Chemical Looping Combustion – Reduction of nickel oxide/nickel aluminate with hydrogen

Chemical Looping Combustion (CLC) has been proposed as a power/heat generating process with inherent CO2 separation, as the fuel is not combusted in direct contact with nitrogen in the air. In CLC the combustion of fossil fuels is split into separate oxidation and reduction reactions. A reducible metal oxide is cycled between the reactors, and acts as an oxygen carrier. The development of suitable oxygen carriers is therefore a major challenge in order to make CLC a commercially viable technology. In the present study, particles of NiO:NiAl2O4 are alternately oxidized by air and regenerated by reduction with hydrogen. The reaction is carried out in a heated fluidized/fixed bed reactor. The net reaction is conversion of hydrogen to H2O by reduction of NiO to Ni. The produced water vapor is absorbed in dry silica gel. The instantaneous mass increase of the silica gel is measured and used to calculate the degree of oxidation (X), thus monitoring the course of the reaction. The rate of oxygen transfer in the reduction reactor is a critical design criterion in CLC. Optimizing the oxygen carrying potential of the metal- metal oxide is therefore an important engineering aspect of CLC. This can be achieved by reducing the content o