Fused salt secondary heat exchange system for compressed air energy storage and control method

Abstract

The invention discloses a fused salt secondary heat exchange system for compressed air energy storage and a control method, and relates to the technical field of compressed air energy storage, the system comprises a fused salt heat storage and exchange subsystem, an intermediate heat exchange subsystem and a compressed air energy storage subsystem, and through two-stage heat transfer among fused salt, an intermediate medium and compressed air, the energy storage efficiency of the compressed air is improved. Fused salt and compressed air are isolated through an intermediate medium, and the leakage risk is reduced; multiplexing of equipment such as a hot molten salt pump and an intermediate medium pump in an energy storage / release stage is realized, and the cost and complexity are optimized; by means of coordination and switching among different valves, the countercurrent flow heat exchange efficiency is improved; in the energy storage stage, fused salt heat storage, intermediate medium heat absorption and compressed air heat release are conducted in a gradient mode according to the specific valve state; in the energy release stage, fused salt heat release, intermediate medium heat transfer and air acting power generation are achieved through the reverse flow. Safety, economy and reliability of the system can be improved, and large-scale application of the compressed air energy storage technology is assisted.

Description

Technical Field

[0001] This invention relates to the field of compressed air energy storage technology, and in particular to a molten salt secondary heat exchange system and control method for compressed air energy storage. Background Technology

[0002] In compressed air energy storage systems, molten salt thermal energy storage technology has attracted attention due to its advantages such as high thermal density and wide operating temperature range. However, directly using molten salt to exchange heat with compressed air has significant problems. For example, when compressed air and molten salt directly exchange heat, the pressure difference across the heat exchanger is large, and the probability of leakage increases exponentially with the increase of the pressure difference. After molten salt leaks, its high temperature and corrosiveness will cause the system to shut down, and the repair time after solidification usually takes several months, which seriously affects reliability. In existing systems, hot molten salt pumps, intermediate medium pumps, etc. are configured independently in the energy storage and energy release stages, which increases costs and complexity and does not take advantage of the equipment's adaptability to operating conditions. Furthermore, direct heat exchange limits the choice of medium for molten salt heat exchangers, making it difficult to flexibly use media such as heat transfer oil and water. Moreover, the pressure on both sides of the heat exchanger is not actively balanced, causing it to be frequently damaged due to alternating stress and high pressure difference. The larger the pressure difference, the shorter the lifespan.

[0003] In recent years, compressed air energy storage molten salt heat exchange solutions have emerged. However, existing compressed air energy storage molten salt heat exchange solutions cannot meet the safety, economy, and long-cycle operation requirements of 300MW units. For example, in a certain 300MW demonstration project, due to the risk of molten salt leakage in direct heat exchange, redundant heat exchangers need to be added, increasing investment costs; the equipment reuse rate is low, increasing operation and maintenance costs by approximately [amount missing]. Therefore, there is an urgent need to innovate heat exchange systems to solve the above problems. Summary of the Invention

[0004] In view of the problems existing in the above or prior art, the present invention is proposed.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a molten salt secondary heat exchange system for compressed air energy storage, comprising a molten salt storage and heat exchange subsystem, wherein the molten salt storage and heat exchange subsystem comprises a hot molten salt tank, a cold molten salt tank disposed on one side of the hot molten salt tank, a molten salt heat exchanger disposed on one side of the cold molten salt tank, and a molten salt circulation pipeline for connecting the hot molten salt tank and the cold molten salt tank and flowing through the molten salt heat exchanger;

[0006] An intermediate heat exchange subsystem includes an intermediate medium pump, a plurality of intermediate medium heat exchangers disposed on one side of the intermediate medium pump, and an intermediate medium circulation pipeline for connecting the intermediate medium pump and the molten salt heat exchanger and flowing through the plurality of intermediate medium heat exchangers.

[0007] A compressed air energy storage subsystem includes an expansion device, a compression device, and a heat exchange device connected to the intermediate heat exchange subsystem, as well as an air storage tank disposed on one side of the heat exchange device.

[0008] The molten salt heat exchange subsystem and the intermediate heat exchange subsystem exchange heat through the molten salt heat exchanger, and the intermediate heat exchange subsystem and the compressed air energy storage subsystem exchange heat through the multiple intermediate medium heat exchangers.

[0009] As a preferred embodiment of the molten salt secondary heat exchange system for compressed air energy storage described in this invention, wherein: a hot molten salt pump and a plurality of first control switches for controlling the flow direction of molten salt are provided on the molten salt circulation pipeline;

[0010] The intermediate medium circulation pipeline is equipped with a pressure stabilizing tank and multiple second control switches for controlling the flow direction of the intermediate medium.

[0011] By switching between the first and second control switches, the flow direction of molten salt and intermediate medium can be guided, and the hot molten salt pump and intermediate medium pump can be reused in the energy storage / release stage, reducing the number of pumps and significantly reducing the system equipment investment cost and floor space. The pressure stabilizing tank can regulate the pressure on both sides of the molten salt heat exchanger, which can effectively reduce heat exchanger seal failure, structural deformation and other failures caused by high pressure difference, extend the service life of the heat exchanger and reduce maintenance costs.

[0012] As a preferred embodiment of the molten salt secondary heat exchange system for compressed air energy storage according to the present invention, the first control switch includes a high-temperature molten salt outlet valve disposed at the outlet of the hot molten salt tank, a low-temperature molten salt outlet valve disposed at the outlet of the cold molten salt tank, a high-temperature molten salt pump outlet valve disposed at the outlet of the molten salt heat exchanger, and a low-temperature molten salt pump outlet valve disposed at the outlet of the molten salt heat exchanger.

[0013] The second control switch includes a hot-side inlet valve and a cold-side inlet valve located at the inlet of the intermediate medium pump, and a high-temperature outlet valve and a low-temperature outlet valve located at the outlet of the intermediate medium pump.

[0014] In a preferred embodiment of the molten salt secondary heat exchange system for compressed air energy storage described in this invention, the first control switch further includes:

[0015] A high-temperature molten salt reflux valve is installed at the reflux point of the hot molten salt tank, and a low-temperature molten salt reflux valve is installed at the reflux point of the cold molten salt tank;

[0016] The second control switch also includes,

[0017] The cold-side reflux valve and the hot-side reflux valve are installed at the reflux point of the molten salt heat exchanger, and the high-temperature reflux valve and the low-temperature reflux valve are installed on the intermediate medium circulation pipeline.

[0018] By coordinating the opening and closing of various valves, the system achieves countercurrent heat exchange, media isolation, and equipment reuse under both energy storage and energy release conditions, ensuring that the intermediate medium can flow along the preset path and enhancing the feasibility and controllability of the system's workflow.

[0019] As a preferred embodiment of the molten salt secondary heat exchange system for compressed air energy storage according to the present invention, the plurality of intermediate medium heat exchangers include a first intermediate medium heat exchanger, a second intermediate medium heat exchanger disposed on one side of the first intermediate medium heat exchanger, a third intermediate medium heat exchanger disposed on one side of the second intermediate medium heat exchanger, and a fourth intermediate medium heat exchanger disposed on one side of the third intermediate medium heat exchanger.

[0020] By setting up multiple intermediate medium heat exchangers, the heat of compressed air can be recovered in stages during the energy storage stage and preheated in stages during the energy release stage. Multi-stage heat exchange can make fuller use of temperature differences, reduce irreversible losses, and improve the overall heat exchange efficiency of the entire secondary heat exchange system.

[0021] As a preferred embodiment of the molten salt secondary heat exchange system for compressed air energy storage according to the present invention, the expansion device includes a first expander and a second expander disposed on one side of the first expander;

[0022] The compression device includes a first compressor and a second compressor disposed on one side of the first compressor;

[0023] The heat exchange device includes a first energy storage heat exchanger, a second energy storage heat exchanger disposed on one side of the first energy storage heat exchanger, a third energy storage heat exchanger disposed on one side of the second energy storage heat exchanger, and a fourth energy storage heat exchanger disposed on one side of the third energy storage heat exchanger.

[0024] As a preferred embodiment of the molten salt secondary heat exchange system for compressed air energy storage according to the present invention, the compressed air energy storage subsystem further includes a heat storage tank disposed on one side of the first energy storage heat exchanger and a cold storage tank disposed on one side of the third energy storage heat exchanger.

[0025] By setting up multiple expanders and compressors, the system can adapt to the power requirements of large-scale units, achieving parallel power output or segmented compression. Multi-stage energy storage heat exchangers enable the graded recovery and utilization of heat / cold energy from compressed air and expander exhaust. Combined with heat storage tanks and cold storage tanks, this forms a complete thermal management system. Heat storage tanks store the high-temperature heat generated during compression, while cold storage tanks store the low-temperature cold energy generated after expansion. This temperature-graded energy storage method allows the system to more effectively utilize high-quality thermal energy to preheat air during the energy release phase, while simultaneously using stored cold energy to cool the air entering the compressor. This maximizes the recovery and utilization of energy throughout the entire system process, further improving cycle efficiency.

[0026] The beneficial effects of this solution are as follows: This invention, through a two-stage indirect heat exchange system between molten salt, an intermediate medium, and compressed air, isolates high-pressure compressed air from direct contact with atmospheric / low-pressure molten salt. This fundamentally solves the risk of system shutdown due to high-pressure differential leakage caused by direct contact between high-pressure compressed air and atmospheric / low-pressure molten salt. By using the intermediate medium as a physical barrier for heat transfer, it effectively isolates two working fluids with vastly different properties. Even if leakage occurs, it is limited to the intermediate heat exchange subsystem, preventing high-temperature, corrosive molten salt from directly entering the compressed air energy storage subsystem. This eliminates prolonged system downtime and expensive maintenance costs caused by molten salt leakage and solidification, significantly improving the operational safety and reliability of a 300MW-class large-scale compressed air energy storage system. This solution improves counter-current heat exchange efficiency. During the energy storage phase, molten salt heat storage, intermediate medium heat absorption, and compressed air heat release occur in stages according to specific valve states. During the energy release phase, the reverse process realizes molten salt heat release, intermediate medium heat transfer, and air power generation. This can facilitate the large-scale application of compressed air energy storage technology.

[0027] Another object of the present invention is to provide a control method for a molten salt secondary heat exchange system for compressed air energy storage, comprising the following steps:

[0028] During the energy storage phase, multiple first control switches of the molten salt heat exchange subsystem are controlled to allow cold molten salt to flow into the molten salt heat exchanger to absorb heat, and multiple second control switches of the intermediate heat exchange subsystem are controlled to allow the intermediate medium to absorb heat from the compressed air and then release heat to the molten salt.

[0029] During the energy release phase, multiple first control switches of the molten salt storage and heat exchange subsystem are controlled to allow hot molten salt to flow into the molten salt heat exchanger and release heat, while multiple second control switches of the intermediate heat exchange subsystem are controlled to allow the intermediate medium to absorb heat from the molten salt and release heat to the compressed air.

[0030] The hot molten salt pump and the intermediate medium pump can be reused by switching between the first control switch and the second control switch;

[0031] In a preferred embodiment of the control method for the molten salt secondary heat exchange system for compressed air energy storage, during the energy storage phase, by opening the low-temperature outlet valve, the high-temperature reflux valve, the cold-side inlet valve, and the cold-side reflux valve, and closing the high-temperature outlet valve, the low-temperature reflux valve, the hot-side inlet valve, and the hot-side reflux valve, it is ensured that the intermediate medium forms countercurrent heat exchange with the compressed air in the plurality of intermediate medium heat exchangers.

[0032] By opening and closing specific valves, efficient countercurrent heat exchange between the intermediate medium and compressed air is ensured in multiple intermediate medium heat exchangers, thereby improving the heat exchange efficiency during the energy storage stage.

[0033] In a preferred embodiment of the control method for the molten salt secondary heat exchange system for compressed air energy storage, during the energy release phase, by opening the high-temperature outlet valve, the low-temperature reflux valve, the hot-side inlet valve, and the hot-side reflux valve, and closing the low-temperature outlet valve, the high-temperature reflux valve, the cold-side inlet valve, and the cold-side reflux valve, it is ensured that the intermediate medium forms countercurrent heat exchange with the air entering the expansion device within the plurality of intermediate medium heat exchangers.

[0034] By opening and closing specific valves, efficient countercurrent heat exchange is ensured between the intermediate medium and the air entering the expansion device within the multiple intermediate medium heat exchangers, thereby improving the heat exchange efficiency during the energy release phase.

[0035] The beneficial effects of this plan are:

[0036] This invention achieves the switching of the flow direction of molten salt and intermediate medium by controlling the first control switch and the second control switch respectively in the energy storage and energy release stages, ensuring the correctness of the heat transfer path. Through the coordinated control between various valves, the hot molten salt pump and the intermediate medium pump can be reused in two working conditions. This not only saves the high cost of configuring pumps separately for different working conditions, but also simplifies the complex pipeline, reduces the footprint and maintenance complexity, and greatly improves the economy and compactness of the system. Attached Figure Description

[0037] 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 accompanying 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.

[0038] Figure 1 This is a schematic diagram of the overall structure of a molten salt secondary heat exchange system for compressed air energy storage.

[0039] Among them, the red line represents the molten salt heat storage and exchange subsystem process; the orange line represents the intermediate heat exchange subsystem process; the blue line represents the compressed air energy storage subsystem process; the green line represents the cold storage medium system process; and the yellow line represents the heat storage medium system process.

[0040] 101. Hot molten salt tank; 102. Cold molten salt tank; 103. Hot molten salt pump; 104. Molten salt heat exchanger; 105. High-temperature molten salt outlet valve; 106. Low-temperature molten salt outlet valve; 107. High-temperature molten salt pump outlet valve; 108. Low-temperature molten salt pump outlet valve; 109. High-temperature molten salt reflux valve; 110. Low-temperature molten salt reflux valve; 201. Intermediate medium pump; 202. First intermediate medium heat exchanger; 203. Second intermediate medium heat exchanger; 204. Third intermediate medium heat exchanger; 205. Fourth intermediate medium heat exchanger; 210. High-temperature outlet valve; 211. Low-temperature outlet valve ; 212, Low-temperature reflux valve; 213, High-temperature reflux valve; 214, Pressure stabilizing tank; 220, Hot-side inlet valve; 221, Cold-side inlet valve; 222, Cold-side reflux valve; 223, Hot-side reflux valve; 310, Generator; 311, First expander; 312, Second expander; 313, Gas storage tank; 314, First compressor; 315, Second compressor; 316, Motor; 320, Heat storage tank; 321, Cold storage tank; 322, First energy storage heat exchanger; 323, Second energy storage heat exchanger; 324, Third energy storage heat exchanger; 325, Fourth energy storage heat exchanger. Detailed Implementation

[0041] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0042] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0043] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0044] Example 1

[0045] Reference Figure 1 This is the first embodiment of the present invention, which provides a molten salt secondary heat exchange system for compressed air energy storage, comprising:

[0046] The molten salt heat storage and exchange subsystem is used to store and release thermal energy. The molten salt heat storage and exchange subsystem includes a hot molten salt tank 101, a cold molten salt tank 102 disposed on one side of the hot molten salt tank 101, a molten salt heat exchanger 104 disposed on one side of the cold molten salt tank 102, and a molten salt circulation pipeline for connecting the hot molten salt tank 101 and the cold molten salt tank 102 and flowing through the molten salt heat exchanger 104.

[0047] The intermediate heat exchange subsystem, serving as an intermediate medium for heat transfer, includes an intermediate medium pump 201, multiple intermediate medium heat exchangers located on one side of the intermediate medium pump 201, and intermediate medium circulation pipelines connecting the intermediate medium pump 201 and the molten salt heat exchanger 104 and flowing through the multiple intermediate medium heat exchangers. The molten salt heat exchanger 104 can be made of heat transfer oil (operating temperature 200-350℃) or water (temperature must be controlled <100℃, flow rate adjusted to satisfy Q = m³ / s). water ·c p-water Liquids such as ΔT have broadened the application scenarios.

[0048] It should be noted that, in this embodiment, the molten salt heat exchanger 104 is compatible with liquid heat exchange media such as heat transfer oil and water, and the heat exchange process satisfies the heat exchange calculation formula Q=m·c p • ΔT, in other embodiments, can be adjusted according to the characteristics of different media.

[0049] The compressed air energy storage subsystem includes an expansion device, a compression device, and a heat exchange device connected to the intermediate heat exchange subsystem, as well as an air storage tank 313 located on one side of the heat exchange device.

[0050] The molten salt heat exchange subsystem and the intermediate heat exchange subsystem exchange heat through the molten salt heat exchanger 104. The intermediate heat exchange subsystem and the compressed air energy storage subsystem exchange heat through multiple intermediate medium heat exchangers. Heat is first exchanged between the compressed air and the intermediate medium, and then exchanged a second time between the intermediate medium and the molten salt, thus realizing two-stage heat transfer.

[0051] This invention transforms the direct heat exchange between molten salt and compressed air into a secondary heat exchange involving molten salt, intermediate medium, and compressed air by using an intermediate medium. This significantly reduces the risk of molten salt leaking directly into the compressed air system. Even in extreme cases where a small amount of molten salt leaks, the intermediate medium can initially intercept and buffer the leaking molten salt, especially preventing the molten salt from entering the expander generator. This allows for more time for maintenance and repair, and avoids molten salt directly entering the main compressed air process, which could cause large-scale equipment damage and prolonged shutdown.

[0052] Example 2

[0053] Reference Figure 1 This is the second embodiment of the present invention, which differs from the first embodiment in that...

[0054] The molten salt circulation pipeline is equipped with a hot molten salt pump 103 and multiple first control switches for controlling the flow direction of molten salt;

[0055] A pressure stabilizing tank 214 and multiple second control switches for controlling the flow direction of the intermediate medium are installed on the intermediate medium circulation pipeline. Using the pressure stabilizing tank 214 and the multiple second control switches, the pressure difference ΔP across the molten salt heat exchanger is maintained at ≤0.1MPa, satisfying the pressure balance formula where the allowable pressure on the molten salt side is P. 熔盐侧 =P 介质侧 +ΔP 允许 (where ΔP is allowed) 允许 To minimize the allowable pressure difference, reduce the possibility of damage to the molten salt heat exchanger; thus extending the equipment lifespan from L... original Extended operating time reduces the probability of heat exchanger damage. Compared to traditional structures without pressure balancing measures, the probability of heat exchanger seal failure and structural deformation due to excessive pressure differential is significantly reduced, resulting in significantly improved equipment operational stability and ensuring long-term continuous operation of 300MW-class compressed air energy storage units.

[0056] It should be noted that the molten salt pump 103 and the intermediate medium pump 201 are reused in both the energy storage and energy release stages. By switching between the first and second control switches to change the flow direction of the molten salt and intermediate medium, the function of the equipment is converted, allowing the molten salt pump 103 and the intermediate medium pump 201 to be reused in both stages. This reduces the number of additional pumps required in traditional solutions. Taking a 300MW unit as an example, equipment procurement costs are reduced by approximately 15%-20%. Simultaneously, due to the reduced number of devices, the system footprint is reduced, and the costs of supporting infrastructure construction, installation, and commissioning are also reduced. During the operation and maintenance phase, equipment reuse allows for more focused maintenance, reducing the workload by approximately 25% and consequently lowering maintenance costs, resulting in significant long-term economic benefits. The reuse control logic of the intermediate medium pump 201 and the molten salt pump 103 can be implemented using a programmable logic controller (PLC) or a distributed control system (DCS) to achieve automatic valve switching and pump start / stop control, adjusting the system flow based on the operating instructions from the energy storage and energy release stages.

[0057] Example 3

[0058] Reference Figure 1 This is the third embodiment of the present invention, which differs from the first two embodiments in that...

[0059] The first control switch includes a high-temperature molten salt outlet valve 105 located at the outlet of the hot molten salt tank 101, a low-temperature molten salt outlet valve 106 located at the outlet of the cold molten salt tank 102, a high-temperature molten salt pump outlet valve 107 located at the outlet of the molten salt heat exchanger 104, and a low-temperature molten salt pump outlet valve 108 located at the outlet of the molten salt heat exchanger 104.

[0060] The second control switch includes a hot-side inlet valve 220 and a cold-side inlet valve 221 located at the inlet of the intermediate medium pump 201, and a high-temperature outlet valve 210 and a low-temperature outlet valve 211 located at the outlet of the intermediate medium pump 201.

[0061] Furthermore, the first control switch also includes,

[0062] A high-temperature molten salt reflux valve 109 is installed at the reflux point of the hot molten salt tank 101, and a low-temperature molten salt reflux valve 110 is installed at the reflux point of the cold molten salt tank 102;

[0063] The second control switch also includes,

[0064] The cold-side reflux valve 222 and the hot-side reflux valve 223 are installed at the reflux point of the molten salt heat exchanger 104, and the low-temperature reflux valve 212 and the high-temperature reflux valve 213 are installed on the intermediate medium circulation pipeline.

[0065] By switching the valve states of the intermediate medium pump hot-side inlet valve 220, intermediate medium pump cold-side inlet valve 221, intermediate medium hot-side return valve 223, and intermediate medium cold-side return valve 222, the countercurrent heat exchange process adjustment in the energy storage and release stages is achieved. During the energy storage stage, the cold-side inlet valve 221 and cold-side return valve 222 are opened to ensure the intermediate medium's cold-side inlet and cold-side return flow; during the energy release stage, the hot-side inlet valve 220 and hot-side return valve 223 are opened to ensure the intermediate medium's hot-side inlet and hot-side return flow, meeting the temperature gradient matching requirements of countercurrent heat exchange and improving heat exchange efficiency. This increases the logarithmic mean temperature difference between the intermediate medium and compressed air by approximately 10% during the energy storage stage and by approximately 12% during the energy release stage.

[0066] The optimized counter-current heat exchange process achieved by switching different valves allows for precise control of the heat exchange process based on the energy demand and temperature characteristics at different stages of energy storage and release. Whether it's large-scale energy storage during off-peak hours or rapid energy release for power generation during peak hours, the system can efficiently match energy storage and release needs through valve status adjustments and process switching. This enhances the ability of compressed air energy storage systems to participate in ancillary services such as peak shaving, frequency regulation, and backup power in the power system, and better integrates them into the modern smart grid system.

[0067] Furthermore, the plurality of intermediate medium heat exchangers include a first intermediate medium heat exchanger 202, a second intermediate medium heat exchanger 203 disposed on one side of the first intermediate medium heat exchanger 202, a third intermediate medium heat exchanger 204 disposed on one side of the second intermediate medium heat exchanger 203, and a fourth intermediate medium heat exchanger 205 disposed on one side of the third intermediate medium heat exchanger 204.

[0068] Furthermore, the expansion device includes a first expander 311 and a second expander 312 disposed on one side of the first expander 311;

[0069] The compression device includes a first compressor 314 and a second compressor 315 disposed on one side of the first compressor 314;

[0070] The heat exchange equipment includes a first energy storage heat exchanger 322, a second energy storage heat exchanger 323 disposed on one side of the first energy storage heat exchanger 322, a third energy storage heat exchanger 324 disposed on one side of the second energy storage heat exchanger 323, and a fourth energy storage heat exchanger 325 disposed on one side of the third energy storage heat exchanger 324.

[0071] The system employs a multi-stage expander, multi-stage compressor, and multi-stage heat exchanger configuration, which can meet the energy processing requirements of large-scale units of 300MW. The multi-stage structure can more efficiently complete the air compression and expansion process, improve the operating efficiency of the main equipment, and enable the system to smoothly cope with large-scale energy storage and release, meeting the application requirements of grid-level energy storage.

[0072] Furthermore, the compressed air energy storage subsystem also includes a heat storage tank 320 located on one side of the first energy storage heat exchanger 322, which is used to store the high-temperature heat generated during the compression process; and a cold storage tank 321 located on one side of the third energy storage heat exchanger 324, which is used to store the low-temperature cold energy generated after expansion. This temperature-level energy storage method enables the system to more effectively utilize high-quality thermal energy to preheat the air during the energy release phase, while using the stored cold energy to cool the air entering the compressor, thereby maximizing the recovery and utilization of energy in the system process, further improving cycle efficiency and reducing dependence on external energy.

[0073] The system of this invention is applicable to compressed air energy storage units of 10MW and above. Through parameter optimization and process control, it meets the energy storage and release requirements of large-scale energy storage systems and ensures the safe, efficient and long-term operation of the units.

[0074] Example 4: This example is a case study of a 300MW compressed air energy storage unit.

[0075] The specific system parameters are as follows:

[0076] Molten salt parameters: A sodium nitrate-potassium nitrate molten salt with a mass ratio of 60:40 was selected, with a specific heat capacity at constant pressure of ℃. cp-salt = 1.5 kJ / (kg·℃), design mass flow rate m salt =1200 kg / s, cold molten salt temperature (°C / T) during energy storage stage cold-salt =250℃, molten salt temperature (℃T) hot-salt =400℃.

[0077] Intermediate medium parameters: L-QB300 heat transfer oil was selected, with a specific heat capacity at constant pressure (°C). p-oil = 2.0 kJ / (kg·℃), mass flow rate m oil =1000 kg / s, inlet temperature (°C / T) during energy storage stage oil-in =200℃, outlet temperature ℃T oil-out =300℃.

[0078] Compressed air parameters: mass flow rate (m³) air =800kg / s, inlet temperature of the energy storage stage, 205℃T before entering the fourth intermediate medium heat exchanger air-in205 =450℃, inlet temperature of the expansion equipment during the energy release stage (℃T) air-in-turbine =380℃, expansion equipment efficiency η=0.85, air constant pressure specific heat capacity ℃c p-air = 1.0 kJ / (kg·℃).

[0079] Reference Figure 1 This is the fourth embodiment of the present invention, which provides a control method for a molten salt secondary heat exchange system for compressed air energy storage, including the following steps:

[0080] During the energy storage stage, multiple first control switches of the molten salt heat exchange subsystem are controlled to allow cold molten salt to flow into the molten salt heat exchanger 104 to absorb heat, and multiple second control switches of the intermediate heat exchange subsystem are controlled to allow the intermediate medium to absorb heat from the compressed air and then release heat to the molten salt.

[0081] The operational verification during the energy storage phase is as follows:

[0082] Molten salt thermal storage calculation: Q salt-store =1200×1.5×(400-250)=2.7×10 5 kW;

[0083] Calculation of heat absorption by intermediate medium: Q oil-absorb =1000×2.0×(300-200)=2.0×10 5 kW, considering the system heat loss rate δ = 5%, the molten salt flow rate or temperature needs to be adjusted to make Q salt-store =Q oil-absorb / (1-δ), ensuring energy matching;

[0084] Compressed air heat release calculation: Q air-release =800×1.0×(450-T) air-out25 ), let Q air-release =Q oil-absorb Solving for ℃T air-out25 =450-(2.0×10 5 (800 × 1.0) = 200℃, verifying the law of conservation of energy;

[0085] Valve configuration effect: Opening the cold side inlet valve 221 and the cold side return valve 222, and closing the hot side inlet valve 220 and the hot side return valve 223, ensures the cold side circulation of the intermediate medium. Simulation shows that the logarithmic mean temperature difference between the intermediate medium and the compressed air is increased by 10%, and the heat exchange efficiency is increased by 8%.

[0086] During the energy release phase, multiple first control switches of the molten salt storage and heat exchange subsystem are controlled to allow hot molten salt to flow into the molten salt heat exchanger 104 to release heat, and multiple second control switches of the intermediate heat exchange subsystem are controlled to allow the intermediate medium to absorb heat from the molten salt and release heat to the compressed air.

[0087] The energy release phase operation verification is as follows:

[0088] Calculation of exothermic reaction of molten salt: Q salt-release =2.7×10 5 kW (matching the energy storage stage);

[0089] Calculation of heat release in intermediate medium: Q oil-release =1000×2.0×(300-200)=2.0×10 5 kW, considering heat loss, parameters need to be adjusted to ensure energy transfer;

[0090] Expander work calculation: Air enthalpy drop Δh = c p-air ×(T air-in-turbine -T0)=1.0×(380-20)=360kJ / kg (T0=20℃ is the ambient temperature), power P=0.85×800×360=2.448×10 5 kW, suitable for the power requirements of 300MW units, with multiple expanders connected in parallel;

[0091] Valve configuration effect: Opening the hot-side inlet valve 220 and the hot-side return valve 223, and closing the cold-side inlet valve 221 and the cold-side return valve 222, ensures the hot-side circulation of the intermediate medium. Simulation shows that the logarithmic mean temperature difference between the intermediate medium and air is increased by 12%, and the heat exchange efficiency is increased by 10%.

[0092] The hot molten salt pump 103 and the intermediate medium pump 201 can be reused by switching between the first control switch and the second control switch;

[0093] Furthermore, during the energy storage phase, by opening the low-temperature outlet valve 211, the high-temperature reflux valve 213, the cold-side inlet valve 221, and the cold-side reflux valve 222, and closing the high-temperature outlet valve 210, the low-temperature reflux valve 212, the hot-side inlet valve 220, and the hot-side reflux valve 223, it is ensured that the intermediate medium forms countercurrent heat exchange with the compressed air in multiple intermediate medium heat exchangers.

[0094] The specific operation method in the energy storage stage is as follows: Motor 316 drives the first compressor 314 and the second compressor 315 to do work; Motor 316, first compressor 314 and second compressor 315 are coaxially connected.

[0095] Molten salt storage and heat exchange subsystem process: Open cryogenic molten salt outlet valve 106, cryogenic molten salt pump outlet valve 108, and high-temperature molten salt reflux valve 109; close high-temperature molten salt outlet valve 105, high-temperature molten salt pump outlet valve 107, and cryogenic molten salt reflux valve 110; start hot molten salt pump 103 to allow molten salt (temperature T) in cold molten salt tank 102 to flow. cold-salt After passing through the aforementioned valves and pumps, the molten salt flows into the molten salt heat exchanger 104, absorbs heat, and becomes high-temperature molten salt (temperature T). hot-salt ) Store in hot molten salt tank 101, molten salt heat exchange Q salt-store =m salt ·c p-salt ·(T hot-salt -T cold-salt (where m) salt c is the molten salt mass flow rate. p-salt T is the specific heat capacity of molten salt at constant pressure. hot-salt T is the temperature of the molten salt. cold-salt (This refers to the temperature of the cold molten salt).

[0096] Intermediate heat exchange subsystem flow: Open cryogenic outlet valve 211, high-temperature reflux valve 213, intermediate medium pump cold-side inlet valve 221, and intermediate medium cold-side reflux valve 222; close high-temperature outlet valve 210, cryogenic reflux valve 212, intermediate medium pump hot-side inlet valve 220, and intermediate medium hot-side reflux valve 223; start intermediate medium pump 201, causing compressed air to flow through the third intermediate medium heat exchanger 204 and the fourth intermediate medium heat exchanger 205 to transfer heat to the intermediate medium (such as heat transfer oil, constant pressure specific heat capacity c). p-oil The intermediate medium carries heat into the molten salt heat exchanger 104 and transfers heat to the molten salt. The intermediate medium absorbs heat Q. oil-absorb =m oil ·c p-oil ·(T oil-out -T oil-in (where m) oil c represents the mass flow rate of the intermediate medium. p-oil T is the isobaric specific heat capacity of the intermediate medium. oil-in T represents the inlet temperature of the intermediate medium. oil-out (where Q is the outlet temperature of the intermediate medium), and Q oil-absorb =Q salt-store (Ignoring heat loss);

[0097] Compressed air energy storage subsystem process: Compressed air, cooled by the fourth intermediate medium heat exchanger 205, enters the fourth energy storage heat exchanger 325, where it reacts with the working fluid (such as heat transfer oil, with a constant pressure specific heat capacity c) in the heat storage tank 320.p-heat Heat exchange occurs, with heat stored in a heat storage tank and heat Q released from the air. air-release =m air ·c p-air ·(T air-in205 -T air-out25 (where m) air For air mass flow rate, c p-air T is the specific heat capacity of air at constant pressure. air-in205 T is the temperature of air before it enters the fourth intermediate medium heat exchanger 205. air-out25 (The temperature of the air after it flows out of the fourth energy storage heat exchanger 325).

[0098] Furthermore, during the energy release phase, by opening the high-temperature outlet valve 210, the low-temperature reflux valve 212, the hot-side inlet valve 220, and the hot-side reflux valve 223, and closing the low-temperature outlet valve 211, the high-temperature reflux valve 213, the cold-side inlet valve 221, and the cold-side reflux valve 222, it is ensured that the intermediate medium forms countercurrent heat exchange with the air entering the expansion equipment in multiple intermediate medium heat exchangers.

[0099] The specific operational methods during the energy storage phase are as follows:

[0100] Molten salt storage and heat exchange subsystem process: Open high-temperature molten salt outlet valve 105, high-temperature molten salt pump outlet valve 107, and low-temperature molten salt reflux valve 110; close low-temperature molten salt outlet valve 106, low-temperature molten salt pump outlet valve 108, and high-temperature molten salt reflux valve 109; start hot molten salt pump 103, causing high-temperature molten salt in hot molten salt tank 101 to flow into molten salt heat exchanger 104, release heat, and then become cold molten salt stored in cold molten salt tank 102. The heat released by the molten salt is Q. salt-release =m salt ·c p-salt ·(T hot-salt -T cold- s salt );

[0101] Intermediate heat exchange subsystem flow: Open high-temperature outlet valve 210, low-temperature reflux valve 212, intermediate medium pump hot-side inlet valve 220, and intermediate medium hot-side reflux valve 223; close low-temperature outlet valve 211, high-temperature reflux valve 213, intermediate medium pump cold-side inlet valve 221, and intermediate medium cold-side reflux valve 222; start intermediate medium pump 201, so that the intermediate medium absorbs heat in molten salt heat exchanger 104, and then flows through the first intermediate medium heat exchanger 202 and the second intermediate medium heat exchanger 203 to preheat the inlet air of the first expander 311 and the second expander 312. The intermediate medium releases heat Q. oil-release =m oil ·c p-oil ·(T oil-out -T oil-in ), and Q oil-release =Q salt-release(Ignoring heat loss);

[0102] Compressed air energy storage subsystem process: Air preheated by the first intermediate medium heat exchanger 202 and the second intermediate medium heat exchanger 203 (temperature T) air-in-turbine The power generated by the expansion tubes 311 and 312 is P = η·m. air •Δh (where η is the expander efficiency and Δh is the air enthalpy drop); the exhaust gas from the first expander 311 and the second expander 312 enters the first energy storage heat exchanger 322 and the second energy storage heat exchanger 323, and the heat is stored in the cold storage tank 321. The exhaust gas releases heat Q. exhaust-release =m air ·c p-air ·(T exhaust-in -T exhaust-out (where T) exhaust-in T is the temperature of the exhaust gas before it enters the heat exchanger. exhaust-out (The temperature of the exhaust gas after exiting the heat exchanger). Generator 310, first expander 311 and second expander 312 are coaxially connected.

[0103] This invention uses an intermediate medium to isolate the molten salt, avoiding the adverse effects of impurities and moisture in the compressed air on the molten salt-side equipment. It also reduces the risk of corrosion of the compressed air-side equipment by the molten salt, thereby improving the operational reliability of the entire secondary heat exchange system and the associated compressed air energy storage main equipment, reducing the number of downtime due to failure, ensuring that the unit can stably output power, and meeting the high reliability requirements of application scenarios such as grid peak shaving and large-scale industrial and commercial energy storage.

[0104] Molten salt heat exchanger 104 is compatible with various liquid media such as heat transfer oil and water. When water is used as the intermediate medium, by controlling the flow rate and temperature, such as controlling the molten salt outlet temperature to be lower than the boiling point of water, the heat exchange medium requirements of different application scenarios can be met. In some projects where water resource utilization is more convenient or where the cost of the medium is strictly controlled, it can be flexibly switched to water as the medium, which expands the adaptability of the technical solution under different regions and project conditions and enhances the breadth of technology promotion and application.

[0105] By using a pressure stabilizing tank 214 to balance the pressure and coordinating the control of various valves in the first and second control switches, the damage to the molten salt heat exchanger 104 caused by alternating stress and high pressure difference is mitigated. Through fatigue life simulation analysis, the life of the molten salt heat exchanger 104 can be extended, significantly reducing the cost of equipment replacement and the impact of system downtime.

[0106] Importantly, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A molten salt secondary heat exchange system for compressed air energy storage, characterized in that: include, A molten salt storage and heat exchange subsystem includes a hot molten salt tank (101), a cold molten salt tank (102) disposed on one side of the hot molten salt tank (101), a molten salt heat exchanger (104) disposed on one side of the cold molten salt tank (102), and a molten salt circulation pipeline for connecting the hot molten salt tank (101) and the cold molten salt tank (102) and flowing through the molten salt heat exchanger (104); An intermediate heat exchange subsystem includes an intermediate medium pump (201), a plurality of intermediate medium heat exchangers disposed on one side of the intermediate medium pump (201), and an intermediate medium circulation pipeline for connecting the intermediate medium pump (201) and the molten salt heat exchanger (104) and flowing through the plurality of intermediate medium heat exchangers. The compressed air energy storage subsystem includes an expansion device, a compression device, and a heat exchange device connected to the intermediate heat exchange subsystem, as well as an air storage tank (313) disposed on one side of the heat exchange device. The molten salt heat exchange subsystem and the intermediate heat exchange subsystem exchange heat through the molten salt heat exchanger (104), and the intermediate heat exchange subsystem and the compressed air energy storage subsystem exchange heat through the multiple intermediate medium heat exchangers.

2. The molten salt secondary heat exchange system for compressed air energy storage as described in claim 1, characterized in that: The molten salt circulation pipeline is equipped with a hot molten salt pump (103) and multiple first control switches for controlling the flow direction of molten salt; The intermediate medium circulation pipeline is equipped with a pressure stabilizing tank (214) and multiple second control switches for controlling the flow direction of the intermediate medium.

3. The molten salt secondary heat exchange system for compressed air energy storage as described in claim 2, characterized in that: The first control switch includes a high-temperature molten salt outlet valve (105) located at the outlet of the hot molten salt tank (101), a low-temperature molten salt outlet valve (106) located at the outlet of the cold molten salt tank (102), a high-temperature molten salt pump outlet valve (107) located at the outlet of the molten salt heat exchanger (104), and a low-temperature molten salt pump outlet valve (108). The second control switch includes a hot-side inlet valve (220) and a cold-side inlet valve (221) disposed at the inlet of the intermediate medium pump (201), and a high-temperature outlet valve (210) and a low-temperature outlet valve (211) disposed at the outlet of the intermediate medium pump (201).

4. The molten salt secondary heat exchange system for compressed air energy storage as described in claim 3, characterized in that: The first control switch also includes, A high-temperature molten salt reflux valve (109) is provided at the reflux point of the hot molten salt tank (101), and a low-temperature molten salt reflux valve (110) is provided at the reflux point of the cold molten salt tank (102); The second control switch also includes, The cold-side reflux valve (222) and hot-side reflux valve (223) are installed at the reflux point of the molten salt heat exchanger (104), and the low-temperature reflux valve (212) and high-temperature reflux valve (213) are installed on the intermediate medium circulation pipeline.

5. A molten salt secondary heat exchange system for compressed air energy storage as described in claim 1, characterized in that: The plurality of intermediate medium heat exchangers include a first intermediate medium heat exchanger (202), a second intermediate medium heat exchanger (203) disposed on one side of the first intermediate medium heat exchanger (202), a third intermediate medium heat exchanger (204) disposed on one side of the second intermediate medium heat exchanger (203), and a fourth intermediate medium heat exchanger (205) disposed on one side of the third intermediate medium heat exchanger (204).

6. The molten salt secondary heat exchange system for compressed air energy storage as described in claim 1, characterized in that: The expansion device includes a first expander (311) and a second expander (312) disposed on one side of the first expander (311); The compression device includes a first compressor (314) and a second compressor (315) disposed on one side of the first compressor (314); The heat exchange device includes a first energy storage heat exchanger (322), a second energy storage heat exchanger (323) disposed on one side of the first energy storage heat exchanger (322), a third energy storage heat exchanger (324) disposed on one side of the second energy storage heat exchanger (323), and a fourth energy storage heat exchanger (325) disposed on one side of the third energy storage heat exchanger (324).

7. A molten salt secondary heat exchange system for compressed air energy storage as described in claim 6, characterized in that: The compressed air energy storage subsystem also includes a heat storage tank (320) disposed on one side of the first energy storage heat exchanger (322) and a cold storage tank (321) disposed on one side of the third energy storage heat exchanger (324).

8. A control method for a molten salt secondary heat exchange system for compressed air energy storage, characterized in that, Includes the following steps: During the energy storage phase, multiple first control switches of the molten salt heat exchange subsystem are controlled to allow cold molten salt to flow into the molten salt heat exchanger (104) to absorb heat, and multiple second control switches of the intermediate heat exchange subsystem are controlled to allow the intermediate medium to absorb heat from the compressed air and then release heat to the molten salt. During the energy release phase, multiple first control switches of the molten salt storage and heat exchange subsystem are controlled to allow hot molten salt to flow into the molten salt heat exchanger (104) to release heat, and multiple second control switches of the intermediate heat exchange subsystem are controlled to allow the intermediate medium to absorb heat from the molten salt and release heat to the compressed air. The hot molten salt pump (103) and the intermediate medium pump (201) can be reused by switching between the first control switch and the second control switch.

9. The control method for a molten salt secondary heat exchange system for compressed air energy storage as described in claim 8, characterized in that: During the energy storage phase, by opening the low-temperature outlet valve (211), the high-temperature reflux valve (213), the cold-side inlet valve (221), and the cold-side reflux valve (222), and closing the high-temperature outlet valve (210), the low-temperature reflux valve (212), the hot-side inlet valve (220), and the hot-side reflux valve (223), it is ensured that the intermediate medium forms countercurrent heat exchange with the compressed air in the plurality of intermediate medium heat exchangers.

10. The control method for a molten salt secondary heat exchange system for compressed air energy storage as described in claim 8, characterized in that: During the energy release phase, by opening the high-temperature outlet valve (210), the low-temperature reflux valve (212), the hot-side inlet valve (220), and the hot-side reflux valve (223), and closing the low-temperature outlet valve (211), the high-temperature reflux valve (213), the cold-side inlet valve (221), and the cold-side reflux valve (222), it is ensured that the intermediate medium forms countercurrent heat exchange with the air entering the expansion device in the plurality of intermediate medium heat exchangers.

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