Gas-solid flow characteristics at the riser wall were studied in a 60-meter-high transparent circulating fluidized bed (CFB) riser. The flowing processes of clusters were recorded by a high-speed camera. Through analyzing the pictures obtained in the 60 m riser, the coverage fraction of clusters at the riser wall f(c), the descent velocities of clusters at the riser wall U-c, the cluster-wall contact length L-c and the cluster-wall contact time r were measured. Based on the experimental data, empirical formulas for estimating f(c), U-c, L-c in the 60 m riser (10 m above the distributor) were proposed. The results showed that both U-c and L-c obtained in the 60 m riser (10 m above the distributor) were larger than those obtained in risers lower than 15 m.tau c varied between 0.07 s and 0.20 s under the experimental conditions. (C) 2018 Elsevier B.V. All rights reserved.