Steam and air fed biomass gasification: Comparisons based on energy and exergy

Results are reported of thermodynamic analyses of a biomass gasification unit in which sawdust is the biomass feed and the gasifying medium is either air or steam. Energy and exergy analyses are performed for the system and each of its components. A parametric study reveals the effect of design and operating parameters on the system's performance and energy and exergy efficiencies. The results show that the adiabatic temperature of biomass gasification significantly changes with the type of the gasifying medium. In addition, the exergy and energy efficiencies are observed to be higher when air is the gasifying medium rather than steam, while the system performance and exergy efficiencies are dependent on the moisture content of the feed biomass. The results are significant because they quantify the strong dependence of biomass gasification, which can be used for syngas or hydrogen production, on moisture content, and gasifying medium. ► Thermodynamic analyses of air/steam-biomass gasification are performed. ► The energy and exergy efficiencies vary with the amount of air supplied to the gasifier. ► Higher efficiencies are achieved for steam gasification with the change in equivalence ratio. ► Exergy efficiency of steam gasification decreases by 8% with 66% increase in biomass moisture. ► This decrease is only 4% for air-biomass gasification process.