Inert supports enhanced sulphur-resistant of iron-based oxygen carriers in chemical looping combustion of element sulphur

Abstract

Sulphur chemical looping combustion (CLC) produces concentrated SO2 at low reaction temperatures. Here, the reaction mechanism of iron-based oxygen carriers (OCs) with sulphur and the cyclic reaction performance of the OCs were studied. The OCs were prepared on three inert supports (ZrO2, MgAl2O4, and Al2O3) with seven loading ratios using sol-gel method. The effects of the inert support, sulphur gasification temperature, OC reduction temperature, and N2 purge gas flow rate on the reaction between sulphur and OCs were investigated. For both Fe5Al5 and Fe5MgAl5 reductions, the FeO combined with Al2O3 to form FeAl2O4 spinel instead of being reduced further. Nevertheless, no spinel was formed in Fe2O3/ZrO2 (Fe5Zr5) reduction, but the over-reduction of FeO to Fe occurred. The reaction conditions were then optimized. The SO2 yields in the FR reached 87.68–91.61 %, and the FeS and FeS2 formed in the FR released SO2 in the AR. The three oxygen carriers (Fe5Al5, Fe5Zr5, and Fe5MgAl5) exhibited stable reactivity for ten cycles. Overall, Fe5Al5 was the optimal oxygen carrier for sulphur CLC, with respect to oxygen delivery, SO2 concentrations in the FR, and stability in redox cyclic reactions.