Brazil is amongst the top manufacturers and exporters of citric juice and, as a consequence, is one of the major by-products producers from citrus processing plants. Only about 49% of the entire fruit is utilized, the rest being disposed. The wastes from citrus industry contain high organic and moisture contents, which turns them into toxic and hazardous environment pollutants. This means that a pretreatment stage is required before disposal. Drying is an attractive alternative to reduce moisture content and the costs of transportation and increase storage time. It consists essentially of momentum, energy and mass transfer between a solid particulate system and a drying fluid, normally heated air. In the case of organic matter drying, kinetics is essentially diffusion controlled. In this context, the main objective of the present work was to analyze mass transfer during the drying of organic matter from citrus processing plants under different operating conditions. The experiments were done in a fixed bed for thin layer drying with heated air in the range of 110 to 170°C, and air flow velocity in the range of 1 to 4 m/s. Mass transfer was analyzed based on Fick’s second law of diffusion, supposing constant the effective diffusivity. The effective diffusivity was determined by nonlinear regression, which consisted of minimizing the sum of squares of the residuals. All calculations were performed in MatLab. An Arrhenius-like expression was employed to evaluate the effect of the gas temperature on model parameter sensitivity.
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