Modeling the Drying of Grass Seeds (Brachiaria brizantha) in Fluidized Beds

Abstract

A modified three-phase model is developed to simulate the drying of Brachiaria brizantha in fluidized beds. In this new model, the constitutive equation of drying kinetics is formulated including both the constant rate and the falling rate mechanisms; the seed shrinkage is taken into account during all drying operation and the transition between bubbling to slugging regime is delineated for estimating the bubble velocity and size. Such modifications improve the mathematical model to better simulate the drying of coarse particles in fluidized beds. The best estimation of the five adjustable model parameters, which are required to define heat and mass transfer mechanisms between interstitial gas and seed particles and to specify the heat loss from dryer walls to ambient air, is attained by incorporating an optimization routine into the computer model program. Having been specially designed to supply data for this model, experiments are performed in a bath laboratory-scale fluidized bed. Additional data are generated to validate the model and program routines. Results show a good agreement between simulated and experimental data, validating the approach used to describe drying kinetics and particle shrinkage.

Keywords:

• Drying mechanism
• Fluidized bed regimes
• Three-phase model

ACKNOWLEDGMENTS

The authors thank CAPES for the Ph.D. scholarship of A.C. Rizzi, Jr., and Dr. J.F.A. Vitor for the free copies of the model compute programs.