Magnetic tracking of a fuel particle in a fluid-dynamically down-scaled fluidised bed

Artikel i vetenskaplig tidskrift, 2017

The mixing of a fuel particle in a fluid-dynamically down-scaled bubbling fluidised bed was studied using magnetic particle tracking. Both the resulting steady-state fuel distributions and the underlying mixing dynamics (fuel velocity field) were investigated. The experimental set-up applied resembles the mixing of an anthracite coal particle in a bed with a cross-section of 0.85 × 0.85 m2 operated at 900 °C with fluidisation velocities in the range of 0.16–0.45 m/s and bed heights in the range of 0.25–0.35 m. Four different gas distributors with variable pressure drops and orifice configurations were investigated. For the cases studied, 7.5 min of sampling time at a sampling frequency of 20 Hz was found to be sufficient to resolve the spatial distribution of the tracer. However, to provide a reliable estimate of the mixing dynamics, a sampling frequency of at least 100 Hz was required, together with a sampling time of approximately 20 s. Results on axial mixing showed improved mixing with increasing fluidisation velocity and bed height. The lateral dispersion coefficients were in the order of 10− 3–10− 2 m2/s (on an up-scaled basis), increased with fluidisation velocity, and were only moderately influenced by the configuration of the gas distributor.