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In fluidized beds, solids residence time distribution (RTD) measurements can be used to:

-characterize bed hydrodynamics
-identify solids bypassing
-zones of internal recirculation or stagnant flow
-determine the extent of solids mixing or segregation

Solids transport and mixing behaviours have a large impact on process performance such as conversion, heat transfer and reaction rates, deactivation of catalyst particles, and others.

A pulse of solids tracer is injected and detected either in-situ, or by sampling. Existing solids tracer technologies typically rely on radioactive particles, which are great candidates for tracing of commercial reactors and processes but can be more expensive and disruptive to run in the lab due to the additional safety precautions required.

Back in 2010, Coanda developed a unique phosphorescent solids tracer technique to study solids mixing in fluidization applications. Phosphorescent materials absorb UV photons and re-emit visible light photons over time. This tracer afterglow is detected using our in-house designed optical probes, allowing for real-time particle detection at tracer concentrations as low as 200 ppmw.

Tracer particles are energized in a specially designed injector, where they are fluidized while being exposed to UV light. The injector’s borosilicate glass column is surrounded by UV-emitting light tubes, and can be pressurized up to 100 psig. The tracer particles are energized for 5-10 minutes at a constant fluidization velocity and pressure. The injector is then slumped, and the pressurized tracer particles are injected into the process using a dump valve, resulting in a fast and repeatable tracer injection.

The video shows fluidized tracer particles being injected into a riser. In this application, solids were detected at multiple locations within the riser, the reactor dense bed, and the standpipe that returns the solids to the bottom of the riser. For additional information, see “Phosphorescent Tracing to Study Solids Mixing in Fluidized Beds”, AIChE 2012 conference paper – https://bit.ly/3RhjvmA