Axial flow structure of solids holdup in an 18-m high-density CFB riser based on pressure measurements

The axial flow structure in a high-density CFB riser having a height of 18 m is investigated on the basis of pressure measurements.Solids circulation rates reach 1400 kg/(m2 s)at superficial gas velocities of 5-9 m/s and the apparent solids holdup exceeds 0.2,indicating high-density operations have been achieved.The apparent solids holdup increases with the solids circulation rate increasing and/or superficial gas velocity decreasing.Axial distributions of the apparent solids holdup have exponential shapes with denser regions at the bottom and more dilute regions in the upper part.The apparent slip velocity increases with the increasing solids holdup and reaches 14 m/s,showing that there are more opportunities of cluster formation in high-density operation.Furthermore,the apparent slip velocity has a power relation with the apparent solids holdup under a wide range of operating conditions.