An energy storage system using liquid ammonia as storage medium

Abstract

This invention belongs to the field of large-scale energy storage technology and discloses an energy storage system using liquid ammonia as the storage medium. The system includes: a first liquid ammonia mixture storage tank, a first throttling valve, a first thermal storage device, a compressor, a second thermal storage device, a first cooler, a second liquid ammonia mixture storage tank, a second throttling valve, a turbine, and a second cooler. The outlet of the first liquid ammonia mixture storage tank is connected to the inlet of the second liquid ammonia mixture storage tank via the first throttling valve, the first thermal storage device, the compressor, the second thermal storage device, and the first cooler. The outlet of the second liquid ammonia mixture storage tank is connected to the inlet of the first liquid ammonia mixture storage tank via the second throttling valve, the second thermal storage device, the turbine, the first thermal storage device, and the second cooler. This invention uses liquid ammonia as the storage medium, which can be liquefied under ambient temperature and pressure, and can ensure the energy storage density of the system.

Description

Technical Field

[0001] This invention belongs to the field of large-scale energy storage technology, and specifically relates to an energy storage system that uses liquid ammonia as the storage medium. Background Technology

[0002] Currently, existing large-scale energy storage technologies generally employ compressed air or compressed liquid carbon dioxide for energy storage. When using compressed air energy storage for large-scale energy storage, excess electrically driven compressors can compress air to a high-pressure state and store it in salt caverns, underground mines, or artificial underwater airbags during off-peak electricity demand periods. During peak electricity demand periods, the stored compressed air drives turbines to generate electricity, adapting to grid demand and smoothing out power fluctuations. However, compressed air energy storage has certain limitations, including: if air is stored in gaseous form, its density is not very high, preventing a significant increase in system energy storage density and requiring a large storage volume, thus limiting its widespread adoption due to geographical constraints; furthermore, if air is stored in liquid form, an air liquefaction device is required, and the excess energy consumption leads to reduced system efficiency. Given the specific circumstances of compressed air energy storage, some scholars have proposed compressed liquid carbon dioxide (CCCO) energy storage. The main difference between CCCO and compressed air energy storage is that the working medium is replaced with carbon dioxide. Utilizing the high critical temperature (around 31°C) of carbon dioxide, it achieves liquefaction at ambient temperatures, eliminating the need for redundant liquefaction devices and increasing energy density while maintaining high system efficiency. However, CCCO energy storage has gradually revealed some drawbacks during its promotion, including: Since carbon dioxide's critical temperature is around 31°C, it cannot be fully liquefied using ambient water at higher temperatures (e.g., summer); without ambient water liquefaction, CCCO energy storage systems face similar challenges to compressed air energy storage, requiring complex liquefaction devices; furthermore, carbon dioxide's triple point pressure is 527 kPa, and it cannot liquefy below this pressure, necessitating a tank pressure higher than the triple point pressure, which poses certain safety risks.

[0003] To further explain, for the aforementioned existing liquid gas energy storage system, if the tank pressure is close to the ambient pressure, the tank temperature must be lower than the ambient temperature; if the tank temperature is close to the ambient temperature, the tank pressure must be higher than the ambient pressure. Summary of the Invention

[0004] The purpose of this invention is to provide an energy storage system using liquid ammonia as the storage medium to solve one or more of the aforementioned technical problems. The technical solution provided by this invention uses liquid ammonia as the storage medium, which allows for liquefaction at ambient temperature and pressure, eliminating the need for complex liquefaction devices and allowing for lower tank pressure, thus reducing costs and safety risks. Furthermore, the high density of the liquefied ammonia working fluid ensures the system's energy storage density.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides an energy storage system using liquid ammonia water as the storage medium, comprising: a first liquid ammonia water mixture storage tank, a first throttle valve, a first thermal storage device, a compressor, a second thermal storage device, a first cooler, a second liquid ammonia water mixture storage tank, a second throttle valve, a turbine, and a second cooler; the outlet of the first liquid ammonia water mixture storage tank is sequentially connected to the inlet of the second liquid ammonia water mixture storage tank via the first throttle valve, the first thermal storage device, the compressor, the second thermal storage device, and the first cooler; the outlet of the second liquid ammonia water mixture storage tank is sequentially connected to the inlet of the first liquid ammonia water mixture storage tank via the second throttle valve, the second thermal storage device, the turbine, the first thermal storage device, and the second cooler.

[0007] The first liquid ammonia water mixture storage tank and the second liquid ammonia water mixture storage tank are used to store liquid ammonia water working fluid in the energy storage stage and the energy release stage, respectively.

[0008] A further improvement of the present invention is that the energy storage stage of the energy storage system includes:

[0009] The liquid ammonia-water mixture working fluid flows out of the first liquid ammonia-water mixture storage tank, and after being depressurized by the first throttle valve, it absorbs heat in the first heat storage device and vaporizes into a gaseous state. Then it enters the compressor for compression. The high-temperature and high-pressure gaseous ammonia-water mixture working fluid after compression releases heat and stores energy in the second heat storage device. After releasing heat, the ammonia-water mixture working fluid is cooled to ambient temperature by the first cooler and flows into the second liquid ammonia-water mixture storage tank.

[0010] A further improvement of the present invention is that the energy release phase of the energy storage system includes:

[0011] The liquid ammonia mixture working fluid flows out from the second liquid ammonia mixture storage tank, is throttled by the second throttle valve, absorbs heat to a high-temperature gaseous state in the second heat storage device, and expands in the turbine; the gaseous ammonia mixture working fluid at the turbine outlet releases heat in the first heat storage device, is cooled to ambient temperature by the second cooler, and stored in the first liquid ammonia mixture storage tank.

[0012] A further improvement of the present invention is that it also includes: a separator, a liquid pump, and a third throttle valve;

[0013] The separator and the third throttle valve are disposed between the second thermal storage device and the first cooler; wherein, the second thermal storage device is connected to the inlet of the separator via the third throttle valve, the gaseous ammonia working fluid outlet of the separator is connected to the inlet of the compressor, and the liquid ammonia working fluid outlet of the separator is connected to the inlet of the first cooler;

[0014] The liquid pump replaces the second throttle valve; wherein the outlet of the second liquid ammonia mixture storage tank is connected to the inlet of the liquid pump, and the outlet of the liquid pump is connected to the inlet of the second thermal storage device.

[0015] A further improvement of the present invention is that the energy storage stage of the energy storage system includes:

[0016] The liquid ammonia-water mixture working fluid flows out from the first liquid ammonia-water mixture storage tank, and after being depressurized by the first throttle valve, it absorbs heat in the first heat storage device and vaporizes into a gaseous state. Subsequently, it mixes with ammonia-rich vapor from the separator. The mixed gaseous ammonia-water mixture working fluid enters the compressor for compression. The compressed high-temperature and high-pressure gaseous ammonia-water mixture working fluid releases heat and stores energy in the second heat storage device. After releasing heat, the ammonia-water mixture working fluid is depressurized by the third throttle valve and separated into ammonia-rich vapor and ammonia-lean solution in the separator. The ammonia-lean solution is cooled to ambient temperature by the first cooler and flows into the second liquid ammonia-water mixture storage tank.

[0017] A further improvement of the present invention is that the energy release phase of the energy storage system includes:

[0018] The liquid ammonia mixture working fluid flows out from the second liquid ammonia mixture storage tank, is pressurized by the liquid pump, absorbs heat to a high-temperature gaseous state in the second heat storage device, and expands in the turbine; the gaseous ammonia mixture working fluid at the turbine outlet releases heat in the first heat storage device, and is then cooled to ambient temperature by the second cooler 10 and stored in the first liquid ammonia mixture storage tank.

[0019] A further improvement of the present invention is that the first cooler and the second cooler are used for liquefaction using ambient water.

[0020] A further improvement of the present invention is that the maximum temperature during the operation of the energy storage system is below 300°C.

[0021] A further improvement of the present invention is that the operating pressure of the energy storage system is below 0.5 MPa.

[0022] A further improvement of the present invention is that the ammonia concentration in the first liquid ammonia mixture storage tank and the second liquid ammonia mixture storage tank is between 0.15 and 0.25.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The energy storage system provided by this invention uses liquid ammonia as the storage medium. Liquid ammonia can be liquefied under ambient temperature and pressure, eliminating the need for complex liquefaction devices and allowing for lower tank pressure, thus reducing costs and safety risks. In addition, the high density of the liquefied ammonia working medium ensures the energy storage density of the system.

[0025] To further explain, in the energy storage system using liquid ammonia as the storage medium provided by this invention, the ammonia working fluid is stored in a liquid form in the storage tank, and its high density ensures the energy storage density of the system. The maximum temperature during system operation does not exceed 300°C, which reduces the requirements for the materials of the thermal storage equipment. At the same time, the system operating pressure is low, not exceeding 0.5 MPa, which reduces the pressure requirements for pipelines and equipment. In addition, the temperature of the storage tank is the same as the ambient temperature, which can adapt to changes in ambient temperature, eliminating the need to consider the insulation technology of the storage tank, reducing the difficulty of liquefaction and economic requirements. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below; obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of an energy storage system using liquid ammonia as the storage medium provided in an embodiment of the present invention (illustrative, schematic diagram of system 1);

[0028] Figure 2 This is a schematic diagram of another energy storage system using liquid ammonia as the storage medium provided in an embodiment of the present invention (illustrative, schematic diagram of system 2);

[0029] Figure 3 This is a schematic diagram illustrating the change in energy storage efficiency of System 1 and System 2 with ambient temperature in an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram illustrating the change of energy storage density of System 1 and System 2 with ambient temperature in an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram illustrating the change in energy storage efficiency of System 1 and System 2 with respect to the concentration before mixing (ammonia concentration in the storage tank) in an embodiment of the present invention.

[0032] Figure 6 This is a schematic diagram illustrating the change in energy storage density of System 1 and System 2 with the concentration before mixing (ammonia concentration in the storage tank) in an embodiment of the present invention.

[0033] In the diagram, 1. First liquid ammonia-water mixture storage tank; 2. First throttle valve; 3. First thermal storage device; 4. Compressor; 5. Second thermal storage device; 6. First cooler; 7. Second liquid ammonia-water mixture storage tank; 8. Second throttle valve; 9. Turbine; 10. Second cooler; 11. Separator; 12. Liquid pump; 13. Third throttle valve. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0035] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings:

[0037] Please see Figure 1 This invention provides an energy storage system using liquid ammonia as the storage medium, comprising: a first liquid ammonia mixture storage tank 1, a first throttle valve 2, a first thermal storage device 3, a compressor 4, a second thermal storage device 5, a first cooler 6, a second liquid ammonia mixture storage tank 7, a second throttle valve 8, a turbine 9, and a second cooler 10; wherein,

[0038] The connection relationship is as follows: the outlet of the first liquid ammonia mixture storage tank 1 is connected to the inlet of the first throttle valve 2; the outlet of the first throttle valve 2 is connected to the inlet of the first thermal storage device 3; the outlet of the first thermal storage device 3 is connected to the inlet of the compressor 4; the outlet of the compressor 4 is connected to the inlet of the second thermal storage device 5; the outlet of the second thermal storage device 5 is connected to the inlet of the first cooler 6; the outlet of the first cooler 6 is connected to the inlet of the second liquid ammonia mixture storage tank 7; the outlet of the second liquid ammonia mixture storage tank 7 is connected to the inlet of the second throttle valve 8; the outlet of the second throttle valve 8 is connected to the inlet of the second thermal storage device 5; the outlet of the second thermal storage device 5 is connected to the inlet of the turbine 9; the outlet of the turbine 9 is connected to the inlet of the first thermal storage device 3; the outlet of the first thermal storage device 3 is connected to the inlet of the second cooler 10; and the outlet of the second cooler 10 is connected to the inlet of the first liquid ammonia mixture storage tank 1.

[0039] The functions are as follows: the first liquid ammonia water mixture storage tank 1 and the second liquid ammonia water mixture storage tank 7 are used to store liquid ammonia water working fluid in the energy storage stage and the energy release stage, respectively; the first throttle valve 2 and the second throttle valve 8 play a role in reducing pressure; the first heat storage device 3 and the second heat storage device 5 are used to store heat; the compressor 4 is used to compress the gaseous ammonia water working fluid to high pressure and high temperature in the energy storage stage; the turbine 9 is used to expand the gaseous ammonia water working fluid to output work in the energy release stage; and the first cooler 6 and the second cooler 10 reduce the temperature of the ammonia water flowing into the storage tank.

[0040] Please see Figure 1 In this embodiment of the invention,

[0041] The energy storage stage includes: the liquid ammonia-water mixture working fluid flows out from the first liquid ammonia-water mixture storage tank 1, is depressurized by the first throttle valve 2, absorbs heat in the first heat storage device 3 and vaporizes into a gaseous state, and then enters the compressor 4 for compression. The compressed high-temperature and high-pressure gaseous ammonia-water mixture working fluid releases heat and is stored in the second heat storage device 5; subsequently, the ammonia-water mixture working fluid is cooled to ambient temperature by the first cooler 6 and flows into the second liquid ammonia-water mixture storage tank.

[0042] Please see Figure 1 In this embodiment of the invention,

[0043] The energy release stage includes: the liquid ammonia-water mixture working fluid flows out from the second liquid ammonia-water mixture storage tank 7, is throttled by the second throttle valve 8, absorbs heat to a high-temperature gaseous state in the second heat storage device 5, and expands in the turbine 9; after the gaseous ammonia-water mixture working fluid at the turbine outlet releases heat in the first heat storage device 3, it is cooled to the ambient temperature by the second cooler 10 and stored in the first liquid ammonia-water mixture storage tank 1.

[0044] In this embodiment of the invention, the highest temperature during system operation does not exceed 300°C, which places lower requirements on the materials of the thermal storage equipment; at the same time, the system operating pressure is low, not exceeding 0.5MPa, which places lower pressure requirements on pipelines and equipment; in addition, the temperature of the storage tank is the same as the ambient temperature, which can adapt to changes in ambient temperature, eliminating the need to consider the insulation technology of the storage tank, thus reducing the difficulty of liquefaction and economic requirements.

[0045] Please see Figure 2 This invention provides an energy storage system using liquid ammonia as the storage medium, wherein...

[0046] The outlet of the first liquid ammonia mixture storage tank 1 is connected to the inlet of the first throttle valve 2. The outlet of the first throttle valve 2 is connected to the inlet of the first thermal storage device 3. The outlet of the first thermal storage device 3 is connected to the inlet of the compressor 4. The outlet of the compressor 4 is connected to the inlet of the second thermal storage device 5. The outlet of the second thermal storage device 5 is connected to the inlet of the third throttle valve 13. The outlet of the third throttle valve 13 is connected to the inlet of the separator 11. The outlet of the gaseous ammonia working medium of the separator 11 is connected to the inlet of the compressor 4. The outlet of the liquid ammonia working medium of the separator 11 is connected to... The inlet and outlet of the first cooler 6 are connected to the inlet of the second liquid ammonia mixture storage tank 7. The outlet of the second liquid ammonia mixture storage tank 7 is connected to the inlet of the liquid pump 12. The outlet of the liquid pump 12 is connected to the inlet of the second thermal storage device 5. The outlet of the second thermal storage device 5 is connected to the inlet of the turbine 9. The outlet of the turbine 9 is connected to the inlet of the first thermal storage device 3. The outlet of the first thermal storage device 3 is connected to the inlet of the second cooler 10. The outlet of the second cooler 10 is connected to the inlet of the first liquid ammonia mixture storage tank 1.

[0047] In this embodiment of the invention, the first liquid ammonia water mixture storage tank 1 and the second liquid ammonia water mixture storage tank 7 are used to store liquid ammonia water working fluid in the energy storage stage and the energy release stage, respectively; the first throttle valve 2 and the third throttle valve 13 are used to reduce pressure; the first heat storage device 3 and the second heat storage device 5 are used to store heat; the compressor 4 is used to compress the gaseous ammonia water working fluid to high pressure and high temperature in the energy storage stage; the turbine 9 is used to expand the gaseous ammonia water working fluid to output work in the energy release stage; and the first cooler 6 and the second cooler 10 are used to reduce the temperature of the ammonia water flowing into the storage tank.

[0048] Please see Figure 2 In this embodiment of the invention,

[0049] The energy storage stage includes: the concentration of the liquid ammonia-water mixture working fluid in the storage tank is the same as before mixing. The liquid ammonia-water mixture working fluid flows out from the first liquid ammonia-water mixture storage tank 1, is depressurized by the first throttle valve 2, absorbs heat in the first thermal storage device 3 and vaporizes into a gaseous state. It then mixes with ammonia-rich vapor from the upper outlet of the separator 11. The concentration of the mixed gaseous ammonia-water mixture working fluid is the same as after mixing. The high-temperature and high-pressure gaseous ammonia-water mixture working fluid, after being compressed by the compressor 4, releases heat and is stored in the second thermal storage device 5. Subsequently, the ammonia-water mixture working fluid is depressurized by the third throttle valve 13 and separated into ammonia-rich vapor and ammonia-lean solution in the separator 11. The ammonia-lean solution is cooled to ambient temperature by the first cooler 6 and flows into the second liquid ammonia-water mixture storage tank 7.

[0050] Please see Figure 2 In this embodiment of the invention,

[0051] The energy release stage includes: the liquid ammonia-water mixture working fluid flows out from the second liquid ammonia-water mixture storage tank 7, is pressurized by the liquid pump 12, absorbs heat to a high-temperature gaseous state in the second heat storage device 5, and expands in the turbine 9; the gaseous ammonia-water mixture working fluid at the turbine outlet releases heat in the first heat storage device 3, is cooled to ambient temperature by the second cooler 10 and stored in the first liquid ammonia-water mixture storage tank 1.

[0052] The principle of this invention is explained as follows: When using carbon dioxide as the working fluid, the pressure before the compressor is generally lower than the critical pressure, while the pressure after the compressor is higher than the critical pressure. The carbon dioxide after the compressor is liquefied from a supercritical state through cooling (which can be equivalent to a second thermal storage device 5), throttling (which can be equivalent to a third throttling valve 13), and separation (which can be equivalent to a separator 11). Liquid air energy storage often employs a similar liquefaction method. (Invention Embodiment) Figure 1 As shown, the main change lies in eliminating the complex liquefaction device and directly liquefying ambient water through a cooler; after removing the separator, all the flow can enter the turbine to do work, eliminating the need to send a portion of the flow to the compressor inlet, thus further improving the system's energy storage efficiency. Embodiment of the Invention Figure 2 As shown, a cooler was added at the liquid ammonia outlet of the separator to increase the subcooling in the storage tank. This has two effects: first, it prevents the liquid ammonia from entering the two-phase zone due to the ambient temperature, which would generate gas and affect the safety of the storage tank; second, it increases the density of the liquid ammonia in the storage tank, thereby further increasing the energy storage density.

[0053] To be further specific and exemplary, in Figure 1 and Figure 2In the two systems, the pressure and temperature of the liquid ammonia mixture in the first liquid ammonia mixture storage tank are the same as the ambient pressure (1 bar) and temperature (20°C). In System 2, the temperature of the liquid ammonia mixture in the second liquid ammonia mixture storage tank is the same as the ambient temperature, while the pressure is slightly lower than the ambient pressure (0.8 bar). In System 1, the temperature of the liquid ammonia mixture in the second liquid ammonia mixture storage tank is the same as the ambient temperature, while the pressure is higher than the ambient pressure (4.8 bar). Furthermore, when the ambient temperature and pressure are 20°C and 1 bar, the ammonia concentration before mixing must not exceed 0.34, otherwise it cannot remain liquid. In this embodiment, the ammonia concentration in System 1 is 0.2, and the ammonia concentration before mixing in System 2 is also 0.2. The lowest temperature during system operation is the ambient temperature, and the highest temperature does not exceed 300°C, resulting in lower requirements for the materials of the thermal storage equipment; the system operating pressure is between 0.8 bar and 4.8 bar, resulting in lower pressure requirements for pipelines and equipment.

[0054] Table 1. Comparison of physical properties of different fluids

[0055]

[0056] As shown in Table 1, ammonia water with an ammonia concentration of 0.34 can be liquefied at an ambient temperature of 20°C and an ambient pressure of 1 bar. Therefore, its liquefaction is relatively easy, and its liquefied density is similar to that of liquefied air, maintaining a high density while achieving liquefaction. Therefore, this invention proposes a liquid ammonia water energy storage system that can be liquefied at ambient temperature and pressure to solve the problems existing in the prior art.

[0057] Please see Figures 3 to 6 , Figure 3 In the experiment, the energy storage efficiency of System 1 remained unchanged with varying ambient temperature, consistently at 65.42%. The energy storage efficiency of System 2 increased with increasing ambient temperature and decreased concentration after mixing. At an ambient temperature of 35°C and a mixing concentration of 0.21, the system's energy storage efficiency reached its highest value of approximately 63.94%. Furthermore, the system's energy storage efficiency remained above 50% throughout the ambient temperature range of 0–35°C. Figure 4 In the system, the energy storage density of System 1 decreases with increasing ambient temperature, mainly because ambient temperature affects the density of ammonia in the tank. When the ambient temperature is 35℃ and the concentration after mixing is 0.23, the energy storage density of System 1 is higher than that of System 2. The energy storage density of System 2 increases with increasing ambient temperature and also with increasing concentration after mixing. When the ambient temperature varies from 0 to 35℃, the system energy storage density is consistently above 30 kWh·m³. -3 . Figure 5In System 1, the energy storage efficiency slightly decreases with increasing pre-mixing concentration; when the pre-mixing concentration increases from 0.15 to 0.25, the energy storage efficiency decreases by 0.08%. In System 2, the energy storage efficiency increases with increasing pre-mixing concentration and increases with decreasing post-mixing concentration. Although increasing the pre-mixing concentration of ammonia water is beneficial to the system's circulation efficiency, the higher the concentration, the lower the corresponding liquefaction temperature; therefore, the pre-mixing concentration of ammonia water needs to be considered comprehensively. In this embodiment of the invention, when the pre-mixing concentration varies between 0.15 and 0.25, and the post-mixing concentration varies between 0.21 and 0.27, the system energy storage efficiency is within the range of 54% to 62%. Figure 6 In the system, the energy storage density of System 1 decreases with increasing pre-mixing concentration; when the pre-mixing concentration increases from 0.15 to 0.25, the energy storage density decreases by 1.39 kWh·m³. -3 The energy storage density of System 2 decreases with increasing pre-mixing concentration and increases with increasing post-mixing concentration. The pre-mixing concentration affects the ammonia density in the tank, but the effect is relatively small. For example, with a post-mixing concentration of 0.27, when the pre-mixing ammonia concentration increases from 0.19 to 0.25, its energy storage density only decreases by 0.46 kWh·m³. -3 .

[0058] In summary, liquid gas energy storage belongs to large-scale energy storage systems, with liquid air energy storage and liquid carbon dioxide energy storage being the more mature examples. Compared to air and carbon dioxide, ammonia water is easier to liquefy, as it can be liquefied at ambient temperature and pressure while maintaining a high liquefaction density. This invention specifically proposes a liquid ammonia water energy storage system that can be liquefied at ambient temperature and pressure: In this system, the ammonia water working medium can be liquefied from ambient water, and the liquid ammonia water at ambient temperature is stored in two separate tanks. This process can replace complex cryogenic liquefaction equipment, and this energy storage system achieves easy liquefaction while maintaining a high energy storage density.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An energy storage system using liquid ammonia as the storage medium, characterized in that, include: The system comprises a first liquid ammonia mixture storage tank (1), a first throttle valve (2), a first thermal storage device (3), a compressor (4), a second thermal storage device (5), a first cooler (6), a second liquid ammonia mixture storage tank (7), a second throttle valve (8), a turbine (9), and a second cooler (10). The outlet of the first liquid ammonia mixture storage tank (1) is connected to the inlet of the second liquid ammonia mixture storage tank (7) via the first throttle valve (2), the first thermal storage device (3), the compressor (4), the second thermal storage device (5), and the first cooler (6) in sequence. The outlet of the second liquid ammonia mixture storage tank (7) is connected to the inlet of the first liquid ammonia mixture storage tank (1) via the second throttle valve (8), the second thermal storage device (5), the turbine (9), the first thermal storage device (3), and the second cooler (10) in sequence. The first liquid ammonia mixture storage tank (1) and the second liquid ammonia mixture storage tank (7) are used to store liquid ammonia working fluid in the energy storage stage and the energy release stage, respectively. It also includes: a separator (11), a liquid pump (12), and a third throttle valve (13); the separator (11) and the third throttle valve (13) are disposed between the second heat storage device (5) and the first cooler (6); wherein the second heat storage device (5) is connected to the inlet of the separator (11) via the third throttle valve (13), the gaseous ammonia working fluid outlet of the separator (11) is connected to the inlet of the compressor (4), and the liquid ammonia working fluid outlet of the separator (11) is connected to the inlet of the first cooler (6); the liquid pump (12) replaces the second throttle valve (8); wherein the outlet of the second liquid ammonia mixture storage tank (7) is connected to the inlet of the liquid pump (12), and the outlet of the liquid pump (12) is connected to the inlet of the second heat storage device (5); The energy storage stage of the energy storage system includes: a liquid ammonia water mixture working fluid flows out from the first liquid ammonia water mixture storage tank (1), is depressurized by the first throttle valve (2), absorbs heat in the first heat storage device (3) and vaporizes into a gaseous state, and then mixes with ammonia-rich vapor from the separator (11). The mixed gaseous ammonia water mixture working fluid enters the compressor (4) for compression. The compressed high-temperature and high-pressure gaseous ammonia water mixture working fluid releases heat and stores energy in the second heat storage device (5). After releasing heat, the ammonia water mixture working fluid is depressurized by the third throttle valve (13) and separated into ammonia-rich vapor and ammonia-lean solution in the separator (11). The ammonia-lean solution is cooled to ambient temperature by the first cooler (6) and flows into the second liquid ammonia water mixture storage tank (7). The energy release phase of the energy storage system includes: the liquid ammonia water mixture working fluid flows out from the second liquid ammonia water mixture storage tank (7), is pressurized by the liquid pump (12), absorbs heat to a high temperature gaseous state in the second heat storage device (5), and expands in the turbine (9); the gaseous ammonia water mixture working fluid at the outlet of the turbine (9) releases heat in the first heat storage device (3), and is then cooled to the ambient temperature by the second cooler (10) and stored in the first liquid ammonia water mixture storage tank (1).

2. The energy storage system using liquid ammonia as the storage medium according to claim 1, characterized in that, The first cooler (6) and the second cooler (10) are used for liquefaction using ambient water.

3. The energy storage system using liquid ammonia as the storage medium according to claim 1, characterized in that, The highest temperature during the operation of the energy storage system is below 300℃.

4. The energy storage system using liquid ammonia as the storage medium according to claim 1, characterized in that, The energy storage system operates at a pressure below 0.5 MPa.

5. The energy storage system using liquid ammonia as the storage medium according to claim 1, characterized in that, The ammonia concentration in the first liquid ammonia mixture storage tank (1) and the second liquid ammonia mixture storage tank (7) is between 0.15 and 0.25.

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