Numerical study on the cluster flow behavior in the riser of circulating fluidized beds

In this paper, the cluster flow behavior in the riser of circulating fluidized beds (CFBs) was predicted by means of the Euler-Lagrange approach. Gas turbulence was modeled by means of Large Eddy Simulation (LES). Particle collision was modeled by means of the direct simulation Monte Carlo (DSMC) method. An extended cluster identification method was used to obtain the solid concentration and velocities of clusters. The flow behavior of falling clusters in the near wall region and the up-flowing and down-flowing clusters in the core of riser were analyzed respectively. At the same time, some cluster transient flow characteristics observed in the CFBs experimental studies were obtained in present simulation. Simulated results showed that there exists a low-pressure zone between the tails of a down-flowing cluster in the core of riser and a new cluster can be formed in the near wall region and transferred from the near wall region to the core of riser under the effect of upgoing gas. Simulated results have a reasonable agreement with the previous experimental findings.