A thermal-pressure decoupled liquid piston compressed air energy storage system and its operation method

Abstract

This invention discloses a thermo-pressure decoupled liquid piston compressed air energy storage system and its operation method. The system includes a compressed air energy storage unit, a heat exchange and storage unit, and an expansion generator set. A variable compressed air system and a dual-tank near-isothermal compressed air system serve as the low-pressure and high-pressure stages on the energy storage side of the entire system, respectively, sequentially compressing air. The compression ratio of the multi-stage compressor in the variable compressed air system is adjusted, and the compression ratio of the water-air tank in the dual-tank near-isothermal compressed air system is matched and adjusted to achieve the target pressure. This allows the heat of compression generated by the compressed air during the energy storage process to be fully utilized during the energy release process, solving the problem of heat supply and demand imbalance during the energy storage and release process caused by the throttle valve installed at the expander inlet. The heat of compression is stored in the heat storage unit. The flexibility of this compressed air energy storage unit is used to acquire and store pressure potential energy, achieving decoupling of thermal energy and pressure potential energy, and efficiently distributing the thermal energy required for the release of pressure potential energy.

Description

Technical Field

[0001] This invention belongs to the field of physical energy storage technology, specifically relating to a thermo-pressure decoupled liquid piston compressed air energy storage system and its operation method. Background Technology

[0002] With the rapid growth of total installed capacity of new energy sources, addressing the instability and intermittency of new energy power generation has become a major challenge for large-scale utilization of new energy, and energy storage is one of the main solutions. Energy storage involves storing energy through a medium and releasing it when needed. Compressed air energy storage and pumped hydro storage are widely recognized as suitable for high-power and large-capacity energy storage systems of hundreds of megawatts. While pumped hydro storage power plants are highly efficient, the construction of large-scale pumped hydro storage power plants requires huge initial investments, has a long construction period, and is subject to very strict geographical location requirements, making site selection difficult and even potentially submerging vegetation and urban areas. Compared to pumped hydro storage, compressed air energy storage offers greater flexibility in site selection and lower investment costs. In recent years, with increased understanding and research into compressed air energy storage technology, several large-scale compressed air energy storage power plants have been built.

[0003] Compressed air energy storage can be technically categorized into non-insulated, insulated, and isothermal systems. Traditional compressed air energy storage systems are non-insulated systems based on fuel combustion. Their main components include a multi-stage compressor, a gas storage unit, a combustion chamber, and a multi-stage turboexpander. During off-peak electricity demand, surplus off-peak electricity drives an electric motor, which in turn drives the multi-stage compressor to compress air via a coupling. The resulting high-pressure air is stored in the gas storage unit. During peak electricity demand, the high-pressure air is released from the storage unit, mixed with fuel in the combustion chamber, and then combusted. Finally, the air enters the multi-stage turboexpander to generate electricity, which is then fed into the grid. However, its drawbacks include heat dissipation during air compression by the multi-stage compressor, and the need to consume fossil fuels during energy release, causing pollution.

[0004] Adiabatic compressed air energy storage refers to a system based on traditional fuel-heated compressed air energy storage that eliminates the combustion chamber and fuel heating, and adds heat storage equipment and heat exchangers. During the energy storage stage, when air is compressed, heat exchangers are installed between or after the compressor stages. The cold heat storage medium flowing in the heat exchangers absorbs the heat of compression generated during air compression and stores this heat in the heat storage equipment. During the energy release stage, before the gas enters the expander to perform work, heat exchangers are installed before or between the stages. The hot heat storage medium flowing in the heat exchangers heats the high-pressure air to utilize the heat of compression. It retains the basic structure of a compressed air energy storage system and avoids the combustion of fossil fuels. During the energy release stage, in order to stabilize the air conditions entering the expander, a throttle valve is required to obtain a stable airflow. This results in the gas pressure before expansion being lower than its storage pressure, causing the heat generated during gas compression to exceed the heat required for gas expansion, creating an imbalance between heat supply and demand during energy storage and release. Summary of the Invention

[0005] To address the problems in the prior art, the present invention aims to provide a thermo-pressure decoupled liquid piston compressed air energy storage system and its operation method. By adjusting the compression ratio of the multi-stage compressor in the variable compression system and matching the compression ratio of the dual-tank near-isothermal compression system to achieve the target pressure, the compression heat generated by the compressed air during the energy storage process can be fully utilized in the energy release process. The compression heat generated by the compressed air process in the variable compressed air system is stored through the heat accumulator unit, and the pressure potential energy is obtained and stored by utilizing the flexibility of the compressed air energy storage unit, which includes both the variable compressed air system and the dual-tank near-isothermal compressed air energy storage system. This achieves decoupling of thermal energy and pressure potential energy and separate storage of thermal energy and pressure potential energy, efficiently distributing the thermal energy required for releasing pressure potential energy.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a thermo-compression decoupled liquid piston compressed air energy storage system, comprising a variable compressed air system, a dual-tank near-isothermal compressed air energy storage system, a heat exchange and storage unit, and an expansion generator set; the variable compressed air system includes a multi-stage compressor, with a heat exchange and storage unit installed at the outlet of each stage compressor from low to high; the gas outlet of the final stage heat exchange and storage unit is connected to the gas inlet of the dual-tank near-isothermal compressed air energy storage system; the compressor is connected to the hot side of the heat exchange and storage unit; the gas outlet of the dual-tank near-isothermal compressed air energy storage system is sequentially connected to a heat storage tank; the expansion generator set includes a multi-stage expander, with the working fluid inlet of each stage expander connected to the cold side of the heat exchange and storage unit; the outlet of the heat storage tank is connected to the gas inlet on the cold side of the heat exchange and storage unit at the inlet of the highest stage expander; the multi-stage compressor set is driven by an electric motor; the expansion generator set is connected to a generator; the inlet of the dual-tank near-isothermal compressed air energy storage system is connected to a circulating water pump and an underground water tank.

[0007] The heat exchange and storage unit includes a packed bed accumulator, a water cooler, and a water heater. The hot-side inlet of the packed bed accumulator is connected to the compressor outlet, the hot-side outlet of the packed bed accumulator is connected to the hot-side inlet of the water cooler, and the hot-side outlet of the water cooler is connected to the compressor inlet. The cold-side inlet of the highest-level water heater serves as the gas inlet on the cold side of the heat exchange and storage unit. The cold-side outlet of the water heater is connected to the cold-side inlet of the packed bed accumulator, and the cold-side outlet of the packed bed accumulator is connected to the expander. Both the hot side of the water heater and the cold side of the water cooler are connected to an underground water source or an underground water tank.

[0008] The multi-stage compressor unit includes a low-pressure compressor, a medium-pressure compressor, and a high-pressure compressor arranged along the airflow direction. The expander generator unit includes the inlets of a high-pressure expander, a medium-pressure expander, and a low-pressure expander arranged sequentially along the airflow direction. The hot-side outlets of the first and second water coolers are respectively connected to the inlets of the medium-pressure compressor and the high-pressure compressor. The hot-side outlet of the third water cooler is connected to the air inlet of the dual-tank near-isothermal compressed air energy storage system and serves as a connection section between the variable compression system and the near-isothermal compression system. The outlets of the high-pressure expander and the medium-pressure expander are respectively connected to the cold-side inlets of the second and third water heaters. The outlet of the thermal storage tank is connected to the cold-side inlet of the first water heater.

[0009] The thermal storage tank is a vertical tank. Inside the thermal storage tank, there are 5-8 perforated phase change heat storage plates evenly distributed horizontally along the height direction. The perforated phase change heat storage plates are gradually curved and protruding from the edge to the center, and the higher the height, the greater the protrusion of the perforated phase change heat storage plates. The bending radius of the perforated phase change heat storage plates does not exceed the radius of the thermal storage tank body. The perforated phase change heat storage plates are welded to the surrounding pipe wall of the thermal storage tank.

[0010] The perforated phase change heat storage plate inside the thermal storage tank contains phase change heat storage balls. The balls are evenly distributed in the perforated phase change heat storage plate and the number of layers does not exceed one layer. The perforated phase change heat storage plate has a different number of vent holes distributed along different radii. The vent hole spacing is 1 / 2-2 / 3 of the vent hole diameter. Along the direction of increasing radius, the number of vent holes per ring increases by 5-10.

[0011] The dual-tank near-isothermal compressed air energy storage system includes a first high-pressure water-air tank and a second high-pressure water-air tank. The first and second high-pressure water-air tanks are connected by two pipelines to their inlets and outlets. A gas-liquid separator is installed on the connecting pipelines between the inlets and outlets of the first and second high-pressure water-air tanks. Valves are installed at both the inlets and outlets of the first and second high-pressure water-air tanks. Both tanks are equipped with level sensors. The inlets of the first and second high-pressure water-air tanks are connected to an underground water tank via a water pump unit. The air inlets of the first and second high-pressure water-air tanks are connected to the air outlets of a heat exchange and storage unit. Valves are installed on the pipelines from the heat exchange and storage unit to the air inlets of the first and second high-pressure water-air tanks. The air outlets of the first and second high-pressure water-air tanks are connected to a thermal storage tank. Valves are also installed on the pipelines from the air outlets of the first and second high-pressure water-air tanks to the thermal storage tank.

[0012] The generator's electrical output is connected to the power grid and / or to drive a multi-stage compressor and a water pump.

[0013] Based on the operation method of the liquid piston compressed air energy storage system with thermal decoupling described in this invention, in the preset stage, water is added to the dual-tank near-isothermal compressed air energy storage unit to the set water level.

[0014] During system energy storage, air is compressed through a multi-stage compressor. The compressed air releases heat in the heat exchange and storage unit at the outlet of each stage compressor, and then enters the dual-tank near-isothermal compressed air energy storage system through the final stage heat exchange and storage unit, where it is compressed to the target pressure. The air that has reached the target pressure then enters the heat storage tank for energy storage. The dual-tank near-isothermal compressed air energy storage system pressurizes water by pumping from an underground water tank.

[0015] When the system releases energy, compressed air is released from the bottom of the thermal storage tank. After absorbing heat and heating up in the heat exchange and storage unit at the working fluid inlet of each stage expander, the compressed air enters the expander to do work and drive the generator to generate electricity.

[0016] The variable compressed air system serves as the low-pressure stage compressed air on the energy storage side of the entire system, while the dual-tank near-isothermal compressed air system serves as the high-pressure stage compressed air on the energy storage side. The outlet of the variable compressed air system is connected to the inlet of the dual-tank near-isothermal compressed air system. By adjusting the compression ratio of each stage compressor in the variable compressed air system, the compression ratio of the water-air tank in the dual-tank near-isothermal compressed air system is matched and adjusted to achieve the target pressure, so that the heat of compression generated by the compressed air during the energy storage process can be fully utilized in the energy release process. The heat of compression generated by the variable compressed air system during the compressed air process is stored in a heat exchange and heat storage unit.

[0017] The thermal storage tank has 5-8 perforated phase change heat storage plates evenly distributed horizontally along its height. Phase change heat storage balls are distributed in the perforated phase change heat storage plates inside the thermal storage tank. Air is compressed to the target pressure through a dual-tank near-isothermal compressed air energy storage system and enters from the top of the thermal storage tank. The air passes through the perforated phase change heat storage plates layer by layer and gradually fills the entire thermal storage tank. The near-isothermal compression heat is stored in the phase change heat storage balls inside the perforated phase change heat storage plates. The perforated phase change heat storage plates at the top layer absorb the most heat because they have the highest contact temperature with the air.

[0018] When the system releases energy, compressed air is released from the bottom of the thermal storage tank. The expansion and cooling of the air in the thermal storage tank creates a temperature difference with the perforated phase change heat storage plate. The phase change material in the phase change heat storage ball in the perforated phase change heat storage plate releases heat through phase change, and the air absorbs heat and rises in temperature. Subsequently, the compressed air enters the expander unit step by step after pre-heat exchange in the heat exchange and heat storage unit.

[0019] The generator produces electricity that is used in the power grid, compressor motors, and water pump units.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] In the energy storage process described in this invention, the variable compressed air system in the compressed air energy storage unit serves as the low-pressure stage compressed air on the energy storage side of the entire power generation system, while the dual-tank near-isothermal compressed air system serves as the high-pressure stage compressed air on the energy storage side of the entire power generation system. The outlet of the variable compressed air system is connected to the inlet of the dual-tank near-isothermal compressed air system. By adjusting the compression ratios of the low-pressure, medium-pressure, and high-pressure compressors in the variable compressed air system, and matching the compression ratios of the first and second high-pressure water-gas tanks in the dual-tank near-isothermal compressed air system, the target pressure is achieved. This allows the compression heat generated by the compressed air during energy storage to be fully utilized during the energy release process, avoiding system heat loss and improving system efficiency. A heat accumulator unit is used to store the compression heat generated during the compression process of the variable compressed air system. The flexibility of the compressed air energy storage unit, which includes both the variable compressed air system and the dual-tank near-isothermal compressed air energy storage system, is utilized to acquire and store pressure potential energy, achieving decoupling of thermal energy and pressure potential energy and separate storage of thermal energy and pressure potential energy, efficiently distributing the thermal energy required for releasing pressure potential energy.

[0022] Furthermore, the three water coolers use groundwater or water from underground water tanks as their cold-side medium to cool the compressed air to room temperature, thereby reducing the operating energy consumption of the low-pressure compressor, medium-pressure compressor, and high-pressure compressor; the three water heaters use groundwater or water from underground water tanks as their hot-side medium to preheat the outlet air of the thermal storage tank, high-pressure expander, and medium-pressure expander to near ambient temperature, thereby saving stored compression heat.

[0023] Furthermore, by casting perforated phase change heat storage plates with varying degrees of protrusion, different levels of flow resistance are set at different heights to eliminate uneven air intake at the central air inlet at the top of the heat storage tank.

[0024] Furthermore, the bending radius of the perforated phase change heat storage plate should not exceed the radius of the heat storage tank body to prevent excessive flow resistance from causing excessive pressure loss of compressed gas.

[0025] Furthermore, along the direction of increasing radius, the number of vents per ring is increased by 5-10 to achieve uniform ventilation.

[0026] Furthermore, the thermal storage tank is equipped with 5-8 perforated phase change heat storage plates with different degrees of curvature evenly distributed horizontally along the height direction, and the higher the height, the greater the degree of protrusion of the perforated phase change heat storage plates; the heat storage plates are welded to the surrounding pipe wall of the thermal storage tank, and different degrees of flow resistance are set at different heights by casting perforated phase change heat storage plates with different degrees of protrusion, thereby eliminating uneven air intake at the central air inlet at the top of the thermal storage tank.

[0027] Furthermore, the perforated phase change heat storage plates inside the thermal storage tank contain phase change heat storage balls for absorbing heat through phase change. During the energy storage phase, when compressed air enters the thermal storage tank, the air passes through the perforated phase change heat storage plates layer by layer and gradually fills the entire thermal storage tank, storing the near-isothermal compression heat in the phase change heat storage balls within the perforated phase change heat storage plates. During the energy release phase, the compressed air is released from the bottom of the thermal storage tank. Due to the expansion and cooling of the air inside the thermal storage tank, a temperature difference is generated, causing the phase change heat storage balls within the perforated phase change heat storage plates to release heat through phase change, heating the compressed air, reducing heat loss, and improving system efficiency. Attached Figure Description

[0028] Figure 1 This is a diagram of a thermo-pressure decoupled liquid piston compressed air energy storage system according to the present invention.

[0029] Figure 2 This is a schematic diagram of a heat storage gas tank according to the present invention.

[0030] Figure 3 This is a schematic cross-sectional view of a thermal storage gas tank according to the present invention.

[0031] Figure 4 This is a schematic diagram of a perforated phase change heat storage plate according to the present invention.

[0032] Figure 5 This is a partial cross-sectional schematic diagram of a perforated phase change heat storage plate according to the present invention.

[0033] Wherein: 1-Low-pressure compressor, 2-Packed bed accumulator, 3-First water cooler, 4-Medium-pressure compressor, 5-Packed bed accumulator, 6-Second water cooler, 7-High-pressure compressor, 8-Packed bed accumulator, 9-Third water cooler, 10-Regenerative gas storage tank, 11-Electric motor, 12-Generator, 13-Second intake valve, 14-First intake valve, 15-First exhaust valve, 16-Second exhaust valve, 17-First liquid level sensor, 18-Second liquid level sensor, 19-First water inlet valve, 20-Second water inlet valve, 2 1-First drain valve, 22-Second drain valve, 23-Water pump unit, 24-Gas-liquid separator, 25-Water supply valve, 26-Underground water tank, 27-First high-pressure water-gas tank, 28-Second high-pressure water-gas tank, 29-First water heater, 30-High-pressure expander, 31-Second water heater, 32-Medium-pressure expander, 33-Third water heater, 34-Low-pressure expander, 35-Power grid, 36-Perforated phase change heat storage plate, 37-Phase change heat storage ball, 38-Ventilation hole, 39-Air inlet of air storage tank, 40-Air outlet of air storage tank. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings:

[0035] Compared to adiabatic compressed air energy storage, near-isothermal compressed air energy storage not only has higher compression efficiency but also eliminates the need for heat storage equipment, saving significant equipment purchase costs and avoiding heat transfer losses from heat exchangers and heat dissipation during the heat storage process. The dual-tank near-isothermal compressed air energy storage system is one type of near-isothermal air energy storage system. It uses a circulating water pump to drive the liquid levels in two high-pressure water-air tanks to alternately rise, thereby alternately compressing air to the target pressure condition.

[0036] The packed bed accumulator includes a first packed bed accumulator 2, a second packed bed accumulator 5, and a third packed bed accumulator 8; the water cooler includes a first water cooler 3, a second water cooler 6, and a third water cooler 9; the water heater includes a first water heater 29, a second water heater 31, and a third water heater 33.

[0037] Please see Figure 1The present invention provides a thermo-pressure decoupled liquid piston compressed air energy storage system, comprising a compressed air energy storage unit, a heat exchange and storage unit, and an expansion generator set; the compressed air energy storage unit includes a variable compressed air system and a dual-tank near-isothermal compressed air energy storage system; the variable compressed air system includes a low-pressure compressor 1, a medium-pressure compressor 4, and a high-pressure compressor 7, which are connected to an electric motor 11, driven by excess electrical energy; the heat exchange and storage unit includes a first water cooler 3, a second water cooler 6, and a third water cooler... Unit 9, first water heater 29, second water heater 31, third water heater 33, first packed bed accumulator 2, second packed bed accumulator 5, and third packed bed accumulator 8; low-pressure compressor 1, first packed bed accumulator 2 (hot side), first water cooler 3 (hot side), medium-pressure compressor 4, second packed bed accumulator 5 (hot side), second water cooler 6 (hot side), high-pressure compressor 7, third packed bed accumulator 8 (hot side), and third water cooler 9 (hot side) are sequentially connected along the medium flow direction; the outlet of the regenerative gas storage tank 10 is connected to the cold side inlet of the first water heater 29;

[0038] The expander generator set includes a high-pressure expander 30, a medium-pressure expander 32, and a low-pressure expander 34. The high-pressure expander 30, the medium-pressure expander 31, and the low-pressure expander 32 are connected to the generator 12, and the generator is connected to the power grid 35. The cold side of the first water heater 29, the cold side of the third packed bed accumulator 8, the high-pressure expander 30, the cold side of the second water heater 31, the cold side of the second packed bed accumulator 5, the medium-pressure expander 32, the cold side of the third water heater 33, the first packed bed accumulator 2, and the low-pressure expander 34 are connected along the medium flow direction. The outlet of the low-pressure expander 34 is vented, and the inlet of the low-pressure compressor 1 is the air inlet of the system.

[0039] The dual-tank near-isothermal compressed air energy storage system includes a thermal storage tank 10, a first high-pressure water-air tank 27, a second high-pressure water-air tank 28, a water circulation pipeline, a gas inlet and outlet pipeline, and a circulating water pump unit 23. The outlet of the first high-pressure water-air tank 27 is connected to the inlet of the second high-pressure water-air tank 28 via a pipeline, and the pump unit 23 is installed on the pipeline. The inlet of the first high-pressure water-air tank 27 is connected to the outlet of the second high-pressure water-air tank 28, and the pump unit 23 is installed on the pipeline. The inlets of the first high-pressure water-air tank 27 and the second high-pressure water-air tank 28 are equipped with and share a gas-liquid separator 24. The inlets of the first high-pressure water-air tank 27 and the second high-pressure water-air tank 28 are respectively equipped with a first inlet valve 19 and a second inlet valve 20. The outlets of the first high-pressure water-air tank 27 and the second high-pressure water-air tank 28 are respectively equipped with a first drain valve 21 and a second drain valve 22. The first high-pressure water-air tank and the second high-pressure water-air tank are respectively equipped with a first liquid... Level sensor 17 and second liquid level sensor 18, the inlets of the first high-pressure water gas tank 27 and the second high-pressure water gas tank 28 are connected to the underground water tank 26 or other water source via the water pump unit 23, and a water supply valve 25 is installed on the pipeline from the underground water tank 26 or other water source to the water pump unit 23; the air inlets of the first high-pressure water gas tank 27 and the second high-pressure water gas tank 28 are connected to the air outlet of the heat exchange and heat storage unit, and the air outlet of the third water cooler 9 in the highest-level heat exchange and heat storage unit is used as the air outlet of the heat exchange and heat storage unit; a first air inlet valve 14 and a second air inlet valve 13 are respectively installed on the pipeline from the heat exchange and heat storage unit to the air inlets of the first high-pressure water gas tank 27 and the second high-pressure water gas tank 28; the air outlets of the first high-pressure water gas tank 27 and the second high-pressure water gas tank 28 are connected to the heat storage gas tank 10; a first exhaust valve 15 and a second exhaust valve 16 are respectively installed on the pipeline from the air outlets of the first high-pressure water gas tank 27 and the second high-pressure water gas tank 28 to the heat storage gas tank 10.

[0040] refer to Figure 1 To stabilize the air entering the expander, a throttle valve is required to obtain a stable airflow. This results in the gas pressure before expansion being lower than its storage pressure, causing the heat generated during gas compression to exceed the heat required for gas expansion. This leads to an imbalance between heat supply and demand during energy storage and release. To address this, a variable-pressure compressed air system serves as the low-pressure stage for the energy storage side of the entire power generation system, while a dual-tank near-isothermal compressed air system serves as the high-pressure stage. The outlet of the variable-pressure compressed air system is connected to the inlet of the dual-tank near-isothermal compressed air system. By adjusting the compression ratios of the low-pressure compressor 1, medium-pressure compressor 4, and high-pressure compressor 7 in the variable-pressure system, and matching the compression ratios of the first high-pressure water-gas tank 27 and the second high-pressure water-gas tank 28 in the dual-tank near-isothermal compressed air system, the target pressure is achieved, ensuring that the heat generated during compressed air storage is fully utilized during energy release.

[0041] refer to Figure 1 The heat exchange and heat storage unit stores the heat of compression generated during the compression process of the variable compressed air system, and utilizes the flexibility of the compressed air energy storage unit, which includes the variable compressed air system and the dual-tank near isothermal compressed air energy storage system, to obtain and store pressure potential energy. This achieves decoupling of thermal energy and pressure potential energy and separate storage of thermal energy and pressure potential energy, and efficiently distributes the thermal energy required to release pressure potential energy.

[0042] refer to Figure 1 The heat exchange and storage unit includes a packed bed accumulator whose hot-side inlets are connected to the outlets of low-pressure compressor 1, medium-pressure compressor 4, and high-pressure compressor 7, respectively, and whose hot-side outlets are connected to the hot-side inlets of the water coolers included in the heat exchange unit. The cold-side inlets of the three packed bed accumulators are connected to the cold-side outlets of the three water heaters included in the heat exchange unit, respectively, and whose cold-side outlets are connected to the inlets of high-pressure expander 30, medium-pressure expander 32, and low-pressure expander 34, respectively. The hot-side outlets of the first water cooler 3 and the second water cooler 6 are connected to the inlets of medium-pressure compressor 4 and high-pressure compressor 7, respectively, and the hot-side outlet of the third water cooler 9 is connected to the air inlet of the dual-tank near-isothermal compressed air energy storage system, and serves as a variable compression... The system is connected to the dual-tank near-isothermal compressed air energy storage system; three water coolers use groundwater or underground water tank 26 as their cold-side medium to cool the compressed air to ambient temperature, thereby reducing the operating energy consumption of the low-pressure compressor 1, medium-pressure compressor 4 and high-pressure compressor 7; the outlets of the high-pressure expander 30 and medium-pressure expander 32 are respectively connected to the cold-side inlets of the second water heater 31 and the third water heater 33, and the outlet of the thermal storage tank is connected to the cold-side inlet of the first water heater 29. The three water heaters use groundwater or underground water tank water as their hot-side medium to preheat the air at the outlets of the thermal storage tank 10, high-pressure expander 30 and medium-pressure expander 32 to near ambient temperature, saving the stored compression heat.

[0043] refer to Figure 2 , Figure 3 , Figure 4 and Figure 5 The thermal storage tank 10 is a vertical tank. Inside the thermal storage tank 10, 5-8 perforated phase change heat storage plates 36 are horizontally arranged along the height direction. The perforated phase change heat storage plates 36 are gradually curved and protruding from the edge to the center, and the higher the height, the greater the protrusion of the perforated phase change heat storage plates 36. For the perforated phase change heat storage plates 36, the radius of curvature of the vertical surface does not exceed the radius of the tank body of the thermal storage tank 10, so as to prevent excessive flow resistance and excessive pressure loss of compressed air. The heat storage plates are welded to the surrounding pipe wall of the thermal storage tank. Different degrees of flow resistance are set at different heights by casting perforated phase change heat storage plates with different degrees of protrusion, so as to eliminate uneven air intake at the central air inlet at the top of the thermal storage tank 10.

[0044] During energy storage, the near-isothermal compression process generates some heat, causing the air temperature to rise. When air enters from the top of the thermal storage tank 10, the perforated phase change heat storage plates 36 with heat storage function distributed at different heights of the thermal storage tank 10 will gradually absorb the heat from the air. During energy release, the thermal storage tank 10 releases air. The air expands and cools down, creating a temperature difference with the perforated phase change heat storage plates 36. The phase change material inside the phase change heat storage ball 37 undergoes a phase change and releases heat into the air. The air is heated and enters the packed bed heat storage device.

[0045] refer to Figure 4 and Figure 5 The perforated phase change heat storage plate 36 inside the heat storage tank contains phase change heat storage balls 37 for absorbing heat through phase change. The balls are evenly distributed in the perforated phase change heat storage plate 36 and the number of layers does not exceed 2. The perforated phase change heat storage plate has a different number of vent holes 38 distributed along different radii. The vent holes 38 are spaced about 1 / 2 to 2 / 3 of the vent hole diameter. Along the direction of increasing distribution radius, the number of vent holes 38 per ring increases by 5 to 10 to achieve uniform ventilation.

[0046] refer to Figure 1 , Figure 3 , Figure 4 and Figure 5 During energy storage, the near-isothermal compression process generates some heat, causing the air temperature to rise. When air enters from the top of the thermal storage tank 10, the perforated phase change heat storage plates 36 with heat storage function distributed at different heights of the thermal storage tank 10 will gradually absorb the heat of the air. During energy release, the thermal storage tank 10 releases air. The air expands and cools down, creating a temperature difference with the perforated phase change heat storage plates 36. The phase change material in the phase change heat storage ball 37 undergoes a phase change and releases heat into the air. The air is heated and enters the water heater and the packed bed accumulator.

[0047] Based on the above system, the present invention provides a method for thermally decoupled liquid piston compressed air energy storage and release, comprising the following steps:

[0048] During the pre-setting stage, water from the first high-pressure water tank 27 and the second high-pressure water tank 28 is replenished to the pre-set liquid level through the water replenishment pipe. Then, the water replenishment valve 25 is closed, and the water replenishment valve 25 is not opened again for water replenishment if there is no liquid loss.

[0049] During the energy storage stage, the air first enters the variable compressed air system for compression. The air from the atmosphere is compressed sequentially by the low-pressure compressor 1, the medium-pressure compressor 4 and the high-pressure compressor 7. After each stage of the compressor, the air is compressed by the packed bed accumulator and the water cooler, and then reaches a suitable intermediate pressure. The air is then connected to the air inlet of the dual-tank near-isothermal compressed air energy storage system. The air inlet is connected to the air inlet pipeline, and the air outlet of the dual-tank near-isothermal compressed air energy storage system is connected to the air outlet pipeline. Gas reaching intermediate pressure enters through the inlet. Simultaneously, the first inlet valve 14 is opened, and the second inlet valve 13, first exhaust valve 15, and second exhaust valve 16 are closed. As gas enters the first high-pressure water-gas tank 27 through the inlet pipe, the first drain valve 21 and second water inlet valve 20 are opened, while the second drain valve 22 and first water inlet valve 19 are closed. This allows water in the first high-pressure water-gas tank 27 to pass sequentially through the gas-liquid separator 24 and the water pump unit 23, being forced into the second high-pressure water-gas tank 12. As the liquid level in the second high-pressure water-gas tank 28 rises, the internal gas pressure increases. When the gas pressure in the second high-pressure water-gas tank 28 is not less than the gas pressure in the exhaust pipe, the second exhaust valve 16 opens, continuing compression until the liquid level reaches the second level. After the sensor 18 detects the preset liquid level, the second exhaust valve 16 is closed, while the second drain valve 22, the first water inlet valve 19, and the second air inlet valve 13 are opened. The second water inlet valve 20, the first drain valve 21, and the first air inlet valve 14 are closed. At this time, the gas in the air inlet pipe enters the second high-pressure water-gas tank 28. The water in the second high-pressure water-gas tank 28 passes through the gas-liquid separator 24 and the water pump unit 23 in sequence and enters the first high-pressure water-gas tank 27. The liquid level in the first high-pressure water-gas tank rises, and the gas is compressed. When the gas pressure in the first high-pressure water-gas tank 27 is not less than the gas pressure in the exhaust pipe, the first exhaust valve 15 is opened, and compression continues until the liquid level reaches the preset liquid level detected by the first liquid level sensor 17, after which the first exhaust valve 15 is closed. The valves are adjusted repeatedly to circulate and increase the pressure. Compressed air is then introduced from the top of the thermal storage tank 10 through the exhaust pipe. The compressed air passes layer by layer through the perforated phase change heat storage plates 36 and gradually fills the entire thermal storage tank 10. The near-isothermal heat of compression is stored in the phase change heat storage balls 37 within the perforated phase change heat storage plates 36. The top perforated phase change heat storage plate 10 absorbs more heat because it has the highest contact temperature with the air. During the simultaneous intake and drainage of the high-pressure water-gas tank, the gas pressure in the tank remains stable due to the consistent volumetric flow rate.

[0050] When the system releases energy, compressed air is released from the bottom of the thermal storage tank 10. Due to the expansion and cooling of the air in the thermal storage tank 10 and the temperature difference generated by the perforated phase change heat storage plate 36, the phase change material in the phase change heat storage ball 37 in the perforated phase change heat storage plate 36 undergoes phase change and releases heat, and the air absorbs heat and rises in temperature. Subsequently, the compressed air is preheated by the water heater before the high-pressure expander 30, medium-pressure expander 32 and low-pressure expander 34 and heated by the packed bed heat storage device to form high-temperature and high-pressure air. It then enters the high-pressure expander 30, medium-pressure expander 32 and low-pressure expander 34 in stages to expand and drive the generator 12 to generate electricity. The generated electricity is fed into the power grid 35.

Claims

1. A thermo-pressure decoupled liquid piston compressed air energy storage system, characterized in that, The system includes a variable compressed air system, a dual-tank near-isothermal compressed air energy storage system, a heat exchange and storage unit, and an expander generator set. The variable compressed air system includes a multi-stage compressor, with a heat exchange and storage unit installed at the outlet of each stage compressor from low to high temperature. The gas outlet of the final stage heat exchange and storage unit is connected to the gas inlet of the dual-tank near-isothermal compressed air energy storage system. The compressor is connected to the hot side of the heat exchange and storage unit. The gas outlet of the dual-tank near-isothermal compressed air energy storage system is sequentially connected to a heat storage tank (10). The expander generator set includes a multi-stage expander, with the working fluid inlet of each expander connected to... The cold side of the heat exchange and heat storage unit; the outlet of the heat storage tank (10) is connected to the gas inlet of the cold side of the heat exchange and heat storage unit at the inlet of the highest stage expander; the multi-stage compressor unit is driven by an electric motor, and the expander generator unit is connected to the generator; the inlet of the dual-tank near-isothermal compressed air energy storage system is connected to the circulating water pump (23) and the underground water tank (26); the heat exchange and heat storage unit includes a packed bed accumulator, a water cooler and a water heater; the hot side inlet of the packed bed accumulator is connected to the compressor outlet; the hot side outlet of the packed bed accumulator is connected to the hot side inlet of the water cooler; and the hot side outlet of the water cooler is connected to the compressor inlet. The cold-side inlet of the highest-level water heater serves as the gas inlet on the cold side of the heat exchange and storage unit. The cold-side outlet of the water heater is connected to the cold-side inlet of the packed bed accumulator, and the cold-side outlet of the packed bed accumulator is connected to the expander. The hot side of the water heater and the cold side of the water cooler are both connected to an underground water source or an underground water tank (26). The multi-stage compressor unit includes a low-pressure compressor (1), a medium-pressure compressor (4), and a high-pressure compressor (7) arranged along the airflow direction. The expander generator unit includes a high-pressure expander (30), a medium-pressure expander (32), and a low-pressure expander (34) arranged sequentially along the airflow direction. The inlet of the first water cooler (3) and the second water cooler (6) are respectively connected to the inlet of the medium-pressure compressor (4) and the high-pressure compressor (7), and the hot-side outlet of the third water cooler (9) is connected to the air inlet of the dual-tank near-isothermal compressed air energy storage system, and serves as the connection section between the variable compression system and the near-isothermal compression system; the outlet of the high-pressure expander (30) and the medium-pressure expander (32) are respectively connected to the cold-side inlet of the second water heater (31) and the third water heater (33), and the outlet of the heat storage tank (10) is connected to the cold-side inlet of the first water heater (29).

2. The thermo-pressure decoupled liquid piston compressed air energy storage system according to claim 1, characterized in that, The thermal storage tank (10) is a vertical tank. Inside the thermal storage tank (10), there are 5-8 perforated phase change heat storage plates (36) evenly distributed horizontally along the height direction. The perforated phase change heat storage plates (36) are gradually curved and protruded from the edge to the middle. The higher the height, the greater the protrusion of the perforated phase change heat storage plates (36). The bending radius of the perforated phase change heat storage plates (36) does not exceed the radius of the tank body of the thermal storage tank (10). The perforated phase change heat storage plates (36) are welded to the surrounding pipe wall of the thermal storage tank.

3. The thermo-pressure decoupled liquid piston compressed air energy storage system according to claim 2, characterized in that, The perforated phase change heat storage plate (36) inside the heat storage tank has phase change heat storage balls (37) distributed in it. The balls are evenly distributed in the perforated phase change heat storage plate (36) and the number of layers does not exceed (2). The perforated phase change heat storage plate has a different number of vent holes (38) distributed along different radii. The vent holes (38) are spaced at intervals of 1 / 2-2 / 3 of the vent hole diameter. Along the direction of increasing radius, the number of vent holes (38) per ring increases by 5-10.

4. The thermo-pressure decoupled liquid piston compressed air energy storage system according to claim 1, characterized in that, The dual-tank near-isothermal compressed air energy storage system includes a first high-pressure water-air tank (27) and a second high-pressure water-air tank (28). The first high-pressure water-air tank (27) and the second high-pressure water-air tank (28) are connected by two pipelines to their inlets and outlets. A gas-liquid separator (24) is installed on the connecting pipeline between the inlets and outlets of the first high-pressure water-air tank (27) and the second high-pressure water-air tank (28). Valves are installed at both the inlets and outlets of the first high-pressure water-air tank (27) and the second high-pressure water-air tank (28). Both the first high-pressure water-air tank and the second high-pressure water-air tank are equipped with level sensors. The inlet of the water-gas tank (28) is connected to the underground water tank (26) via the circulating water pump (23); the inlets of the first high-pressure water-gas tank (27) and the second high-pressure water-gas tank (28) are connected to the outlet of the heat exchange and heat storage unit. Valves are installed on the pipelines from the heat exchange and heat storage unit to the inlets of the first high-pressure water-gas tank (27) and the second high-pressure water-gas tank (28). The outlets of the first high-pressure water-gas tank (27) and the second high-pressure water-gas tank (28) are connected to the heat storage tank (10). Valves are installed on the pipelines from the outlets of the first high-pressure water-gas tank (27) and the second high-pressure water-gas tank (28) to the heat storage tank (10).

5. The thermo-pressure decoupled liquid piston compressed air energy storage system according to claim 1, characterized in that, The generator’s power output is connected to the power grid (35) and / or to a motor that drives a multi-stage compressor and a water pump.

6. An operation method for a liquid piston compressed air energy storage system with thermo-pressure decoupling according to any one of claims 1-5, characterized in that, During the pre-setting stage, water is added to the dual-tank near-isothermal compressed air energy storage unit to the set water level; During system energy storage, air is compressed by a multi-stage compressor. The compressed air releases heat in the heat exchange and heat storage unit at the outlet of each stage compressor. It then enters the dual-tank near-isothermal compressed air energy storage system through the final stage heat exchange and heat storage unit and is compressed to the target pressure. The air that reaches the target pressure enters the heat storage tank (10) for energy storage. The dual-tank near-isothermal compressed air energy storage system pressurizes water from the underground water tank (26). When the system releases energy, compressed air is released from the bottom of the heat storage tank (10). After the compressed air absorbs heat and heats up in the heat exchange and heat storage unit at the working fluid inlet of each stage expander, it enters the expander to do work and drive the generator to generate electricity. The variable compressed air system serves as the low-pressure stage compressed air on the energy storage side of the entire system, while the dual-tank near-isothermal compressed air system serves as the high-pressure stage compressed air on the energy storage side. The outlet of the variable compressed air system is connected to the inlet of the dual-tank near-isothermal compressed air system. By adjusting the compression ratio of each stage compressor in the variable compressed air system, the compression ratio of the water-air tank in the dual-tank near-isothermal compressed air system is matched and adjusted to achieve the target pressure, so that the heat of compression generated by the compressed air during the energy storage process can be fully utilized in the energy release process. The heat of compression generated by the variable compressed air system during the compressed air process is stored in a heat exchange and heat storage unit.

7. The operating method according to claim 6, characterized in that, The heat storage tank (10) has 5-8 perforated phase change heat storage plates (36) evenly distributed horizontally along the height direction inside. The perforated phase change heat storage plates (36) inside the heat storage tank have phase change heat storage balls (37) distributed in them. Air is compressed to the target pressure through the dual-tank near-isothermal compressed air energy storage system and enters from the top of the heat storage tank (10). The air passes through the perforated phase change heat storage plates (36) layer by layer and gradually fills the entire heat storage tank (10). The near-isothermal compression heat is stored in the phase change heat storage balls (37) inside the perforated phase change heat storage plates (36). The perforated phase change heat storage plates (36) at the top layer absorb the most heat because they have the highest contact temperature with the air. When the system releases energy, compressed air is released from the bottom of the thermal storage tank (10). The expansion and cooling of the air in the thermal storage tank (10) and the temperature difference generated by the perforated phase change heat storage plate (36) are generated. The phase change material in the phase change heat storage ball (37) in the perforated phase change heat storage plate releases heat through phase change, and the air absorbs heat and rises in temperature. Then, the compressed air enters the expander unit step by step after preheating through the heat exchange and heat storage unit.

8. The operating method according to claim 6, characterized in that, The generator produces electricity that is fed into the power grid, and is used in the motors of the compressor and the circulating water pump (23).

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