Interaction of heat transfer and particle dynamics in rotary kilns with internals - Experimental study of biomass drying

Abstract

The drying of granular biomass in rotary kilns involves a strong coupling between heat and mass transfer and particle dynamics. To ensure efficient processing, internal constructions are commonly applied to distribute the bulk material within the kiln cross section and to enhance gas-solid interactions. To investigate these mechanisms systematically, experimental studies are conducted using wooden spheres as model material for biomass. The approach decouples the phenomena independently by investigating the motion behavior and the heat treatment separately. The influence of operating parameters such as filling degree (5-20%), rotational speed (3-10 rpm) and the internal configuration (flights and cross internals) on the particle distribution and the drying efficiency is investigated experimentally. The use of flights leads to a more uniform particle distribution in the cross section and increases the presence of particles in the hydraulic section of the drum. Although adding a cross in the middle of the drum does not increase the particle number in this region, faster drying is observed, which can be attributed to an increased residence time of particles within the cross section. The experimental results provide benchmark data for the validation of a Discrete Element Method (DEM) model, which will be presented in a separate study.