Reactivity of Ca-Fe/bentonite oxygen carrier in coal chemical-looping combustion

A Ca-based compound oxygen carrier was prepared with industrial grade natural anhydrite, bentonite (ben) and iron nitrates by using the mechanical mixing-prilling method. The experiments were carried out in a fluidized bed with steam as the gasification-fluidization medium. The influence of active component content, temperature as well as multi-cycle on the reactivity between CaSO₄/bentonite and coal was investigated. The results show that the CaSO₄ mass content of 60% and the adding Fe₂O₃ can make a better reactivity and less attrition of the oxygen carrier particles. The attrition rate is 0.089%/h. The time to reach a carbon conversion of 95% is shortened to 20.8 min, and the average dry concentration of CO₂ approaches 95.99%. Ten redox tests demonstrate that the concentration of CO₂ can be kept in 80% and the CaSO₄-Fe₂O₃/ben (Ca-Fe/ben) oxygen carrier has a good cyclic stability. Moreover, four types of coal are tested, indicating that the coals with high volatile content and high ash content have higher combustion efficiencies with above 90% CO₂ concentration in gasification products in all cases.