The attrition behaviour of oxygen-carriers under inert and reacting conditions

Abstract

The attrition of two potential oxygen-carriers for chemical-looping, 100wt% mechanically-mixed, unsupported iron oxide (400–600μm diameter) and 25wt% copper oxide impregnated on alumina (600–900μm diameter), has been studied. The rates of attrition of batches of these particles whilst they were being fluidised and subjected to successive cycles of reduction and oxidation were determined by measuring the rate of production of fine particles elutriated from the bed, as well as progressive changes in the distribution of particle sizes retained in the bed. The ability of the particles to withstand impacts was also investigated by examining the degree of fragmentation of 1g of reacted particles of known size on projecting them at a target at various velocities. It was found that the mechanical strength of the iron oxide particles deteriorated significantly after repeated cycles of oxidation and reduction. Thus, the rate of elutriation increased ∼35-fold between the 1st and 10th cycle. At an impact velocity of 38m/s, the amount of fragmentation in the impact test, viz. mass fraction of particles after impact having a size less than that before impact, increased from ∼2.3wt% (fresh particles) to 98wt% after the 10th cycle. The CuO particles, in comparison, were able to withstand repeated reaction: no signs of increased rates of elutriation or fragmentation were observed over ten cycles. These results highlight the importance of selecting a durable support for oxygen-carriers.