Combustion reactivity of hydrothermally derived biochar from sugarcane green harvesting residues (GHR): An evaluation as a solid fuel

Abstract

This study presents a novel macro-scale non-isothermal thermogravimetric analysis to evaluate the combustion reactivity of hydrochars derived from hydrothermal carbonization (HTC) of sugarcane green harvesting residues (GHR). HTC was applied to enhance the fuel properties of GHR, a biomass with low mass and energy density and high alkaline and alkaline-earth metal content, assessing its viability as a partial replacement for bagasse and coal in industrial boilers. HTC was conducted in a batch reactor without agitation using a particle size of 0.25 mm. A central composite experimental design was employed to evaluate the effects of temperature (200-300 °C) and water/GHR mass ratio (5/1 to 10/1) on mass yield, higher heating value (HHV), and energy density. Reaction time was 30 min with a heating rate of 10 °C/min. Raw GHR and hydrochars were characterized following ASTM standards. The highest dry mass yield (84.5 %) was obtained at 200 °C and a 5/1 ratio, while the maximum HHV (29.2 MJ/kg daf) and energy density (1.71) were achieved at 300 °C and a 10/1 ratio. HTC increased fixed carbon and reduced volatile matter due to dehydration, hydrolysis, depolymerization, oxidation, and carbonization. Through macro-scale non-isothermal thermogravimetric analysis, hydrochar at 200 °C and water/GHR ratio of 10/1 exhibited the highest combustion index (5.15 × 10^-1⁰ %²min^-2°C^-3) and mass yield (84.5 % db). Despite lower volatile matter, its activation energy (178.52 kJ/mol) remained comparable to raw GHR (116.25 kJ/mol), indicating no significant loss in reactivity. These findings highlight the potential of GHR-derived hydrochar as a sustainable alternative fuel for industrial applications.

Keywords: Biomass; Combustion; Hydrothermal carbonization; Macro TGA; Sugarcane green harvesting residues.