Determination of physical and combustion properties of blended briquettes of carbonized sawdust and banana leaves and pseudo stem waste

Abstract

Instability in the world’s petroleum is occasioned by perpetual escalation in petroleum prices, increasing environmental effect from exhaust emissions has prompted the search for renewable sources of fuel. Currently in Kenya, biomass such as sawdust from sawmill industries and agro wastes, like banana leaves and pseudo stem, are potential sources of renewable energy. However, in most cases biomass is normally discarded in the fields with no value addition and also little information exists on their use as fuel in blended briquettes. Consequently, this study investigated the use of carbonized sawdust and banana waste as raw materials for briquettes production as an alternative energy source. Specifically, the study aimed at characterizing physical properties of the raw materials, fabricating blended briquettes at varying mix ratios/particle sizes and characterizing physical and combustion properties of the blended briquettes. In the study, pseudo stem and banana leaves from Musa acuminata AAA species and sawdust from Eucalyptus tree species were collected, dried to 8 % moisture content, hammer milled, sieved and carbonized in muffle furnace at 400 °C for 5 minutes. Blended briquettes were produced at constant compaction pressure of 5 MPa at varying blend ratios(1:0,4:1,3:2,1:1,2:3,1:4, 0:1)and particle sizes(2.5 mm, 5 mm, 7 mm, 9 mm,11 mm)using molasses as a binder. The briquettes were then characterized in terms of mass density, durability index, ash content, moisture content, volatile matter and calorific value. Raw materials: sawdust, banana waste and molasses had moisture contents of 12.52 %, 14.63 % and 22.23 %; volatile matter of 25.32 %, 31.45 % and 43.25 %; calorific value of 15.92 MJ/kg, 12.35 MJ/kg and 11.24 MJ/kg; ash content of 5.79 %, 6.89 % and 8.00 %, respectively. The density ranged from 392.54 kg/m 3 to 681.21 kg/m 3 , calorific value,23.40 MJ/kg to 25.92 MJ/, ash content, 6.89 % to 5.79 %, moisture content, 11.10 % to 7.45 %, durability index,95.35 % to 99.70 % and CO emission, 5.64 ppm to 1.74 ppm. In addition, as the particle sizes were increased from 2.5 mm to 11 mm, the briquettes’ moisture content ranged from 7.22 % to 6.98 %, ash content,5.82 % to 5.83 %, CO emission,5.87 ppm to 5.20 ppm, calorific value,26.49 MJ/kg to 25.84 MJ/kg, density,763.33 kg/m 3 to 557.68 kg/m 3 and durability index,97.77 % to 93.43 %. In conclusion, sawdust had better calorific value, lower ash and moisture contents, lower volatile matter and higher mass density than banana waste. Mix ratio of 1:1 provided optimal durability and moisture content in briquettes while that of 3:1 gave optimal CO emission. An increase in sawdust content increased both calorific values and ash content of the briquettes. Lastly, blended briquettes with fine particles have higher mass density, calorific value, durability index, and CO emission than those with coarser particles. From the study, it is recommended that briquettes with high and fine sawdust content (50% above) should be used owing to their good durability, low moisture content, low CO emission and higher calorific value. Future studies should determine effects of interaction between variables such as compaction pressure, blend ratio and particle sizes on combustion properties.