回转窑多粒径颗粒流动与偏析的DEM模拟与实验研究

为明晰回转窑内颗粒的运动行为及偏析机理,以绿豆、黄豆和黑豆为颗粒介质,依次对3种装填顺序下的颗粒流动过程进行离散元模拟与实验研究,以颗粒质量分数和平均粒度为判据,对颗粒偏析进行评价。结果表明,回转窑内颗粒流动区可分为自由滚落区、渗流呆滞区以及窑壁携带区,自由滚落区颗粒流速最大,而渗流呆滞区流速最小。窑内颗粒沿轴向输运过程发生径向偏析,形成夹层结构,小颗粒受渗流作用在渗流呆滞区中心形成内核,大粒径和中等粒径颗粒集中在自由滚落区和窑壁携带区。窑内颗粒力链分布不均匀,强力链分布于近窑壁区,弱力链分布于自由滚落区和渗流呆滞区,且渗流呆滞区力链细而密集。当窑头附近不同粒径颗粒存在轴向速度差时,颗粒在轴向发生掺混,并产生径向偏析。

DEM simulation and experimental study on flow and segregation of multi-sized particles in a rotary kiln

In order to clarify the movement behavior and segregation mechanism of particles in a rotary kiln,the DEM simulations and experiments of the particle flow process under three filling sequences were carried out.It is shown that the particle flow zone in a rotary kiln can be divided into free tumbling zone,percolation stagnant zone and kiln wall carrying zone.The particle velocity in the free tumbling zone is the largest,while that in the percolation stagnant zone is the smallest.In the process of axial transport,the particles in the kiln undergo radial segregation to form a sandwich structure.The small particles form a core in the center of the percolation stagnant zone under the percolation effect.The large and medium-sized particles are concentrated in the free tumbling zone and the kiln wall carrying zone.The distribution of particle force chains in the kiln is uneven.The strong force chains are distributed near the kiln wall,and the weak ones are embedded throughout the free tumbling zone and percolation stagnant zone,and those in the percolation stagnant zone are thin and dense.When there is an axial velocity difference between particles with different sizes near the kiln head,the particles mix in the axial direction and undergo radial segregation.