Experimental investigation on an aerated mixing vessel through electrical resistance tomography (ERT) and response surface methodology (RSM)

Aerated mixing vessel is highly applied in such industrial processes as oxidation, hydrogenation, and biological fermentation where gas and liquid are contacted and mixed to reach steady condition. However, the design of an aerated mixing vessel is challenging specially in case of non-Newtonian fluids. To enhance the efficiency of the process, it is essential to assess the effect of the gas sparged to the vessel on the mixing performance. In the present work, an electrical resistance tomography (ERT) system was utilized to assess the mixing of the activated sludge as shear thinning non-Newtonian fluid in presence of aeration. ERT results revealed that shorter mixing time can be achieved in presence of aeration. The following three central impellers were employed: ASI (a combination of A200 and the Scaba impellers), ARI (a combination of A200 and the Rushton impellers), and Rushton (fully radial impeller). An ERT system with a two-plane assembly equipped with 16 sensors on each plane was employed to assess the impact of the impeller type, impeller speed, and gas flow rate on the mixing of activated sludge in terms of mixing time, specific power consumption, and gas flow number. A statistical-based experimental design with RSM (response surface methodology) was applied to evaluate the individual and interactive effects of the design parameters and operating conditions. Experiments and RSM demonstrated that among all independent variables in this study, impeller speed was the common independent variable which impacts mixing time, specific power consumption, and gas flow number significantly.