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



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. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4100–4115, 2013