Chemical Looping Combustion of Coal Chars Using Iron Ore of Different Grades as Oxygen Carriers

Natural ore, which is cost-effective and reserve-abundant, is more attractive to be used as oxygen carriers (OCs) in industrial-scale chemical looping combustion (CLC) units compared to synthetic OCs. In this paper, five kinds of iron ore of different grades (with Fe2O3 contents at around 50, 60, 70, 80, and 90 wt %) are investigated as OCs in a batch fluidized bed reactor by using three kinds of coal char with different ranks as fuels. The aim is to illustrate the matching relationship between coal rank and iron ore grade in CLC applications. The experimental results indicate that five different hematite OCs exhibit diverse reaction performance in CLC of coal char. Generally, the carbon conversion rate is accelerated with the increase of iron ore grades. In contrast, the enhancement for high-grade iron ore is not apparent due to the limited coal char gasification rate in the reaction. For the low-rank coal char, it shows high adaptability to different grades of iron ore. However, the adaptability of the high-rank coal char is relatively poor on account of its slow char gasification rate. Overall, iron ore with Fe2O3 content in the range 70-80 wt % shows sufficient oxygen-carrying capacity in CLC and exhibits the best adaptability toward the conversion of coal char with different ranks.