(170c) Industrial Design and Evaluation of a New Impeller for Liquid Blending and Solids Dissolution in Stirred Tank Reactors

A new impeller was designed for the purpose of improving the mixing in stirred tank reactors by means of faster liquid blending and solids dissolution in liquid. Computational Fluid Dynamics (CFD) simulations were used to estimate the shaft power consumption, power and flow numbers as a function of the impeller Reynolds number. Using these parameters, the blend time of miscible fluid mixing was estimated. An experimental validation of this time was performed using Electrical Resistance Tomography (ERT) of the CFD-simulated system. The ERT technique was also used to visualize the flow, i.e. flow structures for a liquid-liquid system, and spatial distribution of gas bubbles in a gas-liquid system. For the case of solids dissolution in a compatible liquid, the dissolution time was estimated by ERT and compared with CFD. The results indicate that the new impeller, when run at high shaft speeds intended for gas dispersion or solids dissolution, is useful for generating flow along the shaft direction in addition to the strong radially outward flow at observed such high shaft speeds. This axial flow helps in drawing down solids, increasing blending, and increasing bubble residence time. The performance of this impeller is compared with the Cowles blade impeller [1] and the Conn ITT blade impeller [1], which are widely used for generating dispersions under turbulent conditions with high shear. Compared to the Conn ITT blade impeller, this stronger axial flow is achieved by means of a higher power consumption, corresponding to a power number of 1.27 in the turbulent regime, while the Conn ITT blade impeller has a power number of 0.83. Measured k_La is similar to that obtained using Conn ITT blade impeller at the same run conditions.