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

Abstract

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 (PM2.5) respectively, which are below WHO Air Quality Standard safe for domestic uses. Binderless T. cacao pod produced more harmful CO and PM2.5 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.