(13d) Measurement of Residence Time in Calcination Processes
While continuous rotary calcination is a widely used process in large scale catalyst manufacturing, little explanation of the process can be found in scientific literature. Problems arise particularly upon scale-up of the process from the laboratory and pilot plant scales to the manufacturing scale. Developing such fundamental understanding of rotary calcination can improve product quality and cut energy and material costs. This research seeks to provide a methodology for scale-up through understanding of the effects of material properties, operating conditions and calciner geometry on particle residence time and temperature distributions. The two important indices for continuous calcination are: (1) in the axial direction, the residence time of the particles inside the calciner, and (2) in the radial direction, the time required for complete calcination of the particles. To optimize calciner performance, the particle residence time must exceed the time required for heating and calcination. For uniform treatment, the particles must also exhibit low axial dispersion. A combination of discrete element method (DEM) simulations and experiments are used to explore the influence of these competing timescales on scale-up. In this presentation, the impact of operating variables and material properties on the mean residence time and axial dispersion was investigated in a pilot plant rotary calciner. The residence time distribution of a cohesive catalyst powder was measured. The Taylor Dispersion model was successfully applied to predict the mean residence time as the powder flowed through the calciner. It was found that the feed rate did not significantly affect the mean residence time, while calciner incline and rotary speed did.