water-gas tank. Tank (21), fourth water-gas tank (22) and second water pump (23), third water-gas tank (21) and fourth water-gas tank (22) are connected in parallel, the air inlet of the top of the third water-gas tank (21) and fourth water-gas tank (22) is connected to the air outlet of the second buffer heat exchanger (18), the air outlet of the top of the third water-gas tank (21) and fourth water-gas tank (22) is connected to the air inlet of the fourth heat exchanger (26), and the bottom of the third water-gas tank (21) and fourth water-gas tank (22) is connected by the second water pump (23) and liquid conveying pipeline.

2. The heat pump energy storage system with coupled liquid piston according to claim 1, characterized in that, The outlet of the energy release compressor (15) is connected to the air inlet of the first buffer heat exchanger (16). The air outlet of the first buffer heat exchanger (16) is connected to the energy release inlet of the hot storage tank (2). The energy release outlet of the hot storage tank (2) is connected to the air inlet of the energy release expander (17). The outlet of the energy release expander (17) is connected to the air inlet of the second buffer heat exchanger (18). The air outlet of the second buffer heat exchanger (18) is connected to the air inlet of the second double-tank liquid piston (30). The outlet of the second double-tank liquid piston (30) is connected to the energy release inlet of the cold storage tank (13) via the fourth heat exchanger (26). The fourth heat exchanger (26) is used to reduce the air temperature from the outlet of the second double-tank liquid piston (30) to room temperature. The energy release outlet of the cold storage tank (13) is connected to the energy release compressor (15) to form a cycle.

3. The heat pump energy storage system with coupled liquid piston according to claim 1, characterized in that, The first buffer heat exchanger (16) and the second buffer heat exchanger (18) are buffer heat exchangers with the same structure. The buffer heat exchanger is cylindrical in shape and includes a buffer air heat exchange space (38) and a gas-liquid heat exchange space (39). The inner wall of the buffer air heat exchange space (38) is welded with spiral fins (35). Several parallel air heat exchanger pipes (37) are provided in the gas-liquid heat exchange space (39). The air heat exchanger pipes (37) are connected to the buffer air heat exchange space (38). The side wall of the gas-liquid heat exchange space (39) is provided with a heat exchange liquid inlet (31) and a heat exchange liquid outlet (32). The gas-liquid heat exchange space (39) has semi-circular baffles (36) arranged at equal intervals. The semi-circular baffles (36) are provided with through holes for the air heat exchange pipes to pass through.

4. The heat pump energy storage system with coupled liquid piston according to claim 3, characterized in that, The number of through holes in the three rows near the middle surface of the buffer heat exchanger is the same, and the number of through holes in the remaining rows gradually decreases as they are further away from the diameter. The width of the spiral fins (35) is 25-45cm, the pitch is equal, the pitch is 20-30cm, and the radius of the semi-circular baffle (36) is 40-60cm.

5. The heat pump energy storage system with coupled liquid piston according to claim 3, characterized in that, The angle between the semicircular baffle (36) and the buffer heat exchanger cross section increases with the increase of the horizontal distance from the heat exchange liquid inlet (31). The angle between the semicircular baffle (36) closest to the heat exchange liquid inlet (31) and the buffer heat exchanger cross section is 0°. The angle between each semicircular baffle and the buffer heat exchanger cross section increases by 2-5° along the liquid flow direction.

6. The heat pump energy storage system with coupled liquid piston according to claim 3, characterized in that, The buffer air heat exchange space (39) is made entirely of thermally conductive materials, the outer shell and semi-circular baffle (36) of the gas-liquid heat exchange space (38) are made of thermally insulating materials, and the air heat exchange pipe (37) is made of thermally conductive materials and has an anti-corrosion coating sprayed on its outer wall.

7. A heat pump energy storage method coupled with a liquid piston, characterized in that, Based on the heat pump energy storage system with coupled liquid piston as described in any one of claims 1-6, in the energy storage stage, the energy storage compressor (1) compresses the air and stores the heat of compression through the heat storage tank (2), and the high-pressure air with the temperature reduced to room temperature enters the first double-tank liquid piston (29) to complete near-isothermal compression. Then, the room-temperature high-pressure air from the first double-tank liquid piston (29) is input into the energy storage expander (12) to expand and do work, thereby driving the generator to generate electricity. After that, the low-temperature normal-pressure air from the outlet of the energy storage expander (12) is introduced into the cold storage tank (13) to store its cold energy. Finally, the room-temperature normal-pressure air from the outlet of the cold storage tank (13) is introduced into the energy storage compressor (1) to start a new cycle. During the energy release phase, the low-temperature air from the outlet of the cold storage tank (13) is compressed by the energy release compressor (15), and then enters the first buffer heat exchanger (16) for heat exchange. After the compressed air temperature is reduced to room temperature, it is passed into the hot storage tank (2) for heat exchange to absorb the heat energy stored therein. The high-temperature air from the hot storage tank (2) is passed into the energy release expander (17) for expansion and work to drive the generator to generate electricity. Then, the air from the outlet of the energy release expander (17) is passed into the second buffer heat exchanger (18) for heat exchange. After the air temperature is reduced to room temperature, it is passed into the second double-tank liquid piston (30) for near-isothermal compression to increase its pressure energy. Then, the high-pressure air from the outlet of the second double-tank liquid piston (30) is passed into the cold storage tank (13) for heat exchange. After absorbing the cold energy therein, the low-temperature air is passed into the energy release compressor (15) to start a new cycle.

8. The heat pump energy storage method with coupled liquid piston according to claim 7, characterized in that, The high-pressure air at the outlet of the second double-tank liquid piston (30) is cooled by the fourth heat exchanger (26).

9. The heat pump energy storage method with coupled liquid piston according to claim 7, characterized in that, First, air is introduced into the first water-air tank (6). The first water pump (8) pumps water from the bottom of the first water-air tank (6) into the second water-air tank (7). After the air in the second water-air tank (7) is compressed to the set pressure, the compressed air is introduced into the second heat exchanger (11) to cool to room temperature before being introduced into the energy storage expander (12) to generate electricity. After the gas height in the second water-air tank (7) is equal to the clearance height, the first water pump (8) pumps water from the bottom of the second water-air tank (7) into the first water-air tank (6). After the air in the first water-gas tank (6) is compressed to the set pressure, the compressed air is introduced into the second heat exchanger (11) to cool to room temperature and then introduced into the energy storage expander (12) to generate electricity. After the gas height in the first water-gas tank (6) is equal to the clearance height, the air inlet of the second water-gas tank and the exhaust port of the first water-gas tank are closed, and the air inlet of the first water-gas tank is opened. This cycle is repeated to perform near-isothermal compression of the two tanks. The working process of the second double-tank liquid piston (30) is the same as that of the first double-tank liquid piston (29).

Images