Attrition of oxygen carrier particles in fluidized bed – basic theory and screening measurements with a customized jet cup test rig
Conference contribution, 2014
This article provides an overview of expected attrition phenomena during chemical-looping processes in interconnected fluidized-bed reactors, and also describes a customized method for measuring attrition resistance of oxygen-carrier particles. The proposed method is similar to the jet cup method, but has been scaled down in order to be suitable for samples as small as 5 g. Experimental results for materials, which previously have been used in continuous experiments in different reactor systems, are presented in brief. The attrition behaviour of materials during continuous operation was compared to results obtained with the jet cup test rig, and a strong correlation was established. Also, a weaker correlation between oxygen carrier performance and the commonly used crushing strength index was found. Some general guidelines with respect to particle attrition during chemical-looping combustion are provided. Materials that show good attrition resistance in the jet cup tests are much more likely to perform well in real operation. Also particles with a crushing strength greater than 2 N are more likely to perform well compared to softer particles. Composite materials with NiO or Fe2O3 as active phase and Al2O3-, NiAl2O4- or MgAl2O4-based support, as well as materials based on the CaMnO3-δ perovskite structure, are among the materials that were found to have high attrition resistance, and which also improved further following operation with fuel. In contrast, combined iron-manganese oxides (FexMn1-x)2O3, and materials containing smaller or larger amounts of either CuO or ZrO2 experienced reduced attrition resistance during operation with fuel, and usually also had low attrition resistance to begin with.
Fluidized bed combustion