The interest in biomass particulate solids has been increasing over the last decades for their wide use in thermochemical and biochemical processes to produce energy, biofuels and biochemicals. Solid biomass materials include a wide variety of materials of different natural source (forestry and agricultural wastes). Usually, biomass passes through a pre-processing step to obtain granular materials or powders. Industrial practice reports difficulties due to blockage in the discharge from storage units  and difficulties in predicting and controlling biomass flow rates in the feeding of the transformation units . Solutions to these problems involving special ancillary equipment, that are proposed on empirical basis, increase the handling cost of low value materials so that the economic feasibility of the whole process becomes critical. These problems can be correctly addressed by the knowledge of the flow properties of solid biomass. However, standard characterization methods used for conventional granular solids are not always suitable for biomass materials. Moreover, it ought to be considered that current design procedures for hopper flow  were developed for particulates made of rigid and nonfibrous particles. The simple Mohr Coulomb approach followed in these procedures may be inadequate for lignocellulosic biomass, made of elastic irregularly shaped particles. The scope of this paper is to verify the standard design procedures on the flow condition of a plane silo discharging lignocellulosic granular biomass. Discharge experiments were carried out in a plane silo, of total volume of about 0.3 m3, formed by a parallelepiped bin and a wedge-shaped hopper in which it is possible to independently change both the hopper inclination angle and the width of the outlet slot. Two different woody biomass powders, a dry one (A) made of sawdust sieved below 4mm, and a moist one (B) sieved below 2mm were tested. The results of the design procedure by Jenike were compared with the experimental data obtained in the plane silo. The design procedure appeared sufficiently conservative to be used with confidence in the case of damp sawdust Wood Powder B. The same procedure turned out to predict critical outlet values very close to those experimentally found in the case of the dried sawdust Wood Powder B. Therefore, the application of the design procedure in this case requires the adoption of safety coefficients for a reliable hopper design for material flow. Several biomass particulates, such as those deriving from weeds, straws or canes, may present particle elongation ratio much larger than those of the tested materials and, therefore the characterization of the flow properties and the assessment of the silo design procedure for such materials deserve further studies. References  Mattsson J.E., Kofman P.D., Biomass & Bioenergy 2002; 22: 179-185.  Cummer K.R., Brown R.C., Biomass & Bioenergy 2002; 23: 113-128.  Jenike A.W., Bulletin of the University of Utah N. 123, 1964.