Pseudophysical Compartment Modeling of an Industrial Rotary Dryer with Flighted and Unflighted Sections: Solids Transport

A novel pseudophysical compartment model describing the solids transport within a case-study cocurrent industrial rotary dryer is presented. The model is novel and distinctive because it combines both multiscale partial differential equation and ordinary differential equation modeling techniques to represent the five separate sections occurring within the dryer, including both flighted and unflighted sections. The solid phase in the unflighted sections was modeled as an axial dispersed plug flow system. The solid transport in the flighted sections was partitioned into the usual series–parallel formulation of well-mixed tanks representing airborne and flight-borne solids. Parameter values and compartment numbers were estimated using mechanistic geometric modeling, dryer design loading constraints, and solids flow properties. Geometric modeling enabled the effects of internal scaling arising from solid materials sticking to the internal walls of the dryer to be accounted for in a realistic manner. Industrial residence time distribution data were collected for a range of operational scenarios and were used to estimate the remaining model parameters (axial dispersion coefficient and kilning velocity). The model results were well-matched to the collected set of industrial residence time distributions (RTDs), and estimated parameter values were within expected limits. The axial dispersion coefficient and kilning velocity were modeled as functions of operating variables in order to fully embed physical realism into the compartment model, and new correlations are presented. The effect of operating conditions on RTDs and solids distribution within the dryer was investigated. The results matched past observations and provide insights into dryer efficiency