Biomass valorization for energy applications: A preliminary study on millet husk

This study used millet husk which is a waste and gum Arabic as binder to develop briquettes for domestic cooking in Northern Nigeria. The objective was to investigate the effect of particle sizes, compaction pressures and binder concentrations on the physical, mechanical and thermal characteristics of the briquettes. Furthermore, the study also accessed the economic viability of the usage of millet husk briquettes as fuel. Particle sizes of 0.3, 0.4, 0.6 and 1.7mm; compaction pressures of 10, 15, 20 and 25 MPa and binder concentrations (gum Arabic) of 25, 30, 35 and 40% were used to densify the millet husk mixed with gum Arabic at room temperature with the aid of hydraulic press. The caloric value (15.27 MJ/kg) was determined using ASTM D2015, other physical and chemical properties of the millet husk was determined by proximate and ultimate analysis which showed that volatile matter (76%), ash content (6.5%) and sulphur content (0.3%) are within the recommended range for domestic cooking fuels. It was found that the density (438 kg/m³ and 669 kg/m³), impact resistance index (70-93%) and compressive strength of the millet husk briquettes increased with compaction pressures and binder concentrations and decreases with increase in particle sizes, while for porosity of the briquettes, the above case was a reversal. The performance of the briquettes for domestic cooking were accessed by ignition time (109 and 140 s); burning rate (0.09 g/s and 0.18 g/s) and water boiling test which took 5 and 11 min to boil 1 L of water as compared to fuel wood that takes longer. Economic analysis showed that utilizing the millet husk generated in northern Nigeria will lead to huge savings in fuel wood consumption, monetary savings of about ₦ 9,257,869,268.62, and reduction in deforestation and its attendant problems. A structured questionnaire as used to ascertain the acceptability of the produced briquettes. Most of the respondents (90%) in a survey expressed willingness to use millet husk briquette as replacement for wood. The study concludes that millet husk is good for briquetting for energy applications with high potential to reduce energy poverty, minimal waste and reduce indoor pollution for domestic cooking therefore, making millet cultivation more profitable in Northern Nigeria.