Gravity discharge characteristics of biomass-coal blends in a hopper

Adding biomass particles into pulverized coal may significantly improve the flowability of the cohesive pulverized coal particles. Experimental study of solids discharge flow from a cylindrical hopper with no aeration revealed an interesting “needle particle effect”, which was believed to be responsible for the smoother solids discharge and significantly increased discharge rates of the coal-biomass blends within the limits of the study. The mechanisms behind the needle particle effect in a gravity discharge system, including adherence, lowering cohesion, arch-breaking and transition of flow pattern, are analyzed and verified by the experimental results. The blends behaved different when different types of biomass particles were added. The observed flowability of the blends was strongly affected by the aspect ratio and surface roughness of the biomass particles. A revised model based on Crewdson's equation is proposed to predict the gravity discharge rate of biomass-coal blends.