Measurement of gas hold-up distribution in stirred vessels equipped with pitched blade turbines by means of electrical resistance tomography

Gas dispersion is a widespread operation in the process industry. The effectiveness of the dispersion affects fluid mixing, heat and mass transfer rates and, as a consequence, the chemical or biochemical reactions involved. In this work, the gas-liquid dispersion in stirred tanks equipped with pitched blade turbines (PBT) is investigated by means of Electrical Resistance Tomography (ERT). The main goal of this study is the assessment of gas-distribution in the vessel. Measurements are taken in case of different fluid dynamic regimes, which occurrence depends on the operating conditions. The effect of impeller rotational speed on gas-liquid dispersion is investigated in vessels having different sizes. The adoption of ERT allows the assessment of gas distribution through the vessel volume without any particular limitation about the maximum gas volume fraction, so that experimental conditions close to that adopted in industrial operation can be effectively managed. The transition between flooding and loading regime is investigated, in which the impeller starts to effectively distribute the gas throughout the liquid phase. The vessel size is found to play a role in determining the condition at which loading regime occurs. The data could be either used to set up simplified correlations for the transition between flooding/loading regimes or as a valuable benchmark for CFD simulation, given the detailed information available about the spatial distribution the dispersed gas.