Mechanical Performance and Handling Stability of Biochar–Straw Briquettes and Straw–Sunflower Waste–Biochar Pellets

Biochar is a carbon-rich solid with potential as a fuel component, but its friability limits storage and handling. This study evaluated lignocellulosic co-materials for densifying biochar into briquettes and pellets. Briquettes contained straw/biochar ratios of 100/0, 80/20, 60/40 and 40/60; pellets contained straw/biochar/sunflower-waste ratios of 80/0/20, 60/20/20, 40/40/20 and 20/60/20. Mixture moisture was 5.88–6.81% on a wet basis. Peak compressive force was determined from five briquettes and ten pellets per formulation, and retained mass was measured during abrasion. Briquette peak force was greatest at 80/20 straw/biochar (633.02 ± 173.20 N); the formulation effect was significant by Welch ANOVA (p = 0.024) and Kruskal–Wallis testing (p = 0.004). This formulation remained 67.17% mass after 5 min. Pellet peak force was greatest at 60/20/20 straw/biochar/sunflower waste (1130.81 ± 203.69 N). Pellet data were non-normal at 60% biochar; Welch ANOVA was non-significant (p = 0.085), whereas the Kruskal–Wallis test was significant (p = 0.027). Pellet retained mass after 10 min. decreased from 96.19% without biochar to 90.84, 75.80 and 61.40% at 20, 40 and 60% biochar, respectively. A 20% biochar fraction provided the best mechanical compromise. Energy performance requires separate calorimetric and combustion verification.