Fluidized Bed Design and Process Calculations for the Continuous Torrefaction of Tomato Peels with Solid Product Separation

This work reports the Authors’ concept idea and the gross design of a plant system capable of continuously separating the torrefied solids from the inert bed material downstream from a fluidized bed reactor, where biomass torrefaction is performed in a continuous operation mode. It is constituted of three units that process solids: i. a bubbling fluidized bed, equipped with a heat exchanging tube bundle, acting as a torrefaction reactor; ii. an inclined plate sieve separator for collection of the torrefied product as oversize solids; iii. a loop-seal for reinjection of undersize particles, i.e., the inert solids, back into the bed. A simple model of the torrefaction reactor as a well-stirred system has been devised to predict the conversion of feedstock (i.e., tomato peel particles) on the basis of an empirical correlation previously established by the Authors under batch conditions; the variability of biomass particle residence time in the bed as induced by the fluidization of inert solids has been accounted for by introducing a distribution function of the biomass residence time, and this latter has been suitably incorporated within the equations yielding the bed inventory of biomass. The recycling system of undersize inert solids back into the bed through a standpipe and a loop-seal for reinjection has been simply designed according to literature. The resulting set of equations is easily handled and smoothly provides the plant design variables and the relevant process calculations.