Exergy analysis of thermochemical ethanol production via biomass gasification and catalytic synthesis

In this paper an exergy analysis of thermochemical ethanol production from biomass is presented. This process combines a steam-blown indirect biomass gasification of woody feedstock, with a subsequent conversion of produced syngas into ethanol. The production process involves several process sections, including biomass drying and gasification, syngas cleaning, reforming, conditioning, and compression, ethanol synthesis, separation of synthesis products, and heat recovery. The process is simulated with a computer model using the flow-sheeting software Aspen Plus. The exergy analysis is performed for various ethanol catalysts, including Rh-based and MoS2-based (target) catalysts as well as for various gasification temperatures. The exergetic efficiency is 43.5% for Rh-based and 44.4% for MoS2-based (target) catalyst, when ethanol is considered as the only exergetic output. In case when by-products of ethanol synthesis are considered as the additional output the exergetic efficiency for Rh-based catalyst increases to 58.9% and 65.8% for MoS2-based (target) catalyst. The largest exergy losses occur in biomass gasifier and ethanol synthesis reactor. The exergetic efficiency for both ethanol catalysts increases with decreasing gasification temperature.