Assessment of the Redox Characteristics of Iron Ore by Introducing Biomass Ash in the Chemical Looping Combustion Process: Biomass Ash Type, Constituent, and Operating Parameters

Chemical looping combustion (CLC) is a potential CO2 capture and sequestration (CCS) technology that can easily separate CO2 and H2O without energy loss and greatly improve the efficiency of carbon capture. Due to the inherent defects of natural iron ore, such as low reactivity and poor oxygen carrying capacity, four kinds of biomass ashes (rape stalk ash, rice stalk ash, platane wood ash, and U. lactuca ash) that have different constituents of K, Na, Ca, and Si were applied to modify the redox performance of natural iron ore. The effects of biomass ash type, constituent, reaction temperature, H2O vapor flow rate, and redox cycle on the CLC process were assessed experimentally in a batch fluidized bed reactor system. Oxygen carrier physicochemical characteristics were determined by several analytical techniques. The results showed that rape stalk ash, platane wood ash, and U. lactuca ash with a high K content and high K/Si ratio significantly improved the reactivity and cycle stability of iron ore, even after 10 redox cycles, while rice straw ash with a low K/Si ratio showed an inhibitory effect due to the formation of bridge eutectics, which enhanced agglomeration. In a range from 800 to 950 degrees C, higher temperatures led to a much better ability to promote the CLC process than lower temperatures. A higher flow rate of H2O had little effect on the further promotion of the CLC process due to hydrogen inhibition. It is believed that the application of BA-modified iron ore oxygen carriers is an effective strategy to improve the CLC process.