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Summary An agitated fluidised bed dryer was employed to dry lixiviated roselle (Hibiscus sabdariffa L.) calyxes. The effects of operational drying variables on the chemical attributes such as the retention of monomeric anthocyanins (MA), phenolic compounds, polymeric colour, antioxidant activity and drying rate were analysed. Drying curves showed only decreasing falling rate period. To determine the kinetic parameters, the drying data were fitted to a Page's model, based on the moisture content ratio vs. the drying time; the k values ranged from 1.58 × 10−5 to 6.28 × 10−2 s−1. The different drying conditions showed significant differences in the chemical parameters. When processing wet feeds, as lixiviated roselle calyxes, the mechanical assisted fluidisation can be considered as an innovative concept.

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We study the behavior of a multi-stage fluidized bed dryer operated continuously with dowcomers. With the kinetics of silica gel drying depending on the mass of solids in the dryer and the gas feeding temperature, E = 14.5 KJ/mol, and the distribution of residence times of solids through the dryer, modeling by N tanks agitated in series, the experimental moisture content of the solids coming out of the dryer is compared with the predicted by the Vanecek model. Keywords: fluidization; gel of sílice; continuous multistage dryer.