(479d) Theoretical and Experimental Study of Bulk Strength of Fibrous Biomass Materials

Unconfined yield strength governs the ability of a bulk material to be easily handled in a process.  Generally, the greater the strength of a given material, the more difficult it is to handle that material.   Strength of simple systems of closely sized spherical particles can be modeled and used as an analytical tool to predict process behavior.  However, wet fibrous materials do not follow typical models and rules for nearly spherical materials.  This paper explores the relationship between the bulk yield strength and the moisture content, particle aspect ratio, particle size, particle density, and bulk density.  Typical biomass materials are of very light density until they are milled.  After milling the density increases, creating a more tightly packed product.  In general, cohesive flow properties depend on the particle interaction forces.  The strength of smaller sized material is generally higher than a corresponding large particle.  However, the tendency to exhibit cohesive flow problems is directly proportional to the strength and inversely proportional to the density.  Smaller particles produce stronger bulk strength, but larger densities.  Thus, it is not easy to predict if a finer or coarser material will flow better in any given process.  In addition, interlocking of particles results in large frictional forces between particles that increase bulk strength effects due to particle shape and geometry.  This paper presents data of various biomass samples as a function of particle size, particle shape, moisture content, and particle density.  These effects are explained using a particle scale theoretical approach and compared to data generated from strength measurements.