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Emergency Rescue Plan for Boiler Accidents. Author: Anonymous. Source: Mech-Electrical Home. Boilers are important devices used in industrial production processes as well as for daily use. They are special equipment that must withstand high temperatures and pressures, and they pose an explosion risk. In the event of an emergency, such as a boiler explosion, pipe rupture, or water shortage, if one does not know how to respond appropriately, serious accidents can occur, putting the lives of employees at risk and causing significant financial losses to the company. I. Characteristics of boilers 1. Boilers must operate with high reliability; any failure can lead to power outages, production stops, and equipment damage, resulting in severe losses. 2. Boilers are subject to high temperatures, pressure, and corrosion during operation, which can easily lead to accidents. 3. A boiler is a sealed pressure vessel that operates under high temperature and pressure, and there is a risk of explosion. Once an explosion occurs, it will destroy equipment and buildings, cause injuries and deaths, and its destructive power is extremely significant. II. Causes of boiler accidents 1. Too low a water level in the boiler can lead to serious water shortage accidents ； Excessively high boiler water levels can lead to a full-steam accident. Operating at high water levels for an extended period can also cause scaling to form at the pressure gauge connections, resulting in blockages and rendering the pressure gauge ineffective, which in turn may cause overpressure accidents in the boiler. 2. Poor water quality management. Excessive boiler scale, combined with a lack of regular blowdown, leads to the accumulation of sludge and scale on the water side of the heating surfaces, increasing thermal resistance and causing damage to the metal components of those heating surfaces ； Oil present in the feed water or acidic feed water can cause the metal walls to overheat or corrode ； Excessively high alkalinity can cause caustic embrittlement in steel plates. 3. The water cycle is disrupted. Scaling can disrupt the water circulation; for example, if the alkalinity in a boiler is too high, foaming on the water surface of the boiler drum and steam-water splashing can easily interfere with the water circulation. The water circulation is disrupted, causing chaos in the water conditions inside the boiler. Some of the heat exchange tubes may experience backflow or stagnation, or a \"vapor plug\" may form; sludge and scale accumulate in the tubes where the water flow is stagnant, which can damage the heat exchange tubes or even lead to explosions. 4. Operation at excessive temperature. Due to poor flue gas flow or unstable combustion conditions, the steam temperature at the boiler outlet becomes too high, which in turn raises the temperature of the heating surfaces and leads to metal degradation or tube burst accidents. 5. Overpressure operation. If the safety valve fails, or if there is a malfunction in the water circulation system, it can cause the boiler to operate under excessive pressure, and in severe cases, this may lead to a boiler explosion. 6. Grate failures can cause plant shutdown accidents. 7. Mistakes by boiler operators, incorrect maintenance methods, and irregular inspections of the boiler can all lead to accidents. III. Emergency Handling of Boiler Accidents (I) Water Deficiency Accident 1. Symptoms of a water deficiency accident: When the water level indicated by the water gauge is below the lowest level line while the boiler is in operation, it is considered a water deficiency accident. In boiler accidents, the most common type is water shortage. Water shortage occurs in two situations: 1) Mild water shortage – a mild water shortage in a boiler refers to a situation where the water level inside the boiler disappears from the gauge; however, this level can be restored by flushing the gauge and using the \"call for water\" method. 2) Severe water shortage: When the method of \"calling for water\" is used and the water level in the boiler still does not appear on the gauge, this is referred to as a severe water shortage in the boiler. When the steam drum runs out of water, it disrupts the water circulation, leading to stagnation, separation of steam and water, and evacuation of the downcomer. Severe water shortage can even dry out the boiler, resulting in serious accidents. At the same time, water shortage can cause the steam temperature to rise significantly, even affecting the safe operation of the equipment. 2. The main signs of low water level in a boiler are: the water level in the gauge being below the lower limit, or no water level being visible; furthermore, the negative value indicated by the low-water-level gauge increases ； The two-color water level gauge is green ； The water level alarm emits a sound and the low water level indicator light turns on ； The water supply volume is abnormally lower than the steam flow rate. 3. Causes of water shortage: 1) Operators fail to perform their duties properly and lack a sense of responsibility. 2) The boiler operators have low technical skills, make misjudgments and perform incorrect operations; they even mistake a lack of water for an adequate water level. 3) Water shortage is caused by issues with the water level indicator itself. 4) Caused by a fault in the water supply system. 5) Leakage in the furnace waste discharge pipeline and waste discharge valve. 6) A single main water supply pipeline supplies water to multiple boilers simultaneously, resulting in competition for water. 4. Handling of water shortage incidents: First, check the boiler water level using the water intake method to determine whether it is a severe water shortage or only a slight one. When the water level cannot be seen on all of the boiler’s visual water level gauges, the boiler must be stopped immediately, and the following procedures should be followed: 1) Immediately perform the \"call for water\" operation on boilers that allow such a procedure. The method is as follows: First, open the drain valve, then close the water valve to purge the steam valve; after that, open the water valve and close the steam valve to purge the water valve. After purging is complete, open the steam valve and the drain valve. At this point, the water level should quickly return to its actual position and fluctuate up and down. “The key to performing the “call for water” operation is not to turn the water knob on the water level gauge. 2) After performing the “call for water” operation and the water level is displayed on the gauge, the combustion equipment of the boiler can be started slowly to allow it to continue operating. If there is a loud noise inside the boiler when the boiler feed water valve is opened, or if the water level does not rise even when more feed water is added, under no circumstances should the boiler’s combustion equipment be started; the boiler must be shut down for inspection. 3) For boilers that can be subjected to a \"water call\" operation, if no water level is indicated on the gauge after such an operation, it is strictly prohibited to add more water to the boiler; the boiler must be shut down immediately. Boilers that are not suitable for a \"water call\" operation should also be shut down urgently. 4) During boiler operation, when severe water shortage or water overfill is detected ； Failure of safety components such as level gauges, pressure gauges, or safety valves ； The boiler should be shut down urgently in cases where all the water supply systems fail, or when it suffers severe deformation and leakage due to heating, making normal operation impossible. Main steps for shutting down the furnace: stop supplying fuel and air, reduce exhaust airflow ； Extinguish and remove the fuel from the furnace (referring to bed-fired boilers); note that watering the furnace should not be used to put out the fire, instead yellow sand or wet coal ash should be used to suppress the glowing flames ； Open the furnace door, ash door, flue dampers, etc., to cool the furnace ； Disconnect the boiler from the main steam pipe, and open the vent or safety valve on the boiler drum, as well as the superheater outlet header and drain valves ； Water is added to and removed from the boiler in order to accelerate its cooling. In the event of a severe water shortage, do not feed water into the boiler. 5. Methods to prevent boiler water shortage: 1) Strengthen the safety and technical training for boiler operators to rapidly improve their operational skills. 2) Regularly flush the water level gauge to ensure that it indicates the correct water level. 3) Strengthen the maintenance and management of the water supply system and water level alarm system, and conduct regular calibration and adjustment. 4) Install the water level gauge properly, and conduct regular inspections during operation to prevent an increase in water level. (II) Full-water accident 1. Methods for dealing with a full-water accident: (1) When the boiler’s steam pressure is normal and the water level is above the highest safe water level but below the upper visible edge, the water gauge should be flushed to determine whether the water level indicates a false reading; once the accuracy of the water level reading is confirmed, measures should be taken to reduce the feedwater supply in order to restore the water level to normal. (2) As the water level continues to rise, the drain valve and the emergency discharge valve should be opened to release water. (3) After the above treatments, if the water level in the boiler drum continues to rise and exceeds the visible upper edge, it is necessary to identify the cause of the fault and eliminate the underlying problems before resuming operation. (III) Steam-water slugging accidents 1. Handling of steam-water slugging accidents (1) Reduce combustion by closing the main steam valve and lowering the load. (2) Fully open the surface blowdown valve of the boiler drum, and partially open the periodic blowdown valve as well; at the same time increase the feed water to maintain a normal water level, in order to reduce the salt content in the boiler water and improve its quality. (3) Take effective measures to improve the quality of the boiler water, and increase the frequency of analytical tests on it. When water hammer occurs in the steam pipes, the steam pipe and steam distribution valve traps should be activated to drain the water. (4) After troubleshooting, the water level gauge should be flushed to restore normal operation; if the fault persists despite the above measures, the furnace should be stopped immediately for inspection. And report to the relevant supervisors immediately. (IV) Furnace tube explosion accidents 1. Handling of furnace tube explosion accidents (1) When the tube is only slightly damaged and the normal water level can be maintained with no further expansion of the accident, operation can continue at reduced load; once the backup furnace is started, the furnace should be shut down immediately for maintenance ； (2) When the pipes are severely damaged and it is no longer possible to maintain normal water level and steam pressure, emergency shutdown measures must be taken. At this time, the exhaust fan must not be stopped, and the water supply should continue in order to try to maintain the water level and prevent other pipes from being damaged. (3) If several boilers supply steam in parallel, the boiler with a burst tube should be disconnected from the steam main. (5) Economizer damage accidents 1. Handling of economizer damage accidents (1) For non-boiling economizers, the bypass flue dampers should be opened, the main flue dampers should be closed, and the use of the economizer should be suspended. At the same time, the valves for the water supply to the economizer’s bypass should be opened to continue supplying water to the boiler. (2) If the smoke inlet and outlet dampers of the economizer are highly airtight, maintenance can be carried out without shutting down the furnace after the economizer is isolated. (3) When the boiler is operating with a faulty economizer in isolation, the flue gas temperature shall not exceed the value specified on the draft fan nameplate; otherwise, the load should be reduced. (VI) Air preheater damage accidents 1. Handling of air preheater damage accidents (1) In the case of minor damage, the unit can continue to operate; maintenance should be carried out after the backup furnace comes online. (2) When severe damage prevents the boiler from operating properly, it should be shut down for maintenance. (7) Accidents of rupture of the water level gauge glass plate (tube) during boiler operation 1. In the event of a rupture of the water level gauge glass plate (tube) while the boiler is in operation, the boiler must be shut down urgently for maintenance. (8) Boiler overpressure accident 1. Handling of boiler overpressure accidents (1) Reduce combustion. (2) If the safety valve fails and emergency steam release is not possible, steam can be released manually. (3) Maintain the normal water level on the water gauge. (4) Carry out water supply and drainage to lower the furnace temperature. (5) After identifying the cause of the overpressure, decide whether to shut down the system or resume operation.