A Dynamic Two-Dimensional Model for Deep-Bed Drying of Mate Leaves (Ilex paraguariensis) in a Single-Pass/Single-Zone Conveyor-Belt Dryer

Abstract

A fundamental model for deep-bed drying of mate leaves in a cross-flow, single-pass/single-zone conveyor-belt dryer is suggested. It involves a set of four partial differential equations obtained by solute mass and energy balances in the solid and fluid phase of the dryer. A set of experimental results of moisture content, absolute humidity, air temperature, and solid temperature available in the literature for deep-bed drying of corn and rough rice in batch dryers was preliminarily used to validate the model. To confirm the reliability of the model for current purposes, drying experiments were carried out at steady-state conditions by feeding 0.05 m, 0.10 m, and 0.15 m deep beds of mate leaves in a bench-scale conveyor-belt dryer at inlet average drying temperatures close to 39°C, 47°C, and 53°C. Air and solid temperature at the top of the beds and average moisture content were well-captured by the model. A good agreement between experimental and calculated open-loop transient responses of average moisture of mate leaves in the discharge of the dryer, in the presence of imposed disturbances in the speed of the conveyor, was also observed. In all cases, the dynamic model was solved numerically by the method of lines without involving any adjustable parameter.