The mixing process in biogas plants is fundamental for effectiveness. Unfortunately, difficulties at full scale mean that research must usually be performed at lab‐scale and the results up‐scaled. This study presents a scale‐up strategy for the fluid flow in shear‐thinning non‐Newtonian fluids. Dimensional analysis was applied to connect the influencing parameters, i.e., geometric dimensions, rotational speed, and rheological properties, to key figures. By using the Reynolds and Hedström number, standards for adapting the rotational speed and rheological properties were defined as a function of the scale. A sliding‐mesh model was selected for numerical simulations of a plant with a paddle agitator at two different scales. The scale‐up approach leads to similar velocity fields, which result in equal normalized mixing times.
An elutriation particle separator is described which provides an inexpensive, efficient, and accurate method of obtaining from an original mixed sample sizable fractions of particles with diameters within preselected size ranges. Preliminary results for three size ranges between 10 and 100 μ are presented, together with proposed modifications (including a connected series of separators) for more efficient operation.
Die Auslegung und Optimierung von Rührsystemen in Biogasanlagen erfolgt nach wie vor auf Basis empirischer Erfahrungswerte. Mithilfe der particle image velocimetry (PIV) wurde das Strömungsfeld eines Paddelrührwerks unter dem Einfluss der Einbaulage und der Fluidviskosität im Labormaßstab untersucht. Dabei wurden die Viskositätseigenschaften von Fermentersuspensionen mithilfe eines Rohrviskosimeters bestimmt. Über Maßstabsgesetze konnten die Viskositätseigenschaften der Modellsuspensionen für den Versuch angepasst werden. Als Ergebnis zeigt sich, dass eine geänderte Einbaulage Totzonen um bis zu 55 % reduzieren kann.
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