Nozzle zone agglomeration in spray dryers: Influence of total solid content on agglomerate properties

During agglomeration in the nozzle zone of spray dryers, dry particles are forced to collide with drying droplets. These collisions ideally form agglomerates with improved flowability and reconstitution properties. However, the interactions of feed parameters on the collision outcomes are unclear. This study examines the influence of a varied total solid content of the feed solution on agglomerate formation in a pilot plant spray dryer. An increase in total solid content (TS) from 30 to 50% TS (w/w) resulted in an increase in porosity of the primary particles, whereby particle size development was reasoned by this effect. Agglomerate porosity increased but agglomerate size increased more due to a changed particle viscosity. By adding a marker powder, it was found that higher total solid contents resulted in less coalescence of the agglomerates. The counter-current air classification in the drying chamber affected the agglomerate properties such as size, density and shape.