Influence of process conditions on the product properties in a continuous fluidized bed spray granulation process

Abstract

This work focuses on continuously operated spray granulation processes in horizontal fluidized beds highlighting the influence of process conditions on the particle properties of the resulting product granules. The drying process has a decisive influence on the kinetics of the growth rate and thus also on the properties of the particles, such as the morphological structure, particle moisture content and porosity as well as density, compression strength and the wetting behavior. This influence has been considered in this study in more detail on the basis of the model material sodium benzoate. In order to compare the produced granules at different drying conditions and spray rates of the suspension an external product classification was used to achieve a certain product granule size. The obtained experimental results show a deep influence of the thermal conditions onto granule morphology and structural properties, which is in qualitative agreement with recent experimental observations (Rieck et al., 2015; Hoffmann et al., 2015a; Schmidt et al., 2017b). The overall trend of the results reveal smoother product granules with decreasing spray rates of the suspension and increasing drying temperatures. These smoother surface morphologies lead to a more homogeneous layering which has as a consequence that the internal particle porosity is decreasing while the solids density and the compression strength of the particles are increasing at the same time. In this study the purely qualitative classification of the surface texture from previous experimental studies was extended by the topographic analysis of the product granules, giving the possibility to quantify the morphological structure by means of roughness measurements. This makes the morphological design accessible as product property and permits the utilization of models that describe the morphology according to the process conditions.