Particle and gas dynamics of high density circulating fluidized beds

High Density Circulating Fluidized Bed (HDCFB) reactors have found applications in a number of important industrial processes including fluid catalytic cracking and other catalytic reactors, but received little attention in academic research. This project is a continuation of a series of HDCFB studies at the University of British Columbia. The dual-loop CFB unit was modified to further increase the solids circulation flux to ∼600 kg/m2s, compared with the maximum of ∼400 kg/m2s in the original design. Experiments were conducted in a 0.076 m diameter, and 6.4 m tall riser at superficial air velocities between 4 and 9 m/s. FCC particles with mean diameter 70 pm and density 1600 kg/m3 are used as the bed material.; An integrated dual-functional optical fiber probe was developed to provide simultaneous determination of local instantaneous solids volume concentration, particle velocity and solids flux in multi-phase suspensions. The probe has 3 fibers in parallel with the middle fiber projecting light into the riser and the other two fibers receiving reflected light from moving particles. The local instantaneous solids flux was calculated as the product of the simultaneously determined suspension density (volume concentration times particle density) and particle velocity. The probe was confirmed to provide reasonably accurate simultaneous measurements of local instantaneous particle velocities, solids concentrations and solids fluxes.; Local particle velocity and concentration were measured simultaneously for high solids fluxes and high-density conditions using the optical fiber probe. The results show that the local time-mean velocity and flux profiles are both high in the central region and decrease toward the wall. Downward particle velocity and solids flux occur in the near-wall region for a range of operating conditions. The downward flow of particles is reduced or even eliminated, leading to Dense Suspension Upflow regime for high superficial gas velocities and high solids fluxes.; For a certain range of conditions, there was net upflow at the wall in the lower part of the riser and downflow at higher levels, indicating that the onset of the dense suspension upflow regime is height-dependent and that fast fluidization and dense suspension upflow regime can coexist in a single riser. A correlation was developed to predict the transition and a new regime map is obtained.; Gas residence time distributions were obtained using helium tracer and a step-change input. For high solids density conditions, axial gas dispersion decreases as the riser is dominated by dense suspension upflow conditions. (Abstract shortened by UMI.)...