Effects of Operating Parameters on Hydrodynamic Behavior of Spout-fluid Beds without and with a Draft Tube

Abstract

The spout-fluid bed (SFB) is one of many modifications to conventional spouted bed, which is achieved by introducing an auxiliary gas flow into the annular region of a spouted bed through a distributor. Therefore, the SFB has better gas-solid contact and mixing, and reduces the risks of particle agglomeration and dead zone. In addition, the gas-solid contact and the solids circulation rate can be controlled more easily and flexibly by installing a draft tube in the bed (DSFB). In this study, the effects of operating parameters on flow characteristics of the SFB and the DSFB were investigated and they were compared, using the same semi-cylindrical column and the same particles. As the results, the flow regime maps were recognized based on pressure fluctuation data and the DSFB had wide range of operating conditions for stable spouting, comparing with the SFB. The minimum spouting gas velocity for stable spouting state (spouting with aeration) decreased with increasing the auxiliary gas velocity. Also, longitudinal and radial distributions of particle velocity in the spout and the annulus were obtained in detail for the stable spouting state by means of the particle image velocimetry (PIV). Particle velocities in the spout and the annulus were increased with increasing the auxiliary gas velocity. Moreover, the distributions of particle velocities in the DSFB showed that particles in the draft tube were accelerated remarkably and particles in the annulus descended uniformly with small velocity, comparing with the SFB.