(723g) Solids Mixing Studies in Fluidized Beds Using Fluorescent Tracer Technique

A fluorescent solid tracer technique has been used to study various properties such as solids mixing time, solids residence distribution time and the effects of internals on mixing in fluidized beds. Studying these parameters is of great importance in controlling the back-mixing of solids or verifying that solids segregate in a fluidized bed. The technique may also be used to compare the flow patterns of different solids, understand the hydrodynamics associated with different internals at different operating conditions, and to optimize the size and the shape of a reactor. In these sets of experiments, FCC catalyst was coated with a suitable UV dye in a 12-in (30-cm)-diameter spray column using a suitable solvent to dissolve the dye. The dyed catalyst was then injected into a 6-in (15-cm)- diameter Plexiglas column fluidized at superficial gas velocities of 1 ft/s (0.31 m/s) and 0.25 ft/s (0.08 m/s) to analyze mixing of FCC equilibrium catalyst. Fluorescent probes, which were inserted at different locations in the bed, captured the mixing phenomena of the catalyst in the bed. A photodiode converted an optical signal to an electrical signal and the data were recorded using a data acquisition system and was analyzed to study the mixing behavior of particulate solids in a small scale fluidized bed.