Impregnated CuO/Al2O3 Oxygen Carriers for Chemical-Looping Combustion: Avoiding Fluidized Bed Agglomeration

Abstract

Chemical-looping combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2 that involves the use of an oxygen carrier, which transfers oxygen from air to the fuel avoiding the direct contact between them. An oxygen carrier in a CLC power plant must show high reaction rates and sufficient durability in successive cycle reactions. Furthermore, the oxygen carrier particles must not agglomerate. To produce materials with these characteristics, different Cu-based oxygen carriers with a range of CuO content between 10 and 26 wt % were prepared by impregnation using alumina as support. The particles were calcined at different temperatures in the range of 550−950 °C. The oxygen carriers were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray, and thermogravimetry. The samples were evaluated in a fluidized bed facility in order to determine their behavior in multicycle reduction−oxidation tests. A number of 100 cycles was done when the carrier did not agglomerate. The effects of metal content, calcination temperature, and method of preparation on the oxygen carriers reactivity, gas product distribution, attrition rate, and agglomeration were analyzed for the different oxygen carriers. It was observed that the CuO content in the oxygen carrier, the calcination temperature used in the preparation, and the conversion reached by the oxygen carrier during the reduction period affected the agglomeration process. In this work, the preparation conditions to produce Cu-based oxygen carriers with high reactivities, and small attrition rates were found. Moreover, the agglomeration of these oxygen carriers in the fluidized reactor, which is the main reason adduced in the literature to reject the Cu-based oxygen carriers for the CLC process, was avoided.