Reactivity and Stability of Different Red Muds as Oxygen Carriers for Chemical Looping Combustion of Methane and Biomass in a Fluidized Bed

The reactivity and stability of two low-cost red muds (LuShan and XinFa) as oxygen carriers for chemical looping combustion (CLC) were experimentally investigated in a fluidized bed, with methane and biomass char, respectively. CH4 conversions using the present red muds were quite low, <20% after stable cycles. The XinFa red mud had better reactivity and stability in comparison with the LuShan red mud, with its CO2 selectivity maintained at about 80% during 50 cycles. Due to the high content of Ca in the LuShan red mud, its promoting effect on the water-gas shift reaction led to continuous high H2 production during biomass char-fueled experiments. The XinFa red mud achieved a complete conversion of char with only CO2 as the gaseous product. Further, it showed better resistance to attrition. The agglomeration affinity in the case of using biomass char as fuel was stronger than that when using methane as fuel. NaAlSiO4 with a high melting point was detected in both fresh and cycled oxygen carriers. Ca2Al2SiO7 was found in the LuShan red mud due to the interactions among Ca, Al, and Si at elevated temperatures.