Effect of hydrothermal carbonisation temperature on the ignition properties of grape marc hydrochar fuels

The ignition properties of solid hydrochars and their slurries derived from the hydrothermal carbonisation (HTC) of grape marc were evaluated and compared using radiation heating methods. Solid hydrochar samples produced at 180 °C, 220 °C and 260 °C with median particle sizes of 10 – 14 μm were mixed with water to prepare the hydrochar slurries for ignition experiments. The 260 °C solid hydrochar exhibited the shortest ignition delay time (0.2 s) and the lowest ignition temperature (179 °C). It might be due to the presence of secondary char, which was evident by a unique peak appearing in both thermogravimetric and radiation heating profiles of the 260 °C solid hydrochar. This property also demonstrated a significant impact on the combustion characteristics of its slurry. The 220 °C solid hydrochar was ignited after the 260 °C solid hydrochar (0.28 s) while its slurry experienced the longest ignition delay time among the rest (2.38 s). These observations could be related to the hydrophilic content on the outer layer of 220 °C solid hydrochar. This hydrochar and its slurry, however, ignited at the similar temperature with the 180 °C solid hydrochar and its slurry respectively, indicating that the volatile matter content had a more significant effect on the ignition temperature of the 220 °C solid hydrochar than its hydrophilic components. Results from this study further demonstrated that the hydrochar slurry derived from grape marc is highly ignitable which might provide an alternative pathway to recycle grape marc into a sustainable liquid fuel.