Use of synthetic oxygen carriers for Chemical Looping Combustion of Victorian brown coal

Abstract

Chemical Looping Combustion (CLC) is a promising alternative technology for inherent capture of CO2 at a lower cost and energy penalty relative to other Carbon Capture and Storage (CCS) options. This paper details the use of synthetic oxygen carriers composed of 20wt% CuO, Mn2O3 and NiO impregnated on Fe2O3 in CLC with Victorian brown coal as a fuel. The investigation used a variety of experimental equipment including a fluidized bed reactor, Thermogravimetric Analyser (TGA) and Temperature Programmed Reduction (TPR) unit. The oxygen carrier samples were characterized using techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Accelerated Surface Area and Porosimetry (ASAP). The characterization also included in situ high temperature XRD using synchrotron radiation to study the changes in the lattice parameter and crystal size of Fe2O3 as a function of temperature in a CLC-like environment. It was observed that the synthetic oxygen carriers demonstrated greater performance and enhanced reactivity over Fe2O3 with the NiO impregnated sample having the highest CO2 conversion efficiency. The synchrotron based in situ XRD study showed that the crystal size of the oxygen carrier increased after one redox cycle. This was also observed in the SEM micrographs of the used samples and is due to coalescence of the grains. Thermochemical modelling was carried out to generate an Ellingham diagram and it was found that the theoretical and experimental values did not conform well and this was attributed to the algorithm used by the software. It was found that all the synthetic oxygen carriers demonstrated superior performance over Fe2O3. However, the viability of using synthetic oxygen carriers in a larger scale will depend on the economics of their production.