A MODEL OF COAL COMBUSTION DYNAMICS IN A FLUIDIZED-BED COMBUSTOR

A model of coal combustion dynamics in a fluidized bed is developed in this study. The model is carried out on the premise that the total combustion response can be decomposed into two distinct processes: volatile combustion and char combustion. In this investigation, combustion dynamics are examined through CO2 transient responses. For an impulse in the feed rate of coal, volatile combustion is modeled as an exponential decay. In contrast with volatile combustion, the transient response of char combustion cannot be approximated by an exponential decay. Instead, the transient model of char combustion is based on a closed-form solution to a population balance equation. This solution is used in conjunction with fragmentation distributions to explain the wide differences observed between the impulse responses of small and large coal particles. To verify this model, theoretical responses are compared with experimental data obtained from batch tests of coal with known initial particle size distributions. Experimental results suggest that particle size distributions -even narrow distributions-significantly affect the transient responses of coal combustion in fluidized beds.