(344d) Phosphorescent Tracing to Study Solids Mixing in Fluidized Beds

A phosphorescent solids tracer technique has been designed to study the solids mixing in a pressurized circulating fluidized bed (CFB) model of a FLUID COKING Reactor. Using pure phosphorescent pigment as a tracer, an external fluidized bed injector was used to activate and then inject a pulse of tracer into the riser. This provided a quick, repeatable, and well-distributed injection of tracer into the top of the Reactor fluidized bed. The light emitted from the tracer particles was collected at various locations in the Reactor fluidized bed and the standpipe using a single-fiber optical probe assembly. Measurements obtained from the tracer tests demonstrate that both standpipe time-of-flight and Reactor solids residence time distributions (RTDs) can be measured in the model. Standpipe time-of-flight data was correlated against the riser constriction pressure drop to provide a calibration for external circulation. Leading edge times from the solids RTD illustrated the extent of solids by-passing through the Reactor. The by-passing phenomenon observed corresponds to the bed turnover time predicted by the correlation of Geldart (Gas Fluidization Technology, John Wiley & Sons, 1986). Beyond this, the technique allows for multiple tracer injections to be conducted in a short period of time with limited noise build-up due to the nature decay of light emitted from the phosphorescent pigment. This allows statistical information regarding the measurements to be considered.