Environmental and exergetic evaluation of hydrogen production via lignocellulosic biomass gasification

Gasification is a promising pathway for the conversion of biomass into energy products. In particular, the syngas generated through biomass gasification is of great interest for hydrogen production. Based on an overview of technological options, a base-case system for hydrogen production via biomass gasification is defined, and its environmental and thermodynamic performance is evaluated through a life cycle assessment and an exergetic analysis. The case study involves poplar gasification in a low-pressure char indirect gasifier, catalytic tar destruction, cold wet gas cleaning, syngas conversion and hydrogen purification. The calculated exergetic efficiency of the plant is 48%, a value comparable to that of conventional coal gasification technologies for hydrogen production. The total exergy loss of the plant (mainly associated with the flue gas streams) is found to be 4.6% of the fuel exergy provided to the overall plant, while 47% of the overall fuel exergy vanishes as exergy destruction within the individual components of the plant. The life cycle assessment of the system covers from poplar cultivation to hydrogen purification. Seven impact potentials are considered: cumulative energy demand, global warming, ozone layer depletion, photochemical oxidant formation, land competition, acidification and eutrophication. The life-cycle energy balance of the system suggests a relatively promising energy performance. Poplar cultivation and harvesting, biomass pre-treatment and syngas cleaning are identified as the subsystems with the largest contributions to the environmental impacts. Measures to enhance the environmental and energy performance of the system should focus on minimizing the poplar feedstock demand, improving the logistical planning for biomass supply, reducing the natural gas demand of the steam reforming subsystem, and optimizing the electricity demand of the gas cleaning subsystem. Lower consumption levels of fertilizers and diesel for poplar cultivation and harvesting should also be achieved. (C) 2014 Elsevier Ltd. All rights reserved.