Characterization of fuel mixing in a fluidized bed cold model: An experimental study using magnetic particle tracking

Abstract

An experimental study of the mixing of fuel particles in fluidized beds has been conducted. The study was performed using magnetic particle tracking sensors to track a magnetic tracer particle in a downscaled cold model of an industrial boiler. The fluid dynamical scaling was applied using Glicksman’s simplified scaling laws. Mixing characteristics of the tracer particles were evaluated and mixing cells were studied. The lateral dispersion coefficient was calculated using Einstein's equation for Brownian motion and measuring the residence time in the mixing cells for three different bed heights. This resulted in lateral dispersion coefficient values in the range of 3.3 − 7.6 × 10^(−3) m^2/s for mixing cell sizes between 0.04 and 0.08 m. Dispersion calculations based on mixing cells were performed using larger mixing cell size estimations (between 0.131 and 0.214 m), and the calculated lateral dispersion values converged towards the same values as the Brownian motion calculations when time filtering was applied. By comparing dispersion data from 20 minute and 5 minute measurements it was concluded that the shorter 5 minute measurements gave enough data to properly characterize the mixing. Movement patterns similar to mixing cells could be observed although they were disrupted by the construction of the cold model units distributor plate. No mixing cells unaffected by walls or the mentioned disruption were identified. The tracer particle did not cover the entire bed at the low bed height which indicates that defluidized zones were present.