1 The furnace temperature is too high
The center temperature of the furnace flame is relatively high, and the radiation heat transfer of the high-temperature furnace flue gas to the burner is enhanced, resulting in an increase in the temperature of the burner nozzle wall. This is a cause of burner burnout.
2 The center of the furnace flame is deflected
The burner thermal test results show that the furnace temperature measured from the four corners and the temperature distribution at the burner nozzle are obviously uneven. The center of the furnace flame is deflected, which can also cause burner damage. From the primary air duct wind speed measurement results, the primary air nozzle wind speeds of the four-corner burners on the same floor are obviously uneven, and the primary air speed of the nozzles on each floor is lower than the design value. The large deviation in wind speed at the primary air nozzles on the same floor is one of the reasons for the deflection of the furnace flame center. A large deviation in primary wind speed and a low primary wind speed will cause damage to the burner nozzle.
3 Reasons for operation control
3.1 The pulverized coal fire is too close
3.2 If the primary wind speed is too small, the pulverized coal fire distance will be too close. During operation, if the total controlled primary air pressure is too low, the ignition distance may be too close, which may cause the burner nozzle to overheat, deform, or even be damaged.
3.3 If the secondary air speed is too low, the ignition distance will be too close, causing damage to the burner nozzle.
3.4 Impact of changes in coal type
As the coal quality became better and the volatile content increased, the ignition distance of the pulverized coal from the primary air nozzle became closer. The operating personnel failed to adjust the primary air and secondary air in time to adapt to the change of coal type.
3.5 The fineness of pulverized coal is too fine
Judging from the coal quality analysis report for two months, the combustible volatile content of the coal type operating in the power plant is between 15% and 23%, and the ash content is around 25%. The corresponding controlled fineness of the pulverized coal R90zj should be 14.5% to 21%, while The pulverized coal fineness R90 controlled by the operation is about 12%, which causes the pulverized coal ignition distance at the primary air nozzle to be too close, causing the burner nozzle to overheat and deform until it is damaged.
3.6 Insufficient cooling of the upper primary air nozzle during low load operation
During low-load operation, the primary air nozzle that is not in use is almost in a dry burning state and cannot be sufficiently cooled, causing the burner to overheat, deform, and even be damaged.
4. Reasons for burner design
4.1 Material aspect
The alloy steel material selected for the burner cannot meet the wear resistance and high temperature resistance requirements of the burner during normal operation of the boiler.
4.2 Structural aspects
The design of the nozzle structure of the pulverized coal concentration and preheating burner is not perfect, and strong heat backflow is generated at the nozzle, causing the nozzle temperature to be too high, causing the nozzle to be overheated, deformed, and damaged.
5. Preventive measures for burner damage
5.1 Improve burner design
5.1.1 Improve burner structure and anti-wear performance
For the preheating cylinder of the direct ignition burner of pulverized coal, the thickness of the cylinder wall and the length of the inner cylinder should be appropriately improved during design, and high-quality alloy steel materials should be selected to increase the wear resistance and heat resistance. For pulverized coal concentration and preheating burners, the wear resistance of the burner and the high temperature resistance of the preheating chamber should be fully considered during design.
5.1.2 Increase the perimeter wind design of the upper primary air nozzle
Peripheral wind can play such a role: when the load is high, the perimeter wind is open. At this time, the role of the perimeter wind is to strengthen the primary wind intensity, prevent the expansion of coal powder and wash away the surrounding water walls, and timely replenish the amount of oxygen required for combustion; the existence of perimeter wind It also weakens the reducing atmosphere near the water-cooled wall to avoid high-temperature corrosion of the water-cooled wall; at low load, it can meet the cooling requirements of the upper primary air nozzle when a powder discharge machine is stopped, and prevent the burner from burning out. According to the investigation of boiler burners in power plants in Jiangsu Province, at high loads, the operation perimeter wind can also effectively control the pulverized coal ignition distance of the burner.
5.2 Ensure that the furnace design and cutting are correct
Use the opportunity of stopping the furnace to check the installation angle of the burner to ensure that the furnace design circle is correct. Carry out a cold and hot mixing test of the primary air speed of No. 2 furnace and a cold-state baffle characteristic test of the secondary air to ensure that the center of the furnace flame is not deflected.
5.3 Strengthen operation control and adjustment
5.3.1 The operating personnel should promptly grasp the changes in the type of coal entering the furnace, and adjust the operation of the pulverizing system accordingly based on the coal quality analysis report to ensure that the fineness of the pulverized coal is within the optimal range.
5.3.2 Boiler operators should always observe the ignition situation of pulverized coal and control the ignition distance of pulverized coal to about 500 to 800 mm from the primary air nozzle outlet. Adjust the opening of the air supply valve in time according to the concentration of pulverized coal and the wall temperature of the preheating burner.
5.3.3 Under high and low load conditions, operators should adjust the combustion in the furnace and adjust the ratio of primary and secondary air to ensure that the furnace flame is not deflected.
5.4 Re-carry out burner design calculations
In view of the situation that the current coal type is better than the original designed coal type. Re-do burner design calculations. When designing a new burner, consideration should be given to appropriately reducing the primary air nozzle area and increasing the primary air nozzle wind speed to 25-28 m/s. After the burner is modified, it is necessary to determine the reasonable installation position of the burner wall temperature thermocouple so that it can truly play a monitoring role during operation.
1 The furnace temperature is too high
The center temperature of the furnace flame is relatively high, and the radiation heat transfer of the high-temperature furnace flue gas to the burner is enhanced, resulting in an increase in the temperature of the burner nozzle wall. This is a cause of burner burnout.
2 The center of the furnace flame is deflected
The burner thermal test results show that the furnace temperature measured from the four corners and the temperature distribution at the burner nozzle are obviously uneven. The center of the furnace flame is deflected, which can also cause burner damage. From the primary air duct wind speed measurement results, the primary air nozzle wind speeds of the four-corner burners on the same floor are obviously uneven, and the primary air speed of the nozzles on each floor is lower than the design value. The large deviation in wind speed at the primary air nozzles on the same floor is one of the reasons for the deflection of the furnace flame center. A large deviation in primary wind speed and a low primary wind speed will cause damage to the burner nozzle.
3 Reasons for operation control
3.1 The pulverized coal fire is too close
3.2 If the primary wind speed is too small, the pulverized coal fire distance will be too close. During operation, if the total controlled primary air pressure is too low, the ignition distance may be too close, which may cause the burner nozzle to overheat, deform, or even be damaged.
3.3 If the secondary air speed is too low, the ignition distance will be too close, causing damage to the burner nozzle.
3.4 Impact of changes in coal type
As the coal quality became better and the volatile content increased, the ignition distance of the pulverized coal from the primary air nozzle became closer. The operating personnel failed to adjust the primary air and secondary air in time to adapt to the change of coal type.
3.5 The fineness of pulverized coal is too fine
Judging from the coal quality analysis report for two months, the combustible volatile content of the coal type operating in the power plant is between 15% and 23%, and the ash content is around 25%. The corresponding controlled fineness of the pulverized coal R90zj should be 14.5% to 21%, while The pulverized coal fineness R90 controlled by the operation is about 12%, which causes the pulverized coal ignition distance at the primary air nozzle to be too close, causing the burner nozzle to overheat and deform until it is damaged.
3.6 Insufficient cooling of the upper primary air nozzle during low load operation
During low-load operation, the primary air nozzle that is not in use is almost in a dry burning state and cannot be sufficiently cooled, causing the burner to overheat, deform, and even be damaged.
4. Reasons for burner design
4.1 Material aspect
The alloy steel material selected for the burner cannot meet the wear resistance and high temperature resistance requirements of the burner during normal operation of the boiler.
4.2 Structural aspects
The design of the nozzle structure of the pulverized coal concentration and preheating burner is not perfect, and strong heat backflow is generated at the nozzle, causing the nozzle temperature to be too high, causing the nozzle to be overheated, deformed, and damaged.
5. Preventive measures for burner damage
5.1 Improve burner design
5.1.1 Improve burner structure and anti-wear performance
For the preheating cylinder of the direct ignition burner of pulverized coal, the thickness of the cylinder wall and the length of the inner cylinder should be appropriately improved during design, and high-quality alloy steel materials should be selected to increase the wear resistance and heat resistance. For pulverized coal concentration and preheating burners, the wear resistance of the burner and the high temperature resistance of the preheating chamber should be fully considered during design.
5.1.2 Increase the perimeter wind design of the upper primary air nozzle
Peripheral wind can play such a role: when the load is high, the perimeter wind is open. At this time, the role of the perimeter wind is to strengthen the primary wind intensity, prevent the expansion of coal powder and wash away the surrounding water walls, and timely replenish the amount of oxygen required for combustion; the existence of perimeter wind It also weakens the reducing atmosphere near the water-cooled wall to avoid high-temperature corrosion of the water-cooled wall; at low load, it can meet the cooling requirements of the upper primary air nozzle when a powder discharge machine is stopped, and prevent the burner from burning out. According to the investigation of boiler burners in power plants in Jiangsu Province, at high loads, the operation perimeter wind can also effectively control the pulverized coal ignition distance of the burner.
5.2 Ensure that the furnace design and cutting are correct
Use the opportunity of stopping the furnace to check the installation angle of the burner to ensure that the furnace design circle is correct. Carry out a cold and hot mixing test of the primary air speed of No. 2 furnace and a cold-state baffle characteristic test of the secondary air to ensure that the center of the furnace flame is not deflected.
5.3 Strengthen operation control and adjustment
5.3.1 The operating personnel should promptly grasp the changes in the type of coal entering the furnace, and adjust the operation of the pulverizing system accordingly based on the coal quality analysis report to ensure that the fineness of the pulverized coal is within the optimal range.
5.3.2 Boiler operators should always observe the ignition situation of pulverized coal and control the ignition distance of pulverized coal to about 500 to 800 mm from the primary air nozzle outlet. Adjust the opening of the air supply valve in time according to the concentration of pulverized coal and the wall temperature of the preheating burner.
5.3.3 Under high and low load conditions, operators should adjust the combustion in the furnace and adjust the ratio of primary and secondary air to ensure that the furnace flame is not deflected.
5.4 Re-carry out burner design calculations
In view of the situation that the current coal type is better than the original designed coal type. Re-do burner design calculations. When designing a new burner, consideration should be given to appropriately reducing the primary air nozzle area and increasing the primary air nozzle wind speed to 25-28 m/s. After the burner is modified, it is necessary to determine the reasonable installation position of the burner wall temperature thermocouple so that it can truly play a monitoring role during operation.