Droplet Agglomeration

In the droplet agglomeration process the powder particles are wetted with droplets of liquid atomized by means of a nozzle or a rotary atomizer while suspended in air, as described in Figure 1. The powder may either be introduced around the rotary atomizer or the nozzle by means of gravity or pressure air conveying, or from below by means of pressure conveying.

Figure 1 Feed System for a rewet plant (wetting by means of warm water atomized by an atomizer)

The actual agglomeration takes places by collision of the single particles wetted and sticky on the surface, and when they reach the agglomeration chamber wall they will roll down whereby the compactness of the agglomerates is obtained.

Droplet agglomeration can also be performed by spraying the wetting agent through a number of nozzles positioned right above the fluidized powder layer in a Vibro-Fluidizer®. To obtain stable agglomerates the powder should contain sufficient binding material, like carbohydrates.

Some powders (containing a high content of fat and sugar) become so sticky when wetted, that heavy deposits in the conical part of the agglomeration chamber develop. A mechanically revolving scraper or similar is therefore necessary in order to get the powder out of the chamber. Another and technically better solution is to let the conical part of the agglomeration chamber rotate slowly and have a stationary scraping device such as a knife scraping off the powder. The droplet agglomeration process is especially used for powders containing fat such as whole milk powder and powders with a high content of sugar such as cocoa-milk-sugar mixtures, whereas the rotating cone is mainly used when the powder contains cereals and starch, such as baby foods.