The use of iron oxide as an oxygen carrier in chemical-looping combustion of methane with inherent separation of CO2

Chemical-looping combustion (CLC) has been suggested as an energy efficient method for capture of carbon dioxide from combustion. The technique involves the use of a metal oxide as an oxygen carrier which transfers oxygen from the combustion air to the fuel, and the direct contact between fuel and combustion air is avoided. Thus, the products of combustion, i.e. carbon dioxide and water, are kept separate from the rest of the flue gas. After condensation of the water almost pure CO2 is obtained, without any energy lost for the separation. In this paper, the feasibility of using Fe2O3 as an oxygen carrier has been investigated in a fixed bed quartz reactor. Iron oxide was exposed to repeated cycles of air and methane at 950 degreesC, with the outlet gas concentrations measured. The time under reducing conditions and the amount of bed material were varied in a wide range. The reduction rate of Fe2O3 to Fe (dX/dt) with 100% methane was between 1-8%/Min and was a function of both the conversion range of the solid material, AX, as well as the yield of methane to carbon dioxide, gamma (red). The rate of oxidation was also a function of DeltaX and the gas conversion, gamma (ox), and was considerably faster than the reduction, with rates up to 90%/min. The parameters dX/dt, DeltaX, and gamma are closely related and can be used to establish design criteria of a CLC system based on interconnected fluidized beds. The rates of both reduction and oxidation found should be sufficient to be employed in a CLC system based on two interconnected fluidized beds. (C) 2001 Elsevier Science Ltd. All rights reserved.