Avaliação teórico-experimental do revestimento de partículas em leito de jorro

Abstract

The spouted bed has been increasingly used in coating of particles like pills and seeds, due to the excellent mobility of particles in the bed, to the biggest coating uniformity and the simultaneous coating and drying of the particles. The coating improves the physical and chemical properties of the particles. The spouted has advantages as no mechanical moving components, simultaneous coating and drying, possibility of working with a wide range of particles few agglomerates. Therefore, it requires care when used with fragile particles and coatings, which increase the elutriation. In this work experimental data obtained for the soybean's coating in a spouted bed with draft tube conducted by Duarte (2002) were subjected to a detailed statistical analysis to study the influence of the initial distribution of seeds and effect of the operating variables on the final coating distribution. Besides it, two dynamic balance population models were analyzed, both applied to functional characteristics areas of the conical cylindrical spouted bed with draft tube, to predict the population density function and to evaluate the effect of operational variables on the coating uniformity: the model of Liu and Litster (1993-b) applied to a single domain and the model of Wnukowski and Setterwall (1989) applied to two perfectly mixed regions where occur drying and coating of the particles. Both population balance models have been solved through the Coating1.0 code developed in Maple® and the obtained results were validated against the Duarte (2002) data. The single domain model is used as the basis for the parametric sensitivity and elasticity analysis of the spout air flow, atomization air flow, suspension flow and concentration of the suspension for each of the sixteen experiments through the DDASPK.F code. The analyses showed a great influence of the flow of spout air jet and the flow of suspension on the coating's uniformity. The growth takes place mainly at intermediate mass seeds according to a normal distribution, which is not affected by the initial distribution of uncoated seeds. The parametric sensitivity was more pronounced in seeds of intermediate mass, presenting its highest values for the spout flow air, while the elasticity was more pronounced for seeds of small and big masses.