Exergy analysis of hydrogen production methods from biomass

Hydrogen is considered as a universal energy carrier for the future. Currently 95% of hydrogen comes from fossil fuels but biomass has the potential to become a sustainable source of hydrogen. This paper presents a second law analysis of hydrogen production processes from a variety of biomass feedstocks by thermochemical methods (gasification of wood, straw, vegetable oil, manure, sludge) as well as biochemical methods (fermentation and anaerobic digestion of organic wastes). It is shown that the exergetic efficiency of H-2-from-biomass processes increases with decreasing moisture content in the biomass feedstock. The exergetic efficiency of H-2 production by gasification of more dry biomass is comparable to that of the commonly used steam methane reforming. The detailed exergy analysis of H-2 production by biomass gasification shows that the largest exergy losses occur in the gasifier followed by water separation and syngas compression.