Coal combustion: Effects of process conditions on char reactivity. Quarterly technical report No. 5, September 1, 1992--December 1, 1992

摘要

During the past quarter, we carried out a study of the kinetics of char combustion, assessed the reproducibility error of our experiments, and continued our systematic study of the effects of particle size and oxygen concentration on the reactivity of chars. The results from the kinetic study indicated that the rate expression for combustion of Illinois No. 6 chars is first order with respect to the oxygen concentration. The activation energy and the preexponential factor for this reaction were also calculated. The reproducibility error assessment shows that the average relative error increases with increasing particle size. Thus, the number of combustion runs needed for accurate measurements of the reaction rate increases with increasing particle size. For combustion in the regime of diffusional limitations, our results show the ignition temperature decreases with increasing pyrolysis heating rates, increasing coal particle size, decreasing heat treatment temperatures and increasing oxygen concentrations. The kinetic parameters (activation energy, preexponential rate factor, and order of reaction) for the combustion of Illinois No. 6 coal were determined using our thermogravimetric reactor with video microscopy imaging (TGA/VMI). In order to obtain a constant slope from the Arrhenius plot, the experiments were performed in the kinetic control regime. Our previous results demonstrated that in this regime char reactivity is independent of pyrolysis heating rate, heat treatment temperature (HTT), soak time and particle size. For this study therefore, we chose to pyrolyze and combust particles from the 28--32 mesh (500--600 (mu)m) fraction of Illinois No. 6 coal.