Circulating fluidized bed (CFB) is used for a wide range of gas−solid reactions. However, most of the data reported on CFBs are for Geldart's group A particles, although the applications of Geldart's group B CFBs are numerous. In the current work, the solid flow field is deciphered in a pilot-plant-scale Geldart's group B CFB riser. Solid motion is tracked by using a radioactive particle tracking technique. The data are reported in a fully developed flow region of 0.1 m diameter and 6.5 m height CFB riser at different inlet gas velocities (7.6−9.2 m/s) and solid fluxes (100−200 kg/m 2 s). The different flow quantities such as mean axial and radial velocities, rootmean-square velocities, granular temperature, and turbulent intensities are calculated for all the cases. It is observed that solid motion predominantly lies in the axial direction. The probability distribution function of instantaneous solid velocity shows wider distribution near the wall as compared to the center of the riser. This shows that the probability of mesoscale metastable structure formation increases while moving from the center to the wall. Furthermore, the results show that the mean solid velocity largely depends on gas−solid interactions. However, for the fluctuating velocity, both gas−solid and solid−solid interactions are critical. The results indicate that the solid turbulent intensity in Geldart's group B riser is significantly higher than that in the group A riser. Hence, solid velocity fluctuations are higher in the group B riser.

Solid flow in a Geldart’s group B circulating fluidized bed (CFB) riser is complex, and it exhibits backflow and recirculation in the riser. A single radioactive tracer particle is used to measure the overall and sectional residence time distribution in a CFB riser at a gas velocity of 7.6–9.2 m/s and a solid flux of 100–200 kg/m2s. At the same time, radioactive particle tracking (RPT) data are used to measure the trajectories of the tracer particle and its length distribution at the bottom and middle sections of the riser. Both residence time distribution (RTD) and trajectory length distribution data obtained from RPT and RTD experiments are processed and compared. Results show that the bottom section has higher back mixing than the middle section. The results also show that back mixing in both the sections reduces with an increase in the gas inlet velocity and reduces marginally with an increase in the solid flux. Results confirm that RPT and RTD data are highly correlated and can be used with the same accuracy to quantify the macromixing behavior of any process vessel/reactor.

Solid phase velocity measurements are performed at the bottom section of a pilot plant scale cold-flow circulating fluidized bed riser with Geldart group B solids using a radioactive particle tracking technique. Experiments are performed at different gas velocities and solid fluxes to evaluate the effect of gas velocity and solid flux on solid phase velocity in the bottom section of the riser. Different flow quantities such as mean velocity, root-mean-square velocities, and granular temperature are calculated and presented at different heights. Solid motion is seen to occur in the axial direction primarily. It is observed that axial velocity fluctuation increases with the height where radial solid velocity fluctuation decreases. Both gas–solid and solid–solid interactions are vital in determining the solid flow field. Gas–solid interaction is critical in the axial direction, while solid–solid interaction is important in the radial direction.