Flexible and safe coal-fired boiler starting system and operation method

Abstract

The invention belongs to the technical field of coal-fired boilers, and discloses a coal-fired boiler flexible and safe starting system and an operation method.In the shutdown and load reduction process of the boiler, heat is stored in fused salt and steam in a cascade mode through bypass main steam flow, and the working medium flow of a high-temperature heating surface is increased so that the working medium cooling capacity of the high-temperature heating surface can be guaranteed; the bypass separator produces water to store a high-temperature working medium and quickly reduce the load, so that flexible and safe shutdown is realized; in the starting and load increasing process, through multi-medium energy storage cross-space-time regulation and control, the output power is rapidly increased, a steam-water working medium circulation path is reconstructed, the water cooling wall working medium flow is increased, multi-medium cascade heating water supply is adopted, under-enthalpy of a working medium at an inlet of the water cooling wall is rapidly reduced on the premise that safe operation of the water cooling wall is guaranteed, and flexible and safe starting is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coal-fired boilers, and particularly relates to a flexible and safe starting system for a coal-fired boiler and a running method. BACKGROUND

[0002] With the accelerating pace of global energy structure transformation towards green and low carbon, the installed capacity of renewable energy such as solar and wind energy is showing explosive growth. However, the volatility, intermittency and unpredictability of new energy itself lead to the dramatic fluctuation of its output power with the change of weather conditions and day and night, which brings great challenges to the balance regulation and safe and stable operation of the power system. In order to ensure the safety of the power grid, the traditional coal-fired generating unit as the basic regulation resource must bear the frequent start-stop and peak regulation tasks to cope with the uncertainty of new energy output and the dynamic change of system load. However, compared with the stable working condition under the benchmark load, the running flexibility of the coal-fired boiler is severely limited under the non-conventional working condition of frequent start-stop, deep peak regulation and low load operation. On the one hand, during the start-stop process, the equipment needs to undergo repeated thermal expansion and cold contraction, and the boiler heating surface metal is frequently subjected to alternating stress, which aggravates the thermal fatigue, creep and aging of the metal, significantly shortening the service life of the key components. On the other hand, during the low load operation stage, due to the significant reduction of the main steam flow and the circulating water flow, the cooling capacity of the boiler body and the auxiliary equipment is significantly weakened, and the overheat easily occurs in some high-temperature parts, and even the safety hazards such as local dry burning and deformation occur. Especially during the rapid start-stop and load change of the boiler, the dramatic fluctuation of the working fluid velocity aggravates the temperature difference stress and flow erosion risk, which easily induces serious faults such as boiler leakage and pipe explosion.

[0003] In the prior art, in view of the above problems, an external heat storage device is gradually explored to alleviate the energy impact of the boiler start-stop. By adding a multi-temperature zone energy storage device such as molten salt, steam or feed water outside the boiler system, the excess heat energy can be stored in the form of high temperature during the boiler load reduction or shutdown process, and the energy can be released back to the boiler during the subsequent boiler start-up and load increase stage, realizing the time and space transfer and smooth output of energy. This helps to reduce the temperature difference stress of the boiler during the start-stop and peak regulation process, reduce the number of cold and hot impact, and delay the fatigue failure of the key metal components. At the same time, the heat storage system can cooperate with the state monitoring and active safety protection technology of the boiler equipment, intelligently predict the equipment health status through real-time acquisition and analysis of the multi-source monitoring data such as boiler wall temperature, stress and vibration, actively intervene in the high-risk working condition, and improve the safety and reliability of the boiler start-stop and peak regulation process. However, the coupling of the multi-temperature zone heat storage device and the boiler system and its dynamic control strategy are not mature, and there are still many technical bottlenecks in energy transfer efficiency, system response speed and safety protection mechanism. In addition, how to efficiently coordinate the heat storage system and the grid dispatching demand to ensure the optimal energy management and fault warning of the boiler and its auxiliary equipment during the dynamic start-stop process is also a key technical problem to be solved. SUMMARY

[0004] The purpose of the present invention is to overcome the problems of insufficient flexibility and difficulty in ensuring safety in starting and stopping peak-shaving of the above-mentioned coal-fired boilers, and to provide a flexible and safe starting system and operation method for coal-fired boilers.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a flexible and safe starting system for a coal-fired boiler, comprising a coal-fired boiler system, a heat storage and release circuit, and a safety monitoring system; The coal-fired boiler system includes a boiler, in which a high-temperature heating surface pipeline, an economizer pipeline and a water-cooled wall pipeline are provided. The boiler feed water flows through the economizer pipeline and the water-cooled wall pipeline into the steam-water separator. The high-temperature steam generated by the steam-water separator enters the high-temperature heating surface pipeline. The high-temperature water generated by the steam-water separator is connected to a first water storage tank on one path and to a second water storage tank on another path. The outlet of the first water storage tank is connected to the water-cooled wall pipeline, the outlet of the economizer pipeline is connected to the water-cooled wall pipeline, the steam at the outlet of the high-temperature heating surface pipeline leaves the boiler on one path, the second path is connected to the steam-molten salt heat exchanger via the main steam bypass, the steam-molten salt heat exchanger is connected to the second water storage tank, the third path is connected to the second water storage tank, the working medium outlet of the second water storage tank is connected to the steam-molten salt heat exchanger, and the working medium heated by the steam-molten salt heat exchanger leaves the boiler; The heat storage circuit includes a cold tank, the outlet of the cold tank is connected to the molten salt inlet of the steam-molten salt heat exchanger, and the outlet of the hot tank is connected to the molten salt inlet of the steam-molten salt heat exchanger. The molten salt outlet of the steam-molten salt heat exchanger enters the hot tank in the first route, is connected to the cold tank in the second route, and is connected to the molten salt-feed water heat exchanger in the third route. The molten salt-feed water heat exchanger is connected to the cold tank, and the outlet feed water of the molten salt-feed water heat exchanger enters the economizer pipeline of the boiler; The safety monitoring system includes: The high-temperature heating surface safety status acquisition module is used to collect the working fluid temperature and pressure of the high-temperature heating surface pipeline in the boiler and transmit it to the high-temperature heating surface active safety assurance instruction execution module; The high-temperature heating surface active safety assurance instruction execution module is used to control the temperature and pressure of the working fluid in the high-temperature heating surface pipeline according to the data collected by the high-temperature heating surface safety status acquisition module; The water-wall safety status acquisition module is used to collect the wall temperature operating data of the water-wall pipeline in the boiler and transmit it to the water-wall active safety assurance instruction execution module; The water-cooled wall active safety assurance instruction execution module is used to control the wall temperature operation data of the water-cooled wall pipeline in the boiler according to the data collected by the water-cooled wall safety status collection module.

[0006] A further improvement of the present invention is that a first water storage valve is provided between the steam-water separator and the first water storage tank, and a second water storage valve is provided between the steam-water separator and the second water storage tank.

[0007] The further improvement of the present application is that a recirculation pump and a recirculation valve are arranged on the connecting pipeline of the first water storage tank and the water-cooled wall pipeline.

[0008] The further improvement of the present application is that a main steam regulating valve is arranged on the pipeline of the high-temperature heating surface pipeline leaving the boiler, a first regulating valve is arranged on the pipeline of the high-temperature heating surface pipeline and the steam-salt heat exchanger, and a main steam storage valve is arranged on the connecting pipeline of the high-temperature heating surface pipeline and the second water storage tank.

[0009] The further improvement of the present application is that a main steam bypass second regulating valve is arranged on the connecting pipeline of the steam-salt heat exchanger and the second water storage tank, a second water storage tank water supply valve is arranged on the connecting pipeline of the second water storage tank and the steam-salt heat exchanger, and a steam-salt heat exchanger steam regulating valve is arranged on the pipeline of the steam-salt heat exchanger leaving the boiler.

[0010] The further improvement of the present application is that a cold tank outlet pump and a cold tank outlet regulating valve are arranged on the connecting pipeline of the cold tank and the steam-salt heat exchanger.

[0011] The further improvement of the present application is that a hot tank outlet pump and a hot tank outlet regulating valve are arranged on the connecting pipeline of the hot tank and the steam-salt heat exchanger.

[0012] The further improvement of the present application is that a steam-salt heat exchanger first salt regulating valve is arranged on the connecting pipeline of the steam-salt heat exchanger and the cold tank, and a steam-salt heat exchanger second salt regulating valve is arranged on the connecting pipeline of the steam-salt heat exchanger and the salt-feedwater heat exchanger.

[0013] In the second aspect, the present application provides a running method of a flexible and safe starting system of a coal-fired boiler, which comprises the following steps: In the process of stopping and reducing the load of the boiler, the first water storage valve and the recirculation valve are closed, the second water storage tank water supply valve and the steam-salt heat exchanger steam regulating valve are closed, the hot tank outlet regulating valve, the steam-salt heat exchanger first salt regulating valve and the steam-salt heat exchanger second salt regulating valve are closed; the process of stopping and reducing the load of the boiler system is divided into three stages, when being in the first stage, the second water valve and the main steam storage valve are closed, the cold tank outlet regulating valve is opened, and the main steam regulating valve, the main steam bypass second regulating valve and the main steam bypass first regulating valve are adjusted; when being in the second stage, the main steam storage valve is opened, the main steam bypass second regulating valve and the main steam bypass first regulating valve are closed, the cold tank outlet regulating valve is closed, and the main steam storage valve and the main steam regulating valve are adjusted; when being in the third stage, the main steam regulating valve is closed, and the second water valve is opened. During the boiler startup and load increase process, the second water storage valve is closed, the second main steam bypass regulating valve, the first main steam bypass regulating valve and the main steam storage valve are closed, and the cold tank outlet regulating valve is closed. The boiler system startup and load increase process is divided into two stages. When in stage one, the recirculation valve is closed, the first water storage valve is opened, the main steam regulating valve is closed, the water supply valve of the second water storage tank and the steam-molten salt heat exchanger steam regulating valve are opened, and the hot tank outlet regulating valve is opened. In the initial temperature and pressure increase stage of startup, the high-temperature working medium generated by the separator is stored in the first water storage tank, and the high-temperature molten salt heats the high-temperature water in the second water storage tank to replace the main steam. The first molten salt regulating valve and the second molten salt regulating valve of the steam-molten salt heat exchanger are adjusted; when in stage two, the recirculation valve is opened, the main steam regulating valve is opened, the recirculation valve, the first molten salt regulating valve and the second molten salt regulating valve of the steam-molten salt heat exchanger are adjusted, and the main steam regulating valve and the water supply valve of the second water storage tank and the steam-molten salt heat exchanger steam regulating valve are adjusted.

[0014] A further improvement of the present invention is that, for the boiler shutdown and load reduction process, when the main steam temperature is higher than 370°C, it is in stage one; when the main steam temperature is lower than 370°C and higher than 250°C, it is in stage two; when the main steam temperature is lower than 250°C, it is in stage three; During the boiler startup and load increase process, when the steam-water separator temperature is lower than 250°C, it is in stage one; when the steam-water separator temperature is higher than 250°C, it is in stage two.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention bypasses the main steam flow to store heat in molten salt and steam during boiler shutdown and load reduction, increases the flow of high-temperature heating surface working fluid to ensure the cooling capacity of high-temperature heating surface working fluid, and produces water in the bypass separator to store high-temperature working fluid and quickly reduce the load, thereby realizing flexible and safe shutdown; the present invention quickly increases the output power through multi-media energy storage and spatial and temporal control during startup and load increase, reconstructs the steam-water working fluid flow path to increase the flow of water-cooled wall working fluid, adopts multi-media cascade heating feed water, and quickly reduces the working fluid under-enthalpy at the water-cooled wall inlet while ensuring the safe operation of the water-cooled wall, thereby realizing flexible and safe startup; the present invention configures a heat storage and release circuit and a safety monitoring system in the coal-fired boiler system, couples the energy cascade utilization of multi-temperature zone energy storage systems such as molten salt / steam / feed water in the storage and release process, integrates boiler equipment safety status monitoring and active safety assurance technology, can realize flexible and safe startup of coal-fired boilers, and improves the start-stop peak-shaving capability of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a system diagram of the present invention; DETAILED DESCRIPTION For further understanding of the present application, the following will make a detailed description of the present application in combination with the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for the purpose of explaining the present application but not for limiting the present application.

[0017] Referring to Figure 1 , including coal-fired boiler system, storage and release heat circuit and safety monitoring system.

[0018] The coal-fired boiler system comprises a boiler 1, a first water storage valve 6, a first water storage tank 7, a recirculation pump 8, a recirculation valve 9, a second water storage valve 10, a second water storage tank 11, a main steam regulating valve 12, a main steam bypass second regulating valve 13, a main steam bypass first regulating valve 14, a main steam storage valve 16, a second water storage tank water supply valve 17, wherein the boiler 1 has a high-temperature heating surface pipeline 2, an economizer pipeline 3, a water wall pipeline 4, and a steam-water separator 5; the feed water of the boiler 1 flows through the economizer pipeline 3 and the water wall pipeline 4 into the steam-water separator 5, the high-temperature steam generated by the steam-water separator 5 enters the high-temperature heating surface pipeline 2, the high-temperature water generated by the steam-water separator is connected to the first water storage tank 7 through the first water storage valve 6 in one way and connected to the second water storage tank 11 through the second water storage valve 10 in another way, the outlet of the first water storage tank 7 is connected to the outlet of the economizer pipeline 3 through the recirculation pump 8 and the recirculation valve 9, the steam at the outlet of the high-temperature heating surface pipeline 2 flows through the main steam regulating valve 12 to leave the boiler 1 in one way, flows through the main steam bypass first regulating valve 14, the steam-salt heat exchanger 15 and the main steam bypass second regulating valve 13 to enter the second water storage tank 11 in another way, and flows through the main steam storage valve 16 to directly enter the second water storage tank 11 in another way, the working medium at the outlet of the second water storage tank 11 flows through the second water storage tank water supply valve 17, is heated by the steam-salt heat exchanger 15, and then flows through the steam-salt heat exchanger steam regulating valve 18 to leave the boiler 1; The heat storage circuit comprises the steam-salt heat exchanger 15, a cold tank 19, a cold tank outlet pump 20, a cold tank outlet regulating valve 21, a hot tank 22, a hot tank outlet pump 23, a hot tank outlet regulating valve 24, a steam-salt heat exchanger steam regulating valve 18, a steam-salt heat exchanger first salt regulating valve 25, a steam-salt heat exchanger second salt regulating valve 26, a salt-feed water heat exchanger 27, and pipelines connecting various devices; the molten salt at the outlet of the cold tank 19 is connected to the molten salt inlet of the steam-salt heat exchanger 15 through the cold tank outlet pump 20 and the cold tank outlet regulating valve 21, the molten salt at the outlet of the hot tank 22 is connected to the molten salt inlet of the steam-salt heat exchanger 15 through the hot tank outlet pump 23 and the hot tank outlet regulating valve 24, the molten salt outlet of the steam-salt heat exchanger 15 enters the hot tank 22 in one way, enters the cold tank 19 through the steam-salt heat exchanger first salt regulating valve 25 in another way, and flows through the steam-salt heat exchanger second salt regulating valve 26 and the salt-feed water heat exchanger 27 to return to the cold tank 19 in another way, the feed water at the outlet of the salt-feed water heat exchanger 27 enters the economizer pipeline 3 of the boiler 1; The safety monitoring system comprises a high-temperature heating surface safety state acquisition module 28, a high-temperature heating surface active safety guarantee instruction execution module 29, a water wall safety state acquisition module 30, and a water wall active safety guarantee instruction execution module 31. The high-temperature heating surface safety state acquisition module 28 and the water wall safety state acquisition module 30 are responsible for collecting the working medium temperature and pressure and wall temperature in the high-temperature heating surface pipeline 2 and the water wall pipeline 4 of the boiler 1 respectively, and transmitting the operation data to the high-temperature heating surface active safety guarantee instruction execution module 29 and the water wall active safety guarantee instruction execution module 31 for information processing and active intervention of the operation parameters.

[0019] The operation method of the boiler shutdown and load reduction process of the application: close the first water storage valve 6 and the recirculation valve 9, close the second water storage tank water supply valve 17 and the steam-salt heat exchanger steam regulating valve 18, close the hot tank outlet regulating valve 24, the steam-salt heat exchanger first salt regulating valve 25, and the steam-salt heat exchanger second salt regulating valve 26; the boiler system shutdown and load reduction process is divided into three stages: when the main steam temperature is higher than 370°C, it is in stage one; when the main steam temperature is lower than 370°C and higher than 250°C, it is in stage two; when the main steam temperature is lower than 250°C, it is in stage three.

[0020] When in the shutdown and load reduction stage one, close the second water storage valve 10 and the main steam storage valve 16, open the cold tank outlet regulating valve 21, adjust the main steam regulating valve 12, the main steam bypass second regulating valve 13 and the main steam bypass first regulating valve 14, and the adjustment target is to ensure that the boiler outlet steam flow meets the demand of the load reduction rate and to store the high-temperature steam heat of the boiler in the molten salt, at this time, the high-temperature heating surface working medium flow is large, which ensures sufficient cooling capacity to guarantee the safe operation of the high-temperature heating surface.

[0021] When in the shutdown and load reduction stage two, open the main steam storage valve 16, close the main steam bypass second regulating valve 13 and the main steam bypass first regulating valve 14, close the cold tank outlet regulating valve 21, adjust the main steam storage valve 16 and the main steam regulating valve 12, and the adjustment target is to ensure that the boiler outlet steam flow meets the demand of the load reduction rate and to store the high-temperature steam heat of the boiler in the second water storage tank 11, at this time, the high-temperature heating surface outlet steam temperature and flow are reduced, and the molten salt efficiency is reduced, and the direct steam storage method is adopted.

[0022] When in the shutdown and load reduction stage three, close the main steam regulating valve 12 and open the second water storage valve 10, at this time, the boiler system no longer produces steam, and the steam-water separator produces steam and water, which flows through the high-temperature heating surface to guarantee the safe shutdown of the high-temperature heating surface.

[0023] The operating method of the present invention during the boiler startup and load increase process includes closing the second water storage valve 10, closing the second main steam bypass regulating valve 13, the first main steam bypass regulating valve 14, and the main steam storage valve 16, and closing the cold tank outlet regulating valve 21. The boiler system startup and load increase process is divided into two stages. When the steam-water separator temperature is lower than 250°C, it is in stage one, and when the steam-water separator temperature is higher than 250°C, it is in stage two.

[0024] When in the first stage of startup and load increase, close the recirculation valve 9, open the first water storage valve 6, close the main steam regulating valve 12, open the second water storage tank water supply valve 17 and the steam-molten salt heat exchanger steam regulating valve 18, open the hot tank outlet regulating valve 24, and in the initial stage of startup, store the high-temperature working medium generated by the separator in the first water storage tank 7, and the high-temperature molten salt heats the high-temperature water in the second water storage tank 11 to replace the main steam. Regulate the first molten salt regulating valve 25 of the steam-molten salt heat exchanger and the second molten salt regulating valve 26 of the steam-molten salt heat exchanger. The regulation goal is to use the waste heat after the high-temperature molten salt heats the high-temperature water to continue to heat the feed water, so as to realize the cascade utilization of energy. The regulation limit is to ensure that the economizer does not vaporize and the water-cooled wall does not overheat; When in the second stage of starting and increasing load, open the recirculation valve 9 and the main steam regulating valve 12. At this time, it is in the late stage of load increase, the feed water flow is large, the cooling capacity is strong, and the working capacity needs to be quickly improved. Regulate the recirculation valve 9, the first molten salt regulating valve 25 of the steam-molten salt heat exchanger and the second molten salt regulating valve 26 of the steam-molten salt heat exchanger, and preheat the feed water with molten salt before the economizer and high-temperature water after the economizer respectively, quickly reduce the water wall inlet enthalpy deficiency, and increase the steam production of the separator. The adjustment limit is to ensure that the economizer does not vaporize and the water wall does not overheat. Regulate the main steam regulating valve 12 and the second water storage tank water supply valve 17 and the steam-molten salt heat exchanger steam regulating valve 18. The adjustment target is to make the boiler outlet steam flow meet the requirements of the rapid load increase rate.

[0025] During the boiler shutdown and load reduction process, the present invention bypasses the main steam flow to store heat in molten salt and steam in a cascaded manner, while ensuring the cooling capacity of the high-temperature heating surface working medium. The bypass separator produces water to store the high-temperature working medium and quickly reduce the load, achieving flexible and safe shutdown. During the startup and load increase process, the output power is quickly increased through multi-media energy storage and time-space control, the steam-water working medium flow path is reconstructed to increase the water-cooled wall working medium flow, and multi-media cascade heating of the feed water is used to quickly reduce the working medium enthalpy at the water-cooled wall inlet while ensuring the safe operation of the water-cooled wall, thereby achieving flexible and safe startup. By coupling the cascade utilization of energy in the storage and release process of multi-temperature zone energy storage systems such as molten salt / steam / feed water, the present invention integrates boiler equipment safety status monitoring and active safety assurance technology to achieve flexible and safe startup of coal-fired boilers and improve the start-stop peak-shaving capability of the unit.

[0026] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it. Although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A flexible and safe starting system for a coal-fired boiler, characterized in that: Including coal-fired boiler system, heat storage and release circuit and safety monitoring system; The coal-fired boiler system includes a boiler (1), wherein a high-temperature heating surface pipeline (2), an economizer pipeline (3) and a water-cooled wall pipeline (4) are arranged in the boiler (1), the feed water of the boiler (1) flows through the economizer pipeline (3) and the water-cooled wall pipeline (4) and enters the steam-water separator (5), the high-temperature steam generated by the steam-water separator (5) enters the high-temperature heating surface pipeline (2), the high-temperature water generated by the steam-water separator (5) is connected to the first water storage tank (7) on one path and to the second water storage tank (11) on the other path, and the outlet of the first water storage tank (7) is connected to the outlet of the first water storage tank (11). The outlet of the economizer pipeline (3) is connected to the water-cooled wall pipeline (4), the outlet of the high-temperature heating surface pipeline (2) is connected to the boiler (1) in one way, the second way is connected to the steam-molten salt heat exchanger (15) via the main steam bypass, the steam-molten salt heat exchanger (15) is connected to the second water storage tank (11), the third way is connected to the second water storage tank (11), the working medium outlet of the second water storage tank (11) is connected to the steam-molten salt heat exchanger (15), and the working medium heated by the steam-molten salt heat exchanger (15) leaves the boiler (1); The heat storage circuit includes a cold tank (19), the outlet of the cold tank (19) is connected to the molten salt inlet of the steam-molten salt heat exchanger (15), and the outlet of the hot tank (22) is connected to the molten salt inlet of the steam-molten salt heat exchanger (15). The molten salt outlet of the steam-molten salt heat exchanger (15) enters the hot tank (22) in the first route, is connected to the cold tank (19) in the second route, is connected to the molten salt-feed water heat exchanger (27) in the third route, the molten salt-feed water heat exchanger (27) is connected to the cold tank (19), and the outlet feed water of the molten salt-feed water heat exchanger (27) enters the economizer pipeline (3) of the boiler (1); The safety monitoring system includes: A high-temperature heating surface safety status acquisition module (28) is used to collect the working fluid temperature and pressure of the high-temperature heating surface pipeline (2) of the boiler (1) and transmit it to the high-temperature heating surface active safety assurance instruction execution module (29); A high-temperature heating surface active safety assurance instruction execution module (29) is used to control the working fluid temperature and pressure of the high-temperature heating surface pipeline (2) based on the data collected by the high-temperature heating surface safety status collection module (28); A water-cooled wall safety status acquisition module (30) is used to collect wall temperature operation data of the water-cooled wall pipeline (4) in the boiler (1) and transmit the data to the water-cooled wall active safety assurance instruction execution module (31); The water-cooled wall active safety assurance instruction execution module (31) is used to control the wall temperature operation data of the water-cooled wall pipeline (4) in the boiler (1) based on the data collected by the water-cooled wall safety status collection module (30).

2. A coal-fired boiler flexible and safe starting system according to claim 1, characterized in that: A first water storage valve (6) is provided between the steam-water separator (5) and the first water storage tank (7), and a second water storage valve (10) is provided between the steam-water separator (5) and the second water storage tank (11).

3. A coal-fired boiler flexible and safe starting system according to claim 1, characterized in that: A recirculation pump (8) and a recirculation valve (9) are provided on the connecting pipeline between the first water storage tank (7) and the water-cooled wall pipeline (4).

4. A coal-fired boiler flexible and safe starting system according to claim 1, characterized in that: A main steam regulating valve (12) is provided on the pipeline where the high-temperature heating surface pipeline (2) leaves the boiler (1), a first regulating valve (14) is provided on the pipeline between the high-temperature heating surface pipeline (2) and the steam-molten salt heat exchanger (15), and a main steam storage valve (16) is provided on the connecting pipeline between the high-temperature heating surface pipeline (2) and the second water storage tank (11).

5. A coal-fired boiler flexible and safe starting system according to claim 1, characterized in that: A main steam bypass second regulating valve (13) is provided on the connecting pipeline between the steam-molten salt heat exchanger (15) and the second water storage tank (11), a second water storage tank water supply valve (17) is provided on the connecting pipeline between the second water storage tank (11) and the steam-molten salt heat exchanger (15), and a steam-molten salt heat exchanger steam regulating valve (18) is provided on the pipeline of the steam-molten salt heat exchanger (15) leaving the boiler (1).

6. A coal-fired boiler flexible and safe starting system according to claim 1, characterized in that: A cold tank outlet pump (20) and a cold tank outlet regulating valve (21) are provided on the connecting pipeline between the cold tank (19) and the steam-molten salt heat exchanger (15).

7. A coal-fired boiler flexible and safe starting system according to claim 1, characterized in that: A hot tank outlet pump (23) and a hot tank outlet regulating valve (24) are provided on the connecting pipeline between the hot tank (22) and the steam-molten salt heat exchanger (15).

8. The coal-fired boiler flexible and safe starting system according to claim 1, characterized in that: A first molten salt regulating valve (25) of the steam-molten salt heat exchanger is provided on the connecting pipeline between the steam-molten salt heat exchanger (15) and the cold tank (19), and a second molten salt regulating valve (26) of the steam-molten salt heat exchanger is provided on the connecting pipeline between the steam-molten salt heat exchanger (15) and the molten salt-feed water heat exchanger (27).

9. An operating method of the flexible and safe starting system for a coal-fired boiler according to any one of claims 1 to 8, characterized in that: The following steps are involved: During the boiler shutdown and load reduction process, the first water storage valve (6) and the recirculation valve (9) are closed, the second water storage tank water supply valve (17) and the steam-molten salt heat exchanger steam regulating valve (18) are closed, the hot tank outlet regulating valve (24), the steam-molten salt heat exchanger first molten salt regulating valve (25), and the steam-molten salt heat exchanger second molten salt regulating valve (26) are closed; the boiler system shutdown and load reduction process is divided into three stages. When in stage one, the second water storage valve (10) and the main steam storage valve (16) are closed, the cold tank outlet regulating valve (24) is opened, and the main steam storage valve (16) is opened. The throttle valve (21) regulates the main steam regulating valve (12), the second main steam bypass regulating valve (13) and the first main steam bypass regulating valve (14); when in stage two, the main steam storage valve (16) is opened, the second main steam bypass regulating valve (13) and the first main steam bypass regulating valve (14) are closed, the cold tank outlet regulating valve (21) is closed, and the main steam storage valve (16) and the main steam regulating valve (12) are regulated; when in stage three, the main steam regulating valve (12) is closed and the second water storage valve (10) is opened; During the process of boiler startup and load increase, the second water storage valve (10) is closed, the second regulating valve (13) of the main steam bypass, the first regulating valve (14) of the main steam bypass and the main steam storage valve (16) are closed, and the cold tank outlet regulating valve (21) is closed. The process of boiler system startup and load increase is divided into two stages. When in stage 1, the recirculation valve (9) is closed, the first water storage valve (6) is opened, the main steam regulating valve (12) is closed, the water supply valve (17) of the second water storage tank and the steam regulating valve (18) of the steam-molten salt heat exchanger are opened, and the hot tank outlet regulating valve (24) is opened. During the initial temperature and pressure increase stage of startup, the high temperature working fluid generated by the separator is discharged. The high-temperature molten salt is stored in the first water storage tank (7), and the high-temperature molten salt heats the high-temperature water in the second water storage tank (11) to replace the main steam, and the first molten salt regulating valve (25) of the steam-molten salt heat exchanger and the second molten salt regulating valve (26) of the steam-molten salt heat exchanger are regulated; when in the second stage, the recirculation valve (9) is opened, the main steam regulating valve (12) is opened, the recirculation valve (9), the first molten salt regulating valve (25) of the steam-molten salt heat exchanger and the second molten salt regulating valve (26) of the steam-molten salt heat exchanger are regulated, and the main steam regulating valve (12) and the water supply valve (17) of the second water storage tank and the steam regulating valve (18) of the steam-molten salt heat exchanger are regulated.

10. The method for operating a flexible and safe starting system for a coal-fired boiler according to claim 9, characterized in that: For the boiler shutdown and load reduction process, when the main steam temperature is higher than 370°C, it is in stage one; when the main steam temperature is lower than 370°C and higher than 250°C, it is in stage two; when the main steam temperature is lower than 250°C, it is in stage three; During the boiler startup and load increase process, when the steam-water separator temperature is lower than 250°C, it is in stage one; when the steam-water separator temperature is higher than 250°C, it is in stage two.

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