Influence of temperature and process water circulation on hydrothermal carbonization of food waste for sustainable fuel production

Abstract

To address the challenge posed by energy shortages, this study focuses on the conversion of food waste (FW) into valuable resources. Employing hydrothermal carbonization (HTC) technology, the research successfully converted FW into an efficient solid fuel. Furthermore, it conducted an extensive investigation into how hydrothermal temperature (ranging from 180 to 260 °C) and the recycling of process water (repeated four times) influence the physical and chemical properties, as well as the combustion characteristics, of hydrochar fuel. The study's findings reveal that with an increase in hydrothermal temperature, the hydrochar yield decreases. However, this reduction can be mitigated by increasing the number of process water cycles. Notably, when the hydrothermal temperature surpasses 220 °C, the O/C and H/C ratios of hydrochar fall within the range characteristic of lignite, resulting in a higher heating value (HHV). Moreover, as the hydrothermal temperature and the number of process water cycles rise, the –C−(C, H)/CC bonds in aromatic vibrations become stronger, indicating the occurrence of aromaticization and polymerization reactions during this process. Hydrochar exhibits a more stable covalent cross-linked structure, which broadens its combustion range and reduces its reactivity. The combustion rate of hydrochar is significantly lower than that of FW, implying that it is more readily combustible. In summary, the utilization of HTC on FW and the recycling of process water can effectively transform it into a more stable solid fuel.