Relationships between structural features and reactivities of coal-chars prepared in CO2 and H2O atmospheres

Under various combustion process, CO2 and H2O both have important effects in the evolution of the structures and reactivities of chars. The purpose of this study is to investigate the characteristics of coal char after reacted under the atmospheres containing CO2 and H2O in the temperature range of 500-1000 degrees C. Micro-Raman and FTIR spectrometer were used to reveal the evolution of char structural characteristic, and char reactivities were measured at isothermal condition under 70%CO2/30% O-2 atmosphere on a thermogravimetric analyzer (TGA). The experimental results indicate that 700 degrees C was the initial temperature for additional weight loss of char which caused by H2O and CO2 gasification, and the influences of H2O gasification were obviously more drastic than that of CO2 gasification along with lower char yield under H2O containing atmospheres. It was found that more O-containing functional groups contained in the chars which prepared in CO2 and H2O atmospheres and the addition of CO2 accelerated the condensation of aromatic rings in the char, which means a more aromatic structure in char, that is, less aromatic monomers and greater condensation of them in cluster. Condensation of H2O-char and CO2/H2O-char greatly decreased at 500-700 degrees C and then drastically increased at 700-1000 degrees C. The positive correlation between the Raman parameters (I(Gr+ Vr+ Vl)/I-D) and the char reactivity parameters (R-20, R-50, R-80, and R-max) was observed, which can be represented by different linear correlation model under different atmospheres.