Experimentally validated computations of heat transfer in granular materials in rotary calciners

Heat transport through flowing particulate materials is an essential component of modern technologies such as heterogeneous catalytic reactors, high performance cryogenic insulation, construction material, and powder metallurgy. In catalyst manufacturing, heat transfer through granular media occurs in the drying and calcination stages. In this paper, we describe the use of experiments and discrete element methods to examine flow, mixing, and mass and heat transport in rotary calciners. Alumina powder (200 μm) and cylindrical silica pellets (2 mm diameter and 3 mm long), which are common support materials for catalysts, are used in our experiments. A parametric study was conducted by varying the material properties of granular material, and rotational speed of the calciner. We use the discrete element model to simulate flow, mixing, and heat transport in granular flow systems in rotary calciners. Simulations and experiments show that the rotation speed has minimal impact on heat transfer. As expected, the material with higher thermal conductivity (alumina) warms up faster in experiments and simulations. Various baffle configurations (rectangular and L-shaped flights) in the calciner and their effect on the flow and heat transfer of granular material are simulated. The average wall-particles heat transfer coefficient of the granular system is also estimated from the experimental findings.