Mathematical modelling of castor oil seeds (Ricinus communis) drying kinetics in fluidized bed at high temperatures

Ricinus communis or castor oil seed is an agricultural product which possesses a large amount of proteins and lipids that could be useful in food and energy industries. Drying process can be helpful to conserve the castor oil seed during long storage periods, for this reason in this research, the drying kinetics of castor oil seeds during fluidized bed drying at a constant air velocity of 7 m/s and high air temperatures (80, 90, 100, 110 degrees C) were studied. Six empirical mathematical models were selected to describe and compare the drying characteristic of R. communis seeds at previous described conditions. Drying rate constants, coefficients and statistical parameters were determined by non-linear regression analysis. Among the tested models used to describe the drying kinetics of castor oil seeds, the diffusion approach model was selected as the best one. The moisture loss from the seeds was described by the Fick's diffusion equation, and based on the obtained results the effective moisture diffusivity was estimated, getting a value in the range from 8.21 x 10(-19) to 2.61 x 10(-9) m(2)/s. The relationship between the temperature and the effective moisture diffusivity was described adequately by means of Arrhenius-type equation. An activation energy value of 41.41 kJ/mol was obtained. The findings allow the successful simulation of R. communis seeds fluidized bed drying between 80 and 110 degrees C. This study provides information to dry castor oil seed by fluidized bed at high temperatures that could be useful for biofuel production. (C) 2012 Elsevier B.V. All rights reserved.