Interactions of H2O and O2 with char during gasification in mixed atmosphere analyzed by isotope tracer method and in-situ DRIFTS

Abstract

The interactions of char with H2O and O2 were important for describing the synergistic mechanism of char gasification in H2O/O2 atmosphere. The gases produced during gasification in specific atmospheres were tracked by isotope-labeled oxygen tracing experiment. The interactions of H2O with char and O2 with char during gasification in H2O and O2 atmospheres were separately studied. This helped to explore the interactions between H2O and char and O2 and char during the gasification in mixed-gas atmosphere. It was found that H2O inhibited oxidation of char during gasification, whereas O2 promoted the char-H2O reaction in mixed atmosphere. The overall gasification reactivity in mixed-gas atmosphere was determined by superimposing the effects of O2 on char-H2O reactions and the effects of H2O on O2-char reactions. This could also explain the reason for the influence of H2O on the overall changes in reactivity, based on O2 concentration. The interactive mechanisms during char gasification with H2O and O2 atmospheres were investigated by in-situ DRIFTS experiment and molecular dynamics simulation. In the H2O/O2 atmosphere, H2O was more likely to promote the curling of char structure. The free H radicals obtained in the decomposition of H2O molecules consumed the active sites of reaction between char and O2 and decreased its reactivity. Oxygen could inhibit the curling of the char structure caused due to water and promote the formation of OH radicals. This in turn, promoted the cracking of aromatic rings, increased the number of sites for reaction between char and H2O, and improved the gasification of char in H2O. In case of mixed-gas atmosphere, the interactions between isotope decoupled single reactions could provide new understanding.