Empirical modeling of mechanical and fuel properties of hazelnut shell briquettes as affected by particle size

Particle size is a critical parameter influencing the quality of biomass briquettes, particularly in char-based systems where bonding mechanisms differ from raw biomass briquetting. This study investigates the effect of particle size on the physical, mechanical, and proximate properties of hazelnut shell (Corylus avellana) char briquettes produced under controlled compaction conditions. Briquettes were prepared from three particle size fractions (0.84, 0.42, and 0.25 mm) using a constant binder content, moisture level, compaction pressure, and dwell time. The results show that reducing particle size led to improved bulk density and compressive strength, with finer briquettes exhibiting higher mechanical stability. Proximate analysis revealed a decrease in ash and volatile matter contents and an increase in fixed carbon as particle size decreased, indicating enhanced fuel quality for finer particles. Empirical relationships between particle size and briquette properties exhibited strong goodness-of-fit, with coefficients of determination (R²) exceeding 0.95 within the tested range. These findings demonstrate that particle size significantly influences both the mechanical integrity and fuel characteristics of hazelnut shell char briquettes. The results provide feedstock-specific experimental insights that can support process optimization in char-based briquetting systems, while emphasizing that the derived relationships are valid only within the investigated particle size range.