Mechanical Properties and Performance Characteristics of Shea Kernel–Groundnut Shell–Derived Bio-Briquettes for Rural Energy Applications

The physicochemical, mechanical, and combustion properties of charred-briquettes, made from shea kernel shell (SKS) and groundnut shell (GS), were studied for rural household applications in northern Ghana. The shells were carbonized through thermal pyrolysis and then mixed with a binder (cassava peel) to fabricate solid briquettes at varied material-binder ratios of 90 wt%:10 wt%, 85 wt%:15 wt%, 80 wt%:20 wt%, and 75 wt%:25 wt% for optimization purposes. The briquette’s mechanical properties including compressed density (D_c), relax density (D_r), relaxation ratio (R_r), shatter resistance index (SRI), water penetration resistance index (WPRI), as well as compressive and tensile strength tests were determined. The D_c, D_r, SRI, and WPRI for both materials’ briquettes largely increased as percentage binder content increased, whereas the R_r decreased. The decreasing R_r improves mechanical stability, while a high WPRI indicates effective heating; both parameters are desirable for quality briquette production. The compressive strength test reported in this work ranged from 392–682 N/mm² for SKS briquettes and 406–687 N/mm² for GS briquettes. Whilst the tensile strength test reported for SKS briquettes ranged from 275–422 N/mm² and 312–474 N/mm² for GS briquettes. The water boiling time recorded for SKS briquette samples was 38.4 min at a burning rate of 2.81 g/min, whilst GS briquettes recorded 43.5 min at 2.305 g/min burning rate, respectively. The calorific values for SKS and GS briquettes were 26.15 MJ/kg and 25.33 MJ/kg, while the thermal efficiencies recorded were 49% and 38%, respectively.