Oxidation kinetics of adsorbent-decorated Fe-based oxygen carrier for chemical-looping combustion

Adsorbent-decorated Fe₂O₃/Al₂O₃ as oxygen carrier (OC) was proposed for restraining the emission of chloride, sulfide and heavy metals during the chemical-looping combustion process of gaseous or solid fuels. Three adsorbents (K₂O, Na₂O and CaO) were selected for decorating these OC particles. First, the raw Fe₂O₃/Al₂O₃ and three adsorbent-decorated Fe₂O₃/Al₂O₃ were reduced by synthesis gas and then the oxidation kinetics of four reduced OCs (raw FeO/Al₂O₃ and three adsorbent-decorated FeO/Al₂O₃) were investigated by using thermogravimetric analysis (TGA) technique in air atmosphere at four temperatures (850, 875, 900 and 925℃). It was found that the translation of FeO to Fe₂O₃ can be described by the phase boundary-controlled (contracting cylinder) model, and the apparent activation energy (E) was calculated to be 13.71, 20.21, 21.62 and 24.20 kJ/mol for raw FeO/Al₂O₃, K₂O-decorated FeO/Al₂O₃, Na₂O-decorated FeO/Al₂O₃ and CaO-decorated FeO/Al₂O₃, respectively. Last, the reaction mechanism was evaluated through comparing the calculated data from the obtained kinetic parameters and the experimental results, which demonstrated the reliability of the phase boundary-controlled (contracting cylinder) model.