Examining particle size growth in twin screw granulation up to steady state with acoustic emissions

The transient evolution of granules was studied to learn new details about the underlying mechanism for continuous wet granulation in a twin-screw extruder. Sieving and a new inline PAT for particle size development was used to gain these insights. The onset for steady state was established based on observing a consistent PSD, which occurred at five times the mean residence time of the process, over a range of degrees of fill (DF; 12–30 %). The early stages of startup for granulation were captured by the inline PAT, showing different stages of granule growth for particle sizes ranging from 102 to 2230 μm. The analysis found that conveying elements have a stronger influence on granule growth at a low DF whereas the kneading zone had a stronger influence on granule growth at a higher DF. This study presents new details on this black-box process while highlighting the unique value of PAT to twin-screw granulation. • Granulation at a higher degree of fill (DF) becoming increasingly dependent on the kneading zone. • Steady state will be reached by 5 times the mean residence time independent of DF. • Inline PAT can output a representative particle size distribution with only 5 s sampling.