A MODEL OF THE COMBUSTION OF A SINGLE SMALL COAL PARTICLE USING KINETIC-PARAMETERS BASED ON THERMOGRAVIMETRIC ANALYSIS

A mathematical model for the combustion in air of a single entrained s pherical coal particle, 30 mu m in diameter, has been developed incorp orating thermogravimetric analysis data of Whitwick coal. The model is based on a set of ordinary differential equations, describing the rea ction rates and the mass and heat transport processes. The system of e quations was solved numerically. The combustion mechanism of the parti cle was described by locating the reaction zone at the solid surface, where gas-phase combustion of volatiles and heterogeneous reaction bet ween gaseous oxygen and the carbon and hydrogen in the solid occurred in parallel. The combustion process was chemical-reaction-rate-control led, with the oxygen partial pressure at the surface almost that of th e surrounding bulk gas. The simulation results using this model, with the kinetic parameters for devolatilization and combustion derived fro m the experimental thermogravimetric data, are consistent with previou sly reported combustion lifetimes of approximately 1 s, for particles of this size and rank. They are also consistent with the anticipation that higher ambient gas temperatures should result in shorter burn-out times. The use of thermogravimetric data in the modelling of the comb ustion of small particles of these low-rank coals is a potentially val uable method for characterization of feedstocks for pulverized coal-fi red boilers. (C) 1998 John Wiley & Sons, Ltd.