Effect of formulation of steady-state heat balance for char particles on AFBC modelling

Abstract

For the solution of population balances of char particles burning in the bed in modelling of an atmospheric fluidized-bed combustor (AFBC), a submodel for calculating the surface temperature of reacting char particles is included by solving the corresponding heat balance. This particle heat balance is strongly interrelated with other submodels through the kinetic term of heat generation at the reaction surface. Three possible formulations for calculating the particle temperature are analysed: 1. (a) without particle heat balance; 2. (b) heat balance around the particle with a log mean of oxygen concentration; 3. (c) heat balance around the particle at each height in the bed. These assumptions are introduced into a model for an AFBC without a plume of volatiles, with slow bubble regime in the bed and with plug flow of gas, using the shrinking unreacted-core model and considering char losses by carryover and overflow. The effect of incorporating these hypotheses in the model is analysed through the solution of the population balance. The results obtained indicate that the effect is appreciable on the carbon combustion efficiency and carbon loading in the bed.