Multicycle reduction and oxidation of different types of iron oxide particles - Application to chemical-looping combustion

Chemical-looping combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2. The technique involves the use of a metal oxide as an oxygen carrier that transfers oxygen from the combustion air to the fuel. The use of iron oxide as an oxygen carrier has been investigated. Particles composed of 40-80 wt % Fe2O3, together with Al2O3, ZrO2, TiO2, or MgAl2O4, have been prepared by freeze granulation. Particles have been sintered at different temperatures in the range of 950-1400 degreesC, and particles 0.125-0.180 mm in diameter have been obtained by sieving. The reactivity of the oxygen-carrier particles has been evaluated in a laboratory fluidized bed of quartz, where the alternating atmosphere that an oxygen carrier encounters in a CLC system is simulated by exposing the sample to alternating reducing (50% CH4, 50% H2O) and oxidizing (5% O-2) conditions at a temperature of 950 degreesC. The oxides are characterized prior to, and following, reactivity testing, with respect to crushing strength, surface structure, and chemical composition. Of the 27 investigated oxygen carriers, 20 show reactivity, which would mean that <500 kg/MWth of material would be needed in the fuel reactor. Some oxygen carriers have shown agglomeration in the bed and may not be suitable for a CLC system of interconnected fluidized beds.