Comparative study of solid biofuels derived from sugarcane leaves with two different thermochemical conversion methods: wet and dry torrefaction

This work describes the conversion of sugarcane leaves into biocoal with two thermal processes: wet torrefaction (subcritical water, 175-250 degrees C) and dry torrefaction (nitrogen atmosphere, 225-300 degrees C). The residence time was 30 min for both processes. The effects on physical and energy characteristics, including mass and energy yield, proximate and ultimate analyses, fiber analysis, higher heating value (HHV), structural parameters determined by Fourier-transform infrared spectroscopy, and O/C and H/C atomic ratios were used for comparisons. The results showed that increasing the reaction temperature lowers the mass yield; however, it also significantly improves the fuel ratio of torrefied samples. The highest HHV of wet and dry-torrefied samples were 23.31 and 22.07 MJ/kg, respectively. The best removal of ash and sulfur content was obtained under wet torrefaction. Moreover, wet torrefaction was recommended as a suitable process for hemicellulose depolymerization. At 250 degrees C, the wet-torrefied sample had the highest fuel ratio (0.48) and was suited for biomass co-firing. The finding that wet-torrefied samples reached the same range of lignite at lower reaction temperatures than dry-torrefied samples was particularly intriguing. Torrefaction at the temperatures below 250 degrees C did not prove to have a statistically significant effect on the energy properties of the dry-torrefied samples. Therefore, wet torrefaction is a promising process in the thermochemical conversion of sugarcane leaves into solid biofuel.

Automated summary

This study investigated the conversion of sugarcane leaves into biocoal through wet and dry torrefaction processes. Wet torrefaction showed better removal of ash and sulfur content, as well as being recommended for hemicellulose depolymerization. Wet-torrefied samples also exhibited higher fuel ratios than dry-torrefied samples at lower reaction temperatures. Overall, wet torrefaction was found to be a promising method for converting sugarcane leaves into solid biofuel.