A dual-medium compressed air energy storage system based on phase change thermal storage

Abstract

This application relates to the field of air energy storage technology, and particularly to a dual-medium compressed air energy storage system based on phase change heat storage. The system includes: a multi-stage compression and expansion unit, comprising an air compressor, an air expander, a first phase change heat accumulator, and a cooler, connected sequentially at each stage; a liquid storage unit, a second phase change heat accumulator, and a waste heat utilization unit, wherein the waste heat utilization unit exchanges heat with the first phase change heat accumulator of each stage of the compression and expansion unit, and the second phase change heat accumulator is connected to both the liquid storage unit and the waste heat utilization unit; the gas storage tank is a spherical tank-type rigid container, internally divided into an air chamber and a liquid chamber by a flexible diaphragm. The air chamber stores compressed air and is connected to the final stage of the compression and expansion unit, while the liquid chamber stores liquid carbon dioxide and is connected to the waste heat utilization unit. The working pressures of the two chambers are equal. This solves the problems of poor sealing, low gas density, low energy storage efficiency, and difficulty in achieving constant pressure operation in related technologies.

Description

Technical Field

[0001] This application relates to the field of air energy storage technology, and in particular to a dual-medium compressed air energy storage system based on phase change thermal storage. Background Technology

[0002] To achieve efficient and stable constant-pressure compressed air energy storage, research has been conducted on air energy storage technologies in recent years. Studies have shown that current related technologies mostly adopt underwater flexible compressed air energy storage schemes, relying on flexible energy storage packs, but the sealing performance is difficult to guarantee, and increased air pressure and water depth can easily lead to leakage; supercritical air-carbon dioxide energy storage schemes achieve adjustable pressure and constant-pressure operation by introducing supercritical carbon dioxide circulation, but carbon dioxide is stored in a gaseous state with low density, resulting in limited energy storage efficiency and utilization. Summary of the Invention

[0003] This application provides a dual-medium compressed air energy storage system based on phase change thermal storage to solve problems such as high technical complexity, poor sealing, low gas density, low energy storage efficiency, low energy storage utilization rate, and difficulty in achieving constant pressure operation.

[0004] The first aspect of this application provides a dual-medium compressed air energy storage system based on phase change heat storage, comprising the following steps: a multi-stage compression and expansion unit, each stage including an air compressor, an air expander, a first phase change heat accumulator, and a cooler, the multi-stage compression and expansion units being connected sequentially; a liquid storage unit, a second phase change heat accumulator, and a waste heat utilization unit, the waste heat utilization unit exchanging heat with the first phase change heat accumulator of each stage of the compression and expansion unit, the second phase change heat accumulator being connected to both the liquid storage unit and the waste heat utilization unit; and a gas storage tank, comprising a spherical rigid container, the spherical rigid container being divided into an air chamber and a liquid chamber by a flexible diaphragm, the air chamber being connected to the final stage of the compression and expansion unit, the liquid chamber being connected to the waste heat utilization unit, the air chamber being used to store compressed air, the liquid chamber being used to store liquid carbon dioxide, and the working pressures of the air chamber and the liquid chamber being equal.

[0005] Optionally, in one embodiment of this application, the spherical rigid container is composed of an outer gas storage wall, a vacuum layer, an inner gas storage wall, an air cavity, a flexible diaphragm, and a liquid cavity, from the outside to the inside.

[0006] Optionally, in one embodiment of this application, both the first phase change accumulator and the second phase change accumulator include a tube side and a shell side, with compressed air flowing through the tube side and the shell side filled with a solid-liquid phase change heat storage medium.

[0007] Optionally, in one embodiment of this application, the solid-liquid phase change heat storage medium includes one or more combinations of molten salt high-temperature phase change heat storage materials and neopentyl glycol or some salt low-temperature phase change heat storage materials.

[0008] Optionally, in one embodiment of this application, the air compressor and the air expander are connected to a valve, the valve is connected to one end of the first phase change heat accumulator, the other end of the first phase change heat accumulator is connected to the first port of the cooler, the second end of the cooler is connected to the valve of the next stage compression and expansion unit, the third end of the cooler is connected to the waste heat utilization unit, and the fourth end of the cooler is connected to the condenser.

[0009] Optionally, in one embodiment of this application, the waste heat utilization unit includes a regenerator and a carbon dioxide expander. The regenerator receives external waste heat and is connected to the carbon dioxide expander. The carbon dioxide expander is connected to the liquid chamber of the gas storage tank through a first control valve, and the carbon dioxide expander is connected to the third end of the cooler and the second phase change heat accumulator through a second control valve.

[0010] Optionally, in one embodiment of this application, the condenser is connected to the second control valve via a third control valve.

[0011] Optionally, in one embodiment of this application, the liquid storage unit includes a booster pump and a liquid storage tank, the booster pump being connected to the second phase change accumulator and the liquid storage tank respectively, and the liquid storage tank being connected to the second phase change accumulator.

[0012] Optionally, in one embodiment of this application, during the energy storage stage, both the air chamber and the liquid storage tank in the gas storage tank are vented, and the liquid chamber is filled with liquid carbon dioxide. After opening the valve and starting the air compressor to compress the air to a medium-high pressure and high temperature state, the high-temperature air enters the tube side of the first phase change accumulator. It is then cooled by the solid-liquid phase change heat storage medium in the shell side of the first phase change accumulator, and enters the cooler for further cooling. After being compressed and cooled stage by stage by stage compression and expansion units, the compressed air is stored in the air chamber of the gas storage tank. The solid-liquid phase change heat storage medium of the first phase change accumulator... The heat is absorbed and melted, and the heat of compression is stored in the solid-liquid phase change heat storage medium of the first phase change heat accumulator. The heat exchange medium in the cooler is the liquid carbon dioxide discharged from the liquid chamber in the gas storage tank. When the compressor continuously charges the gas storage tank with compressed air, the third control valve is closed. The liquid carbon dioxide stored in the liquid chamber of the gas storage tank is discharged and enters the cooler through the first control valve to absorb the heat of compression and then vaporize. At this time, the second control valve and valve are opened to allow the gaseous carbon dioxide to enter the second phase change heat accumulator to release heat and reduce to a low temperature state. Then, it is pressurized to a liquid state by the booster pump and finally stored in the liquid storage tank.

[0013] Optionally, in one embodiment of this application, during the energy release phase, the valve is first opened in reverse, and the high-pressure liquid carbon dioxide stored in the storage tank enters the second phase change heat accumulator through the valve for heat exchange. The high-pressure liquid carbon dioxide is heated to gaseous carbon dioxide, and then the gaseous carbon dioxide is further heated to a high temperature by the regenerator and enters the carbon dioxide expander to expand and do work. The pressure of the expanded carbon dioxide is equivalent to the pressure of the compressed air stored in the air chamber of the gas storage tank. Then, the gaseous carbon dioxide discharged after expansion enters the cooler in reverse through the second control valve to exchange heat with the compressed air discharged from the air chamber of the gas storage tank. At this time, the third control valve is opened, and the carbon dioxide after heat exchange is first cooled and then enters the condenser for further cooling and condensation into liquid. Finally, the liquid carbon dioxide is injected into the liquid chamber in the gas storage tank through the first control valve, while the air in the gas storage tank is gradually discharged at a constant pressure to power the air expander for electricity generation, thus forming a cycle until the air in the air chamber of the gas storage tank is completely released.

[0014] Therefore, this application has the following beneficial effects: This application embodiment controls air temperature and pressure through a multi-stage compression and expansion unit, achieving efficient compressed air energy storage and reducing energy consumption during compression. The liquid storage unit works in conjunction with a second phase change accumulator and a waste heat utilization unit. The waste heat utilization unit exchanges heat with each stage of the first phase change accumulator. The second phase change accumulator connects the liquid storage unit and the waste heat utilization unit. By recovering and utilizing compression heat and waste heat, heat storage efficiency is improved, and the overall system power consumption is reduced through cascaded phase change. The gas storage tank adopts a spherical rigid container, internally divided into an air chamber and a liquid chamber by a flexible diaphragm. The air chamber connects to the final stage compression and expansion unit for storing compressed air, and the liquid chamber connects to the waste heat utilization unit for storing liquid carbon dioxide. The air chamber and liquid chamber operate at equal pressures, achieving constant-pressure gas storage, increasing the liquid carbon dioxide storage density, improving energy storage efficiency and system operational stability, while ensuring pressure balance between the air and liquid chambers for controlled energy release and utilization. This solves the problems of high complexity, poor sealing, low gas density, low energy storage efficiency, low energy utilization rate, and difficulty in achieving constant-pressure operation associated with related technologies.

[0015] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0016] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is an example diagram of a dual-medium compressed air energy storage system based on phase change thermal storage according to an embodiment of this application; Figure 2 This is a schematic diagram illustrating the working principle of the energy storage stage according to an embodiment of this application; Figure 3 This is a schematic diagram of the gas storage facility structure according to an embodiment of this application; Figure 4 This is a schematic diagram of a phase change heat storage device according to an embodiment of this application; Figure 5 This is a schematic diagram illustrating the working principle of the energy release stage according to an embodiment of this application. Detailed Implementation

[0017] The embodiments of this application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0018] The following describes an embodiment of the dual-medium compressed air energy storage system based on phase change thermal storage, with reference to the accompanying drawings. To address the problems mentioned in the background section, this application provides a dual-medium compressed air energy storage system based on phase change thermal storage. In this embodiment, multi-stage compression and expansion units control air temperature and pressure to achieve efficient compressed air energy storage and reduce energy consumption during compression. A liquid storage unit works in conjunction with a second phase change thermal accumulator and a waste heat utilization unit. The waste heat utilization unit exchanges heat with each stage of the first phase change thermal accumulator. The second phase change thermal accumulator connects the liquid storage unit and the waste heat utilization unit. By recovering and utilizing compression heat and waste heat, the thermal storage efficiency is improved, and the overall system power consumption is reduced through cascaded phase change. The gas storage tank is a spherical rigid container, internally divided into an air chamber and a liquid chamber by a flexible diaphragm. The air chamber connects to the final compression and expansion unit for storing compressed air, and the liquid chamber connects to the waste heat utilization unit for storing liquid carbon dioxide. The air chamber and liquid chamber operate at equal pressures, enabling constant-pressure gas storage, increasing the liquid carbon dioxide storage density, improving energy storage efficiency and system operational stability, while ensuring pressure balance between the air and liquid chambers for controlled energy release and utilization. This solves the problems of high technical complexity, poor sealing, low gas density, low energy storage efficiency, low energy storage utilization, and difficulty in achieving constant pressure operation.

[0019] Specifically, Figure 1 This is a block diagram of a dual-medium compressed air energy storage system based on phase change thermal storage, provided as an embodiment of this application.

[0020] like Figure 1 As shown, the dual-medium compressed air energy storage system 10 based on phase change heat storage includes: a multi-stage compression and expansion unit 100, an air storage tank 200, a waste heat utilization unit 300, a second phase change heat storage device 400, and a liquid storage unit 500.

[0021] Among them, such as Figure 2As shown, the multi-stage compression and expansion unit 100 includes an air compressor 110, an air expander 150, a first phase change heat accumulator 130, and a cooler 140, which are connected sequentially. It also includes a liquid storage unit 500, a second phase change heat accumulator 400, and a waste heat utilization unit 300. The waste heat utilization unit 300 exchanges heat with the first phase change heat accumulator 130 of each compression and expansion unit. The second phase change heat accumulator 400 is connected to both the liquid storage unit 500 and the waste heat utilization unit 300. An air storage tank 200 includes a spherical rigid container. The spherical rigid container is divided into an air chamber 240 and a liquid chamber 260 by a flexible diaphragm 250. The air chamber 240 is connected to the final compression and expansion unit, and the liquid chamber 260 is connected to the waste heat utilization unit 300. The air chamber 240 stores compressed air, and the liquid chamber 260 stores liquid carbon dioxide. The working pressures of the air chamber 240 and the liquid chamber 260 are equal.

[0022] It is understood that the embodiments of this application use a spherical rigid container with a flexible diaphragm 250 to separate the air chamber 240 and the liquid chamber 260, which can achieve efficient energy storage and release through gas-liquid coupling; the multi-stage compression and expansion unit 100 is used to recover and release energy, thereby improving the energy density and round-trip efficiency of compressed air energy storage; the first phase change heat accumulator 130 and the second phase change heat accumulator 400 are used to recover the waste heat of compression and supplement heat during energy release, which simplifies the system configuration, reduces system power consumption, and improves the stability of output power; the pressure of the air chamber 240 is adjusted by the pressure change of liquid carbon dioxide in the liquid chamber 260, thereby achieving balanced control of the pressure of the gas storage tank 200, reducing energy loss, and improving energy storage efficiency.

[0023] Specifically, such as Figure 2As shown, the multi-stage compression and expansion unit 100 is a unit formed by sequentially connecting a multi-stage air compressor 110, an air expander 150, a first phase change heat accumulator 130, and a cooler 140, used to realize the compression and energy storage of air and the expansion and energy release of air; the air compressor 110 is a device for compressing outside air to increase its pressure and temperature; the air expander 150 is a device for expanding high-pressure air to do work and release energy; the first phase change heat accumulator 130 is a high-temperature heat accumulator used to absorb heat during compression and release heat during expansion to achieve heat recovery; the cooler 140 is a device used to reduce the temperature of compressed air to improve efficiency and protect the equipment; the liquid storage unit 5 Unit 00 is a unit consisting of a storage tank 520 and a booster pump 510, used for storing and pressurizing liquid carbon dioxide; the second phase change accumulator 400 is a low-temperature accumulator used to regulate the temperature of carbon dioxide and realize energy recovery; the waste heat utilization unit 300 is a unit used to exchange heat with each stage of the first phase change accumulator 130 to recover compression waste heat or provide expansion heating; both the first phase change accumulator 130 and the second phase change accumulator 400 include a tube side 410 and a shell side 420. The tube side 410 specifically includes: a head 411, a tube box 412, an air inlet pipe 413, an air outlet pipe 414, a heat storage medium inlet 415, and a heat storage medium outlet 416. The gas storage tank 200 is a gas storage device constructed from a rigid spherical tank-type container, with its interior divided into an air chamber 240 and a liquid chamber 260 by a flexible diaphragm 250. The flexible diaphragm 250 is a diaphragm structure used to isolate the air chamber 240 and the liquid chamber 260 and to transmit pressure. The air chamber 240 is a space used to store compressed air and connected to the final stage compression and expansion unit. The liquid chamber 260 is a space used to store liquid carbon dioxide and to regulate the pressure of the air chamber 240 by pressure changes.

[0024] In one embodiment of this application, such as Figure 3 As shown, the spherical rigid container consists of an outer gas storage wall 210, a vacuum layer 220, an inner gas storage wall 230, an air cavity 240, a flexible diaphragm 250, and a liquid cavity 260, from the outside to the inside.

[0025] Among them, the spherical rigid container is a spherical high-pressure vessel that can withstand high internal pressure and reduce stress concentration, and is used to store compressed air and liquid carbon dioxide; the outer wall 210 is the outermost shell of the spherical rigid container, which provides the main pressure resistance and protects the internal structure; the vacuum layer 220 is a heat insulation layer set between the outer wall 210 and the inner wall 230, which reduces heat transfer and maintains stable internal temperature; the inner wall 230 is the inner shell of the spherical rigid container, which is used to seal and withstand the pressure of the internal medium.

[0026] It is understandable that by designing the spherical rigid container from the outside to the inside as an outer gas storage wall 210, a vacuum layer 220, an inner gas storage wall 230, an air cavity 240, a flexible diaphragm 250, and a liquid cavity 260, the pressure-bearing capacity and overall strength of the container can be significantly improved, and stress concentration can be reduced. The vacuum layer 220 provides effective heat insulation, reduces heat transfer, ensures the temperature stability of the gas storage cavity and the liquid cavity 260, and improves energy storage efficiency. The flexible diaphragm 250 completely isolates the air cavity 240 and the liquid cavity 260, preventing gas-liquid mixing, while allowing pressure to be transmitted between them, achieving a dynamic balance of gas and hydraulic pressure.

[0027] Specifically, such as Figure 3 As shown, the gas storage tank 200 is composed of a spherical rigid container, which includes an outer gas storage wall 210, a vacuum layer 220, an inner gas storage wall 230, an air cavity 240, a flexible diaphragm 250, and a liquid cavity 260.

[0028] The gas storage tank 200 uses a spherical rigid container for gas storage. Inside the spherical tank, a flexible diaphragm 250 divides it into an air chamber 240 and a liquid chamber 260. The flexible diaphragm 250 forms a liquid chamber 260. The air chamber 240 is located between the flexible diaphragm 250 and the inner wall of the spherical tank. The flexible diaphragm 250 is a deformable and flexible membrane structure free from tension. The working pressures of the air chamber 240 and the liquid chamber 260 are equal, preferably greater than 6.5 MPa. The air chamber 240 stores compressed air, and the liquid chamber 260 stores liquid carbon dioxide. The air chamber 240 and the liquid CO2... The pressure in cavity 260 is equal and the volume distribution between the two can be adjusted by the scaling of the flexible diaphragm 250. The diaphragm can prevent the mixing of air and liquid carbon dioxide and is not permeable. The spherical rigid container consists of an outer gas storage wall 210, a vacuum layer 220, an inner gas storage wall 230, an air cavity 240, a flexible diaphragm 250, and a liquid cavity 260 from the outside to the inside. The vacuum layer 220 serves to insulate heat and balance the internal and external pressure difference, and does not need to be filled with heat insulation material. The inner and outer walls of the gas storage are made of high-strength steel, and the surface should be smooth and burr-free. The thickness and steel type are determined according to the gas storage pressure of the system.

[0029] In one embodiment of this application, such as Figure 4 As shown, both the first phase change heat accumulator 130 and the second phase change heat accumulator 400 include a tube side 410 and a shell side 420. Compressed air is passed through the tube side 410, and the shell side 420 is filled with a solid-liquid phase change heat storage medium.

[0030] The tube side 410 is the pipe section in the heat exchanger that supplies fluid flow and is used to introduce compressed air; the shell side 420 is the shell space section in the heat exchanger that surrounds the tube side 410 and is used to fill the solid-liquid phase change heat storage medium and exchange heat with the tube side 410.

[0031] It is understood that the embodiments of this application, by employing a structure in which compressed air flows through the tube side 410 and the shell side 420 is filled with a solid-liquid phase change heat storage medium, improve the heat exchange area and heat exchange efficiency, ensure uniform and controllable compressed air temperature, and avoid local overheating or overcooling. Each heat storage unit is independent and has a thermal insulation design, adopts a pure counter-current heat exchange method, and uses carbon steel or stainless steel as materials. The solid-liquid phase change heat storage medium includes high-temperature phase change heat storage materials and low-temperature phase change heat storage materials, wherein the high-temperature phase change heat storage material is selected from molten salts, and the low-temperature phase change heat storage material is selected from neopentyl glycol or some salts; the heat storage form is latent heat storage; the phase change temperature is distributed according to the heat exchange temperature gradient, the solid-liquid phase change temperature range of the high-temperature phase change heat storage material is 90℃-425℃, and the solid-liquid phase change temperature range of the low-temperature phase change heat storage material is 5-80℃.

[0032] In one embodiment of this application, such as Figure 2 As shown, the air compressor 110 and the air expander 150 are connected to valve 120. Valve 120 is connected to one end of the first phase change heat accumulator 130. The other end of the first phase change heat accumulator 130 is connected to the first port of the cooler 140. The second end of the cooler 140 is connected to valve 120 of the next stage compression and expansion unit. The third end of the cooler 140 is connected to the waste heat utilization unit 300. The fourth end of the cooler 140 is connected to the condenser 280.

[0033] Among them, valve 120 is a device for controlling the flow direction and flow rate of compressed air or expanded air; the first port of cooler 140 is the interface connecting cooler 140 and the first phase change heat storage device 130, for air to flow into cooler 140; the second end of cooler 140 is the interface connecting cooler 140 and valve 120 of the next stage compression and expansion unit, for air to flow to the next stage unit; the third end of cooler 140 is the interface connecting cooler 140 and waste heat utilization unit 300, for recovering waste heat from compressed air; the fourth end of cooler 140 is the interface connecting cooler 140 and condenser 280, for directing carbon dioxide to condense and cool it in condenser 280 before storing it in the liquid chamber of the gas storage tank.

[0034] It is understood that, in the embodiments of this application, by arranging the air compressor 110, air expander 150, valve 120, first phase change heat accumulator 130, cooler 140, waste heat utilization unit 300, and condenser 280 in the above connection manner, the compressed air can sequentially pass through the heat accumulator and cooler 140 to achieve heat recovery, and the air flow direction and flow rate can be precisely controlled by the valve 120; the next-stage compression and expansion unit can be smoothly connected to the system to ensure graded energy utilization; the waste heat utilization unit 300 can effectively recover the residual heat in the compressed air, improve the overall thermal efficiency of the system, realize the heat transfer of carbon dioxide, and ensure the continuous and reliable operation of the system; the connection of the condenser 280 ensures that the carbon dioxide is cooled and condensed into a liquid state; the entire process realizes the orderly distribution of air flow and the gradient utilization of heat energy, improving the energy utilization rate, operational stability, and safety of the system.

[0035] In one embodiment of this application, such as Figure 2 As shown, the waste heat utilization unit 300 includes a regenerator 310 and a carbon dioxide expander 320. The regenerator 310 receives external waste heat and is connected to the carbon dioxide expander 320. The carbon dioxide expander 320 is connected to the liquid chamber 260 of the gas storage tank 200 through a first control valve 610. The carbon dioxide expander 320 is connected to the third end of the cooler 140 and the second phase change heat accumulator 400 through a second control valve 620.

[0036] Among them, the waste heat utilization unit 300 is a functional module used to recover and utilize external waste heat. It can convert thermal energy into usable energy from carbon dioxide working fluid, thereby improving system energy efficiency. Figure 2 As shown, the first control valve 610 is located between the carbon dioxide expander 320 and the liquid chamber 260 of the gas storage tank 200. It is used to regulate the flow rate and pressure of liquid carbon dioxide entering the expander 320 to ensure stable operation. The second control valve 620 is a three-way switching valve located at the outlet of the carbon dioxide expander 320. Its function is to switch the flow direction of the expanded carbon dioxide gas according to different operating conditions, which can be directed to the cooler 140 or the second phase change heat accumulator 400 to achieve complex flow path switching. The third end of the cooler 140 is one of its interfaces, used to receive or discharge the expanded carbon dioxide gas, cooling it before it recirculates or is discharged.

[0037] Understandably, by setting up the waste heat utilization unit 300 and opening the first control valve 610, the flow rate of liquid carbon dioxide in the gas storage tank 200 can be adjusted to ensure stable liquid carbon dioxide pressure during system energy storage or release, maintaining a constant pressure state in the gas storage tank. The external waste heat from the regenerator 310 can preferentially heat the carbon dioxide working fluid, increasing the inlet expansion temperature of the gaseous carbon dioxide and ensuring the power generation efficiency of the carbon dioxide expander. The second control valve 620 can either direct the carbon dioxide to the third end of the cooler 140 for cooling or to the second phase change heat accumulator 400 for energy storage. By setting it to a three-way structure, the second control valve 620 can flexibly regulate the flow path of the expanded gas, meeting the system's operational needs under different conditions, thereby improving the energy efficiency of the waste heat utilization unit 300 and the overall operational stability of the system.

[0038] The types of air compressor 110 and expander used in this application are not limited and can be common types such as piston, axial flow, and centrifugal. Different combinations of these types can be selected according to specific operating conditions, such as series or parallel configuration of piston and centrifugal types to meet the requirements of high pressure ratio and high flow rate. The structure of cooler 140 and regenerator 310 is not limited and can be conventional heat exchanger types such as shell-and-tube, regenerative, plate, or plate-fin. Other equivalent heat exchanger structures can be selected according to the requirements of heat exchange efficiency, volume, weight, or installation space, or multiple heat exchangers can be combined to improve overall heat exchange performance and meet the thermal management requirements under different operating conditions.

[0039] In one embodiment of this application, such as Figure 2 As shown, the condenser 280 is connected to the cooler 140 via the third control valve 630.

[0040] The third control valve 630 is a control valve installed between the condenser 280 and the first control valve 610. It is used to control whether the expanded carbon dioxide gas enters the condenser 280 for condensation, thereby flexibly switching the gas flow direction and realizing heat management and recovery under different operating modes.

[0041] Understandably, by connecting the condenser 280 to the first control valve 610 via the third control valve 630, the expanded carbon dioxide gas can enter the condenser 280 for condensation when needed, thereby reducing the gas temperature and facilitating subsequent recovery or recycling. The third control valve 630 allows for flexible switching of whether the gas enters the condenser 280, enabling the selection of direct discharge, heat exchange, or heat storage paths based on the system's operating status.

[0042] In one embodiment of this application, such as Figure 2As shown, the liquid storage unit 500 includes a booster pump 510 and a liquid storage tank 520. The booster pump 510 is connected to the second phase change accumulator 400 and the liquid storage tank 520, respectively. The liquid storage tank 520 is connected to the second phase change accumulator 400.

[0043] The liquid storage unit 500 is a functional module used to store and regulate the liquid working fluid within the system, ensuring a stable liquid supply capacity under different operating conditions. The booster pump 510 is a pump capable of increasing liquid pressure, used to pressurize the liquid in the liquid storage tank 520 or the liquid in the second phase change accumulator 400 and then deliver it to other components of the system, ensuring stable liquid flow and meeting the working fluid pressure requirements. The liquid storage tank 520 is a container for storing the liquid working fluid, serving to buffer, regulate, and stabilize the liquid level, preventing system instability due to insufficient or fluctuating liquid levels.

[0044] Understandably, by setting up the liquid storage unit 500, the system can stably provide liquid working fluid under different operating conditions. The booster pump 510 can pressurize and transport the liquid in the liquid storage tank 520 or the second phase change accumulator 400, ensuring the liquid can smoothly enter subsequent stages; simultaneously, the buffering effect of the liquid storage tank 520 can balance liquid level fluctuations within the system and reduce pressure shocks.

[0045] In one embodiment of this application, during the energy storage stage, both the air chamber 240 and the liquid storage tank 520 in the gas storage 200 are vented, and the liquid chamber 260 is filled with liquid carbon dioxide. After opening valve 120 and starting air compressor 110 to compress air to a medium-high pressure and high temperature state, the high-temperature air enters the tube side 410 of the first phase change accumulator. It is cooled by the solid-liquid phase change heat storage medium in the shell side 420 of the first phase change accumulator, and then enters cooler 140 for further cooling. After being compressed and cooled stage by stage-by-stage compression and expansion units 100, the compressed air is stored in the air chamber 240 of the gas storage 200. The solid-liquid phase change heat storage medium of the first phase change accumulator 130 absorbs heat. The heat of melting and compression is stored in the solid-liquid phase change heat storage medium of the first phase change heat accumulator 130. The heat exchange medium in the cooler 140 is the liquid carbon dioxide discharged from the liquid chamber 260 in the gas storage tank 200. When the compressor continuously charges the gas storage tank 200 with compressed air, the third control valve 630 is closed. The liquid carbon dioxide stored in the liquid chamber 260 of the gas storage tank is discharged and enters the cooler through the first control valve 610 to absorb the heat of compression and then vaporize. At this time, the second control valve 620 and valve 120 are opened to allow the gaseous carbon dioxide to enter the second phase change heat accumulator 400 to release heat and reduce to a low temperature state. Then, it is pressurized to a liquid state by the booster pump 510 and finally stored in the liquid storage tank 520.

[0046] Understandably, during the energy storage phase, after the air compressor 110 is started and compresses the air to medium-high pressure and high temperature, the high-temperature air enters the tube side 410 of the first phase change heat accumulator. It is cooled by the solid-liquid phase change heat storage medium in the shell side 420 and then enters the cooler 140 for further cooling. After passing through the multi-stage compression and expansion unit 100, it is stored in the air chamber 240 of the gas storage tank 200. Simultaneously, the solid-liquid phase change heat storage medium in the first phase change heat accumulator 130 absorbs heat and melts, storing the heat of compression. The heat exchange medium stored in the cooler 140 is liquid carbon dioxide discharged from the liquid chamber 260 of the gas storage tank. When the compressor continuously charges compressed air, the third control valve 630 is closed, allowing the liquid carbon dioxide to enter the cooler 140 at constant pressure through the first control valve 610 to absorb heat and vaporize. It then enters the second phase change heat accumulator 400 through the second control valve 620 to absorb heat and cool down. After being pressurized by the booster pump 510, it is stored in the liquid storage tank 520, achieving high-pressure stable storage. This step can fully recover the heat of compressed air, improve energy utilization, and at the same time provide a stable high-pressure liquid carbon dioxide for the energy release stage, thereby improving system efficiency and response speed.

[0047] Specifically, during the energy storage phase, in the initial state, both the air chamber 240 and the liquid storage tank 520 of the gas storage tank 200 are vented, while the liquid chamber 260 is filled with liquid carbon dioxide at a pressure of at least 7 MPa. Firstly, as... Figure 4 As shown, the air compressor 110 is started to compress air to a medium-high pressure and high temperature state. The high-temperature air enters the tube side 410 of the first phase change heat accumulator 130, where it exchanges heat with the solid-liquid phase change heat storage medium in the shell side 420 of the first phase change heat accumulator 130 to cool down. Then, it enters the cooler 140 for further cooling to about 30°C. Subsequently, the air sequentially passes through the next stage compressor, the first phase change heat accumulator 130, and the cooler 140 to complete multi-stage compression and cooling, and finally enters the air chamber 240 of the air storage tank 200. During this process, the solid-liquid phase change heat storage medium absorbs heat and melts, thus storing the heat of compression.

[0048] The heat exchange medium in cooler 140 comes from liquid carbon dioxide discharged from liquid chamber 260 of gas storage tank 200. When the compressor continuously charges high-pressure, low-temperature compressed air into gas storage tank 200 at a constant pressure, the third control valve 630 is first closed, allowing the liquid carbon dioxide in liquid chamber 260 (below 30°C) to be discharged through the first control valve 610 and enter cooler 140 to absorb the heat of compression, turning into gaseous carbon dioxide at 80-100°C. Then, the second control valve 620 is opened, allowing the high-temperature carbon dioxide to enter the second phase change heat accumulator 400, where it exchanges heat with the cooling medium and cools to approximately 20°C. After being pressurized to 15MPa by booster pump 510, it is then transported to liquid storage tank 520 for storage.

[0049] In one embodiment of this application, during the energy release phase, valve 120 is first opened in reverse, allowing high-pressure liquid carbon dioxide stored in the storage tank 520 to enter the second phase change heat accumulator 400 for heat exchange. The high-pressure liquid carbon dioxide is heated to gaseous carbon dioxide, which is then further heated to a high temperature by the regenerator 310 before entering the carbon dioxide expander 320 to expand and perform work. The pressure of the expanded carbon dioxide is comparable to the pressure of the compressed air stored in the air chamber 240 of the gas storage tank. The expanded gaseous carbon dioxide is then discharged through the second phase change heat accumulator 400. The second control valve 620 enters the cooler 140 in reverse to exchange heat with the compressed air discharged from the air chamber 240 of the gas storage tank 200. At this time, the third control valve 630 is opened. The carbon dioxide after heat exchange is first cooled and then enters the condenser 280 for further cooling and condensation into liquid. Finally, the liquid carbon dioxide is injected into the liquid chamber 260 in the gas storage tank 200 through the first control valve 610. Meanwhile, the air in the gas storage tank 200 is gradually discharged at a constant pressure to power the air expander 150 for electricity generation, thus forming a cycle until the air in the air chamber 240 of the gas storage tank 200 is completely released.

[0050] The energy release stage involves releasing stored energy to perform work or generate electricity. The second phase change accumulator 400 is a low-temperature heat storage device containing a solid-liquid phase change heat storage medium, used to absorb or release heat to regulate the temperature of gaseous carbon dioxide. The regenerator 310 is a heat exchange device used to heat gaseous carbon dioxide using external or system waste heat, increasing its temperature. The carbon dioxide expander 320 is an expansion device that uses high-pressure carbon dioxide expansion to perform work, converting thermal and pressure energy into mechanical or electrical energy. The second control valve 620 controls the flow of gaseous carbon dioxide between the expander, cooler 140, and accumulator. The third control valve 630 controls the flow of cooled carbon dioxide into the condenser 280; the condenser 280 is a heat exchanger. The equipment is used to cool gaseous carbon dioxide to a liquid state and release heat to the cooling medium. The first control valve 610 is used to control the injection of liquid carbon dioxide into the liquid chamber 260 of the gas storage tank 200, so as to replenish the liquid and allow the compressed air stored in the air chamber 240 of the gas storage tank 200 to be discharged at a constant pressure for expansion and power generation, or to control the discharge of liquid carbon dioxide for the storage of compressed air. The liquid chamber 260 of the gas storage tank 200 is the part of the gas storage tank 200 that stores liquid carbon dioxide. It is used to form a pressure balance with the air chamber 240 and to provide a heating medium during the energy release stage, so that the air can achieve constant pressure power generation, thereby improving the energy storage capacity and power generation efficiency. The air expander 150 is connected to the air chamber 240 of the gas storage tank 200 and converts the energy of the stored compressed air into mechanical energy or electrical energy.

[0051] It is understood that in this embodiment, the high-pressure liquid carbon dioxide in the storage tank 520 is gradually released through a multi-stage heat exchange and expansion process, which efficiently converts thermal energy and pressure energy into mechanical energy or electrical energy, thereby achieving constant pressure discharge of air from the gas storage tank 200 and providing stable power for the air expander 150. At the same time, the system's thermal energy utilization rate is improved through the second phase change heat accumulator 400 and the cooler 140. Finally, the liquid carbon dioxide is reinjected into the storage tank 520 to complete the energy cycle.

[0052] like Figure 5 As shown, in the energy release stage, in this embodiment, the high-pressure liquid carbon dioxide in the storage tank 520 is first introduced in reverse through valve 120 into the second phase change heat accumulator 400, where it exchanges heat with the solid-liquid phase change heat storage medium, heating the liquid carbon dioxide to approximately 80-100°C and converting it into a gaseous state. Subsequently, the gaseous carbon dioxide enters the regenerator 310 for further heating to a high temperature of not less than 220°C, and then enters the carbon dioxide expander 320 to expand and perform work, so that the pressure of the expanded carbon dioxide is equivalent to the pressure of the compressed air stored in the air chamber 240 of the gas storage tank 200. At this time, the working pressure is at least 7 MPa.

[0053] Next, the gaseous carbon dioxide discharged from the expander enters the cooler 140 in reverse through the second control valve 620, where it exchanges heat with the compressed air discharged from the air chamber 240 of the gas storage tank 200. At this time, the third control valve 630 is opened, so that the carbon dioxide after heat exchange is cooled to about 35-40°C and then enters the condenser 280 for further cooling to about 20°C and liquefaction.

[0054] Finally, the liquefied carbon dioxide is injected into the liquid chamber 260 of the gas storage tank 200 at constant pressure through the first control valve 610, which pushes the compressed air in the air chamber 240 of the gas storage tank 200 to be gradually discharged at constant pressure, supplying the air expander 150 to generate electricity, until the air in the air chamber 240 is completely released, completing the entire cycle power generation process.

[0055] The solid-liquid phase change heat storage medium in the first phase change heat storage device 130 and the second phase change heat storage device 400 releases the stored heat and solidifies during this process; the heat required by the regenerator 310 to heat carbon dioxide comes from external waste heat.

[0056] The dual-medium compressed air energy storage system based on phase change heat storage proposed in this application controls air temperature and pressure through multi-stage compression and expansion units, achieving efficient compressed air energy storage and reducing energy consumption during compression. The liquid storage unit works in conjunction with a second phase change heat accumulator and a waste heat utilization unit. The waste heat utilization unit exchanges heat with each stage of the first phase change heat accumulator. The second phase change heat accumulator connects the liquid storage unit and the waste heat utilization unit. By recovering and utilizing compression heat and waste heat, the heat storage efficiency is improved, and the overall system power consumption is reduced through cascaded phase change. The gas storage tank adopts a spherical rigid container, internally divided into an air chamber and a liquid chamber by a flexible diaphragm. The air chamber connects to the final stage compression and expansion unit for storing compressed air, and the liquid chamber connects to the waste heat utilization unit for storing liquid carbon dioxide. The air chamber and liquid chamber operate at equal pressures, achieving constant-pressure gas storage, increasing the liquid carbon dioxide storage density, improving energy storage efficiency and system operational stability, while ensuring pressure balance between the air and liquid chambers, facilitating controllable energy release and utilization. This solves the problems of poor sealing, low gas density, low energy storage efficiency, and difficulty in achieving constant-pressure operation in related technologies.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0058] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0059] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A dual-medium compressed air energy storage system based on phase change thermal storage, characterized in that, include: A multi-stage compression and expansion unit, comprising an air compressor, an air expander, a first phase change heat accumulator, and a cooler, wherein the multi-stage compression and expansion units are connected sequentially. The system includes a liquid storage unit, a second phase change accumulator, and a waste heat utilization unit. The waste heat utilization unit exchanges heat with the first phase change accumulator of each stage of compression and expansion unit. The second phase change accumulator is connected to the liquid storage unit and the waste heat utilization unit, respectively. A gas storage facility includes a spherical rigid container, which is divided into an air chamber and a liquid chamber by a flexible diaphragm. The air chamber is connected to a final-stage compression and expansion unit, and the liquid chamber is connected to a waste heat utilization unit. The air chamber is used to store compressed air, and the liquid chamber is used to store liquid carbon dioxide. The working pressures of the air chamber and the liquid chamber are equal. A flexible diaphragm is used to completely isolate the air chamber from the liquid chamber, preventing gas-liquid mixing, while allowing pressure to be transmitted between them, thus achieving a dynamic balance of gas and hydraulic pressure. Both the first phase change accumulator and the second phase change accumulator include a tube side and a shell side. Compressed air is passed through the tube side, and the shell side is filled with a solid-liquid phase change heat storage medium. The air compressor and the air expander are connected by a valve, which is connected to one end of the first phase change heat accumulator. The other end of the first phase change heat accumulator is connected to the first port of the cooler. The second end of the cooler is connected to the valve of the next-stage compression and expansion unit. The third end of the cooler is connected to the waste heat utilization unit. The fourth end of the cooler is connected to the condenser. The waste heat utilization unit includes a regenerator and a carbon dioxide expander. The regenerator receives external waste heat and is connected to the carbon dioxide expander. The carbon dioxide expander is connected to the liquid chamber of the gas storage tank through a first control valve. The carbon dioxide expander is connected to the third end of the cooler and the second phase change heat accumulator through a second control valve.

2. The dual-medium compressed air energy storage system based on phase change thermal storage according to claim 1, characterized in that, The spherical rigid container consists of, from the outside to the inside, an outer gas storage wall, a vacuum layer, an inner gas storage wall, an air cavity, a flexible diaphragm, and a liquid cavity.

3. The dual-medium compressed air energy storage system based on phase change thermal storage according to claim 1, characterized in that, The solid-liquid phase change heat storage medium includes one or more combinations of molten salt high-temperature phase change heat storage materials and neopentyl glycol or some salt low-temperature phase change heat storage materials.

4. The dual-medium compressed air energy storage system based on phase change thermal storage according to claim 1, characterized in that, The condenser is connected to the second control valve via a third control valve.

5. The dual-medium compressed air energy storage system based on phase change thermal storage according to claim 1, characterized in that, The liquid storage unit includes a booster pump and a liquid storage tank. The booster pump is connected to the second phase change accumulator and the liquid storage tank, respectively. The liquid storage tank is connected to the second phase change accumulator.

6. The dual-medium compressed air energy storage system based on phase change thermal storage according to claim 5, characterized in that, During the energy storage phase, both the air chamber and the liquid storage tank in the gas storage tank are vented, and the liquid chamber is filled with liquid carbon dioxide. The valve is opened, and the air compressor is started to compress the air to a medium-high pressure and high temperature state. The high-temperature air enters the tube side of the first phase change accumulator, where it is cooled by the solid-liquid phase change heat storage medium in the shell side. It then enters the cooler for further cooling. After being compressed and cooled stage by stage-by-stage compression and expansion units, the compressed air is stored in the air chamber of the gas storage tank. The solid-liquid phase change heat storage medium of the first phase change accumulator absorbs heat and melts... The heat of compression is stored in the solid-liquid phase change heat storage medium of the first phase change heat accumulator. The heat exchange medium in the cooler is the liquid carbon dioxide discharged from the liquid chamber in the gas storage tank. When the compressor continuously charges the gas storage tank with compressed air, the third control valve is closed. The liquid carbon dioxide stored in the liquid chamber of the gas storage tank is discharged through the first control valve and enters the cooler to absorb the heat of compression and then vaporizes. At this time, the second control valve and valve are opened to allow the gaseous carbon dioxide to enter the second phase change heat accumulator to release heat and reduce to a low temperature state. Then, it is pressurized to a liquid state by the booster pump and finally stored in the liquid storage tank.

7. The dual-medium compressed air energy storage system based on phase change thermal storage according to claim 6, characterized in that, During the energy release phase, the valve is first opened in reverse, allowing the high-pressure liquid carbon dioxide stored in the storage tank to enter the second phase change accumulator for heat exchange. The high-pressure liquid carbon dioxide is heated to gaseous carbon dioxide, which is then further heated to a high temperature by the regenerator and enters the carbon dioxide expander to expand and do work. The pressure of the expanded carbon dioxide is equivalent to the pressure of the compressed air stored in the air chamber of the gas storage tank. The gaseous carbon dioxide discharged after expansion then enters the cooler in reverse through the second control valve to exchange heat with the compressed air discharged from the air chamber of the gas storage tank. At this time, the third control valve is opened, and the carbon dioxide after heat exchange is first cooled and then enters the condenser for further cooling and condensation into liquid. Finally, the liquid carbon dioxide is injected into the liquid chamber in the gas storage tank through the first control valve, while the air in the gas storage tank is gradually discharged at a constant pressure to power the air expander for electricity generation, thus forming a cycle until the air in the air chamber of the gas storage tank is completely released.

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