Thermal Behaviour and Household-Energy Implications of Rice-Husk–Palm-Kernel-Shell Blends

Agricultural residues such as rice husk (RH) and palm kernel shell (PKS) are abundant, low-cost biomass wastes that can be valorised into briquettes as a sustainable alternative to conventional solid fuels. This study investigated the physico-chemical and thermal properties of briquettes produced from RH and PKS powders blended at RH: PKS weight ratios of 100:0, 90:10 (A), 80:20 (B), 70:30 (C), 60:40 (D), 50:50 (E) and 0:100, with structural and thermal characterisation performed using XRD, FTIR, SEM-EDX, TGA/DTG and DSC. Proximate analysis gave moisture, ash, volatile matter and fixed carbon contents of up to 5.57%, 19.32%, 81.38% and 2.11%, respectively, for the briquettes, with fixed carbon calculated by difference. Compositional analysis showed that RH contained a higher cellulose content (18.24%) than PKS (15.91%), in addition to having more hemicellulose (29.82%) than PKS (17.44%), while PKS was markedly richer in lignin (58.72% against 30.06%). Ultimate analysis indicated carbon, hydrogen, oxygen, nitrogen and sulfur contents ranging from 28.86-43.62%, 13.58-29.25%, 28.79-47.83%, 0.56-1.06% and 0.80-1.08%, respectively. Sample E (50:50) exhibited the highest experimental higher heating value (19.19 MJ/kg), which was 18% above the value predicted from proximate data (15.65 MJ/kg). XRD showed a broad amorphous halo centred near 2θ = 22° in all samples, whereas FTIR confirmed cellulose-, hemicellulose- and lignin-related functional groups, together with silica-related bands in RH. TGA/DTG showed that RH-rich samples decompose at lower temperature than PKS-rich blends. Overall, the findings demonstrate that the optimal RH: PKS blend ratio is property-dependent, providing guidance for tailoring briquette composition to specific fuel applications.