Granulation rate processes in the kneading elements of a twin screw granulator

Abstract

To characterize the granulation rate processes in the kneading section of the twin screw granulator, separate experiments were conducted using exclusively conveying elements as the baseline in addition to different configurations of kneading elements. The configuration parameters examined were the length of the kneading section, the advance angle, and the angle direction. Granule size, shape and liquid distribution were measured. Two main rate processes were observed (1) breakage and layering, and (2) Shear elongation and layering. Breakage was dominant in the 90 configuration while shear elongation dominated in the 30 reverse configurations, with other configurations giving some combination of the two rate processes. The distinct three-dimensional (3-D) shape characteristics of granules obtained from each configuration were crucial in elucidating the dominant granulation rate process in each case. The proposed granulation mechanisms explain the events leading to particular granule attributes, but more importantly provide insight into future optimization of twin screw granulation process.

Distributive mixing elements: Towards improved granule attributes from a twin screw granulation process

“…The kneading elements provide a shearintensive zone that allows granule formation by intimate mixing of liquid and powder. However, the granules obtained are characterized by a broad bimodal size distribution, with the presence of lumps and un-granulated fines (El Hagrasy et al, 2012;Kleinebudde, 2008, 2010;El Hagrasy and Litster, 2013;Dhenge et al, 2010Djuric et al, 2009;Melkebeke et al, 2008). A broad size distribution is undesirable in a wet granulation process due to potential issues with drying uniformity and powder segregation.…”

“…The flexible equipment design introduces additional manipulated variables, including screw configuration, screw speed, and shaft length. Earlier research work has demonstrated that screw configuration has a strong impact on granule attributes Kleinebudde, 2008, 2010;El Hagrasy and Litster, 2013;Thompson and Sun, 2010).…”

“…However, there is little fundamental understanding about granulation mechanisms taking place in this type of screw elements. The purpose of this work is to characterize the distributive mixing elements by investigating the effect of orientation (forward versus reverse) and placement (adjacent versus spaced) of DME on granule attributes using a similar approach to that adopted with conveying and kneading elements (El Hagrasy and Litster, 2013). The results of granule size, shape, porosity, and liquid distribution characterization from the different DME configurations are presented.…”

“…A broad size distribution is undesirable in a wet granulation process due to potential issues with drying uniformity and powder segregation. Hence, a more quantitative understanding of the mechanisms occurring in each screw element type is necessary to improve the efficiency and control of granulation processes and develop a systematic design approach (El Hagrasy and Litster, 2013;Thompson and Sun, 2010;Faure et al, 2001).…”

Representing spray zone with cross flow as a well-mixed compartment in a high shear granulator

“…Recent development of granulation technique can be seen (e.g. [2], [3], [4], [5], [6], [7], [8], [9], [10], [11])…”