填充床中细小颗粒渗流行为的DEM模拟

为进一步探索COREX过程固体物料的运动状态,对COREX过程中涉及到的细小颗粒渗流行为进行了DEM模拟。考察不同颗粒直径比、阻尼系数及滑动摩擦系数对细小颗粒渗流行为的影响,特别是计算得到不同模拟参数下细小颗粒在填充床内的运动轨迹。模拟结果显示,渗流过程中细小颗粒的平均渗流速度为一定值。随着颗粒直径比的增加,颗粒竖直方向的渗流速度逐渐减小,停留时间与径向弥散逐渐变大。随着颗粒间阻尼系数的增加,颗粒渗流速度逐渐增加,停留时间逐渐减小,径向弥散逐渐变小。滑动摩擦系数对细小颗粒的渗流行为影响较小。从细小颗粒运动轨迹分析可知,颗粒直径比变大时,细小颗粒易在空隙中缓慢移动,易趋于静止床层中,导致颗粒沉积。随着颗粒间阻尼系数变小,颗粒运动轨迹向填充床边缘发展,偏离床层中心。

Analyses on percolation behaviour of small particles in a packed bed by DEM

In order to further reveal the solid flow behaviour in COREX, the phenomenon of small particle percolation under gravity, which involves in COREX process, is investigated by means of discrete element method. The effects of material properties on the percolation behaviour are simulated in this paper, including diameter ratios of percolation to packing particles, damping and sliding friction coefficients between percolating and packing particles. The trajectories of percolation particles under different simulation parameters are also examined. The results show that the mean percolation velocity of small particle moving down through the bed is a constant. It is shown that increasing the diameter ratio would decrease the mean percolation velocity and increase the radial dispersion and the mean residence time. With the increase of damping coefficient, the mean percolation velocity increases and the residence time and radial dispersion of the percolation particles decrease. The sliding friction coefficient has limited effects on the percolation behaviour. From the analyses of the trajectory of small particle, it can be seen that small particle would move down slowly and even trend to be static as the diameter ratios of percolation to packing particles increase. With the decrease of damping coefficient, the trajectory of small particle would deviate from the centre and close to the boundary of the bed.