Drying of pasty and granular materials in mechanically and conventional spouted beds

Abstract

A contactor vessel was built to operate as either a mechanically or a conventional spouted bed for the purpose of analyzing the drying of pasty and granular materials under comparable conditions in both configurations. A classical conical–cylindrical spouted bed with a 60° conical base and an air inlet central orifice was modified to enable the switch by introducing in the vessel’s center an open helicoidal conveyor screw placed above the air inlet orifice. This screw is removable and conveniently returns the bed to its conventional spouted configuration. Experiments on drying solutions (calcium carbonate suspensions and skimmed milk) and granular materials (porous alumina particles) were performed for various bed parameter settings. The spouting pressure drop, outlet air temperature, and relative humidity were measured over time under different conditions. Mechanical agitation is proved effective in drying diluted carbonate calcium liquid suspensions and coarse porous alumina particles at an air velocity approximately 50% lower in comparison to drying in a conventional spouted bed. The conventional spouted bed performed better at drying liquid skimmed milk as the mechanical agitation combined with the axial inlet air flow is not effective in mitigating sticking and powder agglomeration in the bed when handling pastes of complex composition. Introducing mechanical agitation in the designed setup broadens the operating range of a conventional spouted bed with axial air flow in the inlet.