Improving the energy balance of microalgae biodiesel: Synergy with an autonomous sugarcane ethanol distillery

Abstract

This study analyzed the algal biodiesel production system via dry-route, based on Chlorella vulgaris cultivated in raceways, by comparing the Net Energy Balance (NEB) and the Fossil Energy Ratio (FER) of five scenarios: C0 (single system of biomass production); C1 (C0 + pyrolysis of the microalgae press cake); C2 (C0 + anaerobic co-digestion of the microalgae press cake); C3 and C4 (same conditions of C1 and C2, but integrating both scenarios into an autonomous ethanol distillery). Each scenario was analyzed under de perspective of energy allocation (a) and system expansion with avoided product (b). The results showed that with the energy allocation, only C3a and C4a improved the values of baseline scenario (C0a) for NEB, in 120% and 72% respectively. When the system expansion is considered, none of the scenarios was better than the respective baseline scenario (C0b), in relation to the NEB. Considering the FER, C3a increased in 3.4% the values of C0a, while C3b and C4b increased the values of C0b in 54.1% and 28.8%, respectively. In general, system expansion showed the best scenarios: for the NEB C0b showed the highest average values while C3b showed the highest average values for the FER.