Performance Evaluation of Torrefaction Coupled with a Chemical Looping Gasification Process under Autothermal Conditions: Flexible Syngas Production from Biomass

Abstract

Herein, a coupled biomass torrefaction and chemical looping gasification (BTCLG) process was proposed, and process simulations were performed under autothermal conditions. The effects of operational parameters on product distribution with torrefaction temperatures from 240 to 300 °C, gasification temperatures from 700 to 880 °C, and steam/biomass (S/B) ratios from 0.5 to 1.5 were explored. The results showed that the process could stably operate under autothermal conditions. Torrefaction increased the syngas yield, heating value, and cold gas efficiency by 12.44, 5.11, and 36.73%, respectively. Moreover, it reduced the bed material circulation rate required for autothermal operation by 59.03%. At the torrefaction temperature of 240 °C, the syngas yield reached a maximum value of 0.78 Nm3/kg. Increases in the gasification temperature also positively impacted syngas production. However, the optimal gasification temperature was 810 °C based on the bed material circulation rate constraint. The syngas H2/CO ratio could be flexibly adjusted from 1.62 to 3.34 by changing the S/B ratio to meet downstream demands. Overall, the simulation results support the technical viability and demonstrate the excellent performance of the BTCLG process compared to the biomass CLG process.