Flow properties and arching behavior of biomass particulate solids

This paper addresses the problem of estimating solid biofuel flowability, with particular reference to arching phenomena in silo discharge. The flow properties and the tendency to arch formation over openings of three different biomass particulate solids, two cuts of sawdust and a dried ground olive husk, were studied. Shear testing experiments indicated that flow properties of particulate biomass could be measured by shear cells when the particle size is below 2 mm and that, however, particle elasticity or irregular shape could determine uncommon flow behavior. The pipe to arch transition was characterized for the biomass samples and a gypsum powder in a new tester, in which the critical opening size for arching was characterized as a function of the consolidation stress. This test allowed the ranking of material flowability which compared well with the ranking obtained according to the Jenike classification. A new procedure, derived from the Jenike's classical arch stability analysis, was proposed to evaluate the flow function of the materials from the critical orifice diameter for arching. An optimized procedure was suggested to obtain an estimate of material flow function from arching tests with a limited knowledge of other particulate biomass flow properties. (C) 2012 Elsevier B.V. All rights reserved.