F.J. Muzzio, M. G. Ierapetritou, Y. Gao
Chemical Engineering Science
While continuous powder mixing has been an area of active research in recent years, effects of operating conditions on the mixing performance has not been well understood yet. Based on our previously developed periodic section modeling (Gao et al., 2012), this paper examines the effects of operating conditions on two significant parameters of the continuous blending processes: axial velocity and local mixing rate of the mixture. Four mixing cases differing in particle size, density and cohesiveness are simulated. Results show that when the local mixing rate improves at low fill levels and high blade speed, particles also move faster in the axial direction and reside for a shorter time inside the mixer. This trade-off between ascending local mixing rate and descending residence time indicates a non-optimal overall blending performance even when the best operating condition is applied. Based on these results, strategies that can further improve the blending performance are performed, which are proposed by increasing the blade speed while keeping a constant axial velocity. These strategies guarantee that the variance decay rate along the mixing axis is proportional to the blade speed in continuous blending processes. Dramatic improvements are observed when these strategies are applied, which shows the merit of this work on design and optimization of continuous power blending processes.
Continuous Powder Mixing, Discrete element method, optimization, Periodic section modeling, RSD, RTD