Sintering and agglomeration of Fe_2O_3-MgAl_2O_4 oxygen carriers with different Fe_2O_3 loadings in chemical looping processes

摘要

Fe2O3-based chemical looping combustion can be combined with steam-iron reaction and dry reform of methane for high-value-added products if Fe2O3 is deeply reduced. However, the deactivation caused by sintering and agglomeration worsens, which is an essential issue to be solved. In this study, the stability of Fe2O3-MgAl2O4 oxygen carriers was investigated not only in a packed bed reactor but also a fluidized bed reactor using CO as fuel and air as oxidant at 850 degrees C. Four oxygen carriers, with Fe2O3 loadings of 20 wt%, 30 wt%, 40 wt% and 50 wt%, were prepared through coprecipitation method. The results of 30 cycles in the packed bed reactor showed that the rate of CO2 production for each oxygen carrier deteriorated with cycling, indicating each oxygen carrier suffered deactivation. The CO2 yield of the oxygen carrier with 20 wt% Fe2O3 during the reduction stage dropped from 4.23 mol/kg Fe2O3 to 2.46 mol/kg Fe2O3, while that of the oxygen carrier with 50 wt% Fe2O3 changed from 7.26 mol/kg Fe2O3 to 2.56 mol/kg Fe2O3. Also, the SEM images after cyclic experiments demonstrated the size of crystallite for oxygen carrier with 20 wt% Fe2O3 was the smallest. In addition, the cycles in the fluidized bed reactor exhibited that defluidization occurred to all oxygen carriers except the one with Fe2O3 content of 20 wt%. These results proved the positive effects of decreasing Fe2O3 proportion on sintering and agglomeration.