Chemical-looping with oxygen uncoupling using combined Mn-Fe oxides, testing in batch fluidized bed

Chemical-looping with oxygen uncoupling (CLOU) has been studied with gaseous and solid fuel in a small fluidized bed batch reactor, using new Fe-Mn-based oxygen carriers. CLOU is a development of chemical-looping combustion, using oxygen carriers with the ability to release oxygen, which can react directly with the fuel. The carbon dioxide from the combustion is inherently obtained as separated from the rest of the flue gases. In this work manganese is combined with iron oxides, giving new bimetallic oxide compounds with different thermodynamic properties compared to pure manganese oxides. Four different combinations of iron manganese oxide have been examined by decomposition in N2 and also reaction with methane and syn-gas. F3, a material with a molar ratio of Fe:Mn of 2:1, showed the best behaviour in terms of its release of oxygen, take up of oxygen, fluidizability and methane conversion. Therefore, F3 was also tested with solid fuel using inert fludization gas, N2. The char particles effectively remove oxygen released as it is converted to CO2. Thus, CO2 will represent the oxygen release. The tests show that the particles release oxygen corresponding to approximately 0.5% of their mass. Moreover, a test where steam was added in the fluidization gas showed high gas conversion, with essentially no unconverted gas. Thus, the tests indicate that the F3 particles, if used in chemical-looping of solid fuels, could contribute both to faster fuel conversion and to higher conversion of gas, as compared to a normal oxygen carrier that does not release oxygen.