Graded heat storage Carnot battery system based on Brayton cycle and operation method of graded heat storage Carnot battery system

Abstract

The invention provides a graded heat storage Carnot battery system based on Brayton cycle and an operation method thereof, and belongs to the technical field of energy storage. The graded heat storage Carnot battery system based on the Brayton cycle comprises an energy storage cycle subsystem which comprises a first compressor, a first heat exchanger and a preheating module and is suitable for converting external electric energy into heat energy and storing the heat energy; the heat storage subsystem is suitable for storing a low-temperature first heat storage medium, a high-temperature first heat storage medium, a low-temperature second heat storage medium and a high-temperature second heat storage medium; and the energy release circulation subsystem comprises a second heat exchanger, a first expansion machine and a cooling compression module and is suitable for converting the heat energy stored by the energy storage circulation subsystem into electric energy. The system does not need a low-temperature cold storage unit, the structure is simplified, the cost is reduced, and the engineering feasibility is improved; graded heat storage realizes gradient utilization of heat energy, optimizes circulation, improves energy conversion efficiency, and is suitable for power consumption of power grid-level renewable energy sources.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology, specifically relating to a graded thermal Carnot battery system based on the Brayton cycle and its operation method. Background Art

[0002] Renewable energy power generation is characterized by intermittency and volatility, and its output capacity is significantly affected by natural resource conditions. It often has sufficient output when user load is low, but insufficient output during peak electricity demand periods. This leads to a significant mismatch between its output and user electricity demand in terms of timing. To achieve large-scale and efficient utilization of redundant renewable energy power, and to ensure power supply to users during peak load periods when renewable energy output is insufficient, there is an urgent need to develop large-scale energy storage systems with long-term energy storage capabilities and good economics.

[0003] Current mainstream energy storage technologies include pumped hydro storage, compressed air storage (CASS), and battery storage, but each technology has certain limitations. For example, while pumped hydro storage and CASS offer large storage capacity and low cost, they are limited by geographical factors, making flexible deployment difficult—pumped hydro storage requires a significant water level difference. CASS requires large-scale salt caverns for air storage; if such conditions are not available, additional costs must be incurred to build storage tanks. Battery storage offers rapid response, but typically only supports a few hours of storage time, failing to meet long-term energy storage needs across day and night or even seasons. Furthermore, its large-scale application faces challenges such as high cost, poor safety, and limited lifespan.

[0004] As a novel physical energy storage method, the Carnot battery system stores electrical energy as thermal energy, enabling long-term, large-scale energy storage. Among them, the Carnot battery based on the Brayton cycle is considered the most engineering-feasible Carnot battery system due to its high system efficiency and mature components.

[0005] Carnot batteries based on the Brayton cycle compress and heat air during the energy storage phase, storing its thermal energy. During the energy release phase, the stored thermal energy is used to heat the air, driving an expander to generate electricity. To further improve system efficiency, such Carnot battery systems typically incorporate a cold storage unit to reduce compression power consumption and optimize system energy efficiency. The cold storage medium generally uses low-temperature materials such as alkanes and methanol; however, cold storage units still face the following significant challenges in practical applications.

[0006] First, the cold storage unit requires thermal insulation structure and cryogenic materials, which significantly increases the complexity of the system structure and initial investment, reducing the feasibility and economy of engineering applications. Second, the low thermal conductivity of the cold storage medium results in slow heat transfer and limited dynamic response capabilities, making it difficult to adapt to rapidly changing power loads. In addition, most thermal storage systems (such as solar molten salt thermal storage systems) only support high-temperature thermal storage scenarios, lack the necessary cold storage facilities, and have poor integration compatibility with the cold storage unit, which restricts the integrated design of the system.

[0007] Therefore, there is an urgent need to explore a Carnot battery system configuration that does not require a cold storage unit, has a simple system structure, and is highly feasible in engineering, in order to meet the current power system's urgent need for efficient, large-scale, long-term energy storage. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a graded thermal storage Carnot battery system based on the Brayton cycle and its operation method, aiming to at least partially solve the above-mentioned technical problems. The specific technical solution provided by this invention is as follows.

[0009] As a first aspect of the present invention, a graded Carnot battery system based on the Brayton cycle is provided, comprising:

[0010] The energy storage cycle subsystem includes:

[0011] The first compressor is suitable for compressing preheated air to increase its temperature and pressure.

[0012] A first heat exchanger is adapted to store heat energy from compressed air from a first compressor into a first heat storage medium by exchanging heat with a low-temperature first heat storage medium, thereby forming a high-temperature first heat storage medium; and

[0013] The preheating module is suitable for heating the heat-exchanged air from the first heat exchanger to form preheated air;

[0014] The thermal storage subsystem is suitable for storing a low-temperature first thermal storage medium, a high-temperature first thermal storage medium, a low-temperature second thermal storage medium, and a high-temperature second thermal storage medium.

[0015] The energy release cycle subsystem includes:

[0016] The second heat exchanger is suitable for heating compressed air by exchanging heat with a high-temperature first heat storage medium to form a low-temperature first heat storage medium;

[0017] The first expander is suitable for expanding and discharging work using heated air from the second heat exchanger; and

[0018] The cooling and compression module is suitable for cooling the air from the first expander multiple times and compressing it at least once to form compressed air.

[0019] As a second aspect of the present invention, a method for operating a graded thermal storage Carnot battery system based on the Brayton cycle is provided, comprising:

[0020] In the energy storage stage, the energy storage cycle subsystem is used to convert electrical energy into thermal energy and store the thermal energy in the thermal storage subsystem, thereby realizing the conversion and storage of electrical energy into thermal energy.

[0021] During the energy release phase, the thermal energy stored in the thermal storage subsystem is converted into electrical energy using the energy release cycle subsystem, thus realizing the conversion of thermal energy into electrical energy.

[0022] In this embodiment of the invention, a tiered thermal energy storage subsystem, in conjunction with an energy storage cycle subsystem and an energy release cycle subsystem, achieves cascaded utilization and efficient conversion of thermal energy. In the energy storage stage, the compressed air thermal energy is stored as a high-temperature primary thermal energy storage medium through a first heat exchanger, and a preheating module reduces the power consumption of the first compressor. In the energy release stage, the high-temperature primary thermal energy storage medium heats the compressed air to drive the first expander to generate electricity, and a cooling compression module optimizes the air compression process, significantly improving the system's electrothermal conversion efficiency. The invention eliminates the need for a cold storage unit, simplifying the system structure, reducing initial investment and operational complexity, enhancing dynamic response capabilities, adapting to the large-scale consumption needs of renewable energy, balancing long-term energy storage with economic efficiency, and demonstrating strong engineering feasibility. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a graded thermal storage Carnot battery system based on the Brayton cycle in an embodiment of the present invention.

[0024] Explanation of reference numerals in the attached figures:

[0025] A - Energy storage cycle subsystem; B - Energy release cycle subsystem; C - Thermal storage subsystem;

[0026] 1-First compressor; 2-First heat exchanger; 3-Second heat exchanger; 4-First expander; 5-Second expander; 6-Third heat exchanger; 7-Fourth heat exchanger; 8-First radiator; 9-Second compressor; 10-Second radiator; 11-Third compressor; 12-First hot tank; 13-First cold tank; 14-Second hot tank; 15-Second cold tank. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0028] Given the technical and economic requirements of energy storage technology in terms of long duration, large scale, and low cost, related technologies such as Carnot batteries can be adopted. As a novel physical energy storage technology, Carnot batteries can convert electrical energy into thermal energy for storage through a reverse Brayton cycle when there is excess electricity, and convert thermal energy into electrical energy through a Brayton cycle when renewable energy generation is insufficient. They offer advantages such as high efficiency, long storage time, and low cost, meeting the needs of large-scale, long-term energy storage. However, existing Brayton cycle-based Carnot battery systems typically incorporate cold storage units to reduce compression power consumption and improve system efficiency. However, cold storage units face several technical challenges, such as complex system construction, high cost, low thermal conductivity of the cold storage medium, slow heat transfer rate, limited dynamic response capability, and poor integration compatibility with existing high-temperature thermal storage systems. Therefore, this invention provides a staged thermal storage Carnot battery system based on the Brayton cycle, achieving staged thermal storage to solve many problems caused by cold storage units in existing technologies and meet the technical and economic requirements of large-scale, long-term energy storage.

[0029] Figure 1 This is a schematic diagram of the structure of a graded thermal storage Carnot battery system based on the Brayton cycle in an embodiment of the present invention.

[0030] As a first aspect of the present invention, a graded Carnot battery system based on the Brayton cycle is provided, such as... Figure 1 As shown, it includes:

[0031] Energy storage cycle subsystem A includes:

[0032] First compressor 1, suitable for compressing preheated air to increase air temperature and pressure;

[0033] The first heat exchanger 2 is adapted to store the heat energy from the compressed air from the first compressor 1 into the first heat storage medium by exchanging heat with the low-temperature first heat storage medium, thereby forming a high-temperature first heat storage medium; and

[0034] The preheating module is suitable for heating the heat-exchanged air from the first heat exchanger 2 to form preheated air;

[0035] Thermal storage subsystem C is suitable for storing a low-temperature first thermal storage medium, a high-temperature first thermal storage medium, a low-temperature second thermal storage medium, and a high-temperature second thermal storage medium.

[0036] Energy release cycle subsystem B includes:

[0037] The second heat exchanger 3 is suitable for heating compressed air by exchanging heat with a high-temperature first heat storage medium and forming a low-temperature first heat storage medium;

[0038] The first expander 4 is suitable for expanding and discharging work using heated air from the second heat exchanger 3; and

[0039] The cooling and compression module is suitable for cooling the air from the first expander 4 multiple times and compressing it at least once to form compressed air.

[0040] In this embodiment of the invention, the thermal energy storage subsystem C, with its staged thermal storage, works in conjunction with the energy storage cycle subsystem A and the energy release cycle subsystem B to achieve efficient cascaded utilization of thermal energy. During the energy storage phase, the first heat exchanger 2 stores the thermal energy of compressed air, and a preheating module reduces compression power consumption. During the energy release phase, the second heat exchanger 3 heats the compressed air to drive the first expander 4 to generate electricity, and a cooling compression module optimizes the compression process. This eliminates the need for a cold storage unit, simplifying the structure, reducing costs, improving dynamic response and integration compatibility, and efficiently adapting to large-scale, long-term energy storage needs.

[0041] In some embodiments, the preheating module includes: a second expander 5 adapted to expand and perform work discharge of heat-exchanged air from the first heat exchanger 2; and a third heat exchanger 6 adapted to heat the air from the second expander 5 by exchanging heat with a high-temperature second heat storage medium, and to form preheated air and a low-temperature second heat storage medium.

[0042] In this embodiment of the invention, the air output from the first heat exchanger 2 is expanded by the second expander 5 to perform work, recovering some energy to reduce system energy consumption. Simultaneously, the air is preheated by the third heat exchanger 6 and the high-temperature second heat storage medium before being sent to the first compressor 1, reducing energy loss during compression. This preheating module achieves both tiered energy recovery and utilization, and optimizes compressor operating conditions through preheating, improving overall system energy efficiency, further strengthening the synergistic advantages of tiered heat storage, and enhancing system economy and operational efficiency.

[0043] In some embodiments, the cooling compression module includes: a fourth heat exchanger 7, adapted to perform secondary cooling of the cooled air from the first expander 4 by exchanging heat with a low-temperature second heat storage medium, and to form a high-temperature second heat storage medium.

[0044] In this embodiment of the invention, the fourth heat exchanger 7 of the cooling compression module exchanges heat with the low-temperature second heat storage medium to perform secondary cooling on the air discharged from the first expander 4. Simultaneously, the waste heat from the air is transferred to the low-temperature second heat storage medium, causing it to heat up and form a high-temperature second heat storage medium. This design not only enhances the air cooling effect to optimize the subsequent compression process but also achieves efficient recovery and utilization of waste heat, further improving the staged heat storage system and enhancing the system's energy utilization rate and operational economy.

[0045] In some embodiments, the cooling and compression module further includes: a first radiator 8, adapted to perform a third cooling on the air that has been cooled twice; a second compressor 9, adapted to perform a first compression on the air that has been cooled three times; a second radiator 10, adapted to perform a fourth cooling on the air that has been compressed once; and a third compressor 11, adapted to perform a second compression on the air that has been cooled four times, and to form compressed air, thereby increasing the energy storage capacity of the compressed air.

[0046] The second compressor 9, the second radiator 10, and the third compressor 11 form a bi-stage inter-stage cold compression structure. The second radiator 10 is used to cool the air between the two compression stages. The air compressed twice by the third compressor 11 is then sent to the second heat exchanger 3 for heat exchange. The first radiator 8 is used to cool the air at the outlet of the fourth heat exchanger 7 and sends the cooled air to the second compressor 9.

[0047] In this embodiment of the invention, the cooling compression module comprises a bi-stage cold compression structure consisting of the second compressor 9, the second radiator 10, and the third compressor 11. By placing the second radiator 10 between the two compression stages to cool the air, the compression power consumption is significantly reduced. The first radiator 8 pre-cools the air exiting the fourth heat exchanger 7 before sending it to the second compressor 9, further optimizing the compression conditions. This design increases the air energy storage capacity while reducing energy loss and enhancing the heat exchange efficiency with the second heat exchanger 3 through the synergy of staged cooling and compression, thereby improving the overall energy efficiency and operational stability of the system.

[0048] In some embodiments, the thermal storage subsystem C includes a first hot tank 12, a first cold tank 13, a second hot tank 14, and a second cold tank 15. The first hot tank 12 is used to store a first thermal storage medium at high temperatures, the first cold tank 13 is used to store a first thermal storage medium at low temperatures, the second hot tank 14 is used to store a second thermal storage medium at high temperatures, and the second cold tank 15 is used to store a second thermal storage medium at low temperatures.

[0049] In some embodiments, the temperature of the high-temperature first heat storage medium is 500-800°C; the temperature of the low-temperature first heat storage medium is 250-300°C; the temperature of the high-temperature second heat storage medium is 200-250°C; and the temperature of the low-temperature second heat storage medium is 50-100°C.

[0050] In some embodiments, the first heat storage medium is molten salt. The second heat storage medium includes any one of water, heat transfer oil, and molten salt.

[0051] Specifically, the output of the first hot tank 12 is connected to the input of the first cold tank 13 via the second heat exchanger 3, and the output of the first cold tank 13 is connected to the input of the first hot tank 12 via the first heat exchanger 2, so as to realize a closed loop of the first heat storage medium in the first hot tank 12, the second heat exchanger 3, the first cold tank 13, and the first heat exchanger 2. The output of the second hot tank 14 is connected to the input of the second cold tank 15 via the third heat exchanger 6, and the output of the second cold tank 15 is connected to the input of the second hot tank 15 via the fourth heat exchanger 7, so as to realize a closed loop of the second heat storage medium in the second hot tank 14, the third heat exchanger 6, the second cold tank 15, and the fourth heat exchanger 7.

[0052] In this embodiment of the invention, a staged Carnot battery system based on the Brayton cycle is provided. This system eliminates the need for a cold storage unit, uses air as the circulating working fluid, and employs a first (high-temperature) and a second (medium-temperature) heat storage medium as heat storage materials, significantly reducing the system's structural complexity and construction costs. During the energy storage phase, electrical energy drives a first compressor 1 to compress air, increasing its temperature and pressure. The heat of compression is stored in the first heat storage medium via a first heat exchanger 2, converting electrical energy into thermal energy. Part of the residual heat from the air drives a second expander 5 to recover electrical energy. The cooled air is preheated by the high-temperature second heat storage medium and then compressed again, completing the energy storage cycle. During the energy release phase, air undergoes bipolar intercooling compression (composed of a second compressor 9, a second radiator 10, and a third compressor 11), absorbing heat from the high-temperature first thermal storage medium to reach a high-temperature, high-pressure state. It then enters the first expander 4 to expand and release electrical energy. The residual heat from this expansion is stored in the second thermal storage medium, used to preheat the cold air exiting the second expander 5 in subsequent energy storage phases, achieving efficient heat recovery. After cooling, the air re-enters the second compressor 9, completing the energy release cycle. This system possesses excellent energy storage efficiency, thermal efficiency, and engineering feasibility. It offers long storage time, large scale, and low cost, meeting the power system's demand for long-term, large-scale energy storage. It is suitable for absorbing redundant renewable energy power, ensuring peak load supply, and has the capability to integrate with existing molten salt thermal storage solar power plants.

[0053] As a second aspect of the present invention, a method for operating a graded thermal storage Carnot battery system based on the Brayton cycle is provided, comprising:

[0054] In the energy storage stage, the energy storage cycle subsystem is used to convert electrical energy into thermal energy and store the thermal energy in the thermal storage subsystem, thereby realizing the conversion and storage of electrical energy into thermal energy.

[0055] During the energy release phase, the thermal energy stored in the thermal storage subsystem is converted into electrical energy using the energy release cycle subsystem, thus realizing the conversion of thermal energy into electrical energy.

[0056] In this embodiment of the invention, the operating method converts electrical energy into thermal energy for storage during the energy storage phase and converts the thermal energy back into electrical energy during the energy release phase, achieving efficient energy conversion and recycling. The tiered thermal storage design enables cascaded storage and release of thermal energy, reducing energy loss and improving overall system efficiency. The elimination of a cold storage unit simplifies the operation process, reduces energy consumption and costs, and is suitable for long-term, large-scale energy storage scenarios. It can efficiently absorb redundant renewable energy power and ensure peak power supply, demonstrating strong engineering practicality.

[0057] In some specific embodiments, the energy storage cycle process includes:

[0058] External electrical energy drives the first compressor 1 to compress air, increasing the air temperature and pressure;

[0059] The compressed air enters the first heat exchanger 2 for heat exchange, forming a high-temperature first heat storage medium, which cools the compressed air while maintaining its pressure after compression.

[0060] The cooled air enters the second expander 5, expands to do work and drive power generation, and recovers some electrical energy.

[0061] After being cooled and depressurized, the air enters the third heat exchanger 6 and exchanges heat with the high-temperature second heat storage medium, raising its temperature to the preheating temperature at the inlet of the first compressor 1, thus completing a closed loop.

[0062] In some specific embodiments, the energy release cycle process includes:

[0063] Compressed air enters the second heat exchanger 3 and exchanges heat with the high-temperature first heat storage medium, which raises the temperature of the compressed air and maintains the pressure after compression.

[0064] The heated air enters the first expander 4, expands to do work and drive power generation, and the temperature and pressure of the air decrease.

[0065] Air from the first expander 4 enters the fourth heat exchanger 7 for heat exchange, forming a high-temperature second heat storage medium;

[0066] The first radiator 8 is used to cool the air from the fourth heat exchanger 7 three times.

[0067] The second compressor 9 is powered by electricity to compress the air that has been cooled three times.

[0068] The second radiator 10 is used to cool the compressed air four times.

[0069] The third compressor 11 is driven by electric energy to perform secondary compression on the air medium that has been cooled four times, forming compressed air. The compressed air is then input into the second heat exchanger 3 to complete a closed loop.

[0070] As an example, embodiments of the present invention provide a graded thermal storage Carnot battery system based on the Brayton cycle and its operation method, using molten salt as the first thermal storage medium and water as the second thermal storage medium.

[0071] like Figure 1 As shown, the system includes an energy storage cycle subsystem A, an energy release cycle subsystem B, and a thermal storage subsystem C.

[0072] The energy storage cycle subsystem A includes a first compressor 1, a first heat exchanger 2, a second expander 5, and a third heat exchanger 6. The first compressor 1 uses electrical energy to compress air to a high temperature and high pressure state (compressing air from 221.00℃ and 1.0 bar to 610.01℃ and 7.3 bar). The second heat exchanger 3 transfers the air's heat energy to molten salt (cooling the air to 270.00℃ and 7.3 bar after heat exchange). The second expander 5 uses air expansion to generate electricity (cooling and depressurizing the air to 59.85℃ and 1.0 bar after expansion). The third heat exchanger 6 transfers hot water's heat energy to the air, heating it to the inlet temperature of the first compressor 1 (221.00℃), thus completing the cycle.

[0073] The thermal storage subsystem C includes a first hot tank 12, a first cold tank 13, a second hot tank 14, and a second cold tank 15. The first hot tank 12 stores molten salt heated by air in the first heat exchanger 2 at a temperature of 600.00℃. The first cold tank 13 stores molten salt heated by air in the second heat exchanger 3 at a temperature of 260.00℃. Both the first hot tank 12 and the first cold tank 13 are stored at atmospheric pressure (1.0 bar). The second hot tank 14 stores hot water heated by air in the fourth heat exchanger 7 at a temperature of 231.00℃. The second cold tank 15 stores cold water heated by air in the third heat exchanger 6 at a temperature of 70.00℃. Both the second hot tank 14 and the second cold tank 15 are maintained at a pressure of 30.0 bar to ensure the hot water remains in a liquid state.

[0074] The energy release cycle subsystem B includes a second compressor 9, a second radiator 10, a third compressor 11, a second heat exchanger 3, a first expander 4, a fourth heat exchanger 7, and a first radiator 8. The second compressor 9 is used to compress air to a medium-temperature and medium-pressure state (compressing air from 25.00℃ and 1.0 bar to 65.84℃ and 1.5 bar). The second radiator 10 is used to cool the air to room temperature (25.00℃) with cooling water. The third compressor 11 is used to compress the air again to a medium-temperature and high-pressure state (245.32℃ and 9.0 bar). The second heat exchanger 3 is used to transfer the heat energy of molten salt to the air, heating the air to a high-temperature and high-pressure state (589.37℃ and 9.0 bar). The first expander 4 is used to generate electricity by expanding the air (the air is cooled and depressurized to 242.29℃ and 1.0 bar after expansion). The fourth heat exchanger 7 is used to transfer the waste heat of the air to hot water (the air is cooled to 80.36℃ and 1.0 bar after heat exchange). The first radiator 8 is used to cool the air to room temperature (25.00℃) with cooling water, thus completing the cycle.

[0075] like Figure 1 As shown, in the energy release cycle, the waste heat of the air at the outlet of the first expander 4 is stored in the second heat tank 14. This part of the hot water heat energy is used to preheat the air at the outlet of the second expander 5 in the energy storage cycle, so as to achieve efficient utilization of heat energy.

[0076] Table 1 provides an example of... Figure 1 The thermodynamic parameters at the inlet of each device in the system shown.

[0077] Table 1 Thermodynamic parameters of key system nodes

[0078]

[0079] Table 2 provides an example of, for instance, the following... Figure 1 The main design parameters of each device in the system shown are as follows.

[0080] Table 2 Main Design Parameters of the System

[0081]

[0082] As shown in Table 1, in the energy release cycle, the air outlet temperature of the first expander 4 is 242.29℃. In order to efficiently utilize this part of the air heat energy, the air heat energy is transferred to the hot water and stored through the fourth heat exchanger 7. The air outlet temperature of the fourth heat exchanger 7 drops to 80.36℃, reducing the heat loss in the first radiator 8. In the energy storage cycle, the hot water heat energy in the second heat tank 14 is used to heat the outlet air of the second expander 5 to 221.00℃ to achieve preheating of the inlet air of the first compressor 1, thereby improving the system energy utilization efficiency.

[0083] As shown in Table 1, in the energy release cycle, bipolar intercooling compression is achieved through the second compressor 9, the second radiator 10, and the third compressor 11. The second compressor 9 compresses the air from 25.00℃ and 1.0 bar to 65.84℃ and 1.5 bar, and then the second radiator 10 cools the air to 25.00℃ and 1.5 bar. Subsequently, the third compressor 11 compresses the air to 245.32℃ and 9.0 bar, thereby greatly reducing the compression power consumption of the energy release cycle. The high pressure ratio of bipolar compression also allows the air to expand more fully in the first expander 4, increasing the expansion power generation of the energy release cycle and thus improving the system efficiency.

[0084] This system eliminates the need for complex cold storage units, uses air as the circulating medium, and selects low-cost, readily available molten salt and water as the heat storage medium. This significantly reduces the complexity of the system structure and construction costs, and can meet the power system's demand for large-scale energy storage systems with long-term energy storage capabilities and good economic efficiency.

[0085] To illustrate the technical effectiveness of the energy storage system according to the embodiments of the present invention, the energy balance of the system was calculated, and the round-trip efficiency of the embodiments of the present invention was also calculated. The round-trip efficiency is defined as the ratio of the net work done in the energy release phase to the net work done in the energy storage phase.

[0086] Table 3 shows the following: Figure 1 The system's energy balance table is shown, where round-trip efficiency is represented by the ratio of energy output to energy input.

[0087] Table 3 System Energy Balance Table

[0088]

[0089] As shown in Table 3, the system input electrical energy is 4049.46kW and the output electrical energy is 2131.40kW, corresponding to a round-trip efficiency of 52.63%, demonstrating a high energy storage conversion efficiency. The system energy loss is mainly concentrated in the first radiator 8 (accounting for 27.25%) used for cooling the outlet air of the fourth heat exchanger 7 and the second radiator 10 (accounting for 20.11%) used for interstage cooling of the compressor.

[0090] The Brayton cycle-based graded thermal storage Carnot battery system provided by this invention mainly includes: an energy storage cycle subsystem, a thermal storage subsystem, and an energy release cycle subsystem. When there is a power surplus, the system converts electrical energy into thermal energy for storage via a reverse Brayton cycle; when renewable energy generation is insufficient, it converts thermal energy into electrical energy via a Brayton cycle. This system eliminates the need for complex cold storage units, uses air as the system's circulating working fluid, and selects a first thermal storage medium (high temperature) and a second thermal storage medium (medium temperature) as thermal storage materials. This significantly reduces the system's structural complexity and construction costs, and can meet the power system's demand for large-scale energy storage systems with long-term energy storage capabilities and good economic efficiency.

[0091] In summary, the Brayton cycle-based staged thermal storage Carnot battery system provided by this invention optimizes the operating temperature range, extending the entire operating range to the mid-to-high temperature range above ambient temperature. This fundamentally eliminates the need for a cold storage unit, avoids complex insulation structures and the use of low-temperature materials, reduces system complexity and construction costs, and significantly improves engineering feasibility and economy. Simultaneously, by setting up a mid-temperature thermal storage stage of 70-231℃, direct preheating of the working fluid and waste heat recovery are achieved, eliminating the need for a large temperature difference regeneration section, simplifying the system configuration and circulation process, and improving the electro-thermal conversion efficiency. Regarding the thermal storage medium configuration, molten salt is used for high-temperature thermal storage, and pressurized water is preferred for mid-temperature thermal storage. Compared to heat transfer oil or mid-temperature molten salt, water is inexpensive and readily available, improving the economy and versatility of the thermal storage stage. Furthermore, the embodiment provides the system's operating thermal storage temperature range, pressure ratio parameters, and round-trip efficiency, verifying the system's feasibility and engineering application value. This invention achieves cascaded utilization of thermal energy through innovative configuration and operational optimization of graded thermal storage, while taking into account system efficiency, economy, and engineering feasibility, and can meet the application needs of large-scale renewable energy consumption.

[0092] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A graded Carnot battery system for thermal storage based on the Brayton cycle, characterized in that, include: The energy storage cycle subsystem includes: The first compressor is suitable for compressing preheated air to increase its temperature and pressure. A first heat exchanger is adapted to store heat energy from compressed air from the first compressor into a first heat storage medium by exchanging heat with a low-temperature first heat storage medium, thereby forming a high-temperature first heat storage medium; and The preheating module is adapted to heat the air that has been heated from the first heat exchanger to form the preheated air; The thermal storage subsystem is suitable for storing a low-temperature first thermal storage medium, a high-temperature first thermal storage medium, a low-temperature second thermal storage medium, and a high-temperature second thermal storage medium. The energy release cycle subsystem includes: The second heat exchanger is suitable for heating compressed air by exchanging heat with a high-temperature first heat storage medium to form a low-temperature first heat storage medium; The first expander is suitable for expanding and discharging work using heated air from the second heat exchanger; and The cooling and compression module is suitable for cooling the air from the first expander multiple times and compressing it at least once to form the compressed air.

2. The graded thermal storage Carnot battery system according to claim 1, characterized in that, The preheating module includes: The second expander is suitable for expanding and discharging heat-exchanged air from the first heat exchanger; and The third heat exchanger is adapted to heat the air from the second expander by exchanging heat with the high-temperature second heat storage medium, and to form the preheated air and the low-temperature second heat storage medium.

3. The graded thermal storage Carnot battery system according to claim 1, characterized in that, The cooling compression module includes: The fourth heat exchanger is suitable for further cooling of the air from the first expander by exchanging heat with the low-temperature second heat storage medium, and forming a high-temperature second heat storage medium.

4. The graded thermal storage Carnot battery system according to claim 3, characterized in that, The cooling compression module also includes: The first radiator is suitable for cooling the air that has undergone secondary cooling a third time; The second compressor is suitable for compressing the air that has been cooled three times in one operation; The second radiator is suitable for cooling the compressed air four times; and The third compressor is suitable for performing secondary compression on the air that has been cooled four times, and forming the compressed air, thereby increasing the energy storage capacity of the compressed air.

5. The graded thermal storage Carnot battery system according to any one of claims 1-4, characterized in that, The first heat storage medium is molten salt.

6. The graded thermal storage Carnot battery system according to claim 5, characterized in that, The second heat storage medium includes any one of water, heat transfer oil, and molten salt.

7. The graded thermal storage Carnot battery system according to claim 6, characterized in that, The temperature of the first high-temperature heat storage medium is 500-800℃; The temperature of the first low-temperature heat storage medium is 250-300℃; The temperature of the high-temperature second heat storage medium is 200-250℃; The temperature of the second thermal storage medium at low temperature is 50-100℃.

8. A method for operating a graded thermal storage Carnot battery system as described in any one of claims 1-7, characterized in that, include: In the energy storage stage, the energy storage cycle subsystem is used to convert electrical energy into thermal energy and store the thermal energy in the thermal storage subsystem, thereby realizing the conversion and storage of electrical energy into thermal energy. During the energy release phase, the thermal energy stored in the thermal storage subsystem is converted into electrical energy using the energy release cycle subsystem, thus realizing the conversion of thermal energy into electrical energy.

9. The operating method according to claim 8, characterized in that, The process of converting electrical energy into thermal energy using an energy storage cycle subsystem and storing the thermal energy in a thermal storage subsystem includes: External electrical energy drives the first compressor to compress air, increasing the air temperature and pressure; The compressed air enters the first heat exchanger for heat exchange, forming a high-temperature first heat storage medium, which cools the compressed air while maintaining its pressure after compression. The cooled air enters the second expander, expands to do work and drive power generation, and recovers some electrical energy. After being cooled and depressurized, the air enters the third heat exchanger and exchanges heat with the high-temperature second heat storage medium, raising its temperature to the preheating temperature at the inlet of the first compressor, thus completing a closed loop.

10. The operating method according to claim 8, characterized in that, The process of converting the thermal energy stored in the thermal storage subsystem into electrical energy using the energy release cycle subsystem includes: Compressed air enters the second heat exchanger and exchanges heat with the high-temperature first heat storage medium, which raises the temperature of the compressed air and maintains the pressure after compression. The heated air enters the first expander, expands to do work and drive power generation, and the temperature and pressure of the air decrease. Air from the first expander enters the fourth heat exchanger for heat exchange, forming a high-temperature second heat storage medium; The first radiator is used to cool the air from the second cooling of the fourth heat exchanger three times. The second compressor is driven by electricity to compress the air that has been cooled three times. The compressed air is cooled four times using a second radiator. The third compressor is driven by electricity to perform secondary compression on the air medium that has been cooled four times, forming compressed air. The compressed air is then input into the second heat exchanger to complete a closed loop.

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