Study of cluster characteristics in a circulating fluidized bed riser

摘要

The paper presents an analysis of measurement results on cluster and cluster core properties in a rectangular circulating fluidized bed riser. Experiments were carried out under different superficial gas velocities in the range of 4.5 m/s to 5.5 m/s along with solids circulation rate up to 272 kg/m(2)center dot s. High-speed images of the bed were taken in a controlled lighting environment. Analysis of the experimental images was conducted to demonstrate the microscopic structure of particle clusters. A cluster always consists of a dense core with highest solids holdup and the relatively dilute cluster cloud. Additionally, the horizontal length scale distribution as well as the solids concentration inside the clusters were evaluated, respectively. The effects of superficial gas velocity, solid circulation rate and the elevation on the measured cluster properties were determined. Results indicate that both a higher solid circulation rate and a lower gas velocity are benefited for cluster formation. Besides, at the top of the riser, the impact of the riser outlet structure becomes serious under high gas velocities, giving rise to wider clusters. Furthermore, narrow clusters with widths below several millimeters, which insensitive to the variation of operating conditions, are common in all position of the CFB riser.