Hydrothermal carbonization of waste ginkgo leaf residues for solid biofuel production: Hydrochar characterization and its pelletization

This study explored the potential of hydrothermal carbonization (HTC) for the production of a carbon-rich solid fuel from Ginkgo leaf residues (GLRs). Density, durability, hardness, hydrophobicity, and energy input estimates for HTC treated and untreated GLRs pellets were determined. Results showed that hydrothermal treatment significantly improved the physical properties of pellets made from GLRs, especially, at the temperature treatment of 220 degrees C. Pellet durability and hardness from samples treated at 220 degrees C (HT220) increased from 70.1% and 0.8 N/mm(2) to 96.8% and 2.1 N/mm(2) when compared to those made from untreated GLR (control). Hydrochar pellets had higher fixed carbon contents, elevated heating values, and enhanced energy densification ratio in comparison to the control pellets. The equilibrium moisture content decreased from 13.9% to 4.8% for HT220 pellets. The activation energy of HT220 pellets decreased from 44.6 to 26.8 kJ/mol in the first order reaction model and from 93.9 to 61.2 kJ/mol in the 3D diffusion model compared to the control pellets. The comprehensive combustibility index S was enhanced twice for HT220 pellets. The high durability, low moisture uptake, and improved pyrolysis property indicated that combining hydrothermal carbonization with pelletization is an efficient way for GLRs utilization as solid biofuel.