The Reclaim Screw in Mammoth Silos Operating on a Free Surface: Comparison Between Horizontal and Inclined Operation on Free Flowing Bulk Solids

Although the screw conveyor, operating on a free surface, has been used for years as reclaim and storage equipment in mammoth silos, there is no documented knowledge about its spill characteristics. Research at Delft University of Technology together with ESI Eurosilo B.V. on the inclined use of the reclaim screw to achieve homogenization in mammoth silos made this lack of knowledge apparent. This paper presents the results of experiments to gain insight into the spill during reclaiming. Experiments were conducted reclaiming a horizontal surface and up- and downwards along an inclined surface, using a free-flowing bulk material. A relationship was found between the theoretical and effective fill ratio. This relationship shows a certain maximum effective fill ratio and a dependence on the reclaim-depth. As expected, the effective fill ratio drops quickly when reclaiming upwards, mostly due to flow- and throwback: the fill is spilled behind the screw blades and over the axis. Unexpectedly, the effective fill ratio also decreases when reclaiming downwards due to a shift of material towards the non-reclaiming side where it is left behind forming ridges on the surface. It is expected that all three mechanisms will cause less spill when reclaiming a cohesive material. The experiments provide the desired insight into spill mechanisms during reclaiming. Indeed, the inclined use of the reclaim screw to achieve homogenization is thought feasible when reclaiming downwards.