A Feasibility Study on Pellet Coating Using a High-Speed Quasi-continuous Coater

Pellet coating is traditionally carried out using the Wurster coater. This study investigated the feasibility of pellet coating in a newly developed coater built with a unique airflow system, the Supercell? coater (GEA Pharma Systems, UK). A full factorial design study was carried out to evaluate the influences of the spray rate of the coating dispersion, batch size of the pellet load, pellet size fraction and plenum pressure of the fluidizing air on the color coating of pellets in the Supercell? coater. Results showed that pellets could be successfully coated using the Supercell? coater. Higher plenum pressures and lower spray rates were found to minimize pellet agglomeration during coating. Although coating efficiencies were comparable amongst the different pellet size fractions, larger batch sizes of pellets were coated with higher efficiencies. Process optimization was carried out for each pellet size fraction and a large batch size (120 g) in combination with a high plenum pressure (1,500 mm WC) were deemed optimal. Optimal spray rates differed according to pellet size fraction and a lower spray rate was required for smaller pellets. Pellet flow patterns observed during coating were dependent on the pressure drop across the fluidized load. A ‘swirling’ pellet flow pattern was generally observed at coating conditions which led to optimal outcomes.KEY WORDS: fluid bed, fluidization, pellet coating, pellet flow patterns, pressure drop, process optimization, Supercell? coater