In certain kinds of spray drying plants, agglomeration is used to produce non-dusty, free-flowing and easily dispersible powders. In these plants, air classifiers may be used to separate product-size particles from fine particles, the latter of which are recycled for agglomeration. The classifiers used should give a sharp cut and it should be possible to control the cut size. Zigzag air classifiers have been shown in measurements to hve these properties. A number of tests on spray drying plants including zigzag air classifiers have demonstrated that non-dusty, large-particle powders can be obtained, and that the mean particle size produced by a plant can be controlled by varying the classifier air velocity.
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