Compressed air energy storage system based on high-temperature heat pump and low-melting-point fused salt

Abstract

The invention relates to a compressed air energy storage system based on a high-temperature heat pump and low-melting-point fused salt. The compressed air energy storage system comprises a compression module, a control module and a power supply module. The compression module receives input electric energy and generates a high-pressure air signal and a first medium-low-temperature compression heat signal. The air storage module is connected with the compression module and receives and stores the high-pressure air signal; the first-stage fused salt heat storage module is connected with the compression module, and receives and stores the first medium-low temperature compression heat signal; the evaporator side of the high-temperature heat pump module is connected with the low-temperature section of the first-stage fused salt heat storage module, and part of first fused salt heat medium signals are received to serve as low-temperature heat source signals. The power generation module is connected with the air storage module to receive released high-pressure air signals and connected with the high-temperature section of the first-stage fused salt heat storage module and the condenser side of the high-temperature heat pump module to receive first fused salt heat medium signals and high-temperature heat energy signals correspondingly. The compressed air energy storage system based on the high-temperature heat pump and the low-melting-point molten salt can solve the problems that traditional compressed air energy storage is low in efficiency and depends on fossil fuel and geographical conditions.

Description

Technical Field

[0001] This invention relates to the field of large-scale physical energy storage technology, specifically to a compressed air energy storage system based on a high-temperature heat pump and a low-melting-point molten salt. Background Technology

[0002] The transformation of the energy structure relies heavily on large-scale energy storage technologies to achieve smooth grid connection of renewable energy and peak shaving and valley filling. Compressed air energy storage is considered one of the most promising large-scale energy storage technologies due to its large capacity, long lifespan, and relatively low cost. Its traditional approach involves consuming electricity during off-peak hours to compress air and store it in underground gas storage caverns. When power generation is needed, the high-pressure air is released to drive a turbine expander. However, early traditional compressed air energy storage systems have two inherent drawbacks: first, a large amount of heat is generated during compression, which is directly dissipated into the environment through interstage coolers in traditional designs, resulting in significant energy waste; second, before expansion and power generation, the high-pressure air needs to be reheated to prevent turbine icing and improve efficiency. This process usually relies on burning fossil fuels such as natural gas, which not only leads to carbon emissions, making the energy storage system less "green," but also makes its operation subject to fuel supply and price constraints.

[0003] To address the aforementioned issues, adiabatic compressed air energy storage technology has been developed. Its core idea is to store the heat of compression using solid or liquid heat storage media and then use it to heat air during power generation, theoretically eliminating the need for fossil fuels. However, this technology faces significant challenges in practice. The main bottleneck lies in the extremely wide temperature range of the heat generated during compression, from near ambient temperature to hundreds of degrees Celsius. Traditional molten salts, widely used in concentrated solar power (CSP), have high freezing points and are prone to solidification when used to store low-temperature heat, clogging pipelines and equipment and preventing the system from operating safely and stably. Therefore, how to safely and economically recover and store low-temperature compression heat and efficiently use it for power generation has become a core technical challenge hindering the further development and wider application of compressed air energy storage technology. While attempts have been made to utilize other heat transfer media or complex multi-stage heat storage systems, these solutions often introduce new shortcomings in terms of system complexity, cost, or efficiency. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a compressed air energy storage system based on a high-temperature heat pump and low-melting-point molten salt, to solve the problems of low efficiency and dependence on fossil fuels and geographical conditions in traditional compressed air energy storage. This invention uses low-melting-point molten salt as the heat storage medium to safely and efficiently capture and store the full spectrum of thermal energy generated during compression, especially in the medium and low temperature range. Simultaneously, it innovatively integrates a high-temperature heat pump cycle to raise the grade of low-grade thermal energy and ambient thermal energy that are difficult to use directly in the system to a high usable temperature. Finally, during the power generation stage, the stored multi-grade thermal energy is used to perform cascade heating of the high-pressure air, thereby significantly improving system efficiency and completely eliminating dependence on fossil fuels.

[0005] This invention provides a compressed air energy storage system based on a high-temperature heat pump and a low-melting-point molten salt, comprising:

[0006] The compression module receives input electrical energy and generates a high-pressure air signal and a first medium-low temperature compression heat signal.

[0007] The gas storage module is connected to the compression module and receives and stores high-pressure air signals.

[0008] A primary molten salt thermal storage module is connected to a compression module, which receives and stores a first low-temperature compression thermal signal and forms a first molten salt thermal medium signal.

[0009] The high-temperature heat pump module has its evaporator side connected to the low-temperature section of the first-stage molten salt heat storage module. It receives part of the first molten salt heat medium signal as a low-temperature heat source signal. Its condenser side consumes auxiliary power and generates a high-temperature heat energy signal by improving the quality of the low-temperature heat source signal.

[0010] The power generation module is connected to the gas storage module to receive the released high-pressure air signal, and is connected to the high-temperature section of the first-stage molten salt thermal storage module and the condenser side of the high-temperature heat pump module to receive the first molten salt thermal medium signal and the high-temperature thermal energy signal respectively. The high-pressure air signal is heated by the thermal energy signal and then expands to do work, generating an output electrical energy signal.

[0011] In one embodiment of the present invention, the molten salt medium circulating in the primary molten salt thermal storage module is a low-melting-point molten salt. The freezing point of this low-melting-point molten salt is significantly lower than that of molten salt used in conventional solar thermal power generation, thereby enabling the safe and efficient capture and storage of low-temperature compression heat signals from the compression module over a wide temperature range without concern about the medium solidifying and clogging the flow channels. Its chemical composition includes a eutectic mixture of various nitrates, and these nitrate cations include at least sodium and potassium ions. A third cation may be selectively introduced to give the mixture a lower eutectic point and more stable thermophysical properties, ensuring that it remains liquid and has good thermal conductivity throughout the expected operating temperature range of the entire system.

[0012] In one embodiment of the present invention, the high-temperature heat pump module employs a special working medium that can operate stably at a high condensation temperature and raise the low-temperature heat energy signal absorbed from the evaporator side to a higher temperature level. It is preferably a non-azeotropic working medium that exhibits temperature slip during phase change, thereby enabling better temperature matching with external heat sources and heat sinks to reduce irreversible losses during heat transfer. Alternatively, it may be a carbon dioxide working medium with excellent thermodynamic properties, which can provide a large temperature range to adapt to different heating requirements when operating in a supercritical state.

[0013] In one embodiment of the present invention, a secondary molten salt thermal storage module is further included. This secondary molten salt thermal storage module is specifically used to receive and store the high-temperature thermal energy signal released from the condenser side of the high-temperature heat pump module. The internal circulating thermal storage medium can be a molten salt suitable for high-temperature scenarios. The output end of the secondary molten salt thermal storage module is connected to the high-temperature heater of the power generation module, and is specifically responsible for heating the high-pressure air signal to a higher initial expansion temperature during the energy release and power generation stage. This forms a stepped heating configuration with the primary molten salt thermal storage module, realizing temperature matching and efficient utilization of thermal energy in stages.

[0014] In one embodiment of the present invention, the heat source on the evaporator side of the high-temperature heat pump module is not limited to the low-temperature section of the primary molten salt thermal storage module. The system also integrates an environmental heat source acquisition module, which can extract low-grade environmental heat energy from the surrounding air, water or soil and generate a stable environmental heat source signal to provide to the evaporator of the high-temperature heat pump module as a supplementary or alternative heat source, thereby increasing the total heat energy input of the system and improving its energy utilization efficiency, so that the system can still maintain excellent performance under partial load or specific environment.

[0015] In one embodiment of the present invention, the compression module adopts a multi-stage compression and intercooling structure. Each stage of compression is equipped with an intercooler, and the first-stage molten salt heat storage module includes multiple corresponding stage heat exchange units. Each stage heat exchange unit is connected to the hot side of an intercooler, thereby enabling the recovery of compression heat signals at different temperature levels after each stage of compression in stages and temperature ranges. This achieves refined recovery and management of the full spectrum of heat energy generated during the compression process, and avoids the improper degradation and utilization of high-quality heat energy.

[0016] In one embodiment of the present invention, the power generation module adopts a multi-stage expansion and intermediate reheat structure, which includes a high-pressure turbine and a low-pressure turbine. After the high-pressure turbine expands and does work, the high-pressure air signal is guided to flow through a reheater connected to the molten salt circuit for heating. After absorbing the stored heat energy signal and restoring the temperature, it enters the low-pressure turbine to continue expanding and doing work. This process can significantly increase the total power generation output and improve the overall operating efficiency of the turbine, so that the heat energy stored in the molten salt can be more fully and thoroughly utilized.

[0017] In one embodiment of the present invention, the power generation module adopts a multi-stage expansion and intermediate reheat structure, which includes a high-pressure turbine and a low-pressure turbine. After the high-pressure turbine expands and does work, the high-pressure air signal is guided to flow through a reheater connected to the molten salt circuit for heating. After absorbing the stored heat energy signal and restoring the temperature, it enters the low-pressure turbine to continue expanding and doing work. This process can significantly increase the total power generation output and improve the overall operating efficiency of the turbine, so that the heat energy stored in the molten salt can be more fully and thoroughly utilized.

[0018] In one embodiment of the present invention, the exhaust gas discharged by the power generation module after completing the expansion work still carries a considerable amount of usable waste heat. The system is equipped with a waste heat recovery module, which captures the waste heat signal carried in the low-temperature exhaust gas discharged by the power generation module through a waste heat exchanger, and transmits the recovered waste heat signal to the evaporator side of the high-temperature heat pump module as its additional low-temperature heat source, thereby realizing the deep mining and utilization of energy throughout the entire system process, and further improving the energy conversion efficiency of the entire system.

[0019] In one embodiment of the present invention, the operation of the system is coordinated by a central control module. The central control module receives dispatch signals from the power grid and temperature, pressure and flow signals fed back by each node in the system. After calculation by the built-in optimization algorithm, it generates control signals and sends them to the expansion valve of the high-temperature heat pump module and the regulating valves on each pipeline of the variable frequency drive of the compression module. The control module dynamically adjusts the energy storage power, energy release power and the heat pump's temperature rise to achieve optimal economic operation and the longest equipment life under different operating conditions.

[0020] This invention provides a compressed air energy storage system based on a high-temperature heat pump and low-melting-point molten salt. By using low-melting-point molten salt as the heat storage medium, this invention safely and efficiently captures and stores the full spectrum of thermal energy generated during compression, especially the medium and low temperature range. At the same time, it innovatively integrates a high-temperature heat pump cycle to raise the grade of low-grade thermal energy and ambient thermal energy that are difficult to use directly in the system to a high usable temperature. Finally, during the power generation stage, the stored multi-grade thermal energy is used to perform cascade heating of high-pressure air, thereby significantly improving system efficiency and completely eliminating dependence on fossil fuels. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a system architecture diagram of a compressed air energy storage system based on a high-temperature heat pump and a low-melting-point molten salt. Detailed Implementation

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0024] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0025] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0026] Please see Figure 1The diagram illustrates a compressed air energy storage system based on a high-temperature heat pump and low-melting-point molten salt according to the present invention. The system includes a compression module that receives input electrical energy and generates a high-pressure air signal and a first medium-low temperature compression heat signal; a gas storage module connected to the compression module that receives and stores the high-pressure air signal; a primary molten salt heat storage module connected to the compression module that receives and stores the first medium-low temperature compression heat signal and forms a first molten salt heat medium signal; a high-temperature heat pump module whose evaporator side is connected to the low-temperature section of the primary molten salt heat storage module, receiving a portion of the first molten salt heat medium signal as a low-temperature heat source signal, and whose condenser side consumes auxiliary electrical energy to enhance the quality of the low-temperature heat source signal to generate a high-temperature heat energy signal; and a power generation module connected to the gas storage module to receive the released high-pressure air signal, and connected to the high-temperature section of the primary molten salt heat storage module and the condenser side of the high-temperature heat pump module to receive the first molten salt heat medium signal and the high-temperature heat energy signal respectively. The high-pressure air signal is heated by the heat energy signal and expands to perform work, generating an output electrical energy signal.

[0027] Figure 1 As shown, its core architecture consists of five functional units: a compression module, an air storage module, a primary molten salt thermal storage module, a high-temperature heat pump module, and a power generation module. These modules are tightly coupled into a highly efficient and collaborative whole through a series of energy flow signals. The compression module is the energy input starting point and power source of the entire system. Its core function is to receive input electrical energy signals from the power grid or other power sources and convert them into mechanical energy to drive a multi-stage compressor to progressively pressurize the intake atmospheric air. During this compression process, the intermolecular distance of air is forcibly reduced, and its internal energy and temperature rise sharply, thereby simultaneously generating two core output signals: one is the high-pressure air signal compressed to tens or even hundreds of atmospheres, which contains enormous pressure potential energy waiting to be released; the other is the large amount of heat energy inevitably generated during the compression process, namely the first medium-low temperature compression heat signal. This part of the heat signal has an extremely wide temperature range, from the low temperature range close to the ambient temperature to the medium-high temperature range of several hundred degrees Celsius generated by compression. Its total energy is very considerable, and improper handling of it in traditional technology is the main reason for the low system efficiency. The gas storage module is physically and functionally directly connected downstream of the compression module. Its core mission is to safely, reliably, and with low loss receive and temporarily store the high-pressure air signal generated by the compression module. The implementation of this module can be diversified according to geographical conditions and project scale. For example, it can be used to build a large-scale, low-cost gas storage facility using abandoned salt caverns, mined-out mine shafts, or artificial hard rock caverns. Alternatively, it can be stored using a series of high-pressure container arrays on the ground. Regardless of the form, the module must have excellent sealing performance and pressure bearing capacity to ensure that the pressure and total amount of the high-pressure air signal remain stable during the energy storage cycle, without significant leakage or attenuation, thus laying a solid foundation for subsequent stable power generation.

[0028] Furthermore, the primary molten salt thermal storage module is a revolutionary component for the system to achieve heat energy recovery and management. It is tightly thermocoupled with the compression outlets and interstage coolers of the compression module through one or more sets of high-efficiency heat exchangers. Its core function is to receive and store the first medium-low temperature compression heat signal from the compression module in a real-time and efficient manner. To achieve this, the medium circulating in the closed loop of this module is not ordinary heat transfer oil or water, but a low-melting-point molten salt medium with a special formula. After receiving heat signals at different temperature levels, the temperature of this molten salt medium rises and stores the heat energy in the form of sensible heat inside itself, thus forming a primary molten salt thermal medium signal with both temperature and heat. The unique feature of this signal is that its temperature level corresponds to the real-time temperature of the molten salt medium, and the heat value it contains is related to the flow rate and heat capacity of the molten salt. The high-temperature heat pump module is a key innovation in this system, achieving improved energy quality and a significant leap in efficiency. It is an active energy-consuming device, requiring some auxiliary electrical energy to operate, but its benefits far outweigh this consumption. The module thermodynamically follows the reverse Carnot cycle principle and contains four core components: an evaporator, a compressor, a condenser, and a throttling valve. Its evaporator side is coupled to the low-temperature section of the first-stage molten salt heat storage module via a heat exchanger, specifically to extract the portion of the first-stage molten salt heat medium that has already cooled and is difficult for the power generation module to directly and efficiently utilize. The high-temperature heat pump module defines its low-temperature heat source signal as a signal. The core function of the high-temperature heat pump module is that it can consume a small amount of high-grade electrical energy to drive the phase change cycle of its internal working fluid. It successfully transports and raises the low-grade heat energy contained in the low-temperature heat source signal absorbed from the evaporator side to a significantly higher temperature level. Finally, it releases this energy with improved grade as a high-temperature heat energy signal through its condenser side. This process is essentially the conversion of a large amount of low-grade waste heat that is difficult to utilize into a small amount of high-grade heat energy that is highly valuable, thus achieving a qualitative leap in energy.

[0029] In one embodiment of the present invention, the power generation module is the endpoint of energy release and the window for external work in the entire system. It undertakes the important task of converting the stored pressure potential energy and thermal energy back into high-grade electrical energy. Physically, the module's air inlet is connected to the output of the gas storage module, enabling it to receive and retrieve the high-pressure air signal released by the gas storage module as needed. Simultaneously, its thermal connection is more complex, with its preheating system connected to both the high-temperature section of the first-stage molten salt thermal storage module and the condenser-side output of the high-temperature heat pump module, allowing it to receive the first molten salt thermal medium signal from the former and the high-temperature thermal energy signal from the latter in parallel. The power generation module typically includes a multi-stage turboexpander and its associated reheater. The preheater unit operates as follows: First, the cold, high-pressure air signal from the gas storage module is sequentially fed into a high-temperature preheater connected to the condenser side of the high-temperature heat pump module and a low-temperature preheater connected to the high-temperature section of the first-stage molten salt thermal storage module. Utilizing the received high-temperature thermal energy signals of varying grades and the first molten salt thermal medium signal, the high-pressure air is heated step-by-step, raising its temperature to the optimal expansion and work range. Subsequently, this high-temperature, high-pressure air is guided into the turbine expander, driving the blades to rotate at high speed, converting its internal energy (thermal energy) and pressure potential energy into mechanical energy. Finally, this energy is converted into pure output electrical energy signals via a coupled generator and fed into the power grid to complete the entire energy storage-release cycle. Through the precise coordination of these modules, the system cleverly solves two core pain points of traditional technologies: compression heat waste and dependence on fossil fuels.

[0030] like Figure 1As shown, the key circulating medium in the primary molten salt thermal storage module—low-melting-point molten salt—has been specifically defined and optimized. This molten salt medium is not the binary nitrate mixture widely used in conventional solar thermal power plants, whose freezing point is typically around 220 degrees Celsius. This property greatly limits their application in capturing and storing medium- and low-temperature heat below this temperature, because once the medium solidifies, it will completely clog pipes and heat exchangers, leading to system failure. The present invention uses a special low-melting-point molten salt formulation with a significantly reduced freezing point. Its superior thermophysical properties enable it to safely, efficiently, and economically capture and store medium- and low-temperature compression heat signals from the entire wide temperature range of the compression module, without any concern about the catastrophic risk of medium solidification and blockage of flow channels during system start-up and shutdown, low-load operation, or ambient temperature fluctuations. Its chemical composition typically includes a eutectic mixture of various nitrates. The eutectic point is lowered by carefully adjusting the proportions of different components. These nitrates contain at least sodium and potassium ions as cations to form a relatively stable matrix. However, to further lower the eutectic point temperature of the mixture and improve its overall thermal properties, a third or even a fourth cation, such as lithium or calcium ions, is selectively introduced into the formulation. The introduction of lithium ions can significantly reduce the melting point and viscosity of the molten salt, but it also increases the cost of the formulation. The introduction of calcium ions, on the other hand, helps to improve the thermal stability and upper limit of the operating temperature of the molten salt. This carefully designed multi-element eutectic mixture ensures that the molten salt medium maintains good liquid fluidity throughout the entire system's expected operating temperature range, from the low temperature range close to ambient temperature to the highest temperature range generated by compression. At the same time, it has high specific heat capacity and thermal conductivity. The former ensures that it has a huge heat storage density, while the latter ensures that it has extremely high rate and efficiency in the heat absorption and release process in the heat exchanger. This makes the entire heat storage and release process respond quickly and minimize heat loss, providing a cornerstone guarantee for the efficient and stable operation of the system from the material level.

[0031] like Figure 1As shown, the heart of a high-temperature heat pump module—its working medium—poses stringent requirements and provides optimal solutions. This working medium must be able to operate stably and efficiently even at high condensing temperatures. Its core mission is to elevate the low-grade heat contained in the low-temperature thermal energy signal absorbed from the evaporator side to a higher temperature level sufficient to effectively heat high-pressure air during power generation. The magnitude of this elevation directly determines the system efficiency gain. To meet this stringent requirement, one of the preferred options for the working medium is a non-azeotropic mixture. This type of working medium is composed of two or more pure substances with different boiling points mixed in a specific ratio. Its unique characteristic is that it exhibits a temperature glide phenomenon during the isobaric phase change process (whether evaporation or condensation). That is, its phase change process is not completed at a constant temperature, but rather spans a temperature range. This characteristic allows its temperature change curve to better match the temperature change curves of external heat sources and heat sinks. For example, when heating a stream of molten salt or air that gradually heats up from a low temperature to a high temperature, the temperature glide of the non-azeotropic working medium can achieve a near-perfect match, thereby greatly reducing the huge irreversible heat transfer losses that exist in the heat exchange process of traditional fixed-temperature phase change working media and improving the intrinsic efficiency of the heat pump cycle. Another highly promising alternative is to use carbon dioxide, which possesses excellent environmental friendliness and thermodynamic properties, as the working fluid. When operating in a supercritical state, carbon dioxide does not exhibit a clear gas-liquid boundary when heated or cooled, but rather remains in a fluid state, providing a wide range of temperature variations. This allows a single-stage cycle to generate temperature glides approaching 100 degrees Celsius, making it highly suitable for heating needs in various scenarios, especially applications requiring high-temperature heating. Carbon dioxide also boasts advantages such as being non-toxic, non-flammable, inexpensive, and having no ozone-depleting effect. Whether using a non-azeotropic mixture or carbon dioxide, both enable the high-temperature heat pump module to become a powerful energy level enhancer, converting previously unusable waste heat and ambient heat into valuable driving energy. This is one of the core technological means by which this invention achieves efficiency breakthroughs.

[0032] Furthermore, a specialized secondary molten salt thermal storage module was introduced. The addition of this module is a strategic move for the system to achieve refined thermal energy management and targeted utilization. This secondary molten salt thermal storage module functionally complements and has a clear division of labor with the primary molten salt thermal storage module. Its core design mission is specifically to receive, store, and subsequently release high-quality, high-temperature thermal energy signals output from the condenser side of the high-temperature heat pump module. The high-temperature heat pump module, as an energy quality enhancer, outputs energy characterized by high temperature and high availability. While direct use is not impossible, buffering and storing it through a dedicated thermal storage module offers several significant advantages: First, it decouples the operation of the high-temperature heat pump module from the power generation module's electricity demand in terms of time. The high-temperature heat pump can operate continuously when grid electricity prices are low or the system has sufficient reserve power, storing heat for centralized release when power generation is needed, thus enhancing the system's operational flexibility and economy. Second, it provides the power generation module with a stable, reliable, and extremely high-temperature heat source. The internal circulating heat storage medium of this secondary molten salt thermal storage module can be selected based on the overall system design temperature and cost considerations. It can be a traditional molten salt suitable for higher temperature scenarios than the primary molten salt, such as binary nitrate commonly used in concentrated solar power (CSP), because it does not pose a solidification risk under these high-temperature conditions and the technology is mature. Its output end is precisely connected to the high-temperature heater or reheater at the inlet of the power generation module through a high-temperature valve and piping system. Thus, during the energy release and power generation phase, when high-pressure air is released from the gas storage module, it first flows through this high-temperature heater coupled to the secondary molten salt thermal storage module and is... The stored high-grade thermal energy is instantly heated to a very high initial expansion temperature, laying a solid foundation for its full expansion and work in the turbine. Subsequently, this preheated high-pressure air flows sequentially through subsequent heating equipment, such as a low-temperature preheater coupled to the primary molten salt thermal storage module, forming a clear chain of cascaded thermal energy utilization. This configuration ensures that the highest-temperature heat is used for the final and most critical heating stage, while slightly lower-temperature heat is used for preliminary preheating and intermediate heating, strictly adhering to the fundamental thermodynamic principle of "temperature matching and cascaded utilization," minimizing heat loss during the heat exchange process. This minimizes losses, thereby ensuring the ultimate efficiency of energy conversion from a system architecture perspective.

[0033] like Figure 1As shown, the high-temperature heat pump module's range of low-temperature heat source selection expands beyond the waste heat generated within the system, enabling it to actively extract energy from the environment, thus becoming a more powerful energy amplifier. This system achieves this leap forward by integrating a dedicated environmental heat source acquisition module. This module is essentially a low-grade heat collection loop, which can be implemented in various forms. For example, it can be an array of finned tube heat exchangers deployed outdoors, exchanging air with the surrounding environment, using a fan to drive ambient air through the heat exchanger, thereby absorbing the vast but dispersed environmental heat energy contained in the atmosphere; it can also be a buried pipe heat exchanger loop embedded in the soil, utilizing the soil's stable temperature and certain heat capacity, allowing for slow and continuous heat exchange between the circulating fluid and the soil; it can also be a water-to-water heat exchanger placed in nearby water bodies such as ponds, lakes, or cooling water pools. Regardless of its specific form, the core function of this module is to continuously and stably extract ubiquitous low-grade environmental heat energy from the surrounding air, water, or soil, and convert it into a usable hot fluid, generating a stable environmental heat source signal. This environmental heat source signal is then transmitted and provided to the evaporator side of the high-temperature heat pump module as a supplementary or, under certain operating conditions, even primary source of low-temperature heat. The revolutionary significance of this design lies in the fact that it allows the total heat energy input of the system to no longer be limited to the waste heat generated during compression, but to inject a huge amount of free "environmental energy." This is equivalent to increasing the system's energy input, but with almost no additional operating costs (only a small amount of pump power loss), thereby significantly improving its overall energy utilization efficiency. That is, the ratio of the system's output electrical energy to the sum of the input electrical energy and the free environmental energy becomes very high. This allows the system to maintain exceptionally good and stable performance by extracting environmental heat sources even under partial load operation or in specific environments where the low-temperature waste heat available in the primary molten salt circuit is insufficient, greatly enhancing the system's environmental adaptability and reliability.

[0034] Specifically, the structure of the compression module was optimized, adopting a classic and efficient structure of multi-stage compression combined with intercooling, and precisely coupling this structure with molten salt heat storage. The compression module does not consist of a single compressor completing the entire compression process; instead, it comprises multiple compressors connected in series, with a heat exchange device called an intercooler between each two compressor stages. After air is compressed by the first-stage compressor, its pressure and temperature increase simultaneously. Before entering the next stage compressor with even higher pressure, it is first introduced into the first-stage intercooler for cooling. The purpose of cooling is twofold: first, to lower the air temperature, reducing the power consumption required for the next stage of compression (because compressing hotter gases requires more work); and second, to extract the heat of compression at the very first moment. This is precisely the ingenuity of the system. The primary molten salt heat storage module is designed to contain multiple corresponding staged heat exchange units, each precisely connected to the hot side of a specific intercooler. For example, the highest-temperature portion of the compression heat generated by the first-stage intercooler is guided to a high-temperature staged heat exchange unit, where it is recovered by a high-temperature stream of molten salt. The pre-cooled air enters the second-stage compressor for further compression, raising its temperature again, and then enters the second-stage intercooler, where the second-highest heat generated is received by a medium-temperature staged heat exchange unit; and so on. This design makes the system... The system can recover compression heat signals at different temperature levels after each compression stage in a precise manner, according to different levels and temperature ranges. Each heat stream is guided into the corresponding temperature range in the molten salt circuit for storage according to its quality, realizing the precise recovery and management of the full spectrum of heat energy generated during the compression process. This avoids the overall quality degradation caused by mixing heat of different qualities together, i.e., the thermodynamic waste of high-quality heat energy being used in a low-quality manner. It ensures that every joule of heat energy can be released in the subsequent power generation stage as much as possible in a stage that matches its quality, thus providing a guarantee for the high efficiency of the system from the source.

[0035] Specifically, the expansion and power generation process of the power generation module has been optimized, adopting a multi-stage expansion and intermediate reheat structure corresponding to the compression module. This is a key step in maximizing the extraction of air energy and improving power generation efficiency. The power generation module does not simply allow high-pressure air to expand to its full extent in a single turbine; instead, it decomposes it into at least two stages, or even more, high-pressure and low-pressure turbines. The high-pressure air first enters the high-pressure turbine for initial expansion, driving its rotation to generate electricity. During this process, the air pressure and temperature drop significantly. If this cooled and depressurized air were directly allowed into the low-pressure turbine, its power generation capacity would be greatly reduced. Therefore, the system incorporates a crucial heat exchange device called a reheater on the connecting pipe between the high-pressure and low-pressure turbines. This reheater is connected to a molten salt circuit storing thermal energy (which, depending on the design, can be a two-stage high-temperature molten salt circuit or the high-temperature section of a single-stage molten salt circuit). When the partially cooled air discharged from the high-pressure turbine flows through this reheater, it absorbs a new thermal energy signal from the molten salt, thus increasing its temperature. The air is reheated to near its initial intake temperature, and then this revitalized high-temperature, high-pressure air re-enters the low-pressure turbine to continue expanding and doing work. This process is called intermediate reheat, and its thermodynamic benefits are extremely significant. On the one hand, it increases the total power output because the air has a higher enthalpy after reheating for a second work. On the other hand, it greatly improves the overall isentropic efficiency of the turbine by avoiding the various problems caused by the low-pressure turbine operating in the low-temperature wet steam region and reducing irreversible losses from excessive single-stage expansion. This allows every bit of thermal energy stored in the molten salt to be utilized more fully and thoroughly, ultimately converting into more net power output. This successfully completes the last link of the entire energy storage cycle, maximizing the conversion of stored thermal energy signals and pressure potential energy signals of various grades into valuable output electrical energy signals.

[0036] This invention discloses a compressed air energy storage system based on a high-temperature heat pump and a low-melting-point molten salt. By using a low-melting-point molten salt as the heat storage medium, it safely and efficiently captures and stores the full spectrum of thermal energy generated during compression, especially the medium and low temperature range. At the same time, it innovatively integrates a high-temperature heat pump cycle to raise the grade of low-grade thermal energy and ambient thermal energy that are difficult to use directly in the system to a high usable temperature. Finally, during the power generation stage, the stored multi-grade thermal energy is used to perform cascade heating of high-pressure air, thereby significantly improving system efficiency and completely eliminating dependence on fossil fuels.

[0037] Therefore, the compressed air energy storage system based on high-temperature heat pump and low-melting-point molten salt of the present invention can solve the problems of low efficiency and dependence on fossil fuels and geographical conditions of traditional compressed air energy storage.

[0038] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A compressed air energy storage system based on high temperature heat pumps and low melting point molten salts, characterized in that, Comprise: a compression module receiving input electrical energy and generating a high-pressure air signal and a first medium-low temperature compressed heat signal; a gas storage module connected to the compression module, receiving and storing the high-pressure air signal; a primary molten salt thermal storage module connected to the compression module, receiving and storing the first medium-low temperature compressed heat signal, and forming a first molten salt heat medium signal; a high-temperature heat pump module, whose evaporator side is connected to the low-temperature section of the primary molten salt thermal storage module, receiving part of the first molten salt heat medium signal as a low-temperature heat source signal, and its condenser side consumes auxiliary electrical energy and generates a high-temperature heat energy signal after upgrading the low-temperature heat source signal in grade; a power generation module connected to the gas storage module to receive the released high-pressure air signal, and connected to the high-temperature section of the primary molten salt thermal storage module and the condenser side of the high-temperature heat pump module to respectively receive the first molten salt heat medium signal and the high-temperature heat energy signal, which uses the heat energy signal to heat and expand the high-pressure air signal to generate an output electrical energy signal.

2. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt according to claim 1, characterized in that, The molten salt medium circulating in the primary molten salt thermal storage module is a low-melting-point molten salt, whose freezing point is significantly lower than that of conventional molten salts used in solar thermal power generation, so it can safely and efficiently capture and store the medium-low temperature compressed heat signal from the compression module without worrying about medium freezing and blocking the flow passage. Its chemical composition contains a eutectic mixture of multiple nitrate salts, which at least includes sodium ions and potassium ions, and optionally introduces a third kind of cation to make the mixture have a lower eutectic point and more stable thermophysical properties, ensuring that it always remains liquid and has good thermal conductivity within the expected operating temperature range of the entire system.

3. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt according to claim 1, characterized in that, The high-temperature heat pump module uses a special working medium that can operate stably at a higher condensing temperature and raise the low-temperature heat energy signal absorbed from the evaporator side to a higher temperature level. Its preferred non-azeotropic mixed working medium has a temperature glide phenomenon during phase change, which can better match the temperature of external heat source and heat sink to reduce irreversible loss in heat transfer process, or is a carbon dioxide working medium with excellent thermodynamic properties, which can provide a large temperature range in supercritical state to adapt to different heating demands.

4. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt according to claim 1, characterized in that, It also includes a secondary molten salt thermal storage module, which is specially used to receive and store the high-temperature heat energy signal released from the condenser side of the high-temperature heat pump module. The heat storage medium circulating inside can be a molten salt suitable for higher temperature scenarios. The output end of the secondary molten salt thermal storage module is connected to the high-temperature heater of the power generation module, which is responsible for heating the high-pressure air signal to a higher initial expansion temperature during the energy release and power generation stage, forming a cascade heating configuration with the primary molten salt thermal storage module, and realizing temperature matching and staged efficient utilization of heat energy.

5. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt according to claim 1, characterized in that, The evaporator side heat source of the high-temperature heat pump module is not limited to the low-temperature section from the primary molten salt heat storage module. The system also integrates an ambient heat source collection module that can absorb low-grade ambient heat energy from the surrounding air or water or soil and generate a stable ambient heat source signal to provide the evaporator of the high-temperature heat pump module as a supplementary or alternative heat source, thereby increasing the total heat energy input of the system and improving its energy utilization efficiency, so that the system can still maintain excellent performance under partial load or in certain environments.

6. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt as claimed in claim 1, wherein, The compression module adopts a multi-stage compression intermediate cooling structure, and an intermediate cooler is arranged after each stage of compression. The primary molten salt heat storage module includes a plurality of staged heat exchange units corresponding thereto, and each staged heat exchange unit is connected to the hot side of an intermediate cooler, thereby recovering the compression heat signals of different temperature levels generated after each stage of compression in a staged and temperature-segmented manner, achieving fine recovery and management of the full spectrum of heat energy generated during the compression process, and avoiding the improper degradation of high-quality heat energy.

7. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt as claimed in claim 1, wherein, The power generation module adopts a multi-stage expansion intermediate reheating structure, which includes a high-pressure turbine and a low-pressure turbine. After the high-pressure turbine expands and does work, the high-pressure air signal is again guided to flow through a reheater connected to the molten salt circuit for heating. After the temperature of the absorbed and stored heat energy signal is restored, it enters the low-pressure turbine for further expansion and work. This process can significantly increase the total power generation output and improve the overall operating efficiency of the turbine, allowing the stored heat energy in the molten salt to be more fully utilized.

8. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt as claimed in claim 1, wherein, The power generation module adopts a multi-stage expansion intermediate reheating structure, which includes a high-pressure turbine and a low-pressure turbine. After the high-pressure turbine expands and does work, the high-pressure air signal is again guided to flow through a reheater connected to the molten salt circuit for heating. After the temperature of the absorbed and stored heat energy signal is restored, it enters the low-pressure turbine for further expansion and work. This process can significantly increase the total power generation output and improve the overall operating efficiency of the turbine, allowing the stored heat energy in the molten salt to be more fully utilized.

9. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt as claimed in claim 1, wherein, The exhaust gas from the power generation module still carries considerable available waste heat after completing the expansion and work. The system is provided with a waste heat recovery module that captures the waste heat signal carried by the low-temperature exhaust gas from the power generation module through a waste heat exchanger and delivers the recovered waste heat signal to the evaporator side of the high-temperature heat pump module as an additional low-temperature heat source, thereby achieving deep excavation and utilization of the system's full-process energy and further improving the energy conversion efficiency of the entire system.

10. A compressed air energy storage system based on high temperature heat pump and low melting point molten salt as claimed in claim 1, wherein, The operation of the system is coordinated by a central control module that receives dispatch signals from the power grid and temperature, pressure, and flow signals from internal nodes of the system. After calculation by the built-in optimization algorithm, control signals are generated and sent to the frequency drive of the compression module, the expansion valve of the high-temperature heat pump module, and the regulating valves on the pipelines to dynamically adjust the energy storage and release power and the temperature of the heat pump, achieving optimal economic operation and longest equipment life under different operating conditions.

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