Effect of hydrothermal carbonization temperature on reactivity and synergy of co-gasification of biomass hydrochar and coal

Abstract

In this study, co-gasification reactivity, synergy and kinetics of blended char of bituminous coal (SF) and raw/hydrothermal-carbonization-treated (HTC) rice straw (RS/RSH) at different HTC temperatures (180–240 °C) and gasification temperatures (800–950 °C) were investigated. Moreover, mineral matter transformation and chemical structure evolution during co-gasification were quantitatively investigated to reveal the influence mechanism of binary particle interaction on co-gasification synergy behavior. Reactivity results indicate that co-gasification reactivity of SF-RSH blended char was lower than SF-RS blended char and was decreased with increasing HTC temperature. Synergy factor results show that the existence of synergistic effect during co-gasification contributed to the higher actual blended char reactivity than the corresponding calculated value, which was mainly due to the inhibition effect on active K transformation and the positive effect on carbon structure evolution (i.e., the decrease of ordering degree of carbon structure and the increase of amorphous carbon structure amount) resulted from binary particle interaction during co-gasification. Moreover, synergistic effect was weaker for SF-RSH blended char than SF-RS blended char and was reduced as HTC temperature and gasification temperature increased, which could be well correlated by the weakened inhibition effect on active K transformation, the enhanced promotion effect on active Ca transformation and the weakened inhibition effect on carbon structure graphitization process at higher HTC temperature and gasification temperature. Kinetics analysis demonstrates that activation energies of SF, RS, RSH, SF-RS and SF-RSH char samples were 208.21, 144.74, 160.62–174.01, 161.09, 169.20–178.97 kJ·mol−1, respectively. Moreover, binary particle interaction improved blended char co-gasification kinetics with activation energy reduction of 19.96–31.41 kJ·mol−1 than the calculated values.