Heat Transfer in Granular Flow in Rotary Calciners: Experiments and Particle Dynamics Simulations

Introduction Heat transport in particulate materials is an essential component of modern technologies such as high performance cryogenic insulation, heterogeneous catalytic reactors, 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 experiments and particle dynamics simulations to examine flow, mixing, and mass & heat transport in rotary calciners. A cylindrical vessel made of aluminum, representing a slice of a calciner (8 inches diameter and 3 inches long) is used for the experiments. In parallel to the experimental studies we also use Discrete Element Method (DEM) simulations to model flow, mixing, and heat transport in granular flow systems in rotary calciners. Granular flow and heat transport properties of alumina and silica are studied systematically in order to develop a fundamental understanding of their effect on calcination performance. Two basic mechanisms of heat transfer are involved: the transient conduction in the particle bed during its contact with the wall and convective thermal mixing originated by the rotation of the calciner. Heat transport processes are simulated accounting for initial material temperature, wall temperature, specific heat capacity, effective granular bed heat transfer coefficient, baffle configuration, and granular flow properties (cohesion and friction).