Reactivity and stability of Co‐Ni/Al2O3 oxygen carrier in multicycle CLC

Abstract

AbstractThis study deals with the development of a bimetallic Co‐Ni/Al2O3 oxygen carrier suitable for a fluidized bed chemical‐looping combustion process. Temperature programmed characterization shows that the addition of Co enhances the reducibility of the oxygen carrier by influencing the metal‐support interactions helping the formation of reducible nickel species. Reactive characterization of the prepared oxygen carriers in a CREC fluidized riser simulator, using multiple reduction/oxidation cycles, demonstrates that the Co‐Ni/Al2O3 particles display excellent reactivity and stability. The addition of Co in the bimetallic Co‐Ni/Al2O3 influences the state of the surface minimizing the formation of nickel aluminate. The addition of Co also inhibits metal particle agglomeration by maintaining consistent metal dispersion during the cyclic oxidation/reduction processes. A solid‐state kinetics for both reduction and oxidation cycles is established using a clarified Avrami‐Erofeev model at nonisothermal conditions. This random nucleation model describes solid phase changes adequately. The activation energy for Co‐Ni/Al2O3 reduction is found to be significantly lower than the activation energy for the unpromoted Ni/Al2O3 sample, with this observation confirming the positive influence of adding Co on the Ni‐Al2O3 oxygen carrier. © 2007 American Institute of Chemical Engineers AIChE J, 2007