Effects of the Moisture Content on the Flow Behavior of Milled Woody Biomass

Abstract

Handling milled biomass particles in equipment like hoppers and feeders has been a long-lasting challenge in the bioenergy industry because of the poor flowability of these low density, high aspect ratio, and irregularly shaped particles. The inner pores of woody biomass particles complicate the granular flow behavior. When water exists in these intra- and inter-particle pores with sizes ranging from nanometers to micrometers, intricate processes such as hydrogen bonding, capillary effects, liquid bridge, and lubrication occur. However, knowledge of how these processes alter the bulk flow behavior of woody biomass particles is severely lacking. This study investigates the bulk flow behavior of loblolly pine chips in wedge-shaped hoppers considering moisture content. The fiber saturation point (FSP) of the material (30%) was determined through the differential scanning calorimetry analysis. The compressibility and shear resistance were found to increase with the increased moisture content through meso-scale testing. Moreover, hopper flow simulations suggest that the effective discharge rate decreases by 50% with the increasing moisture content up to the FSP, beyond which moisture content has no apparent influence on the effective discharge. This study highlights the importance of quantifying the biomass FSP in understanding biomass flowability at various moisture contents and sheds light on the trouble-free handling of wet woody biomass particles in the bioenergy industry.