Air–Steam Gasification of Wheat Straw for Bio-hydrogen Production

Conversion of the agro-residues into syngas using air–steam gasification provides a renewable route for hydrogen production from organic material. The study reports the experimental investigation on gasification of wheat straw into hydrogen-enriched syngas using air–steam gasification in a bubbling fluidized bed gasifier. The gasifier was operated at an atmospheric pressure gasifier with fuel processing capacity of 5 kg/h and used low-temperature steam for gasification mixed with air. The wheat straw of particle size 0.6–1.0 mm was used as a feed material for gasification, whereas different bed materials used were sand and olivine. In this study, the temperature was maintained at 800 °C during gasification and the steam-to-biomass ratio was varied between 0.3, 0.4, and 0.5, at a fixed equivalence ratio of 0.3. It was observed that hydrogen (H2) reached the maximum concentration of 7.44% for air gasification, which was enhanced to 13.27% at a steam-to-biomass ratio of 0.5. The highest H2 yield obtained was 0.29 Nm3/kg for the S/B ratio of 0.5 as compared to air gasification, which was about 0.15 Nm3/kg. The higher heating value of the syngas is ranged between 4.22 and 4.60 MJ/Nm3. As the steam used in the present study was lower temperature steam, the narrow steam-to-biomass ratio was used to take care of bed temperature; a more steam introduction at a lower temperature can reduce the reaction temperature, drastically disturbing the gasification process. The gas yield was increased from 2.03 to 2.21 Nm3/kg with an increase in steam-to-biomass ratio from 0.3 to 0.5, whereas a substantial increase in carbon conversion efficiency from 78.91 to 89.38% as the S/B ratio increased from 0.3 to 0.5 was observed. A bubbling fluidized bed (BFB) gasifier was found appropriate for the gasification of agricultural waste residues.