Conversion of biomass into biofuel by microwave pyrolysis: Assessment of energy and exergy aspect

Higher heating value, energy and exergy analysis of bio-oil and biochar from microwave pyrolysis have been assessed. The energy efficiency for the pyrolysis system has been analyzed by the comparisons of energy based on heating values. The exergy analysis was done using standard relationships by the fraction of energy actually available for practical uses as biofuel. The yield of bio-oil and its higher heating value (HHV) were increased by 2–13% and 25–130% respectively when the microwave power increased from 500 W to 700 W, then both are decreased at 900 W. Using activated carbon (AC) had a remarkable effect on increasing the yield and HHV of bio-oil by 18–31% and 3–7 times respectively more than other cases. By using the additives, the yield of biochar decreased remarkably, while its HHV increased by 12%-40% compared to without additive. The maximum energy and exergy rate (1.74 MJ/h) of the bio-oil were obtained at 700 W level of microwave power using AC additive, while for biochar were 1.95 MJ/h and 2 MJ/h when no additive used. The maximum values of energy and exergy of the bio-oil were computed to be 27% and 26% respectively at 700 W using AC as an additive. The maximum values of energy and exergy efficiency of biochar were calculated to be 33% and 32% respectively when pyrolyzed at 500 W using AC. The energy and exergy efficiencies of the pyrolysis system were computed to be maximum value of 53.3% and 52.8% respectively at 700 W using AC additive.