Experimental Investigation of a CuO/Al2O3 Oxygen Carrier for Chemical-Looping Combustion

Chemical-looping combustion (CLC) has emerged as an interesting alternative for conventional power production technologies, intrinsically combining power production and CO2 capture. The performance of the oxygen carrier particles used in this technology is of vital importance for the overall technical and economical feasibility of CLC technology, and therefore, the behavior of a selected oxygen carrier (CuO/Al2O3) has been investigated in more detail using thermogravimetry. The experimental study focused on the reactivity during the oxidation and reduction cycles and the stability of the particles over multiple alternating sequences of these cycles. Particles of relatively large size were used, to investigate the possibility of using the material in packed-bed CLC. Interpretation of the experimental results on a quantitative level was achieved through comparison with numerical simulations using a detailed particle model in which the effects of both reaction kinetics and intraparticle mass-transfer limitations were fully taken into account. It was found that the experimentally determined conversion rate of the particles during oxidation could be very well described by the particle model that accounts for changes in the particle morphology. The average pore size needed in the simulations to reproduce the experimental results matched well with the most common pore size found by nitrogen adsorption−desorption experiments using the BET and BJH methods. For the reduction cycles using hydrogen as the reducing agent, it was concluded that the conversion characteristics could be described reasonably well for moderate conversions, but for higher conversions, the discrepancies were larger, especially at rather low operating temperatures. When reduction cycles were carried out with methane, carbon deposition was observed. The generated data and insights help in assessing the optimal reactor configuration for CLC and its feasibility.