A comparative study on the intrinsic reactivity and structural evolution during gasification of chars from biomass and different rank coals

Abstract

This study aims to investigate the intrinsic reactivity and structural evolution of chars that were originated from biomass, lignite and bituminous coal during steam gasification. A cornstalk, a lignite and a bituminous coal were selected to prepare chars by heating up to 1000 °C at a heating rate of 10 °C/min under inert atmosphere. The intrinsic reactivities of chars were then investigated using a fixed-bed reactor along with an on-line gas analysis system. The results showed that the determining factors that affected the intrinsic reactivities of the chars varied with the nature of the precursors. Besides the effect of surface area, the increase of Alkali and Alkaline Earth Metallic species (AAEMs) concentrations in cornstalk char played a key catalytic role in the intrinsic reactivity. The evolution of chemical structure was the main factor affecting the intrinsic reactivity of the lignite char. The relatively stable chemical structures and non-catalytic minerals in the bituminous char led to a constant intrinsic reactivity. The intrinsic reaction rates of the blends of lignite char and cornstalk char were slightly lower than that of the cornstalk char or lignite char, which suggests that their co-gasification caused inhibition on the intrinsic reaction rate. The intrinsic reaction rates of the blends of bituminous char and cornstalk char were higher than that of the bituminous char, and increased with the increasing ratio of cornstalk char. Therefore, a suitable strategy of blending biomass with specific rank coal is expected to bring significantly synergistic effect on the gasification reactivity and further improve the efficiency of co-gasification process.