(506d) 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.