Thermodynamic potential of high temperature chemical looping combustion with molten iron oxide as the oxygen carrier

Abstract

The thermodynamic potential of a chemical looping combustion (CLC) system using molten iron slag as the oxygen carrier (OC) for the combustion of methane is reported. A configuration of two inter-connected bubbling column reactors is proposed as a plausible configuration for the air and fuel reactors to facilitate the heating of a pressurised hot gas stream to an estimated temperature of 1350 °C. This approach has potential to avoid the technical challenges associated with the use of the solid OC employed in conventional CLC systems such as particle breakage, attrition, agglomeration and structural change that arise from successive reduction and oxidation (Red-Ox) cycles. However, it brings alternative challenges associated with the handling of molten metal oxides such as proper material selection and solidification of the LOC, which will require further work to full identify and resolve. The process has been modelled using codes developed with MATLAB and HSC Chemistry 7.0 software and compared with published data. The model was used to estimate that a fuel conversion efficiency of more than 97% can be achieved with molten iron oxide as the oxygen carrier, together with a mole fraction of the iron and iron oxides in the product gas of less than 10−6. A sensitivity to molar ratios of liquid oxygen carrier, steam to fuel flow rate and the operating pressure is also reported.