Effect of Weathering on Steel Converter Slag Used as an Oxygen Carrier

Steel converter slag, also called LD slag, is a material that has been suggested for use as a low-cost oxygen carrier for chemical looping applications. Low-cost oxygen carriers are especially relevant for the conversion of solid fuels, which may contain large amounts of reactive ashes. Ash may limit the lifetime of the bed material, which is why a high-cost oxygen carrier will likely not be competitive. Applying LD slag on an industrial scale as an oxygen carrier makes the storage properties of the material highly interesting. LD slag has been known to be affected by weathering, thus limiting the possibilities of the material to be used in construction, e.g., as fillers in concrete. In this study, pretreated LD slag for use as an oxygen carrier was weathered outdoors for roughly 1.5 years in southwest Sweden. Afterward, the particles were characterized and used in a laboratory batch fluidized bed reactor system to evaluate the effects of storage on the oxygen carrier properties. It was found that the reactivity with the fuel of the weathered LD slag was similar to that of the original sample when used in a laboratory fluidized bed. However, the physical properties were severely degraded due to weathering. Dissolved CaO formed CaCO₃, agglomerating the top layer of the sample. The particles in the bulk of the sample were found to have decreased density and increased attrition rate. This suggests that LD slag particles for use as oxygen carriers should be stored dry to avoid weathering of the particles.