Estimation of kinetic rate parameters for coal combustion from measurements of the ignition temperature

Combustion reactivity plays a significant role in the development of optimal strategies for the efficient utilization of coal. A promising technique for characterization of combustion reactivity involves measurement of the gas temperatures which lead to the ignition of coal particles of different sizes, and the use of classical ignition theory to extract the relevant reaction rate parameters. This paper examines the influence of the modeling assumptions, within the framework of heterogeneous ignition theory, on the combustion rate parameters calculated from experimental data. It is shown that unequivocal determination of reaction order from ignition data is difficult. Further, the manner in which the rate constant is defined-whether it is based on the external or the internal surface area-exerts a significant influence on the reactivity parameters. The effect of radiation is included in the energy balance and shown to influence the results substantially, for larger particles in particular. Finally, it is shown that combustion reactivity determined from ignition measurements does not differ significantly from other measurement techniques if the effects of radiation and mass transport limitations are accounted for. (C) 1998 Elsevier Science Ltd. All rights reserved.