开孔形式对盘环形挡板汽提器特性影响的模拟分析

Numerical analysis of effect of pore-opening on disc-donut baffle in stripper

采用CFD方法对安置盘环挡板的汽提器进行了模拟计算,对比了盘环挡板上有无开孔情况下的颗粒流动分布。结果表明,在盘环挡板上进行开孔可有效减少“气垫”区域,使气体与颗粒更顺利地穿透挡板进行高效接触。此外,通过对比不同开孔形式下的催化剂颗粒流动与气泡分布特性,可以发现均匀开孔时,随着开孔尺寸的增加,气相流动阻力下降,可以携带颗粒更加均匀地穿过盘环挡板,使得挡板以下的“气垫”区域减小,颗粒在汽提器内分布更加均匀,有利于汽提蒸汽与催化剂颗粒之间的接触。但是,随着开孔尺寸增加,汽提器内气泡的平均尺寸有所增加,气泡数量减小,气泡所占的总体积及气泡所能提供的相界面积有所减少。对比均匀开孔与非均匀开孔的颗粒流动与气泡特性,结果表明,在盘形挡板顶部附近开孔12mm,其他区域均匀开孔9mm的非均匀开孔形式在确保催化剂颗粒流动的均匀性分布、汽提蒸汽与催化剂颗粒之间的接触效果的同时,容易产生更小的气泡,可以提供更高的气固相界面积,更加有利于汽提器性能的改善,因此是比较优选的开孔方式。本文关于挡板开孔形式影响的模拟分析对设计高性能的汽提器内构件具有重要意义。

Computational fluid dynamics(CFD)model was developed to study the gas-solids flow in a stripper with pore-opening on disc-donut baffle.Solids flow behaviors in the stripper with and without pore-opening on disc-donut baffle were compared.It was predicted that the disc-donut baffle with poreopening can reduce the area of“air cushion”.As a result,gas and particle could flow through the pore easily,which was beneficial for their contact.Effects of different types of pore-opening on the solids flow behaviors as well as on the bubble behaviors were further analyzed with the model.Simulation results showed that with the size of pore increasing,the gas flow resistance decreased.Therefore,more particles can be carried through the baffle by the gas,and the area of“air cushion”was reduced,which distributed particles more uniformly in the stripper and was beneficial for improving the contact efficiency of stripping steam and catalyst particles.However,at larger pore size,the average bubble size increased,the bubble number decreased,and the total bubble volume and interfacial area decreased,which may be detrimental for the stripping process.Considering the uniform particle distribution and bubble behaviors,it was concluded that the type of pore with 12mm near the top of the disc baffle and 9mm on the donut baffle was promising in providing improved stripping performance.The present work is meaningful for guiding the design of efficient internals in the stripper.