Development and performance of binder-supported CaSO4 oxygen carriers for chemical looping combustion

Chemical-looping combustion (CLC) has been recognized as an energy-efficient method for CO2 capture. For calcium sulfate (CaSO4) oxygen carrier, the rapid fall in the mechanical strength and reactivity limits its application in CLC. In this study, Taguchi robust design method with L9 orthogonal array was implemented to optimize extrusion condition for the preparation of binder-supported CaSO4 oxygen carriers. The orthogonal experiment results showed the addition of SB powder enhanced both mechanical strength and conversion of CaSO4, and the optimal extrusion condition was 30 g CaSO4, 12 g SB powder, 2.5 mL acetic acid, and 15 mL water. The favorable oxygen carriers were comprehensively studied in a fixed bed reactor. The results of reduction test showed the mass-based reaction rates of the binder-supported CaSO4 were significantly increased, because the fresh samples had the higher surface area which was evidenced by pore structure analysis. Moreover, the favorable performance of binder-supported CaSO4 was explained by formation of CaAl2O4 which had excellent thermal stability and provided a stable nanosized framework between the crystal grains observed by field emission scanning electron microscope (FESEM).