A comparison of compartment models for solids transport in flighted rotary dryers

Flighted rotary dryers are used extensively in a number of industries to control moisture content and temperature of particulate materials. In order to predict and control the operations of these units, it is necessary to understand the complicated solids transport and heat and mass transfer operations that occur. Most previous attempts to model the solids transport fail to characterise the dispersion seen in experimental measurements. Recently, a model has been developed using combinations of perfectly mixed reactors to reproduce the solids residence time distribution for a dryer based all geometric and physical analysis. While this model has shown promise in accurately fitting the experimental data, a geometric study of the local residence time distribution for falling particles within the dryer differs significantly from the CSTR residence time distribution used to represent the airborne mass. This paper presents a discussion of these concerns and proposes an alternative model for a rotary dryer using a combination of perfectly mixed reactors and plug flow reactors to better represent these aspects of a dryer. The two models are compared Gild shown to produce similar steady-state results.