Effect of pretreatment on chemical characteristic and thermal degradation behavior of corn stalk digestate: Comparison of dry and wet torrefaction.

In this study, the dry torrefaction (DT) and wet torrefaction (WT) were compared at different temperatures to explore the effect of these pretreatments on the characteristic of corn stalk digestate (CSD) and the thermal degradation behaviors. The results indicated the both torrefactions improved the fuel properties of CSD, including the lower volatiles content, higher carbon content and HHV. The WT showed higher removals of organics and alkali metals, while DT retained more carbon and ash. The SEM, FTIR and XRD analyses indicated the existence of organic coverings of WT samples, and showed richer surface functional groups, relative complete lignin structure and higher crystallinity compared to DT samples. The thermogravimetric analysis displayed the torrefied temperature above 260 °C (DT) or 220 °C (WT) was not suitable for CSD pyrolysis. Besides, the WT samples showed the more concentrated combustion range, while DT tends the burning of CSD to the behavior of coal.