Fluidized Bed Torrefaction of Industrial Tomato Peels: Set-Up of a New Batch Lab-Scale Test Rig and Preliminary Experimental Results

This paper reports on preliminary results of an experimental investigation aimed at examining the potential of energy valorization of difficult biogenic agro-industrial residues (i.e., tomato peels) by means of fluidized bed torrefaction pretreatment. To this end a new atmospheric bench scale experimental apparatus, described in the paper, has been purposely designed and set up. The centerpiece of the system is represented by the torrefaction unit consisting of a batch double-walled tubular glass 100 mm ID reactor in which the double wall is kept under vacuum to ensure a thermal isolation without losing the advantage of its transparency. Therefore, the fluidization pattern and movement of particles in the bed can be monitored visually anytime at any temperature during experiments. Preliminary, but rather encouraging, results on the effect of the fluidized bed torrefaction severity (i.e., temperature) on some physicochemical properties (i.e., LHV, bulk and energy density, proximate and ultimate composition) of the torrefied tomato peels are presented in this paper. Additional findings from an experimental investigation on fluidization characteristics of different TP and sand mixtures are also included. They allowed determining the best bed operating conditions in terms of biomass particles size and maximum batch loading, i.e. the critical biomass-to-inert particles mass ratio in the bed, beyond which the fluidization properties deteriorate. The outcomes of this study show that a bubbling sand bed reactor could be successfully used for the torrefaction of agro-industrial residues by carefully setting the superficial gas velocity as the onset of complete fluidization occurs at a higher value compared to that of the initial fluidization velocity.