Quality enhancement for spray granulation with design of experiments

Spray granulation (spray drying) is a process for drying dispersed, emulsified or dissolved substances in a liquid phase. The small components combine to form coarser particles, also known as granulates, which allows the targeted adjustment of properties. The granulate can then be processed using molding processes. 

Better understanding of complex processes with statistical experimental design

Spray granulation is a very complex process, in which many factors influence the result (Fig. 1). Essentially, the raw materials, process parameters, technological conditions and ambient conditions affect the quality of the granulate. Statistical Design of Experience (DoE) can be used to analyze the influence of various parameters on relevant properties of the granulates obtained.

A two-stage full-factorial experimental design for high-purity Al₂O₃ powders and MgAl₂O₄ spinel powders was created at Fraunhofer IKTS, so that up to 31 influencing factors on the granulate properties could be investigated. Figure 2 shows an example of the evaluation of the granulate size of spinel (characterized by the d50 and d95 values of the particle size distribution) in relation to the solids content in the slurry. This diagram shows that a higher solids content leads on average to larger granulates. 

The application of DoE also makes it possible to identify the interactions of the influencing factors with the greatest impact on the targeted properties, to optimize the target values and to control the quality. The knowledge gained forms a foundation for understanding the interrelationships. Material developments on a laboratory scale can thus be efficiently scaled up to an industrial scale.