More fundamentals of dilute suspension collapse and choking for vertical conveying systems

Using gas-solid flows in circulating fluidized-bed risers to analogize vertical pneumatic conveying systems, the collapse of dilute suspension, that is, the choking of accumulative type, was studied in three different risers with respect to different particles. The collapse of dilute suspension was dominated by an identical differential pressure drop over the measuring section. This differential pressure drop was independent of gas velocity and riser diameter, but varied with particle properties. The saturation carrying capacity, the solid flow rate at the dilute suspension collapse, was closely related to particle characteristics and riser diameter. With an increase in the riser diameter, it increased for lighter and smaller particles, but decreased for heavier and larger particles. Based on these experimental measurements, as well as the related literature reports, a correlation was developed for the saturation carrying capacity by analyzing its dependencies on gas velocity and riser diameter. More than 150 experimental data of the saturation carrying capacity available in the literature were compiled to evaluate the accuracy of the proposed correlation by comparing with 13 other literature correlations, demonstrating that this new method has the highest accuracy.