Coal-fired unit and operation control method of coal-fired unit

Abstract

This application provides a coal-fired power unit and its operation control method, including a coal-fired boiler system, a molten salt system, and a condenser. The coal-fired power unit also includes a boiler feedwater regeneration system and a molten salt feedwater regeneration system located downstream of the condenser, which are connected in parallel. The boiler feedwater regeneration system is connected to the feedwater inlet of the coal-fired boiler system via a first feedwater circuit, and the molten salt feedwater regeneration system is connected to the feedwater inlet of the molten salt system via a second feedwater circuit. The molten salt system includes a molten salt heater, and the coal-fired boiler system includes a coal-fired steam circuit connected to the molten salt heater to heat the molten salt. The molten salt system also includes a molten salt steam circuit, and the steam outlet of the molten salt heater is connected to the molten salt feedwater regeneration system via the molten salt steam circuit to heat the condensate in the molten salt feedwater regeneration system. This can improve the load change rate and meet the flexible peak-shaving requirements for complementarity with new energy sources.

Description

Technical Field

[0001] This invention relates to the field of coal-fired power generation technology, specifically to a coal-fired unit and a method for controlling its operation. Background Technology

[0002] Under the current energy policy of "dual carbon emission reduction," power generating units need to complement new energy sources to ensure power supply and fully utilize their flexible peak-shaving capabilities. While gas turbine generator units have a fast load change rate and can flexibly shaving peaks, they are insufficient to achieve a sufficient scale for complementing new energy sources. Although coal-fired generator units have a sufficient scale, their inherent high thermal inertia and equipment safety limitations result in a lower load change rate, far lower than that of gas turbine power plants, making it difficult to meet the flexible peak-shaving requirements for complementing new energy sources. Summary of the Invention

[0003] The purpose of this application is to provide a coal-fired power unit and a method for controlling its operation, which can improve the rate of change of load and meet the flexible peak-shaving requirements of complementing new energy sources.

[0004] This application provides a coal-fired power unit, including a coal-fired boiler system, a molten salt system, and a condenser. The coal-fired power unit also includes a boiler feedwater regeneration system and a molten salt feedwater regeneration system located downstream of the condenser. The boiler feedwater regeneration system and the molten salt feedwater regeneration system are arranged in parallel. The boiler feedwater regeneration system is connected to the feedwater inlet of the coal-fired boiler system through a first feedwater circuit, and the molten salt feedwater regeneration system is connected to the feedwater inlet of the molten salt system through a second feedwater circuit.

[0005] The molten salt system includes a molten salt heater, and the coal-fired boiler system includes a coal-fired steam circuit. The coal-fired steam circuit is connected to the molten salt heater to heat the molten salt. The molten salt system includes a molten salt steam circuit, and the steam outlet of the molten salt heater is connected to the molten salt feedwater regeneration system through the molten salt steam circuit to heat the condensate in the molten salt feedwater regeneration system.

[0006] Optionally, the molten salt heater includes a molten salt reheat heater, the molten salt steam circuit includes a fifth steam circuit, the steam outlet of the molten salt reheat heater is connected to the fifth steam circuit, and the molten salt feedwater regeneration system includes a second low-pressure heater system, the fifth steam circuit is connected to the second low-pressure heater system.

[0007] Optionally, the molten salt feedwater regeneration system includes a hot water tank for storing condensate heated by the second low-temperature heating system.

[0008] Optionally, a second deaerator is provided between the second low-pressure heating system and the second high-pressure heating system. The second deaerator includes a deaerator head and a water tank located below the deaerator head, wherein the water tank is the hot water tank.

[0009] Optionally, the molten salt steam circuit further includes a sixth steam circuit, the steam outlet of the molten salt reheater is connected to the sixth steam circuit, and the sixth steam circuit is connected to the deaerator head of the second deaerator.

[0010] Optionally, the hot water tank is also connected to the boiler feedwater regeneration system.

[0011] Optionally, the molten salt steam circuit further includes a seventh steam circuit, and the steam outlet of the molten salt reheater is connected to the seventh steam circuit; the coal-fired boiler system includes a low-pressure cylinder, and the seventh steam circuit is connected to the inlet of the low-pressure cylinder.

[0012] Optionally, it also includes a cold water tank located between the second low-pressure heater system and the condenser.

[0013] Optionally, the molten salt steam circuit includes a fourth steam circuit, the steam outlet of the molten salt reheat heater is connected to the fourth steam circuit, the molten salt feedwater reheat system includes a second high-pressure heater system located downstream of the second low-pressure heater system, the second high-pressure heater system is connected to the second feedwater circuit, and the fourth steam circuit is connected to the second high-pressure heater system.

[0014] Optionally, the molten salt steam circuit includes a first steam circuit, the molten salt heater includes a molten salt superheater, the steam outlet of the molten salt superheater is connected to the first steam circuit, the molten salt feedwater regeneration system includes a second high-pressure heater system, the second high-pressure heater system is connected to the second feedwater circuit, and the first steam circuit is connected to the second high-pressure heater system.

[0015] Optionally, the molten salt steam circuit includes a second steam circuit, and the steam outlet of the molten salt superheater is also connected to the second steam circuit; the coal-fired boiler system includes a boiler reheater, and the second steam circuit is connected to the steam inlet of the boiler reheater.

[0016] Optionally, the molten salt steam circuit includes a third steam circuit, and the steam outlet of the molten salt superheater is also connected to the third steam circuit; the molten salt system further includes a molten salt phase change heater, which is located upstream of the molten salt superheater, and the third steam circuit is connected to the molten salt phase change heater.

[0017] Optionally, the molten salt steam circuit includes a high-pressure condensate circuit, and the high-pressure condensate outlet of the molten salt phase change heater is connected to the high-pressure condensate circuit; the molten salt feedwater regeneration system includes a second deaerator, and the high-pressure condensate circuit is connected to the second deaerator.

[0018] This application also provides an operation control method for a coal-fired power unit, applicable to any of the coal-fired power units described above.

[0019] During load increases, including:

[0020] Step S1: Control the coal-fired boiler to increase the load for a first predetermined time using a first predetermined variable load capacity;

[0021] Step S2: Control the molten salt exothermic system to increase the load for a first predetermined time with a second predetermined variable load capacity;

[0022] Step S3: Control the molten salt heating system to maintain the minimum operating state, or reduce the load for a first predetermined time with the third predetermined load change capability;

[0023] After simultaneously performing steps S1, S2, and S3 to reach the total load increase, the coal-fired boiler is controlled to continue increasing the load, while the molten salt exothermic system and the molten salt heating system are both reduced to the minimum operating state.

[0024] When reducing the load, including:

[0025] Step S4: Control the coal-fired boiler to reduce the load for a second predetermined time using a first predetermined load-changing capacity;

[0026] Step S5: Control the molten salt heating system to increase the load for a second predetermined time with a third predetermined variable load capacity;

[0027] Step S6: Control the molten salt exothermic system to maintain the minimum operating state, or reduce the load for a second predetermined time with the second predetermined variable load capacity.

[0028] After simultaneously performing steps S4, S5, and S6 to achieve the total load reduction, the coal-fired boiler is controlled to continue reducing its load, and both the molten salt exothermic system and the molten salt heating system are reduced to their minimum operating states.

[0029] Optionally,

[0030] When the total load increase exceeds the full load of the molten salt exothermic system, in step S2, the molten salt exothermic system is controlled to increase the load to its full load for a first predetermined time with a second predetermined load change capability.

[0031] When the total load reduction exceeds the full load of the molten salt heating system, in step S5, the molten salt heating system is controlled to increase the load to its full load for a second predetermined time using a third predetermined load change capability.

[0032] In this application, the steam outlet of the molten salt heater is connected to the molten salt feedwater regeneration system via a molten salt steam loop to heat the condensate in the molten salt feedwater regeneration system. The steam heated by the molten salt in the molten salt heater is introduced into the molten salt feedwater regeneration system to provide condensate separately for the molten salt system. This condensate absorbs the latent heat of the steam, thus fully utilizing the heat of the steam to provide hot water for the molten salt system. In this way, the molten salt system can improve its heat storage and release capabilities, becoming a comprehensive energy storage system with molten salt energy storage as the primary method and hot water energy storage as a secondary method. This gives the molten salt system the ability to rapidly change loads, assisting coal-fired boiler systems and enabling coal-fired units to have rapid peak-shaving capabilities, meeting the flexible peak-shaving requirements of complementarity with new energy sources. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the coal-fired unit in this embodiment.

[0034] The reference numerals in the above figures are explained as follows:

[0035] 100-Coal-fired boiler system;

[0036] 11-Coal-fired boiler; 12-Coal-fired superheater; 13-Coal-fired reheater; 14-Pressure reducer; 15-High-pressure cylinder; 16-Medium-pressure cylinder; 17-Low-pressure cylinder;

[0037] P - First steam branch; E - Second steam branch; R - Third steam branch;

[0038] S - Fourth steam branch; F - Fifth steam branch; Q - Sixth steam branch;

[0039] C-Seventh Steam Branch;

[0040] T-Steam reflux path;

[0041] 200-molten salt system;

[0042] 21-High-temperature molten salt tank; 22-Low-temperature molten salt tank; 23-Molten salt superheater; 24-Molten salt evaporator; 25-Molten salt feedwater preheater; 26-Molten salt reheater; 27-Molten salt phase change heater; 28-Molten salt superheater; 29-Molten salt reheater;

[0043] A - First steam replenishment circuit; B - Second steam replenishment circuit;

[0044] K - First steam circuit; D - Second steam circuit; U - Third steam circuit;

[0045] L - Fourth steam circuit; M - Fifth steam circuit; N - Sixth steam circuit; G - Seventh steam circuit; J - High-pressure condensate circuit;

[0046] 300 - Water supply system;

[0047] 301 - Boiler feedwater regeneration system; 302 - Molten salt feedwater regeneration system;

[0048] 31-First high-pressure heater system; 32-First low-pressure heater system; 33-First fine treatment device; 34-First deaerator; 35-Cold water tank; 36-Second low-pressure heater system; 37-Second fine treatment device; 38-Second high-pressure heater system; 39-Second deaerator; 391-Deaerator head; 392-Hot water tank;

[0049] H - First water supply circuit; I - Second water supply circuit; O - Connecting water circuit;

[0050] 400-generator;

[0051] 500-Condenser. Detailed Implementation

[0052] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the coal-fired unit in this embodiment.

[0054] The coal-fired unit in this embodiment includes a coal-fired boiler system 100, a molten salt system 200, a condenser 500, and a generator 400. The coal-fired unit also includes a feedwater system 300 located downstream of the condenser 500. Specifically, the feedwater system 300 includes a boiler feedwater regeneration system 301 and a molten salt feedwater regeneration system 302, i.e., it includes two feedwater systems. Because the coal-fired unit in this embodiment has a relatively complex structure, Figure 1 The same letters are used to represent the same circuit, thus establishing the connection between multiple systems of a coal-fired unit in a more concise way. For example, the coal-fired boiler system 100 has a second steam branch E, and the steam of the molten salt superheater 28 of the molten salt system 200 comes from the second steam branch E. That is, the molten salt superheater 28 is connected to the second steam branch E of the coal-fired boiler system 100.

[0055] The components of the coal-fired unit in this embodiment will be discussed in detail below.

[0056] 100 coal-fired boiler systems

[0057] Coal-fired boiler system 100 includes Figure 1The coal-fired boiler 11, high-pressure cylinder 15, intermediate-pressure cylinder 16, and low-pressure cylinder 17 shown are used to provide steam power to the generator 400 of the coal-fired unit for power generation. The coal-fired boiler 11 has a coal-fired superheater 12 and a coal-fired reheater 13. The heat generated by the combustion of the coal-fired boiler 11 can heat the condensate entering the coal-fired boiler 11 to form steam through the superheater 12 and reheater 13. The coal-fired boiler system 100 includes a coal-fired steam circuit connected to the coal-fired boiler 11. The steam generated can flow along the coal-fired steam circuit after being discharged from the coal-fired boiler 11. Specifically, in this embodiment, the coal-fired steam circuit includes one coal-fired steam circuit connected to the superheater 12 and another coal-fired steam circuit connected to the reheater 13. The coal-fired steam circuit connected to the coal-fired superheater 12 comprises three parts, defined as the first steam branch P, the second steam branch E, and the third steam branch R. The coal-fired steam circuit connected to the coal-fired reheater 13 also comprises three parts, defined as the fourth steam branch S, the fifth steam branch F, and the sixth steam branch Q. Wherein:

[0058] The first steam branch P is connected to the high-pressure cylinder 15, providing high-pressure and high-temperature steam to the high-pressure cylinder 15;

[0059] The second steam branch E is connected Figure 1 The molten salt superheater 28 of the molten salt system 200 heats the molten salt and serves as the main steam source for heating the molten salt;

[0060] The third steam branch R serves as a bypass to connect to the steam inlet of the coal-fired reheater 13. The third steam branch R is equipped with a control valve, which is normally closed and opens during shutdown or emergency conditions to return steam to the coal-fired reheater 13 inside the coal-fired boiler 11.

[0061] The fourth steam branch S is connected to the intermediate pressure cylinder 16 and serves as the main steam source for the intermediate pressure cylinder 16.

[0062] Fifth steam branch F connected Figure 1 The molten salt reheat heater 29 of the molten salt system 200 is used to heat the molten salt;

[0063] The sixth steam branch Q serves as a bypass and can connect to the condenser 400. The sixth steam branch Q is equipped with a control valve, which is normally closed but opens during shutdown or emergency conditions to direct steam to the condenser 500. Both the third steam branch R and the sixth steam branch Q serve as temporary protection.

[0064] The coal-fired boiler system 100 also includes a steam return path T, which connects the steam outlet of the high-pressure cylinder 15 and the steam inlet of the coal-fired reheater 13. The aforementioned third steam branch R can be connected to the steam inlet of the coal-fired reheater 13 via the steam return path T.

[0065] Molten Salt System 200

[0066] Molten salt system 200 includes Figure 1 The high-temperature molten salt tank 21 and the low-temperature molten salt tank 22 shown in the diagram allow molten salt to flow between them to store and release heat. Specifically, the molten salt system 200 includes multiple heat exchangers. A portion of these heat exchangers stores heat in the molten salt; this portion is defined as the molten salt heating system. A corresponding portion of these heat exchangers also releases heat; this portion is defined as the molten salt exothermic system. The heat exchangers in the molten salt heating system can be defined as molten salt heaters, including… Figure 1 The molten salt superheater 28 and molten salt reheater 29 shown in the diagram, and the heat exchanger in the molten salt exothermic system include... Figure 1 The molten salt superheater 23 and molten salt reheater 26 are shown. To more fully utilize the heat of the steam and further facilitate system stability, the heat exchangers of the molten salt heating system also include… Figure 1 The molten salt phase change heater 27 shown, and the heat exchanger of the molten salt exothermic system also include Figure 1 The molten salt evaporator 24 and the molten salt feedwater preheater 25 are shown.

[0067] from Figure 1 As can be seen, the high-temperature and high-pressure steam flowing out from the second steam branch E enters the molten salt superheater 28 of the molten salt system 200, transferring heat to a portion of the molten salt flowing out from the low-temperature molten salt tank 22. The molten salt then flows into the high-temperature molten salt tank 21 for heat storage. The steam flowing out from the fifth steam branch F enters the molten salt reheater 29, transferring heat to another portion of the molten salt flowing out from the low-temperature molten salt tank 22. The molten salt also flows into the high-temperature molten salt tank 21 for heat storage.

[0068] Water supply system 300

[0069] Water supply system 300 includes Figure 1 The boiler feedwater regeneration system 301 and the molten salt feedwater regeneration system 302 shown are both located downstream of the condenser 500. The condensate flowing out of the condenser 500 enters the boiler feedwater regeneration system 301 and the molten salt feedwater regeneration system 302 respectively.

[0070] The boiler feedwater regeneration system 301 includes a first low-pressure heater system 32, a first deaerator 34, and a first high-pressure heater system 31. The low-pressure heater system described in this application includes multiple low-pressure heater heat exchangers, and the high-pressure heater system includes multiple high-pressure heater heat exchangers. A first fine treatment device 33 can also be installed between the first low-pressure heater system 32 and the condenser 500 to ensure water quality and protect downstream components. A portion of the water discharged from the condenser 500 passes through the first low-pressure heater system 32, the first deaerator 34, and the first high-pressure heater system 31, and is then connected to the feedwater inlet of the coal-fired superheater 12 in the coal-fired boiler 11 via the first feedwater circuit H.

[0071] The molten salt feedwater regeneration system 302 also includes a second low-pressure heater system 36, a second deaerator 39, and a second high-pressure heater system 38. A second fine treatment device 37 can be installed between the second low-pressure heater system 36 and the condenser 500 in the molten salt feedwater regeneration system 302. Another portion of the water discharged from the condenser 500 passes through the second low-pressure heater system 36, the second deaerator 39, and the second high-pressure heater system 38, and is then connected to the feedwater inlet of the molten salt system 200 via the second feedwater circuit I. Specifically... Figure 1 In the middle, that is, the feedwater inlet of the molten salt feedwater preheater 25 in the molten salt exothermic system.

[0072] It is worth noting that in this embodiment, the steam outlet of the molten salt heater is connected to the molten salt feedwater regeneration system 302 through a molten salt steam circuit to heat the condensate in the molten salt feedwater regeneration system 302. As mentioned above, the molten salt heater specifically includes a molten salt superheater 28 and a molten salt reheater 29. The inventors have found that the molten salt superheater 28 and the molten salt reheater 29 mainly absorb the sensible heat of the steam and cannot effectively absorb the latent heat of the steam. In this embodiment, a portion of the steam heated by the molten salt in the molten salt superheater 28 and most of the steam heated by the molten salt in the molten salt reheater 29 are introduced into the molten salt feedwater regeneration system 302 to provide water separately to the molten salt system 200, and this portion of water absorbs the latent heat of the steam, thereby fully utilizing the heat of the steam to provide hot water to the molten salt system 200. In this way, the molten salt system 200 can improve the heat storage and release capacity, that is, it is a comprehensive energy storage system with molten salt energy storage as the main component and hot water energy storage as the auxiliary component. This enables the molten salt system to have the ability to quickly change loads, which can assist the coal-fired boiler system 100 and enable the coal-fired unit to have the ability to quickly adjust peak loads.

[0073] Specifically, the molten salt steam circuit connected to the molten salt heater includes a first steam circuit K, a second steam circuit D, and a third steam circuit U connected to the steam outlet of the molten salt superheater 28, and also includes a fourth steam circuit L, a fifth steam circuit M, a sixth steam circuit N, and a seventh steam circuit G connected to the steam outlet of the molten salt reheater 29. Wherein:

[0074] The first steam circuit K is connected to the second high-pressure heater system 38 of the molten salt feedwater regeneration system 302, and directly heats the feedwater supplied to the molten salt system 200;

[0075] The second steam circuit D is connected to the steam inlet of the coal-fired reheater 13. Specifically, a pressure reducer 14 can be installed. After the pressure is reduced by the pressure reducer 14, the second steam circuit D is connected to the steam return flow path T of the coal-fired boiler system 100, thereby connecting to the steam inlet of the coal-fired reheater 13.

[0076] The third steam circuit U is connected to the molten salt phase change heater 27, which is located between the low-temperature molten salt tank 22 and the molten salt superheater 28. The third steam circuit U can preheat the low-temperature molten salt entering the molten salt phase change heater 27 to improve the heat exchange efficiency of the molten salt after entering the molten salt superheater 28.

[0077] The fourth steam circuit L is connected to the second high-pressure heater system 38 of the molten salt feedwater regeneration system 302, and together with the first steam circuit K, heats the condensate passing through the second high-pressure heater system 38.

[0078] The fifth steam circuit M is connected to the second low-pressure heater system 36 of the molten salt feedwater regeneration system 302, which can provide preliminary heating for the condensate of the molten salt feedwater regeneration system 302;

[0079] The sixth steam circuit N is connected to the second deaerator 39, which is located between the second low-pressure heater system 36 and the second high-pressure heater system 38. That is, the sixth steam circuit N continues to heat the condensate after it has been heated by the second low-pressure heater system 36.

[0080] The seventh steam circuit G is connected to the steam inlet of the low-pressure cylinder 17, specifically through the outlet pipeline of the intermediate-pressure cylinder 16, to provide steam replenishment for the low-pressure cylinder 17.

[0081] The aforementioned steam circuits can be depressurized in stages according to specific application requirements before entering the corresponding systems for heat exchange. It is understood that the steam flowing from the molten salt superheater 28 is divided into three parts, and the steam flowing from the molten salt reheater 29 is divided into four parts. However, the utilization of steam heat is not limited to this; more steam circuits can be created or the number of steam circuits can be reduced, but at least one steam circuit must be connected to the molten salt feedwater regeneration system 302. For example, the molten salt reheater 29 can be equipped with only one, two, or three of the four steam circuits. However, for coal-fired units, the steam capacity of each component is relatively limited. For instance, the steam capacity of the second high-pressure heater system 38, the second low-pressure heater system 36, and the second deaerator 39 cannot completely consume the latent heat of steam from the molten salt reheater 29. Therefore, by setting a seventh steam circuit G, a portion of the excess steam is added to the low-pressure cylinder 17. Thus, the number and flow rate of steam circuits can be designed and adjusted according to actual steam demand. The design of the number of steam circuits for the molten salt superheater 28 is similar and will not be elaborated further.

[0082] Please look again. Figure 1 In this embodiment, the molten salt system 200 also includes a high-pressure condensate circuit J. The third steam circuit U, which is connected to the molten salt superheater 28, is connected to the molten salt phase change heater 27. The molten salt phase change heater 27 has a high-pressure condensate outlet. That is, after the steam enters the molten salt phase change heater 27 and preheats the molten salt, the steam becomes liquid and forms a high-pressure condensate. The high-pressure condensate still has a high temperature and can be connected to the second deaerator 39 through the high-pressure condensate circuit J. Together with the sixth steam circuit N, it heats the condensate that has passed through the second deaerator 39, thereby further utilizing the heat of the steam.

[0083] In addition, the molten salt feedwater regeneration system 302 in this embodiment also includes a hot water tank 392, which is used to store condensate heated by the second low-pressure heater system 36. It should be understood that the molten salt exothermic system of the molten salt system 200 operates intermittently, that is, it operates when the load needs to be increased, and when the load does not need to be increased, the molten salt exothermic system maintains a minimum operating state. At this time, the requirements for feedwater are not high, as long as the minimum flow rate requirement is met. However, the excess latent heat of steam in the molten salt heating system of the molten salt system 200 needs to be stored using hot water storage. Therefore, the hot water tank 392 facilitates the storage of hot water while also providing water to maintain the operation of the molten salt exothermic system.

[0084] Specifically, in this embodiment, the second deaerator 39 includes a deaerator head 391 and a water tank located below the deaerator head 391, the water tank being a hot water tank 392. That is, the second deaerator 39 is a storage-type deaerator, and its water tank is set to a relatively large capacity water tank to achieve the purpose of storing water, eliminating the need for a separate hot water tank 392, which simplifies the system structure. Of course, the second deaerator 39 can also be equipped with a separate hot water tank 392.

[0085] Let's look again. Figure 1 In this embodiment, the hot water tank 392 is also connected to the boiler feedwater regeneration system 301, specifically to the first deaerator 34 of the boiler feedwater regeneration system 301. When the hot water stored in the hot water tank 392 cannot be fully used by the molten salt system 200, the remaining portion can slowly enter the first deaerator 34 of the boiler feedwater regeneration system 301 at a low flow rate to heat the feedwater of the coal-fired boiler system 100, making full use of thermal energy. At this time, the condensate flow rate of the boiler feedwater regeneration system 301 can be slightly reduced to maintain the stability of the feedwater flow rate of the coal-fired boiler system 100.

[0086] It should be emphasized that this embodiment provides the molten salt system 200 with rapid load change capability by heating the feedwater of the molten salt system 200, thereby assisting the coal-fired boiler system 100 in achieving flexible peak shaving. For this purpose, a separate molten salt feedwater regeneration system 302 is set up and connected in parallel with the boiler feedwater regeneration system 301 downstream of the condenser 500. This ensures that both feedwater regeneration systems can operate safely, while absorbing the latent heat that is not fully utilized in the molten salt heating system, and minimizing the connection between the molten salt system 200 and the boiler feedwater regeneration system 301 that supplies water to the coal-fired boiler system 100, so as to obtain a relatively independent and stable working environment.

[0087] Furthermore, the molten salt feedwater regeneration system 302 also includes a cold water tank 35, which is located between the second low-pressure heater system 36 and the condenser 500. To prevent the molten salt feedwater regeneration system 302 from interfering with the stable operation of the system during the hot water storage process, a cold water tank 35 for storing condensate is also provided. This ensures that while the molten salt feedwater regeneration system 302 operates stably, there is also sufficient condensate to absorb the latent heat of steam and store it in the hot water tank 392.

[0088] The main technological processes of the aforementioned coal-fired power units include:

[0089] 1) Molten salt thermal storage process:

[0090] The molten salt thermal storage process is achieved through the molten salt heating system of the molten salt system 200. On the molten salt side of the molten salt system 200, i.e., in the flow path of the molten salt, the low-temperature molten salt in the low-temperature molten salt tank 22 is pumped into the molten salt phase change heater 27, the molten salt superheater 28, and the molten salt reheater 29 via a molten salt pump. The molten salt superheater 28 and the molten salt reheater 29 are connected in parallel, while the molten salt superheater 28 and the molten salt phase change heater 27 are connected in series. On the steam-water side of the molten salt system 200, in this embodiment, the molten salt is heated by the main steam generated by the coal-fired superheater 12 in the coal-fired boiler 11 and the reheat steam generated by the coal-fired reheater 13, i.e., the main steam of the second steam branch E and the reheat steam of the fifth steam branch F. After the main steam heats the molten salt in the molten salt superheater 28, the temperature of the main steam drops to near the exhaust temperature of the high-pressure cylinder 15, and then it is divided into three parts: the first steam circuit K, the second steam circuit D, and the third steam circuit U. The steam in the first steam circuit K enters the second high-pressure heater system 38 of the molten salt feedwater reheat system 302 to heat the feedwater of the molten salt exothermic system. The steam in the second steam circuit D can be depressurized by the pressure reducer 14 and then reach the same temperature as the exhaust temperature of the high-pressure cylinder 15, and enters the coal-fired reheater 13 through the steam return flow path T. The third steam circuit U enters the molten salt phase change heater 27.

[0091] After the reheated steam heats the molten salt in the molten salt reheat heater 29, the steam temperature drops to near the exhaust temperature of the intermediate-pressure cylinder 16. It then divides into four parts: the fourth steam circuit L, the fifth steam circuit M, the sixth steam circuit N, and the seventh steam circuit G. The steam in the fourth steam circuit L, after being depressurized in stages, enters the second high-pressure heater system 38 of the molten salt feedwater reheat system 302. The steam in the fifth steam circuit M, after being depressurized in stages, enters the second low-pressure heater system 36 of the molten salt feedwater reheat system 302. The steam in the sixth steam circuit N, after being depressurized, enters the second deaerator 39, storing its heat in hot water, specifically in the hot water tank 392. Finally, the steam in the seventh steam circuit G, after being depressurized to the same temperature as the exhaust temperature of the intermediate-pressure cylinder 16, enters the low-pressure cylinder 17 to perform work.

[0092] 2) Molten salt exothermic process

[0093] The molten salt exothermic process is realized through the molten salt exothermic system of the molten salt system 200. On the molten salt side of the molten salt system 200, i.e. in the passage of flowing molten salt, the high-temperature molten salt in the high-temperature molten salt tank 21 is pumped into the molten salt superheater 23, molten salt reheater 26, molten salt evaporator 24 and molten salt feedwater preheater 25 through the molten salt pump. The molten salt superheater 23 and the molten salt reheater 26 are connected in parallel, and the molten salt superheater 23, the molten salt evaporator 24 and the molten salt feedwater preheater 25 are connected in series. On the steam-water side of the molten salt system 200, i.e., in the flowing water passage, the hot water stored in the hot water tank 392 is pumped by the feedwater pump into the second high-pressure heater system 38 of the molten salt feedwater regeneration system 302, and then sequentially enters the molten salt feedwater preheater 25, molten salt evaporator 24, and molten salt superheater 23 of the molten salt system 200. That is, the hot water provided by the molten salt feedwater regeneration system 302 undergoes further progressive heating within the molten salt system 200 to generate high-temperature steam more quickly. The high-temperature steam enters the appropriate position of the high-pressure cylinder 15 of the steam turbine via the first supplementary steam circuit A to perform work. After the steam generated by the molten salt system 200 performs work in the high-pressure cylinder 15, a corresponding portion of the steam flow from the exhaust of the high-pressure cylinder 15 can be diverted into the molten salt reheater 26. Figure 1 The steam return path T of the coal-fired boiler system 100 shown is connected to the seventh steam branch C. The steam in the seventh steam branch C is heated by molten salt in the molten salt reheater 26 and then enters the intermediate pressure cylinder 16 at a suitable position through the second supplementary steam circuit B to do work, thereby making fuller use of the heat energy stored in the molten salt system 200 and keeping the flow of the superheater and reheater of the coal-fired boiler 100 balanced.

[0094] 3) Operation and insulation of molten salt system 200

[0095] The molten salt system 200 includes a molten salt heating system and a molten salt heat release system, which is also known as a molten salt boiler. To prevent the molten salt from solidifying and to ensure that all equipment, auxiliary pumps, pipelines, and valves in the molten salt system 200 are always ready for operation, heat preservation and preheating are required. Therefore, the molten salt system 200 is always in operation, for example, operating within a 10%-100% capacity range. That is, the molten salt circuit and steam-water circuit of the molten salt system 200 are always kept flowing. If necessary, electric heat tracing can be considered locally.

[0096] 4) Hot water storage process

[0097] As mentioned earlier, the main steam from the second steam branch E and the reheat steam from the fifth steam branch F heat the molten salt, primarily utilizing the sensible heat portion of the steam. Because the saturation temperature is low, this heat is difficult for the molten salt to effectively utilize. Therefore, this embodiment also includes a dedicated molten salt feedwater regeneration system 302 to heat the feedwater of the molten salt system 200, while simultaneously fully utilizing the latent heat of the steam. Specifically, the molten salt feedwater regeneration system 302 is equipped with a hot water tank 392. A portion of the near-saturated steam at a lower temperature after heating the molten salt can enter the second low-temperature heater system 36 and the second deaerator 39 of the molten salt feedwater regeneration system 302, heating the condensate to a higher temperature before storing it in the hot water tank 392. This achieves combined heat storage of molten salt and hot water, improving the problem of the difficulty in utilizing the latent heat of steam. To prevent the hot water heat storage process from interfering with the stable operation of the system, a cold water tank 35 for storing condensate is also provided; specifically, the cold water tank 35 is a demineralized cold water tank.

[0098] 5) Hot water heat release process

[0099] When a coal-fired unit needs to flexibly adjust peak load and quickly change load, the molten salt system 200 needs to be put into use. The hot water stored in the hot water tank 392 enters the second high-temperature heater system 38, which can heat it to about 300°C, for example, and then enters the molten salt system 200, and passes through the molten salt feedwater preheater 27, the molten salt evaporator 24 and the molten salt superheater 23 in sequence.

[0100] It is worth mentioning that the heat absorption and release processes of the molten salt system 200 are not balanced, and the hot water stored in the hot water tank 392 may not all be usable by the molten salt system 200. Therefore, this embodiment also provides a connecting water passage O, which can slowly introduce a portion of the hot water in the hot water tank 392 that cannot be used by the molten salt system 200 into the first deaerator 34 of the boiler feedwater regeneration system 301 at a small flow rate. At the same time, it can slightly reduce the condensate flow rate of the boiler feedwater regeneration system 301.

[0101] This embodiment also provides an operation control method for a coal-fired power unit, applicable to any of the coal-fired power units mentioned above. As mentioned earlier, since the latent heat of steam is stored in the molten salt feedwater regenerator system 302, the molten salt system 200 has the ability to rapidly change loads. Specifically, this operation control method achieves the purpose of flexible peak-shaving operation of the coal-fired power unit by jointly controlling the heating and heat-releasing parts of the coal-fired boiler system 100 and the molten salt system 200. As mentioned earlier, the molten salt system 200 includes a molten salt heating system and a molten salt heat-releasing system. Specifically, in this embodiment, the molten salt heat-releasing system includes a molten salt superheater 23, a molten salt reheater 26, a molten salt evaporator 24, and a molten salt feedwater preheater 25. The molten salt heating system in the molten salt system 200 includes a molten salt superheater 28, a molten salt reheater 29, and a molten salt phase change heater 27.

[0102] During operation control, different controls are applied for load increases and load decreases, as follows:

[0103] Load ramp-up process:

[0104] Step S1: The coal-fired boiler 11 increases the load for a first predetermined time t1 according to the first predetermined variable load capacity a;

[0105] Step S2: The molten salt exothermic system increases the load according to the second predetermined variable load capacity b within the first predetermined time t1;

[0106] Regardless of whether it is in the minimum operating state or above the minimum operating state, the molten salt exothermic system needs to increase the load within the first predetermined time t1 according to the second predetermined variable load capacity b. The ratio of the full load of the molten salt exothermic system to the maximum steam inlet of the turbine is also defined as c, for example, when the molten salt exothermic system is at full load, it is 35% of the maximum steam inlet of the turbine.

[0107] Step S3: Control the molten salt heating system to maintain the minimum operating state, or reduce the load for a first predetermined time t1 by the third predetermined variable load capacity d.

[0108] At this time, if the molten salt heating system is in its minimum operating state, it will remain in that state, meaning it will not store heat to facilitate load increase. However, if the molten salt heating system is in a state higher than the minimum (for example, if the load of the coal-fired boiler 11 is greater than the load required by the turbine, then the molten salt heating system will be at high or full load), it will need to simultaneously reduce the heating flow rate, meaning it will no longer store heat to facilitate a rapid response to load increase. The amount of heating load that the molten salt heating system reduces within a first predetermined time t1 according to a third predetermined load change capability d is defined as the amount of heat the molten salt heating system reduces within a first predetermined time t1. The ratio of the full load of the molten salt heating system to the maximum steam inlet of the turbine is e, for example, 25% of the maximum steam inlet of the turbine. The aforementioned load change capabilities are all ratios of change compared to the corresponding full load within a unit of time, which is in minutes in this embodiment. Assume the load increase demand is Q. 升 Then the first predetermined time t1 can be calculated using the following formula:

[0109] Q 升 = a*t1+b*t1*c+d*t1*e

[0110] Among them, Q 升The first predetermined load change capacity a, the proportional capacity c, and the proportional capacity e are all known. As long as t1, b, and d are obtained, the relationship can be satisfied. When adjusting b and d, the value of t1 can be made smaller to achieve the purpose of rapid load increase. After performing steps S1, S2, and S3 to reach the total amount of load increase required, i.e., after rapid load increase, the coal-fired boiler 11 continues to increase the load at the first predetermined load change capacity a until the total load increase is reached. Both the molten salt heat release system and the molten salt heating system can gradually reduce the flow rate until the minimum flow rate is reached, thus completing one load increase process.

[0111] Load reduction process:

[0112] Step S4: The coal-fired boiler 11 reduces its load for a second predetermined time t2 according to the first predetermined load change capacity a;

[0113] Step S5: Control the molten salt heating system to increase the load for a second predetermined time t2 with the third predetermined variable load capacity d;

[0114] Regardless of whether the molten salt heating system is in the minimum operating state or above the minimum operating state, the molten salt heating system needs to increase the heating flow rate within the second predetermined time t2 according to the third predetermined variable load capacity d.

[0115] Step S6: Control the molten salt exothermic system to maintain the minimum operating state, or reduce the load for a second predetermined time t2 with the second predetermined variable load capacity.

[0116] At this point, if the molten salt exothermic system is in its minimum operating state, it will remain in that state, meaning it will not release heat. If the molten salt exothermic system is in a state higher than the minimum (for example, if the load of the coal-fired boiler 11 is lower than the load required by the turbine, the molten salt exothermic system will be at high or full load), then the molten salt exothermic system needs to synchronously reduce its flow rate using the second predetermined load-changing capacity b, meaning it will no longer release heat, to facilitate a rapid response to load reduction. Assume the load reduction demand is Q. 降 Then the second predetermined time t2 can be calculated using the following formula:

[0117] Q 降 = a*t1+b*t1*c+d*t1*e

[0118] Among them, Q 降The first predetermined load change capacity a, the proportional load c, and the proportional load e are all known. As long as t2, b, and d are obtained, the relationship can be satisfied. b and d can be adjusted to make the value of t2 smaller, thereby achieving the purpose of rapid load reduction. After performing steps S4, S5, and S6 to reach the total amount of load reduction required, i.e., after rapid load reduction, the coal-fired boiler 11 continues to reduce the load at the first predetermined load change capacity a until the total load reduction is reached. Both the molten salt exothermic system and the molten salt heating system can gradually reduce the flow rate until the minimum flow rate is reached, completing one load reduction process.

[0119] The following provides a specific example of the coal-fired unit operation control method in this embodiment. The components of the molten salt exothermic system and the molten salt heating system, based on the molten salt feedwater regenerative system 302, have enhanced variable load capacity and can be configured with a larger variable load capacity, such as a rapid variable load capacity of approximately 25%, meaning the second predetermined variable load capacity b and the third predetermined variable load capacity d are no greater than 25%. The molten salt exothermic system can be designed and selected based on 35% of the turbine's maximum steam inlet flow rate as the evaporation rate under the BMCR (Boiler Maximum Continuous Rating) condition, i.e., ratio c = 35%; the molten salt heating system can be designed and selected based on 25% of the turbine's maximum steam inlet flow rate as the evaporation rate under the BMCR condition, i.e., ratio e = 25%. Furthermore, the current first predetermined variable load capacity of the coal-fired boiler 11 is approximately 2%. According to the above settings, the theoretical maximum load increase / decrease rate of the steam turbine can reach Pe% = a + b * c + d * e = 2% + 25% * 35% + 25% * 25% = 17%. Considering the minimum maintenance flow rate of the molten salt exothermic system and the molten salt heating system, and for the convenience of the following description, the relevant time and variable load have been rounded, but this does not affect the process flow description of the relevant load adjustment.

[0120] 1) Load increase process of 50%-100%

[0121] In this case, the total change in turbine load Q 升 The current operating load of the coal-fired boiler 11 is 50% and 75%, respectively.

[0122] The first scenario is: the coal-fired boiler is operating at 50% load.

[0123] Both the molten salt heating system and the molten salt exothermic system are in their minimum operating state. At this time, the molten salt exothermic system can rapidly increase its load at a rate of 12%, i.e., the second predetermined load change capacity b = 12%, reaching full load (approximately 96%) in about 8 minutes, i.e., the first predetermined time t1 = 8. The coal-fired boiler 11 increases its load at a rate of 2%, i.e., the first predetermined load change capacity a = 2%, increasing by approximately 16% in 8 minutes. The molten salt heating system maintains its minimum operating state, i.e., the third predetermined load change capacity d = 0. At this time, the total load increase is:

[0124] Q 升 =a*t1+b*t1*c+d*t1*e=2%*8+12%*8*35%+0=49.6%

[0125] That is, within 8 minutes, the total load can increase by nearly 50%, completing a rapid load increase. However, it is known that only 16% of the load increase is completed by the coal-fired boiler 11, which still needs to continue increasing its load at a rate of 2% until it reaches 100%. Correspondingly, the molten salt exothermic system gradually reduces its flow rate, at a rate roughly equal to the rate of increase of the coal-fired boiler 11, maintaining the 50% load increase until the minimum flow rate is reached. Since the coal-fired boiler 11 only increases its load by 16% at 8 minutes, and still needs to complete the remaining 34% load increase, the load increase will be completed approximately after 17 minutes. In this case, the turbine's load increase rate is approximately 49.6% ÷ 8 = 6.2%.

[0126] It is understandable that the molten salt exothermic system can quickly change load to full load, meaning the maximum increase in turbine load is 35%. At this point, based on the total load change Q... 升 The difference between the values ​​and the first predetermined load change capacity a of the coal-fired boiler 11 can be used to obtain the first predetermined time t1, where t1 = (50% - 35%) ÷ 2% = 7.5 minutes. In this embodiment, 8 minutes is selected. From the first predetermined time t1, the value of the second predetermined load change capacity b of the molten salt exothermic system can be calculated, which is 100% ÷ 8 = 12.5%. In this embodiment, 12% is selected. If the molten salt exothermic system is not changed to full load, the load increase required by the coal-fired boiler 11 will be greater, and the first predetermined time t1 will obviously be longer. Therefore, the preferred solution is to directly and quickly change the load of the molten salt exothermic system to full load. In addition, in the first case, the load of the coal-fired boiler 11 is 50%. Under normal operating conditions, the load of the coal-fired boiler 11 is required to be no less than 50%. Therefore, in the first case, the molten salt heating system operates in the minimum operating state. Under the condition of increased load, the molten salt heating system does not need to store heat further and still maintains the minimum operating state.

[0127] The second scenario is: the coal-fired boiler is operating at 75% load.

[0128] The molten salt exothermic system is in its lowest operating state, while the molten salt heating system is operating at full load. Full load operation of the molten salt heating system mainly includes three scenarios: 1. The turbine has finished reducing its load but has not yet increased it; 2. It is storing heat; 3. The coal-fired boiler 11 and the molten salt heating system are operating together, participating in peak shaving and frequency regulation, in which case the molten salt heating system can operate at a higher load or full load. At this time, the molten salt exothermic system begins to rapidly increase its load at a rate of 25%, i.e., the second predetermined load change capacity b = 25%, reaching full load in approximately 4 minutes, i.e., the first predetermined time t1 = 4. The molten salt heating system begins to reduce its heating flow rate at a rate of 25%, i.e., the third predetermined load change capacity d = 25%, reaching minimum flow state in approximately 4 minutes. The coal-fired boiler 11 increases its load at a rate of 2% of the first predetermined load change capacity a = 2%, increasing by approximately 8% in 4 minutes. At this time, the total load increase is:

[0129] Q 升 =a*t1+b*t1*c+d*t1*e=2%*4+25%*4*35%+25%*4*25%

[0130] =35% + 25% + 8% = 58%

[0131] At this point, the target load of coal-fired boiler 11, which is 75% to 100%, is still 25% - 8% = 17% short. If the load is increased at a rate of 2%, the required time is 17% ÷ 2 = 8.5 minutes, meaning approximately 8 to 9 minutes more is needed for the load to increase. That is, in the following 8 to 9 minutes, coal-fired boiler 11 continues to increase the load until it reaches 100%. The molten salt heat release system gradually reduces the flow rate until it reaches the minimum flow rate, completing one load increase process. In this case, the turbine's load increase rate can reach 58% ÷ 4 = 14.5%.

[0132] 2) Load reduction process from 100% to 50%

[0133] In this situation, the total change in turbine load is 50%. The following operation control is based on the current load of coal-fired boiler 11 being 100% and 65%.

[0134] The first scenario is: the coal-fired boiler is operating at 100% load.

[0135] Both the molten salt heating system and the molten salt exothermic system are operating at their lowest operating levels. At this time, the molten salt heating system begins to increase its heating flow rate at a rate of 8%, i.e., the third predetermined variable load capacity d = 8%, reaching its maximum flow rate in approximately 12 minutes. The molten salt exothermic system remains in its lowest operating state, not releasing heat, in order to reduce the load accordingly as quickly as possible. The coal-fired boiler 11 reduces its load at a rate of 2%, i.e., the first predetermined variable load capacity a = 2%, reducing it by 24% within 12 minutes. The total load reduction is:

[0136] Q降 = a*t1+b*t1*c+d*t1*e

[0137] =2%*12 + 0%*12*35% + 8%*12*25% = 24% + 24% = 48%

[0138] This means that approximately 50% of the load increase target has been achieved. Similarly, coal-fired boiler 11 then continues to reduce its load over a period of (50% - 24%) ÷ 2% = 13 minutes. That is, in the following approximately 12 to 13 minutes, coal-fired boiler 11 continues to reduce its load until it reaches 50%. During the load reduction process, the molten salt exothermic system maintains its minimum operating state, and the molten salt heating system gradually reduces its flow rate until it reaches minimum flow, completing one load reduction cycle. In this case, the turbine's load reduction rate is approximately 48% ÷ 12 = 4%.

[0139] The second scenario is: the coal-fired boiler 11 is operating at 65% load.

[0140] The molten salt heating system is operating at its lowest operating state, while the molten salt exothermic system is operating at full load. Full load operation of the molten salt exothermic system mainly includes three scenarios: 1. The assist system has completed its load increase but has not yet reduced its load; 2. The high-temperature molten salt tank 21 of the molten salt system 200 is full and needs to release heat; 3. The coal-fired boiler 11 and the molten salt exothermic system are operating together, participating in peak shaving and frequency regulation, in which case the molten salt exothermic system can maintain operation at a higher or even full load. At this time, the molten salt exothermic system begins to rapidly reduce its load at a rate of 25%, i.e., the second predetermined load change capacity b = 25%, reaching the minimum flow state in approximately 4 minutes. The molten salt heating system begins to increase its heating flow rate at a rate of 25%, i.e., the third predetermined load change capacity d = 25%, reaching the maximum flow rate in approximately 4 minutes. The coal-fired boiler 11 reduces its load at a rate of 2% of the first predetermined load change capacity a = 2%, reducing it by approximately 8% in 4 minutes. The total load reduction is:

[0141] Q 降 =a*t1+b*t1*c+d*t1*e=2%*4+25%*4*35%+25%*4*25%=58%.

[0142] At this point, the target load reduction of coal-fired boiler 11 from 65% to 50% is still 15% - 8% = 7%. Therefore, at a load reduction rate of 2%, it will require approximately 3.5 minutes of further load reduction time. That is, in the following 3 to 4 minutes, coal-fired boiler 11 continues to reduce its load until it reaches 50%. The molten salt heating system gradually reduces its flow rate until it reaches its minimum flow rate, completing one load reduction cycle. Under these circumstances, the turbine's load reduction rate can reach 58% ÷ 4 = 14.5%.

[0143] 3) Segmented load increase process of 50%-75% and 75%-100%

[0144] In this case, the total change in turbine load is 25%, and the process calculation can also be illustrated under various conditions.

[0145] The first scenario is that the coal-fired boiler's load is either 50% or 75%, meaning the load is increased from 50% to 75%, or from 75% to 100%.

[0146] Both the molten salt heating system and the molten salt exothermic system are in their lowest operating state. At this time, the molten salt exothermic system begins to rapidly increase its load at a rate of 25% of its second predetermined variable load capacity (b = 25%). Since the maximum capacity of the molten salt exothermic system is 35%, which is greater than the total load change of the turbine (25%), the load increase rate of the molten salt exothermic system and the coal-fired boiler 11 working together is approximately (25% * 35% + 2%). Therefore, the time t1 = 25% / (25% * 35% + 2%), which is approximately 2.32 minutes. We can take t1 = 2.5 minutes, allowing the molten salt exothermic system to reach nearly 60% of its capacity within 2.5 minutes, i.e., a load increase of 60% * 35% = 21%. The coal-fired boiler 11 increases its load at a rate of 2% of its first predetermined variable load capacity (a = 2%), increasing by approximately 5% within 2.5 minutes. Total load increase:

[0147] Q 升 =60% * 35% + 5% = 26%.

[0148] At this point, the 25% load increase target of coal-fired boiler 11 is still 25% - 5% = 20% short. Therefore, reducing the load at a rate of 2% requires approximately 10 minutes of further load reduction. Over the next 10 minutes, coal-fired boiler 11 continues to increase the load until it reaches 75% or 100%. The molten salt heat release system gradually reduces its flow rate until it reaches its minimum flow rate, completing one load increase process. In this case, the turbine's load increase rate is approximately 26% ÷ 2.5 = 10.4%.

[0149] The second scenario involves the coal-fired boilers operating at 66% or 91% load, meaning the load is increased from 66% to 75%, or from 91% to 100%.

[0150] The molten salt exothermic system is in its lowest operating state, while the molten salt heating system is operating at high load. At this time, the molten salt exothermic system begins to rapidly increase its load at a rate of 25% of its second predetermined load change capacity (b = 25%), reaching 50% in approximately t1 = 2 minutes. The molten salt heating system then begins to reduce its heating flow rate at a rate of 25% of its third predetermined load change capacity (d = 25%). The combined load increase rate of the molten salt exothermic system, the molten salt heating system, and the coal-fired boiler 11 is approximately (25% * 35% + 25% * 25% + 2%), so the time t1 = 25% / (25% * 35% + 25% * 25% + 2%), t1 is approximately 1.47 minutes, rounded down to 2 minutes. Therefore, the load can be reduced by 50% in approximately 2 minutes. The coal-fired boiler 11 increases its load at a rate of 2% of its first predetermined load change capacity (a = 2%), increasing by approximately 4% in 2 minutes. The total load increase is:

[0151] Q 升 =50% * 35% + 50% * 25% + 4% = 29%

[0152] At this point, the 25% load increase target of coal-fired boiler 11 is still 9% - 4% = 5% short. Therefore, reducing the load at a rate of 2% requires approximately 2.5 minutes of load reduction time. Over the next 2 to 3 minutes, coal-fired boiler 11 continues to increase the load until it reaches 75% or 100%. The molten salt heat release system gradually reduces its flow rate until it reaches its minimum flow rate. The molten salt heating system continues to reduce its flow rate until it reaches its minimum flow rate, completing one load increase process. In this case, the turbine's load increase rate is approximately 29% ÷ 2 = 14.5%.

[0153] 4) Segmented load reduction processes of 100%-75% and 75%-50%

[0154] In this case, the total change in turbine load is 25%, and the process calculation can also be illustrated under various conditions.

[0155] The first scenario is: the load of the coal-fired boiler is 100% or 75% respectively, that is, the load is reduced from 100% to 75%, or from 75% to 50%.

[0156] Both the molten salt heating system and the molten salt exothermic system are in their lowest operating state. At this time, the molten salt heating system begins to increase its heating flow rate at a rate of 25% of its third predetermined load change capacity (b = 25%). The load reduction rate of the molten salt heating system and the coal-fired boiler 11 working together is approximately (25% * 25% + 2%). Therefore, the time t2 = 25% / (25% * 25% + 2%), which is approximately 3.03 minutes. For ease of calculation and comparison, it is rounded up to 4 minutes. The molten salt heating system reaches its maximum flow rate in approximately t2 = 4 minutes. The coal-fired boiler 11 reduces its load at a rate of 2% of its first predetermined load change capacity (a = 2%), reducing it by approximately 8% within 4 minutes. Therefore, the total load reduction is:

[0157] Q 降 =25% + 8% = 33%

[0158] At this point, the coal-fired boiler 11 is still 17% short of its 25% load reduction target (25% - 8% = 17%). Therefore, at a load reduction rate of 2%, it will require approximately 8.5 minutes of further load reduction time. Over the next 8 to 9 minutes, the coal-fired boiler 11 continues to reduce its load until it reaches 75% or 50%. The molten salt heating system gradually reduces its flow rate until it reaches its minimum flow rate, completing one load reduction cycle. In this scenario, the turbine's load reduction rate is approximately 33% ÷ 4 = 8.25%.

[0159] The second scenario is: the coal-fired boiler load is 59% or 83%, that is, the load is reduced from 59% to 50%, or from 83% to 75%.

[0160] The molten salt heating system is in its lowest operating state, while the molten salt exothermic system is operating at high load. At this time, the molten salt exothermic system begins to rapidly reduce its load at a rate of 25% of its second predetermined load change capacity (b = 25%), reducing it by 50% in approximately t2 = 2 minutes. The molten salt heating system then begins to increase its heating flow rate at a rate of 25% of its third predetermined load change capacity (d = 25%). The load reduction rate of the molten salt exothermic system, the molten salt heating system, and the coal-fired boiler 11 working together is approximately (25% * 35% + 25% * 25% + 2%). Therefore, the time t1 = 25% / (25% * 35% + 25% * 25% + 2%), t1 is approximately 1.47 minutes. Rounded to 2 minutes, the molten salt heating system and the molten salt exothermic system can reach 50% load reduction in approximately 2 minutes. The coal-fired boiler 11 reduces its load at a rate of 2%, decreasing by approximately 4% in 2 minutes. The total load reduction is:

[0161] Q 降 =50% * 35% + 50% * 25% + 4% = 29%.

[0162] At this point, the 25% load reduction target of coal-fired boiler 11 is still 9% - 4% = 5% short. Therefore, at a load reduction rate of 2%, it will require approximately 2.5 minutes of further load reduction time. Over the next 2 to 3 minutes, coal-fired boiler 11 continues to reduce its load until it reaches 75% or 50%. The molten salt exothermic system gradually reduces its flow rate until it reaches its minimum flow rate. The molten salt heating system gradually reduces its flow rate until it reaches its minimum flow rate, completing one load reduction cycle. In this scenario, the turbine's load reduction rate can reach 29% ÷ 2 = 14.5%.

[0163] 5) Load increase / decrease process from 30% to 100%

[0164] In this case, the total change in turbine load is 75%. This is because the main steam pressure and temperature parameters of coal-fired boiler 11 are too low under 30% operating conditions. The situation where coal-fired boiler 11 is below 50% load is not considered.

[0165] During load increase, in this scenario, coal-fired boiler 11 operates at 55% load, the molten salt heat release system is at its lowest operating state, and the molten salt heating system is operating at full load. At this time, the molten salt heat release system begins to rapidly increase its load at a rate of 10% of the second predetermined load change capacity (b = 10%), reaching full load in approximately t1 = 10 minutes. The molten salt heating system then begins to decrease its heating flow rate at a rate of 10% of the third predetermined load change capacity (d = 10%), reaching minimum flow in approximately 10 minutes. Coal-fired boiler 11 increases its load at a rate of 2%, increasing by approximately 20% within 10 minutes. The total load increase is:

[0166] Q 升 =35% + 25% + 20% = 70%

[0167] At this point, the load of coal-fired boiler 11 is 75%. The target load increase is still 25% short of 100% - 75%. Therefore, if the load continues to increase at a rate of 2%, it will require approximately 12.5 minutes more to reach 100%. That is, over the next 12 to 13 minutes, coal-fired boiler 11 will continue to increase its load until it reaches 100%. The molten salt heat release system gradually reduces its flow rate until it reaches its minimum flow rate, completing one load increase process. In this case, the turbine's load increase rate can reach 70% ÷ 10 = 7%.

[0168] In the first scenario of load reduction, coal-fired boiler 11 is at 100% load, and both the molten salt heating system and the molten salt heat release system are operating at their lowest possible levels. At this time, the molten salt heating system begins to increase the heating flow rate at a rate of 4.5% of its first predetermined load change capacity c, reaching its maximum flow rate (approximately 99%) within approximately t2 = 22 minutes. Coal-fired boiler 11 then reduces its load at a rate of 2%, decreasing by approximately 45% within 22 minutes. The total load reduction is:

[0169] Q 降 =25% + 45% = 70%

[0170] Subsequently, the load on coal-fired boiler 11 remained unchanged. The molten salt heating system could operate at maximum flow for more than 10 hours, meeting the requirements for deep peak shaving. Under these conditions, the turbine's load reduction rate was approximately 70% ÷ 22 = 3.2%.

[0171] In the second scenario of load reduction, the coal-fired boiler 11 is operating at 65% load, the molten salt heating system is at its lowest operating state, and the molten salt heat release system is operating at full load. At this time, the molten salt heat release system begins to rapidly reduce its load at a rate of 20% of the second predetermined load change capacity (b = 20%), reaching its minimum flow rate in approximately t2 = 5 minutes. The molten salt heating system then begins to increase its heating flow rate at a rate of 20% of the third predetermined load change capacity (d = 20%), reaching its maximum flow rate in approximately 5 minutes. The coal-fired boiler 11 reduces its load at a rate of 2% of the first predetermined load change capacity, decreasing by approximately 10% in 5 minutes. The total load reduction is:

[0172] Q 降 =35% + 25% + 10% = 70%

[0173] Subsequently, the load on coal-fired boiler 11 remained unchanged. The molten salt heating system could operate at maximum flow for more than 10 hours, meeting the requirements for deep peak shaving. Under these conditions, the turbine's load reduction rate could reach 70% ÷ 5 = 14%.

[0174] During load increases and decreases, the above operating mode results in only a small amount of energy loss. However, in some cases, the load reduction rate may be too low. Considering that the actual load reduction capacity of the coal-fired boiler 11 is greater than its load increase capacity, and that high and low pressure bypasses can be opened to assist in load reduction, the actual load reduction rate can reach over 7%. Of course, opening high and low pressure bypasses to assist in load reduction results in steam energy loss and can be used as a backup measure.

[0175] The following example illustrates the parameters of a specific coal-fired unit that enables the above-described operation control method.

[0176] Taking a conventional supercritical 350MW coal-fired unit as an example, the maximum steam inlet of the turbine, i.e., the boiler BMCR evaporation capacity, is 1055 t / h. According to the capacity ratio requirements of this application, the system configuration is as follows:

[0177] Table 1. Configuration of Integrated Energy Storage System for Conventional Supercritical 350MW Coal-fired Units

[0178]

[0179]

[0180] In the table above, THA for the steam turbine represents "turbine heat acceptance," meaning the heat rate acceptance condition; VWO for the steam turbine represents "valve wide open," meaning the valve is fully open. In this embodiment, the molten salt system 200 can be designed and selected based on a 3-hour operating time. The high-temperature molten salt tank 21 and the low-temperature molten salt tank 22 have equal volumes, with the larger volume chosen. The volumes of both the high-temperature and low-temperature molten salt tanks are equal to the total molten salt storage capacity. Based on this capacity, the molten salt system 200 can be used for approximately 6 hours during load increases and decreases. This roughly matches the daily peak and trough fluctuations in grid load after integrating wind and solar power. However, considering factors such as molten salt prices, the capacity of the molten salt system 200 can be appropriately reduced from 3 hours of full flow to 1 hour, achieving a short-term, rapid peak-shaving effect, but timely energy storage replenishment is required. In this embodiment, the capacity of the hot water tank 392 and the cold water tank 35 in the molten salt feedwater regeneration system 302 is designed according to the water supply required by the molten salt system 200, and is also designed to last for 3 hours. The capacity of the cold water tank 35 can be slightly larger than that of the hot water tank 392.

[0181] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A coal-fired power unit, characterized in that, The unit includes a coal-fired boiler system, a molten salt system, and a condenser. The coal-fired unit also includes a boiler feedwater regeneration system and a molten salt feedwater regeneration system located downstream of the condenser. The boiler feedwater regeneration system and the molten salt feedwater regeneration system are connected in parallel. The boiler feedwater regeneration system is connected to the feedwater inlet of the coal-fired boiler system through a first feedwater circuit, and the molten salt feedwater regeneration system is connected to the feedwater inlet of the molten salt system through a second feedwater circuit. The molten salt system includes a molten salt heater, and the coal-fired boiler system includes a coal-fired steam circuit. The coal-fired steam circuit is connected to the molten salt heater to heat the molten salt. The molten salt system includes a molten salt steam circuit, and the steam outlet of the molten salt heater is connected to the molten salt feedwater regeneration system through the molten salt steam circuit to heat the condensate in the molten salt feedwater regeneration system. The molten salt heater includes a molten salt reheat heater, the molten salt steam circuit includes a fifth steam circuit, the steam outlet of the molten salt reheat heater is connected to the fifth steam circuit, and the molten salt feedwater reheat system includes a second low-pressure heater system, the fifth steam circuit is connected to the second low-pressure heater system.

2. The coal-fired power unit according to claim 1, characterized in that, The molten salt feedwater regeneration system includes a hot water tank for storing condensate heated by the second low-temperature heating system.

3. The coal-fired power unit according to claim 2, characterized in that, A second deaerator is provided between the second low-pressure heating system and the second high-pressure heating system. The second deaerator includes a deaerator head and a water tank located below the deaerator head. The water tank is the hot water tank.

4. The coal-fired power unit according to claim 3, characterized in that, The molten salt steam circuit also includes a sixth steam circuit, the steam outlet of the molten salt reheat heater is connected to the sixth steam circuit, and the sixth steam circuit is connected to the deaerator head of the second deaerator.

5. The coal-fired power unit according to claim 3, characterized in that, The hot water tank is also connected to the boiler feedwater regeneration system.

6. The coal-fired power unit according to claim 1, characterized in that, The molten salt steam circuit also includes a seventh steam circuit, and the steam outlet of the molten salt reheat heater is connected to the seventh steam circuit; the coal-fired boiler system includes a low-pressure cylinder, and the seventh steam circuit is connected to the inlet of the low-pressure cylinder.

7. The coal-fired power unit according to claim 1, characterized in that, It also includes a cold water tank, which is located between the second low-pressure heater system and the condenser.

8. The coal-fired power unit according to claim 1, characterized in that, The molten salt steam circuit includes a fourth steam circuit, the steam outlet of the molten salt reheat heater is connected to the fourth steam circuit, the molten salt feedwater reheat system includes a second high-pressure heater system located downstream of the second low-pressure heater system, the second high-pressure heater system is connected to the second feedwater circuit, and the fourth steam circuit is connected to the second high-pressure heater system.

9. The coal-fired power unit according to any one of claims 1-8, characterized in that, The molten salt steam circuit includes a first steam circuit, the molten salt heater includes a molten salt superheater, the steam outlet of the molten salt superheater is connected to the first steam circuit, the molten salt feedwater regeneration system includes a second high-pressure heater system, the second high-pressure heater system is connected to the second feedwater circuit, and the first steam circuit is connected to the second high-pressure heater system.

10. The coal-fired power unit according to claim 9, characterized in that, The molten salt steam circuit includes a second steam circuit, and the steam outlet of the molten salt superheater is also connected to the second steam circuit; the coal-fired boiler system includes a boiler reheater, and the second steam circuit is connected to the steam inlet of the boiler reheater.

11. The coal-fired power unit according to claim 10, characterized in that, The molten salt steam circuit includes a third steam circuit, and the steam outlet of the molten salt superheater is also connected to the third steam circuit; the molten salt system also includes a molten salt phase change heater, which is located upstream of the molten salt superheater, and the third steam circuit is connected to the molten salt phase change heater.

12. The coal-fired power unit according to claim 11, characterized in that, The molten salt steam circuit includes a high-pressure condensate circuit, and the high-pressure condensate outlet of the molten salt phase change heater is connected to the high-pressure condensate circuit; the molten salt feedwater regeneration system includes a second deaerator, and the high-pressure condensate circuit is connected to the second deaerator.

13. A method for operating and controlling a coal-fired power unit, applied to the coal-fired power unit according to any one of claims 1-12, characterized in that, During load increases, including: Step S1: Control the coal-fired boiler to increase the load for a first predetermined time using a first predetermined variable load capacity; Step S2: Control the molten salt exothermic system to increase the load for a first predetermined time using the second predetermined variable load capacity; Step S3: Control the molten salt heating system to maintain the minimum operating state, or reduce the load for a first predetermined time with the third predetermined variable load capacity; After simultaneously performing steps S1, S2, and S3 to reach the total load increase, the coal-fired boiler is controlled to continue increasing the load, while the molten salt exothermic system and the molten salt heating system are both reduced to the minimum operating state. When reducing the load, including: Step S4: Control the coal-fired boiler to reduce the load for a second predetermined time using a first predetermined load-changing capacity; Step S5: Control the molten salt heating system to increase the load for a second predetermined time with a third predetermined variable load capacity; Step S6: Control the molten salt exothermic system to maintain it in the lowest operating state, or reduce the load for a second predetermined time with the second predetermined variable load capacity; After simultaneously performing steps S4, S5, and S6 to achieve the total load reduction, the coal-fired boiler is controlled to continue reducing its load, and both the molten salt exothermic system and the molten salt heating system are reduced to their minimum operating states.

14. The operation control method for a coal-fired power unit as described in claim 13, characterized in that, When the total load increase exceeds the full load of the molten salt exothermic system, in step S2, the molten salt exothermic system is controlled to increase the load to its full load for a first predetermined time with a second predetermined load change capability. When the total load reduction exceeds the full load of the molten salt heating system, in step S5, the molten salt heating system is controlled to increase the load to its full load for a second predetermined time using a third predetermined load change capability.

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