Modeling the motion of fuel particles in a fluidized bed

Artikel i vetenskaplig tidskrift, 2021

A semiempirical model for the mixing of fuel particles in a fluidized bed is presented and validated against experimental data from the literature regarding lateral fuel mixing. The model of fuel particle mixing categorizes the fluidized bed into three mixing zones: a rising bubble wake solid zone, an emulsion zone with sinking bulk solids, and a splash zone located above the dense bed. In the emulsion zone, the axial motion of the fuel particle is described by a force balance, applying a viscoplastic stress model, i.e., with a dominant yield stress and only a minor contribution of the shear stress, using an empirical expression from the literature. In the lateral direction, the model is divided into so-called ‘recirculation cells’, which are crucial for the lateral mixing. Comparisons of the modeled and measured lateral dispersion coefficients of different fuel types measured in three different large-scale fluidized bed units under both hot and cold conditions (covering a broad range of coefficients: 10−4–10−1 m2/s) reveal satisfactory agreement. The validated model was used to investigate how the lateral mixing of fuel particles depends on the excess gas velocity, the bed height, and the lateral distribution of bubbles over the bed cross-section (which is typically uneven in industrial FB furnaces), as well as the size and density of the fuel particles.