Energy and exergy analysis and optimization of biomass gasification process for hydrogen production (based on air, steam and air/steam gasifying agents)

Growing the consumption of fossil fuels and emerging global warming issue have driven the research interests toward renewable and environmentally friendly energy sources. Biomass gasification is identified as an efficient technology to produce sustainable hydrogen. In this work, energy and exergy analysis coupled with thermodynamic equilibrium model were implemented in biomass gasification process for production of hydrogen. In this regard, a detailed comparison of the performance of a downdraft gasifier was implemented using air, steam, and air/steam as the gasifying agents for horse manure, pinewood and sawdust as the biomass materials. The comparison results indicate that the steam gasification of pinewood generates a more desired product gas compositions with a much higher hydrogen exergy efficiency and low exergy values of unreacted carbon and irreversibility. Then the effects of the inherent operating factors were investigated and optimized applying a response surface methodology to maximize hydrogen exergy efficiency of the process. A hydrogen exergy efficiency of 44% was obtained when the product gas exergy efficiency reaches to the highest value (88.26%) and destruction and unreacted carbon efficiencies exhibit minimum values of 7.96% and 1.9%. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.