ABSTRACT
In this study, a simple four-mould hydraulic piston press biomass hollow briquette making machine, suitable for household and small-scale production of circular briquettes with a centre hole was developed. The briquetting machine was operated using a 4-tons hydraulic jack. Other members of the machine include: the mould, pistons, lower and upper compression plates, jack head and jack seat plates, and the machine stand. The performance evaluation of the machine was carried out using sorghum and millet stalk at moisture content of 8% and 6 % respectively. The biomass material was milled using hammer mill with sieve sizes 7mm (P1), 5mm (P2), and 3mm (P3). Briquettes were produced from mixture of biomass at these three particle sizes P1, P2 and P3 and cassava starch binder at three binder ratios of 20% (B1), 30% (B2) and 40% (B3) by weight of biomass material. Four physical properties namely - compressed density, relaxed density, relaxation ratio, and shattered index of the briquettes; and five thermal properties namely - heat calorific value, ash content, volatile matter, fixed carbon content and thermal efficiency of briquetting materials were determined. The machine evaluation was based on Complete Randomized Design (CRD). The data obtained was statistically analyzed using Statistical Analysis System (SAS 9.1) software. Biomass particle size was found to be significant at 1% probability level on physical properties for sorghum-stalk briquette except on relaxation ratio, which was significant only at 5% probability level. The physical properties of sorghum-stalk briquettes improved with decrease in particle size. Mean values of 727.67kg/m3, 222.35kg/m3, 89.57% and 3.28 were recorded for compressed density, relaxed density, shattered index and relaxation ratio, respectively at sorghum-stalk particle size P1(3mm). Binder ratio B2 was found to have the best effect on the compressed density and relaxed density of sorghum-stalk briquettes while relaxation ratio and shattered index of sorghum-stalk briquettes improved with increase in binder ratio to B3. Particle sizes and binder ratio were found to be significant at 1% probability level on the thermal properties of sorghum-stalk briquettes, with optimum mean values of 17.726 MJ/kg, 1.6%, 24.60 % and 24.66% for calorific value, ash content, volatile matter and thermal efficiency respectively at P3. The thermal properties of sorghum-stalk briquette and Millet-stalk briquette were found to improve with decrease in binder ratio. However, starch binder was found to have no significant difference on the physical properties of millet-stalk briquettes. The physical properties of millet-stalk briquettes increased with decrease in particle size. Mean values of 814.41kg/m3, 225.34kg/m3 and 99.49% was obtained for compressed density, relaxed density and shattered index, respectively for millet-stalk briquette at particle size P1(3mm). While particle size has no significant difference on the relaxation ratio of millet-stalk briquettes. On the other hand, particle size P2 gave optimum mean thermal property values of 16.692 MJ/kg, 2.9%, 26.20 % and 28.15% for calorific value, ash content, volatile matter and thermal fuel efficiency respectively. Generally, the constructed briquetting machine is capable of producing quality briquettes from sorghum and millet stalk biomass at particle sizes 3mm (P3) and 5mm (P2) respectively. The developed prototype briquetting machine has a production capacity range of 4.64 kg/hr - 5.26 kg/hr depending on the material used in producing the briquette
