PROCESS INTENSIFICATION OF TOMATO RESIDUES DRYING BY MICROWAVE HEATING: EXPERIMENTS AND SIMULATION

Drying of wet wastes from tomato processing industry was investigated as a critical step prior to their valorization to energy and/or to value-added chemicals. Microwave drying (MWD) was considered because of its advantages over conventional drying. A lab-scale MW oven equipped with automatic temperature control allowed operating at “constant temperature” rather than at “constant magnetron power”, as occurred in past research. MWD tests were performed in batch mode at three temperatures (50, 60 and 70 °C) and the results were compared with those from hot air drying (HAD) experiments. Based on experimental data, an empirical kinetic equation was developed for the microwave drying of tomato wastes as a function of moisture content and temperature. The rate equation was incorporated into a lumped-parameter mathematical model for a steady-state MWD process, which in turn was embedded in an Aspen PlusTM flowsheet used for the gross sizing of a continuous microwave belt dryer. Compared with HAD, MWD allows reducing the drying time up to one order of magnitude (i.e., from 320 to 100 min at 50 °C and from 190 to 60 min at 70 °C), but implies an investment cost one order of magnitude larger (i.e., from about 0.2 to 0.9 M€).