CHARACTERISATION OF FUEL BRIQUETTES FROM Gmelina arborea (Roxb) SAWDUST AND MAIZE COB PARTICLES USING Cissus populnea GUM AS BINDER

Abstract

Large quantities of agricultural and mill residues which are generated annually in Nigeria constitute environmental health hazards. Densification of these residues which is a major way of converting them to high quality fuel has not been adequately studied in Nigeria. The objective of this study was to develop and evaluate a system for briquetting and combusting Gmelina arborea sawdust and maize cob particles. Gmelina arborea Sawdust (GS) was obtained from a small-scale sawmill in Ibadan while maize cobs were obtained from Oja – Oba market, Ibadan and milled. Moisture Contents (MC) and Bulk Densities (BD) of GS and Maize Cob Particles (MCP) were determined. Gum extracted from Cissus populnea stems was evaluated for its suitability as binding agent for fuel briquettes. The viscosity of the crude gum powder was determined at concentrations of 1-10 % (w/v). A manual briquetting machine and a briquetting stove were developed and evaluated. Briquetting of the GS and MCP was done at gum concentrations of 1-30 % (w/w) and pressure levels of 1.5-5.0MPa using 0.6 mm fine and 1.18 mm coarse particles. Briquette stability was measured in terms of linear expansion with time (1-10080 minutes) while the Compressive Strength (CS), Durability Index (DRI) and Water Resistance Index (WRI) were determined in accordance with ASABE standards. Briquette burn rate and thermal efficiency of the stove were determined using the standard water boiling test. Data were analysed using ANOVA. The MC and BD of GS (10.0 % and 150.0 kg/m3) were higher than those of MCP (9.0 % and 134.0 kg/m3). The gum yield of C. populnea was 1.40±0.05 % at 12.60±0.02 % MC. There was positive correlation between gum concentration and viscosity (R2=0.958). The piston press type briquetting machine produced 50.0 mm diameter and 60.0 mm long hollow cylindrical briquettes and gave a maximum through-put of 0.6 kg/h. The combustion chamber of the clay-lined steel stove accommodated a maximum of 5 briquettes. Minimum gum contents required for durable briquette production were 10.0% and 15.0% for GS and MCP respectively. Increase in binder concentration enhanced the linear expansion of both Gmelina arborea Sawdust Briquette (GSB) and Maize Cob Briquette (MCB) with the increase more pronounced in the MCB than GSB. There was significant difference (p<0.001) in the CS and WRI of the briquettes whereas there was no significant difference (p>0.05) between the DRI values. The strongest and most durable briquettes were obtained using fine particle size at a pressure of 1.5 MPa and 25.0% gum content. The burning rate of GSB was 0.800±0.003 kg/h while that of MCB was 1.000±0.018 kg/h. There was no significant difference (p>0.05) in their burn rate values. However, it took more time to boil one litre of water with GSB (22-24 min) than MCB (16-18 min). Maximum thermal efficiency of the stove was 38.0 %. Cissus populnea gum was suitable for the production of briquettes from Gmelina sawdust and maize cob particles. However, Gmelina arborea Sawdust Briquettes were stronger and more durable but less efficient in combustion than Maize Cob Briquettes.