Coal-fired unit peak shaving system with molten salt heat storage and operation method

Abstract

The present application relates to coal-fired power generation technology field, specifically relates to a kind of coal-fired unit peak shaving system and operating method with fused salt heat storage, the system includes: coal-fired system and heat storage system;Coal-fired system includes coal-fired boiler, high, medium, low pressure cylinder, generator, deaerator, high-pressure heater, low-pressure heater, condenser, condensate pump and feedwater pump, heat storage system includes flue gas-fused salt heat exchanger, steam heat storage tank, high-temperature fused salt tank, low-temperature fused salt tank, high-temperature fused salt pump, low-temperature fused salt pump, high-temperature feedwater heat exchanger, low-temperature feedwater heat exchanger, superheated steam-fused salt heat exchanger and reheat steam-fused salt heat exchanger.By the coal-fired unit peak shaving system and operating method with fused salt heat storage provided in the present application, the flexible operation capability of coal-fired unit can be further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coal-fired power generation technology, in particular to a coal-fired unit peak shaving system with molten salt heat storage and an operation method to realize flexible operation of the unit. BACKGROUND

[0002] With the larger-scale development of new energy, the proportion of power generation is becoming higher and higher, and it is estimated that the proportion of new energy power generation will reach 40% by 2040. The clean energy consumption problem needs to be prepared in advance, and the coal-fired unit, especially the coal-fired unit, needs to dig the potential of flexible regulation and actively participate in flexible transformation to promote the consumption of clean energy in a larger range. Overall, the flexible market of thermal power has broad prospects. At present, it is crucial to improve the flexible operation capability of the coal-fired unit, that is, to improve the variable load rate of the unit to cope with the current complex operating environment, but due to the large inertia of the boiler, the superheated steam and reheated steam temperature of the unit is easy to exceed the maximum allowable temperature of the unit. In addition, during the variable load process of the unit, the flue gas temperature of the unit is easy to lose heat, resulting in a decrease in the power generation efficiency of the unit, and more seriously, causing safety accidents of the unit. At present, there is still no corresponding solution to meet the more excellent flexible operation capability and operation safety of the unit, and the problems to be solved are as follows: (1) when the unit is in the peak shaving process, the superheated steam temperature, reheated steam temperature and flue gas temperature of the unit need to be always within the reasonable operating range of the unit; (2) when the unit is in the process of rapid variable load operation, the coal-fired system and the heat storage system need to be reasonably operated to improve the variable load capacity of the coal-fired unit.

[0003] Therefore, in view of the above problems, scholars have proposed a coal-fired unit integrated with a heat storage system. A coal-fired power generation system coupled with steam energy storage and an operation method (application patent number 202210980571.0) has proposed using steam as a heat storage method for the unit, but in the operation process, the steam extracted from the coal-fired boiler is directly stored, which requires a storage device that can withstand high temperature and high pressure, increasing the overall equipment cost. Moreover, a coal-fired boiler flue gas and steam combined heat storage deep peak shaving system and operation method (patent number 202111066086.4) has proposed using reheated steam for heat storage to improve the variable load rate of the unit, but since the reheated steam is directly used to heat the feedwater after heating the molten salt heat storage medium, the reheated steam extraction heat storage capacity is not fully utilized, and therefore the unit still has room for improvement. SUMMARY

[0004] In order to solve the problems existing in the prior art, the purpose of the present application is to propose a coal-fired unit peak shaving system with molten salt heat storage and an operation method, which can improve the flexible operation capability and power generation efficiency of the unit.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following use scheme:

[0006] The coal-fired unit peak shaving system with molten salt heat storage and an operation method thereof, characterized in that, comprising a coal-fired system and a heat storage system:

[0007] The coal-fired system comprises a coal-fired boiler 1, a high-pressure cylinder 2, a medium-pressure cylinder 3, a low-pressure cylinder 4, a generator 5, a deaerator 6, a high-pressure heater 7, a low-pressure heater 8, a condenser 9, a high-temperature feedwater heat exchanger 10, a low-temperature feedwater heat exchanger 11, a superheated steam-molten salt heat exchanger 13, a reheated steam-molten salt heat exchanger 14, a condensate pump P1, a feedwater pump P2, a first valve V1, a second valve V2, a third valve V3, a fourth valve V4 and a fifth valve V5; a superheated steam outlet end of the coal-fired boiler 1 is connected to a hot end inlet of the superheated steam-molten salt heat exchanger 13 through a ninth valve V9; a reheated steam outlet end of the coal-fired boiler 1 is connected to a hot end inlet of the reheated steam-molten salt heat exchanger 14 through a tenth valve V10; the superheated steam outlet end of the coal-fired boiler 1 is connected to the high-pressure cylinder 2; the reheated steam outlet end of the coal-fired boiler 1 is connected to the medium-pressure cylinder 3; an outlet of the high-pressure cylinder 2 is connected to the coal-fired boiler 1 and a hot end inlet of the high-pressure heater 7; an outlet of the medium-pressure cylinder 3 is connected to the hot end inlet of the high-pressure heater 7 through the first valve V1; the outlet of the medium-pressure cylinder 3 is connected to the deaerator 6 and the low-pressure cylinder 4; an outlet of the low-pressure cylinder 4 is connected to a hot end inlet of the low-pressure heater 8; the outlet of the low-pressure cylinder 4 is connected to the condenser 9; the high-pressure cylinder 2, the medium-pressure cylinder 3, the low-pressure cylinder 4 and the generator 5 share a bearing connection; an outlet of the deaerator 6 is connected to a cold end inlet of the high-pressure heater 7 through the feedwater pump P2 and the second valve V2; the outlet of the deaerator 6 is connected to a cold end inlet of the high-temperature feedwater heat exchanger 10 through the feedwater pump P2 and the fourth valve V4; a cold end outlet of the high-pressure heater 7 and a cold end outlet of the high-temperature feedwater heat exchanger 10 are connected to the coal-fired boiler 1; an outlet of the condenser 9 is connected to a cold end inlet of the low-pressure heater 8 through the condensate pump P1 and the third valve V3; the outlet of the condenser 9 is connected to a cold end inlet of the low-temperature feedwater heat exchanger 11 through the condensate pump P1 and the fifth valve V5; a cold end outlet of the low-pressure heater 8 and a cold end outlet of the low-temperature feedwater heat exchanger 11 are connected to an inlet of the deaerator 6;

[0008] The heat storage system comprises a flue gas-molten salt heat exchanger 12, a steam heat storage tank 15, a high-temperature molten salt tank 16, a low-temperature molten salt tank 17, a high-temperature molten salt pump P3, a low-temperature molten salt pump P4, a sixth valve V6, a seventh valve V7, an eighth valve V8, a ninth valve V9 and a tenth valve V10, a hot end outlet of the superheated steam-molten salt heat exchanger 13 and the reheated steam-molten salt heat exchanger 14 is communicated with an inlet of the steam heat storage tank 15; a cold end outlet of the flue gas-molten salt heat exchanger 12, a cold end outlet of the superheated steam-molten salt heat exchanger 13 and a cold end outlet of the reheated steam-molten salt heat exchanger 14 are communicated with an inlet of the high-temperature molten salt tank 16; an outlet of the high-temperature molten salt tank 16 is communicated with a hot end inlet of the high-pressure feedwater heat exchanger 10 through the seventh valve V7 and the high-temperature molten salt pump P3; a hot end outlet of the high-pressure feedwater heat exchanger 10 is communicated with a hot end inlet of the low-pressure feedwater heat exchanger 11; a hot end outlet of the low-pressure feedwater heat exchanger 11 is communicated with an inlet of the low-temperature molten salt tank 17; a cold end inlet of the superheated steam-molten salt heat exchanger 13 is communicated with an outlet of the low-temperature molten salt tank 17 through the low-temperature molten salt pump P4 and the eighth valve V8; a cold end inlet of the reheated steam-molten salt heat exchanger 14 is communicated with the outlet of the low-temperature molten salt tank 17 through the low-temperature molten salt pump P4 and the eighth valve V8; a cold end inlet of the flue gas-molten salt heat exchanger 12 is communicated with the outlet of the low-temperature molten salt tank 17 through the low-temperature molten salt pump P4 and the eighth valve V8; an outlet of the steam heat storage tank 15 is communicated with a hot end inlet of the high-pressure heater 7 through the sixth valve V6.

[0009] In the coal-fired system, a superheated steam flow divider F1 is arranged between a superheated steam outlet end of the coal-fired boiler 1 and a hot end inlet of the superheated steam-molten salt heat exchanger 13 and the high-pressure cylinder 2; a reheated steam flow divider F2 is arranged between a reheated steam outlet end of the coal-fired boiler 1 and a hot end inlet of the reheated steam-molten salt heat exchanger 14 and the medium-pressure cylinder 3; a second feedwater flow divider F5 is arranged between an outlet of the feedwater pump P2 and a cold end inlet of the high-pressure heater 7 and a cold end inlet of the high-temperature feedwater heat exchanger 10; a first feedwater flow divider F4 is arranged between the condensate pump P1 and a cold end inlet of the low-pressure heater 8 and a cold end inlet of the low-temperature feedwater heat exchanger 11; a first feedwater flow combiner M1 is arranged between the coal-fired boiler 1 and a cold end outlet of the high-pressure heater 7 and a cold end outlet of the high-temperature feedwater heat exchanger 10; a steam flow divider M3 is arranged between the high-pressure heater 7 and an extraction outlet of the medium-pressure cylinder 3 and the steam heat storage tank 15; a second feedwater flow combiner M2 is arranged between an inlet of the deaerator 6 and a cold end outlet of the low-pressure heater 8 and a cold end outlet of the low-temperature feedwater heat exchanger 11.

[0010] The molten salt shunt F3 is arranged between the outlet of the low-temperature molten salt pump P4 and the cold end inlet of the flue gas-molten salt heat exchanger 12, the cold end inlet of the superheated steam-molten salt heat exchanger 13 and the cold end inlet of the reheated steam-molten salt heat exchanger 14; the molten salt merger M5 is arranged between the inlet of the high-temperature molten salt tank 16 and the cold end outlet of the flue gas-molten salt heat exchanger 12, the cold end outlet of the superheated steam-molten salt heat exchanger 13 and the cold end outlet of the reheated steam-molten salt heat exchanger 14; and the steam merger M4 is arranged between the hot end outlet of the superheated steam-molten salt heat exchanger 13 and the hot end outlet of the reheated steam-molten salt heat exchanger 14.

[0011] The steam temperature of the reheated steam outlet of the coal-fired boiler 1 is 560-620 DEG C, and the pressure is greater than 2 MPa; the steam temperature of the superheated steam outlet of the coal-fired boiler 1 is 560-620 DEG C, and the pressure is greater than 10 MPa; the flue gas temperature of the flue gas-molten salt heat exchanger 12 is greater than 560 DEG C; and the steam storage pressure of the steam storage tank 15 is 3-5 MPa.

[0012] The molten salt used in the heat storage system is a ternary mixed nitrate of 53% potassium nitrate, 40% sodium nitrite and 7% sodium nitrate, and the melting point of the molten salt is low, so that the molten salt is not prone to "frozen pipe phenomenon" in use.

[0013] In the operation system of the coal-fired power generating unit with flue gas and steam heat storage, when the coal-fired unit needs to operate at a reduced load, the ninth valve V9 and the tenth valve V10 of the steam outlet of the coal-fired boiler 1 can be adjusted respectively to control the flow of the molten salt heat storage medium flowing out of the low-temperature molten salt tank 17 and the steam extraction amount of the coal-fired boiler 1, so that the coal-fired unit can operate more flexibly to cope with the complex operation environment of the coal-fired unit, and the flue gas temperature of the coal-fired boiler 1 can be controlled to enable the coal-fired unit to operate safely and efficiently.

[0014] In the operation system of the coal-fired power generating unit with flue gas and steam heat storage, when the coal-fired unit operates at a reduced load, the superheated steam and the reheated steam are merged into the steam storage tank 15 after heating the molten salt heat storage medium, and when the load is increased, the steam in the steam storage tank 15 can replace the steam extracted from the high-pressure cylinder and the medium-pressure cylinder to heat the feed water, so that the power generation capacity of the coal-fired unit can be rapidly increased, and therefore the variable load rate of the unit can be improved.

[0015] The coal-fired boiler 1 uses a three-flue gas damper to adjust the temperature, and the flue gas-molten salt heat exchanger 12 can be arranged in the third flue, so that the flue gas heat storage can be more reasonably utilized during the peak shaving of the unit, and the flexibility of the coal-fired unit can be improved.

[0016] The operation method of the coal-fired unit peak shaving system with molten salt heat storage opens the first valve V1, the second valve V2 and the third valve V3, closes the fourth valve V4, the fifth valve V5, the sixth valve V6, the seventh valve V7, the eighth valve V8, the ninth valve V9 and the tenth valve V10, only operates the coal-fired system, and does not operate the heat storage system when the coal-fired unit is normally operated;

[0017] When the coal-fired unit needs to be operated at a reduced load, on the basis of normal operation of the coal-fired unit, the eighth valve V8, the ninth valve V9 and the tenth valve V10 are opened, the low-temperature molten salt heat storage medium in the low-temperature molten salt tank 17 flows out, and the flow of the outflowing molten salt heat storage medium can be adjusted by using the low-temperature molten salt pump P4, the outflowing molten salt heat storage medium enters the flue gas-molten salt heat exchanger 12, the superheated steam-molten salt heat exchanger 13 and the reheated steam-molten salt heat exchanger 14, respectively, the molten salt heat storage medium entering the flue gas-molten salt heat exchanger 12 is heated by the flue gas in the coal-fired boiler 1, the molten salt heat storage medium entering the superheated steam-molten salt heat exchanger 13 is heated by the superheated steam of the coal-fired boiler 1, the molten salt heat storage medium entering the reheated steam-molten salt heat exchanger 14 is heated by the reheated steam of the coal-fired boiler 1, and the molten salt heat storage medium all flows into the high-temperature molten salt tank 16 after being heated, and the superheated steam and the reheated steam all flow into the steam heat storage tank 15 for storage after being discharged.

[0018] When the coal-fired unit needs to be operated at a reduced load, on the basis of normal operation of the coal-fired unit, the eighth valve V8, the ninth valve V9 and the tenth valve V10 are opened, the low-temperature molten salt heat storage medium in the low-temperature molten salt tank 17 flows out, and the flow of the outflowing molten salt heat storage medium can be adjusted by using the low-temperature molten salt pump P4, the outflowing molten salt heat storage medium enters the flue gas-molten salt heat exchanger 12, the superheated steam-molten salt heat exchanger 13 and the reheated steam-molten salt heat exchanger 14, respectively, the molten salt heat storage medium entering the flue gas-molten salt heat exchanger 12 is heated by the flue gas in the coal-fired boiler 1, the molten salt heat storage medium entering the superheated steam-molten salt heat exchanger 13 is heated by the superheated steam of the coal-fired boiler 1, the molten salt heat storage medium entering the reheated steam-molten salt heat exchanger 14 is heated by the reheated steam of the coal-fired boiler 1, and the molten salt heat storage medium all flows into the high-temperature molten salt tank 16 after being heated, and the superheated steam and the reheated steam all flow into the steam heat storage tank 15 for storage after being discharged.

[0019] The advantage of the present application is that when the thermal power unit is in load reduction operation, the flue gas and steam can be used to heat the molten salt heat storage medium stored in the high-temperature molten salt tank 16 to realize heat storage, and the steam after heat release can also be stored in the steam heat storage tank 15, which can improve the load reduction rate of the unit, and control the flue gas temperature of the coal-fired boiler 1 to make the unit operate safely and efficiently. When the load is increased, the high-temperature molten salt heat storage medium in the high-temperature molten salt tank 16 can be used to heat the feed water to partially replace the high-pressure heater 7 and the low-pressure heater 8, thereby reducing the steam extraction amount of the cylinder, and in addition, the steam stored in the steam heat storage tank 15 is used to heat the feed water, which further reduces the steam extraction amount of the high-pressure cylinder and the medium-pressure cylinder, thereby greatly improving the load increasing rate of the coal-fired unit. In addition, storing the heated steam in the steam heat storage tank 15 can avoid using high-temperature and high-pressure storage equipment to reduce equipment cost.

[0020] Compared with other energy storage media, molten salt is a medium with low cost, long service life and good heat transfer and heat storage performance, and because the melting point of nitrate is low and the corrosion is small, the molten salt used in heat storage is usually a mixture of nitrates. In addition, compared with two-component mixed nitrates, three-component mixed nitrates (i.e. the composition is 53% potassium nitrate, 40% sodium nitrite and 7% sodium nitrate) can greatly reduce the melting point of the system and are not prone to "freezing pipe phenomenon" in use. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A structure principle diagram of a coal-fired unit peak shaving system with molten salt heat storage according to the present application.

[0022] In the figure, 1. coal-fired boiler; 2. high-pressure cylinder; 3. medium-pressure cylinder; 4. low-pressure cylinder; 5. generator; 6. deaerator; 7. high-pressure heater; 8. low-pressure heater; 9. condenser; 10. high-temperature feed water heat exchanger; 11. low-temperature feed water heat exchanger; 12. flue gas-molten salt heat exchanger; 13. superheated steam-molten salt heat exchanger; 14. reheat steam-molten salt heat exchanger; 15. steam heat storage tank; 16. high-temperature molten salt tank; 17. low-temperature molten salt tank; P1. condensate pump; P2. feed water pump; P3. high-temperature molten salt pump; P4. low-temperature molten salt pump; V1-V10. valves; M1. first feed water combiner; M2. second feed water combiner; M3. steam splitter; M4. steam combiner; M5. molten salt combiner; F1. superheated steam splitter; F2. reheat steam splitter; F3. molten salt splitter; F4. first feed water splitter; F5. second feed water splitter. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be described clearly and completely in combination with the drawings. The solutions in the embodiments are not used to limit the protection scope of the present application, and any equivalent implementation or change without departing from the present application is included in the protection scope of the present application.

[0024] As Figure 1 shown, the coal-fired power generating unit of the present application, which stores heat by flue gas and steam, comprises a coal-fired system and a heat storage system. The coal-fired system comprises a coal-fired boiler 1, a high-pressure cylinder 2, a medium-pressure cylinder 3, a low-pressure cylinder 4, a generator 5, a deaerator 6, a high-pressure heater 7, a low-pressure heater 8, a condenser 9, a high-temperature feedwater heat exchanger 10, a low-temperature feedwater heat exchanger 11, a superheated steam-molten salt heat exchanger 13, a reheated steam-molten salt heat exchanger 14, a condensate pump P1, a feedwater pump P2, a first valve V1, a second valve V2, a third valve V3, a fourth valve V4, and a fifth valve V5. The superheated steam outlet of the coal-fired boiler 1 is connected to the hot end inlet of the superheated steam-molten salt heat exchanger 13 through a ninth valve V9. The reheated steam outlet of the coal-fired boiler 1 is connected to the hot end inlet of the reheated steam-molten salt heat exchanger 14 through a tenth valve V10. The superheated steam outlet of the coal-fired boiler 1 is connected to the high-pressure cylinder 2. The reheated steam outlet of the coal-fired boiler 1 is connected to the medium-pressure cylinder 3. The outlet of the high-pressure cylinder 2 is connected to the hot end inlet of the coal-fired boiler 1 and the high-pressure heater 7. The outlet of the medium-pressure cylinder 3 is connected to the hot end inlet of the high-pressure heater 7 through the first valve V1. The outlet of the medium-pressure cylinder 3 is connected to the deaerator 6 and the low-pressure cylinder 4. The outlet of the low-pressure cylinder 4 is connected to the hot end inlet of the low-pressure heater 8. The outlet of the low-pressure cylinder 4 is connected to the condenser 9. The high-pressure cylinder 2, the medium-pressure cylinder 3, the low-pressure cylinder 4, and the generator 5 share a bearing connection. The outlet of the deaerator 6 is connected to the cold end inlet of the high-pressure heater 7 through the feedwater pump P2 and the second valve V2. The outlet of the deaerator 6 is connected to the cold end inlet of the high-temperature feedwater heat exchanger 10 through the feedwater pump P2 and the fourth valve V4. The cold end outlet of the high-pressure heater 7 and the cold end outlet of the high-temperature feedwater heat exchanger 10 are connected to the coal-fired boiler 1. The outlet of the condenser 9 is connected to the cold end inlet of the low-pressure heater 8 through the condensate pump P1 and the third valve V3. The outlet of the condenser 9 is connected to the cold end inlet of the low-temperature feedwater heat exchanger 11 through the condensate pump P1 and the fifth valve V5. The cold end outlet of the low-pressure heater 8 and the cold end outlet of the low-temperature feedwater heat exchanger 11 are connected to the inlet of the deaerator 6.

[0025] The heat storage system comprises a flue gas-molten salt heat exchanger 12, a steam heat storage tank 15, a high-temperature molten salt tank 16, a low-temperature molten salt tank 17, a high-temperature molten salt pump P3, a low-temperature molten salt pump P4, a sixth valve V6, a seventh valve V7, an eighth valve V8, a ninth valve V9 and a tenth valve V10, a hot end outlet of the superheated steam-molten salt heat exchanger 13 and the reheated steam-molten salt heat exchanger 14 is communicated with an inlet of the steam heat storage tank 15; a cold end outlet of the flue gas-molten salt heat exchanger 12, a cold end outlet of the superheated steam-molten salt heat exchanger 13 and a cold end outlet of the reheated steam-molten salt heat exchanger 14 are communicated with an inlet of the high-temperature molten salt tank 16; an outlet of the high-temperature molten salt tank 16 is communicated with a hot end inlet of the high-temperature feedwater heat exchanger 10 through the seventh valve V7 and the high-temperature molten salt pump P3; a hot end outlet of the high-temperature feedwater heat exchanger 10 is communicated with a hot end inlet of the low-temperature feedwater heat exchanger 11; a hot end outlet of the low-temperature feedwater heat exchanger 11 is communicated with an inlet of the low-temperature molten salt tank 17; a cold end inlet of the superheated steam-molten salt heat exchanger 13 is communicated with an outlet of the low-temperature molten salt tank 17 through the low-temperature molten salt pump P4 and the eighth valve V8; a cold end inlet of the reheated steam-molten salt heat exchanger 14 is communicated with the outlet of the low-temperature molten salt tank 17 through the low-temperature molten salt pump P4 and the eighth valve V8; a cold end inlet of the flue gas-molten salt heat exchanger 12 is communicated with the outlet of the low-temperature molten salt tank 17 through the low-temperature molten salt pump P4 and the eighth valve V8; an outlet of the steam heat storage tank 15 is communicated with a hot end inlet of the high-pressure heater 7 through the sixth valve V6.

[0026] When the coal-fired unit is normally operated, the first valve V1, the second valve V2 and the third valve V3 are opened, and the fourth valve V4, the fifth valve V5, the sixth valve V6, the seventh valve V7, the eighth valve V8, the ninth valve V9 and the tenth valve V10 are closed, only the coal-fired system is operated, and the heat storage system is not operated.

[0027] When the coal-fired unit needs to be operated at a reduced load, on the basis of the normal operation of the coal-fired unit, the eighth valve V8, the ninth valve V9 and the tenth valve V10 are opened, the low-temperature molten salt heat storage medium in the low-temperature molten salt tank 17 flows out, and the flow of the outflowing molten salt heat storage medium can be adjusted by using the low-temperature molten salt pump P4, the outflowing molten salt heat storage medium enters the flue gas-molten salt heat exchanger 12, the superheated steam-molten salt heat exchanger 13 and the reheated steam-molten salt heat exchanger 14 respectively, the molten salt heat storage medium entering the flue gas-molten salt heat exchanger 12 is heated by the flue gas in the coal-fired boiler 1, the molten salt heat storage medium entering the superheated steam-molten salt heat exchanger 13 is heated by the superheated steam of the coal-fired boiler 1, and the molten salt heat storage medium entering the reheated steam-molten salt heat exchanger 14 is heated by the reheated steam of the coal-fired boiler 1, the molten salt heat storage medium after being heated all flows into the high-temperature molten salt tank 16, and the superheated steam and the reheated steam after being discharged all flow into the steam heat storage tank 15 for storage.

[0028] When the coal-fired unit needs to increase load operation, on the basis of normal operation of the coal-fired unit, the fourth valve 4, the fifth valve 5, the sixth valve 6 and the seventh valve V7 are opened, and the first valve V1 and the third valve V3 are closed, the high-temperature molten salt heat storage medium in the high-temperature molten salt tank 16 flows out, and the flow of the outflowing molten salt heat storage medium can be adjusted by using the high-temperature molten salt pump P3, the molten salt heat storage medium first flows into the high-temperature feedwater heat exchanger 10 to heat the feedwater flowing out of the deaerator 6, and then flows into the low-temperature feedwater heat exchanger 11 to heat the condensate flowing out of the condenser 9, the molten salt heat storage medium flows into the low-temperature molten salt tank 17 after heat release, and the outflowing steam in the steam heat storage tank 15 heats the feedwater.

[0029] The steam temperature at the reheated steam outlet of the coal-fired boiler 1 is 560-620℃, and the pressure is greater than 2MPa; the steam temperature at the superheated steam outlet of the coal-fired boiler 1 is 560-620℃, and the pressure is greater than 10MPa; the flue gas temperature at the position of the flue gas-molten salt heat exchanger 12 in the flue of the coal-fired boiler 1 is greater than 560℃; the steam storage pressure of the steam heat storage tank 15 is 3-5MPa.

[0030] The molten salt used in the heat storage system is a ternary mixed nitrate of 53% potassium nitrate, 40% sodium nitrite and 7% sodium nitrate, and the melting point of the molten salt is low, so that the molten salt is not prone to "frozen pipe phenomenon" in use.

[0031] When the coal-fired unit needs to decrease load operation, the ninth valve V9 and the tenth valve V10 at the steam outlet of the coal-fired boiler 1 can be adjusted respectively to control the flow of the molten salt heat storage medium flowing out of the low-temperature molten salt tank 17 and the steam extraction amount of the coal-fired boiler 1, so that the coal-fired unit can be operated more flexibly to cope with complex operating environment of the unit, and the flue gas temperature of the coal-fired boiler 1 can be controlled to make the unit operate safely and efficiently.

[0032] When the coal-fired unit decreases load operation, the superheated steam and the reheated steam are merged into the steam heat storage tank 15 after heating the molten salt heat storage medium, and when the load is increased, the steam in the steam heat storage tank 15 can replace the steam extraction of the high-pressure cylinder and the intermediate-pressure cylinder to heat the feedwater, so that the power generation capacity of the unit is rapidly increased, and therefore the variable load rate of the unit can be increased.

[0033] The coal-fired boiler 1 uses three-flue gas damper temperature regulation, and the flue gas-molten salt heat exchanger 12 can be arranged in the third flue, so that the flue gas heat storage is more reasonably utilized during the peak shaving of the unit, and the flexibility of the unit is improved.

Claims

1. A coal-fired unit peak shaving system with molten salt thermal storage, characterized in that, The coal-fired system and the heat storage system are connected through the high-temperature molten salt heat exchanger and the low-temperature molten salt heat exchanger. The coal-fired system comprises a coal-fired boiler (1), a high-pressure cylinder (2), a medium-pressure cylinder (3), a low-pressure cylinder (4), a generator (5), a deaerator (6), a high-pressure heater (7), a low-pressure heater (8), a condenser (9), a high-temperature feedwater heat exchanger (10), a low-temperature feedwater heat exchanger (11), a superheated steam-molten salt heat exchanger (13), a reheated steam-molten salt heat exchanger (14), a condensate pump (P1), a feedwater pump (P2), a first valve (V1), a second valve (V2), a third valve (V3), a fourth valve (V4) and a fifth valve (V5); the superheated steam outlet of the coal-fired boiler (1) is connected to the hot end inlet of the superheated steam-molten salt heat exchanger (13) through a ninth valve (V9); the reheated steam outlet of the coal-fired boiler (1) is connected to the hot end inlet of the reheated steam-molten salt heat exchanger (14) through a tenth valve (V10); the superheated steam outlet of the coal-fired boiler (1) is connected to the high-pressure cylinder (2); the reheated steam outlet of the coal-fired boiler (1) is connected to the medium-pressure cylinder (3); the outlet of the high-pressure cylinder (2) is connected to the hot end inlet of the coal-fired boiler (1) and the high-pressure heater (7); the outlet of the medium-pressure cylinder (3) is connected to the hot end inlet of the high-pressure heater (7) through the first valve (V1); the outlet of the medium-pressure cylinder (3) is connected to the deaerator (6) and the low-pressure cylinder (4); the outlet of the low-pressure cylinder (4) is connected to the hot end inlet of the low-pressure heater (8); the outlet of the low-pressure cylinder (4) is connected to the condenser (9); the high-pressure cylinder (2), the medium-pressure cylinder (3), the low-pressure cylinder (4) and the generator (5) share a bearing connection; the outlet of the deaerator (6) is connected to the cold end inlet of the high-pressure heater (7) through the feedwater pump (P2) and the second valve (V2); the outlet of the deaerator (6) is connected to the cold end inlet of the high-temperature feedwater heat exchanger (10) through the feedwater pump (P2) and the fourth valve (V4); the cold end outlet of the high-pressure heater (7) and the cold end outlet of the high-temperature feedwater heat exchanger (10) are connected to the coal-fired boiler (1); the outlet of the condenser (9) is connected to the cold end inlet of the low-pressure heater (8) through the condensate pump (P1) and the third valve (V3); the outlet of the condenser (9) is connected to the cold end inlet of the low-temperature feedwater heat exchanger (11) through the condensate pump (P1) and the fifth valve (V5); the cold end outlet of the low-pressure heater (8) and the cold end outlet of the low-temperature feedwater heat exchanger (11) are connected to the inlet of the deaerator (6). The heat storage system comprises a flue gas-molten salt heat exchanger (12), a steam heat storage tank (15), a high-temperature molten salt tank (16), a low-temperature molten salt tank (17), a high-temperature molten salt pump (P3), a low-temperature molten salt pump (P4), a sixth valve (V6), a seventh valve (V7), an eighth valve (V8), a ninth valve (V9) and a tenth valve (V10), a hot end outlet of a superheated steam-molten salt heat exchanger (13) and a reheated steam-molten salt heat exchanger (14) is communicated with an inlet of the steam heat storage tank (15); a cold end outlet of the flue gas-molten salt heat exchanger (12), the superheated steam-molten salt heat exchanger (13) and the reheated steam-molten salt heat exchanger (14) is communicated with an inlet of the high-temperature molten salt tank (16); an outlet of the high-temperature molten salt tank (16) is communicated with a hot end inlet of the high-temperature feed water heat exchanger (10) through the seventh valve (V7) and the high-temperature molten salt pump (P3); a hot end outlet of the high-temperature feed water heat exchanger (10) is communicated with a hot end inlet of the low-temperature feed water heat exchanger (11); a hot end outlet of the low-temperature feed water heat exchanger (11) is communicated with an inlet of the low-temperature molten salt tank (17); a cold end inlet of the superheated steam-molten salt heat exchanger (13) is communicated with an outlet of the low-temperature molten salt tank (17) through the low-temperature molten salt pump (P4) and the eighth valve (V8); a cold end inlet of the reheated steam-molten salt heat exchanger (14) is communicated with the outlet of the low-temperature molten salt tank (17) through the low-temperature molten salt pump (P4) and the eighth valve (V8); a cold end inlet of the flue gas-molten salt heat exchanger (12) is communicated with the outlet of the low-temperature molten salt tank (17) through the low-temperature molten salt pump (P4) and the eighth valve (V8); an outlet of the steam heat storage tank (15) is communicated with a hot end inlet of the high-pressure heater (7) through the sixth valve (V6).

2. The coal-fired unit peak shaving system with molten salt heat storage according to claim 1, characterized in that, In the coal-fired system, a superheated steam flow divider (F1) is arranged between a superheated steam outlet end of the coal-fired boiler (1) and a hot end inlet of the superheated steam-molten salt heat exchanger (13) and a high-pressure cylinder (2); a reheated steam flow divider (F2) is arranged between a reheated steam outlet end of the coal-fired boiler (1) and a hot end inlet of the reheated steam-molten salt heat exchanger (14) and a medium-pressure cylinder (3); a second feed water flow divider (F5) is arranged between an outlet of the feed water pump (P2) and a cold end inlet of the high-pressure heater (7) and a cold end inlet of the high-temperature feed water heat exchanger (10); a first feed water flow divider (F4) is arranged between the condensate pump (P1) and a cold end inlet of the low-pressure heater (8) and a cold end inlet of the low-temperature feed water heat exchanger (11); a first feed water flow combiner (M1) is arranged between the coal-fired boiler (1) and a cold end outlet of the high-pressure heater (7) and a cold end outlet of the high-temperature feed water heat exchanger (10); a steam flow divider (M3) is arranged between the high-pressure heater (7) and an exhaust outlet of the medium-pressure cylinder (3) and the steam heat storage tank (15); a second feed water flow combiner (M2) is arranged between an inlet of the deaerator (6) and a cold end outlet of the low-pressure heater (8) and a cold end outlet of the low-temperature feed water heat exchanger (11).

3. The coal-fired unit peak shaving system with molten salt heat storage according to claim 1, characterized in that, The molten salt shunt (F3) is arranged between the outlet of the low-temperature molten salt pump (P4) and the cold end inlet of the flue gas-molten salt heat exchanger (12), the cold end inlet of the superheated steam-molten salt heat exchanger (13) and the cold end inlet of the reheated steam-molten salt heat exchanger (14); the molten salt combiner (M5) is arranged between the inlet of the high-temperature molten salt tank (16) and the cold end outlet of the flue gas-molten salt heat exchanger (12), the cold end outlet of the superheated steam-molten salt heat exchanger (13) and the cold end outlet of the reheated steam-molten salt heat exchanger (14); and the steam combiner (M4) is arranged between the hot end outlet of the superheated steam-molten salt heat exchanger (13) and the hot end outlet of the reheated steam-molten salt heat exchanger (14).

4. The coal-fired unit peak shaving system with molten salt heat storage according to claim 1, characterized in that, The steam temperature of the reheated steam outlet of the coal-fired boiler (1) is 560-620 DEG C, and the pressure is greater than 2 MPa; the steam temperature of the superheated steam outlet of the coal-fired boiler (1) is 560-620 DEG C, and the pressure is greater than 10 MPa; the flue gas temperature of the flue gas-molten salt heat exchanger (12) is greater than 560 DEG C; and the steam storage pressure of the steam storage tank (15) is 3-5 MPa.

5. The coal-fired unit peak shaving system with molten salt heat storage according to claim 1, characterized in that, The molten salt used in the heat storage system is a ternary mixed nitrate of 53% potassium nitrate, 40% sodium nitrite and 7% sodium nitrate, and the melting point of the molten salt is low, so that the molten salt is not prone to "frozen pipe phenomenon" in use.

6. The coal-fired unit peak shaving system with molten salt heat storage according to claim 1, characterized in that, When the coal-fired unit needs to operate at a reduced load, the ninth valve (V9) and the tenth valve (V10) of the coal-fired boiler (1) are adjusted respectively to control the flow of the molten salt storage medium flowing out of the low-temperature molten salt tank (17) and the steam extraction amount of the coal-fired boiler (1), so that the coal-fired unit can operate more flexibly to cope with complex operating environments of the coal-fired unit, and the flue gas temperature of the coal-fired boiler (1) can be controlled, so that the coal-fired unit can operate safely and efficiently.

7. The coal-fired unit peak shaving system with molten salt heat storage according to claim 1, characterized in that, When the coal-fired unit operates at a reduced load, the superheated steam and the reheated steam are merged into the steam storage tank (15) after heating the molten salt storage medium, and when the load is increased, the steam in the steam storage tank (15) replaces the steam extracted from the high-pressure cylinder and the medium-pressure cylinder to heat the feed water, so that the power generation capacity of the coal-fired unit can be rapidly increased, and the load change rate of the coal-fired unit can be increased.

8. The coal-fired unit peak shaving system with molten salt heat storage according to claim 1, characterized in that, The coal-fired boiler (1) uses a three-flue gas damper to adjust the temperature, and the flue gas-molten salt heat exchanger (12) is arranged in the third flue, so that the flue gas heat storage can be reasonably utilized during unit peak shaving, and the flexibility of the coal-fired unit can be improved.

9. The method of operating a molten salt thermal energy storage enabled coal-fired unit peaking system of any of claims 1 to 8, characterized in that, When the coal-fired unit operates normally, the first valve (V1), the second valve (V2) and the third valve (V3) are opened, and the fourth valve (V4), the fifth valve (V5), the sixth valve (V6), the seventh valve (V7), the eighth valve (V8), the ninth valve (V9) and the tenth valve (V10) are closed, so that only the coal-fired system operates, and the heat storage system does not operate. When the coal-fired unit needs to be operated at a reduced load, on the basis of normal operation of the coal-fired unit, the eighth valve (V8), the ninth valve (V9) and the tenth valve (V10) are opened, the low-temperature molten salt heat storage medium in the low-temperature molten salt tank (17) flows out, and the flow of the molten salt heat storage medium flowing out can be adjusted by using the low-temperature molten salt pump (P4), the molten salt heat storage medium flowing out enters the flue gas-molten salt heat exchanger (12), the superheated steam-molten salt heat exchanger (13) and the reheated steam-molten salt heat exchanger (14) respectively, the molten salt heat storage medium entering the flue gas-molten salt heat exchanger (12) is heated by the flue gas in the coal-fired boiler (1), the molten salt heat storage medium entering the superheated steam-molten salt heat exchanger (13) is heated by the superheated steam of the coal-fired boiler (1), the molten salt heat storage medium entering the reheated steam-molten salt heat exchanger (14) is heated by the reheated steam of the coal-fired boiler (1), and the molten salt heat storage medium after being heated all flows into the high-temperature molten salt tank (16), and the superheated steam and the reheated steam after being discharged all flow into the steam heat storage tank (15) for storage; When the coal-fired unit needs to be operated at a reduced load, on the basis of normal operation of the coal-fired unit, the eighth valve (V8), the ninth valve (V9) and the tenth valve (V10) are opened, the low-temperature molten salt heat storage medium in the low-temperature molten salt tank (17) flows out, and the flow of the molten salt heat storage medium flowing out can be adjusted by using the low-temperature molten salt pump (P4), the molten salt heat storage medium flowing out enters the flue gas-molten salt heat exchanger (12), the superheated steam-molten salt heat exchanger (13) and the reheated steam-molten salt heat exchanger (14) respectively, the molten salt heat storage medium entering the flue gas-molten salt heat exchanger (12) is heated by the flue gas in the coal-fired boiler (1), the molten salt heat storage medium entering the superheated steam-molten salt heat exchanger (13) is heated by the superheated steam of the coal-fired boiler (1), the molten salt heat storage medium entering the reheated steam-molten salt heat exchanger (14) is heated by the reheated steam of the coal-fired boiler (1), and the molten salt heat storage medium after being heated all flows into the high-temperature molten salt tank (16), and the superheated steam and the reheated steam after being discharged all flow into the steam heat storage tank (15) for storage;

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