Chemical looping gasification of biomass char in fluidized bed and CO2-enriched atmosphere

Chemical looping gasification (CLG) of biomass is an emerging technology for producing synthetic gas with high content in H₂, CO, and other valuable compounds in alternative to O₂-enriched gasification, an oxygen carrier delivering O₂ to the fuel. In the present paper, the results of CLG experiments at the bench scale are presented with a particular focus on the conversion of biomass char that is the least reactive but most energetic constituent of biomass. Synthetic Cu oxygen carrier and CO₂-enriched atmosphere were used at temperatures of 900 and 945 °C in a fluidized bed. In inert conditions, the char conversion was not complete for the fixed equivalence ratio that was adopted. Conversely, char was fully converted in the presence of CO₂, thanks to the inverse Boudouard reaction. The results show that higher temperature is preferable for thermodynamic reasons, although the related energy balance reduces the range of auto-thermal operability. The CO produced upon combined gasification by O₂ and CO₂ achieved a yield very close to the theoretical value of 78 mmol per gram of char at 100vol% CO₂ and 945 °C.