Sustainable biomass briquettes from rice husk blended with coconut and palm kernel shells: a charcoal alternative for clean cooking in Tanzania

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Biomass briquettes are sustainable alternatives to charcoal and firewood, especially where agricultural residues are abundant. This study examined briquettes from carbonized rice husk blended with coconut shell and palm kernel shell using starch, molasses, and clay binders. Properties evaluated included proximate composition, calorific value, combustion behavior, and mechanical durability. Rice husk briquettes showed poor fuel quality, with ash content of 38–52%, fixed carbon of 21–40%, and calorific values of 2441–3859 kcal/kg, below the recommended ≥ 4300 kcal/kg. Starch binder performed best, achieving 3859 kcal/kg and improved strength over molasses and clay. Blending with higher-energy biomass significantly improved performance. The coconut shell blend (CR40: 40% rice husk, 60% coconut shell) achieved 20% ash, 7% moisture, 18% volatile matter, 55% fixed carbon, and 5277 kcal/kg (∼37–116% increase). The palm kernel shell blend (PR40: 40% rice husk, 60% palm kernel shell) showed 25% ash, 6% moisture, 22% volatile matter, 47% fixed carbon, and 4741 kcal/kg (∼22–94% increase). In contrast, 50:50 blends (CR50, PR50) had lower calorific values (4051–4225 kcal/kg) and higher ash, indicating reduced performance, though still suitable for domestic cooking. Combustion tests for CR40 and PR40 showed burning rates of 5–6 g/min and ignition times of 4–5 min. Mechanical properties were high, with water resistance of 93–95% and shatter resistance of 98–99%, exceeding the 80% standard. Overall, blending rice husk with coconut shell or palm kernel shell enhances fuel quality, combustion performance, and durability, offering a sustainable alternative to charcoal for household cooking and agricultural waste valorization in Tanzania and other developing countries.