Investigation of mechanical and combustion characteristics of cashew nut and mango seed shells composite briquettes

Abstract

The ever increasing world energy demand, with over dependency on fossil fuel is hampered by adverse environmental effects due to global warming resulting from carbon dioxide emitted during combustion. Majority of Kenyans rely on biomass, whose sustainability is faced with diminishing forest cover, currently at 1.7 %. Hence, there is need to search for alternative environmentally friendly and accessible sources. Availability of mango seed and cashew nut shells, currently considered of no economic value, may be an option for alternative fuel. Although studies have been done on the mechanical and combustion characteristics of varieties of biomass, there is little information on composite briquette produced from the cashew nut and mango seed shells. This study focused on mechanical and combustion characteristics of cashew nut and mango seed shells composite briquette. Cashew nut and mango seed shells were collected, dried, hammer milled, carbonized in muffle furnace at 400oC for 5 mins and cooled. The carbonized shell fines were mixed at varying ratios and particle sizes and bonded with banana peels before compacting at different pressures. Resulting composite briquettes were dried and mechanical and combustion characteristics determined. Density of the briquettes varied from 381.3 Kg/m3, to 763.45 Kg/m3 at the mango: cashew nut shell ratios 5:0, 4:1, 3:2, 2.5:2.5, 2:3, 1:4, 0:5. Moisture content, ash content and calorific value increased from 7.30 %, 5.28 % 16.47 MJ/kg to 11.27 %, 10.37 % and 26.61 MJ/kg respectively as the cashew nut fines in the mix ratios was increased. Durability index, compressive strength and carbon monoxide rose from 95.59 %, 7.44 KN/m2,, 1.80 ppm to 99.1 % , 7.89 KN/m2 and 5.96 ppm respectively. As the particle sizes increased from 3mm to 11mm, the density, moisture, ash content reduced from 729.08 Kg/m3, 7.56 %, 5.94 % to 492.41Kg/m3, 6.88 %, 5.93 % respectively but no significant effect on calorific value. Durability index, compressive strength and carbon monoxide reduced significantly with change in particle sizes from 98.41 %, 7.75 KN/m2 and 5.64 ppm to 95.52 % , 6.37 KN/m2 and 5.21 ppm respectively. As the compaction pressure increased from 5 MPa to 11 MPa, the briquette density changed from 492.41Kg/m3 to 729.08 Kg/m3 but no significant reduction of ash content from 5.94 % to 5.92 %. Calorific value, Carbon Monoxide and durability index increased from 21.60 MJ/kg, 5.21 ppm, 97.14 % to 25.74 MJ/kg, 5.64 ppm and 98.87 % respectively which could be attributed to increased bonding of particles at higher pressure. The resulting briquettes had similar mechanical and combustion characteristics to wood and charcoal, hence could serve as alternative source of energy