On the attrition evaluation of oxygen carriers in Chemical Looping Combustion

Abstract

Chemical Looping Combustion (CLC) is one of the most promising processes for the low-cost capture of CO2. It is based on the transfer of oxygen from air to the fuel by means of a solid oxygen carrier that circulates between two interconnected fluidized bed reactors: the fuel reactor and the air reactor. CO2 capture is inherent to this process since air does not become mixed with the fuel. A key issue for the large-scale development of CLC technology is the selection of oxygen carrier materials with suitable properties such as high reactivity and good fluidization. Another important feature that an oxygen carrier must fulfil is to have high resistance to attrition. For this purpose, several particle characteristics related to attrition resistance were analysed in this work on 23 oxygen carriers, both natural and synthetic, prepared by different methods and using different metal oxides. Particle crushing strength and Air Jet Index (AJI) were determined for the fresh materials, as well as the attrition rate and the corresponding particle lifetime during multi-cycle redox reactions in a continuously operated CLC unit for gaseous fuels. A comparison was made of the different methods used to evaluate attrition behaviour.

The AJI-ASTM test for particles subjected to long-term CLC operation was used as a standard screening tool to evaluate the attrition behaviour of the oxygen carriers. Finally, a methodology was proposed for the selection of oxygen carriers as eligible materials for CLC scale-up based on attrition behaviour.