Closed compressed carbon dioxide heat pump energy storage system and using method thereof

Abstract

The invention provides a closed compressed carbon dioxide heat pump energy storage system and a use method thereof, and the system is additionally provided with a variable volume gas storage tank, an actuating mechanism and a plurality of regulating valves on the basis of a traditional compressor, an expansion machine, a heat exchanger and a heat regenerator. The variable-volume gas storage tank is connected to the outlet side of the expansion machine, and the volume of the variable-volume gas storage tank is changed through driving of the executing mechanism, so that the overall pressure and working medium density of the system are rapidly adjusted on the premise that the total mass of working media of the system is not changed, and rapid and efficient lifting of loads is achieved. And meanwhile, the volume of the gas storage tank can be actively expanded to the maximum when the system is shut down, so that the stagnation pressure of the system is rapidly reduced to a safe range, and the overpressure risk of low-pressure side equipment is effectively avoided. The closed type carbon dioxide energy storage system solves the technical problems that an existing closed type carbon dioxide energy storage system is low in load adjusting speed, low in efficiency and high in shutdown pressure, and has the advantages of being fast in response, high in energy efficiency and good in safety.

Description

Technical Field

[0001] This invention relates to the field of heat pump energy storage technology, and in particular to a closed-loop compressed carbon dioxide heat pump energy storage system and its usage method. Background Technology

[0002] Carbon dioxide, due to its moderate critical parameters (critical pressure 7.38 MPa, critical temperature 31℃) and advantages such as high density and good heat transfer performance in the supercritical state, has become one of the ideal working fluids for novel compressed gas energy storage and heat pump energy storage systems. In closed-loop compressed carbon dioxide heat pump energy storage systems, flexible adjustment of system load is the core capability for coping with grid demand fluctuations and maintaining efficient and stable system operation. Common load adjustment methods in existing technologies mainly suffer from the following problems: Capacity regulation: This method involves changing the system pressure and mass flow rate by introducing or discharging carbon dioxide as the working fluid, thereby achieving load regulation. While this method can maintain the compressor's efficient operation at its design point, it is limited by the working fluid's charging and discharging speed, resulting in a relatively long system response time and making rapid load adjustment impossible.

[0003] Temperature regulation: This method affects power consumption and mass flow rate by changing the temperature of the working fluid at the compressor inlet. This method is inefficient and deviates significantly from the design operating conditions, impacting the overall system energy efficiency.

[0004] Throttling regulation: A regulating valve is installed at the compressor inlet to change the compressor performance through throttling losses. This method has significant throttling losses, leading to a decrease in system efficiency, and the adjustment range is limited. If the valve opening is too small, it can easily cause compressor surge.

[0005] Bypass regulation: This involves directly bypassing a portion of the high-pressure working fluid from the compressor outlet to the inlet. While this can quickly reduce the load, it significantly sacrifices system efficiency and is unsuitable for long-term operation.

[0006] Furthermore, after a closed-loop system shuts down (especially in an emergency), the working fluid in all equipment and pipelines reaches a static equilibrium state. At this point, the overall system pressure (stagnation pressure) is usually significantly higher than the low-pressure side design pressure during normal operation. This leads to two unfavorable options: either significantly increase the pressure resistance of all pipelines and equipment on the low-pressure side, significantly increasing costs and design complexity; or transfer a large amount of working fluid to an external storage tank before shutdown. However, due to limitations in tank capacity and transfer speed, this is difficult to achieve during abnormal shutdowns, posing a safety risk of equipment overpressure operation.

[0007] Therefore, there is an urgent need for a technical solution that can enable rapid and efficient load adjustment of a closed-loop carbon dioxide heat pump energy storage system, while also quickly and proactively reducing system stagnation pressure during shutdown to ensure system safety. Summary of the Invention

[0008] The purpose of this invention is to provide a closed-loop compression carbon dioxide heat pump energy storage system and its usage method. By introducing a variable-volume gas storage tank into the system and linking it with an actuator, the effective volume of the system can be rapidly changed without altering the total mass of the working fluid. This allows for rapid and precise control of the system pressure, thereby enabling rapid load increases and decreases. Furthermore, when the system is shut down, this method can quickly expand the system volume to its maximum, minimizing stagnation pressure and effectively avoiding the risk of overpressure on the low-pressure side.

[0009] According to one objective of the present invention, a closed-loop compression carbon dioxide heat pump energy storage system is provided, comprising a compressor, an expander, a motor, a first heat exchanger, a regenerator, a second heat exchanger, and connecting pipelines, and further comprising: A variable volume gas storage tank, the inlet of which is connected to the outlet of the expander, and the outlet of which is connected to the inlet of the first heat exchanger; The actuator is mechanically connected to the variable volume gas storage tank; Multiple regulating valves are connected to the actuator; Specifically, by operating the regulating valve, the driving fluid is controlled to act on the actuator, thereby driving the volume of the variable volume gas storage tank to change.

[0010] Furthermore, the variable volume gas storage tank is equipped with a first piston, which divides the inside of the tank into a working fluid chamber and a back chamber, and the first piston is connected to a first piston rod extending out of the back chamber.

[0011] Furthermore, the actuator is a double-acting hydraulic cylinder or a double-acting pneumatic cylinder, and a second piston is provided inside the actuator. The second piston divides the inner cavity of the actuator into a first chamber and a second chamber, and the second piston is connected to a second piston rod; the first piston rod is connected to the second piston rod.

[0012] Furthermore, the plurality of regulating valves include: A first regulating valve, the outlet of which is connected to the first chamber; The second regulating valve has its outlet connected to the second chamber; The third regulating valve has its inlet connected to the first chamber; The fourth regulating valve has its inlet connected to the second chamber.

[0013] Furthermore, it also includes a cold salt tank and a hot salt tank; the first heat exchanger and the cold salt tank form a cold-end heat storage cycle, and the second heat exchanger and the hot salt tank form a hot-end heat storage cycle.

[0014] Furthermore, it also includes a displacement sensor for monitoring the volume of the variable-volume gas storage tank or the position of the piston.

[0015] Furthermore, it also includes a pressure sensor for monitoring system pressure, the pressure sensor being disposed at the working fluid chamber of the variable volume gas storage tank and / or the inlet of the compressor.

[0016] Furthermore, the actuator is an electromechanical actuator driven by a servo motor, and is connected to the first piston rod or the second piston rod through a ball screw or gear rack mechanism.

[0017] According to another objective of the present invention, the present invention provides a method of using the above-described closed-loop compression carbon dioxide heat pump energy storage system, comprising the following steps: Load increase step: Control the volume of the variable volume gas storage tank to decrease, thereby increasing the system pressure, increasing the working fluid mass flow rate, and realizing the increase of system load; Load reduction step: Control the increase of the volume of the variable volume gas storage tank to reduce the system pressure, thereby reducing the mass flow rate of the working fluid and reducing the system load.

[0018] Furthermore, it also includes: Before or during system shutdown, the actuator is controlled to increase the volume of the variable volume gas storage tank to its design maximum value, thereby reducing the system stagnation pressure to below a safe level.

[0019] This invention introduces a variable-volume gas storage tank and a linked actuator at the expander outlet, enabling rapid changes in the effective volume of the closed-loop system while maintaining a constant total mass of the working fluid, thereby precisely controlling system pressure. This structure significantly improves load regulation speed, overcoming the problems of slow response and low efficiency of traditional capacity regulation, such as bypass or throttling. Simultaneously, during shutdown, the tank volume can be actively expanded to its maximum, rapidly reducing system stagnation pressure and fundamentally avoiding overpressure risks on the low-pressure side, thus enhancing system safety and reliability. This solution is compact, flexible in control, and achieves a balance between rapid load response and proactive safety protection without affecting the operating efficiency of the main equipment. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention.

[0022] In the diagram: 1. Compressor; 2. First coupling; 3. Motor; 4. Second coupling; 5. Expander; 6. First heat exchanger; 7. Regenerator; 8. Second heat exchanger; 9. Cold salt tank; 10. Hot salt tank; 11. Variable volume gas storage tank; 11.1. First piston; 11.2. First piston rod; 12. Actuator; 12.1. Second piston; 12.2. Second piston rod; 13. First regulating valve; 14. Second regulating valve; 15. Third regulating valve; 16. Fourth regulating valve. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0025] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] Example 1 like Figure 1 As shown, a closed-loop compression carbon dioxide heat pump energy storage system includes a compressor 1, an expander 5, a motor 3, a first heat exchanger 6, a regenerator 7, a second heat exchanger 8, and connecting pipelines, and further includes: A variable volume gas storage tank 11 is located in the working fluid circuit on the outlet side of the expander 5; the outlet of the variable volume gas storage tank 11 is connected to the inlet of the subsequent first heat exchanger 6. The actuator 12 is mechanically connected to the variable volume gas storage tank 11 and is used to drive the volume change of the variable volume gas storage tank 11. Multiple regulating valves are connected to the actuator 12 to control the flow of driving fluid into and out of the actuator 12 to drive its action.

[0027] Specifically, a sliding first piston 11.1 is provided inside the variable volume gas storage tank 11. The first piston 11.1 divides the inside of the tank into a working fluid chamber and a back chamber that are connected to the system; the first piston 11.1 is connected to a first piston rod 11.2 that extends out of the back chamber.

[0028] The actuator 12 is a hydraulic or pneumatic cylinder, and a second piston 12.1 is provided inside it. The second piston 12.1 divides the inner cavity of the actuator 12 into a first chamber and a second chamber. The second piston 12.1 is connected to a second piston rod 12.2. The first piston rod 11.2 and the second piston rod 12.2 are rigidly connected or coaxially connected through a connector.

[0029] Specifically, the multiple control valves include: The first regulating valve 13 has its outlet connected to the first chamber; The second regulating valve 14 has its outlet connected to the second chamber; The third regulating valve 15 has its inlet connected to the first chamber; The fourth regulating valve 16 has its inlet connected to the second chamber; The inlets of the first regulating valve 13 and the second regulating valve 14 are used to receive high-pressure driving fluid, while the outlets of the third regulating valve 15 and the fourth regulating valve 16 are used to discharge the driving fluid. By controlling the opening and closing of different regulating valves, the driving fluid can push the second piston to move, which in turn links the first piston through the piston rod, changing the effective volume of the variable-volume gas storage tank.

[0030] The system in this embodiment also includes a cold salt tank 9 and a hot salt tank 10. The first heat exchanger 6 and the cold salt tank 9 form a cold-end heat storage cycle, and the second heat exchanger 8 and the hot salt tank 10 form a hot-end heat storage cycle.

[0031] The system in this embodiment also includes a displacement sensor for monitoring the volume of the variable volume gas storage tank 11 or the position of the piston.

[0032] The system in this embodiment also includes pressure sensors for monitoring the pressure at key points of the system, including the working fluid chamber of the variable volume gas storage tank 11 and / or the inlet of the compressor 1.

[0033] This embodiment includes a compressor 1 and an expander 5 as rotating devices, which are coaxially connected to a motor 3 via a first coupling 2 or a second coupling 4, respectively, to form an energy storage / release unit.

[0034] The working fluid circuit in this embodiment is as follows: the outlet of the expander 5 is sequentially connected to the variable volume gas storage tank 11, the first heat exchanger 6 (low temperature side), and the low pressure side of the regenerator 7, and then enters the inlet of the compressor 1; the outlet of the compressor 1 is sequentially connected to the second heat exchanger 8 (high temperature side) and the high pressure side of the regenerator 7, and finally enters the inlet of the expander 5.

[0035] In this embodiment, the first heat exchanger 6 and the cold brine tank 9 form a cold-end heat storage cycle, and the second heat exchanger 8 and the hot brine tank 10 form a hot-end heat storage cycle. The regenerator 7 is used to recover waste heat from the working fluid and improve system efficiency.

[0036] The core improvement of this embodiment lies in the variable volume gas storage tank 11 and its drive unit. The variable volume gas storage tank 11 is arranged on a low-pressure pipeline after the outlet of the expander 5 and before the first heat exchanger 6. A sliding first piston 11.1 is provided inside the tank, dividing the tank body into a working fluid chamber (connected to the system) and a back chamber. The first piston rod 11.2 extends from the back chamber and is rigidly connected to the second piston rod 12.2 of the actuator 12.

[0037] The actuator 12 is a hydraulic (pneumatic) cylinder, whose internal second piston 12.1 divides the cylinder body into a first chamber on the left and a second chamber on the right. A first regulating valve 13 (inlet valve) and a third regulating valve 15 (outlet valve) are connected to the first chamber; a second regulating valve 14 (inlet valve) and a fourth regulating valve 16 (outlet valve) are connected to the second chamber. The other end of each regulating valve is connected to a high-pressure drive source (such as a hydraulic station) and a return hydraulic (pneumatic) pipeline, respectively.

[0038] The working method of the system in this embodiment is as follows: Energy storage process (charging): Motor 3 drives compressor 1 to compress the low-pressure carbon dioxide working fluid into a high-temperature, high-pressure supercritical state. The heat is stored in the hot salt tank 10 in the second heat exchanger 8. After being cooled by the regenerator 7, the high-pressure working fluid enters the expander 5 to expand and do work, driving motor 3 to generate electricity. At the same time, the working fluid temperature is further reduced, and it absorbs heat from the cold salt tank 9 through the first heat exchanger 6, completing the cycle. At this time, the system adjusts the load as needed according to the grid command or its own status.

[0039] Rapid Load Increase: When the power grid needs to increase power output (energy release) or energy storage capacity, the control system opens the second regulating valve 14 and the fourth regulating valve 16. High-pressure driving fluid (e.g., hydraulic oil) enters the second chamber, pushing the second piston 12.1 to the left. Through the linkage of the first piston rod 11.2 and the second piston rod 12.2, the first piston 11.1 in the variable volume gas storage tank 11 moves to the left, compressing its back chamber, resulting in a decrease in the working fluid chamber volume of the variable volume gas storage tank. Since the system is closed and the total mass of the working fluid remains constant, the overall system pressure rises rapidly. The increased pressure increases the working fluid density, and with the compressor 1 and expander 5 operating at stable speeds, the mass flow rate through them increases, and the system load (power) increases rapidly. Since no losses such as throttling are introduced, the compressor 1 and expander 5 still operate near their high-efficiency range.

[0040] Rapid load reduction: When system load needs to be reduced, the control system opens the first regulating valve 13 and the third regulating valve 15. High-pressure driving fluid enters the first chamber, pushing the second piston 12.1 to the right, which in turn drives the first piston 11.1 to the right, increasing the working fluid chamber volume of the variable volume gas storage tank 11. The system pressure then drops rapidly, the working fluid density decreases, and the mass flow rate decreases, thereby achieving a rapid load reduction while maintaining unit efficiency.

[0041] Safe Shutdown: When the system is scheduled to shut down or receives an emergency shutdown signal, it immediately executes a "rapid load reduction" operation to its limit position, i.e., driving the first piston 11.1 to move to the far right, so that the volumetric gas storage tank 11 reaches its design maximum volume. At this time, the volume of the entire closed system is at its maximum, and the system pressure drops to its minimum. After the rotating equipment has completely stopped, the stagnation pressure reached by the system is far lower than the low-pressure side pressure during normal operation, and even lower than its design pressure, thus ensuring the safety of all low-pressure equipment, including the compressor inlet pipe, the first heat exchanger, and the low-pressure side of the regenerator. This process is rapid and proactive, does not rely on external storage tanks, and has high reliability.

[0042] Example 2 like Figure 1 As shown, in this embodiment, based on embodiment 1, the actuator 12 can take various forms: Double-acting hydraulic cylinder: As described in Example 1, this is the most straightforward form. The high-pressure drive source is a hydraulic pump station, providing a stable supply of high-pressure oil. The regulating valve is a solenoid directional valve or an electro-hydraulic servo valve, enabling precise control and rapid response of the piston position.

[0043] Pneumatic actuators: When the system itself has high-pressure carbon dioxide gas, some of the high-pressure gas can be used as the driving medium. In this case, a dedicated high-pressure gas source is required, or the gas must be drawn from the high-pressure side of the system (pressure reduction and stabilization are necessary). The pneumatic method also has a very rapid response, and since the medium and working fluid are from the same source, there is no risk of contamination.

[0044] Electromechanical actuator: Actuator 12 can also be a ball screw or rack and pinion mechanism driven by a servo motor, directly pushing the second piston rod 12.2. This method offers high control precision, but it is necessary to consider whether the power and response speed can meet the requirements for rapid adjustment.

[0045] In addition, to more intelligently adjust the load and protect the system, the following components and control logic can be added: Position sensor: A displacement sensor is installed on the first piston rod 11.2 or the second piston rod 12.2 to monitor the volume change of the variable volume gas storage tank 11 in real time and realize closed-loop control.

[0046] Pressure sensor: Pressure sensors are installed in the working fluid chamber of the variable volume gas storage tank 11 and at key low-pressure points of the system (such as the compressor inlet), and the system pressure is directly used as the adjustment target.

[0047] Control logic integration: The load regulation logic is integrated with the unit's main controller. The controller receives grid dispatch instructions or internal status signals, calculates the target load or target pressure, and then controls the opening degree or switching sequence of the regulating valves through algorithms such as PID control. This ensures that the volume of the variable-volume gas storage tank 11 smoothly and accurately reaches the target value, achieving stepless and rapid load regulation. The shutdown protection logic has the highest priority.

[0048] This embodiment regulates system pressure and load by actively and rapidly changing the volume of a certain node within a closed system. This can be achieved through different actuators and technical means, all of which should fall within the protection scope of this invention.

[0049] This invention regulates pressure and mass flow rate by changing the system volume, avoiding throttling losses, bypass losses, or significant deviations from design conditions. It can achieve rapid increases and decreases in system load while maintaining efficient compressor operation, with a fast response speed.

[0050] This invention can quickly and reliably reduce the system stagnation pressure to a safe range by actively expanding the system volume before shutdown, fundamentally solving the risk of overpressure during shutdown of closed systems, without the need for expensive high-pressure equipment or reliance on slow working fluid discharge.

[0051] This invention features a compact structure and flexible control. The integrated design of the variable-volume gas storage tank and actuator makes the system adjustment mechanism relatively simple and reliable. Through valve control logic, precise and flexible load adjustment and safe shutdown procedures can be achieved.

[0052] This invention significantly improves system reliability. This regulation method is not only used for load tracking, but also serves as an active safety measure, enhancing the entire energy storage system's ability to cope with grid fluctuations and abnormal operating conditions, thereby improving the overall reliability and economy of the system.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A closed-loop compressed carbon dioxide heat pump energy storage system, characterized in that, Includes a compressor, expander, motor, first heat exchanger, regenerator, second heat exchanger, and connecting piping, and also includes: A variable volume gas storage tank, the inlet of which is connected to the outlet of the expander, and the outlet of which is connected to the inlet of the first heat exchanger; The actuator is mechanically connected to the variable volume gas storage tank; Multiple regulating valves are connected to the actuator; Specifically, by operating the regulating valve, the driving fluid is controlled to act on the actuator, thereby driving the volume of the variable volume gas storage tank to change.

2. The closed-loop compression carbon dioxide heat pump energy storage system according to claim 1, characterized in that, The variable volume gas storage tank is equipped with a first piston, which divides the inside of the tank into a working fluid chamber and a back chamber. The first piston is connected to a first piston rod that extends out of the back chamber.

3. The closed-loop compression carbon dioxide heat pump energy storage system according to claim 2, characterized in that, The actuator is a double-acting hydraulic cylinder or a double-acting pneumatic cylinder. A second piston is provided inside the actuator, which divides the inner cavity of the actuator into a first chamber and a second chamber. The second piston is connected to a second piston rod. The first piston rod is connected to the second piston rod.

4. The closed-loop compression carbon dioxide heat pump energy storage system according to claim 3, characterized in that, The plurality of regulating valves include: A first regulating valve, the outlet of which is connected to the first chamber; The second regulating valve has its outlet connected to the second chamber; The third regulating valve has its inlet connected to the first chamber; The fourth regulating valve has its inlet connected to the second chamber.

5. The closed-loop compression carbon dioxide heat pump energy storage system according to claim 1, characterized in that, It also includes a cold salt tank and a hot salt tank; the first heat exchanger and the cold salt tank form a cold-end heat storage cycle, and the second heat exchanger and the hot salt tank form a hot-end heat storage cycle.

6. The closed-loop compression carbon dioxide heat pump energy storage system according to any one of claims 1 to 5, characterized in that, It also includes a displacement sensor for monitoring the volume of the variable-volume gas storage tank or the position of the piston.

7. The closed-loop compression carbon dioxide heat pump energy storage system according to any one of claims 1 to 5, characterized in that, It also includes a pressure sensor for monitoring system pressure, the pressure sensor being disposed at the working fluid chamber of the variable volume gas storage tank and / or the inlet of the compressor.

8. The closed-loop compression carbon dioxide heat pump energy storage system according to claim 3, characterized in that, The actuator is an electromechanical actuator driven by a servo motor, and is connected to the first piston rod or the second piston rod through a ball screw or gear rack mechanism.

9. The method of using the closed-loop compression carbon dioxide heat pump energy storage system according to any one of claims 1-8, characterized in that, Includes the following steps: Load increase step: Control the volume of the variable volume gas storage tank to decrease, thereby increasing the system pressure, increasing the working fluid mass flow rate, and realizing the increase of system load; Load reduction step: Control the increase of the volume of the variable volume gas storage tank to reduce the system pressure, thereby reducing the mass flow rate of the working fluid and reducing the system load.

10. The method of using the closed-loop compression carbon dioxide heat pump energy storage system according to claim 9, characterized in that, Also includes: Before or during system shutdown, the actuator is controlled to increase the volume of the variable volume gas storage tank to its design maximum value, thereby reducing the system stagnation pressure to below a safe level.

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