Observed Mixing Behavior of Single Particles in a Bubbling Fluidized Bed of Higher-Density Particles

Abstract

We report experimental observations of the dynamic behavior of single, magnetically tagged 3–4 mm particles varying in density from 0.55 g/cm3 to 1.2 g/cm3 as they migrate freely in a bubbling air-fluidized bed of 177–250 μm glass beads of 2.5 g/cm3 density over a range of air flows. The densities of the tracer particles (made by imbedding small magnets in wooden particles) were chosen to span a range typical for many biomass materials and exhibited both segregated and well-mixed behavior. Using high-speed measurements from externally mounted magnetic probes, we were able to reconstruct three-dimensional spatial and temporal information about the tracers’ trajectories over periods of five minutes. Based on this information, we describe general trends in how the tracers moved and redistributed themselves as functions of their density, fluidization air flow, and the overall concentration of low density particles present. One key finding was that the time average vertical probability distribution of the tracer particles locations is consistent with a Weibull distribution. The effective Weibull parameters appear to vary systematically with the degree of fluidization and particle density. Also, we observed that temporal autocorrelations in the vertical position of the tracer particles vary systematically with fluidization intensity and reveal important information about the dominant bed circulation time scales. Our results suggest that it may be possible to develop relatively simple statistical models or correlations for describing the spatial distribution and circulation of mm sized particles in bubbling beds of this type. Such tools should be useful for simulating some types of fluidized biomass processing and for validating kinetic-theory models of fluidized bed systems.

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

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Improved magnetic particle tracking technique in dense gas fluidized beds

“…They were able to follow a rather large magnetic marker at 62.5 Hz. Halow et al studied segregation effects in fluidized beds using just four Hall effect sensors. Finally, Neuwirth et al have used MPT to enable comparison of measured particle motion in a rotor granulator with simulated results obtained from discrete element model.…”

CFD–DEM Investigation of Fuel Dispersion Behaviors in a 3D Fluidized Bed

“…Although using these novel experimental techniques (e.g., RPT and PEPT) has provided some valuable insights into the particle motions in a fluidized bed, the high expense and the concomitant safety concerns of such techniques still highly hinder their wider applications in a large number of repetitive experiments. Based on this, Mohs et al 10 for the first time utilized the so-called magnetic particle tracking (MPT) technology, which is non-intrusive and relatively cheap, to track single solid particles in a prismatic spouted bed, and later this technology was successfully employed in a spouted fluidized bed 11 and a bubbling fluidized bed, 12 demonstrating its great potential in particle tracking. Buist et al 13 improved the accuracy of MPT by sequential quadratic programming and wavelet filtering.…”