PARTICLE MASS DITRIBUTION IN BATCH FLUIDIZED BED COATING PROCESS

The paper deals with mathematical modeling the coating process of particulate materials. Inter-particle coating variability is one of the main indicators of the encapsulated product quality. The function of particle distribution according to the mass of coverage was shown can be used to characterize the inter-particle coating variability when the thick shells are applied. The paper presents a mathematical model of the batch fluidized bed coating. The model allows predicting the function of particle distribution according to the mass of coverage. The model bases on the population balance equations, derived for the two compartments: a spraying zone and a drying zone. An algorithm for the numerical solution of the function of particle distribution according to the mass of coverage is described. The influences of the main process parameters on the coating uniformity are shown. As the growth rate of the coating mass decreases, the coating variability of the particles decreases too. This is achieved by reducing the flow rate of the coating solution sprayed by the nozzle. As the flow rate of particles through the spraying zone decreases, the coating variability increases at a fixed processing time. The coating variability value CV was proposed for assessment of the coating substance distribution over the encapsulated particles. The simulation results showed a decrease in the CV value during the process, which indicates a decrease in the ununiformity distribution of the mass of the film-forming substance between the particles at the selected process parameters.