Process simulation and economic and environmental evaluation of a corncob-based biorefinery system

Abstract

A new biorefinery system of producing bioethanol, xylose, electricity and steam from corncob was analyzed by a systematic methodology of process simulation, pinch analysis, economic analysis and life cycle assessment (LCA). The biorefinery system processing 875 kt/a corncob and operating 8400 h/a was first simulated in Aspen Plus. Through process integration in Aspen Energy Analyzer, the biorefinery system reduced 36.8% of cooling utilities and 60.6% of heating utilities, achieved by the installation of 10 heat exchangers. The yield of bioethanol, 194.2 L/t dry corncob, was lower than other biorefineries because hemicellulose in corncob was employed to produce high-valued xylose. However, the production cost, 0.50 $/L bioethanol, made it quite competitive due to the sale price of xylose being more than two times higher than bioethanol. Lastly, the new biorefinery system was evaluated by environmental performance of using LCA method in SimaPro software. Two other biorefinery systems involved with same feedstock and capacity, but different conversion routes were conducted as base cases. The results showed that pretreatment, bioethanol production and wastewater treatment contributed most to the fossil fuels depletion (FDP) and global warming potential (GWP) impacts. The new biorefinery system showed significantly better performance compared with other cases, FDP 25.5 MJ/t dry corncob (0.05 MJ/MJ bioethanol) and GWP 0.45 t CO2 eq/t dry corncob (0.11 kg CO2 eq/MJ bioethanol).