Scale-up of mixing processes of highly concentrated suspensions using electrical resistance tomography

Qualification and quantification of mixing processes are crucial requirements for process engineering and energetic optimization in chemical and pharmaceutical industry as well as in wastewater treatment and biogas production. The analysis of mixing processes in stirred systems becomes a challenging task, especially when using opaque substrates. With Electrical Resistance Tomography (ERT), a powerful measuring 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 experimental tests presented in this paper are carried out in reactor systems with volumes of 0.1 m(3) and 1 m(3). The validity of scale-up methodologies was ensured by comparable flow conditions and velocity distributions between the lab and pilot plant scale. For biogas plants, as an example of 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 the Fraunhofer Institute for Ceramic Technologies arid Systems (IKTS). Within the scope of further investigations, reliable information related with Computational Fluid Dynamics (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.