Highly attrition resistant oxygen carrier for chemical looping combustion

Chemical looping combustion (CLC) is expected to become one of the most competitive combustion technologies to reduce the cost of carbon capture and the cost of electricity for power generation. An oxygen carrier is used in the CLC to supply oxygen necessary for the fuel combustion. The oxygen carrier requires high reactivity and mechanical strength for a long time use under a cyclic redox reaction at high temperatures. This work was carried out to confirm that Mg-added NiO oxygen carrier with a high attrition resistant and high oxygen transfer capacity could be obtainable by using γ-Al2O3 mixed with MgO as support material. A NiO oxygen carrier was successfully formed by spray drying slurry containing 70 wt% NiO and 30 wt% support on a dry solid basis. The prepared oxygen carrier was characterized in terms of the physical properties related to the fluidization, such as shape, particle size, packing density, and mechanical strength. The prepared oxygen carrier was, especially, notified with its excellent spherical shape and high mechanical strength at a sintering temperature of 1,300 °C. The redox reactivity of the spray-dried oxygen carrier was measured with a thermogravimetric analyzer using 10 vol.% CH4 in CO2 balance as a fuel gas and air as an oxidizing gas. Water vapor addition to the fuel gas was performed to observe its effect on the reactivity. The oxygen transfer capacity of the oxygen carrier at the reaction temperature of 950 °C was over 12 wt%, indicating more than 80% of the total oxygen in the originally added NiO was transferred to the fuel. Water vapor addition made little change in the oxygen transfer capacity. This work indicates that γ-Al2O3 mixed with MgO could be a good support material for a highly attrition resistant spray-dried NiO oxygen carrier containing Mg component.