(622d) Cu Oxidation Kinetics In a Chemical Looping Combustion Systems

Knowledge of intrinsic chemistry will greatly facilitate the optimization of fuel and air reactors in Chemical Looping Combustion (CLC) power systems.  In order to determine intrinsic Cu oxidation rates, Cu particles having diameters within the size range of 5 to 50 microns were oxidized with dry air in a thermogravimetric analyzer (TGA) at temperatures ranging from 200 °C to 800 °C.  In the case of Cu oxidation (and CuO reduction), morphological changes in surface area, porosity, diameter and density influence observed mass loss rates and must be accounted for when extracting intrinsic kinetics from experimental data.  In order to determine how these properties (i.e. surface area, porosity, diameter, and density) vary with oxidation, additional experiments were performed in a tube furnace with the same Cu particles at the same temperature / pressure and gas composition conditions as in the TGA experiments.  Particles used in the tube furnace experiments were collected at different extents of conversion and analyzed to determine the parameters in the models developed to describe how surface area, diameter, porosity and density vary as a function of particle conversion.  Intrinsic chemical rates were then determined by fitting a direct numerical simulation (DNS) of a single Cu particle to the TGA and tube furnace data.

The tube furnace experiments show that as the Cu particles are oxidized, pores within the particle close up, surface area decreases, and oxidation rates go from being chemically controlled to mass transport controlled.  The copper oxidation mechanism employed, takes into account dissociative chemisorption of oxygen on to Cu and Cu₂O surfaces and CuO dissociation.  Calculated results agree with a cascading pathway of Cu going to Cu₂O then to CuO, as experimentally observed.