Characterization of combined Fe-Cu oxides as oxygen carrier in chemical looping gasification of biomass

Abstract

Chemical looping gasification (CLG) of biomass is an innovative biomass gasification technology, where oxygen carrier (OC) has the effects of oxygen supply, heat transfer and catalyst for syngas production. In order to integrate the synergistic effect between Fe and Cu oxides, a novel combined OC containing Fe2O3 and CuO was produced for biomass gasification and investigated in a batch fluidized bed reactor in this work. At first, an OC with 50 wt.% Fe2O3 and 10 wt.% CuO (Fe50Cu10) was selected as the representative OC to evaluate the superiority of combined OC. The mono-metallic OC of CuO is unsuitable as oxygen carrier in the CLG of biomass due to its too low syngas yield, although CuO can greatly accelerate biomass gasification process. In addition, combined Fe-Cu oxides OC is also superior to mono-metallic OC of Fe2O3 at enhancing carbon conversion efficiency on the premise that syngas yield tended to be close. Then the blending ratio of Fe/Cu was optimized and Fe50Cu10 had been proven to be the optimal combined Fe-Cu oxides OC in CLG. Next, the influences of the factors including gasification temperature, steam mole fraction and O/C ratio on the performance of Fe50Cu10 were investigated. 900 °C is the best temperature for gasification and higher team mole fraction gave rise to higher carbon conversion efficiency and syngas yield, while O/C ratio was somewhat different. The optimal O/C ratio was deemed to be 0.78. Besides, 10 redox cycles were conducted to investigate the stability of combined OC reactivity. The combined OC after 3 cycles performed worst reactivity, while better performance was demonstrated after 7–10 cycles. Based on the analysis of SEM-EDX, it was found that sintering caused by Cu atomic was the main cause of the reactivity decline. In addition, it was inferred that the distribution of Cu atomic in the combined OC was more uniform with the cycle number.