X-ray diffraction parameters and reaction rate modeling for gasification and combustion of chars derived from inertinite-rich coals

Abstract

An investigation was undertaken to determine the effect of carbon structural properties on the reactivity of chars derived from inertinite-rich coal. The structures of chars were characterized by X-ray diffraction and the reactivity evaluation with respect to gasification and combustion involving experimentation and reaction rate modeling was carried out. The effect of the aromaticity on the intrinsic reaction rates and associated activation energy for gasification and combustion of chars were determined based on chemical reaction rate controlled kinetics. Two sets of results were examined consisting of gasification with four char samples derived from different inertinite-rich coals prepared with a devolitalization temperature of 900°C (Set 1) and three chars from the same parent coal also rich in inertinites prepared at different devolitalization temperatures, namely 550, 700 and 850°C (Set 2). It was found that the aromaticity and fraction of crystalline carbon of the four chars prepared at the same temperature (Set 1) varied in the ranges 0.85–0.95 and 0.52–0.72 respectively and the chars prepared at different temperatures (Set 2) in the ranges 0.82–0.92 and 0.44–0.74 respectively. The structural properties of the chars within each set of results were also very different which required reaction rate modeling for the determination of intrinsic reactivities. The random pore model with chemical reaction controlling described the reaction kinetics accurately and it was found that the intrinsic reactivity of the char decreased with increasing aromaticity while the activation energies decreased (aromaticity<0.92) which indicated the effect of the variation of the distribution of aromatic/aliphatic structures on the intrinsic reaction rate. It is proposed that the aromaticity of chars be used as a predictive index for char reactivity under chemical reaction controlled conditions.