Structural evolution of a bituminous coal char related to its synchronized gasification behavior with H₂O and/or CO₂

This work aims to investigate the structural evolution of the char during gasification under a single or mixed atmosphere of H₂O and/or CO₂ with the synchronized investigation of the effect of the varying char structure on the gasification reactivity. The experimental char was prepared from a bituminous coal at 1000℃. The changes of the char structure along with the progress of the carbon conversion during gasification were characterized using N₂ adsorption, SEM, and Raman spectroscopy. The results revealed that H₂O showed a more dramatically change on the char structure than CO₂ and two reactants had different reaction pathways. The different pathways of reactants affected the evolution manners of the char structure and different gasification reactivity of char was related to structural evolution. The specific reaction rate between the char and CO₂ decreased monotonously with increasing carbon conversion. However, the opposite trends are observed when H₂O exist, either H₂O alone or the mixtures of H₂O and CO₂. The char gasification reactivity was under the common effect of physical and chemical structure. In terms of the mixture of H₂O and CO₂, the significant specific surface area caused by H₂O provided more active sites for CO₂. The interactions between H₂O and CO₂ promoted reaction between C and CO₂ (C + CO₂ → CO) in mixtures of H₂O and CO₂, leading to higher amount of CO and higher specific reaction rate than calculated.