Abstract:

Most of the particles in industrial production have a non-spherical shape. However, the study of particle shape effect and liquid phase mechanism is insufficient, which is the main limiting factor for the application of draft tube spout-fluid bed in particle coating. In this study, the spherical and non-spherical cylindrical particles with similar particle size and density were selected as experimental materials. The pressure pulsation signal spectrum analysis and information entropy analysis of the two types of particles under different gas velocities and droplet introduction amounts were compared, and it is divided based on the gas-solid flow convection pattern in the bed. Meanwhile, the effect of particle shape and liquid phase under spouted-fluidized state were clarified by signal analysis method. The results show that non-spherical particles have a smaller minimum spouting velocity, multiple main frequency peaks and higher information entropy than spherical particles. These indicate that non-spherical particles have a high degree of chaos in the system. The solid circulation rate is reduced due to the friction and collision between particles in the draft tube. The minimum spouting velocity and the minimum spout fluidizing velocity are decrease owing to the introduction of liquid in the bed. Meanwhile, the liquid bridging force between particles is increased in the annular region, resulting in an increasing of the minimum fluidization velocity. However, the gas velocity is increased with the evaporating of liquid, resulting in a decrease in the minimum spouting velocity and the minimum spouting fluidization velocity. Due to the introduction of liquid during the spouted-fluidized flow pattern, the dominant frequency of pressure drop Δp_DT is reduced for the spherical particle. However, the dominant frequency of pressure drop Δp_DT is increased for the non-spherical particle. Moreover, owing to the liquid adhering, the spectrum analysis of non-spherical particles show a single dominant frequency peak with a larger amplitude. This indicates an enhanced regularity of pressure fluctuations for non-spherical wet particles.

Key words: spout-fluid bed, draft tube, non-spherical, wet particle, liquid phase effect

摘要：

实际工业生产中颗粒多为非球形颗粒，对颗粒形状效应和液相作用机制的研究不足，是导向管喷动流化床在颗粒涂层改性、包膜等工业应用的关键限制因素。选取粒径、密度相似的球形和圆柱形非球形颗粒为实验物料，对比两种颗粒在不同气速和雾滴引入量下的压力脉动信号频谱分析、信息熵分析，并结合床内气固流动对流型进行划分，绘制非球形湿颗粒流动相图，进而探究喷动流化过程中颗粒形状效应及液相作用机制。相比于球形颗粒，粒径、密度相似的非球形颗粒有较小的最小喷动速度，在喷动过程中有两个及以上较低的主频峰且信息熵较大，显示出非球形颗粒在系统内较高的混乱程度，颗粒之间摩擦、碰撞等降低了导向管内颗粒的固体循环速率。液体的引入增大了环形区颗粒间液桥力，使最小流化速度变大，但液体挥发引起喷动气量增大，使最小喷动速度与最小喷动流化速度减小。在喷动流化流型下引入液体，球形颗粒导向管两端压降Δp_DT的脉动主频降低，而非球形颗粒Δp_DT的主频升高。而且非球形颗粒黏附液体后频谱分析结果显示幅值较大的单一主频峰，表明非球形湿颗粒压力脉动规律性的增强。

关键词: 喷动流化床, 导向管, 非球形, 湿颗粒, 液相效应