Maximum stable drop size measurements indicate turbulence attenuation by aeration in a 3 m3 aerated stirred tank

• We measured hydromechanical stress in a 3 m3 aerated stirred tank.
• Two different setups of Rushton type impellers were used.
• Results for unaerated conditions were in line with literature data.
• Results for aerated conditions show strong turbulence attenuation by aeration.
• Aeration reduced ϕ = ϵmax/ϵ∅ by 64% and 52%, respectively.

In this study, break-up controlled drop dispersion experiments in a 3 m3 pilot scale reactor with 1.2 m inner diameter are presented that allow a correlation of the maximum local energy dissipation rate in stirred reactors with intense aeration. Experiments with two different setups of 6-bladed Rushton turbine impellers with diameters of d = 0.41 m (d/DR = 0.34) and d = 0.51 m (d/DR = 0.43) in a 3 impeller configuration were conducted. The results from experiments without aeration are well in agreement with the existing literature on drop dispersion. The results from experiments with aeration indicate a strong attenuation of turbulence intensity in stirred tank reactors by the presence of air. The ratio between maximum and volume-averaged energy dissipation rate was reduced by aeration by 64% for the d/DR = 0.34 impeller and by 52% for the d/DR = 0.43 impeller when compared with unaerated operating conditions on the basis of equal volumetric power input. The value of the aeration rate had no measurable effect in the range of aeration rates applied, which was between 0.1 vvm (volume of gas/volume liquid/minute) and 1 vvm.