Preparation and performance of the Fe₂O₃/ATP oxygen carriers in coal chemical looping combustion

Through mechanical-mixing, impregnating and sol-gel methods, Fe₂O₃-based oxygen carriers (OC) were prepared with natural attapulgite (ATP) as an inert support and characterized by X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and nitrogen adsorption-desorption measurements. The reactivity of Fe₂O₃-based oxygen carriers (Fe₂O₃/ATP OCs) in coal chemical looping combustion (CLC) was investigated in a fluidized-bed reactor at 900 ℃ by using steam as the gasification agent. The results indicated that the surface area and attrition resistance of Fe₂O₃/ATP OCs are improved significantly by using ATP as the support. Owing the synergy between ATP and Fe₂O₃, both are catalytic active, carbon conversion is enhanced significantly. ATP is an appropriate support for Fe₂O₃ oxygen carriers, whereas the sol-gel method gives the carriers best performance. U-Fe4ATP6 prepared by the sol-gel method, with a surface area of 4.920 7 m²/g and Ca content of 4.3%, exhibits much better performance than other two oxygen carriers. When used in CLC, the initial carbon conversion rate reaches 0.168 min^-1, with an average CO₂ concentration of 98.6% and a combustion efficiency of 98.7%. The catalytic activity of U-Fe4ATP6 is slightly decreased after twenty cycles; the initial carbon conversion rate is decreased to 0.108 min^-1 and the residence time (t₉₅) is extended to 18 min, whereas the CO₂ capture efficiency and combustion efficiency remain at about 98.6% and 96.7%, respectively.