Performance Evaluation of a Cu-Based Oxygen Carrier Impregnated onto ZrO2 for Chemical-Looping Combustion (CLC)

Chemical-looping combustion (CLC) has been introduced as a promising technique with inherent advantages for efficient, low-cost CO2 separation. The type of oxygen carrier employed plays a vital role in improving the overall efficiency and economic penalty of the system. This study investigates the performance of a CuO oxygen carrier impregnated onto ZrO2 in a continuously operated 500 W-th CLC unit over 30 h of CH4 combustion. A decrease in combustion efficiency was observed during the initial 10 h followed by stabilization. A loss of CuO of between 13 and 5 wt % was recorded during the first 5 h of combustion before the CuO content was kept constant. This loss was due to the Cu layer peeling off the surface of particles and the clustering and migration of CuO from internal areas to the surface and then attrited. The effect of the oxygen carrier-to-fuel ratio (phi) on the combustion efficiency of the impregnated Cu-based oxygen carrier was studied. In order to reach a combustion efficiency of 99%, phi values of 3.9 were needed. The particle attrition rate was stabilized after 30 h of operation at 0.06%/h, and the estimated lifetime was 1500 h of operation. XRD and TPR analyses confirmed very low interaction between CuO and the support (ZrO2), which was unable to retain CuO inside the particles. Therefore, the lack of interaction between CuO and the ZrO2 support is not positive for oxygen carrier behavior in the CLC process.