Qualification and quantification of mixing processes of highly concentrated suspensions using electrical resistance tomography

In chemical and pharmaceutical industry as well as in wastewater treatment and biogas production, the qualification and quantification of mixing processes is a crucial requirement for process engineering and energetic optimization. The analysis of mixing processes in stirred systems becomes a challenging task, especially when using opaque substrates. With electrical resistance tomography (ERT), a powerful technique is provided to allow a comprehensive and non-intrusive quantification of mixing processes of complex suspensions. Combined with advanced cross-correlation techniques, ERT offers the possibility to derive the axial flow velocity profile inside a stirred system. Investigations in different scales are an essential prerequisite regarding the evaluation and optimization of large-scale mixing processes under consideration of similarity laws. The validity of scale-up methods was ensured by comparable flow conditions and velocity distributions between the lab and pilot plant scale. For biogas plants, as an example for the importance of efficient mixing, the scale-up principles 'geometric similarity', 'constant impeller tip speed', 'similar viscosity and flow characteristics' as well as 'scale-up of particles and fibers of the dispersed phase' are proved to be valid by Fraunhofer IKTS. Within the scope of further investigations, reliable information related with CFD are ought to be derived for the continuing evaluation of mixing processes at any scale to establish a foundation for the dimensioning and operation of stirring systems, especially for highly concentrated, non-Newtonian fluids.