Combined calcium looping and chemical looping combustion cycles with CaO-CuO pellets in a fixed bed reactor

The feasibility of using integrated CaO/CuO-based pellets in combined calcium and chemical looping cycles in a fixed bed was investigated with emphasis on CO2 capture performance. Three types of pellets were tested, namely; integrated core-in-shell CaO/CuO-based pellets; integrated homogeneous CaO/CuO-based pellets; and mixed CaO-based pellets and CuO-based pellets. Redox cycles consisted of oxidation/carbonation at 650 °C in 15% CO2; 4% O2, and N2 balance, and reduction/calcination at 850 °C in a CO/H2 mixture. The results showed that mixed pellets exhibited the highest CO2 uptakes of 0.11 g CO2/g bed in the first cycle and 0.07 g/g after 11 cycles (corresponding to CaO conversions of 32.1% and 19%, respectively). This enhanced performance was attributed to the significantly higher pore volume and surface area in the calcined CaO-based pellets, which were superior to those of integrated CaO/CuO-based pellets. The reduction of CuO to Cu2O was found to be partially irreversible, with ∼45% of copper oxide in the pellets in the form of Cu2O despite the excess O2 in the oxidizing environment. It was also noted that cycled core-in-shell pellets were the most susceptible to fragmentation, indicating the low mechanical strength of these pellets. It was concluded that combined calcium and chemical looping cycles in a fixed bed system is a feasible process providing suitable pellets are used. Incorporating CuO in CaO-based pellets reduces the porosity of the pellets, thus compromises CO2 uptake. Among the three groups of pellets, mixed pellets are the most promising for CaL-CLC processes due to their better performance, easier manufacturing, and better quality control than integrated pellets.