An experimental study to investigate the impact of solar drying on emission products of woody biomass in the torrefaction process

Abstract Biomass torrefaction is a thermochemical process that transforms biomass into a more energy-dense fuel, producing solid biochar, volatile organic compounds, and gases such as carbon dioxide (CO₂), carbon monoxide (CO), and nitrogen oxides (NOx). In this study, the effects of solar drying, as a sustainable preprocessing method, and subsequent torrefaction were evaluated under varying initial moisture content levels of 5%, 10%, 15%, and 20%. The drying conditions of wood chips and the torrefaction process were documented for a sustainable biomass drying system using solar energy. Comprehensive proximate and final analysis and flue gas monitoring analyzed the torrefied biomass’s emission characteristics and combustion efficiency. Results showed that higher initial moisture content increased hydrogen and volatile matter, decreased fixed carbon, and marginally raised the higher heating value. This study shows that solar drying optimizes biomass pretreatment and is a cost-effective and environmentally friendly alternative to conventional drying. This work sheds light on the relationship between initial moisture content, emission characteristics, and combustion behavior, aiding bioenergy development.