MATHEMATICAL-MODELING OF FLUIDIZED-BED COMBUSTION .1. COMBUSTION OF CARBON IN BUBBLING BEDS

A three-phase model for carbon combustion in fluidized beds has been d eveloped to take into account the effects of gas backmixing and solids circulation. Inclusion of these phenomena is expected ultimately to b e important in extending the fluidized bed combustion model to predict N2O emissions. Transient mass and energy balance equations are presen ted in this paper for the fast bubble regime; these equations can be e asily modified for the slow bubble operating regime. The system of nin e first-order semilinear hyperbolic partial differential equations has been solved numerically. The transient solution permits comparison of the predictive capability of the model with published data on combust ion rates, burnout times and particle temperatures obtained from batch experiments. The comparisons reveal that the agreement with data on c ombustion rates and burnout times is in most cases within similar to 3 0%. In addition, these comparisons show that improvement in the predic tive capabilities of the model depends on ability to predict the produ ct CO/CO2 ratio. Copyright (C) 1996 Elsevier Science Ltd.