The performance of Fe₂O₃-CaO Oxygen Carriers and the Interaction of Iron Oxides with CaO during Chemical Looping Combustion and H₂ production

Chemical-looping combustion (CLC) has emerged as a promising and low cost carbon capture process which produces a pure stream of CO₂. In CLC, oxygen from a solid oxygen carrier (OC) is used to combust fuels. Iron oxide is a promising material, being relatively cheap and environmentally benign. The thermodynamics of the Fe- O system allows reduced iron oxides to be also used for partial oxidation or hydrogen production. However, pure Fe₂O₃ has the problem of degradation in reactivity over repeated CLC cycles. This work is concerned with inclusion of a suitable CaO support material within the Fe-based OCs to increase its strength and cycle ability. OCs were made from Fe₂O₃ powder by granulation and followed by impregnation with Ca(NO₃)₂.4H₂O. The reactivity and cyclic stability of the OCs were tested by being subjected to alternating reducing (using H₂ or CO) and oxidizing environments (using air and / CO₂) for many cycles, in a thermogravimetric analyser and a fluidized bed reactor at 850-950°C. It was found that, for samples with a range of loading of CaO, from 2 to 30 mol%, the one containing 20 mol% CaO showed optimal performances, whereas others showed improvements in oxygen carrying capacity, cyclic stability and reactivity over unmodified iron oxide but to a lesser extent.