Coal-fired unit coupled with a cascade thermal storage system and operation method thereof

Abstract

The embodiment of the present application provides a coal-fired unit coupled with a cascade heat storage system and an operation method, the unit comprising: a coal-fired system and a cascade heat storage system; the coal-fired system comprising a coal-fired boiler; steam generated by the coal-fired boiler is heat-exchanged with a steam heat exchange system through a steam bypass; wherein superheated steam is condensed after heat release in the steam heat exchange system and is returned to an outlet end of a deaerator of the coal-fired system; reheat steam is conducted to a low-pressure cylinder of the coal-fired system after heat release in the steam heat exchange system; a steam generation system is used for heat exchange with a feedwater bypass of the coal-fired system; wherein steam generated by low-pressure water extraction from the outlet end of the deaerator is used for work in the low-pressure cylinder of the coal-fired system; steam generated by high-pressure water extraction from a boiler inlet is used for work in a high-pressure cylinder of the coal-fired system; a molten salt pump is used for providing pressure to make heat storage medium at each cascade temperature of the cascade heat storage device flow between heat storage devices; and the cascade heat storage device is used for storing and releasing heat exchanged with steam.

Description

Technical Field

[0001] The embodiments of the present invention belong to the field of energy storage technology, specifically relating to a coal-fired unit and its operation method for a coupled cascade thermal storage system. Background Technology

[0002] The proportion of renewable energy generation is rapidly increasing, leading to a widening peak-to-valley load difference in the power grid. Coal-fired power generation is the largest power source in my country's power system, bearing enormous pressure for peak and frequency regulation to maintain grid stability. Existing coal-fired units were designed with base load in the initial power generation phase, making it difficult for them to participate in significant thermal regulation later on.

[0003] Energy storage, as a technology unrestricted by time and space, can be coupled with thermal power generating units to meet peak-shaving and valley-filling load regulation needs and frequency regulation needs arising from the grid's impact from new energy integration. Thermal energy storage technology is widely used and mature. With the further deepening of my country's power system reform, adding energy storage systems to thermal power plants to meet peak-shaving and frequency regulation assessment standards, and obtaining economic compensation through peak-shaving auxiliary market transactions, is an innovative profit model. Currently, this energy storage technology mainly utilizes high-parameter steam and electric heaters as heat sources for the energy storage system. However, the output steam parameters decrease, or the feedwater is directly heated, resulting in a significant decline in energy quality and low utilization efficiency. On the thermal energy storage system side, due to temperature differences at the heat exchange pinch points, the temperature difference between the two thermal storage tanks is too small, the flow rate of the thermal storage medium increases, and the circulation efficiency decreases. Alternatively, designs with multiple thermal storage tanks and multiple thermal storage media may be necessary, increasing system costs.

[0004] Therefore, how to solve the above problems has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The embodiments of the present invention aim to at least solve one of the technical problems existing in the prior art, and provide a coal-fired unit and its operation method with a coupled cascade thermal storage system.

[0006] A first aspect of the present invention provides a coal-fired power unit coupled with a cascade thermal storage system, comprising: a coal-fired system and a cascade thermal storage system;

[0007] The coal-fired system includes a coal-fired boiler;

[0008] The cascade thermal storage system includes a cascade thermal storage device, a steam generation system, a steam heat exchange system, and a molten salt pump;

[0009] The superheated steam of the coal-fired boiler exchanges heat with the steam heat exchange system through a superheated steam bypass; wherein, the condensate after the superheated steam releases heat and condenses in the steam heat exchange system flows back to the deaerator outlet of the coal-fired system; the reheated steam of the coal-fired boiler exchanges heat with the steam heat exchange system through a reheated steam bypass; wherein, the steam after the reheated steam of the coal-fired boiler releases heat in the steam heat exchange system is conducted to the low-pressure cylinder of the coal-fired system; the steam generation system is used to exchange heat with the feedwater bypass of the coal-fired system; wherein, the steam generated by the low-pressure pumping heat absorption at the deaerator outlet enters the low-pressure cylinder of the coal-fired system to do work; the steam generated by the high-pressure pumping heat absorption at the boiler inlet enters the high-pressure cylinder of the coal-fired system to do work.

[0010] The molten salt pump is used to provide pressure to allow the heat storage medium at each stage temperature of the cascaded heat storage device to flow between the heat storage devices; wherein, the cascaded heat storage device uses the heat storage medium to store the heat of steam in the steam heat exchange system; the cascaded heat storage device uses the heat storage medium to release heat in the steam heat exchange system to evaporate feedwater.

[0011] Optionally, the coal-fired system may also include a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a generator, a condenser, a first circulating water pump, a low-pressure heater, a deaerator, a second circulating water pump, and a high-pressure heater.

[0012] The superheated steam outlet of the coal-fired boiler is connected to the high-pressure cylinder; the reheated steam outlet of the coal-fired boiler is connected to the intermediate-pressure cylinder; the outlet of the intermediate-pressure cylinder is connected to the deaerator and the low-pressure cylinder respectively; the outlet of the low-pressure cylinder is connected to the hot-end inlet of the low-pressure heater and the condenser respectively; the outlet of the condenser is connected to the inlet of the first circulating water pump; the outlet of the first circulating water pump is connected to the cold-end inlet of the low-pressure heater; the cold-end outlet of the low-pressure heater is connected to the inlet of the deaerator; the outlet of the deaerator is connected to the inlet of the second circulating water pump; the outlet of the second circulating water pump is connected to the cold-end inlet of the high-pressure heater; and the cold-end outlet of the high-pressure heater is connected to the feedwater inlet of the coal-fired boiler.

[0013] Optionally, the cascade thermal storage device includes a high-temperature thermal storage tank, a medium-temperature thermal storage tank, and a low-temperature thermal storage tank; wherein, the steam heat exchange system is located at the heat absorption end of the high-temperature thermal storage tank, the medium-temperature thermal storage tank, and the low-temperature thermal storage tank; and the steam generation system is located at the heat release end of the high-temperature thermal storage tank, the medium-temperature thermal storage tank, and the low-temperature thermal storage tank.

[0014] Optionally, the steam heat exchange system includes a first superheated steam heat exchanger, a steam condenser, a condensate heat exchanger, and a second superheated steam heat exchanger.

[0015] The first superheated steam heat exchanger is installed in the heat absorption pipeline between the medium-temperature heat storage tank and the high-temperature heat storage tank; the steam condenser, the condensate heat exchanger, and the second superheated steam heat exchanger are installed in the heat absorption pipeline between the low-temperature heat storage tank and the medium-temperature heat storage tank.

[0016] Optionally, the steam generation system includes a first feedwater preheater, a first steam generator, a first steam superheater, a second steam generator, and a second steam superheater.

[0017] The first steam generator and the first steam superheater are installed in the heat release pipeline between the medium-temperature heat storage tank and the high-temperature heat storage tank; the first feedwater preheater, the second steam generator and the second steam superheater are installed in the heat release pipeline between the low-temperature heat storage tank and the medium-temperature heat storage tank.

[0018] Optionally, the molten salt pump includes a first high-temperature molten salt pump, a first low-temperature molten salt pump, a second high-temperature molten salt pump, and a second low-temperature molten salt pump;

[0019] The first high-temperature molten salt pump is installed in the heat release pipeline between the high-temperature thermal storage tank and the medium-temperature thermal storage tank; the first low-temperature molten salt pump is installed in the heat release pipeline between the medium-temperature thermal storage tank and the low-temperature thermal storage tank; the second high-temperature molten salt pump is installed in the heat absorption pipeline between the high-temperature thermal storage tank and the medium-temperature thermal storage tank; and the second low-temperature molten salt pump is installed in the heat absorption pipeline between the low-temperature thermal storage tank and the medium-temperature thermal storage tank.

[0020] A second aspect of the present invention provides an operation method for a coal-fired unit with a coupled cascade thermal storage system, comprising:

[0021] The superheated steam from the coal-fired boiler exchanges heat with the steam heat exchange system through a superheated steam bypass; wherein, the condensate after the superheated steam releases heat and condenses in the steam heat exchange system flows back to the deaerator outlet of the coal-fired system.

[0022] The reheat steam from the coal-fired boiler exchanges heat with the steam heat exchange system through a reheat steam bypass; wherein, the reheat steam from the coal-fired boiler, after releasing heat in the steam heat exchange system, is conducted to the low-pressure cylinder of the coal-fired system.

[0023] The steam generation system exchanges heat with the feedwater bypass of the coal-fired system; wherein, the steam generated by the low-pressure pumping heat absorption at the deaerator outlet enters the low-pressure cylinder of the coal-fired system to do work; the steam generated by the high-pressure pumping heat absorption at the boiler inlet enters the high-pressure cylinder of the coal-fired system to do work.

[0024] A molten salt pump provides pressure to allow the heat storage medium at each stage temperature of the cascaded heat storage device to flow between the devices; wherein, the cascaded heat storage device uses the heat storage medium to store the heat of steam in the steam heat exchange system; the cascaded heat storage device uses the heat storage medium to release heat in the steam heat exchange system to evaporate feedwater;

[0025] A molten salt pump provides pressure to allow the heat storage medium at each stage of the cascaded heat storage device to flow between the devices. The cascaded heat storage device uses the heat storage medium to store the heat of steam in the steam heat exchange system. The cascaded heat storage device also uses the heat storage medium to release heat in the steam heat exchange system to evaporate feedwater.

[0026] Optionally, the operating states of the cascade thermal storage system include thermal storage state, thermal release state, and thermal standby state;

[0027] The molten salt flow rate in the low-temperature path between the low-temperature storage tank and the medium-temperature storage tank of the steam heat exchange system is Q. s The molten salt flow rate in the high-temperature path between the medium-temperature and high-temperature heat storage tanks of the steam heat exchange system is Q. s ';

[0028] The molten salt flow rate in the cryogenic path between the cryogenic and intermediate-temperature thermal storage tanks of the steam generation system is Q. r The molten salt flow rate in the high-temperature path between the medium-temperature and high-temperature heat storage tanks of the steam heat exchange system is Q. r '; Wherein, the molten salt flow rates of the low-temperature path and high-temperature path corresponding to the steam heat exchange system and the steam generation system satisfy the condition: Q s / Q s '=Q r / Q r The molten salt flow rates in the low-temperature and high-temperature paths of the steam heat exchange system satisfy the condition: Q s ≥3Q s The molten salt flow rates in the low-temperature and high-temperature paths of the steam generation system satisfy the condition: Q r ≥3Q r '.

[0029] Optionally, when the cascade thermal storage system is in hot standby mode, the molten salt flow rate of the low-temperature path of the steam heat exchange system is Q. s min The molten salt flow rate in the high-temperature path of the steam heat exchange system is Q. s ' min The molten salt flow rate in the cryogenic path of the steam generation system is Q. r min The molten salt flow rate in the cryogenic path of the steam generation system is Q. r ' min; wherein, the molten salt flow rates of the steam heat exchange system and the corresponding low-temperature and high-temperature paths of the steam heat exchange system satisfy the condition: Q s min =Q r min Q s ' min =Q r ' min .

[0030] Optionally, when the cascade thermal storage system is in thermal storage state, the molten salt flow rate of the low-temperature path of the steam heat exchange system is Q. s w The molten salt flow rate in the high-temperature path of the steam heat exchange system is Q. s ' w ;

[0031] When the cascade thermal storage system is in a heat release state, the molten salt flow rate of the low-temperature path of the steam generation system is Q. r w The molten salt flow rate in the cryogenic path of the steam generation system is Q. r ' w ;

[0032] The flow difference coefficient is defined to satisfy the following condition: This flow difference coefficient is used to measure the relative difference in molten salt flow rates between the heat storage and heat release of the unit; where, the weighting coefficient is... The closer α is to 1, the more balanced the entire molten salt circuit is.

[0033] The beneficial effects of the embodiments of the present invention include:

[0034] In this invention, superheated steam and reheated steam generated by a coal-fired boiler are connected to a steam heat exchange system. The heat storage medium is heated through the steam heat exchange system and flows between the various heat storage devices under the action of a molten salt pump. The exhaust steam from the reheated steam after heat exchange is incorporated into the low-pressure cylinder of the coal-fired system to perform work, while the condensate from the superheated steam is incorporated into the feedwater inlet of the coal-fired boiler to complete the circulation. With the above configuration, this invention achieves a closed-loop circulation of steam and water between the coal-fired system and the cascade heat storage system without adding any other heating equipment, resulting in high energy utilization efficiency and improved system economy. In addition, by utilizing the heat storage medium between the cascade heat storage systems to absorb the heat from the extracted steam or generate high-quality steam, a faster load change rate is achieved. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a coal-fired unit with a coupled cascade thermal storage system according to an embodiment of the present invention.

[0036] In the diagram, 1. Coal-fired boiler; 2. High-pressure cylinder; 3. Medium-pressure cylinder; 4. Low-pressure cylinder; 5. Generator; 6. Condenser; 7. First circulating water pump; 8. Low-pressure heater; 9. Deaerator; 10. Second circulating water pump; 11. High-pressure heater; 12. High-temperature thermal storage tank; 13. Medium-temperature thermal storage tank; 14. Low-temperature thermal storage tank; 15. First feedwater preheater; 16. First steam generator; 17. First steam superheater; 18. Second steam generator; 19. Second steam superheater; 20. First... 21. Superheated steam heat exchanger; 22. Steam condenser; 23. Drain heat exchanger; 24. Second superheated steam heat exchanger; 25. First high-temperature molten salt pump; 26. First low-temperature molten salt pump; 27. Second low-temperature molten salt pump; F1. Superheated steam distributor; F2. Reheated steam distributor; F3. Low-pressure feedwater distributor; F4. High-pressure feedwater distributor; M1. Feedwater mixer; M2. First steam mixer; M3. Second steam mixer; M4. Superheated steam mixer. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The detailed descriptions and accompanying drawings of the following embodiments are used to exemplarily illustrate the principles of this application, but should not be used to limit the scope of this application; that is, this application is not limited to the described embodiments. In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this application 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 this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range.

[0039] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joining" 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 direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application depending on the specific circumstances.

[0040] like Figure 1As shown, this invention provides a coal-fired power unit with a coupled cascade thermal storage system. The coal-fired power unit includes a coal-fired system and a cascade thermal storage system. The coal-fired system includes a coal-fired boiler 1. The cascade thermal storage system includes cascade thermal storage devices, a steam generation system, a steam heat exchange system, and a molten salt pump.

[0041] The superheated steam from coal-fired boiler 1 exchanges heat with the steam heat exchange system via a superheated steam bypass. The condensate from the superheated steam, after releasing heat and condensing within the steam heat exchange system, flows back to the outlet of the deaerator 9 in the coal-fired system. The reheated steam from coal-fired boiler 1 also exchanges heat with the steam heat exchange system via a reheat steam bypass. The reheated steam from coal-fired boiler 1, after releasing heat within the steam heat exchange system, is conducted to the low-pressure cylinder of the coal-fired system. The steam generation system exchanges heat with the feedwater bypass of the coal-fired system. The steam generated by the low-pressure pumping at the outlet of deaerator 9, which absorbs heat, enters the low-pressure cylinder 4 of the coal-fired system to perform work. The steam generated by the high-pressure pumping at the inlet of coal-fired boiler 1, which absorbs heat, enters the high-pressure cylinder 2 of the coal-fired system to perform work.

[0042] Molten salt pumps are used to provide pressure to allow the heat storage medium at each stage temperature of the cascaded heat storage device to flow between the heat storage devices. The cascaded heat storage device uses the heat storage medium to store the heat of steam in the steam heat exchange system, and uses the heat storage medium to release heat in the steam heat exchange system to evaporate feedwater.

[0043] In this invention, superheated steam and reheated steam generated by coal-fired boiler 1 are connected to a steam heat exchange system. The heat storage medium is heated through the steam heat exchange system and flows between the various heat storage devices under the action of a molten salt pump. The exhaust steam after heat exchange of the reheated steam is incorporated into the low-pressure cylinder of the coal-fired system to perform work, while the condensate after heat exchange of the superheated steam is incorporated into the feedwater inlet of coal-fired boiler 1 to complete the circulation. With the above configuration, this invention achieves a closed-loop circulation of steam and water between the coal-fired system and the cascade heat storage system without adding other heating equipment, resulting in high energy utilization efficiency and improved system economy. In addition, by utilizing the heat storage medium between the cascade heat storage systems to absorb the heat extracted from the steam or generate high-quality steam, a faster load change rate is obtained.

[0044] In some embodiments, the coal-fired system further includes a high-pressure cylinder 2, a medium-pressure cylinder 3, a low-pressure cylinder 4, a generator 5, a condenser 6, a first circulating water pump 7, a low-pressure heater 8, a deaerator 9, a second circulating water pump 10, and a high-pressure heater 11.

[0045] The superheated steam outlet of the coal-fired boiler 1 is connected to the high-pressure cylinder 2, and the reheated steam outlet of the coal-fired boiler 1 is connected to the intermediate-pressure cylinder 3. The outlet of the intermediate-pressure cylinder 3 is connected to the deaerator 9 and the low-pressure cylinder 4, respectively. The outlet of the low-pressure cylinder 4 is connected to the hot-end inlet of the low-pressure heater 8 and the condenser 6, respectively. The outlet of the condenser 6 is connected to the inlet of the first circulating water pump 7, and the outlet of the first circulating water pump 7 is connected to the cold-end inlet of the low-pressure heater 8. The cold-end outlet of the low-pressure heater 8 is connected to the inlet of the deaerator 9. The outlet of the deaerator 9 is connected to the inlet of the second circulating water pump 10, and the outlet of the second circulating water pump 10 is connected to the cold-end inlet of the high-pressure heater 11. The cold-end outlet of the high-pressure heater 11 is connected to the feedwater inlet of the coal-fired boiler 1.

[0046] In some embodiments, the cascade thermal storage device includes a high-temperature thermal storage tank 12, a medium-temperature thermal storage tank 13, and a low-temperature thermal storage tank 14, wherein a steam heat exchange system is disposed at the heat absorption end of the high-temperature thermal storage tank 12, the medium-temperature thermal storage tank 13, and the low-temperature thermal storage tank 14, and a steam generation system is disposed at the heat release end of the high-temperature thermal storage tank 12, the medium-temperature thermal storage tank 13, and the low-temperature thermal storage tank 14.

[0047] In some embodiments, the steam heat exchange system includes a first superheated steam heat exchanger 20, a steam condenser 21, a condensate heat exchanger 22, and a second superheated steam heat exchanger 23.

[0048] The first superheated steam heat exchanger 20 is installed in the heat absorption pipeline between the medium-temperature heat storage tank 13 and the high-temperature heat storage tank 12, and the steam condenser 21, the condensate heat exchanger 22, and the second superheated steam heat exchanger 23 are installed in the heat absorption pipeline between the low-temperature heat storage tank 14 and the medium-temperature heat storage tank 13.

[0049] In some embodiments, the steam generation system includes a first feedwater preheater 15, a first steam generator 16, a first steam superheater 17, a second steam generator 18, and a second steam superheater 19.

[0050] The first steam generator 16 and the first steam superheater 17 are installed in the heat release pipeline between the medium-temperature heat storage tank 13 and the high-temperature heat storage tank 12, and the first water preheater 15, the second steam generator 18 and the second steam superheater 19 are installed in the heat release pipeline between the low-temperature heat storage tank 14 and the medium-temperature heat storage tank 13.

[0051] In some embodiments, the molten salt pump includes a first high-temperature molten salt pump 24, a first low-temperature molten salt pump 25, a second high-temperature molten salt pump 27, and a second low-temperature molten salt pump 26.

[0052] The first high-temperature molten salt pump 24 is installed in the heat release pipeline between the high-temperature heat storage tank 12 and the medium-temperature heat storage tank 13, and the first low-temperature molten salt pump 25 is installed in the heat release pipeline between the medium-temperature heat storage tank 13 and the low-temperature heat storage tank 14. The second high-temperature molten salt pump 27 is installed in the heat absorption pipeline between the high-temperature heat storage tank 12 and the medium-temperature heat storage tank 13, and the second low-temperature molten salt pump 26 is installed in the heat absorption pipeline between the low-temperature heat storage tank 14 and the medium-temperature heat storage tank 13.

[0053] Specifically, the outlet of the high-temperature thermal storage tank 12 is connected to the hot-end inlet of the first steam superheater 17, and the hot-end outlet of the first steam superheater 17 is connected to the hot-end inlet of the first steam generator 16. The hot-end outlet of the first steam generator 16 is connected to the inlet of the medium-temperature thermal storage tank 13, and the outlet of the medium-temperature thermal storage tank 13 is connected to the hot-end inlet of the first feedwater preheater 15. The hot-end outlet of the first feedwater preheater 15 is connected to the hot-end inlet of the second steam superheater 19, and the hot-end outlet of the second steam superheater 19 is connected to the hot-end inlet of the second steam generator 18. The hot-end outlet of the second steam generator 18 is connected to the inlet of the low-temperature thermal storage tank 14, and the outlet of the low-temperature thermal storage tank 14 is connected to the hot-end inlet of the condensate heat exchanger 22. The hot-end outlet of the condensate heat exchanger 22 is connected to the hot-end inlet of the steam condenser 21, and the hot-end outlet of the steam condenser 21 is connected to the hot-end inlet of the second superheated steam heat exchanger 23. The hot end outlet of the second superheated steam heat exchanger 23 is connected to the inlet of the medium-temperature heat storage tank 13, the outlet of the medium-temperature heat storage tank 13 is connected to the hot end inlet of the first superheated steam heat exchanger 20, and the hot end outlet of the first superheated steam heat exchanger 20 is connected to the high-temperature heat storage tank 12.

[0054] In some embodiments, the coal-fired unit further includes: a superheated steam diverter F1 is provided in the superheated steam bypass between the superheated steam outlet end of the coal-fired boiler 1 and the high-pressure cylinder 2, wherein the superheated steam diverter F1 is used to divert the superheated steam, so that a part of the superheated steam enters the high-pressure cylinder 2 and the other part of the superheated steam enters the steam heat exchange system for heat release.

[0055] A reheat steam diverter F2 is provided in the reheat steam bypass between the reheat steam outlet of the coal-fired boiler 1 and the intermediate pressure cylinder 3. The reheat steam diverter F2 is used to divert the reheat steam, so that part of the reheat steam enters the intermediate pressure cylinder 3 and the other part of the reheat steam enters the steam heat exchange system for heat release.

[0056] In some embodiments, the feedwater bypass includes a low-pressure feedwater bypass, which connects to the outlet of the deaerator 9 and the inlet of the second circulating water pump 10. The coal-fired system also includes a low-pressure feedwater diverter F3 and a second steam mixer M3, wherein feedwater in the low-pressure feedwater bypass enters the steam generation system through the low-pressure feedwater diverter F3 to absorb heat and evaporate into steam, and the steam enters the low-pressure cylinder 4 through the second steam mixer M3 to perform work.

[0057] In some embodiments, the feedwater bypass includes a high-pressure feedwater bypass, which connects the outlet of the second circulating water pump 10 and the feedwater inlet of the coal-fired boiler 1. The coal-fired system also includes a high-pressure feedwater diverter F4 and a superheated steam mixer M4, wherein the feedwater in the high-pressure feedwater bypass enters the steam generation system through the high-pressure feedwater diverter F4 to absorb heat and evaporate into steam, and the steam enters the intermediate-pressure cylinder 3 through the superheated steam mixer M4 to perform work.

[0058] A specific example provided by the present invention includes, for example: Figure 1 As shown, a coal-fired power unit with a coupled cascade thermal storage system includes a coal-fired system and a cascade thermal storage system. The coal-fired system includes a coal-fired boiler 1, a high-pressure cylinder 2, an intermediate-pressure cylinder 3, a low-pressure cylinder 4, a generator 5, a condenser 6, a first circulating water pump 7, a low-pressure heater 8, a deaerator 9, a second circulating water pump 10, and a high-pressure heater 11.

[0059] The superheated steam outlet of coal-fired boiler 1 is connected to high-pressure cylinder 2, and the reheated steam outlet of coal-fired boiler 1 is connected to intermediate-pressure cylinder 3. The outlet of high-pressure cylinder 2 is connected to the hot end of the reheater of coal-fired boiler 1 and to the hot end inlet of high-pressure heater 11. The outlet of intermediate-pressure cylinder 3 is connected to deaerator 9 and low-pressure cylinder 4. The outlet of low-pressure cylinder 4 is connected to the hot end inlet of low-pressure heater 8 and to condenser 6. The outlet of condenser 6 is connected to the inlet of first circulating water pump 7. The outlet of first circulating water pump 7 is connected to the cold end inlet of low-pressure heater 8, and the cold end outlet of low-pressure heater 8 is connected to the inlet of deaerator 9. The outlet of deaerator 9 is connected to the inlet of second circulating water pump 10, the outlet of second circulating water pump 10 is connected to the cold end inlet of high-pressure heater 11, and the cold end outlet of high-pressure heater 11 is connected to the feedwater inlet of coal-fired boiler 1.

[0060] Specifically, the coal-fired boiler 1 has a reheater. The superheated steam outlet of the coal-fired boiler 1 is connected to the steam inlet of the high-pressure cylinder 2, and the superheated steam enters the high-pressure cylinder 2 to do work. The outlet of the high-pressure cylinder 2 is connected to the inlet of the reheater, and the outlet of the reheater of the coal-fired boiler 1 is connected to the inlet of the intermediate-pressure cylinder 3. The exhaust steam from the high-pressure cylinder 2 is heated by the reheater of the coal-fired boiler 1 to generate reheated steam, which enters the intermediate-pressure cylinder 3 to do work. The exhaust steam from the intermediate-pressure cylinder 3 enters the low-pressure cylinder 4 to do work. Finally, the high-pressure cylinder 2, the intermediate-pressure cylinder 3, and the low-pressure cylinder 4 are connected to the generator 5 through bearings to generate electricity.

[0061] Furthermore, the steam discharged from the low-pressure cylinder 4 sequentially enters the condenser 6, the first circulating water pump 7, the low-pressure heater 8, the deaerator 9, the second circulating water pump 10, and the high-pressure heater 11. The steam discharged from the low-pressure cylinder 4 enters the condenser 6 and condenses into condensate, which is then extracted from the condenser 6 by the first circulating water pump 7 and transported to the low-pressure heater 8. The steam extracted from the low-pressure cylinder 4 serves as a heat source to heat the condensate in the low-pressure heater 8 and sends it to the deaerator 9. The steam extracted from the intermediate-pressure cylinder 3 provides a heat source to complete the heating and deaeration process of the condensate in the deaerator 9, and the deaerated condensate is extracted from the deaerator 9 by the second circulating water pump 10 and sent to the high-pressure heater 11. The steam extracted from the high-pressure cylinder 2 continues to heat the condensate in the high-pressure heater 11 and finally sends it to the boiler feedwater inlet through a connected pipeline.

[0062] A superheated steam distributor F1 is installed between the superheated steam outlet of the coal-fired boiler 1 and the high-pressure cylinder 2, and a reheated steam distributor F2 is installed between the reheated steam outlet of the coal-fired boiler 1 and the intermediate-pressure cylinder 3. A low-pressure feedwater distributor F3 is installed in the pipeline between the outlet of the deaerator 9 and the inlet of the second circulating water pump 10. A high-pressure feedwater distributor F4 is installed in the pipeline between the outlet of the high-pressure heater 11 and the feedwater inlet of the coal-fired boiler 1. A feedwater mixer M1 is installed in the pipeline between the outlet of the deaerator 9 and the inlet of the second circulating water pump 10, wherein the feedwater mixer M1 is located downstream of the low-pressure feedwater distributor F3. A first steam mixer M2 and a second steam mixer M3 are respectively installed in the pipeline between the intermediate-pressure cylinder 3 and the low-pressure cylinder 4, wherein the first steam mixer M2 is located upstream of the second steam mixer M3. A superheated steam mixer M4 is installed in the pipeline between the superheated steam outlet of the coal-fired boiler 1 and the high-pressure cylinder 2.

[0063] The cascade thermal energy storage system includes cascade thermal energy storage equipment, a steam heat exchange system, a steam generation system, and molten salt pumps. The molten salt pumps include a first high-temperature molten salt pump 24, a first low-temperature molten salt pump 25, a second high-temperature molten salt pump 27, and a second low-temperature molten salt pump 26.

[0064] The cascade thermal storage equipment includes a high-temperature thermal storage tank 12, a medium-temperature thermal storage tank 13, and a low-temperature thermal storage tank 14.

[0065] The steam generation system includes a first feedwater preheater 15, a first steam generator 16, a first steam superheater 17, a second steam generator 18, and a second steam superheater.

[0066] The steam heat exchange system includes a first superheated steam heat exchanger 20, a steam condenser 21, a condensate heat exchanger 22, and a second superheated steam heat exchanger 23.

[0067] The energy transfer process of the steam heat exchange system is as follows: Superheated steam bypasses the hot steam distributor F1 and enters the steam heat exchange system to transfer heat to the thermal storage equipment. After releasing heat and condensing, the condensate returns to the outlet of the deaerator 9. Reheated steam bypasses the reheated steam distributor F2 and enters the steam heat exchange system to transfer heat to the thermal storage equipment. The released low-temperature steam returns to the inlet of the low-pressure cylinder 4 via the first steam mixer M2 and continues to do work inside the low-pressure cylinder 4. Low-temperature molten salt is pressurized from the low-temperature thermal storage tank 14 by the second low-temperature molten salt pump 26, and medium-temperature molten salt is pressurized from the medium-temperature thermal storage tank 13 by the second high-temperature molten salt pump 27. After absorbing heat, the molten salt flows into the medium-temperature thermal storage tank 13 and the high-temperature thermal storage tank 12 for storage, respectively.

[0068] Specifically, the superheated steam from the gas-fired boiler is transported via a superheated steam bypass and split by a hot steam distributor F1. Part of the superheated steam enters the high-pressure cylinder 2, while the other part enters the first superheated steam heat exchanger 20 to release heat to the higher-temperature heat storage medium. The outlet of the first superheated steam heat exchanger 20 is connected to the inlet of the steam condenser 21. Steam exiting the first superheated steam heat exchanger 20 enters the steam condenser 21 to release heat in the middle section of the lower-temperature heat storage medium and condenses into condensate. The outlet of the steam condenser 21 is connected to the inlet of the drain heat exchanger 22, where the condensate releases heat in the cold section of the lower-temperature heat storage medium. The outlet of the drain heat exchanger 22 is connected to the feedwater mixer M1. After heat exchange, the condensate enters the low-pressure feedwater header from the feedwater mixer M1 and recirculates back into the coal-fired system.

[0069] The reheat steam from the coal-fired boiler 1 is transported via a reheat steam bypass. The reheat steam is then split by the reheat steam distributor F2. A portion of the reheat steam enters the intermediate-pressure cylinder 3, while the other portion flows out into the second superheated steam heat exchanger 23 to release heat in the hot section of the lower-temperature heat storage medium. The outlet of the second superheated steam heat exchanger 23 is connected to the first steam mixer M2. After heat exchange, the exhaust steam enters the low-pressure cylinder 4 from the first steam mixer M2 to continue performing work. The low-temperature heat storage medium flows out from the low-temperature heat storage tank 14 and is pumped by the second low-temperature molten salt pump 26. It is heated to the ideal temperature sequentially by the condensate heat exchanger 22 in the cold section, the steam condenser 21 in the middle section, and the second superheated steam heat exchanger 23 in the hot section, and finally sent to the medium-temperature heat storage tank 13 for storage. The medium-temperature heat storage medium flows out from the medium-temperature heat storage tank 13 and is pumped by the second high-temperature molten salt pump 27, heated to the ideal temperature by the first superheated steam heat exchanger 20, and then sent to the high-temperature heat storage tank 12 for storage. The terms "cold section," "middle section," and "hot section" only indicate the order of the physical location of the thermal storage medium in the thermal storage system.

[0070] The energy transfer process of the steam generation system is as follows: Low-pressure feedwater bypass enters the steam generation system from low-pressure feedwater distributor F3, absorbs heat and evaporates, then returns to low-pressure cylinder 4 via second steam mixer M3 to perform work. High-pressure feedwater bypass enters the steam generation system from high-pressure feedwater distributor F4, absorbs heat and evaporates, then returns to intermediate-pressure cylinder 3 via hot steam mixer M4 to perform work. High-temperature molten salt is pressurized from high-temperature storage tank 12 by first high-temperature molten salt pump 24, and medium-temperature molten salt is pressurized from medium-temperature storage tank 13 by first low-temperature molten salt pump 25, flows through the steam generation system to release heat, and then flows into medium-temperature storage tank 13 and low-temperature storage tank 14 for storage.

[0071] Specifically, the low-pressure feedwater bypass flows out from the low-pressure feedwater distributor F3 and enters the second steam generator 18, where it is heated and evaporated by the cold section of the lower-temperature heat storage medium. The outlet of the second steam generator 18 is connected to the inlet of the second steam superheater 19. The low-pressure steam exits from the second steam generator 18 and enters the second steam superheater 19, where it is heated into superheated steam by the middle section of the lower-temperature heat storage medium. The outlet of the second steam superheater 19 is connected to the second steam mixer M3. After heat exchange, the low-pressure superheated steam enters the low-pressure cylinder 4 from the second steam mixer M3 to perform work.

[0072] High-pressure feedwater bypass flows out from high-pressure feedwater diverter F4 and enters the first feedwater preheater 15, where it is heated by the lower-temperature heat storage medium in the hot section. The outlet of the first feedwater preheater 15 is connected to the inlet of the first steam generator 16. High-pressure feedwater exits from the first feedwater preheater 15 and enters the first steam generator 16, where it is heated and evaporated by the higher-temperature heat storage medium in the cold section. The outlet of the first steam generator 16 is connected to the inlet of the first steam superheater 17. The evaporated high-pressure steam enters the first steam superheater 17 and is heated by the higher-temperature heat storage medium in the hot section to become superheated steam that meets the steam parameters required for the high-pressure cylinder 2 to perform work. The outlet of the first steam superheater 17 is connected to the superheated steam mixer M4, and the superheated steam enters the high-pressure cylinder 2 from the superheated steam mixer M4 to perform work. It can be understood that the terms "cold section," "middle section," and "hot section" only indicate the physical order of the heat storage medium in the heat storage system.

[0073] High-temperature thermal storage medium flows out of high-temperature thermal storage tank 12 and is pumped by the first high-temperature molten salt pump 24, releasing heat sequentially through the hot section (first steam superheater 17) and the cold section (first steam generator 16) of the higher-temperature thermal storage medium until it reaches the ideal temperature, and is finally sent to the medium-temperature thermal storage tank 13 for storage. Medium-temperature thermal storage medium flows out of medium-temperature thermal storage tank 13 and is pumped by the first low-temperature molten salt pump 25, releasing heat sequentially through the hot section (first feedwater preheater 15), the middle section (second steam superheater 19), and the cold section (second steam generator 18) of the lower-temperature thermal storage medium until it reaches the ideal temperature, and is then sent to the low-temperature thermal storage tank 14 for storage. It is understood that "cold section," "middle section," and "hot section" only indicate the physical order of the thermal storage medium within the thermal storage system.

[0074] It is understandable that all heat exchangers in the steam heat exchange system and steam generation system, including the first feedwater preheater 15, the first steam generator 16, the first steam superheater 17, the second steam generator 18, the second steam superheater 19, the first superheated steam heat exchanger 20, the steam condenser 21, the condensate heat exchanger 22, and the second superheated steam heat exchanger 23, have independent cold and hot sides, so that the heat source and the cold source flow through the hot side and the cold side respectively for heat exchange.

[0075] In this invention, based on the load requirements of the coal-fired power generation unit, reheat steam and superheated steam are extracted from the coal-fired boiler 1 to reduce the unit load. Heating and evaporation are carried out by a high-temperature thermal storage tank 12, a medium-temperature thermal storage tank 13, and a low-temperature thermal storage tank 14. Low-pressure feedwater is diverted by a low-pressure feedwater distributor F3, and the steam generation system releases heat onto the low-pressure feedwater. The resulting steam then enters the pressure cylinder through a second steam mixer M3 to perform work. High-pressure feedwater is diverted by a high-pressure feedwater distributor F4, and the steam generation system releases heat onto the high-pressure feedwater. The resulting steam then enters the pressure cylinder through a superheated steam mixer M4 to perform work, thereby increasing the unit load.

[0076] In some embodiments, three tanks—a high-temperature thermal storage tank, a medium-temperature thermal storage tank, and a low-temperature thermal storage tank—are connected in sequence, with tank temperatures ranging from 180°C to 600°C.

[0077] In some embodiments, the ratio of superheated steam flow rate to reheated steam flow rate is between 0.9 and 1.1 to ensure the safety of the boiler superheater and reheater.

[0078] In this invention, the flow rate of the thermal storage medium in the cascade thermal storage system can be selected according to the load requirements of the coal-fired power generation unit to achieve rapid changes in the unit load, thereby improving the response rate and peak-shaving and frequency regulation capabilities.

[0079] In some embodiments, the flow rate of the medium flowing from the high-temperature thermal storage tank 12 into the medium-temperature thermal storage tank 13 is different from the flow rate of the medium flowing from the medium-temperature thermal storage tank 13 into the low-temperature thermal storage tank 14. The flow rate of the medium flowing from the low-temperature thermal storage tank 14 into the medium-temperature thermal storage tank 13 is different from the flow rate of the medium flowing from the medium-temperature thermal storage tank 13 into the high-temperature thermal storage tank 12.

[0080] In some embodiments, the ratio of the flow rate of the medium from the high-temperature thermal storage tank 12 into the medium-temperature thermal storage tank 13 and the flow rate of the medium from the medium-temperature thermal storage tank 13 into the low-temperature thermal storage tank 14 is inversely proportional to the ratio of the flow rate of the medium from the low-temperature thermal storage tank 14 into the medium-temperature thermal storage tank 13 and the flow rate of the medium from the medium-temperature thermal storage tank 13 into the high-temperature thermal storage tank 12, thereby achieving a balance of medium flow rates.

[0081] In summary, in this invention, when the unit needs to reduce load, the surplus superheated steam and reheated steam generated by the coal-fired boiler are connected to the steam heat exchange system of the cascade thermal storage system through superheated steam distributor F1 and reheated steam distributor F2. Molten salt is heated from the low-temperature and medium-temperature thermal storage tanks through the steam heat exchange system and flows into the medium-temperature and high-temperature thermal storage tanks respectively under the action of the molten salt pump. The exhaust steam after reheating is connected to the intermediate-pressure cylinder 3 through the first steam mixer M2, and the exhaust steam from the intermediate-pressure cylinder 3 enters the low-pressure cylinder 4 to do work. The condensate after superheating is connected to the deaerator 9 outlet through the feedwater mixer M1 and enters the feedwater header to complete the circulation.

[0082] When the unit needs to increase load, the steam generation system processes the feedwater pumped from the coal-fired system as follows: the first feedwater preheater 15 heats the feedwater to a critical temperature below the evaporation temperature; the first steam generator heats the feedwater at the critical evaporation temperature to slightly superheated steam, accounting for 40% to 90% of the heat in the heat exchange system; the first steam superheater heats the slightly superheated steam to the required superheated steam temperature, and then sends it to the high-pressure cylinder and low-pressure cylinder of the steam turbine to perform work.

[0083] The advantages of this invention lie in the absence of additional heating equipment. The steam and water complete a closed loop between the coal-fired system and the cascade thermal storage system, resulting in high energy efficiency and improved system economy. Furthermore, the coordinated flow of different molten salts among the three storage tanks in the cascade thermal storage system rapidly absorbs extracted steam heat or generates high-quality steam, achieving a faster load change rate. Moreover, when the unit reduces load, the cascade thermal storage system extracts nearly proportional amounts of superheated and reheated steam; when the unit increases load, it generates nearly proportional amounts of superheated and reheated steam. This avoids safety hazards to the boiler and turbine caused by uneven flow changes during the steam-water circulation process, thus improving system safety.

[0084] A first aspect of the present invention provides an operation method for a coal-fired power unit with a coupled cascade thermal storage system, comprising:

[0085] S101. The superheated steam of the coal-fired boiler 1 is exchanged with the steam heat exchange system through the superheated steam bypass. The condensate after the superheated steam releases heat and condenses in the steam heat exchange system is returned to the outlet end of the deaerator 9 of the coal-fired system.

[0086] S102. The reheat steam of the coal-fired boiler 1 is exchanged with the steam heat exchange system through the reheat steam bypass, wherein the reheat steam of the coal-fired boiler 1, after releasing heat in the steam heat exchange system, is conducted to the low-pressure cylinder of the coal-fired system.

[0087] S103. Heat exchange is performed between the steam generation system and the feedwater bypass of the coal-fired system. Specifically, the steam generated by the low-pressure pumping heat absorption at the deaerator outlet enters the low-pressure cylinder of the coal-fired system to perform work, and the steam generated by the high-pressure pumping heat absorption at the boiler inlet enters the high-pressure cylinder of the coal-fired system to perform work.

[0088] S104. A molten salt pump provides pressure to allow the heat storage medium at each stage temperature of the cascaded heat storage device to flow between the heat storage devices. The cascaded heat storage device uses the heat storage medium to store the heat of steam in the steam heat exchange system, and also uses the heat storage medium to release heat in the steam heat exchange system to evaporate feedwater.

[0089] This invention provides a specific example of an operation method for a coal-fired power unit with a coupled cascade thermal storage system, including the following operation process:

[0090] 1. When a coal-fired power generation unit needs to start reducing its load, steam corresponding to the load reduction target flow rate is drawn from the superheated steam distributor F1 and the reheated steam distributor F2 and introduced into the steam heat exchange system of the cascade thermal storage system.

[0091] 2. The condensate after the superheated steam heat exchange is connected from the feedwater mixer M1 to the feedwater header at the outlet of the deaerator 9. The steam after the reheated steam releases heat is discharged from the intermediate pressure cylinder of the first steam mixer M2 to complete the heat storage cycle.

[0092] 3. The low-temperature molten salt of the steam heat exchange system of the cascade thermal storage system flows from the low-temperature thermal storage tank 14 through the second low-temperature molten salt pump 26, through the condenser heat exchanger 22, the steam condenser 21, and the second superheated steam heat exchanger 23 to absorb the heat of superheated steam and reheated steam before flowing into the medium-temperature thermal storage tank 13 for storage. The medium-temperature molten salt flows from the medium-temperature thermal storage tank 13 through the second high-temperature molten salt pump 27, through the first superheated steam heat exchanger 20 to absorb the heat of steam before flowing into the high-temperature thermal storage tank 12 for storage.

[0093] In this embodiment, when the coal-fired power generation unit needs to increase its load, feedwater is drawn from the low-pressure feedwater distributor F3 and the high-pressure feedwater distributor F4 into the steam generation system of the cascade thermal storage system. The two feedwater streams with different parameters are converted into superheated steam by the steam generation system and fed into the high-pressure cylinder 2 via the superheated steam pipeline, and into the low-pressure cylinder 4 via the exhaust pipeline of the intermediate-pressure cylinder 3 to perform work. The high-temperature molten salt from the steam generation system of the cascade thermal storage system is pumped from the high-temperature thermal storage tank 12 through the first high-temperature molten salt pump 24, through the first steam superheater 17 and the first steam generator 16, releasing heat before entering the medium-temperature thermal storage tank 13 for storage. The medium-temperature molten salt is pumped from the medium-temperature thermal storage tank 13 through the first low-temperature molten salt pump 25, through the first feedwater preheater 15, the second steam superheater 19 and the second steam generator 18, releasing heat before entering the low-temperature thermal storage tank 14 for storage.

[0094] In this embodiment, based on the variable load requirements of frequency regulation of the coal-fired power generation unit, the outlet flow rates of the superheated steam distributor F1, reheated steam distributor F2, low-pressure feedwater distributor F3, and high-pressure feedwater distributor F4 are adjusted. The output of the first high-temperature molten salt pump 24, the first low-temperature molten salt pump 25, the second low-temperature molten salt pump 26, and the second high-temperature molten salt pump 27 are adjusted, i.e., the flow rate of the heat storage medium, to rapidly consume or generate steam, directly acting on the rapidly operating steam turbine, quickly changing the unit load, improving the response rate and frequency regulation capability. The superheated steam distributor F1, reheated steam distributor F2, low-pressure feedwater distributor F3, high-pressure feedwater distributor F4, the first high-temperature molten salt pump 24, the first low-temperature molten salt pump 25, the second low-temperature molten salt pump 26, and the second high-temperature molten salt pump 27 act as controllable loads in response to the frequency regulation commands of the coal-fired power generation unit.

[0095] In some embodiments, the ratio of superheated steam flow rate to reheated steam flow rate extracted during the thermal storage process is between 0.9 and 1.1, ensuring the safety of the boiler superheater and reheater.

[0096] In some embodiments, the flow rate of the medium flowing from the high-temperature thermal storage tank 12 into the medium-temperature thermal storage tank 13 is different from the flow rate of the medium flowing from the medium-temperature thermal storage tank 13 into the low-temperature thermal storage tank 14.

[0097] In some embodiments, the flow rate of the medium flowing from the low-temperature thermal storage tank 14 into the medium-temperature thermal storage tank 13 is different from the flow rate of the medium flowing from the medium-temperature thermal storage tank 13 into the high-temperature thermal storage tank 12.

[0098] In some embodiments, the ratio of the flow rate of the medium from the high-temperature thermal storage tank 12 into the medium-temperature thermal storage tank 13 and the flow rate of the medium from the medium-temperature thermal storage tank 13 into the low-temperature thermal storage tank 14 is inversely proportional to the ratio of the flow rate of the medium from the low-temperature thermal storage tank 14 into the medium-temperature thermal storage tank 13 and the flow rate of the medium from the medium-temperature thermal storage tank 13 into the high-temperature thermal storage tank 12, thereby achieving a balance of medium flow rates.

[0099] In some embodiments, the operating states of the cascade thermal storage system include thermal storage state, thermal release state, and thermal standby state.

[0100] The molten salt flow rate in the low-temperature path between the low-temperature and medium-temperature heat storage tanks of the steam heat exchange system is Q. s The molten salt flow rate in the high-temperature path between the medium-temperature and high-temperature heat storage tanks of the steam heat exchange system is Q. s '.

[0101] The molten salt flow rate in the cryogenic path between the cryogenic and intermediate-temperature thermal storage tanks of the steam generation system is Q. r The molten salt flow rate in the high-temperature path between the medium-temperature and high-temperature heat storage tanks of the steam heat exchange system is Q. r ', where the molten salt flow rates of the low-temperature and high-temperature paths corresponding to the steam heat exchange system and steam generation system satisfy the condition: Q s / Q s'=Q r / Q r The molten salt flow rates in the low-temperature and high-temperature paths of the steam heat exchange system satisfy the condition: Q s ≥3Q s The molten salt flow rates in the low-temperature and high-temperature paths of the steam generation system satisfy the condition: Q r ≥3Q r '.

[0102] With the above setup, the high and low temperature molten salt flow rates of the steam heat exchange system and the steam generation system correspond, and the flow rate and quality balance of the molten salt can be controlled by the working time to avoid the accumulation of molten salt in a certain tank.

[0103] In some embodiments, when the cascade thermal storage system is in hot standby mode, the molten salt flow rate in the low-temperature path of the steam heat exchange system is Q. s min The molten salt flow rate in the high-temperature path of the steam heat exchange system is Q. s ' min The molten salt flow rate in the low-temperature path of the steam generation system is Q. r min The molten salt flow rate in the high-temperature path of the steam generation system is Q. r ' min Among them, the molten salt flow rates of the steam heat exchange system and the corresponding low-temperature and high-temperature paths of the steam heat exchange system satisfy the condition: Q s min =Q r min Q s ' min =Q r ' min .

[0104] Understandably, Q max and Q min It represents the flow limit for all molten salt pipes in the thermal storage system loop, and the minimum flow rate Q within the pipes. min Highest traffic Q max The heat storage state, heat release state, and thermal standby state of a thermal storage system are collectively referred to as its operating state, denoted by Q. w This indicates that the size relationship is Q. min ≤Q w ≤Q max In the hot standby state, the molten salt flow rate Q in the low-temperature path of the steam heat exchange system is... s For Q s min molten salt flow rate Q in high-temperature circuit s 'For Q s ' min The molten salt flow rate Q in the cryogenic path of the steam generation system. r For Qr min molten salt flow rate Q in high-temperature circuit r 'For Q r ' min .

[0105] In some embodiments, the thermal storage power is P s min The heat release power is P r min Molten salt flow rate relationship Q under hot standby conditions s min =Q r min Q s ' min =Q r ' min The relationship between heat storage power and heat release power satisfies P s min =P r min With this setup, molten salt flow balance can be achieved in hot standby mode, and the mass of molten salt in the molten salt tank can be dynamically balanced, making the thermal storage system equivalent to a heat exchanger.

[0106] In some embodiments, when the cascade thermal storage system is in thermal storage state, the molten salt flow rate in the low-temperature path of the steam heat exchange system is Q. s w The molten salt flow rate in the high-temperature path of the steam heat exchange system is Q. s ' w When the cascade thermal storage system is in a heat release state, the molten salt flow rate in the low-temperature path of the steam generation system is Q. r w The molten salt flow rate in the low-temperature path of the steam generation system is Q. r ' w .

[0107] It is understandable that when the thermal storage system is in thermal storage mode, the molten salt flow rate Q in the low-temperature path of the steam heat exchange system is... s For Q s w molten salt flow rate Q in high-temperature circuit s 'For Q s ' w The molten salt flow rate Q in the cryogenic path of the steam generation system. r For Q r w molten salt flow rate Q in high-temperature circuit r 'For Q r ' w .

[0108] Furthermore, the flow difference coefficient is defined to satisfy the following condition: This flow rate difference coefficient is used to measure the relative difference in molten salt flow rates for heat storage and heat release within the unit. In the formula, the weighting coefficient... The closer α is to 1, the more balanced the entire molten salt circuit is.

[0109] The weighting coefficient 'a' is calculated based on the molten salt flow rate of each loop. The molten salt flow rate is determined by the steam-water flow rate, which is affected by changes in generator power. Changes in generator power lead to changes in the steam-water flow rate and the molten salt flow rate. The power of the thermal storage system can be calculated using the molten salt flow rate. If the thermal storage system operates at maximum power, then Q... w =Q max .

[0110] Understandable Q s w Q s ' w Q r w Q r ' w Q in the condition s Q s '、Q r Q r 'The input corresponding to the parameter.' Q s Q represents the molten salt flow rate in the cryogenic path of the steam heat exchange system at any given time. s min Q represents the minimum flow rate limit for the cryogenic path of a steam heat exchange system. s w This represents the flow rate of the cryogenic path in the steam heat exchange system during operation, where Q... s Includes Q s w Q s w Includes Q s min .

[0111] In some embodiments, when the unit reduces load, the generator power change decreases from P0 to P1, and the unit output decreases by ΔP = f(a, Q). s Calculate the steady-state operating flow rate Q of the molten salt circuit (T1, T2, T3). sw Q s ' w And control the output of the molten salt pump. In the formula, ΔP is the power output of the generator set, a is the weighting coefficient for the difference in flow rate in the molten salt circuit, and Q... s The flow rate of molten salt in the low-temperature circuit of the steam heat exchange system is given by T1, T2, and T3, which represent the temperatures of the high, medium, and low-temperature tanks of the thermal storage system, respectively. ΔP determines the steam flow rate entering the thermal storage system. Based on the proportional relationship between steam flow rate, tank temperature, and molten salt flow rate, and the first law of thermodynamics, the steady-state operating flow rate Q of the molten salt circuit can be calculated. sw Q s ' w Thus, the molten salt pump has an output power target.

[0112] When the unit increases its load, the power change increases from P0 to P2, and the unit output increases by ΔP = f(a, Q). r Calculate the steady-state operating flow rate Q of the molten salt circuit (T1, T2, T3). rw Q rw And control the output of the molten salt pump.

[0113] Understandably, Q s Includes Q s w Q s w and Q s ' w The relationship is represented by a weighting coefficient 'a', which is variable and influenced by the power of the thermal storage system. The power of the thermal storage system is affected by the steam-water flow rate, which in turn is affected by the generator power. Changes in generator power (load fluctuations) control changes in the steam-water flow rate (entry and exit from the thermal storage system), thus controlling Q. s From Q s min To Q s w (Example) If the thermal storage system operates at maximum power, Q s w =Q max .

[0114] In some embodiments, the thermal storage system assists the unit's step response process, starting from the unit's response action. A step increase occurs, reaching the response load in 5 seconds, with P0 increasing to P2, and the molten salt circuit flow rate increasing from Q. s min Q s ' min Arrival at Q sw Q sw The system operates for 2 minutes, waiting for the boiler load to respond. After 2 minutes, the molten salt circuit flow rate slowly decreases to Q. s min Q s ' min The system is in hot standby mode. A step-down descent occurs, reaching the response load in 5 seconds, with P0 decreasing to P1, and the molten salt circuit flow rate changing from Q... r min Q r ' min Arrival at Q rw Q rw The system operates for 2 minutes, waiting for the boiler load to respond. After 2 minutes, the molten salt circuit flow rate slowly decreases to Q. r min Qr ' min Hot standby status.

[0115] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A coal-fired power unit with a coupled cascade thermal storage system, characterized in that, include: Coal-fired systems and cascade thermal storage systems; The coal-fired system includes a coal-fired boiler; The cascade thermal storage system includes a cascade thermal storage device, a steam generation system, a steam heat exchange system, and a molten salt pump; The superheated steam of the coal-fired boiler exchanges heat with the steam heat exchange system through a superheated steam bypass; wherein, the condensate after the superheated steam releases heat and condenses in the steam heat exchange system flows back to the deaerator outlet of the coal-fired system; the reheated steam of the coal-fired boiler exchanges heat with the steam heat exchange system through a reheated steam bypass; wherein, the steam after the reheated steam of the coal-fired boiler releases heat in the steam heat exchange system is conducted to the low-pressure cylinder of the coal-fired system; the steam generation system is used to exchange heat with the feedwater bypass of the coal-fired system; wherein, the steam generated by the low-pressure pumping heat absorption at the deaerator outlet enters the low-pressure cylinder of the coal-fired system to do work; the steam generated by the high-pressure pumping heat absorption at the boiler inlet enters the high-pressure cylinder of the coal-fired system to do work. The molten salt pump is used to provide pressure to allow the heat storage medium at each stage temperature of the cascaded heat storage device to flow between the heat storage devices; wherein, the cascaded heat storage device uses the heat storage medium to store the heat of steam in the steam heat exchange system; the cascaded heat storage device uses the heat storage medium to release heat in the steam generation system to evaporate feedwater; The cascade thermal storage device includes a high-temperature thermal storage tank, a medium-temperature thermal storage tank, and a low-temperature thermal storage tank; wherein, the steam heat exchange system is located at the heat absorption end of the high-temperature thermal storage tank, the medium-temperature thermal storage tank, and the low-temperature thermal storage tank; and the steam generation system is located at the heat release end of the high-temperature thermal storage tank, the medium-temperature thermal storage tank, and the low-temperature thermal storage tank.

2. A coal-fired unit with a coupled cascade thermal storage system according to claim 1, characterized in that, The coal-fired system also includes a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a generator, a condenser, a first circulating water pump, a low-pressure heater, a deaerator, a second circulating water pump, and a high-pressure heater. The superheated steam outlet of the coal-fired boiler is connected to the high-pressure cylinder; the reheated steam outlet of the coal-fired boiler is connected to the intermediate-pressure cylinder; the outlet of the intermediate-pressure cylinder is connected to the deaerator and the low-pressure cylinder respectively; the outlet of the low-pressure cylinder is connected to the hot-end inlet of the low-pressure heater and the condenser respectively; the outlet of the condenser is connected to the inlet of the first circulating water pump; the outlet of the first circulating water pump is connected to the cold-end inlet of the low-pressure heater; the cold-end outlet of the low-pressure heater is connected to the inlet of the deaerator; the outlet of the deaerator is connected to the inlet of the second circulating water pump; the outlet of the second circulating water pump is connected to the cold-end inlet of the high-pressure heater; and the cold-end outlet of the high-pressure heater is connected to the feedwater inlet of the coal-fired boiler.

3. A coal-fired unit with a coupled cascade thermal storage system according to claim 1, characterized in that, The steam heat exchange system includes a first superheated steam heat exchanger, a steam condenser, a condensate heat exchanger, and a second superheated steam heat exchanger. The first superheated steam heat exchanger is installed in the heat absorption pipeline between the medium-temperature heat storage tank and the high-temperature heat storage tank; the steam condenser, the condensate heat exchanger, and the second superheated steam heat exchanger are installed in the heat absorption pipeline between the low-temperature heat storage tank and the medium-temperature heat storage tank.

4. A coal-fired unit with a coupled cascade thermal storage system according to claim 1, characterized in that, The steam generation system includes a first feedwater preheater, a first steam generator, a first steam superheater, a second steam generator, and a second steam superheater. The first steam generator and the first steam superheater are installed in the heat release pipeline between the medium-temperature heat storage tank and the high-temperature heat storage tank; the first feedwater preheater, the second steam generator and the second steam superheater are installed in the heat release pipeline between the low-temperature heat storage tank and the medium-temperature heat storage tank.

5. A coal-fired unit with a coupled cascade thermal storage system according to claim 1, characterized in that, The molten salt pump includes a first high-temperature molten salt pump, a first low-temperature molten salt pump, a second high-temperature molten salt pump, and a second low-temperature molten salt pump; The first high-temperature molten salt pump is installed in the heat release pipeline between the high-temperature thermal storage tank and the medium-temperature thermal storage tank; the first low-temperature molten salt pump is installed in the heat release pipeline between the medium-temperature thermal storage tank and the low-temperature thermal storage tank; the second high-temperature molten salt pump is installed in the heat absorption pipeline between the high-temperature thermal storage tank and the medium-temperature thermal storage tank; and the second low-temperature molten salt pump is installed in the heat absorption pipeline between the low-temperature thermal storage tank and the medium-temperature thermal storage tank.

6. A method for operating a coal-fired unit with a coupled cascade thermal storage system, wherein the method is implemented using a coal-fired unit with a coupled cascade thermal storage system according to any one of claims 1-5, characterized in that, include: The superheated steam from the coal-fired boiler exchanges heat with the steam heat exchange system through a superheated steam bypass; wherein, the condensate after the superheated steam releases heat and condenses in the steam heat exchange system flows back to the deaerator outlet of the coal-fired system. The reheat steam from the coal-fired boiler is exchanged with the steam heat exchange system through a reheat steam bypass; wherein, the reheat steam from the coal-fired boiler, after releasing heat in the steam heat exchange system, is conducted to the low-pressure cylinder of the coal-fired system. The steam generation system exchanges heat with the feedwater bypass of the coal-fired system; wherein, the steam generated by the low-pressure pumping heat absorption at the deaerator outlet enters the low-pressure cylinder of the coal-fired system to do work; the steam generated by the high-pressure pumping heat absorption at the boiler inlet enters the high-pressure cylinder of the coal-fired system to do work. A molten salt pump provides pressure to allow the heat storage medium at each stage of the cascaded heat storage device to flow between the devices. The cascaded heat storage device uses the heat storage medium to store the heat of steam in the steam heat exchange system. The cascaded heat storage device also uses the heat storage medium to release heat in the steam generation system to evaporate feedwater.

7. The operation method of a coal-fired unit with a coupled cascade thermal storage system according to claim 6, characterized in that, The working states of the cascade thermal storage system include thermal storage state, thermal release state, and thermal standby state. The molten salt flow rate in the low-temperature path between the low-temperature storage tank and the medium-temperature storage tank of the steam heat exchange system is Q. s The molten salt flow rate in the high-temperature path between the medium-temperature and high-temperature heat storage tanks of the steam heat exchange system is Q. s ’ ; The molten salt flow rate in the cryogenic path between the cryogenic and intermediate-temperature thermal storage tanks of the steam generation system is Q. r The molten salt flow rate in the high-temperature path between the medium-temperature and high-temperature heat storage tanks of the steam heat exchange system is Q. r ’ The molten salt flow rates of the low-temperature and high-temperature paths corresponding to the steam heat exchange system and the steam generation system satisfy the condition: Q s / Q s ’ =Q r / Q r ’ The molten salt flow rates in the low-temperature and high-temperature paths of the steam heat exchange system satisfy the condition: Q s ≥3Q s ’ The molten salt flow rates in the low-temperature and high-temperature paths of the steam generation system satisfy the condition: Q r ≥3Q r ’ .

8. The operation method of a coal-fired unit with a coupled cascade thermal storage system according to claim 7, characterized in that, When the cascade thermal storage system is in hot standby mode, the molten salt flow rate of the low-temperature path of the steam heat exchange system is Q. s min The molten salt flow rate in the high-temperature path of the steam heat exchange system is Q. s ' min The molten salt flow rate in the cryogenic path of the steam generation system is Q. r min The molten salt flow rate in the cryogenic path of the steam generation system is Q. r ' min ; wherein, the molten salt flow rates of the steam heat exchange system and the corresponding low-temperature and high-temperature paths of the steam heat exchange system satisfy the condition: Q s min =Q r min Q s ' min =Q r ' min .

9. The operation method of a coal-fired unit with a coupled cascade thermal storage system according to claim 8, characterized in that, When the cascade thermal storage system is in thermal storage state, the molten salt flow rate of the low-temperature path of the steam heat exchange system is Q. s w The molten salt flow rate in the high-temperature path of the steam heat exchange system is Q. s ' w ; When the cascade thermal storage system is in a heat release state, the molten salt flow rate of the low-temperature path of the steam generation system is Q. r w The molten salt flow rate in the cryogenic path of the steam generation system is Q. r ' w ; The flow difference coefficient is defined to satisfy the following condition: This flow difference coefficient is used to measure the relative difference in molten salt flow rates between the heat storage and heat release of the unit; where, the weighting coefficient is... The closer α is to 1, the more balanced the entire molten salt circuit is.

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