Upgrading fuel quality of moso bamboo via low temperature thermochemical treatments: Dry torrefaction and hydrothermal carbonization

- Fuel potential was enhanced via hydrothermal carbonization and torrefaction.
- Hydrochar performed better than torrefied bamboo produced at the same temperature.
- Hydrophobicity was obtained at higher treating temperature.
- Removal of hemicellulose was the dominant reaction in hydrothermal carbonization.
- 260 °C was determined to be suitable for hydrochar production.

The application of raw bamboo as biomass energy is restricted due to its large particle size, high oxygen content, low energy density and weak water resistance. In order to upgrade the fuel quality of moso bamboo, dry torrefaction (DT) and hydrothermal carbonization (HTC) have been investigated in this study. The physicochemical properties, thermal stability and microstructures of solid products were examined by varying the reaction temperature among 220, 260 and 300 °C. The results showed that increasing temperature reduced the mass yield and energy yield, however, it significantly improved the calorific value of solid products. Through the HTC process, the bamboo hydrochar obtained the calorific value of 28.29 MJ/kg, the energy yield of 59.77% and the fixed carbon content of 63.08% at the temperature of 260 °C, indicating enhanced potential as a solid fuel. In comparison, the grindability (including particle size and bulk density), hydrophobicity, and thermal stability of torrefied bamboo were considerably lower than that of bamboo hydrochar produced at the same temperature. Furthermore, the transformation of chemical bonds demonstrated that hydrolysis, dehydration and decarboxylation took place during the HTC process. The porous structure was only slightly enhanced with increasing reaction temperature, exhibiting variation consistent with that of hydrophobicity.