Optimizing Continuous Powder Mixing Processes Using Periodic Section Modeling

Optimizing continuous powder mixing processes using periodic section modeling

Yijie Gao, Fernando Muzzio and Marianthi G. Ierapetritou

Dept. of Chemical and Biochemical Engineering, Rutgers University, Piscataway, NJ 08854

Continuous powder mixing is considered as an advantageous choice to batch mixing for better controllability and easier scale-up of production rate. Many works have been performed on the performance improvement of the continuous mixing process. In this study, the effects of operating conditions are investigated. Using the periodic section modeling developed in our previous study ¹, we investigated the effects on cross-sectional mixing, and on axial mixing and motion. The variance decay rate of the batch-like mixing in the cross-sectional directions (k_b), as well as the mean particle velocity in the axial direction (v_x), is used as key indices of performance in the continuous mixing process.

We consider mixing at different fill levels and blade speeds in order to characterize their effects on powder mixing. Mixing cases with materials of different particle size, particle density and cohesiveness are also compared. Results show similar contours for both k_b and v_x among the studied cases, indicating that the optimal operation obtained in continuous mixing of one mixing case can be directly used as the optimal condition at another case. Based on the characteristics of contours, it is also noticeable that both variance decay rate k_b and axial velocity v_x increase with the blade speed. This leads to a trade-off on the improvement of the overall cross-sectional mixing efficiency. To resolve this issue, two operating parameters are changed simultaneously, i.e. increase of blade speed and decrease of blade angle, or increase of both blade speed and weir height. While variance decay rate k_b increases proportionally with blade speed, an approximately constant axial velocity v_x is obtained using this strategy. Results show dramatic improvement of the overall cross-sectional mixing efficiency, and provide a promising direction towards optimizing continuous powder mixing design and operating conditions.

Reference

1.         Gao Y, Ierapetritou MG, Muzzio FJ. Periodic section modeling of convective continuous powder mixing processes. AIChE Journal. 2011; In Press: DOI: 10.1002/aic.12348.