Prospect demonstration of spray granulation in the fast fluidized bed

Using commercially available fine sugar particles as bed material and sugar-water solution containing 60% (mass fraction) sugar as spray liquid, spray granulation was tested in a circulating fluidized bed of 100 mm in diameter at two distinctively different gas velocities to demonstrate the prospects of the operation in the high-velocity fast fluidized bed. The results show that the spray granulation in the fast fluidized bed allows granules to grow gradually and uniformly so that the granulation process is easily controllable and the product is free of extremely big granules. The low particle suspension concentration and short interaction time between spray droplets and bed-material particles prevailing in the bed were considered to be the cause. Benefiting from its high gas velocity, the fast fluidized-bed granulator also enables low inlet temperatures of drying gas (358 K in this work) and suppresses vertical segregation of differently sized particles inside the granulator. Consequently, the spray granulation in the fast fluidized bed was found to be free of any "hot spot" near the gas distributor and the bed temperature along the bed column was almost uniform. On these bases, we urged that the spray granulation in the fast fluidized bed, in comparison with that in low-velocity bubbling fluidized bed, is hopefully an attractive technology for producing size-uniform granules at tens to hundreds micrometers from solutions of heat-sensitive materials.