A supercritical boiler flexibility peak shaving system and method

Abstract

The present invention discloses a supercritical boiler flexible peak shaving system and method. The cold inlets of the steam boiler water heaters are respectively connected to the outlet of the main pipe of the economizer outlet and the lower header of the water wall. The steam pulverized coal heater is arranged on the primary air pulverized coal pipeline. The inlet and outlet of the hot steam extraction pipeline are respectively connected to the hot reheat steam header and the hot inlet of the steam boiler water heater. The hot outlet of the steam boiler water heater is connected to the hot inlet of the steam pulverized coal heater, and the hot outlet of the steam pulverized coal heater is connected with a waste steam pipeline. The present invention overcomes the problem of a relatively high wet state conversion load during the ultra-low load operation of a supercritical boiler. Under the condition that the unit is in ultra-low load operation and the boiler needs to be converted to wet state operation, the boiler water from the economizer outlet to the lower header of the water wall is heated, the ignition environment of pulverized coal is improved, and the conversion to wet state is postponed during the load reduction process; the primary air pulverized coal airflow is heated by steam, 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

Technical Field

[0001] The invention belongs to the technical field of comprehensive transformation of flexible peak-shaving of supercritical boilers, and relates to a flexible peak-shaving system and method for supercritical boilers. Background Art

[0002] Vigorously developing new energy is the direction of energy development and the requirement for accelerating the construction of ecological civilization. In recent years, new energy and nuclear power have continued to develop rapidly, with installed capacity and power generation increasing significantly year by year. With the adjustment of energy structure and the accelerated development of clean energy, the power grid in some areas has insufficient peak-shaving capacity during the winter heating period, resulting in difficulties in absorbing new energy. In some areas, the problems of wind, solar and water abandonment are prominent. Further tapping the deep peak-shaving capacity of traditional coal-fired units, which account for the majority of power generation, is the most convenient, fast and effective means to alleviate the current difficulties in absorbing new energy.

[0003] Large thermal power units, especially supercritical thermal power units, participate in wide load and deep peak regulation, which makes the boilers and related main and auxiliary equipment of the units often under low load and large load change rate conditions, and requires the units to have lower load limits. This extremely low load operation requirement and large load change rate directly affect the safety and economy of the units, and may cause the following problems:

[0004] 1) The boiler combustion stability is poor and the system operation safety and economy are reduced. The minimum stable combustion load design value of large thermal power unit boilers is generally 30%~40%BMCR. For the purpose of safe operation, the minimum stable combustion load controlled by the power plant is above 40%BMCR. During deep peak-shaving operation, the boiler combustion condition is lower than the original designed minimum stable combustion load, the furnace temperature level drops sharply, the coal powder ignition stability is poor, and there is a major hidden danger of furnace fire extinguishing and cannon. When the boiler is started and stopped and operated under extremely low load conditions, the boiler needs to add oil to assist combustion, and the deterioration of coal powder ignition and burnout may cause accidents such as tail secondary combustion, electrostatic precipitator explosion and desulfurization slurry poisoning, and the safety and economy of the system's long-term operation is significantly reduced.

[0005] 2) The temperature deviation of the flue gas temperature of the water-cooled wall and the heating surface increases, the hydrodynamic safety decreases, and the main reheat steam temperature is insufficient. When the unit is in deep peak regulation, the amount of fuel entering the furnace decreases, the influence of the primary air powder non-uniformity becomes more prominent, the flue gas temperature deviation increases, the steam pressure decreases, the hydrodynamic force is insufficient or changes dramatically, and the combustion and steam-water system are difficult to coordinate. The water-cooled wall and the heating surface metal are prone to overheating. In addition, the long-term low-load operation of the boiler and the limited soot blowing of the heating surface lead to overheating of the unit heating surface, the main and reheat steam temperatures are out of balance and fail to reach the design value, and the risks of overheating of the water-cooled wall and the heating surface bursting and the furnace coking and damaging the water-cooled wall increase. For ultra-supercritical units, it is more likely to aggravate the formation and peeling of oxide scale on the steam-water side, posing a greater threat to the safety of unit operation.

[0006] 3) Threaten the safe and economic operation of the steam turbine. When the unit operates at deep peak shaving and rapid load change, the steam turbine operates under low-flow and low-load conditions for a long time, which will make the internal flow field of the steam turbine's flow path components extremely complex, seriously deviating from the design conditions. As a result, it is easy to cause problems such as thermal deformation of the cylinder and rotor, high-cycle fatigue of the blades, and erosion of the low-pressure last-stage blades, seriously shortening the service life of the steam turbine and affecting the economic performance of the unit, threatening the safe operation of the steam turbine.

[0007] 4) Affect the long-term safe operation of the key components of the unit. When the unit operates at deep peak shaving and rapid load change, the stress levels of the key components of the unit, such as the steam drum or steam-water separator, headers, four major pipelines, boiler tubes, main valves, steam turbine rotor, cylinder, and generator rotor, are greatly increased, and the fatigue damage and life damage are aggravated, affecting the operation safety of the unit. It is urgent to carry out research on the analysis, inspection, monitoring, and safety analysis and evaluation of the key components of the unit during deep peak shaving.

[0008] 5) The AGC load change rate response ability of the unit is insufficient. The characteristics of the boiler combustion control and the steam-water system regulation of current large-scale coal-fired generating units determine that the coordinated control of the large-scale boiler combustion system and the steam-water system presents the regulation control characteristics of large inertia. Limited by environmental protection regulations, the widespread adoption of low-nitrogen combustion methods further reduces the flexibility of the boiler combustion and the steam-water system regulation and the speed of load change response. How to improve the AGC rapid response ability of the unit under the condition of ensuring the safe and economic operation of the unit and environmental protection indicators by optimizing the coordinated control of the combustion system and the steam-water system under large-scale load change is also an important problem that needs to be solved currently.

[0009] 6) Affect the safe and economic operation of auxiliary equipment. When the boiler operates at low load for a long time, the furnace flue gas temperature is low, the pulverized coal combustion is incomplete, and coupled with the low flue gas flow velocity, it affects the normal operation of the denitration equipment and causes increased ash accumulation and corrosion of equipment such as air preheaters and low-temperature economizers. The auxiliary equipment deviates from the design conditions, not only reducing the operation efficiency of the auxiliary equipment and increasing the plant power consumption rate, but also bringing safety risks to the operation of the auxiliary equipment. If the output of the boiler fan is too low, it may cause air robbing and stall of the fan, and then surge and trip; if the number of coal mills in use is small, it will bring the risk of boiler flameout caused by coal mill tripping, and if the number of coal mills in use is large, it will also bring hazards such as large vibration.

[0010] The problem of power grid peak shaving has become an issue that cannot be ignored. Research scholars have proposed to enhance the peak shaving ability of thermal power units through technical means. Conduct low-load stable combustion tests on deep peak shaving units to understand the peak shaving ability of the units. At the same time, combined with technical transformation measures such as advanced low-load stable combustion technology, determine the transformation plan of the unit and propose a feasible supporting plan. When conducting low-load stable combustion performance tests, air dynamic field tests, combustion adjustment tests, thermal efficiency tests, and in-furnace combustion condition tests of the unit under cold conditions should be carried out simultaneously to ensure the safe and stable operation of the unit while ensuring that the generator set maximally meets the needs of power grid operation and meets the requirements of deep peak shaving.

[0011] For supercritical units, generally 30% load is the critical point of the dry-wet state conversion. When the load is lower than 30% of the rated load, the boiler needs to enter the wet state operation, which causes a significant reduction in the reheat steam temperature and seriously affects the operation safety of the steam turbine. At present, there is no very effective technology to delay the transition to the wet state. Summary of the Invention

[0012] To solve the problems existing in the prior art, the purpose of the present invention is to provide a flexible peak shaving system and method for a supercritical boiler to overcome the problem of a relatively high wet state conversion load during ultra-low load operation of the supercritical boiler.

[0013] The technical solution adopted by the present invention is as follows:

[0014] A flexible peak shaving system for a supercritical boiler includes a reheater hot steam header, a 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;

[0015] The cold inlet of the steam-boiler water heater is connected to the outlet of the economizer outlet main pipe, and the cold outlet of the steam-boiler water heater is connected to the water wall lower header;

[0016] The steam-pulverized coal heater is arranged on the primary air pulverized coal pipeline;

[0017] The inlet of the hot steam extraction pipeline is connected to the reheater hot steam header and / or the superheated steam header, the outlet of the hot steam extraction pipeline is connected to the hot inlet of the steam-boiler water heater, the hot outlet of the steam-boiler water heater is connected to the hot inlet of the steam-pulverized coal heater, and a waste steam pipeline is connected to the hot outlet of the steam-pulverized coal heater.

[0018] Preferably, a steam flow regulating valve is provided on the hot steam extraction pipeline.

[0019] Preferably, an extraction steam pipeline isolation shut-off valve is provided upstream of the steam flow regulating valve on the hot steam extraction pipeline.

[0020] Preferably, the steam-boiler water heater adopts a shell-and-tube heater, and the steam-pulverized coal heater adopts a surface heater.

[0021] Preferably, the steam pulverized coal heater is arranged on the straight pipe section before the furnace inlet of the primary air pulverized coal pipeline, and the primary air pulverized coal pipeline is the pulverized coal pipe corresponding to the single-layer burner in the lower layer or the sub-lower layer of the boiler.

[0022] Preferably, a steam shut-off valve is provided on the exhaust steam pipeline.

[0023] Preferably, temperature sensors and pressure sensors are provided on the connecting pipeline between the hot outlet of the steam boiler water heater and the hot inlet of the steam pulverized coal heater and on the exhaust steam pipeline.

[0024] Preferably, the exhaust steam pipeline is connected to the heating pipeline;

[0025] Alternatively, the exhaust steam pipeline is connected to the boiler regular blowdown flash tank.

[0026] The present invention also provides a supercritical boiler flexible peak shaving method, which is carried out by using the supercritical boiler flexible peak shaving system as described above in the present invention, and includes the following processes:

[0027] When the unit is operating at an ultra-low load and continues to reduce the load, and the boiler needs to switch to the wet state, a part of the steam is extracted from the hot reheat steam header and / or the superheated steam header through the hot steam extraction pipeline and sent into the steam boiler water heater. The steam and the boiler water in the main pipe at the outlet of the economizer exchange heat through the steam boiler water heater, so that the steam temperature decreases and the boiler water temperature increases. The heated boiler water enters the lower header of the water wall, and the steam after temperature reduction flows through the steam pulverized coal heater and heats the pulverized coal air flow in the primary air pulverized coal pipeline. After the steam is cooled again, it becomes condensate and is discharged through the exhaust steam pipeline.

[0028] Preferably, the steam temperature at the hot inlet of the steam boiler water heater is 500 - 570 °C, and the steam temperature at the outlet of the steam boiler water heater is 320 ± 10 °C;

[0029] The temperature of the boiler water is increased to 300 ± 5 °C after being heated by the steam boiler water heater;

[0030] The steam temperature at the hot inlet of the steam pulverized coal heater is 320 ± 10 °C, the steam temperature at the hot outlet of the steam pulverized coal heater is 100 ± 10 °C, and the temperature of the pulverized coal in the primary air pulverized coal pipeline is increased by 30 - 50 °C.

[0031] The present invention has the following beneficial effects:

[0032] The flexible peak shaving system for the supercritical boiler of the present invention can operate when the unit is at an ultra-low load (below 30% of the rated load), and the boiler needs to switch to the wet state. In this condition, part of the steam is extracted from the hot reheat steam header and / or the superheated steam header through the hot steam extraction pipeline to heat the boiler water in the main economizer outlet pipe from the economizer outlet to the lower header of the water wall, and increase the temperature of the boiler water in the main economizer outlet pipe, so as to increase the water temperature (wall temperature) in the water wall, which is beneficial to improving the ignition environment of pulverized coal and enabling stable combustion; when the temperature of the boiler water increases, the intermediate point temperature increases by the same amplitude under the same heat absorption, and the switch to the wet state can be postponed during the load reduction process. The load point at which the boiler enters the wet state can be reduced to about 20% - 25% of the rated load; the extracted steam does not generate electricity by doing work, and the steam consumption increases, which increases the fuel quantity, and the combustion in the furnace is stable and safe; the steam coming out of the steam-boiler water heater is still in the superheated state. Therefore, the steam-pulverized coal heater can use the heat in the superheated steam to heat the primary air pulverized coal flow, increase the temperature of the pulverized coal flow, reduce the ignition heat of the pulverized coal, and is beneficial to improving the combustion stability. After heat exchange in the steam-pulverized coal heater, the temperature of the steam decreases, causing the steam to form condensate, which can be used for other purposes or recycled. Brief Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of the flexible peak shaving system for the supercritical boiler of the present invention.

[0034] Among them, 1 is the hot steam extraction pipeline, 2 is the main economizer outlet pipe, 3 is the steam-boiler water heater, 4 is the steam intermediate pipeline, 5 is the primary air pulverized coal pipeline, 6 is the steam-pulverized coal heater, 7 is the waste steam pipeline, 8 is the isolation shut-off valve for the extracted steam pipeline, 9 is the steam quantity regulating valve, and 10 is the waste steam shut-off valve. Detailed Embodiment

[0035] The following further describes the present invention in detail with reference to the drawings:

[0036] The present invention aims to overcome the problem of a relatively high load when transitioning to the wet state during the ultra-low load operation of a supercritical boiler. During the low load operation of the boiler, the internal heat load of the furnace decreases, and the distribution deviation also increases. After the boiler feed water volume decreases, the distribution uniformity also decreases significantly. Therefore, the increase in the distribution deviation will surely cause local overheating, increasing the operation risk of the boiler. Transitioning to the wet state operation is an effective method to increase the water circulation volume of the water wall and reduce the wall temperature deviation. However, during the wet state operation, due to the low load, the flue gas volume and temperature in the furnace decrease, the main steam temperature slightly decreases, but the reheat steam temperature will drop significantly, deteriorating the economic indicators of the unit operation. Generally, a supercritical boiler needs to transition to the wet state operation when the load drops to 30% ECR and enters the dry state operation mode when the load rises to 30% ECR. Therefore, during the flexible peak shaving operation of a supercritical boiler, the minimum load needs to be controlled above 30% to avoid the adverse effects of frequent conversion between the wet and dry states on the large fluctuations of the metal wall temperature and the boiler life. Therefore, to enable the supercritical boiler to perform peak shaving operation at a lower load, it is necessary to reduce the load of the wet state transition operation.

[0037] Referring to Figure 1 , the flexible peak shaving system of the supercritical boiler of the present invention includes a reheat hot steam header, a total economizer outlet pipe 2, a water wall lower header, a primary air pulverized coal pipeline 5, a hot steam extraction pipeline 1, a steam-water heater 3, and a steam-pulverized coal heater 6; the cold inlet of the steam-water heater 3 is connected to the outlet of the total economizer outlet pipe 2, and the cold outlet of the steam-water heater 3 is connected to the water 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 connected to the reheat hot steam header and / or the superheated steam header, the outlet of the hot steam extraction pipeline 1 is connected to the hot inlet of the steam-water heater 3, the hot outlet of the steam-water heater 3 is connected to the hot inlet of the steam-pulverized coal heater 6, and a waste steam pipeline 7 is connected to the hot outlet of the steam-pulverized coal heater 6. The hot steam extraction pipeline 1 is connected to the reheat hot steam header, and the steam from the reheat hot steam header heats the boiler water coming from the total economizer outlet pipe 2 through the steam-water heater 3, increasing the temperature of the boiler water by 20 - 30 °C before entering the water wall lower header. The steam temperature after heating the boiler water is still above 300 °C and remains in the superheated state. It is connected to the steam-pulverized coal heater 6 on the primary air pulverized coal pipeline 5 through an intermediate steam pipeline 4 to heat the pulverized coal air flow, which can increase the pulverized coal temperature by 30 - 50 °C, and the waste steam pipeline 7 with reduced temperature discharges into the boiler regular blowdown flash tank or the heat supply pipeline.

[0038] As a preferred embodiment of the present invention, a steam flow regulating valve 9 is provided on the hot steam extraction pipeline 1, and the extraction amount of the reheat steam can be adjusted through the steam flow regulating valve 9 to control the degree of increase in the boiler water temperature.

[0039] As a preferred embodiment of the present invention, an extraction steam pipeline isolation shut-off valve 8 is provided upstream of the steam quantity regulating valve 9 on the hot steam extraction pipeline 1, and the extraction steam pipeline isolation shut-off valve 8 can isolate and withdraw the entire system.

[0040] As a preferred embodiment of the present invention, the steam boiler water heater 3 adopts a shell-and-tube heater, and the steam pulverized coal heater 6 adopts a surface heater.

[0041] As a preferred embodiment of the present invention, the steam pulverized coal heater 6 is arranged on the straight pipe section before entering the furnace of the primary air pulverized coal pipeline 5, and the primary air pulverized coal pipeline 5 is the pulverized coal pipe corresponding to the single-layer burner in the lower layer or the sub-lower layer of the boiler, and the heating section is on the straight pipe section as close to the furnace as possible.

[0042] As a preferred embodiment of the present invention, a waste steam shut-off valve 10 is provided on the waste steam pipeline 7.

[0043] As a preferred embodiment of the present invention, temperature sensors and pressure sensors are provided on the 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 on the waste steam pipeline 7.

[0044] As a preferred embodiment of the present invention, the waste steam can be mixed into the heating pipeline under suitable conditions, and can be introduced into the boiler regular blowdown flash tank for working medium recovery when conditions are not met. Therefore, the waste steam pipeline 7 is connected to the heating pipeline; alternatively, the waste steam pipeline 7 is connected to the boiler regular blowdown flash tank.

[0045] When the supercritical boiler flexibility peak shaving system of the present invention is specifically operated, when the unit is operating at an ultra-low load (below 30% of the rated load) and the boiler needs to switch to the wet state operation, part of the steam is extracted from the reheater steam hot section header and / or the superheater steam header to heat the boiler water from the economizer outlet to the water wall lower header to increase the temperature. The water temperature (wall temperature) in the water wall increases, which is beneficial to improving the ignition environment of the pulverized coal and facilitating stable combustion; when the boiler water temperature increases, the intermediate point temperature increases by the same amplitude under the same heat absorption, and the switch to the wet state can be postponed during the load reduction process, and the load point at which the boiler enters the wet state can be reduced to about 20% - 25% of the rated load; the extracted steam does not do work for power generation, the steam consumption increases, the fuel quantity increases, and the combustion in the furnace is stable and safe; the staged steam heats the primary air pulverized coal air flow, increasing the temperature of the pulverized coal air flow by 30 - 50 °C and reducing the ignition heat of the pulverized coal, which is beneficial to improving combustion stability. The reheater steam after staged utilization can be discharged into the regular blowdown flash tank, or can be connected to the heating pipeline system under permitted conditions to recover the working medium or make full use of the energy.

[0046] Embodiment

[0047] The peak shaving system for supercritical boilers in this embodiment includes a hot steam extraction pipeline 1, a shell-and-tube steam-water heater, an intermediate steam pipeline 4 that leads the steam to the primary air pulverized coal pipeline 5 for surface heating after the steam temperature drops to about 300 °C, a steam pulverized coal heater 6, a waste steam pipeline 7, a steam extraction pipeline isolation shut-off valve 8, a waste steam shut-off valve 10, and a steam flow regulating valve 9;

[0048] The steam extraction position is the reheater hot steam header. The extraction steam pressure and temperature vary slightly with different boiler capacity parameters. Generally, it is 2 - 3 MPa under low load, and the steam temperature is 500 - 570 °C. The extracted reheated steam heats the boiler water at the outlet of the economizer through a shell-and-tube heat exchanger (i.e., the steam-boiler water heater 3), raising the temperature of the boiler water in the economizer outlet main pipe by 20 - 30 °C. The temperature increase level of the boiler water can be determined through tests or calculations. During operation, only minor adjustments are allowed, and large changes are not advisable. Too low a temperature increase of the boiler water is not conducive to reducing the wet state load, and too high a temperature increase is not conducive to the working medium distribution and the safety of the wall temperature.

[0049] The amount of reheated steam extraction can be adjusted through the steam flow regulating valve 9.

[0050] Under low load, the temperature of the boiler water at the outlet of the economizer is 270 ± 5 °C, and the saturated water temperature corresponding to the pressure is 311 - 318 °C. The heated boiler water temperature retains an under-temperature of 10 °C and can only reach a maximum of 308 °C. Therefore, from the perspective of the safe operation of the water wall and reducing the wet state load, the boiler water temperature is controlled at 300 °C, that is, the extraction steam volume is adjusted to raise the temperature of the boiler water by 20 - 30 °C.

[0051] After the steam heats the boiler water, the temperature is 320 ± 10 °C, which can be led to the pulverized coal pipeline in front of the furnace to preheat the pulverized coal, increase the pulverized coal temperature, reduce the ignition heat of the pulverized coal air flow, and improve the stable combustion ability of the boiler under low load. For bituminous coal, the mixed temperature of the primary air and pulverized coal in the direct-fired system is generally 70 - 80 °C. After being heated by steam, it increases by 30 - 50 °C, and the steam temperature drops to about 100 ± 10 °C, becoming drain water. The steam heating of the pulverized coal is carried out through a surface heater, which is set on the straight pipe section before entering the furnace. A steam extraction pipeline isolation shut-off valve 8 and a steam flow regulating valve 9 are set on the steam extraction pipeline for system isolation and steam volume adjustment. A waste steam shut-off valve 10 is set on the waste steam pipeline 7 for system isolation and is not put into use under high load. Temperature and pressure measuring points of the working medium are set on the intermediate steam pipeline 4 and the waste steam pipeline 7.

[0052] When the supercritical boiler flexibility peak shaving system in this embodiment is in use, when the unit continues to reduce the load during the ultra-low load (below 30% of the rated load) and the boiler needs to switch to the wet state, a part of the steam is extracted from the hot reheat steam header to heat the boiler water from the economizer outlet to the lower water wall header, increasing the temperature by 20 - 30 °C, reducing the wet state load to 20 - 25% of the rated load, the steam temperature drops from above 500 °C to 320 ± 10 °C, and the steam flow is adjusted by a control valve to control the temperature of the boiler water entering the water wall at 300 ± 5 °C; the steam above 300 °C is still in the superheated state and is led to the lower or the second lower pulverized coal pipeline (straight section) in front of the furnace, where it heats the pulverized coal air flow through a surface heater, increasing the temperature by 30 - 50 °C, while the steam temperature drops to 100 ± 10 °C, and it is discharged to the regular blowdown flash tank or the heating pipeline through the exhaust gas pipeline.

Claims

1. A supercritical boiler flexibility peak shaving system, characterized in that It includes a reheater hot steam header, a total economizer outlet 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 connected to the outlet of the total economizer outlet pipe (2), and the cold outlet of the steam boiler water heater (3) is connected to the water 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 connected to the reheater hot steam header and / or the superheated steam header, the outlet of the hot steam extraction pipeline (1) is connected to the hot inlet of the steam boiler water heater (3), the hot outlet of the steam boiler water heater (3) is connected to 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 waste steam pipeline (7); A steam flow regulating valve (9) is provided on the hot steam extraction pipeline (1); An extraction steam pipeline isolation shut-off valve (8) is provided on the hot steam extraction pipeline (1) upstream of the steam flow regulating valve (9); The steam boiler water heater (3) adopts a shell-and-tube heater, and the steam pulverized coal heater (6) adopts a surface heater; 2. The supercritical boiler flexibility peak shaving system according to claim 1, wherein The steam pulverized coal heater (6) is arranged on the straight pipe section of the primary air pulverized coal pipeline (5) before entering the furnace, and the primary air pulverized coal pipeline (5) is the pulverized coal pipe corresponding to the single-layer burner in the lower layer or the second lower layer of the boiler; 3. The supercritical boiler flexibility peak shaving system according to claim 1, characterized in that, A waste steam shut-off valve (10) is provided on the waste steam pipeline (7); 4. A supercritical boiler flexibility peak shaving system according to claim 1, characterized in that Temperature sensors and pressure sensors are provided on the 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 on the waste steam pipeline (7); 5. A supercritical boiler flexibility peak shaving system according to claim 1, characterized in that, The waste steam pipeline (7) is connected to the heating pipeline; Or, the waste steam pipeline (7) is connected to the boiler regular blowdown flash tank; 6. A flexible peak shaving method for a supercritical boiler, characterized in that, It is carried out by using the supercritical boiler flexibility peak shaving system described in any one of claims 1-5, including the following process: When the unit is operating at an ultra-low load and continues to reduce the load, and the boiler needs to switch to the wet state, a part of the steam is extracted from the reheater hot steam header and / or the superheated steam header through the hot steam extraction pipeline (1) and sent into the steam boiler water heater (3). The steam and the boiler water in the total economizer outlet pipe (2) exchange heat through the steam boiler water heater (3), so that the steam temperature decreases and the boiler water temperature increases. The heated boiler water enters the water wall lower header, and the steam after temperature reduction flows through the steam pulverized coal heater (6) and heats the pulverized coal air flow in the primary air pulverized coal pipeline (5). The steam becomes condensate after further temperature reduction and is discharged through the waste steam pipeline (7).

7. A method for flexible peak shaving of a supercritical boiler according to claim 6, characterized in that, The steam temperature at the hot inlet of the steam boiler water heater (3) is 500-570°C, and the steam temperature at the outlet of the steam boiler water heater (3) is 320±10°C; The temperature of the boiler water is increased to 300±5°C after being heated by the steam boiler water heater (3); The steam temperature at the hot inlet of the steam pulverized coal heater (6) is 320±10°C, the steam temperature at the hot outlet of the steam pulverized coal heater (6) is 100±10°C, and the temperature of the pulverized coal in the primary air pulverized coal pipeline (5) is increased by 30-50°C.

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