超超临界电站锅炉储水罐用调节阀及管配系统流场特性分析

Analysis on characteristics of flow in regulating valve and pipe system of water storage tank for boiler in ultra-supercritical power plants

针对超超临界电站锅炉储水罐用调节阀国产化研制中流场结构设计面临的问题,结合前期配置于某电站储水罐用调节阀及管配系统底板汽蚀击穿故障现象,基于两相空化流动控制方程和Fluent流场数值模拟手段,采用RNG k-ε湍流模型及耦合算法,对该调节阀流场结构及管配系统流场特性进行数值模拟分析计算,并进行流场结构及特性验证,结构改进优化设计.重点分析了压锥式调节阀及管配系统流场特性,结果表明:压锥式调节阀在设计工况下,由于阀门开度较小,高温介质在喉口处发生严重的汽化现象,气化率达90%以上,介质速度较高达到143 m/s,以至于管配系统底板被冲击至击穿.针对失效原因,提出了一种新型笼罩式调节阀,优化结构流场模拟结果表明,在阀门喉口含汽量减少了21.6%,盲板附近的速度降低了80%,表明汽化现象得到了抑制,管配系统能够安全运行.模拟结果较好展示了阀门流场的分布规律,为该类调节阀结构设计与优化提供可借鉴的理论依据,对电站锅炉调节阀国产化推进具有一定促进作用.

In view of faced problems in flow structure design in the research and development of regulating valve of water storage tank for boiler in ultra-supercritical power plants in China,combining the cavitation erosion of valve plate in the previously designed regulating valve in a specific plant,a series of numerical simulations of two-phase cavitating flow field in a regulating valve and pipe system are carried out by using CFD code in Fluent. In the simulations,the RNG k- ε turbulence model and full cavitation model are used to validate fluid flow structure and to optimize the valve structure,especially,a cone valve and its pipe system are paid attention. The results show that cavitation occurs seriously in the throat of the original cone valve under design condition due to the very narrow opening. Particu-larly,the vapour volume fraction is above 90% and the flow velocity is as high as 143 m / s,leading to damage to the valve plate by cavitation eventually. To eliminate the cavitation,a new type of valve structure is put forward. The results show that the vapour volume fraction is reduced by 21. 6% and the fluid velocity is decreased by 80% near the throat,suggesting the cavitation phenomenon has been suppressed to some extend and the pipe system is capable of safe operation. The simulated results exhibit the flow field distribution in the valve and pipe system more clearly,and provide theoretical references for the design and optimization of regulating valves,as well as promote the nationalization of this kind of valve.