Common accidents during boiler operation

These are common accidents that occur during the operation of boilers in power plants: 1. Excessive water in the feedwater pump drum due to increased operation. 2. Low drum water level caused by a failure in the feedwater pump. 3. Low drum water level when the load drops suddenly. 4. Boiler shuts down due to an emergency stop of the grinding machine. 5. Boiler shuts down because the powder feeder starts operating automatically in excess. 6. Boiler shuts down due to an emergency stop of both grinding machines. 7. Boiler shuts down when oil supply is stopped during startup. 8. Secondary combustion occurs when the load is increased. 9. Severe overheating due to powder carried by the third air stream. 10. Sudden drop in steam temperature after the boiler shuts down and the drum becomes full of water. 11. High steam temperature during the process of restarting the boiler after it has shut down. 12. Boiler overpressures when all loads are removed suddenly. 13. Overheating leads to shutdown due to improper operation. 14. Uncontrolled operation of the cooling water valve causes fluctuations in steam temperature, leading to shutdown of the turbine. 15. Accidental activation of the fan’s emergency switch due to misalignment. 16. Blockage of the fine powder separator. 17. High temperature in the powder bin due to air leakage in the auger system. 18. Local overheating of the water wall resulting in tube rupture. 19. Tube rupture due to overheating in the rear section of the boiler. 20. Vibration of the fan’s support rods causes the fan blades to fall off. 21. Startup of the fan while it is still under load, resulting in damage to the motor

Handling of common boiler accidents. Common boiler accidents include: 1. Economizer accidents. When the economizer is damaged, the following symptoms occur: 1. The water level indicated by the boiler gauge drops, or the water supply volume is abnormally high compared to the evaporation rate； 2. There are noises near the economizer; steam is escaping from the cracks in the furnace wall and at the bottom of the economizer, along with moisture issues ； 3. The temperature difference of the flue gas on both sides of the economizer increases (the temperature on the leaking side is lower). Handling when the economizer is damaged: 1. Isolate the economizer by opening the bypass flue damper and closing the economizer’s flue gas inlet damper. Water can be supplied directly into the furnace without going through the economizer; to do this, open the boiler’s direct feed valve and close the economizer’s water inlet valve ； 2. After using the economizer bypass flue, ventilation should be adjusted to maintain an appropriate negative pressure in the furnace chamber ； 3. For a faulty economizer, once it is isolated from both flue gas and feedwater, water should be drained promptly if necessary ； 4. If the smoke inlet and outlet dampers of the economizer are airtight and leak-free, repairs to the economizer can be carried out while the boiler is in operation; however, these repairs must be done under conditions that ensure personal safety, and the economizer should then be put back into use. If repairs cannot be carried out while the boiler is running, it should be shut down as soon as possible for maintenance. II. Water shortage incidents – Symptoms of water shortage incidents: 1. The water level is below the minimum safe level, or the water level is not visible; the glass tube of the water gauge turns white ； 2. The high and low water level alarms emit alarm signals. 3. The water supply is less than the evaporation rate. If water shortage occurs due to the rupture of furnace tubes or economizer tubes, the opposite phenomenon occurs ； 4. A burnt smell can be detected in cases of severe water shortage ； Reasons for water shortage incidents: 1. Inadequate monitoring of water level by operators, along with errors in judgment and operation. 2. The steam-water connection pipe of the level gauge became blocked, resulting in a failure of the water level alarm; as a result, the operators failed to detect the false water level in time. 3. Water supply machinery failure, automatic water supply regulation malfunction ； 4. Leakage in the drain valve or improper operation of the drain system. Procedure for dealing with water shortage incidents: In cases where the water level in the gauge is below the lower visible edge and the level cannot be seen even after calling for water, an emergency shutdown of the boiler should be carried out. If the water level does not drop below the lower edge of the gauge, increase the water supply to restore the water level to normal. III. Flood accident Phenomena of a flood accident: 1. The water level is above the maximum level mark, and the water level alarm emits a high-level alarm signal ； 2. The water supply volume is abnormally higher than the steam flow rate. In severe cases, water hammer occurs in the steam pipes. Reasons for full water level: 1. Inadequate monitoring of the water level by the operators, incorrect adjustments, or the formation of an artificial water level ； 2. The water level alarm is malfunctioning, and the automatic water supply control system is also malfunctioning. Methods for dealing with a full-water accident: 1. Immediately flush the water level gauge; if a full-water accident is confirmed, quickly close the feedwater valve and open the economizer recirculation valve or the bypass flue to prevent damage to the economizer. 2. Open the drain valve to increase drainage, but the water release time must not exceed 30 seconds (per valve). When releasing water, pay close attention to the water level in the gauge to prevent water shortage accidents caused by excessive discharge. 3. Reduce the air damper, decrease fuel and air supply, and weaken combustion. 4. Open the drain valves on the steam cylinders and steam main pipes. 5. Once the water level returns to normal, resume normal combustion and bring the system back into normal operation. IV. Azeotrope formation in soda water: Phenomena of azeotrope formation: 1. The water level inside the gauge fluctuates violently, with a large number of bubbles and foam appearing, making it impossible to see the actual water level. 2. Water hammer occurs in the steam pipeline, resulting in steam leakage and water leakage at the flange connections. Reasons for soda water azeotropy: 1. Poor quality of boiler water, with excessive levels of oil, salts, and suspended impurities ； 2. Wastewater was not discharged in accordance with regulations ； 3. When the load increases suddenly or units are connected, the steam pressure in the new boiler is higher than that in the steam main, causing a large amount of steam to escape from the boiler. Treatment methods for soda azeotrope: 1. Water treatment personnel should take effective measures to improve the quality of boiler water and increase the frequency of analyses of it. The boiler load shall not be increased until the quality of the boiler water improves ； 2. Fully open the surface blowdown valve of the boiler drum; at the same time, appropriate bottom blowdown should be carried out, and the feed water supply should be increased to maintain a normal water level, in order to reduce the salt content in the boiler water ； 3. Open the drain valves on the steam pipeline and the steam distributor. 4. After the accident is resolved, the water level gauge should be flushed to restore normal operation. If the accident persists despite the above measures, it is necessary to report it immediately to the relevant supervisors in order to decide whether to shut down the furnace. V. Damage to the water level gauge glass tube (plate) Causes of damage: 1. Poor quality of the glass tube (plate). When cutting the glass tube, fine cracks were formed at the end. 2. The upper and lower packing on the glass tube is too tight, or the upper and lower packing glands are not aligned during installation. 3. When using a new glass tube, it was not properly preheated, and the operation for flushing the water level gauge was incorrect. 4. During normal operation, when exposed to cold water droplets or suddenly in contact with cold air. Handling methods and precautions: 1. When preheating new glass tubes, first slightly open the steam and water valves. Once moisture appears inside the tube, then slightly open the water valve to discharge the mixture of steam and water. After that, slowly close the water valve, gradually adjusting the steam and water valves to their normal positions ； 2. If both level gauges are damaged at the same time, the furnace should be shut down urgently, and new glass tubes should be installed. 3. If one gauge is damaged, the other gauge should be used to monitor the water level, and emergency measures should be taken to repair the damaged gauge. 4. When replacing the glass tube of the water level gauge, the steam and water valves should be closed, while the drain valve should be opened. VI. Secondary combustion in the flue: Phenomena of secondary combustion in the flue: 1. A sharp increase in exhaust gas temperature, a decrease in negative pressure in the flue or the formation of positive pressure; sometimes the explosion-proof door at the rear operates ； 2. The smoke turns abnormally black, and in severe cases, sparks are emitted. Reasons for secondary combustion in the flue: 1. Improper adjustment of fuel and air volume ； 2. Improper ignition or shutdown procedures led to the accumulation of large amounts of combustible material in the furnace and flue ducts ； 3. Prolonged operation at low load results in a very low flue gas flow rate, leading to the accumulation of large amounts of combustible material inside the flue ； 4. Excessive negative pressure in the furnace causes unburned combustible materials to be drawn into the flue. Handling method: 1. Immediately stop feeding fuel into the furnace and shut down the furnace urgently ； 2. Close the flue dampers, air dampers, and all access doors; ventilation is strictly prohibited ； 3. Steam can be injected into the flue, or a carbon dioxide fire extinguisher can be used to put out the fire ； 4. After the accident is resolved, carefully inspect the equipment; if nothing is abnormal, ventilate it for 10–20 minutes first, then ignite it in accordance with the operating procedures. VII. Water hammer in the boiler drum, pipes, and economizer. Symptoms of water hammer: 1. Knocking sounds and vibrations inside the boiler drum or pipes. 2. When water hammer occurs in the economizer or water pipes, the gauge pointer moves rapidly and significantly. Reasons for water hammer in the boiler drum: 1. The water level in the boiler drum is too low, or the flange connections between the feed water pipes and the water tank are not secure; the check valves on the feed water pipes are malfunctioning or not properly sealed, allowing steam to flow into the feed water pipes. 2. The connection flanges of the steam heating tubes inside the lower part of the boiler drum are loose, or they are installed in an incorrect position. Solutions: 1. Check the water level in the boiler drum; if it is too low, increase the feed water volume to the normal level ； 2. Water should be added to the drum in a uniform and steady manner ； 3. During shutdown inspections or maintenance, pay attention to eliminating defects in the steam heating equipment inside the lower drum and in the flanges of the feed water tank in the upper drum. Causes of water hammer in the water supply pipes: 1. Air or steam present in the water supply pipes, and malfunctioning of the water supply check valve; 2. Excessively high water supply temperature or vaporization. Solution: 1. Activate the backup water supply pipeline and repair the faulty check valve on the main water supply pipeline to ensure its proper functioning ； 2. Reduce the feedwater temperature. Reasons for water hammer in steam pipes: 1. Poor pipe warming and drainage before steam is supplied ； 2. The main air valve or the valve in the air supply pipeline is opened too quickly when supplying steam ； 3. An excessive rapid increase in load, or full water level in the boiler and azeotrope formation between water and steam, cause steam to carry water into the pipes. Solution: 1. Turn on the steam trap on the steam pipeline to drain water ； 2. Check the water level inside the boiler; if it exceeds the specified limit, it should be reduced to the normal level ； 3. Improve the quality of the feed water, increase wastewater discharge appropriately, and avoid azeotrope formation. Reasons for water impact in the economizer: 1. The air inside the economizer was not completely removed when starting the fire ； 2. The outlet temperature of the economizer is too high, resulting in localized vaporization ； 3. The check valve on the economizer feedwater pipeline is not functioning properly, causing inertial shock to the feedwater. Solution: 1. Close the main flue and open the bypass flue ； 2. Slowly open the economizer air valve to discharge the air ； 3. Optimize the economizer recirculation conditions; the boiler uses continuous feedwater ； 4. Repair the check valve to make it function properly. VIII. Sudden Power Outage: In the event of a sudden power outage, the emergency shutdown procedure should be followed. Close the main steam valve and maintain the water level.