Pure compressed air energy storage graded expansion gas-liquid coupling stable output device and method

Abstract

The application relates to a pure compressed air energy storage graded expansion gas-liquid coupling stable output device and method. The device comprises a high-pressure gas storage unit, a gas-liquid working unit, an intermediate pressure buffer unit, a high-pressure liquid power generation unit, a low-pressure expansion power generation unit and a control unit. The high-pressure gas storage unit and the gas-liquid working unit are independently arranged and are connected in time through a high-pressure inlet valve only in the working stage, and the high-pressure gas storage unit is free of liquid throughout the process. The control unit is configured to: in the working stage, after the high-pressure gas enters the working tank through the high-pressure inlet valve, the high-pressure inlet valve is closed before the expansion end point according to the real-time state parameters in the tank to form a closed expansion cavity, so that the gas continues to expand in the closed expansion cavity, pushes the liquid out through a liquid discharge pipeline and drives the liquid power prime mover to work. The application can realize continuous and stable power output of the system and significantly improve the energy utilization rate without throttling, changing the gas storage condition and relying on large-capacity power compensation.

Description

Technical Field

[0001] This application relates to the field of compressed air energy storage technology, and in particular to a pure compressed air energy storage staged expansion gas-liquid coupling stable output device and method. Background Technology

[0002] Compressed air energy storage is currently a core technology for large-scale, long-duration physical energy storage. It boasts significant advantages such as long service life, high operational safety, and compatibility with renewable energy consumption, making it a crucial support for building a new power system and achieving dual-carbon goals. Currently, most operational traditional compressed air energy storage projects employ a technology that uses high-pressure gas to directly drive an expander to generate electricity.

[0003] However, under constant-volume gas storage conditions, the gas pressure continuously decreases from the rated value to a lower level during energy release, forcing the expander to operate over an extremely wide range of conditions. This leads to the following prominent technical problems: Firstly, to cover the surge uncertainty under wide operating conditions, the expander back pressure design is forced to be increased, resulting in a significant decrease in the expansion ratio and the waste of a large amount of usable energy in the low-pressure section. Secondly, the drastic fluctuations in inlet pressure and flow rate force the system to be equipped with large-capacity power voltage stabilizers to maintain grid connection stability, significantly increasing system costs. Some existing solutions introduce gas-liquid coupling paths, but they generally adopt a gas-liquid co-storage structure, where the effective gas storage volume is continuously occupied by the liquid medium. Furthermore, at the end of the expansion of the work tank, the residual gas pressure is much higher than the return liquid source pressure, leading to difficulties in liquid return, gas release losses, or additional pumping energy consumption. The usable pressure energy of the residual gas is also not effectively recovered.

[0004] The aforementioned problems, such as the contradiction between constant volume and variable pressure, the cost of wide operating conditions, the loss of gas-liquid co-storage volume, and the waste of residual energy, are superimposed on each other, which seriously restrict the energy conversion efficiency and economy of compressed air energy storage systems.

[0005] Based on the above, how to solve the problems of low efficiency and poor grid connection stability caused by the wide operating conditions of expanders under constant volume gas storage is a problem to be solved in this technical field. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this application provides a pure compressed air energy storage staged expansion gas-liquid coupling stable output device and method. This method artificially establishes an intermediate pressure buffer unit between the high-pressure gas storage unit and the atmosphere, divides the compressed air expansion work into two stages: a high-pressure gas-liquid expansion stage and a low-pressure pure gas expansion stage. Dynamic valve control ensures that after the expansion tank reaches its final pressure near the intermediate pressure buffer unit's operating pressure, there is no pressure difference causing liquid return and efficient transfer of residual gas. Simultaneously, bidirectional real-time balance between the hydraulic and expansion sides locks the intermediate pressure within the expander's efficient operating range. Thus, without throttling, altering gas storage conditions, or relying on large-capacity power compensation, the system achieves continuous and stable power output and significantly improved energy utilization.

[0007] The embodiments of this application adopt the following technical solutions: In a first aspect, this application provides a pure compressed air energy storage staged expansion gas-liquid coupling stable output device, comprising: a high-pressure gas storage unit for storing high-pressure compressed air; a gas-liquid working unit including at least one working tank, wherein the working tank is provided with a high-pressure inlet valve and a vent valve at the top and a drain pipe at the bottom; an intermediate pressure buffer unit including a gas-liquid coexistence container, wherein the gas phase volume is larger than the single expansion gas volume of the working tank, and its working pressure is within the high-efficiency inlet pressure range of the expander; a high-pressure section hydraulic power generation unit including at least one hydraulic prime mover, wherein the hydraulic prime mover is connected to the drain pipe of the working tank; a low-pressure section expansion power generation unit including an expander, wherein the air inlet of the expander is connected to the gas phase space of the intermediate pressure buffer unit; and a control unit; The high-pressure gas storage unit and the gas-liquid work unit are arranged independently and are only connected through the high-pressure gas inlet valve during the work phase. No liquid enters the high-pressure gas storage unit throughout the process. The control unit is configured to: during the power-operating phase, control the high-pressure gas to enter the power tank through the high-pressure inlet valve, and close the high-pressure inlet valve before the expansion endpoint according to the real-time state parameters inside the tank to form a sealed expansion chamber, allowing the gas to continue expanding in the sealed expansion chamber, pushing the liquid out through the drain pipe and driving the hydraulic prime mover to perform work; at the expansion endpoint, control the opening of the vent valve to connect the power tank with the intermediate pressure buffer unit to balance the pressure, and then control the liquid to flow back to the power tank, replacing the residual gas in the tank with the intermediate pressure buffer unit as the gas source for the expander; and, according to the real-time pressure of the intermediate pressure buffer unit, coordinately adjust the load of the hydraulic prime mover and the load of the expander to maintain the pressure of the intermediate pressure buffer unit within the high-efficiency intake pressure range of the expander and maintain stable system power output.

[0008] The above technical solution adopts an architecture where the high-pressure gas storage unit and the gas-liquid work unit are independently arranged and coupled in a time-sharing manner. The high-pressure gas storage unit has no liquid entering throughout the process, and its entire volume is used to store high-pressure compressed gas, maximizing the utilization rate of the gas storage volume. The control unit realizes the formation of a sealed expansion chamber to fully extract the expansion work of the high-pressure section. The residual gas is replaced to the intermediate pressure buffer unit to become the gas source of the expander, thereby recovering the residual usable energy. Through the coordinated load regulation of the hydraulic prime mover and the expander, the pressure of the intermediate pressure buffer unit is maintained within the high-efficiency inlet pressure range of the expander. The expander operates stably in a narrow operating condition high-efficiency range, and the back pressure can be designed to a very low level. Without throttling, without changing the gas storage conditions, and without relying on large-capacity power compensation equipment, the system achieves continuous and stable power output and significantly improves energy utilization. This solves the technical problems of low efficiency and poor grid connection stability caused by the wide operating condition of the expander under constant volume gas storage conditions in the existing technology.

[0009] In some embodiments, the control unit includes a dynamic valve closing module and a differential pressure return module; The dynamic valve closing module is configured to: calculate the total gas volume Ve at the expansion endpoint based on the shape and size of the working tank and the expected liquid level at the end of expansion, and determine the expansion endpoint pressure Pe and temperature Te; collect the instantaneous pressure P1, instantaneous temperature T1, and liquid level h1 in the working tank in real time, and calculate the current gas volume V1 through the liquid level h1; close the high-pressure inlet valve when P1V1 / T1=PeVe / Te, so that the working tank forms the sealed expansion chamber and continues to discharge liquid to perform work until the expansion endpoint; wherein the expansion endpoint pressure Pe is the sum of the working pressure of the intermediate pressure buffer unit and the minimum working pressure difference of the hydraulic prime mover; The differential pressure return module is configured such that: when the gas in the working tank expands to the expansion endpoint pressure Pe, the vent valve is opened to connect the working tank with the intermediate pressure buffer unit to balance the pressure; after the pressure is balanced, the liquid in the intermediate pressure buffer unit flows back to the working tank by gravity or a return pump, and the liquid occupies the gas space, displacing the residual gas in the tank through the vent valve to the intermediate pressure buffer unit; when the liquid level is higher than the vent valve, the vent valve is closed, and the working tank is filled with liquid and enters a standby state; The control unit also sets a minimum liquid level as a safety protection threshold. If the gas expansion in the working tank does not reach the expansion endpoint pressure Pe but has reached the minimum liquid level, the high-pressure air inlet valve is closed and the vent valve is opened. After pressure balancing, the liquid is returned.

[0010] Through the above technical solution, dynamic valve closing control is achieved based on the ideal gas law, so that the expansion endpoint pressure is precisely close to the working pressure of the intermediate pressure buffer unit, creating near-zero pressure difference conditions for liquid return without pressure difference; the residual gas is completely replaced to the intermediate pressure buffer unit to become the gas source of the expander, avoiding the gas release loss or additional pumping energy consumption caused by the pressure difference margin in the traditional solution; the minimum liquid level safety protection logic prevents gas from rushing into the hydraulic prime mover, improving the system's operational safety.

[0011] In some embodiments, the control unit further includes a coordinated pressure stabilization module configured to: monitor the pressure of the intermediate pressure buffer unit in real time; when the pressure of the intermediate pressure buffer unit is higher than a set value, reduce the load of the hydraulic prime mover to reduce the air supply to the intermediate pressure buffer unit, while increasing the load of the expander to increase the air extraction from the intermediate pressure buffer unit; when the pressure of the intermediate pressure buffer unit is lower than the set value, increase the load of the hydraulic prime mover to increase the air supply, while reducing the load of the expander to reduce the air extraction.

[0012] Through the above technical solution, the hydraulic prime mover side and the expander side form a bidirectional real-time balance adjustment through the intermediate pressure buffer unit, which dynamically matches the gas rate entering the intermediate pressure buffer unit with the expander pumping rate, thereby locking the pressure of the intermediate pressure buffer unit within the high-efficiency working range of the expander, so that the expander back pressure can be designed to a very low level, maintaining the continuous and stable power output of the system.

[0013] In some embodiments, the gas-liquid working unit includes multiple working tanks connected in parallel; the control unit further includes a multi-working-tank coordination module, which is configured to: control the opening sequence of the high-pressure air inlet valves of each working tank, causing each working tank to work cyclically and independently controlling the real-time liquid output of each working tank; when the number of working tanks is even, they can share the hydraulic prime mover in pairs to alternately perform work and be grouped and cyclically operated. It should be noted that when the number is even, alternation or cyclic operation is possible.

[0014] Through the above technical solutions, the multi-tank operation can be cyclically carried out in sequence, which can realize flexible configuration from alternating output of two tanks to cyclic output of multiple tanks, ensuring continuous gas and liquid supply on the hydraulic side, reducing power output fluctuations, and improving the continuous operation capability of the system.

[0015] In some embodiments, the working tank is either non-isolated or isolated from the liquid chamber; When a non-isolated system is used, the bottom of each working tank is connected to the inlet of the hydraulic prime mover via a pipe, and the outlet of the hydraulic prime mover is connected to the intermediate pressure buffer unit; the liquid in the intermediate pressure buffer unit is returned to the working tank by a return pump or gravity to complete the return process. When an isolated type is used, the working tanks are set in groups of two, and each group drives one of the hydraulic prime movers. Each working tank has two one-way valves at the bottom, which are respectively connected to the inlet and outlet of the hydraulic prime mover. During the expansion process, the pressure difference between the back pressure of the hydraulic prime mover and the working pressure of the intermediate pressure buffer unit pushes the isolation component of the other working tank to reset and complete the return of liquid. The two tanks work alternately.

[0016] The above technical solutions provide two types of working tank structures: non-isolated and isolated. The non-isolated structure is simple and suitable for low-viscosity media such as clean water, while the isolated structure can achieve zero-energy reset and fluid return by utilizing the internal pressure difference of the system and is suitable for hydraulic oil media. This allows the system to flexibly select the working tank structure according to different scales and working media.

[0017] In some embodiments, the hydraulic prime mover includes impulse turbines, each with an independently arranged shaft. Each impulse turbine is equipped with an independent controllable nozzle or needle valve and drives a variable frequency generator. Each variable frequency generator is connected to a common DC bus via an independent machine-side converter and then connected to the grid at a constant frequency via a unified grid-side converter. Each impulse turbine is installed in the gas space inside the intermediate pressure buffer unit or encapsulated in a pressure-bearing shell. The pressure-bearing shell is connected to the gas space of the intermediate pressure buffer unit through a top gas phase balance pipe and to the liquid phase space of the intermediate pressure buffer unit through a bottom liquid connection pipe, so that the operating environment pressure of the impulse turbine follows the operating pressure of the intermediate pressure buffer unit. Optionally, the gas phase and liquid connection pipes are respectively equipped with shut-off valves for shutting off during maintenance. The liquid connection pipes must ensure that the liquid in the turbine casing flows smoothly into the intermediate pressure buffer unit, avoiding liquid accumulation at the turbine tail.

[0018] The above technical solution places the impulse turbine in an environment with the same pressure as the intermediate pressure buffer unit, and the outlet liquid naturally flows into the same pressure environment, eliminating back pressure loss; the electrical parallel scheme of independent variable speed constant frequency of the split shaft enables each turbine to adaptively adjust its speed according to the real-time head to maintain the optimal speed ratio, which is suitable for large-scale compressed air energy storage scenarios.

[0019] In some embodiments, an energy storage compression unit is also included, comprising a first-stage compressor and a second-stage compressor; the inlet of the first-stage compressor is connected to the atmosphere, and the outlet is connected to the gas phase space of the intermediate pressure buffer unit; the inlet of the second-stage compressor is connected to the gas phase space of the intermediate pressure buffer unit, and the outlet is connected to the high-pressure gas storage unit; the intermediate pressure buffer unit serves as both a first-stage exhaust buffer and a second-stage intake pressure stabilizing container during the energy storage stage, enabling the first-stage compressor to operate under stable conditions where the intake pressure is constant and the exhaust pressure is locked by the intermediate pressure buffer unit.

[0020] Through the above technical solution, the intermediate pressure buffer unit is reused as the intermediate pressure stabilization node in the energy storage stage. The first stage compressor always operates in the narrow operating condition high efficiency range, and the second stage compressor has a reduced pressure ratio and increased surge margin, which systematically improves the compression efficiency and operational safety in the energy storage stage.

[0021] In some embodiments, a three-stage heating system is also included: a first-stage heating system, in which hot fluid is injected into the working tank through a top spray nozzle to perform heat and mass exchange on the high-pressure gas, and / or the gas is preheated by a heat exchanger before it enters the working tank; a second-stage heating system, in which hot fluid is injected into the intermediate pressure buffer unit through a spray nozzle to increase the temperature of the gas entering the expander; and a third-stage heating system, in which heat exchangers are used to heat the gas at the expander inlet and / or between stages, and when the expander is a screw expander, hot fluid is also injected into the working chamber for continuous heating during the expansion process.

[0022] Through the above technical solutions, the three-stage heat compensation precisely addresses the thermodynamic characteristics of the three stages: high-pressure section closed expansion, intermediate buffer zone air intake, and low-pressure section dynamic expansion. It systematically compensates for the temperature drop loss during the expansion process and significantly improves power generation efficiency.

[0023] In some embodiments, a waste energy recovery unit is also included, which includes a turbocharger with a variable cross-section nozzle. The turbine end inlet of the turbocharger is connected to the exhaust outlet of the expander. The exhaust gas from the expander drives the turbine end to do work, and the turbine exhaust gas provides a cold source for the cooling and heat exchange components. The compressor end of the turbocharger compresses ambient air to generate high-temperature compressed air, which provides a heat source for the heating and heat exchange components. The excess heat is recycled to the system's heat storage and heat replenishment circuit.

[0024] The above technical solution utilizes the residual pressure of the expanded exhaust gas to drive the turbocharger. The turbine end recovers the waste cooling and the compressor end generates waste heat, realizing a closed-loop recovery of combined cooling, heating and power and energy cascade utilization, thereby improving the overall energy utilization efficiency of the system.

[0025] Secondly, this application provides a method for stable output of pure compressed air energy storage staged expansion gas-liquid coupling, applied to the pure compressed air energy storage staged expansion gas-liquid coupling stable output device described in the first aspect, including an energy release and power generation stage, wherein the energy release and power generation stage includes the following steps: High-pressure gas-liquid expansion steps: High-pressure gas enters the power tank through the high-pressure inlet valve, pushes the liquid out of the tank and enters the hydraulic prime mover to do work and generate electricity, and the tail liquid enters the intermediate pressure buffer unit; After the high-pressure gas enters the power tank, the high-pressure inlet valve is closed before the expansion endpoint according to the real-time state parameters in the tank, so that the power tank forms a closed expansion chamber and continues to discharge liquid to do work until the expansion endpoint. Expansion endpoint triggering and liquid return steps: When the gas in the sealed expansion chamber expands to the preset expansion endpoint pressure, the vent valve is opened to connect the working tank and the intermediate pressure buffer unit to balance the pressure. Then, the liquid flows back to the working tank to replace the residual gas in the tank to the intermediate pressure buffer unit. After the working tank is filled with liquid, it enters the standby state and is recycled. Low-pressure section pure gas expansion step: The gas in the intermediate pressure buffer unit is separated into gas and liquid and then enters the expander to expand and generate electricity; Collaborative pressure stabilization steps: The pressure of the intermediate pressure buffer unit is monitored in real time. When the pressure of the intermediate pressure buffer unit is higher than the set value, the load of the hydraulic prime mover is reduced while the load of the expander is increased. When the pressure of the intermediate pressure buffer unit is lower than the set value, the load of the hydraulic prime mover is increased while the load of the expander is reduced. Through bidirectional real-time balance between the high-pressure section and the low-pressure section, the pressure of the intermediate pressure buffer unit is maintained within the high-efficiency intake pressure range of the expander, and the system power output is kept stable.

[0026] Through the above technical solution, in the energy release and power generation stage, the high-pressure gas expands fully in the working tank to drive the liquid to do work, and the residual gas is efficiently replaced to the intermediate pressure buffer unit to become the gas source of the expander. The hydraulic prime mover and the expander maintain the intermediate pressure within the high-efficiency air intake pressure range of the expander through bidirectional real-time balance adjustment. The expander always operates in the high-efficiency range and the back pressure can be designed to a very low level, so as to achieve continuous and stable power output of the system and significantly improve energy utilization.

[0027] In summary, this application includes at least the following beneficial technical effects: 1. By establishing an intermediate pressure buffer unit between the high-pressure gas storage unit and the atmosphere, the work done by compressed air expansion is divided into two stages: high-pressure gas-liquid expansion and low-pressure pure gas expansion. The high-pressure gas storage unit and the gas-liquid work unit are arranged independently and coupled in a time-sharing manner. The high-pressure gas storage unit has no liquid entering throughout the process, thus maximizing the utilization rate of the gas storage volume. The control unit realizes the formation of a sealed expansion chamber to fully extract the expansion work of the high-pressure stage. The gas after the first expansion is replaced by the intermediate pressure buffer unit to become the gas source of the expander for secondary expansion work. The intermediate pressure is maintained within the high-efficiency inlet pressure range of the expander through the coordinated load regulation of the hydraulic prime mover and the expander. The expander operates stably in the narrow operating condition high-efficiency range, and the back pressure can be designed to a very low level. There is no throttling loss throughout the process. Without changing the gas storage conditions and without relying on large-capacity power compensation equipment, the system achieves continuous and stable power output and significantly improves energy utilization. 2. The system adopts an architecture that separates the functions of the high-pressure gas storage unit and the gas-liquid power unit. The system pressure stabilization function is fully undertaken by the expander through collaborative pressure stabilization. The number of power tanks is decoupled from the system's stable output performance. Only a small number of power tanks are needed to ensure continuous gas supply, and the total number of high-pressure bearing components is significantly reduced. The power tanks are available in both non-isolated and isolated structural forms. The hydraulic prime mover offers a variety of options, including hydraulic motors and impulse turbines. The system architecture is simplified, flexible, and cost-effective. 3. The intermediate pressure buffer unit is reused as an intermediate pressure stabilizing node in the two-stage compression during the energy storage stage and as a physical coupling platform for the two-stage expansion during the energy release stage. Combined with the three-stage heat replenishment system and the waste energy recovery unit, it realizes combined cooling, heating and power and closed-loop recovery of energy cascade utilization. The system's storage and release efficiency are improved in both directions, and the overall energy utilization efficiency is maximized. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A block diagram of a pure compressed air energy storage staged expansion gas-liquid coupling stable output device provided in the embodiments of this application; Figure 2 A module block diagram of the control unit provided in the embodiments of this application; Figure 3 A schematic diagram of a pure compressed air energy storage staged expansion gas-liquid coupling stable output device, taking a small-scale park distributed energy storage system as an example, provided in an embodiment of this application. Figure 4 A schematic diagram of the structure of a pure compressed air energy storage staged expansion gas-liquid coupling stable output device, taking a large-scale artificial chamber energy storage system as an example, provided for the embodiments of this application; Figure 5 A flowchart of a stable output method for staged expansion gas-liquid coupling in pure compressed air energy storage provided in this application embodiment.

[0030] Figure 3In the middle section: High-pressure gas storage unit 11, compressor 12, compression heat recovery device 13, external heating device 14, heat storage device 15, circulating heat pump 16, heating unit 17, turbocharger 18, cooling unit 19, gas-liquid separator 110, generator 111, secondary expansion 112, primary expansion 113, second heat exchanger 114, filter separator 115, intermediate pressure buffer unit 116, vent valve 117, high-pressure inlet valve 118, power tank 119, piston 120, check valve 121, hydraulic motor 122, generator 123, first heat exchanger 124; Figure 4 Medium: High-pressure gas storage unit 21, two-stage compressor 22, one-stage compressor 23, compression heat recovery device 24, external heating device 25, heat storage device 26, heat extraction circulation pump 27, intermediate pressure buffer unit 28, hot spray 29, return liquid pump and one-way valve 210, gas-liquid separator 211, first-stage expansion 212, interstage heat exchanger 213, second-stage expansion 214, generator 215, cooling unit 216, turbocharger 217, heating unit 218, water turbine 219, variable frequency generator 220, vent valve 221, power tank 222, high-pressure gas supply valve 223, spray valve 224. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, the technical features involved in the various embodiments described below can be combined with each other as long as they do not conflict with each other.

[0032] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Example 1

[0033] It should be noted that currently operational traditional compressed air energy storage projects are mostly large-scale centralized power plants with a capacity of hundreds of megawatts. These projects heavily rely on special geological gas storage spaces such as salt caverns, natural rock caves, and underground chambers, resulting in extremely stringent site selection constraints, long construction periods, and high overall costs. Furthermore, the gas pressure gradually decreases during compressed air expansion for power generation, making it impossible to guarantee efficient operation of the expander under a wide range of operating conditions, leading to low overall efficiency and hindering flexible widespread adoption. At the same time, industrial parks, production plants, and industrial clusters are continuously increasing their demand for distributed energy storage, peak shaving and valley filling, self-contained emergency power supplies, and integrated cooling and heating power supply. Small and medium-sized compressed air energy storage technologies without special geological dependencies have become a necessity in the industry.

[0034] Existing gas-liquid coupled compressed air energy storage solutions have been explored in small and medium-sized scenarios, but they generally suffer from the following technical shortcomings: 1. The Cost of Passive Adaptation to the Constant-Capacity Transformer Contradiction. Existing compressed air energy storage systems face a contradiction between pressure decay caused by constant-capacity gas storage and the pressure stabilization requirements of the expander. To address this contradiction, existing technologies typically employ three paths: First, configuring large-capacity power regulation equipment (lithium batteries, supercapacitors, SVG, etc.) on the power side to transfer the pressure stabilization requirements of the mechanical side to power electronic compensation. While this approach can achieve stable output, the investment in power voltage regulation equipment can reach 15%-20% of the total system investment. Furthermore, the continuous high-power operation of the equipment leads to short lifespan and high replacement costs, severely eroding the project's economic viability. Secondly, modifying the gas storage side to constant pressure conditions, such as the constant pressure compressed air energy storage systems developed by some research institutions, can simulate a constant hydrostatic pressure environment at a water depth of 700 meters. This constant hydrostatic pressure enables constant pressure energy storage and release, ensuring the expander always operates near its design point. However, this approach is severely limited by coastal geographical conditions, resulting in extremely high engineering construction costs and making large-scale promotion difficult in vast inland areas and ordinary industrial parks. Existing technologies even introduce special structures such as dual-working-medium systems and flexible diaphragm gas storage facilities, significantly increasing engineering complexity and system costs. Thirdly, throttling the fluctuating high-pressure gas to the expander's design pressure using a throttling valve can achieve constant inlet pressure, but the usable energy of the high-pressure gas is irreversibly lost during the throttling process. For example, throttling a 10MPa-level gas storage system to 7MPa can result in a usable energy loss of over 10%. The common characteristic of these three approaches is that they all passively adapt to system defects through external conditions: either through "post-event compensation" on the power side, "pre-event modification" on the gas storage side, or exchanging irreversible energy loss for pressure stability. Existing technologies rarely explore a technical route to achieve stable gas intake for expanders by actively extracting expansion work in the high-pressure section through a gas-liquid work unit and coordinating with staged expansion control, without throttling, changing gas storage conditions, or relying on power compensation.

[0035] 2. Systemic Costs of Wide Operating Conditions. To fully utilize the stored air energy, existing compressed air energy storage systems generally employ a deep discharge strategy, allowing the stored air pressure to drop significantly from its rated value to a lower level during energy release. This necessitates that the expander operate over an extremely wide range of conditions. To cover the surge uncertainties under these wide operating conditions, the back pressure design is forced to be increased, directly leading to a significant decrease in the expansion ratio and expansion work loss, resulting in a significant increase in the proportion of work loss in the low-pressure section. For example, with a back pressure discharge of 0.3 MPa (gauge pressure, absolute pressure 0.4 MPa), the pressure approximately RT0ln(0.4 / 0.1) ≈ 118.6 kJ / kg is completely wasted. In comparison, the pressure loss when throttling from 15 MPa (gauge pressure, absolute pressure 15.1 MPa) to 10 MPa (gauge pressure, absolute pressure 10.1 MPa) is approximately RT0ln(15.1 / 10.1)≈34.4 kJ / kg; the gas release loss at 0.3 MPa in the low-pressure section (118.6 kJ / kg) is about 3.4 times that of the throttling loss from 15 MPa to 10 MPa (34.4 kJ / kg).

[0036] Meanwhile, the drastic fluctuations in intake pressure and flow rate force the system to be equipped with large-capacity power voltage regulators to maintain grid connection stability, further increasing system costs. This chain of contradictions is interconnected: constant-volume deep discharge → wide operating condition operation → high back pressure compromise → power loss + increased grid connection costs. Existing technology fails to recognize that locking the expander in a narrow, high-efficiency operating range through front-end constant current control can achieve full gas release while designing a very low back pressure level and eliminating the need for large-capacity power compensation equipment, thereby breaking this systemic contradiction.

[0037] 3. Gas-liquid co-storage structures and the resulting engineering challenges in continuous operation. To address the aforementioned constant-volume, variable-pressure contradiction, some existing technologies employ a gas-liquid coupling approach, introducing a gas-liquid co-storage structure within the same tank: gas and liquid coexist within the high-pressure vessel for extended periods, achieving pressure stabilization or constant-pressure energy release through liquid displacement or liquid column pressure. This structure results in the effective gas storage volume being continuously occupied by an incompressible, non-expandable liquid medium, leading to a mismatch between energy storage density and equipment cost. More importantly, the gas-liquid co-tank structure leads to an engineering compromise dilemma for continuous operation of the system: in order to reduce the liquid content and improve the utilization rate of the gas storage volume, a multi-tank work-return-work cycle is adopted. However, at the end of the expansion of the work tank, the residual gas pressure in the tank is still at a high level (it is necessary to maintain the minimum working pressure difference of the hydraulic prime mover). This residual pressure is much higher than the return liquid source pressure, and the liquid cannot rely on gravity to overcome the back pressure and achieve self-reset. If the gas is not actively released to reduce the pressure, a high-power return liquid pump is required to overcome the pressure difference, or multiple tanks are connected in series to reduce the pressure step by step, which leads to a doubling of equipment investment and complex control logic. If the gas is actively released to atmospheric pressure, a large amount of low-pressure gas is wasted, just like in point 2 above.

[0038] 4. Mismatch in power distribution caused by gas-liquid co-storage. The work done by isothermal gas expansion equation W=RT·ln(P1 / P2) shows that the gas's work capacity is determined by the expansion ratio, not the pressure difference. In compressed air energy storage scenarios with gas-liquid co-storage, the proportion of work done in the low-pressure, high-expansion-ratio section is much higher than that in the high-pressure hydraulic section. Previous energy loss analysis also shows that the avoidable energy loss of the turbine expander on the energy release side is greater than the unavoidable loss, and optimizing the low-pressure section can significantly reduce the total energy loss of the system. Existing technologies are limited by the structural constraints of gas-liquid co-storage: the high-pressure container is occupied by incompressible liquid media for a long time, resulting in low effective gas storage volume utilization, which limits the total gas storage capacity and the total work capacity. To compensate for the total output gap, existing technologies are forced to excessively configure expensive hydraulic equipment in the high-pressure section to extract relatively limited work, or to use the hydraulic prime mover and expander as parallel dual main loops, failing to achieve optimal matching between equipment capacity and power distribution.

[0039] This application employs a functionally separated and time-coupled architecture between the high-pressure gas storage unit and the gas-liquid working unit. Liquid circulates only between working tanks or between the working tank and the intermediate pressure buffer unit, fundamentally eliminating volume constraints. By establishing the intermediate pressure buffer unit as a physical coupling platform for the two working stages, the expander's intake conditions are confined to a narrow, high-efficiency operating range. Dynamic valve control ensures the working tank's expansion endpoint pressure approaches the intermediate pressure buffer unit's operating pressure. After opening the vent valve to balance the pressure, zero-pressure-difference liquid return is achieved. Residual gas is replaced by the intermediate pressure buffer unit under near-zero-pressure-difference conditions, becoming the expander's gas source. This avoids the venting losses or additional pumping losses caused by pressure differential margins in traditional solutions. Controllable expansion on the hydraulic side, rather than throttling and pressure reduction, actively controls the gas expansion rhythm using a hydraulic prime mover to keep the intermediate pressure within the expander's high-efficiency operating range, eliminating throttling losses. This application is applicable to both new systems and upgrades of existing compressed air energy storage power stations. It can be implemented using an energy performance contracting model, with low upgrade costs and quantifiable energy-saving benefits.

[0040] The purpose of this application is to overcome the shortcomings of existing compressed air energy storage technologies, such as low gas-liquid co-storage volume utilization, rigid demand for multi-tank pressure stabilization, poor adaptability to dynamic operating conditions, large expansion temperature drop loss, insufficient output stability, serious waste of residual energy, high-pressure potential energy throttling loss, violent front-end fluctuations, high power stabilization cost, and systemic contradictions caused by deep discharge utilization and wide operating conditions leading to back pressure loss and grid connection cost. The application provides a pure compressed air energy storage staged expansion gas-liquid coupling stable output device and method.

[0041] This application adopts an architecture that separates the functions of the high-pressure gas storage unit and the gas-liquid work unit, effectively decoupling energy storage and work functions. By artificially establishing an intermediate pressure buffer unit between the high-pressure gas storage unit and the atmosphere, the compressed air expansion work is divided into two stages: high-pressure gas-liquid expansion and low-pressure pure gas expansion. Dynamic valve control ensures that the work tank forms a sealed expansion chamber, guaranteeing that the high-pressure gas fully expands to drive the liquid to do work. Residual gas is efficiently transferred through pressure differential-free liquid return control. After one expansion, the gas is replaced by the intermediate pressure buffer unit and directly becomes the expander's gas source. Its expansion work is then recovered by the low-pressure expander, avoiding the problems encountered in traditional solutions. The system mitigates losses due to pressure differential margin, including venting losses and additional pumping losses. Controllable expansion on the hydraulic side, utilizing a hydraulic prime mover to actively control the gas expansion rhythm, adjusts the load on the high-pressure and low-pressure sections based on pressure changes in the intermediate pressure buffer unit, and maintains the intermediate pressure within the expander's efficient operating range through real-time bidirectional balancing between the high-pressure and low-pressure sections. The expander operates in reverse, prioritizing grid-connected power quality, ensuring stable operation within a narrow, efficient operating range, with back pressure designed to be very low. The hydraulic and expansion sides are gently coupled and linked through the gas-capacity buffer of the intermediate pressure buffer unit, jointly maintaining stable overall system output. The modified system can achieve the same power generation as the original deep discharge using a shallow discharge strategy, retaining a higher termination pressure to save recharge compression energy consumption, or maintaining a deep discharge strategy to achieve greater power generation capacity. Improved cycle efficiency provides an economic basis for applying for expanded energy storage capacity.

[0042] For details, please refer to Figure 1 As shown, this application provides a pure compressed air energy storage staged expansion gas-liquid coupling stable output device, including a high-pressure gas storage unit, a gas-liquid working unit composed of one or more sets of parallel pressurized gas-liquid working tanks, an intermediate pressure buffer unit, a high-pressure section hydraulic power generation unit, a low-pressure section expansion power generation unit, an energy storage compression unit, and a control unit.

[0043] The high-pressure gas storage unit and the gas-liquid power unit are arranged independently, connected only during the power-generating phase via controllable valves. No liquid enters the high-pressure gas storage unit throughout its operation; its entire volume is used to store high-pressure compressed gas. The gas-liquid power unit is responsible for the complete expansion and hydraulic work of the gas in the high-pressure section and for supplying gas to the intermediate pressure buffer unit. The number of power tanks depends only on the operating conditions of the hydraulic prime mover, continuous operation requirements, and the structural form of the power tanks, and is not necessarily related to the stable output performance of the entire power supply system. The proportion of work done in the high-pressure section is less than that in the low-pressure section; the low-pressure section expander regulation undertakes the main task of stabilizing the power supply system's output.

[0044] The intermediate pressure buffer unit includes a gas-liquid coexistence container, whose working pressure varies slightly within the high-efficiency inlet pressure range of the expander (the high-efficiency inlet pressure range of the expander is an inherent and determinable parameter of the equipment); the gas phase volume of the intermediate pressure buffer unit is much larger than the single expansion gas volume of the power tank, so as to suppress pressure fluctuations within the range that the expander can adaptively adjust.

[0045] The high-pressure section hydraulic power generation unit includes at least one hydraulic prime mover and a corresponding generator; each hydraulic prime mover is connected to the drain pipe of the corresponding working tank; the low-pressure section expansion power generation unit includes a turbine expander or a screw expander and a generator driven by it.

[0046] The energy storage compression unit includes a first-stage compressor and a second-stage compressor. The first-stage compressor compresses atmospheric air to the working pressure of the intermediate pressure buffer unit and operates continuously under stable conditions where the intake pressure is constant and the exhaust pressure is locked by the intermediate pressure buffer unit. The second-stage compressor further compresses the air in the intermediate pressure buffer unit to the working pressure of the high-pressure gas storage unit and dynamically adjusts it according to the real-time pressure of the gas storage unit. During the energy storage stage, the intermediate pressure buffer unit also serves as the first-stage exhaust buffer and the second-stage intake pressure stabilizing container, so that the two compressors operate decoupled through gas capacity buffering. The first stage is constant and efficient, while the second stage has a lower pressure ratio and increased surge margin.

[0047] The hydraulic power generation unit and the expansion power generation unit each achieve speed matching with the generator through a speed change device; when a variable hydraulic motor is used, multiple motors can be combined through shafts or the transfer case can output in reverse to drive the same generator, or they can be combined with the low-pressure expansion power generation unit to form a single shaft system to drive a generator to generate electricity.

[0048] The hydraulic prime mover is flexibly selected based on system scale, medium characteristics, and operating conditions, including but not limited to variable speed constant frequency turbines, hydraulic turbines, and variable displacement hydraulic motors, each driving a corresponding generator. Variable displacement hydraulic motors are suitable for small to medium scale scenarios with high pressure differentials and precise flow regulation; hydraulic turbines are suitable for clean water media and highly standardized scenarios; and impulse turbines are suitable for large-scale, high-power scenarios. When using an impulse turbine, the liquid after work needs to be discharged into an intermediate pressure buffer unit with a higher working pressure. Therefore, the turbine is installed within the gas space of the intermediate pressure buffer unit, or entirely encapsulated in a pressure-bearing shell connected to the intermediate pressure buffer unit. This ensures that the turbine's operating environment pressure follows the intermediate pressure buffer unit's working pressure in real time, forming an equivalent atmospheric working environment. The outlet liquid naturally flows into the same pressure environment, avoiding back pressure loss.

[0049] refer to Figure 2 As shown, the control unit is configured as follows: Dynamic valve closing module: After the high-pressure inlet valve is connected to the working tank, the total gas volume Ve at the expansion endpoint needs to be calculated based on the shape and size of the working tank and the expected liquid level at the end of expansion, and the expansion endpoint pressure Pe and expansion temperature Te are determined; the instantaneous pressure P1, instantaneous temperature T1 and liquid level h1 in the current working tank are collected in real time, and the current gas volume V1 is calculated based on the liquid level h1; when P1V1 / T1=PeVe / Te, the high-pressure inlet valve is closed, so that the current working tank forms a closed expansion chamber and continues to discharge liquid to do work until the expansion endpoint.

[0050] Pressure-differential return module: When the gas expansion in the working tank reaches the preset expansion endpoint pressure Pe, the vent valves of the working tank and the intermediate pressure buffer unit are opened first to balance the pressure between the working tank and the intermediate pressure buffer unit. The liquid at the bottom of the intermediate pressure buffer unit returns to the intermediate pressure buffer unit without pressure difference by gravity or a return pump, and replaces the gas in the working tank to the intermediate pressure buffer unit. When the liquid level is higher than the vent valve, the vent valve is closed, and the tank enters the standby state after being completely filled with liquid. At the same time, a minimum liquid level is set as a safety protection threshold. If the gas expansion in the working tank has not reached the preset expansion endpoint pressure Pe, but has reached the set minimum liquid level, the vent valve is opened directly and the high-pressure air inlet valve is confirmed to be closed to end the expansion and prevent gas from rushing into the hydraulic prime mover.

[0051] Multi-power tank coordination module: When there is more than one power tank, the working sequence of the power tanks (opening time of the high-pressure air inlet valve) is controlled, so that the power tanks work in a cycle and the real-time liquid output is independently controlled to reduce power output fluctuations. When the number of power tanks is even, they can share the hydraulic prime mover in pairs to work alternately and be grouped in a cycle.

[0052] Collaborative grid connection module: When the hydraulic prime mover of the high-voltage section hydraulic power generation unit adopts a variable speed constant frequency water turbine to drive the variable frequency generator, it must be rectified and then connected to the grid with the power of the low-voltage section expansion power generation unit.

[0053] The collaborative pressure stabilization module monitors the pressure of the intermediate pressure buffer unit in real time and adjusts the loads of the high-pressure and low-pressure sections according to the pressure changes. This ensures that the intermediate pressure buffer unit pressure varies slightly within the high-efficiency intake pressure range of the expander. When the intermediate pressure buffer unit pressure is higher than the set value, the hydraulic prime mover load is reduced to supply less gas, while the expander load is increased to extract more gas, ensuring stable power output and lowering the intermediate pressure buffer unit pressure. Conversely, when the intermediate pressure buffer unit pressure is lower than the set value, the hydraulic prime mover load is increased to supply more gas, while the expander load is reduced to extract more gas, ensuring stable power output and raising the intermediate pressure buffer unit pressure. Through bidirectional real-time balancing between the high-pressure and low-pressure sections, the system maintains continuous and stable power output while ensuring that the expander always operates within its high-efficiency range, allowing for very low back pressure design.

[0054] Explanation of the core principles behind the above settings: 1. Principle of staged expansion and intermediate pressure buffer unit: This application artificially establishes a controllable intermediate pressure buffer unit between the high-pressure gas storage unit and the atmosphere, dividing the work done by compressed air expansion into two stages: a high-pressure gas-liquid expansion stage and a low-pressure pure gas expansion stage. In the high-pressure stage, the high-pressure gas enters the work tank and pushes the liquid out, driving the hydraulic prime mover to generate electricity. The gas outputs shaft work as it expands from high pressure to intermediate pressure. In the low-pressure stage, the gas in the intermediate pressure buffer unit serves as the gas source, and after gas-liquid separation, it enters the expander to continue expanding and doing work.

[0055] This intermediate pressure buffer unit does not simply provide intermediate parameters, but rather a physical boundary condition that is actively designed, maintained, and utilized. Its operating pressure is locked within the expander's efficient intake pressure range, with only minor fluctuations. The expander always operates within a narrow, efficient operating range, allowing back pressure to be designed to a very low level, significantly reducing surge margin and substantially improving the expansion ratio.

[0056] 2. The essential difference between work done by controlled expansion and throttling: The core thermodynamic essence of this application lies in the fact that after high-pressure gas enters the working tank, it does not expand freely through a valve to reduce pressure (throttling), but instead is first sealed and then fully expanded to push the liquid inside the tank out, driving a hydraulic prime mover to generate electricity. During the process of the gas expanding from high pressure to intermediate pressure, each step outputs shaft work, making it a controllable expansion and work process.

[0057] Dynamic valve control ensures that the high-pressure inlet valve closes in advance when the gas in the work tank reaches the preset expansion condition, creating a sealed expansion chamber in the work tank. The gas continues to expand within this chamber, pushing the liquid until it is completely discharged. This process ensures that the expansion work of the high-pressure gas is fully extracted, rather than being irreversibly dissipated through the throttling valve.

[0058] The flow regulation mechanism of a hydraulic prime mover (such as the swashplate / axis / eccentric cylinder of a hydraulic motor, the nozzle / guide vane of a hydraulic turbine, or the nozzle / needle valve of a water turbine) functions to regulate the expansion load in the high-pressure section: reducing the flow rate increases the resistance to liquid discharge and slows down gas expansion, but it still pushes the liquid to do work; increasing the flow rate reduces the resistance and accelerates expansion. Regardless of how the flow regulation mechanism operates, every step of the gas expansion process does work externally, and there is no irreversible loss due to free expansion or throttling.

[0059] 3. The principle of thermodynamic work distribution: Existing gas-liquid coupled compressed air energy storage technologies generally regard the hydraulic work-doping link as the main power output means of the system, or regard the hydraulic prime mover and the expander as parallel dual main loops. The root cause of this technical route selection is that the distribution law of work done by expansion is not understood from the thermodynamic essence.

[0060] It should be noted that in the following thermodynamic calculations, the commonly used gas storage pressures in engineering (such as 25MPa, 10MPa, 4MPa, 2MPa, etc.) are all gauge pressures. When calculating the expansion ratio, they must be converted to absolute pressure (Absolute Pressure = Gauge Pressure + 0.1MPa atmospheric pressure). The expansion endpoint of 0.1MPa is gauge pressure (i.e., absolute pressure of 0.2MPa, slightly higher than standard atmospheric pressure, to ensure smooth exhaust of the expander).

[0061] According to the gas law, the work done by the isothermal expansion of an ideal gas is W = RT·ln(P1 / P2), where P1 and P2 are the absolute pressures, and ln(P1 / P2) is the natural logarithm of the expansion ratio. Due to the nonlinear nature of the natural logarithm function, the work done by expansion is mainly concentrated in the low-pressure, high-expansion-ratio range.

[0062] Taking the expansion of 25MPa gas storage (gauge pressure, absolute pressure 25.1MPa) to 0.1MPa gauge pressure (absolute pressure 0.2MPa) as an example, the total expansion ratio is 125.5. If the process is divided into a high-pressure section (25MPa gauge pressure → 4MPa gauge pressure, i.e., absolute pressure 25.1MPa → 4.1MPa, expansion ratio 6.12) and a low-pressure section (4MPa gauge pressure → 0.1MPa gauge pressure, i.e., absolute pressure 4.1MPa → 0.2MPa, expansion ratio 20.5), then: Isothermal expansion condition (ideal limit, sufficient heat compensation): Work done in the high-voltage section: W_high = RT·ln(6.12) = 1.814RT; Work done in the low-pressure section: W_low = RT·ln(20.5) = 3.020RT; Total work done: W_total = RT·ln(125.5) = 4.834RT; High-voltage section accounts for 37.5%; low-voltage section accounts for 62.5%.

[0063] Adiabatic expansion condition (no heat compensation limit, maximum temperature drop loss): High-pressure section: Air expands adiabatically from 298K to 4.1MPa (absolute pressure), temperature drops to 177.6K, and work is done by 121.0kJ / kg; Low-pressure section: Air adiabatically expands from 177.6K to 0.2MPa (absolute pressure), temperature drops to 75.0K, and work is done by 103.0kJ / kg; Total work done: 224.0 kJ / kg; High-voltage section accounted for 54.0%; low-voltage section accounted for 46.0%.

[0064] The above calculations show that even under extremely unfavorable conditions of adiabatic heating without reheating, the work done in the low-pressure section still accounts for 46%; while under ideal isothermal conditions, the work done in the low-pressure section is absolutely dominant (62.5%). This application sets up a multi-stage, multi-stage reheating system (preheating before expansion + in-tank spraying + inlet air heating + interstage heating + in-cavity injection) to make the actual operating conditions closer to isothermal conditions, thus the work done in the low-pressure section accounts for 55%-65%.

[0065] Taking the expansion of 10MPa gas storage (gauge pressure, absolute pressure 10.1MPa) to 0.1MPa gauge pressure (absolute pressure 0.2MPa) as an example, the total expansion ratio is 50.5, divided into a high-pressure section (10MPa gauge pressure → 2MPa gauge pressure, i.e., absolute pressure 10.1MPa → 2.1MPa, expansion ratio 4.81) and a low-pressure section (2MPa gauge pressure → 0.1MPa gauge pressure, i.e., absolute pressure 2.1MPa → 0.2MPa, expansion ratio 10.5): Isothermal expansion condition: Work done in the high-voltage section: W_high = RT·ln(4.81) = 1.571RT; Work done in the low-pressure section: W_low = RT·ln(10.5) = 2.351RT; Total work done: W_total = RT·ln(50.5) = 3.922RT; High-voltage section accounted for 40.1%; low-voltage section accounted for 59.9%.

[0066] Adiabatic expansion condition: High-pressure section: Air expands adiabatically from 298K to 2.1MPa (absolute pressure), temperature drops to 190.1K, and work is done by 108.4kJ / kg; Low-pressure section: Air adiabatically expands from 190.1K to 0.2MPa (absolute pressure), the temperature drops to 97.2K, and the work done is 93.3kJ / kg; Total work done: 201.7 kJ / kg; High-voltage section accounted for 53.7%; low-voltage section accounted for 46.3%.

[0067] This shows that even under the typical operating conditions of a hydraulic prime mover at 10 MPa, the low-pressure section still accounts for 59.9% under isothermal conditions; The summary and comparison are as follows: More importantly, the above calculations are based on peak operating conditions with the gas storage facility at full pressure. In actual energy release, the expansion ratio of the high-pressure section will gradually decrease, and the proportion of work done by the high-pressure section will show a monotonically decreasing trend throughout the entire cycle. Under the average operating conditions throughout the entire cycle, the proportion of work done by the high-pressure section will definitely be lower than that under peak operating conditions. Furthermore, when the gas storage pressure decreases from 10 MPa to 7 MPa, the changes in the proportion of work done by the high and low pressure sections are shown in the table below: This further verifies that although the instantaneous pressure of the high-pressure section is high, its cumulative work output over the entire cycle is limited; while the instantaneous pressure of the low-pressure section is low, its cumulative work output over the entire cycle is absolutely dominant. Therefore, matching the high-pressure, low-power section with a low-cost, high-pressure-resistant hydraulic prime mover, and matching the low-pressure, high-power section with a high-efficiency, wide-range-operating-condition expander, fully conforms to the objective laws of energy conversion and achieves the optimal match between equipment investment and power output.

[0068] This thermodynamic law determines the rationality of the division of labor between primary and secondary functions in this application: although the peak pressure of the high-pressure section is high, its proportion of extractable mechanical work over the entire cycle is small; while the peak pressure of the low-pressure section is low, its proportion of extractable mechanical work over the entire cycle is large. Therefore, setting the main power generation unit to account for more than 60% of the total rated power of the system has sufficient thermodynamic basis and allows for engineering margins.

[0069] 4. Timing matching and venting pressure linkage control principle: Existing solutions use "expansion ratio" or "fixed liquid level" as the core indicators for valve closure determination. However, these indicators cannot directly reflect the actual operating constraints of the engineering system and do not consider the full utilization of the working tank volume and the optimized balance of switching frequency.

[0070] The dynamic matching algorithm in this application aims to fully utilize the effective volume of the work tank and reduce the number of switching operations. Based on the ideal gas law, it calculates the expansion endpoint state in real time: according to the shape and size of the work tank and the expected liquid level at the end of expansion, it calculates the total gas volume Ve, the expansion endpoint pressure Pe, and the temperature Te at the expansion endpoint, where Pe ≥ the working pressure Pl of the intermediate pressure buffer unit to ensure smooth gas release; it also collects the current tank pressure P1, temperature T1, and liquid level h1 in real time, and calculates the current gas volume V1 using the liquid level h1. When P1V1 / T1 = PeVe / Te, the main valve is closed. This algorithm maximizes the liquid discharge volume per work cycle and minimizes the switching frequency.

[0071] Simultaneously, a minimum safe liquid level is set as a rigid protection threshold: if the liquid level in the tank drops to the minimum safe liquid level but the expansion endpoint condition has not been met, an emergency valve closure and switching are executed to prevent gas from entering the hydraulic prime mover. The control unit also has a parameter adaptive correction function, dynamically optimizing the expansion endpoint parameters based on actual operating deviations, continuously approaching the optimal operating state throughout its entire life cycle.

[0072] 5. Bidirectional real-time balanced voltage regulation principle: This application, through the coordinated regulation of the hydraulic prime mover's flow rate and the expander's load, keeps the pressure of the intermediate pressure buffer unit within the upper and lower limits of the expander's efficient operating range. When the pressure of the intermediate pressure buffer unit is higher than the set value, the load of the hydraulic prime mover is reduced to supply less air, while the load of the expander is increased (the guide vanes / nozzles are opened to extract more air), and the pressure is reduced by the combined force of the two directions.

[0073] When the pressure of the intermediate pressure buffer unit is lower than the set value, the flow regulation mechanism of the hydraulic prime mover increases the load to discharge more liquid and supply more gas, while reducing the load of the expander (closing the guide vanes / nozzles) to reduce the extraction of gas, thus increasing the pressure through bidirectional combined force.

[0074] This is a flow balance control system: by simultaneously adjusting in opposite directions on both sides, the gas rate entering the intermediate pressure buffer unit is dynamically matched with the expander's pumping rate, thereby locking the intermediate pressure within the expander's high-efficiency range. The two sides automatically balance like a seesaw, fixing the intermediate pressure at a set point or within an extremely narrow range. This bidirectional real-time balanced operation also naturally achieves the gas consumption pattern of low gas volume at high pressure and high gas volume at low pressure: when the storage pressure is high and the intermediate pressure approaches the lower limit, the expander's expansion ratio is large, its work capacity is strong, and its gas consumption per unit power is low; when the storage pressure is low and the intermediate pressure approaches the upper limit, the expander's expansion ratio is small, its work capacity is weak, and its gas consumption per unit power increases. This pattern matches the natural decay characteristics of the storage pressure, allowing for more efficient gas usage in the high-pressure section and more efficient usage in the low-pressure section, achieving optimal gas volume distribution throughout the entire cycle without additional control.

[0075] 6. Principle of zero-pressure differential liquid return and efficient transfer of residual energy: In traditional solutions, the expansion endpoint pressure of the work tank must be higher than the working pressure of the low-pressure gas storage unit by a pressure differential margin. Before liquid return, gas must be released or pumped to overcome this margin. This application uses dynamic valve closure control to precisely lock the expansion endpoint pressure to a level close to the current intermediate pressure buffer unit's working pressure.

[0076] At this point, the vent valve at the top of the working tank and the connecting valve to the intermediate pressure buffer unit are opened. With the pressures on both sides essentially equal, the gas flows naturally under zero pressure difference. The gas from the initial expansion in the working tank is completely replaced by the intermediate pressure buffer unit, supplying gas to the expander. The expansion work is then recovered by the low-pressure expander, achieving secondary utilization of the energy from the high-pressure expansion. Subsequently, the return pump is started or gravity is used for return, and the liquid flows back to the working tank under zero back pressure. This process achieves efficient transfer of secondary expansion capacity and zero-pressure-difference drive for the return process.

[0077] To minimize losses, the pressure at the expansion endpoint should be set as low as possible (close to the pressure of the intermediate pressure buffer unit plus the minimum working pressure difference of the hydraulic prime mover). However, in practical engineering, the pressure can be set higher to increase the circulation speed of the power tank. Under the condition that the hydraulic prime mover still has the capacity to perform work at the end of the expansion, the expansion work of the high-pressure section should be utilized as much as possible.

[0078] Although expansion losses are unavoidable, they are far lower than the gas release losses near atmospheric pressure. From the perspective of the second law of thermodynamics, the essence of the aforementioned liquid return dilemma is the irreversible degradation of available energy (ν), and the degree of this degradation is directly related to the liquid return reference pressure. Under a high-pressure liquid return reference (e.g., 4.0 MPa gauge pressure), the irreversible loss corresponding to the same 0.3 MPa pressure differential margin is only RT0ln(4.4 / 4.1)≈6.2 kJ / kg, and the gas still retains a high-pressure ν of 315.5 kJ / kg after equilibrium, directly entering the intermediate pressure buffer unit as the expander gas source. As mentioned earlier, under an atmospheric pressure liquid return reference, the ν loss corresponding to the same 0.3 MPa pressure differential margin is approximately 119.4 kJ / kg, and the residual gas pressure ν returns to zero. In contrast, this application uses the pressure of the intermediate pressure buffer unit as the liquid return reference, which can significantly reduce the liquid return loss compared with the traditional atmospheric pressure liquid return method, and fundamentally reduce the irreversible degradation of residual gas from the high pressure level to the low pressure level.

[0079] 7. Expander reverse adjustment and stabilizing anchor principle: This application's expander control does not aim to track intermediate pressure, but rather uses the system's output grid-connected frequency and power as the ultimate goal for reverse regulation. The process involves monitoring grid-connected parameters → adjusting the expander guide vanes / nozzles → stabilizing power output quality. Taking a typical operating condition of 10MPa-level gas storage (absolute pressure 10.1MPa), intermediate pressure 4MPa (absolute pressure 4.1MPa), and back pressure 0.05MPa gauge pressure (absolute pressure 0.15MPa) as an example, two energy release strategies are analyzed: Strategy 1 (shallow discharge, high power, short duration): Energy release stops when the gas storage tank pressure reaches 6.1MPa. The total system power is based on the output power at 6.1MPa in the gas storage tank as the grid-connected power benchmark. During energy release, the expander output smoothly transitions from 84.8% initially (when the hydraulic side is at full power) to 100% at the end (when the hydraulic side is deactivated). The adjustment range based on the expander's highest value is only 15.2%, completely within the narrow operating condition high-efficiency range. The gas release ratio is 39.6%, suitable for high-power, short-duration discharge scenarios. Strategy Two (Deep Discharge, Low Power, Long Duration): Energy release stops when the gas tank pressure reaches 4.1 MPa (hydraulic side completely disconnected). The total system power is based on the output power of the expander when it operates alone. During energy release, the expander output transitions from 72.7% initially to 100% at the end, an adjustment range of 27.3%, still within the narrow operating condition high-efficiency range. The gas release ratio is 59.4%, and the total energy is 1.34 times that of Strategy One, suitable for long-duration discharge scenarios. Therefore, the expander acts as the system's "stabilizing anchor," and its adjustment range is naturally constrained by the upper limit of the hydraulic side's proportion, without needing to cover wide operating condition drift. Within the narrow operating condition high-efficiency range, only minute adjustments at the second level are needed to completely absorb residual fluctuations on the hydraulic side. Due to stable intake conditions, the expander's operating point is rigidly locked at the center of the high-efficiency range, significantly compressing the surge margin, and allowing the back pressure to be designed to a very low level.

[0080] 8. Principle of Two-Layer Wave Suppression: The first layer is a gas-capacity passive buffer: the intermediate pressure buffer unit has sufficient gas phase volume to absorb and convert the periodic flow fluctuations on the hydraulic side into extremely small pressure pulsations.

[0081] The second layer is hydraulic active fine-tuning: the flow regulation mechanism of each hydraulic prime mover adjusts in coordination according to the real-time fluctuation trend of the intermediate pressure. When the intermediate pressure is too high, the flow rate is reduced to slow down the intake pressure drop, and when it is too low, the flow rate is increased to accelerate the intake pressure rise, further compressing the fluctuations within the range that the expander can adaptively absorb.

[0082] 9. Principle of equivalent atmospheric environment for pressure-bearing shell: After performing work, the liquid from an impulse turbine needs to be discharged into an intermediate pressure buffer unit with a higher operating pressure. If the turbine is installed directly in an atmospheric pressure environment, its outlet back pressure must overcome the high-pressure back pressure to discharge the liquid, resulting in a sharp increase in runner outlet pressure loss and a drastic drop in hydraulic efficiency. This application installs each impulse turbine within the gas space inside the intermediate pressure buffer unit, or encapsulates it entirely in a pressure-bearing shell connected to the intermediate pressure buffer unit, so that the turbine's operating environment pressure follows the intermediate pressure buffer unit's operating pressure in real time, forming an equivalent atmospheric operating environment. When the turbine operates in this environment, its outlet liquid naturally flows into the same pressure environment, and the flow channel design completely follows the conventional turbine hydraulic model.

[0083] This design allows the pressure at the end of the expansion of the working tank to drop to a level only slightly higher than the working pressure of the intermediate pressure buffer unit, resulting in more complete gas expansion and a significant improvement in the utilization rate of the high-pressure gas storage volume.

[0084] 10. Principle of parallel connection of split-shaft speed-changing constant frequency electrical circuit: The efficient operation of impulse turbines relies heavily on the optimal speed ratio. This application employs a split-shaft independent arrangement: each turbine has its own independent shaft system, independent variable frequency generator, and independent turbine-side converter. The turbine-side converter adaptively adjusts the speed based on real-time head to maintain the optimal speed ratio. The turbine-side converter rectifies the variable frequency AC power from each generator into DC power, which is then fed into a common DC bus. Since there is no frequency concept on the DC side, the speed differences between the turbines are naturally eliminated during rectification. The power is then connected to the grid at a constant frequency via a unified grid-side converter. The grid side only perceives the constant output of a single standard converter.

[0085] 11. Principle of work tank cycle scheduling: This application provides various configuration and scheduling schemes for power tanks and hydraulic prime movers: single tank per machine, dual tanks sharing a single machine, and multiple tanks operating in rotation or in groups. A single tank achieves fluctuating output through a cycle of power-return-power; dual tanks achieve alternating operation by controlling a high-pressure intake valve, allowing both tanks to share a single hydraulic prime mover; multiple tanks adopt a cyclical operation mode of power-return-standby-power, alternating in rotation. The core purpose of the multi-tank configuration is to ensure continuous system operation. Pressure stabilization is entirely handled by the gas-capacity buffer of the intermediate pressure buffer unit and the fine-tuning of the expander. The number of power tanks is not necessarily related to stable output performance.

[0086] 12. Modification of applications and shallow discharge strategies or principles for improving discharge capacity: This application applies to both new systems and upgrades of existing compressed air energy storage power stations. A gas-liquid power generation unit, an intermediate pressure buffer unit, and a high-pressure hydraulic power generation unit are connected in series or parallel between the existing high-pressure gas storage unit and the expander. The original expander continues to operate as a low-pressure section, with intake conditions locked within a narrow, high-efficiency operating range. Back pressure can be lowered, and the expansion work from the high-pressure section is recovered on the hydraulic side. The existing gas storage facilities are 100% retained; the expander itself is retained, requiring only adjustments to the control logic. This can be implemented using an energy performance contracting model.

[0087] After modification, a shallow discharge strategy can be adopted: each discharge retains a relatively high final pressure, without complete deep discharge. Due to the improved system efficiency, shallow discharge can meet the output requirements, and the retained high-pressure gas saves the compression energy consumption for the next refill (the high-pressure section has the highest compression energy consumption), significantly improving the cycle efficiency.

[0088] The upgraded discharge energy enhancement strategy retains the original termination pressure and discharge depth for each discharge. Due to improved system efficiency, higher output demands can be met, providing an economically viable basis for applying to expand energy storage capacity or power generation duration.

[0089] 13. Principle of cascade matching and non-throttling of heterogeneous equipment: Existing compressed air energy storage systems generally employ a direct expansion mode for high-pressure gas. Taking the expansion from 10MPa storage pressure to atmospheric pressure as an example, the single-stage expansion ratio is as high as 100:1, far exceeding the optimal expansion ratio range of a centripetal turbine expander. The actual isentropic efficiency decreases by 10-15 percentage points compared to the design conditions, and the high-pressure intake causes severe erosion of the impeller. If a multi-stage turbine expansion is adopted, reheaters must be installed between stages for heat replenishment, significantly increasing system complexity, equipment investment, and heat loss. More seriously, when the storage pressure (e.g., 25MPa) is much higher than the expander's rated intake pressure (e.g., 10MPa), existing systems generally use throttle valves to reduce pressure, resulting in a direct loss of more than 30% of the available pressure energy.

[0090] Based on the differences in energy conversion characteristics across different pressure ranges, this application employs a tiered matching strategy for heterogeneous equipment: the high-pressure range features high gas density and potential energy, making it suitable for hydraulic prime movers (hydraulic motors / turbines), fully utilizing the high efficiency and standardization advantages of hydraulic equipment under high-pressure conditions; the low-pressure range features a large gas expansion ratio and high flow velocity, making it suitable for adjustable expanders (screw expanders / turbine expanders), leveraging the expander's load regulation capabilities and work efficiency across a wide operating range. The two stages of equipment complement each other in terms of pressure-efficiency characteristics, eliminating the need for throttling valves throughout the process and avoiding irreversible throttling losses.

[0091] 14. The synergistic effect principle of three-stage heat replenishment: The temperature drop during the adiabatic expansion of air is a key factor limiting system efficiency. This application incorporates a three-stage heat compensation system: First stage (high-pressure closed expansion stage): Hot fluid is sprayed into the gas-liquid working tank through the top atomizing spray nozzle to directly exchange heat and mass with the high-pressure gas, compensating for the temperature drop during the closed expansion stage; the gas can also be heated by a heat exchanger before entering the working tank; or both methods can be used simultaneously.

[0092] Second stage (heat replenishment in intermediate pressure buffer unit): Hot fluid is sprayed into the intermediate pressure buffer unit through the top atomizing spray nozzle to directly exchange heat and mass with the gas in the tank, thereby increasing the temperature of the gas entering the expander. The third stage (low-pressure dynamic expansion stage): The gas is reheated through heat exchange at the expander inlet and between stages. If a screw expander is used, the hot fluid can also be directly injected into the compression chamber or interstage chamber to continuously replenish heat during rotor meshing expansion, thus alleviating the temperature drop during low-pressure expansion.

[0093] The three-stage heat exchange system precisely addresses the thermodynamic characteristics of the high-pressure and low-pressure sections: the high-pressure section has high gas density and specific heat capacity, making it suitable for high-flow-rate spray heat exchange; the low-pressure section has high gas velocity and short residence time, making it suitable for direct injection into the screw expander chamber for thorough mixing with the gas; and under conditions where injection is not possible, heat exchange is achieved through a heat exchanger. The three-stage synergy can maintain the average temperature of the entire expansion process at a high level, systematically improving power generation efficiency.

[0094] 15. Functional topology reconfiguration principle: Existing gas-liquid coupled compressed air energy storage systems exhibit a mismatched topology, characterized by "high-pressure hydraulics as the primary method and low-pressure expansion as a secondary method," or even "high-pressure direct throttling and waste." This stems from the fact that in existing gas-liquid hybrid storage schemes, a large amount of incompressible liquid occupies the high-pressure container space, resulting in a small gas capacity and limited energy storage. This contradicts the characteristics of low energy release under high pressure differentials and high energy release under low pressure differentials and high pressure differentials. This application fundamentally reconstructs the system's functional topology based on the nonlinear characteristics of the gas state equation W=RT·ln(P1 / P2): Energy flow topology: High-pressure section (25-10MPa) → hydraulic prime mover (auxiliary power generation, accounting for 0%-40% of total rated power); Low-pressure section (10-0.5MPa) → expander (main power generation, accounting for 60%-100% of total rated power). This topology ensures a high degree of matching between equipment capacity and power distribution, avoiding the waste of expensive expanders in high-pressure, low-expansion-ratio sections, or the irreversible loss of high-pressure energy through throttling valves.

[0095] Temporal topology: The high-pressure gas storage unit and the gas-liquid work unit are "time-sharing coupled," connected only through controllable valves during the energy release and work phase, and completely decoupled during the energy storage phase. The high-pressure gas storage unit is 100% dedicated to storing high-pressure compressed gas, while the gas-liquid work unit serves only as a short-term coupled work chamber. This topology completely overturns the inherent architecture of existing schemes that "store gas and liquid together in the same container for a long period of time."

[0096] The pressure stabilization topology consists of three stages: front-end hydraulic equipment providing "purely passive natural power output" → back-end expander providing "full-power steady-state regulation" → inertial flywheel filling "transient gaps." Existing solutions rely on frequent switching of multiple tanks or continuous high-power compensation from power electronic devices, resulting in complex, costly, and short-life pressure stabilization topologies. This application concentrates the pressure stabilization function entirely in the back-end expander, requiring only 2-3 sets of small-volume working tanks at the front end to ensure continuous gas supply, making the pressure stabilization topology extremely simple and reliable.

[0097] Waste energy flow topology: Expansion exhaust gas waste cooling → cooling heat exchange components → turbine secondary waste cooling → cold storage or cooling supply; Turbine supercharging waste heat → heating heat exchange components → heat storage or heating supply; Surplus heat → thermal storage unit → supplementary heat loop. This topology realizes energy cascade utilization and closed-loop recovery, breaking the linear energy flow of traditional energy storage and single power generation.

[0098] The aforementioned functional topology reconstruction fundamentally solves the structural defects of the existing gas-liquid coupling scheme, which features "co-storage of gas and liquid, multi-tank pressure stabilization, high pressure as the main factor, and residual energy venting," resulting in a significant improvement in system efficiency, stability, and economy.

[0099] 16. Principle of isolated differential pressure reset: When the working tank uses a piston-type or diaphragm-type isolation structure, after expansion, the gas pressure inside the tank drops to balance with the pressure of the intermediate pressure buffer unit. During this process, a pressure difference exists between the back pressure on the outlet side of the hydraulic prime mover and the gas back pressure of the intermediate pressure buffer unit. This pressure difference acts on the effective area of ​​the piston or diaphragm, forming a reset thrust that pushes the isolation component to move, increasing the liquid chamber volume. Under the action of the pressure difference, liquid flows into the working tank's liquid chamber, completing the return liquid reset. This process requires no external pumping and relies entirely on the internal pressure difference of the system, resulting in zero energy consumption. The control unit monitors the total liquid volume of the two working tanks (for piston-type tanks, it monitors the sum of the two piston heights). When the volume deviates from the set value, the auxiliary liquid replenishment module replenishes the liquid to ensure a constant system liquid volume.

[0100] 17. Two-stage compression principle in the energy storage stage: The intermediate pressure buffer unit in this application not only plays a stabilizing role during the energy release phase, but also serves as an intermediate pressure stabilizing node during the compression process in the energy storage phase, achieving bidirectional operational isolation between storage and release. The compression process in the energy storage phase is divided into two stages: The first stage of compression compresses atmospheric air to the operating pressure of the intermediate pressure buffer unit (e.g., 4 MPa). Since both the intake (atmospheric pressure) and exhaust (intermediate pressure buffer unit lock-in pressure) are stable, this stage of the compressor can always operate at its design efficiency peak, with an isentropic efficiency of 85%–88%, and does not require frequent adjustments to match downstream fluctuations.

[0101] The second stage of compression compresses the air in the intermediate pressure buffer unit to the pressure of the high-pressure gas storage unit (e.g., 20 MPa). Although the operating conditions change as the gas storage pressure increases, the pressure ratio decreases from the total pressure ratio of 200 to the second stage pressure ratio of 5, significantly increasing the surge margin and greatly improving operational safety; even if it deviates from the design point, it is not easy to enter the surge zone.

[0102] Calculated using the polytropic compression work formula, the first stage of compression work (0.1→4MPa) accounts for over 70% of the total compression work, and its efficient operation significantly contributes to the system's round-trip efficiency. The second stage of compression work (4→20MPa) accounts for less than 30%, and even though its efficiency is slightly lower, its impact on the overall system is limited. The intermediate pressure buffer unit's gas-capacity buffering function during the energy storage stage decouples the two compressor stages, with the first stage operating at a constant full load and the second stage adjusting as needed, thus systematically improving energy storage efficiency and equipment utilization.

[0103] Compared with the prior art, this application has at least the following advantages: 1. Maximize the utilization rate of high-pressure volume. Adopting a functionally separate high-pressure gas storage unit and gas-liquid working unit, no liquid enters the high-pressure gas storage tank throughout the process, and the entire high-pressure volume is used to store high-pressure gas. Under the same cost of high-pressure containers, the gas storage capacity and energy storage capacity are maximized to achieve the utilization rate of high-pressure gas storage volume.

[0104] 2. Pressure stabilization and continuous operation are completely decoupled. The system's pressure stabilization function is entirely undertaken by the downstream wide-condition expander, and a single small-capacity working tank can achieve stable output; only a small number of working tanks need to operate alternately to achieve continuous and uninterrupted gas and liquid supply, significantly reducing the total number of high-pressure bearing components.

[0105] 3. Precise timing matching of the working tank ensures high operational continuity. Employing a multi-parameter linkage dynamic valve-closing algorithm, the system tracks the current liquid discharge progress of the working tank and the recharge progress of the standby tank in real time. This ensures that the time deviation between the two tanks is controlled within seconds, and the switching interval can be flexibly set according to requirements. For small-capacity distributed scenarios, this can be set to the minute level, while for large-scale, long-term energy storage scenarios, it can be extended to over one hour. This completely eliminates the timing mismatch problem of "working tank waiting for recharge" or "recharge tank waiting idly" caused by large parameter variations and complex multi-tank control, significantly improving the reliability of continuous system operation.

[0106] 4. Smooth venting with no residue and high circulation efficiency. The expansion endpoint pressure and the intermediate pressure buffer unit working pressure are rigidly linked to ensure that residual gas in the tank can be smoothly discharged after each cycle of liquid drainage, without any effective volume loss due to gas retention.

[0107] 5. Flexible selection of hydraulic equipment with strong closed-loop adaptability. For small-scale energy storage, auxiliary power generation units should prioritize the use of positive displacement hydraulic prime movers such as hydraulic motors, which have a high degree of standardization, stable efficiency, and a complete maintenance system under high pressure, variable flow, and back pressure closed-loop return fluid conditions. For large-scale energy storage, water turbines are preferred to achieve high power output.

[0108] 6. Three-stage heat compensation and efficiency enhancement throughout the entire expansion process. The three stages of operation—high-pressure expansion, expansion intake, and low-pressure dynamic expansion—are optimized to systematically improve the air insulation and cooling problem.

[0109] 7. The control architecture is streamlined and reliable. The front-end auxiliary hydraulic prime mover accounts for a small proportion of the work and does not require complex adjustment for forced stabilization; the load regulation and pressure stabilization are mainly completed by the back-end expander. There are fewer control links and fewer failure points, and the fluctuation of the total output frequency of the system can be controlled within ±0.5Hz.

[0110] 8. Combined cooling, heating and power (CCHP) maximizes comprehensive utilization value. It fully recovers the waste cooling from expansion exhaust gas and the waste pressure and heat from turbines, achieving free cooling and zero-carbon heating, breaking the traditional profit model of energy storage and single power generation.

[0111] 9. Adaptable to all scenarios and regions. It is not limited by power scale, gas storage form, or water source. It can be directly applied to the upgrading and transformation of traditional large-scale salt cavern / rock cave compressed air energy storage power stations. It can also be implemented in distributed small and medium-sized energy storage scenarios such as parks and factories by relying on conventional high-pressure storage tanks and CNG gas storage wells.

[0112] 10. Throttling losses are largely eliminated, ensuring full utilization of high-pressure investment. The mismatch in pressure levels between the high-pressure gas storage unit and the expander leads to throttling losses. This application directly recovers the pressure energy of the high-pressure section through a gas-liquid work unit, eliminating the need for throttling valves throughout the process (only a small differential pressure loss occurs during the minimum operation of the motor or turbine). Every unit of investment in the high-pressure gas storage container corresponds to effective energy storage capacity, significantly improving the overall energy conversion efficiency and economy of the system.

[0113] 11. Adhering to the thermodynamic work distribution law, the equipment capacity and work distribution are optimally matched. The expansion work W=RT·ln(P1 / P2), determined by the gas law, has nonlinear characteristics, with the low-pressure, high-expansion-ratio segment accounting for the absolute majority of the total work. Taking 25MPa gauge pressure → 4MPa gauge pressure → 0.1MPa gauge pressure as an example, under isothermal conditions, the low-pressure segment accounts for 62.5% (peak) / 71% (average), and under adiabatic conditions, it also accounts for 46.0% (peak). Taking 10MPa gauge pressure → 2MPa gauge pressure → 0.1MPa gauge pressure as an example, under isothermal conditions, the low-pressure segment accounts for 59.9% (peak) / 70.5% (average). This application matches the high-pressure, low-work-rate segment with low-cost hydraulic equipment and the low-pressure, high-work-rate segment with a high-efficiency expander, avoiding the waste of expensive wide-condition expanders in the high-pressure, low-expansion-ratio segment. The equipment investment and work output are highly matched, and the system's economic efficiency is significantly better than traditional solutions.

[0114] 12. This application effectively suppresses the power fluctuation caused by gas storage pressure decay and multi-tank switching through a two-layer synergy of "timing matching to reduce switching impact + expander to ensure steady state", thus significantly improving power quality.

[0115] 13. Compression efficiency is simultaneously improved during the energy storage stage. The intermediate pressure buffer unit acts as a pressure stabilization node during the energy storage stage, dividing the compression process into a first stage (atmospheric pressure → intermediate pressure) and a second stage (intermediate pressure → high-pressure gas storage). The first-stage compressor operates under stable conditions with efficiency close to the design peak; the second-stage pressure ratio is significantly reduced, increasing surge margin. The first-stage compression work accounts for approximately 70% of the total compression work, and its efficient operation systematically improves the system's round-trip efficiency.

[0116] Summary of advantages of this application: Regarding high-pressure gas storage volume utilization, this application adopts a gas-liquid separation architecture, ensuring no liquid enters the high-pressure gas storage unit throughout the process. Regarding the number of high-pressure working tanks, this application requires only a small number of working tanks operating alternately, with the downstream expander handling all pressure stabilization. Regarding system pressure stabilization dependence, this application relies entirely on the expander for pressure stabilization, with only a small number of small-volume working tanks at the front end ensuring continuous gas supply, resulting in a highly simple and reliable pressure stabilization topology. Regarding power distribution and equipment matching, this application follows the thermodynamic law that work is absolutely dominant in the low-pressure, high-expansion-ratio section. The high-pressure section is matched with a hydraulic prime mover, and the low-pressure section with an expander, achieving a high degree of matching between equipment investment and power output. Regarding the heat compensation stage, this application employs a three-stage heat compensation (high-pressure sealed + expansion inlet + low-pressure power) spray and heat exchange method, precisely targeting the thermodynamic characteristics of the high-pressure and low-pressure sections to systematically improve efficiency. In terms of minimum economic installed capacity, this application benefits from dual-tank rapid switching and expander full-power pressure stabilization, and the minimum economic scale can be reduced to 100kW, which is suitable for distributed scenarios such as parks and factories. Example 2

[0117] This embodiment 2 uses a small-scale park distributed energy storage system (isolated working tank + hydraulic motor + screw expander) as an example to illustrate the solution of this application.

[0118] It should be noted that in small-scale distributed energy storage scenarios, CNG underground gas wells are used as high-pressure gas storage units, with storage pressures reaching up to 25 MPa (gauge pressure), while the rated inlet pressure of conventional screw expanders is only 3-5 MPa. Existing technologies generally use throttle valves to reduce the pressure of the high-pressure gas to an acceptable range for the expander, resulting in the irreversible dissipation of a large amount of usable energy in the high-pressure section. Simultaneously, the gas pressure continuously decreases during energy release, forcing the expander to operate under a wide range of conditions, increasing the back pressure design, and causing a significant amount of usable energy in the low-pressure section to be wasted.

[0119] refer to Figure 3 As shown, the pure compressed air energy storage staged expansion gas-liquid coupling stable output device provided in this embodiment 2 includes: a high-pressure gas storage unit 11, a compressor 12, a compression heat recovery device 13, an external heating device 14, a heat storage device 15, a circulating heat pump 16, a heating unit 17, a turbocharger 18, a cooling unit 19, a gas-liquid separator 110, a generator 111, a secondary expander 112, a primary expander 113, a second heat exchanger 114, a filter separator 115, an intermediate pressure buffer unit 116, a vent valve 117, a high-pressure inlet valve 118, a power tank 119 (piston-type hydraulic accumulator), a piston 120, a one-way valve 121, a hydraulic motor 122, a generator 123, and a first heat exchanger 124.

[0120] In this embodiment, the high-pressure gas storage unit 11 adopts a 22m³ CNG underground gas storage well with a rated working pressure of 25MPa (gauge pressure) and an absolute pressure of 25.1MPa. The working pressure of the intermediate pressure buffer unit 115 is dynamically adjusted between 3.0MPa (gauge pressure, 3.1MPa absolute pressure) and 4.0MPa (gauge pressure, 4.1MPa absolute pressure), which is located within the high-efficiency working range of the screw expander. The expander back pressure is set to 0.05MPa (gauge pressure) and 0.15MPa absolute pressure, fully utilizing the non-surge structural advantage of the screw expander. The target energy release time is 3 hours, and the total system output power is set to 100kW.

[0121] The high-pressure gas storage unit and the gas-liquid work unit are functionally separated: the high-pressure gas storage unit 11 and the gas-liquid work unit are arranged independently. No liquid enters the high-pressure gas storage unit 11 throughout the entire process, and its 22m³ volume is entirely used to store high-pressure compressed gas, maximizing the utilization rate of the gas storage volume. The work tank 119 of the gas-liquid work unit is only connected to the high-pressure gas storage unit 11 during the energy release and work phase through the high-pressure air inlet valve 118.

[0122] Configuration of the gas-liquid working unit: This embodiment adopts an isolated working tank structure. The working tank 119 is a piston-type hydraulic accumulator with an internal piston 120 to achieve gas-liquid isolation. Two working tanks 119 are arranged as a group, each group driving one hydraulic motor 122. Each working tank 119 has two one-way valves 121 at its bottom, one connected to the inlet of the hydraulic motor 122 and the other to the outlet of the hydraulic motor 122, automatically opening and closing according to the pressure difference between the two working tanks. Liquid in the high-pressure working tank flows into the inlet of the hydraulic motor 122 under gas pressure, while liquid at the outlet of the hydraulic motor 122 flows into the low-pressure return tank. This embodiment sets up two groups of isolated working tanks, totaling four working tanks 119 and two hydraulic motors 122, which work alternately. The two hydraulic motors 122 drive the generator 123 through a rigid parallel connection on the coaxial axis.

[0123] The hydraulic motor 122 is equipped with an independently controllable variable displacement mechanism (swashplate / swashplate / eccentric cylinder), which achieves constant speed and variable flow operation by adjusting the displacement. In the initial stage of energy release, the gas storage pressure is around 25 MPa, and the working pressure of the intermediate pressure buffer unit 116 is 3.0 MPa (gauge pressure). The hydraulic pressure differential is 22 MPa, providing strong work capacity. By partially closing the variable displacement mechanism, the flow rate is limited, maintaining the power within the target range while controlling gas consumption to prevent intermediate pressure surges. In the final stage of energy release, the gas storage pressure decreases to around 11 MPa, and the working pressure of the intermediate pressure buffer unit 116 is increased to 4.0 MPa (gauge pressure). The hydraulic pressure differential is 7.1 MPa, and the variable displacement mechanism is fully opened to increase the flow rate, maintaining the total gas supply to ensure the expander's intake.

[0124] The system also includes an auxiliary fluid replenishment module, comprising a storage tank, a replenishment pump, and valves, used to compensate for leakage from piston 120 and hydraulic motor 122, maintaining a constant total fluid volume in the two working tanks. Multiple auxiliary fluid replenishment modules can be shared.

[0125] Intermediate pressure buffer unit design: The intermediate pressure buffer unit 116 is a gas-liquid coexistence container. Its gas phase volume is designed to be 8 times the volume of the working tank during a single expansion. This can suppress pressure fluctuations caused by switching between single tanks to within ±6%, which is within the adaptive adjustment range of the screw expander. The working pressure of the intermediate pressure buffer unit 115 is 3.0~4.0MPa (gauge pressure), which is the same range as the inlet pressure of the screw expander. The expansion ratio range is 20.7~27.3.

[0126] Low-pressure expansion power generation unit: Employs a screw expander, consisting of a primary expander 113 and a secondary expander 112. The screw expander inlet pressure is 3.0–4.0 MPa (gauge pressure), the back pressure is 0.05 MPa (gauge pressure), and the isentropic efficiency is 75%. The screw expander drives the generator 111. The expander's inlet and outlet are equipped with an inlet filter separator 115 and a tail gas-liquid separator 110, respectively, to separate liquid components from the gas. Furthermore, the gas-liquid separator 110 also collects liquid for recycling to the heat storage module for reheating the expansion module.

[0127] Dynamic valve closing control: The dynamic valve closing module in the control unit collects the instantaneous pressure P1, instantaneous temperature T1, and liquid level h1 in the working tank 119 in real time (in this embodiment, the liquid level is determined by monitoring the position of piston 120). The current gas volume V1 is calculated based on the liquid level h1. The total gas volume Ve at the expansion endpoint is calculated based on the shape and size of the working tank 119 and the expected liquid level at the end of expansion, and combined with the expansion endpoint pressure Pe and temperature Te. Wherein, the expansion endpoint pressure Pe = the working pressure of the intermediate pressure buffer unit + the minimum working pressure difference of the hydraulic motor (e.g., Pe = 3.05MPa gauge pressure). When P1V1 / T1 = PeVe / Te, the dynamic valve closing module commands the high-pressure inlet valve 118 to close, so that the working tank 119 forms a sealed expansion chamber. The gas continues to expand in the chamber, pushing piston 120, and the liquid continues to be discharged, driving hydraulic motor 122 to do work until the expansion endpoint.

[0128] Pressure-free return control: After the isolated working tank completes expansion, the gas pressure inside the tank drops to near equilibrium with the working pressure of the intermediate pressure buffer unit 116. At this time, the pressure-free return module in the control unit instructs the vent valve 117 to open, connecting the working tank 119 to the intermediate pressure buffer unit 116. The residual gas flows into the intermediate pressure buffer unit 116 through the vent valve 117, becoming the expander's gas source. Simultaneously, a pressure difference exists between the back pressure at the outlet side of the hydraulic motor 122 and the gas back pressure of the intermediate pressure buffer unit 116. This pressure difference acts on the effective area of ​​the piston 120, forming a reset thrust that pushes the piston 120 to move, increasing the volume of the liquid chamber. Under the action of the pressure difference, liquid flows from the outlet side of the hydraulic motor 122 into the liquid chamber of the working tank 119, completing the return reset. This process requires no external pumping and relies entirely on the internal pressure difference of the system, resulting in zero energy consumption. After the liquid level exceeds the vent valve 117, the vent valve 117 is closed, the working tank 119 is filled with liquid, and the high-pressure inlet valve is opened to enter the next working cycle, continuing the cycle.

[0129] At the same time, a minimum safe liquid level (monitored by piston position) is set as a rigid protection threshold. If the gas expansion in the working tank 119 does not reach the preset expansion endpoint pressure Pe, but the piston 120 has reached the minimum safe position, the control unit directly closes the high-pressure air inlet valve 118 and opens the vent valve 117. After confirming that the high-pressure air inlet valve 118 is in the closed state, the expansion ends to prevent gas from rushing into the hydraulic motor 122.

[0130] Multi-operation tank coordinated control: The multi-operation tank coordination module in the control unit controls the working sequence of two sets of isolated operation tanks. By controlling the opening time of each set of high-pressure intake valves 118, the two sets of operation tanks alternate or cycle through the operation sequence. The two hydraulic motors 122 coordinately control the output flow through their respective controllable variable mechanisms to reduce power output fluctuations.

[0131] Collaborative pressure stabilization control: The collaborative pressure stabilization module in the control unit monitors the pressure of the intermediate pressure buffer unit 116 in real time. At the initial stage of energy release, the intermediate pressure is 3.0 MPa. If it is too high, the variable mechanism of the hydraulic motor 122 is reduced to supply less air, while the screw expander opens its slide valve to extract more air, resulting in a bidirectional pressure reduction. At the end of energy release, the intermediate pressure is 4.0 MPa. If it is too low, the variable mechanism of the hydraulic motor 122 is opened to supply more air, while the screw expander reduces its slide valve opening to extract less air, resulting in a bidirectional pressure increase. This forms a dual-layer fluctuation suppression mechanism of passive gas-capacity buffering and active hydraulic fine-tuning. Through bidirectional real-time balance between the high-pressure and low-pressure sections, the intermediate pressure is maintained within a small range of 3.0–4.0 MPa (gauge pressure), ensuring stable overall system output.

[0132] Cooperative grid connection control: When the hydraulic motor 122 drives the generator 123 in a variable speed constant frequency mode, the cooperative grid connection module in the control unit rectifies its output power and combines it with the power of the low-voltage expansion power generation unit (generator 111) to form the total output of the system and connect it to the grid.

[0133] Two-stage compression in the energy storage stage: The compressor 12 of the energy storage compression unit in this embodiment needs to meet the requirements of high pressure and low flow rate, and can be set as a two-stage positive displacement compression. The discharge pressure of the first stage compressor is set to 2-4 MPa. In this stage, the pressure rise is low and the pressure ratio is high, so a screw compressor is used. The second stage compresses from 2-4 MPa to 25 MPa, with a high pressure difference and low pressure ratio, and a reciprocating compressor that flexibly adapts to the compression ratio is used. The compression heat recovery device 13 recovers the heat generated during the compression process and stores it in the heat storage device 15. The external heating device 14 can use external heat sources such as solar energy to supplement the heat storage.

[0134] Three-stage heat recovery system: During the energy release and power generation process, the circulating heat pump 16 extracts heat from the heat storage device 15. First-stage heat replenishment: Before the expansion stage of the working tank 119, the hot fluid preheats the high-pressure gas through the first heat exchanger 124. Second-stage heat exchange: A second heat exchanger 114 is used between the intermediate pressure buffer unit 116 and the first-stage expansion to preheat the gas before the second expansion, thereby increasing the temperature of the gas entering the expander. Third-stage heat replenishment: Hot fluid is directly injected into the working chamber of the screw expander to continuously replenish heat during the rotor meshing expansion process, alleviating the temperature drop during expansion in the low-pressure section; at the same time, heat replenishment is carried out between stages through heat exchangers.

[0135] Waste heat recovery and supplementary heating unit: The low-temperature exhaust gas from the expansion power generation unit recovers its cooling capacity through the cooling unit 19. The heat-exchanged exhaust gas drives the turbocharger 18, and the turbine exhaust gas can be further recovered for cooling. The compressor end of the turbocharger 18 compresses ambient air to generate high-temperature compressed air. The high-temperature airflow recovers heat through the heating unit 17 to produce heating hot water and domestic hot water. Excess heat can be reused in the heat storage device 15 and the supplementary heating circuit. The turbocharger 18 is equipped with variable section nozzles, which can adaptively adjust according to the pressure and flow rate of the expansion exhaust gas.

[0136] Parameter adaptive correction: The control unit also has a parameter adaptive correction function. Based on the deviation of the expansion endpoint parameters of the dynamic valve closing module (such as the difference between the actual expansion endpoint pressure and the preset value), the liquid return time deviation of the differential pressure return module, and the pressure regulation deviation of the collaborative pressure stabilizing module, the calculated parameters of expansion endpoint gas volume Ve, expansion endpoint pressure Pe and expansion endpoint temperature Te are dynamically corrected to continuously approach the optimal operating state throughout the entire life cycle.

[0137] Calculation of usable energy from the gas storage well: From 25.1 MPa absolute pressure to 11.2 MPa absolute pressure, the energy released from the gas storage well, calculated using isothermal expansion integration, yields approximately 488.1 MJ of ideal work from hydraulic work in the high-pressure section (25.1 → 11.2 MPa absolute pressure, dynamic expansion from 3.1 → 4.1 MPa absolute pressure in the intermediate section); and approximately 971.4 MJ of ideal work from expansion work in the low-pressure section (expansion from 3.1 → 4.1 MPa absolute pressure to 0.15 MPa absolute pressure). Considering an 85% efficiency for the hydraulic motor, 75% for the screw expander, and 95% for the generator: the actual output of the hydraulic section is approximately 95.2 kWh (average 31.7 kW), the actual output of the expander section is approximately 189.5 kWh (average 63.2 kW), and the total system output is approximately 284.7 kWh. The system is rated to operate at 100 kW for 2.85 hours, or drive 90 kW electrical equipment for more than 3 hours.

[0138] Expander stability anchor characteristics: The total output power of the system is based on the output power of the expander when it is operating alone. During the energy release process, the expander output smoothly transitions from approximately 59.2% initially (when the hydraulic side is at full power, with an intermediate pressure of 3.0 MPa) to approximately 76.7% at the end (when the hydraulic side is attenuating, with an intermediate pressure of 4.0 MPa). The adjustment range based on the expander's highest value is only 17.6%, which is entirely within the narrow operating high-efficiency range of the screw expander.

[0139] Liquid and auxiliary components in the power tank: The liquid in the power tank 119 uses hydraulic oil as the working medium, which is compatible with the sealing system of the hydraulic motor 122 and piston 120. The top of the power tank 119 is provided with an air inlet (connected to the high-pressure air inlet valve 118), an air vent (connected to the air vent valve 117) and a first heat exchanger 124, and the bottom is provided with a liquid outlet (connected to the check valve 121 and the hydraulic prime mover pipeline).

[0140] It should be noted that the system in this embodiment is small in scale and uses hydraulic oil. To save hydraulic oil, the intermediate pressure buffer unit 116 is empty of liquid and adopts a pure dry tank mode. The first two stages of supplementary heating do not use spray heating, but use heat exchangers. For the small scale, heat exchangers are sufficient and there is no need to set up spray heating.

[0141] This implementation uses a functional separation architecture to utilize the entire volume of the 22m³ CNG storage well for storing high-pressure gas. A combination of an isolated working tank and a hydraulic motor ensures full extraction of expansion work in the high-pressure section. Zero-energy piston resetting and liquid return are achieved through internal system pressure differential. Residual gas is efficiently transferred to an intermediate pressure buffer unit to become the gas source for the screw expander. The screw expander operates stably within an intake range of 3.0–4.0 MPa, with back pressure dropping to 0.05 MPa (gauge pressure). There is no throttling loss throughout the process, and the total system output remains stable at 90–100 kW. The minimum economical installed capacity is reduced to the 100 kW level, making it suitable for distributed scenarios such as industrial parks and factories. Example 3

[0142] This embodiment 3 uses a large-scale artificial chamber energy storage system (non-isolated working tank + impulse turbine + turbine expander) as an example to illustrate the solution of this application.

[0143] It should be noted that in inland areas without salt cavern geological conditions, artificial hard rock chambers are used as high-pressure gas storage units, with large gas storage scales (200,000 m³ level) and system rated power reaching 100MW level. Existing technologies face more prominent contradictions in large-scale scenarios: the gas storage pressure in constant-volume chambers continuously and significantly decreases during long-term energy release, forcing the expander to operate under extremely wide operating conditions, and the power loss in the low-pressure section caused by the increased back pressure design is extremely large in absolute terms in large-scale systems; at the same time, if the pressure energy in the high-pressure section is reduced through a throttling valve, the usable energy lost in a 100MW-level system can reach tens of megawatt-hours.

[0144] Reference Figure 4 As shown, the pure compressed air energy storage staged expansion gas-liquid coupling stable output device provided in this embodiment 3 includes: a high-pressure gas storage unit 21, a two-stage compressor 22, a one-stage compressor 23, a compression heat recovery device 24, an external heating device 25, a heat storage device 26, a heat extraction circulation pump 27, an intermediate pressure buffer unit 28, a hot spray 29, a return liquid pump and a one-way valve 210, a gas-liquid separator 211, a first-stage expansion 212, an interstage heat exchanger 213, a second-stage expansion 214, a generator 215, a cooling unit 216, a turbocharger 217, a heating unit 218, a water turbine 219 (in the container), a variable frequency generator 220, a venting valve 221, a power tank 222, a high-pressure gas supply valve 223, and a spray valve 224.

[0145] In this embodiment, the high-pressure gas storage unit 21 adopts a 200,000 m³ artificial hard rock chamber, with a designed gas storage pressure of 10 MPa (gauge pressure) and an absolute pressure of 10.1 MPa. The working pressure of the intermediate pressure buffer unit 28 is dynamically adjusted between 4.0 MPa (gauge pressure, absolute pressure 4.1 MPa) and 4.5 MPa (gauge pressure, absolute pressure 4.6 MPa), located within the high-efficiency operating range of the turbine expander. The expander back pressure is set at 0.05 MPa (gauge pressure) and 0.15 MPa (absolute pressure). The heat replenishment method adopts gas-heat co-storage (compression heat recovery + solar thermal collector external heat source), and the polytropic index n≈1.1 during the expansion process. The target energy release time is 6 hours, and the total system output power is set at 100 MW.

[0146] The high-pressure gas storage unit and the gas-liquid work unit are functionally separated: the high-pressure gas storage unit 21 and the gas-liquid work unit are arranged independently. No liquid enters the high-pressure gas storage unit 21 throughout its operation, and the entire 200,000 m³ chamber volume is used to store high-pressure compressed gas. The work tank 222 of the gas-liquid work unit is only connected to the high-pressure gas storage unit 21 during the energy release and work phase via a high-pressure gas supply valve 223. The tank volume of the work tank 222 is much smaller than the total volume of the high-pressure gas storage unit 21; the liquid medium exists only in the gas-liquid work unit, the intermediate pressure buffer unit 28, and the connecting pipelines.

[0147] Configuration of the gas-liquid working unit: This embodiment adopts a non-isolated working tank structure. Three working tanks 222 are connected in parallel, and each working tank 222 is equipped with one impulse turbine 219, with one tank and one turbine working in a cyclical manner. Clean water is used as the working medium in the working tanks 222. Air diffusers, buffer baffles, buffer floats, float balls, and other defoaming devices can be added to the working tanks 222 to suppress the disturbance of the liquid surface by high-pressure air intake. The top of the working tank 222 is equipped with an air inlet (connected to the high-pressure air supply valve 223), an air vent (connected to the air vent valve 221), and a hot fluid spray port (connected to the spray valve 224), and the bottom is equipped with a liquid outlet. The bottom of each non-isolated working tank 222 is connected to the inlet of the corresponding impulse turbine 219 through a pipe, and the liquid at the outlet of the turbine 219 is discharged into the intermediate pressure buffer unit 28.

[0148] The power tank 222 adopts a cyclical operation mode of power-return-standby-power, with the three tanks taking turns to drive the liquid into the impulse turbine 219. The next set of power tanks is dynamically triggered based on the pressure of the intermediate pressure buffer unit 28 and the rectified power status.

[0149] The equivalent atmospheric environment arrangement of the pressure-bearing shell of the impulse turbines: Each impulse turbine 219 is independently arranged with its shaft, and is encapsulated within the pressure-bearing shell. The pressure-bearing shell is connected to the gas phase space of the intermediate pressure buffer unit 28 through a top gas phase balance pipe, and to the liquid phase space of the intermediate pressure buffer unit 28 through a bottom liquid connection pipe, and can discharge liquid to the intermediate pressure buffer unit 28. Both the gas phase balance pipe and the liquid connection pipe are equipped with isolation valves. The pressure inside the pressure-bearing shell follows the working pressure of the intermediate pressure buffer unit 28 (4.0~4.5MPa gauge pressure) in real time, forming an equivalent atmospheric working environment. When the turbine 219 operates in this environment, the outlet liquid naturally flows into the same pressure environment. The flow channel design completely follows the conventional turbine hydraulic model, eliminating back pressure loss. A monitoring and control device is installed at the bottom of the pressure-bearing shell to ensure that the liquid level does not become too high and affect the normal operation of the turbine 219.

[0150] Each impulse turbine 219 is equipped with an independent controllable nozzle or needle valve, each driving a variable frequency generator 220. Each variable frequency generator 220 is connected to a common DC bus via an independent turbine-side converter. After inversion, its AC output is synchronously coupled with the AC output of the generator 215, and then connected to the grid at a constant frequency. The grid side only senses the constant output after synchronous coupling. Each turbine 219 adaptively adjusts its speed according to the real-time head to maintain the optimal speed ratio. The turbine-side converter rectifies the variable frequency AC power from each variable frequency generator 220 into DC power, which is then connected to the common DC bus. Since there is no frequency concept on the DC side, the speed differences between the turbines are naturally eliminated during the rectification process.

[0151] Intermediate pressure buffer unit design: Intermediate pressure buffer unit 28 is a gas-liquid coexistence container. The inlet pressure of the high-efficiency range of the turbine expander is 3.5–5.0 MPa (gauge pressure), and an inlet pressure of 4.0–4.5 MPa is selected as the design operating condition. The gas phase volume of intermediate pressure buffer unit 28 is designed to be 10 times the single expansion gas volume of power tank 222, which can suppress pressure fluctuations caused by switching between multiple tanks to within ±5%, and can completely absorb the turbine expander guide vane adjustment. The specific volume is determined comprehensively based on the expander guide vane adjustment response characteristics and the continuous operation requirements of the hydraulic prime mover.

[0152] Low-pressure section expansion power generation unit: Employs a two-stage turboexpander, including a primary expander 212 and a secondary expander 214, with an interstage heat exchanger 213 for interstage reheat. Rated power 100MW, inlet pressure 4.0–4.5MPa (gauge pressure), back pressure 0.05MPa (gauge pressure), expansion ratio range 27.3–30.7, isentropic efficiency above 75%. The turboexpander drives the generator 215. A gas-liquid separator 211 is installed at the input end where the expander connects to the intermediate pressure buffer unit 28 to protect the expander.

[0153] Dynamic valve closure control: The dynamic valve closure module in the control unit calculates the total gas volume Ve at the expansion endpoint based on the shape and size of the work tank 222 and the expected liquid level at the end of expansion, combined with the expansion endpoint pressure Pe and temperature Te. The expansion endpoint pressure Pe = intermediate pressure buffer unit working pressure + minimum working pressure difference of the impulse turbine, with the difference being kept as small as possible. Real-time acquisition of instantaneous pressure P1, instantaneous temperature T1, and liquid level h1 within the work tank 222 is used to calculate the current gas volume V1. When P1V1 / T1 = PeVe / Te, the dynamic valve closure module commands the high-pressure gas supply valve 223 to close, forming a sealed expansion chamber in the work tank 222. The gas continues to expand within the chamber, pushing the liquid until it is completely discharged, fully extracting the expansion work from the high-pressure section.

[0154] Pressure-free return liquid control: After the working tank 222 completes expansion, the pressure-free return liquid module in the control unit instructs it to open its top vent valve 221 to connect with the intermediate pressure buffer unit 28 to balance the pressure. After pressure balance, the liquid at the bottom of the intermediate pressure buffer unit 28 is transported to the working tank 222 through the return liquid pump and one-way valve 210. The liquid occupies the gas space, pushing the expanded gas in the working tank 222 to the intermediate pressure buffer unit 28 through the vent valve 221. The expanded gas directly becomes the gas source for the expander. When the liquid level is higher than the vent valve 221, the return liquid is completed, and the vent valve 221 is closed to enter the standby state. For multiple tanks, the return liquid pump can be shared by switching valves.

[0155] When conditions permit, the intermediate pressure buffer unit 28 can be placed on top of the working tank 222, with its bottom connected to the top of the working tank 222 via a vent valve 221 and a pipe. After the working tank 222 has expanded, the vent valve 221 is opened, and the liquid at the bottom of the intermediate pressure buffer unit 28 flows into the working tank 222 under gravity through the bottom straight pipe. Simultaneously, the expanded gas inside the tank rises and enters the upper part of the intermediate pressure buffer unit 28 until the working tank 222 is filled with liquid, completing the liquid return process. Then, the vent valve 221 is closed, and the system enters a standby state. The vent pipe diameter must be sufficient to ensure a short liquid return time and eliminate the need for additional power consumption.

[0156] At the same time, a minimum liquid level is set as a safety protection threshold. If the gas expansion in the working tank 222 does not reach the preset expansion endpoint pressure Pe but has reached the set minimum liquid level, the control unit directly opens the vent valve 221 and confirms that the high-pressure gas supply valve 223 is in the closed state, ending the expansion and preventing gas from rushing into the impulse turbine 219.

[0157] Multi-operation tank coordinated control: The multi-operation tank coordinated module in the control unit controls the working sequence of the three operation tanks 222, controls the opening sequence of the high-pressure air supply valve 223 to make the three operation tanks 222 alternate or cycle to participate in the working sequence, and controls the output through the nozzle / needle valve of each turbine 219 to reduce power output fluctuations.

[0158] Collaborative pressure stabilization control: The collaborative pressure stabilization module in the control unit monitors the pressure of the intermediate pressure buffer unit 28 in real time. The pressure in the pre-release chamber is around 10 MPa, the intermediate pressure is 4.0 MPa, and the hydraulic side pressure difference is 6.0 MPa, indicating strong work capacity. The turbine 219 nozzle actively closes to limit the flow rate, preventing the intermediate pressure from exceeding the upper limit of the expander's high-efficiency zone. Simultaneously, the expander opens its guide vanes to increase air extraction, resulting in bidirectional pressure reduction. At the end of the release phase, the chamber pressure decreases to 6.45 MPa, the intermediate pressure increases to 4.5 MPa, and the maximum hydraulic side pressure difference is only 1.85 MPa. The nozzle actively opens to increase the flow rate, maintaining the total air supply to ensure air intake for the expander. Simultaneously, the expander reduces the guide vane opening to decrease air extraction, resulting in bidirectional pressure increase. The hydraulic power naturally decreases to approximately 9 MW, with the expander providing a safety net of 91 MW, maintaining a constant total system power output of 100 MW. Through a dual-layer fluctuation suppression mechanism of passive gas-capacity buffering and active hydraulic fine-tuning, the intermediate pressure can be varied slightly within the range of 4.0 to 4.5 MPa (gauge pressure).

[0159] Coordinated grid connection control: The coordinated grid connection module in the control unit rectifies the variable frequency generators 220 of the three impulse turbines 219 through independent machine-side converters and then connects them to the common DC bus. After inversion, the power is combined with the power of the low-voltage expansion power generation unit (generator 215) and then connected to the grid synchronously on the unified grid side to form the total output of the system.

[0160] The energy storage stage employs a two-stage compression system: the energy storage compression unit comprises a first-stage compressor 23 and a second-stage compressor 22. The first-stage compressor 23 has its inlet connected to the atmosphere and its outlet connected to the gas phase space of the intermediate pressure buffer unit 28. It compresses atmospheric air to the operating pressure (4.0–4.5 MPa) of the intermediate pressure buffer unit 28. Under stable operating conditions with constant inlet pressure and outlet pressure locked by the intermediate pressure buffer unit 28, it operates continuously, achieving an isentropic efficiency of 85%–88%. The second-stage compressor 22 has its inlet connected to the gas phase space of the intermediate pressure buffer unit 28 and its outlet connected to the high-pressure gas storage unit 21. It further compresses the air within the intermediate pressure buffer unit 28 to the operating pressure of the high-pressure gas storage unit 21 (energy release end pressure – energy storage end pressure), dynamically adjusting the outlet pressure based on the real-time pressure of the high-pressure gas storage unit 21. The intermediate pressure buffer unit 28 serves as both a first-stage exhaust buffer and a second-stage intake pressure stabilizing container during the energy storage phase. The two compressor stages operate decoupled through gas-capacity buffering, with the first stage operating at a constant full load and high efficiency, while the second-stage pressure ratio decreases from a total pressure ratio of 100 to approximately 2.5, significantly increasing the surge margin. The compression heat recovery device 24 recovers the heat generated during the compression process and stores it in the heat storage device 26. The external heating device 25 can utilize external heat sources such as solar energy to supplement the heat storage.

[0161] Three-stage heat recovery system: During the energy release and power generation process, the heat extraction circulation pump 27 pumps the liquid from the intermediate pressure buffer unit 28 into the heat storage device 26 to extract heat, and then provides heat fluid to each stage of the heat recovery process. First-stage heat exchange: During the expansion phase of the working tank 222, a hot fluid is injected through the hot fluid spray port at the top of the working tank 222 via the spray valve 224, directly exchanging heat and mass with the high-pressure gas to compensate for the temperature drop during the closed expansion phase. Alternatively, the high-pressure gas can be heated by a heat exchanger before entering the working tank 222, or both methods can be used simultaneously.

[0162] Second-stage reheating: Hot fluid is sprayed into the intermediate pressure buffer unit 28 through the hot spray 29 to directly exchange heat and mass with the gas in the tank, thereby increasing the temperature of the gas entering the expander.

[0163] Third-stage heat replenishment: The gas is heated at the inlet of the expander and between stages through the interstage heat exchanger 213, so that the temperature of the gas rises between the two stages of expansion.

[0164] The liquid circulates from the intermediate pressure buffer unit 28 to the heat storage device 26 to extract heat, and then sprays it into the working tank 222 and the intermediate pressure buffer unit 28, and supplies heat to the interstage heat exchanger 213, realizing the combined use of multiple methods such as high-pressure preheating heat exchange, working tank spraying, low-pressure expansion preheating, and expansion interstage heating.

[0165] Waste Energy Recovery and Replenishment Unit: The low-temperature exhaust gas from the low-pressure expansion power generation unit recovers its cooling capacity through the cooling unit 216. The heat-exchanged exhaust gas drives the turbocharger 217. The turbocharger 217 is equipped with variable geometry nozzles, and the turbine inlet is connected to the exhaust gas outlet of the expansion power generation unit. The turbine exhaust gas can be recovered again to provide a cooling source for the cooling and heat exchange components. The compressor end of the turbocharger 217 compresses ambient air to generate high-temperature compressed air. The high-temperature airflow recovers heat through the heating unit 218 to produce heating hot water and domestic hot water. Excess heat is reused as needed in the heat storage device 26 and the replenishment circuit, realizing energy cascade utilization and closed-loop recovery. If the cleanliness of the expanded gas is sufficient, the exhaust gas can also be used directly for cooling, and the compressed air can be used directly for heating.

[0166] Parameter adaptive correction: The control unit also has a parameter adaptive correction function, which dynamically optimizes the expansion endpoint parameters (Ve, Pe, Te) according to the actual operating deviation, and continuously approaches the optimal operating state throughout the entire life cycle.

[0167] Energy calculation for the gas storage chamber: Energy is released from the chamber from 10.1 MPa absolute pressure to 6.45 MPa absolute pressure. After polytropic expansion (n=1.1) integration calculation: The ideal work done by hydraulic force in the high-pressure section (10.1→6.45 MPa absolute pressure, dynamic intermediate pressure 4.1→4.6 MPa absolute pressure) is about 464,000 MJ; The ideal work done by expansion in the low-pressure section (expansion from intermediate pressure 4.1→4.6 MPa absolute pressure to 0.15 MPa absolute pressure) is about 2,455,000 MJ. Considering an efficiency of 85% for the impulse turbine, 75% for the turbine expander, and 95% for the generator: the actual output of the hydraulic section is approximately 103.8 MWh (average 17.3 MW), the actual output of the expander section is approximately 486.2 MWh (average 81.0 MW), and the total system output is approximately 590.0 MWh. The system can operate for 5.90 hours at a rated capacity of 100 MW, or precisely for 6 hours at a rated capacity of 98.3 MW. The high-pressure section accounts for approximately 17% of the work, and the low-pressure section accounts for approximately 83%. The equipment capacity and power distribution are highly matched, conforming to the thermodynamic law that the low-pressure, high-expansion-ratio section is absolutely dominant in terms of work done by the nonlinear characteristics of isothermal gas expansion, W=RT·ln(P1 / P2).

[0168] Expander stability anchor characteristics: The total system output power is based on the grid-connected power when the expander is operating alone. The expander output smoothly transitions from approximately 78.6% initially (when the hydraulic side is at full power) to 100% at the end (when the hydraulic side is deactivated), with an adjustment range of 21.4%, which is entirely within the narrow operating efficiency range of the turbine expander. Because the intake pressure is stabilized within the narrow operating range of 4.0–4.5 MPa, the surge margin is significantly reduced, the back pressure can be lowered to 0.05 MPa (gauge pressure), and the expansion ratio is significantly improved.

[0169] Selection of high-pressure gas storage unit type: This embodiment adopts artificial hard rock chamber, but high-pressure gas storage unit 1 can also be selectively matched with natural chamber, salt cavern, abandoned oil and gas well, high-pressure tubular storage tank or CNG gas storage well, etc. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device and method of this application are applicable to various gas storage forms.

[0170] This implementation utilizes a functional separation architecture to store high-pressure gas within a 200,000 m³ chamber. A high-power extraction of expansion work in the high-pressure section is achieved through an impulse turbine in an equivalent atmospheric environment within the pressure-bearing shell. Residual gas is efficiently transferred to an intermediate pressure buffer unit via a non-isolated power tank with zero pressure differential return, becoming the gas source for the turbine expander. The turbine expander operates stably within an intake range of 4.0–4.5 MPa, with back pressure dropping to 0.05 MPa (gauge pressure). A split-shaft, independently variable-speed, constant-frequency turbine is electrically connected in parallel with the turbine expander and then connected to the grid at a constant frequency. There is no throttling loss throughout the process, and no large-capacity power compensation equipment is required. The average hydraulic power is 17.3 MW, and the average expander power is 81.0 MW, achieving a stable 100 MW-level grid-connected output under ordinary constant-volume gas storage conditions. This solution can also be directly applied to the upgrading and transformation of traditional large-scale salt cavern / rock cave compressed air energy storage power stations. After the transformation, a shallow discharge strategy can be adopted to retain a higher termination pressure in order to save energy consumption for refilling and compression. After the cycle efficiency is improved, it has the economic basis to apply for expansion of energy storage scale. Example 4

[0171] Example 4 illustrates the proposed solution using the energy storage application of abandoned gas wells in an oil and gas field (abandoned natural gas wells + wind and solar power consumption + combined cooling, heating and power).

[0172] It should be noted that in remote oil and gas field operating areas, the power grid is weak and the energy supply is unstable. When using abandoned gas wells as high-pressure gas storage units to absorb local wind and solar power, complex problems are faced, such as unstable wind and solar power output, low energy storage and release efficiency, and reliance on external energy sources for cooling and heating in remote areas. At the same time, abandoned gas wells have different pressure levels, requiring the system to have wide-range pressure adaptability.

[0173] The system architecture of this embodiment 4 is similar to the basic architecture of the previous embodiments, except that: the high-pressure gas storage unit adopts abandoned natural gas wells, and the gas storage pressure level is determined according to the actual conditions of the gas wells; the energy storage side uses local wind and solar power to drive a two-stage compressor; the energy release side flexibly selects a hydraulic prime mover according to the gas storage pressure level (an impulse turbine is selected for high pressure and large capacity, and a hydraulic motor is selected for medium and low pressure and small capacity); the expander is selected as a screw expander or a turbine expander according to the scale.

[0174] The key feature of this implementation lies in the integrated utilization of combined cooling, heating, and power (CCHP) and waste energy recovery. Based on the staged expansion gas-liquid synergistic coupling architecture of this application, the high-pressure section uses a hydraulic prime mover to recover pressure energy, while the low-pressure section uses an expander to perform work, with no throttling losses throughout the entire process. Based on this: Cold energy utilization: The low-temperature exhaust gas from the expansion power generation unit recovers its cooling capacity through a cooling heat exchange component, providing a cooling source for the work area (air conditioning, equipment cooling, etc.). The turbine exhaust gas from the turbocharger can also be recovered for cooling capacity again, or, if the expansion gas is clean enough, it can be used directly for cooling.

[0175] Thermal energy utilization: The compressor end of the turbocharger compresses ambient air to generate high-temperature compressed air. Heat is recovered through heat exchange components to produce heating hot water and domestic hot water, providing a heat source for the work area. The heat stored in the compression heat recovery device and external heating device (which can utilize solar collectors) improves power generation efficiency through a three-stage heat supplementation system during the energy release process, while surplus heat can be supplied as needed.

[0176] Power supply: The high-voltage hydraulic power generation unit and the low-voltage expansion power generation unit combine to form a stable power output, providing a stable power supply to the work area.

[0177] Through coordinated pressure stabilization control, the pressure of the intermediate pressure buffer unit is monitored in real time, and the load of the hydraulic prime mover and the expander are adjusted in both directions to maintain the continuous and stable power output of the system while ensuring the quality stability of the combined cooling and heating supply.

[0178] This implementation utilizes abandoned gas wells as high-pressure gas storage units to achieve zero investment in new gas storage facilities, absorbs local wind and solar power to reduce curtailment rates, and achieves efficient energy storage and release through a staged expansion gas-liquid synergistic coupling architecture. Simultaneously, it fully recovers waste cooling from expansion exhaust gas and waste pressure and heat from turbines, realizing integrated combined cooling, heating, and power (CCHP). This solves the complex problems of weak power grids and unstable energy supply in remote oil and gas fields, breaking the traditional profit model of single-generation energy storage, and possesses good engineering feasibility and economic viability. This application is not limited by power scale, gas storage form, or water source, and can be directly applied to various distributed small and medium-sized energy storage scenarios.

[0179] The thermodynamic parameters, efficiency data, and control parameters in the above embodiments are all derived from theoretical calculations and simulation analysis. In actual engineering applications, they need to be verified and optimized according to specific working conditions. Example 5

[0180] Based on the aforementioned embodiments, this embodiment 5 provides a method for stable output of pure compressed air energy storage through staged expansion gas-liquid coupling, including an energy release and power generation stage, as referenced. Figure 5 As shown, the energy release and power generation stage includes the following steps: S1. High-pressure gas-liquid expansion steps: High-pressure gas enters the power tank through the high-pressure inlet valve, pushes the liquid out of the tank and enters the hydraulic prime mover to generate electricity, and the tail liquid enters the intermediate pressure buffer unit; After the high-pressure gas enters the power tank, the high-pressure inlet valve is closed before the expansion endpoint according to the real-time state parameters inside the tank, so that the power tank forms a closed expansion chamber and continues to discharge liquid to do work until the expansion endpoint; S2. Expansion endpoint triggering and liquid return steps: When the gas in the sealed expansion chamber expands to the preset expansion endpoint pressure, the vent valve is opened to connect the working tank and the intermediate pressure buffer unit to balance the pressure. Then, the liquid flows back to the working tank to replace the residual gas in the tank to the intermediate pressure buffer unit. After the working tank is filled with liquid, it enters the standby state and is recycled. S3, Low-pressure section pure gas expansion step: The gas in the intermediate pressure buffer unit enters the expander after gas-liquid separation to expand and generate electricity; S4. Collaborative pressure stabilization step: Real-time monitoring of the pressure of the intermediate pressure buffer unit. When the pressure of the intermediate pressure buffer unit is higher than the set value, the load of the hydraulic prime mover is reduced while the load of the expander is increased. When the pressure of the intermediate pressure buffer unit is lower than the set value, the load of the hydraulic prime mover is increased while the load of the expander is reduced. Through bidirectional real-time balance between the high-pressure section and the low-pressure section, the pressure of the intermediate pressure buffer unit is maintained within the high-efficiency intake pressure range of the expander, and the system power output is kept stable.

[0181] The specific principles of each step have been described in detail in other embodiments, and will not be repeated here.

[0182] Through the above scheme, during the energy release and power generation stage, the high-pressure gas expands fully in the work tank to drive the liquid to do work. The residual gas is efficiently replaced to the intermediate pressure buffer unit to become the gas source for the expander. The hydraulic prime mover and the expander maintain the intermediate pressure within the high-efficiency intake pressure range of the expander through bidirectional real-time balance adjustment. The expander always operates in the high-efficiency range and the back pressure can be designed to a very low level, achieving continuous and stable power output and significantly improving energy utilization.

[0183] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A pure compressed air energy storage staged expansion gas-liquid coupling stable output device, characterized in that, include: The system includes: a high-pressure gas storage unit for storing high-pressure compressed air; a gas-liquid power unit including at least one power tank, with a high-pressure inlet valve and a vent valve at the top and a drain pipe at the bottom; an intermediate pressure buffer unit including a gas-liquid coexistence container, the gas phase volume of which is larger than the single expansion gas volume of the power tank, and its working pressure is within the high-efficiency inlet pressure range of the expander; a high-pressure section hydraulic power generation unit including at least one hydraulic prime mover connected to the drain pipe of the power tank; a low-pressure section expansion power generation unit including an expander, the inlet of which is connected to the gas phase space of the intermediate pressure buffer unit; and a control unit. The high-pressure gas storage unit and the gas-liquid work unit are arranged independently and are only connected through the high-pressure gas inlet valve during the work phase. No liquid enters the high-pressure gas storage unit throughout the process. The control unit is configured to: during the power-operating phase, control the high-pressure gas to enter the power tank through the high-pressure inlet valve, and close the high-pressure inlet valve before the expansion endpoint according to the real-time state parameters inside the tank to form a sealed expansion chamber, allowing the gas to continue expanding in the sealed expansion chamber, pushing the liquid out through the drain pipe and driving the hydraulic prime mover to perform work; at the expansion endpoint, control the opening of the vent valve to connect the power tank with the intermediate pressure buffer unit to balance the pressure, and then control the liquid to flow back to the power tank, replacing the residual gas in the tank with the intermediate pressure buffer unit as the gas source for the expander; and, according to the real-time pressure of the intermediate pressure buffer unit, coordinately adjust the load of the hydraulic prime mover and the load of the expander to maintain the pressure of the intermediate pressure buffer unit within the high-efficiency intake pressure range of the expander and maintain stable system power output.

2. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 1, characterized in that, The control unit includes a dynamic valve closing module and a differential pressure return module; The dynamic valve closing module is configured to: calculate the total gas volume Ve at the expansion endpoint based on the shape and size of the working tank and the expected liquid level at the end of expansion, and determine the expansion endpoint pressure Pe and temperature Te; collect the instantaneous pressure P1, instantaneous temperature T1, and liquid level h1 in the working tank in real time, and calculate the current gas volume V1 through the liquid level h1; close the high-pressure inlet valve when P1V1 / T1=PeVe / Te, so that the working tank forms the sealed expansion chamber and continues to discharge liquid to perform work until the expansion endpoint; wherein the expansion endpoint pressure Pe is the sum of the working pressure of the intermediate pressure buffer unit and the minimum working pressure difference of the hydraulic prime mover; The differential pressure return module is configured such that: when the gas in the working tank expands to the expansion endpoint pressure Pe, the vent valve is opened to connect the working tank with the intermediate pressure buffer unit to balance the pressure; after the pressure is balanced, the liquid in the intermediate pressure buffer unit flows back to the working tank by gravity or a return pump, and the liquid occupies the gas space, displacing the residual gas in the tank through the vent valve to the intermediate pressure buffer unit; when the liquid level is higher than the vent valve, the vent valve is closed, and the working tank is filled with liquid and enters a standby state; The control unit also sets a minimum liquid level as a safety protection threshold. If the gas expansion in the working tank does not reach the expansion endpoint pressure Pe but has reached the minimum liquid level, the high-pressure air inlet valve is closed and the vent valve is opened. After pressure balancing, the liquid is returned.

3. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 1, characterized in that, The control unit further includes a coordinated pressure stabilization module, which is configured to: monitor the pressure of the intermediate pressure buffer unit in real time; when the pressure of the intermediate pressure buffer unit is higher than a set value, reduce the load of the hydraulic prime mover to reduce the air supply to the intermediate pressure buffer unit, and simultaneously increase the load of the expander to increase the air extraction from the intermediate pressure buffer unit; when the pressure of the intermediate pressure buffer unit is lower than the set value, increase the load of the hydraulic prime mover to increase the air supply, and simultaneously decrease the load of the expander to reduce the air extraction.

4. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 1, characterized in that, The gas-liquid working unit includes multiple working tanks connected in parallel; the control unit also includes a multi-working-tank coordination module, which is configured to: control the opening sequence of the high-pressure air inlet valve of each working tank, so that each working tank works in a cycle and independently controls the real-time liquid output of each working tank; when the number of working tanks is even, they share the hydraulic prime mover in pairs to work alternately and are grouped in a cycle.

5. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 1 or 4, characterized in that, The working tank adopts either a non-isolated or isolated expansion chamber and liquid chamber; When a non-isolated system is used, the bottom of each working tank is connected to the inlet of the hydraulic prime mover via a pipe, and the outlet of the hydraulic prime mover is connected to the intermediate pressure buffer unit; the liquid in the intermediate pressure buffer unit is returned to the working tank by a return pump or gravity to complete the return process. When an isolated type is used, the working tanks are set in groups of two, and each group drives one of the hydraulic prime movers. Each working tank has two one-way valves at the bottom, which are respectively connected to the inlet and outlet of the hydraulic prime mover. During the expansion process, the pressure difference between the back pressure of the hydraulic prime mover and the working pressure of the intermediate pressure buffer unit pushes the isolation component of the other working tank to reset and complete the return of liquid. The two tanks work alternately.

6. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 1, characterized in that, The hydraulic prime mover includes impulse turbines, each with an independent shaft arrangement. Each impulse turbine is equipped with an independent controllable nozzle or needle valve and drives a variable frequency generator. Each variable frequency generator is connected to a common DC bus via an independent machine-side converter and then connected to the grid at a constant frequency via a unified grid-side converter. Each impulse turbine is installed in the gas space inside the intermediate pressure buffer unit or encapsulated in a pressure-bearing shell. The pressure-bearing shell is connected to the gas phase space of the intermediate pressure buffer unit through a top gas phase balance pipe and to the liquid phase space of the intermediate pressure buffer unit through a bottom liquid phase connection pipe, so that the working environment pressure of the impulse turbine follows the working pressure of the intermediate pressure buffer unit.

7. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 1, characterized in that, It also includes an energy storage compression unit, which includes a first-stage compressor and a second-stage compressor. The inlet of the first-stage compressor is connected to the atmosphere, and the outlet is connected to the gas phase space of the intermediate pressure buffer unit. The inlet of the second-stage compressor is connected to the gas phase space of the intermediate pressure buffer unit, and the outlet is connected to the high-pressure gas storage unit. During the energy storage stage, the intermediate pressure buffer unit also serves as the first-stage exhaust buffer and the second-stage intake pressure stabilizing container, so that the first-stage compressor operates under stable conditions with constant intake pressure and exhaust pressure locked by the intermediate pressure buffer unit.

8. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 1, characterized in that, It also includes a three-stage heating system: the first stage of heating involves injecting hot fluid into the working tank through a top spray nozzle to perform heat and mass exchange on the high-pressure gas, and / or preheating the gas through a heat exchanger before the high-pressure gas enters the working tank; the second stage of heating involves injecting hot fluid into the intermediate pressure buffer unit through a spray nozzle to increase the temperature of the gas entering the expander; the third stage of heating involves heating the gas through a heat exchanger at the expander inlet and / or between stages, and when the expander is a screw expander, hot fluid is also injected into the working chamber for continuous heating during the expansion process.

9. The pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to claim 8, characterized in that, It also includes a waste energy recovery unit, which includes a turbocharger with a variable cross-section nozzle. The turbine end air inlet of the turbocharger is connected to the exhaust outlet of the expander. The expanded exhaust gas drives the turbine end to do work, and the turbine exhaust gas provides a cold source for the cooling and heat exchange components. The compressor end of the turbocharger compresses ambient air to generate high-temperature compressed air, which provides a heat source for the heating and heat exchange components. The excess heat is recycled to the system's heat storage and heat replenishment circuit.

10. A method for stable output of pure compressed air energy storage staged expansion gas-liquid coupling, applied to the pure compressed air energy storage staged expansion gas-liquid coupling stable output device according to any one of claims 1-9, characterized in that, The energy release and power generation stage includes the following steps: High-pressure gas-liquid expansion steps: High-pressure gas enters the power tank through the high-pressure inlet valve, pushes the liquid out of the tank and enters the hydraulic prime mover to do work and generate electricity, and the tail liquid enters the intermediate pressure buffer unit; After the high-pressure gas enters the power tank, the high-pressure inlet valve is closed before the expansion endpoint according to the real-time state parameters in the tank, so that the power tank forms a closed expansion chamber and continues to discharge liquid to do work until the expansion endpoint. Expansion endpoint triggering and liquid return steps: When the gas in the sealed expansion chamber expands to the preset expansion endpoint pressure, the vent valve is opened to connect the working tank and the intermediate pressure buffer unit to balance the pressure. Then, the liquid flows back to the working tank to replace the residual gas in the tank to the intermediate pressure buffer unit. After the working tank is filled with liquid, it enters the standby state and is recycled. Low-pressure section pure gas expansion step: The gas in the intermediate pressure buffer unit is separated into gas and liquid and then enters the expander to expand and generate electricity; Collaborative pressure stabilization steps: The pressure of the intermediate pressure buffer unit is monitored in real time. When the pressure of the intermediate pressure buffer unit is higher than the set value, the load of the hydraulic prime mover is reduced while the load of the expander is increased. When the pressure of the intermediate pressure buffer unit is lower than the set value, the load of the hydraulic prime mover is increased while the load of the expander is reduced. Through bidirectional real-time balance between the high-pressure section and the low-pressure section, the pressure of the intermediate pressure buffer unit is maintained within the high-efficiency intake pressure range of the expander, and the system power output is kept stable.

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