Influence of binder rate, pyrolysis temperature and volume of biochar briquettes on CO and PM2.5 emission factors and thermal efficiency

Abstract

Several combustions tests using biochar briquettes of peanut shells and charcoal from Ziguinchor town in a locally named “jambar” stove are reported in this article. The biochar briquettes were produced following a 23 factorial plan for testing the influence of the rate (R) of binder on a dry basis, the pyrolysis temperature (T), and the volume (V) of ellipsoid shape biochar briquette on emission factors (CO and PM2.5) and thermal efficiency. The minimal and maximal levels were defined as following R = [6%; 10%], T = [400 °C; 800 °C], and V = [7 cm3; 31 cm3]. Wheat flour was used as a binder. A specially designed hood with an extractor fan is used to collect the overall emissions produced during a simulated household cooking task. Physicochemical characterizations are conducted to determine immediate analysis, elemental analysis, and calorific value of the produced biochar briquettes and the charcoal from Ziguinchor town. The results of the physicochemical characterizations show that all produced biochar briquettes had a content of fixed carbon greater than 60%, ashes content below 18%, and moisture content below 8%. All biochar briquettes presented a lower heating value (between 24.35 MJ/kg and 26.55 MJ/kg) below those from Ziguinchor charcoal (28.02 MJ/kg). The results show that the CO emission factors varied from 140.08 g/kg to 217.09 g/kg when the levels of factors changed. The CO emission factor of charcoal from Ziguinchor was 178.46 g/kg. The lowest CO emission factor, 140.08 g/kg, was obtained for the lower levels of the factors (R = 6%, T = 400 °C, and V = 7 cm3). The PM2.5 emission factors of the biochar briquettes varied from 0.57 mg/kg to 1.53 mg/kg and were equal to 7.91 mg/kg for Ziguinchor charcoal. The lowest PM2.5 emission factor, 0.57 mg/kg, was obtained for the levels of the factors (R = 6%, T = 800 °C, and V = 31 cm3). It was generally observed that the more is the rate of binder and the volume of the briquette, the more is the emissions of PM2.5 and CO, respectively.