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.