气固逆流式流化床颗粒团聚特性实验研究

Experimental Study on Cluster Characteristics of Gas-solid Countercurrent Fluidized Bed

气固逆流式流化床可结合气固并行上行床和下行床的优点,即较高的固含率和较低的返混,近年来逐渐受到关注。搭建可视化气固逆流式流化床实验台,采用石英砂(d_(p)=113.5 μm)颗粒为物料,对光纤探针在不同操作工况下获得的瞬时信号,采用阈值法研究了团聚物颗粒浓度、团聚物频率、团聚物持续时间和团聚物时间分率在不同轴向高度的径向分布。结果表明:输运管边壁处团聚物颗粒浓度较高且团聚物生成与破碎严重,团聚物尺寸大小在径向分布上较为均匀。随着颗粒在输运管内下降,所有团聚物特征参数均有降低的趋势。此外,表观气速和颗粒质量流量的增大有利于大尺寸团聚物的形成。研究结果可弥补气固逆流领域的不足并为团聚物的模型构建提供相关依据。

Gas-solid countercurrent fluidized bed has the potential to combine the merits of both cocurrent fluidized bed and downer.Recently,the concept of gas-solid counterflow gets more attention due to its high solid holdup and lower solid backing.In this study,a visualized gas-solid countercurrent fluidized bed is constructed.The radial distribution of cluster characteristics(cluster solid volume fraction,frequency,existence time and time fraction)under different axial positions are comprehensive investigated with the threshold method in gas-solid counterflow with quartz particles(dp=113.5 μm)using optical fiber probe.The superficial gas velocities and solid mass flux are in the range of 0.79~1.37 m/s and 55.10~92.84 kg-m^(-2)-s^(-1),respectively.The results indicate that the cluster solid volume fraction is much higher and the regeneration of cluster is much severe in the near-wall region.The radial distribution of cluster existence time presents respectively uniform.All of the cluster characteristic parameters are decreased with the downward movement of particles.Besides,the increase of superficial gas velocity and solid mass flux are beneficial for the formation of large-scale cluster.The results can make up the research deficiency in the gas-solid countercurrent fluidized bed filed.