Use of chemically and physically mixed iron and nickel oxides as oxygen carriers for gas combustion in a CLC process

Different bimetallic Fe–Ni-based OCs have been prepared and evaluated in a TGA, a batch fluidised bed reactor, and a continuous CLC unit in order to analyse the effect of NiO content on the CLC performance when CH4 or a PSA-offgas was used as fuel. A set of experiments was conducted in continuous operation in a 500 Wth CLC unit, firstly working with a chemically mixed OC, with the iron and nickel oxides impregnated over the same alumina particle, and secondly working with a physical mixture of two impregnated Fe- and Ni-based OCs. The results were also compared with those obtained with an unmixed Fe-based OC. The effect on the combustion efficiency of different operating conditions, such as fuel composition, oxygen carrier to fuel ratio and fuel reactor temperature has been determined in the continuous unit. It was found that the use of a chemically mixed OC had a negative effect on the combustion efficiency since the formation of Fe–Ni compounds reduced the catalytic effect of Ni addition. On the other hand, a physically mixed OC with 2% of NiO increased significantly the combustion efficiency at low temperatures.