Mechanism of particle coating granulation with RESS process in a fluidized bed

In this study, the rapid expansion of supercritical fluid solution (RESS) process was employed for the coating granulation of fine particles in a fluidized bed and its mechanism was examined. The rapid expansion of the supercritical solution causes very high supersaturating ratio of solute in the spraying flow, forming a large number of superfine nuclei. The superfine nuclei deposited on the surface of the particles form a thin film. It was found that the fine particles were all covered with the thin film. This coating mechanism has been confirmed by SEM inspection. The granules with fine particles adhered were circulated through the spraying region and were covered with the binder or coating material (solute) in the region in the form of a film, resulting in the fine particles being cumulatively coated on core particles layer by layer. The temperature at the nozzle inlet was found to be an important factor affecting the coating granulation process.