Frequency modulation and peak shaving system for coal-fired power unit coupled with multi-level heat storage system and its operation method

Abstract

The present invention discloses a frequency modulation and peak shaving system for a coal-fired unit coupled with a multi-stage heat storage system and an operation method thereof. Through two hybrid energy storage methods of extracting main steam at low load and using part of the auxiliary power, and utilizing multi-stage heat storage of sensible heat storage and phase change heat storage, the frequency modulation and peak shaving capacity of the coal-fired unit is greatly improved, and at the same time, a relatively high cycle efficiency is maintained. The present invention adopts a hybrid energy storage method of electric heating and extraction steam heating, taking into account the rapid regulation of electric heating and the high round-trip efficiency of extraction steam heating; adopts a multi-stage heat storage method of sensible heat storage and latent heat storage, avoiding the limitation of sensible heat storage by the pinch temperature difference. The present invention adopts a partial electric heating energy storage method, solving the problem of insufficient auxiliary power capacity when a large-capacity electric energy storage is configured for the coal-fired unit, and at the same time avoiding the situation that the temperature of the released energy steam is not of high enough grade affected by the end temperature difference of the heat exchanger.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired power generation, and in particular to a frequency modulation and peak shaving system for a coal-fired unit coupled with a multi-stage energy storage system and an operation method thereof. Background Art

[0002] With the continuous increase in the proportion of renewable energy power generation, the structure and operation mode of the power system are becoming increasingly complex. Coal power has gradually changed from the main power source for providing electricity and power to a power and power regulation type power source, and will participate more in auxiliary services such as system peak shaving and spinning reserve to improve the emergency reserve capacity of the power system.

[0003] The energy storage system can improve the load response speed of thermal power units, improve the efficiency of rapid regulation of thermal power units, reduce carbon emissions, avoid damage to the unit life caused by large-scale regulation, and reduce the costs of equipment maintenance and replacement. According to the characteristics of each energy storage technology, the energy storage technologies that can assist thermal power units in frequency modulation and peak shaving include: battery energy storage, flywheel energy storage, hot water storage tank, molten salt energy storage, etc. Among them, the energy storage technology has been widely used at present due to its low price, mature technology, and suitability for large-scale energy storage.

[0004] According to different energy storage methods, the energy storage technology can be divided into two types: extraction steam energy storage and electric heating. For extraction steam energy storage, the round-trip efficiency of the energy storage system is relatively high, but limited by the pinch temperature difference, the heat transfer temperature difference of the sensible heat storage system is large, and the steam temperature often fails to meet the requirements during energy release; for electric heating, the system has a fast response speed and a large depth of regulation, but it violates the principle of energy gradient utilization, and the overall efficiency of the energy storage system is relatively low. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to some extent.

[0006] To this end, an embodiment of the present invention proposes a frequency modulation and peak shaving system for a coal-fired unit coupled with a multi-stage energy storage system and an operation method thereof.

[0007] On the one hand, the present invention proposes a frequency modulation and peak shaving system for a coal-fired unit coupled with a multi-stage energy storage system, including:

[0008] A coal-fired unit, the coal-fired unit includes a boiler, a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder arranged in sequence from upstream to downstream, wherein the extraction steam of the intermediate-pressure cylinder provides heat source for the deaerator;

[0009] Multi - stage heat storage system, the multi - stage heat storage system includes a first heat exchange path, a second heat exchange path connected between the main steam outlet end of the boiler and the boiler feed water inlet end, and a third heat exchange path connected between the outlet end of the deaerator and the steam inlet end of the intermediate - pressure cylinder. Among them, the first heat exchange path uses the electric energy generated by the low - pressure cylinder to heat the sensible heat storage medium to store electric energy, the second heat exchange path is used to use the main steam flowing through it to heat the phase - change heat storage medium and the sensible heat storage medium on its cold side to store the heat energy of the main steam, and the third heat exchange path is used to use the phase - change heat storage medium and the sensible heat storage medium on its hot side to heat the deaerated condensate flowing through its cold side to generate reheated steam.

[0010] In some embodiments, the low - pressure cylinder does work on the generator arranged downstream of it to generate electric energy. A three - winding transformer, an electric heater, and a high - temperature sensible heat storage tank are sequentially arranged upstream and downstream on the first heat exchange path. The electric energy generated by the generator is stepped down by the three - winding transformer to supply electric energy to the electric heater, and the electric heater heats the sensible heat storage medium and stores it in the high - temperature sensible heat storage tank.

[0011] In some embodiments, a primary energy storage heat exchanger, a phase - change heat storage heat exchanger, and a secondary energy storage heat exchanger are sequentially arranged on the second heat exchange path along the main steam flow direction. The main steam flowing through the hot sides of the primary energy storage heat exchanger and the secondary energy storage heat exchanger is used to heat the sensible heat storage medium flowing through the cold sides of the primary energy storage heat exchanger and the secondary energy storage heat exchanger, and the main steam flowing through the hot side of the phase - change heat storage heat exchanger is used to heat the phase - change heat storage medium on its cold side.

[0012] In some embodiments, the cold - side outlet end of the primary energy storage heat exchanger is connected to the inlet end of the electric heater.

[0013] In some embodiments, the cold - side inlet end of the secondary energy storage heat exchanger is connected to the outlet end of the low - temperature sensible heat storage tank, and a low - temperature pump is arranged between the secondary energy storage heat exchanger and the low - temperature sensible heat storage tank.

[0014] In some embodiments, an energy storage boost water pump is arranged between the hot - side outlet end of the secondary energy storage heat exchanger and the boiler feed water inlet end.

[0015] In some embodiments, a primary steam generator, the phase - change heat storage heat exchanger, and a secondary steam generator are sequentially arranged on the third heat exchange path along the condensate flow direction. The high - temperature sensible heat storage medium flowing through the hot side of the primary steam generator heats the condensate on its cold side to generate saturated water, the saturated water is heated to saturated steam in the phase - change heat exchanger, and the saturated steam exchanges heat with the high - temperature sensible heat storage medium flowing through the hot side of the secondary steam generator to generate reheated steam, and the reheated steam enters the intermediate - pressure cylinder to do work.

[0016] In some embodiments, the hot-side outlet end of the primary steam generator is connected to the inlet end of the low-temperature sensible heat storage tank, the cold-side inlet end of the primary steam generator is connected to the outlet end of the deaerator, and an energy-releasing booster pump is arranged between the primary steam generator and the deaerator.

[0017] In some embodiments, the hot-side inlet end of the secondary steam generator is connected to the outlet end of the high-temperature sensible heat storage tank, and a high-temperature pump is arranged between the secondary steam generator and the high-temperature sensible heat storage tank.

[0018] On the other hand, the present invention proposes an operation method for a coal-fired power unit frequency modulation and peak shaving system coupled with a multi-stage heat storage system, including the following processes:

[0019] When the coal-fired power generation system needs deep peak shaving, the first heat exchange path and the second heat exchange path are opened, and part of the electric energy and part of the heat energy of the main steam are converted into sensible heat and latent heat and stored by using the first heat exchange path and the second heat exchange path;

[0020] When the coal-fired power generation system needs to quickly increase the load, the third heat exchange path is opened, and the stored sensible heat and latent heat are used to heat the deaerated condensate water to generate reheated steam through the third heat exchange path, and the reheated steam enters the intermediate pressure cylinder to do work;

[0021] When the coal-fired power generation system needs frequency modulation, the first heat exchange path and the second heat exchange path are opened, and the electric heater responds to the coal-fired power unit frequency modulation instruction as a controllable load.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] By using two hybrid energy storage methods of extracting main steam at low load and using part of the plant electricity, and using multi-stage heat storage of sensible heat storage and phase change heat storage, the present invention greatly improves the frequency modulation and peak shaving capabilities of the coal-fired power unit, and at the same time maintains a high cycle efficiency.

[0024] The present invention adopts a hybrid energy storage method of electric heating and extraction steam heating, taking into account the rapid regulation of electric heating and the round-trip efficiency of extraction steam heating; adopts a multi-stage heat storage method of sensible heat storage and latent heat storage, avoiding the limitation of sensible heat storage by the pinch temperature difference.

[0025] The present invention adopts a partial electric heating energy storage method, which solves the problem of insufficient plant electricity capacity when the coal-fired power unit is configured with a large-capacity electric energy storage, and at the same time avoids the situation that the temperature of the energy-releasing steam is not high enough due to the influence of the heat exchanger end difference. Description of the Drawings

[0026] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0027] Figure 1 Schematic diagram of the frequency regulation and peak shaving system for a coal-fired unit with a coupled multi-stage energy storage system according to the present invention;

[0028] Figure 2 T-Q diagram during the energy storage process under the 30% THA condition of a certain unit;

[0029] Figure 3 T-Q diagram during the energy release process under the 75% THA condition of a certain unit;

[0030] Explanation of the reference numerals in the drawings:

[0031] Boiler 1, high-pressure cylinder 2, intermediate-pressure cylinder 3, low-pressure cylinder 4, generator 5, condenser 6, condensate pump 7, low-pressure heater 8, deaerator 9, high-pressure heater 10, feed water pump 11, energy release booster pump 12, energy storage booster pump 13, three-winding transformer 14, electric heater 15, primary energy storage heat exchanger 16, secondary energy storage heat exchanger 17, low-temperature pump 18, low-temperature sensible heat storage tank 19, phase change heat storage heat exchanger 20, high-temperature sensible heat storage tank 21, high-temperature pump 22, secondary steam generator 23, primary steam generator 24. Detailed implementation manners

[0032] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0033] The frequency regulation and peak shaving system for a coal-fired unit with a coupled multi-stage energy storage system according to an embodiment of the present invention and its operation method will be described below with reference to the drawings.

[0034] As Figure 1 shown, the frequency regulation and peak shaving system for a coal-fired unit with a coupled multi-stage energy storage system according to the present invention includes a coal-fired power generation unit. The coal-fired unit includes a boiler 1, a high-pressure cylinder 2, an intermediate-pressure cylinder 3, and a low-pressure cylinder 4 arranged in sequence from upstream to downstream. Among them, the boiler 1 includes a reheater. The main steam outlet end of the boiler 1 is connected to the steam inlet end of the high-pressure cylinder 2. The main steam generated by the boiler 1 enters the high-pressure cylinder 2 to do work. The exhaust port of the high-pressure cylinder 2 is connected to the inlet end of the reheater. The exhaust steam generated by the high-pressure cylinder 2 enters the reheater to be heated to generate reheated steam. The reheated steam generated by the reheater enters the intermediate-pressure cylinder 3 to do work. The exhaust steam of the intermediate-pressure cylinder 3 enters the low-pressure cylinder 4 to do work. The low-pressure cylinder 4 is connected to the generator 5 through a bearing. The low-pressure cylinder 4 does work on the generator 5 to generate electric energy.

[0035] Downstream of the low-pressure cylinder 4, a condenser 6, a low-pressure heater 8, a deaerator 9, and a high-pressure heater 10 are arranged in sequence. The exhaust steam of the low-pressure cylinder 4 enters the condenser 6 and condenses into condensate. The condensate is pumped into the low-pressure heater 8 by a condensate pump 7 arranged between the condenser 6 and the low-pressure heater 8. The extraction steam of the low-pressure cylinder 4 provides heat source for the low-pressure heater 8. After being heated in the low-pressure heater 8, the condensate enters the deaerator 9. The extraction steam of the intermediate-pressure cylinder 3 provides heat source for the deaerator 9 to carry out heating and deaeration. The deaerated condensate is pumped into the high-pressure heater 10 by a feed water pump 11 arranged between the deaerator 9 and the high-pressure heater 10. The extraction steam of the high-pressure cylinder 2 provides heat source for the high-pressure heater 10. The outlet end of the high-pressure heater 10 is connected to the feed water inlet end of the boiler 1. The condensate becomes feed water after being pressurized by the high-pressure heater 10 and enters the boiler 1.

[0036] The multi-stage heat storage system includes a first heat exchange path, a second heat exchange path, and a third heat exchange path. Among them, the first heat exchange path uses electric energy to heat the sensible heat storage medium to store electric energy. The second heat exchange path is connected between the main steam outlet end and the feed water inlet end of the boiler 1. The second heat exchange path is used to use the main steam flowing through it to heat the phase change heat storage medium and the sensible heat storage medium on its cold side to store the heat energy of the main steam. The third heat exchange path is connected between the outlet end of the deaerator 9 and the steam inlet end of the intermediate-pressure cylinder 3. The third heat exchange path is used to use the phase change heat storage medium and the sensible heat storage medium on its hot side to heat the deaerated condensate flowing through its cold side to generate reheated steam.

[0037] On the first heat exchange path, a three-winding transformer 14, an electric heater 15, and a high-temperature sensible heat storage tank 21 are arranged in sequence from upstream to downstream. The electric energy generated by the generator 5 is stepped down by the three-winding transformer 14 and provided to the electric heater 15. After the electric heater 15 heats the sensible heat storage medium, it stores it in the high-temperature sensible heat storage tank 21.

[0038] Specifically, the voltage of the electric energy generated by the generator 5 is relatively high and cannot be directly used for the electric heater 15. Therefore, a three-winding transformer 14 is arranged between the generator 5 and the electric heater 15 to step down the voltage, and the stepped-down electric energy is used by the electric heater 15. The outlet end of the electric heater 15 is connected to the inlet end of the high-temperature sensible heat storage tank 21, and the inlet end of the electric heater 15 is connected to the cold-side outlet end of the first-stage energy storage heat exchanger 16. The sensible heat storage medium flowing out from the cold-side outlet end of the first-stage energy storage heat exchanger 16 becomes a high-temperature sensible heat storage medium after being heated by the electric heater 15, and the high-temperature sensible heat storage medium is stored in the high-temperature sensible heat storage tank 21. The electric heater 15 has a fast start response speed and heating speed, and can quickly heat the sensible heat storage medium into a high-temperature sensible heat storage medium for storage.

[0039] On the second heat exchange path, a primary energy storage heat exchanger 16, a phase change heat storage heat exchanger 20, and a secondary energy storage heat exchanger 17 are sequentially arranged along the main steam flow direction. The main steam flowing through the hot sides of the primary energy storage heat exchanger 16 and the secondary energy storage heat exchanger 17 is used to heat the sensible heat storage medium flowing through the cold sides of the primary energy storage heat exchanger 16 and the secondary energy storage heat exchanger 17, and the main steam flowing through the hot side of the phase change heat storage heat exchanger 20 is used to heat the phase change heat storage medium on its cold side.

[0040] Specifically, the second heat exchange path is used to store the thermal energy of a part of the main steam generated by the boiler 1. The primary energy storage heat exchanger 16, the phase change heat storage heat exchanger 20, and the secondary energy storage heat exchanger 17 are arranged in sequence upstream and downstream in the direction of the main steam flow. The hot side inlet end of the primary energy storage heat exchanger 16 is connected to the main steam outlet end of the boiler 1, the hot side outlet end of the primary energy storage heat exchanger 16 is connected to the hot side inlet end of the phase change energy storage heat exchanger, the hot side outlet end of the phase change energy storage heat exchanger is connected to the hot side inlet end of the secondary energy storage heat exchanger 17, and the hot side outlet end of the secondary energy storage heat exchanger 17 is connected to the feed water inlet end of the boiler 1. An energy storage booster pump 13 is arranged between the hot side outlet end of the secondary energy storage heat exchanger 17 and the feed water inlet end of the boiler 1. The condensate formed after the main steam flowing out of the hot side outlet end of the secondary energy storage heat exchanger 17 is cooled enters the boiler 1 as feed water under the action of the energy storage booster pump 13. A low-temperature pump 18 is arranged between the secondary energy storage heat exchanger 17 and the low-temperature sensible heat storage tank 19. The cold side inlet end of the secondary energy storage heat exchanger 17 is connected to the outlet end of the low-temperature sensible heat storage tank 19. The low-temperature sensible heat storage medium stored in the low-temperature sensible heat storage tank 19 is pumped into the cold side of the secondary energy storage heat exchanger 17 under the action of the low-temperature pump 18 to exchange heat with the main steam flowing through the hot side of the secondary energy storage heat exchanger 17.

[0041] The cold side outlet end of the secondary energy storage heat exchanger 17 is connected to the cold side inlet end of the primary energy storage heat exchanger 16. The sensible heat storage medium flowing out of the cold side outlet end of the secondary energy storage heat exchanger 17 enters the cold side of the primary energy storage heat exchanger 16 to exchange heat with the main steam flowing through the hot side of the primary energy storage heat exchanger 16. The cold side outlet end of the primary energy storage heat exchanger 16 is connected to the inlet end of the electric heater 15. The sensible heat storage medium flowing out of the cold side outlet end of the primary energy storage heat exchanger 16 is reheated by the electric heater 15 and then stored in the high-temperature sensible heat storage tank 21. In the phase change heat storage heat exchanger 20, the main steam flowing through it serves as the hot side to heat the phase change heat storage medium on the cold side, causing the phase change heat storage medium to undergo a phase change to store the thermal energy of the main steam.

[0042] It can be understood that both the primary energy storage heat exchanger 16 and the secondary energy storage heat exchanger 17 have independent cold sides and hot sides, such that the heat source and the cold source flow through the hot side and the cold side respectively for heat exchange. The phase change energy storage heat exchanger 20 has a phase change energy storage medium side and a tube side. During the phase change energy storage process, its tube side is the hot side, and during the phase change energy release process, its tube side is the cold side. It can be understood that multiple tube sides can also be provided in the phase change energy storage heat exchanger 20 to make the tube sides of the phase change energy release process and the phase change energy storage process independent of each other.

[0043] On the third heat exchange path, a primary steam generator 24, a phase change energy storage heat exchanger 20, and a secondary steam generator 23 are sequentially arranged along the condensate flow direction. The high-temperature sensible heat storage medium flowing through the hot side of the primary steam generator 24 heats the condensate on its cold side to generate saturated water. The saturated water is heated to saturated steam in the phase change heat exchanger. The saturated steam exchanges heat with the high-temperature sensible heat storage medium flowing through the hot side of the secondary steam generator 23 to generate reheated steam, and the reheated steam enters the intermediate pressure cylinder 3 to do work.

[0044] Specifically, the primary steam generator 24, the phase change energy storage heat exchanger 20, and the secondary steam generator 23 are arranged upstream and downstream in sequence in the condensate flow direction. The cold side inlet end of the primary steam generator 24 is connected to the outlet end of the deaerator 9. An energy release booster pump 12 is arranged between the primary steam generator 24 and the deaerator 9. Part of the deaerated condensate is pumped into the cold side of the primary steam generator 24 under the action of the energy release booster pump 12. In the primary steam generator 24, the condensate on the cold side exchanges heat with the sensible heat storage medium on the hot side, and the condensate is heated to saturated water at a certain pressure. The cold side outlet end of the primary steam generator 24 is connected to the cold side inlet end of the phase change energy storage heat exchanger 20, and the saturated water exchanges heat with the phase change energy storage medium in the phase change energy storage heat exchanger 20 and is heated to saturated steam. The cold side outlet end of the phase change energy storage heat exchanger 20 is connected to the cold side inlet end of the secondary steam generator 23. In the secondary steam generator 23, the saturated steam on the cold side exchanges heat with the sensible heat storage medium on the hot side, and the saturated steam is heated to reheated steam. The cold side outlet end of the secondary steam generator 23 is connected to the steam inlet end of the intermediate pressure cylinder 3, and the reheated steam enters the intermediate pressure cylinder 3 to do work.

[0045] The hot-side inlet end of the secondary steam generator 23 is connected to the outlet end of the high-temperature sensible heat storage tank 21. A high-temperature pump 22 is provided between the secondary steam generator 23 and the high-temperature sensible heat storage tank 21. The sensible heat storage medium in the high-temperature sensible heat storage tank 21 enters the hot side of the secondary steam generator 23 under the action of the high-temperature pump 22 to heat the saturated steam on its cold side. The hot-side outlet end of the secondary steam generator 23 is connected to the hot-side inlet end of the primary steam generator 24. The sensible heat storage medium flowing out from the hot-side outlet end of the secondary steam generator 23 enters the hot side of the primary steam generator 24 to heat the condensate water on its cold side. The hot-side outlet end of the primary steam generator 24 is connected to the inlet end of the low-temperature sensible heat storage tank 19. The sensible heat storage medium flowing out from the hot-side outlet end of the primary steam generator 24 enters the low-temperature sensible heat storage tank 19 for storage.

[0046] It can be understood that both the primary steam generator 24 and the secondary steam generator 23 have independent cold sides and hot sides, enabling the heat source and the cold source to flow through the hot side and the cold side respectively for heat exchange.

[0047] T-Q diagram of the energy storage process under 30% THA condition of a certain unit, as Figure 2 shown. It can be seen from the figure that the main steam extraction of the boiler 1 and the electric heater 15 heat the sensible heat storage medium and the phase change heat storage medium. Due to the existence of the terminal difference, the sensible heat storage medium heated by the main steam extraction is lower than the initial temperature of the main steam. The present invention eliminates the terminal difference through the re-heating of the electric heater 15, and adopts a multi-stage heat storage method of sensible heat storage and latent heat storage, avoiding the limitation of sensible heat storage by the pinch temperature difference.

[0048] T-Q diagram of the energy storage process under 75% THA condition of a certain unit, as Figure 3 shown. It can be seen from the figure that the sensible heat storage medium and the latent heat storage medium heat the steam, and the steam is heated to reheat steam and enters the intermediate pressure cylinder 3 to do work.

[0049] Operation method of the frequency modulation and peak shaving system of a coal-fired unit with a coupled multi-stage heat storage system. Using the frequency modulation and peak shaving system of a coal-fired unit with the coupled multi-stage heat storage system of the present invention, it includes the following operation processes:

[0050] When the coal-fired power generation system needs deep peak shaving, the first heat exchange path and the second heat exchange path are opened, and part of the electric energy and part of the heat energy of the main steam are converted into sensible heat and latent heat and stored. At this time, the energy storage booster water pump 13 and the low-temperature pump 18 are started, and the first-stage energy storage heat exchanger 16, the phase change heat storage heat exchanger 20, the second-stage energy storage heat exchanger 17, and the electric heater 15 work to convert part of the electric energy and part of the main steam of the coal-fired unit into sensible heat and latent heat and store them.

[0051] When the coal-fired power generation system needs to quickly increase the load, the third heat exchange path is opened. Through the third heat exchange path, the stored sensible heat and latent heat are used to heat the deaerated condensate to generate reheated steam, and the reheated steam enters the intermediate pressure cylinder 3 to do work. At this time, the energy release booster pump 12 and the high-temperature pump 22 are started, and the secondary steam generator 23, the primary steam generator 24 and the phase change heat storage heat exchanger 20 work. The stored sensible heat and latent heat heat the condensate to reheated steam, and the reheated steam enters the intermediate pressure cylinder 3 to do work.

[0052] When the coal-fired power generation system needs to perform frequency modulation, the first heat exchange path and the second heat exchange path are opened, and the electric heater 15 responds to the frequency modulation command of the coal-fired unit as a controllable load. At this time, the energy storage booster pump 13 and the low-temperature pump 18 are started, and the primary energy storage heat exchanger 16, the phase change heat storage heat exchanger 20, the secondary energy storage heat exchanger 17 and the electric heater 15 work. Since the start-up response speed and heating speed of the electric heater 15 are relatively fast, the electric heater 15 responds to the frequency modulation command of the coal-fired unit as a controllable load.

[0053] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms may be directed to different embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, without conflict, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0054] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0055] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A frequency modulation and peak shaving system for a coal-fired unit coupled with a multi-stage heat storage system, characterized in that, Comprising: A coal-fired unit, which includes a boiler, a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder arranged in sequence from upstream to downstream. Among them, the extraction steam from the intermediate-pressure cylinder provides heat source for the deaerator. A multi-stage heat storage system, which includes a first heat exchange path, a second heat exchange path connected between the main steam outlet end of the boiler and the boiler feed water inlet end, and a third heat exchange path connected between the outlet end of the deaerator and the steam inlet end of the intermediate-pressure cylinder. Among them, the first heat exchange path uses the electric energy generated by the work of the low-pressure cylinder to heat the sensible heat storage medium to store electric energy, the second heat exchange path is used to use the main steam flowing through it to heat the phase change heat storage medium and the sensible heat storage medium on its cold side to store the heat energy of the main steam, and the third heat exchange path is used to use the phase change heat storage medium and the sensible heat storage medium on its hot side to heat the deaerated condensate flowing through its cold side to generate reheated steam.

2. The system according to claim 1, wherein The low-pressure cylinder does work on the generator arranged downstream of it to generate electric energy. On the first heat exchange path, a three-winding transformer, an electric heater, and a high-temperature sensible heat storage tank are arranged in sequence from upstream to downstream. The electric energy generated by the generator is stepped down by the three-winding transformer and then provides electric energy for the electric heater. The electric heater heats the sensible heat storage medium and stores it in the high-temperature sensible heat storage tank.

3. The system according to claim 2, wherein On the second heat exchange path, a primary energy storage heat exchanger, a phase change heat storage heat exchanger, and a secondary energy storage heat exchanger are arranged in sequence along the main steam flow direction. The main steam flowing through the hot sides of the primary energy storage heat exchanger and the secondary energy storage heat exchanger is used to heat the sensible heat storage medium flowing through the cold sides of the primary energy storage heat exchanger and the secondary energy storage heat exchanger, and the main steam flowing through the hot side of the phase change heat storage heat exchanger is used to heat the phase change heat storage medium on its cold side.

4. The system according to claim 3, characterized in that, The cold side outlet end of the primary energy storage heat exchanger is connected to the inlet end of the electric heater.

5. The system according to claim 3, wherein The cold side inlet end of the secondary energy storage heat exchanger is connected to the outlet end of the low-temperature sensible heat storage tank, and a low-temperature pump is arranged between the secondary energy storage heat exchanger and the low-temperature sensible heat storage tank.

6. The system according to claim 3, wherein An energy storage boost water pump is arranged between the hot side outlet end of the secondary energy storage heat exchanger and the boiler feed water inlet end.

7. The system according to claim 5, characterized in that, On the third heat exchange path, a primary steam generator, the phase change heat storage heat exchanger, and a secondary steam generator are arranged in sequence along the condensate flow direction. The high-temperature sensible heat storage medium flowing through the hot side of the primary steam generator heats the condensate on its cold side to generate saturated water. The saturated water is heated to saturated steam in the phase change heat storage heat exchanger. The saturated steam exchanges heat with the high-temperature sensible heat storage medium flowing through the hot side of the secondary steam generator to generate reheated steam, and the reheated steam enters the intermediate-pressure cylinder to do work.

8. The system according to claim 7, wherein The hot side outlet end of the primary steam generator is connected to the inlet end of the low-temperature sensible heat storage tank, the cold side inlet end of the primary steam generator is connected to the outlet end of the deaerator, and an energy release boost water pump is arranged between the primary steam generator and the deaerator.

9. The system according to claim 7, wherein The hot side inlet end of the secondary steam generator is connected to the outlet end of the high-temperature sensible heat storage tank, and a high-temperature pump is arranged between the secondary steam generator and the high-temperature sensible heat storage tank.

10. An operating method of a frequency modulation and peak shaving system for a coal-fired unit coupled with a multi-stage thermal energy storage system, characterized in that, Using the system according to any one of claims 2-9, It includes the following processes: When the coal-fired power generation system needs deep peak shaving, the first heat exchange path and the second heat exchange path are opened, and part of the electric energy and part of the heat energy of the main steam are converted into sensible heat and latent heat by the first heat exchange path and the second heat exchange path and stored; When the coal-fired power generation system needs to quickly increase the load, the third heat exchange path is opened, and the stored sensible heat and latent heat are used through the third heat exchange path to heat the deaerated condensate to generate reheated steam, and the reheated steam enters the intermediate pressure cylinder to do work; When the coal-fired power generation system needs frequency modulation, the first heat exchange path and the second heat exchange path are opened, and the electric heater responds to the frequency modulation command of the coal-fired unit as a controllable load.

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