Heat storage system coupled with multi-stage steam heat accumulator and operation method of heat storage system

Abstract

The invention discloses a heat storage system coupled with a multi-stage steam heat accumulator and an operation method of the heat storage system, and belongs to the technical field of heat energy storage. The heat storage system coupled with the multi-stage steam heat accumulator comprises a boiler, a steam turbine system, a high-pressure steam heat accumulator, a low-pressure steam heat accumulator and a valve assembly, steam and hot water are adopted as heat storage media, and heat energy is directly stored and released through the high-pressure steam heat accumulator and the low-pressure steam heat accumulator; the indirect heat exchange process of media such as fused salt is omitted, heat energy is released back to a steam turbine system through the coupling relation of the high-pressure steam heat accumulator, the low-pressure steam heat accumulator and the steam turbine system and used for assisting the short-time frequent peak and frequency regulation work of a coal-fired power unit, and the dynamic response capacity of the coal-fired power unit is improved; in actual operation, the operation mode of the heat storage system can be flexibly changed according to the load change of the power grid and the operation state of the coal-fired power generation unit.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage technology, specifically to a thermal energy storage system coupled with a multi-stage steam accumulator and its operation method. Background Technology

[0002] With the continuous optimization and adjustment of the energy structure, the operation mode of the power industry is undergoing profound changes. Under the new power grid, due to the uncertainty of renewable energy power generation and the complexity of electricity load, coal-fired power generating units need to perform peak shaving and frequency regulation operations more frequently. This places extremely high demands on the flexibility and response speed of thermal energy storage technology. The basic principle of thermal energy storage technology is to store excess heat and release it when needed, achieving a balance between heat and energy supply and demand. In the power system, thermal energy storage technology is combined with coal-fired power generating units to store excess heat generated during power generation. When the electricity load increases or the power generation capacity needs to be adjusted, the stored heat is released to drive the power generation equipment to increase the power output, thereby achieving efficient operation of the coal-fired power generating unit system.

[0003] Thermal energy storage technology, primarily based on molten salt thermal storage, is relatively mature and has been widely applied in the power industry. However, due to the high viscosity and poor thermal conductivity of molten salt, when a rapid increase in power generation is needed, the molten salt thermal storage system may not be able to release the stored heat in time, resulting in a lag in power generation adjustment and affecting the frequency regulation performance of the power grid. Conversely, when a rapid decrease in power generation is needed, the molten salt thermal storage system may not be able to store excess heat quickly enough, leading to energy waste and grid instability, making it difficult to meet the demands of rapid peak shaving and frequency regulation under new power grid conditions.

[0004] Therefore, how to design a new thermal storage system that meets the needs of frequent peak shaving and frequency regulation of coal-fired power generating units has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a thermal storage system coupled with a multi-stage steam accumulator and its operation method, so as to overcome the problem that the existing thermal storage system cannot meet the requirements of coal-fired power generation units for rapid peak shaving and frequency regulation due to its slow heat exchange response speed.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution: A thermal storage system coupled with a multi-stage steam accumulator includes a boiler, a steam turbine system, a high-pressure steam accumulator, a low-pressure steam accumulator, and a valve assembly. The valve assembly includes a main steam bypass valve, a feedwater bypass valve, a first steam valve, a reheat steam bypass valve, a condensate bypass valve, and a second steam valve. The main steam outlet of the boiler is divided into two paths. The first path is connected to the first inlet of the high-pressure steam accumulator via the main steam bypass valve. The outlet of the high-pressure steam accumulator is connected to the cold reheat steam inlet of the boiler via the first steam valve. The second path is connected to the first inlet of the steam turbine system. The first outlet of the steam turbine system is connected to the cold reheat steam inlet and the feedwater inlet of the boiler, respectively. The boiler's hot reheat steam outlet is divided into two paths. The first path passes sequentially through the condensate bypass valve, the first inlet of the low-pressure steam accumulator, the outlet of the low-pressure steam accumulator, the second steam valve, the second inlet of the turbine system, the second outlet of the turbine system, and the reheat steam bypass valve to connect to the second inlet of the low-pressure steam accumulator. The second path connects to the third inlet of the turbine system. The third outlet of the turbine system is divided into two paths: one path merges into the boiler's feedwater inlet, and the other path connects to the second inlet of the high-pressure steam accumulator via the feedwater bypass valve.

[0007] A further improvement of the present invention is that the steam turbine system includes a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a generator, a deaerator, a low-pressure heater group, a condenser, and a high-pressure heater group; the high-pressure cylinder, intermediate-pressure cylinder, low-pressure cylinder, and generator are coaxially connected in sequence; the second main steam outlet of the boiler is connected to the inlet of the high-pressure cylinder, and the outlet of the high-pressure cylinder is divided into two paths, one path is connected to the cold reheat steam inlet of the boiler, and the other path is connected to the feedwater inlet of the boiler via the first inlet of the high-pressure heater group; The boiler's hot reheat steam outlet first path sequentially passes through the condensate bypass valve, the first inlet of the low-pressure steam accumulator, the outlet of the low-pressure steam accumulator, and the second steam valve to connect to the inlet of the low-pressure cylinder. The low-pressure cylinder outlet is divided into two paths: one path connects to the first inlet of the low-pressure heater group, and the other path connects to the second inlet of the low-pressure heater group via the condenser. The low-pressure steam accumulator outlet is also divided into two paths: one path connects to the first inlet of the deaerator, and the other path connects to the second inlet of the low-pressure steam accumulator via the reheat steam bypass valve. The second reheat steam outlet of the boiler is connected to the inlet of the intermediate pressure cylinder. The outlet of the intermediate pressure cylinder is divided into two paths via the deaerator. One path is connected to the second inlet of the high-pressure heater group, and the other path is connected to the second inlet of the high-pressure steam accumulator via the feedwater bypass valve.

[0008] A further improvement of the present invention is that the turbine system further includes a condensate pump, which is located between the deaerator and the feedwater bypass valve.

[0009] A further improvement of the present invention is that the turbine system further includes a feedwater pump, which is located between the condenser and the low-pressure heater group.

[0010] This invention also provides an operation method for a thermal storage system coupled with a multi-stage steam accumulator. The system employs the aforementioned coupled multi-stage steam accumulator. During operation, the thermal storage system includes a thermal storage state and a heat release state. When the first steam valve and the second steam valve are closed, the thermal storage system is in the thermal storage state. If only the main steam bypass valve and the feedwater bypass valve are opened in the thermal storage state, the high-pressure steam accumulator operates independently. If only the reheat steam bypass valve and the condensate bypass valve are opened in the thermal storage state, the low-pressure steam accumulator operates independently. If the reheat steam bypass valve, the condensate bypass valve, the main steam bypass valve, and the feedwater bypass valve are opened simultaneously in the thermal storage state, the high-pressure steam accumulator and the low-pressure steam accumulator operate simultaneously. When the first steam valve and the second steam valve are opened, and the main steam bypass valve, the feedwater bypass valve, the reheat steam bypass valve, and the condensate bypass valve are closed, the thermal storage system is in the heat release state.

[0011] A further improvement of the present invention is that the working pressure range of the high-pressure steam accumulator before heat storage is 2.0~4.0MPa.

[0012] A further improvement of the present invention is that the working pressure range of the high-pressure steam accumulator after heat storage is 6.0~8.0MPa.

[0013] A further improvement of the present invention is that the working pressure range of the low-pressure steam accumulator before heat storage is 0.5~1.0MPa.

[0014] A further improvement of the present invention is that the working pressure range of the low-pressure steam accumulator after heat storage is 2.0~3.0MPa.

[0015] A further improvement of the present invention is that the liquid water volume content of the high-pressure steam accumulator and the low-pressure steam accumulator is 40-60% before heat storage and not more than 90% after heat storage.

[0016] Compared with the prior art, the positive and progressive effects of the present invention are as follows: The thermal storage system provided by this invention, which couples multiple stages of steam accumulators, includes a boiler, a steam turbine system, a high-pressure steam accumulator, a low-pressure steam accumulator, and valve components. It uses steam and hot water as the thermal storage medium, directly storing and releasing heat energy through the high-pressure and low-pressure steam accumulators, eliminating the indirect heat exchange process of molten salt or other media. Through the coupling relationship between the high-pressure and low-pressure steam accumulators and the steam turbine system, the heat energy is released back to the steam turbine system to assist in the short-term, frequent peak-shaving and frequency regulation of coal-fired power units, improving the dynamic response capability of coal-fired power generating units. In actual operation, the system can flexibly change its operating mode according to changes in grid load and the operating status of the coal-fired power generating units, effectively solving the problem that molten salt, due to its slow heat exchange response, cannot meet the rapid peak-shaving and frequency regulation requirements of coal-fired power generating units.

[0017] Furthermore, the specific structure of the steam turbine system is defined, including the coordinated connection method of the high-pressure cylinder, intermediate-pressure cylinder, low-pressure cylinder, generator, deaerator, high and low pressure heater group and condenser, so that the thermal storage system can optimize the thermodynamic cycle and improve the overall system efficiency while responding quickly.

[0018] Furthermore, the condensate pump enables precise regulation of the feedwater flow into the high-pressure steam accumulator, allowing the thermal storage system to dynamically adjust the heat storage and release rate of the high-pressure steam accumulator according to load demand. At the same time, it ensures that the pressure gradient between the deaerator and the high-pressure steam accumulator is maintained even when the feedwater bypass valve is open, preventing steam backflow.

[0019] Furthermore, installing a feedwater pump between the condenser and the low-pressure heater group helps maintain the optimal operating pressure of the low-pressure heater group, reduces the amount of steam extracted from the turbine, and allows more steam to be used for power generation. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a connection diagram of a thermal storage system coupled with a multi-stage steam accumulator according to the present invention; The components are as follows: 1. Boiler; 2. High-pressure steam accumulator; 3. Low-pressure steam accumulator; 4. High-pressure cylinder; 5. Medium-pressure cylinder; 6. Low-pressure cylinder; 7. Generator; 8. Low-pressure heater group; 9. Deaerator; 10. High-pressure heater group; 11. Condenser; 12. Feedwater pump; 13. Condensate pump; 14. Main steam bypass valve; 15. Feedwater bypass valve; 16. First steam valve; 17. Reheat steam bypass valve; 18. Condensate bypass valve; 19. Second steam valve. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, 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, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] Furthermore, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can 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 according to the specific circumstances.

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This is an explanation of the present invention and not a limitation thereof.

[0028] A thermal storage system coupled with a multi-stage steam accumulator includes a boiler 1, a steam turbine system, a high-pressure steam accumulator 2, a low-pressure steam accumulator 3, and a valve assembly. The valve assembly includes a main steam bypass valve 14, a feedwater bypass valve 15, a first steam valve 16, a reheat steam bypass valve 17, a condensate bypass valve 18, and a second steam valve 19. The main steam outlet of boiler 1 is divided into two paths. The first path is connected to the first inlet of high-pressure steam accumulator 2 via main steam bypass valve 14. The outlet of high-pressure steam accumulator 2 is connected to the cold reheat steam inlet of boiler 1 via first steam valve 16. The second path is connected to the first inlet of the steam turbine system. The first outlet of the steam turbine system is connected to the cold reheat steam inlet and the feedwater inlet of boiler 1, respectively. The hot reheat steam outlet of boiler 1 is divided into two paths. The first path passes through condensate bypass valve 18, the first inlet of low-pressure steam accumulator 3, the outlet of low-pressure steam accumulator 3, the second steam valve 19, the second inlet of the turbine system, the second outlet of the turbine system, and reheat steam bypass valve 17 to connect to the second inlet of low-pressure steam accumulator 3. The second path connects to the third inlet of the turbine system. The third outlet of the turbine system is divided into two paths. One path flows into the feedwater inlet of boiler 1, and the other path passes through feedwater bypass valve 15 to connect to the second inlet of high-pressure steam accumulator 2.

[0029] The thermal storage system provided by this invention, which couples multiple stages of steam accumulators, includes a boiler 1, a steam turbine system, a high-pressure steam accumulator 2, a low-pressure steam accumulator 3, and valve components. It uses steam and hot water as the thermal storage medium, directly storing and releasing heat energy through the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3, eliminating the indirect heat exchange process of molten salt or other media. Through the coupling relationship between the high-pressure steam accumulator 2, the low-pressure steam accumulator 3, and the steam turbine system, the heat energy is released back to the steam turbine system to assist in the short-term, frequent peak-shaving and frequency regulation of coal-fired power units, improving the dynamic response capability of the coal-fired power generation units. In actual operation, the system can flexibly change its operating mode according to changes in grid load and the operating status of the coal-fired power generation units, effectively solving the problem that molten salt, due to its slow heat exchange response, cannot meet the rapid peak-shaving and frequency regulation requirements of the coal-fired power generation units.

[0030] Specifically, the turbine system includes a high-pressure cylinder 4, an intermediate-pressure cylinder 5, a low-pressure cylinder 6, a generator 7, a deaerator 9, a low-pressure heater group 8, a condenser 11, and a high-pressure heater group 10; the high-pressure cylinder 4, the intermediate-pressure cylinder 5, the low-pressure cylinder 6, and the generator 7 are connected coaxially in sequence; the second main steam outlet of the boiler 1 is connected to the inlet of the high-pressure cylinder 4, and the outlet of the high-pressure cylinder 4 is divided into two paths, one of which is connected to the cold reheat steam inlet of the boiler 1, and the other is connected to the feedwater inlet of the boiler 1 via the first inlet of the high-pressure heater group 10; The first reheat steam outlet of boiler 1 is connected to the inlet of low-pressure cylinder 6 via condensate bypass valve 18, the first inlet of low-pressure steam accumulator 3, the outlet of low-pressure steam accumulator 3, and the second steam valve 19. The outlet of low-pressure cylinder 6 is divided into two paths: one path is connected to the first inlet of low-pressure heater group 8, and the other path is connected to the second inlet of low-pressure heater group 8 via condenser 11. The outlet of low-pressure steam accumulator 3 is divided into two paths: one path is connected to the first inlet of deaerator 9, and the other path is connected to the second inlet of low-pressure steam accumulator 3 via reheat steam bypass valve 17. The second reheat steam outlet of boiler 1 is connected to the inlet of intermediate pressure cylinder 5. The outlet of intermediate pressure cylinder 5 is divided into two paths via deaerator 9. One path is connected to the second inlet of high pressure heater group 10, and the other path is connected to the second inlet of high pressure steam accumulator 2 via feedwater bypass valve 15.

[0031] By defining the specific structure of the steam turbine system, including the coordinated connection of the high-pressure cylinder 4, intermediate-pressure cylinder 5, low-pressure cylinder 6, generator 7, deaerator 9, high and low pressure heater group 8, and condenser 11, the thermal storage system can optimize the thermodynamic cycle and improve the overall system efficiency while responding quickly.

[0032] Specifically, the turbine system also includes a condensate pump 13, which is located between the deaerator 9 and the feedwater bypass valve 15.

[0033] The condensate pump 13 enables precise regulation of the feedwater flow into the high-pressure steam accumulator 2, allowing the thermal storage system to dynamically adjust the heat storage and release rate of the high-pressure steam accumulator 2 according to load demand. At the same time, it ensures that the pressure gradient between the deaerator 9 and the high-pressure steam accumulator 2 can still be maintained when the feedwater bypass valve 15 is open, thus preventing steam backflow.

[0034] Specifically, the turbine system also includes a feedwater pump 12, which is located between the condenser 11 and the low-pressure heater group 8.

[0035] A feedwater pump 12 is installed between the condenser 11 and the low-pressure heater group 8, which helps to maintain the optimal operating pressure of the low-pressure heater group 8, reduces the amount of steam extracted by the turbine, and allows more steam to be used for power generation.

[0036] This invention also provides an operation method for a thermal storage system coupled with a multi-stage steam accumulator. The system employs the aforementioned coupled multi-stage steam accumulator. During operation, the thermal storage system includes a thermal storage state and a heat release state. When the first steam valve 16 and the second steam valve 19 are closed, the thermal storage system is in the thermal storage state. If only the main steam bypass valve 14 and the feedwater bypass valve 15 are opened in the thermal storage state, the high-pressure steam accumulator 2 operates independently. If only the reheat steam bypass valve 17 and the condensate bypass valve 15 are opened in the thermal storage state, the system operates independently. When the first steam valve 16 and the second steam valve 19 are opened, and the main steam bypass valve 14 and the feedwater bypass valve 15 are opened simultaneously, the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 operate simultaneously. When the first steam valve 16 and the second steam valve 19 are opened, and the main steam bypass valve 14, the feedwater bypass valve 15, the reheat steam bypass valve 17 and the condensate bypass valve 18 are closed, the heat storage system is in a heat release state.

[0037] This method utilizes a steam accumulator to directly store the working fluid of the steam turbine, reducing the heat exchange process, providing rapid response, and also serving as an auxiliary peak-shaving and frequency regulation function. The stored working fluids are steam and hot water, which are inexpensive and have a significant economic advantage compared to molten salt thermal storage. By adopting a multi-stage storage approach, it can meet the high-efficiency operation requirements under different peak-shaving and frequency regulation needs.

[0038] Specifically, the operating pressure range of the high-pressure steam accumulator 2 before heat storage is 2.0~4.0 MPa.

[0039] Specifically, the operating pressure range of the high-pressure steam accumulator 2 after heat storage is 6.0~8.0 MPa.

[0040] Specifically, the operating pressure range of the low-pressure steam accumulator 3 before heat storage is 0.5~1.0 MPa.

[0041] Specifically, the operating pressure range of the low-pressure steam accumulator 3 after heat storage is 2.0~3.0 MPa.

[0042] Specifically, the liquid water volume content of the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 before heat storage is 40-60%, and the liquid water volume content after heat storage is no more than 90%.

[0043] The heat storage efficiency of high-pressure steam accumulator 2 and low-pressure steam accumulator 3 depends on the heat exchange area between steam and liquid water. Too much liquid water (e.g., over 60%) reduces the contact area between the gas phase and liquid water, slowing down the steam condensation rate. Too little liquid water (e.g., below 40%) prevents sufficient absorption of the latent heat of the steam (the latent heat released when steam condenses into water is the main form of heat storage). A liquid water content of 40-60% maximizes the gas-liquid interface area, accelerating steam condensation and increasing the heat storage rate and the amount of heat stored per unit volume. Controlling the liquid water volume content after heat storage to below 90% means that there is still more than 10% gas phase area, providing space for liquid water evaporation during heat release. This ensures that water vaporizes smoothly into steam during pressure reduction, releasing the stored latent heat. It also avoids increased evaporation resistance due to excessive liquid water content, ensuring stable steam output pressure and improving heat release efficiency.

[0044] Example 1 See Figure 1A thermal storage system coupled with multi-stage steam accumulators includes a high-pressure steam accumulator 2, a main steam bypass valve 14, a feedwater bypass valve 15, a first steam valve 16, a low-pressure steam accumulator 3, a reheat steam bypass valve 17, a condensate bypass valve 18, and a second steam valve 19. The main steam outlet of boiler 1 is connected to the inlet of high-pressure cylinder 4 and the steam inlet of high-pressure steam accumulator 2, respectively. The outlet of high-pressure cylinder 4 and the steam outlet of high-pressure steam accumulator 2 are both connected to the reheat steam inlet of boiler 1. The reheat steam outlet of boiler 1 is connected to the inlet of intermediate-pressure cylinder 5 and the steam inlet of low-pressure steam accumulator 3, respectively. The outlet of intermediate-pressure cylinder 5 and the low-pressure steam accumulator 3 are connected to the reheat steam inlet of boiler 1. The steam outlet of the high-pressure steam accumulator 3 is connected to the inlet of the low-pressure cylinder 6. The outlet of the low-pressure cylinder 6 is connected in sequence to the condenser 11, feedwater pump 12, low-pressure heater group 8, deaerator 9, condensate pump 13 and high-pressure heater group 10. The outlet of the high-pressure heater group 10 is connected to the feedwater inlet of the boiler 1. The high-pressure cylinder 4, intermediate-pressure cylinder 5 and low-pressure cylinder 6 are coaxially connected to drive the generator 7 to rotate. The extraction steam outlets of the three are respectively connected to the steam inlets of the high-pressure heater group 10, deaerator 9 and low-pressure heater group 8. The outlet of the feedwater pump 12 is connected to the hot water inlet of the high-pressure steam accumulator 2, and the outlet of the low-pressure heater group 8 is connected to the hot water inlet of the low-pressure steam accumulator 3.

[0045] The high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 contain a certain amount of saturated water and steam before heat storage. During the heat storage process, steam and hot water are injected to increase the pressure in the steam accumulators. During the heat release process, the steam valves of the steam accumulators are opened, causing flash evaporation inside the steam accumulators and releasing saturated steam. The main steam bypass valve 14 and the feedwater bypass valve 15 are used to control the flow rate of steam and hot water entering the high-pressure steam accumulator 2. The reheat steam bypass valve 17 and the condensate bypass valve 18 are used to control the flow rate of steam and hot water entering the low-pressure steam accumulator 3. The first steam valve 16 and the second steam valve 19 are used to control the steam flow rate and pressure at the steam outlet. The operating pressure range of the high-pressure steam accumulator 2 before heat storage is 2.0~4.0 MPa, and the operating range after heat storage is 6.0~8.0 MPa. The operating pressure range of the low-pressure steam accumulator 3 before heat storage is 0.5~1.0 MPa, and the operating range after heat storage is 2.0~3.0 MPa. MPa; the liquid water volume content of the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 before heat storage is between 40% and 60%, and the maximum liquid water volume content after heat storage does not exceed 90%; the total mass of steam and hot water charged into the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 during the heat storage process should be equal to the steam flow rate released during the heat release process, so as to ensure that the water level of the steam accumulator remains unchanged before and after heat storage.

[0046] The heat storage process of the coupled multi-stage steam accumulator system is as follows: the first steam valve 16 and the second steam valve 19 are closed, and the main steam bypass valve 14, feedwater bypass valve 15, reheat steam bypass valve 17, and condensate bypass valve 18 are opened, allowing the main steam and feedwater of the coal-fired generator set 7 to enter the high-pressure steam accumulator 2, and the reheat steam and condensate to enter the low-pressure steam accumulator 3, thereby increasing the pressure of the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3, thus reducing the unit's output power; specifically, a portion of the steam at the turbine inlet is stored in the steam accumulator, thus reducing the amount of steam entering the turbine to perform work, and reducing the output power; at the same time, due to the injection of high-temperature and high-pressure steam, the pressure inside the steam accumulator increases.

[0047] The heat release process of the multi-stage steam accumulator storage system is as follows: Open the first steam valve 16 and the second steam valve 19, close the main steam bypass valve 14, feedwater bypass valve 15, reheat steam bypass valve 17 and condensate bypass valve 18, and release the steam in the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 into the cold reheat steam and the inlet steam of the low-pressure cylinder 6, respectively, thereby increasing the unit's output power. Specifically, by releasing steam, the amount of steam entering the turbine to do work increases, the power generation increases, and the unit's output power is increased.

[0048] During the thermal storage process, the main steam bypass valve 14, feedwater bypass valve 15, reheat steam bypass valve 17, and condensate bypass valve 18 are opened to store superheated steam in the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3. The superheated steam directly contacts and exchanges heat with the saturated steam and saturated water in the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3, and does not return to the regenerative system. The unit's output power and frequency will decrease rapidly the moment the valves are opened. When superheated steam is used to heat molten salt, the steam is generally cooled to a higher temperature and returned to the regenerative system. Some steam will still be pushed back to the turbine. The rate at which the unit's output power and frequency are reduced is not as good as that of steam thermal storage.

[0049] During the heat release process, the first steam valve 16 and the second steam valve 19 are opened. The molten salt cannot release heat quickly, but the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 will generate a pressure difference at the moment the valves are opened. Thus, steam is quickly generated through flash evaporation and returned to the steam turbine, which can achieve a rapid increase in power and frequency.

[0050] High-pressure steam accumulator 2 and low-pressure steam accumulator 3 store superheated steam and release saturated steam. From the perspective of mass and energy conservation, if 1 kg of superheated steam is stored, the mass of the released saturated steam will definitely be greater than 1 kg. This will cause the water level inside the steam accumulator to change (become lower). When the heat storage system is in the process of frequent heat storage and release, it cannot replenish the water level of high-pressure steam accumulator 2 and low-pressure steam accumulator 3. When the water level of high-pressure steam accumulator 2 and low-pressure steam accumulator 3 changes significantly, there will be safety hazards. Therefore, a feedwater bypass valve 15 and a reheat steam bypass valve 17 are installed to store superheated steam and hot water simultaneously during the heat storage process. In this way, by controlling the flow rate, energy and mass are conserved during the heat storage and release process, maintaining the water level balance in high-pressure steam accumulator 2 and low-pressure steam accumulator 3 before and after the heat storage and release process, thus achieving stable control and safety assurance of the heat storage system.

[0051] The thermal storage system provided by this invention is suitable for assisting the peak shaving and frequency regulation of 7 coal-fired power generator sets. In the thermal storage state, the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 can achieve different operating modes according to the different needs of the units. These operating modes specifically include: independent operating mode of the high-pressure steam accumulator 2, independent operating mode of the low-pressure steam accumulator 3, and simultaneous operation mode of both the high-pressure and low-pressure steam accumulators 2 and 3. When the demand for peak shaving and frequency regulation is high, only the main steam bypass valve 14 and the feedwater bypass valve 15 are opened, while other valve components are closed. The main steam outlet steam of boiler 1 and the outlet hot water of feedwater pump 12 enter the high-pressure steam accumulator 2. At this time, the high-pressure steam accumulator 2 operates independently, extracting more main steam, reducing the amount of steam entering the turbine to perform work, thereby reducing the output power; the losses in the steam accumulator are relatively large, resulting in low efficiency.

[0052] When the peak-shaving and frequency regulation demand is slightly low, only the reheat steam bypass valve 17 and the condensate bypass valve 18 are opened, while other valve components are closed. The hot reheat steam outlet steam of boiler 1 and the hot water outlet of low-pressure heater group 8 enter the low-pressure steam accumulator 3. At this time, the low-pressure steam accumulator 3 operates independently.

[0053] When peak-shaving and frequency regulation demands are low, the main steam bypass valve 14, feedwater bypass valve 15, reheat steam bypass valve 17, and condensate bypass valve 18 are opened simultaneously, while other valve components are closed. The main steam outlet steam of boiler 1 and the outlet hot water of feedwater pump 12 enter the high-pressure steam accumulator 2, and the hot reheat steam outlet steam of boiler 1 and the outlet hot water of low-pressure heater group 8 enter the low-pressure steam accumulator 3. At this time, the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 operate simultaneously.

[0054] When the high-pressure steam accumulator 2 and the low-pressure steam accumulator 3 operate simultaneously or when the low-pressure steam accumulator 3 operates independently, the unit's output power decreases, the steam accumulator losses decrease, and the efficiency increases. When the unit needs to increase the load or the turbine frequency, the heat storage system starts to release heat. At this time, the steam flow and pressure are adjusted according to the heat storage situation and different peak-shaving and frequency regulation requirements to achieve efficient operation under different requirements.

[0055] This invention utilizes steam accumulators to store steam and hot water from the turbines of coal-fired power units, and releases the steam back to the turbine system during the heat release process. This assists the coal-fired power units in short-term peak shaving and frequency regulation. Because there are fewer heat exchange processes, this heat storage method has a faster response speed, which greatly helps the unit to quickly change loads and regulate frequencies. Furthermore, by using multi-stage steam accumulators for heat storage, the operating mode of the heat storage system can be changed under different needs, achieving efficient operation under different requirements. This is a new type of energy storage technology with promising applications.

[0056] Finally, it should be noted that the embodiments listed above are merely one or more specific manifestations of the technical solution of this invention. Their purpose is to clearly illustrate the concept, principle, and application of this invention through specific examples, and is by no means intended to limit the scope of protection of this invention to these specific embodiments. In fact, the true value of this invention lies in its proposed technical ideas and innovations, rather than its manifestations or implementation methods.

[0057] For those skilled in the art, after thoroughly reading and understanding the technical solution of this invention, they are fully capable of making various changes, modifications, or equivalent substitutions to the specific implementation of the invention based on their own professional knowledge and skills. These changes may include, but are not limited to: adjusting the range of technical parameters, optimizing the algorithm flow to improve efficiency, and replacing some technical components to achieve better compatibility or reduce costs. As long as these modified technical solutions substantially retain the technical features claimed by the original invention, that is, they can still achieve the core functions and effects of this invention, then these changes should be considered to fall within the scope of protection of the pending claims of this invention.

[0058] Furthermore, with the continuous progress and development of technology, new technical means and methods are constantly emerging, which provides ample space for further improvement and perfection of this invention. Therefore, the scope of protection of this invention should also include reasonable and foresightful improvements and extensions based on existing technology. As long as these improvements and extensions do not depart from the basic principles and core concepts of this invention, they should be considered equivalents of this invention and are equally protected by patent rights.

Claims

1. A thermal storage system coupled with a multi-stage steam accumulator, characterized in that, It includes a boiler (1), a steam turbine system, a high-pressure steam accumulator (2), a low-pressure steam accumulator (3), and a valve assembly, wherein the valve assembly includes a main steam bypass valve (14), a feedwater bypass valve (15), a first steam valve (16), a reheat steam bypass valve (17), a condensate bypass valve (18), and a second steam valve (19). The main steam outlet of the boiler (1) is divided into two paths. The first path is connected to the first inlet of the high-pressure steam accumulator (2) via the main steam bypass valve (14). The outlet of the high-pressure steam accumulator (2) is connected to the cold reheat steam inlet of the boiler (1) via the first steam valve (16). The second path is connected to the first inlet of the turbine system. The first outlet of the turbine system is connected to the cold reheat steam inlet of the boiler (1) and the feedwater inlet of the boiler (1) respectively. The hot reheat steam outlet of the boiler (1) is divided into two paths. The first path passes through the condensate bypass valve (18), the first inlet of the low-pressure steam accumulator (3), the outlet of the low-pressure steam accumulator (3), the second steam valve (19), the second inlet of the turbine system, the second outlet of the turbine system, and the reheat steam bypass valve (17) to connect to the second inlet of the low-pressure steam accumulator (3). The second path connects to the third inlet of the turbine system. The third outlet of the turbine system is divided into two paths. One path flows into the feedwater inlet of the boiler (1), and the other path connects to the second inlet of the high-pressure steam accumulator (2) through the feedwater bypass valve (15).

2. The thermal storage system with coupled multi-stage steam accumulators according to claim 1, characterized in that, The turbine system includes a high-pressure cylinder (4), an intermediate-pressure cylinder (5), a low-pressure cylinder (6), a generator (7), a deaerator (9), a low-pressure heater group (8), a condenser (11), and a high-pressure heater group (10); the high-pressure cylinder (4), the intermediate-pressure cylinder (5), the low-pressure cylinder (6), and the generator (7) are connected coaxially in sequence; the second main steam outlet of the boiler (1) is connected to the inlet of the high-pressure cylinder (4), and the outlet of the high-pressure cylinder (4) is divided into two paths, one path is connected to the cold reheat steam inlet of the boiler (1), and the other path is connected to the feedwater inlet of the boiler (1) through the first inlet of the high-pressure heater group (10); The first reheat steam outlet of the boiler (1) passes through the condensate bypass valve (18), the first inlet of the low-pressure steam accumulator (3), the outlet of the low-pressure steam accumulator (3), and the second steam valve (19) to the inlet of the low-pressure cylinder (6). The outlet of the low-pressure cylinder (6) is divided into two paths: one path connects to the first inlet of the low-pressure heater group (8), and the other path connects to the second inlet of the low-pressure heater group (8) via the condenser (11). The outlet of the low-pressure steam accumulator (3) is divided into two paths: one path connects to the first inlet of the deaerator (9), and the other path connects to the second inlet of the low-pressure steam accumulator (3) via the reheat steam bypass valve (17). The second reheat steam outlet of the boiler (1) is connected to the inlet of the intermediate pressure cylinder (5). The outlet of the intermediate pressure cylinder (5) is divided into two paths via the deaerator (9). One path is connected to the second inlet of the high pressure heater group (10), and the other path is connected to the second inlet of the high pressure steam accumulator (2) via the feedwater bypass valve (15).

3. The thermal storage system with coupled multi-stage steam accumulators according to claim 2, characterized in that, The turbine system also includes a condensate pump (13), which is located between the deaerator (9) and the feedwater bypass valve (15).

4. A thermal storage system with coupled multi-stage steam accumulators according to claim 2, characterized in that, The turbine system also includes a feedwater pump (12), which is located between the condenser (11) and the low-pressure heater group (8).

5. A method for operating a thermal storage system coupled with multi-stage steam accumulators, characterized in that, The heat storage system using the coupled multi-stage steam accumulator as described in any one of claims 1 to 4, during operation, includes a heat storage state and a heat release state. When the first steam valve (16) and the second steam valve (19) are closed, the heat storage system is in the heat storage state. If only the main steam bypass valve (14) and the feedwater bypass valve (15) are opened in the heat storage state, the high-pressure steam accumulator (2) operates independently; if only the reheat steam bypass valve (17) and the condensate bypass valve (18) are opened in the heat storage state, the low-pressure steam accumulator (2) operates independently. 3) Independent operation; if the reheat steam bypass valve (17), condensate bypass valve (18), main steam bypass valve (14) and feedwater bypass valve (15) are opened simultaneously in the heat storage state, the high-pressure steam accumulator (2) and the low-pressure steam accumulator (3) will operate simultaneously; when the first steam valve (16) and the second steam valve (19) are opened, and the main steam bypass valve (14), feedwater bypass valve (15), reheat steam bypass valve (17) and condensate bypass valve (18) are closed, the heat storage system is in the heat release state.

6. The operation method of a thermal storage system with coupled multi-stage steam accumulators according to claim 5, characterized in that, The working pressure range of the high-pressure steam accumulator (2) before heat storage is 2.0~4.0 MPa.

7. The operation method of a thermal storage system with coupled multi-stage steam accumulators according to claim 6, characterized in that, The working pressure range of the high-pressure steam accumulator (2) after heat storage is 6.0~8.0 MPa.

8. The operation method of a thermal storage system with coupled multi-stage steam accumulators according to claim 5, characterized in that, The working pressure range of the low-pressure steam accumulator (3) before heat storage is 0.5~1.0 MPa.

9. A method for operating a thermal storage system with coupled multi-stage steam accumulators according to claim 8, characterized in that, The working pressure range of the low-pressure steam accumulator (3) after heat storage is 2.0~3.0 MPa.

10. The operation method of a thermal storage system with coupled multi-stage steam accumulators according to claim 5, characterized in that, The liquid water volume content of the high-pressure steam accumulator (2) and the low-pressure steam accumulator (3) before heat storage is 40-60%, and the liquid water volume content after heat storage is no more than 90%.

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