Exergy analysis of alternative configurations of biomass gasification-mixed alcohol production system via catalytic synthesis and fermentation

In-depth exergy analysis of three conceptual biomass-mixed alcohol systems using syngas platform has been studied, according to the distribution strategy of synthesis tail gas and syngas. The system configurations are base case, cascade case and parallel case. The results show that higher alcohol yield (C2+OH) is highest in base case, which is a catalytic synthesis process with synthesis tail gas recycling. Yet its exergy efficiency is lower than that of 43.8% in the hybrid conversion configuration of cascade case, of which synthesis tail gas is recycled to an additional subsystem for gas fermentation. And it has increased bioconversion of COX components (CO and CO2) in tail gas for ethanol production under moderate bioreaction condition and biomass carbon utilization ratio of 38.8% is obtained in cascade case. With the detailed exergy analysis at the levels of system, subsystem, and operation component, it highlights that the subsystems of gasification and steam & power generation contribute above 70% of total system exergy destruction, mainly from gasifier and combustor. The results of this study provide a further understanding towards bio-mixed alcohol production configuration to improve its thermodynamic performance as exergy efficiency via the hybrid conversion processes of catalytic synthesis and metabolic fermentation pathway.