| Abstract: | A mathematical model for the combustion in air of a single entrained spherical coal particle, 30 μm in diameter, has been developed incorporating thermogravimetric analysis data of Whitwick coal. The model is based on a set of ordinary differential equations, describing the reaction rates and the mass and heat transport processes. The system of equations was solved numerically. The combustion mechanism of the particle was described by locating the reaction zone at the solid surface, where gas-phase combustion of volatiles and heterogeneous reaction between gaseous oxygen and the carbon and hydrogen in the solid occurred in parallel. The combustion process was chemical-reaction-rate-controlled, with the oxygen partial pressure at the surface almost that of the surrounding bulk gas. The simulation results using this model, with the kinetic parameters for devolatilization and combustion derived from the experimental thermogravimetric data, are consistent with previously 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 combustion of small particles of these low-rank coals is a potentially valuable method for characterization of feedstocks for pulverized coal-fired boilers. © 1998 John Wiley & Sons, Ltd. |
