Experimental analysis of heat transport in the solid bed of rotary kilns

Rotary kilns processes are energy intensive, thus the efficiency and performance of the kilns must be enhanced in order to optimize the processes where the understanding of heat transport and the temperature distribution inside the solid bed is crucial. Nevertheless, the heat transport phenomena as well as the temperature distribution inside the solid bed are still not well understood at present. In the present work, the heat transport into the solid bed for directly and indirectly heated rotary drum was analyzed. Experimental works were carried out to study the contact heat transfer from the covered wall to the covered bed, the heat transfer at the free bed surface and the transient mixing inside the solid bed. The experiments were conducted with different operational parameters such as rotational speed and filling degree, material parameters such as effective thermal conductivity, bulk density, specific heat capacity, particle size and dispersity. Various materials such as glass beads, steel spheres, quartz sand, animal powder, expanded clay and cement clinker have been used as test materials. The heat transfer from the covered wall to the covered bed was defined by contact heat transfer coefficient. In addition, the heat transport from the free bed surface was defined with the effective thermal conductivity of the active layer, since continuous renewal of active layer play important role in heat transport inside the solid bed. The mixing quality was characterized by the mixing time which is the time required to reach the preferred mixing state. Experimental results for all the three heat transport phenomena were compared with previous literature models.