Sustainable fuel production: briquetting and characterization of torrefied pine needle biochar

The sustainable conversion of lignocellulosic residues into solid biofuels provides an environmentally sound approach to renewable energy generation. This study investigates the production and characterization of briquettes from torrefied pine needle biochar using four locally available binders – animal fat, molasses, starch and bentonite powder – at varying concentrations (15–30 wt%). Briquetting was performed via densification using a hydraulic press, followed by comprehensive physicomechanical and combustion analyses in accordance with International Organization for Standardization (ISO) and American Society for Testing and Materials (ASTM) standards. Results demonstrated that binder type and proportion significantly influenced briquette quality. Animal fat at 20 wt% (A20) achieved the highest calorific value (31.20 MJ/kg), favourable ignition and burning behaviour (5 s and 45 min) and minimal emissions (CO = 27.35 ppm; no detectable SOx or NOx). Bentonite produced the most durable briquettes (compressive strength = 3.00 MPa; shatter index = 96.20%) but exhibited high ash and SOx emissions. The findings confirm that torrefied pine needle biochar can serve as an effective feedstock for clean solid biofuel production and that animal fat is an optimal binder balancing mechanical integrity, energy efficiency and environmental performance for decentralized rural energy systems.