In-situ decoupling effect of H2O on the whole process of coal gasification in MFBRA and TG-FTIR-MS

Abstract

O2/H2O oxy-fuel combustion, as one of the most promising combustion technologies for CO2 reduction, has become a hot spot around the world. In oxyfuel combustion, H2O gasification has an important effect on the overall reaction process. This paper used Chinese Shenhua coal as raw material to decouple the effect of H2O on the whole process of raw coal-H2O gasification reaction. At 800 °C in 15 vol.% H2O, the changes of gas-liquid-solid phase product concentration and the development of char structure in the coal-H2O gasification were investigated. The MFBRA was used to analyze the rapid coal-H2O gasification reaction, while the slow-heating-rate gasification of coal was analyzed by TG-FTIR-MS. The results show that in the rapid single-particle reaction at 800 °C, H2O promotes the whole devolatilization of coal, with a certain inhibitory effect on the secondary gas-phase reaction, especially for the H2 release. H2O increases the oxygen-containing functional groups on the char surface and increases the structural defects in char. H2O would increase the −COO- groups, and promotes the consumption of CC on the surface. H2O has an obvious etching effect on the char surface. For slow-heating-rate gasification of coal, the reaction has obvious secondary weightlessness, and H2O promotes initial devolatilization, but has an inhibitory effect on the secondary one. At >700 °C, the H2O gasification is more pronounced than that of a single-particle rapid reaction. H2O reduces the activation energy of the initial stage and increases the reaction activation energy of the secondary one during devolatilization. H2O can promote the consumption of aromatic liquid-phase products such as toluene and phenol during devolatilization of pulverized coal under the slow-heating condition.