(232d) Solids Dynamics in Gas-Solid Risers Inferred from Carpt Experiments

A thorough conception of the particle motion in the risers of Circulating Fluidized Beds (CFB) is very important to develop fundamental models for proper design and scale-up of these units. Existing and new models used to represent the complex particle dynamics in CFBs require experimental data for validation and improvement. Computed Automated Radioactive Particle Tracking (CARPT) technique has the capability of non-intrusively exploring the 3D solids structure and the complex solids motion in large opaque systems.

The trajectories of a solid tracer with the same characteristics as the circulating solids in the risers of two pilot-scale CFBs are examined in detail to get insights into the complex solid dynamics of these systems. The analysis uses tools from the theory of non-linear dynamics and symbolic dynamics. Features of the solid dynamics within the fast fluidization and the dilute phase transport flow regimes are highlighted and related to the operating conditions.

Non-linear dynamics theory has provided a framework and a new set of tools suitable for analysis of experimental time series, which frequently contributes to get insights into the dynamics of complex systems. Iterated maps have been obtained from successive crossings of the tracer through a given location in the inspected test sections. Distinct structures according to the flow regime have been found. They point to a more deterministic and regular motion in the DPT regime than in the FF regime.

Likewise, symbolic dynamics is a methodology that can be employed to enhance certain features of experimental time series of observables in continuous systems. The time series of an observed variable is transformed into a series of symbols, following certain criteria. A high relative frequency of a certain symbol-sequence implies the recurrence of specific patterns of the time series, which can be related to properties of the underlying system. Relative frequencies of symbol-sequences derived from the time series of the tracer positions were found to be strongly influenced by the flow regime and can be used as pointers for regime identification.

Finally, fast descending paths of the tracer, particularly within the column core, are closely examined to check the hypothesis of cluster formation at certain conditions.