凝汽式汽轮机后轴承振动过大原因及解决

Cause and Solution of Excessive Vibration of Condensing Turbine Rear Bearing

汽轮机轴承振动值作为汽轮机运行重要的安全指标而备受关注,后轴承相比前轴承发生振动超标的几率更大。某些凝汽式汽轮机在启动阶段汽轮机正常运行时,切换循环水泵或凝汽器单侧运行单侧清洗的过程中,汽轮机后轴承振动过大引发机组停机。对此现象进行了分析,结合汽轮机在后轴承振动超标前后过程中汽轮机的外观和数据变化,逐一排查后轴承振动大的原因。结果发现凝汽器的进出水口膨胀节被拉起,汽轮机后汽缸出现“顶缸”现象,导致后轴承振动过大。根据汽轮机和凝汽器的受力状态,建立力学几何模型,找到从源头上消除水压内推合力过大的方法。对于采用弹簧支承的凝汽器,调整循环水进出口处膨胀节的安装位置,可大幅消除循环水进出水口的内推力,以一台凝汽器进出水口规格DN700,水压0.3 MPa为例,通过调整膨胀节的安装位置,其水压内推合力由423 kN大幅下调至38 kN,避免汽轮机后轴承端产生过大的推力造成振动超值。对于采用固定支承的凝汽器,汽轮机本体及凝汽器需要注意结构强度问题。通过上述理论分析并将整改措施应用于凝汽式汽轮机,凝汽式汽轮机后轴承振动过大现象得到彻底解决,汽轮机故障停机率下降。

As an important safety index of turbine operation,the vibration value of turbine bearing has attracted much attention.The rear bearing is more likely to exceed the standard than the front bearing.When certain condensing steam turbines are operating normally during the start-up phase,during the process of switching the circulating water pump or cleaning the condenser on one side,excessive vibration of the rear bearing of the turbine causes the unit to shut down.An analysis is conducted on this phenomenon,and combined with the changes in the appearance and data of the steam turbine before and after the excessive vibration of the rear bearing,the reasons for the large vibration of the rear bearing are investigated one by one.It is found that the expansion joint of the inlet and outlet of the condenser is pulled up,and the phenomenon of"jackup casing"appears in the rear casing of the turbine,resulting in excessive vibration of the rear bearing.According to the stress state of steam turbine and condenser,a mechanical and geometric model is established to find a way to solve the problem of excessive internal pushing force of water pressure from the source.For condensers supported by springs,adjusting the installation position of expansion joints at the inlet and outlet of the circulating water can significantly eliminate the internal thrust of the circulating water inlet and outlet.Taking a condenser inlet and outlet specification DN700 and water pressure 0.3 MPa as an example,by adjusting the installation position of the expansion joint,the internal pushing force of the water pressure is greatly reduced from 423 kN to 38 kN,so as to avoid excessive thrust at the rear bearing of the steam turbine resulting in excessive vibration.For the condenser with fixed support,attention must be paid to the structural strength of the turbine body and condenser.Through the above rectification,the rear bearing vibration phenomenon of condensing steam turbine has been completely solved.Turbine failure and shutdown rate decreased.