Abstract
Particle elasticity and particle fibrous shapes are the main characteristics of biomass and both may be a possible cause of deviation of the biomass behavior from the Coulomb model. In this work we intend to evaluate the possibility to successfully apply the Jenike procedure to the design of storage units containing biomass solids. On this purpose two sawdust samples, a dry one and a humid one, were taken into account. Internal flow properties were characterized by a Schulze ring shear tester while wall friction properties was characterized by a Brookfield Powder Flow Tester. The critical outlet size to allow arch freeflow of powder was directly evaluated on a purposely built 0.3 m3 plane silo. In this silo the wedge shaped hopper allowed to continuously and independently change the hopper angle and the hopper outlet size. Finally, the relationship between the measured flow functions and the arching conditions was assessed by comparing the experimental critical outlet size values with those calculated according to the Jenike design procedure. The results obtained from this comparison indicate that the Jenike procedure is adequate for design purposes with the tested materials. However, it has to be noted that in some cases the difference between the experimental values and the design values of the critical outlet size for an arch free silo is so small to suggest the use of safety coefficients in the application of the design procedure. Furthermore, several biomass particulates, such as those deriving from weeds, straws or canes, may present particle elongation ratios much larger than those of the tested materials and, therefore, the assessment of the flow properties and of the silo design procedure for such materials deserve further studies.
