Chemical Engineering Research & Design, Vol.141, 481-491, 2019
Kinetics of the reduction and oxidation of Mg added NiO/Al2O3 for chemical looping combustion
Reduction and oxidation kinetics of Mg added Ni-based oxygen carriers with different types of NiO and Mg contents were investigated for chemical looping combustion (CLC) using thermogravimetric analyzer (TGA) in the temperature range of 825-900 degrees C. The Johnson-Mehl-Avrami (JMA) model was adopted for determination of kinetic parameters of both reduction and oxidation reaction of the three oxygen carriers. It was found that the reduction reaction consists of (1) fast surface reaction in which the reaction rate is independent of both the reaction temperature and the fuel gas concentration, (2) nucleation with short duration, and (3) kinetic controlled reaction under influence of gas diffusion rate. In oxidation reaction, the reaction rates were not heavily dependent on reaction temperature because of the low activation energies. Instead, the concentration of 02 strongly affected the pre-exponential factors, and the reaction rate constant k, consequently. Unlike the reduction reaction, the fast surface reaction was not observed in the oxidation reaction. The type of NiO used for preparation of the oxygen carriers was found to be more important factor than Mg contents for determination of the kinetic parameters for both reduction and oxidation. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.