Analysis of reactivity of Fe-based oxygen carrier with coal during chemical-looping combustion

Chemical-looping combustion (CLC) has been suggested as an energy-efficient method for the capture of the greenhouse gas carbon dioxide from combustion. The reactivity of using Fe2O3 as an oxygen carrier during CLC of coal has been investigated experimentally at 800–950°C. The experiments were carried out in a fluidized bed, where the steam acted as the gasification-fluidization medium. The reactivity of Fe2O3 as a function of the reactor temperature, reaction time, and cyclic reduction number was discussed. The reactivity of Fe2O3 oxygen carriers was enhanced as temperature increased at 800–950°C. Moreover, the time of chemical reaction control between the oxygen carrier and coal gasification products decreased with increased reaction temperature. When the reaction temperature was above 900°C, the rate of carbon to form CO2 was higher than 90%; however, it was lower than 75% below 850°C. At 900°C, the dry basis concentration of CO2 decreased with increased cyclic reduction period, while that of CO and CH4 increased. Moreover, the value of the CO concentration was less than that of CH4. The performance of the reacted Fe2O3-based oxygen carriers was also evaluated using an X-ray diffractometer and a scanning electron microscope to characterize the solid residues of oxygen carrier. The results show that Fe2O3-based oxygen carriers are only reduced to Fe3O4. With the increase of cyclic reduction period, the oxygen carrier sinters gradually.