Experimental investigation of the influence of drying conditions on process stability of continuous spray fluidized bed layering granulation with external product separation

This work presents a systematic experimental study of continuous spray fluidized bed(SFB) layering granulation with external product separation. Inlayering granulation processes the product particle morphology is controlled by the drying conditions during operation. But varying drying conditions during continuous SFB layering granulation have a significant influence on process stability. High fluidizing gas inlet temperature, high fluidizing gas mass flow rate and low spray mass flow rate, resulting in intense drying conditions, led to stable steady state operation. An equilibrium between seed particle production, particle growth and product discharge was established. In contrast, low fluidizing gas inlet temperature, low fluidizing gas mass flow rate and high spray mass flow rates, resulting in moderate drying conditions, led to self-sustained oscillations of the particle size distribution (PSD) in the fluidized bed. The oscillations in PSD where partly transmitted to the PSD of the product, but they were limited by the mesh widths of the sieves, which were used for external separation. For the cases with an oscillatory steady state, equilibrium between seed particle formation, particle growth and product discharge could not be achieved due to temporarily excessive seed particle formation. (C) 2017 Elsevier B.V. All rights reserved.