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

Abstract

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 Fe 2O 3 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 Fe 2O 3 as a function of the reactor temperature, reaction time, and cyclic reduction number was discussed. The reactivity of Fe 2O 3 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 CO 2 was higher than 90%; however, it was lower than 75% below 850°C. At 900°C, the dry basis concentration of CO 2 decreased with increased cyclic reduction period, while that of CO and CH 4 increased. Moreover, the value of the CO concentration was less than that of CH 4. The performance of the reacted Fe 2O 3-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 Fe 2O 3-based oxygen carriers are only reduced to Fe 3O 4. With the increase of cyclic reduction period, the oxygen carrier sinters gradually.