Optimizing torrefaction of banana waste (peels and rachis) for sustainable biocoal production in rural communities

Abstract

This study investigates the optimization of banana residue's torrefaction, specifically rachis and peel, by evaluating their potential as biocoal. This research aligns with circular economy principles, aiming to reduce waste and enhance the agro-industrial production chain. It also seeks to benefit small-scale farmers, particularly in remote areas without access to advanced technologies or biorefinery systems. Torrefaction conditions were optimized for biocoal quality and combustion emissions reduction using Response Surface Methodology, evaluating temperature (155–325 °C), time (12–68 min), and a 10 °C min⁻¹ heating rate under an inert atmosphere. Analytical assessments included yields, proximate, ultimate and calorific (Higher Heating Value, HHV) analyses, and combustion emissions estimations (CO, CO₂, and NOx). Results demonstrated solid yields ranging from 92.02 to 52.62 % for rachis and 91.92–56.46 % for peel, while HHVs ranged from 15.61 to 17.26 MJ kg⁻¹ and 17.11–20.16 MJ kg⁻¹, respectively. The optimized torrefaction conditions were 255 °C for 60 min for rachis and 249 °C for 20 min for peel. These conditions resulted in an SY of 63.21 % for rachis and 72.15 % for peel, with HHVs of 17.01 MJ kg⁻¹ and 19.87 MJ kg⁻¹ and ash content of 15.78 % and 14.92 %, respectively, suggesting greater energy yield for biofuel application. High ash content suggests the need for pre-treatment techniques or material blending to enhance the usability of biocoal as biofuel. CO₂ emissions for the combustion of optimized biocoal were 1310.75 for peel and 1142.78 kg ton⁻¹ for rachis, with the potential for reduced carbon intensity compared to conventional fuels.