Performance of Fe2O3/CaSO4 composite oxygen carrier on inhibition of sulfur release in calcium-based chemical looping combustion

Chemical-looping combustion (CLC) is very promising with thanks to its efficient and low cost CO2 capture. For calcium sulfate (CaSO4) oxygen carrier, sulfur dioxide (SO2) emission in CLC process limits its practical application. In this study, Fe2O3/CaSO4 composite oxygen carriers with different Fe2O3 loading contents were prepared using impregnation method with natural anhydrite as active support and Fe2O3 as additive. Experiments on the evaluation of their capacities to inhibit SO2 release and enhance the reactivity of CaSO4 were conducted in a laboratory scale fixed-bed reactor under CO-H2-N2 atmosphere. The effects of temperature and Fe2O3 loading content on the performance of Fe2O3/CaSO4 oxygen carriers were investigated in terms of fuel conversion and sulfur inhibition efficiency. Fe2O3 could intensify the reduction of CaSO4 to CaS and raise the calcium sulfide yield, over 85% SO2 released from the decomposition of CaSO4 alone was inhibited by Fe2O3/CaSO4 oxygen carriers with the Fe2O3 loading content higher than 5 wt% at 950 °C. Temperature and Fe2O3 loading content had pronounced positive effect on the reactivity enhancement of CaSO4, with higher conversion of CO and H2 obtained at higher temperature and Fe2O3 loading content. Redox cyclic tests showed that Fe2O3/CaSO4 oxygen carrier could keep a better recyclability and stability than CaSO4. The higher the Fe2O3 loading content, the higher the reactivity and sulfur inhibition ability Fe2O3/CaSO4 oxygen carriers could possess. Overall, the results show that Fe2O3/CaSO4 oxygen carrier displays its promising aspect and could be a good candidate in CLC.