Interaction effects between sugarcane bagasse and sawdust during their co-hydrothermal carbonisation and co-gasification

Hydrothermal carbonisation (HTC) coupled with gasification presents a promising approach for the effective and clean utilisation of biomass. However, the complex composition of biomass complicates the understanding of its gasification mechanisms. This study examined the individual and co-HTC processes combined with gasification of sugarcane bagasse (SB) and sawdust (SD) to explore their interactions and assess how HTC severity and biomass ratios influence gasification reactivity. The results demonstrated a notable positive synergistic effect during co-HTC of SB and SD at elevated HTC temperatures and increased SB proportions, leading to improvements in mass yield and fuel ratio of the resulting co-hydrochars. Conversely, higher HTC temperatures also led to greater anti-synergistic effects on higher heating value. HTC treatment generally diminished the gasification reactivity of SB and SD, primarily due to the removal of reactive minerals and increased aromatisation. However, raising the SB mass ratio significantly enhanced reactivity, owing to the strong synergistic interaction among their hydrochars. The presence of calcium and iron species, along with the higher volatile content in SB, are likely key factors contributing to this synergistic effect during the co-gasification due to their catalytic activity. Among the kinetic models tested, the grain model (GM), having the highest goodness of fit (R²) value of 0.9984, provided the best fit for describing the gasification behaviour of the samples. Overall, HTC effectively converts biomass into solid with high energy content, offering a robust foundation for expanding the application scope of hydrochars from biomass.