Control method to prevent oxide scale from falling off on heating surfaces during peak load regulation and start-up / shutdown of coal-fired units

Abstract

The present invention discloses a control method for preventing oxide scale shedding from the heating surface during peak-shaving startup and shutdown of a coal-fired unit. By controlling the rate of change of steam temperature and pressure during startup and shutdown, sudden changes in steam and wall temperatures are prevented. The method also adjusts the opening of the boiler's additional air and fuel air dampers to control the flue gas temperature at the furnace outlet and prevent overheating and dry burning of the heating surface. The method also adjusts the opening of the high-pressure bypass to control the steam flow rate on the heating surface and prevent sudden changes in superheated steam temperature. During turbine run-up and generator grid connection, the method adjusts the reheat flue gas damper to prevent a sudden rise in reheated steam temperature. During shutdown, the method controls the superheat after the desuperheater to prevent water plugging in the superheater. Thus, without upgrading or renovating the heating surface materials, and only by optimizing the operation control method, it is possible to achieve a state where oxide scale is not detected on the heating surface throttle orifices and the bottom of the U-bend within a single maintenance cycle, and tube bursts are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal-fired power generation, and particularly relates to a control method for preventing oxide scale from falling off on a heating surface of a coal-fired unit during peak load regulation and start-up and shutdown. Background Art

[0002] With the rapid growth of renewable energy installations and the widespread adoption of renewable energy, coal-fired units are facing frequent peak-shaving starts and stops. Due to the mismatch in expansion coefficients between the boiler heating surface (made of TP347H and SUP304 pipes) and the oxide scale, large temperature fluctuations during the start-up and shutdown process can cause oxide scale to fall off, even leading to blockage and bursting. Existing methods for controlling oxide scale include upgrading the heating surface material or spraying, which are both costly.

[0003] Based on the above situation, a control method for preventing the oxide scale from falling off the heating surface during the peak load start and stop of the coal-fired unit was invented to solve the above problem. Summary of the Invention

[0004] The purpose of the present invention is to provide a control method for preventing oxide scale from falling off on the heating surface during peak load regulation and start-up and shutdown of coal-fired units, thereby solving the problem of blockage and burst of heating surface caused by oxide scale falling off during peak load regulation and start-up and shutdown of units.

[0005] The technical solution adopted by the present invention is: a control method for preventing oxide scale from falling off the heating surface during peak load start and stop of coal-fired units, including controlling the steam temperature change rate of the unit to be less than 1.5℃ / min or the steam pressure change rate to be less than 0.1MPa / min.

[0006] The present invention is also characterized in that:

[0007] When the unit is started, control the unit main steam temperature rise rate to be less than 1℃ / min, the reheat steam temperature rise rate to be less than 2℃ / min, the main steam pressure rise rate to be less than 0.1MPa / min, the water-cooled wall temperature rise rate to be less than 1.5℃ / min, the superheater wall temperature rise rate to be less than 2℃ / min, the additional air U damper opening of the secondary air system to 30%-50%, the additional air L damper opening of the secondary air system to 50%-80%, the fuel air damper opening to 20%-30%, the furnace outlet flue gas temperature before turbine start-up to be less than 500℃ or adjust the high-pressure bypass opening to 10%-50%.

[0008] Starting a cold boiler involves the following steps:

[0009] Step 1: Ignite the cold boiler and control the water wall temperature rise rate to be less than a preset water wall temperature rise rate value, which is 1°C / min.

[0010] Step 2: Adjust the opening of the additional air U damper of the secondary air system to 30%-50%, the opening of the additional air L damper of the secondary air system to 50%-80%, the opening of the fuel air damper to 20%-30%, and the secondary air box differential pressure to 0.1kPa-0.2kPa;

[0011] Step 3: When the boiler separator pressure reaches 0.2 MPa, open the high-pressure bypass regulating valve to 40%-50%;

[0012] Step 4: During the boiler heating process, the superheater wall temperature rise rate is controlled to be less than a predetermined value of the superheater wall temperature rise rate, which is 2°C / min.

[0013] Step 5: Before the turbine is started up, the flue gas temperature at the furnace outlet is controlled to be lower than a predetermined value of the flue gas temperature at the furnace outlet, which is 500° C.

[0014] Step 6: Control the main steam temperature rise rate to be less than the preset value of the main steam temperature rise rate, which is 1°C / min; and the main steam pressure rise rate to be less than the preset value of the main steam pressure rise rate, which is 0.1 MPa / min.

[0015] Step 7: During the turbine run-up and grid connection period, adjust the flue gas damper system so that the superheated flue gas damper opening of the flue gas damper system is 90%-100%, and the reheated flue gas damper opening is 20%-30%; the reheated steam temperature rise rate is less than the preset reheated steam temperature rise rate, which is 2°C / min.

[0016] Starting a warm boiler involves the following steps:

[0017] Step 1: Supply water to the warm boiler, with the supply water temperature controlled at 150°C-160°C and the supply water flow rate controlled at 30t / h-50t / h; control the temperature drop rate of the water-cooled wall at the middle header outlet to be less than a predetermined temperature drop rate of the water-cooled wall at the middle header outlet, which is 50°C / 10min;

[0018] Step 2: Ignite the warm boiler and control the water wall temperature rise rate to be less than a preset water wall temperature rise rate value, which is 1.5°C / min.

[0019] Step 3: Adjust the opening of the additional air U damper of the secondary air system to 30%-50%, the opening of the additional air L damper of the secondary air system to 50%-80%, the opening of the fuel air damper to 30%-40%, and the secondary air box differential pressure to 0.2kPa-0.4kPa;

[0020] Step 4: When the boiler separator pressure reaches 0.2 MPa, the high-pressure bypass regulating valve is opened to 10%-20%. During the high-pressure bypass process, the superheater wall temperature drop rate is less than the superheater temperature drop rate preset value, which is 0.5°C / min.

[0021] Step 5: When the boiler separator pressure reaches 0.5 MPa, the high-pressure bypass regulating valve is opened to 40%-50%. During the high-pressure bypass process, the superheater wall temperature drop rate is less than the superheater temperature drop rate preset value, which is 0.5°C / min.

[0022] Step 6: During the boiler heating process, the superheater wall temperature rise rate is controlled to be less than a predetermined value of the superheater temperature rise rate, which is 2°C / min.

[0023] Step 7: Before the turbine is started up, the flue gas temperature at the furnace outlet is controlled to be lower than a predetermined value of the flue gas temperature at the furnace outlet, which is 500° C.

[0024] Step 8: Control the main steam temperature rise rate to be less than a preset value of the main steam temperature rise rate, which is 1°C / min; and the main steam pressure rise rate to be less than a preset value of the main steam pressure rise rate, which is 0.1 MPa / min.

[0025] Step 9: During the turbine run-up and grid connection period, adjust the flue gas damper system so that the superheated flue gas damper opening of the flue gas damper system is 90%-100%, and the reheated flue gas damper opening is 30%-50%; the reheated steam temperature rise rate is less than the preset reheated steam temperature rise rate, which is 2°C / min.

[0026] The following steps are involved when the boiler is shut down:

[0027] Step 1: Control the load reduction rate to be less than a preset load reduction rate, wherein the preset load reduction rate is 3MW / min;

[0028] Step 2: Control the main steam and reheat steam temperature drop rates to be less than the preset values of the main steam and reheat steam temperature drop rates, and the preset values of the main steam and reheat steam temperature drop rates are both 1.5°C / min;

[0029] Step 3: Control the main steam pressure drop rate to be less than a preset main steam pressure drop rate value, wherein the preset main steam pressure drop rate value is 0.1 MPa / min;

[0030] Step 4: When the unit load is higher than 200MW, use desuperheating water to ensure that the steam superheat of the partition screen superheater and the rear screen superheater is greater than 20℃, and the steam superheat of the high-temperature superheater is greater than 50℃; when the unit load is lower than 200MW, it is prohibited to use desuperheating water;

[0031] Step 5: After the boiler is turned off, close all smoke and wind dampers to suffocate the furnace; if the metal temperature of any heating surface is higher than 300℃, natural ventilation cooling is not allowed;

[0032] Step 6: When the metal temperature of any heating surface of the boiler is higher than 200°C, forced ventilation cooling is not performed;

[0033] Step 7: Depressurize the boiler to 0. After 3-4 hours, close the air and water vent valves and perform vacuum maintenance. Maintain the vacuum in the heating surface pipelines above -80kPa for 2-3 hours. Stop after the drain temperature of the main and reheat steam pipelines stabilizes. Keep the boiler in a completely stuffy state and cool naturally.

[0034] The beneficial effects of the present invention are as follows: the control method for preventing oxide scale from falling off on the heating surface during peak-shaving start-up and shutdown of a coal-fired unit does not require any upgrading or modification of the heating surface material, and only requires optimization of the operation control method, thereby achieving the goal of no oxide scale being detected on the throttle hole and the bottom of the U-bend on the heating surface within one maintenance cycle, and no pipe bursting occurring. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to specific embodiments.

[0036] The present invention provides a control method for preventing oxide scale from falling off the heating surface during peak load start-up and shutdown of coal-fired units. By controlling the rate of change of steam temperature and steam pressure during start-up and shutdown of the unit, sudden changes in steam temperature and wall temperature are prevented; the opening of the boiler additional air and fuel air dampers are adjusted to control the flue gas temperature at the furnace outlet to prevent overheating and dry burning of the heating surface; the opening of the high-pressure bypass is adjusted to control the steam flow rate of the heating surface to prevent sudden changes in superheated steam temperature; during the turbine run-up and generator grid connection process, the reheated flue gas damper is adjusted to prevent a sudden rise in the reheated steam temperature; during the shutdown process, the superheat after the superheater is controlled to prevent water plugs from forming in the superheater. Therefore, without upgrading or modifying the heating surface material, only the operation control method is optimized, so that no oxide scale is detected at the throttle hole and the bottom of the U-bend of the heating surface within one maintenance cycle, and no pipe burst occurs. It is specifically implemented according to the following steps:

[0037] 1. Start a cold boiler

[0038] Step 1: Ignite the cold boiler, and the water-cooled wall temperature rise rate is less than a predetermined value of the water-cooled wall temperature rise rate; the predetermined value of the water-cooled wall temperature rise rate is 1°C / min;

[0039] Step 2: Adjust the additional air U damper of the secondary air system to 30%-50%, the additional air L damper to 50%-80%, the fuel air damper to 20%-30%, and the secondary air box differential pressure to 0.1-0.2 kPa;

[0040] Step 3: When the boiler separator pressure reaches 0.2 MPa, open the high-pressure bypass regulating valve to 40%-50%;

[0041] Step 4: During the boiler heating process, the superheater wall temperature rise rate is less than a predetermined value of the superheater wall temperature rise rate; the predetermined value of the superheater wall temperature rise rate is 2°C / min;

[0042] Step 5: Before the turbine is started up, the flue gas temperature at the furnace outlet is less than a predetermined value of the flue gas temperature at the furnace outlet; the predetermined value of the flue gas temperature at the furnace outlet is 500° C.

[0043] Step 6: The main steam temperature rise rate is less than the main steam temperature rise rate preset value, which is 1°C / min; the main steam pressure rise rate is less than the main steam pressure rise rate preset value, which is 0.1 MPa / min;

[0044] Step 7: During the turbine run-up and grid connection period, adjust the flue gas damper system so that the superheated flue gas damper of the flue gas damper system is set to 90%-100%, and the reheated flue gas damper is set to 20%-30%; the reheated steam temperature rise rate is less than the preset reheated steam temperature rise rate, which is 2°C / min.

[0045] 2. Start the warm boiler

[0046] Step 1: Supply water to the warm boiler, raising the supply water temperature to 150-160°C and the supply water flow rate to 30-50 t / h; the temperature drop rate of the water-cooled wall at the middle header outlet is less than the preset temperature drop rate of the water-cooled wall at the middle header outlet; the preset temperature drop rate of the water-cooled wall at the middle header outlet is 50°C / 10 min;

[0047] Step 2: The warm boiler is ignited, and the water wall temperature rise rate is less than a predetermined value of the water wall temperature rise rate, which is 1.5°C / min.

[0048] Step 3: Adjust the additional air U damper of the secondary air system to 30%-50%, the additional air L damper to 50%-80%, the fuel air damper to 30%-40%, and the secondary air box differential pressure to 0.2-0.4kPa;

[0049] Step 4: When the boiler separator pressure reaches 0.2 MPa, gradually open the high-pressure bypass regulating valve to 10%-20%; during the high-pressure bypass opening process, the superheater wall temperature drop rate is less than the superheater temperature drop rate preset value; the superheater wall temperature drop rate preset value is 0.5°C / min;

[0050] Step 5: When the boiler separator pressure reaches 0.5 MPa, gradually open the high-pressure bypass regulating valve to 40%-50%; during the high-pressure bypass opening process, the superheater wall temperature drop rate is less than the superheater temperature drop rate preset value; the superheater wall temperature drop rate preset value is 0.5°C / min;

[0051] Step 6: During the boiler heating process, the superheater wall temperature rise rate is less than a predetermined value of the superheater temperature rise rate; the predetermined value of the superheater wall temperature rise rate is 2°C / min;

[0052] Step 7: Before the turbine is started up, the flue gas temperature at the furnace outlet is less than a predetermined value of the flue gas temperature at the furnace outlet; the predetermined value of the flue gas temperature at the furnace outlet is 500° C.

[0053] Step 8: The main steam temperature rise rate is less than a preset value of the main steam temperature rise rate, which is 1°C / min; the main steam pressure rise rate is less than a preset value of the main steam pressure rise rate, which is 0.1 MPa / min;

[0054] Step 9: During the turbine run-up and grid connection period, adjust the flue gas damper system so that the superheated flue gas damper of the flue gas damper system is set to 90%-100%, and the reheated flue gas damper is set to 30%-50%; the reheated steam temperature rise rate is less than the preset reheated steam temperature rise rate, which is 2°C / min.

[0055] 3. Boiler shutdown

[0056] Step 1: The load reduction rate is less than a preset load reduction rate; the preset load reduction rate is 3MW / min;

[0057] Step 2: The main and reheat steam temperature drop rates are less than the preset values of the main and reheat steam temperature drop rates; the preset values of the main and reheat steam temperature drop rates are 1.5°C / min;

[0058] Step 3: The main steam pressure drop rate is less than a predetermined value of the main steam pressure drop rate; the predetermined value of the main steam pressure drop rate is 0.1 MPa / min;

[0059] Step 4: If the unit load is higher than 200MW, use desuperheating water to ensure that the steam superheat of the partition panel superheater and the rear panel superheater is greater than 20℃, and the steam superheat of the high-temperature superheater is greater than 50℃; if the unit load is lower than 200MW, do not use desuperheating water;

[0060] Step 5: Turn off the boiler and close all smoke and wind dampers; if the metal temperature of any heating surface is higher than 300℃, natural ventilation and cooling are not allowed;

[0061] Step 6: If the metal temperature of any heating surface of the boiler is higher than 200°C, no forced ventilation cooling is performed;

[0062] Step 7: Depressurize the boiler to 0. After 3-4 hours, close the air and water vent valves and perform vacuum maintenance. Maintain the vacuum in the heating surface pipelines above -80kPa for 2-3 hours. Stop after the drain temperature of the main and reheat steam pipelines stabilizes. Keep the boiler in a completely stuffy state and cool naturally.

Claims

1. A control method for preventing oxide scale from falling off the heating surface during peak load start and stop of coal-fired units, characterized in that: Starting a warm boiler involves the following steps: Step 1: Supply water to the warm boiler, with the supply water temperature controlled at 150°C-160°C and the supply water flow rate controlled at 30t / h-50t / h; control the temperature drop rate of the water-cooled wall at the middle header outlet to be less than a predetermined temperature drop rate of the water-cooled wall at the middle header outlet, which is 50°C / 10min; Step 2: Ignite the warm boiler and control the water wall temperature rise rate to be less than a preset water wall temperature rise rate value, which is 1.5°C / min. Step 3: Adjust the opening of the additional air U damper of the secondary air system to 30%-50%, the opening of the additional air L damper of the secondary air system to 50%-80%, the opening of the fuel air damper to 30%-40%, and the secondary air box differential pressure to 0.2kPa-0.4kPa; Step 4: When the boiler separator pressure reaches 0.2 MPa, the high-pressure bypass regulating valve is opened to 10%-20%. During the high-pressure bypass process, the superheater wall temperature drop rate is less than the superheater temperature drop rate preset value, which is 0.5°C / min. Step 5: When the boiler separator pressure reaches 0.5 MPa, the high-pressure bypass regulating valve is opened to 40%-50%. During the high-pressure bypass process, the superheater wall temperature drop rate is less than the superheater temperature drop rate preset value, which is 0.5°C / min. Step 6: During the boiler heating process, the superheater wall temperature rise rate is controlled to be less than a predetermined value of the superheater temperature rise rate, which is 2°C / min. Step 7: Before the turbine is started up, the flue gas temperature at the furnace outlet is controlled to be lower than a predetermined value of the flue gas temperature at the furnace outlet, which is 500° C. Step 8: Control the main steam temperature rise rate to be less than a preset value of the main steam temperature rise rate, which is 1°C / min; and the main steam pressure rise rate to be less than a preset value of the main steam pressure rise rate, which is 0.1 MPa / min. Step 9: During the turbine run-up and grid connection period, adjust the flue gas damper system so that the superheated flue gas damper opening of the flue gas damper system is 90%-100%, and the reheated flue gas damper opening is 30%-50%; the reheated steam temperature rise rate is less than the preset reheated steam temperature rise rate, which is 2°C / min.

2. A control method for preventing oxide scale from falling off the heating surface during peak load start and stop of coal-fired units, characterized in that: The following steps are involved when the boiler is shut down: Step 1: Control the load reduction rate to be less than a preset load reduction rate, wherein the preset load reduction rate is 3MW / min; Step 2: Control the main steam and reheat steam temperature drop rates to be less than the preset values of the main steam and reheat steam temperature drop rates, and the preset values of the main steam and reheat steam temperature drop rates are both 1.5°C / min; Step 3: Control the main steam pressure drop rate to be less than a preset main steam pressure drop rate value, wherein the preset main steam pressure drop rate value is 0.1 MPa / min; Step 4: When the unit load is higher than 200MW, use desuperheating water to ensure that the steam superheat of the partition screen superheater and the rear screen superheater is greater than 20℃, and the steam superheat of the high-temperature superheater is greater than 50℃; when the unit load is lower than 200MW, it is prohibited to use desuperheating water; Step 5: After the boiler is turned off, close all smoke and wind dampers to suffocate the furnace; if the metal temperature of any heating surface is higher than 300℃, natural ventilation cooling is not allowed; Step 6: When the metal temperature of any heating surface of the boiler is higher than 200°C, forced ventilation cooling is not performed; Step 7: Depressurize the boiler to 0. After 3-4 hours, close the air and water vent valves and perform vacuum maintenance. Maintain the vacuum in the heating surface pipelines above -80kPa for 2-3 hours. Stop after the drain temperature of the main and reheat steam pipelines stabilizes. Keep the boiler in a completely stuffy state and cool naturally.