Systematic effects of coal rank and type on the kinetics of coal pyrolysis

In this work, the global pyrolysis kinetics of a broad range of coals was studied by means of thermogravimetric experiments (heating rate = 25 degreesC/min). An Arrhenius-based deconvolution model was applied to the experimental DTG curves in order to obtain reliable kinetic parameters for the different DTG peaks. The model assumes that the weight loss rate ascribed to volatile release during primary and secondary pyrolysis is a result of the parallel occurrence of three pseudo-unimolecular nth-order reactions (peaks 1, 2, and 3). The kinetic results were expressed as a function of coal rank (0.43 less than or equal to R-r < 1.14%) and maceral composition in order to obtain reliable kinetic trends. By error minimization, an average apparent reaction order of 1.67 was found. The mass fractions corresponding to peaks 1, 2, and 3 were found to follow definite trends with rank and maceral composition. The temperature of maximum reactivity for peak 1 was almost coincident with that of the maximum overall reactivity and followed clear trends with coal rank and type. The activation energies of peaks 2 and 3 were found to be independent of coal type and clearly related to coal rank. The kinetic parameters (activation energy and preexponential factor) of the three peaks exhibited clear isokinetic effects. It is thought that the deviations of the obtained activation energies from those calculated by the isokinetic effect trends are a consequence of a narrow distribution of activation energies within each peak.