It is sometimes desirable to have product particles that are larger than those produced by a single stage spray drying process. Agglomeration is the process of enlarging particles by getting them to stick to each other. Agglomerated particles may have improved solubility, higher bulk density, improved flow properties and less dust.
Occasionally, the second stage of a two stage dryer is used to agglomerate product particles. Since the particles leaving the first stage are still sticky, they will bond with other particles during the second stage drying.
Some installations spray wet particles from the first stage with additional feed in the second stage. The fresh feed softens the surface of the particles and allows them to grow. This process is called “instantizing” or “re-wetting agglomeration”.
Most dryer operations include the recycling of fine particles fines captured by the separation equipment into the spray zone. Returning fines promotes an agglomerating effect, leading to the production of a powder that is coarser, freer flowing and “dust free”.