Magnetic tracer-particle tracking in a fluid dynamically down-scaled bubbling fluidized bed

Artikel i vetenskaplig tidskrift, 2015

A method for 3-dimensional (3D) magnetic tracer particle tracking in a fluid dynamically downscaled fluidized bed is presented. The method applies Anisotropic Magneto Resistive (AMR) sensors to track a magnetic tracer particle in the form of an NdFeB-based permanent magnet. The fluid dynamically downscaled bed has a cross-section of 0.17x0.17 m2 and is operated at ambient conditions with bronze powder as bulk solids and the tracer particle corresponding to a fuel particle. After up-scaling the bed corresponds to a 0.85x0.85 m2 bed of fuel ash or silica sand operated with air at 900°C using anthracite coal as a fuel. Thus, the method provides continuous tracking of the tracer particle trajectory which, combined with the fluid dynamic scaling yields quantitative information applicable to the study of fuel mixing in large-scale fluidized-bed processes operating under hot conditions. Application of the method represents a significant step forward compared to other experimental studies which are limited to qualitative interpretations; performed in 2D units and in cold 3D units which are not fluid dynamically scaled. It is shown that the AMR sensor system is able to work with the (non-magnetic) bronze powder resulting from the fluid dynamical downscaling, i.e. overcoming the limitation in signal penetration which prevents tracking of radioactive objects in such dense media. Thus, successful application of the AMR method for continuous 3D object tracking in a fluid dynamically downscaled unit is demonstrated for the first time. The measurement system provides both translational and rotational data, unleashing possibilities also as validation tool of CFD models. The preliminary results show a spatial resolution in the order of 1 mm, while temporal resolution is in the order of milliseconds.