(163e) Influence of Surface Stickiness of Food Products to Agglomeration in Spray Drying

The agglomeration of droplets and particles during spray drying is desired to obtain better product properties, like dust reduction and better dissolution. Agglomeration can occur between two primary droplets or between droplets and returned fines. In the latter case the distance of the fines return from the atomization device (either pressure nozzle or rotary) is important. When fines are returned close to the nozzle coalescence will occur with the surface tension dominated droplets, resulting in layering on primary particles or lumps with a large size. Further from the nozzle the droplets have dried to form particles which are likely to rebound (either sliding or non-sliding) with the returned fines, due to low Van der Waals forces between the particles. In the transition region viscous forces dominate the droplets. These droplets are able to produce agglomerates.

The surface stickiness of droplets of a food product is measured as a function of drying time (and thus distance from the atomizer, as the velocity at which the particle falls in the spray dryer is known). A probe tack test has been used to investigate the in situ surface stickiness of hemispherical drops of food product. The effect of different amounts of added salt on drop stickiness was studied. With this method we can correlate the stickiness of droplets to drying time (and subsequently distance from atomizer). This enables us to return the fines at the point where agglomeration is most likely to occur.

This research is a part of a larger project aimed at validating and improving the existing model of collisions between a viscous droplet and another viscous droplet or a dry particle in spray drying.