Energy release unit and control method thereof, compressed energy storage system

Abstract

The application discloses a kind of energy release units and its control method, compressed energy storage system.The energy release unit includes turbine with rotating shaft assembly, the first end of rotating shaft assembly is connected with first generator and the second end is connected with second generator;First generator is used to convert the mechanical energy of rotating shaft assembly into electric energy in the stable operation stage of energy release unit and is delivered to power grid;Second generator is permanent magnet DC generator and is used to convert the mechanical energy of rotating shaft assembly into electric energy in the shutdown stage of energy release unit and is delivered to battery assembly, whereby the rotating kinetic energy of rotating shaft assembly can be recycled to generate electricity and reduce energy waste;Second generator can also provide electromagnetic resistance to rotating shaft assembly while generating electricity, so that rotating shaft assembly reaches stop rotation faster and thus shortens the shutdown time of energy release unit, and auxiliary system can also stop running in advance accordingly to reduce plant power consumption, improve the overall economic benefits of energy storage system operation.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and in particular to an energy release unit and its control method, and a compressed energy storage system. Background Technology

[0002] Currently, energy storage technology based on carbon dioxide gas-liquid phase change cycle has gradually attracted widespread attention. During periods of low electricity demand, excess electricity or clean energy is used to compress and condense gaseous carbon dioxide at room temperature and pressure into liquid carbon dioxide, which is then stored in a liquid storage unit. The heat energy generated during the compression process is stored. During periods of high electricity demand, the stored heat energy is used to heat the liquid carbon dioxide back to a gaseous state. The gaseous carbon dioxide drives a turbine to generate electricity, and the gaseous carbon dioxide after doing work is returned to the gas storage unit for recycling. It has advantages such as simple structure, flexible layout, and high energy storage efficiency.

[0003] In the existing carbon dioxide energy storage technology system design, the energy storage mode and the energy release mode operate intermittently. The energy storage unit and the energy release unit need to complete at least one start-up and shutdown operation every day to match the diurnal fluctuation pattern of the grid load. When the energy release unit enters the shutdown stage during load reduction, it first needs to close the intake valve to cut off the supply of high-pressure carbon dioxide. Then, the turbine's rotating shaft assembly (including the rotor and connecting shaft) needs to gradually reduce from high speed to zero speed until the shutdown is completed by relying on the frictional resistance between itself, the gas and the bearing. This process is called "rotor coasting". The following problems exist in this stage: (1) Rotor kinetic energy is completely wasted: The large amount of rotational kinetic energy contained in the rotor during coasting is only converted into heat energy and dissipated through friction, without any recovery or utilization, resulting in energy waste; (2) Increased plant power consumption: Due to the limited frictional resistance, the rotor coasting time is usually long, while the auxiliary systems (such as cooling water system, shaft seal system, oil pump, cooling fan system, etc.) need to continue to run until the rotor stops completely before they can be shut down, resulting in additional plant power consumption of the auxiliary systems during coasting, which reduces the operating economy of the energy storage system. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides an energy release unit and its control method, as well as a compressed energy storage system, to solve the problems of how to recover rotational kinetic energy to reduce energy waste during the unloading and shutdown phase of the energy release unit, and how to shorten the shutdown time to reduce plant power consumption.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A first aspect of the present invention is to provide an energy release unit comprising a turbine having a rotating shaft assembly, wherein a first end of the rotating shaft assembly is connected to a first generator and a second end of the rotating shaft assembly is connected to a second generator.

[0007] The first generator is connected to the power grid and is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and transmit it to the power grid during the stable operation phase of the energy release unit.

[0008] The second generator is a permanent magnet DC generator connected to the battery pack. The second generator is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and deliver it to the battery pack during the shutdown phase of the energy release unit, and to provide electromagnetic resistance to the rotating shaft assembly to shorten the shutdown time of the energy release unit.

[0009] In one specific embodiment, the second generator is connected to a power regulator, which is used to regulate the output power of the second generator.

[0010] In one specific embodiment, the first generator is connected to the power grid via a first switching assembly, and the second generator is connected to the battery assembly via a second switching assembly.

[0011] In one specific embodiment, the battery assembly is electrically connected to the plant's electrical equipment.

[0012] In one specific embodiment, the energy release unit includes a superheater, a high-pressure turbine, a reheater, and a low-pressure turbine connected in sequence, with the high-pressure turbine and the low-pressure turbine coaxially connected via the rotating shaft assembly.

[0013] A second aspect of the present invention is to provide a control method for the energy release unit as described above, the control method comprising: when the energy release unit enters the shutdown operation phase, turning off the first generator and turning on the second generator, the second generator converting the mechanical energy of the rotating shaft assembly into electrical energy and delivering it to the battery assembly and providing electromagnetic resistance, thereby reducing the coasting time of the rotating shaft assembly and shortening the shutdown time of the energy release unit.

[0014] In one specific embodiment, the control method further includes: when the energy release unit starts running, the high-voltage turbine and the low-voltage turbine operate under no-load conditions to accelerate; when the high-voltage turbine and the low-voltage turbine reach their rated speeds, the first generator is started and connected to the grid to generate electricity, the energy release unit enters a stable operation phase, the high-voltage turbine and the low-voltage turbine operate under load, and the first generator converts the mechanical energy of the rotating shaft assembly into electrical energy and transmits it to the power grid.

[0015] A third aspect of the present invention is to provide a compressed energy storage system comprising a gas storage unit, an energy storage unit, a liquid storage unit, and an energy release unit connected in a closed loop in sequence, wherein the energy release unit is the energy release unit as described above and is controlled by the control method described above.

[0016] In one specific embodiment, the compressed energy storage system further includes a condenser connected between the energy storage unit and the liquid storage unit, and an evaporator connected between the liquid storage unit and the energy release unit.

[0017] In one specific embodiment, the energy storage unit includes a compressor and an energy storage heat exchanger connected in sequence.

[0018] The present invention provides an energy release unit and its control method, and a compressed energy storage system. The energy release unit includes a turbine with a rotating shaft assembly. A first generator is connected to a first end of the rotating shaft assembly, and a second generator is connected to a second end of the rotating shaft assembly. The first generator is connected to the power grid and is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and transmit it to the power grid during the stable operation phase of the energy release unit. The second generator is a permanent magnet DC generator and is connected to a battery assembly. The second generator is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and transmit it to the battery assembly during the shutdown phase of the energy release unit, and to provide electromagnetic resistance to the rotating shaft assembly to shorten the shutdown time of the energy release unit. By setting up a second generator, specifically a permanent magnet DC generator, during the shutdown phase of the energy release unit: on the one hand, the second generator recovers the rotational kinetic energy of the rotating shaft assembly to generate electricity and store it in the battery assembly. The electrical energy stored in the battery assembly can be used as plant power, thereby reducing energy waste; on the other hand, while generating electricity, the second generator can also provide electromagnetic resistance to the rotating shaft assembly, enabling the rotating shaft assembly to stop rotating more quickly, thus shortening the shutdown time of the energy release unit. Auxiliary systems (such as cooling water system, shaft sealing system, oil pump, cooling fan system, etc.) can also stop operating earlier, thereby reducing plant power consumption and improving the overall economic efficiency of the energy storage system. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the energy release unit and the corresponding compressed energy storage system in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the drawings. The embodiments of the present invention shown in and described with reference to the drawings are merely exemplary, and the present invention is not limited to these embodiments.

[0021] It should be noted that the same or similar reference numerals in the accompanying drawings of the embodiments of the present invention correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing the present 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, the terms used to describe positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0022] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0023] This invention first provides an energy release unit and a compressed energy storage system including the energy release unit. The compressed energy storage system can be a compressed energy storage system using carbon dioxide or air as the working fluid. This embodiment uses carbon dioxide as an example for specific explanation.

[0024] See Figure 1 The compressed energy storage system mainly includes a gas storage unit 10, an energy storage unit 20, a liquid storage unit 30, and an energy release unit 40 connected in a closed loop. The gas storage unit 10 stores gaseous carbon dioxide at atmospheric pressure, and the liquid storage unit 30 stores liquid carbon dioxide. The gaseous carbon dioxide flowing from the gas storage unit 10 is converted into liquid carbon dioxide at a preset energy storage pressure by the energy storage unit 20 and flows into the liquid storage unit 30, completing energy storage in this process. The liquid carbon dioxide output from the liquid storage unit 30 releases energy by the energy release unit 40, converting back into gaseous carbon dioxide at atmospheric pressure, and flows into the gas storage unit 10, completing energy release and application in this process. Typically, during off-peak electricity demand periods or by utilizing wind and solar power curtailment, the energy storage unit 20 compresses and liquefies the gaseous carbon dioxide into liquid carbon dioxide, storing it in the liquid storage unit 30, converting energy into compressible energy and thermal energy for storage. During peak electricity demand periods, the energy release unit 40 vaporizes and expands the liquid carbon dioxide, releasing the stored energy and converting it into electrical energy for use.

[0025] As a specific example, in this embodiment, such as Figure 1As shown, the energy storage unit 20 mainly includes a compressor 21 and an energy storage heat exchanger 22 connected between the gas storage unit 10 and the liquid storage unit 30. Further, a condenser 50 is installed on the connecting pipeline between the energy storage unit 20 and the liquid storage unit 30. The gaseous carbon dioxide in the gas storage unit 10 is compressed by the compressor 21, cooled by the energy storage heat exchanger 22, and then liquefied by the condenser 50 to form liquid carbon dioxide, which is stored in the liquid storage unit 30.

[0026] As a specific example, in this embodiment, such as Figure 1 As shown, the energy release unit 40 mainly includes a superheater 41, a high-pressure turbine 42, a reheater 43, and a low-pressure turbine 44 connected between the liquid storage unit 30 and the gas storage unit 10. Further, a first evaporator 60 is installed on the connecting pipeline between the liquid storage unit 30 and the energy release unit 40. The liquid carbon dioxide in the liquid storage unit 30 is heated and evaporated by the first evaporator 60, then fed into the superheater 41 for further heating and temperature increase. It then enters the high-pressure turbine 42 to expand and release energy. The carbon dioxide gas discharged from the high-pressure turbine 42 is reheated by the reheater 43 and enters the low-pressure turbine 44 to expand and release energy, finally forming atmospheric pressure gaseous carbon dioxide stored in the gas storage unit 10.

[0027] In existing technologies, when the energy release unit enters the shutdown phase due to load reduction, the high-speed rotating mechanism in the turbine generator set gradually reduces its speed from high to zero until shutdown is completed, relying on the frictional resistance between itself, the gas, and the bearings. This process not only results in the ineffective utilization of rotor kinetic energy, leading to energy waste, but also causes additional plant power consumption in the auxiliary systems, reducing the operational economy of the energy storage system. To address this problem, the present invention improves the energy release unit 40, such as... Figure 1 As shown, in the energy release unit 40, the high-pressure turbine 42 and the low-pressure turbine 44 are coaxially connected via a rotating shaft assembly (including a rotor and connecting shaft, etc.) 45. A first generator 1 is connected to the first end of the rotating shaft assembly 45, and a second generator 4 is connected to the second end of the rotating shaft assembly 45. The first generator 1 is connected to the power grid 2 and is used to convert the mechanical energy of the rotating shaft assembly 45 into electrical energy and supply it to the power grid 2 during the stable operation phase of the energy release unit 40. The second generator 4 is a permanent magnet DC generator connected to the battery assembly 5. During the shutdown phase of the energy release unit 40, the second generator 4 is used to convert the mechanical energy of the rotating shaft assembly 45 into electrical energy and supply it to the battery assembly 5, and to provide electromagnetic resistance to the rotating shaft assembly 45, thereby shortening the shutdown time of the energy release unit 40.

[0028] Specifically, when the energy release condition ends and the first generator 1, used for grid-connected power generation, drops to its minimum load, the output switch of the second generator 4 is closed. The high-voltage turbine 42 and the low-voltage turbine 44 are tripped and enter a coasting state. The second generator 4 generates electricity and supplies it to the battery assembly 5. Due to the electromagnetic resistance of the permanent magnet DC generator (second generator 4) when the turbine rotor is outputting electrical energy, the turbine rotor will stop quickly, recovering the coasting energy of the turbine rotor, shortening the turbine downtime, and the auxiliary equipment system will stop operating earlier accordingly, reducing plant power consumption. The electrical energy stored in the battery assembly 5 can be used for DC power systems such as plant lighting and will continue to charge during the next energy release condition.

[0029] It should be noted that in some other embodiments, the energy release unit 40 may contain only one turbine, or more turbines may be coaxially connected via the rotating shaft assembly 45. This requires connecting the first generator 1 and the second generator 4 to both ends of the rotating shaft assembly 45, respectively. The first generator 1 is preferably an AC generator.

[0030] Based on the energy release unit and its corresponding compressed energy storage system provided in this embodiment, during the shutdown phase of the energy release unit 40: on the one hand, the second generator 4 recovers the rotational kinetic energy of the rotating shaft assembly 45 to generate electricity and store it in the battery assembly 5, thereby reducing energy waste; on the other hand, while generating electricity, the second generator 4 can also provide electromagnetic resistance to the rotating shaft assembly 45, so that the rotating shaft assembly 45 can stop rotating more quickly, thereby shortening the shutdown time of the energy release unit 40. Auxiliary systems (such as cooling water system, shaft seal system, oil pump, cooling fan system, etc.) can also stop operating in advance accordingly, thereby reducing plant power consumption, thereby improving the overall economic efficiency of the energy storage system operation.

[0031] In this embodiment, the first generator 1 is connected to the power grid 2 via the first switch assembly 3, and the second generator 4 is connected to the battery assembly 5 via the second switch assembly 6.

[0032] Furthermore, such as Figure 1 As shown, the second generator 4 is connected to a power regulator 7, which is used to regulate the output power of the second generator 4. The battery pack 5 is electrically connected to the plant auxiliary equipment 8, and the electrical energy stored in the battery pack 5 can be used as plant auxiliary power. The plant auxiliary equipment 8 is, for example, a lighting device.

[0033] Based on the energy release unit provided in the above embodiments, the present invention also provides a control method for the energy release unit. The control method includes: when the energy release unit 40 enters the shutdown operation stage, turning off the first generator 1 and turning on the second generator 4. The second generator 4 converts the mechanical energy of the rotating shaft assembly 45 into electrical energy and delivers it to the battery assembly 5, providing electromagnetic resistance, reducing the coasting time of the rotating shaft assembly 45, thereby shortening the shutdown time of the energy release unit 40.

[0034] Specifically, during the energy release phase of the compressed energy storage unit, the control method for the energy release unit includes the following steps:

[0035] S11. When the energy release unit 40 starts to run, the high-pressure turbine 42 and the low-pressure turbine 44 start to accelerate under no-load conditions.

[0036] S12. After the high-pressure turbine 42 and the low-pressure turbine 44 reach their rated speeds, the first generator 1 is started and connected to the grid for power generation.

[0037] Specifically, after the high-voltage turbine 42 and the low-voltage turbine 44 reach their rated speed, the first generator 1 is started and the first switch assembly 3 is closed. The first generator 1 is connected to the power grid 2, the energy release unit 40 enters the stable operation stage, the high-voltage turbine 42 and the low-voltage turbine 44 operate under load, and the first generator 1 converts the rotational kinetic energy of the rotating shaft assembly 45 into electrical energy and transmits it to the power grid 2.

[0038] S13. When the energy release unit 40 enters the shutdown operation stage, the first generator 1 is turned off and the second generator 4 is turned on. The second generator 4 converts the mechanical energy of the rotating shaft assembly 45 into electrical energy and delivers it to the battery assembly 5, providing electromagnetic resistance, reducing the coasting time of the rotating shaft assembly 45, thereby shortening the shutdown time of the energy release unit 40.

[0039] Specifically, when the energy release operation ends, the first generator 1 is shut down, the high-pressure turbine 42 and the low-pressure turbine 44 are tripped and their inlet valves are closed, and the high-pressure turbine 42 and the low-pressure turbine 44 enter a coasting state. At this time, the second generator 4 is started and the second switch assembly 6 is closed. The second generator 4 is connected to the battery assembly 5, and the output power of the second generator 4 is adjusted by the power regulator 7. The second generator 4 converts the rotational kinetic energy of the rotating shaft assembly 45 into electrical energy and delivers it to the battery assembly 5. Thus, during the shutdown operation phase of the energy release unit 40, the second generator 4 can recover the rotational kinetic energy of the rotating shaft assembly 45 to generate electricity, thereby reducing energy waste. Furthermore, while generating electricity, the second generator 4 can also provide electromagnetic resistance to the rotating shaft assembly 45, enabling the rotating shaft assembly 45 to stop rotating more quickly, thereby shortening the shutdown time of the energy release unit 40.

[0040] In summary, the energy release unit and its control method, as well as the compressed energy storage system provided by the embodiments of the present invention, can not only recover the kinetic energy of rotor rotation for power generation during the "rotor coasting" stage, thereby reducing energy waste, but also reduce the coasting time and shorten the downtime of the energy release unit. This allows auxiliary systems such as cooling water systems, shaft sealing systems, oil pumps, and cooling fan systems to stop operating earlier, thereby reducing plant power consumption and improving the overall economic efficiency of the energy storage system operation.

[0041] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A control method for an energy-releasing unit, characterized in that, The energy release unit includes a superheater, a high-pressure turbine, a reheater, and a low-pressure turbine connected in sequence. The high-pressure turbine and the low-pressure turbine are coaxially connected via a rotating shaft assembly. A first generator is connected to the first end of the rotating shaft assembly, and a second generator is connected to the second end of the rotating shaft assembly. The first generator is connected to the power grid and is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and supply it to the power grid during the stable operation phase of the energy release unit. The second generator is a permanent magnet DC generator connected to a battery pack. The second generator is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and supply it to the battery pack during the shutdown phase of the energy release unit, and to provide electromagnetic resistance to the rotating shaft assembly to shorten the shutdown time of the energy release unit. The control method includes: When the energy release unit starts running, the high-pressure turbine and the low-pressure turbine start up and accelerate under no-load conditions; when the high-pressure turbine and the low-pressure turbine reach their rated speed, the first generator is started and connected to the grid to generate electricity, the energy release unit enters the stable operation stage, the high-pressure turbine and the low-pressure turbine operate under load, and the first generator converts the mechanical energy of the rotating shaft assembly into electrical energy and transmits it to the power grid; When the energy release unit enters the shutdown operation phase, the first generator is turned off and the second generator is turned on. The second generator converts the mechanical energy of the rotating shaft assembly into electrical energy and delivers it to the battery assembly, providing electromagnetic resistance to reduce the coasting time of the rotating shaft assembly and thus shorten the shutdown time of the energy release unit.

2. The control method for the energy-releasing unit according to claim 1, characterized in that, The second generator is connected to a power regulator, which is used to regulate the output power of the second generator.

3. The control method for the energy-releasing unit according to claim 1, characterized in that, The first generator is connected to the power grid via a first switching assembly, and the second generator is connected to the battery assembly via a second switching assembly.

4. The control method for the energy-releasing unit according to claim 1, characterized in that, The battery assembly is electrically connected to the plant's electrical equipment.

5. A compressed energy storage system, comprising a gas storage unit, an energy storage unit, a liquid storage unit, and an energy release unit connected in a closed loop in sequence, characterized in that, The energy release unit is controlled using the control method described in any one of claims 1-4.

6. The compressed energy storage system according to claim 5, characterized in that, The compressed energy storage system also includes a condenser connected between the energy storage unit and the liquid storage unit, and an evaporator connected between the liquid storage unit and the energy release unit.

7. The compressed energy storage system according to claim 5, characterized in that, The energy storage unit includes a compressor and an energy storage heat exchanger connected in sequence.

Images