Incipient spray fluidized bed agglomeration at the border to coating

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First aim of the present work is to track the border between spray fluidized bed agglomeration and coating, as adjoining and competitive processes of key importance for advanced particle engineering. We will investigate experimentally agglomeration in the vicinity of this border (borderline agglomeration), focusing on the starting period of it (incipient agglomeration), in which dimers are formed from primary particles. Simplest agglomerate structure and clearest conditions of spray fluidized bed agglomeration support decisively our second project aim, which is improved modeling. Here, we can capitalize on own Monte Carlo models, which are stochastic and discrete, able of representing micro-scale events and processes. The goal is to radically improve these models in two stages. In the first stage (present project) crucial model constituents will be revised, namely the sub-models for breakage and drying, based on separate experiments without spraying (for breakage) or without binder in the spray (for drying). The criterion for aggregation or rebound after wet collision will also be revisited, though still based on normal momentum dissipation. The improved model will provide direct and unconditional access to the agglomeration-coating border, making regime maps obsolete. In a second stage (continuation proposal), a still more radical revision of the aggregation sub-model is planned. Based on the hypothesis that many collisions on a wet spot are unsuccessful due to tangential and rotational motion of the colliding particles, we will evaluate those usually neglected components of motion by means of CFD-DEM on primary particles, and correlate them with a rebound probability in the model by use of measured results from the first project period. Final goal is to operate the agglomeration model with direct input from CFD-DEM, i.e. without the presently necessary adaption of collision frequency. Model applicability to stronger agglomeration far-off the border will also be tested in the second project period.