Study on the aggregate motion for gas–liquid–solid agitated tank reactors design using radioactive particle tracking

This work provides a detailed study on the agitation rate influence on the solid motion within a pilot-scale slurry tank containing nickel oxide particle agglomerates suspended in iso-octane by the action of an axial impeller and slight bubbling nitrogen gas. The behaviour of a tracer particle representing solid aggregates is determined from radioactive particle tracking measurements with a spatial accuracy of ∼2 mm. An increase in the overall space occupied by the tracer is observed with increasing stirring speed. The instantaneous velocities, calculated by time differentiation of successive tracer positions, are significantly higher than the dynamic error. A measure based on the Reynolds stress as the turbulence level estimator is reliably mapped in three dimensions from the ensemble-averaged correlation matrix of the Lagrangian tracer velocity, enabling studying the influence of agitation on the turbulence levels distribution. This study offers an improved understanding of three-phase stirred reactors, which efficiencies are heavily coupled to complex fluid mechanics, especially in a turbulent flow. The axisymmetry is broken due to the presence of baffles. Incrementing the agitation intensity reduces the axial coherence of the thrust on the solid phase, raising turbulence levels, especially nearby the impeller tip.