气固顺/逆流间歇移动床内颗粒速度分布特性

Characteristics of solid velocity distribution in gas-solid concurrent/counter-current intermittent moving bed

采用颗粒示踪方法考察了顺流和逆流间歇移动床内颗粒流动状态和速度分布随表观气速和时间的变化规律,进行定量化分析并建立颗粒速度计算式。结果表明,示踪层颗粒始终近似为V形分布,表明颗粒速度呈“慢-快-慢”的形式分布,且变化幅度随时间的推移更加明显。不同于重力条件,顺流和逆流条件下气体和颗粒间相互影响更为复杂。同一时刻下,顺流床内颗粒速度变化幅度随表观气速增加而增大;逆流床与之相反。然而在同一料位高度下,随表观气速增大,顺流床内流动区域宽度增大,时间不均匀指数和流动死区占比减小,表明颗粒速度分布更加均匀;逆流床与之相反。借助料仓中常用的颗粒运动模型(Particle Kinematic Model,PKM),引入雷诺数Re和斯特哈尔数St,建立气固顺流和逆流条件下的颗粒速度计算式,以期为顺/逆流间歇移动床的操作和设计提供参考。

The particle tracer method is applied to investigate both the solid flow state and the solid velocity distribution under different superficial gas velocities and times in the gas-solid concurrent/counter-current intermittent moving bed.The quantitative analysis is made and the calculation formula of the solid velocity is also established.The results show that,an approximate V-shaped distribution is presented in the particle tracer layers,which indicates that the horizontal distribution of the solid velocity is in the form of the "slow-fast-slow".Moreover,the variation of the solid velocity distribution is more obvious with the passage of time.Different from the gravity condition,the interaction between the gas and the solid phases is more complex under both the concurrent and the counter-current conditions.At the same time,with increasing superficial gas velocity,the variation range of the solid velocity distribution increases in the concurrent moving bed;while it decreases in the counter-current moving bed.Besides,at the same height of the particle layers,with increasing superficial gas velocity,the width of the flow area increases in the concurrent moving bed,and both the inhomogeneity index of the flow time and the percentage of solid flow dead zone decrease,which indicates a more uniform solid velocity distribution appears under concurrent condition.However,it is opposite in the counter-current moving bed.Based on the widely used solid velocity model of particle kinematic model(PKM) in the silo,with the introduction of both the Reynolds number Re and the Stehar number St,the calculation formula of the solid velocity is established under both the concurrent and the counter-current conditions in this work.It is anticipated to provide a reference for the operation and design of the gas-solid concurrent/counter-current moving bed.