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

Set-up and Mass Balances on Soxhlet Extraction Tests in "Learning by Doing" of Process Engineering Students

International audienceA group of bachelor students undertaking a training in a chemical engineering lab class has been involved by the lecturer in the Soxhlet extraction of compounds of interest from agri-food residues. Beyond pursuing experimental practice and investigating solid-liquid extraction, the lab training received added value by the engineering objectives to which the students were oriented: 1) setting up and verifying the closure of the macroscopic mass balances – never reported in the literature according to the authors’ investigation – on the Soxhlet apparatus; 2) quantifying the heat duty of a Soxhlet test as a function of the solvent choice.Roasted hazelnut cuticles and tomato pomace from industrial food transformation processes were used for testing. Two cases were raised to the students’ attention: I. the solvent and the solid to be extracted are perfectly anhydrous; II. water is present in both the tested solids and the extraction solvent. A scheme of the material flows in the Soxhlet experimental procedure was developed together with the trained students. Based on this, the mass balances were written, yielding three simple equations for dry solids, solvent and water. Their solution, after some simplifying assumptions, was quite straightforward and intuitive for the students. All in all, the Soxhlet experimental activity proved to be not only reliable and accurate, but also attractive and mind-opening

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