Development of a control system to anticipate agglomeration in fluidised bed coating

Fluidised bed coating is a technology commonly used to modify the properties of pharmaceuticals or powdered food. However, too high moisture content during the process, due generally to insufficient drying or the use of a temperature above glass transition of the polymer solution, usually induces particle agglomeration. Various processing elements can be involved however, and this paper provides an analysis of these variables in order to determine which parameters should be controlled and which can be manipulated. It was found that the pressure must be controlled and that the flow of the coating solution can be manipulated to do this. Since a bang-bang controller can manipulate the flow of the coating solution, it was adopted here, with agglomeration avoided by maintaining the pressure in an adequate range. The system was used successfully to coat microcellulose beads with gum Arabic; moreover, it was possible to increase the quality of production.

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► The pressure is more sensitive to the appearance of agglomeration.
► The pressure at DP1 was selected as the controller variable.
► The flow of the coating solution is the only parameter that affects positively both.
► It was thus chosen as the variable for manipulation.