The dynamic properties of clusters were studied in a concurrent downflow CFB reactor (downer) using optical fiber solids concentration signals. The downer reactor (0.1 m i. d. and 10 m high) was operated at gas velocities ranging from 3.5 to 10 m·s-1 and solids flux from 50 to 200 kg·m-2·s-1. The particles used in this research were FCC catalyst

with average size of 67 μm and a density of 1500 kg·m-3. Sensitivity analysis was first conducted to establish the optimum settings for determining cluster parameters. Aggregate properties (frequency

time fraction

existence time and average solids concentration) were established using transient solids concentration data

based on the results of the sensitivity analysis. The cluster properties were affected strongly by the operating conditions (gas velocity and solids flux) and by the local mean solids concentration. The cluster properties also varied strongly with axial and radial positions in the downer. In the fully developed section

the core region shows high clustering tendency than the wall region. Smooth axial profiles of cluster properties were observed towards the bottom.