Effects of solids feeder and riser exit configuration on establishing high density circulating fluidized beds

Influences of configurations of solids feeding device and riser exit on the flow behaviors of gas–solid in a solids circulation system were studied in order to investigate a highly dense solids circulation at high velocity. Experiments were carried out in a lab-scale circulating fluidized bed (0.05 m-ID × 4.5 m-H) cold model with FCC particles (dp = 70 μm, ρs = 1740 kg/m3) as a bed material. Three kinds of solids feeders (Loop-seal, J-valve and L-valve type) and three different shapes of riser exits (C, L and T-shape) were employed. It was found that the solids mass flux (Gs) increased with increasing the primary gas velocity (U1) in all configurations, and the level of Gs with the L-valve was much higher than the other feeders and the high Gs enabled solids holdup (εs) in the riser to be relatively dense at high U1. Among the three riser exit configurations investigated (C, L and T-shape), on the other hand, C-shape exit provided high Gs and εs at high U1. In this study, a highly dense solids circulation was observed under conditions such as LV solids feeder and C-shape riser exit with sufficient solids inventory (Is). The effects of the inlet and exit configurations on the gas–solid flow behaviors from a dilute to a dense-phase were discussed based on correlation dimension (Dc) and Kolmogorov entropy (K) obtained by chaos analysis of pressure fluctuations.