In-depth system parameters of transition flow pattern between turbulent and fast fluidization regimes in high solid particle density circulating fluidized bed reactor

•Transition flow between turbulent and fast fluidization regimes was discussed.•Circulating-turbulent transition flow was found with only primary gas injection.•The results showed the unique system characteristics for the transition flow.•Circulating-turbulent flow had unique power spectrum peak at the center region.•The collision governs the system characteristic in circulating-turbulent flow.

The transition flow between turbulent and fast fluidization regimes in high solid particle density circulating fluidized bed reactor was successfully investigated in this study. In addition, the effects of computational cell and simulation time were compared. Then, the comprehensive explanation and in-depth system parameters were discussed. The results showed the unique system characteristics. For the transition flow between turbulent and fast fluidization regimes, lower range of energy spectrum than the turbulent and fast fluidization regimes was found. As the increasing of gas inlet velocity, the axial and radial solid particle dispersion coefficients increased and decreased, respectively. For the axial and radial gas dispersion coefficients, both of them were increased with the increasing of gas inlet velocity. At the near wall region, the transition flow had no obvious power spectrum peak except the one below 0.2 Hz, while, at the center region, the maximum peak at 5.0 Hz was found. All the velocities had no significant correlation with solid volume fraction. The solid particle–solid particle interaction or collision then governs the system characteristic. The transition flow between turbulent and fast fluidization regimes will be an alternative choice for applying with circulating fluidized bed reactor in other new physical and chemical processes.

Graphical abstractThe instantaneous contours and snapshot pictures of solid particle inside circulating fluidized bed riser with three different gas inlet velocities (vg, inlet).Figure optionsDownload full-size imageDownload as PowerPoint slide