Gas–solids flow structure and prediction of solids concentration distribution inside a novel multi-regime riser

• Systematic study of axial and radial flow structure in a novel multi-regime riser.
• Comprehensive analysis of flow development along the diameter-enlarged section.
• Correlation of solids concentration in turbulent section of multi-regime risers.
• Prediction of solids concentration distribution in the diameter-enlarged section.

In this study, a novel multi-regime riser featured by combination of a dense-phase bottom region operated in turbulent fluidization and a dilute upper region was presented. Systematic research was conducted to investigate both axial and radial solids concentration distributions and the flow development in this riser. Experimental results indicated that high solids concentration and uniform flow structure were achieved in the diameter-enlarged bottom section, and the flow development was comprehensively analyzed in terms of local solids concentration, radial nonuniformity index and one-dimensional slip velocity. An empirical correlation of solids concentration in the turbulent section of various multi-regime risers was also developed. This correlation was further extended to predict axial solids concentration distribution in the diameter-enlarged section of this novel riser. Moreover, Boltzman function was adopted to correlate local solids concentration with cross-sectional averaged solids concentration and radial position in bottom dense region and upper flow developing region of the diameter-enlarged section, respectively. In general, a satisfactory agreement between predictions of these correlations and experimental results was obtained.