Visualization of particle aggregation and effects of particle properties on cluster characteristics in a CFB riser

The particle aggregation was studied in a circulating fluidized bed riser. The flow structure and the formation of clusters were visualized by a high-speed digital image system. The particle aggregation is characterized by analyzing the images frame by frame, as well as the instantaneous solids concentration data obtained by the optical fiber probe. The results indicated the smaller and the lighter particles have higher potential to aggregate than the larger and heavier particles. The effects of particle sphericity were not as significant as the effects of particle density and size. A new cluster characteristic, cluster number fraction, was defined in this study. Other aggregate properties, including cluster time fraction, cluster mean existence time and cluster frequency were also compared with the analyses of solids concentration. The study elucidated the effects of particle density, size and sphericity on particle aggregation properties.