Granule transformation in a twin screw granulator: Effects of conveying, kneading, and distributive mixing elements

This work presents experimental data from granule transformation studies in a Twin Screw Granulator (TSG). Three types of screw elements were considered: conveying elements (CEs), kneading elements (KEs) with 60 degrees forward (F) and 60 degrees reverse (R)configurations, and distributive mixing elements (DMEs) with F and R configurations. The TSG was divided into three sections: an upstream CE section, a mixing section that contained either CEs, KEs (F/R), or DMEs (F/R), and a downstream CE section. The screw pullout method was used to collect granules from the upstream and downstream CE sections. For the powder feed number used in the experiments, the granule properties in the upstream CE section were nearly identical in all of the experiments regardless of the element type used in the mixing section. For the experiments with CEs in the mixing section, the granule properties in the downstream CE section were similar to those in the upstream section, indicating that CEs do not significantly modify the granule properties. The average granule size increased, porosity decreased, and liquid binder concentration uniformity increased downstream of the mixing section in comparison to the upstream granule properties when either KE or DME elements were used. The granules downstream of the 60 degrees R KE section had larger average size, smaller porosity, and higher liquid binder concentration uniformity compared to the granules collected downstream of the 60 degrees F KE section. The granules downstream of the DME section had a uniform liquid binder concentration distribution and showed little difference in size and porosity whether forward or reverse configurations were used. This work extends previously published granule transformation studies by examining a larger range of operating parameters and element types. In addition, a new model for predicting the granule size distribution in conveying elements is presented. (C) 2018 Elsevier B.V. All rights reserved.