ANALYSIS OF LATERAL FUEL MIXING IN A FLUIDDYNAMICALLY DOWN-SCALED BUBBLING FLUIDIZED BED

Paper i proceeding, 2013

A method to evaluate the lateral mixing process of fuel particles in bubbling fluidized beds is proposed. The method determines the lateral dispersion coefficient of the fuel particles by means of digital image analysis to video recordings of tracer particle measurements in a fluid-dynamically downscaled 3-dimensional cold-flow model. The work applies direct measurements of tracer particles coated with fluorescent paint, which are irradiated with an ultraviolet light emitting lamp, mounted above the bed. The cold-flow model has cross-sectional dimensions of 0.3 m x 0.3 m and can be operated with bed heights up to 0.16 m. According to the scaling laws this setup is assumed to fluid-dynamically resemble a bubbling fluidized bed operated at 900°C with crosssectional dimensions of 1.5 m x 1.5 m and bed heights up to 0.8 m. The measurements were made for fluidization velocities ranging from 0.17 to 0.83 m/s (up-scaled). The lateral fuel dispersion coefficient is found to increase with superficial velocity over the entire range of velocities investigated. The results show up-scaled (i.e. at hot conditions) dispersion coefficients ranging from 10-2 to 10-1 m2/s, which is similar to values obtained previously in large-scale bubbling beds under hot conditions.