Mixing Indices Allow Scale-up of Stirred Tank Slurry Reactor Conditions for Equivalent Homogeneity

Publication date: Available online 25 November 2019Source: Chemical Engineering Research and DesignAuthor(s): S.T.L. Harrison, A. Kotsiopoulos, R. Stevenson, J.J. CilliersAbstractThe influence of reactor scale, impeller tip speed and specific power on the overall homogeneity (multi-phasic mixing) of two dimensionally similar stirred tanks of 50 mm and 220 mm internal diameter (ID) are compared using data collected from electrical resistance tomography for 5 and 15% v/v 600 – 800 μm particle suspensions. The data collected is used to quantify the suspension quality of the system by defining mixing indices in the axial MIz and radial MIr directions as well as the overall mixing index MIo. Analyses across the vessels indicated that axial and radial homogeneity improved with increasing impeller tip speed for both large and small vessels with more consistent suspensions observed in the former. Improved homogeneity was consistently found in the 10 to 20% (v/v) solids loading range (data only shown for 15%) than at 5%, across both reactors. In either vessel, optimum homogeneity was achieved at impeller tip speeds ca. 20% lower than the critical suspension speed, as shown previously. Analysis of the local concentration of particles in the lowest region of the vessels indicated that absolute homogeneity was unattainable as the decreasing local concentration displayed an asymptotic character with increasing power per unit volume. The suspension quality during reactor scale-up ...

Source: Chemical Engineering Research and Design - November 26, 2019 Category: Chemistry Source Type: research