A strong flexible coal-fired power generation system and operation method

Abstract

The application discloses a strong-flexible coal-fired power generation system and an operation method. The system comprises a recompression and reheating discharge cycle, a heat storage cycle and a heat release cycle. The heat storage cycle comprises high-temperature and low-temperature molten salt tanks, a No. 2 molten salt heat exchanger, a molten salt-flue gas heat exchanger, a split turbine and a medium-temperature regenerator. The heat release cycle comprises high-temperature and low-temperature molten salt tanks, a No. 1 molten salt heat exchanger, a heat release cycle turbine and a regenerator. During heat storage, part of flue gas and turbine working medium are split to heat molten salt, so that the working medium flow on the cycle side is reduced, the output power of the unit is further reduced, and the heat is stored in the molten salt storage tank. During heat release, the stored heat in the molten salt tank is released to heat the split working medium of the main compressor, so that the recompression cycle and the heat release cycle jointly generate power, the output power of the unit is improved. The application integrates the heat storage cycle and the heat release cycle, improves the flexibility of the coal-fired power generation unit, reduces the minimum operating load of the unit, improves the variable load rate, realizes the strong-flexibility of the coal-fired unit, promotes the consumption of new energy power generation and the transformation of the power structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power generation, and particularly relates to a strong-flexibility coal-fired power generation system and an operation method. BACKGROUND

[0002] Compared with the conventional steam power cycle, the supercritical carbon dioxide power cycle has higher energy conversion efficiency, and the turbine and heat exchange equipment have very small volume and compact structure, so the supercritical carbon dioxide power cycle has great application potential in the field of coal-fired power generation.

[0003] With the acceleration of the transformation of the power system in China, higher efficiency and more flexibility are urgently required in the coal-fired power generation industry, so as to better provide peak shaving services for new energy consumption. One of the flexibility requirements of the coal-fired power generation unit is that the unit can be operated at a large variable load and achieve ultra-low load operation in the steady state condition, and the load can be quickly raised and lowered in the variable condition transient process. For the supercritical carbon dioxide coal-fired power generation unit, the minimum stable combustion load of the boiler and the boiler-turbine energy flow coupling limit the load that can be reduced, and the operation flexibility is insufficient. SUMMARY

[0004] In order to further reduce the minimum operating load of the low-coal-fired unit, widen the variable load range, and improve the variable load rate, the application provides a strong-flexibility coal-fired power generation system and an operation method.

[0005] In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] A strong-flexibility coal-fired power generation system adopts supercritical carbon dioxide as the circulating working medium, and includes a recompression reheat power cycle, a heat storage cycle and a heat release cycle.

[0007] The re-compression reheat power generation cycle specifically comprises a high-pressure turbine 7, a low-pressure turbine 8, a re-compressor 10, a main compressor 11, a cooler 12, a low-temperature regenerator 13, a high-temperature regenerator 15 and a boiler 16; the outlet of the main compressor 11 is connected with the cold side inlet of the low-temperature regenerator 13, the cold side outlet of the low-temperature regenerator 13 is connected with the cold side inlet of the high-temperature regenerator 15, the cold side outlet of the high-temperature regenerator 15 is connected with the inlet of the boiler 16, the outlet of the boiler 16 is connected with the high-pressure turbine 7, the outlet of the high-pressure turbine 7 is connected with the boiler 16, the outlet of the boiler 16 is connected with the low-pressure turbine 8, the outlet of the low-pressure turbine 8 is connected with the high-temperature regenerator 15 and the low-temperature regenerator 13 in sequence, the hot side outlet of the low-temperature regenerator 13 is connected with the inlet of the re-compressor 10 and the inlet of the cooler 12 respectively, the outlet of the re-compressor 10 is connected with the cold side outlet of the low-temperature regenerator 13, and the outlet of the cooler 12 is connected with the inlet of the main compressor 11; the cold side inlet of the high-temperature regenerator 15 is also connected with the tail inlet of the boiler 16, and the outlet of the tail of the boiler 16 is connected with the cold side outlet of the high-temperature regenerator 15.

[0008] The heat storage cycle specifically comprises a low-temperature molten salt tank 2, a high-temperature molten salt tank 3, a No. 2 molten salt heat exchanger 4, a split turbine 9 and a medium-temperature regenerator 14; the hot side inlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-pressure turbine 7, the hot side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the split turbine 9, the outlet of the split turbine 9 is connected with the hot side inlet of the medium-temperature regenerator 14, the hot side outlet of the medium-temperature regenerator 14 is connected with the hot side inlet of the low-temperature regenerator 13, the cold side inlet of the medium-temperature regenerator 14 is connected with the cold side outlet of the low-temperature regenerator 13, and the cold side outlet of the medium-temperature regenerator 14 is connected with the tail inlet of the boiler 16; the cold side inlet of the No. 2 molten salt heat exchanger 4 is connected with the outlet of the low-temperature molten salt tank 2, and the cold side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-temperature molten salt tank 3.

[0009] The heat storage cycle specifically comprises a low-temperature molten salt tank 2, a high-temperature molten salt tank 3, a No. 2 molten salt heat exchanger 4, a split turbine 9 and a medium-temperature regenerator 14; the hot side inlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-pressure turbine 7, the hot side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the split turbine 9, the outlet of the split turbine 9 is connected with the hot side inlet of the medium-temperature regenerator 14, the hot side outlet of the medium-temperature regenerator 14 is connected with the hot side inlet of the low-temperature regenerator 13, the cold side inlet of the medium-temperature regenerator 14 is connected with the cold side outlet of the low-temperature regenerator 13, and the cold side outlet of the medium-temperature regenerator 14 is connected with the tail inlet of the boiler 16; the cold side inlet of the No. 2 molten salt heat exchanger 4 is connected with the outlet of the low-temperature molten salt tank 2, and the cold side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-temperature molten salt tank 3.

[0010] The heat storage cycle specifically comprises a low-temperature molten salt tank 2, a high-temperature molten salt tank 3, a No. 2 molten salt heat exchanger 4, a split turbine 9 and a medium-temperature regenerator 14; the hot side inlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-pressure turbine 7, the hot side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the split turbine 9, the outlet of the split turbine 9 is connected with the hot side inlet of the medium-temperature regenerator 14, the hot side outlet of the medium-temperature regenerator 14 is connected with the hot side inlet of the low-temperature regenerator 13, the cold side inlet of the medium-temperature regenerator 14 is connected with the cold side outlet of the low-temperature regenerator 13, and the cold side outlet of the medium-temperature regenerator 14 is connected with the tail inlet of the boiler 16; the cold side inlet of the No. 2 molten salt heat exchanger 4 is connected with the outlet of the low-temperature molten salt tank 2, and the cold side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-temperature molten salt tank 3.

[0011] The boiler 16 is provided with a bypass flue, and the bypass flue is provided with a flue gas-molten salt heat exchanger 5.

[0012] The high-temperature molten salt tank 3 is provided with a first valve 171, the low-temperature molten salt tank 2 is provided with a second valve 172, the second molten salt heat exchanger 4 is provided with a third valve 173, the outlet of the main compressor 11 is provided with a fourth valve 174, the tail outlet of the boiler 16 is provided with a fifth valve 175, the tail inlet of the boiler 16 is provided with a sixth valve 176, and the cold side outlet of the low-temperature regenerator 13 is provided with a seventh valve 177.

[0013] The inlet temperature of the main compressor 11 is 32-42℃.

[0014] The inlet pressure of the main compressor 11 is 7.5-9.0MPa.

[0015] The operation method of the strong-flexible coal-fired power generation system comprises a conventional operation mode, a heat storage operation mode and a heat release operation mode.

[0016] In the conventional operation mode, all valves and the bypass flue damper 6 are in a default closed state, the high-temperature and high-pressure carbon dioxide working medium at the outlet of the boiler 16 first enters the high-pressure turbine 7 to do work, the working medium at the outlet of the high-pressure turbine 7 is reheated by the boiler 16 and then enters the low-pressure turbine 8 to do work, the working medium at the outlet of the low-pressure turbine 8 is sequentially heat-released by the high-temperature regenerator 15 and the low-temperature regenerator 13 and then is divided into two parts: one part is compressed and boosted by the re-compressor 10; the other part is cooled by the cooler 12 and then enters the main compressor 11 to be compressed and boosted, the working medium at the outlet of the main compressor 11 enters the low-temperature regenerator 13 to be heated, the working medium at the cold side outlet of the low-temperature regenerator 13 is combined with the working medium at the outlet of the re-compressor 10, and then enters the boiler after being heated by the high-temperature regenerator 15; the fifth valve 175 and the sixth valve 176 are opened, and the bypass is formed in front of the cold side inlet of the high-temperature regenerator 15, and the bypass working medium enters the tail of the boiler 16 to absorb the heat of the medium and low-temperature flue gas and then is combined with the working medium at the cold side outlet of the high-temperature regenerator 15.

[0017] The heat storage operation mode, on the basis of the normal operation mode, opens the bypass flue damper 6, opens the second valve 172, the third valve 173 and the seventh valve 177, and closes the sixth valve 176; a bypass flue is formed inside the boiler, part of the flue gas is bypassed to heat the molten salt from the low-temperature molten salt tank 2, and the molten salt is stored in the high-temperature molten salt tank 3 after being heated to a high-temperature state; similarly, part of the high-pressure turbine 7 inlet working medium is bypassed to heat the molten salt from the low-temperature molten salt tank 2 in the second molten salt heat exchanger 4, and the molten salt is stored in the high-temperature molten salt tank 3 after being heated to a high-temperature state;

[0018] The heat release operation mode, on the basis of the normal operation mode, opens the first valve 171 and the fourth valve 174; the main compressor 11 outlet working medium is bypassed: part of it generates power according to the normal operation mode; the other part enters the heat release cycle to generate power; in the heat release cycle, the main compressor 11 bypassed working medium first enters the heat release cycle regenerator 19 for preheating, then releases the high-temperature molten salt stored in the high-temperature molten salt tank 3 in the first molten salt heat exchanger 1 to heat the bypassed working medium from the cold side outlet of the heat release cycle regenerator 19, the heated working medium enters the heat release cycle turbine 18 to do work, and the heat release cycle turbine 18 outlet working medium is cooled by the heat release cycle regenerator 19 and then flows into the cooler 12 inlet main stream.

[0019] In the heat storage operation mode, the carbon dioxide working medium at the outlet of the second molten salt heat exchanger 4 enters the bypass turbine 9 to expand and do work, and at the same time, the pressure is reduced, the bypass turbine 9 outlet working medium heats the low-temperature regenerator 13 cold side outlet bypassed working medium in the medium-temperature regenerator 14, the medium-temperature regenerator 14 cold side outlet working medium is absorbed by the boiler 16 tail after being heated, and then flows into the high-temperature regenerator 15 cold side outlet, and the medium-temperature regenerator 14 hot side outlet working medium flows into the low-temperature regenerator 13 hot side inlet.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] 1) The present application is based on a supercritical carbon dioxide Brayton recompression cycle, which can improve the efficiency of a coal-fired power generation system.

[0022] 2) The present application integrates a heat storage system, which can reduce the circulating power generation side working medium through heat storage, thereby reducing the minimum operating load of the coal-fired power generation unit, or can increase the unit output power through heat release without changing the boiler load, thereby widening the unit variable load range.

[0023] 3) The present application can release the heat of the molten salt heat storage tank when the coal-fired power generation system is increasing the load, and start the heat release cycle, so that the recompression cycle and the heat release cycle jointly generate power to improve the load increasing rate; when the load is decreasing, the flow rate entering the high-pressure and low-pressure turbines is quickly reduced to improve the load decreasing rate. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1This is a schematic diagram of the highly flexible coal-fired power generation system of the present invention.

[0025] Figure 2(a) is a schematic diagram of the conventional operation mode of a highly flexible coal-fired power generation system.

[0026] Figure 2(b) is a schematic diagram of the thermal storage operation mode of a highly flexible coal-fired power generation system.

[0027] Figure 2(c) is a schematic diagram of the heat release operation mode of a highly flexible coal-fired power generation system. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 The illustrated highly flexible coal-fired power generation system uses supercritical carbon dioxide as the circulating working fluid and mainly includes a recompression-reheat discharge cycle, a thermal storage cycle, and a heat release cycle.

[0030] The recompression and reheat power generation cycle specifically includes a high-pressure turbine 7, a low-pressure turbine 8, a recompressor 10, a main compressor 11, a cooler 12, a low-temperature regenerator 13, a high-temperature regenerator 15, and a boiler 16. The outlet of the main compressor 11 is connected to the cold-side inlet of the low-temperature regenerator 13, the cold-side outlet of the low-temperature regenerator 13 is connected to the cold-side inlet of the high-temperature regenerator 15, the cold-side outlet of the high-temperature regenerator 15 is connected to the inlet of the boiler 16, the working fluid at the outlet of the boiler 16 is connected to the high-pressure turbine 7, and the reheat working fluid at the outlet of the high-pressure turbine 7 is connected to the boiler 16. The reheat working fluid at the outlet of boiler 16 is connected to low-pressure turbine 8. The outlet of low-pressure turbine 8 is connected in sequence to the hot side of high-temperature regenerator 15 and the hot side of low-temperature regenerator 13. The hot side outlet of low-temperature regenerator 13 is connected to the inlet of re-compressor 10 and the inlet of cooler 12, respectively. The outlet of re-compressor 10 is connected to the cold side outlet of low-temperature regenerator 13. The outlet of cooler 12 is connected to the inlet of main compressor 11. The cold side inlet of high-temperature regenerator 15 is also connected to the tail inlet of boiler 16. The working fluid at the tail outlet of boiler 16 is connected to the cold side outlet of high-temperature regenerator 15.

[0031] The heat storage cycle, in particular, comprises a low-temperature molten salt tank 2, a high-temperature molten salt tank 3, a No. 2 molten salt heat exchanger 4, a split turbine 9 and a medium-temperature regenerator 14; a molten salt-flue gas heat exchanger 5 is arranged in the boiler 16, the molten salt-flue gas heat exchanger 5 is connected with the outlet of the low-temperature molten salt tank 2, and the molten salt-flue gas heat exchanger 5 is connected with the inlet of the high-temperature molten salt tank 3; the outlet of the low-temperature molten salt tank 2 is also connected with the cold side inlet of the No. 2 molten salt heat exchanger 4, the inlet of the high-temperature molten salt tank 3 is also connected with the cold side outlet of the No. 2 molten salt heat exchanger 4, the hot side inlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-pressure turbine 7, the hot side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the split turbine 9, the outlet of the split turbine 9 is connected with the hot side inlet of the medium-temperature regenerator 14, the hot side outlet of the medium-temperature regenerator 14 is connected with the hot side inlet of the low-temperature regenerator 13, the cold side inlet of the medium-temperature regenerator 14 is connected with the cold side outlet of the low-temperature regenerator 13, and the cold side outlet of the medium-temperature regenerator 14 is connected with the tail end working medium inlet of the boiler 16.

[0032] The heat storage cycle, in particular, comprises a low-temperature molten salt tank 2, a high-temperature molten salt tank 3, a No. 2 molten salt heat exchanger 4, a split turbine 9 and a medium-temperature regenerator 14; a molten salt-flue gas heat exchanger 5 is arranged in the boiler 16, the molten salt-flue gas heat exchanger 5 is connected with the outlet of the low-temperature molten salt tank 2, and the molten salt-flue gas heat exchanger 5 is connected with the inlet of the high-temperature molten salt tank 3; the outlet of the low-temperature molten salt tank 2 is also connected with the cold side inlet of the No. 2 molten salt heat exchanger 4, the inlet of the high-temperature molten salt tank 3 is also connected with the cold side outlet of the No. 2 molten salt heat exchanger 4, the hot side inlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the high-pressure turbine 7, the hot side outlet of the No. 2 molten salt heat exchanger 4 is connected with the inlet of the split turbine 9, the outlet of the split turbine 9 is connected with the hot side inlet of the medium-temperature regenerator 14, the hot side outlet of the medium-temperature regenerator 14 is connected with the hot side inlet of the low-temperature regenerator 13, the cold side inlet of the medium-temperature regenerator 14 is connected with the cold side outlet of the low-temperature regenerator 13, and the cold side outlet of the medium-temperature regenerator 14 is connected with the tail end working medium inlet of the boiler 16.

[0033] The boiler 16 is provided with a split flue damper 6 to realize flue bypass, and the bypass flue is provided with a flue gas-molten salt heat exchanger 5.

[0034] The connection pipeline between the high-temperature molten salt tank 3 and the No. 1 molten salt heat exchanger 1 is provided with a No. 1 valve 171, the connection pipeline between the low-temperature molten salt tank 2 and the molten salt-flue gas heat exchanger 5 is provided with a No. 2 valve 172, the connection pipeline between the No. 2 molten salt heat exchanger 4 and the high-pressure turbine 7 is provided with a No. 3 valve 173, the connection pipeline between the outlet of the main compressor 11 and the heat release cycle regenerator 19 is provided with a No. 4 valve 174, the connection pipeline between the tail end outlet of the boiler 16 and the cold side outlet of the high-temperature regenerator 15 is provided with a No. 5 valve 175, the connection pipeline between the tail end inlet of the boiler 16 and the cold side inlet of the high-temperature regenerator 15 is provided with a No. 6 valve 176, and the connection pipeline between the cold side outlet of the low-temperature regenerator 13 and the cold side inlet of the medium-temperature regenerator 14 is provided with a No. 7 valve 177.

[0035] The inlet temperature of the main compressor 11 is 32-42℃, and the inlet pressure of the main compressor 11 is 7.5-9.0 MPa.

[0036] The operation method of the strong flexible coal-fired power generation system mainly includes a normal operation mode, a heat storage operation mode and a heat release operation mode.

[0037] The normal operation mode: all valves and the diversion flue damper 6 are in a default closed state, high-temperature and high-pressure carbon dioxide working medium at the outlet of the boiler 16 enters the high-pressure turbine 7 to do work, the working medium at the outlet of the high-pressure turbine 7 is reheated by the boiler 16 and then enters the low-pressure turbine 8 to do work, the working medium at the outlet of the low-pressure turbine 8 is sequentially heat-released by the high-temperature regenerator 15 and the low-temperature regenerator 13 and then is divided into two parts: one part is compressed and boosted by the re-compressor 10; the other part is cooled by the cooler 12 and then enters the main compressor 11 to be compressed and boosted, the working medium at the outlet of the main compressor 11 enters the low-temperature regenerator 13 to be heated, the working medium at the cold side outlet of the low-temperature regenerator 13 is combined with the working medium at the outlet of the re-compressor 10, and then enters the boiler after being heated by the high-temperature regenerator 15; the fifth valve 175 and the sixth valve 176 are opened to form diversion before the cold side inlet of the high-temperature regenerator 15, and the diverted working medium enters the tail of the boiler 16 to absorb heat of the medium and low-temperature flue gas and then is combined with the working medium at the cold side outlet of the high-temperature regenerator 15; the normal operation mode is shown in FIG. 2(a);

[0038] The heat storage operation mode: based on the normal operation mode, the diversion flue damper 6, the second valve 172, the third valve 173 and the seventh valve 177 are opened, and the sixth valve 176 is closed; a bypass flue is formed in the boiler, and the diverted flue gas heats the molten salt from the low-temperature molten salt tank 2, and the molten salt is stored in the high-temperature molten salt tank 3 after being heated to a high-temperature state; similarly, the diverted working medium at the inlet of the high-pressure turbine 7 heats the molten salt from the low-temperature molten salt tank 2 in the second molten salt heat exchanger 4, and the molten salt is stored in the high-temperature molten salt tank 3 after being heated to a high-temperature state; the carbon dioxide working medium at the outlet of the second molten salt heat exchanger 4 enters the diversion turbine 9 to expand and do work, and the pressure is reduced, the working medium at the outlet of the diversion turbine 9 heats the diverted working medium at the cold side outlet of the low-temperature regenerator 13 in the medium-temperature regenerator 14, the working medium at the cold side outlet of the medium-temperature regenerator 14 enters the tail of the boiler 16 to absorb heat and then is combined with the working medium at the cold side outlet of the high-temperature regenerator 15, and the working medium at the hot side outlet of the medium-temperature regenerator 14 is combined with the working medium at the hot side inlet of the low-temperature regenerator 13; the heat storage operation mode is shown in FIG. 2(b);

[0039] The heat release operation mode: on the basis of the normal operation mode, the first valve 171 and the fourth valve 174 are opened; the working medium at the outlet of the main compressor 11 is branched: one part does work to generate electricity according to the normal operation mode; the other part enters the heat release cycle to do work to generate electricity. In the heat release cycle, the branched working medium of the main compressor 11 first enters the heat release cycle regenerator 19 for preheating, then releases the high-temperature molten salt stored in the high-temperature molten salt tank 3 to heat the branched working medium from the cold side outlet of the heat release cycle regenerator 19 in the first molten salt heat exchanger 1, the heated working medium enters the heat release cycle turbine 18 to do work, and the working medium at the outlet of the heat release cycle turbine 18 is cooled by the heat release cycle regenerator 19 and then merged into the main stream at the inlet of the cooler 12; the heat release operation mode is shown in Fig. 2(c).

[0040] When the heat is stored, the branched part of the flue gas and the turbine working medium heat the molten salt, so as to reduce the flow of the working medium on the circulating side and further reduce the output power of the unit, and at the same time, the heat is stored in the molten salt storage tank; when the heat is released, the stored heat in the molten salt tank is released to heat the branched working medium of the main compressor, so as to realize the combined work of the recompression cycle and the heat release cycle to generate electricity and improve the output power of the unit. The present application integrates the heat storage cycle and the heat release cycle, improves the flexibility of the coal-fired power generation unit, reduces the minimum operating load of the unit, improves the variable load rate, realizes the strong flexibility of the coal-fired unit, promotes the consumption of new energy power generation and the transformation of the power structure.

Claims

1. A highly flexible coal-fired power generation system employing supercritical carbon dioxide as a cycle working fluid, characterized by, The heat storage cycle comprises a low-temperature molten salt tank (2), a high-temperature molten salt tank (3), a No. 2 molten salt heat exchanger (4), a split turbine (9) and a medium-temperature regenerator (14); the hot side inlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-pressure turbine (7), the hot side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the split turbine (9), the outlet of the split turbine (9) is connected with the hot side inlet of the medium-temperature regenerator (14), the hot side outlet of the medium-temperature regenerator (14) is connected with the hot side inlet of the low-temperature regenerator (13), the cold side inlet of the medium-temperature regenerator (14) is connected with the cold side outlet of the low-temperature regenerator (13), and the cold side outlet of the medium-temperature regenerator (14) is connected with the tail end working medium inlet of the boiler (16); the cold side inlet of the No. 2 molten salt heat exchanger (4) is connected with the outlet of the low-temperature molten salt tank (2), and the cold side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-temperature molten salt tank (3). The heat storage cycle comprises a low-temperature molten salt tank (2), a high-temperature molten salt tank (3), a No. 2 molten salt heat exchanger (4), a split turbine (9) and a medium-temperature regenerator (14); the hot side inlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-pressure turbine (7), the hot side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the split turbine (9), the outlet of the split turbine (9) is connected with the hot side inlet of the medium-temperature regenerator (14), the hot side outlet of the medium-temperature regenerator (14) is connected with the hot side inlet of the low-temperature regenerator (13), the cold side inlet of the medium-temperature regenerator (14) is connected with the cold side outlet of the low-temperature regenerator (13), and the cold side outlet of the medium-temperature regenerator (14) is connected with the tail end working medium inlet of the boiler (16); the cold side inlet of the No. 2 molten salt heat exchanger (4) is connected with the outlet of the low-temperature molten salt tank (2), and the cold side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-temperature molten salt tank (3). The heat storage cycle comprises a low-temperature molten salt tank (2), a high-temperature molten salt tank (3), a No. 2 molten salt heat exchanger (4), a split turbine (9) and a medium-temperature regenerator (14); the hot side inlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-pressure turbine (7), the hot side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the split turbine (9), the outlet of the split turbine (9) is connected with the hot side inlet of the medium-temperature regenerator (14), the hot side outlet of the medium-temperature regenerator (14) is connected with the hot side inlet of the low-temperature regenerator (13), the cold side inlet of the medium-temperature regenerator (14) is connected with the cold side outlet of the low-temperature regenerator (13), and the cold side outlet of the medium-temperature regenerator (14) is connected with the tail end working medium inlet of the boiler (16); the cold side inlet of the No. 2 molten salt heat exchanger (4) is connected with the outlet of the low-temperature molten salt tank (2), and the cold side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-temperature molten salt tank (3). The heat storage cycle comprises a low-temperature molten salt tank (2), a high-temperature molten salt tank (3), a No. 2 molten salt heat exchanger (4), a split turbine (9) and a medium-temperature regenerator (14); the hot side inlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-pressure turbine (7), the hot side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the split turbine (9), the outlet of the split turbine (9) is connected with the hot side inlet of the medium-temperature regenerator (14), the hot side outlet of the medium-temperature regenerator (14) is connected with the hot side inlet of the low-temperature regenerator (13), the cold side inlet of the medium-temperature regenerator (14) is connected with the cold side outlet of the low-temperature regenerator (13), and the cold side outlet of the medium-temperature regenerator (14) is connected with the tail end working medium inlet of the boiler (16); the cold side inlet of the No. 2 molten salt heat exchanger (4) is connected with the outlet of the low-temperature molten salt tank (2), and the cold side outlet of the No. 2 molten salt heat exchanger (4) is connected with the inlet of the high-temperature molten salt tank (3).

2. A high flexibility coal-fired power plant according to claim 1, characterized in that The boiler (16) is arranged with a molten salt-flue gas heat exchanger (5), the molten salt inlet of the molten salt-flue gas heat exchanger (5) is connected with the outlet of the low-temperature molten salt tank (2), and the molten salt outlet of the molten salt-flue gas heat exchanger (5) is connected with the inlet of the high-temperature molten salt tank (3).

3. A high flexibility coal-fired power plant according to claim 2, wherein The boiler (16) is arranged with a split flue damper (6) to realize flue bypass, and the molten salt-flue gas heat exchanger (5) is arranged in the bypass flue.

4. A high flexibility coal-fired power plant according to claim 1, wherein, The connection pipeline of the high-temperature molten salt tank (3) and the No. 1 molten salt heat exchanger (1) is provided with a No. 1 valve (171), the connection pipeline of the low-temperature molten salt tank (2) and the molten salt-flue gas heat exchanger (5) is provided with a No. 2 valve (172), the connection pipeline of the No. 2 molten salt heat exchanger (4) and the high-pressure turbine (7) is provided with a No. 3 valve (173), the connection pipeline of the outlet of the main compressor (11) and the heat-releasing regenerator (19) is provided with a No. 4 valve (174), the connection pipeline of the tail outlet of the boiler (16) and the cold side outlet of the high-temperature regenerator (15) is provided with a No. 5 valve (175), the connection pipeline of the tail inlet of the boiler (16) and the cold side inlet of the high-temperature regenerator (15) is provided with a No. 6 valve (176), and the connection pipeline of the cold side outlet of the low-temperature regenerator (13) and the cold side inlet of the medium-temperature regenerator (14) is provided with a No. 7 valve (177).

5. A highly flexible coal-fired power system as claimed in claim 1, wherein, The inlet temperature of the main compressor (11) is 32-42 ℃.

6. A highly flexible coal-fired power system as claimed in claim 1, wherein, The inlet pressure of the main compressor (11) is 7.5-9.0 MPa.

7. A method of operating a highly flexible coal-fired power system as defined in any one of claims 1 to 6, characterized in that The main compressor (11) is provided with a No. 4 valve (174), the connection pipeline of the tail outlet of the boiler (16) and the cold side outlet of the high-temperature regenerator (15) is provided with a No. 5 valve (175), the connection pipeline of the tail inlet of the boiler (16) and the cold side inlet of the high-temperature regenerator (15) is provided with a No. 6 valve (176), and the connection pipeline of the cold side outlet of the low-temperature regenerator (13) and the cold side inlet of the medium-temperature regenerator (14) is provided with a No. 7 valve (177). The conventional operation mode, the heat storage operation mode and the heat release operation mode are included. In the conventional operation mode, all the valves and the split flue damper (6) are in the default closed state, the high-temperature and high-pressure carbon dioxide working medium at the outlet of the boiler (16) first enters the high-pressure turbine (7) to do work, the working medium at the outlet of the high-pressure turbine (7) is reheated by the boiler (16) and then enters the low-pressure turbine (8) to do work, the working medium at the outlet of the low-pressure turbine (8) is sequentially heat-released by the high-temperature regenerator (15) and the low-temperature regenerator (13) and is divided into two parts: one part is compressed and boosted by the re-compressor (10); the other part is cooled by the cooler (12) and then enters the main compressor (11) to be compressed and boosted, the working medium at the outlet of the main compressor (11) enters the low-temperature regenerator (13) to be heated, the working medium at the cold side outlet of the low-temperature regenerator (13) is combined with the working medium at the outlet of the re-compressor (10), is heated by the high-temperature regenerator (15) and then enters the boiler; the No. 5 valve (175) and the No. 6 valve (176) are opened, a split is formed in front of the cold side inlet of the high-temperature regenerator (15), and the split-out part of the working medium enters the tail of the boiler (16) to absorb the heat of the medium and low-temperature flue gas and is combined with the connection part of the boiler (16) at the cold side outlet of the high-temperature regenerator (15); The heat storage mode, on the basis of the normal operation mode, opens the bypass flue damper (6), opens the second valve (172), the third valve (173) and the seventh valve (177), and closes the sixth valve (176); a bypass flue is formed inside the boiler, a part of flue gas is bypassed to heat the molten salt from the low-temperature molten salt tank (2), and the molten salt is stored in the high-temperature molten salt tank (3) after being heated to a high-temperature state; similarly, a part of the high-pressure turbine (7) inlet working medium is bypassed to heat the molten salt from the low-temperature molten salt tank (2) in the second molten salt heat exchanger (4), and the molten salt is stored in the high-temperature molten salt tank (3) after being heated to a high-temperature state; The heat release mode, on the basis of the normal operation mode, opens the first valve (171) and the fourth valve (174); the main compressor (11) outlet working medium is divided into two parts: one part generates power according to the normal operation mode; the other part generates power in the heat release cycle; in the heat release cycle, the main compressor (11) divided working medium first enters the heat release cycle regenerator (19) for preheating, then releases the high-temperature molten salt stored in the high-temperature molten salt tank (3) in the first molten salt heat exchanger (1) to heat the divided working medium from the cold side outlet of the heat release cycle regenerator (19), the heated working medium enters the heat release cycle turbine (18) to do work, and the heat release cycle turbine (18) outlet working medium is cooled by the heat release cycle regenerator (19) and then flows into the cooler (12) inlet main stream.

8. The method of operating a highly flexible coal-fired power plant according to claim 7, wherein, In the heat storage mode, the carbon dioxide working medium at the outlet of the second molten salt heat exchanger (4) enters the bypass turbine (9) to expand and do work, while reducing the pressure, the bypass turbine (9) outlet working medium heats the low-temperature regenerator (13) cold side outlet divided working medium in the medium-temperature regenerator (14), the medium-temperature regenerator (14) cold side outlet working medium enters the boiler (16) tail to absorb heat, then flows into the high-temperature regenerator (15) cold side outlet, and the medium-temperature regenerator (14) hot side outlet working medium flows into the low-temperature regenerator (13) hot side inlet.

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