Implementation of a Control Loop for a Continuous Powder Mixing Process

Powder mixing is an essential operation in various industrial fields, such as pharmaceutics, agro-food, cements, etc. While important advances on modeling and simulation of powder flow have been made over the past years, the understanding of powder behavior inside a mixer is still too poor to be implemented in a model that may be used in real-time in the frame of a process control loop. Whatever the mixture considered, the efficiency of a continuous powder mixer strongly depends on various operating variables, such as flow rates and stirrer’s rotational speed. Performing the regulation of these is therefore essential to guarantee the homogeneity of the mixture produced.

This work is part of an overall study on the elaboration of a process control loop to minimize the impact of current perturbations, such as changing the inlet dosage mode, and reach the required homogeneity at the outlet of the vessel. For this, we have used a Gericke GCM500 continuous mixer, for which a method of on-line image analysis had previously been developed to derive the homogeneity of mixtures in real time. Different modes of regulation for the rotational speed of the stirrer have been studied, based on either the mean content or the coefficient of variation. Case studies are defined and presented to evaluate the impact of the regulation modes on the mixer’s efficiency during strong perturbation of the inflow rate and inlet composition.