Discrete element study of solid circulating and resident behaviors in an internally circulating fluidized bed

Three-dimensional modeling of the gas-solid flow in an internally circulating fluidized bed is conducted based on the computational fluid dynamics coupled with discrete element method. The gas flow is resolved at the computational grid level while the solid motion is tracked individually. General circulation pattern and the circulating path of solid phase in the system are investigated. Then, the distribution pattern of solid cycle time is studied. Moreover, the solid resident behaviors from the scales of both the computational grid and particle level are explored. Simultaneously, the influences of operating parameters and bed geometrical configuration on these two aspects are discussed. The results show that solid circulation is constructed in the two chambers with the formations of three local circulation rolls of solid motion. A global path can be identified for solid circulation in the system. Solid cycle time in the bed shows an early-occurred peak with a long tail and distributes in a log-normal probability histogram. Increasing the fluidizing velocity introduced into each chamber or the gap height lowers the solid cycle time. In addition, large solid residence time (SRT) appears in the two corners of the bed. At the particlescale level, larger SRT is observed in the right chamber as compared with that of the left one, and the increase of fluidizing velocity reduces the SRTs in the two chambers. No-linear evolutionary tendencies of both the cycle time and the SRT in each chamber can be observed with changing the geometrical configuration, which raises a caution on the geometry design of the apparatus. (C) 2014 Elsevier B.V. All rights reserved.