Binary-ore oxygen carriers prepared by extrusion–spheronization method for chemical looping combustion of coal

Abstract

In this study, composite oxygen carriers (OCs) were prepared by the extrusion–spheronization method, using disused fine (<100 μm) iron and copper ores as raw materials. A range of inert aluminosilicates (namely diatomite, montmorillonite, rectorite, pseudo-boehmite, pumice, and attapulgite) were tested as binders to achieve uniform physical mixing of iron ore and copper ore powders in a single OC particle, one-step particle shaping, and synergistic effect between active components. Firstly, the extrusion-spheronization process was optimized to achieve a sufficient crushing strength. It was found that FeCu-10 M (72 wt% iron ore, 18 wt% copper ore, and 10 wt% montmorillonite added as a binder) and FeCu-5P (76 wt% iron ore, 19 wt% copper ore, and 5 wt% pumice) OCs showed a relatively high crushing strength (greater than 2 N). Subsequently, the coal chemical looping combustion performance tests were conducted in a batch-fluidized bed. FeCu-10 M performed better at a bed temperature of 950 °C and for an oxygen-to-fuel ratio of 2.5 to 3.1. The OC also demonstrated excellent reactivity and stability during multiple redox cycles. The X-ray diffraction (XRD) pattern revealed that no obvious interphase side reaction occurred among different components within the particles. Scanning electron microscopy (SEM) characterization indicated no obvious sintering within the particle or agglomeration between the particles. The experimental results demonstrated that the extrusion–spheronization method is suitable for large-scale preparation of OC particles. The binary-ore OCs prepared by extrusion–spheronization exhibited good performance in terms of reactivity, stability, and economy.