Influence of Moisture Content and Fine Levels on Angle of Repose for Pelletized Materials

HighlightsThe influence of moisture content and fine levels on the angle of repose (AoR) was evaluated for multiple pellet types.Filling angle of repose (AoR) show some increases with moisture, but values remained in the “free-flowing” range.Emptying and tilting table AoR were more impacted by additional moisture and fines.Image analysis was successfully used to measure the angle of repose.Abstract. Biomass and feed pellets can be handled and stored using similar equipment to that used for other bulk materials; however, their unique physical characteristics can lead to handling challenges. Understanding the flow characteristics of these materials is essential for handling and storage system design, but these characteristics are not well defined in less-than-ideal conditions. The overall objective of this study was to evaluate how moisture content and level of fines influence the angle of repose (AoR) of hardwood, pine bedding, and feed pellets. Three moisture levels (unconditioned, two and four percentage points above equilibrium) and four particle fine levels (0%, 5%, 10%, and 15% fines) were evaluated. Multiple methods for measuring AoR were assessed, including the fixed funnel (both lose and confined base), tilting table, and a clear-sided test fixture to measure emptying and filling AoR simultaneously. An image analysis tool using a polyline fit to the pellet boundary was developed and used to measure the respective angles. The impact of increasing moisture and fine levels varied by pellet type and AoR measurement method, but generally resulted in an increase in AoR. The filling (dynamic) AoR was least impacted by moisture and fine levels, showing no differences among fine levels, and limit differences among moisture levels. Emptying (static) AoR was linearly correlated with the tilting table method, but the tilting table AoR was on average 15.5° higher. Utilizing the combined test fixture, the overall filling (dynamic) AoR for hardwood, pine bedding, and feed pellets inclusive of all moisture contents and percent fine levels were 33.8°, 35.0°, and 35.4°, respectively, while emptying (static) AoR’s were 39.9°, 44.2°, and 42.7°. Keywords: Angle of repose, Biomass, Moisture content, Particle size, Pellets, Physical properties.