It has hcen noticed that, the flows in risers of circula,ting fluidixed beds (CFI3s) is con- trolled by meso-scale structure of particles, that is clusters. The clusters largely changes fiow structure, consequently, they have considerable effect on the transport phenomena in risers of CFBs. Many experiments on the struct,ure of clusters have been performed, for example, Yerushalmi ct al. (1978), Rhodes ct, .al. (1992), Horio & Kuroki (1994), Hatano ct, al. (1994), zou et al. (1994), Li et al. (1995) and Tsukada ct al. (1997). Most of them intended to study the flows in the conditions of industriad applications, thus the conditions with respect, to the properties of gases aad solid particles are restrictfed to a small range. There are few experimental data on the structure of clusters in nonstandard conditions. For example, concerning the pressurised CFBs, it is difficult, to make observation. Therefore, it has been dcsircd to dcvclop a prediction method that is available for ra wide range of conditions.
Numerical simulation is a promising method to study these phenomena, because the presence of particles does not make the flow fields less acccssible, and it is easy to change parameters. Tsuo and Gidaspow (1990) calculated flow patterns in circulating fluid beds. They used a two-fluid model in which solid phase is rnodeled as a viscous fluid with constant effective viscosity, and predicted unstable flows with clusters. Our group proposed another simulation method for particle flows. We applied the Lagrangian approach coupled with direct simulation Monte-Carlo (DSMC) method, which was proposed for numerical simulations of rarcficd gas flows by Bird (1976), to the calculations of flow with clusters (Tanaka et al., 1995, 1996; Tsuji et al. 1997, 1998). The advantage of this method is that the properties of gas and particles can be easily taken into account. Tanaka, et, al. (1995) simulated two-dimensional flow under the same condition by Horio & Kuroki (1994) by using this method, and showed that the predicted structure and size of clusters are sirnilar to the experiments.
This project aims to produce numerical predictions that, are available to improve the understanding of the flows in CFB risers by using our method mentioned above. In this report, we present, a three-dimensional calculation that assumes the same conditions of gases and particles as Louge’s experiments (1997), in which riser flows of pressurised CFBs were studied by using high density gases. The effect, of the pressurised condition on the structure of clusters is discussed. Furthermore, correlations that appear in continuum rnodels are given.