DEM–PBM modeling of impact dominated ribbon milling

Abstract

Ribbon milling is a critical step in dry granulation using roll compaction as it determines the properties of granules, and subsequently the properties of final products. During ribbon milling, fragmentation of ribbons or flakes (i.e., compressed agglomerates from dry powders) are induced by either impact or abrasion. Understanding these fragmentation mechanisms is critical in optimizing ribbon milling processes. In the current study, the discrete element method (DEM) was used to model fragmentation at the microscopic level, providing a detailed insight into the underlying breakage mechanism. In DEM modeling, virtual ribbons were created by introducing an appropriate interfacial energy using the cohesive particle model based on the JKR theory. A set of three‐dimensional parallelepiped ribbons with solid fraction φ=0.7422 and surface energies ranging from γ=0.03normalJ/m2 and γ=2 normalJ/m2 were created and then fractured during impacts with a plane at various impact velocities, to model impact dominated milling. The fragmentation rate, and the number and size of fragments (i.e., granules) resulting from the breakage of a ribbon during the impact were determined. The DEM simulations showed that the granules size distribution had a bimodal pattern and there was a strong correlation between the size of fines generated from fragmentation during impact and the size of the feed powder (i.e., the size of the primary particles in this study), which was consistent with the observation from physical experiments. Two quantities were calculated from the DEM simulations: the number of fragments p and the fraction of fines z for each breakage event which were then used as input parameters for population balance models (PBM) to develop a DEM–PBM modeling framework. Comparision with published experimental data shows that the developed DEM‐PBM model is a promising tool for analysing ribbon milling, but all breakage mechanisms involved need to to considered in order to achieve an accurate prediction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3692–3705, 2017

DEM–PBM modeling of abrasion dominated ribbon breakage

“…An OscilloWitt screen mill (Frewitt, Switzerland) was then employed to break the ribbons and produce granules, for which the size distributions were measured using a QicPic (Sympatec, Germany). The experimental setup was described in detail in Mirtič and Reynolds, and in Loreti et al…”

“…A polydisperse cuboidal agglomerate with 1460 autoadhesive elastic spherical particles was modeled, by using the JKR‐Thornton models for the adhesion. The virtual agglomerate was created with identical initial particles size distribution, material properties (see Table ) and the same technique as presented in Loreti et al The size distribution of the spheres used was spheres with diameter , spheres with diameter , spheres with diameter , spheres with diameter , and spheres with diameter , which mimics the particle size distribution of the feed powder used in the experimental study. Also the values of solid fraction and surface energy used in this study are identical to that used in Loreti et al, i.e., and , respectively.…”

“…The fragments resulting in abrasion were calculated with a breadth‐first search algorithm discovered independently by Moore and Lee and implemented in our in‐house code by Loreti et al By summing each particle mass composing the fragment, the size of each fragment was estimated. From the total mass of the fragment, the diameter of the sphere with equivalent diameter was calculated, i.e., the mass equivalent diameter.…”

“…and , but emphasized the necessity to determine them accurately. To address this challenge, Loreti et al developed a robust predictive DEM–PBM framework for the parameter estimation through the integration of two mechanistic modeling techniques, i.e., DEM and PBM. The DEM–PBM simulations were performed for impact dominant ribbon milling, and compared with the experimental results.…”

“…Our recent study highlighted that it is necessary to considered abrasion dominant ribbon breakage, in order to more accurately predict the ribbon milling behavior using the developed DEM–PBM. Therefore, in the current study, ribbon milling dominated by abrasion is considered using the approach developed by Loreti et al…”