AN IMPROVED MODEL FOR FIXED-BED COAL COMBUSTION AND GASIFICATION

An improved one-dimensional model for countercurrent oxidation and gasification of coal in fixed or slowly moving beds has been developed. The model incorporates an advanced devolatilization submodel that can predict the evolution rates and the yields of individual gas species and tar. A split, back-and-forth, shooting method is implemented to satisfy exactly the boundary conditions for both the feed coal and the feed gas streams. An option to switch between equilibrium and non-equilibrium gas phase composition has been added. The model yields improved predictions for product gas composition and product tar flow rate. The model predictions are compared with the experimental data for two coals: a Jetson bituminous coal and a Rosebud subbituminous coal. An illustrative simulation for an atmospheric, airblown, dry ash, Wellman-Galusha gasifier, fired with the Jetson bituminous coal, is presented. Areas which need additional improvements are identified.