Undesired agglomeration in agitated filter dryers: A critical review

Agitated filter dryers (AFDs) are commonly used in many industries, however the mechanisms driving undesired agglomeration remain poorly understood. Undesired agglomeration can have several consequences, including out of specification product, equipment damage, additional downstream processing and increased cycle times and cost. This review explores the influence of key material and process parameters on agglomeration in AFDs, highlighting the lack of mechanistic understanding that has hindered the development of accurate predictive models.

To address this, insights from wet granulation are applied to propose a novel mechanism consisting of three rate processes governing agglomeration during agitated drying: (1) formation of loosely bound agglomerates, (2) consolidation and coalescence, and (3) solidification of liquid bridges. The review examines how various parameters influence each rate process in this mechanism, offering a more predictive framework for agglomeration behaviour.

Additionally, existing modelling efforts for AFDs are reviewed, revealing that many studies focus on heat transfer while neglecting agglomeration. Comparisons with wet granulation models highlight opportunities to integrate established agglomeration and scale-up approaches into AFD models. By advancing the mechanistic understanding, this work aims to improve prediction, control, and scalability of agglomeration in agitated drying.