Scale-Up Effect of Riser Reactors (1): Axial and Radial Solids Concentration Distribution and Flow Development

The influence of the riser diameter on the axial and radial solids holdup profiles and flow development is studied by measuring local solids holdups with a fiber-optic probe in a 10-m twin-riser system with 0.076- and 0.203-m inner diameters, at solids circulation rates of up to 200 kg/(m2 s) and superficial gas velocities of up to 8 m/s. It was found that the solids concentration increases with increasing riser diameter. Furthermore, the radial profiles of the solids concentration are steeper with larger-diameter risers. For both risers, the flow development in the riser center is nearly instantaneous, with the solids concentration remaining low under all operating conditions. In the wall region, the flow development slows down. Moreover, the flow development is slower in the larger-diameter riser. Increasing the solids flux also slows the flow development. However, increasing the superficial gas velocity makes the flow development faster while also lengthening the fully developed region.