CN113251412A

CN113251412A - Flexible peak shaving system and method for supercritical boiler

Info

Publication number: CN113251412A
Application number: CN202110699532.9A
Authority: CN
Inventors: 薛宁; 魏铜生; 姬海民; 张知翔; 温寒健; 韩键平; 杜南京; 李亮辉
Original assignee: Xian Thermal Power Research Institute Co Ltd
Current assignee: Xian Thermal Power Research Institute Co Ltd
Priority date: 2021-06-23
Filing date: 2021-06-23
Publication date: 2021-08-13

Abstract

The invention discloses a flexible peak regulation system and a method for a supercritical boiler.A cold inlet of a water heater of a steam boiler is respectively communicated with an outlet of a main pipe of an outlet of an economizer and a lower header of a water-cooled wall, and the steam pulverized coal heater is arranged on a primary air pulverized coal pipeline; the inlet and the outlet of the hot steam extraction pipeline are respectively communicated with the reheating hot section steam main pipe and the hot inlet of the steam furnace water heater, the hot outlet of the steam furnace water heater is connected with the hot inlet of the steam pulverized coal heater, and the hot outlet of the steam pulverized coal heater is connected with a steam exhaust pipeline. The invention overcomes the problem of high wet-state load when the supercritical boiler operates at ultra-low load. Under the working conditions that the unit is in ultra-low load operation and the boiler needs to be in a wet state operation, boiler water from an outlet of the economizer to the lower header of the water-cooled wall is heated, the ignition environment of pulverized coal is improved, and the wet state is delayed in the load reduction process; the primary air pulverized coal airflow is heated by the steam, so that the temperature of the pulverized coal airflow is increased, the ignition heat of the pulverized coal is reduced, and the combustion stability is improved.

Description

Flexible peak shaving system and method for supercritical boiler

Technical Field

The invention belongs to the technical field of flexible peak shaving comprehensive transformation of a supercritical boiler, and relates to a flexible peak shaving system and a flexible peak shaving method of the supercritical boiler.

Background

The rapid development of new energy is the direction of energy development and is the requirement for accelerating the promotion of ecological civilization construction. In recent years, new energy and nuclear power are continuously and rapidly developed, and installation and power generation are greatly increased year by year. With the adjustment of an energy structure, the development of clean energy is accelerated, the peak regulation capacity of a power grid in a local area in a winter heating period is insufficient, new energy consumption is difficult, and the problems of wind abandonment, light abandonment and water abandonment in partial areas are obvious. The deep peak regulation capability of the traditional coal-fired unit occupying the main position of the generated energy is further excavated, and the method is the most convenient, rapid and effective means for relieving the new energy consumption dilemma at present.

Large-scale thermal power generating units, particularly ultra (supercritical) thermal power generating units, participate in wide-load deep peak shaving, so that unit boilers and related main and auxiliary equipment are always under the conditions of low load and large load change rate, and the units are required to have lower load limit values. The extremely low load operation requirement and the large load change rate directly affect the safety and the economical efficiency of the unit, and may cause the following problems:

1) the combustion stability of the boiler is poor, and the safety and the economical efficiency of the system operation are reduced. The minimum stable combustion load design value of a large thermal power generating unit boiler is generally 30% -40% BMCR, and the minimum stable combustion load controlled by a power plant is above 40% BMCR due to the requirement of safe operation. During deep peak regulation operation, the combustion working condition of the boiler is lower than the originally designed minimum stable combustion load, the temperature level of the hearth is sharply reduced, the ignition stability of pulverized coal is poor, and the great hidden danger of fire extinguishing and blasting of the hearth exists. When the system is operated under the conditions of starting and stopping the boiler and extremely low load, the boiler needs to be oiled to support combustion, and the ignition and burnout of pulverized coal are deteriorated, so that accidents such as tail secondary combustion, electric precipitation deflagration, desulfurization slurry poisoning and the like can be caused, and the safety and the economical efficiency of the long-period operation of the system are obviously reduced.

2) The temperature deviation of the water wall and the heating surface smoke temperature wall is increased, the hydrodynamic safety is reduced, and the main reheat steam temperature is insufficient. Under the condition of deep peak regulation of a unit, the amount of fuel fed into the boiler is reduced, the influence of primary air powder nonuniformity is more obvious, the over-temperature of metals on a water wall and a heating surface is easily caused due to the reasons of increased smoke temperature deviation, reduced steam pressure, insufficient or severe hydrodynamic force, difficult coordination of combustion and a steam-water system and the like, and the over-temperature of the heating surface of the unit is caused due to the long-term low-load operation of a boiler and limited soot blowing of the heating surface, so that the temperature of main and reheated steam is imbalanced and cannot reach the designed value, the risks of over-temperature explosion of the water wall and the heating surface, coke falling of a hearth and smashing the water wall and the like are increased, the generation and the stripping of steam-water side oxide skin of an ultra (ultra) critical unit are more likely to be aggravated, and the operation safety of the unit is greatly threatened.

3) Threatens the safe and economic operation of the steam turbine. When a unit operates in deep peak shaving and rapid variable load, the steam turbine operates in a low-flow and low-load working condition for a long time, so that the internal flow field of the through-flow component of the steam turbine becomes abnormal and complex and deviates from the design condition seriously, thereby easily causing the problems of thermal deformation of a cylinder body and a rotor, high-cycle fatigue of blades, water erosion of low-pressure last-stage blades and the like, shortening the service life of the steam turbine seriously, influencing the economic performance of the unit and threatening the safe operation of the steam turbine.

4) The long-period safe operation of key parts of the unit is influenced. When the unit is operated in deep peak shaving and rapid load variation, the stress level of key units of a steam drum or a steam-water separator, a header, four pipelines, a boiler pipe, a main valve, a steam turbine rotor, a cylinder, a generator rotor and the like is greatly improved, fatigue damage and service life damage are aggravated, and the operation safety of the unit is influenced. The analysis, inspection, monitoring and research and safety analysis and evaluation of the key components of the unit during deep peak regulation are urgently needed to be carried out.

5) The unit AGC load change rate response capability is insufficient. The characteristics of boiler combustion control and steam-water system regulation of the existing large-scale coal-fired generating set determine that the coordination control of a large-scale boiler combustion system and a steam-water system presents the regulation control characteristic of large inertia, and are limited by the limitation of environmental regulations. How to improve the quick response capability of the AGC of the unit under the condition of ensuring the safe and economic operation and environmental protection indexes of the unit by optimizing the coordination control under the condition of large-range variable load of a combustion system and a steam-water system is also an important problem to be solved at present.

6) The safety and the economical efficiency of the operation of the auxiliary machine are influenced. When the boiler operates under low load for a long time, the smoke temperature of a hearth is low, pulverized coal is not completely combusted, and the flow rate of the smoke is low, so that the normal operation of denitration equipment is influenced, and the dust deposition and corrosion of equipment such as an air preheater, a low-temperature economizer and the like are aggravated. The auxiliary machine equipment deviates from the design working condition, so that the operation efficiency of the auxiliary machine is reduced, the plant power consumption rate is increased, and the safety risk of the operation of the auxiliary machine is brought. The too low output of the boiler fan can bring the wind rush and stall of the fan, and further surge and trip occur; the fire extinguishing danger of the boiler caused by the tripping of the coal mill can be brought by a small number of coal mills, and the damage of large vibration and the like can be brought by a large number of coal mills.

The problem of power grid peak regulation is already a considerable problem, and researchers propose to enhance the peak regulation capability of a thermal power generating unit by technical means. And carrying out a low-load stable combustion test aiming at the deep peak regulation unit, and obtaining the peak regulation capability of the unit. Meanwhile, the method combines the advanced low-load stable combustion technology and other technical reconstruction measures to determine the reconstruction scheme of the unit and provide a feasible matching scheme. When a low-load stable combustion performance test is carried out, an aerodynamic field test, a combustion adjustment test, a thermal efficiency test, a combustion working condition test in a furnace and the like of the unit in a cold state are carried out at the same time, so that the safe and stable operation of the unit is ensured, the generator set is ensured to meet the operation requirement of a power grid to the maximum extent, and the requirement of deep peak regulation is met.

For a supercritical unit, the 30% load is a critical point of dry-wet state conversion generally, and a boiler which is lower than the 30% rated load needs to be operated in a wet state, so that the temperature of reheated steam is greatly reduced, and the operation safety of a steam turbine is seriously influenced. At present, no effective technology exists for delaying the transition to the wet state.

Disclosure of Invention

In order to solve the problems in the prior art, the invention aims to provide a flexible peak shaving system and a method for a supercritical boiler so as to solve the problem that the wet-state load is high when the supercritical boiler operates at ultra-low load.

The technical scheme adopted by the invention is as follows:

a flexible peak regulation system of a supercritical boiler comprises a reheating hot section steam main pipe, an economizer outlet main pipe, a water wall lower header, a primary air pulverized coal pipeline, a hot steam extraction pipeline, a steam boiler water heater and a steam pulverized coal heater;

the cold inlet of the steam boiler water heater is communicated with the outlet of the coal economizer outlet main pipe, and the cold outlet of the steam boiler water heater is connected with the water-cooled wall lower header;

the steam pulverized coal heater is arranged on the primary air pulverized coal pipeline;

the inlet of the hot steam extraction pipeline is communicated with the reheating hot section steam main pipe and/or the superheated steam main pipe, the outlet of the hot steam extraction pipeline is connected with the hot inlet of the steam boiler water heater, the hot outlet of the steam boiler water heater is connected with the hot inlet of the steam pulverized coal heater, and the hot outlet of the steam pulverized coal heater is connected with a spent steam pipeline.

Preferably, a steam quantity adjusting door is arranged on the hot steam extraction pipeline.

Preferably, the hot steam extraction pipeline is provided with a steam extraction pipeline isolation shutoff valve at the upstream of the steam quantity regulating valve.

Preferably, the steam boiler water heater adopts a shell-and-tube heater, and the steam coal powder heater adopts a surface heater.

Preferably, the steam pulverized coal heater is arranged on a straight pipe section before entering the boiler of the primary air pulverized coal pipeline, and the primary air pulverized coal pipeline is a pulverized coal pipe corresponding to a single-layer burner at the lower layer or the next lower layer of the boiler.

Preferably, a spent steam shutoff valve is arranged on the spent steam pipeline.

Preferably, a connecting pipeline between a hot outlet of the steam furnace water heater and a hot inlet of the steam pulverized coal heater and a steam exhaust pipeline are respectively provided with a temperature sensor and a pressure sensor.

Preferably, the steam-depleted pipeline is connected to the heat supply pipeline;

or the spent steam pipeline is connected with the fixed-row flash tank of the boiler.

The invention also provides a flexible peak regulation method of the supercritical boiler, which is carried out by adopting the flexible peak regulation system of the supercritical boiler, and comprises the following processes:

under the working condition that the unit is in ultralow load continuous load reduction operation and the boiler needs to be in a wet state, part of steam is pumped from a reheat steam hot section main pipe and/or a superheated steam main pipe through a hot steam extraction pipeline and sent into a steam boiler water heater, the steam and boiler water in an economizer outlet main pipe are subjected to heat exchange through the steam boiler water heater, so that the steam temperature is reduced, the boiler water temperature is increased, the boiler water with the increased temperature enters a water-cooled wall lower header, the steam with the decreased temperature flows through the steam coal powder heater and heats coal powder airflow in a primary air coal powder pipeline, and the steam becomes hydrophobic after being cooled again and is discharged through a steam exhaust pipeline.

Preferably, the steam temperature at the hot inlet of the steam furnace water heater is 500-570 ℃, and the steam temperature at the outlet of the steam furnace water heater is 320 +/-10 ℃;

the temperature of the furnace water is increased to 300 +/-5 ℃ after the furnace water is heated by a steam furnace water heater;

the steam temperature of the hot inlet of the steam pulverized coal heater is 320 +/-10 ℃, the steam temperature of the hot outlet of the steam pulverized coal heater is 100 +/-10 ℃, and the pulverized coal temperature in the primary air pulverized coal pipeline is increased by 30-50 ℃.

The invention has the following beneficial effects:

the supercritical boiler flexibility peak regulation system can run when a unit is in an ultralow load (below 30% of rated load), and under the working condition that the boiler needs to be in a wet state, a hot steam extraction pipeline is used for extracting partial steam from a reheat steam hot section main pipe and/or a superheated steam main pipe to heat boiler water in an economizer outlet main pipe from an economizer outlet to a water-cooled wall lower header, so that the temperature of the boiler water in the economizer outlet main pipe is increased, the water temperature (wall temperature) in the water-cooled wall is increased, the ignition environment of pulverized coal is favorably improved, and stable combustion is utilized; the temperature of furnace water is increased, the temperature of the middle point is increased by the same amplitude under the same heat absorption capacity, the transition to the wet state can be delayed in the load reduction process, and the load point of the boiler entering the wet state can be reduced to about 20-25% of rated load; the extracted steam does not work to generate electricity, the steam consumption is increased, the fuel quantity is increased, and the combustion in the furnace is stable and safe; the steam from the steam boiler water heater is still in an overheated state, so that the steam coal powder heater can be used for collecting heat in the overheated steam to heat primary air coal powder airflow, the temperature of the coal powder airflow is increased, the ignition heat of the coal powder is reduced, and the combustion stability is improved. The temperature of the steam after heat exchange of the steam pulverized coal heater is reduced, so that the steam is hydrophobic and can be used for other purposes or recovered.

Drawings

FIG. 1 is a schematic structural diagram of a flexible peak shaving system of a supercritical boiler according to the present invention.

Wherein, 1 is a hot steam extraction pipeline, 2 is an economizer outlet header pipe, 3 is a steam boiler water heater, 4 is a steam intermediate pipeline, 5 is a primary air pulverized coal pipeline, 6 is a steam pulverized coal heater, 7 is a steam exhaust pipeline, 8 is a steam extraction pipeline isolation shutoff door, 9 is a steam quantity regulating door, and 10 is a steam exhaust shutoff door.

Detailed Description

The invention is described in further detail below with reference to the accompanying drawings:

the invention aims to solve the problem that the wet-state load is higher when the supercritical boiler operates at ultra-low load. The boiler operates under low load, the heat load in the boiler is reduced, the distribution deviation is increased, and the distribution uniformity is greatly reduced after the water supply quantity of the boiler is reduced, so that the increase of the distribution deviation can certainly cause local overtemperature, and the operation risk of the boiler is improved. The wet-state operation is an effective method for improving the water circulation volume of the water wall and reducing the wall temperature deviation. However, the moisture state operation is low in load, the smoke gas amount and the smoke temperature in the furnace are reduced, the temperature of the main steam is slightly reduced, but the temperature of the reheated steam is greatly reduced, and the economic index of the unit operation is poor. Supercritical boilers generally require wet-to-wet operation when the load is reduced to 30% ECR and dry-to-dry operation when the load is increased to 30% ECR. Therefore, the minimum load of the supercritical boiler needs to be controlled to be more than 30% in the flexible peak shaving operation state, so as to avoid the adverse effect on the service life of the boiler and the large fluctuation of the metal wall temperature caused by frequent switching of the boiler between the dry state and the wet state. Therefore, to peak-load operate the supercritical boiler at a lower load, the load of the wet-to-wet operation must be reduced.

Referring to fig. 1, the flexible peak regulation system of the supercritical boiler comprises a reheating hot section steam main pipe, an economizer outlet main pipe 2, a water wall lower header, a primary air pulverized coal pipeline 5, a hot steam extraction pipeline 1, a steam boiler water heater 3 and a steam pulverized coal heater 6; the cold inlet of the steam boiler water heater 3 is communicated with the outlet of the coal economizer outlet header pipe 2, and the cold outlet of the steam boiler water heater 3 is connected with the water-cooled wall lower header; the steam pulverized coal heater 6 is arranged on the primary air pulverized coal pipeline 5; the inlet of the hot steam extraction pipeline 1 is communicated with the reheating hot section steam main pipe and/or the superheated steam main pipe, the outlet of the hot steam extraction pipeline 1 is connected with the hot inlet of the steam furnace water heater 3, the hot outlet of the steam furnace water heater 3 is connected with the hot inlet of the steam pulverized coal heater 6, and the hot outlet of the steam pulverized coal heater 6 is connected with the steam exhaust pipeline 7. The hot steam extraction pipeline 1 is communicated with a reheating hot section steam main pipe, and furnace water from an economizer outlet main pipe 2 is heated by a steam furnace water heater 3, so that the temperature of the furnace water is increased by 20-30 ℃ and then enters a water-cooled wall lower header. The steam temperature of the heated boiler water is still above 300 ℃ and still in an overheated state, and the steam is communicated with a steam pulverized coal heater 6 on a primary air pulverized coal pipeline 5 through an intermediate steam pipeline 4 to heat pulverized coal airflow, so that the pulverized coal temperature can be increased by 30-50 ℃, and the temperature-reduced exhaust steam is discharged into a boiler fixed-row flash tank or a heat supply pipeline through a pipeline 7.

In a preferred embodiment of the present invention, a steam amount adjusting gate 9 is provided on the hot steam extraction pipe 1, and the extraction amount of the reheated steam can be adjusted by the adjusting gate 9 to control the degree of the temperature increase of the furnace water.

As a preferred embodiment of the invention, a steam extraction pipeline isolation shut-off door 8 is arranged on the hot steam extraction pipeline 1 at the upstream of the steam quantity regulating door 9, and the steam extraction pipeline isolation shut-off door 8 can realize the isolation exit of the whole system.

As the preferred embodiment of the invention, the steam furnace water heater 3 adopts a shell-and-tube heater, and the steam coal powder heater 6 adopts a surface heater.

As a preferred embodiment of the invention, the steam pulverized coal heater 6 is arranged on a straight pipe section before the primary air pulverized coal pipeline 5 enters the boiler, the primary air pulverized coal pipeline 5 is a pulverized coal pipe corresponding to a single-layer burner at the lower layer or the next lower layer of the boiler, and the heating section is a straight pipe section which is as close to a hearth as possible.

As a preferred embodiment of the present invention, a spent steam shutoff valve 10 is provided on the spent steam pipeline 7.

As the preferred embodiment of the invention, a connecting pipeline between the hot outlet of the steam boiler water heater 3 and the hot inlet of the steam pulverized coal heater 6 and a steam lack pipeline 7 are respectively provided with a temperature sensor and a pressure sensor.

As a preferred embodiment of the present invention, the spent steam can be mixed into the heat supply pipeline under appropriate conditions, and can be introduced into the boiler fixed discharge flash tank for working medium recovery without conditions, so that the spent steam pipeline 7 is connected to the heat supply pipeline; or the spent steam pipeline 7 is connected with a fixed-row flash tank of the boiler.

When the supercritical boiler flexibility peak shaving system is specifically operated, a unit runs under ultra-low load (below 30% rated load), and under the working condition that the boiler needs to be in wet state running, partial steam is pumped from a reheat steam hot section main pipe and/or a superheated steam main pipe to heat boiler water from an economizer outlet to a water-cooled wall lower header, so that the temperature is increased, the water temperature (wall temperature) in the water-cooled wall is increased, the ignition environment of pulverized coal is favorably improved, and stable combustion is utilized; the temperature of furnace water is increased, the temperature of the middle point is increased by the same amplitude under the same heat absorption capacity, the wet state can be delayed in the load reduction process, and the load point of the boiler entering the wet state can be reduced to about 20-25% of rated load; the extracted steam does not work to generate electricity, the steam consumption is increased, the fuel quantity is increased, and the combustion in the furnace is stable and safe; the cascade steam heats the primary air coal dust airflow, the temperature of the coal dust airflow is increased by 30-50 ℃, the ignition heat of the coal dust is reduced, and the combustion stability is improved. The reheated steam after cascade utilization can be discharged into a fixed-discharge flash tank, and can also be connected into a heat supply pipeline system under the condition permission to recover working media or fully utilize energy.

Examples

The supercritical boiler flexibility peak regulation system comprises a hot steam extraction pipeline 1, a shell-and-tube steam-water heater, an intermediate steam pipeline 4, a steam pulverized coal heater 6, a steam exhaust pipeline 7, a steam extraction pipeline isolation shutoff door 8, a steam exhaust shutoff door 10 and a steam quantity adjusting door 9, wherein the steam temperature is reduced to about 300 ℃ and then is led to a primary air pulverized coal pipeline 5 for surface heating;

the steam extraction position is a reheating hot section steam main pipe, the steam extraction pressure and temperature slightly differ along with different boiler capacity parameters, the pressure and temperature are generally 2-3 MPa under low load, and the steam temperature is 500-570 ℃. The extracted reheat steam heats the boiler water at the outlet of the economizer through a shell-and-tube heat exchanger (namely a steam boiler water heater 3), so that the temperature of the boiler water in an outlet main pipe of the economizer is increased by 20-30 ℃, the temperature increase level of the boiler water can be determined through tests or calculation, and the boiler water can be slightly adjusted in operation and is not suitable for being greatly changed. Too low temperature rise of furnace water is unfavorable for reducing the wet load, and too high temperature rise is unfavorable for working medium distribution and wall temperature safety.

The amount of reheat steam extraction can be regulated by a steam amount regulation gate 9.

The furnace water temperature at the outlet of the coal economizer is 270 +/-5 ℃ under low load, the saturated water temperature is 311-318 ℃ under corresponding pressure, the temperature of the heated furnace water is kept 10 ℃ of the lower temperature, and can only reach 308 ℃ at most, so the operation safety of the water-cooled wall is realized, the wet-state load angle is reduced, the furnace water temperature is controlled to be 300 ℃, and the steam extraction quantity is adjusted to enable the furnace water temperature to rise by 20-30 ℃.

After the steam heats the boiler water, the temperature is 320 +/-10 ℃, the steam can be led to a coal powder pipeline in front of the boiler to preheat the coal powder, the temperature of the coal powder is increased, the ignition heat of coal powder airflow is reduced, and the stable combustion capacity of the low-load boiler is improved. The mixing temperature of the direct-blowing primary air powder is generally 70-80 ℃ for bituminous coal, the temperature is increased by 30-50 ℃ through steam heating, and the steam temperature is reduced to about 100 +/-10 ℃ to become hydrophobic. The coal powder is heated by steam to improve the operation of the surface heater, and the heater is arranged on the straight pipe section before entering the furnace. The steam extraction pipeline is provided with a steam extraction pipeline isolation shutoff valve 8 and a steam quantity adjusting valve 9, so that system isolation and steam quantity adjustment can be performed. And a spent steam shutoff door 10 is arranged on the spent steam pipeline 7 to isolate the system, so that high load is not used. Temperature and pressure measuring points of working media are arranged on the middle steam pipeline 4 and the exhaust steam pipeline 7.

When the supercritical boiler flexibility peak regulation system is used, the unit is under the ultra-low load (below 30% of rated load) and continues to operate in a load reduction mode, under the working condition that the boiler needs to be in a wet state, partial steam is pumped from a reheat steam hot section main pipe to heat boiler water from an economizer outlet to a water wall lower header, the temperature is increased by 20-30 ℃, the wet state load is reduced to 20-25% of rated load, the steam temperature is reduced to 320 +/-10 ℃ from above 500 ℃, the steam flow is regulated through a regulating valve, and the boiler water entering the water wall is controlled to be at 300 +/-5 ℃; and (3) introducing the steam with the temperature of more than 300 ℃ to a lower layer or a lower layer coal powder pipeline (straight section) in front of the furnace to heat coal powder airflow through a surface heater, increasing the temperature by 30-50 ℃, reducing the temperature of the steam to 100 +/-10 ℃, and discharging the steam to a fixed-row flash tank or a heat supply pipeline through a waste gas pipeline.

Claims

1. A supercritical boiler flexible peak regulation system is characterized by comprising a reheating hot section steam main pipe, an economizer outlet main pipe (2), a water wall lower header, a primary air pulverized coal pipeline (5), a hot steam extraction pipeline (1), a steam boiler water heater (3) and a steam pulverized coal heater (6);

a cold inlet of the steam boiler water heater (3) is communicated with an outlet of the coal economizer outlet header pipe (2), and a cold outlet of the steam boiler water heater (3) is connected with a water-cooled wall lower header;

the steam pulverized coal heater (6) is arranged on the primary air pulverized coal pipeline (5);

the inlet of the hot steam extraction pipeline (1) is communicated with a reheating hot section steam main pipe and/or a superheated steam main pipe, the outlet of the hot steam extraction pipeline (1) is connected with the hot inlet of the steam boiler water heater (3), the hot outlet of the steam boiler water heater (3) is connected with the hot inlet of the steam pulverized coal heater (6), and the hot outlet of the steam pulverized coal heater (6) is connected with a steam exhaust pipeline (7).

2. The supercritical boiler flexibility peak shaving system according to claim 1, characterized in that the hot steam extraction pipe (1) is provided with a steam amount adjusting door (9).

3. The supercritical boiler flexibility peak shaving system according to claim 2, characterized in that the hot steam extraction duct (1) is provided with a steam extraction duct isolation shut-off gate (8) upstream of the steam amount regulating gate (9).

4. The supercritical boiler flexibility peak shaving system according to claim 1, characterized in that the steam boiler water heater (3) is a shell-and-tube heater, and the steam pulverized coal heater (6) is a surface heater.

5. The supercritical boiler flexibility peak regulation system according to claim 1, characterized in that the steam pulverized coal heater (6) is arranged on the straight pipe section before the primary air pulverized coal pipeline (5) enters the boiler, and the primary air pulverized coal pipeline (5) is a pulverized coal pipe corresponding to a single-layer burner at the lower layer or the next lower layer of the boiler.

6. The supercritical boiler flexibility peak shaving system according to claim 1, characterized in that the spent steam pipeline (7) is provided with a spent steam shut-off valve (10).

7. The supercritical boiler flexibility peak shaving system according to claim 1, characterized in that a connection pipeline between the hot outlet of the steam boiler water heater (3) and the hot inlet of the steam pulverized coal heater (6) and a steam exhaust pipeline (7) are both provided with a temperature sensor and a pressure sensor.

8. The supercritical boiler flexibility peak shaving system according to claim 1, characterized by that the spent steam pipeline (7) is connected to the heat supply pipeline;

or the spent steam pipeline (7) is connected with the fixed-row flash tank of the boiler.

9. A method for the flexible peak regulation of a supercritical boiler is characterized by being carried out by adopting the flexible peak regulation system of the supercritical boiler as claimed in any one of claims 1 to 8, and comprising the following processes:

under the working condition that the unit is in ultralow load continuous load reduction operation and the boiler needs to be in a wet state, partial steam is pumped from a reheat steam hot section main pipe and/or a superheated steam main pipe through a hot steam extraction pipeline (1) and sent into a steam boiler water heater (3), the steam and boiler water in an economizer outlet main pipe (2) exchange heat through the steam boiler water heater (3), so that the steam temperature is reduced, the boiler water temperature is increased, the boiler water with the increased temperature enters a water-cooled wall lower header, the steam flows through a steam coal powder heater (6) and heats coal powder airflow in a primary air coal powder pipeline (5) after the temperature is reduced, and the steam becomes hydrophobic after being cooled again and is discharged through a steam exhaust pipeline (7).

10. The method for the peak shaving flexibility of the supercritical boiler according to claim 9, wherein the steam temperature at the hot inlet of the steam boiler water heater (3) is 500-570 ℃, and the steam temperature at the outlet of the steam boiler water heater (3) is 320 ± 10 ℃;

the temperature of the furnace water is increased to 300 +/-5 ℃ after the furnace water is heated by the steam furnace water heater (3);

the steam temperature of the hot inlet of the steam pulverized coal heater (6) is 320 +/-10 ℃, the steam temperature of the hot outlet of the steam pulverized coal heater (6) is 100 +/-10 ℃, and the pulverized coal temperature in the primary air pulverized coal pipeline (5) is increased by 30-50 ℃.