锅炉热态启动过程汽包瞬态应力有限元分析

Finite element analysis of transient stress in boiler drum during hot start-up process

为研究锅炉热态启动速度对汽包应力的影响,本文根据某电厂汽包实际结构尺寸,通过ANSYS软件建立了汽包有限元模型,结合运行规程中给定的热态启动曲线以及不同温升率的5条热态启动曲线,对汽包瞬态应力场进行研究。结果表明:热态启动过程中,最大机械应力和总应力的位置位于汽包与下降管接口的纵向截面内转角处;最大热应力的位置在与正常水位线相交的水冷壁上升管开孔处横向截面的内转角处;当温升率从2℃/min增加到5℃/min,热态启动速度对汽包在应力最危险点的机械应力最大值没有影响,而热应力最大值随温升率的增加而增加;启动后期,热应力不再起作用,总应力主要受机械应力影响,总应力最大值与机械应力最大值相同且不随热态启动速度的变化而改变,仅与汽包内压有关,可见汽包可承受比运行规程中给定的更快的锅炉启动速度。

A complete finite element model for boiler drum,which is based on the actual boiler drum structure size,was established by pre-processor of ANSYS,to study the effects of hot start-up speed on stresses in boiler drum.Combining with the hot start-up curves given by operation rules and five hot start-up curves at different temperature rising rates,the transient stress field of the boiler drum was investigated.The results indicate that,during the hot start-up,the maximum mechanical stress intensity and the maximum total stress intensity locate at the inner joint corner of drum shell and downcomer in the longitudinal cross section.The maximum thermal stress intensity locates at the inner joint corners of drum shell and risers which are in contact with the normal water line in the horizontal cross section.As the temperature rising rate increases from 2 ℃/min to 5℃/min,the hot start-up speed has no effect on the maximum mechanical stress intensity of the most dangerous point on the boiler drum,but the maximum thermal stress intensity increases with the temperature rising rate.In the latter stage of hot start-up process,the thermal stress is not going to work.The total stress is largely driven by the mechanical stress.So the maximum total stress intensity is the same as the maximum mechanical stress intensity,and they don＇t change with the temperature rising rate but with the pressure in the drum.Therefore,the boiler drum can suffer a higher temperature rising rate during the hot start-up,compared with the value given by the operation rule.