Methodology for Attrition Evaluation of Oxygen Carriers in Chemical Looping Systems

Existing methodologies for attrition evaluation of oxygen carriers in Chemical Looping Combustion systems do not adequately reflect the unique process conditions to which oxygen carriers are exposed, specifically high temperatures and cyclically reacting oxidizing and reducing atmospheres. This proposed Small Business Innovation Research (SBIR/STTR) project targets the development of novel equipment and methodologies that address the shortcomings of existing attrition evaluation methods through use of test conditions that broadly account for the process requirements of coal-based chemical looping systems. Phase I successfully demonstrated the dramatically improved attrition evaluation methodology, and allowed the ability to isolate the relative attrition effects due to mechanical, thermal and chemical stresses to which oxygen carriers are subjected. Phase I performed a detailed analysis of an iron-based oxygen carrier hematite and demonstrated dramatically higher attrition rates under the cyclic reacting conditions compared to non-reacting test conditions. Phase II will include more extensive testing with several additional oxygen carriers over a wider range of process conditions. A new test system will also be constructed to examine the effect of a second important attrition mechanism, and associated methodologies developed. An extensive test campaign will be completed using this new equipment. Additionally, Phase II will develop empirical models that describe the attrition behavior of oxygen carriers as a function of process conditions and attrition mechanism. Focus will be on not only the attrition of the oxygen carriers, but also the reactivity, in order to accurately project the lifetime of oxygen carriers in chemical looping systems.

The main benefit of the proposed work is an enabling service for expedited development of chemical looping combustion technology, an emerging strategy for reducing carbon dioxide emissions from fossil- fuel based energy production systems. The information gathered will be useful in designing not only the oxygen carriers themselves, but also the processes and equipment which employ those materials. Additionally, the proposed work will provide a low-cost and expedited approach to material screening. In addition to chemical looping combustion, several other potential markets have been identified, with commercial interest already expressed, including characterization of the following: limestone for fluidized bed combustors, sorbents for carbon dioxide capture, catalysts for fluid catalytic cracking, and materials for thermal energy storage.