(493b) Power Dissipation in Pharmaceutical Reactors and Vessels Equipped with a Retreat-Blade Impeller

Glass-lined stirred reactors and tanks are commonly used in the pharmaceutical industry because of their corrosion resistance, ease of cleanliness and minimization of product contamination. Most industrial glass-lined tank reactors are provided with a torispherical tank bottom and a retreat curve impeller with low impeller clearance from the vessel bottom. The power, P, dissipated by the impeller is a critical process parameter to mixing processes to achieve the desired mixing effect, especially since the power per unit volume, P/V, controls directly mass transfer processes and other mixing phenomena. However, little information has been published about the power dissipation and the corresponding power number Po. The objective of this study was to determine experimentally the impeller power dissipation in the vessel and obtain power correlations for a retreat-blade impeller under various types of baffling conditions. In this study the power P was measured in fluids of different viscosities and densities at different agitation speeds, and the non-dimensional Power Number, Po, was obtained in a scaled-down version of a typical glass-lined tank reactor for a large range of the Reynolds Number (1<Re<1,000,000) for pharmaceutical active ingredient (API) synthesis. Po depends significantly depends on baffling type and Reynolds number, Re. Correlating equations were obtained to predict Po as a function of Re and baffling type. These equations can be used by the industry practitioner to optimize pharmaceutical mixing processes, especially during API synthesis in reactors.