MODELING OF THE 3-DOMAIN FLUIDIZED-BED PARTICULATE COATING PROCESS

Three-compartment representation is applied in the modelling of partic ulate coating in a fluidized-bed granulator. The model based on the ra ndom surface renewal concept was employed to develop population balanc e equations for the coated particles. The model is used in assessing t he effect of stagnant regions, large beds and unequal rate of transfer between domains on the coating distribution. It was found that the ex istence of stagnant regions within the bed will widen the coating dist ribution, while increasing the rate of transfer to the active spraying domain relative to; the rate of transfer to the non-active domain wil l produce coating with a narrow distribution. The model results shows that large beds widen the coating distribution as they are normally as sociated with a large non-active domain. Also, vigorous mixing of the bed was found to be instrumental in narrowing the coaling distribution and minimizing the effects caused by the presence of the non-active d omain. The combination of bed size, rate of spraying and rates of exch ange between domains can be used to obtain particles with a required c oating distribution. (C) 1997 Elsevier Science Ltd.