Chemical-Looping Combustion of Methane Using CaSO4 as an Oxygen Carrier: Effects of MgO Addition

This work focused on the performance of CaSO4 as an oxygen carrier with the addition of varying levels of MgO. The reduction of the oxygen carrier by CH4 was investigated in a laboratory-scale fixed-bed reactor. The effect of the reaction temperature was examined on the reduction of CaSO4. The results indicated that a higher temperature led to high combustion efficiency and induced CaO formation, which decreased the performance and recyclability of CaSO4. The addition of MgO to the CaSO4 accelerated the reduction reaction and impeded the formation of CaO. Moreover, the MgO/CaSO4 composite oxygen carriers manifested a better recyclability with increasing MgO levels of up to 50 wt% by reducing the formation of CaO. However, the combustion efficiency of CH4 was optimal at 30 wt% MgO. Therefore, the mass fraction of MgO must be controlled to confine the side reactions that are catalyzed by MgO itself, yet still help improve the overall performance of the CaSO4-based oxygen carrier.