Method for controlling the wall temperature difference of a steam drum after shutdown of a power plant boiler

Abstract

The present application relates to the technical field of boiler temperature control, and specifically discloses a method for controlling the wall temperature difference of a steam pocket after a power station boiler is shut down, which comprises the following steps: after the boiler is shut down and extinguished, steam pocket water is replenished, the adjacent boiler heating system is warmed up, the bottom heating is kept in a standby state, the boiler is naturally depressurized in a first time section, natural ventilation cooling or bottom heating is performed according to the change of the wall temperature difference of the steam pocket, when the wall temperature difference of the steam pocket is less than a third temperature difference set threshold, all manhole doors are opened for ventilation, the ventilation cooling is started by starting the induced draft fan according to the maintenance requirement, until the steam pocket pressure is reduced to below 1.0 Mpa, the upper wall temperature of the steam pocket is reduced to below 180 DEG C, when the wall temperature of the steam pocket is reduced to below 150 DEG C, the steam pocket pressure is reduced to below 0.5 MPa, and the wall temperature difference of the steam pocket is reduced to below a fourth temperature difference set threshold, the bottom heating is exited, and the water is discharged under pressure, the present application utilizes the adjacent boiler heating system to reduce the descending speed of the lower wall temperature of the steam pocket after the boiler is shut down, and reduces the wall temperature difference of the steam pocket, thereby meeting the production requirement.

Description

Technical Field

[0001] This invention relates to the field of boiler temperature control technology, and in particular to a method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down. Background Technology

[0002] Subcritical boilers in power plants, due to their thicker and longer steam drum walls and the exceptionally high pressure they withstand, are prone to developing temperature differences between the upper and lower walls of the steam drum during unit start-up and shutdown. This generates significant thermal stress, leading to steam drum bending and deformation, which impacts the safe operation and lifespan of the steam drum. Therefore, effectively controlling the temperature difference of the steam drum walls is crucial during unit operation.

[0003] When the boiler is shut down, the pressure in the steam drum decreases. The saturated steam inside the drum is heated by the upper drum wall and becomes superheated steam. Superheated steam has a lower density than saturated steam, forming a protective film of superheated steam on the upper inner wall of the drum. Superheated steam has poor thermal conductivity and cannot form convective heat transfer, resulting in very slow cooling of the upper drum wall. Meanwhile, the lower drum wall, in contact with the boiler water, continues to circulate naturally and cools faster. Therefore, during the shutdown process, the upper part of the drum has a higher temperature, while the lower part has a lower temperature. Normally, after a boiler is shut down, pressurized water is released when the steam drum pressure is between 0.5 and 0.8 MPa. This involves opening the blowdown valve, economizer, and all drain and air valves in the boiler body. In some units, the temperature difference between the upper and lower walls of the steam drum rises rapidly within 30 to 40 minutes after water release, sometimes reaching 70 to 90°C. However, according to production regulations, the temperature difference between the upper and lower parts of the steam drum should not exceed 50°C. Therefore, it is necessary to control the steam pressure to prevent a sharp drop. Otherwise, the lower part of the steam drum will cool down too quickly, resulting in a temperature difference exceeding 50°C, which would not meet production requirements.

[0004] Since the boiler is equipped with an adjacent furnace heating system, and the adjacent furnace heating system is usually used when the boiler is started up, this application applies the adjacent furnace heating system to the shutdown period in order to solve the above-mentioned technical problems. Summary of the Invention

[0005] To address the technical problems in the prior art, this invention provides a method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down.

[0006] This invention includes a method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, comprising:

[0007] After the boiler is shut down and the flame is extinguished, water is added to the steam drum, and the heating system of the adjacent boiler is warmed up at the same time, keeping the bottom heating in standby mode.

[0008] The boiler is naturally depressurized within the first time period after shutdown.

[0009] After the boiler is shut down, natural ventilation cooling or bottom heating is carried out according to the temperature difference of the steam drum wall.

[0010] Once the temperature difference of the steam drum wall is less than the third temperature difference set threshold, open all manhole doors in the furnace, high-temperature reheater and high-temperature superheater for ventilation, and start the induced draft fan for ventilation and cooling as needed for maintenance, until the steam drum pressure drops below 1.0 MPa and the upper wall temperature of the steam drum drops below 180°C.

[0011] When the steam drum wall temperature drops below 150℃, the steam drum pressure drops below 0.5MPa, and the steam drum wall temperature difference drops below the fourth temperature difference setting threshold, stop bottom heating and drain water under pressure.

[0012] After the water is drained, monitor the temperature difference of the steam drum wall. If the temperature difference of the steam drum wall increases, close all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves to seal and insulate the furnace. If the temperature of the upper wall of the steam drum drops to the set temperature threshold, open all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves.

[0013] Furthermore, replenishing the steam drum with water includes:

[0014] During the water replenishment process, monitor the temperature change of the upper wall of the steam drum. If the rate of temperature drop does not exceed the temperature drop rate threshold, continue water replenishment. If the rate of temperature drop exceeds the temperature drop rate threshold, stop water replenishment and wait until the rate of temperature drop does not exceed the temperature drop rate threshold before continuing water replenishment until the water level reaches the maximum level and then stop water replenishment.

[0015] Furthermore, the threshold for the rate of temperature decrease is 10℃ / hour.

[0016] Furthermore, natural pressure reduction of the boiler includes:

[0017] Check the manual valves for fixed discharge, continuous discharge, and drainage. If there is internal leakage, manually close the valves. At the same time, close all dampers, coke holes, and manholes to seal the furnace and allow for natural pressure reduction.

[0018] Furthermore, the first time segment is 6 to 8 hours.

[0019] Furthermore, natural ventilation cooling is implemented based on the temperature difference changes in the steam drum walls, including:

[0020] If the temperature difference of the steam drum wall is greater than the first temperature difference setting threshold, the bottom heating manual main valve and the manual valves of each branch of the bottom heating are slightly opened to deliver heat into the furnace. By adjusting the opening of the bottom heating manual main valve, the steam drum pressure drop rate is controlled to be no less than the first pressure drop setting threshold, and the steam drum wall temperature difference is controlled to be less than the second temperature difference setting threshold.

[0021] If the temperature difference of the steam drum wall is not greater than the first temperature difference setting threshold, the coke-breaking door is opened for natural ventilation cooling; the first temperature difference setting threshold is less than the second temperature difference setting threshold.

[0022] Furthermore, the first temperature difference setting threshold is 25℃; the first pressure drop setting threshold is 0.05Mpa / hour; and the second temperature difference setting threshold is 30℃.

[0023] Furthermore, pressurized waterproofing is performed, including:

[0024] The electric drain valve of the lower water-cooled wall header is opened in turn to drain water.

[0025] During water discharge, if the temperature difference of the steam drum wall increases to the third temperature difference threshold, the scorch gate and manhole door will be sealed and water discharge will be stopped; and the bottom heating will be slightly opened to maintain pressure stability for 2 hours.

[0026] If the temperature difference of the steam drum wall drops to the fourth temperature difference threshold, continue to release water;

[0027] After the water is drained, close the electric drain valve of the lower header of the cold wall.

[0028] Furthermore, the third temperature difference threshold is set at 20℃; the fourth temperature difference threshold is set at 15℃.

[0029] Furthermore, the temperature threshold is set at 60°C.

[0030] The method for controlling the drum wall temperature difference after a power plant boiler shutdown according to the present invention involves, firstly, replenishing water to the drum after the boiler is shut down, and simultaneously warming the adjacent boiler heating system, keeping the bottom heating system in standby mode. Then, within the first time period after shutdown, the boiler is naturally depressurized. Afterwards, natural ventilation cooling or bottom heating is performed based on the changes in the drum wall temperature difference. When the drum wall temperature difference is less than a third set threshold, all manholes in the furnace, high-temperature reheater, and high-temperature superheater are opened for ventilation. The induced draft fan is started for ventilation and cooling as needed for maintenance, until the drum pressure drops below 1.0 MPa and the upper drum wall temperature drops below 180°C, and further until the drum wall temperature drops to 15°C. When the temperature drops below 0℃, the steam drum pressure drops below 0.5MPa, and the steam drum wall temperature difference drops below the fourth temperature difference setting threshold, bottom heating is stopped, and pressurized water is discharged. After the water discharge is completed, the change in the steam drum wall temperature difference is monitored. If the steam drum wall temperature difference increases, all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves are closed to seal and insulate the furnace. If the upper wall temperature of the steam drum drops to the temperature setting threshold, all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves are opened. This utilizes the adjacent boiler heating system to reduce the rate of temperature drop of the lower wall of the steam drum after boiler shutdown, thereby reducing the steam drum wall temperature difference and meeting production requirements. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0032] Figure 1 This is a flowchart illustrating the steps of a method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, according to an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of bottom heating according to an embodiment of the present invention. Detailed Implementation

[0034] The technical solutions in 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 protection scope of the present invention.

[0035] This invention includes a method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, such as... Figure 1 As shown, the method includes the following steps:

[0036] Step S10: After the boiler is shut down and the flame is extinguished, water is added to the steam drum, and the heating system of the adjacent boiler is warmed up at the same time, keeping the bottom heating in standby mode.

[0037] like Figure 2 As shown, the bottom heating system includes water-cooled wall lower headers on four walls: front, rear, left, and right. Each wall has eight branches, and each branch can have two manual doors (not shown).

[0038] In this step, the process of replenishing the steam drum with water includes:

[0039] During the water replenishment process, the temperature change of the upper wall of the steam drum is monitored. If the temperature drop rate does not exceed the temperature drop rate threshold, water replenishment continues. If the temperature drop rate exceeds the temperature drop rate threshold, it indicates that the temperature of the upper wall of the steam drum is dropping too quickly, so water replenishment is stopped. Water replenishment resumes only when the temperature drop rate does not exceed the temperature drop rate threshold, until the water level reaches the maximum and then water replenishment is stopped. In this embodiment, the temperature drop rate threshold can be set to 10℃ / hour. Those skilled in the art can also make appropriate modifications to this value according to the boiler model and production requirements, which are not limited here.

[0040] After the steam drum is replenished with water and the bottom heating is ready, proceed to step S20.

[0041] Step S20: Naturally reduce the pressure of the boiler during the first time period after shutdown.

[0042] Specifically, in this embodiment, the natural pressure reduction of the boiler includes:

[0043] Check the manual valves for fixed-flow, continuous-flow, and drainage. If any valves have internal leaks, manually close them. At the same time, close all dampers, coke holes, and manholes to seal the furnace and allow for natural pressure reduction. Based on actual operation, set the first time period to 6-8 hours, that is, allow for natural pressure reduction within 6-8 hours after furnace shutdown. After 6-8 hours, continue with step S30.

[0044] Step S30: After the first time interval following the shutdown, perform natural ventilation cooling or bottom heating based on the temperature difference changes in the steam drum wall.

[0045] Specifically, this step involves natural ventilation cooling based on the temperature difference changes in the steam drum walls, including:

[0046] If the temperature difference of the drum wall is greater than the first temperature difference setting threshold, the bottom heating manual main valve and the manual valves of each branch of the bottom heating are slightly opened to transfer heat into the furnace. By adjusting the opening of the bottom heating manual main valve, the pressure drop rate of the drum is controlled to be no less than the first pressure drop setting threshold, and the temperature difference of the drum wall is controlled to be less than the second temperature difference setting threshold. If the temperature difference of the drum wall is not greater than the first temperature difference setting threshold, the coking door is opened for natural ventilation cooling.

[0047] In this embodiment of the invention, the first temperature difference setting threshold is less than the second temperature difference setting threshold. For example, the first temperature difference setting threshold is set to 25°C, the first pressure drop setting threshold is set to 0.05 MPa / hour, and the second temperature difference setting threshold is set to 30°C. When the drum wall temperature difference is greater than 25°C, the main manual valve for bottom heating and the manual valves for each branch of bottom heating are slightly opened to deliver heat into the furnace. By adjusting the opening of the main manual valve for bottom heating, the pressure drop rate of the drum is controlled to be no less than 0.05 MPa / hour, and the drum wall temperature difference is controlled to be less than 30°C. If the drum wall temperature difference is less than or equal to 25°C, the coking valve is opened for natural ventilation cooling.

[0048] Step S40: Once the temperature difference of the steam drum wall is less than the third temperature difference set threshold, open all manhole doors in the furnace, high-temperature reheater and high-temperature superheater for ventilation, and start the induced draft fan for ventilation and cooling as needed for maintenance, until the steam drum pressure drops below 1.0 MPa and the upper wall temperature of the steam drum drops below 180°C.

[0049] In this embodiment, the third temperature difference setting threshold is less than the first temperature difference setting threshold, for example, it is set to 20°C. When the temperature difference of the steam drum wall is less than 20°C, all manhole doors at the furnace, high-temperature reheater and high-temperature superheater are opened for ventilation, and the induced draft fan is started for ventilation and cooling as needed for maintenance, until the steam drum pressure drops below 1.0 MPa and the upper wall temperature of the steam drum drops below 180°C.

[0050] After the steam drum pressure drops below 1.0 MPa and the steam drum upper wall temperature drops below 180°C, continue ventilation and cooling until the steam drum wall temperature drops below 150°C and the steam drum pressure drops below 0.5 MPa, then proceed to step S50.

[0051] Step S50: When the steam drum wall temperature drops below 150℃, the steam drum pressure drops below 0.5MPa, and the steam drum wall temperature difference drops below the fourth temperature difference setting threshold, exit bottom heating and perform pressurized water discharge.

[0052] In this embodiment, the fourth temperature difference setting threshold is lower than the third temperature difference setting threshold in the above steps. For example, the value of the fourth temperature difference setting threshold is set to 15°C. When the temperature difference of the steam drum wall drops below 15°C, bottom heating is stopped, and pressurized water is discharged.

[0053] Specifically, this step involves pressurized waterproofing, including:

[0054] The electric drain valve of the lower water-cooled wall header is opened in turn to drain water.

[0055] During water discharge, if the temperature difference of the steam drum wall increases to 20°C, the coking door and manhole door will be sealed and water discharge will be stopped; the bottom heating will be slightly opened to maintain stable pressure for 2 hours, thereby reducing the rate of temperature drop of the lower wall of the steam drum and causing the temperature difference of the steam drum wall to gradually decrease.

[0056] If the temperature difference between the steam drum walls drops to 15°C, continue releasing water.

[0057] After the water is drained, close the electric drain valve of the lower header of the cold wall.

[0058] Step S60: After the water is drained, monitor the temperature difference of the steam drum wall. If the temperature difference of the steam drum wall increases, close all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves to seal and insulate the furnace. If the temperature of the upper wall of the steam drum drops to the set temperature threshold, open all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves.

[0059] The temperature threshold in this step can be set to 60℃. After the temperature of the upper wall of the steam drum drops to 60℃, open all drain valves, drain valves, economizer recirculation valves, air valves, venting steam to the air, continuous venting, and fixed venting to achieve orderly cooling after the boiler is shut down.

[0060] The method for controlling the drum wall temperature difference after a power plant boiler shutdown according to the present invention involves, firstly, replenishing water to the drum after the boiler is shut down, and simultaneously warming the adjacent boiler heating system, keeping the bottom heating system in standby mode. Then, within the first time period after shutdown, the boiler is naturally depressurized. Afterwards, natural ventilation cooling or bottom heating is performed based on the changes in the drum wall temperature difference. When the drum wall temperature difference is less than a third set threshold, all manholes in the furnace, high-temperature reheater, and high-temperature superheater are opened for ventilation. The induced draft fan is started for ventilation and cooling as needed for maintenance, until the drum pressure drops below 1.0 MPa and the upper drum wall temperature drops below 180°C, and further until the drum wall temperature drops to 15°C. When the temperature drops below 0℃, the steam drum pressure drops below 0.5MPa, and the steam drum wall temperature difference drops below the fourth temperature difference setting threshold, bottom heating is stopped, and pressurized water is discharged. After the water discharge is completed, the change in the steam drum wall temperature difference is monitored. If the steam drum wall temperature difference increases, all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves are closed to seal and insulate the furnace. If the upper wall temperature of the steam drum drops to the temperature setting threshold, all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves are opened. This utilizes the adjacent boiler heating system to reduce the rate of temperature drop of the lower wall of the steam drum after boiler shutdown, thereby reducing the steam drum wall temperature difference and meeting production requirements.

[0061] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, characterized in that, include: After the boiler is shut down and the flame is extinguished, water is added to the steam drum, and the heating system of the adjacent boiler is warmed up at the same time, keeping the bottom heating in standby mode. The boiler is naturally depressurized in the first period after shutdown; After the boiler is shut down, natural ventilation cooling or bottom heating is carried out according to the temperature difference of the steam drum wall. Once the temperature difference of the steam drum wall is less than the third temperature difference set threshold, all manhole doors in the furnace, high-temperature reheater, and high-temperature superheater are opened for ventilation, and the induced draft fan is started for ventilation and cooling as needed for maintenance, until the steam drum pressure drops below 1.0 MPa and the upper wall temperature of the steam drum drops below 180°C; the third temperature difference set threshold is 20°C. When the steam drum wall temperature drops below 150℃, the steam drum pressure drops below 0.5MPa, and the steam drum wall temperature difference drops below the fourth temperature difference setting threshold, stop bottom heating and drain water under pressure. After the water is drained, monitor the temperature difference of the steam drum wall. If the temperature difference of the steam drum wall increases, close all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves to seal and insulate the furnace. If the temperature of the upper wall of the steam drum drops to the set temperature threshold, open all drain valves, drain valves, economizer recirculation valves, air valves, venting valves, continuous exhaust valves, and fixed exhaust valves.

2. The method for controlling the temperature difference of the steam drum wall after shutdown of a power plant boiler as described in claim 1, characterized in that, Steam drum water replenishment includes: During the water replenishment process, monitor the temperature change of the upper wall of the steam drum. If the rate of temperature drop does not exceed the temperature drop rate threshold, continue water replenishment. If the rate of temperature drop exceeds the temperature drop rate threshold, stop water replenishment and wait until the rate of temperature drop does not exceed the temperature drop rate threshold before continuing water replenishment until the water level reaches the maximum level and then stop water replenishment.

3. The method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, as described in claim 2, is characterized in that... The threshold for the rate of temperature decrease is 10°C / hour.

4. The method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, as described in claim 2, is characterized in that... Natural pressure reduction of the boiler includes: Check the manual valves for fixed discharge, continuous discharge, and drainage. If there is internal leakage, manually close the valves. At the same time, close all dampers, coke holes, and manholes to seal the furnace and allow for natural pressure reduction.

5. The method for controlling the temperature difference of the steam drum wall after shutdown of a power plant boiler as described in claim 4, characterized in that, The first time period is 6 to 8 hours.

6. The method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, as described in claim 5, is characterized in that... Natural ventilation cooling is implemented based on the temperature difference changes in the steam drum wall, including: If the temperature difference of the steam drum wall is greater than the first temperature difference setting threshold, the bottom heating manual main valve and the manual valves of each branch of the bottom heating are slightly opened to deliver heat into the furnace. By adjusting the opening of the bottom heating manual main valve, the steam drum pressure drop rate is controlled to be no less than the first pressure drop setting threshold, and the steam drum wall temperature difference is controlled to be less than the second temperature difference setting threshold. If the temperature difference of the steam drum wall is not greater than the first temperature difference setting threshold, the coke-breaking door is opened for natural ventilation cooling; the first temperature difference setting threshold is less than the second temperature difference setting threshold.

7. The method for controlling the temperature difference of the steam drum wall after shutdown of a power plant boiler as described in claim 6, characterized in that, The first temperature difference setting threshold is 25℃; the first pressure drop setting threshold is 0.05Mpa / hour; and the second temperature difference setting threshold is 30℃.

8. The method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, as described in claim 6, is characterized in that... Performing pressurized water release includes: The electric drain valve of the lower water-cooled wall header is opened in turn to drain water. During water discharge, if the temperature difference of the steam drum wall increases to the third temperature difference threshold, the scorch gate and manhole door will be sealed and water discharge will be stopped; and the bottom heating will be slightly opened to maintain pressure stability for 2 hours. If the temperature difference of the steam drum wall drops to the fourth temperature difference threshold, continue to release water; After the water is drained, close the electric drain valve of the lower header of the cold wall.

9. The method for controlling the temperature difference of the steam drum wall after a power plant boiler is shut down, as described in claim 8, is characterized in that... The fourth temperature difference threshold is set at 15°C.

10. The method for controlling the temperature difference of the steam drum wall after shutdown of a power plant boiler as described in claim 8, characterized in that, The temperature setting threshold is 60℃.

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