Coal-fired boiler direct-drive high-temperature molten salt two-stage heat storage power generation heat supply peak regulation system and method

Abstract

The invention relates to the field of peak regulation of coal-fired power plants, in particular to a coal-fired boiler direct-drive high-temperature molten salt two-stage heat storage power generation heat supply peak regulation system and method, and the system comprises a coal-fired boiler unit which comprises a coal-fired boiler capable of generating flue gas carrying heat and a flue gas pipeline allowing flue gas to circulate; the fused salt heat storage unit comprises a fused salt storage vessel such as a fused salt tank capable of containing fused salt and a fused salt pipeline allowing the fused salt to circulate, and the fused salt can exchange heat with flue gas in the flue gas pipeline so as to store heat; the one or more power generation units are used for generating power through part of the heat stored by the fused salt heat storage unit, and under the condition that the multiple power generation units are arranged, the multiple power generation units can be independently adjusted; and the heat supply unit is used for supplying heat by using part of the heat stored by the fused salt heat storage unit. With such a configuration, it is possible to achieve power generation and heat supply by coupling the coal-fired boiler and the two-stage molten salt.

Description

Technical Field

[0001] This invention relates to the field of flexible deep peak shaving in coal-fired power plants, specifically providing a direct-drive high-temperature molten salt two-stage thermal storage power generation and heating peak shaving system and method for coal-fired boilers. Background Technology

[0002] Although the installed capacity of renewable energy power generation equipment such as wind and solar power has reached 42% of the total installed capacity in the country, coal-fired power generation, which accounts for 35.7% of the country's installed power generation capacity, still contributes 63.2% of the power generation (e.g., the power generation in 2024 was 6.3743 trillion kWh). Therefore, coal-fired power generation is still the mainstay of power supply for various industries.

[0003] With the integration of a large amount of renewable energy with cyclical, fluctuating, and random characteristics into the grid, the power supply stability of power grids (such as coal-fired power plants) has been severely challenged. Compared with renewable energy generation, coal-fired power generation has the advantage of relative stability. Therefore, by using coal-fired power generation as a supplement, it is expected to achieve deep peak shaving (15-100%) for thermal power plants, and it has the advantage of complete decoupling of heat and electricity.

[0004] However, due to the high inertia and instability of the energy output regulation of coal-fired boilers under low load conditions, the depth of peak shaving for power generation based on coal-fired boilers is limited (currently about 60-100%). Therefore, under the premise of decoupling heat and power, there is still room for improvement in how to flexibly carry out deep peak shaving of thermal power plants through energy coupling. Summary of the Invention

[0005] The present invention aims to solve at least to some extent the above-mentioned technical problems and / or solve at least a part of the above-mentioned technical problems. Specifically, through energy coupling, the peak-shaving level of thermal power plants can be improved to some extent, such as the ability to flexibly perform deep peak-shaving of thermal power plants.

[0006] In a first aspect, the present invention provides a direct-drive high-temperature molten salt two-stage thermal energy storage power generation and heating peak-shaving system for a coal-fired boiler. The system comprises: a coal-fired boiler unit, including a coal-fired boiler capable of generating heat-carrying flue gas and a flue gas duct allowing flue gas flow; a molten salt thermal energy storage unit, including a molten salt storage vessel capable of containing molten salt and a molten salt duct allowing molten salt flow, wherein the molten salt can exchange heat with the flue gas in the flue gas duct to store heat; one or more power generation units, used to generate electricity using a portion of the heat stored in the molten salt thermal energy storage unit, wherein, in the case of multiple power generation units, the multiple power generation units can be independently regulated; and a heating unit, used to provide heating using a portion of the heat stored in the molten salt thermal energy storage unit.

[0007] This configuration allows for the coupling of a coal-fired boiler with two stages of molten salt to achieve both power generation and heating.

[0008] In one possible implementation of the above-mentioned direct-drive high-temperature molten salt two-stage thermal energy storage power generation and heating peak-shaving system for coal-fired boilers, the molten salt thermal energy storage unit includes: (1) a molten salt tank group, which includes a high-temperature molten salt tank, an ultra-high-temperature molten salt tank, a medium-temperature molten salt tank and a low-temperature molten salt tank; the high-temperature molten salt tank contains a first molten salt, and the low-temperature molten salt tank contains a second molten salt; (2) a heat exchanger group, which includes: a first flue gas heat exchanger, which is installed in the rear flue gas well of the flue gas pipeline; and a second flue gas heat exchanger, which is installed in the front flue gas well of the flue gas pipeline and / or the furnace of the coal-fired boiler. The wall surface or near the wall surface; a third flue gas heat exchanger, which is installed in the front flue gas well of the flue gas duct; wherein, the first molten salt from the high-temperature molten salt tank, after exchanging heat with the second flue gas heat exchanger and the third flue gas heat exchanger in sequence, can reach the ultra-high temperature molten salt tank (i.e., the ultra-high temperature molten salt tank contains the first molten salt after being heated); wherein, the second molten salt from the low-temperature molten salt tank, after exchanging heat with the first flue gas heat exchanger, can reach the medium-temperature molten salt tank (i.e., the medium-temperature molten salt tank contains the second molten salt after being heated).

[0009] In one possible implementation of the above-mentioned direct-drive high-temperature molten salt two-stage thermal energy storage power generation and heating peak-shaving system for coal-fired boilers, the heat exchanger group further includes: a first water heat exchanger, through which the second molten salt from the intermediate-temperature molten salt tank can reach the low-temperature molten salt tank after exchanging heat with the first water heat exchanger in sequence; a second water heat exchanger, through which the first molten salt from the ultra-high-temperature molten salt tank can reach the high-temperature molten salt tank after exchanging heat with the second water heat exchanger; and a third water heat exchanger, through which the second molten salt from the intermediate-temperature molten salt tank can reach the low-temperature molten salt tank after exchanging heat with the third water heat exchanger; wherein, the first water heat exchanger and the second water heat exchanger also constitute the power generation unit (specifically: the medium of the power generation unit arrives at the power generation unit sequentially via the first water heat exchanger and the second water heat exchanger), and the third water heat exchanger also constitutes the heating unit (specifically: the medium of the return water network of the heating unit arrives at the water supply network via the condenser and the third water heat exchanger).

[0010] This configuration provides the possible flow modes of the first and second molten salts and the corresponding heat exchange modes.

[0011] In one possible implementation, the second flue gas heat exchanger has a dimension along the axial direction of the front flue gas well that is larger than the dimension of the third flue gas heat exchanger along the axial direction of the front flue gas well; and / or the first flue gas heat exchanger has a dimension along the axial direction of the rear flue gas well that is larger than the dimension of the third flue gas heat exchanger along the axial direction of the front flue gas well.

[0012] In one possible implementation of the above-mentioned direct-drive high-temperature molten salt two-stage thermal energy storage power generation and peak-shaving system for coal-fired boilers, the first molten salt is a mixture of nitrates, carbonates, fluorides, chlorides, or molten metal; and / or the second molten salt is a mixture of nitrates, carbonates, fluorides, or chlorides.

[0013] Taking mixed nitrates as an example, it should be noted that mixed nitrates here should be understood as multi-component eutectic nitrate molten salts prepared by uniformly mixing two or more nitrates. The types, quantities, and ratios of the nitrates can be flexibly determined according to actual needs.

[0014] This configuration provides the possible forms of the first and second molten salts.

[0015] In a second aspect, the present invention provides a control method for a direct-drive high-temperature molten salt thermal energy storage power generation and heating peak-shaving system for a coal-fired boiler. The system includes a first molten salt pump, and the control method includes: operating the first molten salt pump so that molten salt from a low-temperature molten salt tank undergoes heat exchange in a first flue gas heat exchanger and then reaches the medium-temperature molten salt tank; and / or the system includes a third molten salt pump, and the control method includes: operating the third molten salt pump so that molten salt from a high-temperature molten salt tank undergoes heat exchange sequentially in a second flue gas heat exchanger and the third flue gas heat exchanger before reaching the ultra-high-temperature molten salt tank.

[0016] With this configuration, it is possible to fully recover heat from the flue gas duct by controlling the operation of the first / third molten salt pump.

[0017] In one possible implementation of the above control method, the system includes a second molten salt pump and a fourth molten salt pump, and the control method includes: operating the second molten salt pump so that molten salt from the intermediate-temperature molten salt tank undergoes heat exchange in the first water heat exchanger constituting the power generation unit and then reaches the low-temperature molten salt tank; and / or operating the fourth molten salt pump so that molten salt from the ultra-high-temperature molten salt tank undergoes heat exchange in the second water heat exchanger constituting the power generation unit and then reaches the high-temperature molten salt tank.

[0018] This configuration illustrates the possible operating modes of the power generation unit. For example, the power generation unit consisting of the first and second water heat exchangers can be understood as follows: after the power generation medium exchanges heat in the first and second water heat exchangers, it can generate electrical energy.

[0019] In one possible implementation of the above control method, the system includes a fifth molten salt pump, and the control method includes: operating the fifth molten salt pump so that: molten salt from the medium-temperature molten salt tank undergoes heat exchange in the third water heat exchanger constituting the heating unit, and then reaches the low-temperature molten salt tank.

[0020] This configuration illustrates possible operating modes of the heating unit. For example, a heating unit consisting of a third water heat exchanger can be understood as follows: after the heating medium, such as water, undergoes heat exchange within the third water heat exchanger, it can supply heat to the heating terminal. Exemplarily, a booster pump is installed on the heating unit, and the specific method of supplying heat to the heating terminal is to operate the booster pump so that: water from the upstream return water network undergoes heat exchange within the third water heat exchanger and then reaches the downstream supply water network.

[0021] In one possible implementation of the above control method, the control method includes: detecting the liquid levels of the first molten salt in the high-temperature molten salt tank and / or the second molten salt in the low-temperature molten salt tank; and adjusting the operating parameters of the first molten salt pump and the third molten salt pump based on the detection results. This step includes: when the liquid level of the first molten salt in the high-temperature molten salt tank drops to a first set liquid level, reducing the operating parameters of the third molten salt pump and / or reducing the fuel delivery speed of the coal-fired boiler unit to ensure that the liquid level of the first molten salt in the high-temperature molten salt tank is not lower than the lower limit of the total molten salt depth; and / or when the liquid level of the first molten salt in the high-temperature molten salt tank rises to a second set liquid level, increasing the operating parameters of the third molten salt pump. And / or reduce the fuel delivery speed of the coal-fired boiler unit to ensure that the level of the first molten salt in the high-temperature molten salt tank is not higher than the upper limit of the total molten salt depth; and / or when the level of the second molten salt in the low-temperature molten salt tank drops to a third set level, reduce the operating parameters of the first molten salt pump and / or reduce the fuel delivery speed of the coal-fired boiler unit to ensure that the level of molten salt in the low-temperature molten salt tank is not lower than the lower limit of the total molten salt depth; and / or when the level of the second molten salt in the low-temperature molten salt tank rises to a fourth set level, increase the operating parameters of the first molten salt pump and / or the fuel delivery speed of the coal-fired boiler unit to ensure that the level of molten salt in the low-temperature molten salt tank is not higher than the upper limit of the total molten salt depth.

[0022] This configuration ensures the reliability of the molten salt circulation loop.

[0023] In one possible implementation, the first / third set liquid level is 20% of the total molten salt depth, wherein the lower limit liquid level is the lowest liquid level that can ensure the normal operation of the cryogenic molten salt tank, such as 10%. The second / fourth set liquid level is 80% of the total molten salt depth, wherein the upper limit liquid level is the highest liquid level that can ensure the cryogenic molten salt tank is continuously at the normal operation level, such as 90%.

[0024] In one possible implementation of the above control method, the system further includes a salt discharge unit, and the control method includes: stopping the first molten salt pump and putting the salt discharge unit in a salt dischargeable state when it is necessary to shut down the coal-fired boiler unit.

[0025] This configuration allows for the timely removal of molten salt from the molten salt circuit when faults, potential hazards, or maintenance periods are detected in coal-fired boiler units.

[0026] In one possible implementation of the above control method, the salt discharge unit includes: a first salt discharge assembly comprising a first valve and a first storage tank, wherein molten salt in the molten salt pipe of the second flue gas heat exchanger and / or the second flue gas heat exchanger can reach the first storage tank via the first valve, wherein the first storage tank can be connected to the high-temperature molten salt tank; a second salt discharge assembly comprising a second valve and a second storage tank, wherein molten salt in the molten salt pipe of the first flue gas heat exchanger can reach the second storage tank via the second valve, wherein the second storage tank can be connected to the low-temperature molten salt tank; the phrase "the salt discharge unit is in a salt dischargeable state" includes: opening the first valve so that: molten salt in the second flue gas heat exchanger and / or the third flue gas heat exchanger is discharged into the first storage tank through the first valve; and / or opening the second valve so that: molten salt in the first flue gas heat exchanger is discharged into the second storage tank through the second valve.

[0027] This configuration provides an overview of the salt removal unit and its possible operating modes.

[0028] In one possible implementation, the salt removal unit includes a fourth valve (connected to a molten salt pipe to a third flue gas heat exchanger), a ninth valve (connected to a molten salt pipe to a second flue gas heat exchanger), and a nitrogen cylinder. By opening the fourth and ninth valves, salt removal is achieved under the action of high-pressure nitrogen gas in the nitrogen cylinder and the gravity of the molten salt itself.

[0029] In one possible implementation, the first storage tank is equipped with a sixth molten salt pump and a seventh molten salt pump. By operating the sixth and seventh molten salt pumps, the molten salt in the first and second storage tanks is discharged into the high-temperature molten salt tank and the low-temperature molten salt tank, respectively.

[0030] In a preferred embodiment of the invention, by using molten salt as the heat storage medium, a high temperature difference can be achieved between the flue gas in the coal-fired boiler and the heat storage medium in the heat exchanger. The coal-fired boiler does not require water / steam pipelines, effectively avoiding the problem of heat transfer deterioration. By using heat exchange at different locations in the flue gas passage with the molten salt, it is expected to fully recover the heat from the flue gas. By using a combination of two molten salts with different temperature properties, deeper peak shaving of coal-fired power plants can be achieved more flexibly. For example, the output power and heating power of the coal-fired power plant can be adjusted within the range of 0-120%, achieving a more thorough decoupling of thermoelectricity in the coal-fired power plant. For instance, the heat storage temperature of the first molten salt can reach 700℃ (and above). The first molten salt can heat steam to a supercritical state through the heat exchanger, greatly improving the efficiency of the coal-fired unit. Attached Figure Description

[0031] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0032] Figure 1 This diagram illustrates the principle of a direct-drive high-temperature molten salt two-stage thermal storage power generation and heating peak-shaving system for a coal-fired boiler, according to an embodiment of the present invention.

[0033] List of reference numerals in the attached diagram:

[0034] 101. Central controller;

[0035] 201. Furnace; 202. Front flue; 203. Cyclone separator; 204. Horizontal flue; 205. Rear flue; 206. Air preheater; 207. Flue gas treatment device.

[0036] 301. Low-temperature molten salt tank; 302. First molten salt pump; 303. First flue gas heat exchanger; 304. Medium-temperature molten salt tank; 305. High-temperature molten salt tank; 306. Third molten salt pump; 307. Second flue gas heat exchanger; 308. Third flue gas heat exchanger; 309. Ultra-high temperature molten salt tank; 310. First liquid level sensor; 311. Second liquid level sensor;

[0037] 401. First valve; 402. Second valve; 403. Fourth valve; 404. Ninth valve; 405. Nitrogen cylinder; 406. First storage tank; 407. Second storage tank; 408. Sixth molten salt pump; 409. Seventh molten salt pump.

[0038] 501. Second molten salt pump; 502. First water heat exchanger; 503. Fourth molten salt pump; 504. Second water heat exchanger; 505. Third valve; 506. Steam turbine unit; 508. Condenser; 509. First water pump; 510. Second water pump; 511. Low temperature water tank; 512. High temperature water tank; 513. Deaerator; 514. Feed water pump.

[0039] 601. Return water network; 602. Water source heat pump; 603. Booster pump; 604. Third water heat exchanger; 605. Fifth valve; 606. Sixth valve; 607. Seventh valve; 608. Eighth valve; 609. Water supply network; 610. Fifth molten salt pump; 6021. Evaporator; 6022. Condenser. Detailed Implementation

[0040] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0041] It should be noted that in the description of this invention, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0042] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection, an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced even without certain specific details. In some instances, heat exchangers, power generation principles, and other aspects well-known to those skilled in the art are not described in detail, in order to highlight the main points of the present invention.

[0044] Main reference Figure 1In one possible implementation, the direct-drive high-temperature molten salt two-stage thermal energy storage power generation and heating peak-shaving system for coal-fired boilers mainly includes a coal-fired boiler unit, a molten salt thermal energy storage unit, a salt discharge unit, a power generation unit, and a heating unit. The coal-fired boiler unit includes a coal-fired boiler capable of generating heat-carrying flue gas and a flue gas duct that allows the flue gas to flow (e.g., the heat-carrying flue gas generated by the coal-fired boiler enters the flue gas duct via its upstream side, and during its flow through the flue gas duct, it exchanges heat with molten salt, thereby storing the heat in the molten salt, and finally discharges it via its downstream side). The molten salt thermal energy storage unit includes a molten salt storage vessel capable of holding molten salt and a molten salt duct that allows the molten salt to flow, and the molten salt can exchange heat with the flue gas in the flue gas duct. The system stores heat through heat exchange. The molten salt discharge unit is primarily used to discharge molten salt from the system before system shutdown. The discharged molten salt can be further incorporated into the molten salt flow path or separately configured to store molten salt. The power generation unit can generate electricity using a portion of the heat stored in the molten salt thermal storage unit. The heating unit can provide heat using a portion of the heat stored in the molten salt thermal storage unit. In this example, the generator is a steam turbine (the power generation unit may include one or more units; in the case of multiple units, each unit can generate / regulate heat relatively independently), and the heating unit can supply hot water to the load through a water supply network. The coal-fired boiler unit can be a pulverized coal boiler, a circulating fluidized bed boiler, or a chain grate boiler.

[0045] In one possible implementation, the flue gas duct includes a front flue, a horizontal flue, a rear flue, an air preheater, and a chimney. The mixed flue gas, carrying heat and particles, generated from coal combustion in the furnace of the flue gas-fired coal-fired boiler, flows from the bottom to the top of the furnace, passing sequentially through the front flue, horizontal flue, rear flue, and air preheater before being discharged through the chimney. In this example, the coal-fired boiler unit is a circulating fluidized bed boiler; therefore, a cyclone separator is installed between the front flue and the horizontal flue. As the mixed flue gas flows through the cyclone separator, particles are separated from the flue gas, and coarse particles in the mixed flue gas return to the furnace through the lower part of the cyclone separator.

[0046] In one possible implementation, a dust collector is installed downstream of the air preheater. Fine particles in the mixed flue gas, after passing through the horizontal flue, the rear flue, and the air preheater, are separated and collected by the dust collector as they flow through it. The flue gas duct also includes an induced draft fan. After the mixed flue gas particles are separated twice within the duct, they are guided by the induced draft fan and discharged into the external environment through the chimney.

[0047] In one possible implementation, the molten salt thermal storage unit includes a molten salt pipeline that allows molten salt to flow, a low-temperature molten salt tank (containing a second molten salt), a first flue gas heat exchanger, a medium-temperature molten salt tank (containing a heated second molten salt), a high-temperature molten salt tank (containing a first molten salt with an upper limit operating temperature higher than that of the second molten salt), a second flue gas heat exchanger, a third flue gas heat exchanger, and an ultra-high-temperature molten salt tank (containing a heated first molten salt).

[0048] In one possible implementation, the first molten salt is a mixture of nitrates, carbonates, fluorides, chlorides, or molten metal, and the second molten salt is a mixture of nitrates, carbonates, fluorides, or chlorides. The lower limit of the operating temperature of the first molten salt is lower than the upper limit of the operating temperature of the second molten salt, but higher than the lower limit of the operating temperature of the second molten salt.

[0049] In one possible implementation, the temperature of the first molten salt (unheated first molten salt) in the high-temperature molten salt tank is 400-600°C, and the temperature of the first molten salt (heated first molten salt) in the ultra-high-temperature molten salt tank is 700-900°C. The temperature of the second molten salt (unheated second molten salt) in the low-temperature molten salt tank is 150-300°C, and the temperature of the second molten salt (heated second molten salt) in the medium-temperature molten salt tank is 500-600°C.

[0050] For example, the first molten salt is a ternary nitrate, and the second molten salt is a quaternary mixed nitrate. The quaternary nitrate in the low-temperature molten salt tank 301 maintains a lower limit heat storage temperature of 170°C, the quaternary nitrate in the medium-temperature molten salt tank 304 maintains an upper limit heat storage temperature of 500°C, the ternary chloride in the high-temperature molten salt tank 305 maintains a lower limit heat storage temperature of 390°C, and the ternary chloride in the ultra-high-temperature molten salt tank 309 maintains an upper limit heat storage temperature of 700°C. Specifically, the quaternary nitrate is a quaternary nitrate with a melting point of 120°C, a lower limit heat storage temperature of 170°C, and an upper limit heat storage temperature of 500°C; the ternary chloride is a ternary chloride with a melting point of 343°C, a lower limit heat storage temperature of 390°C, and an upper limit heat storage temperature of 700°C. Clearly, the composition and properties of the first / second molten salts, as well as the difference in the upper limit operating temperatures of the first and second molten salts, can be flexibly adjusted according to actual needs.

[0051] In one possible implementation, the sub-unit corresponding to the second molten salt in the molten salt thermal storage unit mainly includes a low-temperature molten salt tank, a first flue gas heat exchanger (located in the rear flue gas well of the flue gas duct), and a medium-temperature molten salt tank. After exchanging heat with the first flue gas heat exchanger, the second molten salt from the low-temperature molten salt tank reaches the medium-temperature molten salt tank, meaning the medium-temperature molten salt contains the heated second molten salt. Under the action of the first molten salt pump, the second molten salt in the low-temperature molten salt tank is extracted and sent into the pipe of the first flue gas heat exchanger at a position corresponding to the downstream side of the rear flue gas well. After entering the pipe, it rises in the pipe and is heated. The heated second molten salt then flows to the medium-temperature molten salt tank for storage.

[0052] In one possible implementation, viewed along the flue gas discharge direction, the first flue gas heat exchanger is located near the upstream side of the rear flue gas shaft, and the air preheater is located near the downstream side of the rear flue gas shaft. In this example, the flue gas flow section of the rear flue gas shaft generally includes the upstream portion, the midstream portion, and the downstream portion, and the first flue gas heat exchanger is generally located in the upstream and midstream portions of the rear flue gas shaft.

[0053] For example, the upper outlet of the front flue 202 is connected to the upper inlet of the cyclone separator 203, the upper flue gas outlet of the cyclone separator 203 is connected to the inlet of the rear flue 205 through the horizontal flue 204, the air preheater 206 is installed in the lower hollow part of the rear flue 205, and the lower exhaust port of the rear flue 205 is connected to the flue gas treatment device 207; the coal-fired boiler unit is connected to the control unit such as the central controller 101 through signal lines.

[0054] In one possible implementation, the sub-unit corresponding to the second molten salt in the molten salt thermal storage unit further includes a first water heat exchanger. After exchanging heat with the first water heat exchanger constituting the power generation unit, the second molten salt from the intermediate-temperature molten salt tank can reach the cryogenic molten salt tank. Under the action of a second molten salt pump, the second molten salt (the heated second molten salt) in the intermediate-temperature molten salt tank is drawn and sent into the molten salt pipe of the first water heat exchanger, and the cooled second molten salt returns to the cryogenic molten salt tank.

[0055] In one possible implementation, the sub-unit corresponding to the second molten salt in the molten salt storage unit further includes a third water heat exchanger. After exchanging heat with the third water heat exchanger constituting the heating unit, the second molten salt from the intermediate-temperature molten salt tank can reach the low-temperature molten salt tank. For example, under the action of a fifth molten salt pump, the second molten salt in the intermediate-temperature molten salt tank is drawn and sent into the molten salt pipe in the third water heat exchanger. Heat is exchanged between the molten salt pipe and the water pipe (connected to the water supply network) in the third water heat exchanger, thus cooling the second molten salt and returning it to the low-temperature molten salt tank.

[0056] In one possible implementation, the sub-unit corresponding to the first molten salt in the molten salt thermal storage unit mainly includes a high-temperature molten salt tank, a second flue gas heat exchanger, a third flue gas heat exchanger (both the second and third flue gas heat exchangers are located in the front flue gas well of the flue gas duct), an ultra-high temperature molten salt tank, and a second water heat exchanger. The first molten salt from the high-temperature molten salt tank, after exchanging heat sequentially with the second and third flue gas heat exchangers, can reach the ultra-high temperature molten salt tank (i.e., the ultra-high temperature molten salt tank contains the heated first molten salt). The first molten salt from the ultra-high temperature molten salt tank, after exchanging heat with the second water heat exchanger constituting the power generation unit, can reach the high-temperature molten salt tank. For example, under the action of the third molten salt pump, the first molten salt in the high-temperature molten salt tank is extracted and sequentially sent to the second / third flue gas heat exchangers at a position downstream of the front flue gas well. After sufficient heat exchange with the mixed flue gas, the first molten salt is heated and sent to the ultra-high temperature molten salt tank for storage. Under the action of the fourth molten salt pump, the first molten salt (the first molten salt being heated) in the ultra-high temperature molten salt tank is drawn and sent to the molten salt pipe in the second water heat exchanger that constitutes the power generation unit. The molten salt pipe in the second water heat exchanger exchanges heat with the water pipe, further heating the saturated steam or supercritical steam into ultra-high temperature superheated steam. The first molten salt is cooled down accordingly, and the cooled first molten salt is returned to the high temperature molten salt tank for storage.

[0057] In one possible implementation, the second flue gas heat exchanger is disposed in close contact with the wall of the front flue (e.g., close contact with the wall of the front flue approximately throughout the entire area of ​​the front flue), and the third flue gas heat exchanger is disposed in the front flue near the downstream side, such as in the middle or upper part of the front flue, and is located in the hollow part inside the second flue gas heat exchanger.

[0058] For example, the flue gas flow section of the front flue duct 202 consists of an upstream section, a midstream section, and a downstream section. The second flue gas heat exchanger 307 is arranged near the wall of the furnace 201 and the front flue duct 202, and the third flue gas heat exchanger 308 is arranged in a screen-like manner in the hollow position of the front flue duct 202. The flue gas flow section of the rear flue duct 205 includes an upstream section, a midstream section, and a downstream section. The first flue gas heat exchanger 303 is arranged in the upstream and midstream sections of the rear flue duct 205, and the air preheater 206 is arranged in the downstream section of the rear flue duct 205. Fuel is fed into the furnace at a calculated rate. Primary air (60% of the total air volume) is heated to 100°C by an air preheater before being fed into the furnace, and secondary air (40% of the total air volume) is heated to 380°C by an air preheater before being fed into the furnace. The fuel burns in the furnace, creating a high-temperature flue gas flow field of 800-950°C in the furnace and the front flue. The high-temperature flue gas generated in the furnace 201 flows sequentially through the front flue 202, cyclone separator 203, horizontal flue 204, rear flue 205, and air preheater 206. After being treated by the flue gas treatment device 207 to meet standards, it is discharged into the external environment. Specifically, when the flue gas flows through the cyclone separator 203, particles are separated from the flue gas. The particles in the flue gas return to the furnace 201 through the lower part of the cyclone separator 203.

[0059] The molten salt thermal storage unit is used to store heat through heat exchange between molten salt and flue gas. It consists of a low-temperature molten salt tank 301, a first molten salt pump 302, a first flue gas heat exchanger 303, a medium-temperature molten salt tank 304, a high-temperature molten salt tank 305, a third molten salt pump 306, a second flue gas heat exchanger 307, a third flue gas heat exchanger 308, an ultra-high-temperature molten salt tank 309, a first liquid level sensor 310, and a second liquid level sensor 311. The inlet of the first molten salt pump 302 is connected to the low-temperature molten salt tank 301, and the outlet of the first molten salt pump 302 is connected to the lower inlet of the first flue gas heat exchanger 303 through a molten salt pipe. The upper outlet of the first flue gas heat exchanger 303 is connected to the medium-temperature molten salt tank 304 through a molten salt pipe. The inlet of the third molten salt pump 306 is connected to the high-temperature molten salt tank 305. The outlet of the third molten salt pump 306 is connected to the upper inlet of the second flue gas heat exchanger 307 through a molten salt pipe. The lower outlet of the second flue gas heat exchanger 307 is connected to the lower inlet of the third flue gas heat exchanger 308 through a molten salt pipe. The upper outlet of the third flue gas heat exchanger 308 is connected to the ultra-high temperature molten salt tank 309 through a molten salt pipe. The central controller 101 is connected to the first molten salt pump 302, the third molten salt pump 306, the first liquid level sensor 310, and the second liquid level sensor 311 through signal lines. The first liquid level sensor 310 is located at the upper part of the high-temperature molten salt tank 305, and the second liquid level sensor 311 is located at the upper part of the low-temperature molten salt tank 301. During the heat storage process, the first molten salt pump 302 draws 170°C quaternary nitrate from the low-temperature molten salt tank 301 and sends it into the first flue gas heat exchanger 303 through the lower inlet of the heat exchange pipe. As the quaternary nitrate flows upward within the first flue gas heat exchanger 303, it is gradually heated to 500°C and then stored in the medium-temperature molten salt tank 304. The third molten salt pump 306 draws 390°C ternary chloride from the high-temperature molten salt tank 305 and sends it sequentially into the second flue gas heat exchanger 307 and the third flue gas heat exchanger 308 through the upper inlet pipe of the second flue gas heat exchanger 307. After sufficient heat exchange with the flue gas, it is heated to 700°C and then stored in the ultra-high temperature molten salt tank 309.

[0060] In one possible implementation, the salt discharge unit includes a first valve 401, a second valve 402, a fourth valve 403, a ninth valve 404, a nitrogen cylinder 405, a first storage tank 406, a second storage tank 407, a sixth molten salt pump 408, and a seventh molten salt pump 409. The first valve 401 is connected to the lowest point heat exchange pipe of the second flue gas heat exchanger 307 and the first storage tank 406, respectively. The second valve 402 is connected to the lowest point heat exchange pipe of the first flue gas heat exchanger 303 and the second storage tank 407, respectively. One end of the fourth valve 403 is connected to the pipe connecting the second flue gas heat exchanger 307 and the high-temperature molten salt tank 305. The highest point is connected, and the other end is connected to nitrogen cylinder 405; one end of the ninth valve 404 is connected to the highest point of the connecting pipe between the third flue gas heat exchanger 308 and the ultra-high temperature molten salt tank 309, and the other end is connected to nitrogen cylinder 405; the sixth molten salt pump 408 is connected to the first storage tank 406 and the high temperature molten salt tank 305 respectively, and the seventh molten salt pump 409 is connected to the second storage tank 407 and the low temperature molten salt tank 301 respectively. The first valve 401, the second valve 402, the fourth valve 403, the ninth valve 404, the sixth molten salt pump 408, and the seventh molten salt pump 409 are respectively connected to the central controller 101 via signal lines. After the molten salt thermal storage unit starts and stops, valves (403, 404, 401) open. The ternary chloride (first molten salt) in the second flue gas heat exchanger 307 and the third flue gas heat exchanger 308 is discharged into the first storage tank 406 through the first valve 401 under the action of gravity and high-pressure nitrogen in the nitrogen cylinder 405. The sixth molten salt pump 408 starts and sends all the ternary chloride in the first storage tank 406 to the high-temperature molten salt tank 305 for storage. At the same time, the second valve 402 opens, and the quaternary nitrate (second molten salt) in the first flue gas heat exchanger is discharged into the second storage tank 407 through the second valve 402 under the action of gravity. The seventh molten salt pump 409 starts and sends all the quaternary nitrate in the second storage tank 407 to the low-temperature molten salt tank 301 for storage, completing the salt discharge process of the molten salt thermal storage system.

[0061] In one possible implementation, the power generation unit includes a second molten salt pump 501, a first water heat exchanger 502, a fourth molten salt pump 503, a second water heat exchanger 504, a third valve 505, a steam turbine 506, a condenser 508, a first water pump 509, a second water pump 510, a low-temperature water tank 511, a high-temperature water tank 512, a deaerator 513, and a feedwater pump 514. The inlet and outlet of the second molten salt pump 501 are respectively connected to the molten salt side inlet pipes of the medium-temperature molten salt tank 304 and the first water heat exchanger 502. The molten salt side outlet pipe of the first water heat exchanger 502 is connected to the low-temperature molten salt tank 301 through a molten salt pipe. The inlet and outlet of the fourth molten salt pump 503 are respectively connected to the molten salt side inlet pipes of the ultra-high temperature molten salt tank 309 and the second water heat exchanger 504. The molten salt side outlet pipe of the second water heat exchanger 504 is connected to the high-temperature molten salt tank 305 through a molten salt pipe. The inlet and outlet of the circulating water side pipeline of condenser 508 are connected to the exhaust port of turbine unit 506 and the circulating water inlet of deaerator 513 via pipelines, respectively. The inlet and outlet of feedwater pump 514 are connected to the outlet of deaerator 513 and the circulating water side pipeline inlet of first water heat exchanger 502 via pipelines, respectively. The outlet of the circulating water side pipeline of first water heat exchanger 502 is connected to the circulating water side pipeline inlet of second water heat exchanger 504. The water side outlet of second water heat exchanger 504 is connected to the steam inlet of turbine unit 506 via pipeline. The inlet and outlet of first water pump 509 are connected to the outlet of low-temperature water tank 511 and the cooling water side pipeline inlet of condenser 508 via pipelines, respectively. The inlet and outlet of water tank 512 are connected to the cooling water side pipe outlet of condenser 508 and the inlet of second water pump 510 via pipelines, respectively. The cooling water side pipe inlet and outlet of evaporator 6021 of water source heat pump 602 are connected to the outlet of second water pump 510 and the inlet of low temperature water tank 511 via pipelines, respectively. One end of third valve 505 is connected to the highest point of the circulating water pipeline between second water heat exchanger 504 and turbine unit 506. First water pump 509, second water pump 510, feed water pump 514, second molten salt pump 501, fourth molten salt pump 503, third valve 505, and turbine unit 506 are connected to central controller 101 via signal lines. During power generation, the second molten salt pump 501 draws 500°C quaternary nitrate from the medium-temperature molten salt tank 304 and sends it into the molten salt side pipe of the first water heat exchanger 502. The quaternary nitrate exchanges heat with the circulating water in the circulating water side pipe through the heat exchange wall, cools down to 170°C, and is then stored in the low-temperature molten salt tank 301. At the same time, the fourth molten salt pump 503 draws 700°C ternary chloride from the ultra-high temperature molten salt tank 309 and sends it into the molten salt side pipe of the second water heat exchanger 504. The ternary chloride exchanges heat with the saturated steam in the circulating water side pipe, cools down to 390°C, and is then stored in the high-temperature molten salt tank 305.Meanwhile, feedwater pump 514 draws circulating water from deaerator 513, pressurizes it to 30 MPa, and sends it into the circulating water side pipeline of the first water heat exchanger 502. The circulating water is heated to 374°C saturated steam and then enters the circulating water side pipeline of the second water heat exchanger 504, where it is heated to 680°C superheated steam. This superheated steam then enters turbine unit 506 to drive generator 507 to generate electricity. After turbine unit 506 has done its work, it discharges exhaust steam at 42°C and 5.6 kPa. At the same time, first water pump 509 draws 20°C cryogenic cold water from cryogenic water tank 511. The exhaust steam is cooled and condensed into subcooled circulating water in the cooling water side pipe of the condenser 508. The exhaust steam is cooled and condensed into subcooled circulating water after exchanging heat with the low-temperature cooling water through the heat exchange wall in the circulating water side pipe of the condenser 508 and then returned to the deaerator 513. The low-temperature cooling water is heated to 32°C and then enters the high-temperature water tank 512. The second water pump 510 draws 32°C high-temperature cooling water from the high-temperature water tank 512 and sends it into the cooling water side pipe of the condenser 6022 of the water source heat pump 602. The high-temperature cooling water is cooled down to 20°C and then returned to the low-temperature water tank 511 for storage.

[0062] In one possible implementation, the heating unit comprises a return water network 601, a water source heat pump 602, a booster pump 603, a third water heat exchanger 604, a fifth valve 605, a sixth valve 606, a seventh valve 607, an eighth valve 608, a supply water network 609, and a fifth molten salt pump 610. The water source heat pump 602 includes an evaporator 6021 and a condenser 6022. The inlet and outlet of the hot water supply side pipe of the condenser 6022 of the water source heat pump 602 are connected to the return water network 601 and the inlet of the booster pump 603, respectively. The inlet and outlet of the hot water supply side pipe of the third water heat exchanger 604 are connected to the outlet of the booster pump 603 and the seventh valve 607, respectively. The seventh valve 607 is connected to the supply water network 609 via a pipe. The eighth valve 608 is connected to the seventh valve 607 via a pipe between the eighth valve 608 and the third water heat exchanger 604. The fifth valve 605... The fifth molten salt pump 610 is connected to the inlet of the hot water supply pipe of the condenser 6022 of the water source heat pump 602 and the high-temperature water tank 512. The sixth valve 606 is connected to the inlet of the hot water supply pipe of the condenser 6022 of the water source heat pump 602 and the return water network 601. The inlet and outlet of the fifth molten salt pump 610 are connected to the outlet of the medium-temperature molten salt tank 304 and the inlet of the molten salt side pipe of the third water heat exchanger 604, respectively. The outlet of the molten salt side pipe of the third water heat exchanger 604 is connected to the inlet of the low-temperature molten salt tank 301. During the heating process, the fifth molten salt pump draws 500°C quaternary nitrate from the medium-temperature molten salt tank 304 and sends it into the molten salt side pipe of the third water heat exchanger 604. After exchanging heat with the hot water supply pipe of the third water heat exchanger 604 and cooling down to 170°C, it is stored in the low-temperature molten salt tank 301. Meanwhile, the 30°C low-temperature hot water in the return water network 601 absorbs heat and rises to 65°C on the water side of the condenser 6022 of the water source heat pump 602 through the sixth valve 606. After being pressurized to 10MPa by the booster pump 603, it is sent to the hot water supply side pipeline of the third water heat exchanger 604 and further heated into superheated steam at 490°C. It is then sent to the water supply network 609 for heating through the seventh valve 607.

[0063] In one possible implementation, both the molten salt pipes and heat exchangers are equipped with temperature-controlled heaters (e.g., molten salt pipes and heat exchangers located outside of coal-fired boilers need to be equipped with temperature-controlled heaters, which can be configured by wrapping around the outer wall of the molten salt pipes and heat exchangers). The temperature-controlled heaters are mainly used to heat the internal temperature of the molten salt pipes and heat exchangers to at least 50°C above the melting point of the molten salt flowing inside and maintain a constant temperature. In addition, the insulation layers of molten salt pipes, steam pipes, and water pipes should meet the requirements of national standards, and heat exchangers and pipes outside of coal-fired boilers should be insulated.

[0064] Based on the above structure, the present invention also provides a control method for a direct-drive high-temperature molten salt two-stage thermal energy storage power generation and heating peak-shaving system for coal-fired boilers. This method is mainly used to realize the power generation function and the terminal heating requirements through heat exchange between flue gas and power generation working medium and between flue gas and water body.

[0065] (a) Starting at rated power:

[0066] After configuring according to the conditions in Tables 1 and 2, the rated power generation and heating load can be started by the operation and maintenance personnel following these steps.

[0067] Table 1. Main parameters of molten salt thermal storage system under rated operating conditions

[0068]

[0069] Table 2 Main parameters of circulating water / steam system under rated operating conditions

[0070]

[0071] The central controller 101 calculates and sets the operating frequencies of the first molten salt pump 302, the second molten salt pump 501, the third molten salt pump 306, the fourth molten salt pump 503, the fifth molten salt pump 610, the first water pump 509, the second water pump 510, the booster pump 603, the feed water pump 514, and the water source heat pump 602 based on the rated power generation and rated heating load. It also calculates and sets the opening and closing states of the first valve 401, the second valve 402, the third valve 505, the fourth valve 403, the fifth valve 605, the sixth valve 606, the seventh valve 607, the eighth valve 608, and the ninth valve 404. Finally, it calculates and sets the coal delivery rate, primary air volume, and secondary air flow rate of the coal-fired boiler.

[0072] The central controller 101 sends an ignition command to the coal-fired boiler unit, which starts up according to the built-in operating program of the coal-fired boiler unit until the flue gas temperature and flue gas flow rate generated by the coal-fired boiler unit reach the calculated operating conditions and remain stable. The flue gas temperature in the front smoke well 202 and the rear smoke well 205 rises and stabilizes to the calculated operating conditions, thus completing the rated operating condition start-up of the coal-fired boiler unit.

[0073] At the same time, the central controller 101 sends a control signal to the heating tube to start the heating tube to heat the molten salt contact pipe and equipment (except for the molten salt pump), and heats the molten salt contact pipe and equipment to the lower limit heat storage temperature (390℃, 170℃) of the molten salt they are in contact with (first molten salt, second molten salt), and maintains a stable state.

[0074] The central controller 101 sends a start signal to the first molten salt pump 302 and the third molten salt pump 306, and starts the first molten salt pump 302 and the third molten salt pump 306 according to the calculated frequency. The first molten salt pump 302 sends quaternary nitrate into the first flue gas heat exchanger 303. After the quaternary nitrate is heated to 500°C, it is stored in the medium-temperature molten salt tank 304. The third molten salt pump 306 sends ternary chloride into the second flue gas heat exchanger 307 and the third flue gas heat exchanger 308 in sequence. After the ternary chloride is heated to 700°C, it is stored in the ultra-high temperature molten salt tank 309.

[0075] The central controller 101 sends start signals to the second molten salt pump 501 and the fourth molten salt pump 503 respectively. The second molten salt pump 501 and the fourth molten salt pump 503 start according to the calculated frequency. The second molten salt pump 501 draws 500℃ quaternary nitrate from the medium-temperature molten salt tank 304 and sends it into the molten salt side pipeline of the first water heat exchanger 502 to heat the first water heat exchanger 502 to a stable temperature before entering the low-temperature molten salt tank 301. The fourth molten salt pump 503 draws ternary chloride from the ultra-high temperature molten salt tank 309 and sends it into the molten salt side pipeline of the second water heat exchanger 504 to heat the second water heat exchanger 504 to a stable temperature before entering the high-temperature molten salt tank 305, until the molten salt flow rate and temperature at each location in the thermal power generation unit reach the calculated value and remain stable.

[0076] The central controller 101 sends a start signal to the feedwater pump 514. The feedwater pump 514 draws circulating water from the deaerator 513 according to the calculated flow rate and pressurizes it to 30MPa before sending it sequentially into the circulating water side pipes of the first water heat exchanger 502 and the second water heat exchanger 504. The circulating water is then heated to saturated steam at 274.9℃ and superheated steam at 680℃, respectively. The superheated steam enters the turbine unit 506 to do work and generate electricity. The turbine unit 506 discharges exhaust steam at 42℃ and 5.6kPa into the circulating water side pipes of the condenser 508 for cooling and condensation until the circulating water reaches a stable circulation state.

[0077] The central controller 101 sends a start signal to the first water pump 509. The first water pump 509 draws low-temperature cooling water from the low-temperature water tank 511 according to the calculated flow rate and sends it into the cooling water side pipeline of the condenser 508 to cool and condense the exhaust steam in the circulating water side pipeline of the condenser 508 into subcooled circulating water at 32°C and 5.6 kPa. The subcooled circulating water returns to the deaerator 513 for degassing treatment and then re-enters the feed water pump 514. The heated 38°C cooling water enters the high-temperature water tank 512 for storage until the flow rate, pressure and temperature of the circulating water and cooling water in the condenser 508 reach and remain stable.

[0078] The central controller 101 sends a start signal to the fifth molten salt pump. The fifth molten salt pump extracts 500°C quaternary nitrate from the medium-temperature molten salt tank 304 according to the calculated flow rate and sends it into the molten salt side pipeline of the third water heat exchanger 604 to preheat the third water heat exchanger 604 to a stable temperature. The quaternary nitrate, after cooling to the lower limit of the heat storage temperature, is returned to the low-temperature molten salt tank 301 until the temperature of the molten salt contact pipeline and equipment of the heating unit reaches and remains stable.

[0079] The central controller 101 sends start signals to the second water pump 510, the booster pump 603, and the water source heat pump 602, and sends opening signals to the sixth valve 606 and the seventh valve 607. According to the calculated flow rate, the second water pump 510 is started to draw high-temperature cooling water from the high-temperature water tank 512 and deliver it to the cooling water side pipe of the evaporator 6021 of the water source heat pump 602. Simultaneously, the booster pump 603 is started to draw 30°C low-temperature hot water from the return water network 601 and deliver it to the hot water side pipe of the condenser 6022 of the water source heat pump 602. The water source heat pump 602 is then started to draw heat from the high-temperature cooling water in the evaporator 6021. The condenser 6022 heats the 30°C hot water from the return water network 601. After being cooled to 20°C by the water source heat pump 602, the hot water is returned to the low-temperature water tank 511 for storage. The hot water absorbs heat and is heated to 65°C. It then enters the hot water supply side pipeline of the third water heat exchanger 604 via the booster pump 603. It is further heated to 490°C by quaternary nitrates and sent to the water supply network 609 as superheated steam. The quaternary nitrates are cooled to the lower limit heat storage temperature of 170°C and then stored in the low-temperature molten salt tank 301. This process continues until the flow rate and temperature of the quaternary nitrates, cooling water, and hot water in the heating unit reach the calculated values ​​and remain stable.

[0080] At this point, the system enters the operating state of generating electricity and supplying heat at rated load.

[0081] (ii) Regulation of power generation and heating load:

[0082] When changes are detected in the power generation signal transmitted by the power grid and the heating load signal transmitted by heat users, the power generation and heating load can be adjusted in the following ways:

[0083] The central controller 101 calculates the operating frequencies of the second molten salt pump 501, the fourth molten salt pump 503, the fifth molten salt pump, the feed water pump 514, the booster pump 603, the first water pump 509, the second water pump 510, and the water source heat pump 602 according to the changed power generation and heating load. The central controller 101 resets the operating frequencies of the second molten salt pump 501, the fourth molten salt pump 503, the feed water pump 514, and the first water pump 509, respectively. The second molten salt pump 501, the fourth molten salt pump 503, the feed water pump 514, and the first water pump 509 operate according to the newly set frequencies until the power generation unit reaches a new stable state and continues to operate, completing a rapid adjustment of the power generation.

[0084] The central controller 101 resets the operating frequencies of the fifth molten salt pump, the second water pump 510, the water source heat pump 602, and the booster pump 603. The fifth molten salt pump, the second water pump 510, the water source heat pump 602, and the booster pump 603 operate at the newly set frequencies until the heating unit reaches a stable state and continues to operate, thus completing a rapid adjustment of the heating load.

[0085] By repeating the above steps, the central controller 101 can quickly adjust the power generation and heating load.

[0086] (III) Liquid level control in the molten salt tank:

[0087] The central controller 101 cyclically detects the molten salt levels in the low-temperature molten salt tank 301 and the high-temperature molten salt tank 305 through the first liquid level sensor 310 and the second liquid level sensor 311, respectively. When:

[0088] (1) When the central controller 101 detects that the quaternary nitrate level in the cryogenic molten salt tank 301 has dropped to 20%, the central controller 101 sends signals to the first molten salt pump 302 and the coal-fired boiler unit respectively to reduce the operating frequency and reduce the fuel delivery speed, until the flow rate of the first molten salt pump 302 is reduced to close to the sum of the flow rates of the second molten salt pump 501 and the fifth molten salt pump, ensuring that the quaternary nitrate level in the cryogenic molten salt tank 301 is not lower than 10% of the total molten salt depth. And when the central controller 101 detects that the quaternary nitrate level in the cryogenic molten salt tank 301 has risen to 80%, the central controller 101 sends signals to the first molten salt pump 302 and the coal-fired boiler respectively to increase the operating frequency and fuel delivery speed, until the flow rate of the first molten salt pump 302 is increased to close to the sum of the flow rates of the second molten salt pump 501 and the fifth molten salt pump, ensuring that the quaternary nitrate level in the cryogenic molten salt tank 301 is not higher than 90%.

[0089] (2) When the central controller 101 detects that the ternary chloride level in the high-temperature molten salt tank 305 has dropped to 20%, the central controller 101 sends signals to the third molten salt pump 306 and the coal-fired boiler to reduce the operating frequency and fuel delivery speed, respectively, until the flow rate of the third molten salt pump 306 is reduced to near the flow rate of the fourth molten salt pump 503, ensuring that the ternary chloride level in the high-temperature molten salt tank 305 is not lower than 10%. And, when the central controller 101 detects that the ternary chloride level in the high-temperature molten salt tank 305 has risen to 80%, the central controller 101 sends signals to the third molten salt pump 306 and the coal-fired boiler to increase the operating frequency and fuel delivery speed, respectively, until the flow rate of the third molten salt pump 306 is increased to near the flow rate of the fourth molten salt pump 503, ensuring that the ternary chloride level in the high-temperature molten salt tank 305 is not higher than 90%.

[0090] (iv) Shutdown of coal-fired boiler units and molten salt thermal storage units:

[0091] When the coal-fired boiler unit / molten salt thermal storage unit needs to be shut down for maintenance or other reasons, if the maintenance personnel press the "Coal-fired Boiler Shutdown" button, the central controller 101 will send shutdown signals to the first molten salt pump 302 and the third molten salt pump 306 respectively, and send opening signals to the first valve 401, the second valve 402, the fourth valve 403, and the ninth valve 404 respectively. Under the influence of gravity and nitrogen pressure, the ternary chloride in the second flue gas heat exchanger 307 and the third flue gas heat exchanger 308 will be completely discharged into the first storage tank 406 through the first valve 401, and the quaternary nitrate in the first flue gas heat exchanger 303 will be completely discharged into the second storage tank 407 through the second valve 402. Additionally, the central controller 101 will send start signals to the sixth molten salt pump 408 and the seventh molten salt pump 409 respectively, discharging the ternary chloride in the first storage tank 406 and the quaternary nitrate in the second storage tank 407 into the high-temperature molten salt tank 305 and the low-temperature molten salt tank 301 respectively. In addition, the central controller 101 sends signals to the coal-fired boiler unit to stop coal supply, primary air supply, and secondary air supply, and the fuel in the furnace 201 gradually shuts off and cools to ambient temperature. In this way, the coal-fired boiler unit and the molten salt thermal storage unit can be shut down before maintenance, preparing for maintenance of the coal-fired boiler unit and the molten salt thermal storage unit.

[0092] (v) Shutdown of the power generation unit:

[0093] When the power generation unit needs to be shut down, if the maintenance personnel press the "Power Generation Unit Shutdown" button, the central controller 101 sends a shutdown signal to the feed water pump 514 and an opening signal to the third valve 505. The circulating water and steam in the power generation unit are all discharged into the deaerator 513 under the action of gravity and nitrogen pressure. (2) The central controller 101 sends shutdown signals to the second molten salt pump 501 and the fourth molten salt pump 503 respectively. The quaternary nitrates in the power generation unit are all discharged into the low temperature molten salt tank 301 and the medium temperature molten salt tank 304 respectively under the action of gravity; the ternary chlorides in the power generation unit are all discharged into the high temperature molten salt tank 305 and the ultra-high temperature molten salt tank 309 respectively under the action of gravity. If the temperature and pressure of the power generation unit's thermal system drop to the ambient temperature and atmospheric pressure, the power generation unit will be shut down and maintenance work can be carried out.

[0094] (vi) Shutdown of heating unit:

[0095] When the heating unit needs to be shut down, maintenance personnel can press the "Heating Unit Shutdown" button. Correspondingly, the central controller 101 sends a shutdown signal to the booster pump 603, a shut-off signal to the sixth valve 606 and the seventh valve 607, and an opening signal to the fifth valve 605 and the eighth valve 608. The hot water and steam in the heating unit are then discharged into the high-temperature water tank 512 under gravity. The central controller 101 sends a shutdown signal to the fifth molten salt pump, and the quaternary nitrate in the heating unit is discharged into the low-temperature molten salt tank 301 and the medium-temperature molten salt tank 304 under gravity. After all the quaternary nitrate, hot water, and steam in the heating unit have been emptied, and the temperature and pressure of the thermal system have dropped to ambient temperature and pressure, the heating unit has shut down and maintenance work can be carried out.

[0096] In this example, the coal-fired boiler unit is a 660MW coal-fired unit, and the coal-fired boiler adopts a circulating fluidized bed boiler. Lignite is crushed into 6-10mm particles, and limestone with a particle size of 0.5mm and a purity of 85% is mixed evenly in a mass ratio of 5:1 to produce the boiler fuel. Softened water that has undergone chemical treatment is selected for circulating water.

[0097] The first flue gas heat exchanger 303 is made of 304 stainless steel, with an operating temperature of 600℃ and a nominal pressure of 2.0MPa. The second flue gas heat exchanger 307 and the third flue gas heat exchanger 308 are made of 316L stainless steel, with an operating temperature of 1000℃ and a nominal pressure of 2MPa. The first, second, and third water heat exchangers are all shell-and-tube type. The first and second water heat exchangers have a nominal pressure of 35MPa and operating temperatures of 550℃ and 750℃ respectively. The third water heat exchanger 604 has a nominal pressure of 10MPa and an operating temperature of 550℃. The first and third water heat exchangers are made of 304 stainless steel, while the second water heat exchanger 504 is made of 316L stainless steel.

[0098] The first through seventh molten salt pumps are all submersible pumps with variable frequency control. Among them, the first molten salt pump 302, the seventh molten salt pump 409, and the low-temperature molten salt tank 301 are made of carbon steel and operate at a temperature of 170℃. The second molten salt pump 501, the third molten salt pump 306, the fifth molten salt pump 610, the sixth molten salt pump 408, the medium-temperature molten salt tank 304, and the high-temperature molten salt tank 305 are made of 304 stainless steel and operate at a temperature of 550℃. The fourth molten salt pump 503 and the ultra-high temperature molten salt tank 309 are made of 316L stainless steel and operate at a temperature of 750℃. The first valve 401 and the ninth valve 404 are made of 316L stainless steel, with an operating temperature of 750℃ and a nominal pressure of 2MPa. The second valve 402 and the fourth valve 403 are made of 304 stainless steel, with an operating temperature of 550℃ and a nominal pressure of 2MPa. The fifth valve 605 and the sixth valve 606 are made of carbon steel, with an operating temperature of 100℃ and a nominal pressure of 1.0MPa. The third valve 505 is made of 316L stainless steel, with an operating temperature of 700℃ and a nominal pressure of 35MPa. The seventh valve 607 and the eighth valve 608 are made of 304 stainless steel, with an operating temperature of 500℃ and a nominal pressure of 10MPa. The feed water pump 514 and the booster pump 603 are multistage centrifugal pumps. The feed water pump 514 has an operating temperature of 200℃, a head of 3000 meters, and a nominal pressure of 35MPa. The booster pump 603 has an operating temperature of 100℃, a head of 100 meters, and a nominal pressure of 3MPa. Both the first and second water pumps are centrifugal pumps, operating at 60℃, with a head of 30 meters and a nominal pressure of 1MPa. The water source heat pump 602 has frequency regulation capabilities and a rated heating temperature of 65℃. The steam turbine unit 506 is equipped with its own water delivery system and uses a multi-stage centrifugal turbine unit, with an exhaust back pressure of 5kPa and an exhaust temperature of 42℃.

[0099] The external walls of the molten salt pipes, low-temperature molten salt tanks 301, medium-temperature molten salt tanks 304, high-temperature molten salt tanks 305, ultra-high-temperature molten salt tanks 309, first storage tank 406, second storage tank 407, first valve 401, second valve 402, fourth valve 403, first water heat exchanger 502, second water heat exchanger 504, and third water heat exchanger 604 of the coal-fired boiler unit are all tightly wrapped with heating tubes to heat the wall surface temperature and maintain it at the lower limit of the heat storage temperature for internal flow or contact with molten salt. A 300mm thick composite silicate insulation layer is wrapped around the heating tubes. The external walls of the circulating water pipes, cooling water pipes, hot water supply pipes, low-temperature water tank 511, high-temperature water tank 512, condenser 508, deaerator 513, turbine unit 506, third valve 505, fifth valve 605, sixth valve 606, seventh valve 607, and eighth valve 608 are respectively wrapped with insulation layers of a thickness that meets national standards.

[0100] Obviously, the structural form, model, component ratio, temperature properties, etc. in the above embodiments can be flexibly adjusted according to actual needs.

[0101] Based on the preferred embodiments of the present invention, the beneficial effects that can be achieved include:

[0102] (1) The peak-shaving system achieves complete decoupling of power generation and heating. Specifically, coal-fired units can independently and flexibly adjust power generation and heating load within the range of 0% to 100%. Therefore, it can meet the grid's demand for flexible and deep peak shaving of coal-fired units according to actual electricity and heat demand. Among them, under the premise of using high-temperature molten salt for two-stage thermal storage, such as the first molten salt with ultra-high thermal storage temperature (700~1000℃), it is easier to achieve high-temperature supercritical power generation of water vapor at 700℃ and above, which can improve the power generation efficiency of coal-fired units to no less than 60%, and the energy-saving and carbon reduction effects are obvious.

[0103] (2) When coal-fired units are used for peak shaving of power generation and heating, the coal-fired boiler unit can still operate under rated conditions or only need to adjust the heating load within a small range, which greatly improves the conversion rate from coal to heat. Correspondingly, the coal consumption and carbon emissions per unit of heat production are greatly reduced, and the coal consumption and carbon emissions for the same power generation and heat supply are also greatly reduced. The power generation cost, heating cost and system operation and maintenance cost are reduced simultaneously. It is especially suitable for the construction, expansion and renovation of coal-fired units. The speed of power generation and heating load adjustment is much higher than that of traditional coal-fired units with thermal storage peak shaving.

[0104] (3) Using molten salt as the heat transfer medium in the coal-fired boiler unit, the flue gas heat exchanger in the boiler is in a near-atmospheric pressure state, which improves the safety factor of the coal-fired boiler and effectively avoids the problem of heat transfer deterioration in the heat exchanger of the coal-fired boiler unit. In addition, the molten salt and water / steam in the power generation unit can achieve relatively uniform heat transfer, which completely avoids the safety accidents such as tube rupture caused by non-uniform heat transfer of water / steam on the cold wall in the traditional coal-fired boiler process of coal-fired units, and significantly reduces the safety hazards and equipment failure rate of coal-fired units.

[0105] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A direct-drive high-temperature molten salt two-stage thermal storage power generation, heating, and peak-shaving system for a coal-fired boiler, characterized in that, The system includes: A coal-fired boiler unit, comprising a coal-fired boiler capable of generating heat-carrying flue gas and flue gas ducts that allow flue gas to flow. A molten salt thermal storage unit includes a molten salt storage vessel capable of holding molten salt and a molten salt pipe that allows the molten salt to flow through. The molten salt can exchange heat with the flue gas in the flue gas pipe to store heat. One or more power generation units are used to generate electricity using a portion of the heat stored in the molten salt thermal storage unit. In the case of multiple power generation units, the multiple power generation units can be adjusted independently of each other. A heating unit that uses a portion of the heat stored in a molten salt thermal storage unit for heating.

2. The direct-drive high-temperature molten salt two-stage thermal storage power generation and heating peak-shaving system for coal-fired boilers according to claim 1, characterized in that, The molten salt thermal storage unit includes: (1) A molten salt tank group, comprising a high-temperature molten salt tank, an ultra-high-temperature molten salt tank, a medium-temperature molten salt tank and a low-temperature molten salt tank; wherein the high-temperature molten salt tank contains a first molten salt and the low-temperature molten salt tank contains a second molten salt; (2) A heat exchanger assembly, comprising: The first flue gas heat exchanger is installed in the rear flue gas shaft of the flue gas duct; The second flue gas heat exchanger is installed on the wall or near the wall of the flue gas duct's front flue gas shaft and / or the furnace of the flue gas coal-fired boiler. The third flue gas heat exchanger is installed in the front flue gas shaft of the flue gas duct; The first molten salt from the high-temperature molten salt tank can reach the ultra-high temperature molten salt tank after exchanging heat with the second flue gas heat exchanger and the third flue gas heat exchanger in sequence. The second molten salt from the low-temperature molten salt tank exchanges heat with the first flue gas heat exchanger and then reaches the medium-temperature molten salt tank.

3. The direct-drive high-temperature molten salt two-stage thermal storage power generation and heating peak-shaving system for coal-fired boilers according to claim 2, characterized in that, The heat exchanger assembly also includes: The first water heat exchanger allows the second molten salt from the medium-temperature molten salt tank to reach the low-temperature molten salt tank after sequentially exchanging heat with the first water heat exchanger. The second water heat exchanger allows the molten salt from the ultra-high temperature molten salt tank to reach the high temperature molten salt tank after heat exchange with the first molten salt in the ultra-high temperature molten salt tank; and The second molten salt from the intermediate-temperature molten salt tank can reach the low-temperature molten salt tank after exchanging heat with the third water heat exchanger. The first water heat exchanger and the second water heat exchanger also constitute the power generation unit, and the third water heat exchanger also constitutes the heating unit.

4. The direct-drive high-temperature molten salt two-stage thermal storage power generation and heating peak-shaving system for coal-fired boilers according to claim 2, characterized in that, The first molten salt is a mixture of nitrates, carbonates, fluorides, chlorides, or molten metal; and / or The second molten salt is a mixture of nitrates, carbonates, fluorides, or chlorides.

5. A control method for a direct-drive high-temperature molten salt thermal energy storage power generation and heating peak-shaving system for a coal-fired boiler as described in claim 3, characterized in that, The system includes a first molten salt pump, and the control method includes: The first molten salt pump is operated so that: After the molten salt from the low-temperature molten salt tank undergoes heat exchange in the first flue gas heat exchanger, it reaches the medium-temperature molten salt tank. And / or The system includes a third molten salt pump, and the control method includes: The third molten salt pump is operated so as to: The molten salt from the high-temperature molten salt tank undergoes heat exchange in the second flue gas heat exchanger and the third flue gas heat exchanger in sequence before reaching the ultra-high temperature molten salt tank.

6. The control method according to claim 5, characterized in that, The system includes a second molten salt pump and a fourth molten salt pump, and the control method includes: The second molten salt pump is operated so that: After the molten salt from the medium-temperature molten salt tank undergoes heat exchange in the first water heat exchanger that constitutes the power generation unit, it reaches the low-temperature molten salt tank. And / or The fourth molten salt pump is operated so that: Molten salt from the ultra-high temperature molten salt tank undergoes heat exchange in the second water heat exchanger that constitutes the power generation unit before reaching the high temperature molten salt tank.

7. The control method according to claim 5, characterized in that, The system includes a fifth molten salt pump, and the control method includes: The fifth molten salt pump is operated so as to: After the molten salt from the medium-temperature molten salt tank undergoes heat exchange in the third water heat exchanger that constitutes the heating unit, it reaches the low-temperature molten salt tank.

8. The control method according to claim 6, characterized in that, The control method includes: Detect the liquid levels of the first molten salt in the high-temperature molten salt tank and / or the second molten salt in the low-temperature molten salt tank; Based on the test results, the operating parameters of the first molten salt pump and the third molten salt pump are adjusted. This step includes: When the level of the first molten salt in the high-temperature molten salt tank drops to the first set level, the operating parameters of the third molten salt pump are reduced and / or the fuel delivery speed of the coal-fired boiler unit is reduced to ensure that the level of the first molten salt in the high-temperature molten salt tank is not lower than the lower limit of the total molten salt depth. And / or When the level of the first molten salt in the high-temperature molten salt tank rises to the second set level, the operating parameters of the third molten salt pump are increased and / or the fuel delivery speed of the coal-fired boiler unit is reduced to ensure that the level of the first molten salt in the high-temperature molten salt tank is not higher than the upper limit of the total molten salt depth. And / or When the level of the second molten salt in the cryogenic molten salt tank drops to the third set level, the operating parameters of the first molten salt pump and / or the fuel delivery speed of the coal-fired boiler unit are reduced to ensure that the level of molten salt in the cryogenic molten salt tank is not lower than the lower limit of the total molten salt depth. And / or When the level of the second molten salt in the cryogenic molten salt tank rises to the fourth set level, the operating parameters of the first molten salt pump and / or the fuel delivery speed of the coal-fired boiler unit are increased to ensure that the level of molten salt in the cryogenic molten salt tank does not exceed the upper limit of the total molten salt depth.

9. The control method according to claim 8, characterized in that, The system also includes a salt removal unit, and the control method includes: In cases where it is necessary to shut down the coal-fired boiler unit, the first molten salt pump shall be stopped, and... The salt removal unit is in a salt removal state.

10. The control method according to claim 9, characterized in that, The salt removal unit includes: The first salt discharge assembly includes a first valve and a first storage tank. Molten salt in the molten salt pipe of the second flue gas heat exchanger and / or the second flue gas heat exchanger can reach the first storage tank via the first valve. The first storage tank can be connected to the high-temperature molten salt tank. The second salt discharge assembly includes a second valve and a second storage tank. Molten salt in the molten salt pipe of the first flue gas heat exchanger can reach the second storage tank via the second valve. The second storage tank can be connected to the cryogenic molten salt tank. The phrase "the salt removal unit is in a salt-removing state" includes: Open the first valve so that: Molten salt in the second flue gas heat exchanger and / or the third flue gas heat exchanger is discharged into the first storage tank through the first valve; and / or Open the second valve so that: The molten salt in the first flue gas heat exchanger is discharged into the second storage tank through the second valve.

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