BIOCHARS FROM SLOW PYROLYSIS OF PEANUT SHELLS, CASHEW NUT SHELLS, AND MILLET STALKS AS VALUE-ADDED PRODUCTS FOR BRIQUETTE PRODUCTION

Abstract

Biomass is nowadays used for producing biochar briquettes through slow pyrolysis technologies namely for cooking purposes in developing countries. This article investigated some properties of biochar obtained from tropical biomasses like peanut shells, cashew nut shells, and millet stalks, pyrolyzed at 400 °C and 800 °C. Firstly the mass yield and energy yield of the biochar were determined. The main properties investigated were obtained by conducting proximate and ultimate analysis, determination of calorific value, FTIR (Fourier-transform infrared) analysis, and thermogravimetric analysis. The results showed that depending on the biomass and the pyrolysis temperature, the biochar yields varied from 20.26 % to 42.79 % while the energy yields varied from 24.24 % to 60.71 %. The highest yields are obtained with the lowest temperature and are all more important with peanut shells. All the biochars had fixed carbon contents greater than 60%, except biochar obtained at 400°C with millet stalks. The millet stalks biochar obtained at 400 °C was the one with the highest ash content (21.41%) and the lowest fixed carbon content (59.31%). It was observed that the more the pyrolysis temperature increased, the more the carbon content increased. The lower heating value of raw biomasses and biochars varied respectively between 18.36 and 22.51 MJ/kg and between 23.83 and 30.85 MJ/kg. FTIR analysis results showed that the O-H and C-O bonds disappeared in the case of biochars obtained at 800 °C. The reactivity of biochars towards O2 showed that for all biochars, ignition temperatures (Ti) were up to 317 °C and the temperatures at maximum mass loss rate were between 438 °C and 501 °C.