Growth mechanism and the dependence of granule size on drop size in fluidized-bed granulation

Closey sized granules have been formed in a fluidized bed by adding a series of precisely sized drops of binder solution. Resulting size data together with that from previous binder distribution and spray drop-size measurements provide a wide ranging correlation between granule size and drop size of the form D_g 8 D_dⁿ. For lactose and ballotini particles under specified conditions, values of n were 0.80 and 0.85, respectively. The correlation applied over a wide size range, granules from 150 to 5000 µm and drops from 35 to 3000 µm diameter. An explanation for the correlation has been sought in terms of partial liquid filling of pores in the initially formed wet granule. This model appears most appropriate for a granule formed by engulfment of particles by a single drop rather than by a succession of agglomeration events involving several drops. © 1991.