Kinetics model for the reduction of Fe2O3/Al2O3 by CO in Chemical Looping Combustion

Abstract

Kinetics model which describes intrinsic characteristics of reactions involved in Chemical Looping Combustion (CLC) can be used as a basic tool for reactor design and reactor modeling. To further develop previously studied sol-gel Fe2O3/Al2O3 oxygen carrier, this work performed a detailed kinetics investigation for the reduction from Fe2O3/Al2O3 to Fe3O4/Al2O3 by CO. In order to derive a reliable kinetics model, thermodynamics calculations were first performed to identify the reaction pathways with full CO2 capture and no carbon deposition, excluding their influence. Experimental data at 673–773 K during thermogravimetric analyzer (TGA) tests was considered for kinetics analysis to attain good CLC performance. Finally, a widely used model-free method was employed to develop the kinetics model. Accordingly, a 3D nucleation and nuclei growth model with the model function g(X) = [-ln(1-X)]1/3, activation energy 270 kJ/mol and pre-exponential factor 1.6·1012s−1 was developed to describe the first half reduction from Fe2O3/Al2O3 to Fe3O4/Al2O3 by CO (0 < X≤ 0.5). Following this, the diffusion effects dominated the reduction process (0.5 < X ≤1), which can be described by a 2D diffusion model function g(X) = (1-X)·ln(1-X) + X with the activation energy and pre-exponential factor as 131 kJ/mol and 3.1·103 s−1, respectively. The whole kinetics model can be considered for the future application.