Chemical Engineering Science, Vol.65, No.1, 98-106, 2010
Reduction and oxidation kinetics of Co-Ni/Al2O3 oxygen carrier involved in a chemical-looping combustion cycles
The solid-state kinetics of Co-Ni/Al2O3 oxygen carrier is studied using non-isothermal reaction data and a non-linear regression analysis. XRD analysis of the fresh samples shows that NiO is the dominant reducible phase of the oxygen carrier. Pulse chemisorption suggests a negligible nuclei growth over the repeated reduction/oxidation cycles. Mercury porosimetry confirms that the pore size of the carrier particle is slightly increased following reduction. A nucleation and nuclei growth model and an unreacted shrinking-core model are developed based on the oxygen carrier texture change during reduction/oxidation, as observed by pulse chemisorption and mercury porosimetry. Model parameters are calculated using H-2-TPR and O-2-TPO data. It is found that the random nucleation model describes solid phase changes adequately. The determined apparent activation energies are 45 and 44 kJ/mol for the reduction and oxidation, respectively. The established kinetic model is successfully evaluated for the reduction cycle using a CREC mini-fluidized Riser Simulator reactor operating under expected conditions of large industrial scale fluidized CLC units. (C) 2009 Published by Elsevier Ltd.
Keywords:CO2 capture;CLC;Gas-solid reaction kinetics;Nucleation and nuclei growth model;Shrinking-core model