Abstract:
This work studied the effect of the binary and ternary combinations of pine needle (Pinus pinaster ) dust and bambara nut (Vigna subterranea) chaff with coal dust for briquette production. Briquettes of 100% of the pure coal and the biomass were produced first. The ratios for the blending were as follows 1:1 for the binary combination of each biomass with coal and with themselves, and 1:1:1 for the ternary combination of the two biomass with coal. The feed stocks were dried to a moisture content of 5-10% and ground to a particle size of 0.8 mm. Desulphurization, homogeneity and binding were successfully achieved by addition of calcium hydroxide (Ca(OH)2), water and starch, respectively. The mixture was compacted into a rectangular briquetting mould of about 3.8 cm in diameter and height of about 2.5 cm using a manual briquetting machine at a pressure of 5 Mpa for 2 hour. The briquettes were brought out and sun dried for 10 days for further removal of moisture and curing. Proximate analyses, calorific value, combustion and emission analyses, thermogravimetric analyses (TGA) and differential thermogravimetric analyses (DTA) were carried out in line with ASTM D-3173 specifications. The result of the calorific values showed that coal briquette had the highest heating value (23,471 KJ/kg) while the briquette made from Bambara nut chaff had the least calorific value (16,150 KJ/kg). It was found out that the binary and ternary blends with biomass reduced the calorific value of coal briquette. The result of the TGA/DTA analyses showed that coal briquette was the most stable at higher temperatures when compared with the two biomass while pine needle briquette had the least stability during combustion. The thermal stability as well as the percentage combustible fuels increased in the binary and ternary blends with coal. The combustion and emission analyses showed that the blended briquettes had better combustion characteristics than the single coal and biomass briquettes in terms of burning rate, time required to boil water, specific fuel consumption and thermal efficiency. The concentration of CO and CO2 emitted by the coal briquette was the highest (33 ppm and 99 ppm respectively) even though they were within the permissible range stipulated by the World Health Organization Ambient Air Quality Standard (WHO-AAQS) and National Ambient Air Quality Standard (NAAQS) which is 35 ppm for CO and 600 ppm for CO2. However, it was observed that blending the various biomass with coal reduced the concentration of the CO and CO2 evolved during combustion. Therefore, the binary and ternary blends of coal with the two biomass reduced the CO and CO2 emissions. The ternary blend had the highest particulate matter (3,359 µg/m3) followed by the coal briquette (3,051 µg/m3). However, even though the binary combinations of the biomass with coal reduced the concentration of PM evolved, they were still higher than the permissible range in the atmosphere as stipulated by WHO-AAQS and NAAQS which is 150 µg/m3.
