Binder-type effect on the physico-mechanical, combustion and emission properties of Alstonia boonei De Wild. sawdust and Theobroma cacao L. pod biochar briquettes for energy applications

by Mark Glalah, Charles Antwi-Boasiako, Derrick Adu-Gyamfi

Energy application potential from the abundant biomass residues is inadequately exploited. Over-dependence on forest trees, its negative environmental impacts, and ever-rising energy costs require alternative production technologies including briquetting. The physico-mechanical and combustion properties of binderless and bindered Alstonia boonei sawdust and Theobroma cacao (cocoa) pod briquettes, carbonized in a steel kiln (at 410±5°C, and a heating rate of 4°C/min from the ambient temperature of 25°C), piston-pressed at 9.0 MPa, were studied. The binders were starch, wax, and clay. Starch-bindered T. cacao pod briquettes recorded the maximum bulk density (640 kg/cm³), while basic density was greatest for sawdust/clay briquette (433 kg/cm³). Sawdust/wax briquette produced much Water Resistance Capacity (76.76%) with safer carbon monoxide (CO) emissions (0.67 ppm). A. boonei sawdust/starch briquettes recorded the greatest calorific value (24.023 MJ/kg), least specific fuel consumption (0.0483 kg/l), and slowest burning rate (0.0005 kg/min). All but T. cacao pod/starch and Sawdust/starch emitted CO below the safe air quality Standard of ≤ 6ppm (24h mean). Binderless sawdust, sawdust/starch and T. cacao pod/starch briquettes recorded 47.86, 20.95 and 11.40 μg/m³ particulate matter (PM_2.5) respectively, which are below WHO Air Quality Standard safe for domestic uses. Binderless T. cacao pod produced more harmful CO and PM_2.5 than its non-bindered A. boonei sawdust counterpart. Clay-bindered briquettes were the most durable. Briquetting, ‘a waste-to-energy technology’, enhances bio-residue management for domestic and industrial spaces in the global energy mix.