Redox performance of Cu-based oxygen carrier used in chemical looping air separation combined oxy-fuel combustion technology

Highlights: • Thermodynamics of CuO in flue gas atmosphere was carried out. • CuO/MgAl₂O₄ was selected as oxygen carrier in the new prototype. • Reduction and oxidation reactivity of oxygen carrier was investigated in TGA. • Redox performance of oxygen carrier was investigated in the fixed-bed reactor. - Abstract: Chemical looping air separation offering the oxygen source to oxy-fuel combustion is an effective CO₂ and NO_x reduction technology in fossil fuel combustion. In the technology, oxygen carrier releases oxygen to flue gas and the reduced oxygen carrier absorbs oxygen from air in two separated reactors. And then the oxygen enriched flue gas returns to the combustor. The redox performance of oxygen carrier is essential to this technology. Thermodynamic calculations on CuO/Cu₂O in flue gas atmosphere indicate that the redox reaction of copper oxides is not affected by the compositions in the flue gas. The optimization reduction temperatures are determined as 850~1050 °C. The redox performance of Cu-based oxygen carriers with 40wt%, 50wt%, 60wt% MgAl₂O₄ as inert binder was investigated in TGA and fixed-bed reactor. The reduction rate increases with temperature increasing and with oxygen concentration decreasing. The oxidation rate increases with temperature increasing when temperature is lower than 850 °C, while it begins to decrease when temperature is higher than 850 °C. The highest oxygen concentration in the reduction period is not limited to the gas flow but to the P_e at that temperature. The reduction and oxidation rates all increase with binder adding ratio decreasing. The average reaction rate of oxygen carrier begins to decrease when conversion is higher than 80%. The reduced oxygen carrier can be oxidized in low oxygen concentration.