Model studies of solid flow and size segregation in packed and moving beds

摘要

This work examines the fundamental behaviour of granular materials in packed/moving beds under simplified blast furnace conditions. Such study has a significant impact on the development of new technology such as pulverized coal injection and the performance of blast furnace operation.Experiments have shown that a number of interesting phenomena appear in blast furnace operation. These phenomena involve rich granular dynamics which currently attract strong interest from a wide scientific and engineering. However, previous work on this area, limited by the research techniques, is predominantly at large scales focusing on phenomenological descriptions, but rarely touching on the basic fundamentals governing these phenomena. A novel discrete element simulation at an individual particle level can overcome these problems. For this purpose, this work conducts a systematic study of these important phenomena, including crater formation, coke collapse, creep motion and particle percolation, by use of the discrete element method (DEM).The experiments and simulations conducted in the impact of a particle stream onto a particle bed using a 20 slot model suggest that the DEM can reproduce the experimental results well under comparative conditions. The crater size is shown to be affected by the discharging rate, discharging height and materials properties, and is related to the ratio of the input energy from the falling stream to the inertial energy from the original packing. Fundamental understanding of coke collapse based on three different configurations: batch charging, self loading and load impact have been investigated. It was found that coke collapse is a kind of continuous avalanche due to top layer particles spreading. Apparent frozen layer under rapidly flowing layer is not stationary and slowly creep motion can be detected at an arbitrary depth. The mean velocity of creep motion decays exponentially with depth. Percolation happens due to both gravity and strain. The percolation velocity under gravity is much greater than that under shear. Size ratio effect is most significant. For size ratio smaller than threshold gravity induced percolation dominate otherwise shear due to the descending of the packed bed.Additionally, this work demonstrates the value of DEM as a tool for complementing experimental observations.