DETERMINATION OF REACTIVITY AND THERMODYNAMIC ANALYSIS OF NICKEL-BASED OXYGEN CARRIERS FOR CHEMICAL-LOOPING COMBUSTION

Abstract This work aimed to study nickel-based oxygen carriers (OC) for Chemical Looping Combustion (CLC) using H2 and CH4 as fuel. The reactivity and reaction kinetics of the OC were investigated, applying the shrinking core, nucleation and diffusion models in three dimensions, as well as whether the OC is thermodynamically favorable for the reaction. The results showed that the OC achieved high conversion for both fuels, proving to be quite reactive, while the fuel gas concentration and the temperature have a strong effect on the solids conversion. For the H2 combustion, the reaction rate can be described well by the shrinking core model, whereas for CH4 the nucleation model may better represent the experimental data. With respect to reactions that occur in the reduction reactor with the NiO/Ni redox system, it was observed that, for the investigated temperatures used in CLC, high values of the equilibrium constant were obtained, showing that practically complete conversion of the fuels is possible.