State-of-the-art review of erosion modeling in fluid/solids systems
Résumé
Erosion in fluidized-bed combustors, commercial process units used to burn coal cleanly, has surfaced as a serious issue that may have adverse economic effects. The evidence suggests that the key to understanding this erosion is detailed knowledge of the coupled and complex phenomena of solids circulation and bubble motion. The FLUFIX computer code has been developed for this purpose. Computed hydrodynamic results compare well with experimental data (including the bubble frequency and size and the time-averaged porosity and pressure distributions) taken in a thin 'two-dimensional' rectangular fluidized beds containing a rectangular obstacle and a few-tube approximation of the International Energy Agency Grimethorpe tube bank 'C1' configuration. Six representative erosion models selected from the literature, comprising both single-particle and fluidized-bed models are critiqued. A methodology is described whereby the computed hydrodynamic results can be used with such erosion models. Previous attempts (none involving fluidized beds) to couple fluid mechanics and erosion models are reviewed. The energy dissipation models are developed, and are shown to generalize the so-called power dissipation model used to analyze slurry jet pump erosion. It is demonstrated, by explicitly introducing the force of the particle on the eroding material surface, that impaction and abrasive erosion mechanisms are basically the same. In doing so, it has been possible to unify the entire erosion literature developed for over a century. Linkage is made to two previously developed single-particle erosion models: Finnie's and Neilson and Gilchrist's. The implementation methodology, which can be applied to any erosion model, be it single-particle or fluidized bed, is summarized. The monolayer energy dissipation (MED) erosion model is developed. The erosion rates computed from the EROSION code are compared with each other and for the cold few-tube approximation of the IEA Grimethorpe tube bank 'C1' fluidized-bed experiment, and with other available erosion data literature to validate the calculations. The simplified closed form MED (SCFMED) erosion models and erosion guidelines are developed using semi-empirical correlations in order to allow quick engineering estimates of erosion. Alternative methodologies to couple hydrodynamics and erosion using the kinetic theory of granular flow and discrete element method (DEM) models are briefly reviewed. Finally, a critical review of the integrated experimental and computational fluid dynamics (CFD) pressurized fluidized-bed hydrodynamics and erosion research ongoing at Chalmers University is presented. This body of work has been influenced by the research at Argonne National Laboratory (ANL) and Illinois Institute of Technology (IIT) and reinforces the trends and conclusions reported in this review.