Modeling and cost analysis of drying of citrus residues as biomass in rotary dryer for bioenergy

The valorization of residues in any industrial processing activities aims at the reuse, recycling or composting of solid wastes, in such a way as to generate useful products or sources of energy. Citrus residues have been recognized as a promising biomass for renewable energy and liquid fuels. Drying is an interesting alternative to add value to solid waste, as long as it is economically viable, and one of the most important operations for efficient performance of the energy conversion technologies. In this work, a dynamic model of drying citrus residues in a rotating drum was developed and verified experimentally. From overall heat and mass balances, a series of perfectly stirred tanks was added together for each solid recycle and residence time in order to fully describe citrus solid wastes drying in the semi-industrial rotary drum. Process cost analysis was also performed to assess the most suitable drying level to balance process costs with the biomass quality in terms of the moisture content. Results showed that the model performed reasonably well so that simulation and measurements were in good agreement to be part of process optimization strategies.