Compilation of Common Problems in Boiler Operation

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Please, **don’t be stingy with a little money – give some away! Common problems in boiler operation (1) 1. After the boiler shuts down, when should load reduction be initiated? How should the magnitude and speed of load reduction be controlled? Answer: After extinguishing the fire, load reduction should be initiated immediately when the steam pressure begins to drop. The speed and extent of load reduction should not cause the boiler to overpressure and discharge steam; the value of load reduction should be determined based on the degree of drop in steam pressure and temperature, as well as the time required to restart ignition after the fire is extinguished. Based on experience, normally, a 220T/H boiler reduces its load to 20MW after the fire is extinguished, while a 400T/H boiler reduces its load to 40MW under similar conditions. 2. Why are explosion vents installed on boilers? Answer: When a furnace explosion occurs, pressure relief is activated automatically to reduce the impact of the explosion on the boiler, thereby preventing damage to the furnace’s water wall, furnace walls, and flues. 3. When dealing with coal feeder failures on short notice during operation, what measures should the coal grinding system take to prevent the boiler from going out? Answer: Reduce the opening of the inlet damper of the powder discharge fan to keep the current flowing through it 1–1.5 A below the operating current; keep the circulation door fully open to maintain the temperature at the outlet of the mill around 80 degrees. If it is difficult to stabilize the combustion, consult the furnace operator to shut down this powder production system. 4. Add oil when combustion is unstable; withdraw the oil injector once negative pressure turns positive – can this prevent large positive pressure shocks? Why? Answer: No ； Since a negative pressure in the furnace turning positive indicates that some of the extinguished coal powder has been ignited, the impact force generated by the ignition of this extinguished coal powder does not decrease even if the oil injectors are shut down; shutting down the oil injectors could lead to another fireout. 5. When the steam injection pressure is automatically too high, the powder feeder operates at a low speed; high oxygen levels should be avoided to prevent flameout? Answer: First, oil should be injected to stabilize combustion; then the automatic control of steam pressure should be disabled. Depending on the situation, the speed of the operating feed powder pumps should be increased, and 1–2 feed powder pumps should be shut down. If necessary, the air supply volume should be reduced to help restore oxygen levels and steam pressure to normal levels quickly. The rotation speed of the powder feeder in the lowest row is ≮ 800 revolutions per minute. 6. Why is it necessary to open the economizer recirculation valve when stopping water inflow? Answer: When water supply to the boiler is stopped, if the economizer continues to be heated, water circulates through the circulation pipes between the economizer and the steam drum, thereby ensuring the safety of the economizer ； 7. Why should air supply be reduced and the small secondary air be turned off after extinguishing the fire and before restarting the burner with oil? Answer: After extinguishing the fire, the temperature in the furnace is low; excessive secondary air supply and high air intake rates will result in too much air at the base of the oil gun, making it difficult to ignite the nozzle, or they may shift the ignition point of the oil backward, extinguishing the burning nozzle and hindering re-ignition. 8. Why should a slightly lower oxygen level be maintained during low-load operation, as long as safety is not compromised? Answer: During low-load operation, the furnace temperature is relatively low, making it difficult for the coal dust airflow to ignite; as a result, combustion stability is poor. Maintaining a high oxygen level further lowers the furnace temperature and reduces the concentration of coal dust undergoing combustion, which in turn diminishes the combustion process’s resistance to disturbances and can lead to flameout. 9. Why is it necessary to turn on the moisture absorption tube of the powder bin during operation? Answer: Remove moisture from the powder bin and the powder conveyor to prevent the coal powder in the bin from becoming damp and clumping, which could affect its fluidity. By removing moisture, the temperature inside the powder bin is maintained at an appropriate level, thereby preventing spontaneous combustion and explosion of the coal powder. 10. What is the purpose of hot water soakback flushing in the superheater? Answer: The water-soluble salts such as silicic acid that accumulate inside the superheater tubes can be dissolved by soaking; once softened, they detach from the tube walls and are flushed out of the superheater via the steam drum, thereby preventing severe scaling in the superheater as well as in the flow passages of the turbine. 11. When a boiler is severely overfilled with water, the steam temperature drops sharply; then why is it still necessary to shut down the boiler urgently? Answer: 1. After the boiler stops operating, the pressure drops rapidly, increasing the superheat of the steam and reducing the damage to the turbine ； 2. The water in the furnace contracts rapidly after the engine is turned off. It will cause the water level in the steam drum to drop sharply in a short period of time, reducing the amount of water carried by the steam ； 3. After the engine is turned off, the heat load drops sharply, resulting in a significant reduction in evaporation volume. This lowers the steam’s carrying capacity, and thus the amount of water carried by the steam decreases. 12. What is the role of activating the exhaust to atmosphere when the steam temperature drops sharply, posing a threat to the safety of the turbine? Answer: The function of opening the overhead steam vent is to reduce steam pressure and increase the superheat of the steam ； Another side effect is that, after the pressure decreases, it creates conditions for increasing the heat load and raising the temperature; however, the first one is the main one ； Reducing the pressure lowers the steam flow rate; as a result, the steam’s ability to carry water droplets in the steam drum decreases, and the steam load is reduced, which helps to minimize damage to the turbine. 13. Under what circumstances can oil be injected to stabilize combustion, and under what circumstances is it strictly prohibited to use oil for combustion enhancement? Answer: If there are signs of unstable combustion in the boiler, such as a sharp increase in oxygen levels, increased fluctuations in negative pressure, a drop in steam pressure, or individual flame sensors for the flame-out protection flashing or going out, it is necessary to introduce oil to stabilize the combustion promptly or take other measures to maintain stable combustion. If the combustion instability is severe, with the negative pressure indicating values of –200 Pa or lower, and one or more of the flame indicator lights in the fire suppression system going out, it is strictly prohibited to initiate oil injection for detonation combustion when there is serious combustion instability in the boiler (before the fire suppression system has activated). 14. What combustion stabilization measures other than oil injection should be taken when the lower-row powder feeder fails and stops operating? Answer: Monitoring and adjustment of combustion should be strengthened. Measures to stabilize combustion include disabling the automatic operation of the powder feeder that is not in use, increasing the output of other powder feeders at that angle, reducing the primary air supply to the burner that is not in use, raising the temperature level in the area of downstream burners, and operating with a slightly lower oxygen level within the limits permitted by safety regulations. And promptly notify maintenance to address the issues. 15. Why is it necessary to control the outlet temperature of the coal grinder? Answer: Ensure the dry output of the grinding system ； Avoid an increase in coal powder moisture due to low outlet temperature, which can lead to poor fluidity and system blockages ； Prevent coal powder from self-igniting and exploding due to excessive temperature. 16. What are the conditions for extinguishing the flame in the entire furnace through fire suppression? What are the conditions for the layer flame to go out? Answer: The flames on the three layers are extinguished ； 3/4 of the corner flames have gone out. 17. Sometimes, no overheating is detected in the temperature of the superheater tube walls, yet tube bursts still occur. What is the reason? Answer: 1. Due to the limited number of temperature measurement points installed on the pipe walls and the poor representativeness of these points, it is not possible to obtain the true values of the temperature across all pipe walls. As a result, the pipe walls without such measurement points may have experienced overheating during actual operation, but this overheating cannot be detected through the temperature readings ； 2. The wall temperature sensors installed are those for the outer wall of the furnace; there is a temperature difference with the inner wall of the furnace. In some tubes, the temperature on the inner wall of the furnace may **exceed the specified allowable temperature difference, leading to overheating and tube rupture ； 3. The error of the primary element measuring the wall temperature of the pipe is large, or the secondary instrument is inaccurate; as a result, the wall temperature indication is wrong, leading to misguidance of operators. 18. Why does rapid fire acceleration and voltage increase cause overheating and tube rupture in the superheater? Answer: A sudden increase in the boiler’s heat load leads to a sharp rise in both the flow rate of flue gas passing through the superheater tubes and the steam temperature. However, the amount of steam generated by the water wall tubes increases more slowly than the rise in the heat load; as a result, the steam flow rate in the superheater cannot increase in step with this change. This worsens the cooling conditions of the superheater tubes, causing their temperatures to rise rapidly in a short period of time, which can lead to overheating and tube failure ； Furthermore, rapid increase in fire pressure can cause the temperature of the superheated steam to rise sharply; the adjustment of the steam temperature often fails to keep up with these changes, which can lead to overheating of the steam and tube rupture due to poor cooling of the tube walls. 19. What is the purpose of closing the inlet baffle of the powder exhaust fan and opening the recirculation valve of the grinding system? Answer: The low temperature, high speed, and large volume of the tertiary air have a significant impact on the stability of combustion in the boiler. Reducing the damper at the inlet of the powder discharge fan can minimize the interference caused by the tertiary air on combustion, thereby stabilizing it and preventing extinguishment. The purpose of increasing the recirculation rate is mainly to boost the ventilation volume of the system, thereby increasing the output of the powder production system and preventing a significant drop in output due to reducing the inlet damper settings. It also helps to reduce the amount of tertiary air while maintaining stable combustion under the same ventilation conditions. 20. How is the superheater and reheater protected during the boiler startup process? Answer: During the low-pressure phase, the steam flow rate passing through the heating surfaces is low, resulting in poor cooling conditions for the tube walls; therefore, overheaters and reheaters are protected by keeping the flue gas temperature below the temperature limit that the tube materials can withstand ； When the pressure reaches a certain level, steam discharge to the atmosphere, the primary and secondary bypasses, as well as the superheater drain are activated, primarily by adjusting the amount of steam flowing through the superheater and reheater, so that there is sufficient steam available to cool the heated surfaces and ensure the safety of the tube walls ； During the startup phase, the temperature and pressure should be increased in strict accordance with the specified heating and pressurization curves and relevant technical standards, to prevent the tube walls from overheating due to a sudden increase in thermal load. 21. Why, in the event of severe combustion instability in the boiler and when the flame-out protection does not activate, can oil be used to stabilize the combustion? Answer: It is set according to the operation requirements of the fire suppression protection system. When there is localized extinguishment or unstable combustion in the furnace, on the verge of extinguishment, the signal indicating that the entire furnace has lost its flame may not trigger any action. Moreover, the negative pressure pipe used for fire suppression protection might become blocked; if the negative pressure signal cannot detect unstable combustion or localized extinguishment, then the fire suppression protection system will not activate either. As a result, severe unstable combustion leading to the use of oil for combustion can cause a deflagration, resulting in a large positive pressure surge or a high furnace pressure signal that triggers the fire suppression mechanism. 22. What are the common conventional measures for stable combustion? Answer: Common conventional measures to maintain stable combustion include reducing air supply, lowering the flow rate of the primary air to the powder feeder and shutting it down temporarily, decreasing the pressure and velocity of the primary air, reducing the flow rate of the secondary air at the bottom as well as the intermediate secondary air (for boilers #5–#6). Operation with a slightly lower excess air coefficient and a higher rotation speed of the powder feeder is maintained, provided that safety is not compromised. 23. Why is it strictly prohibited to reduce the powder discharge flap of the powder feeder to control the powder supply during operation? Answer: Controlling the amount of coal fed by adjusting the coal feed control valve will result in uneven coal feeding by the feeder. Reducing the amount of coal fed by this feeder significantly when the coal level is high lowers the concentration of coal dust in the primary air, which may lead to the boiler going out of operation. 24. What is the allowable deviation in powder level during operation? What is the significance of controlling powder level deviation? Answer: The difference in powder level between the two sides must not exceed 0.5 meters ； Controlling the deviation in powder level can reduce uneven powder distribution among the feeders, preventing situations such as excessive or sudden fluctuations in the amount of powder discharged by the feeders on the side with a lower powder level, as well as a decrease in the amount of powder discharged by the feeders on the side with a higher powder level. This helps to maintain stable combustion and avoids shutdowns due to lack of fuel. 25. What are the symptoms of poor powder discharge from the powder feeder? What are the symptoms of interruption in powder feeding by the powder feeder? Answer: The problem of poor powder distribution: sudden fluctuations in primary air pressure and velocity ； Large fluctuations in steam pressure and temperature ； An increased fluctuation in the negative pressure in the furnace, along with unstable oxygen levels, can lead to unstable combustion or even the shutdown of the boiler. Phenomenon of interrupted coal feeding: The unit load, steam pressure, and temperature decrease; oxygen level rises; the negative pressure in the furnace becomes more negative; primary air pressure drops while the primary air velocity increases; the temperature of the short pipe used for coal feeding decreases, and no coal powder is present at the burner outlet. In severe cases of unstable combustion, the fire may go out. 26. The wall temperature of the rear screen tube on the right side of the 400T/H furnace is too high; what measures can be taken to reduce this wall temperature? Answer: 1. Increase the feed amount to the right-side feeder and reduce it for the left-side feeder ； 2. Increase the flow rate of the cooling water at the left primary stage to reduce the temperature at the outlet of that cooling unit ； 3. Take measures to reduce the flue gas temperature at the inlet of the right-side screen superheater; increase the opening degree of the tertiary air or primary/secondary air dampers on the right side, and decrease the opening degree of the tertiary air and primary/secondary air dampers on the left side ； 4. Increase steam pressure and temperature, reduce steam consumption ； 5. If the high-pressure heater is not in operation, the steam turbine should be started to operate the high-pressure heater. 27. What are the signs of unstable boiler combustion? Answer: 1. Large fluctuations in chamber negative pressure or swings in the negative direction ； 2. Unstable steam temperature, steam pressure, and load with large fluctuations ； 3. The flame detection intensity for fire suppression protection decreases, and some detection lights go out ； 4. The fire extinguishing protection system features automatic oil injection, with the oil gun engaging automatically ； 5. Fire extinguishing occurs in severe cases ； 6. Large fluctuations or swings in primary air pressure or wind speed ； 7. The oxygen level at the furnace outlet fluctuates significantly.