Case Studies of Boiler Operation Accidents--6
Thread Content
An accident occurred at Xinxiang Power Plant due to a full water condition in Boiler No. 2, which led to the failure of the shafting of Unit No. 2. Details of the accident: At 03:20 on January 25, 1990, after the fire was extinguished in Boiler No. 2, during the process of restoring normal operation, high leakage rates from the feedwater control valves (with a leakage rate of 120 T/H) prevented the operators from effectively controlling the water level in the steam drum. As a result, the water level in the steam drum rose sharply while the steam temperature dropped rapidly, causing water hammer in the turbine.
Cause analysis of the accident: The operators failed to detect the sudden drop in steam temperature in time, allowing low-temperature steam to enter the turbine for an extended period. Low-temperature steam enters the turbine, causing the stationary components such as the cylinders to deform under thermal stress, the rotating shaft to bend, severe radial friction between the moving and stationary components to occur, and ultimately the shafting to break. Faulty water level gauges and incorrect readings, failure of the boiler water level protection system, faults in the feedwater system, violations of operating procedures, misjudgments, and improper operations are the main causes of overfilling and underfilling accidents in boiler drums. Accident summary: Appropriate countermeasures against accidents are formulated based on aspects such as the configuration, installation, and operation of the drum water level measurement system, as well as the maintenance of the feedwater system.
Could we consider this from another angle? Is there something wrong with our design? If we had taken such issues into account during the initial risk assessment, we could have set a maximum opening degree for the water supply valve; in other words, the maximum flow rate of water supplied couldn’t exceed a certain safe value. This would have allowed us to completely avoid such problems. After all, it is under abnormal conditions that human error is more likely to occur. Additionally, if the temperature drops to a certain level, we can simply close the water supply valve, which might help prevent problems from arising. We can’t always rely on humans to control things and avoid accidents, as humans may make mistakes.