Porosity distributions in a fluidized bed with an immersed obstacle

Abstract

Erosion in bubbling fluidized-bed combustors is a serious issue that may affect their reliability and economics. Available evidence suggests that the key to understanding this erosion is detailed knowledge of the coupled and complex phenomena of solids circulation and bubble motion. A thin transparent “two-dimensional” rectangular fluidized bed with an obstacle served as a rough model for a fluidized-bed combustor. This model was studied experimentally and computationally using two hydrodynamic equation sets. The computed hydrodynamic results agree reasonably well with experimental data. Bubble frequencies and sizes compare well with those obtained from analyzing a high-speed motion picture frame-by-frame. Time-averaged porosities computed from both models agree with time-averaged porosity distributions measured with a gamma-ray densitometer. The principal diferences between the data and the computations in this paper are due to asymmetries present in the experiment and to the simplified solids rheology used in the hydrodynamic models.