Gas-liquid phase change compressed carbon dioxide energy storage system and control method thereof

Abstract

The invention discloses a gas-liquid phase change compressed carbon dioxide energy storage system which comprises a gas storage unit, an energy storage unit, a liquid storage unit and an energy release unit which are sequentially connected in a closed loop mode, the energy release unit comprises a superheater, a high-pressure turbine, a reheater and a low-pressure turbine which are sequentially connected, and a second evaporator is arranged in an exhaust cylinder of the low-pressure turbine. The input end of the second evaporator is connected to the outlet end of the liquid storage unit, and the output end of the second evaporator is connected to the inlet end of the reheater. The second evaporator is configured to receive the liquid working medium from the liquid storage unit in the no-load starting stage of the energy release unit so that the liquid working medium can be evaporated and gasified, and therefore the exhaust temperature of the low-pressure turbine can be reduced, and the gaseous working medium formed through evaporation and gasification is input into the low-pressure turbine through the reheater to continue acting. Therefore, the risk of equipment damage caused by overhigh exhaust temperature during turbine operation is reduced, the exhaust heat of the turbine is recovered, the total air inflow of the turbine is reduced, and the overall efficiency of a system unit is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a gas-liquid phase change compressed carbon dioxide energy storage system and a control method thereof. BACKGROUND

[0002] At present, the energy storage technology based on carbon dioxide gas-liquid phase change cycle compresses and condenses the gaseous carbon dioxide at normal temperature and pressure in the gas storage unit into liquid carbon dioxide and stores it in the liquid storage unit by using excess power or clean energy during the off-peak period, and stores the heat energy generated during the compression process, and uses the stored heat energy to heat the liquid carbon dioxide to gaseous carbon dioxide during the peak period, and the gaseous carbon dioxide drives the turbine to drive the generator to generate electricity, and the gaseous carbon dioxide after work returns to the gas storage unit for recycling, which has the advantages of simple structure, flexible layout, high energy storage efficiency, etc., and has gradually attracted widespread attention.

[0003] In the system design of the existing carbon dioxide energy storage technology, the energy storage mode and the energy release mode are intermittent operation, and the energy storage unit and the energy release unit need to complete at least one start and stop operation per day to match the day and night fluctuation of the power grid load. When the energy release unit starts, the turbine in it needs to go through the process of accelerating from zero speed to rated speed, and when the speed reaches the rated value, it can be connected to the power grid and output power externally. During the process of accelerating the turbine, the turbine is in an empty load running state, and the turbine cannot do work externally in this state. Due to the mechanical characteristics of the turbine, the energy conversion efficiency is very low when the turbine is in an empty load running state, and a large amount of high-pressure carbon dioxide energy is not effectively utilized, resulting in the turbine exhaust temperature often exceeding the safety alarm value set by the system. Moreover, since the turbine needs to be started every day, frequent high-temperature exhaust will cause continuous damage to the metal stress of the turbine low-pressure cylinder bearing, the performance of the lubricating oil, and the material strength of the last-stage blade, and long-term operation will greatly shorten the service life of the equipment, increase the maintenance cost and operation risk of the energy storage system. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a gas-liquid phase change compressed carbon dioxide energy storage system and a control method thereof to solve the problem of how to reduce the turbine exhaust temperature during the start-up phase of the energy release unit and effectively utilize the energy of high-pressure carbon dioxide.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: The first aspect of the present application provides a gas-liquid phase change compression carbon dioxide energy storage system, comprising a gas storage unit, an energy storage unit, a liquid storage unit and a energy release unit connected in sequence in a closed loop, wherein the energy release unit comprises a superheater, a high-pressure turbine, a reheater and a low-pressure turbine connected in sequence, a second evaporator is arranged in the exhaust cylinder of the low-pressure turbine, the input end of the second evaporator is connected to the outlet end of the liquid storage unit, and the output end of the second evaporator is connected to the inlet end of the reheater; wherein the second evaporator is configured to receive liquid working medium from the liquid storage unit in the idle start stage of the energy release unit to evaporate and gasify the liquid working medium so as to reduce the exhaust temperature of the low-pressure turbine, and input the gaseous working medium formed by evaporation and gasification into the low-pressure turbine through the reheater.

[0006] In one specific embodiment, the input end of the second evaporator is connected to the outlet end of the liquid storage unit through a first pipeline, the output end of the second evaporator is connected to the inlet end of the reheater through a second pipeline, and a gate valve and a throttling regulating valve are arranged on the first pipeline.

[0007] In one specific embodiment, the second evaporator is an expansion evaporator.

[0008] In one specific embodiment, the gas-liquid phase change compression carbon dioxide energy storage system further comprises a condenser connected between the energy storage unit and the liquid storage unit, and a first evaporator connected between the liquid storage unit and the energy release unit.

[0009] In one specific embodiment, the high-pressure turbine and the low-pressure turbine are coaxially connected through 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; wherein the first generator is connected to a power grid, and the first generator is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and transmit the electrical energy to the power grid in the stable operation stage of the energy release unit; wherein the second generator is a permanent magnet direct current generator and is connected to a battery assembly, and the second generator is used to convert the mechanical energy of the rotating shaft assembly into electrical energy and transmit the electrical energy to the battery assembly in the shutdown stage of the energy release unit, and to provide electromagnetic resistance to the rotating shaft assembly so as to shorten the shutdown time of the energy release unit.

[0010] In one specific embodiment, the second generator is connected with a power regulator, and the power regulator is used to adjust the output power of the second generator.

[0011] In one specific embodiment, the first generator is connected to the power grid through a first switch assembly, and the second generator is connected to the battery assembly through a second switch assembly.

[0012] In one specific embodiment, the battery assembly is electrically connected to the plant's electrical equipment.

[0013] A second aspect of the present invention is to provide a control method for the gas-liquid phase change compressed carbon dioxide energy storage system as described above, the control method comprising: When the energy release unit starts running, the high-pressure turbine and the low-pressure turbine start up and accelerate under no-load conditions. At this time, the liquid working fluid in the liquid storage unit is transported to the second evaporator for evaporation and vaporization, and the gaseous working fluid formed by evaporation and vaporization is input to the low-pressure turbine through the reheater. After the high-pressure turbine and the low-pressure turbine reach their rated speeds, the high-pressure turbine and the low-pressure turbine operate under load, at which point the delivery of the liquid working fluid from the storage unit to the second evaporator is stopped.

[0014] A third aspect of the present invention is to provide another control method for the gas-liquid phase change compression carbon dioxide energy storage system as described above, the control method comprising: When the energy release unit starts to run, the high-pressure turbine and the low-pressure turbine run under no-load to accelerate. At this time, the liquid working fluid in the liquid storage unit is transported to the second evaporator for evaporation and vaporization, and the gaseous working fluid formed by evaporation and vaporization is input to the low-pressure turbine through the reheater. After 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 a stable operation phase. The high-pressure turbine and the low-pressure turbine operate under load. At this time, the liquid working fluid in the liquid storage unit is stopped from being transported to the second evaporator. 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, reducing the coasting time of the rotating shaft assembly, and thus shortening the shutdown time of the energy release unit.

[0015] The gas-liquid phase change compression carbon dioxide energy storage system and its control method provided in this invention involve installing a second evaporator in the exhaust cylinder of the low-pressure turbine in the energy release unit. The input end of the second evaporator is connected to the outlet end of the liquid storage unit, and the output end is connected to the inlet end of the reheater. During the no-load start-up phase of the energy release unit, the second evaporator receives liquid working fluid from the liquid storage unit, causing the liquid working fluid to evaporate and vaporize, thereby reducing the exhaust temperature of the low-pressure turbine. The gaseous working fluid formed by evaporation and vaporization is then heated by the reheater and input into the low-pressure turbine to continue performing work. This not only reduces the risk of equipment damage caused by excessively high exhaust temperature during turbine operation but also recovers the exhaust heat from the turbine, reduces the total turbine intake, and improves the overall efficiency of the system unit. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the gas-liquid phase change compression carbon dioxide energy storage system in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the gas-liquid phase change compression carbon dioxide energy storage system in Embodiment 2 of the present invention. Detailed Implementation

[0017] 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.

[0018] 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.

[0019] 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.

[0020] Example 1 This embodiment first provides a gas-liquid phase change compressed carbon dioxide energy storage system, such as Figure 1As shown, the gas-liquid phase change compressed carbon dioxide 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 out of 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 compression 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.

[0021] As a specific example, in this embodiment, such as Figure 1 As 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.

[0022] 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.

[0023] Among them, such as Figure 1As 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 the first generator 1 is connected to the power grid 2, specifically via a first switch assembly 3. The first generator 1 is used to convert the mechanical energy of the rotating shaft assembly 45 into electrical energy and transmit it to the power grid 2 during the stable operation phase of the energy release unit 40. Preferably, the first generator 1 is an AC generator.

[0024] In the existing technology, during the energy release phase, when the energy release unit starts to run, the turbine is in an unloaded operating state and cannot perform external work. A large amount of energy from high-pressure carbon dioxide is not effectively utilized. Furthermore, since the turbine needs to be started every day, frequent high-temperature exhaust will cause continuous damage to the bearing metal stress, lubricating oil performance, and material strength of the last stage blades of the low-pressure turbine. Long-term operation will significantly shorten the service life of the equipment and increase the maintenance cost and operational risks of the energy storage system.

[0025] To address the above issues, the gas-liquid phase change compression carbon dioxide energy storage system provided in this embodiment is described in reference to... Figure 1 A second evaporator 100 is installed in the exhaust cylinder of the low-pressure turbine 44. The input end of the second evaporator 100 is connected to the outlet end of the liquid storage unit 30, and the output end of the second evaporator 100 is connected to the inlet end of the reheater 43. The second evaporator 100 is configured to receive liquid working fluid from the liquid storage unit 30 during the no-load start-up phase of the energy release unit 40, causing the liquid working fluid to evaporate and vaporize, thereby reducing the exhaust temperature of the low-pressure turbine 44. The gaseous working fluid formed by the evaporation and vaporization is then input to the low-pressure turbine through the reheater 43. Preferably, the second evaporator 100 is selected as an expansion evaporator.

[0026] Based on the gas-liquid phase change compression carbon dioxide energy storage system provided in this embodiment, during the no-load start-up phase of the energy release unit 40, the second evaporator 100 receives liquid working fluid from the liquid storage unit 30. The liquid working fluid evaporates and vaporizes in the second evaporator 100, absorbing heat and thus reducing the exhaust temperature of the low-pressure turbine 44. This not only reduces the risk of equipment damage due to excessively high exhaust temperature during turbine operation but also recovers the exhaust heat from the turbine. Furthermore, the gaseous working fluid formed by evaporation and vaporization is heated by the reheater 43 and then input into the low-pressure turbine 44 to continue performing work. This reduces the total turbine intake of the energy release unit 40 and improves the overall efficiency of the system unit.

[0027] In specific plans, such as Figure 1As shown, the input end of the second evaporator 100 is connected to the outlet end of the liquid storage unit 30 via a first pipe 200, and the output end of the second evaporator 100 is connected to the inlet end of the reheater 43 via a second pipe 300. A gate valve 400 and a throttling regulating valve 500 are provided on the first pipe 200. The flow rate of the liquid working fluid input to the second evaporator 100 is regulated by controlling the gate valve 400 and the throttling regulating valve 500. Specifically, when the high-pressure turbine 42 and the low-pressure turbine 44 start under no-load conditions, as the turbine speed increases, the exhaust temperature of the exhaust cylinder of the low-pressure turbine 44 gradually rises. At this time, the gate valve 400 and the throttling valve 500 are opened, and the high-pressure liquid carbon dioxide enters the second evaporator 100 for expansion and heat absorption after throttling. The exhaust temperature of the exhaust cylinder of the low-pressure turbine 44 decreases, and the high-pressure liquid carbon dioxide evaporates into high-pressure carbon dioxide gas in the second evaporator 100. The high-pressure carbon dioxide gas enters the reheater 43 for further heating and then enters the low-pressure turbine 44 to do work, thereby recovering heat, and the total intake flow of the turbines (high-pressure turbine 42 and low-pressure turbine 44) decreases. When the turbine reaches its rated speed, it successfully synchronizes with the power grid and outputs electrical energy. When the turbine is running under load, the exhaust temperature of the exhaust cylinder of the low-pressure turbine 44 decreases. At this time, the gate valve 400 and the throttling valve 500 are closed, and the turbine operates stably under load.

[0028] Based on the gas-liquid phase change compressed carbon dioxide energy storage system described above, this embodiment also provides a control method for the gas-liquid phase change compressed carbon dioxide energy storage system. The control method includes an energy storage stage and an energy release stage. Specifically, in the energy release stage, the operation of the energy release unit 40 includes the following steps: S11. When the energy release unit 40 starts to run, the high-pressure turbine 42 and the low-pressure turbine 44 run under no-load to accelerate. At this time, the liquid working fluid in the liquid storage unit 30 is transported to the second evaporator 100 for evaporation and vaporization, and the gaseous working fluid formed by evaporation and vaporization is input to the low-pressure turbine 44 through the reheater 43.

[0029] In the above process, the liquid working fluid evaporates and vaporizes in the second evaporator 100, absorbing heat from the exhaust cylinder of the low-pressure turbine 44. This reduces the temperature of the gaseous working fluid in the exhaust cylinder of the low-pressure turbine 44, i.e., lowers the exhaust temperature of the low-pressure turbine 44, effectively reducing the risk of equipment damage caused by excessively high exhaust temperatures during turbine operation. On the other hand, the gaseous working fluid formed by evaporation and vaporization is heated by the reheater 43 and then input into the low-pressure turbine 44 to continue performing work, realizing the recovery and reuse of exhaust heat. This reduces the total intake flow rate required at the turbine front end and improves the overall efficiency of the system unit.

[0030] S12. After the high-pressure turbine 42 and the low-pressure turbine 44 reach their rated speed, the first generator 1 is started and connected to the grid for power generation. The energy release unit 40 enters the stable operation stage. The high-pressure turbine 42 and the low-pressure turbine 44 operate under load. At this time, the liquid working fluid in the liquid storage unit 30 is stopped from being transported to the second evaporator 100. The first generator 1 converts the mechanical energy of the rotating shaft assembly 45 into electrical energy and transmits it to the power grid 2.

[0031] Specifically, after the high-pressure turbine 42 and the low-pressure turbine 44 reach their rated speeds, 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 for grid-connected power generation. The high-pressure turbine 42 and the low-pressure turbine 44 operate under load. The exhaust temperature of the low-pressure turbine 44 gradually decreases, and there is no need to absorb heat and cool down through the second evaporator 100. Therefore, at this time, the gate valve 400 and the throttling regulating valve 500 are closed to stop the delivery of the liquid working fluid in the liquid storage unit 30 to the second evaporator 100.

[0032] S13. When the energy release unit 40 enters the shutdown operation stage, the first generator 1 is turned off, and the rotating shaft assembly 45 gradually reduces its speed until it finally stops rotating.

[0033] Specifically, when the energy release condition ends, the first generator 1 is shut down, the high-pressure turbine 42 and the low-pressure turbine 44 are tripped and the inlet valves are closed, the high-pressure turbine 42 and the low-pressure turbine 44 enter a coasting state, and the rotating shaft assembly 45 gradually slows down until it finally stops.

[0034] Example 2 In the gas-liquid phase change compression carbon dioxide energy storage system provided in Example 1, in step S13 of the operation process of the energy release unit 40, during the shutdown operation phase of the energy release unit 40, the high-pressure turbine 42 and the low-pressure turbine 44 enter the coasting state, and the rotating shaft assembly 45 needs to gradually reduce from high speed to zero speed until the shutdown is completed by relying on its own frictional resistance with the gas and bearings. 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 the coasting process is only converted into heat energy and dissipated through friction, without any recovery and 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 system (such as cooling water system, shaft seal system, oil pump, cooling fan system, etc.) needs to continue to run until the rotor stops completely before it can be shut down, resulting in additional plant power consumption of the auxiliary system during the coasting period, which reduces the operating economy of the energy storage system.

[0035] To address the above issues, Example 2 provides a gas-liquid phase change compression carbon dioxide energy storage system, which is an improvement upon the gas-liquid phase change compression carbon dioxide energy storage system provided in Example 1. The following only details the differences between the gas-liquid phase change compression carbon dioxide energy storage system of this example and Example 1, while the identical parts will not be repeated.

[0036] See Figure 2 In the gas-liquid phase change compressed carbon dioxide energy storage system provided in this embodiment, a second generator 4 is connected to the second end of the rotating shaft assembly 45 in the energy release unit 40. The second generator 4 is a permanent magnet DC generator and is connected to the battery assembly 5, specifically through a second switch assembly 6. The second generator 4 is used to convert the mechanical energy of the rotating shaft assembly 45 into electrical energy and deliver it to the battery assembly 5 during the shutdown phase of the energy release unit 40, and to provide electromagnetic resistance to the rotating shaft assembly 45, thereby shortening the shutdown time of the energy release unit 40.

[0037] 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.

[0038] Based on the gas-liquid phase change compressed carbon dioxide energy storage system provided in this embodiment, during the shutdown phase of the energy release unit 40: on the one hand, the rotational kinetic energy of the rotating shaft assembly 45 is recovered by the second generator 4 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.

[0039] Among them, such as Figure 2As 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.

[0040] Based on the gas-liquid phase change compressed carbon dioxide energy storage system provided in this embodiment, this embodiment also provides a control method for the gas-liquid phase change compressed carbon dioxide energy storage system. The control method for the gas-liquid phase change compressed carbon dioxide energy storage system includes an energy storage stage and an energy release stage. Specifically, in the energy release stage, the operation of the energy release unit 40 includes the following steps: S21. When the energy release unit 40 starts running, the high-pressure turbine 42 and the low-pressure turbine 44 start up under no-load conditions. At this time, the liquid working fluid in the liquid storage unit 30 is transported to the second evaporator 100 for evaporation and vaporization, and the gaseous working fluid formed by evaporation and vaporization is input to the low-pressure turbine 44 through the reheater 43. That is, step S21 is the same as step S11 in embodiment 1.

[0041] S22. 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. The energy release unit 40 enters a stable operation phase, and the high-pressure turbine 42 and the low-pressure turbine 44 operate under load. At this time, the transfer of the liquid working fluid in the liquid storage unit 30 to the second evaporator 100 is stopped. The first generator 1 converts the mechanical energy of the rotating shaft assembly 45 into electrical energy and transmits it to the power grid 2. That is, step S22 is the same as step S12 in Embodiment 1.

[0042] S23. 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.

[0043] 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 mechanical 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, thereby shortening the shutdown time of the energy release unit 40.

[0044] 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 gas-liquid phase change compressed carbon dioxide 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 includes a superheater, a high-pressure turbine, a reheater, and a low-pressure turbine connected in sequence. A second evaporator is provided in the exhaust cylinder of the low-pressure turbine. The input end of the second evaporator is connected to the outlet end of the liquid storage unit, and the output end of the second evaporator is connected to the inlet end of the reheater. The second evaporator is configured to receive liquid working fluid from the liquid storage unit during the no-load start-up phase of the energy release unit, thereby reducing the exhaust temperature of the low-pressure turbine by evaporating and vaporizing the liquid working fluid, and input the gaseous working fluid formed by evaporation and vaporization to the low-pressure turbine through the reheater.

2. The gas-liquid phase change compressed carbon dioxide energy storage system according to claim 1, characterized in that, The input end of the second evaporator is connected to the outlet end of the liquid storage unit through a first pipe, and the output end of the second evaporator is connected to the inlet end of the reheater through a second pipe. A gate valve and a throttling regulating valve are provided on the first pipe.

3. The gas-liquid phase change compressed carbon dioxide energy storage system according to claim 1, characterized in that, The second evaporator is an expanded capacity evaporator.

4. The gas-liquid phase change compressed carbon dioxide energy storage system according to claim 1, characterized in that, The gas-liquid phase change compressed carbon dioxide energy storage system further includes a condenser connected between the energy storage unit and the liquid storage unit, and a first evaporator connected between the liquid storage unit and the energy release unit.

5. The gas-liquid phase change compressed carbon dioxide energy storage system according to any one of claims 1-4, characterized in that, The high-pressure turbine and the low-pressure turbine are coaxially connected by 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 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 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.

6. The gas-liquid phase change compressed carbon dioxide energy storage system according to claim 5, characterized in that, The second generator is connected to a power regulator, which is used to regulate the output power of the second generator.

7. The gas-liquid phase change compressed carbon dioxide energy storage system according to claim 5, 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.

8. The gas-liquid phase change compressed carbon dioxide energy storage system according to claim 5, characterized in that, The battery assembly is electrically connected to the plant's electrical equipment.

9. A control method for a gas-liquid phase change compressed carbon dioxide energy storage system as described in any one of claims 1-8, characterized in that, 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. At this time, the liquid working fluid in the liquid storage unit is transported to the second evaporator for evaporation and vaporization, and the gaseous working fluid formed by evaporation and vaporization is input to the low-pressure turbine through the reheater. After the high-pressure turbine and the low-pressure turbine reach their rated speeds, the high-pressure turbine and the low-pressure turbine operate under load, at which point the delivery of the liquid working fluid from the storage unit to the second evaporator is stopped.

10. A control method for a gas-liquid phase change compressed carbon dioxide energy storage system as described in any one of claims 5-8, characterized in that, The control method includes: When the energy release unit starts to run, the high-pressure turbine and the low-pressure turbine run under no-load to accelerate. At this time, the liquid working fluid in the liquid storage unit is transported to the second evaporator for evaporation and vaporization, and the gaseous working fluid formed by evaporation and vaporization is input to the low-pressure turbine through the reheater. After 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 a stable operation phase. The high-pressure turbine and the low-pressure turbine operate under load. At this time, the liquid working fluid in the liquid storage unit is stopped from being transported to the second evaporator. 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, reducing the coasting time of the rotating shaft assembly, and thus shortening the shutdown time of the energy release unit.

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