Drying Applications for the Reflux Classifier
Drying of fine and cohesive particles has a wide range of industrial applications. This is commonly performed in fluidised bed systems; however, problems arise with high drying rates, as the required gas velocities encourage elutriation of ultra fine particles. To prevent this, gas velocities and drying rates are maintained below certain levels, or extensive recycle systems are required to recover the fines that are lost. This study attempts to resolve the above shortcoming using a novel system referred to as the Reflux Classifier. The Reflux Classifier is a fluidised bed arrangement that has been successful in retaining particles as small as 10 microns (Callen et al., Chem. Eng Sci., 2006). It features an arrangement of parallel inclined channels situated above the freeboard zone, increasing the effective sedimentation area of the vessel, and providing an internal recycle and hence greater solids retention. The current study is concerned with the drying rates of milk powder in the Reflux classifier versus those obtained in a more traditional fluidised bed of the same dimensions. The results show that the geometry of the reflux classifier allows higher superficial gas velocities to be used within the bed, with nominal elutriation. This minimises the load on recycle systems, in some cases negating it altogether.