Operating conditions-induced changes in product yield and characteristics during thermal-conversion of peanut shell to biochar in relation to economic analysis

The influences of pyrolysis conditions on the products yield distribution and physico-chemical characteristics of biochar derived from peanut shell in a fixed-bed reactor were investigated in this study. The pyrolysis conditions included the pyrolysis temperature (300-700 °C), retention time (15-90 min), heating rate (1-10 °C min−1), gas flow rate (20-200 mL min−1) and feedstock particle size (<0.075, 0.075-0.150, 0.150-0.300 and 0.300-2.00 mm). Various analytical techniques were used to characterize the biochar for ultimate and proximate analyses, higher heating value (23.99-30.44 MJ kg−1), pH (8.11-12.89), electrical conductivity (22.78-34.44 mS cm−1), surface functional groups (acidic, carboxylic and basic groups), Fourier transform infrared spectroscopy analysis, pore volume (0.055-1.241 cm3 g−1) and specific surface area (7.12-20.96 m2 g−1). The results demonstrated that the temperature predominantly regulated the product yields distribution and characteristics of produced biochar. Furthermore, the heating rate considerably influenced the biochar proximate composition, micropore surface area and pore size. Particle size had significant influences on biochar surface porosity and bio-oil yield. The economic analysis of the pyrolysis system indicated its feasibility and superiority with a positive net present value of 12.07 × 106 USD after twenty-five years of operation.