(466e) Power Dissipation and Power Numbers for a Retreat-Blade Impeller in Pharmaceutical Mixing Tanks and Reactors Using an Experimentally Validated Computational Approach

Mixing in stirred vessels is a very common operation in many pharmaceutical processes. Glass-lined tanks and reactors are especially commonly used in the in pharmaceutical industry for the synthesis of Active Pharmaceutical Ingredients (APIs) because of their corrosion resistance, cleanability, and reduced contamination levels. In such cases, a retreat-blade impeller with a low impeller clearance off the tank bottom is commonly used in and the reactors are cylindrical and provided with a torispherical vessel bottom and equipped with a single baffle and a retreat-blade impeller (RBI). The power, P, dissipated by the impeller is critical to any mixing process since mechanical energy dissipation is needed to homogenize the vessel content, disperse immiscible phases, suspend solids, increase mass transfer, and, in general, produce the desired mixing level. P depends not only on the type of impeller used, agitation speed, and physical properties of fluid but also on the geometry of the system, including the location of the impeller in the mixing vessel. Despite their common use, little information is available on the hydrodynamics of RBI’s is such systems and their mixing performance, including their power dissipation. In this work the power, P, dissipated by a RBI, and the non-dimensional Power Number, Po, in different fluids were obtained both computationally via Computational Fluid Dynamics (CFD) and experimentally, using a strain-gage based torque measuring device, for different Reynold’s Number values in a 61-Liter, scaled-down version of a typical glass-lined reactor for the synthesis of pharmaceutical APIs. Additionally, P and Po were obtained for a fully baffled system (four rectangular baffles) and for an unbaffled system. P and Po were obtained for a very large range of the Reynolds Number, Re (1<Re<1,000,000). Po was found to vary significantly with baffling type and Re. Excellent agreement was obtained between the CFD-predicted and the experimentally obtained values for Po. Correlation equations relating Po with Re using baffling type as the parameter were additionally obtained. These equations can be used by industrial practitioners to obtain Po and hence P for their system and thus help quantify and optimize pharmaceutical mixing processes typically involving the synthesis of APIs in this type of reactors.