Characterisation of Australian ilmenite oxygen carrier during chemical looping combustion of Victorian brown coal

Chemical looping combustion (CLC) offers a low emission route for fossil fuel-based power generation. In this study, a compact fully looped chemical looping reactor was developed in-house, and operated continuously with a Victorian brown coal as fuel and an Australian ilmenite as oxygen carrier at 940–980 °C and atmospheric pressure for 36 h. The study found that the CLC performance increased with increasing operation time. The CO₂/CO molar ratio, used to evaluate the CLC reaction degree, increased from 2.3 to 8.9 over the 36 h of operation. Specifically, this paper provides a comprehensive study and evaluation of the ilmenite characteristics on morphology changes and ash interaction, due to the continuous operation. No noticeable effect by ash interaction on the CLC performance or operation was observed during the continuous operation. The characterisation results revealed a clear segregation of iron species from the iron‑titanium matrix, its migration to and enrichment over the particle surfaces. Hematite (Fe₂O₃) formation became more pronounced while pores developed internal and external of the ilmenite particles. These changes are believed to improve the carrier reactivity, and so the CLC performance, but also to weaken the mechanical strength of the carrier, promoting particle attrition and leading to its loss by elutriation.