Powder Flow Cell: Granulation to Overcome Segregation of an Animal Feed Powder Mix

Segregation of powders leads to various unwanted effects such as concentration variations, inhomogeneities or volatile dust during powder transfer. Industrial mixes are often composed of multiple powders with differences in shape, size and chemical nature. In these mixtures, segregation is often not easy to avoid. Granulation is often used to counteract these differences by producing aggregates which are easier to deal with. In this report, a powder mix is first characterized in the powder cell with air fluidization regarding its segregation sensibility, and then granulated in-situ with a custom-designed injector & stirrer. After drying under dry air circulation, segregation sensibility is once again characterized in the cell to evaluate the impact of granulation and to compare the powder mix with visual observations.


Segregation of powders is the source of some undesired effects such as concentration inhomogeneities, volatile dust, cohesion discrepancies, etc. Segregation can take place when the product is composed of powders with differing chemical composition, density, particle size distribution or particle shape. The presence of humidity can alter or enhance segregation as well.

The segregation of powders can be estimated in the Anton Paar powder flow cell (more information can be found in the application report “A Qualitative Fluidization Segregation Test for Pneumatic Transport”) by computing the rise of torque needed to rotate an impeller in the powder bulk before and after an intense fluidization step. Before fluidization, the recorded torque reflects the ability to move the untreated powder at a given speed. The fluidization step is controlled with the flowmeter of the cell. The air flow is set high enough to provoke elutriation inside the bulk (if the powder is responsive to this mechanism). Consequently, the fine fraction of the powder is mainly deposited at the surface of the bulk and the large particles sink to the bottom (Figure 2).

Then, the torque to rotate the same impeller in the bulk as before is usually higher than the one before the fluidization step. A qualitative analysis is possible by looking at the increase of torque – a larger increase meaning the sample is more prone to segregate. This protocol can then be used each time the segregation sensitivity needs to be estimated.

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