Steam turbine casing after speeding accident
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At about 21:15 on the evening of July 3, a steam turbine accident occurred in a Hebei steel plant. According to the description of the on-site personnel, the impeller fragments flew nearly 100 meters, the colored steel tiles on the roof of the factory building were overturned, and the window glass was shattered. Since the scene has been cordoned off and the specific cause is unknown, there are currently no reports of casualties at the scene. The unit was shut down on July 1. The unit was started during the day yesterday, and an accident occurred at night. During the operation of the unit, the air exhaust valve was opened (possibly due to misoperation), and the turbine ran over after one minute. It is possible that after the empty row is opened, the generator reverse power icon causes the generator main protection to operate, and the main steam valve or extraction check valve is not closed tightly, causing the turbine to overspeed and eventually cause a speeding accident.
What is a speeding accident? Let me introduce some science to you
Steam turbine overspeed accidents are caused by faults in the speed regulation and protection systems of the steam turbine and its own defects, but they are often directly related to operation and maintenance. Analysis and discussion will be conducted according to different accident causes and fault links. 1. The speed control system is defective: The task of the steam turbine speed control system is not only to ensure the normal operation of the steam turbine at the rated speed, but also to ensure that the speed does not increase beyond the specified allowable value after the turbine load is shed. Therefore, the speed control system is the first measure to prevent the steam turbine from overspeeding. If the turbine cannot maintain no-load operation after the load is shed, overspeeding may occur. The reasons why the speed of the steam turbine rises too high after load shedding are as follows. (1) The speed regulating valve cannot be closed or the amount of steam leakage is large. (2) The extraction steam check valve is not tight or refuses to operate. (3) The retardation rate of the speed control system is too large or the adjustment components are stuck. (4) The operation mode is unreasonable or improperly adjusted. (5) The droop of the speed control system is too large. (6) The dynamic characteristics of the speed control system are inappropriate. (7) The speed control system is improperly adjusted, such as the synchronizer adjustment range and the expansion gap of the steam distribution mechanism not meeting the requirements. 2. Turbine overspeed protection system failure: (1) The emergency safety device does not operate or the operating speed is too high. The operating speed of the emergency safety device is generally specified to be 10-12% higher than the rated speed. This is the main protection device to protect the turbine from excessively increasing its speed. In addition, different units are also equipped with additional protection or electric overspeed devices that specify the operating speed to be slightly higher than the emergency safety device. If the turbine speed increases, the main reasons for the emergency safety device not operating or operating excessively are:: ① The weight or fly ring guide rod is stuck. ② The dynamic and static parts of the heavy hammer or flying ring are not concentric, causing tension during operation. ③ The spring undergoes excessive radial deformation under force, causing friction with the hole wall. ④The gap between the impact plates is too large and the emergency safety device slide valve cannot operate after the impactor flies out. (2) The slide valve of the emergency safety device is stuck and cannot operate. (3) The automatic main steam valve and speed regulating valve are stuck. 3. Improper adjustment during operation: (1) The oil quality is not well managed. The oil is of inferior quality or has a different label. When it is returned, it is not tested and added to the main oil tank for operation. Furthermore, the quality of maintenance is poor. The adjustment of the shaft seal gap is not within the standard range. The adjustment is improper. The shaft seal pressure is adjusted too high during operation. Steam leaks to the oil gear, causing water to enter the oil, causing the speed regulation and protection components to jam. (2) When the synchronizer is operated manually or electrically, if the load is increased or decreased beyond the specified adjustment range, it will not only cause the unit's speed to rise sharply after load shedding, but also cause the adjusting sleeve to lose pulsation, causing jamming and overspeeding accidents. (3) The steam quality during operation is poor, and the chemical supervision does not comply with the standards issued by the ministry. Long-term operation will cause the main steam valve and the speed regulating valve to become stuck. (4) After major or minor repairs or after 2000 hours or after the speed control system is disassembled, the engine is turned on for an overspeed test. The speed increase does not meet the standard and the operation is improper, causing the speed to rise too fast.
I collected them, there are many on the Internet, mostly in power plants, and there are turbines for steam turbines in chemical plants. I collected them as a special topic.
There are currently no reports of casualties at the scene. Judging from the casing, the pressure of this steam turbine should not be high.
[Steam turbine speed accidents in recent years] Summary, with pictures and analysis! https://bbs.hcbbs.com/thread-3236469-1-1.html (Source: Haichuan Chemical Forum-Haichuanliu)