Nine abnormal phenomena and eight mechanical failures in boiler operation, and their solutions.

Boilers often malfunction during operation, and if not addressed promptly, can lead to serious safety accidents. Early detection and resolution of abnormalities can minimize losses. Today, we've compiled nine common abnormal boiler operating phenomena and eight major mechanical malfunctions, along with their solutions. Let's take a look!

Boiler water level abnormal

1. Boiler is full of water

Phenomena:

① The water level alarm sounds, and the high water level indicator light illuminates;

② All indicator lights on the electrical contact water level gauge are on;

③ The steam drum water level is higher than the highest visible water level;

④ The feedwater flow rate is abnormally greater than the steam flow rate;

⑤ The steam salinity increases;

⑥ The superheated steam temperature drops;

⑦ In cases of severe overfilling, water hammer occurs in the steam pipeline, and steam leaks from the flange.

Causes:

① The automatic feedwater control system malfunctions, or the feedwater regulating device malfunctions.

② The water level gauge, steam flow meter, and feedwater flow meter are indicating incorrect readings, leading to misjudgment and misoperation by operators.

③ The feedwater pressure suddenly increases.

④ Operator negligence, insufficient monitoring of the water level, untimely adjustments, or misoperation.

Solutions:

① When the boiler steam pressure and feedwater pressure are normal, and the steam drum water level exceeds +75mm, confirming overfilling, immediately investigate the cause.

② If the water level is affected by automatic feedwater control malfunction, immediately switch from automatic to manual control and reduce feedwater by closing the regulating valve. If the water level continues to rise, open the emergency drain valve to release water.

③ If the steam drum water level still rises above +100mm, close or shut off the feedwater valve (open the economizer recirculation valve when feedwater is stopped) and increase water release.

④ Depending on the steam temperature drop, close or shut off the desuperheating valve, and open the superheater drain valve if necessary.

⑤ If the steam drum water level exceeds the visible portion of the level gauge, immediately shut down the boiler, close the main steam valve, and notify the electrical and turbine departments. Increase water release until the steam drum water level returns to normal. If the water level rise is caused by abnormal feedwater pressure, immediately contact the turbine department to restore normal operation as soon as possible.

⑥ After the fault is cleared, restore boiler unit operation as soon as possible.

II. Boiler water shortage phenomenon

① The water level alarm sounds, and the low water level indicator light illuminates.

② All negative indicator lights on the electrical contact water level gauge are on.

③ The steam drum water level is below the lowest visible level.

④ The feedwater flow rate is abnormally lower than the steam flow rate.

⑤ The superheated steam temperature is rising.

Causes:

① Automatic feedwater control malfunction.

② Incorrect readings from the water level gauge, steam flow meter, and feedwater flow meter, leading to misjudgment and misoperation by operators.

③ Sudden reduction in boiler load.

④ Feedwater pump malfunction causing a drop in feedwater pressure.

⑤ Leaks in the boiler blowdown pipe or valves, resulting in excessive blowdown volume.

⑥ Rupture in the water-cooled wall or economizer tubes.

⑦ Operator negligence, insufficient monitoring of the water level, untimely adjustments, or misoperation.

Handling Procedures:

① When boiler steam pressure and feedwater pressure are normal, but the drum water level is below -75mm, verify the accuracy of the water level gauge. If automatic adjustment fails, switch to manual control and appropriately increase the feedwater flow.

② If the water level continues to drop below -100mm, in addition to increasing the feedwater flow, check that the blowdown valve and drain valve are tightly closed. Reduce the load if necessary.

③ If the drum water level continues to drop and disappears from the drum water level gauge, immediately shut down the boiler, close the main steam valve, and continue feeding water into the boiler.

④ If the water level disappears from the drum water level gauge due to operator negligence, and the electric contact water level gauge cannot detect it, immediately shut down the boiler, close the main steam valve and feedwater valve. After shutdown, call for water. If no water is detected, do not feed water into the boiler. After calling for water, if the water level gauge shows a level, increase the boiler feedwater and ensure the water level recovers.

⑤ If the water level drops due to low feedwater pressure, immediately notify the turbine to increase the feedwater pressure.

III. Soda and Water Soaring Together

Phenomena:

① The boiler drum water level fluctuates violently; in severe cases, the water level is obscured.

② The superheated steam temperature drops sharply; in severe cases, water hammer occurs in the steam pipes, and steam leaks from the flanges.

③ The salt content of the steam and boiler water increases, and the conductivity rises.

Causes:

① The boiler water quality does not meet standards, with excessive suspended solids and salt content.

② Blowout is not performed according to regulations.

③ The continuous blowout is too small or not opened at all.

④ The load increases significantly.

⑤ The boiler drum water level remains too high.

Solutions:

① Appropriately reduce the boiler evaporation rate and maintain stability.

② Fully open the continuous blowout; if necessary, open the emergency drain valve and the scheduled blowout valve, increase the inlet and outlet water flow, and maintain the water level slightly below the normal value.

③ Stop chemical dosing.

④ Open the superheater drain valve and notify the turbine to increase drainage.

⑤ Notify the laboratory personnel to analyze the boiler water and take measures to improve water quality. ⑥ The boiler load must not be increased until the boiler water quality is improved.

⑦ After the fault is cleared, the water level gauge must be flushed.

Boiler Combustion Abnormality

I. Boiler coking

Phenomena:

① Bed temperature rises sharply and exceeds 1000℃.

② Oxygen level drops, even to zero.

③ When observing the flame, fluidization is poor, and the flame appears white in localized or large areas.

④ Ash discharge is low or nonexistent.

⑤ In severe cases, negative pressure continuously increases, and the primary air fan current decreases.

Causes:

① Coal is added too quickly or excessively during ignition and pressurization, or coal is added without sufficient air.

② Improper operation during ignition suppression.

③ Primary air is too low, below the monitoring fluidization air volume.

④ Combustion load is too high, and combustion temperature is too high.

⑤ Coal particles are too large, or ash deformation temperature is too low.

⑥ Excessive ash discharge results in low bed material or complete discharge.

⑦ Abnormal or blocked return feeder.

⑧ Coal feeder stops supplying coal; improper handling.

⑨ Load increases too quickly; improper operation.

⑩ Damaged air cap allows ash and slag to fall into the air chamber, causing uneven air distribution.

⑪ Inaccurate or malfunctioning bed thermometer leads to misjudgment by operators.

⑫ Excessively thick bed material and failure to remove slag in a timely manner.

⑬ Poor separation by the magnetic separator allows iron parts to enter the furnace, causing poor boiling.

Remedies:

① Immediately shut down the furnace.

② Drain the circulating ash and remove as much slag as possible from the furnace chamber.

③ Check for coking.

④ Open the manhole and loosen as much coke as possible, removing it from the furnace promptly.

⑤ If coking is not severe, ignite and put the furnace back into operation after removing the coke.

⑥ If coking is severe and cannot be eliminated while hot, treat after cooling.

Coking Prevention:

① Control the particle size of the coal fed into the furnace to below 8mm.

② Strictly control the coal feed rate during ignition.

③ When increasing or decreasing the load, strictly adhere to the principle of adding air before coal when increasing the load, and reducing coal before air when decreasing the load.

④ When adjusting combustion, use a "small amount, multiple times" adjustment method to avoid large fluctuations in bed temperature.

⑤ Regularly check the coal feeder's operation, observe the furnace flame color, and ensure the return feeder is functioning properly.

⑥ When discharging slag, release small amounts frequently based on the pressure difference in the material bed. After slag discharge, carefully check to ensure the slag discharge door is tightly closed before leaving the site.

II. Boiler shutdown

Phenomena:

① Fluidized bed temperature drops sharply, and flue gas temperature decreases.

② Steam temperature and pressure decrease.

③ Combustion chamber darkens, flame becomes invisible.

④ Oxygen level indicator rises significantly.

Causes:

① Faulty coal feeder or undetected coal blockage, resulting in prolonged coal shortage.

② Abnormal secondary material return, excessive ash accumulation, suddenly flooding into the furnace.

③ Poor coal quality or changes in coal quality, with untimely adjustments leading to poor combustion and flameout.

④ Improper air-coal ratio.

Solutions:

① If the coal feeder is faulty, immediately shut down the furnace and quickly re-ignite.

② If the material return is abnormal, urgently release ash while increasing the ash discharge rate; at this time, strictly prohibit feeding coal into the boiler.

③ Strictly control steam temperature, close the desuperheating water supply, and open the superheater drain valve.

3. Clogged return feeder

Phenomena:

① Bed temperature is difficult to control; even a slight increase in coal feed causes the bed temperature to rise rapidly and become uncontrollable.

② Steam pressure drops.

③ Differential pressure between the upper and lower parts of the furnace decreases.

Solutions:

① First, increase ash discharge to restore unobstructed flow of return material as much as possible.

② If the blockage is severe and cannot be resolved, report to the shift supervisor and the responsible leader, and shut down the furnace. Inspect the return feeder; if any foreign objects are found, remove them and drain all the ash from the return feeder.

③ After resolving the blockage, ignite and increase the pressure.

IV. Slag Discharge Pipe Blockage

Causes:

① Large foreign objects were not cleaned from the furnace before startup.

② Localized coke lumps were not cleaned during the shutdown process.

③ Localized detachment of the furnace wall.

④ Poor combustion; high carbon content in the slag causes re-combustion and coking inside the pipe.

Solutions:

① Reduce the load or maintain operation at no load.

② Take safety precautions and use a steel bar to poke at the bottom of the slag discharge pipe to break up and release as much foreign matter as possible.

③ If the problem cannot be resolved quickly, shut down the furnace.

V. Coal feeder malfunction

Causes:

① Large debris gets stuck in the coal feeder.

② The coupling pin is broken.

③ The frequency converter motor is faulty.

④ The motor is damaged.

Solutions:

① If two coal feeders are damaged, stop the operation of that feeder and increase the coal feed rate of the other feeder (under the design coal quality, one feeder can operate at full load).

② If all three coal feeders are damaged simultaneously, immediately shut down the furnace and reduce the fire intensity.

③ Notify maintenance for emergency repairs, and restart the furnace after normal operation is restored.

VI. Secondary Combustion of Combustibles in the Flue

Phenomena:

① The exhaust gas temperature increases sharply.

② The negative pressure in the flue and furnace changes drastically.

③ The primary and secondary air temperatures rise and exceed the specified values.

④ Black smoke is emitted from the chimney.

⑤ Sparks are emitted from areas with loose air ducts.

⑥ In severe cases, the flue explosion-proof door activates.

Causes:

① Excessive induced draft volume and negative pressure.

② Malfunctioning return feeder, resulting in a large amount of unburned fuel being carried into the flue.

③ Damaged separator, unable to separate fuel properly.

Solutions:

① Upon detecting an abnormal rise in flue gas temperature, first identify the cause and verify the accuracy of instrument readings.

② Strengthen combustion regulation to maintain stable combustion.

③ Maintain stable operating parameters.

④ If the flue gas temperature continues to rise and exceeds 220℃, immediately shut down the furnace.

⑤ Close all orifices and dampers; ventilation is strictly prohibited.

⑥ After the temperature drops and it is confirmed that there is no ignition source, the induced draft fan can be started for ventilation for 5-10 minutes to remove accumulated ash, then re-ignite.

Damage to boiler pressure-bearing components  

I. Damage to the water-cooled wall

Phenomena:

① Rapid drop in boiler drum water level.

② Abnormally higher feedwater flow rate than steam flow rate.

③ Minor leaks are accompanied by a hissing sound of steam ejection; severe leaks result in a popping sound and steam ejection within the furnace, leading to furnace shutdown.

④ Drop in steam and feedwater pressure.

⑤ Decreased flue gas temperature.

Causes:

① Poor boiler feedwater quality, inadequate chemical monitoring, and failure to discharge wastewater according to regulations, leading to scaling and corrosion within the pipes.

② During maintenance and installation, pipes are blocked by debris, resulting in poor water circulation and causing overheating and rupture.

③ Manufacturing defects, substandard materials, improper installation, and poor welding quality.

④ Severe boiler water shortage and improper operation.

⑤ Improper start-up and shutdown operations, causing localized excessively high pipe wall temperatures.

⑥ Inadequate anti-wear layer on the water-cooled wall, resulting in severe wear.

⑦ Poor pipe expansion, leading to weld cracks.

Handling Procedures:

① If a water-cooled wall tube ruptures and the steam drum water level cannot be maintained, immediately shut down the boiler, report to the shift supervisor and relevant leaders, and keep the induced draft fan running.

② Increase the feedwater pressure and flow rate to maintain the steam drum water level.

③ If the damage is severe and the boiler steam pressure drops rapidly, and increasing the feedwater flow rate still cannot maintain the steam drum water level, stop the feedwater supply.

④ After all the steam in the boiler has been vented, stop the induced draft fan.

⑤ If the damage to the boiler water-cooled wall is minor, and the normal water level can be maintained without rapidly escalating the fault, the boiler evaporation rate can be appropriately reduced. Simultaneously, report to the shift supervisor and relevant leaders and await shutdown instructions. However, if the fault continues to worsen (increased noise, increased leakage, or endangering adjacent tubes), the boiler must be shut down immediately.

II. Economizer tube damage

Phenomena:

① Feedwater flow rate abnormally exceeds steam flow rate, leading to a drop in steam drum water level in severe cases.

② Abnormal material return from the secondary return feeder, resulting in either no ash being discharged from the ash discharge pipe or water being discharged (Burn #1).

③ Increased flue gas resistance and increased induced draft fan current.

④ Decreased flue gas temperature in the economizer and air preheater, with a widening temperature difference between the two sides.

⑤ Leaking sound in the economizer flue.

Causes:

① Large fluctuations in economizer water temperature and flow rate, severe water hammer, and improper operation of the recirculation loop.

② Poor feedwater quality causing pipe wall corrosion.

③ Fly ash abrasion.

④ Poor material, manufacturing, or welding of the economizer tubes.

⑤ Pipe blockage by debris causing localized overheating.

Solutions:

① Reduce boiler evaporation rate and quickly put the standby boiler into operation or increase the evaporation rate of other boilers. Report to the shift supervisor and management, and only shut down the boiler after obtaining approval. ② If the normal water level cannot be maintained during operation, or if the damage worsens, immediately shut down the boiler, keep the induced draft fan running, and stop the induced draft fan after all steam has been vented.

③ To maintain the steam drum water level, water can continue to be fed into the boiler, all drain valves must be closed, and the economizer recirculation valve must not be opened.

III. Superheater tube damage

Phenomena:

① Steam flow rate is abnormally lower than feedwater flow rate.

② In severe cases of damage, boiler steam pressure drops sharply.

③ Boiler outlet negative pressure is biased towards positive; in severe cases, steam may leak outwards from leaks.

④ Low flue gas temperature after the superheater or large temperature difference between the two sides.

⑤ Changes in superheated steam temperature: high temperature due to inlet leakage; low temperature due to outlet leakage.

⑥ Noise is heard at the superheater leak point.

Causes:

① Inadequate chemical monitoring; poor steam-water separator separation leading to poor steam quality; scale buildup inside the superheater tubes causing tube wall overheating.

② Improper operation during ignition and pressurization; insufficient steam flow to the superheater, causing overheating.

③ Excessively high operating temperature during normal operation; improper operation causing overheating.

④ Excessive desuperheating water flow; leaks in the desuperheating water pipes; water plugs in the superheater, causing localized overheating.

⑤ Superheater material does not meet standards; poor manufacturing and installation. ⑥ The superheater tubes are clogged with debris.

⑦ Severe fly ash wear, years of neglect, and pipe creep.

Remedies:

① Reduce the load appropriately and disconnect the desuperheater.

② If necessary, open the drain condensate drains on the superheater and main steam pipeline.

③ Report to the supervisor and shift leader.

IV. Desuperheater damage

Phenomenon:

① The superheated steam temperature drops, and the temperature difference between the various steam pipes increases.

② In severe cases, the steam pipeline experiences impact, causing a rapid temperature drop.

Causes:

① Excessive fluctuation in the desuperheating water flow rate.

② Scale buildup or defects in the desuperheater, or excessive bends in the water pipes.

③ Improper installation or maintenance.

Solutions:

① Appropriately reduce the load and disconnect the desuperheater.

② If necessary, open the drain valves on the superheater and main steam pipeline.

③ Report to the supervisor and shift leader.

V. Damage to steam and water supply pipes

Phenomena:

① When a minor leak occurs in the pipeline, the insulation layer becomes damp, leaks steam, or drips water.

② When a pipeline bursts, a noticeable sound is heard, and water and steam are ejected.

③ The steam or water flow meter shows abnormal changes; the flow rate decreases before the burst point and increases after the burst point.

Causes:

① Poor pipeline installation; materials, manufacturing, or welding do not meet requirements.

② Incorrect installation of pipe supports and hangers, affecting the free expansion of the pipeline.

③ Substandard water supply quality, causing pipe wall corrosion.

④ Abnormal operation of the water supply system, with large pressure fluctuations, causing water hammer or vibration.

⑤ Insufficient warm-up of the steam pipeline, resulting in severe water hammer.

Handling:

Water supply pipe damage:

① If normal water supply can be maintained, operation can be continued for a short period. Report to the shift supervisor and relevant leaders, await further action, or shut down the boiler. If the fault escalates and normal water levels cannot be maintained, threatening equipment and personal safety, the boiler must be shut down immediately.

② In the event of a water supply pipeline burst, the boiler must be shut down immediately. Steam Pipeline 

Damage:

① For minor leaks that can sustain operation for a short time, report to the shift supervisor and senior management, and await further instructions.

② In case of serious leaks or rupture, immediately shut down the boiler.

③ In case of a ruptured steam main pipe, immediately disconnect it from the system.

VI. Water hammer in boiler piping

Phenomena:

① Pressure gauge readings on the pipeline experiencing water hammer fluctuate unpredictably, or the gauges may even be damaged.

② There is a water hammer sound; in severe cases, the pipeline vibrates and steam escapes from the flanges.

Causes:

① Drastic changes in feedwater pressure and temperature.

② Malfunction of the feedwater check valve or feedwater regulating valve.

③ Insufficient air removal during feedwater pressurization, or excessive feedwater flow.

④ Insufficient desuperheating water flow, causing vaporization of the desuperheating water; excessively high feedwater temperature also causes vaporization.

⑤ Excessively high or rapid temperature of the cold furnace inlet water.

⑥ Insufficient pipeline warm-up, or incomplete drainage of condensate.

⑦ Insufficient steam temperature or water carryover in the steam.

Solutions:

① When water hammer occurs in the feedwater pipeline, partially close or completely shut off the feedwater valve; slowly open it after the hammer subsides.

② When water hammer occurs in the pipeline downstream of the feedwater valve, partially close the feedwater valve and open the economizer recirculation valve; close it after the hammer subsides.

③ During desuperheater impact, reduce the load and disconnect the desuperheater; restart it after the impact subsides.

④ During steam pipeline water hammer, shut off the desuperheating water supply, open the drain valve on the main steam pipeline, notify the turbine to monitor the steam temperature, and increase drainage.

Electrical system failure

I. Sudden load reduction

Phenomena:

① Boiler steam pressure rises sharply.

② Steam flow rate decreases sharply.

③ Steam drum water level drops momentarily and then rises.

④ In severe cases, safety valves activate (superheater, steam drum).

⑤ Electrical load decreases suddenly.

Solutions:

① Immediately open the vent valve to release steam.

② Reduce coal and air flow accordingly; stop coal feeding if necessary.

③ Switch all automatic modes to manual.

④ Adjust air flow, coal flow, and feedwater flow based on steam pressure and water level.

⑤ Reduce or shut off desuperheating water flow based on steam temperature; open superheater drain valves if necessary.

⑥ If the safety valve does not activate or return to its designated position at the specified value, manually operate the valve to raise and lower it.

II. Power outage at the boiler plant

Symptoms:

① Motor trips, indicator lights flash, and the emergency alarm sounds.

② Thermal instruments lose power, and readings malfunction.

③ Voltmeter and ammeter readings return to zero.

④ Boiler steam temperature, steam pressure, and water level all drop sharply.

Handling:

① Immediately switch the motor switch to the stop position and shut down the boiler.

② If the entire plant loses power, immediately stop coal feeding, shut down the boiler, close the main steam valve and feedwater valve, open the economizer recirculation valve, close the connecting valve, and try to maintain the water level.

③ If the feedwater pump has power, maintain normal boiler water supply.

④ If the boiler control panel loses power, a designated person must monitor the water level on-site and maintain normal boiler water supply.

⑤ After power is restored, the shift supervisor will give unified command to start the motors sequentially to prevent simultaneous starting.

⑥ If the power outage lasts for a long time and the water level gauge of the steam drum cannot be seen, you must call for water first. If water is detected, you can add water. If water is not detected, it is strictly forbidden to add water. All bed material should be drained and water can only be added to the boiler after the boiler has completely cooled down.

                                                                                            Qingdao Huayuan Equipment Manufacturing Co., Ltd.