Effects of CO 2 /H 2 O on the characteristics of chars prepared in CO 2 /H 2 O/N 2 atmospheres

Abstract CO 2 and H 2 O play vital roles in the evolution of char structures and reactivities, particularly in wet oxy-fuel combustion. This work aims to investigate the effects of CO 2 /H 2 O gasification on the characteristics of char prepared in CO 2 /H 2 O/N 2 atmospheres. Lignite samples from Zhundong coalfield in China were pyrolyzed and gasified in different atmospheres at a slow heating rate of 20 °C/min to generate char. Raman spectroscopy was used to identify the microstructure of coal chars, which was correlated with the char combustion reactivity measured with thermogravimetric analyzer in O 2 /H 2 O/CO 2 atmosphere. The combustion reactivity index T index was correlated with Raman structural parameters to demonstrate the applicability of Raman spectroscopy in evaluating char-combustion reactivity. Results indicated that the gasification of CO 2 and H 2 O with coal significantly contributed to the weight loss of char. The Raman band ratio I (Gr+Vl+Vr) / I D decreased and the total Raman peak area increased upon adding CO 2 and H 2 O. Thus, the char became more condensed and contained additional O-containing functional groups. Char-combustion reactivity in oxy-fuel combustion was decreased which originated from the changes in char structures induced by CO 2 and H 2 O gasification. Moreover, T index had positive and negative linear correlations with the Raman parameters I (Gr+Vl+Vr) / I D and I All , respectively. For char prepared in CO 2 -containing atmosphere, the correlation among T index , I (Gr+Vl+Vr) / I D , and I All can be expressed by the function T index  = 13.2299 I (Gr+Vl+Vr) / I D  − 1.7255E-4 I All  + 421.260 with R  = 0.94.