(749d) Measurement of the Axial Dispersion of Cohesive Powders in Rotary Kilns

With applications in a wide range of solids manufacturing processes including blending, drying, and disposing of waste, the rotary kiln has been established as an essential device in chemical and metallurgical industries. In the preparation of catalysts in particular, a better scientific understanding of rotary kilns will improve continuous calcination processes for increased throughput with improved product quality. While widely used in large-scale catalyst manufacturing, fundamental understanding of rotary calcination is absent from scientific literature. Thus, the goal of this research is to improve fundamental understanding of rotary calcination processes to aid in scale-up from laboratory and pilot plant scales to the manufacturing scale. For successful calcination to occur, the residence time of the particles must exceed the time required for heating and subsequent treatment. The optimal residence time therefore depends on both of these competing time scales, which are functions of feed material properties, kiln geometry and kiln operating conditions. For uniform treatment of the feed, the particles must also exhibit low axial dispersion. In this work, the residence time distribution and axial dispersion coefficient for two cohesive fluid catalytic cracking powders were measured in pilot plant kilns using a tracer study developed by Danckwerts. Results were successfully matched to the Taylor fit of the axial dispersion model and the Sullivan prediction for mean residence time. It was found that an increase in feed rate, kiln incline and rotary speed decreased mean residence time and overall dispersion. The axial dispersion coefficient was found to vary with kiln conditions. Such results have not been previously reported for cohesive powders.