Nonintrusive particle motion studies in the near-wall region of a pilot-scale circulating fluidized bed

A backscatter LDV system was used to record velocities of solid particles in the near-wall region of the riser section of a pilot-scale cold-flow CFB. The riser was 30.5 cm in diameter and 15.2 m in height. The bed material comprised cork particles with a Sauter mean diameter of 812 mum and a particle density of 189 kg/m(3). The superficial gas velocity was varied from 3.75 to 5.4 m/s with a solids circulation rate ranging from 3.4 to 17.1 kg/m(2.)s. A bimodal velocity distribution was observed near the wall region. The mean velocity of solids was found to increase with increasing superficial gas velocity and decreasing solids circulation rate. The mean velocity of particles moving in the downward direction was relatively insensitive to changes in operating conditions. A criterion for defining clusters was proposed and justified, and the effects of operating conditions on the mean velocity and size of clusters were examined. The mean cluster velocity for most of the operating conditions was in the range of 0.8-1.4 m/s in the downward direction. The mean cluster size was found to increase with increasing solids-to-gas load ratio.