Chemical looping combustion of lignite using iron ore modified by foreign ions: Alkaline-earth and transition metal ions

Abstract

In the chemical looping combustion (CLC) of lignite, oxygen carrier reactivity is the key to combustion performance. In this paper, the effects of particle size and temperature upon the CLC of lignite are investigated in a fixed bed reactor using iron ore as the oxygen carrier. Under optimized working conditions, the iron ores are loaded with alkaline-earth metals (K, Na and Ca) and transition metals (Ni, Mn and Cu) in a mass ratio of 10%, and their effect upon its CLC reactivity are studied. The carbon conversion rate, carbon capture rate, CO2 capture rate, CO2 selectivity, and other parameters are obtained. The size of lignite particles had a direct effect on the carbon capture rate of the fuel reactor. The particle size with the best effect on carbon and CO2 capture for both the Yunnan and Yizhong lignite is 80–200 mesh. The increase in temperature effectively promotes the reaction between oxygen carrier and volatiles, thereby resulting in an increase in CO2 concentration. The capacity of the oxygen carrier to transform the lignite is effectively enhanced by the modification with Cu, K, Na, Ca and Mn. In particular, the CO2 selectivity is greatly improved (up to 94.84%) for the Cu-modified oxygen carrier. These results provide important references for the CLC process, especially for the design of the oxygen carrier.