Method for stress regulation of thick-walled components of a boiler

Abstract

The application discloses a boiler thick-wall part stress regulation method and relates to the technical field of boilers. The method comprises the following steps: heating the inside heating surface of a boiler by introducing heated air into the boiler until the boiler is ready for water filling; simultaneously with the introduction of the heated air into the boiler, electric heating is performed on the medium tangential inlet pipeline of the steam-water separator of the boiler until the wall temperature of the medium tangential inlet pipeline exceeds the preset limit power of the electric heating; and electric heating is performed on the outer wall of the water storage tank of the boiler until the wall temperature of the water storage tank exceeds the preset limit power of the electric heating. The application reduces the temperature and pressure rising time of the boiler.

Description

A method for stress control of thick-walled components in boilers Technical Field

[0001] This invention relates to the field of boiler technology, and in particular to a method for stress control of thick-walled components in boilers. Background Technology

[0002] Coal-fired power will shift from its past role as the "main power source, fundamental position, and supporting role" to a "balanced role as base load power source and regulating power source" in the near to medium term (2021-2030). Coal-fired power will play a fundamental role in coal conversion, power and heat supply, and system peak shaving. In the long term (2031-2050), coal-fired power will become a purely "regulating power source," providing a safety net for power supply security and peak shaving for the full absorption of clean energy. As the annual utilization hours of coal-fired power plants gradually decrease, flexible operation of coal-fired power plants has become the norm. However, the original design life of the main pressure-bearing components of the boiler in the unit was 30 years. Taking a certain supercritical boiler design as an example, the cold start-stop life is >500 times, the warm start-stop life is >1200 times, the hot start life is >5000 times, and the extremely hot start life is >500 times. With the increasingly frequent requirements for flexible operation of coal-fired units, the number of rapid load changes and cold, warm, hot, and extremely hot start-ups of coal-fired units will increase significantly. How to ensure the safety of thick-walled components under flexible operation has become a concern. Currently, the highest variable load range of once-through boilers has reached 30%-100% of the boiler's maximum continuous rating (BMCR), while the lowest stable operating load has reached below 20% of the BMCR. Therefore, the stress amplitude variation range experienced by the unit during startup has become larger than the original design range.

[0003] Figure 2 shows the stress superposition of thick-walled components during the entire start-up and shutdown process of the unit. In Figure 2, (a) represents cold start, (b) represents warm start, and (c) represents hot start. 1 represents thermal stress, 2 represents internal pressure membrane stress, and 3 represents total stress. The stress is mainly composed of internal pressure stress and thermal stress. Among them, internal pressure stress is mainly related to the operating pressure of the unit, while thermal stress is related to the load change rate of the unit. Since the operating parameters of the working fluid during unit startup are determined by the load, and the working fluid pressure is basically a fixed parameter at a certain load, the membrane stress caused by internal pressure tends to a constant value throughout the startup process. Due to different start-up and shutdown rates, thick-walled components will have different internal and external wall temperature differences (where the greater the change rate, the greater the unit wall temperature; in Figure 2, the internal and external wall temperature difference 1' < 1”), causing the superposition amplitude of the combined stress during the entire start-up and shutdown process to increase with the increase of the internal and external wall temperature difference (in Figure 2, the superposition stress Δσ' < Δσ”). Both 1' and 1” represent thermal stress, caused by temperature difference, specifically the temperature difference between the inner and outer walls. In Figure 2, the rate of change of the inner wall temperature represented by 1' is less than that represented by 1”, meaning: the temperature difference between the inner and outer walls 1' < 1”. 3' and 3” represent the total stress resulting from their combination with 2 (the membrane stress caused by internal pressure). That is, 1' and 2 combine to form 3', and 1” and 2 combine to form 3”. Different start-up methods result in varying stress superposition amplitudes due to the initial wall temperature of the unit (due to the influence of the working fluid, the temperature difference between the inner and outer walls is greatest during cold start-up and least during hot start-up), depending on the thickness of the furnace wall temperature (superposition stress Δσ). 冷态启动 >Δσ 温态启动 >Δσ 热态启动 ).

[0004] According to stress design principles, the stress amplitude of a coal-fired power unit is mainly composed of internal pressure stress and thermal stress. During the initial cold start-up phase, drastic changes in internal pressure cause significant changes in thermal stress. Therefore, during this initial phase, the pressure cannot change rapidly to prevent large temperature fluctuations. These drastic temperature changes during startup result in a negative combined stress. The greater the rate of temperature change, the smaller the negative thermal stress becomes, leading to an increase in the final combined stress amplitude. Therefore, if active external heating is used to preheat thick-walled components during the initial cold start-up phase, the internal temperature difference of these components can be effectively reduced, and thermal stress can be effectively controlled.

[0005] During the initial cold start-up of thick-walled components in a once-through boiler, drastic changes in thermal stress are concentrated primarily in these components. Using external heating to raise the temperature of these components during the initial startup phase effectively reduces the limitation of thermal stress on the start-up and shutdown speed. To prevent localized metal thermal fatigue caused by uneven thermal stress in these heat storage components, a very long startup time is often required during the development of the startup curve. The long water filling stage during cold start-up and the temperature and pressure rise stage during cold and hot start-up significantly limit the rate of change in deep peak shaving for coal-fired boilers. Summary of the Invention

[0006] The purpose of this invention is to provide a method for stress control of thick-walled components in boilers, thereby reducing the heating and pressurization time of the boiler.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A method for stress control of thick-walled components in a boiler includes:

[0009] The heated air is introduced into the boiler to heat the internal heating surfaces until the boiler is ready to be filled with water.

[0010] While the heated air is introduced into the boiler, the tangential inlet pipe of the boiler's steam-water separator is electrically heated until the wall temperature of the tangential inlet pipe exceeds the preset limit power of the electric heating. The outer wall of the boiler's water storage tank is also electrically heated until the wall temperature of the water storage tank exceeds the preset limit power of the electric heating.

[0011] Optionally, the step of introducing heated air into the boiler to heat the internal heating surfaces until the boiler is ready to be filled with water specifically includes:

[0012] The air output from the compressed air system is electrically heated;

[0013] The heated air is introduced into the boiler in three separate streams to heat the internal heating surfaces of the boiler until the boiler is ready to be filled with water.

[0014] Optionally, the step of introducing heated air into the boiler through three channels to heat the internal heating surfaces of the boiler until the boiler is ready to be filled with water specifically includes:

[0015] The heated air from the first path is introduced through the drain valve after the main water supply valve and discharged through the exhaust valve of the high-temperature superheater.

[0016] The heated air from the second path is introduced from the water storage tank to the drain valve in front of the condenser drain valve and discharged through the high-temperature superheater exhaust valve.

[0017] The heated air from the third path is discharged from the high-pressure cylinder and connected to the drain valve after the valve of the low-temperature reheater, and then discharged through the exhaust valve of the high-temperature reheater.

[0018] Optionally, the first heated air accounts for 50% of the total compressed air output flow, the second heated air accounts for 30% of the total compressed air output flow, and the third heated air accounts for 20% of the total compressed air output flow.

[0019] Optionally, the electric heating of the air output from the compressed air system specifically includes:

[0020] An electric heater is used to electrically heat the air output from the compressed air system, and the target temperature of the electric heater is twice the wall temperature of the steam-water separator.

[0021] Optionally, the step of introducing heated air into the boiler through three channels to heat the internal heating surfaces of the boiler until the boiler is ready to be filled with water further includes:

[0022] The valve opening of the first-path heated air output is controlled by the wall temperature of the high-temperature superheater.

[0023] The valve opening of the second-path heated air output is controlled by the wall temperature of the steam-water separator;

[0024] The opening degree of the valve for the third-path heated air output is controlled by the wall temperature of the high-temperature reheater.

[0025] Optionally, a first mica electric heating element is wrapped around the outside of each medium tangential inlet pipe on the steam-water separator.

[0026] Optionally, a second mica electric heating element is covered on the portion of the outer wall of the water storage tank between the water outlet and the water inlet, and a third mica electric heating element is covered on the portion of the outer wall of the water storage tank between the water inlet and the inlet of the water storage tank.

[0027] Optionally, the step of simultaneously introducing heated air into the boiler and electrically heating the tangential inlet pipe of the boiler's steam-water separator until the wall temperature of the tangential inlet pipe exceeds a preset limit power for electric heating, and electrically heating the outer wall of the boiler's water storage tank until the wall temperature of the water storage tank exceeds a preset limit power for electric heating, specifically includes:

[0028] The heating power of the first mica electric heating element is controlled by the wall temperature of the steam-water separator and the inlet steam temperature of the roof superheater.

[0029] When the boiler is in the water filling period, the power for electric heating of the second mica electric heating element and the third mica electric heating element is set to be the same;

[0030] After the boiler is filled with water, the power of the second mica electric heating element is controlled according to the boiler wall temperature corresponding to the second mica electric heating element, and the power of the third mica electric heating element is controlled according to the boiler wall temperature corresponding to the third mica electric heating element.

[0031] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0032] Before the boiler is filled with water, this invention heats the internal heating surfaces of the boiler by introducing heated air into the boiler. At the same time as the heated air is introduced into the boiler, the tangential inlet pipe of the steam-water separator is electrically heated, and the outer wall of the boiler's water storage tank is electrically heated until the corresponding wall temperature exceeds the preset limit power of the electric heating. This ensures a higher wall temperature for thick-walled components, reduces the boiler's heating and pressurization time, and enables the boiler to start up quickly to meet the needs of deep peak shaving. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 is a schematic flowchart of a stress control method for thick-walled components of a boiler provided by an embodiment of the present invention;

[0035] Figure 2 is a schematic diagram of stress superposition under different start-up modes;

[0036] Figure 3 is a schematic cross-sectional view of a DC boiler provided in an embodiment of the present invention;

[0037] Figure 4 is a schematic diagram of the compressed air system heating provided in an embodiment of the present invention;

[0038] Figure 5 is a schematic diagram of the compressed air-assisted heating control principle provided in an embodiment of the present invention;

[0039] Figure 6 is a simplified diagram of the DC boiler start-up system provided in an embodiment of the present invention;

[0040] Figure 7 is a partial cross-sectional front view of the steam-water separator provided in an embodiment of the present invention;

[0041] Figure 8 is a partial cross-sectional top view of the steam-water separator provided in an embodiment of the present invention;

[0042] Figure 9 is an unfolded view of the mica electric heating element in the tangential inlet pipe of the medium provided in an embodiment of the present invention;

[0043] Figure 10 is a partial cross-sectional front view of the water storage tank provided in an embodiment of the present invention;

[0044] Figure 11 is a partial cross-sectional top view of the water storage tank provided in an embodiment of the present invention;

[0045] Figure 12 is a front cross-sectional view of the thick-walled electric heating cover of the water storage tank provided in an embodiment of the present invention;

[0046] Figure 13 is a schematic diagram of the external auxiliary heating control principle provided in an embodiment of the present invention.

[0047] Symbol explanation:

[0048] 1-Main feedwater valve, 2-Main steam valve, 3-High-pressure cylinder exhaust valve to low-temperature reheater valve, 4-Reheat steam valve, 5-Steam-water separator valve to water tank valve, 6-Water tank valve to condenser valve, 7-High-temperature superheater exhaust valve, 8-High-temperature reheat exhaust valve, 9-Heat exchanger attached to the furnace wall, 10-First compressed air inlet to boiler, 11-Second compressed air inlet to boiler, 12-Third compressed air inlet to boiler, 13-Electric heater, 14-Filter screen, 15-Saturated steam outlet, 16-Tangential medium inlet, 17-First wall temperature measuring point, 18-Saturated water outlet, 19-Steam outlet, 20-Upper water level measuring point, 21-Second wall temperature measuring point, 22-Water inlet, 23-Lower water level measuring point, 24-Third wall temperature measuring point, 25-Drain outlet, 26-Thick wall of water tank. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] The purpose of this invention is to provide a method for stress control of thick-walled components in boilers, thereby reducing the heating and pressurization time of the boiler.

[0051] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] The boiler of this invention is a once-through boiler. This embodiment of the stress control method for thick-walled components of a boiler is implemented using supercritical spiral tube once-through boiler technology, and is also applicable to supercritical boilers with vertical tube panel arrangement.

[0053] Before a cold start, the temperature of a once-through boiler is generally at or slightly above ambient temperature. To reduce the damage of thermal stress to the thick-walled pressure-bearing components of the boiler body, strict limits are placed on the boiler's water filling temperature and the temperature difference between the inner and outer walls of the thick-walled components during water filling. If the water filling rate is too low, although it ensures uniform expansion throughout the boiler, the time required for heating and pressurization will be further prolonged, which is unsuitable for the current deep peak-shaving requirements of the power grid. If the water filling rate is too high, although it reduces the time required for heating and pressurization, the rapid heating of the pressure-bearing components will cause uneven expansion of the thick-walled components, increasing the starting thermal stress on these components, increasing the stress amplitude during full-load cycling, and shortening the boiler's service life.

[0054] This invention provides a method for stress control of thick-walled components in a boiler, as shown in Figure 1. The method includes the following steps.

[0055] Step 101: Introduce heated air into the boiler to heat the internal heating surfaces until the boiler is ready to be filled with water.

[0056] Figure 3 shows a boiler including a main feedwater valve 1, a main steam valve 2, a high-pressure cylinder exhaust valve to the low-temperature reheater 3, a reheat steam valve 4, a steam-water separator to the water storage tank valve 5, a water storage tank to the condenser valve 6, a high-temperature superheater exhaust valve 7, a high-temperature reheat exhaust valve 8, a heat exchanger attached to the furnace wall 9, a first compressed air inlet to the boiler 10, a second compressed air inlet to the boiler 11, and a third compressed air inlet to the boiler 12. The heat exchangers attached to the furnace wall include roof superheaters and wall-mounted superheaters. In Figure 3, "low reheat" is short for low-temperature reheater, "low superheater" is short for low-temperature superheater, "high reheat" is short for high-temperature reheater, "high superheater" is short for high-temperature superheater, and "screen superheater" is short for screen-type superheater.

[0057] As shown in Figures 3 and 4, the present invention uses an electric heating rapid heating device to preheat compressed air before it flows through the boiler working fluid side, thereby increasing the wall temperature of the metal pipes and thick-walled components of the water supply system.

[0058] The electric heater 13 heats the air output from the compressed air system, and the heated air is divided into three paths after passing through the filter 14.

[0059] Step 101 specifically includes:

[0060] The air output from the compressed air system is electrically heated.

[0061] The heated air is introduced into the boiler in three separate streams to heat the internal heating surfaces of the boiler until the boiler is ready to be filled with water.

[0062] The process of introducing heated air into the boiler through three channels to heat the boiler's internal heating surfaces until the boiler is ready to be filled with water specifically includes:

[0063] The heated air from the first path is introduced through the drain valve after the main water supply valve and discharged through the exhaust valve of the high-temperature superheater.

[0064] The heated air from the second path is introduced from the water storage tank to the drain valve in front of the condenser drain valve and discharged through the high-temperature superheater exhaust valve.

[0065] The heated air from the third path is discharged from the high-pressure cylinder and connected to the drain valve after the valve of the low-temperature reheater, and then discharged through the exhaust valve of the high-temperature reheater.

[0066] The first heated air accounts for 50% of the total compressed air output flow, the second heated air accounts for 30% of the total compressed air output flow, and the third heated air accounts for 20% of the total compressed air output flow.

[0067] As shown in Figure 3, compressed air flows through various heat exchangers in the once-through boiler, and the temperature of each heat exchanger decreases. The plant-use compressed air is heated to a certain temperature by an electric heater and then enters the boiler in three separate streams at different mass flow rates. The first stream enters after the drain valve behind the main feedwater valve, passing through the economizer, water-cooled walls, low-temperature superheater, roof superheater, wall-mounted superheater, screen superheater, and high-temperature superheater, before exiting through the exhaust valve of the high-temperature superheater. Due to the large number of heat exchangers involved and their vast heat exchange areas, this first stream accounts for 50% of the total compressed air flow. The second stream runs from the water storage tank to the condenser drain valve. The air enters through the drain valve behind the valve of the high-pressure reheater, passes through the heated water tank, steam-water separator, screen-type superheater, and high-temperature superheater, and exits through the exhaust valve of the high-temperature superheater. Because the water tank and steam-water separator are thick-walled heat storage components, the second route accounts for 30% of the total compressed air flow. The third route connects to the drain valve behind the valve of the low-temperature reheater after the exhaust of the high-pressure cylinder, heats the low-temperature reheater and high-temperature reheater, and exits through the exhaust valve of the high-temperature reheater. This part accounts for 20% of the total compressed air flow. The definition of "before" and "after" is that when a valve is connected to a pipeline, the part flowing into the valve is the "before" part, and the part flowing out of the valve is the "after" part.

[0068] The electric heating of the air output from the compressed air system specifically includes:

[0069] An electric heater is used to electrically heat the air output from the compressed air system, and the target temperature of the electric heater is twice the current wall temperature of the steam-water separator.

[0070] The electric heater is powered by 380V plant power, and the relevant feedback temperature measurement points are the existing wall temperature measurement points of the unit. As shown in Figure 5, the process of introducing heated air into the boiler in three paths to heat the internal heating surfaces of the boiler until the boiler is ready to fill with water specifically includes:

[0071] The opening degree of the electric valve for the first path of heated air output is controlled by the end wall of the high-temperature superheater.

[0072] The opening degree of the electric valve for the second-path heated air output is controlled by the end wall of the steam-water separator.

[0073] The opening degree of the electric valve for the third-path heated air output is controlled by the end wall temperature of the high-temperature reheater.

[0074] All three channels are enabled by default.

[0075] The detailed process of electrically heating the air output from the compressed air system includes the following steps.

[0076] Step 1011: Before the boiler starts up and fills with water during cold start of the unit, open the exhaust valves of the boiler high-temperature superheater and high-temperature reheater; open the manual valves for the first, second, and third compressed air to the boiler; close the drain valves after the main feedwater valve, the drain valves before the water tank to the condenser drain valve, and the drain valves after the high-pressure cylinder exhaust (cold reheat) to the low-temperature reheater valve.

[0077] Step 1012: Start the electric heater.

[0078] Step 1013: Start the compressed air system.

[0079] Step 1014: Monitor the temperature rise of each heated surface of the boiler, the target temperature of the electric heater, and the outlet pressure of the compressed air system.

[0080] Step 1015: When the temperature of each heated surface of the boiler rises to the boiler water temperature, check whether the first, second and third compressed air to boiler ventilation electric valves are in the correct position to maintain the minimum compressed air flow rate and ensure that the furnace wall temperature is constant.

[0081] Step 1016: After the water filling preparation is completed, close the manual valves for the first, second, and third compressed air supply to the boiler, and stop the electric heating operation.

[0082] Step 1017: Exit the compressed air auxiliary heating control system.

[0083] This invention applies mica electric heating to some thick-walled components used for heat storage in coal-fired power boilers. By utilizing its customizable shape, block or strip electric heating is applied to the entire outer side of the thick-walled component, thereby regulating the temperature difference between the inner and outer walls during operation and reducing the impact of thermal stress on the boiler.

[0084] During the ignition of a once-through boiler, to reduce flow instability and maintain the water-cooled wall tube temperature below the allowable value, the flow rate in the furnace water-cooled wall tubes must be ensured to be no less than the minimum flow rate. During boiler startup, a startup system needs to be installed before the superheater to drain excess water. Since the startup system (Figure 6) only operates during boiler startup and ultra-low load conditions, its heat storage container wall thickness is often an order of magnitude less than that of a drum boiler. Therefore, the external wall preheating section before water filling is unnecessary; auxiliary heating (circled areas in Figure 6) is sufficient to meet the requirements.

[0085] Step 102: While the heated air is introduced into the boiler, the medium tangential inlet pipe of the boiler's steam-water separator is electrically heated until the wall temperature of the medium tangential inlet pipe exceeds the preset limit power of the electric heating. The outer wall of the boiler's water storage tank is electrically heated until the wall temperature of the water storage tank exceeds the preset limit power of the electric heating.

[0086] The steam-water separator (Figures 7 and 8) is a core component in the startup and heating / pressurization processes of a once-through boiler. It has a cylindrical body with spherical heads. Each separator body has six tangential inlet pipe joints at a 15° angle to the horizontal plane at its upper part. When the steam-water mixture enters the separator tangentially along the body, the centrifugal force generated by rotation separates the steam and water. The separated steam flows from the top outlet pipe to the roof superheater, while the separated water is discharged from the bottom of the separator to a water storage tank. The steam-water separator includes a saturated steam outlet 15, a tangential medium inlet 16, a first temperature measuring point 17, and a saturated water outlet 18. The wall temperature of the steam-water separator is obtained at the first temperature measuring point 17.

[0087] For steam-water separators, the present invention provides the following solution:

[0088] During the process of water filling and heating / pressurization of the DC boiler, the steam-water separator only serves as a medium for separating the working medium and does not participate in the storage of the working medium. Therefore, the present invention only sets an electric heating layer at the tangential inlet interface and adjacent pipes. The electric heating of the tangential inlet pipe of the medium is shown in Figure 9. Block or strip electric heating is laid on the outer surface of the steam-water separator connected thereto.

[0089] A water storage tank (Figures 10 and 11) is located below the steam-water separator to collect the separator's drainage. A vent pipe is located at the top of the tank to release steam carried in by the separator's drainage, and a drain outlet at the bottom is used to adjust the water level and connect to the start-up expansion steam trap. A lower water level measuring point monitors the tank's water level to maintain heat storage, while an upper water level measuring point serves as a warning to prevent the tank from overflowing. Two sets of wall temperature measuring points detect the wall temperature near the upper and lower water level measuring points, respectively. The water storage tank includes a steam vent 19, an upper water level measuring point 20, a second wall temperature measuring point 21, a water inlet 22, a lower water level measuring point 23, a third wall temperature measuring point 24, and a drain outlet 25.

[0090] The outer side of each medium tangential inlet pipe of the gas-water separator is covered with a first mica electric heating element.

[0091] As shown in Figure 12, a second mica electric heating element is installed on the portion of the outer wall of the water storage tank between the upper water level point (upper water level measuring point) and the lower water level point (lower water level measuring point). A third mica electric heating element is installed on the portion of the outer wall of the water storage tank between the lower water level point and the inlet of the water storage tank. No electric heating is installed above the upper water level measuring point because it is above the warning water level and contains steam. The thick wall 26 of the water storage tank is shown in Figure 12.

[0092] The second and third mica electric heating elements are either strip-shaped or block-shaped. The second and third mica electric heating elements are powered by different power supply modules. Block-shaped electric heating elements are installed near the water inlet of the storage tank, with their power supply connected to the corresponding power supply module for the second mica electric heating element. Block-shaped electric heating elements are installed on other small pipes or measuring point interfaces, with their power supply connected to the power supply module of the adjacent area.

[0093] As shown in Figure 13, step 102 specifically includes:

[0094] The heating power of the first mica electric heating element is controlled by the wall temperature of the steam-water separator and the inlet steam temperature of the roof superheater.

[0095] When the boiler is in the water filling period, the power for electric heating of the second mica electric heating element and the third mica electric heating element is set to be the same.

[0096] After the boiler is filled with water, the power of the second mica electric heating element is controlled according to the boiler wall temperature corresponding to the second mica electric heating element, and the power of the third mica electric heating element is controlled according to the boiler wall temperature corresponding to the third mica electric heating element.

[0097] The power supply for the electric heating of the steam-water separator and water storage tank is connected to 380V plant power. The electric heating section of the steam-water separator uses data from the wall temperature measuring point located below the tangential inlet of the medium and the steam temperature data from the inlet of the roof superheater to adjust the corresponding electric heating power in real time. During the boiler water filling period, the A and B groups of heaters in the water storage tank operate at the same power according to the feedwater temperature. During the heating and pressurization phase, the water level in the storage tank fluctuates frequently between the upper and lower water level measuring points. Based on the water level, the power of groups A and B is controlled accordingly. The two groups of heaters in group A use the second mica electric heating element, and the two groups of heaters in group B use the third mica electric heating element. The two groups of heaters in group A are the low-power heating section, and the two groups of heaters in group B are the high-power heating section.

[0098] This invention, while heating the boiler working fluid side system with compressed air, also introduces an external auxiliary heating system for the boiler's thick-walled pressure-bearing components. By installing an electric heating system on the outside of the steam-water separator, water storage tank, and large tee, the wall temperature of the thick-walled components is increased. This method ensures that the boiler obtains sufficient wall temperature, improves the uniform expansion of the thick-walled components, shortens the boiler water filling time, and, due to the increased wall temperature, also increases the feedwater temperature to exceed the current limitations of cold-state water filling temperature for coal-fired units.

[0099] Since the electric heating system has a certain upper temperature limit, after the water filling is completed and the boiler is ignited, the external auxiliary heating system of the boiler pressure-bearing components is kept running. During this process, the operation of the auxiliary heating system and the temperature difference between the inner and outer walls of each thick wall are monitored.

[0100] When the corresponding wall temperature exceeds the limit power of the electric heating, the auxiliary heating system for the corresponding thick wall is shut down. This shortens the time required for the boiler to heat up and pressurize during startup.

[0101] This invention proposes a stress control method for thick-walled boiler components. It employs a combined heating system: a compressed air-assisted heating system preheats the internal heating surfaces of the boiler system, and an electric auxiliary heating system is installed outside the thick-walled pressure-bearing components. By preheating the working fluid side with air and installing electric heating blankets on the outside of the thick-walled pressure-bearing components, the metal wall temperature on the working fluid side is increased. This increased metal wall temperature minimizes the water filling time during boiler operation. Simultaneously, heating ensures the increased temperature of the inner and outer walls of the thick-walled pressure-bearing components, reducing the water filling speed limitation caused by thermal stress. This ensures a corresponding reduction in boiler heating and pressurization time, thereby achieving rapid boiler startup to meet the needs of deep peak shaving.

[0102] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0103] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for stress control of thick-walled components in a boiler, characterized in that, include: The heated air is introduced into the boiler to heat the internal heating surfaces until the boiler is ready to be filled with water. While heated air is introduced into the boiler, the tangential inlet pipe of the boiler's steam-water separator is electrically heated until its wall temperature exceeds a preset power limit. The outer wall of the boiler's water storage tank is also electrically heated until its wall temperature exceeds a preset power limit. Steam separated by the steam-water separator flows from the top outlet pipe to the roof superheater. A first mica electric heating element is wrapped around the outside of each tangential inlet pipe of the steam-water separator. A second mica electric heating element is wrapped around the portion of the outer wall of the water storage tank between the water level point and the lower water level point. The portion of the outer wall of the water storage tank between the water outlet and the inlet of the water storage tank is covered with a third mica electric heating element; the process of electrically heating the medium tangential inlet pipe of the boiler's steam-water separator while the heated air is introduced into the boiler, until the wall temperature of the medium tangential inlet pipe exceeds the preset limit power of the electric heating, and electrically heating the outer wall of the boiler's water storage tank until the wall temperature of the water storage tank exceeds the preset limit power of the electric heating, specifically includes: controlling the heating power of the first mica electric heating element by the wall temperature of the steam-water separator and the inlet steam temperature of the roof superheater; When the boiler is in the water filling period, the power for electric heating of the second mica electric heating element and the third mica electric heating element is set to be the same; after the boiler water filling is completed, the power for electric heating of the second mica electric heating element is controlled according to the boiler wall temperature corresponding to the second mica electric heating element, and the power for electric heating of the third mica electric heating element is controlled according to the boiler wall temperature corresponding to the third mica electric heating element.

2. The stress control method for thick-walled boiler components according to claim 1, characterized in that, The process of introducing heated air into the boiler to heat the internal heating surfaces until the boiler is ready to be filled with water specifically includes: electrically heating the air output from the compressed air system; and introducing the heated air into the boiler in three separate streams to heat the internal heating surfaces until the boiler is ready to be filled with water.

3. The stress control method for thick-walled boiler components according to claim 2, characterized in that, The process of introducing heated air into the boiler in three separate streams to heat the boiler's internal heating surfaces until the boiler is ready to be filled with water includes: introducing the first stream of heated air through the drain valve after the main feedwater valve and discharging it through the high-temperature superheater exhaust valve; introducing the second stream of heated air through the drain valve before the condenser drain valve from the water storage tank and discharging it through the high-temperature superheater exhaust valve; and introducing the third stream of heated air through the drain valve after the high-pressure cylinder exhaust valve to the low-temperature reheater valve and discharging it through the high-temperature reheater exhaust valve.

4. The stress control method for thick-walled boiler components according to claim 3, characterized in that, The first heated air accounts for 50% of the total compressed air output flow, the second heated air accounts for 30% of the total compressed air output flow, and the third heated air accounts for 20% of the total compressed air output flow.

5. The stress control method for thick-walled boiler components according to claim 2, characterized in that, The electric heating of the air output from the compressed air system specifically includes: using an electric heater to electrically heat the air output from the compressed air system, wherein the target temperature of the electric heater is twice the wall temperature of the steam-water separator.

6. The stress control method for thick-walled boiler components according to claim 3, characterized in that, The process of introducing heated air into the boiler in three separate channels to heat the boiler's internal heating surfaces until the boiler is ready to be filled with water further includes: controlling the valve opening of the first channel heated air output by controlling the wall temperature of the high-temperature superheater; controlling the valve opening of the second channel heated air output by controlling the wall temperature of the steam-water separator; and controlling the valve opening of the third channel heated air output by controlling the wall temperature of the high-temperature reheater.

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