Energy densification of sugarcane leaves through torrefaction under minimized oxidative atmosphere

Worldwide, the annual energy content of sugarcane leaves (SCL) amounts to 4.21 EJ. However, its direct use as a solid fuel is hindered by its inherent characteristics, such as its low bulk density, low energy density, and hygroscopic nature. These characteristics of SCL could be improved through torrefaction. However, in addition to these characteristics, combustion and flow characteristics, expressed in their respective indices, should also meet their desired values as they have direct influence in the later performance of boilers and furnaces. Torrefaction of SCL at various temperatures (250-350 °C) and times (0-75 min) under minimized oxidative atmosphere was investigated in this study to improve its characteristics as solid fuel. The torrefaction performance was not only assessed through the mass and energy yields, but also changes in the combustion and flow indices. Torrefaction at 300 °C & 45 min led to the increase in fixed carbon to as much as 21 g for every 100 g of raw SCL being torrefied, which originally contains 18 g of fixed carbon. Devolatilization during torrefaction not only involves the volatilization of the volatiles but also the formation of additional fixed carbon. The higher heating value (HHV) of SCL increased to as much as ~ 22 MJ/kg after the torrefaction. The resulting SCL torrefied at 300 °C for at least 45 min was found to be suitable for industrial and domestic applications having fuel ratio (FR), combustibility index (CI), volatile ignitability (VI), Hausner ratio (HR), and Carr compressibility index (CCI) falling within prescribed values of 0.5-2.0, 12-23 MJ/kg, > 14 MJ/kg, < 1.34, and < 25, respectively.