Numerical Simulation of Wet Particles Motion in a Vertical Powder Dryer

Abstract

In this study, the motion of wet particles in the drying unit of a vertical powder dryer is investigated by using a Discrete element method (DEM) coupled with a liquid bridge force. In particular, by varying parameters such as the particle mass flow rates, the superficial gas velocities, and superficial gas temperatures, the influence of the moisture content on the flow behavior is examined. The results show that when the moisture content increases, the mean particle velocity decreases while the bed mean solid "holdup" and the mean residence time (MRT) of particles grow. It is also found that the local solid holdup is relatively higher in the near-wall region and decreases towards the near-fluid region. Two regression models are introduced accordingly for the mean particle velocity and the bed mean solid holdup by means of the RSM-BBD (Response surface methodology-Box-Behnken design) method to obtain the optimal combination of parameters for flooding prevention. Finally, the optimal results are compared with numerical observations. As the relative error is less than 10%, this demonstrates that the proposed methodology can accurately describe the particle flow dynamics in the drying unit.