| In recent years, chemical-looping combustion (CLC) has received growing interest as an efficient combustion technology for the capture of CO 2 and the substantial reduction of NOx emissions from fossil fuel based power generation stations. This non-conventional technique involves the use of a solid oxygen carrier to supply oxygen, instead of air, during fuel combustion, thereby preventing the dilution of CO2 in the flue gas with the N2 from air. Consequently, CO2 is delivered without any extra energy penalty for disposal. Formation of NO x is also negligible because the fuel burns in the absence of air and without a flame.; This study deals with the development of a bimetallic Co-Ni/Al2 O3 oxygen carrier suitable for fluidized bed CLC. Temperature programmed characterization shows that the addition of Co enhances the reducibility of the oxygen carrier by influencing the state of the surface minimizing the formation of nickel aluminate. Temperature programmed H2 desorption kinetics reveal that the activation energy of hydrogen desorption for Co-Ni/Al 2O3 is significantly decreased while compared to the one of an unpromoted Ni/Al2O3 sample. This result suggests that doping the fluidizable oxygen carrier with Co diminishes metal support interactions and the binding energy between the metals and the H2 molecules. This effect increases the availability of the reactive species in a Co-Ni/Al2O3 sample. Reactive characterization of the prepared oxygen carriers in a CREC (Chemical Reactor Engineering Center) fluidized bed Riser Simulator, demonstrates that the Co-Ni/Al2O 3 particles are highly reactive and stable over multiple reduction/oxidation cycles. XRD analysis shows similar phases (NiO and NiCoO2 on both the fresh and used samples, confirming that no phase transformation occurred during the CLC processes. The addition of Co also inhibits metal particle agglomeration by maintaining consistent metal dispersion during the cyclic reduction/oxidation processes, with this finding being confirmed by pulse (H2) chemisorption analysis over repeated reduction/oxidation cycles. SEM images of a fresh and a used carrier sample evidences similar distribution of the metal crystallites suggesting minimum agglomeration of the nickel species at the high temperatures of the CLC process.; The solid-state kinetics for both the reduction and oxidation cycles is established using a clarified Avrami-Erofeev model at non-isothermal conditions. This random nucleation model describes the 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/Al 2O3 sample, indicating the positive effect of Co on the Co-Ni/Al 2O3 oxygen carrier.; Keywords. CO2 capture, NOx, CLC, Co-Ni/Al2O3 oxygen carrier, bimetallic oxygen carrier, reactivity, stability, solid-state kinetics. |
