Scale-up effect of riser reactors (3) axial and radial solids flux distribution and flow development

The influence of riser diameter on the axial and radial solids flux and flow development is studied in three riser circulating fluidized bed reactors of different diameters (76, 100 and 203 mm i.d. risers). A suction probe was used for the direct measurement, while the calculated local solids flux data obtained from solids velocity and concentration measured by two separate fibre optic probes were used to compare. Two shapes were found for the radial profile of the solids flux, a parabolic shape and a flat core shape. The shapes obtained could be predicted, based on the operating conditions, using a new concept of the effective solids saturation carrying capacity. The radial profile of solids flux is less uniform in a larger riser than in a smaller riser. Flow development is slower with the increase of riser diameter. The operating conditions were found to affect the solids flux in each reactor in the same general fashion: increasing gas velocity decreased the amount of downflow solids in the risers; increases in the solids circulation rate caused more solids to flow downwards.